Sparse spectral-tau method for the three-dimensional helically reduced wave equation on two-center domains

We describe a multidomain spectral-tau method for solving the three-dimensional helically reduced wave equation on the type of two-center domain that arises when modeling compact binary objects in astrophysical applications. A global two-center domain may arise as the union of Cartesian blocks, cylindrical shells, and inner and outer spherical shells. For each such subdomain, our key objective is to realize certain (differential and multiplication) physical-space operators as matrices acting on the corresponding set of modal coefficients. We then achieve sparse realizations through the integration “preconditioning” of Coutsias, Hagstrom, Hesthaven, and Torres. Since ours is the first three-dimensional multidomain implementation of the technique, we focus on the issue of convergence for the global solver, here the alternating Schwarz method accelerated by GMRES. Our methods may prove relevant for numerical solution of other mixed-type or elliptic problems, and in particular for the generation of initial data in general relativity

Post-Stagnation Behavior in the Upstream Regions of Ice Stream C, West Antarctica

The region where two active tributaries feed into the now stagnant Ice Stream C (ISC), West Antarctica, is thickening. In this region, we observe a correlation between faster ice flow (the tributaries) and elevated topography. We conclude that stagnation of ISC resulted in compression and thickening along the tributaries, eventually forming a bulge on the ice-sheet surface. Modern hydraulic potential gradients would divert basal meltwater from ISC to Ice Stream B (ISB). These gradients are primarily controlled by the bulge topography, and so likely formed subsequent to trunk stagnation. As such, we argue against water piracy as being the cause for ISC\u27s stagnation. Kinematic-wave theory suggests that thickness perturbations propagate downstream over time, but that kinematic-wave speed decreases near the stagnant trunk. This and modest diffusion rates combine to trap most of the tributary-fed ice in the bulge region. Using interferometric synthetic aperture radar velocity measurements, we observe that half of the ice within ISC\u27s southern tributary flows into ISB. That flow pattern and other observations of non-steady flow in the region likely result from stagnation-induced thickening along upper ISC combined with a longer period of thinning on upper ISB. If current trends in thickness change continue, more ice from upper ISC will be diverted to ISB

Assessing and monitoring intratumor heterogeneity in glioblastoma: how far has multimodal imaging come?

Glioblastoma demonstrates imaging features of intratumor heterogeneity that result from underlying heterogeneous biological properties. This stems from variations in cellular behavior that result from genetic mutations that either drive, or are driven by, heterogeneous microenvironment conditions. Among all imaging methods available, only T1-weighted contrast-enhancing and T2-weighted fluid-attenuated inversion recovery are used in standard clinical glioblastoma assessment and monitoring. Advanced imaging modalities are still considered emerging techniques as appropriate end points and robust methodologies are missing from clinical trials. Discovering how these images specifically relate to the underlying tumor biology may aid in improving quality of clinical trials and understanding the factors involved in regional responses to treatment, including variable drug uptake and effect of radiotherapy. Upon validation and standardization of emerging MR techniques, providing information based on the underlying tumor biology, these images may allow for clinical decision-making that is tailored to an individual's response to treatment.Stephen Price is funded by a Clinician Scientist Award from the National Institute for Health Research.This is the author accepted manuscript. The final version is available from Future Medicine via http://dx.doi.org/10.2217/cns.15.2

Millimeter Observations of GRB 030329: Continued Evidence for a Two-Component Jet

We present the results of a dedicated campaign on the afterglow of GRB 030329 with the millimeter interferometers of the Owens Valley Radio Observatory (OVRO), the Berkeley-Illinois-Maryland Association (BIMA), and with the MAMBO-2 bolometer array on the IRAM 30-m telescope. These observations allow us to trace the full evolution of the afterglow of GRB 030329 at frequencies of 100 GHz and 250 GHz for the first time. The millimeter light curves exhibit two main features: a bright, constant flux density portion and a steep power-law decline. The absence of bright, short-lived millimeter emission is used to show that the GRB central engine was not actively injecting energy well after the burst. The millimeter data support a model, advocated by Berger et al., of a two-component jet-like outflow in which a narrow angle jet is responsible for the high energy emission and early optical afterglow, and a wide-angle jet carrying most of the energy is powering the radio and late optical afterglow emissionComment: Accepted to ApJ

Sources And Remedies Of High-Frequency Piping Vibration And Noise.

Tutorialpg. 189-212In large diameter piping, high-frequency energy can produce excessive noise and vibration, and failures of thermowells, instrumentation, and attached small-bore piping. In severe cases, the pipe itself can fracture. Perhaps more precisely called "high wave number" problems, these problems most often manifest themselves in centrifugal compressors, screw compressors, heat exchangers, and silencers. Two high-frequency energy generation mechanisms predominate in most industrial processes; flow induced (vortex 189 shedding) and pulsation at multiples of running speed (blade-pass in centrifugal compressors and pocket-passing frequency in screw compressors). Once this energy is generated, amplification may occur from acoustical and/or structural resonances, resulting in high amplitude vibration and noise. To resolve these problems successfully, an understanding of the underlying physics of two- and three-dimensional acoustics is necessary. With these principles in mind, modifications to the piping system can be considered for the particular application. The three-dimensional wave equation is used to analyze the propagation of the high-order (cross-wall) acoustical modes in the duct or pipe. These cross-wall modes can be diametrical (m) modes, annular (n) modes, or combined (m, n) modes. By reformulating the resulting differential equations into polar coordinates and applying the appropriate boundary conditions, an equation for the "cut-on" frequencies,/ (m,n)• for cross-wall modes can be developed that incorporates zeroes of the first order Bessel function, f3(m,n)• the speed of sound, and pipe diameter. Several references provide lists of the zeroes of the Bessel function; however, most of these references only provide solutions up to m, n = 6. Field tests have identified cross-wall modes up to m = 30. Therefore, a table is provided for zeros of f3(m,n) for m= 0 to 32 and n = 0 to 8. This paper discusses the excitation and amplification mechanisms relevant to high-frequency energy generation in piping systems. Mechanisms that allow efficient coupling of this energy with the surroundings (either structural or acoustical) are discussed. Data from various systems are presented, as well as design modifications that have been shown to be effective at reducing the high-frequency energy

Upland Habitat Quality and Historic Landscape Composition Influence Genetic Variation of a Pond-Breeding Salamander

Understanding the temporal and spatial scale at which habitat alteration impacts populations is important for conservation and management. Amphibians have declined more than other vertebrates, and pond-breeding species are particularly susceptible to habitat loss and fragmentation because they have terrestrial and aquatic life stages. One approach to management of pond-breeding species is protection of core upland habitat surrounding the breeding pond. We used genetic variation as an indicator of population status in a common amphibian species, spotted salamanders (Ambystoma maculatum), to determine how amount of suitable upland habitat relates to population status in the greater Charlotte, North Carolina, USA metropolitan area. We developed candidate models to evaluate the relative influence of historical and contemporary forested habitat availability on population genetic variation at two spatial scales of upland area (164 m and 2000 m) at four time intervals over the past seven decades (1938, 1978, 1993, 2005). We found that historical land cover best predicted contemporary allelic richness. Inbreeding coefficient and observed heterozygosity were not effectively predicted by forest cover at either spatial or temporal scales. Allelic richness was best predicted at the smaller spatial scale in the 1993 time interval. Predicting and understanding how future landscape configuration affects genetic variation of common and rare species is imperative for the conservation of amphibian and other wildlife populations

The assembly of developing motor neurons depends on an interplay between spontaneous activity, type II cadherins and gap junctions

A core structural and functional motif of the vertebrate central nervous system is discrete clusters of neurons or ‘nuclei’. Yet the developmental mechanisms underlying this fundamental mode of organisation are largely unknown. We have previously shown that the assembly of motor neurons into nuclei depends on cadherin-mediated adhesion. Here, we demonstrate that the emergence of mature topography among motor nuclei involves a novel interplay between spontaneous activity, cadherin expression and gap junction communication. We report that nuclei display spontaneous calcium transients, and that changes in the activity patterns coincide with the course of nucleogenesis. We also find that these activity patterns are disrupted by manipulating cadherin or gap junction expression. Furthermore, inhibition of activity disrupts nucleogenesis, suggesting that activity feeds back to maintain integrity among motor neurons within a nucleus. Our study suggests that a network of interactions between cadherins, gap junctions and spontaneous activity governs neuron assembly, presaging circuit formation

Ligand biological activity predicted by cleaning positive and negative chemical correlations.

Predicting ligand biological activity is a key challenge in drug discovery. Ligand-based statistical approaches are often hampered by noise due to undersampling: The number of molecules known to be active or inactive is vastly less than the number of possible chemical features that might determine binding. We derive a statistical framework inspired by random matrix theory and combine the framework with high-quality negative data to discover important chemical differences between active and inactive molecules by disentangling undersampling noise. Our model outperforms standard benchmarks when tested against a set of challenging retrospective tests. We prospectively apply our model to the human muscarinic acetylcholine receptor M1, finding four experimentally confirmed agonists that are chemically dissimilar to all known ligands. The hit rate of our model is significantly higher than the state of the art. Our model can be interpreted and visualized to offer chemical insights about the molecular motifs that are synergistic or antagonistic to M1 agonism, which we have prospectively experimentally verified

A Neural Network Approach to Identify the Peritumoral Invasive Areas in Glioblastoma Patients by Using MR Radiomics

The challenge in the treatment of glioblastoma is the failure to identify the cancer invasive area outside the contrast-enhancing tumour which leads to the high local progression rate. Our study aims to identify its progression from the preoperative MR radiomics. 57 newly diagnosed cerebral glioblastoma patients were included. All patients received 5-aminolevulinic acid (5-ALA) fluorescence guidance surgery and postoperative temozolomide concomitant chemoradiotherapy. Preoperative 3 T MRI data including structure MR, perfusion MR, and DTI were obtained. Voxel-based radiomics features extracted from 37 patients were used in the convolutional neural network to train and as internal validation. Another 20 patients of the cohort were tested blindly as external validation. Our results showed that the peritumoural progression areas had higher signal intensity in FLAIR (p = 0.02), rCBV (p = 0.038), and T1C (p = 0.0004), and lower intensity in ADC (p = 0.029) and DTI-p (p = 0.001) compared to non-progression area. The identification of the peritumoural progression area was done by using a supervised convolutional neural network. There was an overall accuracy of 92.6% in the training set and 78.5% in the validation set. Multimodal MR radiomics can demonstrate distinct characteristics in areas of potential progression on preoperative MRI.</p