Multilevel convergence analysis of multigrid-reduction-in-time

This paper presents a multilevel convergence framework for multigrid-reduction-in-time (MGRIT) as a generalization of previous two-grid estimates. The framework provides a priori upper bounds on the convergence of MGRIT V- and F-cycles, with different relaxation schemes, by deriving the respective residual and error propagation operators. The residual and error operators are functions of the time stepping operator, analyzed directly and bounded in norm, both numerically and analytically. We present various upper bounds of different computational cost and varying sharpness. These upper bounds are complemented by proposing analytic formulae for the approximate convergence factor of V-cycle algorithms that take the number of fine grid time points, the temporal coarsening factors, and the eigenvalues of the time stepping operator as parameters. The paper concludes with supporting numerical investigations of parabolic (anisotropic diffusion) and hyperbolic (wave equation) model problems. We assess the sharpness of the bounds and the quality of the approximate convergence factors. Observations from these numerical investigations demonstrate the value of the proposed multilevel convergence framework for estimating MGRIT convergence a priori and for the design of a convergent algorithm. We further highlight that observations in the literature are captured by the theory, including that two-level Parareal and multilevel MGRIT with F-relaxation do not yield scalable algorithms and the benefit of a stronger relaxation scheme. An important observation is that with increasing numbers of levels MGRIT convergence deteriorates for the hyperbolic model problem, while constant convergence factors can be achieved for the diffusion equation. The theory also indicates that L-stable Runge-Kutta schemes are more amendable to multilevel parallel-in-time integration with MGRIT than A-stable Runge-Kutta schemes.Comment: 26 pages; 17 pages Supplementary Material

The Digital Revolution to Come: Photogrammetry in Archaeological Practice

The three-dimensional (3D) revolution promised to transform archaeological practice. Of the technologies that contribute to the proliferation of 3D data, photogrammetry facilitates the rapid and inexpensive digitization of complex subjects in both field and lab settings. It finds additional use as a tool for public outreach, where it engages audiences ranging from source communities to artifact collectors. But what has photogrammetry’s function been in advancing archaeological analysis? Drawing on our previous work, we review recent applications to understand the role of photogrammetry for contemporary archaeologists. Although photogrammetry is widely used as a visual aid, its analytical potential remains underdeveloped. Considering various scales of inquiry—graduating from objects to landscapes—we address how the technology fits within and expands existing documentation and data visualization routines, while evaluating the opportunity it presents for addressing archaeological questions and problems in innovative ways. We advance an agenda advocating that archaeologists move from proof-of concept papers toward greater integration of photogrammetry with research

Anti-Screening by Quarks and the Structure of the Inter-Quark Potential

The inter-quark potential is dominated by anti-screening effects which underly asymptotic freedom. We calculate the order g^6 anti-screening contribution from light fermions and demonstrate that these effects introduce a non-local divergence. These divergences are shown to make it impossible to define a coupling renormalisation scheme that renormalises this minimal, anti-screening potential. Hence the beta function cannot be divided into screening and anti-screening parts beyond lowest order. However, we then demonstrate that renormalisation can be carried out in terms of the anti-screening potential.Comment: 11 pages, some clarifications and typographical corrections, to appear in Physics Letters

UV/Ozone treatment to reduce metal-graphene contact resistance

We report reduced contact resistance of single-layer graphene devices by using ultraviolet ozone (UVO) treatment to modify the metal/graphene contact interface. The devices were fabricated from mechanically transferred, chemical vapor deposition (CVD) grown, single layer graphene. UVO treatment of graphene in the contact regions as defined by photolithography and prior to metal deposition was found to reduce interface contamination originating from incomplete removal of poly(methyl methacrylate) (PMMA) and photoresist. Our control experiment shows that exposure times up to 10 minutes did not introduce significant disorder in the graphene as characterized by Raman spectroscopy. By using the described approach, contact resistance of less than 200 {\Omega} {\mu}m was achieved, while not significantly altering the electrical properties of the graphene channel region of devices.Comment: 17 pages, 5 figure

Temperature Response of 129 Xe Depolarization Transfer and Its Application for Ultrasensitive NMR Detection

Trapping xenon in functionalized cryptophane cages makes the sensitivity of hyperpolarized (HP) 129Xe available for specific NMR detection of biomolecules. Here, we study the signal transfer onto a reservoir of unbound HP xenon by gating the residence time of the nuclei in the cage through the temperature-dependant exchange rate. Temperature changes larger than ∼0.6  K are detectable as an altered reservoir signal. The temperature response is adjustable with lower concentrations of caged xenon providing more sensitivity at higher temperatures. Ultrasensitive detection of functionalized cryptophane at 310 K is demonstrated with a concentration of 10 nM, corresponding to a ∼4000−fold sensitivity enhancement compared to conventional detection. This makes HPNMR capable of detecting such constructs in concentrations far below the detection limit of benchtop uv-visible light absorbance

Data-driven normalization strategies for high-throughput quantitative RT-PCR

Background: High-throughput real-time quantitative reverse transcriptase polymerase chain reaction (qPCR) is a widely used technique in experiments where expression patterns of genes are to be profiled. Current stage technology allows the acquisition of profiles for a moderate number of genes (50 to a few thousand), and this number continues to grow. The use of appropriate normalization algorithms for qPCR-based data is therefore a highly important aspect of the data preprocessing pipeline

Macrofauna and biostratigraphy of the Rollrock Section, northern Ellesmere Island, Canadian Arctic Islands - a comprehensive high latitude archive of the Jurassic - Cretaceous Transition

Working in the Arctic would not be possible without manifold support. Our sincere thanks go to the following people in Canada who helped to make our research a success: Sylvie LeBlanc (Department of Culture and Heritage, Iglooik, Canada); Jane Chisholm (Parks Canada, Iqaluit, Canada); John Innis (Universal Helicopters); the rangers of Parks Canada at Quttinirpaaq National Park (Ellesmere Island, Canada); the Polar Continental Shelf Programme team at Resolute (Cornwallis Island, Canada); Margaret Currie, Laura Smyk and Kieran Sheperd (all Canadian Museum of Nature, Ottawa, Canada). Alex Chavanne (California, USA) joined our team as an excellent field assistant, helped logging and sampling the Rollrock Section and found the giant Dorsoplanites specimen. Sarah Wallace-Jones (Sedgwick Museum, Department of Earth Sciences, University of Cambridge, UK) provided access to preparation labs. Magdalena Biszczuk (CASP) prepared the maps in Fig. 1; and Michael Pointon (CASP) polished the English. Ashton F. Embry (Geological Survey of Canada, Calgary) kindly shared his field observations and analytical results on the Rollrock Section. Mikhail Rogov (Geologicheskij Institut, Rossijskaja Akademija Nauk, Moscow) greatly helped by sharing expert knowledge regarding ammonites of the Jurassic-Cretaceous boundary interval and by providing literature. CASP's industry sponsors are acknowledged for funding the Canadian Arctic Islands Project. Peter Alsen (Geological Survey of Denmark and Greenland, Copenhagen, Denmark) and Terence Poulton (Natural Resources Canada, Calgary, Canada) provided careful and detailed reviews, which greatly improved the manuscript.Peer reviewedPostprin

Impedance analysis of Al2O3/H-terminated diamond metal-oxide-semiconductor structures

Impedance spectroscopy (IS) analysis is carried out to investigate the electrical properties of the metal-oxide-semiconductor (MOS) structure fabricated on hydrogen-terminated single crystal diamond. The low-temperature atomic layer deposition Al2O3 is employed as the insulator in the MOS structure. By numerically analysing the impedance of the MOS structure at various biases, the equivalent circuit of the diamond MOS structure is derived, which is composed of two parallel capacitive and resistance pairs, in series connection with both resistance and inductance. The two capacitive components are resulted from the insulator, the hydrogenated-diamond surface, and their interface. The physical parameters such as the insulator capacitance are obtained, circumventing the series resistance and inductance effect. By comparing the IS and capacitance-voltage measurements, the frequency dispersion of the capacitance-voltage characteristic is discussed

NADPH oxidase 4 modulates hepatic responses to lipopolysaccharide mediated by Toll-like receptor-4.

Chronic inflammation plays a key role in development of many liver diseases. Stimulation of Toll-like receptor 4 (TLR4) by bacterial lipopolysaccharide (LPS) initiates inflammation and promotes development of hepatocellular carcinoma and other liver diseases. NADPH oxidases contribute to LPS-induced reactive oxygen species (ROS) production and modulate TLR responses, but whether these enzymes function in TLR4 responses of hepatocytes is unknown. In the present work, we examined the role of NADPH oxidase 4 (Nox4) in LPS-induced TLR4 responses in human hepatoma cells and wildtype and Nox4-deficient mice. We found that LPS increased expression of Nox4, TNF-α, and proliferating cell nuclear antigen (PCNA). Nox4 silencing suppressed LPS-induced TNF-α and PCNA increases in human cells. The LPS-induced TNF-α increases were MyD88-dependent, and were attenuated in primary hepatocytes isolated from Nox4-deficient mice. We found that Nox4 mediated LPS-TLR4 signaling in hepatocytes via NF-ĸB and AP-1 pathways. Moreover, the effect of Nox4 depletion was time-dependent; following six weeks of repeated LPS stimulation in vivo, hepatic TNF-α and PCNA responses subsided in Nox4-deficient mice compared with wildtype mice. Therefore, our data suggest that Nox4 mediates LPS-TLR4 signaling in human hepatoma cells and murine hepatocytes and may contribute to the ability of LPS to stimulate liver pathology