Pseudospectral techniques for non -smooth evolutionary problems

A pseudospectral approach is used to solve non-smooth evolutionary problems using Fourier collocation and Chebyshev collocation. It is well known that pseudospectral methods for smooth problems can offer superior accuracy over finite difference and finite element methods.;This paper explores the use of pseudospectral methods for non-smooth evolutionary problems in the area of hyperbolic heat transfer. Boundary and initial conditions are considered which cause instantaneous jumps, in the temperature and flux, prior to the propagation of a thermal wave into the medium. There is a considerable amount of literature that has investigated hyperbolic heat transfer under similar conditions, the common problems throughout theses investigations is the presence of numerical oscillation at the wave front. Finite difference and finite element methods have both been used, and both methods exhibit severe numerical oscillation at the wave front. In an attempt to reduce this oscillation extremely fine grids and severe timestep restrictions had to be introduced, but even these attempts still exhibited some oscillation.;This paper will demonstrate that pseudospectral methods, when used correctly, can eliminate the numerical oscillation at the wave front and accurately resolve the instantaneous jump at the boundary. Furthermore, pseudospectral methods can be used successfully with coarser grids and larger timesteps and still provide superior results.;This paper will also investigate hyperbolic heat transfer with boundary conditions that contain a continuous periodic flux with surface radiation. These boundary conditions have never before been investigated in the literature on hyperbolic heat transfer. Previous research has only considered boundary conditions that contain a constant flux with radiation r a periodic on-off pulse with radiation. In either case, extremely fine grids were needed to prevent severe numerical oscillation. This paper will compare the hyperbolic and parabolic thermal response due to the periodic flux, under a wide range of frequencies, as well as show how pseudospectral methods can be used successfully in the case of periodic flux with surface radiation without the need to introduce fine spatial grids and prohibitively small timesteps

A Longitudinal Study of Identifying and Paying Down Architectural Debt

Architectural debt is a form of technical debt that derives from the gap between the architectural design of the system as it "should be" compared to "as it is". We measured architecture debt in two ways: 1) in terms of system-wide coupling measures, and 2) in terms of the number and severity of architectural flaws. In recent work it was shown that the amount of architectural debt has a huge impact on software maintainability and evolution. Consequently, detecting and reducing the debt is expected to make software more amenable to change. This paper reports on a longitudinal study of a healthcare communications product created by Brightsquid Secure Communications Corp. This start-up company is facing the typical trade-off problem of desiring responsiveness to change requests, but wanting to avoid the ever-increasing effort that the accumulation of quick-and-dirty changes eventually incurs. In the first stage of the study, we analyzed the status of the "before" system, which indicated the impacts of change requests. This initial study motivated a more in-depth analysis of architectural debt. The results of this analysis were used to motivate a comprehensive refactoring of the software system. The third phase of the study was a follow-on architectural debt analysis which quantified the improvements made. Using this quantitative evidence, augmented by qualitative evidence gathered from in-depth interviews with Brightsquid's architects, we present lessons learned about the costs and benefits of paying down architecture debt in practice.Comment: Submitted to ICSE-SEIP 201

REPRODUCTIVE POTENTIAL WITHIN THE LANDSCAPE: A SPATIALLY-EXPLICIT, AGENT-BASED MODEL OF ASYNCHRONY

Reproductive asynchrony, which can be a beneficial life-history strategy in healthy insect populations, may contribute to an Allee effect at small population densities. A spatially explicit, agent-based model is used to investigate quantitative effects of asynchrony on reproductive potential. Temporal and spatial isolation effects are treated independently and together. Three behaviors are explored: clustered emergence from host plants, hilltopping, and mating discretion by females. The magnitude of the reduction in overall spatial overlap within the simulated population is shown to be governed by the radius of circular, random-walk movement and potential interaction distance. Hilltopping behavior and clustered emergence partially alleviate detrimental effects of spatial isolation; female selectivity in mating can exacerbate the loss of reproductive potential. Among these three behaviors, hilltopping produced the largest differential in spatial/temporal overlap

Technical Report on NETL's Non Newtonian Multiphase Slurry Workshop: A path forward to understanding non-Newtonian multiphase slurry flows

The Department of Energy’s (DOE) National Energy Technology Laboratory (NETL) sponsored a workshop on non-Newtonian multiphase slurry at NETL’s Morgantown campus August 19 and 20, 2013. The objective of this special two-day meeting of 20-30 invited experts from industry, National Labs and academia was to identify and address technical issues associated with handling non-Newtonian multiphase slurries across various facilities managed by DOE. Particular emphasis during this workshop was placed on applications managed by the Office of Environmental Management (EM). The workshop was preceded by two webinars wherein personnel from ORP and NETL provided background information on the Hanford WTP project and discussed the critical design challenges facing this project. In non-Newtonian fluids, viscosity is not constant and exhibits a complex dependence on applied shear stress or deformation. Many applications under EM’s tank farm mission involve non-Newtonian slurries that are multiphase in nature; tank farm storage and handling, slurry transport, and mixing all involve multiphase flow dynamics, which require an improved understanding of the mechanisms responsible for rheological changes in non-Newtonian multiphase slurries (NNMS). To discuss the issues in predicting the behavior of NNMS, the workshop focused on two topic areas: (1) State-of-the-art in non-Newtonian Multiphase Slurry Flow, and (2) Scaling up with Confidence and Ensuring Safe and Reliable Long-Term Operation

Quantification of Cell Movement Reveals Distinct Edge Motility Types During Cell Spreading

Actin-based motility is central to cellular processes such as migration, bacterial engulfment, and cancer metastasis, and requires precise spatial and temporal regulation of the cytoskeleton. We studied one such process, fibroblast spreading, which involves three temporal phases: early, middle, and late spreading, distinguished by differences in cell area growth. In these studies, aided by improved algorithms for analyzing edge movement, we observed that each phase was dominated by a single, kinematically and biochemically distinct cytoskeletal organization, or motility type. Specifically, early spreading was dominated by periodic blebbing; continuous protrusion occurred predominantly during middle spreading; and periodic contractions were prevalent in late spreading. Further characterization revealed that each motility type exhibited a distinct distribution of the actin-related protein VASP, while inhibition of actin polymerization by cytochalasin D treatment revealed different dependences on barbed-end polymerization. Through this detailed characterization and graded perturbation of the system, we observed that although each temporal phase of spreading was dominated by a single motility type, in general cells exhibited a variety of motility types in neighboring spatial domains of the plasma membrane edge. These observations support a model in which global signals bias local cytoskeletal biochemistry in favor of a particular motility type

Active Turbulence and Scalar Transport near the Forest–Atmosphere Interface

Turbulent velocity, temperature, water vapor concentration, and other scalars were measured at the canopyatmosphere interface of a 13-14-m-tall uniform pine forest and a 33-m-tall nounuiform hardwood forest. These measurement were used to investigate whether the mixing layer (ML) analogy of Raupach et al. predicts eddy sizes and now characteristics responsible for much of the turbulent stresses and vertical scalar fluxes. For this purpose, wavelet spectra and cospectra were derived and analyzed. It was found that the MI. analogy predicts well vertical velocity variances and integral timescales. However, at low wavenumbers, inactive eddy motion signatures were present in horizontol velocity wavelet spectra, suggesting that MI. may not be suitable for scaling horizontal velocity perturbations. Momentum and scalar wavelet cospectra of turbulent stresses and scalar fluxes demonstrated that active eddy motion, which was shown by Raupach et al. to be the main energy contributor to vertical velocity (w) spectral energy (Em). is also the main scalar flux-transporting eddy motion. Predictions using ML of the peak E, frequency are in excellent agreement with measured waveled cospectral peaks of vertical fluxes (Kh = 1.5, where K is wavenumber and h is canopy height). Using Lorentz wavelet thresholding of vertical velocity time series, wavelet coefficients associated with active turbulence were identified. It was demonstrated that detection frequency of organized structures, as predicted from Lorentz wavelet filtering, relate to the arrival frequency /h and integral timescale, where is the mean horizontal velocity at height z = h. The newly proposed wavelet thresholding approach, which relies on a"global" wavelet threshold formulation for the energy in w, provides simultaneous energy-covariance-preserving characterization of "active" turbulence at the canopy-atmosphere interface

Stable and unstable accretion in the classical T Tauri stars IM Lup and RU Lup as observed by MOST

Results of the time variability monitoring of the two classical T Tauri stars, RU Lup and IM Lup, are presented. Three photometric data sets were utilised: (1) simultaneous (same field) MOST satellite observations over four weeks in each of the years 2012 and 2013, (2) multicolour observations at the SAAO in April - May of 2013, (3) archival V-filter ASAS data for nine seasons, 2001 - 2009. They were augmented by an analysis of high-resolution, public-domain VLT-UT2 UVES spectra from the years 2000 to 2012. From the MOST observations, we infer that irregular light variations of RU Lup are caused by stochastic variability of hot spots induced by unstable accretion. In contrast, the MOST light curves of IM Lup are fairly regular and modulated with a period of about 7.19 - 7.58 d, which is in accord with ASAS observations showing a well defined 7.247+/-0.026 d periodicity. We propose that this is the rotational period of IM Lup and is due to the changing visibility of two antipodal hot spots created near the stellar magnetic poles during the stable process of accretion. Re-analysis of RU Lup high-resolution spectra with the Broadening Function approach reveals signs of a large polar cold spot, which is fairly stable over 13 years. As the star rotates, the spot-induced depression of intensity in the Broadening Function profiles changes cyclically with period 3.71058 d, which was previously found by the spectral cross-correlation method.Comment: 14 pages, 7 figures. Accepted by MNRA

Collaborative navigation as a solution for PNT applications in GNSS challenged environments: report on field trials of a joint FIG / IAG working group

PNT stands for Positioning, Navigation, and Timing. Space-based PNT refers to the capabilities enabled by GNSS, and enhanced by Ground and Space-based Augmentation Systems (GBAS and SBAS), which provide position, velocity, and timing information to an unlimited number of users around the world, allowing every user to operate in the same reference system and timing standard. Such information has become increasingly critical to the security, safety, prosperity, and overall qualityof-life of many citizens. As a result, space-based PNT is now widely recognized as an essential element of the global information infrastructure. This paper discusses the importance of the availability and continuity of PNT information, whose application, scope and significance have exploded in the past 10–15 years. A paradigm shift in the navigation solution has been observed in recent years. It has been manifested by an evolution from traditional single sensor-based solutions, to multiple sensor-based solutions and ultimately to collaborative navigation and layered sensing, using non-traditional sensors and techniques – so called signals of opportunity. A joint working group under the auspices of the International Federation of Surveyors (FIG) and the International Association of Geodesy (IAG), entitled ‘Ubiquitous Positioning Systems’ investigated the use of Collaborative Positioning (CP) through several field trials over the past four years. In this paper, the concept of CP is discussed in detail and selected results of these experiments are presented. It is demonstrated here, that CP is a viable solution if a ‘network’ or ‘neighbourhood’ of users is to be positioned / navigated together, as it increases the accuracy, integrity, availability, and continuity of the PNT information for all users