347 research outputs found
Extension of effort for lunar flight handbook detailed technical report
Lunar flight handbook - orbital departure windows, libration points, and lunar flight orbit estimation, theory, and operation
Distributed-Pair Programming can work well and is not just Distributed Pair-Programming
Background: Distributed Pair Programming can be performed via screensharing
or via a distributed IDE. The latter offers the freedom of concurrent editing
(which may be helpful or damaging) and has even more awareness deficits than
screen sharing. Objective: Characterize how competent distributed pair
programmers may handle this additional freedom and these additional awareness
deficits and characterize the impacts on the pair programming process. Method:
A revelatory case study, based on direct observation of a single, highly
competent distributed pair of industrial software developers during a 3-day
collaboration. We use recordings of these sessions and conceptualize the
phenomena seen. Results: 1. Skilled pairs may bridge the awareness deficits
without visible obstruction of the overall process. 2. Skilled pairs may use
the additional editing freedom in a useful limited fashion, resulting in
potentially better fluency of the process than local pair programming.
Conclusion: When applied skillfully in an appropriate context, distributed-pair
programming can (not will!) work at least as well as local pair programming
A Model of Vertical Oligopolistic Competition
This paper develops a model of successive oligopolies with endogenous market entry, allowing for varying degrees of product differentiation and entry costs in both markets. Our analysis shows that the downstream conditions dominate the overall profitability of the two-tier structure while
the upstream conditions mainly affect the distribution of profits. We compare the welfare effects of upstream versus downstream deregulation policies and show that the impact of deregulation may be overvalued when ignoring feedback effects from the other market. Furthermore, we analyze how different forms of vertical restraints influence the endogenous market structure and show when they are welfare enhancing
Massively parallel linear stability analysis with P_ARPACK for 3D fluid flow modeled with MPSalsa
Capillary Condensation and Interface Structure of a Model Colloid-Polymer Mixture in a Porous Medium
We consider the Asakura-Oosawa model of hard sphere colloids and ideal
polymers in contact with a porous matrix modeled by immobilized configurations
of hard spheres. For this ternary mixture a fundamental measure density
functional theory is employed, where the matrix particles are quenched and the
colloids and polymers are annealed, i.e. allowed to equilibrate. We study
capillary condensation of the mixture in a tiny sample of matrix as well as
demixing and the fluid-fluid interface inside a bulk matrix. Density profiles
normal to the interface and surface tensions are calculated and compared to the
case without matrix. Two kinds of matrices are considered: (i) colloid-sized
matrix particles at low packing fractions and (ii) large matrix particles at
high packing fractions. These two cases show fundamentally different behavior
and should both be experimentally realizable. Furthermore, we argue that
capillary condensation of a colloidal suspension could be experimentally
accessible. We find that in case (ii), even at high packing fractions, the main
effect of the matrix is to exclude volume and, to high accuracy, the results
can be mapped onto those of the same system without matrix via a simple
rescaling.Comment: 12 pages, 9 figures, submitted to PR
Recommended from our members
Modeling Transport in Gas Chromatography Columns for the Micro-ChemLab
The gas chromatography (GC) column is a critical component in the microsystem for chemical detection ({mu}ChemLab{trademark}) being developed at Sandia. The goal is to etch a meter-long GC column onto a 1-cm{sup 2} silicon chip while maintaining good chromatographic performance. Our design strategy is to use a modeling and simulation approach. We have developed an analytical tool that models the transport and surface interaction process to achieve an optimized design of the GC column. This analytical tool has a flow module and a separation module. The flow module considers both the compressibility and slip flow effects that may significantly influence the gas transport in a long and narrow column. The separation module models analyte transport and physico-chemical interaction with the coated surface in the GC column. It predicts the column efficiency and performance. Results of our analysis will be presented in this paper. In addition to the analytical tool, we have also developed a time-dependent adsorption/desorption model and incorporated this model into a computational fluid dynamics (CFD) code to simulate analyte transport and separation process in GC columns. CFD simulations can capture the complex three-dimensional flow and transport dynamics, whereas the analytical tool cannot. Different column geometries have been studied, and results will be presented in this paper. Overall we have demonstrated that the modeling and simulation approach can guide the design of the GC column and will reduce the number of iterations in the device development
Local Embeddedness and Economic and Social Upgrading in Madagascar's Export Apparel Industry
MPAS-Albany Land Ice (MALI): a variable-resolution ice sheet model for Earth system modeling using Voronoi grids
We introduce MPAS-Albany Land Ice (MALI) v6.0, a new variable-resolution land ice model that uses unstructured Voronoi grids on a plane or
sphere. MALI is built using the Model for Prediction Across Scales (MPAS)
framework for developing variable-resolution Earth system model components
and the Albany multi-physics code base for the solution of coupled systems of
partial differential equations, which itself makes use of Trilinos solver
libraries. MALI includes a three-dimensional first-order momentum balance
solver (BlatterâPattyn) by linking to the Albany-LI ice sheet velocity
solver and an explicit shallow ice velocity solver. The evolution of ice
geometry and tracers is handled through an explicit first-order horizontal
advection scheme with vertical remapping. The evolution of ice temperature is
treated using operator splitting of vertical diffusion and horizontal
advection and can be configured to use either a temperature or enthalpy
formulation. MALI includes a mass-conserving subglacial hydrology model that
supports distributed and/or channelized drainage and can optionally be
coupled to ice dynamics. Options for calving include eigencalving, which
assumes that the calving rate is proportional to extensional strain rates. MALI is
evaluated against commonly used exact solutions and community benchmark
experiments and shows the expected accuracy. Results for the MISMIP3d
benchmark experiments with MALI's BlatterâPattyn solver fall between
published results from Stokes and L1L2 models as expected. We use the model
to simulate a semi-realistic Antarctic ice sheet problem following the
initMIP protocol and using 2 km resolution in marine ice sheet regions. MALI
is the glacier component of the Energy Exascale Earth System Model (E3SM)
version 1, and we describe current and planned coupling to other E3SM
components.</p
Factors and processes shaping the population structure and distribution of genetic variation across the species range of the freshwater snail radix balthica (Pulmonata, Basommatophora)
Background: Factors and processes shaping the population structure and spatial distribution of genetic diversity across a species' distribution range are important in determining the range limits. We comprehensively analysed the influence of recurrent and historic factors and processes on the population genetic structure, mating system and the distribution of genetic variability of the pulmonate freshwater snail Radix balthica. This analysis was based on microsatellite variation and mitochondrial haplotypes using Generalised Linear Statistical Modelling in a Model Selection framework. Results: Populations of R. balthica were found throughout North-Western Europe with range margins marked either by dispersal barriers or the presence of other Radix taxa. Overall, the population structure was characterised by distance independent passive dispersal mainly along a Southwest-Northeast axis, the absence of isolation-by-distance together with rather isolated and genetically depauperated populations compared to the variation present in the entire species due to strong local drift. A recent, climate driven range expansion explained most of the variance in genetic variation, reducing at least temporarily the genetic variability in this area. Other factors such as geographic marginality and dispersal barriers play only a minor role. Conclusions: To our knowledge, such a population structure has rarely been reported before. It might nevertheless be typical for passively dispersed, patchily distributed taxa (e.g. freshwater invertebrates). The strong local drift implied in such a structure is expected to erode genetic variation at both neutral and coding loci and thus probably diminish evolutionary potential. This study shows that the analysis of multiple factors is crucial for the inference of the processes shaping the distribution of genetic variation throughout species ranges. Additional files Additional file 1: Distribution of Radix taxa. Spatial distribution of the Radix MOTU as defined in Pfenninger et al. 2006 plus an additional, newly discovered taxon. This map is the basis for the inference of the species range of R. balthica. Additional file 2: Sampling site table and spatial distribution of diversity indices, selfing estimates and inferred population bottlenecks for R. balthica. Table of sampling site code, geographical position in decimal degrees latitude and longitude, number of individuals analysed with microsatellites (Nnuc), expected heterozygosity (HE) and standard deviation across loci, mean rarefied number of alleles per microsatellite locus (A) and their standard deviation, number of individuals analysed for mitochondrial variation (Nmt), rarefied number of mitochondrial COI haplotypes (Hmt), number of individuals measured for body size (Nsize). Figures A1 - A3 show a graphical representation of the spatial distribution of He, Hmt and, s, respectively. Additional file 3: Assessment of environmental marginality. PCA (principle component analysis) on 35 climatic parameters for the period from 1960 - 2000 from publicly availableWorldClim data. Additional file 4: Inference of a recent climate driven range expansion in R. balthica. Analysis of the freshwater benthos long term monitoring data of the Swedish national monitoring databases at the Swedish University of Agricultural Sciences SLU with canonical correspondence analysis
Description and evaluation of the Community Ice Sheet Model (CISM) v2.1
We describe and evaluate version 2.1 of the Community Ice Sheet Model (CISM).
CISM is a parallel, 3-D thermomechanical model, written mainly in Fortran,
that solves equations for the momentum balance and the thickness and
temperature evolution of ice sheets. CISM's velocity solver incorporates a
hierarchy of Stokes flow approximations, including shallow-shelf,
depth-integrated higher order, and 3-D higher order. CISM also includes a
suite of test cases, links to third-party solver libraries, and
parameterizations of physical processes such as basal sliding, iceberg
calving, and sub-ice-shelf melting. The model has been verified for standard
test problems, including the Ice Sheet Model Intercomparison Project for
Higher-Order Models (ISMIP-HOM) experiments, and has participated in the
initMIP-Greenland initialization experiment. In
multimillennial simulations with modern climate forcing on a 4 km grid, CISM
reaches a steady state that is broadly consistent with observed flow patterns
of the Greenland ice sheet. CISM has been integrated into version 2.0 of the
Community Earth System Model, where it is being used for Greenland
simulations under past, present, and future climates. The code is open-source
with extensive documentation and remains under active development.</p
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