Papers by David A. Joiner
Linearly Polarized Radiation Transport in a Spherical Dust Shell
Infrared and visible observations of classical novae show that these objects are associated with ... more Infrared and visible observations of classical novae show that these objects are associated with substantial dust shells. The time variability of novae makes them ideal candidates for time-dependent modeling. Past models of nucleation and grain growth in novae have not successfully reproduced the grain sizes observed in these objects. The interplay of the harsh radiation field, density inhomogeneities in the ejecta, and the photochemistry of small carbonaceous molecules in determining the grain formation rate is still not well understood. We have applied the kinetic nucleation theory to study the formation and growth of dust grains in the nova environment. Grain formation is modeled using kinetic equations for small cluster growth coupled to moments of the grain size distribution to determine the growth of larger particles. We consider the effects of photodissociation and sticking probability. The dust formation stage of the novae outflow produces a blackbody spectrum which can be u...
The National Computational Science Institute: Computational Astronomy for Astronomy Educators
The mission of the National Computational Science Institute is to improve science, math, engineer... more The mission of the National Computational Science Institute is to improve science, math, engineering, and technology education at all levels by training undergraduate faculty in the use of computational science as a means of increasing inquiry based learning in their classrooms. Formed in the summer of 2001, NCSI plans to sponsor faculty workshops and produce online material to assist educators in all areas of SMET, including astronomy. NCSI is an extension of a National Science Foundation Undergraduate Faculty Enhancement program, the Shodor Computational Science Institute, which ran summer workshops in North Carolina for educators in the southeastern United States from 1998-2001. NCSI is currently seeking NSF funding to increase its efforts throughout the US. One program in development by NCSI is an online course entitled Computational Astronomy for Astronomy Educators, which will focus on the needs of introductory undergraduate and pre-college astronomy courses.
Novae vary in their visible luminosity by orders of magnitude over a period of months to a few ye... more Novae vary in their visible luminosity by orders of magnitude over a period of months to a few years, and often show the occurrence of a large dip in their visible light, associated with the growth of carbon dust grains. Previous models have had difficulty simultaneously matching observed optical depths, grain sizes, temperatures, formation times, and infrared reradiation. This thesis will test the hypothesis that the presence of hydrogen on small carbon molecules improves the accuracy of a kinetic model applied to grain formation in novae. A kinetic model with photodissociation limited by hydrogenation of carbon molecules is implemented, including line of sight effects due to density inhomogeneities in the outflow. Also, a comparison of the methods of binning and of taking moments of the kinetic equations is made. The bin and moment methods are found to both be capable of reproducing the results of a set of kinetic equations, and the relative efficiency of each method differs depen...
A CONSISTENT ORBITAL STABILITY ANALYSIS FOR THE GJ 581 SYSTEM
The Astrophysical Journal, 2014
ABSTRACT We apply a combination of N-body modeling techniques and automated data fitting with Mon... more ABSTRACT We apply a combination of N-body modeling techniques and automated data fitting with Monte Carlo Markov Chain uncertainty analysis of Keplerian orbital models to radial velocity data to determine long term stability of the planetary system GJ 581. We find that while there are stability concerns with the 4-planet model as published by Forveille et al. (2011), when uncertainties in the system are accounted for, particularly stellar jitter, the hypothesis that the 4-planet model is gravitationally unstable is not statistically significant. Additionally, the system including proposed planet g by Vogt et al. (2012) also shows some stability concerns when eccentricities are allowed to float in the orbital fit, yet when uncertainties are included in the analysis the system including planet g also can not be proven to be unstable. We present revised reduced chi-squared values for Keplerian astrocentric orbital fits assuming 4-planet and 5-planet models for GJ~581 under the condition that best fits must be stable, and find no distinguishable difference by including planet g in the model. Additionally we present revised orbital element estimates for each assuming uncertainties due to stellar jitter under the constraint of the system being gravitationally stable.
Scaffolding the infrastructure of the computational science digital library
Proceedings of the 6th ACM/IEEE-CS joint conference on Digital libraries - JCDL '06, 2006
... Science Digital Library Diana Tanase Shodor Education Foundation 60 Forty Avenue London, UK, ... more ... Science Digital Library Diana Tanase Shodor Education Foundation 60 Forty Avenue London, UK, HA9 8LQ 44-7960-221124 diana@shodor.org Michael Bruce Ohio Supercomputer Center 1224 Kinnear Road Columbus, Ohio, 43212 614-292-9248 mbruce@osc.edu ...
Teaching parallel computing to science faculty
Proceedings of the eleventh ACM SIGPLAN symposium on Principles and practice of parallel programming - PPoPP '06, 2006
... Paul Gray University of Northern Iowa 1227 West 27th St Cedar Falls, IA 50614 1-319-273-5917 ... more ... Paul Gray University of Northern Iowa 1227 West 27th St Cedar Falls, IA 50614 1-319-273-5917 gray@cs.uni.edu ... In each of the NCSI workshops, Computational Science and Engineering (CSE) is presented in the context of its use in Science, Technology, Engineering, and ...
Proceedings of the 5th ACM/IEEE-CS joint conference on Digital libraries - JCDL '05, 2005
We propose to address the issue of quality of digital library objects in the Computational Scienc... more We propose to address the issue of quality of digital library objects in the Computational Science Education Reference Desk by applying a verification, validation, and accreditation workflow to the review of learning objects.
19th IEEE International Parallel and Distributed Processing Symposium
This paper confronts the issue of bringing high performance computing (HPC) education to those wh... more This paper confronts the issue of bringing high performance computing (HPC) education to those who do not have access to a dedicated clustering environments in an easy, fully-functional, inexpensive manner through the use of the "Bootable Cluster CD" (BCCD). As an example, many primarily undergraduate institutions (PUI's) do not have the facilities, time, or money to purchase hardware, maintain user accounts, configure software components, and keep ahead of the latest security advisories for a dedicated clustering environment. The BCCD project's primary goal is to support an instantaneous, drop-in distributed computing environment. A consequence of providing such an environment is the ability to promote the education of high performance computing issues at the undergraduate level through the ability to turn an ordinary lab of networked workstations temporarily into a non-invasive, fully-functional clustering classroom. The BCCD itself is a self-contained clustering environment in a bootable CD format. Using the BCCD, students, educators and researchers are able to gain insight into configuration, utilization, troubleshooting, debugging, and administration issues uniquely associated with parallel computing in a live, easy to use "drop-in" clustering environment. As the name implies, the BCCD provides a full, cohesive clustering environment running GNU/Linux when booted from the CDROM drives of networked workstations.
Incorporating computational science activities in high school algebra
Proceedings of the 6th ACM/IEEE-CS joint conference on Digital libraries - JCDL '06, 2006
ABSTRACT Despite great increases in the role of computation in Science, Technology, Engineering a... more ABSTRACT Despite great increases in the role of computation in Science, Technology, Engineering and Mathematics (STEM), there has been no comprehensive curriculum for computational science in K-12 education [5]. The June 2005 President's Information Technology Advisory Committee (PITAC) report stated that "only a small fraction of the potential of computational science is being realized", and "the diverse technical skills and technologies ... constitute a critical U.S. infrastructure that we under appreciate and undervalue at our peril [4]." Despite a growing focus on STEM education, a substantial shortage exists of Americans qualified to work in STEM professions, including scientific research [1]. Progress in training computational scientists is lagging demand in the U.S. today. As this decade is seeing growth in the number of graduate, undergraduate, and teacher training programs in computational science [7], it is vital that the curriculum and materials to infuse computation into K-12 schools are made avail.Previous studies have shown how interactive learning objects can be incorporated into teaching, allowing teachers to make classrooms more engaging and student active, provided faculty using the resources have adequate training, a willingness to modify their teaching styles, and access to or time to create quality interactive assignments [6]. The Computational Science Education Reference Desk (CSERD), a Pathway project of the National Science Digital Library, collects learning objects for teaching about and teaching with computation, reviewing items in its catalog on the basis of verification, validation, and accreditation to help provide faculty with information regarding the quality of the learning objects [3].This study attempts to determine the effectiveness of a set of interactive learning materials from the CSERD collection in teaching concepts in a freshman Algebra I class. Materials from the CSERD resource Project Interactivate [2] will be used in a series of 4 lessons through February and March 2006 at a parochial school in Northeastern New Jersey. Students will take a pre- and post-test on topics covered in this period. Students and teachers will be surveyed to determine their attitudes towards the use of computation in learning and towards mathematics in general. Additionally, students will submit a daily feedback statement after each augmented lesson.
Proceedings of the 2010 TeraGrid Conference on - TG '10, 2010
... Skylar Thompson Genome Sciences Department University of Washington Seattle, WA 98195skylar@c... more ... Skylar Thompson Genome Sciences Department University of Washington Seattle, WA 98195skylar@cs.earlham.edu ... 2.1 Workshop Content The general format of the workshops is to start on Sun-day evening, with introductory presentations and a tour of the local HPC facility if ...
The Astrophysical Journal, 2003
To study the dependence of scattering-induced polarization on source properties in reflection neb... more To study the dependence of scattering-induced polarization on source properties in reflection nebulae and circumstellar envelopes, the transport of polarized radiation in a dusty medium is solved for spherical geometry with spherical dust grains. The Stokes parameters for linear polarization are calculated by iterating between a short characteristic solution of the linear ray equations that determines the angular distribution of the radiation field and a numerical integration of the scattering kernel. The combined moment equation is used to determine the mean intensities, which are used to improve the iteration process. The scattering phase matrix is calculated for non-Rayleigh (Mie) scattering in a model circumstellar dust shell using a sum over Fourier coefficients and general spherical functions. Specific intensity is calculated for a resolved source, from which polarization maps are constructed, and the variance of polarization with properties of the dust and of the circumstellar shell is studied. Polarization in the near-IR, visible, and UV is ubiquitous for all models in this study and should be observable in any marginally resolved source, even for a beam size as large as onefourth the source size. The critical wavelength c at which polarization remains significant in the infrared is related to the grain albedo ! and dust temperature T d by log ! c ð Þ ½ / c T d ð Þ À1 . For models applicable to circumstellar shells of asymptotic giant branch stars, this wavelength ranges from 1 to 5 lm. In general, c increases with the dust shell opacity, grain size, and albedo. Although c is insensitive to the dust density distribution and the ambient interstellar radiation field, the polarization spectrum and peak polarization depend strongly on these parameters. To test the realism of our models, a model is constructed for a source similar to IRC +10216. The results are found to be consistent with available observations.
Computational Science Educational Reference Desk
D-Lib Magazine, 2006
The Computational Science Education Reference Desk (CSERD) is a portal to the National Science Di... more The Computational Science Education Reference Desk (CSERD) is a portal to the National Science Digital Library (NSDL) that opens its virtual shelves to those interested in educational resources for computational science. If one wants to find trustworthy resources on the behavior of ...
Applications of Computational Science: Data-Intensive Computing for Student Projects
Computing in Science & Engineering, 2000
A research course for juniors and seniors has been designed to offer students a chance to work wi... more A research course for juniors and seniors has been designed to offer students a chance to work with the tools of computational science for large, data-intensive computations on publicly available datasets.
Reaching future computer scientists
Communications of the ACM, 2011
ABSTRACT Think teachers, not students.
Journal of Computing Sciences in …, 2010
N-body Stability Analysis of Gliese 581
ABSTRACT We present N-body stability analysis results of a 4 planet model of Gliese 581. We find ... more ABSTRACT We present N-body stability analysis results of a 4 planet model of Gliese 581. We find that previously published values by Forveille et. al. (2011) of the eccentricity of GJ 581 E lead to a system that is dynamically unstable. Limitations are placed on the range of eccentricities that would allow for a stable system, such that eccentricities much higher than 0.1 to 0.15 for GJ 581 E are unlikely. Simulation results are performed using the hybrid symplectic integrator code Mercury for 10 Myrs and a timestep of 0.1 days. Additionally, the effect of the inclination of the orbit on limitations on eccentricity and stability results of proposed 5 and 6 planet systems will also be discussed.
American Journal of Physics, 2008
The increase in availability of open source research quality simulation software coupled with a r... more The increase in availability of open source research quality simulation software coupled with a reduction in barriers to high performance computer hardware access and new methods for adding interactivity to server-side web services have created a rich environment for the development of supercomputer based laboratories to augment the many personal computer based activities currently in use in the physics classroom. An exemplary supercomputer based laboratory is presented using the N-body problem applied to galactic structure.
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Papers by David A. Joiner