Page Not Found
Page not found. Your pixels are in another canvas.
Sitemap
A list of all the posts and pages found on the site. For you robots out there is an XML version available for digesting as well.
Pages
About Me
About me
Page not in menu
This is a page not in th emain menu
Posts
Future Blog Post
Published:
This post will show up by default. To disable scheduling of future posts, edit config.yml and set future: false.
Blog Post number 4
Published:
This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.
Blog Post number 3
Published:
This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.
Blog Post number 2
Published:
This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.
Blog Post number 1
Published:
This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.
portfolio
Portfolio item number 1
Short description of portfolio item number 1
Portfolio item number 2
Short description of portfolio item number 2
publications
Probing spatial variation of the fine-structure constant using the CMB
Published in Phys. Rev. D., 2019
This paper includes results from a summer research project that Davy Qi and I worked on with Tristan Smith at Swarthmore College, where we examined the effects of spatial variation of the fine-structure constant on the CMB.
Recommended citation: Smith, Tristan, Dan Grin, David Robinson, and Davy Qi. “Probing Spatial Variation of the Fine-Structure Constant Using the CMB.” Physical Review D 99.4 (2019). https://journals.aps.org/prd/abstract/10.1103/PhysRevD.99.043531
Can Cooling and Heating Functions Be Modeled with Homogeneous Radiation Fields?
Published in ApJ, 2022
We explore the cooling and heating functions of Epoch of Reionization galaxies from the Cosmic Reionization on Computers (CROC) project. We find that the actual cooling and heating rates of CROC galaxies cannot be adequately described by assuming a spatially homogeneous radiation field.
Recommended citation: Robinson, David, Camille Avestruz, and Nickolay Y. Gnedin. “Can Cooling and Heating Functions be Modeled with Homogeneous Radiation Fields?” ApJ 936 50 (2022). https://iopscience.iop.org/article/10.3847/1538-4357/ac85e1
Exploring the dependence of gas cooling and heating functions on the incident radiation field with Machine Learning
Published in MNRAS, 2024
In this paper, we use the machine learning algorithm XGBoost to approximate cooling and heating functions with a general incident radiation field calculated with CLOUDY. We are able to reduce the frequency of large prediction errors compared to interpolation table approaches. We also use feature importance techniques to explore what aspects of the incident radiation field most strongly affect the cooling and heating functions.
Recommended citation: Robinson, David, Camille Avestruz, and Nickolay Y. Gnedin. “Exploring the Dependence of Gas Cooling and Heating Functions on the Incident Radiation Field with Machine Learning.” MNRAS 528 1 (2024). https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stad3880/7478000
Emergence of the temperature-density relation in the low-density intergalactic medium
Published in MNRAS, 2024
In this paper, we explore the evolution of the phase diagram of low-density gas in the intergalactic medium in four different simulated boxes from the Cosmic Reionization on Computers (CROC) project. We show that the evolution of the fraction of cold gas is approximately universal across the four different reionization histories, when parameterized by the hydrogen neutral fraction. We also explore the emergence of a tight temperature-density relationship through the decreasing width of the scatter around a power-law relationship. This decrease in width is also a nearly universal function of the neutral fraction.
Recommended citation: Wells, Alexandra, David Robinson, Camille Avestruz, and Nickolay Y Gnedin. "Emergence of the temperature–density relation in the low-density intergalactic medium." MNRAS 528 4 (2024). https://academic.oup.com/mnras/article/528/4/5845/7602414
On the minimum number of radiation field parameters to specify gas cooling and heating functions
Published in OJA (in revision), 2024
In this paper, we modify our previous implementation of XGBoost to approximate atomic gas cooling and heating functions. We now use radiation field intensity averaged in various energy bins to describe the incident radiation field (instead of photoionization rates). We use feature importance tools to find the most important energy bins for predicting cooling and heating functions. We find that a sample of only 3 energy bins (or photoionization rates) are sufficient to accurately interpolate atomic gas cooling and heating functions at fixed metallicity.
Recommended citation: Robinson, David, Camille Avestruz, and Nickolay Y. Gnedin. “On the minimum number of radiation field parameters to specify gas cooling and heating functions.” arXiv:2406.19446 (2024). https://arxiv.org/abs/2406.19446
The effects of different cooling and heating function models on a simulated analog of NGC300
Published in OJA (submitted), 2024
In this paper, we incorporate our machine learning approximation for gas cooling and heating functions into a hydrodynamic isolated galaxy simulation. We compare the gas thermodynamics across two runs of the simulation: one using our machine learning models to compute the atomic gas cooling and heating functions, and one using an interpolation table. We find that our machine learning model predicts systematically hotter low-density gas.
Recommended citation: Robinson, David, Camille Avestruz, Nickolay Y. Gnedin, and Vadim A. Semenov. “The effects of different cooling and heating function models on a simulated analog of NGC300.” arXiv:2412.15324 (2024). https://arxiv.org/abs/2412.15324
Cosmic Reionization on Computers: Statistical Properties of the Distributions of Mean Opacities
Published in OJA (in prep), 2025
In this paper, we explore the distribution of Lyman alpha optical depth along simulated quasar sightlines in the Cosmic Reionization on Computers (CROC) simulations. We compare the cumulative distribution function (CDF) of optical depths to observations, subsampling the simulated sightlines appropriately. We quantify the variance in the simulated CDFs due to this subsampling.
Recommended citation: Werre, Ella, David Robinson, Camille Avestruz, and Nickolay Y. Gnedin. "Cosmic Reionization on Computers: Statistical Properties of the Distributions of Mean Opacities". OJA 2025 (in prep). TBA
talks
The dependence of cooling and heating functions on local radiation fields
Published:
Abstract: Cooling and heating functions determine the thermal pressure support of gas clouds and the energy budget of gas. These functions are a key component in how gas clouds collapse to form stars and subsequently galaxies. The radiative transfer physics underlying cooling and heating functions is known but is too computationally expensive to include in hydrodynamic simulations for realistic local radiation fields within galactic halos. Hence, a fast approximation to the dependence on the incident radiation field is needed to include local effects. We first discuss results from an existing approximation to heating and cooling functions in a simulation from the Cosmic Reionization on Computers project. We find that the simulated gas thermodynamics cannot be adequately described by functions computed with a spatially constant radiation field. We also discuss ongoing work using machine learning to investigate what wavelength bands of the radiation field most strongly affect cooling and heating functions.
The dependence of cooling and heating functions on local radiation fields
Published:
Abstract: Cooling and heating functions of gas determine its energy budget and the thermal pressure support it can provide. These functions are thus a key ingredient in the physics that control how stars and galaxies form. The radiative transfer physics shaping cooling and heating functions is known, but is too computationally expensive to include in hydrodynamic simulations for realistic local radiation fields within galactic halos. Instead, a fast approximation scheme is needed. We use machine learning to investigate which wavelength bands of the radiation field most strongly affect cooling and heating functions. We use these results to develop more accurate approximation schemes to cooling and heating functions in the presence of a local radiation field.
Exploring the Dependence of Gas Cooling and Heating Functions on the Incident Radiation Field with Machine Learning
Published:
Abstract: Gas cooling and heating functions control gas thermodynamics and play a crucial role in galaxy formation. These functions depend on both gas properties (temperature, density, metallicity) and the incident radiation field. While they can be computed exactly with photoionization codes, this is computationally expensive and impractical to do on-the-fly in hydrodynamic simulations. As an alternative to interpolation tables of pre-computed values, we explore the capacity of machine learning to approximate cooling and heating functions with a generalized radiation field. Specifically, we use the machine learning algorithm XGBoost to predict cooling and heating functions calculated with the photoionization code Cloudy at fixed metallicity, using different combinations of photoionization rates as features. Our XGBoost models outperform a traditional interpolation approach at each fixed metallicity, regardless of feature selection. At arbitrary metallicity, we are able to reduce the frequency of the largest cooling and heating function errors compared to an interpolation table. We find that the primary bottleneck to increasing accuracy lies in accurately capturing the metallicity dependence.
teaching
Physics 141: Elementary Lab 1
Undergraduate lab, University of Michigan, LSA Physics, 2019
Graduate Student Instructor (GSI) for 2 sections (Fall 2019) and 4 sections (Winter 2021, virtual) of an introductory mechanics lab for scientists and engineers. Gave a five-minute introductory lecture on each week’s lab, guided groups of 2-3 students through completing the experiment and filling out a lab template (Excel sheets and Jupyter notebooks), and graded each group’s completed lab sheets. In Fall 2019, I also wrote weekly five-minute quizzes with multiple choice and short answers questions on the content of that week’s lab manual.
Physics 236: Life Sciences Lab II
Undergraduate lab, University of Michigan, LSA Physics, 2020
Graduate Student Instructor (GSI) for 2 sections of an introductory electromagnetism lab for life sciences students in Winter 2020. Gave a five-minute introductory lecture on each week’s lab, guided groups of 2-3 students through completing the experiment and filling out a lab template (Excel sheets), and graded each group’s completed lab sheets.
Astronomy 107: The Dark Side of the Universe
Undergraduate course, University of Michigan, LSA Astronomy, 2020
Graduate Student Instructor (GSI) for 4 sections of a virtual, asynchronous half-semester survey course on dark energy, dark matter, and black holes (2 sections each half-semester) in Fall 2020. I held weekly office hours, and graded student papers (2 page creative assignments on each of the three topics), as well as short-answer questions on quizzes and optional extra credit mathematical problems.
Physics 360: Waves, Heat, and Light
Undergraduate course, University of Michigan, LSA Physics, 2021
Graduate Student Instructor (GSI) for the honors version of the third course in the introductory physics sequence, covering special relativity, thermodynamics (with some statistical mechanics), and waves in Fall 2021 and Winter 2022. I led two weekly discussion sections (50 minutes each), where students worked in small groups on worksheets covering problems related to the topics covered in class. I provided a short introduction to the topics on the worksheet, helped individual groups with questions, and then went over the solutions to the worksheet problems at the end of the section. I also graded the weekly problem sets, as well as some short-answer questions on weekly quizzes.
Physics 391: Introduction to Modern Physics Lab
Undergraduate lab, University of Michigan, LSA Physics, 2024
Graduate Student Instructor (GSI) for 2 sections of a sophomore-level modern physics lab in Winter 2024. I assisted the professor with helping groups of 2 students work through each experiment, held weekly office hours for student questions about the data analysis and report components, and (for one section) graded the students’ data analysis codes for each lab.