Physical Sciences and Mathematics Commons^™

Interpreting An Archaean Paleoenvironment Through 3d Imagery Of Microbialites, Cecilia M. Howard, Nathan D. Sheldon, Selena Y. Smith, Nora Noffke

OES Faculty Publications

While stromatolites, and to a lesser extent thrombolites, have been extensively studied in order to unravel Precambrian (>539 Ma) biological evolution, studies of clastic-dominated microbially induced sedimentary structures (MISS) are relatively scarce. The lack of a consolidated record of clastic microbialites creates questions about how much (and what) information on depositional and taphonomic settings can be gleaned from these fossils. We used μCT scanning, a non-destructive X-ray-based 3D imaging method, to reconstruct morphologies of ancient MISS and mat textures in two previously described coastal Archaean samples from the ~3.48 Ga Dresser Formation, Pilbara, Western Australia. The aim of this …

Heterogeneity Of Nitrogen Fixation In The Mesopelagic Zone Of The South China Sea, Siqi Wu, Xianhui Sean Wan, Moge Du, Xirong Chen, Corday R. Selden, Mar Benavides, Sophie Bonnet, Carolin R. Löscher, M. Robert Hamersley, Margaret R. Mulholland, Xiuli Yan, Shuh-Ji Kao

OES Faculty Publications

Biological dinitrogen (N₂) fixation, the energetically expensive conversion of N₂ gas to ammonia, plays an essential role in balancing the nitrogen budget in the ocean. Accumulating studies show detectable N₂ fixation rates below the euphotic zone in various marine systems, revealing new insights of marine N₂ fixation. However, the reported rates are highly variable and frequently fall close to detection limits, raising the question of the ubiquity and significance of N₂ fixation in the global dark ocean. Using highly sensitive isotopic labeling incubation including a set of control incubations, we confirm the occurrence of mesopelagic N₂ fixation in the South …

Marine Emissions Of Methanethiol Increase Aerosol Cooling In The Southern Ocean, Charel Wohl, Julián Villamayor, Martí Galí, Anoop S. Mahajan, Rafael P. Fernández, Carlos A. Cuevas, Adriana Bossolasco, Qinyi Li, Anthony J. Kettle, Tara Williams, Roland Sarda-Esteve, Valérie Gros, Rafel Simó, Alfonso Saiz-Lopez

OES Faculty Publications

Ocean-emitted dimethyl sulfide (DMS) is a major source of climate-cooling aerosols. However, most of the marine biogenic sulfur cycling is not routed to DMS but to methanethiol (MeSH), another volatile whose reactivity has hitherto hampered measurements. Therefore, the global emissions and climate impact of MeSH remain unexplored. We compiled a database of seawater MeSH concentrations, identified their statistical predictors, and produced monthly fields of global marine MeSH emissions adding to DMS emissions. Implemented into a global chemistry-climate model, MeSH emissions increase the sulfate aerosol burden by 30 to 70% over the Southern Ocean and enhance the aerosol cooling effect while …

Governing Dynamic Watersheds Under Static Institutions – Examining How Local Governments Respond To Floods And Droughts In The United States, Jonathon R. Loos

Dartmouth College Ph.D Dissertations

The U.S. has seen a shift towards decentralized watershed governance in recent decades that has increased the delegation of management responsibilities to local governments and community organizations. This shift has precipitated the emergence of multilevel watershed governance systems (e.g. national, state, regional, local management levels) that are hypothesized to be more adaptive and responsive to local needs. However, multilevel governance systems risk complicating and overburdening the role of local governments within watershed management, and little is known about how local governments address socio-ecological change within multilevel institutions. Working within several U.S. watershed geographies, this dissertation seeks to interrogate theories of …

Consistent Monte Carlo Methods For Non-Linear Applications In Light Transport, Zackary T. Misso

Dartmouth College Ph.D Dissertations

The study of light transport focuses on describing the propagation of light from emitters to sensors through accurately describing the interactions light can undergo with everything in between. Physically-based rendering is the process of applying the laws of light transport to formulate practical algorithms which simulate the flow of light for the purpose of synthesizing images of virtual environments.

Unfortunately, there are very few interesting scene configurations which can be computed analytically. Instead, modern solutions predominantly rely on Monte Carlo integration to stochastically estimate the transfer of light since the process is both unbiased and consistent. Meaning, it is expected …

Mitigating Safety Issues In Pre-Trained Language Models: A Model-Centric Approach Leveraging Interpretation Methods, Weicheng Ma

Dartmouth College Ph.D Dissertations

Pre-trained language models (PLMs), like GPT-4, which powers ChatGPT, face various safety issues, including biased responses and a lack of alignment with users' backgrounds and expectations. These problems threaten their sociability and public application. Present strategies for addressing these safety concerns primarily involve data-driven approaches, requiring extensive human effort in data annotation and substantial training resources. Research indicates that the nature of these safety issues evolves over time, necessitating continual updates to data and model re-training—an approach that is both resource-intensive and time-consuming. This thesis introduces a novel, model-centric strategy for understanding and mitigating the safety issues of PLMs by …

Scalable Methods For Resource-Constrained Adaptive Sampling, Kizito Masaba

Dartmouth College Ph.D Dissertations

As the global community confronts the pressing issues of climate change, the importance of environment monitoring cannot be overstated. This process is essential in identifying and tracking critical environmental trends to facilitate efficient and effective conservation efforts. Traditionally, scientists perform this task using hand-held, in-situ instruments. With the recent robot advancements, this task can be fully automated by applying multi-robot systems to a task referred to as multi-robot adaptive sampling. However, the cost of purchasing and operating robot systems for this application are still prohibitive due to various environmental, technological, and logistical constraints. Some of the outstanding constraints to the …

Leveraging Uncertainty To Understand The Causes And Consequences Of Observed Climate Change, Alexander Reid Gottlieb

Dartmouth College Ph.D Dissertations

Detecting and attributing climate change to date is essential to understanding the harm global warming has caused and the threat it poses in the future. Yet detecting and attributing historical climate change and its attendant impacts is challenging owing to observational uncertainties in the historical record, the difficulty of isolating the forced response from unforced variability, and the methodological ambiguity on how to best map climate variability and change onto climate impacts. In this thesis, I use the study system of Northern Hemisphere snow to demonstrate how synthesizing a wide array of observational and climate model data with methods from …

An Early Byzantine Ecclesiastical Complex At Ashdod-Yam: Correlating Geophysical Prospection With Excavated Remains, Yaniv Darvasi, Alexander Fantalkin, Paul Brindza, Amotz Agnon

Physics Faculty Publications

In this study we show the successful deployment of Ground Penetrating Radar (GPR) together with Electrical Resistivity Surveys (ERS) in guiding the archeological excavations at Ashdod-Yam (southern coast of Israel). This approach enabled the precise identification of excavation targets relating to an Early Byzantine ecclesiastical complex located in a residential neighborhood of the modern city of Ashdod. Applied over the course of five years, the combined use of GPR and ERS, interspersed with phases of archeological excavation, not only facilitated an efficient exploration but also ensured the preservation of valuable historical structures. The geophysical data, corroborated by drone images of …

Shock-Discharge Interaction Model Extended Into The Third Dimension, Anna Markhotok

Physics Faculty Publications

This work is an addition to the previously developed two-dimensional model of the shock-plasma interaction, extending it into the third dimension. The model can trace the evolution of the state of the hypersonic flow and the shock front refracted at a thermal discontinuity. The advantages of using the spherical coordinate system for this type of problem include increased transparency in interpreting the solution and a shortened calculation procedure, because all the changes to the front are reduced to one distortion component. Although the vorticity generation triggered at the interface is a consequence of the refraction and tied to the steep …

Investigation Of Hot-Spots Due To Trapped Flux In Niobium Superconducting Radiofrequency Cavities, B. Khanal, P. Dhakal

Physics Faculty Publications

One of the significant sources of residual losses in superconducting radio-frequency cavities is magnetic flux trapped during the cool-down due to the incomplete Messier effect. If the trapped vortices are non-uniformly distributed on the cavity surface, the temperature mapping revealed the “hot-spots” at the location of high density of pinned vortices. Here, we performed a rf test on 1.3 GHz single cell cavity with the combination of the temperature mapping system. The temperature mapping reveled the development of the hot spots with the increase in rf field inside the cavity. When magnetic field is trapped locally on the surface of …

Novel Measurement Of The Neutron Magnetic Form Factor From A=3 Mirror Nuclei, S. N. Sentiesteban, S. Li, D. Abrams, S. Alsalmi, D. Androic, K. Aniol, J. Arrington, T. Averett, C. Ayerbe Gayoso, J. Bane, S. Barcus, J. Barrow, A. Beck, V. Bellini, H. Bhatt, D. Bhetuwal, D. Biswas, A. Camsonne, J. Castellanos, J. Chen, J. P. Chen, D. Chrisman, M. E. Christy, C. Clarke, S. Covrig, R. Cruz-Torres, D. Day, D. Dutta, E. Fuchey, C. Gal, F. Garibaldi, T. N. Gautam, T. Gogami, J. Gomez, P. Guèye, T. J. Hague, J. O. Hansen, F. Hauenstein, W. Henry, D. W. Higinbotham, R. J. Holt, C. Hyde, K. Itabashi, M. Kaneta, A. Karki, A. T. Katramatou, C. E. Keppel, P. M. King, L. Kurbany, T. Kutz, N. Lashley-Colthirst, W. B. Li, H. Liu, N. Liyange, E. Long, A. Lovato, J. Mammei, P. Markowitz, R. E. Mcclellan, F. Meddi, D. Meekins, R. Michaels, M. Mihovilovič, A. Moyer, S. Nagao, D. Nguyen, M. Nycz, M. Olson, L. Ou, V. Owen, C. Palatchi, B. Pandey, A. Papadopoulou, S. Park, T. Petkovic, S. Premathilake, V. Punjabi, R. D. Ransome, P. E. Reimer, J. Reinhold, S. Riordan, N. Rocco, V.M. Rodriguez, A. Schmidt, B. Schmookler, E. P. Segarra, A. Shahinyan, S. Širca, K. Slifer, P. Solvignon, T. Su, R. Suleiman, L. Tang, Y. Tian, W. Tireman, F. Tortorici, Y. Toyama, K Uehara, G. M. Urciuoli, D. Votaw, J. Williamson, B. Wojtsekhowski, S. Wood, Z. H. Ye, J. Zhang, X. Zheng

Physics Faculty Publications

The electromagnetic form factors of the proton and neutron encode information on the spatial structure of their charge and magnetization distributions. While measurements of the proton are relatively straightforward, the lack of a free neutron target makes measurements of the neutron’s electromagnetic structure more challenging and more sensitive to experimental or model-dependent uncertainties. Various experiments have attempted to extract the neutron form factors from scattering from the neutron in deuterium, with different techniques providing different, and sometimes large, systematic uncertainties. We present results from a novel measurement of the neutron magnetic form factor using quasielastic scattering from the mirror nuclei …

Evolution Of Efimov States, Sebastian M. Dawid, Md Habib E. Islam, Raúl A. Briceño, Andrew W. Jackura

Physics Faculty Publications

The Efimov phenomenon manifests itself as an emergent discrete scaling symmetry in the quantum three-body problem. In the unitarity limit, it leads to an infinite tower of three-body bound states with energies forming a geometric sequence. In this work, we study the evolution of these so-called Efimov states using relativistic scattering theory. We identify them as poles of the three-particle 𝑆 matrix in the complex energy plane, and we study how they transform from virtual states through bound states to resonances when we change the interaction strength. We dial the scattering parameters toward the unitarity limit and observe the emergence …

A Formalism For Extracting Track Functions From Jet Measurements, Kyle Lee, Ian Moult, Felix Ringer, Wouter J. Waalewijn

Physics Faculty Publications

The continued success of the jet substructure program will require widespread use of tracking information to enable increasingly precise measurements of a broader class of observables. The recent reformulation of jet substructure in terms of energy correlators has simplified the incorporation of universal non-perturbative matrix elements, so called “track functions”, in jet substructure calculations. These advances make it timely to understand how these universal non-perturbative functions can be extracted from hadron collider data, which is complicated by the use jet algorithms. In this paper we introduce a new class of jet functions, which we call (semi-inclusive) track jet functions, which …

Understanding Sextupole, T. Zolkin, I. Morozov, S. Nagaitsev

Physics Faculty Publications

In this study, we reassess the dynamics within a simple accelerator lattice featuring a single degree of freedom and incorporating a sextupole magnet. In the initial segment, we revisit the Hénon quadratic map, a representation of a general transformation with quadratic nonlinearity. In the subsequent section, we unveil that a conventional sextupole is essentially a composite structure, comprising an integrable McMillan sextupole and octupole, along with non-integrable corrections of higher orders. This fresh perspective sheds light on the fundamental nature of the sextupole magnet, providing a more nuanced understanding of its far-from-trivial chaotic dynamics. Importantly, it enables the description of …

Particle Accelerator Spin-Transparent Storage Rings For Beyond State-Of-The-Art Science, R. Suleiman, Y. Derbenev, M. Grau, V. Morozov

Physics Faculty Publications

We will describe spin-transparent storage rings that exhibit spin-coherence times of several hours and store a large number of particles and their use in novel applications. For example, these rings can be used to directly measure the electric dipole moment of the electron, relevant to CP violation and matter-antimatter asymmetry in the universe, and to search for dark energy and ultra-light dark matter*. These rings can also serve as a compelling platform for quantum computing. In this presentation, we will describe how spin-transparent rings can be used in conjunction with ion traps to enhance scalability and increase quantum coherence times …

1/Q² Power Corrections To Tmd Factorization For Drell-Yan Hadronic Tensor, I. Balitsky

Physics Faculty Publications

I calculate 1/Q² power corrections to unpolarized Drell-Yan hadronic tensor for electromagnetic (EM) current at large N-c and demonstrate the EM gauge invariance at this level.

Analytic Solutions Of The Dglap Evolution And Theoretical Uncertainties, A. Simonelli

Physics Faculty Publications

The energy dependence for the singlet sector of Parton Distributions Functions (PDFs) is described by an entangled pair of ordinary linear differential equations. Although there are no exact analytic solutions, it is possible to provide approximated results depending on the assumptions and the methodology adopted. These results differ in their sub-leading, neglected terms and ultimately they are associated with different treatments of the theoretical uncertainties. In this work, a novel analytic approach in Mellin space is presented and a new methodology for obtaining closed and exponentiated analytic solutions is devised. Different results for the DGLAP evolution at Next-Leading-Order are compared, …

Towards Unpolarized Gpds From Pseudo-Distributions, Hervé Dutrieux, Robert G. Edwards, Colin Egerer, Joseph Karpie, Christopher Monahan, Kostas Orginos, Anatoly Radyushkin, David Richards, Eloy Romero, Savvas Zafeiropoulos

Physics Faculty Publications

We present an exploration of the unpolarized isovector proton generalized parton distributions (GPDs) H^u−d(x, ξ, t) and E^u−d(x, ξ, t) in the pseudo-distribution formalism using distillation. Taking advantage of the large kinematic coverage made possible by this approach, we present results on the moments of GPDs up to the order x³ — including their skewness dependence — at a pion mass m_π = 358 MeV and a lattice spacing a = 0.094 fm.

Hubble Tension And Gravitational Self-Interaction, Corey Sargent, William Clark, Alexander Deur, Balša Terzić

Physics Faculty Publications

One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g. the Type IA supernova, tend to yield larger values than measurements from quantities originating at high-redshift, e.g. fits of cosmic microwave background radiation. It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements. Here we explore whether the self-interaction of gravitational fields in General Relativity, which are traditionally neglected when studying the evolution …

Non-Symmetry In The Shock Refraction At A Closed Interface As A Recovery Mechanism, Anna Markhotok

Physics Faculty Publications

The possibility of a shock wave recovery at a discrete closed interface with a heated gas has been investigated. A two-dimensional model applied to conditions of optical discharges featuring spherical, elliptical, and drop-like configurations demonstrated that non-symmetry in the shock refraction contributes to the specific mechanism of recovery other than simply its compensation. Even though the full restoration of the hypersonic flow state does not occur in a strict sense of it, clear reverse changes toward the initial shape of the shock front eventually take place, thus creating an appearance of a full recovery seen in experiments. From analysis of …

Proof Of Principle For A Self-Governing Prediction And Forecasting Reward Algorithm, Jose Osvaldo Gonzalez-Hernandez, Jonathan Marino, Ted Rogers, Brandon Velasco

Physics Faculty Publications

We use Monte Carlo techniques to simulate an organized prediction competition between a group of scientific experts acting under the influence of a "self-governing" prediction reward algorithm. Our aim is to illustrate the advantages of a specific type of reward distribution rule that is designed to address some of the limitations of traditional forecast scoring rules. The primary extension of this algorithm as compared with standard forecast scoring is that it incorporates measures of both group consensus and question relevance directly into the reward distribution algorithm. Our model of the prediction competition includes parameters that control both the level of …

The Discharge-Induced Polarity-Dependent Propagation Characteristics Of A Strong Shock Wave, Anna Markhotok

Physics Faculty Publications

The specifics of a shock wave propagation down a positive column of a DC discharge in molecular chemically inert gases has been investigated. It was shown that axial gradients caused by the imbalance in the charged particle momentum transfer to the gas molecules can be a reason for the shock velocity dependence on the electric field direction. In pure nitrogen gas, the calculated shock velocity difference of up to 13.5% is in good agreement with the 12% value obtained in the experiment. A returning gas flow organizing in the discharge as a possible mechanism for an extended shock structure and …

F₀(1370) And F₀(980) Controversies From Dispersive Data Analyses, Jose R. Pelaez, A. Rodas, J. Ruiz De Elvira

Physics Faculty Publications

We report on our recent works on dispersive analyses of ππ → ππ and ππ → K ¯ K scattering data and their use to address two controversial aspects of the f₀(1370) and f₀(980) scalar mesons. First, we show with model-independent techniques that the f₀(1370) pole does indeed appear in meson–meson scattering data, although there is tension between its values in the ππ and K ¯ K channels. Second, we explain the proper interpretation of the f₀(980) pole residue, which would otherwise lead to branching ratios larger than one. We have also provided simple ππ → ππ data parameterizations that …

Phenomenology Of Tmd Parton Distributions In Drell-Yan And Z⁰ Boson Production In A Hadron Structure Oriented Approach, F. Aslan, M. Boglione, J. O. Gonzalez-Hernandez, T. Rainaldi, T. C. Rogers, A. Simonelli

Physics Faculty Publications

We present a first practical implementation of a recently proposed hadron structure oriented (HSO) approach to transverse momentum dependent (TMD) phenomenology applied to Drell-Yan-like processes, including lepton pair production at moderate Q² and Z⁰ boson production. We compare and contrast general features of our methodology with other common practices and emphasize aspects that we view as improvements. Separately, we discuss the importance of treatments that preserve various theoretical properties of the nonperturbative parts of TMD parametrizations for future applications that have the extraction of hadron structure as a primary goal. These include the HSO’s preservation of a basic TMD parton-model-like …

New Spin Structure Constraints On Hyperfine Splitting And Proton Zemach Radius, David Ruth, Karl Slifer, Jian-Ping Chen, Carl E. Carlson, Franziska Hagelstein, Vladimir Pasculutsa, Alexandre Deur, Sebastian Kuhn, Marco Ripani, Xiaochao Zheng, Ryan Zielinski, Chao Gu

Physics Faculty Publications

The 1S hyperfine splitting in hydrogen is measured to an impressive ppt precision and will soon be measured to ppm precision in muonic hydrogen. The latter measurement will rely on theoretical predictions, which are limited by knowledge of the proton polarizability effect Δ_pol. Data-driven evaluations of Δ_pol have long been in significant tension with baryon chiral perturbation theory. Here we present improved results for Δ_pol driven by new spin structure data, reducing the long-standing tension between theory and experiment and halving the dominating uncertainty in hyperfine splitting calculations.

Fully Relativistic Derivation Of The Thermal Sunyaev-Zel'dovich Effect, Balša Terzić, Geoffrey A. Krafft, William Clark, Alexandre Deur, Emerson Rogers, Ioannis Sakiotis, Brandon Velasco

Physics Faculty Publications

We present the first fully and inherently relativistic derivation of the thermal Sunyaev-Zel'dovich effect. This work uses the formalism historically applied to compute radiation spectra emerging from inverse Thomson/Compton sources of x-ray radiation. Comparing our results to the traditional approach based on relativistically-corrected classical Kompaneets equation, we find small, but systematic differences. Most notable are the modest (⩽10%) differences in the crossover frequency where the spectral distortion due to the Sunyaev-Zel'dovich effect vanishes, and the quadratic scaling of the energy shift with the electron cloud temperatures.

Charge Lifetime Improvement Of The Continuous Electron Beam Accelerator Facility Photogun With A Biased Anode, J. T. Yoskowitz, G. A. Krafft, G. Palacios-Serrano, S.A.K. Wijethunga, J. Grames, J. Hansknecht, C. Hernandez-Garcia, M. Poelker, M. L. Stutzman, R. Suleiman, C. A. Valerio-Lizarraga, S. B. Van Der Geer

Physics Faculty Publications

GaAs photocathodes in dc high-voltage photoguns are highly susceptible to ion back-bombardment, which reduces the photocathode quantum efficiency and limits the useful operating lifetime for producing polarized electron beams. This paper demonstrates that applying a small positive bias to the photogun anode can significantly suppress ion back-bombardment and increase charge lifetime. This technique was studied extensively using the Continuous Electron Beam Accelerator Facility photogun, where highly polarized electron beams created using a strained-superlattice GaAs/GaAsP photocathode were used and charge lifetimes improved by almost a factor of 2. A new simulation code ionator was developed to model ion production and tracking …

Coulomb Confinement In The Hamiltonian Limit, Sebastian M. Dawid, Wyatt A. Smith, Arkaitz Rodas, Robert J. Perry, César Fernández-Ramírez, Eric S. Swanson, Adam P. Szczepaniak

Physics Faculty Publications

The Gribov-Zwanziger scenario attributes the phenomenon of confinement to the instantaneous interaction term in the QCD Hamiltonian in the Coulomb gauge. For a static quark-antiquark pair, it leads to a potential energy that increases linearly with the distance between them. Lattice studies of the SU(2) Yang-Mills theory determined the corresponding (Coulomb) string tension for sources in the fundamental representation, 𝜎_𝐶, to be about 3 times larger than the Wilson loop string tension, 𝜎_𝐹. It is far above the Zwanziger variational bound, 𝜎_𝐶 ≥𝜎_𝐹. We argue that the value often reported in the literature …

Counting Linearly Polarized Gluons With Lattice Qcd, Shuai Zhao

Physics Faculty Publications

We outline an approach to calculate the transverse-momentum-dependent distribution of linearly polarized gluons inside an unpolarized hadron on the lattice with the help of large momentum effective theory. To achieve this purpose, we propose calculating a Euclidean version of the degree of polarization for a fast-moving hadron on the lattice, which is ultraviolet finite, and no soft function subtraction is needed. It indicates a practical way to explore the distribution of the linearly polarized gluons in a proton and the linearly polarized gluon effects in hadron collisions on the lattice.