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Marko Gacesa

Publications and source records attributed to Marko Gacesa.

At least 19 recordsLinked to original sources
arXiv2026

Physicochemical properties of lunar regolith simulant for in situ oxygen production

Permanent lunar settlements will rely on in situ oxygen production from regolith for life support and propulsion. While oxygen is abundant in lunar materials, it is chemically bound within metal oxides whose extractability depends strongly on regolith composition and processing strategy. In this study, we validate and characterize high-fidelity lunar regolith simulants representative of the lunar highlands and south pole using scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area and pore structure analysis, and hydrogen temperature-programmed reduction. The simulants exhibit strong mineralogical and compositional fidelity to returned Apollo and Chang'e samples, with ilmenite confirmed as the most readily reducible oxygen-bearing phase. However, despite low ilmenite abundance, bulk highland simulants display favorable reduction behavior arising from distributed Fe-bearing silicate and glassy phases, as well as surface and microstructural properties that influence gas-solid interactions. Adsorption experiments with gases (H2, CH4, and CO2) and water indicate that mineralogical heterogeneity and pore accessibility influence their uptake in simulants. These results indicate that oxygen extraction behavior in realistic lunar regolith is governed by whole-regolith response rather than ilmenite content alone, supporting the option of whole-regolith processing strategies for oxygen production in lunar in situ resource utilization architectures.

physics.space-ph↗
arXiv2025

Quantum scattering of hot H/D on CO$_2$: Cross sections and rate coefficients for planetary atmospheres and their evolution

Collisions between hot hydrogen atoms and CO$_2$ play a central role in energy transfer and atmospheric escape in CO$_2$-rich planetary atmospheres. We present quantum mechanical $j_z$-conserving coupled-states calculations of state-resolved cross sections for H/D--CO$_2$ collisions at energies up to 5~eV, benchmarked to within 7\% of close-coupling results. Scattering is strongly forward-peaked, yielding momentum-transfer cross sections substantially smaller than commonly assumed: mass-scaling from O/C--CO$_2$ systems overestimates H--CO$_2$ total cross sections by factors of 30--45, while existing empirical fits underestimate the low-energy regime by up to $\sim$45\%. Isotopic substitution (H/D) produces energy-dependent differences of up to 35\% at $E<0.1$~eV, invalidating uniform scaling approaches for D/H fractionation. Maxwellian-averaged rate coefficients derived from our cross sections are significantly smaller than mass-scaled values, implying reduced H--CO$_2$ energy transfer efficiency. In atmospheric escape modelling, these revisions can shift Martian exobase altitudes by 10--20~km, leading to order-unity changes in thermal escape rates, and have implications for hydrogen loss in early CO$_2$-dominated planetary atmospheres. Our results provide essential quantum-mechanical inputs for revisiting atmospheric evolution scenarios on Mars, early Earth, and CO$_2$-rich exoplanets.

astro-ph.EP↗
arXiv2025

Auto-ML Graph Neural Network Hypermodels for Outcome Prediction in Event-Sequence Data

This paper introduces HGNN(O), an AutoML GNN hypermodel framework for outcome prediction on event-sequence data. Building on our earlier work on graph convolutional network hypermodels, HGNN(O) extends four architectures-One Level, Two Level, Two Level Pseudo Embedding, and Two Level Embedding-across six canonical GNN operators. A self-tuning mechanism based on Bayesian optimization with pruning and early stopping enables efficient adaptation over architectures and hyperparameters without manual configuration. Empirical evaluation on both balanced and imbalanced event logs shows that HGNN(O) achieves accuracy exceeding 0.98 on the Traffic Fines dataset and weighted F1 scores up to 0.86 on the Patients dataset without explicit imbalance handling. These results demonstrate that the proposed AutoML-GNN approach provides a robust and generalizable benchmark for outcome prediction in complex event-sequence data.

cs.LG↗
arXiv2025

Energy relaxation in superthermal collisions of carbon with oxygen: the influence of isotopic substitution

The transition from a once-dense Martian atmosphere to the thin one observed today implies a substantial loss of carbon, either through atmospheric escape or surface deposition. Accurately modeling this carbon escape necessitates accounting for collisions between energetic carbon atoms and the primary atmospheric constituents, including oxygen. To this end, we computed a highly accurate and comprehensive set of potential energy curves (PECs) for the C($^3$P) + O($^3$P) system. Based on these PECs, we derived statistically averaged total elastic and differential cross sections. Comparison with literature data for O($^3$P) + O($^3$P) collisions reveals that cross sections involving carbon can differ by up to a factor of two, indicating that oxygen is not a good proxy for modeling carbon escape. Furthermore, we evaluated the impact of all possible isotopic combinations in C($^3$P) + O($^3$P) collisions and found variations in cross sections of up to 8\%. Given the observed isotopic enrichment of carbon and oxygen in the Martian atmosphere, even such moderate differences can have a significant effect on escape models and the interpretation of planetary evolution.

astro-ph.EP↗
arXiv2024

Semi-strong Efficient Market of Bitcoin and Twitter: an Analysis of Semantic Vector Spaces of Extracted Keywords and Light Gradient Boosting Machine Models

This study extends the examination of the Efficient-Market Hypothesis in Bitcoin market during a five year fluctuation period, from September 1 2017 to September 1 2022, by analyzing 28,739,514 qualified tweets containing the targeted topic "Bitcoin". Unlike previous studies, we extracted fundamental keywords as an informative proxy for carrying out the study of the EMH in the Bitcoin market rather than focusing on sentiment analysis, information volume, or price data. We tested market efficiency in hourly, 4-hourly, and daily time periods to understand the speed and accuracy of market reactions towards the information within different thresholds. A sequence of machine learning methods and textual analyses were used, including measurements of distances of semantic vector spaces of information, keywords extraction and encoding model, and Light Gradient Boosting Machine (LGBM) classifiers. Our results suggest that 78.06% (83.08%), 84.63% (87.77%), and 94.03% (94.60%) of hourly, 4-hourly, and daily bullish (bearish) market movements can be attributed to public information within organic tweets.

econ.GN↗
arXiv2023

Quantum scattering cross sections of O($^3P$) + N$_2$ collisions for planetary aeronomy

"Hot atoms", which are atoms in their excited states, transfer their energy to the surrounding atmosphere through collisions. This process of energy transfer is known as thermalization, and it plays a crucial role in various astrophysical and atmospheric processes. Thermalization of hot atoms is mainly governed by the amount of species present in the surrounding atmosphere and the collision cross-section between the hot atoms and surrounding species. In this work, we investigated the elastic and inelastic collisions between hot oxygen atoms and neutral N$_2$ molecules, relevant to oxygen gas escape from the martian atmosphere and for characterizing the chemical reactions in hypersonic flows. We conducted a series of quantum scattering calculations between various isotopes of O($^3P$) atoms and N$_2$ molecules across a range of collision energies (0.3 to 4 eV), and computed both their differential and collision cross-sections using quantum time$-$independent coupled-channel approach. Our differential cross-section results indicate a strong preference for forward scattering over sideways or backward scattering, and this anisotropy in scattering is further pronounced at higher collision energies. By comparing the cross-sections of three oxygen isotopes, we find that the heavier isotopes consistently have larger collision cross-sections than the lighter isotopes over the entire collision energy range examined. However, for all the isotopes, the variation of collision cross-section with respect to collision energy is the same. As a whole, the present study contributes to a better understanding of the energy distribution and thermalization processes of hot atoms within atmospheric environments. Specifically, the cross$-$sectional data presented in this work is directly useful in improving the accuracy of energy relaxation modeling of O and N$_2$ collisions over Mars and Venus atmospheres.

astro-ph.EP↗
arXiv2023

Elastic and inelastic cross sections for $^{12}$C+CO$_2$ and $^{13}$C+CO$_2$ scattering at superthermal energies

We report elastic and inelastic cross sections for fast superthermal $^{12}$C($^3P$) and $^{13}$C($^3P$) atoms scattering on $^{12}$CO$_2$. The cross sections were computed using quantum-mechanical rotationally close-coupling formalism with the electronic interaction described by a newly constructed potential energy surface correlating to the lowest energy asymptote of the complex. State-to-state cross sections, differential cross sections, and derived transport properties of interest for energy relaxation are also reported. The computed elastic cross sections are strongly anisotropic, show significant energy dependence, and differ by up to 2% between the two isotopes of carbon.

astro-ph.EP↗
arXiv2022

A quantum-mechanical investigation of O($^3P$) + CO scattering cross sections at superthermal collision energies

The kinetics and energetic relaxation associated with collisions between fast and thermal atoms are of fundamental interest for escape and therefore also for the evolution of the Mars atmosphere. The total and differential cross-sections of fast O($^3P$) atom collisions with CO have been calculated from quantum mechanical calculations. The cross-sections are computed at collision energies from 0.4 to 5 eV in the center-of-mass frame relevant to the planetary science and astrophysics. All the three potential energy surfaces ($^3$A', $^3$A" and 2 $^3$A" symmetry) of O($^3P$) + CO collisions separating to the atomic ground state have been included in calculations of cross-sections. The cross-sections are computed for all three isotopes of energetic O($^3P$) atoms collisions with CO. The isotope dependence of the cross-sections are compared. Our newly calculated data on the energy relaxation of O atoms and their isotopes with CO molecules will be very useful to improve the modeling of escape and energy transfer processes in the Mars' upper atmosphere.

physics.chem-ph↗
arXiv2020

Photoassociation of ultracold long-range polyatomic molecules

We explore the feasibility of optically forming long-range tetratomic and larger polyatomic molecules in their ground electronic state from ultracold pairs of polar molecules aligned by external fields. Depending on the relative orientation of the interacting diatomic molecules, we find that a tetratomic can be formed either as a weakly bound complex in a very extended halo state or as a pure long-range molecule composed of collinear or nearly-collinear diatomic molecules. The latter is a novel type of tetratomic molecule comprised of two diatomic molecules bound at long intermolecular range and predicted to be stable in cold and ultracold regimes. Our numerical studies were conducted for ultracold KRb and RbCs, resulting in production of (KRb)$_2$ and (RbCs)$_2$ complexes, respectively. Based on universal properties of long-range interactions between polar molecules, we identify triatomic and tetratomic linear polar molecules with favorable ratio of dipole and quadrupole moments for which the apporach could be generalized to form polyatomic molecules.

physics.atom-ph↗
arXiv2019

O($^3P$)+CO$_2$ scattering cross sections at superthermal collision energies for planetary aeronomy

We report new elastic and inelastic cross sections for O($^3P$)+CO$_2$ scattering at collision energies from 0.03 to 5 eV, of major importance to O escape from Mars, Venus, and CO$_2$-rich atmospheres. The cross sections were calculated from first principles using three newly constructed ab-initio potential energy surfaces correlating to the lowest energy asymptote of the complex. The surfaces were restricted to a planar geometry with the CO$_2$ molecule assumed to be in linear configuration fixed at equilibrium. Quantum-mechanical coupled-channel formalism with a large basis set was used to compute state-to-state integral and differential cross sections for elastic and inelastic O($^3P$)+CO$_2$ scattering between all pairs of rotational states of CO$_2$ molecule. The elastic cross sections are 35\% lower at 0.5 eV and more than 50\% lower at 4+ eV than values commonly used in studies of processes in upper and middle planetary atmospheres of Mars, Earth, Venus, and CO$_2$-rich planets. Momentum transfer cross sections, of interest for energy transport, were found to be lower than predicted by mass-scaling.

astro-ph.EP↗
arXiv2019

Impacts of Quantum Chemistry Calculations on Exoplanetary Science, Planetary Astronomy, and Astrophysics

Several of NASA missions (TESS, JWST, WFIRST, etc.) and mission concepts (LUVOIR, HabEx, and OST) emphasize the exploration and characterization of exoplanets, and the study of the interstellar medium. We anticipate that a much broader set of chemical environments exists on exoplanets, necessitating data from a correspondingly broader set of chemical reactions. Similarly, the conditions that exist in astrophysical environments are very different from those traditionally probed in laboratory chemical kinetics studies. These are areas where quantum mechanical theory, applied to important reactions via well-validated chemical kinetics models, can fill a critical knowledge gap. Quantum chemical calculations are also introduced to study interior of planets, photochemical escape, and many critical chemical pathways (e.g. prebiotic environments, contaminations, etc.) After years of development of the relevant quantum chemical theories and significant advances in computational power, quantum chemical simulations have currently matured enough to describe real systems with an accuracy that competes with experiments. These approaches, therefore, have become the best possible alternative in many circumstances where performing experiments is too difficult, too expensive, or too dangerous, or simply not possible. In this white paper, several existing quantum chemical studies supporting exoplanetary science, planetary astronomy, and astrophysics are described, and the potential positive impacts of improved models associated with scientific goals of missions are addressed. In the end, a few recommendations from the scientific community to strengthen related research efforts at NASA are provided.

astro-ph.EP↗
arXiv2018

Strange messenger: A new history of hydrogen on Earth, as told by Xenon

Atmospheric xenon is strongly mass fractionated, the result of a process that apparently continued through the Archean and perhaps beyond. Previous models that explain Xe fractionation by hydrodynamic hydrogen escape cannot gracefully explain how Xe escaped when Ar and Kr did not, nor allow Xe to escape in the Archean. Here we show that Xe is the only noble gas that can escape as an ion in a photo-ionized hydrogen wind, possible in the absence of a geomagnetic field or along polar magnetic field lines that open into interplanetary space. To quantify the hypothesis we construct new 1-D models of hydrodynamic diffusion-limited hydrogen escape from highly-irradiated CO$_2$-H$_2$-H atmospheres. The models reveal three minimum requirements for Xe escape: solar EUV irradiation needs to exceed $10\times$ that of the modern Sun; the total hydrogen mixing ratio in the atmosphere needs to exceed 1% (equiv. to 0.5% CH$_4$); and transport amongst the ions in the lower ionosphere needs to lift the Xe ions to the base of the outflowing hydrogen corona. The long duration of Xe escape implies that, if a constant process, Earth lost the hydrogen from at least one ocean of water, roughly evenly split between the Hadean and the Archean. However, to account for both Xe's fractionation and also its depletion with respect to Kr and primordial $^{244}$Pu, Xe escape must have been limited to small apertures or short episodes, which suggests that Xe escape was restricted to polar windows by a geomagnetic field, or dominated by outbursts of high solar activity, or limited to transient episodes of abundant hydrogen, or a combination of these. Xenon escape stopped when the hydrogen (or methane) mixing ratio became too small, or EUV radiation from the aging Sun became too weak, or charge exchange between Xe$^+$ and O$_2$ rendered Xe neutral.

astro-ph.EP↗
arXiv2016

Charge transfer in ultracold gases via Feshbach resonances

We investigate the prospects of controlling charge-exchange in ultracold collisions of heteroisotopic combinations of atoms and ions of the same element. The treatment, readily applicable to alkali or alkanine-earth metals, is illustrated in the process $^9$Be$^{+}$ + $^{10}$Be $\leftrightarrow$ $^{9}$Be + $^{10}$Be$^{+}$, which exhibits favorable electronic, nuclear, and hyperfine structure. Feshbach resonances are obtained from quantum scattering calculations in a standard coupled-channel formalism with non-BO terms originating from the nuclear kinetic operator. Near a narrow resonance predicted at 322 G, we find the charge-exchange rate coefficient to rise from practically zero to values larger than $10^{-12}$ cm$^3$/s. Our results suggest controllable charge-exchange reactions between different isotopes of suitable atom-ion pairs with potential applications to quantum systems engineered to study charge diffusion in trapped cold atom-ion mixtures and emulate many-body physics.

physics.atom-ph↗
arXiv2016

Non-thermal production and escape of OH from the upper atmosphere of Mars

We present a theoretical analysis of formation and kinetics of hot OH molecules in the upper atmosphere of Mars produced in reactions of thermal molecular hydrogen and energetic oxygen atoms. Two major sources of energetic O considered are the photochemical production, via dissociative recombination of O$_{2}^{+}$ ions, and energizing collisions with fast atoms produced by the precipitating Solar Wind (SW) ions, mostly H$^+$ and He$^{2+}$, and energetic neutral atoms (ENAs) originating in the charge-exchange collisions between the SW ions and atmospheric gases. Energizing collisions of O with atmospheric secondary hot atoms, induced by precipitating SW ions and ENAs, are also included in our consideration. The non-thermal reaction O + H$_2(v,j) \rightarrow$ H + OH$(v',j')$ is described using recent quantum-mechanical state-to-state cross sections, which allow us to predict non-equilibrium distributions of excited rotational and vibrational states $(v',j')$ of OH and expected emission spectra. A fraction of produced translationally hot OH is sufficiently energetic to overcome Mars' gravitational potential and escape into space, contributing to the hot corona. We estimate the total escape flux from dayside of Mars for low solar activity conditions at about $5\times10^{22}$ s$^{-1}$, or about 0.1\% of the total escape rate of atomic O and H. The described non-thermal OH production mechanism is general and expected to contribute to the evolution of atmospheres of the planets, satellites, and exoplanets with similar atmospheric compositions.

astro-ph.EP↗
arXiv2016

Production of NaCa$^+$ molecular ions in the ground state from cold atom-ion mixtures by photoassociation via an intermediate state

We present a theoretical analysis of optical pathways for formation of cold Ca($^1$S)Na$^+$($^1$S) molecular ions via an intermediate state. The formation schemes are based on ab initio potential energy curves and transition dipole moments calculated using effective-core-potential methods of quantum chemistry. In the proposed approach, starting from a mixture of cold trapped Ca$^+$ ions immersed into an ultracold gas of Na atoms, (NaCa)$^+$ molecular ions are photoassociated in the excited E$^{1}Σ^+$ electronic state and allowed to spontaneously decay either to the ground electronic state or an intermediate state from which the population is transferred to the ground state via an additional optical excitation. By analyzing all possible pathways, we find that the efficiency of a two-photon scheme, via either B$^{1}Σ^+$ or C$^{1}Σ^+$ potential, is sufficient to produce significant quantities of ground state (NaCa)$^+$ molecular ions. A single-step process results in lower formation rates that would require either a high density sample or a very intense photoassociation laser to be viable.

physics.atom-ph↗
arXiv2014

Rydberg Electrons in a Bose-Einstein Condensate

We investigate a hybrid system composed of ultracold Rydberg atoms immersed in an atomic Bose-Einstein condensate (BEC). The coupling between the Rydberg electrons and BEC atoms leads to the excitation of phonons, the exchange of which induces Yukawa interaction between Rydberg atoms. Due to the small electron mass, the effective charge associated with this quasi-particle-mediated interaction can be large, while its range is equal to the healing length of the BEC, which can be tuned by adjusting the scattering length of the BEC atoms. We find that for small healing lengths, the distortion of the BEC can "image" the wave function density of the Rydberg electron, while large healing lengths induce an attractive Yukawa potential between the two Rydberg atoms that can form a new type of ultra-long-range molecule. We discuss both cases for a realistic system.

cond-mat.quant-gas↗
arXiv2014

Quantum reactive scattering of O($^3$P)+H$_2$ at collision energies up to 4.4 eV

We report the results of quantum scattering calculations for the O($^3$P)+H$_2$ reaction for a range of collision energies from 0.4 to 4.4 eV, important for astrophysical and atmospheric processes. The total and state-to-state reactive cross sections are calculated using a fully quantum time-independent coupled-channel approach on recent potential energy surfaces of $^{3}A'$ and $^{3}A''$ symmetry. A larger basis set than in the previous studies was used to ensure convergence at higher energies. Our results agree well with the published data at lower energies and indicate the breakdown of reduced dimensionality approach at collision energies higher than 1.5 eV. Differential cross sections and momentum transfer cross sections are also reported.

physics.chem-ph↗
arXiv2014

Photoassociation of ultracold molecules near a Feshbach resonance as a probe of the electron-proton mass ratio variation

We show that the photoassociation (PA) rate of ultracold diatomic molecules in the vicinity of a Feshbach resonance could be used to probe variations of the electron-to-proton mass ratio $β= m_e/m_p$, a quantity related to other fundamental constants via the $Λ_{\mathrm{QCD}}$ scale. The PA rate exhibits two features near a Feshbach resonance, a minimum and a maximum, which are very sensitive to the details of the interactions and the exact mass of the system. The effect and detection threshold are illustrated in the formation rates of ultracold Li$_2$ and LiNa molecules by performing coupled-channel calculations in an external magnetic field. We find that the PA rate is particularly sensitive near narrow Feshbach resonances in heavy molecules, where it might be possible to detect relative variability of $β$ on the order of $10^{-15}-10^{-16}$. We also use a two-channel model to derive a proportionality relation between the variation of the PA rate and $β$ applicable to diatomic molecules.

physics.atom-ph↗