Physical Sciences and Mathematics Commons^™

Role Of Electronegativity In Environmentally Persistent Free Radicals (Epfrs) Formation On Zno, Syed Monjur Ahmed, Reuben Oumnov, Orhan Kizilkaya, Randall W. Hall, Philip T. Sprunger, Robert L. Cook

Natural Sciences and Mathematics | Faculty Scholarship

Environmentally persistent free radicals (EPFRs), a group of emerging pollutants, have significantly longer lifetimes than typical free radicals. EPFRs form by the adsorption of organic precursors on a transition metal oxide (TMO) surface involving electron charge transfer between the organic and TMO. In this paper, dihalogenated benzenes were incorporated to study the role of electronegativity in the electron transfer process to obtain a fundamental knowledge of EPFR formation mechanism on ZnO. Upon chemisorption on ZnO nanoparticles at 250 °C, electron paramagnetic resonance (EPR) confirms the formation of oxygen adjacent carbon-centered organic free radicals with concentrations between 1016 and 1017 spins/g. …

New Features Of Laboratory-Generated Epfrs From 1,2-Dichlorobenzene (Dcb) And 2‑Monochlorophenol (Mcp), Lavrent Khachatryan, Marwan Y. Rezk, Divine Nde, Farhana Hasan, Slawomir Lomnicki, Dorin Boldor, Robert Cook, Phillip Sprunger, Randall W. Hall, Stephania Cormier

Natural Sciences and Mathematics | Faculty Scholarship

The present research is primarily focused on investigating the characteristics of environmentally persistent free radicals (EPFRs) generated from commonly recognized aromatic precursors, namely, 1,2-dichlorobenzene (DCB) and 2- monochlorophenol (MCP), within controlled laboratory conditions at a temperature of 230 °C, termed as DCB230 and MCP230 EPFRs, respectively. An intriguing observation has emerged during the creation of EPFRs from MCP and DCB utilizing a catalyst 5% CuO/SiO2, which was prepared through various methods. A previously proposed mechanism, advanced by Dellinger and colleagues (a conventional model), postulated a positive correlation between the degree of hydroxylation on the catalyst’s surface (higher hydroxylated, HH and …

Pine Needle Pyrolysis: Bio-Waste Into Biofuel, Alexandra Fuentes

Honors Theses

This project explores the alternate uses of biomass. In particular it focuses on pine needles as a source for biofuels. Pine needles are of interest because in certain Mountain communities they are collected and removed from residential properties. By removing the pine needles, communities create a “defensible space” to prevent wild fires from destroying homes and property. These needles are often placed in regional landfills. The South Tahoe Refuse and Recycling Services alone has more than 4,340 tons of pine needles dumped at their facility annually. This large amount of biomass can be a potential energy source.

The focus of …

Formation Of Environmentally Persistent Free Radicals (Epfrs) On Zno At Room Temperature: Implications For The Fundamental Model Of Epfr Generation., Matthew C. Patterson, Mark F. Ditusa, Cheri A. Mcferrin, R. L. Kurtz, Randall W. Hall, E. D. Poliakoff, P. T. Sprunger

Natural Sciences and Mathematics | Faculty Scholarship

Environmentally persistent free radicals (EPFRs) have significant environmental and public health impacts. In this study, we demonstrate that EPFRs formed on ZnO nanoparticles provide two significant surprises. First, EPR spectroscopy shows that phenoxy radicals form readily on ZnO nanoparticles at room temperature, yielding EPR signals similar to those previously measured after 250°C exposures. Vibrational spectroscopy supports the conclusion that phenoxy-derived species chemisorb to ZnO nanoparticles under both exposure temperatures. Second, DFT calculations indicate that electrons are transferred from ZnO to the adsorbed organic (oxidizing the Zn), the opposite direction proposed by previous descriptions of EPFR formation on metal oxides.

Titanium-Oxides As A Stabilizing Agent For Environmentally Persistent Free Radicals (Epfrs), Josef Baylis

Scholarly and Creative Works Conference (2015 - 2021)

The mechanism of formation for surface bound radicals were studied using ab initio quantum methods. The shift in electron density from transition metal surfaces to surface bound radical groups was studied to learn the mechanism for the binding. Results indicate an oxidation-reduction based mechanism of formation.

Sign Learning Kink-Based (Silk) Quantum Monte Carlo For Molecular Systems, Xiaoyao Ma, Randall W. Hall, Frank Loffler, Karol Kowalski, Kiran Bhaskaran-Nair, Mark Jarrell, Juana Moreno

Collected Faculty and Staff Scholarship

The Sign Learning Kink (SiLK) based Quantum Monte Carlo (QMC) method is used to calculate the ab initioground state energies for multiple geometries of the H₂O, N₂, and F₂ molecules. The method is based on Feynman’s path integral formulation of quantum mechanics and has two stages. The first stage is called the learning stage and reduces the well-known QMC minus sign problem by optimizing the linear combinations of Slater determinants which are used in the second stage, a conventional QMC simulation. The method is tested using different vector spaces and compared to the results of …

Scale Up Isolation Of Aaptamine For In Vivo Evaluation Indicates Its Neurobiological Activity Is Linked To The Delta Opioid Receptor, Nicole L. Mcintosh, Eptisam Lambu, Laura Millan-Lobo, Fei Li, Li He, Phillip Crews, Jennifer L. Whistler, Tyler Johnson

Student Research Posters

Opioid receptors belong to the large superfamily of seven transmembrane-spanning (7TM) G protein-coupled receptors (GPCRs). As a class, GPCRs are of fundamental physiological importance mediating the actions of the majority of known neurotransmitters and hormones. The Mu, Delta, and Kappa (MOP, DOP, KOP) opioid receptors are particularly intriguing members of this receptor family as they are the targets involved in many neurobiological diseases such as addiction, pain, stress, anxiety, and depression. Recently we discovered that the aaptamine class of marine sponge derived natural products exhibit selective agonist activity in vitro for the DOP versus MOP receptor. Our findings may explain …

Environmentally Persistent Free Radicals (Epfrs). 3. Free Versus Bound Hydroxyl Radicals In Epfr Aqueous Solutions, Lavrent Khachatryan, Cheri A. Mcferrin, Randall W. Hall, Barry Dellinger

Collected Faculty and Staff Scholarship

Additional experimental evidence is presented for in vitro generation of hydroxyl radicals because of redox cycling of environmentally persistent free radicals (EPFRs) produced after adsorption of 2-monochlorophenol at 230 °C (2-MCP-230) on copper oxide supported by silica, 5% Cu(II)O/silica (3.9% Cu). A chemical spin trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed. Experiments in spiked O¹⁷ water have shown that ∼15% of hydroxyl radicals formed as a result of redox cycling. This amount of hydroxyl radicals arises from an exogenous Fenton reaction and may stay either partially trapped on the surface …

Potential Role Of Micro-Algae On Global Energy Supply, Sage Callaway-Keeley, Stephanie Huynh

Student Research Posters

The most effective ways to reduce CO2 emissions are to improve the energy efficiency of each economic sector and to reduce the cutting of tropical and temperate forests around the world. These options, however, may not fully reach their technical and economic potential due to various political and socioeconomic. The most practical of these is to increase CO2 sinks through photosynthesis in both standing tree biomass and in ocean primary producers. The use of marine algae as CO2 sinks is for large-scale CO2 mitigation: the use of phytoplankton through Fe fertilization and macro algal (kelp) farms, which can be used …

Biofuels: A Hands-On Approach, Learning The Potential Of Utilizing Non-Food Sources, Alexandra Ham, Gabrielle Pecora, Hoaithuong Bui, Timothy Camarella, Victor Pham, Marc Ting

Student Research Posters

The global energy economy is huge and thoughts of replacing large amounts of petroleum based fuels by massive levels of fermentation of grains are not realistic. On an energy basis what global agriculture produces for food will almost cover the energy demands if all of it is redirected to the production of fuels—either as alcohols for gasoline or as fat derivatives for diesel fuel. This means that chemical processes need to be developed that allow inclusion of non-food based agricultural and urban wastes as well as forest debris into the energy economy. These represent opportunities to capture new sources of …

Constructing Explicit Magnetic Analogies For The Dynamics Of Glass Forming Liquids, Jacob D. Stevenson, Aleksandra M. Walczak, Randall W. Hall, Peter G. Wolynes

Collected Faculty and Staff Scholarship

By defining a spatially varying replica overlap parameter for a supercooled liquid referenced to an ensemble of fiducial liquid state configurations, we explicitly construct a constrained replica free energy functional that maps directly onto an Ising Hamiltonian with both random fields and random interactions whose statistics depend on the liquid structure. Renormalization group results for random magnets when combined with these statistics for the Lennard-Jones glass suggest that discontinuous replica symmetry breaking would occur if a liquid with short range interactions could be equilibrated at a sufficiently low temperature where its mean field configurational entropy would vanish, even though the …

Making Soap From Readily Available Agricultural And Household Wastes Can Increase Cleanless In Rural Area, Eugenia Lucas, Thomas Ciaglo

Student Research Posters

In some areas of the world, soap is too expensive for many people to afford. For these people an alternative exists. They can make their own soap. In general, soap is made by the reaction of triglycerides and caustic soda. However, caustic soda, too, may be difficult to find or too expensive. The aim of this project is to develop a process for making soap from readily available agricultural and household waste materials, and other inexpensive chemicals. By using this process, rural people can get the benefits of readily available, inexpensive soap. Soap is made from animal fats or vegetable …

Divergence, Recombination And Retention Of Functionality During Protein Evolution, Yanong O. Xu, Randall W. Hall, Richard A. Goldstein, David D. Pollock

Collected Faculty and Staff Scholarship

We have only a vague idea of precisely how protein sequences evolve in the context of protein structure and function. This is primarily because structural and functional contexts are not easily predictable from the primary sequence, and evaluating patterns of evolution at individual residue positions is also difficult. As a result of increasing biodiversity in genomics studies, progress is being made in detecting context-dependent variation in substitution processes, but it remains unclear exactly what context-dependent patterns we should be looking for. To address this, we have been simulating protein evolution in the context of structure and function using lattice models …

Simulation Of Electronic And Geometric Degrees Of Freedom Using A Kink-Based Path Integral Formulation: Application To Molecular Systems, Randall W. Hall

Collected Faculty and Staff Scholarship

A kink-based path integral method, previously applied to atomic systems, is modified and used to study molecular systems. The method allows the simultaneous evolution of atomic and electronic degrees of freedom. Results for CH₄, NH₃, and H₂O demonstrate this method to be accurate for both geometries and energies. Comparison with DFT and MP2 level calculations show the path integral approach to produce energies in close agreement with MP2 energies and geometries in close agreement with both DFT and MP2 results.

Microscopic Theory Of Network Glasses, Randall W. Hall, Peter G. Wolynes

Collected Faculty and Staff Scholarship

A theory of the glass transition of network liquids is developed using self-consistent phonon and liquid state approaches. The dynamical transition and entropy crisis characteristic of random first-order transitions are mapped as a function of the degree of bonding and density. Using a scaling relation for a soft-core model to crudely translate the densities into temperatures, theory predicts that the ratio of the dynamical transition temperature to the laboratory transition temperature rises as the degree of bonding increases, while the Kauzmann temperature falls explaining why highly coordinated liquids are “strong” while van der Waals liquids without coordination are “fragile.”

Kink-Based Path Integral Calculations Of Atoms He-Ne, Randall W. Hall

Collected Faculty and Staff Scholarship

An adaptive, kink-based path integral formalism is used to calculate the ground state energies of the atoms He–Ne. The method uses an adaptive scheme to virtually eliminate the sign difficulties. This is done by using a Monte Carlo scheme to identify states that contribute significantly to the canonical partition function and then include them in the wavefunctions to calculate the canonical averages. The calculations use the 6-31G basis set and obtain both precision and accuracy.

An Adaptive, Kink-Based Approach To Path Integral Calculations, Randal W. Hall

Collected Faculty and Staff Scholarship

A kink-based expression for the canonical partition function is developed using Feynman’s path integral formulation of quantum mechanics and a discrete basis set. The approach is exact for a complete set of states. The method is tested on the 3×3 Hubbard model and overcomes the sign problem seen in traditional path integral studies of fermion systems. Kinks correspond to transitions between different N-electron states, much in the same manner as occurs in configuration interaction calculations in standard ab initio methods. The different N-electron states are updated, based on which states occur frequently during a Monte Carlo simulation, giving better estimates …

Photoabsorption Spectra Of Argon Cation Clusters: Monte Carlo Simulations Using Many-Body Polarization, Jose A. Gascon, Randall W. Hall

Collected Faculty and Staff Scholarship

A simple, semiempirical model that includes many-body polarization is used to study the ground and excited stateproperties of Ar+N clusters (N=3–23) at 80 K. For purposes of comparison, a model that does not include many-body polarization is used to study clusters with N=3–27.Monte Carlo simulations are used to calculate the average properties of these clusters. The model is similar to one previously used to study argon cation clusters without many-body polarization. The photoabsorptionspectrum is in good agreement with experiment; in particular, the photoabsorptionspectra for cluster sizes 4–10 do not show the blueshift that is seen with models that do not …

Electronic Properties Of Small Neutral And Charged Beryllium Clusters, Andrew M. Kolchin, Randall W. Hall

Collected Faculty and Staff Scholarship

We determine the atomic and electronic structures for neutral and singly positively chargedberyllium clusters containing from two to six atoms using density functional theory in the local spin density approximation. Ions are moved with a steepest descent method and the electronic wave functions optimized using a fictitious dynamics with simulated annealing, as conceived by Car and Parrinello [Phys. Rev. Lett. 55, 2471 (1985)]. Shell-like orbitals, filling angular momentum states in the order: 1s 1p 2s 1d are obtained. We employ a Mulliken population analysis using an atomic basis to examine how the shell orbitals arise from atomic orbitals. This analysis …

Development, Justification, And Use Of A Projection Operator In Path Integral Calculations In Continuous Space, Randall W. Hall, Melissa R. Prince

Collected Faculty and Staff Scholarship

A projection operator, similar to one previously used by us for problems with a finite set of basis functions, is suggested for use with continuous basis sets. This projection operator requires knowledge of the nodes of the density matrix at all temperatures. We show that a class of nodes, determined from the noninteracting density matrix and present at high temperatures in the interacting system are preserved to first order in the interaction at low temperatures. While we cannot show that the nodes are present at intermediate temperatures, we suspect they do exist and, as a test of this conjecture, we …

Path Integral Studies Of The 2d Hubbard Model Using A New Projection Operator, Randall W. Hall

Collected Faculty and Staff Scholarship

Feynman’s path integral formulation of quantum mechanics, supplemented by an approximate projection operator (exact in the case of noninteracting particles), is used to study the 2D Hubbard model. The projection operator is designed to study Hamiltonians defined on a finite basis set, but extensions to continuous basis sets are suggested. The projection operator is shown to reduce the variance by a significant amount relative to straightforward Monte Carlo integration. Approximate calculations are usually within one standard deviation of exact results and virtually always within two to three standard deviations. In addition, the algorithm scales with the number of discretization points …

Path Integral Study Of The Correlated Electronic States Of Na4–Na6, Randall W. Hall

Collected Faculty and Staff Scholarship

Feynman’s path integral formulation of quantum mechanics is used to study the correlated electronic states of Na4–Na6. Two types of simulations are performed: in the first, the nuclei are allowed to move at finite temperature in order to find the most stable geometries. In agreement with previous calculations, we find that planar structures are the most stable and that there is significant vibrational amplitude at finite temperatures, indicating that the Born–Oppenheimer surface is relatively flat. In the second type of simulation, the nuclei are held fixed at symmetric and asymmetric geometries and the correlated electron density is found. Our results …

The Exchange Potential In Path Integral Studies: Analytical Justification, Randall W. Hall

Collected Faculty and Staff Scholarship

We present analytical justification for our previously described exchange pseudopotential. We show how the fermi quantum partition function can be constructed from the Boltzmann (distinguishable particle) wave functions if the states that correspond to like‐spin electrons occupying the same quantum state are excluded. A class of weighting functions that satisfy this constraint approximately is discussed. Our previous pseudopotential falls under this class. Essentially, our pseudopotential forces the unwanted states to have high energy and, hence, to make negligible contribution to the partition function. Exchange potentials of the form discussed in this article should be useful for studying systems where the …

The Treatment Of Exchange In Path Integral Simulations Via An Approximate Pseudopotential, Randall W. Hall

Collected Faculty and Staff Scholarship

An approximate form that includes the effects of exchange is suggested for the short time propagator used in path integral simulations. The form is inspired physically by the approximation made in Hartree–Fock treatments of atoms and molecules. The approximate propagator is used with q u a n t i t a t i v e accuracy in two systems: an ideal gas of fermions localized in a three‐dimensional harmonic well and the triplet state of the sodium dimer.

The Aperiodic Crystal Picture And Free Energy Barriers In Glasses, Randall W. Hall, Peter G. Wolynes

Collected Faculty and Staff Scholarship

The aperiodic crystal picture associates the glass transition with freezing into a nonperiodic structure. Dynamics in the glassy state involves activated jumps between different aperiodic free energy minima. Activation barriers may be estimated through the use of freezing theory and the theory of dense solids. The results resemble, but are distinct from, free volume theory. Reasonable fits to experimental data are obtained.

Solvent Influence On Atomic Spectra: The Effect Of Finite Size, Randall W. Hall, Peter G. Wolynes

Collected Faculty and Staff Scholarship

Time dependent Hartree theory is used to determine the solvent effect on atomic spectra for a given solvent configuration. Configuration averaging is performed as in the mean spherical approximation, resulting in an upper bound to the polarizability. Comparisons are made with previous, more approximate theories, including path integral treatments. It is found that deviations from previous theories can be significant in certain regimes.