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At least 1,099 records · Page 61

An equation of state for partially ionized plasmas: The Coulomb contribution to the free energy

We have previously developed an equation of state (EOS) model called ChemEOS (Hakel and Kilcrease, Atomic Processes in Plasmas, Eds., J. Cohen et al., AIP, 2004) for a plasma of interacting ions, atoms and electrons. It is based on a chemical picture of the plasma and is derived from an expression for the Helmholtz free energy of the interacting species. All other equilibrium thermodynamic quantities are then obtained by minimizing this free energy subject to constraints, thus leading to a thermodynamically consistent EOS. The contribution to this free energy from the Coulomb interactions among the particles is treated using the method of Chabrier and Potekhin (Phys. Rev. E 58, 4941 (1998)) which we have adapted for partially ionized plasmas. This treatment is further examined and is found to give rise to unphysical behavior for various elements at certain values of the density and temperature where the Coulomb coupling begins to become significant and the atoms are partially ionized. We examine the source of this unphysical behavior and suggest corrections that produce acceptable results. The sensitivity of the thermodynamic properties and frequency-dependent opacity of iron is examined with and without these corrections. Lastly, the corrected EOS is used to determine the fractional ion populations and level populations for a new generation of OPLIB low-Z opacity tables currently being prepared at Los Alamos National Laboratory with the ATOMIC code.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Intercellular Adhesion Molecule-1 and Vascular Cell Adhesion Molecule Are Induced by Ionizing Radiation on Lymphatic Endothelium

Purpose/Objectives: The goal of this study was to assess the effects of ionizing radiation on the expression of the integrin ligands ICAM-1 and VCAM that control leucocyte transit by lymphatic endothelial cells. Materials/Methods: Confluent monolayers of primary human lymphatic endothelial cells (LEC) were irradiated with single dose of 2, 5, 10 or 20 Gy, with 6 MeV-x-rays using a Linear-Accelerator. ICAM-1 and VCAM expression was determined by flow cytometry. Human tissue specimens received a single dose of 20 Gy with 15 MeV-x-rays. MC38, B16-OVA or B16-VEGF-C tumors grown in C57BL/6 mice were irradiated with single dose of 20Gy using a Linear-Accelerator fitted with a 10mm Radiosurgery collimator. Clinical samples were obtained from patients previous and 4 weeks after complete standard radiotherapy. ICAM-1 and VCAM expression was detected in all tissue specimens by confocal microscopy. To understand the role of TGFβ in this process anti-TGFβ blocking mAb were injected i.p. 30min before radiotherapy. Cell adhesion to irradiated LEC was analyzed in adhesion experiments performed in the presence or in the absence of anti- TGFβ and /or anti-ICAM1 blocking mAb. Results: We demonstrate that lymphatic endothelial cells in tumor samples experience induction of surface ICAM-1 and VCAM when exposed to ionizing radiation in a dose- and time-dependent manner. These effects can be recapitulated in cultured LEC, and are in part mediated by TGFβ. These data are consistent with increases in ICAM-1 and VCAM expression on LYVE-1+ endothelial cells in freshly explanted human tumor tissue and in mouse transplanted tumors after radiotherapy. Finally, ICAM-1 and VCAM expression accounts for enhanced adherence of human T lymphocytes to irradiated LEC. Conclusion: Our results show induction of ICAM-1 and VCAM on LVs in irradiated lesions and offer a starting point for elucidating the biological and therapeutic implications of targeting leukocyte traffic in combination to immunotherapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Electron and ion transport equations in computational weakly-ionized plasmadynamics

A new set of ion and electron transport equations is proposed to simulate steady or unsteady quasi-neutral or non-neutral multicomponent weakly-ionized plasmas through the drift–diffusion approximation. The proposed set of equations is advantaged over the conventional one by being considerably less stiff in quasi-neutral regions because it can be integrated in conjunction with a potential equation based on Ohm's law rather than Gauss's law. The present approach is advantaged over previous attempts at recasting the system by being applicable to plasmas with several types of positive ions and negative ions and by not requiring changes to the boundary conditions. Several test cases of plasmas enclosed by dielectrics and of glow discharges between electrodes show that the proposed equations yield the same solution as the standard equations but require 10 to 100 times fewer iterations to reach convergence whenever a quasi-neutral region forms. Further, several grid convergence studies indicate that the present approach exhibits a higher resolution (and hence requires fewer nodes to reach a given level of accuracy) when ambipolar diffusion is present. Because the proposed equations are not intrinsically linked to specific discretization or integration schemes and exhibit substantial advantages with no apparent disadvantage, they are generally recommended as a substitute to the fluid models in which the electric field is obtained from Gauss's law as long as the plasma remains weakly-ionized and unmagnetized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Monte Carlo simulation of excitation and ionization collisions with complexity reduction

Kinetic simulation of plasmas with detailed excitation and ionization collisions presents a significant computational challenge due to the multiscale feature of the collisional rates. In the present work, we propose a complexity reduction method based on atomic level grouping for modeling excitation and ionization collisions. High order of accuracy of the reduction method is realized by allowing an internal distribution within each group. We apply the reduction method to the standard Monte Carlo collision algorithm to model an atomic Hydrogen plasma. Numerical results suggest that the stiffness of the collisional kinetics can be significantly reduced with minimal loss in accuracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Two regimes of ionization-induced recovery in SrTiO 3 under irradiation

Irradiation of pre-damaged SrTiO 3 with 2 MeV He, 1.2 MeV C, 5 MeV C and 12 MeV O ions reveals two regimes of ionization-induced recovery. For C and O ions, with electronic energy loss between 1.6 and 3 keV/nm, recovery cross-sections range from 0.27 to 0.38 nm 2 , and molecular dynamics confirms recovery related to ionization-induced thermal spikes via electron-phonon coupling. Lastly, at lower electronic energy losses, recovery cross-sections decrease to about 5.5 × 10 -4 nm 2 for 2 MeV He ions and 1.0 × 10 -5 nm 2 for 200 keV electrons, which suggests recovery associated with local electronic excitation processes.

36 MATERIALS SCIENCE↗

Rapid Determination of Uranium Isotopic Abundance from Cotton Swipes: Direct Extraction via a Planar Surface Reader and Coupling to a Microplasma Ionization Source

The collection of solid particulates and liquids from surfaces by the use of cloth swipes is fairly ubiquitous. In such methods, there is a continuous concern regarding the ability to locate and quantitatively sample the analyte species from the material. In this effort, we demonstrate the initial coupling of an Advion Plate Express plate reader to a liquid sampling–atmospheric pressure glow discharge (LS-APGD) microplasma ionization source with an Orbitrap mass spectrometer to perform uranium isotopic analyses of solution residues on cotton swipes. The Plate Express employs a sampling probe head to engage and seal against the swipe surface. Subsequentially, the analyte residues are desorbed and transported within a 2% HNO 3 electrolyte flow to the ionization source. Quantitative recoveries were observed following a single 30 s extraction step, with the absolute mass sampled per extraction being ~100 ng. While the intrasample variability in the analytical responses for triplicate sampling of the same swipe yield ~30% RSD, this lack of precision is offset by the ability to determine isotope ratios for enriched uranium specimens with a precision of better than 10% RSD. Pooled, intersample precision ( n = 9) was found to be <5%RSD across the various sample compositions. Finally, 235 U/ 238 U determinations (ranging from 0.053 to 1.806) were accurate with errors of <10%, absolute. The 234 U- and 236 U-inclusive ratios were determined with similar accuracy in enriched samples. While the driving force for the effort is in the realm of nuclear nonproliferation efforts, the ubiquitous use of cloth swipes across many application areas could benefit from this convenient approach, including the use of versatile, reduced-format mass spectrometer systems.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

Isotopic Heterogeneity Imaged in a Uranium Fuel Pellet with Extreme Ultraviolet Laser Ablation and Ionization Time-of-Flight Mass Spectrometry

We use extreme ultraviolet laser ablation and ionization time-of-flight mass spectrometry (EUV TOF) to map uranium isotopic heterogeneity at the nanoscale (=100 nm). Using low-enriched uranium fuel pellets that were made by blending two isotopically distinct feedstocks, we show that EUV TOF can map the 235U/238U content in 100 nm-sized pixels. The two-dimensional (2D) isotope maps reveal U ratio variations in sub-microscale to =1 µm areas of the pellet that had not been fully exposed by microscale or bulk mass spectrometry analyses. Compared to the ratio distribution measured in a homogeneous U reference material, the ratios in the enriched pellet follow a ~3× wider distribution. These results indicate U heterogeneity in the fuel pellet from incomplete blending of the different source materials. EUV TOF results agree well with those obtained on the same enriched pellets by nanoscale secondary ionization mass spectrometry (NanoSIMS), which reveals a comparable U isotope ratio distribution at the same spatial scale. EUV TOF’s ability to assess and map isotopic heterogeneity at the nanoscale makes it a promising tool in fields such as nuclear forensics, geochemistry, and biology that could benefit from uncovering sub-microscale sources of chemical modifications.

Rush, Lydia A.↗

Anatomy of Protein Electrospray Ionization Mass Spectra by Superconducting Tunnel Junction Mass and Energy Spectrometry

Cryogenic superconducting tunnel junction (STJ) detectors have the advantage of single-particle sensitivity, high quantum efficiency, low noise, and the ability to detect the time and relative impact energy of deposited ions. This makes them attractive for use in mass spectrometry (MS) and as a form of energy spectrometry. STJ cryodetectors have been coupled to time-offlight (TOF) mass spectrometers equipped with a matrix-assisted laser desorption ionization (MALDI) source and to an electrospray ionization (ESI) TOF mass spectrometer. Here, a lab-made linear ion trap (LIT) mass spectrometer system was coupled to an ESI source and a 16-channel Nb-STJ array with improved readout electronics. The goal was to investigate fundamentals of ESI-generated protein ions by further exploiting the advantage of resolving these ions in a third dimension of the relative energy deposited into the STJs. The proteins equine cytochrome c, bovine carbonic anhydrase, bovine serum albumin, and murine immunoglobulin G were studied using this ESI-LIT-STJ-MS instrument. Multiply charged monomers, multimers, and fragments from metastable ions were resolved from monomer peaks by differences in ion deposition energy even when these ions have the same mass-to-charge ratio as the corresponding monomer. The determination of fragment mass from metastable decomposition is accomplished without knowing the charge state of the fragment. The average charge state of the multimers is reduced with each addition of a protein which is a direct reflection of the surface area available for charging. Multiply charged in-source fragments have also been observed and distinguished in the mass spectrum of carbonic anhydrase by using the differences in the energy deposited in the STJs.

42 ENGINEERING↗

Rapid assessment of human amylin aggregation and its inhibition by copper(II) ions by laser ablation electrospray ionization mass spectrometry with ion mobility separation

Native electrospray ionization (ESI) mass spectrometry (MS) is often used to monitor noncovalent complex formation between peptides and ligands. The relatively low throughput of this technique, however, is not compatible with extensive screening. Laser ablation electrospray ionization (LAESI) MS combined with ion mobility separation (IMS) can analyze complex formation and provide conformation information within a matter of seconds. Islet amyloid polypeptide (IAPP) or amylin, a 37-amino acid residue peptide, is produced in pancreatic beta-cells through proteolytic cleavage of its prohormone. Both amylin and its precursor can aggregate and produce toxic oligomers and fibrils leading to cell death in the pancreas that can eventually contribute to the development of type 2 diabetes mellitus. The inhibitory effect of the copper(II) ion on amylin aggregation has been recently discovered, but details of the interaction remain unknown. Finding other more physiologically tolerated approaches requires large scale screening of potential inhibitors. In this paper, we demonstrate that LAESI-IMS-MS can reveal the binding stoichiometry, copper oxidation state, and the dissociation constant of human amylin–copper(II) complex. The conformations of hIAPP in the presence of copper(II) ions were also analyzed by IMS, and preferential association between the β-hairpin amylin monomer and the metal ion was found. The copper(II) ion exhibited strong association with the —HSSNN– residues of the amylin. In the absence of copper(II), amylin dimers were detected with collision cross sections consistent with monomers of β-hairpin conformation. When copper(II) was present in the solution, no dimers were detected. Thus, the copper(II) ions disrupt the association pathway to the formation of β-sheet rich amylin fibrils. Using LAESI-IMS-MS for the assessment of amylin–copper(II) interactions demonstrates the utility of this technique for the high-throughput screening of potential inhibitors of amylin oligomerization and fibril formation. Finally and more generally, this rapid technique opens the door for high-throughput screening of potential inhibitors of amyloid protein aggregation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Quantitative Mass Spectrometry Imaging of Prostaglandins as Silver Ion Adducts with Nanospray Desorption Electrospray Ionization

Prostaglandins (PG) are an important class of lipid biomolecules that are essential in many biological processes, including inflammation and successful pregnancy. Despite a high bioactivity, physiological concentrations are typically low, which makes direct mass spectrometric analysis of endogenous PG species challenging. Consequently, there have not been any studies investigating the localization of PG species to specific morphological regions in tissue sections using mass spectrometry imaging (MSI) techniques. Herein, we show that silver ions, added to the solvent used for nanospray desorption electrospray ionization (nano-DESI) MSI, enhances the ionization of PG species and enables nano-DESI MSI of several PG species in day 4 pregnant uterine tissue. It was found that detection of [PG+Ag]+ ions increased the sensitivity by ~ 30 times, when compared to [PG-H]- ions. Further, the addition of isotopically labeled internal standards enabled generation of quantitative ion images for the detected PG species. Increased sensitivity and quantitative MSI enabled the first proof-of-principle results detailing the localization of PG species in mouse uterus tissue sections. These results show that PG species are primarily localizing to the cellular regions of the luminal epithelium and glandular epithelium in uterine tissue. Further, this study provides a unique scaffold for future studies investigating the distribution of PG species within biological tissue samples.

Duncan, Kyle D.↗

Threshold Ionization Spectroscopy and Theoretical Calculations of LnO (Ln = La and Ce)

Mass-analyzed threshold ionization (MATI) spectroscopy was used to measure the vibronic spectra of LnO (Ln = La and Ce). Single-reference coupled cluster and relativistic multireference configuration calculations were carried out to compare with the measured vibronic energies. The spectrum of LaO displays a single vibronic band system, while that of CeO shows multiple ones. The ionization energies of LaO and CeO are measured as 5.2446 (6) and 5.3332(6) eV, respectively, which are a hundredfold improvement over the literature values. The vibrational energies of the neutral molecule and corresponding ion reveal the charge effect on the metal-oxygen bond of both species. The single band system in the spectrum of LaO arises from the transition of the ground state of the neutral molecule with the La(6s 1 )O(2p 6 ) valence configuration to the ground state of the singly charged ion with the La(6s o )O(2p 6 ) configuration. Here, the multiple band systems in the spectrum of CeO are attributed to the spin-orbit coupling for the Ce(4f 1 6s 1 )O(2p 6 ) configuration of the neutral molecule and an excited state for the Ce(4f 1 )O(2p 6 ) configuration of the ion.

74 ATOMIC AND MOLECULAR PHYSICS↗

Coupled Cluster Studies of Ionization Potentials and Electron Affinities of Single-Walled Carbon Nanotubes

In this paper we apply equation-of-motion coupled cluster (EOMCC) methods in studies of vertical ionization potentials (IP) and electron affinities (EA) for sin- gled walled carbon nanotubes. EOMCC formulations for ionization potentials and electron affinities employing excitation manifolds spanned by single and double ex- citations (IP/EA-EOMCCSD) are used to study IPs and EAs of nanotubes as a function of nanotube length. Several armchair nanotubes corresponding to C20nH20 models with n = 2 - 6 have been used in benchmark calculations. In agreement with previous studies, we demonstrate that the electronegativity of C20nH20 systems remains, to a large extent, independent of nanotube length. We also compare IP/EA- EOMCCSD results with those obtained with the coupled cluster models with single and double excitations corrected by perturbative triples, CCSD(T), and density func- tional theory (DFT) using global and range-separated hybrid exchange-correlation functionals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Multiphoton Ionization of One-Electron Relativistic Diatomic Quasimolecules in Strong Laser Fields

We perform a theoretical and computational study of relativistic one-electron homonuclear diatomic quasimolecules subject to strong electromagnetic fields linearly polarized along the molecular axis. Several quasimolecules with the nuclear charges 1 to 92 and appropriately scaled internuclear distances and field parameters are used in the calculations. The time-dependent Dirac equation is solved with the help of the generalized pseudospectral method in prolate spheroidal coordinates. We have found that employing this coordinate system makes it possible to avoid emergence of spurious states, which usually show up when solving the Dirac equation numerically. For lower carrier frequencies, interaction with the driving field is described within the dipole approximation. Relativistic effects in the multiphoton ionization probabilities are investigated with respect to the internuclear distance in the quasimolecule. In conclusion, for higher frequencies, the interaction with the field is described beyond the dipole approximation. Nondipole effects in the ionization probability are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Geometries, Binding Energies, Ionization Potentials, and Electron Affinities of Metal Clusters: Mg n 0, ± 1 , n = 1–7

Equilibrium geometries, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for neutral and singly charged magnesium clusters, Mg n 0, ± 1 , n = 1–7, have been computed using 39 exchange-correlation (XC) functionals in Kohn–Sham density functional theory and several coupled-cluster methods with single, double, and triple excitations, including CCSD(T) for all species, CCSD(2)T and CR-CC(2,3) for species with n = 1–3, and CCSDt, CC(t;3), and CCSDT for species with n = 1 and 2. We have used augmented polarized–valence and polarized–core–valence correlation-consistent basis sets. We have found that the geometry and binding energy of the weakly bound Mg 2 dimer requires a robust treatment of connected triple excitations, represented in this work by the CR-CC(2,3), CC(t;3), and full CCSDT methods, which are more accurate than the popular quasi-perturbative CCSD(T) approximation, but CCSD(T) is sufficiently accurate to be applied to other Mg clusters. We have also demonstrated that for all Mg clusters examined in this study, hybrid XC functionals generally have higher accuracy than local ones, with PW6B95, SOGGA11-X, M11, and PWB6K being the most accurate, both for the geometries and for the binding energies, ionization potentials, and electron-detachment energies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Tolerance of Perovskite Solar Cells to Targeted Proton Irradiation and Electronic Ionization Induced Healing

Mixed organic–inorganic halide perovskite solar cells (PSCs) are of interest for space photovoltaic applications due to their apparent tolerance to high-energy proton radiation. Here, the use of a more stable wide-bandgap FA0.8Cs0.2PbI2.4Br0.6Cl0.02 perovskite with thin encapsulation enables, for the first time, the detailed dependence of fluence and energy of energetic protons on device performance. Energies were chosen to provide the highest concentration of displacements within the active region, and therefore the highest amount of degradation. Not only are these devices tolerant when compared to conventional technologies, but an unexpected increase in open circuit voltage and power density is observed for increased electronic ionization when the proton energy is increased. This study aims to expand the description of the proton radiation tolerance to include not only nonionizing nuclear energy losses that are most detrimental to current technologies, but electronic ionization, which is shown to yield benefits in PSCs.

device performance↗

Molecular Characterization of Organosulfates in Organic Aerosols from Shanghai and Los Angeles Urban Areas by Nanospray-Desorption Electrospray Ionization High-Resolution Mass Spectrometry

Aerosol samples collected in the urban areas of Shanghai and Los Angeles were analyzed by nanospray-desorption electrospray ionization mass spectrometry (nano-DESI MS) with high mass resolution (m/Δm=100,000). Solvent mixtures of acetonitrile/water and acetonitrile/toluene were used to extract and ionize polar and non-polar compounds, respectively. A diverse mixture of oxygenated hydrocarbons, organosulfates, organonitrates, and organics with reduced nitrogen were detected in the Los Angeles sample. Majority of the organics in the Shanghai sample were detected as organosulfates. The dominant organosulfates in the two samples have distinctly different molecular characteristics. Specifically, organosulfates in the Los Angeles sample were dominated by isoprene- or monoterpene-derived products, while organosulfates of yet unknown origin in the Shanghai sample had distinctive characteristics of long aliphatic carbon chains and low degree of oxidation and unsaturation. The use of acetonitrile/toluene solvent facilitated identification of this type of organosulfates, suggesting they could be missed in previous studies relying on sample extraction using common polar solvents. The high molecular weight and low degree of unsaturation and oxidization of the organosulfates detected in the Shanghai sample suggest that they may act as surfactants, and plausibly affect the surface tension and hygroscopicity of the atmospheric particulate matter. We propose that direct esterification of carbonyl or hydroxyl compounds by sulfates or sulfuric acid in liquid phase could be the formation pathway of these special organosulfates. Finally, long-chain alkanes from vehicle emissions might be their precursors.

Environmental Molecular Sciences Laboratory↗

Ambient Single-Cell Analysis and Native Tissue Imaging Using Laser-Ablation Electrospray Ionization Mass Spectrometry with Increased Spatial Resolution

Laser ablation electrospray ionization mass spectrometry (LAESI-MS) is an emerging method that has the potential to transform the field of metabolomics. This is in part due to LAESI-MS being an ambient ionization method that requires minimal sample preparation and uses (endogenous) water for in situ analysis. This application note details the employment of the ‘LAESI microscope’ source to perform spatially resolved MS analysis of cells and MS imaging (MSI) of tissues at high spatial resolution. This source configuration utilizes a long-working distance reflective objective that permits both visualization of the sample and a smaller LAESI laser beam profile than conventional LAESI setups. In this work, we analyzed 200 single cells of Allium cepa (red onion) and imaged Fittonia argyroneura (nerve plant) in high spatial resolution using this source coupled to a Fourier transform mass spectrometer for high mass resolution and high mass accuracy metabolomics.

59 BASIC BIOLOGICAL SCIENCES↗

Desorption Electrospray Ionization–Mass Spectrometry Imaging Provides Spatiochemical Information on Potential Biocontrol Agents against Phytophthora capsici Infection in Tomato Plants

Biological control agents can offer an eco-friendly and more sustainable alternative to conventional chemical pesticides, providing protection against destructive pathogens, such as Phytophthora capsici, while reducing potential environmental harm associated with synthetic pesticide use in agricultural systems. This work evaluates the biocontrol effectiveness of Bacillus vallismortis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Bacillus subtilis, against the widespread plant pathogen Phytophthora capsici. Our studies showed that Bacillus thuringiensis and Bacillus subtilis promote plant growth and provide protection against Phytophthora capsici in both in vitro and in vivo greenhouse studies, while Bacillus vallismortis and Bacillus amyloliquefaciens were effective in vitro but not in vivo. Specifically, Bacillus thuringiensis was observed to both hinder the growth of Phytophthora capsici and enhance plant resilience to this pathogen, with B. thuringiensis-treated, pathogen-exposed plants displaying a 94.4% increase in root length and a 74.0% increase in shoot height compared to plants with only oomycete exposure. To probe the molecular interactions between the biocontrol agent and pathogen, a dual culture of Bacillus thuringiensis and Phytophthora capsici was analyzed in situ using a desorption electrospray ionization–mass spectrometry imaging (DESI-MSI) workflow. This approach interrogated the spatially oriented biochemical interactions that may serve as the molecular foundation for the effectiveness of these biological control agents in crop protection, identifying seven unique phenotypic regions within the dual culture. Herein, we demonstrate the benefits of biological control agent application in tomato cultivation and showcase the strengths of desorption electrospray ionization–mass spectrometry imaging when applied to the spatially resolved molecular characterization of agriculturally relevant microorganisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗