Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization.

PubMed

Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

2016-08-01

The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M(+.) decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques. Graphical Abstract ᅟ.

LTC1877 High Efficiency Regulator Total Ionizing Dose Test Report

NASA Technical Reports Server (NTRS)

Oldham, Timothy; Pellish, Jonathan; Boutte, Alvin

2012-01-01

This report presents total ionizing dose evaluation data for the Linear Technology Corporation LTC1877 high efficiency monolithic synchronous step-down regulator. Data sheet parameters were tracked as a function of ionizing dose up to a total of 20 krad(SiO2). Control devices were also used.

Development Status of the Helicon Hall Thruster

DTIC Science & Technology

2009-09-15

Hall thruster , the Helicon Hall Thruster , is presented. The Helicon Hall Thruster combines the efficient ionization mechanism of a helicon source with the favorable plasma acceleration properties of a Hall thruster . Conventional Hall thrusters rely on direct current electron bombardment to ionize the flow in order to generate thrust. Electron bombardment typically results in an ionization cost that can be on the order of ten times the ionization potential, leading to reduced efficiency, particularly at low

Ionization Mechanism of Positive-Ion Nitrogen Direct Analysis in Real Time.

PubMed

Song, Liguo; Chuah, Wei Chean; Lu, Xinyi; Remsen, Edward; Bartmess, John E

2018-04-01

Nitrogen can be an inexpensive alternative to helium used by direct analysis in real time (DART), especially in consideration of the looming helium shortage. Therefore, the ionization mechanism of positive-ion N 2 DART has been systematically investigated. Our experiments suggest that a range of metastable nitrogen species with a variety of internal energies existed and all of them were less energetic than metastable helium atoms. However, compounds with ionization energies (IE) equal to or lower than 10.2 eV (all organic compounds except the extremely small ones) can be efficiently ionized. Because N 2 DART was unable to efficiently ionize ambient moisture and common organic solvents such as methanol and acetonitrile, the most important ionization mechanism was direct Penning ionization followed by self-protonation of polar compounds generating [M+H] + ions. On the other hand, N 2 DART was able to efficiently ionize ammonia, which was beneficial in the ionization of hydrogen-bonding compounds with proton affinities (PA) weaker than ammonia generating [M+NH 4 ] + ions and large PAHs generating [M+H] + ions through proton transfer. N 2 DART was also able to efficiently ionize NO, which led to the ionization of nonpolar compounds such as alkanes and small aromatics generating [M-(2m+1)H] + (m=0,1…) ions. Lastly, metastable nitrogen species was also able to produce oxygen atoms, which resulted in increased oxygen adducts as the polarity of organic compounds decreased. In comparison with He DART, N 2 DART was approximately one order of magnitude less sensitive in generating [M+H] + ions, but could be more sensitive in generating [M+NH 4 ] + ions. Graphical Abstract ᅟ.

Ionization Mechanism of Positive-Ion Nitrogen Direct Analysis in Real Time

NASA Astrophysics Data System (ADS)

Song, Liguo; Chuah, Wei Chean; Lu, Xinyi; Remsen, Edward; Bartmess, John E.

2018-02-01

Nitrogen can be an inexpensive alternative to helium used by direct analysis in real time (DART), especially in consideration of the looming helium shortage. Therefore, the ionization mechanism of positive-ion N2 DART has been systematically investigated. Our experiments suggest that a range of metastable nitrogen species with a variety of internal energies existed and all of them were less energetic than metastable helium atoms. However, compounds with ionization energies (IE) equal to or lower than 10.2 eV (all organic compounds except the extremely small ones) can be efficiently ionized. Because N2 DART was unable to efficiently ionize ambient moisture and common organic solvents such as methanol and acetonitrile, the most important ionization mechanism was direct Penning ionization followed by self-protonation of polar compounds generating [M+H]+ ions. On the other hand, N2 DART was able to efficiently ionize ammonia, which was beneficial in the ionization of hydrogen-bonding compounds with proton affinities (PA) weaker than ammonia generating [M+NH4]+ ions and large PAHs generating [M+H]+ ions through proton transfer. N2 DART was also able to efficiently ionize NO, which led to the ionization of nonpolar compounds such as alkanes and small aromatics generating [M-(2m+1)H]+ (m=0,1…) ions. Lastly, metastable nitrogen species was also able to produce oxygen atoms, which resulted in increased oxygen adducts as the polarity of organic compounds decreased. In comparison with He DART, N2 DART was approximately one order of magnitude less sensitive in generating [M+H]+ ions, but could be more sensitive in generating [M+NH4]+ ions. [Figure not available: see fulltext.

The great importance of normalization of LC-MS data for highly-accurate non-targeted metabolomics.

PubMed

Mizuno, Hajime; Ueda, Kazuki; Kobayashi, Yuta; Tsuyama, Naohiro; Todoroki, Kenichiro; Min, Jun Zhe; Toyo'oka, Toshimasa

2017-01-01

The non-targeted metabolomics analysis of biological samples is very important to understand biological functions and diseases. LC combined with electrospray ionization-based MS has been a powerful tool and widely used for metabolomic analyses. However, the ionization efficiency of electrospray ionization fluctuates for various unexpected reasons such as matrix effects and intraday variations of the instrument performances. To remove these fluctuations, normalization methods have been developed. Such techniques include increasing the sensitivity, separating co-eluting components and normalizing the ionization efficiencies. Normalization techniques allow simultaneously correcting of the ionization efficiencies of the detected metabolite peaks and achieving quantitative non-targeted metabolomics. In this review paper, we focused on these normalization methods for non-targeted metabolomics by LC-MS. Copyright © 2016 John Wiley & Sons, Ltd.

A discharge flow-photoionization mass spectrometric study of the FO(X 2 Pi i) radical. Photoionization efficiency spectrum and ionization energy

NASA Technical Reports Server (NTRS)

Zhang, Zhengyu; Kuo, Szu-Cherng; Klemm, R. Bruce; Monks, Paul S.; Stief, Louis J.

1994-01-01

Photoionization efficiency spectra of FO were measured over the wavelength range 80.0-100.0 nm and in the ionization threshold region, 94.0-100.0 nm, using a discharge flow-photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. FO was generated by the reaction of F2P atoms with NO3 and via a F2O2 discharge. A value of 12.78 +/- 0.03 eV was obtained for the adiabatic ionization energy of FO from photoion thresholds which corresponds to FO(+)(X 3 Sigma -) from FO(X 2 Pi i). These results, which are the first to be obtained by direct Photo-ionization mass spectrometry (PIMS) measurements, corroborate those of a photoelectron spectroscopy (PES) study; however, the ionization energy determined here is free from interferences due to other species which complicated the PES measurement. A value of 109.5 +/- 8.0 kJ/mol for Delta f H 0 298(FO) is computed from the present value of IE(FO) and a previous appearance energy measurement, and a value for the proton affinity of FO is calculated to be 511.5 +/- 10.0 kJ/mol.

Covalent organic framework as efficient desorption/ionization matrix for direct detection of small molecules by laser desorption/ionization mass spectrometry.

PubMed

Feng, Dan; Xia, Yan

2018-07-19

Covalent organic framework (COF) was explored as a novel matrix with a high desorption/ionization efficiency for direct detection of small molecules by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS). By using COF as an LDI MS matrix, we could detect not only biological micro molecules such as amino acids and fatty acids, but also emerging environmental pollutants like bisphenol S (BPS) and pyrene. With COF as the matrix, higher desorption/ionization efficiency, and less background interference were achieved than the conventional organic matrices. Good salt tolerance (as high as 500 mM NaCl) and repeatability allowed the detection limit of amino acids was 90 fmol. In addition, COF matrix performed well for amino acids analysis in the honey sample. The ionization mechanism was also discussed. These results demonstrate that COF is a powerful matrix for small molecules analysis in real samples by MS. Copyright © 2018 Elsevier B.V. All rights reserved.

Vortex focusing of ions produced in corona discharge.

PubMed

Kolomiets, Yuri N; Pervukhin, Viktor V

2013-06-15

Completeness of the ion transportation into an analytical path defines the efficiency of ionization analysis techniques. This is of particular importance for atmospheric pressure ionization sources like corona discharge, electrospray, ionization with radioactive ((3)H, (63)Ni) isotopes that produce nonuniform spatial distribution of sample ions. The available methods of sample ion focusing are either efficient at reduced pressure (~1Torr) or feature high sample losses. This paper deals with experimental research into atmospheric pressure focusing of unipolar (positive) ions using a highly swirled air stream with a well-defined vortex core. Effects of electrical fields from corona needle and inlet capillary of mass spectrometer on collection efficiency is considered. We used a corona discharge to produce an ionized unipolar sample. It is shown experimentally that with an electrical field barrier efficient transportation and focusing of an ionized sample are possible only when a metal plate restricting the stream and provided with an opening covered with a grid is used. This gives a five-fold increase of the transportation efficiency. It is shown that the electric field barrier in the vortex sampling region reduces the efficiency of remote ionized sample transportation two times. The difference in the efficiency of light ion focusing observed may be explained by a high mobility and a significant effect of the electric field barrier upon them. It is possible to conclude based on the experimental data that the presence of the field barrier narrows considerably (more than by one and half) the region of the vortex sample ion focusing. Copyright © 2013 Elsevier B.V. All rights reserved.

Evaluation of species-dependent detection efficiencies in the aerosol mass spectrometer

USDA-ARS?s Scientific Manuscript database

Mass concentrations of chemical species calculated from the aerosol mass spectrometer (AMS) depend on two factors: particle collection efficiency (CE) and relative ionization efficiency (RIE, relative to the primary calibrant ammonium nitrate). While previous studies have characterized CE, RIE is re...

Low-sample flow secondary electrospray ionization: improving vapor ionization efficiency.

PubMed

Vidal-de-Miguel, G; Macía, M; Pinacho, P; Blanco, J

2012-10-16

In secondary electrospray ionization (SESI) systems, gaseous analytes exposed to an elecrospray plume become ionized after charge is transferred from the charging electrosprayed particles to the sample species. Current SESI systems have shown a certain potential. However, their ionization efficiency is limited by space charge repulsion and by the high sample flows required to prevent vapor dilution. As a result, they have a poor conversion ratio of vapor into ions. We have developed and tested a new SESI configuration, termed low-flow SESI, that permits the reduction of the required sample flows. Although the ion to vapor concentration ratio is limited, the ionic flow to sample vapor flow ratio theoretically is not. The new ionizer is coupled to a planar differential mobility analyzer (DMA) and requires only 0.2 lpm of vapor sample flow to produce 3.5 lpm of ionic flow. The achieved ionization efficiency is 1/700 (one ion for every 700 molecules) for TNT and, thus, compared with previous SESI ionizers coupled with atmospheric pressure ionization-mass spectrometry (API-MS) (Mesonero, E.; Sillero, J. A.; Hernández, M.; Fernandez de la Mora, J. Philadelphia PA, 2009) has been improved by a large factor of at least 50-100 (our measurements indicate 70). The new ionizer coupled with the planar DMA and a triple quadrupole mass spectrometer (ABSciex API5000) requires only 20 fg (50 million molecules) to produce a discernible signal after mobility and MS(2) analysis.

Enhanced ionization efficiency in TIMS analyses of plutonium and americium using porous ion emitters

DOE PAGES

Baruzzini, Matthew L.; Hall, Howard L.; Watrous, Matthew G.; ...

2016-12-05

Investigations of enhanced sample utilization in thermal ionization mass spectrometry (TIMS) using porous ion emitter (PIE) techniques for the analyses of trace quantities of americium and plutonium were performed. Repeat ionization efficiency (i.e., the ratio of ions detected to atoms loaded on the filament) measurements were conducted on sample sizes ranging from 10–100 pg for americium and 1–100 pg for plutonium using PIE and traditional (i.e., a single, zone-refined rhenium, flat filament ribbon with a carbon ionization enhancer) TIMS filament sources. When compared to traditional filaments, PIEs exhibited an average boost in ionization efficiency of ~550% for plutonium and ~1100%more » for americium. A maximum average efficiency of 1.09% was observed at a 1 pg plutonium sample loading using PIEs. Supplementary trials were conducted using newly developed platinum PIEs to analyze 10 pg mass loadings of plutonium. As a result, platinum PIEs exhibited an additional ~134% boost in ion yield over standard PIEs and ~736% over traditional filaments at the same sample loading level.« less

Ion-recombination correction for different ionization chambers in high dose rate flattening-filter-free photon beams

NASA Astrophysics Data System (ADS)

Lang, Stephanie; Hrbacek, Jan; Leong, Aidan; Klöck, Stephan

2012-05-01

Recently, there has been an increased interest in flattening-filter-free (FFF) linear accelerators. Removal of the filter results in available dose rates up to 24 Gy min-1 (for nominal energy 10 MV in depth of maximum dose, a source-surface distance of 100 cm and a field size of 10×10 cm2). To guarantee accurate relative and reference dosimetry for the FFF beams, we investigated the charge collection efficiency of multiple air-vented and one liquid ionization chamber for dose rates up to 31.9 Gy min-1. For flattened beams, the ion-collection efficiency of all air-vented ionization chambers (except for the PinPoint chamber) was above 0.995. By removing the flattening filter, we found a reduction in collection efficiency of approximately 0.5-0.9% for a 10 MV beam. For FFF beams, the Markus chamber showed the largest collection efficiency of 0.994. The observed collection efficiencies were dependent on dose per pulse, but independent of the pulse repetition frequency. Using the liquid ionization chamber, the ion-collection efficiency for flattened beams was above 0.990 for all dose rates. However, this chamber showed a low collection efficiency of 0.940 for the FFF 10 MV beam at a dose rate of 31.9 Gy min-1. All investigated air-vented ionization chambers can be reliably used for relative dosimetry of FFF beams. The order of correction for reference dosimetry is given in the manuscript. Due to their increased saturation in high dose rate FFF beams, liquid ionization chambers appear to be unsuitable for dosimetry within these contexts.

Large-area field-ionization detector for the study of Rydberg atoms.

PubMed

Jones, A C L; Piñeiro, A M; Roeder, E E; Rutbeck-Goldman, H J; Tom, H W K; Mills, A P

2016-11-01

We describe here the development and characterization of a micro-channel plate (MCP) based detector designed for the efficient collection and detection of Rydberg positronium (Ps) atoms for use in a time-of-flight apparatus. The designed detector collects Rydberg atoms over a large area (∼4 times greater than the active area of the MCP), ionizing incident atoms and then collecting and focusing the freed positrons onto the MCP. Here we discuss the function, design, and optimization of the device. The detector has an efficiency for Rydberg Ps that is two times larger than that of the γ-ray scintillation detector based scheme it has been designed to replace, with half the background signal. In principle, detectors of the type described here could be readily employed for the detection of any Rydberg atom species, provided a sufficient field can be applied to achieve an ionization rate of ≥10 8 /s. In such cases, the best time resolution would be achieved by collecting ionized electrons rather than the positive ions.

Study of Conical Pulsed Inductive Thruster with Multiple Modes of Operation

NASA Technical Reports Server (NTRS)

Miller, Robert; Eskridge, Richard; Martin, Adam; Rose, Frank

2008-01-01

An electrodeless, pulsed, inductively coupled thruster has several advantages over current electric propulsion designs. The efficiency of a pulsed inductive thruster is dependent upon the pulse characteristics of the device. Therefore, these thrusters are throttleable over a wide range of thrust levels by varying the pulse rate without affecting the thruster efficiency. In addition, by controlling the pulse energy and the mass bit together, the ISP of the thruster can also be varied with minimal efficiency loss over a wide range of ISP levels. Pulsed inductive thrusters will work with a multitude of propellants, including ammonia. Thus, a single pulsed inductive thruster could be used to handle a multitude of mission needs from high thrust to high ISP with one propulsion solution that would be variable in flight. A conical pulsed inductive lab thruster has been built to study this form of electric propulsion in detail. This thruster incorporates many advantages that are meant to enable this technology as a viable space propulsion technology. These advantages include incorporation of solid state switch technology for all switching needs of the thruster and pre-ionization of the propellant gas prior to acceleration. Pre-ionizing will significantly improve coupling efficiency between drive and bias fields and the plasma. This enables lower pulse energy levels without efficiency reduction. Pre-ionization can be accomplished at a small fraction of the drive pulse energy.

Laser-Induced Ionization Efficiency Enhancement On A Filament For Thermal Ionization Mass Spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siegfried, M.

2015-10-14

The evaluation of trace Uranium and Plutonium isotope ratios for nanogram to femtogram material quantities is a vital tool for nuclear counter-proliferation and safeguard activities. Thermal Ionization Mass Spectrometry (TIMS) is generally accepted as the state of the art technology for highly accurate and ultra-trace measurements of these actinide ratios. However, the very low TIMS ionization yield (typically less than 1%) leaves much room for improvement. Enhanced ionization of Nd and Sm from a TIMS filament was demonstrated using wavelength resonance with a nanosecond (pulse width) laser operating at 10 Hz when light was directed toward the filament.1 For thismore » study, femtosecond and picosecond laser capabilities were to be employed to study the dissociation and ionization mechanisms of actinides/lanthanides and measure the enhanced ionization of the metal of interest. Since the underlying chemistry of the actinide/lanthanide carbides produced and dissociated on a TIMS filament is not well understood, the experimental parameters affecting the photodissociation and photoionization with one and two laser beams were to be investigated.« less

First results on Ge resonant laser photoionization in hollow cathode lamp

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scarpa, Daniele, E-mail: daniele.scarpa@lnl.infn.it; Andrighetto, Alberto; Barzakh, Anatoly

2016-02-15

In the framework of the research and development activities of the SPES project regarding the optimization of the radioactive beam production, a dedicated experimental study has been recently started in order to investigate the possibility of in-source ionization of germanium using a set of tunable dye lasers. Germanium is one of the beams to be accelerated by the SPES ISOL facility, which is under construction at Legnaro INFN Laboratories. The three-step, two color ionization schemes have been tested using a Ge hollow cathode lamp. The slow and the fast optogalvanic signals were detected and averaged by an oscilloscope as amore » proof of the laser ionization inside the lamp. As a result, several wavelength scans across the resonances of ionization schemes were collected with the fast optogalvanic signal. Some comparisons of ionization efficiency for different ionization schemes were made. Furthermore, saturation curves of the first excitation transitions have been obtained. This investigation method and the setup built in the laser laboratory of the SPES project can be applied for the photo-ionization scheme studies also for the other possible radioactive elements.« less

Gas engineering studies for high pressure self-sustained diffuse discharge closing switches

NASA Astrophysics Data System (ADS)

Hunter, S. R.; Christophorou, L. G.; Carter, J. G.

The operating voltage and discharge stability of diffuse discharges for fast-closing switch applications are critically dependent on the variation of the ionization (alpha/N) and attachment (eta/N) coefficients with E/N (gas density normalized electric field strength). Gases and gas mixtures which possess low (E/N)/sub lim/ values (i.e., the E/N value when anti alpha/N = alpha/N - eta/N = 0) and effective ionization coefficients, anti alpha/N, which vary slowly with E/N near (E/N)(sub lim) lead to lower voltage (i.e., more efficient) operation with increased discharge stability. Several gas mixtures with these characteristics are discussed. It is argued that further improvements in switch efficiency and discharge stability can be obtained by adding a low ionization onset gas additive to these binary mixtures, such that at low E/N, alpha/N is greater than eta/N, while at higher E/N, eta/N is greater than alpha/N over a restricted E/N range. Several low ionization onset gas additives are suggested and the electron attachment and ionization coefficients in selected gas mixtures which possess these desirable characteristics are given.

Attachment of chloride anion to sugars: mechanistic investigation and discovery of a new dopant for efficient sugar ionization/detection in mass spectrometers.

PubMed

Boutegrabet, Lemia; Kanawati, Basem; Gebefügi, Istvan; Peyron, Dominique; Cayot, Philippe; Gougeon, Régis D; Schmitt-Kopplin, Philippe

2012-10-08

A new method for efficient ionization of sugars in the negative-ion mode of electrospray mass spectrometry is presented. Instead of using strongly hydrophobic dopants such as dichloromethane or chloroform, efficient ionization of sugars has been achieved by using aqueous HCl solution for the first time. This methodology makes it possible to use hydrophilic dopants, which are more appropriate for chromatographic separation techniques with efficient sugar ionization and detection in mass spectrometry. The interaction between chloride anions and monosaccharides (glucose and galactose) was studied by DFT in the gas phase and by implementing the polarizable continuum model (PCM) for calculations in solution at the high B3LYP/6-31+G(d,p)//B3LYP/6-311+G(2d,p) level of theory. In all optimized geometries of identified [M+Cl](-) anions, a non-covalent interaction exists. Differences were revealed between monodentate and bidentate complex anions, with the latter having noticeably higher binding energies. The calculated affinity of glucose and galactose toward the chloride anion in the gas phase and their chloride anion binding energies in solution are in excellent agreement with glucose and galactose [M+Cl](-) experimental intensity profiles that are represented as a function of the chloride ion concentration. Density functional calculations of gas-phase affinities toward chloride anion were also performed for the studied disaccharides sucrose and gentiobiose. All calculations are in excellent agreement with the experimental data. An example is introduced wherein HCl was used to effectively ionize sugars and form chlorinated adduct anions to detect sugars and glycosylated metabolites (anthocyanins) in real biological systems (Vitis vinifera grape extracts and wines), whereas they would not have been easily detectable under standard infusion electrospray mass spectrometry conditions as deprotonated species. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Efficient and robust photo-ionization loading of beryllium ions

NASA Astrophysics Data System (ADS)

Wolf, Sebastian; Studer, Dominik; Wendt, Klaus; Schmidt-Kaler, Ferdinand

2018-02-01

We demonstrate the efficient generation of Be^+ ions with a 60 ns and 150 nJ laser pulse near 235 nm for two-step photo-ionization, proven by subsequent counting of the number of ions loaded into a linear Paul trap. The bandwidth and power of the laser pulse are chosen in such a way that a first, resonant step fully saturates the entire velocity distribution of beryllium atoms effusing from a thermal oven. The second excitation step is driven by the same light field causing efficient non-resonant ionization. Our ion-loading scheme has a similar efficiency as compared to former pathways using two-photon continuous wave laser excitation, but with an order of magnitude lower than average UV light power.

Towards high-resolution laser ionization spectroscopy of the heaviest elements in supersonic gas jet expansion

PubMed Central

Ferrer, R.; Barzakh, A.; Bastin, B.; Beerwerth, R.; Block, M.; Creemers, P.; Grawe, H.; de Groote, R.; Delahaye, P.; Fléchard, X.; Franchoo, S.; Fritzsche, S.; Gaffney, L. P.; Ghys, L.; Gins, W.; Granados, C.; Heinke, R.; Hijazi, L.; Huyse, M.; Kron, T.; Kudryavtsev, Yu.; Laatiaoui, M.; Lecesne, N.; Loiselet, M.; Lutton, F.; Moore, I. D.; Martínez, Y.; Mogilevskiy, E.; Naubereit, P.; Piot, J.; Raeder, S.; Rothe, S.; Savajols, H.; Sels, S.; Sonnenschein, V.; Thomas, J-C; Traykov, E.; Van Beveren, C.; Van den Bergh, P.; Van Duppen, P.; Wendt, K.; Zadvornaya, A.

2017-01-01

Resonant laser ionization and spectroscopy are widely used techniques at radioactive ion beam facilities to produce pure beams of exotic nuclei and measure the shape, size, spin and electromagnetic multipole moments of these nuclei. However, in such measurements it is difficult to combine a high efficiency with a high spectral resolution. Here we demonstrate the on-line application of atomic laser ionization spectroscopy in a supersonic gas jet, a technique suited for high-precision studies of the ground- and isomeric-state properties of nuclei located at the extremes of stability. The technique is characterized in a measurement on actinium isotopes around the N=126 neutron shell closure. A significant improvement in the spectral resolution by more than one order of magnitude is achieved in these experiments without loss in efficiency. PMID:28224987

Reduced Sampling Size with Nanopipette for Tapping-Mode Scanning Probe Electrospray Ionization Mass Spectrometry Imaging

PubMed Central

Kohigashi, Tsuyoshi; Otsuka, Yoichi; Shimazu, Ryo; Matsumoto, Takuya; Iwata, Futoshi; Kawasaki, Hideya; Arakawa, Ryuichi

2016-01-01

Mass spectrometry imaging (MSI) with ambient sampling and ionization can rapidly and easily capture the distribution of chemical components in a solid sample. Because the spatial resolution of MSI is limited by the size of the sampling area, reducing sampling size is an important goal for high resolution MSI. Here, we report the first use of a nanopipette for sampling and ionization by tapping-mode scanning probe electrospray ionization (t-SPESI). The spot size of the sampling area of a dye molecular film on a glass substrate was decreased to 6 μm on average by using a nanopipette. On the other hand, ionization efficiency increased with decreasing solvent flow rate. Our results indicate the compatibility between a reduced sampling area and the ionization efficiency using a nanopipette. MSI of micropatterns of ink on a glass and a polymer substrate were also demonstrated. PMID:28101441

Air ionization as a control technology for off-gas emissions of volatile organic compounds.

PubMed

Kim, Ki-Hyun; Szulejko, Jan E; Kumar, Pawan; Kwon, Eilhann E; Adelodun, Adedeji A; Reddy, Police Anil Kumar

2017-06-01

High energy electron-impact ionizers have found applications mainly in industry to reduce off-gas emissions from waste gas streams at low cost and high efficiency because of their ability to oxidize many airborne organic pollutants (e.g., volatile organic compounds (VOCs)) to CO 2 and H 2 O. Applications of air ionizers in indoor air quality management are limited due to poor removal efficiency and production of noxious side products, e.g., ozone (O 3 ). In this paper, we provide a critical evaluation of the pollutant removal performance of air ionizing system through comprehensive review of the literature. In particular, we focus on removal of VOCs and odorants. We also discuss the generation of unwanted air ionization byproducts such as O 3 , NOx, and VOC oxidation intermediates that limit the use of air-ionizers in indoor air quality management. Copyright © 2017. Published by Elsevier Ltd.

Multiphoton ionization of many-electron atoms and highly-charged ions in intense laser fields: a relativistic time-dependent density functional theory approach

NASA Astrophysics Data System (ADS)

Tumakov, Dmitry A.; Telnov, Dmitry A.; Maltsev, Ilia A.; Plunien, Günter; Shabaev, Vladimir M.

2017-10-01

We develop an efficient numerical implementation of the relativistic time-dependent density functional theory (RTDDFT) to study multielectron highly-charged ions subject to intense linearly-polarized laser fields. The interaction with the electromagnetic field is described within the electric dipole approximation. The resulting time-dependent relativistic Kohn-Sham (RKS) equations possess an axial symmetry and are solved accurately and efficiently with the help of the time-dependent generalized pseudospectral method. As a case study, we calculate multiphoton ionization probabilities of the neutral argon atom and argon-like xenon ion. Relativistic effects are assessed by comparison of our present results with existing non-relativistic data.

Selective ionization of dissolved organic nitrogen by positive ion atmospheric pressure photoionization coupled with Fourier transform ion cyclotron resonance mass spectrometry.

PubMed

Podgorski, David C; McKenna, Amy M; Rodgers, Ryan P; Marshall, Alan G; Cooper, William T

2012-06-05

Dissolved organic nitrogen (DON) comprises a heterogeneous family of organic compounds that includes both well-known biomolecules such as urea or amino acids and more complex, less characterized compounds such as humic and fulvic acids. Typically, DON represents only a small fraction of the total dissolved organic carbon pool and therefore presents inherent problems for chemical analysis and characterization. Here, we demonstrate that DON may be selectively ionized by atmospheric pressure photionization (APPI) and characterized at the molecular level by Fourier transform ion cyclotron resonance mass spectrometry. Unlike electrospray ionization (ESI), APPI ionizes polar and nonpolar compounds, and ionization efficiency is not determined by polarity. APPI is tolerant to salts, due to the thermal treatment inherent to nebulization, and thus avoids salt-adduct formation that can complicate ESI mass spectra. Here, for dissolved organic matter from various aquatic environments, we selectively ionize DON species that are not efficiently ionized by other ionization techniques and demonstrate significant signal-to-noise increase for nitrogen species by use of APPI relative to ESI.

Threshold ionization spectroscopic investigation of supersonic jet-cooled, laser-desorbed Tryptophan

NASA Astrophysics Data System (ADS)

Taherkhani, Mehran; Armentano, Antonio; Černý, Jiří; Müller-Dethlefs, Klaus

2016-07-01

Tryptophan (Trp) was studied by two-colour Photoionization Efficiency (PIE) and Mass Analysed Threshold Ionization (MATI) spectroscopy using a laser desorption apparatus. Conformer A of Trp was excited into the S1 state (34,878 cm-1) and the second laser was scanned around the D0 cation ground and the D1 excited state. No ionization signal into the D0 state could be found, but a clear threshold was observed for the D1 state with an ionization energy of 66,704 ± 3 cm-1 (8.27 eV). This observation is explained in terms of the electronic configurations of the S1 and cationic states.

Ionization of EPA Contaminants in Direct and Dopant-Assisted Atmospheric Pressure Photoionization and Atmospheric Pressure Laser Ionization

NASA Astrophysics Data System (ADS)

Kauppila, Tiina J.; Kersten, Hendrik; Benter, Thorsten

2015-06-01

Seventy-seven EPA priority environmental pollutants were analyzed using gas chromatography-mass spectrometry (GC-MS) equipped with an optimized atmospheric pressure photoionization (APPI) and an atmospheric pressure laser ionization (APLI) interface with and without dopants. The analyzed compounds included e.g., polycyclic aromatic hydrocarbons (PAHs), nitro compounds, halogenated compounds, aromatic compounds with phenolic, acidic, alcohol, and amino groups, phthalate and adipatic esters, and aliphatic ethers. Toluene, anisole, chlorobenzene, and acetone were tested as dopants. The widest range of analytes was ionized using direct APPI (66/77 compounds). The introduction of dopants decreased the amount of compounds ionized in APPI (e.g., 54/77 with toluene), but in many cases the ionization efficiency increased. While in direct APPI the formation of molecular ions via photoionization was the main ionization reaction, dopant-assisted (DA) APPI promoted ionization reactions, such as charge exchange and proton transfer. Direct APLI ionized a much smaller amount of compounds than APPI (41/77 compounds), showing selectivity towards compounds with low ionization energies (IEs) and long-lived resonantly excited intermediate states. DA-APLI, however, was able to ionize a higher amount of compounds (e.g. 51/77 with toluene), as the ionization took place entirely through dopant-assisted ion/molecule reactions similar to those in DA-APPI. Best ionization efficiency in APPI and APLI (both direct and DA) was obtained for PAHs and aromatics with O- and N-functionalities, whereas nitro compounds and aliphatic ethers were the most difficult to ionize. Halogenated aromatics and esters were (mainly) ionized in APPI, but not in APLI.

Sensitive screening of abused drugs in dried blood samples using ultra-high-performance liquid chromatography-ion booster-quadrupole time-of-flight mass spectrometry.

PubMed

Chepyala, Divyabharathi; Tsai, I-Lin; Liao, Hsiao-Wei; Chen, Guan-Yuan; Chao, Hsi-Chun; Kuo, Ching-Hua

2017-03-31

An increased rate of drug abuse is a major social problem worldwide. The dried blood spot (DBS) sampling technique offers many advantages over using urine or whole blood sampling techniques. This study developed a simple and efficient ultra-high-performance liquid chromatography-ion booster-quadrupole time-of-flight mass spectrometry (UHPLC-IB-QTOF-MS) method for the analysis of abused drugs and their metabolites using DBS. Fifty-seven compounds covering the most commonly abused drugs, including amphetamines, opioids, cocaine, benzodiazepines, barbiturates, and many other new and emerging abused drugs, were selected as the target analytes of this study. An 80% acetonitrile solvent with a 5-min extraction by Geno grinder was used for sample extraction. A Poroshell column was used to provide efficient separation, and under optimal conditions, the analytical times were 15 and 5min in positive and negative ionization modes, respectively. Ionization parameters of both electrospray ionization source and ion booster (IB) source containing an extra heated zone were optimized to achieve the best ionization efficiency of the investigated abused drugs. In spite of their structural diversity, most of the abused drugs showed an enhanced mass response with the high temperature ionization from an extra heated zone of IB source. Compared to electrospray ionization, the ion booster (IB) greatly improved the detection sensitivity for 86% of the analytes by 1.5-14-fold and allowed the developed method to detect trace amounts of compounds on the DBS cards. The validation results showed that the coefficients of variation of intra-day and inter-day precision in terms of the signal intensity were lower than 19.65%. The extraction recovery of all analytes was between 67.21 and 115.14%. The limits of detection of all analytes were between 0.2 and 35.7ngmL -1 . The stability study indicated that 7% of compounds showed poor stability (below 50%) on the DBS cards after 6 months of storage at room temperature and -80°C. The reported method provides a new direction for abused drug screening using DBS. Copyright © 2017 Elsevier B.V. All rights reserved.

Carbon Nanotube Fiber Ionization Mass Spectrometry: A Fundamental Study of a Multi-Walled Carbon Nanotube Functionalized Corona Discharge Pin for Polycyclic Aromatic Hydrocarbons Analysis.

PubMed

Nahan, Keaton S; Alvarez, Noe; Shanov, Vesselin; Vonderheide, Anne

2017-11-01

Mass spectrometry continues to tackle many complicated tasks, and ongoing research seeks to simplify its instrumentation as well as sampling. The desorption electrospray ionization (DESI) source was the first ambient ionization source to function without extensive gas requirements and chromatography. Electrospray techniques generally have low efficiency for ionization of nonpolar analytes and some researchers have resorted to methods such as direct analysis in real time (DART) or desorption atmospheric pressure chemical ionization (DAPCI) for their analysis. In this work, a carbon nanotube fiber ionization (nanoCFI) source was developed and was found to be capable of solid phase microextraction (SPME) of nonpolar analytes as well as ionization and sampling similar to that of direct probe atmospheric pressure chemical ionization (DP-APCI). Conductivity and adsorption were maintained by utilizing a corona pin functionalized with a multi-walled carbon nanotube (MWCNT) thread. Quantitative work with the nanoCFI source with a designed corona discharge pin insert demonstrated linearity up to 0.97 (R 2 ) of three target PAHs with phenanthrene internal standard. Graphical Abstract ᅟ.

Carbon Nanotube Fiber Ionization Mass Spectrometry: A Fundamental Study of a Multi-Walled Carbon Nanotube Functionalized Corona Discharge Pin for Polycyclic Aromatic Hydrocarbons Analysis

NASA Astrophysics Data System (ADS)

Nahan, Keaton S.; Alvarez, Noe; Shanov, Vesselin; Vonderheide, Anne

2017-09-01

Mass spectrometry continues to tackle many complicated tasks, and ongoing research seeks to simplify its instrumentation as well as sampling. The desorption electrospray ionization (DESI) source was the first ambient ionization source to function without extensive gas requirements and chromatography. Electrospray techniques generally have low efficiency for ionization of nonpolar analytes and some researchers have resorted to methods such as direct analysis in real time (DART) or desorption atmospheric pressure chemical ionization (DAPCI) for their analysis. In this work, a carbon nanotube fiber ionization (nanoCFI) source was developed and was found to be capable of solid phase microextraction (SPME) of nonpolar analytes as well as ionization and sampling similar to that of direct probe atmospheric pressure chemical ionization (DP-APCI). Conductivity and adsorption were maintained by utilizing a corona pin functionalized with a multi-walled carbon nanotube (MWCNT) thread. Quantitative work with the nanoCFI source with a designed corona discharge pin insert demonstrated linearity up to 0.97 (R2) of three target PAHs with phenanthrene internal standard. [Figure not available: see fulltext.

Heating of the solar chromosphere by ionization pumping

NASA Technical Reports Server (NTRS)

Lindsey, C. A.

1981-01-01

A new theory is proposed to explain the heating of the solar chromosphere, and possibly the corona, by the dissipation of hydrodynamic compression waves. The basis of the dissipative mechanism, here referred to as ionization pumping, is hysteresis caused by irreversible relaxation of the chromospheric medium to ionization equilibrium following pressure perturbations. In the middle chromosphere, where hydrogen is partially ionized, it is shown that ionization pumping will cause strong dissipation of waves whose periods are 200s or less. This could cause heating of the chromosphere sufficient to compensate for the radiative losses. The mechanism retains a high efficiency for waves of arbitrarily small amplitude and, thus, can be more efficient than shock dissipation for small perturbations in pressure. The formation of shocks therefore is not required for the dissipation of waves whose periods are several minutes or less.

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

PubMed Central

Short, Luke Chandler; Cai, Sheng-Suan; Syage, Jack A.

2009-01-01

The technique of atmospheric pressure photoionization (APPI) has several advantages over electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), including efficient ionization of non-polar or low charge affinity compounds, reduced susceptibility to ion suppression, high sensitivity, and large linear dynamic range. These benefits are greatest at low flow rates (i.e., ≤100 μL/min), while at a higher flow, photon absorption and ion-molecule reactions become significant. Under certain circumstances, APPI signal and S/N have been observed to excel at higher flow, which may be due to a non-photoionzation mechanism. To better understand APPI at higher flow rates, we have selected three lamps (Xe, Kr and Ar) and four mobile phases typical for reverse-phase, high-pressure liquid chromatography: acetonitrile, methanol, (1:1) acetonitrile:water and (1:1) methanol:water. As test compounds, three polyaromatic hydrocarbons are studied: benzo[a]pyrene, indeno[1,2,3-c,d]pyrene and benz[a]anthracene. We find that solvent photoabsorption cross-section is not the only parameter in explaining relative signal intensity, but that solvent photo-ion chemistry can also play a significant role. Three conclusions from this investigation are: (i) Methanol photoionization leads to protonated methanol clusters that can result in chemical ionization of analyte molecule; (ii) Use of the Ar lamp often results in greater signal and S/N; (iii) Acetonitrile photoionization is less efficient and resulting clusters are too strongly bound to efficiently chemically ionize the analyte, so that analyte ion formation is dominated by direct photoionization. PMID:17188507

APPI-MS: effects of mobile phases and VUV lamps on the detection of PAH compounds.

PubMed

Short, Luke Chandler; Cai, Sheng-Suan; Syage, Jack A

2007-04-01

The technique of atmospheric pressure photoionization (APPI) has several advantages over electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), including efficient ionization of nonpolar or low charge affinity compounds, reduced susceptibility to ion suppression, high sensitivity, and large linear dynamic range. These benefits are greatest at low flow rates (i.e.,

Effect of matching between the magnetic field and channel length on the performance of low sputtering Hall thrusters

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Boyang, Jia; Sun, Hezhi; Wei, Liqiu; Peng, Wuji; Li, Peng; Yu, Daren

2018-02-01

Discharge characteristics of a non-wall-loss Hall thruster were studied under different channel lengths using a design based on pushing a magnetic field through a double permanent magnet ring. The effect of different magnetic field intensities and channel lengths on ionization, efficiency, and plume divergence angle were studied. The experimental results show that propellant utilization is improved for optimal matching between the magnetic field and channel length. While matching the magnetic field and channel length, the ionization position of the neutral gas changes. The ion flow is effectively controlled, allowing the thrust force, specific impulse, and efficiency to be improved. Our study shows that the channel length is an important design parameter to consider for improving the performance of non-wall-loss Hall thrusters.

Was Star Formation Suppressed in High-Redshift Minihalos?

NASA Astrophysics Data System (ADS)

Haiman, Zoltán; Bryan, Greg L.

2006-10-01

The primordial gas in the earliest dark matter halos, collapsing at redshifts z~20, with masses Mhalo~106 Msolar and virial temperatures Tvir<104 K, relied on the presence of molecules for cooling. Several theoretical studies have suggested that gas contraction and star formation in these minihalos was suppressed by radiative, chemical, thermal, and dynamical feedback processes. The recent measurement by the Wilkinson Microwave Anisotropy Probe (WMAP) of the optical depth to electron scattering, τ~0.09+/-0.03, provides the first empirical evidence for this suppression. The new WMAP result is consistent with vanilla models of reionization, in which ionizing sources populate cold dark matter halos down to a virial temperature of Tvir=104 K. On the other hand, we show that in order to avoid overproducing the optical depth, the efficiency for the production of ionizing photons in minihalos must have been about an order of magnitude lower than expected from massive metal-free stars and lower than the efficiency in large halos that can cool via atomic hydrogen (Tvir>104 K). This conclusion is insensitive to assumptions about the efficiency of ionizing photon production in the large halos, as long as reionization ends by z=6, as required by the spectra of bright quasars at z<~6. Our conclusion is strengthened if the clumping of the ionized gas evolves with redshift, as suggested by semianalytical predictions and three-dimensional numerical simulations.

Current developments with TRIUMF's titanium-sapphire laser based resonance ionization laser ion source. An overview

NASA Astrophysics Data System (ADS)

Lassen, J.; Li, R.; Raeder, S.; Zhao, X.; Dekker, T.; Heggen, H.; Kunz, P.; P. Levy, C. D.; Mostanmand, M.; Teigelhöfer, A.; Ames, F.

2017-11-01

Developments at TRIUMF's isotope separator and accelerator (ISAC) resonance ionization laser ion source (RILIS) in the past years have concentrated on increased reliability for on-line beam delivery of radioactive isotopes to experiments, as well as increasing the number of elements available through resonance ionization and searching for ionization schemes with improved efficiency. The current status of these developments is given with a list of two step laser ionization schemes implemented recently.

A New Electrospray Aerosol Generator with High Particle Transmission Efficiency

PubMed Central

Fu, Huijing; Patel, Anand C.; Holtzman, Michael J.; Chen, Da-Ren

2012-01-01

A new single-capillary electrospray (ES) aerosol generator has been developed for monodisperse particle production with maximal transmission efficiency. The new generator consists of both a spray chamber in a point-to-orifice-plate configuration and a charge reduction chamber that can hold up to 4 Nuclespot ionizers (Model P-2042, NRD Inc.). The 2 chambers are partitioned by an orifice plate. To optimize the particle transmission efficiency of the prototype, a systematic study was performed on the generator by varying the system setup and operation. Two key dimensions of the generator setup, the orifice diameter and the distance from the capillary tip to the orifice plate, were varied. Fluorescence analysis was applied to characterize the loss of ES-generated particles at different locations of the prototype. It was found that particle loss in the generator could be reduced by either increasing the orifice diameter or decreasing the distance between the capillary tip and the orifice plate. Increasing either the total radioactivity of the ionizers or the flowrate of the particle carrier gas also further decreased the particle loss in the system. The maximum particle transmission efficiency of 88.0% was obtained with the spray chamber fully opened to the charge reduction chamber, the capillary tip at the same level as the orifice plate, and 4 bipolar ionizers installed. PMID:22829715

Synthetic oligomer analysis using atmospheric pressure photoionization mass spectrometry at different photon energies.

PubMed

Desmazières, Bernard; Legros, Véronique; Giuliani, Alexandre; Buchmann, William

2014-01-15

Atmospheric pressure photoionization (APPI) followed by mass spectrometric detection was used to ionize a variety of polymers: polyethylene glycol, polymethyl methacrylate, polystyrene, and polysiloxane. In most cases, whatever the polymer or the solvent used (dichloromethane, tetrahydrofuran, hexane, acetone or toluene), only negative ion mode produced intact ions such as chlorinated adducts, with no or few fragmentations, in contrast to the positive ion mode that frequently led to important in-source fragmentations. In addition, it was shown that optimal detection of polymer distributions require a fine tuning of other source parameters such as temperature and ion transfer voltage. Series of mass spectra were recorded in the negative mode, in various solvents (dichloromethane, tetrahydrofuran, hexane, toluene, and acetone), by varying the photon energy from 8eV up to 10.6eV using synchrotron radiation. To these solvents, addition of a classical APPI dopant (toluene or acetone) was not necessary. Courtesy of the synchrotron radiation, it was demonstrated that the photon energy required for an efficient ionization of the polymer was correlated to the ionization energy of the solvent. As commercial APPI sources typically use krypton lamps with energy fixed at 10eV and 10.6eV, the study of the ionization of polymers over a wavelength range allowed to confirm and refine the previously proposed ionization mechanisms. Moreover, the APPI source can efficiently be used as an interface between size exclusion chromatography or reverse phase liquid chromatography and MS for the study of synthetic oligomers. However, the photoionization at fixed wavelength of polymer standards with different molecular weights showed that it was difficult to obtain intact ionized oligomers with molecular weights above a few thousands. Copyright © 2013 Elsevier B.V. All rights reserved.

Spectroscopy of the UO+2 cation and the delayed ionization of UO2.

PubMed

Merritt, Jeremy M; Han, Jiande; Heaven, Michael C

2008-02-28

Vibronically resolved spectra for the UO+2 cation have been recorded using the pulsed field ionization zero electron kinetic energy (PFI-ZEKE) technique. For the ground state, long progressions in both the bending and symmetric stretch vibrations were observed. Bend and stretch progressions of the first electronically excited state were also observed, and the origin was found at an energy of 2678 cm(-1) above the ground state zero-point level. This observation is consistent with a recent theoretical prediction [Infante et al., J. Chem. Phys. 127, 124308 (2007)]. The ionization energy for UO2, derived from the PFI-ZEKE spectrum, namely, 6.127(1) eV, is in excellent agreement with the value obtained from an earlier photoionization efficiency measurement. Delayed ionization of UO2 in the gas phase has been reported previously [Han et al., J. Chem. Phys. 120, 5155 (2004)]. Here, we extend the characterization of the delayed ionization process by performing a quantitative study of the ionization rate as a function of the energy above the ionization threshold. The ionization rate was found to be 5 x 10(6) s(-1) at threshold, and increased linearly with increasing energy in the range investigated (0-1200 cm(-1)).

F--Ray: A new algorithm for efficient transport of ionizing radiation

NASA Astrophysics Data System (ADS)

Mao, Yi; Zhang, J.; Wandelt, B. D.; Shapiro, P. R.; Iliev, I. T.

2014-04-01

We present a new algorithm for the 3D transport of ionizing radiation, called F2-Ray (Fast Fourier Ray-tracing method). The transfer of ionizing radiation with long mean free path in diffuse intergalactic gas poses a special challenge to standard numerical methods which transport the radiation in position space. Standard methods usually trace each individual ray until it is fully absorbed by the intervening gas. If the mean free path is long, the computational cost and memory load are likely to be prohibitive. We have developed an algorithm that overcomes these limitations and is, therefore, significantly more efficient. The method calculates the transfer of radiation collectively, using the Fast Fourier Transform to convert radiation between position and Fourier spaces, so the computational cost will not increase with the number of ionizing sources. The method also automatically combines parallel rays with the same frequency at the same grid cell, thereby minimizing the memory requirement. The method is explicitly photon-conserving, i.e. the depletion of ionizing photons is guaranteed to equal the photoionizations they caused, and explicitly obeys the periodic boundary condition, i.e. the escape of ionizing photons from one side of a simulation volume is guaranteed to be compensated by emitting the same amount of photons into the volume through the opposite side. Together, these features make it possible to numerically simulate the transfer of ionizing photons more efficiently than previous methods. Since ionizing radiation such as the X-ray is responsible for heating the intergalactic gas when first stars and quasars form at high redshifts, our method can be applied to simulate thermal distribution, in addition to cosmic reionization, in three-dimensional inhomogeneous cosmological density field.

Analysis of nonderivatized steroids by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using C70 fullerene as matrix.

PubMed

Montsko, Gergely; Vaczy, Alexandra; Maasz, Gabor; Mernyak, Erzsebet; Frank, Eva; Bay, Csaba; Kadar, Zalan; Ohmacht, Robert; Wolfling, Janos; Mark, Laszlo

2009-10-01

Neutral steroid hormones are currently analyzed by gas or liquid chromatography/mass spectrometry based methods. Most of the steroid compounds, however, lack volatility and do not contain polar groups, which results in inadequate chromatographic behavior and low ionization efficiency. Derivatization of the steroids to form more volatile, thermostable, and charged products solves this difficulty, but the derivatization of compounds with unknown chemical moieties is not an easy task. In this study, a rapid, high-throughput, sensitive matrix-assisted laser desorption/ionization time-of-flight mass spectrometry method is described using C(70) fullerene as a matrix compound. The application of the method is demonstrated for five general sex steroids and for synthetic steroid compounds in both negative and positive ionization modes.

Design of a secondary ionization target for direct production of a C- beam from CO2 pulses for online AMS.

PubMed

Salazar, Gary; Ognibene, Ted

2013-01-01

We designed and optimized a novel device "target" that directs a CO 2 gas pulse onto a Ti surface where a Cs + beam generates C - from the CO 2 . This secondary ionization target enables an accelerator mass spectrometer to ionize pulses of CO 2 in the negative mode to measure 14 C/ 12 C isotopic ratios in real time. The design of the targets were based on computational flow dynamics, ionization mechanism and empirical optimization. As part of the ionization mechanism, the adsorption of CO 2 on the Ti surface was fitted with the Jovanovic-Freundlich isotherm model using empirical and simulation data. The inferred adsorption constants were in good agreement with other works. The empirical optimization showed that amount of injected carbon and the flow speed of the helium carrier gas improve the ionization efficiency and the amount of 12 C - produced until reaching a saturation point. Linear dynamic range between 150 and 1000 ng of C and optimum carrier gas flow speed of around 0.1 mL/min were shown. It was also shown that the ionization depends on the area of the Ti surface and Cs + beam cross-section. A range of ionization efficiency of 1-2.5% was obtained by optimizing the described parameters.

Electron-muon ranger: performance in the MICE muon beam

NASA Astrophysics Data System (ADS)

Adams, D.; Alekou, A.; Apollonio, M.; Asfandiyarov, R.; Barber, G.; Barclay, P.; de Bari, A.; Bayes, R.; Bayliss, V.; Bene, P.; Bertoni, R.; Blackmore, V. J.; Blondel, A.; Blot, S.; Bogomilov, M.; Bonesini, M.; Booth, C. N.; Bowring, D.; Boyd, S.; Bradshaw, T. W.; Bravar, U.; Bross, A. D.; Cadoux, F.; Capponi, M.; Carlisle, T.; Cecchet, G.; Charnley, C.; Chignoli, F.; Cline, D.; Cobb, J. H.; Colling, G.; Collomb, N.; Coney, L.; Cooke, P.; Courthold, M.; Cremaldi, L. M.; Debieux, S.; DeMello, A.; Dick, A.; Dobbs, A.; Dornan, P.; Drielsma, F.; Filthaut, F.; Fitzpatrick, T.; Franchini, P.; Francis, V.; Fry, L.; Gallagher, A.; Gamet, R.; Gardener, R.; Gourlay, S.; Grant, A.; Graulich, J. S.; Greis, J.; Griffiths, S.; Hanlet, P.; Hansen, O. M.; Hanson, G. G.; Hart, T. L.; Hartnett, T.; Hayler, T.; Heidt, C.; Hills, M.; Hodgson, P.; Hunt, C.; Husi, C.; Iaciofano, A.; Ishimoto, S.; Kafka, G.; Kaplan, D. M.; Karadzhov, Y.; Kim, Y. K.; Kuno, Y.; Kyberd, P.; Lagrange, J.-B.; Langlands, J.; Lau, W.; Leonova, M.; Li, D.; Lintern, A.; Littlefield, M.; Long, K.; Luo, T.; Macwaters, C.; Martlew, B.; Martyniak, J.; Masciocchi, F.; Mazza, R.; Middleton, S.; Moretti, A.; Moss, A.; Muir, A.; Mullacrane, I.; Nebrensky, J. J.; Neuffer, D.; Nichols, A.; Nicholson, R.; Nicola, L.; Noah Messomo, E.; Nugent, J. C.; Oates, A.; Onel, Y.; Orestano, D.; Overton, E.; Owens, P.; Palladino, V.; Pasternak, J.; Pastore, F.; Pidcott, C.; Popovic, M.; Preece, R.; Prestemon, S.; Rajaram, D.; Ramberger, S.; Rayner, M. A.; Ricciardi, S.; Roberts, T. J.; Robinson, M.; Rogers, C.; Ronald, K.; Rothenfusser, K.; Rubinov, P.; Rucinski, P.; Sakamato, H.; Sanders, D. A.; Sandström, R.; Santos, E.; Savidge, T.; Smith, P. J.; Snopok, P.; Soler, F. J. P.; Speirs, D.; Stanley, T.; Stokes, G.; Summers, D. J.; Tarrant, J.; Taylor, I.; Tortora, L.; Torun, Y.; Tsenov, R.; Tunnell, C. D.; Uchida, M. A.; Vankova-Kirilova, G.; Virostek, S.; Vretenar, M.; Warburton, P.; Watson, S.; White, C.; Whyte, C. G.; Wilson, A.; Wisting, H.; Yang, X.; Young, A.; Zisman, M.

2015-12-01

The Muon Ionization Cooling Experiment (MICE) will perform a detailed study of ionization cooling to evaluate the feasibility of the technique. To carry out this program, MICE requires an efficient particle-identification (PID) system to identify muons. The Electron-Muon Ranger (EMR) is a fully-active tracking-calorimeter that forms part of the PID system and tags muons that traverse the cooling channel without decaying. The detector is capable of identifying electrons with an efficiency of 98.6%, providing a purity for the MICE beam that exceeds 99.8%. The EMR also proved to be a powerful tool for the reconstruction of muon momenta in the range 100-280 MeV/c.

Quantum Phenomena in High Energy Density Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murnane, Margaret; Kapteyn, Henry

The possibility of implementing efficient (phase matched) HHG upconversion of deep- UV lasers in multiply-ionized plasmas, with potentially unprecedented conversion efficiency is a fascinating prospect. HHG results from the extreme nonlinear response of matter to intense laser light:high harmonics are radiated as a result of a quantum coherent electron recollision process that occurs during laser field ionization of an atom. Under current support from this grant in work published in Science in 2015, we discovered a new regime of bright HHG in highly-ionized plasmas driven by intense UV lasers, that generates bright harmonics to photon energies >280eV

The ionization efficiency of aluminum and iron at meteoric velocities

NASA Astrophysics Data System (ADS)

DeLuca, Michael; Munsat, Tobin; Thomas, Evan; Sternovsky, Zoltan

2018-07-01

The ionization efficiency of aluminum was measured in the laboratory over an extended velocity range of 10.8-73.4 km/s and compared to available models. The measurements were made by shooting submicron-sized aluminum dust particles into an air chamber using the University of Colorado's dust accelerator facility. The ionization efficiency, β, is calculated from the total charge generated in the chamber during the complete ablation of particles of known mass. An array of photomultiplier tubes observed the light production by a subset of particles in the chamber to confirm that a moderate deceleration of the ablating particles occurred at low velocities. This information allows the interpretation of the β measurements to be extended to velocities <20 km/s, with the understanding that the low-velocity β measurements are lower limits. Updated β measurements for iron particles are also reported over an extended velocity range compared to previously published data: 10.5-87.3 km/s. The measurements are fit to functions for the ionization efficiency across the entire velocity range, and a semi-empirical function is presented which matches the shape of the measured β curves for aluminum and iron at both high and low velocities.

Cosmic distribution of highly ionized metals and their physical conditions in the EAGLE simulations

NASA Astrophysics Data System (ADS)

Rahmati, Alireza; Schaye, Joop; Crain, Robert A.; Oppenheimer, Benjamin D.; Schaller, Matthieu; Theuns, Tom

2016-06-01

We study the distribution and evolution of highly ionized intergalactic metals in the Evolution and Assembly of Galaxies and their Environment (EAGLE) cosmological, hydrodynamical simulations. EAGLE has been shown to reproduce a wide range of galaxy properties while its subgrid feedback was calibrated without considering gas properties. We compare the predictions for the column density distribution functions (CDDFs) and cosmic densities of Si IV, C IV, N V, O VI and Ne VIII absorbers with observations at redshift z = 0 to ˜6 and find reasonable agreement, although there are some differences. We show that the typical physical densities of the absorbing gas increase with column density and redshift, but decrease with the ionization energy of the absorbing ion. The typical metallicity increases with both column density and time. The fraction of collisionally ionized metal absorbers increases with time and ionization energy. While our results show little sensitivity to the presence or absence of AGN feedback, increasing/decreasing the efficiency of stellar feedback by a factor of 2 substantially decreases/increases the CDDFs and the cosmic densities of the metal ions. We show that the impact of the efficiency of stellar feedback on the CDDFs and cosmic densities is largely due to its effect on the metal production rate. However, the temperatures of the metal absorbers, particularly those of strong O VI, are directly sensitive to the strength of the feedback.

Electrochemical Ionization and Analyte Charging in the Array of Micromachined UltraSonic Electrospray (AMUSE) Ion Source

PubMed Central

Forbes, Thomas P.; Degertekin, F. Levent; Fedorov, Andrei G.

2010-01-01

Electrochemistry and ion transport in a planar array of mechanically-driven, droplet-based ion sources are investigated using an approximate time scale analysis and in-depth computational simulations. The ion source is modeled as a controlled-current electrolytic cell, in which the piezoelectric transducer electrode, which mechanically drives the charged droplet generation using ultrasonic atomization, also acts as the oxidizing/corroding anode (positive mode). The interplay between advective and diffusive ion transport of electrochemically generated ions is analyzed as a function of the transducer duty cycle and electrode location. A time scale analysis of the relative importance of advective vs. diffusive ion transport provides valuable insight into optimality, from the ionization prospective, of alternative design and operation modes of the ion source operation. A computational model based on the solution of time-averaged, quasi-steady advection-diffusion equations for electroactive species transport is used to substantiate the conclusions of the time scale analysis. The results show that electrochemical ion generation at the piezoelectric transducer electrodes located at the back-side of the ion source reservoir results in poor ionization efficiency due to insufficient time for the charged analyte to diffuse away from the electrode surface to the ejection location, especially at near 100% duty cycle operation. Reducing the duty cycle of droplet/analyte ejection increases the analyte residence time and, in turn, improves ionization efficiency, but at an expense of the reduced device throughput. For applications where this is undesirable, i.e., multiplexed and disposable device configurations, an alternative electrode location is incorporated. By moving the charging electrode to the nozzle surface, the diffusion length scale is greatly reduced, drastically improving ionization efficiency. The ionization efficiency of all operating conditions considered is expressed as a function of the dimensionless Peclet number, which defines the relative effect of advection as compared to diffusion. This analysis is general enough to elucidate an important role of electrochemistry in ionization efficiency of any arrayed ion sources, be they mechanically-driven or electrosprays, and is vital for determining optimal design and operation conditions. PMID:20607111

Fundamental Studies of Molecular Secondary Ion Mass Spectrometry Ionization Probability Measured With Femtosecond, Infrared Laser Post-Ionization

NASA Astrophysics Data System (ADS)

Popczun, Nicholas James

The work presented in this dissertation is focused on increasing the fundamental understanding of molecular secondary ion mass spectrometry (SIMS) ionization probability by measuring neutral molecule behavior with femtosecond, mid-infrared laser post-ionization (LPI). To accomplish this, a model system was designed with a homogeneous organic film comprised of coronene, a polycyclic hydrocarbon which provides substantial LPI signal. Careful consideration was given to signal lost to photofragmentation and undersampling of the sputtered plume that is contained within the extraction volume of the mass spectrometer. This study provided the first ionization probability for an organic compound measured directly by the relative secondary ions and sputtered neutral molecules using a strong-field ionization (SFI) ionization method. The measured value of ˜10-3 is near the upper limit of previous estimations of ionization probability for organic molecules. The measurement method was refined, and then applied to a homogeneous guanine film, which produces protonated secondary ions. This measurement found the probability of protonation to occur to be on the order of 10-3, although with less uncertainty than that of the coronene. Finally, molecular depth profiles were obtained for SIMS and LPI signals as a function of primary ion fluence to determine the effect of ionization probability on the depth resolution of chemical interfaces. The interfaces chosen were organic/inorganic interfaces to limit chemical mixing. It is shown that approaching the inorganic chemical interface can enhance or suppress the ionization probability for the organic molecule, which can lead to artificially sharpened or broadened depths, respectively. Overall, the research described in this dissertation provides new methods for measuring ionization efficiency in SIMS in both absolute and relative terms, and will inform both innovation in the technique, as well as increase understanding of depth-dependent experiments.

Peptides Labeled with Pyridinium Salts for Sensitive Detection and Sequencing by Electrospray Tandem Mass Spectrometry

NASA Astrophysics Data System (ADS)

Waliczek, Mateusz; Kijewska, Monika; Rudowska, Magdalena; Setner, Bartosz; Stefanowicz, Piotr; Szewczuk, Zbigniew

2016-11-01

Mass spectrometric analysis of trace amounts of peptides may be problematic due to the insufficient ionization efficiency resulting in limited sensitivity. One of the possible ways to overcome this problem is the application of ionization enhancers. Herein we developed new ionization markers based on 2,4,6-triphenylpyridinium and 2,4,6-trimethylpyridinium salts. Using of inexpensive and commercially available pyrylium salt allows selective derivatization of primary amino groups, especially those sterically unhindered, such as ɛ-amino group of lysine. The 2,4,6-triphenylpyridinium modified peptides generate in MS/MS experiments an abundant protonated 2,4,6-triphenylpyridinium ion. This fragment is a promising reporter ion for the multiple reactions monitoring (MRM) analysis. In addition, the fixed positive charge of the pyridinium group enhances the ionization efficiency. Other advantages of the proposed ionization enhancers are the simplicity of derivatization of peptides and the possibility of convenient incorporation of isotopic labels into derivatized peptides.

Applications of High-Resolution Electrospray Ionization Mass Spectrometry to Measurements of Average Oxygen to Carbon Ratios in Secondary Organic Aerosols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bateman, Adam P.; Laskin, Julia; Laskin, Alexander

2012-07-02

The applicability of high resolution electrospray ionization mass spectrometry (HR ESI-MS) to measurements of the average oxygen to carbon ratio (O/C) in organic aerosols was investigated. Solutions with known average O/C containing up to 10 standard compounds representative of secondary organic aerosol (SOA) were analyzed and corresponding electrospray ionization efficiencies were quantified. The assumption of equal ionization efficiency commonly used in estimating O/C ratios of organic aerosols was found to be reasonably accurate. We found that the accuracy of the measured O/C ratios increases by averaging the values obtained from both (+) and (-) modes. A correlation was found betweenmore » the ratio of the ionization efficiencies in the positive and negative ESI modes with the octanol-water partition constant, and more importantly, with the compound's O/C. To demonstrate the utility of this correlation for estimating average O/C values of unknown mixtures, we analyzed the ESI (+) and ESI (-) data for SOA produced by oxidation of limonene and isoprene and compared to online O/C measurements using an aerosol mass spectrometer (AMS). This work demonstrates that the accuracy of the HR ESI-MS methods is comparable to that of the AMS, with the added benefit of molecular identification of the aerosol constituents.« less

Efficient ionisation of calcium, strontium and barium by resonant laser pumping

NASA Technical Reports Server (NTRS)

Skinner, C. H.

1980-01-01

Efficient ionization has been observed when an atomic vapor of strontium, barium or calcium was illuminated with a long pulse tunable laser at the frequency of the atomic resonance line. The variation in the degree of ionization with neutral density and laser intensity has been measured using the 'hook' method. The maximum ionization observed was 94%. Excited state populations were measured yielding an excitation temperature (depending on exact experimental conditions) in the region of 0.4 eV. The decay of ion density after the laser pulse was monitored and the recombination coefficients determined. The results are interpreted in terms of an electron heating model.

Large scale nanoparticle screening for small molecule analysis in laser desorption ionization mass spectrometry

DOE PAGES

Yagnik, Gargey B.; Hansen, Rebecca L.; Korte, Andrew R.; ...

2016-08-30

Nanoparticles (NPs) have been suggested as efficient matrixes for small molecule profiling and imaging by laser-desorption ionization mass spectrometry (LDI-MS), but so far there has been no systematic study comparing different NPs in the analysis of various classes of small molecules. Here, we present a large scale screening of 13 NPs for the analysis of two dozen small metabolite molecules. Many NPs showed much higher LDI efficiency than organic matrixes in positive mode and some NPs showed comparable efficiencies for selected analytes in negative mode. Our results suggest that a thermally driven desorption process is a key factor for metalmore » oxide NPs, but chemical interactions are also very important, especially for other NPs. Furthermore, the screening results provide a useful guideline for the selection of NPs in the LDI-MS analysis of small molecules.« less

Large scale nanoparticle screening for small molecule analysis in laser desorption ionization mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yagnik, Gargey B.; Hansen, Rebecca L.; Korte, Andrew R.

Nanoparticles (NPs) have been suggested as efficient matrixes for small molecule profiling and imaging by laser-desorption ionization mass spectrometry (LDI-MS), but so far there has been no systematic study comparing different NPs in the analysis of various classes of small molecules. Here, we present a large scale screening of 13 NPs for the analysis of two dozen small metabolite molecules. Many NPs showed much higher LDI efficiency than organic matrixes in positive mode and some NPs showed comparable efficiencies for selected analytes in negative mode. Our results suggest that a thermally driven desorption process is a key factor for metalmore » oxide NPs, but chemical interactions are also very important, especially for other NPs. Furthermore, the screening results provide a useful guideline for the selection of NPs in the LDI-MS analysis of small molecules.« less

Control of nitromethane photoionization efficiency with shaped femtosecond pulses.

PubMed

Roslund, Jonathan; Shir, Ofer M; Dogariu, Arthur; Miles, Richard; Rabitz, Herschel

2011-04-21

The applicability of adaptive femtosecond pulse shaping is studied for achieving selectivity in the photoionization of low-density polyatomic targets. In particular, optimal dynamic discrimination (ODD) techniques exploit intermediate molecular electronic resonances that allow a significant increase in the photoionization efficiency of nitromethane with shaped near-infrared femtosecond pulses. The intensity bias typical of high-photon number, nonresonant ionization is accounted for by reference to a strictly intensity-dependent process. Closed-loop adaptive learning is then able to discover a pulse form that increases the ionization efficiency of nitromethane by ∼150%. The optimally induced molecular dynamics result from entry into a region of parameter space inaccessible with intensity-only control. Finally, the discovered pulse shape is demonstrated to interact with the molecular system in a coherent fashion as assessed from the asymmetry between the response to the optimal field and its time-reversed counterpart.

Study of the ionization rate of the released deuterium in vacuum arc discharges with metal deuteride cathodes

NASA Astrophysics Data System (ADS)

Liu, Fei-Xiang; Long, Ji-Dong; Zheng, Le; Dong, Pan; Li, Chen; Chen, Wei

2018-02-01

The ionization rate of the released deuterium from a metal deuteride cathode in vacuum arc discharges is investigated by both experiments and modeling analysis. Experimental results show that the deuterium ionization rate increases from 2% to 30% with the increasing arc current in the range of 2-100 A. Thus the full ionization assumption, as is widely used in arc plasma simulations, is not satisfied for the released deuterium at low discharge current. According to the modeling results, the neutral-to-ion conversion efficiency for the deuterium traveling across the cathodic spot region can be significantly less than one, due to the fast plasma expansion and rarefaction in the vacuum. In addition, the model also reveals that, unlike the metal atoms which are mainly ionized in the sheath region and flow back to the cathode, the deuterium ionization primarily occurs in the quasi-neutral region and moves towards the anode. Consequently, the cathodic sheath layer acts like a filter that increases the deuterium fraction beyond the sheath region.

Particle in cell simulation on plasma grating contrast enhancement induced by infrared laser pulse

NASA Astrophysics Data System (ADS)

Li, M.; Yuan, T.; Xu, Y. X.; Wang, J. X.; Luo, S. N.

2018-05-01

The dynamics of plasma grating contrast enhancement (PGCE) irradiated by an infrared laser pulse is investigated with one dimensional particle-in-cell simulation where field ionization and impact ionization are simultaneously considered for the first time. The numeric results show that the impact ionization dominates the PGCE process. Upon the interaction with the laser pulse, abundant free electrons are efficiently accelerated and subsequently triggered massive impact ionizations in the density ridges of the plasma grating for the higher local plasma energy density, which efficiently enhances the grating contrast. Besides the dynamic analysis of PGCE, we explore the parameter space of the incident infrared laser pulse to optimize the PGCE effect, which can provide useful guidance to experiments related to laser-plasma-grating interactions and may find applications in prolonging the duration of the plasma grating.

Heavy component of spent nuclear fuel: Efficiency of model-substance ionization by electron-induced discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antonov, N. N., E-mail: antonovnickola@gmail.com; Gavrikov, A. V.; Samokhin, A. A.

The method of plasma separation of spent nuclear fuel can be tested with a model substance which has to be transformed from the condensed to plasma state. For this purpose, electron-induced discharge in lead vapor injected into the interelectrode gap is simulated using the kinetic approach. The ionization efficiency, the electrostatic-potential distribution, and those of the ion and electron densities in the discharge gap are derived as functions of the discharge-current density and concentration of the vapor of the model substance. Given a discharge-current density of 3.5 A/cm{sup 2} and a lead-vapor concentration of 2 × 10{sup 12} cm{sup –3},more » the simulated ionization efficiency proves to be nearly 60%. The discharge in lead vapor is also investigated experimentally.« less

Quantitative Surface Analysis of a Binary Drug Mixture—Suppression Effects in the Detection of Sputtered Ions and Post-Ionized Neutrals

NASA Astrophysics Data System (ADS)

Karras, Gabriel; Lockyer, Nicholas P.

2014-05-01

A systematic mass spectrometric study of two of the most common analgesic drugs, paracetamol and ibuprofen, is reported. The drugs were studied by means of secondary ion mass spectrometry (SIMS) and secondary neutral mass spectrometry (SNMS) using laser post-ionization (LPI) both in pure samples and in a two-component mixture. Ion suppression within the two-component system observed in SIMS mode is ameliorated using LPI under room temperature analysis. However, suppression effects are apparent in LPI mode on performing the analysis at cryogenic temperatures, which we attribute to changes in the desorption characteristics of sputtered molecules, which influences the subsequent post-ionization efficiency. This suggests different mechanisms of ion suppression in SIMS and LPI modes.

Electron-Muon Ranger: Performance in the MICE muon beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, D.

2015-12-16

The Muon Ionization Cooling Experiment (MICE) will perform a detailed study of ionization cooling to evaluate the feasibility of the technique. To carry out this program, MICE requires an efficient particle-identification (PID) system to identify muons. The Electron-Muon Ranger (EMR) is a fully-active tracking-calorimeter that forms part of the PID system and tags muons that traverse the cooling channel without decaying. The detector is capable of identifying electrons with an efficiency of 98.6%, providing a purity for the MICE beam that exceeds 99.8%. Lastly, the EMR also proved to be a powerful tool for the reconstruction of muon momenta inmore » the range 100–280 MeV/c.« less

Iron oxide nanomatrix facilitating metal ionization in matrix-assisted laser desorption/ionization mass spectrometry.

PubMed

Obena, Rofeamor P; Lin, Po-Chiao; Lu, Ying-Wei; Li, I-Che; del Mundo, Florian; Arco, Susan dR; Nuesca, Guillermo M; Lin, Chung-Chen; Chen, Yu-Ju

2011-12-15

The significance and epidemiological effects of metals to life necessitate the development of direct, efficient, and rapid method of analysis. Taking advantage of its simple, fast, and high-throughput features, we present a novel approach to metal ion detection by matrix-functionalized magnetic nanoparticle (matrix@MNP)-assisted MALDI-MS. Utilizing 21 biologically and environmentally relevant metal ion solutions, the performance of core and matrix@MNP against conventional matrixes in MALDI-MS and laser desorption ionization (LDI) MS were systemically tested to evaluate the versatility of matrix@MNP as ionization element. The matrix@MNPs provided 20- to >100-fold enhancement on detection sensitivity of metal ions and unambiguous identification through characteristic isotope patterns and accurate mass (<5 ppm), which may be attributed to its multifunctional role as metal chelator, preconcentrator, absorber, and reservoir of energy. Together with the comparison on the ionization behaviors of various metals having different ionization potentials (IP), we formulated a metal ionization mechanism model, alluding to the role of exciton pooling in matrix@MNP-assisted MALDI-MS. Moreover, the detection of Cu in spiked tap water demonstrated the practicability of this new approach as an efficient and direct alternative tool for fast, sensitive, and accurate determination of trace metal ions in real samples.

On the SIMS Ionization Probability of Organic Molecules.

PubMed

Popczun, Nicholas J; Breuer, Lars; Wucher, Andreas; Winograd, Nicholas

2017-06-01

The prospect of improved secondary ion yields for secondary ion mass spectrometry (SIMS) experiments drives innovation of new primary ion sources, instrumentation, and post-ionization techniques. The largest factor affecting secondary ion efficiency is believed to be the poor ionization probability (α + ) of sputtered material, a value rarely measured directly, but estimated to be in some cases as low as 10 -5 . Our lab has developed a method for the direct determination of α + in a SIMS experiment using laser post-ionization (LPI) to detect neutral molecular species in the sputtered plume for an organic compound. Here, we apply this method to coronene (C 24 H 12 ), a polyaromatic hydrocarbon that exhibits strong molecular signal during gas-phase photoionization. A two-dimensional spatial distribution of sputtered neutral molecules is measured and presented. It is shown that the ionization probability of molecular coronene desorbed from a clean film under bombardment with 40 keV C 60 cluster projectiles is of the order of 10 -3 , with some remaining uncertainty arising from laser-induced fragmentation and possible differences in the emission velocity distributions of neutral and ionized molecules. In general, this work establishes a method to estimate the ionization efficiency of molecular species sputtered during a single bombardment event. Graphical Abstract .

Electrospray-assisted laser desorption/ionization and tandem mass spectrometry of peptides and proteins.

PubMed

Peng, Ivory X; Shiea, Jentaie; Ogorzalek Loo, Rachel R; Loo, Joseph A

2007-01-01

We have constructed an electrospray-assisted laser desorption/ionization (ELDI) source which utilizes a nitrogen laser pulse to desorb intact molecules from matrix-containing sample solution droplets, followed by electrospray ionization (ESI) post-ionization. The ELDI source is coupled to a quadrupole ion trap mass spectrometer and allows sampling under ambient conditions. Preliminary data showed that ELDI produces ESI-like multiply charged peptides and proteins up to 29 kDa carbonic anhydrase and 66 kDa bovine albumin from single-protein solutions, as well as from complex digest mixtures. The generated multiply charged polypeptides enable efficient tandem mass spectrometric (MS/MS)-based peptide sequencing. ELDI-MS/MS of protein digests and small intact proteins was performed both by collisionally activated dissociation (CAD) and by nozzle-skimmer dissociation (NSD). ELDI-MS/MS may be a useful tool for protein sequencing analysis and top-down proteomics study, and may complement matrix-assisted laser desorption/ionization (MALDI)-based measurements. Copyright (c) 2007 John Wiley & Sons, Ltd.

Thrust performance, propellant ionization, and thruster erosion of an external discharge plasma thruster

NASA Astrophysics Data System (ADS)

Karadag, Burak; Cho, Shinatora; Funaki, Ikkoh

2018-04-01

It is quite a challenge to design low power Hall thrusters with a long lifetime and high efficiency because of the large surface area to volume ratio and physical limits to the magnetic circuit miniaturization. As a potential solution to this problem, we experimentally investigated the external discharge plasma thruster (XPT). The XPT produces and sustains a plasma discharge completely in the open space outside of the thruster structure through a magnetic mirror configuration. It eliminates the very fundamental component of Hall thrusters, discharge channel side walls, and its magnetic circuit consists solely of a pair of hollow cylindrical permanent magnets. Thrust, low frequency discharge current oscillation, ion beam current, and plasma property measurements were conducted to characterize the manufactured prototype thruster for the proof of concept. The thrust performance, propellant ionization, and thruster erosion were discussed. Thrust generated by the XPT was on par with conventional Hall thrusters [stationary plasma thruster (SPT) or thruster with anode layer] at the same power level (˜11 mN at 250 W with 25% anode efficiency without any optimization), and discharge current had SPT-level stability (Δ < 0.2). Faraday probe measurements revealed that ion beams are finely collimated, and plumes have Gaussian distributions. Mass utilization efficiencies, beam utilization efficiencies, and plume divergence efficiencies ranged from 28 to 62%, 78 to 99%, and 40 to 48%, respectively. Electron densities and electron temperatures were found to reach 4 × 1018 m-3 ( ∂ n e / n e = ±52%) and 15 eV ( ∂ T e / T e = ±10%-30%), respectively, at 10 mm axial distance from the anode centerline. An ionization mean free path analysis revealed that electron density in the ionization region is substantially higher than the conventional Hall thrusters, which explain why the XPT is as efficient as conventional ones even without a physical ionization chamber. Our findings propose an alternative approach for low power Hall thruster design and provide a successful proof of concept experiment of the XPT.

Laser stripping of hydrogen atoms by direct ionization

DOE PAGES

Brunetti, E.; Becker, W.; Bryant, H. C.; ...

2015-05-08

Direct ionization of hydrogen atoms by laser irradiation is investigated as a potential new scheme to generate proton beams without stripping foils. The time-dependent Schrödinger equation describing the atom-radiation interaction is numerically solved obtaining accurate ionization cross-sections for a broad range of laser wavelengths, durations and energies. Parameters are identified where the Doppler frequency up-shift of radiation colliding with relativistic particles can lead to efficient ionization over large volumes and broad bandwidths using currently available lasers.

Laser stripping of hydrogen atoms by direct ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brunetti, E.; Becker, W.; Bryant, H. C.

Direct ionization of hydrogen atoms by laser irradiation is investigated as a potential new scheme to generate proton beams without stripping foils. The time-dependent Schrödinger equation describing the atom-radiation interaction is numerically solved obtaining accurate ionization cross-sections for a broad range of laser wavelengths, durations and energies. Parameters are identified where the Doppler frequency up-shift of radiation colliding with relativistic particles can lead to efficient ionization over large volumes and broad bandwidths using currently available lasers.

Novel high power impulse magnetron sputtering enhanced by an auxiliary electrical field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Chunwei, E-mail: lcwnefu@126.com, E-mail: xiubotian@163.com; State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001; Tian, Xiubo, E-mail: lcwnefu@126.com, E-mail: xiubotian@163.com

2016-08-15

The high power impulse magnetron sputtering (HIPIMS) technique is a novel highly ionized physical vapor deposition method with a high application potential. However, the electron utilization efficiency during sputtering is rather low and the metal particle ionization rate needs to be considerably improved to allow for a large-scale industrial application. Therefore, we enhanced the HIPIMS technique by simultaneously applying an electric field (EF-HIPIMS). The effect of the electric field on the discharge process was studied using a current sensor and an optical emission spectrometer. Furthermore, the spatial distribution of the electric potential and electric field during the EF-HIPIMS process wasmore » simulated using the ANSYS software. The results indicate that a higher electron utilization efficiency and a higher particle ionization rate could be achieved. The auxiliary anode obviously changed the distribution of the electric potential and the electric field in the discharge region, which increased the plasma density and enhanced the degree of ionization of the vanadium and argon gas. Vanadium films were deposited to further compare both techniques, and the morphology of the prepared films was investigated by scanning electron microscopy. The films showed a smaller crystal grain size and a denser growth structure when the electric field was applied during the discharge process.« less

Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets.

PubMed

LaForge, A C; Stumpf, V; Gokhberg, K; von Vangerow, J; Stienkemeier, F; Kryzhevoi, N V; O'Keeffe, P; Ciavardini, A; Krishnan, S R; Coreno, M; Prince, K C; Richter, R; Moshammer, R; Pfeifer, T; Cederbaum, L S; Mudrich, M

2016-05-20

We report the observation of electron-transfer-mediated decay (ETMD) involving magnesium (Mg) clusters embedded in helium (He) nanodroplets. ETMD is initiated by the ionization of He followed by removal of two electrons from the Mg clusters of which one is transferred to the He ion while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. For Mg clusters larger than five atoms we observe stable doubly ionized clusters. Thus, ETMD provides an efficient pathway to the formation of doubly ionized cold species in doped nanodroplets.

Ionization cross section, pressure shift and isotope shift measurements of osmium

NASA Astrophysics Data System (ADS)

Hirayama, Yoshikazu; Mukai, Momo; Watanabe, Yutaka; Oyaizu, Michihiro; Ahmed, Murad; Kakiguchi, Yutaka; Kimura, Sota; Miyatake, Hiroari; Schury, Peter; Wada, Michiharu; Jeong, Sun-Chan

2017-11-01

In-gas-cell laser resonance ionization spectroscopy of neutral osmium atoms was performed with the use of a two-color two-step laser resonance ionization technique. Saturation curves for the ionization scheme were measured, and the ionization cross section was experimentally determined by solving the rate equations for the ground, intermediate and ionization continuum populations. The pressure shift and pressure broadening in the resonance spectra of the excitation transition were measured. The electronic factor {F}247 for the transition {λ }1=247.7583 nm to the intermediate state was deduced from the measured isotope shifts of stable {}{188,189,{190,192}}Os isotopes. The efficient ionization scheme, pressure shift, nuclear isotope shift and {F}247 are expected to be useful for applications of laser ion sources to unstable nuclei and for nuclear spectroscopy based on laser ionization techniques.

The study of lead vapor ionization in discharge with a hot cathode and efficiency of its deposition on the substrates applied for plasma separation method

NASA Astrophysics Data System (ADS)

Antonov, N. N.; Samokhin, A. A.; Zhabin, S. N.; Gavrikov, A. V.; Smirnov, V. P.

2016-11-01

Spent nuclear fuel plasma separation method approbation implies the use of model substances. Thus it is necessary to solve the problem of material conversion into a cold plasma flow, as well as the problem of deposition on collectors. For this purpose, we carried out a kinetic and hydrodynamic simulation of the discharge with hot cathode in the lead vapor (lead vapor was injected into the interelectrode gap). Dependencies of the ionization efficiency, electrostatic potential distribution, density distribution of ions and electrons in the discharge gap on the discharge current density and the model substance vapor concentration were obtained. The simulation results show that at discharge current density of about 3.5 A/cm2 and the lead vapor concentration of 2 × 1012 cm-3, the ionization efficiency is close to 60%. Experimental research of the discharge with a hot cathode in the lead vapor was carried out. We also carried out the research of the Pb condensation coefficients on various substrates. For experimental data analysis the numerical model based on Monte Carlo method was used. The research results show that deposition coefficients at medium temperatures of substrates near 70 °C do not drop lower than 75%.

A combined thermal dissociation and electron impact ionization source for RIB generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alton, G.D.; Williams, C.

1995-12-31

The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for RIB applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, in principle, overcome thismore » handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility (HRIBF), now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article.« less

Axial Structure of High-Vacuum Planar Magnetron Discharge Space

NASA Astrophysics Data System (ADS)

Miura, Tsutomu

1999-09-01

The spatial structure of high-vacuum planar magnetron discharge is theoretically investigated taking into account the electron confinement. The boundary xes of the electron confinement region depends on BA with Ea/BA as the parameter (BA: the magnetic flux density at the anode, Ea: the average electric field strength). The location at which the frequency of ionization events takes the maximum is expressed as CnNxiep (CnN: a factor related to the electron density distribution, xiep: the distance of the location from the cathode at which the ionization is most efficient). With increasing Ea and BA at a fixed Ea/BA, the density of the confined energetic electrons increases. With increasing Ea, the region where ionization is efficient shifts to the cathode side to give a high efficiency of the magnet. The boundary xes as determined by the probe method agreed with the theoretical prediction.

Time-dependent Cooling in Photoionized Plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gnat, Orly, E-mail: orlyg@phys.huji.ac.il

I explore the thermal evolution and ionization states in gas cooling from an initially hot state in the presence of external photoionizing radiation. I compute the equilibrium and nonequilibrium cooling efficiencies, heating rates, and ion fractions for low-density gas cooling while exposed to the ionizing metagalactic background radiation at various redshifts ( z = 0 − 3), for a range of temperatures (10{sup 8}–10{sup 4} K), densities (10{sup −7}–10{sup 3} cm{sup −3}), and metallicities (10{sup −3}–2 times solar). The results indicate the existence of a threshold ionization parameter, above which the cooling efficiencies are very close to those in photoionization equilibriummore » (so that departures from equilibrium may be neglected), and below which the cooling efficiencies resemble those in collisional time-dependent gas cooling with no external radiation (and are thus independent of density).« less

Collective Autoionization in Multiply-Excited Systems: A novel ionization process observed in Helium Nanodroplets

PubMed Central

LaForge, A. C.; Drabbels, M.; Brauer, N. B.; Coreno, M.; Devetta, M.; Di Fraia, M.; Finetti, P.; Grazioli, C.; Katzy, R.; Lyamayev, V.; Mazza, T.; Mudrich, M.; O'Keeffe, P.; Ovcharenko, Y.; Piseri, P.; Plekan, O.; Prince, K. C.; Richter, R.; Stranges, S.; Callegari, C.; Möller, T.; Stienkemeier, F.

2014-01-01

Free electron lasers (FELs) offer the unprecedented capability to study reaction dynamics and image the structure of complex systems. When multiple photons are absorbed in complex systems, a plasma-like state is formed where many atoms are ionized on a femtosecond timescale. If multiphoton absorption is resonantly-enhanced, the system becomes electronically-excited prior to plasma formation, with subsequent decay paths which have been scarcely investigated to date. Here, we show using helium nanodroplets as an example that these systems can decay by a new type of process, named collective autoionization. In addition, we show that this process is surprisingly efficient, leading to ion abundances much greater than that of direct single-photon ionization. This novel collective ionization process is expected to be important in many other complex systems, e.g. macromolecules and nanoparticles, exposed to high intensity radiation fields. PMID:24406316

Possible influence of the Kuramoto length in a photo-catalytic water splitting reaction revealed by Poisson-Nernst-Planck equations involving ionization in a weak electrolyte

NASA Astrophysics Data System (ADS)

Suzuki, Yohichi; Seki, Kazuhiko

2018-03-01

We studied ion concentration profiles and the charge density gradient caused by electrode reactions in weak electrolytes by using the Poisson-Nernst-Planck equations without assuming charge neutrality. In weak electrolytes, only a small fraction of molecules is ionized in bulk. Ion concentration profiles depend on not only ion transport but also the ionization of molecules. We considered the ionization of molecules and ion association in weak electrolytes and obtained analytical expressions for ion densities, electrostatic potential profiles, and ion currents. We found the case that the total ion density gradient was given by the Kuramoto length which characterized the distance over which an ion diffuses before association. The charge density gradient is characterized by the Debye length for 1:1 weak electrolytes. We discuss the role of these length scales for efficient water splitting reactions using photo-electrocatalytic electrodes.

Single electron dynamics in a Hall thruster electromagnetic field profile

NASA Astrophysics Data System (ADS)

Marini, Samuel; Pakter, Renato

2017-05-01

In this work, the single electron dynamics in a simplified three dimensional Hall thruster model is studied. Using Hamiltonian formalism and the concept of limiting curves, one is able to determine confinement conditions for the electron in the acceleration channel. It is shown that as a given parameter of the electromagnetic field is changed, the particle trajectory may transit from regular to chaotic without affecting the confinement, which allows one to make a detailed analysis of the role played by the chaos. The ionization volume is also computed, which measures the probability of an electron to ionize background gas atoms. It is found that there is a great correlation between chaos and increased effective ionization volume. This indicates that a complex dynamical behavior may improve the device efficiency by augmenting the ionization capability of each electron, requiring an overall lower electron current.

Selected cis- and trans-3-fluorostyrene rotamers studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

NASA Astrophysics Data System (ADS)

Wu, Pei Ying; Tzeng, Wen Bih

2015-10-01

We applied two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibronic, photoionization efficiency, and cation spectra of the selected rotamers of 3-fluorostyrene. The adiabatic ionization energies of cis- and trans-3-fluorostyrene were determined to be 69 960 ± 5 and 69 856 ± 5 cm-1, respectively. Cation vibrations 10a, 15, 6b, and 12 of both rotamers have been found to have frequencies of 218, 404, 452, and 971 cm-1, respectively. This finding shows that the relative orientation of the vinyl group with respect to the F atom does not affect these vibrations of the 3-fluorostyrene cation. Our one-dimensional potential energy surface calculations support that the cis-trans isomerization of 3-fluorostyrene does not occur under the present experimental conditions.

Bipolar Mass Spectrometry of Labile Coordination Complexes, Redox Active Inorganic Compounds, and Proteins Using a Glass Nebulizer for Sonic-Spray Ionization

NASA Astrophysics Data System (ADS)

Antonakis, Manolis M.; Tsirigotaki, Alexandra; Kanaki, Katerina; Milios, Constantinos J.; Pergantis, Spiros A.

2013-08-01

In this study, we report on the development of a novel nebulizer configuration for sonic-spray ionization (SSI) mass spectrometry (MS), more specifically for a version of SSI that is referred to as Venturi easy ambient sonic-spray ionization (V-EASI) MS. The developed nebulizer configuration is based on a commercially available pneumatic glass nebulizer that has been used extensively for aerosol formation in atomic spectrometry. In the present study, the nebulizer was modified in order to achieve efficient V-EASI-MS operation. Upon evaluating this system, it has been demonstrated that V-EASI-MS offers some distinct advantages for the analysis of coordination compounds and redox active inorganic compounds over the predominantly used electrospray ionization (ESI) technique. Such advantages, for this type of compounds, are demonstrated here for the first time. More specifically, a series of labile heptanuclear heterometallic [CuII 6LnIII] clusters held together with artificial amino acid ligands, in addition to easily oxidized inorganic oxyanions of selenium and arsenic, were analyzed. The observed advantages pertain to V-EASI appearing to be a "milder" ionization source than ESI, not requiring electrical potentials for gas phase ion formation, thus eliminating the possibility of unwanted redox transformations, allowing for the "simultaneous" detection of negative and positive ions (bipolar analysis) without the need to change source ionization conditions, and also not requiring the use of syringes and delivery pumps. Because of such features, especially because of the absence of ionization potentials, EASI can be operated with minimal requirements for source parameter optimization. We observed that source temperature and accelerating voltage do not seem to affect labile compounds to the extent they do in ESI-MS. In addition, bipolar analysis of proteins was demonstrated here by acquiring both positive and negative ion mass spectra from the same protein solutions, without the need to independently adjust solution and source conditions in each mode. Finally, the simple and efficient operation of a dual-nebulizer configuration was demonstrated for V-EASI-MS for the first time.

Bipolar mass spectrometry of labile coordination complexes, redox active inorganic compounds, and proteins using a glass nebulizer for sonic-spray ionization.

PubMed

Antonakis, Manolis M; Tsirigotaki, Alexandra; Kanaki, Katerina; Milios, Constantinos J; Pergantis, Spiros A

2013-08-01

In this study, we report on the development of a novel nebulizer configuration for sonic-spray ionization (SSI) mass spectrometry (MS), more specifically for a version of SSI that is referred to as Venturi easy ambient sonic-spray ionization (V-EASI) MS. The developed nebulizer configuration is based on a commercially available pneumatic glass nebulizer that has been used extensively for aerosol formation in atomic spectrometry. In the present study, the nebulizer was modified in order to achieve efficient V-EASI-MS operation. Upon evaluating this system, it has been demonstrated that V-EASI-MS offers some distinct advantages for the analysis of coordination compounds and redox active inorganic compounds over the predominantly used electrospray ionization (ESI) technique. Such advantages, for this type of compounds, are demonstrated here for the first time. More specifically, a series of labile heptanuclear heterometallic [Cu(II) 6Ln(III)] clusters held together with artificial amino acid ligands, in addition to easily oxidized inorganic oxyanions of selenium and arsenic, were analyzed. The observed advantages pertain to V-EASI appearing to be a "milder" ionization source than ESI, not requiring electrical potentials for gas phase ion formation, thus eliminating the possibility of unwanted redox transformations, allowing for the "simultaneous" detection of negative and positive ions (bipolar analysis) without the need to change source ionization conditions, and also not requiring the use of syringes and delivery pumps. Because of such features, especially because of the absence of ionization potentials, EASI can be operated with minimal requirements for source parameter optimization. We observed that source temperature and accelerating voltage do not seem to affect labile compounds to the extent they do in ESI-MS. In addition, bipolar analysis of proteins was demonstrated here by acquiring both positive and negative ion mass spectra from the same protein solutions, without the need to independently adjust solution and source conditions in each mode. Finally, the simple and efficient operation of a dual-nebulizer configuration was demonstrated for V-EASI-MS for the first time.

Determination of polycyclic aromatic hydrocarbons and their nitro-, amino-derivatives absorbed on particulate matter 2.5 by multiphoton ionization mass spectrometry using far-, deep-, and near-ultraviolet femtosecond lasers.

PubMed

Tang, Yuanyuan; Imasaka, Tomoko; Yamamoto, Shigekazu; Imasaka, Totaro

2016-06-01

Multiphoton ionization processes of parent-polycyclic aromatic hydrocarbons (PPAHs), nitro-PAHs (NPAHs), and amino-PAHs (APAHs) were examined by gas chromatography combined with time-of-flight mass spectrometry using a femtosecond Ti:sapphire laser as the ionization source. The efficiency of multiphoton ionization was examined using lasers emitting in the far-ultraviolet (200 nm), deep-ultraviolet (267 nm), and near-ultraviolet (345 nm) regions. The largest signal intensities were obtained when the far-ultraviolet laser was employed. This favorable result can be attributed to the fact that these compounds have the largest molar absorptivities in the far-ultraviolet region. On the other hand, APAHs were ionized more efficiently than NPAHs in the near-ultraviolet region because of their low ionization energies. A sample extracted from a real particulate matter 2.5 (PM2.5) sample was measured, and numerous signal peaks arising from PAH and its analogs were observed at 200 nm. On the other hand, only a limited number of signed peaks were observed at 345 nm, some of which were signed to PPAHs, NPAHs, and APAHs. Thus, multiphoton ionization mass spectrometry has potential for the use in comprehensive analysis of toxic environmental pollutants. Copyright © 2016 Elsevier Ltd. All rights reserved.

Electron ionization and dissociation of aliphatic amino acids

NASA Astrophysics Data System (ADS)

Papp, P.; Shchukin, P.; Kočíšek, J.; Matejčík, Š.

2012-09-01

We present experimental and theoretical study of electron ionization and dissociative ionization to the gas phase amino acids valine, leucine, and isoleucine. A crossed electron/molecular beams technique equipped with quadrupole mass analyzer has been applied to measure mass spectra and ion efficiency curves for formation of particular ions. From experimental data the ionization energies of the molecules and the appearance energies of the fragment ions were determined. Ab initio calculations (Density Functional Theory and G3MP2 methods) were performed in order to calculate the fragmentation paths and interpret the experimental data. The experimental ionization energies of parent molecules [P]+ 8.91 ± 0.05, 8.85 ± 0.05, and 8.79 ± 0.05 eV and G3MP2 ionization energies (adiabatic) of 8.89, 8.88, and 8.81 eV were determined for valine, leucine, and isoleucine, respectively, as well as the experimental and theoretical threshold energies for dissociative ionization channels. The comparison of experimental data with calculations resulted in identification of the ions as well as the neutral fragments formed in the dissociative reactions. Around 15 mass/charge ratio fragments were identified from the mass spectra by comparison of experimental appearance energies with calculated reaction enthalpies for particular dissociative reactions.

Fabrication and characterization of a 3D Positive ion detector and its applications

NASA Astrophysics Data System (ADS)

Venkatraman, Pitchaikannu; Sureka, Chandrasekaran Senbagavadivoo

2017-11-01

There is a growing interest to experimentally evaluate the track structure induced by ionizing particles in order to characterize the radiobiological quality of ionizing radiation for applications in radiotherapy and radiation protection. To do so, a novel positive ion detector based on the multilayer printed circuit board (PCB) technology has been proposed previously, which works under the principle of ion induced impact ionization. Based on this, an upgraded 3D positive ion detector was fabricated in order to improve its efficiency and use it for various applications. To improve the efficiency of the detector, cathodes with different insulators (Bakelite plate and Steatite Ceramics) and conducting layers (ITO, FTO, and Gold coated cathode) were studied under various gaseous media (methane, nitrogen, and air) using Am-241, Co-60, Co-57, Na-22, Cs-137, and Ba-133 sources. From this study, it is confirmed that the novel 3D positive ion detector that has been upgraded using gold as strip material, tungsten (87%) coated copper (13%) as the core wire, gold coated ceramic as cathode, and thickness of 3.483 mm showed 9.2% efficiency under methane medium at 0.9 Torr pressure using an Am-241 source. It is also confirmed that when the conductivity of the cathode and thickness of the detector is increased, the performance of the detector is improved significantly. Further, the scope of the detector to use in the field of radiation protection, radiation dosimetry, gamma spectrometry, radiation biology, and oncology are reported here.

High efficiency photoionization detector

DOEpatents

Anderson, David F.

1984-01-01

A high efficiency photoionization detector using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36.+-.0.02 eV, and a vapor pressure of 0.35 torr at 20.degree. C.

Recombination in liquid-filled ionization chambers beyond the Boag limit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brualla-González, L.; Roselló, J.

Purpose: The high mass density and low mobilities of charge carriers can cause important recombination in liquid-filled ionization chambers (LICs). Saturation correction methods have been proposed for LICs. Correction methods for pulsed irradiation are based on Boag equation. However, Boag equation assumes that the charge ionized by one pulse is fully collected before the arrival of the next pulse. This condition does not hold in many clinical beams where the pulse repetition period may be shorter than the charge collection time, causing overlapping between charge carriers ionized by different pulses, and Boag equation is not applicable there. In this work,more » the authors present an experimental and numerical characterization of collection efficiencies in LICs beyond the Boag limit, with overlapping between charge carriers ionized by different pulses. Methods: The authors have studied recombination in a LIC array for different dose-per-pulse, pulse repetition frequency, and polarization voltage values. Measurements were performed in a Truebeam Linac using FF and FFF modalities. Dose-per-pulse and pulse repetition frequency have been obtained by monitoring the target current with an oscilloscope. Experimental collection efficiencies have been obtained by using a combination of the two-dose-rate method and ratios to the readout of a reference chamber (CC13, IBA). The authors have also used numerical simulation to complement the experimental data. Results: The authors have found that overlap significantly increases recombination in LICs, as expected. However, the functional dependence of collection efficiencies on the dose-per-pulse does not change (a linear dependence has been observed in the near-saturation region for different degrees of overlapping, the same dependence observed in the nonoverlapping scenario). On the other hand, the dependence of collection efficiencies on the polarization voltage changes in the overlapping scenario and does not follow that of Boag equation, the reason being that changing the polarization voltage also affects the charge collection time, thus changing the amount of overlapping. Conclusions: These results have important consequences for saturation correction methods for LICs. On one hand, the two-dose-rate method, which relies on the functional dependence of the collection efficiencies on dose-per-pulse, can also be used in the overlapping situation, provided that the two measurements needed to feed the method are performed at the same pulse repetition frequency (monitor unit rate). This result opens the door to computing collection efficiencies in LICs in many clinical setups where charge overlap in the LIC exists. On the other hand, correction methods based on the voltage-dependence of Boag equation like the three-voltage method or the modified two-voltage method will not work in the overlapping scenario due to the different functional dependence of collection efficiencies on the polarization voltage.« less

Resonance ionization spectroscopy of sodium Rydberg levels using difference frequency generation of high-repetition-rate pulsed Ti:sapphire lasers

NASA Astrophysics Data System (ADS)

Naubereit, P.; Marín-Sáez, J.; Schneider, F.; Hakimi, A.; Franzmann, M.; Kron, T.; Richter, S.; Wendt, K.

2016-05-01

The generation of tunable laser light in the green to orange spectral range has generally been a deficiency of solid-state lasers. Hence, the formalisms of difference frequency generation (DFG) and optical parametric processes are well known, but the DFG of pulsed solid-state lasers was rarely efficient enough for its use in resonance ionization spectroscopy. Difference frequency generation of high-repetition-rate Ti:sapphire lasers was demonstrated for resonance ionization of sodium by efficiently exciting the well-known D1 and D2 lines in the orange spectral range (both ≈589 nm). In order to prove the applicability of the laser system for its use at resonance ionization laser ion sources of radioactive ion beam facilities, the first ionization potential of Na was remeasured by three-step resonance ionization into Rydberg levels and investigating Rydberg convergences. A result of EIP=41449.455 (6) stat(7) syscm-1 was obtained, which is in perfect agreement with the literature value of EIPlit =41449.451(2)cm-1 . A total of 41 level positions for the odd-parity Rydberg series n f 2F5/2,7/2o for principal quantum numbers of 10 ≤n ≤60 were determined experimentally.

Efficient thermoelectric device

NASA Technical Reports Server (NTRS)

Ila, Daryush (Inventor)

2010-01-01

A high efficiency thermo electric device comprising a multi nanolayer structure of alternating insulator and insulator/metal material that is irradiated across the plane of the layer structure with ionizing radiation. The ionizing radiation produces nanocrystals in the layered structure that increase the electrical conductivity and decrease the thermal conductivity thereby increasing the thermoelectric figure of merit. Figures of merit as high as 2.5 have been achieved using layers of co-deposited gold and silicon dioxide interspersed with layers of silicon dioxide. The gold to silicon dioxide ratio was 0.04. 5 MeV silicon ions were used to irradiate the structure. Other metals and insulators may be substituted. Other ionizing radiation sources may be used. The structure tolerates a wide range of metal to insulator ratio.

A singly charged ion source for radioactive {sup 11}C ion acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katagiri, K.; Noda, A.; Nagatsu, K.

2016-02-15

A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive {sup 11}C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source wasmore » found to have favorable performance as a singly charged ion source.« less

Nuclear microprobe investigation of the effects of ionization and displacement damage in vertical, high voltage GaN diodes

DOE PAGES

Vizkelethy, G.; King, M. P.; Aktas, O.; ...

2016-12-02

Radiation responses of high-voltage, vertical gallium-nitride (GaN) diodes were investigated using Sandia National Laboratories’ nuclear microprobe. Effects of the ionization and the displacement damage were studied using various ion beams. We found that the devices show avalanche effect for heavy ions operated under bias well below the breakdown voltage. Here, the displacement damage experiments showed a surprising effect for moderate damage: the charge collection efficiency demonstrated an increase instead of a decrease for higher bias voltages.

Nuclear microprobe investigation of the effects of ionization and displacement damage in vertical, high voltage GaN diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vizkelethy, G.; King, M. P.; Aktas, O.

Radiation responses of high-voltage, vertical gallium-nitride (GaN) diodes were investigated using Sandia National Laboratories’ nuclear microprobe. Effects of the ionization and the displacement damage were studied using various ion beams. We found that the devices show avalanche effect for heavy ions operated under bias well below the breakdown voltage. Here, the displacement damage experiments showed a surprising effect for moderate damage: the charge collection efficiency demonstrated an increase instead of a decrease for higher bias voltages.

PHD TUTORIAL: A complete numerical approach to electron hydrogen collisions

NASA Astrophysics Data System (ADS)

Bartlett, Philip L.

2006-11-01

This tutorial presents an extensive computational study of electron-impact scattering and ionization of atomic hydrogen and hydrogenic ions, through the solution of the non-relativistic Schrödinger equation in coordinate space using propagating exterior complex scaling (PECS). It details the complete numerical and computational development of the PECS method, which enables highly computationally-efficient solution of these collision systems. Benchmark results are presented for a complete range of electron-hydrogen collisions, including discrete elastic and inelastic scattering both below and above the ionization threshold energy, very low-energy ionizing collisions through to moderately high-energy ionizing collisions, ground-state and excited-state targets and charged hydrogenic targets with Z <= 4. Total ionization cross sections through to fully differential cross sections, both in-plane and out-of-plane, are given and are found to be in excellent accord with other state-of-the-art methods and measurements, where available. We also review our recent confirmation (Bartlett and Stelbovics 2004 Phys. Rev. Lett. 93 233201) of the Wannier and related threshold laws for e-H collisions.

Modeling of metal thin film growth: Linking angstrom-scale molecular dynamics results to micron-scale film topographies

NASA Astrophysics Data System (ADS)

Hansen, U.; Rodgers, S.; Jensen, K. F.

2000-07-01

A general method for modeling ionized physical vapor deposition is presented. As an example, the method is applied to growth of an aluminum film in the presence of an ionized argon flux. Molecular dynamics techniques are used to examine the surface adsorption, reflection, and sputter reactions taking place during ionized physical vapor deposition. We predict their relative probabilities and discuss their dependence on energy and incident angle. Subsequently, we combine the information obtained from molecular dynamics with a line of sight transport model in a two-dimensional feature, incorporating all effects of reemission and resputtering. This provides a complete growth rate model that allows inclusion of energy- and angular-dependent reaction rates. Finally, a level-set approach is used to describe the morphology of the growing film. We thus arrive at a computationally highly efficient and accurate scheme to model the growth of thin films. We demonstrate the capabilities of the model predicting the major differences on Al film topographies between conventional and ionized sputter deposition techniques studying thin film growth under ionized physical vapor deposition conditions with different Ar fluxes.

Insight into doping efficiency of organic semiconductors from the analysis of the density of states in n-doped C60 and ZnPc

NASA Astrophysics Data System (ADS)

Gaul, Christopher; Hutsch, Sebastian; Schwarze, Martin; Schellhammer, Karl Sebastian; Bussolotti, Fabio; Kera, Satoshi; Cuniberti, Gianaurelio; Leo, Karl; Ortmann, Frank

2018-05-01

Doping plays a crucial role in semiconductor physics, with n-doping being controlled by the ionization energy of the impurity relative to the conduction band edge. In organic semiconductors, efficient doping is dominated by various effects that are currently not well understood. Here, we simulate and experimentally measure, with direct and inverse photoemission spectroscopy, the density of states and the Fermi level position of the prototypical materials C60 and zinc phthalocyanine n-doped with highly efficient benzimidazoline radicals (2-Cyc-DMBI). We study the role of doping-induced gap states, and, in particular, of the difference Δ1 between the electron affinity of the undoped material and the ionization potential of its doped counterpart. We show that this parameter is critical for the generation of free carriers and influences the conductivity of the doped films. Tuning of Δ1 may provide alternative strategies to optimize the electronic properties of organic semiconductors.

Influence of oxygen on the chemical stage of radiobiological mechanism

NASA Astrophysics Data System (ADS)

Barilla, Jiří; Lokajíček, Miloš V.; Pisaková, Hana; Simr, Pavel

2016-07-01

The simulation of the chemical stage of radiobiological mechanism may be very helpful in studying the radiobiological effect of ionizing radiation when the water radical clusters formed by the densely ionizing ends of primary or secondary charged particle may form DSBs damaging DNA molecules in living cells. It is possible to study not only the efficiency of individual radicals but also the influence of other species or radiomodifiers (mainly oxygen) being present in water medium during irradiation. The mathematical model based on Continuous Petri nets (proposed by us recently) will be described. It makes it possible to analyze two main processes running at the same time: chemical radical reactions and the diffusion of radical clusters formed during energy transfer. One may study the time change of radical concentrations due to the chemical reactions running during diffusion process. Some orientation results concerning the efficiency of individual radicals in DSB formation (in the case of Co60 radiation) will be presented; the influence of oxygen present in water medium during irradiation will be shown, too.

High efficiency photoionization detector

DOEpatents

Anderson, D.F.

1984-01-31

A high efficiency photoionization detector is described using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36 [+-] 0.02 eV, and a vapor pressure of 0.35 torr at 20 C. 6 figs.

Coherent control of strong-field two-pulse ionization of Rydberg atoms.

PubMed

Fedorov, M; Poluektov, N

2000-02-28

Strong-field ionization of Rydberg atoms is investigated in its dependence on phase features of the initial coherent population of Rydberg levels. In the case of a resonance between Rydberg levels and some lower-energy atomic level (V-type transitions), this dependence is shown to be very strong: by a proper choice of the initial population an atom can be made either completely or very little ionized by a strong laser pulse. It is shown that phase features of the initial coherent population of Rydberg levels and the ionization yield can be efficiently controlled in a scheme of ionization by two strong laser pulses with a varying delay time between them.

Clinical translation of human microRNA 21 as a potential biomarker for exposure to ionizing radiation.

PubMed

Halimi, Mohammad; Parsian, Hadi; Asghari, S Mohsen; Sariri, Reyhaneh; Moslemi, Dariush; Yeganeh, Farshid; Zabihi, Ebrahim

2014-06-01

This study investigated to what extent the serum microRNA 21 (miR-21) level alters in response to ionizing radiation (IR). Initially, we evaluated the appropriateness of our RNA extraction efficiency and microRNA assay in serum, and then investigated the serum miR-21 level in 4 patients with breast cancer in 4 stages: pre- and postoperation, at the beginning radiotherapy, and after 25 sessions of radiotherapy with a total of 50 Gy irradiation, as well as in 20 healthy volunteers. The initial analysis showed the appropriateness of our RNA extraction efficiency and microRNA assay in serum for identifying people exposed to IR. We then analyzed the serum miR-21 level in another group of 40 patients with breast cancer before and after radiotherapy. During our large-scale analysis, the miR-21 level before radiotherapy was comparable with healthy volunteers (P = 0.10) and increased significantly after radiotherapy (P < 0.001)-an indication that this could discriminate irradiated patients from nonirradiated ones with high specificity (75%) and sensitivity (80%). According to this study, serum miR-21 has the potential to be used as a biomarker for the identification of people exposed to ionizing radiation. Copyright © 2014 Mosby, Inc. All rights reserved.

Laser separation of lithium isotopes by double resonance enhanced multiphoton ionization of Li/sub 2/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balz, J.G.; Bernheim, R.A.; Gold, L.P.

1987-01-01

Multiphoton ionization spectra of /sup 7/Li/sub 2/, /sup 6/Li/sub 2/, and /sup 7/Li/sup 6/Li vapors have been measured in the 570--650 nm region using a single, low resolution, multimode cw dye laser. A number of wavelengths provide selective multiphoton ionization of one isotopic species demonstrating the possibility of efficient laser-driven isotopic separation in lithium in this wavelength region.

The absorption of energetic electrons by molecular hydrogen gas

NASA Technical Reports Server (NTRS)

Cravens, T. E.; Victor, G. A.; Dalgarno, A.

1975-01-01

The processes by which energetic electrons lose energy in a weakly ionized gas of molecular hydrogen are analyzed, and calculations are carried out taking into account the discrete nature of the excitation processes. The excitation, ionization, and heating efficiencies are computed for electrons with energies up to 100 eV absorbed in a gas with fractional ionizations up to 0.01, and the mean energy per pair of neutral hydrogen atoms is calculated.

Electron energy deposition in N2 gas

NASA Technical Reports Server (NTRS)

Fox, J. L.; Victor, G. A.

1988-01-01

The processes by which energetic electrons lose energy in a weakly ionized gas of molecular nitrogen are analyzed and calculations are carried out taking into account the discrete nature of the excitation processes. The excitation, ionization, dissociation and heating efficiencies are computed for energies up to 200 eV absorbed in a gas with fractional ionizations varying from 10(-6) to 10(-2). Individual vibrational excitations up to the seventh vibrational level are presented.

A combined thermal dissociation and electron impact ionization source for radioactive ion beam generation{sup a}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alton, G.D.; Williams, C.

1996-04-01

The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for radioactive ion beam (RIB) applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, inmore » principle, overcome this handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility, now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article. {copyright} {ital 1996 American Institute of Physics.}« less

A combined thermal dissociation and electron impact ionization source for radioactive ion beam generation (abstract){sup a}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alton, G.D.; Williams, C.

1996-03-01

The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for radioactive ion beam (RIB) applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, inmore » principle, overcome this handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility, now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article. {copyright} {ital 1996 American Institute of Physics.}« less

Resonant ionization spectroscopy of autoionizing Rydberg states in cobalt and redetermination of its ionization potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yuan; Gottwald, T.; Mattolat, C.

We obtained multi-step resonance ionization spectroscopy of cobalt using a hot-cavity laser ion source and three Ti:Sapphire lasers. Furthermore, the photoionization spectra revealed members of five new autoionizing Rydberg series that originate from three different lower levels of 3d 74s5s h 4F 9/2, 3d 74s4d f 4G 11/2, and 3d 74s4d f 4H 13/2 and converge to the first four excited states of singly ionized Co. Our analyses of the Rydberg series yield 63564.689 0.036 cm -1 as the first ionization potential of Co, which is an order of magnitude more accurate than the previous estimation. Using a three-step resonancemore » ionization scheme that employs an autoinizing Rydberg state in the last transition, we obtained an overall ionization efficiency of about 18% for Co.« less

Resonant ionization spectroscopy of autoionizing Rydberg states in cobalt and redetermination of its ionization potential

DOE PAGES

Liu, Yuan; Gottwald, T.; Mattolat, C.; ...

2017-03-20

We obtained multi-step resonance ionization spectroscopy of cobalt using a hot-cavity laser ion source and three Ti:Sapphire lasers. Furthermore, the photoionization spectra revealed members of five new autoionizing Rydberg series that originate from three different lower levels of 3d 74s5s h 4F 9/2, 3d 74s4d f 4G 11/2, and 3d 74s4d f 4H 13/2 and converge to the first four excited states of singly ionized Co. Our analyses of the Rydberg series yield 63564.689 0.036 cm -1 as the first ionization potential of Co, which is an order of magnitude more accurate than the previous estimation. Using a three-step resonancemore » ionization scheme that employs an autoinizing Rydberg state in the last transition, we obtained an overall ionization efficiency of about 18% for Co.« less

Cycling excitation process: An ultra efficient and quiet signal amplification mechanism in semiconductor

NASA Astrophysics Data System (ADS)

Liu, Yu-Hsin; Yan, Lujiang; Zhang, Alex Ce; Hall, David; Niaz, Iftikhar Ahmad; Zhou, Yuchun; Sham, L. J.; Lo, Yu-Hwa

2015-08-01

Signal amplification, performed by transistor amplifiers with its merit rated by the efficiency and noise characteristics, is ubiquitous in all electronic systems. Because of transistor thermal noise, an intrinsic signal amplification mechanism, impact ionization was sought after to complement the limits of transistor amplifiers. However, due to the high operation voltage (30-200 V typically), low power efficiency, limited scalability, and, above all, rapidly increasing excess noise with amplification factor, impact ionization has been out of favor for most electronic systems except for a few applications such as avalanche photodetectors and single-photon Geiger detectors. Here, we report an internal signal amplification mechanism based on the principle of the phonon-assisted cycling excitation process (CEP). Si devices using this concept show ultrahigh gain, low operation voltage, CMOS compatibility, and, above all, quantum limit noise performance that is 30 times lower than devices using impact ionization. Established on a unique physical effect of attractive properties, CEP-based devices can potentially revolutionize the fields of semiconductor electronics.

Action-FRET of a Gaseous Protein

NASA Astrophysics Data System (ADS)

Daly, Steven; Knight, Geoffrey; Halim, Mohamed Abdul; Kulesza, Alexander; Choi, Chang Min; Chirot, Fabien; MacAleese, Luke; Antoine, Rodolphe; Dugourd, Philippe

2017-01-01

Mass spectrometry is an extremely powerful technique for analysis of biological molecules, in particular proteins. One aspect that has been contentious is how much native solution-phase structure is preserved upon transposition to the gas phase by soft ionization methods such as electrospray ionization. To address this question—and thus further develop mass spectrometry as a tool for structural biology—structure-sensitive techniques must be developed to probe the gas-phase conformations of proteins. Here, we report Förster resonance energy transfer (FRET) measurements on a ubiquitin mutant using specific photofragmentation as a reporter of the FRET efficiency. The FRET data is interpreted in the context of circular dichroism, molecular dynamics simulation, and ion mobility data. Both the dependence of the FRET efficiency on the charge state—where a systematic decrease is observed—and on methanol concentration are considered. In the latter case, a decrease in FRET efficiency with methanol concentration is taken as evidence that the conformational ensemble of gaseous protein cations retains a memory of the solution phase conformational ensemble upon electrospray ionization.

Enhanced one-photon double ionization of atoms and molecules in an environment of different species.

PubMed

Stumpf, V; Kryzhevoi, N V; Gokhberg, K; Cederbaum, L S

2014-05-16

The correlated nature of electronic states in atoms and molecules is manifested in the simultaneous emission of two electrons after absorption of a single photon close to the respective threshold. Numerous observations in atoms and small molecules demonstrate that the double ionization efficiency close to threshold is rather small. In this Letter we show that this efficiency can be dramatically enhanced in the environment. To be specific, we concentrate on the case where the species in question has one or several He atoms as neighbors. The enhancement is achieved by an indirect process, where a He atom of the environment absorbs a photon and the resulting He(+) cation is neutralized fast by a process known as electron transfer mediated decay, producing thereby doubly ionized species. The enhancement of the double ionization is demonstrated in detail for the example of the Mg · He cluster. We show that the double ionization cross section of Mg becomes 3 orders of magnitude larger than the respective cross section of the isolated Mg atom. The impact of more neighbors is discussed and the extension to other species and environments is addressed.

Preliminary studies for a beam-generated plasma neutralizer test in NIO1

NASA Astrophysics Data System (ADS)

Sartori, E.; Veltri, P.; Balbinot, L.; Cavenago, M.; Veranda, M.; Antoni, V.; Serianni, G.

2017-08-01

The deployment of neutral beam injectors in future fusion plants is beset by the particularly poor efficiency of the neutralization process. Beam-generated plasma neutralizers were proposed as a passive and intrinsically safe scheme of efficient plasma neutralizers. The concept is based on the natural ionization of the gas target by the beam, and on a suitable confinement of the secondary plasma. The technological challenge of such a concept is the magnetic confinement of the secondary plasma: a proof-of-principle for the concept is needed. The possibility to test of such a system in the small negative ion beam system NIO1 is discussed in this paper. The constraints given by the facility are first discussed. A model of beam-gas interaction is developed to provide the charge-state of beam particles along the neutralizer, and to provide the source terms of plasma generation. By using a cylindrical model of plasma diffusion in magnetic fields, the ionization degree of the target is estimated. In the absence of magnetic fields the diffusion model is validated against experimental measurements of the space-charge compensation plasma in the drift region of NIO1. Finally, the feasibility study for a beam-generated plasma neutralizer in NIO is presented. The neutralizer length, required gas target thickness, and a very simple magnetic setup were considered, taking into account the integration in NIO1. For the basic design a low ionization degree (1%) is obtained, however a promising plasma density up to hundred times the beam density was calculated. The proposed test in NIO1 can be the starting point for studying advanced schemes of magnetic confinement aiming at ionization degrees in the order of 10%.

High-order harmonic generation in a capillary discharge

DOEpatents

Rocca, Jorge J.; Kapteyn, Henry C.; Mumane, Margaret M.; Gaudiosi, David; Grisham, Michael E.; Popmintchev, Tenio V.; Reagan, Brendan A.

2010-06-01

A pre-ionized medium created by a capillary discharge results in more efficient use of laser energy in high-order harmonic generation (HHG) from ions. It extends the cutoff photon energy, and reduces the distortion of the laser pulse as it propagates down the waveguide. The observed enhancements result from a combination of reduced ionization energy loss and reduced ionization-induced defocusing of the driving laser as well as waveguiding of the driving laser pulse. The discharge plasma also provides a means to spectrally tune the harmonics by tailoring the initial level of ionization of the medium.

Argon laser phototherapy could eliminate the damage effects induced by the ionizing radiation "gamma radiation" in irradiated rabbits.

PubMed

Abdul-Aziz, Karolin Kamel; Tuorkey, M J

2010-04-02

The ionizing radiations could be taken in considerate as an integral part in our life, since, living organisms are actually exposed to a constant shower of ionizing radiations whether from the natural or artificial resources. The radio-protective efficiency of several chemicals has been confirmed in animal trails, whereas, due to their accumulative toxicity, their clinical utility is limited. Therefore, we aimed in the present work to investigate the possibility of using argon laser to recuperate the damaged tissues due to exposing to the ionizing radiation. The rabbits were used in this study, and they were designed as control, gamma irradiated, laser, and gamma plus laser groups. Lipid peroxidation, reduced glutathione (GSH), glutathione peroxidase (GSH-Px) and glucose-6-phosphate dehydrogenase (G-6-PD) in blood and liver were evaluated. As well as, the level of protein thiol was evaluated in the plasma among each group. Results of this study revealed the potential therapeutic performance of the treatment by laser argon to decline the damaging effect of the ionized radiation whether at systematic or local levels. In conclusion, argon laser therapy appears propitious protective effect against the hazard effects of gamma radiation. Copyright 2010 Elsevier B.V. All rights reserved.

Optimizing the ionization and energy absorption of laser-irradiated clusters

NASA Astrophysics Data System (ADS)

Kundu, M.; Bauer, D.

2008-03-01

It is known that rare-gas or metal clusters absorb incident laser energy very efficiently. However, due to the intricate dependencies on all the laser and cluster parameters, it is difficult to predict under which circumstances ionization and energy absorption are optimal. With the help of three-dimensional particle-in-cell simulations of xenon clusters (up to 17256 atoms), it is shown that for a given laser pulse energy and cluster, an optimum wavelength exists that corresponds to the approximate wavelength of the transient, linear Mie-resonance of the ionizing cluster at an early stage of negligible expansion. In a single ultrashort laser pulse, the linear resonance at this optimum wavelength yields much higher absorption efficiency than in the conventional, dual-pulse pump-probe setup of linear resonance during cluster expansion.

Measurement of the ionization produced by sub-keV silicon nuclear recoils in a CCD dark matter detector

DOE PAGES

Chavarria, A. E.; Collar, J. I.; Peña, J. R.; ...

2016-10-15

We report a measurement of the ionization efficiency of silicon nuclei recoiling with sub-keV kinetic energy in the bulk silicon of a charge-coupled device (CCD). Nuclear recoils are produced by low-energy neutrons (<24 keV) from a 124Sb– 9Be photoneutron source, and their ionization signal is measured down to 60 eV electron equivalent. This energy range, previously unexplored, is relevant for the detection of low-mass dark matter particles. The measured efficiency is found to deviate from the extrapolation to low energies of the Lindhard model. Furthermore, this measurement also demonstrates the sensitivity to nuclear recoils of CCDs employed by DAMIC, amore » dark matter direct detection experiment located in the SNOLAB underground laboratory.« less

Nanomanipulation-Coupled Matrix-Assisted Laser Desorption/ Ionization-Direct Organelle Mass Spectrometry: A Technique for the Detailed Analysis of Single Organelles

NASA Astrophysics Data System (ADS)

Phelps, Mandy S.; Sturtevant, Drew; Chapman, Kent D.; Verbeck, Guido F.

2016-02-01

We describe a novel technique combining precise organelle microextraction with deposition and matrix-assisted laser desorption/ionization (MALDI) for a rapid, minimally invasive mass spectrometry (MS) analysis of single organelles from living cells. A dual-positioner nanomanipulator workstation was utilized for both extraction of organelle content and precise co-deposition of analyte and matrix solution for MALDI-direct organelle mass spectrometry (DOMS) analysis. Here, the triacylglycerol (TAG) profiles of single lipid droplets from 3T3-L1 adipocytes were acquired and results validated with nanoelectrospray ionization (NSI) MS. The results demonstrate the utility of the MALDI-DOMS technique as it enabled longer mass analysis time, higher ionization efficiency, MS imaging of the co-deposited spot, and subsequent MS/MS capabilities of localized lipid content in comparison to NSI-DOMS. This method provides selective organellar resolution, which complements current biochemical analyses and prompts for subsequent subcellular studies to be performed where limited samples and analyte volume are of concern.

Influence of Ionization and Beam Quality on Interaction of TW-Peak CO2 Laser with Hydrogen Plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samulyak, Roman

3D numerical simulations of the interaction of a powerful CO2 laser with hydrogen jets demonstrating the role of ionization and laser beam quality are presented. Simulations are performed in support of the plasma wakefield accelerator experiments being conducted at the BNL Accelerator Test Facility (ATF). The CO2 laser at BNL ATF has several potential advantages for laser wakefield acceleration compared to widely used solid-state lasers. SPACE, a parallel relativistic Particle-in-Cell code, developed at SBU and BNL, has been used in these studies. A novelty of the code is its set of efficient atomic physics algorithms that compute ionization and recombinationmore » rates on the grid and transfer them to particles. The primary goal of the initial BNL experiments was to characterize the plasma density by measuring the sidebands in the spectrum of the probe laser. Simulations, that resolve hydrogen ionization and laser spectra, help explain several trends that were observed in the experiments.« less

Improving N-Glycan Coverage using HPLC-MS with Electrospray Ionization at Subambient Pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marginean, Ioan; Kronewitter, Scott R.; Moore, Ronald J.

Human serum glycan profiling with mass spectrometry (MS) has been employed to study several disease conditions and is demonstrating promise for e.g. clinical biomarker discovery. However, the poor glycan ionization efficiency and the large dynamic range of glycan concentrations in human sera hinder comprehensive profiling. In particular, large glycans are problematic because they are present at low concentrations and prone to fragmentation. Here we show that the sub-ambient pressure ionization with nanoelectrospray (SPIN)-MS can expand the serum glycome profile when compared with the conventional atmospheric pressure electrospray ionization (ESI)-MS with a heated capillary inlet. Notably, the ions generated by themore » SPIN interface were observed at higher charge states for 50% of the annotated glycans. Out of a total of 130 detected glycans, 34 were only detected with the SPIN-MS, resulting in improved coverage of glycan families as well as of glycans with larger numbers of labile monosaccharides.« less

Development of a High Ionization Efficiency Molten Glass Ion Emitter for TIMS

NASA Astrophysics Data System (ADS)

Cheversia, M. B.; Farmer, G.; Koval, C.; David, D.

2006-12-01

Thermal ionization mass spectrometry (TIMS) remains the method of choice for many high precision isotope ratio determinations but is handicapped by the use of low efficiency ion emitters. For example, ionization efficiencies from molten glass emitters (Si-gel) used for such elements as Pb, Cr, Ru, and Ag are in the range of 0.05-2%, which limits the sample size and the precision to which isotope ratio determinations for these elements can be made. Our aim is to improve the ionization efficiency of the molten glass ion emitter using electrochemical methods. This work builds on recent observations indicating that many metals doped in borosilicate glasses (eg. Bi, Ag), are emitted from the liquid glass (in vacuo) primarily as the neutral metal atom. Our goal is to increase the proportion of singly charged metal atoms in metal-doped molten glasses via oxidation induced by electrochemical methods and to assess whether such in situ oxidation of metal atoms leads to an increase in emitted metal ions. Our experiments are performed in a vacuum chamber that mimics conditions in the sample chamber of the TIMS. A borosilicate glass sample is placed in a miniature ceramic crucible. The crucible contains working and reference Pt electrodes, and a Pt thermocouple. The entire apparatus is wrapped with a resistively heated Ta wire until temperatures in the glass reach approximately 1400°C, to ensure that the glass is molten. By this method, we have produced simple cyclic voltammograms that suggest that over a 100°C temperature range, the borosilicate glass undergoes a transition from resistive behavior as a solid, to a conductive electrolyte, as a molten liquid glass, as expected. The change is evident as an order of magnitude decrease in resistivity of the glass, as interpreted from the voltammograms. The voltammograms produced for the pure borosilicate glasses represent the baseline against which we will compare the electrochemical characteristics of Pb doped glasses. These experiments are currently underway and are designed to determine the speciation of lead in the glass, and to determine the voltages required to induce cathodic currents in the glass corresponding to ionization to Pb+ and Pb2+. By generating a cathodic current and an increased concentration of the oxidized species, we hope to ultimately generate a higher intensity ion beam, higher ionization efficiency for low efficiency elements, and higher precision analyses on small sample sizes for the TIMS.

Absorption and dissociative photoionization cross sections of NH3 from 80 to 1120 A

NASA Technical Reports Server (NTRS)

Samson, James A. R.; Haddad, G. N.; Kilcoyne, L. D.

1987-01-01

The total absorption, photoionization, and dissociative photoionization cross sections of ammonia have been measured from 80 to 1120 A. All possible fragment ions have been observed including doubly ionized ammonia. The absolute ionization efficiencies have also been measured in this spectral range. The appearance potentials of the fragment ions have been measured and are compared with the calculated appearance potentials derived from published heats of formation and ionization potentials of the fragments.

Soft Argon-Propane Dielectric Barrier Discharge Ionization.

PubMed

Schütz, Alexander; Lara-Ortega, Felipe J; Klute, Felix David; Brandt, Sebastian; Schilling, Michael; Michels, Antje; Veza, Damir; Horvatic, Vlasta; García-Reyes, Juan F; Franzke, Joachim

2018-03-06

Dielectric barrier discharges (DBDs) have been used as soft ionization sources (DBDI) for organic mass spectrometry (DBDI-MS) for approximately ten years. Helium-based DBDI is often used because of its good ionization efficiency, low ignition voltage, and homogeneous plasma conditions. Argon needs much higher ignition voltages than helium when the same discharge geometry is used. A filamentary plasma, which is not suitable for soft ionization, may be produced instead of a homogeneous plasma. This difference results in N 2 , present in helium and argon as an impurity, being Penning-ionized by helium but not by metastable argon atoms. In this study, a mixture of argon and propane (C 3 H 8 ) was used as an ignition aid to decrease the ignition and working voltages, because propane can be Penning-ionized by argon metastables. This approach leads to homogeneous argon-based DBDI. Furthermore, operating DBDI in an open environment assumes that many uncharged analyte molecules do not interact with the reactant ions. To overcome this disadvantage, we present a novel approach, where the analyte is introduced in an enclosed system through the discharge capillary itself. This nonambient DBDI-MS arrangement is presented and characterized and could advance the novel connection of DBDI with analytical separation techniques such as gas chromatography (GC) and high-pressure liquid chromatography (HPLC) in the near future.

Quantum mechanical calculations related to ionization and charge transfer in DNA

NASA Astrophysics Data System (ADS)

Cauët, E.; Valiev, M.; Weare, J. H.; Liévin, J.

2012-07-01

Ionization and charge migration in DNA play crucial roles in mechanisms of DNA damage caused by ionizing radiation, oxidizing agents and photo-irradiation. Therefore, an evaluation of the ionization properties of the DNA bases is central to the full interpretation and understanding of the elementary reactive processes that occur at the molecular level during the initial exposure and afterwards. Ab initio quantum mechanical (QM) methods have been successful in providing highly accurate evaluations of key parameters, such as ionization energies (IE) of DNA bases. Hence, in this study, we performed high-level QM calculations to characterize the molecular energy levels and potential energy surfaces, which shed light on ionization and charge migration between DNA bases. In particular, we examined the IEs of guanine, the most easily oxidized base, isolated and embedded in base clusters, and investigated the mechanism of charge migration over two and three stacked guanines. The IE of guanine in the human telomere sequence has also been evaluated. We report a simple molecular orbital analysis to explain how modifications in the base sequence are expected to change the efficiency of the sequence as a hole trap. Finally, the application of a hybrid approach combining quantum mechanics with molecular mechanics brings an interesting discussion as to how the native aqueous DNA environment affects the IE threshold of nucleobases.

Ion Clouds in the Inductively Coupled Plasma Torch: A Closer Look through Computations.

PubMed

Aghaei, Maryam; Lindner, Helmut; Bogaerts, Annemie

2016-08-16

We have computationally investigated the introduction of copper elemental particles in an inductively coupled plasma torch connected to a sampling cone, including for the first time the ionization of the sample. The sample is inserted as liquid particles, which are followed inside the entire torch, i.e., from the injector inlet up to the ionization and reaching the sampler. The spatial position of the ion clouds inside the torch as well as detailed information on the copper species fluxes at the position of the sampler orifice and the exhausts of the torch are provided. The effect of on- and off-axis injection is studied. We clearly show that the ion clouds of on-axis injected material are located closer to the sampler with less radial diffusion. This guarantees a higher transport efficiency through the sampler cone. Moreover, our model reveals the optimum ranges of applied power and flow rates, which ensure the proper position of ion clouds inside the torch, i.e., close enough to the sampler to increase the fraction that can enter the mass spectrometer and with minimum loss of material toward the exhausts as well as a sufficiently high plasma temperature for efficient ionization.

Developing a Vacuum Electrospray Source To Implement Efficient Atmospheric Sampling for Miniature Ion Trap Mass Spectrometer.

PubMed

Yu, Quan; Zhang, Qian; Lu, Xinqiong; Qian, Xiang; Ni, Kai; Wang, Xiaohao

2017-12-05

The performance of a miniature mass spectrometer in atmospheric analysis is closely related to the design of its sampling system. In this study, a simplified vacuum electrospray ionization (VESI) source was developed based on a combination of several techniques, including the discontinuous atmospheric pressure interface, direct capillary sampling, and pneumatic-assisted electrospray. Pulsed air was used as a vital factor to facilitate the operation of electrospray ionization in the vacuum chamber. This VESI device can be used as an efficient atmospheric sampling interface when coupled with a miniature rectilinear ion trap (RIT) mass spectrometer. The developed VESI-RIT instrument enables regular ESI analysis of liquid, and its qualitative and quantitative capabilities have been characterized by using various solution samples. A limit of detection of 8 ppb could be attained for arginine in a methanol solution. In addition, extractive electrospray ionization of organic compounds can be implemented by using the same VESI device, as long as the gas analytes are injected with the pulsed auxiliary air. This methodology can extend the use of the proposed VESI technique to rapid and online analysis of gaseous and volatile samples.

Cross sections for direct and dissociative ionization of NH3 and CS2 by electron impact

NASA Technical Reports Server (NTRS)

Rao, M. V. V. S.; Srivastava, S. K.

1991-01-01

A crossed electron beam-molecular beam collision geometry is used to measure cross sections for the production of positive ions by electron impact on NH3 and CS2. Ionization cross-section data for NH3 and the values of various cross sections are presented, as well as ionization efficiency curves for CS2. Considerable differences are found between the various results on NH3. The present values are close to the data of Djuric et al. (1981). The semiempirical calculations of Hare and Meath (1987) differ considerably in the absolute values of cross sections. Discrepancies were observed in comparisons of cross sections of other fragment ions resulting from the ionization and dissociate ionization of NH3.

Scaling-law equilibria for calcium in canopy-type models of the solar chromosphere

NASA Technical Reports Server (NTRS)

Jones, H. P.

1982-01-01

Scaling laws for resonance line formation are used to obtain approximate excitation and ionization equilibria for a three-level model of singly ionized calcium. The method has been developed for and is applied to the study of magnetograph response in the 8542 A infrared triplet line to magnetostatic canopies which schematically model diffuse, nearly horizontal fields in the low solar chromosphere. For this application, the method is shown to be efficient and semi-quantitative, and the results indicate the type and range of effects on calcium-line radiation which result from reduced gas pressure inside the magnetic regions.

How does ionizing radiation escape from galaxies?

NASA Astrophysics Data System (ADS)

Orlitova, Ivana

2016-10-01

Search for sources that reionized the Universe from z 15 to z 6 is one of the main drivers of present-day astronomy. Low-mass star-forming galaxies are the most favoured sources of ionizing photons, but the searches of escaping Lyman continuum (LyC) have not been extremely successful. Our team has recently detected prominent LyC escape from five Green Pea galaxies at redshift 0.3, using the HST/COS spectrograph, which represents a significant breakthrough. We propose here to study the LyC escape of the strongest among these leakers, J1152, with spatial resolution. From the comparison of the ionizing and non-ionizing radiation maps, and surface brightness profiles, we will infer the major mode in which LyC is escaping: from the strongest starburst, from the galaxy edge, through a hole along our line-of-sight, through clumpy medium, or directly from all the production sites due to highly ionized medium in the entire galaxy. In parallel, we will test the predictive power of two highly debated indirect indicators of LyC leakage: the [OIII]5007/[OII]3727 ratio, and Lyman-alpha. We predict that their spatial distribution should closely follow that of the ionizing continuum if column densities of the neutral gas are low. This combined study, which relies on the HST unique capabilities, will bring crucial information on the structure of the leaking galaxies, provide constraints for hydrodynamic simulations, and will lead to efficient future searches for LyC leakers across a large range of redshifts.

Preliminary Ionization Efficiencies of {sup 11}C and {sup 14}O with the LBNL ECR Ion Sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Z.Q.; Cerny, J.; Guo, F.Q.

1998-10-05

High charge states, up to fully stripped {sup 11}C and {sup 14}O ion, beams have been produced with the electron cyclotron resonance ion sources (LBNL, ECR and AECR-U) at Lawrence Berkeley National Laboratory. The radioactive atoms of {sup 11}C and {sup 14}O were collected in batch mode with an LN{sub 2} trap and then bled into the ECR ion sources. Ionization efficiency as high as 11% for {sup 11}C{sup 4+} was achieved.

Development of a Microfluidic Open Interface with Flow Isolated Desorption Volume for the Direct Coupling of SPME Devices to Mass Spectrometry.

PubMed

Tascon, Marcos; Alam, Md Nazmul; Gómez-Ríos, Germán Augusto; Pawliszyn, Janusz

2018-02-20

Technologies that efficiently integrate the sampling and sample preparation steps with direct introduction to mass spectrometry (MS), providing simple and sensitive analytical workflows as well as capabilities for automation, can generate a great impact in a vast variety of fields, such as in clinical, environmental, and food-science applications. In this study, a novel approach that facilitates direct coupling of Bio-SPME devices to MS using a microfluidic design is presented. This technology, named microfluidic open interface (MOI), which operates under the concept of flow-isolated desorption volume, consists of an open-to-ambient desorption chamber (V ≤ 7 μL) connected to an ionization source. Subsequently, compounds of interest are transported to the ionization source by means of the self-aspiration process intrinsic of these interfaces. Thus, any ionization technology that provides a reliable and constant suction, such as electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), or inductively coupled plasma ionization (ICP), can be hyphenated to MOI. Using this setup, the desorption chamber is used to release target compounds from the coating, while the isolation of the flow enables the ionization source to be continuously fed with solvent, all without the necessity of employment of additional valves. As a proof of concept, the design was applied to an ESI-MS/MS system for experimental validation. Furthermore, numerical simulations were undertaken to provide a detailed understanding of the fluid flow pattern inside the interface, then used to optimize the system for better efficiency. The analytical workflow of the developed Bio-SPME-MOI-MS setup consists of the direct immersion of SPME fibers into the matrix to extract/enrich analytes of interest within a short period of time, followed by a rinsing step with water to remove potentially adhering proteins, salts, and/or other interfering compounds. Next, the fiber is inserted into the MOI for desorption of compounds of interest. Finally, the volume contained in the chamber is drained and moved toward the electrospray needle for ionization and direct introduction to MS. Aiming to validate the technology, the fast determination of selected immunosuppressive drugs (e.g., tacrolimus, cyclosporine, sirolimus, and everolimus) from 100 μL of whole blood was assessed. Limits of quantitation in the subppb range were obtained for all studied compounds. Good linearity (r 2 ≥ 0.99) and excellent precision, with (8%) and without (14%) internal standard correction, were attained.

Quantitative Profiling of Major Neutral Lipid Classes in Human Meibum by Direct Infusion Electrospray Ionization Mass Spectrometry

PubMed Central

Chen, Jianzhong; Green, Kari B.; Nichols, Kelly K.

2013-01-01

Purpose. The purpose of this investigation was to better understand lipid composition in human meibum. Methods. Intact lipids in meibum samples were detected by direct infusion electrospray ionization mass spectrometry (ESI-MS) analysis in positive detection mode using sodium iodide (NaI) as an additive. The peak intensities of all major types of lipid species, that is, wax esters (WEs), cholesteryl esters (CEs), and diesters (DEs) were corrected for peak overlapping and isotopic distribution; an additional ionization efficiency correction was performed for WEs and CEs, which was simplified by the observation that the corresponding ionization efficiency was primarily dependent on the specific lipid class and saturation degree of the lipids while independent of the carbon chain length. A set of WE and CE standards was spiked in meibum samples for ionization efficiency determination and absolute quantitation. Results. The absolute amount (μmol/mg) for each of 51 WEs and 31 CEs in meibum samples was determined. The summed masses for 51 WEs and 31 CEs accounted for 48 ± 4% and 40 ± 2%, respectively, of the total meibum lipids. The mass percentages of saturated and unsaturated species were determined to be 75 ± 2% and 25 ± 1% for CEs and 14 ± 1% and 86 ± 1% for WEs. The profiles for two types of DEs were also obtained, which include 42 α,ω Type II DEs, and 21 ω Type I-St DEs. Conclusions. Major neutral lipid classes in meibum samples were quantitatively profiled by ESI-MS analysis with NaI additive. PMID:23847307

Three-photon resonance ionization of atomic Mn in a hot-cavity laser ion source using Ti:sapphire lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Y.; Gottwald, T.; Mattolat, C.

We have demonstrated three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti: sapphire lasers. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d 54s5s f 6S 5/2 level at 49 415.35 cm -1, while Rydberg transitions were reached from the 3d 54s4d e 6D 9/2,7/2,5/2) levels at around 47 210 cm -1. Analyses of the strong Rydberg transitions associated with the 3d 54s4d e 6D 7/2 lower level indicate that they belong to the dipole-allowed 4dmore » → nf 6F° 9/2,7/2,5/2 series converging to the 3d 54s 7S 3 ground state of Mn II. From this series, an ionization potential of 59 959.56 ± 0.01 cm -1 is obtained for Mn. At high ion source temperatures the semi-forbidden 4d → nf 8 F°9/2,7/2,5/2 series was also observed. The overall ionization efficiency for Mn has been measured to be about 0.9% when using the strong AI transition in the third excitation step and 0.3% when employing an intense Rydberg transition. Experimental data indicate that the ionization efficiency was limited by the interaction of Mn atoms with ion source materials at high temperatures.« less

Three-photon resonance ionization of atomic Mn in a hot-cavity laser ion source using Ti:sapphire lasers

DOE PAGES

Liu, Y.; Gottwald, T.; Mattolat, C.; ...

2015-05-08

We have demonstrated three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti: sapphire lasers. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d 54s5s f 6S 5/2 level at 49 415.35 cm -1, while Rydberg transitions were reached from the 3d 54s4d e 6D 9/2,7/2,5/2) levels at around 47 210 cm -1. Analyses of the strong Rydberg transitions associated with the 3d 54s4d e 6D 7/2 lower level indicate that they belong to the dipole-allowed 4dmore » → nf 6F° 9/2,7/2,5/2 series converging to the 3d 54s 7S 3 ground state of Mn II. From this series, an ionization potential of 59 959.56 ± 0.01 cm -1 is obtained for Mn. At high ion source temperatures the semi-forbidden 4d → nf 8 F°9/2,7/2,5/2 series was also observed. The overall ionization efficiency for Mn has been measured to be about 0.9% when using the strong AI transition in the third excitation step and 0.3% when employing an intense Rydberg transition. Experimental data indicate that the ionization efficiency was limited by the interaction of Mn atoms with ion source materials at high temperatures.« less

Determination of drugs and drug-like compounds in different samples with direct analysis in real time mass spectrometry.

PubMed

Chernetsova, Elena S; Morlock, Gertrud E

2011-01-01

Direct analysis in real time (DART), a relatively new ionization source for mass spectrometry, ionizes small-molecule components from different kinds of samples without any sample preparation and chromatographic separation. The current paper reviews the published data available on the determination of drugs and drug-like compounds in different matrices with DART-MS, including identification and quantitation issues. Parameters that affect ionization efficiency and mass spectra composition are also discussed. Copyright © 2011 Wiley Periodicals, Inc.

A Numerical Simulation of the Energy Conversion Process in Microwave Rocket

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shibata, Teppei; Oda, Yasuhisa; Komurasaki, Kimiya

2008-04-28

In Microwave Rocket, a high power microwave beam ionizes atmospheric air inside of the thruster and the ionization front drives a shock wave. In this paper, CFD simulation was conducted using measured propagation velocity of the ionization front to evaluate the engine performance. As a result, maximum cycle efficiency was obtained at the power density of about 200 kW/m{sup 2} which is the transitional beam power condition between Microwave Supported Combustion and Microwave Supported Detonation regimes.

Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization.

PubMed

Neustetter, M; Jabbour Al Maalouf, E; Limão-Vieira, P; Denifl, S

2016-08-07

Electron ionization of neat tungsten hexacarbonyl (W(CO)6) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO)6 clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO)n (+) (0 ≤ n ≤ 6) and W2(CO)n (+) (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO)n (+) (0 ≤ n ≤ 3) and W2C(CO)n (+) (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.

Röntgen spheres around active stars

NASA Astrophysics Data System (ADS)

Locci, Daniele; Cecchi-Pestellini, Cesare; Micela, Giuseppina; Ciaravella, Angela; Aresu, Giambattista

2018-01-01

X-rays are an important ingredient of the radiation environment of a variety of stars of different spectral types and age. We have modelled the X-ray transfer and energy deposition into a gas with solar composition, through an accurate description of the electron cascade following the history of the primary photoelectron energy deposition. We test and validate this description studying the possible formation of regions in which X-rays are the major ionization channel. Such regions, called Röntgen spheres may have considerable importance in the chemical and physical evolution of the gas embedding the emitting star. Around massive stars the concept of Röntgen sphere appears to be of limited use, as the formation of extended volumes with relevant levels of ionization is efficient just in a narrow range of gas volume densities. In clouds embedding low-mass pre-main-sequence stars significant volumes of gas are affected by ionization levels exceeding largely the cosmic-ray background ionization. In clusters arising in regions of vigorous star formation X-rays create an ionization network pervading densely the interstellar medium, and providing a natural feedback mechanism, which may affect planet and star formation processes.

CF3+ fragmentation by electron impact ionization of perfluoro-propyl-vinyl-ethers, C5F10O, in gas phase

NASA Astrophysics Data System (ADS)

Kondo, Yusuke; Ishikawa, Kenji; Hayashi, Toshio; Miyawaki, Yudai; Takeda, Keigo; Kondo, Hiroki; Sekine, Makoto; Hori, Masaru

2015-04-01

The gas phase fragmentations of perfluoro-propyl-vinyl ether (PPVE, C5F10O) are studied experimentally. Dominant fragmentations of PPVE are found to be the result of a dissociative ionization reaction, i.e., CF3+ via direct bond cleavage, and C2F3O- and C3F7O- via electron attachment. Regardless of the appearance energy of around 14.5 eV for the dissociative ionization of CF3+, the observed ion efficiency for the CF3+ ion was extremely large the order of 10-20 cm-2, compared with only 10-21 cm-2 for the other channels. PPVE characteristically generated CF3+ as the largest abundant ion are advantageous for use of feedstock gases in plasma etching processes.

A rapid and sensitive method for the simultaneous analysis of aliphatic and polar molecules containing free carboxyl groups in plant extracts by LC-MS/MS

PubMed Central

2009-01-01

Background Aliphatic molecules containing free carboxyl groups are important intermediates in many metabolic and signalling reactions, however, they accumulate to low levels in tissues and are not efficiently ionized by electrospray ionization (ESI) compared to more polar substances. Quantification of aliphatic molecules becomes therefore difficult when small amounts of tissue are available for analysis. Traditional methods for analysis of these molecules require purification or enrichment steps, which are onerous when multiple samples need to be analyzed. In contrast to aliphatic molecules, more polar substances containing free carboxyl groups such as some phytohormones are efficiently ionized by ESI and suitable for analysis by LC-MS/MS. Thus, the development of a method with which aliphatic and polar molecules -which their unmodified forms differ dramatically in their efficiencies of ionization by ESI- can be simultaneously detected with similar sensitivities would substantially simplify the analysis of complex biological matrices. Results A simple, rapid, specific and sensitive method for the simultaneous detection and quantification of free aliphatic molecules (e.g., free fatty acids (FFA)) and small polar molecules (e.g., jasmonic acid (JA), salicylic acid (SA)) containing free carboxyl groups by direct derivatization of leaf extracts with Picolinyl reagent followed by LC-MS/MS analysis is presented. The presence of the N atom in the esterified pyridine moiety allowed the efficient ionization of 25 compounds tested irrespective of their chemical structure. The method was validated by comparing the results obtained after analysis of Nicotiana attenuata leaf material with previously described analytical methods. Conclusion The method presented was used to detect 16 compounds in leaf extracts of N. attenuata plants. Importantly, the method can be adapted based on the specific analytes of interest with the only consideration that the molecules must contain at least one free carboxyl group. PMID:19939243

Extending semi-numeric reionization models to the first stars and galaxies

NASA Astrophysics Data System (ADS)

Koh, Daegene; Wise, John H.

2018-03-01

Semi-numeric methods have made it possible to efficiently model the epoch of reionization (EoR). While most implementations involve a reduction to a simple three-parameter model, we introduce a new mass-dependent ionizing efficiency parameter that folds in physical parameters that are constrained by the latest numerical simulations. This new parametrization enables the effective modelling of a broad range of host halo masses containing ionizing sources, extending from the smallest Population III host haloes with M ˜ 106 M⊙, which are often ignored, to the rarest cosmic peaks with M ˜ 1012 M⊙ during EoR. We compare the resulting ionizing histories with a typical three-parameter model and also compare with the latest constraints from the Planck mission. Our model results in an optical depth due to Thomson scattering, τe = 0.057, that is consistent with Planck. The largest difference in our model is shown in the resulting bubble size distributions that peak at lower characteristic sizes and are broadened. We also consider the uncertainties of the various physical parameters, and comparing the resulting ionizing histories broadly disfavours a small contribution from galaxies. The smallest haloes cease a meaningful contribution to the ionizing photon budget after z = 10, implying that they play a role in determining the start of EoR and little else.

Laser resonance ionization spectroscopy on lutetium for the MEDICIS project

NASA Astrophysics Data System (ADS)

Gadelshin, V.; Cocolios, T.; Fedoseev, V.; Heinke, R.; Kieck, T.; Marsh, B.; Naubereit, P.; Rothe, S.; Stora, T.; Studer, D.; Van Duppen, P.; Wendt, K.

2017-11-01

The MEDICIS-PROMED Innovative Training Network under the Horizon 2020 EU program aims to establish a network of early stage researchers, involving scientific exchange and active cooperation between leading European research institutions, universities, hospitals, and industry. Primary scientific goal is the purpose of providing and testing novel radioisotopes for nuclear medical imaging and radionuclide therapy. Within a closely linked project at CERN, a dedicated electromagnetic mass separator system is presently under installation for production of innovative radiopharmaceutical isotopes at the new CERN-MEDICIS laboratory, directly adjacent to the existing CERN-ISOLDE radioactive ion beam facility. It is planned to implement a resonance ionization laser ion source (RILIS) to ensure high efficiency and unrivaled purity in the production of radioactive ions. To provide a highly efficient ionization process, identification and characterization of a specific multi-step laser ionization scheme for each individual element with isotopes of interest is required. The element lutetium is of primary relevance, and therefore was considered as first candidate. Three two-step excitation schemes for lutetium atoms are presented in this work, and spectroscopic results are compared with data of other authors.

High Sensitivity Combined with Extended Structural Coverage of Labile Compounds via Nanoelectrospray Ionization at Subambient Pressures

DOE PAGES

Cox, Jonathan T.; Kronewitter, Scott R.; Shukla, Anil K.; ...

2014-09-15

Subambient pressure ionization with nanoelectrospray (SPIN) has proven to be effective in producing ions with high efficiency and transmitting them to low pressures for high sensitivity mass spectrometry (MS) analysis. Here we present evidence that not only does the SPIN source improve MS sensitivity but also allows for gentler ionization conditions. The gentleness of a conventional heated capillary electrospray ionization (ESI) source and the SPIN source was compared by the liquid chromatography mass spectrometry (LC-MS) analysis of colominic acid. Colominic acid is a mixture of sialic acid polymers of different lengths containing labile glycosidic linkages between monomer units necessitating amore » gentle ion source. By coupling the SPIN source with high resolution mass spectrometry and using advanced data processing tools, we demonstrate much extended coverage of sialic acid polymer chains as compared to using the conventional ESI source. Additionally we show that SPIN-LC-MS is effective in elucidating polymer features with high efficiency and high sensitivity previously unattainable by the conventional ESI-LC-MS methods.« less

In-situ Probing of Radiation-induced Processing of Organics in Astrophysical Ice Analogs—Novel Laser Desorption Laser Ionization Time-of-flight Mass Spectroscopic Studies

NASA Astrophysics Data System (ADS)

Gudipati, Murthy S.; Yang, Rui

2012-09-01

Understanding the evolution of organic molecules in ice grains in the interstellar medium (ISM) under cosmic rays, stellar radiation, and local electrons and ions is critical to our understanding of the connection between ISM and solar systems. Our study is aimed at reaching this goal of looking directly into radiation-induced processing in these ice grains. We developed a two-color laser-desorption laser-ionization time-of-flight mass spectroscopic method (2C-MALDI-TOF), similar to matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectroscopy. Results presented here with polycyclic aromatic hydrocarbon (PAH) probe molecules embedded in water-ice at 5 K show for the first time that hydrogenation and oxygenation are the primary chemical reactions that occur in astrophysical ice analogs when subjected to Lyα radiation. We found that hydrogenation can occur over several unsaturated bonds and the product distribution corresponds to their stabilities. Multiple hydrogenation efficiency is found to be higher at higher temperatures (100 K) compared to 5 K—close to the interstellar ice temperatures. Hydroxylation is shown to have similar efficiencies at 5 K or 100 K, indicating that addition of O atoms or OH radicals to pre-ionized PAHs is a barrierless process. These studies—the first glimpses into interstellar ice chemistry through analog studies—show that once accreted onto ice grains PAHs lose their PAH spectroscopic signatures through radiation chemistry, which could be one of the reason for the lack of PAH detection in interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks.

Charge collection efficiency degradation induced by MeV ions in semiconductor devices: Model and experiment

DOE PAGES

Vittone, Ettore; Pastuovic, Zeljko; Breese, Mark B. H.; ...

2016-02-08

This study investigates both theoretically and experimentally the charge collection efficiency (CCE) degradation in silicon diodes induced by energetic ions. Ion Beam Induced Charge (IBIC) measurements carried out on n- and p-type silicon diodes which were previously irradiated with MeV He ions show evidence that the CCE degradation does not only depend on the mass, energy and fluence of the damaging ion, but also depends on the ion probe species and on the polarization state of the device. A general one-dimensional model is derived, which accounts for the ion-induced defect distribution, the ionization profile of the probing ion and themore » charge induction mechanism. Using the ionizing and non-ionizing energy loss profiles resulting from simulations based on the binary collision approximation and on the electrostatic/transport parameters of the diode under study as input, the model is able to accurately reproduce the experimental CCE degradation curves without introducing any phenomenological additional term or formula. Although limited to low level of damage, the model is quite general, including the displacement damage approach as a special case and can be applied to any semiconductor device. It provides a method to measure the capture coefficients of the radiation induced recombination centres. They can be considered indexes, which can contribute to assessing the relative radiation hardness of semiconductor materials.« less

Cycling excitation process: An ultra efficient and quiet signal amplification mechanism in semiconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yu-Hsin; Yan, Lujiang; Zhang, Alex Ce

2015-08-03

Signal amplification, performed by transistor amplifiers with its merit rated by the efficiency and noise characteristics, is ubiquitous in all electronic systems. Because of transistor thermal noise, an intrinsic signal amplification mechanism, impact ionization was sought after to complement the limits of transistor amplifiers. However, due to the high operation voltage (30-200 V typically), low power efficiency, limited scalability, and, above all, rapidly increasing excess noise with amplification factor, impact ionization has been out of favor for most electronic systems except for a few applications such as avalanche photodetectors and single-photon Geiger detectors. Here, we report an internal signal amplification mechanismmore » based on the principle of the phonon-assisted cycling excitation process (CEP). Si devices using this concept show ultrahigh gain, low operation voltage, CMOS compatibility, and, above all, quantum limit noise performance that is 30 times lower than devices using impact ionization. Established on a unique physical effect of attractive properties, CEP-based devices can potentially revolutionize the fields of semiconductor electronics.« less

Commentary: Ethical Issues of Current Health-Protection Policies on Low-Dose Ionizing Radiation

PubMed Central

Socol, Yehoshua; Dobrzyński, Ludwik; Doss, Mohan; Feinendegen, Ludwig E.; Janiak, Marek K.; Miller, Mark L.; Sanders, Charles L.; Scott, Bobby R.; Ulsh, Brant; Vaiserman, Alexander

2014-01-01

The linear no-threshold (LNT) model of ionizing-radiation-induced cancer is based on the assumption that every radiation dose increment constitutes increased cancer risk for humans. The risk is hypothesized to increase linearly as the total dose increases. While this model is the basis for radiation safety regulations, its scientific validity has been questioned and debated for many decades. The recent memorandum of the International Commission on Radiological Protection admits that the LNT-model predictions at low doses are “speculative, unproven, undetectable and ‘phantom’.” Moreover, numerous experimental, ecological, and epidemiological studies show that low doses of sparsely-ionizing or sparsely-ionizing plus highly-ionizing radiation may be beneficial to human health (hormesis/adaptive response). The present LNT-model-based regulations impose excessive costs on the society. For example, the median-cost medical program is 5000 times more cost-efficient in saving lives than controlling radiation emissions. There are also lives lost: e.g., following Fukushima accident, more than 1000 disaster-related yet non-radiogenic premature deaths were officially registered among the population evacuated due to radiation concerns. Additional negative impacts of LNT-model-inspired radiophobia include: refusal of some patients to undergo potentially life-saving medical imaging; discouragement of the study of low-dose radiation therapies; motivation for radiological terrorism and promotion of nuclear proliferation. PMID:24910586

Chemical vapor deposition of aminopropyl silanes in microfluidic channels for highly efficient microchip capillary electrophoresis-electrospray ionization-mass spectrometry.

PubMed

Batz, Nicholas G; Mellors, J Scott; Alarie, Jean Pierre; Ramsey, J Michael

2014-04-01

We describe a chemical vapor deposition (CVD) method for the surface modification of glass microfluidic devices designed to perform electrophoretic separations of cationic species. The microfluidic channel surfaces were modified using aminopropyl silane reagents. Coating homogeneity was inferred by precise measurement of the separation efficiency and electroosmotic mobility for multiple microfluidic devices. Devices coated with (3-aminopropyl)di-isopropylethoxysilane (APDIPES) yielded near diffusion-limited separations and exhibited little change in electroosmotic mobility between pH 2.8 and pH 7.5. We further evaluated the temporal stability of both APDIPES and (3-aminopropyl)triethoxysilane (APTES) coatings when stored for a total of 1 week under vacuum at 4 °C or filled with pH 2.8 background electrolyte at room temperature. Measurements of electroosmotic flow (EOF) and separation efficiency during this time confirmed that both coatings were stable under both conditions. Microfluidic devices with a 23 cm long, serpentine electrophoretic separation channel and integrated nanoelectrospray ionization emitter were CVD coated with APDIPES and used for capillary electrophoresis (CE)-electrospray ionization (ESI)-mass spectrometry (MS) of peptides and proteins. Peptide separations were fast and highly efficient, yielding theoretical plate counts over 600,000 and a peak capacity of 64 in less than 90 s. Intact protein separations using these devices yielded Gaussian peak profiles with separation efficiencies between 100,000 and 400,000 theoretical plates.

Increasing Polyaromatic Hydrocarbon (PAH) Molecular Coverage during Fossil Oil Analysis by Combining Gas Chromatography and Atmospheric-Pressure Laser Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)

PubMed Central

Benigni, Paolo; DeBord, J. Daniel; Thompson, Christopher J.; Gardinali, Piero; Fernandez-Lima, Francisco

2016-01-01

Thousands of chemically distinct compounds are encountered in fossil oil samples that require rapid screening and accurate identification. In the present paper, we show for the first time, the advantages of gas chromatography (GC) separation in combination with atmospheric-pressure laser ionization (APLI) and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for the screening of polyaromatic hydrocarbons (PAHs) in fossil oils. In particular, reference standards of organics in shale oil, petroleum crude oil, and heavy sweet crude oil were characterized by GC-APLI-FT-ICR MS and APLI-FT-ICR MS. Results showed that, while APLI increases the ionization efficiency of PAHs, when compared to other ionization sources, the complexity of the fossil oils reduces the probability of ionizing lower-concentration compounds during direct infusion. When gas chromatography precedes APLI-FT-ICR MS, an increase (more than 2-fold) in the ionization efficiency and an increase in the signal-to-noise ratio of lower-concentration fractions are observed, giving better molecular coverage in the m/z 100–450 range. That is, the use of GC prior to APLI-FT-ICR MS resulted in higher molecular coverage, higher sensitivity, and the ability to separate and characterize molecular isomers, while maintaining the ultrahigh resolution and mass accuracy of the FT-ICR MS separation. PMID:27212790

Real time analysis of brain tissue by direct combination of ultrasonic surgical aspiration and sonic spray mass spectrometry.

PubMed

Schäfer, Karl-Christian; Balog, Júlia; Szaniszló, Tamás; Szalay, Dániel; Mezey, Géza; Dénes, Júlia; Bognár, László; Oertel, Matthias; Takáts, Zoltán

2011-10-15

Direct combination of cavitron ultrasonic surgical aspirator (CUSA) and sonic spray ionization mass spectrometry is presented. A commercially available ultrasonic surgical device was coupled to a Venturi easy ambient sonic-spray ionization (V-EASI) source by directly introducing liquified tissue debris into the Venturi air jet pump. The Venturi air jet pump was found to efficiently nebulize the suspended tissue material for gas phase ion production. The ionization mechanism involving solely pneumatic spraying was associated with that of sonic spray ionization. Positive and negative ionization spectra were obtained from brain and liver samples reflecting the primary application areas of the surgical device. Mass spectra were found to feature predominantly complex lipid-type constituents of tissues in both ion polarity modes. Multiply charged peptide anions were also detected. The influence of instrumental settings was characterized in detail. Venturi pump geometry and flow parameters were found to be critically important in ionization efficiency. Standard solutions of phospholipids and peptides were analyzed in order to test the dynamic range, sensitivity, and suppression effects. The spectra of the intact tissue specimens were found to be highly specific to the histological tissue type. The principal component analysis (PCA) and linear discriminant analysis (LDA) based data analysis method was developed for real-time tissue identification in a surgical environment. The method has been successfully tested on post-mortem and ex vivo human samples including astrocytomas, meningeomas, metastatic brain tumors, and healthy brain tissue. © 2011 American Chemical Society

A Versatile Integrated Ambient Ionization Source Platform.

PubMed

Ai, Wanpeng; Nie, Honggang; Song, Shiyao; Liu, Xiaoyun; Bai, Yu; Liu, Huwei

2018-04-30

The pursuit of high-throughput sample analysis from complex matrix demands development of multiple ionization techniques with complementary specialties. A versatile integrated ambient ionization source (iAmIS) platform is proposed in this work, based on the idea of integrating multiple functions, enhancing the efficiency of current ionization techniques, extending the applications, and decreasing the cost of the instrument. The design of the iAmIS platform combines flowing atmospheric pressure afterglow (FAPA) source/direct analysis in real time (DART), dielectric barrier discharge ionization (DBDI)/low-temperature plasma (LTP), desorption electrospray ionization (DESI), and laser desorption (LD) technique. All individual and combined ionization modes can be easily attained by modulating parameters. In particular, the FAPA/DART&DESI mode can realize the detection of polar and nonpolar compounds at the same time with two different ionization mechanisms: proton transfer and charge transfer. The introduction of LD contributes to the mass spectrometry imaging and the surface-assisted laser desorption (SALDI) under ambient condition. Compared with other individual or multi-mode ion source, the iAmIS platform provides the flexibility of choosing different ionization modes, broadens the scope of the analyte detection, and facilitates the analysis of complex samples. Graphical abstract ᅟ.

A Versatile Integrated Ambient Ionization Source Platform

NASA Astrophysics Data System (ADS)

Ai, Wanpeng; Nie, Honggang; Song, Shiyao; Liu, Xiaoyun; Bai, Yu; Liu, Huwei

2018-04-01

The pursuit of high-throughput sample analysis from complex matrix demands development of multiple ionization techniques with complementary specialties. A versatile integrated ambient ionization source (iAmIS) platform is proposed in this work, based on the idea of integrating multiple functions, enhancing the efficiency of current ionization techniques, extending the applications, and decreasing the cost of the instrument. The design of the iAmIS platform combines flowing atmospheric pressure afterglow (FAPA) source/direct analysis in real time (DART), dielectric barrier discharge ionization (DBDI)/low-temperature plasma (LTP), desorption electrospray ionization (DESI), and laser desorption (LD) technique. All individual and combined ionization modes can be easily attained by modulating parameters. In particular, the FAPA/DART&DESI mode can realize the detection of polar and nonpolar compounds at the same time with two different ionization mechanisms: proton transfer and charge transfer. The introduction of LD contributes to the mass spectrometry imaging and the surface-assisted laser desorption (SALDI) under ambient condition. Compared with other individual or multi-mode ion source, the iAmIS platform provides the flexibility of choosing different ionization modes, broadens the scope of the analyte detection, and facilitates the analysis of complex samples. [Figure not available: see fulltext.

Optimization of carrier multiplication for more effcient solar cells: the case of Sn quantum dots.

PubMed

Allan, Guy; Delerue, Christophe

2011-09-27

We present calculations of impact ionization rates, carrier multiplication yields, and solar-power conversion efficiencies in solar cells based on quantum dots (QDs) of a semimetal, α-Sn. Using these results and previous ones on PbSe and PbS QDs, we discuss a strategy to select QDs with the highest carrier multiplication rate for more efficient solar cells. We suggest using QDs of materials with a close to zero band gap and a high multiplicity of the bands in order to favor the relaxation of photoexcited carriers by impact ionization. Even in that case, the improvement of the maximum solar-power conversion efficiency appears to be a challenging task. © 2011 American Chemical Society

Equation of motion coupled cluster methods for electron attachment and ionization potential in polyacenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhaskaran-Nair, Kiran; Kowalski, Karol; Jarrell, Mark

2015-11-05

Polyacenes have attracted considerable attention due to their use in organic based optoelectronic materials. Polyacenes are polycyclic aromatic hydrocarbons composed of fused benzene rings. Key to understanding and design of new functional materials is an understanding of their excited state properties starting with their electron affinity (EA) and ionization potential (IP). We have developed a highly accurate and com- putationally e*fficient EA/IP equation of motion coupled cluster singles and doubles (EA/IP-EOMCCSD) method that is capable of treating large systems and large basis set. In this study we employ the EA/IP-EOMCCSD method to calculate the electron affinity and ionization potential ofmore » naphthalene, anthracene, tetracene, pentacene, hex- acene and heptacene. We have compared our results with other previous theoretical studies and experimental data. Our EA/IP results are in very good agreement with experiment and when compared with the other theoretical investigations our results represent the most accurate calculations as compared to experiment.« less

Desorption atmospheric pressure photoionization and direct analysis in real time coupled with travelling wave ion mobility mass spectrometry.

PubMed

Räsänen, Riikka-Marjaana; Dwivedi, Prabha; Fernández, Facundo M; Kauppila, Tiina J

2014-11-15

Ambient mass spectrometry (MS) is a tool for screening analytes directly from sample surfaces. However, background impurities may complicate the spectra and therefore fast separation techniques are needed. Here, we demonstrate the use of travelling wave ion mobility spectrometry in a comparative study of two ambient MS techniques. Desorption atmospheric pressure photoionization (DAPPI) and direct analysis in real time (DART) were coupled with travelling wave ion mobility mass spectrometry (TWIM-MS) for highly selective surface analysis. The ionization efficiencies of DAPPI and DART were compared. Test compounds were: bisphenol A, benzo[a]pyrene, ranitidine, cortisol and α-tocopherol. DAPPI-MS and DART-TWIM-MS were also applied to the analysis of chloroquine from dried blood spots, and α-tocopherol from almond surface, and DAPPI-TWIM-MS was applied to analysis of pharmaceuticals and multivitamin tablets. DAPPI was approximately 100 times more sensitive than DART for bisphenol A and 10-20 times more sensitive for the other compounds. The limits of detection were between 30-290 and 330-8200 fmol for DAPPI and DART, respectively. Also, from the authentic samples, DAPPI ionized chloroquine and α-tocopherol more efficiently than DART. The mobility separation enabled the detection of species with low signal intensities, e.g. thiamine and cholecalciferol, in the DAPPI-TWIM-MS analysis of multivitamin tablets. DAPPI ionized the studied compounds of interest more efficiently than DART. For both DAPPI and DART, the mobility separation prior to MS analysis reduced the amount of chemical noise in the mass spectrum and significantly increased the signal-to-noise ratio for the analytes. Copyright © 2014 John Wiley & Sons, Ltd.

Characteristics of light reflected from a dense ionization wave with a tunable velocity.

PubMed

Zhidkov, A; Esirkepov, T; Fujii, T; Nemoto, K; Koga, J; Bulanov, S V

2009-11-20

An optically dense ionization wave (IW) produced by two femtosecond (approximately 10/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses.

Ionization of biomolecular targets by ion impact: input data for radiobiological applications

NASA Astrophysics Data System (ADS)

de Vera, Pablo; Abril, Isabel; Garcia-Molina, Rafael; Solov'yov, Andrey V.

2013-06-01

In this work we review and further develop a semiempirical model recently proposed for the ion impact ionization of complex biological media. The model is based on the dielectric formalism, and makes use of a semiempirical parametrization of the optical energy-loss function of bioorganic compounds, allowing the calculation of single and total ionization cross sections and related quantities for condensed biological targets, such as liquid water, DNA and its components, proteins, lipids, carbohydrates or cell constituents. The model shows a very good agreement with experimental data for water, adenine and uracil, and allows the comparison of the ionization efficiency of different biological targets, and also the average kinetic energy of the ejected secondary electrons.

Ionization imaging—A new method to search for 0- ν ββ decay

NASA Astrophysics Data System (ADS)

Chinowski, W.; Goldschmidt, A.; Nygren, D.; Bernstein, A.; Heffner, M.; Millaud, J.

2007-10-01

We present a new method to search for 0- ν ββ decay in 136Xe, the Ionization Imaging Chamber. This concept is based on 3-D track reconstruction by detection of ionization, without avalanche gain, in a novel time projection chamber (TPC) geometry. The rejection efficiency of external charged particle backgrounds is optimized by the realization of a maximal, fully active, closed, and ex post facto variable fiducial surface. Event localization within the fiducial volume and detailed event reconstruction mitigate external neutral particle backgrounds; larger detectors offer higher rejection efficiencies. Energy resolution at the Q-value of 2.5 MeV is expected to be better than 1% FWHM, reducing the potential impact of allowed 2- ν ββ decays. Scaling from ˜25 kg prototype to 1000+ kg target mass is graceful. A new possible methodology for the identification of the daughter barium nucleus is also described.

A DUAL PLATFORM FOR SELECTIVE ANALYTE ENRICHMENT AND IONIZATION IN MASS SPECTROMETRY USING APTAMER-CONJUGATED GRAPHENE OXIDE

PubMed Central

Gulbakan, Basri; Yasun, Emir; Shukoor, M. Ibrahim; Zhu, Zhi; You, Mingxu; Tan, Xiaohong; Sanchez, Hernan; Powell, David H.; Dai, Hongjie; Tan, Weihong

2010-01-01

This study demonstrates the use of aptamer-conjugated graphene oxide as an affinity extraction and detection platform for analytes from complex biological media. We have shown that cocaine and adenosine can be selectively enriched from plasma samples and that direct mass spectrometric readout can be obtained without a matrix and with greatly improved signal-to-noise ratios. The aptamer conjugated graphene oxide has clear advantages in target enrichment and in generating highly efficient ionization of target molecules for mass spectrometry. These results demonstrate the utility of the approach for analysis of small molecules in real biological samples. PMID:21090719

Escape of ionizing radiation from high redshift dwarf galaxies: role of AGN feedback

NASA Astrophysics Data System (ADS)

Trebitsch, Maxime; Volonteri, Marta; Dubois, Yohan; Madau, Piero

2018-05-01

While low mass, star forming galaxies are often considered as the primary driver of reionization, their actual contribution to the cosmic ultraviolet background is still uncertain, mostly because the escape fraction of ionizing photons is only poorly constrained. Theoretical studies have shown that efficient supernova feedback is a necessary condition to create paths through which ionizing radiation can escape into the intergalactic medium. We investigate the possibility that accreting supermassive black holes in early dwarf galaxies may provide additional feedback and enhance the leakage of ionizing radiation. We use a series of high resolution cosmological radiation hydrodynamics simulations where we isolate the different sources of feedback. We find that supernova feedback prevents the growth of the black hole, thus quenching its associated feedback. Even in cases where the black hole can grow, the structure of the interstellar medium is strongly dominated by supernova feedback. We conclude that, in the dwarf galaxy regime, supermassive black holes do not appear to play a significant role in enhancing the escape fraction and in contributing to the early UV background.

A simple resonance enhanced laser ionization scheme for CO via the A1Π state

NASA Astrophysics Data System (ADS)

Sun, Z. F.; von Zastrow, A. D.; Parker, D. H.

2017-07-01

We investigate the laser ionization process taking place when the CO molecule is exposed to vacuum ultraviolet (VUV) radiation resonant with the CO A1Π (v = 0) ← X1Σ+ (v = 0) transition around 154 nm, along with the ultraviolet (UV) and visible (Red) radiation used to generate VUV by four-wave difference-frequency mixing. By measuring the CO+ ion recoil and a room temperature gas spectrum, it is possible to assign the ionization process as 1 + 1' + 1'' REMPI where the one-photon steps refer to the VUV, UV, and Red radiation, respectively. Resonance enhanced ionization of rotational states around J = 12 arise due to the overlap of the fixed wavelength UV (˜250 nm) with the R band-head of a transition assigned to CO E1Π (v = 6) ← A1Π (v = 0) with a term value of 104 787.5 cm-1. The REMPI process is efficient and polarization sensitive and should be useful in a wide range of studies involving nascent CO.

Ionization dynamics of the water trimer: A direct ab initio MD study

NASA Astrophysics Data System (ADS)

Tachikawa, Hiroto; Takada, Tomoya

2013-03-01

Ionization dynamics of the cyclic water trimer (H2O)3 have been investigated by means of direct ab initio molecular dynamics (AIMD) method. Two reaction channels, complex formation and OH dissociation, were found following the ionization of (H2O)3. In both channels, first, a proton was rapidly transferred from H2O+ to H2O (time scale is ˜15 fs after the ionization). In complex channel, an ion-radical contact pair (H3O+-OH) solvated by the third water molecule was formed as a long-lived H3O+(OH)H2O complex. In OH dissociation channel, the second proton transfer further takes place from H3O+(OH) to H2O (time scale is 50-100 fs) and the OH radical is separated from the H3O+. At the same time, the OH dissociation takes place when the excess energy is efficiently transferred into the kinetic energy of OH radical. The OH dissociation channel is significantly minor, and almost all product channels were the complex formation. The reaction mechanism was discussed on the basis of theoretical results.

Chemi-ionization reactions of La, Pr, Tb, and Ho with atomic O and La with N{sub 2}O from 200 to 450 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ard, Shaun G.; Shuman, Nicholas S.; Martinez, Oscar

2016-08-28

The chemi-ionization rate coefficients of La, Pr, Tb, and Ho with O have been measured from 200 to 450 K using a thermalized flow tube apparatus. Both La and Tb were found to react near the calculated hard sphere collision limit, while the Pr and Ho reactions proceeded at roughly 40% of that limit at all temperatures. The efficiencies of these reactions are considered and the near thermoneutral character of the reaction with Ho can explain this case, whereas an explanation for the inefficiency of the Pr reaction remains elusive. The chemi-ionization reaction of La with N{sub 2}O was alsomore » studied and found to proceed roughly 2 orders of magnitude slower than the competing neutral oxidation pathway. The latter result disagrees with previous literature reports.« less

Derivatization reagents in liquid chromatography/electrospray ionization tandem mass spectrometry.

PubMed

Santa, Tomofumi

2011-01-01

Liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is one of the most prominent analytical techniques owing to its inherent selectivity and sensitivity. In LC/ESI-MS/MS, chemical derivatization is often used to enhance the detection sensitivity. Derivatization improves the chromatographic separation, and enhances the mass spectrometric ionization efficiency and MS/MS detectability. In this review, an overview of the derivatization reagents which have been applied to LC/ESI-MS/MS is presented, focusing on the applications to low molecular weight compounds. 2010 John Wiley & Sons, Ltd.

Gas chromatography/chemical ionization triple quadrupole mass spectrometry analysis of anabolic steroids: ionization and collision-induced dissociation behavior.

PubMed

Polet, Michael; Van Gansbeke, Wim; Van Eenoo, Peter; Deventer, Koen

2016-02-28

The detection of new anabolic steroid metabolites and new designer steroids is a challenging task in doping analysis. Switching from electron ionization gas chromatography triple quadrupole mass spectrometry (GC/EI-MS/MS) to chemical ionization (CI) has proven to be an efficient way to increase the sensitivity of GC/MS/MS analyses and facilitate the detection of anabolic steroids. CI also extends the possibilities of GC/MS/MS analyses as the molecular ion is retained in its protonated form due to the softer ionization. In EI it can be difficult to find previously unknown but expected metabolites due to the low abundance or absence of the molecular ion and the extensive (and to a large extent unpredictable) fragmentation. The main aim of this work was to study the CI and collision-induced dissociation (CID) behavior of a large number of anabolic androgenic steroids (AAS) as their trimethylsilyl derivatives in order to determine correlations between structures and CID fragmentation. Clarification of these correlations is needed for the elucidation of structures of unknown steroids and new metabolites. The ionization and CID behavior of 65 AAS have been studied using GC/CI-MS/MS with ammonia as the reagent gas. Glucuronidated AAS reference standards were first hydrolyzed to obtain their free forms. Afterwards, all the standards were derivatized to their trimethylsilyl forms. Full scan and product ion scan analyses were used to examine the ionization and CID behavior. Full scan and product ion scan analyses revealed clear correlations between AAS structure and the obtained mass spectra. These correlations were confirmed by analysis of multiple hydroxylated, methylated, chlorinated and deuterated analogs. AAS have been divided into three groups according to their ionization behavior and into seven groups according to their CID behavior. Correlations between fragmentation and structure were revealed and fragmentation pathways were postulated. Copyright © 2016 John Wiley & Sons, Ltd.

An evaluation of krypton propellant in Hall thrusters

NASA Astrophysics Data System (ADS)

Linnell, Jesse Allen

Due to its high specific impulse and low price, krypton has long sparked interest as an alternate Hall thruster propellant. Unfortunately at the moment, krypton's relatively poor performance precludes it as a legitimate option. This thesis presents a detailed investigation into krypton operation in Hall thrusters. These findings suggest that the performance gap can be decreased to 4% and krypton can finally become a realistic propellant option. Although krypton has demonstrated superior specific impulse, the xenon-krypton absolute efficiency gap ranges between 2 and 15%. A phenomenological performance model indicates that the main contributors to the efficiency gap are propellant utilization and beam divergence. Propellant utilization and beam divergence have relative efficiency deficits of 5 and 8%, respectively. A detailed characterization of internal phenomena is conducted to better understand the xenon-krypton efficiency gap. Krypton's large beam divergence is found to be related to a defocusing equipotential structure and a weaker magnetic field topology. Ionization processes are shown to be linked to the Hall current, the magnetic mirror topology, and the perpendicular gradient of the magnetic field. Several thruster design and operational suggestions are made to optimize krypton efficiency. Krypton performance is optimized for discharge voltages above 500 V and flow rates corresponding to an a greater than 0.015 mg/(mm-s), where alpha is a function of flow rate and discharge channel dimensions (alpha = m˙alphab/Ach). Performance can be further improved by increasing channel length or decreasing channel width for a given flow rate. Also, several magnetic field design suggestions are made to enhance ionization and beam focusing. Several findings are presented that improve the understanding of general Hall thruster physics. Excellent agreement is shown between equipotential lines and magnetic field lines. The trim coil is shown to enhance beam focusing, ionization processes, and electron dynamics. Electron mobility and the Hall parameter are studied and compared to different mobility models. Azimuthal electron current is studied using a fluid and particle drift approach. Analyses of several magnetic field features are conducted and simple tools are suggested for the development of future Hall thrusters. These findings have strong implications for future Hall thruster design, lifetimes, and modeling.

Using Quasi-3D OSIRIS simulations of LWFA to study generating high brightness electron beams using ionization and density downramp injection

NASA Astrophysics Data System (ADS)

Dalichaouch, Thamine; Davidson, Asher; Xu, Xinlu; Yu, Peicheng; Tsung, Frank; Mori, Warren; Li, Fei; Zhang, Chaojie; Lu, Wei; Vieira, Jorge; Fonseca, Ricardo

2016-10-01

In the past few decades, there has been much progress in theory, simulation, and experiment towards using Laser wakefield acceleration (LWFA) as the basis for designing and building compact x-ray free-electron-lasers (XFEL) as well as a next generation linear collider. Recently, ionization injection and density downramp injection have been proposed and demonstrated as a controllable injection scheme for creating higher quality and ultra-bright relativistic electron beams using LWFA. However, full-3D simulations of plasma-based accelerators are computationally intensive, sometimes taking 100 millions of core-hours on today's computers. A more efficient quasi-3D algorithm was developed and implemented into OSIRIS using a particle-in-cell description with a charge conserving current deposition scheme in r - z and a gridless Fourier expansion in ϕ. Due to the azimuthal symmetry in LWFA, quasi-3D simulations are computationally more efficient than 3D cartesian simulations since only the first few harmonics in are needed ϕ to capture the 3D physics of LWFA. Using the quasi-3D approach, we present preliminary results of ionization and down ramp triggered injection and compare the results against 3D LWFA simulations. This work was supported by DOE and NSF.

Instantaneous and efficient surface wave excitation of a low pressure gas or gases

DOEpatents

Levy, Donald J.; Berman, Samuel M.

1988-01-01

A system for instantaneously ionizing and continuously delivering energy in the form of surface waves to a low pressure gas or mixture of low pressure gases, comprising a source of rf energy, a discharge container, (such as a fluorescent lamp discharge tube), an rf shield, and a coupling device responsive to rf energy from the source to couple rf energy directly and efficiently to the gas or mixture of gases to ionize at least a portion of the gas or gases and to provide energy to the gas or gases in the form of surface waves. The majority of the rf power is transferred to the gas or gases near the inner surface of the discharge container to efficiently transfer rf energy as excitation energy for at least one of the gases. The most important use of the invention is to provide more efficient fluorescent and/or ultraviolet lamps.

In situ analysis of plant tissue underivatized carbohydrates and on-probe enzymatic degraded starch by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry by using carbon nanotubes as matrix.

PubMed

Gholipour, Yousef; Nonami, Hiroshi; Erra-Balsells, Rosa

2008-12-15

Underivatized carbohydrates of tulip bulb and leaf tissues were characterized in situ by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) by using carbon nanotubes (CNTs) as matrix. Two sample preparation methods--(i) depositing CNTs on the fresh tissue slices placed on the probe and (ii) locating semitransparent tissues on a dried layer of CNTs on the probe--were examined. Furthermore, practicability of in situ starch analysis by MALDI-TOF MS was examined by detection of glucose originated from on-probe amyloglucosidase-catalyzed degradation of starch on the tissue surface. Besides, CNTs could efficiently desorb/ionize natural mono-, di-, and oligosaccharides extracted from tulip bulb tissues as well as glucose resulting from starch enzymatic degradation in vitro. These results were compared with those obtained by in situ MALDI-TOF MS analysis of similar tissues. Positive ion mode showed superior signal reproducibility. CNTs deposited under semitransparent tissue could also desorb/ionize neutral carbohydrates, leading to nearly complete elimination of matrix cluster signals but with an increase in tissue-originated signals. Furthermore, several experiments were carried out to compare the efficiency of 2,5-dihydroxybenzoic acid, nor-harmane, alpha-cyano-4-hydroxycinnamic acid, and CNTs as matrices for MALDI of neutral carbohydrates from the intact plant tissue surface and for enzymatic tissue starch degradation; these results are discussed in brief. Among matrices studied, the lowest laser power was needed to acquire carbohydrate signals with high signal-to-noise ratio and resolution when CNTs were used.

Distinctive plume formation in atmospheric Ar and He plasmas in microwave frequency band and suitability for biomedical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, H. Wk.; Kang, S. K.; Won, I. H.

Distinctive discharge formation in atmospheric Ar and He plasmas was observed in the microwave frequency band using coaxial transmission line resonators. Ar plasmas formed a plasma plume whereas He formed only confined plasmas. As the frequency increased from 0.9 GHz to 2.45 GHz, the Ar plasma exhibited contraction and filamentation, and the He plasmas were constricted. Various powers and gas flow rates were applied to identify the effect of the electric field and gas flow rate on plasma plume formation. The He plasmas were more strongly affected by the electric field than the Ar plasmas. The breakdown and sustain powersmore » yielded opposite results from those for low-frequency plasmas (∼kHz). The phenomena could be explained by a change in the dominant ionization process with increasing frequency. Penning ionization and the contribution of secondary electrons in sheath region reduced as the frequency increased, leading to less efficient ionization of He because its ionization and excitation energies are higher than those of Ar. The emission spectra showed an increase in the NO and N{sub 2} second positive band in both the Ar and He plasmas with increasing frequency whereas the hydroxyl radical and atomic O peaks did not increase with increasing frequency but were highest at particular frequencies. Further, the frequency effect of properties such as the plasma impedance, electron density, and device efficiency were presented. The study is expected to be helpful for determining the optimal conditions of plasma systems for biomedical applications.« less

Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neustetter, M.; Jabbour Al Maalouf, E.; Denifl, S., E-mail: Stephan.Denifl@uibk.ac.at, E-mail: plimaovieira@fct.unl.pt

2016-08-07

Electron ionization of neat tungsten hexacarbonyl (W(CO){sub 6}) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO){sub 6} clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO){sub n}{sup +} (0 ≤ n ≤ 6) and W{sub 2}(CO){sub n}{sup +} (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO){sub n}{sup +} (0 ≤more » n ≤ 3) and W{sub 2}C(CO){sub n}{sup +} (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.« less

New developments of the in-source spectroscopy method at RILIS/ISOLDE

NASA Astrophysics Data System (ADS)

Marsh, B. A.; Andel, B.; Andreyev, A. N.; Antalic, S.; Atanasov, D.; Barzakh, A. E.; Bastin, B.; Borgmann, Ch.; Capponi, L.; Cocolios, T. E.; Day Goodacre, T.; Dehairs, M.; Derkx, X.; De Witte, H.; Fedorov, D. V.; Fedosseev, V. N.; Focker, G. J.; Fink, D. A.; Flanagan, K. T.; Franchoo, S.; Ghys, L.; Huyse, M.; Imai, N.; Kalaninova, Z.; Köster, U.; Kreim, S.; Kesteloot, N.; Kudryavtsev, Yu.; Lane, J.; Lecesne, N.; Liberati, V.; Lunney, D.; Lynch, K. M.; Manea, V.; Molkanov, P. L.; Nicol, T.; Pauwels, D.; Popescu, L.; Radulov, D.; Rapisarda, E.; Rosenbusch, M.; Rossel, R. E.; Rothe, S.; Schweikhard, L.; Seliverstov, M. D.; Sels, S.; Sjödin, A. M.; Truesdale, V.; Van Beveren, C.; Van Duppen, P.; Wendt, K.; Wienholtz, F.; Wolf, R. N.; Zemlyanoy, S. G.

2013-12-01

At the CERN ISOLDE facility, long isotope chains of many elements are produced by proton-induced reactions in target materials such as uranium carbide. The Resonance Ionization Laser Ion Source (RILIS) is an efficient and selective means of ionizing the reaction products to produce an ion beam of a chosen isotope. Coupling the RILIS with modern ion detection techniques enables highly sensitive studies of nuclear properties (spins, electromagnetic moments and charge radii) along an isotope chain, provided that the isotope shifts and hyperfine structure splitting of the atomic transitions can be resolved. At ISOLDE the campaign to measure the systematics of isotopes in the lead region (Pb, Bi, Tl and Po) has been extended to include the gold and astatine isotope chains. Several developments were specifically required for the feasibility of the most recent measurements: new ionization schemes (Po, At); a remote controlled narrow line-width mode of operation for the RILIS Ti:sapphire laser (At, Au, Po); isobar free ionization using the Laser Ion Source Trap, LIST (Po); isobar selective particle identification using the multi-reflection time-of-flight mass separator (MR-ToF MS) of ISOLTRAP (Au, At). These are summarized as part of an overview of the current status of the in-source resonance ionization spectroscopy setup at ISOLDE.

A highly sensitive electron spectrometer for crossed-beam collisional ionization: A retarding-type magnetic bottle analyzer and its application to collision-energy resolved Penning ionization electron spectroscopy

NASA Astrophysics Data System (ADS)

Yamakita, Yoshihiro; Tanaka, Hideyasu; Maruyama, Ryo; Yamakado, Hideo; Misaizu, Fuminori; Ohno, Koichi

2000-08-01

A highly sensitive electron energy analyzer which utilizes a "magnetic bottle" combined with a retarding electrostatic field has been developed for Penning ionization electron spectroscopy. A beam of metastable rare-gas atoms is crossed with a continuous supersonic sample beam in the source region of the analyzer. The emitted electrons are collected by an inhomogeneous magnetic field (the magnetic bottle effect) with a high efficiency of nearly 4π solid angle, which is more than 103 times higher than that of a conventional hemispherical analyzer. The kinetic energy of electrons is analyzed by scanning the retarding field in a flight tube of the analyzer in the presence of a weak magnetic field. The velocity of the metastable atoms can also be resolved by a time-of-flight method in the present instrument. Examples of Penning ionization electron energy spectra as a function of collision energy are presented for Ar and N2 with metastable He*(2 3S) atoms. This instrument has opened the possibility for extensive studies of Penning ionization electron spectroscopy for low-density species, such as clusters, ions, electronically excited species, unstable or transient species, and large molecules with low volatility.

A Corona Discharge Initiated Electrochemical Electrospray Ionization Technique

PubMed Central

Lloyd, John R.; Hess, Sonja

2009-01-01

We report here the development of a corona discharge (CD) initiated electrochemical (EC) electrospray ionization (ESI) technique using a standard electrospray ion source. This is a new ionization technique distinct from ESI, electrochemistry inherent to ESI, APCI, and techniques using hydroxyl radicals produced under atmospheric pressure conditions. By maximizing the observable CD at the tip of a stainless steel ESI capillary, efficient electrochemical oxidation of electrochemically active compounds is observed. For electrochemical oxidation to be observed, the ionization potential of the analyte must be lower than Fe. Ferrocene labeled compounds were chosen as the electrochemically active moiety. The electrochemical cell in the ESI source was robust and generated ions with selectivity according to the ionization potential of the analytes and up to zeptomolar sensitivity. Our results indicate that CD initiated electrochemical ionization has the potential to become a powerful technique to increase the dynamic range, sensitivity and selectivity of ESI experiments. Synopsis Using a standard ESI source a corona discharge initiated electrochemical ionization technique was established resulting from the electrochemistry occurring at the CD electrode surface. PMID:19747843

Modeling the gain of inner-shell X-ray laser transitions in neon, argon, and copper driven by X-ray free electron laser radiation using photo-ionization and photo-excitation processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nilsen, Joseph

2015-12-16

Using an X-ray free electron laser (XFEL) at 960 eV to photo-ionize the 1s electron in neutral neon followed by lasing on the 2p-1s transition in singly-ionized neon, an inner-shell X-ray laser was demonstrated at 849 eV in singly-ionized neon gas several years ago. It took decades to demonstrate this scheme, because it required a very strong X-ray source that could photo-ionize the 1s (K shell) electron in neon on a timescale comparable to the intrinsic Auger lifetime in neon of 2 fs. In this paper, we model the neon inner shell X-ray laser under similar conditions to those usedmore » in the XFEL experiments at the SLAC Linac Coherent Light Source (LCLS), and show how we can improve the efficiency of the neon laser and reduce the drive requirements by tuning the XFEL to the 1s-3p transition in neutral neon in order to create gain on the 2p-1s line in neutral neon. We also show how the XFEL could be used to photo-ionize L-shell electrons to drive gain on n = 3–2 transitions in singly-ionized Ar and Cu plasmas. Furthermore, these bright, coherent, and monochromatic X-ray lasers may prove very useful for doing high-resolution spectroscopy and for studying non-linear process in the X-ray regime.« less

Smoothed particle hydrodynamic simulations of expanding HII regions

NASA Astrophysics Data System (ADS)

Bisbas, Thomas G.

2009-09-01

This thesis deals with numerical simulations of expanding ionized regions, known as HII regions. We implement a new three dimensional algorithm in Smoothed Particle Hydrodynamics for including the dynamical effects of the interaction between ionizing radiation and the interstellar medium. This interaction plays a crucial role in star formation at all epochs. We study the influence of ionizing radiation in spherically symmetric clouds. In particular, we study the spherically symmetric expansion of an HII region inside a uniform-density, non-self-gravitating cloud. We examine the ability of our algorithm to reproduce the known theoretical solution and we find that the agreement is very good. We also study the spherically symmetric expansion inside a uniform-density, self-gravitating cloud. We propose a new differential equation of motion for the expanding shell that includes the effects of gravity. Comparing its numerical solution with the simulations, we find that the equation predicts the position of the shell accurately. We also study the expansion of an off-centre HII region inside a uniform-density, non- self-gravitating cloud. This results in an evolution known as the rocket effect, where the ionizing radiation pushes and accelerates the cloud away from the exciting star leading to its dispersal. During this evolution, cometary knots appear as a result of Rayleigh-Taylor and Vishniac instabilities. The knots are composed of a dense head with a conic tail behind them, a structure that points towards the ionizing source. Our simulations show that these knots are very reminiscent of the observed structures in planetary nebula, such as in the Helix nebula. The last part of this thesis is dedicated to the study of cores ionized by an exciting source which is placed outside and far away from them. The evolution of these cores is known as radiation driven compression (or implosion). We perform simulations and compare our findings with results of other workers and we find that they agree very well. Using stable Bonnor-Ebert spheres, we extend our study to modelling triggered star formation within these cores as they are overrun and compressed by the incident ionizing flux. We construct a parameter space diagram and we map regions where star formation is expected to be observed. All the above results indicate that the algorithm presented in this thesis works well for treating the propagation of ionizing radiation. This new algorithm provides the means to explore and evaluate the role of ionizing radiation in regulating the efficiency and statistics of star formation.

Evaluation of the influence of ionization states and spacers in the thermotropic phase behaviour of amino acid-based cationic lipids and the transfection efficiency of their assemblies.

PubMed

Sarker, Satya Ranjan; Arai, Satoshi; Murate, Motohide; Takahashi, Hiroshi; Takata, Masaki; Kobayashi, Toshihide; Takeoka, Shinji

2012-01-17

The influence of both the ionization states and the hydrocarbon chain spacer of a series of amino acid-based cationic lipids was evaluated in terms of gene delivery efficiency and cytotoxicity to the COS-7 cell line and compared with that of Lipofectamine 2000. We synthesized a series of amino acid-based cationic lipids with different ionization states (i.e., -NH(2), -NH(3)(+)Cl(-) or -NH(3)(+)TFA(-)) in the lysine head group and different hydrocarbon chain spacers (i.e., 0, 3, 5 or 7 carbon atoms) between the hydrophilic head group and hydrophobic moieties. In the 3-carbon series, the cationic assemblies formed a micellar structure in the presence of -NH(3)(+)Cl(-) and a vesicular structure both in the presence of -NH(2) and -NH(3)(+)TFA(-). Differential scanning calorimetry (DSC) data revealed a significantly lower (8.1°C) gel-to-liquid crystalline phase transition temperature for cationic assemblies bearing -NH(3)(+)TFA(-) when compared to their -NH(2) counterparts. Furthermore, the zeta potential of cationic assemblies having -NH(3)(+)TFA(-) in the hydrophilic head group was maximum followed by -NH(3)(+)Cl(-) and -NH(2) irrespective of their hydrocarbon chain spacer length. The gene delivery efficiency in relation to the ionization states of the hydrophilic head group was as follows: -NH(3)(+)TFA(-)>-NH(3)(+)Cl(-)>-NH(2). Copyright © 2011 Elsevier B.V. All rights reserved.

Biomedical applications of laser photoionization

NASA Astrophysics Data System (ADS)

Xiong, Xiaoxiong; Moore, Larry J.; Fassett, John R.; O'Haver, Thomas C.

1991-07-01

Trace elements are important for many essential metabolic functions. Zinc is a structural/functional component in more than 200 enzymes active in the biochemistry of cell division and tissue growth, neurology and endocrine control. Calcium is involved in intracellular control mechanisms and in skeletal bone building and resorption processes related to osteoporosis. Sensitive and selective laser photoionization is being developed to understand mechanisms in smaller samples and biological units approaching the cellular domain. Zinc has an ionization potential of 9.4 eV, or 75766.8 cm-1. Several processes are being explored, including two-photon resonant, three- photon ionization utilizing sequential UV transitions, e.g., 4s2 1S0 yields 4s4p 3P1 and 4s4p 3P1 yields 4s5d 3D1. Preliminary zinc stable isotope ratio data obtained by thermal atomization and laser photoionization agree with accepted values within 2 to 5%, except for anomalous 67Zn. Photoionization of calcium is being studied for isotope enrichment and ratio measurement using narrow and medium bandwidth lasers. Several ionization pathways, e.g., 4s2 1S0 - 2hv1 yields 4s10s - hv2 yields Ca+ (4s2S), are being investigated for isotopically selective ionization. Auto-ionization pathways are explored for greater efficiency in isotopic analysis. All studies have utilized a Nd:YAG- pumped laser system with one or two frequency-doubled tunable dye lasers coupled either to a magnetic sector or time-of-flight mass spectrometer.

Asymmetric soft-error resistant memory

NASA Technical Reports Server (NTRS)

Buehler, Martin G. (Inventor); Perlman, Marvin (Inventor)

1991-01-01

A memory system is provided, of the type that includes an error-correcting circuit that detects and corrects, that more efficiently utilizes the capacity of a memory formed of groups of binary cells whose states can be inadvertently switched by ionizing radiation. Each memory cell has an asymmetric geometry, so that ionizing radiation causes a significantly greater probability of errors in one state than in the opposite state (e.g., an erroneous switch from '1' to '0' is far more likely than a switch from '0' to'1'. An asymmetric error correcting coding circuit can be used with the asymmetric memory cells, which requires fewer bits than an efficient symmetric error correcting code.

Electron gyroharmonic effects in ionization and electron acceleration during high-frequency pumping in the ionosphere.

PubMed

Gustavsson, B; Leyser, T B; Kosch, M; Rietveld, M T; Steen, A; Brändström, B U E; Aso, T

2006-11-10

Optical emissions and incoherent scatter radar data obtained during high-frequency electromagnetic pumping of the ionospheric plasma from the ground give data on electron energization in an energy range from 2 to 100 eV. Optical emissions at 4278 A from N2+ that require electrons with energies above the 18 eV ionization energy give the first images ever of pump-induced ionization of the thermosphere. The intensity at 4278 A is asymmetric around the ionospheric electron gyroharmonic, being stronger above the gyroresonance. This contrasts with emissions at 6300 A from O(1D) and of electron temperature enhancements, which have minima at the gyroharmonic but have no apparent asymmetry. This direct evidence of pump-induced ionization contradicts previous indirect evidence, which indicated that ionization is most efficiently produced when the pump frequency was below the gyroharmonic.

The epoch of cosmic heating by early sources of X-rays

NASA Astrophysics Data System (ADS)

Eide, Marius B.; Graziani, Luca; Ciardi, Benedetta; Feng, Yu; Kakiichi, Koki; Di Matteo, Tiziana

2018-05-01

Observations of the 21 cm line from neutral hydrogen indicate that an epoch of heating (EoH) might have preceded the later epoch of reionization. Here we study the effects on the ionization state and the thermal history of the intergalactic medium (IGM) during the EoH induced by different assumptions on ionizing sources in the high-redshift Universe: (i) stars; (ii) X-ray binaries (XRBs); (iii) thermal bremsstrahlung of the hot interstellar medium (ISM); and (iv) accreting nuclear black holes (BHs). To this aim, we post-process outputs from the (100 h-1 comoving Mpc)3 hydrodynamical simulation MassiveBlack-II with the cosmological 3D radiative transfer code CRASH, which follows the propagation of ultraviolet and X-ray photons, computing the thermal and ionization state of hydrogen and helium through the EoH. We find that stars determine the fully ionized morphology of the IGM, while the spectrally hard XRBs pave way for efficient subsequent heating and ionization by the spectrally softer ISM. With the seeding prescription in MassiveBlack-II, BHs do not contribute significantly to either ionization or heating. With only stars, most of the IGM remains in a cold state (with a median T = 11 K at z = 10), however, the presence of more energetic sources raises the temperature of regions around the brightest and more clustered sources above that of the cosmic microwave background, opening the possibility to observing the 21 cm signal in emission.

A Combined Desorption Ionization by Charge Exchange (DICE) and Desorption Electrospray Ionization (DESI) Source for Mass Spectrometry

NASA Astrophysics Data System (ADS)

Chan, Chang-Ching; Bolgar, Mark S.; Miller, Scott A.; Attygalle, Athula B.

2011-01-01

A source that couples the desorption ionization by charge exchange (DICE) and desorption electrospray ionization (DESI) techniques together was demonstrated to broaden the range of compounds that can be analyzed in a single mass spectrometric experiment under ambient conditions. A tee union was used to mix the spray reagents into a partially immiscible blend before this mixture was passed through a conventional electrospray (ES) probe capillary. Using this technique, compounds that are ionized more efficiently by the DICE method and those that are ionized better with the DESI procedure could be analyzed simultaneously. For example, hydroquinone, which is not detected when subjected to DESI-MS in the positive-ion generation mode, or the sodium adduct of guaifenesin, which is not detected when examined by DICE-MS, could both be detected in one experiment when the two techniques were combined. The combined technique was able to generate the molecular ion, proton and metal adduct from the same compound. When coupled to a tandem mass spectrometer, the combined source enabled the generation of product ion spectra from the molecular ion and the [M + H]+ or [M + metal]+ ions of the same compound without the need to physically change the source from DICE to DESI. The ability to record CID spectra of both the molecular ion and adduct ions in a single mass spectrometric experiment adds a new dimension to the array of mass spectrometric methods available for structural studies.

Tailoring Ion Charge State Distribution in Tetramethyltin Clusters under Influence of Moderate Intensity Picosecond Laser Pulse: Role of Laser Wavelength and Rate of Energy Deposition

NASA Astrophysics Data System (ADS)

Sharma, Pramod; Das, Soumitra; Vatsa, Rajesh K.

2017-07-01

Systematic manipulation of ionic-outcome in laser-cluster interaction process has been realized for studies carried out on tetramethyltin (TMT) clusters under picosecond laser conditions, determined by choice of laser wavelength and intensity. As a function of laser intensity, TMT clusters exhibit gradual enhancement in overall ionization of its cluster constituents, up to a saturation level of ionization, which was distinct for different wavelengths (266, 355, and 532 nm). Simultaneously, systematic appearance of higher multiply charged atomic ions and shift in relative abundance of multiply charged atomic ions towards higher charge state was observed, using time-of-flight mass spectrometer. At saturation level, multiply charged atomic ions up to (C2+, Sn2+) at 266 nm, (C4+, Sn4+) at 355 nm, and (C4+, Sn6+) at 532 nm were detected. In addition, at 355 nm intra-cluster ion chemistry within the ionized cluster leads to generation of molecular hydrogen ion (H2 +) and triatomic molecular hydrogen ion (H3 +). Generation of multiply charged atomic ions is ascribed to efficient coupling of laser pulse with the cluster media, facilitated by inner-ionized electrons produced within the cluster, at the leading edge of laser pulse. Role of inner-ionized electrons is authenticated by measuring kinetic energy distribution of electrons liberated upon disintegration of excessively ionized cluster, under the influence of picosecond laser pulse.

Atmospheric Gaseous Plasma with Large Dimensions

NASA Astrophysics Data System (ADS)

Korenev, Sergey

2012-10-01

The forming of atmospheric plasma with large dimensions using electrical discharge typically uses the Dielectric Barrier Discharge (DBD). The study of atmospheric DBD was shown some problems related to homogeneous volume plasma. The volume of this plasma determines by cross section and gas gap between electrode and dielectric. The using of electron beam for volume ionization of air molecules by CW relativistic electron beams was shown the high efficiency of this process [1, 2]. The main advantage of this approach consists in the ionization of gas molecules by electrons in longitudinal direction determines by their kinetic energy. A novel method for forming of atmospheric homogeneous plasma with large volume dimensions using ionization of gas molecules by pulsed non-relativistic electron beams is presented in the paper. The results of computer modeling for delivered doses of electron beams in gases and ionization are discussed. The structure of experimental bench with plasma diagnostics is considered. The preliminary results of forming atmospheric plasma with ionization gas molecules by pulsed nanosecond non-relativistic electron beam are given. The analysis of potential applications for atmospheric volume plasma is presented. Reference: [1] S. Korenev. ``The ionization of air by scanning relativistic high power CW electron beam,'' 2002 IEEE International Conference on Plasma Science. May 2002, Alberta, Canada. [2] S. Korenev, I. Korenev. ``The propagation of high power CW scanning electron beam in air.'' BEAMS 2002: 14th International Conference on High-Power Particle Beams, Albuquerque, New Mexico (USA), June 2002, AIP Conference Proceedings Vol. 650(1), pp. 373-376. December 17.

Fully correcting the meteor speed distribution for radar observing biases

NASA Astrophysics Data System (ADS)

Moorhead, Althea V.; Brown, Peter G.; Campbell-Brown, Margaret D.; Heynen, Denis; Cooke, William J.

2017-09-01

Meteor radars such as the Canadian Meteor Orbit Radar (CMOR) have the ability to detect millions of meteors, making it possible to study the meteoroid environment in great detail. However, meteor radars also suffer from a number of detection biases; these biases must be fully corrected for in order to derive an accurate description of the meteoroid population. We present a bias correction method for patrol radars that accounts for the full form of ionization efficiency and mass distribution. This is an improvement over previous methods such as that of Taylor (1995), which requires power-law distributions for ionization efficiency and a single mass index. We apply this method to the meteor speed distribution observed by CMOR and find a significant enhancement of slow meteors compared to earlier treatments. However, when the data set is severely restricted to include only meteors with very small uncertainties in speed, the fraction of slow meteors is substantially reduced, indicating that speed uncertainties must be carefully handled.

A novel APPI-MS setup for in situ degradation product studies of atmospherically relevant compounds: capillary atmospheric pressure photo ionization (cAPPI).

PubMed

Kersten, Hendrik; Derpmann, Valerie; Barnes, Ian; Brockmann, Klaus J; O'Brien, Rob; Benter, Thorsten

2011-11-01

We report on the development of a novel atmospheric pressure photoionization setup and its applicability for in situ degradation product studies of atmospherically relevant compounds. A custom miniature spark discharge lamp was embedded into an ion transfer capillary, which separates the atmospheric pressure from the low pressure region in the first differential pumping stage of a conventional atmospheric pressure ionization mass spectrometer. The lamp operates with a continuous argon flow and produces intense light emissions in the VUV. The custom lamp is operated windowless and efficiently illuminates the sample flow through the transfer capillary on an area smaller than 1 mm(2). Limits of detection in the lower ppbV range, a temporal resolution of milliseconds in the positive as well as the quasi simultaneously operating negative ion mode, and a significant reduction of ion transformation processes render this system applicable to real time studies of rapidly changing chemical systems. The method termed capillary atmospheric pressure photo ionization (cAPPI) is characterized with respect to the lamp emission properties as a function of the operating conditions, temporal response, and its applicability for in situ degradation product studies of atmospherically relevant compounds, respectively.

Desorption Mass Spectrometry for Nonvolatile Compounds Using an Ultrasonic Cutter

NASA Astrophysics Data System (ADS)

Habib, Ahsan; Ninomiya, Satoshi; Chen, Lee Chuin; Usmanov, Dilshadbek T.; Hiraoka, Kenzo

2014-07-01

In this work, desorption of nonvolatile analytes induced by friction was studied. The nonvolatile compounds deposited on the perfluoroalkoxy substrate were gently touched by an ultrasonic cutter oscillating with a frequency of 40 kHz. The desorbed molecules were ionized by a dielectric barrier discharge (DBD) ion source. Efficient desorption of samples such as drugs, pharmaceuticals, amino acids, and explosives was observed. The limits of detection for these compounds were about 1 ng. Many compounds were detected in their protonated forms without undergoing significant fragmentation. When the DBD was off, no ions for the neutral samples could be detected, meaning that only desorption along with little ionization took place by the present technique.

Desorption mass spectrometry for nonvolatile compounds using an ultrasonic cutter.

PubMed

Habib, Ahsan; Ninomiya, Satoshi; Chen, Lee Chuin; Usmanov, Dilshadbek T; Hiraoka, Kenzo

2014-07-01

In this work, desorption of nonvolatile analytes induced by friction was studied. The nonvolatile compounds deposited on the perfluoroalkoxy substrate were gently touched by an ultrasonic cutter oscillating with a frequency of 40 kHz. The desorbed molecules were ionized by a dielectric barrier discharge (DBD) ion source. Efficient desorption of samples such as drugs, pharmaceuticals, amino acids, and explosives was observed. The limits of detection for these compounds were about 1 ng. Many compounds were detected in their protonated forms without undergoing significant fragmentation. When the DBD was off, no ions for the neutral samples could be detected, meaning that only desorption along with little ionization took place by the present technique.

Modeling photoionization of aqueous DNA and its components.

PubMed

Pluhařová, Eva; Slavíček, Petr; Jungwirth, Pavel

2015-05-19

Radiation damage to DNA is usually considered in terms of UVA and UVB radiation. These ultraviolet rays, which are part of the solar spectrum, can indeed cause chemical lesions in DNA, triggered by photoexcitation particularly in the UVB range. Damage can, however, be also caused by higher energy radiation, which can ionize directly the DNA or its immediate surroundings, leading to indirect damage. Thanks to absorption in the atmosphere, the intensity of such ionizing radiation is negligible in the solar spectrum at the surface of Earth. Nevertheless, such an ionizing scenario can become dangerously plausible for astronauts or flight personnel, as well as for persons present at nuclear power plant accidents. On the beneficial side, ionizing radiation is employed as means for destroying the DNA of cancer cells during radiation therapy. Quantitative information about ionization of DNA and its components is important not only for DNA radiation damage, but also for understanding redox properties of DNA in redox sensing or labeling, as well as charge migration along the double helix in nanoelectronics applications. Until recently, the vast majority of experimental and computational data on DNA ionization was pertinent to its components in the gas phase, which is far from its native aqueous environment. The situation has, however, changed for the better due to the advent of photoelectron spectroscopy in liquid microjets and its most recent application to photoionization of aqueous nucleosides, nucleotides, and larger DNA fragments. Here, we present a consistent and efficient computational methodology, which allows to accurately evaluate ionization energies and model photoelectron spectra of aqueous DNA and its individual components. After careful benchmarking, the method based on density functional theory and its time-dependent variant with properly chosen hybrid functionals and polarizable continuum solvent model provides ionization energies with accuracy of 0.2-0.3 eV, allowing for faithful modeling and interpretation of DNA photoionization. The key finding is that the aqueous medium is remarkably efficient in screening the interactions within DNA such that, unlike in the gas phase, ionization of a base, nucleoside, or nucleotide depends only very weakly on the particular DNA context. An exception is the electronic interaction between neighboring bases which can lead to sequence-specific effects, such as a partial delocalization of the cationic hole upon ionization enabled by presence of adjacent bases of the same type.

Joint neutron crystallographic and NMR solution studies of Tyr residue ionization and hydrogen bonding: Implications for enzyme-mediated proton transfer

DOE PAGES

Michalczyk, Ryszard; Unkefer, Clifford J.; Bacik, John -Paul; ...

2015-05-05

Proton transfer is a fundamental mechanism at the core of many enzyme-catalyzed reactions. It is also exquisitely sensitive to a number of factors, including pH, electrostatics, proper active-site geometry, and chemistry. Carbonic anhydrase has evolved a fast and efficient way to conduct protons through a combination of hydrophilic amino acid side chains that coordinate a highly ordered H-bonded water network. This study uses a powerful approach, combining NMR solution studies with neutron protein crystallography, to determine the effect of pH and divalent cations on key residues involved in proton transfer in human carbonic anhydrase. Lastly, the results have broad implicationsmore » for our understanding of proton transfer and how subtle changes in ionization and H-bonding interactions can modulate enzyme catalysis.« less

Effect of low-frequency oscillation on performance of Hall thrusters

NASA Astrophysics Data System (ADS)

Liqiu, WEI; Wenbo, LI; Yongjie, DING; Daren, YU

2018-07-01

In this paper, a direct connection between the discharge current amplitude and the thruster performance is established by varying solely the capacitance of the filter unit of the Hall thrusters. To be precise, the variation characteristics of ion current, propellant utilization efficiency, and divergence angle of plume at different low-frequency oscillation amplitudes are measured. The findings demonstrate that in the case of the propellant in the discharge channel just meets or falls below the full ionization condition, the increase of low-frequency oscillation amplitude can significantly enhance the ionization degree of the neutral gas in the channel and increase the thrust and anode efficiency of thruster. On the contrary, the increase in the amplitude of low-frequency oscillation will lead to increase the loss of plume divergence, therefore the thrust and anode efficiency of thruster decrease.

Effect of an InxGa1-xAs-GaAs blocking heterocathode metal contact on the GaAs TED operation

NASA Astrophysics Data System (ADS)

Arkusha, Yu. V.; Prokhorov, E. D.; Storozhenko, I. P.

2004-09-01

The frequency dependence of the generation efficiency of an mm- -nn:In:InxGaGa1-1-xAs- As-nn:GaAs-:GaAs-nn++:GaAs TED with the 2.5-mm long active region is calculated. The optimum values - which yield the diode maximum generation efficiency - for the :GaAs TED with the 2.5-mm long active region is calculated. The optimum values - which yield the diode maximum generation efficiency - for the nn:In:InxGaGa1-1-xAs cathode length, the cathode concentration of ionized impurities, and the height of the potential barrier on metal contact are determined.As cathode length, the cathode concentration of ionized impurities, and the height of the potential barrier on metal contact are determined.

Fragmentation of neutral amino acids and small peptides by intense, femtosecond laser pulses.

PubMed

Duffy, Martin J; Kelly, Orla; Calvert, Christopher R; King, Raymond B; Belshaw, Louise; Kelly, Thomas J; Costello, John T; Timson, David J; Bryan, William A; Kierspel, Thomas; Turcu, I C Edmond; Cacho, Cephise M; Springate, Emma; Williams, Ian D; Greenwood, Jason B

2013-09-01

High power femtosecond laser pulses have unique properties that could lead to their application as ionization or activation sources in mass spectrometry. By concentrating many photons into pulse lengths approaching the timescales associated with atomic motion, very strong electric field strengths are generated, which can efficiently ionize and fragment molecules without the need for resonant absorption. However, the complex interaction between these pulses and biomolecular species is not well understood. To address this issue, we have studied the interaction of intense, femtosecond pulses with a number of amino acids and small peptides. Unlike previous studies, we have used neutral forms of these molecular targets, which allowed us to investigate dissociation of radical cations without the spectra being complicated by the action of mobile protons. We found fragmentation was dominated by fast, radical-initiated dissociation close to the charge site generated by the initial ionization or from subsequent ultrafast migration of this charge. Fragments with lower yields, which are useful for structural determinations, were also observed and attributed to radical migration caused by hydrogen atom transfer within the molecule.

Multi-purpose two- and three-dimensional momentum imaging of charged particles for attosecond experiments at 1 kHz repetition rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Månsson, Erik P., E-mail: erik.mansson@sljus.lu.se; Sorensen, Stacey L.; Gisselbrecht, Mathieu

2014-12-15

We report on the versatile design and operation of a two-sided spectrometer for the imaging of charged-particle momenta in two dimensions (2D) and three dimensions (3D). The benefits of 3D detection are to discern particles of different mass and to study correlations between fragments from multi-ionization processes, while 2D detectors are more efficient for single-ionization applications. Combining these detector types in one instrument allows us to detect positive and negative particles simultaneously and to reduce acquisition times by using the 2D detector at a higher ionization rate when the third dimension is not required. The combined access to electronic andmore » nuclear dynamics available when both sides are used together is important for studying photoreactions in samples of increasing complexity. The possibilities and limitations of 3D momentum imaging of electrons or ions in the same spectrometer geometry are investigated analytically and three different modes of operation demonstrated experimentally, with infrared or extreme ultraviolet light and an atomic/molecular beam.« less

Desorption electrospray ionization mass spectrometry for the analysis of pharmaceuticals and metabolites.

PubMed

Kauppila, Tiina J; Wiseman, Justin M; Ketola, Raimo A; Kotiaho, Tapio; Cooks, R Graham; Kostiainen, Risto

2006-01-01

The performance of desorption electrospray ionization (DESI) in the analysis of a group of pharmaceuticals and their glucuronic acid conjugates is reported. The suitability of different sprayer solvents and different surfaces was examined. In the positive ion mode, water/methanol/trifluoroacetic acid performed best, whereas, in the negative ion mode, water/methanol/ammonium hydroxide was found to be the most suitable spray solvent. Of the surfaces investigated, polymethylmethacrylate (PMMA) was found to give the best performance in terms of sensitivity. Spray solution flow rate and the distance of the sprayer tip from the surface were also found to have significant effects on the signal intensity. Analytes with basic groups efficiently formed the corresponding protonated molecules in the positive ion mode, whereas acidic analytes, such as the glucuronic acid conjugates, formed intense signals due to the deprotonated molecules in the negative ion mode. Ionization of neutral compounds was less efficient and in many cases it was achieved through adduct formation with simple anions or cations. Copyright (c) 2005 John Wiley & Sons, Ltd.

Direct evidence of two interatomic relaxation mechanisms in argon dimers ionized by electron impact

PubMed Central

Ren, Xueguang; Jabbour Al Maalouf, Elias; Dorn, Alexander; Denifl, Stephan

2016-01-01

In weakly bound systems like liquids and clusters electronically excited states can relax in inter-particle reactions via the interplay of electronic and nuclear dynamics. Here we report on the identification of two prominent examples, interatomic Coulombic decay (ICD) and radiative charge transfer (RCT), which are induced in argon dimers by electron collisions. After initial ionization of one dimer constituent ICD and RCT lead to the ionization of its neighbour either by energy transfer to or by electron transfer from the neighbour, respectively. By full quintuple-coincidence measurements, we unambiguously identify ICD and RCT, and trace the relaxation dynamics as function of the collisional excited state energies. Such interatomic processes multiply the number of electrons and shift their energies down to the critical 1–10 eV range, which can efficiently cause chemical degradation of biomolecules. Therefore, the observed relaxation channels might contribute to cause efficient radiation damage in biological systems. PMID:27000407

Capillary electrophoresis electrospray ionization mass spectrometry interface

DOEpatents

Smith, Richard D.; Severs, Joanne C.

1999-01-01

The present invention is an interface between a capillary electrophoresis separation capillary end and an electrospray ionization mass spectrometry emitter capillary end, for transporting an anolyte sample from a capillary electrophoresis separation capillary to a electrospray ionization mass spectrometry emitter capillary. The interface of the present invention has: (a) a charge transfer fitting enclosing both of the capillary electrophoresis capillary end and the electrospray ionization mass spectrometry emitter capillary end; (b) a reservoir containing an electrolyte surrounding the charge transfer fitting; and (c) an electrode immersed into the electrolyte, the electrode closing a capillary electrophoresis circuit and providing charge transfer across the charge transfer fitting while avoiding substantial bulk fluid transfer across the charge transfer fitting. Advantages of the present invention have been demonstrated as effective in providing high sensitivity and efficient analyses.

Effect of oblique channel on discharge characteristics of 200-W Hall thruster

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Peng, Wuji; Sun, Hezhi; Xu, Yu; Wei, Liqiu; Li, Hong; Zeng, Ming; Wang, Fufeng; Yu, Daren

2017-02-01

In an experiment involving a 200-W Hall thruster, partial ionization occurs in the plume area because of the extrapolation of the magnetic field. To improve the thruster performance, the concept of an oblique channel is proposed for improving the ionization degree in the plume area. Calculations performed using a Particle-in-cell (PIC) simulator and the experimental results both show that an oblique channel structure can reduce the wall loss. Compared with a straight channel under similar conditions of the discharge voltage and current, the ionization degree in the plume area, thrust, specific impulse, propellant utilization, and anode efficiency are improved by ˜20%. The oblique channel is an important design consideration for improving the partial ionization of the plume area in the thruster.

The SPES surface ionization source

NASA Astrophysics Data System (ADS)

Manzolaro, M.; D'Agostini, F.; Monetti, A.; Andrighetto, A.

2017-09-01

Ion sources and target systems play a crucial role in isotope separation on line facilities, determining the main characteristics of the radioactive ion beams available for experiments. In the context of the selective production of exotic species (SPES) facility, a 40 MeV, 200 μA proton beam directly impinges a uranium carbide target, generating approximately 1013 fissions per second. The radioactive isotopes produced by the 238U fissions are delivered to the 1+ ion source by means of a tubular transfer line. Here they can be ionized and subsequently accelerated toward the experimental areas. In this work, the characterization of the surface ionization source currently adopted for the SPES facility is presented, taking as a reference ionization efficiency and transversal emittance measurements. The effects of long term operation at high temperature are also illustrated and discussed.

High-current fast electron beam propagation in a dielectric target.

PubMed

Klimo, Ondrej; Tikhonchuk, V T; Debayle, A

2007-01-01

Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10(12) A cm(-2). The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.

Study on the characteristics of a two gap capillary discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, D.; Yang, L. J., E-mail: yanglj@mail.xjtu.edu.cn; Huo, P.

2015-02-15

The paper presents a new two-gap capillary (TGC) discharge structure. The prominent innovation is the introduction of the middle electrode, which divides the capillary into the trigger gap and the main gap. The discharge circuit of the TGC comprises the trigger circuit and the main circuit. The two circuits are used for the pre-ionization of the trigger gap and providing energy of 450 J for the main gap arc discharging, respectively. When the discharge initiates, the trigger gap is pre-ionized under high voltage pulse produced by trigger circuit, and meanwhile, the weakly ionized plasma is generated. The main circuit then maintainsmore » the expansion of the plasma, which is called soft capillary discharge. Afterwards, the main gap is shorted and discharges under a relatively low voltage. With the optimization of the circuit parameter, both the energy deposition ratio in main gap and the degree of plasma ionization are enhanced. The efficiency of the energy deposition is almost twice higher compared with that of the conventional capillary structure. The life performance test indicates that the erosion of the middle electrode and the trigger gap carbonization are the key factors that limit the life performance of the TGC.« less

Classical vs. evolved quenching parameters and procedures in scintillation measurements: The importance of ionization quenching

NASA Astrophysics Data System (ADS)

Bagán, H.; Tarancón, A.; Rauret, G.; García, J. F.

2008-07-01

The quenching parameters used to model detection efficiency variations in scintillation measurements have not evolved since the decade of 1970s. Meanwhile, computer capabilities have increased enormously and ionization quenching has appeared in practical measurements using plastic scintillation. This study compares the results obtained in activity quantification by plastic scintillation of 14C samples that contain colour and ionization quenchers, using classical (SIS, SCR-limited, SCR-non-limited, SIS(ext), SQP(E)) and evolved (MWA-SCR and WDW) parameters and following three calibration approaches: single step, which does not take into account the quenching mechanism; two steps, which takes into account the quenching phenomena; and multivariate calibration. Two-step calibration (ionization followed by colour) yielded the lowest relative errors, which means that each quenching phenomenon must be specifically modelled. In addition, the sample activity was quantified more accurately when the evolved parameters were used. Multivariate calibration-PLS also yielded better results than those obtained using classical parameters, which confirms that the quenching phenomena must be taken into account. The detection limits for each calibration method and each parameter were close to those obtained theoretically using the Currie approach.

Improvement in ionization efficiency of direct analysis in real time-mass spectrometry (DART-MS) by corona discharge.

PubMed

Sekimoto, Kanako; Sakakura, Motoshi; Kawamukai, Takatomo; Hike, Hiroshi; Shiota, Teruhisa; Usui, Fumihiko; Bando, Yasuhiko; Takayama, Mitsuo

2016-08-02

Herein it is shown that a combination of direct analysis in real time (DART) with a corona discharge system consisting of only a needle electrode easily improves DART ionization efficiency. Positive and negative DC corona discharges led to a formation of abundant excited helium atoms as well as the reactant ions H3O(+)(H2O)n and O2˙(-) in the DART analyte ionization area. These phenomena resulted in an increase in the absolute intensities of (de)protonated analytes by a factor of 2-20 over conventional DART. The other analyte ions detected in this corona-DART system (i.e., molecular ions, fragment ions, oxygenated (de)protonated analytes, dehydrogenated deprotonated analytes, and negative ion adducts) were quite similar to those obtained from DART alone. This indicates a lack of side reactions due to the corona discharge. The change in the relative intensities of individual analyte-related ions due to the combination of a corona discharge system with DART suggests that there is no effect of the abundant excited helium in the analyte ionization area on the fragmentation processes or enhancement of oxidation due to hydroxyl radicals HO˙. Furthermore, it was found that the corona-DART combination can be applied to the highly sensitive analysis of n-alkanes, in which the alkanes are ionized as positive ions via hydride abstraction and oxidation, independent of the type of alkane or the mass spectrometer used.

Comparison of Internal Energy Distributions of Ions Created by Electrospray Ionization and Laser Ablation-Liquid Vortex Capture-Electrospray Ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cahill, John F.; Kertesz, Vilmos; Ovchinnikova, Olga S.

2015-06-27

Recently a number of techniques have combined laser ablation with liquid capture for mass spectrometry spot sampling and imaging applications. The newly developed non-contact liquid-vortex capture probe has been used to efficiently collect 355 nm UV laser ablated material in a continuous flow solvent stream in which the captured material dissolves and then undergoes electrospray ionization. This sampling and ionization approach has produced what appear to be classic electrospray ionization spectra; however, the softness of this sampling/ionization process versus simple electrospray ionization has not been definitely determined. A series of benzlypyridinium salts, known as thermometer ions, were used to comparemore » internal energy distributions between electrospray ionization and the UV laser ablation liquid-vortex capture probe electrospray combination. Measured internal energy distributions were identical between the two techniques, even with differences in laser fluence (0.7-3.1 J cm-2) and when using UV-absorbing or non-UV-absorbing sample substrates. This data indicates ions formed directly by UV laser ablation, if any, are likely an extremely small constituent of the total ion signal observed. Instead, neutral molecules, clusters or particulates ejected from the surface during laser ablation, subsequently captured and dissolved in the flowing solvent stream then electrosprayed are the predominant source of ion signal observed. The electrospray ionization process used controls the softness of the technique.« less

Virtual quantification of metabolites by capillary electrophoresis-electrospray ionization-mass spectrometry: predicting ionization efficiency without chemical standards.

PubMed

Chalcraft, Kenneth R; Lee, Richard; Mills, Casandra; Britz-McKibbin, Philip

2009-04-01

A major obstacle in metabolomics remains the identification and quantification of a large fraction of unknown metabolites in complex biological samples when purified standards are unavailable. Herein we introduce a multivariate strategy for de novo quantification of cationic/zwitterionic metabolites using capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) based on fundamental molecular, thermodynamic, and electrokinetic properties of an ion. Multivariate calibration was used to derive a quantitative relationship between the measured relative response factor (RRF) of polar metabolites with respect to four physicochemical properties associated with ion evaporation in ESI-MS, namely, molecular volume (MV), octanol-water distribution coefficient (log D), absolute mobility (mu(o)), and effective charge (z(eff)). Our studies revealed that a limited set of intrinsic solute properties can be used to predict the RRF of various classes of metabolites (e.g., amino acids, amines, peptides, acylcarnitines, nucleosides, etc.) with reasonable accuracy and robustness provided that an appropriate training set is validated and ion responses are normalized to an internal standard(s). The applicability of the multivariate model to quantify micromolar levels of metabolites spiked in red blood cell (RBC) lysates was also examined by CE-ESI-MS without significant matrix effects caused by involatile salts and/or major co-ion interferences. This work demonstrates the feasibility for virtual quantification of low-abundance metabolites and their isomers in real-world samples using physicochemical properties estimated by computer modeling, while providing deeper insight into the wide disparity of solute responses in ESI-MS. New strategies for predicting ionization efficiency in silico allow for rapid and semiquantitative analysis of newly discovered biomarkers and/or drug metabolites in metabolomics research when chemical standards do not exist.

Study of Auger effect in DNA when bound to molecules containing platinum. A possible application to hadrontherapy

NASA Astrophysics Data System (ADS)

Kobayashi, K.; Usami, N.; Sasaki, I.; Frohlich, H.; Le Sech, C.

2003-01-01

Complexes made of DNA and Cyclo-Pt bound to plasmid DNA, were placed in aqueous solution and irradiated with monochromatic X-rays in the range E=8.5-13 keV, including the resonant photoabsorption energy of the L III shell of the platinum atom. The number of single- and double-strand breaks (ssb and dsb) induced by irradiation on a supercoiled DNA plasmid was measured by the production of circular-nicked and linear forms. In order to disentangle the contribution of the direct effects imparted to ionization, and the indirect effects due to a free radical attack, experiments have been performed in the presence of a small concentration (64 mmol l -1) of hydroxyl free radical scavenger dimethyl sulfoxide (DMSO). An enhancement of the number of ssb and dsb is observed when the plasmids contain the Pt intercalating molecules. Even when off-resonant X-rays are used, the strand break efficiency remains higher than expected based upon the absorption cross-section, as if the Pt bound to DNA is increasing the yield of strand breaks. A mechanism is suggested, involving photoelectrons generated from the ionization of water which efficiently ionize Pt atoms. This observation may provide an insight to understanding the effects of new radiotherapy protocols, associated chemotherapeutic agents such as cisplatin and ordinary radiotherapy for tumoral treatments.

A Radical-Mediated Pathway for the Formation of [M + H](+) in Dielectric Barrier Discharge Ionization.

PubMed

Wolf, Jan-Christoph; Gyr, Luzia; Mirabelli, Mario F; Schaer, Martin; Siegenthaler, Peter; Zenobi, Renato

2016-09-01

Active capillary plasma ionization is a highly efficient ambient ionization method. Its general principle of ion formation is closely related to atmospheric pressure chemical ionization (APCI). The method is based on dielectric barrier discharge ionization (DBDI), and can be constructed in the form of a direct flow-through interface to a mass spectrometer. Protonated species ([M + H](+)) are predominantly formed, although in some cases radical cations are also observed. We investigated the underlying ionization mechanisms and reaction pathways for the formation of protonated analyte ([M + H](+)). We found that ionization occurs in the presence and in the absence of water vapor. Therefore, the mechanism cannot exclusively rely on hydronium clusters, as generally accepted for APCI. Based on isotope labeling experiments, protons were shown to originate from various solvents (other than water) and, to a minor extent, from gaseous impurities and/or self-protonation. By using CO2 instead of air or N2 as plasma gas, additional species like [M + OH](+) and [M - H](+) were observed. These gas-phase reaction products of CO2 with the analyte (tertiary amines) indicate the presence of a radical-mediated ionization pathway, which proceeds by direct reaction of the ionized plasma gas with the analyte. The proposed reaction pathway is supported with density functional theory (DFT) calculations. These findings add a new ionization pathway leading to the protonated species to those currently known for APCI. Graphical Abstract ᅟ.

Improving low-level plasma protein mass spectrometry-based detection for candidate biomarker discovery and validation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Page, Jason S.; Kelly, Ryan T.; Camp, David G.

2008-09-01

Methods. To improve the detection of low abundance protein candidate biomarker discovery and validation, particularly in complex biological fluids such as blood plasma, increased sensitivity is desired using mass spectrometry (MS)-based instrumentation. A key current limitation on the sensitivity of electrospray ionization (ESI) MS is due to the fact that many sample molecules in solution are never ionized, and the vast majority of the ions that are created are lost during transmission from atmospheric pressure to the low pressure region of the mass analyzer. Two key technologies, multi-nanoelectrospray emitters and the electrodynamic ion funnel have recently been developed and refinedmore » at Pacific Northwest National Laboratory (PNNL) to greatly improve the ionization and transmission efficiency of ESI MS based analyses. Multi-emitter based ESI enables the flow from a single source (typically a liquid chromatography [LC] column) to be divided among an array of emitters (Figure 1). The flow rate delivered to each emitter is thus reduced, allowing the well-documented benefits of nanoelectrospray 1 for both sensitivity and quantitation to be realized for higher flow rate separations. To complement the increased ionization efficiency afforded by multi-ESI, tandem electrodynamic ion funnels have also been developed at PNNL, and shown to greatly improve ion transmission efficiency in the ion source interface.2, 3 These technologies have been integrated into a triple quadrupole mass spectrometer for multiple reaction monitoring (MRM) of probable biomarker candidates in blood plasma and show promise for the identification of new species even at low level concentrations.« less

An approach toward quantification of organic compounds in complex environmental samples using high-resolution electrospray ionization mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Tran B.; Nizkorodov, Sergey; Laskin, Alexander

2013-01-07

Quantitative analysis of individual compounds in complex mixtures using high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) is complicated by differences in the ionization efficiencies of analyte molecules in the mixture, resulting in signal suppression during ionization. However, the ability to obtain concentration estimates of compounds in an environmental sample is important for data interpretation and comparison. We introduce an approach for estimating mass concentrations of analytes observed in a multicomponent mixture by HR-ESI-MS, without prior separation. The approach relies on a calibration of the instrument using appropriate standards added to the mixture of studied analytes. An illustration of how the proposedmore » calibration can be applied in practice is provided for aqueous extracts of isoprene photooxidation organic aerosol, with multifunctional organic acids standards. We show that the observed ion sensitivities in ESI-MS are positively correlated with the “adjusted mass,” defined as a product of the molecular mass and the H/C ratio in the molecule (adjusted mass = H/C x molecular mass). The correlation of the observed ESI sensitivity with adjusted mass is justified by considering trends of the physical and chemical properties of organic compounds that affect ionization in the positive ion mode, i.e., gas-phase basicity, polarizability, and molecular size.« less

Analysis of Intrinsic Peptide Detectability via Integrated Label-Free and SRM-Based Absolute Quantitative Proteomics.

PubMed

Jarnuczak, Andrew F; Lee, Dave C H; Lawless, Craig; Holman, Stephen W; Eyers, Claire E; Hubbard, Simon J

2016-09-02

Quantitative mass spectrometry-based proteomics of complex biological samples remains challenging in part due to the variability and charge competition arising during electrospray ionization (ESI) of peptides and the subsequent transfer and detection of ions. These issues preclude direct quantification from signal intensity alone in the absence of a standard. A deeper understanding of the governing principles of peptide ionization and exploitation of the inherent ionization and detection parameters of individual peptides is thus of great value. Here, using the yeast proteome as a model system, we establish the concept of peptide F-factor as a measure of detectability, closely related to ionization efficiency. F-factor is calculated by normalizing peptide precursor ion intensity by absolute abundance of the parent protein. We investigated F-factor characteristics in different shotgun proteomics experiments, including across multiple ESI-based LC-MS platforms. We show that F-factors mirror previously observed physicochemical predictors as peptide detectability but demonstrate a nonlinear relationship between hydrophobicity and peptide detectability. Similarly, we use F-factors to show how peptide ion coelution adversely affects detectability and ionization. We suggest that F-factors have great utility for understanding peptide detectability and gas-phase ion chemistry in complex peptide mixtures, selection of surrogate peptides in targeted MS studies, and for calibration of peptide ion signal in label-free workflows. Data are available via ProteomeXchange with identifier PXD003472.

Synergistic effect of ozonation and ionizing radiation for PVA decomposition.

PubMed

Sun, Weihua; Chen, Lujun; Zhang, Yongming; Wang, Jianlong

2015-08-01

Ozonation and ionizing radiation are both advanced oxidation processes (AOPs) without chemical addition and secondary pollution. Also, the two processes' efficiency is determined by different pH conditions, which creates more possibilities for their combination. Importantly, the combined process of ozonation and ionizing radiation could be suitable for treating wastewaters with extreme pH values, i.e., textile wastewater. To find synergistic effects, the combined process of ozonation and ionizing radiation mineralization was investigated for degradation of polyvinyl alcohol (PVA) at different pH levels. A synergistic effect was found at initial pH in the range 3.0-9.4. When the initial pH was 3.0, the combined process of ozonation and ionizing radiation gave a PVA mineralization degree of 17%. This was 2.7 times the sum achieved by the two individual processes, and factors of 2.1 and 1.7 were achieved at initial pH of 7.0 and 9.4, respectively. The combined process of ozonation and ionizing radiation was demonstrated to be a feasible strategy for treatment of PVA-containing wastewater. Copyright © 2015. Published by Elsevier B.V.

Sensitive ion detection device and method for analysis of compounds as vapors in gases

DOEpatents

Denton, M. Bonner; Sperline, Roger P.

2015-09-15

An ion mobility spectrometer (IMS) for the detection of trace gaseous molecular compounds dissolved or suspended in a carrier gas, particularly in ambient air, without preconcentration or the trapping of analyte particles. The IMS of the invention comprises an ionization volume of greater than 5 cm.sup.3 and preferably greater than 100 cm.sup.3. The larger size ionizers of this invention enable analysis of trace (<1 ppb) of sample compounds in the gas phase. To facilitate efficient ion motion through the large volume ionization and reaction regions of the IMS, an electric field gradient can be provided in the ionization region or in both the ionization and reaction regions. The systems can be implemented with radioactive ionization sources, corona discharge ion sources or ions can be formed by photoionization. In specific embodiments, particularly when the sample gas is ambient air, the sample gas is heater prior to entry into the instrument, the instrument is run at temperatures above ambient, and the instrument can be heated by contact with heated sample gas exiting the instrument.

Sensitive ion detection device and method for analysis of compounds as vapors in gases

DOEpatents

Denton, M. Bonner; Sperline, Roger P

2014-02-18

An ion mobility spectrometer (IMS) for the detection of trace gaseous molecular compounds dissolved or suspended in a carrier gas, particularly in ambient air, without preconcentration or the trapping of analyte particles. The IMS of the invention comprises an ionization volume of greater than 5 cm.sup.3 and preferably greater than 100 cm.sup.3. The larger size ionizers of this invention enable analysis of trace (<1 ppb) of sample compounds in the gas phase. To facilitate efficient ion motion through the large volume ionization and reaction regions of the IMS, an electric field gradient can be provided in the ionization region or in both the ionization and reaction regions. The systems can be implemented with radioactive ionization sources, corona discharge ion sources or ions can be formed by photoionization. In specific embodiments, particularly when the sample gas is ambient air, the sample gas is heater prior to entry into the instrument, the instrument is run at temperatures above ambient, and the instrument can be heated by contact with heated sample gas exiting the instrument.

Alkali metal cation complexation by 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds

DOE PAGES

Surowiec, Malgorzata A.; Custelcean, Radu; Surowiec, Kazimierz; ...

2014-04-23

Alkali metal cation extraction behavior for two series of 1,3-alternate, mono-ionizable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionizable group is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the proton-ionizable group is attached to one para position in the calixarene framework, thus positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs+ efficiency and selectivity. Single-species extraction pH profiles of Cs+ for Series 1 and 2 ligands with the same proton-ionizable groupmore » are very similar. Thus, association of Cs+ with the calixcrown ring is more important than the the proton-ionizable group’s position in relation to the crown ether cavity. Solid-state structures are presented for two unionized ligands from Series 2, as is a crystal containing two different ionized ligand–Cs+ complexes.« less

GaN Light-Emitting Triodes (LETs) for High-Efficiency Hole Injection and for Assessment of the Physical Origin of the Efficiency Droop

DTIC Science & Technology

2007-07-06

quantum efficiency . In AlGaN-based UV LEDs, an electron-blocking layer (EBL) is frequently inserted between the p-type cladding layer and the active...me). This limits the hole injection efficiency into the active region, and hence internal quantum efficiency . Figure 1: (a) Schematic band...less efficient than along the lateral direction because most of the holes ionized from the acceptors are localized inside the quantum wells which are

Nanoengineering of strong field processes in solids

NASA Astrophysics Data System (ADS)

Almalki, S.; Parks, A. M.; Brabec, T.; McDonald, C. R.

2018-04-01

We present a theoretical investigation of the effect of quantum confinement on high harmonic generation in semiconductor materials by systematically varying the confinement width along one or two directions transverse to the laser polarization. Our analysis shows a growth in high harmonic efficiency concurrent with a reduction of ionization. This decrease in ionization comes as a consequence of an increased band gap resulting from the confinement. The increase in harmonic efficiency results from a restriction of wave packet spreading, leading to greater recollision probability. Consequently, nanoengineering of one and two-dimensional nanosystems may prove to be a viable means to increase harmonic yield and photon energy in semiconductor materials driven by intense laser fields.

Efficiencies for production of atomic nitrogen and oxygen by relativistic proton impact in air

NASA Technical Reports Server (NTRS)

Porter, H. S.; Jackman, C. H.; Green, A. E. S.

1976-01-01

Relativistic electron and proton impact cross sections are obtained and represented by analytic forms which span the energy range from threshold to 1 GeV. For ionization processes, the Massey-Mohr continuum generalized oscillator strength surface is parameterized. Parameters are determined by simultaneous fitting to (1) empirical data, (2) the Bethe sum rule, and (3) doubly differential cross sections for ionization. Branching ratios for dissociation and predissociation from important states of N2 and O2 are determined. The efficiency for the production of atomic nitrogen and oxygen by protons with kinetic energy less than 1 GeV is determined using these branching ratio and cross section assignments.

Circular dichroism in photoelectron images from aligned nitric oxide molecules

DOE PAGES

Sen, Ananya; Pratt, S. T.; Reid, K. L.

2017-05-03

We have used velocity map photoelectron imaging to study circular dichroism of the photoelectron angular distributions (PADs) of nitric oxide following two-color resonanceenhanced two-photon ionization via selected rotational levels of the A 2Σ +, v' = 0 state. By using a circularly polarized pump beam and a counter-propagating, circularly polarized probe beam, cylindrical symmetry is preserved in the ionization process, and the images can be reconstructed using standard algorithms. The VMI set up enables individual ion rotational states to be resolved with excellent collection efficiency, rendering the measurements considerably simpler to perform than previous measurements conducted with a conventional photoelectronmore » spectrometer. The results demonstrate that circular dichroism is observed even when cylindrical symmetry is maintained, and serve as a reminder that dichroism is a general feature of the multiphoton ionization of atoms and molecules. Furthermore, the observed PADs are in good agreement with calculations based on parameters extracted from previous experimental results obtained by using a time-offlight electron spectrometer.« less

Micrometeoroid ablation simulated in the laboratory

NASA Astrophysics Data System (ADS)

Sternovsky, Zoltan; Thomas, Evan W.; DeLuca, Michael; Horanyi, Mihaly; Janches, Diego; Munsat, Tobin L.; Plane, John M. C.

2016-04-01

A facility is developed to simulate the ablation of micrometeoroids in laboratory conditions, which also allows measuring the ionization probability of the ablated material. An electrostatic dust accelerator is used to generate iron and meteoric analog particles with velocities 10-50 km/s. The particles are then introduced into a cell filled with nitrogen, air or carbon dioxide gas with pressures adjustable in the 0.02 - 0.5 Torr range, where the partial or complete ablation of the particle occurs over a short distance. An array of biased electrodes is used to collect the ionized products with spatial resolution along the ablating particles' path, allowing thus the study of the temporal resolution of the process. A simple ablation model is used to match the observations. For completely ablated particles the total collected charge directly yields the ionization efficiency for. The measurements using iron particles in N2 and air are in relatively good agreement with earlier data. The measurements with CO2 and He gases, however, are significantly different from the expectations.

Circular dichroism in photoelectron images from aligned nitric oxide molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sen, Ananya; Pratt, S. T.; Reid, K. L.

We have used velocity map photoelectron imaging to study circular dichroism of the photoelectron angular distributions (PADs) of nitric oxide following two-color resonanceenhanced two-photon ionization via selected rotational levels of the A 2Σ +, v' = 0 state. By using a circularly polarized pump beam and a counter-propagating, circularly polarized probe beam, cylindrical symmetry is preserved in the ionization process, and the images can be reconstructed using standard algorithms. The VMI set up enables individual ion rotational states to be resolved with excellent collection efficiency, rendering the measurements considerably simpler to perform than previous measurements conducted with a conventional photoelectronmore » spectrometer. The results demonstrate that circular dichroism is observed even when cylindrical symmetry is maintained, and serve as a reminder that dichroism is a general feature of the multiphoton ionization of atoms and molecules. Furthermore, the observed PADs are in good agreement with calculations based on parameters extracted from previous experimental results obtained by using a time-offlight electron spectrometer.« less

Ionizing radiation delivered by specific antibody is therapeutic against a fungal infection

PubMed Central

Dadachova, Ekaterina; Nakouzi, Antonio; Bryan, Ruth A.; Casadevall, Arturo

2003-01-01

There is an urgent need for new antimicrobial therapies to combat drug resistance, new pathogens, and the relative inefficacy of current therapy in compromised hosts. Ionizing radiation can kill microorganisms quickly and efficiently, but this modality has not been exploited as a therapeutic antimicrobial strategy. We have developed methods to target ionizing radiation to a fungal cell by labeling a specific mAb with the therapeutic radioisotopes Rhenium-188 and Bismuth-213. Radiolabeled antibody killed cells of human pathogenic fungus Cryptococcus neoformans in vitro, thus converting an antibody with no inherent antifungal activity into a microbicidal molecule. Administration of radiolabeled antibody to mice with C. neoformans infection delivered 213Bi and 188Re to the sites of infection, reduced their organ fungal burden, and significantly prolonged their survival without apparent toxicity. This study establishes the principle that targeted radiation can be used for the therapy of an infectious disease, and suggests that it may have wide applicability as an antimicrobial strategy. PMID:12930899

Ionizing radiation delivered by specific antibody is therapeutic against a fungal infection

NASA Astrophysics Data System (ADS)

Dadachova, Ekaterina; Nakouzi, Antonio; Bryan, Ruth A.; Casadevall, Arturo

2003-09-01

There is an urgent need for new antimicrobial therapies to combat drug resistance, new pathogens, and the relative inefficacy of current therapy in compromised hosts. Ionizing radiation can kill microorganisms quickly and efficiently, but this modality has not been exploited as a therapeutic antimicrobial strategy. We have developed methods to target ionizing radiation to a fungal cell by labeling a specific mAb with the therapeutic radioisotopes Rhenium-188 and Bismuth-213. Radiolabeled antibody killed cells of human pathogenic fungus Cryptococcus neoformans in vitro, thus converting an antibody with no inherent antifungal activity into a microbicidal molecule. Administration of radiolabeled antibody to mice with C. neoformans infection delivered 213Bi and 188Re to the sites of infection, reduced their organ fungal burden, and significantly prolonged their survival without apparent toxicity. This study establishes the principle that targeted radiation can be used for the therapy of an infectious disease, and suggests that it may have wide applicability as an antimicrobial strategy.

Photo-ionization of aluminum in a hot cavity for the selective production of exotic species project

NASA Astrophysics Data System (ADS)

Scarpa, D.; Makhathini, L.; Tomaselli, A.; Grassi, D.; Corradetti, S.; Manzolaro, M.; Vasquez, J.; Calderolla, M.; Rossignoli, M.; Monetti, A.; Andrighetto, A.; Prete, G.

2014-02-01

SPES (Selective Production of Exotic Species) is an Isotope Separation On-Line (ISOL) based accelerator facility that will be built in the Legnaro-Istituto Nazionale di Fisica Nucleare (INFN) Laboratory (Italy), intended to provide intense neutron-rich radioactive ion beams obtained by proton-induced fission of a uranium carbide (UCx) target. Besides this main target material, silicon carbide (SiC) will be the first to be used to deliver p-rich beams. This target will also validate the functionality of the SPES facility with aluminum beam as result of impinging SiC target with proton beam. In the past, off line studies on laser photoionization of aluminum have been performed in Pavia Spectroscopy Laboratory and in Laboratori Nazionali di Legnaro; a XeCl excimer laser was installed in order to test the laser ionization in the SPES hot cavity. With the new Wien filter installed a better characterization of the ionization process in terms of efficiency was performed and results are discussed.

Test study of boron nitride as a new detector material for dosimetry in high-energy photon beams.

PubMed

Poppinga, D; Halbur, J; Lemmer, S; Delfs, B; Harder, D; Looe, H K; Poppe, B

2017-09-05

The aim of this test study is to check whether boron nitride (BN) might be applied as a detector material in high-energy photon-beam dosimetry. Boron nitride exists in various crystalline forms. Hexagonal boron nitride (h-BN) possesses high mobility of the electrons and holes as well as a high volume resistivity, so that ionizing radiation in the clinical range of the dose rate can be expected to produce a measurable electrical current at low background current. Due to the low atomic numbers of its constituents, its density (2.0 g cm -3 ) similar to silicon and its commercial availability, h-BN appears as possibly suitable for the dosimetry of ionizing radiation. Five h-BN plates were contacted to triaxial cables, and the detector current was measured in a solid-state ionization chamber circuit at an applied voltage of 50 V. Basic dosimetric properties such as formation by pre-irradiation, sensitivity, reproducibility, linearity and temporal resolution were measured with 6 MV photon irradiation. Depth dose curves at quadratic field sizes of 10 cm and 40 cm were measured and compared to ionization chamber measurements. After a pre-irradiation with 6 Gy, the devices show a stable current signal at a given dose rate. The current-voltage characteristic up to 400 V shows an increase in the collection efficiency with the voltage. The time-resolved detector current behavior during beam interrupts is comparable to diamond material, and the background current is negligible. The measured percentage depth dose curves at 10 cm  ×  10 cm field size agreed with the results of ionization chamber measurements within  ±2%. This is a first study of boron nitride as a detector material for high-energy photon radiation. By current measurements on solid ionization chambers made from boron nitride chips we could demonstrate that boron nitride is in principle suitable as a detector material for high-energy photon-beam dosimetry.

Test study of boron nitride as a new detector material for dosimetry in high-energy photon beams

NASA Astrophysics Data System (ADS)

Poppinga, D.; Halbur, J.; Lemmer, S.; Delfs, B.; Harder, D.; Looe, H. K.; Poppe, B.

2017-09-01

The aim of this test study is to check whether boron nitride (BN) might be applied as a detector material in high-energy photon-beam dosimetry. Boron nitride exists in various crystalline forms. Hexagonal boron nitride (h-BN) possesses high mobility of the electrons and holes as well as a high volume resistivity, so that ionizing radiation in the clinical range of the dose rate can be expected to produce a measurable electrical current at low background current. Due to the low atomic numbers of its constituents, its density (2.0 g cm-3) similar to silicon and its commercial availability, h-BN appears as possibly suitable for the dosimetry of ionizing radiation. Five h-BN plates were contacted to triaxial cables, and the detector current was measured in a solid-state ionization chamber circuit at an applied voltage of 50 V. Basic dosimetric properties such as formation by pre-irradiation, sensitivity, reproducibility, linearity and temporal resolution were measured with 6 MV photon irradiation. Depth dose curves at quadratic field sizes of 10 cm and 40 cm were measured and compared to ionization chamber measurements. After a pre-irradiation with 6 Gy, the devices show a stable current signal at a given dose rate. The current-voltage characteristic up to 400 V shows an increase in the collection efficiency with the voltage. The time-resolved detector current behavior during beam interrupts is comparable to diamond material, and the background current is negligible. The measured percentage depth dose curves at 10 cm  ×  10 cm field size agreed with the results of ionization chamber measurements within  ±2%. This is a first study of boron nitride as a detector material for high-energy photon radiation. By current measurements on solid ionization chambers made from boron nitride chips we could demonstrate that boron nitride is in principle suitable as a detector material for high-energy photon-beam dosimetry.

Assessment of ionization chamber correction factors in photon beams using a time saving strategy with PENELOPE code.

PubMed

Reis, C Q M; Nicolucci, P

2016-02-01

The purpose of this study was to investigate Monte Carlo-based perturbation and beam quality correction factors for ionization chambers in photon beams using a saving time strategy with PENELOPE code. Simulations for calculating absorbed doses to water using full spectra of photon beams impinging the whole water phantom and those using a phase-space file previously stored around the point of interest were performed and compared. The widely used NE2571 ionization chamber was modeled with PENELOPE using data from the literature in order to calculate absorbed doses to the air cavity of the chamber. Absorbed doses to water at reference depth were also calculated for providing the perturbation and beam quality correction factors for that chamber in high energy photon beams. Results obtained in this study show that simulations with phase-space files appropriately stored can be up to ten times shorter than using a full spectrum of photon beams in the input-file. Values of kQ and its components for the NE2571 ionization chamber showed good agreement with published values in the literature and are provided with typical statistical uncertainties of 0.2%. Comparisons to kQ values published in current dosimetry protocols such as the AAPM TG-51 and IAEA TRS-398 showed maximum percentage differences of 0.1% and 0.6% respectively. The proposed strategy presented a significant efficiency gain and can be applied for a variety of ionization chambers and clinical photon beams. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Silver nanostructures in laser desorption/ionization mass spectrometry and mass spectrometry imaging.

PubMed

Sekuła, Justyna; Nizioł, Joanna; Rode, Wojciech; Ruman, Tomasz

2015-09-21

Silver nanoparticles have been successfully applied as a matrix replacement for the laser desorption/ionization time-of-flight mass spectrometry (LDI-ToF-MS). Nanoparticles, producing spectra with highly reduced chemical background in the low m/z region, are perfectly suited for low-molecular weight compound analysis and imaging. Silver nanoparticles (AgNPs) can efficiently absorb ultraviolet laser radiation, transfer energy to the analyte and promote analyte desorption, but also constitute a source of silver ions suitable for analyte cationisation. This review provides an overview of the literature on silver nanomaterials as non-conventional desorption and ionization promoters in LDI-MS and mass spectrometry imaging.

Observation of novel photochemistry in the multiphoton ionization of Mo(CO) sub 6 van der Waals clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peifer, W.R.; Garvey, J.F.

1989-07-27

van der Waals clusters of Mo(CO){sub 6} generated in the free-jet expansion of a pulsed beam of seeded helium are subjected to multiphoton ionization and the product ions analyzed by quadrupole mass spectrometry. Oxomolybdenum and dioxomolybdenum ions are observed to be produced with high efficiency. This behavior is in striking contrast to that of metal carbonyl monomers and covalently bound cluster carbonyls, which under complete ligand loss prior to ionization. The observed photochemistry is ascribed to reactions between a photoproduced molybdenum atom and the ligands of neighboring Mo(CO){sub 6} solvent molecules within the van der Waals cluster.

Protonation enhancement by dichloromethane doping in low-pressure photoionization

PubMed Central

Shu, Jinian; Zou, Yao; Xu, Ce; Li, Zhen; Sun, Wanqi; Yang, Bo; Zhang, Haixu; Zhang, Peng; Ma, Pengkun

2016-01-01

Doping has been used to enhance the ionization efficiency of analytes in atmospheric pressure photoionization, which is based on charge exchange. Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH2Cl2) doping. CH2Cl2 is not a common dopant due to its high ionization energy (11.33 eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6 eV and was operated at ~500–1000 Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7 ± 122.4, 197.8 ± 18.8, 87.3 ± 7.8, and 93.5 ± 35.5 times after doping 291 ppmv CH2Cl2, meanwhile CH2Cl2 almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization. PMID:27905552

Protonation enhancement by dichloromethane doping in low-pressure photoionization.

PubMed

Shu, Jinian; Zou, Yao; Xu, Ce; Li, Zhen; Sun, Wanqi; Yang, Bo; Zhang, Haixu; Zhang, Peng; Ma, Pengkun

2016-12-01

Doping has been used to enhance the ionization efficiency of analytes in atmospheric pressure photoionization, which is based on charge exchange. Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH 2 Cl 2 ) doping. CH 2 Cl 2 is not a common dopant due to its high ionization energy (11.33 eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6 eV and was operated at ~500-1000 Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7 ± 122.4, 197.8 ± 18.8, 87.3 ± 7.8, and 93.5 ± 35.5 times after doping 291 ppmv CH 2 Cl 2 , meanwhile CH 2 Cl 2 almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization.

Graphene oxide membrane as an efficient extraction and ionization substrate for spray-mass spectrometric analysis of malachite green and its metabolite in fish samples.

PubMed

Wei, Shih-Chun; Fan, Shen; Lien, Chia-Wen; Unnikrishnan, Binesh; Wang, Yi-Sheng; Chu, Han-Wei; Huang, Chih-Ching; Hsu, Pang-Hung; Chang, Huan-Tsung

2018-03-20

A graphene oxide (GO) nanosheet-modified N + -nylon membrane (GOM) has been prepared and used as an extraction and spray-ionization substrate for robust mass spectrometric detection of malachite green (MG), a highly toxic disinfectant in liquid samples and fish meat. The GOM is prepared by self-deposition of GO thin film onto an N + -nylon membrane, which has been used for efficient extraction of MG in aquaculture water samples or homogenized fish meat samples. Having a dissociation constant of 2.17 × 10 -9  M -1 , the GOM allows extraction of approximately 98% of 100 nM MG. Coupling of the GOM-spray with an ion-trap mass spectrometer allows quantitation of MG in aquaculture freshwater and seawater samples down to nanomolar levels. Furthermore, the system possesses high selectivity and sensitivity for the quantitation of MG and its metabolite (leucomalachite green) in fish meat samples. With easy extraction and efficient spray ionization properties of GOM, this membrane spray-mass spectrometry technique is relatively simple and fast in comparison to the traditional LC-MS/MS methods for the quantitation of MG and its metabolite in aquaculture products. Copyright © 2017 Elsevier B.V. All rights reserved.

Establishment of a Charge Reversal Derivatization Strategy to Improve the Ionization Efficiency of Limaprost and Investigation of the Fragmentation Patterns of Limaprost Derivatives Via Exclusive Neutral Loss and Survival Yield Method

NASA Astrophysics Data System (ADS)

Sun, Dong; Meng, Xiangjun; Ren, Tianming; Fawcett, John Paul; Wang, Hualu; Gu, Jingkai

2018-04-01

Sensitivity is generally an issue in bioassays of prostaglandins and their synthetic analogs due to their extremely low concentration in vivo. To improve the ionization efficiency of limaprost, an oral prostaglandin E1 (PGE1) synthetic analog, we investigated a charge reversal derivatization strategy in electrospray ionization mass spectrometry (ESI-MS). We established that the cholamine derivative exhibits much greater signal intensity in the positive-ion mode compared with limaprost in the negative ion mode. Collision-induced dissociation (CID) involved exclusive neutral mass loss and positive charge migration to form stable cationic product ions with the positive charge on the limaprost residue rather than on the modifying group. This has the effect of maintaining the efficiency and specificity of multiple reaction monitoring (MRM) and avoiding cross talk. CID fragmentation patterns of other limaprost derivatives allowed us to relate the dissociation tendency of different neutral leaving groups to an internal energy distribution scale based on the survival yield method. Knowledge of the energy involved in the production of stabilized positive ions will potentially assist the selection of suitable derivatization reagents for the analysis of a wide variety of lipid acids. [Figure not available: see fulltext.

IONIZED GAS KINEMATICS AT HIGH RESOLUTION. V. [Ne ii], MULTIPLE CLUSTERS, HIGH EFFICIENCY STAR FORMATION, AND BLUE FLOWS IN HE 2–10

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beck, Sara; Turner, Jean; Lacy, John

2015-11-20

We measured the 12.8 μm [Ne ii] line in the dwarf starburst galaxy He 2–10 with the high-resolution spectrometer TEXES on the NASA IRTF. The data cube has a diffraction-limited spatial resolution of ∼1″ and a total velocity resolution, including thermal broadening, of ∼5 km s{sup −1}. This makes it possible to compare the kinematics of individual star-forming clumps and molecular clouds in the three dimensions of space and velocity, and allows us to determine star formation efficiencies. The kinematics of the ionized gas confirm that the starburst contains multiple dense clusters. From the M/R of the clusters and themore » ≃30%–40% star formation efficiencies, the clusters are likely to be bound and long lived, like globulars. Non-gravitational features in the line profiles show how the ionized gas flows through the ambient molecular material, as well as a narrow velocity feature, which we identify with the interface of the H ii region and a cold dense clump. These data offer an unprecedented view of the interaction of embedded H ii regions with their environment.« less

Hydrazide and hydrazine reagents as reactive matrices for MALDI-MS to detect gaseous aldehydes.

PubMed

Shigeri, Yasushi; Ikeda, Shinya; Yasuda, Akikazu; Ando, Masanori; Sato, Hiroaki; Kinumi, Tomoya

2014-08-01

The reagents 19 hydrazide and 14 hydrazine were examined to function as reactive matrices for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to detect gaseous aldehydes. Among them, two hydrazide (2-hydroxybenzohydrazide and 3-hydroxy-2-naphthoic acid hydrazide) and two hydrazine reagents [2-hydrazinoquinoline and 2,4-dinitrophenylhydrazine (DNPH)] were found to react efficiently with carbonyl groups of gaseous aldehydes (formaldehyde, acetaldehyde and propionaldehyde); these are the main factors for sick building syndrome and operate as reactive matrices for MALDI-MS. Results from accurate mass measurements by JMS-S3000 Spiral-TOF suggested that protonated ion peaks corresponding to [M + H](+) from the resulting derivatives were observed in all cases with the gaseous aldehydes in an incubation, time-dependent manner. The two hydrazide and two hydrazine reagents all possessed absorbances at 337 nm (wavelength of MALDI nitrogen laser), with, significant electrical conductivity of the matrix crystal and functional groups, such as hydroxy group and amino group, being important for desorption/ionization efficiency in MALDI-MS. To our knowledge, this is the first report that gaseous molecules could be derivatized and detected directly in a single step by MALDI-MS using novel reactive matrices that were derivatizing agents with the ability to enhance desorption/ionization efficiency. Copyright © 2014 John Wiley & Sons, Ltd.

STARLIFE-An International Campaign to Study the Role of Galactic Cosmic Radiation in Astrobiological Model Systems.

PubMed

Moeller, Ralf; Raguse, Marina; Leuko, Stefan; Berger, Thomas; Hellweg, Christine Elisabeth; Fujimori, Akira; Okayasu, Ryuichi; Horneck, Gerda

2017-02-01

In-depth knowledge regarding the biological effects of the radiation field in space is required for assessing the radiation risks in space. To obtain this knowledge, a set of different astrobiological model systems has been studied within the STARLIFE radiation campaign during six irradiation campaigns (2013-2015). The STARLIFE group is an international consortium with the aim to investigate the responses of different astrobiological model systems to the different types of ionizing radiation (X-rays, γ rays, heavy ions) representing major parts of the galactic cosmic radiation spectrum. Low- and high-energy charged particle radiation experiments have been conducted at the Heavy Ion Medical Accelerator in Chiba (HIMAC) facility at the National Institute of Radiological Sciences (NIRS) in Chiba, Japan. X-rays or γ rays were used as reference radiation at the German Aerospace Center (DLR, Cologne, Germany) or Beta-Gamma-Service GmbH (BGS, Wiehl, Germany) to derive the biological efficiency of different radiation qualities. All samples were exposed under identical conditions to the same dose and qualities of ionizing radiation (i) allowing a direct comparison between the tested specimens and (ii) providing information on the impact of the space radiation environment on currently used astrobiological model organisms. Key Words: Space radiation environment-Sparsely ionizing radiation-Densely ionizing radiation-Heavy ions-Gamma radiation-Astrobiological model systems. Astrobiology 17, 101-109.

Nanostructured solid substrates for efficient laser desorption/ionization mass spectrometry (LDI-MS) of low molecular weight compounds.

PubMed

Silina, Yuliya E; Volmer, Dietrich A

2013-12-07

Analytical applications often require rapid measurement of compounds from complex sample mixtures. High-speed mass spectrometry approaches frequently utilize techniques based on direct ionization of the sample by laser irradiation, mostly by means of matrix-assisted laser desorption/ionization (MALDI). Compounds of low molecular weight are difficult to analyze by MALDI, however, because of severe interferences in the low m/z range from the organic matrix used for desorption/ionization. In recent years, surface-assisted laser desorption/ionization (SALDI) techniques have shown promise for small molecule analysis, due to the unique properties of nanostructured surfaces, in particular, the lack of a chemical background in the low m/z range and enhanced production of analyte ions by SALDI. This short review article presents a summary of the most promising recent developments in SALDI materials for MS analysis of low molecular weight analytes, with emphasis on nanostructured materials based on metals and semiconductors.

Initiation of air ionization by ultrashort laser pulses: evidence for a role of metastable-state air molecules

NASA Astrophysics Data System (ADS)

Bulgakov, A. V.; Mirza, I.; Bulgakova, N. M.; Zhukov, V. P.; Machulka, R.; Haderka, O.; Campbell, E. E. B.; Mocek, T.

2018-06-01

Transmission measurements for femtosecond laser pulses focused in air with spectral analysis of emission from the focal region have been carried out for various pulse energies and air pressures. The air breakdown threshold and pulse attenuation due to plasma absorption are evaluated and compared with calculations based on the multiphoton ionization model. The plasma absorption is found to depend on the pulse repetition rate and is considerably stronger at 1 kHz than at 1–10 Hz. This suggests that accumulation of metastable states of air molecules plays an important role in initiation of air breakdown, enhancing the ionization efficiency at high repetition rates. Possible channels of metastable-state-assisted air ionization and the role of the observed accumulation effect in laser material processing are discussed.

Ionizing Organic Compound Based Nanocomposites for Efficient Gamma-Ray Sensor

NASA Technical Reports Server (NTRS)

Singh, N. B.; Dayal, Vishall; Su, Ching-Hua; Arnold, Bradley; Choa, Fow-Sen; Kabandana, Monia G. K.; House, David

2017-01-01

Thin film and nanocrystalline materials of oxides have been very attractive choice as low cost option for gamma-ray detection and have shown great promise. Our studies on pure oxide films indicated that thickness and microstructure have pronounced effect on sensitivity. Since the interaction of gamma-ray with composites involves all three interaction processes; photoelectric effect, Compton scattering, and pair production, composites containing ionic organics have better chance for enhancing sensitivity. In the composites of ionizing organics oxidation effect of unusual oxides changes much faster and hence increases the sensitivity of radiation. In this study, we have used nickel oxide and titanium oxide in ionic organics to develop composite materials for low energy gamma-ray sensing. We prepared composites containing ethylene carbonate and evaluated the effect of commercial Cs-137 radiation source by studying current-voltage relationship at several frequencies. Radiated samples showed higher resistivity compared to as prepared composites.

Ionized gas (plasma) delivery of reactive oxygen species (ROS) into artificial cells

NASA Astrophysics Data System (ADS)

Hong, Sung-Ha; Szili, Endre J.; Jenkins, A. Toby A.; Short, Robert D.

2014-09-01

This study was designed to enhance our understanding of how reactive oxygen species (ROS), generated ex situ by ionized gas (plasma), can affect the regulation of signalling processes within cells. A model system, comprising of a suspension of phospholipid vesicles (cell mimics) encapsulating a ROS reporter, was developed to study the plasma delivery of ROS into cells. For the first time it was shown that plasma unequivocally delivers ROS into cells over a sustained period and without compromising cell membrane integrity. An important consideration in cell and biological assays is the presence of serum, which significantly reduced the transfer efficiency of ROS into the vesicles. These results are key to understanding how plasma treatments can be tailored for specific medical or biotechnology applications. Further, the phospholipid vesicle ROS reporter system may find use in other studies involving the application of free radicals in biology and medicine.

Investigation of ionizing radiation shielding effectiveness of decorative building materials used in Bangladeshi dwellings

NASA Astrophysics Data System (ADS)

Yesmin, Sabina; Sonker Barua, Bijoy; Uddin Khandaker, Mayeen; Tareque Chowdhury, Mohammed; Kamal, Masud; Rashid, M. A.; Miah, M. M. H.; Bradley, D. A.

2017-11-01

Following the rapid growing per capita income, a major portion of Bangladeshi dwellers is upgrading their non-brick houses by rod-cement-concrete materials and simultaneously curious to decorate the houses using luxurious marble stones. Present study was undertaken to investigate the gamma-ray attenuation co-efficient of decorative marble materials leading to their suitability as shielding of ionizing radiation. A number of commercial grades decorative marble stones were collected from home and abroad following their large-scale uses. A well-shielded HPGe γ-ray spectrometer combined with associated electronics was used to evaluate the mass attenuation coefficients of the studied materials for high energy photons. Some allied parameters such as half-value layer and radiation protection efficacy of the investigated marbles were calculated. The results showed that among the studied samples, the marble 'Carrara' imported from Italy is suitable to be used as radiation shielding material.

Anion-Tunable Properties and Electrochemical Performance of Functionalized Ferrocene Compounds

NASA Astrophysics Data System (ADS)

Cosimbescu, Lelia; Wei, Xiaoliang; Vijayakumar, M.; Xu, Wu; Helm, Monte L.; Burton, Sarah D.; Sorensen, Christina M.; Liu, Jun; Sprenkle, Vincent; Wang, Wei

2015-09-01

We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Finally, the electrochemical performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability.

Anion-Tunable Properties and Electrochemical Performance of Functionalized Ferrocene Compounds.

PubMed

Cosimbescu, Lelia; Wei, Xiaoliang; Vijayakumar, M; Xu, Wu; Helm, Monte L; Burton, Sarah D; Sorensen, Christina M; Liu, Jun; Sprenkle, Vincent; Wang, Wei

2015-09-16

We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Finally, the electrochemical performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cosimbescu, Lelia; Wei, Xiaoliang; Vijayakumar, M.

We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Lastly, the electrochemicalmore » performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability.« less

Mechanisms of Nanophase-Induced Desorption in LDI-MS. A Short Review

PubMed Central

Picca, Rosaria Anna; Calvano, Cosima Damiana; Cioffi, Nicola; Palmisano, Francesco

2017-01-01

Nanomaterials are frequently used in laser desorption ionization mass spectrometry (LDI-MS) as DI enhancers, providing excellent figures of merit for the analysis of low molecular weight organic molecules. In recent years, literature on this topic has benefited from several studies assessing the fundamental aspects of the ion desorption efficiency and the internal energy transfer, in the case of model analytes. Several different parameters have been investigated, including the intrinsic chemical and physical properties of the nanophase (chemical composition, thermal conductivity, photo-absorption efficiency, specific heat capacity, phase transition point, explosion threshold, etc.), along with morphological parameters such as the nanophase size, shape, and interparticle distance. Other aspects, such as the composition, roughness and defects of the substrate supporting the LDI-active nanophases, the nanophase binding affinity towards the target analyte, the role of water molecules, have been taken into account as well. Readers interested in nanoparticle based LDI-MS sub-techniques (SALDI-, SELDI-, NALDI- MS) will find here a concise overview of the recent findings in the specialized field of fundamental and mechanistic studies, shading light on the desorption ionization phenomena responsible of the outperforming MS data offered by these techniques. PMID:28368330

Liquid-chromatography thermospray mass-spectrometric study of n-acylamino dilactones and 4-butyrolactones derived from Antimycin-A

USGS Publications Warehouse

Abidi, S.L.; Ha, S.C.; Rosen, R.T.

1990-01-01

Reversed-phase high-performance liquid chromatography—thermospray mass spectrometric (HPLC—MS) characteristics of four sets of lactonic complexes (one 4-butyrolactones and three dilactone complexes) derived from antimycin A were investigated. Three types of 8-hydroxy analogues were also included in the study. Pairs of a–b structures isomeric at the 8-acyloxy ester side-chains were best separated with a high-efficiency octadecylsilica column prior to analysis by HPLC—MS. Mass spectra of the a–b pairs each with identical molecular weights exhibited virtually indistinguishable fragmentation patterns, although their relative intensities were not superimposable. In some cases, HPLC—MS of the title compounds yielded mass chromatograms showing the minor components more easily recognizable than the HPLC—UV counter parts because of the apparent higher ionization efficiency of the minor isomers and increased resolution of subcomponents in the MS system. Under the mobile phase conditions employed, analyte ionization occurred with variable degrees of gas phase ammonolysis depending upon the ammonia concentration of the buffer. Potential applicability of the on-line HPLC—MS technique for the characterization of components in mixtures of antimycin analogues and isomers is demonstrated.

Combination of electrospray ionization, atmospheric pressure photoionization and laser desorption ionization Fourier transform ion cyclotronic resonance mass spectrometry for the investigation of complex mixtures - Application to the petroleomic analysis of bio-oils.

PubMed

Hertzog, Jasmine; Carré, Vincent; Le Brech, Yann; Mackay, Colin Logan; Dufour, Anthony; Mašek, Ondřej; Aubriet, Frédéric

2017-05-29

The comprehensive description of complex mixtures such as bio-oils is required to understand and improve the different processes involved during biological, environmental or industrial operation. In this context, we have to consider how different ionization sources can improve a non-targeted approach. Thus, the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been coupled to electrospray ionization (ESI), laser desorption ionization (LDI) and atmospheric pressure photoionization (APPI) to characterize an oak pyrolysis bio-oil. Close to 90% of the all 4500 compound formulae has been attributed to C x H y O z with similar oxygen class compound distribution. Nevertheless, their relative abundance in respect with their double bound equivalent (DBE) value has evidenced significant differences depending on the ion source used. ESI has allowed compounds with low DBE but more oxygen atoms to be ionized. APPI has demonstrated the efficient ionization of less polar compounds (high DBE values and less oxygen atoms). The LDI behavior of bio-oils has been considered intermediate in terms of DBE and oxygen amounts but it has also been demonstrated that a significant part of the features are specifically detected by this ionization method. Thus, the complementarity of three different ionization sources has been successfully demonstrated for the exhaustive characterization by petroleomic approach of a complex mixture. Copyright © 2017 Elsevier B.V. All rights reserved.

Study of EHD flow generator's efficiencies utilizing pin to single ring and multi-concentric rings electrodes

NASA Astrophysics Data System (ADS)

Sumariyah; Kusminart; Hermanto, A.; Nuswantoro, P.

2016-11-01

EHD flow or ionic wind yield corona discharge is a stream coming from the ionized gas. EHD is generated by a strong electric field and its direction follows the electric field lines. In this study, the efficiency of the EHD flow generators utilizing pin-multi concentric rings electrodes (P-MRE) and the EHD pin-single ring electrode (P-SRE) have been measured. The comparison of efficiencies two types of the generator has been done. EHD flow was generated by using a high-voltage DC 0-10 KV on the electrode pin with a positive polarity and electrode ring/ multi-concentric rings of negative polarity. The efficiency was calculated by comparison between the mechanical power of flow to the electrical power that consumed. We obtained that the maximum efficiency of EHD flow generator utilizing pin-multi concentric rings electrodes was 0.54% and the maximum efficiency of EHD flow generator utilizing a pin-single ring electrode was 0.23%. Efficiency of EHD with P-MRE 2.34 times Efficiency of EHD with P-SRE

Capillary atmospheric pressure electron capture ionization (cAPECI): a highly efficient ionization method for nitroaromatic compounds.

PubMed

Derpmann, Valerie; Mueller, David; Bejan, Iustinian; Sonderfeld, Hannah; Wilberscheid, Sonja; Koppmann, Ralf; Brockmann, Klaus J; Benter, Thorsten

2014-03-01

We report on a novel method for atmospheric pressure ionization of compounds with elevated electron affinity (e.g., nitroaromatic compounds) or gas phase acidity (e.g., phenols), respectively. The method is based on the generation of thermal electrons by the photo-electric effect, followed by electron capture of oxygen when air is the gas matrix yielding O2(-) or of the analyte directly with nitrogen as matrix. Charge transfer or proton abstraction by O2(-) leads to the ionization of the analytes. The interaction of UV-light with metals is a clean method for the generation of thermal electrons at atmospheric pressure. Furthermore, only negative ions are generated and neutral radical formation is minimized, in contrast to discharge- or dopant assisted methods. Ionization takes place inside the transfer capillary of the mass spectrometer leading to comparably short transfer times of ions to the high vacuum region of the mass spectrometer. This strongly reduces ion transformation processes, resulting in mass spectra that more closely relate to the neutral analyte distribution. cAPECI is thus a soft and selective ionization method with detection limits in the pptV range. In comparison to standard ionization methods (e.g., PTR), cAPECI is superior with respect to both selectivity and achievable detection limits. cAPECI demonstrates to be a promising ionization method for applications in relevant fields as, for example, explosives detection and atmospheric chemistry.

Assessment of strontium oxide functionalized graphene nanoflakes for enhanced photocatalytic activity: A density functional theory approach

NASA Astrophysics Data System (ADS)

Divya, A.; Mathavan, T.; Asath, R. Mohamed; Archana, J.; Hayakawa, Y.; Benial, A. Milton Franklin

2016-05-01

A series of strontium oxide functionalized graphene nanoflakes were designed and their optoelectronic properties were studied for enhanced photocatalytic activity. The efficiency of designed molecules was studied using various parameters such as HOMO-LUMO energy gap, light harvesting efficiency and exciton binding energy. The computed results show that by increasing the degree of functionalization of strontium oxide leads to lowering the band gap of hydrogen terminated graphene nanoflakes. Furthermore, the study explores the role of strontium oxide functionalization in Frontier Molecular Orbitals, ionization potential, electron affinity, exciton binding energy and light harvesting efficiency of designed molecules. The infrared and Raman spectra were simulated for pure and SrO functionalized graphene nanoflakes. The electron rich and electron deficient regions which are favorable for electrophilic and nucleophilic attacks respectively were analyzed using molecular electrostatic potential surface analysis.

Coupling of metal-organic frameworks-containing monolithic capillary-based selective enrichment with matrix-assisted laser desorption ionization-time-of-flight mass spectrometry for efficient analysis of protein phosphorylation.

PubMed

Li, Daojin; Yin, Danyang; Chen, Yang; Liu, Zhen

2017-05-19

Protein phosphorylation is a major post-translational modification, which plays a vital role in cellular signaling of numerous biological processes. Mass spectrometry (MS) has been an essential tool for the analysis of protein phosphorylation, for which it is a key step to selectively enrich phosphopeptides from complex biological samples. In this study, metal-organic frameworks (MOFs)-based monolithic capillary has been successfully prepared as an effective sorbent for the selective enrichment of phosphopeptides and has been off-line coupled with matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) for efficient analysis of phosphopeptides. Using š-casein as a representative phosphoprotein, efficient phosphorylation analysis by this off-line platform was verified. Phosphorylation analysis of a nonfat milk sample was also demonstrated. Through introducing large surface areas and highly ordered pores of MOFs into monolithic column, the MOFs-based monolithic capillary exhibited several significant advantages, such as excellent selectivity toward phosphopeptides, superb tolerance to interference and simple operation procedure. Because of these highly desirable properties, the MOFs-based monolithic capillary could be a useful tool for protein phosphorylation analysis. Copyright © 2016 Elsevier B.V. All rights reserved.

Ambient diode laser desorption dielectric barrier discharge ionization mass spectrometry of nonvolatile chemicals.

PubMed

Gilbert-López, Bienvenida; Schilling, Michael; Ahlmann, Norman; Michels, Antje; Hayen, Heiko; Molina-Díaz, Antonio; García-Reyes, Juan F; Franzke, Joachim

2013-03-19

In this work, the combined use of desorption by a continuous wave near-infrared diode laser and ionization by a dielectric barrier discharge-based probe (laser desorption dielectric barrier discharge ionization mass spectrometry (LD-DBDI-MS)) is presented as an ambient ionization method for the mass spectrometric detection of nonvolatile chemicals on surfaces. A separation of desorption and ionization processes could be verified. The use of the diode laser is motivated by its low cost, ease of use, and small size. To achieve an efficient desorption, the glass substrates are coated at the back side with a black point (target point, where the sample is deposited) in order to absorb the energy offered by the diode laser radiation. Subsequent ionization is accomplished by a helium plasmajet generated in the dielectric barrier discharge source. Examples on the application of this approach are shown in both positive and negative ionization modes. A wide variety of multiclass species with low vapor pressure were tested including pesticides, pharmaceuticals and explosives (reserpine, roxithromycin, propazine, prochloraz, spinosad, ampicillin, dicloxacillin, enrofloxacin, tetracycline, oxytetracycline, erythromycin, spinosad, cyclo-1,3,5,7-tetramethylene tetranitrate (HMX), and cyclo-1,3,5-trimethylene trinitramine (RDX)). A comparative evaluation revealed that the use of the laser is advantageous, compared to just heating the substrate surface.

Enhancing Sensitivity of Liquid Chromatography-Mass Spectrometry of Peptides and Proteins Using Supercharging Agents.

PubMed

Nshanian, Michael; Lakshmanan, Rajeswari; Chen, Hao; Ogorzalek Loo, Rachel R; Loo, Joseph A

2018-04-01

Trifluoroacetic acid (TFA) is often used as a mobile phase modifier to enhance reversed phase chromatographic performance. TFA adjusts solution pH and is an ion-pairing agent, but it is not typically suitable for electrospray ionization-mass spectrometry (ESI-MS) and liquid chromatography/MS (LC/MS) because of its significant signal suppression. Supercharging agents elevate peptide and protein charge states in ESI, increasing tandem MS (MS/MS) efficiency. Here, LC/MS protein supercharging was effected by adding agents to LC mobile phase solvents. Significantly, the ionization suppression generally observed with TFA was, for the most part, rescued by supercharging agents, with improved separation efficiency (higher number of theoretical plates) and lowered detection limits.

A theoretical analysis of vacuum arc thruster performance

NASA Technical Reports Server (NTRS)

Polk, James E.; Sekerak, Mike; Ziemer, John K.; Schein, Jochen; Qi, Niansheng; Binder, Robert; Anders, Andre

2001-01-01

In vacuum arc discharges the current is conducted through vapor evaporated from the cathode surface. In these devices very dense, highly ionized plasmas can be created from any metallic or conducting solid used as the cathode. This paper describes theoretical models of performance for several thruster configurations which use vacuum arc plasma sources. This analysis suggests that thrusters using vacuum arc sources can be operated efficiently with a range of propellant options that gives great flexibility in specific impulse. In addition, the efficiency of plasma production in these devices appears to be largely independent of scale because the metal vapor is ionized within a few microns of the cathode electron emission sites, so this approach is well-suited for micropropulsion.

Predicting ESI/MS Signal Change for Anions in Different Solvents.

PubMed

Kruve, Anneli; Kaupmees, Karl

2017-05-02

LC/ESI/MS is a technique widely used for qualitative and quantitative analysis in various fields. However, quantification is currently possible only for compounds for which the standard substances are available, as the ionization efficiency of different compounds in ESI source differs by orders of magnitude. In this paper we present an approach for quantitative LC/ESI/MS analysis without standard substances. This approach relies on accurately predicting the ionization efficiencies in ESI source based on a model, which uses physicochemical parameters of analytes. Furthermore, the model has been made transferable between different mobile phases and instrument setups by using a suitable set of calibration compounds. This approach has been validated both in flow injection and chromatographic mode with gradient elution.

Intense laser pulse propagation in ionizing gases

NASA Astrophysics Data System (ADS)

Bian, Zhigang

2003-10-01

There have been considerable technological advances in the development of high intensity, short pulse lasers. However, high intensity laser pulses are subject to various laser-plasma instabilities. In this thesis, a theory is developed to study the scattering instability that occurs when a laser pulse propagates through and ionizes a gas. The instability is due to the intensity dependence of the ionization rate, which leads to a transversely structured free electron density. The instability is convective in the frame of laser pulse, but can have a relatively short growth length scaling as Lg˜k0/k2p where k0 is the laser wave number, k2p=w2p/c 2 and op is the plasma frequency. The most unstable perturbations correspond to a scattering angle for which the transverse wave number is around the plasma wave number, k p. The scattered light is frequency upshifted. The comparison between simple analytic theory and numerical simulation shows good agreement. Instabilities can drastically change the shape of the laser pulse and reduce the propagation distance of the laser pulse. Therefore, we change the propagation conditions and reduce the laser-plasma interaction possibilities in applications which require an interaction length well in excess of the Rayleigh length of the laser beam. One of the methods is to use a capillary to propagate the laser pulse. We studied the propagation of short pulses in a glass capillary. The propagation is simulated using the code WAKE, which has been modified to treat the case in which the simulation boundary is the wall of a capillary. Parameters that were examined include transmission efficiency of the waveguides as a function of gas pressure, laser intensity, and waveguide length, which is up to 40 Rayleigh lengths. The transmission efficiency decreases with waveguide length due to energy loss through the side-walls of the capillary. The loss increases with gas pressure due to ionization of the gas and scattering of the radiation. The intensity on the inner wall of the capillary is monitored to assure realistic simulations, consistent with optical breakdown of the waveguide material. Generally speaking the intensity on the wall increases with gas pressure due to the scattering of the lowest order capillary mode. Finally, the high order harmonic generation (HHG) in a capillary is investigated. The phase matching condition is studied to increase the conversion efficiency for high order harmonics generation. The phase matching occurs as a balance of the dispersion of the neutral gas, plasma and the waveguide.

Epoch of Reionization : An Investigation of the Semi-Analytic 21CMMC Code

NASA Astrophysics Data System (ADS)

Miller, Michelle

2018-01-01

After the Big Bang the universe was filled with neutral hydrogen that began to cool and collapse into the first structures. These first stars and galaxies began to emit radiation that eventually ionized all of the neutral hydrogen in the universe. 21CMMC is a semi-numerical code that takes simulated boxes of this ionized universe from another code called 21cmFAST. Mock measurements are taken from the simulated boxes in 21cmFAST. Those measurements are thrown into 21CMMC and help us determine three major parameters of this simulated universe: virial temperature, mean free path, and ionization efficiency. My project tests the robustness of 21CMMC on universe simulations other than 21cmFAST to see whether 21CMMC can properly reconstruct early universe parameters given a mock “measurement” in the form of power spectra. We determine that while two of the three EoR parameters (Virial Temperature and Efficiency) have some reconstructability, the mean free path parameter in the code is the least robust. This requires development of the 21CMMC code.

Cellular Response to Ionizing Radiation: A MicroRNA Story

PubMed Central

Halimi, Mohammad; Asghari, S. Mohsen; Sariri, Reyhaneh; Moslemi, Dariush; Parsian, Hadi

2012-01-01

MicroRNAs (miRNAs) represent a class of small non-coding RNA molecules that regulate gene expression at the post-transcriptional level. They play a crucial role in diverse cellular pathways. Ionizing radiation (IR) is one of the most important treatment protocols for patients that suffer from cancer and affects directly or indirectly cellular integration. Recently it has been discovered that microRNA-mediated gene regulation interferes with radio-related pathways in ionizing radiation. Here, we review the recent discoveries about miRNAs in cellular response to IR. Thoroughly understanding the mechanism of miRNAs in radiation response, it will be possible to design new strategies for improving radiotherapy efficiency and ultimately cancer treatment. PMID:24551775

Scattering of hydrogen, nitrogen and water ions from micro pore optic plates for application in spaceborne plasma instrumentation

NASA Astrophysics Data System (ADS)

Stude, Joan; Wieser, Martin; Barabash, Stas

2016-10-01

Time-of-flight mass spectrometers for upcoming space missions into enhanced radiation environments need to be small, light weight and energy efficient. Time-of-flight systems using surface interactions as start-event generation can be smaller than foil-type instruments. Start surfaces for such applications need to provide narrow angular scattering, high ionization yields and high secondary electron emissions to be effective. We measured the angular scattering, energy distribution and positive ionization yield of micro pore optics for incident hydrogen, nitrogen and water ions at 2 keV. Positive ionization yields of 2% for H+ , 0.5% for N+ and 0.2% for H2O+ were detected.

Resonance Ionization Mass Spectrometry System for Measurement of Environmental Samples

NASA Astrophysics Data System (ADS)

Pibida, L.; McMahon, C. A.; Nörtershäuser, W.; Bushaw, B. A.

2002-10-01

A resonance ionization mass spectrometry (RIMS) system has been developed at the National Institute of Standards and Technology (NIST) for sensitive and selective determination of radio-cesium in the environment. The overall efficiency was determined to be 4×10-7 with a combined (laser and mass spectrometer) selectivity of 108 for both 135Cs and 137Cs with respect to 133Cs. RIMS isotopic ratio measurements of 135Cs/ 137Cs were performed on a nuclear fuel burn-up sample and compared to measurements on a similar system at Pacific Northwest National Laboratory (PNNL) and to conventional thermal ionization mass spectrometry (TIMS). Results of preliminary RIMS investigations on a freshwater lake sediment sample are also discussed.

Feasibility of atmospheric pressure desorption/ionization on silicon mass spectrometry in analysis of drugs.

PubMed

Huikko, K; Ostman, P; Sauber, C; Mandel, F; Grigoras, K; Franssila, S; Kotiaho, T; Kostiainen, R

2003-01-01

The feasibility of atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS) for drug analysis was investigated. It was observed that only compounds with relative high proton affinity are efficiently ionized under AP-DIOS conditions. The limits of detection (LODs) achieved in MS mode with midazolam, propranolol, and angiotensin II were 80 fmol, 20 pmol, and 1 pmol, respectively. In MS/MS mode the LODs for midazolam and propranolol were 10 fmol and 5 pmol, respectively. The good linearity (r(2) > 0.991), linear dynamic range of 3 orders of magnitude, and reasonable repeatability showed that the method is suitable for quantitative analysis. Copyright 2003 John Wiley & Sons, Ltd.

Evidence for impact ionization in vanadium dioxide

DOE PAGES

Holleman, Joshua; Bishop, Michael M.; Garcia, Carlos; ...

2016-10-17

Pump-probe optical spectroscopy was used to investigate charge carrier multiplication via impact ionization in the M 1 insulating phase of VO 2. By comparing the transient reflectivities of the film when pumped at less than and then more than twice the band-gap energy, we observed an enhancement of the ultrafast response with the higher energy pump color while the film was still transiently in the insulating phase. We additionally identified multiple timescales within the charge dynamics and analyzed how these changed when the pump and probe wavelengths were varied. This experiment provided evidence that impact ionization acts efficiently as amore » carrier multiplication process in this prototypical strongly-correlated insulator.« less

Identification of Microalgae by Laser Desorption/Ionization Mass Spectrometry Coupled with Multiple Nanomatrices.

PubMed

Peng, Lung-Hsiang; Unnikrishnan, Binesh; Shih, Chi-Yu; Hsiung, Tung-Ming; Chang, Jeng; Hsu, Pang-Hung; Chiu, Tai-Chia; Huang, Chih-Ching

2016-04-01

In this study, we demonstrate a simple method to identify microalgae by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using three different substrates: HgSe, HgTe, and HgTeSe nanostructures. The fragmentation/ionization processes of complex molecules in algae varied according to the heat absorption and transfer efficiency of the nanostructured matrices (NMs). Therefore, the mass spectra obtained for microalgae showed different patterns of m/z values for different NMs. The spectra contained both significant and nonsignificant peaks. Constructing a Venn diagram with the significant peaks obtained for algae when using HgSe, HgTe, and HgTeSe NMs in m/z ratio range 100-1000, a unique relationship among the three sets of values was obtained. This unique relationship of sets is different for each species of microalgae. Therefore, by observing the particular relationship of sets, we successfully identified different algae such as Isochrysis galbana, Emiliania huxleyi, Thalassiosira weissflogii, Nannochloris sp., Skeletonema cf. costatum, and Tetraselmis chui. This simple and cost-effective SALDI-MS analysis method coupled with multi-nanomaterials as substrates may be extended to identify other microalgae and microorganisms in real samples. Graphical Abstract Identification of microalgae by surface-assisted laser desorption/ionization mass spectrometry coupled with three different mercury-based nanosubstrates.

Characteristics of soft x-ray spectra from ultra-fast micro-capillary discharge plasmas

NASA Astrophysics Data System (ADS)

Li, Jing; Avaria, Gonzalo; Shlyaptsev, Vyacheslav; Tomasel, Fernando; Grisham, Michael; Dawson, Quincy; Rocca, Jorge; NSF CenterExtreme Ultraviolet Science; Technology Collaboration

2013-10-01

The efficient generation of high aspect ratio (e.g. 300:1) plasma columns ionized to very high degrees of ionization (e.g. Ni-like Xenon) by an ultrafast current pulses of moderate amplitude in micro-capillary channels is of interest for fundamental plasma studies and for applications such as the generation of discharge-pumped soft x-ray lasers. Spectra and simulations for plasmas generated in 500 um alumina capillary discharges driven by 35-40 kA current pulses with 4 ns rise time were obtained in Xenon and Neon discharges. The first shows the presence of lines corresponding to ionization stages up to Fe-like Xe. The latter show that Al impurities from the walls and Si (from injected SiH4) are ionized to the H-like and He-like stages. He-like spectra containing the resonance line significantly broaden by opacity, the intercombination line, and Li-like satellites are analyzed and modeled. For Xenon discharges, the spectral lines from the Ni-like transitions the 3d94d(3/2, 3/2)J=0 to the 3d94p(5/2, 3/2)J=1 and to 3d94p(3/2, 1/2)J=1 are observed at gas pressures up to 2.0 Torr. Work supported by NSF Award PHY-1004295.

Laser desorption ionization of small molecules assisted by tungsten oxide and rhenium oxide particles.

PubMed

Bernier, Matthew C; Wysocki, Vicki H; Dagan, Shai

2015-07-01

Inorganic metal oxides have shown potential as matrices for assisting in laser desorption ionization with advantages over the aromatic acids typically used. Rhenium and tungsten oxides are attractive options due to their high work functions and relative chemical inertness. In this work, it is shown that ReO3 and WO3 , in microparticle (μP) powder forms, can efficiently facilitate ionization of various types of small molecules and provide minimized background contamination at analyte concentrations below 1 ng/µL. This study shows that untreated inorganic WO3 and ReO3 particles are valid matrix options for detection of protonatable, radical, and precharged species under laser desorption ionization. Qualitatively, the WO3 μP showed improved detection of apigenin, sodiated glucose, and precharged analyte choline, while the ReO3 μP allowed better detection of protonated cocaine, quinuclidine, ametryn, and radical ions of polyaromatic hydrocarbons at detection levels as low as 50 pg/µL. For thermometer ion survival yield experiments, it was also shown that the ReO3 powder was significantly softer than α-cyano-4-hydroxycinnaminic acid. Furthermore, it provided higher intensities of cocaine and polyaromatic hydrocarbons, at laser flux values equal to those used with α-cyano-4-hydroxycinnaminic acid. Copyright © 2015 John Wiley & Sons, Ltd.

GAS-PHASE SYNTHESIS OF PRECURSORS OF INTERSTELLAR GLYCINE: A COMPUTATIONAL STUDY OF THE REACTIONS OF ACETIC ACID WITH HYDROXYLAMINE AND ITS IONIZED AND PROTONATED DERIVATIVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barrientos, Carmen; Redondo, Pilar; Largo, Laura

2012-04-01

A computational study of the reactions of hydroxylamine and its ionized and protonated derivatives with acetic acid is provided. The reaction of neutral hydroxylamine with acetic acid, despite being clearly exothermic, involves a very large energy barrier. The reaction of ionized hydroxylamine with acetic acid is also clearly exothermic, but again a significant energy barrier is found (around 24 kcal mol{sup -1} at the CCSD(T) level). The reaction of the most stable protonated isomer of hydroxylamine, NH{sub 3}OH{sup +}, with acetic acid also involves a high barrier (more than 27 kcal mol{sup -1} at the CCSD(T) level). Only the highermore » energy isomer, NH{sub 2}OH{sup +}{sub 2}, leads to a sensibly lower energy barrier (about 2.3 kcal mol{sup -1} at the CCSD(T) level). Nevertheless, an estimate of the reaction coefficient at low temperatures such as those reigning in the interstellar medium gives very low values. Therefore, it seems that precursors of interstellar glycine could not be efficiently produced from the reactions of hydroxylamine-derived ions with acetic acid.« less

UV + V UV double-resonance studies of autoionizing Rydberg states of the hydroxyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Green, Amy M.; Liu, Fang; Lester, Marsha I., E-mail: milester@sas.upenn.edu

2016-05-14

The hydroxyl radical (OH) is a key oxidant in atmospheric and combustion chemistry. Recently, a sensitive and state-selective ionization method has been developed for detection of the OH radical that utilizes UV excitation on the A{sup 2}Σ{sup +}–X{sup 2}Π transition followed by fixed 118 nm vacuum ultraviolet (VUV) radiation to access autoionizing Rydberg states [J. M. Beames et al., J. Chem. Phys. 134, 241102 (2011)]. The present study uses tunable VUV radiation generated by four-wave mixing to examine the origin of the enhanced ionization efficiency observed for OH radicals prepared in specific A{sup 2}Σ{sup +} intermediate levels. The enhancement ismore » shown to arise from resonant excitation to distinct rotational and fine structure levels of two newly identified {sup 2}Π Rydberg states with an A{sup 3}Π cationic core and a 3d electron followed by ionization. Spectroscopic constants are derived and effects due to uncoupling of the Rydberg electron are revealed for the OH {sup 2}Π Rydberg states. The linewidths indicate a Rydberg state lifetime due to autoionization on the order of a picosecond.« less

Laser-induced dissociation processes of protonated glucose: dehydration reactions vs cross-ring dissociation

NASA Astrophysics Data System (ADS)

Dyakov, Y. A.; Kazaryan, M. A.; Golubkov, M. G.; Gubanova, D. P.; Bulychev, N. A.; Kazaryan, S. M.

2018-04-01

Studying the processes occurring in biological systems under irradiation is critically important for understanding the principles of working of biological systems. One of the main problems, which stimulate interest to the processes of photo-induced excitation and ionization of biomolecules, is the necessity of their identification by various mass spectrometry (MS) methods. While simple analysis of small molecules became a standard MS technique long time ago, recognition of large molecules, especially carbohydrates, is still a difficult problem, and requires sophisticated techniques and complicated computer analysis. Due to the large variety of substances in the samples, as far as the complexity of the processes occurring after excitation/ionization of the molecules, the recognition efficiency of MS technique in terms of carbohydrates is still not high enough. Additional theoretical and experimental analysis of ionization and dissociation processes in various kinds of polysaccharides, beginning from the simplest ones, is necessary. In our work, we extent previous theoretical and experimental studies of saccharides, and concentrate our attention to protonated glucose. In this article we paid the most attention to the cross-ring dissociation and water loss reactions due to their importance for identification of various isomers of hydrocarbon molecules (for example, distinguish α- and β-glucose).

Research on the degradation mechanism of dimethyl phthalate in drinking water by strong ionization discharge

NASA Astrophysics Data System (ADS)

Hong, ZHAO; Chengwu, YI; Rongjie, YI; Huijuan, WANG; Lanlan, YIN; I, N. MUHAMMAD; Zhongfei, MA

2018-03-01

The degradation mechanism of dimethyl phthalate (DMP) in the drinking water was investigated using strong ionization discharge technology in this study. Under the optimized condition, the degradation efficiency of DMP in drinking water was up to 93% in 60 min. A series of analytical techniques including high-performance liquid chromatography, liquid chromatography mass spectrometry, total organic carbon analyzer and ultraviolet-visible spectroscopy were used in the study. It was found that a high concentration of ozone (O3) produced by dielectric barrier discharge reactor was up to 74.4 mg l-1 within 60 min. Tert-butanol, isopropyl alcohol, carbonate ions ({{{{CO}}}3}2-) and bicarbonate ions ({{{{HCO}}}3}-) was added to the sample solution to indirectly prove the presence and effect of hydroxyl radicals (·OH). These analytical findings indicate that mono-methyl phthalate, phthalic acid (PA) and methyl ester PA were detected as the major intermediates in the process of DMP degradation. Finally, DMP and all products were mineralized into carbon dioxide (CO2) and water (H2O) ultimately. Based on these analysis results, the degradation pathway of DMP by strong ionization discharge technology were proposed.

Evolution of magnetic fields in collapsing star-forming clouds under different environments

NASA Astrophysics Data System (ADS)

Higuchi, Koki; Machida, Masahiro N.; Susa, Hajime

2018-04-01

In nearby star-forming clouds, amplification and dissipation of the magnetic field are known to play crucial roles in the star-formation process. The star-forming environment varies from place to place and era to era in galaxies. In this study, amplification and dissipation of magnetic fields in star-forming clouds are investigated under different environments using magnetohydrodynamics (MHD) simulations. We consider various star-forming environments in combination with the metallicity and the ionization strength, and prepare prestellar clouds having two different mass-to-flux ratios. We calculate the cloud collapse until protostar formation using ideal and non-ideal (inclusion and exclusion of ohmic dissipation and ambipolar diffusion) MHD calculations to investigate the evolution of the magnetic field. We perform 288 runs in total and show the diversity of the density range within which the magnetic field effectively dissipates, depending on the environment. In addition, the dominant dissipation process (Ohmic dissipation or ambipolar diffusion) is shown to strongly depend on the star-forming environment. Especially, for the primordial case, magnetic field rarely dissipates without ionization source, while it efficiently dissipates when very weak ionization sources exist in the surrounding environment. The results of this study help to clarify star formation in various environments.

Flagged uniform particle splitting for variance reduction in proton and carbon ion track-structure simulations

NASA Astrophysics Data System (ADS)

Ramos-Méndez, José; Schuemann, Jan; Incerti, Sebastien; Paganetti, Harald; Schulte, Reinhard; Faddegon, Bruce

2017-08-01

Flagged uniform particle splitting was implemented with two methods to improve the computational efficiency of Monte Carlo track structure simulations with TOPAS-nBio by enhancing the production of secondary electrons in ionization events. In method 1 the Geant4 kernel was modified. In method 2 Geant4 was not modified. In both methods a unique flag number assigned to each new split electron was inherited by its progeny, permitting reclassification of the split events as if produced by independent histories. Computational efficiency and accuracy were evaluated for simulations of 0.5-20 MeV protons and 1-20 MeV u-1 carbon ions for three endpoints: (1) mean of the ionization cluster size distribution, (2) mean number of DNA single-strand breaks (SSBs) and double-strand breaks (DSBs) classified with DBSCAN, and (3) mean number of SSBs and DSBs classified with a geometry-based algorithm. For endpoint (1), simulation efficiency was 3 times lower when splitting electrons generated by direct ionization events of primary particles than when splitting electrons generated by the first ionization events of secondary electrons. The latter technique was selected for further investigation. The following results are for method 2, with relative efficiencies about 4.5 times lower for method 1. For endpoint (1), relative efficiency at 128 split electrons approached maximum, increasing with energy from 47.2  ±  0.2 to 66.9  ±  0.2 for protons, decreasing with energy from 51.3  ±  0.4 to 41.7  ±  0.2 for carbon. For endpoint (2), relative efficiency increased with energy, from 20.7  ±  0.1 to 50.2  ±  0.3 for protons, 15.6  ±  0.1 to 20.2  ±  0.1 for carbon. For endpoint (3) relative efficiency increased with energy, from 31.0  ±  0.2 to 58.2  ±  0.4 for protons, 23.9  ±  0.1 to 26.2  ±  0.2 for carbon. Simulation results with and without splitting agreed within 1% (2 standard deviations) for endpoints (1) and (2), within 2% (1 standard deviation) for endpoint (3). In conclusion, standard particle splitting variance reduction techniques can be successfully implemented in Monte Carlo track structure codes.

Specific interaction between negative atmospheric ions and organic compounds in atmospheric pressure corona discharge ionization mass spectrometry.

PubMed

Sekimoto, Kanako; Sakai, Mami; Takayama, Mitsuo

2012-06-01

The interaction between negative atmospheric ions and various types of organic compounds were investigated using atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. Atmospheric negative ions such as O(2)(-), HCO(3)(-), COO(-)(COOH), NO(2)(-), NO(3)(-), and NO(3)(-)(HNO(3)) having different proton affinities served as the reactant ions for analyte ionization in APCDI in negative-ion mode. The individual atmospheric ions specifically ionized aliphatic and aromatic compounds with various functional groups as atmospheric ion adducts and deprotonated analytes. The formation of the atmospheric ion adducts under certain discharge conditions is most likely attributable to the affinity between the analyte and atmospheric ion and the concentration of the atmospheric ion produced under these conditions. The deprotonated analytes, in contrast, were generated from the adducts of the atmospheric ions with higher proton affinity attributable to efficient proton abstraction from the analyte by the atmospheric ion.

Detection limits of organic compounds achievable with intense, short-pulse lasers.

PubMed

Miles, Jordan; De Camillis, Simone; Alexander, Grace; Hamilton, Kathryn; Kelly, Thomas J; Costello, John T; Zepf, Matthew; Williams, Ian D; Greenwood, Jason B

2015-06-21

Many organic molecules have strong absorption bands which can be accessed by ultraviolet short pulse lasers to produce efficient ionization. This resonant multiphoton ionization scheme has already been exploited as an ionization source in time-of-flight mass spectrometers used for environmental trace analysis. In the present work we quantify the ultimate potential of this technique by measuring absolute ion yields produced from the interaction of 267 nm femtosecond laser pulses with the organic molecules indole and toluene, and gases Xe, N2 and O2. Using multiphoton ionization cross sections extracted from these results, we show that the laser pulse parameters required for real-time detection of aromatic molecules at concentrations of one part per trillion in air and a limit of detection of a few attomoles are achievable with presently available commercial laser systems. The potential applications for the analysis of human breath, blood and tissue samples are discussed.

Detection of polychlorinated biphenyls in transformer oils in Vietnam by multiphoton ionization mass spectrometry using a far-ultraviolet femtosecond laser as an ionization source.

PubMed

Duong, Vu Thi Thuy; Duong, Vu; Lien, Nghiem Thi Ha; Imasaka, Tomoko; Tang, Yuanyuan; Shibuta, Shinpei; Hamachi, Akifumi; Hoa, Do Quang; Imasaka, Totaro

2016-03-01

Polychlorinated biphenyls (PCBs) in transformer and food oils were measured using gas chromatography combined with multiphoton ionization mass spectroscopy. An ultrashort laser pulse emitting in the far-ultraviolet region was utilized for efficient ionization of the analytes. Numerous signal peaks were clearly observed for a standard sample mixture of PCBs when the third and fourth harmonic emissions (267 and 200nm) of a femtosecond Ti:sapphire laser (800nm) were employed. The signal intensities were found to be greater when measured at 200nm compared with those measured at 267nm, providing lower detection limits especially for highly chlorinated PCBs at shorter wavelengths. After simple pretreatment using disposable columns, PCB congeners were measured and found to be present in the transformer oils used in Vietnam. Copyright © 2015 Elsevier B.V. All rights reserved.

Effects of ionizing radiation in ginkgo and guarana [rapid communication

NASA Astrophysics Data System (ADS)

Rabelo Soriani, Renata; Cristina Satomi, Lucilia; Pinto, Terezinha de Jesus A.

2005-07-01

Raw plant materials normally carry high bioburden due to their origin, offering potential hazards to consumers. The use of decontamination processes is therefore an important step towards the consumer safety and therapeutical efficiency. Several authors have reported the treatment of medicinal herbs with ionizing radiation. This work evaluated the effects of different radiation doses on the microbial burden and chemical constituents of ginkgo ( Ginkgo biloba L.) and guaraná ( Paullinia cupana H.B.K.).

Efficient approach for the detection and identification of new androgenic metabolites by applying SRM GC-CI-MS/MS: a methandienone case study.

PubMed

Polet, Michael; Van Gansbeke, Wim; Van Eenoo, Peter; Deventer, Koen

2016-07-01

Identification of anabolic androgenic steroids (AAS) is a vital issue in doping control and toxicology, and searching for metabolites with longer detection times remains an important task. Recently, a gas chromatography chemical ionization triple quadrupole mass spectrometry (GC-CI-MS/MS) method was introduced, and CI, in comparison with electron ionization (EI), proved to be capable of increasing the sensitivity significantly. In addition, correlations between AAS structure and fragmentation behavior could be revealed. This enables the search for previously unknown but expected metabolites by selection of their predicted transitions. The combination of both factors allows the setup of an efficient approach to search for new metabolites. The approach uses selected reaction monitoring which is inherently more sensitive than full scan or precursor ion scan. Additionally, structural information obtained from the structure specific CI fragmentation pattern facilitates metabolite identification. The procedure was demonstrated by a methandienone case study. Its metabolites have been studied extensively in the past, and this allowed an adequate evaluation of the efficiency of the approach. Thirty three metabolites were detected, including all relevant previously discovered metabolites. In our study, the previously reported long-term metabolite (18-nor-17β-hydroxymethyl,17α-methyl-androst-1,4,13-trien-3-one) could be detected up to 26 days by using GC-CI-MS/MS. The study proves the validity of the approach to search for metabolites of new synthetic AAS and new long-term metabolites of less studied AAS and illustrates the increase in sensitivity by using CI. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Studies of ionizing radiation shielding effectiveness of silica-based commercial glasses used in Bangladeshi dwellings

NASA Astrophysics Data System (ADS)

Yasmin, Sabina; Barua, Bijoy Sonker; Khandaker, Mayeen Uddin; Chowdhury, Faruque-Uz-Zaman; Rashid, Md. Abdur; Bradley, David A.; Olatunji, Michael Adekunle; Kamal, Masud

2018-06-01

Following the rapid growing economy, the Bangladeshi dwellers are replacing their traditional (mud-, bamboo-, and wood-based) houses to modern multistoried buildings, where different types of glasses are being used as decorative as well as structural materials due to their various advantageous properties. In this study, we inquire the protective and dosimetric capability of commercial glasses for ionizing radiation. Four branded glass samples (PHP-Bangladesh, Osmania-Bangladesh, Nasir-Bangladesh, and Rider-China) of same thickness and color but different elemental weight fractions were analyzed for shielding and dosimetric properties. The chemical composition of the studied material was evaluated by EDX technique. A well-shielded HPGe γ-ray spectrometer combined with associated electronics was used to evaluate the attenuation coefficients of the studied materials for 59 keV, 661 keV, 1173 keV and 1332 keV photon energies. A number of shielding parameters- half value layer (HVL), radiation protection efficiency (RPE) and effective atomic number (Zeff) were also evaluated. The data were compared with the available literature (where applicable) to understand its shielding capability relative to the standard materials such as lead. Among the studied brands, Rider (China) shows relatively better indices to be used as ionizing radiation shielding material. The obtained, Zeff of the studied glass samples showed comparable values to the TLD-200 dosimeter, thus considered suitable for environmental radiation monitoring purposes.

Saturation current and collection efficiency for ionization chambers in pulsed beams.

PubMed

DeBlois, F; Zankowski, C; Podgorsak, E B

2000-05-01

Saturation currents and collection efficiencies in ionization chambers exposed to pulsed megavoltage photon and electron beams are determined assuming a linear relationship between 1/I and 1/V in the extreme near-saturation region, with I and V the chamber current and polarizing voltage, respectively. Careful measurements of chamber current against polarizing voltage in the extreme near-saturation region reveal a current rising faster than that predicted by the linear relationship. This excess current combined with conventional "two-voltage" technique for determination of collection efficiency may result in an up to 0.7% overestimate of the saturation current for standard radiation field sizes of 10X10 cm2. The measured excess current is attributed to charge multiplication in the chamber air volume and to radiation-induced conductivity in the stem of the chamber (stem effect). These effects may be accounted for by an exponential term used in conjunction with Boag's equation for collection efficiency in pulsed beams. The semiempirical model follows the experimental data well and accounts for both the charge recombination as well as for the charge multiplication effects and the chamber stem effect.

A Virtual Mixture Approach to the Study of Multistate Equilibrium: Application to Constant pH Simulation in Explicit Water

PubMed Central

Wu, Xiongwu; Brooks, Bernard R.

2015-01-01

Chemical and thermodynamic equilibrium of multiple states is a fundamental phenomenon in biology systems and has been the focus of many experimental and computational studies. This work presents a simulation method to directly study the equilibrium of multiple states. This method constructs a virtual mixture of multiple states (VMMS) to sample the conformational space of all chemical states simultaneously. The VMMS system consists of multiple subsystems, one for each state. The subsystem contains a solute and a solvent environment. The solute molecules in all subsystems share the same conformation but have their own solvent environments. Transition between states is implicated by the change of their molar fractions. Simulation of a VMMS system allows efficient calculation of relative free energies of all states, which in turn determine their equilibrium molar fractions. For systems with a large number of state transition sites, an implicit site approximation is introduced to minimize the cost of simulation. A direct application of the VMMS method is for constant pH simulation to study protonation equilibrium. Applying the VMMS method to a heptapeptide of 3 ionizable residues, we calculated the pKas of those residues both with all explicit states and with implicit sites and obtained consistent results. For mouse epidermal growth factor of 9 ionizable groups, our VMMS simulations with implicit sites produced pKas of all 9 ionizable groups and the results agree qualitatively with NMR measurement. This example demonstrates the VMMS method can be applied to systems of a large number of ionizable groups and the computational cost scales linearly with the number of ionizable groups. For one of the most challenging systems in constant pH calculation, SNase Δ+PHS/V66K, our VMMS simulation shows that it is the state-dependent water penetration that causes the large deviation in lysine66’s pKa. PMID:26506245

A Virtual Mixture Approach to the Study of Multistate Equilibrium: Application to Constant pH Simulation in Explicit Water.

PubMed

Wu, Xiongwu; Brooks, Bernard R

2015-10-01

Chemical and thermodynamic equilibrium of multiple states is a fundamental phenomenon in biology systems and has been the focus of many experimental and computational studies. This work presents a simulation method to directly study the equilibrium of multiple states. This method constructs a virtual mixture of multiple states (VMMS) to sample the conformational space of all chemical states simultaneously. The VMMS system consists of multiple subsystems, one for each state. The subsystem contains a solute and a solvent environment. The solute molecules in all subsystems share the same conformation but have their own solvent environments. Transition between states is implicated by the change of their molar fractions. Simulation of a VMMS system allows efficient calculation of relative free energies of all states, which in turn determine their equilibrium molar fractions. For systems with a large number of state transition sites, an implicit site approximation is introduced to minimize the cost of simulation. A direct application of the VMMS method is for constant pH simulation to study protonation equilibrium. Applying the VMMS method to a heptapeptide of 3 ionizable residues, we calculated the pKas of those residues both with all explicit states and with implicit sites and obtained consistent results. For mouse epidermal growth factor of 9 ionizable groups, our VMMS simulations with implicit sites produced pKas of all 9 ionizable groups and the results agree qualitatively with NMR measurement. This example demonstrates the VMMS method can be applied to systems of a large number of ionizable groups and the computational cost scales linearly with the number of ionizable groups. For one of the most challenging systems in constant pH calculation, SNase Δ+PHS/V66K, our VMMS simulation shows that it is the state-dependent water penetration that causes the large deviation in lysine66's pKa.

Enhanced adsorption of ionizable antibiotics on activated carbon fiber under electrochemical assistance in continuous-flow modes.

PubMed

Wang, Sitan; Li, Xiaona; Zhao, Huimin; Quan, Xie; Chen, Shuo; Yu, Hongtao

2018-05-01

Ionizable antibiotics have attracted serious concerns because of their variable dissociation forms and thereby rendering unique toxicity and microorganism resistance. Developing an efficient and environmentally friendly method for removing these micropollutants from environmental media remains very challenging. Here, electro-assisted adsorption onto activated carbon fiber in continuous-flow mode was used to remove three ionizable antibiotics, sulfadimethoxine (SDM), ciprofloxacin (CIP), and clarithromycin (CLA), from water. Benefiting from strengthened electrostatic interactions, the adsorption capacities for the target antibiotics (10 mg/L) in flow mode (70.9-202.2 mg/g) increased by ∼5 times under a potential of 1.0 V (SDM) or -1.0 V (CIP and CLA) relative to those of open circuit (OC) adsorption. Meanwhile, effluent concentration decreased from >100 μg/L to 9.6 μg/L with removal efficiency increasing from 99.0% to 99.9%. Moreover, high recovery efficiency of ACF up to 96.35 ± 0.65% was achieved by imposing a reverse potential (-1.0 V) relative to that used for SDM adsorption. In addition, trace levels of antibiotics (364-580 ng/L) in surface water could be removed effectively to achieve low effluent concentration (0.4-1.2 ng/L) and high removal efficiency (99.9%) upon treating up to ∼1560 bed volumes (BVs), demonstrating the potential of electro-assisted adsorption for practical application in water treatment. Copyright © 2018 Elsevier Ltd. All rights reserved.

Efficient ECH-assisted plasma start-up using trapped particle configuration in the versatile experiment spherical torus

NASA Astrophysics Data System (ADS)

An, YoungHwa; Lee, Jeongwon; Jo, JongGab; Jung, Bong-Ki; Lee, HyunYeong; Chung, Kyoung-Jae; Na, Yong-Su; Hahm, T. S.; Hwang, Y. S.

2017-01-01

An efficient and robust ECH (electron cyclotron heating)-assisted plasma start-up scheme with a low loop voltage and low volt-second consumption utilizing the trapped particle configuration (TPC) has been developed in the versatile experiment spherical torus (VEST). The TPC is a mirror-like magnetic field configuration providing a vertical magnetic field in the same direction as the equilibrium field. It significantly enhances ECH pre-ionization with enhanced particle confinement due to its mirror effect, and intrinsically provides an equilibrium field with a stable decay index enabling prompt plasma current initiation. Consequently, the formation of TPC before the onset of the loop voltage allows the plasma to start up with a lower loop voltage and lower volt-second consumption as well as a wider operation range in terms of ECH pre-ionization power and H2 filling pressure. The TPC can improve the widely-used field null configuration significantly for more efficient start-up when ECH pre-ionization is used. This can then be utilized in superconducting tokamaks requiring a low loop voltage start-up, such as ITER, or in spherical tori with limited volt-seconds. The TPC can be particularly useful in superconducting tokamaks with a limited current slew-rate of superconducting PF coils, as it can save volt-second consumption before plasma current initiation by providing prompt initiation with an intrinsic stable equilibrium field.

High Sensitivity and High Detection Specificity of Gold-Nanoparticle-Grafted Nanostructured Silicon Mass Spectrometry for Glucose Analysis.

PubMed

Tsao, Chia-Wen; Yang, Zhi-Jie

2015-10-14

Desorption/ionization on silicon (DIOS) is a high-performance matrix-free mass spectrometry (MS) analysis method that involves using silicon nanostructures as a matrix for MS desorption/ionization. In this study, gold nanoparticles grafted onto a nanostructured silicon (AuNPs-nSi) surface were demonstrated as a DIOS-MS analysis approach with high sensitivity and high detection specificity for glucose detection. A glucose sample deposited on the AuNPs-nSi surface was directly catalyzed to negatively charged gluconic acid molecules on a single AuNPs-nSi chip for MS analysis. The AuNPs-nSi surface was fabricated using two electroless deposition steps and one electroless etching step. The effects of the electroless fabrication parameters on the glucose detection efficiency were evaluated. Practical application of AuNPs-nSi MS glucose analysis in urine samples was also demonstrated in this study.

Multiphoton laser ionization for energy conversion in barium vapor

NASA Astrophysics Data System (ADS)

Makdisi, Y.; Kokaj, J.; Afrousheh, K.; Mathew, J.; Nair, R.; Pichler, G.

2013-03-01

We have studied the ion detection of barium atoms in special heated ovens with a tungsten rod in the middle of the stainless steel tube. The tungsten rod was heated indirectly by the oven body heaters. A bias voltage between the cell body and the tungsten rod of 9 V was used to collect electrons, after the barium ions had been created. However, we could collect the electrons even without the bias voltage, although with ten times less efficiency. We studied the conditions for the successful bias-less thermionic signal detection using excimer/dye laser two-photon excitation of Rydberg states below and above the first ionization limit (two-photon wavelength at 475.79 nm). We employed a hot-pipe oven and heat-pipe oven (with inserted mesh) in order to generate different barium vapor distributions inside the oven. The thermionic signal increased by a factor of two under heat-pipe oven conditions.

Anion-Tunable Properties and Electrochemical Performance of Functionalized Ferrocene Compounds

PubMed Central

Cosimbescu, Lelia; Wei, Xiaoliang; Vijayakumar, M.; Xu, Wu; Helm, Monte L.; Burton, Sarah D.; Sorensen, Christina M.; Liu, Jun; Sprenkle, Vincent; Wang, Wei

2015-01-01

We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Finally, the electrochemical performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability. PMID:26374254

Anion-tunable properties and electrochemical performance of functionalized ferrocene compounds

DOE PAGES

Cosimbescu, Lelia; Wei, Xiaoliang; Vijayakumar, M.; ...

2015-09-16

We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Lastly, the electrochemicalmore » performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability.« less

Decomposition reaction of the veterinary antibiotic ciprofloxacin using electron ionizing energy.

PubMed

Cho, Jae Young; Chung, Byung Yeoup; Lee, Kyeong-Bo; Lee, Geon-Hwi; Hwang, Seon Ah

2014-12-01

The application of electron ionizing energy for degrading veterinary antibiotic ciprofloxacin (CFX) in aqueous solution was elucidated. The degradation efficiency of CFX after irradiation with electron ionizing energy was 38% at 1 kGy, 80% at 5kGy, and 97% at 10 kGy. Total organic carbon of CFX in aqueous solution after irradiation with electron ionizing energy decreased 2% at 1 kGy, 18% at 5 kGy, and 53% at 10 kGy. The CFX degradation products after irradiation with electron ionizing energy were CFX1 ([M+H] m/z 330), CFX2 ([M+H] m/z 314), and CFX3 ([M+H] m/z 263). CFX1 had an F atom substituted with OH and CFX2 was expected to originate from CFX via loss of F or H2O. CFX3 was expected to originate from CFX via loss of the piperazynilic ring. Among the several radicals, hydrate electron (eaq(-)) is expected to play an important role in degradation of veterinary antibiotic during irradiation with electron ionizing energy. The toxicity of the degraded products formed during irradiation with electron ionizing energy was evaluated using microbes such as Escherichia coli, Pseudomonas putida, and Bacillus subtilis, and the results revealed that the toxicity decreased with irradiation. These results demonstrate that irradiation technology using electron ionizing energy is an effective was to remove veterinary antibiotics from an aquatic ecosystem. Copyright © 2014 Elsevier Ltd. All rights reserved.

The role of exciton ionization processes in bulk heterojunction organic photovoltaic cells

NASA Astrophysics Data System (ADS)

Zou, Yunlong; Holmes, Russell

2015-03-01

Dissociating photogenerated excitons into their constituent charges is essential for efficient photoconversion in organic semiconductors. Organic photovoltaics cells (OPV) widely adopt a heterojunction architecture where dissociation is facilitated by charge transfer at a donor-acceptor (D-A) interface. Interestingly, recent work on MoOx/C60 Schottky OPVs has demonstrated that excitons in C60 may also undergo bulk-ionization to generate photocurrent, driven by the built-in field at the MoOx/C60 interface. Here, we show that bulk-ionization processes also contribute to the photocurrent in bulk heterojunction (BHJ) OPVs with fullerene-rich compositions. The short-circuit current density (JSC) in a MoOx/C60 Schottky OPVs shows almost no dependence on temperature down to 80 K. This characteristic of bulk-ionization allows the use of temperature-dependent measurements of JSC to distinguish dissociation by bulk-ionization from charge transfer at a D-A interface. For BHJ OPVs constructed using the D-A pairing of boron subphthalocyanine chloride (SubPc)-C60, bulk-ionization is found to contribute >10% of the total photocurrent and >30% of the photocurrent from C60. We further find that fullerene-rich SubPc-C60 BHJ OPVs show a larger open-circuit voltage (VOC) than evenly mixed BHJs due to the presence of bulk-ionization. This talk will examine the dependence of JSC and VOC on the relative fraction of dissociation by charge transfer and bulk-ionization processes.

Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen Atom Donors

PubMed Central

Jing, Linhong; Nash, John J.

2009-01-01

The factors that control the reactivities of aryl radicals toward hydrogen-atom donors were studied by using a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer (FT – ICR). Hydrogen-atom abstraction reaction efficiencies for two substrates, cyclohexane and isopropanol, were measured for twenty-three structurally different, positively-charged aryl radicals, which included dehydrobenzenes, dehydronaphthalenes, dehydropyridines, and dehydro(iso)quinolines. A logarithmic correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) vertical electron affinities (EA) of the aryl radicals. Transition state energies calculated for three of the aryl radicals with isopropanol were found to correlate linearly with their (calculated) EAs. No correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) enthalpy changes for the reactions. Measurement of the reaction efficiencies for the reactions of several different hydrogen-atom donors with a few selected aryl radicals revealed a logarithmic correlation between the hydrogen-atom abstraction reaction efficiencies and the vertical ionization energies (IE) of the hydrogen-atom donors, but not the lowest homolytic X – H (X = heavy atom) bond dissociation energies of the hydrogen-atom donors. Examination of the hydrogen-atom abstraction reactions of twenty-nine different aryl radicals and eighteen different hydrogen-atom donors showed that the reaction efficiency increases (logarithmically) as the difference between the IE of the hydrogen-atom donor and the EA of the aryl radical decreases. This dependence is likely to result from the increasing polarization, and concomitant stabilization, of the transition state as the energy difference between the neutral and ionic reactants decreases. Thus, the hydrogen-atom abstraction reaction efficiency for an aryl radical can be “tuned” by structural changes that influence either the vertical EA of the aryl radical or the vertical IE of the hydrogen atom donor. PMID:19061320

Radiation protection and mitigation by natural antioxidants and flavonoids; implications to radiotherapy and radiation disasters.

PubMed

Yahyapour, Rasoul; Shabeeb, Dheyauldeen; Cheki, Mohsen; Musa, Ahmed Eleojo; Farhood, Bagher; Rezaeyan, Abolhasan; Amini, Peyman; Fallah, Hengameh; Najafi, Masoud

2018-06-19

Nowadays, ionizing radiations are used for various medical and terroristic aims. These purposes involve exposure to ionizing radiations. Hence, people are at risk for acute or late effects. Annually, millions of cancer patients undergo radiotherapy during their course of treatment. Also, some radiological or nuclear events in recent years pose a threat to people, hence the need for radiation mitigation strategies. Amifostine, the first FDA approved radioprotector, has shown some toxicities that limit its usage and efficiency. Due to these side effects, scientists have researched for other agents with less toxicity for better radioprotection and possible mitigation of the lethal effects of ionizing radiations after an accidental exposure. Flavonoids have shown promising results for radioprotection and can be administered in higher doses with less toxicity. Studies for mitigation of ionizing radiation-induced toxicities has concentrated on natural antioxidants. Detoxification of free radicals, management of inflammatory responses and attenuation of apoptosis signaling pathways in radiosensitive organs are the main mechanisms for radiation protection and mitigation with flavonoids and natural antioxidants. However, several studies have proposed that a combination in the form of some antioxidants may alleviate radiation toxicities more effectively in comparison to a single form of antioxidants. In this review, we focus on recent findings about natural radioprotectors and mitigators which are clinically applicable for radiotherapy patients, as well as injured people in possible radiation accidents. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Ionization asymmetry effects on the properties modulation of atmospheric pressure dielectric barrier discharge sustained by tailored voltage waveforms

NASA Astrophysics Data System (ADS)

Zhang, Z. L.; Nie, Q. Y.; Zhang, X. N.; Wang, Z. B.; Kong, F. R.; Jiang, B. H.; Lim, J. W. M.

2018-04-01

The dielectric barrier discharge (DBD) is a promising technology to generate high density and uniform cold plasmas in atmospheric pressure gases. The effective independent tuning of key plasma parameters is quite important for both application-focused and fundamental studies. In this paper, based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of ionization asymmetry effects on the properties modulation of atmospheric DBD sustained by tailored voltage waveforms are reported. The driving voltage waveform is characterized by an asymmetric-slope fundamental sinusoidal radio frequency signal superimposing one or more harmonics, and the effects of the number of harmonics, phase shift, as well as the fluctuation of harmonics on the sheath dynamics, impact ionization of electrons and key plasma parameters are investigated. The results have shown that the electron density can exhibit a substantial increase due to the effective electron heating by a spatially asymmetric sheath structure. The strategic modulation of harmonics number and phase shift is capable of raising the electron density significantly (e.g., nearly three times in this case), but without a significant increase in the gas temperature. Moreover, by tailoring the fluctuation of harmonics with a steeper slope, a more profound efficiency in electron impact ionization can be achieved, and thus enhancing the electron density effectively. This method then enables a novel alternative approach to realize the independent control of the key plasma parameters under atmospheric pressure.

Toward single-cell analysis by plume collimation in laser ablation electrospray ionization mass spectrometry.

PubMed

Stolee, Jessica A; Vertes, Akos

2013-04-02

Ambient ionization methods for mass spectrometry have enabled the in situ and in vivo analysis of biological tissues and cells. When an etched optical fiber is used to deliver laser energy to a sample in laser ablation electrospray ionization (LAESI) mass spectrometry, the analysis of large single cells becomes possible. However, because in this arrangement the ablation plume expands in three dimensions, only a small portion of it is ionized by the electrospray. Here we show that sample ablation within a capillary helps to confine the radial expansion of the plume. Plume collimation, due to the altered expansion dynamics, leads to greater interaction with the electrospray plume resulting in increased ionization efficiency, reduced limit of detection (by a factor of ~13, reaching 600 amol for verapamil), and extended dynamic range (6 orders of magnitude) compared to conventional LAESI. This enhanced sensitivity enables the analysis of a range of metabolites from small cell populations and single cells in the ambient environment. This technique has the potential to be integrated with flow cytometry for high-throughput metabolite analysis of sorted cells.

Immuno-affinity Capture Followed by TMPP N-Terminus Tagging to Study Catabolism of Therapeutic Proteins.

PubMed

Kullolli, Majlinda; Rock, Dan A; Ma, Ji

2017-02-03

Characterization of in vitro and in vivo catabolism of therapeutic proteins has increasingly become an integral part of discovery and development process for novel proteins. Unambiguous and efficient identification of catabolites can not only facilitate accurate understanding of pharmacokinetic profiles of drug candidates, but also enables follow up protein engineering to generate more catabolically stable molecules with improved properties (pharmacokinetics and pharmacodynamics). Immunoaffinity capture (IC) followed by top-down intact protein analysis using either matrix-assisted laser desorption/ionization or electrospray ionization mass spectrometry analysis have been the primary methods of choice for catabolite identification. However, the sensitivity and efficiency of these methods is not always sufficient for characterization of novel proteins from complex biomatrices such as plasma or serum. In this study a novel bottom-up targeted protein workflow was optimized for analysis of proteolytic degradation of therapeutic proteins. Selective and sensitive tagging of the alpha-amine at the N-terminus of proteins of interest was performed by immunoaffinity capture of therapeutic protein and its catabolites followed by on-bead succinimidyloxycarbonylmethyl tri-(2,4,6-trimethoxyphenyl N-terminus (TMPP-NTT) tagging. The positively charged hydrophobic TMPP tag facilitates unambiguous sequence identification of all N-terminus peptides from complex tryptic digestion samples via data dependent liquid chromatgraphy-tandem mass spectroscopy. Utility of the workflow was illustrated by definitive analysis of in vitro catabolic profile of neurotensin human Fc (NTs-huFc) protein in mouse serum. The results from this study demonstrated that the IC-TMPP-NTT workflow is a simple and efficient method for catabolite formation in therapeutic proteins.

Pretreatment of grass waste using combined ionizing radiation-acid treatment for enhancing fermentative hydrogen production.

PubMed

Yang, Guang; Wang, Jianlong

2018-05-01

In this study, the combined ionizing radiation-acid pretreatment process was firstly applied to enhance hydrogen fermentation of grass waste. Results showed that the combined pretreatment synergistically enhanced hydrogen fermentation of grass waste. The SCOD and soluble polysaccharide contents of grass waste increased by 1.6 and 2.91 times after the combined pretreatment, respectively. SEM observation and crystallinity test showed the combined pretreatment effectively disrupted the grass structure. Owing to the more favorable substrate conditions, the hydrogen yield achieved 68 mL/g-dry grass added after the combined pretreatment, which was 161.5%, 112.5% and 28.3% higher than those from raw, ionizing radiation pretreated and acid pretreated grass waste, respectively. The VS removal also increased from 13.9% to 25.6% by the combined pretreatment. Microbial community analysis showed that the abundance of dominant hydrogen producing genus Clostridium sensu stricto 1 increased from 37.9% to 69.4% after the combined pretreatment, which contributed to more efficient hydrogen fermentation. Copyright © 2018 Elsevier Ltd. All rights reserved.

Enhanced MALDI-TOF MS Analysis of Phosphopeptides Using an Optimized DHAP/DAHC Matrix

PubMed Central

Hou, Junjie; Xie, Zhensheng; Xue, Peng; Cui, Ziyou; Chen, Xiulan; Li, Jing; Cai, Tanxi; Wu, Peng; Yang, Fuquan

2010-01-01

Selecting an appropriate matrix solution is one of the most effective means of increasing the ionization efficiency of phosphopeptides in matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In this study, we systematically assessed matrix combinations of 2, 6-dihydroxyacetophenone (DHAP) and diammonium hydrogen citrate (DAHC), and demonstrated that the low ratio DHAP/DAHC matrix was more effective in enhancing the ionization of phosphopeptides. Low femtomole level of phosphopeptides from the tryptic digests of α-casein and β-casein was readily detected by MALDI-TOF-MS in both positive and negative ion mode without desalination or phosphopeptide enrichment. Compared with the DHB/PA matrix, the optimized DHAP/DAHC matrix yielded superior sample homogeneity and higher phosphopeptide measurement sensitivity, particularly when multiple phosphorylated peptides were assessed. Finally, the DHAP/DAHC matrix was applied to identify phosphorylation sites from α-casein and β-casein and to characterize two phosphorylation sites from the human histone H1 treated with Cyclin-Dependent Kinase-1 (CDK1) by MALDI-TOF/TOF MS. PMID:20339515

Theoretical and observational determinations of the ionization coefficient of meteors

NASA Astrophysics Data System (ADS)

Jones, William

1997-07-01

We examine the problem of the determination of the ionization coefficient beta from both the theoretical and observational points of view. In the past, theoretical evaluations of beta in terms of the relevant scattering cross-sections have used the Massey-Sida formula, which we show to give results which are plainly incorrect. We derive an integral equation for beta and compare the results of its application to copper and iron with laboratory simulations. Agreement for the variation of the ionization coefficient with velocity is good. The ionization coefficient has been determined observationally by Verniani & Hawkins from a comparison of radar and visual observations, employing the luminous efficiency tau also obtained observationally by Verniani. However, this determination of tau would appear to be invalidated by fragmentation. There is good evidence that the radiation of cometary meteors is dominated by that of iron in the visual range, and we have accordingly re-analysed the data of Verniani & Hawkins using the luminous efficiency of iron obtained in simulation experiments. However, it is not possible to choose an iron concentration which gives agreement between the determination of the ionization coefficient by this means and its determination from the theoretical equation in terms of either scattering coefficients or simulation methods. The observational ionization coefficients are much lower than predicted by the present theory and we provisionally explain this as a consequence of transfer of charge from the meteoric ion to a molecule of the air. It is now possible for the meteoric atom to be re-ionized, but it is also possible at sufficiently high initial line densities for significant dissociative recombination of the electrons and nitrogen or oxygen to take place. This recombination will not take place in meteor trains simulated in an ionization chamber. We thus conclude that the present theory is limited to faint radio meteors at lower velocities (v<~35 km s^-1), for which no significant secondary ionization or recombination will take place. The theoretical results may be approximated by the analytic form beta~=9.4x10^-6 (v-10)^2v^0.8, where the velocity v is in km s^-1. For visual meteors in the range of about 30 to 60 km s^-1, we propose as a reasonable approximation the result we have obtained from the Verniani-Hawkins observational data using simulation results for the luminosity: beta=4.91x10^-6v^2.25. At present, however, we are unable to propose estimates of beta for slow bright meteors or fast radio meteors.

Reversal electron attachment ionizer for detection of trace species

NASA Technical Reports Server (NTRS)

Bernius, Mark T. (Inventor); Chutjian, Ara (Inventor)

1990-01-01

An in-line reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region and executing a reversal of said electrons, such that the electrons possess zero kinetic energy at the point of reversal, may be used to produce both negative and positive ions. A sample gas is introduced at the point of electron reversal for low energy electron-(sample gas) molecule attachment with high efficiency. The attachment process produces negative ions from the sample gas, which includes species present in trace (minute) amounts. These ions are extracted efficiently and directed to a mass analyzer where they may be detected and identified. The generation and detection of positive ions is accomplished in a similar fashion with minimal adjustment to potentials applied to the apparatus.

Reversal electron attachment ionizer for detection of trace species

NASA Technical Reports Server (NTRS)

Bernius, Mark T. (Inventor); Chutjian, Ara (Inventor)

1989-01-01

An in-line reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region and executing a reversal of the electrons, such that the electrons possess zero kinetic energy at the point of reversal, may be used to produce both negative and positive ions. A sample gas is introduced at the point of electron reversal for low energy electron-(sample gas) molecule attachment with high efficiency. The attachment process produces negative ions from the sample gas, which includes species present in trace (minute) amounts. These ions are extracted efficiently and directed to a mass analyzer where they may be detected and identified. The generation and detection of positive ions is accomplished in a similar fashion with minimal adjustment to potentials applied to the apparatus.

Effect of azimuthal diversion rail on an ATON-type Hall thruster

NASA Astrophysics Data System (ADS)

Xu, Zhang; Liqiu, Wei; Liang, Han; Yongjie, Ding; Daren, Yu

2017-03-01

A newly designed azimuthal diversion rail (ADR) is studied and used to enhance the ionization process in an ATON-type Hall thruster. The diversion rail efficiently reduces the neutral flow axial velocity, and hence, increases the resistance time of atoms in the discharge channel of the Hall thruster. Thrust performances, in terms of thrust, anode efficiency and ion beam divergence, are found to be improved because of the application of the diversion rail, especially at low mass flow rate conditions. Experiment results reveal that the ADR increases the mass utilization under insufficient mass flow rate operating conditions. The design of the ADR broadens the efficient operating range of Hall thrusters and has significant contribution to multi-mode Hall thruster development.

Single photon ionization and chemical ionization combined ion source based on a vacuum ultraviolet lamp for orthogonal acceleration time-of-flight mass spectrometry.

PubMed

Hua, Lei; Wu, Qinghao; Hou, Keyong; Cui, Huapeng; Chen, Ping; Wang, Weiguo; Li, Jinghua; Li, Haiyang

2011-07-01

A novel combined ion source based on a vacuum ultraviolet (VUV) lamp with both single photon ionization (SPI) and chemical ionization (CI) capabilities has been developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). The SPI was accomplished using a commercial 10.6 eV krypton discharge lamp with a photon flux of about 10(11) photons s(-1), while the CI was achieved through ion-molecule reactions with O(2)(+) reactant ions generated by photoelectron ionization at medium vacuum pressure (MVP). To achieve high ionization efficiency, the ion source pressure was elevated to 0.3 mbar and the photoionization length was extended to 36 mm. As a result, limits of detection (LODs) down to 3, 4, and 6 ppbv were obtained for benzene, toluene, and p-xylene in MVP-SPI mode, and values of 8 and 10 ppbv were obtained for toluene and chloroform, respectively, in SPI-CI mode. As it is feasible to switch between MVP-SPI mode and SPI-CI mode rapidly, this system is capable of monitoring complex organic mixtures with a wide range of ionization energies (IEs). The analytical capacity of this system was demonstrated by measuring dehydrogenation products of long-chain paraffins to olefins through direct capillary sampling and drinking water disinfection byproducts from chlorine through a membrane interface.

Helicon thruster plasma modeling: Two-dimensional fluid-dynamics and propulsive performances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahedo, Eduardo; Navarro-Cavalle, Jaume

2013-04-15

An axisymmetric macroscopic model of the magnetized plasma flow inside the helicon thruster chamber is derived, assuming that the power absorbed from the helicon antenna emission is known. Ionization, confinement, subsonic flows, and production efficiency are discussed in terms of design and operation parameters. Analytical solutions and simple scaling laws for ideal plasma conditions are obtained. The chamber model is then matched with a model of the external magnetic nozzle in order to characterize the whole plasma flow and assess thruster performances. Thermal, electric, and magnetic contributions to thrust are evaluated. The energy balance provides the power conversion between ionsmore » and electrons in chamber and nozzle, and the power distribution among beam power, ionization losses, and wall losses. Thruster efficiency is assessed, and the main causes of inefficiency are identified. The thermodynamic behavior of the collisionless electron population in the nozzle is acknowledged to be poorly known and crucial for a complete plasma expansion and good thrust efficiency.« less

Critical factors determining the quantification capability of matrix-assisted laser desorption/ionization– time-of-flight mass spectrometry

PubMed Central

Wang, Chia-Chen; Lai, Yin-Hung; Ou, Yu-Meng; Chang, Huan-Tsung; Wang, Yi-Sheng

2016-01-01

Quantitative analysis with mass spectrometry (MS) is important but challenging. Matrix-assisted laser desorption/ionization (MALDI) coupled with time-of-flight (TOF) MS offers superior sensitivity, resolution and speed, but such techniques have numerous disadvantages that hinder quantitative analyses. This review summarizes essential obstacles to analyte quantification with MALDI-TOF MS, including the complex ionization mechanism of MALDI, sensitive characteristics of the applied electric fields and the mass-dependent detection efficiency of ion detectors. General quantitative ionization and desorption interpretations of ion production are described. Important instrument parameters and available methods of MALDI-TOF MS used for quantitative analysis are also reviewed. This article is part of the themed issue ‘Quantitative mass spectrometry’. PMID:27644968

Application of irradiation in bait production to the control of crawling insects in urban areas

NASA Astrophysics Data System (ADS)

Migdał, W.; Owczarczyk, H. B.; Świ ȩtosławski, J.; Świ ȩtosławski, J.

2000-03-01

The efficiency and palatability of two baits were studied to the control of crawling insects in urban areas: "Cockroach Kill Gel" for control of cockroaches and Faratox B for control of ants. Ionizing energy was used in producing the baits. It was concluded, that after irradiation the palatability of Faratox B improved and palatability of Cockroach Kill Gel did not change.

Effects of ultrashort laser pulses on angular distributions of photoionization spectra.

PubMed

Ooi, C H Raymond; Ho, W L; Bandrauk, A D

2017-07-27

We study the photoelectron spectra by intense laser pulses with arbitrary time dependence and phase within the Keldysh framework. An efficient semianalytical approach using analytical transition matrix elements for hydrogenic atoms in any initial state enables efficient and accurate computation of the photoionization probability at any observation point without saddle point approximation, providing comprehensive three dimensional photoelectron angular distribution for linear and elliptical polarizations, that reveal the intricate features and provide insights on the photoionization characteristics such as angular dispersions, shift and splitting of photoelectron peaks from the tunneling or above threshold ionization(ATI) regime to non-adiabatic(intermediate) and multiphoton ionization(MPI) regimes. This facilitates the study of the effects of various laser pulse parameters on the photoelectron spectra and their angular distributions. The photoelectron peaks occur at multiples of 2ħω for linear polarization while  odd-ordered peaks are suppressed in the direction perpendicular to the electric field. Short pulses create splitting and angular dispersion where the peaks are strongly correlated to the angles. For MPI and elliptical polarization with shorter pulses the peaks split into doublets and the first peak vanishes. The carrier envelope phase(CEP) significantly affects the ATI spectra while the Stark effect shifts the spectra of intermediate regime to higher energies due to interference.

A novel magnet focusing plate for matrix-assisted laser desorption/ionization analysis of magnetic bead-bound analytes.

PubMed

Gode, David; Volmer, Dietrich A

2013-05-15

Magnetic beads are often used for serum profiling of peptide and protein biomarkers. In these assays, the bead-bound analytes are eluted from the beads prior to mass spectrometric analysis. This study describes a novel matrix-assisted laser desorption/ionization (MALDI) technique for direct application and focusing of magnetic beads to MALDI plates by means of dedicated micro-magnets as sample spots. Custom-made MALDI plates with magnetic focusing spots were made using small nickel-coated neodymium micro-magnets integrated into a stainless steel plate in a 16 × 24 (384) pattern. For demonstrating the proof-of-concept, commercial C-18 magnetic beads were used for the extraction of a test compound (reserpine) from aqueous solution. Experiments were conducted to study focusing abilities, the required laser energies, the influence of a matrix compound, dispensing techniques, solvent choice and the amount of magnetic beads. Dispensing the magnetic beads onto the micro-magnet sample spots resulted in immediate and strong binding to the magnetic surface. Light microscope images illustrated the homogeneous distribution of beads across the surfaces of the magnets, when the entire sample volume containing the beads was pipetted onto the surface. Subsequent MALDI analysis of the bead-bound analyte demonstrated excellent and reproducible ionization yields. The surface-assisted laser desorption/ionization (SALDI) properties of the strongly light-absorbing γ-Fe2O3-based beads resulted in similar ionization efficiencies to those obtained from experiments with an additional MALDI matrix compound. This feasibility study successfully demonstrated the magnetic focusing abilities for magnetic bead-bound analytes on a novel MALDI plate containing small micro-magnets as sample spots. One of the key advantages of this integrated approach is that no elution steps from magnetic beads were required during analyses compared with conventional bead experiments. Copyright © 2013 John Wiley & Sons, Ltd.

Surface tuning laser desorption/ionization mass spectrometry (STLDI-MS) for the analysis of small molecules using quantum dots.

PubMed

Abdelhamid, Hani Nasser; Chen, Zhen-Yu; Wu, Hui-Fen

2017-08-01

In most applications of quantum dots (QDs) for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS), one side of QDs is supported by a solid substrate (stainless - steel plate), whereas the other side is in contact with the target analytes. Therefore, the surface capping agent of QDs is a key parameter for laser desorption/ionization mass spectrometry (LDI-MS). Cadmium telluride quantum dots (CdTe QDs) modified with different capping agents are synthesized, characterized, and applied for surface tuning laser desorption/ionization mass spectrometry (STLDI-MS). Data shows that CdTe quantum dot modified cysteine (cys@CdTe QDs) has an absorption that matches with the wavelength of the N 2 laser (337 nm). The synergistic effect of large surface area and absorption of the laser irradiation of cys@CdTe QDs enhances the LDI-MS process for small - molecule analysis, including α-, β-, and γ-cyclodextrin, gramicidin D, perylene, pyrene, and triphenylphosphine. Cys@CdTe QDs are also applied using Al foils as substrates. Aluminum foil combined with cys@CdTe QDs enhances the ionization efficiency and is cheap compared to traditional matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) with a stainless - steel plate.

Photochemistry of PAHs in cosmic water ice. The effect of concentration on UV-VIS spectroscopy and ionization efficiency

NASA Astrophysics Data System (ADS)

Cuylle, Steven H.; Allamandola, Louis J.; Linnartz, Harold

2014-02-01

Context. Observations and models show that polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium. Like other molecules in dense clouds, PAHs accrete onto interstellar dust grains, where they are embedded in an ice matrix dominated by water. In the laboratory, mixed molecular ices (not containing PAHs) have been extensively studied using Fourier transform infrared absorption spectroscopy. Experiments including PAHs in ices have started, however, the concentrations used are typically much higher than the concentrations expected for interstellar ices. Optical spectroscopy offers a sensitive alternative. Aims: We report an experimental study of the effect PAH concentration has on the electronic spectra and the vacuum UV (VUV) driven processes of PAHs in water-rich ices. The goal is to apply the outcome to cosmic ices. Methods: Optical spectroscopic studies allow us to obtain in-situ and quasi real-time electronic solid state spectra of two prototypical PAHs (pyrene and coronene) embedded in water ice under VUV photoprocessing. The study is carried out on PAH:H2O concentrations in the range of 1:30 000 to pure PAH, covering the temperature range from 12 to 125 K. Results: PAH concentration strongly influences the efficiency of PAH cation formation. At low concentrations, ionization efficiencies are over 60% dropping to about 15% at 1:1000. Increasing the PAH concentration reveals spectral broadening in neutral and cation PAH spectra attributed to PAH clustering inside the ice. At the PAH concentrations expected for interstellar ices, some 10 to 20% may be present as cations. The presence of PAHs in neutral and ion form will add distinctive absorption bands to cosmic ice optical spectra and this may serve as a tool to determine PAH concentrations.

Influence of Triply-Charged Ions and Ionization Cross-Sections in a Hybrid-PIC Model of a Hall Thruster Discharge

NASA Technical Reports Server (NTRS)

Smith, Brandon D.; Boyd, Iain D.; Kamhawi, Hani

2014-01-01

The sensitivity of xenon ionization rates to collision cross-sections is studied within the framework of a hybrid-PIC model of a Hall thruster discharge. A revised curve fit based on the Drawin form is proposed and is shown to better reproduce the measured crosssections at high electron energies, with differences in the integrated rate coefficients being on the order of 10% for electron temperatures between 20 eV and 30 eV. The revised fit is implemented into HPHall and the updated model is used to simulate NASA's HiVHAc EDU2 Hall thruster at discharge voltages of 300, 400, and 500 V. For all three operating points, the revised cross-sections result in an increase in the predicted thrust and anode efficiency, reducing the error relative to experimental performance measurements. Electron temperature and ionization reaction rates are shown to follow the trends expected based on the integrated rate coefficients. The effects of triply-charged xenon are also assessed. The predicted thruster performance is found to have little or no dependence on the presence of triply-charged ions. The fraction of ion current carried by triply-charged ions is found to be on the order of 1% and increases slightly with increasing discharge voltage. The reaction rates for the 0?III, I?III, and II?III ionization reactions are found to be of similar order of magnitude and are about one order of magnitude smaller than the rate of 0?II ionization in the discharge channel.

Real-Time Food Authentication Using a Miniature Mass Spectrometer.

PubMed

Gerbig, Stefanie; Neese, Stephan; Penner, Alexander; Spengler, Bernhard; Schulz, Sabine

2017-10-17

Food adulteration is a threat to public health and the economy. In order to determine food adulteration efficiently, rapid and easy-to-use on-site analytical methods are needed. In this study, a miniaturized mass spectrometer in combination with three ambient ionization methods was used for food authentication. The chemical fingerprints of three milk types, five fish species, and two coffee types were measured using electrospray ionization, desorption electrospray ionization, and low temperature plasma ionization. Minimum sample preparation was needed for the analysis of liquid and solid food samples. Mass spectrometric data was processed using the laboratory-built software MS food classifier, which allows for the definition of specific food profiles from reference data sets using multivariate statistical methods and the subsequent classification of unknown data. Applicability of the obtained mass spectrometric fingerprints for food authentication was evaluated using different data processing methods, leave-10%-out cross-validation, and real-time classification of new data. Classification accuracy of 100% was achieved for the differentiation of milk types and fish species, and a classification accuracy of 96.4% was achieved for coffee types in cross-validation experiments. Measurement of two milk mixtures yielded correct classification of >94%. For real-time classification, the accuracies were comparable. Functionality of the software program and its performance is described. Processing time for a reference data set and a newly acquired spectrum was found to be 12 s and 2 s, respectively. These proof-of-principle experiments show that the combination of a miniaturized mass spectrometer, ambient ionization, and statistical analysis is suitable for on-site real-time food authentication.

Model study of modern oil-based paint media by triacylglycerol profiling in positive and negative ionization modes.

PubMed

Degano, Ilaria; La Nasa, Jacopo; Ghelardi, Elisa; Modugno, Francesca; Colombini, Maria Perla

2016-12-01

Lipid binders have traditionally been determined in paintings by using gas chromatography/mass spectrometry (GC/MS) to identify the characteristic profiles and ratios of fatty acids . However, the presence of mixtures in contemporary and modern oil paints makes the GC/MS determination of fatty acids insufficient to fully characterize the lipid binding media. In this study we prove that triacylglycerol (TAG) profiling by high-performance liquid chromatography with high-resolution tandem mass spectrometry, using ESI in positive and negative ionization modes is highly effective. We exploited this analytical approach to study the curing and degradation processes undergone by six plant oils used in the formulation of media in modern paints, using both natural and artificial ageing experiments. We believe that is the first time that a negative ionization mode has been applied for this purpose and that a survey with HPLC-ESI-Q-ToF has been carried out to study the ageing kinetics of plant oils. TAG profiling enabled us to study the evolution over time of the constituents of modern oils, with respect to curing and ageing. The data analyzed in this study demonstrate that our approach is efficient to study the oxidation of TAGs during ageing. The data also improve current knowledge on the properties of vegetable oils, which could lead to the development of new paint materials and conservation treatments for modern and contemporary works of art. Copyright © 2016 Elsevier B.V. All rights reserved.

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry of beta-(1 --> 3), beta-(1 --> 4)-xylans from Nothogenia fastigiata using nor-harmane as matrix.

PubMed

Fukuyama, Yuko; Kolender, Adriana A; Nishioka, Masae; Nonami, Hiroshi; Matulewicz, María C; Erra-Balsells, Rosa; Cerezo, Alberto S

2005-01-01

Three xylan fractions isolated from the red seaweed Nothogenia fastigiata (Nemaliales) were analyzed by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOFMS). UV-MALDI-TOFMS was carried out in the linear and reflectron modes, and as routine in the positive and negative ion modes. Of the several matrices tested, nor-harmane was the only effective one giving good spectra in the positive ion mode. The number-average molar masses of two of the fractions, calculated from the distribution profiles, were lower than those determined previously by (1)H NMR analysis, suggesting a decrease in the ionization efficiency with increasing molecular weight; weight-average molar mass and polydispersity index were also determined. As the xylans retained small but significant quantities of calcium salts, the influence of added Ca(2+) as CaCl(2) on UV-MALDI-MS was investigated. The simultaneous addition of sodium chloride and calcium chloride was also analyzed. Addition of sodium chloride did not change the distribution profile of the native sample showing that the inhibitory effect is due to Ca(2+) and not to Cl(-). Addition of calcium chloride with 1:1 analyte/salt molar ratio gave spectra with less efficient desorption/ionization of oligomers; the signals of these oligomers were completely suppressed when the addition of the salt became massive (1:100 analyte/salt molar ratio). Copyright (c) 2005 John Wiley & Sons, Ltd.

Organic–inorganic binary mixture matrix for comprehensive laser-desorption ionization mass spectrometric analysis and imaging of medium-size molecules including phospholipids, glycerolipids, and oligosaccharides

DOE PAGES

Feenstra, Adam D.; Ames Lab., Ames, IA; O'Neill, Kelly C.; ...

2016-10-13

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a widely adopted, versatile technique, especially in high-throughput analysis and imaging. However, matrix-dependent selectivity of analytes is often a severe limitation. In this work, a mixture of organic 2,5-dihydroxybenzoic acid and inorganic Fe 3O 4 nanoparticles is developed as a binary MALDI matrix to alleviate the well-known issue of triacylglycerol (TG) ion suppression by phosphatidylcholine (PC). In application to lipid standards and maize seed cross-sections, the binary matrix not only dramatically reduced the ion suppression of TG, but also efficiently desorbed and ionized a wide variety of lipids such as cationic PC, anionicmore » phosphatidylethanolamine (PE) and phosphatidylinositol (PI), and neutral digalactosyldiacylglycerol (DGDG). The binary matrix was also very efficient for large polysaccharides, which were not detected by either of the individual matrices. As a result, the usefulness of the binary matrix is demonstrated in MS imaging of maize seed sections, successfully visualizing diverse medium-size molecules and acquiring high-quality MS/MS spectra for these compounds.« less

Preliminary Spectroscopic Measurements for a Gallium Electromagnetic (GEM) Thruster

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Burton, Rodney L.; Glumac, Nick G.; Polzin, Kurt A.

2007-01-01

As a propellant option for electromagnetic thrusters, liquid ,gallium appears to have several advantages relative to other propellants. The merits of using gallium in an electromagnetic thruster (EMT) are discussed and estimates of discharge current levels and mass flow rates yielding efficient operation are given. The gallium atomic weight of 70 predicts high efficiency in the 1500-2000 s specific impulse range, making it ideal for higher-thrust, near-Earth missions. A spatially and temporally broad spectroscopic survey in the 220-520 nm range is used to determine which species are present in the plasma and estimate electron temperature. The spectra show that neutral, singly, and doubly ionized gallium species are present in a 20 J, 1.8 kA (peak) are discharge. With graphite present on the insulator to facilitate breakdown, singly and doubly ionized carbon atoms are also present, and emission is observed from molecular carbon (CZ) radicals. A determination of the electron temperature was attempted using relative emission line data, and while the spatially and temporally averaged, spectra don't fit well to single temperatures, the data and presence of doubly ionized gallium are consistent with distributions in the 1-3 eV range.

Ionization-induced star formation - IV. Triggering in bound clusters

NASA Astrophysics Data System (ADS)

Dale, J. E.; Ercolano, B.; Bonnell, I. A.

2012-12-01

We present a detailed study of star formation occurring in bound star-forming clouds under the influence of internal ionizing feedback from massive stars across a spectrum of cloud properties. We infer which objects are triggered by comparing our feedback simulations with control simulations in which no feedback was present. We find that feedback always results in a lower star formation efficiency and usually but not always results in a larger number of stars or clusters. Cluster mass functions are not strongly affected by feedback, but stellar mass functions are biased towards lower masses. Ionization also affects the geometrical distribution of stars in ways that are robust against projection effects, but may make the stellar associations more or less subclustered depending on the background cloud environment. We observe a prominent pillar in one simulation which is the remains of an accretion flow feeding the central ionizing cluster of its host cloud and suggest that this may be a general formation mechanism for pillars such as those observed in M16. We find that the association of stars with structures in the gas such as shells or pillars is a good but by no means foolproof indication that those stars have been triggered and we conclude overall that it is very difficult to deduce which objects have been induced to form and which formed spontaneously simply from observing the system at a single time.

Electron Attenuation Measurement using Cosmic Ray Muons at the MicroBooNE LArTPC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meddage, Varuna

2017-10-01

The MicroBooNE experiment at Fermilab uses liquid argon time projection chamber (LArTPC) technology to study neutrino interactions in argon. A fundamental requirement for LArTPCs is to achieve and maintain a low level of electronegative contaminants in the liquid to minimize the capture of drifting ionization electrons. The attenuation time for the drifting electrons should be long compared to the maximum drift time, so that the signals from particle tracks that generate ionization electrons with long drift paths can be detected efficiently. In this talk we present MicroBooNE measurement of electron attenuation using cosmic ray muons. The result yields a minimummore » electron 1/e lifetime of 18 ms under typical operating conditions, which is long compared to the maximum drift time of 2.3 ms.« less

Response of GaAs charge storage devices to transient ionizing radiation

NASA Astrophysics Data System (ADS)

Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

Interatomic Coulombic decay cascades in multiply excited neon clusters

PubMed Central

Nagaya, K.; Iablonskyi, D.; Golubev, N. V.; Matsunami, K.; Fukuzawa, H.; Motomura, K.; Nishiyama, T.; Sakai, T.; Tachibana, T.; Mondal, S.; Wada, S.; Prince, K. C.; Callegari, C.; Miron, C.; Saito, N.; Yabashi, M.; Demekhin, Ph. V.; Cederbaum, L. S.; Kuleff, A. I.; Yao, M.; Ueda, K.

2016-01-01

In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold. However on tuning the laser to the lowest resonant transition, the system becomes multiply excited, and more efficient, indirect ionization pathways become operative. These mechanisms are known as interatomic Coulombic decay (ICD), where one of the species de-excites to its ground state, transferring its energy to ionize another excited species. Here we show that on tuning to a higher resonant transition, a previously unknown type of interatomic Coulombic decay, intra-Rydberg ICD occurs. In it, de-excitation of an atom to a close-lying Rydberg state leads to electron emission from another neighbouring Rydberg atom. Moreover, systems multiply excited to higher Rydberg states will decay by a cascade of such processes, producing even more ions. The intra-Rydberg ICD and cascades are expected to be ubiquitous in weakly-bound systems exposed to high-intensity resonant radiation. PMID:27917867

Spontaneous Charge Separation and Sublimation Processes are Ubiquitous in Nature and in Ionization Processes in Mass Spectrometry

NASA Astrophysics Data System (ADS)

Trimpin, Sarah; Lu, I.-Chung; Rauschenbach, Stephan; Hoang, Khoa; Wang, Beixi; Chubatyi, Nicholas D.; Zhang, Wen-Jing; Inutan, Ellen D.; Pophristic, Milan; Sidorenko, Alexander; McEwen, Charles N.

2018-02-01

Ionization processes have been discovered by which small and large as well as volatile and nonvolatile compounds are converted to gas-phase ions when associated with a matrix and exposed to sub-atmospheric pressure. Here, we discuss experiments further defining these simple and unexpected processes. Charge separation is found to be a common process for small molecule chemicals, solids and liquids, passed through an inlet tube from a higher to a lower pressure region, with and without heat applied. This charge separation process produces positively- and negatively-charged particles with widely different efficiencies depending on the compound and its physical state. Circumstantial evidence is presented suggesting that in the new ionization process, charged particles carry analyte into the gas phase, and desolvation of these particles produce the bare ions similar to electrospray ionization, except that solid particles appear likely to be involved. This mechanistic proposition is in agreement with previous theoretical work related to ion emission from ice.

Dustbuster: a New Generation Impact-ionization Time-of-flight Mass Spectrometer for in situ Analysis of Cosmic Dust

NASA Astrophysics Data System (ADS)

Austin, D. E.; Ahrens, T. J.; Beauchamp, J. L.

2000-10-01

We have developed and tested a small impact-ionization time-of-flight mass spectrometer for analysis of cosmic dust, suitable for use on deep space missions. This mass spectrometer, named Dustbuster, incorporates a large target area and a reflectron, simultaneously optimizing mass resolution, sensitivity, and collection efficiency. Dust particles hitting the 65-cm2 target plate are partially ionized. The resulting ions are accelerated through a modified reflectron that focuses the ions in space and time to produce high-resolution spectra. The instrument, shown below, measures 10 x 10 x 20 cm, has a mass of 500 g, and consumes little power. Laser desorption ionization of metal and mineral samples (embedded in the impact plate) simulates particle impacts for instrument performance tests. Mass resolution in these experiments is near 200, permitting resolution of isotopes. The mass spectrometer can be combined with other instrument components to determine dust particle trajectories and sizes. This project was funded by NASA's Planetary Instrument Definition and Development Program.

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

NASA Astrophysics Data System (ADS)

Louchev, Oleg A.; Saito, Norihito; Oishi, Yu; Miyazaki, Koji; Okamura, Kotaro; Nakamura, Jumpei; Iwasaki, Masahiko; Wada, Satoshi

2016-09-01

We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α ) radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i) multi-photon ionization, (ii) step-wise (2+1)-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii) laser-induced avalanche ionization produced by generated free electrons. Developed expressions validated by order of magnitude estimations and available experimental data allow us to identify the area for the operation under high input laser intensities avoiding the onset of full-scale discharge, loss of efficiency and inhibition of generated L-α radiation. Calculations made reveal an opportunity for scaling up the output energy of the experimentally generated pulsed L-α radiation without significant enhancement of photoionization.

High efficiency direct detection of ions from resonance ionization of sputtered atoms

DOEpatents

Gruen, Dieter M.; Pellin, Michael J.; Young, Charles E.

1986-01-01

A method and apparatus are provided for trace and other quantitative analysis with high efficiency of a component in a sample, with the analysis involving the removal by ion or other bombardment of a small quantity of ion and neutral atom groups from the sample, the conversion of selected neutral atom groups to photoions by laser initiated resonance ionization spectroscopy, the selective deflection of the photoions for separation from original ion group emanating from the sample, and the detection of the photoions as a measure of the quantity of the component. In some embodiments, the original ion group is accelerated prior to the RIS step for separation purposes. Noise and other interference are reduced by shielding the detector from primary and secondary ions and deflecting the photoions sufficiently to avoid the primary and secondary ions.

High efficiency direct detection of ions from resonance ionization of sputtered atoms

DOEpatents

Gruen, D.M.; Pellin, M.J.; Young, C.E.

1985-01-16

A method and apparatus are provided for trace and other quantitative analysis with high efficiency of a component in a sample, with the analysis involving the removal by ion or other bombardment of a small quantity of ion and neutral atom groups from the sample, the conversion of selected neutral atom groups to photoions by laser initiated resonance ionization spectroscopy, the selective deflection of the photoions for separation from original ion group emanating from the sample, and the detection of the photoions as a measure of the quantity of the component. In some embodiments, the original ion group is accelerated prior to the RIS step for separation purposes. Noise and other interference are reduced by shielding the detector from primary and secondary ions and deflecting the photoions sufficiently to avoid the primary and secondary ions.

Creating space plasma from the ground

NASA Astrophysics Data System (ADS)

Carlson, H. C.; Djuth, F. T.; Zhang, L. D.

2017-01-01

We have performed an experiment to compare as directly as realizable the ionization production rate by HF radio wave energy versus by solar EUV. We take advantage of the commonality that ionization production by both ground-based high-power HF radio waves and by solar EUV is driven by primary and secondary suprathermal electrons near and above 20 eV. Incoherent scatter radar (ISR) plasma-line amplitudes are used as a measure of suprathermal electron fluxes for ISR wavelengths near those for 430 MHz and are indeed a clean measure of such for those fluxes sufficiently weak to have negligible self-damping. We present data from an HF heating experiment on November 2015 at Arecibo, which even more directly confirm the only prior midlatitude estimate, of order 10% efficiency for conversion of HF energy to ionospheric ionization. We note the theoretical maximum possible is 1/3, while 1% or less reduces the question to near practical irrelevance. Our measurements explicitly confirm the prediction that radio-frequency production of artificial ionospheres can be practicable, even at midlatitudes. Furthermore, that this midlatitude efficiency is comparable to efficiencies measured at high latitudes (which include enhancements unique to high latitudes including magnetic zenith effect, gyrofrequency multiples, and double resonances) requires reexamination of current theoretical thinking about soft-electron acceleration processes in weakly magnetized plasmas. The implications are that electron acceleration by any of a variety of processes may be a fundamental underpinning to energy redistribution in space plasmas.

Ultrafast Screening and Quantitation of Pesticides in Food and Environmental Matrices by Solid-Phase Microextraction-Transmission Mode (SPME-TM) and Direct Analysis in Real Time (DART).

PubMed

Gómez-Ríos, Germán Augusto; Gionfriddo, Emanuela; Poole, Justen; Pawliszyn, Janusz

2017-07-05

The direct interface of microextraction technologies to mass spectrometry (MS) has unquestionably revolutionized the speed and efficacy at which complex matrices are analyzed. Solid Phase Micro Extraction-Transmission Mode (SPME-TM) is a technology conceived as an effective synergy between sample preparation and ambient ionization. Succinctly, the device consists of a mesh coated with polymeric particles that extracts analytes of interest present in a given sample matrix. This coated mesh acts as a transmission-mode substrate for Direct Analysis in Real Time (DART), allowing for rapid and efficient thermal desorption/ionization of analytes previously concentrated on the coating, and dramatically lowering the limits of detection attained by sole DART analysis. In this study, we present SPME-TM as a novel tool for the ultrafast enrichment of pesticides present in food and environmental matrices and their quantitative determination by MS via DART ionization. Limits of quantitation in the subnanogram per milliliter range can be attained, while total analysis time does not exceed 2 min per sample. In addition to target information obtained via tandem MS, retrospective studies of the same sample via high-resolution mass spectrometry (HRMS) were accomplished by thermally desorbing a different segment of the microextraction device.

Study of solid-conversion gaseous detector based on GEM for high energy X-ray industrial CT.

PubMed

Zhou, Rifeng; Zhou, Yaling

2014-01-01

The general gaseous ionization detectors are not suitable for high energy X-ray industrial computed tomography (HEICT) because of their inherent limitations, especially low detective efficiency and large volume. The goal of this study was to investigate a new type of gaseous detector to solve these problems. The novel detector was made by a metal foil as X-ray convertor to improve the conversion efficiency, and the Gas Electron Multiplier (hereinafter "GEM") was used as electron amplifier to lessen its volume. The detective mechanism and signal formation of the detector was discussed in detail. The conversion efficiency was calculated by using EGSnrc Monte Carlo code, and the transport course of photon and secondary electron avalanche in the detector was simulated with the Maxwell and Garfield codes. The result indicated that this detector has higher conversion efficiency as well as less volume. Theoretically this kind of detector could be a perfect candidate for replacing the conventional detector in HEICT.

Microwave Driven Magnetic Plasma Accelerator Studies (CYCLOPS)

NASA Technical Reports Server (NTRS)

Crimi, G. F.; Eckert, A. C.; Miller, D. B.

1967-01-01

A microwave-driven cyclotron resonance plasma acceleration device was investigated using argon, krypton, xenon, and mercury as propellants. Limited ranges of propellant flow rate, input power, and magnetic field strength were used. Over-all efficiencies (including the 65% efficiency of the input polarizer) less than 10% were obtained for specific impulse values between 500 and 1500 sec. Power transfer efficiencies, however, approached 100% of the input power available in the right-hand component of the incident circularly polarized radiation. Beam diagnostics using Langmuir probes, cold gas mapping, r-f mapping and ion energy analyses were performed in conjunction with an engine operating in a pulsed mode. Measurements of transverse electron energies at the position of cyclotron resonant absorption yielded energy values more than an order of magnitude lower than anticipated. The measured electron energies were, however, consistent with the low values of average ion energy measured by retarding potential techniques. The low values of average ion energy were also consistent with the measured thrust values. It is hypothesized that ionization and radiation limit the electron kinetic energy to low-values thus limiting the energy which is finally transferred to the ion. Thermalization by electron-electron collision was also identified as an additional loss mechanism. The use of light alkali metals, which have relatively few low lying energy levels to excite, with the input power to mass ratio selected so as to limit the electron energies to less than the second ionization potential, is suggested. It is concluded, however, that the over-all efficiency for such propellants would be less than 40 per cent.

Electrically driven plasmon-exciton coupled random lasing in ZnO metal-semiconductor-metal devices

NASA Astrophysics Data System (ADS)

Suja, Mohammad; Debnath, Bishwajit; Bashar, Sunayna B.; Su, Longxing; Lake, Roger; Liu, Jianlin

2018-05-01

Electrically driven plasmon-exciton coupled random lasing is demonstrated by incorporating Ag nanoparticles on Cu-doped ZnO metal-semiconductor-metal (MSM) devices. Both photoluminescence and electroluminescence studies show that emission efficiencies have been enhanced significantly due to coupling between ZnO excitons and Ag surface plasmons. With the incorporation of Ag nanoparticles on ZnO MSM structures, internal quantum efficiency up to 6 times is demonstrated. Threshold current for lasing is decreased by as much as 30% while the output power is increased up to 350% at an injection current of 40 mA. A numerical simulation study reveals that hole carriers are generated in the ZnO MSM devices from impact ionization processes for subsequent plasmon-exciton coupled lasing.

Electron-Atom Ionization Calculations using Propagating Exterior Complex Scaling

NASA Astrophysics Data System (ADS)

Bartlett, Philip

2007-10-01

The exterior complex scaling method (Science 286 (1999) 2474), pioneered by Rescigno, McCurdy and coworkers, provided highly accurate ab initio solutions for electron-hydrogen collisions by directly solving the time-independent Schr"odinger equation in coordinate space. An extension of this method, propagating exterior complex scaling (PECS), was developed by Bartlett and Stelbovics (J. Phys. B 37 (2004) L69, J. Phys. B 39 (2006) R379) and has been demonstrated to provide computationally efficient and accurate calculations of ionization and scattering cross sections over a large range of energies below, above and near the ionization threshold. An overview of the PECS method for three-body collisions and the computational advantages of its propagation and iterative coupling techniques will be presented along with results of: (1) near-threshold ionization of electron-hydrogen collisions and the Wannier threshold laws, (2) scattering cross section resonances below the ionization threshold, and (3) total and differential cross sections for electron collisions with excited targets and hydrogenic ions from low through to high energies. Recently, the PECS method has been extended to solve four-body collisions using time-independent methods in coordinate space and has initially been applied to the s-wave model for electron-helium collisions. A description of the extensions made to the PECS method to facilitate these significantly more computationally demanding calculations will be given, and results will be presented for elastic, single-excitation, double-excitation, single-ionization and double-ionization collisions.

A 200 W Hall thruster with hollow indented anode

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Sun, Hezhi; Wei, Liqiu; Li, Peng; Su, Hongbo; Peng, Wuji; Yu, Daren

2017-10-01

A hollow indented anode is proposed for increasing the neutral gas density in a discharge channel, in order to improve the performance of the thruster. The experimental results show that a hollow indented anode structure can effectively improve the performance, compared to a hollow straight anode under similar operating conditions, in terms of thrust, propellant utilization, ionization rate, and anode efficiency. Furthermore, simulations show that the indented anode can effectively increase the neutral gas density in a discharge channel and on the centerline of the channel, compared to a hollow straight anode. In addition, it can increase the ionization rate in the channel and the pre-ionization in the anode. Therefore, the hollow indented anode could be considered as an important design idea for improving thruster performance.

Effect of external applied electric field on the silicon solar cell's thermodynamic efficiency

NASA Astrophysics Data System (ADS)

Zieba Falama, R.; Mibaile, Justin; Guemene Dountio, E.; Djongyang, Noël; Doka, Serge Y.; Kofane, Timoleon C.

2017-03-01

This paper presents a possible solution to improve the efficiency of photovoltaic solar cells. An external electric field is applied on a silicon photovoltaic solar cell, inducing band-trap ionization of charge carriers. Output current is then monitored and the thermodynamic efficiency is calculated. Results show on the one hand a significant increase in efficiency for a certain margin of applied electric field, and on the another hand the instabilities of efficiency. A simple approach is then suggested for the implementation of these results. An efficiency of 67% has been reached for an applied electric of 1586 V/Cm.

Determination of short chain carboxylic acids in vegetable oils and fats using ion exclusion chromatography electrospray ionization mass spectrometry.

PubMed

Viidanoja, Jyrki

2015-02-27

A new method for quantification of short chain C1-C6 carboxylic acids in vegetable oils and fats by employing Liquid Chromatography Mass Spectrometry (LC-MS) has been developed. The method requires minor sample preparation and applies non-conventional Electrospray Ionization (ESI) liquid phase chemistry. Samples are first dissolved in chloroform and then extracted using water that has been spiked with stable isotope labeled internal standards that are used for signal normalization and absolute quantification of selected acids. The analytes are separated using Ion Exclusion Chromatography (IEC) and detected with Electrospray Ionization Mass Spectrometry (ESI-MS) as deprotonated molecules. Prior to ionization the eluent that contains hydrochloric acid is modified post-column to ensure good ionization efficiency of the analytes. The averaged within run precision and between run precision were generally lower than 8%. The accuracy was between 85 and 115% for most of the analytes. The Lower Limit of Quantification (LLOQ) ranged from 0.006 to 7mg/kg. It is shown that this method offers good selectivity in cases where UV detection fails to produce reliable results. Copyright © 2015 Elsevier B.V. All rights reserved.

Theoretical considerations on the optogalvanic detection of laser induced fluorescence in atmospheric pressure atomizers

NASA Astrophysics Data System (ADS)

Omenetto, N.; Smith, B. W.; Winefordner, J. D.

1989-01-01

Several theoretical considerations are given on the potential and practical capabilities of a detector of fluorescence radiation whose operating principle is based on a multi-step excitation-ionization scheme involving the fluorescence photons as the first excitation step. This detection technique, which was first proposed by MATVEEVet al. [ Zh. Anal Khim.34, 846 (1979)], combines two independent atomizers, one analytical cell for the excitation of the sample fluorescence and one cell, filled with pure analyte atomic vapor, acting as the ionization detector. One laser beam excites the analyte fluorescence in the analytical cell and one (or two) laser beams are used to ionize the excited atoms in the detector. Several different causes of signal and noise are evaluated, together with a discussion on possible analytical atom reservoirs (flames, furnaces) and laser sources which could be used with this approach. For properly devised conditions, i.e. optical saturation of the fluorescence and unity ionization efficiency, detection limits well below pg/ml in solution and well below femtograms as absolute amounts in furnaces can be predicted. However, scattering problems, which are absent in a conventional laser-enhanced ionization set-up, may be important in this approach.

The Evolution of Electrospray Generated Droplets is Not Affected by Ionization Mode

NASA Astrophysics Data System (ADS)

Liigand, Piia; Heering (Suu), Agnes; Kaupmees, Karl; Leito, Ivo; Girod, Marion; Antoine, Rodolphe; Kruve, Anneli

2017-10-01

Ionization efficiency and mechanism in ESI is strongly affected by the properties of mobile phase. The use of mobile-phase properties to accurately describe droplets in ESI source is convenient but may be inadequate as the composition of the droplets is changing in the plume due to electrochemical reactions occurring in the needle tip as well as continuous drying and fission of droplets. Presently, there is paucity of research on the effect of the polarity of the ESI mode on mobile phase composition in the droplets. In this paper, the change in the organic solvent content, pH, and droplet size are studied in the ESI plume in both ESI+ and ESI- ionization mode. We introduce a rigorous way - the absolute pH (pHabs H 2 O) - to describe pH change in the plume that takes into account organic solvent content in the mobile phase. pHabs H 2 O enables comparing acidities of ESI droplets with different organic solvent contents. The results are surprisingly similar for both ionization modes, indicating that the dynamics of the change of mobile-phase properties is independent from the ESI mode used. This allows us to conclude that the evolution of ESI droplets first of all proceeds via the evaporation of the organic modifier and to a lesser extent via fission of smaller droplets from parent droplets. Secondly, our study shows that qualitative findings related to the ESI process obtained on the ESI+ mode can almost directly be applied also in the ESI- mode. [Figure not available: see fulltext.

Fluorescence spectroscopy of UV-MALDI matrices and implications of ionization mechanisms

NASA Astrophysics Data System (ADS)

Lin, Hou-Yu; Hsu, Hsu Chen; Lu, I.-Chung; Hsu, Kuo-Tung; Liao, Chih-Yu; Lee, Yin-Yu; Tseng, Chien-Ming; Lee, Yuan-Tseh; Ni, Chi-Kung

2014-10-01

Matrix-assisted laser desorption ionization (MALDI) has been widely used in the mass analysis of biomolecules; however, there are a lot of debates about the ionization mechanisms. Previous studies have indicated that S1-S1 annihilation might be a key process in the generation of primary ions. This study investigates S1-S1 annihilation by examining the time-resolved fluorescence spectra of 12 matrices. No S1-S1 annihilation was observed in six of these matrices (3-hydroxy-picolinic acid, 6-aza-2-thiothymine, 2,4-dihydroxy-acetophenone, 2,6-dihydroxy-acetophenone, 2,4,6-trihydroxy-acetophenone, and ferulic acid). We observed two matrix molecules reacting in an electronically excited state (S1) in five of these matrices (2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxy-acetophenone, 2,3-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid), and S1-S1 annihilation was a possible reaction. Among these five matrices, no S1-S1 annihilation was observed for 2,3-dihydroxybenzoic acid in typical peak power region of nanosecond laser pulses in MALDI, but a very small value of reaction rate constant was observed only in the high peak power region. The excited-state lifetime of sinapinic acid was too short to determine whether the molecules reacted in an electronically excited state. No correlation was observed between the ion generation efficiency of MALDI and S1-S1 annihilation. The results indicate that the proposal of S1-S1 annihilation is unnecessary in MALDI and energy pooling model for MALDI ionization mechanism has to be modified.

Benchmark study of ionization potentials and electron affinities of armchair single-walled carbon nanotubes using density functional theory

NASA Astrophysics Data System (ADS)

Zhou, Bin; Hu, Zhubin; Jiang, Yanrong; He, Xiao; Sun, Zhenrong; Sun, Haitao

2018-05-01

The intrinsic parameters of carbon nanotubes (CNTs) such as ionization potential (IP) and electron affinity (EA) are closely related to their unique properties and associated applications. In this work, we demonstrated the success of optimal tuning method based on range-separated (RS) density functionals for both accurate and efficient prediction of vertical IPs and electron affinities (EAs) of a series of armchair single-walled carbon nanotubes C20n H20 (n  =  2–6) compared to the high-level IP/EA equation-of-motion coupled-cluster method with single and double substitutions (IP/EA-EOM-CCSD). Notably, the resulting frontier orbital energies (–ε HOMO and –ε LUMO) from the tuning method exhibit an excellent approximation to the corresponding IPs and EAs, that significantly outperform other conventional density functionals. In addition, it is suggested that the RS density functionals that possess both a fixed amount of exact exchange in the short-range and a correct long-range asymptotic behavior are suitable for calculating electronic structures of finite-sized CNTs. Next the performance of density functionals for description of various molecular properties such as chemical potential, hardness and electrophilicity are assessed as a function of tube length. Thanks to the efficiency and accuracy of this tuning method, the related behaviors of much longer armchair single-walled CNTs until C200H20 were studied. Lastly, the present work is proved to provide an efficient theoretical tool for future materials design and reliable characterization of other interesting properties of CNT-based systems.

Attosecond-recollision-controlled selective fragmentation of polyatomic molecules.

PubMed

Xie, Xinhua; Doblhoff-Dier, Katharina; Roither, Stefan; Schöffler, Markus S; Kartashov, Daniil; Xu, Huailiang; Rathje, Tim; Paulus, Gerhard G; Baltuška, Andrius; Gräfe, Stefanie; Kitzler, Markus

2012-12-14

Control over various fragmentation reactions of a series of polyatomic molecules (acetylene, ethylene, 1,3-butadiene) by the optical waveform of intense few-cycle laser pulses is demonstrated experimentally. We show both experimentally and theoretically that the responsible mechanism is inelastic ionization from inner-valence molecular orbitals by recolliding electron wave packets, whose recollision energy in few-cycle ionizing laser pulses strongly depends on the optical waveform. Our work demonstrates an efficient and selective way of predetermining fragmentation and isomerization reactions in polyatomic molecules on subfemtosecond time scales.

Total and dissociative photoionization cross sections of N2 from threshold to 107 eV

NASA Technical Reports Server (NTRS)

Samson, James A. R.; Masuoka, T.; Pareek, P. N.; Angel, G. C.

1986-01-01

The absolute cross sections for the production of N(+) and N2(+) were measured from the dissociative ionization threshold of 115 A. In addition, the absolute photoabsorption and photoionization cross sections were tabulated between 114 and 796 A. The ionization efficiencies were also given at several discrete wave lengths between 660 and 790 A. The production of N(+) fragment ions are discussed in terms of the doubly excited N2(+) states with binding energies in the range of 24 to 44 eV.

Total and dissociative photoionization cross sections of N2 from threshold to 107 eV

NASA Technical Reports Server (NTRS)

Samson, James A. R.; Masuoka, T.; Pareek, P. N.; Angel, G. C.

1987-01-01

The absolute cross sections for the production of N(+) and N2(+) have been measured from the dissociative ionization threshold to 115 A. In addition, the absolute photoabsorption and photoionization cross sections are tabulated between 114 and 796 A. The ionization efficiencies are also given at several discrete wavelengths between 660 and 790 A. The production of N(+) fragment ions are discussed in terms of the doubly excited N2(+) states with binding energies in the range 24 to 44 eV.

Design for gas chromatography-corona discharge-ion mobility spectrometry.

PubMed

Jafari, Mohammad T; Saraji, Mohammad; Sherafatmand, Hossein

2012-11-20

A corona discharge ionization-ion mobility spectrometry (CD-IMS) with a novel sample inlet system was designed and constructed as a detector for capillary gas chromatography. In this design, a hollow needle was used instead of a solid needle which is commonly used for corona discharge creation, helping us to have direct axial interfacing for GC-IMS. The capillary column was passed through the needle, resulting in a reaction of effluents with reactant ions on the upstream side of the corona discharge ionization source. Using this sample introduction design, higher ionization efficiency was achieved relative to the entrance direction through the side of the drift tube. In addition, the volume of the ionization region was reduced to minimize the resistance time of compounds in the ionization source, increasing chromatographic resolution of the instrument. The effects of various parameters such as drift gas flow, makeup gas flow, and column tip position inside the needle were investigated. The designed instrument was exhaustively validated in terms of sensitivity, resolution, and reproducibility by analyzing the standard solutions of methyl isobutyl ketone, heptanone, nonanone, and acetophenone as the test compounds. The results obtained by CD-IMS detector were compared with those of the flame ionization detector, which revealed the capability of the proposed GC-IMS for two-dimensional separation (based on the retention time and drift time information) and identification of an analyte in complex matrixes.

Microhydration of LiOH: Insight from electronic decays of core-ionized states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kryzhevoi, Nikolai V., E-mail: nikolai.kryzhevoi@pci.uni-heidelberg.de

2016-06-28

We compute and compare the autoionization spectra of a core-ionized LiOH molecule both in its isolated and microhydrated states. Stepwise microhydration of LiOH leads to gradual elongation of the Li–OH bond length and finally to molecular dissociation. The accompanying changes in the local environment of the OH{sup −} and Li{sup +} counterions are reflected in the computed O 1s and Li 1s spectra. The role of solvent water molecules and the counterion in the spectral shape formation is assessed. Electronic decays of the microhydrated LiOH are found to be mostly intermolecular since the majority of the populated final states havemore » at least one outer-valence vacancy outside the initially core-ionized ion, mainly on a neighboring water molecule. The charge delocalization occurs through the intermolecular Coulombic and electron transfer mediated decays. Both mechanisms are highly efficient that is partly attributed to hybridization of molecular orbitals. The computed spectral shapes are sensitive to the counterion separation as well as to the number and arrangement of solvent molecules. These sensitivities can be used for studying the local hydration structure of solvated ions in aqueous solutions.« less

Physical Conditions in Shocked Interstellar Gas Interacting with the Supernova Remnant IC 443

NASA Astrophysics Data System (ADS)

Ritchey, Adam M.; Federman, Steven Robert; Jenkins, Edward B.; Caprioli, Damiano; Wallerstein, George

2018-06-01

We present the results of a detailed investigation into the physical conditions in interstellar material interacting with the supernova remnant IC 443. Our analysis is based on an examination of high-resolution HST/STIS spectra of two stars probing predominantly neutral gas located both ahead of and behind the supernova shock front. The pre-shock neutral gas is characterized by densities and temperatures typical of diffuse interstellar clouds, while the post-shock material exhibits a range of more extreme physical conditions, including high temperatures (>104 K) in some cases, which may require a sudden heating event to explain. The ionization level is enhanced in the high-temperature post-shock material, which could be the result of enhanced radiation from shocks or from an increase in cosmic-ray ionization. The gas-phase abundances of refractory elements are also enhanced in the high-pressure gas, suggesting efficient destruction of dust grains by shock sputtering. Observations of highly-ionized species at very high velocity indicate a post-shock temperature of 107 K for the hot X-ray emitting plasma of the remnant’s interior, in agreement with studies of thermal X-ray emission from IC 443.

Measurements of trap dynamics of cold OH molecules using resonance-enhanced multiphoton ionization

NASA Astrophysics Data System (ADS)

Gray, John M.; Bossert, Jason A.; Shyur, Yomay; Lewandowski, H. J.

2017-08-01

Trapping cold, chemically important molecules with electromagnetic fields is a useful technique to study small molecules and their interactions. Traps provide long interaction times, which are needed to precisely examine these low-density molecular samples. However, the trapping fields lead to nonuniform molecular density distributions in these systems. Therefore, it is important to be able to experimentally characterize the spatial density distribution in the trap. Ionizing molecules at different locations in the trap using resonance-enhanced multiphoton ionization (REMPI) and detecting the resulting ions can be used to probe the density distribution even at the low density present in these experiments because of the extremely high efficiency of detection. Until recently, one of the most chemically important molecules, OH, did not have a convenient REMPI scheme identified. Here, we use a newly developed 1 +1' REMPI scheme to detect trapped cold OH molecules. We use this capability to measure the trap dynamics of the central density of the cloud and the density distribution. These types of measurements can be used to optimize loading of molecules into traps, as well as to help characterize the energy distribution, which is critical knowledge for interpreting molecular collision experiments.

Laser Desorption Ionization of small molecules assisted by Tungsten oxide and Rhenium oxide particles

PubMed Central

Bernier, Matthew; Wysocki, Vicki; Dagan, Shai

2015-01-01

Inorganic metal oxides have shown potential as matrices for assisting in laser desorption ionization (LDI) with advantages over the aromatic acids typically used. Rhenium and tungsten oxides are an attractive option due to their high work functions and relative chemical inertness. In this work, it is shown that ReO3 and WO3, in microparticle (μP) powder forms, can efficiently ionize various types of small molecules and provide minimized background contamination at analyte concentrations below 1 ng/μL. This study shows that untreated inorganic WO3 and ReO3 particles are valid matrix options for detection of protonatable, radical, and precharged species under LDI. Qualitatively, the WO3 μP showed an improved detection of apigenin, sodiated glucose, and the precharged analyte choline, while the ReO3 μP allowed detection of protonated cocaine, quinuclidine, ametryn, and radical ions of polyaromatic hydrocarbons at detection levels as low as 50 pg/μL. For thermometer ion survival yield experiments, it was also shown that the ReO3 powder was significantly softer than CCA. Furthermore, it provided higher intensities of cocaine and polyaromatic hydrocarbons, at laser flux values equal to that used with CCA. PMID:26349643

A vacuum ultraviolet laser pulsed field ionization-photoion study of methane (CH 4): Determination of the appearance energy of methylium from methane with unprecedented precision and the resulting impact on the bond dissociation energies of CH 4 and CH 4 +

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Yih -Chung; Xiong, Bo; Bross, David H.

Here, we report on the successful implementation of a high-resolution vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection method for the study of unimolecular dissociation of quantum-state- or energy-selected molecular ions. As a test case, we have determined the 0 K appearance energy (AE 0) for the formation of methylium, CH 3 +, from methane, CH 4, as AE 0 (CH 3 +/CH 4) = 14.32271 ± 0.00013 eV. This value has a significantly smaller error limit, but is otherwise consistent with previous laboratory and/or synchrotron-based studies of this dissociative photoionization onset. Furthermore, the sum of the VUV lasermore » PFI-PI spectra obtained for the parent CH 4 + ion and the fragment CH 3 + ions of methane is found to agree with the earlier VUV pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of methane, providing unambiguous validation of the previous interpretation that the sharp VUV-PFI-PE step observed at the AE 0 (CH 3 +/CH 4) threshold ensues because of higher PFI detection efficiency for fragment CH 3 + than for parent CH 4 +. This, in turn, is a consequence of the underlying high- n Rydberg dissociation mechanism for the dissociative photoionization of CH 4, which was proposed in previous synchrotron-based VUV-PFI-PE and VUV-PFI-PEPICO studies of CH 4. The present highly accurate 0 K dissociative ionization threshold for CH 4 can be utilized to derive accurate values for the bond dissociation energies of methane and methane cation. For methane, the straightforward application of sequential thermochemistry via the positive ion cycle leads to some ambiguity because of two competing VUV-PFI-PE literature values for the ionization energy of methyl radical. The ambiguity is successfully resolved by applying the Active Thermochemical Tables (ATcT) approach, resulting in D 0 (H-CH 3) = 432.463 ± 0.027 kJ/mol and D 0(H-CH 3 +) = 164.701 ± 0.038 kJ/mol.« less

A vacuum ultraviolet laser pulsed field ionization-photoion study of methane (CH 4): Determination of the appearance energy of methylium from methane with unprecedented precision and the resulting impact on the bond dissociation energies of CH 4 and CH 4 +

DOE PAGES

Chang, Yih -Chung; Xiong, Bo; Bross, David H.; ...

2017-03-27

Here, we report on the successful implementation of a high-resolution vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection method for the study of unimolecular dissociation of quantum-state- or energy-selected molecular ions. As a test case, we have determined the 0 K appearance energy (AE 0) for the formation of methylium, CH 3 +, from methane, CH 4, as AE 0 (CH 3 +/CH 4) = 14.32271 ± 0.00013 eV. This value has a significantly smaller error limit, but is otherwise consistent with previous laboratory and/or synchrotron-based studies of this dissociative photoionization onset. Furthermore, the sum of the VUV lasermore » PFI-PI spectra obtained for the parent CH 4 + ion and the fragment CH 3 + ions of methane is found to agree with the earlier VUV pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of methane, providing unambiguous validation of the previous interpretation that the sharp VUV-PFI-PE step observed at the AE 0 (CH 3 +/CH 4) threshold ensues because of higher PFI detection efficiency for fragment CH 3 + than for parent CH 4 +. This, in turn, is a consequence of the underlying high- n Rydberg dissociation mechanism for the dissociative photoionization of CH 4, which was proposed in previous synchrotron-based VUV-PFI-PE and VUV-PFI-PEPICO studies of CH 4. The present highly accurate 0 K dissociative ionization threshold for CH 4 can be utilized to derive accurate values for the bond dissociation energies of methane and methane cation. For methane, the straightforward application of sequential thermochemistry via the positive ion cycle leads to some ambiguity because of two competing VUV-PFI-PE literature values for the ionization energy of methyl radical. The ambiguity is successfully resolved by applying the Active Thermochemical Tables (ATcT) approach, resulting in D 0 (H-CH 3) = 432.463 ± 0.027 kJ/mol and D 0(H-CH 3 +) = 164.701 ± 0.038 kJ/mol.« less

Ionization behavior of amino lipids for siRNA delivery: determination of ionization constants, SAR, and the impact of lipid pKa on cationic lipid-biomembrane interactions.

PubMed

Zhang, Jingtao; Fan, Haihong; Levorse, Dorothy A; Crocker, Louis S

2011-03-01

Ionizable amino lipids are being pursued as an important class of materials for delivering small interfering RNA (siRNA) therapeutics, and research is being conducted to elucidate the structure-activity relationships (SAR) of these lipids. The pK(a) of cationic lipid headgroups is one of the critical physiochemical properties of interest due to the strong impact of lipid ionization on the assembly and performance of these lipids. This research focused on developing approaches that permit the rapid determination of the relevant pK(a) of the ionizable amino lipids. Two distinct approaches were investigated: (1) potentiometric titration of amino lipids dissolved in neutral surfactant micelles; and (2) pH-dependent partitioning of a fluorescent dye to cationic liposomes formulated from amino lipids. Using the approaches developed here, the pK(a) values of cationic lipids with distinct headgroups were measured and found to be significantly lower than calculated values. It was also found that lipid-lipid interaction has a strong impact on the pK(a) values of lipids. Lysis of model biomembranes by cationic lipids was used to evaluate the impact of lipid pK(a) on the interaction between cationic lipids and cell membranes. It was found that cationic lipid-biomembrane interaction depends strongly on lipid pK(a) and solution pH, and this interaction is much stronger when amino lipids are highly charged. The presence of an optimal pK(a) range of ionizable amino lipids for siRNA delivery was suggested based on these results. The pK(a) methods reported here can be used to support the SAR screen of cationic lipids for siRNA delivery, and the information revealed through studying the impact of pK(a) on the interaction between cationic lipids and cell membranes will contribute significantly to the design of more efficient siRNA delivery vehicles.

Beacons in the dark: using the most distant galaxies to probe cosmic reionization

NASA Astrophysics Data System (ADS)

De Barros, Stephane

2017-08-01

One of the major unresolved problems in modern cosmology is when and how the universe was ionized. The consensus scenario is that ultra-faint, low-mass galaxies contributed most to the UV background at high-redshift and that reionization was an inhomogeneous process, with ionized bubbles created first around galaxy overdensities. The very surprising discovery of Ly-alpha emission lines around a large fraction of the most luminous galaxies at z=7.4-8.7, when we expect the universe to be highly neutral, could thus be explained by the fact that they lie in large HII bubbles which were ionized thanks to yet undetected fainter neighbors. Theoretical models indeed predict a boost of up to 6x larger galaxy counts around the brightest sources compared to the general field, when probing down to luminosities as faint as 0.1L_UV of the central source. Here we propose a direct test of these models by searching for fainter neighbors around three bright z>7.4 galaxies emitting Ly-alpha, including two sources that lie only 9 Mpc from each other and could share the same ionized bubble, as well as the most distant confirmed Ly-alpha emitter EGSY-8p7 at z=8.68. Given the expected overdensities, we have the opportunity to detect 20 (and up to 50) new z 7-9 galaxies with only a modest investment of HST time. These observations are thus maximally efficient at providing a large number of precious high-redshift targets for early JWST spectroscopy to directly study the galaxies that are in the process of ionizing the universe. Our imaging will further enhance the legacy of the CANDELS/EGS field, and we will make the reduced data available to the community immediately for JWST follow-up.

Transit dosimetry in IMRT with an a-Si EPID in direct detection configuration

NASA Astrophysics Data System (ADS)

Sabet, Mahsheed; Rowshanfarzad, Pejman; Vial, Philip; Menk, Frederick W.; Greer, Peter B.

2012-08-01

In this study an amorphous silicon electronic portal imaging device (a-Si EPID) converted to direct detection configuration was investigated as a transit dosimeter for intensity modulated radiation therapy (IMRT). After calibration to dose and correction for a background offset signal, the EPID-measured absolute IMRT transit doses for 29 fields were compared to a MatriXX two-dimensional array of ionization chambers (as reference) using Gamma evaluation (3%, 3 mm). The MatriXX was first evaluated as reference for transit dosimetry. The accuracy of EPID measurements was also investigated by comparison of point dose measurements by an ionization chamber on the central axis with slab and anthropomorphic phantoms in a range of simple to complex fields. The uncertainty in ionization chamber measurements in IMRT fields was also investigated by its displacement from the central axis and comparison with the central axis measurements. Comparison of the absolute doses measured by the EPID and MatriXX with slab phantoms in IMRT fields showed that on average 96.4% and 97.5% of points had a Gamma index<1 in head and neck and prostate fields, respectively. For absolute dose comparisons with anthropomorphic phantoms, the values changed to an average of 93.6%, 93.7% and 94.4% of points with Gamma index<1 in head and neck, brain and prostate fields, respectively. Point doses measured by the EPID and ionization chamber were within 3% difference for all conditions. The deviations introduced in the response of the ionization chamber in IMRT fields were<1%. The direct EPID performance for transit dosimetry showed that it has the potential to perform accurate, efficient and comprehensive in vivo dosimetry for IMRT.

Fundamental Scaling of Microplasmas and Tunable UV Light Generation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manginell, Ronald P.; Sillerud, Colin Halliday; Hopkins, Matthew M.

2016-11-01

The temporal evolution of spectral lines from microplasma devices (MD) was studied, including impurity transitions. Long-wavelength emission diminishes more rapidly than deep UV with decreasing pulse width and RF operation. Thus, switching from DC to short pulsed or RF operation, UV emissions can be suppressed, allowing for real-time tuning of the ionization energy of a microplasma photo-ionization source, which is useful for chemical and atomic physics. Scaling allows MD to operate near atmospheric pressure where excimer states are efficiently created and emit down to 65 nm; laser emissions fall off below 200 nm, making MD light sources attractive for deepmore » UV use. A first fully-kinetic three-dimensional model was developed that explicitly calculates electron-energy distribution function. This, and non-continuum effects, were studied with the model and how they are impacted by geometry and transient or DC operation. Finally, a global non-dimensional model was developed to help explain general trends MD physics.« less

Electrospray Ionization Efficiency Is Dependent on Different Molecular Descriptors with Respect to Solvent pH and Instrumental Configuration

PubMed Central

Kiontke, Andreas; Oliveira-Birkmeier, Ariana; Opitz, Andreas

2016-01-01

Over the past decades, electrospray ionization for mass spectrometry (ESI-MS) has become one of the most commonly employed techniques in analytical chemistry, mainly due to its broad applicability to polar and semipolar compounds and the superior selectivity which is achieved in combination with high resolution separation techniques. However, responsiveness of an analytical method also determines its suitability for the quantitation of chemical compounds; and in electrospray ionization for mass spectrometry, it can vary significantly among different analytes with identical solution concentrations. Therefore, we investigated the ESI-response behavior of 56 nitrogen-containing compounds including aromatic amines and pyridines, two compound classes of high importance to both, synthetic organic chemistry as well as to pharmaceutical sciences. These compounds are increasingly analyzed employing ESI mass spectrometry detection due to their polar, basic character. Signal intensities of the peaks from the protonated molecular ion (MH+) were acquired under different conditions and related to compound properties such as basicity, polarity, volatility and molecular size exploring their quantitative impact on ionization efficiency. As a result, we found that though solution basicity of a compound is the main factor initially determining the ESI response of the protonated molecular ion, other factors such as polarity and vaporability become more important under acidic solvent conditions and may nearly outweigh the importance of basicity under these conditions. Moreover, we show that different molecular descriptors may become important when using different types of instruments for such investigations, a fact not detailed so far in the available literature. PMID:27907110

Direct characterization of commercial lecithins by easy ambient sonic-spray ionization mass spectrometry.

PubMed

Fernandes, Gabriel D; Alberici, Rosana M; Pereira, Gustavo G; Cabral, Elaine C; Eberlin, Marcos N; Barrera-Arellano, Daniel

2012-12-01

Commercial lecithins are composed mainly of phospholipids and triacylglycerols. The analysis of the commercial lecithins, including their fraction of phospholipids, normally involves laborious and expensive protocols. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) is shown to be an efficient technique for the analysis of lipids. Samples of commercial lecithins including standards, refined, deoiled and modified soy lecithin were tested. Characteristic profiles of phosphatidylcholines and triacylglycerols are detected by EASI(+)-MS, whereas EASI(-)-MS provided phosphatidylethanolamines, glycophospholipids and free fatty acids profiles. Acetylated lecithins also displayed characteristic acetylated derivatives. EASI-MS data was also compared to MALDI-MS, and found to display richer compositional information. The industrial process applied to lecithin fabrication was also characterised via typical EASI-MS profiles. EASI-MS both in its positive and negative ion modes offers a direct, fast and efficient technique able to characterise commercial lecithin. Copyright © 2012 Elsevier Ltd. All rights reserved.

Determination of hexabromocyclododecane by flowing atmospheric pressure afterglow mass spectrometry.

PubMed

Smoluch, Marek; Silberring, Jerzy; Reszke, Edward; Kuc, Joanna; Grochowalski, Adam

2014-10-01

The first application of a flowing atmospheric-pressure afterglow ion source for mass spectrometry (FAPA-MS) for the chemical characterization and determination of hexabromocyclododecane (HBCD) is presented. The samples of technical HBCD and expanded polystyrene foam (EPS) containing HBCD as a flame retardant were prepared by dissolving the appropriate solids in dichloromethane. The ionization of HBCD was achieved with a prototype FAPA source. The ions were detected in the negative-ion mode. The ions corresponding to a deprotonated HBCD species (m/z 640.7) as well as chlorine (m/z 676.8), nitrite (m/z 687.8) and nitric (m/z 703.8) adducts were observed in the spectra. The observed isotope pattern is characteristic for a compound containing six bromine atoms. This technique is an effective approach to detect HBCD, which is efficiently ionized in a liquid phase, resulting in high detection efficiency and sensitivity. Copyright © 2014 Elsevier B.V. All rights reserved.

Dependence of optimal initial density on laser parameters for multi-keV x-ray radiators generated by nanosecond laser-produced underdense plasma

NASA Astrophysics Data System (ADS)

Tu, Shao-yong; Yuan, Yong-teng; Hu, Guang-yue; Miao, Wen-yong; Zhao, Bin; Zheng, Jian; Jiang, Shao-en; Ding, Yong-kun

2016-01-01

Efficient multi-keV x-ray sources can be produced using nanosecond laser pulse-heated middle-Z underdense plasmas generated using gas or foam. Previous experimental results show that an optimal initial target density exists for efficient multi-keV x-ray emission at which the laser ionization wave is supersonic. Here we explore the influence of the laser intensity and the pulse duration on this optimal initial target density via a one-dimensional radiation hydrodynamic simulation. The simulation shows that the optimal initial density is sensitive to both the laser intensity and the pulse duration. However, the speed of the supersonic ionization wave at the end of the laser irradiation is always maintained at 1.5 to 1.7 times that of the ion acoustic wave under the optimal initial density conditions.

Efficient Enrichment and Analysis of Vicinal-Diol-Containing Flavonoid Molecules Using Boronic-Acid-Functionalized Particles and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry.

PubMed

Kim, Eunjin; Kang, Hyunook; Choi, Insung; Song, Jihyeon; Mok, Hyejung; Jung, Woong; Yeo, Woon-Seok

2018-05-09

Detection and quantitation of flavonoids are relatively difficult compared to those of other small-molecule analytes because flavonoids undergo rapid metabolic processes, resulting in their elimination from the body. Here, we report an efficient enrichment method for facilitating the analysis of vicinal-diol-containing flavonoid molecules using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In our strategy, boronic-acid-functionalized polyacrylamide particles were used, where boronic acids bound to vicinal diols to form boronate monoesters at basic pH. This complex remained intact during the enrichment processes, and the vicinal-diol-containing flavonoids were easily separated by centrifugation and subsequent acidic treatments. The selectivity and limit of detection of our strategy were confirmed by mass spectrometry analysis, and the validity was assessed by performing the detection and quantitation of quercetin in mouse organs.

On plate graphite supported sample processing for simultaneous lipid and protein identification by matrix assisted laser desorption ionization mass spectrometry.

PubMed

Calvano, Cosima Damiana; van der Werf, Inez Dorothé; Sabbatini, Luigia; Palmisano, Francesco

2015-05-01

The simultaneous identification of lipids and proteins by matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) after direct on-plate processing of micro-samples supported on colloidal graphite is demonstrated. Taking advantages of large surface area and thermal conductivity, graphite provided an ideal substrate for on-plate proteolysis and lipid extraction. Indeed proteins could be efficiently digested on-plate within 15 min, providing sequence coverages comparable to those obtained by conventional in-solution overnight digestion. Interestingly, detection of hydrophilic phosphorylated peptides could be easily achieved without any further enrichment step. Furthermore, lipids could be simultaneously extracted/identified without any additional treatment/processing step as demonstrated for model complex samples such as milk and egg. The present approach is simple, efficient, of large applicability and offers great promise for protein and lipid identification in very small samples. Copyright © 2015 Elsevier B.V. All rights reserved.

A velocity-map imaging study of methyl non-resonant multiphoton ionization from the photodissociation of CH3I in the A-band

PubMed Central

Poullain, Sonia Marggi; Chicharro, David V.; Rubio-Lago, Luis; García-Vela, Alberto

2017-01-01

Chemical reaction dynamics and, particularly, photodissociation in the gas phase are generally studied using pump–probe schemes where a first laser pulse induces the process under study and a second one detects the produced fragments. Providing an efficient detection of ro-vibrationally state-selected photofragments, the resonance enhanced multiphoton ionization (REMPI) technique is, without question, the most popular approach used for the probe step, while non-resonant multiphoton ionization (NRMPI) detection of the products is scarce. The main goal of this work is to test the sensitivity of the NRMPI technique to fragment vibrational distributions arising from molecular photodissociation processes. We revisit the well-known process of methyl iodide photodissociation in the A-band at around 280 nm, using the velocity-map imaging technique in conjunction with NRMPI of the methyl fragment. The detection wavelength, carefully selected to avoid any REMPI transition, was scanned between 325 and 335 nm seeking correlations between the different observables—the product vibrational, translational and angular distributions—and the excitation wavelength of the probe laser pulse. The experimental results have been discussed on the base of quantum dynamics calculations of photofragment vibrational populations carried out on available ab initio potential-energy surfaces using a four-dimensional model. This article is part of the themed issue ‘Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces’. PMID:28320907

Optimal control of the strong-field ionization of silver clusters in helium droplets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Truong, N. X.; Goede, S.; Przystawik, A.

Optimal control techniques combined with femtosecond laser pulse shaping are applied to steer and enhance the strong-field induced emission of highly charged atomic ions from silver clusters embedded in helium nanodroplets. With light fields shaped in amplitude and phase we observe a substantial increase of the Ag{sup q+} yield for q>10 when compared to bandwidth-limited and optimally stretched pulses. A remarkably simple double-pulse structure, containing a low-intensity prepulse and a stronger main pulse, turns out to produce the highest atomic charge states up to Ag{sup 20+}. A negative chirp during the main pulse hints at dynamic frequency locking to themore » cluster plasmon. A numerical optimal control study on pure silver clusters with a nanoplasma model converges to a similar pulse structure and corroborates that the optimal light field adapts to the resonant excitation of cluster surface plasmons for efficient ionization.« less

Scintillator Non-Proportionality: Present Understanding and Future Challenges

NASA Astrophysics Data System (ADS)

Moses, W. W.; Payne, S. A.; Choong, W.-S.; Hull, G.; Reutter, B. W.

2008-06-01

Scintillator non-proportionality (the fact that the conversion factor between the energy deposited in a scintillator and the number of visible photons produced is not constant) has been studied both experimentally and theoretically for 50 years. Early research centered on the dependence of the conversion factor on the species of the ionizing radiation (gamma, alpha, beta, proton, etc.), and researchers during the 1960s discovered a strong correlation between the scintillation efficiency and the ionization density. In more recent years, non-proportionality has been proposed as the reason why the energy resolution of most scintillators is worse than that predicted by counting statistics. While much progress has been made, there are still major gaps in our understanding of both the fundamental causes of non-proportionality and their quantitative link to scintillator energy resolution. This paper summarizes the present state of knowledge on the nature of the light-yield non-proportionality and its effect on energy resolution.

Efficient G0W0 using localized basis sets: a benchmark for molecules

NASA Astrophysics Data System (ADS)

Koval, Petr; Per Ljungberg, Mathias; Sanchez-Portal, Daniel

Electronic structure calculations within Hedin's GW approximation are becoming increasingly accessible to the community. In particular, as it has been shown earlier and we confirm by calculations using our MBPT_LCAO package, the computational cost of the so-called G0W0 can be made comparable to the cost of a regular Hartree-Fock calculation. In this work, we study the performance of our new implementation of G0W0 to reproduce the ionization potentials of all 117 closed-shell molecules belonging to the G2/97 test set, using a pseudo-potential starting point provided by the popular density-functional package SIESTA. Moreover, the ionization potentials and electron affinities of a set of 24 acceptor molecules are compared to experiment and to reference all-electron calculations. PK: Guipuzcoa Fellow; PK,ML,DSP: Deutsche Forschungsgemeinschaft (SFB1083); PK,DSP: MINECO MAT2013-46593-C6-2-P.

The galaxy NGC 1566 - Distribution and kinematics of the ionized gas

NASA Astrophysics Data System (ADS)

Comte, G.; Duquennoy, A.

1982-10-01

H-alpha narrowband observations are the basis of a study of ionized hydrogen in the large spiral galaxy NGC 1566 which has yielded a catalog of 418 H II regions covering the main body of the galaxy, supplemented by 59 positions and estimated H-alpha luminosities for regions located in the pseudo-outer ring where no H-alpha plate is available. A discussion of luminosity function, diameter distribution and spiral structure notes evidence for a double two-armed spiral pattern. The plane of the galaxy appears warped, and the efficiency of the two different spiral patterns in star formation is different. A preliminary radial velocity field is determined from three interferograms in H-alpha light, and is found to be acceptably fitted by a simple bulge-plus-disk dynamical model in which the apparent disk mass-to-light ratio sharply increases from center to edge.

High Resolution Separations and Improved Ion Production and Transmission in Metabolomics

PubMed Central

Metz, Thomas O.; Page, Jason S.; Baker, Erin S.; Tang, Keqi; Ding, Jie; Shen, Yufeng; Smith, Richard D.

2008-01-01

The goal of metabolomics analyses is the detection and quantitation of as many sample components as reasonably possible in order to identify compounds or “features” that can be used to characterize the samples under study. When utilizing electrospray ionization to produce ions for analysis by mass spectrometry (MS), it is important that metabolome sample constituents be efficiently separated prior to ion production, in order to minimize ionization suppression and thereby extend the dynamic range of the measurement, as well as the coverage of the metabolome. Similarly, optimization of the MS inlet and interface can lead to increased measurement sensitivity. This perspective review will focus on the role of high resolution liquid chromatography (LC) separations in conjunction with improved ion production and transmission for LC-MS-based metabolomics. Additional emphasis will be placed on the compromise between metabolome coverage and sample analysis throughput. PMID:19255623

Effects of ionizing radiation on bio-active plant extracts useful for preventing oxidative damages.

PubMed

Mulinacci, Nadia; Valletta, Alessio; Pasqualetti, Valentina; Innocenti, Marzia; Giuliani, Camilla; Bellumori, Maria; De Angelis, Giulia; Carnevale, Alessia; Locato, Vittoria; Di Venanzio, Cristina; De Gara, Laura; Pasqua, Gabriella

2018-04-02

Humans are exposed to ionizing radiations in medical radiodiagnosis and radiotherapy that cause oxidative damages and degenerative diseases. Airplane pilots, and even more astronauts, are exposed to a variety of potentially harmful factors, including cosmic radiations. Among the phytochemicals, phenols are particularly efficient in countering the oxidative stress. In the present study, different extracts obtained from plant food, plant by-products and dietary supplements, have been compared for their antioxidant properties before and after irradiation of 140 cGy, a dose absorbed during a hypothetical stay of three years in the space. All the dry extracts, characterized in terms of vitamin C and phenolic content, remained chemically unaltered and maintained their antioxidant capability after irradiation. Our results suggest the potential use of these extracts as nutraceuticals to protect humans from oxidative damages, even when these extracts must be stored in an environment exposed to cosmic radiations as in a space station.

PHOTON STUDY WITH SPUTNIK III

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chudakov, A.E.

1961-01-01

>A scintillation counter with twice the efficiency of a Geiger counter for photon recording was placed in the third Soviet satellite. The counter consisted of a cylindrical crystal of sodium iodide and a photomuitiplier. It was found that the total ionization in the crystal was much greater than expected. This excess seemed to depend on geomagnetic longitude as well as latitude. The most probable explanation is the bremsstrahlung radiation of electrons of energy less than 100 kev. (L.N.N.)

Modeling VLF signal modulation during solar flares with GEANT4 Monte Carlo simulation, a simple chemical model and LWPC

NASA Astrophysics Data System (ADS)

Palit, Sourav; Chakrabarti, Sandip Kumar; Pal, Sujay; Basak, Tamal

Extra ionization by X-rays during solar flares affects VLF signal propagation through D-region ionosphere. Ionization produced in the lower ionosphere due to X-ray spectra of solar flares are simulated with an efficient detector simulation program, GEANT4. The balancing between the ionization and loss processes, causing the lower ionosphere to settle back to its undisturbed state is handled with a simple chemical model consisting of four broad species of ion densities. Using the electron densities, modified VLF signal amplitude is then computed with LWPC code. VLF signal along NWC (Australia) to IERC/ICSP (India) propagation path is examined during a M and a X-type solar flares and observational deviations are compared with simulated results. The agreement is found to be excellent.

Driving Turbulence and Triggering Star Formation by Ionizing Radiation

NASA Astrophysics Data System (ADS)

Gritschneder, Matthias; Naab, Thorsten; Walch, Stefanie; Burkert, Andreas; Heitsch, Fabian

2009-03-01

We present high-resolution simulations on the impact of ionizing radiation of massive O stars on the surrounding turbulent interstellar medium (ISM). The simulations are performed with the newly developed software iVINE which combines ionization with smoothed particle hydrodynamics (SPH) and gravitational forces. We show that radiation from hot stars penetrates the ISM, efficiently heats cold low-density gas and amplifies overdensities seeded by the initial turbulence. The formation of observed pillar-like structures in star-forming regions (e.g. in M16) can be explained by this scenario. At the tip of the pillars gravitational collapse can be induced, eventually leading to the formation of low-mass stars. Detailed analysis of the evolution of the turbulence spectra shows that UV radiation of O stars indeed provides an excellent mechanism to sustain and even drive turbulence in the parental molecular cloud.

Characterization of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source for mass spectrometry.

PubMed

Forbes, Thomas P; Dixon, R Brent; Muddiman, David C; Degertekin, F Levent; Fedorov, Andrei G

2009-09-01

An initial investigation into the effects of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source is reported to gain understanding of ionization mechanisms and to improve analyte ionization efficiency and operation stability. In RF-only mode, AMUSE ejects, on average, an equal number of slightly positive and slightly negative charged droplets due to random charge fluctuations, providing inefficient analyte ionization. Charge separation at the nozzle orifice is achieved by the application of an external electric field. By bringing the counter electrode close to the nozzle array, strong electric fields can be applied at relatively low DC potentials. It has been demonstrated, through a number of electrode/electrical potential configurations, that increasing charge separation leads to improvement in signal abundance, signal-to-noise ratio, and signal stability.

The MOSDEF Survey: Direct Observational Constraints on the Ionizing Photon Production Efficiency, ξ ion, at z ∼ 2

NASA Astrophysics Data System (ADS)

Shivaei, Irene; Reddy, Naveen A.; Siana, Brian; Shapley, Alice E.; Kriek, Mariska; Mobasher, Bahram; Freeman, William R.; Sanders, Ryan L.; Coil, Alison L.; Price, Sedona H.; Fetherolf, Tara; Azadi, Mojegan; Leung, Gene; Zick, Tom

2018-03-01

We combine Hα and Hβ spectroscopic measurements and UV photometry for a sample of 673 galaxies from the MOSDEF survey to constrain hydrogen-ionizing photon production efficiencies ({ξ }ion}) at z = 1.4–2.6. We find < {log}({ξ }ion}/[{{{s}}}-1/{erg} {{{s}}}-1 {Hz}}-1])> = 25.06 (25.34), assuming the Calzetti (SMC) curve for the UV dust correction and a scatter of 0.28 dex in the {ξ }ion} distribution. After accounting for observational uncertainties and variations in dust attenuation, we conclude that the remaining scatter in {ξ }ion} is likely dominated by galaxy-to-galaxy variations in stellar populations, including the slope and upper-mass cutoff of the initial mass function, stellar metallicity, star formation burstiness, and stellar evolution (e.g., single/binary star evolution). Moreover, {ξ }ion} is elevated in galaxies with high ionization states (high [O III]/[O II]) and low oxygen abundances (low [N II]/Hα and high [O III]/Hβ) in the ionized ISM. However, {ξ }ion} does not correlate with the offset from the z ∼ 0 star-forming locus in the BPT diagram, suggesting no change in the hardness of the ionizing radiation accompanying the offset from the z ∼ 0 sequence. We also find that galaxies with blue UV spectral slopes (< β > =-2.1) have {ξ }ion} elevated by a factor of ∼2 relative to the average {ξ }ion} of the sample (< β > =-1.4). If these blue galaxies are similar to those at z > 6, our results suggest that a lower Lyman-continuum escape fraction is required for galaxies to maintain reionization, compared to the canonical {ξ }ion} predictions from stellar population models. Furthermore, we demonstrate that even with robustly dust-corrected Hα, the UV dust attenuation can cause on average a ∼0.3 dex systematic uncertainty in {ξ }ion} calculations.

Nuclear-Recoil Energy Scale in CDMS II Silicon Dark-Matter Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agnese, R.; et al.

The Cryogenic Dark Matter Search (CDMS II) experiment aims to detect dark matter particles that elastically scatter from nuclei in semiconductor detectors. The resulting nuclear-recoil energy depositions are detected by ionization and phonon sensors. Neutrons produce a similar spectrum of low-energy nuclear recoils in such detectors, while most other backgrounds produce electron recoils. The absolute energy scale for nuclear recoils is necessary to interpret results correctly. The energy scale can be determined in CDMS II silicon detectors using neutrons incident from a broad-spectrummore » $$^{252}$$Cf source, taking advantage of a prominent resonance in the neutron elastic scattering cross section of silicon at a recoil (neutron) energy near 20 (182) keV. Results indicate that the phonon collection efficiency for nuclear recoils is $$4.8^{+0.7}_{-0.9}$$% lower than for electron recoils of the same energy. Comparisons of the ionization signals for nuclear recoils to those measured previously by other groups at higher electric fields indicate that the ionization collection efficiency for CDMS II silicon detectors operated at $$\\sim$$4 V/cm is consistent with 100% for nuclear recoils below 20 keV and gradually decreases for larger energies to $$\\sim$$75% at 100 keV. The impact of these measurements on previously published CDMS II silicon results is small.« less

Top-down approach for the direct characterization of low molecular weight heparins using LC-FT-MS.

PubMed

Li, Lingyun; Zhang, Fuming; Zaia, Joseph; Linhardt, Robert J

2012-10-16

Low molecular heparins (LMWHs) are structurally complex, heterogeneous, polydisperse, and highly negatively charged mixtures of polysaccharides. The direct characterization of LMWH is a major challenge for currently available analytical technologies. Electrospray ionization (ESI) liquid chromatography-mass spectrometry (LC-MS) is a powerful tool for the characterization complex biological samples in the fields of proteomics, metabolomics, and glycomics. LC-MS has been applied to the analysis of heparin oligosaccharides, separated by size exclusion, reversed phase ion-pairing chromatography, and chip-based amide hydrophilic interaction chromatography (HILIC). However, there have been limited applications of ESI-LC-MS for the direct characterization of intact LMWHs (top-down analysis) due to their structural complexity, low ionization efficiency, and sulfate loss. Here we present a simple and reliable HILIC-Fourier transform (FT)-ESI-MS platform to characterize and compare two currently marketed LMWH products using the top-down approach requiring no special sample preparation steps. This HILIC system relies on cross-linked diol rather than amide chemistry, affording highly resolved chromatographic separations using a relatively high percentage of acetonitrile in the mobile phase, resulting in stable and high efficiency ionization. Bioinformatics software (GlycReSoft 1.0) was used to automatically assign structures within 5-ppm mass accuracy.

Constraining the sensitivity of iodide adduct chemical ionization mass spectrometry to multifunctional organic molecules using the collision limit and thermodynamic stability of iodide ion adducts

DOE PAGES

Lopez-Hilfiker, Felipe D.; Iyer, Siddarth; Mohr, Claudia; ...

2016-04-06

The sensitivity of a chemical ionization mass spectrometer (ions formed per number density of analytes) is fundamentally limited by the collision frequency between reagent ions and analytes, known as the collision limit, the ion–molecule reaction time, and the transmission efficiency of product ions to the detector. We use the response of a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) to N 2O 5, known to react with iodide at the collision limit, to constrain the combined effects of ion–molecule reaction time, which is strongly influenced by mixing and ion losses in the ion–molecule reaction drift tube. A mass spectrometric voltage scanningmore » procedure elucidates the relative binding energies of the ion adducts, which influence the transmission efficiency of molecular ions through the electric fields within the vacuum chamber. Together, this information provides a critical constraint on the sensitivity of a ToF-CIMS towards a wide suite of routinely detected multifunctional organic molecules for which no calibration standards exist. Lastly, we describe the scanning procedure and collision limit determination, and we show results from the application of these constraints to the measurement of organic aerosol composition at two different field locations.« less

Investigation of Recombination Processes In A Magnetized Plasma

NASA Technical Reports Server (NTRS)

Chavers, Greg; Chang-Diaz, Franklin; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

Interplanetary travel requires propulsion systems that can provide high specific impulse (Isp), while also having sufficient thrust to rapidly accelerate large payloads. One such propulsion system is the Variable Specific Impulse Magneto-plasma Rocket (VASIMR), which creates, heats, and exhausts plasma to provide variable thrust and Isp, optimally meeting the mission requirements. A large fraction of the energy to create the plasma is frozen in the exhaust in the form of ionization energy. This loss mechanism is common to all electromagnetic plasma thrusters and has an impact on their efficiency. When the device operates at high Isp, where the exhaust kinetic energy is high compared to the ionization energy, the frozen flow component is of little consequence; however, at low Isp, the effect of the frozen flow may be important. If some of this energy could be recovered through recombination processes, and re-injected as neutral kinetic energy, the efficiency of VASIMR, in its low Isp/high thrust mode may be improved. In this operating regime, the ionization energy is a large portion of the total plasma energy. An experiment is being conducted to investigate the possibility of recovering some of the energy used to create the plasma. This presentation will cover the progress and status of the experiment involving surface recombination of the plasma.

Applicability of post-ionization theory to laser-assisted field evaporation of magnetite

DOE PAGES

Schreiber, Daniel K.; Chiaramonti, Ann N.; Gordon, Lyle M.; ...

2014-12-15

Analysis of the mean Fe ion charge state from laser-assisted field evaporation of magnetite (Fe3O4) reveals unexpected trends as a function of laser pulse energy that break from conventional post-ionization theory for metals. For Fe ions evaporated from magnetite, the effects of post-ionization are partially offset by the increased prevalence of direct evaporation into higher charge states with increasing laser pulse energy. Therefore the final charge state is related to both the field strength and the laser pulse energy, despite those variables themselves being intertwined when analyzing at a constant detection rate. Comparison of data collected at different base temperaturesmore » also show that the increased prevalence of Fe2+ at higher laser energies is possibly not a direct thermal effect. Conversely, the ratio of 16O+:16O2+ is well-correlated with field strength and unaffected by laser pulse energy on its own, making it a better overall indicator of the field evaporation conditions than the mean Fe charge state. Plotting the normalized field strength versus laser pulse energy also elucidates a non-linear dependence, in agreement with previous observations on semiconductors, that suggests a field-dependent laser absorption efficiency. Together these observations demonstrate that the field evaporation process for laser-pulsed oxides exhibits fundamental differences from metallic specimens that cannot be completely explained by post-ionization theory. Further theoretical studies, combined with detailed analytical observations, are required to understand fully the field evaporation process of non-metallic samples.« less

Isomer and Fluorination Effects among Fluorine Substituted Hydrocarbon C3/C4 Molecules in Electron Impact Ionization

NASA Astrophysics Data System (ADS)

Patel, U. R.; Joshipura, K. N.

2015-05-01

Electron collision processes are very important in both man-made and natural plasmas, for determining the energy balances and transport properties of electrons. Electron -molecule scattering leading to ionization represents one of the most fundamental processes in collision physics. In the gas phase, the total efficiency of the process is described by the absolute total electron impact ionization cross section. Carbon based materials are some of the widely used materials for a divertor plate and magnetically confined fusion devices. In the ``ITER,'' it is very important for steady state operation to have an estimate of the lifetime of carbon plasma facing components. Apart from fusion plasma relevance, the present theoretical study is very important in modeling and controlling other electron assisted processes in many areas. Hydrocarbons play an important role for plasma diagnostics as impurities in the Tokamak fusion divertor, as seed gases for the production of radicals and ions in low temperature plasma processing. Fluorine substituted hydrocarbons (perfluorocarbons) are important as reactants in plasma assisted fabrication processes. In the present work, we have calculated total ionization cross sections Qion for C3/C4 Hydrocarbon isomers by electron impact, and comparisons are made mutually to observe isomer effect. Comparisons are also made by substituting H atom by F atom and revealing fluorination effect. The present calculations are quite significant owing to the lack of experimental data, with just an isolated previous theoretical work in some cases.

Indirect dark matter signatures in the cosmic dark ages. II. Ionization, heating, and photon production from arbitrary energy injections

NASA Astrophysics Data System (ADS)

Slatyer, Tracy R.

2016-01-01

Any injection of electromagnetically interacting particles during the cosmic dark ages will lead to increased ionization, heating, production of Lyman-α photons and distortions to the energy spectrum of the cosmic microwave background, with potentially observable consequences. In this paper we describe numerical results for the low-energy electrons and photons produced by the cooling of particles injected at energies from keV to multi-TeV scales, at arbitrary injection redshifts (but focusing on the post-recombination epoch). We use these data, combined with existing calculations modeling the cooling of these low-energy particles, to estimate the resulting contributions to ionization, excitation and heating of the gas, and production of low-energy photons below the threshold for excitation and ionization. We compute corrected deposition-efficiency curves for annihilating dark matter, and demonstrate how to compute equivalent curves for arbitrary energy-injection histories. These calculations provide the necessary inputs for the limits on dark matter annihilation presented in the accompanying paper I, but also have potential applications in the context of dark matter decay or deexcitation, decay of other metastable species, or similar energy injections from new physics. We make our full results publicly available at http://nebel.rc.fas.harvard.edu/epsilon, to facilitate further independent studies. In particular, we provide the full low-energy electron and photon spectra, to allow matching onto more detailed codes that describe the cooling of such particles at low energies.

Non-traditional applications of laser desorption/ionization mass spectrometry

NASA Astrophysics Data System (ADS)

McAlpin, Casey R.

Seven studies were carried out using laser desorption/ionization mass spectrometry (LDI MS) to develop enhanced methodologies for a variety of analyte systems by investigating analyte chemistries, ionization processes, and elimination of spectral interferences. Applications of LDI and matrix assisted laser/desorption/ionization (MALDI) have been previously limited by poorly understood ionization phenomena, and spectral interferences from matrices. Matrix assisted laser desorption ionization MS is well suited to the analysis of proteins. However, the proteins associated with bacteriophages often form complexes which are too massive for detection with a standard MALDI mass spectrometer. As such, methodologies for pretreatment of these samples are discussed in detail in the first chapter. Pretreatment of bacteriophage samples with reducing agents disrupted disulfide linkages and allowed enhanced detection of bacteriophage proteins. The second chapter focuses on the use of MALDI MS for lipid compounds whose molecular mass is significantly less than the proteins for which MALDI is most often applied. The use of MALDI MS for lipid analysis presented unique challenges such as matrix interference and differential ionization efficiencies. It was observed that optimization of the matrix system, and addition of cationization reagents mitigated these challenges and resulted in an enhanced methodology for MALDI MS of lipids. One of the challenges commonly encountered in efforts to expand MALDI MS applications is as previously mentioned interferences introduced by organic matrix molecules. The third chapter focuses on the development of a novel inorganic matrix replacement system called metal oxide laser ionization mass spectrometry (MOLI MS). In contrast to other matrix replacements, considerable effort was devoted to elucidating the ionization mechanism. It was shown that chemisorption of analytes to the metal oxide surface produced acidic adsorbed species which then protonated free analyte molecules. Expanded applications of MOLI MS were developed following description of the ionization mechanism. A series of experiments were carried out involving treatment of metal oxide surfaces with reagent molecules to expand MOLI MS and develop enhanced MOLI MS methodologies. It was found that treatment of the metal oxide surface with a small molecule to act as a proton source expanded MOLI MS to analytes which did not form acidic adsorbed species. Proton-source pretreated MOLI MS was then used for the analysis of oils obtained from the fast, anoxic pyrolysis of biomass (py-oil). These samples are complex and produce MOLI mass spectra with many peaks. In this experiment, methods of data reduction including Kendrick mass defects and nominal mass z*-scores, which are commonly used for the study of petroleum fractions, were used to interpret these spectra and identify the major constituencies of py-oils. Through data reduction and collision induced dissociation (CID), homologous series of compounds were rapidly identified. The final chapter involves using metal oxides to catalytically cleave the ester linkage on lipids containing fatty acids in addition to ionization. The cleavage process results in the production of spectra similar to those observed with saponification/methylation. Fatty acid profiles were generated for a variety of micro-organisms to differentiate between bacterial species. (Abstract shortened by UMI.)

Closed Cycle Magnetohydrodynamic Nuclear Space Power Generation Using Helium/Xenon Working Plasma

NASA Technical Reports Server (NTRS)

Litchford, R. J.; Harada, N.

2005-01-01

A multimegawatt-class nuclear fission powered closed cycle magnetohydrodynamic space power plant using a helium/xenon working gas has been studied, to include a comprehensive system analysis. Total plant efficiency was expected to be 55.2 percent including pre-ionization power. The effects of compressor stage number, regenerator efficiency, and radiation cooler temperature on plant efficiency were investigated. The specific mass of the power generation plant was also examined. System specific mass was estimated to be 3 kg/kWe for a net electrical output power of 1 MWe, 2-3 kg/kWe at 2 MWe, and approx.2 kg/KWe at >3 MWe. Three phases of research and development plan were proposed: (1) Phase I-proof of principle, (2) Phase II-demonstration of power generation, and (3) Phase III-prototypical closed loop test.

Investigation of theoretical efficiency limit of hot carriers solar cells with a bulk indium nitride absorber

NASA Astrophysics Data System (ADS)

Aliberti, P.; Feng, Y.; Takeda, Y.; Shrestha, S. K.; Green, M. A.; Conibeer, G.

2010-11-01

Theoretical efficiencies of a hot carrier solar cell considering indium nitride as the absorber material have been calculated in this work. In a hot carrier solar cell highly energetic carriers are extracted from the device before thermalisation, allowing higher efficiencies in comparison to conventional solar cells. Previous reports on efficiency calculations approached the problem using two different theoretical frameworks, the particle conservation (PC) model or the impact ionization model, which are only valid in particular extreme conditions. In addition an ideal absorber material with the approximation of parabolic bands has always been considered in the past. Such assumptions give an overestimation of the efficiency limits and results can only be considered indicative. In this report the real properties of wurtzite bulk InN absorber have been taken into account for the calculation, including the actual dispersion relation and absorbance. A new hybrid model that considers particle balance and energy balance at the same time has been implemented. Effects of actual impact ionization (II) and Auger recombination (AR) lifetimes have been included in the calculations for the first time, considering the real InN band structure and thermalisation rates. It has been observed that II-AR mechanisms are useful for cell operation in particular conditions, allowing energy redistribution of hot carriers. A maximum efficiency of 43.6% has been found for 1000 suns, assuming thermalisation constants of 100 ps and ideal blackbody absorption. This value of efficiency is considerably lower than values previously calculated adopting PC or II-AR models.

Quantitative Method for Simultaneous Analysis of Acetaminophen and 6 Metabolites.

PubMed

Lammers, Laureen A; Achterbergh, Roos; Pistorius, Marcel C M; Romijn, Johannes A; Mathôt, Ron A A

2017-04-01

Hepatotoxicity after ingestion of high-dose acetaminophen [N-acetyl-para-aminophenol (APAP)] is caused by the metabolites of the drug. To gain more insight into factors influencing susceptibility to APAP hepatotoxicity, quantification of APAP and metabolites is important. A few methods have been developed to simultaneously quantify APAP and its most important metabolites. However, these methods require a comprehensive sample preparation and long run times. The aim of this study was to develop and validate a simplified, but sensitive method for the simultaneous quantification of acetaminophen, the main metabolites acetaminophen glucuronide and acetaminophen sulfate, and 4 Cytochrome P450-mediated metabolites by using liquid chromatography with mass spectrometric (LC-MS) detection. The method was developed and validated for the human plasma, and it entailed a single method for sample preparation, enabling quick processing of the samples followed by an LC-MS method with a chromatographic run time of 9 minutes. The method was validated for selectivity, linearity, accuracy, imprecision, dilution integrity, recovery, process efficiency, ionization efficiency, and carryover effect. The method showed good selectivity without matrix interferences. For all analytes, the mean process efficiency was >86%, and the mean ionization efficiency was >94%. Furthermore, the accuracy was between 90.3% and 112% for all analytes, and the within- and between-run imprecision were <20% for the lower limit of quantification and <14.3% for the middle level and upper limit of quantification. The method presented here enables the simultaneous quantification of APAP and 6 of its metabolites. It is less time consuming than previously reported methods because it requires only a single and simple method for the sample preparation followed by an LC-MS method with a short run time. Therefore, this analytical method provides a useful method for both clinical and research purposes.

Efficient encapsulation of antisense oligonucleotides in lipid vesicles using ionizable aminolipids: formation of novel small multilamellar vesicle structures.

PubMed

Semple, S C; Klimuk, S K; Harasym, T O; Dos Santos, N; Ansell, S M; Wong, K F; Maurer, N; Stark, H; Cullis, P R; Hope, M J; Scherrer, P

2001-02-09

Typical methods used for encapsulating antisense oligodeoxynucleotides (ODN) and plasmid DNA in lipid vesicles result in very low encapsulation efficiencies or employ cationic lipids that exhibit unfavorable pharmacokinetic and toxicity characteristics when administered intravenously. In this study, we describe and characterize a novel formulation process that utilizes an ionizable aminolipid (1,2-dioleoyl-3-dimethylammonium propane, DODAP) and an ethanol-containing buffer system for encapsulating large quantities (0.15--0.25 g ODN/g lipid) of polyanionic ODN in lipid vesicles. This process requires the presence of up to 40% ethanol (v/v) and initial formulation at acidic pH values where the DODAP is positively charged. In addition, the presence of a poly(ethylene glycol)-lipid was required during the formulation process to prevent aggregation. The 'stabilized antisense-lipid particles' (SALP) formed are stable on adjustment of the external pH to neutral pH values and the formulation process allows encapsulation efficiencies of up to 70%. ODN encapsulation was confirmed by nuclease protection assays and (31)P NMR measurements. Cryo-electron microscopy indicated that the final particles consisted of a mixed population of unilamellar and small multilamellar vesicles (80--140 nm diameter), the relative proportion of which was dependent on the initial ODN to lipid ratio. Finally, SALP exhibited significantly enhanced circulation lifetimes in mice relative to free antisense ODN, cationic lipid/ODN complexes and SALP prepared with quaternary aminolipids. Given the small particle sizes and improved encapsulation efficiency, ODN to lipid ratios, and circulation times of this formulation compared to others, we believe SALP represent a viable candidate for systemic applications involving nucleic acid therapeutics.

Development of the MICROMEGAS detector for measuring the energy spectrum of alpha particles by using a 241Am source

NASA Astrophysics Data System (ADS)

Kim, Do Yoon; Ham, Cheolmin; Shin, Jae Won; Park, Tae-Sun; Hong, Seung-Woo; Andriamonje, Samuel; Kadi, Yacine; Tenreiro, Claudio

2016-05-01

We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting a particles emitted from an 241Am standard source. The voltage applied to the ionization region of the detector is optimized for stable operation at room temperature and atmospheric pressure. The energy of a particles from the 241Am source can be varied by changing the flight path of the a particle from the 241Am source. The channel numbers of the experimentally-measured pulse peak positions for different energies of the a particles are associated with the energies deposited by the alpha particles in the ionization region of the detector as calculated by using GEANT4 simulations; thus, the energy calibration of the MICROMEGAS detector for a particles is done. For the energy calibration, the thickness of the ionization region is adjusted so that a particles may completely stop in the ionization region and their kinetic energies are fully deposited in the region. The efficiency of our MICROMEGAS detector for a particles under the present conditions is found to be ~97.3%.

Is electrospray emission really due to columbic forces?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aliotta, Francesco, E-mail: aliotta@ipcf.cnr.it; Ponterio, Rosina C.; Salvato, Gabriele

2014-09-15

Electrospray ionization (ESI) is a widely adopted soft ionization method for mass spectroscopy (MS). In spite of the undeniable success of the technique, its mechanisms are difficult to be analytically modelled because the process is characterized by non-equilibrium conditions. The common belief is that the formation of gas-phase ions takes place at the apex of the Taylor cone via electrophoretic charging. The charge balance implies that a conversion of electrons to ions should occur at the metal-liquid interface of the injector needle. We have detected that the above description is based on unproved assumptions which are not consistent with themore » correct evaluation of the problem. The comparison between experiments performed under the usual geometry and observations obtained under symmetric field configurations suggests that the emitted droplets cannot be significantly charged or, at least, that any possible ionization mechanism is so poorly efficient to ensure that columbic forces cannot play a major role in jet formation, even in cases where the liquid consists of a solution of ionic species. Further work is required to clearly understand how ionization occurs in ESI-MS.« less

Experimental Determination of the Ionization Energies of MoSe 2, WS 2, and MoS 2 on SiO 2 Using Photoemission Electron Microscopy

DOE PAGES

Keyshar, Kunttal; Berg, Morgann; Zhang, Xiang; ...

2017-07-19

Here, the values of the ionization energies of transition metal dichalcogenides (TMDs) are needed to assess their potential usefulness in semiconductor heterojunctions for high-performance optoelectronics. Here, we report on the systematic determination of ionization energies for three prototypical TMD monolayers (MoSe 2, WS 2, and MoS 2) on SiO 2 using photoemission electron microscopy with deep ultraviolet illumination. The ionization energy displays a progressive decrease from MoS 2, to WS 2, to MoSe 2, in agreement with predictions of density functional theory calculations. Combined with the measured energy positions of the valence band edge at the Brillouin zone center, wemore » deduce that, in the absence of interlayer coupling, a vertical heterojunction comprising any of the three TMD monolayers would form a staggered (type-II) band alignment. This band alignment could give rise to long-lived interlayer excitons that are potentially useful for valleytronics or efficient electron–hole separation in photovoltaics.« less

Metabolomics relative quantitation with mass spectrometry using chemical derivatization and isotope labeling

DOE PAGES

O'Maille, Grace; Go, Eden P.; Hoang, Linh; ...

2008-01-01

Comprehensive detection and quantitation of metabolites from a biological source constitute the major challenges of current metabolomics research. Two chemical derivatization methodologies, butylation and amination, were applied to human serum for ionization enhancement of a broad spectrum of metabolite classes, including steroids and amino acids. LC-ESI-MS analysis of the derivatized serum samples provided a significant signal elevation across the total ion chromatogram to over a 100-fold increase in ionization efficiency. It was also demonstrated that derivatization combined with isotopically labeled reagents facilitated the relative quantitation of derivatized metabolites from individual as well as pooled samples.

State-resolved three-dimensional electron-momentum correlation in nonsequential double ionization of benzene

NASA Astrophysics Data System (ADS)

Winney, Alexander H.; Lin, Yun Fei; Lee, Suk Kyoung; Adhikari, Pradip; Li, Wen

2016-03-01

We report state-resolved electron-momentum correlation measurement of strong-field nonsequential double ionization in benzene. With a novel coincidence detection apparatus, highly efficient triple coincidence (electron-electron dication) and quadruple coincidence (electron-electron-cation-cation) are used to resolve the final ionic states and to characterize three-dimensional (3D) electron-momentum correlation. The primary states associated with dissociative and nondissociative dications are assigned. A 3D momentum anticorrelation is observed for the electrons in coincidence with dissociative benzene dication states whereas such a correlation is absent for nondissociative dication states.

Diode-laser-based RIMS measurements of strontium-90

NASA Astrophysics Data System (ADS)

Bushaw, B. A.; Cannon, B. D.

1998-12-01

Double- and triple-resonance excitation schemes for the ionization of strontium are presented. Use of single-mode diode lasers for the resonance excitations provides a high degree of optical isotopic selectivity: with double-resonance, selectivity of >104 for 90Sr against the stable Sr isotopes has been demonstrated. Measurement of lineshapes and stable isotope shifts in the triple-resonance process indicate that optical selectivity should increase to ˜109. When combined with mass spectrometer selectivity this is sufficient for measurement of 90Sr at background environmental levels. Additionally, autoionizing resonances have been investigated for improving ionization efficiency with lower power lasers.

Direct Analyses of Secondary Metabolites by Mass Spectrometry Imaging (MSI) from Sunflower (Helianthus annuus L.) Trichomes.

PubMed

Brentan Silva, Denise; Aschenbrenner, Anna-Katharina; Lopes, Norberto Peporine; Spring, Otmar

2017-05-10

Helianthus annuus (sunflower) displays non-glandular trichomes (NGT), capitate glandular trichomes (CGT), and linear glandular trichomes (LGT), which reveal different chemical compositions and locations in different plant tissues. With matrix-assisted laser desorption/ionization (MALDI) and laser desorption/ionization (LDI) mass spectrometry imaging (MSI) techniques, efficient methods were developed to analyze the tissue distribution of secondary metabolites (flavonoids and sesquiterpenes) and proteins inside of trichomes. Herein, we analyzed sesquiterpene lactones, present in CGT, from leaf transversal sections using the matrix 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA) (mixture 1:1) with sodium ions added to increase the ionization in positive ion mode. The results observed for sesquiterpenes and polymethoxylated flavones from LGT were similar. However, upon desiccation, LGT changed their shape in the ionization source, complicating analyses by MSI mainly after matrix application. An alternative method could be applied to LGT regions by employing LDI (without matrix) in negative ion mode. The polymethoxylated flavones were easily ionized by LDI, producing images with higher resolution, but the sesquiterpenes were not observed in spectra. Thus, the application and viability of MALDI imaging for the analyses of protein and secondary metabolites inside trichomes were confirmed, highlighting the importance of optimization parameters.

Lifetime of inner-shell hole states of Ar (2p) and Kr (3d) using equation-of-motion coupled cluster method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, Aryya; Vaval, Nayana, E-mail: np.vaval@ncl.res.in; Pal, Sourav

2015-07-14

Auger decay is an efficient ultrafast relaxation process of core-shell or inner-shell excited atom or molecule. Generally, it occurs in femto-second or even atto-second time domain. Direct measurement of lifetimes of Auger process of single ionized and double ionized inner-shell state of an atom or molecule is an extremely difficult task. In this paper, we have applied the highly correlated complex absorbing potential-equation-of-motion coupled cluster (CAP-EOMCC) approach which is a combination of CAP and EOMCC approach to calculate the lifetime of the states arising from 2p inner-shell ionization of an Ar atom and 3d inner-shell ionization of Kr atom. Wemore » have also calculated the lifetime of Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}D, Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}S, and Ar{sup 2+}(2p{sup −1}3s{sup −1}) {sup 1}P double ionized states. The predicted results are compared with the other theoretical results as well as experimental results available in the literature.« less

Solvent jet desorption capillary photoionization-mass spectrometry.

PubMed

Haapala, Markus; Teppo, Jaakko; Ollikainen, Elisa; Kiiski, Iiro; Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

2015-03-17

A new ambient mass spectrometry method, solvent jet desorption capillary photoionization (DCPI), is described. The method uses a solvent jet generated by a coaxial nebulizer operated at ambient conditions with nitrogen as nebulizer gas. The solvent jet is directed onto a sample surface, from which analytes are extracted into the solvent and ejected from the surface in secondary droplets formed in collisions between the jet and the sample surface. The secondary droplets are directed into the heated capillary photoionization (CPI) device, where the droplets are vaporized and the gaseous analytes are ionized by 10 eV photons generated by a vacuum ultraviolet (VUV) krypton discharge lamp. As the CPI device is directly connected to the extended capillary inlet of the MS, high ion transfer efficiency to the vacuum of MS is achieved. The solvent jet DCPI provides several advantages: high sensitivity for nonpolar and polar compounds with limit of detection down to low fmol levels, capability of analyzing small and large molecules, and good spatial resolution (250 μm). Two ionization mechanisms are involved in DCPI: atmospheric pressure photoionization, capable of ionizing polar and nonpolar compounds, and solvent assisted inlet ionization capable of ionizing larger molecules like peptides. The feasibility of DCPI was successfully tested in the analysis of polar and nonpolar compounds in sage leaves and chili pepper.

A Systems Approach to Evaluating Ionizing Radiation: Six Focus Areas to Improve Quality, Efficiency, and Patient Safety

PubMed Central

Mower, Laura; Bushe, Chris

2015-01-01

Abstract: Ionizing radiation is an essential component of the care process. However, providers and patients may not be fully aware of the risks involved, the level of ionizing radiation delivered with various procedures, or the potential for harm through incidental overexposure or cumulative dose. Recent high-profile incidents demonstrating the devastating short-term consequences of radiation overexposure have drawn attention to these risks, but applicable solutions are lacking. Although various recommendations and guidelines have been proposed, organizational variability challenges providers to identify their own practical solutions. To identify potential failure modes and develop solutions to preserve patient safety within a large, national healthcare system, we assembled a multidisciplinary team to conduct a comprehensive analysis of practices surrounding the delivery of ionizing radiation. Workgroups were developed to analyze existing culture, processes, and technology to identify deficiencies and propose solutions. Six focus areas were identified: competency and certification; equipment; monitoring and auditing; education; clinical pathways; and communication and marketing. This manuscript summarizes this comprehensive, multidisciplinary, and systemic analysis of risk and provides examples to illustrate how these focus areas can be used to improve the use of ionizing radiation. The proposed solutions, once fully implemented, may advance patient safety and care. PMID:26042626

Interfacing Capillary-Based Separations to Mass Spectrometry Using Desorption Electrospray Ionization

PubMed Central

Barbula, Griffin K.; Safi, Samir; Chingin, Konstantin; Perry, Richard H.; Zare, Richard N.

2014-01-01

The powerful hybrid analysis method of capillary-based separations followed by mass spectrometric analysis gives substantial chemical identity and structural information. It is usually carried out using electrospray ionization. However, the salts and detergents used in the mobile phase for electrokinetic separations suppress ionization efficiencies and contaminate the inlet of the mass spectrometer. This report describes a new method that uses desorption electrospray ionization (DESI) to overcome these limitations. Effluent from capillary columns is deposited on a rotating Teflon disk that is covered with paper. As the surface rotates, the temporal separation of the eluting analytes (i.e., the electropherogram) is spatially encoded on the surface. Then, using DESI, surface-deposited analytes are preferentially ionized, reducing the effects of ion suppression and inlet contamination on signal. With the use of this novel approach, two capillary-based separations were performed: a mixture of the rhodamine dyes at milligram/milliliter levels in a 10 mM sodium borate solution was separated by capillary electrophoresis, and a mixture of three cardiac drugs at milligram/milliliter levels in a 12.5 mM sodium borate and 12.5 mM sodium dodecyl sulfate solution was separated by micellar electrokinetic chromatography. In both experiments, the negative effects of detergents and salts on the MS analyses were minimized. PMID:21319740

CHEMICAL ANALYSIS OF A DIFFUSE CLOUD ALONG A LINE OF SIGHT TOWARD W51: MOLECULAR FRACTION AND COSMIC-RAY IONIZATION RATE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Indriolo, Nick; Neufeld, D. A.; Gerin, M.

2012-10-20

Absorption lines from the molecules OH{sup +}, H{sub 2}O{sup +}, and H{sup +} {sub 3} have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. Together, OH{sup +} and H{sub 2}O{sup +} are used to determine the molecular hydrogen fraction in the outskirts of the observed cloud, as well as the cosmic-ray ionization rate of atomic hydrogen. H{sup +} {sub 3} is used to infer the cosmic-ray ionization rate of H{sub 2} in the molecular interior ofmore » the cloud, which we find to be {zeta}{sub 2} = (4.8 {+-} 3.4) Multiplication-Sign 10{sup -16} s{sup -1}. Combining the results from all three species we find an efficiency factor-defined as the ratio of the formation rate of OH{sup +} to the cosmic-ray ionization rate of H-of {epsilon} = 0.07 {+-} 0.04, much lower than predicted by chemical models. This is an important step in the future use of OH{sup +} and H{sub 2}O{sup +} on their own as tracers of the cosmic-ray ionization rate.« less

Degradation spectra and ionization yields of electrons in gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inokuti, M.; Douthat, D.A.; Rau, A.R.P.

1975-01-01

Progress in the microscopic theory of electron degradation in gases by Platzman, Fano, and co-workers is outlined. The theory consists of (1) the cataloging of all major inelastic-collision cross sections for electrons (including secondary-electron energy distribution in a single ionizing collision) and (2) the evaluation of cumulative consequences of individual electron collisions for the electrons themselves as well as for target molecules. For assessing the data consistency and reliability and extrapolating the data to the unexplored ranges of variables (such as electron energy), a series of plots devised by Platzman are very powerful. Electron degradation spectra were obtained through numericalmore » solution of the Spencer--Fano equation for all electron energies down to the first ionization thresholds for a few examples such as He and Ne. The systematics of the solutions resulted in the recognition of approximate scaling properties of the degradation spectra for different initial electron energies and pointed to new methods of more efficient treatment. Systematics of the ionization yields and their energy dependence on the initial electron energy were also recognized. Finally, the Spencer--Fano equation for the degradation spectra and the Fowler equation for the ionization and other yields are tightly linked with each other by a set of variational principles. (52 references, 7 figures) (DLC)« less

X-ray and multiwavelength insights into the inner structure of high-luminosity disc-like emitters

NASA Astrophysics Data System (ADS)

Luo, B.; Brandt, W. N.; Eracleous, M.; Wu, Jian; Hall, P. B.; Rafiee, A.; Schneider, D. P.; Wu, Jianfeng

2013-02-01

We present X-ray and multiwavelength studies of a sample of eight high-luminosity active galactic nuclei (AGN) with disc-like Hβ emission-line profiles selected from the Sloan Digital Sky Survey Data Release 7. These sources have higher redshift (z ≈ 0.6) than the majority of the known disc-like emitters, and they occupy a largely unexplored space in the luminosity-redshift plane. Seven sources have typical AGN X-ray spectra with power-law photon indices of Γ ≈ 1.4-2.0; two of them show some X-ray absorption (column density NH ≈ 1021-1022 cm-2 for neutral gas). The other source, J0850+4451, has only three hard X-ray photons detected and is probably heavily obscured (NH ≳ 3 × 1023 cm-2). This object is also identified as a low-ionization broad absorption line (BAL) quasar based on Mg II λ2799 absorption; it is the first disc-like emitter reported that is also a BAL quasar. The infrared-to-ultraviolet (UV) spectral energy distributions (SEDs) of these eight sources are similar to the mean SEDs of typical quasars with a UV `bump', suggestive of standard accretion discs radiating with high efficiency, which differs from low-luminosity disc-like emitters. Studies of the X-ray-to-optical power-law slope parameters (αOX) indicate that there is no significant excess X-ray emission in these high-luminosity disc-like emitters. Energy budget analysis suggests that for disc-like emitters in general, the inner disc must illuminate and ionize the outer disc efficiently (≈15 per cent of the nuclear ionizing radiation is required on average) via direct illumination and/or scattering. Warped accretion discs are probably needed for direct illumination to work in high-luminosity objects, as their geometrically thin inner discs decrease the amount of direct illumination possible for a flat disc.

N2 Dissociation In The Mesosphere Due To Secondary Electrons During A Solar Proton Event: The Effect On Atomic Nitrogen and Nitric Oxide

NASA Astrophysics Data System (ADS)

Verronen, P. T.; Shematovich, V. I.; Bisikalo, D. V.; Turunen, E.; Ulich, Th.

Solar proton events have an effect on the middle atmospheric odd nitrogen chem- istry. During a solar proton event high energy protons enter Earth's middle atmosphere where they ionize ambient gas. Ionization leads to production of atomic nitrogen, and further to production of nitric oxide, through ion chemistry. In addition, ionization processes produce secondary electrons that, if possessing 9.76 eV or more energy, dissociate N2 providing an additional source of atomic nitrogen. We have calculated mesospheric N2 dissociation rate due to secondary electrons dur- ing a solar proton event. Further, we have studied the effect on atomic nitrogen and nitric oxide at altitudes between 50 and 90 km. It was found that N2 is efficiently dis- sociated in the lower mesosphere by secondary electrons, with rates up to 103 cm-3 s-1 at 50 km. Thus, secondary electrons significantly add to odd nitrogen produc- tion. As a result of N2 dissociation, atomic nitrogen is greatly enhanced in both N(4S) and N(2D) states by 259% and 1220% maximum increases at 50 km, respectively. This further leads to a maximum increase of 16.5% in NO concentration at 61 km via chemical reactions. In our study a Monte Carlo model was used to calculate the total ionization rate and secondary electrons flux due to precipitating protons. These where then used as input to a detailed ion and neutral chemistry model and a steady-state solution was calcu- lated for two cases: With and without N2 dissociation due to secondary electrons.

Fluorescence spectroscopy of UV-MALDI matrices and implications of ionization mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Hou-Yu; Hsu, Hsu Chen; Lu, I-Chung

2014-10-28

Matrix-assisted laser desorption ionization (MALDI) has been widely used in the mass analysis of biomolecules; however, there are a lot of debates about the ionization mechanisms. Previous studies have indicated that S{sub 1}-S{sub 1} annihilation might be a key process in the generation of primary ions. This study investigates S{sub 1}-S{sub 1} annihilation by examining the time-resolved fluorescence spectra of 12 matrices. No S{sub 1}-S{sub 1} annihilation was observed in six of these matrices (3-hydroxy-picolinic acid, 6-aza-2-thiothymine, 2,4-dihydroxy-acetophenone, 2,6-dihydroxy-acetophenone, 2,4,6-trihydroxy-acetophenone, and ferulic acid). We observed two matrix molecules reacting in an electronically excited state (S{sub 1}) in five of thesemore » matrices (2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxy-acetophenone, 2,3-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid), and S{sub 1}-S{sub 1} annihilation was a possible reaction. Among these five matrices, no S{sub 1}-S{sub 1} annihilation was observed for 2,3-dihydroxybenzoic acid in typical peak power region of nanosecond laser pulses in MALDI, but a very small value of reaction rate constant was observed only in the high peak power region. The excited-state lifetime of sinapinic acid was too short to determine whether the molecules reacted in an electronically excited state. No correlation was observed between the ion generation efficiency of MALDI and S{sub 1}-S{sub 1} annihilation. The results indicate that the proposal of S{sub 1}-S{sub 1} annihilation is unnecessary in MALDI and energy pooling model for MALDI ionization mechanism has to be modified.« less

Freeze-drying process monitoring using a cold plasma ionization device.

PubMed

Mayeresse, Y; Veillon, R; Sibille, P H; Nomine, C

2007-01-01

A cold plasma ionization device has been designed to monitor freeze-drying processes in situ by monitoring lyophilization chamber moisture content. This plasma device, which consists of a probe that can be mounted directly on the lyophilization chamber, depends upon the ionization of nitrogen and water molecules using a radiofrequency generator and spectrometric signal collection. The study performed on this probe shows that it is steam sterilizable, simple to integrate, reproducible, and sensitive. The limitations include suitable positioning in the lyophilization chamber, calibration, and signal integration. Sensitivity was evaluated in relation to the quantity of vials and the probe positioning, and correlation with existing methods, such as microbalance, was established. These tests verified signal reproducibility through three freeze-drying cycles. Scaling-up studies demonstrated a similar product signature for the same product using pilot-scale and larger-scale equipment. On an industrial scale, the method efficiently monitored the freeze-drying cycle, but in a larger industrial freeze-dryer the signal was slightly modified. This was mainly due to the positioning of the plasma device, in relation to the vapor flow pathway, which is not necessarily homogeneous within the freeze-drying chamber. The plasma tool is a relevant method for monitoring freeze-drying processes and may in the future allow the verification of current thermodynamic freeze-drying models. This plasma technique may ultimately represent a process analytical technology (PAT) approach for the freeze-drying process.

Novel ionic liquid matrices for qualitative and quantitative detection of carbohydrates by matrix assisted laser desorption/ionization mass spectrometry.

PubMed

Zhao, Xiaoyong; Shen, Shanshan; Wu, Datong; Cai, Pengfei; Pan, Yuanjiang

2017-09-08

Analysis of carbohydrates based on matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is still challenging and researchers have been devoting themselves to efficient matrices discovery. In the present study, the design, synthesis, qualitative and quantitative performance of non-derivative ionic liquid matrices (ILMs) were reported. DHB/N-methylaniline (N-MA) and DHB/N-ethylaniline (N-EA), performing best for carbohydrate detection, have been screened out. The limit of detection for oligosaccharide provided by DHB/N-MA and DHB/N-EA were as low as 10 fmol. DHB/N-MA and DHB/N-EA showed significantly higher ion generation efficiency than DHB. The comparison of capacity to probe polysaccharide between these two ILMs and DHB also revealed their powerful potential. Their outstanding performance were probably due to lower proton affinities and stronger UV absorption at λ = 355 nm. What is more, taking DHB/N-MA as an example, quantitative analysis of fructo-oligosaccharide mixtures extracted and identified from rice noodles has been accomplished sensitively using an internal standard method. Overall, DHB/N-MA and DHB/N-EA exhibited excellent performance and might be significant sources as the carbohydrate matrices. Copyright © 2017 Elsevier B.V. All rights reserved.

Diamond Pixel Detectors

NASA Astrophysics Data System (ADS)

Adam, W.; Berdermann, E.; Bergonzo, P.; Bertuccio, G.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Doroshenko, J.; Dulinski, W.; van Eijk, B.; Fallou, A.; Fizzotti, F.; Foster, J.; Foulon, F.; Friedl, M.; Gan, K. K.; Gheeraert, E.; Gobbi, B.; Grim, G. P.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Kass, R.; Koeth, T.; Krammer, M.; Lander, R.; Logiudice, A.; Lu, R.; mac Lynne, L.; Manfredotti, C.; Meier, D.; Mishina, M.; Moroni, L.; Oh, A.; Pan, L. S.; Pernicka, M.; Perera, L.; Pirollo, S.; Plano, R.; Procario, M.; Riester, J. L.; Roe, S.; Rott, C.; Rousseau, L.; Rudge, A.; Russ, J.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R. J.; Tesarek, R.; Trischuk, W.; Tromson, D.; Vittone, E.; Wedenig, R.; Weilhammer, P.; White, C.; Zeuner, W.; Zoeller, M.

2001-06-01

Diamond based pixel detectors are a promising radiation-hard technology for use at the LHC. We present first results on a CMS diamond pixel sensor. With a threshold setting of 2000 electrons, an average pixel efficiency of 78% was obtained for normally incident minimum ionizing particles.

Instantaneous characterization of vegetable oils via TAG and FFA profiles by easy ambient sonic-spray ionization mass spectrometry.

PubMed

Simas, Rosineide C; Catharino, Rodrigo R; Cunha, Ildenize B S; Cabral, Elaine C; Barrera-Arellano, Daniel; Eberlin, Marcos N; Alberici, Rosana M

2010-04-01

A fast and reliable method is presented for the analysis of vegetable oils. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) is shown to efficiently desorb and ionize the main oil constituents from an inert surface under ambient conditions and to provide comprehensive triacylglyceride (TAG) and free fatty acid (FFA) profiles detected mainly as either [TAG + Na](+) or [FFA-H](-) ions. EASI(+/-)-MS analysis is simple, easily implemented, requires just a tiny droplet of the oil and is performed without any pre-separation or chemical manipulation. It also causes no fragmentation of TAG ions hence diacylglyceride (DAG) and monoacylglyceride (MAG) profiles and contents can also be measured. The EASI(+/-)-MS profiles of TAG and FFA permit authentication and quality control and can be used, for instance, to access levels of adulteration, acidity, oxidation or hydrolysis of vegetable oils in general.

1-(3-aminopropyl)-3-butylimidazolium bromide for carboxyl group derivatization: potential applications in high sensitivity peptide identification by mass spectrometry.

PubMed

Qiao, Xiaoqiang; Zhou, Yuan; Hou, Chunyan; Zhang, Xiaodan; Yang, Kaiguang; Zhang, Lihua; Zhang, Yukui

2013-03-01

The cationic reagent 1-(3-aminopropyl)-3-butylimidazolium bromide (BAPI) was exploited for the derivatization of carboxyl groups on peptides. Nearly 100% derivatization efficiency was achieved with the synthetic peptide RVYVHPI (RI-7). Furthermore, the peptide derivative was stable in a 0.1% TFA/water solution or a 0.1% (v/v) TFA/acetonitrile/water solution for at least one week. The effect of BAPI derivatization on the ionization of the peptide RI-7 was further investigated, and the detection sensitivity was improved >42-fold via matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), thus outperforming the commercial piperazine derivatization approach. Moreover, the charge states of the peptide were largely increased via BAPI derivatization by electrospray ionization (ESI) MS. The results indicate the potential merits of BAPI derivatization for high sensitivity peptide analysis by MS.

Characterization of Charge Separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) Ion Source for Mass Spectrometry

PubMed Central

Forbes, Thomas P.; Dixon, R. Brent; Muddiman, David C.; Degertekin, F. Levent; Fedorov, Andrei G.

2009-01-01

An initial investigation into the effects of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source is reported in order to gain understanding of ionization mechanisms and to improve analyte ionization efficiency and operation stability. In RF-only mode, AMUSE ejects on average, an equal number of slightly positive and slightly negative charged droplets due to random charge fluctuations, providing inefficient analyte ionization. Charge separation at the nozzle orifice is achieved by the application of an external electric field. By bringing the counter electrode close to the nozzle array, strong electric fields can be applied at relatively low DC potentials. It has been demonstrated, through a number of electrode/electrical potential configurations that increasing charge separation leads to improvement in signal abundance, signal-to-noise ratio, and signal stability. PMID:19525123

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keyshar, Kunttal; Berg, Morgann; Zhang, Xiang

Here, the values of the ionization energies of transition metal dichalcogenides (TMDs) are needed to assess their potential usefulness in semiconductor heterojunctions for high-performance optoelectronics. Here, we report on the systematic determination of ionization energies for three prototypical TMD monolayers (MoSe 2, WS 2, and MoS 2) on SiO 2 using photoemission electron microscopy with deep ultraviolet illumination. The ionization energy displays a progressive decrease from MoS 2, to WS 2, to MoSe 2, in agreement with predictions of density functional theory calculations. Combined with the measured energy positions of the valence band edge at the Brillouin zone center, wemore » deduce that, in the absence of interlayer coupling, a vertical heterojunction comprising any of the three TMD monolayers would form a staggered (type-II) band alignment. This band alignment could give rise to long-lived interlayer excitons that are potentially useful for valleytronics or efficient electron–hole separation in photovoltaics.« less

Recent progress in microchip electrophoresis-mass spectrometry.

PubMed

Kitagawa, Fumihiko; Otsuka, Koji

2011-06-25

This review highlights the methodological and instrumental developments in microchip electrophoresis (MCE)-mass spectrometry (MS) from 1997. In MCE-MS, the development of ionization interface is one of the most important issues to realize highly sensitive detection and high separation efficiency. Among several interfaces, electrospray ionization (ESI) has been mainly employed to MCE-MS since a simple structure of the ESI interface is suitable for coupling with the microchips. Although the number of publications is still limited, laser desorption ionization (LDI) interface has also been developed for MCE-MS. The characteristics of the ESI and LDI interfaces applied to the electrophoresis microchips are presented in this review. The scope of applications in MCE-MS covers mainly biogenic compounds such as bioactive amines, peptides, tryptic digests and proteins. This review provides a comprehensive table listing the applications in MCE-MS. Copyright © 2010 Elsevier B.V. All rights reserved.

Composite glycerol/graphite/aromatic acid matrices for thin-layer chromatography/matrix-assisted laser desorption/ionization mass spectrometry of heterocyclic compounds.

PubMed

Esparza, Cesar; Borisov, R S; Varlamov, A V; Zaikin, V G

2016-10-28

New composite matrices have been suggested for the analysis of mixtures of different synthetic organic compounds (N-containing heterocycles and erectile dysfunction drugs) by thin layer chromatography/matrix-assisted laser desorption ionization time-of-flight mass spectrometry (TLC/MALDI-TOF). Different mixtures of classical MALDI matrices and graphite particles dispersed in glycerol were used for the registration of MALDI mass spectra directly from TLC plates after analytes separation. In most of cases, the mass spectra possessed [M+H] + ions; however, for some analytes only [M+Na] + and [M+K] + ions were observed. These ions have been used to generate visualized TLC chromatograms. The described approach increases the desorption/ionization efficiencies of analytes separated by TLC, prevent spot blurring, simplifies and decrease time for sample preparation. Copyright © 2016 Elsevier B.V. All rights reserved.

Hole-transport material variation in fully vacuum deposited perovskite solar cells

NASA Astrophysics Data System (ADS)

Polander, Lauren E.; Pahner, Paul; Schwarze, Martin; Saalfrank, Matthias; Koerner, Christian; Leo, Karl

2014-08-01

This work addresses the effect of energy level alignment between the hole-transporting material and the active layer in vacuum deposited, planar-heterojunction CH3NH3PbIx-3Clx perovskite solar cells. Through a series of hole-transport materials, with conductivity values set using controlled p-doping of the layer, we correlate their ionization potentials with the open-circuit voltage of the device. With ionization potentials beyond 5.3 eV, a substantial decrease in both current density and voltage is observed, which highlights the delicate energetic balance between driving force for hole-extraction and maximizing the photovoltage. In contrast, when an optimal ionization potential match is found, the open-circuit voltage can be maximized, leading to power conversion efficiencies of up to 10.9%. These values are obtained with hole-transport materials that differ from the commonly used Spiro-MeO-TAD and correspond to a 40% performance increase versus this reference.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Custelcean, Radu; Bartsch, Richard A.

Two series of novel mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations are synthesized. In one series, the proton-ionizable group (PIG) is attached to the para position of one aromatic ring in the calixarene framework, thereby positioning it over the polyether ring cavity. In the other series, the PIG is a substituent on the benzo group in the polyether ring. This orients the PIG away from the crown ether cavity. In addition to carboxylic acid functions, the PIGs include N-(X)sulfonyl carboxamide groups. With X group variation from methyl to phenyl to 4-nitrophenyl to trifluoromethyl, the acidity of the PIG is 'tuned'. Solventmore » extraction of Ag{sup +} from aqueous solutions into chloroform is used to probe the influence of structural variation within the mono-ionizable calixcrown ligand on metal ion extraction efficiency, including the identity and acidity of the PIG and its orientation with respect to the polyether ring.« less

The laser and optical system for the RIBF-PALIS experiment

NASA Astrophysics Data System (ADS)

Sonoda, T.; Iimura, H.; Reponen, M.; Wada, M.; Katayama, I.; Sonnenschein, V.; Takamatsu, T.; Tomita, H.; Kojima, T. M.

2018-01-01

This paper describes the laser and optical system for the Parasitic radioactive isotope (RI) beam production by Laser Ion-Source (PALIS) in the RIKEN fragment separator facility. This system requires an optical path length of 70 m for transporting the laser beam from the laser light source to the place for resonance ionization. To accomplish this, we designed and implemented a simple optical system consisting of several mirrors equipped with compact stepping motor actuators, lenses, beam spot screens and network cameras. The system enables multi-step laser resonance ionization in the gas cell and gas jet via overlap with a diameter of a few millimeters, between the laser photons and atomic beam. Despite such a long transport distance, we achieved a transport efficiency for the UV laser beam of about 50%. We also confirmed that the position stability of the laser beam stays within a permissible range for dedicated resonance ionization experiments.

A Penning discharge as a dc source for multiply ionized atoms.

NASA Astrophysics Data System (ADS)

Rainer, Kling; Manfred, Kock

1997-10-01

We report upon a specially designed Penning discharge which has been further developed from a source published by Finley et al.(Finley, D. S., Bowyer, S., Paresce, F., Malina, R. F.: Appl. Opt. 18) (1979) 649 towards a radiation standard for the XUV.(Heise, C., Hollandt, J., Kling, R., Kock, M., Kuehne, M.: Appl. Opt. 33) (1994) 5111 The discharge stands out for low buffer gas pressure, high electric power input and a strong superimposed magnetic field. That leads to intense sputtering of the cathodes which can be made of nearly any material. The efficient excitation and ionization of the sputtered atoms permit spectroscopy on multiply ionized spezies. W III and Fe III spectra will be given as examples. We also will present kinetic temperatures of the nonthermal plasma showing that the ionic component is decoupled from the cold neutral gas component.

Energy Conversion Alternatives Study (ECAS), Westinghouse phase 1. Volume 9: Closed-cycle MHD. [energy conversion efficiency of electric power plants using magnetohydrodynamics

NASA Technical Reports Server (NTRS)

Tsu, T. C.

1976-01-01

A closed-cycle MHD system for an electric power plant was studied. It consists of 3 interlocking loops, an external heating loop, a closed-cycle cesium seeded argon nonequilibrium ionization MHD loop, and a steam bottomer. A MHD duct maximum temperature of 2366 K (3800 F), a pressure of 0.939 MPa (9.27 atm) and a Mach number of 0.9 are found to give a topping cycle efficiency of 59.3%; however when combined with an integrated gasifier and optimistic steam bottomer the coal to bus bar efficiency drops to 45.5%. A 1978 K (3100 F) cycle has an efficiency of 55.1% and a power plant efficiency of 42.2%. The high cost of the external heating loop components results in a cost of electricity of 21.41 mills/MJ (77.07 mills/kWh) for the high temperature system and 19.0 mills/MJ (68.5 mills/kWh) for the lower temperature system. It is, therefore, thought that this cycle may be more applicable to internally heated systems such as some futuristic high temperature gas cooled reactor.

Hydrazinonicotinic acid derivatization for selective ionization and improved glycan structure characterization by MALDI-MS.

PubMed

Jiao, Jing; Yang, Lijun; Zhang, Ying; Lu, Haojie

2015-08-21

The analysis of glycan is important for understanding cell biology and disease processes because the glycans play a key role in many important biological behaviors, such as cell division, cellular localization, tumor immunology and inflammation. Nevertheless, it is still hard work to analyze glycans by MALDI-MS, which generally stems from the inherent low abundance and the low ionization efficiency of glycans. Moreover, the difficulty in generating informative fragmentations further hinders glycans structure characterization. In this work, hydrazinonicotinic acid (HYNIC) was used as a novel derivatized reagent for improved and selective detection of glycans. Through tagging the reducing terminus of glycans with the diazanyl group of HYNIC, significant enhancement of the ionization efficiency of glycans was achieved. After derivatization, the signal to noise ratio (S/N) of the maltoheptaose was improved by more than one order of magnitude in positive mode. HYNIC derivatization also allowed the sensitive detection of sialylated glycan in negative mode, with a 15 fold enhancement of S/N. Interestingly, it is noteworthy that the HYNIC reagent not only effectively labeled the reducing end of glycans in the presence of tryptic peptides, but also suppressed the ionization of peptides, enabling the direct detection of glycans from glycoprotein without separation. Therefore, analysis of glycans became easier due to the omission of a pre-separation step. Importantly, by using different acid reagents as the catalyst, derivatized product signals corresponding to [M + Na](+) or [M + H](+) were obtained respectively, which yield complementary fragmentation patterns for the structure elucidation of glycans. Finally, more than 40 N-glycans were successfully detected in 10 μL human serum using this method.

Molecular-level characterization of reactive and refractory dissolved natural organic nitrogen compounds by atmospheric pressure photoionization coupled to Fourier transform ion cyclotron resonance mass spectrometry.

PubMed

Osborne, Daniel M; Podgorski, David C; Bronk, Deborah A; Roberts, Quinn; Sipler, Rachel E; Austin, David; Bays, James S; Cooper, William T

2013-04-30

Dissolved organic nitrogen (DON) represents a significant fraction of the total dissolved nitrogen pool in most surface waters and serves as an important nitrogen source for phytoplankton and bacteria. As with other natural organic matter mixtures, ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) is the only technique currently able to provide molecular composition information on DON. Although electrospray ionization (ESI) is the most commonly used ionization method, it is not very efficient at ionizing most DON components. Positive- and negative-mode atmospheric pressure photoionization (APPI) coupled with ultrahigh resolution FTICRMS at 9.4 T were compared for determining the composition of DON before and after bioassays. Toluene was added as the APPI dopant to the solid-phase DON extracts, producing a final sample that was 90% methanol and 10% toluene by volume. Positive-mode (+) APPI proved significantly more efficient at ionizing DON; 62% of the formulas that could be assigned in the positive-ion spectrum contained at least one nitrogen atom vs. 31% in the negative-ion spectrum. FTICR mass spectral data indicated that most of the refractory DON compounds (i.e. nonreactive during the 5 days of the incubation) had molecular compositions representative of lignin-like molecules, while lipid-like and protein-like molecules comprised most of the small reactive component of the DON pool. From these data we conclude that (+) APPI FTICRMS is a promising technique for describing the molecular composition of DON mixtures. The technique is particularly valuable in assessing the bioavailability of individual components of DON when combined with bioassays. Copyright © 2013 John Wiley & Sons, Ltd.

Zero kinetic energy photoelectron spectroscopy of tryptamine and the dissociation pathway of the singly hydrated cation cluster.

PubMed

Gu, Quanli; Knee, J L

2012-09-14

The relative ionization energies of tryptamine conformations are determined by zero kinetic energy photoelectron spectroscopy and photoionization efficiency measurements. The relative cationic conformational stabilities are compared to the published results for the neutral molecule. In the cation, the interaction strength changes significantly between amino group and either the phenyl or the pyrrole moiety of the indole chromophore where most of the positive charge is located, leading to different conformational structures and relative conformer energies in the cation. In particular, the measured adiabatic ionization potential of isomer B is 60,928 ± 5 cm(-1), at least 400 cm(-1) higher than any of the 6 other tryptamine isomers which all have ionization potentials within 200 cm(-1) of each other. In addition to the monomer, measurements were made on the A conformer of the tryptamine(+)-H(2)O complex including the ionization threshold and cation dissociation energy measured using a threshold photoionization fragmentation method. The water cluster exhibits an unexpectedly high ionization potential of 60,307 ± 100 cm(-1), close to the conformer A monomer of 60 320 ± 100 cm(-1). It also exhibits surprisingly low dissociation energy of 1750 ± 150 cm(-1) compared to other H-bonding involved cation-H(2)O complexes which are typically several thousands of wavenumbers higher. Quantum chemical calculations indicate that upon ionization the structure of the parent molecule in the water complex remains mostly unchanged due to the rigid intermolecular double hydrogen bonded water molecule bridging the monomer backbone and its side chain thus leading to the high ionization potential in the water cluster. The surprisingly low dissociation energy measured in the cationic water complex is attributed to the formation of a much more stable structural isomer H(+) in the exit channel.

Direct olive oil analysis by mass spectrometry: A comparison of different ambient ionization methods.

PubMed

Lara-Ortega, Felipe J; Beneito-Cambra, Miriam; Robles-Molina, José; García-Reyes, Juan F; Gilbert-López, Bienvenida; Molina-Díaz, Antonio

2018-04-01

Analytical methods based on ambient ionization mass spectrometry (AIMS) combine the classic outstanding performance of mass spectrometry in terms of sensitivity and selectivity along with convenient features related to the lack of sample workup required. In this work, the performance of different mass spectrometry-based methods has been assessed for the direct analyses of virgin olive oil for quality purposes. Two sets of experiments have been setup: (1) direct analysis of untreated olive oil using AIMS methods such as Low-Temperature Plasma Mass Spectrometry (LTP-MS) or paper spray mass spectrometry (PS-MS); or alternatively (2) the use of atmospheric pressure ionization (API) mass spectrometry by direct infusion of a diluted sample through either atmospheric pressure chemical ionization (APCI) or electrospray (ESI) ionization sources. The second strategy involved a minimum sample work-up consisting of a simple olive oil dilution (from 1:10 to 1:1000) with appropriate solvents, which originated critical carry over effects in ESI, making unreliable its use in routine; thus, ESI required the use of a liquid-liquid extraction to shift the measurement towards a specific part of the composition of the edible oil (i.e. polyphenol rich fraction or lipid/fatty acid profile). On the other hand, LTP-MS enabled direct undiluted mass analysis of olive oil. The use of PS-MS provided additional advantages such as an extended ionization coverage/molecular weight range (compared to LTP-MS) and the possibility to increase the ionization efficiency towards nonpolar compounds such as squalene through the formation of Ag + adducts with carbon-carbon double bounds, an attractive feature to discriminate between oils with different degree of unsaturation. Copyright © 2017 Elsevier B.V. All rights reserved.

Determination of multislice computed tomography dose index (CTDI) using optically stimulated luminescence technology.

PubMed

Ruan, Chun; Yukihara, Eduardo G; Clouse, William J; Gasparian, Patricia B R; Ahmad, Salahuddin

2010-07-01

The extensive use of multislice computed tomography (MSCT) and the associated increase in patient dose calls for an accurate dose evaluation technique. Optically stimulated luminescence (OSL) dosimetry provides a potential solution to the arising concerns over patient dose. This study was intended to evaluate the feasibility and accuracy of OSL dosimeter systems in the diagnostic CT x-ray beam energy range. MSCT dose profiles were measured by irradiating OSL strips placed inside the extended PMMA head and body phantoms at different scan conditions by varying kVp settings (100, 120, and 140 kVp) and collimated beam widths (5, 10, 20, and 40 mm). All scans in this study were performed using a GE Lightspeed VCT scanner in axial mode. The exposed strips were then read out using a custom-made OSL strip reader and corrected with field-specific conversion factors. Based on the corrected OSL dose profile, the CTDI(450-OSL) and CTDI(l00-OSL) were evaluated. CTDI(100-IC) was also obtained using a 100 mm long pencil ionization chamber for accuracy verification. CTDI(100-efficiency) can be further evaluated by calculating the ratio of CTDI(100-OSL) and CTDI(450-OSL), which was compared to results from previous studies as well. The OSL detectors were found to have good sensitivity and dose response over a wide range of diagnostic CT x-ray beam energy viz. the primary beam and the scatter tail section of the dose profile. The differences between CTDI100 values obtained using the OSL strips and those obtained with 100 mm long pencil ionization chamber were < +/- 5% for all scan conditions, indicating good accuracy of the OSL system. It was also found that the CTDI(100-efficiency) did not significantly change as the beam width increased and tube voltage changed. The average CTDI(100-efficiency) at the center of the head and body phantoms were 72.6% and 56.2%, respectively. The corresponding values for the periphery of the head and body phantoms were 85.0% and 81.7%. These results agreed very well with previous results from the literature using other detection techniques or Monte Carlo simulations. The LED-based OSL system can be an accurate alternative device for CT dose evaluations. CTDI100 measurement with the use of a 100 mm pencil ionization chamber substantially underestimates the CTDIinfinity value even with 5 mm collimated beam width. The established complete set of CTDI(100-efficiency) correction factors for various scan parameters allows for accurately estimating CTDIinfinity with the current use of pencil chamber and dose phantoms. Combined with the simple calibration, it gives this work great potential to be used not only in routine clinical quality assurance checks but also as a promising tool for patient organ dose assessment.

The performance and the characterization of laser ablation aerosol particle time-of-flight mass spectrometry (LAAP-ToF-MS)

NASA Astrophysics Data System (ADS)

Gemayel, Rachel; Hellebust, Stig; Temime-Roussel, Brice; Hayeck, Nathalie; Van Elteren, Johannes T.; Wortham, Henri; Gligorovski, Sasho

2016-05-01

Hyphenated laser ablation-mass spectrometry instruments have been recognized as useful analytical tools for the detection and chemical characterization of aerosol particles. Here we describe the performances of a laser ablation aerosol particle time-of-flight mass spectrometer (LAAP-ToF-MS) which was designed for aerodynamic particle sizing using two 405 nm scattering lasers and characterization of the chemical composition of single aerosol particle via ablation/ionization by a 193 nm excimer laser and detection in a bipolar time-of-flight mass spectrometer with a mass resolving power of m/Δm > 600.

We describe a laboratory based optimization strategy for the development of an analytical methodology for characterization of atmospheric particles using the LAAP-ToF-MS instrument in combination with a particle generator, a differential mobility analyzer and an optical particle counter. We investigated the influence of particle number concentration, particle size and particle composition on the detection efficiency. The detection efficiency is a product of the scattering efficiency of the laser diodes and the ionization efficiency or hit rate of the excimer laser. The scattering efficiency was found to vary between 0.6 and 1.9 % with an average of 1.1 %; the relative standard deviation (RSD) was 17.0 %. The hit rate exhibited good repeatability with an average value of 63 % and an RSD of 18 %. In addition to laboratory tests, the LAAP-ToF-MS was used to sample ambient air during a period of 6 days at the campus of Aix-Marseille University, situated in the city center of Marseille, France. The optimized LAAP-ToF-MS methodology enables high temporal resolution measurements of the chemical composition of ambient particles, provides new insights into environmental science, and a new investigative tool for atmospheric chemistry and physics, aerosol science and health impact studies.

Laser ion source for multi-nucleon transfer reaction products

NASA Astrophysics Data System (ADS)

Hirayama, Y.; Watanabe, Y. X.; Imai, N.; Ishiyama, H.; Jeong, S. C.; Miyatake, H.; Oyaizu, M.; Kimura, S.; Mukai, M.; Kim, Y. H.; Sonoda, T.; Wada, M.; Huyse, M.; Kudryavtsev, Yu.; Van Duppen, P.

2015-06-01

We have developed a laser ion source for the target-like fragments (TLFs) produced in multi-nucleon transfer (MNT) reactions. The operation principle of the source is based on the in-gas laser ionization and spectroscopy (IGLIS) approach. In the source TLFs are thermalized and neutralized in high pressure and high purity argon gas, and are extracted after being selectively re-ionized in a multi-step laser resonance ionization process. The laser ion source has been implemented at the KEK Isotope Separation System (KISS) for β-decay spectroscopy of neutron-rich isotopes with N = 126 of nuclear astrophysical interest. The simulations of gas flow and ion-beam optics have been performed to optimize the gas cell for efficient thermalization and fast transporting the TLFs, and the mass-separator for efficient transport with high mass-resolving power, respectively. To confirm the performances expected at the design stage, off-line experiments have been performed by using 56Fe atoms evaporated from a filament in the gas cell. The gas-transport time of 230 ms in the argon cell and the measured KISS mass-resolving power of 900 are consistent with the designed values. The high purity of the gas-cell system, which is extremely important for efficient and highly-selective production of laser ions, was achieved and confirmed from the mass distribution of the extracted ions. After the off-line tests, on-line experiments were conducted by directly injecting energetic 56Fe beam into the gas cell. After thermalization of the injected 56Fe beam, laser-produced singly-charged 56Fe+ ions were extracted. The extraction efficiency and selectivity of the gas cell in the presence of plasma induced by 56Fe beam injection as well as the time profile of the extracted ions were investigated; extraction efficiency of 0.25%, a beam purity of >99% and an extraction time of 270 ms. It has been confirmed that the performance of the KISS laser ion source is satisfactory to start the measurements of lifetimes of the β-decayed nuclei with N = 126 .

Silver-gold alloy nanoparticles as tunable substrates for systematic control of ion-desorption efficiency and heat transfer in surface-assisted laser desorption/ionization.

PubMed

Lai, Samuel Kin-Man; Cheng, Yu-Hong; Tang, Ho-Wai; Ng, Kwan-Ming

2017-08-09

Systematically controlling heat transfer in the surface-assisted laser desorption/ionization (SALDI) process and thus enhancing the analytical performance of SALDI-MS remains a challenging task. In the current study, by tuning the metal contents of Ag-Au alloy nanoparticle substrates (AgNPs, Ag55Au45NPs, Ag15Au85NPs and AuNPs, ∅: ∼2.0 nm), it was found that both SALDI ion-desorption efficiency and heat transfer can be controlled in a wide range of laser fluence (21.3 mJ cm -2 to 125.9 mJ cm -2 ). It was discovered that ion detection sensitivity can be enhanced at any laser fluence by tuning up the Ag content of the alloy nanoparticle, whereas the extent of ion fragmentation can be reduced by tuning up the Au content. The enhancement effect of Ag content on ion desorption was found to be attributable to the increase in laser absorption efficiency (at 355 nm) with Ag content. Tuning the laser absorption efficiency by changing the metal composition was also effective in controlling the heat transfer from the NPs to the analytes. The laser-induced heating of Ag-rich alloy NPs could be balanced or even overridden by increasing the Au content of NPs, resulting in the reduction of the fragmentation of analytes. In the correlation of experimental measurement with molecular dynamics simulation, the effect of metal composition on the dynamics of the ion desorption process was also elucidated. Upon increasing the Ag content, it was also found that phase transition temperatures, such as melting, vaporization and phase explosion temperature, of NPs could be reduced. This further enhanced the desorption of analyte ions via phase-transition-driven desorption processes. The significant cooling effect on the analyte ions observed at high laser fluence was also determined to be originated from the phase explosion of the NPs. This study revealed that the development of alloy nanoparticles as SALDI substrates can constitute an effective means for the systematic control of ion-desorption efficiency and the extent of heat transfer, which could potentially enhance the analytical performance of SALDI-MS.

New Experimental Results of Simulating Micrometeoroid Ablation in the Laboratory

NASA Astrophysics Data System (ADS)

Sternovsky, Zoltan; Thomas, Evan; DeLuca, Michael; Janches, Diego; Munsat, Tobin; Plane, John

2017-04-01

A facility is developed to simulate the ablation of micrometeoroids in laboratory conditions, which also allows measuring the ionization probability of the ablated material. An electrostatic dust accelerator is used to generate iron, aluminum and meteoric analog particles with velocities 10-50 km/s. The particles are then introduced into a cell filled with nitrogen, air or carbon dioxide gas with pressures adjustable in the 0.02 - 0.5 Torr range, where the partial or complete ablation of the particle occurs over a short distance. An array of biased electrodes is used to collect the ionized products with spatial resolution along the ablating particles' path, allowing thus the study of the temporal resolution of the process. A new optical observation setup using a 64 channel PMT system was added to the setup to allow the observation of the ablating particle and deceleration of the particle from the neutral drag. A simple ablation model is used to match the observations. For completely ablated particles the total collected charge directly yields the ionization efficiency. The measurements using iron particles in N2 and air are in relatively good agreement with earlier data. The new experimental data using aluminum particles suggest that the neutral drag acting of the particle is smaller than expected.

Low temperature plasmas induced in SF6 by extreme ultraviolet (EUV) pulses

NASA Astrophysics Data System (ADS)

Bartnik, A.; Skrzeczanowski, W.; Czwartos, J.; Kostecki, J.; Fiedorowicz, H.; Wachulak, P.; Fok, T.

2018-06-01

In this work, a comparative study of extreme ultraviolet (EUV) induced low temperature SF6-based plasmas, created using two different irradiation systems, was performed. Both systems utilized laser-produced plasma (LPP) EUV sources. The essential difference between the systems concerned the formation of the driving EUV beam. The first one contained an efficient ellipsoidal EUV collector allowing for focusing of the EUV radiation at a large distance from the LPP source. The spectrum of focused radiation was limited to the long-wavelength part of the total LPP emission, λ > 8 nm, due to the reflective properties of the collector. The second system did not contain any EUV collector. The gas to be ionized was injected in the vicinity of the LPP, at a distance of the order of 10 mm. In both systems, energies of the driving photons were high enough for dissociative ionization of the SF6 molecules and ionization of atoms or even singly charged ions. Plasmas, created due to these processes, were investigated by spectral measurements in the EUV, ultraviolet (UV), and visible (VIS) spectral ranges. These low temperature plasmas were employed for preliminary experiments concerning surface treatment. The formation of pronounced nanostructures on the silicon surface after plasma treatment was demonstrated.

Hydrodynamic and shock heating instabilities of liquid metal strippers for RIA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassanein, Ahmed

2013-05-24

Stripping of accelerated ions is a key problem for the design of RIA to obtain high efficiency. Thin liquid Lithium film flow is currently considered as stripper for RIA ion beams to obtain higher Z for following acceleration: in extreme case of Uranium from Z=29 to Z=60-70 (first stripper) and from Z=70 till full stripping Z=92 (second stripper). Ionization of ion occurs due to the interaction of the ion with electrons of target material (Lithium) with the loss of parts of the energy due to ionization, Q{sub U}, which is also accompanied with ionization energy losses, Q{sub Li} of themore » lithium. The resulting heat is so high that can be removed not by heat conduction but mainly by convection, i.e., flowing of liquid metal across beam spot area. The interaction of the beam with the liquid metal generates shock wave propagating along direction perpendicular to the beam as well as excites oscillations along beam direction. We studied the dynamics of these excited waves to determine conditions for film stability at the required velocities for heat removal. It will allow optimizing jet nozzle shapes and flow parameters to prevent film fragmentation and to ensure stable device operation.« less

A Sleeping Giant Awakened: Reignition of AGN Activity, Reborn Star Formation, and a Multiphase Outflow in one of the Largest Radio Galaxies Known

NASA Astrophysics Data System (ADS)

Tremblay, Grant; O'Dea, Christopher; Labiano, Alvaro; Baum, Stefi; McDermid, Richard; Combes, Francoise; Garcia-Burillo, Santiago; Davis, Timothy

2014-08-01

3C 236 is the second largest known radio galaxy and one of the largest objects in the known Universe. Its central AGN has recently reignited after a 10 Myr dormancy period, giving rise to a very young and compact radio source and a 1000 km/sec outflow of warm ionized and atomic HI gas. We propose GMOS-N IFU observations to resolve this outflow, determine its driver, and estimate the relative coupling efficiencies between the warm ionized, atomic, and cold molecular gas phases. We will assemble a much-needed spatially resolved Balmer decrement (extinction map) across the dramatic double dust lanes of this source, enabling high spatial resolution star formation rate, efficiency, and gas excitation and velocity maps. These will address several mysteries related to the very high star formation efficiency and the unique nature of the multiphase outflow in this source. 3C 236 is such a remarkable galaxy that whatever the results of the proposed observations, they will have wide-ranging implications for the triggering of star formation and AGN activity, their possibly coupled co-evolution, and the feedback effects of the latter on the former.

Production of thymine glycols in DNA by radiation and chemical carcinogens as detected by a monoclonal antibody.

PubMed Central

Leadon, S. A.

1987-01-01

In order to understand the role in carcinogenesis of damage indirectly induced by chemical carcinogens, it is important to identify the primary DNA lesions. We have measured the formation and repair of one type of DNA modification, 5,6-dihydroxydihydrothymine (thymine glycol), following exposure of cultured human cells to the carcinogens N-hydroxy-2-naphthylamine or benzo(a)pyrene. The efficiency of production of thymine glycols in DNA by these carcinogens was compared to that by ionizing radiation and ultraviolet light. Thymine glycols were detected using a monoclonal antibody against this product in a sensitive immunoassay. We found that thymine glycols were produced in DNA in a dose dependent manner after exposure to the carcinogens and that their production was reduced if either catalase or superoxide dismutase or both were present at the time of treatment. The efficiency of thymine glycol production following exposure to the chemical carcinogens was greater than that following equi-toxic doses of radiation. Thymine glycols were efficiently removed from the DNA of human cells following treatment with either the chemical carcinogens, ionizing radiation or ultraviolet light. PMID:3477281

Research and development program, fiscal year 1966

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1964-04-01

The biomedical program of the Laboratory of Nuclear Medicine and Radiation Biology for FY 1966 is conducted within the scope of the following categories: Somatic Effects of Radiation; Combating Detrimental Effects of Radiation; Molecular and Cellular Level Studies; Environmental Radiation Studies; Radiological and Health Physics and Instrumentation; Chemical Toxicity; Cancer Research; and Selected Beneficial Applications. The overall objectives of the Laboratory within these areas of the Biology and Medicine program may be summarized as follows: (1) investigation of the effects of ionizing radiation on living organisms and systems of biological significance; (2) investigation of the dynamic aspects of physiological andmore » biochemical processes in man, animals and plants and how these processes are modified by radiation and related pathological states; (3) the assessment and study of the immediate and long term consequences of the operation or detonation of nuclear devices on the fauna, and flora in man's environment and on man; (4) the development of methods of minimizing or preventing the detrimental effects of ionizing radiation; (5) research in, and development of, beneficial uses of ionizing radiation and radioactive substances in medicine and biology; (6) research in the development of new and more efficient radiation detection devices; (7) research, including field studies, as mutually agreed upon by the Commission and the University, in connection with the conduct of weapon tests and biomedical and civil effects experiments at such tests conducted at continental and overseas test sites; and (8) the conduct of training and educational activities in the biological and medical aspects of radiation and related fields.« less

THz field engineering in two-color femtosecond filaments using chirped and delayed laser pulses

NASA Astrophysics Data System (ADS)

Nguyen, A.; González de Alaiza Martínez, P.; Thiele, I.; Skupin, S.; Bergé, L.

2018-03-01

We numerically study the influence of chirping and delaying several ionizing two-color light pulses in order to engineer terahertz (THz) wave generation in air. By means of comprehensive 3D simulations, it is shown that two chirped pulses can increase the THz yield when they are separated by a suitable time delay for the same laser energy in focused propagation geometry. To interpret these results, the local current theory is revisited and we propose an easy, accessible all-optical criterion that predicts the laser-to-THz conversion efficiencies given any input laser spectrum. In the filamentation regime, numerical simulations display evidence that a chirped pulse is able to produce more THz radiation due to propagation effects, which maintain the two colors of the laser field more efficiently coupled over long distances. A large delay between two pulses promotes multi-peaked THz spectra as well as conversion efficiencies above 10‑4.

Electrophoretic extraction of low molecular weight cationic analytes from sodium dodecyl sulfate containing sample matrices for their direct electrospray ionization mass spectrometry.

PubMed

Kinde, Tristan F; Lopez, Thomas D; Dutta, Debashis

2015-03-03

While the use of sodium dodecyl sulfate (SDS) in separation buffers allows efficient analysis of complex mixtures, its presence in the sample matrix is known to severely interfere with the mass-spectrometric characterization of analyte molecules. In this article, we report a microfluidic device that addresses this analytical challenge by enabling inline electrospray ionization mass spectrometry (ESI-MS) of low molecular weight cationic samples prepared in SDS containing matrices. The functionality of this device relies on the continuous extraction of analyte molecules into an SDS-free solvent stream based on the free-flow zone electrophoresis (FFZE) technique prior to their ESI-MS analysis. The reported extraction was accomplished in our current work in a glass channel with microelectrodes fabricated along its sidewalls to realize the desired electric field. Our experiments show that a key challenge to successfully operating such a device is to suppress the electroosmotically driven fluid circulations generated in its extraction channel that otherwise tend to vigorously mix the liquid streams flowing through this duct. A new coating medium, N-(2-triethoxysilylpropyl) formamide, recently demonstrated by our laboratory to nearly eliminate electroosmotic flow in glass microchannels was employed to address this issue. Applying this surface modifier, we were able to efficiently extract two different peptides, human angiotensin I and MRFA, individually from an SDS containing matrix using the FFZE method and detect them at concentrations down to 3.7 and 6.3 μg/mL, respectively, in samples containing as much as 10 mM SDS. Notice that in addition to greatly reducing the amount of SDS entering the MS instrument, the reported approach allows rapid solvent exchange for facilitating efficient analyte ionization desired in ESI-MS analysis.

Characterization and biocompatibility studies of lead free X-ray shielding polymer composite for healthcare application

NASA Astrophysics Data System (ADS)

Singh, Anil Kumar; Singh, Rakesh Kumar; Sharma, Bhupesh; Tyagi, Ajay Kumar

2017-09-01

Lead based X-ray shielding systems are widely being used in healthcare and radiation processing centers to protect technicians, operators and patients from unwanted exposure to ionizing radiation. However, the use of lead is avoided mainly due to its toxic effects on human health and environment, and also discomfort due to heavier in weight. Hence, production of non-toxic, environment friendly, lead-free X-ray shielding system with less weight and good radiation shielding efficiency compared to conventional lead-based shielding systems is a challenging issue and need of the day. The objectives of present study are to develop, characterize and establish synergy of the materials making radiation shielding composition and their biocompatibility without compromising on radiation shielding efficiency and physico-mechanical attributes vis-à-vis lead based systems.

Picoelectrospray Ionization Mass Spectrometry Using Narrow-bore Chemically Etched Emitters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marginean, Ioan; Tang, Keqi; Smith, Richard D.

2014-01-01

Electrospray ionization mass spectrometry (ESI-MS) at flow rates below ~10 nL/min has been only sporadically explored due to difficulty in reproducibly fabricating emitters that can operate at lower flow rates. Here we demonstrate narrow orifice chemically etched emitters for stable electrospray at flow rates as low as 400 pL/min. Depending on the analyte concentration, we observe two types of MS signal response as a function of flow rate. At low concentrations, an optimum flow rate is observed slightly above 1 nL/min, while the signal decreases monotonically with decreasing flow rates at higher concentrations. In spite of lower MS signal, themore » ion utilization efficiency increases exponentially with decreasing flow rate in all cases. No unimolecular response was observed within this flow rate range during the analysis of an equimolar mixture of peptides, indicating that ionization efficiency is an analyte-dependent characteristic in given experimental conditions. While little to no gain in signal-to-noise was achieved at ultralow flow rates for concentration-limited analyses, experiments consuming the same amount of analyte suggest that mass-limited analyses will benefit strongly from the use of low flow rates and avoiding unnecessary sample dilution. By operating under optimal conditions, consumption of just 500 zmol of sample yielded signal-to-noise ratios ~10 for some peptides. These findings have important implications for the analysis of trace biological samples.« less

Molecular Insights into the pH-Dependent Adsorption and Removal of Ionizable Antibiotic Oxytetracycline by Adsorbent Cyclodextrin Polymers

PubMed Central

Zhang, Yu; Cai, Xiyun; Xiong, Weina; Jiang, Hao; Zhao, Haitong; Yang, Xianhai; Li, Chao; Fu, Zhiqiang; Chen, Jingwen

2014-01-01

Effects of pH on adsorption and removal efficiency of ionizable organic compounds (IOCs) by environmental adsorbents are an area of debate, because of its dual mediation towards adsorbents and adsorbate. Here, we probe the pH-dependent adsorption of ionizable antibiotic oxytetracycline (comprising OTCH2 +, OTCH±, OTC−, and OTC2−) onto cyclodextrin polymers (CDPs) with the nature of molecular recognition and pH inertness. OTCH± commonly has high adsorption affinity, OTC− exhibits moderate affinity, and the other two species have negligible affinity. These species are evidenced to selectively interact with structural units (e.g., CD cavity, pore channel, and network) of the polymers and thus immobilized onto the adsorbents to different extents. The differences in adsorption affinity and mechanisms of the species account for the pH-dependent adsorption of OTC. The mathematical equations are derived from the multiple linear regression (MLR) analysis of quantitatively relating adsorption affinity of OTC at varying pH to adsorbent properties. A combination of the MLR analysis for OTC and molecular recognition of adsorption of the species illustrates the nature of the pH-dependent adsorption of OTC. Based on this finding, γ-HP-CDP is chosen to adsorb and remove OTC at pH 5.0 and 7.0, showing high removal efficiency and strong resistance to the interference of coexisting components. PMID:24465975

Ion microscopy with resonant ionization mass spectrometry : time-of-flight depth profiling with improved isotopic precision.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pellin, M. J.; Veryovkin, I. V.; Levine, J.

2010-01-01

There are four generally mutually exclusive requirements that plague many mass spectrometric measurements of trace constituents: (1) the small size (limited by the depth probed) of many interesting materials requires high useful yields to simply detect some trace elements, (2) the low concentrations of interesting elements require efficient discrimination from isobaric interferences, (3) it is often necessary to measure the depth distribution of elements with high surface and low bulk contributions, and (4) many applications require precise isotopic analysis. Resonant ionization mass spectrometry has made dramatic progress in addressing these difficulties over the past five years.

Investigation of critical parameters controlling the efficiency of associative ionization

NASA Astrophysics Data System (ADS)

Le Padellec, A.; Launoy, T.; Dochain, A.; Urbain, X.

2017-05-01

This paper compiles our merged-beam experimental findings for the associative ionization (AI) process from charged reactants, with the aim of guiding future investigations with e.g. the double electrostatic ion storage ring DESIREE in Stockholm. A reinvestigation of the isotopic effect in H-(D-) + He+ collisions is presented, along with a review of {{{H}}}3+ and NO+ production by AI involving ion pairs or excited neutrals, and put in perspective with the mutual neutralization and radiative association reactions. Critical parameters are identified and evaluated for their systematic role in controlling the magnitude of the cross section: isotopic substitution, exothermicity, electronic state density, and spin statistics.

Tunnel ionization of atoms and molecules: How accurate are the weak-field asymptotic formulas?

NASA Astrophysics Data System (ADS)

Labeye, Marie; Risoud, François; Maquet, Alfred; Caillat, Jérémie; Taïeb, Richard

2018-05-01

Weak-field asymptotic formulas for the tunnel ionization rate of atoms and molecules in strong laser fields are often used for the analysis of strong field recollision experiments. We investigate their accuracy and domain of validity for different model systems by confronting them to exact numerical results, obtained by solving the time dependent Schrödinger equation. We find that corrections that take the dc-Stark shift into account are a simple and efficient way to improve the formula. Furthermore, analyzing the different approximations used, we show that error compensation plays a crucial role in the fair agreement between exact and analytical results.

Focused analyte spray emission apparatus and process for mass spectrometric analysis

DOEpatents

Roach, Patrick J [Kennewick, WA; Laskin, Julia [Richland, WA; Laskin, Alexander [Richland, WA

2012-01-17

An apparatus and process are disclosed that deliver an analyte deposited on a substrate to a mass spectrometer that provides for trace analysis of complex organic analytes. Analytes are probed using a small droplet of solvent that is formed at the junction between two capillaries. A supply capillary maintains the droplet of solvent on the substrate; a collection capillary collects analyte desorbed from the surface and emits analyte ions as a focused spray to the inlet of a mass spectrometer for analysis. The invention enables efficient separation of desorption and ionization events, providing enhanced control over transport and ionization of the analyte.

Interaction of cholesterol-conjugated ionizable amino lipids with biomembranes: lipid polymorphism, structure-activity relationship, and implications for siRNA delivery.

PubMed

Zhang, Jingtao; Fan, Haihong; Levorse, Dorothy A; Crocker, Louis S

2011-08-02

Delivery of siRNA is a major obstacle to the advancement of RNAi as a novel therapeutic modality. Lipid nanoparticles (LNP) consisting of ionizable amino lipids are being developed as an important delivery platform for siRNAs, and significant efforts are being made to understand the structure-activity relationship (SAR) of the lipids. This article uses a combination of small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) to evaluate the interaction between cholesterol-conjugated ionizable amino lipids and biomembranes, focusing on an important area of lipid SAR--the ability of lipids to destabilize membrane bilayer structures and facilitate endosomal escape. In this study, cholesterol-conjugated amino lipids were found to be effective in increasing the order of biomembranes and also highly effective in inducing phase changes in biological membranes in vitro (i.e., the lamellar to inverted hexagonal phase transition). The phase transition temperatures, determined using SAXS and DSC, serve as an indicator for ranking the potency of lipids to destabilize endosomal membranes. It was found that the bilayer disruption ability of amino lipids depends strongly on the amino lipid concentration in membranes. Amino lipids with systematic variations in headgroups, the extent of ionization, tail length, the degree of unsaturation, and tail asymmetry were evaluated for their bilayer disruption ability to establish SAR. Overall, it was found that the impact of these lipid structure changes on their bilayer disruption ability agrees well with the results from a conceptual molecular "shape" analysis. Implications of the findings from this study for siRNA delivery are discussed. The methods reported here can be used to support the SAR screening of cationic lipids for siRNA delivery, and the information revealed through the study of the interaction between cationic lipids and biomembranes will contribute significantly to the design of more efficient siRNA delivery vehicles.

Are clusters important in understanding the mechanisms in atmospheric pressure ionization? Part 1: Reagent ion generation and chemical control of ion populations.

PubMed

Klee, Sonja; Derpmann, Valerie; Wißdorf, Walter; Klopotowski, Sebastian; Kersten, Hendrik; Brockmann, Klaus J; Benter, Thorsten; Albrecht, Sascha; Bruins, Andries P; Dousty, Faezeh; Kauppila, Tiina J; Kostiainen, Risto; O'Brien, Rob; Robb, Damon B; Syage, Jack A

2014-08-01

It is well documented since the early days of the development of atmospheric pressure ionization methods, which operate in the gas phase, that cluster ions are ubiquitous. This holds true for atmospheric pressure chemical ionization, as well as for more recent techniques, such as atmospheric pressure photoionization, direct analysis in real time, and many more. In fact, it is well established that cluster ions are the primary carriers of the net charge generated. Nevertheless, cluster ion chemistry has only been sporadically included in the numerous proposed ionization mechanisms leading to charged target analytes, which are often protonated molecules. This paper series, consisting of two parts, attempts to highlight the role of cluster ion chemistry with regard to the generation of analyte ions. In addition, the impact of the changing reaction matrix and the non-thermal collisions of ions en route from the atmospheric pressure ion source to the high vacuum analyzer region are discussed. This work addresses such issues as extent of protonation versus deuteration, the extent of analyte fragmentation, as well as highly variable ionization efficiencies, among others. In Part 1, the nature of the reagent ion generation is examined, as well as the extent of thermodynamic versus kinetic control of the resulting ion population entering the analyzer region.

Target Plate Material Influence on Fullerene-C60 Laser Desorption/Ionization Efficiency

NASA Astrophysics Data System (ADS)

Zeegers, Guido P.; Günthardt, Barbara F.; Zenobi, Renato

2016-04-01

Systematic laser desorption/ionization (LDI) experiments of fullerene-C60 on a wide range of target plate materials were conducted to gain insight into the initial ion formation in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The positive and negative ion signal intensities of precursor, fragment, and cluster ions were monitored, varying both the laser fluence (0-3.53 Jcm-2) and the ion extraction delay time (0-950 ns). The resulting species-specific ion signal intensities are an indication for the ionization mechanisms that contribute to LDI and the time frames in which they operate, providing insight in the (MA)LDI primary ionization. An increasing electrical resistivity of the target plate material increases the fullerene-C60 precursor and fragment anion signal intensity. Inconel 625 and Ti90/Al6/V4, both highly electrically resistive, provide the highest anion signal intensities, exceeding the cation signal intensity by a factor ~1.4 for the latter. We present a mechanism based on transient electrical field strength reduction to explain this trend. Fullerene-C60 cluster anion formation is negligible, which could be due to the high extraction potential. Cluster cations, however, are readily formed, although for high laser fluences, the preferred channel is formation of precursor and fragment cations. Ion signal intensity depends greatly on the choice of substrate material, and careful substrate selection could, therefore, allow for more sensitive (MA)LDI measurements.

Calculation of H2-He Flow with Nonequilibrium Ionization and Radiation: an Interim Report

NASA Technical Reports Server (NTRS)

Furudate, Michiko; Chang, Keun-Shik

2005-01-01

The nonequilibrium ionization process in hydrogen-helium mixture behind a strong shock wave is studied numerically using the detailed ionization rate model developed recently by Park which accounts for emission and absorption of Lyman lines. The study finds that, once the avalanche ionization is started, the Lyman line is self-absorbed. The intensity variation of the radiation at 5145 Angstroms found by Leibowitz in a shock tube experiment can be numerically reproduced by assuming that ionization behind the shock wave prior to the onset of avalanche ionization is 1.3%. Because 1.3% initial ionization is highly unlikely, Leibowitz s experimental data is deemed questionable. By varying the initial electron density value in the calculation, the calculated ionization equilibration time is shown to increase approximately as inverse square-root of the initial electron density value. The true ionization equilibration time is most likely much longer than the value found by Leibowitz.

Development of a Computationally Efficient, High Fidelity, Finite Element Based Hall Thruster Model

NASA Technical Reports Server (NTRS)

Jacobson, David (Technical Monitor); Roy, Subrata

2004-01-01

This report documents the development of a two dimensional finite element based numerical model for efficient characterization of the Hall thruster plasma dynamics in the framework of multi-fluid model. Effect of the ionization and the recombination has been included in the present model. Based on the experimental data, a third order polynomial in electron temperature is used to calculate the ionization rate. The neutral dynamics is included only through the neutral continuity equation in the presence of a uniform neutral flow. The electrons are modeled as magnetized and hot, whereas ions are assumed magnetized and cold. The dynamics of Hall thruster is also investigated in the presence of plasma-wall interaction. The plasma-wall interaction is a function of wall potential, which in turn is determined by the secondary electron emission and sputtering yield. The effect of secondary electron emission and sputter yield has been considered simultaneously, Simulation results are interpreted in the light of experimental observations and available numerical solutions in the literature.

Leaky Integrate and Fire Neuron by Charge-Discharge Dynamics in Floating-Body MOSFET.

PubMed

Dutta, Sangya; Kumar, Vinay; Shukla, Aditya; Mohapatra, Nihar R; Ganguly, Udayan

2017-08-15

Neuro-biology inspired Spiking Neural Network (SNN) enables efficient learning and recognition tasks. To achieve a large scale network akin to biology, a power and area efficient electronic neuron is essential. Earlier, we had demonstrated an LIF neuron by a novel 4-terminal impact ionization based n+/p/n+ with an extended gate (gated-INPN) device by physics simulation. Excellent improvement in area and power compared to conventional analog circuit implementations was observed. In this paper, we propose and experimentally demonstrate a compact conventional 3-terminal partially depleted (PD) SOI- MOSFET (100 nm gate length) to replace the 4-terminal gated-INPN device. Impact ionization (II) induced floating body effect in SOI-MOSFET is used to capture LIF neuron behavior to demonstrate spiking frequency dependence on input. MHz operation enables attractive hardware acceleration compared to biology. Overall, conventional PD-SOI-CMOS technology enables very-large-scale-integration (VLSI) which is essential for biology scale (~10 11 neuron based) large neural networks.

Electrochemically Initiated Tagging of Thiols Using an Electrospray Ionization-Based Liquid Microjunction Surface Sampling Probe Two-Electrode Cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Berkel, Gary J; Kertesz, Vilmos

2009-01-01

This paper reports on the conversion of a liquid microjunction surface sampling probe (LMJ-SSP) into a two electrode electrochemical cell using a conductive sample surface and the probe as the two electrodes with an appropriate battery powered circuit. With this LMJ-SSP, two-electrode cell arrangement, tagging of analyte thiol functionalities (in this case peptide cysteine residues) with hydroquinone tags was initiated electrochemically using a hydroquinone doped solution when the analyte either was initially in solution or was sampled from a surface. Efficient tagging (~90%), at flow rates of 5-10 L/min, could be achieved for up to at least two cysteines onmore » a peptide. The high tagging efficiency observed was explained with a simple kinetic model. In general, the incorporation of a two-electrode electrochemical cell, or other multiple electrode arrangement, into the LMJ-SSP is expected to add to the versatility of this approach for surface sampling and ionization coupled with mass spectrometric detection.« less

Study of the 20,22Ne+20,22Ne and 10,12,13,14,15C+12C Fusion Reactions with MUSIC

NASA Astrophysics Data System (ADS)

Avila, M. L.; Rehm, K. E.; Almaraz-Calderon, S.; Carnelli, P. F. F.; DiGiovine, B.; Esbensen, H.; Hoffman, C. R.; Jiang, C. L.; Kay, B. P.; Lai, J.; Nusair, O.; Pardo, R. C.; Santiago-Gonzalez, D.; Talwar, R.; Ugalde, C.

2016-05-01

A highly efficient MUlti-Sampling Ionization Chamber (MUSIC) detector has been developed for measurements of fusion reactions. A study of fusion cross sections in the 10,12,13,14,15C+12C and 20,22Ne+20,22Ne systems has been performed at ATLAS. Experimental results and comparison with theoretical predictions are presented. Furthermore, results of direct measurements of the 17O(α, n)20Ne, 23Ne(α, p)26Mg and 23Ne(α, n)26Al reactions will be discussed.

Young Stellar Objects from Soft to Hard X-rays

NASA Astrophysics Data System (ADS)

Güdel, Manuel

2009-05-01

Magnetically active stars are the sites of efficient particle acceleration and plasma heating, processes that have been studied in detail in the solar corona. Investigation of such processes in young stellar objects is much more challenging due to various absorption processes. There is, however, evidence for violent magnetic energy release in very young stellar objects. The impact on young stellar environments (e.g., circumstellar disk heating and ionization, operation of chemical networks, photoevaporation) may be substantial. Hard X-ray devices like those carried on Simbol-X will establish a basis for detailed studies of these processes.

Ionization degree measurement in the gain medium of a hydrocarbon-free rubidium vapor laser operating in pulsed and CW modes.

PubMed

Zhao, Xiaofan; Yang, Zining; Hua, Weihong; Wang, Hongyan; Xu, Xiaojun

2017-04-17

Although the diode pumped alkali laser (DPAL) works in a three-level scheme, higher energy-state excitation and ionization processes exist during operation, which may lead to deleterious effects on laser performance. In this paper, we report the ionization degree measurement in the gain medium of an operational hydrocarbon-free Rb DPAL by using the optogalvanic method. The results show that, at the pulsed mode with a duration of ~1 ms, a maximal ionization degree of ~0.06% is obtained at a pump power of 140 W. While in the CW mode, the plasma reaches an ionization degree as high as ~2% at a pump power of 110 W, which is mainly due to the enough time for sufficient plasma development. A comparison with our previous work [Opt. Lett.39, 6501 (2014)] as well as modeling results is made and discussed. The influences of different population transfer channels on laser performance are simulated and analyzed. The results show that, for a typical hydrocarbon-free Rb laser (pump intensity of 15 kW/cm², helium pressure of 10 atm and cell temperature of 438 K), all the high-energy excitation effects give an overall negative influence on laser efficiency of ~3.78%, while the top two influencing channels are the photoionization (~1.8%) and the energy pooling (~1.53%). The work in this paper experimentally reveals the influence of the macroscopic ionization evolution process on an operational DPAL for the first time, which would be helpful for a more comprehensive understanding of the physics in DPALs.

Design and Validation of In-Source Atmospheric Pressure Photoionization Hydrogen/Deuterium Exchange Mass Spectrometry with Continuous Feeding of D2O.

PubMed

Acter, Thamina; Lee, Seulgidaun; Cho, Eunji; Jung, Maeng-Joon; Kim, Sunghwan

2018-01-01

In this study, continuous in-source hydrogen/deuterium exchange (HDX) atmospheric pressure photoionization (APPI) mass spectrometry (MS) with continuous feeding of D 2 O was developed and validated. D 2 O was continuously fed using a capillary line placed on the center of a metal plate positioned between the UV lamp and nebulizer. The proposed system overcomes the limitations of previously reported APPI HDX-MS approaches where deuterated solvents were premixed with sample solutions before ionization. This is particularly important for APPI because solvent composition can greatly influence ionization efficiency as well as the solubility of analytes. The experimental parameters for APPI HDX-MS with continuous feeding of D 2 O were optimized, and the optimized conditions were applied for the analysis of nitrogen-, oxygen-, and sulfur-containing compounds. The developed method was also applied for the analysis of the polar fraction of a petroleum sample. Thus, the data presented in this study clearly show that the proposed HDX approach can serve as an effective analytical tool for the structural analysis of complex mixtures. Graphical abstract ᅟ.

Gold nanoparticles as a platform for creating a multivalent poly-SUMO chain inhibitor that also augments ionizing radiation.

PubMed

Li, Yi-Jia; Perkins, Angela L; Su, Yang; Ma, Yuelong; Colson, Loren; Horne, David A; Chen, Yuan

2012-03-13

Protein-protein interactions mediated by ubiquitin-like (Ubl) modifications occur as mono-Ubl or poly-Ubl chains. Proteins that regulate poly-SUMO (small ubiquitin-like modifier) chain conjugates play important roles in cellular response to DNA damage, such as those caused by cancer radiation therapy. Additionally, high atomic number metals, such as gold, preferentially absorb much more X-ray energy than soft tissues, and thus augment the effect of ionizing radiation when delivered to cells. In this study, we demonstrate that conjugation of a weak SUMO-2/3 ligand to gold nanoparticles facilitated selective multivalent interactions with poly-SUMO-2/3 chains leading to efficient inhibition of poly-SUMO-chain-mediated protein-protein interactions. The ligand-gold particle conjugate significantly sensitized cancer cells to radiation but was not toxic to normal cells. This study demonstrates a viable approach for selective targeting of poly-Ubl chains through multivalent interactions created by nanoparticles that can be chosen based on their properties, such as abilities to augment radiation effects.

Gold nanoparticles as a platform for creating a multivalent poly-SUMO chain inhibitor that also augments ionizing radiation

PubMed Central

Li, Yi-Jia; Perkins, Angela L.; Su, Yang; Ma, Yuelong; Colson, Loren; Horne, David A.; Chen, Yuan

2012-01-01

Protein-protein interactions mediated by ubiquitin-like (Ubl) modifications occur as mono-Ubl or poly-Ubl chains. Proteins that regulate poly-SUMO (small ubiquitin-like modifier) chain conjugates play important roles in cellular response to DNA damage, such as those caused by cancer radiation therapy. Additionally, high atomic number metals, such as gold, preferentially absorb much more X-ray energy than soft tissues, and thus augment the effect of ionizing radiation when delivered to cells. In this study, we demonstrate that conjugation of a weak SUMO-2/3 ligand to gold nanoparticles facilitated selective multivalent interactions with poly-SUMO-2/3 chains leading to efficient inhibition of poly-SUMO-chain-mediated protein-protein interactions. The ligand-gold particle conjugate significantly sensitized cancer cells to radiation but was not toxic to normal cells. This study demonstrates a viable approach for selective targeting of poly-Ubl chains through multivalent interactions created by nanoparticles that can be chosen based on their properties, such as abilities to augment radiation effects. PMID:22388745

Micro Corona Ionizer as an Ozone Source for Bacterial Cell Lysis

NASA Astrophysics Data System (ADS)

Lee, Eun-Hee; Lim, Hyun Jeong; Chua, Beelee; Son, Ahjeong

2015-04-01

DNA extraction is a critical process of DNA assays including polymerase chain reaction (PCR), microarrays, molecular cloning, and DNA hybridization which has been well established and can be implemented by commercial kits. DNA extraction involves cell lysis, precipitation, and purification through the combination of physical and chemical processes. Cell lysis is essential to high DNA recovery yield which can be achieved via a variety of physical, chemical, and enzymatic methods. However, these methods were originally developed for bioassays that were labor intensive, time consuming, and vulnerable to contamination and inhibition. Here, we proposed to employ a micro corona ionizer as an ozone source to lyse bacterial cells. Ozone has been well known and used as a disinfectant which allows cell lysis and DNA extraction. Previously, we have shown that a micro corona ionizer is capable of generating a significant amount of ozone. In this study, we employed the micro corona ionizer for the bacterial cell lysis which consists of a 50 μm diameter cantilever wire as the discharge cathode and a 50 μm thick copper foil as anode. Applied voltages varied from 1900 to 2200 V with corresponding corona currents from 16 to 28 μA. The resultant ozone (concentration > 0.14 ppm) generated from the micro corona ionizer was bubbled into the sample via a miniature pump. We demonstrated the cell lysis of Pseudomonas putida as the target bacterium using the micro corona ionizer. At a flow rate of 38 ml/min and applied corona voltage of 2000 V, 98.5 ± 0.2% lysis (normalized to sonication result) was achieved after 10 min. In comparison, untreated and air-treated samples showed normalized % lysis of 11.9 ± 2.4 and 36.1 ± 1.7%, respectively. We also showed that the cell lysis efficiency could be significantly increased by increasing the flow rate and the applied corona voltage. By comparing the experimental results for continuous and pulsed treatment, we verified that the percentage of lysis is primarily determined by the total ozone treatment time.

Cascaded chirped photon acceleration for efficient frequency conversion

NASA Astrophysics Data System (ADS)

Edwards, Matthew R.; Qu, Kenan; Jia, Qing; Mikhailova, Julia M.; Fisch, Nathaniel J.

2018-05-01

A cascaded sequence of photon acceleration stages using the instantaneous creation of a plasma density gradient by flash ionization allows the generation of coherent and chirped ultraviolet and x-ray pulses with independently tunable frequency and bandwidth. The efficiency of the cascaded process scales with 1/ω in energy, and multiple stages produce significant frequency up-conversion with gas-density plasmas. Chirping permits subsequent pulse compression to few-cycle durations, and output frequencies are not limited to integer harmonics.

Mechanisms of Ionizing Radiation-Induced Cell Death in Primary Lung Cells

DTIC Science & Technology

2013-03-05

haemocytometer, and plated on 60 mm dishes coated with 0.5% gelatin (modification to allow attachment of PAEC). The cells were incubated for 14 days...we performed delayed plating where PAEC were first cultured to 70-90% confluence, exposed to varying doses of X-rays, incubated, and seeded then for...calculated as a function of plating efficiency of non-irradiated controls. The plating efficiency (PE) was defined as the percentage of the number

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phipps, Arran T.J.

Determining the composition of dark matter is at the forefront of modern scientific research. There is compelling evidence for the existence of vast quantities of dark matter throughout the universe, however it has so-far eluded all direct detection efforts and its identity remains a mystery. Weakly interacting massive particles (WIMPs) are a favored dark matter candidate and have been the primary focus of direct detection for several decades. The Cryogenic Dark Matter Search (CDMS) has developed the Z-dependent Ionization and Phonon (ZIP) detector to search for such particles. Typically made from germanium, these detectors are capable of distinguishing between electromagneticmore » background and a putative WIMP signal through the simultaneous measurement of ionization and phonons produced by scattering events. CDMS has operated several arrays of these detectors at the Soudan Underground Laboratory (Soudan, MN, USA) resulting in many competitive (often world-leading) WIMP exclusion limits. This dissertation focuses on ionization collection in these detectors under the sub-Kelvin, low electric field, and high crystal purity conditions unique to CDMS. The design and performance of a fully cryogenic HEMT-based amplifier capable of achieving the SuperCDMS SNOLAB ionization energy resolution goal of 100 eVee is presented. The experimental apparatus which has been used to record electron and hole properties under CDMS conditions is described. Measurements of charge transport, trapping, and impact ionization as a function of electric field in two CDMS detectors are shown, and the ionization collection efficiency is determined. The data is used to predict the error in the nuclear recoil energy scale under both CDMSlite and iZIP operating modes. A two species, two state model is developed to describe how ionization collection and space charge generation in CDMS detectors are controlled by the presence of “overcharged” D- donor and A+ acceptor impurity states. The thermal stability of these states is exclusive to sub-Kelvin operation, explaining why ionization collection in CDMS detectors differs from similar semiconductor detectors operating at higher temperature. This work represents a solid foundation for the understanding ionization collection in CDMS detectors.« less

Fast, low-level detection of strontium-90 and strontium-89 in environmental samples by collinear resonance ionization spectroscopy

NASA Astrophysics Data System (ADS)

Monz, L.; Hohmann, R.; Kluge, H.-J.; Kunze, S.; Lantzsch, J.; Otten, E. W.; Passler, G.; Senne, P.; Stenner, J.; Stratmann, K.; Swendt, K.; Zimmer, K.; Herrmann, G.; Trautmann, N.; Walter, K.

1993-12-01

Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 10 8 atoms in the presence of about 10 18 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 10 6. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 10 10 and an overall efficiency of ξ = 5 × 10 -6 have been achieved. The desired detection limit of 10 8 atoms 90Sr has been demonstrated with synthetic samples.

Hybrid quadrupole mass filter/quadrupole ion trap/time-of-flight-mass spectrometer for infrared multiple photon dissociation spectroscopy of mass-selected ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gulyuz, Kerim; Stedwell, Corey N.; Wang Da

2011-05-15

We present a laboratory-constructed mass spectrometer optimized for recording infrared multiple photon dissociation (IRMPD) spectra of mass-selected ions using a benchtop tunable infrared optical parametric oscillator/amplifier (OPO/A). The instrument is equipped with two ionization sources, an electrospray ionization source, as well as an electron ionization source for troubleshooting. This hybrid mass spectrometer is composed of a quadrupole mass filter for mass selection, a reduced pressure ({approx}10{sup -5} Torr) quadrupole ion trap (QIT) for OPO irradiation, and a reflectron time-of-flight drift tube for detecting the remaining precursor and photofragment ions. A helium gas pulse is introduced into the QIT to temporarilymore » increase the pressure and hence enhance the trapping efficiency of axially injected ions. After a brief pump-down delay, the compact ion cloud is subjected to the focused output from the continuous wave OPO. In a recent study, we implemented this setup in the study of protonated tryptophan, TrpH{sup +}, as well as collision-induced dissociation products of this protonated amino acid [W. K. Mino, Jr., K. Gulyuz, D. Wang, C. N. Stedwell, and N. C. Polfer, J. Phys. Chem. Lett. 2, 299 (2011)]. Here, we give a more detailed account on the figures of merit of such IRMPD experiments. The appreciable photodissociation yields in these measurements demonstrate that IRMPD spectroscopy of covalently bound ions can be routinely carried out using benchtop OPO setups.« less

Matrix-assisted laser desorption/ionization mass spectrometric analysis of aliphatic biodegradable photoluminescent polymers using new ionic liquid matrices.

PubMed

Serrano, Carlos A; Zhang, Yi; Yang, Jian; Schug, Kevin A

2011-05-15

In this study, two novel ionic liquid matrices (ILMs), N,N-diisopropylethylammonium 3-oxocoumarate and N,N-diisopropylethylammonium dihydroxymonooxoacetophenoate, were tested for the structural elucidation of recently developed aliphatic biodegradable polymers by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The polymers, formed by a condensation reaction of three components, citric acid, octane diol, and an amino acid, are fluorescent, but the exact mechanism behind their luminescent properties has not been fully elucidated. In the original studies, which introduced the polymer class (J. Yang et al., Proc. Natl. Acad. Sci. USA 2009, 106, 10086-10091), a hyper-conjugated cyclic structure was proposed as the source for the photoluminescent behavior. With the use of the two new ILMs, we present evidence that supports the presence of the proposed cyclization product. In addition, the new ILMs, when compared with a previously established ILM, N,N-diisopropylethylammonium α-cyano-3-hydroxycinnimate, provided similar signal intensities and maintained similar spectral profiles. This research also established that the new ILMs provided good spot-to-spot reproducibility and high ionization efficiency compared with corresponding crystalline matrix preparations. Many polymer features revealed through the use of the ILMs could not be observed with crystalline matrices. Ultimately, the new ILMs highlighted the composition of the synthetic polymers, as well as the loss of water that was expected for the formation of the proposed cyclic structure on the polymer backbone. Copyright © 2011 John Wiley & Sons, Ltd.

Dissociation reactions of potassiated glucose: deionization, potassium hydroxide loss, and cross-ring dissociation

NASA Astrophysics Data System (ADS)

Dyakov, Y. A.; Kazaryan, M. A.; Golubkov, M. G.; Gubanova, D. P.; Asratyan, A. A.

2018-04-01

Photochemical properties of carbohydrates, including mono- and polysaccharides, as well as various kinds of glycoproteins, proteoglycans, and glycolipids, take great attention last decades due to their significance for clarifying physical and chemical processes happening in biological molecules under irradiation. Understanding of excitation and ionization processes is important for interpretation of mass spectrometric (MS) experiments, which is the main instrument for quick and reliable analysis of biological samples. While polynucleotides and simple proteins can be easily studied by standard MS techniques (MALDI, ESI, and CID), carbohydrates and complicated biomolecules containing oligosaccharide residues are difficult to be ionized. Carbohydrates give a low signal yield. Their detection and analysis requires the special equipment and technology. Therefore, the development of new efficient methods for identification of carbohydrates in biological samples currently is the critical scientific and technical problem. In this work we study dissociation processes taking place in potassiated α- and β-glucose, which can be concerned as the modelling molecule for investigation of wide range of carbohydrates and carbohydrate fragments of biomolecules containing potassium ion as the ionization source. Here we compare deionization process with H2O and KOH elimination channels, as far as their competition with cross-ring dissociation processes. Potential energy surface were optimized by the density functional B3LYP/6-31G* method. Single point energy calculations in minima and transition state points were performed by G3(MP2,CCSD) ab initio method.

Energetics and dynamics through time-resolved measurements in mass spectrometry

NASA Astrophysics Data System (ADS)

Lifshitz, Chava

Results of recent work on time-resolved photoionization and electron ionization mass spectrometry carried out in Jerusalem are reviewed. Time-resolved photoionization mass spectrometry in the vacuum ultraviolet is applied to polycyclic aromatic hydrocarbons, for example naphthalene, pyrene and fluoranthene as well as to some bromo derivatives (bromonaphthalene and bromoanthracene). Time-resolved photoionization efficiency curves are modelled by Rice-Ramsperger-Kassel-Marcus QET rate-energy k ( E ) dependences of the unimolecular dissociative processes and by the rate process infrared radiative relaxation k . Experimental results are augmented by time-resolved photorad dissociation data for the same species, whenever available. Kinetic shifts, conventional and intrinsic (due to competition between dissociative and radiative decay), are evaluated. Activation parameters (activation energies and entropies) are deduced. Thermochemical information is obtained including bond energies and ionic heats of formation. Fullerenes, notably C , are studied by time-resolved electron ionization and a large intrinsic shift, due to competition with black-bodylike radiative decay in the visible is discussed.

AP-MALDI Mass Spectrometry Imaging of Gangliosides Using 2,6-Dihydroxyacetophenone

NASA Astrophysics Data System (ADS)

Jackson, Shelley N.; Muller, Ludovic; Roux, Aurelie; Oktem, Berk; Moskovets, Eugene; Doroshenko, Vladimir M.; Woods, Amina S.

2018-03-01

Matrix-assisted laser/desorption ionization (MALDI) mass spectrometry imaging (MSI) is widely used as a unique tool to record the distribution of a large range of biomolecules in tissues. 2,6-Dihydroxyacetophenone (DHA) matrix has been shown to provide efficient ionization of lipids, especially gangliosides. The major drawback for DHA as it applies to MS imaging is that it sublimes under vacuum (low pressure) at the extended time necessary to complete both high spatial and mass resolution MSI studies of whole organs. To overcome the problem of sublimation, we used an atmospheric pressure (AP)-MALDI source to obtain high spatial resolution images of lipids in the brain using a high mass resolution mass spectrometer. Additionally, the advantages of atmospheric pressure and DHA for imaging gangliosides are highlighted. The imaging of [M-H]- and [M-H2O-H]- mass peaks for GD1 gangliosides showed different distribution, most likely reflecting the different spatial distribution of GD1a and GD1b species in the brain. [Figure not available: see fulltext.

Simulation of double stage hall thruster with double-peaked magnetic field

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Li, Peng; Sun, Hezhi; Wei, Liqiu; Xu, Yu; Peng, Wuji; Su, Hongbo; Li, Hong; Yu, Daren

2017-07-01

This study adopts double permanent magnetic rings and four permanent magnetic rings to form two symmetrical magnetic peaks and two asymmetrical magnetic peaks in the channel of a Hall thruster, and uses a 2D-3V PIC-MCC model to analyze the influence of magnetic strength on the discharge characteristic and performance of Hall thrusters with an intermediate electrode and double-peaked magnetic field. As opposed to the two symmetrical magnetic peaks formed by double permanent magnetic rings, increasing the magnetic peak value deep within the channel can cause propellant ionization to occur; with the increase in the magnetic peak deep in the channel, the propellant utilization, thrust, and anode efficiency of the thruster are significantly improved. Double-peaked magnetic field can realize separate control of ionization and acceleration in a Hall thruster, and provide technical means for further improving thruster performance. Contribution to the Topical Issue "Physics of Ion Beam Sources", edited by Holger Kersten and Horst Neumann.

Covariance mapping of two-photon double core hole states in C 2 H 2 and C 2 H 6 produced by an x-ray free electron laser

DOE PAGES

Mucke, M; Zhaunerchyk, V; Frasinski, L J; ...

2015-07-01

Few-photon ionization and relaxation processes in acetylene (C 2H 2) and ethane (C 2H 6) were investigated at the linac coherent light source x-ray free electron laser (FEL) at SLAC, Stanford using a highly efficient multi-particle correlation spectroscopy technique based on a magnetic bottle. The analysis method of covariance mapping has been applied and enhanced, allowing us to identify electron pairs associated with double core hole (DCH) production and competing multiple ionization processes including Auger decay sequences. The experimental technique and the analysis procedure are discussed in the light of earlier investigations of DCH studies carried out at the samemore » FEL and at third generation synchrotron radiation sources. In particular, we demonstrate the capability of the covariance mapping technique to disentangle the formation of molecular DCH states which is barely feasible with conventional electron spectroscopy methods.« less

Size dependent fragmentation of argon clusters in the soft x-ray ionization regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gisselbrecht, Mathieu; Lindgren, Andreas; Burmeister, Florian

Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters ({>=}100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slowermore » processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ('heat') dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.« less

Studying Townsend and glow modes in an atmospheric-pressure DBD using mass spectrometry

NASA Astrophysics Data System (ADS)

McKay, Kirsty; Donaghy, David; He, Feng; Bradley, James W.

2018-01-01

Ambient molecular beam mass spectrometry has been employed to examine the effects of the mode of operation and the excitation waveform on the ionic content of a helium-based atmospheric-pressure parallel plate dielectric barrier discharge. By applying 10 kHz microsecond voltage pulses with a nanosecond rise times and 10 kHz sinusoidal voltage waveforms, distinctly different glow and Townsend modes were produced, respectively. Results showed a significant difference in the dominant ion species between the two modes. In the Townsend mode, molecular oxygen ions, atomic oxygen anions and nitric oxide anions are the most abundant species, however, in the glow mode water clusters ions and hydrated nitric oxygen anions dominate. Several hypotheses are put forward to explain these differences, including low electron densities and energies in the Townsend mode, more efficient ionization of water molecules through penning ionization and charge exchange with other species in glow mode, and large temperature gradients due to the pulsed nature of the glow mode, leading to more favorable conditions for cluster formation.

Quaternary ammonium isobaric tag for a relative and absolute quantification of peptides.

PubMed

Setner, Bartosz; Stefanowicz, Piotr; Szewczuk, Zbigniew

2018-02-01

Isobaric labeling quantification of peptides has become a method of choice for mass spectrometry-based proteomics studies. However, despite of wide variety of commercially available isobaric tags, none of the currently available methods offers significant improvement of sensitivity of detection during MS experiment. Recently, many strategies were applied to increase the ionization efficiency of peptides involving chemical modifications introducing quaternary ammonium fixed charge. Here, we present a novel quaternary ammonium-based isobaric tag for relative and absolute quantification of peptides (QAS-iTRAQ 2-plex). Upon collisional activation, the new stable benzylic-type cationic reporter ion is liberated from the tag. Deuterium atoms were used to offset the differential masses of a reporter group. We tested the applicability of QAS-iTRAQ 2-plex reagent on a series of model peptides as well as bovine serum albumin tryptic digest. Obtained results suggest usefulness of this isobaric ionization tag for relative and absolute quantification of peptides. Copyright © 2017 John Wiley & Sons, Ltd.

Application of elevated temperature-dispersive liquid-liquid microextraction for determination of organophosphorus pesticides residues in aqueous samples followed by gas chromatography-flame ionization detection.

PubMed

Farajzadeh, Mir Ali; Afshar Mogaddam, Mohammad Reza; Rezaee Aghdam, Samaneh; Nouri, Nina; Bamorrowat, Mahdi

2016-12-01

In the present study, an elevated temperature, dispersive, liquid-liquid microextraction/gas chromatography-flame ionization detection was investigated for the determination, pre-concentration, and extraction of six organophosphorus pesticides (malathion, phosalone, dichlorvos, diazinon, profenofos, and chlorpyrifos) residues in fruit juice and aqueous samples. A mixture of 1,2-dibromoethane (extraction solvent) and dimethyl sulfoxide (disperser solvent) was injected rapidly into the sample solution heated at an elevated temperature. Analytical parameters, including enrichment factors (1600-2075), linearity (r>0.994), limits of detection (0.82-2.72ngmL(-1)) and quantification (2.60-7.36ngmL(-1)), relative standard deviations (<7%) and extraction recoveries (64-83%), showed the high efficiency of the method developed for analysis of the target analytes. The proposed procedure was used effectively to analyse selected analytes in river water and fruit juice, and diazinon was found at ngmL(-1) concentrations in apple juice. Copyright © 2016 Elsevier Ltd. All rights reserved.

Unusual Complex Formation and Chemical Reaction of Haloacetate Anion on the Exterior Surface of Cucurbit[6]uril in the Gas Phase

NASA Astrophysics Data System (ADS)

Choi, Tae Su; Ko, Jae Yoon; Heo, Sung Woo; Ko, Young Ho; Kim, Kimoon; Kim, Hugh I.

2012-10-01

Noncovalent interactions of cucurbit[6]uril (CB[6]) with haloacetate and halide anions are investigated in the gas phase using electrospray ionization ion mobility mass spectrometry. Strong noncovalent interactions of monoiodoacetate, monobromoacetate, monochloroacetate, dichloroacetate, and trichloroacetate on the exterior surface of CB[6] are observed in the negative mode electrospray ionization mass spectra. The strong binding energy of the complex allows intramolecular SN2 reaction of haloacetate, which yields externally bound CB[6]-halide complex, by collisional activation. Utilizing ion mobility technique, structures of exteriorly bound CB[6] complexes of haloacetate and halide anions are confirmed. Theoretically determined low energy structures using density functional theory (DFT) further support results from ion mobility studies. The DFT calculation reveals that the binding energy and conformation of haloacetate on the CB[6] surface affect the efficiency of the intramolecular SN2 reaction of haloacetate, which correlate well with the experimental observation.

Photoionization studies with molecular beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ng, C.Y.

1976-09-01

A molecular beam photoionization apparatus which combines the advantages of both the molecular beam method with photoionization mass spectrometry has been designed and constructed for carrying out some unique photoionization experiments. Rotational cooling during the supersonic expansion has resulted in high resolution photoionization efficiency curves for NO, ICl, C/sub 2/H/sub 2/ and CH/sub 3/I. The analysis of these spectra has yielded ionization potentials for these molecules to an accuracy of +- 3 MeV. Detailed autoionization structures were also resolved. This allows the investigation of the selection rules for autoionization, and the identification of the Rydberg series which converge to themore » excited states of the molecular ions. The degree of relaxation for thermally populated excited states has been examined using NO and ICl as examples. As a result of adiabatic cooling, a small percentage of dimers is also formed during the expansion. The photoionization efficiency curves for (NO)/sub 2/, ArICl, Ar/sub 2/, Kr/sub 2/ and Xe/sub 2/ have been obtained near the thresholds. Using the known dissociation energies of the (NO)/sub 2/, Ar/sub 2/, Kr/sub 2/ and Xe/sub 2/ van der Waals molecules, the corresponding dissociation energies for NO-NO/sup +/, Ar/sub 2//sup +/, Kr/sub 2//sup +/, and Xe/sub 2//sup +/ have been determined. The ionization mechanisms for this class of molecules are examined and discussed.« less

Band Edge Positions and Their Impact on the Simulated Device Performance of ZnSnN 2-Based Solar Cells

DOE PAGES

Arca, Elisabetta; Fioretti, Angela; Lany, Stephan; ...

2017-12-07

ZnSnN 2 (ZTN) has been proposed as a new earth abundant absorber material for PV applications. While carrier concentration has been reduced to values suitable for device implementation, other properties such as ionization potential, electron affinity and work function are not known. Here, we experimentally determine the value of ionization potential (5.6 eV), electron affinity (4.1 eV) and work function (4.4 eV) for ZTN thin film samples with Zn cation composition Zn/(Zn+Sn) = 0.56 and carrier concentration n = 2x10 19cm -3. Using both experimental and theoretical results, we build a model to simulate the device performance of a ZTN/Mg:CuCrOmore » 2 solar cell, showing a potential efficiency of 23% in the limit of no defects present. We also investigate the role of band tails and recombination centers on the cell performance. In particular device simulations show that band tails are highly detrimental to the cell efficiency, and recombination centers are a major limitation if present in concentration comparable to the net carrier density. The effect of the position of the band edges of the p-type junction partner was assessed too. Through this study, we determine the major bottlenecks for the development of ZTN-based solar cell and identify avenues to mitigate them.« less

Fabrication of Nanostructured Mesoporous Germanium for Application in Laser Desorption Ionization Mass Spectrometry.

PubMed

Abdelmaksoud, Hazem H; Guinan, Taryn M; Voelcker, Nicolas H

2017-02-15

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is a high-throughput analytical technique ideally suited for small-molecule detection from different bodily fluids (e.g., saliva, urine, and blood plasma). Many SALDI-MS substrates require complex fabrication processes and further surface modifications. Furthermore, some substrates show instability upon exposure to ambient conditions and need to be kept under special inert conditions. We have successfully optimized mesoporous germanium (meso-pGe) using bipolar electrochemical etching and efficiently applied meso-pGe as a SALDI-MS substrate for the detection of illicit drugs such as in the context of workplace, roadside, and antiaddictive drug compliance. Argon plasma treatment improved the meso-pGe efficiency as a SALDI-MS substrate and eliminated the need for surface functionalization. The resulting substrate showed a precise surface geometry tuning by altering the etching parameters, and an outstanding performance for illicit drug detection with a limit of detection in Milli-Q water of 1.7 ng/mL and in spiked saliva as low as 5.3 ng/mL for cocaine. The meso-pGe substrate had a demonstrated stability over 56 days stored in ambient conditions. This proof-of-principle study demonstrates that meso-pGe can be reproducibly fabricated and applied as an analytical SALDI-MS substrate which opens the door for further analytical and forensic high-throughput applications.

Palladium modified porous silicon as multi-functional MALDI chip for serum peptide detection.

PubMed

Li, Xiao; Chen, Xiaoming; Tan, Jie; Liang, Xiao; Wu, Jianmin

2017-02-14

Interest in using mesoporous materials for peptidomic research has increased recently. The present study reports a new type of matrix assisted laser desorption/ionization (MALDI) plate derived from electrochemically etched porous silicon (PSi) whose surface was modified with palladium nanoparticles (PdNPs). Owing to the well-tailored pore size and the molecular filtration effect of the PSi, peptides in serum samples can be selectively captured and enriched in the pore channel, thereby eliminating the interference from large proteins in subsequent MALDI-MS detection. On the other hand, the PdNPs with localized surface plasmon resonance (LSPR) effect can help to enhance the efficiency of energy absorption in the UV region. Meanwhile, the charge separation effect between the PSi semiconductor and PdNPs also can be applied to promote the accumulation of positive charges on PdNPs, resulting in an improvement in laser desorption/ionization (LDI) efficiency under positive linear detection mode. The interplay among these unique properties of PSi and PdNPs can synergistically increase the overall sensitivity in serum peptide detection. Using this technology, serum sample can be directly detected on the PSi-PdNPs chip without complicated pretreatment process. Therefore, a high fidelity serum peptide fingerprint can be acquired in a high throughput way. With the assistance of statistical analysis, colorectal cancer patients and healthy people can be accurately distinguished based on the serum peptide fingerprints.

FastChem: A computer program for efficient complex chemical equilibrium calculations in the neutral/ionized gas phase with applications to stellar and planetary atmospheres

NASA Astrophysics Data System (ADS)

Stock, Joachim W.; Kitzmann, Daniel; Patzer, A. Beate C.; Sedlmayr, Erwin

2018-06-01

For the calculation of complex neutral/ionized gas phase chemical equilibria, we present a semi-analytical versatile and efficient computer program, called FastChem. The applied method is based on the solution of a system of coupled nonlinear (and linear) algebraic equations, namely the law of mass action and the element conservation equations including charge balance, in many variables. Specifically, the system of equations is decomposed into a set of coupled nonlinear equations in one variable each, which are solved analytically whenever feasible to reduce computation time. Notably, the electron density is determined by using the method of Nelder and Mead at low temperatures. The program is written in object-oriented C++ which makes it easy to couple the code with other programs, although a stand-alone version is provided. FastChem can be used in parallel or sequentially and is available under the GNU General Public License version 3 at https://github.com/exoclime/FastChem together with several sample applications. The code has been successfully validated against previous studies and its convergence behavior has been tested even for extreme physical parameter ranges down to 100 K and up to 1000 bar. FastChem converges stable and robust in even most demanding chemical situations, which posed sometimes extreme challenges for previous algorithms.

Chemical Enhancements in Shock-Accelerated Particles: Ab initio Simulations.

PubMed

Caprioli, Damiano; Yi, Dennis T; Spitkovsky, Anatoly

2017-10-27

We study the thermalization, injection, and acceleration of ions with different mass/charge ratios, A/Z, in nonrelativistic collisionless shocks via hybrid (kinetic ions-fluid electrons) simulations. In general, ions thermalize to a postshock temperature proportional to A. When diffusive shock acceleration is efficient, ions develop a nonthermal tail whose extent scales with Z and whose normalization is enhanced as (A/Z)^{2} so that incompletely ionized heavy ions are preferentially accelerated. We discuss how these findings can explain observed heavy-ion enhancements in Galactic cosmic rays.

Self-induced optogalvanic effect in a segmented hollow-cathode discharge

NASA Astrophysics Data System (ADS)

Steflekova, V.; Zhechev, D.

2018-03-01

Optogalvanic (OG) interaction is simulated and studied in a segmented hollow-cathode discharge (SHCD). HCD-lamps are used to induce an OG signal by their own emission or by that of another lamp. The efficiency of the OG of a Ne/Cu HCD lamp in the range 320-380 nm is estimated theoretically. An irregular galvanic peak arising near the inflection point in the i-V curve (∂V/∂i<0) is detected. Its origin is related to Penning ionization of the sputtered cathode material.

Scintillating fibres coupled to silicon photomultiplier prototypes for fast beam monitoring and thin timing detectors

NASA Astrophysics Data System (ADS)

Papa, A.; Kettle, P.-R.; Ripiccini, E.; Rutar, G.

2016-07-01

Several scintillating fibre prototypes (single- and double-layers) made of 250 μm multi-clad square fibres coupled to silicon photomultiplier have been studied using electrons, positrons and muons at different energies. Current measurements show promising results: already for a single fibre layer and minimum ionizing particles we obtain a detection efficiency ≥ 95 % (mean collected light/fibre ≈ 8 phe), a timing resolution of 550 ps/fibre and a foreseen spatial resolution < 100 μm, based on the achieved negligible optical cross-talk between fibres (< 1 %). We will also discuss the performances of a double-layer staggered prototype configuration, for which a full detection efficiency (≥ 99 %) has been measured together with a timing resolution of ≈ 400 ps for double hit events.

High-field plasma acceleration in a high-ionization-potential gas

DOE PAGES

Corde, S.; Adli, E.; Allen, J. M.; ...

2016-06-17

Plasma accelerators driven by particle beams are a very promising future accelerator technology as they can sustain high accelerating fields over long distances with high energy efficiency. They rely on the excitation of a plasma wave in the wake of a drive beam. To generate the plasma, a neutral gas can be field-ionized by the head of the drive beam, in which case the distance of acceleration and energy gain can be strongly limited by head erosion. In our research, we overcome this limit and demonstrate that electrons in the tail of a drive beam can be accelerated by upmore » to 27 GeV in a high-ionization-potential gas (argon), boosting their initial 20.35 GeV energy by 130%. Particle-in-cell simulations show that the argon plasma is sustaining very high electric fields, of ~150 GV m -1, over ~20 cm. Lastly, the results open new possibilities for the design of particle beam drivers and plasma sources.« less

A physics-based model for the ionization of samarium by the MOSC chemical releases in the upper atmosphere

NASA Astrophysics Data System (ADS)

Bernhardt, Paul A.; Siefring, Carl L.; Briczinski, Stanley J.; Viggiano, Albert; Caton, Ronald G.; Pedersen, Todd R.; Holmes, Jeffrey M.; Ard, Shaun; Shuman, Nicholas; Groves, Keith M.

2017-05-01

Atomic samarium has been injected into the neutral atmosphere for production of electron clouds that modify the ionosphere. These electron clouds may be used as high-frequency radio wave reflectors or for control of the electrodynamics of the F region. A self-consistent model for the photochemical reactions of Samarium vapor cloud released into the upper atmosphere has been developed and compared with the Metal Oxide Space Cloud (MOSC) experimental observations. The release initially produces a dense plasma cloud that that is rapidly reduced by dissociative recombination and diffusive expansion. The spectral emissions from the release cover the ultraviolet to the near infrared band with contributions from solar fluorescence of the atomic, molecular, and ionized components of the artificial density cloud. Barium releases in sunlight are more efficient than Samarium releases in sunlight for production of dense ionization clouds. Samarium may be of interest for nighttime releases but the artificial electron cloud is limited by recombination with the samarium oxide ion.

Results on nucleon life-time from the Kolar gold field experiment

NASA Technical Reports Server (NTRS)

Krishnaswamy, M. R.; Menon, M. G. K.; Mondal, N. K.; Narasimham, V. S.; Sreekantan, B. V.; Hayashi, Y.; Ito, N.; Kawakami, S.; Miyake, S.

1985-01-01

The KGF nucleon decay experiment has been in operation since October 1980 with a 140 ton calorimetric detector at a depth of 2.3 Km underground. The detector comprises 34 layers of proportional counters arranged in an orthogonal geometry with 12 mm thick iron plates in between successive layers. The proportional counters are made up of square (10 x 10 square centimeters) iron plates of wall thickness 2.3 mm. Each of the 1600 counters is instrumented to provide data on ionization, DE/dx and arrival time. The visible energy of a particle is determined to an accuracy of approximately 20% from the ionization and range of its track. The end point ionization of a stopping track provides the direction of motion as well as the nature of the particle (mu/pi,k,p). Decay of mu is recorded with an overall efficiency of only 20% in view of the thickness of 13 g/square centimeters between successive layers.

Lif Spectroscopy of ThF and the Preparation of ThF^{+} for the Jila eEDM Experiment

NASA Astrophysics Data System (ADS)

Ng, Kia Boon; Zhou, Yan; Gresh, Dan; Cairncross, William; Roussy, Tanya; Shagam, Yuval; Cheng, Lan; Ye, Jun; Cornell, Eric

2017-06-01

ThF^{+} is a promising candidate for a second-generation molecular ion-based measurement of the permanent electric dipole moment of the electron (eEDM). Compared to the current HfF^{+} eEDM experiment, ThF^{+} has several advantages: (i) the eEDM-sensitive ^{3}Δ_1 electronic state is the ground state, which facilitates a long measurement coherence time; (ii) its effective electric field (38 GV/cm) is 50% larger than that of HfF+, which promises a direct increase of the eEDM sensitivity; and (iii) the ionization energy of neutral ThF is lower than its dissociation energy, which introduces a greater flexibility for rotational state-selective photoionization via core-nonpenetrating Rydberg states. We use laser-induced fluorescence (LIF) spectroscopy to find suitable intermediate states required for the state selective ionization process. We present the results of our LIF spectroscopy of ThF, and our current progress on efficient ThF ionization and on ThF^{+} dissociation.

A Simple Sonication Improves Protein Signal in Matrix-Assisted Laser Desorption Ionization Imaging

NASA Astrophysics Data System (ADS)

Lin, Li-En; Su, Pin-Rui; Wu, Hsin-Yi; Hsu, Cheng-Chih

2018-02-01

Proper matrix application is crucial in obtaining high quality matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI). Solvent-free sublimation was essentially introduced as an approach of homogeneous coating that gives small crystal size of the organic matrix. However, sublimation has lower extraction efficiency of analytes. Here, we present that a simple sonication step after the hydration in standard sublimation protocol significantly enhances the sensitivity of MALDI MSI. This modified procedure uses a common laboratory ultrasonicator to immobilize the analytes from tissue sections without noticeable delocalization. Improved imaging quality with additional peaks above 10 kDa in the spectra was thus obtained upon sonication treatment. [Figure not available: see fulltext.

Would Dissociative Recombination of DNA+ be a Possible Pathway of DNA Damage?

NASA Astrophysics Data System (ADS)

Kwon, H. C.; Chen, Z. P.; Strom, R. A.; Andrianarijaona, V. M.

2015-05-01

It is known that dissociative recombination (DR) is one of the very efficient processes of destruction of molecular cations into neutral particles. During the past few years, the focus of DR has been expanded from small inorganic molecules to macromolecular cation. We are probing the possibility of the DR of DNA+ after ionization of DNA, for example due to ionizing radiation. Therefore we are investigating the existence of autoionization states within nucleotide bases (Guanine, Adenine, Cytosine, and Thymine). Our results from computational analysis using the modern electronic structure program ORCA will be presented. Authors wish to give special thanks to Pacific Union College Student Senate for their financial support.

Ionization tube simmer current circuit

DOEpatents

Steinkraus, R.F. Jr.

1994-12-13

A highly efficient flash lamp simmer current circuit utilizes a fifty percent duty cycle square wave pulse generator to pass a current over a current limiting inductor to a full wave rectifier. The DC output of the rectifier is then passed over a voltage smoothing capacitor through a reverse current blocking diode to a flash lamp tube to sustain ionization in the tube between discharges via a small simmer current. An alternate embodiment of the circuit combines the pulse generator and inductor in the form of an FET off line square wave generator with an impedance limited step up output transformer which is then applied to the full wave rectifier as before to yield a similar simmer current. 6 figures.

MULTI-PLATE IONIZATION CHAMBER FOR THE DETECTION OF SLOW NEUTRONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bubzanowski, A.; Grotowski, K.

1957-01-01

A description is given of an ionization chamber, the electrodes of which are coated with a layer of natural boron of thickness 3 mg/cm/sup 2/. Each electrode of the chamber consists of three disks, placed between plates of the other electrodes. The capacitance between the electrodes does not exceed 15 micromicrofarads. The technology of coating the layer is as follows: the boron is mixed with alcohol and a small amount of Canada balsam and is coated in the form of an emulsion on the plates. The chamber efficiency is approximately 2%. The filler is argon at atmospheric pressure. The durationmore » of the output pulses after forming is approximately 5 microseconds.« less

Mode transition induced by the magnetic field gradient in Hall thrusters

NASA Astrophysics Data System (ADS)

Han, Liang; Wei, Liqiu; Yu, Daren

2016-09-01

A mode transition phenomenon was found in Hall thrusters, which was induced by the increase of the magnetic field gradient. In the transition process, we observed experimentally that there have been obvious changes in the oscillation, the mean value of the discharge current, the thrust, the anode efficiency, and the plume pattern. The shifting and compression of the high magnetic field causes the electron density in the discharge channel to decrease and the ionization zone to move towards the exit plane. This also corresponds to a low atom density in the discharge channel, resulting in a loss of stability of the ionization at a high magnetic field gradient, which presents the transition of the discharge mode.

GASEOUS DISCHARGE DEVICE

DOEpatents

Gow, J.D.

1961-01-10

An extremely compact two-terminal gaseous discharge device is described that is capable of producing neutrons in copious quantities, relatively high energy ions, intense x rays, and the like. Principal novelty resides in the provision of a crossed electric-magnetic field region in the discharge envelope that traps electrons and accelerates them to very high energies to provide an intense ionizing medium adjacent the anode of the device for ionizing gas therein with extremely high efficiency. In addition, the crossed-field trapping region holds the electrons close to the anode whereby the acceleration of ions to the cathode is not materially effected by the electron sheath and the ions assume substantially the full energy of the anodecathode potential drop. (auth)

Ionization tube simmer current circuit

DOEpatents

Steinkraus, Jr., Robert F.

1994-01-01

A highly efficient flash lamp simmer current circuit utilizes a fifty percent duty cycle square wave pulse generator to pass a current over a current limiting inductor to a full wave rectifier. The DC output of the rectifier is then passed over a voltage smoothing capacitor through a reverse current blocking diode to a flash lamp tube to sustain ionization in the tube between discharges via a small simmer current. An alternate embodiment of the circuit combines the pulse generator and inductor in the form of an FET off line square wave generator with an impedance limited step up output transformer which is then applied to the full wave rectifier as before to yield a similar simmer current.

LLE review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley, D.K.

1989-01-01

This volume of the LLE Review, covering the period October--December 1989, contains an article discussing saturation effects and power-balance considerations in the design of high-power lasers and an article describing numerical modeling of the effects of power imbalances on target behavior. The advanced technology section reports on the development of a liquid crystal laser-beam apodizer and an experiment to study the high-intensity ionization of noble gases. Finally, the activities of the National Laser Users Facility and the GDL and OMEGA laser facilities are summarized. The highlights of this issue are: The problem of achieving power balance in high-efficiency, multibeam lasersmore » has been studied in terms of gain-saturation effects and the nonlinear nature of harmonic frequency conversion. It is shown that power imbalance can be minimized by balancing the gains and losses in equivalent amplification stages in each beamline. The effects of target implosion behavior of various power-imbalance sources in the OMEGA laser system have been studied using the two-dimensional hydrodynamics code ORCHID. The simulations show good agreement with an experiment in which a deliberate power imbalance was applied to the target drive. Laser-beam apodizers with large clear apertures have been fabricated using cholesteric liquid crystals. A soft-edge profile has been achieved by filling a cell with two separate liquid crystals with different selective-reflection bands, and allowing them to partially mix at the interface. A study of the ionization of noble gases in the tunneling regime using high- intensity, 1-ps pulses from the tabletop terawatt laser (T{sup 3}) has been carried out. The measured ion production is well predicted by a Coulomb barrier suppression ionization theory.« less

Modelling massive star feedback with Monte Carlo radiation hydrodynamics: photoionization and radiation pressure in a turbulent cloud

NASA Astrophysics Data System (ADS)

Ali, Ahmad; Harries, Tim J.; Douglas, Thomas A.

2018-07-01

We simulate a self-gravitating, turbulent cloud of 1000 M⊙ with photoionization and radiation pressure feedback from a 34 M⊙ star. We use a detailed Monte Carlo radiative transfer scheme alongside the hydrodynamics to compute photoionization and thermal equilibrium with dust grains and multiple atomic species. Using these gas temperatures, dust temperatures, and ionization fractions, we produce self-consistent synthetic observations of line and continuum emission. We find that all material is dispersed from the (15.5 pc)3 grid within 1.6 Myr or 0.74 free-fall times. Mass exits with a peak flux of 2 × 10-3 M⊙ yr-1, showing efficient gas dispersal. The model without radiation pressure has a slight delay in the breakthrough of ionization, but overall its effects are negligible. 85 per cent of the volume, and 40 per cent of the mass, become ionized - dense filaments resist ionization and are swept up into spherical cores with pillars that point radially away from the ionizing star. We use free-free emission at 20 cm to estimate the production rate of ionizing photons. This is almost always underestimated: by a factor of a few at early stages, then by orders of magnitude as mass leaves the volume. We also test the ratio of dust continuum surface brightnesses at 450 and 850 µm to probe dust temperatures. This underestimates the actual temperature by more than a factor of 2 in areas of low column density or high line-of-sight temperature dispersion; the H II region cavity is particularly prone to this discrepancy. However, the probe is accurate in dense locations such as filaments.

Reionization of Hydrogen and Helium by Early Stars and Quasars

NASA Astrophysics Data System (ADS)

Wyithe, J. Stuart B.; Loeb, Abraham

2003-04-01

We compute the reionization histories of hydrogen and helium caused by the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar luminosity function at high redshifts. The less constrained properties of the ionizing radiation produced by stars are modeled with two free parameters: (i) a transition redshift, ztran, above which the stellar population is dominated by massive, zero-metallicity stars and below which it is dominated by a Scalo mass function; and (ii) the product of the escape fraction of stellar ionizing photons from their host galaxies and the star formation efficiency, fescf*. We constrain the allowed range of these free parameters at high redshifts on the basis of the lack of the H I Gunn-Peterson trough at z<~6 and the upper limit on the total intergalactic optical depth for electron scattering, τes<0.18, from recent cosmic microwave background (CMB) experiments. We find that quasars ionize helium by a redshift z~4, but cannot reionize hydrogen by themselves before z~6. A major fraction of the allowed combinations of fescf* and ztran leads to an early peak in the ionized fraction because of the presence of metal-free stars at high redshifts. This sometimes results in two reionization epochs, namely, an early H II or He III overlap phase followed by recombination and a second overlap phase. Even if early overlap is not achieved, the peak in the visibility function for scattering of the CMB often coincides with the early ionization phase rather than with the actual reionization epoch. Consequently, τes does not correspond directly to the reionization redshift. We generically find values of τes>~7%, which should be detectable by the MAP satellite.

Exploring matrix effects and quantifying organic additives in hydraulic fracturing associated fluids using liquid chromatography electrospray ionization mass spectrometry.

PubMed

Nell, Marika; Helbling, Damian E

2018-05-23

Hydraulic fracturing (HF) operations utilize millions of gallons of water amended with chemical additives including biocides, corrosion inhibitors, and surfactants. Fluids injected into the subsurface return to the surface as wastewaters, which contain a complex mixture of additives, transformation products, and geogenic chemical constituents. Quantitative analytical methods are needed to evaluate wastewater disposal alternatives or to conduct adequate exposure assessments. However, our narrow understanding of how matrix effects change the ionization efficiency of target analytes limits the quantitative analysis of polar to semi-polar HF additives by means of liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS). To address this limitation, we explored the ways in which matrix chemistry influences the ionization of seventeen priority HF additives with a modified standard addition approach. We then used the data to quantify HF additives in HF-associated fluids. Our results demonstrate that HF additives generally exhibit suppressed ionization in HF-associated fluids, though HF additives that predominantly form sodiated adducts exhibit significantly enhanced ionization in produced water samples, which is largely the result of adduct shifting. In a preliminary screening, we identified glutaraldehyde and 2-butoxyethanol along with homologues of benzalkonium chloride (ADBAC), polyethylene glycol (PEG), and polypropylene glycol (PPG) in HF-associated fluids. We then used matrix recovery factors to provide the first quantitative measurements of individual homologues of ADBAC, PEG, and PPG in HF-associated fluids ranging from mg L-1 levels in hydraulic fracturing fluid to low μg L-1 levels in PW samples. Our approach is generalizable across sample types and shale formations and yields important data to evaluate wastewater disposal alternatives or implement exposure assessments.

Low- and high-LET radiation drives clonal expansion of lung progenitor cells in vivo

PubMed Central

Farin, Alicia M.; Manzo, Nicholas D.; Kirsch, David G.; Stripp, Barry R.

2015-01-01

Abundant populations of epithelial progenitor cells maintain the epithelium along the proximal-to-distal axis of the airway. Exposure of lung tissue to ionizing radiation leads to tissue remodeling and potential cancer initiation or progression. However, little is known about the effects of ionizing radiation on airway epithelial progenitor cells. We hypothesized that ionizing radiation exposure will alter the behavior of airway epithelial progenitor cells in a radiation dose- and quality-dependent manner. To address this hypothesis, we cultured primary airway epithelial cells isolated from mice exposed to various doses of 320 kVp X-ray or 600 MeV/nucleon 56Fe ions in a 3D epithelial-fibroblast co-culture system. Colony-forming efficiency of the airway epithelial progenitor cells was assessed at culture day 14. In vivo clonogenic and proliferative potentials of airway epithelial progenitor cells were measured after exposure to ionizing radiation by lineage tracing and IdU incorporation. Exposure to both X-rays and 56Fe resulted in a dose dependent decrease in the ability of epithelial progenitors to form colonies in vitro. In vivo evidence for increased clonogenic expansion of epithelial progenitors was observed after exposure to both X-rays and 56Fe. Interestingly, we found no significant increase in the epithelial proliferative index, indicating that ionizing radiation does not promote increased turnover of the airway epithelium. Therefore, we propose a model in which radiation induces a dose-dependent decrease in the pool of available progenitor cells, leaving fewer progenitors able to maintain the airway long-term. This work provides novel insights into the effects of ionizing radiation exposure on airway epithelial progenitor cell behavior. PMID:25564721

Modelling massive-star feedback with Monte Carlo radiation hydrodynamics: photoionization and radiation pressure in a turbulent cloud

NASA Astrophysics Data System (ADS)

Ali, Ahmad; Harries, Tim J.; Douglas, Thomas A.

2018-04-01

We simulate a self-gravitating, turbulent cloud of 1000M⊙ with photoionization and radiation pressure feedback from a 34M⊙ star. We use a detailed Monte Carlo radiative transfer scheme alongside the hydrodynamics to compute photoionization and thermal equilibrium with dust grains and multiple atomic species. Using these gas temperatures, dust temperatures, and ionization fractions, we produce self-consistent synthetic observations of line and continuum emission. We find that all material is dispersed from the (15.5pc)3 grid within 1.6Myr or 0.74 free-fall times. Mass exits with a peak flux of 2× 10-3M⊙yr-1, showing efficient gas dispersal. The model without radiation pressure has a slight delay in the breakthrough of ionization, but overall its effects are negligible. 85 per cent of the volume, and 40 per cent of the mass, become ionized - dense filaments resist ionization and are swept up into spherical cores with pillars that point radially away from the ionizing star. We use free-free emission at 20cm to estimate the production rate of ionizing photons. This is almost always underestimated: by a factor of a few at early stages, then by orders of magnitude as mass leaves the volume. We also test the ratio of dust continuum surface brightnesses at 450 and 850μ to probe dust temperatures. This underestimates the actual temperature by more than a factor of 2 in areas of low column density or high line-of-sight temperature dispersion; the HII region cavity is particularly prone to this discrepancy. However, the probe is accurate in dense locations such as filaments.

The relative impact of photoionizing radiation and stellar winds on different environments

NASA Astrophysics Data System (ADS)

Haid, S.; Walch, S.; Seifried, D.; Wünsch, R.; Dinnbier, F.; Naab, T.

2018-05-01

Photoionizing radiation and stellar winds from massive stars deposit energy and momentum into the interstellar medium (ISM). They might disperse the local ISM, change its turbulent multi-phase structure, and even regulate star formation. Ionizing radiation dominates the massive stars' energy output, but the relative effect of winds might change with stellar mass and the properties of the ambient ISM. We present simulations of the interaction of stellar winds and ionizing radiation of 12, 23, and 60 M⊙ stars within a cold neutral (CNM, n0 = 100 cm-3), warm neutral (WNM, n0 = 1, 10 cm-3) or warm ionized (WIM, n0 = 0.1 cm-3) medium. The FLASH simulations adopt the novel tree-based radiation transfer algorithm TREERAY. With the On-the-Spot approximation and a temperature-dependent recombination coefficient, it is coupled to a chemical network with radiative heating and cooling. In the homogeneous CNM, the total momentum injection ranges from 1.6× 104 to 4× 105 M⊙ km s-1 and is always dominated by the expansion of the ionized HII region. In the WIM, stellar winds dominate (2× 102 to 5× 103 M⊙ km s-1), while the input from radiation is small (˜ 102 M⊙ km s-1). The WNM (n0 = 1 cm-3) is a transition regime. Energetically, stellar winds couple more efficiently to the ISM (˜ 0.1 percent of wind luminosity) than radiation (< 0.001 percent of ionizing luminosity). For estimating the impact of massive stars, the strongly mass-dependent ratios of wind to ionizing luminosity and the properties of the ambient medium have to be considered.