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1

Profiling Neurosteroids in Cerebrospinal Fluids and Plasma by Gas Chromatography\\/Electron Capture Negative Chemical Ionization Mass Spectrometry  

Microsoft Academic Search

A quantitative method for the determination of allopregnanolone (5?,3?-THP) and related neurosteroids in CSF and plasma was established using gas chromatography\\/electron capture negative chemical ionization mass spectrometry (GC\\/ECNCI\\/MS). Neurosteroids were converted to carboxymethoxime, pentafluorobenzyl and trimethylsilyl derivatives and detected as intense (M-181)? fragment ions generated under the negative ion chemical ionization process. The response curves constructed using d4-dihydrotestosterone (DHT) and

Yang-Suk Kim; Hongjian Zhang; Hee-Yong Kim

2000-01-01

2

Detection of trace levels of triclopyr using capillary gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry.  

PubMed

Triclopyr, after esterification, is shown to be a suitable candidate for detection by gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry forming a characteristic carboxylate anion which offers a high detection sensitivity. A detection limit of 70 fg reaching the ionizer is indicated. Low backgrounds and an absence of chemical interferences are shown for vegetation extracts, using a simple method of extraction and derivatisation. A similar behaviour is demonstrated for 2,4-D and 2,4,5-T. PMID:3379116

Begley, P; Foulger, B E

1988-04-01

3

Study of the fragmentation pattern of ketamine-heptafluorobutyramide by gas chromatography/electron ionization mass spectrometry.  

PubMed

Ketamine is an anaesthetic compound used in human and veterinary medicine with hallucinogen properties that have resulted in its increased illicit use by teenagers at rave parties. Although several gas chromatography/mass spectrometry (GC/MS) methods have been reported for the quantification of the drug both in urine and in hair, its electron ionization (EI) fragmentation after derivatization with different reagents has been not yet fully investigated. The present work reports the study of the fragmentation of ketamine, derivatized with heptafluorobutyric anhydride (HFBA-Ket), using gas chromatography/electron ionization mass spectrometry (GC/EI-MS). The complete characterization of the fragmentation pattern represented an intriguing exercise and required tandem mass spectrometry (MS(n)) experiments, high-resolution accurate mass measurements and the use of deuterated d(4)-ketamine to corroborate the proposed structures and to characterize the fragment ions carrying the unchanged aromatic moiety. Extensive fragmentation was observed, mainly located at the cyclohexanone ring followed by rearrangement of the fragment ions, as confirmed by the mass spectra obtained from the deuterated molecule. The GC/EI-MS analysis of HFBA-Ket will represent a useful tool in forensic science since high-throughput analyses are enabled, preserving both the GC stationary phase and the cleanliness of the mass spectrometer ion optics. PMID:19957293

Pieri, Maria; Castiglia, Loredana; Miraglia, Nadia; Guadagni, Rossella; Malorni, Livia; Sannolo, Nicola; Acampora, Antonio; Della Casa, Elvira

2010-01-01

4

An Examination of Pentafluorobenzoyl Derivatization Strategies for the Analysis of Fatty Alcohols using Gas Chromatography/Electron Capture Negative Ion Chemical Ionization-Mass Spectrometry  

PubMed Central

Gas chromatography/electron capture negative ion chemical ionization-mass spectrometry (GC/ECNICI-MS) combined with pentafluorobenzoyl derivatization (PFBoyl) is frequently used for the sensitive detection of fatty alcohols (FOH). However, this derivatization technique suffers from a lack of established reaction protocols, time-consuming reactions, and the presence of reagent artifacts or unwanted derivatization byproducts which can hinder analyte detection. Here, strategies are presented to reduce the problems associated with PFBoyl-derivatization, including 1) the optimization of reaction conditions (derivatization time and temperature) for a variety of PFBoyl-derivatized FOH, 2) an investigation of microwave-accelerated derivatization (MAD) as a rapid alternative heating mechanism for the PFBoyl-derivatization of FOH, and 3) an analysis of an alternative strategy employing a solvent extraction procedure post-derivatization to reduce the detrimental effects commonly associated with PFBoyl derivatization reagents. The optimal reaction conditions for the PFBoyl-derivatization of FOH was determined to be 60 °C for 45 min. The investigation in MAD demonstrated the potential of obtaining comparable PFBoyl-derivatizations to those obtained using traditional heating methods, albeit in a reaction time of 3 min. An examination of several solvents for post-derivatization extraction revealed improved relative response factors in comparison to those obtained without solvent extraction. The best solvents for the PFBoyl-FOH extraction, dichloromethane and tert-butyl methyl ether, were also compared to the no solvent extraction samples with standard response curves and PFBoyl-derivatized FOH in Bligh-Dyer extracted rat plasma.

Bowden, John A.; Ford, David A.

2010-01-01

5

Evaluation of BDE-47 Hydroxylation Metabolic Pathways Based on a Strong Electron-Withdrawing Pentafluorobenzoyl Derivatization Gas Chromatography/Electron Capture Negative Ionization Quadrupole Mass Spectrometry.  

PubMed

Understanding the metabolic pathways of polybrominated diphenyl ethers (PBDEs) is a key issue in the evaluation of their cytotoxicity after they enter the biota. In order to obtain more information concerning the metabolic pathways of PBDEs, we developed a strong electron-withdrawing pentafluorobenzoyl (PFBoyl) derivatization capillary gas chromatography/electron capture negative ionization quadrupole mass spectrometry (GC/ECNI-qMS). PFBoyl esterification greatly improves separation of the metabolites of PBDEs such as hydroxylated PBDEs (OH-PBDEs) and bromophenols (BPs) metabolites in rat liver microsomes (RLMs). On the other hand, the strong electron-withdrawing property of PFBoyl derivatized on OH-PBDEs and/or BPs makes cleavage of the ester bond on ECNI easier resulting in higher abundance of the structure-informative characteristic fragment ions at a high m/z region, which facilitate the identification of OH-PBDEs metabolites. Subsequent quantification can be performed by monitoring not only (79)Br(-) (or (81)Br(-)) but also their characteristic fragment ions, achieving more accurate isotope dilution quantification using GC/ECNI-qMS. These merits allow us to identify totally 12 metabolites of BDE-47, a typical example of PBDEs, in the RLMs in vitro incubation systems. In addition to the already known metabolites of BDE-47, one dihydroxylated 3,6-di-OH-BDE-47 and one dihydroxylated 3,5-di-OH-tetrabrominated dioxin were found. Moreover, the second hydroxylation took place on the same bromophenyl ring, where the first hydroxyl group was located, and was further confirmed via the identification of the dihydroxylated 2',6'-di-OH-BDE-28 of an asymmetric 2'-OH-BDE-28. This methodological development and its subsequent findings of the metabolic pathways of BDE-47 provided experimental evidence for understanding its dioxin-like behavior and endocrine disrupting risk. PMID:24925108

Zhai, Chao; Peng, Shunv; Yang, Limin; Wang, Qiuquan

2014-07-15

6

Evaluation of gas chromatography-atmospheric pressure chemical ionization-mass spectrometry as an alternative to gas chromatography-electron ionization-mass spectrometry: avocado fruit as example.  

PubMed

Although GC-APCI-MS was developed more than 40 years ago this coupling is still far from being a routine technique. One of the reasons explaining the limited use of GC-APCI so far is the lack of spectral database which facilitates the identification of the compounds under study. The first application of a very recently developed GC-APCI database to identify as many compounds as possible in a complex matrix such as avocado fruit is presented here. The results achieved by using this database has been checked against those obtained using traditional GC-EI-MS and a comparison of the MS signals observed in both ionization sources has been carried out. 100 compounds belonging to different chemical families were identified in the matrix under study. Considering the results of this study, the wide range of application (in terms of polarity and size of analytes) and the robustness of APCI as interface, the high quality of TOF spectra, and our library as a publicly available resource, GC-APCI-TOF MS is definitively a valuable addition to the "metabolomics toolbox". PMID:24054422

Hurtado-Fernández, Elena; Pacchiarotta, Tiziana; Longueira-Suárez, Enrique; Mayboroda, Oleg A; Fernández-Gutiérrez, Alberto; Carrasco-Pancorbo, Alegría

2013-10-25

7

A rapid novel derivatization of amphetamine and methamphetamine using 2,2,2-trichloroethyl chloroformate for gas chromatography electron ionization and chemical ionization mass spectrometric analysis.  

PubMed

Amphetamine and methamphetamine are commonly abused central nervous system stimulants. We describe a rapid new derivatization of amphetamine and methamphetamine using 2,2,2-trichloroethyl chloroformate for gas chromatography-mass spectrometric analysis. Amphetamine and methamphetamine, along with N-propyl amphetamine (internal standard), were extracted from urine using 1-chlorobutane. The derivatization with 2,2,2-trichloroethyl chloroformate can be achieved at room temperature in 10 minutes. The electron ionization mass spectrum of amphetamine 2,2,2-trichloroethyl carbamate showed two weak molecular ions at m/z 309 and 311, but showed diagnostic strong peaks at m/z 218, 220, and 222. In contrast, chemical ionization of the mass spectrum of amphetamine 2,2,2-trichloroethyl carbamate showed strong (M + 1) ions at m/z 310 and 312 and other strong diagnostic peaks at m/z 274 and 276. The major advantages of this derivative are the presence of a diagnostic cluster of peaks due to the isotopic effect of three chlorine atoms (isotopes 35 and 37) in the derivatized molecule and the relative ease of its preparation. We also observed strong molecular ions for derivatized methamphetamine in the chemical ionization mass spectrum, but the molecular ions were very weak in the electron ionization mass spectrum. We used the scan mode of mass spectrometry in all analyses. When using a urine standard containing 1,000 ng/mL of amphetamine (a 7.4-micromol/L concentration) and methamphetamine (a 6.7-micromol/L concentration), the within-run precisions were 4.8% for amphetamine and 3.6% for methamphetamine. The corresponding between-run precisions were 5.3% for amphetamine and 6.7% for methamphetamine. The assay was linear for amphetamine and methamphetamine concentrations of 250 to 5,000 ng/mL (amphetamine, 1.9-37.0 micromol/L; methamphetamine, 1.7-33.6 micromol/L). The detection limit was 100 ng/mL (amphetamine, 0.74 micromol/L; methamphetamine, 0.67 micromol/L) using the scan mode of electron ionization mass spectrometry. We observed good a correlation between the concentrations of amphetamine and methamphetamine in five urine specimens positive for amphetamines using the more conventional pentafluoropropionyl derivative and our new derivative using 2,2,2-trichloroethyl chloroformate. PMID:9576569

Dasgupta, A; Spies, J

1998-05-01

8

Gas chromatography-electron ionization-mass spectrometry analysis of O,O'- dialkyl methylphosphonites for verification analysis of the Chemical Weapons Convention.  

PubMed

Gas chromatography-mass spectrometry (GC-MS) analysis of O,O'-dialkyl methylphosphonites (DAMPs) was carried out with a view to developing a database and understanding the mechanism of fragmentation. DAMPs are included in the list of schedule 2B4 chemicals of the Chemical Weapons Convention. GC-MS analysis of DAMPs and their deuterated analogs revealed that their fragmentations were dominated by ?-cleavages, alkenyl radical loss and hydrogen rearrangements. Based on fragment ions of deuterated analogs and density functional theory calculations, the fragmentation routes were rationalized. PMID:21625030

Pardasani, Deepak; Tak, Vijay; Purohit, Ajay K; Kanaujia, Pankaj K; Dubey, Devendra K

2011-01-01

9

Determination of Acrylamide in Rat Serum and Sciatic Nerve by Gas Chromatography-Electron-Capture Detection.  

National Technical Information Service (NTIS)

A modified method for the derivatization and determination of acrylamide as 2-bromopropenamide by gas chromatography-electron-capture detection was developed and applied to serum and sciatic nerve from rats. The method was accurate and precise over the ca...

J. H. Raymer C. M. Sparacino G. R. Velez S. Padilla R. C. MacPhail

1993-01-01

10

DETERMINATION OF ACRYLAMIDE IN RAT SERUM AND SCIATIC NERVE BY GAS CHROMATOGRAPHY-ELECTRON-CAPTURE DETECTION  

EPA Science Inventory

A modified method for the derivatization and analysis of acrylamide as 2-bromopropenamide by gas chromatography/electron capture detection was validated in serum and sciatic nerve from rats. he method was accurate and precise over the concentration range of 2240 to 74700 ppm (w/v...

11

Nano-high-performance liquid chromatography–electron ionization mass spectrometry approach for environmental analysis  

Microsoft Academic Search

We describe a method, based on a new nano-HPLC gradient generator coupled to a modified direct electron ionization (EI) LC–MS interface, for the analysis of several compounds of environmental interest. The gradient generator was installed on a conventional HPLC system and the nano-flow rate was achieved using a double splitter. Reproducible gradients of different shapes (i.e. linear, convex, concave) can

Achille Cappiello; Giorgio Famiglini; Filippo Mangani; Pierangela Palma; Antonella Siviero

2003-01-01

12

Determination of thiazolidine-4-carboxylates in urine by chloroformate derivatization and gas chromatography-electron impact mass spectrometry.  

PubMed

The derivatization method of thiazolidine-4-carboxylic acid (TZCA) and methyl-thiazolidine-4-carboxylic acid (Me-TZCA) in urine with alcohol/chloroformate was achieved. TZCA and Me-TZCA were derivatized in one step in urine with ethyl chloroformate in 1 min at room temperature. The derivatives of TZCA and Me-TZCA had very good chromatographic properties and offered very sensitive response for gas chromatography-electron impact ionization-mass spectrometry (GC-EI-MS). On the basis of derivatization, the method for simultaneous determination of TZCA and Me-TZCA in human urine was developed. Deuterated Me-TZCA (Me-TZCA-d(4)) was synthesized as the internal standard (IS) for the analysis of urine samples. TZCA and Me-TZCA were derivatized and extracted from urine at pH 9.5 with toluene, and then the dried extract was dissolved with 100 microl ethyl acetate and injected in GC/MS system. The recoveries of TZCA and Me-TZCA were about 102 and 103%, respectively, at the concentration of 0.05 mg/l. The method detection limits (MDL) were 1.0 and 0.5 microg/l, respectively, for TZCA and Me-TZCA in 1 ml human urine. The coefficients of variation of TZCA and Me-TZCA were less than 6% at the concentrations of 0.05 and 0.2 mg/l, respectively. To assess the formation of TZCA during inhalation with formaldehyde (FA) (about 3.1 and 38.1 ppm FA in air), urine samples from rats were taken during 3 days after initiation of treatment. The mean amount of TZCA determined was 0.07 mg/l in control group and 0.18 mg/l during treatment with 3.1 ppm. The TZCA levels increased up to about 1.01 mg/l during treatment with 38.1 ppm. It is planned to study whether urinary TZCA can be used as an indicator in the biological monitoring of exposure to FA. PMID:17610311

Shin, Ho-Sang; Ahn, Hye-Sil; Lee, Byung-Hoon

2007-09-01

13

Determination of indicator polychlorinated biphenyls (PCBs) by gas chromatography-electron capture detector.  

PubMed

An effective method for determination of indicator polychlorinated biphenyls (PCBs) has been validated using gas chromatography (GC) equipped with electron capture detector (ECD). The GC-ECD method was validated by determining the linear range (working range) for determination of the compounds, minimum detectable quantities (MDQ), the precision and accuracy of the method for the analysis of the compounds. MDQ obtained for the compounds ranges from 0.0005 to 0.002 ng. Indeed the method was found to be more sensitive as the number of chlorine atoms attached to the biphenyl increases. The precision and accuracy of the GC method validated ranges from 2.4% to 14.5% and -7.0% to 14.6% respectively. Coefficient of variation associated with the repeatability of the retention times and corresponding peak areas was found to be 0.0001-0.0007 for the retention times and 0.0014-0.059 for the peak areas. Percentage recoveries for the compounds were in the range of 95.7-101.0%. The validated method was then applied to determine levels of indicator PCBs in sediments sampled from eleven sampling points along the Lake Bosuntwi in Ghana and the highest PCB load of 19.17 ng g(-1) was recorded at Pipie No. 2. PCB 52 and PCB 101 were found to be the most ubiquitous indicator PCBs in the study area, both with 90.91% occurrence. PMID:24016628

Afful, Samuel; Awudza, Johannes A M; Twumasi, Stevester K; Osae, Shiloh

2013-11-01

14

Photocatalytic oxidation of aqueous trichloroethylene using dye sensitized buoyant photocatalyst monitored via micro-headspace solid-phase microextration gas chromatography\\/electron capture detection and mass spectrometry  

Microsoft Academic Search

Trichloroethylene (TCE), a useful industrial agent which unfortunately exhibits carcinogenic properties, has become an extremely prevalent environmental contaminant. As such, new rapid, sensitive, and cost effective detection methods are needed for the identification of potential point sources of contamination. A new analytic micro-headspace method is described, utilizing solid phase micro-extraction (SPME) fibers and routine gas chromatography\\/electron capture detection (GC\\/ECD) for

Matt V. Alexander; Jeffrey J. Rosentreter

2008-01-01

15

Determination of chlorophenols in water samples using simultaneous dispersive liquid–liquid microextraction and derivatization followed by gas chromatography-electron-capture detection  

Microsoft Academic Search

Simultaneous dispersive liquid–liquid microextraction (DLLME) and derivatization combined with gas chromatography-electron-capture detection (GC-ECD) was used to determine chlorophenols (CPs) in water sample. In this derivatization\\/extraction method, 500?L acetone (disperser solvent) containing 10.0?L chlorobenzene (extraction solvent) and 50?L acetic anhydride (derivatization reagent) was rapidly injected by syringe in 5.00mL aqueous sample containing CPs (analytes) and K2CO3 (0.5%, w\\/v). Within a few

Nazir Fattahi; Yaghoub Assadi; Mohammad Reza Milani Hosseini; Elham Zeini Jahromi

2007-01-01

16

Determination of pentachlorophenol residue in meat and fish by gas chromatography-electron capture detection and gas chromatography-mass spectrometry with accelerated solvent extraction.  

PubMed

A novel analytical method, using gas chromatography-electron capture detection (GC-ECD) and GC-mass spectrometry detection (MS), was developed for the qualitative and quantitative measurement of pentachlorophenol in meat and fish. The analyte was extracted by methanol-2% trichloroacetic acid (3/1, v/v) with accelerated solvent extraction (ASE). The eluted fraction was evaporated and derivatized with acetic anhydride-pyridine (1/1, v/v) for GC-ECD analysis and GC-MS confirmation. The parameters for extraction pressure, temperature and cycle of ASE, cleanup, derivatization and analysis procedure were optimized. The averaged decision limits and detection capability of the method were in the ranges of 0.25-0.41 and 0.49-1.01 µg/kg in the muscle and liver of swine and bovine and in the muscle of carp and finless eel, respectively. Spiked recoveries from levels of 0.5-2.0 µg/kg were found to be more than 71.1%, with relative standard deviation less than 14.7% in GC-ECD and GC-MS. This rapid and reliable method can be used for the characterization and quantification of residues of pentachlorophenol in animal and fish tissues. PMID:23690067

Zhao, Dongmei

2014-05-01

17

Analysis of N-nitrosamines in water by isotope dilution gas chromatography-electron ionisation tandem mass spectrometry.  

PubMed

A method has been developed for the determination of eight N-nitrosamines in drinking water and treated municipal effluent. The method uses solid phase extraction (SPE), gas chromatography (GC) and analysis by tandem mass spectrometry (MS-MS) with electron ionization (EI). The target compounds are N-nitrosodimethylamine (NDMA), N-nitrosomethyethylamine (NMEA), N-nitrosodiethylamine NDEA), N-nitrosodipropylamine (NDPA), N-nitrosodi-n-butylamine (NDBuA), N-nitrosodiphenylamine (NDPhA), N-nitrosopyrrolidine (NPyr), N-nitrosopiperidine (NPip), N-nitrosomorpholine (NMorph). The use of direct isotope analogues for isotope dilution analysis of all analytes ensures accurate quantification, accounting for analytical variabilities that may occur during sample processing, extraction and instrumental analysis. Method detection levels (MDLs) were determined to describe analyte concentrations sufficient to provide a signal with 99% certainty of detection. The established MDLs for all analytes were 0.4-4 ng L(-1) in a variety of aqueous matrices. Sample matrices were observed to have only a minor impact on MDLs and the method validation confirmed satisfactory method stability over intra-day and inter-day analyses of tap water and tertiary treated effluent samples. PMID:22967534

McDonald, James A; Harden, Nick B; Nghiem, Long D; Khan, Stuart J

2012-09-15

18

Gas amplified ionization detector for gas chromatography  

DOEpatents

A gas-amplified ionization detector for gas chromatrography which possesses increased sensitivity and a very fast response time. Solutes eluding from a gas chromatographic column are ionized by UV photoionization of matter eluting therefrom. The detector is capable of generating easily measured voltage signals by gas amplification/multiplication of electron products resulting from the UV photoionization of at least a portion of each solute passing through the detector.

Huston, Gregg C. (LaBelle, PA)

1992-01-01

19

Improved method for the in vitro assessment of antioxidant activity of plant extracts by headspace solid-phase microextraction and gas chromatography-electron capture detection.  

PubMed

The simultaneous monitoring of malondialdehyde, pentanal and hexanal, final products of lipid peroxidation is reported, using a headspace solid-phase microextraction (HS-SPME) technique with on-fibre derivatisation. The aldehydes are extracted and subjected to on-sorbent derivatisation into stable hydrazones with 2,4,6-trichlorophenylhydrazine (TCPH) and analyzed. The degree of inhibition of oxidation is performed by monitoring the chlorinated hydrazones after thermal desorption, by gas chromatography-electron capture detection. The procedure was employed to evaluate in vitro the antioxidant activity of Hypericum perforatum L. extracts and of the well-known antioxidant vitamin E following induction of oxidation of sunflower oil, as a model lipid system. Prior to the measurement of antioxidant activity, the optimal process conditions, i.e. headspace volume, temperature, agitation, extraction/derivatisation time and desorption time and temperature were properly established. Aqueous extracts of H. perforatum L. exhibited the highest antioxidative effect. The method is shown to be promising for screening purposes for antioxidant substances and natural extracts. PMID:17316667

Gioti, Eleni M; Fiamegos, Yiannis C; Skalkos, Dimitris C; Stalikas, Constantine D

2007-06-01

20

Solid phase extraction with silicon dioxide microsphere adsorbents in combination with gas chromatography-electron capture detection for the determination of DDT and its metabolites in water samples.  

PubMed

The goal of the present study was to investigate the feasibility of silicon dioxide (SiO(2)) microspheres without special modification to enrich dichlorodiphenyltrichloroethane (DDT) and its main metabolites, p,p'-dichlorodiphenyl-2,2-dichloroethylene (p,p'-DDD) and p,p'-dichlorodiphenyldichloroethylene (DDE) in combination with gas chromatography-electron-capture detection. The experimental results indicated that an excellent linear relationship between the recoveries and the concentrations of DDT and its main metabolites was obtained in the range of 0.2-30 ng mL(-1) and the correlation coefficients were in the range of 99.96-99.99%. The detection limits based on the ratio of signal to the baseline noise (S/N = 3) were 2.2, 2.9, 3.8 and 4.1 ng L(-1) for p,p'-DDD, p,p'-DDT, o,p'-DDT, and p,p'-DDE, respectively. The precisions of the proposed method were all below 10% (n = 6). Four real water samples were utilized for validation of the proposed method, and satisfactory spiked recoveries in the range of 72.4-112.9% were achieved. These results demonstrated that the developed method was a simple, sensitive, and robust analytical method for the monitoring of pollutants in the environment. PMID:23356340

Zhou, Qingxiang; Wu, Wei; Xie, Guohong

2013-01-01

21

Group-selective enrichment and determination of pyrethroid insecticides in aquaculture seawater via molecularly imprinted solid phase extraction coupled with gas chromatography-electron capture detection.  

PubMed

Two types of molecularly imprinted polymers (MIPs) for the simultaneous determination of six pyrethroid insecticides have been developed using deltamethrin (D-MIPs) and cypermethrin (C-MIPs) as template molecules. A comparison of the performance of D-MIPs, C-MIPs, and the corresponding non-imprinted polymers (NIPs) were conducted. Stronger group-selective interactions between the C-MIPs and the six pyrethroid insecticides were achieved. The MISPE method based on the C-MIPs displayed higher extraction recoveries (86.4-96.0%) with RSD values ranging from 2.4 to 7.8% for the six pyrethroid insecticides in aquaculture seawater. After the C-MIP cartridge procedure, the limits of detection and quantification for fenvalerate, deltamethrin, cypermethrin, cyfluthrin, and bifenthrin were in the 16.6-37.0 and 55.3-109.1 ng L?¹ ranges, respectively, and 0.68 and 2.26 ?g L?¹ for phenothrin, respectively. The proposed MISPE method coupled with gas chromatography-electron capture detection was successfully used for the determination of the six pyrethroid insecticides in aquaculture seawater. PMID:22265776

Shi, Xizhi; Liu, Jinghua; Sun, Aili; Li, Dexiang; Chen, Jiong

2012-03-01

22

Relativistic ionization fronts in gas jets  

NASA Astrophysics Data System (ADS)

A high-power ultra-short laser pulse propagating through a gas jet, ionizes the gas by tunnelling ionization, creating a relativistic plasma-gas interface. The relativistic ionization front that is created can be used to frequency up-shift electromagnetic radiation either in co-propagation or in counter-propagation configurations. In the counter-propagation configuration, ionization fronts can act as relativistic mirrors for terahertz radiation, leading to relativistic double Doppler frequency up-shift to the visible range. In this work, we identified and explored, the parameters that optimize the key features of relativistic ionization fronts for terahertz radiation reflection. The relativistic ionization front generated by a high power laser (TOPS) propagating in a supersonic gas jet generated by a Laval nozzle has been fully characterized. We have also performed detailed two-dimensional relativistic particle-in-cell simulations with Osiris 2.0 to analyze the generation and propagation of the ionization fronts.

Lemos, Nuno; Dias, J. M.; Gallacher, J. G.; Issac, R. C.; Fonseca, R. A.; Lopes, N. C.; Silva, L. O.; Mendonça, J. T.; Jaroszynski, D. A.

2006-10-01

23

Ionizing Shock Structure in a Monatomic Gas.  

National Technical Information Service (NTIS)

The structure of an ionizing shock front in a monatomic gas is described. Both atom-atom and electron-atom collisional ionization are considered. The ionization rates for either of these processes is assumed to be controlled by the rate of excitation from...

D. L. Chubb

1967-01-01

24

Several versions of forward gas ionization calorimeter.  

National Technical Information Service (NTIS)

The properties of several versions of a gas ionization calorimeter are analyzed by means of the simulation with the GEANT code. The jet energy and coordinate resolutions are evaluated. Some calorimeter versions meet the ATLAS requirements. 13 refs., 15 fi...

V. V. Babintsev A. G. Kholodenko Y. Rodnov

1994-01-01

25

Miniaturized gas ionization sensors using carbon nanotubes  

NASA Astrophysics Data System (ADS)

Gas sensors operate by a variety of fundamentally different mechanisms. Ionization sensors work by fingerprinting the ionization characteristics of distinct gases, but they are limited by their huge, bulky architecture, high power consumption and risky high-voltage operation. Here we report the fabrication and successful testing of ionization microsensors featuring the electrical breakdown of a range of gases and gas mixtures at carbon nanotube tips. The sharp tips of nanotubes generate very high electric fields at relatively low voltages, lowering breakdown voltages several-fold in comparison to traditional electrodes, and thereby enabling compact, battery-powered and safe operation of such sensors. The sensors show good sensitivity and selectivity, and are unaffected by extraneous factors such as temperature, humidity, and gas flow. As such, the devices offer several practical advantages over previously reported nanotube sensor systems. The simple, low-cost, sensors described here could be deployed for a variety of applications, such as environmental monitoring, sensing in chemical processing plants, and gas detection for counter-terrorism.

Modi, Ashish; Koratkar, Nikhil; Lass, Eric; Wei, Bingqing; Ajayan, Pulickel M.

2003-07-01

26

Highly Ionized Gas in Galactic Halos  

NASA Astrophysics Data System (ADS)

We have calculated the time-dependent, nonequilibrium thermal and ionization history of gas cooling radiatively from 10(6) K in a one-dimensional, planar, steady-state flow model of the galactic fountain, including the effects of radiative transfer. We show that the inclusion of the effects of photoionizing radiation emitted by the cooling gas itself or "self-ionization" is sufficient to cause the flow to match the observed galactic halo column densities of C IV, Si IV, and N V and UV emission from C IV and O III, for cooling region sizes, i.e. D0 (>}_{ ~ ) 15pc. For an initial flow velocity v0 ~ 100km/s, comparable to the sound speed of a 10(6) K gas, the initial density is found to be n_{H,0} ~ 2times 10(-2) cm(-3) , in reasonable agreement with other observational estimates of ionized halo gas, and D0 ~ 40pc. We also compare predicted H alpha fluxes, total ionizing flux, free-free radio emission, and broadband X-ray fluxes with observed values. In addition we apply the same fountain flow model to Lyman limit quasar metal absorption lines at higher redshift, showing that such models are also capable of matching the observational data. A unique prediction of our models is the presence of appreciable and potentially detectable column densities of Ne VIII. We demonstrate the possibility that a transverse magnetic field in a radiative shock provides an alternative explanation for the occurrence of the isochoric cooling phase required in our steady state cooling flow model. Such a field can lead naturally to a constant downstream gas density once magnetic pressure increases enough to dominate the total pressure of the gas. We find that preshock parameters of n_{H,1}=0.005cm(-3) and B1=0.5 mu G with a shock velocity of vs=300 km/s matches the observed column density ratios. We have calculated theoretical UV absorption line profiles and show how these profiles may be used to distinguish between different models for the origin of highly ionized gas.

Benjamin, Robert A.

1994-12-01

27

Direct and simultaneous determination of trace-level carbon tetrachloride, peroxyacetyl nitrate, and peroxypropionyl nitrate using gas chromatography-electron capture detection.  

PubMed

Gas chromatography equipped with electron capture detector (GC-ECD) has been widely used for detecting atmospheric peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN). However, to the best of our knowledge, only a few capillary columns have been adopted for separation to achieve the direct and simultaneous analysis of the two atmospheric pollutants. This paper demonstrates a novel method for directly and simultaneously measuring atmospheric carbon tetrachloride (CCl(4)), PAN, and PPN using GC-ECD with a DB-1 separation column. The responses of the GC-ECD to PAN, PPN, and CCl(4) were individually calibrated by using gas mixtures prepared via volatilization of synthesized solutions of PAN and PPN or high-purity CCl(4) reagent in a Teflon Bag. The concentrations of PAN and PPN in the synthesized solutions were quantified by ion chromatography (IC). Further calibration of the GC-ECD for PAN was conducted by in situ photochemical formation of gaseous PAN which was quantified by a NO(x) analyzer. The two calibration methods agreed well with each other, and the overall uncertainties for measuring atmospheric PAN were estimated to be ± 13% and ± 15% based on the calibrations of IC and NO(x), respectively. The detection limits (three times the signal to noise ratio) for PAN, PPN, and CCl(4) were estimated to be 22, 36, and 5 pptv (parts per trillion by volume), respectively. The atmospheric concentrations of these compounds were measured for several days in August in Beijing, and the values obtained in this study were found to be in good agreement with the data reported in the literature for Beijing using other GC-ECD methods. PMID:23107119

Zhang, Gen; Mu, Yujing; Liu, Junfeng; Mellouki, Abdelwahid

2012-11-30

28

Diffuse Ionized Gas in Nearby Spiral Galaxies  

NASA Astrophysics Data System (ADS)

Sensitive H? images have been obtained for nine nearby spiral galaxies typically permitting detection of DIG down to a surface brightness of 1-2 × 10-17 ergs s-1 cm -2 arcsecond-2, or 5-10 pc cm -6 in emission measure. For four of these galaxies, SII images were obtained to permit analysis of the spectral properties of the DIG on galactic scales. Both the intensity and the diffuse nature of the emission were incorporated into an automated masking technique to distinguish the DIG and HII regions in all galaxies studied. For this reason, selection effects were minimized when comparing DIG properties between galaxies. Additionally, optical spectra of DIG regions with various surface brightness levels in M31 permitted detailed analysis of the ionization state for these regions. From these spectra, H?, H?, H?, H?, NII (?6583), SII (?6717 + ?6731), OIII (?5007), and OII (?3727) line intensities were measured and provided a test to typical ionization models. Diffuse ionized gas is present in all galaxies observed, occurring as smooth, diffuse emission in distant galaxies, but resolving into clumps and filaments in nearby galaxies. It is responsible for roughly 35%-50% of the total H? emission from each galaxy. The SII (?6717 + ?6731)/H? ratio observed in DIG is elevated compared to values in HII regions. Typical values for DIG are 0.40-0.60, while HII region values are 0.20- 0.25. The line ratio increases steadily from values around 0.2 to values of 0.7 as the surface brightness decreases from the brightest HII regions to the faintest DIG. This smooth decrease is a natural consequence of photo-ionization models with increasingly more dilute radiation fields ionizing the fainter regions. In M31, spectroscopic observations suggested that photoionization models in which dilute radiation fields are responsible for the ionization of DIG were the most successful at reproducing the observed optical line ratios.

Greenawalt, Bruce Emerson

29

Extraction of ultra traces of polychlorinated biphenyls in aqueous samples using suspended liquid-phase microextraction and gas chromatography-electron capture detection.  

PubMed

This study reports the feasibility of applying directly suspended liquid-phase microextraction (DSLPME)-gas chromatography detection for the pre-concentration and determination of low levels of eight polychlorinated biphenyls (PCBs) in aqueous samples. The technique requires minimal sample preparation, analysis time and solvent consumption and represents significant advantages over conventional analytical methods. The experimental parameters such as salt content, sample temperature, stirring rate, extraction time, micro-drop volume and breakthrough volume were investigated and found to have significant influences on DSLPME. Under the optimal experimental conditions, the enrichment factor ranged from 578 to 729, and the recovery was above 93 %. Calibration curves possessed good linearity (R(2) > 0.99) over a wide concentration range of 0.1-10.0 ?g L(-1) with limits of detection ranging from 0.01 to 0.07 ?g L(-1). The relative standard deviations for 1.0 ?g L(-1) of PCBs in water by using internal standard were in the range 2-14 % (n = 3). The proposed simple, accurate and sensitive analytical method was applied successfully to the determination of trace amounts of PCBs in water samples. PMID:22892997

Hassan, Jalal; Shamsipur, Mojtaba

2013-05-01

30

Ultrasonic enhancement of leaching and in situ derivatization of haloacetic acids in vegetable foods prior to gas chromatography-electron capture detection.  

PubMed

A continuous ultrasound-assisted approach to enhance the extraction of nine haloacetic acids (HAAs) from vegetables with in situ derivatization to methyl esters for their gas chromatography (GC) analysis is presented. The optimization of simultaneous extraction (using acidic methanol as extractant) and derivatization enabled the completion of both steps in 15 min. Ultrasound assistance has proved to enhance both linked steps, which results in a considerable shortening of the overall analysis time (i.e. 552.1 and 552.2 EPA methods for analysis of these compounds in drinking water require 1 and 2 h, respectively, only for derivatization). After sample preparation, the esterified HAAs were isolated by liquid-liquid extraction with n-hexane and analysed by GC-electron capture detection. The proposed method is an interesting alternative to present methods for the determination of HAAs in vegetable foods. This is an area unjustifiably forgotten by reference laboratory organisms as proved by the absence of official methods for analysis of the target compounds in these samples. The proposed method can be applied to the analysis of HAAs in any solid sample after optimization of the main variables involved in the extraction-derivatization step. PMID:18586256

Alvarez Sánchez, B; Priego Capote, F; Luque de Castro, M D

2008-08-01

31

Quantification of multi-residue levels in peach juices, pulps and peels using dispersive liquid-liquid microextraction based on floating organic droplet coupled with gas chromatography-electron capture detection.  

PubMed

In this paper, polychlorinated biphenyl (PCB), organochlorine pesticide (OCP) and pyrethroid pesticides in peach was investigated by comparing their residual level in peach juice, pulps and peels using dispersive liquid-liquid microextraction based on solidification of floating organic droplet (DLLME-SFO) combined with gas chromatography-electron capture detection (GC-ECD). Extraction conditions such as the type of extractant, volume of extractant and dispersant, salt effect and extraction time were optimized. For juice samples, the linearity of the method was obtained in the range of 10-2000 ng L(-1),with determination coefficients>0.99. The limits of detection (LOD) of the method were ranged between 2.8 and 18.5 ng L(-1). For pulp and peel samples, the developed method is linear over the range assayed, 1-20 ?g kg(-1),with coefficients also >0.99. The relative recoveries of compounds analyzed from juice, pulp and peel samples were in the range of 73-106% with a relative standard deviation between 2.6 and 11.8%. The proposed method was applied to the simultaneous analysis of residues in real peach juice, pulp and peel samples. As a result, there were no target analytes found in peach juices and pulps while 3.3 ?g kg(-1) cyhalothrin and 3.5 ?g kg(-1) fenvalerate were found in peels. The experiment results revealed that the pyrethroid residues just deposited on the peels of the fruits, but did not move into pulps and juices. PMID:21703950

Matsadiq, Guzalnur; Hu, Hai-Li; Ren, Hai-Bo; Zhou, Yi-Wen; Liu, Lu; Cheng, Jing

2011-07-15

32

Molecular and Ionized Gas in Galaxies  

NASA Astrophysics Data System (ADS)

The thesis consists of three parts. The first is a study of distribution of molecular and ionized gas in our Galaxy. We collect data of Galactic HII regions, giant molecular clouds (GMCs) and 6.7 GHz methanol masers from literature, which are used as tracers to outline the spiral structure (Hou et al. 2009a; Hou & Han 2013). In the second part, we work on the galaxies with a lot of gas, which appear as ultraluminous infrared galaxies (ULIRGs). We find 308 ULIRGs from SDSS-DR6, and study the relationship between black hole masses (MBH) and the velocity dispersion ? of the Type I ULIRGs (Hou et al. 2009b), and then analyse the gas content and stellar populations of diverse ULIRGs (Hou et al. 2011). In the third part, we review the research on radio spectral lines at low frequencies (<9 GHz), and present our observation results of CH lines for a few nearby galaxies.

Hou, L. G.

2013-05-01

33

Confirmation of identity by gas chromatography/tandem mass spectrometry of sulfathiazole, sulfamethazine, sulfachloropyridazine, and sulfadimethoxine from bovine or swine liver extracts after quantitation by gas chromatography/electron-capture detection.  

PubMed

Four sulfonamide veterinary drug residues were quantitated by electron-capture detection (ECD) after separation by gas chromatography (GC). The identities of sulfathiazole (ST), sulfamethazine (SM), sulfachloropyridazine (SCP), and sulfadimethoxine (SDM) were confirmed in bovine or swine liver residues by tandem mass spectrometry (MS/MS). Bovine or swine liver tissues were extracted by using either the Tishler or the Manuel-Steller cleanup. The methylated residues containing ST, SM, SCP, and SDM were separated by GC prior to MS/MS daughter ion analysis. Control tissue, control tissue fortified at 0.1 ppm, and incurred tissue residues at approximately 0.1 ppm were analyzed for these 4 sulfonamides. A Finnigan Model TSQ-46 operating in the chemical ionization mode was used to perform the MS/MS daughter ion experiments. The identities of all 4 sulfonamides were confirmed in a single GC/MS/MS analysis. PMID:2211474

Matusik, J E; Sternal, R S; Barnes, C J; Sphon, J A

1990-01-01

34

The Ionized Gas Around Starforming Galaxies  

NASA Astrophysics Data System (ADS)

We consider the evolution of metal- enriched gas exposed to a superposition of time- dependent radiation field of a nearby starburt galaxy and nearly invariant (on timescales 100 Myr) extragalactic ionization background. We study the evolution of ionic species (particularly those commonly observed in galactic circumference) depending on the galactic mass and star formation rate, and derive conditions for the highly ionized oxygen, OVI, to appear in extended galactic haloes in absorption or emission spectra. We have found that the maximum OVI fraction can reach ˜ 0.4 - 0.6 under the action of both ionizing radiation field, which is typical in haloes of starforming galaxies, and the extragalactic background, the fraction remains high in a wide temperature range. We have shown that the OVI fraction is high enough that even for ˜ 0.1Zsun metallicity we can explain large OVI column densities (log[N(OVI), cm-2] ˜ 14.5 - 15.3) observed in the haloes of starforming galaxies by Tumlinson et al. (2011). Thus, the requirements to the sources of oxygen supply into the extended haloes become reasonably conservative.

Vasiliev, E. O.; Ryabova, M. V.; Shchekinov, Yu. A.

35

The Diffuse Ionized Gas in the large telescopes era  

NASA Astrophysics Data System (ADS)

In this workshop we summarize the ``state of the art'' of the Diffuse Ionized Gas. We present all the possible situations which can produce ionization outside an H II region, as well as some of the observations that can be performed with the GTC instrumentation and how relevant they can be in the undestanding of the ionization mechanisms of the DIG.

Hidalgo-Gámez, A. M.

2005-12-01

36

The Ionization of the Diffuse Ionized Gas Halo of NGC 891  

NASA Astrophysics Data System (ADS)

The ionization of Diffuse Ionized Gas (DIG) layers in galaxies remains a critical but unsolved problem for our understanding of galaxy energetics. Work using optical emission lines has indicated that photo-ionization by massive stars in the disk dominates the energy input, but no pure photo-ionization model can reproduce all the observed line ratios, leading to the possibility that non-ionizing heat sources and/or secondary ionization sources may be important for the energetics. However, the optical diagnostics present three main problems: sensitivity to extinction, gas temperature, and (for some crucial lines) weak emission. The MIR diagnostic ratio [Ne III]/[Ne II] provides a measurable, extinction-free diagnostic of the hardness of the ionizing spectrum with little temperature sensitivity. Thus this ratio will provide an excellent test of whether photo-ionization alone can maintain the DIG, or whether a second source of ionization is required. We therefore propose to use the SH module on the Spitzer IRS to observe two fields in the lower halo (z=1 kpc) and one field in the disk of the well studied edge-on NGC 891 to determine how this ratio changes with distance from the thin disk of ionizing sources. We will compare our results with predictions from our own 2-d and 3-d simulations of the ionization structure, where such inputs as the ionizing spectrum, spectral hardening by propagation through intervening gas, and additional heat sources can be modeled.

Rand, Richard; Benjamin, Robert; Wood, Kenneth

2005-06-01

37

Kinematics of Diffuse Ionized Gas Halos  

NASA Astrophysics Data System (ADS)

Existing long-slit spectral data for edge-on spiral galaxies suggesting that their Diffuse Ionized Gas (DIG) halos rotate slower than their underlying disks are summarized. An attempt to characterize lagging halos using a model of purely ballistic disk-halo flow is discussed, with the result that the model fails badly for the lagging halo of NGC 891, but is somewhat more successful for NGC 5775. New two-dimensional kinematic data on the DIG halo of NGC 4302 are presented, along with a preliminary analysis of its rotation. Two-dimensional data on NGC 5775 and a preliminary analysis of its halo rotation is discussed by Heald et al. (this volume). The halo of NGC 4302 shows clear signs of lagging on its approaching side, but also strong indications of peculiar kinematics. The kinematics of the receding side are more complex.

Rand, R. J.

2005-06-01

38

Simultaneous screening for and determination of 128 date-rape drugs in urine by gas chromatography-electron ionization-mass spectrometry.  

PubMed

Date-rape drugs (DRDs) are used for the purpose of "drugging" unsuspected victims and raping or robbing them while under the influence of the drug. The wide variety of substances used for criminal purposes, their low concentrations in body fluids and, often, a long time delay between the event and clinical examination make comprehensive screening analysis of biological materials collected from crime victims for the presence of these drugs very difficult. Detection of a drug used to facilitate sexual assault in biological fluids can be very important evidence of a committed crime. The purpose of this study was to develop a simple GC-EI-MS screening procedure for date-rape drugs in urine. Target analytes were isolated by solid-phase extraction. 2-mL urine samples were extracted and then derivatized by using BSTFA+1%TMCS reagent. Detection of all compounds was based on full-scan mass spectra and for each compound one ion was chosen for further quantification. The method allowed the simultaneous screening, detection and quantification of 128 compounds from different groups (number of compounds): opioids (20), amphetamines (11), GHB and related products (3), hallucinogens (9), benzodiazepines (18), antihistamines (9), antidepressants (14), selective serotonin-reuptake inhibitors (4), antipsychotics (7), barbiturates (7), other sedatives (5), muscle relaxants (2) and other drugs (19). The procedure can easily be expanded to encompass more substances. The developed method appeared to be suitable for screening for the target DRDs. The procedure was successfully applied to the analysis of authentic urine samples collected from victims of rapes and other crimes in routine casework. PMID:20207513

Adamowicz, Piotr; Ka?a, Maria

2010-05-20

39

Gas chromatography-electron ionization mass spectrometry and liquid chromatography-electrospray tandem mass spectrometry for determination of impurities in the anti-cancer drug isophosphoramide mustard  

NASA Astrophysics Data System (ADS)

Isophosphoramide mustard (IPM) is known to have substantial anti-cancer activities in various animal models. Liquid chromatography-electrospray mass spectrometry (LC-ES-MS) and LC-ES-MS/MS methodologies have been developed and applied to the analysis of synthesized preparations of IPM. Our studies reveal that the principal impurity in IPM is N-(2-chloroethyl)-N'-ethylphosphorodiamidic acid (MC-IPM) formed by dehydrochlorination of IPM with subsequent hydrogenation during synthesis. This impurity is present at levels in the range of 2-5% depending upon synthesis conditions. In addition, a second IPM derivative has been characterized by LC-ES-MS/MS and has been shown to be the product of a reaction of IPM with the dilute perchloric acid mobile phase used for liquid chromatography separations. The LC-ES-MS/MS method has been successfully employed to detect IPM spiked into a blood plasma sample. This work establishes that LC-ES-MS/MS is a viable tool for the detailed characterization of IPM and related products.

Cole, Richard B.; Chou, Chau-Wen; Boué, Stephen M.; Leblanc, Blaise W.; Rodgers, Andrew H.; Struck, Robert F.; Morgan, Lee Roy

2004-02-01

40

Energy Exchange between Weakly Ionized Gas and a Metal Surface  

NASA Astrophysics Data System (ADS)

An attempt to describe heat exchange of low ionized gas with a metal surface has been made with the use of DSMC approach and kinetic Monte-Carlo method. Modeling is adhered to concrete experimental conditions at which thin tungsten wire is placed in plasma and dependence of a heat flow on wire surface temperature, gas pressure, gas nature and a degree of ionization is investigated. As a result of simulation temperature profiles near the wire surface for nitrogen and argon as well as dependence of relative heat flow in a gas/surface system on temperature and degree of ionization with consideration of energy accommodation have been obtained. In the case of nitrogen the chemical charge-transfer reaction is taken into account.

Polikarpov, A. Ph.; Polikarpov, Ph. J.; Borisov, S. F.

2008-12-01

41

Transport Phenomena in a Completely Ionized Gas  

Microsoft Academic Search

The coefficients of electrical and thermal conductivity have been computed for completely ionized gases with a wide variety of mean ionic charges. The effect of mutual electron encounters is considered as a problem of diffusion in velocity space, taking into account a term which previously had been neglected. The appropriate integro-differential equations are then solved numerically. The resultant conductivities are

Lyman Spitzer; Richard Härm

1953-01-01

42

Relative Ionizations in the Nearest Interstellar Gas  

NASA Astrophysics Data System (ADS)

We compare CLOUDY predictions for the equilibrium ionization in the interstellar cloud surrounding the solar system with pick-up ion data. The incident radiation field includes contributions from hot stars, the emission from the conductive cloud boundary and the diffuse FUV back-ground. To within the observational uncertainties, CLOUDY predictions for the ratios n(He?)/n(O?), n(N?)/n(O?), n(Ne?)/n(O?), and n(He?)/n(Ne?) are consistent with pick-up ion data, provided that O? and N? are filtered by ˜ 50% in the heliopause region and the outer heliosphere as predicted by others. Thus, the steady-state ionization model and assumed radiation field appear approximately valid. However, the youth and low intervening column density towards the Vela pulsar leave open the possibility that the parent supernova explosion ˜ 10,500 years ago, and 200 pc distant, may also have affected LISM ionization, although the mechanism is uncertain. Support for this last possibility is provided by the apparent signature of the Vela explosion in the terrestrial geological record.

Frisch, P. C.; Slavin, J. D.

1996-10-01

43

IONIZED GAS IN THE GALACTIC CENTER: NEW OBSERVATIONS AND INTERPRETATION  

SciTech Connect

We present new observations of the [Ne II] emission from the ionized gas in Sgr A West with improved resolution and sensitivity. About half of the emission comes from gas with kinematics indicating it is orbiting in a plane tipped about 25 Degree-Sign from the Galactic plane. This plane is consistent with that derived previously for the circumnuclear molecular disk and the northern arm and western arc ionized features. However, unlike most previous studies, we conclude that the ionized gas is not moving along the ionized features, but on more nearly circular paths. The observed speeds are close to, but probably somewhat less than expected for orbital motions in the potential of the central black hole and stars and have a small inward component. The spatial distribution of the emission is well fitted by a spiral pattern. We discuss possible physical explanations for the spatial distribution and kinematics of the ionized gas, and conclude that both may be best explained by a one-armed spiral density wave, which also accounts for both the observed low velocities and the inward velocity component. We suggest that a density wave may result from the precession of elliptical orbits in the potential of the black hole and stellar mass distribution.

Irons, Wesley T.; Lacy, John H. [Department of Astronomy, University of Texas, Austin, TX 78712 (United States); Richter, Matthew J., E-mail: lacy@astro.as.utexas.edu [Department of Physics, University of California, Davis, CA 95616 (United States)

2012-08-20

44

The kinematics of the diffuse ionized gas in NGC 4666  

NASA Astrophysics Data System (ADS)

Context. The global properties of the interstellar medium with processes such as infall and outflow of gas and a large scale circulation of matter and its consequences for star formation and chemical enrichment are important for the understanding of galaxy evolution. Aims: In this paper we studied the kinematics and morphology of the diffuse ionized gas (DIG) in the disk and in the halo of the star forming spiral galaxy NGC 4666 to derive information about its kinematical properties. Especially, we searched for infalling and outflowing ionized gas. Methods: We determined surface brightness, radial velocity, and velocity dispersion of the warm ionized gas via high spectral resolution (R ? 9000) Fabry-Pérot interferometry. This allows the determination of the global velocity field and the detection of local deviations from this velocity field. We calculated models of the DIG distribution and its kinematics for comparison with the measured data. In this way we determined fundamental parameters such as the inclination and the scale height of NGC 4666, and established the need for an additional gas component to fit our observed data. Results: We found individual areas, especially along the minor axis, with gas components reaching into the halo which we interpret as an outflowing component of the DIG. As the main result of our study, we were able to determine that the vertical structure of the DIG distribution in NGC 4666 is best modeled with two components of ionized gas, a thick and a thin disk with 0.8 kpc and 0.2 kpc scale height, respectively. Therefore, the enhanced star formation in NGC 4666 drives an outflow and also maintains a thick ionized gas layer reminiscent of the Reynold's layer in the Milky Way.

Voigtländer, P.; Kamphuis, P.; Marcelin, M.; Bomans, D. J.; Dettmar, R.-J.

2013-06-01

45

Similarity of ionized gas nebulae around unobscured and obscured quasars  

NASA Astrophysics Data System (ADS)

Quasar feedback is suspected to play a key role in the evolution of massive galaxies, by removing or reheating gas in quasar host galaxies and thus limiting the amount of star formation. In this paper, we continue our investigation of quasar-driven winds on galaxy-wide scales. We conduct Gemini Integral Field Unit spectroscopy of a sample of luminous unobscured (type 1) quasars, to determine the morphology and kinematics of ionized gas around these objects, predominantly via observations of the [O III] ?5007 Å emission line. We find that ionized gas nebulae extend out to ˜13 kpc from the quasar, that they are smooth and round, and that their kinematics are inconsistent with gas in dynamical equilibrium with the host galaxy. The observed morphological and kinematic properties are strikingly similar to those of ionized gas around obscured (type 2) quasars with matched [O III] luminosity, with marginal evidence that nebulae around unobscured quasars are slightly more compact. Therefore, in samples of obscured and unobscured quasars carefully matched in [O III] luminosity, we find support for the standard geometry-based unification model of active galactic nuclei, in that the intrinsic properties of the quasars, of their hosts and of their ionized gas appear to be very similar. Given the apparent ubiquity of extended ionized regions, we are forced to conclude that either the quasar is at least partially illuminating pre-existing gas or that both samples of quasars are seen during advanced stages of quasar feedback. In the latter case, we may be biased by our [O III]-based selection against quasars in the early `blow-out' phase, for example due to dust obscuration.

Liu, Guilin; Zakamska, Nadia L.; Greene, Jenny E.

2014-08-01

46

Diffuse ionized gas and chemical abundances in IC 1727  

NASA Astrophysics Data System (ADS)

Long-slit spectroscopy results of the dwarf spiral galaxy IC 1727, which is interacting with NGC 672, are presented. The extinction, excitation, density and shocks throughout the galaxy are studied, as well as the oxygen abundances of a total of 22 H II regions. The interstellar medium of this galaxy is very perturbed, with high values of the [S II]/H? ratio and high excitation values throughout the galaxy (inside the H II regions and in the diffuse ionized gas). Such values might be an indication of strong perturbations resulting from the interaction between IC 1727 and NGC 672. Shocks are the second source of ionization of the diffuse ionized gas, after leaking photons from H II regions. The chemical abundance of this galaxy is well below solar and closer to the values of the Large Magellanic Cloud. The abundances differ between the various H II regions of the galaxy, as observed in other spiral galaxies.

Ramirez-Ballinas, I.; Hidalgo-Gámez, A. M.

2014-08-01

47

The ionization sources of the diffuse ionized gas in nearby disk galaxies  

NASA Astrophysics Data System (ADS)

Diffuse ionized gas (DIG) has been shown to be an important component of the interstellar medium (ISM), with its large filling factor (>= 20%) and a mass that makes it the most massive component of the Galactic ionized ISM. Given that it has been found to be ubiquitous in both the Galaxy and external disk galaxies, the energy source to create and maintain the DIG must necessarily be large. Massive OB stars are the only known sources with enough energy to power the DIG, and DIG is also linked morphologically to OB stars as it is brightest near bright star forming regions. However, the details of the location and spectral types of the ionizing stars, as well as the relevance of other ionizing mechanisms, are still not clear. I present the results of three different studies aimed at exploring the ionization sources of the DIG. Optical spectroscopy of DIG in M33 and NGC 891 using the Gemini-North telescope has been obtained to compare diagnostic emission line ratios with photoionization models. The first detection of (O I] l6300 was made in the DIG of M33. In M33, models in which ionizing photons leaking from H II regions are responsible for the ionization of the DIG best fit our observed line ratios. In NGC 891, we found evidence that shock ionization may need to be included along with photoionization in order to explain our observed emission line ratios. The diffuse Ha fraction in eight nearby galaxies was studied as a function of radius and star formation rate per unit area. We found no correlation with radius, but we did find that regions with higher star formation rates have lower diffuse fractions. Neither of these results had any dependence on galaxy type. These results have implications regarding the circumstances under which H II regions may be leaking ionizing photons and thus ionizing DIG. We also compared observed and predicted ionizing photon emission rates for 39 H II regions in the Large Magellanic Cloud. Our results indicate that five of the H II regions are reliably density bounded, with the remaining regions consistent with being either radiation or density bounded. All three of these studies suggest that OB stars, both in H II regions and in the field, play a major role in creating and maintaining the DIG, and that other mechanisms, such as shocks, may also contribute to the ionization of the DIG.

Voges, Erica Susan

48

Highly ionized gas in the Galactic halo  

NASA Technical Reports Server (NTRS)

We reexamine the values of electron density n(sub e) and gas pressure P/k in the interstellar medium (ISM) of the Galactic halo, as inferred from C IV emission and absorption lines and using current C IV atomic data. In a homogeneous model with 4.7 less than or equal to log T less than or equal to 5.3, the data are consistent with 0.01 less than or equal to n(sub e) less than or equal to 0.02/cu cm and 2200 less than or equal to P/k less than or equal to 3700/cu cm K, a factor of 2-3 higher than advocated by Martin & Bowyer (1990) and comparable to the thermal pressure in the disk. If some of the C IV absorption arises from nonemitting, photoionized gas, then the inferred density and pressure will increase accordingly. The volume filling factor for homogeneous models ranges from 0.5% to 5%. Because of the constraints arising from filling factor and radiated power, most of the C IV must arise from gas near the peak of the cooling curve, at log t less than or equal to 5.6. We relate both emission-line and absorption-line observations to recent models in which turbulent mixing layers and isobarically cooling supernova remnants (SNRs) provide significant amounts of halo gas at approximately 10(exp 5.3) K and process 20-40 solar mass/yr with a power of approximately 10(exp 41) ergs/sec. Since the observed C IV and N V absorption scale heights have been reported to differ, at 4.9 kpc and 1.6 kpc, respectively, we examine inhomogeneous models with different exponential scale heights of T, P, and SN energy input. The ISM may change its character with distance above the Galactic plane, as superbubbles and mixing layers dominate over isolated SNRs as the source of the C IV. For appropiate scale heights, the midplane pressure is twice the homogeneous values quoted above. The O IV lambda 1034 diffuse emission line, which can be used as a temperature diagnostic of the hot gas, is predicted to be comparable in strength to that of C IV lambda 1549 (approximately 6000 photons/cu cm/s/sr. The ions C IV, N V, and O VI are predicted to show a decreasing trend in vertical extent, with the O IV scale height perhaps as low as approximately 1 kpc.

Shull, J. Michael; Slavin, Jonathan D.

1994-01-01

49

Viscosity Coefficient Curve Fits for Ionized Gas Species Grant Palmer  

NASA Technical Reports Server (NTRS)

Viscosity coefficient curve fits for neutral gas species are available from many sources. Many do a good job of reproducing experimental and computational chemistry data. The curve fits are usually expressed as a function of temperature only. This is consistent with the governing equations used to derive an expression for the neutral species viscosity coefficient. Ionized species pose a more complicated problem. They are subject to electrostatic as well as intermolecular forces. The electrostatic forces are affected by a shielding phenomenon where electrons shield the electrostatic forces of positively charged ions beyond a certain distance. The viscosity coefficient for an ionized gas species is a function of both temperature and local electron number density. Currently available curve fits for ionized gas species, such as those presented by Gupta/Yos, are a function of temperature only. What they did was to assume an electron number density. The problem is that the electron number density they assumed was unrealistically high. The purpose of this paper is two-fold. First, the proper expression for determining the viscosity coefficient of an ionized species as a function of both temperature and electron number density will be presented. Then curve fit coefficients will be developed using the more realistic assumption of an equilibrium electron number density. The results will be compared against previous curve fits and against highly accurate computational chemistry data.

Palmer, Grant; Arnold, James O. (Technical Monitor)

2001-01-01

50

Ionization chamber for measurements of high-level tritium gas  

SciTech Connect

The construction and calibration of a simple ionization-chamber apparatus for measurement of high level tritium gas is described. The apparatus uses an easily constructed but rugged chamber containing the unknown gas and an inexpensive digital multimeter for measuring the ion current. The equipment after calibration is suitable for measuring 0.01 to 100% tritium gas in hydrogen-helium mixes with an accuracy of a few percent. At both the high and low limits of measurements deviations from the predicted theoretical current are observed. These are briefly discussed.

Carstens, D.H.W.; David, W.R.

1980-01-01

51

The effect of recombination radiation on the temperature and ionization state of partially ionized gas  

NASA Astrophysics Data System (ADS)

A substantial fraction of all ionizing photons originate from radiative recombinations. However, in radiative transfer calculations this recombination radiation is often assumed to be absorbed `on-the-spot' because for most methods the computational cost associated with the inclusion of gas elements as sources is prohibitive. We present a new, CPU and memory efficient implementation for the transport of ionizing recombination radiation in the TRAPHIC radiative transfer scheme. TRAPHIC solves the radiative transfer equation by tracing photon packets at the speed of light and in a photon-conserving manner in spatially adaptive smoothed particle hydrodynamics simulations. Our new implementation uses existing features of the TRAPHIC scheme to add recombination radiation at no additional cost in the limit in which the fraction of the simulation box filled with radiation approaches 1. We test the implementation by simulating an H II region in photoionization equilibrium and comparing to reference solutions presented in the literature, finding excellent agreement. We apply our implementation to discuss the evolution of the H II region to equilibrium. We show that the widely used case A and B approximations yield accurate ionization profiles only near the source and near the ionization front, respectively. We also discuss the impact of recombination radiation on the geometry of shadows behind optically thick absorbers. We demonstrate that the shadow region may be completely ionized by the diffuse recombination radiation field and discuss the important role of heating by recombination radiation in the shadow region.

Rai?evi?, Milan; Pawlik, Andreas H.; Schaye, Joop; Rahmati, Alireza

2014-01-01

52

Warm Gas and Ionizing Photons in the Local Group  

NASA Astrophysics Data System (ADS)

Several lines of argument suggest that a large fraction of the baryons in the universe may be in the form of warm (T~105-107 K) gas. In particular, loose groups of galaxies may contain substantial reservoirs of such gas. Observations of the cosmic microwave background by COBE place only weak constraints on such an intragroup medium within the Local Group. The idea of a Local Group corona dates back at least 40 years (Kahn & Woltjer). Here we show that gas at T~(2-3)×106 K (the approximate virial temperature of the Local Group)--extremely difficult to observe directly--can in principle radiate a large enough flux of ionizing photons to produce detectable H? emission from embedded neutral clouds. However, additional constraints on the corona--the most stringent being pulsar dispersion measures toward the Magellanic Clouds, and the timing mass--rule out an intragroup medium whose ionizing flux dominates over the cosmic background or the major Local Group galaxies. A cosmologically significant coronal gas mass could remain invisible to H? observations. More massive galaxy groups could contain extensive coronae which are important for the baryon mass and produce a strong, local ionizing flux.

Maloney, Philip R.; Bland-Hawthorn, J.

1999-09-01

53

Kinematics of the Diffuse Ionized Gas in NGC 891  

NASA Astrophysics Data System (ADS)

In some external edge-on spirals, the azimuthal velocity of halo gas is observed to decrease with height above the midplane (z). This effect has been observed in both the neutral and ionized components of halos. Models of the disk-halo interaction which consider the effects of moving gas out of the disk and into the halo predict such a velocity gradient as a consequence of the conservation of angular momentum. In order to observationally test the predictions of such models, high spectral resolution emission line data with two-dimensional coverage are required to first estimate the form of the radial density profile in the halo, and subsequently extract the azimuthal velocities as a function of z. We present high spectral resolution WIYN SparsePak observations of the diffuse ionized gas (DIG) in NGC 891. Preliminary results of an analysis of the azimuthal velocity field will also be summarized. This work is part of an ongoing project to investigate the vertical azimuthal velocity gradient of the ionized halo gas in a select sample of edge-on spirals with a range of DIG halo morphology. This material is based on work partially supported by the National Science Foundation under Grant No. AST 99-86113.

Heald, G. H.; Rand, R. J.; Benjamin, R. A.; Bershady, M. A.

2005-05-01

54

Monte Carlo photoionization simulations of diffuse ionized gas  

NASA Astrophysics Data System (ADS)

We demonstrate that the observed increase of some nebular line ratios with height above the midplane in the diffuse ionized gas (DIG) in the Milky Way and other galaxies is a natural consequence of the progressive hardening of the radiation field far from the midplane ionizing sources. To obtain increasing temperatures and line ratios away from the midplane, our photoionization simulations of a multicomponent interstellar medium do not require as much additional heating (over and above that from photoionization) as previous studies that employed one-dimensional, spherically averaged models. Radiation leaking into the DIG from density bounded HII regions is generally harder in the H-ionizing continuum and has its He-ionizing photons suppressed compared to the ionizing source of the HII region. In line with other recent investigations, we find that such leaky HII region models can provide elevated temperatures and line ratios, and a lower He+ fraction in the DIG. For a composite model representing the relative spectral types of O stars in the solar neighbourhood, we find that the natural hardening of the radiation field reaching large heights in our simulations can explain most of the observed line ratios. However, additional heating is required to reproduce the largest line ratios in the DIG.

Wood, Kenneth; Mathis, John S.

2004-10-01

55

Field emission model of carbon nanotubes to simulate gas breakdown in ionization gas sensor  

NASA Astrophysics Data System (ADS)

A new field emission model of carbon nanotubes (CNTs) to simulate gas detection mechanism in CNT based ionization gas sensor has been developed. The new model consists of three modules which are combined together and embedded in the standard particle-in-cell/Monte Carlo collision codes. The functionality of the enhanced model is checked by varying the gas pressure and gap spacing in the simulations. From the results, around one order of magnitude decrease in the breakdown voltages and two orders of magnitude faster response time is observed. The lowest breakdown voltages are observed when intertube spacing is equal to height of the nanotube. The field enhancement factor ? is calculated from our model and compared with the ? of the well established model. The closeness among the values of ? validates the performance of our field emission model. Furthermore, the ? of our model is compared with the ? of the existing ionization gas sensors. It was found that the ? of our sensor is around 3 times better than the ? of the gold nanowire based ionization gas sensor and 28 times better than the ? of the other CNT based ionization gas sensor. These results suggest that by properly controlling the growth of CNT structures, an optimized CNT based ionization gas sensor can be realized.

Mahmood, Salman; Arif Burhanudin, Zainal; Salman, Aysha

2013-01-01

56

Resonance ionization spectroscopy: counting noble-gas atoms  

SciTech Connect

New work on the counting of noble gas atoms, using lasers for the selective ionization and detectors for counting individual particles (electrons or positive ions) is reported. When positive ions are counted, various kinds of mass analyzers (magnetic, quadrupole, or time-of-flight) can be incorporated to provide A selectivity. It is shown that a variety of interesting and important applications can be made with atom-counting techniques which are both atomic number (Z) and mass number (A) selective.

Hurst, G.S.; Payne, M.G.; Chen, C.H.; Willis, R.D.; Lehmann, B.E.; Kramer, S.D.

1981-06-01

57

Electron-impact double ionization of rare-gas ions  

NASA Astrophysics Data System (ADS)

Cross sections for the removal of two electrons from rare-gas ions by single collisions with incident electrons have been both measured using crossed beams of ions and electrons, and calculated using Hartree-Fock distorted-wave theory. For initial ions Ar4+, Kr4+, and Xe4+ the measured peak cross sections are 1.4 × 10-18, 6.5 × 10-18 cm2, respectively. These measurements confirm and extend the measurements of Müller and Frodl and of Achenbach et al. Calculations were performed for the charge-state-4 + ions and for Xe+, Xe2+, and Xe3+. Comparison of experiment and theory indicates that the double ionization of rare-gas ions is dominated by the indirect mechanism of inner-shell single ionization followed by autoionization. The distorted-wave calculations for the 4d ionization cross section of Xeq+ (q=1 to 4) ions are strongly influenced by term dependence in the ejected-electron continuum, and by ground-state correlations.

Pindzola, M. S.; Griffin, D. C.; Bottcher, C.; Crandall, D. H.; Phaneuf, R. A.; Gregory, D. C.

1984-04-01

58

Development of a portable gas-filled ionization chamber  

NASA Astrophysics Data System (ADS)

A new portable gas-filled ionization chamber has been designed and constructed at the Physics Department of Sung Kyun Kwan University. To overcome the maximum count rate of ˜105 particles per second of a conventional ionization chamber, which utilizes a Frisch grid, and to enhance the portability of a detector, we adopted the design of multiple electrodes and modified it from the original designs by Kimura et al. and Chae et al. The new design utilizes a stack of multiple electrodes installed perpendicular to the optical beam axis. This configuration provides a fast response time for the detector, which is essential for high-rate counting. The device has been tested with a 241Am ( t 1/2 = 432.2 years) radioactive ? source, which mainly emits 5.486-MeV (branching ratio of 85%) and 5.443-MeV (branching ratio of 13%) ? particles. An energy resolution of 6.3% was achieved.

Chae, K. Y.; Cha, S. M.; Gwak, M. S.

2014-02-01

59

Approximate Thermodynamics State Relations in Partially Ionized Gas Mixtures  

SciTech Connect

In practical applications, the thermodynamic state relations of partially ionized gas mixtures are usually approximated in terms of the state relations of the pure partially ionized constituent gases or materials in isolation. Such approximations are ordinarily based on an artificial partitioning or separation of the mixture into its constituent materials, with material k regarded as being confined by itself within a compartment or subvolume with volume fraction {alpha}k and possessing a fraction {beta}k of the total internal energy of the mixture. In a mixture of N materials, the quantities {alpha}k and {beta}k constitute an additional 2N--2 independent variables. The most common procedure for determining these variables, and hence the state relations for the mixture, is to require that the subvolumes all have the same temperature and pressure. This intuitively reasonable procedure is easily shown to reproduce the correct thermal and caloric state equations for a mixture of neutral (non-ionized) ideal gases. Here we wish to point out that (a) this procedure leads to incorrect state equations for a mixture of partially ionized ideal gases, whereas (b) the alternative procedure of requiring that the subvolumes all have the same temperature and free electron density reproduces the correct thermal and caloric state equations for such a mixture. These results readily generalize to the case of partially degenerate and/or relativistic electrons, to a common approximation used to represent pressure ionization effects, and to two-temperature plasmas. This suggests that equating the subvolume electron number densities or chemical potentials instead of pressures is likely to provide a more accurate approximation even in nonideal plasma mixtures.

Ramshaw, J D

2003-12-30

60

Constraining stellar feedback: Ionized gas structures in local starburst galaxies  

NASA Astrophysics Data System (ADS)

Stellar feedback, i.e., the return of mechanical energy from supernova explosions, and massive star and AGN winds to the interstellar medium, is one of the fundamental processes that shape galaxy evolution. Yet, some of its fundamental parameters, such as the efficiency of feedback, have not been solidly constrained from an observational point of view. In this thesis, we aim at addressing this issue. First, we investigate the kinematics of Damped Ly-alpha Absorbers (DLAs) at z = 3 using high-resolution cosmological hydrodynamical simulations. Our simulations include a heuristic model for galactic outflows driven by stellar feedback to test how these components affect the kinematics of neutral gas in high redshift systems. We determine that, without outflows, our simulations fail to yield a sufficient number of DLAs with broad velocity dispersion ('wide DLAs'), as in previous studies. With outflows, our predicted DLA kinematics are in much better agreement with observations. In the second part of the thesis, I investigate stellar feedback within 8 nearby star-forming galaxies, selected to fill the 2-dimensional parameter space of host galaxy stellar mass and star formation rate density. Here, I employ forbidden-line diagnostic diagrams, [O III](5007A)/Hbeta versus [S II](6716A+6731A)/Halpha (or [N II](6584A)/Halpha) to separate shock--ionized from photo--ionized gas within and outside the central star forming regions in these galaxies. I find that the Halpha luminosity from the shock--ionized gas correlates with the SFR density, in the sense of more luminous shocks for higher SFR density. The ratio of Halpha luminosity from shocks to the total Ha luminosity is related to the galaxy's stellar mass; increasing ratios are observed for decreasing stellar mass. The accepted HST proposal (GO-12497; P.I.: Hong) will expand on the observed correlations by adding two more starbursts to our sample.

Hong, Sungryong

61

Diffuse Ionized Gas in the Dwarf Galaxy DDO 53  

NASA Astrophysics Data System (ADS)

We study the diffuse ionized gas (DIG) in the M81 group dwarf irregular galaxy DDO 53. We use long-slit spectroscopy in order to determine the most interesting line ratios. We compare these ratios with classical and leaking photoionization, shocks and turbulent layer models. As other dwarf irregular galaxies, the spectral characteristics are very diferent to those of the DIG in spiral galaxies: the excitation is higher and the [SII/H?] much lower. A combination of leakage photoionization models plus shocks will be able to explain these characteristics.

Flores-Fajardo, N.; Hidalgo-Gámez, A. M.

62

Optical Breakdown Based on Resonant Enhanced Multi-Photon Ionization and Electron Avalanche Ionization in Gas Mixtures  

NASA Astrophysics Data System (ADS)

We present the results of the experimental and theoretical study of a new kind of optical breakdown in gases with ionization amplification by the combination of Resonant Enhanced Multi-Photon Ionization (REMPI) and subsequent avalanche ionization. As an example, the Ar:Xe mixture was studied. Coherent microwave Rayleigh scattering (radar REMPI) was used to measure REMPI and avalanche ionization. It was shown that REMPI ionization of a relatively small density component (Ar) can catalyze the avalanche ionization process in a buffer gas (Xe) by the use of a laser beam at very low intensity. Theoretical plasma dynamic model verifies the finding. Based on the presented results, several important applications are possible. First, it can improve the detection sensitivity of Radar REMPI. Second, it suggests that plasma generation can be achieved at reduced gas densities or laser beam intensities. Here we can suggest the following two methods: 1. Long laser pulse: The pulse front generates REMPI and subsequent pulse initiates avalanche ionization and Joule heating. 2. Two subsequent laser pulses: A short laser pulse tuned on a REMPI of mixture component generates weakly ionized REMPI plasma and a long off-resonant laser pulse for the avalanche ionization and Joule heating.

Shneider, Mikhail; Zhang, Zhili; Miles, Richard

2008-10-01

63

Diffuse Ionized Gas inside the Dwarf Irregular Galaxy NGC 6822  

NASA Astrophysics Data System (ADS)

We have studied the differences between the diffuse ionized gas (DIG) and the H II regions along a slit position in the local dwarf irregular galaxy NGC 6822. The slit position passes through the two most prominent H II regions: Hubble V and Hubble X. Important differences have been found in the excitation, ionization, and [N II] ?6584/H? and [S II] ?6717/H? line ratios between the DIG and the H II locations. Moreover, the values of all the line ratios are not similar to those in the DIG locations of spiral galaxies but are very similar to the values in other irregular galaxies, such as IC 10. We also determined the rate of recombination using the He I ?5875 line. Finally, we obtained a picture of the ionization sources of the DIG. We consider that the leakage of photons from the H II regions might explain most of the line ratios, except [N II]/H?, which might be explained by turbulence. Based on observations collected at the European Southern Observatory, Chile, proposal 69.C-0203(A).

Hidalgo-Gámez, A. M.; Peimbert, A.

2007-05-01

64

3D Photoionization Models of Diffuse Ionized Gas  

NASA Astrophysics Data System (ADS)

We present 3D photoionization simulations of the diffuse ionized gas (DIG) in the Milky Way to examine the possibility of using [N II]/H? line ratios to probe the 3D structure of the DIG. Compared to data from the Perseus arm, smooth density models produce [N II]/H? values that are lower than observed at small distances above the midplane. This is because N is mostly N2+ close to the midplane ionizing sources, so [N II]/H? is small. As we make our density grid more porous, a smaller luminosity is required to ionize the grid. At small distances from the sources N changes from being being mostly N2+ for the smooth model to mostly N+ in a model with a very small DIG filling factor. We find that simulations with a DIG volume filling factor of around 20% give the best match to observations. This filling factor is remarkably close to that derived from traditional analyses of emission and dispersion measures in the DIG. Clearly, there is no limit to the parameter space that could be investigated using 3D photoionization codes. We comment on future directions for using 3D radiation transfer techniques to critically test 3D dynamical models of the ISM.

Wood, K.

2005-06-01

65

Gas electron multiplier (GEM) enhanced ionization chamber for fluorescence detector  

NASA Astrophysics Data System (ADS)

Detecting dilute elements in thin materials using extended X-ray absorption fluorescence spectroscopy (EXAFS) method requires a detector capable of high count rate and low noise. For detection of dilute elements, the fluorescence signal amplitude is often overcome by the presence of noise or background interference. In this paper we have used a gas ionization chamber enhanced by a gas electron multiplier (GEM) to amplify the primary ionized electrons due to the X-ray fluorescence of a dilute element. The GEM provides an essentially noise free electron amplification of the signal primary photoelectrons. It provides a larger output current prior to the electronic amplification, allowing a lower gain amplifier with lower electronic circuit noise contribution and hence improved S/ N ratio. In addition, since the signal is produced only by electrons, and not from ion motion, the detector is capable of recording rapidly changing signals. Iron in an arbitrary tree leaf was used as a test sample. This sample was measured using our detector SUBRSAB, and also with Lytle and passivated implanted planar silicon (PIPS) detectors. An improvement in the signal amplitude by a factor of 20 and a factor of 2 are recorded for the proposed detector with respect to the Lytle and PIPS detectors, respectively. Although the gain in signal over the PIPS detector is small for this detector, its lack of sensitivity to light and its low and temperature-independent dark current are further advantages.

Shaban, E. H.; Siddons, D. P.; Kuczewski, A.

2007-11-01

66

Photoionized Mixing Layer Models of the Diffuse Ionized Gas  

NASA Astrophysics Data System (ADS)

It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer (TML) models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated, and mixed. The emission spectrum of such layers is compared with observations of Rand of the DIG in the edge-on spiral NGC 891. We generate two sequence of models that fit the line ratio correlations between [S II]/H?, [O I]/H?, [N II]/[S II], and [O III]/H? reasonably well. In one sequence of models, the hot wind velocity increases, while in the other, the ionization parameter and layer opacity increase. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.

Binette, Luc; Flores-Fajardo, Nahiely; Raga, Alejandro C.; Drissen, Laurent; Morisset, Christophe

2009-04-01

67

A Novel Gas Sensor Based on Tunneling-Field-Ionization on Whisker-Covered Gold Nanowires  

Microsoft Academic Search

Typical gas ionization sensors (GISs) work by fingerprinting the ionization breakdown voltages of the gases to be identified. In this work, we developed a GIS that operates by field-ionizing the unknown gas at exceptionally low voltages. The resultant field-ion current-voltage (I-V) characteristic was then used to identify the gas. Freestanding gold nanowires (AuNW), terminated with nanoscale whisker-like features, were employed

Ramin Banan Sadeghian; Mojtaba Kahrizi

2008-01-01

68

Diffuse Ionized Gas Line Strengths from Echelle Spectroscopy  

NASA Astrophysics Data System (ADS)

We discuss serendipitous detections of several emission lines from the diffuse interstellar medium in high-resolution spectra of stars in Baade's Window and globular clusters near the Galactic center. Following Lehnert & Heckman (1994, ApJ, 426, L27), we show that the ratios of the strengths of the emission lines of H? , [N II], and [S II] are inconsistent with those of H II regions, but match those of the diffuse ionized gas, suggesting this as its origin. We discuss these ratios and upper limits to the line strengths of [O I] lambda 6300 and He I lambda 5879. It is difficult to specify where the emitting gas is located along the line of sight to Baade's Window, since this is along the Galaxy's minor axis where the (low) gas velocity poses no constraint. However, we note that the two spectra acquired 1 arcmin apart in Baade's Window are indistinguishable, with equal line strengths and velocity widths. The emission lines are significantly fainter in the sky spectrum of a star in the globular cluster NGC 5927, where the gas velocity indicates that the emission probably does arise in or near the galactic disk.

Terndrup, D. M.; Peterson, R. C.

1996-05-01

69

Diffused ionized gas in the spiral galaxy M31  

NASA Technical Reports Server (NTRS)

We present a study of diffuse ionized gas (DIG, or WIM for warm ionized medium) in the nearby spiral M31, based on charge coupled device (CCD) imagery in H alpha and (S II) emission lines. We find that the DIG in M31 contributes 40% of the observed total H alpha luminosity, and at least 20% of the total after correction for extinction. This fraction is constant across the disk of M31. The total H alpha luminosity of M31, corrected for extinction, is about 4.1 x 10(exp 40) ergs/s. This implies a low star formation rate of about 0.35 M solar mass/yr, in agreement with earlier estimates. DIG is concentrated near regions of star formation. The average emission measure (EM) perpendicular to the disk ranges from about 6 pc cm(exp-6) in weaker spiral arms to 15 pc cm(exp-6) in the main spiral arms, with (rare) peak values reaching 50 pc cm(exp-6). Overall, the EM in the main arms is substantially higher than that of DIG in the solar neighborhood, implying higher power requirements per unit area in these regions of M31. However, the strong concentration of DIG near regions of star formation keeps the total area covered by DIG in M31 relatively small, which makes it possible to sustain this gas in spite of the low star formation rate. We argue that the DIG extent in vertical direction in M31 may well be lower than in our Galaxy, because of its low star formation rate. A simple parameterization of the electron distribution then shows that the DIG in the spiral arms may contribute between 15% and 40% of the total atomic gas column. The average electron densities implied by the high EMs reached in some regions seem to indicate a higher thermal pressure in the DIG than in the diffuse H I gas in M31. This pressure in-equilibrium can be avoided if part of the diffuse emissions due to a denser component, as proposed most recently by Miller & Cox, because this would reduce the EM and implied pressures for the actual widespread DIG. Column densities of the ionized gas might then be lower as well. We also show, however, that it is not possible to attribute all of the diffuse emission to a relatively dense component, such as earlier proposed extended low-density H II regions. The DIG in M31 shows an overall (S II)/H alpha intensity ratio of 0.5, significantly higher than in discrete H II regions, and similar to that in other galaxies. This number does not vary with radius in M31. There is a suggestion that (S II)/H alpha intensity may be higher at the lowest detectable emission measures, up to 0.7 or even 1. The discrete source population in M31 also shows a trend toward increasing (S II)/H alpha flux ratios as the sources become more diffuse. Few sources (apart from supernova remnants), however, reach the value of 0.5 found in the DIG as a whole. The distinct spectral signature of the DIG in M31, and its energy requirements favor photoionization of the gas, although it is likely that shock ionization occurs in selected regions.

Walterbos, Rene A. M.; Braun, Robert

1994-01-01

70

Amonia gas: an improved reagent for chemical ionization mass spectrometry of bile acid methyl ester acetates  

Microsoft Academic Search

The ammonia chemical ionization mass spectra of 28 methyl ester acetate derivatives of bile acids and related compounds have been determined by gas-liquid chromatography-mass spectrometry. Advantages of ammonia ionization over the previously studied isobutane ionization include a 130 to 270% enhancement in the sensitivity of base peak monitoring, and direct determination of molecular weight from the base peak (M +

B. R. DeMark; P. D. Klein

1981-01-01

71

A MEMS-based ionization gas sensor using carbon nanotubes and dielectric barrier  

Microsoft Academic Search

We have demonstrated here the successful operation of an ionization gas sensor with gap spacing 2~10 mum and using CNTs (carbon nanotubes) as the electrode material. By set up an appropriate threshold current, the application of less than 20 V DC bias could generate electric field enough to effectively ionize various gases in atmospheric pressure. Working by the fingerprinting ionization

Jiahao Wu; Hai Liu; Yanyan Wang; Dong Xu; Yafei Zhang

2008-01-01

72

Diffuse Ionized Gas in Three Sculptor Group Galaxies  

NASA Astrophysics Data System (ADS)

We present a study of the diffuse ionized gas (DIG) in three Sculptor group galaxies: NGC 55, NGC 253, and NGC 300. The study is based on narrow band imagery in H? + [N II](6548+6583 A) and [S II] (6717+6731 A). We find that DIG contributes 33 to 58% of the total H? luminosity in these galaxies, or 30 to 54% after correcting for scattered light. We find that NGC 300 has a higher fractional DIG luminosity than the other galaxies in our sample, but it is not clear whether this is a significant difference or an effect of the high inclination of the other galaxies. The diffuse emission, averaged over the optical extent of the disk, has a face-on emission measure of 5 to 10 pc cm^-6^. The DIG is concentrated near H II regions, although significant emission is seen at large distances from H II regions, up to 0.5 to 1 kpc. The [S II]/(H? +[N II]) ratio is enhanced in the DIG, typically around 0.3 to 0.5, compared to 0.2 for the H II regions in these galaxies. These properties are similar to those measured for the DIG in the Milky Way and in other nearby spirals. The line ratios, large- scale distribution, and energy requirement suggest that photoionization is the dominant ionization mechanism.

Hoopes, Charles G.; Walterbos, Rene A. M.; Greenwalt, Bruce E.

1996-10-01

73

GBT and VLA investigation of the ionized gas towards the Galactic center  

NASA Astrophysics Data System (ADS)

We report results of a study of the ionized gas towards the Galactic center with radio recombination lines at cm wavelengths. Both the Green Bank Telescope and the Very Large Array were utilized to probe the kinematics of the ionized gas on a global scale for both diffuse and discrete sources within the inner 2.0° × 0.5° (l × b). A diffuse ˜0 km s-1 gas, a thermal flux continuum fraction exceeding 40%, and an asymmetry where ˜70% of the ionized gas is found at positive Galactic longitudes are the preliminary results briefly discussed here.

Royster, M. J.; Yusef-Zadeh, F.

2014-05-01

74

IC 5181: An S0 Galaxy with Ionized Gas on Polar Orbits  

NASA Astrophysics Data System (ADS)

The nearby S0 galaxy IC 5181 is studied to address the origin of the ionized gas component that orbits the galaxy on polar orbit. We perform detailed photometric and spectroscopic observations measuring the surface brightness distribution of the stars (I band), ionized gas of IC 5181 (H? narrow band), the ionized-gas and stellar kinematics along both the major and minor axis, and the corresponding line strengths of the Lick indices. We conclude that the galaxy hosts a geometrically and kinematically decoupled component of ionized gas. It is elongated along the galaxy minor axis and in orthogonal rotation with respect to the galaxy disk. The result is suggesting that the gas component is not related to the stars having an external origin. The gas was accreted by IC 5181 on polar orbits from the surrounding environment.

Pizzella, A.; Morelli, L.; Corsini, E. M.; Dalla Bontá, E.; Cesetti, M.

2014-05-01

75

Supernova remnants and diffuse ionized gas in M31  

NASA Technical Reports Server (NTRS)

Researchers have compiled an initial list of radio/optical supernova remnants (SNRs) in M31, by searching for radio identifications of emission-line sources with a high (SII)/H alpha ratio (greater than 0.60). The (SII) filter included both sulfur lines and the H alpha filter did not include (NII). This search revealed 11 SNRs, of which only two were known. In addition, researchers detected radio emission from 3 SNRs that were identified in previous optical surveys (D'Odorico et al., 1980), but that were outside the charge coupled device (CCD) fields. The 14 objects only include the most obvious candidates, but a full search is in progress and the researchers expect to find several more SNRs. Also not all optical SNRs show detectable radio emission and a pure optical list of SNR candidates based only on the ratio of (SII)/H alpha emission contains many more objects. Two conclusions are apparent. First, the radio properties of the SNRs in M31 are quite similar to those of Galactic SNRs as is illustrated. The brightnesses are not systematically lower as has been suggested in the past (Dickel and D'Odorico, 1984). Second, the slope of the relation is close to -2; this slope is expected from the intrinsic dependence between surface brightness and diameter. The radio luminosity of the SNRs does not seem to depend strongly on diameter, or age, contrary to model predictions. Selection effects, however, play an important role in these plots. The CCD images show widespread diffuse ionized gas with a ratio of (SII)/H alpha that is higher than that of discrete HII regions. Discrete HII regions typically show ratios between 0.2 to 0.3, while the diffuse gas in the arms consistently shows ratios of 0.5. Researchers can trace this gas across the spiral arms to emission measures below 5 pc cm (-6). Its properties seem to be similar to that of the diffuse gas in the solar neighborhood.

Walterbos, Rene; Braun, Robert

1990-01-01

76

Analysis of the diffuse ionized gas database: DIGEDA  

NASA Astrophysics Data System (ADS)

Studies of the Diffuse Ionized Gas (DIG) have progressed without providing so far any strict criterion to distinguish DIGs from H II regions. In this work, we compile the emission line measurements of 29 galaxies that are available in the scientific literature, thereby setting up the first DIG database (DIGEDA). Making use of this database, we proceed to analyze the global properties of the DIG using the [NII]?6583/H?, [O I]?6300/H?, [O III]?5007/H? and [SII]?6716/H? lines ratios, including the H ? emission measure. This analysis leads us to conclude that the [N II]/H? ratio provides an objective criterion for distinguishing whether an emission region is a DIG or an H II region, while the EM(H?) is a useful quantity only when the galaxies are considered individually. Finally, we find that the emission regions of Irr galaxies classified as DIG in the literature appear in fact to be much more similar to H II regions than to the DIGs of spiral galaxies.

Flores-Fajardo, N.; Morisset, C.; Binette, L.

2009-10-01

77

Galaxy-Scale Clouds of Ionized Gas around AGN  

NASA Astrophysics Data System (ADS)

The serendipitous 2007 discovery of the object now known (even by NED) as "Hanny's Voorwerp" (Lintott et al. 2009) set into motion a search for more examples of galaxy-scale clouds of highly-ionized gas in the vicinity of active galactic nuclei (AGN). Using a sample assembled primarily by 'citizen scientists' via a dedicated thread in the Galaxy Zoo Forum, we carried out the first part of a larger long- slit spectroscopic survey of such objects with the 2.1m telescope at Kitt Peak National Observatory (KPNO). Of the 30 objects targeted during seven nights (multiple exposures for several), extended emission clouds were observed in 15 objects, with [OIII]?5007 emission occasionally extending >30 kpc from galaxy cores. A strong majority (11/15) of the extended emission clouds coincide with merging or otherwise violently disrupted systems, but more relevant to our search were the handful of clouds coinciding with isolated, symmetric galaxies lacking an obvious excitation mechanism. We present the results of part one in the hunt for Voorwerp analogues, much of which served to weed-out the more interesting objects to be targeted for future, multi-wavelength studies.

Chojnowski, S. Drew; Keel, William C.

2012-02-01

78

Cross-phase modulation between lasers in a tunnel ionizing gas  

SciTech Connect

The phase modulation of a low power long pulse probe laser beam in a rapidly tunnel ionizing gas (helium) under a relativistic short pulse laser is investigated. The relativistic pulse creates a fast increasing plasma density at its front, far ahead of the intensity peak. The probe pulse sees these changes as modulation in its phase and undergoes large frequency upshift. The spectral content of the blueshifted potion of the probe pulse is large when its intensity peak commoves with the ionization front. There are two ionization front created by first and second ionizations, and the separation between the two increases as laser propagates through the gas. The rate of density variation by first and second ionizations, however, is fairly the same and varies little as the spot size of the laser beam increases up to three times its initial value. The ionization front velocity, as well as the upshift in probe pulse frequency, is bigger for sharper laser pulse.

Liu, C. S. [Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States); Pathak, Vishwa Bandhu; Tripathi, V. K. [Department of Physics, IIT Delhi, New Delhi 110016 (India)

2009-05-15

79

Experimental and theoretical study of the gas-phase interaction between ionized nitrile sulfides and pyridine  

Microsoft Academic Search

The gas-phase reactivity of ionized nitrile sulfides, R-C?N+-S·, towards neutral pyridine was studied both experimentally (six sector hybrid mass spectrometer) and theoretically (density\\u000a functional theory and Møller-Plesset ab initio calculations). An ionized sulfur atom transfer and a cycloaddition process\\u000a respectively yielding ionized pyridine N-thioxide and a thiazolopyridinium cation were observed. Whereas the very efficient S·+ transfer reaction probably involves the

Pascal Gerbaux; Yves Van Haverbeke; Robert Flammang

2003-01-01

80

CNT-Based MEMS\\/NEMS Gas Ionizers for Portable Mass Spectrometry Applications  

Microsoft Academic Search

We report the fabrication and experimental characterization of a carbon nanotube (CNT)-based MEMS\\/NEMS electron impact gas ionizer with an integrated extractor gate for portable mass spectrometry. The ionizer achieves low-voltage ionization using sparse forests of plasma-enhanced chemical-vapor-deposited CNTs as field emitters and a proximal extractor grid with apertures aligned to the CNT forests to facilitate electron transmission. The extractor gate

Luis Fernando Velasquez-Garcia; Blaise Laurent Patrick Gassend; Akintunde Ibitayo Akinwande

2010-01-01

81

Gas Accretion is Dominated by Warm Ionized Gas in Milky Way Mass Galaxies at z ~ 0  

NASA Astrophysics Data System (ADS)

We perform high-resolution hydrodynamic simulations of a Milky Way mass galaxy in a fully cosmological setting using the adaptive mesh refinement code, Enzo, and study the kinematics of gas in the simulated galactic halo. We find that the gas inflow occurs mostly along filamentary structures in the halo. The warm-hot (105 K 106 K) ionized gases are found to dominate the overall mass accretion in the system (with \\dot{M} = 3-5 M ? yr-1) over a large range of distances, extending from the virial radius to the vicinity of the disk. Most of the inflowing gas (by mass) does not cool, and the small fraction that manages to cool does so primarily close to the galaxy (R <~ 100 kpc, with more pronounced cooling at smaller R), perhaps comprising the neutral gas that may be detectable as, e.g., high-velocity clouds. The neutral clouds are embedded within larger, accreting filamentary flows, and represent only a small fraction of the total mass inflow rate. The inflowing gas has relatively low metallicity (Z/Z ? < 0.2). The outer layers of the filamentary inflows are heated due to compression as they approach the disk. In addition to the inflow, we find high-velocity, metal-enriched outflows of hot gas driven by supernova feedback. Our results are consistent with observations of halo gas at low z.

Joung, M. Ryan; Putman, Mary E.; Bryan, Greg L.; Fernández, Ximena; Peek, J. E. G.

2012-11-01

82

Nearby early-type galaxies with ionized gas. IV. Origin and powering mechanism of the ionized gas  

NASA Astrophysics Data System (ADS)

Aims: A significant fraction of early-type galaxies (ETGs) exhibit emission lines in their optical spectra. We attempt to identify the producing the emission mechanism and the ionized gas in ETGs, and its connection with the host galaxy evolution. Methods: We analyzed intermediate-resolution optical spectra of 65 ETGs, mostly located in low density environments and exhibiting spectros-copic diagnostic lines of ISM from which we had previously derived stellar population properties. To extract the emission lines from the galaxy spectra, we developed a new fitting procedure that accurately subtracts the underlying stellar continuum, and accounts for the uncertainties caused by the age-metallicity degeneracy. Results: Optical emission lines are detected in 89% of the sample. The incidence and strength of emission correlate with neither the E/S0 classification, nor the fast/slow rotator classification. By means of the classical [OIII]/H? versus [NII]/H? diagnostic diagram, the nuclear galaxy activity is classified such that 72% of the galaxies with emission are LINERs, 9% are Seyferts, 12% are composite/transition objects, and 7% are non-classified. Seyferts have young luminostiy-weighted ages (?5 Gyr), and appear, on average, significantly younger than LINERs and composites. Excluding the Seyferts from our sample, we find that the spread in the ([OIII], H?, or [NII]) emission strength increases with the galaxy central velocity dispersion ?_c. Furthermore, the [NII]/H? ratio tends to increase with ?_c. The [NII]/H? ratio decreases with increasing galactocentric distance, indicative of either a decrease in the nebular metallicity, or a progressive “softening” of the ionizing spectrum. The average nebular oxygen abundance is slightly less than solar, and a comparison with the results obtained in Paper III from Lick indices shows that it is ?0.2 dex lower than that of stars. Conclusions: The nuclear (r < re/16) emission can be attributed to photoionization by PAGB stars alone only for ?22% of the LINER/composite sample. On the other hand, we cannot exclude an important role of PAGB star photoionization at larger radii. For the major fraction of the sample, the nuclear emission is consistent with excitation caused by either a low-accretion rate AGN or fast shocks (200-500 km s-1) in a relatively gas poor environment (n ? 100 cm-3), or both. The derived [SII]6717/6731 ratios are consistent with the low gas densities required by the shock models. The derived nebular metallicities are indicative of either an external origin of the gas, or an overestimate of the oxygen yields by SN models. Based on observations obtained at the European Southern Observatory, La Silla, Chile.Appendix and Tables 2 and 3 are only available in electronic form at http://www.aanda.org

Annibali, F.; Bressan, A.; Rampazzo, R.; Zeilinger, W. W.; Vega, O.; Panuzzo, P.

2010-09-01

83

Evaluation of Gas-filled Ionization Chamber Method for Radon Measurement at Two Reference Facilities  

SciTech Connect

For quality assurance, gas-filled ionization chamber method was tested at two reference facilities for radon calibration: EML (USA) and PTB (Germany). Consequently, the radon concentrations estimated by the ionization chamber method were in good agreement with the reference radon concentrations provided by EML as well as PTB.

Ishikawa, Tetsuo; Tokonami, Shinji; Kobayashi, Yosuke; Sorimachi, Atsuyuki; Yatabe, Yoshinori; Miyahara, Nobuyuki [National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555 (Japan)

2008-08-07

84

Fabrication of gas ionization sensors using well-aligned MWCNT arrays grown in porous AAO templates  

Microsoft Academic Search

Gas ionization sensors based on the field ionization from well-aligned MWCNT arrays grown in porous AAO templates were fabricated. The breakdown voltages were measured in different gases of different concentrations. The changes of the breakdown voltage were related to the type of detected gases and its concentration. At the same time, the pre-discharge processes had also been studied to test

Xing Chen; Zhenhua Guo; Jarui Huang; Fanli Meng; Meiyun Zhang; Jinhuai Liu

2008-01-01

85

Dielectrophoresis of ionized gas microbubbles: Dipole reversal due to diffusive double-layer polarization  

Microsoft Academic Search

Gas bubbles generated by electrolysis reactions are shown to exhibit anomalous induced ac dipoles and dielectrophoretic behavior that cannot be described by classical Maxwell-Wagner theory. Normal charging and screening of conducting ionized gas in the gas-phase double layer are shown to render the bubble insulating at low ac field frequencies to affect negative dielectrophoresis. This screening effect couples with dielectric

Zachary R. Gagnon; Hsueh-Chia Chang

2008-01-01

86

Dielectrophoresis of ionized gas microbubbles: Dipole reversal due to diffusive double-layer polarization  

Microsoft Academic Search

Gas bubbles generated by electrolysis reactions are shown to exhibit anomalous induced ac dipoles and dielectrophoretic behavior that cannot be described by classical Maxwell-Wagner theory. Normal charging and screening of conducting ionized gas in the gas-phase double layer are shown to render the bubble insulating at low ac field frequencies to affect negative dielectrophoresis. This screening effect couples with dielectric

Zachary R. Gagnon; Hsueh-Chia Chang

2009-01-01

87

The ionizing radiation of gas discharge and electret effect in polyolefin dielectrics  

NASA Astrophysics Data System (ADS)

The results of studies of ionizing radiation of an electric gas discharge, the penetrating power, and the influence on the electret effect and electrical relaxation in polyolefin cable dielectrics are discussed.

Novikov, G. K.

2011-09-01

88

Infrared spectroscopy of ionized corannulene in the gas phase  

NASA Astrophysics Data System (ADS)

The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H2, and C2Hx losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp3 hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C5v geometry induced by the Jahn-Teller effect as a consequence of the degenerate 2E1 ground electronic state. As indicated by the calculations, the five equivalent Cs minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm-1 region show the largest discrepancy with the harmonic predictions. In addition to CH ``in-plane'' bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

Galué, Héctor Alvaro; Rice, Corey A.; Steill, Jeffrey D.; Oomens, Jos

2011-02-01

89

Infrared spectroscopy of ionized corannulene in the gas phase.  

PubMed

The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H(2), and C(2)H(x) losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp(3) hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C(5v) geometry induced by the Jahn-Teller effect as a consequence of the degenerate (2)E(1) ground electronic state. As indicated by the calculations, the five equivalent C(s) minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm(-1) region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation. PMID:21303123

Alvaro Galué, Héctor; Rice, Corey A; Steill, Jeffrey D; Oomens, Jos

2011-02-01

90

Gas ionization sensors using well-aligned MWCNT arrays grown in porous AAO template  

Microsoft Academic Search

Porous anodic aluminum oxide (AAO) templates were prepared by a two-step anodization process, then chemical vapor deposition (CVD) method was used to prepare well-aligned open-ended multiwall carbon nanotube (MWCNT) arrays in the AAO templates that also served as catalyst. Gas ionization sensors were fabricated using the MWCNT arrays. The gas ionization sensors featured the electrical breakdown of the ethanol vapor

Xing Chen; Zhongying Huang; Jiarui Huang; Jinhuai Liu; Mingguang Kong

2005-01-01

91

Influence of ionization on ultrafast gas-based nonlinear fiber optics.  

PubMed

We numerically investigate the effect of ionization on ultrashort high-energy pulses propagating in gas-filled kagomé-lattice hollow-core photonic crystal fibers by solving an established uni-directional field equation. We consider the dynamics of two distinct regimes: ionization induced blue-shift and resonant dispersive wave emission in the deep-UV. We illustrate how the system evolves between these regimes and the changing influence of ionization. Finally, we consider the effect of higher ionization stages. PMID:21997110

Chang, W; Nazarkin, A; Travers, J C; Nold, J; Hölzer, P; Joly, N Y; Russell, P St J

2011-10-10

92

PHYSICS OF A PARTIALLY IONIZED GAS RELEVANT TO GALAXY FORMATION SIMULATIONS-THE IONIZATION POTENTIAL ENERGY RESERVOIR  

SciTech Connect

Simulation codes for galaxy formation and evolution take on board as many physical processes as possible beyond the standard gravitational and hydrodynamical physics. Most of this extra physics takes place below the resolution level of the simulations and is added in a ''sub-grid'' fashion. However, these sub-grid processes affect the macroscopic hydrodynamical properties of the gas and thus couple to the ''on-grid'' physics that is explicitly integrated during the simulation. In this paper, we focus on the link between partial ionization and the hydrodynamical equations. We show that the energy stored in ions and free electrons constitutes a potential energy term which breaks the linear dependence of the internal energy on temperature. Correctly taking into account ionization hence requires modifying both the equation of state and the energy-temperature relation. We implemented these changes in the cosmological simulation code GADGET2. As an example of the effects of these changes, we study the propagation of Sedov-Taylor shock waves through an ionizing medium. This serves as a proxy for the absorption of supernova feedback energy by the interstellar medium. Depending on the density and temperature of the surrounding gas, we find that up to 50% of the feedback energy is spent ionizing the gas rather than heating it. Thus, it can be expected that properly taking into account ionization effects in galaxy evolution simulations will drastically reduce the effects of thermal feedback. To the best of our knowledge, this potential energy term is not used in current simulations of galaxy formation and evolution.

Vandenbroucke, B.; De Rijcke, S.; Schroyen, J. [Department of Physics and Astronomy, Ghent University, Krijgslaan 281, S9, B-9000 Gent (Belgium); Jachowicz, N. [Department of Physics and Astronomy, Ghent University, Proeftuinstraat 86, B-9000 Gent (Belgium)

2013-07-01

93

Observations of extended and counterrotating disks of ionized gas in S0 galaxies  

NASA Technical Reports Server (NTRS)

While many E/S0 galaxies have been found to show emission line spectra in their nuclear regions, the question of the presence and nature of extended disks of ionized gas in these galaxies has been addressed only in recent years. Typically the ionized gas is detected in the inner region on a scale of approx. 1 kpc (e.g., Phillips et al. 1986, Caldwell 1984). Here researchers present evidence that the disks of ionized gas of at least some S0 galaxies are much more extended than previously believed. In addition, with the detection of the counterrotation of gas and stars in NGC 7007 they strengthen the basis for arguments that the source of gas in S0 galaxies is external

Dettmar, Ralf-Juergen; Jullien-Dettmar, Marlies; Barteldrees, Andreas

1990-01-01

94

Shock Structure Analysis and Aerodynamics in a Weakly Ionized Gas Flow  

NASA Technical Reports Server (NTRS)

The structure of a shock wave propagating through a weakly ionized gas is analyzed using an electrofluid dynamics model composed of classical conservation laws and Gauss Law. A viscosity model is included to correctly model the spatial scale of the shock structure, and quasi-neutrality is not assumed. A detailed analysis of the structure of a shock wave propagating in a weakly ionized gas is presented, together with a discussion of the physics underlying the key features of the shock structure. A model for the flow behind a shock wave propagating through a weakly ionized gas is developed and used to analyze the effect of the ionization on the aerodynamics and performance of a two-dimensional hypersonic lifting body.

Saeks, R.; Popovic, S.; Chow, A. S.

2006-01-01

95

Mass spectrometric behavior of anabolic androgenic steroids using gas chromatography coupled to atmospheric pressure chemical ionization source. Part I: Ionization.  

PubMed

The detection of anabolic androgenic steroids (AAS) is one of the most important topics in doping control analysis. Gas chromatography coupled to (tandem) mass spectrometry (GC-MS(/MS)) with electron ionization and liquid chromatography coupled to tandem mass spectrometry have been traditionally applied for this purpose. However, both approaches still have important limitations, and, therefore, detection of all AAS is currently afforded by the combination of these strategies. Alternative ionization techniques can minimize these drawbacks and help in the implementation of a single method for the detection of AAS. In the present work, a new atmospheric pressure chemical ionization (APCI) source commercialized for gas chromatography coupled to a quadrupole time-of-flight analyzer has been tested to evaluate the ionization of 60 model AAS. Underivatized and trimethylsylil (TMS)-derivatized compounds have been investigated. The use of GC-APCI-MS allowed for the ionization of all AAS assayed irrespective of their structure. The presence of water in the source as modifier promoted the formation of protonated molecules ([M+H](+) ), becoming the base peak of the spectrum for the majority of studied compounds. Under these conditions, [M+H](+) , [M+H-H2 O](+) and [M+H-2·H2 O](+) for underivatized AAS and [M+H](+) , [M+H-TMSOH](+) and [M+H-2·TMSOH](+) for TMS-derivatized AAS were observed as main ions in the spectra. The formed ions preserve the intact steroid skeleton, and, therefore, they might be used as specific precursors in MS/MS-based methods. Additionally, a relationship between the relative abundance of these ions and the AAS structure has been established. This relationship might be useful in the structural elucidation of unknown metabolites. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24913403

Raro, M; Portolés, T; Sancho, J V; Pitarch, E; Hernández, F; Marcos, J; Ventura, R; Gómez, C; Segura, J; Pozo, O J

2014-06-01

96

The ionization conditions in the Milky Way halo - Infalling gas toward the North Galactic Pole  

NASA Technical Reports Server (NTRS)

Observations of gas in the Milky Way halo are studied with an eye toward the theoretical predictions of the Galactic Fountain model for the production of halo gas. Data are shown that indicate significant variations in the ionization conditions in infalling halo gas in the northern galactic hemisphere. Understanding the nature of Milky Way halo gas plays a critical role in interpreting QSO absorption lines in the investigation of galaxies at high redshift.

Danly, Laura

1992-01-01

97

Ionization gas sensor using aligned multiwalled carbon nanotubes (MWCNTs) array  

Microsoft Academic Search

Carbon nanotubes (CNTs) have drawn a lot of interest as the sensing element in sensor technology because of their unique electronic properties and remarkable mechanical properties. CNTs' extremely high surface-to-volume ratio makes it a very good candidate for the adsorption of gas molecules. Gas sensors are divided into two types, namely; physical gas sensors and chemical gas sensors. In the

Atieh Ranjbar Kermany; Norani Muti Mohamed; B. S. M. Singh

2010-01-01

98

Conical Electrostatic Probe Response in a Weakly Ionized Gas Flow.  

National Technical Information Service (NTIS)

Conical electrostatic probes of lengths 0.153, 0.393 and 1.0 cm were placed in partially ionized argon flows in the laboratory in order to study the use of their current-voltage characteristics in the measurement of ion number densities over a wide range....

C. F. Bruce L. Talbot

1974-01-01

99

Highly Ionized Gas Surrounding High-Velocity Cloud Complex C  

Microsoft Academic Search

We present Far Ultraviolet Spectroscopic Explorer and Hubble Space Telescope observations of high-, intermediate-, and low-ion absorption in high-velocity cloud (HVC) Complex C along the lines of sight toward five active galaxies. Our purpose is to investigate the idea that Complex C is surrounded by an envelope of highly ionized material, arising from the interaction between the cloud and a

Andrew J. Fox; Blair D. Savage; Bart P. Wakker; Philipp Richter; Kenneth R. Sembach; Todd M. Tripp

2004-01-01

100

Prediction of Shock Wave Structure in Weakly Ionized Gas Flow by Solving MGD Equation  

NASA Technical Reports Server (NTRS)

This paper reports the recent research results of shockwave structure predictions using a new developed code. The modified Rankine-Hugoniot relations across a standing normal shock wave are discussed and adopted to obtain jump conditions. Coupling a electrostatic body force to the Burnett equations, the weakly ionized flow field across the shock wave was solved. Results indicated that the Modified Rankine-Hugoniot equations for shock wave are valid for a wide range of ionization fraction. However, this model breaks down with small free stream Mach number and with large ionization fraction. The jump conditions also depend on the value of free stream pressure, temperature and density. The computed shock wave structure with ionization provides results, which indicated that shock wave strength may be reduced by existence of weakly ionized gas.

Deng, Z. T.; Oviedo-Rojas, Ruben; Chow, Alan; Litchford, Ron J.; Cook, Stephen (Technical Monitor)

2002-01-01

101

Effect of laser self-defocusing on third harmonic generation in a tunnel ionizing gas  

SciTech Connect

A paraxial theory of third harmonic generation by a finite spot size laser in a tunnel ionizing gas is developed. The laser, with intensity close to tunnel ionization threshold, creates plasma whose density rises in a stepwise manner in every half wave period, giving a strong second harmonic component in electron density. The density beats with the oscillatory velocity at the fundamental to produce a nonlinear current, driving the third harmonic. The region of harmonic generation is localized near the laser axis. Further, the strong radial nonuniformity, created in electron density by the ionization process, causes defocusing of the laser, limiting the efficiency of harmonic generation.

Verma, Updesh; Sharma, A. K. [Center for Energy Studies, Indian Institute of Technology Delhi, New Delhi-110016 (India)

2009-01-15

102

Gas-phase chemiluminescence and chemi-ionization  

SciTech Connect

The phenomena of chemiluminescence (or more broadly chemi-excitation) and chemi-ionization have major similarities from a fundamental kinetic and dynamic point of view. However, since the former has primarily been investigated using optical spectroscopic techniques and the latter largely by mass spectroscopic (and other gaseous electronic) methods, the two phenomena have apparently never, explicitly been discussed together in one volume. In addition to a number of review articles on each individual subject, several meetings and books have had chemiluminescence and bioluminescence as their theme and those have been dominated by condensed phase work. On the other hand, chemi-ionization is often discussed in the contest of gaseous electronics, plasma chemistry and combustion. It is the goal of this book to present a more unified understanding of the two phenomena.

Fontijn, A.

1985-01-01

103

The structure of the Orion Nebula: The partially ionized gas  

Microsoft Academic Search

The H109-alpha, He109-alpha, C109-alpha, He137-beta, and C137-beta lines toward Orion A have been mapped with an angular resolution of 2.6 arcmin. C85-alpha spectra at three positions have also been taken, with a resolution of 2.8 arcmin. The C109-alpha data reveal that there are three distinct regions of ionized carbon characterized by radial velocities of 6, 8.5, and 11 km\\/s. The

D. T. Jaffe; V. Pankonin

1978-01-01

104

Study of the surface ionization detector for gas chromatography  

Microsoft Academic Search

The structure of the surface ionization detector (SID) and the operation parameters of GC–SID were investigated to reduce peak tailing and to enhance sensitivity. The performances of the GC–SID, including its repeatability, linearity, sensitivity, selectivity, and tolerance towards water vapor, were evaluated systematically. Compared with nitrogen–phosphorus detector (NPD), the SID was able to detect fg level triethylamine, and selectively respond

Weiwei Li; Dapeng Wu; Shiheng Chen; Hong Peng; Yafeng Guan

2011-01-01

105

Wavelength scaling of terahertz generation by gas ionization.  

PubMed

Low-frequency currents induced by ultrashort laser-driven ionization can emit extremely broadband, single-cycle terahertz pulses. We present a model that predicts a strong wavelength dependence of the THz emission in good agreement with our experimental study. This reveals that the combined effects of plasma currents rising proportionally to the square of the pump wavelength and wavelength-dependent focusing conditions lead to 30 times higher THz emission at 1800 nm compared to an 800 nm wavelength. Unrivaled single-cycle electric field strengths of 4.4??MV/cm are achieved with this compact table-top setup. PMID:23829737

Clerici, Matteo; Peccianti, Marco; Schmidt, Bruno E; Caspani, Lucia; Shalaby, Mostafa; Giguère, Mathieu; Lotti, Antonio; Couairon, Arnaud; Légaré, François; Ozaki, Tsuneyuki; Faccio, Daniele; Morandotti, Roberto

2013-06-21

106

The in-gas-jet laser ion source: Resonance ionization spectroscopy of radioactive atoms in supersonic gas jets  

NASA Astrophysics Data System (ADS)

New approaches to perform efficient and selective step-wise resonance ionization spectroscopy (RIS) of radioactive atoms in different types of supersonic gas jets are proposed. This novel application results in a major expansion of the in-gas laser ionization and spectroscopy (IGLIS) method developed at KU Leuven. Implementation of resonance ionization in the supersonic gas jet allows to increase the spectral resolution by one order of magnitude in comparison with the currently performed in-gas-cell ionization spectroscopy. Properties of supersonic beams, obtained from the de Laval-, the spike-, and the free jet nozzles that are important for the reduction of the spectral line broadening mechanisms in cold and low density environments are discussed. Requirements for the laser radiation and for the vacuum pumping system are also examined. Finally, first results of high-resolution spectroscopy in the supersonic free jet are presented for the 327.4 nm 3d104s 2S1/2? 3d104p 2P1/2 transition in the stable 63Cu isotope using an amplified single mode laser radiation.

Kudryavtsev, Yu.; Ferrer, R.; Huyse, M.; Van den Bergh, P.; Van Duppen, P.

2013-02-01

107

Observations and modeling of diffuse ionized gas in edge-on galaxies  

NASA Astrophysics Data System (ADS)

The present PhD theses deals with observations of diffuse ionized gas (DIG) in edge-on galaxies and their corresponding modeling. A still unexplained issue concerns possible ionization mechanisms of the DIG. Based upon energy estimations photoionization by young O stars appears to be the most likely ionizing source. Within the scope of this work, spectroscopic line ratios have been obtained which are compared to predictions of common photoionization models. As these codes cannot explain the observational data consistently, a new photoionization model code has been developed which is based on Monte Carlo techniques and assumes a more realistic geometry. First model iterations of the ionization structure of the DIG reveal encouraging results. In order to simulate individual galaxies in detail, a comprehensive investigation of the free parameter space is required.

Tuellmann, Ralph

2002-04-01

108

Anomalous propagation of planar shock wave in weakly ionized gas  

NASA Astrophysics Data System (ADS)

Shock propagation velocity along the centerline of a cylindrical glow discharge has to be much higher in the cathode region than in the positive column in order to account for the measured propagation time. This is an outcome of detailed analysis of planar shock waves propagating along a cylindrical glow discharge [B. N. Ganguly, P. Bletzinger, and A. Garscadden, Phys. Lett. A 230, 218 (1997)]. The analysis was restricted to shock front propagation time to the two well-defined positions at the centerline where the motion can be considered one dimensional. Although there is not yet a comprehensive interpretation of the anomalous propagation velocity, it seems to increase wherever number density of excited states increases. Intensified local ionization due to excessive presence of excited states combined with the excitation of ion acoustic waves could be the mechanism for anomalous shock propagation velocity.

Popovic, S.; Vuskovic, L.

1999-05-01

109

Multimedia imaging detectors operating on gas-solid-state ionization principles  

Microsoft Academic Search

The engineering design of a novel imaging detector, operating on gaseous solid-state ionization principles for slot-scan imaging radiation in two dimensions, is presented. The detector has two basic functional components: a noble gas filled detector volume operating on gas microstrip principles and a solid-state detector volume. An experimental arrangement has been established, where incident X-rays spend part of their energy

George C. Giakos; Samir Chowdhury

1998-01-01

110

Noble gas detection using resonance ionization spectroscopy and a quadrupole mass spectrometer  

SciTech Connect

The technique of Resonance Ionization Spectroscopy (RIS) is being extended to develop a means for counting individual atoms of a selected isotope of a noble gas. In this method, lasers are used for RIS to obtain atomic species (Z) selectivity and a small quadrupole mass spectrometer provides isotopic (A) selectivity. A progress report on the objective of counting each atom of a particular isotope of a noble gas is given. 11 references, 4 figures.

Chen, C.H.; Hurst, G.S.

1983-01-01

111

Isotopically selective counting of noble gas atoms, using resonance ionization spectroscopy  

SciTech Connect

The technique of Resonance Ionization Spectroscopy (RIS) is being extended to develop a means for counting individual atoms of a selected isotope of a noble gas. In this method, lasers are used for RIS to obtain atomic species (Z) selectivity and a small quadrupole mass spectrometer provides isotopic (A) selectivity. A progress report on the objective of counting each atom of a particular isotope of a noble gas is given. 10 references, 4 figures.

Chen, C.H.

1984-04-01

112

Sparsepak Observations of Diffuse Ionized Gas Halo Kinematics in NGC891  

NASA Astrophysics Data System (ADS)

We present WIYN SparsePak observations of the diffuse ionized gas (DIG) hallo of NGC891. Preliminary results of an analysis of the halo velocity field reveal a clear gradient of the azimuthal velocity with z which agrees with results for the neutral gas. The magnitude of the gradient has been determined, using two independent methods, to be approximately 15 km s-1 kpc-1.

Heald, George H.; Rand, Richard J.; Benjamin, Robert A.; Bershady, Matthew A.

113

Isotopically Selective Counting of Noble Gas Atoms, Using Resonance Ionization Spectroscopy.  

National Technical Information Service (NTIS)

The technique of Resonance Ionization Spectroscopy (RIS) is being extended to develop a means for counting individual atoms of a selected isotope of a noble gas. In this method, lasers are used for RIS to obtain atomic species (Z) selectivity and a small ...

C. H. Chen

1984-01-01

114

Noble gas detection using resonance ionization spectroscopy and a quadrupole mass spectrometer  

Microsoft Academic Search

The technique of Resonance Ionization Spectroscopy (RIS) is being extended to develop a means for counting individual atoms of a selected isotope of a noble gas. In this method, lasers are used for RIS to obtain atomic species (Z) selectivity and a small quadrupole mass spectrometer provides isotopic (A) selectivity. A progress report on the objective of counting each atom

C. H. Chen; G. S. Hurst

1983-01-01

115

Isotopically selective counting of noble gas atoms, using resonance ionization spectroscopy  

Microsoft Academic Search

The technique of Resonance Ionization Spectroscopy (RIS) is being extended to develop a means for counting individual atoms of a selected isotope of a noble gas. In this method, lasers are used for RIS to obtain atomic species (Z) selectivity and a small quadrupole mass spectrometer provides isotopic (A) selectivity. A progress report on the objective of counting each atom

C. H. Chen

1984-01-01

116

Collisions of Fast Multicharged Ions in Gas Targets: Charge Transfer and Ionization.  

National Technical Information Service (NTIS)

Measurements of cross sections for charge transfer and ionization of H sub 2 and rare-gas targets have been made with fast, highly stripped projectiles in charge states as high as 59+. We have found an empirical scaling rule for electron-capture cross sec...

A. S. Schlachter

1981-01-01

117

Gas Ionization During Carbothermal Reduction in Microwave Field and Its Effect  

Microsoft Academic Search

The reduction kinetic condition of the direct solid-phase reduction of metal oxide powder containing coal by microwave heating is better than that by the conventional heating process. The research shows that the gas ionization during carbothermal reduction accelerates the carbon gasification reaction and interface chemical reaction, and it also improves the kinetic conditions of carbothermal reduction. Thus, the formation mechanism

Jin CHEN; Xue-hong SHI; Meng ZHANG; Jing ZHAO

2009-01-01

118

Field ionization kinetic and electron impact studies of gas phase transition states - The cyclic bromonium ion  

NASA Technical Reports Server (NTRS)

Cis- and trans-isomers of 4-t-butylcyclohexyl bromide were studied to determine the mechanism of cyclic bromonium ion formation. The field ionization kinetic and electron impact data indicate that the formation of the cyclic structure occurs simultaneously with loss of the neutral fragment. The data also show that little or no gas-phase cis-trans isomerization occurs.

Green, M. M.; Giguere, R. J.; Falick, A. M.; Aberth, W.; Burlingame, A. L.

1978-01-01

119

Spatial interference during the ionization of noble gas atoms by few-cycle XUV laser pulses  

NASA Astrophysics Data System (ADS)

We have investigated the spatial interference effects, which appear during the ionization of noble gas atoms by few-cycle XUV laser pulses. By using ab initio calculations, and single active electron model potentials, we have studied how the spatial interference pattern is influenced by the atomic species of the target.

Borbély, S.; Tóth, A.; Tökésit, K.; Nagy, L.

2014-04-01

120

Monte Carlo simulation of charged particle diffusion through an ionized gas: contributions of simultaneous multiple collisions  

Microsoft Academic Search

When a charged particle moves through fully or partially ionized plasmas, energy loss and momentum transfer occur through various kinds of elastic and inelastic collisions.In ordinary gases, composed primarily of neutral particles, the interactions are mainly close binary collisions, being the impact parameter well shorter than the mean free path. In a gas composed of charged particles, neglecting simultaneous multiple

V. Molinari; F. Teodori

2004-01-01

121

Properties of the highly ionized disk and halo gas toward two distant high-latitude stars  

NASA Technical Reports Server (NTRS)

Goddard High Resolution Spectrograph (GHRS) intermediate -resolution observations of S III, Si III, Al III, Si IV, C IV, and N V absorption along the sight lines to HD 18100 (l = 217.9 deg, b = -62.7, d = 3.1 kpc, z = -2.8 kpc) and HD 100340 (l = 258.9 deg, b = +61.2 deg, d = 5.3 kpc, z = 4.6 kpc) are presented. These small science aperture spectra have resolutions ranging from 11 to 20 km/s full width at half maximum (FWHM) and S/N from 30 to 65 per diode substep. Strong absorption by moderately and highly ionized gas is seen in each direction. The absorption in the direction of the south Galactic polar region (HD 18100) is kinematically simple, while the absorption in the direction of north Galactic polar region (HD 100304) is kinematically complex. In each case the absorption by the highly ionized gas lies within the velocity range of absorption by neutral and weakly ionized gas. Along each sight line, the velocity dispersion determined from the unsaturated absorption lines increases with the energy required to create each ion. The logarithmic column densities for Al III, Si IV, C IV, and N V are log N(atoms/sq cm = 12.71, 13.10, 13.58, and 12.75 toward HD 18100 and log N = 12.88, 13.31, 13.83, and 13.04 toward HD 100340. Average ionic ratios among these species are very similar along the two sight lines. Differences in profile shape between the absorption for AL II, Si IV, C IV, and N V provide additional support for the claim of Savage, Sembach, & Cardelli (1994) that there exists two types of highly ionized gas in the interstellar medium. One type of highly ionized gas is responsible for the structured Si IV absorption and part of the C IV absorption. In this gas N(C IV)/N(Si IV) approximately 3.0 and N(C IV)/N(N V) greater than 6. The absorption by this gas seems to be associated with some type of self-regulating interface or mixing layer between the warm and hot interstellar medium. The other type of highly ionized gas is responsible for most of the N V absorption, part of the C IV absorption, and has very little associated Si IV absorption. In this gas N(C IV)/N(N V) is approximately 1 to 3. This gas is hot (T greater than 2 x 10(exp 5) K) and may be tracing the cooling gas of supernova (SN) bubbles or a Galactic fountain. The relative mixture of these two types of highly ionized gas varies from one sight line to the next. The two sight lines in this study sample halo gas in the solar neighborhood and have a smaller percentage of the more highly ionized gas than inner Galaxy sight lines.

Savage, Blair D.; Sembach, K. R.

1994-01-01

122

Neutral Gas and Low-Redshift Starbursts: From Infall to Ionization  

NASA Astrophysics Data System (ADS)

The interplay of gas inflows, star formation, and feedback drives galaxy evolution, and starburst galaxies provide important laboratories for probing these processes at their most extreme. With two samples of low-redshift starburst galaxies, we examine the conversion of neutral gas into stars and the subsequent effects of stellar feedback on the neutral interstellar medium (ISM). The ALFALFA H? survey represents a complete, volume-limited sample of HI-selected galaxies with 21 cm spectra and H? and R-band imaging. By contrasting the starburst galaxies with the rest of the gas-rich galaxy population, we investigate the roles of galaxy morphology, HI kinematics, and the atomic gas supply in triggering extreme levels of star formation. Both an elevated HI gas supply and an external disturbance are necessary to drive the starbursts. While neutral gas may fuel a starburst, it may also increase starbursts' optical depths and hinder the transport of ionizing radiation. In contrast to the expectations for high-redshift star-forming galaxies, neutral gas appears to effectively bar the escape of ionizing radiation in most low-redshift starbursts. To evaluate the impact of radiative feedback in extreme starbursts, we analyze optical spectra of the Green Pea galaxies, a low-redshift sample selected by their intense [O III] ?5007 emission and compact sizes. We use nebular photoionization and stellar population models to constrain the Peas' burst ages, ionizing sources, and optical depths and find that the Peas are likely optically thin to Lyman continuum (LyC) radiation. These young starbursts still generate substantial ionizing radiation, while recent supernovae may have carved holes in the ISM that enhance LyC photon escape into the intergalactic medium. While the ALFALFA survey demonstrates the role of external processes in triggering starbursts, the Green Peas show that starbursts' radiation can escape to affect their external environment.

Jaskot, Anne; Oey, M. S.; Salzer, J. J.; Van Sistine, A.; Haynes, M. P.

2014-01-01

123

Development of a new electron ionization/field ionization ion source for gas chromatography/time-of-flight mass spectrometry.  

PubMed

We have developed a combined EI/FI source for gas chromatography/orthogonal acceleration time-of-flight mass spectrometry (GC/oaTOFMS). In general, EI (electron ionization) and FI (field ionization) mass spectra are complementary: the EI mass spectrum contains information about fragment ions, while the FI mass spectrum contains information about molecular ions. Thus, the comparative study of EI and FI mass spectra is useful for GC/MS analyses. Unlike the conventional ion sources for FI and EI measurements, the newly developed source can be used for both measurements without breaking the ion source vacuum or changing the ion source. Therefore, the combined EI/FI source is more preferable than the conventional EI or FI ion source from the viewpoint of the reliability of measurements and facility of operation. Using the combined EI/FI source, the complementarity between EI and FI mass spectra is demonstrated experimentally with n-hexadecane (100 pg): characteristic fragment ions for the n-alkane such as m/z 43, 57, 71, and 85 are obtained in the EI mass spectrum, while only the parent peak of m/z 226 (M+) without any fragment ions is observed in the FI mass spectrum. Moreover, the field desorption (FD) measurement is also demonstrated with poly(ethylene glycol)s M600 (10 ng) and M1000 (15 ng). Signals of [M+H]+, [M+Na]+ and [M+K]+ are clearly detected in the FD mass spectra. PMID:19764073

Miyamoto, Kenji; Fujimaki, Susumu; Ueda, Yoshihisa

2009-10-30

124

Identification of Isoflavone Metabolites Dihydrodaidzein, Dihydrogenistein, 6?OH O-dma, and cis-4OHequol in Human Urine by Gas Chromatography–Mass Spectroscopy Using Authentic Reference Compounds  

Microsoft Academic Search

The metabolic products of daidzein and genistein, the principal isoflavones of soy, were examined. Six volunteers included soy into their normal diet for a 2-week period and urine samples were analyzed before and after soy consumption. Isolation and characterization of the urinary metabolites were carried out with absorption chromatography on Sephadex LH-20 and gas chromatography–electron ionization mass spectrometry (GC–EIMS). The

S. Heinonen; K. Wähälä; H. Adlercreutz

1999-01-01

125

Dust and ionized gas in active radio elliptical galaxies  

NASA Technical Reports Server (NTRS)

The authors present broad and narrow bandwidth imaging of three southern elliptical galaxies which have flat-spectrum active radio cores (NGC 1052, IC 1459 and NGC 6958). All three contain dust and extended low excitation optical line emission, particularly extensive in the case of NGC 1052 which has a large H alpha + (NII) luminosity. Both NGC 1052 and IC 1459 have a spiral morphology in emission-line images. All three display independent strong evidence that a merger or infall event has recently occurred, i.e., extensive and infalling HI gas in NGC 1052, a counter-rotating core in IC 1459 and Malin-Carter shells in NGC 6958. This infall event is the most likely origin for the emission-line gas and dust, and the authors are currently investigating possible excitation mechanisms (Sparks et al. 1990).

Forbes, D. A.; Sparks, W. B.; Macchetto, F. D.

1990-01-01

126

A compact apparatus for mass selective resonance ionization spectroscopy in a buffer gas cell  

NASA Astrophysics Data System (ADS)

An ultra-sensitive laser spectroscopic method for the investigation of transuranium nuclides has been developed based on resonance ionization in an argon buffer gas cell. This method has been combined with ion-guide extraction and mass selective direct detection of the resonantly ionized atoms. Using argon as a buffer gas, recoils of fusion reactions can be thermalized even at low pressure. The differential pumping system consists of only one roots pump and two turbo molecular pumps. The set-up has been tested with m243Am evaporated from a filament located inside the optical gas cell. Resonance ionization is performed using a two-step excitation with an excimer-dye-laser combination. The ions are transported by a suitable electrical field to the nozzle, and are ejected with the ion-guide gas jet into an electrostatic lens system followed by a quadrupole mass spectrometer and a channeltron detector. The total sensitivity has been measured to be 1.0 × 10-4. The extraction time for ions based on electric field guidance amounts to 1.5 ms, which is two orders of magnitude faster than the ion-guide gas exchange time of this set-up.

Backe, H.; Feldmann, R.; Hies, M.; Kunz, H.; Lauth, W.; Martin, R.; Schöpe, H.; Schwamb, P.; Sewtz, M.; Eberhardt, K.; Thörle, P.; Trautmann, N.; Zauner, S.

1996-04-01

127

Dissociation and ionization of molecular gas in the spiral arms of M51  

NASA Technical Reports Server (NTRS)

Researchers derive the star formation rate and efficiency in the arm and interarm regions of M51 from observations of the molecular (Lo et al. 1987) and ionized (van der Hulst et al. 1988) phases of the interstellar medium, and show that the HI observations of Tilanus and Allen (1989) are consistent with dissociation of molecular gas by these young, massive stars if n sub H greater than or equal to 200 cm (-2). However, these stars are not able to dissociate or ionize all the gas, and at least 60 percent must remain molecular in the interarm regions. The efficiency of star formation in M51 seems to be similar to that in the Galaxy, and does not appear to be enhanced in the spiral arms. Therefore, the effect of the strong density wave may be only to concentrate the gas, and hence the young stars, to the arm regions.

Lees, J. F.; Lo, K. Y.

1990-01-01

128

An Experimental Study of the Ionization of Low-Density Gas Flows by Induced Discharges  

NASA Technical Reports Server (NTRS)

Induced discharges are advantageous for ionizing low-density flows in that they introduce no electrode contamination into the flow and they provide a relatively high degree of ionization with good coupling of power into the gas. In this investigation a 40-megacycle oscillator was used to produce and maintain induced discharges in argon and mercury-vapor flows. Methods for preventing blowout of the discharge were determined, and power measurements were made with an in-line wattmeter. Some results with damped oscillations pulsed at 1,000 pulses per second are also presented.

Barger, R. L.; Brooks, J. D.; Beasley, W. D.

1960-01-01

129

A three-dimensional Monte Carlo photoionization code for modelling diffuse ionized gas  

NASA Astrophysics Data System (ADS)

We have developed a three-dimensional Monte Carlo photoionization code tailored for the study of Galactic HII regions and the percolation of ionizing photons in diffuse ionized gas. We describe the code, our calculation of photoionization, heating and cooling, and the approximations we have employed for the low-density HII regions we wish to study. Our code gives results in agreement with the Lexington HII region benchmarks. We show an example of a two-dimensional shadowed region and point out the very significant effect that diffuse radiation produced by recombinations of He has on the temperature within the shadow.

Wood, Kenneth; Mathis, John S.; Ercolano, Barbara

2004-03-01

130

DYNAMO - II. Coupled stellar and ionized-gas kinematics in two low-redshift clumpy discs  

NASA Astrophysics Data System (ADS)

We study the spatially resolved stellar kinematics of two star-forming galaxies at z ˜ 0.1 from the larger DYnamics of Newly Assembled Massive Objects (DYNAMO) sample. These galaxies, which have been characterized by high levels of star formation and large ionized-gas velocity dispersions, are considered possible analogues to high-redshift clumpy discs. They were observed using the Gemini Multi-Object Spectrograph instrument in integral field spectroscopy (IFS) mode at the Gemini Observatory with high spectral resolution (R ? 5400, equivalent to ? ? 24 km s-1 at the observed wavelengths) and ˜6 h exposure times in order to measure the resolved stellar kinematics via absorption lines. We also obtain higher quality emission-line kinematics than previous observations. The spatial resolution (1.2 kpc) is sufficient to show that the ionized gas in these galaxies (as traced by H? emission) is morphologically irregular, forming multiple giant clumps while stellar continuum light is smooth and well described by an exponential profile. Clumpy gas morphologies observed in IFS data are confirmed by complementary narrow-band H? imaging from the Hubble Space Telescope. Morphological differences between the stars and ionized gas are not reflected dynamically as stellar kinematics are found to be closely coupled to the kinematics of the ionized gas: both components are smoothly rotating with large velocity dispersions (˜40 km s-1) suggesting that the high gas dispersions are not primarily driven by star formation feedback. In addition, the stellar population ages of these galaxies are estimated to be quite young (60-500 Myr). The large velocity dispersions measured for these young stars suggest that we are seeing the formation of thick discs and/or stellar bulges in support of recent models which produce these from clumpy galaxies at high redshift.

Bassett, Robert; Glazebrook, Karl; Fisher, David B.; Green, Andrew W.; Wisnioski, Emily; Obreschkow, Danail; Cooper, Erin Mentuch; Abraham, Roberto G.; Damjanov, Ivana; McGregor, Peter J.

2014-08-01

131

Dielectrophoresis of ionized gas microbubbles: Dipole reversal due to diffusive double-layer polarization  

NASA Astrophysics Data System (ADS)

Gas bubbles generated by electrolysis reactions are shown to exhibit anomalous induced ac dipoles and dielectrophoretic behavior that cannot be described by classical Maxwell-Wagner theory. Normal charging and screening of conducting ionized gas in the gas-phase double layer are shown to render the bubble insulating at low ac field frequencies to affect negative dielectrophoresis. This screening effect couples with dielectric polarization at high frequencies to produce no crossover frequency for small bubbles and two crossover frequencies for bubbles larger than a critical size of 40 ?m. A double-layer theory accurately captures the two crossover frequencies and critical bubble size behavior.

Gagnon, Zachary R.; Chang, Hsueh-Chia

2008-12-01

132

Amonia gas: an improved reagent for chemical ionization mass spectrometry of bile acid methyl ester acetates  

SciTech Connect

The ammonia chemical ionization mass spectra of 28 methyl ester acetate derivatives of bile acids and related compounds have been determined by gas-liquid chromatography-mass spectrometry. Advantages of ammonia ionization over the previously studied isobutane ionization include a 130 to 270% enhancement in the sensitivity of base peak monitoring, and direct determination of molecular weight from the base peak (M + NH/sub 4//sup +/) in the mass spectrum of any of the derivatives. Minor ions in the ammonia spectra also allow selective detection of 3-keto compounds and can indicate unsaturation or double bond conjugation in the molecule. The significance of these studies for the detection and quantitation of bile acids is discussed. 2 tables.

DeMark, B.R.; Klein, P.D.

1981-01-01

133

Role of gas dynamics in negative ion formation in an atmospheric sampling glow discharge ionization source  

SciTech Connect

A version of the atmospheric sampling glow discharge ionization (ASGDI) source was developed to study the role of gas dynamics on anion formation. This source, which is used in conjunction with mass spectrometry for direct air monitoring, was designed so several key instrumental dimensions as well as operating parameters could be readily changed. Such flexibility permitted the study of ionization processes in ASGDI and the parameters that can be controlled to favor a particular ion product. One aspect of ASGDI that was found to influence ionization yield was the hydrodynamic properties of the sample inlet free-jet expansion. From these investigations, it was found that mean molecular flow of species expanding toward the skimmer could be manipulated to favor kinetically fast reactions over more thermodynamically preferred reactions. In the case of 2,4-dinitrotoluene, observation of the M[sup [minus

Chambers, D.M.; McLuckey, S.A.; Glish, G.L. (Oak Ridge National Lab., TN (United States))

1993-03-15

134

Generation of naphthoquinone radical anions by electrospray ionization: solution, gas-phase, and computational chemistry studies.  

PubMed

Radical anions are present in several chemical processes, and understanding the reactivity of these species may be described by their thermodynamic properties. Over the last years, the formation of radical ions in the gas phase has been an important issue concerning electrospray ionization mass spectrometry studies. In this work, we report on the generation of radical anions of quinonoid compounds (Q) by electrospray ionization mass spectrometry. The balance between radical anion formation and the deprotonated molecule is also analyzed by influence of the experimental parameters (gas-phase acidity, electron affinity, and reduction potential) and solvent system employed. The gas-phase parameters for formation of radical species and deprotonated species were achieved on the basis of computational thermochemistry. The solution effects on the formation of radical anion (Q(•-)) and dianion (Q(2-)) were evaluated on the basis of cyclic voltammetry analysis and the reduction potentials compared with calculated electron affinities. The occurrence of unexpected ions [Q+15](-) was described as being a reaction between the solvent system and the radical anion, Q(•-). The gas-phase chemistry of the electrosprayed radical anions was obtained by collisional-induced dissociation and compared to the relative energy calculations. These results are important for understanding the formation and reactivity of radical anions and to establish their correlation with the reducing properties by electrospray ionization analyses. PMID:21561138

Vessecchi, Ricardo; Naal, Zeki; Lopes, José N C; Galembeck, Sérgio E; Lopes, Norberto P

2011-06-01

135

Qualitative Gas Chromatography-Mass Spectrometry Analyses Using Amines as Chemical Ionization Reagent Gases  

NASA Astrophysics Data System (ADS)

Ammonia is a very useful chemical ionization (CI) reagent gas for the qualitative analyses of compounds by positive ion gas chromatography-mass spectrometry (GCMS). The gas is readily available, inexpensive, and leaves no carbon contamination in the MS source. Compounds of interest to our laboratory typically yield abundant protonated or ammoniated species, which are indicative of a compound's molecular weight. Nevertheless, some labile compounds fragment extensively by substitution and elimination reactions and yield no molecular weight information. In these cases, a CI reagent gas mixture of methylamine in methane prepared dynamically was found to be very useful in obtaining molecular weight data. Likewise, deuterated ammonia and deuterated methylamine are useful CI reagent gases for determining the exchangeable protons in organic compounds. Deuterated methylamine CI reagent gas is conveniently prepared by dynamically mixing small amounts of methylamine with excess deuterated ammonia.

Little, James L.; Howard, Adam S.

2013-12-01

136

STS-39 Critical Ionization Velocity (CIV) gas release from OV-103 payload bay  

NASA Technical Reports Server (NTRS)

A plume of nitrous oxide gas is released from a compressed gas canister mounted on the increased capacity adaptive payload carrier 1 (ICAPC-1) on the forward port side of Discovery's, Orbiter Vehicle (OV) 103's, payload bay (PLB). The gas release is part of the Critical Ionization Velocity (CIV) experiment conducted during STS-39. The Shuttle Pallet Satellite II (SPAS-II) 'parked' about two kilometers (km) away, is taking infrared, visible, and ultraviolet radiometric spatial, spectral, and temporal measurements of the gas plumes. Surrounding the CIV ICAPC-1 are: the ICAPC-2 payload support subsystem, radiometer, and Langmuir probe also mounted on the port side; the Space Test Payload 1 (STP-1) multipurpose experiment support structure (MPESS) (just beyond gas beam); and the Air Force Program 675 (AFP-675) experiment support structure (ESS).

1991-01-01

137

Gas-phase recombination, grain neutralization and cosmic-ray ionization in diffuse gas  

Microsoft Academic Search

Atomic ions are mostly neutralized by small grains (or PAH molecules) in current theories of heating and cooling in cool diffuse clouds; in the main they do not recombine with free electrons. This alters the ionization balance by depressing n(H+) and n(He+) while carbon generally remains nearly fully once-ionized: charge exchange with atomic oxygen and formation of H2 and OH

H. Liszt

2003-01-01

138

Ionized gas discs in elliptical and S0 galaxies at z < 1  

NASA Astrophysics Data System (ADS)

We analyse the extended, ionized-gas emission of 24 early-type galaxies (ETGs) at 0 < z < 1 from the ESO Distant Cluster Survey (EDisCS). We discuss different possible sources of ionization and favour star formation as the main cause of the observed emission. 10 galaxies have disturbed gas kinematics, while 14 have rotating gas discs. In addition, 15 galaxies are in the field, while 9 are in the infall regions of clusters. This implies that, if the gas has an internal origin, this is likely stripped as the galaxies get closer to the cluster centre. If the gas instead comes from an external source, then our results suggest that this is more likely acquired outside the cluster environment, where galaxy-galaxy interactions more commonly take place. We analyse the Tully-Fisher relation of the ETGs with gas discs, and compare them to EDisCS spirals. Taking a matched range of redshifts, MB < -20, and excluding galaxies with large velocity uncertainties, we find that, at fixed rotational velocity, ETGs are 1.7 mag fainter in MB than spirals. At fixed stellar mass, we also find that ETGs have systematically lower specific star formation rates than spirals. This study constitutes an important step forward towards the understanding of the evolution of the complex ISM in ETGs by significantly extending the look-back-time baseline explored so far.

Jaffé, Yara L.; Aragón-Salamanca, Alfonso; Ziegler, Bodo; Kuntschner, Harald; Zaritsky, Dennis; Rudnick, Gregory; Poggianti, Bianca M.; Hoyos, Carlos; Halliday, Claire; Demarco, Ricardo

2014-06-01

139

The quantification of synthetic corticosteroids using isotope dilution gas chromatography negative chemical ionization mass spectrometry.  

PubMed

Prednisolone, dexamethasone and betamethasone were labelled with deuterium via a simple synthetic procedure and used as internal standards in the gas chromatographic/mass spectrometric analysis of the corresponding undeuterated compounds. The mass spectrometer was used in the negative chemical ionization mode, which gave fragmentation of the methoxime trimethylsilyl ether derivatives favourable for their quantification. The method was applicable to the quantification of synthetic corticosteroids contained in human aqueous humour in the 0.1-10-ng range. PMID:3382802

Midgley, J M; Watson, D G; Healey, T; Noble, M

1988-05-01

140

TIME-VARYING FLAME IONIZATION SENSING APPLIED TO NATURAL GAS AND PROPANE BLENDS IN A PRESSURIZED LEAN PREMIXED (LPM) COMBUSTOR  

Microsoft Academic Search

In-situ monitoring of combustion phenomena is a critical need for optimal operation and control of advanced gas turbine combustion systems. The concept described in this paper is based on naturally occurring flame ionization processes that accompany the combustion of hydrocarbon fuels. Previous work has shown that flame ionization techniques may be applied to detect flashback, lean blowout, and some aspects

D. L. Straub; B. T. Chorpening; E. D. Huckaby; J. D. Thornton; W. L. Fincham

2008-01-01

141

Breakdown voltage reduction by field emission in multi-walled carbon nanotubes based ionization gas sensor  

NASA Astrophysics Data System (ADS)

Ionization gas sensors using vertically aligned multi-wall carbon nanotubes (MWCNT) are demonstrated. The sharp tips of the nanotubes generate large non-uniform electric fields at relatively low applied voltage. The enhancement of the electric field results in field emission of electrons that dominates the breakdown mechanism in gas sensor with gap spacing below 14 ?m. More than 90% reduction in breakdown voltage is observed for sensors with MWCNT and 7 ?m gap spacing. Transition of breakdown mechanism, dominated by avalanche electrons to field emission electrons, as decreasing gap spacing is also observed and discussed.

Saheed, M. Shuaib M.; Muti Mohamed, Norani; Arif Burhanudin, Zainal

2014-03-01

142

Ionized gas dynamics in the inner 2 pc of Sgr A West  

NASA Astrophysics Data System (ADS)

We present a data cube of the [NeII] (12.8 ?m) emission from the inner 2 pc of Sgr A West with 1? and 4 km s-1 resolution, and with substantially better SNR and velocity resolution than previous observations of the ionized gas. We compare the observations to two proposed models of the gas motions and distribution: flows along tidally stretched streamers, and more nearly circular motions with density wave compression. The density wave model provides a considerably better fit to the kinematics of the northern arm and western arc. Neither model fits the eastern arm and bar kinematics well.

Lacy, John H.; Irons, Wesley T.; Richter, Matthew J.

2014-05-01

143

H-alpha LEGUS: Unveiling the Interplay Between Stars, Star Clusters, and Ionized Gas  

NASA Astrophysics Data System (ADS)

We propose to obtain narrow-band, H-alpha observations for a significant subset of the star-forming, nearby galaxies recently targeted by the LEGUS treasury program {GO-13364}. LEGUS is observing these galaxies in five broad-band filters: NUV, U, B, V, and I. The new H-alpha observations will reveal thousands of previously undetected HII regions, including those ionized by stellar clusters and single massive stars, allow us to measure their luminosities and sizes, and to separate discrete sources from diffuse ionized gas. We will use our narrow-band imaging survey to: {1} establish the connection between star and cluster formation, and determine the prevelance with which isolated massive stars form in different galaxies; {2} determine whether the initial cluster mass function is universal; {3} investigate the size evolution of ionized gas bubbles, and how this depends on cluster age and mass, as well as on local galactic conditions; and {4} place stringent limits on the leakage of ionizing photons from HII regions, and better understand how the interplay between properties of the ionizing source and the morphology of the HII region impacts leakage. The broad goal of this study is to better understand how feedback from massive stars affects the surrounding medium. Ultimately, the interplay between feedback and the ISM on these scales will enable a better understanding of galaxy-scale outflows in the early universe, a process critical to galaxy evolution. This program naturally lends itself to an improvement of the scientific output by involving the general public via an already established Citizen Science program.;

Chandar, Rupali

2013-07-01

144

The Cygnus X region. XVI - The ionized gas behind the dark cloud between the North America and Pelican nebulae  

NASA Astrophysics Data System (ADS)

Radio recombination line observations are presented for the ionized gas at selected positions behind the dark cloud separating the North America and Pelican nebulae. The high angular resolution of about 3 arcmin makes it possible to sample the different structural components. The lines are dominated by ionized gas physically similar to that of the visible nebulae. A further extended background source is identified and briefly discussed in terms of an Ori A-type H II region in the Perseus spiral arm.

Heske, A.; Wendker, H. J.

1985-07-01

145

Atmospheric pressure ionization and gas phase ion mobility studies of isomeric dihalogenated benzenes using different ionization techniques  

NASA Astrophysics Data System (ADS)

Ion mobility spectrometry (IMS) featuring different ionization techniques was used to analyze isomeric ortho-, meta- and para-dihalogenated benzenes in order to assess how structural features affect ion formation and drift behavior. The structure of the product ions formed was investigated by atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) and IMS-MS coupling. Photoionization provided [M]+ ions for chlorinated and fluorinated compounds while bromine was cleaved from isomers of dibromobenzene and bromofluorobenzene. This ionization technique does not permit the different isomers to be distinguished. Comparable ions and additional clustered ions were obtained using 63Ni ionization. Depending on the chemical constitution, different clustered ions were observed in ion mobility spectra for the separate isomers of dichlorobenzene and dibromobenzene. Corona discharge ionization permits the most sensitive detection of dihalogenated compounds. Only clustered product ions were obtained. Corona discharge ionization enables the classification of different structural isomers of dichlorobenzene, dibromobenzene and bromofluorobenzene.

Borsdorf, H.; Nazarov, E. G.; Eiceman, G. A.

2004-03-01

146

GAS ACCRETION IS DOMINATED BY WARM IONIZED GAS IN MILKY WAY MASS GALAXIES AT z {approx} 0  

SciTech Connect

We perform high-resolution hydrodynamic simulations of a Milky Way mass galaxy in a fully cosmological setting using the adaptive mesh refinement code, Enzo, and study the kinematics of gas in the simulated galactic halo. We find that the gas inflow occurs mostly along filamentary structures in the halo. The warm-hot (10{sup 5} K 10{sup 6} K) ionized gases are found to dominate the overall mass accretion in the system (with M-dot = 3-5 M {sub Sun} yr{sup -1}) over a large range of distances, extending from the virial radius to the vicinity of the disk. Most of the inflowing gas (by mass) does not cool, and the small fraction that manages to cool does so primarily close to the galaxy (R {approx}< 100 kpc, with more pronounced cooling at smaller R), perhaps comprising the neutral gas that may be detectable as, e.g., high-velocity clouds. The neutral clouds are embedded within larger, accreting filamentary flows, and represent only a small fraction of the total mass inflow rate. The inflowing gas has relatively low metallicity (Z/Z {sub Sun} < 0.2). The outer layers of the filamentary inflows are heated due to compression as they approach the disk. In addition to the inflow, we find high-velocity, metal-enriched outflows of hot gas driven by supernova feedback. Our results are consistent with observations of halo gas at low z.

Joung, M. Ryan; Putman, Mary E.; Bryan, Greg L.; Fernandez, Ximena; Peek, J. E. G., E-mail: moo@astro.columbia.edu [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)

2012-11-10

147

Dense clumps of ionized gas near Pi Scorpii, as revealed by the fine-structure excitation of N II  

NASA Technical Reports Server (NTRS)

The column density and the emission of the ionized gas along the line of sight toward the B1 V + B2 V binary star Pi Sco are measured on the basis of the fine-structure absorption lines of the ground state N II. It is found that the bulk of this ionized gas must be clumped on a length scale of 0.025 pc, which is far smaller than the observed size of the diffuse H II region surrounding Pi Sco of about 6 pc. The observed column density of S III toward Pi Sco yields an upper limit on the distance of the absorbing, clumped gas from the star of less than about 0.02 pc, assuming that both the N II and S III absorption arise from the same gas. The possibility that the ionized gas originates from a photoevaporating circumstellar disk directly surrounding Pi Sco is excluded, since such a disk would have an unusual size of order 0.025 pc and would have had to survive for the estimated age of Pi Sco of 5-8 Myr. The derived mean density of the clumped gas is of order 40/cu cm, so that the gas is at a pressure that far exceeds the mean pressure in the H II region. It is concluded that the ionized gas could originate from evaporation flows off a cluster of compact neutral objects that evaporate due to the ionizing radiation of Pi Sco.

Bertoldi, Frank; Jenkins, Edward B.

1992-01-01

148

Ionization effects in the generation of wake-fields by ultra-high contrast femtosecond laser pulses in argon gas  

NASA Astrophysics Data System (ADS)

Difference in mechanisms of wake-field generation and electron self-injection by high contrast femtosecond laser pulses in an initially neutral Argon gas and in pre-ionized plasma without ionization is studied via 2D particle-in-cell simulations including optical ionization of the media. For shorter laser pulses, 40 fs, ionization results only in an increase of the charge of accelerated electrons by factor of ~3 with qualitatively the same energy distribution. For longer pulses, 80 fs, a more stable wake field structure is observed in the neutral gas with the maximal energy of the accelerated electrons exceeding that in the fixed density plasma. In higher density Argon, an ionizing laser pulse converts itself to a complex system of solitons at a self-induced, critical density ramp.

Makito, K.; Zhidkov, A.; Hosokai, T.; Shin, J.-H.; Masuda, S.; Kodama, R.

2012-10-01

149

Fabrication of gas ionization sensor based on titanium oxide nanotube arrays  

NASA Astrophysics Data System (ADS)

Gas sensors have been fabricated based on field ionization from titanium oxide nanotubes grown on titanium foil. Ordered nanaotube arrays of titanium oxides were grown by the anodization method. We measured breakdown voltages and discharge currents of the device for various gases. Our gas ionization sensors (GIS) presented good sensitivity, selectivity, and short response time. The GISs based on TiO2 nanotube arrays showed lower breakdown voltage, higher discharge current, and good selectivity. An excellent response observed for Ar compared to other gases. Besides, by introducing 2 % CO and 4 % H2 to N2 flow gas, the amount of breakdown voltage shifts about 20 and 70 volts to the lower values, respectively. The GIS works at room temperature and has the ability of detect inert gases with high stability and good linearity. Besides, short response time of about 1 second for the GISs based on TiO2 nanotube arrays makes them excellent for gas sensing applications. Sharp edges of the nanotubes, through enhancing the applied electric field, reduce operating voltage to the reasonable values and power consumption.

Nikfarjam, Alireza; Mohammadpour, Raheleh; Iraji zad, Azam

2014-06-01

150

Diffuse Ionized Gas in Irregular Galaxies. I. GR 8 and ESO 245-G05  

NASA Astrophysics Data System (ADS)

We have studied the spectral characteristics of the diffuse ionized gas (DIG) in two irregular galaxies with low metallicities and intermediate star formation rates: ESO 245-G05 and GR 8. The [O III]/H? ratio in these galaxies is higher than in the DIG of spiral galaxies but not as high as in other irregular galaxies previously studied, such as IC 10 and NGC 6822. The [N II]/H? and [S II]/H? ratios have very small values, indicating the absence of shocks as the ionization source for this gas. This ionization can be explained in both galaxies with photon leakage from the H II regions as the only source. The percentage of photons that have escaped from the H II regions is small in ESO 245-G05, only 35%, but varies from 35% up to 60% in GR 8. We also investigated whether the differences found between spiral and irregular galaxies in the [O III]/H? and the [N II]/H? ratios are due to differences in the metal content between these types of galaxies. Although the number of galaxies studied is not very large, it can be concluded that the [O III]/H? ratio is not related to the oxygen content, while the situation is more ambiguous for the [N II]/H? ratio.

Hidalgo-Gámez, A. M.

2006-04-01

151

A study of the ionized gas in Stephan's Quintet from integral field spectroscopy observations?  

NASA Astrophysics Data System (ADS)

Stephan's Quintet (SQ) is a famous interacting compact group of galaxies in an important stage of dynamical evolution, but surprisingly very few spectroscopic studies are found in the literature. We present optical integral field spectroscopy (IFS) observations of the SQ from the PPAK IFS Nearby Galaxies Survey, that provide a powerful way of studying with spatial resolution the physical characteristics of the ionized gas within the group. The nature of the gas emission is analysed using 2D maps of continuum-subtracted, pure emission-line intensities, stacked spectra, diagnostic diagrams, and photoionization model predictions. In the case of NGC 7319, we study the galaxy-wide high-velocity outflow emission by comparing the emission properties with theoretical shock and AGN models. We conclude that the excitation mechanism of the gas in this galaxy is a mixture of AGN photoionization and shocks with a photoionizing precursor. The emission spectra from the large-scale shock front in the interacting pair NGC 7318A/B is analysed, confirming the presence of several kinematic components. Comparison with predictions from theoretical shock models suggests that the gas emission is consistent with shocks without a photoionizing precursor, low pre-shock density, and velocities in the range of ˜200-400 km s-1. The gas oxygen abundance for NGC 7318B is determined using an updated O3N2 calibration. Although NGC 7317 shows no significant gas emission, an ionizing cluster is found southwest of this galaxy, probably the result of tidal interaction. As a by-product, we analyse the gas emission of the foreground galaxy NGC 7320.

Rodríguez-Baras, M.; Rosales-Ortega, F. F.; Díaz, A. I.; Sánchez, S. F.; Pasquali, A.

2014-07-01

152

Study of dust and ionized gas in early-type galaxies  

NASA Astrophysics Data System (ADS)

We present results of optical broad-band and narrow-band H? observations of a sample of forty nearby early-type galaxies. The majority of sample galaxies are known to have dust in various forms viz. dust lanes, nuclear dust and patchy/filamentary dust. A detailed study of dust was performed for 12 galaxies with prominent dust features. The extinction curves for these galaxies run parallel to the Galactic extinction curve, implying that the properties of dust in these galaxies are similar to those of the Milky-Way. The ratio of total to selective extinction (RV) varies between 2.1 and 3.8, with an average of 2.9 ± 0.2, fairly close to its canonical value of 3.1 for our Galaxy. The average relative grain size {}/{aGal} of dust particles in these galaxies turns out to be 1.01 ± 0.2, while dust mass estimated using optical extinction lies in the range ?102 to 104 M?. The H? emission was detected in 23 out of 29 galaxies imaged through narrow-band filters with the H? luminosities in the range 1038-1041 erg s-1. The mass of the ionized gas is in the range ?103-105 M?. The morphology and extent of ionized gas is found similar to those of dust, indicating possible coexistence of dust and ionized gas in these galaxies. The absence of any apparent correlation between blue luminosity and normalized IRAS dust mass is suggestive of merger related origin of dust and gas in these galaxies.

Kulkarni, Samridhi; Sahu, D. K.; Chaware, Laxmikant; Chakradhari, N. K.; Pandey, S. K.

2014-07-01

153

Ionized gas velocity dispersion in nearby dwarf galaxies: looking at supersonic turbulent motions  

NASA Astrophysics Data System (ADS)

We present the results of an ionized gas turbulent motions study in several nearby dwarf galaxies using a scanning Fabry-Perot interferometer with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). Combining the ‘intensity-velocity dispersion’ diagrams (?) with two-dimensional maps of radial velocity dispersion, we found a number of common patterns pointing to the relation between the value of chaotic ionized gas motions and processes of current star formation. In five out of the seven analysed galaxies, we identified expanding shells of ionized gas with diameters of 80-350 pc and kinematic ages of 1-4 Myr. We also demonstrate that the ? diagrams may be useful for the search of supernova remnants, other small expanding shells or unique stars in nearby galaxies. As an example, a candidate luminous blue variable (LBV) was found in UGC 8508. We propose some additions to the interpretation, previously used by Muñoz-Tuñón et al. to explain the ? diagrams for giant star formation regions. In the case of dwarf galaxies, a major part of the regions with high velocity dispersion belongs to the diffuse low surface brightness emission, surrounding the star-forming regions. We attribute this to the presence of perturbed low-density gas with high values of turbulent velocities around the giant H II regions. Based on observations obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The observations were carried out with the financial support of the Ministry of Education and Science of Russian Federation (contracts no. 16.518.11.7073 and 16.552.11.7028).

Moiseev, Alexei V.; Lozinskaya, Tatiana A.

2012-06-01

154

Ionized Gas in E/S0 Galaxies with Dust Lanes  

NASA Astrophysics Data System (ADS)

We present results from an ongoing program to study the properties of dust and ionized gas in E/S0 galaxies with dust lanes. Our observational program comprises of H-alpha and broad-band images obtained with the SAAO 1.9m, the VATT 1.8m and the 1m telescope on WO. A detailed analysis of 30 galaxies shows the presence of a diffusely distributed ionized gas component in most objects. The extended gas morphology is typically smooth and closely follows the dust structure, with a clear correlation between the mass of both components. The dust content in each galaxy is estimated by measuring the extinction by the extragalactic dust in the dark lanes. The derived extinction law is used to correct the measured colors for intrinsic dust extinction and the data are fitted with a stellar population synthesis model. We find that the line-emission and colors of most objects are consistent with the presence of an “old” stellar population ( 10 Gyr) and a small fraction of a “young” population ( 10- 100 Myr). The younger stellar population may have formed at a later stage of the evolution of the galaxy through either a merger event or a secondary star-formation burst. Strong evidence for the external origin of the ISM is provided by the apparent inclination of the dust and ionized gas disks with respect to the galactic plane in a large fraction of our sample galaxies. Further spectroscopic observations will be obtained to study the gaseous disks dynamics and to characterize the underlying stellar populations for evidence of multiple phases of star formation and assembly history.

Funes, Jose G.; J., S.; Finkelman, I.; Borsch, N.; Vaisanen, P.; Kniazev, A.

2011-01-01

155

The Level of Ionization and Chemical Composition of QSO BAL Region Gas - Repeat for Hopr 230  

NASA Astrophysics Data System (ADS)

FROM PROGRAM 5455: About 10% of all radio quiet QSOs exhibit broad absorption lines (BALs) in their spectra. The BALs come from a mostly highly ionized region outflowing from the central source at speeds up to many tens of thousands of km/s. Observational constraints on models require that the covering factor of the BAL region be small (e.g., normally < 0.2), therefore many QSOs must have BAL regions which do not lie along our lines-of-sight. For assumptions which should reasonably apply to BAL regions, accurate (algorithm independent) ionic column densities can be derived as a function of outflow velocity for BAL gas. This is unlike the case for broad emission lines in QSOs, which at any observed velocity originates in various components with a range of ionizations. Based on column density analyses, evidence suggests that the chemical composition of the BAL region gas is enhanced by factors of 10 to 100 or more times solar values. Since this conclusion is remarkable, we propose to carefully checked it. One possible problem is that our assumptions about the ability of BAL gas to cover the central source are not universally correct. Another problem with past analyses is that different ionic species of the same element in an object have not been studied. We will remedy these problems by observing the UV spectrum of three specially selected BAL QSOs which currently show the best evidence for enhanced abundances. Constraints on the ionization and chemical composition of the BAL region gas will be derived using Ferland's

Turnshek, David

1994-07-01

156

Multiple ionization of rare gas dimers by slow highly charged ions: screening effect during a collision  

NASA Astrophysics Data System (ADS)

Multiple ionization dynamics of rare gas dimers by slow highly charged ions has been investigated using the three-center Coulombic over-barrier model. The outermost electrons at two atomic sites in the dimer are sequentially removed by forming a quasi-molecule with a projectile, where partial screening is taken into account in the non-active site ionized during a collision. It is found that the fragment ion pair (Q,Q?) distribution is remarkably sensitive to the screening effect, which enhances the population of highly charge-asymmetric pairs such as (2,0) and (3,1). Recent measurement of the ion pair distribution in Ar9+ + Ar2 collisions is best reproduced with the present model by taking a screening parameter of s = 0.4.

Ohyama-Yamaguchi, Tomoko; Ichimura, Atsushi

2013-09-01

157

Electron capture and ionization of 33-TeV Pb ions in gas targets  

SciTech Connect

We have measured the total cross sections for electron capture by bare Pb{sup 82+} ions and for the ionization of hydrogenlike Pb{sup 81+}(1s) ions at 158GeV/A, {gamma}=168, in Ar, Kr, and Xe gas targets. At this energy, the total capture cross sections are dominated by electron capture from pair production. The capture measurements are compared with the results of several theoretical calculations and with similar measurements made with solid targets. The Pb{sup 81+}(1s) ionization cross sections obtained, which are substantially lower than those measured in solids, agree well with recent calculations that predict saturation at high energies from target screening effects.

Krause, H. F.; Vane, C. R.; Datz, S.; Grafstro''m, P.; Knudsen, H.; Mikkelsen, U.; Scheidenberger, C.; Schuch, R. H.; Vilakazi, Z.

2001-03-01

158

Ionized Gas Velocities from Multi-slit Spectroscopy for Nearby, Edge-on Galaxies  

NASA Astrophysics Data System (ADS)

Extra-planar (EP) gas in several spiral galaxies shows a decrease in rotational velocity with increasing height above the disk. The majority of this EP gas likely originates from disk-halo cycling driven by star formation in the disk via galactic fountains, which predict a lagging EP component. However, observations for a handful of galaxies show a steeper gradient than predicted by galactic fountains alone. A possible remedy for this is EP gas originating from infalling material, such as accreted satellites or the IGM. Accreted material with lower initial angular momentum than the disk could contribute to a steeper rotational velocity gradient. Studying the kinematics of EP gas can therefore provide constraints for how widespread accretion may be. We present optical observations and modeling of the ionized EP gas in our sample of 10 nearby, edge-on galaxies. For a subset of our targets, we compare our results to those from the HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) project. HALOGAS is WSRT deep HI survey studying cold gas accretion in the local universe. Our optical observations are from a multi-slit spectroscopic setup on the ARC 3.5m telescope, which allows us to measure velocities of Ha-emitting gas as a function of height above the disk in 11 radial distance bins in a single exposure. RW acknowledges support from NSF grant AST-0908126 and from a grant from Research Corporation for the Advancement of Science.

Wu, Catharine J.; Walterbos, R. A.; Rand, R. J.; Heald, G.; HALOGAS Team

2014-01-01

159

Imaging spectrophotometry of ionized gas in NGC 1068. I. Kinematics of the narrow-line region  

SciTech Connect

The kinematics of collisionally excited forbidden N II 6548, 6583 across the inner 1 arcmin diameter of the nearby Seyfert galaxy NGC 1068 is mapped using an imaging Fabry-Perot interferometer and low-noise CCD. The stack of monochromatic images, which spatially resolved the high-velocity gas, was analyzed for kinematic and photometric content. Profiles agree well with previous long-slit work, and their complete spatial coverage makes it possible to constrain the gas volume distribution. It is found that the narrow-line region is distributed in a thick center-darkened, line-emitting cylinder that envelopes the collimated radio jet. Three distinct kinematic subsystems, of which the cylinder is composed, are discussed in detail. Detailed behavior of the emission-line profiles, at the few points in the NE quadrant with simple kinematics, argues that the ionized gas develops a significant component of motion perpendicular to the jet axis. 67 refs.

Cecil, G.; Bland, J.; Tully, R.B. (Institute for Advanced Study, Princeton, NJ (USA) Hawaii Univ., Honolulu (USA))

1990-05-01

160

OI and OIII in Sgr A: neutral and ionized gas at the Galactic center  

SciTech Connect

We have mapped the /sup 3/P/sub 1/-/sup 3/P/sub 2/ fine structure line emission at 63 microns from neutral oxygen in the vicinity of the galactic center. The emission is extended over more than 4' and is centered on Sgr A West. We conclude that the bulk of the OI emission arises in a predominantly neutral region outside of the ionized central 3 pc of our galaxy. Assuming that the oxygen is collisionally excited by neutral hydrogen impact, we estimate that the gas temperatures in this region are >130K, that is, significantly higher than the dust temperature of 70K. The OI line center velocities change systematically along the galactic plane in a manner consistent with galactic rotation. However, the unusual velocity distribution and linewidths suggest that the motions have a large noncircular component and that there are large scale inhomogeneities in the OI-emitting gas. We also have detected the 88 micron /sup 3/P/sub 1/-/sup 3/P/sub 0/ fine structure line of OIII in a 45triangle-solid FWHM beam centered on Sgr A West. The ratio of this line intensity to that of 52 micron /sup 3/P/sub 2/-/sup 3/P/sub 1/ line indicates that most of the ionized gas in this region has electron density >10/sup 4/ cm/sup -3/.

Genzel, R.; Watson, D.; Townes, C.; Lester, D.; Dinerstein, H.; Werner, M.; Storey, J.

1982-05-01

161

Ionized gas outflow in the isolated S0 galaxy NGC 4460  

NASA Astrophysics Data System (ADS)

We used integral-field and long-slit spectroscopy to study a bright extended nebulosity recently discovered in the isolated lenticular galaxy NGC 4460 during an H? survey of nearby galaxies. An analysis of archival Sloan Digital Sky Survey, GALEX and Hubble Space Telescope images indicates that current star formation is entirely concentrated in the central kiloparsec of the galaxy disc. The observed ionized gas parameters (morphology, kinematics and ionization state) can be explained by a gas outflow above the plane of the galaxy, caused by star formation in the circumnuclear region. Galactic wind parameters in NGC 4460 (outflow velocity, total kinetic energy) are several times smaller, compared with the known galactic wind in NGC 253, which is explained by the substantially lower total star formation rate. We discuss the cause of the star formation processes in NGC 4460 and in two other known isolated lenticular (S0) and elliptical (E) galaxies of the Local Volume: NGC 404 and 855. We provide evidence suggesting that the feeding of isolated galaxies by intergalactic gas on a cosmological time-scale is a steady process without significant variations. Based on observations collected with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, which is operated under the financial support of the Science Department of Russia (registration number 01-43). E-mail: moisav@gmail.com

Moiseev, Alexei; Karachentsev, Igor; Kaisin, Serafim

2010-04-01

162

Highly ionized atoms in cooling gas. [in model for cooling of hot Galactic corona  

NASA Technical Reports Server (NTRS)

The ionization of low density gas cooling from a high temperature was calculated. The evolution during the cooling is assumed to be isochoric, isobaric, or a combination of these cases. The calculations are used to predict the column densities and ultraviolet line luminosities of highly ionized atoms in cooling gas. In a model for cooling of a hot galactic corona, it is shown that the observed value of N(N V) can be produced in the cooling gas, while the predicted value of N(Si IV) falls short of the observed value by a factor of about 5. The same model predicts fluxes of ultraviolet emission lines that are a factor of 10 lower than the claimed detections of Feldman, Bruna, and Henry. Predictions are made for ultraviolet lines in cooling flows in early-type galaxies and clusters of galaxies. It is shown that the column densities of interest vary over a fairly narrow range, while the emission line luminosities are simply proportional to the mass inflow rate.

Edgar, Richard J.; Chevalier, Roger A.

1986-01-01

163

Non-equilibirum ionization and cooling of metal-enriched gas in the presence of a photoionization background  

NASA Astrophysics Data System (ADS)

Simulations of the formation of galaxies, as well as ionization models used to interpret observations of quasar absorption lines, generally either assume ionization equilibrium or ignore the presence of the extragalactic background (EGB) radiation. We introduce a method to compute the non-equilibrium ionization and cooling of diffuse gas exposed to the EGB. Our method iterates the ionization states of the 11 elements that dominate the cooling (H, He, C, N, O, Ne, Si, Mg, S, Ca and Fe) and uses tabulated ion-by-ion cooling and photo-heating efficiencies to update the temperature of the gas. Our reaction network includes radiative and di-electric recombination, collisional ionization, photoionization, Auger ionization and charge transfer. We verify that our method reproduces published results for collisional equilibrium, collisional non-equilibrium and photoionized equilibrium. Non-equilibrium effects can become very important in cooling gas, particularly below 106 K. Photoionization and non-equilibrium effects both tend to boost the degree of ionization and to reduce cooling efficiencies. The effect of the EGB is larger for lower densities (i.e. higher ionization parameters). Hence, photoionization affects (equilibrium and non-equilibrium) cooling more under isochoric than under isobaric conditions. Non-equilibrium effects are smaller in the presence of the EGB and are thus overestimated when using collisional-only processes. The inclusion of the EGB alters the observational diagnostics of diffuse, metal-enriched gas (e.g. metal absorption lines probed in quasar sight lines) even more significantly than the cooling efficiencies. We argue that the cooling efficiency should be considered if ionization models are used to infer physical conditions from observed line ratios, as the a priori probability of observing gas is lower if its cooling time is shorter. We provide online tables of ionization fractions and cooling efficiencies, as well as other data, for equilibrium and non-equilibrium scenarios, and both with and without an EGB. Cooling efficiencies and diagnostics of the physical state of diffuse gas can become highly inaccurate if ionization equilibrium is assumed or if the existence of the ionizing background is ignored.

Oppenheimer, Benjamin D.; Schaye, Joop

2013-09-01

164

Can the Lyman Continuum Leaked Out of H II Regions Explain Diffuse Ionized Gas?  

NASA Astrophysics Data System (ADS)

We present an attempt to explain the diffuse H? emission of a face-on galaxy M 51 with the "standard" photoionization model, in which the Lyman continuum (Lyc) escaping from H II regions propagates large distances into the diffuse interstellar medium (ISM). The diffuse H? emission of M 51 is analyzed using thin slab models and exponential disk models in the context of the "on-the-spot" approximation. The scale height of the ionized gas needed to explain the diffuse H? emission with the scenario is found to be of the order of ~1-2 kpc, consistent with those of our Galaxy and edge-on galaxies. The model also provides a vertical profile, when the galaxy is viewed edge-on, consisting of two-exponential components. However, it is found that an incredibly low absorption coefficient of ?0 ? 0.4-0.8 kpc-1 at the galactic plane, or, equivalently, an effective cross section as low as ?eff ~ 10-5 of the photoionization cross section at 912 Å is required to allow the stellar Lyc photons to travel through the H I disk. Such a low absorption coefficient is out of accord with the properties of the ISM. Furthermore, we found that even the model that has the diffuse ionized gas (DIG) phase only and no H I gas phase shows highly concentrated H? emissions around H II regions, and can account for only lsim26% of the H? luminosity of the DIG. This result places a strong constraint on the ionizing source of the DIG. We also report that the H? intensity distribution functions not only of the DIG, but also of H II regions in M 51, appear to be lognormal.

Seon, Kwang-Il

2009-09-01

165

Development of a resonant laser ionization gas cell for high-energy, short-lived nuclei  

NASA Astrophysics Data System (ADS)

A new laser ion source configuration based on resonant photoionization in a gas cell has been developed at RIBF RIKEN. This system is intended for the future PArasitic RI-beam production by Laser Ion-Source (PALIS) project which will be installed at RIKEN's fragment separator, BigRIPS. A novel implementation of differential pumping, in combination with a sextupole ion beam guide (SPIG), has been developed. A few small scroll pumps create a pressure difference from 1000 hPa-10-3 Pa within a geometry drastically miniaturized compared to conventional systems. This system can utilize a large exit hole for fast evacuation times, minimizing the decay loss for short-lived nuclei during extraction from a buffer gas cell, while sufficient gas cell pressure is maintained for stopping high energy RI-beams. In spite of the motion in a dense pressure gradient, the photo-ionized ions inside the gas cell are ejected with an assisting force gas jet and successfully transported to a high-vacuum region via SPIG followed by a quadrupole mass separator. Observed behaviors agree with the results of gas flow and Monte Carlo simulations.

Sonoda, T.; Wada, M.; Tomita, H.; Sakamoto, C.; Takatsuka, T.; Furukawa, T.; Iimura, H.; Ito, Y.; Kubo, T.; Matsuo, Y.; Mita, H.; Naimi, S.; Nakamura, S.; Noto, T.; Schury, P.; Shinozuka, T.; Wakui, T.; Miyatake, H.; Jeong, S.; Ishiyama, H.; Watanabe, Y. X.; Hirayama, Y.; Okada, K.; Takamine, A.

2013-01-01

166

Monte Carlo simulation of charged particle diffusion through an ionized gas: contributions of simultaneous multiple collisions  

NASA Astrophysics Data System (ADS)

When a charged particle moves through fully or partially ionized plasmas, energy loss and momentum transfer occur through various kinds of elastic and inelastic collisions. In ordinary gases, composed primarily of neutral particles, the interactions are mainly close binary collisions, being the impact parameter well shorter than the mean free path. In a gas composed of charged particles, neglecting simultaneous multiple collisions can be a very poor approximation because the electromagnetic forces decrease much more slowly with distance than do the forces between neutral atoms. Here we present a Monte Carlo code, where the effects of large impact parameter multiple scattering are considered.

Molinari, V.; Teodori, F.

2004-01-01

167

Filling factors and scale heights of the diffuse ionized gas in the Milky Way  

NASA Astrophysics Data System (ADS)

The combination of dispersion measures of pulsars, distances from the model of Cordes & Lazio (\\cite{cordes+lazio02}) and emission measures from the WHAM survey enabled a statistical study of electron densities and filling factors of the diffuse ionized gas (DIG) in the Milky Way. The emission measures were corrected for absorption and contributions from beyond the pulsar distance. For a sample of 157 pulsars at |b|>5° and 60° < ? < 360°, located in mainly interarm regions within about 3 kpc from the Sun, we find that: (1) The average volume filling factor along the line of sight /line{f}v and the mean density in ionized clouds /line{n}c are inversely correlated: /line{f}v(/line{n}c ) = (0.0184± 0.0011) /line{n}c{ -1.07± 0.03} for the ranges 0.03 < /line{n}c < 2 {cm-3 and 0.8 > /line{f}v > 0.01. This relationship is very tight. The inverse correlation of /line{f}v and /line{n}c causes the well-known constancy of the average electron density along the line of sight. As /line{f}v(z) increases with distance from the Galactic plane |z|, the average size of the ionized clouds increases with |z|. (2) For |z| < 0.9 kpc the local density in clouds nc (z) and local filling factor f(z) are inversely correlated because the local electron density ne (z) = f(z) nc (z) is constant. We suggest that f(z) reaches a maximum value of >0.3 near |z| = 0.9 kpc, whereas nc (z) continues to decrease to higher |z|, thus causing the observed flattening in the distribution of dispersion measures perpendicular to the Galactic plane above this height. (3) For |z| < 0.9 kpc the local distributions nc (z), f(z) and ne2(z) have the same scale height which is in the range 250 < h ? 500 pc. (4) The average degree of ionization of the warm atomic gas /line{I}w (z) increases towards higher |z| similarly to /line{f}v (z). Towards |z| = 1 kpc, /line{f}v (z) = 0.24± 0.05 and /line{I}w (z) = 0.24± 0.02. Near |z| = 1 kpc most of the warm, atomic hydrogen is ionized.

Berkhuijsen, E. M.; Mitra, D.; Mueller, P.

2006-01-01

168

Isothermal flow measurements in a gas turbine combustor using a fast flame ionization detector  

NASA Astrophysics Data System (ADS)

A fast-response flame ionization detector (FFID) has been used to study isothermal gas transport and mixing inside a gas turbine combustion chamber. The large, highly linear dynamic range of the FFID coupled with a frequency response that extends up to approximately 200 Hz can reveal large-scale features of interest in turbulent flows. Experiments were performed in a ground-based test facility simulating high-altitude restart conditions. Pulses of propane were discharged into the core swirler of a fuel injector through a high-speed valve. The mole fraction of this tracer was monitored at various locations inside the combustion chamber. These measurements allowed the identification of recirculation timescales and flow instabilities at different points inside the combustion chamber, providing important insights into the altitude restart process.

Read, R. W.; Hochgreb, S.

2010-05-01

169

Interrelated structures of the transport shock and collisional relaxation layer in a multitemperature, multilevel ionized gas  

NASA Technical Reports Server (NTRS)

The gas dynamic structures of the transport shock and the downstream collisional relaxation layer are evaluated for partially ionized monatomic gases. Elastic and inelastic collisional nonequilibrium effects are taken into consideration. Three electronic levels are accounted for in the microscopic model of the atom. Nonequilibrium processes with respect to population of levels and species plus temperature are considered. By using an asymptotic technique the shock morphology is found on a continuum flow basis. The asymptotic procedure gives two distinct layers in which the nonequilibrium effects to be considered are different. A transport shock appears as the inner solution to an outer collisional relaxation layer in which the gas reaches local equilibrium. A family of numerical examples is displayed for different flow regimes. Argon and helium models are used in these examples.

Vinolo, A. R.; Clarke, J. H.

1972-01-01

170

The ionization of the emission-line gas in young radio galaxies  

NASA Astrophysics Data System (ADS)

This paper is the second in a series in which we present intermediate-resolution, wide-wavelength coverage spectra for a complete sample of 14 compact radio sources, taken with the aim of investigating the impact of the nuclear activity on the circumnuclear interstellar medium (ISM) in the early stages of radio source evolution. In the first paper (Holt, Tadhunter & Morganti), we presented the kinematic results from the nuclear emission-line modelling and reported fast outflows in the circumnuclear gas. In this paper, we use the line fluxes to investigate the physical conditions and dominant ionization mechanisms of the emission-line gas. We find evidence for large electron densities and high reddening in the nuclear regions, particularly in the broader, blueshifted components. These results are consistent with the idea that the young, recently triggered radio sources still reside in dense and dusty cocoons deposited by the recent activity triggering event (merger/interaction). In addition, we find that the quiescent nuclear and extended narrow components are consistent with active galactic nucleus (AGN) photoionization, split between simple-slab AGN photoionization and mixed-medium photoionization models. For the nuclear broader and shifted components, the results are less clear. Whilst there are suggestions that the broader components may be closer to shock plus precursor models on the diagnostic diagrams, and that the electron temperatures and densities are high, we are unable to unambiguously distinguish the dominant ionization mechanism using the optical emission-line ratios. This is surprising given the strong evidence for jet-cloud interactions (broad emission lines, large outflow velocities and strong radio-optical alignments), which favours the idea that the warm gas has been accelerated in shocks driven by the radio lobes expanding through a dense cocoon of gas deposited during the triggering event.

Holt, J.; Tadhunter, C. N.; Morganti, R.

2009-12-01

171

Gas kinematics and ionization along the extended sight line to HD 116852  

NASA Technical Reports Server (NTRS)

We present Goddard High-Resolution Spectrograph intermediate observations of the interstellar medium toward HD 116852, a low halo star at a distance of 4.8 kpc (z = -1.3 kpc) in the direction l = 304. deg 9, b = 16.deg 1. The small science aperture observations have signal-to-noise ratios ranging from 30 to 90 and resolutions of 11 to 18 km/s (FWHM). We confirm the optical MK classification of this star through an analysis of its ultraviolet photosperic and stellar wind profiles. We detect interstellar lines of Al III, Si IV, C IV, and N V together with lines of C I, C I*, C I**, Si II, Ge II, P II, and Ni II. We convert the Mg II, P II, S II, Al III, Si IV, C IV, and N V profiles into measure of apparent column density as a function of LSR velocity. Gas scale height, velocity dispersion, and differential Galactic rotation effects govern the profile shapes. A simple computer model of the expected sight line column density profiles for the low and high ion species indicates that the gas velocity dispersions and scale heights increase as the ionization level of the gas increases. We find scale heigts H greater than or = 1 kpc for the high ions, which are comparable to the z-distance of the star, whereas we find H approximatley = 0.6 to 0.7 kpc for A1 III and H approximatley 0.1 kpc for P II and Ge II. An enhancement in the Al II profile near -15 km/s accounts for approximately 25% of the A1 III column along the sight line and probably arises within gas located approximately 500 pc below the Sagittarius-Carina spiral arm link. Portions of the broad underlying A1 III distribution are associated with the higher ionization lines, perhaps in conductive interfaces. The presence of N V and the column density ratios of Si IV, C IV, and N V favor the interpretation that much of the high ion absorption is produced by collisional ionization in gas with T = 1-3 x 10(exp 5) K. An enhancement near -35 km/s in both the Si IV and C IV profiles may be due to an outflow from the Norma spiral arm at a z-distance of about -1 kpc. The smooth decrease of the N(C IV)/N(Si IV) ratio at negative velocities may be due to an ISM ionization structure for hot gas that changes distance from the Galactic plane or to a two phase gas distribution in which the relative contribution from each phase changes with distance from the Galactic plane.

Sembach, Kenneth R.; Savage, Blair D.

1994-01-01

172

Numerical models for the diffuse ionized gas in galaxies. I. Synthetic spectra of thermally excited gas with turbulent magnetic reconnection as energy source  

NASA Astrophysics Data System (ADS)

Aims: The aim of this work is to verify whether turbulent magnetic reconnection can provide the additional energy input required to explain the up to now only poorly understood ionization mechanism of the diffuse ionized gas (DIG) in galaxies and its observed emission line spectra. Methods: We use a detailed non-LTE radiative transfer code that does not make use of the usual restrictive gaseous nebula approximations to compute synthetic spectra for gas at low densities. Excitation of the gas is via an additional heating term in the energy balance as well as by photoionization. Numerical values for this heating term are derived from three-dimensional resistive magnetohydrodynamic two-fluid plasma-neutral-gas simulations to compute energy dissipation rates for the DIG under typical conditions. Results: Our simulations show that magnetic reconnection can liberate enough energy to by itself fully or partially ionize the gas. However, synthetic spectra from purely thermally excited gas are incompatible with the observed spectra; a photoionization source must additionally be present to establish the correct (observed) ionization balance in the gas.

Hoffmann, T. L.; Lieb, S.; Pauldrach, A. W. A.; Lesch, H.; Hultzsch, P. J. N.; Birk, G. T.

2012-08-01

173

Development of a portable greenhouse gas analyzer based on Penning ionization electron spectroscopy (PIES) in a pulsed glow discharge plasma  

NASA Astrophysics Data System (ADS)

A greenhouse gas (GHG) analyzer currently under development at Lenterra, Inc. is described which utilizes Penning ionization electron spectroscopy (PIES) in a glow discharge plasma. A population of helium metastable atoms (2^3S, 19.8 eV) is produced in a pulsed (50 ?s duration, 5 kHz rep rate) glow discharge in helium/analyte gas mixtures. In the afterglow electrons are produced due to Penning ionization of GHG analyte molecules (including carbon dioxide and methane) by the helium metastables. These electrons possess energies equal to the energy stored in the helium metastable minus the ionization potential of the analyte molecule. Electron energy spectra are measured using the current-voltage characteristic obtained during the afterglow with a swept-voltage collector electrode. These spectra exhibit peaks that allow for the determination of the ionization potential of each analyte, and therefore selective gas detection. Experimental results are presented and components of the portable PIES device are described, including the glow discharge apparatus, as well as a carbon nanotube gas micro-concentrator and a micro gas chromatography column.

Denning, C. Mark; Stepaniuk, Vadim; Sheverev, Valery

2009-10-01

174

Measurement of photon flux with a miniature gas ionization chamber in a Material Testing Reactor  

NASA Astrophysics Data System (ADS)

Nuclear heating measurements in Material Testing Reactors (MTR) are crucial for the design of the experimental devices and the prediction of the temperature of the hosted samples. Nuclear heating in MTR materials (except fuel) is mainly due to the energy deposition by the photon flux. Therefore, the photon flux is a key input parameter for the computer codes which simulate nuclear heating and temperature reached by samples/devices under irradiation. In the Jules Horowitz MTR under construction at the CEA Cadarache, the maximal expected nuclear heating levels will be about 15 to 18 W g-1 and it will be necessary to assess this parameter with the best accuracy. An experiment was performed at the OSIRIS reactor to combine neutron flux, photon flux and nuclear heating measurements to improve the knowledge of the nuclear heating in MTR. There are few appropriate sensors for selective measurement of the photon flux in MTR even if studies and developments are ongoing. An experiment, called CARMEN-1, was conducted at the OSIRIS MTR and we used in particular a gas ionization chamber based on miniature fission chamber design to measure the photon flux. In this paper, we detail Monte-Carlo simulations to analyze the photon fluxes with ionization chamber measurements and we compare the photon flux calculations to the nuclear heating measurements. These results show a good accordance between photon flux measurements and nuclear heating measurement and allow improving the knowledge of these parameters.

Fourmentel, D.; Filliatre, P.; Villard, J. F.; Lyoussi, A.; Reynard-Carette, C.; Carcreff, H.

2013-10-01

175

Fabrication of gas sensor based on field ionization from SWCNTs with tripolar microelectrode  

NASA Astrophysics Data System (ADS)

We report the nanofabrication of a sulfur dioxide (SO2) sensor with a tripolar on-chip microelectrode utilizing a film of single-walled carbon nanotubes (SWCNTs) as the field ionization cathode, where the ion flow current and the partial discharge current generated by the field ionization process of gaseous molecules can be gauged to gas species and concentration. The variation of the sensitivity is less than 4% for all of the tested devices, and the sensor has selectivity against gases such as He, NO2, CO, H2, SO2 and O2. Further, the sensor response presents well-defined and reproducible linear behavior with regard to concentration in the range investigated and a detection limitation of <˜0.5 ppm for SO2. More importantly, a tripolar on-chip microelectrode with SWCNTs as a cathode exhibits an impressive performance with respect to stability and anti-oxidation behavior, which are significantly better than had been possible before in the traditional bipolar sensor under explicit circumstances at room temperature.

Cai, Shengbing; Zhang, Yong; Duan, Zhemin

2012-12-01

176

Determination of Residual Epichlorohydrin in Sevelamer Hydrochloride by Static Headspace Gas Chromatography with Flame Ionization Detection  

PubMed Central

A sensitive static headspace gas chromatographic method was developed and validated for the determination of residual epichlorohydrin (ECH) in sevelamer hydrochloride (SVH) drug substance. This method utilized a Phenomenex Zebron ZB-WAX GC column, helium as carrier gas with flame ionization detection. The critical experimental parameters, such as, headspace vial incubation time and incubation temperature were studied and optimized. The method was validated as per United States Pharmacopoeia (USP) and International Conference on Harmonization (ICH) guidelines in terms of detection limit (DL), quantitation limit (QL), linearity, precision, accuracy, specificity and robustness. A linear range from 0.30 to 10 ?g/mL was obtained with the coefficient of determination (r2) 0.999. The DL and QL of ECH were 0.09 ?g/mL and 0.30 ?g/mL, respectively. The recovery obtained for ECH was between 91.7 and 96.6%. Also, the specificity of the method was proved through gas chromatography mass spectrometry (GC-MS). This method was applied successfully to determine the content of residual ECH in SVH bulk drug.

Karthikeyan, Kaliaperumal; Arularasu, Govindasamy T.; Devaraj, Perumalsamy; Pillai, Karnam Chandrasekara

2010-01-01

177

Detection of traces of formaldehyde in pure air by gas chromatography and helium ionization detection.  

PubMed

The sensitive helium ionization detector (HID) was used for the direct determination of ppm to ppb levels of formaldehyde in air. Two methods to generate formaldehyde in an air stream were evaluated. The first method utilized a paraformaldehyde permeation tube and the second utilized a motor driven syringe and a dilute solution of formaldehyde. The two methods were evaluated using gas chromatography with HID and spectrophotometry. The paraformaldehyde permeation tube generates only about 60% of the theoretical value, while the motor driven syringe was accurate for levels below 2 ppm; however, at a concentration of 13 ppm or above, oligomers or other chemical forms of CH2O are formed to decrease the concentration of gaseous CH2O produced. PMID:6501532

Andrawes, F F

1984-11-01

178

Prediction of gas chromatography flame ionization detector response factors from molecular structures  

SciTech Connect

The prediction of flame ionization detector response factors as a function of molecular structure components is evaluated with modern capillary column gas chromatography equipment that included an on-column injector. The effect on the standard carbon content based response by electronegative atoms is analyzed for various functional groups. This study updates much earlier work that characterized the decrease in signal response by using average correction factors for each functional group. The effective carbon number concept based on naphthalene as the internal standard was used. For 56 compounds containing a single functional group, predictions based on these average responses reproduced the actual response to within 1.7% on average. This model was then extended to bifunctional groups with similar success for several molecules. The effects of changes in temperature programming and concentration were found to be minimal within the range studied.

Jorgensen, A.D. (Univ. of Toledo, OH (USA)); Picel, K.C.; Stamoudis, V.C. (Argonne National Laboratory, IL (USA))

1990-04-01

179

Identification of volatiles by headspace gas chromatography with simultaneous flame ionization and mass spectrometric detection.  

PubMed

Volatiles are frequently abused as inhalants. The methods used for identification are generally nonspecific if analyzed concurrently with ethanol or require an additional analytical procedure that employs mass spectrometry. A previously published technique utilizing a capillary flow technology splitter to simultaneously quantitate and confirm ethyl alcohol by flame ionization and mass spectrometric detection after headspace sampling and gas chromatographic separation was evaluated for the detection of inhalants. Methanol, isopropanol, acetone, acetaldehyde, toluene, methyl ethyl ketone, isoamyl alcohol, isobutyl alcohol, n-butyl alcohol, 1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane (Norflurane, HFC-134a), chloroethane, trichlorofluoromethane (Freon®-11), dichlorodifluoromethane (Freon®-12), dichlorofluoromethane (Freon®-21), chlorodifluoromethane (Freon®-22) and 1,2-dichlorotetrafluoroethane (Freon®-114) were validated for qualitative identification by this method. The validation for qualitative identification included evaluation of matrix effects, sensitivity, carryover, specificity, repeatability and ruggedness/robustness. PMID:24005155

Tiscione, Nicholas B; Yeatman, Dustin Tate; Shan, Xiaoqin; Kahl, Joseph H

2013-10-01

180

The Effect of the Argon Carrier Gas in the Multiphoton Dissociation-Ionization of Tetracene  

PubMed Central

The multiphoton dissociation-ionization of tetracene at 355 nm using 6.5 nanosecond laser pulses, with and without argon as a carrier gas (CG), has been studied and compared. Ion fragments were analyzed in a time-of-flight mass spectrometer and separated according to their mass-to-charge ratio (m/z). The results show that the dynamic of photodissociation at ?1010 W cm?2 intensities is strongly influenced by the CG. The suppression of fragmentation channels primarily those relating to the formation of the CHm+ (m = 2, 4), C2H4+ and C5H4+2 ions. CH5+ and CH6+ were observed which have not been reported before in photodissociation tetracene experiments.

Poveda, Juan Carlos; Roman, Alejandro San; Guerrero, Alfonso; Alvarez, Ignacio; Cisneros, Carmen

2008-01-01

181

Determination of 17 ?-Estradiol in Rabbit Plasma by Gas Chromatography with Flame Ionization Detection  

PubMed Central

This article describes gas chromatography-flame ionization detection method for determination of 17 ?-estradiol in rabbit plasma. 17 ?-estradiol and internal standard progesterone were extracted from plasma using liquid–liquid extraction method. Linearity was found between 0.25 and 20 ?g/ml (r2=0.994) for plasma samples. Intra-day and inter-day precision, expressed as the relative standard deviation were less than 5.5%, and accuracy (relative error) was less than 3.5%. The mean recovery of 17 ?-estradiol samples was 94.4%. The limits of detection and quantification of method for plasma samples were 0.10 ?g/ml and 0.15 ?g/ml, respectively. Also, clinically used other 10 drugs were investigated to check for potential interferences and the method was successfully applied to the determination of 17 ?-estradiol in New Zealand white rabbits.

Yilmaz, B; Kadioglu, Y.

2012-01-01

182

A reservoir of ionized gas in the galactic halo to sustain star formation in the Milky Way.  

PubMed

Without a source of new gas, our Galaxy would exhaust its supply of gas through the formation of stars. Ionized gas clouds observed at high velocity may be a reservoir of such gas, but their distances are key for placing them in the galactic halo and unraveling their role. We have used the Hubble Space Telescope to blindly search for ionized high-velocity clouds (iHVCs) in the foreground of galactic stars. We show that iHVCs with 90 ? |v(LSR)| ? 170 kilometers per second (where v(LSR) is the velocity in the local standard of rest frame) are within one galactic radius of the Sun and have enough mass to maintain star formation, whereas iHVCs with |v(LSR)| ? 170 kilometers per second are at larger distances. These may be the next wave of infalling material. PMID:21868626

Lehner, Nicolas; Howk, J Christopher

2011-11-18

183

Determination of BROMATE AT PARTS-PER-TRILLION LEVELS BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY WITH NEGATIVE CHEMICAL IONIZATION  

EPA Science Inventory

The ozonation of bromide-containing source waters produces bromate as a class 2B carcinogenic disinfection by-product. The present work describes the determination of bromate by gas chromatography-negative chemical ionization mass spectrometry (GC-NCIMS) following a bromate react...

184

Highly Ionized High-Velocity Gas in the Vicinity of the Galaxy  

NASA Astrophysics Data System (ADS)

We report the results of a FUSE study of high-velocity O VI absorption along complete sight lines through the Galactic halo in directions toward 100 extragalactic objects and two halo stars. The high-velocity O VI traces a variety of phenomena, including tidal interactions with the Magellanic Clouds, accretion of gas, outflowing material from the Galactic disk, warm/hot gas interactions in a highly extended Galactic corona, and intergalactic gas in the Local Group. We identify 84 high-velocity O VI features at >=3 ? confidence at velocities of -500=13.95+/-0.34 with a median value of 13.97. Values of b greater than the 17.6 km s-1 thermal width expected for O VI at T~3×105 K indicate that additional nonthermal broadening mechanisms are common. The O VI ?1031.926 absorption is detected at >=3 ? confidence along 59 of the 102 sight lines surveyed. The high-velocity O VI detections indicate that ~60% of the sky (and perhaps as much as ~85%, depending on data quality considerations) is covered by high-velocity H+ associated with the O VI. We find that N(H+)>~1018 cm-2 if the high-velocity hot gas has a metallicity similar to that of the Magellanic Stream; this detection rate is considerably higher than that of high-velocity warm H I traced through its 21 cm emission at a comparable column density level. Some of the high-velocity O VI is associated with known H I structures (the Magellanic Stream, Complex A, Complex C, the Outer Spiral Arm, and several discrete H I HVCs). Some of the high-velocity O VI features have no counterpart in H I 21 cm emission, including discrete absorption features and positive velocity absorption wings extending from ~100 to ~300 km s-1 that blend with lower velocity absorption produced by the Galactic thick disk/halo. The discrete features may typify clouds located in the Local Group, while the O VI absorption wings may be tidal debris or material expelled from the Galactic disk. Most of the O VI features have velocities incompatible with those of the Galactic halo, even if the halo has decoupled from the underlying Galactic disk. The reduction in the dispersion about the mean of the high-velocity O VI centroids when the velocities are converted from the LSR to the GSR and LGSR reference frames is necessary (but not conclusive) evidence that some of the clouds are located outside the Galaxy. Most of the O VI cannot be produced by photoionization, even if the gas is irradiated by extragalactic ultraviolet background radiation. Several observational quantities indicate that collisions in hot gas are the primary ionization mechanism responsible for the production of the O VI. These include the ratios of O VI column densities to those of other highly ionized species (C IV, N V) and the strong correlation between N(O VI) and O VI line width. Consideration of the possible sources of collisional ionization favors production of some of the O VI at the boundaries between cool/warm clouds of gas and a highly extended (R>~70 kpc), hot (T>106 K), low-density (n<~10-4-10-5 cm-3) Galactic corona or Local Group medium. The existence of a hot, highly extended Galactic corona or Local Group medium and the prevalence of high-velocity O VI are consistent with predictions of current galaxy formation scenarios. Distinguishing between the various phenomena producing high-velocity O VI in and near the Galaxy will require continuing studies of the distances, kinematics, elemental abundances, and physical states of the different types of high-velocity O VI found in this study. Descriptions of galaxy evolution will need to account for the highly ionized gas, and future X-ray studies of hot gas in the Local Group will need to consider carefully the relationship of the X-ray absorption/emission to the complex high-velocity absor

Sembach, K. R.; Wakker, B. P.; Savage, B. D.; Richter, P.; Meade, M.; Shull, J. M.; Jenkins, E. B.; Sonneborn, G.; Moos, H. W.

2003-05-01

185

Signature of superradiance from a nitrogen-gas plasma channel produced by strong-field ionization  

NASA Astrophysics Data System (ADS)

Recently, Yao et al. demonstrated the creation of coherent emissions in nitrogen gas with two-color (800 nm + 400 nm) ultrafast laser pulses [J. Yao, G. Li, C. Jing, B. Zeng, W. Chu, J. Ni, H. Zhang, H. Xie, C. Zhang, H. Li, H. Xu, S. L. Chin, Y. Cheng, and Z. Xu, New J. Phys. 15, 023046 (2013), 10.1088/1367-2630/15/2/023046]. Based on this two-color scheme, here we report on systematic investigation of temporal characteristics of the radiation emitted at 391 nm [N2+: B2?u+(? =0) -X2?g+(? =0)] by experimentally examining its temporal profiles with the increase of the plasma channel induced by the intense 800-nm femtosecond laser pulses at a nitrogen-gas pressure of ˜25 mbar. We reveal unexpected temporal profiles of the coherent emissions, which show significant superradiance signatures owing to the cooperation of an ensemble of excited N2+ molecules that are coherently radiating in phase. Our findings shed more light on the mechanisms behind the coherent laserlike emissions induced by strong-field ionization of molecules.

Li, Guihua; Jing, Chenrui; Zeng, Bin; Xie, Hongqiang; Yao, Jinping; Chu, Wei; Ni, Jielei; Zhang, Haisu; Xu, Huailiang; Cheng, Ya; Xu, Zhizhan

2014-03-01

186

Kinematics of the Diffuse Ionized Gas Halos of NGC 891 and NGC 5775  

NASA Astrophysics Data System (ADS)

As part of an ongoing effort to characterize the nature of the disk-halo interaction in spiral galaxies, we present an investigation into the kinematics of the diffuse ionized gas (DIG) halos of two edge-on spirals, NGC 891 and NGC 5775. Observations of optical emission lines were obtained at high spectral resolution with the SparsePak fiber array at WIYN, and the TAURUS-II Fabry-Perot interferometer at the AAT, respectively. Detailed three-dimensional models of the galaxies were created and compared with the data, revealing the presence of a vertical gradient in rotational velocity in each case. The sense of the gradient corresponds to decreasing rotation speed with increasing height above the disk; the magnitude is approximately 15 km s-1 kpc-1 in NGC 891, and 8 km s-1 kpc-1 in NGC 5775. Qualitatively, this behavior is predicted by models of the disk-halo interaction which consider gas being lifted out of the disk, but quantitative agreement has not yet been achieved. We describe the results of our observations, present a comparison with a purely ballistic model of disk-halo flow, and discuss prospects for a better understanding of this critical process in the evolution of galaxies. This material is based on work partially supported by the National Science Foundation under Grant No. AST 99-86113.

Heald, G. H.; Rand, R. J.; Benjamin, R. A.; Bershady, M. A.; Collins, J. A.; Bland-Hawthorn, J.

2005-12-01

187

Diffuse Ionized Gas in the Magellanic System: Early Results from WHAM-South  

NASA Astrophysics Data System (ADS)

From its new vantage point at CTIO, the Wisconsin H? Mapper is poised to explore the full distribution and kinematics of diffuse plasma in extended gaseous structures near the Magellanic Clouds. Shaped by the interaction between the Clouds and the Milky Way, the Bridge, Stream, and Leading Arm gas complexes have been studied extensively in 21 cm emission and optical/UV absorption. With spectral resolution of 12 km/s, WHAM is able to separate optical emission from these structures and brighter local gas near vLSR 0 km/s. Combined with its unprecedented sensitivity to the limit of atmospheric line confusion ( 10s of mR), we are embarking on a survey of the ionized component of the Magellanic System with WHAM. With observations of the southern component of our all-sky survey nearly completed, we have begun to examine some emission features toward the Magellanic System. Here we present a sample of several regions observed recently with WHAM in H?. WHAM was built and continues to operate with ongoing support from NSF. The research presented here is currently funded by award AST-0607512 and an International Program Development Fund from the University of Sydney.

Haffner, L. Matthew; Madsen, G. J.

2011-01-01

188

Emission spectrum of ionized gas in the irregular galaxy Holmberg II  

NASA Astrophysics Data System (ADS)

We studied the ionized gas spectra of star-forming regions in the Holmberg II galaxy using optical long-slit spectroscopic observations made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). We estimated the oxygen, nitrogen, sulphur, neon and argon abundances in individual H II regions and found the average metallicity in the galaxy to be Z ? 0.1 or 0.3 Z?, depending on the estimation method employed. We used these observations combined with the results of our earlier studies of the irregular galaxy IC 10 and the blue compact dwarf galaxy VII Zw 403 to compare the currently most popular methods of gas metallicity estimation in order to select from among them the techniques that are most reliable for analysing irregular galaxies. To this end, we used the `direct' Te method and six empirical and theoretical methods. The results of our observations mostly confirmed the conclusions of López-Sánchez et al. based on the analysis of systematic deviations of metallicity estimates derived by applying different methods to `model' H II regions.

Egorov, O. V.; Lozinskaya, T. A.; Moiseev, A. V.

2013-02-01

189

Ion impact induced ionization/fragmentation dynamics of rare gas Dimers  

NASA Astrophysics Data System (ADS)

We have measured the ionization and fragmentation of Helium, Neon and Argon Dimers induced by ion impact and observed two different pathways, the sequential ionization on each atom and the interatomic Cou-lombic decay.

Kim, H.-K.; Titze, J.; Schöffler, M.; Trinter, F.; Waitz, M.; Voigtsberger, J.; Sann, H.; Meckel, M.; Stuck, C.; Lenz, U.; Metz, D.; Jung, A.; Odenweller, M.; Neumann, N.; Ulrich, B.; Costa Fraga, R.; Petridis, N.; Schössler, S.; Ullmann-Pfleger, K.; Grisenti, R.; Czasch, A.; Jagutzki, O.; Schmidt, L.; Jahnke, T.; Schmidt-Böcking, H.; Becht, J.; Gassert, H.; Merabet, H.; Rangama, J.; Zhou, C. L.; Cassimi, A.; Dörner, R.

2014-04-01

190

The Properties and the Evolution of the Highly Ionized Gas in MR 2251-178  

NASA Technical Reports Server (NTRS)

We present the first XMM-Newton observations of the radio-quiet quasar MR 2251-178 obtained in 2000 and 2002. The EPIC-pn spectra show a power-law continuum with a slope of Gamma = 1.6 at high energies absorbed by at least two warm absorbers (WAs) intrinsic to the source. The underlying continuum in the earlier observation shows a soft excess at low X-ray energies which can be modeled as an additional power-law with Gamma = 2.9. The spectra also show a weak narrow iron K alpha emission line. The high-resolution grating spectrum obtained in 2002 shows emission lines from N VI, O VII, O VIII, Ne IX, and Ne X, as well as absorption lines from the low-ionization ions of O III, O IV, and O V, and other confirmed and suspected weaker absorption lines. The O III - O V lines are consistent with the properties of the emission line gas observed as extended optical (O III) emission in this source. The signal-to-noise of the 2000 grating data is too low to detect any lines. We suggest a model for the high-resolution spectrum which consist of two or three warm-absorber (WA) components. The two-components model has a high-ionization WA with a column density of 10(exp 21.5)-10 (exp 21.8) sq cm and a low-ionization absorber with a column density of 10(exp 20.3) sq cm. In the three-components model we add a lower ionization component that produces the observed iron M-shell absorption lines. We investigate the spectral variations in MR 2251-178 over a period of 8.5 years using data from ASCA, BeppoSAX, and XMM-Newton. All X-ray observations can be fitted with the above two power laws and the two absorbers. The observed luminosity variations seems to correlate with variations in the soft X-ray continuum. The 8.5 year history of the source suggests a changing X-ray absorber due to material that enters and disappears from the line-of-sight on timescales of several months. We also present, for the first time, the entire FUSE spectrum of MR 2251-178. We detect emission from N III, C III, and O VI and at least 4 absorption systems in C III, H I, and O VI, one at -580 km/s and at least 3 others which are blended together and form a wide trough covering the velocity range of 0 to -500 km/s. The general characteristics of the UV and X-ray absorbers are consistent with an origin in the same gas.

Kaspi, Shai; Netzer, hagai; Chelouche, Doron; George, Ian M.; Nandra, Kirpal; Turner, T. J.

2004-01-01

191

Densities and filling factors of the diffuse ionized gas in the Solar neighbourhood  

NASA Astrophysics Data System (ADS)

Aims: We analyse electron densities and filling factors of the diffuse ionized gas (DIG) in the Solar neighbourhood. Methods: We have combined dispersion measures and emission measures towards 38 pulsars at distances known to better than 50%, from which we derived the mean density in clouds, N_c, and their volume filling factor, F_v, averaged along the line of sight. The emission measures were corrected for absorption by dust and contributions from beyond the pulsar distance. Results: The scale height of the electron layer for our sample is 0.93± 0.13 kpc and the midplane electron density is 0.023± 0.004 cm-3, in agreement with earlier results. The average density along the line of sight is < n_e> = 0.018± 0.002 cm-3 and is nearly constant. Since < n_e> = F_vN_c, an inverse relationship between Fv and Nc is expected. We find F_v(N_c) = (0.011± 0.003) N_c-1.20± 0.13, which holds for the ranges N_c= 0.05-1 cm-3 and F_v= 0.4-0.01. Near the Galactic plane the dependence of Fv on Nc is significantly stronger than away from the plane. Fv does not systematically change along or perpendicular to the Galactic plane, but the spread about the mean value of 0.08± 0.02 is considerable. The total pathlength through the ionized regions increases linearly to about 80 pc towards |z| = 1 kpc. Conclusions: Our study of Fv and Nc of the DIG is the first one based on a sample of pulsars with known distances. We confirm the existence of a tight, nearly inverse correlation between Fv and Nc in the DIG. The exact form of this relation depends on the regions in the Galaxy probed by the pulsar sample. The inverse F_v-Nc relation is consistent with a hierarchical, fractal density distribution in the DIG caused by turbulence. The observed near constancy of < n_e> then is a signature of fractal structure in the ionized medium, which is most pronounced outside the thin disk.

Berkhuijsen, E. M.; Müller, P.

2008-10-01

192

Very metal-poor galaxies: ionized gas kinematics in nine objects  

NASA Astrophysics Data System (ADS)

The study of ionized gas morphology and kinematics in nine extremely metal-deficient (XMD) galaxies with the scanning Fabry-Perot interferometer on the Special Astrophysical Observatory (SAO) 6-m telescope is presented. Some of these very rare objects (with currently known range of O/H of 7.12 < 12 + log(O/H) < 7.65, or ) are believed to be the best proxies of `young' low-mass galaxies in the high-redshift Universe. One of the main goals of this study is to look for possible evidence of star formation (SF) activity induced by external perturbations. Recent results from HI mapping of a small subsample of XMD star-forming galaxies provided confident evidence for the important role of interaction-induced SF. Our observations provide complementary or new information that the great majority of the studied XMD dwarfs have strongly disturbed gas morphology and kinematics or the presence of detached components. We approximate the observed velocity fields by simple models of a rotating tilted thin disc, which allows us the robust detection of non-circular gas motions. These data, in turn, indicate the important role of current/recent interactions and mergers in the observed enhanced SF. As a by-product of our observations, we obtained data for two Low Surface Brightness (LSB) dwarf galaxies: Anon J012544+075957 that is a companion of the merger system UGC 993, and SAO 0822+3545 which shows off-centre, asymmetric, low star formation rate star-forming regions, likely induced by the interaction with the companion XMD dwarf HS 0822+3542. Based on observations obtained with the Special Astrophysical Observatory RAS 6-m telescope. E-mail: moisav@gmail.com (AVM); sap@sao.ru (SAP); akniazev@saao.ac.za (AYK)

Moiseev, A. V.; Pustilnik, S. A.; Kniazev, A. Y.

2010-07-01

193

The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies  

NASA Astrophysics Data System (ADS)

Following our study on the incidence, morphology and kinematics of the ionized gas in early-type galaxies, we now address the question of what is powering the observed nebular emission. To constrain the likely sources of gas excitation, we resort to a variety of ancillary data we draw from complementary information on the gas kinematics, stellar populations and galactic potential from the SAURON data, and use the SAURON-specific diagnostic diagram juxtaposing the [OIII] ?5007/H? and [NI] ??5197, 5200/H? line ratios. We find a tight correlation between the stellar surface brightness and the flux of the H? recombination line across our sample, which points to a diffuse and old stellar source as the main contributor of ionizing photons in early-type galaxies, with post-asymptotic giant branch (pAGB) stars being still the best candidate based on ionizing balance arguments. The role of AGN photoionization is confined to the central 2-3arcsec of an handful of objects with radio or X-ray cores. OB-stars are the dominant source of photoionization in 10 per cent of the SAURON sample, whereas for another 10 per cent the intense and highly ionized emission is powered by the pAGB population associated to a recently formed stellar subcomponent. Fast shocks are not an important source of ionization for the diffuse nebular emission of early-type galaxies since the required shock velocities can hardly be attained in the potential of our sample galaxies. Finally, in the most massive and slowly or non-rotating galaxies in our sample, which can retain a massive X-ray halo, the finding of a spatial correlation between the hot and warm phases of the interstellar medium (ISM) suggests that the interaction with the hot ISM provides an additional source of ionization besides old ultraviolet-bright stars. This is also supported by a distinct pattern towards lower values of the [OIII]/H? ratio. These results lead us to investigate the relative role of stellar and AGN photoionization in explaining the ionized gas emission observed in early-type galaxies by the Sloan Digital Sky Survey (SDSS). By simulating how our sample galaxies would appear if placed at further distance and targeted by the SDSS, we conclude that only in very few, if any, of the SDSS galaxies which display modest values for the equivalent width of the [OIII] line (less than ~2.4 Å) and low-ionization nuclear emission-line region like [OIII]/H? values the nebular emission is truly powered by an AGN.

Sarzi, Marc; Shields, Joseph C.; Schawinski, Kevin; Jeong, Hyunjin; Shapiro, Kristen; Bacon, Roland; Bureau, Martin; Cappellari, Michele; Davies, Roger L.; de Zeeuw, P. Tim; Emsellem, Eric; Falcón-Barroso, Jesús; Krajnovi?, Davor; Kuntschner, Harald; McDermid, Richard M.; Peletier, Reynier F.; van den Bosch, Remco C. E.; van de Ven, Glen; Yi, Sukyoung K.

2010-03-01

194

Charging of a conducting sphere moving in a weakly ionized gas under an arbitrarily oriented external uniform electric field  

Microsoft Academic Search

.  A charging conducting sphere moving in a weakly ionized gas\\u000a is investigated. An external uniform electric field is applied with arbitrary orientation\\u000a relative to the gas flow.\\u000a The ion current is obtained analytically and investigated numerically\\u000a in ballistic assumption.\\u000a It is shown that charging regimes depend not only on the net charge of the sphere but\\u000a also on the gas

A. E. Sorokin

2008-01-01

195

Kinematics of the diffuse ionized gas in spiral galaxy disk-halo interactions  

NASA Astrophysics Data System (ADS)

Multiphase gas has been observed in the halos of the Milky Way and some external spiral galaxies. The origin of this gas is still unknown, but observational evidence indicates that star formation-driven disk-halo flows likely play an important role: a correlation is observed between more prominent gaseous halos and higher disk star formation rates; moreover, loop and filamentary structures, often rooted in disk H II regions, extend well into some halos. Whether this process is characterized by hydrodynamic flows of diffuse gas, or ballistic motion of denser clouds, may be addressed by examining the kinematics of the gaseous halos. Accretion of material from the surrounding environment may also be important in driving the kinematics of halo gas. In this thesis, I present an investigation into the kinematics of the warm ionized phase of halo gas in three external edge-on, late type spiral galaxies: NGC 5775, NGC 891, and NGC 4302. The extraction of rotation curves from edge-on systems is a non-trivial task, particularly in the faint halo region, and requires detailed analysis of position-velocity (PV) diagrams. Spectra covering two-dimensional areas of each galaxy have been obtained using Fabry-Perot imaging spectroscopy in the case of NGC 5775, and multi-fiber spectroscopy in the cases of NGC 891 and NGC 4302. PV diagrams constructed from the data are analyzed to investigate whether the rotation speed of the halo gas varies with height above the disk. In each case, a gradient in rotational velocity with height is revealed, with approximate magnitudes 8 km s -1 kpc -1 (NGC 5775), 15 km s -1 kpc -1 (NGC 891), and 30 km s -1 kpc -1 (NGC 4302). All three gradients represent a decrease in rotation speed with increasing distance from the star forming disk. The gradient measured in NGC 891 agrees with an earlier H I study. These three results, together with the H I result, are the first robust measurements of rotation speeds in gaseous halos and their variation with height above the disk. A model of disk-halo flow which considers pure ballistic motion of gas clouds through a galactic gravitational potential is utilized in an attempt to match the results for each galaxy. In each case, the change in rotation speed with height predicated by the ballistic model is found to be significantly lower than the measured value from the data. The model also predicts a large amount of radial redistribution of halo gas, which is not seen in the data. The discrepancy between the kinematics in the data and model is most severe in NGC 4302, and least severe in NGC 5775. The magnitude of the discrepancy decreases as the prominence of filamentary structures in each halo increases, suggesting that the motion of gas in halos of smoother appearance may be intrinsically less ballistic in nature. Evidence from other modeling studies indicates that a hydrodynamic treatment may be more successful. The variation in the observed gradient in rotational velocity appears to be related to the morphology of the gaseous halo, and to the level of star formation in the underlying disk.

Heald, George Herbert, Jr.

196

WFPC2 Imaging of the Multiphase Halos of Two Spiral Galaxies: Dust and Ionized Gas  

NASA Astrophysics Data System (ADS)

We present high-resolution optical images of the interstellar medium (ISM) in the thick disks of the spiral galaxies NGC 4013 and NGC 4302. Our broadband (BVI) images acquired with the Hubble Space Telescope’s WFPC2 show extensive extraplanar dust clouds seen in absorption against the background stellar light, while our narrow-band H-alpha images taken with the WIYN 3.5-m telescope show the diffuse ionized gas (DIG) in these galaxies. The dusty, thick disk clouds visible in our WFPC2 images, which can be found to heights approaching 2 kpc from the midplanes of these galaxies, trace a phase of the ISM that shows significant structure on quite small scales. In general this material is seen to be highly filamentary. By contrast, the thick disk DIG in these galaxies has significantly smoother distribution. We note several unresolved knots of H-alpha emission which may represent thick disk H II regions. We discuss the relationship of the dust-bearing clouds and the DIG in these galaxies.

Rueff, Katherine; Pitterle, M.; Hirschauer, A.; Lehner, N.; Howk, C.

2006-12-01

197

Micro-flame ionization detector with a novel structure for portable gas chromatograph.  

PubMed

A micro-flame ionization detector (micro-FID) for portable gas chromatograph (GC) based on conventional mechanical fabrication techniques was developed and evaluated. Structure was redesigned and dimensions were optimized for best performance. Air is introduced from upper part of the detector, flowing downwards into the burning chamber along a narrow round gap between the collection electrode and the inner wall of the detector body, forming a uniform flow field around the burning jet. The lowest detection limit of the mu-FID was 5x10(-13)g/s for n-decane, with a linear response range of five orders of magnitude. The consumption of gases is only 10 ml/min for hydrogen, and 120 ml/min for air, that is about 1/3 of the gases required for conventional FIDs. A comparative study between the micro-FID and commercial FID was also performed that proved the advantages of the micro-FID. The micro-FID is simple in structure, low heating power, and low consumption of gases that not only decrease the cost of running, but also increase the portability of GC for filed applications. PMID:20678662

Wang, Jianwei; Wang, Hua; Duan, Chunfeng; Guan, Yafeng

2010-08-15

198

H? and [SII] Emission from Warm Ionized Gas in the Scutum-Centaurus Arm  

NASA Astrophysics Data System (ADS)

We present Wisconsin H-Alpha Mapper [SII] ?6716 and H? spectroscopic maps of the warm ionized medium (WIM) in the Scutum-Centaurus Arm at Galactic longitudes 310° < l < 345°. Using extinction-corrected H? intensities (I_{{H} \\alpha }^c), we measure an exponential scale height of electron density squared in the arm of H_{n_e^2}= 0.30 \\, {kpc} (assuming a distance of 3.5 kpc), intermediate between that observed in the inner Galaxy and in the Perseus Arm. The [S II]/H? line ratio is enhanced at large |z| and in sightlines with faint I_{{H} \\alpha }^c. We find that the [S II]/H? line ratio has a power-law relationship with I_{{H} \\alpha }^c from a value of ?1.0 at I_{{H} \\alpha }^c< 0.2 \\, {R} (Rayleighs) to a value of ?0.08 at I_{{H} \\alpha }^c\\gtrsim 100 \\, {R}. The line ratio is better correlated with H? intensity than with height above the plane, indicating that the physical conditions within the WIM vary systematically with electron density. We argue that the variation of the line ratio with height is a consequence of the decrease of electron density with height. Our results reinforce the well-established picture in which the diffuse H? emission is due primarily to emission from in situ photoionized gas, with scattered light only a minor contributor.

Hill, Alex S.; Benjamin, Robert A.; Haffner, L. Matthew; Gostisha, Martin C.; Barger, Kathleen A.

2014-06-01

199

Improved gas chromatography-flame ionization detector analytical method for the analysis of epoxy fatty acids.  

PubMed

In this study an improved method for analysis of epoxy fatty acids is reported. Data obtained from analysis of polar fatty acids has previously been presented, but due to the high number of compounds that co-elute in the polar fraction, the resultant chromatograms are complex which may lead to compromising the accuracy of the data. A three steps separation of fatty acid methyl esters (FAMEs) by solid-phase extraction (SPE) on a silica gel column to remove hydroxy fatty acid interferences was proposed. This approach is opposed to a two step separation procedure that has been often used to prevent analytical interferences caused by non-altered fatty acids. A gas chromatograph with a flame ionization detector (GC-FID) equipped with a polar CP-Sil 88™ column was used. Quantification was based on the use of methyl nonadecanoate (C19:0), as an internal standard. Individual mono epoxy fatty acids were well separated without co-eluting compounds. The optimized method was finally applied to screen epoxy fatty acids in 37 fresh oil samples. Results obtained for the total epoxy fatty acids were in the range 0.03-2mgg(-1) of oil with repeatability coefficient of variation (CV) ranging from 2.8 to 9.9% for duplicate analysis showing that the results obtained are repeatable. PMID:24161147

Mubiru, Edward; Shrestha, Kshitij; Papastergiadis, Antonios; De Meulenaer, Bruno

2013-11-29

200

Quantification of cholesterol tracers by gas chromatography--negative ion chemical ionization mass spectrometry.  

PubMed

Because of its high sensitivity, gas chromatography negative ion chemical ionization mass spectrometry (GC-NCI-MS) is a potentially valuable analytical tool for the study of cholesterol metabolism. Of several derivatives prepared for potential use in tracer studies pentafluorobenzoyl cholesterol was selected because it formed rapidly at ambient temperature and was stable for long periods, could be detected at a level of 1 fmol, and yielded a mass spectrum in which the molecular ion was the principal component. Hexadeuterated cholesterol tracer ([26,26,26,27,27,27-2H6]cholesterol) could be detected in dilutions up to 2700 in unlabeled cholesterol by selected ion monitoring with a coefficient of variation averaging 3.2%. In seven normal subjects tracer cholesterol was infused intravenously and plasma cholesterol enrichment was determined after 4 h. The measured rapidly miscible cholesterol pool was 391.0 +/- 38.6 mg cholesterol/kg. Negative ion mass spectrometry of pentafluorobenzyol cholesterol will facilitate analysis of both small amounts of natural cholesterol and labeled cholesterol in applications where sensitivity is critical. PMID:8946736

Ostlund, R E; Hsu, F F; Bosner, M S; Stenson, W F; Hachey, D L

1996-11-01

201

Ethanol analysis by headspace gas chromatography with simultaneous flame-ionization and mass spectrometry detection.  

PubMed

Ethanol is the most frequently identified compound in forensic toxicology. Although confirmation involving mass spectrometry is desirable, relatively few methods have been published to date. A novel technique utilizing a Dean's Switch to simultaneously quantitate and confirm ethyl alcohol by flame-ionization (FID) and mass spectrometric (MS) detection after headspace sampling and gas chromatographic separation is presented. Using 100 ?L of sample, the limits of detection and quantitation were 0.005 and 0.010 g/dL, respectively. The zero-order linear range (r(2) > 0.990) was determined to span the concentrations of 0.010 to 1.000 g/dL. The coefficient of variation of replicate analyses was less than 3.1%. Quantitative accuracy was within ±8%, ±6%, ±3%, and ±1.5% at concentrations of 0.010, 0.025, 0.080, and 0.300 g/dL, respectively. In addition, 1,1-difluoroethane was validated for qualitative identification by this method. The validated FID-MS method provides a procedure for the quantitation of ethyl alcohol in blood by FID with simultaneous confirmation by MS and can also be utilized as an identification method for inhalants such as 1,1-difluoroethane. PMID:21871160

Tiscione, Nicholas B; Alford, Ilene; Yeatman, Dustin Tate; Shan, Xiaoqin

2011-09-01

202

[Determination of difenoconazole residue in foods by gas chromatography-negative chemical ionization mass spectrometry].  

PubMed

A method is presented for the determination of difenoconazole residue in all kinds of foods by solid phase extraction-gas chromatography-negative chemical ionization mass spectrometry (SPE-GC-MS/NCI). Difenoconazole residue was extracted with ethyl acetate from different samples, such as perilla leaves, carrots, spinach powder, rice, gram, jasmine flower tea, oolong tea, strawberries, sauce, bee honey, beef, chicken and eels, etc. The extracts were cleaned-up by active carbon SPE column connected to alumina neutral SPE column or Florisil SPE column only. Analytical screening was determined by the technique of GC-MS/NCI on selected ion monitoring mode. The recoveries of difenoconazole in most samples were in the range from 70% to 120% at three spiked levels, 0.01 mg/kg, 0.04 mg/kg and 0.10 mg/kg, and the relative standard deviations (RSDs) were below 9.5%. The linearity of the method is good from 0.02 to 1.00 mg/L, and limit of detection (LOD) was 0.000 5 or 0.001 mg/kg for different type samples. The method is selective without interference and is suitable for determination and conformation of difenoconazole residue in all kinds of foods. PMID:17679443

Shen, Weijian; Yang, Wenquan; Shen, Chongyu; Zhao, Zengyun; Xu, Jinzhong; Ding, Tao

2007-05-01

203

The ionized gas at the centre of IC 10: a possible localized chemical pollution by Wolf-Rayet stars  

NASA Astrophysics Data System (ADS)

We present results from integral field spectroscopy with the Potsdam Multi-Aperture Spectrograph at the 3.5-m telescope at Calar Alto Observatory of the intense star-forming region [HL90] 111 at the centre of the starburst galaxy IC 10. We have obtained maps with a spatial sampling of 1 × 1 arcsec2= 3.9× 3.9 pc2 of different emission lines and analysed the extinction, physical conditions, nature of the ionization and chemical abundances of the ionized gas, as well determined locally the age of the most recent star formation event. By defining several apertures, we study the main integrated properties of some regions within [HL90] 111. Two contiguous spaxels show an unambiguous detection of the broad He II?4686 emission line, this feature seems to be produced by a single late-type WN star. We also report a probable N and He enrichment in the precise spaxels where the Wolf-Rayet (WR) features are detected. The enrichment pattern is roughly consistent with that expected for the pollution of the ejecta of a single or a very small number of WR stars. Furthermore, this chemical pollution is very localized (˜2 arcsec ˜7.8 pc) and it should be difficult to detect in star-forming galaxies beyond the Local Volume. We also discuss the use of the most common empirical calibrations to estimate the oxygen abundances of the ionized gas in nearby galaxies from 2D spectroscopic data. The ionization degree of the gas plays an important role when applying these empirical methods, as they tend to give lower oxygen abundances with increasing ionization degree. Based on observations collected at the Centro Astrónomico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Plank Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Visiting Astronomer at the Instituto de Astrofísica de Canarias.

López-Sánchez, Á. R.; Mesa-Delgado, A.; López-Martín, L.; Esteban, C.

2011-03-01

204

LARGE-SCALE SHOCK-IONIZED AND PHOTOIONIZED GAS IN M83: THE IMPACT OF STAR FORMATION  

SciTech Connect

We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 A)/H{beta} versus [S II](6716 A+6731 A)/H{alpha}, with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (0.''2 x 0.''2) basis and compare it with several photo- and shock-ionization models. We select four regions from the center to the outer spiral arm and compare them in the diagnostic diagram. For the photoionized gas, we observe a gradual increase of the log ([O III]/H{beta}) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super-solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photoionized from the shock-ionized component of the gas. We find that the shock-ionized H{alpha} emission ranges from {approx}2% to about 15%-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is a horizontal distribution around log ([O III]/H{beta}) {approx} 0. This feature is well fit by a shock-ionization model with 2.0 Z{sub sun} metallicity and shock velocities in the range of 250-350 km s{sup -1}. A low-velocity shock component, <200 km s{sup -1}, is also detected and is spatially located at the boundary between the outer ring and the spiral arm. The low-velocity shock component can be due to (1) supernova remnants located nearby, (2) dynamical interaction between the outer ring and the spiral arm, and (3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83.

Hong, Sungryong; Calzetti, Daniela [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Dopita, Michael A. [Research School of Astronomy and Astrophysics, Australian National University, ACT 2611 (Australia); Blair, William P. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Whitmore, Bradley C.; Bond, Howard E. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Balick, Bruce [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Carollo, Marcella [Department of Physics, ETH-Zurich, Zurich 8093 (Switzerland); Disney, Michael J. [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom); Frogel, Jay A. [Association of Universities for Research in Astronomy, Washington, DC 20005 (United States); Hall, Donald [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Holtzman, Jon A. [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Kimble, Randy A. [NASA-Goddard Space Flight Center, Greenbelt, MD 20771 (United States); McCarthy, Patrick J. [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101-1292 (United States); O'Connell, Robert W. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Paresce, Francesco [Istituto di Astrofisica Spaziale e Fisica Cosmica, INAF, Via Gobetti 101, 40129 Bologna (Italy); Saha, Abhijit [National Optical Astronomy Observatories, Tucson, AZ 85726-6732 (United States); Silk, Joseph I. [Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom); Trauger, John T. [NASA-Jet Propulsion Laboratory, Pasadena, CA 91109 (United States); Walker, Alistair R., E-mail: wpb@pha.jhu.edu [Cerro Tololo Inter-American Observatory, La Serena (Chile)

2011-04-10

205

Highly Ionized Gas in the Galactic Halo and the High-Velocity Clouds toward PG 1116+215  

NASA Astrophysics Data System (ADS)

We have obtained high-resolution Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) echelle observations of the quasar PG 1116+215 (zem=0.1765, l=223.36d, b=+68.21d). The semicontinuous coverage of the ultraviolet spectrum over the wavelength range 916-2800 Å provides detections of Galactic and high-velocity cloud (HVC) absorption over a wide range of ionization species: H I, C II-IV, N I-II, O I, O VI, Mg II, Si II-IV, P II, S II, and Fe II over the velocity range -100kms-1ionization species consist of five discrete components: three at low and intermediate velocities (vLSR~-44, -7, +56 km s-1) and two at high velocities (vLSR~+100, +184 km s-1). Over the same velocity range, the higher ionization species (C III-IV, O VI, Si IV)-those with ionization potentials larger than 40 eV-show continuous absorption with column density peaks at vLSR~10 km s-1, the expected velocity of halo gas corotating with the Galactic disk, and vLSR~+184 km s-1, the velocity of the higher velocity HVC. The velocity coincidence of both low- and high-ionization species in the vLSR~+184 km s-1 HVC gas suggests that they arise in a common structure, though not necessarily in the same gaseous phase. The absorption structure in the high-ionization gas, which extends to very low velocities, suggests a scenario in which a moderately dense cloud of gas is streaming away from the Galaxy through a hot external medium (either the Galactic halo or corona) that is stripping gas from this cloud. The cloud core produces the observed neutral atoms and low-ionization species. The stripped material is the likely source of the high-ionization species. Among the host of collisionally ionized nonequilibrium models, we find that shock ionization and conductive interfaces can account for the column density ratios of high-ionization species. The nominal metallicity of the neutral gas using the O I and H I column densities is [O/H]~-0.66, with a substantial uncertainty caused by the saturation of the H I Lyman series in the FUSE band. The ionization of the cloud core is likely dominated by photons, and assuming the source of ionizing photons is the extragalactic UV background, we estimate the cloud has a density of 10-2.7 cm-3 with a thermal pressure p/k~24 cm-3 K. If photons escaping the Galactic disk are also included (i.e., if the cloud lies closer than the outer halo), the density and thermal pressure could be higher by as much as 2 dex. In either case, the relative abundances of O, Si, and Fe in the cloud core are readily explained without departures from the solar pattern. We compare the column density ratios of the HVCs toward the PG 1116+215 to other isolated HVCs as well as Complex C. Magellanic Stream gas (either a diffuse extension of the leading arm or gas stripped from a prior passage) is a possible origin for this gas and is consistent with the location of the high-velocity gas on the sky, as well as its high positive velocity, the ionization, and metallicity. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Also based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which is operated for NASA by Johns Hopkins University under NASA contract NAS 5-32985.

Ganguly, Rajib; Sembach, Kenneth R.; Tripp, Todd M.; Savage, Blair D.

2005-04-01

206

Ionized Gas Kinematics at High Resolution. IV. Star Formation and a Rotating Core in the Medusa (NGC 4194)  

NASA Astrophysics Data System (ADS)

NGC 4194 is a post-merger starburst known as The Medusa for its striking tidal features. We present here a detailed study of the structure and kinematics of ionized gas in the central 0.65 kpc of the Medusa. The data include radio continuum maps with resolution up to 0.''18 (35 pc) and a 12.8 ?m [Ne II] data cube with spectral resolution ~4 km s-1: the first high-resolution, extinction-free observations of this remarkable object. The ionized gas has the kinematic signature of a core in solid-body rotation. The starburst has formed a complex of bright compact H II regions, probably excited by deeply embedded super star clusters, but none of these sources is a convincing candidate for a Galactic nucleus. The nuclei of the merger partners that created the Medusa have not yet been identified.

Beck, Sara C.; Lacy, John; Turner, Jean; Greathouse, Thomas; Neff, Susan

2014-05-01

207

Ionized gas in elliptical and S0 galaxies. I. A survey for H-alpha and forbidden N II emission  

SciTech Connect

A spectroscopic survey of a large sample of southern E and S0 galaxies in order to detect ionized gas in the nuclei is reported. The strongest line in the 6000-7000 A range was nearly always forbidden N II 6584 A, followed by H-alpha and forbidden S II 6716, 6731 A. Identical detection rates of about 50 percent were obtained for the forbidden N II line in both E and S0 galaxies. The mass of ionized gas in early-type galaxies was very small, with values typically in the range 1000-10,000 solar masses. The relative emission-line strengths in virtually every case were indistinguishable from those of LINER nuclei. The observed values of the forbidden N II 6584 A/H-alpha ratios fell mostly between one and three and seem correlated with galaxy absolute magnitude. The existence of such a correlation may be indicative of metallicity differences. 58 references.

Phillips, M.M.; Jenkins, C.R.; Dopita, M.A.; Sadler, E.M.; Binette, L.

1986-05-01

208

Gas-phase halo alkylation of C60-fullerene by ion-molecule reaction under chemical ionization.  

PubMed

Chemical ionization (CI) mass spectra of C60-fullerene were studied using 1,2-dibromoethane and 1,2-dichloroethane as CI reagents. The ion-molecule reaction between C60 and C2H4X(+) (X=Br and Cl) leads to the formation of (C60+C2H4X)(+) adducts. The collision-induced dissociation of the adducts reveal gas phase halo alkylation of C60-fullerence involving the C-C bond formation. PMID:24227533

Srinivas, R; Vairamani, M; Mathews, C K

1993-11-01

209

The Effects of Ionized Gas Exposure on the Toughness and Fatigue Properties of Aluminum Alloys and Composites  

Microsoft Academic Search

The effects of an oxygen ionized gas from simulated space exposure on the toughness and fatigue properties of several aerospace aluminum alloys and aluminum composites have been analyzed. The test matrix consisted of four aluminum systems: the 6000 and 1100 series and two 8090 aluminum-lithium alloys. The test specimens were prepared as Charpy V-notched impact and disk-shaped compact fracture toughness

Stephen Vincent Zaat

1992-01-01

210

Determination of organophosphorus pesticide residues in human tissues by capillary gas chromatography–negative chemical ionization mass spectrometry analysis  

Microsoft Academic Search

We describe an analytical method that allows the determination of organophosphorus pesticides (OPs) in different human tissues. It involves an extraction procedure with ethanol–ethyl acetate, followed by gel permeation chromatography clean-up step and analysis by capillary gas chromatography–negative chemical ionization mass spectrometry in the selected ion monitoring mode. The method was tested for 37 OPs and the recoveries obtained vary

Mario Vincenzo Russo; Luigi Campanella; Pasquale Avino

2002-01-01

211

In gas laser ionization and spectroscopy experiments at the Superconducting Separator Spectrometer (S3): Conceptual studies and preliminary design  

NASA Astrophysics Data System (ADS)

The results of preparatory experiments and the preliminary designs of a new in-gas laser ionization and spectroscopy setup, to be coupled to the Super Separator Spectrometer S3 of SPIRAL2-GANIL, are reported. Special attention is given to the development and tests to carry out a full implementation of the in-gas jet laser spectroscopy technique. Application of this novel technique to radioactive species will allow high-sensitivity and enhanced-resolution laser spectroscopy studies of ground- and excited-state properties of exotic nuclei.

Ferrer, R.; Bastin, B.; Boilley, D.; Creemers, P.; Delahaye, P.; Liénard, E.; Fléchard, X.; Franchoo, S.; Ghys, L.; Huyse, M.; Kudryavtsev, Yu.; Lecesne, N.; Lu, H.; Lutton, F.; Mogilevskiy, E.; Pauwels, D.; Piot, J.; Radulov, D.; Rens, L.; Savajols, H.; Thomas, J. C.; Traykov, E.; Van Beveren, C.; Van den Bergh, P.; Van Duppen, P.

2013-12-01

212

The ATLAS3D project - X. On the origin of the molecular and ionized gas in early-type galaxies  

NASA Astrophysics Data System (ADS)

We make use of interferometric CO and H I observations, and optical integral-field spectroscopy from the ATLAS3D survey, to probe the origin of the molecular and ionized interstellar medium (ISM) in local early-type galaxies. We find that 36 ± 5 per cent of our sample of fast-rotating early-type galaxies have their ionized gas kinematically misaligned with respect to the stars, setting a strong lower limit on the importance of externally acquired gas (e.g. from mergers and cold accretion). Slow rotators have a flat distribution of misalignments, indicating that the dominant source of gas is external. The molecular, ionized and atomic gas in all the detected galaxies are always kinematically aligned, even when they are misaligned from the stars, suggesting that all these three phases of the ISM share a common origin. In addition, we find that the origin of the cold and warm gas in fast-rotating early-type galaxies is strongly affected by environment, despite the molecular gas detection rate and mass fractions being fairly independent of group/cluster membership. Galaxies in dense groups and the Virgo cluster nearly always have their molecular gas kinematically aligned with the stellar kinematics, consistent with a purely internal origin (presumably stellar mass loss). In the field, however, kinematic misalignments between the stellar and gaseous components indicate that at least 42 ± 5 per cent of local fast-rotating early-type galaxies have their gas supplied from external sources. When one also considers evidence of accretion present in the galaxies' atomic gas distributions, ?46 per cent of fast-rotating field ETGs are likely to have acquired a detectable amount of ISM from accretion and mergers. We discuss several scenarios which could explain the environmental dichotomy, including preprocessing in galaxy groups/cluster outskirts and the morphological transformation of spiral galaxies, but we find it difficult to simultaneously explain the kinematic misalignment difference and the constant detection rate. Furthermore, our results suggest that galaxy mass may be an important independent factor associated with the origin of the gas, with the most massive fast-rotating galaxies in our sample (MK?-24 mag; stellar mass of ?8 × 1010 M?) always having kinematically aligned gas. This mass dependence appears to be independent of environment, suggesting it is caused by a separate physical mechanism.

Davis, Timothy A.; Alatalo, Katherine; Sarzi, Marc; Bureau, Martin; Young, Lisa M.; Blitz, Leo; Serra, Paolo; Crocker, Alison F.; Krajnovi?, Davor; McDermid, Richard M.; Bois, Maxime; Bournaud, Frédéric; Cappellari, Michele; Davies, Roger L.; Duc, Pierre-Alain; de Zeeuw, P. Tim; Emsellem, Eric; Khochfar, Sadegh; Kuntschner, Harald; Lablanche, Pierre-Yves; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Scott, Nicholas; Weijmans, Anne-Marie

2011-10-01

213

SIGGMA: A SURVEY OF IONIZED GAS IN THE GALAXY, MADE WITH THE ARECIBO TELESCOPE  

SciTech Connect

A Survey of Ionized Gas in the Galaxy, made with the Arecibo telescope (SIGGMA), uses the Arecibo L-band Feed Array (ALFA) to fully sample the Galactic plane (30 Degree-Sign {<=} l {<=} 75 Degree-Sign and -2 Degree-Sign {<=} b {<=} 2 Degree-Sign ; 175 Degree-Sign {<=} l {<=} 207 Degree-Sign and -2 Degree-Sign {<=} b {<=} 1 Degree-Sign ) observable with the telescope in radio recombination lines (RRLs). Processed data sets are being produced in the form of data cubes of 2 Degree-Sign (along l) Multiplication-Sign 4 Degree-Sign (along b) Multiplication-Sign 151 (number of channels), archived and made public. The 151 channels cover a velocity range of 600 km s{sup -1} and the velocity resolution of the survey changes from 4.2 km s{sup -1} to 5.1 km s{sup -1} from the lowest frequency channel to the highest frequency channel. RRL maps with 3.'4 resolution and a line flux density sensitivity of {approx}0.5 mJy will enable us to identify new H II regions, measure their electron temperatures, study the physics of photodissociation regions with carbon RRLs, and investigate the origin of the extended low-density medium. Twelve Hn{alpha} lines fall within the 300 MHz bandpass of ALFA; they are resampled to a common velocity resolution to improve the signal-to-noise ratio (S/N) by a factor of three or more and preserve the line width. SIGGMA will produce the most sensitive fully sampled RRL survey to date. Here, we discuss the observing and data reduction techniques in detail. A test observation toward the H II region complex S255/S257 has detected Hn{alpha} and Cn{alpha} lines with S/N > 10.

Liu, B. [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); McIntyre, T. [University of New Mexico, Albuquerque, NM 87131 (United States); Terzian, Y. [Cornell University, Ithaca, NY 14853 (United States); Minchin, R. [Arecibo Observatory, HC03 Box 53995, Arecibo 00612, PR (United States); Anderson, L. [West Virginia University, Morgantown, WV 26506 (United States); Churchwell, E. [University of Wisconsin-Madison, Madison, WI 53706 (United States); Lebron, M. [University of Puerto Rico, P.O. Box 23323, 00931-3323, San Juan (Puerto Rico); Roshi, D. Anish [National Radio Astronomy Observatory, Green Bank and Charlottesville, VA 22903 (United States)

2013-10-01

214

Internally heated membrane interfaced to a gas chromatography flame ionization detector.  

PubMed

Volatile Organic Compounds (VOCs) mixtures in aqueous solutions have been investigated using a simple and efficient all-in-one on-line sampling, isolation, enrichment and pre-concentration internally heated membrane connected to a gas chromatography flame ionization detector (GC-FID). In our previous study with the internally heated membrane, no GC column was used in the instrument. In this new study, we introduce a GC column in the instrument design and this makes it possible for mixtures to be investigated. This new experimental design enabled high resolution separation of analyte mixtures capable of being adsorbed, diffused, and desorbed from the device for detection with an FID. With the new design we present data from investigation of competitive adsorption effects on the membrane. The data showed that analyte adsorption and diffusion onto the membrane can be affected when mixtures of analytes are introduced. The application of multiple linear regressions approach to the data enabled us to correct for the problem of competitive adsorption. Analyte adsorption and diffusion was affected by the diffusion coefficients of the analytes; the higher the diffusion coefficient the better the extraction from the membrane. Increasing the sampling time from 1 to 4 min increases the response by 77%. The sampling time responses were linear up to 4 min sampling time. Above 4 min sampling time, the data deviate from linearity. The effect of adding salt to standards has no effect on analyte absorption onto the membrane. The detection limits for key VOCs studied with an internal standard calibration ranged from 0.2 to 194 ng cm(-3). PMID:23622547

Kanu, A Bakarr; Thomas, C L P

2013-07-15

215

Integral Field Unit Observations of NGC 891: Kinematics of the Diffuse Ionized Gas Halo  

NASA Astrophysics Data System (ADS)

We present high and moderate spectral resolution spectroscopy of diffuse ionized gas (DIG) emission in the halo of NGC 891. The data were obtained with the SparsePak integral field unit at the WIYN Observatory. The wavelength coverage includes the [N II] ??6548, 6583, H?, and [S II] ??6716, 6731 emission lines. Position-velocity (PV) diagrams, constructed using spectra extracted from four SparsePak pointings in the halo, are used to examine the kinematics of the DIG. Using two independent methods, a vertical gradient in azimuthal velocity is found to be present in the northeast quadrant of the halo, with magnitude approximately 15-18 km s-1 kpc-1, in agreement with results from H I observations. The kinematics of the DIG suggests that this gradient begins at approximately 1 kpc above the midplane. In another part of the halo, the southeast quadrant, the kinematics is markedly different and suggest rotation at about 175 km s-1, much slower than the disk but with no vertical gradient. We use an entirely ballistic model of disk-halo flow in an attempt to reproduce the kinematics observed in the northeast quadrant. Analysis shows that the velocity gradient predicted by the ballistic model is far too shallow. Based on intensity cuts made parallel to the major axis in the ballistic model and an H? image of NGC 891 from the literature, we conclude that the DIG halo is much more centrally concentrated than the model, suggesting that hydrodynamics dominate over ballistic motion in shaping the density structure of the halo. Velocity dispersion measurements along the minor axis of NGC 891 seem to indicate a lack of radial motions in the halo, but the uncertainties do not allow us to set firm limits.

Heald, George H.; Rand, Richard J.; Benjamin, Robert A.; Bershady, Matthew A.

2006-08-01

216

SIGGMA: A Survey of Ionized Gas in the Galaxy, Made with the Arecibo Telescope  

NASA Astrophysics Data System (ADS)

A Survey of Ionized Gas in the Galaxy, made with the Arecibo telescope (SIGGMA), uses the Arecibo L-band Feed Array (ALFA) to fully sample the Galactic plane (30° <= l <= 75° and -2° <= b <= 2° 175° <= l <= 207° and -2° <= b <= 1°) observable with the telescope in radio recombination lines (RRLs). Processed data sets are being produced in the form of data cubes of 2° (along l) × 4° (along b) × 151 (number of channels), archived and made public. The 151 channels cover a velocity range of 600 km s-1 and the velocity resolution of the survey changes from 4.2 km s-1 to 5.1 km s-1 from the lowest frequency channel to the highest frequency channel. RRL maps with 3.'4 resolution and a line flux density sensitivity of ~0.5 mJy will enable us to identify new H II regions, measure their electron temperatures, study the physics of photodissociation regions with carbon RRLs, and investigate the origin of the extended low-density medium. Twelve Hn? lines fall within the 300 MHz bandpass of ALFA; they are resampled to a common velocity resolution to improve the signal-to-noise ratio (S/N) by a factor of three or more and preserve the line width. SIGGMA will produce the most sensitive fully sampled RRL survey to date. Here, we discuss the observing and data reduction techniques in detail. A test observation toward the H II region complex S255/S257 has detected Hn? and Cn? lines with S/N > 10.

Liu, B.; McIntyre, T.; Terzian, Y.; Minchin, R.; Anderson, L.; Churchwell, E.; Lebron, M.; Anish Roshi, D.

2013-10-01

217

Determination of polycyclic aromatic hydrocarbons [PAHs] in processed meat products using gas chromatography - flame ionization detector.  

PubMed

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in smoked, grilled and boiled meats were determined using gas chromatography - flame ionization detector (GC-FID). PAHs in the processed meats were extracted in n-hexane after hydrolysis with methanolic KOH. Clean-up was achieved using solid phase extraction in neutral-Si/basic-Si/acidic-Si/neutral-Si frits. The fractions, benzo[k]fluoranthene (BkP), benzo[a]pyrene (BaP), indeno[123-cd]pyrene (IP) and benzo[ghi]perylene (BghiP) were separated and quantified using GC-FID. The method and instrument limits of detections were 0.1, 0.1, 0.2, 0.3?g/kg and 0.5, 0.5, 1.0, 1.5?g/kg, respectively, for BkP, BaP, IP and BghiP. The method's recovery and precision generally varied between 83.69% and 94.25% with relative standard deviation (RSD) of 3.18-15.60%; and 90.38-96.71% with relative standard deviation (RSD) of 1.82-12.87% respectively. The concentration of BkP, BaP, IP and BghiP in smoked, grilled and boiled meat samples were ranged 0.64-31.54?g/kg, 0.07-7.04?g/kg, 0.09-15.03, 0.51-46.67?g/kg and 0.01-5.11?g/kg, respectively. PMID:24629971

Olatunji, Olatunde S; Fatoki, Olalekan S; Opeolu, Beatrice O; Ximba, Bhekumusa J

2014-08-01

218

High-velocity clouds as streams of ionized and neutral gas in the halo of the Milky Way  

NASA Astrophysics Data System (ADS)

High-velocity clouds (HVCs), fast-moving ionized and neutral gas clouds found at high galactic latitudes, may play an important role in the evolution of the Milky Way. The extent of this role depends sensitively on their distances and total sky covering factor. We search for HVC absorption in Hubble Space Telescope high-resolution ultraviolet (UV) spectra of a carefully selected sample of 133 active galactic nuclei (AGN) using a range of atomic species in different ionization stages (e.g. O I, C II, C IV, Si II, Si III, Si IV). This allows us to identify neutral, weakly ionized or highly ionized HVCs over several decades in H I column densities. The sky covering factor of UV-selected HVCs with |vLSR| ? 90 km s-1 is about 68 per cent for the Galactic sky at |b|?20?. About 74 per cent of the HVC directions have N(H i)<3×1018 cm-2 and 46 per cent have N(H i)<8×1017 cm-2. We show that our survey is essentially complete, i.e. an undetected population of HVCs with extremely low H (H I + H II) column density is unlikely to be important for the HVC mass budget. We confirm that the predominantly ionized HVCs contain at least as much mass as the traditional H I HVCs and show that large H I HVC complexes have generally ionized envelopes extending far from the H I contours. There are also large regions of the Galactic sky that are covered with ionized high-velocity gas with little H I emission nearby. We show that the covering factors of HVCs with 90?|v LSR |?170 km s-1 drawn from the AGN and stellar (with stars at d > 3 kpc) samples are similar. This confirms that most of the HVCs are within 5-15 kpc of the sun. The HVCs with |vLSR |?170 km s-1 are largely associated with the Magellanic Stream at b < -20° and its leading arm at b > 20° as well as other large known H I complexes. We conclude that there is no evidence in the Local Group that any galaxy shows a population of HVCs extending much farther away than 50 kpc from its host, except possibly for those tracing remnants of galaxy interaction. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract no. NAS5-26555.

Lehner, N.; Howk, J. C.; Thom, C.; Fox, A. J.; Tumlinson, J.; Tripp, T. M.; Meiring, J. D.

2012-08-01

219

Highly ionized gas absorption in the disk and halo toward HD 167756 at 3.5 kilometers per second resolution  

NASA Technical Reports Server (NTRS)

High-resolution spectra of interstellar Si IV, C IV, and N V absorption lines along the 4 kpc path to the inner Galaxy star HD 167756 at z = -0.85 kpc are presented. The spectra were obtained with the echelle mode of Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) and have signal-to-noise ratios ranging from 23 to 38. The high resolution of the measurements full width at half maximum (FWHM = 3.5 km/s) results in fully resolved line profiles for the highly ionized gas absorption. The measurements provide information on the column density per unit velocity, N(v), as a function of velocity for Si IV, C IV, and N V. The C IV and N V profiles extend from -70 to +70 km/s, while the Si IV profiles extend from -40 to +70 km/s. The integrated logarithmic column densities are long N(Si IV) = 13.09 +/- 0.02, log N(C IV) = 13.83 +/- 0.02, and log N(N V) = 13.56 +/- 0.03. The N V profile is broad, asymmetric, and featureless, while the Si IV profile contains narrow absorption components near V(sub LSR) = -19, 0, +20, and +52 km/s with Doppler spread parameters, b about = 10-12 km/s. The C IV profile contains both broad and narrow structure. The high ion feature near +52 km/s is also detected in the low-ionization lines of Ca II, O I, Si II, and Fe II. The other narrow Si IV and C IV components occur within several km/s of components seen in low-ionization species. The sight line contains at least two types of highly ionized gas. One type gives rise to a broad N V profile, and the other results in the more structured Si IV profile. The C IV profile contains contributions from both types of highly ionized gas. The broad but asymmetric N V profile is well represented by a large Galactic scale height gas which is participating in Galactic rotation and has a combination of thermal and turbulent broadening with b(sub tot) about = 42 km/s. The C IV to N V abundance ratio of 1.0 +/- 0.3 for the gas implies T about 1.6 x 10(exp 5) K or about 8 x 10(exp 5) K if the gas is in collisional ionization equilibrium and has a solar carbon to nitrogen abundance ratio. This absorption may be associated with cooling hot gas situated in Galactic shells and supershells along the sight line. The gas producing the narrow Si IV and C IV absorption components has line widths that are compatible with origins in conductive interfaces between the warm and hot interstellar medium. Kinematic flows associated with the photoionized edges of clouds might also produce Si IV and C IV lines with Doppler spread parameters similar to those observed, but the C IV to Si IV ratio in this gas is 3.5, which leads us to favor the conductive interface interpretation.

Savage, Blair D.; Sembach, Kenneth R.; Cardelli, Jason A.

1994-01-01

220

Ionization of the diffuse gas in galaxies: Hot low-mass evolved stars at work  

NASA Astrophysics Data System (ADS)

The Diffuse Ionized Medium (DIG) is visible through its faint optical line emission outside classical HII regions (Reynolds 1971) and turns out to be a major component of the interstellar medium in galaxies. OB stars in galaxies likely represent the main source of ionizing photons for the DIG. However, an additional source is needed to explain the increase of [NII]/H?, [SII]/H? with galactic height.

Flores-Fajardo, N.; Morisset, C.; Stasinska, G.; Binette, L.

2011-10-01

221

Ionization of Local Interstellar Gas Based on STIS and FUSE spectra of Nearby Stars  

NASA Astrophysics Data System (ADS)

The ultraviolet contains many resonance line transitions that are sensitive to a range of ionization stages of ions present in the local interstellar medium (LISM). We couple observations of high resolution ultraviolet spectrographs, STIS and GHRS on the Hubble Space Telescope (HST) and the Far-Ultraviolet Spectroscopic Explorer (FUSE) in order to make a comprehensive survey of the ionization structure of the local interstellar medium. In particular, we focus on the sight line toward G191-B2B, a nearby (69 pc) white dwarf. We present interstellar detections of highly ionized elements (e.g., SiIII, CIII, CIV, etc) and compare them directly to neutral or singly ionized LISM detections (e.g., SiII, CII, etc). The extensive observations of G191-B2B provides an opportunity for a broad study of ionization stages of several elements, while a survey of several sight lines provides a comprehensive look at the ionization structure of the LISM. We acknowledge support for this project through NASA FUSE Grant NNX06AD33G.

Redfield, Seth; Linsky, J. L.

2009-01-01

222

PRESENT-DAY GALACTIC EVOLUTION: LOW-METALLICITY, WARM, IONIZED GAS INFLOW ASSOCIATED WITH HIGH-VELOCITY CLOUD COMPLEX A  

SciTech Connect

The high-velocity cloud Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin H{alpha} Mapper kinematically resolved observations of Complex A over the velocity range of -250 to -50 km s{sup -1} in the local standard of rest reference frame. These observations include the first full H{alpha} intensity map of Complex A across (l, b) = (124 Degree-Sign , 18 Degree-Sign ) to (171 Degree-Sign , 53 Degree-Sign ) and deep targeted observations in H{alpha}, [S II] {lambda}6716, [N II] {lambda}6584, and [O I] {lambda}6300 toward regions with high H I column densities, background quasars, and stars. The H{alpha} data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than 10{sup 6} M{sub Sun }. We find that the Bland-Hawthorn and Maloney model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7-8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 10{sup 4} K or for gas with a high fraction of singly ionized nitrogen and sulfur.

Barger, K. A.; Haffner, L. M.; Wakker, B. P.; Hill, Alex S. [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Madsen, G. J. [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Duncan, A. K., E-mail: kbarger@astro.wisc.edu, E-mail: haffner@astro.wisc.edu, E-mail: Alex.Hill@csiro.au, E-mail: wakker@astro.wisc.edu, E-mail: greg.madsen@sydney.edu.au [Rose-Hulman Institute of Technology, Terre Haute, IN 47803 (United States)

2012-12-20

223

Present-day Galactic Evolution: Low-metallicity, Warm, Ionized Gas Inflow Associated with High-velocity Cloud Complex A  

NASA Astrophysics Data System (ADS)

The high-velocity cloud Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin H? Mapper kinematically resolved observations of Complex A over the velocity range of -250 to -50 km s-1 in the local standard of rest reference frame. These observations include the first full H? intensity map of Complex A across (\\mathit {l, b}) = (124{^\\circ }, 18{^\\circ }) to (171°, 53°) and deep targeted observations in H?, [S II] ?6716, [N II] ?6584, and [O I] ?6300 toward regions with high H I column densities, background quasars, and stars. The H? data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than 106 M ?. We find that the Bland-Hawthorn & Maloney model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7-8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 104 K or for gas with a high fraction of singly ionized nitrogen and sulfur.

Barger, K. A.; Haffner, L. M.; Wakker, B. P.; Hill, Alex. S.; Madsen, G. J.; Duncan, A. K.

2012-12-01

224

Al III, Si IV, and C IV absorption toward zeta Ophiuchi: Evidence for photionized and collisionally ionized gas  

NASA Technical Reports Server (NTRS)

We present Goddard High-Resolution Spectrograph observations at 3.5 km/s resolution and signal-to-noise ratios of 30 to 60 for the Al III, Si IV, and N V absorption lines in the far-ultraviolet spectrum of the O9.5 V star zeat Ophiuchi. The measurement reveal three types of highly ionized gas along the 140 pc line of sight. (1) Narrow components of Al III (b = 4.3 km/s, the mean value of (v(helio)) = -7.8 km/s; b = 3.2 km/s, the mean value of (v(sub helio)) = -14.4 km/s) and Si IV (b = 5.3 km/s, the mean value of (v(sub helio)) = -15.0 km/s) trace photionized gas in the expanding H II region surrounding zeta Oph. The observed magnitude and direction of the velocity offset between the Al III and Si IV profiles can be explained by models of H II regions that incorporate expansion. Narrow C IV absorption associated with the H II region is not detected. Predictions of the expected amounts of Si IV and C IV overestimate the column densities of these ions by factors of 30 and more than 10, respectively. The discrepancy may be due to the effects of elemental depletions in the gas and/or to the interaction of the stellar wind with surrounding matter. (2) Broad (b = 15 to 18 km/s) and weak Si IV and C IV absorption components are detected near the mean value of (v(sub helio)) = -26 km/s. The high-ionization species associated with these absorption components are probably produced by electron collisional ionization in a heated gas. This absorption may be physically related to the zeta Oph bow shock ot to a cloud complex situated within the local interstellar medium at d less than 60 pc. The C IV to Si IV column density ratio in this gas is 8, a factor of 6 less than conductive interface models predict, but this discrepancy may be removed by considering the effects of self-photoionization within the cooling gas in the model calculations. (3) A broad (b = 13 km/s) and weak C IV absorption feature detected at the mean value of (v(sub helio)) = -61 km/s is not seen in other species. We tentatively ascribe this absorption to gas in a postshock ragion of an optically thin shock in the zeta Oph stellar wind.

Sembach, Kenneth R.; Savage, Blair D.; Jenkins, Edward B.

1994-01-01

225

Ultraviolet interstellar absorption toward stars in the Small Magellanic Cloud. IV - Highly ionized gas associated with the Small Magellanic Cloud  

NASA Technical Reports Server (NTRS)

High-dispersion International Ultraviolet Explorer satellite spectra of seven stars in the Small Magellanic Cloud (SMC) are examined to study the properties of interstellar C IV and Si IV absorption in the SMC. Absorption by C IV or Si IV or both is found near 160 km/s for all the stars. The velocity and the relative C IV and Si IV strengths suggest UV-photoionized nebular gas as the origin of this absorption. In addition, the stars show absorption by C IV and, sometimes, Si IV in the velocity range 100-130 km/s. This velocity is 30-60 km/s more negative than that expected for normal nebular gas, and the relative C IV and Si IV strengths indicate an ionization source other than stellar UV photoionization by normal Population I stars. Possible global origins are considered for this absorption, including a hot phase of the SMC interstellar medium and a circum-SMC distribution of highly ionized gas. The only detection of interstellar N V toward a SMC star is for HD 5980. The line is broad, possibly complex, and spans the velocity range of the nebular absorption and the 100-130 km/s absorption.

Fitzpatrick, E. L.; Savage, B. D.

1985-01-01

226

Electronic spectroscopy and ionization potential of UO2 in the gas phase.  

PubMed

The electronic spectroscopy of UO(2) has been examined using multiphoton ionization with mass-selected detection of the UO(2) (+) ions. Supersonic jet cooling was used to reduce the spectral congestion. Twenty-two vibronic bands of neutral UO(2) were observed in the range from 17,400 to 32,000 cm(-1). These bands originated from the U(5fphi(u)7ssigma(g))O(2) X (3)Phi(2u) and (3)Phi(3u) states. The stronger band systems are attributed to metal-centered 7p<--7s transitions. Threshold ionization measurements were used to determine the ionization potentials of UO and UO(2). These were found to be higher than the values obtained previously from electron impact measurements but in agreement with the results of recent theoretical calculations. PMID:15267385

Han, Jiande; Goncharov, Vasiliy; Kaledin, Leonid A; Komissarov, Anatoly V; Heaven, Michael C

2004-03-15

227

Fuel cell with ionization membrane  

NASA Technical Reports Server (NTRS)

A fuel cell is disclosed comprising an ionization membrane having at least one area through which gas is passed, and which ionizes the gas passing therethrough, and a cathode for receiving the ions generated by the ionization membrane. The ionization membrane may include one or more openings in the membrane with electrodes that are located closer than a mean free path of molecules within the gas to be ionized. Methods of manufacture are also provided.

Hartley, Frank T. (Inventor)

2007-01-01

228

Dynamical theory of low-energy ionization of inert-gas atoms at surfaces  

NASA Astrophysics Data System (ADS)

A quasi-ab-initio calculation of the ionization probability of a low-energy He atom at the surface of a linear chain of n atoms (modeling Si) has been made using the technique of numerical solution of the equations of motion for scrNij(t)?ionization effect below 1 keV has been explained on the basis of impact scattering, in which the projectile valence orbital overlaps the target core orbitals. Two conditions are established for seeing the effect: (1) The hopping integral Vak(z) between the orbitals centered on the He atom and the target atom must go through zero at distances z~=RC (the distance of closest approach). (2) The diabatic level centered on the projectile must shift up to near ?F there. Fortunately, the first condition will be rather generally encountered, because of the oscillations in the target valence orbitals at small radius. On the other hand, feature (2) is more specific to the projectile-target material combination and leads to some target material dependencies. At energies higher than 2 keV, the ionization probabilities with and without the level shift ? become identical, and only condition (1) is necessary. Thus, in this energy region the surface ionization effect will be more generally expected for such systems as, e.g., the He-->Cu surface, which has a noncrossing energy-level diagram or ?=0, in good agreement with experiment. For energies greater than 50 or 100 keV, neither condition is necessary, and Pion oscillates as a function of E0, representing the quasiresonant ionization process. It is also found that the ionization probability Pion in surface scattering (n>=30) is nearly 1 order of magnitude greater than that in a binary collision (n=1), at an energy of 1 keV. The effect of the energy-band occupation has also been shown to be of essential importance.

Muda, Y.; Newns, D. M.

1988-04-01

229

Fast gas chromatography and negative-ion chemical ionization tandem mass spectrometry for forensic analysis of cannabinoids in whole blood  

Microsoft Academic Search

The present work describes a fast gas chromatography\\/negative-ion chemical ionization tandem mass spectrometric assay (Fast GC\\/NICI-MS\\/MS) for analysis of tetrahydrocannabinol (THC), 11-hydroxy-tetrahydrocannabinol (THC-OH) and 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH) in whole blood. The cannabinoids were extracted from 500?L of whole blood by a simple liquid–liquid extraction (LLE) and then derivatized by using trifluoroacetic anhydride (TFAA) and hexafluoro-2-propanol (HFIP) as fluorinated agents. Mass spectrometric

Aurélien Thomas; Christèle Widmer; Gérard Hopfgartner; Christian Staub

2007-01-01

230

Determination of 3,4-dihydroxyphenylethyleneglycol in urine by gas chromatography with a flame ionization detector: a new rapid method.  

PubMed

3,4-Dihydroxyphenylethyleneglycol, a major metabolite of noradrenaline in rat brain, is estimated alone or with 4-hydroxy-3-methoxyphenylethyleneglycol in rat and human urine by gas chromatography with a flame ionization detector. The samples are hydrolyzed and extracted at pH 2 with ethyl acetate. Then, to analyze only 3,4-dihydroxyphenylethyleneglycol the reaction with n-butaneboronic acid is carried out directly; if 4-hydroxy-3-methoxyphenylethyleneglycol also has to be estimated, preliminary acetylation in alkaline aqueous solution is performed. The advantages of the specificity due to the reagents used is discussed. PMID:378468

Biondi, P A; Fedele, G; Motta, A; Secchi, C

1979-06-01

231

Far-IR spectroscopy of the galactic center: Neutral and ionized gas in the central 10 pc of the galaxy  

NASA Technical Reports Server (NTRS)

The 3P1 - 3P2 fine structure line emission from neutral atomic oxygen at 63 microns in the vicinity of the galactic center was mapped. The emission is extended over more than 4' (12 pc) along the galactic plane, centered on the position of Sgr A West. The line center velocities show that the O I gas is rotating around the galactic center with an axis close to that of the general galactic rotation, but there appear also to be noncircular motions. The rotational velocity at R is approximately 1 pc corresponds to a mass within the central pc of about 3 x 10(6) solar mass. Between 1 and 6 pc from the center the mass is approximately proportional to radius. The (O I) line probability arises in a predominantly neutral, atomic region immediately outside of the ionized central parsec of out galaxy. Hydrogen densities in the (O I) emitting region are 10(3) to 10(6) cm(-3) and gas temperatures are or = 100 K. The total integrated luminosity radiated in the line is about 10(5) solar luminosity, and is a substantial contribution to the cooling of the gas. Photoelectric heating or heating by ultraviolet excitation of H2 at high densities (10(5) cm(-3)) are promising mechanisms for heating of the gas, but heating due to dissipation of noncircular motions of the gas may be an alternative possibility. The 3P1 - 3P0 fine structure line of (O III) at 88 microns toward Sgr A West was also detected. The (O III) emission comes from high density ionized gas (n 10(4) cm(-3)), and there is no evidence for a medium density region (n 10(3) cm(-3)), such as the ionized halo in Sgr A West deduced from radio observations. This radio halo may be nonthermal, or may consist of many compact, dense clumps of filaments on the inner edges of neutral condensations at R or = 2 pc.

Hollenbach, D. J.; Watson, D. M.; Townes, C. H.; Dinerstein, H. L.; Hollenbach, D.; Lester, D. F.; Werner, M.; Storey, J. W. V.

1983-01-01

232

Measuring the Obscured Ionized Gas in the Center of the Nearby Face-on Spiral IC 342 with the GBT and EVLA  

NASA Astrophysics Data System (ADS)

Galactic centers represent a unique environment for star formation. Their high gas surface densities and short crossing times may lead to more efficient star formation than found in the disks of galaxies. Measuring the properties of the young massive clusters in galactic centers is critical to understanding star formation in this environment. One way to do this is to measure the properties of the gas ionized by the young massive clusters. Unfortunately, this gas is still obscured by the natal clouds of dust and gas surrounding the young massive clusters. Therefore, measuring the properties of this gas requires the use of an extinction-free ionized gas tracer like radio recombination lines. This poster presents radio recombination line observations of the center of the nearby face-on spiral galaxy IC 342. These observations constrain the density, filling factor, and kinematics of the obscured ionized gas in the center of this galaxy. The properties of the ionized gas are then used to constrain the properties of the young massive clusters and star formation efficiency in the center of IC 342.

Kepley, Amanda A.; Balser, D. S.; Chomiuk, L.; Goss, M.; Johnson, K. E.; Meier, D. S.; Pisano, D. J.

2013-01-01

233

Rapid characterization of artemether and its in vitro metabolites on incubation with bovine hemoglobin, rat blood and dog blood by capillary gas chromatography–chemical ionization mass spectrometry  

Microsoft Academic Search

A fast and sensitive analytical method was developed to characterize artemether and its metabolites in small amounts in body fluids. The extracts were derivatized with N-methyl-N-trimethylsilyltrifluoroacetamide, separated on an optimized capillary gas chromatographic system and identified by chemical ionization mass spectrometry by using ammonia as reagent gas. The analytical assay is demonstrated on samples extracted from bovine hemoglobin, rat blood

Wolfgang Blum; Ulrike Pfaar; Jürgen Kühnöl

1998-01-01

234

Ionization chamber  

DOEpatents

An ionization chamber has separate drift and detection regions electrically isolated from each other by a fine wire grid. A relatively weak electric field can be maintained in the drift region when the grid and another electrode in the chamber are connected to a high voltage source. A much stronger electric field can be provided in the detection region by connecting wire electrodes therein to another high voltage source. The detection region can thus be operated in a proportional mode when a suitable gas is contained in the chamber. High resolution output pulse waveforms are provided across a resistor connected to the detection region anode, after ionizing radiation enters the drift region and ionize the gas.

Walenta, Albert H. (Port Jefferson Station, NY)

1981-01-01

235

Hydrogen ionization at the positive electrodes of lead-acid batteries with positive gas feed  

Microsoft Academic Search

In sealed electric storage batteries such as lead-acid batteries, the gases evolved during charging or storing must be absorbed. A highly promising and economic solution to this problem is obtained when the acid battery is built with bifunctional electrodes. A thermodynamic analysis is presented which reveals that molecular hydrogen can be ionized at lead dioxide electrodes. Data obtained at model

E. A. Khouskaya; N. F. Gorbacheva

1985-01-01

236

Gas phase studies on terpenes by ion mobility spectrometry using different atmospheric pressure chemical ionization techniques  

NASA Astrophysics Data System (ADS)

The ionization pathways and drift behavior were determined for sets of constitutional isomeric and stereoisomeric non-polar hydrocarbons (unsaturated monocyclic terpenes, unsaturated and saturated bicyclic terpenes) using ion mobility spectrometry (IMS) with different techniques of atmospheric pressure chemical ionization (APCI) to assess how structural and stereochemical differences influence ion formation. Depending on the structural features, different ions were observed for constitutional isomers using ion mobility spectrometry with photoionization (PI) and corona discharge (CD) ionization. Photoionization provides ion mobility spectra containing one major peak for saturated compounds while at two peaks were observed for unsaturated compounds, which can be assigned to product ions related to monomer and dimer ions. However, differences in relative abundance of product ions were found depending on the position of the double bond. Although IMS using corona discharge ionization permits the most sensitive detection of non-polar hydrocarbons, the spectra are complex and differ from those obtained using photoionization. Additional cluster ions and fragment ions were detected. Only small differences in ion mobility spectra were observed for the diastereomers while the enantiomers provide identical spectra. The structure of the product ions formed was checked by investigations using the coupling of ion mobility spectrometry with mass spectrometry (IMS-MS).

Borsdorf, H.; Stone, J. A.; Eiceman, G. A.

2005-11-01

237

Interaction of rare gas metastable atoms. [Differential and total cross sections, elastic scattering, ionization, potential scattering, phase shifts, rate constants  

SciTech Connect

The physical and chemical properties of metastable rare gas atoms are discussed and summarized. This is followed by a detailed examination of the various possible pathways whereby the metastable's excess electronic energy can be dissipated. The phenomenon of chemi-ionization is given special emphasis, and a theoretical treatment based on the use of complex (optical) potential is presented. This is followed by a discussion on the unique advantages offered by elastic differential cross section measurements in the apprehension of the fundamental forces governing the ionization process. The methodology generally adopted to extract information about the interaction potential for scattering data is also systematically outlined. Two widely studied chemi-ionization systems are then closely examined in the light of accurate differential cross section measurements obtained in this work. The first system is He(2/sup 3/S) + Ar for which one can obtain an interaction potential which is in good harmony with the experimental results of other investigators. The validity of using the first-order semiclassical approximation for the phase shifts calculation in the presence of significant opacities is also discussed. The second reaction studied is He*+D/sub 2/ for which measurements were made on both spin states of the metastable helium. A self-consistent interaction potential is obtained for the triplet system, and reasons are given for not being able to do likewise for the singlet system. The anomalous hump proposed by a number of laboratories is analyzed. Total elastic and ionization cross sections as well as rate constants are calculated for the triplet case. Good agreement with experimental data is found. Finally, the construction and operation of a high power repetitively pulsed nitrogen laser pumped dye laser system is described in great details. Details for the construction and operation of a flashlamp pumped dye laser are likewise given.

Wang, A.Z.F.

1977-11-01

238

Advantages of atmospheric pressure chemical ionization in gas chromatography tandem mass spectrometry: pyrethroid insecticides as a case study.  

PubMed

Gas chromatography coupled to mass spectrometry (GC/MS) has been extensively applied for determination of volatile, nonpolar, compounds in many applied fields like food safety, environment, or toxicology. The wide majority of methods reported use electron ionization (EI), which may result in extensive fragmentation of analytes compromising selectivity and sensitivity. This might also complicate the application of tandem MS due to lack of specific/abundant precursor ions. Pyrethroids are examples of compounds with this behavior. In this work, the potential of atmospheric pressure chemical ionization (APCI), a softer form of ionization, combined with GC and a triple quadrupole mass analyzer was investigated, taking pyrethroids as a case study and their determination in fruit and vegetables as example application. Ionization and fragmentation behavior of eight pyrethroids (bifenthrin, cyfluthrin, cypermethrin, permethrin, ?-cyhalothrin, fluvalinate, fenvalerate, and deltamethrin) by APCI were studied. The formation of a highly abundant (quasi) molecular ion was the main goal because of the enhanced selectivity when used as precursor ion in tandem MS. The addition of water as a modifier was tested to promote the generation of protonated molecules, resulting in notable improvement of sensitivity and selectivity for most compounds. The excellent detectability (low detection limits (LODs) <20 fg achieved) when using APCI combined with state-of-the-art tandem MS was demonstrated for real samples. Additionally, matrix effects were evaluated in terms of signal enhancement/suppression. Depending on the matrix, different degrees of suppression were observed, on average reducing the signal in matrix to 55% of that in solvent. The results presented in this paper demonstrate the potential of APCI as new source for GC/MS that could be applied to other analytical problems apart from those illustrated in this work. PMID:23006011

Portolés, T; Mol, J G J; Sancho, J V; Hernández, F

2012-11-20

239

Production of Neutron-rich Co and Ni Isotopes in a Gas Catcher Cell followed by Resonant Laser Ionization.  

NASA Astrophysics Data System (ADS)

An ion source for producing short-lived neutron-rich nuclei has been developed and connected to the LISOL mass separator. This source consists of a gas cell for capturing recoiling fission products which become neutralized in and transported by the gas flow to the exit hole. Specific elements are selectively ionized and subsequently guided via an RF ion guide to the mass separator. This source has been used to produce ^69-74Ni and ^66-71Co nuclei from which the ?-delayed ? rays were studied. The details of the ion-source setup and performance and some of the key results of the ?-decay studies will be presented. Future prospects as well as other applications of this technique will also be discussed.

Mueller, W. F.; Bruyneel, B.; Franchoo, S.; Huyse, M.; Kruglov, K.; Kudryavtsev, Y.; Prasad, N. V. S. V.; Raabe, R.; Reusen, I.; van Duppen, P.; van Roosbroeck, J.; Vermeeren, L.; Weissman, L.; Janas, Z.; Karny, M.; Kszczot, T.; Plochocki, A.; Kratz, K.-L.; Pfeiffer, B.; Köster, U.; Thirolf, P.; Walters, W. B.

1999-10-01

240

The Ionized Gas and Nuclear Environment in NGC 3783. IV; Variability and Modeling of the 900 ks CHANDRA Spectrum  

NASA Technical Reports Server (NTRS)

We present a detailed analysis of the 900 ks spectrum of NGC3783 obtained by Chandra in 2000-2001 (Kaspi et al. 2002). We split the data in various ways to look for time dependent and luminosity dependent spectral variations. This analysis, the measured equivalent widths of a large number of X-ray lines, and our photoionization calculations, lead us to the following conclusions: 1) NGC 3783 fluctuated in luminosity, by a factor N 1.5, during individual 170 ks observations. The fluctuations were not associated with significant spectral variations. 2) On a longer time scale, of 20-120 days, we discovered two very different spectral shapes that are noted the high state and the low state spectra. The observed changes between the two can be described as the appearance and disappearance of a soft continuum component. The spectral variations are not related, in a simple way, to the brightening or the fading of the short wavelength continuum, as observed in other objects. NGC3783 seems to be the first AGN to show this unusual behavior. 3) The appearance of the soft continuum component is consistent with beeing the only spectral variation and there is no need to invoke changes in the absorber s opacity. In particular, all absorption lines with reliable measurements show the same equivalent width, within the observational uncertainties, during high and low states. 4) Photoionization model calculations show that a combination of three ionization components, each split into two kinematic components, explain very well the intensity of almost all absorption lines and the bound-free absorption. The components span a large range of ionization and a total column of about 3 x 10(exp 22) per square centimeter Moreover, all components are thermally stable and are situated on the vertical branch of the stability curve.. This means that they are in pressure equilibrium and perhaps occupy the same volume of space. This is the first detection of such a multi-component equilibrium gas in AGN. 5) The only real discrepancy between the model and the observations is the wavelength of the iron M-shell UTA feature. This is most likely due to an underestimation of the dielectronic recombination O VI and discuss its possible origin. 6) The lower limit on the distance of the absorbing gas in NGC3783 is between 0.2 and 3.2 pc, depending of the specific ionization component. The constant pressure assumption imposes an upper limit of about 25 pc on the distance of the least ionized gas from the central sourec.

Netzer, Hagai; Kaspi, Shai; Behar, Ehud; Brandt, W. N.; Chelouche, Doron; George, Ian M.; Crenshaw, D. Michael; Gabel, Jack R.; Hamann, Frederick W.; George, Steven B.

2003-01-01

241

Narrowband HST images of M87: Evidence for a disk of ionized gas around a massive black hole  

NASA Technical Reports Server (NTRS)

We present Hubble Space Telescope Wide Field/Planetary Camera-2 (HST WFPC2) narrowband H-alpha + (N II) images of M87 which show a small disk of ionized gas with apparent spiral structure surrounding the nucleus of M87. The jet projects approximately 19.5 deg from the minor axis of the disk, which suggests that the jet is approximately normal to the disk. In a companion Letter, Harms et al. measure the radial velocities at r = +/- 0.25 sec along a line perpendicular to the jet, showing that one side of the disk is approaching at 500 +/- 50 km/s and the other side of the disk is receding at 500 +/- 50 km/s. Absorption associated with the disk and the sense of rotation imply that the apparent spiral arms trail the rotation. The observed radial velocites corrected for a 42 deg inclination of the disk imply rotation at +/- 750 km/s. Analysis of velocity measurements at four positions near the nucleus gives a total mass of approximately 2.4 +/- 0.7 x 10(exp 9) solar mass within 18 pc of the nucleus, and a mass-to-light ratio (M/L)(sub I) = 170. We conclude that there is a disk of ionized gas feeding a massive black hole in the center of M87.

Ford, Holland C.; Harms, Richard J.; Tsvetanov, Zlatan I.; Hartig, George F.; Dressel, Linda L.; Kriss, Gerard A.; Bohlin, Ralph C.; Davidsen, Arthur F.; Margon, Bruce; Kochhar, Ajay K.

1994-01-01

242

Transfer Ionization in MeV p-He Collisions Studied by Pulsed Recoil-Ion-Momentum Spectroscopy in a Storage Ring/Gas Target Experiment  

NASA Astrophysics Data System (ADS)

We have investigated the transfer ionization process in fast collisions between protons, stored in the heavy-ion storage and cooler ring CRYRING, and a cold supersonic helium gas-jet target: H+ + He --> H + He2+ + e-. We have refined the COLTRIMS (COLd Target Recoil-Ion-Momentum Spectroscopy) technique by applying time-varying fields in the recoil-ion-momentum spectrometer to block random singly charged helium ions from single-ionization events.

Schmidt, H. T.; Cocke, C. L.; Fardi, A.; Jensen, J.; Schmidt-Böcking, H.; Schmidt, L.; Schuch, R.; Zettergren, H.; Cederquist, H.

2003-08-01

243

Resonantly enhanced vacuum-ultraviolet generation and multiphoton ionization in carbon monoxide gas  

SciTech Connect

Competition between three-photon resonantly enhanced vacuum ultraviolet third-harmonic generation and six-photon multiphoton ionization using the A state in gaseous carbon monoxide is observed. Excitation spectra of the third-harmonic emission exhibit increasing blue shifts and broadening with increasing pressure due to the phase matching requirements. Estimates for the efficiency and tunability show that third-harmonic generation in carbon monoxide molecules is a promising source for coherent vacuum ultraviolet light.

Glownia, J.H.; Sander, R.K.

1982-01-01

244

Ionized gas and stars in the central kiloparsec of the type 2 Seyfert galaxy NGC 2110 - I. The data  

NASA Astrophysics Data System (ADS)

In this paper, we present new results from an extensive set of Hubble Space Telescope (HST) and ground-based observations of the Seyfert galaxy NGC 2110. The HST data sets include Wide Field Planetary Camera 2 (WFPC2) observations as well as the first high-spatial resolution spectroscopy ([OI], [NII], H? and [SII] lines) of this galaxy obtained using the Space Telescope Imaging Spectrograph (STIS). The ground-based data are three-dimensional (x, y, ?) spectrographic observations obtained using the integral field spectrograph OASIS on the Canada-France-Hawaii Telescope, complemented by near-infrared long-slit spectroscopy obtained using NIRSPEC on the Keck-II telescope. The OASIS observations cover regions containing both stellar absorption lines and major optical emission lines. The NIRSPEC observations cover the H and K bands. Combined with archival HST observations, the WFPC2 data provide us with a high-spatial resolution extinction map. The OASIS data allowed bidimensional mapping of the stellar and gaseous kinematics, as well as of the spectral properties of the ionized gas. These results are compared to those obtained in the near-infrared with NIRSPEC/Keck. Last, we used the STIS data to probe the ionized gas kinematics and properties in the inner 4arcsec along PA = 156° at unprecedented spatial resolution. Our two-dimensional (2D) map of the stellar velocity field and the near-infrared stellar velocity profile are symmetric about the nucleus, confirming the results of previous long-slit observations. The asymmetry of the velocity field of the ionized gas is present at the same level for visible and near-infrared lines, indicating this is not a reddening effect. Multiple Gaussian fitting of the emission-line profile allowed the contributions of the broad and a narrow components to be disentangled. The intensity peak of the [OIII] narrow component is located north of the nucleus, indicating that the bulk of the narrow [OIII] emission comes from the jet-like structure (Mulchaey et al.) and not from the nucleus itself. We suggest that the northern arm is the anomalous one, contrary to what has been claimed earlier. Last, we also show that the elongated region of high gas velocity dispersion located close to the nucleus and discovered by Gonzàlez Delgado et al. is intrinsic to the narrow component.

Ferruit, P.; Mundell, C. G.; Nagar, N. M.; Emsellem, E.; Pécontal, E.; Wilson, A. S.; Schinnerer, E.

2004-08-01

245

Analysis of tert-butyldimethylsilyl derivatives in heavy gas oil from Brazilian naphthenic acids by gas chromatography coupled to mass spectrometry with electron impact ionization.  

PubMed

Naphthenic acids, C(n)H(2n+Z)O(2), are a complex mixture of alkyl-substituted acyclic and cycle-aliphatic carboxylic acids. The content of naphthenic acids and their derivatives in crude oils is very small, which hinders their extraction from matrixes of wide and varied composition. In this work, liquid-liquid extraction, followed by solid phase extraction with an ion exchange resin (Amberlyst A-27) and ultrasound desorption were used to isolate the acid fraction from heavy gas oil of Marlim petroleum (Campos, Rio de Janeiro, Brazil). The analysis was accomplished through gas chromatography coupled to mass spectrometry with electron impact ionization, after derivatization with N-methyl-N-(tert-butyldimethylsilyl)trifluoracetamide (MTBDMSTFA). The results indicate the presence of carboxylic acids belonging to families of alicyclic and naphthenic compounds which contain up to four rings in the molecule. PMID:16439253

Vaz de Campos, Maria Cecília; Oliveira, Eniz Conceição; Filho, Pedro José Sanches; Piatnicki, Clarisse Maria Sartori; Caramão, Elina Bastos

2006-02-10

246

40 CFR 1065.267 - Gas chromatograph with a flame ionization detector.  

Code of Federal Regulations, 2013 CFR

...267 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Hydrocarbon Measurements § 1065.267 Gas chromatograph with a flame...

2013-07-01

247

Thermal desorption-gas chromatography-mass spectrometry-flame ionization detection-sniffer multi-coupling: A device for the determination of odorous volatile organic compounds in air  

Microsoft Academic Search

A multi-coupling analytical system is described, consisting of a thermal desorber installed with a gas chromatograph, a flame ionization detector, a mass spectrometer and a sniffer. The sniffer was connected at the output of the GC column leading to the flame ionization detector. The retention times obtained by the flame ionization detector and the sniffer are well correlated, allowing the

P. Karpe; S. Kirchner; P. Rouxel

1995-01-01

248

Kinematics of the diffuse ionized gas in spiral galaxy disk-halo interactions  

Microsoft Academic Search

Multiphase gas has been observed in the halos of the Milky Way and some external spiral galaxies. The origin of this gas is still unknown, but observational evidence indicates that star formation-driven disk-halo flows likely play an important role: a correlation is observed between more prominent gaseous halos and higher disk star formation rates; moreover, loop and filamentary structures, often

George Herbert Heald Jr.

2006-01-01

249

A Desorbed Gas Molecular Ionization Mechanism for Arcing Onset in Solar Arrays Immersed in a Low-Density Plasma  

NASA Technical Reports Server (NTRS)

Previous experimental studies have hypothesized that the onset of Solar Array Arc (SAA) initiation in low-density space plasmas is caused by a desorbed gas molecular ionization mechanism. Indeed past investigations performed at the NASA Glenn Plasma Interaction Facility tend to not only support the desorbed gas molecular ionization mechanism, but have gone as far as identifying the crucial molecular species that must be present for molecular ion dominated process to occur. When electrical breakdown occurs at a triple junction site on a solar array panel, a quasi-neutral plasma cloud is ejected. Assuming the main component of the expelled plasma cloud by weight is due to water vapor, the fastest process available is due to HO molecules and OH(+) ions, or more succinctly, dissociative molecular-ion dominated recombination processes: H2O(+) + e(-) yields H* + OH*. Recently published spectroscopic observations of solar array arc spectra in ground tests have revealed the well-known molecular OH band (302 to 309nm), as well as the molecular SiH band (387nm peak), and the molecular CH band (432nm peak). Note that the OH band is observed in emission arcs where water vapor is present. Strong atomic lines were also observed for H(sub beta) at 486nm and H(sub alpha) at 656.3nm in prior ground testing. Independent supporting evidence of desorbed gas molecular ionization mechanisms also come from measurements of arc current pulse widths at different capacitances. We will revisit an earlier first order approximation demonstrating the dependence of arc current pulse widths on the square root of the capacitance. The simple arc current pulse width model will be then be used to estimate the temperature of the arc plasma (currently believed to be somewhere in the range of 3 to 5 eV). The current paper then seeks to extend the outlined work by including numerous vacuum chamber measurements obtained with a quadrupole mass spectrometer. A small solar array was mounted inside the vacuum chamber. A plasma source, also mounted inside the vacuum chamber, is used to simulate a low-density plasma environment. The solar array is then biased to a high negative potential and allowed to arc while a mass spectrometer is used to record the partial pressure of H2O and to track other significant changes in mass (1 to 150) AMU.

Galofaro, J.; Vayner, B.; Ferguson, D.; Degroot, W.

2002-01-01

250

Acceleration of electrons generated during ionization of a gas by a nearly flat profile laser pulse  

SciTech Connect

A scheme of acceleration of electrons generated during ionization of krypton by nearly flat radial and nearly flat temporal laser pulse profiles has been suggested. The energy spectrum of the electrons suggests that energy of the electrons is higher for a nearly flat temporal profile than that for a nearly flat radial profile. The suppression of scattering of the electrons is better for a nearly flat radial profile than that for a nearly flat temporal profile. The energy of the electrons increases, scattering decreases, and beam quality improves with an increase in flatness of radial and temporal profiles.

Singh, Kunwar Pal [Department of Physics, MSJ College, Bharatpur, Rajasthan 321201 (India)

2009-09-15

251

Determination of nitrosamines in water by gas chromatography/chemical ionization/selective ion trapping mass spectrometry.  

PubMed

A gas chromatography/mass spectrometry (GC/MS) method for determination of nine N-nitrosamines (NAs) in water is described. Two ionization modes, electron impact (EI) and chemical ionization (CI) with methanol, as well as different ion analysis techniques, i.e. full scan, selected ion storage (SIS) and tandem mass spectrometry (MS/MS) were tested. Chemical ionization followed by SIS resulted the mass spectrometric method of choice, with detection limits in the range of 1-2ng/L. Solid Phase Extraction (SPE) with coconut charcoal cartridges was applied to extract NAs from real samples, according EPA Method 521. Drinking water samples were collected from seven surface- and two groundwater treatment plants. Three surface water treatment plants were sampled before and after addition of O(3)/ClO(2) to observe the effect of disinfection on NAs' formation. N-nitrosodiethylamine (NDEA), n-nitrosodipropylamine (NDPA), n-nitrosomorpholine (NMOR) and n-nitrosodibutylamine (NDBA) were found up to concentrations exceeding three times the risk level of 10ng/L set by the California Department of Public Health. Because dermal adsorption has been recently indicated as a new contamination route of exposure to NAs for people who practice swimming activity, water samples from five swimming pools in the Bologna (Italy) area were collected. N-nitrosopyrrolidine (NPYR) was detected in all samples at concentrations larger than 50ng/L, likely as a disinfection by-product from the amino acid precursor proline, a main constituent of skin collagen. PMID:21377686

Pozzi, Romina; Bocchini, Paola; Pinelli, Francesca; Galletti, Guido C

2011-04-01

252

Detection of [O I] ?6300 and Other Diagnostic Emission Lines in the Diffuse Ionized Gas of M33 with Gemini-North  

NASA Astrophysics Data System (ADS)

We present spectroscopic observations of diffuse ionized gas (DIG) in M33 near the H II region NGC 604. We present the first detection of [O I] ?6300 in the DIG of M33, one of the critical lines for distinguishing photoionization from shock ionization models. We measure [O I]/H? in the range of 0.04-0.10 and an increase in this ratio with decreasing emission measure. Our measurements of [S II]/H? and [N II]/H? also rise with decreasing emission measure, while our [O III]/H? measurements remain fairly constant. We have one tentative detection of He I in the region of brightest emission measure, with a ratio of He I/H? = 0.033 +/- 0.019, indicating that the helium is at least partially ionized. We compare our observed emission-line ratios to photoionization models and find that field star ionization models do not fit our data well. Leaky H II region models are consistent with our data, without the need to invoke additional ionization mechanisms to fit our [O I] or [O III] measurements. The closest large H II region is NGC 604 and is therefore a likely candidate for the source of the ionizing photons for the gas in this region.

Voges, E. S.; Walterbos, R. A. M.

2006-06-01

253

Stability studies of carbamate pesticides and analysis by gas chromatography with flame ionization and nitrogen-phosphorus detection.  

PubMed

As a result of thermal stability studies of carbamate pesticides, a method has been proposed for their direct determination by gas chromatography in the ranges 1-20 and 0.1-1 mg l(-1), using flame ionization and nitrogen-phosphorus detection, respectively. The method allows the determination of propham, propoxur, carbofuran, carbaryl, methiocarb, isopropoxyphenol and naphthol in powdered potato samples. The analytes were previously extracted with a light petroleum-dichloromethane (1:1, v/v) mixture and preconcentred by solid-phase extraction through a C8 cartridge. The recoveries obtained from spiked potato samples (n=4 replicates) at two concentration levels, 10 and 0.5 mg of pesticide per kg of sample, were in the ranges 72-115 and 50-73%, with relative standard deviations of 2-7 and 5-8%, respectively. The detection limits were 50-210 and 41-53 microg kg(-1) with flame ionization and nitrogen-phosphorus detection, respectively, and reaching the maximum residue levels, 0.05 mg kg(-1) for methiocarb and propoxur, set by the Real Decreto 280/1994 (based on the European directive). PMID:11471812

Santos Delgado, M J; Rubio Barroso, S; Fernández-Tostado, G T; Polo-Díez, L M

2001-07-01

254

Analysis of solids with a secondary-neutral microprobe based on electron-gas post-ionization.  

PubMed

The detection sensitivity and the lateral resolution in electron-gas SNMS have been improved in a newly developed secondary-neutral microprobe. This instrument combines the high post-ionization efficiency provided by the electron component of an rf-plasma (post-ionization probability alpha(0) of some 10(-2)) with a high-transmission magnetic mass spectrometer. Using the plasma as an effective primary ion source, secondary-neutral intensities of up to 10(9) cps can be realized for 1 keV Ar(+) ion bombardment and a primary current density of 1 mA/cm(2). To obtain laterally resolved secondary-neutral micrographs, a 20 keV-Ga(+)-ion beam produced in a liquid-metal ion source (LMIS) is utilized for sputter excitation. At Ga(+)-ion-beam currents of about 6 nA a spot size on the target of 1 microm is possible. The detection sensitivity in this operation mode is on the order of

Bieck, W; Gnaser, H; Oechsner, H

1995-10-01

255

Unified First Principles Description from Warm Dense Matter to Ideal Ionized Gas Plasma: Electron-Ion Collisions Induced Friction  

SciTech Connect

Electron-ion interactions are central to numerous phenomena in the warm dense matter (WDM) regime and at higher temperature. The electron-ion collisions induced friction at high temperature is introduced in the procedure of ab initio molecular dynamics using the Langevin equation based on density functional theory. In this framework, as a test for Fe and H up to 1000 eV, the equation of state and the transition of electronic structures of the materials with very wide density and temperature can be described, which covers a full range of WDM up to high energy density physics. A unified first principles description from condensed matter to ideal ionized gas plasma is constructed.

Dai Jiayu; Hou Yong; Yuan Jianmin [Department of Physics, College of Science, National University of Defense Technology, Changsha 410073 (China)

2010-06-18

256

The study of hydrodenitrification by the use of ammonia chemical ionization gas chromatography/tandem mass spectrometry  

SciTech Connect

Ammonia chemical ionization gas chromatography tandem mass spectrometry NH{sub 3}/CI GC/MS/MS was used to differentiate the partially hydrogenated intermediates formed during the catalytic hydrodenitrification (HDN) of model compounds, 2,6-dimethylquinoline and acridine. It was found that the initial hydrogenation proceeds by two competing pathways involving the heterocyclic as well as the adjacent aromatic rings. Several alkyl pyridines and four methylcarbazoles were also used to examine the effect of steric hindrance on HDN. The concentration of 1-methylcarbazole relative to the other methylcarbazole isomers was found to be higher in the HDN product than the cat cracker feed, indicating that the steric hindrance retards the HDN of this relative to the other methylcarbazoles. The similar effect of HDN was observed when alkyl groups were substituted at positions 1 and 5 of the pyridine ring.

Dzidic, I.; Petersen, H.A.; Nowlin, J.G.; Evans, W.E.; Siegel, H.; Hart, H.V. (Shell Development Co., Houston, TX (United States))

1990-08-01

257

Determination of elemental compositions by gas chromatography/time-of-flight mass spectrometry using chemical and electron ionization.  

PubMed

Many metabolomic applications use gas chromatography/mass spectrometry (GC/MS) under standard 70 eV electron ionization (EI) parameters. However, the abundance of molecular ions is often extremely low, impeding the calculation of elemental compositions for the identification of unknown compounds. On changing the beam-steering voltage of the ion source, the relative abundances of molecular ions at 70 eV EI were increased up to ten-fold for alkanes, fatty acid methyl esters and trimethylsilylated metabolites, concomitant with 2-fold absolute increases in ion intensities. We have compared the abundance, mass accuracy and isotope ratio accuracy of molecular species in EI with those in chemical ionization (CI) with methane as reagent gas under high-mass tuning. Thirty-three peaks of a diverse set of trimethylsilylated metabolites were analyzed in triplicate, resulting in 342 ion species ([M+H](+), [M-CH(3)](+) for CI and [M](+.), [M-CH(3)](+.) for EI). On average, CI yielded 8-fold more intense molecular species than EI. Using internal recalibration, average mass errors of 1.8 +/- 1.6 mm/z units and isotope ratio errors of 2.3 +/- 2.0% (A+1/A ratio) and 1.7 +/- 1.8% (A+2/A ratio) were obtained. When constraining lists of calculated elemental compositions by chemical and heuristic rules using the Seven Golden Rules algorithm and PubChem queries, the correct formula was retrieved as top hit in 60% of the cases and within the top-3 hits in 80% of the cases. PMID:20301109

Abate, Salvatore; Ahn, Yun Gyong; Kind, Tobias; Cataldi, Tommaso R I; Fiehn, Oliver

2010-04-30

258

Far-Ultraviolet and H? Imaging of Nearby Spiral Galaxies: The OB Stellar Population in the Diffuse Ionized Gas  

NASA Astrophysics Data System (ADS)

We have compared H? and far-ultraviolet (FUV) images of 10 nearby spirals, with the goal of understanding the contribution of field OB stars to the ionization of the diffuse ionized gas (DIG) in spiral galaxies. The FUV images were obtained by the Ultraviolet Imaging Telescope (UIT), and the H? images were obtained using various ground-based telescopes. In all of the galaxies, the FH?/FUIT flux ratio is lower in the DIG than in the H II regions. This is likely an indication that the mean spectral type for OB stars in the field is later than that in H II regions. Comparison of the NLyc/LUIT ratio with models of evolving stellar populations shows that the stellar population in the DIG is consistent with either an older single-burst population or a steady state model with constant star formation and an initial mass function (IMF) slope steeper than ?=2.35. The steady state model is probably a more realistic representation of the stellar population outside of H II regions. The steep IMF slope simulates the steep present-day mass function slope expected for field OB stars and does not necessarily indicate that the IMF slope is actually steeper than ?=2.35. We compared the FH?/FUIT ratio in the DIG of these galaxies with that in M33, in which the field OB stellar population has previously been investigated using Hubble Space Telescope images. If the mean spectral types of stars in H II regions and in the DIG are the same as in M33 and the difference in extinction between DIG and H II regions is constant among galaxies, then the analysis suggests that field stars are important sources of ionization in most galaxies and may be the dominant source in some galaxies. The FH?/FUIT ratio is correlated with H? surface brightness in both DIG and H II regions, although there is a large scatter in faint H II regions, which may be due to undersampling the IMF in regions with a low total mass of stars formed. The FH?/FUIT ratio is often highest in the centers of galaxies and in the spiral arms, which is also where the DIG is brightest. This can be explained if the extinction is greater in these regions or if the fraction of DIG ionized by leakage is lower in the interarm regions.

Hoopes, Charles G.; Walterbos, René A. M.; Bothun, Gregory D.

2001-10-01

259

Density of warm ionized gas near the Galactic center: low radio frequency observations  

NASA Astrophysics Data System (ADS)

We have detected 62 compact likely extragalactic sources in the Galactic center (GC) region at 0.154 and 0.255 GHz with the Giant Metrewave Radio Telescope (GMRT). Their scattering sizes go down linearly with angular distance from the GC up to about 1°. These are more than 10 times lower than the proposed Hyperstrong scattering model within 0.5° from the GC. We also detect 7 out of 10 EG sources expected in the region from existing catalogs. Ionized interfaces of dense molecular clouds to the ambient medium are likely responsible for strong scattering. However, dense GC clouds traced by CS J = (1 - 0) emission are found to have a narrow distribution of ˜0.2° across the Galactic plane. Lack of strong scattering towards EG sources within ˜ 0.5° from GC with |b| ? 0.2° could explain our results.

Roy, Subhashis

2014-05-01

260

Penning Ionization Electron Spectroscopy in Glow Discharge: A New Dimension for Gas Chromatography Detectors  

NASA Technical Reports Server (NTRS)

Admixtures to helium of 100 ppm and 5 ppm of nitrogen, and 100 ppm and 10 ppm of carbon monoxide were identified and measured in the helium discharge afterglow using an electrical probe placed into the plasma. For nitrogen and carbon monoxide gases, the measured electron energy spectra display distinct characteristic peaks (fingerprints). Location of the peaks on the energy scale is determined by the ionization energies of the analyte molecules. Nitrogen and carbon monoxide fingerprints were also observed in a binary mixture of these gases in helium, and the relative concentration analytes has been predicted. The technically simple and durable method is considered a good candidate for a number of analytical applications, and in particular, in GC and for analytical flight instrumentation.

Sheverev, V. A.; Khromov, N. A.; Kojiro, D. R.; Fonda, Mark (Technical Monitor)

2002-01-01

261

Noise characteristics of the gas ionization cascade used in low vacuum scanning electron microscopy  

SciTech Connect

The noise characteristics of gas cascade amplified electron signals in low vacuum scanning electron microscopy (LVSEM) are described and analyzed. We derive expressions for each component contributing to the total noise culminating in a predictive, quantitative model that can be used for optimization of LVSEM operating parameters. Signal and noise behavior is characterized experimentally and used to validate the model. Under most operating conditions, the noise is dominated by the excess noise generated in the gas amplification cascade. At high gains, the excess noise increases proportionally with gain such that the signal-to-noise ratio is constant. The effects of several instrument operating parameters, including working distance, gas pressure, beam current, and detector bias, are condensed and presented in the form of a master curve.

Tileli, Vasiliki; Thiel, Bradley L. [College of Nanoscale Science and Engineering, University at Albany-SUNY, 257 Fuller Road, Albany, New York 12203 (United States); Knowles, W. Ralph; Toth, Milos [FEI Company, 5350 NE Dawson Creek Drive, Hillsboro, Oregon 97124 (United States)

2009-07-01

262

Measurement of phospholipid fatty acids at picomolar concentrations in biofilms and deep subsurface sediments using gas chromatography and chemical ionization mass spectrometry  

Microsoft Academic Search

Summary Examination of ester-linked phospholipid fatty acids (PLFA) have provided a means to characterize the community structure of microbial assemblies. Attempts to analyze such acids at low picomolar levels in environmental samples by gas chromatography and chemical ionization mass spectrometry (CIMS) using positive or negative ion detection, showed that the limit of detection (LOD) was mainly dependent on the background

A. Tunlid; D. Ringelberg; T. J. Phelps; C LOW; D WHITE

1989-01-01

263

Analysis of Trace Levels of Volatile Organic Contaminants in Municipal Drinking Water by Glass Capillary Gas Chromatography Using Simultaneous Flame Ionization and Electron Capture Detection  

Microsoft Academic Search

A glass capillary gas chromatographic system using simultaneous flame ionization (FID) and electron capture (ECD) detection has been employed for the analysis of trace volatile organic pollutants in a municipal drinking water supply. The use of dual detectors with glass capillary columns allows resolution and detection of both halogenated and non-halogenated compounds simultaneously at less than microgram per liter (ppb)

L. V. McCarthy; E. B. Overton; C. K. Raschke; J. L. Laseter

1980-01-01

264

Study of solid/gas phase photocatalytic reactions by electron ionization mass spectrometry.  

PubMed

This paper describes a novel methodology for the real-time study of solid-gas phase photocatalytic reactions in situ. A novel reaction chamber has been designed and developed to facilitate the investigation of photoactive materials under different gas compositions. UV irradiation in the wavelength of ranges 376-387 and 381-392?nm was provided using specially designed high efficiency light emitting diode arrays. The experiments used air containing 190?ppm NO2 in a moist environment with a relative humidity of 0.1%. Photocatalytic samples consisting of pressed pellets of rutile and anatase crystalline forms of TiO2 were monitored over a period of 150?min. An ultra-high vacuum right angled bleed valve allowed a controlled flow of gas from the main reaction chamber at atmospheric pressure to a residual gas analyser operating at a vacuum of 10(-5) ?mbar. The apparatus and methodology have been demonstrated to provide high sensitivity (ppb). The rate of degradation of NO2 attributed to reaction at the TiO2 surface was sensitive to both crystal structures (anatase or rutile) and wavelength of irradiation. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25044899

Nuño, Manuel; Ball, Richard J; Bowen, Chris R

2014-08-01

265

The Black Hole in IC 1459 from Hubble Space Telescope Observations of the Ionized Gas Disk  

NASA Astrophysics Data System (ADS)

The peculiar elliptical galaxy IC 1459 (MV=-21.19, D=16.5 h-1 Mpc) has a fast counterrotating stellar core, stellar shells and ripples, a blue nuclear point source, and strong radio core emission. We present results of a detailed Hubble Space Telescope study of IC 1459, and in particular its central gas disk, aimed at constraining the central mass distribution. We obtained WFPC2 narrowband imaging centered on the H?+[N II] emission lines to determine the flux distribution of the gas emission at small radii, and we obtained FOS spectra at six aperture positions along the major axis to sample the gas kinematics. We construct dynamical models for the H?+[N II] and H? kinematics that include a supermassive black hole and in which the stellar mass distribution is constrained by the observed surface brightness distribution and ground-based stellar kinematics. In one set of models we assume that the gas rotates on circular orbits in an infinitesimally thin disk. Such models adequately reproduce the observed gas fluxes and kinematics. The steepness of the observed rotation velocity gradient implies that a black hole must be present. There are some differences between the fluxes and kinematics for the various line species that we observe in the wavelength range 4569-6819 Å. Species with higher critical densities generally have a flux distribution that is more concentrated toward the nucleus, and have observed velocities that are higher. This can be attributed qualitatively to the presence of the black hole. There is some evidence that the gas in the central few arcsec has a certain amount of asymmetric drift, and we therefore construct alternative models in which the gas resides in collisionless cloudlets that move isotropically. All models are consistent with a black hole mass in the range M•=1-4×108 Msolar, and models without a black hole are always ruled out at high confidence. The implied ratio of black holes mass to galaxy mass is in the range 0.4-1.5×10-3, which is not inconsistent with results obtained for other galaxies. These results for the peculiar galaxy IC 1459 and its black hole add an interesting data point for studies on the nature of galactic nuclei. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

Verdoes Kleijn, Gijs A.; van der Marel, Roeland P.; Carollo, C. Marcella; de Zeeuw, P. Tim

2000-09-01

266

Effect of ammonium on liquid- and gas-phase protonation and deprotonation in electrospray ionization mass spectrometry.  

PubMed

The electrospray ionization (ESI) is a complex process and there has been a long debate regarding the gas-phase effect on ion generation in the process. In this paper we investigated the effect of liquid chromatographic mobile phase additives (formic acid, aqueous ammonia and their combination) on the ESI signal intensities for a wide variety of compounds. The addition of a trace amount of aqueous ammonia to the common formic acid-methanol mobile phase significantly enhances the ESI signals of protonated molecules and suppresses the formation of sodium adduct ions. This effect is well observed for the compounds containing the -N-C=O group but not for those without N or O atoms. The ESI signal intensity of deprotonated molecules increases with increase in pH of the mobile phase for neutral compounds, such as substituted urea, whereas this trend is not observed for acidic compounds such as phenoxy acids. The mechanistic analysis regarding liquid- and gas-phase protonation and deprotonation is discussed. PMID:23181258

Yang, X Jin; Qu, Yixin; Yuan, Qipeng; Wan, Pingyu; Du, Zhenxia; Chen, Dazhou; Wong, Choon

2013-01-21

267

Evidence for the interaction of the IRS 16 wind with the ionized and molecular gas at the Galactic center  

NASA Technical Reports Server (NTRS)

We present a number of high-resolution radio images showing evidence for the dynamical interaction of the outflow arising from the IRS 16 complex with the ionized gas associated with the Northern Arm of Sgr A West, and with the northwestern segment of the circumnuclear molecular disk which engulfs the inner few parsecs of the Galactic center. We suggest that the wind disturbs the dynamics of the Northern Arm within 0.1 pc of the center, is responsible for the waviness of the arm at larger distances, and is collimated by Sgr A West and the circumnuclear disk. The waviness is discussed in terms of the Rayleigh-Taylor instability induced by the ram pressure of the wind incident on the surface of the Northern Arm. Another consequence of this interaction is the strong mid-IR polarization of the Northern Arm in the vicinity of the IRS 16 complex which is explained as a result of the ram pressure of the wind compressing the gas and the magnetic field.

Yusef-Zadeh, Farhad; Wardle, Mark

1993-01-01

268

Determination of allergenic hydroperoxides in essential oils using gas chromatography with electron ionization mass spectrometry.  

PubMed

Fragrance monoterpenes are widely used commercially due to their pleasant scent. In previous studies, we have shown that air-exposed monoterpenes form hydroperoxides that are strong skin sensitizers. Methods for detection and quantification of the hydroperoxides in essential oils and scented products are thus desirable. Due to thermolability and low UV absorbance, this is a complicated task. We have recently developed a sensitive LC-ESI-MS method, but with limited structural information and separation efficiency for positional isomers and stereoisomers. In the present study, we investigated derivatization with a trimethyl silyl reagent and subsequent GC with electron ionization MS for the determination of monoterpene hydroperoxides. All investigated monoterpene hydroperoxides could be chromatographed as thermostable trimethyl silyl derivatives and yielded the fragment m/z 89 ([OSi(CH3 )3 ](+) ) at a higher extent compared to corresponding alcohols. Limonene-2-hydroperoxide and four other hydroperoxide isomers of limonene were separated and detected in sweet orange oil autoxidized for two months. The concentration of limonene-2-hydroperoxide isomers was found to be 19 ?g/mg in total. Also isomers of linalyl acetate hydroperoxide and linalool hydroperoxide were detected in autoxidized petitgrain oil (two months). The presented GC-MS method showed concentrations in the same order as previous LC-MS/MS analysis of the same type of oils. PMID:24482420

Rudbäck, Johanna; Ramzy, Ahmed; Karlberg, Ann-Therese; Nilsson, Ulrika

2014-04-01

269

Ionization of the diffuse gas in galaxies: hot low-mass evolved stars at work  

NASA Astrophysics Data System (ADS)

We revisit the question of the ionization of the diffuse medium in late-type galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The most important challenge for the models considered so far was the observed increase of [O III]/H?, [O II]/H? and [N II]/H? with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic altitude z we look for the models which simultaneously fit the observed values of the [O III]/H?, [O II]/H? and [N II]/H? ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.

Flores-Fajardo, N.; Morisset, C.; Stasi?ska, G.; Binette, L.

2011-08-01

270

[S IV] IN THE NGC 5253 SUPERNEBULA: IONIZED GAS KINEMATICS AT HIGH RESOLUTION  

SciTech Connect

The nearby dwarf starburst galaxy NGC 5253 hosts a deeply embedded radio-infrared supernebula excited by thousands of O stars. We have observed this source in the 10.5 {mu}m line of S{sup +3} at 3.8 km s{sup -1} spectral and 1.''4 spatial resolution, using the high-resolution spectrometer TEXES on the IRTF. The line profile cannot be fit well by a single Gaussian. The best simple fit describes the gas with two Gaussians, one near the galactic velocity with FWHM 33.6 km s{sup -1} and another of similar strength and FWHM 94 km s{sup -1} centered {approx}20 km s{sup -1} to the blue. This suggests a model for the supernebula in which gas flows toward us out of the molecular cloud, as in a 'blister' or 'champagne flow' or in the H II regions modelled by Zhu.

Beck, Sara C. [Department of Physics and Astronomy, Tel Aviv University, Ramat Aviv (Israel); Lacy, John H. [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Turner, Jean L. [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States); Kruger, Andrew; Richter, Matt [Department of Physics, University of California at Davis, Davis, CA 95616 (United States); Crosthwaite, Lucian P., E-mail: sara@wise.tau.ac.il [Northrop Grumman Aerospace Systems, San Diego, CA 92127 (United States)

2012-08-10

271

Ion Velocity Distribution of a Weakly Ionized Gas in a Uniform Electric Field of Arbitrary Strength  

Microsoft Academic Search

The velocity-distribution function of ions in a neutral gas is studied. A uniform electric field of arbitrary strength is assumed and only binary-ion-neutral-particle collisions are considered. Under these conditions part of the Boltzmann-equation collision operator is replaced by a kinetic model which enables the ion velocity distribution to be found in compact analytical form if the mean free time between

John H. Whealton; Shien-Biau Woo

1972-01-01

272

Ionized Gas and Dust Distributions in Ten Nearby Early-Type Galaxies  

Microsoft Academic Search

We present broad-band V and I images and Halpha+[N II] emission-line maps of ten nearby early-type galaxies observed with the Wide Field Channel (WFC) of the Advanced Camera for Surveys (ACS) as part of the ACS Guaranteed-Time-Observer (GTO) program. The galaxies cover a wide range of velocity dispersions (50-400 km\\/sec) and three possess nuclear dust and gas disks (ESO 208-G021,

A. R. Martel; H. D. Tran; W. B. Sparks; F. Menanteau; H. C. Ford; G. D. Illingworth; Z. I. Tsvetanov

2003-01-01

273

Influence of Gas Heating and Vibrational Kinetics on the Ionization Dynamics of Preformed Air Plasma Channels  

NASA Astrophysics Data System (ADS)

An extensive self-consistent air-plasma model based upon the Boltzmann equation for the electron energy distribution function, coupled with a heavy particle kinetics was developed to study electric discharges in a preexisting air plasma column [1]. Incorporated in the model are the steady-state balance equations for various nitrogen and oxygen species in ground and excited states, as well as atomic and molecular ions. The influence of the gas temperature is accounted for by reduction of the neutral density, collisional processes such as recombination, dissociation, V-V and V-T reactions [2], and by reactions involving electronically excited states of O2. The model was applied to study the influence of the gas temperature and vibrational kinetics on the breakdown processes in a preformed air plasma channel. Numerical calculations predict that electrical breakdown occurs at relatively low electric field. The calculated self-consistent breakdown electric field is ˜10 kV/cm for gas temperature of 300 K, while at temperature of 600 K it drops to ˜5.7 kV/cm, in excellent agreement with the experimentally determined breakdown electric field [1]. * NRC-NRL Postdoc [1] Tz.B. Petrova, H.D. Ladouceur, and A.P. Baronavski, 58th Gaseous Electronics Conference, 2005; San Jose, California, FM.00062 [2] J. Loureiro and C.M. Ferreira, J. Phys. D: Appl. Phys 19 (1986) 17-35

Ladouceur, Harold; Baronavski, Andrew; Petrova, Tzvetelina

2006-03-01

274

Colliding Ionization Fronts. Pt. 1. Ionized Shells in HII Regions.  

National Technical Information Service (NTIS)

The gas dynamical effects produced by the subsequent formation of stars within and around HII regions are studied. The evolution of ionization fronts and their interaction with shock waves and other ionization fronts are numerically followed. The appearan...

G. Tenorio-Tagle

1977-01-01

275

KINEMATICS AND EXCITATION OF THE RAM PRESSURE STRIPPED IONIZED GAS FILAMENTS IN THE COMA CLUSTER OF GALAXIES  

SciTech Connect

We present the results of deep imaging and spectroscopic observations of very extended ionized gas (EIG) around four member galaxies of the Coma Cluster of galaxies: RB 199, IC 4040, GMP 2923, and GMP 3071. The EIGs were serendipitously found in an H{alpha} narrowband imaging survey of the central region of the Coma Cluster. The relative radial velocities of the EIGs with respect to the systemic velocities of the parent galaxies from which they emanate increase almost monotonically with the distance from the nucleus of the respective galaxies, reaching {approx} - 400 to - 800 km s{sup -1} at around 40-80 kpc from the galaxies. The one-sided morphologies and the velocity fields of the EIGs are consistent with the predictions of numerical simulations of ram pressure stripping. We found a very low velocity filament (v{sub rel} {approx} -1300 km s{sup -1}) at the southeastern edge of the disk of IC 4040. Some bright compact knots in the EIGs of RB 199 and IC 4040 exhibit blue continuum and strong H{alpha} emission. The equivalent widths of the H{alpha} emission exceed 200 A and are greater than 1000 Angstrom-Sign for some knots. The emission-line intensity ratios of the knots are basically consistent with those of sub-solar abundance H II regions. These facts indicate that intensive star formation occurs in the knots. Some filaments, including the low-velocity filament of the IC 4040 EIG, exhibit shock-like emission-line spectra, suggesting that shock heating plays an important role in ionization and excitation of the EIGs.

Yoshida, Michitoshi [Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Yagi, Masafumi; Komiyama, Yutaka; Kashikawa, Nobunari [Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Furusawa, Hisanori [Astronomical Data Center, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Hattori, Takashi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'Ohoku Place, Hilo, HI 96720 (United States); Okamura, Sadanori, E-mail: yoshidam@hiroshima-u.ac.jp [Department of Astronomy, University of Tokyo, Tokyo 113-0033 (Japan)

2012-04-10

276

Kinematics and Excitation of the Ram Pressure Stripped Ionized Gas Filaments in the Coma Cluster of Galaxies  

NASA Astrophysics Data System (ADS)

We present the results of deep imaging and spectroscopic observations of very extended ionized gas (EIG) around four member galaxies of the Coma Cluster of galaxies: RB 199, IC 4040, GMP 2923, and GMP 3071. The EIGs were serendipitously found in an H? narrowband imaging survey of the central region of the Coma Cluster. The relative radial velocities of the EIGs with respect to the systemic velocities of the parent galaxies from which they emanate increase almost monotonically with the distance from the nucleus of the respective galaxies, reaching ~ - 400 to - 800 km s-1 at around 40-80 kpc from the galaxies. The one-sided morphologies and the velocity fields of the EIGs are consistent with the predictions of numerical simulations of ram pressure stripping. We found a very low velocity filament (v rel ~ -1300 km s-1) at the southeastern edge of the disk of IC 4040. Some bright compact knots in the EIGs of RB 199 and IC 4040 exhibit blue continuum and strong H? emission. The equivalent widths of the H? emission exceed 200 Å and are greater than 1000 Å for some knots. The emission-line intensity ratios of the knots are basically consistent with those of sub-solar abundance H II regions. These facts indicate that intensive star formation occurs in the knots. Some filaments, including the low-velocity filament of the IC 4040 EIG, exhibit shock-like emission-line spectra, suggesting that shock heating plays an important role in ionization and excitation of the EIGs. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Yoshida, Michitoshi; Yagi, Masafumi; Komiyama, Yutaka; Furusawa, Hisanori; Kashikawa, Nobunari; Hattori, Takashi; Okamura, Sadanori

2012-04-01

277

The Effects of Ionized Gas Exposure on the Toughness and Fatigue Properties of Aluminum Alloys and Composites.  

NASA Astrophysics Data System (ADS)

The effects of an oxygen ionized gas from simulated space exposure on the toughness and fatigue properties of several aerospace aluminum alloys and aluminum composites have been analyzed. The test matrix consisted of four aluminum systems: the 6000 and 1100 series and two 8090 aluminum-lithium alloys. The test specimens were prepared as Charpy V-notched impact and disk-shaped compact fracture toughness specimens. A small specimen size is used for the compact tension specimens to facilitate exposure in a Radio Frequency (RF) Plasma Prep II unit. Radio frequency plasma, sometimes referred to as the "electrodeless plasma", is used in disassociative ionization of molecular oxygen to simulate high fluence, relatively low energy, low earth orbit (LEO) space atomic oxygen. The plasma reacts with the aluminum alloy systems and forms a thin scale of alumina a few microns thick. Monolayer sensitive Variable Angle Spectroscopic Ellipsometry (VASE) is used to determine the growth characteristics and effect on optical constants, the reflective index, n and absorption coefficient, k. Atomic Force Microscopy (AFM) was also employed to determine the effect of short exposure to the oxygen plasma environment. AFM indicates that sharp spikes of oxygen rich material are produced above the aluminum specimen surface resulting in stress concentrations with gradual roughing of the surface. After 10 years of simulated exposure, the increased roughness results in a 34% increase in the fatigue crack growth, da/dN, for the 6000 series; the crack growth rate of the aluminum-lithium material was increased about 28%. The results of instrumented Charpy V-notched impact specimens indicated that exposure reduced the energy for fracture initiation by 29%. Plane strain fracture toughness effects could not be established because the influence of oxygen was concentrated at the surface of the specimens.

Zaat, Stephen Vincent

278

Ionization compression impact on dense gas distribution and star formation. Probability density functions around H II regions as seen by Herschel  

NASA Astrophysics Data System (ADS)

Aims: Ionization feedback should impact the probability distribution function (PDF) of the column density of cold dust around the ionized gas. We aim to quantify this effect and discuss its potential link to the core and initial mass function (CMF/IMF). Methods: We used Herschel column density maps of several regions observed within the HOBYS key program in a systematic way: M 16, the Rosette and Vela C molecular clouds, and the RCW 120 H ii region. We computed the PDFs in concentric disks around the main ionizing sources, determined their properties, and discuss the effect of ionization pressure on the distribution of the column density. Results: We fitted the column density PDFs of all clouds with two lognormal distributions, since they present a "double-peak" or an enlarged shape in the PDF. Our interpretation is that the lowest part of the column density distribution describes the turbulent molecular gas, while the second peak corresponds to a compression zone induced by the expansion of the ionized gas into the turbulent molecular cloud. Such a double peak is not visible for all clouds associated with ionization fronts, but it depends on the relative importance of ionization pressure and turbulent ram pressure. A power-law tail is present for higher column densities, which are generally ascribed to the effect of gravity. The condensations at the edge of the ionized gas have a steep compressed radial profile, sometimes recognizable in the flattening of the power-law tail. This could lead to an unambiguous criterion that is able to disentangle triggered star formation from pre-existing star formation. Conclusions: In the context of the gravo-turbulent scenario for the origin of the CMF/IMF, the double-peaked or enlarged shape of the PDF may affect the formation of objects at both the low-mass and the high-mass ends of the CMF/IMF. In particular, a broader PDF is required by the gravo-turbulent scenario to fit the IMF properly with a reasonable initial Mach number for the molecular cloud. Since other physical processes (e.g., the equation of state and the variations among the core properties) have already been said to broaden the PDF, the relative importance of the different effects remains an open question. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Tremblin, P.; Schneider, N.; Minier, V.; Didelon, P.; Hill, T.; Anderson, L. D.; Motte, F.; Zavagno, A.; André, Ph.; Arzoumanian, D.; Audit, E.; Benedettini, M.; Bontemps, S.; Csengeri, T.; Di Francesco, J.; Giannini, T.; Hennemann, M.; Nguyen Luong, Q.; Marston, A. P.; Peretto, N.; Rivera-Ingraham, A.; Russeil, D.; Rygl, K. L. J.; Spinoglio, L.; White, G. J.

2014-04-01

279

Use of electron ionization and atmospheric pressure chemical ionization in gas chromatography coupled to time-of-flight mass spectrometry for screening and identification of organic pollutants in waters.  

PubMed

A new approach has been developed for multiclass screening of organic contaminants in water based on the use of gas chromatography coupled to hybrid quadrupole high-resolution time-of-flight mass spectrometry with atmospheric pressure chemical ionization (GC-(APCI)QTOF MS). The soft ionization promoted by the APCI source allows effective and wide-scope screening based on the investigation of the molecular ion and/or protonated molecule. This is in contrast to electron ionization (EI) where ionization typically results in extensive fragmentation, and diagnostic ions and/or spectra need to be known a priori to facilitate detection of the analytes in the raw data. Around 170 organic contaminants from different chemical families were initially investigated by both approaches, i.e. GC-(EI)TOF and GC-(APCI)QTOF, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and a notable number of pesticides and relevant metabolites. The new GC-(APCI)QTOF MS approach easily allowed widening the number of compounds investigated (85 additional compounds), with more pesticides, personal care products (UV filters, musks), polychloronaphthalenes (PCNs), antimicrobials, insect repellents, etc., most of them considered as emerging contaminants. Both GC-(EI)TOF and GC-(APCI)QTOF methodologies have been applied, evaluating their potential for a wide-scope screening in the environmental field. PMID:24674644

Portolés, Tania; Mol, Johannes G J; Sancho, Juan V; Hernández, Félix

2014-04-25

280

Infrared imaging spectroscopy of the Galactic center - Distribution and motions of the ionized gas  

NASA Technical Reports Server (NTRS)

High spatial spectral resolution IR images of the Galactic center in the Br-gamma recombination line of hydrogen were taken. A coherent filament of gas extending from north of IRS 1, curving around IRS 16/Sgr A complex, and continuing to the southwest, is seen. Nine stellar sources have associated Br-gamma emission. The total Br-gamma line flux in the filament is approximately 3 x 10 exp -15 W/sq m. The distribution and kinematics of the northern arm suggest orbital motion; the observations are accordingly fit with elliptical orbits in the field of a central point of mass.

Herbst, T. M.; Beckwith, S. V. W.; Forrest, W. J.; Pipher, J. L.

1993-01-01

281

A kinematic study of the neutral and ionized gas in the irregular dwarf galaxies IC4662 and NGC5408  

NASA Astrophysics Data System (ADS)

The feedback between massive stars and the interstellar medium is one of the most important processes in the evolution of dwarf galaxies. This interaction results in numerous neutral and ionized gas structures that have been found both in the disc and in the halo of these galaxies. However, their origin and fate are still poorly understood. We here present new HI and optical data of two Magellanic irregular dwarf galaxies in the Local Volume: IC4662 and NGC5408. The HI line data were obtained with the Australia Telescope Compact Array and are part of the `Local Volume HI Survey'. They are complemented by optical images and spectroscopic data obtained with the European Southern Observatory (ESO) New Technology Telescope and the ESO 3.6-m telescope. Our main aim is to study the kinematics of the neutral and ionized gas components in order to search for outflowing gas structures and to make predictions about their fate. Therefore, we perform a Gaussian decomposition of the HI and H? line profiles. We find the HI gas envelopes of IC4662 and NGC5408 to extend well beyond the optical discs, with HI to optical diameter ratios of above 4. The optical disc is embedded into the central HI maximum in both galaxies. However, higher resolution HI maps show that the HI intensity peaks are typically offset from the prominent HII regions. While NGC5408 shows a fairly regular HI velocity field, which allows us to derive a rotation curve, IC4662 reveals a rather twisted HI velocity field, possibly caused by a recent merger event. We detect outflows with velocities between 20 and 60 kms-1 in our H? spectra of both galaxies, sometimes with HI counterparts of similar velocity. We suggest the existence of expanding superbubbles, especially in NGC5408. This is also supported by the detection of full width at half-maxima as high as 70 kms-1 in H?, which cannot be explained by thermal broadening alone. In the case of NGC5408, we compare our results with the escape velocity of the galaxy, which shows that the measured expansion velocities are in all cases too low to allow the gas to escape from the gravitational potential of NGC5408. This result is consistent with studies of other dwarf galaxies. The radio observations were obtained with the Australia Telescope which is funded by the Commonwealth of Australia for operations as a National Facility managed by CSIRO. All optical observations were collected at the European Southern Observatory, Chile, Proposal-Nos.: 047.01-003, 51.1-0067, 69.D-0143(A) and 077B.-0115(A). E-mail: janine.vaneymeren@uni-due.de (JVE); Baerbel.Koribalski@csiro.au (BSK)

van Eymeren, Janine; Koribalski, Bärbel S.; López-Sánchez, Ángel R.; Dettmar, Ralf-Jürgen; Bomans, Dominik J.

2010-09-01

282

Gas-phase ionization\\/desolvation processes and their effect on protein charge state distribution under matrix-assisted laser desorption\\/ionization conditions  

Microsoft Academic Search

The charge state distribution of proteins was studied as a function of experimental conditions, to improve the understanding of the matrix-assisted laser desorption \\/ionization (MALDI) mechanisms. The relative abundances of the multiply-charged ions appear to be a function of the matrix chosen, the laser fluence and the matrix-to-analyte molar ratio. A correlation is found between the matrix proton affinity and

Sandra Alves; Françoise Fournier; Carlos Afonso; Franck Wind; Jean-Claude Tabet

2006-01-01

283

Gas-Phase Stability of G-quadruplex DNA Determined by Electrospray Ionization Tandem Mass Spectrometry and Molecular Dynamics Simulations  

PubMed Central

The relative gas-phase stabilities of seven quadruplex DNA structures, [d(TG4T)]4, [d(T2G3T)]4, [d(G4T4G4)]2, [d(T2AG3)2]2, d(T2AG3)4, d(T2G4)4, and d(G2T4)4, were investigated using molecular dynamics simulations and electrospray ionization mass spectrometry (ESI-MS). MD simulations revealed that the G-quadruplexes maintained their structures in the gas phase although the G-quartets were distorted to some degree and ammonium ions, retained by [d(TG4T)]4 and [d(T2G3T)]4, played a key role in stabilizing the tetrad structure. Energy-variable collisional activated dissociation was used to assess the relative stabilities of each quadruplex based on E1/2 values, and the resulting order of relative stabilities was found to be [d(TG4T)]4 ? d(T2AG3)4 ? d(T2G4)4 > [d(T2G3T)]4 > [d(T2AG3)2]2 ? d(G2T4)4 ? [d(G4T4G4)]2. The stabilities from the E1/2 values generally paralleled the RMSD and relative free energies of the quadruplexes based on the MD energy analysis. One exception to the general agreement is [d(G4T4G4)]2 which had the lowest E1/2 value, but was determined to be the most stable quadruplex according to the free energy analysis and ranked fourth based on the RMSD comparison. This discrepancy is attributed to differences in the fragmentation pathway of the quadruplex.

Mazzitelli, Carolyn L.; Wang, Junmei; Smith, Suncerae I.; Brodbelt, Jennifer S.

2007-01-01

284

Plasma amino acid quantitation using gas chromatography chemical ionization mass spectrometry and 13C amino acids as internal standards.  

PubMed

A specific and sensitive method for the quantitation of 16 alpha amino acids has been developed. The technique employed uses methane chemical ionization gas chromatography mass spectrometry of the carboxy-n-butyl, N-trifluoroacetyl amino acid derivatives. A commercial 13C amino acid mixture provided individual internal standards for 14 alpha amino acids. A computer controlled quadrupole mass spectrometer was used for selected ion monitoring of those ions characteristic of each N-trifluoroacetyl amino acid/13C amino acid pair. A BASIC computer program located peak maxima and background intensities in each selected ion recording. Standard curves for each amino acid/13C amino acid pair were utilized by the program to calculate the plasma concentration of each detected amino acid. The total instrumental analysis occupied 30 min with sample preparation and derivatization accounting for an additional 2 h. Based on the detection of known amounts of standard amino acids the method will quantitate at the 1-5 nanogram level of detection. PMID:749957

Kingston, E E; Duffield, A M

1978-11-01

285

Ionized Gas Kinematics at High Resolution. II. Discovery of a Double Infrared Cluster in II Zw 40  

NASA Astrophysics Data System (ADS)

The nearby dwarf galaxy II Zw 40 hosts an intense starburst. At the center of the starburst is a bright compact radio and infrared source, thought to be a giant dense H II region containing ?14, 000 O stars. Radio continuum images suggest that the compact source is actually a collection of several smaller emission regions. We accordingly use the kinematics of the ionized gas to probe the structure of the radio-infrared emission region. With TEXES on the NASA-IRTF we measured the 10.5 ?m [S IV] emission line with effective spectral resolutions, including thermal broadening, of ~25 and ~3 km s-1 and spatial resolution ~1''. The line profile shows two distinct, spatially coextensive, emission features. The stronger feature is at galactic velocity and has FWHM 47 km s-1. The second feature is ~44 km s-1 redward of the first and has FWHM 32 km s-1. We argue that these are two giant embedded clusters, and estimate their masses to be ?3 × 105 M ? and ?1.5 × 105 M ?. The velocity shift is unexpectedly large for such a small spatial offset. We suggest that it may arise in a previously undetected kinematic feature remaining from the violent merger that formed the galaxy.

Beck, Sara; Turner, Jean; Lacy, John; Greathouse, Thomas; Lahad, Ohr

2013-04-01

286

IONIZED GAS KINEMATICS AT HIGH RESOLUTION. II. DISCOVERY OF A DOUBLE INFRARED CLUSTER IN II Zw 40  

SciTech Connect

The nearby dwarf galaxy II Zw 40 hosts an intense starburst. At the center of the starburst is a bright compact radio and infrared source, thought to be a giant dense H II region containing Almost-Equal-To 14, 000 O stars. Radio continuum images suggest that the compact source is actually a collection of several smaller emission regions. We accordingly use the kinematics of the ionized gas to probe the structure of the radio-infrared emission region. With TEXES on the NASA-IRTF we measured the 10.5 {mu}m [S IV] emission line with effective spectral resolutions, including thermal broadening, of {approx}25 and {approx}3 km s{sup -1} and spatial resolution {approx}1''. The line profile shows two distinct, spatially coextensive, emission features. The stronger feature is at galactic velocity and has FWHM 47 km s{sup -1}. The second feature is {approx}44 km s{sup -1} redward of the first and has FWHM 32 km s{sup -1}. We argue that these are two giant embedded clusters, and estimate their masses to be Almost-Equal-To 3 Multiplication-Sign 10{sup 5} M{sub Sun} and Almost-Equal-To 1.5 Multiplication-Sign 10{sup 5} M{sub Sun }. The velocity shift is unexpectedly large for such a small spatial offset. We suggest that it may arise in a previously undetected kinematic feature remaining from the violent merger that formed the galaxy.

Beck, Sara; Lahad, Ohr [School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978 (Israel)] [School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978 (Israel); Turner, Jean [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States)] [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States); Lacy, John [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States)] [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Greathouse, Thomas [Southwest Research Institute, San Antonio, TX 78228-0510 (United States)] [Southwest Research Institute, San Antonio, TX 78228-0510 (United States)

2013-04-10

287

[Determination of 17 pyrethroid pesticide residues in vegetables by gas chromatography-mass spectrometry with negative chemical ionization].  

PubMed

A method was established for the determination of 17 pyrethroid pesticide residues in vegetables using QuEChERS (quick, easy, cheap, effective, rugged and safe) clean-up method and gas chromatography-mass spectrometry (GC-MS) with negative chemical ionization (NCI). The pyrethroid pesticides in the sample were extracted with acetonitrile. After QuEChERS clean-up with a mixture of primary secondary amine and graphitized carbon black packings, the extract was analyzed by GC-NCI-MS in selected ion monitoring (SIM) mode. An isotope internal standard of cypermethrin was employed to the quantification. The limits of quantification ranged from 0.02 to 5 microg/kg. The recoveries of the pyrethroid pesticides spiked in three different matrixes (peas, broccoli and Chinese onion green) at four spiked levels of 10, 20, 30 and 100 microg/kg were from 71.0% to 139.0%, and the relative standard deviations were less than 12.8%. This method can be used as a conclusive evidence method of the 17 pyrethroid pesticide residues in vegetables. PMID:23451521

Shen, Weijian; Cao, Xiaowen; Liu, Yijun; Zhang, Rui; Fan, Xin; Zhao, Zengyun; Shen, Chongyu; Wu, Bin

2012-11-01

288

Determination of 17 pyrethroid residues in troublesome matrices by gas chromatography/mass spectrometry with negative chemical ionization.  

PubMed

An analytical method with the technique of QuEChERS (quick, easy, cheap, effective, rugged and safe) and gas chromatography (GC)/mass spectrometry (MS) in negative chemical ionization (NCI) has been developed for the determination of 17 pyrethroid pesticide residues in troublesome matrices, including garlic, onion, spring onion and chili. Pyrethroid residues were extracted with acidified acetonitrile saturated by hexane. After a modified QuEChERS clean-up step, the extract was analyzed by GC-NCI/MS in selected ion monitoring (SIM) mode. An isotope internal standard of trans-cypermethrin-D(6) was employed for quantitation. Chromatograms of pyrethroids obtained in all these matrices were relatively clean and without obvious interference. The limits of detection (LODs) ranged from 0.02 to 6 ?g kg(-1) and recovery yields were from 54.0% to 129.8% at three spiked levels (20, 40 and 60 ?g kg(-1) for chili, and 10, 20 and 30 ?g kg(-1) for others) in four different matrices depending on the compounds determined. The relative standard deviations (RSDs) were all below 14%. Isomerization enhancement of pyrethroids in chili extract was observed and preliminarily explained, especially for acrinathrin and deltamethrin. PMID:21315911

Shen, Chong-yu; Cao, Xiao-wen; Shen, Wei-jian; Jiang, Yuan; Zhao, Zeng-yun; Wu, Bin; Yu, Ke-yao; Liu, Han; Lian, Hong-zhen

2011-03-15

289

Time-of-flight ERD with a 200 mm2 Si3N4 window gas ionization chamber energy detector  

NASA Astrophysics Data System (ADS)

Low energy heavy ion elastic recoil detection work has been carried out in Jyväskylä since 2009 using home made timing detectors, a silicon energy detector and a timestamping data acquisition setup forming a time-of-flight-energy telescope. In order to improve the mass resolution of the setup a new energy detector was designed to replace the silicon solid state detector, which suffered from radiation damage and had poor resolution for heavy recoils. In this paper the construction and operation of an isobutane filled gas ionization chamber with a 14 × 14 mm2 100 nm thick silicon nitride window are described. In addition to greatly improved energy resolution for heavy ions, the detector is also able to detect hydrogen recoils simultaneously in the energy range of 100-1000 keV. Additionally the detector has position sensitivity by means of timing measurement, which can be performed without compromising the performance of the detector in any other way. The achieved position sensitivity improves the depth resolution near the surface.

Julin, Jaakko; Laitinen, Mikko; Sajavaara, Timo

2014-08-01

290

Ambient Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Mass spectrometric ionization methods that operate under ambient conditions and require minimal or no sample pretreatment have attracted much attention in such fields as biomedicine, food safety, antiterrorism, pharmaceuticals, and environmental pollution. These technologies usually involve separate ionization and sample-introduction events, allowing independent control over each set of conditions. Ionization is typically performed under ambient conditions through use of existing electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) techniques. Rapid analyses of gas, liquid, and solid samples are possible with the adoption of various sample-introduction methods. This review sorts different ambient ionization techniques into two main subcategories, primarily on the basis of the ionization processes, that are further differentiated in terms of the approach used for sampling.

Huang, Min-Zong; Yuan, Cheng-Hui; Cheng, Sy-Chyi; Cho, Yi-Tzu; Shiea, Jentaie

2010-07-01

291

Resolved Spectroscopy of the Narrow-Line Region in NGC 1068: Kinematics of the Ionized Gas  

NASA Astrophysics Data System (ADS)

We have determined the radial velocities of the [O III]-emitting gas in the inner narrow-line region of the Seyfert 2 galaxy NGC 1068, along a slit at position angle 202 deg, from STIS observations at a spatial resolution of 0.1" and a spectral resolving power of ?/??~1000. We use these data to investigate the kinematics of the narrow-line region within 6" (~430 pc) of the nucleus. The emission-line knots show evidence for radial acceleration to a projected angular distance of 1.7" in most cases, followed by deceleration that approaches the systemic velocity at a projected distance of ~4". We find that a simple kinematic model of biconical radial outflow can match the general trend of observed radial velocities. In this model, the emitting material is evacuated along the bicone axis, and the axis is inclined 5 deg out of the plane of the sky. The acceleration of the emission-line clouds provides support for dynamical models that invoke radiation and/or wind pressure. We suggest that the deceleration of the clouds is due to their collision with a patchy and anistropically distributed ambient medium. Based on observations with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Crenshaw, D. Michael; Kraemer, Steven B.

2000-04-01

292

Confirmatory method for sulfonamide residues in animal tissues by gas chromatography and pulsed positive ion-negative ion-chemical ionization mass spectrometry.  

PubMed

A confirmatory method has been developed for determination of 13 sulfonamides in edible tissues. The assay involves extraction from a solution resulting from a screening procedure by liquid chromatography and subsequent derivatization. Sulfachloropyridazine (SCP), sulfadiazine (SDA), sulfadimethoxine (SDM), sulfamethazine (SMZ), sulfamerazine (SME), sulfamethoxazole (SMX), sulfamethoxypyridazine (SMP), sulfapyridine (SPR), sulfaquinoxaline (SQX), and sulfathiazole (STA) were detected as the N1-methyl-N4-trifluoroacetyl derivatives, sulfaguanidine (SGU) as the same derivative after cyclization by hexafluoroacetylacetone, and sulfacetamide (SAC) as the methyl derivative. These sulfonamides were detected by gas chromatography and pulsed positive ion-negative ion-chemical ionization mass spectrometry with methane as the reactant gas, whereas sulfanilamide (SAA) was determined as the methyl derivative by electron-impact ionization. PMID:8241826

Mooser, A E; Koch, H

1993-01-01

293

Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation  

NASA Astrophysics Data System (ADS)

Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy n- and VxOyCln- ions (x = 1-14, y = 2-36, n = 1-3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N+, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCln- and VxOyCl(L)(n-1)- clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/?m = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl(1-2)- and VxOy (1-2)- anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of VxOyCl and VxOy anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a wide range of singly and multiply charged gas-phase metal oxide cluster anions for subsequent investigations of structure and reactivity using mass spectrometry and ion spectroscopy techniques.

Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

2013-09-01

294

Thermospray ionization liquid chromatography-mass spectrometry and chemical ionization gas chromatography-mass spectrometry of hexazinone metabolites in soil and vegetation extracts  

Microsoft Academic Search

We have used thermospray LC-MS to confirm three highly polar metabolites (A, B, and G) of the herbicide hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and chemical ionization GC-MS to confirm two other metabolites (D and E) in extracts of soil and vegetation from a forest in the Central Alabama Piedmont. Selected-ion monitoring (SIM) of the protonated molecular ions of metabolite A [3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at mass-to-charge

Joseph B. Fischer; Jerry L. Michael

1995-01-01

295

In-source pyrolysis-field ionization mass spectrometry and Curie-point pyrolysis-gas chromatography\\/mass spectrometry of amino acids in humic substances and soils  

Microsoft Academic Search

With the aid of in-source pyrolysis-field ionization mass spectrometry (Py-FIMS) and Curie-point pyrolysis-gas chromatography\\/mass spectrometry (cPy-GC\\/MS) in the conventional electron impact mode, characteristic signals of 23 amino acid standards were described. Thermal and mass spectrometric fragmentation pathways of these amino acids differed with each method and complemented each other. Pyrolysis products assigned by Py-FIMS extended the range of signals for

C. Sorge; M. Schnitzer; H.-R. Schulten

1993-01-01

296

Determination of alkyltrimethylammonium surfactants in hair conditioners and fabric softeners by gas chromatography–mass spectrometry with electron-impact and chemical ionization  

Microsoft Academic Search

The commercial hair conditioners and fabric softeners were analyzed for the content of alkyltrimethylammonium compounds (ATMACs) by gas chromatography–mass spectrometry (GC–MS) with electron impact (EI) and low-pressure positive-ion chemical ionization (PICI) modes. The method involves mixed diluted samples (adjust pH to 10.0) with potassium iodide to enhance the extraction of iodide–ATMA+ ion pairs by direct liquid–liquid extraction. The iodide–ATMA+ pairs

Pei-Chuan Tsai; Wang-Hsien Ding

2004-01-01

297

Determination of melamine and cyanuric acid in powdered milk using injection-port derivatization and gas chromatography–tandem mass spectrometry with furan chemical ionization  

Microsoft Academic Search

A reliable, sensitive and eco-friendly injection-port trimethylsilylated (TMS) derivatization and gas chromatography–tandem mass spectrometry (GC–MS\\/MS) with furan chemical ionization (furan-CI) method was developed to determine melamine and cyanuric acid in powdered milk samples. The effects of several parameters related to the TMS-derivatization process (i.e., injection-port temperature, residence time and volume of silylating agent) and of various CI agents were investigated.

Shin-Hwa Tzing; Wang-Hsien Ding

2010-01-01

298

Development, validation and application of a method to analyze phenols in water samples by solid phase micro extraction-gas chromatography-flame ionization detector  

Microsoft Academic Search

In this work the development, validation and application of method using Solid Phase Microexctration (SPME) for the analyses of five pollutants (phenol, 2-nitrophenol, 2,4-dimethylphenol, 2,4-dichlorophenol and 4-chloro, 3-methyl phenol) in supplying water, using gas chromatography (GC) with flame ionization detector (FID) is described. The optimal conditions obtained for SPME were: fiber type: Poliacrylate (PA); extraction time: 40 minutes; extraction temperature:

Fernando M. Lanças; Igor R. B. Olivares; Priscila M. Alves

2007-01-01

299

Flame ionization gas chromatographic determination of phthalate esters in water, surface sediments and fish species in the Ogun river catchments, Ketu, Lagos, Nigeria  

Microsoft Academic Search

The detection and quantification of four phthalate esters—dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate\\u000a (DBP), and diethylhexyl phthalate (DEHP)—in water, sediment, and some fish species were carried out using flame ionization\\u000a gas chromatography. The samples were collected from the Ogun river catchments, Ketu, Lagos. The DMP was not detected in the\\u000a water and fish samples but was detected in

Adeleke A. Adeniyi; Olumuyiwa O. Okedeyi; Khafilat A. Yusuf

2011-01-01

300

Transfer Ionization in MeV p-He Collisions Studied by Pulsed Recoil-Ion-Momentum Spectroscopy in a Storage Ring\\/Gas Target Experiment  

Microsoft Academic Search

We have investigated the transfer ionization process in fast collisions between protons, stored in the heavy-ion storage and cooler ring CRYRING, and a cold supersonic helium gas-jet target: H+ + He --> H + He2+ + e-. We have refined the COLTRIMS (COLd Target Recoil-Ion-Momentum Spectroscopy) technique by applying time-varying fields in the recoil-ion-momentum spectrometer to block random singly charged

H. T. Schmidt; C. L. Cocke; A. Fardi; J. Jensen; H. Schmidt-Böcking; L. Schmidt; R. Schuch; H. Zettergren; H. Cederquist

2003-01-01

301

Reactions of metal ions and their clusters in the gas phase using laser ionization: Fourier transform mass spectrometry. Progress report, February 1, 1993--January 31, 1994  

SciTech Connect

This report focuses on progress in seven areas: (1) Gas-Phase Reactions of Fe(Benzyne){sup +} with Simple Alkyl Halides; (2) Photodissociation and Collision-Induced Dissociation of Molecular Ions From Methylphenol and Chloromethylphenol; (3) Isotopomer Differentiation Using Metal Ion Chemical Ionization Reagents; (4) Multiple Excitation Collisional Activation (MECA) in Fourier Transform Mass Spectrometry; (5) Chemistry of Fe{sup +}-Arene Ions with Halobenzenes; (6) Gas-Phase Photodissociaton Study of Ag(Benzene){sup +} and Ag(Toluene){sup +}; and (7) Reactivity of Ti{sup 2+} and V{sup 2+} with Small Alkanes.

Freiser, B.S.

1993-09-01

302

Simulations of a surface glow discharge in a supersonic gas flow in the presence of external ionization  

SciTech Connect

Results of two-dimensional hydrodynamic simulations of a surface glow discharge operating at pressures of 0.2-0.5 Torr in a nitrogen flow propagating with a velocity of 1000 m/s in the presence of external ionization are presented. The effect of the external ionization rate on discharge operation is analyzed. The current-voltage characteristics of the discharge are calculated for different intensities of external ionization in both the presence and absence of secondary electron emission from the cathode. The discharge structure and plasma parameters in the vicinity of the loaded electrode are considered. It is shown that, when the discharge operates at the expense of secondary emission from the cathode, the discharge current and cathode sheath configuration are insensitive to external ionization. It is also demonstrated that, even at a high rate of external ionization, the discharge operates due to secondary emission from the cathode.

Aleksandrov, A. L. [Russian Academy of Sciences, Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch (Russian Federation)

2011-09-15

303

Highly Ionized Gas in the Galactic Halo: A FUSE Survey of O VI Absorption toward 22 Halo Stars  

NASA Astrophysics Data System (ADS)

Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of 22 Galactic halo stars are studied to determine the amount of O VI in the Galactic halo between ~0.3 and ~10 kpc from the Galactic midplane. Strong O VI ?1031.93 absorption was detected toward 21 stars, and a reliable 3 ? upper limit was obtained toward HD 97991. The weaker member of the O VI doublet at 1037.62 Å could be studied toward only six stars because of stellar and interstellar blending problems. The measured logarithmic total column densities vary from 13.65 to 14.57 with =14.17+/-0.28 (1 ?). The observed columns are reasonably consistent with a patchy exponential O VI distribution with a midplane density of 1.7×10-8 cm-3 and scale height between 2.3 and 4 kpc. We do not see clear signs of strong high-velocity components in O VI absorption along the Galactic sight lines, which indicates the general absence of high-velocity O VI within 2-5 kpc of the Galactic midplane. This result is in marked contrast to the findings of Sembach et al., who reported high-velocity O VI absorption toward ~60% of the complete halo sight lines observed by FUSE. The line centroid velocities of the O VI absorption do not reflect Galactic rotation well. The O VI velocity dispersions range from 33 to 78 km s-1, with an average of =45+/-11 km s-1 (1 ?). These values are much higher than the value of ~18 km s-1 expected from thermal broadening for gas at T~3×105 K, the temperature at which O VI is expected to reach its peak abundance in collisional ionization equilibrium. Turbulence, inflow, and outflow must have an effect on the shape of the O VI profiles. Kinematical comparisons of O VI with Ar I reveal that eight of 21 sight lines are closely aligned in LSR velocity (|?VLSR|<=5 km s-1), while nine of 21 exhibit significant velocity differences (|?VLSR|>=15 km s-1). This dual behavior may indicate the presence of two different types of O VI-bearing environments toward the Galactic sight lines. The correlation between the H I and O VI intermediate-velocity absorption is poor. We could identify the known H I intermediate-velocity components in the Ar I absorption but not in the O VI absorption in most cases. Comparison of O VI with other highly ionized species suggests that the high ions are produced primarily by cooling hot gas in the Galactic fountain flow and that turbulent mixing also has a significant contribution. The role of turbulent mixing varies from negligible to dominant. It is most important toward sight lines that sample supernova remnants like Loops I and IV. The average N(C IV)/N(O VI) ratios for the nearby halo (this work) and complete halo (Savage et al.) are similar (~0.6), but the dispersion is larger in the sample of nearby halo sight lines. We are able to show that the O VI enhancement toward the Galactic center region that was observed in the FUSE survey of complete halo sight lines (Savage et al.) is likely associated with processes occurring near the Galactic center by comparing the observations toward the nearby HD 177566 sight line to those toward extragalactic targets.

Zsargó, J.; Sembach, K. R.; Howk, J. C.; Savage, B. D.

2003-04-01

304

The aroma development during storage of Castlebrite apricots as evaluated by gas chromatography, electronic nose, and sensory analysis  

Microsoft Academic Search

One of the most important factors limiting apricot quality is the loss of flavor during storage, particularly overall aroma. To characterize fruit aroma, several techniques have been used, including both instrumental- and sensory-based methodologies. Despite the importance of aroma in fruit quality, limited information is available regarding the effects of long-term cold storage and ripening on the apricot’s volatile compound

B. G. Defilippi; H. Valdés; M. A. Moya-León; R. Infante; R. Campos-Vargas

2009-01-01

305

Deciphering the Ionized Gas Content in the Massive Star-forming Complex G75.78+0.34  

NASA Astrophysics Data System (ADS)

We present subarcsecond observations toward the massive star-forming region G75.78+0.34. We used the Very Large Array to study the centimeter continuum and H2O and CH3OH maser emission, and the Owens Valley Radio Observatory and Submillimeter Array to study the millimeter continuum and recombination lines (H40? and H30?). We found radio continuum emission at all wavelengths, coming from three components: (1) a cometary ultracompact (UC) H II region with an electron density ~3.7 × 104 cm-3, excited by a B0 type star, and with no associated dust emission; (2) an almost unresolved UCH II region (EAST), located ~6'' to the east of the cometary UCH II region, with an electron density ~1.3 × 105 cm-3, and associated with a compact dust clump detected at millimeter and mid-infrared wavelengths; and (3) a compact source (CORE), located ~2'' to the southwest of the cometary arc, with a flux density increasing with frequency, and embedded in a dust condensation of 30 M ?. The CORE source is resolved into two compact and unresolved sources which can be well fit by two homogeneous hypercompact H II regions each one photoionized by a B0.5 zero-age main sequence star, or by free-free radiation from shock-ionized gas resulting from the interaction of a jet/outflow system with the surrounding environment. The spatial distribution and kinematics of water masers close to the CORE-N and S sources, together with excess emission at 4.5 ?m and the detected dust emission, suggest that the CORE source is a massive protostar driving a jet/outflow.

Sánchez-Monge, Álvaro; Kurtz, Stan; Palau, Aina; Estalella, Robert; Shepherd, Debra; Lizano, Susana; Franco, José; Garay, Guido

2013-04-01

306

Determination of deltamethrin in rat plasma and brain using gas chromatography-negative chemical ionization mass spectrometry.  

PubMed

Quantification of the pyrethroid deltamethrin (DLM) in small (100?L) biological samples from rodents is essential for toxicokinetic studies of trace levels of the insecticide in foods. Such empirical kinetic data are necessary for construction of valid physiologically-based toxicokinetic models. There are no validated methods in the literature for determining deltamethrin in 100?L plasma and brain samples. Plasma and brain samples were stabilized using sodium fluoride as an esterase inhibitor, and the DLM was extracted by protein precipitation using acetonitrile and phosphoric acid. The samples were vortexed, centrifuged, evaporated to dryness, and reconstituted in toluene prior to injection into a gas chromatograph equipped with a quadrupole mass analyzer. Samples were ionized via electron capture in the negative ion mode using methane, and the molecular ion and fragment ions of DLM were monitored using Selected-Ion Monitoring (SIM) for quantitation and verification of the analyte. Cis-permethrin was used as the internal standard for the method, which was validated according to current US FDA guidelines. Linearity was determined between 0.3 and 1000ng/mL, with a limit of detection of 150pg/mL. The intra- and inter-batch variation for precision (as % relative standard deviation, RSD) and accuracy (as % bias) of the method were better than 20% at the limit of quantitation and better than 15% across the remaining linear range (n=18), with recoveries of 113% and 68% for plasma and brain respectively. Benchtop stability, autosampler stability, and freeze/thaw stability studies of the method (over a 3-day freeze/thaw cycle) were found to be within the acceptance criteria of 20% RSD and bias. This optimized method was applied to the quantitation of DLM in plasma and brain homogenate samples obtained up to 12h after oral dosing of Sprague-Dawley rats with 1mg DLM/kg body weight. PMID:24814001

Gullick, Darren; Popovici, Andrew; Young, Holly C; Bruckner, James V; Cummings, Brian S; Li, Pei; Bartlett, Michael G

2014-06-01

307

On-line derivatization gas chromatography with furan chemical ionization tandem mass spectrometry for screening of amphetamines in urine.  

PubMed

A simple alternative method with minimal sample pretreatment is investigated for screening of amphetamines in small volume (using only 20 microL) of urine sample. The method is sensitive and selective. The method uses gas chromatography (GC) direct sample introduction (DSI) for on-line derivatization (acylation) of amphetamines to improve sensitivity. Furan as chemical ionization (CI) reagent in conjunction with tandem mass spectrometry (MS/MS) is used to improve selectivity. Low background with sharp protonated molecular ion peaks of analytes is the evidence of improvement in sensitivity and selectivity. Blank urine samples spiked with known amounts of amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine and 3,4-methylenedioxyethylamphetamine is analyzed. Selected ion monitoring of the characteristic product ions (m/z 119+136+150+163) using furan CI-MS/MS in positive ion mode is used for quantification. Limits of detection (LOD) between 0.4 and 1.0 ng mL(-1) and limits of quantitation (LOQ) between 1.0 and 2.0 ng mL(-1) are established. Linear response over the range of 1-1000 ng mL(-1) (r(2)>0.997) is observed for all analytes, except for methamphetamine (2.0-1000 ng mL(-1)). Good accuracy between 86 and 113% and precision ranging from 4 to 18% is obtained. The method is also tested on real samples of urine from suspected drug abusers. This method could be used for screening and determination of amphetamines in urine samples, however needs additional work for full validation. PMID:17034801

Tzing, Shin-Hwa; Ghule, Anil; Liu, Jen-Yu; Ling, Yong-Chien

2006-12-22

308

Method development for the characterization of biofuel intermediate products using gas chromatography with simultaneous mass spectrometric and flame ionization detections.  

PubMed

Accurate analytical methods are required to develop and evaluate the quality of new renewable transportation fuels and intermediate organic liquid products (OLPs). Unfortunately, existing methods developed for the detailed characterization of petroleum products, are not accurate for many of the OLPs generated from non-petroleum feedstocks. In this study, a method was developed and applied to the detailed characterization of complex OLPs formed during triacylglyceride (TG) pyrolysis which is the basis for generating one class of emerging biofuels. This method uses gas chromatography coupled simultaneously with flame ionization and mass spectrometry detectors (GC-FID/MS). The FID provided accurate quantification of carbonaceous species while MS enabled identification of unknown compounds. A programed temperature vaporizer using a 25 °C, 0.1 min, 720 °C min(-1), 350 °C, 5 min temperature program is employed which minimizes compound discrimination better than the more commonly utilized split/splitless injector, as verified with injections at 250 and 350 °C. Two standard mixtures featuring over 150 components are used for accurate identification and a designed calibration standard accounts for compound discrimination at the injector and differing FID responses of various classes of compounds. This new method was used to identify and quantify over 250 species in OLPs generated from canola oil, soybean oil, and canola methyl ester (CME). In addition to hydrocarbons, the method was used to quantify polar (upon derivatization) and unidentified species, plus the unresolved complex mixture that has not typically been determined in previous studies. Repeatability of the analytical method was below 5% RSD for all individual components. Using this method, the mass balance was closed for samples derived from canola and soybean oil but only ca. 77 wt% of the OLP generated from CME could be characterized. The ability to close the mass balance depended on sample origin, demonstrating the need for an accurate quantification method for biofuels at various stages of production. PMID:22245174

S?ávová, Jana; Stahl, Danese C; Seames, Wayne S; Kubátová, Alena

2012-02-10

309

Hydrogen Recombination Lines near 327 MHZ. I. Distribution of Low-Density Ionized Gas in the Galactic Disk  

NASA Astrophysics Data System (ADS)

We present the results of a low-resolution (2deg×2deg) survey of radio recombination lines (RRLs) near 327 MHz in the Galactic plane made with the Ooty Radio Telescope (ORT). Although the angular resolution is coarse, these observations represent the first contiguous survey of low-frequency RRL emission in the longitude range l=330deg-0°-89° (inner Galaxy). Hydrogen RRLs were detected in almost all directions in the inner Galaxy and carbon lines in several positions. In the outer Galaxy (l=172deg-252deg), an unbiased set of 14 positions were observed and lines were detected toward three of them. To study the extent of the ionized gas above the Galactic disk, we have observed RRLs along the Galactic latitude at two specific longitudes (l=0.0d and 13.9d). RRLs were detected up to b=+/-3deg. The l-v diagram and the radial distribution, obtained from RRL emission near 327 MHz, show good similarity with that of RRL emission near 1.4 GHz, ``intense'' 12CO emission and to some extent with the RRLs observed near 3 cm from normal H II region. These distributions are distinctly different from those of H? and H I emission from the Galactic disk. Based on a comparison of the radial distribution of different components in the Galactic disk, we conclude that the diffuse RRL emission is associated with star-forming regions and possibly with a low-density component of known H II regions in the inner Galaxy.

Roshi, D. Anish; Anantharamaiah, K. R.

2000-05-01

310

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection.  

PubMed

Dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-flame ionization detection (GC-FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 microL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 microL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04-1000.25 and 54.76-74.02%, respectively. The linear range was (0.005-16 microg mL(-1)) and limits of detection were between 0.005 and 0.01 microg mL(-1) for each of the analytes. The relative standard deviations (R.S.D.) for 4 microg mL(-1) of TCAs in water were in the range of 5.6-6.4 (n=6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma. PMID:18585215

Yazdi, Ali Sarafraz; Razavi, Nourolhoda; Yazdinejad, Samaneh Raouf

2008-06-15

311

What happens to hydrophobic interactions during transfer from the solution to the gas phase? The case of electrospray-based soft ionization methods.  

PubMed

The disappearance of the hydrophobic effect in the gas phase due to the absence of an aqueous surrounding raises a long-standing question: can noncovalent complexes that are exclusively bound by hydrophobic interactions in solution be preserved in the gas phase? Some reports of successful detection by mass spectrometry of complexes largely stabilized by hydrophobic effect are questionable by the presence of electrostatic forces that hold them together in the gas phase. Here, we report on the MS-based analysis of model supramolecular complexes with a purely hydrophobic association in solution, ?-cyclodextrin, and synthetic adamantyl-containing ligands with several binding sites. The stability of these complexes in the gas phase is investigated by quantum chemical methods (DFT-M06). Compared with the free interaction partners, the inclusion complex between ?-cyclodextrin and adamantyl-containing ligand is shown to be stabilized in the gas phase by ?G = 9.6 kcal mol(-1). The host-guest association is mainly enthalpy-driven due to strong dispersion interactions caused by a large nonpolar interface and a high steric complementarity of the binding partners. Interference from other types of noncovalent binding forces is virtually absent. The complexes are successfully detected via electrospray ionization mass spectrometry, although a high dissociation yield is also observed. We attribute this pronounced dissociation of the complexes to the collisional activation of ions in the atmospheric interface of mass spectrometer. The comparison of several electrospray-based ionization methods reveals that cold spray ionization provides the softest ion generation conditions for these complexes. PMID:21953099

Barylyuk, Konstantin; Balabin, Roman M; Grünstein, Dan; Kikkeri, Raghavendra; Frankevich, Vladimir; Seeberger, Peter H; Zenobi, Renato

2011-07-01

312

What Happens to Hydrophobic Interactions during Transfer from the Solution to the Gas Phase? The Case of Electrospray-Based Soft Ionization Methods  

NASA Astrophysics Data System (ADS)

The disappearance of the hydrophobic effect in the gas phase due to the absence of an aqueous surrounding raises a long-standing question: can noncovalent complexes that are exclusively bound by hydrophobic interactions in solution be preserved in the gas phase? Some reports of successful detection by mass spectrometry of complexes largely stabilized by hydrophobic effect are questionable by the presence of electrostatic forces that hold them together in the gas phase. Here, we report on the MS-based analysis of model supramolecular complexes with a purely hydrophobic association in solution, ?-cyclodextrin, and synthetic adamantyl-containing ligands with several binding sites. The stability of these complexes in the gas phase is investigated by quantum chemical methods (DFT-M06). Compared with the free interaction partners, the inclusion complex between ?-cyclodextrin and adamantyl-containing ligand is shown to be stabilized in the gas phase by ? G = 9.6 kcal mol-1. The host-guest association is mainly enthalpy-driven due to strong dispersion interactions caused by a large nonpolar interface and a high steric complementarity of the binding partners. Interference from other types of noncovalent binding forces is virtually absent. The complexes are successfully detected via electrospray ionization mass spectrometry, although a high dissociation yield is also observed. We attribute this pronounced dissociation of the complexes to the collisional activation of ions in the atmospheric interface of mass spectrometer. The comparison of several electrospray-based ionization methods reveals that cold spray ionization provides the softest ion generation conditions for these complexes.

Barylyuk, Konstantin; Balabin, Roman M.; Grünstein, Dan; Kikkeri, Raghavendra; Frankevich, Vladimir; Seeberger, Peter H.; Zenobi, Renato

2011-07-01

313

Nearby early-type galaxies with ionized gas. VI. The Spitzer-IRS view. Basic data set analysis and empirical spectral classification  

NASA Astrophysics Data System (ADS)

Context. A large fraction of early-type galaxies (ETGs) shows emission lines in their optical spectra, mostly with LINER characteristics. Despite the number of studies, the nature of the ionization mechanisms is still debated. Many ETGs also show several signs of rejuvenation episodes. Aims: We aim to investigate the ionization mechanisms and the physical processes of a sample of ETGs using mid-infrared spectra. Methods: We present here low resolution Spitzer-IRS spectra of 40 ETGs, 18 of which from our proposed Cycle 3 observations, selected from a sample of 65 ETGs showing emission lines in their optical spectra. We homogeneously extract the mid-infrared (MIR) spectra, and after the proper subtraction of a "passive" ETG template, we derive the intensity of the ionic and molecular lines and of the polycyclic aromatic hydrocarbon (PAH) emission features. We use MIR diagnostic diagrams to investigate the powering mechanisms of the ionized gas. Results: The mid-infrared spectra of early-type galaxies show a variety of spectral characteristics. We empirically sub-divide the sample into five classes of spectra with common characteristics. Class-0, accounting for 20% of the sample, are purely passive ETGs with neither emission lines nor PAH features. Class-1 show emission lines but no PAH features, and account for 17.5% of the sample. Class-2, in which 50% of the ETGs are found, as well as having emission lines, show PAH features with unusual ratios, e.g. 7.7 ?m/11.3 ?m ? 2.3. Class-3 objects (7.5% of the sample) have emission lines and PAH features with ratios typical of star-forming galaxies. Class-4, containing only 5% of the ETGs, is dominated by a hot dust continuum. The diagnostic diagram [Ne iii]15.55 ?m/[Ne ii]12.8 ?m vs. [S iii]33.48 ?m/[Si ii]34.82 ?m, is used to investigate the different mechanisms ionizing the gas. According to the above diagram most of our ETGs contain gas ionized via either AGN-like or shock phenomena, or both. Conclusions: Most of the spectra in the present sample are classified as LINERs in the optical window. The proposed MIR spectral classes show unambiguously the manifold of the physical processes and ionization mechanisms, from star formation, low level AGN activity, to shocks (H2), present in LINER nuclei. Based on Spitzer observations: Cycle3 ID 30256 PI R. Rampazzo.Table 3 is only available in electronic form at http://www.aanda.org

Panuzzo, P.; Rampazzo, R.; Bressan, A.; Vega, O.; Annibali, F.; Buson, L. M.; Clemens, M. S.; Zeilinger, W. W.

2011-04-01

314

Comprehensive two-dimensional gas chromatography with flame ionization and time-of-flight mass spectrometry detection: qualitative and quantitative analysis of West Australian sandalwood oil.  

PubMed

The use of gas chromatography (GC)-mass spectrometry (MS), GC-time-of-flight MS (TOFMS), comprehensive two-dimensional GC (GCxGC)-flame ionization detection (FID), and GCxGC-TOFMS is discussed for the characterization of the eight important representative components, including Z-alpha-santalol, epi-alpha-bisabolol, Z-alpha-trans-bergamotol, epi-beta-santalol, Z-beta-santalol, E,E-farnesol, Z-nuciferol, and Z-lanceol, in the oil of west Australian sandalwood (Santalum spicatum). Single-column GC-MS lacks the resolving power to separate all of the listed components as pure peaks and allow precise analytical measurement of individual component abundances. With enhanced peak resolution capabilities in GCxGC, these components are sufficiently well resolved to be quantitated using flame ionization detection, following initial characterization of components by using GCxGC-TOFMS. PMID:15516281

Shellie, Robert; Marriott, Philip; Morrison, Paul

2004-09-01

315

Simple pretreatment procedure combined with gas chromatography/multiphoton ionization/mass spectrometry for the analysis of dioxins in soil samples obtained after the T?hoku earthquake.  

PubMed

A simple pretreatment procedure was developed for the analysis of dioxins in soil samples using gas chromatography/multiphoton ionization/time-of-flight mass spectrometry. The sample was subjected to a pressurized liquid extraction procedure, followed by separation using a pair of Sulfoxide and Ag-ION columns for cleanup. Due to the high selectivity of laser ionization, the procedure was simplified and the time required for an analysis was decreased to 3 h. The sample collected after the earthquake and tsunami contained relatively high concentrations of PCBs and PCDD/Fs. This simple and rapid pretreatment procedure can be useful for monitoring the environment to prevent unexpected exposure of toxic dioxins for the workers who have to process more than 20 million tons of the wastes in a few years. PMID:23199015

Chang, Yu-Ching; Imasaka, Totaro

2013-01-01

316

Imaging spectrophotometry of ionized gas in NGC 1068. III - Anisotropic excitation of the large-scale disk by scattering of nuclear continuum  

SciTech Connect

Photoionization of the solar abundance diffuse ionized media (DIM) in NGC 1068 by anisotropic nuclear emission is studied. It is shown that the emission characteristics can be understood in the light of the developing picture of the galaxy in which its intrinsic type 1 Seyfert nucleus, concealed by an obscuring medium, is visible only through scattered, polarized light. The gas excitation is anisotropic, the high-excitation gas along the jet axis being photoionized by direct nuclear continuum, while the lower excitation gas away from the axis sees only indirect nuclear emission scattered into it. A model of low optical depth, near-nuclear Thomson scattering is considered in detail, and it is shown that, even with moderate dust extinction, this mechanism is sufficient to energize the DIM. 56 refs.

Sokolowski, J.; Bland-hawthorn, J.; Cecil, G. (Rice University, Houston, TX (USA) North Carolina, University, Chapel Hill (USA))

1991-07-01

317

Data on Ionization, Excitation, Dissociation and Dissociative Ionization of Targets by Helium Ion Bombardments, (1). Target Ionization, Excitation, Dissociation and Dissociative Ionization Induced by Several KeV to 3.5 MeV Helium Ions Incident on Thin Gas Targets.  

National Technical Information Service (NTIS)

This report presents a compilation of the experimental data on cross sections for the ionization, excitation, dissociation and dissociative ionization processes of targets in helium ion impacts on atoms and molecules under a single collision condition. Th...

N. Oda J. Urakawa

1984-01-01

318

Ultrafast relaxation and coherent oscillations in aminobenzonitriles in the gas phase probed by intense-field ionization.  

PubMed

4-Aminobenzonitrile derivatives have two excited states of similar energy: besides the benzene-like L(b) state (also termed "locally excited" or LE state) one with charge-transfer (CT) character that is slightly higher in the isolated molecules. The CT state can be lowered by solvents of suitable polarity, so that dual fluorescence can be observed in them. It is controversial along which coordinate this state is displaced, although the amino-group twist is a wide-spread assumption. We investigated a number of such compounds by transient ionization in the gas phase, initially exciting the higher-lying L(a) state (S(2)). Here we briefly review the previous results on 4-(dimethylamino)benzonitrile (the prototype of this class of molecules), 4-piperidino-, pyrrolidino- and pyrrolyl-benzonitrile and compare them with new results on 4-aminobenzonitrile and on the bridged derivative N-methyl-6-cyano-1,2,3,4-tetrahydroquinoline (NMC6). Although in the latter two molecules the CT state has never been detected before, we find the same relaxation path for all compounds: From S(2), the wave packet passes through a conical intersection (CI); from there part of it reaches the S(1) (L(b)) state directly, whereas another part temporarily populates the CT state (also in NMC6), from where it goes around the CI also to the L(b) well. The wave packet directly reaching the L(b) well oscillates there along coordinates involving amino-group twist and wagging or molecular arching and a quinoidal distortion. These coordinates must be components of the CI displacement vector. A vibration involving bond-length alternation of the benzene ring is ascribed to a momentum caused by the electronic symmetry change in the CI, i.e., to the nonadiabatic coupling vector. Also the CT state involves amino-group twist, as to conclude from the anisotropy of the corresponding signal. The six-membered aliphatic ring in NMC6 hinders the twist and raises the CT state to an energy that is, however, still below the L(a) state, so that it can be temporarily populated in a barrierless process. Also in aminobenzonitrile the CT state is between L(a) and L(b) and is reached from L(a) without a barrier. The twist is rationalized by vibronic interaction with a higher state that is pi-antibonding between the amino group and the aromatic ring. PMID:17325762

Fuss, Werner; Schmid, Wolfram E; Kuttan Pushpa, Kumbil; Trushin, Sergei A; Yatsuhashi, Tomoyuki

2007-03-14

319

Triboelectric spray ionization.  

PubMed

Triboelectric spray ionization (TESI) is a variation of electrospray ionization (ESI) using common instrumental components, including gas flow, solvent flow rate and heat, the only difference being the use of a high-voltage power supply for ESI or a static charge for TESI. The ionization of solvent or analyte is due to the electrostatic potential difference formed between the spray electrode and counter electrode. The ion source contains a pneumatic spray operated over a range of flow rates (0.15-1.5 µl/min) and gas pressures (0-100). This new design contains a standalone spray assembly and an optional metal mesh in front of the spray. There are several parameters that affect the performance during ionization of molecules including the flow rate of solvent, gas pressure, temperature, solvent acidity, distance and potential difference between emitter and counter electrode. A variable electrostatic potential can be applied for higher ionization efficiency. The new ionization method was successfully applied to solutions of various proteins under different conditions. The same charge-state distributions compared to other ESI techniques are observed for all the protein samples. The unique feature of TESI is very efficient spraying by using a natural electrostatic potential even at the potential that a human body can produce. This provides very gentle ionization efficiency of peptides and proteins in different solvents. PMID:23378087

Özdemir, Abdil; Lin, Jung-Lee; Gillig, Kent J; Chen, Chung-Hsuan

2013-02-01

320

Dynamics of Ionized Gas at the Galactic Center: Very Large Array Observations of the Three-dimensional Velocity Field and Location of the Ionized Streams in Sagittarius A West  

NASA Astrophysics Data System (ADS)

We present new results based on high-resolution observations of Sgr A West at the Galactic center with the Very Large Array (VLA) at 1.3 cm. By combining recent observations with those made at earlier epochs with the VLA at wavelengths of 1.3 and 3.6 cm, we measured proper motions for 71 compact H II components in the central 80'' (3 pc, assuming D = 8 pc). Using VLA archival data for the H92? radio recombination line, we also investigated radial velocities in the LSR velocity range from +200 to -415 km s-1. Combining proper motion and radial velocity measurements, we have determined the three-dimensional velocity distribution in Sgr A West. We find that the three ionized streams (Northern Arm, Eastern Arm, and Western Arc) in the central 3 pc can be modeled with three bundles of Keplerian orbits around Sgr A*. Assuming that each of the observed streams of ionized gas follows a single orbit, we determined the five orbital parameters (a, e, ?, ?, i) for each of them using least-square fitting to the loci of the streams. The degeneracy in the orbital solutions for both the direction of flow and the two mirror images can be further resolved using the information obtained from the velocity measurements. Our results confirm earlier results on the streams in the Western Arc and the Northern Arm to be in Keplerian orbits, suggesting that the stream in the Eastern Arm is also consistent with an elliptical orbit. All three are confined within the central 3 pc. Both the Northern and Eastern Arm streams have high eccentricities (e = 0.83 ± 0.10 and 0.82 ± 0.05, respectively), while the Western Arc stream is nearly circular, with e = 0.2 ± 0.15. All three streams orbit around Sgr A* in a counterclockwise sense (viewed from the Earth) and have orbital periods in the range 4-8 × 104 yr. To verify the fit, the distributions of radial and transverse velocity vectors in Sgr A West were also computed using the Keplerian model and they show good agreement with both the proper motion and radial velocity data. In addition, the computed orbits suggest that the Northern and Eastern Arm streams may collide in the "Bar" region (a few arcsec south of Sgr A*) and that most of the orbiting ionized gas in the "Bar" region is located behind Sgr A*. We also report an ionized nebula associated with IRS 8, including a bow shock in radio continuum emission which shows excellent agreement with near infrared observations. From the H92? line data, we find evidence of substantial interaction between the IRS 8 nebula and the Northern Arm stream occurring in the bow-shock region. Other new morphological features revealed in our high-resolution image include (1) a helical structure in the Northern Arm, suggesting that MHD plays an important role in the motion of the ionized gas, in addition to the dynamics determined by the central gravitational field, and (2) a linear feature in the IRS 16 region, suggesting that the compressed edge of the Northern Arm may result from the collective winds and radiation pressure from the high mass stars in the IRS16 cluster.

Zhao, Jun-Hui; Morris, Mark R.; Goss, W. M.; An, Tao

2009-07-01

321

The ionized and hot gas in M17 SW. SOFIA/GREAT THz observations of [C II] and 12CO J = 13-12  

NASA Astrophysics Data System (ADS)

Aims: With new THz maps that cover an area of ~3.3 × 2.1 pc2 we probe the spatial distribution and association of the ionized, neutral and molecular gas components in the M17 SW nebula. Methods: We used the dual band receiver GREAT on board the SOFIA airborne telescope to obtain a 5.'7 × 3.'7 map of the 12CO J = 13-12 transition and the [C II] 158 ?m fine-structure line in M17 SW and compare the spectroscopically resolved maps with corresponding ground-based data for low- and mid-J CO and [C I] emission. Results: For the first time SOFIA/GREAT allow us to compare velocity-resolved [C II] emission maps with molecular tracers. We see a large part of the [C II] emission, both spatially and in velocity, that is completely non-associated with the other tracers of photon-dominated regions (PDR). Only particular narrow channel maps of the velocity-resolved [C II] spectra show a correlation between the different gas components, which is not seen at all in the integrated intensity maps. These show different morphology in all lines but give hardly any information on the origin of the emission. The [C II] 158 ?m emission extends for more than 2 pc into the M17 SW molecular cloud and its line profile covers a broader velocity range than the 12CO J = 13-12 and [C I] emissions, which we interpret as several clumps and layers of ionized carbon gas within the telescope beam. The high-J12CO emission emerges from a dense region between the ionized and neutral carbon emissions, indicating the presence of high-density clumps that allow the fast formation of hot CO in the irradiated complex structure of M17 SW. The [C II] observations in the southern PDR cannot be explained with stratified or clumpy PDR models.

Pérez-Beaupuits, J. P.; Wiesemeyer, H.; Ossenkopf, V.; Stutzki, J.; Güsten, R.; Simon, R.; Hübers, H.-W.; Ricken, O.

2012-06-01

322

Pulsed large volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry for simultaneous determination of typical halogenated persistent organic pollutants  

Microsoft Academic Search

A pulsed large-volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry\\u000a (pLVI-GC\\/ECNI-qMS) was developed for the simultaneous determination of typical halogenated persistent organic pollutants (H-POPs).\\u000a By monitoring the characteristic ions of large mass-to-charge ratio (m\\/z) for each of the H-POPs rather than the chlorine and\\/or bromine ions, this method avoided the possible interferences arising\\u000a from the H-POPs

Yuli Zhao; Limin Yang; Qiuquan Wang

2007-01-01

323

Application of gas chromatography-(triple quadrupole) mass spectrometry with atmospheric pressure chemical ionization for the determination of multiclass pesticides in fruits and vegetables.  

PubMed

A multi-residue method for the determination of 142 pesticide residues in fruits and vegetables has been developed using a new atmospheric pressure chemical ionization (APCI) source for coupling gas chromatography (GC) to tandem mass spectrometry (MS). Selected reaction monitoring (SRM) mode has been applied, acquiring three transitions for each compound. In contrast to the extensive fragmentation typically obtained in classical electron ionization (EI), the soft APCI ionization allowed the selection of highly abundant protonated molecules ([M+H](+)) as precursor ions for most compounds. This was favorable for both sensitivity and selectivity. Validation of the method was performed in which both quantitative and qualitative parameters were assessed using orange, tomato and carrot samples spiked at two levels, 0.01 and 0.1mg/kg. The QuEChERS method was used for sample preparation, followed by a 10-fold dilution of the final acetonitrile extract with a mixture of hexane and acetone. Recovery and precision were satisfactory in the three matrices, at both concentration levels. Very low limits of detection (down 0.01?g/kg for the most sensitive compounds) were achieved. Ion ratios were consistent and identification according to EU criteria was possible in 80% (0.01mg/kg) to 96% (0.1mg/kg) of the pesticide/matrix combinations. The method was applied to the analysis of various fruits and vegetables from the Mediterranean region of Spain. PMID:24070626

Cherta, Laura; Portolés, Tania; Beltran, Joaquim; Pitarch, Elena; Mol, Johannes G J; Hernández, Félix

2013-11-01

324

Kelvin spray ionization.  

PubMed

A novel self-powered dual spray ionization source has been developed for applications in mass spectrometry. This new source does not use any power supply and produces both positive and negative ions simultaneously. The idea behind this ionization source comes from the Kelvin water dropper. The source employs one or two syringes, two pneumatic sprays operated over a range of flow rates (0.15-15 ?L min(-1)) and gas pressures (0-150 psi), and two double layered metal screens for ion formation. A variable electrostatic potential from 0 to 4 kV can be produced depending on solvent and gas flow rates that allow gentle ionization of compounds. There are several parameters that affect the performance during ionization of molecules including the flow rate of solvent, gas pressure, solvent acidity, position of spray and metal screens with respect to each other and distance between metal screens and the counter electrode. This ionization method has been successfully applied to solutions of peptides, proteins and non-covalent complexes. In comparison with ESI, the charge number of the most populated state is lower than that from ESI. It indicates that this is a softer ionization technique and it produces more protein ions with folded structures. The unique features of Kelvin spray ionization (KeSI) are that the method is self-powered and ionization occurs at very low potentials by providing very low internal energy to the ions. This advantage can be used for the ionization of very fragile molecules and investigation of non-covalent interactions. PMID:24080942

Özdemir, Abdil; Lin, Jung-Lee; Gillig, Kent J; Chen, Chung-Hsuan

2013-11-21

325

Partially ionized gas flow and heat transfer in the separation, reattachment, and redevelopment regions downstream of an abrupt circular channel expansion.  

NASA Technical Reports Server (NTRS)

Heat transfer and pressure measurements obtained in the separation, reattachment, and redevelopment regions along a tube and nozzle located downstream of an abrupt channel expansion are presented for a very high enthalpy flow of argon. The ionization energy fraction extended up to 0.6 at the tube inlet just downstream of the arc heater. Reattachment resulted from the growth of an instability in the vortex sheet-like shear layer between the central jet that discharged into the tube and the reverse flow along the wall at the lower Reynolds numbers, as indicated by water flow visualization studies which were found to dynamically model the high-temperature gas flow. A reasonably good prediction of the heat transfer in the reattachment region where the highest heat transfer occurred and in the redevelopment region downstream can be made by using existing laminar boundary layer theory for a partially ionized gas. In the experiments as much as 90 per cent of the inlet energy was lost by heat transfer to the tube and the nozzle wall.

Back, L. H.; Massier, P. F.; Roschke, E. J.

1972-01-01

326

A differentially pumped argon plasma in the linear plasma generator Magnum-PSI: gas flow and dynamics of the ionized fraction  

NASA Astrophysics Data System (ADS)

Magnum-PSI is a linear plasma generator designed to reach the plasma-surface interaction (PSI) regime of ITER and nuclear fusion reactors beyond ITER. To reach this regime, the influx of cold neutrals from the source must be significantly lower than the plasma flux reaching the target. This is achieved by a differential pumping scheme, where the vacuum vessel is divided by skimmers into separate chambers which are individually pumped. The non-magnetized expansion of 5 Pa m3 s-1 (3 slm) argon in a low background pressure was studied in the differentially pumped vacuum vessel fitted with non-cooled flat skimmers. The behavior of the neutral component was studied with direct simulation Monte Carlo simulations and Rayleigh scattering measurements. Thomson scattering and double Langmuir probe measurements were performed on the ionized fraction. It was found that the electrons and neutral particles are not completely coupled in the shock front. The neutral fraction shows clear signs of invasion from hotter background gas, causing the average temperature and density to increase before the shock. This is also shown in the ionization ratio, which has been determined in front of and behind the first skimmer. This study helps us to understand the behavior of the gas flow in the machine and validates our modeling.

van Eck, H. J. N.; Hansen, T. A. R.; Kleyn, A. W.; van der Meiden, H. J.; Schram, D. C.; Zeijlmans van Emmichoven, P. A.

2011-08-01

327

Highly Ionized Gas in the Galactic Halo and the High-Velocity Clouds toward PG 1116+215  

Microsoft Academic Search

We have obtained high-resolution Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) echelle observations of the quasar PG 1116+215 (zem=0.1765, l=223.36d, b=+68.21d). The semicontinuous coverage of the ultraviolet spectrum over the wavelength range 916-2800 Å provides detections of Galactic and high-velocity cloud (HVC) absorption over a wide range of ionization species: H I,

Rajib Ganguly; Kenneth R. Sembach; Todd M. Tripp; Blair D. Savage

2005-01-01

328

Practical method for the measurement of Alkyl mercaptans in natural gas by multi-dimensional gas chromatography, capillary flow technology, and flame ionization detection  

Microsoft Academic Search

Volatile sulfur compounds such as alkylmercaptans are undesired impurities in natural gas streams. As a result, natural gas treatment and purification services are essential in many industries that utilize natural gas either as a fuel or in a chemical process. While there are many analytical methods that can be employed for the measurement of mercaptans, a simple, practical, and easy-to-implement

R. Gras; J. Luong; V. Carter; L. Sieben; H. Cortes

2009-01-01

329

The effective ionization coefficients and electron drift velocities in gas mixtures of CF3I with N2 and CO2 obtained from Boltzmann equation analysis  

NASA Astrophysics Data System (ADS)

The electron swarm parameters including the density-normalized effective ionization coefficients (?-?)/N and the electron drift velocities Ve are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend (SST) experiment. The overall density-reduced electric field strength is from 100 Td to 1000 Td (1 Td = 10-17 V·cm2), while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%. From the variation of (?-?)/N with the CF3I mixture ratio k, the limiting field strength (E/N)lim for each CF3I concentration is derived. It is found that for the mixtures with 70% CF3I, the values of (E/N)lim are essentially the same as that for pure SF6. Additionally, the global warming potential (GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.

Deng, Yun-Kun; Xiao, Deng-Ming

2013-03-01

330

A fast gas ionization calorimeter filled with C 3F 8 for operation at high counting rates and hard radiation environment  

NASA Astrophysics Data System (ADS)

The performance of a gas ionization EM calorimeter with planar electrodes and steel absorbers has been studied with a 26.6 GeV/ c electron beam at the 70 GeV IHEP accelerator. The design of the calorimeter is optimized for the operation at high counting rates by minimizing the coupling inductance and by choosing rather fast and heavy perfluoroalkane C 3F 8 ( vdr=0.07 mm/ns at a reduced field E/ N=1.0×10 -16 V cm 2). This gas has been used for the first time in calorimetry applications. The total calorimeter thickness is ?21 X0. The signal readout has been done by remote 25 ? low-noise preamplifiers coupled to towers via 25 ? cable of 3 m length. The choice of a 25 ? input impedance provides a complete matching between preamplifier, cable and tower. The studies of the calorimeter consisted in measuring the signal and noise spectra at different values of HV, ADC gate width and gas pressure. The electron attachment rate in C 3F 8 with a stated purity of 99.99% is quite low (at a given E/ N the mean free path of electrons is ?=2.2 cm at 1 atm). The intrinsic energy resolution of the calorimeter after noise subtraction is found to be independent of the gas pressure and equal to ?7% at E=26.6 GeV/ c.

Denisov, S.; Dushkin, A.; Fedyakin, N.; Gilitsky, Yu.; Ljudmirsky, M.; Spiridonov, A.; Sytnik, V.

1998-12-01

331

Potential of gas chromatography-atmospheric pressure chemical ionization-time-of-flight mass spectrometry for the determination of sterols in human plasma.  

PubMed

The application of Gas Chromatography (GC)-Atmospheric Pressure Chemical Ionization (APCI)-Time-of-Flight Mass Spectrometry (TOF-MS) is presented for sterol analysis in human plasma. A commercial APCI interface was modified to ensure a well-defined humidity which is essential for controlled ionization. In the first step, optimization regarding flow rates of auxiliary gases was performed by using a mixture of model analytes. Secondly, the qualitative and quantitative analysis of sterols including oxysterols, cholesterol precursors, and plant sterols as trimethylsilyl-derivatives was successfully carried out. The characteristics of APCI together with the very good mass accuracy of TOF-MS data enable the reliable identification of relevant sterols in complex matrices. Linear calibration lines and plausible results for healthy volunteers and patients could be obtained whereas all mass signals were extracted with an extraction width of 20 ppm from the full mass data set. One advantage of high mass accuracy can be seen in the fact that from one recorded run any search for m/z can be performed. PMID:24463103

Matysik, S; Schmitz, G; Bauer, S; Kiermaier, J; Matysik, F-M

2014-04-11

332

Use of soft and hard ionization techniques for elucidation of unknown compounds by gas chromatography/time-of-flight mass spectrometry.  

PubMed

Investigation of trace-level non-target compounds by gas chromatography/mass spectrometry (GC/MS) often is a challenging task that requires powerful software tools to detect the unknown components, to obtain the deconvoluted mass spectra, and to interpret the data if no acceptable library match is obtained. In this paper, the complementary use of electron ionization (EI) and chemical ionization (CI) is investigated in combination with GC/time-of-flight (TOF) MS for the elucidation of organic non-target (micro)contaminants in water samples. Based on accurate mass measurement of the molecular and fragment ions from the TOF MS, empirical formulae were calculated. Isotopic patterns, carbon number prediction filter and nitrogen rule were used to reduce the number of possible formulae. The candidate formulae were searched in databases to find possible chemical structures. Selection from possible structure candidates was achieved using information on substructures and observed neutral losses derived from the fragment ions. Four typical examples (bifenazate, boscalid, epoxiconazole, and fenhexamid) are used to illustrate the methodology applied and the various difficulties encountered in this process. Our results indicate that elucidation of unknowns cannot be achieved by following a standardized procedure, as both expertise and creativity are necessary in the process. PMID:21594934

Portolés, Tania; Pitarch, Elena; López, Francisco J; Hernández, Félix; Niessen, Wilfried M A

2011-06-15

333

Influence of wavelength, irradiance, and the buffer gas pressure on high irradiance laser ablation and ionization source coupled with an orthogonal Time of Flight Mass Spectrometer  

NASA Astrophysics Data System (ADS)

Influence of laser wavelength, laser irradiance and the buffer gas pressure were studied in high irradiance laser ablation and ionization source coupled with an orthogonal time-of-flight mass spectrometer. Collisional cooling effects of energetic plasma ions were proved to vary significantly with the elemental mass number. Effective dissociation of interferential polyatomic ions in the ion source, resulting from collision and from high laser irradiance, was verified. Investigation of relative sensitivity coefficients (RSC) of different elements performed on a steel standard GBW01396, which was ablated at 1064 nm, 532 nm, 355 nm, and 266 nm, has demonstrated that the thermal ablation mechanism could play a critical role with the first three wavelengths, while 266 nm induces non-thermal ablation principally. Experimental results also indicated that there is no evident discrepancy for most metal elements on RSCs and LODs among four wavelengths at high irradiance, except that high boiling point elements like Nb, Mo, and W have higher RSCs at higher irradiance regions of 1064 nm, 532 nm, and 355 nm due to thermal ablation. A geological standard and a garnet stone were also used in the experiment subsequently, and their RSCs and LODs for metal elements show nonsignificant dependence on wavelength at designated irradiances. All results reveal that relatively uniform sensitivity can be achieved at any wavelength for metal elements in the solids used in our experiments at an appropriate irradiance for the low pressure high irradiance laser ablation and ionization source.

Huang, Rongfu; Yu, Quan; Tong, Qingguo; Hang, Wei; He, Jian; Huang, Benli

2009-03-01

334

Quantitative Determination of Epinephrine and Norepinephrine in the Picogram Range by Flame Ionization Gas-Liquid Chromatography.  

National Technical Information Service (NTIS)

A gas-liquid chromatographic method has been developed using the hydrogen flame detector for the determination of epinephrine and norepinephrine in blood plasma, red blood cells, serum and urine. The chromatographic method presents several advantages over...

H. G. Lovelady H. A. Schwertner L. L. Foster

1974-01-01

335

In-gas-cell laser ionization spectroscopy in the vicinity of 100Sn: Magnetic moments and mean-square charge radii of N=50-54 Ag  

NASA Astrophysics Data System (ADS)

In-gas-cell laser ionization spectroscopy studies on the neutron deficient 97-101Ag isotopes have been performed with the LISOL setup. Magnetic dipole moments and mean-square charge radii have been determined for the first time with the exception of 101Ag, which was found in good agreement with previous experimental values. The reported results allow tentatively assigning the spin of 97,99Ag to 9/2 and confirming the presence of an isomeric state in these two isotopes, whose collapsed hyperfine structure suggests a spin of 1/2 >. The effect of the N=50 shell closure is not only manifested in the magnetic moments but also in the evolution of the mean-square charge radii of the isotopes investigated, in accordance with the spherical droplet model predictions.

Ferrer, R.; Bree, N.; Cocolios, T. E.; Darby, I. G.; De Witte, H.; Dexters, W.; Diriken, J.; Elseviers, J.; Franchoo, S.; Huyse, M.; Kesteloot, N.; Kudryavtsev, Yu.; Pauwels, D.; Radulov, D.; Roger, T.; Savajols, H.; Van Duppen, P.; Venhart, M.

2014-01-01

336

Determination of volatile residual solvents in traditional Chinese medicines by headspace solid-phase microextraction and cryogenic gas chromatography with flame ionization detection.  

PubMed

A method based on headspace solid-phase microextraction and cryogenic gas chromatography with flame ionization detection was developed for the determination of volatile residual solvents in traditional Chinese medicines. A laboratory-made cryogenic chromatographic system was used for the separation of 15 kinds of residual solvents. During the analysis, a 65 microm PDMS/DVB fiber was used to extract the residual solvents, the extraction time was controlled at 0 degrees C for 15 min, and the NaCl content of the sample was maintained at 30%. The limits of detection ranged from 0.08 (for octane) to 5000 microg/L (for ethanol), and the relative standard deviations were < 8%. The recoveries from spiked samples ranged from 88 to 112%. Trace levels of residual solvents in several traditional Chinese medicines were effectively identified and quantified. PMID:12852559

Liu, Jiemin; Zhou, Qunfang; Jiang, Guibin; Liu, Jingfu; Liu, Jiyan; Wen, Meijuan

2003-01-01

337

Absolute double differential ionization cross sections of gas-phase nucleobase molecules by 0.5- to 2.0-MeV protons  

NASA Astrophysics Data System (ADS)

We have measured absolute ionization cross sections of gas-phase adenine (C5H5N5) and uracil (C4H4N2O2) molecules bombarded by 0.5- to 2.0-MeV protons. Cross sections are given as functions of the energy and angle of ejected electrons. Ejected electrons with energies up to 1000eV were analyzed by a parallel plate electrostatic spectrometer. The angle of ejected electron ranges from 15 to 165 degrees with respect to the incident beam direction. Present data are compared with other data reported previously for various hydrocarbon molecules. We found that the cross sections divided by the number of weakly bound outer-shell electrons are nearly the same for these complex molecules irrespectively of the chemical structure of individual molecules.

Iriki, Y.; Kikuchi, Y.; Doi, K.; Imai, M.; Itoh, A.

2012-11-01

338

Fluorohydrogenate Cluster Ions in the Gas Phase: Electrospray Ionization Mass Spectrometry of the [1-Ethyl-3-methylimidazolium+][F(HF)2.3–] Ionic Liquid  

SciTech Connect

Electrospray ionization of the fluorohydrogenate ionic liquid [1-ethyl-3-methylimidazolium][F(HF)2.3] ionic liquid was conducted to understand the nature of the anionic species as they exist in the gas phase. Abundant fluorohydrogenate clusters were produced; however, the dominant anion in the clusters was [FHF-], and not the fluoride-bound HF dimers or trimers that are seen in solution. Density functional theory (DFT) calculations suggest that HF molecules are bound to the clusters by about 30 kcal/mol. The DFT-calculated structures of the [FHF-]-bearing clusters show that the favored interactions of the anions are with the methynic and acetylenic hydrogen atoms on the imidazolium cation, forming planar structures similar to those observed in the solid state. A second series of abundant negative ions was also formed that contained [SiF5-] together with the imidazolium cation and the fluorohydrogenate anions that originate from reaction of the spray solution with silicate surfaces.

Gary S. Groenewold; James E. Delmore; Michael T. Benson; Tetsuya Tsuda; Rika Hagiwara

2013-12-01

339

The low luminosity AGN in the LINER galaxy M 81: it BeppoSAX discovery of highly ionized gas  

NASA Astrophysics Data System (ADS)

The LINER nucleus of the nearby spiral galaxy M 81 was pointed by BeppoSAX, which caught it at the highest (2-10) keV flux level observed so far. The LECS, MECS and PDS data, extending over (0.1-100) keV, are used to investigate the physical similarities and differences between LINERs and AGNs. The continuum is well fitted by a power law of photon index Gamma ~ 1.84, modified by little absorption due to cold material; this extends to (0.1-100) keV the validity of a similar ASCA result. Superimposed on the continuum BeppoSAX detects a 6.7 keV emission line (confirming another ASCA result) and an absorption edge at ~ 8.6 keV. Both spectral features are consistent with being produced by iron at the same high ionization level, and probably also with the same column density. So, we suggest that they originate from transmission through highly ionized thin material. Concerning the origin of the continuum emission, we do not observe signs of reflection from the optically thick material of an accretion disk, as usually found in Seyfert 1's (a 6.4 keV emission line and a broad bump peaking at 10-20 keV). The low bolometric luminosity of the nucleus of M 81 is consistent with being produced by advection dominated accretion; in this case the X-ray emission should be dominated by Comptonization, rather than by bremsstrahlung, in order to reproduce the steep spectrum observed over the (0.1-100) keV band.

Pellegrini, S.; Cappi, M.; Bassani, L.; Malaguti, G.; Palumbo, G. G. C.; Persic, M.

2000-01-01

340

A Laboratory Experiment To Measure Henry's Law Constants of Volatile Organic Compounds with a Bubble Column and a Gas Chromatography Flame Ionization Detector (GC-FID)  

ERIC Educational Resources Information Center

An undergraduate laboratory experiment is described to measure Henry's law constants of organic compounds using a bubble column and gas chromatography flame ionization detector (GC-FID). This experiment is designed for upper-division undergraduate laboratory courses and can be implemented in conjunction with physical chemistry, analytical…

Lee, Shan-Hu; Mukherjee, Souptik; Brewer, Brittany; Ryan, Raphael; Yu, Huan; Gangoda, Mahinda

2013-01-01

341

Determination of microbial fatty acid profiles at femtomolar levels in human urine and the initial marine microfouling community by capillary gas chromatography-chemical ionization mass spectrometry with negative ion detection  

Microsoft Academic Search

Summary Room temperature esterification with the electron capturing pentafluorobenzyl bromide in glass capillaries, with analysis by capillary gas-liquid chromatography coupled with chemical ionization mass spectrometry and negative ion detection in the selected ion mode, allowed detection and identification of fatty acids from micro- bial biofilms at the femtomolar level. This sensitivity was achieved without loss of specificity of the mass

Goran Odham; Anders Tunlid; Gunilla Westerdahl; Lennart Larsson; James B. Guckert; David C. White

1985-01-01

342

Acetate, propionate and butyrate in plasma: determination of the concentration and isotopic enrichment by gas chromatography/mass spectrometry with positive chemical ionization.  

PubMed

This study describes a rapid and simple method to determine short-chain fatty acid (SCFA) concentrations and their isotopic enrichments (M(0) + 1 and M(0) + 2) in human plasma. Sample preparation involves SCFA extraction and derivatization with 1-(tert-butyldimethylsilyl)imidazole. Gas chromatography/mass spectrometry was performed using chemical ionization with ammonia as the reagent gas. Outstanding resolution, excellent linearity and good detection limits were obtained. Inter-assay and intra-assay repeatability was below 10% and 3% respectively for SCFA concentration. Inter-assay repeatability was below 5%, 4%, 6%, and 14% for isotopic enrichment determination of [1-(13)C]acetate and [1,2-(13)C(2)]acetate, [1-(13)C]propionate and [1-(13)C]butyrate respectively, with intra-assay being below 6%. Such SCFA concentrations and isotopic enrichments were determined in the plasma of rats infused with a (13)C-labeled SCFA. The turnovers of acetate, propionate and butyrate in rats were 19 micromol kg(-1) min(-1), 2.6 micromol kg(-1) min(-1), 0.3 micromol kg(-1) min(-1) respectively. PMID:11473403

Pouteau, E; Meirim, I; Métairon, S; Fay, L B

2001-07-01

343

Simultaneous Determination of Miconazole Nitrate and Metronidazole in Different Pharmaceutical Dosage Forms by Gas Chromatography and Flame Ionization Detector (GC-FID)  

PubMed Central

A simple, rapid and precise gas chromatographic method has been developed for the simultaneous determination of miconazole nitrate (MIZ) and metronidazole (MNZ) in tablets and ovules, using a capillary column AE.SE-54 (15 m × 0.53 mm, i.d.) and nitrogen as a carrier gas at a flow rate of 9 mL min?1. The oven temperature was programmed at 140°C for 3 min, with a rise of 40°C min?1 up to 180°C (held for 2 min) and then increased to a final temperature of 250°C. The injector and detector port temperatures were maintained at 260°C. Detection was carried out using flame ionization detector. Results of assay and recovery studies were statistically evaluated for its accuracy and precision. The retention times were about 3.50 and 12.90 min for MNZ and MIZ, respectively. Linearity ranges were 50.0–6030.0 and 62.5–2000.0 ?g mL?1 for MNZ and MIZ, with limit of detection values of 2.5 and 3.1 ?g mL?1, respectively. Correlation coefficients (R2) of the regression equations were greater than 0.999 in all cases. No interference from any components of pharmaceutical dosage forms or degradation products was observed. According to the validation results, the proposed method was found to be specific, accurate, precise and could be applied to the simultaneous quantitative analysis of MIZ and MNZ in tablets and ovules.

Ashour, Safwan; Kattan, Nuha

2010-01-01

344

Plasma Production via Field Ionization  

SciTech Connect

Plasma production via field ionization occurs when an incoming particle beam is sufficiently dense that the electric field associated with the beam ionizes a neutral vapor or gas. Experiments conducted at the Stanford Linear Accelerator Center explore the threshold conditions necessary to induce field ionization by an electron beam in a neutral lithium vapor. By independently varying the transverse beam size, number of electrons per bunch or bunch length, the radial component of the electric field is controlled to be above or below the threshold for field ionization. Additional experiments ionized neutral xenon and neutral nitric oxide by varying the incoming beam's bunch length. A self-ionized plasma is an essential step for the viability of plasma-based accelerators for future high-energy experiments.

O'Connell, C.L.; Barnes, C.D.; Decker, F.; Hogan, M.J.; Iverson, R.; Krejcik, P.; Siemann, R.; Walz, D.R.; /SLAC; Clayton, C.E.; Huang, C.; Johnson, D.K.; Joshi, C.; Lu, W.; Marsh, K.A.; Mori, W.; Zhou, M.; /UCLA; Deng, S.; Katsouleas, T.; Muggli, P.; Oz, E.; /Southern California U.

2007-01-02

345

Differences between propane in nitrogen versus air matrix analyzed using gas chromatography with flame-ionization detection  

Microsoft Academic Search

New US Federal low-level automobile emission requirements, such as Zero Level Emission Vehicle (ZLEV), for hydrocarbons and other species have resulted in manufacturers need for new certified reference materials. The new emission requirement for hydrocarbons requires the use, by automobile manufacturing testing facilities, of 100nmol\\/mol (ppb) propane in air gas standard. Emission measurement instruments are required, by Federal law, to

George C. Rhoderick

2008-01-01

346

Multiscale approach combining nonadiabatic dynamics with long-time radiative and non-radiative decay: Dissociative ionization of heavy rare-gas tetramers revisited  

NASA Astrophysics Data System (ADS)

A multiscale approach is proposed to address short-time nonadiabatic dynamics and long-time decay. We show the role of both radiative and non-radiative processes in cluster decay mechanisms on examples of rare-gas cluster fragmentation after electron impact ionization. Nonadiabatic molecular dynamics is used as an efficient tool for theoretical study on femto- and picosecond scales and a multiscale approach based on kinetic rates of radiative as well as non-radiative transitions, both considered as parallel reaction channels, is used for the analysis of the long-time system relaxation spanning times over microseconds to infinity. While the radiative processes are typically slow, the system relaxation through non-radiative electronic transitions connected with electron-nuclear interchange of energy may, on the other hand, significantly vary in kinetic rates according to kinetic couplings between relevant adiabatic states. While the predictions of picosecond molecular dynamics themselves fail, the results of the multiscale model for the electron-impact post-ionization fragmentation of krypton and xenon tetramers are in agreement with experiment, namely, in leading to the conclusion that charged monomers prevail. More specifically, on microsecond and longer scales, mainly slow radiative processes are substantial for krypton cluster decay, while for xenon the radiative and slow non-radiative processes compete. In general, the role of slow decay processes through non-radiative transitions is comparable with the role of radiative decay mechanism. The novel multiscale model substantially improves theoretical predictions for the xenon tetramer decay and also further improves the good agreement between theory and experiment we reached previously for krypton.

Jane?ek, Ivan; Jan?a, Tomáš; Naar, Pavel; Kalus, René; Gadea, Florent Xavier

2013-01-01

347

Highly sensitive and selective analysis of urinary steroids by comprehensive two-dimensional gas chromatography combined with positive chemical ionization quadrupole mass spectrometry  

PubMed Central

Comprehensive two dimensional gas chromatography (GC×GC) provides greater separation space than conventional GC. Because of fast peak elution, a time of flight mass spectrometer (TOFMS) is the usual structure-specific detector of choice. The quantitative capabilities of a novel GC×GC fast quadrupole MS were investigated with electron ionization (EI), and CH4 or NH3 positive chemical ionization (PCI) for analysis of endogenous urinary steroids targeted in anti-doping tests. Average precisions for steroid quantitative analysis from replicate urine extractions were 6% (RSD) for EI and 8% for PCI-NH3. The average limits of detection (LOD) calculated by quantification ions for 12 target steroids spiked into steroid-free urine matrix (SFUM) were 2.6 ng mL?1 for EI, 1.3 ng mL?1 for PCI-CH4, and 0.3 ng mL?1 for PCI-NH3, all in mass scanning mode. The measured limits of quantification (LOQ) with full mass scan GC×GC-qMS were comparable with the LOQ values measured by one-dimensional GC-MS in single ion monitoring (SIM) mode. PCI-NH3 yields fewer fragments and greater (pseudo)molecular ion abundances than EI or PCI-CH4. These data show a benchtop GC×GC-qMS system has the sensitivity, specificity, and resolution to analyze urinary steroids at normal urine concentrations, and that PCI-NH3, not currently available on most GC×GC-TOFMS instruments, is of particular value for generation of structure-specific ions.

Zhang, Ying; Tobias, Herbert J.; Brenna, J. Thomas

2014-01-01

348

ON THE ORIGINS OF THE DIFFUSE H{alpha} EMISSION: IONIZED GAS OR DUST-SCATTERED H{alpha} HALOS?  

SciTech Connect

It is known that the diffuse H{alpha} emission outside of bright H II regions not only are very extended, but also can occur in distinct patches or filaments far from H II regions, and the line ratios of [S II] {lambda}6716/H{alpha} and [N II] {lambda}6583/H{alpha} observed far from bright H II regions are generally higher than those in the H II regions. These observations have been regarded as evidence against the dust-scattering origin of the diffuse H{alpha} emission (including other optical lines), and the effect of dust scattering has been neglected in studies on the diffuse H{alpha} emission. In this paper, we reexamine the arguments against dust scattering and find that the dust-scattering origin of the diffuse H{alpha} emission cannot be ruled out. As opposed to the previous contention, the expected dust-scattered H{alpha} halos surrounding H II regions are, in fact, in good agreement with the observed H{alpha} morphology. We calculate an extensive set of photoionization models by varying elemental abundances, ionizing stellar types, and clumpiness of the interstellar medium (ISM) and find that the observed line ratios of [S II]/H{alpha}, [N II]/H{alpha}, and He I {lambda}5876/H{alpha} in the diffuse ISM accord well with the dust-scattered halos around H II regions, which are photoionized by late O- and/or early B-type stars. We also demonstrate that the H{alpha} absorption feature in the underlying continuum from the dust-scattered starlight ({sup d}iffuse galactic light{sup )} and unresolved stars is able to substantially increase the [S II]/H{alpha} and [N II]/H{alpha} line ratios in the diffuse ISM.

Seon, Kwang-Il [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Witt, Adolf N., E-mail: kiseon@kasi.re.kr [Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606 (United States)

2012-10-20

349

Determination of volatile residual solvents in pharmaceutical products by headspace liquid-phase microextraction gas chromatography-flame ionization detector.  

PubMed

This paper demonstrates headspace liquid-phase microextraction (HS-LPME) as used for the determination of volatile residual solvents in pharmaceutical products. This method is based on headspace liquid-phase microextraction capillary column gas chromatography. Under optimum conditions, the linerary of the method ranged from 1 to 1,000 mg l(-1). The limits of detection are 0.2-6.0 [corrected] mg l(-1) and relative standard deviations (RSD) for most of the volatile solvents were below 10%. This novel method is applied to the analysis of volatile residual solvents in pharmaceutical products with satisfactory results. PMID:16770579

Wang, Xia; Jiang, Ting; Yuan, Jinpeng; Cheng, Chuange; Liu, Jianhua; Shi, Junbo; Zhao, Rusong

2006-07-01

350

Ionizing Radiation  

MedlinePLUS

... of Ionizing Radiation Sources Not Covered by Atomic Energy Act of 1954 . STD 01-04-001 [STD ... not the most current version. US Department of Energy (DOE) 10 CFR 835 , Occupational Radiation Protection Health ...

351

Novel analytical methods for flame retardants and plasticizers based on gas chromatography, comprehensive two-dimensional gas chromatography, and direct probe coupled to atmospheric pressure chemical ionization-high resolution time-of-flight-mass spectrometry.  

PubMed

In this study, we assess the applicability of different analytical techniques, namely, direct probe (DP), gas chromatography (GC), and comprehensive two-dimensional gas chromatography (GC × GC) coupled to atmospheric pressure chemical ionization (APCI) with a high resolution (HR)-time-of-flight (TOF)-mass spectrometry (MS) for the analysis of flame retardants and plasticizers in electronic waste and car interiors. APCI-HRTOFMS is a combination scarcely exploited yet with GC or with a direct probe for screening purposes and to the best of our knowledge, never with GC × GC to provide comprehensive information. Because of the increasing number of flame retardants and questions about their environmental fate, there is a need for the development of wider target and untargeted screening techniques to assess human exposure to these compounds. With the use of the APCI source, we took the advantage of using a soft ionization technique that provides mainly molecular ions, in addition to the accuracy of HRMS for identification. The direct probe provided a very easy and inexpensive method for the identification of flame retardants without any sample preparation. This technique seems extremely useful for the screening of solid materials such as electrical devices, electronics and other waste. GC-APCI-HRTOF-MS appeared to be more sensitive compared to liquid chromatography (LC)-APCI/atmospheric pressure photoionization (APPI)-HRTOF-MS for a wider range of flame retardants with absolute detection limits in the range of 0.5-25 pg. A variety of tri- to decabromodiphenyl ethers, phosphorus flame retardants and new flame retardants were found in the samples at levels from microgram per gram to milligram per gram levels. PMID:24016281

Ballesteros-Gómez, Ana; de Boer, Jacob; Leonards, Pim E G

2013-10-15

352

Development, validation and application of a method to analyze phenols in water samples by solid phase micro extraction-gas chromatography-flame ionization detector.  

PubMed

In this work the development, validation and application of method using Solid Phase Microexctration (SPME) for the analyses of five pollutants (phenol, 2-nitrophenol, 2,4-dimethylphenol, 2,4-dichlorophenol and 4-chloro, 3-methyl phenol) in supplying water, using gas chromatography (GC) with flame ionization detector (FID) is described. The optimal conditions obtained for SPME were: fiber type: Poliacrylate (PA); extraction time: 40 minutes; extraction temperature: 70 degrees C; amount of salt added to sample (NaCl): 15%; desorption temperature: 8 minutes. The parameters studied in the method validation were: limit of detection (0.3 and 3.5 microg.L(- 1)); precision, measured by the variation coefficient (between 2.1 and 8.8%); calibration curve and linearity, by using the external standardization method (between 1 and 50 50 microg.L(- 1)). After the methodology development, samples of water collected in Atibaia River (São Paulo - Brazil) were analyzed, using the optimized methodology. Three water samples collected in the rain season showed a peak with retention time close to 4-chloro, 3 methyl phenol further analyzed by Gas Chromatography-Mass Spectrometry for the identity confirmation. In spite of the fact that none target compounds were found in the river water samples analyzed, the presence of two phenols different from those investigated (p-terc butyl phenol; butylated hydroxytoluene) were detected. These results together with the results of the limit of detection (that showed to be lower than the maximum concentration of phenols demanded by different environment control agencies), and the results of the validation, indicate the applicability of this method for the analysis of selected phenols in river water samples. PMID:17562456

Lanças, Fernando M; Olivares, Igor R B; Alves, Priscila M

2007-01-01

353

The determination of cyclophosphamide and its metabolites in blood plasma as stable trifluoroacetyl derivatives by electron capture chemical ionization gas chromatography/mass spectrometry.  

PubMed

A method is described for the determination of the antitumour drug cyclophosphamide and six stable metabolites in plasma of cancer patients, namely dechloroethyl-cyclophosphamide, 4-keto-cyclophosphamide, carboxy-phosphamide, alcophosphamide, nor-nitrogen mustard and the N-chloroethyl-1,3-oxazolidine-2-one, as methyl and/or trifluoroacetyl derivatives by single ion monitoring gas chromatography/mass spectrometry, mostly in the electron capture chemical ionization mode. The isolation of most metabolites was performed by solid-phase C-18 extraction in weakly acidic medium. The phosphoramide mustard isolated under these conditions decomposes readily to the nor-nitrogen mustard during derivatization. The original nor-nitrogen mustard and the chloroethyl-1,3-oxazolidine-2-one were isolated by liquid extraction with ethyl acetate in alkaline medium. Recoveries of 75-99% were measured using spiked blank plasma samples. Quantitation of metabolites in patient plasma samples was performed using two sets of calibration curves for the concentration ranges of 1-100 ng and 0.1-10 micrograms of metabolite per millilitre of original plasma. PMID:8148406

Momerency, G; Van Cauwenberghe, K; Slee, P H; Van Oosterom, A T; De Bruijn, E A

1994-03-01

354

Screening of pesticides and polycyclic aromatic hydrocarbons in feeds and fish tissues by gas chromatography coupled to high-resolution mass spectrometry using atmospheric pressure chemical ionization.  

PubMed

This paper reports a wide-scope screening for detection and identification of pesticides and polycyclic aromatic hydrocarbons (PAHs) in feeds and fish tissues. QuEChERS sample treatment was applied, using freezing as an additional cleanup. Analysis was carried out by gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization (GC-(APCI) QTOF MS). The qualitative validation was performed for over 133 representative pesticides and 24 PAHs at 0.01 and 0.05 mg/kg. Subsequent application of the screening method to aquaculture samples made it possible to detect several compounds from the target list, such as chlorpyrifos-methyl, pirimiphos-methyl, and ethoxyquin, among others. Light PAHs (?4 rings) were found in both animal and vegetable samples. The reliable identification of the compounds was supported by accurate mass measurements and the presence of at least two representative m/z ions in the spectrum together with the retention time of the peak, in agreement with the reference standard. Additionally, the search was widened to include other pesticides for which standards were not available, thanks to the expected presence of the protonated molecule and/or molecular ion in the APCI spectra. This could allow the detection and tentative identification of other pesticides different from those included in the validated target list. PMID:24559176

Nácher-Mestre, Jaime; Serrano, Roque; Portolés, Tania; Berntssen, Marc H G; Pérez-Sánchez, Jaume; Hernández, Félix

2014-03-12

355

Lactone enol cation-radicals: gas-phase generation, structure, energetics, and reactivity of the ionized enol of butane-4-lactone.  

PubMed

The cation-radical of 2-hydroxyoxol-2-ene (1(+*)) represents the first lactone enol ion whose structure and gas-phase ion chemistry have been studied by experiment and theory. Ion 1(+*) was generated by the McLafferty rearrangement in ionized 2-acetylbutane-4-lactone and characterized by accurate mass measurements, isotope labeling, metastable ion and collisionally activated dissociation (CAD) spectra. Metastable 1(+*) undergoes competitive losses of H-4 and CO that show interesting deuterium and (13)C isotope effects. The elimination of CO from metastable 1(+*) shows a bimodal distribution of kinetic energy release and produces (*)CH(2)CH(2)CHdbond;OH(+) (14(+*)) and CH(3)CHdbond;CHOH(+*) (15(+*)) in ratios which are subject to deuterium isotope effects. Ab initio calculations at the G2(MP2) level of theory show that 1(+*) is 105 kJ mol(-1) more stable than its oxo form, [butane-4-lactone](+*)(2(+*)). The elimination of CO from 1(+*) involves multiple isomerizations by hydrogen migrations and proceeds through ion-molecule complexes of CO with 14(+*) and 15(+*). In addition, CO is calculated to catalyze an exothermic isomerization 14(+*) --> 15(+*) in the ion-molecule complexes. Multiple consecutive hydrogen migrations in metastable 1(+*), as modeled by RRKM calculations on the G2(MP2) potential energy surface, explain the unusual deuterium kinetic isotope effects on the CO elimination. PMID:12203676

Turecek, Frantisek; Vivekananda, Shetty; Sadílek, Martin; Polásek, Miroslav

2002-08-01

356

Hollow fiber liquid-phase microextraction coupled with gas chromatography-flame ionization detection for the profiling of fatty acids in vegetable oils.  

PubMed

The development of a two phase hollow fiber liquid-phase microextraction technique, followed by gas-chromatography-flame ionization detection (GC-FID) for the profiling of the fatty acids (FAs) (lauric, myristic, palmitic, stearic, palmitoleic, oleic, linoleic, linolenic and arachidic) in vegetable oils is described. Heptadecanoic acid methyl ester was used as the internal standard. The FAs were transesterified to their corresponding methyl esters prior to the extraction. Extraction parameters such as type of extracting solvent, temperature, extraction time, stirring speed and salt addition were studied and optimized. Recommended conditions were extraction solvent, n-tridecane; extraction time, 35 min; extraction temperature, ambient; without addition of salt. Enrichment factors varying from 37 to 115 were achieved. Calibration curves for the nine FAs were well correlated (r(2)>0.994) within the range of 10-5000 ?g L(-1). The limit of detection (signal:noise, 3) was 4.73-13.21 ng L(-1). The method was successfully applied to the profiling of the FAs in palm oils (crude, olein, kernel, and carotino cooking oil) and other vegetable oils (soybean, olive, coconut, rice bran and pumpkin). The encouraging enrichments achieved offer an interesting option for the profiling of the minor and major FAs in palm and other vegetable oils. PMID:21081239

Siang, Gan Hui; Makahleh, Ahmad; Saad, Bahruddin; Lim, Boey Peng

2010-12-24

357

Application of a multidimensional gas chromatography system with simultaneous mass spectrometric and flame ionization detection to the analysis of sandalwood oil.  

PubMed

The production and trade of Indian sandalwood oil is strictly regulated, due to the impoverishment of the plantations; for such a reason, Australian sandalwood oil has been evaluated as a possible substitute of the Indian type. International directives report, for both the genuine essential oils, specific ranges for the sesquiterpene alcohols (santalols). In the present investigation, a multidimensional gas chromatographic system (MDGC), equipped with simultaneous flame ionization and mass spectrometric detection (FID/MS), has been successfully applied to the analysis of a series of sandalwood oils of different origin. A detailed description of the system utilized is reported. Three santalol isomers, (Z)-?-trans-bergamotol, (E,E)-farnesol, (Z)-nuciferol, epi-?-bisabolol and (Z)-lanceol have been quantified. LoD (MS) and LoQ (FID) values were determined for (E,E)-farnesol, used as representative of the oxygenated sesquiterpenic group, showing levels equal to 0.002% and 0.003%, respectively. A great advantage of the instrumental configuration herein discussed, is represented by the fact that identification and quantitation of target analytes are carried out in one step, without the need to perform two separate analyses. PMID:21112592

Sciarrone, Danilo; Costa, Rosaria; Ragonese, Carla; Tranchida, Peter Quinto; Tedone, Laura; Santi, Luca; Dugo, Paola; Dugo, Giovanni; Joulain, Daniel; Mondello, Luigi

2011-01-01

358

Dispersive micro-solid phase extraction combined with gas chromatography-chemical ionization mass spectrometry for the determination of N-nitrosamines in swimming pool water samples.  

PubMed

A simple sample pretreatment technique, dispersive micro-solid phase extraction, was applied for the extraction of N-nitrosodimethylamine (NDMA) and other four N-nitrosamines (NAs) from samples of swimming pool water. The parameters affecting the extraction efficiency were systematically investigated. The best extraction conditions involved immersing 75 mg of carbon molecular sieve, Carboxen™ 1003 (as an adsorbent), in a 50-mL water sample (pH 7.0) containing 5% sodium chloride in a sample tube. After 20 min of extraction by vigorous shaking, the adsorbent was collected on a filter and the NAs desorbed by treatment with 150 ?L of dichloromethane. A 10-?L aliquot was then directly determined by large-volume injection gas chromatography with chemical ionization mass spectrometry using the selected ion storage mode. The limits of quantitation were <0.9 ng/L. The precision for these analytes, as indicated by relative standard deviations, were <8% for both intra- and inter-day analyses. Accuracy, expressed as the mean extraction recovery, was between 62% and 109%. A preliminary analysis of swimming pool water samples revealed that NDMA was present in the highest concentration, in the range from n.d. to 100 ng/L. PMID:22222914

Fu, Ssu-Chieh; Tzing, Shin-Hwa; Chen, Hsin-Chang; Wang, Yu-Chen; Ding, Wang-Hsien

2012-02-01

359

Measurements of gas-phase inorganic and organic acids from biomass fires by negative-ion proton-transfer chemical-ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

Emissions from 34 laboratory biomass fires were investigated at the combustion facility of the U.S. Department of Agriculture Fire Sciences Laboratory in Missoula, Montana. Gas-phase organic and inorganic acids were quantified using negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS), open-path Fourier transform infrared spectroscopy (OP-FTIR), and proton-transfer-reaction mass spectrometry (PTR-MS). NI-PT-CIMS is a novel technique that measures the mass-to-charge ratio (m/z) of ions generated from reactions of acetate (CH3C(O)O-) ions with inorganic and organic acids. The emission ratios for various important reactive acids with respect to CO were determined. Emission ratios for isocyanic acid (HNCO), 1,2 and 1,3-benzenediols (catechol, resorcinol), nitrous acid (HONO), acrylic acid, methacrylic acid, propionic acid, formic acid, pyruvic acid, and glycolic acid were measured from biomass burning. Our measurements show that there is a significant amount of HONO in fresh smoke. The NI-PT-CIMS measurements were validated by comparison with OP-FTIR measurements of HONO and formic acid (HCOOH) and with PTR-MS measurements of HCOOH.

Veres, Patrick; Roberts, James M.; Burling, Ian R.; Warneke, Carsten; de Gouw, Joost; Yokelson, Robert J.

2010-12-01

360

Fluorohydrogenate cluster ions in the gas phase: electrospray ionization mass spectrometry of the [1-ethyl-3-methylimidazolium(+)][F(HF)2.3(-)] ionic liquid.  

PubMed

Electrospray ionization of the fluorohydrogenate ionic liquid [1-ethyl-3-methylimidazolium][F(HF)2.3] ionic liquid was conducted to understand the nature of the anionic species as they exist in the gas phase. Abundant fluorohydrogenate clusters were produced; however, the dominant anion in the clusters was [FHF(-)], and not the fluoride-bound HF dimers or trimers that are seen in solution. Density functional theory (DFT) calculations suggest that HF molecules are bound to the clusters by about 30 kcal/mol. The DFT-calculated structures of the [FHF(-)]-bearing clusters show that the favored interactions of the anions are with the methynic and acetylenic hydrogen atoms on the imidazolium cation, forming planar structures similar to those observed in the solid state. A second series of abundant negative ions was also formed that contained [SiF5(-)] together with the imidazolium cation and the fluorohydrogenate anions that originate from reaction of the spray solution with silicate surfaces. PMID:24313327

Groenewold, Gary S; Delmore, James E; Benson, Michael T; Tsuda, Tetsuya; Hagiwara, Rika

2013-12-27

361

Environmental PAH analysis by gas chromatography-atmospheric pressure laser ionization-time-of-flight-mass spectrometry (GC-APLI-MS).  

PubMed

The application of polycyclic aromatic hydrocarbon (PAH) analysis by gas chromatography coupled with atmospheric pressure laser ionization and mass spectrometry (GC-APLI-MS) to environmental samples was investigated in the study. The limit of detection for 40 PAH in a standard mixture was 5-100 fg, demonstrating GC-APLI-MS to be a highly sensitive technique and more sensitive by a factor of 100-3,500 compared to GC-MS. Acenaphthylene and cyclopenta[cd]pyrene were not detectable <2,500 fg per injection. To make use of this very high PAH sensitivity, the technique was applied to samples of environmental interest with limited available sample amounts such as particulate matter (PM), soot and a sample from a bioaccumulation test with Lumbriculus variegatus. First, special sample preparation was necessary and ultrasonic extraction proved to be suitable, if a thorough clean-up was performed and plastic materials avoided. By GC-APLI-MS and GC-MS, 224 and 28 single PAH compounds were detected in PM, about 1,000 and 15 in birch soot, and 9 and 2 in worm tissue, respectively, revealing the enormous potential of the method. The selectivity of GC-APLI-MS was shown for a crude oil where >2,200 PAH were detected without any sample preparation. PMID:23852149

Stader, Christian; Beer, Fokko Tjark; Achten, Christine

2013-09-01

362

Optimization of comprehensive two dimensional gas chromatography-flame ionization detection-quadrupole mass spectrometry for the separation of octyl- and nonylphenol isomers.  

PubMed

In the present work, the separation of complex nonylphenol technical mixtures has been optimized using comprehensive two-dimensional gas chromatography coupled with a flame ionization detector and quadrupole mass spectrometer (GC×GC-qMS), using valve-based modulator. The optimization of GC×GC-qMS has been carried out using experimental designs and the optimal separation was obtained at the following conditions: 1st column flow: 1mL/min; 2nd column flow: 17.75 mL/min, oven temperature ramp: 1°C/min, modulation period: 1.5s and discharge time: 0.12s. These values have been used to determinate the previously synthesized 22OP, 33OP, 363NP and 22NP isomers in two different nonylphenol technical mixtures. Percentages obtained were as follows: 4.86% and 0.59% for 22OP, 4.91% and 2.82% for 33OP, 11.79% and 7.71% for 363NP and 2.28% and 1.98% for 22NP, in Fluka and Aldrich mixtures, respectively. The values obtained for NP isomers are in good agreement with the literature. PMID:21489544

Vallejo, A; Olivares, M; Fernández, L A; Etxebarria, N; Arrasate, S; Anakabe, E; Usobiaga, A; Zuloaga, O

2011-05-20

363

Gridded electron reversal ionizer  

NASA Technical Reports Server (NTRS)

A gridded electron reversal ionizer forms a three dimensional cloud of zero or near-zero energy electrons in a cavity within a filament structure surrounding a central electrode having holes through which the sample gas, at reduced pressure, enters an elongated reversal volume. The resultant negative ion stream is applied to a mass analyzer. The reduced electron and ion space-charge limitations of this configuration enhances detection sensitivity for material to be detected by electron attachment, such as narcotic and explosive vapors. Positive ions may be generated by generating electrons having a higher energy, sufficient to ionize the target gas and pulsing the grid negative to stop the electron flow and pulsing the extraction aperture positive to draw out the positive ions.

Chutjian, Ara (Inventor)

1993-01-01

364

Mapping the Ionization State of Laser-Irradiated Ar Gas Jets With Multi-Wavelength Monochromatic X-Ray Imaging  

SciTech Connect

Two-dimensional monochromatic images of fast-electron stimulated Ar K{alpha} and He-{alpha} x-ray self-emission have recorded a time-integrated map of the extent of Ar{sup {approx}6+} and Ar{sup 16+} ions, respectively, within a high density (10{sup 20} cm{sup -3} atomic density) Ar plasma. This plasma was produced by irradiating a 2 mm wide clustering Ar gas jet with an ultra-high intensity (10{sup 19} W/cm{sup 2}, 200 fs) Ti:Sapphire laser operating at 800 nm. Spherically bent quartz crystals in the 200 (for K{alpha}) and 201 (for He-{alpha}) planes were used as near-normal incidence reflective x-ray optics. We see that a large (830 {micro}m long) region of plasma emits K{alpha} primarily along the laser axis, while the He-{alpha} emission is confined to smaller hot spot (230 {micro}m long) region that likely corresponds to the focal volume of the f/8 laser beam. X-ray spectra from a Bragg spectrometer operating in the von Hamos geometry, which images in one dimension, indicate that the centroids of the K{alpha} and He-{alpha} emission regions are separated by approximately 330 {micro}m along the laser axis.

Kugland, N L; Doppner, T; Kemp, A; Schaeffer, D; Glenzer, S H; Niemann, C

2010-04-08

365

Mapping the ionization state of laser-irradiated Ar gas jets with multiwavelength monochromatic x-ray imaging  

NASA Astrophysics Data System (ADS)

Two-dimensional monochromatic images of fast-electron stimulated Ar K? and He-? x-ray self-emission have recorded a time-integrated map of the extent of Ar~6+ and Ar16+ ions, respectively, within a high density (1020 cm-3 atomic density) Ar plasma. This plasma was produced by irradiating a 2 mm wide clustering Ar gas jet with an ultrahigh intensity (1019 W/cm2, 50 TW) Ti:sapphire laser operating at 800 nm. Spherically bent quartz crystals in the 200 (for K?) and 201 (for He-?) planes were used as near-normal incidence reflective x-ray optics. We see that a large (830 ?m long) region of plasma emits K? primarily along the laser axis, while the He-? emission is confined to smaller hot spot (230 ?m long) region that likely corresponds to the focal volume of the f/8 laser beam. X-ray spectra from a Bragg spectrometer operating in the von Hamos geometry indicate that the centroids of the K? and He-? emission regions are separated by approximately 330 ?m along the laser axis.

Kugland, N. L.; Döppner, T.; Kemp, A.; Schaeffer, D.; Glenzer, S. H.; Niemann, C.

2010-10-01

366

Mapping the ionization state of laser-irradiated Ar gas jets with multiwavelength monochromatic x-ray imaging.  

PubMed

Two-dimensional monochromatic images of fast-electron stimulated Ar?K? and He-? x-ray self-emission have recorded a time-integrated map of the extent of Ar(?6+) and Ar(16+) ions, respectively, within a high density (10(20)?cm(-3) atomic density) Ar plasma. This plasma was produced by irradiating a 2 mm wide clustering Ar gas jet with an ultrahigh intensity (10(19)?W/cm(2), 50 TW) Ti:sapphire laser operating at 800 nm. Spherically bent quartz crystals in the 200 (for K?) and 201 (for He-?) planes were used as near-normal incidence reflective x-ray optics. We see that a large (830??m long) region of plasma emits K? primarily along the laser axis, while the He-? emission is confined to smaller hot spot (230??m long) region that likely corresponds to the focal volume of the f/8 laser beam. X-ray spectra from a Bragg spectrometer operating in the von Hamos geometry indicate that the centroids of the K? and He-? emission regions are separated by approximately 330??m along the laser axis. PMID:21034054

Kugland, N L; Döppner, T; Kemp, A; Schaeffer, D; Glenzer, S H; Niemann, C

2010-10-01

367

Monitoring of priority pesticides and other organic pollutants in river water from Portugal by gas chromatography–mass spectrometry and liquid chromatography–atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

Gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–atmospheric pressure chemical ionization mass spectrometry (LC–APCI-MS) were optimized and applied for the trace-level determination of 42 priority pesticides and 33 priority organic pollutants from European Union Directive EC 76\\/464. First, off-line solid-phase extraction of 200 ml of river water using an OASIS solid-phase extraction cartridge, followed by GC–MS was used. Next, selected samples

Débora de Almeida Azevedo; S??lvia Lacorte; Tereza Vinhas; Paula Viana; Damiá Barceló

2000-01-01

368

Development and validation of a gas chromatography–negative chemical ionization tandem mass spectrometry method for the determination of ethyl glucuronide in hair and its application to forensic toxicology  

Microsoft Academic Search

Ethyl glucuronide (EtG) is a minor and direct metabolite of ethanol. EtG is incorporated into the growing hair allowing retrospective investigation of chronic alcohol abuse. In this study, we report the development and the validation of a method using gas chromatography–negative chemical ionization tandem mass spectrometry (GC–NCI-MS\\/MS) for the quantification of EtG in hair. EtG was extracted from about 30mg

Hicham Kharbouche; Frank Sporkert; Stéphanie Troxler; Marc Augsburger; Patrice Mangin; Christian Staub

2009-01-01

369

Determination of ?-sitosterol and cholesterol in oils after reverse micelles with Triton X-100 coupled with ultrasound-assisted back-extraction by a water\\/chloroform binary system prior to gas chromatography with flame ionization detection  

Microsoft Academic Search

Ultrasonic back-extraction of Triton X-100 reverse micelles by a water\\/chloroform binary system and gas chromatography with flame ionization detection (GC-FID) was developed for extraction and determination of ?-sitosterol and cholesterol in soybean and sunflower oil samples. After the homogenization of the oil samples with Triton X-100, an aliquot of 200?L of methanol was added to the samples to form two

Fatemeh Kardani; Ali Daneshfar; Reza Sahrai

2011-01-01

370

Parts per quadrillion level ultra-trace determination of polar and nonpolar compounds via solvent-free capillary microextraction on surface-bonded sol–gel polytetrahydrofuran coating and gas chromatography–flame ionization detection  

Microsoft Academic Search

Sol–gel polytetrahydrofuran (poly-THF) coating was developed for high-sensitivity sample preconcentration by capillary microextraction (CME). Parts per quadrillion (ppq) level detection limits were achieved for both polar and nonpolar analytes through sample preconcentration on sol–gel poly-THF coated microextraction capillaries followed by gas chromatography (GC) analysis of the extracted compounds using a flame ionization detector (FID). The sol–gel coating was in situ

Abuzar Kabir; Christina Hamlet; Abdul Malik

2004-01-01

371

Ionizing radiation  

NASA Technical Reports Server (NTRS)

The biological effects of ionizing radiation encountered in space are considered. Biological experiments conducted in space and some experiences of astronauts during space flight are described. The effects of various levels of radiation exposure and the determination of permissible dosages are discussed.

Tobias, C. A.; Grigoryev, Y. G.

1975-01-01

372

Validation of a qualitative screening method for pesticides in fruits and vegetables by gas chromatography quadrupole-time of flight mass spectrometry with atmospheric pressure chemical ionization.  

PubMed

A wide-scope screening method was developed for the detection of pesticides in fruit and vegetables. The method was based on gas chromatography coupled to a hybrid quadrupole time-of-flight mass spectrometer with an atmospheric pressure chemical ionization source (GC-(APCI)QTOF MS). A non-target acquisition was performed through two alternating scan events: one at low collision energy and another at a higher collision energy ramp (MS(E)). In this way, both protonated molecule and/or molecular ion together with fragment ions were obtained in a single run. Validation was performed according to SANCO/12571/2013 by analysing 20 samples (10 different commodities in duplicate), fortified with a test set of 132 pesticides at 0.01, 0.05 and 0.20mgkg(-1). For screening, the detection was based on one diagnostic ion (in most cases the protonated molecule). Overall, at the 0.01mgkg(-1) level, 89% of the 2620 fortifications made were detected. The screening detection limit for individual pesticides was 0.01mgkg(-1) for 77% of the pesticides investigated. The possibilities for identification according to the SANCO criteria, requiring two ions with a mass accuracy ?±5ppm and an ion-ratio deviation ?±30%, were investigated. At the 0.01mgkg(-1) level, identification was possible for 70% of the pesticides detected during screening. This increased to 87% and 93% at the 0.05 and 0.20mgkg(-1) level, respectively. Insufficient sensitivity for the second ion was the main reason for the inability to identify detected pesticides, followed by deviations in mass accuracy and ion ratios. PMID:25064246

Portolés, T; Mol, J G J; Sancho, J V; López, Francisco J; Hernández, F

2014-08-01

373

Optical ionization detector  

DOEpatents

An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium. 3 figures.

Wuest, C.R.; Lowry, M.E.

1994-03-29

374

Optical ionization detector  

DOEpatents

An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium.

Wuest, Craig R. (Danville, CA); Lowry, Mark E. (Castro Valley, CA)

1994-01-01

375

Two-Dimensional Gas Chromatography\\/ Electron-Impact Mass Spectrometry with Cryofocusing for Simultaneous Quantification of MDMA, MDA, HMMA, HMA, and MDEA in Human Plasma  

Microsoft Academic Search

BACKGROUND: 3,4-Methylenedioxymethamphetamine (MDMA, or Ecstasy) is a popular recreational drug. Analysis of MDMA and metabolites in human plasma, particularly in pharmacokinetic studies, requires low limits of quantification. Two-dimensional GC\\/MS with cryofocusing is a chromatographic technique rec- ognized for its increased selectivity and resolution. METHODS: This method simultaneously quantifies 3,4- methylenedioxyethylamphetamine (MDEA), MDMA, and its metabolites, 3,4-methylenedioxyamphetamine (MDA), 4-hydroxy-3-methoxymethamphetamine (HMMA), and

Erin A. Kolbrich; Ross H. Lowe; Marilyn A. Huestis

376

Determination of isoprostaglandin F 2? type III in human urine by gas chromatography–electronic impact mass spectrometry. Comparison with enzyme immunoassay  

Microsoft Academic Search

F2-Isoprostanes are stable lipid peroxidation products of arachidonic acid, the quantification of which provides an index of oxidative stress in vivo. We describe a method for analysing isoprostaglandin F2? type III (15-F2t-IsoP) in biological fluids. The method involves solid-phase extraction on octadecyl endcapped and aminopropyl cartridges. After conversion to trimethylsilyl ester trimethylsilyl ether derivatives, isoprostaglandin F2? type III is analysed

Janine Bessard; Jean-Luc Cracowski; Françoise Stanke-Labesque; Germain Bessard

2001-01-01

377

2-Phosphoglycolate and glycolate-electrophore detection, including detection of 87 zeptomoles of the latter by gas chromatography-electron-capture mass spectrometry  

Microsoft Academic Search

As a first stage towards a goal of studying some aspects of oxidative damage to DNA and its subsequent repair, we set up three techniques for the detection of 2-phosphoglycolate (PG). This compound is released as a metabolite from the DNA in certain cases of this process. We explored three techniques because we wanted to learn which one(s) would be

Poguang Wang; Veeravagu Murugaiah; Bernice Yeung; Paul Vouros; Roger W. Giese

1996-01-01

378

Optimization of solid-phase extraction and solid-phase microextraction for the determination of ?- and ?-endosulfan in water by gas chromatography–electron-capture detection  

Microsoft Academic Search

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. The 98\\/83\\/European Directive requires to measure residues of pesticides at a target concentration of 1.0 ?g\\/l in surface water and 0.1 ?g\\/l in drinking water. In order to reach the level of detection required, efficient extraction techniques are required. Although solid-phase

M. C López-Blanco; B Reboreda-Rodr??guez; B Cancho-Grande; J Simal-Gándara

2002-01-01

379

Clean-up of aqueous acetone vegetable extracts by solid-matrix partition for pyrethroid residue determination by gas chromatography—electron-capture detection  

Microsoft Academic Search

Disposable, ready-to-use cartridges filled with macroporous diatomaceous material are used to carry out a partition clean-up that, in a single step, is capable of transferring pesticide residues from aqueous acetone extracts into light petroleum-dichloromethane (75:25, v\\/v). This procedure takes the place of some functions (such as separatory-funnel partition, drying over anhydrous sodium sulphate and partial adsorption clean-up) usually performed by

Alfonso Di Muccio; Danilo Attard Barbini; Tiziana Generali; Patrizia Pelosi; Antonella Ausili; Fabio Vergori; Ivano Camoni

1997-01-01

380

Ionic liquid-mediated molecularly imprinted solid-phase extraction coupled with gas chromatography-electron capture detector for rapid screening of dicofol in vegetables.  

PubMed

New ionic liquid-mediated molecularly imprinted polymers (IL-MIPs) were prepared by precipitation polymerization using 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM(+)PF6(-)) as the auxiliary solvent, ?-chloro-DDT as the dummy template, and they were successfully applied as the sorbents of solid-phase extraction (SPE) for rapid screening of dicofol from cabbage, tomato, and carrot samples. The IL-MIPs were characterized by FTIR, FE-SEM, static adsorption and chromatographic evaluation, and the results revealed that the IL-MIPs had higher adsorption capacity and selectivity to dicofol in aqueous solution than that of ionic liquid-mediated non-imprinted polymers (IL-NIPs) and non-imprinted polymers (NIPs). Under the optimized conditions, the IL-MIPs-SPE-GC method offered good linearity (0.4-40.0ngg(-1), r(2)=0.9995) and the average recoveries of dicofol at three spiked levels were in a range of 84.6-104.1% (n=3) with RSD?7.6%. The proposed method obviously improved the selectivity and purification effect, and eliminated the effect of template leakage on dicofol quantitative analysis. PMID:23932224

Yan, Hongyuan; Sun, Ning; Han, Yehong; Yang, Chen; Wang, Mingyu; Wu, Ruijun

2013-09-13

381

Detection and quantitation of fatty acid acyl conjugates of triamcinolone acetonide via gas chromatography–electron-capture negative-ion mass spectrometry  

Microsoft Academic Search

The inherent electron-capture properties of triamcinolone acetonide (TAA) fatty acid conjugates were exploited for development of a GC–MS technique for quantitation of C21 long-chain fatty esters of TAA synthesized in BEAS-2B cells, an immortalized airway epithelium cell line. TAA esters extracted from BEAS-2B cells were purified and detected via selected ion monitoring of the molecular anions generated from the TAA

Walter C Hubbard; Andrew E Blum; Carol A Bickel; Nicola M Heller; Robert P Schleimer

2003-01-01

382

Diffuse Ionized Medium Panel Discussion  

Microsoft Academic Search

The following is a transcript of a 90 minute discussion that took place among tertulia participants at the end of the first\\u000a day. The conversations centered around the origin and nature of wide-spread warm and hot ionized gas in the MilkyWay.

R. J. Reynolds; R. L. Shelton; S. L. Tufte

383

Diffuse Ionized Medium Panel Discussion  

Microsoft Academic Search

The following is a transcript of a 90 minute discussion that took place among tertulia participants at the end of the first day. The conversations centered around the origin and nature of wide-spread warm and hot ionized gas in the MilkyWay.

R. J. Reynolds; R. L. Shelton; S. L. Tufte

2004-01-01

384

Numerical Double Layer Solutions with Ionization.  

National Technical Information Service (NTIS)

Maxwell's equation div D = rho in one dimension is solved numerically, taking ionization into account. Time independent anode sheath and double layer solutions are obtained. By varying voltage, neutral gas pressure, temperature of the trapped ions on the ...

D. Andersson J. Soerensen

1982-01-01

385

Characterization and quantification of 4-methylsterols and 4,4-dimethylsterols from Iberian pig subcutaneous fat by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector and their use to authenticate the fattening systems.  

PubMed

4-Methylsterols and 4,4-dimethylsterols of 47 samples of subcutaneous fat from Iberian pigs reared on two different fattening systems, "Extensive" and "Intensive", have been analyzed by GC-MS and GC-FID. The lipids were extracted by melting the subcutaneous fat in a microwave oven. The unsaponifiable matter was fractionated by thin layer chromatography. Then, the analysis was performed on a capillary SPB-5 column (30 m × 0.25 mm i.d., 0.15 ?m film thickness), with hydrogen as a carrier gas and using a flame ionization detector. n-eicosanol was used as internal standard for quantification of individual methylsterols. These compounds have been analyzed by GC-MS for their identification. The full scan of free and trimethyl silyl ethers was used as acquisition mode. Six compounds have been identified for the first time in this type of samples: (3?,4?,5?)-4-methyl-cholesta-7-en-3-ol, (3?,4?,5?)-4-methyl-cholesta-8(14)-en-3-ol, (3?,5?)-4,4-dimethyl-cholesta-8(14),24-dien-3-ol, (3?)-lanosta-8,24-dien-3-ol, (3?, 5?)-4,4-dimethyl-cholesta-8,14-dien-3-ol and (3?)-lanost-9(11),24-dien-3-ol. The samples were derivatized as trimethyl silyl ethers before their analysis by GC-FID. By using these compounds as chemical descriptors, pattern recognition techniques were applied to differentiate between extensive and intensive fattening systems of Iberian pig. Several pattern recognition techniques, such as principal component analysis, linear discriminant analysis, support vector machines, artificial neural networks, soft independent modeling of class analogy and k nearest neighbors, have been used in order to find out a suitable classification model. A multilayer perceptron artificial neural network based on the contents of the above mentioned compounds allowed the differentiation of the two fattening systems with an overall classification performance of 91.7%. PMID:23598090

Jurado, J M; Jiménez-Lirola, A; Narváez-Rivas, M; Gallardo, E; Pablos, F; León-Camacho, M

2013-03-15

386

Initial results of positron ionization mass spectrometry  

NASA Technical Reports Server (NTRS)

The use of monoenergetic positrons for the ionization of organic molecules in the gas phase is described. The ionic products are analyzed with a time-of-flight mass spectrometer and detected to produce a mass spectrum. The ionization mechanisms which can be studied in this way include positron impact at energies above the ionization limit of the target molecules, positronium formation in the Ore gap energy range, and positron attachment at energies less than 1eV. The technique of positron ionization mass spectrometry (PIMS) may have analytical utility in that chemical selectivity is observed for one or more of these processes.

Donohue, D. L.; Hulett, L. D., Jr.; Mcluckey, S. A.; Glish, G. L.; Eckenrode, B. A.

1990-01-01

387

[Determination of seven toxaphene congeners in ginseng and milkvetch root by gas chromatography tandem mass spectrometry].  

PubMed

A novel method for the determination of representative toxaphene congeners in traditional Chinese herbal medicines was developed. Ginseng and Milkvetch Root were selected as the samples and seven toxaphene congeners were selected as the monitoring objects. The samples were extracted by accelerated solvent extraction with cyclohexane-acetone (9:1, v/v), then cleaned-up by Florisil solid phase extraction with hexane as the eluent and the residues were detected by gas chromatography-electron ionization tandem mass spectrometry (GC-EI-MS/MS) in multiple reaction monitoring (MRM) mode. The performance was demonstrated by the analysis of Ginseng and Milkvetch Root samples spiked with toxaphene congeners at three concentration levels of 0.005, 0.01 and 0.1 mg/kg. The recoveries ranged from 72.4% to 105% with the relative standard deviations (RSDs) of 0.96%-10.4%. The limits of detection (LODs) were 0.2-1.7 microg/kg. This method is sensitive and efficient in the aspect of extraction, and can be applied to monitor the residue of toxaphene congeners in Ginseng and Milkvetch Root. PMID:22667085

Tian, Shaoqiong; Mao, Xiuhong; Miao, Shui; Jia, Zhengwei; Wang, Ke; Ji, Shen

2012-01-01

388

Quantitation of cocaine, benzoylecgonine, cocaethylene, methylecgonine, and norcocaine in human hair by positive ion chemical ionization (PICI) gas chromatography-tandem mass spectrometry.  

PubMed

A total of 30 human head-hair samples were analyzed for cocaine (COC), cocaethylene (CE), benzoylecgonine (BE), methylecgonine (EME), and norcocaine (NCOC) using a sensitive positive ion chemical ionization gas chromatography-tandem mass spectrometry (GC-MS-MS) method. All 30 hair samples had been previously submitted to the laboratory and had confirmed positive for cocaine. Hair samples (20 mg each) were cut into small segments (2-5 mm) and incubated overnight at 45 degrees C in 0.1 N HCl after the addition of 50 microL of an internal standard mix of COC-d3 (1.0 ng/mg), BE-d3 (0.5 ng/mg), EME-d3 (0.25 ng/mg), and NCOC-d3 (0.25 ng/mg). The samples were then extracted with Clean Screen extraction columns from United Chemical Technologies, Inc. The final extract was evaporated to dryness and derivatized with 50 microL of 1,1,1,3,3,3-hexafluoro-2-propanol and 50 microL of trifluoroacetic anhydride at 90 degrees C for 15 min. The derivatized samples were allowed to cool to room temperature, evaporated to dryness, and then reconstituted in 50 microL of ethyl acetate. Parent set masses (unbolded ions) and product ions were m/z 304 and m/z 182 and 82 (COC), m/z 307 and m/z 185 and 85 (COC-d3), m/z 318 and m/z 196 and 82 (CE), m/z 440 and m/z 318 and 105 (BE), m/z 443 and m/z 321 and 105 (BE-d3), m/z 296 and m/z 182, and 82 (EME), m/z 299 and m/z 185 and 85 (EME-d3), m/z 403 and m/z 386 and 105 (NCOC), m/z 406 and m/z 389 and 105 (NCOC-d3). Quantitation was accomplished by calculating the area ratio of the higher mass product ion (underlined ions) of analyte to the respective internal standard based on multilevel calibrations from 0.01 to 10.0 ng/mg. The GC-MS-MS method had a limit of detection of 0.01 ng/mg and a limit of quantitation of 0.05 ng/mg for all five analytes. COC, BE, and EME were detected in all 30 samples, and CE and NCOC were found in 19 and 29 samples, respectively. The average relative percentages of each metabolite normalized to the cocaine concentrations were 12.8%, 15.4%, 1.8%, and 2.5% for BE, CE, EME, and NCOC, respectively. PMID:11043651

Bourland, J A; Hayes, E F; Kelly, R C; Sweeney, S A; Hatab, M M

2000-10-01

389

A multi-residue method for pesticides analysis in green coffee beans using gas chromatography-negative chemical ionization mass spectrometry in selective ion monitoring mode.  

PubMed

In this study, a new gas chromatography-mass spectrometry (GC-MS) method, using the very selective negative chemical ionization (NCI) mode, was developed and applied in combination with a modified acetonitrile-based extraction method (QuEChERS) for the analysis of a large number of pesticide residues (51 pesticides, including isomers and degradation products) in green coffee beans. A previously developed integrated sample homogenization and extraction method for both pesticides and mycotoxins analysis was used. An homogeneous slurry of green milled coffee beans and water (ratio 1:4, w/w) was prepared and extracted with acetonitrile/acetic acid (1%), followed by magnesium sulfate addition for phase separation. Aliquots from this extract could be used directly for LC-MS/MS analysis of mycotoxins and LC-amenable pesticides. For GC-MS analysis, a further clean-up was necessary. C18- and PSA-bonded silica were tested as dispersive solid-phase extraction (d-SPE) sorbents, separate and as a mixture, and the best results were obtained using C18-bonded silica. For the optimal sensitivity and selectivity, GC-MS detection in the NCI-selected ion monitoring (SIM) mode had to be used to allow the fast analysis of the difficult coffee bean matrix. The validation was performed by analyzing recovery samples at three different spike concentrations, 10, 20 and 50 ?g kg(-1), with 6 replicates (n=6) at each concentration. Linearity (r(2)) of calibration curves, estimated instrument and method limits of detection and limits of quantification (LOD(i), LOD(m), LOQ(i) and LOQ(m), respectively), accuracy (as recovery %), precision (as RSD%) and matrix effects (%) were determined for each individual pesticide. From the 51 analytes (42 parent pesticides, 4 isomers and 5 degradation products) determined by GC-MS (NCI-SIM), approximately 76% showed average recoveries between 70-120% and 75% and RSD ? 20% at the lowest spike concentration of 10 ?g kg(-1), the target method LOQ. For the spike concentrations of 20 and 50 ?g kg(-1), the recoveries and RSDs were even better. The validated LOQ(m) was 10, 20 and 50 ?g kg(-1) for respectively 33, 3 and 6 of the analytes studied. For five compounds, the European Union method performance requirements for the validation of a quantitative method (average recoveries between 70-120% and repeatability RSD ? 20%) were not achieved and 4 problematic pesticides (captan, captafol, folpet and dicofol) could not be detected as their parent compound, but only via their degradation products. Although the matrix effect (matrix-enhanced detector response) was high for all pesticides studied, the matrix interference was minimal, due to the high selectivity obtained with the GC-NCI-MS detection. Matrix-matched calibration for applying the method in routine analysis is recommended for reliable quantitative results. PMID:22771261

Pizzutti, Ionara R; de Kok, Andre; Dickow Cardoso, Carmem; Reichert, Bárbara; de Kroon, Marijke; Wind, Wouter; Weber Righi, Laís; Caiel da Silva, Rosselei

2012-08-17

390

Ionizing and Non-Ionizing Radiation  

MedlinePLUS

... Decay Modes Radiation has a wide range of energies that form the electromagnetic spectrum (illustrated below). The ... ionizing radiation ionizing radiation Radiation that has enough energy to move around atoms in a molecule or ...

391

Gas chromatographic determination of benzene, toluene, ethylbenzene and xylenes using flame ionization detector in water samples with direct aqueous injection up to 250 ?l  

Microsoft Academic Search

A simple method of solventless extraction of volatile organic compounds (benzene, toluene, ethylbenzene and xylenes) from aqueous samples was developed. This method allows direct injection of large volume of water sample into a gas chromatograph using the sorption capacity of the sorbent Chromosorb P NAW applied directly in the injection port of gas chromatograph. The system prevent water penetration into

R. Kubinec; J. Adamuš?in; H. Jurdáková; M. Foltin; I. Ostrovský; A. Kraus; L. Soják

2005-01-01

392

Single photon ionization (SPI) via incoherent VUV-excimer light: robust and compact time-of-flight mass spectrometer for on-line, real-time process gas analysis.  

PubMed

Fast on-line detection of organic compounds from complex mixtures, such as industrial process gas streams, require selective and sensitive analytical methods. One feasible approach for this purpose is the use of mass spectrometry (MS) with a selective and soft (fragment-free) ionization technique, such as chemical ionization (CI) or photo ionization (PI). Single photon ionization (SPI) with vacuum ultraviolet (VUV) light is a particularly sof tionization technique, well-suited for detection of both aromatic and aliphatic species. Problematic, however, is the generation of the VUV light. In general, the vacuum ultraviolet (VUV) light sources for SPI-MS are based either on lasers (e.g., 118-nm radiation generated by frequency-tripling of the third harmonic of a Nd:YAG laser) or on conventional VUV lamps, such as deuterium lamps. Althoughthe laser-based techniques are very sophisticated and expensive, the conventional lamps have serious drawbacks regarding their optical parameters, such as low-output power, low spectral power density, and broad emission bands. In this work, a novel excimer VUV light source, in which an electron beam is used to form rare gas excimer species, is used. The excimer VUV light sourceproduces brilliant and intense VUV light. The novel VUV light source was coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). A special interface design, including optical (VUV optics) as well as electronic measures (e.g., pulsed ion extraction) was realized. The use of the excimer VUV lamp for SPI will allow the realization of very compact, rugged, and sensitive SPI-TOFMS devices, which preferably will be adapted for process analytical application or monitoring issues (e.g., chemical warfare detection). The excimer VUV-lamp technology delivers VUV light with a good beam quality and high-output power at low costs. Furthermore, it allows changing the emitted wavelength as well as the bandwidth of the excimer VUV lamp in t he 100-200-nm region by changing the gas filling. Consequently, SPI-TOFMS with an excimer light source is a fast detection technique that can be used for online monitoring, for example, in environmental studies or industrial manufacturing processes. In this paper, technology and characteristics of the new excimer light source, as well as the combination with the TOFMS, are presented. Furthermore, a first characterization of the SPI-TOFMS instrument, regarding analytical parameters such as detection limits and selectivity, is given. This includes a discussion of potential improvements that probably will be achievable within a future prototype genertation. Finally, first applications of the system for on-line measurement of organic trace species in a complex gas mixture (here, motorcycle exhaust gas) are presented. PMID:12175168

Mühlberger, F; Wieser, J; Ulrich, A; Zimmermann, R

2002-08-01

393

Characterization of fatty acid and triacylglycerol composition in animal fats using silver-ion and non-aqueous reversed-phase high-performance liquid chromatography/mass spectrometry and gas chromatography/flame ionization detection.  

PubMed

Fatty acid (FA) and triacylglycerol (TG) composition of natural oils and fats intake in the diet has a strong influence on the human health and chronic diseases. In this work, non-aqueous reversed-phase (NARP) and silver-ion high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry detection and gas chromatography with flame-ionization detection (GC/FID) and mass spectrometry detection are used for the characterization of F