Interpreting closed-loop learning control of molecular fragmentation in terms of wave-packet dynamics and enhanced molecular ionization

International Nuclear Information System (INIS)

Cardoza, David; Baertschy, Mark; Weinacht, Thomas

2005-01-01

We interpret a molecular fragmentation experiment using shaped, ultrafast laser pulses in terms of enhanced molecular ionization during dissociation. A closed-loop learning control experiment was performed to maximize the CF 3 + /CH 3 + production ratio in the dissociative ionization of CH 3 COCF 3 . Using ab inito molecular structure calculations and quasistatic molecular ionization calculations along with data from pump-probe experiments, we identify the primary control mechanism which is quite general and should be applicable to a broad class of molecules

Clusters of DNA damage induced by ionizing radiation: Formation of short DNA fragments. I. Theoretical modeling

International Nuclear Information System (INIS)

Holley, W.R.; Chatterjee, A.

1996-01-01

We have developed a general theoretical model for the interaction of ionizing radiation with chromatin. Chromatin is modeled as a 30-nm-diameter solenoidal fiber composed of 20 turns of nucleosomes, 6 nucleosomes per turn. Charged-particle tracks are modeled by partitioning the energy deposition between primary track core, resulting from glancing collisions with 100 eV or less per event, and δ rays due to knock-on collisions involving energy transfers > 100 eV. A Monte Carlo simulation incorporates damages due to the following molecular mechanisms: (1) ionization of water molecules leading to the formation of circ OH, circ H, e aq , etc.; circ OH attack on sugar molecules leading to strand breaks; circ OH attack on bases; direct ionization of the sugar molecules leading to strand breaks; direct ionization of the bases. Our calculations predict significant clustering of damage both locally, over regions up to 40 hp and over regions extending to several kilobase pairs. A characteristic feature of the regional damage predicted by our model is the production of short fragments of DNA associated with multiple nearby strand breaks. Such fragments have subsequently been detected experimentally and are reported in an accompanying paper after exposure to both high- and low-LET radiation. The overall measured yields agree well quantitatively with the theoretical predictions. Our theoretical results predict the existence of a strong peak at about 85 bp, which represents the revolution period about the nucleosome. Other peaks at multiples of about 1,000 bp correspond to the periodicity of the particular solenoid model of chromatin used in these calculations. Theoretical results in combination with experimental data on fragmentation spectra may help determine the consensus or average structure of the chromatin fibers in mammalian DNA. 27 refs., 7 figs

Supersonic Ionization Wave Driven by Radiation Transport in a Short-Pulse Laser-Produced Plasma

International Nuclear Information System (INIS)

Ditmire, T.; Gumbrell, E.T.; Smith, R.A.; Mountford, L.; Hutchinson, M.H.

1996-01-01

Through the use of an ultrashort (2ps) optical probe, we have time resolved the propagation of an ionization wave into solid fused silica. This ionization wave results when a plasma is created by the intense irradiation of a solid target with a 2ps laser pulse. We find that the velocity of the ionization wave is consistent with radiation driven thermal transport, exceeding the velocity expected from simple electron thermal conduction by nearly an order of magnitude. copyright 1996 The American Physical Society

A multiple sampling time projection ionization chamber for nuclear fragment tracking and charge measurement

International Nuclear Information System (INIS)

Bauer, G.; Bieser, F.; Brady, F.P.; Chance, J.C.; Christie, W.F.; Gilkes, M.; Lindenstruth, V.; Lynen, U.; Mueller, W.F.J.; Romero, J.L.; Sann, H.; Tull, C.E.; Warren, P.

1997-01-01

A detector has been developed for the tracking and charge measurement of the projectile fragment nuclei produced in relativistic nuclear collisions. This device, MUSIC II, is a second generation Multiple Sampling Ionization Chamber (MUSIC), and employs the principles of ionization and time projection chambers. It provides unique charge determination for charges Z≥6, and excellent track position measurement. MUSIC II has been used most recently with the EOS (equation of state) TPC and other EOS collaboration detectors. Earlier it was used with other systems in experiments at the Heavy Ion Superconducting Spectrometer (HISS) facility at Lawrence Berkeley Laboratory and the ALADIN spectrometer at GSI. (orig.)

Line-driven disk winds in active galactic nuclei: The critical importance of ionization and radiative transfer

Energy Technology Data Exchange (ETDEWEB)

Higginbottom, Nick; Knigge, Christian; Matthews, James H. [School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ (United Kingdom); Proga, Daniel [Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154-4002 (United States); Long, Knox S. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sim, Stuart A., E-mail: nick_higginbottom@fastmail.fm [School of Mathematics and Physics, Queens University Belfast, University Road, Belfast, BT7 1NN (United Kingdom)

2014-07-01

Accretion disk winds are thought to produce many of the characteristic features seen in the spectra of active galactic nuclei (AGNs) and quasi-stellar objects (QSOs). These outflows also represent a natural form of feedback between the central supermassive black hole and its host galaxy. The mechanism for driving this mass loss remains unknown, although radiation pressure mediated by spectral lines is a leading candidate. Here, we calculate the ionization state of, and emergent spectra for, the hydrodynamic simulation of a line-driven disk wind previously presented by Proga and Kallman. To achieve this, we carry out a comprehensive Monte Carlo simulation of the radiative transfer through, and energy exchange within, the predicted outflow. We find that the wind is much more ionized than originally estimated. This is in part because it is much more difficult to shield any wind regions effectively when the outflow itself is allowed to reprocess and redirect ionizing photons. As a result, the calculated spectrum that would be observed from this particular outflow solution would not contain the ultraviolet spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so highly ionized that line driving would not actually be efficient. This does not necessarily mean that line-driven winds are not viable. However, our work does illustrate that in order to arrive at a self-consistent model of line-driven disk winds in AGN/QSO, it will be critical to include a more detailed treatment of radiative transfer and ionization in the next generation of hydrodynamic simulations.

Ionization, evaporation and fragmentation of C{sub 60} in collisions with highly charged C, O and F ions-effect of projectile charge state

Energy Technology Data Exchange (ETDEWEB)

Kelkar, A H; Misra, D; Tribedi, L C [Tata Institute of Fundamental Research, Colaba, Mumbai -5 (India)

2007-09-15

We study the various inelastic processes such ionization, fragmentation and evaporation of C{sub 60} molecule in collisions with fast heavy ions. We have used 2.33 MeV/u C, O and F projectile ion beams. Various ionization and fragmentation products were detected using time-of-flight mass spectrometer. The multiply charged C{sub 60}{sup r+} ions were detected for maximum r = 4. The projectile charge state (q{sub p}) dependence of the single and double ionization cross sections is well reproduced by a model based on the giant dipole plasmon resonance (GDPR). The q{sub p}-dependence of the fragmentation yields, was found to be linear. Variation of relative yields of the evaporation products of C{sub 60}{sup 2+} (i.e. C{sub 58}{sup 2+}, C{sub 56}{sup 2+} etc) and C{sub 60}{sup 3+} (i.e. C{sub 58}{sup 3+}, C{sub 56}{sup 3+} etc) with q{sub p} has also been investigated for various projectiles.

Fragmentation study of iridoid glucosides through positive and negative electrospray ionization, collision-induced dissociation and tandem mass spectrometry.

Science.gov (United States)

Es-Safi, Nour-Eddine; Kerhoas, Lucien; Ducrot, Paul-Henri

2007-01-01

Mass spectrometric methodology based on the combined use of positive and negative electrospray ionization, collision-induced dissociation (CID) and tandem mass spectrometry (MS/MS) has been applied to the mass spectral study of a series of six naturally occurring iridoids through in-source fragmentation of the protonated [M+H]+, deprotonated [M--H]- and sodiated [M+Na]+ ions. This led to the unambiguous determination of the molecular masses of the studied compounds and allowed CID spectra of the molecular ions to be obtained. Valuable structural information regarding the nature of both the glycoside and the aglycone moiety was thus obtained. Glycosidic cleavage and ring cleavages of both aglycone and sugar moieties were the major fragmentation pathways observed during CID, where the losses of small molecules, the cinnamoyl and the cinnamate parts were also observed. The formation of the ionized aglycones, sugars and their product ions was thus obtained giving information on their basic skeleton. The protonated, i.e. [M+H]+ and deprotonated [M--H]-, ions were found to fragment mainly by glycosidic cleavages. MS/MS spectra of the [M+Na]+ ions gave complementary information for the structural characterization of the studied compounds. Unlike the dissociation of protonated molecular ions, that of sodiated molecules also provided sodiated sugar fragments where the C0+ fragment corresponding to the glucose ion was obtained as base peak for all the studied compounds. Copyright (c) 2007 John Wiley & Sons, Ltd.

Electron impact ionization of size selected hydrogen clusters (H2)N: ion fragment and neutral size distributions.

Science.gov (United States)

Kornilov, Oleg; Toennies, J Peter

2008-05-21

Clusters consisting of normal H2 molecules, produced in a free jet expansion, are size selected by diffraction from a transmission nanograting prior to electron impact ionization. For each neutral cluster (H2)(N) (N=2-40), the relative intensities of the ion fragments Hn+ are measured with a mass spectrometer. H3+ is found to be the most abundant fragment up to N=17. With a further increase in N, the abundances of H3+, H5+, H7+, and H9+ first increase and, after passing through a maximum, approach each other. At N=40, they are about the same and more than a factor of 2 and 3 larger than for H11+ and H13+, respectively. For a given neutral cluster size, the intensities of the ion fragments follow a Poisson distribution. The fragmentation probabilities are used to determine the neutral cluster size distribution produced in the expansion at a source temperature of 30.1 K and a source pressure of 1.50 bar. The distribution shows no clear evidence of a magic number N=13 as predicted by theory and found in experiments with pure para-H2 clusters. The ion fragment distributions are also used to extract information on the internal energy distribution of the H3+ ions produced in the reaction H2+ + H2-->H3+ +H, which is initiated upon ionization of the cluster. The internal energy is assumed to be rapidly equilibrated and to determine the number of molecules subsequently evaporated. The internal energy distribution found in this way is in good agreement with data obtained in an earlier independent merged beam scattering experiment.

Ability of Accelerator-Driven Systems (ADS) to Transmute Long Lived Fission Fragments

International Nuclear Information System (INIS)

Nguyen Mong Giao; Nguyen Thi Ai Thu; Tu Thanh Danh; Tran Thanh Dung; Huynh, Thi Kim Chi

2010-12-01

This paper presents the research results of the possibility to transmute the long-lived radioactive isotopes into stable or short-lived, mainly the long-lived fission fragments as 99 Tc, 127 I, 129 I, 181 Ta, 107 Ag, 109 Ag by accelerator-driven systems. We use semi-empirical formulas to establish our calculating code with the support of computer programs. (author)

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

Science.gov (United States)

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

2015-04-01

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

SURFACE LAYER ACCRETION IN CONVENTIONAL AND TRANSITIONAL DISKS DRIVEN BY FAR-ULTRAVIOLET IONIZATION

International Nuclear Information System (INIS)

Perez-Becker, Daniel; Chiang, Eugene

2011-01-01

Whether protoplanetary disks accrete at observationally significant rates by the magnetorotational instability (MRI) depends on how well ionized they are. Disk surface layers ionized by stellar X-rays are susceptible to charge neutralization by small condensates, ranging from ∼0.01 μm sized grains to angstrom-sized polycyclic aromatic hydrocarbons (PAHs). Ion densities in X-ray-irradiated surfaces are so low that ambipolar diffusion weakens the MRI. Here we show that ionization by stellar far-ultraviolet (FUV) radiation enables full-blown MRI turbulence in disk surface layers. Far-UV ionization of atomic carbon and sulfur produces a plasma so dense that it is immune to ion recombination on grains and PAHs. The FUV-ionized layer, of thickness 0.01-0.1 g cm -2 , behaves in the ideal magnetohydrodynamic limit and can accrete at observationally significant rates at radii ∼> 1-10 AU. Surface layer accretion driven by FUV ionization can reproduce the trend of increasing accretion rate with increasing hole size seen in transitional disks. At radii ∼<1-10 AU, FUV-ionized surface layers cannot sustain the accretion rates generated at larger distance, and unless turbulent mixing of plasma can thicken the MRI-active layer, an additional means of transport is needed. In the case of transitional disks, it could be provided by planets.

Battery-Powered RF Pre-Ionization System for the Caltech Magnetohydrodynamically-Driven Jet Experiment: RF Discharge Properties and MHD-Driven Jet Dynamics

Science.gov (United States)

Chaplin, Vernon H.

This thesis describes investigations of two classes of laboratory plasmas with rather different properties: partially ionized low pressure radiofrequency (RF) discharges, and fully ionized high density magnetohydrodynamically (MHD)-driven jets. An RF pre-ionization system was developed to enable neutral gas breakdown at lower pressures and create hotter, faster jets in the Caltech MHD-Driven Jet Experiment. The RF plasma source used a custom pulsed 3 kW 13.56 MHz RF power amplifier that was powered by AA batteries, allowing it to safely float at 4-6 kV with the cathode of the jet experiment. The argon RF discharge equilibrium and transport properties were analyzed, and novel jet dynamics were observed. Although the RF plasma source was conceived as a wave-heated helicon source, scaling measurements and numerical modeling showed that inductive coupling was the dominant energy input mechanism. A one-dimensional time-dependent fluid model was developed to quantitatively explain the expansion of the pre-ionized plasma into the jet experiment chamber. The plasma transitioned from an ionizing phase with depressed neutral emission to a recombining phase with enhanced emission during the course of the experiment, causing fast camera images to be a poor indicator of the density distribution. Under certain conditions, the total visible and infrared brightness and the downstream ion density both increased after the RF power was turned off. The time-dependent emission patterns were used for an indirect measurement of the neutral gas pressure. The low-mass jets formed with the aid of the pre-ionization system were extremely narrow and collimated near the electrodes, with peak density exceeding that of jets created without pre-ionization. The initial neutral gas distribution prior to plasma breakdown was found to be critical in determining the ultimate jet structure. The visible radius of the dense central jet column was several times narrower than the axial current channel

A twin Frisch-grid ionization chamber as a selective detector for the delayed gamma-spectroscopy of fission fragments

Energy Technology Data Exchange (ETDEWEB)

Gaudefroy, L., E-mail: laurent.gaudefroy@cea.fr [CEA, DAM, DIF, F-91297 Arpajon (France); Roger, T., E-mail: roger@ganil.fr [GANIL, CEA/DSM-CNRS/IN2P3, BP 55027, F-14076 Caen (France); Pancin, J., E-mail: pancin@ganil.fr [GANIL, CEA/DSM-CNRS/IN2P3, BP 55027, F-14076 Caen (France); Spitaels, C. [GANIL, CEA/DSM-CNRS/IN2P3, BP 55027, F-14076 Caen (France); Aupiais, J. [CEA, DAM, DIF, F-91297 Arpajon (France); Mottier, J. [Institut de Physique Nucléaire, Université Paris-Sud-11-CNRS-IN2P3, F-91406 Orsay (France)

2017-05-21

We present a twin Frisch-grid ionization chamber. The detector is meant to provide high selective power for the study of delayed gamma-ray spectroscopy of fission fragments produced via {sup 252}Cf spontaneous fission. A mean energy resolution on the kinetic energy of fission fragments of 675 keV (FWHM) is achieved and allows us to resolve masses of fragments for fission events where neutron emission is not energetically possible. The mean mass resolution measured for these particular events amounts to 0.54 mass units (FWHM). For fission events with neutron emission a resolution of 4 mass units (FWHM) is reported. Information on fragment emission angle is measured with a resolution of 0.1 on the difference of the cosines determined for both halves of the detector. A charge resolution of 4.5 charge units (FWHM) is also demonstrated.

A mechanism of gene amplification driven by small DNA fragments.

Directory of Open Access Journals (Sweden)

Kuntal Mukherjee

Full Text Available DNA amplification is a molecular process that increases the copy number of a chromosomal tract and often causes elevated expression of the amplified gene(s. Although gene amplification is frequently observed in cancer and other degenerative disorders, the molecular mechanisms involved in the process of DNA copy number increase remain largely unknown. We hypothesized that small DNA fragments could be the trigger of DNA amplification events. Following our findings that small fragments of DNA in the form of DNA oligonucleotides can be highly recombinogenic, we have developed a system in the yeast Saccharomyces cerevisiae to capture events of chromosomal DNA amplification initiated by small DNA fragments. Here we demonstrate that small DNAs can amplify a chromosomal region, generating either tandem duplications or acentric extrachromosomal DNA circles. Small fragment-driven DNA amplification (SFDA occurs with a frequency that increases with the length of homology between the small DNAs and the target chromosomal regions. SFDA events are triggered even by small single-stranded molecules with as little as 20-nt homology with the genomic target. A double-strand break (DSB external to the chromosomal amplicon region stimulates the amplification event up to a factor of 20 and favors formation of extrachromosomal circles. SFDA is dependent on Rad52 and Rad59, partially dependent on Rad1, Rad10, and Pol32, and independent of Rad51, suggesting a single-strand annealing mechanism. Our results reveal a novel molecular model for gene amplification, in which small DNA fragments drive DNA amplification and define the boundaries of the amplicon region. As DNA fragments are frequently found both inside cells and in the extracellular environment, such as the serum of patients with cancer or other degenerative disorders, we propose that SFDA may be a common mechanism for DNA amplification in cancer cells, as well as a more general cause of DNA copy number variation

Fragmentation of size-selected Xe clusters: Why does the monomer ion channel dominate the Xen and Krn ionization?

Czech Academy of Sciences Publication Activity Database

Poterya, Viktoriya; Fárník, Michal; Buck, U.; Bonhomommeneau, D.; Halberstadt, N.

2009-01-01

Roč. 280, 1-3 (2009), s. 78-84 ISSN 1387-3806 R&D Projects: GA AV ČR KAN400400651; GA ČR GA203/06/1290 Institutional research plan: CEZ:AV0Z40400503 Keywords : cluster * fragmentation * ionization * molecular beam scattering Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.117, year: 2009

High molecular weight non-polar hydrocarbons as pure model substances and in motor oil samples can be ionized without fragmentation by atmospheric pressure chemical ionization mass spectrometry.

Science.gov (United States)

Hourani, Nadim; Kuhnert, Nikolai

2012-10-15

High molecular weight non-polar hydrocarbons are still difficult to detect by mass spectrometry. Although several studies have targeted this problem, lack of good self-ionization has limited the ability of mass spectrometry to examine these hydrocarbons. Failure to control ion generation in the atmospheric pressure chemical ionization (APCI) source hampers the detection of intact stable gas-phase ions of non-polar hydrocarbon in mass spectrometry. Seventeen non-volatile non-polar hydrocarbons, reported to be difficult to ionize, were examined by an optimized APCI methodology using nitrogen as the reagent gas. All these analytes were successfully ionized as abundant and intact stable [M-H](+) ions without the use of any derivatization or adduct chemistry and without significant fragmentation. Application of the method to real-life hydrocarbon mixtures like light shredder waste and car motor oil was demonstrated. Despite numerous reports to the contrary, it is possible to ionize high molecular weight non-polar hydrocarbons by APCI, omitting the use of additives. This finding represents a significant step towards extending the applicability of mass spectrometry to non-polar hydrocarbon analyses in crude oil, petrochemical products, waste or food. Copyright © 2012 John Wiley & Sons, Ltd.

Fragmentation dynamics of ionized neon trimer inside helium nanodroplets: a theoretical study.

Science.gov (United States)

Bonhommeau, David; Viel, Alexandra; Halberstadt, Nadine

2004-06-22

We report a theoretical study of the fragmentation dynamics of Ne(3) (+) inside helium nanodroplets, following vertical ionization of the neutral neon trimer. The motion of the neon atoms is treated classically, while transitions between the electronic states of the ionic cluster are treated quantum mechanically. A diatomics-in-molecules description of the potential energy surfaces is used, in a minimal basis set consisting of three effective p orbitals on each neon atom for the missing electron. The helium environment is modeled by a friction force acting on the neon atoms when their speed exceeds the Landau velocity. A reasonable range of values for the corresponding friction coefficient is obtained by comparison with existing experimental measurements. (c) 2004 American Institute of Physics.

Fragmentation of dimethyl ether in femtosecond intense field

Science.gov (United States)

Zhu, Jingyi; Guo, Wei; Wang, Yanqiu; Wang, Li

2006-08-01

The fragmentation of dimethyl ether (DME) in intense femtosecond laser field has been studied at 810, 405 and 270 nm with intensities up to 2.48 × 10 15, 3.86 × 10 15 and 1.62 × 10 14 W/cm 2, respectively. At 405 nm, DME is possibly firstly ionized by multiphoton absorption, and then parent ion DME + dissociates into fragments via filed-induced dissociation. For 810 and 270 nm laser fields, DME firstly dissociates into CH 3O and CH 3 fragments and then these neutral fragments are ionized by field tunneling. Another possible way for DME to dissociate at 810 and 270 nm is that DME is ionized by intense field ejection of inner valance electron and then the excited DME + dissociates into fragment ions. Ultrafast rearrangement of DME or DME + in intense field may be responsible to the unpredictable fragment ions, CHO+/C2H5+andH2+.

Possible ionization ''ignition'' in laser-driven clusters

International Nuclear Information System (INIS)

Rose-Petruck, C.; Schafer, K.J.; Barty, C.P.J.

1995-01-01

The authors use Classical Trajectory Monte Carlo (CTMC) simulations to study the ionization of small rare gas clusters in short pulse, high intensity laser fields. They calculate, for a cluster of 25 neon atoms, the ionization stage reached and the average kinetic energy of the ionized electrons as functions of time and peak laser intensity. The CTMC calculations mimic the results of the much simpler barrier suppression model in the limit of isolated atoms. At solid density the results give much more ionization in the cluster than that predicted by the barrier suppression model. They find that when the laser intensity reaches a threshold value such that on average one electron is ionized from each atom, the cluster atoms rapidly move to higher ionization stages, approaching Ne +8 in a few femtoseconds. This ignition process creates an ultrafast pulse of energetic electrons in the cluster at quite modest laser intensities

BOW SHOCK FRAGMENTATION DRIVEN BY A THERMAL INSTABILITY IN LABORATORY ASTROPHYSICS EXPERIMENTS

Energy Technology Data Exchange (ETDEWEB)

Suzuki-Vidal, F.; Lebedev, S. V.; Pickworth, L. A.; Swadling, G. F.; Skidmore, J.; Hall, G. N.; Bennett, M.; Bland, S. N.; Burdiak, G.; De Grouchy, P.; Music, J.; Suttle, L. [Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BW (United Kingdom); Ciardi, A. [Sorbonne Universités, UPMC Univ. Paris 6, UMR 8112, LERMA, F-75005, Paris (France); Rodriguez, R.; Gil, J. M.; Espinosa, G. [Departamento de Fisica de la Universidad de Las Palmas de Gran Canaria, E-35017 Las Palmas de Gran Canaria (Spain); Hartigan, P. [Department of Physics and Astronomy, Rice University, 6100 S. Main, Houston, TX 77521-1892 (United States); Hansen, E.; Frank, A., E-mail: f.suzuki@imperial.ac.uk [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)

2015-12-20

The role of radiative cooling during the evolution of a bow shock was studied in laboratory-astrophysics experiments that are scalable to bow shocks present in jets from young stellar objects. The laboratory bow shock is formed during the collision of two counterstreaming, supersonic plasma jets produced by an opposing pair of radial foil Z-pinches driven by the current pulse from the MAGPIE pulsed-power generator. The jets have different flow velocities in the laboratory frame, and the experiments are driven over many times the characteristic cooling timescale. The initially smooth bow shock rapidly develops small-scale nonuniformities over temporal and spatial scales that are consistent with a thermal instability triggered by strong radiative cooling in the shock. The growth of these perturbations eventually results in a global fragmentation of the bow shock front. The formation of a thermal instability is supported by analysis of the plasma cooling function calculated for the experimental conditions with the radiative packages ABAKO/RAPCAL.

Fragmentation dynamics of ionized neon clusters (Ne(n), n=3-14) embedded in helium nanodroplets.

Science.gov (United States)

Bonhommeau, David; Halberstadt, Nadine; Viel, Alexandra

2006-01-14

We report a theoretical study of the nonadiabatic fragmentation dynamics of ionized neon clusters embedded in helium nanodroplets for cluster sizes up to n=14 atoms. The dynamics of the neon atoms is modeled using the molecular dynamics with quantum transitions method of Tully [J. Chem. Phys. 93, 1061 (1990)] with the nuclei treated classically and transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model to which induced dipole-induced dipole interactions are added. The effect of the spin-orbit interaction is also discussed. The helium environment is modeled by a friction force acting on charged atoms whose speed exceeds the critical Landau velocity. The dependence of the fragment size distribution on the friction strength and on the initial nanodroplet size is investigated. By comparing with the available experimental data obtained for Ne3+ and Ne4+, a reasonable value for the friction coefficient, the only parameter of the model, is deduced. This value is then used to predict the effect of the helium environment on the dissociation dynamics of larger neon clusters, n=5-14. The results show stabilization of larger fragments than in the gas phase, but fragmentation is not completely caged. In addition, two types of dynamics are characterized for Ne4+: fast and explosive, therefore leaving no time for friction to cool down the process when dynamics starts on one of the highest electronic states, and slower, therefore leading to some stabilization by helium when it starts on one of the lowest electronic states.

An (e, 2e + ion) study of low-energy electron-impact ionization and fragmentation of tetrahydrofuran with high mass and energy resolutions

Science.gov (United States)

Ren, Xueguang; Pflüger, Thomas; Weyland, Marvin; Baek, Woon Yoon; Rabus, Hans; Ullrich, Joachim; Dorn, Alexander

2014-10-01

We study the low-energy (E0 = 26 eV) electron-impact induced ionization and fragmentation of tetrahydrofuran using a reaction microscope. All three final-state charged particles, i.e., two outgoing electrons and one fragment ion, are detected in triple coincidence such that the momentum vectors and, consequently, the kinetic energies for charged reaction products are determined. The ionic fragments are clearly identified in the experiment with a mass resolution of 1 amu. The fragmentation pathways of tetrahydrofuran are investigated by measuring the ion kinetic energy spectra and the binding energy spectra where an energy resolution of 1.5 eV has been achieved using the recently developed photoemission electron source. Here, we will discuss the fragmentation reactions for the cations C4H8O+, C4H7O+, C2H3O+, C3H_6^+, C3H_5^+, C3H_3^+, CH3O+, CHO+, and C2H_3^+.

Electron ionization and dissociation of aliphatic amino acids

Science.gov (United States)

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

2012-09-01

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

Electron impact ionization of the gas-phase sorbitol

Science.gov (United States)

Chernyshova, Irina; Markush, Pavlo; Zavilopulo, Anatoly; Shpenik, Otto

2015-03-01

Ionization and dissociative ionization of the sorbitol molecule by electron impact have been studied using two different experimental methods. In the mass range of m/ z = 10-190, the mass spectra of sorbitol were recorded at the ionizing electron energies of 70 and 30 eV. The ion yield curves for the fragment ions have been analyzed and the appearance energies of these ions have been determined. The relative total ionization cross section of the sorbitol molecule was measured using monoenergetic electron beam. Possible fragmentation pathways for the sorbitol molecule were proposed.

Mass Spectrometric Study of Some Fluoroquinolone Drugs Using Electron Ionization and Chemical Ionization Techniques in Combination With Semi-Empirical Calculations

International Nuclear Information System (INIS)

Abd EL Kareem, M.S.M.

2013-01-01

A mass spectrometer of the type QMS (SSQ710) is used to record the electron ionization mass spectra of some 6-fluoroquinolones molecules, namely: Norfloxacin, Pefloxacin, Ciprofloxacin and Levofloxacin.While the chemical ionization mass spectra of these compounds are recorded using Thermo Finnigan TRACE DSQ GC/MS system.In EI mass spectra, the relative intensities for the molecular ions [M] +. of the studied compounds and the prominent fragment ions are reported and discussed. Furthermore, fragmentation patterns for the four compounds have been suggested and discussed and the most important fragmentation processes such as [M-CO 2 ] +. , [M-C 2 H 4 N] + and [M-CO 2 -C 2 H 4 N] + are investigated.On the other hand, the chemical ionization (CI) mass spectra of the compounds have been recorded using methane as the reagent gas. These spectra are discussed in terms of the structure of the compounds, with particular reference to their conventional electron ionization mass spectra. The protonated molecules [M + H] + are more relatively intense than [M] +. ions in the recorded EI mass spectra indicating higher stability in the case of [M + H] + .Also, fragmentation patterns for the four compounds have been suggested and discussed (using chemical ionization technique) and the most important fragmentation processes such as [MH-CO 2 ] +. , [MH-C 2 H 4 N] + and [MH-H 2 O] + are investigated.

Electron-Impact Ionization and Dissociative Ionization of Biomolecules

Science.gov (United States)

Huo, Winifred M.; Chaban, Galina M.; Dateo, Christopher E.

2006-01-01

It is well recognized that secondary electrons play an important role in radiation damage to humans. Particularly important is the damage of DNA by electrons, potentially leading to mutagenesis. Molecular-level study of electron interaction with DNA provides information on the damage pathways and dominant mechanisms. Our study of electron-impact ionization of DNA fragments uses the improved binary-encounter dipole model and covers DNA bases, sugar phosphate backbone, and nucleotides. An additivity principle is observed. For example, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3(sup prime)- and C5 (sup prime)-deoxyribose-phospate cross sections, differing by less than 5%. Investigation of tandem double lesion initiated by electron-impact dissociative ionization of guanine, followed by proton reaction with the cytosine in the Watson-Crick pair, is currently being studied to see if tandem double lesion can be initiated by electron impact. Up to now only OH-induced tandem double lesion has been studied.

Fundamental study of hydrogen-attachment-induced peptide fragmentation occurring in the gas phase and during the matrix-assisted laser desorption/ionization process.

Science.gov (United States)

Asakawa, Daiki; Takahashi, Hidenori; Iwamoto, Shinichi; Tanaka, Koichi

2018-05-09

Mass spectrometry with hydrogen-radical-mediated fragmentation techniques has been used for the sequencing of proteins/peptides. The two methods, matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) and hydrogen attachment/abstraction dissociation (HAD) are known as hydrogen-radical-mediated fragmentation techniques. MALDI-ISD occurs during laser induced desorption processes, whereas HAD utilizes the association of hydrogen with peptide ions in the gas phase. In this study, the general mechanisms of MALDI-ISD and HAD of peptides were investigated. We demonstrated the fragmentation of four model peptides and investigated the fragment formation pathways using density functional theory (DFT) calculations. The current experimental and computational joint study indicated that MALDI-ISD and HAD produce aminoketyl radical intermediates, which immediately undergo radical-induced cleavage at the N-Cα bond located on the C-terminal side of the radical site, leading to the c'/z˙ fragment pair. In the case of MALDI-ISD, the z˙ fragments undergo a subsequent reaction with the matrix to give z' and matrix adducts of the z fragments. In contrast, the c' and z˙ fragments react with hydrogen atoms during the HAD processes, and various fragment species, such as c˙, c', z˙ and z', were observed in the HAD-MS/MS mass spectra.

A new instrument of VUV laser desorption/ionization mass spectrometry imaging with micrometer spatial resolution and low level of molecular fragmentation.

Science.gov (United States)

Wang, Jia; Liu, Feng; Mo, Yuxiang; Wang, Zhaoying; Zhang, Sichun; Zhang, Xinrong

2017-11-01

Mass spectrometry imaging (MSI) has important applications in material research, biology, and medicine. The MSI method based on UV laser desorption/ionization (UVLDI) can obtain images of intact samples, but has a high level of molecular fragmentation. In this work, we report a new MSI instrument that uses a VUV laser (125.3 nm) as a desorption/ionization source to exploit its advantages of high single photon energy and small focus size. The new instrument was tested by the mass spectra of Nile red and FGB (Fibrinogen beta chain) samples and mass spectrometric images of a fly brain section. For the tested samples, the VUVDI method offers lower levels of molecular fragmentations and higher sensitivities than those of the UVLDI method and second ion mass spectrometry imaging method using a Bi 3 + beam. The ablation crater produced by the focused VUV laser on a quartz plate has an area of 10 μm 2 . The VUV laser is prepared based on the four-wave mixing method using three collimated laser beams and a heated Hg cell.

A new instrument of VUV laser desorption/ionization mass spectrometry imaging with micrometer spatial resolution and low level of molecular fragmentation

Science.gov (United States)

Wang, Jia; Liu, Feng; Mo, Yuxiang; Wang, Zhaoying; Zhang, Sichun; Zhang, Xinrong

2017-11-01

Mass spectrometry imaging (MSI) has important applications in material research, biology, and medicine. The MSI method based on UV laser desorption/ionization (UVLDI) can obtain images of intact samples, but has a high level of molecular fragmentation. In this work, we report a new MSI instrument that uses a VUV laser (125.3 nm) as a desorption/ionization source to exploit its advantages of high single photon energy and small focus size. The new instrument was tested by the mass spectra of Nile red and FGB (Fibrinogen beta chain) samples and mass spectrometric images of a fly brain section. For the tested samples, the VUVDI method offers lower levels of molecular fragmentations and higher sensitivities than those of the UVLDI method and second ion mass spectrometry imaging method using a Bi3+ beam. The ablation crater produced by the focused VUV laser on a quartz plate has an area of 10 μm2. The VUV laser is prepared based on the four-wave mixing method using three collimated laser beams and a heated Hg cell.

Scaling of C{sub 60} ionization and fragmentation with the energy deposited in collisions with H{sup +}, H{sub 2}{sup +}, H{sub 3}{sup +} and He{sup +} ions (2-130 keV)

Energy Technology Data Exchange (ETDEWEB)

Bordenave-Montesquieu, D. [LCAR, IRSAMC, UMR 5589 CNRS, Universite Paul Sabatier, Toulouse (France)]. E-mail: dbm@yosemite.ups-tlse.fr; Moretto-Capelle, P.; Bordenave-Montesquieu, A.; Rentenier, A. [LCAR, IRSAMC, UMR 5589 CNRS, Universite Paul Sabatier, Toulouse (France)

2001-03-14

Fragmentation, ionization and C{sub 2} fragment evaporation of the C{sub 60} molecule induced by collisions with H{sup +}, H{sub 2}{sup +}, H{sub 3}{sup +} and He{sup +} monocharged ions have been measured in coincidence with the electron emission in the 2-130 keV projectile energy range. The time-of-flight mass spectra were found to vary strongly with the collision energy or velocity and the projectile. On the other hand, they scale rather nicely with the energy deposited in the molecule. Relative weights of the total multi-fragmentation into small C{sub n}{sup +} fragments (n=1-14), individual multi-fragmentation (n=1,7 and 11), double ionization of the intact molecule and evaporation of C{sub 2} molecules associated with the doubly charged fullerene ion, are used to illustrate our finding quantitatively. (author). Letter-to-the-editor.

Automated quantum chemistry based molecular dynamics simulations of electron ionization induced fragmentations of the nucleobases Uracil, Thymine, Cytosine, and Guanine.

Science.gov (United States)

Grimme, Stefan; Bauer, Christopher Alexander

2015-01-01

The gas-phase decomposition pathways of electron ionization (EI)-induced radical cations of the nucleobases uracil, thymine, cytosine, and guanine are investigated by means of mixed quantum-classical molecular dynamics. No preconceived fragmentation channels are used in the calculations. The results compare well to a plethora of experimental and theoretical data for these important biomolecules. With our combined stochastic and dynamic approach, one can access in an unbiased way the energetically available decomposition mechanisms. Additionally, we are able to separate the EI mass spectra of different tautomers of cytosine and guanine. Our method (previously termed quantum chemistry electron ionization mass spectra) reproduces free nucleobase experimental mass spectra well and provides detailed mechanistic in-sight into high-energy unimolecular decomposition processes.

Specific cationic emission of cisplatin following ionization by swift protons

International Nuclear Information System (INIS)

Moretto-Capelle, P.; Champeaux, J.P.; Deville, C.; Sence, M.; Cafarelli, P.

2016-01-01

We have investigated collision-induced ionization and fragmentation by 100 keV protons of the radio sensitizing molecule cisplatin, which is used in cancer treatments. A large emission of HCl"+ and NH_2"+ is observed, but surprisingly, no cationic fragments containing platinum are detected, in contrast to ionization-dissociation induced by electronic collision. Theoretical investigations show that the ionization processes take place on platinum and on chlorine atoms. We propose new ionization potentials for cisplatin. Dissociation limits corresponding to the measured fragmentation mass spectrum have been evaluated and the theoretical results show that the non-observed cationic fragments containing platinum are mostly associated with low dissociation energies. We have also investigated the reaction path for the hydrogen transfer from the NH_3 group to the Cl atom, as well as the corresponding dissociation limits from this tautomeric form. Here again the cations containing platinum correspond to lower dissociation limits. Thus, the experimental results suggest that excited states, probably formed via inner-shell ionization of the platinum atom of the molecule, correlated to higher dissociation limits are favored. (authors)

Specific cationic emission of cisplatin following ionization by swift protons

Science.gov (United States)

Moretto-Capelle, Patrick; Champeaux, Jean-Philippe; Deville, Charlotte; Sence, Martine; Cafarelli, Pierre

2016-05-01

We have investigated collision-induced ionization and fragmentation by 100 keV protons of the radio sensitizing molecule cisplatin, which is used in cancer treatments. A large emission of HCl+ and NH2+ is observed, but surprisingly, no cationic fragments containing platinum are detected, in contrast to ionization-dissociation induced by electronic collision. Theoretical investigations show that the ionization processes take place on platinum and on chlorine atoms. We propose new ionization potentials for cisplatin. Dissociation limits corresponding to the measured fragmentation mass spectrum have been evaluated and the theoretical results show that the non-observed cationic fragments containing platinum are mostly associated with low dissociation energies. We have also investigated the reaction path for the hydrogen transfer from the NH3 group to the Cl atom, as well as the corresponding dissociation limits from this tautomeric form. Here again the cations containing platinum correspond to lower dissociation limits. Thus, the experimental results suggest that excited states, probably formed via inner-shell ionization of the platinum atom of the molecule, correlated to higher dissociation limits are favored.

Multicharged Ion-induced simple molecule fragmentation dynamics

International Nuclear Information System (INIS)

Tarisien, M.

2003-10-01

The aim of this work is to study the dynamics of swift multicharged ion-induced fragmentation of diatomic (CO) and triatomic (CO 2 ) molecules. Performed at the GANIL facility, this study used the Recoil Ion Momentum Spectroscopy technique (RIMS), which consists of a time-of-flight mass spectrometer, coupled with a multi-hit capability position sensitive detector (delay line anode). The high-resolution measurement of the kinetic energy distribution released (KER) during the CO fragmentation points out the limitation of the Coulomb Explosion Model, revealing, for example, the di-cation CO 2 + electronic state contribution in the case of C + /O + fragmentation pathway. Furthermore, the multi-ionization cross section dependence with the orientation of the internuclear axis of CO is compared with a geometrical model calculation. Finally, different behaviours are observed for the dissociation dynamics of a triatomic molecule (CO 2 ). While triple ionization leads mainly to a synchronous concerted fragmentation dynamics, a weak fraction of dissociating molecule follows a sequential dynamics involving CO 2 + metastable states. In the case of double ionization, (CO 2 ) 2+ di-cation dissociation dynamics is asynchronously concerted and has been interpreted using a simple model involving an asymmetrical vibration of the molecule. (author)

Ionization in matrix-assisted laser desorption/ionization: singly charged molecular ions are the lucky survivors.

Science.gov (United States)

Karas, M; Glückmann, M; Schäfer, J

2000-01-01

A new model for the ionization processes in UV matrix-assisted laser desorption/ionization (MALDI) which accounts for the major phenomena observed is presented and discussed. The model retains elements of earlier approaches, such as photoionization and photochemical reactions, but it redefines these in the light of new working questions, most importantly why only singly charged ions are detected. Based on experimental evidence, the formation of singly and multiply charged clusters by a deficiency/excess of ions and also by photoionization and subsequent photochemical processes is pointed out to be the major ionization processes, which typically occur in parallel. The generation of electrons and their partial loss into the surrounding vacuum and solid, on the one hand, results in a positively charged ion-neutral plume facilitating a high overall ionization yield. On the other hand, these electrons, and also the large excess of protonated matrix ions in the negative ion mode, induce effective ion reneutralization in the plume. These neutralization processes are most effective for the highly charged cluster ions initially formed. Their fragmentation behaviour is evidenced in fast metastable fragmentation characteristics and agrees well with an electron capture dissociation mechanism and the enthalpy transfer upon neutralization forms the rationale for the prominent fragmentation and intense chemical noise accompanying successful MALDI. Within the course of the paper, cross-correlations with other desorption/ionization techniques and with earlier discussions on their mechanisms are drawn. Copyright 2000 John Wiley & Sons, Ltd.

Fission fragment driven neutron source

Science.gov (United States)

Miller, Lowell G.; Young, Robert C.; Brugger, Robert M.

1976-01-01

Fissionable uranium formed into a foil is bombarded with thermal neutrons in the presence of deuterium-tritium gas. The resulting fission fragments impart energy to accelerate deuterium and tritium particles which in turn provide approximately 14 MeV neutrons by the reactions t(d,n).sup.4 He and d(t,n).sup.4 He.

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

Science.gov (United States)

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

2016-02-28

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

Determination of ramipril in human plasma and its fragmentation by UPLC-Q-TOF-MS with positive electrospray ionization

Directory of Open Access Journals (Sweden)

Szpot Paweł

2015-06-01

Full Text Available This report presents the application of ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry with positive electrospray ionization, to determine ramipril in human plasma. First, the proteins in human plasma were precipitated using acetonitrile, then the supernatant was extracted by ethyl acetate at pH 3 and finally, the extract was analyzed using a UPLC-QTOF- MS system. The method was validated and the coefficient of determination (R2 was > 0.999, the lower limit of quantification (LLOQ was 0.5 ng mL-1. Precision, recovery and stability were determined for three different concentrations of ramipril. RSD for this method ranged from 3.3 to 8.6 %. The intra-day mean recovery was from 65.3 to 97.3 %. In addition, the fragmentation of ramipril was studied. Due to high resolution of the spectrometer, it was possible to measure fragment masses accurately and determine their molecular and chemical formulas with high accuracy.

Surface-ionization field mass-spectrometry studies of nonequilibrium surface ionization

International Nuclear Information System (INIS)

Blashenkov, Nikolai M; Lavrent'ev, Gennadii Ya

2007-01-01

The ionization of polyatomic molecules on tungsten and tungsten oxide surfaces is considered for quasiequilibrium or essentially nonequilibrium conditions (in the latter case, the term nonequilibrium surface ionization is used for adsorbate ionization). Heterogeneous reactions are supposed to proceed through monomolecular decay of polyatomic molecules or fragments of multimolecular complexes. The nonequilibrium nature of these reactions is established. The dependences of the current density of disordered ions on the surface temperature, electric field strength, and ionized particle energy distribution are obtained in analytical form. Heterogeneous dissociation energies, the ionization potentials of radicals, and the magnitude of reaction departure from equilibrium are determined from experimental data, as are energy exchange times between reaction products and surfaces, the number of molecules in molecular complexes, and the number of effective degrees of freedom in molecules and complexes. In collecting the data a new technique relying on surface-ionization field mass-spectrometry was applied. (instruments and methods of investigation)

Non-ideal magnetohydrodynamic simulations of the two-stage fragmentation model for cluster formation

International Nuclear Information System (INIS)

Bailey, Nicole D.; Basu, Shantanu

2014-01-01

We model molecular cloud fragmentation with thin-disk, non-ideal magnetohydrodynamic simulations that include ambipolar diffusion and partial ionization that transitions from primarily ultraviolet-dominated to cosmic-ray-dominated regimes. These simulations are used to determine the conditions required for star clusters to form through a two-stage fragmentation scenario. Recent linear analyses have shown that the fragmentation length scales and timescales can undergo a dramatic drop across the column density boundary that separates the ultraviolet- and cosmic-ray-dominated ionization regimes. As found in earlier studies, the absence of an ionization drop and regular perturbations leads to a single-stage fragmentation on pc scales in transcritical clouds, so that the nonlinear evolution yields the same fragment sizes as predicted by linear theory. However, we find that a combination of initial transcritical mass-to-flux ratio, evolution through a column density regime in which the ionization drop takes place, and regular small perturbations to the mass-to-flux ratio is sufficient to cause a second stage of fragmentation during the nonlinear evolution. Cores of size ∼0.1 pc are formed within an initial fragment of ∼pc size. Regular perturbations to the mass-to-flux ratio also accelerate the onset of runaway collapse.

Supply chain integration in the building industry : The emergence of integrated and repetitive strategies in a fragmented and project-driven industry

NARCIS (Netherlands)

Vrijhoef, R.

2011-01-01

The building industry is a fragmented and project-driven industry with specific characteristics, which can sometimes result in negative effects. Reference has often been made to other industries, particularly manufacturing, that would function more effectively and efficiently. Major differences

Multiphoton above threshold effects in strong-field fragmentation

DEFF Research Database (Denmark)

B Madsen, C; Anis, F; B Madsen, L

2012-01-01

We present a study of multiphoton dissociative ionization from molecules. By solving the time-dependent Schrödinger equation for H2+ and projecting the solution onto double continuum scattering states, we observe the correlated electron-nuclear ionization dynamics in detail. We show—for the first...... time—how multiphoton structure prevails as long as one accounts for the energies of all the fragments. Our current work provides a new avenue to analyze strong-field fragmentation that leads to a deeper understanding of the correlated molecular dynamics....

Attosecond-recollision-controlled selective fragmentation of polyatomic molecules.

Science.gov (United States)

Xie, Xinhua; Doblhoff-Dier, Katharina; Roither, Stefan; Schöffler, Markus S; Kartashov, Daniil; Xu, Huailiang; Rathje, Tim; Paulus, Gerhard G; Baltuška, Andrius; Gräfe, Stefanie; Kitzler, Markus

2012-12-14

Control over various fragmentation reactions of a series of polyatomic molecules (acetylene, ethylene, 1,3-butadiene) by the optical waveform of intense few-cycle laser pulses is demonstrated experimentally. We show both experimentally and theoretically that the responsible mechanism is inelastic ionization from inner-valence molecular orbitals by recolliding electron wave packets, whose recollision energy in few-cycle ionizing laser pulses strongly depends on the optical waveform. Our work demonstrates an efficient and selective way of predetermining fragmentation and isomerization reactions in polyatomic molecules on subfemtosecond time scales.

An unusual case of cerebral penetrating injury by a driven bone fragment secondary to blunt head trauma.

Science.gov (United States)

Lee, Jae Il; Ko, Jun Kyeung; Cha, Seung Heon; Han, In Ho

2011-12-01

Temple trauma that appears initially localized to the skin might possess intracranial complications. Early diagnosis and management of such complications are important, to avoid neurologic sequelae. Non-penetrating head injuries with intracranial hemorrhage caused by a driven bone fragment are extremely rare. A 53-year-old male was referred to our hospital because of intracerebral hemorrhage. He was a mechanic and one day before admission to a local clinic, tip of metallic rod hit his right temple while cutting the rod. Initial brain computed tomography (CT) and magnetic resonance imaging demonstrated scanty subdural hematoma at right temporal lobe and left falx and intracerebral hematoma at both frontal lobes. Facial CT with 3-D reconstruction images showed a small bony defect at the right sphenoid bone's greater wing and a small bone fragment at the left frontal lobe, crossing the falx. We present the unusual case of a temple trauma patient in whom a sphenoid bone fragment migrated from its origin upward, to the contralateral frontal lobe, producing hematoma along its trajectory.

Multicharged Ion-induced simple molecule fragmentation dynamics; Dynamique de la fragmentation de molecules simples induite par impact d'ion multicharge

Energy Technology Data Exchange (ETDEWEB)

Tarisien, M

2003-10-01

The aim of this work is to study the dynamics of swift multicharged ion-induced fragmentation of diatomic (CO) and triatomic (CO{sub 2}) molecules. Performed at the GANIL facility, this study used the Recoil Ion Momentum Spectroscopy technique (RIMS), which consists of a time-of-flight mass spectrometer, coupled with a multi-hit capability position sensitive detector (delay line anode). The high-resolution measurement of the kinetic energy distribution released (KER) during the CO fragmentation points out the limitation of the Coulomb Explosion Model, revealing, for example, the di-cation CO{sub 2}{sup +} electronic state contribution in the case of C{sup +}/O{sup +} fragmentation pathway. Furthermore, the multi-ionization cross section dependence with the orientation of the internuclear axis of CO is compared with a geometrical model calculation. Finally, different behaviours are observed for the dissociation dynamics of a triatomic molecule (CO{sub 2}). While triple ionization leads mainly to a synchronous concerted fragmentation dynamics, a weak fraction of dissociating molecule follows a sequential dynamics involving CO{sub 2}{sup +} metastable states. In the case of double ionization, (CO{sub 2}){sup 2+} di-cation dissociation dynamics is asynchronously concerted and has been interpreted using a simple model involving an asymmetrical vibration of the molecule. (author)

Statistical analysis of fragmentation patterns of electron ionization mass spectra of enolized-trimethylsilylated anabolic androgenic steroids

Science.gov (United States)

Fragkaki, A. G.; Angelis, Y. S.; Tsantili-Kakoulidou, A.; Koupparis, M.; Georgakopoulos, C.

2009-08-01

Anabolic androgenic steroids (AAS) are included in the List of prohibited substances of the World Anti-Doping Agency (WADA) as substances abused to enhance athletic performance. Gas chromatography coupled to mass spectrometry (GC-MS) plays an important role in doping control analyses identifying AAS as their enolized-trimethylsilyl (TMS)-derivatives using the electron ionization (EI) mode. This paper explores the suitability of complementary GC-MS mass spectra and statistical analysis (principal component analysis, PCA and partial least squares-discriminant analysis, PLS-DA) to differentiate AAS as a function of their structural and conformational features expressed by their fragment ions. The results obtained showed that the application of PCA yielded a classification among the AAS molecules which became more apparent after applying PLS-DA to the dataset. The application of PLS-DA yielded a clear separation among the AAS molecules which were, thus, classified as: 1-ene-3-keto, 3-hydroxyl with saturated A-ring, 1-ene-3-hydroxyl, 4-ene-3-keto, 1,4-diene-3-keto and 3-keto with saturated A-ring anabolic steroids. The study of this paper also presents structurally diagnostic fragment ions and dissociation routes providing evidence for the presence of unknown AAS or chemically modified molecules known as designer steroids.

An Unusual Case of Cerebral Penetrating Injury by a Driven Bone Fragment Secondary to Blunt Head Trauma

OpenAIRE

Lee, Jae Il; Ko, Jun Kyeung; Cha, Seung Heon; Han, In Ho

2011-01-01

Temple trauma that appears initially localized to the skin might possess intracranial complications. Early diagnosis and management of such complications are important, to avoid neurologic sequelae. Non-penetrating head injuries with intracranial hemorrhage caused by a driven bone fragment are extremely rare. A 53-year-old male was referred to our hospital because of intracerebral hemorrhage. He was a mechanic and one day before admission to a local clinic, tip of metallic rod hit his right t...

Ir-Driven Dynamics of the 3-AMINOPHENOL-AMMONIA Complex

Science.gov (United States)

Heid, Cornelia G.; Merrill, W. G.; Case, Amanda; Crim, Fleming

2014-06-01

We report on gas-phase experiments investigating the predissociation and possible IR-driven isomerization of the 3-aminophenol-ammonia complex (3-AP-NH3). A molecular beam of 3-AP-NH3 is vibrationally excited with pulsed IR light, initiating an intramolecular vibrational redistribution and subsequent dissociation. The 3-AP fragment is then probed state-selectively via multiphoton ionization (REMPI) and time-of-flight mass spectrometry. Of particular interest is an IR-driven feature which we associate tentatively with a trans-cis isomerization process. We see clear correlation between the excitation of specific vibrational modes (namely the NH3 symmetric and OH stretches) and the presence of this feature, as evidenced by IR-action and IR-depletion spectra. The feature persists atop a broader signal which we assign to the predissociation of the complex and whose cutoff in REMPI-action experiments provides an upper bound on the dissociation energy for 3-AP-NH3.

Comparison of Atmospheric Pressure Chemical Ionization and Field Ionization Mass Spectrometry for the Analysis of Large Saturated Hydrocarbons.

Science.gov (United States)

Jin, Chunfen; Viidanoja, Jyrki; Li, Mingzhe; Zhang, Yuyang; Ikonen, Elias; Root, Andrew; Romanczyk, Mark; Manheim, Jeremy; Dziekonski, Eric; Kenttämaa, Hilkka I

2016-11-01

Direct infusion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was compared to field ionization mass spectrometry (FI-MS) for the determination of hydrocarbon class distributions in lubricant base oils. When positive ion mode APCI with oxygen as the ion source gas was employed to ionize saturated hydrocarbon model compounds (M) in hexane, only stable [M - H] + ions were produced. Ion-molecule reaction studies performed in a linear quadrupole ion trap suggested that fragment ions of ionized hexane can ionize saturated hydrocarbons via hydride abstraction with minimal fragmentation. Hence, APCI-MS shows potential as an alternative of FI-MS in lubricant base oil analysis. Indeed, the APCI-MS method gave similar average molecular weights and hydrocarbon class distributions as FI-MS for three lubricant base oils. However, the reproducibility of APCI-MS method was found to be substantially better than for FI-MS. The paraffinic content determined using the APCI-MS and FI-MS methods for the base oils was similar. The average number of carbons in paraffinic chains followed the same increasing trend from low viscosity to high viscosity base oils for the two methods.

Ionic fragmentation of the isoprene molecule in the VUV energy range (12 to 310 eV)

Energy Technology Data Exchange (ETDEWEB)

Bernini, R.B., E-mail: rafael.bernini@ifrj.edu.br [Instituto Federal de Ciência e Tecnologia do Rio de Janeiro (IFRJ), 25050-100 Duque de Caxias, RJ (Brazil); Coutinho, L.H. [Instituto de Física, Universidade Federal do Rio De Janeiro (UFRJ), 21941-972 Rio de Janeiro, RJ (Brazil); Nunez, C.V. [Laboratório de Bioprospecção e Biotecnologia, Coordenação de Tecnologia e Inovação, Instituto Nacional de Pesquisas da Amazônia (INPA), 69060-001 Manaus, AM (Brazil); Castilho, R.B. de [Departamento de Química, Instituto de Ciências Exatas, Universidade Federal do Amazonas (UFAM), 69077-000 Manaus, AM (Brazil); Souza, G.G.B. de [Instituto de Química, Universidade Federal do Rio de Janeiro (UFRJ), 21949-900 Rio de Janeiro, RJ (Brazil)

2015-07-15

Highlights: • Ionic fragmentation of isoprene following valence-shell and C 1s excitation. • Experimental observation of single and double ionization processes. • Large increase in fragmentation following core excitation. • Similar dissociation pattern bellow (270 eV) and above (310 eV) core edge. • Stable molecular ion observed at all photon energies. - Abstract: Isoprene, C{sub 5}H{sub 8}, is a biogenic volatile compound emitted from plants and animals, playing an important role in atmospheric chemistry. In this work, we have studied the ionic fragmentation of the isoprene molecule induced by high energy photons (synchrotron radiation), both at the valence (12.0, 14.0, 16.0, 18.0, and 21.0 eV) and carbon 1s edge (270 and 310 eV, respectively, below and above edge) energies. The ionic fragments were mass-analyzed using a Wiley–McLaren time-of-flight spectrometer (TOF) and single (PEPICO) and double ionization coincidence (PEPIPICO) spectra were obtained. As expected, the fragmentation degree increases with increasing energy. Below and above the carbon 1s edge, the fragmentation patterns are quite similar, and basically the same fragments are observed as compared to the spectra following valence-shell ionization. Stable doubly-charged ions were not observed. A PEPIPICO spectrum has shown that the main dissociation route for doubly-ionized species corresponds to the [CH{sub 3}]{sup +}/[C{sub 4}H{sub 2–5}]{sup +} ion pair. Intense fragmentation of the isoprene molecule has been observed following valence shell and core electron ionization. The observance of basically the same fragments when moving from valence to inner-shell suggests that basically the same fragmentation routes are present in both cases. All doubly (or multiply)-charged cations are unstable, at least on a microsecond scale.

Effectiveness in detecting fission fragments with ionization chambers

International Nuclear Information System (INIS)

Manrique Garcia, J.; Monne, G.

1991-01-01

Detection of fission fragments is important in nuclear measurements. When a high detection accuracy is required it is necessary to take in account the detection losses due to the absorption of fragments in the fissionable material. The losses corrections might change the final results in 2-3%. The traditional expression used in the calculation of the detection efficiency does not consider neither the density variation of the fissionable substance with its width, because it depends on the target material. That's why actually in many labs it is being searched new methods that allow to find the efficiency for each target. In this work a new method for determination of absorption efficiency is presented. The obtained results are analyzed

Critique of atomic physics instability mechanisms: Ionization-driven and radiative microinstabilities in the tokamak edge plasma

International Nuclear Information System (INIS)

Ross, D.W.

1994-01-01

The theory of atomic-process driven microinstabilities in the tokamak edge plasma is reexamined. It is found that these instabilities, as they are usually presented, do not exist. This assertion applies both to ionization-driven modes and to radiative condensation, or thermal-driven modes. The problem is that there exists no separation of time scales between the approach to equilibrium and the growth rate of the purported instabilities. Therefore, to describe the perturbation of an inhomogeneous plasma, it is essential either to establish an equilibrium that includes both perpendicular transport and the proposed source, or, alternatively, to follow the background evolution simultaneously with the growth of the modes. Neither has been done in theoretical or numerical studies of microinstabilities driven by atomic effects in tokamaks. Very near the density limit, macroscopic modes may be unstable, leading to marfes or disruptions, but perturbations of the equilibrium transport fluxes, when taken into account, are sufficient to stabilize the microscopic modes. If the equilibrium fluxes are not included a priori, the ordering breakdown persists into the nonlinear regime. Since the atomic driving terms are the same as in the linear limit, radial decorrelation lengths would have to approach background scale lengths to yield transport of significant magnitude. Under ordinary tokamak conditions, therefore, atomic processes are unlikely to provide an important driving mechanism for the microturbulence that is presumed to cause anomalous transport

Strategies for mitigating the ionization-induced beam head erosion problem in an electron-beam-driven plasma wakefield accelerator

Directory of Open Access Journals (Sweden)

W. An

2013-10-01

Full Text Available Strategies for mitigating ionization-induced beam head erosion in an electron-beam-driven plasma wakefield accelerator (PWFA are explored when the plasma and the wake are both formed by the transverse electric field of the beam itself. Beam head erosion can occur in a preformed plasma because of a lack of focusing force from the wake at the rising edge (head of the beam due to the finite inertia of the electrons. When the plasma is produced by field ionization from the space charge field of the beam, the head erosion is significantly exacerbated due to the gradual recession (in the beam frame of the 100% ionization contour. Beam particles in front of the ionization front cannot be focused (guided causing them to expand as in vacuum. When they expand, the location of the ionization front recedes such that even more beam particles are completely unguided. Eventually this process terminates the wake formation prematurely, i.e., well before the beam is depleted of its energy. Ionization-induced head erosion can be mitigated by controlling the beam parameters (emittance, charge, and energy and/or the plasma conditions. In this paper we explore how the latter can be optimized so as to extend the beam propagation distance and thereby increase the energy gain. In particular we show that, by using a combination of the alkali atoms of the lowest practical ionization potential (Cs for plasma formation and a precursor laser pulse to generate a narrow plasma filament in front of the beam, the head erosion rate can be dramatically reduced. Simulation results show that in the upcoming “two-bunch PWFA experiments” on the FACET facility at SLAC national accelerator laboratory the energy gain of the trailing beam can be up to 10 times larger for the given parameters when employing these techniques. Comparison of the effect of beam head erosion in preformed and ionization produced plasmas is also presented.

Ionization and bound-state relativistic quantum dynamics in laser-driven multiply charged ions

International Nuclear Information System (INIS)

Hetzheim, Henrik

2009-01-01

The interaction of ultra-strong laser fields with multiply charged hydrogen-like ions can be distinguished in an ionization and a bound dynamics regime. Both are investigated by means of numerically solving the Dirac equation in two dimensions and by a classical relativistic Monte-Carlo simulation. For a better understanding of highly nonlinear physical processes the development of a well characterized ultra-intense relativistic laser field strength has been driven forward, capable of studying e.g. the magnetic field effects of the laser resulting in an additional electron motion in the laser propagation direction. A novel method to sensitively measure these ultra-strong laser intensities is developed and employed from the optical via the UV towards the XUV frequency regime. In the bound dynamics field, the determination of multiphoton transition matrixelements has been investigated between different bound states via Rabi oscillations. (orig.)

Ionization and bound-state relativistic quantum dynamics in laser-driven multiply charged ions

Energy Technology Data Exchange (ETDEWEB)

Hetzheim, Henrik

2009-01-14

The interaction of ultra-strong laser fields with multiply charged hydrogen-like ions can be distinguished in an ionization and a bound dynamics regime. Both are investigated by means of numerically solving the Dirac equation in two dimensions and by a classical relativistic Monte-Carlo simulation. For a better understanding of highly nonlinear physical processes the development of a well characterized ultra-intense relativistic laser field strength has been driven forward, capable of studying e.g. the magnetic field effects of the laser resulting in an additional electron motion in the laser propagation direction. A novel method to sensitively measure these ultra-strong laser intensities is developed and employed from the optical via the UV towards the XUV frequency regime. In the bound dynamics field, the determination of multiphoton transition matrixelements has been investigated between different bound states via Rabi oscillations. (orig.)

Ionization waves of arbitrary velocity driven by a flying focus

Science.gov (United States)

Palastro, J. P.; Turnbull, D.; Bahk, S.-W.; Follett, R. K.; Shaw, J. L.; Haberberger, D.; Bromage, J.; Froula, D. H.

2018-03-01

A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or flying, focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. We present analytical calculations and simulations describing the propagation of the flying focus pulse, the self-similar form of its intensity profile, and ionization wave formation. The ability to control the speed of the ionization wave and, in conjunction, mitigate plasma refraction has the potential to advance several laser-based applications, including Raman amplification, photon acceleration, high-order-harmonic generation, and THz generation.

Electron-impact-ionization dynamics of S F6

Science.gov (United States)

Bull, James N.; Lee, Jason W. L.; Vallance, Claire

2017-10-01

A detailed understanding of the dissociative electron ionization dynamics of S F6 is important in the modeling and tuning of dry-etching plasmas used in the semiconductor manufacture industry. This paper reports a crossed-beam electron ionization velocity-map imaging study on the dissociative ionization of cold S F6 molecules, providing complete, unbiased kinetic energy distributions for all significant product ions. Analysis of these distributions suggests that fragmentation following single ionization proceeds via formation of S F5 + or S F3 + ions that then dissociate in a statistical manner through loss of F atoms or F2, until most internal energy has been liberated. Similarly, formation of stable dications is consistent with initial formation of S F4 2 + ions, which then dissociate on a longer time scale. These data allow a comparison between electron ionization and photoionization dynamics, revealing similar dynamical behavior. In parallel with the ion kinetic energy distributions, the velocity-map imaging approach provides a set of partial ionization cross sections for all detected ionic fragments over an electron energy range of 50-100 eV, providing partial cross sections for S2 +, and enables the cross sections for S F4 2 + from S F+ to be resolved.

DNA fragmentation dynamics allows the assessment of cryptic sperm damage in human: Evaluation of exposure to ionizing radiation, hyperthermia, acidic pH and nitric oxide

Energy Technology Data Exchange (ETDEWEB)

Santiso, Rebeca; Tamayo, Maria [Laboratorio de Genetica Molecular y Radiobiologia, Centro Oncologico de Galicia, Doctor Camilo Veiras 1, 15009-A Coruna (Spain); Genetics Unit, INIBIC-Complejo Hospitalario Universitario A Coruna (CHUAC), As Xubias, 84, 15006-A Coruna (Spain); Gosalvez, Jaime [Genetics Unit, Facultad de Biologia, Universidad Autonoma de Madrid, Ciudad Universitaria de Cantoblanco, 28049 Madrid (Spain); Johnston, Steve [School of Agriculture and Food Science, University of Queensland, Gatton 4343 (Australia); Marino, Alfonso [Servicio de Oncologia Radioterapica, Centro Oncologico de Galicia, Doctor Camilo Veiras 1, 15009-A Coruna (Spain); Fernandez, Carlos; Losada, Carlos [Servicio de Radiofisica, Centro Oncologico de Galicia, Doctor Camilo Veiras 1, 15009-A Coruna (Spain); Fernandez, Jose Luis, E-mail: Jose.Luis.Fernandez.Garcia@sergas.es [Laboratorio de Genetica Molecular y Radiobiologia, Centro Oncologico de Galicia, Doctor Camilo Veiras 1, 15009-A Coruna (Spain); Genetics Unit, INIBIC-Complejo Hospitalario Universitario A Coruna (CHUAC), As Xubias, 84, 15006-A Coruna (Spain)

2012-06-01

Sperm DNA fragmentation (SDF) is not a static seminal parameter, since the longevity of sperm DNA decreases progressively with time following ejaculation or thawing. While the dynamics of SDF is a species-specific characteristic, in the case of humans, there is still significant variation within patients. To evaluate the suitability of the dynamic SDF assay to assess the adverse effects of agents that cause genetic damage, fresh semen samples from different donors were exposed in vitro to (1) increasing acute doses of ionizing radiation, (2) elevated temperature (41 Degree-Sign C and 45 Degree-Sign C), (3) acidic pH (pH 4) and (4) the nitric oxide (NO) donor sodium nitroprusside (SNP). Sperm DNA fragmentation was analyzed after an incubation period of chronic (24 h), or acute (1 h) exposure to each treatment followed by incubation at 37 Degree-Sign C over a period of 24 h. SDF was assessed using the sperm chromatin dispersion (SCD) test. Dynamic SDF for each treatment was analyzed using Kaplan-Meier survival curves. All agents, except for ionizing radiation, accelerated SDF kinetics following chronic exposure over a 24 h period. Transient exposure to NO and heat but not acidic pH increased the basal (T0) level of SDF. Despite the removal of the three toxicants, the remaining sperm following acute exposure showed a decrease in their expected DNA longevity. It is concluded that the assessment of sperm DNA fragmentation dynamics is an effective methodological approach for revealing latent damage associated with toxicants that is not initially expressed following a single initial observation of SDF.

Multiple-electron removal and molecular fragmentation of CO by fast F4+ impact

International Nuclear Information System (INIS)

Ben-Itzhak, I.; Ginther, S.G.; Carnes, K.D.

1993-01-01

Multiple-electron removal from and molecular fragmentation of carbon monoxide molecules caused by collisions with 1-MeV/amu F 4+ ions were studied using the coincidence time-of-flight technique. In these collisions, multiple-electron removal of the target molecule is a dominant process. Cross sections for the different levels of ionization of the CO molecule during the collision were determined. The relative cross sections of ionization decrease with increasing number of electrons removed in a similar way as seen in atomic targets. This behavior is in agreement with a two-step mechanism, where first the molecule is ionized by a Franck-Condon ionization and then the molecular ion dissociates. Most of the highly charged intermediate states of the molecule dissociate rapidly. Only CO + and CO 2+ molecular ions have been seen to survive long enough to be detected as molecular ions. The relative cross sections for the different breakup channels were evaluated for collisions in which the molecule broke into two charged fragments as well as for collisions where only a single charged molecular ion or fragment were produced. The average charge state of each fragment resulting from CO Q+ →C i+ +O j+ breakup increases with the number of electrons removed from the molecule approximately following the relationship bar i=bar j=Q/2 as long as K-shell electrons are not removed. This does not mean that the charge-state distribution is exactly symmetric, as, in general, removing electrons from the carbon fragment is slightly more likely than removing electrons from the oxygen due to the difference in binding energy. The cross sections for molecular breakup into a charged fragment and a neutral fragment drop rapidly with an increasing number of electrons removed

The investigation of substituent effects on the fragmentation pathways of pentacoordinated phenoxyspirophosphoranes by ESI-MSn.

Science.gov (United States)

Cui, Xiaoyan; Sun, Can; Zhao, Pei; Wang, Yanyan; Guo, Yanchun; Zhao, Yufen; Cao, Shuxia

2018-04-01

The fragmentation pathways of pentacoordinated phenoxyspirophosphoranes were investigated in the positive mode by electrospray ionization multistage mass spectrometry. The results demonstrate that the sodium adducts of the title compounds undergo two competitive fragmentation pathways, and the fragmentation patterns are heavily dependent on the various substituent patterns at the phenolic group. An electron-withdrawing substituent at the ortho-position always results in the removal of a corresponding phenol analogue, while cleavage by spiroring opening becomes the predominant fragmentation pathway if an electron-donating substituent is at the phenolic group. The substituent effects on the competitive fragmentation pathways were further elucidated by theoretical calculations, single crystal structure analysis, and high-resolution mass spectrometry. The results contribute to the understanding of the gas-phase fragmentation reactions and the structure identification of spirophosphorane analogues by electrospray ionization multistage mass spectrometry. Copyright © 2018 John Wiley & Sons, Ltd.

Development of soft ionization using direct current pulse glow discharge plasma source in mass spectrometry for volatile organic compounds analysis

Science.gov (United States)

Nunome, Yoko; Kodama, Kenji; Ueki, Yasuaki; Yoshiie, Ryo; Naruse, Ichiro; Wagatsuma, Kazuaki

2018-01-01

This study describes an ionization source for mass analysis, consisting of glow discharge plasma driven by a pulsed direct-current voltage for soft plasma ionization, to detect toxic volatile organic compounds (VOCs) rapidly and easily. The novelty of this work is that a molecular adduct ion, in which the parent molecule attaches with an NO+ radical, [M + NO]+, can be dominantly detected as a base peak with little or no fragmentation of them in an ambient air plasma at a pressure of several kPa. Use of ambient air as the discharge plasma gas is suitable for practical applications. The higher pressure in an ambient air discharge provided a stable glow discharge plasma, contributing to the soft ionization of organic molecules. Typical mass spectra of VOCs toluene, benzene, o-xylene, chlorobenzene and n-hexane were observed as [M + NO]+ adduct ion whose peaks were detected at m/z 122, 108, 136, 142 and 116, respectively. The NO generation was also confirmed by emission bands of NO γ-system. The ionization reactions were suggested, such that NO+ radical formed in an ambient air discharge could attach with the analyte molecule.

Study of Photoionization and Fragmentation on CHClF2 : Experiments and Calculations

International Nuclear Information System (INIS)

Sheng, L.; Yang, B.; Huang, C.; Qi, F.; Zhang, Y.; Wang, Z.; Zhou, S.

2004-01-01

Full text: The photoionization and fragmentation of CHClF 2 are studied with VUV radiation and photoionization mass spectroscopy at NSRL. Ionization potential of Parent molecule CHClF 2 , appearance energies of some fragment ions, and dissociative energy of some fragmentation process are obtained from photoionization efficiency spectroscopy. Dissociative photoionization channels for formation of some fragment ions are proposed on comparison of determined appearance energies and energies predicted with Gaussian-98 calculation

Electron impact ionization of large krypton clusters

Institute of Scientific and Technical Information of China (English)

Li Shao-Hui; Li Ru-Xin; Ni Guo-Quan; Xu Zhi-Zhan

2004-01-01

We show that the detection of ionization of very large van der Waals clusters in a pulsed jet or a beam can be realized by using a fast ion gauge. Rapid positive feedback electron impact ionization and fragmentation processes,which are initially ignited by electron impact ionization of the krypton clusters with the electron current of the ion gauge, result in the appearance of a progressional oscillation-like ion spectrum, or just of a single fast event under critical conditions. Each line in the spectrum represents a correlated explosion or avalanche ionization of the clusters.The phenomena have been analysed qualitatively along with a Rayleigh scattering experiment of the corresponding cluster jet.

Atmospheric pressure ionization-tandem mass spectrometry of the phenicol drug family.

Science.gov (United States)

Alechaga, Élida; Moyano, Encarnación; Galceran, M Teresa

2013-11-01

In this work, the mass spectrometry behaviour of the veterinary drug family of phenicols, including chloramphenicol (CAP) and its related compounds thiamphenicol (TAP), florfenicol (FF) and FF amine (FFA), was studied. Several atmospheric pressure ionization sources, electrospray (ESI), atmospheric pressure chemical ionization and atmospheric pressure photoionization were compared. In all atmospheric pressure ionization sources, CAP, TAP and FF were ionized in both positive and negative modes; while for the metabolite FFA, only positive ionization was possible. In general, in positive mode, [M + H](+) dominated the mass spectrum for FFA, while the other compounds, CAP, TAP and FF, with lower proton affinity showed intense adducts with species present in the mobile phase. In negative mode, ESI and atmospheric pressure photoionization showed the deprotonated molecule [M-H](-), while atmospheric pressure chemical ionization provided the radical molecular ion by electron capture. All these ions were characterized by tandem mass spectrometry using the combined information obtained by multistage mass spectrometry and high-resolution mass spectrometry in a quadrupole-Orbitrap instrument. In general, the fragmentation occurred via cyclization and losses or fragmentation of the N-(alkyl)acetamide group, and common fragmentation pathways were established for this family of compounds. A new chemical structure for the product ion at m/z 257 for CAP, on the basis of the MS(3) and MS(4) spectra is proposed. Thermally assisted ESI and selected reaction monitoring are proposed for the determination of these compounds by ultra high-performance liquid chromatography coupled to tandem mass spectrometry, achieving instrumental detection limits down to 0.1 pg. Copyright © 2013 John Wiley & Sons, Ltd.

Hyperthermal surface ionization mass spectrometry of organic molecules: monoterpenes

International Nuclear Information System (INIS)

Kishi, Hiroshi; Fujii, Toshihiro.

1997-01-01

This paper describes an experimental study on the influence of kinetic energy of fast monoterpene molecules on the surface ionization efficiency and on the mass spectral patterns, using rhenium oxide (ReO 2 ) surface. Molecular kinetic energy, given to the molecules through the acceleration in the seeded supersonic molecular beam, ranged from 1 to 10 eV. Hyperthermal surface ionization mass spectra (HSIMS) were taken for various incident kinetic energies and surface temperatures. The observed mass spectra were interpreted in a purely empirical way, by means of evidence from the previous investigations, and they were compared with conventional EI techniques and with the thermal energy surface ionization technique (SIOMS; Surface Ionization Organic Mass Spectrometry). Ionization efficiency (β) was also studied. Under hyperthermal surface ionization (HSI) conditions, many kinds of fragment ions, including quite abundant odd electron ions (OE +· ) are observed. HSIMS patterns of monoterpenes are different among 6-isomers, contrary to those of SIOMS and EIMS, where very similar patterns for isomers are observed. HSIMS patterns are strongly dependent on the molecular kinetic energies. The surface temperature does not affect much the spectral patterns, but it controls the total amount of ion formation. We conclude from these mass spectral findings, HSI-mechanism contains an impulsive process of ion formation, followed by the fragmentation process as a results of the internal energies acquired through the collision processes. (author)

Fragmentation of organic ions bearing fixed multiple charges observed in MALDI MS.

Science.gov (United States)

Lou, Xianwen; Li, Bao; de Waal, Bas F M; Schill, Jurgen; Baker, Matthew B; Bovee, Ralf A A; van Dongen, Joost L J; Milroy, Lech-Gustav; Meijer, E W

2018-01-01

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) was used to analyze a series of synthetic organic ions bearing fixed multiple charges. Despite the multiple intrinsic charges, only singly charged ions were recorded in each case. In addition to the pseudo-molecular ions formed by counterion adduction, deprotonation and electron capture, a number of fragment ions were also observed. Charge splitting by fragmentation was found to be a viable route for charge reduction leading to the formation of the observed singly charged fragment ions. Unlike multivalent metal ions, organic ions can rearrange and/or fragment during charge reduction. This fragmentation process will evidently complicate the interpretation of the MALDI MS spectrum. Because MALDI MS is usually considered as a soft ionization technique, the fragment ion peaks can easily be erroneously interpreted as impurities. Therefore, the awareness and understanding of the underlying MALDI-induced fragmentation pathways is essential for a proper interpretation of the corresponding mass spectra. Due to the fragment ions generated during charge reduction, special care should be taken in the MALDI MS analysis of multiply charged ions. In this work, the possible mechanisms by which the organic ions bearing fixed multiple charges fragment are investigated. With an improved understanding of the fragmentation mechanisms, MALDI TOF MS should still be a useful technique for the characterization of organic ions with fixed multiple charges. Copyright © 2017 John Wiley & Sons, Ltd.

Measurement of Fragment Mass Distributions in Neutron-induced Fission of 238U and 232Th at Intermediate Energies

International Nuclear Information System (INIS)

Simutkin, V.D.

2008-01-01

Conceptual analysis of accelerator-driven systems assumes extensive use of nuclear data on neutron-induced reactions at intermediate energies. In particular, information about the fission fragment yields from the 238 U(n,f) and 232 Th(n,f) reactions is of particular interest at neutron energies from 10 to 200 MeV. However, there is a lack of such data for both 238 U and 232 Th. Up to now, the intermediate energy measurements have been performed for 238 U only, and there are no data for the 232 Th(n,f) reaction. The aim of the work is to provide such data. Fission fragment mass distributions for the 232 Th(n,f) and 238 U(n,f) reactions have been measured for the incident neutron energies 32.8 MeV, 45.3 MeV and 59.9 MeV. The experiments have been performed at the neutron beam facility of the Universite Catholique de Louvain, Belgium. A multi-section Frisch-gridded ionization chamber has been used as a fission fragment detector. The data obtained have been interpreted in terms of the multimodal random neck-rupture model (MMRNRM). (authors)

Electron Impact Ionization of C60

International Nuclear Information System (INIS)

Duenser, B.; Lezius, M.; Scheier, P.; Deutsch, H.; Maerk, T.D.

1995-01-01

Absolute partial and total cross sections for the electron impact ionization of C 60 have been measured using a novel approach for the absolute calibration. The results obtained reveal not only an anomalous large parent ion cross section (as compared to the other ionization channels), but also anomalies for the production of multiply charged parent and fragment ions. This special behavior has its origin in the specific electronic and geometric structure of C 60 . Semiclassical calculations for singly charged ions support the measured data

Endoergic chemi-ionization in N-O collisions

International Nuclear Information System (INIS)

Nielsen, S.E.; Dahler, J.S.

1979-01-01

A semiclassical theory of endoergic chemi-ionization is developed and applied to the ionizing events that occur when ground state oxygen atoms collide with nitrogen atoms in the ground and first excited states. The approach used is an adaptation and extension of earlier theories due to Bardsley, Nakamura, and Miller. The theory relates the experimental associative (AI) and Penning ionization (PI) cross sections to the following events: formation of a stable diatomic ion (AI), neutral and ionized atomic fragments (PI), or of a metastable diatomic rotational resonance (DI, delayed ionization). The heavy particle motions are treated classically in terms of adiabatic potential energy functions, while localized nonadiabatic transitions also are taken into account by using the Landau-Zener approximation. Finally, the theoretical predictions compare well with the results of Ringer and Gentry's (1978) merged beam experiments

VUV and soft x-ray ionization of a plant volatile: Vanillin (C8H8O3)

Science.gov (United States)

Betancourt, A. Moreno; Coutinho, L. H.; Bernini, R. B.; de Moura, C. E. V.; Rocha, A. B.; de Souza, G. G. B.

2016-03-01

Plant volatiles are emitted by plants in response to several forms of stress, including interaction with energetic photons. In the present work, we discuss the interaction of extreme UV and soft X-ray photons with a plant volatile, vanillin. The single and double (multiple) ionization of the vanillin molecule have been studied for the first time using time-of-flight mass spectrometry and VUV and soft X-ray photons (synchrotron radiation, at 12.0 eV, 21.2 eV, 130 eV, 310 eV, 531 eV, and 550 eV). At 12.0 and 21.2 eV, only singly charged species are observed and the parent ion, C8H8O3+, is the dominant species. Energy differences for some selected fragments were calculated theoretically in this energy region. At 130 eV, direct double and triple ionization of the valence electrons may occur. The fragmentation increases and CHO+ becomes one of the main cations in the mass spectrum. The molecular ion is still the dominant species, but other fragments, such as C6H5O+, begin to present similar intensities. At 310 eV, C 1s electrons may be ionized and Auger processes give rise to dissociative doubly ionized cations. Ionization around the O 1s edge has been studied both at the 531 eV resonance and above the ionization edge. Resonant and normal Auger processes play a significant role in each case and a large fragmentation of the molecule is observed at both photon energies, with intense fragments such as CHO+ and CH3+ being clearly observed. A near edge X-ray absorption fine structure spectrum of the vanillin molecule was obtained around the O 1s ionization threshold. In addition, the fragmentation of vanillin has also been studied using a fast beam of electrons (800 eV), for the sake of comparison.

VUV and soft x-ray ionization of a plant volatile: Vanillin (C8H8O3)

International Nuclear Information System (INIS)

Betancourt, A. Moreno; Moura, C. E. V. de; Rocha, A. B.; Souza, G. G. B. de; Coutinho, L. H.; Bernini, R. B.

2016-01-01

Plant volatiles are emitted by plants in response to several forms of stress, including interaction with energetic photons. In the present work, we discuss the interaction of extreme UV and soft X-ray photons with a plant volatile, vanillin. The single and double (multiple) ionization of the vanillin molecule have been studied for the first time using time-of-flight mass spectrometry and VUV and soft X-ray photons (synchrotron radiation, at 12.0 eV, 21.2 eV, 130 eV, 310 eV, 531 eV, and 550 eV). At 12.0 and 21.2 eV, only singly charged species are observed and the parent ion, C 8 H 8 O 3 + , is the dominant species. Energy differences for some selected fragments were calculated theoretically in this energy region. At 130 eV, direct double and triple ionization of the valence electrons may occur. The fragmentation increases and CHO + becomes one of the main cations in the mass spectrum. The molecular ion is still the dominant species, but other fragments, such as C 6 H 5 O + , begin to present similar intensities. At 310 eV, C 1s electrons may be ionized and Auger processes give rise to dissociative doubly ionized cations. Ionization around the O 1s edge has been studied both at the 531 eV resonance and above the ionization edge. Resonant and normal Auger processes play a significant role in each case and a large fragmentation of the molecule is observed at both photon energies, with intense fragments such as CHO + and CH 3 + being clearly observed. A near edge X-ray absorption fine structure spectrum of the vanillin molecule was obtained around the O 1s ionization threshold. In addition, the fragmentation of vanillin has also been studied using a fast beam of electrons (800 eV), for the sake of comparison.

Enhanced sensitivity of the RET proto-oncogene to ionizing radiation in vitro.

Science.gov (United States)

Volpato, Claudia Béu; Martínez-Alfaro, Minerva; Corvi, Raffaella; Gabus, Coralie; Sauvaigo, Sylvie; Ferrari, Pietro; Bonora, Elena; De Grandi, Alessandro; Romeo, Giovanni

2008-11-01

Exposure to ionizing radiation is a well-known risk factor for a number of human cancers, including leukemia and thyroid cancer. It has been known for a long time that exposure of cells to radiation results in extensive DNA damage; however, a small number of studies have tried to explain the mechanisms of radiation-induced carcinogenesis. The high prevalence of RET/PTC rearrangements in patients who have received external radiation, and the evidence of in vitro induction of RET rearrangements in human cells, suggest an enhanced sensitivity of the RET genomic region to damage by ionizing radiation. To assess whether RET is indeed more sensitive to radiations than other genomic regions, we used a COMET assay coupled with fluorescence in situ hybridization, which allows the measurement of DNA fragmentation in defined genomic regions of single cells. We compared the initial DNA damage of the genomic regions of RET, CXCL12/SDF1, ABL, MYC, PLA2G2A, p53, and JAK2 induced by ionizing radiation in both a lymphoblastoid and a fetal thyroid cell line. In both cell lines, RET fragmentation was significantly higher than in other genomic regions. Moreover, a differential distribution of signals within the COMET was associated with a higher percentage of RET fragments in the tail. RET was more susceptible to fragmentation in the thyroid-derived cells than in lymphoblasts. This enhanced susceptibility of RET to ionizing radiation suggests the possibility of using it as a radiation exposure marker.

Laser desorption/ionization from nanostructured surfaces: nanowires, nanoparticle films and silicon microcolumn arrays

International Nuclear Information System (INIS)

Chen Yong; Luo Guanghong; Diao Jiajie; Chornoguz, Olesya; Reeves, Mark; Vertes, Akos

2007-01-01

Due to their optical properties and morphology, thin films formed of nanoparticles are potentially new platforms for soft laser desorption/ionization (SLDI) mass spectrometry. Thin films of gold nanoparticles (with 12±1 nm particle size) were prepared by evaporation-driven vertical colloidal deposition and used to analyze a series of directly deposited polypeptide samples. In this new SLDI method, the required laser fluence for ion detection was equal or less than what was needed for matrix-assisted laser desorption/ionization (MALDI) but the resulting spectra were free of matrix interferences. A silicon microcolumn array-based substrate (a.k.a. black silicon) was developed as a new matrix-free laser desorption ionization surface. When low-resistivity silicon wafers were processed with a 22 ps pulse length 3xω Nd:YAG laser in air, SF 6 or water environment, regularly arranged conical spikes emerged. The radii of the spike tips varied with the processing environment, ranging from approximately 500 nm in water, to ∼2 μm in SF 6 gas and to ∼5 μm in air. Peptide mass spectra directly induced by a nitrogen laser showed the formation of protonated ions of angiotensin I and II, substance P, bradykinin fragment 1-7, synthetic peptide, pro14-arg, and insulin from the processed silicon surfaces but not from the unprocessed areas. Threshold fluences for desorption/ionization were similar to those used in MALDI. Although compared to silicon nanowires the threshold laser pulse energy for ionization is significantly (∼10x) higher, the ease of production and robustness of microcolumn arrays offer complementary benefits

Multiphoton ionization of (Xe)n and (NO)n clusters using a picosecond laser

International Nuclear Information System (INIS)

Smith, D.B.; Miller, J.C.

1989-01-01

Mass-resolved multiphoton ionization (MPI) spectroscopy is an established technique for detecting and analyzing van der Waals molecules and larger clusters. MPI spectroscopy provides excellent detection sensitivity, moderately high resolution, and selectivity among cluster species. In addition to information provided by the analysis of photoions following MPI, photoelectron spectroscopy can reveal details regarding the structure of ionic states. Unfortunately, the technique is limited by its tendency to produce extensive fragmentation. Fragmentation is also a problem with other ionization techniques (e.g., electron impact ionization), but the intense laser beams required for MPI cause additional dissociation channels to become available. These channels include absorption of additional photons by parent ions (ion ladder mechanism), absorption of additional photons by fragment ions (ladder switching mechanism), and resonances with dissociative states in the neutral manifold. The existence of these dissociation channels can preclude the use of MPI spectroscopy in many situations. Recently, MPI studies of stable molecules using picosecond lasers (pulse length = 1 - 10 ps) have indicated that limitations due to fragmentation might be subdued. With picosecond lasers, dissociation mechanisms can be altered and in some cases fragmentation can be eliminated or reduced. Additional photon absorption competes effectively with dissociation channels when a very short laser pulse or, perhaps more importantly, a sufficiently high peak-power is used. In the case where ionic absorption and fragmentation occurs, it has been shown that picosecond MPI might favor the ion ladder mechanism rather than the ladder switching mechanism

Fragmentation in DNA double-strand breaks

International Nuclear Information System (INIS)

Wei Zhiyong; Suzhou Univ., Suzhou; Zhang Lihui; Li Ming; Fan Wo; Xu Yujie

2005-01-01

DNA double strand breaks are important lesions induced by irradiations. Random breakage model or quantification supported by this concept is suitable to analyze DNA double strand break data induced by low LET radiation, but deviation from random breakage model is more evident in high LET radiation data analysis. In this work we develop a new method, statistical fragmentation model, to analyze the fragmentation process of DNA double strand breaks. After charged particles enter the biological cell, they produce ionizations along their tracks, and transfer their energies to the cells and break the cellular DNA strands into fragments. The probable distribution of the fragments is obtained under the condition in which the entropy is maximum. Under the approximation E≅E 0 + E 1 l + E 2 l 2 , the distribution functions are obtained as exp(αl + βl 2 ). There are two components, the one proportional to exp(βl 2 ), mainly contributes to the low mass fragment yields, the other component, proportional to exp(αl), decreases slowly as the mass of the fragments increases. Numerical solution of the constraint equations provides parameters α and β. Experimental data, especially when the energy deposition is higher, support the statistical fragmentation model. (authors)

The multiphoton ionization of uranium hexafluoride

International Nuclear Information System (INIS)

Armstrong, D.P.

1992-05-01

Multiphoton ionization (MPI) time-of-flight mass spectroscopy and photoelectron spectroscopy studies of UF 6 have been conducted using focused light from the Nd:YAG laser fundamental (λ=1064 nm) and its harmonics (λ=532, 355, or 266 nm), as well as other wavelengths provided by a tunable dye laser. The MPI mass spectra are dominated by the singly and multiply charged uranium ions rather than by the UF x + fragment ions even at the lowest laser power densities at which signal could be detected. The laser power dependence of U n+ ions signals indicates that saturation can occur for many of the steps required for their ionization. In general, the doubly-charged uranium ion (U 2+ ) intensity is much greater than that of the singly-charged uranium ion (U + ). For the case of the tunable dye laser experiments, the U n+ (n = 1- 4) wavelength dependence is relatively unstructured and does not show observable resonance enhancement at known atomic uranium excitation wavelengths. The dominance of the U 2+ ion and the absence or very small intensities of UF x + fragments, along with the unsaturated wavelength dependence, indicate that mechanisms may exist other than ionization of bare U atoms after the stepwise photodissociation of F atoms from the parent molecule

Scaling and universality in binary fragmenting with inhibition

International Nuclear Information System (INIS)

Ploszajczak, M.; Botet, R.

1994-01-01

We investigate a new model of binary fragmentation with inhibition, driven by the white noise. In a broad range of fragmentation probabilities, the power-law spatio-temporal correlations ar found to arise due to self-organized criticality (SOC). We find in the SOC phase a non-trivial power spectrum of the temporal sequence of the fragmentation events. The 1/∫ behaviour is recovered in the irreversible, near-equilibrium part of this phase. (authors). 13 refs., 3 figs., 1 tab

Scaling and universality in binary fragmenting with inhibition

Energy Technology Data Exchange (ETDEWEB)

Ploszajczak, M [Grand Accelerateur National d` Ions Lourds (GANIL), 14 - Caen (France); Botet, R [Paris-11 Univ., 91 - Orsay (France). Lab. de Physique des Solides

1994-12-31

We investigate a new model of binary fragmentation with inhibition, driven by the white noise. In a broad range of fragmentation probabilities, the power-law spatio-temporal correlations ar found to arise due to self-organized criticality (SOC). We find in the SOC phase a non-trivial power spectrum of the temporal sequence of the fragmentation events. The 1/{integral} behaviour is recovered in the irreversible, near-equilibrium part of this phase. (authors). 13 refs., 3 figs., 1 tab.

Dynamic modification of the fragmentation of COq+ excited states generated with high-order harmonics

International Nuclear Information System (INIS)

Cao, W.; De, S.; Singh, K. P.; Chen, S.; Laurent, G.; Ray, D.; Ben-Itzhak, I.; Cocke, C. L.; Schoeffler, M. S.; Belkacem, A.; Osipov, T.; Rescigno, T.; Alnaser, A. S.; Bocharova, I. A.; Zherebtsov, S.; Kling, M. F.; Litvinyuk, I. V.

2010-01-01

The dynamic process of fragmentation of CO q+ excited states is investigated using a pump-probe approach. EUV radiation (32-48 eV) generated by high-order harmonics was used to ionize and excite CO molecules and a time-delayed infrared (IR) pulse (800 nm) was used to influence the evolution of the dissociating multichannel wave packet. Two groups of states, separable experimentally by their kinetic-energy release (KER), are populated by the EUV and lead to C + -O + fragmentation: direct double ionization of the neutral molecule and fragmentation of the cation leading to C + -O*, followed by autoionization of O*. The IR pulse was found to modify the KER of the latter group in a delay-dependent way which is explained with a model calculation.

Measurement of Fragment Mass Distributions in Neutron-induced Fission of {sup 238}U and {sup 232}Th at Intermediate Energies

Energy Technology Data Exchange (ETDEWEB)

Simutkin, V.D. [Uppsala University, P.O Box 525, SE-751 20 Uppsala (Sweden)

2008-07-01

Conceptual analysis of accelerator-driven systems assumes extensive use of nuclear data on neutron-induced reactions at intermediate energies. In particular, information about the fission fragment yields from the {sup 238}U(n,f) and {sup 232}Th(n,f) reactions is of particular interest at neutron energies from 10 to 200 MeV. However, there is a lack of such data for both {sup 238}U and {sup 232}Th. Up to now, the intermediate energy measurements have been performed for {sup 238}U only, and there are no data for the {sup 232}Th(n,f) reaction. The aim of the work is to provide such data. Fission fragment mass distributions for the {sup 232}Th(n,f) and {sup 238}U(n,f) reactions have been measured for the incident neutron energies 32.8 MeV, 45.3 MeV and 59.9 MeV. The experiments have been performed at the neutron beam facility of the Universite Catholique de Louvain, Belgium. A multi-section Frisch-gridded ionization chamber has been used as a fission fragment detector. The data obtained have been interpreted in terms of the multimodal random neck-rupture model (MMRNRM). (authors)

Nonsequential double ionization of D2 molecules with intense 20-fs pulses

DEFF Research Database (Denmark)

Sakai, H.; Larsen, J.J.; Wendt-Larsen, I.

2003-01-01

The kinetic-energy distribution of D+ fragments obtained from the ionization of D2 molecules with intense 20-fs pulses includes a high-energy component extending up to ˜10 eV. These fragments are only present for linearly, or slightly elliptically, polarized light. Both the maximum kinetic...

Fragment-based discovery of a potent NAMPT inhibitor.

Science.gov (United States)

Korepanova, Alla; Longenecker, Kenton L; Pratt, Steve D; Panchal, Sanjay C; Clark, Richard F; Lake, Marc; Gopalakrishnan, Sujatha M; Raich, Diana; Sun, Chaohong; Petros, Andrew M

2017-12-12

NAMPT expression is elevated in many cancers, making this protein a potential target for anticancer therapy. We have carried out both NMR based and TR-FRET based fragment screens against human NAMPT and identified six novel binders with a range of potencies. Co-crystal structures were obtained for two of the fragments bound to NAMPT while for the other four fragments force-field driven docking was employed to generate a bound pose. Based on structural insights arising from comparison of the bound fragment poses to that of bound FK866 we were able to synthetically elaborate one of the fragments into a potent NAMPT inhibitor. Copyright © 2017 Elsevier Ltd. All rights reserved.

Bound-Electron Nonlinearity Beyond the Ionization Threshold

Science.gov (United States)

Wahlstrand, J. K.; Zahedpour, S.; Bahl, A.; Kolesik, M.; Milchberg, H. M.

2018-05-01

We present absolute space- and time-resolved measurements of the ultrafast laser-driven nonlinear polarizability in argon, krypton, xenon, nitrogen, and oxygen up to ionization fractions of a few percent. These measurements enable determination of the strongly nonperturbative bound-electron nonlinear polarizability well beyond the ionization threshold, where it is found to remain approximately quadratic in the laser field, a result normally expected at much lower intensities where perturbation theory applies.

Bound electron nonlinearity beyond the ionization threshold

OpenAIRE

Wahlstrand, J. K.; Zahedpour, S.; Bahl, A.; Kolesik, M.; Milchberg, H. M.

2018-01-01

Although high field laser-induced ionization is a fundamental process underlying many applications, there have been no absolute measurements of the nonlinear polarizability of atoms and molecules in the presence of ionization. Such information is crucial, for example, for understanding the propagation of high intensity ultrashort pulses in matter. Here, we present absolute space- and time-resolved measurements of the ultrafast laser-driven nonlinear polarizability in argon, krypton, xenon, ni...

Tandem mass spectrometry characteristics of polyester anions and cations formed by electrospray ionization.

Science.gov (United States)

Arnould, Mark A; Buehner, Rita W; Wesdemiotis, Chrys; Vargas, Rafael

2005-01-01

Electrospray ionization of polyesters composed of isophthalic acid and neopentyl glycol produces carboxylate anions in negative mode and mainly sodium ion adducts in positive mode. A tandem mass spectrometry (MS/MS) study of these ions in a quadrupole ion trap shows that the collisionally activated dissociation pathways of the anions are simpler than those of the corresponding cations. Charge-remote fragmentations predominate in both cases, but the spectra obtained in negative mode are devoid of the complicating cation exchange observed in positive mode. MS/MS of the Na(+) adducts gives rise to a greater number of fragments but not necessarily more structural information. In either positive or negative mode, polyester oligomers with different end groups fragment by similar mechanisms. The observed fragments are consistent with rearrangements initiated by the end groups. Single-stage ESI mass spectra also are more complex in positive mode because of extensive H/Na substitutions; this is also true for matrix-assisted laser desorption ionization (MALDI) mass spectra. Hence, formation and analysis of anions might be the method of choice for determining block length, end group structure and copolymer sequence, provided the polyester contains at least one carboxylic acid end group that is ionizable to anions.

Multiphoton ionization/dissociation of osmium tetroxide

International Nuclear Information System (INIS)

Ding, D.; Puretzky, A.A.; Compton, R.N.

1993-01-01

The mechanisms leading to laser multiphoton ionization and dissociation (MPI/MPD) of osmium tetroxide (OsO 4 ) have been investigated from measurements of the kinetic energies of product ions (Os + , Os 2+ , OsO + , O 2 + , O + ) and photoelectrons as a function of the laser wavelength. Neutral channels, intermediate to the dominant Os + ionization channel, such as OsO 4 →OsO 4-n +nO are examined using resonance-enhanced multiphoton ionization (REMPI) of the fast O atoms. Equipartition of the available photon energy among the fragments is observed. The wavelength dependence of the Os + ion signal suggests that one or more of the steps leading to Os + ions involve molecular ions and/or excited neutral atoms. The observed preponderance of very slow ( 2+ is shown to result primarily from REMPI of Os +

Knowledge-based Fragment Binding Prediction

Science.gov (United States)

Tang, Grace W.; Altman, Russ B.

2014-01-01

Target-based drug discovery must assess many drug-like compounds for potential activity. Focusing on low-molecular-weight compounds (fragments) can dramatically reduce the chemical search space. However, approaches for determining protein-fragment interactions have limitations. Experimental assays are time-consuming, expensive, and not always applicable. At the same time, computational approaches using physics-based methods have limited accuracy. With increasing high-resolution structural data for protein-ligand complexes, there is now an opportunity for data-driven approaches to fragment binding prediction. We present FragFEATURE, a machine learning approach to predict small molecule fragments preferred by a target protein structure. We first create a knowledge base of protein structural environments annotated with the small molecule substructures they bind. These substructures have low-molecular weight and serve as a proxy for fragments. FragFEATURE then compares the structural environments within a target protein to those in the knowledge base to retrieve statistically preferred fragments. It merges information across diverse ligands with shared substructures to generate predictions. Our results demonstrate FragFEATURE's ability to rediscover fragments corresponding to the ligand bound with 74% precision and 82% recall on average. For many protein targets, it identifies high scoring fragments that are substructures of known inhibitors. FragFEATURE thus predicts fragments that can serve as inputs to fragment-based drug design or serve as refinement criteria for creating target-specific compound libraries for experimental or computational screening. PMID:24762971

Fragmentation and mean kinetic energy release of the nitrogen molecule

International Nuclear Information System (INIS)

Santos, A.C.F.; Melo, W.S.; Sant'Anna, M.M.; Sigaud, G.M.; Montenegro, E.C.

2007-01-01

Ionization and fragmentation of the N 2 molecule in coincidence with the final projectile charge state have been measured for the impact of 0.188-0.875 MeV/amu He + projectiles. The average kinetic energy release (KER) of the target ionic fragments is derived from the peak widths of their time-of-flight distributions. It is shown that the KER's for singly-charged products follow scaling laws irrespectively to the collision channel

Ionization of nitrogen cluster beam

International Nuclear Information System (INIS)

Yano, Katsuki; Be, S.H.; Enjoji, Hiroshi; Okamoto, Kosuke

1975-01-01

A nitrogen cluster beam (neutral particle intensity of 28.6 mAsub(eq)) is ionized by electron collisions in a Bayard-Alpert gauge type ionizer. The extraction efficiency of about 65% is obtained at an electron current of 10 mA with an energy of 50 eV. The mean cluster size produced at a pressure of 663 Torr and temperature of 77.3 K is 2x10 5 molecules per cluster. By the Coulomb repulsion force, multiply ionized cluster ions are broken up into smaller fragments and the cluster ion size reduces to one-fourth at an electron current of 15 mA. Mean neutral cluster sizes depend strongly on the initial degree of saturation PHI 0 and are 2x10 5 , 7x10 4 and 3x10 4 molecules per cluster at PHI 0 's of 0.87, 0.66 and 0.39, respectively. (auth.)

VUV and soft x-ray ionization of a plant volatile: Vanillin (C{sub 8}H{sub 8}O{sub 3})

Energy Technology Data Exchange (ETDEWEB)

Betancourt, A. Moreno; Moura, C. E. V. de; Rocha, A. B.; Souza, G. G. B. de, E-mail: rafael.bernini@ifrj.edu.br, E-mail: gerson@iq.ufrj.br [Instituto de Química, Universidade Federal do Rio de Janeiro (UFRJ) 21949-900 Rio de Janeiro–RJ (Brazil); Coutinho, L. H. [Instituto de Física, Universidade Federal do Rio de Janeiro (UFRJ) 21941-972 Rio de Janeiro–RJ (Brazil); Bernini, R. B., E-mail: rafael.bernini@ifrj.edu.br, E-mail: gerson@iq.ufrj.br [Instituto Federal de Ciência e Tecnologia do Rio de Janeiro (IFRJ), 25050-100 Duque de Caxias–RJ (Brazil)

2016-03-21

Plant volatiles are emitted by plants in response to several forms of stress, including interaction with energetic photons. In the present work, we discuss the interaction of extreme UV and soft X-ray photons with a plant volatile, vanillin. The single and double (multiple) ionization of the vanillin molecule have been studied for the first time using time-of-flight mass spectrometry and VUV and soft X-ray photons (synchrotron radiation, at 12.0 eV, 21.2 eV, 130 eV, 310 eV, 531 eV, and 550 eV). At 12.0 and 21.2 eV, only singly charged species are observed and the parent ion, C{sub 8}H{sub 8}O{sub 3}{sup +}, is the dominant species. Energy differences for some selected fragments were calculated theoretically in this energy region. At 130 eV, direct double and triple ionization of the valence electrons may occur. The fragmentation increases and CHO{sup +} becomes one of the main cations in the mass spectrum. The molecular ion is still the dominant species, but other fragments, such as C{sub 6}H{sub 5}O{sup +}, begin to present similar intensities. At 310 eV, C 1s electrons may be ionized and Auger processes give rise to dissociative doubly ionized cations. Ionization around the O 1s edge has been studied both at the 531 eV resonance and above the ionization edge. Resonant and normal Auger processes play a significant role in each case and a large fragmentation of the molecule is observed at both photon energies, with intense fragments such as CHO{sup +} and CH{sub 3}{sup +} being clearly observed. A near edge X-ray absorption fine structure spectrum of the vanillin molecule was obtained around the O 1s ionization threshold. In addition, the fragmentation of vanillin has also been studied using a fast beam of electrons (800 eV), for the sake of comparison.

[Fragment-based drug discovery: concept and aim].

Science.gov (United States)

Tanaka, Daisuke

2010-03-01

Fragment-Based Drug Discovery (FBDD) has been recognized as a newly emerging lead discovery methodology that involves biophysical fragment screening and chemistry-driven fragment-to-lead stages. Although fragments, defined as structurally simple and small compounds (typically FBDD primarily turns our attention to weakly but specifically binding fragments (hit fragments) as the starting point of medicinal chemistry. Hit fragments are then promoted to more potent lead compounds through linking or merging with another hit fragment and/or attaching functional groups. Another positive aspect of FBDD is ligand efficiency. Ligand efficiency is a useful guide in screening hit selection and hit-to-lead phases to achieve lead-likeness. Owing to these features, a number of successful applications of FBDD to "undruggable targets" (where HTS and other lead identification methods failed to identify useful lead compounds) have been reported. As a result, FBDD is now expected to complement more conventional methodologies. This review, as an introduction of the following articles, will summarize the fundamental concepts of FBDD and will discuss its advantages over other conventional drug discovery approaches.

Negative Ion In-Source Decay Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry for Sequencing Acidic Peptides

Science.gov (United States)

McMillen, Chelsea L.; Wright, Patience M.; Cassady, Carolyn J.

2016-05-01

Matrix-assisted laser desorption/ionization (MALDI) in-source decay was studied in the negative ion mode on deprotonated peptides to determine its usefulness for obtaining extensive sequence information for acidic peptides. Eight biological acidic peptides, ranging in size from 11 to 33 residues, were studied by negative ion mode ISD (nISD). The matrices 2,5-dihydroxybenzoic acid, 2-aminobenzoic acid, 2-aminobenzamide, 1,5-diaminonaphthalene, 5-amino-1-naphthol, 3-aminoquinoline, and 9-aminoacridine were used with each peptide. Optimal fragmentation was produced with 1,5-diaminonphthalene (DAN), and extensive sequence informative fragmentation was observed for every peptide except hirudin(54-65). Cleavage at the N-Cα bond of the peptide backbone, producing c' and z' ions, was dominant for all peptides. Cleavage of the N-Cα bond N-terminal to proline residues was not observed. The formation of c and z ions is also found in electron transfer dissociation (ETD), electron capture dissociation (ECD), and positive ion mode ISD, which are considered to be radical-driven techniques. Oxidized insulin chain A, which has four highly acidic oxidized cysteine residues, had less extensive fragmentation. This peptide also exhibited the only charged localized fragmentation, with more pronounced product ion formation adjacent to the highly acidic residues. In addition, spectra were obtained by positive ion mode ISD for each protonated peptide; more sequence informative fragmentation was observed via nISD for all peptides. Three of the peptides studied had no product ion formation in ISD, but extensive sequence informative fragmentation was found in their nISD spectra. The results of this study indicate that nISD can be used to readily obtain sequence information for acidic peptides.

Time delay between singly and doubly ionizing wavepackets in laser-driven helium

International Nuclear Information System (INIS)

Parker, J S; Doherty, B J S; Meharg, K J; Taylor, K T

2003-01-01

We present calculations of the time delay between single and double ionization of helium, obtained from full-dimensionality numerical integrations of the helium-laser Schroedinger equation. The notion of a quantum mechanical time delay is defined in terms of the interval between correlated bursts of single and double ionization. Calculations are performed at 390 and 780 nm in laser intensities that range from 2 x 10 14 to 14 x 10 14 Wcm -2 . We find results consistent with the rescattering model of double ionization but supporting its classical interpretation only at 780 nm. (letter to the editor)

Effects of ionizing radiations on proteins

International Nuclear Information System (INIS)

Maire, M. le; Foresta, B. de; Viel, A.; Thauvette, L.; Beauregard, G.; Potier, M.

1990-01-01

We have reinvestigated the use of ionizing radiations to measure the molecular mass of water-soluble or membrane proteins. Exposure of purified standard proteins to increasing doses of ionizing radiation causes progressive fragmentation of the native protein into defined peptide patterns. The coloured band corresponding to the intact protein was measured on the SDS gel as a function of dose to determine the dose (D 37.t ) corresponding to 37% of the initial amount of unfragmented protein deposited on the gel. This led to a calibration curve and the known molecular mass of the standard proteins. However, we have to conclude that this method is useless to determine the state of aggregation of a protein, since, for all the oligomers tested, the best fit was obtained by using the protomeric molecular mass, suggesting that there is no energy transfer between protomers. Furthermore, SDS greatly increases the fragmentation rate of proteins, which suggests additional calibration problems for membrane proteins in detergent or in the lipid bilayer. The main drawback of the technique is that some proteins behaved anomalously, leading to very large errors in the apparent target size as compared with true molecular mass. It is thus unreliable to apply the radiation method for absolute molecular-mass determination. We then focused on the novel finding that discrete fragmentation of proteins occurs at preferential sites, and this was studied with aspartate transcarbamylase. (author)

Ionization photophysics and Rydberg spectroscopy of diacetylene

KAUST Repository

Schwell, Martin

2012-11-01

Photoionization of diacetylene was studied using synchrotron radiation over the range 8-24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron-photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IE ad=(10.17±0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE=(16.15±0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions C+ 4, C3H+, C+3 and C 4H+. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11-13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσg, n=4-11), R2(ndσg, n=4-7) and R3(ndδg, n=4-6) converging to the A2Πu state of the cation, and to a new series R01(nsσg, n=3) converging to the B\\' 2Σ+u state of the cation. The autoionization mechanisms and their consistence with specific selection rules are discussed. © 2012 Taylor and Francis.

Ionization photophysics and Rydberg spectroscopy of diacetylene

KAUST Repository

Schwell, Martin; Bé nilan, Yves; Fray, Nicolas; Gazeau, Marie Claire; Es-sebbar, Et-touhami; Gaie-Levrel, Franç ois; Champion, Norbert; Leach, Sydney Sydney

2012-01-01

Photoionization of diacetylene was studied using synchrotron radiation over the range 8-24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron-photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IE ad=(10.17±0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE=(16.15±0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions C+ 4, C3H+, C+3 and C 4H+. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11-13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσg, n=4-11), R2(ndσg, n=4-7) and R3(ndδg, n=4-6) converging to the A2Πu state of the cation, and to a new series R01(nsσg, n=3) converging to the B' 2Σ+u state of the cation. The autoionization mechanisms and their consistence with specific selection rules are discussed. © 2012 Taylor and Francis.

Fission dynamics as brought out in cold fragmentation studies

International Nuclear Information System (INIS)

Signarbieux, G.

1986-10-01

Fission dynamics problem has been addressed since the beginning. This paper is specifically concerned by ''even-odd effects '' in fragment distribution. These effects are reinterpreted, some complementary thoughts on double ionization chamber are given together with a study of fission dymanics at low energy [fr

Fragmentation dynamics of molecular hydrogen in strong ultrashort laser pulses

International Nuclear Information System (INIS)

Rudenko, A; Feuerstein, B; Zrost, K; Jesus, V L B de; Ergler, T; Dimopoulou, C; Schroeter, C D; Moshammer, R; Ullrich, J

2005-01-01

We present the results of a systematic experimental study of dissociation and Coulomb explosion of molecular hydrogen induced by intense ultrashort (7-25 fs) laser pulses. Using coincident recoil-ion momentum spectroscopy we can distinguish the contributions from dissociation and double ionization even if they result in the same kinetic energies of the fragments. The dynamics of all fragmentation channels drastically depends on the pulse duration, and for 7 fs pulses becomes extremely sensitive to the pulse shape

ACE-SWICS In Situ Plasma Composition of Fragmented Comet 73P/Schwassmann-Wachmann 3

Science.gov (United States)

Gilbert, J. A.; Lepri, S. T.; Rubin, M.; Zurbuchen, T.

2013-12-01

The interiors of comets contain some of the most pristine material in the solar system. Comet 73P/Schwassmann-Wachmann 3, discovered in 1930 with a double nucleus, is a Jupiter-family comet with a 5.34-year period. This comet split into 5 fragments in 1995 and disintegrated into nearly 70 pieces in 2006. In May and June of 2006, recently ionized cometary particles originating from some of these fragments were collected with the ACE-SWICS sensor. Due to a combination of the close proximity of the fragments passing between ACE-SWICS and the Sun, and the instrument characteristics, unique measurements regarding the charge state composition and the elemental abundances of both cometary and heliospheric plasma were made during this time. The cometary material released from some of these fragments can be identified by the concentrations of water-group pick-up ions having a mass-per-charge of 16-18 amu/e. With a focus on Helium, Carbon, and water-group ions, we present an analysis of the cometary plasma. Charge state ratios of C+/O+ fall below 0.1 during detection of comet fragment plasma, and there is a clear increase in He+ during fragment crossings. The C/O ratio and He charge states are used to provide constraints on the activity of the cometary fragments and also the spatial distribution of the extended and ionized cometary tail.

Double-electron ionization driven by inhomogeneous fields

Czech Academy of Sciences Publication Activity Database

Chacon, A.; Ortmann, L.; Cucchietti, F.; Suarez, N.; Perez-Hernandez, J.A.; Ciappina, Marcelo F.; Landsman, A.S.; Lewenstein, M.

2017-01-01

Roč. 123, č. 4 (2017), 1-11, č. článku 116. ISSN 0946-2171 R&D Projects: GA MŠk EF15_008/0000162; GA MŠk LQ1606 EU Projects: European Commission(XE) 654148 - LASERLAB-EUROPE Grant - others:ELI Beamlines(XE) CZ.02.1.01/0.0/0.0/15_008/0000162 Institutional support: RVO:68378271 Keywords : nonsequential double-ionization * harmonic-generation * laser fields * helium * model * emission * single * atom * ion * He Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 1.696, year: 2016

Target Plate Material Influence on Fullerene-C60 Laser Desorption/Ionization Efficiency

Science.gov (United States)

Zeegers, Guido P.; Günthardt, Barbara F.; Zenobi, Renato

2016-04-01

Systematic laser desorption/ionization (LDI) experiments of fullerene-C60 on a wide range of target plate materials were conducted to gain insight into the initial ion formation in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The positive and negative ion signal intensities of precursor, fragment, and cluster ions were monitored, varying both the laser fluence (0-3.53 Jcm-2) and the ion extraction delay time (0-950 ns). The resulting species-specific ion signal intensities are an indication for the ionization mechanisms that contribute to LDI and the time frames in which they operate, providing insight in the (MA)LDI primary ionization. An increasing electrical resistivity of the target plate material increases the fullerene-C60 precursor and fragment anion signal intensity. Inconel 625 and Ti90/Al6/V4, both highly electrically resistive, provide the highest anion signal intensities, exceeding the cation signal intensity by a factor ~1.4 for the latter. We present a mechanism based on transient electrical field strength reduction to explain this trend. Fullerene-C60 cluster anion formation is negligible, which could be due to the high extraction potential. Cluster cations, however, are readily formed, although for high laser fluences, the preferred channel is formation of precursor and fragment cations. Ion signal intensity depends greatly on the choice of substrate material, and careful substrate selection could, therefore, allow for more sensitive (MA)LDI measurements.

Thermionic detection of the ionic fragments of continiuum-state pair absorption systems

International Nuclear Information System (INIS)

Hotop, R.; Niemax, K.; Richter, J.; Weber, K.H.

1981-01-01

Using a thermionic diode we have detected the ionic fragments formed by associative ionization and dissociation after continuum-state pair absorption processes in Cs-Cs and Cs-K systems. Assuming an ionization probability of unity of the excited species and calibrating the pair absorption bands by taking into account the known photoionization cross section of the atoms we found excellent agreement with data from classical absorption measurements. (orig.)

Peptides derivatized with bicyclic quaternary ammonium ionization tags. Sequencing via tandem mass spectrometry.

Science.gov (United States)

Setner, Bartosz; Rudowska, Magdalena; Klem, Ewelina; Cebrat, Marek; Szewczuk, Zbigniew

2014-10-01

Improving the sensitivity of detection and fragmentation of peptides to provide reliable sequencing of peptides is an important goal of mass spectrometric analysis. Peptides derivatized by bicyclic quaternary ammonium ionization tags: 1-azabicyclo[2.2.2]octane (ABCO) or 1,4-diazabicyclo[2.2.2]octane (DABCO), are characterized by an increased detection sensitivity in electrospray ionization mass spectrometry (ESI-MS) and longer retention times on the reverse-phase (RP) chromatography columns. The improvement of the detection limit was observed even for peptides dissolved in 10 mM NaCl. Collision-induced dissociation tandem mass spectrometry of quaternary ammonium salts derivatives of peptides showed dominant a- and b-type ions, allowing facile sequencing of peptides. The bicyclic ionization tags are stable in collision-induced dissociation experiments, and the resulted fragmentation pattern is not significantly influenced by either acidic or basic amino acid residues in the peptide sequence. Obtained results indicate the general usefulness of the bicyclic quaternary ammonium ionization tags for ESI-MS/MS sequencing of peptides. Copyright © 2014 John Wiley & Sons, Ltd.

Differentiation of isomeric 2-aryldimethyltetrahydro-5-quinolinones by electron ionization and electrospray ionization mass spectrometry.

Science.gov (United States)

Kumar, Ch Dinesh; Chary, V Naresh; Dinesh, A; Reddy, P S; Srinivas, K; Gayatri, G; Sastry, G N; Prabhakar, S

2011-10-15

A series of isomeric 2-aryl-6,6-dimethyltetrahydro-5-quinolinones (set I) and 2-aryl-7,7-dimethyltetrahydro-5-quinolinones (set II) were studied under positive ion electron ionization (EI) and electrospray ionization (ESI) techniques. Under EI conditions, the molecular ions were found to be less stable in set I isomers, and they resulted in abundant fragment ions, i.e., [M-CH(3)](+), [M-CO](+.), [M-HCO](+), [M-(CH(3),CO)](+), and [M-(CH(3),CH(2)O)](+), when compared with set II isomers. In addition, the set I isomers showed specific fragment ions corresponding to [M-OH](+) and [M-OCH(3)](+). The retro-Diels-Alder (RDA) product ion was always higher in set II isomers. The ESI mass spectra produced [M + H](+) ions, and their decomposition showed favorable loss of CH(3) radical, CH(4) and C(2)H(6) molecules in set I isomers. The set II isomers, however, showed predominant RDA product ions, and specific loss of H(2)O. The selectivity in EI and ESI was attributed to the instability of set I isomers by the presence of a gem-dimethyl group at the α-position, and it was supported by the data from model compounds without a gem-dimethyl group. Density functional theory (DFT) calculations successfully corroborated the fragmentation pathways for diagnostic ions. This study revealed the effect of a gem-dimethyl group located at the α-position to the carbonyl having aromatic/unsaturated carbon on the other side of the carbonyl group. Copyright © 2011 John Wiley & Sons, Ltd.

Ionizing potential waves and high-voltage breakdown streamers.

Science.gov (United States)

Albright, N. W.; Tidman, D. A.

1972-01-01

The structure of ionizing potential waves driven by a strong electric field in a dense gas is discussed. Negative breakdown waves are found to propagate with a velocity proportional to the electric field normal to the wavefront. This causes a curved ionizing potential wavefront to focus down into a filamentary structure, and may provide the reason why breakdown in dense gases propagates in the form of a narrow leader streamer instead of a broad wavefront.

Computational modeling of electrically-driven deposition of ionized polydisperse particulate powder mixtures in advanced manufacturing processes

Science.gov (United States)

Zohdi, T. I.

2017-07-01

A key part of emerging advanced additive manufacturing methods is the deposition of specialized particulate mixtures of materials on substrates. For example, in many cases these materials are polydisperse powder mixtures whereby one set of particles is chosen with the objective to electrically, thermally or mechanically functionalize the overall mixture material and another set of finer-scale particles serves as an interstitial filler/binder. Often, achieving controllable, precise, deposition is difficult or impossible using mechanical means alone. It is for this reason that electromagnetically-driven methods are being pursued in industry, whereby the particles are ionized and an electromagnetic field is used to guide them into place. The goal of this work is to develop a model and simulation framework to investigate the behavior of a deposition as a function of an applied electric field. The approach develops a modular discrete-element type method for the simulation of the particle dynamics, which provides researchers with a framework to construct computational tools for this growing industry.

Photoelectron angular distributions from strong-field ionization of oriented molecules

DEFF Research Database (Denmark)

Holmegaard, Lotte; Hansen, Jonas Lerche; Kalhøj, Line

2010-01-01

The combination of ultrafast light sources with detection of molecular-frame photoelectron angular distributions (MFPADs) is setting new standards for detailed interrogation of molecular dynamics. However, until recently measurement of MFPADs relied on determining the molecular orientation after...... ionization, which is limited to species and processes where ionization leads to fragmentation. An alternative is to fix the molecular frame before ionization. The only demonstrations of such spatial orientation involved aligned small linear nonpolar molecules. Here we extend these techniques to the general...... class of polar molecules. Carbonylsulphide and benzonitrile molecules, fixed in space by combined laser and electrostatic fields, are ionized with intense, circularly polarized 30-fs laser pulses. For carbonylsulphide and benzonitrile oriented in one dimension, the MFPADs exhibit pronounced anisotropies...

Element Distribution and Multiplicity of Heavy Fragments

CERN Multimedia

2002-01-01

This experiment will measure the energy and angular distribution of heavy fragments produced in the reactions of |1|2C on several targets between |2|7Al and |2|3|8U at 86~MeV/u. The systematic investigation of a highly excited interaction region (fireball) by means of a clean N and Z identification of heavy tar fragments, may result in a better understanding of temperature concept and of the degree of equilibration of the local interaction region with respect to the total system. For this investigation a large-area position sensitive ionization chamber of 50~msr solid angle in conjunction with a time-of-flight telescope consisting of parallel-plate detectors will be used. \\\\ \\\\ In order to get information on the transverse momentum transfer and the inelasticity of the collision, the energy of the PROJECTILE-FRAGMENTS will be measured at forward angles with a plastic scintillator hodoscope. In addition to this inclusive measurement correlations between heavy fragments will be investigated by means of three pos...

Theoretical investigation of the ultrafast dissociation of core-ionized water and uracil molecules immersed in liquid water

Energy Technology Data Exchange (ETDEWEB)

Stia, C.R.; Fojon, O.A. [Instituto de Fisica Rosario - CONICET-Universidad Nacional de Rosario, Rosario (Argentina); Gaigeot, M.P. [Laboratoire Analyse et Modelisation pour la Biologie et l' Environnement, LAMBE, UMR-CNRS 8587, Universite d' Evry-Val-d' Essonne, 91 - Evry (France); Institut Universitaire de France, 75 - Paris (France); Vuilleumier, R. [Departement de chimie, Ecole Normale Superieure, 75 - Paris (France); Herve du Penhoat, M.A.; Politis, M.F. [Institut de Mineralogie et de Physique des Milieux Condenses, IMPMC, UMR-CNRS 7590, Universite Pierre et Marie Curie, 75 - Paris (France)

2010-10-15

We present a series of ab initio density functional based calculations of the fragmentation dynamics of core-ionized biomolecules. The computations are performed for pure liquid water, aqueous and isolated Uracil. Core ionization is described by replacing the 1s{sup 2} pseudopotential of one atom of the target molecule (C, N or O) with a pseudopotential for a 1s{sup 1} core-hole state. Our results predict that the dissociation of core-ionized water molecules may be reached during the lifetime of inner-shell vacancy (less than 10 fs), leading to OH bond breakage as a primary outcome. We also observe a second fragmentation channel in which total Coulomb explosion of the ionized water molecule occurs. Fragmentation pathways are found similar for pure water or when the water molecule is in the primary hydration shell of the uracil molecule. In the latter case, the proton may be transferred towards the uracil oxygen atoms. When the core hole is located on the uracil molecule, ultrafast dissociation is only observed in the aqueous environment and for nitrogen-K vacancies, resulting in proton transfers towards the hydrogen-bonded water molecule. (authors)

Ionization and photofragmentation of Ru3(CO)12 and Os3(CO)12

International Nuclear Information System (INIS)

Schalk, Oliver; Josefsson, Ida; Odelius, Michael; Richter, Robert; Prince, Kevin C.; Mucke, Melanie

2015-01-01

In this paper, we use a combination of photoelectron spectroscopy, mass spectrometry, and density functional theory calculations to get a detailed understanding of valence single and double ionization and the subsequent dissociation processes. This is exemplified on benchmark systems, trimetallo-dodecacarbonyls M 3 (CO) 12 with M = Ru, Os, where the energy remaining in the molecule after photoionization can be retrieved by measuring the degree of fragmentation of the molecular ion. The intensity of different mass peaks can thus be directly related to ionization cross sections obtained by photoelectron spectroscopy. We find that the M—CO dissociation energy rises as the number of CO ligands decreases due to dissociation. Moreover, ionization of the CO ligands has a higher cross section than that of the metal center for both single and double ionization. After advanced fragmentation, a CO bond can break and the carbon atom remains bonded to the metal core. In addition, we found that the valence ionization cross sections of M 3 (CO) 12 are maximal at about 40 eV photon energy thus showing a more pronounced shape resonance than Ru and Os-complexes with a single metal atom center. Finally, an np → nd giant resonance absorption causes a significant increase of the ionization cross section above 50 eV for Ru 3 (CO) 12

Molecular-Simulation-Driven Fragment Screening for the Discovery of New CXCL12 Inhibitors.

Science.gov (United States)

Martinez-Rosell, Gerard; Harvey, Matt J; De Fabritiis, Gianni

2018-03-26

Fragment-based drug discovery (FBDD) has become a mainstream approach in drug design because it allows the reduction of the chemical space and screening libraries while identifying fragments with high protein-ligand efficiency interactions that can later be grown into drug-like leads. In this work, we leverage high-throughput molecular dynamics (MD) simulations to screen a library of 129 fragments for a total of 5.85 ms against the CXCL12 monomer, a chemokine involved in inflammation and diseases such as cancer. Our in silico binding assay was able to recover binding poses, affinities, and kinetics for the selected library and was able to predict 8 mM-affinity fragments with ligand efficiencies higher than 0.3. All of the fragment hits present a similar chemical structure, with a hydrophobic core and a positively charged group, and bind to either sY7 or H1S68 pockets, where they share pharmacophoric properties with experimentally resolved natural binders. This work presents a large-scale screening assay using an exclusive combination of thousands of short MD adaptive simulations analyzed with a Markov state model (MSM) framework.

Multiphoton ionization as a probe of molecular photofragmentation: statistical and dynamical energy partitioning in the multiphoton dissociation of nitromethane

International Nuclear Information System (INIS)

Rockney, B.H.

1982-01-01

Multiphoton ionization (MPI) appears in its first use as a probe of laser-induced photofragmentation. Specifically, MPI here reveals the internal and translational energy content of the nascent fragments from the infrared multiphoton dissociation (MPD) of nitromethane (CH 3 NO 2 ). The apparatus for this work consists of a pulsed supersonic molecular beam crossed by two pulsed and focused lasers - a CO 2 laser to induce collision-free unimolecular dissociation of CH 3 NO 2 , and a tunable dye laser following immediately to ionize selectively one of the pair of dissociation fragments for detection by a mass spectrometer and particle multiplier. A computer simulation of each fragment's MPI spectrum, a series of four photon resonances to members of the npsigma/sub u/ Rydberg state of NO 2 and three photon resonances to two vibrational members of the #betta# 1 Rydberg state of CH 3 , aids in determining the fragment's internal energy content. The dye laser is delayed and its focus is traced through a small quarter circle centered at the focus of the CO 2 laser. The flight times of the fragments from the point of dissociation and their laboratory scattering angular distributions at fixed ionizing laser wavelength provide their center of mass recoil velocity distributions. The energy deposited in the fragments evidences a striking mixture of statistical and dynamical energy partitioning. The statistical RRKM theory of unimolecular decomposition accurately predicts the amount of internal energy found in the fragments

Highly informative multiclass profiling of lipids by ultra-high performance liquid chromatography - Low resolution (quadrupole) mass spectrometry by using electrospray ionization and atmospheric pressure chemical ionization interfaces.

Science.gov (United States)

Beccaria, Marco; Inferrera, Veronica; Rigano, Francesca; Gorynski, Krzysztof; Purcaro, Giorgia; Pawliszyn, Janusz; Dugo, Paola; Mondello, Luigi

2017-08-04

A simple, fast, and versatile method, using an ultra-high performance liquid chromatography system coupled with a low resolution (single quadrupole) mass spectrometer was optimized to perform multiclass lipid profiling of human plasma. Particular attention was made to develop a method suitable for both electrospray ionization and atmospheric pressure chemical ionization interfaces (sequentially in positive- and negative-ion mode), without any modification of the chromatographic conditions (mobile phase, flow-rate, gradient, etc.). Emphasis was given to the extrapolation of the structural information based on the fragmentation pattern obtained using atmospheric pressure chemical ionization interface, under each different ionization condition, highlighting the complementary information obtained using the electrospray ionization interface, of support for related molecule ions identification. Furthermore, mass spectra of phosphatidylserine and phosphatidylinositol obtained using the atmospheric pressure chemical ionization interface are reported and discussed for the first time. Copyright © 2017 Elsevier B.V. All rights reserved.

Disturbance driven colony fragmentation as a driver of a coral disease outbreak.

Directory of Open Access Journals (Sweden)

Marilyn E Brandt

Full Text Available In September of 2010, Brewer's Bay reef, located in St. Thomas (U.S. Virgin Islands, was simultaneously affected by abnormally high temperatures and the passage of a hurricane that resulted in the mass bleaching and fragmentation of its coral community. An outbreak of a rapid tissue loss disease among coral colonies was associated with these two disturbances. Gross lesion signs and lesion progression rates indicated that the disease was most similar to the Caribbean coral disease white plague type 1. Experiments indicated that the disease was transmissible through direct contact between colonies, and five-meter radial transects showed a clustered spatial distribution of disease, with diseased colonies being concentrated within the first meter of other diseased colonies. Disease prevalence and the extent to which colonies were bleached were both significantly higher on unattached colony fragments than on attached colonies, and disease occurred primarily on fragments found in direct contact with sediment. In contrast to other recent studies, disease presence was not related to the extent of bleaching on colonies. The results of this study suggest that colony fragmentation and contact with sediment played primary roles in the initial appearance of disease, but that the disease was capable of spreading among colonies, which suggests secondary transmission is possible through some other, unidentified mechanism.

Multiple ionization dynamics of molecules in intense laser fields

International Nuclear Information System (INIS)

Ichimura, Atsushi; Ohyama-Yamaguchi, Tomoko

2005-01-01

A classical field-ionization model is developed for sequential multiple ionization of diatomic and linear triatomic molecules exposed to intense (∼ 10 15 W/cm 2 ) laser fields. The distance R ion of Coulomb explosion is calculated for a combination of fragment charges, by considering nonadiabatic excitation followed by field ionization associated with the inner and outer saddle points. For diatomic molecules (N 2 , NO, and I 2 ), the model explains behaviors observed in experiments, as R ion (21→31) ion (21→22) between competing charge-asymmetric and symmetric channels, and even-odd fluctuation along a principal pathway. For a triatomic molecule CO 2 , a comparison of the model with an experiment suggests that charge-symmetric (or nearly symmetric) channels are dominantly populated. (author)

Resonance ionization laser ion sources for on-line isotope separators (invited)

International Nuclear Information System (INIS)

Marsh, B. A.

2014-01-01

A Resonance Ionization Laser Ion Source (RILIS) is today considered an essential component of the majority of Isotope Separator On Line (ISOL) facilities; there are seven laser ion sources currently operational at ISOL facilities worldwide and several more are under development. The ionization mechanism is a highly element selective multi-step resonance photo-absorption process that requires a specifically tailored laser configuration for each chemical element. For some isotopes, isomer selective ionization may even be achieved by exploiting the differences in hyperfine structures of an atomic transition for different nuclear spin states. For many radioactive ion beam experiments, laser resonance ionization is the only means of achieving an acceptable level of beam purity without compromising isotope yield. Furthermore, by performing element selection at the location of the ion source, the propagation of unwanted radioactivity downstream of the target assembly is reduced. Whilst advances in laser technology have improved the performance and reliability of laser ion sources and broadened the range of suitable commercially available laser systems, many recent developments have focused rather on the laser/atom interaction region in the quest for increased selectivity and/or improved spectral resolution. Much of the progress in this area has been achieved by decoupling the laser ionization from competing ionization processes through the use of a laser/atom interaction region that is physically separated from the target chamber. A new application of gas catcher laser ion source technology promises to expand the capabilities of projectile fragmentation facilities through the conversion of otherwise discarded reaction fragments into high-purity low-energy ion beams. A summary of recent RILIS developments and the current status of laser ion sources worldwide is presented

All-solid-state deep ultraviolet laser for single-photon ionization mass spectrometry.

Science.gov (United States)

Yuan, Chengqian; Liu, Xianhu; Zeng, Chenghui; Zhang, Hanyu; Jia, Meiye; Wu, Yishi; Luo, Zhixun; Fu, Hongbing; Yao, Jiannian

2016-02-01

We report here the development of a reflectron time-of-flight mass spectrometer utilizing single-photon ionization based on an all-solid-state deep ultraviolet (DUV) laser system. The DUV laser was achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2 under the condition of high-purity N2 purging. The unique property of this laser system (177.3-nm wavelength, 15.5-ps pulse duration, and small pulse energy at ∼15 μJ) bears a transient low power density but a high single-photon energy up to 7 eV, allowing for ionization of chemicals, especially organic compounds free of fragmentation. Taking this advantage, we have designed both pulsed nanospray and thermal evaporation sources to form supersonic expansion molecular beams for DUV single-photon ionization mass spectrometry (DUV-SPI-MS). Several aromatic amine compounds have been tested revealing the fragmentation-free performance of the DUV-SPI-MS instrument, enabling applications to identify chemicals from an unknown mixture.

Prompt neutron emission from fragments in spontaneous fission of {sup 244,248}Cm and {sup 252}Cf

Energy Technology Data Exchange (ETDEWEB)

Vorobyev, A. S.; Shcherbakov, O. A. [Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300 (Russian Federation); Dushin, V. N.; Jakovlev, V. A.; Kalinin, V. A.; Petrov, B. F. [V.G. Khlopin Radium Institute, St. Petersburg, 194021 (Russian Federation); Hambsch, F.J [EC-JRC-Institute for Reference Materials and Measurements Retieseweg 111, B-2440 Geel (Belgium); Laptev, A. B. [Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300 (Russian Federation); Japan Nuclear Cycle Development Institute, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan)

2005-07-01

Neutrons emitted in fission were measured separately for each complementary fragment in correlation with fission fragment energies. Two high efficiency Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pin-hole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background and pile-up. The dependencies of these distributions on fragment mass and energy for different energy and mass bins, as well as the mass and energy distribution of the fission fragments are presented and discussed. (authors)

Dynamics of the helium atom close to the full fragmentation threshold: Double ionization

International Nuclear Information System (INIS)

Bouri, C.; Selles, P.; Malegat, L.; Kwato Njock, M. G.

2006-01-01

A complete set of cross sections is presented for photodouble ionization of He at 0.1 eV above the threshold. Special care is taken to clear the asymmetry parameter and the energy differential cross section of any ionization-excitation contribution. As a result, their limiting behaviors for the fully asymmetric partitionings of the excess energy are elucidated, thus shedding light on pending discussions in the field. A reliable scheme follows for computing the fully integrated cross section. Very good agreement is observed between the calculated and measured fully differential cross sections after a detailed reassessment of the experimental normalization procedure. The present findings are compared with the assumptions underlying the Wannier picture of near-threshold double escape

On the SIMS Ionization Probability of Organic Molecules.

Science.gov (United States)

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

2017-06-01

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

A Microchannel Inlet to Reduce High-Velocity Impact Fragmentation of Molecules in Orbital and Fly-by Mass Spectrometers

Science.gov (United States)

Turner, Brandon; Anupriya, Anupriya; Sevy, Eric; Austin, Daniel E.

2017-10-01

Closed source neutral mass spectrometers are often used on flyby missions to characterize the molecular components of planetary exospheres. In a typical closed source, neutrals are thermalized as they deflect off the walls within a spherical antechamber prior to ionization and mass analysis. However, the high kinetic energy of each molecule as it impacts the chamber can lead to fragmentation before the ionization region is reached. Due to this fragmentation, the original composition of the molecule can be altered, leading to ambiguous identification.Even knowing the fragmentation pathways that occur may not allow deconvolution of data to give the correct composition. Only stable, volatile fragments will be observed in the subsequent mass spectrometer and different organic compounds likely give similar fragmentation products. Simply detecting these products will not lead to unambiguous identication of the precursor molecules. Here, we present a hardware solution to this problem—an inlet that reduces the fragmentation of molecules that impact at high velocities.We present a microchannel inlet that reduces the impact fragmentation by allowing the molecules to dissipate kinetic energy faster than their respective dissociation lifetimes. Preliminary calculations indicate that impact-induced fragmentation will be reduced up to three orders of magnitude compared with conventional closed sources by using this inlet. The benefits of such an inlet apply to any orbital or flyby velocity. The microchannel inlet enables detection of semi-volatile molecules that were previously undetectable due to impact fragmentation.

Dose equivalent near the bone-soft tissue interface from nuclear fragments produced by high-energy protons

Science.gov (United States)

Shavers, M. R.; Poston, J. W.; Cucinotta, F. A.; Wilson, J. W.

1996-01-01

During manned space missions, high-energy nucleons of cosmic and solar origin collide with atomic nuclei of the human body and produce a broad linear energy transfer spectrum of secondary particles, called target fragments. These nuclear fragments are often more biologically harmful than the direct ionization of the incident nucleon. That these secondary particles increase tissue absorbed dose in regions adjacent to the bone-soft tissue interface was demonstrated in a previous publication. To assess radiological risks to tissue near the bone-soft tissue interface, a computer transport model for nuclear fragments produced by high energy nucleons was used in this study to calculate integral linear energy transfer spectra and dose equivalents resulting from nuclear collisions of 1-GeV protons transversing bone and red bone marrow. In terms of dose equivalent averaged over trabecular bone marrow, target fragments emitted from interactions in both tissues are predicted to be at least as important as the direct ionization of the primary protons-twice as important, if recently recommended radiation weighting factors and "worst-case" geometry are used. The use of conventional dosimetry (absorbed dose weighted by aa linear energy transfer-dependent quality factor) as an appropriate framework for predicting risk from low fluences of high-linear energy transfer target fragments is discussed.

Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation

Energy Technology Data Exchange (ETDEWEB)

Peters, Thomas; /ZAH, Heidelberg; Klessen, Ralf S.; /ZAH, Heidelberg /KIPAC, Menlo Park; Mac Low, Mordecai-Mark; /Amer. Museum Natural Hist.; Banerjee, Robi; /ZAH, Heidelberg

2010-08-25

Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

Molecular Data for a Biochemical Model of DNA Radiation Damage: Electron Impact Ionization and Dissociative Ionization of DNA Bases and Sugar-Phosphate Backbone

Science.gov (United States)

Dateo, Christopher E.; Fletcher, Graham D.

2004-01-01

As part of the database for building up a biochemical model of DNA radiation damage, electron impact ionization cross sections of sugar-phosphate backbone and DNA bases have been calculated using the improved binary-encounter dipole (iBED) model. It is found that the total ionization cross sections of C3'- and C5'-deoxyribose-phospate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3'- and C5'-deoxyribose-phospate cross sections, differing by less than 10%. Of the four DNA bases, the ionization cross section of guanine is the largest, then in decreasing order, adenine, thymine, and cytosine. The order is in accordance with the known propensity of oxidation of the bases by ionizing radiation. Dissociative ionization (DI), a process that both ionizes and dissociates a molecule, is investigated for cytosine. The DI cross section for the formation of H and (cytosine-Hl)(+), with the cytosine ion losing H at the 1 position, is also reported. The threshold of this process is calculated to be 17.1 eV. Detailed analysis of ionization products such as in DI is important to trace the sequential steps in the biochemical process of DNA damage.

Fragment-Based Drug Discovery of Potent Protein Kinase C Iota Inhibitors.

Science.gov (United States)

Kwiatkowski, Jacek; Liu, Boping; Tee, Doris Hui Ying; Chen, Guoying; Ahmad, Nur Huda Binte; Wong, Yun Xuan; Poh, Zhi Ying; Ang, Shi Hua; Tan, Eldwin Sum Wai; Ong, Esther Hq; Nurul Dinie; Poulsen, Anders; Pendharkar, Vishal; Sangthongpitag, Kanda; Lee, May Ann; Sepramaniam, Sugunavathi; Ho, Soo Yei; Cherian, Joseph; Hill, Jeffrey; Keller, Thomas H; Hung, Alvin W

2018-05-24

Protein kinase C iota (PKC-ι) is an atypical kinase implicated in the promotion of different cancer types. A biochemical screen of a fragment library has identified several hits from which an azaindole-based scaffold was chosen for optimization. Driven by a structure-activity relationship and supported by molecular modeling, a weakly bound fragment was systematically grown into a potent and selective inhibitor against PKC-ι.

Microwave ionization and excitation of Ba Rydberg atoms

International Nuclear Information System (INIS)

Eichmann, U.; Dexter, J.L.; Xu, E.Y.; Gallagher, T.F.

1989-01-01

We have investigated ionization and excitation of the Ba 6sn s 1 S 0 and 6snd 1,3 D 2 series in strong microwave fields. The observed microwave ionization threshold fields, scaling as 0.28 n -5 , and the state mixing fields cannot be completely explained in terms of a single cycle Landau-Zener model. However, by taking into account multiphoton resonant transitions driven by many cycles of the microwave field we have been able to interpret the data. In particular multi-photon transitions have been found to be responsible for apparent resonance structures and for the unexpectedly low mixing fields. Not surprisingly, doubly excited valence states introduce irregularities into both the microwave ionization and the state mixing field values. (orig.)

Dynamics of Neutral Cluster Growth and Cluster Ion Fragmentation for Toluene/Water, Aniline/Argon, and 4-Fluorostyrene/Argon Clusters: Covariance Mapping of the Mass Spectral Data

National Research Council Canada - National Science Library

Foltin, M

1998-01-01

.... To explore sensitivity of the parent ion/fragment ion correlation coefficient to cluster fragmentation, correlation coefficients are measured as a function of ionization photon energy as thresholds...

Comparative study of the dissociative ionization of 1,1,1-trichloroethane using nanosecond and femtosecond laser pulses

CSIR Research Space (South Africa)

Du Plessis, A

2010-03-01

Full Text Available , but different fragmentation patterns. A general trend is that when using femtosecond laser pulses for ionization, the parent molecular ion is observed but not for nanosecond laser ionization. There is also a fundamental interest in laser...-molecule interactions at the high intensities available from femtosecond lasers [12,13]. These papers describe the multiphoton ionization mechanisms termed ladder climbing and ladder switching, which explain the presence of parent molecular ion in ultrashort pulse...

Development of ionization technique for measurement of fast neutron induced fission products yields of {sup 237}Np

Energy Technology Data Exchange (ETDEWEB)

Goverdovski, A.A.; Khryachkov, V.A.; Ketlerov, V.V.; Mitrofanov, V.F.; Ostapenko, Yu.B.; Semenova, N.N.; Fomichev, A.N.; Rodina, L.F. [Institute of Physics and Power Engineering, Obninsk (Russian Federation)

1997-03-01

Twin gridded ionization chamber and corresponding software was designed for measurements of masses, kinetic energies and nuclear charges of fission fragments from fast neutron induced fission of {sup 237}Np. The ionization detector design, electronics, data acquisition and processing system and the test results are presented in this paper. (J.P.N.)

Ionizing and non-ionizing radiations

International Nuclear Information System (INIS)

1994-01-01

The monograph is a small manual to get a knowledge of ionizing and non-ionizing radiations. The main chapters are: - Electromagnetic radiations - Ionizing and non-ionizing radiations - Non-ionizing electromagnetic radiations - Ionizing electromagnetic radiation - Other ionizing radiations - Ionizing radiation effects - The Nuclear Safety Conseil

Matrix-assisted laser desorption/ionization time-of-flight and nano-electrospray ionization ion trap mass spectrometric characterization of 1-cyano-2-substituted-benz[f]isoindole derivatives of peptides for fluorescence detection

DEFF Research Database (Denmark)

Linnemayr, K; Brückner, A; Körner, R

1999-01-01

A series of hexa- to decapeptides (molecular mass range 800-1200) were labeled with naphthalene-2,3-dicarboxaldehyde, which preferentially reacts with the primary amino groups of a peptide. A highly stable peptide conjugate is formed, which allows selective analysis by fluorescence at excitation...... and emission wavelengths of 420 and 490 nm, respectively. After removal of unreacted compounds, the peptide conjugates were characterized by matrix-assisted laser desorption/ionization (MALDI) time-of-flight and nano-electrospray ionization (ESI) ion trap mass spectrometry. They readily form both [M + H]+ ions...... by MALDI and both [M + H]+ and [M + 2H]2+ ions by ESI. Furthermore, the fragmentation behavior of the N-terminally tagged peptides, exhibiting an uncharged N-terminus, was investigated applying post-source decay fragmentation with a curved field reflector and collision-induced dissociation...

An investigation of electronic states of some molecules and molecular cations using mass analyzed threshold ionization and photoinduced Rydberg ionization spectroscopy

Science.gov (United States)

Hofstein, Jason David

1999-11-01

Mass analyzed threshold ionization (MATI) experiments have enabled mapping of the n-dependent Rydberg state survival probability for a series of molecules. Utilizing vacuum and extreme ultraviolet (VUV/XUV) photons, one photon Rydberg manifold spectra of argon, hydrogen chloride, nitrogen, benzene, and oxygen were produced, and the prospects of photoinduced Rydberg ionization (PIRI) experiments examined. It was found that the widths of Rydberg manifolds for the molecules studied are quite different. Hydrogen chloride and nitrogen have the narrowest manifold width, followed by benzene, and then oxygen. These varying widths are most strongly correlated with the angular momentum (i.e., quantum defect) of the initially prepared Rydberg orbital. PIRI experiments required the use of a static cell, rather than a molecular jet assembly, for the more efficient production of higher amounts of VUV/XUV radiation, and hence more Rydberg signal needed to observe PIRI. Armed with the ability to produce tunable VUV/XUV radiation, and to determine the feasibility of a PIRI experiment, the MATI and fragment PIRI spectra of trans-1,3-butadiene (BD) were recorded. The MATI spectrum is vibrationally resolved and was analyzed with the help of ab initio calculations and other published results. The fragment PIRI spectrum of the Aproduction of C3H3+ dominates, but at higher photon energies, C2H4 + is also produced. The production of each fragment showed a definite PIRI wavelength dependence.

Molecular data for a biochemical model of DNA damage: Electron impact ionization and dissociative ionization cross sections of DNA bases and sugar-phosphate backbone

International Nuclear Information System (INIS)

Huo, Winifred M.; Dateo, Christopher E.; Fletcher, Graham D.

2006-01-01

As part of the database for building up a biochemical model of DNA radiation damage, electron impact ionization cross sections of sugar-phosphate backbone and DNA bases have been calculated using the improved binary-encounter dipole (iBED) model. It is found that the total ionization cross sections of C 3 ' - and C 5 ' -deoxyribose-phosphate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C 3 ' - and C 5 ' -deoxyribose-phosphate cross sections, differing by less than 10%, an indication that a building-up principle may be applicable. Of the four DNA bases, the ionization cross section of guanine is the largest, then in decreasing order, adenine, thymine, and cytosine. The order is in accordance with the known propensity of oxidation of the bases by ionizing radiation. Dissociative ionization (DI), a process that both ionizes and dissociates a molecule, is investigated for cytosine. The DI cross section for the formation of H and (cytosine-H1) + , with the cytosine ion losing H at the 1 position, is also reported. The threshold of this process is calculated to be 16.9eV. Detailed analysis of ionization products such as in DI is important to trace the sequential steps in the biochemical process of DNA damage

Frequency of chromosomal aberrations in workers occupationally exposed to ionizing radiations

International Nuclear Information System (INIS)

Spasojevic-Tisma, V.; Joksic, G.; Ilic, Z.; Milanovic, S.; Djuric, J.; Tisma, J.; Celeketic, D.; Cuknic, O.; Perisic, J.; Milacic, S.; Cuknic, O.)

2007-01-01

Subjects occupationally exposed to ionizing radiation (external exposition) are examined for chromosomal aberrations in peripheral blood lymphocytes in comparison to a control group. The average annual absorbed dose, measured by TLD dosimeters, for all three groups did not exceed 2mSv. Continuous exposure to small doses of ionizing radiation causes unstable aberrations in lymphocytes. In this research the largest number of found alterations are of acentric fragments and chromosomal breaks type. The highest occupational risk appears to be for subjects working in manufacturing of radio isotope technetium [sr

Fragmentation of anthracene induced by collisions with 40 keV Ar8+ ions

International Nuclear Information System (INIS)

Brédy, R; Ortéga, C; Ji, M; Bernard, J; Chen, L; Montagne, G; Martin, S

2013-01-01

We report on the fragmentation of anthracene molecular ions C 14 H 10 r+ as a function of the parent ion initial charge r (= 1–4). Neutral anthracene molecules in the gas phase were ionized and excited in collisions with Ar 8+ ions at 40 keV and the mass-to-charge spectra of the parent ions C 14 H 10 r+ (1 ⩽ r ⩽ 4) were obtained. Stable molecular ions C 14 H 10 r+ (1 ⩽ r ⩽ 3) are observed. Branching ratios for the competitive evaporation (loss of neutral fragments) and fragmentation (charge separation) processes were measured for C 14 H 10 2+ parent ions. For C 14 H 10 3+ parent ions, the results indicate that fragmentation is the only dominant process and quasi-symmetric fission is observed. (paper)

Communication: Electron ionization of DNA bases

Energy Technology Data Exchange (ETDEWEB)

Rahman, M. A.; Krishnakumar, E., E-mail: ekkumar@tifr.res.in

2016-04-28

No reliable experimental data exist for the partial and total electron ionization cross sections for DNA bases, which are very crucial for modeling radiation damage in genetic material of living cell. We have measured a complete set of absolute partial electron ionization cross sections up to 500 eV for DNA bases for the first time by using the relative flow technique. These partial cross sections are summed to obtain total ion cross sections for all the four bases and are compared with the existing theoretical calculations and the only set of measured absolute cross sections. Our measurements clearly resolve the existing discrepancy between the theoretical and experimental results, thereby providing for the first time reliable numbers for partial and total ion cross sections for these molecules. The results on fragmentation analysis of adenine supports the theory of its formation in space.

III. Penning ionization, associative ionization and chemi-ionization processes

International Nuclear Information System (INIS)

Cermak, V.

1975-01-01

Physical mechanisms of three important ionization processes in a cold plasma and the methods of their experimental study are discussed. An apparatus for the investigation of the Penning ionization using ionization processes of long lived metastable rare gas atoms is described. Methods of determining interaction energies and ionization rates from the measured energy spectra of the originating electrons are described and illustrated by several examples. Typical associative ionization processes are listed and the ionization rates are compared with those of the Penning ionization. Interactions with short-lived excited particles and the transfer of excitation without ionization are discussed. (J.U.)

Sperm quality and DNA damage in men from Jilin Province, China, who are occupationally exposed to ionizing radiation.

Science.gov (United States)

Zhou, D D; Hao, J L; Guo, K M; Lu, C W; Liu, X D

2016-03-22

Long-term radiation exposure affects human health. Ionizing radiation has long been known to raise the risk of cancer. In addition to high doses of radiation, low-dose ionizing radiation might increase the risk of cardiovascular disease, lens opacity, and some other non-cancerous diseases. Low- and high-dose exposures to ionizing radiation elicit different signaling events at the molecular level, and may involve different response mechanisms. The health risks arising from exposure to low doses of ionizing radiation should be re-evaluated. Health workers exposed to ionizing radiation experience low-dose radiation and have an increased risk of hematological malignancies. Reproductive function is sensitive to changes in the physical environment, including ionizing radiation. However, data is scarce regarding the association between occupational radiation exposure and risk to human fertility. Sperm DNA integrity is a functional parameter of male fertility evaluation. Hence, we aimed to report sperm quality and DNA damage in men from Jilin Province, China, who were occupationally exposed to ionizing radiation. Sperm motility and normal morphology were significantly lower in the exposed compared with the non-exposed men. There was no statistically significant difference in sperm concentration between exposed and non-exposed men. The sperm DNA fragmentation index was significantly higher in the exposed than the non-exposed men. Chronic long-term exposure to low doses of ionizing radiation could affect sperm motility, normal morphology, and the sperm DNA fragmentation index in the Chinese population. Sperm quality and DNA integrity are functional parameters that could be used to evaluate occupational exposure to ionizing radiation.

Electrospray Ionization Mass Spectrometry: A Technique to Access the Information beyond the Molecular Weight of the Analyte

Science.gov (United States)

Banerjee, Shibdas; Mazumdar, Shyamalava

2012-01-01

The Electrospray Ionization (ESI) is a soft ionization technique extensively used for production of gas phase ions (without fragmentation) of thermally labile large supramolecules. In the present review we have described the development of Electrospray Ionization mass spectrometry (ESI-MS) during the last 25 years in the study of various properties of different types of biological molecules. There have been extensive studies on the mechanism of formation of charged gaseous species by the ESI. Several groups have investigated the origin and implications of the multiple charge states of proteins observed in the ESI-mass spectra of the proteins. The charged analytes produced by ESI can be fragmented by activating them in the gas-phase, and thus tandem mass spectrometry has been developed, which provides very important insights on the structural properties of the molecule. The review will highlight recent developments and emerging directions in this fascinating area of research. PMID:22611397

Electrospray ionization mass spectrometry: a technique to access the information beyond the molecular weight of the analyte.

Science.gov (United States)

Banerjee, Shibdas; Mazumdar, Shyamalava

2012-01-01

The Electrospray Ionization (ESI) is a soft ionization technique extensively used for production of gas phase ions (without fragmentation) of thermally labile large supramolecules. In the present review we have described the development of Electrospray Ionization mass spectrometry (ESI-MS) during the last 25 years in the study of various properties of different types of biological molecules. There have been extensive studies on the mechanism of formation of charged gaseous species by the ESI. Several groups have investigated the origin and implications of the multiple charge states of proteins observed in the ESI-mass spectra of the proteins. The charged analytes produced by ESI can be fragmented by activating them in the gas-phase, and thus tandem mass spectrometry has been developed, which provides very important insights on the structural properties of the molecule. The review will highlight recent developments and emerging directions in this fascinating area of research.

Isomeric signatures in the fragmentation of pyridazine and pyrimidine induced by fast ion impact

Energy Technology Data Exchange (ETDEWEB)

Wolff, Wania, E-mail: wania@if.ufrj.br; Luna, Hugo; Montenegro, Eduardo C. [Instituto de Física, Universidade Federal do Rio de Janeiro, 21941-972 Rio de Janeiro, RJ (Brazil)

2015-07-28

We present fast proton impact induced fragmentations of pyrimidine and pyridazine as an experimental resource to investigate isomeric signatures. Major isomeric imprints are identified for few fragment ions and differences of more than an order of magnitude for the cross sections of fragments of the same mass were measured. The observation of the molecular structure of these isomers gives no apparent indication for the reasons for such substantial differences. It is verified that the simple displacement of the position of one nitrogen atom strongly inhibits or favors the production of some ionic fragment species. The dependency of the fragmentation cross sections on the proton impact energy, investigated by means of time of flight mass spectroscopy and of a model calculation based in first order perturbation theory, allows us to disentangle the complex collision dynamics of the ionic fragments. The proton-induced fragmentation discriminates rather directly the association between a molecular orbital ionization and the fragment-ions creation and abundance, as well as how the redistribution of the energy imparted to the molecules takes place, triggering not only single but also double vacancy and leads to specific fragmentation pathways.

Mechanisms of fragmentation and microstructure of debris generated during explosive testing of Al-W granular composite rings

International Nuclear Information System (INIS)

Chiu, Po-Hsun; Nesterenko, V F; Olney, K L; Braithwaite, C; Jardine, A; Collins, A; Benson, D J

2014-01-01

Highly heterogeneous materials comprised of elements with drastically different densities and shock impedances (e.g., Al and W) may provide additional mesoscale fragmentation mechanisms reducing the characteristic fragment size in comparison with solid materials with similar density (e.g., Stainless Steel 304). Explosively driven expanding ring experiments were conducted with Al-W granular composite rings, processed using hot and cold isostatic pressing, with different morphologies (W polyhedral particles or W rods with high aspect ratio and bonded/unbonded Al spherical particles with different sizes). In comparison to homogeneous samples with a similar density, these granular/porous composites generated fragments with a significantly smaller characteristic size. Scanning Electron Microscopy revealed that fragments had a propensity to be composed of clustered Al and W particles. Finite element simulations were conducted to gain an insight into the mesoscale fragmentation mechanisms and the clustering behavior observed in the experiments. Understanding the mesoscale mechanisms of explosively driven pulverization is important for tailoring the size of the fragments through the alteration of mesostructural properties.

Exploration of the fragmentation of laser shock-melted aluminum using x-ray backlighting

Directory of Open Access Journals (Sweden)

Lin Zhang

2016-05-01

Full Text Available The fragmentation of shock-melted metal material is an important scientific problem in shock physics and is suitable for experimentally investigating by the laser-driven x-ray backlighting technique. This letter reports on the exploration of laser shock-melted aluminum fragmentation by means of x-ray backlighting at the SGII high energy facility in China. High-quality and high-resolution radiographs with negligible motion blur were obtained and these images enabled analysis of the mass distribution of the fragmentation product.

Determination of Nerve Agent Metabolites by Ultraviolet Femtosecond Laser Ionization Mass Spectrometry.

Science.gov (United States)

Hamachi, Akifumi; Imasaka, Tomoko; Nakamura, Hiroshi; Li, Adan; Imasaka, Totaro

2017-05-02

Nerve agent metabolites, i.e., isopropyl methylphosphonic acid (IMPA) and pinacolyl methylphosphonic acid (PMPA), were derivatized by reacting them with 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr) and were determined by mass spectrometry using an ultraviolet femtosecond laser emitting at 267 and 200 nm as the ionization source. The analytes of the derivatized compounds, i.e., IMPA-PFB and PMPA-PFB, contain a large side-chain, and molecular ions are very weak or absent in electron ionization mass spectrometry. The use of ultraviolet femtosecond laser ionization mass spectrometry, however, resulted in the formation of a molecular ion, even for compounds such as these that contain a highly bulky functional group. The signal intensity was larger at 200 nm due to resonance-enhanced two-photon ionization. In contrast, fragmentation was suppressed at 267 nm (nonresonant two-photon ionization) especially for PMPA-PFB, thus resulting in a lower background signal. This favorable result can be explained by the small excess energy in ionization at 267 nm and by the low-frequency vibrational mode of a bulky trimethylpropyl group in PMPA.

Electron impact ionization mass spectra of 3-substituted-2-hydroxy-4(3H)-quinazolinones

International Nuclear Information System (INIS)

El Deen, I. M.; Abd El Fattah, M. E.

2003-01-01

2-Amino-2-hydroxy-4(3H)-quinazolinone (3) was prepared via condensation of 1 with hydrazine hydrate. Treatment of 3 with appropriate acid in POCl 3 , ethyl chloroacetate and activated olefinic compounds in DMF yielded the corresponding 3-(substituted)amino-2-hydroxy-4(3H)-quinazolinones 4,5 and 6. The electron impact ionization mass spectra of compounds 3 and 4 show a weak molecular ion peak and a base peak of m/z 146 resulting from a cleavage fragmentation. The compounds 5 and 6 give a characteristics fragmentation pattern with a very stable fragment of benzopyrazolone (m/z 132)

Scaling Relations of Starburst-driven Galactic Winds

International Nuclear Information System (INIS)

Tanner, Ryan; Cecil, Gerald; Heitsch, Fabian

2017-01-01

Using synthetic absorption lines generated from 3D hydrodynamical simulations, we explore how the velocity of a starburst-driven galactic wind correlates with the star formation rate (SFR) and SFR density. We find strong correlations for neutral and low ionized gas, but no correlation for highly ionized gas. The correlations for neutral and low ionized gas only hold for SFRs below a critical limit set by the mass loading of the starburst, above which point the scaling relations flatten abruptly. Below this point the scaling relations depend on the temperature regime being probed by the absorption line, not on the mass loading. The exact scaling relation depends on whether the maximum or mean velocity of the absorption line is used. We find that the outflow velocity of neutral gas can be up to five times lower than the average velocity of ionized gas, with the velocity difference increasing for higher ionization states. Furthermore, the velocity difference depends on both the SFR and mass loading of the starburst. Thus, absorption lines of neutral or low ionized gas cannot easily be used as a proxy for the outflow velocity of the hot gas.

Scaling Relations of Starburst-driven Galactic Winds

Energy Technology Data Exchange (ETDEWEB)

Tanner, Ryan [Department of Chemistry and Physics, Augusta University, Augusta, GA 30912 (United States); Cecil, Gerald; Heitsch, Fabian, E-mail: rytanner@augusta.edu [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States)

2017-07-10

Using synthetic absorption lines generated from 3D hydrodynamical simulations, we explore how the velocity of a starburst-driven galactic wind correlates with the star formation rate (SFR) and SFR density. We find strong correlations for neutral and low ionized gas, but no correlation for highly ionized gas. The correlations for neutral and low ionized gas only hold for SFRs below a critical limit set by the mass loading of the starburst, above which point the scaling relations flatten abruptly. Below this point the scaling relations depend on the temperature regime being probed by the absorption line, not on the mass loading. The exact scaling relation depends on whether the maximum or mean velocity of the absorption line is used. We find that the outflow velocity of neutral gas can be up to five times lower than the average velocity of ionized gas, with the velocity difference increasing for higher ionization states. Furthermore, the velocity difference depends on both the SFR and mass loading of the starburst. Thus, absorption lines of neutral or low ionized gas cannot easily be used as a proxy for the outflow velocity of the hot gas.

Multi-parameter spectroscopy of fission fragments and related emission products

International Nuclear Information System (INIS)

Ruben, A.; Jahnke, U.

1993-01-01

An exclusive measurement of the 252 C f(sf) fragment distribution in mass and energy in coincidence with the related emission products by combining a twin ionization chamber with a 4π-neutron tank, a n-γ-detector, and a solid-state detector telescope is presented. The experimental set-up, data handling and acquisition is described followed by a discussion of the raw data evaluation. (orig.)

Ecological impacts of tropical forest fragmentation: how consistent are patterns in species richness and nestedness?

Science.gov (United States)

Hill, Jane K; Gray, Michael A; Khen, Chey Vun; Benedick, Suzan; Tawatao, Noel; Hamer, Keith C

2011-11-27

Large areas of tropical forest now exist as remnants scattered across agricultural landscapes, and so understanding the impacts of forest fragmentation is important for biodiversity conservation. We examined species richness and nestedness among tropical forest remnants in birds (meta-analysis of published studies) and insects (field data for fruit-feeding Lepidoptera (butterflies and moths) and ants). Species-area relationships were evident in all four taxa, and avian and insect assemblages in remnants typically were nested subsets of those in larger areas. Avian carnivores and nectarivores and predatory ants were more nested than other guilds, implying that the sequential loss of species was more predictable in these groups, and that fragmentation alters the trophic organization of communities. For butterflies, the ordering of fragments to achieve maximum nestedness was by fragment area, suggesting that differences among fragments were driven mainly by extinction. In contrast for moths, maximum nestedness was achieved by ordering species by wing length; species with longer wings (implying better dispersal) were more likely to occur at all sites, including low diversity sites, suggesting that differences among fragments were driven more strongly by colonization. Although all four taxa exhibited high levels of nestedness, patterns of species turnover were also idiosyncratic, and thus even species-poor sites contributed to landscape-scale biodiversity, particularly for insects.

Ionization of water clusters by fast Highly Charged Ions: Stability, fragmentation, energetics and charge mobility

International Nuclear Information System (INIS)

Legendre, S; Maisonny, R; Capron, M; Bernigaud, V; Cassimi, A; Gervais, B; Grandin, J-P; Huber, B A; Manil, B; Rousseau, P; Tarisien, M; Adoui, L; Lopez-Tarifa, P; AlcamI, M; MartIn, F; Politis, M-F; Penhoat, M A Herve du; Vuilleumier, R; Gaigeot, M-P; Tavernelli, I

2009-01-01

We study dissociative ionization of water clusters by impact of fast Ni ions. Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) is used to obtain information about stability, energetics and charge mobility of the ionized clusters. An unusual stability of the (H 2 O) 4 H ''+ ion is observed, which could be the signature of the so called ''Eigen'' structure in gas phase water clusters. High charge mobility, responsible for the formation of protonated water clusters that dominate the mass spectrum, is evidenced. These results are supported by CPMD and TDDFT simulations, which also reveal the mechanisms of such mobility.

Mass spectrometric characterization of a pyrolytic radical source using femtosecond ionization

Energy Technology Data Exchange (ETDEWEB)

Frey, H M; Beaud, P; Mischler, B; Radi, P P; Tzannis, A P; Gerber, T [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1997-06-01

Radicals play, as reactive species, an important role in the chemistry of combustion. In contrast to atmospheric flames where spectra are congested due to high vibrational and rotational excitation, experiments in the cold environment of a molecular beam (MB) yield clean spectra that can be easily attributed to one species by Resonantly Enhanced Multi Photon Ionization (REMP). A pyrolytic radical source has been set up. To characterize the efficiency of the source `soft` ionization with femto second pulses is applied which results in less fragmentation, simplifying the interpretation of the mass spectrum. (author) figs., tabs., refs.

Fragmentation of C2H4 by charge-changing collisions of O2+ ions

International Nuclear Information System (INIS)

Sato, S.; Mizuno, T.; Yamada, T.; Imai, M.; Shibata, H.; Itoh, A.; Tsuchida, H.

2009-01-01

We investigated molecular fragmentation of C 2 H 4 in charge-changing collisions of 1.14MeV O 2+ ions. Branching ratios associated with decaying from temporary produced (C 2 H 4 ) r+ ions into various fragment channels were obtained. Dissociation via a C-C bond breaking is preferential in 1-electron loss collisions in comparison with 1-electron capture collisions. We confirmed that multiple ionization and dissociation rarely occur in electron capture collisions, while they occur rather strongly in electron loss collisions. (author)

Investigation of prompt gamma-ray yields as a function of mass and charge of 236U fission fragments

International Nuclear Information System (INIS)

Bogdzel', A.A.; Gundorin, N.A.; Duka-Zojomi, A.; Kliman, Ya.; Krishtiak, J.

1987-01-01

New experimental results determining yields of the prompt gamma-rays from the excited states decay of fission fragments are presented. 80 gamma-transitions were observed in 51 fission fragments. The measurements were performed by Ge(Li)-spectrometry in coincidence with fast ionization chamber (10g 235 U). The beam of the resonance neutrons with energy range from 0.7 to 36 eV was used

Development of an experimental device based on the digitalization of the signal and dedicated to the characterization of fission fragments and prompt neutrons; Developpement d'un dispositif experimental base sur la digitalisation des signaux et dedie a la caracterisation des fragments de fission et des neutrons prompts emis

Energy Technology Data Exchange (ETDEWEB)

Varapai, N

2006-12-15

The present work demonstrates the application of the digital technique for nuclear measurements. This new technique is based on the digitalization of the signals from the detectors and has several advantages. This technique allows us to extract the maximum amount of information contained in the signal shape. In the case of an ionization chamber this signal contains the necessary information on the particle kinetic energy, emission angle and mass. This method has been implemented for measurements of promptly emitted fission neutrons in coincidence with fission fragments from {sup 252}Cf(sf). A double Frisch-grid ionization chamber is used as fission fragment detector. The promptly emitted neutrons are detected by a NE213 liquid scintillation detector. This work displays how delicate analysis of the digitalized signals permitted us to infer the mass and kinetic energy distributions of the fission fragments as well as the neutron energy spectrum and multiplicity. The outline of this thesis is as follows: Chapter 2 gives an overview of the experimental tools used in this work. Chapter 3 explains the analysis procedure of the digitalized anode signal from an ionization chamber. Chapter 4 gives a detailed explanation of the analysis procedure of the digitalized signal from a neutron detector. In Chapter 5 the analysis procedure of the fission fragment events in coincidence with neutrons is given.

Formation of radical anions of radiosensitizers and related model compounds via electrospray ionization

DEFF Research Database (Denmark)

Feketeová, Linda; Albright, Abigail L; Sørensen, Brita Singers

2014-01-01

Radiosensitizers are used in radiotherapy to enhance tumour control of radioresistant hypoxic tumours. While the detailed mechanism of radiosensitization is still unknown, the formation of radical anions is believed to be a key step. Thus understanding the ionization reactions of radiosensitizers......, misonidazole and related compounds using a hybrid linear ion trap – Fourier Transform Ion Cyclotron Resonance mass spectrometer (Finnigan-LTQ-FT). A key finding is that negative electrospray ionization of these radiosensitizers leads to the formation of radical anions, allowing their fragmentation reactions...

Meta-analysis of the effects of forest fragmentation on interspecific interactions.

Science.gov (United States)

Magrach, Ainhoa; Laurance, William F; Larrinaga, Asier R; Santamaria, Luis

2014-10-01

Forest fragmentation dramatically alters species persistence and distribution and affects many ecological interactions among species. Recent studies suggest that mutualisms, such as pollination and seed dispersal, are more sensitive to the negative effects of forest fragmentation than antagonisms, such as predation or herbivory. We applied meta-analytical techniques to evaluate this hypothesis and quantified the relative contributions of different components of the fragmentation process (decreases in fragment size, edge effects, increased isolation, and habitat degradation) to the overall effect. The effects of fragmentation on mutualisms were primarily driven by habitat degradation, edge effects, and fragment isolation, and, as predicted, they were consistently more negative on mutualisms than on antagonisms. For the most studied interaction type, seed dispersal, only certain components of fragmentation had significant (edge effects) or marginally significant (fragment size) effects. Seed size modulated the effect of fragmentation: species with large seeds showed stronger negative impacts of fragmentation via reduced dispersal rates. Our results reveal that different components of the habitat fragmentation process have varying impacts on key mutualisms. We also conclude that antagonistic interactions have been understudied in fragmented landscapes, most of the research has concentrated on particular types of mutualistic interactions such as seed dispersal, and that available studies of interspecific interactions have a strong geographical bias (arising mostly from studies carried out in Brazil, Chile, and the United States). © 2014 Society for Conservation Biology.

Supersonic propagation of ionization waves in an underdense, laser-produced plasma

International Nuclear Information System (INIS)

Constantin, C.; Back, C.A.; Fournier, K.B.; Gregori, G.; Landen, O.L.; Glenzer, S.H.; Dewald, E.L.; Miller, M.C.

2005-01-01

A laser-driven supersonic ionization wave propagating through a millimeter-scale plasma of subcritical density up to 2-3 keV electron temperatures was observed. Propagation velocities initially ten times the sound speed were measured by means of time-resolved x-ray imaging diagnostics. The measured ionization wave trajectory is modeled analytically and by a two-dimensional radiation-hydrodynamics code. The comparison to the modeling suggests that nonlocal heat transport effects may contribute to the attenuation of the heat-wave propagation

Time-dependent approach to collisional ionization using exterior complex scaling

International Nuclear Information System (INIS)

McCurdy, C. William; Horner, Daniel A.; Rescigno, Thomas N.

2002-01-01

We present a time-dependent formulation of the exterior complex scaling method that has previously been used to treat electron-impact ionization of the hydrogen atom accurately at low energies. The time-dependent approach solves a driven Schroedinger equation, and scales more favorably with the number of electrons than the original formulation. The method is demonstrated in calculations for breakup processes in two dimensions (2D) and three dimensions for systems involving short-range potentials and in 2D for electron-impact ionization in the Temkin-Poet model for electron-hydrogen atom collisions

HIERARCHICAL FRAGMENTATION OF THE ORION MOLECULAR FILAMENTS

International Nuclear Information System (INIS)

Takahashi, Satoko; Ho, Paul T. P.; Su, Yu-Nung; Teixeira, Paula S.; Zapata, Luis A.

2013-01-01

We present a high angular resolution map of the 850 μm continuum emission of the Orion Molecular Cloud-3 (OMC 3) obtained with the Submillimeter Array (SMA); the map is a mosaic of 85 pointings covering an approximate area of 6.'5 × 2.'0 (0.88 × 0.27 pc). We detect 12 spatially resolved continuum sources, each with an H 2 mass between 0.3-5.7 M ☉ and a projected source size between 1400-8200 AU. All the detected sources are on the filamentary main ridge (n H 2 ≥10 6 cm –3 ), and analysis based on the Jeans theorem suggests that they are most likely gravitationally unstable. Comparison of multi-wavelength data sets indicates that of the continuum sources, 6/12 (50%) are associated with molecular outflows, 8/12 (67%) are associated with infrared sources, and 3/12 (25%) are associated with ionized jets. The evolutionary status of these sources ranges from prestellar cores to protostar phase, confirming that OMC-3 is an active region with ongoing embedded star formation. We detect quasi-periodical separations between the OMC-3 sources of ≈17''/0.035 pc. This spatial distribution is part of a large hierarchical structure that also includes fragmentation scales of giant molecular cloud (≈35 pc), large-scale clumps (≈1.3 pc), and small-scale clumps (≈0.3 pc), suggesting that hierarchical fragmentation operates within the Orion A molecular cloud. The fragmentation spacings are roughly consistent with the thermal fragmentation length in large-scale clumps, while for small-scale cores it is smaller than the local fragmentation length. These smaller spacings observed with the SMA can be explained by either a helical magnetic field, cloud rotation, or/and global filament collapse. Finally, possible evidence for sequential fragmentation is suggested in the northern part of the OMC-3 filament.

A multiple sampling ionization chamber for the External Target Facility

International Nuclear Information System (INIS)

Zhang, X.H.; Tang, S.W.; Ma, P.; Lu, C.G.; Yang, H.R.; Wang, S.T.; Yu, Y.H.; Yue, K.; Fang, F.; Yan, D.; Zhou, Y.; Wang, Z.M.; Sun, Y.; Sun, Z.Y.; Duan, L.M.; Sun, B.H.

2015-01-01

A multiple sampling ionization chamber used as a particle identification device for high energy heavy ions has been developed for the External Target Facility. The performance of this detector was tested with a 239 Pu α source and RI beams. A Z resolution (FWHM) of 0.4–0.6 was achieved for nuclear fragments of 18 O at 400 AMeV

Influence of turn (or fold) and local charge in fragmentation of the peptide analogue molecule CH3CO-Gly-NH2 following single-photon VUV (118.22 nm) ionization.

Science.gov (United States)

Bhattacharya, Atanu; Bernstein, Elliot R

2011-10-06

The radical cationic reactivity of the peptide analogue molecule CH(3)CO-Gly-NH(2) is addressed both experimentally and theoretically. The radical cation intermediate of CH(3)CO-Gly-NH(2) is created by single-photon ionization of this molecule at 118.22 nm (~10.5 eV). The two most stable conformers (C(7) and C(5)) of this molecule exhibit different folds along the backbone: the C(7) conformer has a γ-turn structure, and the C(5) conformer has a β-strand structure. The experimental results show that the radical cation intermediate of CH(3)CO-Gly-NH(2) dissociates and generates a fragment-ion signal at 73 amu that is observed through TOFMS. Theoretical results show how the fragment-ion signal at 73 amu is generated by only one conformer of CH(3)CO-Gly-NH(2) (C(7)) and how local charge and specific hydrogen bonding in the molecule influence fragmentation of the radical cation intermediate of CH(3)CO-Gly-NH(2). The specific fold of the molecule controls fragmentation of this reactive radical cation intermediate. Whereas the radical cation of the C(7) conformer dissociates through a hydrogen-transfer mechanism followed by HNCO elimination, the radical cation of the C(5) conformer does not dissociate at all. CASSCF calculations show that positive charge in the radical cationic C(7) conformer is localized at the NH(2)CO moiety of the molecular ion. This site-specific localization of the positive charge enhances the acidity of the terminal NH(2) group, facilitating hydrogen transfer from the NH(2) to the COCH(3) end of the molecular ion. Positive charge in the C(5) conformer of the CH(3)CO-Gly-NH(2) radical cation is, however, localized at the COCH(3) end of the molecular ion, and this conformer does not have enough energy to surmount the energy barrier to dissociation on the ion potential energy surface. CASSCF results show that conformation-specific localization of charge in the CH(3)CO-Gly-NH(2) molecular ion occurs as a result of the different hydrogen

Matrix-assisted laser desorption/ionization mass spectrometry for the structural characterization of modified oligonucleotides

International Nuclear Information System (INIS)

Hurst, G.B.; Hettich, R.L.; Buchanan, M.V.; Stemmler, E.A.

1993-01-01

Matrix-assisted laser desorption ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry (FTMS) and MALDI time-of-flight mass spectrometry (TOFMS) are being used to characterize conditions for the efficient desorption and ionization of normal and modified nucleic acid components. Basic and acidic matrix materials have been evaluated on the components. Basic and acidic matrix materials have been evaluated on the FTMS and TOFMS. Using MALDI-FTMS at 355 nm, less fragmentation has been observed using 2,5-dihydroxybenzoic acid, while more extensive fragmentation is observed for basic matrices, such as 1,5-diaminonaphthalene and 9-aminophenanthrene. Elevation of the cell pressure by the addition of Ar or CO 2 provides collisional cooling of desorbed ions, resulting in an enhancement of [M--H] - and structurally significant high-mass fragment ions. Using MALDI-TOFMS at 337 nm, fragmentation is significantly reduced relative to that observed on the FTMS, perhaps as a consequence of the longer times required for FTMS detection. On the FTMS and TOFMS, cluster ions have been observed in the negative ion mode when metal ions are present in the 2,5-dihydroxybenzoic acid matrix. Metal ion additions and clusters with matrix salts have also been observed for dinucleotides. Applications of MALDI-FTMS and MALDI-TOF to the detection of hydroxylated PAH nucleoside adducts are presented

Dissociation and ionization of molecular ions by ultra-short intense laser pulses probed by coincidence 3D momentum imaging

International Nuclear Information System (INIS)

Ben-Itzhak, Itzik; Wang, Pengqian; Xia, Jiangfan; Max Sayler, A.; Smith, Mark A.; Maseberg, J.W.; Carnes, Kevin D.; Esry, Brett D.

2005-01-01

We have experimentally explored laser-induced dissociation and ionization of diatomic molecular ions using coincidence 3D momentum imaging. The vibrationally excited molecular ion beam (4-8 keV) is crossed by an ultrafast intense laser beam (28-200 fs, 10 13 -10 14 W/cm 2 ). The resulting fragments are recorded in coincidence by a time and position-sensitive detector. Complete angular distributions and kinetic energy release maps are reconstructed from the measured dissociation-momentum vectors. The angular distribution of the H + + H fragments was found to be strongly correlated to their kinetic energy release upon dissociation. Low KER was associated with very narrow angular distributions and high KER with distributions peaking away from the laser polarization. Ionization was found to be smaller than dissociation and increased with laser intensity. The H + + H + fragments have a very narrow angular distribution along the laser polarization

Bond rearrangement caused by sudden single and multiple ionization of water molecules

International Nuclear Information System (INIS)

Ben-Itzhak, I.; Sayler, A. Max; Leonard, M.; Maseberg, J.W.; Hathiramani, D.; Wells, E.; Smith, M.A.; Xia, Jiangfan; Wang, Pengqian; Carnes, K.D.; Esry, B.D.

2005-01-01

Bond rearrangement, namely the dissociation of water into H 2 + +O q+ following ionization by fast proton and highly charged ion impact, was investigated. Single ionization by fast proton impact exhibits a strong isotopic effect, the dissociation of H 2 O + ->H 2 + +O being about twice as likely as D 2 O + ->D 2 + +O, with HDO + ->HD + +O in between. This suggests that the bond rearrangement does not happen during the slow dissociation, but rather during the very fast ionization, and thus H 2 + should also be produced when the water molecule is multiply ionized. We observed that the H 2 + +O + and H 2 + +O 2+ production in 1MeV/amu F 7+ +H 2 O collisions are 0.209+/-0.006% and 0.0665+/-0.003%, respectively, of the main double-ionization dissociation product, H 2 O 2+ ->H + +OH + . This ratio is similar to the triple to double ionization ratio in similar collisions with atomic targets thus suggesting that the bond-rearrangement fraction out of each ionization level is approximately constant. Similar dissociation channels in the heavier water isotopes, which are expected to be smaller, are under study. Finally, the fragmentation of HDO exhibits very strong isotopic preference for breaking the OH bond over the OD bond

Dissociation dynamics of anionic and excited neutral fragments of gaseous SiCl4 following Cl 2p and Si 2p core-level excitations

International Nuclear Information System (INIS)

Chen, J M; Lu, K T; Lee, J M; Chou, T L; Chen, H C; Chen, S A; Haw, S C; Chen, T H

2008-01-01

The state-selective dissociation dynamics for anionic and excited neutral fragments of gaseous SiCl 4 following Cl 2p and Si 2p core-level excitations were characterized by combining measurements of the photon-induced anionic dissociation, x-ray absorption and UV/visible dispersed fluorescence. The transitions of core electrons to high Rydberg states/doubly excited states in the vicinity of both Si 2p and Cl 2p ionization thresholds of gaseous SiCl 4 lead to a remarkably enhanced production of anionic, Si - and Cl - , fragments and excited neutral atomic, Si*, fragments. This enhancement via core-level excitation near the ionization threshold of gaseous SiCl 4 is explained in terms of the contributions from the Auger decay of doubly excited states, shake-modified resonant Auger decay, or/and post-collision interaction. These complementary results provide insight into the state-selective anionic and excited neutral fragmentation of gaseous molecules via core-level excitation.

Determination of the fine structure in the ionization plots obtained from a mass spectrometer with a large energy dispersion

International Nuclear Information System (INIS)

Deruaz, Daniel.

1974-01-01

The precise determination of ionization potentials, fragment ion appearance potentials and different excited state levels of the positive ions formed, together with phenomena due to an electron impact, were studied from ionization efficiency curves obtained by mass spectrometry. A standard ion source and an analytical method of electron energy dispersion reduction were used to study fine structures of ionization efficiency curves. Since the mass spectrometer was not adapted for the acquisition of ionization efficiency curve data an electronic system was designed to record these curves automatically. A precise stepwise potential variation of 45+-0.04mV was obtained, and for each step an intensity proportional to the number of ions created by the fragment considered, the additional gain being 4.4 and the linearity greater than 1% over a 13-volt region. Before each set of measurements the scattering was determined by calculation of the second derivative of a logistic function deduced from the cubic regression of the experimental helium function ionization efficiency curve values. The precision, given by the variance analysis SNEDECOR F test, is higher than 1/1000. For each series of recordings the numerical values were processed by a computer to raise by twenty the signal to noise ratio and calculate the ionization efficiency curve values by the energy difference method and the iterative unfolding method. In this way a high sensitivity was obtained for the determination of the curves near the ionization threshold, and a precision below 50MeV (at least equivalent to that given by ionization cells with quasi-monoenergetic electron beams) for the values of the ionization potentials, the appearance potentials and the excited state energy levels. In order to judge the reliability of the technique the ionization potentials of a set of eleven complex molecules were determined and compared with the results obtained by photoionization and photoelectron spectrometry [fr

FRAGMENTATION STUDIES OF D6,7-ANHIDROERITROMISIN-A BY LIQUID CHROMATOGRAPHY-MASS SPECTROSCOPY (LC-MS

Directory of Open Access Journals (Sweden)

Khairan Khairan

2010-06-01

Full Text Available Semisynthesis of D6,7-Anhydroerythromycin-A was done by biomodification technique by addition of 0.2% INH into a culture fermentation of Saccharopolyspora erythraea ATCC 11635 in medium Hutchinson. The aim of this research is to studies of fragmentation pattern from new matabolite of D6,7-Anhydroerythromycin-A by Liquid Chromatography-Mass Spectroscopy (LC-MS and the ionization of mass spectroscopy is use by ESI (Electrospray Ionization pattern. The FT-IR spectrometric analyzes showed a stretching vibration of C=C conjugated group at wave number 1602.7 cm-1. This C=C conjugated vibration indicated the existence of double bond between C6 and C7 (D6,7, this confirmed that isolate contained D6,7-Anhydroerythromycin-A (the possibility of D6,7 was positive. For complementation, a LC-MS (Liquid Chromatography-Mass Spectroscopy analyzes using ESI-MS (Electrospray Ionization-Mass Spectroscopy ionization pattern was conducted to the isolate which resulted Quassimolecular ions [M+H]+ of D7,8- and D6,7-Anhydroerythromycin-A. LC-MS spectrogram of the isolate, which gave two peaks of m/z 732.2460 and m/z 716.2522, confirmed that the m/z 732.2460 possibly was D7,8-Anhydroerythromycin-A, while the m/z 716.2502 and m/z 715.2522 possibly were D6,7-Anhydroerythromycin-A.   Keywords: isoniazid, enoyl reduction, D6,7-Anhidroeritromisin-A, fragmentation, LC-MS.

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): review.

Science.gov (United States)

Li, Du-Xin; Gan, Lin; Bronja, Amela; Schmitz, Oliver J

2015-09-03

Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. The demand of a "soft" ion source for preserving highly diagnostic molecular ion is desirable, as compared to the "hard" ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS. Copyright © 2015. Published by Elsevier B.V.

Climate-driven range shifts of the king penguin in a fragmented ecosystem

Science.gov (United States)

Cristofari, Robin; Liu, Xiaoming; Bonadonna, Francesco; Cherel, Yves; Pistorius, Pierre; Le Maho, Yvon; Raybaud, Virginie; Stenseth, Nils Christian; Le Bohec, Céline; Trucchi, Emiliano

2018-03-01

Range shift is the primary short-term species response to rapid climate change, but it is often hampered by natural or anthropogenic habitat fragmentation. Different critical areas of a species' niche may be exposed to heterogeneous environmental changes and modelling species response under such complex spatial and ecological scenarios presents well-known challenges. Here, we use a biophysical ecological niche model validated through population genomics and palaeodemography to reconstruct past range shifts and identify future vulnerable areas and potential refugia of the king penguin in the Southern Ocean. Integrating genomic and demographic data at the whole-species level with specific biophysical constraints, we present a refined framework for predicting the effect of climate change on species relying on spatially and ecologically distinct areas to complete their life cycle (for example, migratory animals, marine pelagic organisms and central-place foragers) and, in general, on species living in fragmented ecosystems.

Ionization photophysics and spectroscopy of dicyanoacetylene

International Nuclear Information System (INIS)

Leach, Sydney; Champion, Norbert; Schwell, Martin; Bénilan, Yves; Fray, Nicolas; Gazeau, Marie-Claire; Garcia, Gustavo A.; Gaie-Levrel, François; Guillemin, Jean-Claude

2013-01-01

Photoionization of dicyanoacetylene was studied using synchrotron radiation over the excitation range 8–25 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and detailed spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of dicyanoacetylene was measured as 11.80 ± 0.01 eV. A detailed analysis of the cation spectroscopy involves new aspects and new assignments of the vibrational components to excitation of the quasi-degenerate A 2 Π g , B 2 Σ g + states as well as the C 2 Σ u + and D 2 Π u states of the cation. Some of the structured autoionization features observed in the 12.4–15 eV region of the total ion yield spectrum were assigned to vibrational components of valence shell transitions and to two previously unknown Rydberg series converging to the D 2 Π u state of C 4 N 2 + . The appearance energies of the fragment ions C 4 N + , C 3 N + , C 4 + , C 2 N + , and C 2 + were measured and their heats of formation were determined and compared with existing literature values. Thermochemical calculations of the appearance potentials of these and other weaker ions were used to infer aspects of dissociative ionization pathways

Development of an experimental device based on the digitalization of the signal and dedicated to the characterization of fission fragments and prompt neutrons

International Nuclear Information System (INIS)

Varapai, N.

2006-12-01

The present work demonstrates the application of the digital technique for nuclear measurements. This new technique is based on the digitalization of the signals from the detectors and has several advantages. This technique allows us to extract the maximum amount of information contained in the signal shape. In the case of an ionization chamber this signal contains the necessary information on the particle kinetic energy, emission angle and mass. This method has been implemented for measurements of promptly emitted fission neutrons in coincidence with fission fragments from 252 Cf(sf). A double Frisch-grid ionization chamber is used as fission fragment detector. The promptly emitted neutrons are detected by a NE213 liquid scintillation detector. This work displays how delicate analysis of the digitalized signals permitted us to infer the mass and kinetic energy distributions of the fission fragments as well as the neutron energy spectrum and multiplicity. The outline of this thesis is as follows: Chapter 2 gives an overview of the experimental tools used in this work. Chapter 3 explains the analysis procedure of the digitalized anode signal from an ionization chamber. Chapter 4 gives a detailed explanation of the analysis procedure of the digitalized signal from a neutron detector. In Chapter 5 the analysis procedure of the fission fragment events in coincidence with neutrons is given

Molecular dynamics for irradiation driven chemistry

DEFF Research Database (Denmark)

Sushko, Gennady B.; Solov'yov, Ilia A.; Solov'yov, Andrey V.

2016-01-01

A new molecular dynamics (MD) approach for computer simulations of irradiation driven chemical transformations of complex molecular systems is suggested. The approach is based on the fact that irradiation induced quantum transformations can often be treated as random, fast and local processes...... that describe the classical MD of complex molecular systems under irradiation. The proposed irradiation driven molecular dynamics (IDMD) methodology is designed for the molecular level description of the irradiation driven chemistry. The IDMD approach is implemented into the MBN Explorer software package...... involving small molecules or molecular fragments. We advocate that the quantum transformations, such as molecular bond breaks, creation and annihilation of dangling bonds, electronic charge redistributions, changes in molecular topologies, etc., could be incorporated locally into the molecular force fields...

Multiorbital effects in strong-field ionization and dissociation of aligned polar molecules CH3I and CH3Br

Science.gov (United States)

Luo, Sizuo; Zhou, Shushan; Hu, Wenhui; Li, Xiaokai; Ma, Pan; Yu, Jiaqi; Zhu, Ruihan; Wang, Chuncheng; Liu, Fuchun; Yan, Bing; Liu, Aihua; Yang, Yujun; Guo, Fuming; Ding, Dajun

2017-12-01

Controlling the molecular axis offers additional ways to study molecular ionization and dissociation in strong laser fields. We measure the ionization and dissociation yields of aligned polar CH3X (X =I , Br) molecules in a linearly polarized femtosecond laser field. The current data show that maximum ionization occurs when the laser polarization is perpendicular to the molecular C -X axis, and dissociation prefers to occur at the laser polarization parallel to the C -X axis. The observed angular distributions suggest that the parent ions are generated by ionization from the HOMO. The angular distribution of fragment ions indicates that dissociation occurs mainly from an ionic excited state produced by ionization from the HOMO-1.

Multi-fold correlations between 252Cf (sf) fragments and fission neutrons/γ-rays

International Nuclear Information System (INIS)

Duering, I.; Jahnke, U.

1993-01-01

Direction-sensitive spectroscopy of fission fragments (twin ionization chamber with Frisch grids) was combined with the measurement of neutron multiplicity distribution (P(ν), average total γ-ray energy (2x2 π Gd-loaded scintillator) as well as energy and angular distribution of neutrons and γ-rays. Based on the careful account for necessary corrections, scission configurations given by mass asymmetry, elongation (total kinetic energy of fragments), and shape asymmetry (ν 1 /ν 2 ) can be studied exclusively in correlation with differential distributions of emission products. The scheme for correcting the neutron multiplicity distribution including its separation into the contributions from the complementary fragments is presented in detail. The mass yield for extreme anti ν 1 / anti ν 2 ratios show fine structures indicating the cold shape-asymmetric fission. (orig.)

Investigation and Applications of In-Source Oxidation in Liquid Sampling-Atmospheric Pressure Afterglow Microplasma Ionization (LS-APAG) Source.

Science.gov (United States)

Xie, Xiaobo; Wang, Zhenpeng; Li, Yafeng; Zhan, Lingpeng; Nie, Zongxiu

2017-06-01

A liquid sampling-atmospheric pressure afterglow microplasma ionization (LS-APAG) source is presented for the first time, which is embedded with both electrospray ionization (ESI) and atmospheric pressure afterglow microplasma ionization (APAG) techniques. This ion source is capable of analyzing compounds with diverse molecule weights and polarities. An unseparated mixture sample was detected as a proof-of-concept, giving complementary information (both polarities and non-polarities) with the two ionization modes. It should also be noted that molecular mass can be quickly identified by ESI with clean and simple spectra, while the structure can be directly studied using APAG with in-source oxidation. The ionization/oxidation mechanism and applications of the LS-APAG source have been further explored in the analysis of nonpolar alkanes and unsaturated fatty acids/esters. A unique [M + O - 3H] + was observed in the case of individual alkanes (C 5 -C 19 ) and complex hydrocarbons mixture under optimized conditions. Moreover, branched alkanes generated significant in-source fragments, which could be further applied to the discrimination of isomeric alkanes. The technique also facilitates facile determination of double bond positions in unsaturated fatty acids/esters due to diagnostic fragments (the acid/ester-containing aldehyde and acid oxidation products) generated by on-line ozonolysis in APAG mode. Finally, some examples of in situ APAG analysis by gas sampling and surface sampling were given as well. Graphical Abstract ᅟ.

Surface Ionization and Soft Landing Techniques in Mass Spectrometry

International Nuclear Information System (INIS)

Futrell, Jean H.; Laskin, Julia

2010-01-01

The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has extended mass spectrometric methods to large molecules and molecular complexes. This both greatly expands applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of large molecule mass spectrometry. A corollary of the much greater number of internal degrees of freedom and high density of states associated with molecular complexity is that internal energies much higher than the dissociation energies for competing fragmentation processes are required for observable fragmentation in time scales sampled by mass spectrometers. This article describes the kinetics of surface-induced dissociation (SID), a particularly efficient activation method for complex ions. Two very important characteristics of SID are very rapid, sub-picosecond activation and precise control of ion internal energy by varying ion collision energy. The nature of the surface plays an important role in SID, determining both efficiency and mechanism of ion activation. Surface composition and morphology strongly influence the relative importance of competing reactions of SID, ion capture (soft-landing), surface reaction and neutralization. The important features of SID and ion soft-landing are described briefly in this review and more fully in the recommended reading list.

IN SITU PLASMA MEASUREMENTS OF FRAGMENTED COMET 73P SCHWASSMANN–WACHMANN 3

International Nuclear Information System (INIS)

Gilbert, J. A.; Lepri, S. T.; Combi, M.; Zurbuchen, T. H.; Rubin, M.

2015-01-01

The interiors of comets contain some of the most pristine material in the solar system. Comet 73P/Schwassmann–Wachmann 3, discovered in 1930, is a Jupiter-family comet with a 5.34-year period. This comet split into 5 fragments in 1995 and disintegrated into nearly 70 major pieces in 2006. In 2006 May and June, recently ionized cometary particles originating from fragments including and surrounding some of these major objects were collected with the ACE/SWICS and Wind/STICS sensors. Due to a combination of the instrument characteristics and the close proximity of the fragments passing between those spacecraft and the Sun, unique measurements regarding the charge state composition and the elemental abundances of both cometary and heliospheric plasma were made during that time. The cometary material released from some of these fragments can be identified by the concentrations of water-group pickup ions having a mass-per-charge ratio of 16–18 amu e −1 , indicating that while these fragments are small, they are still actively sublimating. We present an analysis of cometary composition, spatial distribution, and heliospheric interactions, with a focus on helium, C + /O + , and water-group ions

In Situ Plasma Measurements of Fragmented Comet 73P Schwassmann-Wachmann 3

Science.gov (United States)

Gilbert, J. A.; Lepri, S. T.; Rubin, M.; Combi, M.; Zurbuchen, T. H.

2015-12-01

The interiors of comets contain some of the most pristine material in the solar system. Comet 73P/Schwassmann-Wachmann 3, discovered in 1930, is a Jupiter-family comet with a 5.34-year period. This comet split into 5 fragments in 1995 and disintegrated into nearly 70 major pieces in 2006. In 2006 May and June, recently ionized cometary particles originating from fragments including and surrounding some of these major objects were collected with the ACE/SWICS and Wind/STICS sensors. Due to a combination of the instrument characteristics and the close proximity of the fragments passing between those spacecraft and the Sun, unique measurements regarding the charge state composition and the elemental abundances of both cometary and heliospheric plasma were made during that time. The cometary material released from some of these fragments can be identified by the concentrations of water-group pickup ions having a mass-per-charge ratio of 16-18 amu e-1, indicating that while these fragments are small, they are still actively sublimating. We present an analysis of cometary composition, spatial distribution, and heliospheric interactions, with a focus on helium, C+/O+, and water-group ions.

IN SITU PLASMA MEASUREMENTS OF FRAGMENTED COMET 73P SCHWASSMANN–WACHMANN 3

Energy Technology Data Exchange (ETDEWEB)

Gilbert, J. A.; Lepri, S. T.; Combi, M.; Zurbuchen, T. H. [University of Michigan, Ann Arbor, MI 48109 (United States); Rubin, M., E-mail: jagi@umich.edu [Universität Bern, Bern (Switzerland)

2015-12-10

The interiors of comets contain some of the most pristine material in the solar system. Comet 73P/Schwassmann–Wachmann 3, discovered in 1930, is a Jupiter-family comet with a 5.34-year period. This comet split into 5 fragments in 1995 and disintegrated into nearly 70 major pieces in 2006. In 2006 May and June, recently ionized cometary particles originating from fragments including and surrounding some of these major objects were collected with the ACE/SWICS and Wind/STICS sensors. Due to a combination of the instrument characteristics and the close proximity of the fragments passing between those spacecraft and the Sun, unique measurements regarding the charge state composition and the elemental abundances of both cometary and heliospheric plasma were made during that time. The cometary material released from some of these fragments can be identified by the concentrations of water-group pickup ions having a mass-per-charge ratio of 16–18 amu e{sup −1}, indicating that while these fragments are small, they are still actively sublimating. We present an analysis of cometary composition, spatial distribution, and heliospheric interactions, with a focus on helium, C{sup +}/O{sup +}, and water-group ions.

Polymerization, shock cooling and ionization of liquid nitrogen

International Nuclear Information System (INIS)

Ross, M; Rogers, F

2005-01-01

The trajectory of thermodynamic states passed through by the nitrogen Hugoniot starting from the liquid and up to 10 6 GPa has been studied. An earlier report of cooling in the doubly shocked liquid, near 50 to 100 GPa and 7500 K, is revisited in light of the recent discovery of solid polymeric nitrogen. It is found that cooling occurs when the doubly shocked liquid is driven into a volume near the molecular to polymer transition and raising the possibility of a liquid-liquid phase transition (LLPT). By increasing the shock pressure and temperature by an order of magnitude, theoretical calculations predict thermal ionization of the L shell drives the compression maxima to 5-6 fold compression at 10 Mbar (T ∼ 3.5 10 5 K) and at 400 Mbar (T ∼ 2.3 10 6 K) from K shell ionization. Near a pressure of 10 6 GPa the K shell ionizes completely and the Hugoniot approaches the classical ideal gas compression fourfold limit

Mechanics of fragmentation of crocodile skin and other thin films

Science.gov (United States)

Qin, Zhao; Pugno, Nicola M.; Buehler, Markus J.

2014-01-01

Fragmentation of thin layers of materials is mediated by a network of cracks on its surface. It is commonly seen in dehydrated paintings or asphalt pavements and even in graphene or other two-dimensional materials, but is also observed in the characteristic polygonal pattern on a crocodile's head. Here, we build a simple mechanical model of a thin film and investigate the generation and development of fragmentation patterns as the material is exposed to various modes of deformation. We find that the characteristic size of fragmentation, defined by the mean diameter of polygons, is strictly governed by mechanical properties of the film material. Our result demonstrates that skin fragmentation on the head of crocodiles is dominated by that it features a small ratio between the fracture energy and Young's modulus, and the patterns agree well with experimental observations. Understanding this mechanics-driven process could be applied to improve the lifetime and reliability of thin film coatings by mimicking crocodile skin. PMID:24862190

Mechanics of fragmentation of crocodile skin and other thin films

Science.gov (United States)

Qin, Zhao; Pugno, Nicola M.; Buehler, Markus J.

2014-05-01

Fragmentation of thin layers of materials is mediated by a network of cracks on its surface. It is commonly seen in dehydrated paintings or asphalt pavements and even in graphene or other two-dimensional materials, but is also observed in the characteristic polygonal pattern on a crocodile's head. Here, we build a simple mechanical model of a thin film and investigate the generation and development of fragmentation patterns as the material is exposed to various modes of deformation. We find that the characteristic size of fragmentation, defined by the mean diameter of polygons, is strictly governed by mechanical properties of the film material. Our result demonstrates that skin fragmentation on the head of crocodiles is dominated by that it features a small ratio between the fracture energy and Young's modulus, and the patterns agree well with experimental observations. Understanding this mechanics-driven process could be applied to improve the lifetime and reliability of thin film coatings by mimicking crocodile skin.

Glycomics expression analysis of sulfated glycosaminoglycans of human colorectal cancer tissues and non-neoplastic mucosa by electrospray ionization mass spectrometry.

Science.gov (United States)

Marolla, Ana Paula Cleto; Waisberg, Jaques; Saba, Gabriela Tognini; Waisberg, Daniel Reis; Margeotto, Fernando Beani; Pinhal, Maria Aparecida da Silva

2015-01-01

To determine the presence of glycosaminoglycans in the extracellular matrix of connective tissue from neoplastic and non-neoplastic colorectal tissues, since it has a central role in tumor development and progression. Tissue samples from neoplastic and non-neoplastic colorectal tissues were obtained from 64 operated patients who had colorectal carcinoma with no distant metastases. Expressions of heparan sulphate, chondroitin sulphate, dermatan sulphate and their fragments were analyzed by electrospray ionization mass spectrometry, with the technique for extraction and quantification of glycosaminoglycans after proteolysis and electrophoresis. The statistical analysis included mean, standard deviation, and Student'st test. The glycosaminoglycans extracted from colorectal tissue showed three electrophoretic bands in agarose gel. Electrospray ionization mass spectrometry showed characteristic disaccharide fragments from glycosaminoglycans, indicating their structural characterization in the tissues analyzed. Some peaks in the electrospray ionization mass spectrometry were not characterized as fragments of sugars, indicating the presence of fragments of the protein structure of proteoglycans generated during the glycosaminoglycan purification. The average amount of chondroitin and dermatan increased in the neoplastic tissue compared to normal tissue (p=0.01). On the other hand, the average amount of heparan decreased in the neoplastic tissue compared to normal tissue (p= 0.03). The method allowed the determination of the glycosaminoglycans structural profile in colorectal tissue from neoplastic and non-neoplastic colorectal tissue. Neoplastic tissues showed greater amounts of chondroitin sulphate and dermatan sulphate compared to non-neoplastic tissues, while heparan sulphate was decreased in neoplastic tissues.

Glycomics expression analysis of sulfated glycosaminoglycans of human colorectal cancer tissues and non-neoplastic mucosa by electrospray ionization mass spectrometry

Energy Technology Data Exchange (ETDEWEB)

Marolla, Ana Paula Cleto [Universidade Federal de São Paulo, São Paulo, SP (Brazil); Waisberg, Jaques [Hospital do Servidor Público Estadual, São Paulo, SP (Brazil); Faculdade de Medicina do ABC, Santo André, SP (Brazil); Saba, Gabriela Tognini [Faculdade de Medicina do ABC, Santo André, SP (Brazil); Waisberg, Daniel Reis [Faculdade de Medicina da Universidade de São Paulo, São Paulo, SP (Brazil); Margeotto, Fernando Beani; Pinhal, Maria Aparecida da Silva [Faculdade de Medicina do ABC, Santo André, SP (Brazil)

2015-07-01

To determine the presence of glycosaminoglycans in the extracellular matrix of connective tissue from neoplastic and non-neoplastic colorectal tissues, since it has a central role in tumor development and progression. Tissue samples from neoplastic and non-neoplastic colorectal tissues were obtained from 64 operated patients who had colorectal carcinoma with no distant metastases. Expressions of heparan sulphate, chondroitin sulphate, dermatan sulphate and their fragments were analyzed by electrospray ionization mass spectrometry, with the technique for extraction and quantification of glycosaminoglycans after proteolysis and electrophoresis. The statistical analysis included mean, standard deviation, and Student’s t test. The glycosaminoglycans extracted from colorectal tissue showed three electrophoretic bands in agarose gel. Electrospray ionization mass spectrometry showed characteristic disaccharide fragments from glycosaminoglycans, indicating their structural characterization in the tissues analyzed. Some peaks in the electrospray ionization mass spectrometry were not characterized as fragments of sugars, indicating the presence of fragments of the protein structure of proteoglycans generated during the glycosaminoglycan purification. The average amount of chondroitin and dermatan increased in the neoplastic tissue compared to normal tissue (p=0.01). On the other hand, the average amount of heparan decreased in the neoplastic tissue compared to normal tissue (p= 0.03). The method allowed the determination of the glycosaminoglycans structural profile in colorectal tissue from neoplastic and non-neoplastic colorectal tissue. Neoplastic tissues showed greater amounts of chondroitin sulphate and dermatan sulphate compared to non-neoplastic tissues, while heparan sulphate was decreased in neoplastic tissues.

Glycomics expression analysis of sulfated glycosaminoglycans of human colorectal cancer tissues and non-neoplastic mucosa by electrospray ionization mass spectrometry

International Nuclear Information System (INIS)

Marolla, Ana Paula Cleto; Waisberg, Jaques; Saba, Gabriela Tognini; Waisberg, Daniel Reis; Margeotto, Fernando Beani; Pinhal, Maria Aparecida da Silva

2015-01-01

To determine the presence of glycosaminoglycans in the extracellular matrix of connective tissue from neoplastic and non-neoplastic colorectal tissues, since it has a central role in tumor development and progression. Tissue samples from neoplastic and non-neoplastic colorectal tissues were obtained from 64 operated patients who had colorectal carcinoma with no distant metastases. Expressions of heparan sulphate, chondroitin sulphate, dermatan sulphate and their fragments were analyzed by electrospray ionization mass spectrometry, with the technique for extraction and quantification of glycosaminoglycans after proteolysis and electrophoresis. The statistical analysis included mean, standard deviation, and Student’s t test. The glycosaminoglycans extracted from colorectal tissue showed three electrophoretic bands in agarose gel. Electrospray ionization mass spectrometry showed characteristic disaccharide fragments from glycosaminoglycans, indicating their structural characterization in the tissues analyzed. Some peaks in the electrospray ionization mass spectrometry were not characterized as fragments of sugars, indicating the presence of fragments of the protein structure of proteoglycans generated during the glycosaminoglycan purification. The average amount of chondroitin and dermatan increased in the neoplastic tissue compared to normal tissue (p=0.01). On the other hand, the average amount of heparan decreased in the neoplastic tissue compared to normal tissue (p= 0.03). The method allowed the determination of the glycosaminoglycans structural profile in colorectal tissue from neoplastic and non-neoplastic colorectal tissue. Neoplastic tissues showed greater amounts of chondroitin sulphate and dermatan sulphate compared to non-neoplastic tissues, while heparan sulphate was decreased in neoplastic tissues

Ultra-low emittance beam generation using two-color ionization injection in a CO2 laser-driven plasma accelerator

International Nuclear Information System (INIS)

Schroeder, Carl; Benedetti, Carlo; Bulanov, Stepan; Chen, Min; Esarey, Eric; Geddes, Cameron; Vay, J.; Yu, Lule; Leemans, Wim

2015-01-01

Ultra-low emittance (tens of nm) beams can be generated in a plasma accelerator using ionization injection of electrons into a wakefield. An all-optical method of beam generation uses two laser pulses of different colors. A long-wavelength drive laser pulse (with a large ponderomotive force and small peak electric field) is used to excite a large wakefield without fully ionizing a gas, and a short-wavelength injection laser pulse (with a small ponderomotive force and large peak electric field), co-propagating and delayed with respect to the pump laser, to ionize a fraction of the remaining bound electrons at a trapped wake phase, generating an electron beam that is accelerated in the wake. The trapping condition, the ionized electron distribution, and the trapped bunch dynamics are discussed. Expressions for the beam transverse emittance, parallel and orthogonal to the ionization laser polarization, are presented. An example is shown using a 10-micron CO 2 laser to drive the wake and a frequency-doubled Ti:Al 2 O 3 laser for ionization injection.

Differentiating chondroitin sulfate glycosaminoglycans using collision-induced dissociation; uronic acid cross-ring diagnostic fragments in a single stage of tandem mass spectrometry.

Science.gov (United States)

Kailemia, Muchena J; Patel, Anish B; Johnson, Dane T; Li, Lingyun; Linhardt, Robert J; Amster, I Jonathan

2015-01-01

The stereochemistry of the hexuronic acid residues of the structure of glycosaminoglycans (GAGs) is a key feature that affects their interactions with proteins and other biological functions. Electron based tandem mass spectrometry methods, in particular electron detachment dissociation (EDD), have been able to distinguish glucuronic acid (GlcA) from iduronic acid (IdoA) residues in some heparan sulfate tetrasaccharides by producing epimer-specific fragments. Similarly, the relative abundance of glycosidic fragment ions produced by collision-induced dissociation (CID) or EDD has been shown to correlate with the type of hexuronic acid present in chondroitin sulfate GAGs. The present work examines the effect of charge state and degree of sodium cationization on the CID fragmentation products that can be used to distinguish GlcA and IdoA containing chondroitin sulfate A and dermatan sulfate chains. The cross-ring fragments (2,4)A(n) and (0,2)X(n) formed within the hexuronic acid residues are highly preferential for chains containing GlcA, distinguishing it from IdoA. The diagnostic capability of the fragments requires the selection of a molecular ion and fragment ions with specific ionization characteristics, namely charge state and number of ionizable protons. The ions with the appropriate characteristics display diagnostic properties for all the chondroitin sulfate and dermatan sulfate chains (degree of polymerization of 4-10) studied.

Positive and negative ion mode comparison for the determination of DNA/peptide noncovalent binding sites through the formation of "three-body" noncovalent fragment ions.

Science.gov (United States)

Brahim, Bessem; Tabet, Jean-Claude; Alves, Sandra

2018-02-01

Gas-phase fragmentation of single strand DNA-peptide noncovalent complexes is investigated in positive and negative electrospray ionization modes.Collision-induced dissociation experiments, performed on the positively charged noncovalent complex precursor ions, have confirmed the trend previously observed in negative ion mode, i.e. a high stability of noncovalent complexes containing very basic peptidic residues (i.e. R > K) and acidic nucleotide units (i.e. Thy units), certainly incoming from the existence of salt bridge interactions. Independent of the ion polarity, stable noncovalent complex precursor ions were found to dissociate preferentially through covalent bond cleavages of the partners without disrupting noncovalent interactions. The resulting DNA fragment ions were found to be still noncovalently linked to the peptides. Additionally, the losses of an internal nucleic fragment producing "three-body" noncovalent fragment ions were also observed in both ion polarities, demonstrating the spectacular salt bridge interaction stability. The identical fragmentation patterns (regardless of the relative fragment ion abundances) observed in both polarities have shown a common location of salt bridge interaction certainly preserved from solution. Nonetheless, most abundant noncovalent fragment ions (and particularly three-body ones) are observed from positively charged noncovalent complexes. Therefore, we assume that, independent of the preexisting salt bridge interaction and zwitterion structures, multiple covalent bond cleavages from single-stranded DNA/peptide complexes rely on an excess of positive charges in both electrospray ionization ion polarities.

Enhancement of strong-field multiple ionization in the vicinity of the conical intersection in 1,3-cyclohexadiene ring opening

International Nuclear Information System (INIS)

Petrovic, Vladimir S.; Kim, Jaehee; Schorb, Sebastian; White, James; Cryan, James P.; Zipp, Lucas; Glownia, J. Michael; Broege, Douglas; Miyabe, Shungo; Tao, Hongli; Martinez, Todd; Bucksbaum, Philip H.

2013-01-01

Nonradiative energy dissipation in electronically excited polyatomic molecules proceeds through conical intersections, loci of degeneracy between electronic states. We observe a marked enhancement of laser-induced double ionization in the vicinity of a conical intersection during a non-radiative transition. We measured double ionization by detecting the kinetic energy of ions released by laser-induced strong-field fragmentation during the ring-opening transition between 1,3-cyclohexadiene and 1,3,5-hexatriene. The enhancement of the double ionization correlates with the conical intersection between the HOMO and LUMO orbitals

Resonance enhanced multiphoton ionization spectra of molecules and molecular fragments. Annual progress report, March 1992 - February 1993

International Nuclear Information System (INIS)

1993-01-01

In this report, the author will review the progress made in his studies of ion rotational distributions resulting from resonance enhanced multiphoton ionization of excited electronic states and from single-photon ionization of ground electronic states of jet-cooled molecules by coherent VUV and XUV radiation. To do so he will select a few examples from his studies which serve to highlight his progress and to identify the background and significance of the specific spectral features and systems he has chosen to study

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

Science.gov (United States)

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

2018-04-01

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

uv laser induced molecular multiphoton ionization and fragmentation. [Intensity dependence, ion properties and yield

Energy Technology Data Exchange (ETDEWEB)

Rockwood, S; Reilly, J P; Hohla, K; Kompa, K L

1979-02-01

It has been demonstrated that the output from a discharge pumped KrF laser (249 nm) is capable of ionizing a variety of molecules. The nature and yield of ions generated in this process, which were identified by time-of-flight mass spectrometry, exhibit a striking intensity dependence. 12 references, 3 figures.

Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers

International Nuclear Information System (INIS)

Assamagan, K.; Baker, K.; Bayatyan, G.; Carlini, R.; Danagoulian, S.; Eden, T.; Egiyan, K.; Ent, R.; Fenker, H.; Gan, L.; Gasparian, A.; Grigoryan, N.; Greenwood, Z.; Gueye, P.; Hashimoto, O.; Johnston, K.; Keppel, C.; Knyazyan, S.; Majewski, S.; Margaryan, A.; Margaryan, Yu.; Marikyan, G.; Martoff, J.; Mkrtchyan, H.; Parlakyan, L.; Sato, Y.; Sawafta, R.; Simicevic, N.; Tadevosyan, V.; Takahashi, T.; Tang, L.; Vartanyan, G.; Vulcan, W.; Wells, S.; Wood, S.

1999-01-01

A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a 252 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm 2 was achieved

Localization of ionization-induced trapping in a laser wakefield accelerator using a density down-ramp

CERN Document Server

Hansson, M.; Ekerfelt, H.; Aurand, B.; Gallardo Ganzalez, I.; Desforges, F. G.; Davoine, X.; Maitrallain, A.; Reymond, S.; Monot, P.; Persson, A.; Dobosz Dufrénoy S.; Wahlström C-G.; Cros, B.; Lundh, O.

2016-01-01

We report on a study on controlled trapping of electrons, by field ionization of nitrogen ions, in laser wakefield accelerators in variable length gas cells. In addition to ionization-induced trapping in the density plateau inside the cells, which results in wide, but stable, electron energy spectra, a regime of ionization-induced trapping localized in the density down-ramp at the exit of the gas cells, is found. The resulting electron energy spectra are peaked, with 10% shot-to-shot fluctuations in peak energy. Ionization-induced trapping of electrons in the density down-ramp is a way to trap and accelerate a large number of electrons, thus improving the efficiency of the laser-driven wakefield acceleration.

Enhanced signal generation for use in the analysis of synthetic pyrethroids using chemical ionization tandem quadrupole ion trap mass spectrometry.

Science.gov (United States)

Sichilongo, Kwenga

2004-12-01

Synthetic pyrethroids fragment extensively under electron ionization (EI) conditions to give low mass ions, most of them with the same m/z ratios. This fragmentation is primarily due to the labile ester linkage found in these compounds. In this research we established the best gas chromatography (GC) conditions in the EI mode that served as a benchmark in the development of a chemical ionization (CI) protocol for ten selected synthetic pyrethroids. Based on proton affinity data, several reagent gases were evaluated in the positive CI ionization mode. Methanol was found to produce higher average ion counts relative to the other gases evaluated, which led to the development of an optimized method consisting of selective ejection chemical ionization (SECI) and MS/MS. Standard stainless steel ion trap electrodes produced significant degradation of chromatographic performance on late eluting compounds, which was attributed to electrode surface chemistry. A dramatic improvement in signal-to-noise (S/N) ratios was observed when the chromatographically inert Silcosteel coated electrodes were used. The resulting method, that has significant S/N ratio improvements resulting from a combination of septum programmable injections (SPI), optimized CI and inert Silcosteel-coated electrodes, was used to determine instrument detection limits.

Rapid decay of tree-community composition in Amazonian forest fragments

Science.gov (United States)

Laurance, William F.; Nascimento, Henrique E. M.; Laurance, Susan G.; Andrade, Ana; Ribeiro, José E. L. S.; Giraldo, Juan Pablo; Lovejoy, Thomas E.; Condit, Richard; Chave, Jerome; Harms, Kyle E.; D'Angelo, Sammya

2006-01-01

Forest fragmentation is considered a greater threat to vertebrates than to tree communities because individual trees are typically long-lived and require only small areas for survival. Here we show that forest fragmentation provokes surprisingly rapid and profound alterations in Amazonian tree-community composition. Results were derived from a 22-year study of exceptionally diverse tree communities in 40 1-ha plots in fragmented and intact forests, which were sampled repeatedly before and after fragment isolation. Within these plots, trajectories of change in abundance were assessed for 267 genera and 1,162 tree species. Abrupt shifts in floristic composition were driven by sharply accelerated tree mortality and recruitment within ≈100 m of fragment margins, causing rapid species turnover and population declines or local extinctions of many large-seeded, slow-growing, and old-growth taxa; a striking increase in a smaller set of disturbance-adapted and abiotically dispersed species; and significant shifts in tree size distributions. Even among old-growth trees, species composition in fragments is being restructured substantially, with subcanopy species that rely on animal seed-dispersers and have obligate outbreeding being the most strongly disadvantaged. These diverse changes in tree communities are likely to have wide-ranging impacts on forest architecture, canopy-gap dynamics, plant–animal interactions, and forest carbon storage. PMID:17148598

Propagation of a laser-driven relativistic electron beam inside a solid dielectric.

Science.gov (United States)

Sarkisov, G S; Ivanov, V V; Leblanc, P; Sentoku, Y; Yates, K; Wiewior, P; Chalyy, O; Astanovitskiy, A; Bychenkov, V Yu; Jobe, D; Spielman, R B

2012-09-01

Laser probe diagnostics: shadowgraphy, interferometry, and polarimetry were used for a comprehensive characterization of ionization wave dynamics inside a glass target induced by a laser-driven, relativistic electron beam. Experiments were done using the 50-TW Leopard laser at the University of Nevada, Reno. We show that for a laser flux of ∼2 × 10(18) W/cm2 a hemispherical ionization wave propagates at c/3 for 10 ps and has a smooth electron-density distribution. The maximum free-electron density inside the glass target is ∼2 × 10(19) cm-3, which corresponds to an ionization level of ∼0.1%. Magnetic fields and electric fields do not exceed ∼15 kG and ∼1 MV/cm, respectively. The electron temperature has a hot, ringlike structure with a maximum of ∼0.7 eV. The topology of the interference phase shift shows the signature of the "fountain effect", a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields driven by laser. The very low ionization observed after the laser heating pulse suggests a fast recombination on the sub-ps time scale.

FRAGSION: ultra-fast protein fragment library generation by IOHMM sampling.

Science.gov (United States)

Bhattacharya, Debswapna; Adhikari, Badri; Li, Jilong; Cheng, Jianlin

2016-07-01

Speed, accuracy and robustness of building protein fragment library have important implications in de novo protein structure prediction since fragment-based methods are one of the most successful approaches in template-free modeling (FM). Majority of the existing fragment detection methods rely on database-driven search strategies to identify candidate fragments, which are inherently time-consuming and often hinder the possibility to locate longer fragments due to the limited sizes of databases. Also, it is difficult to alleviate the effect of noisy sequence-based predicted features such as secondary structures on the quality of fragment. Here, we present FRAGSION, a database-free method to efficiently generate protein fragment library by sampling from an Input-Output Hidden Markov Model. FRAGSION offers some unique features compared to existing approaches in that it (i) is lightning-fast, consuming only few seconds of CPU time to generate fragment library for a protein of typical length (300 residues); (ii) can generate dynamic-size fragments of any length (even for the whole protein sequence) and (iii) offers ways to handle noise in predicted secondary structure during fragment sampling. On a FM dataset from the most recent Critical Assessment of Structure Prediction, we demonstrate that FGRAGSION provides advantages over the state-of-the-art fragment picking protocol of ROSETTA suite by speeding up computation by several orders of magnitude while achieving comparable performance in fragment quality. Source code and executable versions of FRAGSION for Linux and MacOS is freely available to non-commercial users at http://sysbio.rnet.missouri.edu/FRAGSION/ It is bundled with a manual and example data. chengji@missouri.edu Supplementary data are available at Bioinformatics online. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Wave-driven countercurrent plasma centrifuge

Energy Technology Data Exchange (ETDEWEB)

Fetterman, Abraham J; Fisch, Nathaniel J [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08540 (United States)

2009-11-15

A method for driving rotation and a countercurrent flow in a fully ionized plasma centrifuge is described. The rotation is produced by radiofrequency waves near the cyclotron resonance. The wave energy is transferred into potential energy in a manner similar to the {alpha} channeling effect. The countercurrent flow may also be driven by radiofrequency waves. By driving both the rotation and the flow pattern using waves instead of electrodes, physical and engineering issues may be avoided.

Wave-driven countercurrent plasma centrifuge

International Nuclear Information System (INIS)

Fetterman, Abraham J; Fisch, Nathaniel J

2009-01-01

A method for driving rotation and a countercurrent flow in a fully ionized plasma centrifuge is described. The rotation is produced by radiofrequency waves near the cyclotron resonance. The wave energy is transferred into potential energy in a manner similar to the α channeling effect. The countercurrent flow may also be driven by radiofrequency waves. By driving both the rotation and the flow pattern using waves instead of electrodes, physical and engineering issues may be avoided.

Wave-driven Countercurrent Plasma Centrifuge

International Nuclear Information System (INIS)

Fetterman, A.J.; Fisch, N.J.

2009-01-01

A method for driving rotation and a countercurrent flow in a fully ionized plasma centrifuge is described. The rotation is produced by radiofrequency waves near the cyclotron resonance. The wave energy is transferred into potential energy in a manner similar to the α channeling effect. The countercurrent flow may also be driven by radiofrequency waves. By driving both the rotation and the flow pattern using waves instead of electrodes, physical and engineering issues may be avoided

Photo-electron spectroscopy using synchrotron radiation of molecular radicals and fragments produced by laser photo-dissociation

International Nuclear Information System (INIS)

Nahon, Laurent

1991-01-01

This research thesis reports the combined use of a laser and of a synchrotron radiation in order to respectively photo-dissociate a molecule and to photo-ionize fragments which are analysed by photo-electron spectroscopy. This association allows, on the one hand, radical photo-ionization to be studied, and, on the other hand, polyatomic molecule photo-dissociation to be studied. The author studied the photo-excitation and/or photo-ionization in layer 4d (resp. 3d) of atomic iodine (resp. bromine) produced almost complete laser photo-dissociation of I_2 (resp. Br_2). He discuses the processes of relaxation of transitions from valence 4d to 5p (resp. 3d to 4p) which occur either by direct self-ionization or by resonant Auger effect, and reports the study of photo-dissociation of s-tetrazine (C_2N_4H_2) [fr

Fragmentation characteristics of hydroxycinnamic acids in ESI-MSn by density functional theory.

Science.gov (United States)

Yin, Zhi-Hui; Sun, Chang-Hai; Fang, Hong-Zhuang

2017-07-01

This work aims to analyze the electrospray ionization multistage mass spectrometry (ESI-MS n ) fragmentation characteristics of hydroxycinnamic acids (HCAs) in negative ion mode. The geometric parameters, energies, natural bond orbitals and frontier orbitals of fragments were calculated by density functional theory (DFT) to investigate mass spectral fragmentation mechanisms. The results showed that proton transfer always occurred during fragmentation of HCAs; their quasi-molecular ions ([M - H] - ) existed in more than one form and were mainly with the lowest energy. The fragmentation characteristics included the followings: (1) according to the different substitution position of phenolic hydroxyl group, the ring contraction reaction by CO elimination from benzene was in an increasingly difficult order: m-phenolic hydroxyl > p-phenolic hydroxyl > o-phenolic hydroxyl; and (2) ortho effect always occurred in o-dihydroxycinnamic acids (o-diHCAs), i.e. one phenolic hydroxyl group offered H + , which combined with the other one to lose H 2 O. In addition, there was a nucleophilic reaction during ring contraction in diHCAs that oxygen atom attacked the carbon atom binding with the other phenolic hydroxyl to lose CO 2 . The fragmentation characteristics and mechanism of HCAs could be used for analysis and identification of such compounds quickly and effectively, and as reference for structural analogues by ESI-MS. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

Energy and charge transfer in ionized argon coated water clusters

International Nuclear Information System (INIS)

Kočišek, J.; Lengyel, J.; Fárník, M.; Slavíček, P.

2013-01-01

We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H 2 O) n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar + and water occurs above the threshold; at higher electron energies above ∼28 eV, an excitonic transfer process between Ar + * and water opens leading to new products Ar n H + and (H 2 O) n H + . On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H 2 O) n H 2 2+ and (H 2 O) n 2+ ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent

Resonance multiphoton ionization and dissociation of dimethyl ether via the {\\skew1\\tilde{\\rm C}^{\\prime}}, {\\skew1\\tilde{\\rm C}} and \\tilde{\\rm B} states

Science.gov (United States)

Mejia-Ospino, E.; García, G.; Guerrero, A.; Alvarez, I.; Cisneros, C.

2005-01-01

The three-photon resonance four-photon ionization and dissociation spectra of dimethyl ether (DME) are presented in the wavelength range 450-550 nm at 1 nm intervals. The (3+1) REMPI spectra show three prominent bands corresponding to the \\tildeB \\leftarrow \\skew1\\tildeX, {\\skew1\\tildeC} \\leftarrow \\skew1\\tildeX and {\\skew1\\tildeC^{\\prime}} \\leftarrow \\skew1\\tildeX transitions with origins at 61 457 cm-1 (7.615 eV), 59 055 cm-1 (7.322 eV) and 58 010 cm-1 (7.194 eV), respectively. Several ionized species, CH3+, CHnO+ (n = 1-3) and CH3OCH3+, are observed in the region of wavelengths studied here. In order to compare the results, a shorter wavelength multiphoton dissociation and ionization of DME at 355 nm is also presented. At this wavelength, DME undergoes neutral dissociation to CH3 and CH3O and each fragment is then ionized by multiphoton absorption. The fragmentation at 355 nm is very intense and only small fragments such as CH3+, CHO+, CH2+, CH+ and C+ ions are observed. The measurement of photoelectron energy allows us to establish that the DME ionization potential is at least 9.55 ± 0.15 eV. The experiments were performed using a Nd:YAG-OPO (optical parametric oscillator) tunable laser system coupled to a time-of-flight mass spectrometer and a hemispherical electron energy analyser.

Understanding deposition rate loss in high power impulse magnetron sputtering: I. Ionization-driven electric fields

International Nuclear Information System (INIS)

Brenning, N; Huo, C; Raadu, M A; Lundin, D; Helmersson, U; Vitelaru, C; Stancu, G D; Minea, T

2012-01-01

The lower deposition rate for high power impulse magnetron sputtering (HiPIMS) compared with direct current magnetron sputtering for the same average power is often reported as a drawback. The often invoked reason is back-attraction of ionized sputtered material to the target due to a substantial negative potential profile, sometimes called an extended presheath, from the location of ionization toward the cathode. Recent studies in HiPIMS devices, using floating-emitting and swept-Langmuir probes, show that such extended potential profiles do exist, and that the electric fields E z directed toward the target can be strong enough to seriously reduce ion transport to the substrate. However, they also show that the potential drops involved can vary by up to an order of magnitude from case to case. There is a clear need to understand the underlying mechanisms and identify the key discharge variables that can be used for minimizing the back-attraction. We here present a combined theoretical and experimental analysis of the problem of electric fields E z in the ionization region part of HiPIMS discharges, and their effect on the transport of ionized sputtered material. In particular, we have investigated the possibility of a ‘sweet spot’ in parameter space in which the back-attraction of ionized sputtered material is low. It is concluded that a sweet spot might possibly exist for some carefully optimized discharges, but probably in a rather narrow window of parameters. As a measure of how far a discharge is from such a window, a Townsend product Π Townsend is proposed. A parametric analysis of Π Townsend shows that the search for a sweet spot is complicated by the fact that contradictory demands appear for several of the externally controllable parameters such as high/low working gas pressure, short/long pulse length, high/low pulse power and high/low magnetic field strength. (paper)

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

International Nuclear Information System (INIS)

Alton, G.D.; Williams, C.

1995-01-01

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

Interference effects in double ionization of spatially aligned hydrogen molecules by fast highly charged ions

International Nuclear Information System (INIS)

Landers, A.L.; Alnaser, A.S.; Tanis, J.A.; Wells, E.; Osipov, T.; Carnes, K.D.; Ben-Itzhak, I.; Cocke, C.L.; McGuire, J.H.

2004-01-01

Cross sections differential in target orientation angle were measured for 19 MeV F 8+ +D 2 collisions. Multihit position-sensitive detectors were used to isolate the double-ionization channel and determine a posteriori the full momentum vectors of both ejected D + fragments. A strong dependence of the double ionization cross section on the angle between the incident ion direction and the target molecular axis is observed with a ≅3.5:1 enhancement for molecules aligned perpendicular to the projectile axis. This clear asymmetry is attributed to interference effects, analogous to Young's two-slit experiment, arising from coherent contributions to the ionization from both atomic centers. The data are compared to a simple scattering model based on two center interference

Polymerization, shock cooling and ionization of liquid nitrogen

Energy Technology Data Exchange (ETDEWEB)

Ross, M; Rogers, F

2005-07-21

The trajectory of thermodynamic states passed through by the nitrogen Hugoniot starting from the liquid and up to 10{sup 6} GPa has been studied. An earlier report of cooling in the doubly shocked liquid, near 50 to 100 GPa and 7500 K, is revisited in light of the recent discovery of solid polymeric nitrogen. It is found that cooling occurs when the doubly shocked liquid is driven into a volume near the molecular to polymer transition and raising the possibility of a liquid-liquid phase transition (LLPT). By increasing the shock pressure and temperature by an order of magnitude, theoretical calculations predict thermal ionization of the L shell drives the compression maxima to 5-6 fold compression at 10 Mbar (T {approx} 3.5 10{sup 5} K) and at 400 Mbar (T {approx} 2.3 10{sup 6} K) from K shell ionization. Near a pressure of 10{sup 6} GPa the K shell ionizes completely and the Hugoniot approaches the classical ideal gas compression fourfold limit.

Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers

CERN Document Server

Assamagan, Ketevi A; Bayatyan, G L; Carlini, R; Danagulyan, S; Eden, T; Egiyan, K; Ent, R; Fenker, H; Gan, L; Gasparian, A; Grigoryan, N K; Greenwood, Z; Gueye, P; Hashimoto, O; Johnston, K; Keppel, C; Knyazyan, S; Majewski, S; Margaryan, A; Margaryan, Yu L; Marikian, G G; Martoff, J; Mkrtchyan, H G; Parlakyan, L; Sato, Y; Sawafta, R; Simicevic, N; Tadevosyan, V; Takahashi, T; Tang, L; Vartanian, G S; Vulcan, W; Wells, S; Wood, S

1999-01-01

A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a sup 2 sup 5 sup 2 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm sup 2 was achieved.

Mercury-induced fragmentation of n-decane and n-undecane in positive mode ion mobility spectrometry.

Science.gov (United States)

Gunzer, F

2015-09-21

Ion mobility spectrometry is a well-known technique for trace gas analysis. Using soft ionization techniques, fragmentation of analytes is normally not observed, with the consequence that analyte spectra of single substances are quite simple, i.e. showing in general only one peak. If the concentration is high enough, an extra cluster peak involving two analyte molecules can often be observed. When investigating n-alkanes, different results regarding the number of peaks in the spectra have been obtained in the past using this spectrometric technique. Here we present results obtained when analyzing n-alkanes (n-hexane to n-undecane) with a pulsed electron source, which show no fragmentation or clustering at all. However, when investigating a mixture of mercury and an n-alkane, a situation quite typical in the oil and gas industry, a strong fragmentation and cluster formation involving these fragments has been observed exclusively for n-decane and n-undecane.

Simultaneous atomization and ionization of large organic molecules using femtosecond laser ablation

International Nuclear Information System (INIS)

Kurata-Nishimura, Mizuki; Tokanai, Fuyuki; Matsuo, Yukari; Kobayashi, Tohru; Kawai, Jun; Kumagai, Hiroshi; Midorikawa, Katsumi; Tanihata, Isao; Hayashizaki, Yoshihide

2002-01-01

We have experimentally demonstrated femtosecond laser ablation for simultaneous atomization and ionization (fs-SAI) of organic molecules on solid substrates. We find most of the constituent atoms of organic molecules are atomized and ionized non-resonantly by femtosecond laser ablation. This observation is in contrast with that for the photoionization of cyclic aromatic hydrocarbons by femtosecond laser in the gas phase where little fragmentation has been observed. Crucial contribution of ablation plasma of solid sample to fs-SAI process is suggested. The ratio of natural abundance of stable isotopes contained in sample molecules is well reproduced, which confirms fs-SAI can be applied to the quantitative chemical analysis of isotope-labeled large organic molecules

The coordination between mechanical and chemical subsystems initiates locomotion of Physarum plasmodial fragments

Science.gov (United States)

Zhang, Shun; Guy, Robert; Del Alamo, Juan Carlos

2017-11-01

Physarum polycephalum is a multinucleated slime mold whose endoplasm flows periodically driven by the contraction of its ectoplasm, a dense shell of F-actin cross-linked by myosin molecular motors and attached to the cell membrane. We find that physarum fragments smaller than 100 microns remain round and stay in place. However, larger fragments break symmetry leading to sustained forward locomotion, in process that is reminiscent of an interfacial instability that seems to settle around two different limit cycles (traveling waves and standing waves). We use both theory and experiments to study how coordination emerges between the different mechanical and chemical subsystems of the fragment to initiate locomotion. The role of many involved factors, such as fragment size, substratum adhesiveness, rheological properties, actin polymerization and traction stresses are investigated, and we find they agree well with our predictive model.

MAGNETOACOUSTIC WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA

Energy Technology Data Exchange (ETDEWEB)

Soler, Roberto; Ballester, Jose Luis [Departament de Física, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Carbonell, Marc, E-mail: roberto.soler@uib.es, E-mail: joseluis.ballester@uib.es, E-mail: marc.carbonell@uib.es [Departament de Matemàtiques i Informàtica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)

2013-11-01

Compressible disturbances propagate in a plasma in the form of magnetoacoustic waves driven by both gas pressure and magnetic forces. In partially ionized plasmas the dynamics of ionized and neutral species are coupled due to ion-neutral collisions. As a consequence, magnetoacoustic waves propagating through a partially ionized medium are affected by ion-neutral coupling. The degree to which the behavior of the classic waves is modified depends on the physical properties of the various species and on the relative value of the wave frequency compared to the ion-neutral collision frequency. Here, we perform a comprehensive theoretical investigation of magnetoacoustic wave propagation in a partially ionized plasma using the two-fluid formalism. We consider an extensive range of values for the collision frequency, ionization ratio, and plasma β, so that the results are applicable to a wide variety of astrophysical plasmas. We determine the modification of the wave frequencies and study the frictional damping due to ion-neutral collisions. Approximate analytic expressions for the frequencies are given in the limit case of strongly coupled ions and neutrals, while numerically obtained dispersion diagrams are provided for arbitrary collision frequencies. In addition, we discuss the presence of cutoffs in the dispersion diagrams that constrain wave propagation for certain combinations of parameters. A specific application to propagation of compressible waves in the solar chromosphere is given.

MAGNETOACOUSTIC WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA

International Nuclear Information System (INIS)

Soler, Roberto; Ballester, Jose Luis; Carbonell, Marc

2013-01-01

Compressible disturbances propagate in a plasma in the form of magnetoacoustic waves driven by both gas pressure and magnetic forces. In partially ionized plasmas the dynamics of ionized and neutral species are coupled due to ion-neutral collisions. As a consequence, magnetoacoustic waves propagating through a partially ionized medium are affected by ion-neutral coupling. The degree to which the behavior of the classic waves is modified depends on the physical properties of the various species and on the relative value of the wave frequency compared to the ion-neutral collision frequency. Here, we perform a comprehensive theoretical investigation of magnetoacoustic wave propagation in a partially ionized plasma using the two-fluid formalism. We consider an extensive range of values for the collision frequency, ionization ratio, and plasma β, so that the results are applicable to a wide variety of astrophysical plasmas. We determine the modification of the wave frequencies and study the frictional damping due to ion-neutral collisions. Approximate analytic expressions for the frequencies are given in the limit case of strongly coupled ions and neutrals, while numerically obtained dispersion diagrams are provided for arbitrary collision frequencies. In addition, we discuss the presence of cutoffs in the dispersion diagrams that constrain wave propagation for certain combinations of parameters. A specific application to propagation of compressible waves in the solar chromosphere is given

Nova-driven winds in globular clusters

International Nuclear Information System (INIS)

Scott, E.H.; Durisen, R.H.

1978-01-01

Recent sensitive searches for Hα emission from ionized intracluster gas in globular clusters have set upper limits that conflict with theoretical predictions. We suggest that nova outbursts heat the gas, producing winds that resolve this discrepancy. The incidence of novae in globular clusters, the conversion of kinetic energy of the nova shell to thermal energy of the intracluster gas, and the characteristics of the resultant winds are discussed. Calculated emission from the nova-driven models does not conflict with any observations to date. Some suggestions are made concerning the most promising approaches for future detection of intracluster gas on the basis of these models. The possible relationship of nova-driven winds of globular cluster X-ray sources is also considered

Characterization of nitrated sugar alcohols by atmospheric-pressure chemical-ionization mass spectrometry.

Science.gov (United States)

Ostrinskaya, Alla; Kelley, Jude A; Kunz, Roderick R

2017-02-28

The nitrated sugar alcohols mannitol hexanitrate (MHN), sorbitol hexanitrate (SHN) and xylitol pentanitrate (XPN) are in the same class of compounds as the powerful military-grade explosive pentaerythritol tetranitrate (PETN) and the homemade explosive erythritol tetranitrate (ETN) but, unlike for PETN and ETN, ways to detect MHN, SHN and XPN by mass spectrometry (MS) have not been fully investigated. Atmospheric-pressure chemical-ionization mass spectrometry (APCI-MS) was used to detect ions characteristic of nitrated sugar alcohols. APCI time-of-flight mass spectrometry (APCI-TOF MS) and collision-induced dissociation tandem mass spectrometry (CID MS/MS) were used for confirmation of each ion assignment. In addition, the use of the chemical ionization reagent dichloromethane was investigated to improve sensitivity and selectivity for detection of MHN, SHN and XPN. All the nitrated sugar alcohols studied followed similar fragmentation pathways in the APCI source. MHN, SHN and XPN were detectable as fragment ions formed by the loss of NO 2 , HNO 2 , NO 3 , and CH 2 NO 2 groups, and in the presence of dichloromethane chlorinated adduct ions were observed. It was determined that in MS/MS mode, chlorinated adducts of MHN and SHN had the lowest limits of detection (LODs), while for XPN the lowest LOD was for the [XPN-NO 2 ] - fragment ion. Partially nitrated analogs of each of the three compounds were also present in the starting materials, and ions attributable to these compounds versus those formed from in-source fragmentation of MHN, SHN, and XPN were distinguished and assigned using liquid chromatography APCI-MS and ESI-MS. The APCI-MS technique provides a selective and sensitive method for the detection of nitrated sugar alcohols. The methods disclosed here will benefit the area of explosives trace detection for counterterrorism and forensics. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Gas-phase structure and fragmentation pathways of singly protonated peptides with N-terminal arginine.

Science.gov (United States)

Bythell, Benjamin J; Csonka, István P; Suhai, Sándor; Barofsky, Douglas F; Paizs, Béla

2010-11-25

The gas-phase structures and fragmentation pathways of the singly protonated peptide arginylglycylaspartic acid (RGD) are investigated by means of collision-induced-dissociation (CID) and detailed molecular mechanics and density functional theory (DFT) calculations. It is demonstrated that despite the ionizing proton being strongly sequestered at the guanidine group, protonated RGD can easily be fragmented on charge directed fragmentation pathways. This is due to facile mobilization of the C-terminal or aspartic acid COOH protons thereby generating salt-bridge (SB) stabilized structures. These SB intermediates can directly fragment to generate b(2) ions or facilely rearrange to form anhydrides from which both b(2) and b(2)+H(2)O fragments can be formed. The salt-bridge stabilized and anhydride transition structures (TSs) necessary to form b(2) and b(2)+H(2)O are much lower in energy than their traditional charge solvated counterparts. These mechanisms provide compelling evidence of the role of SB and anhydride structures in protonated peptide fragmentation which complements and supports our recent findings for tryptic systems (Bythell, B. J.; Suhai, S.; Somogyi, A.; Paizs, B. J. Am. Chem. Soc. 2009, 131, 14057-14065.). In addition to these findings we also report on the mechanisms for the formation of the b(1) ion, neutral loss (H(2)O, NH(3), guanidine) fragment ions, and the d(3) ion.

Development of multi-layer ionization chamber for heavy-ion therapy

International Nuclear Information System (INIS)

Yajima, Kaori; Kusano, Yohsuke; Shimojyu, Takuya; Kanai, Tatsuaki

2007-01-01

In heavy-ion radiotherapy, depth dose distributions measured in water phantom are applied to estimate the dose distributions in a patient body. In order to obtain depth dose distributions in water phantom easily and rapidly, Multi-Layer Ionization Chamber (MLIC) was developed and had been adapted as a field dosimeter at NIRS since 2002. Production cross section of fragments in high Z material of the MLIC, however, is very different from those in water material. Then, empirical correction should be required. In order to obtain depth dose distributions with high accuracy, we have to use low Z material as a phantom, which are thought to produce similar fragments with water phantom. From this point of view, we have developed a new MLIC made up of low Z materials, PMMA and graphite film. (author)

Primary and secondary fragmentation of crystal-bearing intermediate magma

Science.gov (United States)

Jones, Thomas J.; McNamara, Keri; Eychenne, Julia; Rust, Alison C.; Cashman, Katharine V.; Scheu, Bettina; Edwards, Robyn

2016-11-01

Crystal-rich intermediate magmas are subjected to both primary and secondary fragmentation processes, each of which may produce texturally distinct tephra. Of particular interest for volcanic hazards is the extent to which each process contributes ash to volcanic plumes. One way to address this question is by fragmenting pyroclasts under controlled conditions. We fragmented pumice samples from Soufriere Hills Volcano (SHV), Montserrat, by three methods: rapid decompression in a shock tube-like apparatus, impact by a falling piston, and milling in a ball mill. Grain size distributions of the products reveal that all three mechanisms produce fractal breakage patterns, and that the fractal dimension increases from a minimum of 2.1 for decompression fragmentation (primary fragmentation) to a maximum of 2.7 by repeated impact (secondary fragmentation). To assess the details of the fragmentation process, we quantified the shape, texture and components of constituent ash particles. Ash shape analysis shows that the axial ratio increases during milling and that particle convexity increases with repeated impacts. We also quantify the extent to which the matrix is separated from the crystals, which shows that secondary processes efficiently remove adhering matrix from crystals, particularly during milling (abrasion). Furthermore, measurements of crystal size distributions before (using x-ray computed tomography) and after (by componentry of individual grain size classes) decompression-driven fragmentation show not only that crystals influence particular size fractions across the total grain size distribution, but also that free crystals are smaller in the fragmented material than in the original pumice clast. Taken together, our results confirm previous work showing both the control of initial texture on the primary fragmentation process and the contributions of secondary processes to ash formation. Critically, however, our extension of previous analyses to characterisation

Ionization photophysics and spectroscopy of dicyanoacetylene

Energy Technology Data Exchange (ETDEWEB)

Leach, Sydney, E-mail: Sydney.Leach@obspm.fr, E-mail: Martin.Schwell@lisa.u-pec.fr; Champion, Norbert [LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon (France); Schwell, Martin, E-mail: Sydney.Leach@obspm.fr, E-mail: Martin.Schwell@lisa.u-pec.fr; Bénilan, Yves; Fray, Nicolas; Gazeau, Marie-Claire [LISA UMR CNRS 7583, Université Paris-Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil (France); Garcia, Gustavo A.; Gaie-Levrel, François [Synchrotron SOLEIL, L’Orme des Merisiers, St. Aubin, B.P. 48, 91192 Gif-sur-Yvette Cedex (France); Guillemin, Jean-Claude [Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708 Rennes Cedex 7 (France)

2013-11-14

Photoionization of dicyanoacetylene was studied using synchrotron radiation over the excitation range 8–25 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and detailed spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of dicyanoacetylene was measured as 11.80 ± 0.01 eV. A detailed analysis of the cation spectroscopy involves new aspects and new assignments of the vibrational components to excitation of the quasi-degenerate A{sup 2}Π{sub g}, B{sup 2}Σ{sub g}{sup +} states as well as the C{sup 2}Σ{sub u}{sup +} and D{sup 2}Π{sub u} states of the cation. Some of the structured autoionization features observed in the 12.4–15 eV region of the total ion yield spectrum were assigned to vibrational components of valence shell transitions and to two previously unknown Rydberg series converging to the D{sup 2}Π{sub u} state of C{sub 4}N{sub 2}{sup +}. The appearance energies of the fragment ions C{sub 4}N{sup +}, C{sub 3}N{sup +}, C{sub 4}{sup +}, C{sub 2}N{sup +}, and C{sub 2}{sup +} were measured and their heats of formation were determined and compared with existing literature values. Thermochemical calculations of the appearance potentials of these and other weaker ions were used to infer aspects of dissociative ionization pathways.

Electron-Nuclear Energy Sharing in Above-Threshold Multiphoton Dissociative Ionization of H2

DEFF Research Database (Denmark)

Wu, J.; Kunitski, M.; Pitzer, M.

2013-01-01

We report experimental observation of the energy sharing between electron and nuclei in above-threshold multiphoton dissociative ionization of H2 by strong laser fields. The absorbed photon energy is shared between the ejected electron and nuclei in a correlated fashion, resulting in multiple...... diagonal lines in their joint energy spectrum governed by the energy conservation of all fragment particles....

Luciferase assay to study the activity of a cloned promoter DNA fragment.

Science.gov (United States)

Solberg, Nina; Krauss, Stefan

2013-01-01

Luciferase based assays have become an invaluable tool for the analysis of cloned promoter DNA fragments, both for verifying the ability of a potential promoter fragment to drive the expression of a luciferase reporter gene in various cellular contexts, and for dissecting binding elements in the promoter. Here, we describe the use of the Dual-Luciferase(®) Reporter Assay System created by Promega (Promega Corporation, Wisconsin, USA) to study the cloned 6.7 kilobases (kb) mouse (m) Tcf3 promoter DNA fragment in mouse embryonic derived neural stem cells (NSC). In this system, the expression of the firefly luciferase driven by the cloned mTcf3 promoter DNA fragment (including transcription initiation sites) is correlated with a co-transfected control reporter expressing Renilla luciferase from the herpes simplex virus (HSV) thymidine kinase promoter. Using an internal control reporter allows to normalize the activity of the experimental reporter to the internal control, which minimizes experimental variability.

Hypothesis-driven and field-validated method to prioritize fragmentation mitigation efforts in road projects.

Science.gov (United States)

Vanthomme, Hadrien; Kolowski, Joseph; Nzamba, Brave S; Alonso, Alfonso

2015-10-01

The active field of connectivity conservation has provided numerous methods to identify wildlife corridors with the aim of reducing the ecological effect of fragmentation. Nevertheless, these methods often rely on untested hypotheses of animal movements, usually fail to generate fine-scale predictions of road crossing sites, and do not allow managers to prioritize crossing sites for implementing road fragmentation mitigation measures. We propose a new method that addresses these limitations. We illustrate this method with data from southwestern Gabon (central Africa). We used stratified random transect surveys conducted in two seasons to model the distribution of African forest elephant (Loxodonta cyclotis), forest buffalo (Syncerus caffer nanus), and sitatunga (Tragelaphus spekii) in a mosaic landscape along a 38.5 km unpaved road scheduled for paving. Using a validation data set of recorded crossing locations, we evaluated the performance of three types of models (local suitability, local least-cost movement, and regional least-cost movement) in predicting actual road crossings for each species, and developed a unique and flexible scoring method for prioritizing road sections for the implementation of road fragmentation mitigation measures. With a data set collected in method was able to identify seasonal changes in animal movements for buffalo and sitatunga that shift from a local exploitation of the site in the wet season to movements through the study site in the dry season, whereas elephants use the entire study area in both seasons. These three species highlighted the need to use species- and season-specific modeling of movement. From these movement models, the method ranked road sections for their suitability for implementing fragmentation mitigation efforts, allowing managers to adjust priority thresholds based on budgets and management goals. The method relies on data that can be obtained in a period compatible with environmental impact assessment

Sodium-doping as a reference to study the influence of intracluster chemistry on the fragmentation of weakly-bound clusters upon vacuum ultraviolet photoionization

OpenAIRE

Litman Jessica H; Yoder Bruce L; Schläppi Bernhard; Signorell Ruth

2012-01-01

The fragmentation of methanol water dimethyl ether and acetic acid clusters upon photoionization with a single vacuum ultraviolet (VUV) photon of 10.1 eV 13.3 eV or 17.5 eV energy is studied with mass spectrometry. The sodium doping method is used as an independent approximate measure of the original cluster size distribution providing information on the degree of fragmentation upon VUV ionization. The experimental results show strong fragmentation for (CH3)2O and CH3CO2H clusters but minor f...

Dynameomics: Data-driven methods and models for utilizing large-scale protein structure repositories for improving fragment-based loop prediction

Science.gov (United States)

Rysavy, Steven J; Beck, David AC; Daggett, Valerie

2014-01-01

Protein function is intimately linked to protein structure and dynamics yet experimentally determined structures frequently omit regions within a protein due to indeterminate data, which is often due protein dynamics. We propose that atomistic molecular dynamics simulations provide a diverse sampling of biologically relevant structures for these missing segments (and beyond) to improve structural modeling and structure prediction. Here we make use of the Dynameomics data warehouse, which contains simulations of representatives of essentially all known protein folds. We developed novel computational methods to efficiently identify, rank and retrieve small peptide structures, or fragments, from this database. We also created a novel data model to analyze and compare large repositories of structural data, such as contained within the Protein Data Bank and the Dynameomics data warehouse. Our evaluation compares these structural repositories for improving loop predictions and analyzes the utility of our methods and models. Using a standard set of loop structures, containing 510 loops, 30 for each loop length from 4 to 20 residues, we find that the inclusion of Dynameomics structures in fragment-based methods improves the quality of the loop predictions without being dependent on sequence homology. Depending on loop length, ∼25–75% of the best predictions came from the Dynameomics set, resulting in lower main chain root-mean-square deviations for all fragment lengths using the combined fragment library. We also provide specific cases where Dynameomics fragments provide better predictions for NMR loop structures than fragments from crystal structures. Online access to these fragment libraries is available at http://www.dynameomics.org/fragments. PMID:25142412

Dynameomics: data-driven methods and models for utilizing large-scale protein structure repositories for improving fragment-based loop prediction.

Science.gov (United States)

Rysavy, Steven J; Beck, David A C; Daggett, Valerie

2014-11-01

Protein function is intimately linked to protein structure and dynamics yet experimentally determined structures frequently omit regions within a protein due to indeterminate data, which is often due protein dynamics. We propose that atomistic molecular dynamics simulations provide a diverse sampling of biologically relevant structures for these missing segments (and beyond) to improve structural modeling and structure prediction. Here we make use of the Dynameomics data warehouse, which contains simulations of representatives of essentially all known protein folds. We developed novel computational methods to efficiently identify, rank and retrieve small peptide structures, or fragments, from this database. We also created a novel data model to analyze and compare large repositories of structural data, such as contained within the Protein Data Bank and the Dynameomics data warehouse. Our evaluation compares these structural repositories for improving loop predictions and analyzes the utility of our methods and models. Using a standard set of loop structures, containing 510 loops, 30 for each loop length from 4 to 20 residues, we find that the inclusion of Dynameomics structures in fragment-based methods improves the quality of the loop predictions without being dependent on sequence homology. Depending on loop length, ∼ 25-75% of the best predictions came from the Dynameomics set, resulting in lower main chain root-mean-square deviations for all fragment lengths using the combined fragment library. We also provide specific cases where Dynameomics fragments provide better predictions for NMR loop structures than fragments from crystal structures. Online access to these fragment libraries is available at http://www.dynameomics.org/fragments. © 2014 The Protein Society.

Fission and fragmentation of silver and bromine nuclei by 1-6 GeV energy photons

International Nuclear Information System (INIS)

Pinheiro Filho, J. de D.

1983-01-01

Fission and fragmentation of silver and bromine nuclei induced by bremsstrahlung photons in the maximum energy range of 1-6 GeV are studied. A special technique of nuclear emulsion for the highly ionizing nuclear fragment detection is used in the discrimination between nuclear fission and fragmentation events. Films of Ilford-KO nuclear emulsion (approximatelly 10 20 atoms/cm 2 of Ag, Br) which had been exposed to bremsstrahlung beams in 'Deutsches Elektronen Synchrotron' (DESY, Hamburg) with total doses of approximatelly 10 11 equivalent photons are used. Through a detailed analysis of range, angular and angle between fragment distributions, and empirical relations which permit to estimate nuclear fragment energy, range and velocity, the discrimination between fission and fragmentation events is made. Results related to fragment range distribution, angular distribution, distribution of angle between fragments, distribution of ratio between ranges, velocity distributions, forward/backward ratio, fission and fragmentation cross sections, nuclear fissionability and ternary fission frequency are presented and discussed. The results show that the mean photofragmentation cross section in the internal 1-6 GeV (0,09+-0,02mb) is significant when compared to the photofission (0,29+-0,05mb). It is also shown that the mean photofission cross section between 1 and 6 GeV is great by a factor of approximatelly 10 when compared to the foreseen by the cascade-evaporation nuclear model for monoenergetic photons of 0,6 GeV. (L.C.) [pt

Laser-driven particle acceleration towards radiobiology and medicine

CERN Document Server

2016-01-01

This book deals with the new method of laser-driven acceleration for application to radiation biophysics and medicine. It provides multidisciplinary contributions from world leading scientist in order to assess the state of the art of innovative tools for radiation biology research and medical applications of ionizing radiation. The book contains insightful contributions on highly topical aspects of spatio-temporal radiation biophysics, evolving over several orders of magnitude, typically from femtosecond and sub-micrometer scales. Particular attention is devoted to the emerging technology of laser-driven particle accelerators and their applicatio to spatio-temporal radiation biology and medical physics, customization of non-conventional and selective radiotherapy and optimized radioprotection protocols.

Ionizing gas breakdown waves in strong electric fields.

Science.gov (United States)

Klingbeil, R.; Tidman, D. A.; Fernsler, R. F.

1972-01-01

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

Microsynthesis and electron ionization mass spectral studies of O(S)-alkyl N,N-dimethyl alkylphosphono(thiolo)thionoamidates for Chemical Weapons Convention verification.

Science.gov (United States)

Saeidian, Hamdollah; Babri, Mehran; Abdoli, Morteza; Sarabadani, Mansour; Ashrafi, Davood; Naseri, Mohammad Taghi

2012-12-15

The availability of mass spectra and interpretation skills are essential for unambiguous identification of the Chemical Weapons Convention (CWC)-related chemicals. The O(S)-alkyl N,N-dimethyl alkylphosphono(thiolo)thionoamidates are included in the list of scheduled CWC-related compounds, but there are very few spectra from these compounds in the literature. This paper examines these spectra and their mass spectral fragmentation routes. The title chemicals were prepared through microsynthetic protocols and were analyzed using electron ionization mass spectrometry with gas chromatography as a MS-inlet system. Structures of fragments were confirmed using analysis of fragment ions of deuterated analogs, tandem mass spectrometry and density functional theory (DFT) calculations. Mass spectrometric studies revealed some interesting fragmentation pathways during the ionization process, such as alkene and amine elimination and McLafferty-type rearrangements. The most important fragmentation route of the chemicals is the thiono-thiolo rearrangement. DFT calculations are used to support MS results and to reveal relative preference formation of fragment ions. The retention indices (RIs) of all the studied compounds are also reported. Mass spectra of the synthesized compounds were investigated with the aim to enrich the Organization for the Prohibition of Chemical Weapons (OPCW) Central Analytical Database (OCAD) which may be used for detection and identification of CWC-related chemicals during on-site inspection and/or off-site analysis such as OPCW proficiency tests. Copyright © 2012 John Wiley & Sons, Ltd.

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): Review

International Nuclear Information System (INIS)

Li, Du-Xin; Gan, Lin; Bronja, Amela; Schmitz, Oliver J.

2015-01-01

Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. The demand of a “soft” ion source for preserving highly diagnostic molecular ion is desirable, as compared to the “hard” ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS. - Highlights: • Atmospheric pressure ion sources (APCI, ESI, APPI, APLC etc) enable the coupling of LC-based high-end MS to GC. • APIs show advantages in selectivity and sensitivity compared with EI in GC-MS. • Accurate mass database in GC-APCI/MS is emerging as an alternative to GC-EI/MS database.

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): Review

Energy Technology Data Exchange (ETDEWEB)

Li, Du-Xin; Gan, Lin; Bronja, Amela [University of Duisburg-Essen, Applied Analytical Chemistry, Universitaetsstr. 5-7, 45141 Essen (Germany); Schmitz, Oliver J., E-mail: oliver.schmitz@uni-due.de [University of Duisburg-Essen, Applied Analytical Chemistry, Universitaetsstr. 5-7, 45141 Essen (Germany)

2015-09-03

Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. The demand of a “soft” ion source for preserving highly diagnostic molecular ion is desirable, as compared to the “hard” ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS. - Highlights: • Atmospheric pressure ion sources (APCI, ESI, APPI, APLC etc) enable the coupling of LC-based high-end MS to GC. • APIs show advantages in selectivity and sensitivity compared with EI in GC-MS. • Accurate mass database in GC-APCI/MS is emerging as an alternative to GC-EI/MS database.

Atrial cardiomyocyte-specific expression of Cre recombinase driven by an Nppa gene fragment

NARCIS (Netherlands)

de Lange, Frederik J.; Moorman, Antoon F. M.; Christoffels, Vincent M.

2003-01-01

To study the development of the atria, we produced a transgenic mouse line that expresses Cre under the regulatory control of a 7 kbp fragment of the Natriuretic peptide precursor type A gene (Nppa), from -3 kbp to +4 kbp relative to the transcription start site. Crossing this line with the R26R and

Fragment-based lead generation: identification of seed fragments by a highly efficient fragment screening technology

Science.gov (United States)

Neumann, Lars; Ritscher, Allegra; Müller, Gerhard; Hafenbradl, Doris

2009-08-01

For the detection of the precise and unambiguous binding of fragments to a specific binding site on the target protein, we have developed a novel reporter displacement binding assay technology. The application of this technology for the fragment screening as well as the fragment evolution process with a specific modelling based design strategy is demonstrated for inhibitors of the protein kinase p38alpha. In a fragment screening approach seed fragments were identified which were then used to build compounds from the deep-pocket towards the hinge binding area of the protein kinase p38alpha based on a modelling approach. BIRB796 was used as a blueprint for the alignment of the fragments. The fragment evolution of these deep-pocket binding fragments towards the fully optimized inhibitor BIRB796 included the modulation of the residence time as well as the affinity. The goal of our study was to evaluate the robustness and efficiency of our novel fragment screening technology at high fragment concentrations, compare the screening data with biochemical activity data and to demonstrate the evolution of the hit fragments with fast kinetics, into slow kinetic inhibitors in an in silico approach.

Universal fragment descriptors for predicting properties of inorganic crystals

Science.gov (United States)

Isayev, Olexandr; Oses, Corey; Toher, Cormac; Gossett, Eric; Curtarolo, Stefano; Tropsha, Alexander

2017-06-01

Although historically materials discovery has been driven by a laborious trial-and-error process, knowledge-driven materials design can now be enabled by the rational combination of Machine Learning methods and materials databases. Here, data from the AFLOW repository for ab initio calculations is combined with Quantitative Materials Structure-Property Relationship models to predict important properties: metal/insulator classification, band gap energy, bulk/shear moduli, Debye temperature and heat capacities. The prediction's accuracy compares well with the quality of the training data for virtually any stoichiometric inorganic crystalline material, reciprocating the available thermomechanical experimental data. The universality of the approach is attributed to the construction of the descriptors: Property-Labelled Materials Fragments. The representations require only minimal structural input allowing straightforward implementations of simple heuristic design rules.

PIC simulations of post-pulse field reversal and secondary ionization in nanosecond argon discharges

Science.gov (United States)

Kim, H. Y.; Gołkowski, M.; Gołkowski, C.; Stoltz, P.; Cohen, M. B.; Walker, M.

2018-05-01

Post-pulse electric field reversal and secondary ionization are investigated with a full kinetic treatment in argon discharges between planar electrodes on nanosecond time scales. The secondary ionization, which occurs at the falling edge of the voltage pulse, is induced by charge separation in the bulk plasma region. This process is driven by a reverse in the electric field from the cathode sheath to the formerly driven anode. Under the influence of the reverse electric field, electrons in the bulk plasma and sheath regions are accelerated toward the cathode. The electron movement manifests itself as a strong electron current generating high electron energies with significant electron dissipated power. Accelerated electrons collide with Ar molecules and an increased ionization rate is achieved even though the driving voltage is no longer applied. With this secondary ionization, in a single pulse (SP), the maximum electron density achieved is 1.5 times higher and takes a shorter time to reach using 1 kV 2 ns pulse as compared to a 1 kV direct current voltage at 1 Torr. A bipolar dual pulse excitation can increase maximum density another 50%–70% above a SP excitation and in half the time of RF sinusoidal excitation of the same period. The first field reversal is most prominent but subsequent field reversals also occur and correspond to electron temperature increases. Targeted pulse designs can be used to condition plasma density as required for fast discharge applications.

Native Frames: Disentangling Sequential from Concerted Three-Body Fragmentation

Science.gov (United States)

Rajput, Jyoti; Severt, T.; Berry, Ben; Jochim, Bethany; Feizollah, Peyman; Kaderiya, Balram; Zohrabi, M.; Ablikim, U.; Ziaee, Farzaneh; Raju P., Kanaka; Rolles, D.; Rudenko, A.; Carnes, K. D.; Esry, B. D.; Ben-Itzhak, I.

2018-03-01

A key question concerning the three-body fragmentation of polyatomic molecules is the distinction of sequential and concerted mechanisms, i.e., the stepwise or simultaneous cleavage of bonds. Using laser-driven fragmentation of OCS into O++C++S+ and employing coincidence momentum imaging, we demonstrate a novel method that enables the clear separation of sequential and concerted breakup. The separation is accomplished by analyzing the three-body fragmentation in the native frame associated with each step and taking advantage of the rotation of the intermediate molecular fragment, CO2 + or CS2 + , before its unimolecular dissociation. This native-frame method works for any projectile (electrons, ions, or photons), provides details on each step of the sequential breakup, and enables the retrieval of the relevant spectra for sequential and concerted breakup separately. Specifically, this allows the determination of the branching ratio of all these processes in OCS3 + breakup. Moreover, we find that the first step of sequential breakup is tightly aligned along the laser polarization and identify the likely electronic states of the intermediate dication that undergo unimolecular dissociation in the second step. Finally, the separated concerted breakup spectra show clearly that the central carbon atom is preferentially ejected perpendicular to the laser field.

Electrostatic field of the large fragment of Escherichia coli DNA polymerase I.

Science.gov (United States)

Warwicker, J; Ollis, D; Richards, F M; Steitz, T A

1985-12-05

The electrostatic field of the large fragment of Escherichia coli DNA polymerase I (Klenow fragment) has been calculated by the finite difference procedure on a 2 A grid. The potential field is substantially negative at physiological pH (reflecting the net negative charge at this pH). The largest regions of positive potential are in the deep crevice of the C-terminal domain, which is the proposed binding site for the DNA substrate. Within the crevice, the electrostatic potential has a partly helical form. If the DNA is positioned to fulfil stereochemical requirements, then the positive potential generally follows the major groove and (to a lesser extent) the negative potential is in the minor groove. Such an arrangement could stabilize DNA configurations related by screw symmetry. The histidine residues of the Klenow fragment give the positive field of the groove a sensitivity to relatively small pH changes around neutrality. We suggest that the histidine residues could change their ionization states in response to DNA binding, and that this effect could contribute to the protein-DNA binding energy.

Use of various ionization modes for the study of molecules of biological interest

International Nuclear Information System (INIS)

Forest, E.

1987-01-01

For the last ten years a revolutionary advance in mass spectrometry applied to molecules of biological interest occurred, chiefly concerning ionization with the emergence of many new modes allowing non volatile, polar or thermally labile sample analysis. Some examples of spectra obtained on high mass molecules such as vitamins, protein fragments, porphyrins (chlorophyll or hemoglobin active site), polysaccharides, are presented using some of the new modes [fr

(e, 2e) ionization-excitation experiment with fixed-in-space H2 molecules

International Nuclear Information System (INIS)

Takahashi, M.; Watanabe, N.; Khajuria, Y.; Udagawa, Y.; Eland, J.H.D.

2005-01-01

This report will introduce an electron-electron-fragment ion triple coincidence spectrometer to the readers with our recent collision dynamics study on ionization-excitation processes of the hydrogen molecule. Following a description of the working principle of the spectrometer, results of the study will be discussed; this includes molecular frame (e, 2e) cross sections that have been observed for the first time. (author)

Microplasma-based flowing atmospheric-pressure afterglow (FAPA) source for ambient desorption-ionization mass spectrometry

Energy Technology Data Exchange (ETDEWEB)

Zeiri, Offer M.; Storey, Andrew P.; Ray, Steven J., E-mail: sjray2@buffalo.edu; Hieftje, Gary M.

2017-02-01

A new direct-current microplasma-based flowing atmospheric pressure afterglow (FAPA) source was developed for use in ambient desorption-ionization mass spectrometry. The annular-shaped microplasma is formed in helium between two concentric stainless-steel capillaries that are separated by an alumina tube. Current-voltage characterization of the source shows that this version of the FAPA operates in the normal glow-discharge regime. A glass surface placed in the path of the helium afterglow reaches temperatures of up to approximately 400 °C; the temperature varies with distance from the source and helium flow rate through the source. Solid, liquid, and vapor samples were examined by means of a time-of-flight mass spectrometer. Results suggest that ionization occurs mainly through protonation, with only a small amount of fragmentation and adduct formation. The mass range of the source was shown to extend up to at least m/z 2722 for singly charged species. Limits of detection for several small organic molecules were in the sub-picomole range. Examination of competitive ionization revealed that signal suppression occurs only at high (mM) concentrations of competing substances. - Highlights: • The first microplasma version of the FAPA source. • Current-voltage behavior reflects the behavior of a normal glow discharge. • Detection limits below 1 pmol for the classes of organic compounds studied over a wide mass range. • Mass spectra show limited fragmentation.

Surface-assisted laser desorption ionization mass spectrometry techniques for application in forensics.

Science.gov (United States)

Guinan, Taryn; Kirkbride, Paul; Pigou, Paul E; Ronci, Maurizio; Kobus, Hilton; Voelcker, Nicolas H

2015-01-01

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is an excellent analytical technique for the rapid and sensitive analysis of macromolecules (>700 Da), such as peptides, proteins, nucleic acids, and synthetic polymers. However, the detection of smaller organic molecules with masses below 700 Da using MALDI-MS is challenging due to the appearance of matrix adducts and matrix fragment peaks in the same spectral range. Recently, nanostructured substrates have been developed that facilitate matrix-free laser desorption ionization (LDI), contributing to an emerging analytical paradigm referred to as surface-assisted laser desorption ionization (SALDI) MS. Since SALDI enables the detection of small organic molecules, it is rapidly growing in popularity, including in the field of forensics. At the same time, SALDI also holds significant potential as a high throughput analytical tool in roadside, work place and athlete drug testing. In this review, we discuss recent advances in SALDI techniques such as desorption ionization on porous silicon (DIOS), nano-initiator mass spectrometry (NIMS) and nano assisted laser desorption ionization (NALDI™) and compare their strengths and weaknesses with particular focus on forensic applications. These include the detection of illicit drug molecules and their metabolites in biological matrices and small molecule detection from forensic samples including banknotes and fingerprints. Finally, the review highlights recent advances in mass spectrometry imaging (MSI) using SALDI techniques. © 2014 Wiley Periodicals, Inc.

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

Energy Technology Data Exchange (ETDEWEB)

Marginean, Ioan; Kronewitter, Scott R.; Moore, Ronald J.; Slysz, Gordon W.; Monroe, Matthew E.; Anderson, Gordon A.; Tang, Keqi; Smith, Richard D.

2012-10-01

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

Gas-phase pesticide measurement using iodide ionization time-of-flight mass spectrometry

Directory of Open Access Journals (Sweden)

T. Murschell

2017-06-01

Full Text Available Volatilization and subsequent processing in the atmosphere are an important environmental pathway for the transport and chemical fate of pesticides. However, these processes remain a particularly poorly understood component of pesticide lifecycles due to analytical challenges in measuring pesticides in the atmosphere. Most pesticide measurements require long (hours to days sampling times coupled with offline analysis, inhibiting observation of meteorologically driven events or investigation of rapid oxidation chemistry. Here, we present chemical ionization time-of-flight mass spectrometry with iodide reagent ions as a fast and sensitive measurement of four current-use pesticides. These semi-volatile pesticides were calibrated with injections of solutions onto a filter and subsequently volatilized to generate gas-phase analytes. Trifluralin and atrazine are detected as iodide–molecule adducts, while permethrin and metolachlor are detected as adducts between iodide and fragments of the parent analyte molecule. Limits of detection (1 s are 0.37, 0.67, 0.56, and 1.1 µg m−3 for gas-phase trifluralin, metolachlor, atrazine, and permethrin, respectively. The sensitivities of trifluralin and metolachlor depend on relative humidity, changing as much as 70 and 59, respectively, as relative humidity of the sample air varies from 0 to 80 %. This measurement approach is thus appropriate for laboratory experiments and potentially near-source field measurements.

On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration.

Science.gov (United States)

Wang, Rui; Gröhn, Arto Juhani; Zhu, Liang; Dietiker, Rolf; Wegner, Karsten; Günther, Detlef; Zenobi, Renato

2012-03-01

Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet-droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet-droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet-droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the sheath gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet-droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be <5 μs. This work gives a clear picture of droplet-droplet interactions in the dual-spray EESI process and detailed information for the optimization of this method for future applications that require higher sensitivity.

The influence of ionizing radiation on the structure of Ca-ATPase hydrophobic fragment of skeletal muscle sarcoplasmic reticulum

International Nuclear Information System (INIS)

Vojtsitskij, V.M.; Fedorov, A.N.; Lugovskoj, Eh.B.; Derzskaya, S.G.; Khizhnyak, S.V.; Kurskij, M.D.; Kucherenko, N.E.

1990-01-01

Early (1 and 24 h) after X-irradiation with a dose of 0.21 C/kg changes occurred in the acceptibility of the polypeptide chain parts of sarcoplasmic reticulum Ca-ATPase for the effect of trypsin. The analysis of the results of studying the structural and functional properties of a hydrophobic fragment of this enzyme in the control and after irradiation permitted to define the part of the Ca-ATPase polypeptide chain that provided ion selectivity of the fragment

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

Science.gov (United States)

Zou, Yunlong; Holmes, Russell

2015-03-01

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

Identifying the Tunneling Site in Strong-Field Ionization of H_{2}^{+}.

Science.gov (United States)

Liu, Kunlong; Barth, Ingo

2017-12-15

The tunneling site of the electron in a molecule exposed to a strong laser field determines the initial position of the ionizing electron and, as a result, has a large impact on the subsequent ultrafast electron dynamics on the polyatomic Coulomb potential. Here, the tunneling site of the electron of H_{2}^{+} ionized by a strong circularly polarized (CP) laser pulse is studied by numerically solving the time-dependent Schrödinger equation. We show that the electron removed from the down-field site is directly driven away by the CP field and the lateral photoelectron momentum distribution (LPMD) exhibits a Gaussian-like distribution, whereas the corresponding LPMD of the electron removed from the up-field site differs from the Gaussian shape due to the Coulomb focusing and scattering by the down-field core. Our current study presents the direct evidence clarifying a long-standing controversy over the tunneling site in H_{2}^{+} and raises the important role of the tunneling site in strong-field molecular ionization.

Giant plasmon excitation in single and double ionization of C60 by fast highly charged Si and O ions

International Nuclear Information System (INIS)

Kelkar, A H; Kadhane, U; Misra, D; Tribedi, L C

2007-01-01

Se have investigated single and double ionization of C 60 molecule in collisions with 2.33 MeV/u Si q+ (q=6-14) and 3.125 MeV/u O q+ (q=5-8) projectiles. The projectile charge state dependence of the single and double ionization yields of C 60 are then compared to those for an ion-atom collision system using Ne gas as a target. A large difference between the gas and the cluster target behaviour was partially explained in terms of a model based on collective excitation namely the giant dipole plasmon resonance (GDPR). The qualitative agreement between the data and GDPR model prediction for single and double ionization signifies the importance of single and double plasmon excitations in the ionization process. A large deviation of the GDPR model for triple and quadruple ionization from the experimental data imply the importance of the other low impact parameter processes such as evaporation, fragmentation and a possible solid-like dynamical screening

Virtual fragment preparation for computational fragment-based drug design.

Science.gov (United States)

Ludington, Jennifer L

2015-01-01

Fragment-based drug design (FBDD) has become an important component of the drug discovery process. The use of fragments can accelerate both the search for a hit molecule and the development of that hit into a lead molecule for clinical testing. In addition to experimental methodologies for FBDD such as NMR and X-ray Crystallography screens, computational techniques are playing an increasingly important role. The success of the computational simulations is due in large part to how the database of virtual fragments is prepared. In order to prepare the fragments appropriately it is necessary to understand how FBDD differs from other approaches and the issues inherent in building up molecules from smaller fragment pieces. The ultimate goal of these calculations is to link two or more simulated fragments into a molecule that has an experimental binding affinity consistent with the additive predicted binding affinities of the virtual fragments. Computationally predicting binding affinities is a complex process, with many opportunities for introducing error. Therefore, care should be taken with the fragment preparation procedure to avoid introducing additional inaccuracies.This chapter is focused on the preparation process used to create a virtual fragment database. Several key issues of fragment preparation which affect the accuracy of binding affinity predictions are discussed. The first issue is the selection of the two-dimensional atomic structure of the virtual fragment. Although the particular usage of the fragment can affect this choice (i.e., whether the fragment will be used for calibration, binding site characterization, hit identification, or lead optimization), general factors such as synthetic accessibility, size, and flexibility are major considerations in selecting the 2D structure. Other aspects of preparing the virtual fragments for simulation are the generation of three-dimensional conformations and the assignment of the associated atomic point charges.

Ion induced fragmentation of biomolecular systems at low collision energies

International Nuclear Information System (INIS)

Bernigaud, V; Adoui, L; Chesnel, J Y; Rangama, J; Huber, B A; Manil, B; Alvarado, F; Bari, S; Hoekstra, R; Postma, J; Schlathoelter, T

2009-01-01

In this paper, we present results of different collision experiments between multiply charged ions at low collision energies (in the keV-region) and biomolecular systems. This kind of interaction allows to remove electrons form the biomolecule without transferring a large amount of vibrational excitation energy. Nevertheless, following the ionization of the target, fragmentation of biomolecular species may occur. It is the main objective of this work to study the physical processes involved in the dissociation of highly electronically excited systems. In order to elucidate the intrinsic properties of certain biomolecules (porphyrins and amino acids) we have performed experiments in the gas phase with isolated systems. The obtained results demonstrate the high stability of porphyrins after electron removal. Furthermore, a dependence of the fragmentation pattern produced by multiply charged ions on the isomeric structure of the alanine molecule has been shown. By considering the presence of other surrounding biomolecules (clusters of nucleobases), a strong influence of the environment of the biomolecule on the fragmentation channels and their modification, has been clearly proven. This result is explained, in the thymine and uracil case, by the formation of hydrogen bonds between O and H atoms, which is known to favor planar cluster geometries.

Stringent limits on the ionized mass loss from A and F dwarfs

International Nuclear Information System (INIS)

Brown, A.; Veale, A.; Judge, P.; Bookbinder, J.A.; Hubeny, I.

1990-01-01

Following the suggestion of Willson et al. (1987) that A- and F-type main-sequence stars might undergo significant mass loss due to pulsationally driven winds, upper limits to the ionized mass loss from A and F dwarfs have been obtained using VLA observations. These stringent upper limits show that the level of ionized mass loss would have at most only a small effect on stellar evolution. Radiative-equilibrium atmospheric and wind models for early A dwarfs indicate that it is highly likely that a wind flowing from such stars would be significantly ionized. In addition, late A and early F dwarfs exhibit chromospheric emission indicative of significant nonradiative heating. The present mass-loss limits are thus representative of the total mass-loss rates for these stars. It is concluded that A and F dwarfs are not losing sufficient mass to cause A dwarfs to evolve into G dwarfs. 24 refs

Measurements of ion velocity separation and ionization in multi-species plasma shocks

Science.gov (United States)

Rinderknecht, Hans G.; Park, H.-S.; Ross, J. S.; Amendt, P. A.; Wilks, S. C.; Katz, J.; Hoffman, N. M.; Kagan, G.; Vold, E. L.; Keenan, B. D.; Simakov, A. N.; Chacón, L.

2018-05-01

The ion velocity structure of a strong collisional shock front in a plasma with multiple ion species is directly probed in laser-driven shock-tube experiments. Thomson scattering of a 263.25 nm probe beam is used to diagnose ion composition, temperature, and flow velocity in strong shocks ( M ˜6 ) propagating through low-density ( ρ˜0.1 mg/cc) plasmas composed of mixtures of hydrogen (98%) and neon (2%). Within the preheat region of the shock front, two velocity populations of ions are observed, a characteristic feature of strong plasma shocks. The ionization state of the Ne is observed to change within the shock front, demonstrating an ionization-timescale effect on the shock front structure. The forward-streaming proton feature is shown to be unexpectedly cool compared to predictions from ion Fokker-Planck simulations; the neon ionization gradient is evaluated as a possible cause.

Ambiguities in the grid-inefficiency correction for Frisch-Grid Ionization Chambers

International Nuclear Information System (INIS)

Al-Adili, A.; Hambsch, F.-J.; Bencardino, R.; Oberstedt, S.; Pomp, S.

2012-01-01

Ionization chambers with Frisch grids have been very successfully applied to neutron-induced fission-fragment studies during the past 20 years. They are radiation resistant and can be easily adapted to the experimental conditions. The use of Frisch grids has the advantage to remove the angular dependency from the charge induced on the anode plate. However, due to the Grid Inefficiency (GI) in shielding the charges, the anode signal remains slightly angular dependent. The correction for the GI is, however, essential to determine the correct energy of the ionizing particles. GI corrections can amount to a few percent of the anode signal. Presently, two contradicting correction methods are considered in literature. The first method adding the angular-dependent part of the signal to the signal pulse height; the second method subtracting the former from the latter. Both additive and subtractive approaches were investigated in an experiment where a Twin Frisch-Grid Ionization Chamber (TFGIC) was employed to detect the spontaneous fission fragments (FF) emitted by a 252 Cf source. Two parallel-wire grids with different wire spacing (1 and 2 mm, respectively), were used individually, in the same chamber side. All the other experimental conditions were unchanged. The 2 mm grid featured more than double the GI of the 1 mm grid. The induced charge on the anode in both measurements was compared, before and after GI correction. Before GI correction, the 2 mm grid resulted in a lower pulse-height distribution than the 1 mm grid. After applying both GI corrections to both measurements only the additive approach led to consistent grid independent pulse-height distributions. The application of the subtractive correction on the contrary led to inconsistent, grid-dependent results. It is also shown that the impact of either of the correction methods is small on the FF mass distributions of 235 U(n th , f).

Molecular dynamics for irradiation driven chemistry: application to the FEBID process*

Science.gov (United States)

Sushko, Gennady B.; Solov'yov, Ilia A.; Solov'yov, Andrey V.

2016-10-01

A new molecular dynamics (MD) approach for computer simulations of irradiation driven chemical transformations of complex molecular systems is suggested. The approach is based on the fact that irradiation induced quantum transformations can often be treated as random, fast and local processes involving small molecules or molecular fragments. We advocate that the quantum transformations, such as molecular bond breaks, creation and annihilation of dangling bonds, electronic charge redistributions, changes in molecular topologies, etc., could be incorporated locally into the molecular force fields that describe the classical MD of complex molecular systems under irradiation. The proposed irradiation driven molecular dynamics (IDMD) methodology is designed for the molecular level description of the irradiation driven chemistry. The IDMD approach is implemented into the MBN Explorer software package capable to operate with a large library of classical potentials, many-body force fields and their combinations. IDMD opens a broad range of possibilities for modelling of irradiation driven modifications and chemistry of complex molecular systems ranging from radiotherapy cancer treatments to the modern technologies such as focused electron beam deposition (FEBID). As an example, the new methodology is applied for studying the irradiation driven chemistry caused by FEBID of tungsten hexacarbonyl W(CO)6 precursor molecules on a hydroxylated SiO2 surface. It is demonstrated that knowing the interaction parameters for the fragments of the molecular system arising in the course of irradiation one can reproduce reasonably well experimental observations and make predictions about the morphology and molecular composition of nanostructures that emerge on the surface during the FEBID process.

Silver nanoparticles as matrix for laser desorption/ionization mass spectrometry of peptides

International Nuclear Information System (INIS)

Hua Lin; Chen Jianrong; Ge Liya; Tan, Swee Ngin

2007-01-01

Silver nanoparticle synthesized from chemical reduction has been successfully utilized as a matrix in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) of peptides. Acting as a substrate to adsorb analytes, as well as a transmission medium for UV laser, silver nanoparticle was found to assist in the desorption/ionization of peptides with little or no induced fragmentation. The size of the nanoparticle was typically in the range of 160 ± 20 nm. One of the key advantages of silver nanoparticle for peptides analysis is its simple step for on-probe sample preparation. In addition, it also minimizes the interferences of sodium dodecyl sulfate (SDS) surfactant background signal, resulting in cleaner mass spectra and more sensitive signal, when compared to α-cyano-4-hydroxycinnamic acid (CCA) matrix

Evidence of site-specific fragmentation on thioacetic acid, CH3C(O)SH, irradiated with synchrotron radiation around the S 2p and O 1s regions.

Science.gov (United States)

Erben, Mauricio F; Geronés, Mariana; Romano, Rosana M; Della Védova, Carlos O

2006-01-26

Site-specific fragmentations following S 2p and O 1s photoexcitation of thioacetic acid, CH3C(O)SH, have been studied by means of synchrotron radiation. Total ion yield (TIY) spectra were measured and multicoincidence techniques, which include photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO) time-of-flight mass spectrometry, were applied. The equivalent-core approximation was employed in order to estimate ionization transition values, and the observed peaks were tentatively assigned. A site-specific fragmentation is moderately observed by comparing the mass spectra collected at resonant energies around the inner and shallow inner shell S 2p and O 1s ionization edges. Beside H+ ion, the most abundant ions observed at the S 2p edge excitation were CH3CO+, SH+, S+, and CH3+. At the O 1s region the large CH3CO+ fragment was depressed, and small CHx+ (x = 0, 1, 2, 3), S+, and SH+ fragments were dominant. The dissociation dynamic for the main ion-pair production has been discussed. Two- and three-body dissociation channels have been observed in the PEPIPICO spectra, and the dissociation mechanisms were proposed.

A large area position-sensitive ionization chamber for heavy-ion-induced reaction studies

CERN Document Server

Pant, L M; Dinesh, B V; Thomas, R G; Saxena, A; Sawant, Y S; Choudhury, R K

2002-01-01

A large area position-sensitive ionization chamber with a wide dynamic range has been developed to measure the mass, charge and energy of the heavy ions and the fission fragments produced in heavy-ion-induced reactions. The split anode geometry of the detector makes it suitable for both particle identification and energy measurements for heavy ions and fission fragments. The detector has been tested with alpha particles from sup 2 sup 4 sup 1 Am- sup 2 sup 3 sup 9 Pu source, fission fragments from sup 2 sup 5 sup 2 Cf and the heavy-ion beams from the 14UD Mumbai Pelletron accelerator facility. Using this detector, measurements on mass and total kinetic energy distributions in heavy-ion-induced fusion-fission reactions have been carried out for a wide range of excitation energies. Results on deep inelastic collisions and mass-energy correlations on different systems using this detector setup are discussed.

Bacterial and archaeal resistance to ionizing radiation

Energy Technology Data Exchange (ETDEWEB)

Confalonieri, F; Sommer, S, E-mail: fabrice.confalonieri@u-psud.fr, E-mail: suzanne.sommer@u-psud.fr [University Paris-Sud, CNRS UMR8621, Institut de Genetique et Microbiologie, Batiments 400-409, Universite Paris-Sud, 91405 Orsay (France)

2011-01-01

Organisms living in extreme environments must cope with large fluctuations of temperature, high levels of radiation and/or desiccation, conditions that can induce DNA damage ranging from base modifications to DNA double-strand breaks. The bacterium Deinococcus radiodurans is known for its resistance to extremely high doses of ionizing radiation and for its ability to reconstruct a functional genome from hundreds of radiation-induced chromosomal fragments. Recently, extreme ionizing radiation resistance was also generated by directed evolution of an apparently radiation-sensitive bacterial species, Escherichia coli. Radioresistant organisms are not only found among the Eubacteria but also among the Archaea that represent the third kingdom of life. They present a set of particular features that differentiate them from the Eubacteria and eukaryotes. Moreover, Archaea are often isolated from extreme environments where they live under severe conditions of temperature, pressure, pH, salts or toxic compounds that are lethal for the large majority of living organisms. Thus, Archaea offer the opportunity to understand how cells are able to cope with such harsh conditions. Among them, the halophilic archaeon Halobacterium sp and several Pyrococcus or Thermococcus species, such as Thermococcus gammatolerans, were also shown to display high level of radiation resistance. The dispersion, in the phylogenetic tree, of radioresistant prokaryotes suggests that they have independently acquired radioresistance. Different strategies were selected during evolution including several mechanisms of radiation byproduct detoxification and subtle cellular metabolism modifications to help cells recover from radiation-induced injuries, protection of proteins against oxidation, an efficient DNA repair tool box, an original pathway of DNA double-strand break repair, a condensed nucleoid that may prevent the dispersion of the DNA fragments and specific radiation-induced proteins involved in

Synthesis and Electrospray Ionization Mass Spectra of N-(1,3,2-Dioxaphosphorinan-2-ylmethyl)thiophosphoramidates

Institute of Scientific and Technical Information of China (English)

MIAO,Zhi-Wei; FU,Cui-Rong; WANG,Bin; CUI,Zhan-Wei; ZHANG,Jian-Feng; CHEN,Ru-Yu

2007-01-01

N-(1,3,2-Dioxaphosphorinan-2-ylmethyl) thiophosphoramidates were synthesized and determined by NMR spectra and positive ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated. The results show that these characteristic ions in ESI mass spectra are useful in the structural determination of N-(1,3,2-dioxaphosphorinan-2-ylmethyl)thiophosphoramidates.

Inhibition of Chk1 by CEP-3891 accelerates mitotic nuclear fragmentation in response to ionizing Radiation

DEFF Research Database (Denmark)

Syljuåsen, Randi G; Sørensen, Claus Storgaard; Nylandsted, Jesper

2004-01-01

The human checkpoint kinase Chk1 has been suggested as a target for cancer treatment. Here, we show that a new inhibitor of Chk1 kinase, CEP-3891, efficiently abrogates both the ionizing radiation (IR)-induced S and G(2) checkpoints. When the checkpoints were abrogated by CEP-3891, the majority (64...

Fast quantitative detection of cocaine in beverages using nanoextractive electrospray ionization tandem mass spectrometry.

Science.gov (United States)

Hu, Bin; Peng, Xuejiao; Yang, Shuiping; Gu, Haiwei; Chen, Huanwen; Huan, Yanfu; Zhang, Tingting; Qiao, Xiaolin

2010-02-01

Without any sample pretreatment, effervescent beverage fluids were manually sprayed into the primary ion plume created by using a nanoelectrospray ionization source for direct ionization, and the analyte ions of interest were guided into an ion trap mass spectrometer for tandem mass analysis. Functional ingredients (e.g., vitamins, taurine, and caffeine, etc.) and spiked impurity (e.g., cocaine) in various beverages, such as Red Bull energy drink, Coco-cola, and Pepsi samples were rapidly identified within 1.5 s. The limit of detection was found to be 7-15 fg (S/N = 3) for cocaine in different samples using the characteristic fragment (m/z 150) observed in the MS(3) experiments. Typical relative standard deviation and recovery of this method were 6.9%-8.6% and 104%-108% for direct analysis of three actual samples, showing that nanoextractive electrospray ionization tandem mass spectrometry is a useful technique for fast screening cocaine presence in beverages. 2010. Published by Elsevier Inc.

A combined thermal dissociation and electron impact ionization source for radioactive ion beam generationa

International Nuclear Information System (INIS)

Alton, G.D.; Williams, C.

1996-01-01

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

Attosecond control of dissociative ionization of O{sub 2} molecules

Energy Technology Data Exchange (ETDEWEB)

Siu, W.; Kelkensberg, F.; Gademann, G. [FOM Institute AMOLF, Science Park 104, NL-1098 XG Amsterdam (Netherlands); Rouzee, A.; Vrakking, M. J. J. [FOM Institute AMOLF, Science Park 104, NL-1098 XG Amsterdam (Netherlands); Max-Born-Institut, Max-Born Strasse 2A, D-12489 Berlin (Germany); Johnsson, P. [FOM Institute AMOLF, Science Park 104, NL-1098 XG Amsterdam (Netherlands); Department of Physics, Lund University, Post Office Box 118, SE-221 00 Lund (Sweden); Dowek, D. [Laboratoire des Collisions Atomiques et Moleculaires (UMR Universite Paris-Sud et CNRS, 8625), Batiment 351, Universite Paris-Sud, F-91405 Orsay Cedex (France); Lucchini, M.; Calegari, F. [Department of Physics, Politecnico di Milano, Istituto di Fotonica e Nanotecnologie CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); De Giovannini, U.; Rubio, A. [Nano-bio Spectroscopy Group, ETSF Scientific Development Centre, Universidad del Pais Vasco, Avenida Tolosa 72, E-20018 San Sebastian (Spain); Lucchese, R. R. [Department of Chemistry, Texas A and M University, Post Office Box 30012, College Station, Texas 77842-3012 (United States); Kono, H. [Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan); Lepine, F. [Universite Lyon 1/CNRS/LASIM, UMR 5579, 43 Boulevard Du 11 Novembre 1918, F-69622 Villeurbane (France)

2011-12-15

We demonstrate that dissociative ionization of O{sub 2} can be controlled by the relative delay between an attosecond pulse train (APT) and a copropagating infrared (IR) field. Our experiments reveal a dependence of both the branching ratios between a range of electronic states and the fragment angular distributions on the extreme ultraviolet (XUV) to IR time delay. The observations go beyond adiabatic propagation of dissociative wave packets on IR-induced quasistatic potential energy curves and are understood in terms of an IR-induced coupling between electronic states in the molecular ion.

Scattering-angle dependence of doubly differential cross sections for fragmentation of H2 by proton impact

International Nuclear Information System (INIS)

Egodapitiya, K. N.; Sharma, S.; Laforge, A. C.; Schulz, M.

2011-01-01

We have measured double differential cross sections (DDCS) for proton fragment formation for fixed projectile energy losses as a function of projectile scattering angle in 75 keV p + H 2 collisions. An oscillating pattern was observed in the angular dependence of the DDCS with a frequency about twice as large as what we found earlier for nondissociative ionization. Possible origins for this frequency doubling are discussed.

Giant plasmon excitation in single and double ionization of C{sub 60} by fast highly charged Si and O ions

Energy Technology Data Exchange (ETDEWEB)

Kelkar, A H; Kadhane, U; Misra, D; Tribedi, L C [Tata Institute of Fundamental Research, Colaba, Mumbai-5 (India)

2007-09-15

Se have investigated single and double ionization of C{sub 60} molecule in collisions with 2.33 MeV/u Si{sup q+} (q=6-14) and 3.125 MeV/u O{sup q+} (q=5-8) projectiles. The projectile charge state dependence of the single and double ionization yields of C{sub 60} are then compared to those for an ion-atom collision system using Ne gas as a target. A large difference between the gas and the cluster target behaviour was partially explained in terms of a model based on collective excitation namely the giant dipole plasmon resonance (GDPR). The qualitative agreement between the data and GDPR model prediction for single and double ionization signifies the importance of single and double plasmon excitations in the ionization process. A large deviation of the GDPR model for triple and quadruple ionization from the experimental data imply the importance of the other low impact parameter processes such as evaporation, fragmentation and a possible solid-like dynamical screening.

RADIATION-DRIVEN IMPLOSION AND TRIGGERED STAR FORMATION

International Nuclear Information System (INIS)

Bisbas, Thomas G.; Wuensch, Richard; Whitworth, Anthony P.; Walch, Stefanie; Hubber, David A.

2011-01-01

We present simulations of initially stable isothermal clouds exposed to ionizing radiation from a discrete external source, and identify the conditions that lead to radiatively driven implosion and star formation. We use the smoothed particle hydrodynamics code SEREN and a HEALPix-based photoionization algorithm to simulate the propagation of the ionizing radiation and the resulting dynamical evolution of the cloud. We find that the incident ionizing flux, Φ LyC , is the critical parameter determining the cloud evolution. At moderate fluxes, a large fraction of the cloud mass is converted into stars. As the flux is increased, the fraction of the cloud mass that is converted into stars and the mean masses of the individual stars both decrease. Very high fluxes simply disperse the cloud. Newly formed stars tend to be concentrated along the central axis of the cloud (i.e., the axis pointing in the direction of the incident flux). For given cloud parameters, the time, t * , at which star formation starts is proportional to Φ -1/3 LyC . The pattern of star formation found in the simulations is similar to that observed in bright-rimmed clouds.

The iQID camera: An ionizing-radiation quantum imaging detector

Energy Technology Data Exchange (ETDEWEB)

Miller, Brian W., E-mail: brian.miller@pnnl.gov [Pacific Northwest National Laboratory, Richland, WA 99352 (United States); College of Optical Sciences, The University of Arizona, Tucson, AZ 85719 (United States); Gregory, Stephanie J.; Fuller, Erin S. [Pacific Northwest National Laboratory, Richland, WA 99352 (United States); Barrett, Harrison H.; Bradford Barber, H.; Furenlid, Lars R. [Center for Gamma-Ray Imaging, The University of Arizona, Tucson, AZ 85719 (United States); College of Optical Sciences, The University of Arizona, Tucson, AZ 85719 (United States)

2014-12-11

We have developed and tested a novel, ionizing-radiation Quantum Imaging Detector (iQID). This scintillation-based detector was originally developed as a high-resolution gamma-ray imager, called BazookaSPECT, for use in single-photon emission computed tomography (SPECT). Recently, we have investigated the detector's response and imaging potential with other forms of ionizing radiation including alpha, neutron, beta, and fission fragment particles. The confirmed response to this broad range of ionizing radiation has prompted its new title. The principle operation of the iQID camera involves coupling a scintillator to an image intensifier. The scintillation light generated by particle interactions is optically amplified by the intensifier and then re-imaged onto a CCD/CMOS camera sensor. The intensifier provides sufficient optical gain that practically any CCD/CMOS camera can be used to image ionizing radiation. The spatial location and energy of individual particles are estimated on an event-by-event basis in real time using image analysis algorithms on high-performance graphics processing hardware. Distinguishing features of the iQID camera include portability, large active areas, excellent detection efficiency for charged particles, and high spatial resolution (tens of microns). Although modest, iQID has energy resolution that is sufficient to discriminate between particles. Additionally, spatial features of individual events can be used for particle discrimination. An important iQID imaging application that has recently been developed is real-time, single-particle digital autoradiography. We present the latest results and discuss potential applications.

Quantum interference in laser-induced nonsequential double ionization

Science.gov (United States)

Quan, Wei; Hao, XiaoLei; Wang, YanLan; Chen, YongJu; Yu, ShaoGang; Xu, SongPo; Xiao, ZhiLei; Sun, RenPing; Lai, XuanYang; Hu, ShiLin; Liu, MingQing; Shu, Zheng; Wang, XiaoDong; Li, WeiDong; Becker, Wilhelm; Liu, XiaoJun; Chen, Jing

2017-09-01

Quantum interference plays an important role in various intense-laser-driven atomic phenomena, e.g., above-threshold ionization and high-order-harmonic generation, and provides a useful tool in ultrafast imaging of atomic and molecular structure and dynamics. However, it has eluded observation in nonsequential double ionization (NSDI), which serves as an ideal prototype to study electron-electron correlation. Thus far, NSDI usually could be well understood from a semiclassical perspective, where all quantum aspects have been ignored after the first electron has tunneled. Here we perform coincidence measurements for NSDI of xenon subject to laser pulses at 2400 nm. It is found that the intensity dependence of the asymmetry parameter between the yields in the second and fourth quadrants and those in the first and third quadrants of the electron-momentum-correlation distributions exhibits a peculiar fast oscillatory structure, which is beyond the scope of the semiclassical picture. Our theoretical analysis indicates that this oscillation can be attributed to interference between the contributions of different excited states in the recollision-excitation-with-subsequent-ionization channel. Our work demonstrates the significant role of quantum interference in NSDI and may create an additional pathway towards manipulation and imaging of the ultrafast atomic and molecular dynamics in intense laser fields.

Nanoparticle assisted laser desorption/ionization mass spectrometry for small molecule analytes.

Science.gov (United States)

Abdelhamid, Hani Nasser

2018-03-01

Nanoparticle assisted laser desorption/ionization mass spectrometry (NPs-ALDI-MS) shows remarkable characteristics and has a promising future in terms of real sample analysis. The incorporation of NPs can advance several methods including surface assisted LDI-MS, and surface enhanced LDI-MS. These methods have advanced the detection of many thermally labile and nonvolatile biomolecules. Nanoparticles circumvent the drawbacks of conventional organic matrices for the analysis of small molecules. In most cases, NPs offer a clear background without interfering peaks, absence of fragmentation of thermally labile molecules, and allow the ionization of species with weak noncovalent interactions. Furthermore, an enhancement in sensitivity and selectivity can be achieved. NPs enable straightforward analysis of target species in a complex sample. This review (with 239 refs.) covers the progress made in laser-based mass spectrometry in combination with the use of metallic NPs (such as AuNPs, AgNPs, PtNPs, and PdNPs), NPs consisting of oxides and chalcogenides, silicon-based NPs, carbon-based nanomaterials, quantum dots, and metal-organic frameworks. Graphical abstract An overview is given on nanomaterials for use in surface-assisted laser desorption/ionization mass spectrometry of small molecules.

A fragmentation study of kaempferol using electrospray quadrupole time-of-flight mass spectrometry at high mass resolution

Science.gov (United States)

March, Raymond E.; Miao, Xiu-Sheng

2004-02-01

A mass spectrometric method based on the combined use of electrospray ionization, collision-induced dissociation and tandem mass spectrometry at high mass resolution has been applied to an investigation of the structural characterization of protonated and deprotonated kaempferol (3,5,7,4'-tetrahydroxyflavone). Low-energy product ion mass spectra of [M+H]+ ions showed simple fragmentations of the C ring that permitted characterization of the substituents in the A and B rings. In addition, four rearrangement reactions accompanied by losses of C2H2O, CHO[radical sign], CO, and H2O were observed. Low-energy product ion mass spectra of [M-H]- ions showed only four rearrangement reactions accompanied by losses of OH[radical sign], CO, CH2O, and C2H2O. The use of elevated cone voltages permitted observation of product ion mass spectra of selected primary and secondary fragment ions so that each fragment ion reported was observed as a direct product of its immediate precursor ion. Product ion mass spectra examined at high mass resolution allowed unambiguous determination of the elemental composition of fragment ions and resolution of two pairs of isobars. Fragmentation mechanisms and ion structures have been proposed.

Inner-shell excitation and site specific fragmentation of poly(methylmethacrylate) thin film

Science.gov (United States)

Tinone, Marcia C. K.; Tanaka, Kenichiro; Maruyama, Junya; Ueno, Nobuo; Imamura, Motoyasu; Matsubayashi, Nobuyuki

1994-04-01

Soft x-ray excitations in the 250-600 eV photon energy range on poly(methylmethacrylate) (PMMA) result in ionic fragmentation of the original polymer with the most intense ions corresponding to CH+3, H+, CH+2, CH+, CHO+, and COOCH+3. The photon energy dependence of ion desorption from thin films of PMMA was measured to investigate the primary steps in radiation induced decomposition following carbon and oxygen 1s electron excitations using monochromatic pulsed-synchrotron radiation. It was clearly found that the decomposition depends on the nature of the electronic states created in the excited species. The fragmentation pattern changes depending on the transitions of the 1s electron to a Rydberg orbital, an unoccupied molecular orbital or the ionization continuum. Moreover, the fragmentation occurs specifically around the site of the atom where the optical excitation takes place. Excitations from carbon and oxygen 1s to σ* states seem to be specially efficient for ion production as observed in the case of CH+3, CH+2, and CH+ at 288.7 and 535.6 eV, and in the case of CHO+ at 539.3 eV.

Impact ionization processes in the steady state of a driven Mott-insulating layer coupled to metallic leads

Science.gov (United States)

Sorantin, Max E.; Dorda, Antonius; Held, Karsten; Arrigoni, Enrico

2018-03-01

We study a simple model of photovoltaic energy harvesting across a Mott-insulating gap consisting of a correlated layer connected to two metallic leads held at different chemical potentials. We address, in particular, the issue of impact ionization, whereby a particle photoexcited to the high-energy part of the upper Hubbard band uses its extra energy to produce a second particle-hole excitation. We find a drastic increase of the photocurrent upon entering the frequency regime where impact ionization is possible. At large values of the Mott gap, where impact ionization is energetically not allowed, we observe a suppression of the current and a piling up of charge in the high-energy part of the upper Hubbard band. Our study is based on a Floquet dynamical mean-field theory treatment of the steady state with the so-called auxiliary master equation approach as impurity solver. We verify that an additional approximation, taking the self-energy diagonal in the Floquet indices, is appropriate for the parameter range we are considering.

Advanced carbon-based material C60 modification using partially ionized cluster and energetic beams

International Nuclear Information System (INIS)

Du Yuancheng; Ren Zhongmin; Ning Zhifeng; Xu Ning; Li Fuming

1997-01-01

Two processes have been undertaken using Partially ionized cluster deposition (PICBD) and energetic ion bombardment beams deposition (IBD) respectively. C 60 films deposited by PICBD at V=0 and 65 V, which result in highly textured close-packed structure in orientation (110) and being more polycrystalline respectively, the resistance of C 60 films to oxygen diffusion contamination will be improved. In the case of PICBD, the ionized C 60 soccer-balls molecules in the evaporation beams will be fragmented in collision with the substrate under the elevated accelerating fields Va. As a new synthetic IBD processing, two low energy (400 and 1000 eV) nitrogen ion beams have been used to bombard C 60 films to synthesize the carbon nitride films

Unraveling nonadiabatic ionization and Coulomb potential effect in strong-field photoelectron holography.

Science.gov (United States)

Song, Xiaohong; Lin, Cheng; Sheng, Zhihao; Liu, Peng; Chen, Zhangjin; Yang, Weifeng; Hu, Shilin; Lin, C D; Chen, Jing

2016-06-22

Strong field photoelectron holography has been proposed as a means for interrogating the spatial and temporal information of electrons and ions in a dynamic system. After ionization, part of the electron wave packet may directly go to the detector (the reference wave), while another part may be driven back and scatters off the ion(the signal wave). The interference hologram of the two waves may be used to extract target information embedded in the collision process. Unlike conventional optical holography, however, propagation of the electron wave packet is affected by the Coulomb potential as well as by the laser field. In addition, electrons are emitted over the whole laser pulse duration, thus multiple interferences may occur. In this work, we used a generalized quantum-trajectory Monte Carlo method to investigate the effect of Coulomb potential and the nonadiabatic subcycle ionization on the photoelectron hologram. We showed that photoelectron hologram can be well described only when the effect of nonadiabatic ionization is accounted for, and Coulomb potential can be neglected only in the tunnel ionization regime. Our results help paving the way for establishing photoelectron holography for probing spatial and dynamic properties of atoms and molecules.

Timeframe Dependent Fragment Ions Observed in In-Source Decay Experiments with β-Casein Using MALDI MS.

Science.gov (United States)

Sekiya, Sadanori; Nagoshi, Keishiro; Iwamoto, Shinichi; Tanaka, Koichi; Takayama, Mitsuo

2015-09-01

The fragment ions observed with time-of-flight (TOF) and quadrupole ion trap (QIT) TOF mass spectrometers (MS) combined with matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) experiments of phosphorylated analytes β-casein and its model peptide were compared from the standpoint of the residence timeframe of analyte and fragment ions in the MALDI ion source and QIT cell. The QIT-TOF MS gave fragment c-, z'-, z-ANL, y-, and b-ions, and further degraded fragments originating from the loss of neutrals such as H(2)O, NH(3), CH(2)O (from serine), C2H4O (from threonine), and H(3)PO(4), whereas the TOF MS merely showed MALDI source-generated fragment c-, z'-, z-ANL, y-, and w-ions. The fragment ions observed in the QIT-TOF MS could be explained by the injection of the source-generated ions into the QIT cell or a cooperative effect of a little internal energy deposition, a long residence timeframe (140 ms) in the QIT cell, and specific amino acid effects on low-energy CID, whereas the source-generated fragments (c-, z'-, z-ANL, y-, and w-ions) could be a result of prompt radical-initiated fragmentation of hydrogen-abundant radical ions [M + H + H](+) and [M + H - H](-) within the 53 ns timeframe, which corresponds to the delayed extraction time. The further degraded fragment b/y-ions produced in the QIT cell were confirmed by positive- and negative-ion low-energy CID experiments performed on the source-generated ions (c-, z'-, and y-ions). The loss of phosphoric acid (98 u) from analyte and fragment ions can be explained by a slow ergodic fragmentation independent of positive and negative charges.

Timeframe Dependent Fragment Ions Observed in In-Source Decay Experiments with β-Casein Using MALDI MS

Science.gov (United States)

Sekiya, Sadanori; Nagoshi, Keishiro; Iwamoto, Shinichi; Tanaka, Koichi; Takayama, Mitsuo

2015-09-01

The fragment ions observed with time-of-flight (TOF) and quadrupole ion trap (QIT) TOF mass spectrometers (MS) combined with matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) experiments of phosphorylated analytes β-casein and its model peptide were compared from the standpoint of the residence timeframe of analyte and fragment ions in the MALDI ion source and QIT cell. The QIT-TOF MS gave fragment c-, z'-, z-ANL, y-, and b-ions, and further degraded fragments originating from the loss of neutrals such as H2O, NH3, CH2O (from serine), C2H4O (from threonine), and H3PO4, whereas the TOF MS merely showed MALDI source-generated fragment c-, z'-, z-ANL, y-, and w-ions. The fragment ions observed in the QIT-TOF MS could be explained by the injection of the source-generated ions into the QIT cell or a cooperative effect of a little internal energy deposition, a long residence timeframe (140 ms) in the QIT cell, and specific amino acid effects on low-energy CID, whereas the source-generated fragments (c-, z'-, z-ANL, y-, and w-ions) could be a result of prompt radical-initiated fragmentation of hydrogen-abundant radical ions [M + H + H]+ and [M + H - H]- within the 53 ns timeframe, which corresponds to the delayed extraction time. The further degraded fragment b/y-ions produced in the QIT cell were confirmed by positive- and negative-ion low-energy CID experiments performed on the source-generated ions (c-, z'-, and y-ions). The loss of phosphoric acid (98 u) from analyte and fragment ions can be explained by a slow ergodic fragmentation independent of positive and negative charges.

Detection and quantification of neurotensin in human brain tissue by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

DEFF Research Database (Denmark)

Gobom, J; Kraeuter, K O; Persson, R

2000-01-01

A method was developed for mass spectrometric detection of neurotensin (NT)-like immunoreactivity and quantification of NT in human brain tissue. The method is based on immunoprecipitation followed by analysis using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF......-MS). The identity of the major component of the immunoprecipitates as neurotensin was confirmed by fragment ion analysis on an electrospray ionization quadrupole time-of-flight instrument. MALDI-TOF-MS quantification of NT was achieved using stable-isotope-labeled NT as the internal standard, yielding an error...

Basic-level categorization of intermediate complexity fragments reveals top-down effects of expertise in visual perception.

Science.gov (United States)

Harel, Assaf; Ullman, Shimon; Harari, Danny; Bentin, Shlomo

2011-07-28

Visual expertise is usually defined as the superior ability to distinguish between exemplars of a homogeneous category. Here, we ask how real-world expertise manifests at basic-level categorization and assess the contribution of stimulus-driven and top-down knowledge-based factors to this manifestation. Car experts and novices categorized computer-selected image fragments of cars, airplanes, and faces. Within each category, the fragments varied in their mutual information (MI), an objective quantifiable measure of feature diagnosticity. Categorization of face and airplane fragments was similar within and between groups, showing better performance with increasing MI levels. Novices categorized car fragments more slowly than face and airplane fragments, while experts categorized car fragments as fast as face and airplane fragments. The experts' advantage with car fragments was similar across MI levels, with similar functions relating RT with MI level for both groups. Accuracy was equal between groups for cars as well as faces and airplanes, but experts' response criteria were biased toward cars. These findings suggest that expertise does not entail only specific perceptual strategies. Rather, at the basic level, expertise manifests as a general processing advantage arguably involving application of top-down mechanisms, such as knowledge and attention, which helps experts to distinguish between object categories. © ARVO

Laser-enhanced ionization spectroscopy around the ionization limit

International Nuclear Information System (INIS)

Axner, O.; Berglind, T.; Sjoestroem, S.

1986-01-01

Laser-induced photoionization and Laser-Enhanced collision Ionization (LEI) of Na, Tl, and Li in flames are detected by measuring the production of charges following a laser excitation. The ionization signal is investigated for excitations of the atoms from lower lying states both to Rydberg states close to the ionization limit, as well as to continuum states, i.e. the process of collision ionization is compared with that of photoionization. The qualitative behaviour of the ionization signal when scanning across the ionization limit is studied. It is shown that the ionization signal has a smooth behaviour when passing from bound states into continuum states. The laser-induced photoionization signal strength of atoms in flames is both calculated and measured and a good agreement is obtained. A calculation of wavelength dependent photoionization signal strengths for a number of elements is also presented. Photoionization is used to determine flame- and geometry-dependent parameters. An implication of photoionization in connection with LEI spectrometry for trace element analysis is that there will be a significant increase in background noise if the sample contains high concentrations of easily photoionizing elements and short wavelength light is used. (orig.)

Drawing a different picture with pencil lead as matrix-assisted laser desorption/ionization matrix for fullerene derivatives.

Science.gov (United States)

Nye, Leanne C; Hungerbühler, Hartmut; Drewello, Thomas

2018-02-01

Inspired by reports on the use of pencil lead as a matrix-assisted laser desorption/ionization matrix, paving the way towards matrix-free matrix-assisted laser desorption/ionization, the present investigation evaluates its usage with organic fullerene derivatives. Currently, this class of compounds is best analysed using the electron transfer matrix trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene] malononitrile (DCTB), which was employed as the standard here. The suitability of pencil lead was additionally compared to direct (i.e. no matrix) laser desorption/ionization-mass spectrometry. The use of (DCTB) was identified as the by far gentler method, producing spectra with abundant molecular ion signals and much reduced fragmentation. Analytically, pencil lead was found to be ineffective as a matrix, however, appears to be an extremely easy and inexpensive method for producing sodium and potassium adducts.

Simulation experiment on total ionization dose effects of linear CCD

International Nuclear Information System (INIS)

Tang Benqi; Zhang Yong; Xiao Zhigang; Wang Zujun; Huang Shaoyan

2004-01-01

We carry out the ionization radiation experiment of linear CCDs operated in unbiased, biased, biased and driven mode respectively by Co-60 γ source with our self-designed test system, and offline test the Dark signal and Saturation voltage and SNR varied with total dose for TCD132D, and get some valuable results. On the basis of above work, we set forth a primary experiment approaches to simulate the total dose radiation effects of charge coupled devices. (authors)

Time-dependent quantum chemistry of laser driven many-electron molecules

International Nuclear Information System (INIS)

Nguyen-Dang, Thanh-Tung; Couture-Bienvenue, Étienne; Viau-Trudel, Jérémy; Sainjon, Amaury

2014-01-01

A Time-Dependent Configuration Interaction approach using multiple Feshbach partitionings, corresponding to multiple ionization stages of a laser-driven molecule, has recently been proposed [T.-T. Nguyen-Dang and J. Viau-Trudel, J. Chem. Phys. 139, 244102 (2013)]. To complete this development toward a fully ab-initio method for the calculation of time-dependent electronic wavefunctions of an N-electron molecule, we describe how tools of multiconfiguration quantum chemistry such as the management of the configuration expansion space using Graphical Unitary Group Approach concepts can be profitably adapted to the new context, that of time-resolved electronic dynamics, as opposed to stationary electronic structure. The method is applied to calculate the detailed, sub-cycle electronic dynamics of BeH 2 , treated in a 3–21G bound-orbital basis augmented by a set of orthogonalized plane-waves representing continuum-type orbitals, including its ionization under an intense λ = 800 nm or λ = 80 nm continuous-wave laser field. The dynamics is strongly non-linear at the field-intensity considered (I ≃ 10 15 W/cm 2 ), featuring important ionization of an inner-shell electron and strong post-ionization bound-electron dynamics

[Ionizing and non-ionizing radiation (comparative risk estimations)].

Science.gov (United States)

Grigor'ev, Iu G

2012-01-01

The population has widely used mobile communication for already more than 15 years. It is important to note that the use of mobile communication has sharply changed the conditions of daily exposure of the population to EME We expose our brain daily for the first time in the entire civilization. The mobile phone is an open and uncontrollable source of electromagnetic radiation. The comparative risk estimation for the population of ionizing and non-ionizing radiation was carried out taking into account the real conditions of influence. Comparison of risks for the population of ionizing and non-ionizing radiation leads us to a conclusion that EMF RF exposure in conditions of wide use of mobile communication is potentially more harmful than ionizing radiation influence.

Effect of molecular structure on fragmentation of isolated organic molecules in solid rare gas matrices

International Nuclear Information System (INIS)

Kobzarenko, A.V.; Sukhov, F.F.; Orlov, A.Yu.; Kovalev, G.V.; Baranova, I.A.; Feldman, V.I.

2012-01-01

The effect of excess energy on the primary radical cations of bifunctional carbonyl compounds and aliphatic alkynes was simulated by matrix isolation method using rare gas matrices with various ionization potentials. The formation of fragmentation products was monitored by EPR and FTIR spectroscopy. It was shown that the radical cations of bifunctional compounds (CH 3 OCH 2 COCH 3 and CH 3 COCOCH 3 ) dissociated effectively yielding · CH 3 radicals upon irradiation in solid argon matrix at T≤16 K. In addition to isolated methyl radicals, the radical pairs consisting of two methyl radicals separated by two CO molecules were detected in the case of diacetyl. The probability of fragmentation decreases with the decreasing excess energy by switching from Ar to Xe. In general, bifunctional molecules were found to be less stable to “hot” ionic fragmentation in low-temperature solids in comparison with simple prototype compounds. In the case of alkynes of the R--C≡CH type, a noticeable yield of fragmentation products was observed when R=–C(CH 3 ) 3 , but it was negligible for R=–CH 3 . The mechanisms of “hot” reactions and excess energy relaxation are discussed. - Highlights: ► Radiolysis of bifunctional organic compounds and alkynes. ► Dependence of “hot” fragmentation probability from molecular structure. ► Ions of bifunctional compounds are less stable than those of monofunctional ones. ► Alkynes are rather stable to “hot” fragmentation.

Sensitivity of clostridium acetobutylicum to oxygen and ionizing radiation

International Nuclear Information System (INIS)

Sozer, A.C.; Adler, H.I.; Machanoff, R.; Haney, S.

1984-01-01

The authors are studying the sensitivity of four strains of the obligate anaerobe, Clostridium acetobutylicum, to oxygen and ionizing radiation. Anaerobic bacteria are useful for such studies because of the absence of elaborate oxygen detoxification mechanisms that are found in aerobes. Their experiments make use of sterile membrane fragments from Escherichia coli that rapidly remove molecular oxygen from media and permit growth of anaerobes without the use of reducing agents or anaerobic chambers. Of the four strains examined for sensitivity to ionizing radiation under anaerobic conditions, one has an LD/sub 50/ of -- 25 krads and the others have an LD/sub 50/ of -- 7 krads. The radiation resistant strain is also relatively resistant to oxygen exposure. Sensitivity to oxygen was determined by diluting cells in buffer at 28 0 and bubbling with air. An exposure to air for 40 min induced only slight inactivation in the radiation resistant strain. All strains are capable of removing oxygen from complex media but there is no apparent correlation between this oxygen consuming reaction and inactivation by either oxygen or radiation

Molecular characterization of thymidine kinase mutants of human cells induced by densely ionizing radiation

Energy Technology Data Exchange (ETDEWEB)

Kronenberg, A; Little, J B

1989-04-01

In order to characterize the nature of mutants induced by densely ionizing radiations at an autosomal locus, the authors have isolated a series of 99 thymidine kinase (tk) mutants of human TK6 lymphoblastoid cells iraadiated with either fast neutrons or accelerated argon ions. Individual muant clones were examined for alterations in their restriction fragment pattern after hybridization with a human cDNA probe for tk. A restriction fragment length polymorphism (RFLP) allowed identification of the active tk allele. Among the neutron-induced mutants, 34/52 exhibited loss of the previously active allele while 6/52 exhibited intragenic rearrangements. Among the argon-induced mutants 27/46 exhibited allele loses and 10/46 showed rearrangements within the tk locus. The remaining mutants had restriction patterns indistinguishable from the TK6 parent. Each of the mutant clones was further examined for structural alterations within the c-erbAl locus which has been localized to chromosome 17q11-q22, at some unknown distance from the human tk locus at chromosome 17q21-q22. A substantial proportion (54%) of tk mutants induced by densely ionizing radiation showed loss of the c-erb locus on the homologous chromosome, suggesting that the mutations involve large-scale genetic changes. (author). 51 refs.; 2 figs.; 6 tabs.

Bird diversity along a gradient of fragmented habitats of the Cerrado.

Science.gov (United States)

Jesus, Shayana DE; Pedro, Wagner A; Bispo, Arthur A

2018-01-01

Understanding the factors that affect biodiversity is of central interest to ecology, and essential to species conservation and ecosystems management. We sampled bird communities in 17 forest fragments in the Cerrado biome, the Central-West region of Brazil. We aimed to know the communities structure pattern and the influence of geographical distance and environmental variables on them, along a gradient of fragmented habitats at both local and landscape scales. Eight structural variables of the fragments served as an environmental distance measurement at the local scale while five metrics served as an environmental distance measurement at the landscape scale. Species presence-absence data were used to calculate the dissimilarity index. Beta diversity was calculated using three indices (βsim, βnes and βsor), representing the spatial species turnover, nestedness and total beta diversity, respectively. Spatial species turnover was the predominant pattern in the structure of the communities. Variations in beta diversity were explained only by the environmental variables of the landscape with spatial configuration being more important than the composition. This fact indicates that, in Cerrado of Goiás avian communities structure, deterministic ecological processes associated to differences in species responses to landscape fragmentation are more important than stochastic processes driven by species dispersal.

Ionization effects in electronic inner-shells of ionized atoms

International Nuclear Information System (INIS)

Shchornak, G.

1983-01-01

A review of the atomic physics of ionization atoms has been presented. Interaction and structure effects in atomic shells, correlated to the occurrence of vacancies in several subshells of the atom have been considered. The methods of calculations of atomic states and wave functions have been reviewed. The energy shift of characteristic X-rays is discussed as a function of the ionization stage of the atom. The influence of inner and outer-shell vacancies on the energy of the X-rays is shown in detail. The influence of chemical effects on the parameters of X-rays is also taken into account. Further on, the change of transition probabilities in radiative and non-radiative transitions by changing stage of ionization is discussed; and among them the leading part of Auger and Coster-Kronig transitions by the arearrangement of the atomic states is shown. The influence of non-radiative electronic transitions on ionization cross-sections for multiple ionization is discussed. Using these results, ionization cross-sections for direct and indirect processes for several ionization stages are given

Jet fragmentation

International Nuclear Information System (INIS)

Saxon, D.H.

1985-10-01

The paper reviews studies on jet fragmentation. The subject is discussed under the topic headings: fragmentation models, charged particle multiplicity, bose-einstein correlations, identified hadrons in jets, heavy quark fragmentation, baryon production, gluon and quark jets compared, the string effect, and two successful models. (U.K.)

Trade and production fragmentation : Central European economies in European Union networks of production and marketing

OpenAIRE

Kaminski, Bartlomiej; Ng, Francis

2001-01-01

Developments driven by trade liberalization and tehcnological progress mean that old development strategies, based on state intervention and trade protection, no longer work. Global competition has brought a growing emphasis on product standards, rapid innovation, adaptability, and speedy response. Technology has made possible the fragmentation of production. Firms that become part of glob...

Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

Science.gov (United States)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P; Fang, Yigang; Kostko, Oleg; Ahmed, Musahid; Head-Gordon, Martin

2017-05-23

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C 2 H 2 ) n + , just like ionized acetylene clusters. The fragmentation products result from reactive ion-molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4 H 4 + and C 6 H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2 H 2 ) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6 H 6 + isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.

Ab initio dynamics and photoionization mass spectrometry reveal ion–molecule pathways from ionized acetylene clusters to benzene cation

Science.gov (United States)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.; Fang, Yigang; Kostko, Oleg

2017-01-01

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion–molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2)n+, just like ionized acetylene clusters. The fragmentation products result from reactive ion–molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C4H4+ and C6H6+ structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C2H2)n+ isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C6H6+ isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM. PMID:28484019

Hydrazinonicotinic acid derivatization for selective ionization and improved glycan structure characterization by MALDI-MS.

Science.gov (United States)

Jiao, Jing; Yang, Lijun; Zhang, Ying; Lu, Haojie

2015-08-21

The analysis of glycan is important for understanding cell biology and disease processes because the glycans play a key role in many important biological behaviors, such as cell division, cellular localization, tumor immunology and inflammation. Nevertheless, it is still hard work to analyze glycans by MALDI-MS, which generally stems from the inherent low abundance and the low ionization efficiency of glycans. Moreover, the difficulty in generating informative fragmentations further hinders glycans structure characterization. In this work, hydrazinonicotinic acid (HYNIC) was used as a novel derivatized reagent for improved and selective detection of glycans. Through tagging the reducing terminus of glycans with the diazanyl group of HYNIC, significant enhancement of the ionization efficiency of glycans was achieved. After derivatization, the signal to noise ratio (S/N) of the maltoheptaose was improved by more than one order of magnitude in positive mode. HYNIC derivatization also allowed the sensitive detection of sialylated glycan in negative mode, with a 15 fold enhancement of S/N. Interestingly, it is noteworthy that the HYNIC reagent not only effectively labeled the reducing end of glycans in the presence of tryptic peptides, but also suppressed the ionization of peptides, enabling the direct detection of glycans from glycoprotein without separation. Therefore, analysis of glycans became easier due to the omission of a pre-separation step. Importantly, by using different acid reagents as the catalyst, derivatized product signals corresponding to [M + Na](+) or [M + H](+) were obtained respectively, which yield complementary fragmentation patterns for the structure elucidation of glycans. Finally, more than 40 N-glycans were successfully detected in 10 μL human serum using this method.

Missing Fragments: Detecting Cooperative Binding in Fragment-Based Drug Design

Science.gov (United States)

2012-01-01

The aim of fragment-based drug design (FBDD) is to identify molecular fragments that bind to alternate subsites within a given binding pocket leading to cooperative binding when linked. In this study, the binding of fragments to human phenylethanolamine N-methyltransferase is used to illustrate how (a) current protocols may fail to detect fragments that bind cooperatively, (b) theoretical approaches can be used to validate potential hits, and (c) apparent false positives obtained when screening against cocktails of fragments may in fact indicate promising leads. PMID:24900472

Electron-impact ionization of SiCl{sub 3} using an improved crossed fast-neutral-beam - electron-beam apparatus

Energy Technology Data Exchange (ETDEWEB)

Mahoney, J M; Gutkin, M V; Tarnovsky, V; Becker, K [Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ 07030 (United States)], E-mail: kbecker@poly.edu

2008-05-15

The fast-neutral-beam technique is a versatile approach to the determination of absolute cross sections for electron-impact ionization of atoms, stable molecules as well as free radicals and metastable species. A fast neutral beam of the species under study is prepared by charge-transfer neutralization of a mass-selected ion beam and the species are subsequently ionized by an electron beam. Mass- and energy-dispersive selection separates singly from multiply charged ions and parent from fragment ions and allows the determination of partial ionization cross sections. Here we describe some major improvements that were made recently to the fast-beam apparatus that has been used extensively for ionization cross section measurements for the past 15 years in our group. Experiments using well-established ionization cross sections in conjunction with extensive ion trajectory simulations were carried out to test the satisfactory performance of the modified fast-neutral-beam apparatus. We also report absolute partial cross sections for the formation of various singly charged positive ions produced by electron impact on SiCl{sub 3} for impact energies from threshold to 200 eV in the modified fast-beam apparatus.

Study of the ionization of H+2 ions in strong laser fields

International Nuclear Information System (INIS)

Odenweller, Matthias

2010-01-01

In the framework of this thesis it has been succeeded to develop a worldwide unique measurement apparatur, by which hydrogen-molecule ions can be ionized by means of short laser pulses and the reaction product kinematically completely measured. For this a detection method following the Coltrims technique, in which both protons and electrons can be detected over the complete spatial angle. The H + 2 ions origin from a high-frequency ion source and are accelerated to 400 keV. This ion beam is overlapped with a 780-nm laser pulse othe pulse length 40 fs. After the reaction the molecule ions fragments either via the dissociation channel H + 2 +nhν→H+H + or via an ionization followed by a Coulomb explosion: H + 2 +nhν→H + +H + +e - . The projectiles are detected after a drift path of about 3 m on an ion detector. For the detection of the electrons a special spectrometer was concipated. In the reaction it comes by the comparatively long pulse length already at low intensities to dissociation processes. The dissociating molecule reaches still during the increasing side of the laser pulse in this way distances, in which the charge-resonance-enhanced-ionization (CREI) can take place. Also the angular distribution of the measured protons lying in a very small angular range around the polarization direction of the laser suggests that CREI is the dominant ionization process. At circular polarization however a netto-acceleration of the electrons perpendicularly to the direction of the electric field at the ionization time takes place, so that the measurement of the electron momenta represents a suited measurement quantity for the study of the ionization process. By this way angular distributions of the electrons relatively to the internuclear axis within the polarization plane could be measured.

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

International Nuclear Information System (INIS)

Alton, G.D.; Williams, C.

1996-01-01

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

Study of Particle Production and Nuclear Fragmentation in Relativistic Heavy-Ion Collisions in Nuclear Emulsions

CERN Multimedia

2002-01-01

% EMU11 \\\\ \\\\ We propose to use nuclear emulsions for the study of nuclear collisions of $^{207}$Pb, $^{197}$Au, and any other heavy-ion beams when they are available. We have, in the past, used $^{32}$S at 200A~GeV and $^{16}$O at 200A and 60A~GeV from CERN (Experiment EMU08) and at present the analysis is going on with $^{28}$Si beam from BNL at 14.5A~GeV. It will be important to compare the previous and the present investigations with the new $^{207}$Pb beam at 60-160A~GeV. We want to measure in nuclear emulsion, on an event by event basis, shower particle multiplicity, pseudorapidity density and density fluctuations of charged particles, charge multiplicity and angular distributions of projectile fragments, production and interaction cross-sections of heavily ionizing particles emitted from the target fragmentation. Special emphasis will be placed on the analysis of events produced in the central collisions which are selected on the basis of low energy fragments emitted from the target excitation. It woul...

Modeling X-ray Absorbers in AGNs with MHD-Driven Accretion-Disk Winds

Science.gov (United States)

Fukumura, Keigo; Kazanas, D.; Shrader, C. R.; Tombesi, F.; Contopoulos, J.; Behar, E.

2013-04-01

We have proposed a systematic view of the observed X-ray absorbers, namely warm absorbers (WAs) in soft X-ray and highly-ionized ultra-fast outflows (UFOs), in the context of magnetically-driven accretion-disk wind models. While potentially complicated by variability and thermal instability in these energetic outflows, in this simplistic model we have calculated 2D kinematic field as well as density and ionization structure of the wind with density profile of 1/r corresponding to a constant column distribution per decade of ionization parameter. In particular we show semi-analytically that the inner layer of the disk-wind manifests itself as the strongly-ionized fast outflows while the outer layer is identified as the moderately-ionized absorbers. The computed characteristics of these two apparently distinct absorbers are consistent with X-ray data (i.e. a factor of ~100 difference in column and ionization parameters as well as low wind velocity vs. near-relativistic flow). With the predicted contour curves for these wind parameters one can constrain allowed regions for the presence of WAs and UFOs.The model further implies that the UFO's gas pressure is comparable to that of the observed radio jet in 3C111 suggesting that the magnetized disk-wind with density profile of 1/r is a viable agent to help sustain such a self-collimated jet at small radii.

Time-resolved investigations of the fragmentation dynamic of H2 (D2) in and with ultra-short laser pulses

International Nuclear Information System (INIS)

Ergler, T.

2006-01-01

In course of this work pump-probe experiments aimed to study ultrafast nuclear motion in H 2 (D 2 ) fragmentation by intense 6-25 fs laser pulses have been carried out. In order to perform time-resolved measurements, a Mach-Zehnder interferometer providing two identical synchronized laser pulses with the time-delay variable from 0 to 3000 fs with 300 as accuracy and long-term stability has been built. The laser pulses at the intensities of up to 10 15 W/cm 2 were focused onto a H 2 (D 2 ) molecular beam leading to the ionization or dissociation of the molecules, and the momenta of all charged reactions fragments were measured with a reaction microscope. With 6-7 fs pulses it was possible to probe the time evolution of the bound H + 2 (D + 2 ) nuclear wave packet created by the first (pump) laser pulse, fragmenting the molecule with the second (probe) pulse. A fast delocalization, or ''collapse'', and subsequent ''revival'' of the vibrational wave packet have been observed. In addition, the signatures of the ground state vibrational excitation in neutral D 2 molecule have been found, and the dominance of a new, purely quantum mechanical wave packet preparation mechanism (the so-called ''Lochfrass'') has been proved. In the experiments with 25 fs pulses the theoretically predicted enhancement of the ionization probability for the dissociating H + 2 molecular ion at large internuclear distances has been detected for the first time. (orig.)

Adhesion of axolemmal fragments to Schwann cells: a signal- and target-specific process closely linked to axolemmal induction of Schwann cell mitosis

International Nuclear Information System (INIS)

Sobue, G.; Pleasure, D.

1985-01-01

Radioiodinated rat CNS axolemmal fragments adhered to cultured rat Schwann cells by a time-, temperature-, and concentration-dependent process independent of extracellular ionized calcium. Adhesion showed target and signal specificity; axolemmal fragments adhered to endoneurial or dermal fibroblasts to a much lesser extent than to Schwann cells, and plasma membrane fragments from skeletal muscle, erythrocytes, or PNS myelin adhered to Schwann cells to a lesser extent than did axolemmal fragments. Brief trypsinization removed 94 to 97% of bound radioactivity from Schwann cells previously incubated with 125 I-axolemmal fragments for up to 24 hr, indicating that adhesion was largely a surface phenomenon rather than the result of rapid internalization of axolemmal fragments by the Schwann cells. When adhesion was compared to the axolemmal mitogenic response of Schwann cells, the concentration of axolemmal fragments yielding half-maximal adhesion was the same as the concentration producing half-maximal stimulation of Schwann cell mitosis. Trypsin digestion, homogenization, or heating of axolemmal fragments before application to cultured Schwann cells diminished adhesion and axolemmal fragment-induced stimulation of Schwann cell mitosis in a parallel fashion. Whereas adhesion of axolemmal fragments to the surfaces of the cultured Schwann cells reached completion within 4 hr in this assay system, induction of Schwann cell mitosis by the fragments required contact with Schwann cells for a minimum of 6 to 8 hr and reached a maximum when the axolemmal fragments had adhered to the Schwann cells for 24 hr or more

Neutronics Assessments for a RIA Fragmentation Line Beam Dump Concept

CERN Document Server

Boles, Jason; Reyes, Susana; Stein, Werner

2005-01-01

Heavy ion and radiation transport calculations are in progress for conceptual beam dump designs for the fragmentation line of the proposed Rare Isotope Accelerator (RIA). Using the computer code PHITS, a preliminary design of a motor-driven rotating wheel beam dump and adjacent downstream multipole has been modeled. Selected results of these calculations are given, including neutron and proton flux in the wheel, absorbed dose and displacements per atom in the hub materials, and heating from prompt radiation and from decay heat in the multipole.

Structures of endothiapepsin-fragment complexes from crystallographic fragment screening using a novel, diverse and affordable 96-compound fragment library.

Science.gov (United States)

Huschmann, Franziska U; Linnik, Janina; Sparta, Karine; Ühlein, Monika; Wang, Xiaojie; Metz, Alexander; Schiebel, Johannes; Heine, Andreas; Klebe, Gerhard; Weiss, Manfred S; Mueller, Uwe

2016-05-01

Crystallographic screening of the binding of small organic compounds (termed fragments) to proteins is increasingly important for medicinal chemistry-oriented drug discovery. To enable such experiments in a widespread manner, an affordable 96-compound library has been assembled for fragment screening in both academia and industry. The library is selected from already existing protein-ligand structures and is characterized by a broad ligand diversity, including buffer ingredients, carbohydrates, nucleotides, amino acids, peptide-like fragments and various drug-like organic compounds. When applied to the model protease endothiapepsin in a crystallographic screening experiment, a hit rate of nearly 10% was obtained. In comparison to other fragment libraries and considering that no pre-screening was performed, this hit rate is remarkably high. This demonstrates the general suitability of the selected compounds for an initial fragment-screening campaign. The library composition, experimental considerations and time requirements for a complete crystallographic fragment-screening campaign are discussed as well as the nine fully refined obtained endothiapepsin-fragment structures. While most of the fragments bind close to the catalytic centre of endothiapepsin in poses that have been observed previously, two fragments address new sites on the protein surface. ITC measurements show that the fragments bind to endothiapepsin with millimolar affinity.

Structures of endothiapepsin–fragment complexes from crystallographic fragment screening using a novel, diverse and affordable 96-compound fragment library

Science.gov (United States)

Huschmann, Franziska U.; Linnik, Janina; Sparta, Karine; Ühlein, Monika; Wang, Xiaojie; Metz, Alexander; Schiebel, Johannes; Heine, Andreas; Klebe, Gerhard; Weiss, Manfred S.; Mueller, Uwe

2016-01-01

Crystallographic screening of the binding of small organic compounds (termed fragments) to proteins is increasingly important for medicinal chemistry-oriented drug discovery. To enable such experiments in a widespread manner, an affordable 96-compound library has been assembled for fragment screening in both academia and industry. The library is selected from already existing protein–ligand structures and is characterized by a broad ligand diversity, including buffer ingredients, carbohydrates, nucleotides, amino acids, peptide-like fragments and various drug-like organic compounds. When applied to the model protease endothiapepsin in a crystallographic screening experiment, a hit rate of nearly 10% was obtained. In comparison to other fragment libraries and considering that no pre-screening was performed, this hit rate is remarkably high. This demonstrates the general suitability of the selected compounds for an initial fragment-screening campaign. The library composition, experimental considerations and time requirements for a complete crystallographic fragment-screening campaign are discussed as well as the nine fully refined obtained endothiapepsin–fragment structures. While most of the fragments bind close to the catalytic centre of endothiapepsin in poses that have been observed previously, two fragments address new sites on the protein surface. ITC measurements show that the fragments bind to endothiapepsin with millimolar affinity. PMID:27139825

Potential for the Vishniac instability in ionizing shock waves propagating into cold gases

Science.gov (United States)

Robinson, A. P. L.; Pasley, J.

2018-05-01

The Vishniac instability was posited as an instability that could affect supernova remnants in their late stage of evolution when subject to strong radiative cooling, which can drive the effective ratio of specific heats below 1.3. The potential importance of this instability to these astrophysical objects has motivated a number of laser-driven laboratory studies. However, the Vishniac instability is essentially a dynamical instability that should operate independently of whatever physical processes happen to reduce the ratio of specific heats. In this paper, we examine the possibility that ionization and molecular dissociation processes can achieve this, and we show that this is possible for a certain range of shock wave Mach numbers for ionizing/dissociating shock waves propagating into cold atomic and molecular gases.

Generation of monoenergetic ion beams via ionization dynamics (Conference Presentation)

Science.gov (United States)

Lin, Chen; Kim, I. Jong; Yu, Jinqing; Choi, Il Woo; Ma, Wenjun; Yan, Xueqing; Nam, Chang Hee

2017-05-01

The research on ion acceleration driven by high intensity laser pulse has attracted significant interests in recent decades due to the developments of laser technology. The intensive study of energetic ion bunches is particularly stimulated by wide applications in nuclear fusion, medical treatment, warm dense matter production and high energy density physics. However, to implement such compact accelerators, challenges are still existing in terms of beam quality and stability, especially in applications that require higher energy and narrow bandwidth spectra ion beams. We report on the acceleration of quasi-mono-energetic ion beams via ionization dynamics in the interaction of an intense laser pulse with a solid target. Using ionization dynamics model in 2D particle-in-cell (PIC) simulations, we found that high charge state contamination ions can only be ionized in the central spot area where the intensity of sheath field surpasses their ionization threshold. These ions automatically form a microstructure target with a width of few micron scale, which is conducive to generate mono-energetic beams. In the experiment of ultraintense (< 10^21 W/cm^2) laser pulses irradiating ultrathin targets each attracted with a contamination layer of nm-thickness, high quality < 100 MeV mono-energetic ion bunches are generated. The peak energy of the self-generated micro-structured target ions with respect to different contamination layer thickness is also examined This is relatively newfound respect, which is confirmed by the consistence between experiment data and the simulation results.

Faunal Communities Are Invariant to Fragmentation in Experimental Seagrass Landscapes.

Directory of Open Access Journals (Sweden)

Jonathan S Lefcheck

Full Text Available Human-driven habitat fragmentation is cited as one of the most pressing threats facing many coastal ecosystems today. Many experiments have explored the consequences of fragmentation on fauna in one foundational habitat, seagrass beds, but have either surveyed along a gradient of existing patchiness, used artificial materials to mimic a natural bed, or sampled over short timescales. Here, we describe faunal responses to constructed fragmented landscapes varying from 4-400 m2 in two transplant garden experiments incorporating live eelgrass (Zostera marina L.. In experiments replicated within two subestuaries of the Chesapeake Bay, USA across multiple seasons and non-consecutive years, we comprehensively censused mesopredators and epifaunal communities using complementary quantitative methods. We found that community properties, including abundance, species richness, Simpson and functional diversity, and composition were generally unaffected by the number of patches and the size of the landscape, or the intensity of sampling. Additionally, an index of competition based on species co-occurrences revealed no trends with increasing patch size, contrary to theoretical predictions. We extend conclusions concerning the invariance of animal communities to habitat fragmentation from small-scale observational surveys and artificial experiments to experiments conducted with actual living plants and at more realistic scales. Our findings are likely a consequence of the rapid life histories and high mobility of the organisms common to eelgrass beds, and have implications for both conservation and restoration, suggesting that even small patches can rapidly promote abundant and diverse faunal communities.

Fragment-based drug discovery and protein–protein interactions

Directory of Open Access Journals (Sweden)

Turnbull AP

2014-09-01

Full Text Available Andrew P Turnbull,1 Susan M Boyd,2 Björn Walse31CRT Discovery Laboratories, Department of Biological Sciences, Birkbeck, University of London, London, UK; 2IOTA Pharmaceuticals Ltd, Cambridge, UK; 3SARomics Biostructures AB, Lund, SwedenAbstract: Protein–protein interactions (PPIs are involved in many biological processes, with an estimated 400,000 PPIs within the human proteome. There is significant interest in exploiting the relatively unexplored potential of these interactions in drug discovery, driven by the need to find new therapeutic targets. Compared with classical drug discovery against targets with well-defined binding sites, developing small-molecule inhibitors against PPIs where the contact surfaces are frequently more extensive and comparatively flat, with most of the binding energy localized in “hot spots”, has proven far more challenging. However, despite the difficulties associated with targeting PPIs, important progress has been made in recent years with fragment-based drug discovery playing a pivotal role in improving their tractability. Computational and empirical approaches can be used to identify hot-spot regions and assess the druggability and ligandability of new targets, whilst fragment screening campaigns can detect low-affinity fragments that either directly or indirectly perturb the PPI. Once fragment hits have been identified and confirmed using biochemical and biophysical approaches, three-dimensional structural data derived from nuclear magnetic resonance or X-ray crystallography can be used to drive medicinal chemistry efforts towards the development of more potent inhibitors. A small-scale comparison presented in this review of “standard” fragments with those targeting PPIs has revealed that the latter tend to be larger, be more lipophilic, and contain more polar (acid/base functionality, whereas three-dimensional descriptor data indicate that there is little difference in their three

Towards a population synthesis model of self-gravitating disc fragmentation and tidal downsizing II: the effect of fragment-fragment interactions

Science.gov (United States)

Forgan, D. H.; Hall, C.; Meru, F.; Rice, W. K. M.

2018-03-01

It is likely that most protostellar systems undergo a brief phase where the protostellar disc is self-gravitating. If these discs are prone to fragmentation, then they are able to rapidly form objects that are initially of several Jupiter masses and larger. The fate of these disc fragments (and the fate of planetary bodies formed afterwards via core accretion) depends sensitively not only on the fragment's interaction with the disc, but also with its neighbouring fragments. We return to and revise our population synthesis model of self-gravitating disc fragmentation and tidal downsizing. Amongst other improvements, the model now directly incorporates fragment-fragment interactions while the disc is still present. We find that fragment-fragment scattering dominates the orbital evolution, even when we enforce rapid migration and inefficient gap formation. Compared to our previous model, we see a small increase in the number of terrestrial-type objects being formed, although their survival under tidal evolution is at best unclear. We also see evidence for disrupted fragments with evolved grain populations - this is circumstantial evidence for the formation of planetesimal belts, a phenomenon not seen in runs where fragment-fragment interactions are ignored. In spite of intense dynamical evolution, our population is dominated by massive giant planets and brown dwarfs at large semimajor axis, which direct imaging surveys should, but only rarely, detect. Finally, disc fragmentation is shown to be an efficient manufacturer of free-floating planetary mass objects, and the typical multiplicity of systems formed via gravitational instability will be low.

Comparing forest fragmentation and its drivers in China and the USA with Globcover v2.2

Science.gov (United States)

Chen, Mingshi; Mao, Lijun; Zhou, Chunguo; Vogelmann, James E.; Zhu, Zhiliang

2010-01-01

Forest loss and fragmentation are of major concern to the international community, in large part because they impact so many important environmental processes. The main objective of this study was to assess the differences in forest fragmentation patterns and drivers between China and the conterminous United States (USA). Using the latest 300-m resolution global land cover product, Globcover v2.2, a comparative analysis of forest fragmentation patterns and drivers was made. The fragmentation patterns were characterized by using a forest fragmentation model built on the sliding window analysis technique in association with landscape indices. Results showed that China’s forests were substantially more fragmented than those of the USA. This was evidenced by a large difference in the amount of interior forest area share, with China having 48% interior forest versus the 66% for the USA. China’s forest fragmentation was primarily attributed to anthropogenic disturbances, driven particularly by agricultural expansion from an increasing and large population, as well as poor forest management practices. In contrast, USA forests were principally fragmented by natural land cover types. However, USA urban sprawl contributed more to forest fragmentation than in China. This is closely tied to the USA’s economy, lifestyle and institutional processes. Fragmentation maps were generated from this study, which provide valuable insights and implications regarding habitat planning for rare and endangered species. Such maps enable development of strategic plans for sustainable forest management by identifying areas with high amounts of human-induced fragmentation, which improve risk assessments and enable better targeting for protection and remediation efforts. Because forest fragmentation is a long-term, complex process that is highly related to political, institutional, economic and philosophical arenas, both nations need to take effective and comprehensive measures to mitigate

Ring magnetron ionizer

International Nuclear Information System (INIS)

Alessi, J.G.

1986-01-01

A ring magnetron D - charge exchange ionizer has been built and tested. An H - current of 500 μA was extracted with an estimated H 0 density in the ionizer of 10 12 cm -3 . This exceeds the performance of ionizers presently in use on polarized H - sources. The ionizer will soon be tested with a polarized atomic beam

Universal elements of fragmentation

International Nuclear Information System (INIS)

Yanovsky, V. V.; Tur, A. V.; Kuklina, O. V.

2010-01-01

A fragmentation theory is proposed that explains the universal asymptotic behavior of the fragment-size distribution in the large-size range, based on simple physical principles. The basic principles of the theory are the total mass conservation in a fragmentation process and a balance condition for the energy expended in increasing the surface of fragments during their breakup. A flux-based approach is used that makes it possible to supplement the basic principles and develop a minimal theory of fragmentation. Such a supplementary principle is that of decreasing fragment-volume flux with increasing energy expended in fragmentation. It is shown that the behavior of the decreasing flux is directly related to the form of a power-law fragment-size distribution. The minimal theory is used to find universal asymptotic fragment-size distributions and to develop a natural physical classification of fragmentation models. A more general, nonlinear theory of strong fragmentation is also developed. It is demonstrated that solutions to a nonlinear kinetic equation consistent with both basic principles approach a universal asymptotic size distribution. Agreement between the predicted asymptotic fragment-size distributions and experimental observations is discussed.

Quasi free mechanism in single photon double ionization of helium

Energy Technology Data Exchange (ETDEWEB)

Schoeffler, Markus; Stuck, Christian [Frankfurt Univ., Frankfurt am Main (Germany). Inst. fuer Kernphysik; Lawrence Berkeley National Lab, Berkeley, CA (United States); Jahnke, Till; Waitz, Markus; Trinter, Florian; Lenz, Ute; Schmidt-Boecking, Horst; Doerner, Reinhard [Frankfurt Univ., Frankfurt am Main (Germany). Inst. fuer Kernphysik; Jones, Mathew; Landers, Allen [Auburn University, Auburn, AL (United States); Belkacem, Ali; Weber, Thorsten [Lawrence Berkeley National Lab, Berkeley, CA (United States); Cocke, Lew [Kansas State University, Manhattan, KS (United States)

2012-07-01

Double ionization of Helium by a single photon is widely believed to proceed through two mechanisms: knock-off (TS1) or shake-off, with the last one dominating at high photon energies. A new mechanism, termed ''Quasi Free Mechanism'' (QFM) was predicted 35 years ago by Amusia and coworkers, but escaped experimental observation till today. Here we provide the first proof of this mechanism using 800 eV photons from the Advanced Light Source. Fragments (electrons and ions) were measured in coincidence using momentum spectroscopy (COLTRIMS). He{sup (}2+) ions with zero momentum were found - the fingerprint for the QFM.

Electrospray ionization of uranyl-citrate complexes

Science.gov (United States)

Somogyi, Árpád; Pasilis, Sofie P.; Pemberton, Jeanne E.

2007-09-01

Results presented here demonstrate the usefulness of electrospray ionization and gas-phase ion-molecule reactions to predict structural and electronic differences in complex inorganic ions. Electrospray ionization of uranyl citrate solutions generates positively and negatively charged ions that participate in further ion-molecule reactions in 3D ion trap and FT-ICR mass analyzers. Most ions observed are derived from the major solution uranyl-citrate complexes and involve species of {(UO2)2Cit2}2-, (UO2)3Cit2, and {(UO2)3Cit3}3-, where Cit indicates the citrate trianion, C6H5O73-. In a 3D ion trap operated at relatively high pressure, complex adducts containing solvent molecules, alkali and ammonium cations, and nitrate or chloride anions are dominant, and proton/alkali cation (Na+, K+) exchange is observed for up to six exchangeable protons in an excess of alkali cations. Adduct formation in a FT-ICR cell that is operated at lower pressures is less dominant, and direct detection of positive and negative ions of the major solution complexes is possible. Multiply charged ions are also detected, suggesting the presence of uranium in different oxidation states. Changes in uranium oxidation state are detected by He-CID and SORI-CID fragmentation, and certain fragments undergo association reactions in trapping analyzers, forming "exotic" species such as [(UO2)4O3]-, [(UO2)4O4]-, and [(UO2)4O5]-. Ion-molecule reactions with D2O in the FT-ICR cell indicate substantial differences in H/D exchange rate and D2O accommodation for different ion structures and charge states. Most notably, the positively charged ions [H2(UO2)2Cit2(H)]+ and [(UO2)2(Cit)]+ accommodate two and three D2O molecules, respectively, which reflects well the structural differences, i.e., tighter uranyl-citrate coordination in the former ion than in the latter. The corresponding negatively charged ions accommodate zero or two D2O molecules, which can be rationalized using suggested solution phase structures

Pulsed radiobiology with laser-driven plasma accelerators

Science.gov (United States)

Giulietti, Antonio; Grazia Andreassi, Maria; Greco, Carlo

2011-05-01

Recently, a high efficiency regime of acceleration in laser plasmas has been discovered, allowing table top equipment to deliver doses of interest for radiotherapy with electron bunches of suitable kinetic energy. In view of an R&D program aimed to the realization of an innovative class of accelerators for medical uses, a radiobiological validation is needed. At the present time, the biological effects of electron bunches from the laser-driven electron accelerator are largely unknown. In radiobiology and radiotherapy, it is known that the early spatial distribution of energy deposition following ionizing radiation interactions with DNA molecule is crucial for the prediction of damages at cellular or tissue levels and during the clinical responses to this irradiation. The purpose of the present study is to evaluate the radio-biological effects obtained with electron bunches from a laser-driven electron accelerator compared with bunches coming from a IORT-dedicated medical Radio-frequency based linac's on human cells by the cytokinesis block micronucleus assay (CBMN). To this purpose a multidisciplinary team including radiotherapists, biologists, medical physicists, laser and plasma physicists is working at CNR Campus and University of Pisa. Dose on samples is delivered alternatively by the "laser-linac" operating at ILIL lab of Istituto Nazionale di Ottica and an RF-linac operating for IORT at Pisa S. Chiara Hospital. Experimental data are analyzed on the basis of suitable radiobiological models as well as with numerical simulation based on Monte Carlo codes. Possible collective effects are also considered in the case of ultrashort, ultradense bunches of ionizing radiation.

Characterization of foot- and mouth disease virus antigen by surface-enhanced laser desorption ionization-time of flight-mass spectrometry in aqueous and oil-emulsion formulations

NARCIS (Netherlands)

Harmsen, M.M.; Jansen, J.; Westra, D.F.; Coco-Martin, J.M.

2010-01-01

We have used a novel method, surface-enhanced laser desorption ionization-time of flight-mass spectrometry (SELDI-TOF-MS), to characterize foot-and-mouth disease virus (FMDV) vaccine antigens. Using specific capture with FMDV binding recombinant antibody fragments and tryptic digestion of FMDV

A Knowledge-Driven Geospatially Enabled Framework for Geological Big Data

Directory of Open Access Journals (Sweden)

Liang Wu

2017-06-01

Full Text Available Geologic survey procedures accumulate large volumes of structured and unstructured data. Fully exploiting the knowledge and information that are included in geological big data and improving the accessibility of large volumes of data are important endeavors. In this paper, which is based on the architecture of the geological survey information cloud-computing platform (GSICCP and big-data-related technologies, we split geologic unstructured data into fragments and extract multi-dimensional features via geological domain ontology. These fragments are reorganized into a NoSQL (Not Only SQL database, and then associations between the fragments are added. A specific class of geological questions was analyzed and transformed into workflow tasks according to the predefined rules and associations between fragments to identify spatial information and unstructured content. We establish a knowledge-driven geologic survey information smart-service platform (GSISSP based on previous work, and we detail a study case for our research. The study case shows that all the content that has known relationships or semantic associations can be mined with the assistance of multiple ontologies, thereby improving the accuracy and comprehensiveness of geological information discovery.

Use of a Minimally Invasive Retractor System for Retrieval of Intracranial Fragments in Wartime Trauma.

Science.gov (United States)

Rymarczuk, George N; Davidson, Laurence; Severson, Meryl A; Armonda, Rocco A

2015-10-01

Wartime penetrating brain injury can result in deep-seated parenchymal and intraventicular shrapnel, bullets, and bone. Large fragments pose a risk of secondary injury from migration, infection, and metal toxicity. It has been recommended that aggressive removal of fragments be avoided. The goal of this study is to report our technique of minimally invasive removal of select deep-seated fragments using a tubular retractor system. A retrospective review of our database of service members presenting with penetrating traumatic brain injuries incurred during Operations Iraqi Freedom and Enduring Freedom and treated at the Walter Reed Army Medical Center and the National Naval Medical Center was performed. Six individuals were identified in which the Vycor ViewSite retractor system (Vycor Medical, Boca Raton, Florida, USA) was used to remove a ventricular or deep intraparenchymal fragment. All patients were male and ranged in age from 21 to 29 years. Fragment location included the foramen of Monro; the atrium of the right lateral ventricle; parasagittally within the right occipital lobe; the occipital horn of the right lateral ventricle; the deep white matter of the dominant temporal lobe; and within the posterior right temporal lobe deep to the junction of the transverse and sigmoid dural venous sinuses. Fragments included in-driven bone, shrapnel from improvised explosive devices, and bullets. In all cases the fragment was successfully removed. No patient had worsening of their neurologic condition following surgery. Deep parenchymal and intraventricular fragments can be safely removed using a tubular retractor system. Published by Elsevier Inc.

UNRAVELLING THE COMPLEX STRUCTURE OF AGN-DRIVEN OUTFLOWS. II. PHOTOIONIZATION AND ENERGETICS

Energy Technology Data Exchange (ETDEWEB)

Karouzos, Marios; Woo, Jong-Hak [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Bae, Hyun-Jin, E-mail: woo@astro.snu.ac.kr [Department of Astronomy and Center for Galaxy EVolution Research, Yonsei University, Seoul 120-749 (Korea, Republic of)

2016-12-20

Outflows have been shown to be prevalent in galaxies hosting luminous active galactic nuclei (AGNs); they present a physically plausible way to couple the AGN energy output with the interstellar medium of their hosts. Despite their prevalence, accurate characterization of these outflows has been challenging. In the second of a series of papers, we use Gemini Multi-Object Spectrograph integral field unit (IFU) data of six local ( z  < 0.1) and moderate-luminosity Type 2 AGNs to study the ionization properties and energetics of AGN-driven outflows. We find strong evidence connecting the extreme kinematics of the ionized gas to the AGN photoionization. The kinematic component related to the AGN-driven outflow is clearly separated from other kinematic components, such as virial motions or rotation, on the velocity and velocity dispersion diagram. Our spatially resolved kinematic analysis reveals that 30 to 90% of the total mass and kinetic energy of the outflow is contained within the central kpc of the galaxy. The spatially integrated mass and kinetic energy of the gas entrained in the outflow correlate well with the AGN bolometric luminosity and results in energy conversion efficiencies between 0.01% and 1%. Intriguingly, we detect ubiquitous signs of ongoing circumnuclear star formation. Their small size, the centrally contained mass and energy, and the universally detected circumnuclear star formation cast doubts on the potency of these AGN-driven outflows as agents of galaxy-scale negative feedback.

Red Geyser: A New Class of Galaxy with Large-scale AGN-driven Winds

Science.gov (United States)

Roy, Namrata; Bundy, Kevin; Cheung, Edmond; MaNGA Team

2018-01-01

A new class of quiescent (non-star-forming) galaxies harboring possible AGN-driven winds have been discovered using the spatially resolved optical spectroscopy from the ongoing SDSS-IV MaNGA (Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory) survey. These galaxies named "red geysers" constitute 5%-10% of the local quiescent galaxy population and are characterized by narrow bisymmetric ionized gas emission patterns. These enhanced patterns are seen in equivalent width maps of Hα, [OIII] and other strong emission lines. They are co-aligned with the ionized gas velocity gradients but significantly misaligned with stellar velocity gradients. They also show very high gas velocity dispersions (~200 km/s). Considering these observations in light of models of the gravitational potential, Cheung et al. argued that red geysers host large-scale AGN-driven winds of ionized gas that may play a role in suppressing star formation at late times. In this work, we test the hypothesis that AGN activity is ultimately responsible for the red geyser phenomenon. We compare the nuclear radio activity of the red geysers to a matched control sample of galaxies of similar stellar mass, redshift, rest frame NUV–r color and axis ratio. and additionally, control for the presence of ionized gas. We have used 1.4 GHz radio continuum data from the VLA FIRST Survey to stack the radio flux from the red geyser sample and control sample. We find that the red geysers have a higher average radio flux than the control galaxies at > 3σ significance. Our sample is restricted to rest-frame NUV–r color > 5, thus ruling out possible radio emission due to star formation activity. We conclude that red geysers are associated with more active AGN, supporting a feedback picture in which episodic AGN activity drives large-scale but relatively weak ionized winds in many in many early-type galaxies.

Effect of molecular structure on fragmentation of isolated organic molecules in solid rare gas matrices

International Nuclear Information System (INIS)

Kobrazenko, A.V.; Sukhov, F.F.; Orlov, A.Yu.; Kovalev, G.V.; Baranova, I.A.; Feldman, V.I.

2011-01-01

Complete text of publication follows. Elucidation of high-energy reaction pathways in the condensed phase is an important issue for basic understanding of the radiation stability of complex organic molecules. As was shown previously, organic radical cations (RC) may undergo fragmentation or rearrangement in solid matrices due to excess energy. The probability of this process depends on both ionization potential (IP) of the molecule and molecular structure. In the present work we have studied the role of 'hot' ionic reaction channels for RC of some bifunctional compounds and alkynes. The effect of excess energy was simulated by matrix isolation method as described in detail earlier. The formation of fragmentation products was monitored by EPR and FTIR spectroscopy. In the present work it was shown that the RC of bifunctional compounds (CH 3 OCH 2 COCH 3 , CH 3 CO(CH 2 ) n COCH 3 , n 0/2) dissociated efficiently producing · CH 3 radicals upon irradiation in solid argon matrix at T ≤ 16 K. The probability of fragmentation decreases with decrease of excess energy by switching from Ar to Xe. It is worth noting that acetone RC does not show fragmentation under these conditions. Thus, bifunctional molecules were found to be less stable to 'hot' ionic fragmentation in low-temperature solids in comparison with simple prototype carbonyl compounds. In the case of alkynes of the R-C ≡ CH type, a noticeable yield of fragmentation products was observed when R = -C(CH 3 ) 3 , but it was negligible for R = -CH 3 . It means that the presence of triple bond stabilizes the molecular skeleton of linear alkynes toward 'hot' fragmentation, similarly as it was shown for alkenes. The mechanisms of 'hot' reactions and excess energy relaxation are discussed. This work was supported by the Russian Foundation for Basic Research (project 09-03-00848a).

Sequential nonadiabatic excitation of large molecules and ions driven by strong laser fields

International Nuclear Information System (INIS)

Markevitch, Alexei N.; Levis, Robert J.; Romanov, Dmitri A.; Smith, Stanley M.; Schlegel, H. Bernhard; Ivanov, Misha Yu.

2004-01-01

Electronic processes leading to dissociative ionization of polyatomic molecules in strong laser fields are investigated experimentally, theoretically, and numerically. Using time-of-flight ion mass spectroscopy, we study the dependence of fragmentation on laser intensity for a series of related molecules and report regular trends in this dependence on the size, symmetry, and electronic structure of a molecule. Based on these data, we develop a model of dissociative ionization of polyatomic molecules in intense laser fields. The model is built on three elements: (i) nonadiabatic population transfer from the ground electronic state to the excited-state manifold via a doorway (charge-transfer) transition; (ii) exponential enhancement of this transition by collective dynamic polarization of all electrons, and (iii) sequential energy deposition in both neutral molecules and resulting molecular ions. The sequential nonadiabatic excitation is accelerated by a counterintuitive increase of a large molecule's polarizability following its ionization. The generic theory of sequential nonadiabatic excitation forms a basis for quantitative description of various nonlinear processes in polyatomic molecules and ions in strong laser fields

Study on effect of ionizing radiation on costimulatory molecular receptor and its relationship with T cell apoptosis

International Nuclear Information System (INIS)

Zhou Jianhua; Su Liaoyuan; Tong Jian; Wang Chunlei; Wang Aiqing

2001-01-01

Effects of different dose γ-ray irradiation on T lymphocyte co-stimulative receptor and apoptosis were investigated to explore the mechanisms of ionizing radiation leading to lymphocyte apoptosis and relationship between CD28 and Fas in T lymphocytes. The effects of irradiation with 0.5, 2, 4 and 8 Gy γ-rays on CD28 and Fas (CD95) molecule expression of human T lymphocytes were measured by flow cytometry (FCM) with direct immunofluorescence technique. Before and after CD28 McAb and IL-18 dealing with T cells the T cells DNA fragmentation and apoptosis were determined by JAM test and FCM technique. With increasing radiation dosage, the CD28 molecule expression decreased and CD95 molecule expression increased in CD3 + T cells, which could affect signal transduction and increase cell DNA fragmentation and apoptosis. However, CD28 McAb and IL-18 could resist DNA fragmentation and the apoptosis

Controlled fragmentation

International Nuclear Information System (INIS)

Arnold, Werner

2002-01-01

Contrary to natural fragmentation, controlled fragmentation offers the possibility to adapt fragment parameters like size and mass to the performance requirements in a very flexible way. Known mechanisms like grooves inside the casing, weaken the structure. This is, however, excluded for applications with high accelerations during launch or piercing requirements for example on a semi armor piercing penetrator. Another method to achieve controlled fragmentation with an additional grid layer is presented with which the required grooves are produced 'just in time' inside the casing during detonation of the high explosive. The process of generating the grooves aided by the grid layer was studied using the hydrocode HULL with respect to varying grid designs and material combinations. Subsequent to this, a large range of these theoretically investigated combinations was contemplated in substantial experimental tests. With an optimised grid design and a suitable material selection, the controlled fragment admits a very flexible adaptation to the set requirements. Additional advantages like the increase of perforation performance or incendiary amplification can be realized with the grid layer

The Statistical Fragmentation Theory of N. F. Mott

Science.gov (United States)

Grady, Dennis

2004-07-01

For a brief period during the height of World War II, Neville F. Mott left his position at the University of Bristol and headed up a concerted theoretical effort at Fort Halstead, UK, to investigate the operational science of weapons and armor technology. The seminal achievements resulting from the efforts of the participating scientists are extraordinary and have provided the basis for much of the continuing research in this field over the intervening six decades. N. F. Mott chose to study the phenomenon of the explosive-driven fragmentation of exploding shell cases. The approaches pursued by Mott are documented in several interim reports and open literature publications and offer a fascinating look into the insightful thinking and scientific methods of one of the preeminent physicists of the last century. This presentation offers a perspective into the several theoretical approaches pursued by Mott. In particular, the hallmark relation for the representation of exploding munitions fragmentation data to the present day is the Mott distribution. The efforts of Mott leading to this distribution are explored and a judgment is offered as to whether Mott himself would use this distribution today.

Ionic fragmentation following core-level photoionization of Sn(CH3)4 by soft X-rays

International Nuclear Information System (INIS)

Ueda, Kiyoshi; Shigemasa, Eiji; Sato, Yukinori; Yagishita, Akira; Hayaishi, Tatsuji

1990-01-01

Ionic fragmentation following the photoionization of Sn(CH 3 ) 4 (TMT) has been studied in the photon energy range of 60-600 eV using synchrotron radiation and time-of-flight mass spectrometry. Each of the Sn:4d, 4p, 3d and C:1s photoionization leads to a type of ionic fragmentation that is characteristic of each ionized core. The Sn:4d photoionization above 60 eV predominantly produces the doubly-charged TMT which dissociates into two singly-charged ions and some neutral fragments. The ions produced in this pathway are CH 3 + , C 2 H 3 + , C 2 H 5 + , SnCH m + and/or Sn + . The Sn:4p photoionization produces the triply-charged TMT and enhances the production of H + , CHsub(m' + ) (m' = 0-3) and Sn + significantly. The Sn:3d photoionization produces multiply-charged TMT whose charges are 3-5 and enhances the production of H + , CHsub(m' + ) (m' = 0-2) and Sn + significantly. The C:1s photoionization produces doubly-charged TMT via the KVV Auger transition and enhances the production of CH 3 + , C 2 H 3 + , SnCH m + and/or Sn + . (orig.)

Fragmentation cross sections outside the limiting-fragmentation regime

CERN Document Server

Sümmerer, K

2003-01-01

The empirical parametrization of fragmentation cross sections, EPAX, has been successfully applied to estimate fragment production cross sections in reactions of heavy ions at high incident energies. It is checked whether a similar parametrization can be found for proton-induced spallation around 1 GeV, the range of interest for ISOL-type RIB facilities. The validity of EPAX for medium-energy heavy-ion induced reactions is also checked. Only a few datasets are available, but in general EPAX predicts the cross sections rather well, except for fragments close to the projectile, where the experimental cross sections are found to be larger.

Occurrence of C-Terminal Residue Exclusion in Peptide Fragmentation by ESI and MALDI Tandem Mass Spectrometry

Science.gov (United States)

Dupré, Mathieu; Cantel, Sonia; Martinez, Jean; Enjalbal, Christine

2012-02-01

By screening a data set of 392 synthetic peptides MS/MS spectra, we found that a known C-terminal rearrangement was unexpectedly frequently occurring from monoprotonated molecular ions in both ESI and MALDI tandem mass spectrometry upon low and high energy collision activated dissociations with QqTOF and TOF/TOF mass analyzer configuration, respectively. Any residue localized at the C-terminal carboxylic acid end, even a basic one, was lost, provided that a basic amino acid such arginine and to a lesser extent histidine and lysine was present in the sequence leading to a fragment ion, usually depicted as (bn-1 + H2O) ion, corresponding to a shortened non-scrambled peptide chain. Far from being an epiphenomenon, such a residue exclusion from the peptide chain C-terminal extremity gave a fragment ion that was the base peak of the MS/MS spectrum in certain cases. Within the frame of the mobile proton model, the ionizing proton being sequestered onto the basic amino acid side chain, it is known that the charge directed fragmentation mechanism involved the C-terminal carboxylic acid function forming an anhydride intermediate structure. The same mechanism was also demonstrated from cationized peptides. To confirm such assessment, we have prepared some of the peptides that displayed such C-terminal residue exclusion as a C-terminal backbone amide. As expected in this peptide amide series, the production of truncated chains was completely suppressed. Besides, multiply charged molecular ions of all peptides recorded in ESI mass spectrometry did not undergo such fragmentation validating that any mobile ionizing proton will prevent such a competitive C-terminal backbone rearrangement. Among all well-known nondirect sequence fragment ions issued from non specific loss of neutral molecules (mainly H2O and NH3) and multiple backbone amide ruptures (b-type internal ions), the described C-terminal residue exclusion is highly identifiable giving raise to a single fragment ion in

Universality of fragment shapes.

Science.gov (United States)

Domokos, Gábor; Kun, Ferenc; Sipos, András Árpád; Szabó, Tímea

2015-03-16

The shape of fragments generated by the breakup of solids is central to a wide variety of problems ranging from the geomorphic evolution of boulders to the accumulation of space debris orbiting Earth. Although the statistics of the mass of fragments has been found to show a universal scaling behavior, the comprehensive characterization of fragment shapes still remained a fundamental challenge. We performed a thorough experimental study of the problem fragmenting various types of materials by slowly proceeding weathering and by rapid breakup due to explosion and hammering. We demonstrate that the shape of fragments obeys an astonishing universality having the same generic evolution with the fragment size irrespective of materials details and loading conditions. There exists a cutoff size below which fragments have an isotropic shape, however, as the size increases an exponential convergence is obtained to a unique elongated form. We show that a discrete stochastic model of fragmentation reproduces both the size and shape of fragments tuning only a single parameter which strengthens the general validity of the scaling laws. The dependence of the probability of the crack plan orientation on the linear extension of fragments proved to be essential for the shape selection mechanism.

TURBULENT DISKS ARE NEVER STABLE: FRAGMENTATION AND TURBULENCE-PROMOTED PLANET FORMATION

Energy Technology Data Exchange (ETDEWEB)

Hopkins, Philip F. [TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125 (United States); Christiansen, Jessie L., E-mail: phopkins@caltech.edu [SETI Institute/NASA Ames Research Center, M/S 244-30, Moffett Field, CA 94035 (United States)

2013-10-10

A fundamental assumption in our understanding of disks is that when the Toomre Q >> 1, the disk is stable against fragmentation into self-gravitating objects (and so cannot form planets via direct collapse). But if disks are turbulent, this neglects a spectrum of stochastic density fluctuations that can produce rare, high-density mass concentrations. Here, we use a recently developed analytic framework to predict the statistics of these fluctuations, i.e., the rate of fragmentation and mass spectrum of fragments formed in a turbulent Keplerian disk. Turbulent disks are never completely stable: we calculate the (always finite) probability of forming self-gravitating structures via stochastic turbulent density fluctuations in such disks. Modest sub-sonic turbulence above Mach number M∼0.1 can produce a few stochastic fragmentation or 'direct collapse' events over ∼Myr timescales, even if Q >> 1 and cooling is slow (t{sub cool} >> t{sub orbit}). In transsonic turbulence this extends to Q ∼ 100. We derive the true Q-criterion needed to suppress such events, which scales exponentially with Mach number. We specify to turbulence driven by magneto-rotational instability, convection, or spiral waves and derive equivalent criteria in terms of Q and the cooling time. Cooling times ∼> 50 t{sub dyn} may be required to completely suppress fragmentation. These gravo-turbulent events produce mass spectra peaked near ∼(Q M{sub disk}/M{sub *}){sup 2} M{sub disk} (rocky-to-giant planet masses, increasing with distance from the star). We apply this to protoplanetary disk models and show that even minimum-mass solar nebulae could experience stochastic collapse events, provided a source of turbulence.

TURBULENT DISKS ARE NEVER STABLE: FRAGMENTATION AND TURBULENCE-PROMOTED PLANET FORMATION

International Nuclear Information System (INIS)

Hopkins, Philip F.; Christiansen, Jessie L.

2013-01-01

A fundamental assumption in our understanding of disks is that when the Toomre Q >> 1, the disk is stable against fragmentation into self-gravitating objects (and so cannot form planets via direct collapse). But if disks are turbulent, this neglects a spectrum of stochastic density fluctuations that can produce rare, high-density mass concentrations. Here, we use a recently developed analytic framework to predict the statistics of these fluctuations, i.e., the rate of fragmentation and mass spectrum of fragments formed in a turbulent Keplerian disk. Turbulent disks are never completely stable: we calculate the (always finite) probability of forming self-gravitating structures via stochastic turbulent density fluctuations in such disks. Modest sub-sonic turbulence above Mach number M∼0.1 can produce a few stochastic fragmentation or 'direct collapse' events over ∼Myr timescales, even if Q >> 1 and cooling is slow (t cool >> t orbit ). In transsonic turbulence this extends to Q ∼ 100. We derive the true Q-criterion needed to suppress such events, which scales exponentially with Mach number. We specify to turbulence driven by magneto-rotational instability, convection, or spiral waves and derive equivalent criteria in terms of Q and the cooling time. Cooling times ∼> 50 t dyn may be required to completely suppress fragmentation. These gravo-turbulent events produce mass spectra peaked near ∼(Q M disk /M * ) 2 M disk (rocky-to-giant planet masses, increasing with distance from the star). We apply this to protoplanetary disk models and show that even minimum-mass solar nebulae could experience stochastic collapse events, provided a source of turbulence

An efficient, selective collisional ejection mechanism for inner-shell population inversion in laser-driven plasmas

Energy Technology Data Exchange (ETDEWEB)

SCHROEDER,W. ANDREAS; NELSON,THOMAS R.; BORISOV,A.B.; LONGWORTH,J.W.; BOYER,K.; RHODES,C.K.

2000-06-07

A theoretical analysis of laser-driven collisional ejection of inner-shell electrons is presented to explain the previously observed anomalous kilovolt L-shell x-ray emission spectra from atomic Xe cluster targets excited by intense sub-picosecond 248nrn ultraviolet radiation. For incident ponderomotively-driven electrons photoionized by strong above threshold ionization, the collisional ejection mechanism is shown to be highly l-state and significantly n-state (i.e. radially) selective for time periods shorter than the collisional dephasing time of the photoionized electronic wavefunction. The resulting preference for the collisional ejection of 2p electrons by an ionized 4p state produces the measured anomalous Xe(L) emission which contains direct evidence for (i) the generation of Xe{sup 27+}(2p{sup 5}3d{sup 10}) and Xe{sup 28+}(2p{sup 5}3d{sup 9}) ions exhibiting inner-shell population inversion and (ii) a coherent correlated electron state collision responsible for the production of double 2p vacancies. For longer time periods, the selectivity of this coherent impact ionization mechanism is rapidly reduced by the combined effects of intrinsic quantum mechanical spreading and dephasing--in agreement with the experimentally observed and extremely strong {minus}{lambda}{sup {minus}6} pump-laser wavelength dependence of the efficiency of inner-shell (2p) vacancy production in Xe clusters excited in underdense plasmas.

Remote control of the dissociative ionization of H2 based on electron-H2 + entanglement

Science.gov (United States)

Wang, Jun-Ping; He, Feng

2018-04-01

The single ionization of H2 in strong laser fields creates the correlated electron-H2 + pair. Based on such a correlation, we conceive a strategy to control the energy spectra of the freed electron or dissociative fragments by simulating the time-dependent Schrödinger equation. Two attosecond pulses in a train produce the replica of electron-H2 + pairs, which are to be steered by a time-delayed phase-stabilized (mid)infrared laser pulse. By controlling the behavior of the freed electron, the dissociation of H2 + can be controlled even though there is no direct laser-H2 + coupling. On the other hand, the photoelectron energy spectra can be manipulated via laser-H2 + coupling. This study demonstrates the entanglement of molecular quantum wave packets, and affords a route to remotely control molecular dissociative ionization.

Anomalous nuclear fragments

International Nuclear Information System (INIS)

Karmanov, V.A.

1983-01-01

Experimental data are given, the status of anomalon problem is discussed, theoretical approaches to this problem are outlined. Anomalons are exotic objects formed following fragmentation of nuclei-targets under the effect of nuclei - a beam at the energy of several GeV/nucleon. These nuclear fragments have an anomalously large cross section of interaction and respectively, small free path, considerably shorter than primary nuclei have. The experimental daa are obtained in accelerators following irradiation of nuclear emulsions by 16 O, 56 Fe, 40 Ar beams, as well as propane by 12 C beams. The experimental data testify to dependence of fragment free path on the distance L from the point of the fragment formation. A decrease in the fragment free path is established more reliably than its dependence on L. The problem of the anomalon existence cannot be yet considered resolved. Theoretical models suggested for explanation of anomalously large cross sections of nuclear fragment interaction are variable and rather speculative

A time-dependent B-spline R-matrix approach to double ionization of atoms by XUV laser pulses

Energy Technology Data Exchange (ETDEWEB)

Guan Xiaoxu; Zatsarinny, O; Noble, C J; Bartschat, K [Department of Physics and Astronomy, Drake University, Des Moines, IA 50311 (United States); Schneider, B I [Physics Division, National Science Foundation, Arlington, Virgina 22230 (United States)], E-mail: xiaoxu.guan@drake.edu, E-mail: oleg.zatsarinny@drake.edu, E-mail: cjn@maxnet.co.nz, E-mail: klaus.bartschat@drake.edu, E-mail: bschneid@nsf.gov

2009-07-14

We present an ab initio and non-perturbative time-dependent approach to the problem of double ionization of a general atom driven by intense XUV laser pulses. After using a highly flexible B-spline R-matrix method to generate field-free Hamiltonian and electric dipole matrices, the initial state is propagated in time using an efficient Arnoldi-Lanczos scheme. Test calculations for double ionization of He by a single laser pulse yield good agreement with benchmark results obtained with other methods. The method is then applied to two-colour pump-probe processes, for which momentum and energy distributions of the two outgoing electrons are presented.

Analysis of Nitro-aromatic and Nitramine Explosives by Atmospheric Pressure Chemical Ionization / High Performance Liquid Chromatography / Mass Spectrometry / Mass Spectrometry

International Nuclear Information System (INIS)

Hicks, B.J.; Han, W.; Robben, J.R.

2009-01-01

This procedure is capable of separating and quantifying twenty-nine high explosives and internal surrogates with a single injection. After the initial preparation step, the sample is introduced to the high performance liquid chromatograph for target separation, ionized by atmospheric pressure chemical ionization and the explosives of interest are isolated / quantified by mass spectrometry / mass spectrometry. Concentrations of the target explosives are measured relative to the response of both internal and external standard concentrations. A C-18 reverse phase high performance liquid chromatograph column is used for separation. Ionization is performed using both positive and negative atmospheric pressure chemical ionization resulting in a molecular ion with little fragmentation. These ions are isolated at the first quadrupole of the mass spectrometer, dissociated by collision with argon in the collision cell and the resulting daughter ions are isolated at the second quadrupole. These daughter ions then reach the detector where they are quantified. To date this procedure represents the most thorough high performance liquid chromatography / mass spectrometry / mass spectrometry explosives analysis available in the environmental chemistry market. (authors)

Ionization

International Nuclear Information System (INIS)

2002-01-01

This document reprints the text of the French by-law from January 8, 2002 relative to the approval and to the controls and verifications of facilities devoted to the ionizing of food products for human beings and animals. The by-law imposes the operators of such facilities to perform measurements and dosimetric verifications all along the ionization process. (J.S.)

Dwarf galaxies with ionizing radiation feedback. II. Spatially resolved star formation relation

International Nuclear Information System (INIS)

Kim, Ji-hoon; Krumholz, Mark R.; Goldbaum, Nathan J.; Wise, John H.; Turk, Matthew J.; Abel, Tom

2013-01-01

We investigate the spatially resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate (SFR). Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially resolved observations of star formation tracers, such as Hα emission. We can also observe how stellar feedback manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3 × 10 11 M ☉ , we find that the correlation between SFR density (estimated from mock Hα emission) and H 2 density shows large scatter, especially at high resolutions of ≲75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution and because Hα traces hot gas around star-forming regions and is displaced from the H 2 peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces and molecular clouds being dispersed via stellar feedback.

Dwarf galaxies with ionizing radiation feedback. II. Spatially resolved star formation relation

Energy Technology Data Exchange (ETDEWEB)

Kim, Ji-hoon; Krumholz, Mark R.; Wise, John H.; Turk, Matthew J.; Goldbaum, Nathan J.; Abel, Tom

2013-11-15

AWe investigate the spatially resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate (SFR). Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially resolved observations of star formation tracers, such as Hα emission. We can also observe how stellar feedback manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3 × 10¹¹ M _⊙, we find that the correlation between SFR density (estimated from mock Hα emission) and H₂ density shows large scatter, especially at high resolutions of ≲ 75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution and because Hα traces hot gas around star-forming regions and is displaced from the H₂ peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces and molecular clouds being dispersed via stellar feedback.

Ionizing radiation

International Nuclear Information System (INIS)

Kruger, J.

1989-01-01

Ionizing radiation results in biological damage that differs from other hazardous substances and is highly dangerous to man. Ionizing radiation cannot be perceived by man's sense organs and the biological damage cannot be detected immediately afterwards (except in very high doses). Every human being is exposed to low doses of radiation. The structure of the atom; sources of ionizing radiation; radiation units; biological effects; norms for radiation protection; and the national control in South Africa are discussed. 1 fig., 5 refs

A Saccharomyces cerevisiae mitochondrial DNA fragment activates Reg1p-dependent glucose-repressible transcription in the nucleus.

Science.gov (United States)

Santangelo, G M; Tornow, J

1997-12-01

As part of an effort to identify random carbon-source-regulated promoters in the Saccharomyces cerevisiae genome, we discovered that a mitochondrial DNA fragment is capable of directing glucose-repressible expression of a reporter gene. This fragment (CR24) originated from the mitochondrial genome adjacent to a transcription initiation site. Mutational analyses identified a GC cluster within the fragment that is required for transcriptional induction. Repression of nuclear CR24-driven transcription required Reg1p, indicating that this mitochondrially derived promoter is a member of a large group of glucose-repressible nuclear promoters that are similarly regulated by Reg1p. In vivo and in vitro binding assays indicated the presence of factors, located within the nucleus and the mitochondria, that bind to the GC cluster. One or more of these factors may provide a regulatory link between the nucleus and mitochondria.

Role of ionization fronts in the colliding wind model of planetary nebulae

International Nuclear Information System (INIS)

Giuliani, J.L. Jr.

1981-01-01

A similarity transformation is used to study the expansion of a planetary nebula which is driven by a fast stellar wind as well as an expanding H II region. The undisturbed gas is taken to be the remnant of a slow, red giant wind. The present analysis improves upon Kwok, Purton, and FitzGerald's colliding wind model for the formation of planetary nebulae since it includes the dynamical influence of ionization fronts, and calculates the variation of velocity and density within the flow

Theory of the corrugation instability of a piston-driven shock wave.

Science.gov (United States)

Bates, J W

2015-01-01

We analyze the two-dimensional stability of a shock wave driven by a steadily moving corrugated piston in an inviscid fluid with an arbitrary equation of state. For h≤-1 or h>h(c), where h is the D'yakov parameter and h(c) is the Kontorovich limit, we find that small perturbations on the shock front are unstable and grow--at first quadratically and later linearly--with time. Such instabilities are associated with nonequilibrium fluid states and imply a nonunique solution to the hydrodynamic equations. The above criteria are consistent with instability limits observed in shock-tube experiments involving ionizing and dissociating gases and may have important implications for driven shocks in laser-fusion, astrophysical, and/or detonation studies.

The unexpected decarbonylation of ionized 2,3-pentanedione and related diketones

Science.gov (United States)

Wang, Xian; Holmes, John L.

2006-03-01

The fragmentation of the 2,3-pentanedione radical cation gives rise to an unexpected composite metastable ion peak, m/z 72, resulting from the isobaric losses of CO and C2H4. These two fragmentation channels are energetically competitive (i.e., the transition states have similar energies). The two processes yield [CH3C(O)CH2CH3]+ and [CH3C(OH)CO]+, respectively. The latter new ion, which is produced by a McLafferty rearrangement, has [Delta]fH° = 604 kJ/mol, obtained from G3 calculations. The four competing processes for metastable [CH3COCOCH2CH3]+, the (intense) losses of CH3CO, CH3CH2CO and the weak losses of C2H4 and CO and their transition states were placed on a potential energy surface computed at the G3 level of theory. The homologous ionized diketone 2,3-butanedione also displays the decarbonylation channel and 3,4-hexanedione loses CO and C2H4.

Electron ionization and the Compton effect in double ionization of helium

International Nuclear Information System (INIS)

Samson, J.

1994-01-01

The author discusses ionization phenomena in helium, both photoionization and electron ionization. In particular he compares double ionization cross sections with total cross sections, as a function of electron energy, and photon energy. Data is discussed over the energy range up to 10 keV

On the fragmentation of filaments in a molecular cloud simulation

Science.gov (United States)

Chira, R.-A.; Kainulainen, J.; Ibáñez-Mejía, J. C.; Henning, Th.; Mac Low, M.-M.

2018-03-01

Context. The fragmentation of filaments in molecular clouds has attracted a lot of attention recently as there seems to be a close relation between the evolution of filaments and star formation. The study of the fragmentation process has been motivated by simple analytical models. However, only a few comprehensive studies have analysed the evolution of filaments using numerical simulations where the filaments form self-consistently as part of large-scale molecular cloud evolution. Aim. We address the early evolution of parsec-scale filaments that form within individual clouds. In particular, we focus on three questions: How do the line masses of filaments evolve? How and when do the filaments fragment? How does the fragmentation relate to the line masses of the filaments? Methods: We examine three simulated molecular clouds formed in kiloparsec-scale numerical simulations performed with the FLASH adaptive mesh refinement magnetohydrodynamic code. The simulations model a self-gravitating, magnetised, stratified, supernova-driven interstellar medium, including photoelectric heating and radiative cooling. We follow the evolution of the clouds for 6 Myr from the time self-gravity starts to act. We identify filaments using the DisPerSe algorithm, and compare the results to other filament-finding algorithms. We determine the properties of the identified filaments and compare them with the predictions of analytic filament stability models. Results: The average line masses of the identified filaments, as well as the fraction of mass in filamentary structures, increases fairly continuously after the onset of self-gravity. The filaments show fragmentation starting relatively early: the first fragments appear when the line masses lie well below the critical line mass of Ostriker's isolated hydrostatic equilibrium solution ( 16 M⊙ pc-1), commonly used as a fragmentation criterion. The average line masses of filaments identified in three-dimensional volume density cubes

Synthesis of refractory organic matter in the ionized gas phase of the solar nebula.

Science.gov (United States)

Kuga, Maïa; Marty, Bernard; Marrocchi, Yves; Tissandier, Laurent

2015-06-09

In the nascent solar system, primitive organic matter was a major contributor of volatile elements to planetary bodies, and could have played a key role in the development of the biosphere. However, the origin of primitive organics is poorly understood. Most scenarios advocate cold synthesis in the interstellar medium or in the outer solar system. Here, we report the synthesis of solid organics under ionizing conditions in a plasma setup from gas mixtures (H2(O)-CO-N2-noble gases) reminiscent of the protosolar nebula composition. Ionization of the gas phase was achieved at temperatures up to 1,000 K. Synthesized solid compounds share chemical and structural features with chondritic organics, and noble gases trapped during the experiments reproduce the elemental and isotopic fractionations observed in primitive organics. These results strongly suggest that both the formation of chondritic refractory organics and the trapping of noble gases took place simultaneously in the ionized areas of the protoplanetary disk, via photon- and/or electron-driven reactions and processing. Thus, synthesis of primitive organics might not have required a cold environment and could have occurred anywhere the disk is ionized, including in its warm regions. This scenario also supports N2 photodissociation as the cause of the large nitrogen isotopic range in the solar system.

The dynamics of target ionization by fast higly charged projectiles

International Nuclear Information System (INIS)

Moshammer, R.; Ullrich, J.; Unverzagt, M.; Olsen, R.E.; Doerner, R.; Mergel, V.; Schmidt-Boecking, H.

1995-12-01

We report on the first kinematically complete investigation of single target ionization by fast heavy ions, on the measurement of all low energy electrons down to zero emission velocities and on the determination of the projectile energy loss on the level of ΔE p /E p ∼10 -7 . This has been achieved by combining a high-resolution recoil-ion momentum spectrometer with a novel 4π electron analyzer. The complete momentum balance between electron, recoil-ion and projectile for single ionization of helium by 3.6 MeV/u Ni 24+ was explored. Low energy electrons are found to be ejected mainly into the forward direction with a most likely longitudinal energy of only 2 eV. The electron momentum is not balanced, as might be expected, by the projectile momentum but is nearly completely compensated by the recoil ion. Surprisingly, the momenta of the helium-atom ''fragments'', the electron and the He 1+ recoil ion, are considerably larger than the total momentum loss of the projectile: the target atom seems to dissociate in the strong, longranging projectile potential. The collision has to be considered as a real three body interaction. (orig.)

Atmospheric pressure chemical ionization Fourier transform ion cyclotron resonance mass spectrometry for complex thiophenic mixture analysis

KAUST Repository

Hourani, Nadim

2013-10-01

Rationale Polycyclic aromatic sulfur heterocycles (PASHs) are detrimental species for refining processes in petroleum industry. Current mass spectrometric Methods that determine their composition are often preceded by derivatization and dopant addition approaches. Different ionization Methods have different impact on the molecular assignment of complex PASHs. The analysis of such species under atmospheric pressure chemical ionization (APCI) is still considered limited due to uncontrolled ion generation with low- and high-mass PASHs. Methods The ionization behavior of a model mixture of five selected PASH standards was investigated using an APCI source with nitrogen as the reagent gas. A complex thiophenic fraction was separated from a vacuum gas oil (VGO) and injected using the same method. The samples were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). RESULTS PASH model analytes were successfully ionized and mainly [M + H]+ ions were produced. The same ionization pattern was observed for the real thiophenic sample. It was found that S1 class species were the major sulfur-containing species found in the VGO sample. These species indicated the presence of alkylated benzothiophenic (BT), dibenzothiophenic (DBT) and benzonaphthothiophenic (BNT) series that were detected by APCI-FTICR MS. CONCLUSIONS This study provides an established APCI-FTICR MS method for the analysis of complex PASHs. PASHs were detected without using any derivatization and without fragmentation. The method can be used for the analysis of S-containing crude oil samples. © 2013 John Wiley & Sons, Ltd.

Seeded inert gas driven disk generator

International Nuclear Information System (INIS)

Joshi, N.K.; Venkatramani, N.; Rohatgi, V.K.

1987-01-01

This report outlines the present status of work being carried out in closed cycle MHD and disk generators. It gives the basic principles and discusses a proposal for setting up an experimental facility to study nonequilibrium plasmas using an inert gas driven disk generator. Disk geometry is a near ideal geometry for plasma studies since it has single or few pair electrodes combined with near perfect insulating walls. The proposed outlay of facility with components and subsystem is given. The facility may also be used to study the concept of fully ionized seed and to develop advanced diagnostic techniques. The absic equation describing the working parameters of such a system is also given in the Appendix. (author). 57 refs

Nuclear fragmentation

International Nuclear Information System (INIS)

Chung, K.C.

1989-01-01

An introduction to nuclear fragmentation, with emphasis in percolation ideas, is presented. The main theoretical models are discussed and as an application, the uniform expansion approximation is presented and the statistical multifragmentation model is used to calculate the fragment energy spectra. (L.C.)

The competition of charge remote and charge directed fragmentation mechanisms in quaternary ammonium salt derivatized peptides--an isotopic exchange study.

Science.gov (United States)

Cydzik, Marzena; Rudowska, Magdalena; Stefanowicz, Piotr; Szewczuk, Zbigniew

2011-12-01

Derivatization of peptides as quaternary ammonium salts (QAS) is a promising method for sensitive detection by electrospray ionization tandem mass spectrometry (Cydzik et al. J. Pept. Sci. 2011, 17, 445-453). The peptides derivatized by QAS at their N-termini undergo fragmentation according to the two competing mechanisms - charge remote (ChR) and charge directed (ChD). The absence of mobile proton in the quaternary salt ion results in ChR dissociation of a peptide bond. However, Hofmann elimination of quaternary salt creates an ion with one mobile proton leading to the ChD fragmentation. The experiments on the quaternary ammonium salts with deuterated N-alkyl groups or amide NH bonds revealed that QAS derivatized peptides dissociate according to the mixed ChR-ChD mechanism. The isotopic labeling allows differentiation of fragments formed according to ChR and ChD mechanisms. © The Author(s) 2011. This article is published with open access at Springerlink.com

Ionization detector

International Nuclear Information System (INIS)

Solomon, E.E.

1980-01-01

A safe and reliable apparatus for detecting products of combustion and aerosols in the atmosphere was developed which uses a beta source. It is easy to adjust for optimum performance. The ionization detector comprises a double chamber; one of the chambers is the basic sensing chamber. The sensing chamber is ported to both the secondary chambers to account for slow ambient changes in the atmosphere outside of the chamber. The voltages from the ionization chamber are adjusted with electrodes in each chamber. The ionization chamber contains baffles to direct the air to be sensed as well as an electrostatic screen. A unique electronic circuit provides an inexpensive and reliable means for detecting the signal change which occurs in the ionization chamber. The decision level of the alarm circuit can be adjusted to allow for any desired sensitivity. (D.N.)

Photo-fragmentation of lithium atoms studied with MOTReMi

Energy Technology Data Exchange (ETDEWEB)

Zhu, Ganjun

2010-02-15

Within this thesis, an experimental study of the photo double ionization (PDI) and the simultaneous ionization-excitation is performed for lithium in different initial states Li(1s{sup 2}2l) (l=s,p). The excess energy of the linearly polarized VUV-light is between 4 and 12 eV above the PDI-threshold. Three forefront technologies are combined: a magneto-optical trap (MOT) for lithium generating an ultra-cold and, by means of optical pumping, a state-prepared target; a reaction microscope (ReMi), enabling the momentum resolved detection of all reaction fragments with high-resolution and the free-electron laser in Hamburg (FLASH), providing an unprecedented brilliant photon beam at favourable time structure to access small cross sections. Close to threshold the total as well as differential PDI cross sections are observed to critically depend on the excitation level and the symmetry of the initial state. For the excited state Li (1s{sup 2}2p) the PDI dynamics strongly depends on the alignment of the 2p-orbital with respect to the VUV-light polarization and, thus, from the population of the magnetic substates (m{sub p}=0,{+-} 1). This alignment sensitivity decreases for increasing excess energy and is completely absent for ionization-excitation. Time-dependent close-coupling calculations are able to reproduce the experimental total cross sections with deviations of at most 30%. All the experimental observations can be consistently understood in terms of the long range electron correlation among the continuum electrons which gives rise to their preferential back-to-back emission. This alignment effect, which is observed here for the first time, allows controlling the PDI dynamics through a purely geometrical modification of the target initial state without changing its internal energy. (orig.)

Photo-fragmentation of lithium atoms studied with MOTReMi

International Nuclear Information System (INIS)

Zhu, Ganjun

2010-02-01

Within this thesis, an experimental study of the photo double ionization (PDI) and the simultaneous ionization-excitation is performed for lithium in different initial states Li(1s 2 2l) (l=s,p). The excess energy of the linearly polarized VUV-light is between 4 and 12 eV above the PDI-threshold. Three forefront technologies are combined: a magneto-optical trap (MOT) for lithium generating an ultra-cold and, by means of optical pumping, a state-prepared target; a reaction microscope (ReMi), enabling the momentum resolved detection of all reaction fragments with high-resolution and the free-electron laser in Hamburg (FLASH), providing an unprecedented brilliant photon beam at favourable time structure to access small cross sections. Close to threshold the total as well as differential PDI cross sections are observed to critically depend on the excitation level and the symmetry of the initial state. For the excited state Li (1s 2 2p) the PDI dynamics strongly depends on the alignment of the 2p-orbital with respect to the VUV-light polarization and, thus, from the population of the magnetic substates (m p =0,± 1). This alignment sensitivity decreases for increasing excess energy and is completely absent for ionization-excitation. Time-dependent close-coupling calculations are able to reproduce the experimental total cross sections with deviations of at most 30%. All the experimental observations can be consistently understood in terms of the long range electron correlation among the continuum electrons which gives rise to their preferential back-to-back emission. This alignment effect, which is observed here for the first time, allows controlling the PDI dynamics through a purely geometrical modification of the target initial state without changing its internal energy. (orig.)

Laser interferometry of radiation driven gas jets

Science.gov (United States)

Swanson, Kyle James; Ivanov, Vladimir; Mancini, Roberto; Mayes, Daniel C.

2017-06-01

In a series of experiments performed at the 1MA Zebra pulsed power accelerator of the Nevada Terawatt Facility nitrogen gas jets were driven with the broadband x-ray flux produced during the collapse of a wire-array z-pinch implosion. The wire arrays were comprised of 4 and 8, 10μm-thick gold wires and 17μm-thick nickel wires, 2cm and 3cm tall, and 0.3cm in diameter. They radiated 12kJ to 16kJ of x-ray energy, most of it in soft x-ray photons of less than 1keV of energy, in a time interval of 30ns. This x-ray flux was used to drive a nitrogen gas jet located at 0.8cm from the axis of the z-pinch radiation source and produced with a supersonic nozzle. The x-ray flux ionizes the nitrogen gas thus turning it into a photoionized plasma. We used laser interferometry to probe the ionization of the plasma. To this end, a Mach-Zehnder interferometer at the wavelength of 266 nm was set up to extract the atom number density profile of the gas jet just before the Zebra shot, and air-wedge interferometers at 266 and 532 nm were used to determine the electron number density of the plasma right during the Zebra shot. The ratio of electron to atom number densities gives the distribution of average ionization state of the plasma. A python code was developed to perform the image data processing, extract phase shift spatial maps, and obtain the atom and electron number densities via Abel inversion. Preliminary results from the experiment are promising and do show that a plasma has been created in the gas jet driven by the x-ray flux, thus demonstrating the feasibility of a new experimental platform to study photoionized plasmas in the laboratory. These plasmas are found in astrophysical scenarios including x-ray binaries, active galactic nuclei, and the accretion disks surrounding black holes1. This work was sponsored in part by DOE Office of Science Grant DE-SC0014451.1R. C. Mancini et al, Phys. Plasmas 16, 041001 (2009)

Ionizing radiation in environment

International Nuclear Information System (INIS)

Jandl, J.; Petr, I.

1988-01-01

The basic terms are explained such as the atom, radioactivity, nuclear reaction, interaction of ionizing radiation with matter, etc. The basic dosimetric variables and units and properties of radionuclides and ionizing radiation are given. Natural and artificial sources of ionizing radiation are discussed with regard to the environment and the propagation and migration of radionuclides is described in the environment to man. The impact is explained of ionizing radiation on the cell and the somatic and genetic effects of radiation on man are outlined. Attention is devoted to protection against ionizing radiation and to radiation limits, also to the detection, dosimetry and monitoring of ionizing radiation in the environment. (M.D.). 92 figs., 40 tabs. 74 refs

Fragment ion distribution in charge-changing collisions of 2-MeV Si ions with C60

Science.gov (United States)

Itoh, A.; Tsuchida, H.; Miyabe, K.; Majima, T.; Nakai, Y.

2001-09-01

We have measured positive fragment ions produced in collisions of 2 MeV Siq+ (q=0, 1, 2, 4) projectiles with a C60 molecular target. The measurement was performed with a time-of-flight coincidence method between fragment ions and charge-selected outgoing projectiles. For all the charge-changing collisions investigated here, the mass distribution of small fragment ions C+n (n=1-12) can be approximated fairly well by a power-law form of n-λ as a function of the cluster size n. The power λ derived from each mass distribution is found to change strongly according to different charge-changing collisions. As a remarkable experimental finding, the values of λ(loss) in electron loss collisions are almost the same for the same final charge states k irrespective of the initial charge q, exhibiting a nearly perfect linear relationship with k. We also performed calculations of the projectile ionization on the basis of the semiclassical approximation and obtained inelastic energy deposition for individual collision processes. The estimated energy deposition is found to have a simple correlation with the experimentally determined values of λ(loss).

Characterization of a facility for the measurement of fission fragment transport effects: experimental determination of the fission rates for fissile and fissionable isotopes

International Nuclear Information System (INIS)

Benetti, P.; Raselli, G.L.; Tigliole, A. Borio di; Cagnazzo, M.; Cesana, A.; Mongelli, S.; Terrani, M.

2002-01-01

The transfer facility of the LENA laboratory allows the direct neutron irradiation of fissionable material in the D channel of the TRIGA reactor. A test measurement carried out with a ionization chamber and a 239 Pu sample shows the possibility to use this tool for the study of the transport effects of the fission fragment emerging from thin layers of fissile materials. (author)

Absolute Charge Transfer and Fragmentation Cross Sections in He2+-C60 Collisions

International Nuclear Information System (INIS)

Rentenier, A.; Moretto-Capelle, P.; Bordenave-Montesquieu, D.; Bordenave-Montesquieu, A.; Ruiz, L. F.; Diaz-Tendero, S.; Alcami, M.; Martin, F.; Zarour, B.; Hanssen, J.; Hervieux, P.-A.; Politis, M. F.

2008-01-01

We have determined absolute charge transfer and fragmentation cross sections in He 2+ +C 60 collisions in the impact-energy range 0.1-250 keV by using a combined experimental and theoretical approach. We have found that the cross sections for the formation of He + and He 0 are comparable in magnitude, which cannot be explained by the sole contribution of pure single and double electron capture but also by contribution of transfer-ionization processes that are important even at low impact energies. The results show that multifragmentation is important only at impact energies larger than 40 keV; at lower energies, sequential C 2 evaporation is the dominant process

Dynamics of NO2 dissociation. Study by resonance-enhanced multi-photon ionisation of energy distribution and of anisotropies in fragments

International Nuclear Information System (INIS)

Mons, Michel

1988-01-01

In this research thesis, the author reports the use of laser resonance-enhanced multi-photon ionization and of time-of-flight mass spectrometry for a detailed characterization of fragments produced by a photo-dissociation process. The author more particularly addressed the case of a NO 2 molecule excited at low energies above the dissociation threshold. In the first part, the author discusses issues and problems related to molecular photo-dissociation. In the second part, he presents the developed method and shows that the combined use of both techniques allows a precise characterisation of photo-fragments in terms of internal or translational energies as well as in terms of angle distributions. Finally, the author presents and discusses results obtained in the case of NO 2 [fr

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

Science.gov (United States)

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

2016-08-01

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

Space-charge effects of the proportional counters in a multiple-ionization chamber

International Nuclear Information System (INIS)

Mang, M.

1993-01-01

At the ALADIN spectrometer of the GSI in october 1991 for the first time the new multiple ionization chamber was applied, in the two anode planes of which are additional multiwire-proportional counters. The proportional counters are required in order to make the detection of light fragments (Z 4 gold projectiles per second by these positive space charges the homogeneous electric field of the MUSIC is disturbed. This effect is especially strong in the beam plane. As consequence of the space charge additionally electrons are focused on the proportional counter so that their amplitudes in dependence on the beam intensity increase up to the 2.5-fold. Furthermore the y coordinate is falsified, because the electrons are diverted to the medium plane. On the measurement of the x coordinate this diversion has with maximally 0.1% only a small influence. These space-charge effects can be qualitatively described by a schematic model, which assumes a stationary positive space charge. Additionally for the proportional counters, which are not in the beam plane, their resolution was determined. In these counters the space-charge effects are small, because essentially fewer particles are registrated than in the medium MWPC's. By this charges of fragments with Z<10 could be separated. The charge resolution amounted at lithium 0.8 charge units. The position resolution of the proportional counters in y direction was determined to less than 8 mm. The detection probability of the fragments amounts for lithium 90% and from boron all fragments are detected

String fragmentation; La fragmentation des cordes

Energy Technology Data Exchange (ETDEWEB)

Drescher, H.J.; Werner, K. [Laboratoire de Physique Subatomique et des Technologies Associees - SUBATECH, Centre National de la Recherche Scientifique, 44 - Nantes (France)

1997-10-01

The classical string model is used in VENUS as a fragmentation model. For the soft domain simple 2-parton strings were sufficient, whereas for higher energies up to LHC, the perturbative regime of the QCD gives additional soft gluons, which are mapped on the string as so called kinks, energy singularities between the leading partons. The kinky string model is chosen to handle fragmentation of these strings by application of the Lorentz invariant area law. The `kinky strings` model, corresponding to the perturbative gluons coming from pQCD, takes into consideration this effect by treating the partons and gluons on the same footing. The decay law is always the Artru-Menessier area law which is the most realistic since it is invariant to the Lorentz and gauge transformations. For low mass strings a manipulation of the rupture point is necessary if the string corresponds already to an elementary particle determined by the mass and the flavor content. By means of the fragmentation model it will be possible to simulate the data from future experiments at LHC and RHIC 3 refs.

Coulomb Fission in Multiply-Charged Ammonia Clusters: Accurate Measurements of the Rayleigh Instability Limit from Fragmentation Patterns.

Science.gov (United States)

Harris, Christopher; Stace, Anthony J

2018-03-15

A series of experiments have been undertaken on the fragmentation of multiply charged ammonia clusters, (NH 3 ) n z+ , where z ≤ 8 and n ≤ 850, to establish Rayleigh instability limits, whereby clusters at certain critical sizes become unstable due to Coulomb repulsion between the resident charges. Experimental results on size-selected clusters are found to be in excellent agreement with theoretical predictions of Rayleigh instability limits at all values of the charge. Electrostatic theory has been used to help identify fragmentation patterns on the assumption that the clusters separate into two dielectric spheres, and the predicted Coulomb repulsion energies used to establish pathways and the sizes of cluster fragments. The results show that fragmentation is very asymmetric in terms of both the numbers of molecules involved and the amount of charge each fragment accommodates. For clusters carrying a charge ≤+4, the results show that fragmentation proceeds via the loss of small, singly charged clusters. When clusters carry a charge of +5 or more, the experimental observations suggest a marked switch in behavior. Although the laboratory measurements equate to fragmentation via the loss of a large dication cluster, electrostatic theory supports an interpretation that involves the sequential loss of two smaller, singly charged clusters possibly accompanied by the extensive evaporation of neutral molecules. It is suggested that this change in fragmentation pattern is driven by the channelling of Coulomb repulsion energy into intermolecular modes within these larger clusters. Overall, the results appear to support the ion evaporation model that is frequently used to interpret electrospray experiments.

Self-focusing and guiding of short laser pulses in ionizing gases and plasmas

International Nuclear Information System (INIS)

Esarey, E.; Sprangle, P.; Krall, J.; Ting, A.

1997-01-01

The propagation of intense laser pulses in gases and plasmas is relevant to a wide range of applications, including laser-driven accelerators, laser-plasma channeling, harmonic generation, supercontinuum generation, X-ray lasers, and laser-fusion schemes. Here, several features of intense, short-pulse (≤1 ps) laser propagation in gases undergoing ionization and in plasmas are reviewed, discussed, and analyzed. The wave equations for laser pulse propagation in a gas undergoing ionization and in a plasma are derived. The source-dependent expansion method is discussed, which is a general method for solving the paraxial wave equation with nonlinear source terms. In gases, the propagation of high-power (near the critical power) laser pulses is considered including the effects of diffraction, nonlinear self-focusing, ionization, and plasma generation. Self-guided solutions and the stability of these solutions are discussed. In plasmas, optical guiding by relativistic effects, ponderomotive effects, and preformed density channels is considered. The self-consistent plasma response is discussed, including plasma wave effects and instabilities such as self-modulation. Recent experiments on the guiding of laser pulses in gases and in plasmas are briefly summarized

Current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization

International Nuclear Information System (INIS)

Stoyanov, D G

2007-01-01

The balances of particles and charges in the volume of parallel-plane ionization chamber are considered. Differential equations describing the distribution of current densities in the chamber volume are obtained. As a result of the differential equations solution an analytical form of the current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization in the volume is obtained

Current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization

Energy Technology Data Exchange (ETDEWEB)

Stoyanov, D G [Faculty of Engineering and Pedagogy in Sliven, Technical University of Sofia, 59, Bourgasko Shaussee Blvd, 8800 Sliven (Bulgaria)

2007-08-15

The balances of particles and charges in the volume of parallel-plane ionization chamber are considered. Differential equations describing the distribution of current densities in the chamber volume are obtained. As a result of the differential equations solution an analytical form of the current-voltage characteristic of parallel-plane ionization chamber with inhomogeneous ionization in the volume is obtained.

Two-particle versus three-particle interactions in single ionization of helium by ion impact

International Nuclear Information System (INIS)

Schulz, M; Moshammer, R; Fischer, D; Ullrich, J

2004-01-01

We have performed kinematically complete experiments on single ionization of He by 100 MeV amu -1 C 6+ and 3.6 MeV amu -1 Au 24,53+ impact. By analysing doubly differential cross sections (DDCS) as a function of the momenta of all two-particle sub-systems we studied the importance of two-particle interactions. Furthermore, presenting the squared momenta of all three collision fragments simultaneously in a Dalitz plot, we evaluated the role of three-particle interactions. Finally, both for the DDCS and the Dalitz plots the corresponding correlation function was analysed. While the absolute cross sections confirm that ionization predominantly leads to a momentum exchange between the electron and the recoil-ion, the correlation function reveals strong correlations between the particles of any two-particle sub-system. Three-particle correlations, which are not accounted for by perturbative calculations, are quite significant as well, at least for certain kinematic conditions

Spatial and temporal dimensions of landscape fragmentation across the Brazilian Amazon.

Science.gov (United States)

Rosa, Isabel M D; Gabriel, Cristina; Carreiras, Joāo M B

2017-01-01

The Brazilian Amazon in the past decades has been suffering severe landscape alteration, mainly due to anthropogenic activities, such as road building and land clearing for agriculture. Using a high-resolution time series of land cover maps (classified as mature forest, non-forest, secondary forest) spanning from 1984 through 2011, and four uncorrelated fragmentation metrics (edge density, clumpiness index, area-weighted mean patch size and shape index), we examined the temporal and spatial dynamics of forest fragmentation in three study areas across the Brazilian Amazon (Manaus, Santarém and Machadinho d'Oeste), inside and outside conservation units. Moreover, we compared the impacts on the landscape of: (1) different land uses (e.g. cattle ranching, crop production), (2) occupation processes (spontaneous vs. planned settlements) and (3) implementation of conservation units. By 2010/2011, municipalities located along the Arc of Deforestation had more than 55% of the remaining mature forest strictly confined to conservation units. Further, the planned settlement showed a higher rate of forest loss, a more persistent increase in deforested areas and a higher relative incidence of deforestation inside conservation units. Distinct agricultural activities did not lead to significantly different landscape structures; the accessibility of the municipality showed greater influence in the degree of degradation of the landscapes. Even with a high proportion of the landscapes covered by conservation units, which showed a strong inhibitory effect on forest fragmentation, we show that dynamic agriculturally driven economic activities, in municipalities with extensive road development, led to more regularly shaped, heavily fragmented landscapes, with higher densities of forest edge.

IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. V. ALFVÉN IONIZATION

International Nuclear Information System (INIS)

Stark, C. R.; Helling, Ch.; Rimmer, P. B.; Diver, D. A.

2013-01-01

Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbor localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfvén ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization (≥10 –7 ) that they constitute plasmas. We outline the criteria required for Alfvén ionization and demonstrate its applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs, and M dwarfs with both solar and sub-solar metallicities. We find that Alfvén ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neutral flows are the smallest. For the model atmospheres considered, our results show that degrees of ionization of 10 –6 -1 can be obtained as a result of Alfvén ionization. Observable consequences include continuum bremsstrahlung emission, superimposed with spectral lines from the plasma ion species (e.g., He, Mg, H 2 , or CO lines). Forbidden lines are also expected from the metastable population. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models. The occurrence of Alfvén ionization may also be applicable to other astrophysical environments such as protoplanetary disks

Modeling laser-driven electron acceleration using WARP with Fourier decomposition

Energy Technology Data Exchange (ETDEWEB)

Lee, P., E-mail: patrick.lee@u-psud.fr [LPGP, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France); Audet, T.L. [LPGP, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France); Lehe, R.; Vay, J.-L. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Maynard, G.; Cros, B. [LPGP, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France)

2016-09-01

WARP is used with the recent implementation of the Fourier decomposition algorithm to model laser-driven electron acceleration in plasmas. Simulations were carried out to analyze the experimental results obtained on ionization-induced injection in a gas cell. The simulated results are in good agreement with the experimental ones, confirming the ability of the code to take into account the physics of electron injection and reduce calculation time. We present a detailed analysis of the laser propagation, the plasma wave generation and the electron beam dynamics.

Fission fragment angular momentum

International Nuclear Information System (INIS)

Frenne, D. De

1991-01-01

Most of the energy released in fission is converted into translational kinetic energy of the fragments. The remaining excitation energy will be distributed among neutrons and gammas. An important parameter characterizing the scission configuration is the primary angular momentum of the nascent fragments. Neutron emission is not expected to decrease the spin of the fragments by more than one unit of angular momentum and is as such of less importance in the determination of the initial fragment spins. Gamma emission is a suitable tool in studying initial fragment spins because the emission time, number, energy, and multipolarity of the gammas strongly depend on the value of the primary angular momentum. The main conclusions of experiments on gamma emission were that the initial angular momentum of the fragments is large compared to the ground state spin and oriented perpendicular to the fission axis. Most of the recent information concerning initial fragment spin distributions comes from the measurement of isomeric ratios for isomeric pairs produced in fission. Although in nearly every mass chain isomers are known, only a small number are suitable for initial fission fragment spin studies. Yield and half-life considerations strongly limit the number of candidates. This has the advantage that the behavior of a specific isomeric pair can be investigated for a number of fissioning systems at different excitation energies of the fragments and fissioning nuclei. Because most of the recent information on primary angular momenta comes from measurements of isomeric ratios, the global deexcitation process of the fragments and the calculation of the initial fragment spin distribution from measured isomeric ratios are discussed here. The most important results on primary angular momentum determinations are reviewed and some theoretical approaches are given. 45 refs., 7 figs., 2 tabs

Biological Effects of Ionizing Radiation

Science.gov (United States)

Ingram, M.; Mason, W. B.; Whipple, G. H.; Howland, J. W.

1952-04-07

This report presents a review of present knowledge and concepts of the biological effects of ionizing radiations. Among the topics discussed are the physical and chemical effects of ionizing radiation on biological systems, morphological and physiological changes observed in biological systems subjected to ionizing radiations, physiological changes in the intact animal, latent changes following exposure of biological systems to ionizing radiations, factors influencing the biological response to ionizing radiation, relative effects of various ionizing radiations, and biological dosimetry.

Ionization chambers

International Nuclear Information System (INIS)

Boag, J.W.

1987-01-01

Although a variety of solid-state and chemical methods for measuring radiation dose have been developed in recent decades and calorimetry can now provide an absolute standard of reference, ionization dosimetry retains its position as the most widely used, most convenient, and, in most situations, most accurate method of measuring either exposure or absorbed dose. The ionization chamber itself is the central element in this system of dosimetry. In this chapter the principles governing the construction and operation of ionization chambers of various types are examined. Since the ionization chambers now in general use are nearly all of commercial manufacture, the emphasis is on operating characteristics and interpretation of measurements rather than on details of construction, although some knowledge of the latter is often required when applying necessary corrections to the measured quantities. Examples are given of the construction of typical chambers designed for particular purposes, and the methods of calibrating them are discussed

On the ultrafast charge migration and subsequent charge directed reactivity in Cl⋯N halogen-bonded clusters following vertical ionization

International Nuclear Information System (INIS)

Chandra, Sankhabrata; Bhattacharya, Atanu; Periyasamy, Ganga

2015-01-01

In this article, we have presented ultrafast charge transfer dynamics through halogen bonds following vertical ionization of representative halogen bonded clusters. Subsequent hole directed reactivity of the radical cations of halogen bonded clusters is also discussed. Furthermore, we have examined effect of the halogen bond strength on the electron-electron correlation- and relaxation-driven charge migration in halogen bonded complexes. For this study, we have selected A-Cl (A represents F, OH, CN, NH 2 , CF 3 , and COOH substituents) molecules paired with NH 3 (referred as ACl:NH 3 complex): these complexes exhibit halogen bonds. To the best of our knowledge, this is the first report on purely electron correlation- and relaxation-driven ultrafast (attosecond) charge migration dynamics through halogen bonds. Both density functional theory and complete active space self-consistent field theory with 6-31 + G(d, p) basis set are employed for this work. Upon vertical ionization of NCCl⋯NH 3 complex, the hole is predicted to migrate from the NH 3 -end to the ClCN-end of the NCCl⋯NH 3 complex in approximately 0.5 fs on the D 0 cationic surface. This hole migration leads to structural rearrangement of the halogen bonded complex, yielding hydrogen bonding interaction stronger than the halogen bonding interaction on the same cationic surface. Other halogen bonded complexes, such as H 2 NCl:NH 3 , F 3 CCl:NH 3 , and HOOCCl:NH 3 , exhibit similar charge migration following vertical ionization. On the contrary, FCl:NH 3 and HOCl:NH 3 complexes do not exhibit any charge migration following vertical ionization to the D 0 cation state, pointing to interesting halogen bond strength-dependent charge migration

Jdpd: an open java simulation kernel for molecular fragment dissipative particle dynamics.

Science.gov (United States)

van den Broek, Karina; Kuhn, Hubert; Zielesny, Achim

2018-05-21

Jdpd is an open Java simulation kernel for Molecular Fragment Dissipative Particle Dynamics with parallelizable force calculation, efficient caching options and fast property calculations. It is characterized by an interface and factory-pattern driven design for simple code changes and may help to avoid problems of polyglot programming. Detailed input/output communication, parallelization and process control as well as internal logging capabilities for debugging purposes are supported. The new kernel may be utilized in different simulation environments ranging from flexible scripting solutions up to fully integrated "all-in-one" simulation systems.

Azimuthal Anisotropies in Nuclear Fragmentation

International Nuclear Information System (INIS)

Dabrowska, A.; Szarska, M.; Trzupek, A.; Wolter, W.; Wosiek, B.

2002-01-01

The directed and elliptic flow of fragments emitted from the excited projectile nuclei has been observed for 158 AGeV Pb collisions with the lead and plastic targets. For comparison the flow analysis has been performed for 10.6 AGeV Au collisions with the emulsion target. The strong directed flow of heaviest fragments is found. Light fragments exhibit directed flow opposite to that of heavy fragments. The elliptic flow for all multiply charged fragments is positive and increases with the charge of the fragment. The observed flow patterns in the fragmentation of the projectile nucleus are practically independent of the mass of the target nucleus and the collision energy. Emission of fragments in nuclear multifragmentation shows similar, although weaker, flow effects. (author)

The ionizing treatment of food

International Nuclear Information System (INIS)

1998-01-01

This book of proceedings contains the talks given by the members of the Society of chemical experts of France (SECF) and by various specialists of the ionizing treatment during the scientific days of September 25-26, 1997. The aim of this meeting was to reconsider the effects of ionization from a scientific point of view and apart from the polemics generated by this domain. The following topics were discussed successively: source and characterization of a ionizing treatment, biological effects of ionization on food and the expected consequences, the ionizing treatment and the reduction of the vitamin C content of fruits and vegetables, is it safe to eat irradiated food?, the organoleptic modifications of food after ionization, quality assurance of dosimetry measurements in an industrial installation of food ionization, the French and European regulations in food ionization, the detection of irradiated foodstuffs, processed food and complex lipid matrices, sterilization of dishes for immuno-depressed patients using ionization. (J.S.)

Analysis of fission-fragment mass distribution within the quantum-mechanical fragmentation theory

Energy Technology Data Exchange (ETDEWEB)

Singh, Pardeep; Kaur, Harjeet [Guru Nanak Dev University, Department of Physics, Amritsar (India)

2016-11-15

The fission-fragment mass distribution is analysed for the {sup 208}Pb({sup 18}O, f) reaction within the quantum-mechanical fragmentation theory (QMFT). The reaction potential has been calculated by taking the binding energies, Coulomb potential and proximity potential of all possible decay channels and a stationary Schroedinger equation has been solved numerically to calculate the fission-fragment yield. The overall results for mass distribution are compared with those obtained in experiment. Fine structure dips in yield, corresponding to fragment shell closures at Z = 50 and N=82, which are observed by Bogachev et al., are reproduced successfully in the present calculations. These calculations will help to estimate the formation probabilities of fission fragments and to understand many related phenomena occurring in the fission process. (orig.)

A qualitative study of amlodipine and its related compounds by electrospray ionization tandem mass spectrometry.

Science.gov (United States)

Gibbons, John; Pugh, Jonathan; Dimopoulos-Italiano, Gina; Pike, Richard

2006-01-01

A comprehensive structural analysis of amlodipine and certain related compounds was performed by electrospray ionization tandem mass spectrometry. Triple quadrupole and quadrupole time-of-flight instruments were used to provide collision-induced dissociation and accurate mass measurement for selected product and second-generation product ions. A unique ion rearrangement was observed, which was found to be characteristic of certain dihydropyridines. This study provides a fundamental understanding of the fragmentation of these compounds. The structural elucidation of an unknown impurity is presented as an example. Copyright (c) 2006 John Wiley & Sons, Ltd.

'Saddle-point' ionization

International Nuclear Information System (INIS)

Gay, T.J.; Hale, E.B.; Irby, V.D.; Olson, R.E.; Missouri Univ., Rolla; Berry, H.G.

1988-01-01

We have studied the ionization of rare gases by protons at intermediate energies, i.e., energies at which the velocities of the proton and the target-gas valence electrons are comparable. A significant channel for electron production in the forward direction is shown to be 'saddle-point' ionization, in which electrons are stranded on or near the saddle-point of electric potential between the receding projectile and the ionized target. Such electrons yield characteristic energy spectra, and contribute significantly to forward-electron-production cross sections. Classical trajectory Monte Carlo calculations are found to provide qualitative agreement with our measurements and the earlier measurements of Rudd and coworkers, and reproduce, in detail, the features of the general ionization spectra. (orig.)

The grain-size distribution of pyroclasts: Primary fragmentation, conduit sorting or abrasion?

Science.gov (United States)

Kueppers, U.; Schauroth, J.; Taddeucci, J.

2013-12-01

Explosive volcanic eruptions expel a mixture of pyroclasts and lithics. Pyroclasts, fragments of the juvenile magma, record the state of the magma at fragmentation in terms of porosity and crystallinity. The grain size distribution of pyroclasts is generally considered to be a direct consequence of the conditions at magma fragmentation that is mainly driven by gas overpressure in bubbles, high shear rates, contact with external water or a combination of these factors. Stress exerted by any of these processes will lead to brittle fragmentation by overcoming the magma's relaxation timescale. As a consequence, most pyroclasts exhibit angular shapes. Upon magma fragmentation, the gas pyroclast mixture is accelerated upwards and eventually ejected from the vent. The total grain size distribution deposited is a function of fragmentation conditions and transport related sorting. Porous pyroclasts are very susceptible to abrasion by particle-particle or particle-conduit wall interaction. Accordingly, pyroclastic fall deposits with angular clasts should proof a low particle abrasion upon contact to other surfaces. In an attempt to constrain the degree of particle interaction during conduit flow, monomodal batches of washed pyroclasts have been accelerated upwards by rapid decompression and subsequently investigated for their grain size distribution. In our set-up, we used a vertical cylindrical tube without surface roughness as conduit. We varied grain size (0.125-0.25; 0.5-1; 1-2 mm), porosity (0; 10; 30 %), gas-particle ratio (10 and 40%), conduit length (10 and 28 cm) and conduit diameter (2.5 and 6 cm). All ejected particles were collected after settling at the base of a 3.3 m high tank and sieved at one sieve size below starting size (half-Φ). Grain size reduction showed a positive correlation with starting grain size, porosity and overpressure at the vent. Although milling in a volcanic conduit may take place, porous pyroclasts are very likely to be a primary product

Heating and ionization in MHD shock waves propagating into partially ionized plasma

International Nuclear Information System (INIS)

Bighel, L.; Collins, A.R.; Cramer, N.F.; Watson-Munro, C.N.

1975-09-01

A model of the structure of MHD switch-on shocks propagating in a partially ionized plasma, in which the primary dissipation mechanism is friction between ions and neutrals, is here compared favourably with experimental results. Four degrees of upstream ionization were studied, ranging from almost complete to very small ionization. (author)

Heating and ionization in MHD shock wave propagating into partially ionized plasma

International Nuclear Information System (INIS)

Bighel, L.; Collins, A.R.; Cramer, N.F.; Watson-Munro, C.N.

1975-09-01

A model of the structure of MHD switch-on shocks propagating in a partially ionized plasma, in which the primary dissipation mechanism is friction between ions and neutrals, is here compared favourably with experimental results. Four degrees of upstream ionization were studied, ranging from almost complete to very small ionization. (author)

Five-photon ionization of atomic hydrogen at wavelengths around the threshold for four-photon ionization

International Nuclear Information System (INIS)

Gontier, Y.; Trahin, M.; Wolff-Rottke, B.; Rottke, H.; Welge, K.H.; Feldmann, D.

1992-01-01

Theoretical and experimental studies show the strong influence of the three-photon nearly resonant 2p state on four- and five-photon ionization of atomic hydrogen near the threshold for four-photon ionization. Changes in five-photon ionization occur when the four-photon ionization channel opens. The angular distributions of photoelectrons from five-photon ionization of H are studied at five wavelengths which cover the range from four-photon resonance with high-lying Rydberg states (n≥10) to direct four-photon ionization into the continuum. The role of resonances in this ionization process is discussed. A fair agreement is found in comparing experimental and theoretical results

Equipment for handling ionization chamber

International Nuclear Information System (INIS)

Altmann, J.

1988-01-01

The device consists of an ionization channel with an ionization chamber, of a support ring, axial and radial bearings, a sleeve, a screw gear and an electric motor. The ionization chamber is freely placed on the bottom of the ionization channel. The bottom part of the channel deviates from the vertical axis. The support ring propped against the axial bearing in the sleeve is firmly fixed to the top part of the ionization channel. The sleeve is fixed to the reactor lid. Its bottom part is provided with a recess for the radial bearing which is propped against a screw wheel firmly connected to the ionization channel. In measuring neutron flux, the screw wheel is rotated by the motor, thus rotating the whole ionization channel such that the ionization chamber is displaced into the reactor core.(J.B.). 1 fig

The effect of isolation, fragmentation, and population bottlenecks on song structure of a Hawaiian honeycreeper

Science.gov (United States)

Pang-Ching, Joshua M.; Paxton, Kristina L.; Paxton, Eben H.; Pack, Adam A.; Hart, Patrick J.

2018-01-01

Little is known about how important social behaviors such as song vary within and among populations for any of the endemic Hawaiian honeycreepers. Habitat loss and non‐native diseases (e.g., avian malaria) have resulted in isolation and fragmentation of Hawaiian honeycreepers within primarily high elevation forests. In this study, we examined how isolation of Hawai'i ‘amakihi (Chlorodrepanis virens) populations within a fragmented landscape influences acoustic variability in song. In the last decade, small, isolated populations of disease tolerant ‘amakihi have been found within low elevation forests, allowing us to record ‘amakihi songs across a large elevational gradient (10–1800 m) that parallels disease susceptibility on Hawai'i island. To understand underlying differences among populations, we examined the role of geographic distance, elevation, and habitat structure on acoustic characteristics of ‘amakihi songs. We found that the acoustic characteristics of ‘amakihi songs and song‐type repertoires varied most strongly across an elevational gradient. Differences in ‘amakihi song types were primarily driven by less complex songs (e.g., fewer frequency changes, shorter songs) of individuals recorded at low elevation sites compared to mid and high elevation populations. The reduced complexity of ‘amakihi songs at low elevation sites is most likely shaped by the effects of habitat fragmentation and a disease‐driven population bottleneck associated with avian malaria, and maintained through isolation, localized song learning and sharing, and cultural drift. These results highlight how a non‐native disease through its influence on population demographics may have also indirectly played a role in shaping the acoustic characteristics of a species.

Hypervelocity Impact Test Fragment Modeling: Modifications to the Fragment Rotation Analysis and Lightcurve Code

Science.gov (United States)

Gouge, Michael F.

2011-01-01

Hypervelocity impact tests on test satellites are performed by members of the orbital debris scientific community in order to understand and typify the on-orbit collision breakup process. By analysis of these test satellite fragments, the fragment size and mass distributions are derived and incorporated into various orbital debris models. These same fragments are currently being put to new use using emerging technologies. Digital models of these fragments are created using a laser scanner. A group of computer programs referred to as the Fragment Rotation Analysis and Lightcurve code uses these digital representations in a multitude of ways that describe, measure, and model on-orbit fragments and fragment behavior. The Dynamic Rotation subroutine generates all of the possible reflected intensities from a scanned fragment as if it were observed to rotate dynamically while in orbit about the Earth. This calls an additional subroutine that graphically displays the intensities and the resulting frequency of those intensities as a range of solar phase angles in a Probability Density Function plot. This document reports the additions and modifications to the subset of the Fragment Rotation Analysis and Lightcurve concerned with the Dynamic Rotation and Probability Density Function plotting subroutines.

Foodstuffs preservation by ionization

International Nuclear Information System (INIS)

1991-12-01

This document contains all the papers presented at the meeting on foodstuffs preservation by ionization. These papers deal especially with the food ionization process, its development and the view of the food industry on ionization. Refs and figs (F.M.)

Ambient ionization mass spectrometry: A tutorial

Energy Technology Data Exchange (ETDEWEB)

Huang, Min-Zong; Cheng, Sy-Chi; Cho, Yi-Tzu [Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan (China); Shiea, Jentaie, E-mail: jetea@fac.nsysu.edu.tw [Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan (China); Cancer Center, Kaohsiung Medical University, Kaohsiung, Taiwan (China)

2011-09-19

Highlights: {yields} Ambient ionization technique allows the direct analysis of sample surfaces with little or no sample pretreatment. {yields} We sort ambient ionization techniques into three main analytical strategies, direct ionization, direct desorption/ionization, and two-step ionization. {yields} The underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques are described and compared. - Abstract: Ambient ionization is a set of mass spectrometric ionization techniques performed under ambient conditions that allows the direct analysis of sample surfaces with little or no sample pretreatment. Using combinations of different types of sample introduction systems and ionization methods, several novel techniques have been developed over the last few years with many applications (e.g., food safety screening; detection of pharmaceuticals and drug abuse; monitoring of environmental pollutants; detection of explosives for antiterrorism and forensics; characterization of biological compounds for proteomics and metabolomics; molecular imaging analysis; and monitoring chemical and biochemical reactions). Electrospray ionization and atmospheric pressure chemical ionization are the two main ionization principles most commonly used in ambient ionization mass spectrometry. This tutorial paper provides a review of the publications related to ambient ionization techniques. We describe and compare the underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques.

Ambient ionization mass spectrometry: A tutorial

International Nuclear Information System (INIS)

Huang, Min-Zong; Cheng, Sy-Chi; Cho, Yi-Tzu; Shiea, Jentaie

2011-01-01

Highlights: → Ambient ionization technique allows the direct analysis of sample surfaces with little or no sample pretreatment. → We sort ambient ionization techniques into three main analytical strategies, direct ionization, direct desorption/ionization, and two-step ionization. → The underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques are described and compared. - Abstract: Ambient ionization is a set of mass spectrometric ionization techniques performed under ambient conditions that allows the direct analysis of sample surfaces with little or no sample pretreatment. Using combinations of different types of sample introduction systems and ionization methods, several novel techniques have been developed over the last few years with many applications (e.g., food safety screening; detection of pharmaceuticals and drug abuse; monitoring of environmental pollutants; detection of explosives for antiterrorism and forensics; characterization of biological compounds for proteomics and metabolomics; molecular imaging analysis; and monitoring chemical and biochemical reactions). Electrospray ionization and atmospheric pressure chemical ionization are the two main ionization principles most commonly used in ambient ionization mass spectrometry. This tutorial paper provides a review of the publications related to ambient ionization techniques. We describe and compare the underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques.

Cross section measurements of the processes occurring in the fragmentation of Hn+ (3 ≤ n ≤ 35) hydrogen clusters induced by high speed (60 keV/u) collisions on helium atoms

International Nuclear Information System (INIS)

Louc, Sandrine

1997-01-01

Different processes involved in the fragmentation of ionised hydrogen clusters H 3 + (H 2 ) (n-3)/2 (n = 5-35) have been studied in the same experiment: the fragmentation of the cluster is induced by the collision with an helium atom at high velocity (≅ c/100). The collision is realised in reversed kinematic - clusters are accelerated - which allows the detection of neutral and charged fragments. The different channels of fragmentation are identified by using coincidence techniques. For all the cluster sizes studied the capture cross sections of one electron of the target by the cluster is equal to the capture cross section of the H 3 + ion. In the same way, the dissociation cross section of the H 3 + core of the cluster does not depend on cluster size. These fragmentation processes are due to the interaction of H 3 + core of the cluster and the helium atom without ionization of another component of the cluster. On the contrary, the cross sections of loss of one, two and three molecules by the cluster and the dissociation cross section of the cluster in all its molecular components depends strongly on the cluster size. This dependence is different from the one measured for the metastable decay of the cluster. Thus, the process of loss of molecules induced by a collision should correspond to a different dissociation mechanism. In regard of the singularities observed for the size dependence, the H 9 + , H 15 + , H 19 + and H 29 + clusters could be the 'core' of the biggest clusters. These observation are in agreement with the size effects of smaller magnitude observed for the dissociation cross section (all the processes). The values of the cross section for the process of at least one ionization of the cluster indicate that about 80% of the fragmentation events result from this process. (author)

Utilize the spectral line pair of the same ionized state ion to measure the ion temperature of tokamak plasma

International Nuclear Information System (INIS)

Lin Xiaodong

2000-01-01

Making use of a Fabry-Perot interferometer driven by a piezoelectric crystal and selecting the suitable separation of plates, the ion temperature is defined by measuring the superimposed profile of the spectral line pair of the same ionized state ions in Tokamak. The advantage of this method is to higher spectral resolution and wider spectral range select

Fragment capture device

Science.gov (United States)

Payne, Lloyd R.; Cole, David L.

2010-03-30

A fragment capture device for use in explosive containment. The device comprises an assembly of at least two rows of bars positioned to eliminate line-of-sight trajectories between the generation point of fragments and a surrounding containment vessel or asset. The device comprises an array of at least two rows of bars, wherein each row is staggered with respect to the adjacent row, and wherein a lateral dimension of each bar and a relative position of each bar in combination provides blockage of a straight-line passage of a solid fragment through the adjacent rows of bars, wherein a generation point of the solid fragment is located within a cavity at least partially enclosed by the array of bars.

Ionization of food products

International Nuclear Information System (INIS)

Vasseur, J.P.

1991-01-01

After general remarks on foods preservation, on international works and on ionization future prospects, main irradiation sources are described. Recalls on radioactivity, on radiation-matter interaction, on toxicology of ionized foods and on ionized foods detection are given. Ionization applications to various products are reviewed, especially in: - Poultry meat - Fishing products - Fresh fruits and vegetables - Dry fruits and vegetables - spices, tea, infusion - prepacked products... An evaluation of economics and sociocultural impacts is presented in connection with recent experiments [fr

The Wolff rearrangement of cyclic 2-diazo-1,3-diketones in electron impact - mass spectrometry - controlling the molecular fragmentation by means of low-energy electrons 18 to 70 eV

International Nuclear Information System (INIS)

Kuruc, J.; Kardosova, E.; Nikolaev, V. A.

2016-01-01

The electron-impact-induced fragmentations (the mass spectra, 17 - 70 eV) of cyclic 2-diazo-1,3-diketones were studied. As the suitable compounds were selected the following cyclic 2-diazo-1,3-diketones: 2-diazo-1,3-cyclohexanedione, Ia; 2-diazo-4,4-dimethyl-1,3-cyclohexanedione, Ib; 2-diazo-5,5-dimethyl-1,3-cyclohexanedione, Ic; 2-diazo-4,6-dioxa-5,5-dimethyl-1,3-cyclohexanedione, Id; and 2-diazo-5-phenyl-1,3-cyclohexanedione, Ie). The mass spectra were measured with Varian MAT 111 instrument with direct introduction of samples, with a source temperature of 120 grad C, energy of ionising electrons was in the range (17 - 70) eV. The elimination of the diazo group is the typical reaction of the fragmentation of the cyclic diazo-1,3-diketones after ionization of molecules by electron impact. All our studied cyclic diazo-1,3-diketones have a molecular ion with a relative intensity from 0.7 to 86.4%. Typical ions are [M]"+·, [M-N"_2]"+"·, [M-N_2-CO]"+"·, [M-N_2-CO-CH_2]"+"·, [M-N_2-CO-CH_3]"+"·. For all treatment cyclic diazo-1,3-diketones have been registered 3D mass spectra, for each cyclic diazo-1,3-diketone was proposed fragmentation scheme, including the general fragmentation scheme. The Wolff rearrangement is observed in all studied cyclic diazo-1,3-diketones after cleavage of nitrogen molecules. The energy of ionizing electrons ∼20 eV in the case of compounds Ib, Id - Ie dominating ions are fragments of the [M-N_2]"+"·, in the compound Ia at 18 and 20 eV is dominant fragment [M-N_2-CO-C_2H_2-H]"+"· and for the Ic at 30 eV becomes a dominant fragment [M-N_2-CH_3]"+"· (m/z = 123) but at (25 - 18) eV the most intensive ion is [M-N_2]"+"· (m/z = 138). (authors)

Coulomb-driven energy boost of heavy ions for laser-plasma acceleration.

Science.gov (United States)

Braenzel, J; Andreev, A A; Platonov, K; Klingsporn, M; Ehrentraut, L; Sandner, W; Schnürer, M

2015-03-27

An unprecedented increase of kinetic energy of laser accelerated heavy ions is demonstrated. Ultrathin gold foils have been irradiated by an ultrashort laser pulse at a peak intensity of 8×10^{19}  W/  cm^{2}. Highly charged gold ions with kinetic energies up to >200  MeV and a bandwidth limited energy distribution have been reached by using 1.3 J laser energy on target. 1D and 2D particle in cell simulations show how a spatial dependence on the ion's ionization leads to an enhancement of the accelerating electrical field. Our theoretical model considers a spatial distribution of the ionization inside the thin target, leading to a field enhancement for the heavy ions by Coulomb explosion. It is capable of explaining the energy boost of highly charged ions, enabling a higher efficiency for the laser-driven heavy ion acceleration.

Chemical data on ionizing and non-ionizing angiographic contrast materials

International Nuclear Information System (INIS)

Bonati, F.

1980-01-01

The cardiovascular effects of ionizing and non-ionizing contrast media are compared in experimental animals and in isolated heart preparations. The following parameters were recorded: peripheric arterial diastolic pressure, heart rate, duration of asystolic period, respiratory rate, contractility of the myocardium (dp/dt, LVSP, Vsub(max), EDV, ESV, SV). The observed changes are mainly due to the higher osmotic activity of the contrast media, as similar alterations were recorded after the injection of hyperosmotic glucose solution. It is concluded that administration of non-ionizing contrast media results in significantly less cardiovascular side effects. (L.E.)

Measurement of projectile-like fragments produced by 80. 6 MeV /sup 16/O on /sup 27/Al

Energy Technology Data Exchange (ETDEWEB)

Wen-Qing, SHEN; Shu-Zhi, YIN; Zhong-Yan, GUO; Wen-Long, ZHAN; Yong-Tai, ZHU; Gen-Ming, JIN; Wei-Min, QIAO; En-Chiu, WU; Cheng-Lie, JIANG

1985-05-01

The projectile-like fragments produced by 80.6 MeV /sup 16/O on /sup 27/Al were measured using the large area position sensitive ionization chamber. The energy spectra, angular distributions, contour plots of d/sup 2/sigma/d..cap omega..dE in the E-theta plane of the reaction products from Li to Na and the Z-distribution were obtained. The cross sections of the quasi and deep inelastic scattering were introduced. A brief discussion of the experimental results is also given.

Exact Solutions of Fragmentation Equations with General Fragmentation Rates and Separable Particles Distribution Kernels

Directory of Open Access Journals (Sweden)

S. C. Oukouomi Noutchie

2014-01-01

Full Text Available We make use of Laplace transform techniques and the method of characteristics to solve fragmentation equations explicitly. Our result is a breakthrough in the analysis of pure fragmentation equations as this is the first instance where an exact solution is provided for the fragmentation evolution equation with general fragmentation rates. This paper is the key for resolving most of the open problems in fragmentation theory including “shattering” and the sudden appearance of infinitely many particles in some systems with initial finite particles number.

Land fragmentation and production diversification

NARCIS (Netherlands)

Ciaian, Pavel; Guri, Fatmir; Rajcaniova, Miroslava; Drabik, Dusan; Paloma, Sergio Gomez Y.

2018-01-01

We analyze the impact of land fragmentation on production diversification in rural Albania. Albania represents a particularly interesting case for studying land fragmentation as the fragmentation is a direct outcome of land reforms. The results indicate that land fragmentation is an important driver

Fragmentation processes in nuclear reactions

International Nuclear Information System (INIS)

Legrain, R.

1984-08-01

Projectile and nuclear fragmentation are defined and processes referred to are recalled. The two different aspects of fragmentation are considered but the emphasis is also put on heavy ion induced reactions. The preliminary results of an experiment performed at GANIL to study peripheral heavy ions induced reactions at intermediate energy are presented. The results of this experiment will illustrate the characteristics of projectile fragmentation and this will also give the opportunity to study projectile fragmentation in the transition region. Then nuclear fragmentation is considered which is associated with more central collisions in the case of heavy ion induced reactions. This aspect of fragmentation is also ilustrated with two heavy ion experiments in which fragments emitted at large angle have been observed

Mottled Protoplanetary Disk Ionization by Magnetically Channeled T Tauri Star Energetic Particles

Science.gov (United States)

Fraschetti, F.; Drake, J. J.; Cohen, O.; Garraffo, C.

2018-02-01

The evolution of protoplanetary disks is believed to be driven largely by angular momentum transport resulting from magnetized disk winds and turbulent viscosity. The ionization of the disk that is essential for these processes has been thought to be due to host star coronal X-rays but could also arise from energetic particles produced by coronal flares, or traveling shock waves, and advected by the stellar wind. We have performed test-particle numerical simulations of energetic protons propagating into a realistic T Tauri stellar wind, including a superposed small-scale magnetostatic turbulence. The isotropic (Kolmogorov power spectrum) turbulent component is synthesized along the individual particle trajectories. We have investigated the energy range [0.1–10] GeV, consistent with expectations from Chandra X-ray observations of large flares on T Tauri stars and recent indications by the Herschel Space Observatory of a significant contribution of energetic particles to the disk ionization of young stars. In contrast with a previous theoretical study finding a dominance of energetic particles over X-rays in the ionization throughout the disk, we find that the disk ionization is likely dominated by X-rays over much of its area, except within narrow regions where particles are channeled onto the disk by the strongly tangled and turbulent magnetic field. The radial thickness of such regions is 5 stellar radii close to the star and broadens with increasing radial distance. This likely continues out to large distances from the star (10 au or greater), where particles can be copiously advected and diffused by the turbulent wind.

Ionizing radiations

International Nuclear Information System (INIS)

Anon.

1999-01-01

This is an update about the radiological monitoring in base nuclear installations. A departmental order of the 23. march 1999 (J.O.28. april, p.6309) determines the enabling rules by the Office of Protection against Ionizing Radiations of person having at one's disposal the results with names of individual exposure of workers put through ionizing radiations. (N.C.)

Chemical characterization of synthetic cannabinoids by electrospray ionization FT-ICR mass spectrometry.

Science.gov (United States)

Kill, Jade B; Oliveira, Izabela F; Tose, Lilian V; Costa, Helber B; Kuster, Ricardo M; Machado, Leandro F; Correia, Radigya M; Rodrigues, Rayza R T; Vasconcellos, Géssica A; Vaz, Boniek G; Romão, Wanderson

2016-09-01

The synthetic cannabinoids (SCs) represent the most recent advent of the new psychotropic substances (NPS) and has become popularly known to mitigate the effects of the Δ(9)-THC. The SCs are dissolved in organic solvents and sprayed in a dry herbal blend. However, little information is reported on active ingredients of SCs as well as the excipients or diluents added to the herbal blend. In this work, the direct infusion electrospray ionization Fourier transform ion cyclotron mass spectrometry technique (ESI-FT-ICR MS) was applied to explore the chemical composition of nine samples of herbal extract blends, where a total of 11 SCs (UR-144, JWH-073, XLR-11, JWH-250, JWH-122, AM-2201, AKB48, JWH-210, JWH-081, MAM-2201 and 5F-AKB48) were identified in the positive ionization mode, ESI(+), and other 44 chemical species (saturated and unsaturated fatty acids, sugars, flavonoids, etc.) were detected in the negative ionization mode, ESI(-). Additionally, CID experiments were performed, and fragmentation pathways were proposed to identify the connectivity of SCs. Thus, the direct infusion ESI-FT-ICR MS technique is a powerful tool in forensic chemistry that enables the rapid and unequivocal way for the determination of molecular formula, the degree of unsaturation (DBE-double bond equivalent) and exact mass (<1ppm) of a total of 55 chemical species without the prior separation step. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

PHOTOIONIZATION OF HIGH-ALTITUDE GAS IN A SUPERNOVA-DRIVEN TURBULENT INTERSTELLAR MEDIUM

International Nuclear Information System (INIS)

Wood, Kenneth; Hill, Alex S.; Haffner, L. Matthew; Reynolds, R. J.; Joung, M. Ryan; Mac Low, Mordecai-Mark; Benjamin, Robert A.; Madsen, G. J.

2010-01-01

We investigate models for the photoionization of the widespread diffuse ionized gas (DIG) in galaxies. In particular, we address the long standing question of the penetration of Lyman continuum photons from sources close to the galactic midplane to large heights in the galactic halo. We find that recent hydrodynamical simulations of a supernova-driven interstellar medium (ISM) have low-density paths and voids that allow for ionizing photons from midplane OB stars to reach and ionize gas many kiloparsecs above the midplane. We find that ionizing fluxes throughout our simulation grids are larger than predicted by one-dimensional slab models, thus allowing for photoionization by O stars of low altitude neutral clouds in the Galaxy that are also detected in Hα. In previous studies of such clouds, the photoionization scenario had been rejected and the Hα had been attributed to enhanced cosmic ray ionization or scattered light from midplane H II regions. We do find that the emission measure distributions in our simulations are wider than those derived from Hα observations in the Milky Way. In addition, the horizontally averaged height dependence of the gas density in the hydrodynamical models is lower than inferred in the Galaxy. These discrepancies are likely due to the absence of magnetic fields in the hydrodynamic simulations and we discuss how magnetohydrodynamic effects may reconcile models and observations. Nevertheless, we anticipate that the inclusion of magnetic fields in the dynamical simulations will not alter our primary finding that midplane OB stars are capable of producing high-altitude DIG in a realistic three-dimensional ISM.

LETTER TO THE EDITOR: Observation of photo-double ionization of carbon monoxide below the adiabatic double-ionization potential by threshold-photoelectron - photoelectron coincidence spectroscopy

Science.gov (United States)

Thompson, David B.; Dawber, Grant; Gulley, Nicola; MacDonald, Michael A.; King, George C.

1997-03-01

The production of 0953-4075/30/5/004/img8 and 0953-4075/30/5/004/img9 ion pairs in carbon monoxide at photon energies below the adiabatic double-ionization threshold of 41.25 eV has been probed in a threshold-photoelectron - photoelectron coincidence (TPEPECO) experiment using tunable VUV radiation and a sensitive electron spectrometer. The TPEPECO spectra provide evidence of 0953-4075/30/5/004/img10 production that does not involve creation and dissociation of a molecular dication, but instead results from complete dissociation of a molecular cation followed by autoionization of the atomic oxygen fragment. Furthermore, an electron - electron coincidence signal has been detected at photon energies as low as 36.5 eV, well below the previously measured onset for 0953-4075/30/5/004/img10 production.

Desulfurization of petroleum induced by ionization radiation: benzothiophene behavior

International Nuclear Information System (INIS)

Andrade, Luana S.; Calvo, Wilson A.P.; Duarte, Celina L.

2013-01-01

Hydrodesulfurization (HDS) is currently the most common method used by refineries; this removes significantly sulfur compounds from petroleum fractions, however, is not highly effective for removing thiophene compounds such as benzothiophene, and generates high costs for the oil industry. Another factor, are the environmental laws, which over the years has become increasingly strict, especially regarding the sulfur content. This compound cause incalculable damage both to the industry and to the environment. Therefore new methods for petroleum desulfurization should be studied in order to minimize the impacts that these compounds cause. In the present study it was used ionizing radiation, a promising method of advanced oxidation in reducing sulfur compounds. The analysis were performed after purge and trap concentration of samples, followed by gas chromatography-mass spectrometry (GC-MS). Then benzothiophene samples with the same concentration from 27 mg.L -1 to 139 mg.L -1 were irradiated with different absorbed doses of radiation ranging from 1 kGy to 20 kGy in gamma irradiator Cobalt-60, Gammacell. These samples were analyzed by the same procedure used for the calibration curve, and the removals of benzothiophene after ionizing radiation treatment were calculated. It was observed that at higher doses there was a greater degradation of this compound and the formation of fragments, such as 1,2-dimethylbenzene and toluene, which may be removed by simple processes. (author)

Universal Fragment Descriptors for Predicting Electronic and Mechanical Properties of Inorganic Crystals

Science.gov (United States)

Oses, Corey; Isayev, Olexandr; Toher, Cormac; Curtarolo, Stefano; Tropsha, Alexander

Historically, materials discovery is driven by a laborious trial-and-error process. The growth of materials databases and emerging informatics approaches finally offer the opportunity to transform this practice into data- and knowledge-driven rational design-accelerating discovery of novel materials exhibiting desired properties. By using data from the AFLOW repository for high-throughput, ab-initio calculations, we have generated Quantitative Materials Structure-Property Relationship (QMSPR) models to predict critical materials properties, including the metal/insulator classification, band gap energy, and bulk modulus. The prediction accuracy obtained with these QMSPR models approaches training data for virtually any stoichiometric inorganic crystalline material. We attribute the success and universality of these models to the construction of new materials descriptors-referred to as the universal Property-Labeled Material Fragments (PLMF). This representation affords straightforward model interpretation in terms of simple heuristic design rules that could guide rational materials design. This proof-of-concept study demonstrates the power of materials informatics to dramatically accelerate the search for new materials.

Large scale meta-analysis of fragment-based screening campaigns: privileged fragments and complementary technologies.

Science.gov (United States)

Kutchukian, Peter S; Wassermann, Anne Mai; Lindvall, Mika K; Wright, S Kirk; Ottl, Johannes; Jacob, Jaison; Scheufler, Clemens; Marzinzik, Andreas; Brooijmans, Natasja; Glick, Meir

2015-06-01

A first step in fragment-based drug discovery (FBDD) often entails a fragment-based screen (FBS) to identify fragment "hits." However, the integration of conflicting results from orthogonal screens remains a challenge. Here we present a meta-analysis of 35 fragment-based campaigns at Novartis, which employed a generic 1400-fragment library against diverse target families using various biophysical and biochemical techniques. By statistically interrogating the multidimensional FBS data, we sought to investigate three questions: (1) What makes a fragment amenable for FBS? (2) How do hits from different fragment screening technologies and target classes compare with each other? (3) What is the best way to pair FBS assay technologies? In doing so, we identified substructures that were privileged for specific target classes, as well as fragments that were privileged for authentic activity against many targets. We also revealed some of the discrepancies between technologies. Finally, we uncovered a simple rule of thumb in screening strategy: when choosing two technologies for a campaign, pairing a biochemical and biophysical screen tends to yield the greatest coverage of authentic hits. © 2014 Society for Laboratory Automation and Screening.

On the ultrafast charge migration and subsequent charge directed reactivity in Cl⋯N halogen-bonded clusters following vertical ionization

Energy Technology Data Exchange (ETDEWEB)

Chandra, Sankhabrata; Bhattacharya, Atanu, E-mail: atanub@ipc.iisc.ernet.in [Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore (India); Periyasamy, Ganga [Department of Chemistry, Central College Campus, Bangalore University, Bangalore (India)

2015-06-28

In this article, we have presented ultrafast charge transfer dynamics through halogen bonds following vertical ionization of representative halogen bonded clusters. Subsequent hole directed reactivity of the radical cations of halogen bonded clusters is also discussed. Furthermore, we have examined effect of the halogen bond strength on the electron-electron correlation- and relaxation-driven charge migration in halogen bonded complexes. For this study, we have selected A-Cl (A represents F, OH, CN, NH{sub 2}, CF{sub 3}, and COOH substituents) molecules paired with NH{sub 3} (referred as ACl:NH{sub 3} complex): these complexes exhibit halogen bonds. To the best of our knowledge, this is the first report on purely electron correlation- and relaxation-driven ultrafast (attosecond) charge migration dynamics through halogen bonds. Both density functional theory and complete active space self-consistent field theory with 6-31 + G(d, p) basis set are employed for this work. Upon vertical ionization of NCCl⋯NH{sub 3} complex, the hole is predicted to migrate from the NH{sub 3}-end to the ClCN-end of the NCCl⋯NH{sub 3} complex in approximately 0.5 fs on the D{sub 0} cationic surface. This hole migration leads to structural rearrangement of the halogen bonded complex, yielding hydrogen bonding interaction stronger than the halogen bonding interaction on the same cationic surface. Other halogen bonded complexes, such as H{sub 2}NCl:NH{sub 3}, F{sub 3}CCl:NH{sub 3}, and HOOCCl:NH{sub 3}, exhibit similar charge migration following vertical ionization. On the contrary, FCl:NH{sub 3} and HOCl:NH{sub 3} complexes do not exhibit any charge migration following vertical ionization to the D{sub 0} cation state, pointing to interesting halogen bond strength-dependent charge migration.

Biological effects of low-level ionizing and non-ionizing radiation

International Nuclear Information System (INIS)

Upton, A.C.

1986-01-01

Early in this century it was recognized that large doses of ionizing radiation could injure almost any tissue in the body, but small doses were generally thought to be harmless. By the middle of the century however it came to be suspected that even the smallest doses of ionizing radiation to the gonads might increase the risk of hereditary disease in subsequently-conceived offspring. Since then the hypothesis that carcinogenic and teratogenic effects also have no threshold has been adopted for purposes of radiological protection. It is estimated nevertheless that the risks that may be associated with natural background levels of ionizing irradiation are too small to be detectable. Hence validation of such risk estimates will depend on further elucidation of the dose-effect relationships and mechanisms of the effects in question, through studies at higher dose levels. In contrast to the situation with ionizing radiation, exposure to natural background levels of ultraviolet radiation has been implicated definitively in the etiology of skin cancers in fair-skinned individuals. Persons with inherited effects in DNA repair capacity are particularly susceptible. Non-ionizing radiations of other types can also affect health at high dose levels, but whether they can cause injury at low levels of exposure is not known

Instantaneous characterization of vegetable oils via TAG and FFA profiles by easy ambient sonic-spray ionization mass spectrometry.

Science.gov (United States)

Simas, Rosineide C; Catharino, Rodrigo R; Cunha, Ildenize B S; Cabral, Elaine C; Barrera-Arellano, Daniel; Eberlin, Marcos N; Alberici, Rosana M

2010-04-01

A fast and reliable method is presented for the analysis of vegetable oils. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) is shown to efficiently desorb and ionize the main oil constituents from an inert surface under ambient conditions and to provide comprehensive triacylglyceride (TAG) and free fatty acid (FFA) profiles detected mainly as either [TAG + Na](+) or [FFA-H](-) ions. EASI(+/-)-MS analysis is simple, easily implemented, requires just a tiny droplet of the oil and is performed without any pre-separation or chemical manipulation. It also causes no fragmentation of TAG ions hence diacylglyceride (DAG) and monoacylglyceride (MAG) profiles and contents can also be measured. The EASI(+/-)-MS profiles of TAG and FFA permit authentication and quality control and can be used, for instance, to access levels of adulteration, acidity, oxidation or hydrolysis of vegetable oils in general.

MAGNETOROTATIONAL-INSTABILITY-DRIVEN ACCRETION IN PROTOPLANETARY DISKS

International Nuclear Information System (INIS)

Bai Xuening

2011-01-01

Non-ideal MHD effects play an important role in the gas dynamics in protoplanetary disks (PPDs). This paper addresses the influence of non-ideal MHD effects on the magnetorotational instability (MRI) and angular momentum transport in PPDs using the most up-to-date results from numerical simulations. We perform chemistry calculations using a complex reaction network with standard prescriptions for X-ray and cosmic-ray ionizations. We first show that whether or not grains are included, the recombination time is at least one order of magnitude less than the orbital time within five disk scale heights, justifying the validity of local ionization equilibrium and strong coupling limit in PPDs. The full conductivity tensor at different disk radii and heights is evaluated, with the MRI active region determined by requiring that (1) the Ohmic Elsasser number Λ be greater than 1 and (2) the ratio of gas to magnetic pressure β be greater than β min (Am) as identified in the recent study by Bai and Stone, where Am is the Elsasser number for ambipolar diffusion. With full flexibility as to the magnetic field strength, we provide a general framework for estimating the MRI-driven accretion rate M-dot and the magnetic field strength in the MRI active layer. We find that the MRI active layer always exists at any disk radius as long as the magnetic field in PPDs is sufficiently weak. However, the optimistically predicted M-dot in the inner disk (r = 1-10 AU) appears insufficient to account for the observed range of accretion rates in PPDs (around 10 -8 M sun yr -1 ) even in the grain-free calculation, and the presence of solar abundance sub-micron grains further reduces M-dot by one to two orders of magnitude. Moreover, we find that the predicted M-dot increases with radius in the inner disk where accretion is layered, which would lead to runaway mass accumulation if disk accretion is solely driven by the MRI. Our results suggest that stronger sources of ionization and

Fragment-based drug design.

Science.gov (United States)

Feyfant, Eric; Cross, Jason B; Paris, Kevin; Tsao, Désirée H H

2011-01-01

Fragment-based drug design (FBDD), which is comprised of both fragment screening and the use of fragment hits to design leads, began more than 15 years ago and has been steadily gaining in popularity and utility. Its origin lies on the fact that the coverage of chemical space and the binding efficiency of hits are directly related to the size of the compounds screened. Nevertheless, FBDD still faces challenges, among them developing fragment screening libraries that ensure optimal coverage of chemical space, physical properties and chemical tractability. Fragment screening also requires sensitive assays, often biophysical in nature, to detect weak binders. In this chapter we will introduce the technologies used to address these challenges and outline the experimental advantages that make FBDD one of the most popular new hit-to-lead process.

Fragment informatics and computational fragment-based drug design: an overview and update.

Science.gov (United States)

Sheng, Chunquan; Zhang, Wannian

2013-05-01

Fragment-based drug design (FBDD) is a promising approach for the discovery and optimization of lead compounds. Despite its successes, FBDD also faces some internal limitations and challenges. FBDD requires a high quality of target protein and good solubility of fragments. Biophysical techniques for fragment screening necessitate expensive detection equipment and the strategies for evolving fragment hits to leads remain to be improved. Regardless, FBDD is necessary for investigating larger chemical space and can be applied to challenging biological targets. In this scenario, cheminformatics and computational chemistry can be used as alternative approaches that can significantly improve the efficiency and success rate of lead discovery and optimization. Cheminformatics and computational tools assist FBDD in a very flexible manner. Computational FBDD can be used independently or in parallel with experimental FBDD for efficiently generating and optimizing leads. Computational FBDD can also be integrated into each step of experimental FBDD and help to play a synergistic role by maximizing its performance. This review will provide critical analysis of the complementarity between computational and experimental FBDD and highlight recent advances in new algorithms and successful examples of their applications. In particular, fragment-based cheminformatics tools, high-throughput fragment docking, and fragment-based de novo drug design will provide the focus of this review. We will also discuss the advantages and limitations of different methods and the trends in new developments that should inspire future research. © 2012 Wiley Periodicals, Inc.

Fragmentation of a single molten copper and silver droplets penetrating a sodium pool with solid crust

International Nuclear Information System (INIS)

Wataru Itagaki; Ken-ichiro Sugiyama; Satoshi Nishimura; Izumi Kinoshita

2005-01-01

As a basic study of molten fuel-coolant interaction in liquid metal fast cooled reactors, we carried out a series of experiments for the fragmentation of molten copper droplet penetrating sodium pool at instantaneous contact interface temperatures below its freezing point. A single molten copper droplet with 5g in weight and with superheating varied from 0 degree C to 131 degree C was dropped into a sodium pool in a wide range of ambient Weber numbers 24 to 228. In addition to the experiment of molten copper droplet, molten silver droplet with 5gs in weight and with superheating varied from 3 degree C to 174 degree C was dropped into the sodium pool at an ambient Weber number of about 80. From the observation of the cross section of solidified silver droplet without fragmentation, it was clearly confirmed that sodium micro jet is driven into the inside from the upper surface of molten droplet keeping liquid phase, which is clear evidence for the thermal fragmentation mechanism proposed in the previous paper. Large scattering in the values of dimensionless mass median diameter observed in the present experimental study is recognized to be dependent on whether latent heat instantaneously released due to the injection of sodium micro jet can be effectively utilized for fragmentation. (authors)

Fragmentation of small molecules induced by 46 keV/amu N+ and N2+ projectiles

International Nuclear Information System (INIS)

Kovacs, S.T.S.; Juhasz, Z.; Herczku, P.; Sulik, B.

2012-01-01

Complete text of publication follows. Collisional molecule fragmentation experiments has gain increasing attention in several research and applied fields. In order to understand the fundamental processes of molecule fragmentation one has to start with collisions of small few-atomic molecules. Moreover, fragments of small molecules such as water can cause damages of large molecules (DNA) very effectively in living tissues. In the last few years a new experimental setup was developed at Atomki. It was designed especially for molecule fragmentation experiments. Now the measurements using this system are running routinely. In 2012 the studied targets were water vapor, methane and nitrogen gases, injected into the collision area by an effusive molecular gas jet system. 650 keV N + and 1,3 MeV N 2 + ions were used as projectiles produced by the VdG-5 electrostatic accelerator. The velocity of the two types of projectiles was the same. Energy and angular distribution of the produced fragments was measured by an energy dispersive electrostatic spectrometer. For atomic ionization a symmetric, diatomic molecular projectile (e.g. N 2 + ) yields about twice more electrons compared to those of singly charged ion projectiles of the same atom (N + ) at the same velocity. In such cases the two atomic centers in the molecular ion can be considered as two individual atomic centers. For the fragmentation of molecular targets the picture is not so simple because in this case close collision of two extended systems is investigated. As figure 1 and 2 show, the measured yields for molecular projectile is not simply twice of the ones for atomic projectile. The shape of the energy spectra are different. The measured data are under evaluation. Acknowledgements. This work was supported by the Hungarian National Science Foundation OTKA (Grant: K73703) and by the TAMOP-4.2.2/B-10/1-2010-0024 project. The project is cofinanced by the European Union and the European Social Fund.

Simulation study of the ionizing front in the critical ionization velocity phenomenon

International Nuclear Information System (INIS)

Machida, S.; Goertz, C.K.; Lu, G.

1988-01-01

Simulations of the Critical Ionization Velocity (CIV) for a neutral gas cloud moving across the static magnetic field are made. We treat a low-β plasma and use a 2-1/2 D electrostatic code linked with our Plasma and Neutral Interaction Code (PANIC). Our study is focused on the understanding of the interface between the neutral gas cloud and the surrounding plasma where the strong interaction takes place. We assume the existence of some hot electrons in the ambient plasma to provide a seed ionization for CIV. When the ionization starts a sheath-like structure is formed at the surface of the neutral gas (Ionizing Front). In that region the crossfield component of the electric field causes the electron to E x B drift with a velocity of the order of the neutral gas velocity times the square root of the ion to electron mass ratio. Thus the kinetic energy of the drifting electrons can be large enough for electron impact ionization. In addition a diamagnetic drift of the electron occurs due to the number density and temperature inhomogeneity in the ionization front. These drift currents excite the lower-hybrid waves with the wave k-vectors almost perpendicular to the neutral flow and magnetic field again resulting in electron heating and additional ionization. The overall structure is studied by developing a simple analytic model as well as making simulation runs. (author)

Studies of the wavelength dependence of non-sequential double ionization of xenon in strong fields

International Nuclear Information System (INIS)

Kaminski, P.; Wiehle, R.; Kamke, W.; Helm, H.; Witzele, B.

2005-01-01

Full text: The non-sequential double ionization of noble gases in strong fields is still a process which is not completely understood. The most challenging question is: what is the dominant physical process behind the knee structure in the yield of doubly charged ions which are produced in the focus of an ultrashort laser pulse in dependence of the intensity? Numerous studies can be explained with the so-called rescattering model, where an electron is freed by the strong laser field and then driven back to its parent ion due to the oscillation of the field. Through this backscattering process it is possible to kick out a second electron. However in the low intensity or multiphoton (MPI) region this model predicts that the first electron can not gain enough energy in the oscillating electric field to further ionize or excite the ion. We present experimental results for xenon in the MPI region which show a significant contribution of doubly charged ions. A Ti:sapphire laser system (800 nm, 100 fs) is used to ionize the atoms. The coincident detection of the momentum distribution of the photoelectrons with an imaging spectrometer and the time of flight spectrum of the ions allows a detailed view into the ionization process. For the first time we also show a systematic study of the wavelength dependence (780-830 nm and 1180-1550 nm) on the non-sequential double ionization. The ratio Xe 2+ /Xe + shows a surprising oscillatory behavior with varying wavelength. Ref. 1 (author)

Introduction to ionizing radiation physics

International Nuclear Information System (INIS)

Musilek, L.

1979-01-01

Basic properties are described of the atom, atomic nucleus and of ionizing radiation particles; nuclear reactions, ionizing radiation sources and ionizing radiation interaction with matter are explained. (J.P.)

Collisional ionization

International Nuclear Information System (INIS)

Arnaud, M.

1985-07-01

In low density, thin plasmas (such as stellar coronae, interstellar medium, intracluster medium) the ionization process is governed by collision between electrons and ions in their ground state. In view of the recent improvements we thought an updating of ionization rates was really needed. The work is based on both experimental data and theoretical works and give separate estimates for the direct and autoionization rates

Assessment of fragment projection hazard: probability distributions for the initial direction of fragments.

Science.gov (United States)

Tugnoli, Alessandro; Gubinelli, Gianfilippo; Landucci, Gabriele; Cozzani, Valerio

2014-08-30

The evaluation of the initial direction and velocity of the fragments generated in the fragmentation of a vessel due to internal pressure is an important information in the assessment of damage caused by fragments, in particular within the quantitative risk assessment (QRA) of chemical and process plants. In the present study an approach is proposed to the identification and validation of probability density functions (pdfs) for the initial direction of the fragments. A detailed review of a large number of past accidents provided the background information for the validation procedure. A specific method was developed for the validation of the proposed pdfs. Validated pdfs were obtained for both the vertical and horizontal angles of projection and for the initial velocity of the fragments. Copyright © 2014 Elsevier B.V. All rights reserved.

Dosimetry of ionizing radiation

International Nuclear Information System (INIS)

Musilek, L.; Seda, J.; Trousil, J.

1992-01-01

The publication deals with a major field of ionizing radiation dosimetry, viz., integrating dosimetric methods, which are the basic means of operative dose determination. It is divided into the following sections: physical and chemical effects of ionizing radiation; integrating dosimetric methods for low radiation doses (film dosimetry, nuclear emulsions, thermoluminescence, radiophotoluminescence, solid-state track detectors, integrating ionization dosemeters); dosimetry of high ionizing radiation doses (chemical dosimetric methods, dosemeters based on the coloring effect, activation detectors); additional methods applicable to integrating dosimetry (exoelectron emission, electron spin resonance, lyoluminescence, etc.); and calibration techniques for dosimetric instrumentation. (Z.S.). 422 refs

First successful ionization of Lr (Z = 103) by a surface-ionization technique

Energy Technology Data Exchange (ETDEWEB)

Sato, Tetsuya K., E-mail: sato.tetsuya@jaea.go.jp; Sato, Nozomi; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Ooe, Kazuhiro; Miyashita, Sunao; Schädel, Matthias [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata-shirane, Tokai-mura, Ibaraki 319-1195 (Japan); Kaneya, Yusuke; Nagame, Yuichiro [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata-shirane, Tokai-mura, Ibaraki 319-1195 (Japan); Graduate School of Science and Engineering, Ibaraki University, 2-1-1, Bunkyo, Mito, Ibaraki 310-8512 (Japan); Osa, Akihiko [Department of Research Reactor and Tandem Accelerator, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata shirane, Tokai-mura, Ibaraki 319-1195 (Japan); Ichikawa, Shin-ichi [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata-shirane, Tokai-mura, Ibaraki 319-1195 (Japan); Nishina Center for Accelerator-Based Science, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Stora, Thierry [ISOLDE, CERN, CH-1211 Geneva 23 (Switzerland); Kratz, Jens Volker [Institut für Kernchemie, Universität Mainz, D-55099 Mainz (Germany)

2013-02-15

We have developed a surface ionization ion-source as part of the JAEA-ISOL (Isotope Separator On-Line) setup, which is coupled to a He/CdI{sub 2} gas-jet transport system to determine the first ionization potential of the heaviest actinide lawrencium (Lr, Z = 103). The new ion-source is an improved version of the previous source that provided good ionization efficiencies for lanthanides. An additional filament was newly installed to give better control over its operation. We report, here, on the development of the new gas-jet coupled surface ion-source and on the first successful ionization and mass separation of 27-s {sup 256}Lr produced in the {sup 249}Cf + {sup 11}B reaction.

Design of a picosecond-laser-driven Ni-like Mo x-ray laser near 20 nm

International Nuclear Information System (INIS)

Nilsen, J.

1997-01-01

The gain is predicted for a solid molybdenum target illuminated by several joules of combined energy from a nanosecond laser pulse to create a preplasma followed by a picosecond laser pulse to drive the gain. Gains greater than 300cm -1 are predicted for the Ni-like Mo 4d 1 S 0 →4p 1 P 1 transition at 18.9 nm, which is driven by the monopole collisional excitation. High gain is also predicted for a self-photo-pumped 4f 1 P 1 →4d 1 P 1 transition at 22.0 nm and several other transitions driven by inner shell collisional ionization. copyright 1997 Optical Society of America

Fragmentation in the branching coral Acropora palmata (Lamarck): growth, survivorship, and reproduction of colonies and fragments.

Science.gov (United States)

Lirman

2000-08-23

Acropora palmata, a branching coral abundant on shallow reef environments throughout the Caribbean, is susceptible to physical disturbance caused by storms. Accordingly, the survivorship and propagation of this species are tied to its capability to recover after fragmentation. Fragments of A. palmata comprised 40% of ramets within populations that had experienced recent storms. While the survivorship of A. palmata fragments was not directly related to the size of fragments, removal of fragments from areas where they settled was influenced by size. Survivorship of fragments was also affected by type of substratum; the greatest mortality (58% loss within the first month) was observed on sand, whereas fragments placed on top of live colonies of A. palmata fused to the underlying tissue and did not experience any losses. Fragments created by Hurricane Andrew on a Florida reef in August 1992 began developing new growth (proto-branches) 7 months after the storm. The number of proto-branches on fragments was dependent on size, but growth was not affected by the size of fragments. Growth-rates of proto-branches increased exponentially with time (1.7 cm year(-1) for 1993-1994, 2.7 cm year(-1) for 1994-1995, 4.2 cm year(-1) for 1995-1996, and 6.5 cm year(-1) for 1996-1997), taking over 4 years for proto-branches to achieve rates comparable to those of adult colonies on the same reef (6.9 cm year(-1)). In addition to the initial mortality and reduced growth-rates, fragmentation resulted in a loss of reproductive potential. Neither colonies that experienced severe fragmentation nor fragments contained gametes until 4 years after the initial damage. Although A. palmata may survive periodic fragmentation, the long-term effects of this process will depend ultimately on the balance between the benefits and costs of this process.

Plasminogen fragments K 1-3 and K 5 bind to different sites in fibrin fragment DD.

Science.gov (United States)

Grinenko, T V; Kapustianenko, L G; Yatsenko, T A; Yusova, O I; Rybachuk, V N

2016-01-01

Specific plasminogen-binding sites of fibrin molecule are located in Аα148-160 regions of C-terminal domains. Plasminogen interaction with these sites initiates the activation process of proenzyme and subsequent fibrin lysis. In this study we investigated the binding of plasminogen fragments K 1-3 and K 5 with fibrin fragment DD and their effect on Glu-plasminogen interaction with DD. It was shown that the level of Glu-plasminogen binding to fibrin fragment DD is decreased by 50-60% in the presence of K 1-3 and K 5. Fragments K 1-3 and K 5 have high affinity to fibrin fragment DD (Kd is 0.02 for K 1-3 and 0.054 μМ for K 5). K 5 interaction is independent and K 1-3 is partly dependent on C-terminal lysine residues. K 1-3 interacts with complex of fragment DD-immobilized K 5 as well as K 5 with complex of fragment DD-immobilized K 1-3. The plasminogen fragments do not displace each other from binding sites located in fibrin fragment DD, but can compete for the interaction. The results indicate that fibrin fragment DD contains different binding sites for plasminogen kringle fragments K 1-3 and K 5, which can be located close to each other. The role of amino acid residues of fibrin molecule Аα148-160 region in interaction with fragments K 1-3 and K 5 is discussed.

Fractal statistics of brittle fragmentation