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Sample records for 2p ionization threshold

  1. Autoionization study of the Argon 2p satellites excited near the argon 2s threshold

    SciTech Connect

    Wang, H.; Glans, P.; Hemmers, O.

    1997-04-01

    The dynamics of near-threshold photoionization is a complex phenomenon in which the many-electron character of the wavefunctions plays an important role. According to generalized time-independent resonant scattering theory, the transition matrix element from an initial state to a final state is the summation of the amplitudes of direct photoionization and an indirect term in which intermediate states are involved and the resonant behavior is embedded. Studies of the interference effects of intermediate states have been explored in the cases where the direct term is negligible. In the present work, electron time-of-flight spectra of the Ar 2p satellites were measured at two angles (magic and 0{degrees}) in the dipole plane with the exciting photon energy tuned in the vicinity of the Ar 2s threshold. For excitation far below or above the 2s threshold, the 2p satellites spectrum is dominated by 3p to np shakeup contributions upon the ionization of a 2p electron.

  2. Mass Analyzed Threshold Ionization of Lutetium Dimer

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Roudjane, Mourad; Liu, Yang; Yang, Dong-Sheng

    2013-06-01

    Lu_2 is produced in a pulsed laser-vaporization metal-cluster source and studied by mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectrum displays several long progressions from the transitions between various vibrational levels of the neutral and ion electronic states. From the spectrum, the upper limit of the ionization energy of the dimer is determined to be 43996 cm^{-1}, and the vibrational frequencies are measured to be 121 cm^{-1} in the neutral state and 90 cm^{-1} in the ion state. By combining with ab initio calculations at CASPT2 level, the ground state of Lu_2 is identified as ^3Σ_g^-. The ^3Σ_g^- state has an electron configuration of 6sσ_g^25dπ_u^15dπ_u^16sσ_u^2, which is formed by the interactions of two Lu atoms in the ^2D(5d6s^2) ground state. Ionization of the neutral state removes a 5dπ_u bonding electron and yields a ion state with a considerably longer bond distance. Lu_2 has a very different bonding feature from La_2, for which a ^1Σ_g^+ ground state was previously identified with an electron configuration of 5dπ_u^46sσ_g^2 formed by the interactions of two La atoms in the ^4F(5d^26s) excited state. Yang Liu, Lu Wu, Chang-Hua Zhang, Serge A. Krasnokutski, and Dong-Sheng Yang, J. Chem. Phys. 135, 034309 (2011).

  3. Mass analyzed threshold ionization (MATI) with VUV radiation

    NASA Astrophysics Data System (ADS)

    Kostko, Oleg; Kim, Sang Kyu; Wilson, Kevin R.; Leone, Stephen R.; Ahmed, Musahid

    2009-05-01

    Mass analyzed threshold ionization is a combination of threshold ionization spectroscopy with mass spectrometry. Similar to zero electron kinetic energy (ZEKE), MATI spectroscopy takes advantage of the field ionization of long lived high Rydberg states to obtain an ionization threshold and perform spectroscopy on the resulting cation. MATI at the synchrotron utilizing tunable VUV light opens up a novel way to perform spectroscopy on ions and improve the resolution in ionization energy determination in comparison with conventional photoionization efficiency curve measurements. This method is implemented at the Advanced Light Source and vibrationally-resolved MATI spectra for simple di- and polyatomic molecules (O2, N2, H2O, N2O, C2H2, and C6H6) are measured. This preliminary work allows us to test the applicability of MATI at a synchrotron and prepare for investigation of more complex systems such as mixtures of molecules, isomers and clusters.

  4. Resonant effects in above-threshold ionization

    NASA Astrophysics Data System (ADS)

    Hertlein, Marcus P.

    2000-09-01

    The ionization of noble gases in high intensity laser fields produces an electron spectrum with characteristic peaks corresponding to atomic levels of the atom. While many of the features in the low energy part of the spectrum have been explained qualitatively, current models are incomplete and are not able to account for the recurrence of ionization probability for higher energy electrons. In particular, one of the basic questions arising is the importance of multiple ionization in these spectra. While the light intensities are in the regime where multiple ionization is known to occur, it was not clear whether the higher energy (or plateau) electrons are a result of this, and whether multiple ionization even leaves a signature in the electron spectrum. In this dissertation, we use several experimental techniques to explore this problem in argon. Our results show that although multiple ionization occurs, electrons from this process do not appear in the observed electron spectrum. Furthermore, the appearance intensities of the peaks visible in the plateau region of the electron spectrum and of the resonance peaks in the well- understood low energy part show a strong correlation, suggestion a common origin of production. Accurate computer simulations of the process, using a single- active-electron model, reproduce all essential features of the experimental spectra. Our results support the conclusion that all high energy electrons observed in our experiments can be explained with single-electron effects.

  5. Above-threshold ionization by chirped laser pulses

    SciTech Connect

    Nakajima, Takashi

    2007-05-15

    We theoretically investigate above-threshold ionization by chirped laser pulses. By comparing the photoelectron energy spectra and the photoelectron angular distributions of Na for the laser pulses with different chirp rates but with the identical spectral profile, we find that the ionization processes have a clear dependence on the chirp rate. Further calculations without excited bound states during the time propagation of the wave function reveal practically no chirp dependence, which is clear evidence that the origin of the chirp dependence in above-threshold ionization is the excited bound states.

  6. Satellite lines at the ionization threshold in charge transfer systems

    NASA Astrophysics Data System (ADS)

    Wardermann, W.; von Niessen, W.

    1992-01-01

    This article deals with the possibility of low-energy ionizations of reduced intensity for larger organic molecules. Possible mechanisms which may lead to this phenomenon are outlined and the necessary structural features are discussed. The lowest ionization energies of some organic unsaturated nitro and nitroso compounds are calculated by the ADC(3) ab initio many-body Green's function method. The π-electron system consists either of fused five- and six-membered rings or of two fused five-membered rings with a variable number of heteroatoms. Some of the molecules contain exocylic double bonds and some are substituted with the donor groups -NH 2, -OH and -NHOH. The strongest many-body effects are found for the nitroso compounds, where in one case the spectral line at the ionization threshold has lost more than 40% of its intensity to satellites. We study the many-body effects at or close to the ionization threshold for these compounds. A particular mechanism which involves the screening of localized valence holes by charge transfer excitations appears to be capable of influencing the profile and intensities of the ionization spectrum already at the ionization threshold. The effect leads to strongly reduced relative intensities of the bands and may cause the appearance of satellite bands nearly at the ionization threshold. The spectral changes in the outermost valence region are discussed by using a simple model calculation in terms of ground-state electronic properties of the molecules.

  7. Mass analyzed threshold ionization spectroscopy of p-fluorostyrene

    NASA Astrophysics Data System (ADS)

    Georgiev, S.; Neusser, H. J.; Chakraborty, Tapas

    2004-05-01

    Adiabatic ionization energy (AIE) and two-color threshold ion vibrational spectra of p-fluorostyrene have been measured by mass analyzed threshold ionization (MATI) method via three different intermediate levels in the first excited state, vibrationless S1 origin, 421411, and 231 vibronic levels. Features of the ion vibrational spectra indicates that the geometry of the molecular ion including the conformation of the vinyl chain in the ionic ground state (D0) is almost identical to that of its neutral ground state (S0), and ionization has very little effect on the vibrational potentials of the aromatic ring modes. Comparison of the AIE with the reported value of styrene shows that fluorination at the para position of the aromatic ring has little effect on energy of the electron ejected in ionization process from the styrene chromophore.

  8. Ionization energy of acetone by vacuum ultraviolet mass-analyzed threshold ionization spectrometry

    NASA Astrophysics Data System (ADS)

    Kim, Jae Han; Kang, Do Won; Hong, Yong Jun; Hwang, Hyonseok; Kim, Hong Lae; Kwon, Chan Ho

    2013-04-01

    Mass-analyzed threshold ionization (MATI) time-of-flight mass spectrometer using coherent vacuum ultraviolet (VUV) laser generated by four-wave difference frequency mixing (FWDFM) in Kr has been constructed and utilized to obtain the accurate ionization energy of acetone. From the MATI onsets measured from various applied pulsed fields, the ionization energy to the ionic ground state of acetone has been determined to be 9.7074 ± 0.0019 eV.

  9. Mass analyzed threshold ionization spectroscopy of indazole cation

    NASA Astrophysics Data System (ADS)

    Su, Huawei; Pradhan, Manik; Tzeng, Wen Bih

    2005-08-01

    We have recorded the two-color resonant two-photon mass analyzed threshold ionization (MATI) spectra of indazole via four intermediate states. The adiabatic ionization energy of this molecule is determined to be 67 534 ± 5 cm -1. The observed MATI bands include in-plane ring bending as well as out-of-plane ring twisting and bending vibrations of the indazole cation. Comparing the present data with those of indole and 7-azaindole leads to a better understanding about the influence of the nitrogen atom in the aza-aromatic bicyclic system.

  10. Threshold behavior of e-H ionizing collisions.

    PubMed

    Bartlett, Philip L; Stelbovics, Andris T

    2004-12-03

    We present accurate ab initio numerical solutions of the full Schrödinger equation for the electron-impact ionization of hydrogen near threshold using the propagating exterior complex scaling method. They provide strong support for the Wannier threshold law [Phys. Rev. 90, 817 (1953)], giving sigma proportional to E(1.122+/-0.015), and also give the energy dependence of the electrons' angular distribution as (pi-theta12) FWHM approximately 3.0E(1/4), in general agreement with classical and semiclassical predictions.

  11. Mass analyzed threshold ionization spectroscopy of 7-azaindole cation

    NASA Astrophysics Data System (ADS)

    Lee Lin, Jung; Tzeng, Wen Bih

    2003-10-01

    The vibrationally resolved mass analyzed threshold ionization (MATI) spectra of jet-cooled 7-azaindole have been recorded by ionizing via four different intermediate levels. The adiabatic ionization energy of this molecule is determined to be 65 462±5 cm -1, which is greater than that of indole by 2871 cm -1. The vibrational spectra of 7-azaindole in the S 1 and D 0 states have been successfully assigned by comparing the measured frequencies with those of indole as well as the predicted values from the ab initio calculations. Detailed analysis on the MATI spectra shows that the structure of the cation is somewhat different from that of this species in the neutral S 1 state.

  12. Mass-Analyzed Threshold Ionization of LaO2

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Zhang, Changhua; Krasnokutski, Sergiy; Yang, Dong-Sheng

    2010-06-01

    Lanthanum oxide, LaO2, is produced in a pulsed laser-vaporization metal-cluster source and studied by mass-analyzed threshold ionization (MATI) spectroscopy. From the MATI spectrum, the adiabatic ionization energy of LaO2 is determined to be 40134 (5) Cm-1 or 4.976 (6) eV, and La+-O stretching and O-La+-O bending frequencies are measured as 656 and 120 Cm-1. The measured ionization energy is about 3.0 eV lower than the value predicted by recent high-level ab initio calculations. In this talk, we will discuss the discrepancy between the experiment and theory and the electronic transition observed in our experiment. T. K. Todorova, I. Infante, L. Gagliardi, and J. M. Dyke, J. Phys. Chem. A 112, 7825 (2008).

  13. Ionization Thresholds of Small Carbon Clusters: Tunable VUVExperiments and Theory

    SciTech Connect

    Belau, Leonid; Wheeler, Steven E.; Ticknor, Brian W.; Ahmed,Musahid; Leone, Stephen R.; Allen, Wesley D.; Schaefer III, Henry F.; Duncan, Michael A.

    2007-07-31

    Small carbon clusters (Cn, n = 2-15) are produced in amolecular beam by pulsed laser vaporization and studied with vacuumultraviolet (VUV) photoionization mass spectrometry. The required VUVradiation in the 8-12 eV range is provided by the Advanced Light Source(ALS) at the Lawrence Berkeley National Laboratory. Mass spectra atvarious ionization energies reveal the qualitative relative abundances ofthe neutral carbon clusters produced. By far the most abundant species isC3. Using the tunability of the ALS, ionization threshold spectra arerecorded for the clusters up to 15 atoms in size. The ionizationthresholds are compared to those measured previously with charge-transferbracketing methods. To interpret the ionization thresholds for differentcluster sizes, new ab initio calculations are carried out on the clustersfor n = 4-10. Geometric structures are optimized at the CCSD(T) levelwith cc-pVTZ (or cc-pVDZ) basis sets, and focal point extrapolations areapplied to both neutral and cation species to determine adiabatic andvertical ionization potentials. The comparison of computed and measuredionization potentials makes it possible to investigate the isomericstructures of the neutral clusters produced in this experiment. Themeasurements are inconclusive for the n = 4-6 species because ofunquenched excited electronic states. However, the data provide evidencefor the prominence of linear structures for the n = 7, 9, 11, 13 speciesand the presence of cyclic C10.

  14. A study to control chemical reactions using Si:2p core ionization: site-specific fragmentation.

    PubMed

    Nagaoka, Shin-ichi; Fukuzawa, Hironobu; Prümper, Georg; Takemoto, Mai; Takahashi, Osamu; Yamaguchi, Katsuhiro; Kakiuchi, Takuhiro; Tabayashi, Kiyohiko; Suzuki, Isao H; Harries, James R; Tamenori, Yusuke; Ueda, Kiyoshi

    2011-08-18

    In an aim to create a "sharp" molecular knife, we have studied site-specific fragmentation caused by Si:2p core photoionization of bridged trihalosilyltrimethylsilyl molecules in the vapor phase. Highly site-specific bond dissociation has been found to occur around the core-ionized Si site in some of the molecules studied. The site specificity in fragmentation and the 2p binding energy difference between the two Si sites depend in similar ways on the intersite bridge and the electronegativities of the included halogen atoms. The present experimental and computational results show that for efficient "cutting" the following conditions for the two atomic sites to be separated by the knife should be satisfied. First, the sites should be located far from each other and connected by a chain of saturated bonds so that intersite electron migration can be reduced. Second, the chemical environments of the atomic sites should be as different as possible.

  15. Mass analyzed threshold ionization (MATI) spectroscopy of p-cresol

    NASA Astrophysics Data System (ADS)

    Shirhatti, P. R.; Wategaonkar, S.

    2012-03-01

    Experimental setup was developed for carrying out the mass analyzed threshold ionization (MATI) spectroscopy. Primary objective has been to carry out the vibronic spectroscopy of the novel hydrogen bonded complexes in the cationic state. To this end MATI spectroscopy is best suited for the purpose. This work presents the successful implementation of the same using p-cresol as a test case. This happens to be the prime substrate in most of our studies on weakly hydrogen bonded complexes that are dominated by the dispersion interaction contrary to the electrostatic nature of the conventional hydrogen bonds. The adiabatic ionization potential of p-cresol was determined as 65,904 ± 10 cm-1 which is in good agreement with the previously reported value. The MATI spectrum also shows a few vibronic bands of p-cresol cation.

  16. Rings in above-threshold ionization: A quasiclassical analysis

    SciTech Connect

    Lewenstein, M.; Kulander, K.C.; Schafer, K.J.; Bucksbaum, P.H. Centrum Fizyki Teoretycznej, Polska Akademia Nauk, Warszawa 02-668 Theoretical Atomic and Molecular Physics , Physics Department, Lawrence Livermore National Laboratory, Livermore, California 94550 Physics Department and Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109-1120 )

    1995-02-01

    A generalized strong-field approximation is formulated to describe atoms interacting with intense laser fields. We apply it to determine angular distributions of electrons in above-threshold ionization (ATI). The theory treats the effects of an electron rescattering from its parent ion core in a systematic perturbation series. Probability amplitudes for ionization are interpreted in terms of quasiclassical electron trajectories. We demonstrate that contributions from the direct tunneling processes in the absence of rescattering are not sufficient to describe the observed ATI spectra. We show that the high-energy portion of the spectrum, including recently discovered rings (i.e., complex features in the angular distributions of outgoing electrons) are due to rescattering processes. We compare our quasiclassical results with exact numerical solutions.

  17. Interference structure of above-threshold ionization versus above-threshold detachment

    NASA Astrophysics Data System (ADS)

    Korneev, Ph A.; Popruzhenko, S. V.; Goreslavski, S. P.; Becker, W.; Paulus, G. G.; Fetić, B.; Milošević, D. B.

    2012-05-01

    Laser-induced electron detachment or ionization of atoms and negative ions is considered. In the context of the saddle-point evaluation of the strong-field approximation (SFA), the velocity maps of the direct electrons (those that do not undergo rescattering) exhibit a characteristic structure due to the constructive and destructive interference of electrons liberated from their parent atoms/ions within certain windows of time. This structure is defined by the above-threshold ionization rings at fixed electron energy and by two sets of curves in momentum space on which destructive interference occurs. The spectra obtained with the SFA are compared with those obtained by numerical solution of the time-dependent Schrödinger equation. For detachment, the agreement is excellent. For ionization, the effect of the Coulomb field is most pronounced for electrons emitted in a direction close to laser polarization, while for near-perpendicular emission the qualitative appearance of the spectrum is unaffected.

  18. Polarization asymmetry in two-electron photodetachment - A cogent test of the ionization threshold law

    NASA Technical Reports Server (NTRS)

    Temkin, A.; Bhatia, A. K.

    1988-01-01

    A very sensitive test of the electron-atom ionization threshold law is suggested: for spin-aligned heavy negative ions it consists of measuring the polarization asymmetry A(PA) coming from double detachment by left- versus right-circularly polarized light. The respective yields are worked out for the Te(-) (5p)5 2P(3/2) ion. The Coulomb-dipole theory predicts A(PA) to be the ratio of two oscillating functions in sharp contrast to any power law (specifically that of Wannier, 1953) for which the ratio is expected to be a smooth function of energy.

  19. Interference oscillations in the angular distribution of laser-ionized electrons near ionization threshold.

    PubMed

    Arbó, D G; Yoshida, S; Persson, E; Dimitriou, K I; Burgdörfer, J

    2006-04-14

    We analyze the two-dimensional momentum distribution of electrons ionized by few-cycle laser pulses in the transition regime from multiphoton absorption to tunneling by solving the time-dependent Schrödinger equation and by a classical-trajectory Monte-Carlo simulation with tunneling (CTMC-T). We find a complex two-dimensional interference pattern that resembles above threshold ionization (ATI) rings at higher energies and displays Ramsauer-Townsend-type diffraction oscillations in the angular distribution near threshold. CTMC-T calculations provide a semiclassical explanation for the dominance of selected partial waves. While the present calculation pertains to hydrogen, we find surprising qualitative agreement with recent experimental data for rare gases [A. Rudenko, J. Phys. B 37, L407 (2004)].

  20. Above-threshold ionization in two electromagnetic fields

    NASA Astrophysics Data System (ADS)

    Bardfield, Rina Shoshana

    1997-11-01

    Above-threshold ionization (ATI) is a process in which a target atom absorbs more than the minimum number of photons from an applied electromagnetic field than are required for ionization, and is characterized by several peaks in the photoelectron spectrum which are separated from each other by the energy of a single photon (Agostini et al. 1979). The experiments of interest in this work involve ATI at microwave frequencies (Gallagher 1988, Gallagher and Scholz 1989), where the frequency of the field is too low to be able to see individual peaks in the spectrum. What is seen is that, in the presence of a weak assisting field, a very large number of microwave photons are absorbed. This problem cannot be treated using standard methods, due both to the intensity of the microwave field and to the large numbers of photons absorbed. The focus of this work is on the development of new analytical techniques to examine the interaction of an atomic system with two simultaneous electromagnetic fields. Specifically, the work focuses on above-threshold ionization in combined microwave and laser fields, where the microwave field is a very strong, very low frequency field, so that standard techniques, such as perturbation theory, do not apply. The work is based on two theoretical methods especially designed for use in intense field problems. These are the Strong Field Approximation (SFA) (Reiss 1980, 1992, 1996), which describes the ionization of an atom by an intense field in which the detached electron remains free in the field after ionization occurs, and the Momentum Translation Approximation (MTA) (Reiss 1970a, 1970b, 1989), which describes the dressing of a bound atomic state by a strong field in which the field can alter the state of the electron without necessarily causing transitions. The laser field, which is much weaker, is treated by traditional techniques. The theory is developed in general terms using S-matrix methods, with particular cases being modeled using

  1. A theoretical analysis on the vibronic spectra with mass analyzed threshold ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Chao, Sheng D.; Peng, Hsin Y.

    2008-01-01

    We have theoretically studied the absorption vibronic spectra with the resonance two-photon (R2P) and non-resonance two-photon (NR2P) mass analyzed threshold ionization (MATI) spectroscopy. The theory uses the inverse Born-Oppenheimer approximation (IBOA) to establish a proper basis set. To analyze the MATI vibronic spectra, we have calculated the Franck-Condon factors involved in the vibronic transitions. Several experimental spectra are analyzed using this theory with emphasis on the importance of the resonance intermediate states. The long vibrational progression in a MATI spectrum can be partly attributed to the result of including the anharmonic correction in the calculated Franck-Condon factors. The experimentally observed isotope effect is also analyzed.

  2. Effects of plasma microfields on radiative transitions from atomic levels above the ionization threshold

    NASA Technical Reports Server (NTRS)

    Davis, J.; Jacobs, V. L.

    1975-01-01

    The effects of plasma electric microfields on line-like optical features arising from atomic levels above the ionization threshold are investigated within the framework of the quasi-static and single-frequency dynamic-field theories of spectral-line broadening. The 2p(23)P to 1s2p(3)P and 2s2p(3)P to 1s2s(3)S transitions in helium and helium-like ions are treated as examples. The mixing of the doubly excited levels in the perturbing microfields produces Stark broadening of the emission lines and induces autoionization of the 2p(23)P level, which, unlike the 2s2p(3)P level, is metastable against autoionization in the field-free environment. Determination of the complete Stark-broadening profiles in thermal plasmas is complicated by the need to include the effects of both the (quasi-static) ion and the (dynamic) electron fields. Under nonequilibrium conditions, where electric fields from either electron or ion plasma waves can far exceed nearby particle fields, the calculation and interpretation of the line shapes may be simplified and could provide a diagnostic probe of the wave-field properties.

  3. Threshold electron attachment and electron impact ionization involving oxygen dimers

    NASA Astrophysics Data System (ADS)

    Kreil, J.; Ruf, M.-W.; Hotop, H.; Ettischer, I.; Buck, U.

    1998-12-01

    Using two different crossed-beams machines we have carried out the first quantitative study of threshold electron attachment and electron impact-induced ionization and fragmentation involving oxygen dimers (O 2) 2. In the electron attachment experiment we study electron transfer from state-selected Ar **(20d) Rydberg atoms to O 2 molecules and dimers in a skimmed supersonic beam at variable nozzle temperatures ( T0) and stagnation pressures ( p0). The relative dimer density is determined through measurements of Penning ionization by metastable Ne *(3s 3P2,0) atoms and used to estimate the absolute cross-section for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 dimers to be nearly 10 -17 m 2, almost four orders of magnitude larger than that for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 monomers. The fragmentation of the oxygen cluster beam is quantitatively characterized by the transverse helium beam scattering method which allows us to spatially separate different clusters. It is shown that in 70 eV electron impact of (O 2) 2 only 3.6(4)% of the dimers are detected as dimer ions (O 2) 2+. In additional experiments involving SF 6 clusters we show that SF 6 dimers fragment nearly completely upon 70 eV electron impact, yielding SF 5+ ions (probability for (SF 6)·SF 5+ production at most 0.3%).

  4. Above-threshold ionization through Rydberg state population

    NASA Astrophysics Data System (ADS)

    Xin, Pei Pei; Yuan, Ming Hu; Wang, Han Mu; Yang, Hai Feng; Liu, Hong Ping

    2017-04-01

    We present a theoretical scenario for the atomic above-threshold ionization (ATI) in an intense laser field by investigating the Rydberg state population in real time. Rather than merely viewing the final distribution of photoelectron yield directly, we monitor the Rydberg state population by projecting the time-dependent wave function onto the bound eigen-states. The calculation shows that the population of resonant Rydberg states is closely related to the peaks in photoelectron kinetic energy spectrum (PKES). For a hydrogen atom, the highest populated Rydberg states are degenerated, exactly corresponding to the first ATI peak if one additional photon is absorbed. While for non-hydrogen atoms, e.g., Ar, the highest Rydberg states are mainly populated on specific states, e.g., 3 d (5 s) and 4f in our case, also giving exact peak positions in PKES, where the state identification is obtained by the angular momentum resolved distribution of excited Rydberg states. This method provides an easy to understand picture for the resonance-enhanced effects in ATI as well as the role of atomic core potential in strong-field ionization.

  5. The Cryogenic Dark Matter Search low ionization-threshold experiment

    SciTech Connect

    Basu Thakur, Ritoban

    2014-01-01

    Over 80 years ago we discovered the presence of Dark Matter in our universe. Endeavors in astronomy and cosmology are in consensus with ever improving precision that Dark Matter constitutes an essential 27% of our universe. The Standard Model of Particle Physics does not provide any answers to the Dark Matter problem. It is imperative that we understand Dark Matter and discover its fundamental nature. This is because, alongside other important factors, Dark Matter is responsible for formation of structure in our universe. The very construct in which we sit is defined by its abundance. The Milky Way galaxy, hence life, wouldn't have formed if small over densities of Dark Matter had not caused sufficient accretion of stellar material. Marvelous experiments have been designed based on basic notions to directly and in-directly study Dark Matter, and the Cryogenic Dark Matter Search (CDMS) experiment has been a pioneer and forerunner in the direct detection field. Generations of the CDMS experiment were designed with advanced scientific upgrades to detect Dark Matter particles of mass O(100) GeV/c2. This mass-scale was set primarily by predictions from Super Symmetry. Around 2013 the canonical SUSY predictions were losing some ground and several observations (rather hints of signals) from various experiments indicated to the possibility of lighter Dark Matter of mass O(10) GeV/c2. While the SuperCDMS experiment was probing the regular parameter space, the CDMSlite experiment was conceived to dedicatedly search for light Dark Matter using a novel technology. "CDMSlite" stands for CDMS - low ionization threshold experiment. Here we utilize a unique electron phonon coupling mechanism to measure ionization generated by scattering of light particles. Typically signals from such low energy recoils would be washed under instrumental noise. In CDMSlite via generation of Luke-Neganov phonons we can detect the small ionization energies, amplified in phonon

  6. Mass-Analyzed Threshold Ionization Spectroscopy of 2-Phenylethanol: Probing of Conformational Changes Caused by Ionization

    NASA Astrophysics Data System (ADS)

    Georgiev, S.; Karaminkov, R.; Chervenkov, S.; Delchev, V.; Neusser, H. J.

    2009-10-01

    The vibrational structure of the ionic ground state of different conformers of the biologically relevant molecule 2-phenylethanol has been investigated by combination of two-photon two-color mass-analyzed threshold ionization spectroscopy (MATI) and quantum chemical calculations at M05, MP2, and coupled cluster (CC) levels of theory with extended basis sets. MATI spectra recorded via gauche vibronic bands are with poor structure and increasing background, whereas the ones measured via vibronic bands of the anti conformers feature well-resolved vibronic structure in the cation. Ab initio computations predict three stable conformers for the 2-phenylethanol cation out of five initial neutral structures. None of the theoretical structures in the cation features a nonclassical OH···π hydrogen bond in conjunction with the analysis of the MATI spectra. This provides clear evidence that the OH···π hydrogen bond stabilizing the lowest-energy gauche conformer in the neutral breaks upon ionization.

  7. The effect of conformation on the ionization energetics of n-butylbenzene. I. A threshold ionization study

    NASA Astrophysics Data System (ADS)

    Tong, Xin; Ford, Mark S.; Dessent, Caroline E. H.; Müller-Dethlefs, Klaus

    2003-12-01

    Conformational isomers of the aromatic hydrocarbon n-butylbenzene have been studied using two-color REMPI (resonance enhanced multiphoton ionization) and MATI (mass analyzed threshold ionization) spectroscopy to explore the effect of conformation on ionization dynamics. Gauche- and anti-cationic conformers were selectively produced by two-color excitation via the respective S1 origins. Adiabatic ionization potentials of the gauche- and anti-conformations were determined to be 70 148 and 69 955±5 cm-1, respectively. Analysis of the REMPI and MATI spectra allowed the determination of the S0 (38 cm-1), S1 (100 cm-1), and D0 (-155 cm-1) gauche- and anti-conformer energy differences. Spectral features and vibrational modes are interpreted with the aid of MP2/cc-pVDZ ab initio calculations, and ionization-induced changes in the molecular conformations discussed.

  8. Rydberg-resolved resonant inelastic soft x-ray scattering: dynamics at core ionization thresholds.

    PubMed

    Rubensson, J-E; Söderström, J; Binggeli, C; Gråsjö, J; Andersson, J; Såthe, C; Hennies, F; Bisogni, V; Huang, Y; Olalde, P; Schmitt, T; Strocov, V N; Föhlisch, A; Kennedy, B; Pietzsch, A

    2015-04-03

    Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.

  9. On the turbulent heating and the threshold condition in the critical ionization velocity interaction

    NASA Technical Reports Server (NTRS)

    Moebius, E.; Papadopoulos, K.; Piel, A.

    1987-01-01

    On the basis of the nonlinear treatment of the ion beam instability and the modified two-stream instability, threshold conditions for the critical ionization velocity interaction are derived. There are three different regimes of interaction: (1) additional ionization for relative velocities smaller than the critical velocity, (2) the self-sustained discharge for velocities greater than the critical velocity which indeed turns out as a sharp threshold, and (3) an explosive growth regime for velocities exceeding 1.5 times the critical velocity. Additional charge exchange collisions of ions and energy loss of electrons due to excitation do not change the basic threshold behavior but modify the value of the critical velocity.

  10. Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of methylcyclohexane in the supersonic jet

    NASA Astrophysics Data System (ADS)

    Han, Songhee; Yoo, Hyun Sik; Ahn, Doo-Sik; Choi, Young S.; Kim, Sang Kyu

    2011-12-01

    Vacuum ultraviolet (VUV) mass-analyzed threshold ionization (MATI) spectrum of supersonically cooled methylcyclohexane has been obtained to give the precise adiabatic ionization energy of 9.6958 ± 0.0025 eV for the chair equatorial conformer. Vibrationally resolved MATI spectrum has been analyzed with the aid of density functional theory and Franck-Condon calculations. The MATI spectrum reflects the structural change upon ionization and its origin is discussed by inspecting the shapes of the valence orbitals involved in the ionization process. The spectroscopic implication of the structural interconversion above the certain energy level is discussed with theoretical calculations of molecular structures and energetics.

  11. Adiabatic theory of Wannier threshold laws and ionization cross sections

    SciTech Connect

    Macek, J.H.; Ovchinnikov, S.Yu.

    1994-12-31

    The Wannier threshold law for three-particle fragmentation is reviewed. By integrating the Schroedinger equation along a path where the reaction coordinate R is complex, anharmonic corrections to the simple power law are obtained. These corrections are found to be non-analytic in the energy E, in contrast to the expected analytic dependence upon E.

  12. Transitions of the type 2s-2p in highly ionized Cu, Zn, Ga, and Ge

    NASA Technical Reports Server (NTRS)

    Behring, W. E.; Cohen, L.; Seely, J. F.; Feldman, U.; Goldsmith, S.; Richardson, M.

    1985-01-01

    Transitions of the type 2s-2p in the F I, O I, N I, and C I isoelectronic sequences of copper, zinc, gallium, and germanium have been identified in the spectra from plasmas produced by the Omega laser system at the University of Rochester. The wavelengths are in the range 50 to 112 A and are measured using silicon and oxygen lines as wavelength standards for gallium and using several lines from the F I, O I, and Na I isoelectronic sequences as wavelength standards for copper, zinc, and germanium. The energy levels that are determined from the measured wavelengths are also presented. Based on these measurements, the wavelengths for a number of magnetic-dipole transitions within the ground configurations of the F I, O I, and N I isoelectronic sequences are predicted.

  13. Intensity-resolved above-threshold ionization of xenon with short laser pulses

    NASA Astrophysics Data System (ADS)

    Hart, N. A.; Strohaber, J.; Kaya, G.; Kaya, N.; Kolomenskii, A. A.; Schuessler, H. A.

    2014-05-01

    We present intensity-resolved above-threshold ionization (ATI) spectra of xenon using an intensity scanning and deconvolution technique. Experimental data were obtained with laser pulses of 58 fs and a central wavelength of 800 nm from a chirped-pulse amplifier. Applying a deconvolution algorithm, we obtained spectra that have higher contrast and are in excellent agreement with characteristic two and ten Up cutoff energies contrary to that found for raw data. The retrieved electron-ionization probability is consistent with the presence of a second electron from double ionization. This recovered ionization probability is confirmed with a calculation based on the Perelomov, Popov, and Terent'ev tunneling ionization model [Sov. Phys. JETP 23, 924 (1966)]. Thus, the measurements of the photoelectron yields and the developed deconvolution technique allowed retrieval of more accurate spectroscopic information from the ATI spectra and ionization probability features that usually are concealed by volume averaging.

  14. Vibrational levels of p-xylene cation determined by mass-analyzed threshold ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Bing; Aigner, Udo; Ludwig Selzle, Heinrich; William Schlag, Edward

    2003-10-01

    Mass-analyzed threshold ionization (MATI) spectroscopy and two-color resonant two-photon ionization method were used for the determination of the vibrational levels of the p-xylene cation. The MATI spectrum was recorded via the 0 0 vibrationless level of the S 1 state of p-xylene. The spectrum shows a rich structure and some vibrational frequencies of the cation are determined. The experimental findings are well supported by ab initio calculation.

  15. Ionization thresholds of small carbon clusters: tunable VUV experiments and theory.

    PubMed

    Belau, Leonid; Wheeler, Steven E; Ticknor, Brian W; Ahmed, Musahid; Leone, Stephen R; Allen, Wesley D; Schaefer, Henry F; Duncan, Michael A

    2007-08-22

    Small carbon clusters (Cn, n = 2-15) are produced in a molecular beam by pulsed laser vaporization and studied with vacuum ultraviolet (VUV) photoionization mass spectrometry. The required VUV radiation in the 8-12 eV range is provided by the Advanced Light Source (ALS) at the Lawrence Berkeley National Laboratory. Mass spectra at various ionization energies reveal the qualitative relative abundances of the neutral carbon clusters produced. By far the most abundant species is C3. Using the tunability of the ALS, ionization threshold spectra are recorded for the clusters up to 15 atoms in size. The ionization thresholds are compared to those measured previously with charge-transfer bracketing methods. To interpret the ionization thresholds for different cluster sizes, new ab initio calculations are carried out on the clusters for n = 4-10. Geometric structures are optimized at the CCSD(T) level with cc-pVTZ (or cc-pVDZ) basis sets, and focal point extrapolations are applied to both neutral and cation species to determine adiabatic and vertical ionization potentials. The comparison of computed and measured ionization potentials makes it possible to investigate the isomeric structures of the neutral clusters produced in this experiment. The measurements are inconclusive for the n = 4-6 species because of unquenched excited electronic states. However, the data provide evidence for the prominence of linear structures for the n = 7, 9, 11, 13 species and the presence of cyclic C10.

  16. Mass analyzed threshold ionization spectroscopy of p-cyanophenol cation and the CN substitution effect

    NASA Astrophysics Data System (ADS)

    Li, Changyong; Pradhan, Manik; Tzeng, Wen Bih

    2005-08-01

    The adiabatic ionization energy of p-cyanophenol has been determined to be 72 698 ± 5 cm -1 (9.0134 ± 0.0006 eV) on the basis of mass analyzed threshold ionization (MATI) spectrscopy. Analysis of the newly obtained MATI spectra gives the respective frequencies of 399, 517 and 820 cm -1 for the ring deformation 6a, C-CN bending, and breathing vibrations of the p-cyanophenol cation. Comparing these experimental data with those of phenol leads to a better understanding about the influence of the CN substituent on the ionization energy and molecular vibration.

  17. Molecular above-threshold-ionization angular distributions with attosecond bichromatic intense XUV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2012-01-01

    Angular distributions of molecular above-threshold ionization (MATI) in bichromatic attosecond extreme ultraviolet (XUV) linear polarization laser pulses have been theoretically investigated. Multiphoton ionization in a prealigned molecular ion H2+ produces clear MATI spectra which show a forward-backward asymmetry in angular and momentum distributions which is critically sensitive to the carrier envelope phase (CEP) φ, the time delay Δτ between the two laser pulses, and the photoelectron kinetic energies Ee. The features of the asymmetry in MATI angular distributions are described well by multiphoton perturbative ionization models. Phase differences of continuum electron wave functions can be extracted from the CEP φ and time delay Δτ dependent ionization asymmetry ratio created by interfering multiphoton ionization pathways. At large internuclear distances MATI angular distributions exhibit more complex features due to laser-induced electron diffraction where continuum electron wavelengths are less than the internuclear distance.

  18. Steplike Intensity Threshold Behavior of Extreme Ionization in Laser-Driven Xenon Clusters

    SciTech Connect

    Doeppner, T.; Mueller, J. P.; Przystawik, A.; Goede, S.; Tiggesbaeumker, J.; Meiwes-Broer, K.-H.; Varin, C.; Ramunno, L.; Brabec, T.; Fennel, T.

    2010-07-30

    The generation of highly charged Xe{sup q+} ions up to q=24 is observed in Xe clusters embedded in helium nanodroplets and exposed to intense femtosecond laser pulses ({lambda}=800 nm). Laser intensity resolved measurements show that the high-q ion generation starts at an unexpectedly low threshold intensity of about 10{sup 14} W/cm{sup 2}. Above threshold, the Xe ion charge spectrum saturates quickly and changes only weakly for higher laser intensities. Good agreement between these observations and a molecular dynamics analysis allows us to identify the mechanisms responsible for the highly charged ion production and the surprising intensity threshold behavior of the ionization process.

  19. Dynamics of the helium atom close to the full fragmentation threshold: Ionization excitation

    SciTech Connect

    Bouri, C.; Selles, P.; Malegat, L.; Teuler, J.M.; Njock, M. Kwato; Kazansky, A.K.

    2005-10-15

    The hyperspherical R-matrix method with semiclassical outgoing waves, designed to provide accurate double-ionization cross sections, is extended to allow for the computation of ionization-excitation data of comparable quality. Accordingly, it appears now as a complete method for treating the correlated dynamics of two-electron atoms, in particular above their full fragmentation threshold. Cross sections {sigma}{sub n} and asymmetry parameters {beta}{sub n} are obtained for single photoionization of helium with excitation of the residual ion up to as high a level as n=50 at 0.1 eV above the double-ionization threshold. These data are extrapolated to infinite values of n in order to check widespread assumptions regarding this limit. Our data are found consistent with the assumed n{sup -3} dependence of the partial ionization cross sections. However, the {beta}{sub {infinity}}=-0.636 obtained still lies far from the -1 value expected at the double-ionization threshold.

  20. Electron-nuclear energy sharing in above-threshold multiphoton dissociative ionization of H2.

    PubMed

    Wu, J; Kunitski, M; Pitzer, M; Trinter, F; Schmidt, L Ph H; Jahnke, T; Magrakvelidze, M; Madsen, C B; Madsen, L B; Thumm, U; Dörner, R

    2013-07-12

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  2. Active vibrations of 1-cyanonaphthalene cation studied by mass-analyzed threshold ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Shivatare, Vidya; Tzeng, Sheng Yuan; Tzeng, Wen Bih

    2013-02-01

    We apply the two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopic technique to record the cation spectra of 1-cyanonaphthalene via four intermediate vibronic levels. The adiabatic ionization energy is determined to be 69 466 ± 5 cm-1. The distinct bands at 416, 472, 516, 669, and 852 cm-1 result from in-plane ring deformation vibrations of the cation. Analysis of these MATI spectra suggests that the molecular geometry and vibrational coordinates of the observed vibrations of the cation in the ground D0 state resemble those of the neutral in the electronically excited S1 state.

  3. One-photon mass-analyzed threshold ionization (MATI) spectroscopy of pyridine: Determination of accurate ionization energy and cationic structure

    NASA Astrophysics Data System (ADS)

    Lee, Yu Ran; Kang, Do Won; Kim, Hong Lae; Kwon, Chan Ho

    2014-11-01

    Ionization energies and cationic structures of pyridine were intensively investigated utilizing one-photon mass-analyzed threshold ionization (MATI) spectroscopy with vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The present one-photon high-resolution MATI spectrum of pyridine demonstrated a much finer and richer vibrational structure than that of the previously reported two-photon MATI spectrum. From the MATI spectrum and photoionization efficiency curve, the accurate ionization energy of the ionic ground state of pyridine was confidently determined to be 73 570 ± 6 cm-1 (9.1215 ± 0.0007 eV). The observed spectrum was almost completely assigned by utilizing Franck-Condon factors and vibrational frequencies calculated through adjustments of the geometrical parameters of cationic pyridine at the B3LYP/cc-pVTZ level. A unique feature unveiled through rigorous analysis was the prominent progression of the 10 vibrational mode, which corresponds to in-plane ring bending, and the combination of other totally symmetric fundamentals with the ring bending overtones, which contribute to the geometrical change upon ionization. Notably, the remaining peaks originate from the upper electronic state (2A2), as predicted by high-resolution photoelectron spectroscopy studies and symmetry-adapted cluster configuration interaction calculations. Based on the quantitatively good agreement between the experimental and calculated results, it was concluded that upon ionization the pyridine cation in the ground electronic state should have a planar structure of C2v symmetry through the C-N axis.

  4. One-photon mass-analyzed threshold ionization (MATI) spectroscopy of pyridine: Determination of accurate ionization energy and cationic structure

    SciTech Connect

    Lee, Yu Ran; Kang, Do Won; Kim, Hong Lae E-mail: hlkim@kangwon.ac.kr; Kwon, Chan Ho E-mail: hlkim@kangwon.ac.kr

    2014-11-07

    Ionization energies and cationic structures of pyridine were intensively investigated utilizing one-photon mass-analyzed threshold ionization (MATI) spectroscopy with vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The present one-photon high-resolution MATI spectrum of pyridine demonstrated a much finer and richer vibrational structure than that of the previously reported two-photon MATI spectrum. From the MATI spectrum and photoionization efficiency curve, the accurate ionization energy of the ionic ground state of pyridine was confidently determined to be 73 570 ± 6 cm{sup −1} (9.1215 ± 0.0007 eV). The observed spectrum was almost completely assigned by utilizing Franck-Condon factors and vibrational frequencies calculated through adjustments of the geometrical parameters of cationic pyridine at the B3LYP/cc-pVTZ level. A unique feature unveiled through rigorous analysis was the prominent progression of the 10 vibrational mode, which corresponds to in-plane ring bending, and the combination of other totally symmetric fundamentals with the ring bending overtones, which contribute to the geometrical change upon ionization. Notably, the remaining peaks originate from the upper electronic state ({sup 2}A{sub 2}), as predicted by high-resolution photoelectron spectroscopy studies and symmetry-adapted cluster configuration interaction calculations. Based on the quantitatively good agreement between the experimental and calculated results, it was concluded that upon ionization the pyridine cation in the ground electronic state should have a planar structure of C{sub 2v} symmetry through the C-N axis.

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

    SciTech Connect

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

    2006-02-15

    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.

  6. Influence of multi-photon excitation on the atomic above-threshold ionization

    NASA Astrophysics Data System (ADS)

    Tian, Yuan-Ye; Wang, Chun-Cheng; Li, Su-Yu; Guo, Fu-Ming; Ding, Da-Jun; Wim-G, Roeterdink; Chen, Ji-Gen; Zeng, Si-Liang; Liu, Xue-Shen; Yang, Yu-Jun

    2015-04-01

    Using the time-dependent pseudo-spectral scheme, we solve the time-dependent Schrödinger equation of a hydrogen-like atom in a strong laser field in momentum space. The intensity-resolved photoelectron energy spectrum in above-threshold ionization is obtained and further analyzed. We find that with the increase of the laser intensity, the above-threshold ionization emission spectrum exhibits periodic resonance structure. By analyzing the population of atomic bound states, we find that it is the multi-photon excitation of bound state that leads to the occurrence of this phenomenon, which is in fairly good agreement with the experimental results. Project supported by the National Basic Research Program of China (Grant No. 2013CB922200), the National Natural Science Foundation of China (Grants Nos. 11274141, 11034003, 11304116, 11274001, and 11247024), and the Jilin Provincial Research Foundation for Basic Research, China (Grant No. 20140101168JC).

  7. Charge-distribution effect of imaging molecular structure by high-order above-threshold ionization

    SciTech Connect

    Wang Bingbing; Fu Panming; Guo Yingchun; Zhang Bin; Zhao Zengxiu; Yan Zongchao

    2010-10-15

    Using a triatomic molecular model, we show that the interference pattern in the high-order above-threshold ionization (HATI) spectrum depends dramatically on the charge distribution of the molecular ion. Therefore the charge distribution can be considered a crucial factor for imaging a molecular geometric structure. Based on this study, a general destructive interference formula for each above-threshold ionization channel is obtained for a polyatomic molecule concerning the positions and charge values of each nuclei. Comparisons are made for the HATI spectra of CO{sub 2}, O{sub 2}, NO{sub 2}, and N{sub 2}. These results may shed light on imaging complex molecular structure by the HATI spectrum.

  8. Unusual under-threshold ionization of neon clusters studied by ion spectroscopy

    NASA Astrophysics Data System (ADS)

    Nagaya, K.; Sugishima, A.; Iwayama, H.; Murakami, H.; Yao, M.; Fukuzawa, H.; Liu, X.-J.; Motomura, K.; Ueda, K.; Saito, N.; Foucar, L.; Rudenko, A.; Kurka, M.; Kühnel, K.-U.; Ullrich, J.; Czasch, A.; Dörner, R.; Feifel, R.; Nagasono, M.; Higashiya, A.; Yabashi, M.; Ishikawa, T.; Togashi, T.; Kimura, H.; Ohashi, H.

    2013-08-01

    We carried out time-of-flight mass spectrometry for neon clusters that were exposed to intense free electron laser pulses with the wavelength of 62 nm, which induce optical transition from the ground state (2s2 2p6) to an excited state (2s2 2p5 nl ) in the Ne atoms. In contrast to Ne+ ions produced by two-photon absorption from isolated Ne atoms, the Ne+ ion yield from Ne clusters shows a linear dependence on the laser intensity (I). We discuss the ionization mechanisms which give the linear behaviour with respect to I and expected features in the electron emission spectrum.

  9. Mass analyzed threshold ionization spectroscopy of p -aminophenol cation and the substitution effect

    NASA Astrophysics Data System (ADS)

    Xie, Yan; Lin, Jung Lee; Tzeng, Wen Bih

    2004-10-01

    The mass analyzed threshold ionization (MATI) spectra of p-aminophenol have been recorded by ionizing via the vibrationless 0 0 and vibrational 6a 1, 12 1, and 1 1 levels in the S 1 state. The adiabatic ionization energy (IE) of this molecule is determined to be 58,822 ± 5 cm -1. The frequencies of ring vibrational modes 6a, 12, 1, and 18b of the cation are measured to be 458, 768, 835, and 1181 cm -1, respectively. Comparing these new data of p-aminophenol with those of several p-substituted anilines and p-substituted phenols leads to a better understanding about the substitution effects on the IE as well as the cation vibration.

  10. Mass-analyzed threshold ionization spectroscopy of 1-bromopropane through dissociative intermediate states

    NASA Astrophysics Data System (ADS)

    Zhang, Song; Wang, Yanmei; Tang, Bifeng; Zheng, Qiusha; Zhang, Bing

    2006-02-01

    One-color two-photon ionization of 1-bromopropane, resulting in the 1-C 3H 7Br + ions in the X2E and X2E electronic states, is investigated using mass-analyzed threshold ionization (MATI) spectroscopy. The adiabatic ionization energies of two spin states are found to be 82 257 ± 5 and 84 823 ± 5 cm -1, respectively. The two-photon MATI spectrum exhibits an extensive vibrational structure. The active modes, including the C-Br stretching, the CH 2-Br wagging, the CH 2 and the CH 3 rocking modes, are observed and reliable values for these vibrational frequencies are obtained. We have also performed ab initio and density functional calculations, which provide interpretation for our experimental finding.

  11. Identification of four rotamers of m-methoxystyrene by resonant two-photon ionization and mass analyzed threshold ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Yanqi; Tzeng, Sheng Yuan; Shivatare, Vidya; Takahashi, Kaito; Zhang, Bing; Tzeng, Wen Bih

    2015-03-01

    We report the vibronic and cation spectra of four rotamers of m-methoxystyrene, recorded by using the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The excitation energies of the S1← S0 electronic transition are found to be 32 767, 32 907, 33 222, and 33 281 cm-1, and the corresponding adiabatic ionization energies are 65 391, 64 977, 65 114, and 64 525 cm-1 for these isomeric species. Most of the observed active vibrations in the electronically excited S1 and cationic ground D0 states involve in-plane ring deformation and substituent-sensitive bending motions. It is found that the relative orientation of the methoxyl with respect to the vinyl group does not influence the vibrational frequencies of the ring-substituent bending modes. The two dimensional potential energy surface calculations support our experimental finding that the isomerization is restricted in the S1 and D0 states.

  12. Identification of four rotamers of m-methoxystyrene by resonant two-photon ionization and mass analyzed threshold ionization spectroscopy

    SciTech Connect

    Xu, Yanqi; Tzeng, Sheng Yuan; Takahashi, Kaito; Shivatare, Vidya; Zhang, Bing; Tzeng, Wen Bih

    2015-03-28

    We report the vibronic and cation spectra of four rotamers of m-methoxystyrene, recorded by using the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The excitation energies of the S{sub 1}← S{sub 0} electronic transition are found to be 32 767, 32 907, 33 222, and 33 281 cm{sup −1}, and the corresponding adiabatic ionization energies are 65 391, 64 977, 65 114, and 64 525 cm{sup −1} for these isomeric species. Most of the observed active vibrations in the electronically excited S{sub 1} and cationic ground D{sub 0} states involve in-plane ring deformation and substituent-sensitive bending motions. It is found that the relative orientation of the methoxyl with respect to the vinyl group does not influence the vibrational frequencies of the ring-substituent bending modes. The two dimensional potential energy surface calculations support our experimental finding that the isomerization is restricted in the S{sub 1} and D{sub 0} states.

  13. Mass-Analyzed Threshold Ionization (MATI) Spectroscopy of Atoms and Molecules Using VUV Synchrotron Radiation

    NASA Astrophysics Data System (ADS)

    Kostko, Oleg; Kim, Sang Kyu; Leone, Stephen R.; Ahmed, Musahid

    2009-05-01

    Mass-analyzed threshold ionization (MATI) spectroscopy using synchrotron radiation (Advanced Light Source, Lawrence Berkeley National Laboratory) has been performed for Ar, N2, O2, N2O, H2O, C2H2, and C6H6. MATI allows for a better determination of ionization energies compared to those derived from photoionization efficiency curves traditionally used in synchrotron photoionization mass spectrometry. The separation of the long-lived Rydberg state from the directly formed prompt ion, essential for a meaningful MATI spectrum, has been accomplished by employing an arrangement of ion optics coupled to unique electric field pulsing schemes. For Ar, a number of resolved bands below the ionization energy are observed, and these are ascribed to high-n,l Rydberg states prepared in the MATI scheme. The first vibrational state resolved MATI spectra of N2 and O2 are reported, and spectral characteristics are discussed in comparison with previously reported threshold photoelectron spectroscopic studies. Although MATI performed with synchrotron radiation is intrinsically less sensitive compared to laser-based sources, this work demonstrates that MATI spectroscopy performed with widely tunable vacuum ultraviolet (VUV) radiation is a complementary technique for studying the ionization spectroscopy of polyatomic molecules.

  14. Mass-analyzed threshold ionization (MATI) spectroscopy of atoms and molecules using VUV synchrotron radiation.

    PubMed

    Kostko, Oleg; Kim, Sang Kyu; Leone, Stephen R; Ahmed, Musahid

    2009-12-31

    Mass-analyzed threshold ionization (MATI) spectroscopy using synchrotron radiation (Advanced Light Source, Lawrence Berkeley National Laboratory) has been performed for Ar, N(2), O(2), N(2)O, H(2)O, C(2)H(2), and C(6)H(6). MATI allows for a better determination of ionization energies compared to those derived from photoionization efficiency curves traditionally used in synchrotron photoionization mass spectrometry. The separation of the long-lived Rydberg state from the directly formed prompt ion, essential for a meaningful MATI spectrum, has been accomplished by employing an arrangement of ion optics coupled to unique electric field pulsing schemes. For Ar, a number of resolved bands below the ionization energy are observed, and these are ascribed to high-n,l Rydberg states prepared in the MATI scheme. The first vibrational state resolved MATI spectra of N(2) and O(2) are reported, and spectral characteristics are discussed in comparison with previously reported threshold photoelectron spectroscopic studies. Although MATI performed with synchrotron radiation is intrinsically less sensitive compared to laser-based sources, this work demonstrates that MATI spectroscopy performed with widely tunable vacuum ultraviolet (VUV) radiation is a complementary technique for studying the ionization spectroscopy of polyatomic molecules.

  15. Mass-Analyzed Threshold Ionization (MATI) Spectroscopy of Atoms and Molecules using VUV Synchrotron Radiation

    SciTech Connect

    Kostko, Oleg; Kim, Sang Kyu; Leone, Stephen R.; Ahmed, Musahid

    2009-01-28

    Mass-analyzed threshold ionization (MATI) spectroscopy using synchrotron radiation (Advanced Light Source, Lawrence Berkeley National Laboratory) has been performed for Ar, N2, O2, N2O, H2O, C2H2, and C6H6. MATI allows for a better determination of ionization energies compared to those derived from photoionization efficiency curves traditionally used in synchrotron photoionization mass spectrometry. The separation of the long-lived Rydberg state from the directly-formed prompt ion, essential for a meaningful MATI spectrum, has been accomplished by employing an arrangement of ion optics coupled to unique electric-field pulsing schemes. For Ar, a number of resolved bands below the ionization energy are observed, and these are ascribed to high-n,l Rydberg states prepared in the MATI scheme. The first vibrational stateresolved MATI spectra of N2 and O2 are reported and spectral characteristics are discussed in comparison with previously-reported threshold photoelectron spectroscopic studies. While MATI performed with synchrotron radiation is intrinsically less sensitive compared to laser based sources, this work demonstrates that MATI spectroscopy performed with widely tunable VUV radiation is a complementary technique for studying the ionization spectroscopy of polyatomic molecules.

  16. Investigation of hydrogen bonding in 3-methylindole · H 2O cluster by mass analyzed threshold ionization

    NASA Astrophysics Data System (ADS)

    Georgiev, S.; Neusser, H. J.

    2004-05-01

    The adiabatic ionization energies and the threshold ion vibrational spectra of 3-methylindole and the 3-methylindole · H 2O cluster and the hydrogen bonding energy of the latter have been measured with mass analyzed threshold ionization (MATI) technique. Dissociation of the cluster has been detected as a breakdown of the threshold ion signal at the parent mass channel and the simultaneous increase of the signal at the fragment mass channel. Comparison with our previous work on indole · H 2O shows that there is only a small influence of the methyl group on the ionization energy and the hydrogen bonding strength.

  17. Fine structure and ionization energy of the 1s2s2p 4P state of the helium negative ion He-.

    PubMed

    Wang, Liming; Li, Chun; Yan, Zong-Chao; Drake, G W F

    2014-12-31

    The fine structure and ionization energy of the 1s2s2p (4)P state of the helium negative ion He(-) are calculated in Hylleraas coordinates, including relativistic and QED corrections up to O(α(4)mc(2)), O((μ/M)α(4)mc(2)), O(α(5)mc(2)), and O((μ/M)α(5)mc(2)). Higher order corrections are estimated for the ionization energy. A comparison is made with other calculations and experiments. We find that the present results for the fine structure splittings agree with experiment very well. However, the calculated ionization energy deviates from the experimental result by about 1 standard deviation. The estimated theoretical uncertainty in the ionization energy is much less than the experimental accuracy.

  18. Is the Kohn-Sham Oscillator Strength Exact at the Ionization Threshold?

    NASA Astrophysics Data System (ADS)

    Yang, Zenghui; van Faassen, Meta; Burke, Kieron

    2009-03-01

    It is well-established that the highest occupied orbital of the exact Kohn-Sham potential of any system is at -I, where I is the ionization energy. Therefore, in optical response, the non-interacting Kohn-Sham electrons in the ground-state potential have a first ionization threshold that exactly matches that of the real system[1]. We show that corresponding the Kohn-Sham oscillator strength is not exact at the first ionization threshold by explicit demonstration for the helium atom. We use a simple fit of the entire photoabsorption spectrum of both the Kohn-Sham potential for helium and that of real helium. We use oscillator strength sum rules[2] to determine the fit parameters, so this fit should be generally useful. [1] M. A. L. Marques, C. A. Ullrich, F. Nogueira, et al. Time-Dependent Density Functional Theory. Springer-Verlag, Berlin, 2006 [2] U. Fano and J. W. Cooper. Rev. Mod. Phys., 40(3), 441-507, 1968

  19. Mass-analyzed threshold ionization of an excited state of lanthanum dioxide

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Liu, Yang; Zhang, Changhua; Li, Shenggang; Dixon, David A.; Yang, Dong-Sheng

    2012-07-01

    LaO2 was produced in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and ab initio electronic structure calculations. The calculations included density functional theory, second-order perturbation theory, coupled cluster theory, and complete active space self-consistent field methods. The adiabatic ionization energy of the molecule and vibrational frequencies of the molecule and its cation were measured accurately for the first time from the MATI spectrum. Numerous ionization processes of lanthanum dioxide, peroxide, and superoxide were considered; the 3B2 ← 4B2 electronic transition of the dioxide was assigned upon comparison with the observed spectrum. The ionization energy and O-La-O bending frequency of the 4B2 neutral state are 4.9760 (6) eV and 92 cm-1, respectively. The La-O stretching and O-La-O bending frequencies of the 3B2 cationic state are 656 and 122 cm-1, respectively. The 4B2 state is formed by two electron transfer from lanthanum to oxygen atoms, and the 3B2 state is produced by the further removal of a lanthanum 6s-based electron.

  20. Mass-analyzed Threshold Ionization Spectroscopy of Rotamers of p-ethoxyphenol Cations and Configuration Effect

    NASA Astrophysics Data System (ADS)

    Zheng, Qiu-sha; Fang, Teng I.; Zhang, Bing; Bih Tzeng, Wen

    2009-12-01

    Two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy was used to record the vibrationally resolved cation spectra of the selected rotamers of p-ethoxyphenol. The adiabatic ionization energies of the trans and cis rotamers are determined to be 61565 ± 5 and 61670 ± 5 cm-1, which are less than that of p-methoxyphenol by 645 and 643 cm-1, respectively. Analysis on the MATI spectra of the selected rotamers of p-ethoxyphenol cation shows that the relative orientation of the ethoxy group has little effect on the in-plane ring vibrations. The low-frequency OC2H5 bending vibrations appear to be active for both forms of the cation.

  1. Reducing the dimensionality of grid based methods for electron-atom scattering calculations below ionization threshold

    NASA Astrophysics Data System (ADS)

    Benda, Jakub; Houfek, Karel

    2017-04-01

    For total energies below the ionization threshold it is possible to dramatically reduce the computational burden of the solution of the electron-atom scattering problem based on grid methods combined with the exterior complex scaling. As in the R-matrix method, the problem can be split into the inner and outer problem, where the outer problem considers only the energetically accessible asymptotic channels. The (N + 1)-electron inner problem is coupled to the one-electron outer problems for every channel, resulting in a matrix that scales only linearly with size of the outer grid.

  2. Threshold for thermal ionization of an aluminum surface by pulsed megagauss magnetic field.

    PubMed

    Awe, T J; Bauer, B S; Fuelling, S; Siemon, R E

    2010-01-22

    The first measurement of the threshold for thermal ionization of the surface of thick metal by pulsed magnetic field (B) is reported. Thick aluminum-with depth greater than the magnetic skin layer-was pulsed with partial differential B/ partial differential t from 30-80 MG/micros. Novel loads avoided nonthermal plasma (from electron avalanche, or energetic particles or photons from arcs). Thermal plasma forms from 6061-alloy aluminum when the surface magnetic field reaches 2.2 MG, in qualitative agreement with numerical simulation results by Garanin et al. [J. Appl. Mech. Tech. Phys. 46, 153 (2005)].

  3. Communication: On the first ionization threshold of the C2H radical.

    PubMed

    Gans, B; Garcia, G A; Holzmeier, F; Krüger, J; Röder, A; Lopes, A; Fittschen, C; Loison, J-C; Alcaraz, C

    2017-01-07

    The slow photoelectron spectrum of the ethynyl radical has been recorded for the first time by using the DESIRS beamline of the SOLEIL synchrotron facility. Ethynyl was generated using a microwave discharge flow tube. The observation of the X(+)Π3←XΣ+2 transition allowed the first direct measurement of the adiabatic ionization threshold of this radical (EI = 11.641(5) eV). The experimental results are supported by ab initio calculations. Our preliminary investigation of the cationic ground state potential energy surfaces predicts a non-negligible Renner-Teller effect which has not been discussed previously.

  4. Benchmark theoretical study of the ionization threshold of benzene and oligoacenes

    NASA Astrophysics Data System (ADS)

    Deleuze, M. S.; Claes, L.; Kryachko, E. S.; François, J.-P.

    2003-08-01

    In straightforward continuation of Green's function studies of the ultraviolet photoelectron spectra of polycyclic aromatic compounds [Deleuze et al., J. Chem. Phys. 115, 5859 (2001); M. S. Deleuze, ibid. 116, 7012 (2002)], we present a benchmark theoretical determination of the ionization thresholds of benzene, naphthalene, anthracene, naphthacene (tetracene), pentacene, and hexacene, within chemical accuracy [0.02-0.07 eV]. The vertical ionization potentials of these compounds have been obtained from series of single-point calculations at the Hartree-Fock, second-, third-, and partial fourth-order Møller-Plesset (MP2, MP3, MP4SDQ) levels, and from coupled cluster calculations including single and double excitations (CCSD) as well as a perturbative estimate of connected triple excitations [CCSD(T)], using basis sets of improving quality, introducing up to 510, 790, 1070, 1350, 1630, and 1910 basis functions in the computations, respectively. A focal point analysis of the convergence of the calculated ionization potentials has been performed in order to extrapolate the CCSD(T) results to an asymptotically (cc-pV∞Z) complete basis set. The present results confirm the adequacy of the outer-valence Green's function scheme for strongly correlated systems. Adiabatic ionization energies have been further determined by incorporating Beck-three-parameter Lee-Yang-Parr functional corrections for zero-point vibrational energies and for geometrical relaxations. Extension of the analysis to the CCSD(T)/cc-pV∞Z level shows that the energy minimum form of the benzene radical cation is an obtuse structure related to the 2B2g state. Isotopic shifts of the adiabatic ionization potentials, due to deuterium substitution of hydrogens, have also been discussed.

  5. Mass-Analyzed Threshold Ionization and Structures of M_3C_2(M=Sc, La)

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Mourad, Roudjane; Yang, D. S.

    2011-06-01

    M_3C_2 (M=Sc, La) clusters are produced by laser vaporization in a pulsed metal-cluster source and identified by photoionization mass spectrometry. Vibrationally resolved ion spectra are obtained with mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectra of M_3C_2 (M=Sc, La) exhibit a weak 0-0 transition, indicating a significant geometry difference between the neutral and ionized clusters. The ionization energies of Sc_2C_2 and La_3C_2 are measured to be 36398 (5) and 30051(5) Cm-1, respectively. In addition, the spectra of the two clusters display a number of vibrational intervals that are associated with M_3 deformations. Preliminary data analysis shows that both clusters have a C2v bi-pyramid structure in the neutral state and a D3h bi-pyramid structure in the ion state, and the spectra may be assigned to the ^1A'_1 (D3h)← ^2B_2 (C2v) transitions.

  6. Resonant two-photon mass-analyzed threshold ionization spectroscopy of 1-fluoronaphthalene and 2-fluoronaphthalene

    NASA Astrophysics Data System (ADS)

    Tzeng, Sheng Yuan; Wu, Jui Yang; Zhang, Shudong; Tzeng, Wen Bih

    2012-11-01

    We applied the resonant two-photon mass-analyzed threshold ionization (MATI) technique to record the cation spectra of 1-fluoronaphthalene (1FN) and 2-fluoronaphthalene (2FN) by ionizing via several intermediate vibronic states. The adiabatic ionization energies of 1FN and 2FN are found to be 66 194 and 66 771 ± 5 cm-1, respectively. Distinct MATI bands resulting from in-plane ring deformation are found at 437, 517, 703, and 779 cm-1 for 1FN; and 286, 455, 494, 764, and 1031 cm-1 for 2FN. Frequencies of these modes are slightly greater than the corresponding ones in the vibronic spectra. This indicates that the molecular geometry in the cationic D0 state is slightly more rigid than that in the neutral S1 state. Comparing the present experimental data with those of naphthalene suggests that the frequency difference of each mode depends on the vibrational pattern, location of the F atom, and degree of the F atom involved in the overall vibration.

  7. Nonconstant ponderomotive energy in above-threshold ionization by intense short laser pulses

    NASA Astrophysics Data System (ADS)

    Della Picca, R.; Gramajo, A. A.; Garibotti, C. R.; López, S. D.; Arbó, D. G.

    2016-02-01

    We analyze the contribution of the quiver kinetic energy acquired by an electron in an oscillating electric field of a short laser pulse to the energy balance in atomic ionization processes. Due to the time dependence of this additional kinetic energy, a temporal average is assumed to preserve a stationary energy conservation rule, which is used to predict the position of the energy peaks observed in the photoelectron (PE) spectra. For a plane wave and a flattop pulse, the mean value of the quiver energy over the whole pulse leads to the concept of ponderomotive energy Up. However, for a short pulse with a fast changing intensity, the stationary approximation loses its validity. We check these concepts by studying first the PE spectrum within the semiclassical model (SCM) for multiple-step pulses. The SCM offers the possibility to establish a connection between emission times and the PE spectrum in the energy domain. We show that PE substructures stem from ionization at different times mapping the pulse envelope. We also analyze the PE spectrum for a realistic sine-squared envelope within the Coulomb-Volkov and ab initio calculations solving the time-dependent Schrödinger equation. We found that the electron emission amplitudes produced at different times interfere with each other producing, in this way, a new additional pattern that modulates the above-threshold ionization (ATI) peaks.

  8. Interference substructure of above-threshold ionization peaks in the stabilization regime

    NASA Astrophysics Data System (ADS)

    Toyota, Koudai; Tolstikhin, Oleg I.; Morishita, Toru; Watanabe, Shinichi

    2008-09-01

    The photoelectron spectra produced in the photodetachment of H- (treated in the single-active-electron approximation) by strong high-frequency laser pulses with adequately chosen laser parameters in the stabilization regime are theoretically studied for elliptic polarization over an extended parameter range. An oscillating substructure in the above-threshold ionization peaks is observed, which confirms similar findings in the one-dimensional (1D) [K. Toyota , Phys. Rev. A 76, 043418 (2007)] and 3D calculations for linear polarization [O. I. Tolstikhin, Phys. Rev. A 77, 032712 (2008)]. The mechanism is an interference between the photoelectron wave packets created in the rising and falling parts of the pulse which is specific to the stabilization regime. We thus conclude that this interference substructure is robust for any polarization and over a wide range of the laser parameters, and hence should be observable experimentally.

  9. Quantum path analysis of high-order above-threshold ionization

    NASA Astrophysics Data System (ADS)

    Kopold, R.; Becker, W.; Kleber, M.

    2000-05-01

    High-order above-threshold ionization spectra are calculated via an improved Keldysh approximation that takes rescattering into account. An approximate method of evaluating the crucial multidimensional integral proceeds via the saddle point method. The saddle points define complex orbits in position space that depart from the ion and return to it to rescatter. The real parts of these orbits are very closely related to the trajectories of the simple-man model. The spectra are analyzed in terms of these quantum orbits whose constructive and destructive interferences generate the spectrum's intricate structures. In most spectral regions, the six trajectories having the shortest travel times between start and return already provide an excellent approximation to the exact calculation. In exceptional cases, more orbits are required. The quantum orbits provide an illuminating illustration of the quantum mechanical path integral.

  10. Phase space path-integral formulation of the above-threshold ionization

    NASA Astrophysics Data System (ADS)

    Milošević, D. B.

    2013-04-01

    Atoms and molecules submitted to a strong laser field can emit electrons of high energies in the above-threshold ionization (ATI) process. This process finds a highly intuitive and also quantitative explanation in terms of Feynman's path integral and the concept of quantum orbits [P. Salières et al., Science 292, 902 (2001)], 10.1126/science.108836. However, the connection with the Feynman path-integral formalism is explained only by intuition and analogy and within the so-called strong-field approximation (SFA). Using the phase space path-integral formalism we have obtained an exact result for the momentum-space matrix element of the total time-evolution operator. Applying this result to the ATI we show that the SFA and the so-called improved SFA are, respectively, the zeroth- and the first-order terms of the expansion in powers of the laser-free effective interaction of the electron with the rest of the atom (molecule). We have also presented the second-order term of this expansion which is responsible for the ATI with double scattering of the ionized electron.

  11. Correspondence of below-threshold high-order-harmonic generation and frustrated tunneling ionization

    NASA Astrophysics Data System (ADS)

    Xiong, Wei-Hao; Xiao, Xiang-Ru; Peng, Liang-You; Gong, Qihuang

    2016-07-01

    Among many of the nonlinear phenomena induced by strong laser pulses, two of the important processes are the harmonic generation and the creation of neutral atoms in the Rydberg states. We carry out a joint study of the below-threshold high-order-harmonic (BTH) generation and the production of low-lying Rydberg atoms driven by an intense few-cycle midinfrared laser pulse. Our results are based on the numerical solution to the three-dimensional time-dependent Schrödinger equation within the single active electron approximation and a semiclassical simulation. The yields of BTH and low-lying Rydberg atoms are found to have a similar carrier envelope phase dependence. We find that both processes can be faithfully described semiclassically in the deep tunneling regime. The trajectory analysis shows that these two processes share the same series of trajectories and can be simultaneously manipulated by the driving pulse shape. Our finding bridges the below-threshold high-order-harmonic generation and the frustrated tunneling ionization.

  12. Photoionization of iodine atoms: Rydberg series which converge to the I{sup +}({sup 1}S{sub 0})<-I({sup 2}P{sub 3/2}) threshold

    SciTech Connect

    Eypper, Marie; Innocenti, Fabrizio; Morris, Alan; Dyke, John M.; Stranges, Stefano; West, John B.; King, George C.

    2010-06-28

    Relative partial photoionization cross sections and angular distribution parameters {beta} have been measured for the first and fourth (5p){sup -1} photoelectron (PE) bands of atomic iodine by performing angle-resolved constant-ionic-state (CIS) measurements on these PE bands between the {sup 1}D{sub 2} and {sup 1}S{sub 0} (5p){sup -1} ionic thresholds in the photon energy region of 12.9-14.1 eV. Rydberg series arising from the 5p{yields}ns and 5p{yields}nd excitations are observed in both the first PE band, I{sup +}({sup 3}P{sub 2})<-I({sup 2}P{sub 3/2}), and the fourth PE band, I{sup +}({sup 1}D{sub 2})<-I({sup 2}P{sub 3/2}), CIS spectra. For each Rydberg state, the resonance energy, quantum defect, linewidth, line shape, and photoelectron angular distribution parameter {beta} have been determined. For the {beta}-plots for each PE band, only resonances corresponding to 5p{yields}nd excitations are observed; no resonances were seen at photon energies corresponding to the 5p{yields}ns resonances in the CIS spectra. The {beta}-plots are interpreted in terms of the parity unfavored channel with j{sub t}=4 being the major contributor at the 5p{yields}nd resonance positions, where j{sub t} is the quantum number for angular momentum transferred between the molecule, and the ion and photoelectron. Comparison of the results obtained with those published for bromine shows reasonably good agreement for the CIS spectra but poor agreement for the {beta}-plots. It appears that parity unfavored channels are playing a greater role in the valence (np){sup -1} ionization of atomic iodine than in the corresponding ionization of atomic bromine.

  13. Atomic, Molecular, and Optical Physics: Optical Excitation Function of H(1s-2p) Produced by electron Impact from Threshold to 1.8 keV

    NASA Technical Reports Server (NTRS)

    James, G. K.; Slevin, J. A.; Shemansky, D. E.; McConkey, J. W.; Bray, I.; Dziczek, D.; Kanik, I.; Ajello, J. M.

    1997-01-01

    The optical excitation function of prompt Lyman-Alpha radiation, produced by electron impact on atomic hydrogen, has been measured over the extended energy range from threshold to 1.8 keV. Measurements were obtained in a crossed-beams experiment using both magnetically confined and electrostatically focused electrons in collision with atomic hydrogen produced by an intense discharge source. A vacuum-ultraviolet mono- chromator system was used to measure the emitted Lyman-Alpha radiation. The absolute H(1s-2p) electron impact excitation cross section was obtained from the experimental optical excitation function by normalizing to the accepted optical oscillator strength, with corrections for polarization and cascade. Statistical and known systematic uncertainties in our data range from +/- 4% near threshold to +/- 2% at 1.8 keV. Multistate coupling affecting the shape of the excitation function up to 1 keV impact energy is apparent in both the present experimental data and present theoretical results obtained with convergent close- coupling (CCC) theory. This shape function effect leads to an uncertainty in absolute cross sections at the 10% level in the analysis of the experimental data. The derived optimized absolute cross sections are within 7% of the CCC calculations over the 14 eV-1.8 keV range. The present CCC calculations converge on the Bethe- Fano profile for H(1s-2p) excitation at high energy. For this reason agreement with the CCC values to within 3% is achieved in a nonoptimal normalization of the experimental data to the Bethe-Fano profile. The fundamental H(1s-2p) electron impact cross section is thereby determined to an unprecedented accuracy over the 14 eV - 1.8 keV energy range.

  14. Measurement of relative cross sections for simultaneous ionization and excitation of the helium 4 2s and 4 2p states

    NASA Technical Reports Server (NTRS)

    Sutton, J. F.

    1972-01-01

    The relative cross sections for simultaneous ionization and excitation of helium by 200-eV electrons into the 4 2s and 4 2p states were measured via a fast delayed coincidence technique. Results show good agreement with the relative cross sections for single electron excitation of helium and hydrogen. An application of the results of the measurement to the development of ultraviolet intensity standard is suggested. This technique involves the use of known branching ratios, a visible light flux reference, and the measured relative cross sections.

  15. Mass-Analyzed Threshold Ionization of M_2O_2 ( M = ce and Pr)

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Dangi, Beni; Rounjane, Mourad; Yang, Dong-Sheng

    2012-06-01

    M_2O_2 ( M = Ce and Pr) is produced in a pulsed laser-vaporization metal-cluster source and studied by mass-analyzed threshold ionization (MATI) spectroscopy. From the MATI spectra, the adiabatic ionization energy is determined to be 37300(5) cm-1 for Ce2O2, and 37885 (5) cm-1 for Pr2O2. Like group 3 transition metal M2O2 (M=Sc, Y, and La) clusters we reported previously, these lanthanide clusters have a D2h planer structure and the vibrational modes observed are from the in-plane motions. However, the ground and other low-energy electronic states of the lanthanide oxides have a much higher electron spin multiplicity due to the existence of 4f electrons in the Ce and Pr atoms. The 4f electron of Ce atom has significantly lower energies than the 5d or 6s electrons and remain uncoupled in Ce2O2. On the other hand, the energy differences between the 4f and 5d/6s electrons of Pr atom are relatively small, and a 4f → 5d electron promotion is required in the formation of Pr2O2. The electronic transitions responsible for the observed MATI spectra are tentatively determined to be ^4B1u ← ^5Ag for Ce2O2 and ^6B1u ← ^7B2g and ^6B1u ← ^5B1u for Pr2O2.

  16. Diffraction at a time grating in above-threshold ionization: The influence of the Coulomb potential

    SciTech Connect

    Arbo, Diego G.; Ishikawa, Kenichi L.; Schiessl, Klaus; Persson, Emil; Burgdoerfer, Joachim

    2010-10-15

    We analyze the photoelectron emission spectrum in atomic above-threshold ionization by a linearly polarized short-laser pulse. Direct electrons can be characterized by both intracycle and intercycle interferences. The former results from the coherent superposition of two different electron trajectories released in the same optical cycle, whereas the latter is the consequence of the superposition of multiple trajectories released in different cycles. In the present article, a semiclassical analytical expression for the complete (both intracycle and intercycle) interference pattern is derived. We show that the recently proposed semiclassical description in terms of a diffraction process at a time grating remains qualitatively unchanged in the presence of the long-range Coulomb potential. The latter causes only a phase shift of the intracycle interference pattern. We verify the predictions of the semiclassical model by comparison with full three-dimensional (3D) time-dependent Schroedinger equation (TDSE) solutions. One key finding is that the subcycle interference structures originating from trajectories launched within a time interval of less than 1 femtosecond should be experimentally observable also in low-resolution spectra for longer multicycle pulses.

  17. Ce-PROMOTED Bond Activation of Ethylene Probed by Mass-Analyzed Threshold Ionization Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Yuchen; Kumari, Sudesh; Cao, Wenjin; Yang, Dong-Sheng

    2015-06-01

    Ce(C_2H_2) and Ce(C_4H_6) complexes were observed in the reaction of Ce atom with ethylene in a supersonic molecular beam source and investigated by mass-analyzed threshold ionization spectroscopy (MATI) and theoretical calculations. Preliminary data analysis shows that Ce(C_2H_2) has a triangle structure (C2v) with Ce binding to C_2H_2 in a two-fold mode and Ce(C_4H_6) has a five-membered metallacyclic structure (Cs) with Ce binding to the two terminal carbon atoms of butadiene. The ground states of both species are triplets with a 4f16s1 Ce-based electron configuration and those of the corresponding ions are doublets from the removal of the 6s1 electron. The Ce(C_2H_2) complex is formed by ethylene dehydrogenation, whereas Ce(C_4H_6) by ethylene dehydrogenation and carbon-carbon bond coupling. The MATI spectra of Ce(C_2H_2) and Ce(C_4H_6) are rather similar to those of the corresponding La complexes previously observed by our group, except that the spectra of the Ce complexes exhibit two electronic transitions with almost identical vibrational intervals. This observation suggests that the existence of a 4f electron results in an increased complexity of the electronic spectra and states of the lanthanide hydrocarbons.

  18. Resonancelike enhancement in high-order above-threshold ionization of polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Wang, C.; Okunishi, M.; Hao, X.; Ito, Y.; Chen, J.; Yang, Y.; Lucchese, R. R.; Zhang, M.; Yan, B.; Li, W. D.; Ding, D.; Ueda, K.

    2016-04-01

    We investigate the resonance-like enhancement (RLE) in high-order above-threshold ionization (ATI) spectra of the polyatomic molecules C2H4 and C2H6 . In the spectrum-intensity maps, strong and weak RLE areas emerge alternatively for both C2H4 and C2H6 but in different sequences. Theoretical calculations using the strong-field approximation reproduce the experimental observation and analysis shows that the different characteristics of the two molecules can be attributed to interference effects of molecular orbitals with different symmetries. For C2H4 , the RLE structures are attributed to C-C centers of the highest occupied molecular orbital (HOMO) orbital. For C2H6 , in contrast, the C-C centers of the HOMO and HOMO-1 orbitals do not contribute to the RLE due to destructive interference but the hydrogen centers of the bonding HOMO-1 orbital give rise to the multiple RLE regions. In addition, clear experimental evidence of the existence of two types of the RLE and their dependence on the parity of ground state is shown. Our result, which strongly supports the channel-closing mechanism of the RLE, for the first time reveals the important role of low-lying orbitals and the differing roles of different atomic centers in the high-order ATI spectrum of molecules.

  19. Correlated electron-nuclear dynamics in above-threshold multiphoton ionization of asymmetric molecule.

    PubMed

    Wang, Zhuo; Li, Min; Zhou, Yueming; Lan, Pengfei; Lu, Peixiang

    2017-02-20

    The partition of the photon energy into the subsystems of molecules determines many photon-induced chemical and physical dynamics in laser-molecule interactions. The electron-nuclear energy sharing from multiphoton ionization of molecules has been used to uncover the correlated dynamics of the electron and fragments. However, most previous studies focus on symmetric molecules. Here we study the electron-nuclear energy sharing in strong-field photoionization of HeH(2+) by solving the one-dimensional time-dependent Schrödinger equation (TDSE). Compared with symmetric molecules, the joint electron-nuclear energy spectrum (JES) of HeH(2+) reveals an anomalous energy shift at certain nuclear energies, while it disappears at higher and lower nuclear energies. Through tracing the time evolution of the wavepacket of bound states, we identify that this energy shift originates from the joint effect of the Stark shift, associated with the permanent dipole, and the Autler-Townes effect due to the coupling of the 2pσ and 2sσ states in strong fields. The energy shift in the JES appears at certain nuclear distances only when both Stark effect and Autler-Townes effect play important roles. We further demonstrate that the electron-nuclei energy sharing can be controlled by varying laser intensity for asymmetric molecules, providing alternative approaches to manipulate photochemical reactions for more complex molecules.

  20. Correlated electron-nuclear dynamics in above-threshold multiphoton ionization of asymmetric molecule

    NASA Astrophysics Data System (ADS)

    Wang, Zhuo; Li, Min; Zhou, Yueming; Lan, Pengfei; Lu, Peixiang

    2017-02-01

    The partition of the photon energy into the subsystems of molecules determines many photon-induced chemical and physical dynamics in laser-molecule interactions. The electron-nuclear energy sharing from multiphoton ionization of molecules has been used to uncover the correlated dynamics of the electron and fragments. However, most previous studies focus on symmetric molecules. Here we study the electron-nuclear energy sharing in strong-field photoionization of HeH2+ by solving the one-dimensional time-dependent Schrödinger equation (TDSE). Compared with symmetric molecules, the joint electron-nuclear energy spectrum (JES) of HeH2+ reveals an anomalous energy shift at certain nuclear energies, while it disappears at higher and lower nuclear energies. Through tracing the time evolution of the wavepacket of bound states, we identify that this energy shift originates from the joint effect of the Stark shift, associated with the permanent dipole, and the Autler-Townes effect due to the coupling of the 2pσ and 2sσ states in strong fields. The energy shift in the JES appears at certain nuclear distances only when both Stark effect and Autler-Townes effect play important roles. We further demonstrate that the electron-nuclei energy sharing can be controlled by varying laser intensity for asymmetric molecules, providing alternative approaches to manipulate photochemical reactions for more complex molecules.

  1. Correlated electron-nuclear dynamics in above-threshold multiphoton ionization of asymmetric molecule

    PubMed Central

    Wang, Zhuo; Li, Min; Zhou, Yueming; Lan, Pengfei; Lu, Peixiang

    2017-01-01

    The partition of the photon energy into the subsystems of molecules determines many photon-induced chemical and physical dynamics in laser-molecule interactions. The electron-nuclear energy sharing from multiphoton ionization of molecules has been used to uncover the correlated dynamics of the electron and fragments. However, most previous studies focus on symmetric molecules. Here we study the electron-nuclear energy sharing in strong-field photoionization of HeH2+ by solving the one-dimensional time-dependent Schrödinger equation (TDSE). Compared with symmetric molecules, the joint electron-nuclear energy spectrum (JES) of HeH2+ reveals an anomalous energy shift at certain nuclear energies, while it disappears at higher and lower nuclear energies. Through tracing the time evolution of the wavepacket of bound states, we identify that this energy shift originates from the joint effect of the Stark shift, associated with the permanent dipole, and the Autler-Townes effect due to the coupling of the 2pσ and 2sσ states in strong fields. The energy shift in the JES appears at certain nuclear distances only when both Stark effect and Autler-Townes effect play important roles. We further demonstrate that the electron-nuclei energy sharing can be controlled by varying laser intensity for asymmetric molecules, providing alternative approaches to manipulate photochemical reactions for more complex molecules. PMID:28218294

  2. Molecular above-threshold ionization spectra as an evidence of the three-point interference of electron wave packets

    NASA Astrophysics Data System (ADS)

    Hasović, Elvedin; Milošević, Dejan B.; Gazibegović-Busuladžić, Azra; Čerkić, Aner; Busuladžić, Mustafa

    2015-03-01

    We consider high-order above-threshold ionization (HATI) of polyatomic molecules ionized by a strong linearly polarized laser field. Improved molecular strong-field approximation by which the HATI process on polyatomic molecular species can be described is developed. Using this theory we calculate photoelectron angular-energy spectra for different triatomic molecules. Special attention is devoted to the minima that are observed in the calculated high-energy electron spectra of the ozone and carbon dioxide molecules. A key difference between these minima and minima that are observed in the corresponding spectra of diatomic molecules are presented.

  3. New results from the search for low-mass weakly interacting massive particles with the CDMS low ionization threshold experiment

    SciTech Connect

    Agnese, R.

    2016-02-17

    The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Our results are presented from the second CDMSlite run with an exposure of 70 kg days, which reached an energy threshold for electron recoils as low as 56 eV. Furthermore, a fiducialization cut reduces backgrounds below those previously reported by CDMSlite. Lastly, new parameter space for the WIMP-nucleon spin-independent cross section is excluded forWIMP masses between 1.6 and 5.5 GeV/c2.

  4. New results from the search for low-mass weakly interacting massive particles with the CDMS low ionization threshold experiment

    DOE PAGES

    Agnese, R.

    2016-02-17

    The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Our results are presented from the second CDMSlite run with an exposure of 70 kg days, which reached an energy threshold for electron recoils as low as 56 eV. Furthermore, a fiducialization cut reduces backgrounds below those previously reported by CDMSlite. Lastly, new parameter space for the WIMP-nucleon spin-independent cross section is excluded forWIMP masses between 1.6 and 5.5 GeV/c2.

  5. Ce-PROMOTED Bond Activation of Propene Probed by Mass-Analyzed Threshold Ionization Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Yuchen; Kumari, Sudesh; Yang, Dong-Sheng

    2016-06-01

    The reaction of Ce + propene (CH2=CH-CH3) was carried out in a laser-ablation supersonic molecular beam source. CeC_2H_2, CeC_3H_4, CeC_3H_6, CeC_4H_6, CeC_6H10, and CeC_6H12 were identified by photoionization time-of-flight mass spectrometric measurements, and their structures and electronic states were investigated with mass-analyzed threshold ionization (MATI) spectroscopy and theoretical calculations. The metal complexes containing two or three carbon atoms were formed by the C-C bond breakage (CeC_2H_2), dehydrogenation (CeC_3H_4), or metal insertion into a C-H bond (CeC_3H_6) of a propene molecule. The larger complexes with four to six carbons are formed through secondary reactions involving C-C bond coupling and dehydrogenation. The ground electronic states of the neutral CeC_2H_2, CeC_3H_4, CeC_3H_6, and CeC_4H_6 complexes are triplets with a 4f16s1 electron configuration on the Ce center, and those of the corresponding ions are doublet with a 4f1 configuration. Their MATI spectra are much more complex than those of the corresponding La species formed in the La + propene reaction previously observed by our group. The spectral complexity arises from possibly multiple electronic transitions due to the existence of a 4f electron of the Ce atom which could be located in any one of the seven f-atomic orbitals or involved in considerable spin-orbit interactions.

  6. Observation of mass analyzed threshold ionization using synchrotron radiation on a new-style time of flight mass spectrometer

    NASA Astrophysics Data System (ADS)

    Zhang, Song; Wang, Yanmei; Cao, Zhenzhou; Zhang, Bing; Wang, Sisheng; Kong, Ruihong; Zhao, Yujie; Shan, Xiaobing; Sheng, Liusi

    2007-04-01

    We have developed an efficient and applicable apparatus that combines mass-analyzed threshold ionization (MATI) with continuous molecular-beam mass spectrometry using tunable vacuum ultraviolet synchrotron radiation at National Synchrotron Radiation Laboratory. The new design, in which the spoiling field and the pulsed ionization field are perpendicular to each other, can obtain efficiently the ionic spectra of molecule. The MATI spectra of Ar and N2 have been recorded in the energy region between 15.5 and 17.5eV to illustrate the feasibility of this scheme. With its unique features, the important experiment considerations are potentially a powerful tool for study of information of ionization energies and ionic states of complex organic compounds.

  7. One-color two-photon mass-analyzed threshold ionization spectroscopy of ethyl bromide through a dissociative intermediate state

    NASA Astrophysics Data System (ADS)

    Tang, Bifeng; Zhang, Song; Wang, Yanmei; Tang, Ying; Zhang, Bing

    2005-10-01

    Mass-analyzed threshold ionization (MATI) spectra of ethyl bromide were obtained using one-color two-photon ionization through a dissociative intermediate state. Accurate values for the adiabatic ionization energy have been obtained, 83099±5 and 85454±5cm-1 for the X˜1E2 and X˜2E2 states of the ethyl bromide cation, respectively, giving a splitting of 2355±10cm-1. Compared with conventional photoelectron data, the two-photon MATI spectrum exhibited a more extensive vibrational structure with a higher resolution, mainly containing the modes involving the dissociation coordinate. The observed modes were analyzed and discussed in terms of wave packet evolving on the potential-energy surface of the dissociative state.

  8. Above-threshold ionization with highly charged ions in superstrong laser fields. I. Coulomb-corrected strong-field approximation

    NASA Astrophysics Data System (ADS)

    Klaiber, Michael; Yakaboylu, Enderalp; Hatsagortsyan, Karen Z.

    2013-02-01

    Aiming at the investigation of above-threshold ionization in superstrong laser fields with highly charged ions, we develop a Coulomb-corrected strong-field approximation (SFA). The influence of the Coulomb potential of the atomic core on the ionized electron dynamics in the continuum is taken into account via the eikonal approximation, treating the Coulomb potential perturbatively in the phase of the quasiclassical wave function of the continuum electron. In this paper the formalism of the Coulomb-corrected SFA for the nonrelativistic regime is discussed, employing velocity and length gauge. Direct ionization of a hydrogenlike system in a strong linearly polarized laser field is considered. The relation of the results in the different gauges to the Perelomov-Popov-Terent'ev imaginary-time method is discussed.

  9. Mass-analyzed threshold ionization spectroscopy of lanthanum-hydrocarbon radicals formed by C—H bond activation of propene

    NASA Astrophysics Data System (ADS)

    Kumari, Sudesh; Cao, Wenjin; Hewage, Dilrukshi; Silva, Ruchira; Yang, Dong-Sheng

    2017-02-01

    La(C3H4) and La(C3H6) are observed from the reaction of laser-vaporized La atoms with propene by photoionization time-of-flight mass spectrometry and characterized by mass-analyzed threshold ionization spectroscopy. Two isomers of La(C3H4) are identified as methyl-lanthanacyclopropene [La(CHCCH3)] (Cs) and lanthanacyclobutene [La(CHCHCH2)] (C1); La(C3H6) is determined to be H—La(η3-allyl) (Cs), a C—H bond inserted species. All three metal-hydrocarbon radicals prefer a doublet ground state with a La 6s-based electron configuration. Ionization of the neutral doublet state of each of these radicals produces a singlet ion state by removing the La-based 6s electron. The threshold ionization allows accurate measurements of the adiabatic ionization energy of the neutral doublet state and metal-ligand and ligand-based vibrational frequencies of the neutral and ionic states. The formation of the three radicals is investigated by density functional theory computations. The inserted species is formed by La inserting into an allylic C—H bond and lanthanacyclopropene by concerted vinylic H2 elimination, whereas lanthanacyclobutene involves both allylic and vinylic dehydrogenations. The inserted species is identified as an intermediate for the formation of lanthanacyclobutene.

  10. Electron-hydrogen atom-impact 1s{yields}2s and 1s{yields}2p excitation with screened Coulomb interaction between the n=2 and n=3 excitation thresholds

    SciTech Connect

    Zhang Songbin; Chen Xiangjun; Wang Jianguo; Janev, R. K.

    2011-03-15

    The effects of Coulomb interaction screening on electron-hydrogen atom 1S {yields} 2S and 1S {yields} 2p excitation scattering between the n = 2 and n = 3 excitation thresholds have been investigated by using the R-matrix method with pseudostates. The excitation collision strengths show dramatic changes when the interaction screening length D varies from {infinity} to 9 a.u., as a result of the convergence of S-type and some p- and D-type Feshbach resonances to the varying 3S or 3p thresholds, and due to the crossover of some other p-, D- and all F-type Feshbach resonances into shape-type resonances when they pass across the 3S or 3p threshold at certain critical values of D. The noncrossover of some p- and D-type Feshbach resonances into shape-type resonances at the 3S (or 3p for those of D-type) threshold is at variance with the behavior of these types of resonances at the 2S (2p for those of D-type) threshold, which results from the threefold splitting of the n = 3 hydrogenic level and, consequently, the more complex nature of the configuration mixing in the n = 3 threshold region. The evolution of the total 1S {yields} 2S, 1S {yields} 2p, and 2S {yields} 2p excitation collision strengths, when the screening strength varies, is presented and discussed.

  11. Photoelectron angular distributions in molecular above threshold ionization by two colour circularly polarized ultrashort UV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2013-10-01

    Photoionization of an aligned molecular ion H? has been investigated with two colour circularly polarized ultrashort UV laser pulses by numerically solving the corresponding time dependent Schrödinger equation. Photoelectron angular distributions (PADs) in molecular above threshold ionization (MATI) exhibit: (i) asymmetry resulting from interference of coherent electron wave packets from multiple pathway ionization, which depends critically on the relative carrier envelope phase (CEP) ? between the two colour laser pulses and photoelectron kinetic energies; (ii) rotation with respect to the molecular symmetry axes due to effects of the nonspherical two center Coulomb potential. Such features are described by multi-photon perturbative theoretical ionization models. The ionization probability is functions of both the CEP ? and the angle ? between the electron emission and the molecular axis. The influence of pulse intensity and ellipticity on PADs in MATI is also investigated. It is found that the asymmetry depends on the pulse intensity whereas the rotation angle is shown to be sensitive to the pulse ellipticity, both reflecting the orientation dependence of molecular ionization probabilities.

  12. Electron ionization of the nucleobases adenine and hypoxanthine near the threshold: a combined experimental and theoretical study.

    PubMed

    Dawley, M Michele; Tanzer, Katrin; Cantrell, William A; Plattner, Peter; Brinkmann, Nicole R; Scheier, Paul; Denifl, Stephan; Ptasińska, Sylwia

    2014-12-07

    Electron ionization of the DNA nucleobase, adenine, and the tRNA nucleobase, hypoxanthine, was investigated near the threshold region (∼5-20 eV) using a high-resolution hemispherical electron monochromator and a quadrupole mass spectrometer. Ion efficiency curves of the threshold regions and the corresponding appearance energies (AEs) are presented for the parent cations and the five most abundant fragment cations of each molecule. The experimental ionization energies (IEs) of adenine and hypoxanthine were determined to be 8.70 ± 0.3 eV and 8.88 ± 0.5 eV, respectively. Quantum chemical calculations (B3LYP/6-311+G(2d,p)) yielded a vertical IE of 8.08 eV and an adiabatic IE of 8.07 eV for adenine and a vertical IE of 8.51 eV and an adiabatic IE of 8.36 eV for hypoxanthine, and the lowest energy optimized structures of the fragment cations and their respective neutral species were calculated. The enthalpies of the possible reactions from the adenine and hypoxanthine cations were also obtained computationally, which assisted in determining the most likely electron ionization pathways leading to the major fragment cations. Our results suggest that the imidazole ring is more stable than the pyrimidine ring in several of the fragmentation reactions from both adenine and hypoxanthine. This electron ionization study contributes to the understanding of the biological effects of electrons on nucleobases and to the database of the electronic properties of biomolecules, which is necessary for modeling the damage of DNA in living cells that is induced by ionizing radiation.

  13. Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of the selected rotamers of m-methoxyaniline and o-methoxyaniline

    NASA Astrophysics Data System (ADS)

    Lin, Jung Lee; Huang, Chen-Jso; Lin, Cheng-Huang; Tzeng, Wen Bih

    2007-07-01

    We report the resonant two-photon ionization and mass-analyzed threshold ionization (MATI) spectra of m-methoxyaniline and o-methoxyaniline. The vibronic features of m-methoxyaniline are built on 34308 ± 2 and 34495 ± 2 cm -1 corresponding to the origins of the S 1 ← S 0 electronic transition ( E1's) of the cis and trans rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 59983 ± 5 and 60879 ± 5 cm -1 for these two species. o-Methoxyaniline is found to have only one stable structure whose E1 and IE are 33875 ± 2 and 58678 ± 5 cm -1, respectively. Most of the active vibrations of m- and o-methoxyaniline in the electronically excited S 1 and cationic ground D 0 states result from the in-plane ring vibrations. Comparing these data with those of p-methoxyaniline allows us to learn about the vicinal substitution effects resulting from the relative locations of the NH 2 and OCH 3 substituents.

  14. Above-threshold ionization in neon produced by combining optical and bichromatic XUV femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Douguet, Nicolas; Grum-Grzhimailo, Alexei N.; Bartschat, Klaus

    2017-01-01

    We consider the ionization of neon induced by a femtosecond laser pulse composed of overlapping, linearly polarized bichromatic extreme ultraviolet and infrared fields. In particular, we study the effects of infrared light on a two-pathway ionization scheme for which Ne 2 s22 p53 s 1P is used as the intermediate state. Using time-dependent calculations, supported by a theoretical approach based on the strong-field approximation, we analyze the ionization probability and the photoelectron angular distributions associated with the different sidebands of the ionization spectrum. Complex oscillations of the angular distribution anisotropy parameters as a function of the infrared light intensity are revealed. Finally, we demonstrate that coherent control of the asymmetry is achievable by tuning the infrared frequency to a nearby electronic transition.

  15. Study of the upper spin--orbit state of the chloroiodomethane cation by mass-analyzed threshold ionization

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Kim, Myung Soo

    2006-11-01

    The vibrational spectrum of CH 2ClI + in the upper spin-orbit state was obtained by one-photon mass-analyzed threshold ionization (MATI) spectrometry. The accurate ionization energy of the upper spin-orbit state was determined to be 10.3045 ± 0.0006 eV. The energy gap between the upper and lower spin-orbit states was 0.5539 ± 0.0012 eV. The frequency of the Cl-C-I bending mode was found to be most affected by the spin-orbit interaction. This suggests that the avoided crossing between the lower and upper spin-orbit states occurs along a direction close to the Cl-C-I bending coordinate.

  16. Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of hexafluorobenzene: The Jahn-Teller effect and vibrational analysis

    NASA Astrophysics Data System (ADS)

    Kwon, Chan Ho; Kim, Myung Soo

    2004-06-01

    One-photon mass-analyzed threshold ionization (MATI) spectrum of hexafluorobenzene was obtained by using vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The ionization energy of hexafluorobenzene determined from the position of the 0-0 band was 9.9108±0.0006 eV. To aid the spectral analysis, the Jahn-Teller coupling parameters for four e2g modes of C6F6+ in the ground electronic state were calculated from the topographical data of the potential energy surface obtained at the density functional theory (DFT) level. These were used in the initial calculation of the energies of the Jahn-Teller states and upgraded through the multimode fit to the experimental data. Excellent agreement between the experimental and calculated frequencies was achieved. The vibrations which are not linear Jahn-Teller active were observed and could be assigned by referring to the frequencies obtained at the DFT level.

  17. Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of vinyl bromide: Franck-Condon analysis and vibrational assignment

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Kim, Myung Soo

    2003-09-01

    Vibrational spectrum of vinyl bromide cation in the ground electronic state was obtained by one-photon mass-analyzed threshold ionization (MATI) spectroscopy using coherent vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. From MATI spectrum, ionization energy to the ground state of the cation was determined to be 9.8171±0.0006 eV (79 180±5 cm-1). Almost complete vibrational assignments for the peaks in the MATI spectrum were possible by utilizing vibrational frequencies and Franck-Condon factors calculated at the Becke three parameter Lee-Yang-Parr (B3LYP)/6-311++G(df,pd) level. Franck-Condon analysis for one-photon MATI spectra is especially useful because calculations of only the ground electronic states are involved while that for two-photon MATI spectra requires excited state calculations.

  18. Near-threshold electron-impact doubly differential cross sections for the ionization of argon and krypton

    SciTech Connect

    Yates, Brent R.; Khakoo, Murtadha A.

    2011-04-15

    We present normalized doubly differential cross sections (DDCS's) for the near-threshold, electron-impact single ionization of argon and krypton, similar to those taken earlier for Ne and Xe [Yates et al., J. Phys. B 42, 095206 (2009)]. The Ar measurements were taken at incident energies of 17, 18, 20, and 30 eV while the Kr measurements were taken at 15, 16, 17.5, and 20 eV. The DDCS scattering angles range from 15 deg. to 120 deg. The differential data are initially normalized to available experimental cross sections for excitation of the ground np{sup 6} to the np{sup 5}(n+1)s excited states of the noble gas and, after integration, to well-established experimental total ionization cross sections of Rapp and Englander-Golden [J. Chem. Phys. 43, 1464 (1965)].

  19. Measurement of the photoionization spectra and ionization thresholds of the H sub 2 CN and D sub 2 CN radicals

    SciTech Connect

    Nesbitt, F.L.; Marston, G.; Stief, L.J. ); Wickramaaratchi, M.A.; Tao, W.; Klemm, R.B. )

    1991-10-03

    The photoionization spectra of the H{sub 2}CN and D{sub 2}CN radicals were obtained by photoionization mass spectroscopy (PIMS) using synchrotron radiation. The radicals were generated by the reaction of N with CH{sub 3} and CD{sub 3}, respectively. For both H{sub 2}CN and D{sub 2}CN a prominent feature was observed near 118.6 nm (10.5 eV) and the ionization threshold was determined to be 9.4 {plus minus} 0.1 eV; both features provide additional signatures for identifying H{sub 2}CN in complex systems. By use of a corrected value for {Delta}H{sub f} (H{sub 2}CN) derived from a recent electron affinity measurement and other available measured or calculated thermochemical quantities for H{sub 2}CN and HCNH radicals and radical ions, a value of 10.8 {plus minus} 0.6 eV for the ionization energy of H{sub 2}CN was derived. The much lower value derived for the ionization energy of HCNH (6.8 and 7.0 eV for the cis and trans isomers, respectively) is consistent with the product of the N + CH{sub 3} reaction being the H{sub 2}CN isomer and not HCNH. The ionization threshold observed at 9.4 eV is attributed to autoionization arising from high Rydberg states of H{sub 2}CN which couple into vibrationally excited states of the linear HCNH{sup +} ground state of the ion. Also discussed are the roles of the H{sub 2}CN radical and HCNH{sup +} radical ion in the chemistry of the atmosphere of Titan and in interstellar clouds.

  20. The threshold laws for electron-atom and positron-atom impact ionization

    NASA Technical Reports Server (NTRS)

    Temkin, A.

    1983-01-01

    The Coulomb-dipole theory is employed to derive a threshold law for the lowest energy needed for the separation of three particles from one another. The study focuses on an electron impinging on a neutral atom, and the dipole is formed between an inner electron and the nucleus. The analytical dependence of the transition matrix element on energy is reduced to lowest order to obtain the threshold law, with the inner electron providing a shield for the nucleus. Experimental results using the LAMPF accelerator to produce a high energy beam of H- ions, which are then exposed to an optical laser beam to detach the negative H- ion, are discussed. The threshold level is found to be confined to the region defined by the upper bound of the inverse square of the Coulomb-dipole region. Difficulties in exact experimental confirmation of the threshold are considered.

  1. Electron-nuclear correlation in above-threshold double ionization of molecules

    NASA Astrophysics Data System (ADS)

    Lu, Peifen; Zhang, Wenbin; Gong, Xiaochun; Song, Qiying; Lin, Kang; Ji, Qinying; Ma, Junyang; He, Feng; Zeng, Heping; Wu, Jian

    2017-03-01

    We report on the experimental observation of photon energy sharing among two electrons and two ions ejected from a doubly ionized molecule exposed to an intense ultraviolet femtosecond laser pulse. Although two electrons are successively released one after the other, bridged by the nuclear motion via their interactions, photon energy sharing among four particles is observed as multiple energy conservation lines in their joint energy spectrum. For sequential double ionization of H2, the electron-nuclear joint energy spectrum allows us to identify three pathways towards the charge-resonance enhanced ionization of the stretching H2+ in strong laser fields. By counting the photon number absorbed by the molecule, we trace the accessibility, enhancement, and suppression of various pathways. The correlated electron-nuclear motion provides profound insights of the complicated strong-field dynamics of molecules.

  2. Effects of ionizing radiation on auditory and visual thresholds. Technical report, 9 Oct 87-28 May 91

    SciTech Connect

    Hienz, R.D.

    1992-03-01

    An experimental analysis of the effects of low-dose ionizing radiation on sensory and motor function was conducted in baboons. Animals were trained using a reaction time procedure to respond to near-threshold acoustic and visual stimuli, and quantitative assessments were made of radiation-induced changes in absolute auditory and visual thresholds and reaction times. Animals received multiple exposures at single fractionated dose levels of 1, 2, and 5 Gy. Single exposures at higher exposure levels of 10 and 15 Gy were also examined. 100-200 cGy exposures produced transient changes in reaction times. Transient Increases in reaction times occurred following low-dose exposures, usually within 1-3 weeks following the exposure. These increases typically recovered to normal baseline levels within 2-3 weeks. 1000 and 1500 cGy exposures produced long-term hearing deficits which were not frequency-specific. The severe hearing loss was most likely due to a sensorineural deficit, since complete loss of function of the tympanic membrane or middle ear ossicles would be expected to produce a hearing loss about 50-55 dB. These higher radiation doses have had less of an effect on visual intensity thresholds, producing a 5-lO dB deficit in visual thresholds. No physical damage to the cornea iris lens or retina was observed.

  3. Rotamers of m-chloroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Huang, Hsin Chang; Shiung, Kui Shiu; Jin, Bih Yaw; Tzeng, Wen Bih

    2013-11-01

    We apply the resonant two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) techniques to record the vibronic and cation spectra of m-chloroanisole. The vibronic features appear in two series, built on 35,822 ± 2 and 35,868 ± 2 cm-1, corresponding to the origins of the S1 ← S0 electronic transition (E1's) of the two rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 67,645 ± 5 and 68,008 ± 5 cm-1 for these two isomeric species. Comparing these data with those of anisole, we find that the chlorine substitution at the meta position leads to a red shift in the E1 and a blue shift in the IE. The observed R2PI and MATI bands mainly result from the in-plane ring deformation and substituent-sensitive bending vibrations of these species in the electronically excited S1 and cationic ground D0 states.

  4. Angle-dependent molecular above-threshold ionization with ultrashort intense linearly and circularly polarized laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2011-07-01

    We present molecular above-threshold ionization (MATI) spectra generated by ultrashort intense linearly and circularly polarized laser pulses from nonperturbative numerical solutions of the corresponding time-dependent Schrödinger equation in the molecular-ion H2+. It is found that high-order MATI spectra with maximum kinetic energy 32Up, where Up=I0/4meω02 is the ponderomotive energy at intensity I0 and frequency ω0, can be obtained in H2+ at great internuclear distances R for both linear and circular polarizations. Quasiclassical laser-induced collision models confirm that such high-order MATIs mainly result from a collision with neighboring ions of the ionized electron. Interference patterns in the high-order MATI spectra are critically sensitive to both the internuclear distance R of the molecules and the polarizations of the driving laser pulses. Moreover, with few-cycle laser pulses, the carrier-envelope phase sensitivity of MATI angular distributions is also investigated for varying internuclear distances R. At critical internuclear distances for charge-resonance-enhanced ionization, we also find that enhanced interference patterns occur.

  5. Mass-analyzed threshold ionization and structural isomers of M3O4 (M = Sc, Y, and La)

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Zhang, Changhua; Krasnokutski, Serge A.; Yang, Dong-Sheng

    2012-08-01

    M3O4 (M = Sc, Y, and La) were produced in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and electronic structure calculations. Adiabatic ionization energies (AIEs) of the neutral clusters and vibrational frequencies of the cations were measured accurately for the first time from the MATI spectra. Five possible structural isomers of M3O4 were considered in the calculations and spectral analysis. A cage-like structure in C3v point group was identified as the most stable one. The structure is formed by fusing three M2O2 fragments together, each sharing two O-M bonds with others. The ground electronic state of the neutral clusters is 2A1 with the unpaired electron being largely a metal-based s character. Ionization of the 2A1 state yields a 1A1 ion state in a similar geometry to the neutral cluster. The AIEs of the clusters are 4.4556 (6), 4.0586(6), and 3.4750(6) eV for M = Sc, Y, and La, respectively. The observed vibrational modes of the cations include metal-oxygen stretching, metal triangle breathing, and oxygen-metal-oxygen rocking in the frequency range of 200-800 cm-1.

  6. Mass-Analyzed Threshold Ionization of Lanthanum Oxide Clusters: La_2O_2 and La_3O_4

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Zhang, Changhua; Krasnokutski, Sergiy; Yang, Dong-Sheng

    2009-06-01

    Lanthanum oxide clusters are produced by laser vaporization in a pulsed cluster source and identified by photoionization mass spectrometry. Vibrationally resolved ion spectra are obtained with mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectra of La_2O_2 and La_3O_4 exhibit a very strong 0-0 transition, indicating similar geometries for the neutral and ionized clusters and a very weakly bonding or non-bonding electron ejected from an outmost molecular orbital. The ionization energies of La_2O_2 and La_3O_4 are measured to be 36937(5) and 28028(5) cm^{-1}, respectively. In addition, the spectra of both clusters display a number of vibrational intervals that are associated with metal-metal, metal-oxygen, and oxygen-oxygen vibrations. Preliminary data analysis shows that the La_2O_2 cluster has a D_{2h} planar structure and La_3O_4 has a C_{3v} cage-like structure, both with alternating La-O-La bonds. The spectra may be assigned to the ^2Ag←^1Ag transition in the case of La_2O_2 and ^1A_1←^2A_1 in La_3O_4 .

  7. Mass-analyzed threshold ionization spectroscopy of p-methylphenol and p-ethylphenol cations and the alkyl substitution effect

    NASA Astrophysics Data System (ADS)

    Lin, Jung Lee; Li, Changyong; Tzeng, Wen Bih

    2004-06-01

    The mass-analyzed threshold ionization (MATI) spectra of p-methylphenol and p-ethylphenol have been recorded by ionizing via various vibronic levels. The adiabatic ionization energies (IEs) of p-methylphenol and p-ethylphenol are determined to be 65918±5 and 65628±5 cm-1, which are less than that of phenol by 2707 and 2997 cm-1, respectively. This redshift indicates that the interaction between the alkyl group and the ring of alkylphenols in the cationic D0 state is greater than that in the neutral S0 state. Moreover, a longer alkyl group gives rise to a greater redshift in the IE. Analysis of the MATI spectra shows that most of the active modes are related to the in-plane ring vibrations of these two cations. However, the length of the alkyl group has an insignificant effect on the frequency of the observed ring vibrations. No band with frequency less than 350 cm-1 is observed for the p-methylphenol cation. In contrast, many low-frequency bands resulting from the characteristic motions (e.g., the C-C2H5 torsion and C-C2H5 and C-OH bending vibrations) appear in the MATI spectra of p-ethylphenol. The present results show that the ethyl group enhances the substituent-sensitive and many large-amplitude vibrations of the cation.

  8. Angle-dependent molecular above-threshold ionization with ultrashort intense linearly and circularly polarized laser pulses

    SciTech Connect

    Yuan, Kai-Jun; Bandrauk, Andre D.

    2011-07-15

    We present molecular above-threshold ionization (MATI) spectra generated by ultrashort intense linearly and circularly polarized laser pulses from nonperturbative numerical solutions of the corresponding time-dependent Schroedinger equation in the molecular-ion H{sub 2}{sup +}. It is found that high-order MATI spectra with maximum kinetic energy 32U{sub p}, where U{sub p}=I{sub 0}/4m{sub e}{omega}{sub 0}{sup 2} is the ponderomotive energy at intensity I{sub 0} and frequency {omega}{sub 0}, can be obtained in H{sub 2}{sup +} at great internuclear distances R for both linear and circular polarizations. Quasiclassical laser-induced collision models confirm that such high-order MATIs mainly result from a collision with neighboring ions of the ionized electron. Interference patterns in the high-order MATI spectra are critically sensitive to both the internuclear distance R of the molecules and the polarizations of the driving laser pulses. Moreover, with few-cycle laser pulses, the carrier-envelope phase sensitivity of MATI angular distributions is also investigated for varying internuclear distances R. At critical internuclear distances for charge-resonance-enhanced ionization, we also find that enhanced interference patterns occur.

  9. Photo-Double Ionization: Threshold Law and Low-Energy Behavior

    NASA Technical Reports Server (NTRS)

    Bhatia, Anand

    2008-01-01

    The threshold law for photoejection of two electrons from atoms (PDI) is derived from a modification of the Coulomb-dipole (C-D) theory. The C-D theory applies to two-electron ejection from negative ions (photo-double detachment:PDD). The modification consists of correctly accounting for the fact that in PDI that the two escaping electrons see a Coulomb field, asymptotically no matter what their relative distances from the residual ion are. We find in the contralinear spherically symmetric model that the analytic threshold law Q(E),i. e. the yield of residual ions, to be Qf(E)approaches E + CwE(sup gamma(w)) + CE(sup 5/4)sin[1/2 ln(E + theta)]/ln(E). The first and third terms are beyond the Wannier law. Our threshold law can only be rigorously justified for residual energies less than or equal to 10(exp -3) eV. Nevertheless in the present experimental range (0.1 - 4 eV), the form, even without the second term, can be fitted to experimental results of PDI for He, Li, and Be, in contrast to the Wannier law which has a larger deviation from the data for Li and Be, for both of which the data show signs of modulation.

  10. Photo-Double Ionization: Threshold Law and Low-Energy Behavior

    NASA Technical Reports Server (NTRS)

    Bhatia, A. K.; Temkin, A.

    2007-01-01

    The threshold law for photoejection of two electrons from atoms (PDI) is derived from a modification of the Coulomb-dipole (C-D) theory. The C-D theory applies to two-electron ejection from negative ions (photo-double detachment:PDD). The modification consists of correctly accounting for the fact that in PDI that the two escaping electrons see a Coulomb field, asymptotically no matter what their relative distances from the residual ion are. We find in the contralinear spherically symmetric model that the analytic threshold law Q(E), i.e. the yield of residual ions, to be Q Integral of (E) varies as E + (C(sub w) E(sup gamma W)) +CE(sup 5/4) sin [1/2 ln E + phi]/ln(E). The first and third terms are beyond the Wannier law. Our threshold law can only be rigorously justified for residual energies <= 10(exp -3) eV. Nevertheless in the present experimental range (0.1 - 4 eV), the form, even without the second term, can be fitted to experimental results of PDI for He, Li, and Be, in contrast to the Wannier law which has a larger deviation from the data for Li and Be.

  11. Mass analyzed threshold ionization spectroscopy of p-methylanisole cation and the substitution effect

    NASA Astrophysics Data System (ADS)

    Huang, Jiangou; Li, Changyong; Tzeng, Wen Bih

    2005-10-01

    The adiabatic ionization energy of p-methylanisole is measured to be 63 972 ± 5 cm -1, which is red-shifted with respect to those of anisole and toluene. This indicates that the interaction of either CH 3 or OCH 3 group with the ring is stronger in the cationic D 0 state than that in the neutral S 0 state. Most of the observed MATI bands result from in-plane ring vibrations. The frequencies of vibrations 9b, 6a, and 1 of the p-methylanisole cation are found to be 407, 515, and 811 cm -1, respectively.

  12. Above-threshold ionization of Mg by linearly and circularly polarized laser fields: Origin of the subpeaks in the photoelectron energy spectra

    SciTech Connect

    Nakajima, Takashi; Buica, Gabriela

    2006-08-15

    We theoretically investigate above-threshold ionization of Mg by linearly and circularly polarized fs laser pulses. We find that the above-threshold ionization peaks are accompanied by small subpeaks for both linearly and circularly polarized pulses. We interpret the physical origin of the subpeaks as above-threshold ionization from the low-lying bound states which are far off-resonantly excited by the spectral wing of the pulse. This interpretation is confirmed by our comparative numerical studies. Furthermore, we provide a clear explanation of why this kind of subpeak in the photoelectron energy spectra has not been reported for smaller photon energies with Mg and other commonly used atoms such as H and rare gas atoms.

  13. Dynamical medium depletion in high-order above-threshold ionization with few-cycle laser pulses

    SciTech Connect

    Altucci, C.; Velotta, R.; Tosa, V.; Nam, C.H.

    2004-12-01

    The influence of dynamical medium depletion in high-order above-threshold ionization (ATI) in left/right asymmetry of photoelectron energy spectra is analyzed. Based on a classical analysis of high-order ATI electrons produced by few-cycle laser pulses, calculated asymmetry maps of electron spectra reproduce very well the experimental results reported in Lindner et al. [Phys. Rev. Lett. 92, 113001 (2004)], utilized for determining the Guoy phase shift of few-cycle laser pulses. The anomalous behavior of the high-energy part of the ATI electron spectra is, then, fully understood in terms of earlier medium depletion occurring in the leading edge of the laser pulse. In order to correctly reproduce the experimental findings a physical temporal envelope of the laser pulse, which only vanishes at the infinity, plays a crucial role.

  14. Effect of rescattering potential on the high-energy above-threshold ionization of a model-H atom

    NASA Astrophysics Data System (ADS)

    Chen, J.-H.; Wang, G.-L.; Zhang, Z.-R.; Zhao, S.-F.

    2017-01-01

    The high-energy above-threshold ionization of a model-H atom (with 1s state and the same binding energy as H atom) in a few-cycle laser pulse is investigated by using the improved strong-field approximation (ISFA), where the spherical shell potential is used as the rescattering potential. The results obtained from numerically solving time-dependent Schrödinger equation(TDSE) are regarded as the benchmark results. Our results show that the energy distributions in high-energy region obtained from ISFA calculations using the spherical shell potential may either match or be better than those from ISFA using Yukawa potential and zero-range potential in the laser with wavelengths of 800 and 1200 nm. In addition, the influence of the rescattering potential on the density of probability at different ejection angles is also discussed in this paper.

  15. Spectroscopy and Ionization Thresholds of Isoelectronic 1-PHENYLALLYL and Benzylallenyl Resonance Stabilized Radicals

    NASA Astrophysics Data System (ADS)

    Sebree, Joshua A.; Kidwell, Nathan; Buchanan, Evan; Zwier, Timothy S.; Zgierski, Marek

    2011-06-01

    In recent years it has been proposed that resonance-stabilized radicals (RSRs) may play an important role as intermediates in the formation of polycyclic aromatic hydrocarbons (PAHs). RSRs gain extra stability by delocalizing the unpaired electron through a neighboring conjugated π-system. Because of this extra stability, RSRs are able to build up in concentration, allowing for the creation of larger, more complex systems through their recombination with other RSRs. Mass-selective two-color resonant two-photon ionization spectra of two RSRs, phenylallyl and benzylallenyl radicals, have been recorded under jet-cooled conditions. These two radicals, while sharing the same radical conjugation, have unique properties. The phenylallyl and benzylallenyl radicals were respectively produced via discharge of trans-β-methylstyrene and benzylallene in argon prior to supersonic expansion. The D0-D1 origin of the phenylallyl radical was found at 19204 wn and was found to have a strong vertical ionization energy of 6.905(2) eV. By comparison, the benzylallenyl radical has an origin at 19703 wn and, while showing similar Franck-Condon activity to phenylallyl, has an IP curve indicative of a large geometry change between the ground state and the ion 7.50(2) eV. Visible-visible holeburning was used to show that each radical exists in one conformeric form in the expansion. The CH stretch region of each radical was taken using D0-Resonant Ion Dip Infrared Spectroscopy in a novel four laser experiment. A combination of this and DFT calculations was used to show that each radical exists in a trans geometry.

  16. Threshold Ionization of La(C_5H_8) Formed by La-MEDIATED Dehydrogenation of 1-PENTENE

    NASA Astrophysics Data System (ADS)

    Cao, Wenjin; Zhang, Yuchen; Yang, Dong-Sheng

    2016-06-01

    La(C_5H_8) was formed by La reaction with 1-pentene (CH2=CH-CH2-CH3) in a laser-vaporization supersonic molecular beam source and characterized with mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectrum displays an origin band at 38988 (5) wn and three vibrational intervals of 130, 294, and 415 wn. The La(C_5H_8) complex is identified as a five-membered metallacycle in C1 point group, with the doublet and singlet being the lowest energy states of the neutral and cation, respectively. The energy at 38998 wn corresponds to the adiabatic ionization energy of the complex, and the three vibration intervals in the order of the frequency increase are assigned to the terminal CH_3 torsion, asymmetric La-ligand stretch, and symmetric La-ligand stretch excitation of the ion. The La + 1-penetene reaction will also be compared with La reactions with other five-carbon hydrocarbon molecules, such as isoprene, 1-pentyne, and 1,4-pentadiene.

  17. Mass-analyzed threshold ionization spectroscopy of the rotamers of p-n-propylphenol cations and configuration effect

    NASA Astrophysics Data System (ADS)

    Li, Changyong; Lin, Jung Lee; Tzeng, Wen Bih

    2005-01-01

    Two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy was used to record the vibrationally resolved cation spectra of the selected rotamers of p-n-propylphenol. The adiabatic ionization energies of the trans, gauche-A, and gauche-B rotamers are determined to be 65 283±5, 65 385±5, and 65 369±5 cm-1, which are less than that of phenol by 3342, 3240, and 3256 cm-1, respectively. This suggests that the n-propyl substitution causes a greater degree in lowering the energy level in the cationic than the neutral ground state. Analysis on the MATI spectra of the selected rotamers of p-n-propylphenol cation shows that the relative orientation of the p-n-alkyl group has little effect on the in-plane ring vibrations. However, the low-frequency C3H7 bending vibrations appear to be active only for the two gauche forms of the cation.

  18. Threshold ionization, structural isomers, and electronic states of M2O2 (M = Sc, Y, and La)

    NASA Astrophysics Data System (ADS)

    Wu, Lu; Zhang, Changhua; Krasnokutski, Serge A.; Yang, Dong-Sheng

    2014-06-01

    M2O2 (M = Sc, Y, and La) were synthesized in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and ab initio calculations. Adiabatic ionization energies (AIEs) and several vibrational frequencies were measured accurately for the first time from the MATI spectra. Six possible structural isomers of M2O2 were considered in the calculations and the three converged structures were used in the spectral analysis. A planar cyclic structure in D2h point group was predicted to be the most stable one by the theory and observed by the experiment. The cyclic structure is formed by joining two MO2 fragments together through two shared oxygen atoms. In forming the ground state clusters, each metal atom loses two (n - 1)d electrons and as a result, has only one ns electron in the metal-based valence orbital. The ground electronic state of Sc2O2 is 1Ag, and those of Y2O2 and La2O2 are 3B1u. Ionization of both 1Ag and 3B1u neutral states yields the 2Ag ion state by removing one of the two ns electrons, and the resultant ion has a similar geometry to the neutral cluster. The AIEs of the clusters are 5.5752 (6), 5.2639 (6), 4.5795 (6) eV for M = Sc, Y, and La, respectively. The vibrational frequencies of the observed modes, including O-M and M-M stretches, are in the range of 200-800 cm-1.

  19. Above-threshold ionization with highly charged ions in superstrong laser fields. II. Relativistic Coulomb-corrected strong-field approximation

    NASA Astrophysics Data System (ADS)

    Klaiber, Michael; Yakaboylu, Enderalp; Hatsagortsyan, Karen Z.

    2013-02-01

    We develop a relativistic Coulomb-corrected strong-field approximation (SFA) for the investigation of spin effects at above-threshold ionization in relativistically strong laser fields with highly charged hydrogenlike ions. The Coulomb-corrected SFA is based on the relativistic eikonal-Volkov wave function describing the ionized electron laser-driven continuum dynamics disturbed by the Coulomb field of the ionic core. The SFA in different partitions of the total Hamiltonian is considered. The formalism is applied for direct ionization of a hydrogenlike system in a strong linearly polarized laser field. The differential and total ionization rates are calculated analytically. The relativistic analog of the Perelomov-Popov-Terent'ev ionization rate is retrieved within the SFA technique. The physical relevance of the SFA in different partitions is discussed.

  20. Above-threshold ionization and laser-induced electron diffraction in diatomic molecules

    NASA Astrophysics Data System (ADS)

    Suárez, Noslen; Chacón, Alexis; Ciappina, Marcelo F.; Wolter, Benjamin; Biegert, Jens; Lewenstein, Maciej

    2016-10-01

    Strong-field photoemission and electron recollision provide a viable route to extract electronic and nuclear dynamics from molecular targets with attosecond temporal resolution. However, since an ab initio treatment of even the simplest diatomic systems is beyond today's capabilities, approximate qualitative descriptions are warranted. In this paper, we develop such a theoretical approach to model the photoelectrons resulting from intense laser-molecule interaction. We present a general theory for symmetric diatomic molecules in the single active electron approximation that, amongst other capabilities, allows adjusting both the internuclear separation and molecular potential in a direct and simple way. More importantly, we derive an analytic approximate solution of the time-dependent Schrödinger equation (TDSE), based on a generalized strong-field approximation (SFA) version. Using that approach, we obtain expressions for electron emitted transition amplitudes from two different molecular centers, and accelerated then in the strong laser field. In addition, our approach directly underpins different underlying physical processes that correspond to (i) direct tunneling ionization; (ii) electron rescattering on the center of origin; and, finally, (iii) electron rescattering on a different center. One innovative aspect of our theory is the fact that the dipole matrix elements are free from nonphysical gauge and coordinate system-dependent terms: this is achieved by adapting the coordinate system, in which SFA is performed, to the center from which the corresponding part of the time-dependent wave function originates. Our analytic results agree very well with the numerical solution of the full three-dimensional TDSE for the H2 + molecule. Moreover, the theoretical model was applied to describe laser-induced electron diffraction measurements of O2 + molecules, obtained at ICFO, and reproduces the main features of the experiment very well. Our approach can be extended in

  1. Photodissociation yield spectroscopy of vinyl bromide cation generated by mass-analyzed threshold ionization: Vibrational spectroscopy and decay dynamics in the B ˜ state

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Kim, Myung Soo

    2007-04-01

    A new technique [mass-analyzed threshold ionization (MATI)-photodissociation yield spectroscopy] to probe bound excited states of a cation was developed, which measures photodissociation yield of the cation generated by mass-analyzed threshold ionization. A vibrational spectrum of vinyl bromide cation in the B ˜ state was obtained using this technique. Optical resolution in the low vibrational energy range of the spectrum was far better than in conventional MATI spectra. The origin of the B ˜ state was found at 2.2578±0.0003eV above the first ionization onset. Almost complete vibrational assignment was possible for peaks appearing in the spectrum. Analysis of time-of-flight profiles of C2H3+ product ion obtained with different laser polarization angles suggested that photoexcited vinyl bromide cation remained in the B ˜ state for several hundred picoseconds prior to internal conversion to the ground state and dissociation therein.

  2. Controlling high-order harmonic generation and above-threshold ionization with an attosecond-pulse train

    SciTech Connect

    Figueira de Morisson Faria, C.; Salieres, P.; Villain, P.; Lewenstein, M.

    2006-11-15

    We perform a detailed analysis of how high-order harmonic generation (HHG) and above-threshold ionization (ATI) can be controlled by a time-delayed attosecond-pulse train superposed to a strong, near-infrared laser field. In particular we show that the high-order harmonic and photoelectron intensities, the high-order harmonic plateau structure and cutoff energies, and the ATI angular distributions can be manipulated by changing this delay. This is a direct consequence of the fact that the attosecond pulse train can be employed as a tool for constraining the instant an electronic wave packet is ejected in the continuum. A change in such initial conditions strongly affects its subsequent motion in the laser field, and thus HHG and ATI. In our studies, we employ the strong-field approximation and explain the features observed in terms of interference effects between various electron quantum orbits. Our results are in agreement with recent experimental findings and theoretical studies employing purely numerical methods.

  3. Surface modification of hexatriacontane by CF_4 plasmas studied by optical emission and threshold ionization mass spectrometries

    NASA Astrophysics Data System (ADS)

    Poncin-Epaillard, F.; Wang, W.; Ausserré, D.; Scharzenbach, W.; Derouard, J.; Sadeghi, N.

    1998-11-01

    The behavior of tetrafluoromethane microwave plasma (2% argon included) has been studied by emission spectroscopy during the treatment of hexatriacontane, a model for high density polyethylene. The evolution of the densities of F* atoms, and CF, CF^*2, radicals has been followed by using the actinometric technique with 2% argon added to the gas. The surface properties, such as surface energy and surface roughness were correlated to the emission intensity of reactives species in the plasma gas phase. We found that the evolution of the fluorinated species emissions in the plasma gas phase can be a direct indication of the surface modifications by the plasma. A mild exposure to the plasma can result in a great decrease of surface energy corresponding to the fluorination. The surface roughness only changes under drastic plasma conditions. Threshold ionization mass spectroscopy is applied to detect the fluorine atoms and CFx radicals. Time resolved measurements in pulsed plasma, give access to the decay rate of F atoms concentration in the afterglow, and to their sticking coefficient on different surfaces. The influences of the discharge parameters and of the surfaces (metal, silicon or hexatriacontane) in contact with the plasma are investigated. The results show that the plasma generated ions and/or UV radiations highly enhance the reactivity of the F atoms on polymer surface.

  4. Two-color above-threshold ionization of atoms and ions in XUV Bessel beams and intense laser light

    NASA Astrophysics Data System (ADS)

    Seipt, D.; Müller, R. A.; Surzhykov, A.; Fritzsche, S.

    2016-11-01

    The two-color above-threshold ionization (ATI) of atoms and ions is investigated for a vortex Bessel beam in the presence of a strong near-infrared (NIR) light field. While the photoionization is caused by the photons from the weak but extreme ultraviolet (XUV) vortex Bessel beam, the energy and angular distribution of the photoelectrons and their sideband structure are affected by the plane-wave NIR field. We here explore the energy spectra and angular emission of the photoelectrons in such two-color fields as a function of the size and location of the target atoms with regard to the beam axis. In addition, analog to the circular dichroism in typical two-color ATI experiments with circularly polarized light, we define and discuss seven different dichroism signals for such vortex Bessel beams that arise from the various combinations of the orbital and spin angular momenta of the two light fields. For localized targets, it is found that these dichroism signals strongly depend on the size and position of the atoms relative to the beam. For macroscopically extended targets, in contrast, three of these dichroism signals tend to zero, while the other four just coincide with the standard circular dichroism, similar as for Bessel beams with a small opening angle. Detailed computations of the dichroism are performed and discussed for the 4 s valence-shell photoionization of Ca+ ions.

  5. Rotations of molecular photoelectron angular distributions in above threshold ionization of H2+ by intense circularly polarized attosecond UV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Chelkowski, Szczepan; Bandrauk, André D.

    2014-10-01

    We present molecular photoelectron angular distributions (MPADs) in multi-photon ionization processes by circularly polarized attosecond UV laser pulses. Simulations are performed on the single electron aligned molecular ion H_2^+ by solving corresponding 3D time-dependent Schrödinger equations. Numerical results of molecular above threshold ionization (MATI) show that rotations of MPADs with respect to the molecular and polarization axes depend on pulse intensities and photoelectron kinetic energies. We attribute the rotation to Γ, the difference between parallel and perpendicular ionization probabilities. It is found that in a resonant ionization process, the rotation angle is also a function of the symmetry of intermediate electronic states. The coherent population transfer between the initial and the resonant electronic states is controlled by pulse intensities. Such dependence of rotations on the pulse intensity is absent in Rydberg resonant ionizations as well as in MATI at large energy photons ℏω > Ip, where ω is angular frequency of photons and Ip is the molecular ionization potential. We describe these processes by a multi-photon perturbation theory model. Effects of molecular alignment and pulse ellipticities on rotations are investigated, confirming the essence of the ionization parameter Γ in rotations of MPADs.

  6. Absolute partial and total electron-impact-ionization cross sections for CF4 from threshold up to 500 eV

    NASA Astrophysics Data System (ADS)

    Ma, Ce; Bruce, M. R.; Bonham, R. A.

    1991-09-01

    Electron-impact dissociative ionization of tetrafluoromethane (CF4) was studied with the use of a pulsed electron beam time-of-flight apparatus. The absolute partial ionization cross sections of CF+3, CF+2, CF2+3, CF+, CF2+2, F+, and C+ were measured from threshold up to 500 eV. The total ionization cross section was obtained by charge weighted summing of all the observed partial ionization cross sections. A total cross section for dissociation into neutral fragments was inferred from our total ionization cross section and the total dissociation cross section of Winters and Inokuti [Phys. Rev. A 25, 1420 (1982)]. The present results for the partial ionization cross sections are as much as 9% (CF+3) to 81% (F+) higher than the previously published absolute measurements of Stephan, Deutsch, and Märk [J. Chem. Phys. 83, 5712 (1985)] at 80 eV, but are in agreement with their recently revised estimates for the singly charged ions. We also found that dissociative ionization was a dominant process for electron-impact energies above 30 eV, accounting for 85% of the total dissociation cross section at 80 eV.

  7. Bond-rearrangement and ionization mechanisms in the photo-double-ionization of simple hydrocarbons (C2H4 , C2H3F , and 1 ,1 -C2H2F2 ) near and above threshold

    NASA Astrophysics Data System (ADS)

    Gaire, B.; Gatton, A.; Wiegandt, F.; Neff, J.; Janke, C.; Zeller, S.; Reedy, D.; Rajput, J.; Ben-Itzhak, I.; Landers, A. L.; Belkacem, A.; Weber, Th.

    2016-09-01

    We investigate bond-rearrangement driven by photo-double-ionization (PDI) near and above the double-ionization threshold in a sequence of carbon-carbon double-bonded hydrocarbon molecules: ethylene, fluoroethylene, and 1,1-difluoroethylene. We employ the kinematically complete cold target recoil ion momentum spectroscopy method to resolve all photo-double-ionization events leading to two-ion fragments. We observe changes in the branching ratios of different dissociative ionization channels depending on the presence of no, one, or two fluorine atoms. The role of the fluorine atom in the bond-rearrangement channels is intriguing, as evident by the reordering of the threshold energies of the PDI in the fluorinated molecules. These effects offer a compelling argument that the electronegativity of the fluorine (or the polarity of the molecule) strongly influences the potential energy surfaces of the molecules and drives bond rearrangement during the dissociation process. The energy sharing and the relative angle between the three-dimensional momentum vectors of the two electrons enable us to distinguish between knockout and other ionization mechanisms of the PDI processes.

  8. One-photon mass-analyzed threshold ionization spectroscopy (MATI) of cis-dichloroethylene (cis-C2H2Cl2)

    NASA Astrophysics Data System (ADS)

    Bae, Yong Jin; Kim, Myung Soo

    2007-11-01

    A high-quality one-photon mass-analyzed threshold ionization (MATI) spectrum of cis-C2H2Cl2 was obtained by using vacuum ultraviolet radiation generated by four-wave mixing in Kr. The ionization energy determined from the position of the 0-0 band in the spectrum was 9.6578 ± 0.0006 eV. Ten vibrational fundamentals for the cation were identified. Most of the overtones and combinations could be assigned properly by comparing with the quantum chemical calculation results. The equilibrium geometry of the cation was determined through Franck-Condon fit.

  9. Numerical Analysis of Threshold between Laser-Supported Detonation and Combustion Wave Using Thermal Non-Equilibrium and Multi-Charged Ionization Model

    NASA Astrophysics Data System (ADS)

    Shiraishi, Hiroyuki; Kumagai, Yuya

    Laser-supported Detonation (LSD), which is one type of Laser-supported Plasma (LSP), is an important phenomenon because it can generate high pressures and temperatures for laser absorption. In this study, using thermal-non-equilibrium model, we numerically simulate LSPs, which are categorized as either LSDs or laser-supported combustion-waves (LSCs). For the analysis model, a two-temperature (heavy particle and electron-temperature) model has been used because the electronic mode excites first in laser absorption and a thermal non-equilibrium state easily arises. In the numerical analysis of the LSDs, laser absorption models are particularly important. Therefore, a multi-charged ionization model is considered to evaluate precisely the propagation and the structure transition of the LSD waves in the proximity of the LSC-LSD threshold. In the new model, the transition of the LSD construction near the threshold, which is indicated by the ionization delay length, becomes more practical.

  10. Preparing transition-metal clusters in known structural forms: The mass-analyzed threshold ionization spectrum of V3

    NASA Astrophysics Data System (ADS)

    Ford, Mark S.; Mackenzie, Stuart R.

    2005-08-01

    The first results are presented of a new experiment designed both to generate and characterize spectroscopically individual isomers of transition-metal cluster cations. As a proof of concept the one-photon mass-analyzed threshold ionization (MATI) spectrum of V3 has been recorded in the region of 44000-45000cm-1. This study extends the range of a previous zero-kinetic-energy (ZEKE) photoelectron study of Yang et al. [Chem. Phys. Lett. 231, 177 (1994)] with which the current results are compared. The MATI spectra reported here exhibit surprisingly high resolution (0.2cm-1) for this technique despite the use of large discrimination and extraction fields. Analysis of the rotational profile of the origin band allows assignment of the V3 ground state as A1'2 and the V3+ ground state as A2'3, both with D3h geometry, in agreement with the density-functional theory study of the V3 ZEKE spectrum by Calaminici et al. [J. Chem. Phys. 114, 4036 (2001)]. There is also some evidence in the spectrum of transitions to the low-lying A1'1 excited state of the ion. The vibrational structure observed in the MATI spectrum is, however, significantly different to and less extensive than that predicted in the density-functional theory study. Possible reasons for the discrepancies are discussed and an alternative assignment is proposed which results in revised values for the vibrational wave numbers of both the neutral and ionic states. These studies demonstrate the efficient generation of cluster ions in known structural (isomeric) forms and pave the way for the study of cluster reactivity as a function of geometrical structure.

  11. Strong-field approximation for above-threshold ionization of polyatomic molecules. II. The role of electron rescattering off the molecular centers

    NASA Astrophysics Data System (ADS)

    Hasović, E.; Milošević, D. B.

    2014-05-01

    We consider high-order above-threshold ionization of polyatomic molecules by a strong laser field. An improved molecular strong-field approximation which takes into account the electron rescattering off the molecular centers is developed. The presented theory is applied to calculate the photoelectron energy and angular distributions for the ozone molecule. The obtained spectra exhibit pronounced minima, and this is explained as a three-point destructive interference of the rescattered electron wave packets.

  12. Bond-rearrangement and ionization mechanisms in the photo-double-ionization of simple hydrocarbons (C2H4, C2H3F, and 1,1-C2H2F2) near and above threshold

    DOE PAGES

    Gaire, B.; Gatton, A. S.; Wiegandt, F.; ...

    2016-09-14

    We have investigated bond-rearrangement driven by photo-double-ionization (PDI) near and above the double ionization threshold in a sequence of carbon-carbon double bonded hydrocarbon molecules: ethylene, fluoroethylene, and 1,1-difluoroethylene. We employ the kinematically complete cold target recoil ion momentum spectroscopy (COLTRIMS) method to resolve all photo-double-ionization events leading to two-ionic fragments. We observe changes in the branching ratios of different dissociative ionization channels depending on the presence of none, one, or two fluorine atoms. The role of the fluorine atom in the bond-rearrangement channels is intriguing as evident by the re-ordering of the threshold energies of the PDI in the fluorinatedmore » molecules. These effects offer a compelling argument that the electronegativity of the fluorine (or the polarity of the molecule) strongly influences the potential energy surfaces of the molcules and drives bond-rearrangement during the dissociation process. The energy sharing and the relative angle between the 3D-momentum vectors of the two electrons provide clear evidence of direct and indirect PDI processes.« less

  13. Bond-rearrangement and ionization mechanisms in the photo-double-ionization of simple hydrocarbons (C2H4, C2H3F, and 1,1-C2H2F2) near and above threshold

    SciTech Connect

    Gaire, B.; Gatton, A. S.; Wiegandt, F.; Neff, J.; Janke, C.; Zeller, S.; Reedy, D.; Rajput, J.; Ben-Itzahk, I.; Landers, A. L.; Belkacem, A.; Weber, Th.

    2016-09-14

    We have investigated bond-rearrangement driven by photo-double-ionization (PDI) near and above the double ionization threshold in a sequence of carbon-carbon double bonded hydrocarbon molecules: ethylene, fluoroethylene, and 1,1-difluoroethylene. We employ the kinematically complete cold target recoil ion momentum spectroscopy (COLTRIMS) method to resolve all photo-double-ionization events leading to two-ionic fragments. We observe changes in the branching ratios of different dissociative ionization channels depending on the presence of none, one, or two fluorine atoms. The role of the fluorine atom in the bond-rearrangement channels is intriguing as evident by the re-ordering of the threshold energies of the PDI in the fluorinated molecules. These effects offer a compelling argument that the electronegativity of the fluorine (or the polarity of the molecule) strongly influences the potential energy surfaces of the molcules and drives bond-rearrangement during the dissociation process. The energy sharing and the relative angle between the 3D-momentum vectors of the two electrons provide clear evidence of direct and indirect PDI processes.

  14. Desorption/Ionization Fluence Thresholds and Improved Mass Spectral Consistency Measured Using a Flattop Laser Profile in the Bioaerosol Mass Spectrometry of Single Bacillus Endospores

    SciTech Connect

    Steele, P T; Srivastava, A; Pitesky, M E; Fergenson, D P; Tobias, H J; Gard, E E; Frank, M

    2004-11-30

    Bioaerosol mass spectrometry (BAMS) is being developed to analyze and identify biological aerosols in real-time. Mass spectra of individual Bacillus endospores were measured here with a bipolar aerosol time-of-flight mass spectrometer in which molecular desorption and ionization were produced using a single laser pulse from a Q-switched, frequency-quadrupled Nd:YAG laser that was modified to have an approximately flattop profile. The flattened laser profile allowed the minimum fluence required to desorb and ionize significant numbers of ions from single aerosol particles to be determined. For Bacillus spores this threshold had a mean value of approximately 1 nJ/{micro}m{sup 2} (0.1 J/cm{sup 2}). Thresholds for individual spores, however, could apparently deviate by 20% or more from the mean. Threshold distributions for clumps of MS2 bacteriophage and bovine serum albumin were subsequently determined. Finally, the flattened profile was observed to increase the reproducibility of single spore mass spectra. This is consistent with the general conclusions of our earlier paper on the fluence dependence of single spore mass spectra and is particularly significant because it is expected to enable more robust differentiation and identification of single bioaerosol particles.

  15. Intensity dependence of the H{sub 2}{sup +} ionization rates in Ti:sapphire laser fields above the Coulomb-explosion threshold

    SciTech Connect

    Sabzyan, Hassan; Vafaee, Mohsen

    2005-06-15

    Ionization rates of the hydrogen molecular ion H{sub 2}{sup +} under linearly polarized pulse of intense laser fields are simulated by direct solution of the fixed-nuclei time-dependent Schroedinger equation for the Ti:sapphire laser lines {lambda}=790 and 800 nm at high intensities starting from just above the Coulomb explosion threshold (i.e., 6.0x10{sup 13}, 1.0x10{sup 14}, 3.2x10{sup 14}, and 1.4x10{sup 15} W cm{sup -2}). Results obtained in this research exhibit a high degree of complexity for the R-dependent enhanced ionization rates for the H{sub 2}{sup +} system in these intense laser fields. The R-dependent ionization peaks move towards small internuclear distances and their structure becomes simpler and smoother with the increase in the intensity of the laser pulse, i.e., with the decrease in the Keldysh parameter. Results obtained in this research are comparable to and even more reliable than the results of other theoretical calculations reported recently and successfully simulate the experimental ionization data.

  16. Strong-field above-threshold ionization in laser-irradiated C60: The signatures of orbital symmetry and intramolecular interference

    NASA Astrophysics Data System (ADS)

    Usachenko, Vladimir; Kim, Vyacheslav; Pyak, Pavel

    2015-05-01

    We report about the results of our theoretical study of strong-field (multiphoton) above-threshold ionization (ATI) in laser-irradiated carbon fullerene molecule C60 under condition of relevant experiment. The problem is addressed within the velocity-gauge (VG) formulation of molecular strong-field approximation (SFA) essentially exploiting the density-functional-theory (DFT) method for numerical composition of initial (laser-free) molecular state using the routines of GAUSSIAN-03 code. The results of our present VG-SFA calculation for C60 photoelectron energy spectra (PES) demonstrate two distinct (well-separated) and pronounced local interference minima - in the low-energy and the high-energy domains of produced PES - both arising due to destructive intramolecular (multislit) quantum interference of strong-field ionization corresponding to photoelectron emission from multiple separate atomic centers.

  17. Cascade L-shell soft-x-ray emission as incident x-ray photons are tuned across the 1s ionization threshold

    SciTech Connect

    Sokaras, D.; Andrianis, M.; Lagoyannis, A.; Kochur, A. G.; Mueller, M.; Kolbe, M.; Beckhoff, B.; Mantler, M.; Zarkadas, Ch.; Karydas, A. G.

    2011-05-15

    The cascade L-shell x-ray emission as an incident polarized and unpolarized monochromatic radiation overpass the 1s ionization threshold is investigated for the metallic Fe by means of moderate resolution, quantitative x-ray spectrometry. A full ab initio theoretical investigation of the L-shell x-ray emission processes is performed based on a detailed straightforward construction of the cascade decay trees within the Pauli-Fock approximation. The agreement obtained between experiments and the presented theory is indicated and discussed with respect to the accuracy of advanced atomic models as well as its significance for the characterization capabilities of x-ray fluorescence (XRF) analysis.

  18. Threshold ionization spectroscopy of H2O, HDO and D2O and low-lying vibrational levels of HDO+ and D2O+

    NASA Astrophysics Data System (ADS)

    Lauzin, Clément; Jacovella, Ugo; Merkt, Frédéric

    2015-12-01

    Rotationally resolved photoelectron spectra of jet-cooled H2O, HDO and D2O have been recorded near the origin of the ? photoionising transition following single-photon ionization using the complementary techniques of mass-analysed threshold-ionization (MATI) and pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy. A gas mixture of H2O, HDO and D2O with Ar was obtained by mixing H2O (ℓ) and D2O (ℓ) in a reservoir and bubbling Ar gas through the mixture. To unambiguously assign the photoelectron bands to H2O, HDO or D2O, the PFI-ZEKE photoelectron spectra of the mixture were compared to MATI spectra and to spectra of H2O. Analysis of the rotational structure of the origin bands (v+1 = 0, v2+ = 0, v+3 = 0) ← (v1 = 0, v2 = 0, v3 = 0) of H2O, HDO and D2O and of the transitions to the (010), (020) and (100) levels of D2O+ and the first excited level of the O-D stretching mode of HDO+ provided new information on the photoionization dynamics of water and the energy level structure of HDO+ and D2O+.

  19. Mass analyzed threshold ionization spectroscopy of deuterium substituted N-methylaniline and N-ethylaniline cations: isotope effect on transition energy and large amplitude vibrations

    NASA Astrophysics Data System (ADS)

    Lin, Jieli; Lin, Jung Lee; Tzeng, Wen Bih

    2003-12-01

    We have recorded the resonant two-photon ionization (R2PI) and mass analyzed threshold ionization (MATI) spectra of deuterium substituted N-methylaniline (NMA-d1) and N-ethylaniline (NEA-d1) to investigate the influence of the N-deuteration on the transition energy and the large amplitude alkyl vibration. The origin of the S 1←S 0 electronic transition (EE) and the adiabatic ionization energy (IE) of NMA-d1 are determined to be 33,294 ± 1 and 59,801 ± 5 cm -1, whereas those of NEA-d1 are 33,301 ± 1 and 59,185 ± 5 cm -1, respectively. Comparing these data with those of NMA and NEA suggests that N-deuteration give rise to a blue shift of 2-4 cm -1 in the EE and a red shift of 19-21 cm -1 in the IE. These isotope shifts are little affected by the length of the alkyl group attached to the nitrogen atom. The present results also show that the N-deuteration influences more on the large amplitude motions of the CH 3 torsion, the C 2H 5 bending, and the N-inversion than the localized benzene ring vibrations.

  20. Measurement of intensity-dependent rates of above-threshold ionization (ATI) of atomic hydrogen at 248 nm

    SciTech Connect

    Nichols, T.D.

    1991-04-01

    Measured rates of multiphoton ionization (MPI) from the ground state of atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at 248 nm wavelength are compared to predictions of lowest-order perturbation theory, Floquet theory, and Keldysh-Faisal-Reiss (KFR) theory with and without Coulomb correction for peak irradiance of 3 {times} 10{sup 12}W/cm{sup 2} to 2 {times} 10{sup 14}W/cm{sup 2}. The Coulomb-corrected Keldysh model falls closest to the measured rates, the others being much higher or much lower. At 5 {times} 10{sup 13}W/cm{sup 2}, the number of ATI electrons decreased by a factor of approximately 40 with each additional photon absorbed. ATI of the molecular hydrogen background and of atoms from photodissociation of the molecules were also observed. The experiment employed a crossed-beam technique at ultrahigh vacuum with an rf-discharge atomic hydrogen source and a magnetic-bottle type electron time-of-flight spectrometer to count the electrons in the different ATI channels separately. The apparatus was calibrated to allow comparison of absolute as well as relative ionization rates to the theoretical predictions. This calibration involved measuring the distribution of irradiance in a focal volume that moved randomly and changed its size from time to time. A data collection system under computer control divided the time-of-flight spectra into bins according to the energy of each laser pulse. This is the first measurement of absolute rates of ATI in atomic hydrogen, and the first measurement of absolute test of MPI in atomic hydrogen without a large factor to account for multiple modes in the laser field. As such, the results of this work are important to the development of ATI theories, which presently differ by orders of magnitude in their prediction of the ionization rates. They are also important to recent calculations of temperatures in laser-heated plasmas, many of which incorporate KFR theory.

  1. One-photon mass-analyzed threshold ionization spectroscopy of 2-bromopropene (2-C3H5Br): Analysis of vibration and internal rotation in the cation

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Kim, Myung Soo

    2003-12-01

    Vibrational spectrum of 2-C3H5Br cation in the ground electronic state was obtained by one-photon mass-analyzed threshold ionization (MATI) spectroscopy using coherent vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. From the MATI spectra, ionization energy of 2-C3H5Br to the ionic ground state has been determined to be 9.4377±0.0006 eV. Vibrational assignments have been made by comparing with the vibrational frequencies and Franck-Condon factors calculated at the B3LYP and BP86 levels with the 6-311++G(3df,3pd) basis set. Several low-frequency bands have been assigned to the torsional motion of the methyl group in the cation. Energies of the torsional states and relative transition intensities to these states have been reproduced well by a one-dimensional rotor model. The torsional barrier and internal rotational constant have been determined to be 80.0 and 5.13 cm-1, respectively.

  2. Rotational state selection of a CH3I+ ion beam using vacuum ultraviolet-mass-analyzed threshold ionization spectroscopy: Characterization using photodissociation spectroscopy

    NASA Astrophysics Data System (ADS)

    Bae, Yong Jin; Kim, Myung Soo

    2008-03-01

    The ÃA12←X˜E3/22 transition of CH3I + was investigated by photodissociation (PD) of the cation generated by one-photon mass-analyzed threshold ionization (MATI). Compared to the PD spectrum obtained by excitation of the cation in the main 0-0 band in the MATI spectrum, those obtained by excitation of the cations in the satellite structures showed substantially simplified rotational structures for nondegenerate vibronic bands. Spectral simplification occurred because each satellite consisted mostly of cations with one K quantum number. Spectroscopic constants in the ground vibronic state and in the 2135, 2138, 39, and 313 nondegenerate vibrational states in ÃA12 were determined via spectral fitting. Also, those in the 213n61 (n=1?) degenerate state, which had been reported previously, was improved. The K quantum number in each satellite determined by the present high resolution study was compatible with the prediction by the symmetry selection rule for photoionization. That is, the K quantum number of the ion core in high Rydberg states accessed by one-photon excitation was found to be conserved upon pulsed field ionization. This work demonstrates generation of mass-selected, vibronically selected, and K-selected ion beam by one-photon MATI.

  3. Vibrational and Geometric Structures of La{_3}C{_2}O and La{_3}C{_2}O^+ from Masse-Analyzed Threshold Ionization

    NASA Astrophysics Data System (ADS)

    Mourad, Roudjane; Wu, Lu; Yang, D. S.

    2011-06-01

    La{_3}C{_2}O is produced for the first time by laser vaporization in a pulsed cluster source and identified by photoionization time-of-flight mass spectrometry. Vibrationally-resolved ion spectra are obtained with mass-analyzed threshold ionization (MATI) spectroscopy. The adiabatic ionization energy of La{_3}C{_2}O is measured to be 30891(5) Cm-1. The spectra display several short vibrational progressions, and these progressions are associated mainly with La-La, La-C and La{_3}C{_2}O stretching excitations. The electron-spin multiplicities and molecular symmetries of La{_3}C{_2}O and La{_3}C{_2}O^+ are determined by combining the experimental measurements with ab initio calculations at MP2 level. Preliminary data analysis shows that the ^1A_1 ← ^2A_1 transition is responsible for the observed MATI spectra. The cluster has C2v symmetry with La{_3}C{_2}O in a bi-pyramid structure and oxygen being attached to the La_3 plane.

  4. Threshold ionization, structural isomers, and electronic states of M{sub 2}O{sub 2} (M = Sc, Y, and La)

    SciTech Connect

    Wu, Lu; Zhang, Changhua; Krasnokutski, Serge A.; Yang, Dong-Sheng

    2014-06-14

    M{sub 2}O{sub 2} (M = Sc, Y, and La) were synthesized in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and ab initio calculations. Adiabatic ionization energies (AIEs) and several vibrational frequencies were measured accurately for the first time from the MATI spectra. Six possible structural isomers of M{sub 2}O{sub 2} were considered in the calculations and the three converged structures were used in the spectral analysis. A planar cyclic structure in D{sub 2h} point group was predicted to be the most stable one by the theory and observed by the experiment. The cyclic structure is formed by joining two MO{sub 2} fragments together through two shared oxygen atoms. In forming the ground state clusters, each metal atom loses two (n − 1)d electrons and as a result, has only one ns electron in the metal-based valence orbital. The ground electronic state of Sc{sub 2}O{sub 2} is {sup 1}A{sub g}, and those of Y{sub 2}O{sub 2} and La{sub 2}O{sub 2} are {sup 3}B{sub 1u}. Ionization of both {sup 1}A{sub g} and {sup 3}B{sub 1u} neutral states yields the {sup 2}A{sub g} ion state by removing one of the two ns electrons, and the resultant ion has a similar geometry to the neutral cluster. The AIEs of the clusters are 5.5752 (6), 5.2639 (6), 4.5795 (6) eV for M = Sc, Y, and La, respectively. The vibrational frequencies of the observed modes, including O-M and M-M stretches, are in the range of 200–800 cm{sup −1}.

  5. Yttrium-Assisted C-H and C-C Bond Activation of Ethylene Probed by Mass-Analyzed Threshold Ionization Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Jong Hyun; Yang, Dong-Sheng

    2016-06-01

    The reaction between Y atom and ethylene (CH2=CH2) was performed in a laser-ablation supersonic molecular beam source. Y(C2H2), Y(C2H4), and Y(C4H6) were observed by time-of-flight mass spectrometry and investigated with mass-analyzed threshold ionization (MATI) spectroscopy and theoretical calculations. Y(C2H2) is formed by hydrogen elimination, Y(C2H4) by simple association, and La(C4H6) by C-C bond coupling and dehydrogenation. Both Y(C2H2) and Y(C2H4) have a C2v triangular structure with a C=C double bond in Y(C2H2) and a C-C single bond in Y(C2H4). Y(C4H6) has a five-membered metallacyclic structure (Cs) with Y binding to the two terminal carbon atoms of butene, which is the exactly same as that of Y(C4H6) formed in the Y + 1-butene reaction. For all three complexes, ionization has a small effect on the metal-carbon bond lengths because the rejected electron has basically a Y 5s character. The adiabatic ionization energies are measured to be 45679(5) wn for Y(C2H2), 45603(5) wn for Y(C2H4) and 43475(5) wn for Y(C4H6). The metal-ligand stretching frequencies of the three complexes are also measured from the MATI spectra.

  6. Photoionization from the 5p {sup 2}P{sub 3/2} state of rubidium

    SciTech Connect

    Nadeem, Ali; Haq, S. U.

    2011-06-15

    We report two-step photoionization studies from the 5p {sup 2}P{sub 3/2} excited state of rubidium using two dye lasers simultaneously pumped by a common Nd:YAG laser in conjunction with a thermionic diode ion detector. The photoionization cross section at the first ionization threshold is measured as 18.8 {+-} 3 Mb and at excess energies of 0.013, 0.106, 0.229, and 0.329 eV is measured as 15, 13.6, 12.6, and 12.5 Mb, respectively. The measured value of the photoionization cross section at the threshold is used to calibrate the oscillator strengths of the 5p {sup 2}P{sub 3/2}{yields}nd {sup 2}D{sub 5/2} (22 {<=}n{<=} 52) Rydberg transitions.

  7. High-order harmonic generation and above-threshold ionization in H: Calculations using expansions over field-free state-specific wave functions

    NASA Astrophysics Data System (ADS)

    Dionissopoulou, S.; Mercouris, Th.; Lyras, A.; Komninos, Y.; Nicolaides, C. A.

    1995-04-01

    We have computed the above-threshold ionization and the emitted harmonic spectra of H interacting with short laser pulses, with photon energies ranging from 1.16 to 5.44 eV and with peak intensities ranging from 6×1013 to 7×1014 W/cm2, by solving the time-dependent Schrödinger equation (TDSE). The method of solution involves the expansion of the time-dependent wave function Ψ(r-->,t) over the exact wave functions of the discrete and the continuous spectrum, computed numerically, and the subsequent integration of the resulting coupled first-order differential equations by a Taylor series expansion technique. This state-specific approach (SSA) to the solution of the TDSE allows systematic understanding of convergence as a function of the number and type of the field-free states for each value of the laser frequency (ω) and peak intensity (I0). For example, the method allows practical numerical study of the degree of participation of high (n,l) (l=0,1,...,n-1) Rydberg, as well as of high-energy scattering states for each partial wave. For the harmonic spectra, comparisons are made between the results obtained by the SSA and those obtained in recent years by a number of researchers from the application of finite-difference grid methods. As regards economy, a general observation is that in the SSA the necessary number of partial waves is smaller than that required in the grid methods. Predictions are made for the case of ħω=2 eV, I0=2×1014 W/cm2, in the context of a study of the effect of the pulse shape on the harmonic-generation spectrum. It is shown that the number of harmonics and the appearance of the plateau depend on the duration of the peak intensity.

  8. One-photon mass-analyzed threshold ionization spectroscopy of CH2BrI: Extensive bending progression, reduced steric effect, and spin-orbit effect in the cation

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Kim, Hyoseok; Lee, Yoon Sup; Kim, Myung Soo

    2005-07-01

    One-photon mass-analyzed threshold ionization (MATI) spectrum of CH2BrI was obtained using coherent vacuum-ultraviolet radiation generated by four-wave difference-frequency mixing in Kr. Unlike CH2ClI investigated previously, a very extensive bending (Br-C-I) progression was observed. Vibrational frequencies of CH2BrI+ were measured from the spectra and the vibrational assignments were made by utilizing frequencies calculated by the density-functional-theory (DFT) method using relativistic effective core potentials with and without the spin-orbit terms. A noticeable spin-orbit effect on the vibrational frequencies was observed from the DFT calculations, even though its influence was not so dramatic as in CH2ClI+. A simple explanation based on the bonding characteristics of the molecular orbitals involved in the ionization is presented to account for the above differences between the MATI spectra of CH2BrI and CH2ClI. The 0-0 band of the CH2BrI spectrum could be identified through the use of combined data from calculations and experiments. The adiabatic ionization energy determined from the position of this band was 9.5944±0.0006eV, which was significantly smaller than the vertical ionization energy reported previously.

  9. Mass-analyzed threshold ionization study of vinyl bromide cation in the first excited electronic state using vacuum-ultraviolet radiation generated by four-wave mixing in Hg

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Kim, Myung Soo

    2005-11-01

    The vibrational spectrum of the vinyl bromide cation in the first excited electronic state ÃA'2 was obtained by one-photon mass-analyzed threshold ionization (MATI) spectroscopy. The use of an improved vacuum-ultraviolet radiation source based on four-wave sum frequency mixing in Hg resulted in excellent sensitivity for MATI signals. From the MATI spectrum, the ionization energy to the ÃA'2 state of the cation was determined to be 10.9150±0.0006eV. Nearly complete vibrational assignments for the MATI peaks were possible by utilizing the vibrational frequencies and Franck-Condon factors calculated at the density-functional theory (DFT) and time-dependent DFT/B3LYP levels with the 6-311+G(df,p) basis set.

  10. Zero kinetic energy spectroscopy: mass-analyzed threshold ionization spectra of chromium sandwich complexes with alkylbenzenes, (η(6)-RPh)(2)Cr (R = Me, Et, i-Pr, t-Bu).

    PubMed

    Ketkov, Sergey Y; Selzle, Heinrich L; Cloke, F Geoffrey N; Markin, Gennady V; Shevelev, Yury A; Domrachev, Georgy A; Schlag, Edward W

    2010-10-28

    For over 25 years zero kinetic energy (ZEKE) spectroscopy has yielded a rich foundation of high-resolution results of molecular ions. This was based on the discovery in the late 60's of long-lived ion states throughout the ionization continuum of molecular ions. Here, an example is chosen from another fundamental system pioneered at this university. The mass-analyzed threshold ionization (MATI) spectra of jet-cooled chromium bisarene complexes (η(6)-RPh)(2)Cr (R = Me (1), Et (2), i-Pr (3), and t-Bu (4)) have been measured and interpreted on the basis of DFT calculations. The MATI spectra of complexes 1 and 2 appear to reveal features arising from ionizations of the isomers formed by the rotation of one arene ring relative to the other. The 1 and 2 MATI spectra show two intense peaks corresponding to the 0(0)(0) ionizations with inverse intensity ratios. As indicated by the DFT calculations, the intensity ratio change on going from 1 to 2 results from different isomers contributing to each MATI peak. The ionization energies corresponding to the 0(0)(0) peaks are 42746 ± 5 and 42809 ± 5 cm(-1) for compound 1 and 42379 ± 5 and 42463 ± 5 cm(-1) for complex 2. The 1 and 2 spectra show also the weaker features representing transitions to the vibrationally excited cationic levels, the signals of individual rotamers being detected and assigned on the basis of calculated vibrational frequencies. The MATI spectra of compounds 3 and 4 reveal only one strong peak because of close ionization potentials of the isomers contributing to the MATI signal. The 3 and 4 ionization energies are 42104 ± 5 and 41917 ± 5 cm(-1), respectively. The precise values of ionization energies obtained from the MATI spectra reveal a nonlinear dependence of the IE on the number of Me groups in the alkyl substituents of (η(6)-RPh)(2)Cr. This can be explained by an increase in the molecular zero point energies on methylation of the substituents.

  11. Analysis of the (1)A' S1 ← (1)A' S0 and (2)A' D0 ← (1)A' S1 band systems in 1,2-dichloro-4-fluorobenzene by means of resonance-enhanced-multi-photon-ionization (REMPI) and mass-analyzed-threshold-ionization (MATI) spectroscopy.

    PubMed

    Krüger, Sascha; Grotemeyer, Jürgen

    2016-03-14

    Resonance enhanced multiphoton ionization (REMPI) and mass analyzed threshold ionization (MATI) spectroscopy have been applied in order to investigate the vibrational structure of 1,2-dichloro-4-fluorobenzene (1,2,4-DCFB) in its first excited state (S1) and the cationic ground state (D0). The selection of the state prior to ionization resulted in MATI spectra with different intensity distributions thus giving access to many vibrational levels. To support the experimental findings, geometry optimizations and frequency analyses at DFT (density functional) and TDDFT (time-dependent density functional) levels of theory have been applied. Additionally, a multidimensional Franck-Condon approach has been used to calculate the vibrational intensities from the DFT calculations. An excellent agreement between simulated and measured REMPI and MATI spectra allowed for a confident assignment of vibrational levels and mechanisms active during excitation and ionization. In order to avoid any ambiguity regarding the assignment of the vibrational bands to normal modes, Duschinsky normal mode analysis has been performed to correlate the ground state (S0) normal modes of 1,2,4-DCFB with the benzene derived Wilson nomenclature. From the REMPI spectra the electronic excitation energy (EE) of 1,2-dichloro-4-fluorobenzene could be determined to be 35 714 ± 2 cm(-1) while the MATI spectra yielded the adiabatic ionization energy (IE) of 1,2-dichloro-4-fluorobenzene which could be determined to be 73 332 ± 7 cm(-1).

  12. Ionization branching ratio control with a resonance attosecond clock.

    PubMed

    Argenti, Luca; Lindroth, Eva

    2010-07-30

    We investigate the possibility to monitor the dynamics of autoionizing states in real-time and control the yields of different ionization channels in helium by simulating extreme ultraviolet (XUV) pump IR-probe experiments focused on the N=2 threshold. The XUV pulse creates a coherent superposition of doubly excited states which is found to decay by ejecting electrons in bursts. Prominent interference fringes in the photoelectron angular distribution of the 2s and 2p ionization channels are observed, along with significant out-of-phase quantum beats in the yields of the corresponding parent ions.

  13. Ionization Branching Ratio Control with a Resonance Attosecond Clock

    NASA Astrophysics Data System (ADS)

    Argenti, Luca; Lindroth, Eva

    2010-07-01

    We investigate the possibility to monitor the dynamics of autoionizing states in real-time and control the yields of different ionization channels in helium by simulating extreme ultraviolet (XUV) pump IR-probe experiments focused on the N=2 threshold. The XUV pulse creates a coherent superposition of doubly excited states which is found to decay by ejecting electrons in bursts. Prominent interference fringes in the photoelectron angular distribution of the 2s and 2p ionization channels are observed, along with significant out-of-phase quantum beats in the yields of the corresponding parent ions.

  14. One-photon mass-analyzed threshold ionization spectroscopy of 2-chloropropene (2-C3H5Cl) and its vibrational assignment based on the density-functional theory calculations

    NASA Astrophysics Data System (ADS)

    Bae, Yong Jin; Lee, Mina; Kim, Myung Soo

    2005-07-01

    A high-quality mass-analyzed threshold ionization (MATI) spectrum of 2-chloropropene, 2-C3H5Cl, is reported. Its ionization energy determined for the first time from the 0-0 band position was 9.5395±0.0006eV. Almost all the peaks in the MATI spectrum could be vibrationally assigned utilizing the frequencies calculated at the B3LYP /6-311++G(3df,3pd) level and the Franck-Condon factors calculated with the molecular parameters obtained at the same level. In particular, the observed methyl torsional progression could be reproduced very well through quantum-mechanical calculations using the molecular parameters obtained at this level. Dramatic lowering of the torsional barrier inferred from the experimental data was entirely compatible with the B3LYP /6-311++G(3df,3pd) results. The torsional barrier and the internal rotational constant determined by fits to six torsional peaks were 53.6 and 5.20cm-1, respectively. A brief discussion at the level of molecular orbital is presented to account for the dramatic lowering of the torsional barrier upon ionization.

  15. K selection in one-photon mass-analyzed threshold ionization of CH3I and CD3I to the X~ 2E3/2 state cations

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Bae, Yong Jin; Kim, Myung Soo

    2008-01-01

    One-photon mass-analyzed threshold ionization (MATI) spectra for the X˜E3/22 states of CH3I+ and CD3I + were measured using vacuum ultraviolet radiation generated by four-wave mixing in Kr. Spin-orbit density functional theory calculations at the B3LYP/aug-cc-pVTZ level and spin-orbit/Jahn-Teller calculations were made to aid vibrational assignment. Each vibrational band consisted of several peaks due to different ΔK transitions, which could be assigned by using molecular parameters determined in the previous high resolution photodissociation spectroscopic study. Possibility of generating mass-selected, vibronically selected and K-selected ion beam with decent intensity by one-photon MATI was demonstrated. The ionization energies to the X˜E3/22 states of CH3I + and CD3I+ corrected for the rotational contribution were 9.5386±0.0006 and 9.5415±0.0006eV, respectively.

  16. Vibrational assignment and Franck-Condon analysis of the mass-analyzed threshold ionization (MATI) spectrum of CH2ClI: The effect of strong spin-orbit interaction

    NASA Astrophysics Data System (ADS)

    Lee, Mina; Kim, Hyoseok; Lee, Yoon Sup; Kim, Myung Soo

    2005-06-01

    Detailed analysis of the one-photon mass-analyzed threshold ionization (MATI) spectrum of CH2ClI is presented. This includes the determination of the ionization energy of CH2ClI, complete vibrational assignments, and quantum-chemical calculations at the spin-orbit density-functional-theory (SODFT) level with various basis sets. Relativistic effective core potentials with effective spin-orbit operators can be used in SODFT calculations to treat the spin-orbit term on an equal footing with other relativistic effects and electron correlations. The comparison of calculated and experimental vibrational frequencies indicate that the spin-orbit effects are essential for the reasonable description of the CH2ClI+ cation. Geometrical parameters and thus the molecular shape of the cation are greatly influenced by the spin-orbit effects even for the ground state. Calculated geometrical parameters deviate substantially for different basis sets or effective core potentials. In an effort to derive the exact geometrical parameters for this cation, SODFT geometries were further improved utilizing Franck-Condon fit of the MATI spectral pattern. This empirical fitting produced the well-converged set of geometrical parameters that are quite insensitive to the choice of SODFT calculations. The C-I bond length and the Cl-C-I bond angle show large deviations among different SODFT calculations, but the empirical spectral fitting yields 2.191±0.003Å for the C-I bond length and 107.09±0.09° for the Cl-C-I angle. Those fitted geometrical parameters along with the experimental vibrational frequencies could serve as a useful reference in calibrating relativistic quantum-chemical methods for radicals.

  17. Rotationally resolved spectroscopy of the A~ 2A1<--X~ 2B1 transition of H2S+ above the barrier to linearity using the mass-analyzed threshold ionization photofragment excitation technique

    NASA Astrophysics Data System (ADS)

    Han, Songhee; Kang, Tae Yeon; Kim, Sang Kyu

    2010-03-01

    The à A21←X˜ B21 transitions of H2S+ above the barrier to linearity have been investigated with the energy resolution high enough to identify individual rotational transition lines for the first time. The rotational cooling of the cation is achieved either by the direct ionization or mass-analyzed threshold ionization (MATI) technique employed in the vacuum-ultraviolet laser excitation of the jet-cooled H2S. Subsequent photoexcitation leads to the H2S+→H2+S+ dissociation and the S+ product yield taken as a function of the excitation energy gives the photofragment excitation (PHOFEX) spectra. The combined use of MATI and PHOFEX techniques greatly simplifies the spectrum allowing the accurate identification of the rotationally resolved bands which is otherwise a formidable task due to the intrinsic complexity of the à A21←X˜ B21 transition. Highly excited states of Ã(0,7,0), Ã(0,8,0), and Ã(0,9,0) vibronic levels with different K quantum numbers which are located above the barrier to linearity are thoroughly investigated. The bent-to-quasilinear transition of H2S+ above the barrier to linearity shows the characteristics of the Renner-Teller effect, showing the large A rotational constant and strong intensity borrowing of the highly vibrationally excited ground levels such as X˜(0,23,0) or X˜(0,24,0) in the dipole-allowed excitation. Spectroscopic parameters of term values, rotational, and spin-orbit coupling constants are precisely determined in this work, providing the most quantitative spectroscopic structure of the H2S+ to date. Quantum-state dependent photodissociation dynamics are also discussed from spectral features of PHOFEX.

  18. Modulated voltage metastable ionization detector

    NASA Technical Reports Server (NTRS)

    Carle, G. C.; Kojiro, D. R.; Humphrey, D. E. (Inventor)

    1985-01-01

    The output current from a metastable ionization detector (MID) is applied to a modulation voltage circuit. An adjustment is made to balance out the background current, and an output current, above background, is applied to an input of a strip chart recorder. For low level concentrations, i.e., low detected output current, the ionization potential will be at a maximum and the metastable ionization detector will operate at its most sensitive level. When the detected current from the metastable ionization detector increases above a predetermined threshold level, a voltage control circuit is activated which turns on a high voltage transistor which acts to reduce the ionization potential. The ionization potential applied to the metastable ionization detector is then varied so as to maintain the detected signal level constant. The variation in ionization potential is now related to the concentration of the constituent and a representative amplitude is applied to another input of said strip chart recorder.

  19. Adaptive Thresholds

    SciTech Connect

    Bremer, P. -T.

    2014-08-26

    ADAPT is a topological analysis code that allow to compute local threshold, in particular relevance based thresholds for features defined in scalar fields. The initial target application is vortex detection but the software is more generally applicable to all threshold based feature definitions.

  20. Gas-Liquid Correlation of Ionization Energies.

    DTIC Science & Technology

    1984-04-01

    ions and water. The threshold and reorganization energies of the hydrated electron are calculated from threshold energies of anions and their absorption...hydroxide ions and water. The threshold and reorganization energies of the hydrated electron are calculated from threshold energies of anions and their...threshold energy of the hydrated electron. 2. Free energy of emission and gas-phase ionization Consider the photoelectron emission by an aqueous

  1. Controlling Two-Electron Threshold Dynamics in Double Photoionization of Lithium by Initial-State Preparation

    NASA Astrophysics Data System (ADS)

    Zhu, G.; Schuricke, M.; Steinmann, J.; Albrecht, J.; Ullrich, J.; Ben-Itzhak, I.; Zouros, T. J. M.; Colgan, J.; Pindzola, M. S.; Dorn, A.

    2009-09-01

    Double photoionization (DPI) and ionization-excitation (IE) of Li(2s) and Li(2p), state-prepared and aligned in a magneto-optical trap, were explored in a reaction microscope at the free-electron laser in Hamburg (FLASH). From 6 to 12 eV above threshold (ℏω=85, 91 eV), total as well as differential DPI cross sections were observed to critically depend on the initial state and, in particular, on the alignment of the 2p orbital with respect to the VUV-light polarization, whereas no effect is seen for IE. The alignment sensitivity is traced back to dynamical electron correlation at threshold.

  2. Controlling Two-Electron Threshold Dynamics in Double Photoionization of Lithium by Initial-State Preparation

    SciTech Connect

    Zhu, G.; Schuricke, M.; Steinmann, J.; Albrecht, J.; Dorn, A.; Ullrich, J.; Ben-Itzhak, I.; Zouros, T. J. M.; Colgan, J.; Pindzola, M. S.

    2009-09-04

    Double photoionization (DPI) and ionization-excitation (IE) of Li(2s) and Li(2p), state-prepared and aligned in a magneto-optical trap, were explored in a reaction microscope at the free-electron laser in Hamburg (FLASH). From 6 to 12 eV above threshold ((Planck constant/2pi)omega=85, 91 eV), total as well as differential DPI cross sections were observed to critically depend on the initial state and, in particular, on the alignment of the 2p orbital with respect to the VUV-light polarization, whereas no effect is seen for IE. The alignment sensitivity is traced back to dynamical electron correlation at threshold.

  3. Ionizing radiation detector

    DOEpatents

    Thacker, Louis H.

    1990-01-01

    An ionizing radiation detector is provided which is based on the principle of analog electronic integration of radiation sensor currents in the sub-pico to nano ampere range between fixed voltage switching thresholds with automatic voltage reversal each time the appropriate threshold is reached. The thresholds are provided by a first NAND gate Schmitt trigger which is coupled with a second NAND gate Schmitt trigger operating in an alternate switching state from the first gate to turn either a visible or audible indicating device on and off in response to the gate switching rate which is indicative of the level of radiation being sensed. The detector can be configured as a small, personal radiation dosimeter which is simple to operate and responsive over a dynamic range of at least 0.01 to 1000 R/hr.

  4. Ionization detection system for aerosols

    DOEpatents

    Jacobs, Martin E.

    1977-01-01

    This invention relates to an improved smoke-detection system of the ionization-chamber type. In the preferred embodiment, the system utilizes a conventional detector head comprising a measuring ionization chamber, a reference ionization chamber, and a normally non-conductive gas triode for discharging when a threshold concentration of airborne particulates is present in the measuring chamber. The improved system utilizes a measuring ionization chamber which is modified to minimize false alarms and reductions in sensitivity resulting from changes in ambient temperature. In the preferred form of the modification, an annular radiation shield is mounted about the usual radiation source provided to effect ionization in the measuring chamber. The shield is supported by a bimetallic strip which flexes in response to changes in ambient temperature, moving the shield relative to the source so as to vary the radiative area of the source in a manner offsetting temperature-induced variations in the sensitivity of the chamber.

  5. Threshold photoelectron spectrum of the Argon 3s satellites

    SciTech Connect

    Medhurst, L.J.; Von Wittenau, A.S.; van Zee, R.D.; Zhang, J.S.; Liu, S.H.; Shirley, D.A.; Lindle, D.W.

    1989-07-01

    Lately a variety of techniques have studied the electron correlation satellites with binding energies between the Argon 3s binding energy (29.24 eV) and the 2p/sup /minus/2/ ionization potential (43.38 eV). One of these techniques, Threshold Photoelectron Spectroscopy, with /approximately/90 meV FWHM resolution, revealed at least 25 individual electronic states. All of these could contribute to any other satellite spectrum, and this helped explain some discrepancies between previous measurements. This technique has been applied to the same region with higher resolution (<60 meV at the Ar 3s/sup /minus/1/peak). In this higher resolution spectrum at least 29 individual electronic states are present. In some cases the multiplet splitting is observed. 12 refs., 2 figs.

  6. Ionizing radiation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This chapter gives a comprehensive review on ionizing irradiation of fresh fruits and vegetables. Topics include principles of ionizing radiation, its effects on pathogenic and spoilage microorganisms, shelf-life, sensory quality, nutritional and phytochemical composition, as well as physiologic and...

  7. Calculations for electron-impact excitation and ionization of beryllium

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg; Bartschat, Klaus; Fursa, Dmitry V.; Bray, Igor

    2016-12-01

    The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the {(2s2p)}3P and {(2s2p)}1P states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications.

  8. Ionization chamber

    DOEpatents

    Walenta, Albert H.

    1981-01-01

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

  9. IONIZATION CHAMBER

    DOEpatents

    Redman, W.C.; Shonka, F.R.

    1958-02-18

    This patent describes a novel ionization chamber which is well suited to measuring the radioactivity of the various portions of a wire as the wire is moved at a uniform speed, in order to produce the neutron flux traverse pattern of a reactor in which the wire was previously exposed to neutron radiation. The ionization chamber of the present invention is characterized by the construction wherein the wire is passed through a tubular, straight electrode and radiation shielding material is disposed along the wire except at an intermediate, narrow area where the second electrode of the chamber is located.

  10. Characterization of P2P Systems

    NASA Astrophysics Data System (ADS)

    Stutzbach, Daniel; Rejaie, Reza

    The combination of large scale and geographically distributed nature of P2P system has led to their significant impact on the Internet. It is essential to characterize deployed P2P system for at least three reasons: (1) Accurately assessing their impact on the Internet, (2) identifying any performance bottleneck as well as any opportunity for performance improvement, (3) understanding user-driven dynamics in P2P systems. To characterize a P2P system, one needs to accurately capture snapshots of the resulting P2P overlay. This is challenging because the overlay is often large and dynamic. While the overlay is discovered by a crawler, it is changing which leads to a distorted view of the system. Capturing unbiased view of the traffic in the overlay is equally challenging because it is difficult to show that the captured behavior represent the observed behavior by all peers. In this chapter, we describe some of the fundamental problems in empirical characterization of widely deployed P2P systems. We present several examples to illustrate the effect of ad-hoc measurement/data collection on the resulting analysis/characterization. We then present two sampling techniques as a powerful approach to capture unbiased view of peer properties in a scalable fashion.

  11. Extremely high magnetic-field sensitivity of charge transport in the Mn/SiO2/p-Si hybrid structure

    NASA Astrophysics Data System (ADS)

    Volkov, N. V.; Tarasov, A. S.; Smolyakov, D. A.; Gustaitsev, A. O.; Rautskii, M. V.; Lukyanenko, A. V.; Volochaev, M. N.; Varnakov, S. N.; Yakovlev, I. A.; Ovchinnikov, S. G.

    2017-01-01

    We report on abrupt changes in dc resistance and impedance of a diode with the Schottky barrier based on the Mn/SiO2/p-Si structure in a magnetic field. It was observed that at low temperatures the dc and ac resistances of the device change by a factor of more than 106 with an increase in a magnetic field to 200 mT. The strong effect of the magnetic field is observed only above the threshold forward bias across the diode. The ratios between ac and dc magnetoresistances can be tuned from almost zero to 108% by varying the bias. To explain the diversity of magnetotransport phenomena observed in the Mn/SiO2/p-Si structure, it is necessary to attract several mechanisms, which possibly work in different regions of the structure. The anomalously strong magnetotransport effects are attributed to the magnetic-field-dependent impact ionization in the bulk of a Si substrate. At the same time, the conditions for this process are specified by structure composition, which, in turn, affects the current through each structure region. The effect of magnetic field attributed to suppression of impact ionization via two mechanisms leads to an increase in the carrier energy required for initiation of impact ionization. The first mechanism is related to displacement of acceptor levels toward higher energies relative to the top of the valence band and the other mechanism is associated with the Lorentz forces affecting carrier trajectories between scatterings events. The estimated contributions of these two mechanisms are similar. The proposed structure is a good candidate for application in CMOS technology-compatible magnetic- and electric-field sensors and switching devices.

  12. Electron ionization of H2O

    NASA Astrophysics Data System (ADS)

    King, Simon J.; Price, Stephen D.

    2008-11-01

    Relative partial ionization cross-sections and precursor-specific relative partial ionization cross-sections for fragment ions formed by electron ionization of H2O have been measured using time-of-flight mass spectrometry coupled with a 2D ion coincidence technique. We report data for the formation of H+, H2+, O2+, O+ and OH+ relative to the formation of H2O+, as a function of ionizing electron energy from 30 to 200 eV. This data includes, for the first time, measurements on the formation all positive ion pairs and ion triples by dissociative multiple electron ionization of H2O. Through determinations of the kinetic energy release involved in ion pair formation we provide further evidence that indirect processes contribute significantly to the yield of H+ + OH+ ion pairs below the vertical double ionization threshold.

  13. Threshold Graph Limits and Random Threshold Graphs

    PubMed Central

    Diaconis, Persi; Holmes, Susan; Janson, Svante

    2010-01-01

    We study the limit theory of large threshold graphs and apply this to a variety of models for random threshold graphs. The results give a nice set of examples for the emerging theory of graph limits. PMID:20811581

  14. Anonymity in P2P Systems

    NASA Astrophysics Data System (ADS)

    Manzanares-Lopez, Pilar; Muñoz-Gea, Juan Pedro; Malgosa-Sanahuja, Josemaria; Sanchez-Aarnoutse, Juan Carlos

    In the last years, the use of peer-to-peer (P2P) applications to share and exchange knowledge among people around the world has experienced an exponential growth. Therefore, it is understandable that, like in any successful communication mechanism used by a lot of humans being, the anonymity can be a desirable characteristic in this scenario. Anonymity in P2P networks can be obtained by means of different methods, although the most significant ones are broadcast protocols, dining-cryptographer (DC) nets and multiple-hop paths. Each of these methods can be tunable in order to build a real anonymity P2P application. In addition, there is a mathematical tool called entropy that can be used in some scenarios to quantify anonymity in communication networks. In some cases, it can be calculated analytically but in others it is necessary to use simulation to obtain the network entropy.

  15. Outer-shell photodetachment of the metastable Be{sup -} 1s{sup 2}2s2p{sup 2} {sup 4}P{sup e} state

    SciTech Connect

    Sanz-Vicario, Jose Luis; Lindroth, Eva

    2003-07-01

    We report calculated photodetachment cross sections from the metastable Be{sup -} 1s{sup 2}2s2p{sup 2} {sup 4}P{sup e} state in the photon energy range 0-10 eV. Outer-shell photodetachment takes place in this energy range, which includes the double-ionization threshold Be{sup +}({sup 2}S{sup e}) at {approx}7 eV as well as doubly excited thresholds of the residual atom up to the Be(1s{sup 2}2p4f) threshold at {approx}10 eV. Therefore, triply excited states of Be{sup -} are reached within the selected photon energy. We have implemented the complex scaled configuration interaction method along with a model potential for the 1s{sup 2} core to uncover the first series of Be{sup -} {sup 4}L{sup o} resonant states. In this work, four {sup 4}P{sup o}, seven {sup 4}D{sup o}, and two {sup 4}S{sup o} resonances are reported and we compare our cross section with other previous theoretical calculations, that reported none or, at most, two resonances.

  16. 2p radioactivity studied by tracking technique

    SciTech Connect

    Mukha, Ivan

    2010-06-01

    The recent advance in experimental studies of short-lived exotic nuclei beyond the proton drip line is presented. In particular, in-flight decays of proton-unbound nuclei with picosecond lifetimes can be probed by a novel technique which tracks all decay products precisely, and the decay vertices as well as the angular correlations of the fragments are deduced from the measured trajectories. The corresponding pioneering experiment which identified a previously-unknown isotope {sup 19}Mg and its two-proton (2p) radioactivity as well as studied the reference 2p decay of the known isotope {sup 16}Ne is described. Systematic studies of other 2p precursors beyond the proton drip line are foreseen with this powerful technique whose sensitivity is larger by factor of 30 in comparison with a conventional invariant-mass method. The 2p radioactivity candidates {sup 30}Ar, {sup 34}Ca and {sup 26}S are discussed. Information about the respective one-proton unbound nuclei can be obtained with this technique by evaluating proton-heavy-fragment correlations. Systematic studies of nuclei beyond the proton drip line, e.g., the well-known proton resonances above the 'waiting points' in the astrophysical rp-process, {sup 69}Br and {sup 73}Br are feasible.

  17. Correlation and relativistic effects in 2p photoelectron spectra of sodium atoms from the initial state 2{p}^{6}3p

    NASA Astrophysics Data System (ADS)

    Liu, Xiaobin; Shi, Yinglong; Xing, Yongzhong; Lu, Feiping; Chen, Zhanbin

    2017-02-01

    We investigate the 2p photoelectron spectra of sodium atoms with the initial state 2{p}63p at a photon energy of 54 eV. The analysis is performed based on the multi-configuration Dirac–Fock method. Special attention is given to the influences of correlation and relativistic effects on the spectra structures. To explore the nature and importance of such influences, calculations were performed based on detailed analyses of the thresholds, relative intensities and corresponding data calculated in the nonrelativistic limit.

  18. Data Sharing in P2P Systems

    NASA Astrophysics Data System (ADS)

    Hayek, Rabab; Raschia, Guillaume; Valduriez, Patrick; Mouaddib, Noureddine

    In this chapter, we survey P2P data sharing systems. All along, we focus on the evolution from simple file-sharing systems, with limited functionalities, to Peer Data Management Systems (PDMS) that support advanced applications with more sophisticated data management techniques. Advanced P2P applications are dealing with semantically rich data (e.g., XML documents, relational tables), using a high-level SQL-like query language. We start our survey with an overview over the existing P2P network architectures, and the associated routing protocols. Then, we discuss data indexing techniques based on their distribution degree and the semantics they can capture from the underlying data. We also discuss schema management techniques which allow integrating heterogeneous data. We conclude by discussing the techniques proposed for processing complex queries (e.g., range and join queries). Complex query facilities are necessary for advanced applications which require a high level of search expressiveness. This last part shows the lack of querying techniques that allow for an approximate query answering.

  19. CARA Risk Assessment Thresholds

    NASA Technical Reports Server (NTRS)

    Hejduk, M. D.

    2016-01-01

    Warning remediation threshold (Red threshold): Pc level at which warnings are issued, and active remediation considered and usually executed. Analysis threshold (Green to Yellow threshold): Pc level at which analysis of event is indicated, including seeking additional information if warranted. Post-remediation threshold: Pc level to which remediation maneuvers are sized in order to achieve event remediation and obviate any need for immediate follow-up maneuvers. Maneuver screening threshold: Pc compliance level for routine maneuver screenings (more demanding than regular Red threshold due to additional maneuver uncertainty).

  20. Threshold π- production on the deuteron

    NASA Astrophysics Data System (ADS)

    Strandberg, B.; Annand, J. R. M.; Briscoe, W.; Feldman, G.; Fissum, K.; Hansen, K.; Isaksson, L.; Myers, L.; O'Reilly, G. V.

    2016-11-01

    An experiment that aims to measure the π- photoproduction cross-section σ(E) on the deuteron γ + 2H → π- + 2p near threshold is discussed. The main concepts of the experimental technique are presented alongside some preliminary signals.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  2. Threshold Concepts in Biochemistry

    ERIC Educational Resources Information Center

    Loertscher, Jennifer

    2011-01-01

    Threshold concepts can be identified for any discipline and provide a framework for linking student learning to curricular design. Threshold concepts represent a transformed understanding of a discipline, without which the learner cannot progress and are therefore pivotal in learning in a discipline. Although threshold concepts have been…

  3. Benchmark calculations for electron-impact excitation and ionization of beryllium

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg; Bartschat, Klaus; Fursa, Dmitry V.; Bray, Igor

    2016-09-01

    The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium for energies from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with previous results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a shape resonance. The ionization from the (2 s 2 p) 3 P and (2 s 2 p) 1 P states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications. This work was supported by the United States National Science Foundation (OZ and KB) and the Australian Research Council (DVF and IB).

  4. Characterization of the CDMS Ionization Readout

    NASA Astrophysics Data System (ADS)

    Phipps, Arran

    2007-10-01

    Current cosmological models predict that a large portion of the total mass of the universe, about eighty percent, consists of putative dark matter. Theory predicts this dark matter may be in the form of particles constantly passing through the Earth. A class of these particles may interact with ordinary matter, earning the name weakly-interacting massive particles (WIMPs). The Cryogenic Dark Matter Search (CDMS) aims to directly detect the existence of WIMPs. CDMS has designed ZIP (Z-dependent Ionization & Phonon) detectors which measure phonon production and ionization of an interaction, making it possible to determine the interacting particle. The low-energy threshold of the ZIP detectors is determined by the signal-to-noise ratio of the ionization readout. A characterization of the signal-to-noise ratio of the ionization readout, along with possible modifications for improved sensitivity will be presented.

  5. Ionization and positronium formation in noble gases

    SciTech Connect

    Marler, J.P.; Sullivan, J.P.; Surko, C.M.

    2005-02-01

    Absolute measurements are presented for the positron-impact cross sections for direct ionization and positronium formation of noble gas atoms in the range of energies from threshold to 90 eV. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. The current data show generally good, quantitative agreement with previous measurements taken using a qualitatively different method. However, significant differences in the cross sections for both direct ionization and positronium formation are also observed. An analysis is presented that yields another, independent measurement of the direct ionization and positronium formation cross sections that is in agreement with the present, direct measurements to within {+-}10% for argon, krypton, and xenon. Comparison with available theoretical predictions yields good quantitative agreement for direct ionization cross sections, and qualitative agreement in the case of positronium formation.

  6. Multielectron coincidence study of the double Auger decay of 3d-ionized krypton

    SciTech Connect

    Andersson, E.; Hedin, L.; Rubensson, J.-E.; Karlsson, L.; Feifel, R.; Fritzsche, S.; Linusson, P.; Eland, J. H. D.

    2010-10-15

    Multielectron coincidence data for triple ionization of krypton have been recorded above the 3d ionization threshold at two photon energies (140 and 150 eV). Three principal transition pathways have been observed, two involving double Auger transitions from Kr{sup +}, and one involving single Auger transitions from Kr{sup 2+} created by direct single-photon double ionization. The decay of the 3d{sup 9} {sup 2}D{sub 5/2,3/2} states in Kr{sup +} has been analyzed in some detail and is found to be strongly dominated by cascade processes where two electrons with well-defined energies are emitted. The decay paths leading to the 4s{sup 2}4p{sup 3} {sup 4}S, {sup 2}D, and {sup 2}P states of Kr{sup 3+} are analyzed and energies of seven intermediate states in Kr{sup 2+} are given. A preliminary investigation of the decay paths from Kr{sup +} 3d{sup 9}4p{sup 5}nl shake-up states has also been carried out.

  7. Extreme-Ultraviolet-Initated High-Order Harmonic Generation: Driving Inner-Valence Electrons Using Below-Threshold-Energy Extreme-Ultraviolet Light.

    PubMed

    Brown, A C; van der Hart, H W

    2016-08-26

    We propose a novel scheme for resolving the contribution of inner- and outer-valence electrons in extreme-ultraviolet (XUV)-initiated high-harmonic generation in neon. By probing the atom with a low-energy (below the 2s ionization threshold) ultrashort XUV pulse, the 2p electron is steered away from the core, while the 2s electron is enabled to describe recollision trajectories. By selectively suppressing the 2p recollision trajectories, we can resolve the contribution of the 2s electron to the high-harmonic spectrum. We apply the classical trajectory model to account for the contribution of the 2s electron, which allows for an intuitive understanding of the process.

  8. Extreme-Ultraviolet-Initated High-Order Harmonic Generation: Driving Inner-Valence Electrons Using Below-Threshold-Energy Extreme-Ultraviolet Light

    NASA Astrophysics Data System (ADS)

    Brown, A. C.; van der Hart, H. W.

    2016-08-01

    We propose a novel scheme for resolving the contribution of inner- and outer-valence electrons in extreme-ultraviolet (XUV)-initiated high-harmonic generation in neon. By probing the atom with a low-energy (below the 2 s ionization threshold) ultrashort XUV pulse, the 2 p electron is steered away from the core, while the 2 s electron is enabled to describe recollision trajectories. By selectively suppressing the 2 p recollision trajectories, we can resolve the contribution of the 2 s electron to the high-harmonic spectrum. We apply the classical trajectory model to account for the contribution of the 2 s electron, which allows for an intuitive understanding of the process.

  9. Laser plasma formation assisted by ultraviolet pre-ionization

    SciTech Connect

    Yalin, Azer P. Dumitrache, Ciprian; Wilvert, Nick; Joshi, Sachin; Shneider, Mikhail N.

    2014-10-15

    We present experimental and modeling studies of air pre-ionization using ultraviolet (UV) laser pulses and its effect on laser breakdown of an overlapped near-infrared (NIR) pulse. Experimental studies are conducted with a 266 nm beam (fourth harmonic of Nd:YAG) for UV pre-ionization and an overlapped 1064 nm NIR beam (fundamental of Nd:YAG), both having pulse duration of ∼10 ns. Results show that the UV beam produces a pre-ionized volume which assists in breakdown of the NIR beam, leading to reduction in NIR breakdown threshold by factor of >2. Numerical modeling is performed to examine the ionization and breakdown of both beams. The modeled breakdown threshold of the NIR, including assist by pre-ionization, is in reasonable agreement with the experimental results.

  10. HRS Threshold Adjustment Test

    NASA Astrophysics Data System (ADS)

    Skapik, Joe

    1991-07-01

    This test will determine the optimal, non-standard discriminator thresholds for the few anomalous channels on each HRS detector. A 15 second flat field observation followed by a 210 second dark count is performed at each of 10 discriminator threshold values for each detector. The result of the test will be the optimal threshold values to be entered into the PDB. Edited 4/30/91 to add comments to disable/re-enable cross-talk tables.

  11. Multi-photon ionization of atoms in intense short-wavelength radiation fields

    NASA Astrophysics Data System (ADS)

    Meyer, Michael

    2015-05-01

    The unprecedented characteristics of XUV and X-ray Free Electron Lasers (FELs) have stimulated numerous investigations focusing on the detailed understanding of fundamental photon-matter interactions in atoms and molecules. In particular, the high intensities (up to 106 W/cm2) giving rise to non-linear phenomena in the short wavelength regime. The basic phenomenology involves the production of highly charged ions via electron emission to which both sequential and direct multi-photon absorption processes contribute. The detailed investigation of the role and relative weight of these processes under different conditions (wavelength, pulse duration, intensity) is the key element for a comprehensive understanding of the ionization dynamics. Here the results of recent investigations are presented, performed at the FELs in Hamburg (FLASH) and Trieste (FERMI) on atomic systems with electronic structures of increasing complexity (Ar, Ne and Xe). Mainly, electron spectroscopy is used to obtain quantitative information about the relevance of various multi-photon ionization processes. For the case of Ar, a variety of processes including above threshold ionization (ATI) from 3p and 3s valence shells, direct 2p two-photon ionization and resonant 2p-4p two-photon excitations were observed and their role was quantitatively determined comparing the experimental ionization yields to ab-initio calculations of the cross sections for the multi-photon processes. Using Ar as a benchmark to prove the reliability of the combined experimental and theoretical approach, the more complex and intriguing case of Xe was studied. Especially, the analysis of the two-photon ATI from the Xe 4d shell reveals new insight into the character of the 4d giant resonance, which was unresolved in the linear one-photon regime. Finally, the influence of intense XUV radiation to the relaxation dynamics of the Ne 2s-3p resonance was investigated by angle-resolved electron spectroscopy, especially be observing

  12. Bayesian Threshold Estimation

    ERIC Educational Resources Information Center

    Gustafson, S. C.; Costello, C. S.; Like, E. C.; Pierce, S. J.; Shenoy, K. N.

    2009-01-01

    Bayesian estimation of a threshold time (hereafter simply threshold) for the receipt of impulse signals is accomplished given the following: 1) data, consisting of the number of impulses received in a time interval from zero to one and the time of the largest time impulse; 2) a model, consisting of a uniform probability density of impulse time…

  13. Ionization potentials of seaborgium

    SciTech Connect

    Johnson, E.; Pershina, V.; Fricke, B.

    1999-10-21

    Multiconfiguration relativistic Dirac-Fock values were calculated for the first six ionization potentials of seaborgium and of the other group 6 elements. No experimental ionization potentials are available for seaborgium. Accurate experimental values are not available for all of the other ionization potentials. Ionic radii for the 4+ through 6+ ions of seaborgium are also presented. The ionization potentials and ionic radii obtained will be used to predict some physiochemical properties of seaborgium and its compounds.

  14. Ionization Energies of Lanthanides

    ERIC Educational Resources Information Center

    Lang, Peter F.; Smith, Barry C.

    2010-01-01

    This article describes how data are used to analyze the pattern of ionization energies of the lanthanide elements. Different observed pathways of ionization between different ground states are discussed, and the effects of pairing, exchange, and orbital interactions on ionization energies of the lanthanides are evaluated. When all the above…

  15. Measurement of the first ionization potential of astatine by laser ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Rothe, S.; Andreyev, A. N.; Antalic, S.; Borschevsky, A.; Capponi, L.; Cocolios, T. E.; de Witte, H.; Eliav, E.; Fedorov, D. V.; Fedosseev, V. N.; Fink, D. A.; Fritzsche, S.; Ghys, L.; Huyse, M.; Imai, N.; Kaldor, U.; Kudryavtsev, Yuri; Köster, U.; Lane, J. F. W.; Lassen, J.; Liberati, V.; Lynch, K. M.; Marsh, B. A.; Nishio, K.; Pauwels, D.; Pershina, V.; Popescu, L.; Procter, T. J.; Radulov, D.; Raeder, S.; Rajabali, M. M.; Rapisarda, E.; Rossel, R. E.; Sandhu, K.; Seliverstov, M. D.; Sjödin, A. M.; van den Bergh, P.; van Duppen, P.; Venhart, M.; Wakabayashi, Y.; Wendt, K. D. A.

    2013-05-01

    The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine.

  16. Determination of the first ionization potential of berkelium and californium by resonance ionization mass spectroscopy

    SciTech Connect

    Nunnemann, M.; Eberhardt, K.; Erdmann, N.; Herrmann, G.; Huber, G.; Koehler, S.; Kratz, J. V.; Naehler, A.; Passler, G.; Trautmann, N.

    1997-01-15

    Resonance ionization mass spectroscopy (RIMS) is used for the precise determination of the first ionization potential (IP) of transuranium elements. Small amounts of material ({approx_equal}0.4 ng) are sufficient for these measurements due to the high sensitivity of RIMS enabling the investigation of the actinides beyond plutonium, which are accessible only in limited amounts and difficult to handle due to their high radioactivity. The method presented takes advantage of the dependence of the ionization threshold on an external static electric field. With samples of 10{sup 12} atoms of {sup 249}Bk and {sup 249}Cf experimental values for the first ionization potentials of IP{sub Bk}=49989(2) cm{sup -1} and IP{sub Cf}=50665(2) cm{sup -1} were obtained.

  17. Determination of the first ionization potential of berkelium and californium by resonance ionization mass spectroscopy

    SciTech Connect

    Nunnemann, M.; Eberhardt, K.; Erdmann, N.; Herrmann, G.; Huber, G.; Koehler, S.; Kratz, J.V.; Naehler, A.; Passler, G.; Trautmann, N.

    1997-01-01

    Resonance ionization mass spectroscopy (RIMS) is used for the precise determination of the first ionization potential ({ital IP}) of transuranium elements. Small amounts of material ({approx}0.4ng) are sufficient for these measurements due to the high sensitivity of RIMS enabling the investigation of the actinides beyond plutonium, which are accessible only in limited amounts and difficult to handle due to their high radioactivity. The method presented takes advantage of the dependence of the ionization threshold on an external static electric field. With samples of 10{sup 12} atoms of {sup 249}Bk and {sup 249}Cf experimental values for the first ionization potentials of IP{sub Bk}=49989(2)cm{sup {minus}1} and IP{sub Cf}=50665(2)cm{sup {minus}1} were obtained. {copyright} {ital 1997 American Institute of Physics.}

  18. Measurement of the first ionization potential of astatine by laser ionization spectroscopy

    PubMed Central

    Rothe, S.; Andreyev, A. N.; Antalic, S.; Borschevsky, A.; Capponi, L.; Cocolios, T. E.; De Witte, H.; Eliav, E.; Fedorov, D. V.; Fedosseev, V. N.; Fink, D. A.; Fritzsche, S.; Ghys, L.; Huyse, M.; Imai, N.; Kaldor, U.; Kudryavtsev, Yuri; Köster, U.; Lane, J. F. W.; Lassen, J.; Liberati, V.; Lynch, K. M.; Marsh, B. A.; Nishio, K.; Pauwels, D.; Pershina, V.; Popescu, L.; Procter, T. J.; Radulov, D.; Raeder, S.; Rajabali, M. M.; Rapisarda, E.; Rossel, R. E.; Sandhu, K.; Seliverstov, M. D.; Sjödin, A. M.; Van den Bergh, P.; Van Duppen, P.; Venhart, M.; Wakabayashi, Y.; Wendt, K. D. A.

    2013-01-01

    The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine. PMID:23673620

  19. Measurement of the first ionization potential of astatine by laser ionization spectroscopy.

    PubMed

    Rothe, S; Andreyev, A N; Antalic, S; Borschevsky, A; Capponi, L; Cocolios, T E; De Witte, H; Eliav, E; Fedorov, D V; Fedosseev, V N; Fink, D A; Fritzsche, S; Ghys, L; Huyse, M; Imai, N; Kaldor, U; Kudryavtsev, Yuri; Köster, U; Lane, J F W; Lassen, J; Liberati, V; Lynch, K M; Marsh, B A; Nishio, K; Pauwels, D; Pershina, V; Popescu, L; Procter, T J; Radulov, D; Raeder, S; Rajabali, M M; Rapisarda, E; Rossel, R E; Sandhu, K; Seliverstov, M D; Sjödin, A M; Van den Bergh, P; Van Duppen, P; Venhart, M; Wakabayashi, Y; Wendt, K D A

    2013-01-01

    The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine.

  20. Double Photoionization Near Threshold

    NASA Technical Reports Server (NTRS)

    Wehlitz, Ralf

    2007-01-01

    The threshold region of the double-photoionization cross section is of particular interest because both ejected electrons move slowly in the Coulomb field of the residual ion. Near threshold both electrons have time to interact with each other and with the residual ion. Also, different theoretical models compete to describe the double-photoionization cross section in the threshold region. We have investigated that cross section for lithium and beryllium and have analyzed our data with respect to the latest results in the Coulomb-dipole theory. We find that our data support the idea of a Coulomb-dipole interaction.

  1. Providing VoD Streaming Using P2P Networks

    NASA Astrophysics Data System (ADS)

    Pedro Muñoz-Gea, Juan; Malgosa-Sanahuja, Josemaria; Manzanares-Lopez, Pilar; Carlos Sanchez-Aarnoutse, Juan

    Overlays and P2P systems, initially developed to support IP multicast and file-sharing, have moved beyond that functionality. They are also proving to be key technologies for the delivery of video streaming. Recently, there have been a number of successful deployments for "live" P2P streaming. However, the question remains open whether similar P2P technologies can be used to provide VoD (Video-On-Demand) services. A P2P VoD service is more challenging to design than a P2P live streaming system because the system should allow users arriving at arbitrary times to watch (arbitrary parts of) the video.

  2. Ionization-chamber smoke detector system

    DOEpatents

    Roe, Robert F.

    1976-10-19

    This invention relates to an improved smoke-detection system of the ionization-chamber type. In the preferred embodiment, the system utilizes a conventional detector head comprising a measuring ionization chamber, a reference ionization chamber, and a normally non-conductive gas triode for discharging when a threshold concentration of airborne particulates is present in the measuring chamber. The improved system is designed to reduce false alarms caused by fluctuations in ambient temperature. Means are provided for periodically firing the gas discharge triode and each time recording the triggering voltage required. A computer compares each triggering voltage with its predecessor. The computer is programmed to energize an alarm if the difference between the two compared voltages is a relatively large value indicative of particulates in the measuring chamber and to disregard smaller differences typically resulting from changes in ambient temperature.

  3. Hydrodynamics of sediment threshold

    NASA Astrophysics Data System (ADS)

    Ali, Sk Zeeshan; Dey, Subhasish

    2016-07-01

    A novel hydrodynamic model for the threshold of cohesionless sediment particle motion under a steady unidirectional streamflow is presented. The hydrodynamic forces (drag and lift) acting on a solitary sediment particle resting over a closely packed bed formed by the identical sediment particles are the primary motivating forces. The drag force comprises of the form drag and form induced drag. The lift force includes the Saffman lift, Magnus lift, centrifugal lift, and turbulent lift. The points of action of the force system are appropriately obtained, for the first time, from the basics of micro-mechanics. The sediment threshold is envisioned as the rolling mode, which is the plausible mode to initiate a particle motion on the bed. The moment balance of the force system on the solitary particle about the pivoting point of rolling yields the governing equation. The conditions of sediment threshold under the hydraulically smooth, transitional, and rough flow regimes are examined. The effects of velocity fluctuations are addressed by applying the statistical theory of turbulence. This study shows that for a hindrance coefficient of 0.3, the threshold curve (threshold Shields parameter versus shear Reynolds number) has an excellent agreement with the experimental data of uniform sediments. However, most of the experimental data are bounded by the upper and lower limiting threshold curves, corresponding to the hindrance coefficients of 0.2 and 0.4, respectively. The threshold curve of this study is compared with those of previous researchers. The present model also agrees satisfactorily with the experimental data of nonuniform sediments.

  4. A Scalable P2P Video Streaming Framework

    NASA Astrophysics Data System (ADS)

    Lee, Ivan

    Peer-to-peer (P2P) networking technique represents a vast potential to overcome many constraints in the conventional content distribution networks, especially for the real-time applications such as P2P streaming. In this chapter, a P2P streaming system is examined, and the proposed system combines multiple-description source coding technique and a scalable streaming infrastructure. The proposed system aims to gradually offload congested traffic from a centralized bottleneck to the under-utilized P2P networks and hence, provides seamless transitions from client/server streaming to centralized P2P streaming and to decentralized P2P streaming. The performance of the proposed framework is evaluated in terms of video frame loss rate, which reflects the probability of freeze video frames.

  5. Mitochondrial threshold effects.

    PubMed Central

    Rossignol, Rodrigue; Faustin, Benjamin; Rocher, Christophe; Malgat, Monique; Mazat, Jean-Pierre; Letellier, Thierry

    2003-01-01

    The study of mitochondrial diseases has revealed dramatic variability in the phenotypic presentation of mitochondrial genetic defects. To attempt to understand this variability, different authors have studied energy metabolism in transmitochondrial cell lines carrying different proportions of various pathogenic mutations in their mitochondrial DNA. The same kinds of experiments have been performed on isolated mitochondria and on tissue biopsies taken from patients with mitochondrial diseases. The results have shown that, in most cases, phenotypic manifestation of the genetic defect occurs only when a threshold level is exceeded, and this phenomenon has been named the 'phenotypic threshold effect'. Subsequently, several authors showed that it was possible to inhibit considerably the activity of a respiratory chain complex, up to a critical value, without affecting the rate of mitochondrial respiration or ATP synthesis. This phenomenon was called the 'biochemical threshold effect'. More recently, quantitative analysis of the effects of various mutations in mitochondrial DNA on the rate of mitochondrial protein synthesis has revealed the existence of a 'translational threshold effect'. In this review these different mitochondrial threshold effects are discussed, along with their molecular bases and the roles that they play in the presentation of mitochondrial diseases. PMID:12467494

  6. Supporting Collaboration and Creativity Through Mobile P2P Computing

    NASA Astrophysics Data System (ADS)

    Wierzbicki, Adam; Datta, Anwitaman; Żaczek, Łukasz; Rzadca, Krzysztof

    Among many potential applications of mobile P2P systems, collaboration applications are among the most prominent. Examples of applications such as Groove (although not intended for mobile networks), collaboration tools for disaster recovery (the WORKPAD project), and Skype's collaboration extensions, all demonstrate the potential of P2P collaborative applications. Yet, the development of such applications for mobile P2P systems is still difficult because of the lack of middleware.

  7. Lifetime of inner-shell hole states of Ar (2p) and Kr (3d) using equation-of-motion coupled cluster method

    SciTech Connect

    Ghosh, Aryya; Vaval, Nayana; Pal, Sourav

    2015-07-14

    Auger decay is an efficient ultrafast relaxation process of core-shell or inner-shell excited atom or molecule. Generally, it occurs in femto-second or even atto-second time domain. Direct measurement of lifetimes of Auger process of single ionized and double ionized inner-shell state of an atom or molecule is an extremely difficult task. In this paper, we have applied the highly correlated complex absorbing potential-equation-of-motion coupled cluster (CAP-EOMCC) approach which is a combination of CAP and EOMCC approach to calculate the lifetime of the states arising from 2p inner-shell ionization of an Ar atom and 3d inner-shell ionization of Kr atom. We have also calculated the lifetime of Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}D, Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}S, and Ar{sup 2+}(2p{sup −1}3s{sup −1}) {sup 1}P double ionized states. The predicted results are compared with the other theoretical results as well as experimental results available in the literature.

  8. Analytical instruments, ionization sources, and ionization methods

    DOEpatents

    Atkinson, David A.; Mottishaw, Paul

    2006-04-11

    Methods and apparatus for simultaneous vaporization and ionization of a sample in a spectrometer prior to introducing the sample into the drift tube of the analyzer are disclosed. The apparatus includes a vaporization/ionization source having an electrically conductive conduit configured to receive sample particulate which is conveyed to a discharge end of the conduit. Positioned proximate to the discharge end of the conduit is an electrically conductive reference device. The conduit and the reference device act as electrodes and have an electrical potential maintained between them sufficient to cause a corona effect, which will cause at least partial simultaneous ionization and vaporization of the sample particulate. The electrical potential can be maintained to establish a continuous corona, or can be held slightly below the breakdown potential such that arrival of particulate at the point of proximity of the electrodes disrupts the potential, causing arcing and the corona effect. The electrical potential can also be varied to cause periodic arcing between the electrodes such that particulate passing through the arc is simultaneously vaporized and ionized. The invention further includes a spectrometer containing the source. The invention is particularly useful for ion mobility spectrometers and atmospheric pressure ionization mass spectrometers.

  9. Ultrafast polychromatic ionization of dielectric solids

    NASA Astrophysics Data System (ADS)

    Jürgens, P.; Jupé, M.; Gyamfi, M.; Ristau, D.

    2016-12-01

    The modeling of the laser-induced damage processes can be divided into thermal and electronic processes. Especially, electronic damage seems to be well understood. In corresponding models, the damage threshold is linked to the excitation of valence electrons into the conduction band, and often the damage is obtained if a critical density of free electrons is exceeded. For the modeling of the electronic excitation, rate equation models are applied which can vary in the different terms representing different excitation channels. According to the current state of the art, photoionization and avalanche ionization contribute the major part to the ionization process, and consequently the determination of laser-induced damage thresholds is based on the calculation of the respective terms. For the theoretical description of both, well established models are available. For the quantitative calculation of the photoionization, the Keldysh theory is used most frequently, and for the avalanche processes the Drude theory is often applied. Both, Drude and Keldysh theory calculations depend on the laser frequency and use a monochromatic approach. For most applications the monochromatic description matches very well with the experimental findings, but in the range of few-cycle pulses the necessary broadening of the laser emission spectrum leads to high uncertainty for the calculation. In this paper, a novel polychromatic approach is presented including photo- and avalanche ionization as well as the critical electron density. The simulation combines different ionization channels in a Monte-Carlo procedure according to the frequency distribution of the spectrum. The resulting influence on the wavelength and material dependency is discussed in detail for various pulse shapes and pulse durations. The main focus of the investigation is concentrated on the specific characteristics in the dispersion and material dependency of the laser-induced damage threshold respecting the polychromatic

  10. HIGH-TEMPERATURE IONIZATION IN PROTOPLANETARY DISKS

    SciTech Connect

    Desch, Steven J.; Turner, Neal J.

    2015-10-01

    We calculate the abundances of electrons and ions in the hot (≳500 K), dusty parts of protoplanetary disks, treating for the first time the effects of thermionic and ion emission from the dust grains. High-temperature ionization modeling has involved simply assuming that alkali elements such as potassium occur as gas-phase atoms and are collisionally ionized following the Saha equation. We show that the Saha equation often does not hold, because free charges are produced by thermionic and ion emission and destroyed when they stick to grain surfaces. This means the ionization state depends not on the first ionization potential of the alkali atoms, but rather on the grains’ work functions. The charged species’ abundances typically rise abruptly above about 800 K, with little qualitative dependence on the work function, gas density, or dust-to-gas mass ratio. Applying our results, we find that protoplanetary disks’ dead zone, where high diffusivities stifle magnetorotational turbulence, has its inner edge located where the temperature exceeds a threshold value ≈1000 K. The threshold is set by ambipolar diffusion except at the highest densities, where it is set by Ohmic resistivity. We find that the disk gas can be diffusively loaded onto the stellar magnetosphere at temperatures below a similar threshold. We investigate whether the “short-circuit” instability of current sheets can operate in disks and find that it cannot, or works only in a narrow range of conditions; it appears not to be the chondrule formation mechanism. We also suggest that thermionic emission is important for determining the rate of Ohmic heating in hot Jupiters.

  11. An intense polarized beam by a laser ionization injection

    NASA Astrophysics Data System (ADS)

    Ohmori, Chihiro; Hiramatsu, Shigenori; Nakamura, Takeshi

    1990-12-01

    Accumulation of protons and polarized protons by photo-ionization injection are described. This method consists of: (1) producing the neutral hydrogen beam by Lorentz stripping; (2) excitation of the neutral hydrogen beam with a laser; and (3) ionization of the hydrogen beam in the 2P excited state with another laser. When the laser for the excitation is circularly polarized, we can get a polarized proton beam. An ionization efficiency of 98 percent and a polarization of 80 percent can be expected by an intense laser beam from a free electron laser (FEL).

  12. A Remedy for Network Operators against Increasing P2P Traffic: Enabling Packet Cache for P2P Applications

    NASA Astrophysics Data System (ADS)

    Nakao, Akihiro; Sasaki, Kengo; Yamamoto, Shu

    We observe that P2P traffic has peculiar characteristics as opposed to the other type of traffic such as web browsing and file transfer. Since they exploit swarm effect — a multitude of end points downloading the same content piece by piece nearly at the same time, thus, increasing the effectiveness of caching — the same pieces of data end up traversing the network over and over again within mostly a short time window. In the light of this observation, we propose a network layer packet-level caching for reducing the volume of emerging P2P traffic, transparently to the P2P applications — without affecting operations of the P2P applications at all — rather than banning it, restricting it, or modifying P2P systems themselves. Unlike the other caching techniques, we aim to provide as generic a caching mechanism as possible at network layer — without knowing much detail of P2P application protocols — to extend applicability to arbitrary P2P protocols. Our preliminary evaluation shows that our approach is expected to reduce a significant amount of P2P traffic transparently to P2P applications.

  13. Isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions

    NASA Astrophysics Data System (ADS)

    Zubova, N. A.; Malyshev, A. V.; Tupitsyn, I. I.; Shabaev, V. M.; Kozhedub, Y. S.; Plunien, G.; Brandau, C.; Stöhlker, Th.

    2016-05-01

    Isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions are evaluated for a wide range of the nuclear charge number: Z =8 -92 . The calculations of the relativistic nuclear recoil and nuclear size effects are performed using a large-scale configuration-interaction Dirac-Fock-Sturm method. The corresponding QED corrections are also taken into account. The results of the calculations are compared with the theoretical values obtained with other methods. The accuracy of the isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions is significantly improved.

  14. Search of truncation of (N-1) electron basis containing full connected triple excitations in computing main and satellite ionization potentials via Fock-space coupled cluster approach.

    PubMed

    Adhikari, Kalipada; Chattopadhyay, Sudip; De, Barin Kumar; Sharma, Amitava; Nath, Ranendu Kumar; Sinha, Dhiman

    2013-06-05

    A valence-universal multireference coupled cluster (VUMRCC) theory, realized via the eigenvalue independent partitioning (EIP) route, has been implemented with full inclusion of triples excitations for computing and analyzing the entire main and several satellite peaks in the ionization potential spectra of several molecules. The EIP-VUMRCC method, unlike the traditional VUMRCC theory, allows divergence-free homing-in to satellite roots which would otherwise have been plagued by intruders, and is thus numerically more robust to obtain more efficient and dependable computational schemes allowing more extensive use of the approach. The computed ionization potentials (IPs) as a result of truncation of the (N-1) electron basis manifold involving virtual functions such as 2h-p and 3h-2p by different energy thresholds varying from 5 to 15 a.u. with 1 a.u. intervals as well as thresholds such as 20, 25, and 30 a.u. have been carefully looked into. Cutoff at around 25 a.u. turns out to be an optimal threshold. Molecules such as C2H4 and C2H2 (X = D,T), and N2 and CO (X = D,T,Q) with Dunning's cc-pVXZ bases have been investigated to determine all main and 2h-p shake-up and 3h-2p double shake-up satellite IPs. We believe that the present work will pave the way to a wider application of the method by providing main and satellite IPs for some problematic N-electron closed shell systems.

  15. Single photon simultaneous K-shell ionization and K-shell excitation. II. Specificities of hollow nitrogen molecular ions

    SciTech Connect

    Carniato, S. Selles, P.; Andric, L.; Palaudoux, J.; Penent, F.; Lablanquie, P.; Žitnik, M.; Bučar, K.; Nakano, M.; Hikosaka, Y.; Ito, K.

    2015-01-07

    The formalism developed in the companion Paper I is used here for the interpretation of spectra obtained recently on the nitrogen molecule. Double core-hole ionization K{sup −2} and core ionization-core excitation K{sup −2}V processes have been observed by coincidence electron spectroscopy after ionization by synchrotron radiation at different photon energies. Theoretical and experimental cross sections reported on an absolute scale are in satisfactory agreement. The evolution with photon energy of the relative contribution of shake-up and conjugate shake-up processes is discussed. The first main resonance in the K{sup −2}V spectrum is assigned to a K{sup −2}π{sup ∗} state mainly populated by the 1s→ lowest unoccupied molecular orbital dipolar excitation, as it is in the K{sup −1}V NEXAFS (Near-Edge X-ray Absorption Fine Structure) signals. Closer to the K{sup −2} threshold Rydberg resonances have been also identified, and among them a K{sup −2}σ{sup ∗} resonance characterized by a large amount of 2s/2p hybridization, and double K{sup −2}(2σ{sup ∗}/1π/3σ){sup −1}1π{sup ∗2} shake-up states. These resonances correspond in NEXAFS spectra to, respectively, the well-known σ{sup ∗} shape resonance and double excitation K{sup −1}(2σ{sup ∗}/1π/3σ){sup −1}1π{sup ∗2} resonances, all being positioned above the threshold.

  16. Universal threshold for femtosecond laser ablation with oblique illumination

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-Long; Cheng, Weibo; Petrarca, Massimo; Polynkin, Pavel

    2016-10-01

    We quantify the dependence of the single-shot ablation threshold on the angle of incidence and polarization of a femtosecond laser beam, for three dissimilar solid-state materials: a metal, a dielectric, and a semiconductor. Using the constant, linear value of the index of refraction, we calculate the laser fluence transmitted through the air-material interface at the point of ablation threshold. We show that, in spite of the highly nonlinear ionization dynamics involved in the ablation process, the so defined transmitted threshold fluence is universally independent of the angle of incidence and polarization of the laser beam for all three material types. We suggest that angular dependence of ablation threshold can be utilized for profiling fluence distributions in ultra-intense femtosecond laser beams.

  17. Linear polarization of the 2p{sup 5}3s{yields}2p{sup 6} lines following the inner-shell photoionization of sodiumlike ions

    SciTech Connect

    Inal, M.K.; Surzhykov, A.; Fritzsche, S.

    2005-10-15

    The inner-shell photoionization of highly charged, many-electron ions and their subsequent radiative decay are studied theoretically within the multiconfiguration Dirac-Fock approach. Special attention is paid to the linear polarization of the characteristic x-ray radiation. Detailed calculations have been carried out, in particular for the 2p{sup 5}3s{yields}2p{sup 6} radiative transitions following ionization of the 2p electron of the sodiumlike iron Fe{sup 15+} and uranium U{sup 81+} ions. For these elements, the inner-shell photoionization was found to induce the (relatively) low linear polarization of the subsequently emitted photons which is strongly affected, moreover, by the higher-order (nondipole) effects in the electron-photon interaction.

  18. Biological Effects of Ionizing Radiation

    DOE R&D Accomplishments Database

    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.

  19. Network problem threshold

    NASA Technical Reports Server (NTRS)

    Gejji, Raghvendra, R.

    1992-01-01

    Network transmission errors such as collisions, CRC errors, misalignment, etc. are statistical in nature. Although errors can vary randomly, a high level of errors does indicate specific network problems, e.g. equipment failure. In this project, we have studied the random nature of collisions theoretically as well as by gathering statistics, and established a numerical threshold above which a network problem is indicated with high probability.

  20. Elaborating on threshold concepts

    NASA Astrophysics Data System (ADS)

    Rountree, Janet; Robins, Anthony; Rountree, Nathan

    2013-09-01

    We propose an expanded definition of Threshold Concepts (TCs) that requires the successful acquisition and internalisation not only of knowledge, but also its practical elaboration in the domains of applied strategies and mental models. This richer definition allows us to clarify the relationship between TCs and Fundamental Ideas, and to account for both the important and the problematic characteristics of TCs in terms of the Knowledge/Strategies/Mental Models Framework defined in previous work.

  1. Vision thresholds revisited

    NASA Astrophysics Data System (ADS)

    Garstang, R. H.

    1999-05-01

    During and just after World War II there was intense interest in the threshold for seeing faint sources against illuminated backgrounds. Knoll, Tousey and Hulburt (1946, 1948) determined the threshold for (effectively) point sources seen against backgrounds ranging in brightness from darkness to subdued daylight. Blackwell (1946) gave contrast ratios for sources of various sizes ranging from point sources up to circular disks of 6 degrees diameter, all seen against the same range of brightnesses, and determined by a very large number of visual observations made by a team of observers. I have combined the two sets of results, and represented them by an improvement on the theoretical formula for threshold illuminance as a function of background brightness which was suggested by Hecht (1934). My formula agrees very well with the observations, and is very suitable for incorporation into computer programs. Applications have been made to problems where the background brightness is caused by light pollution, and the source size is determined by the seeing. These include the optimum magnification and limiting magnitude of telescopes, and the analysis of visual limiting magnitudes determined by Bowen (1947) to determine the night sky brightness at Mount Wilson in 1947.

  2. Three-photon near-threshold photoionization dynamics of isooctane

    NASA Astrophysics Data System (ADS)

    Healy, Andrew T.; Underwood, David F.; Lipsky, Sanford; Blank, David A.

    2005-08-01

    The electron survival probability following three-photon (9.3eV total) near-threshold photoionization of neat isooctane is measured with sub-50fs time resolution. The measured dynamics are nonexponential in time and are well described by a diffusion-controlled electron-cation recombination model. Excitation-power-dependent studies indicate that the unperturbed three-photon threshold ionization is only observed for pump irradiance below 0.5TW/cm2. At excitation fields above this level, the signal is no longer cubic in the excitation irradiance, and the observed electron survival probability dramatically changes, decaying as a single exponential in time.

  3. Three-photon near-threshold photoionization dynamics of isooctane.

    PubMed

    Healy, Andrew T; Underwood, David F; Lipsky, Sanford; Blank, David A

    2005-08-01

    The electron survival probability following three-photon (9.3 eV total) near-threshold photoionization of neat isooctane is measured with sub-50 fs time resolution. The measured dynamics are nonexponential in time and are well described by a diffusion-controlled electron-cation recombination model. Excitation-power-dependent studies indicate that the unperturbed three-photon threshold ionization is only observed for pump irradiance below 0.5 TW cm2. At excitation fields above this level, the signal is no longer cubic in the excitation irradiance, and the observed electron survival probability dramatically changes, decaying as a single exponential in time.

  4. Trisomy 2p: Analysis of unusual phenotypic findings

    SciTech Connect

    Lurie, I.W.; Ilyina, H.G.; Gurevich, D.B.

    1995-01-16

    We present three probands with partial trisomies 2p21-23 due to ins(4;2)(q21;p21p23) pat, 2p23-pter due to t(2;4)(p23;q35)mat, and 2p21-pter due to t(2;11)(p21;q23.3)mat. More than 50 cases of partial trisomy 2p have been reviewed and some abnormalities, unusual for most other types of structural autosomal imbalance, have been found in patients with inherited forms of 2p trisomy and in their non-karyotyped sibs. Neural tube defects (anencephaly, occipital encephalocele, and spina bifida) were found in five probands and 4/6 affected non-karyotyped sibs. The only triplicated segment common to all was 2p24. Different forms of {open_quotes}broncho-pulmonary a/hypoplasia{close_quotes} (including two cases of lung agenesis) were described in four patients (overlapping triplicated segment was 2p21-p25). Three patients (with overlapping triplicated segment 2p23-p25) had diaphragmatic hernia. Abnormal rotation of the heart or L-transposition of large vessels (with or without visceral heterotaxia) was found in two infants (overlapping triplicated segment 2p23-p24). In two patients with common triplicated segment 2p22.3-p25, neuroblastoma has been described. The occurrence of all these defects may be explained either by the action of the same gene(s) mapped to 2p24 or by action of some independent factors located in different segments of the short arm. Although the latter hypothesis is much less probable, it can not be rejected at the present time. We propose the existence of a genetic system controlling surveillance of an abnormal embryo to explain the phenotypic differences between patients with the same imbalance within a family. In some {open_quotes}restrictive{close_quotes} combinations the abnormal embryos will die, although in {open_quotes}permissive{close_quotes} combinations they can survive. 47 refs., 2 figs., 3 tabs.

  5. Network Awareness in P2P-TV Applications

    NASA Astrophysics Data System (ADS)

    Traverso, Stefano; Leonardi, Emilio; Mellia, Marco; Meo, Michela

    The increasing popularity of applications for video-streaming based on P2P paradigm (P2P-TV) is raising the interest of both broadcasters and network operators. The former see a promising technology to reduce the cost of streaming content over the Internet, while offering a world-wide service. The latter instead fear that the traffic offered by these applications can grow without control, affecting other services, and possibly causing network congestion and collapse. The “Network-Aware P2P-TV Application over Wise Networks” FP7 project aims at studying and developing a novel P2P-TV application offering the chance to broadcast high definition video to broadcasters and to carefully manage the traffic offered by peers to the network, therefore avoiding worries to Internet providers about network overload. In such context, we design a simulator to evaluate performance of different P2P-TV solutions, to compare them both considering end-users’ and network providers’ perspectives, such as quality of service perceived by subscribers and link utilization. In this paper, we provide some results that show how effective can be a network aware P2P-TV system.

  6. Improving P2P live-content delivery using SVC

    NASA Astrophysics Data System (ADS)

    Schierl, T.; Sánchez, Y.; Hellge, C.; Wiegand, T.

    2010-07-01

    P2P content delivery techniques for video transmission have become of high interest in the last years. With the involvement of client into the delivery process, P2P approaches can significantly reduce the load and cost on servers, especially for popular services. However, previous studies have already pointed out the unreliability of P2P-based live streaming approaches due to peer churn, where peers may ungracefully leave the P2P infrastructure, typically an overlay networks. Peers ungracefully leaving the system cause connection losses in the overlay, which require repair operations. During such repair operations, which typically take a few roundtrip times, no data is received from the lost connection. While taking low delay for fast-channel tune-in into account as a key feature for broadcast-like streaming applications, the P2P live streaming approach can only rely on a certain media pre-buffer during such repair operations. In this paper, multi-tree based Application Layer Multicast as a P2P overlay technique for live streaming is considered. The use of Flow Forwarding (FF), a.k.a. Retransmission, or Forward Error Correction (FEC) in combination with Scalable video Coding (SVC) for concealment during overlay repair operations is shown. Furthermore the benefits of using SVC over the use of AVC single layer transmission are presented.

  7. Dissociative Ionization of Benzene by Electron Impact

    NASA Technical Reports Server (NTRS)

    Huo, Winifred; Dateo, Christopher; Kwak, Dochan (Technical Monitor)

    2002-01-01

    We report a theoretical study of the dissociative ionization (DI) of benzene from the low-lying ionization channels. Our approach makes use of the fact that electron motion is much faster than nuclear motion and DI is treated as a two-step process. The first step is electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model. For the unimolecular dissociation step, we study the steepest descent reaction path to the minimum of the ion potential energy surface. The path is used to analyze the probability of unimolecular dissociation and to determine the product distributions. Our analysis of the dissociation products and the thresholds of the productions are compared with the result dissociative photoionization measurements of Feng et al. The partial oscillator strengths from Feng et al. are then used in the iBED cross section calculations.

  8. Threshold Concepts in Research Education and Evidence of Threshold Crossing

    ERIC Educational Resources Information Center

    Kiley, Margaret; Wisker, Gina

    2009-01-01

    Most work on threshold concepts has hitherto related to discipline-specific undergraduate education, however, the idea of generic doctoral-level threshold concepts appeared to us to provide a strong and useful framework to support research learning and teaching at the graduate level. The early work regarding research-level threshold concepts is…

  9. Associative ionization reactions involving excited atoms in nitrogen plasma

    SciTech Connect

    Popov, N. A.

    2009-05-15

    A model of kinetic processes in gas-discharge plasmas of pure nitrogen and its mixtures with nitrogen oxide and oxygen is presented. A distinctive feature of the model is that it includes associative ionization reactions involving N({sup 2}P) electronically excited atoms. Taking into account these processes allows one to explain both the anomalously slow decay of gas-discharge nitrogen plasma and the increase in the electron density in the region of the so-called pink afterglow in nitrogen. The possibility of substantially accelerating secondary ionization by adding NO molecules to a partially dissociated nitrogen is demonstrated. It is shown that such acceleration is caused by the associative ionization reaction N({sup 2}P) + O({sup 3}P) {yields} e + NO{sup +}. The calculated results agree well with available experimental data.

  10. Upper Hybrid Effects in Artificial Ionization

    NASA Astrophysics Data System (ADS)

    Papadopoulos, K.; Eliasson, B. E.

    2014-12-01

    A most fascinating result of recent ionospheric experiments has been the discovery of artificial ionization by Pedersen et al. (GRL, 37, L02106, 2010). The Artificial Ionospheric Layers (AIL) were the result of F-region O-mode HF irradiation using the HAARP ionospheric heater operating at 3.6 MW power. As demonstrated by Eliasson et al. (JGR, 117, A10321, 2012) the physics controlling the observed phenomenon and its threshold can be summarized as: " Collisional ionization due to high energy (~ 20 eV) electron tails generated by the interaction of strong Langmuir turbulence with plasma heated at the upper hybrid resonance and transported at the reflection height". The objective of the current presentation is to explore the role of the upper hybrid heating in the formation of AIL and its implications to future experiments involving HF heaters operating in middle and equatorial latitudes.

  11. Electron ionization of acetylene.

    PubMed

    King, Simon J; Price, Stephen D

    2007-11-07

    Relative partial ionization cross sections and precursor specific relative partial ionization cross sections for fragment ions formed by electron ionization of C2H2 have been measured using time-of-flight mass spectrometry coupled with a 2D ion-ion coincidence technique. We report data for the formation of H+, H+2, C2+, C+/C2+ 2, CH+/C2H+2, CH+2, C+2, and C2H+ relative to the formation of C2H+2, as a function of ionizing electron energy from 30-200 eV. While excellent agreement is found between our data and one set of previously published absolute partial ionization cross sections, some discrepancies exist between the results presented here and two other recent determinations of these absolute partial ionization cross sections. We attribute these differences to the loss of some translationally energetic fragment ions in these earlier studies. Our relative precursor-specific partial ionization cross sections enable us, for the first time, to quantify the contribution to the yield of each fragment ion from single, double, and triple ionization. Analysis shows that at 50 eV double ionization contributes 2% to the total ion yield, increasing to over 10% at an ionizing energy of 100 eV. From our ion-ion coincidence data, we have derived branching ratios for charge separating dissociations of the acetylene dication. Comparison of our data to recent ab initio/RRKM calculations suggest that close to the double ionization potential C2H2+2 dissociates predominantly on the ground triplet potential energy surface (3Sigma*g) with a much smaller contribution from dissociation via the lowest singlet potential energy surface (1Delta g). Measurements of the kinetic energy released in the fragmentation reactions of C2H2+2 have been used to obtain precursor state energies for the formation of product ion pairs, and are shown to be in good agreement with available experimental data and with theory.

  12. The lowest ionization potentials of Al2

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Barnes, Leslie A.; Taylor, Peter R.

    1988-01-01

    Potential curves for the lowest two electronic states (X 2 sigma g + and A 2 pi u) of Al2(+) were computed using complete active space SCF/multireference CI wave functions and large Gaussian basis sets. The lowest observable vertical ionization potential (to Al2(+) X 2 sigma g +) of the Al2 X 3 pi u ground state is calculated to occur around 6.1 eV, in excellent agreement with the experimental range of 6.0 to 6.42 eV obtained in recent cluster ionization studies by Cox and co-workers. The second vertical ionization potential (to Al2(+) A 2 pi u) occurs near 6.4 eV, also within the experimental range. The adiabatic IP of 5.90 eV is in good agreement with the value of 5.8 to 6.1 eV deduced by Hanley and co-workers from the difference in thresholds between collision induced dissociation processes of Al3(+). The computed IP values are somewhat larger than those deduced from branching ratios in cluster fragmentation experiments by Jarrold and co-workers. The observation of an ionization threshold below 6.42 eV is shown to be incompatible with an Al2 ground electronic state assignment of 3 sigma g -, but the separation between the two lowest states of Al2 is so small that it is likely that both are populated in the experiments, so that this does not provide unambiguous support for the recent theoretical assignment of the ground state as 3 pi u.

  13. Radiation threshold levels for noise degradation of photodiodes. Technical report

    SciTech Connect

    Aukerman, L.W.; Vernon, F.L.; Song, Y.

    1986-09-30

    Space radiation can increase the noise of photodiodes as a result of either a sustained ionizing-dose-rate effect or displacement damage. Elementary, straightforward models are presented for calculating radiation threshold levels and rad hit susceptibility. Radiation-effects experiments that verify these models are discussed. Calculations for room-temperature silicon p-i-n photodetectors, an avalanche photodiode, and a hypothetical cooled staring detector indicate that this damage mechanism should not be ignored for space and nuclear environments.

  14. Alkali metal ionization detector

    DOEpatents

    Bauerle, James E.; Reed, William H.; Berkey, Edgar

    1978-01-01

    Variations in the conventional filament and collector electrodes of an alkali metal ionization detector, including the substitution of helical electrode configurations for either the conventional wire filament or flat plate collector; or, the substitution of a plurality of discrete filament electrodes providing an in situ capability for transferring from an operationally defective filament electrode to a previously unused filament electrode without removing the alkali metal ionization detector from the monitored environment. In particular, the helical collector arrangement which is coaxially disposed about the filament electrode, i.e. the thermal ionizer, provides an improved collection of positive ions developed by the filament electrode. The helical filament design, on the other hand, provides the advantage of an increased surface area for ionization of alkali metal-bearing species in a monitored gas environment as well as providing a relatively strong electric field for collecting the ions at the collector electrode about which the helical filament electrode is coaxially positioned. Alternatively, both the filament and collector electrodes can be helical. Furthermore, the operation of the conventional alkali metal ionization detector as a leak detector can be simplified as to cost and complexity, by operating the detector at a reduced collector potential while maintaining the sensitivity of the alkali metal ionization detector adequate for the relatively low concentration of alkali vapor and aerosol typically encountered in leak detection applications.

  15. "Magic" Ionization Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Trimpin, Sarah

    2016-01-01

    The systematic study of the temperature and pressure dependence of matrix-assisted ionization (MAI) led us to the discovery of the seemingly impossible, initially explained by some reviewers as either sleight of hand or the misinterpretation by an overzealous young scientist of results reported many years before and having little utility. The "magic" that we were attempting to report was that with matrix assistance, molecules, at least as large as bovine serum albumin (66 kDa), are lifted into the gas phase as multiply charged ions simply by exposure of the matrix:analyte sample to the vacuum of a mass spectrometer. Applied heat, a laser, or voltages are not necessary to achieve charge states and ion abundances only previously observed with electrospray ionization (ESI). The fundamentals of how solid phase volatile or nonvolatile compounds are converted to gas-phase ions without added energy currently involves speculation providing a great opportunity to rethink mechanistic understanding of ionization processes used in mass spectrometry. Improved understanding of the mechanism(s) of these processes and their connection to ESI and matrix-assisted laser desorption/ionization may provide opportunities to further develop new ionization strategies for traditional and yet unforeseen applications of mass spectrometry. This Critical Insights article covers developments leading to the discovery of a seemingly magic ionization process that is simple to use, fast, sensitive, robust, and can be directly applied to surface characterization using portable or high performance mass spectrometers.

  16. "Magic" Ionization Mass Spectrometry.

    PubMed

    Trimpin, Sarah

    2016-01-01

    The systematic study of the temperature and pressure dependence of matrix-assisted ionization (MAI) led us to the discovery of the seemingly impossible, initially explained by some reviewers as either sleight of hand or the misinterpretation by an overzealous young scientist of results reported many years before and having little utility. The “magic” that we were attempting to report was that with matrix assistance, molecules, at least as large as bovine serum albumin (66 kDa), are lifted into the gas phase as multiply charged ions simply by exposure of the matrix:analyte sample to the vacuum of a mass spectrometer. Applied heat, a laser, or voltages are not necessary to achieve charge states and ion abundances only previously observed with electrospray ionization (ESI). The fundamentals of how solid phase volatile or nonvolatile compounds are converted to gas-phase ions without added energy currently involves speculation providing a great opportunity to rethink mechanistic understanding of ionization processes used in mass spectrometry. Improved understanding of the mechanism(s) of these processes and their connection to ESI and matrix-assisted laser desorption/ionization may provide opportunities to further develop new ionization strategies for traditional and yet unforeseen applications of mass spectrometry. This Critical Insights article covers developments leading to the discovery of a seemingly magic ionization process that is simple to use, fast, sensitive, robust, and can be directly applied to surface characterization using portable or high performance mass spectrometers.

  17. Optical thresholding and Max Operation

    DTIC Science & Technology

    Thresholding and Max operations are essential elements in the implementation of neural networks. Although there have been several optical...implementations of neural networks, the thresholding functions are performed electronically. Optical thresholding and Max operations have the advantages of...we propose and study the properties of self-oscillation in nonlinear optical (NLO) four-wave mixing (FWM) and NLO resonators for parallel optical thresholding and Max operation.

  18. Resonance ionization detection of combustion radicals

    SciTech Connect

    Cool, T.A.

    1993-12-01

    Fundamental research on the combustion of halogenated organic compounds with emphasis on reaction pathways leading to the formation of chlorinated aromatic compounds and the development of continuous emission monitoring methods will assist in DOE efforts in the management and disposal of hazardous chemical wastes. Selective laser ionization techniques are used in this laboratory for the measurement of concentration profiles of radical intermediates in the combustion of chlorinated hydrocarbon flames. A new ultrasensitive detection technique, made possible with the advent of tunable VUV laser sources, enables the selective near-threshold photoionization of all radical intermediates in premixed hydrocarbon and chlorinated hydrocarbon flames.

  19. Managing Linguistic Data Summaries in Advanced P2P Applications

    NASA Astrophysics Data System (ADS)

    Hayek, Rabab; Raschia, Guillaume; Valduriez, Patrick; Mouaddib, Noureddine

    As the amount of stored data increases, data localization techniques become no longer sufficient in P2P systems. A practical approach is to rely on compact database summaries rather than raw database records, whose access is costly in large P2P systems. In this chapter, we describe a solution for managing linguistic data summaries in advanced P2P applications which are dealing with semantically rich data. The produced summaries are synthetic, multidimensional views over relational tables. The novelty of this proposal relies on the double summary exploitation in distributed P2P systems. First, as semantic indexes, they support locating relevant nodes based on their data descriptions. Second, due to their intelligibility, these summaries can be directly queried and thus approximately answer a query without the need for exploring original data. The proposed solution consists first in defining a summary model for hierarchical P2P systems. Second, appropriate algorithms for summary creation and maintenance are presented. A query processing mechanism, which relies on summary querying, is then proposed to demonstrate the benefits that might be obtained from summary exploitation.

  20. Determinants of Default in P2P Lending.

    PubMed

    Serrano-Cinca, Carlos; Gutiérrez-Nieto, Begoña; López-Palacios, Luz

    2015-01-01

    This paper studies P2P lending and the factors explaining loan default. This is an important issue because in P2P lending individual investors bear the credit risk, instead of financial institutions, which are experts in dealing with this risk. P2P lenders suffer a severe problem of information asymmetry, because they are at a disadvantage facing the borrower. For this reason, P2P lending sites provide potential lenders with information about borrowers and their loan purpose. They also assign a grade to each loan. The empirical study is based on loans' data collected from Lending Club (N = 24,449) from 2008 to 2014 that are first analyzed by using univariate means tests and survival analysis. Factors explaining default are loan purpose, annual income, current housing situation, credit history and indebtedness. Secondly, a logistic regression model is developed to predict defaults. The grade assigned by the P2P lending site is the most predictive factor of default, but the accuracy of the model is improved by adding other information, especially the borrower's debt level.

  1. Determinants of Default in P2P Lending

    PubMed Central

    2015-01-01

    This paper studies P2P lending and the factors explaining loan default. This is an important issue because in P2P lending individual investors bear the credit risk, instead of financial institutions, which are experts in dealing with this risk. P2P lenders suffer a severe problem of information asymmetry, because they are at a disadvantage facing the borrower. For this reason, P2P lending sites provide potential lenders with information about borrowers and their loan purpose. They also assign a grade to each loan. The empirical study is based on loans’ data collected from Lending Club (N = 24,449) from 2008 to 2014 that are first analyzed by using univariate means tests and survival analysis. Factors explaining default are loan purpose, annual income, current housing situation, credit history and indebtedness. Secondly, a logistic regression model is developed to predict defaults. The grade assigned by the P2P lending site is the most predictive factor of default, but the accuracy of the model is improved by adding other information, especially the borrower’s debt level. PMID:26425854

  2. Protecting Data Privacy in Structured P2P Networks

    NASA Astrophysics Data System (ADS)

    Jawad, Mohamed; Serrano-Alvarado, Patricia; Valduriez, Patrick

    P2P systems are increasingly used for efficient, scalable data sharing. Popular applications focus on massive file sharing. However, advanced applications such as online communities (e.g., medical or research communities) need to share private or sensitive data. Currently, in P2P systems, untrusted peers can easily violate data privacy by using data for malicious purposes (e.g., fraudulence, profiling). To prevent such behavior, the well accepted Hippocratic database principle states that data owners should specify the purpose for which their data will be collected. In this paper, we apply such principles as well as reputation techniques to support purpose and trust in structured P2P systems. Hippocratic databases enforce purpose-based privacy while reputation techniques guarantee trust. We propose a P2P data privacy model which combines the Hippocratic principles and the trust notions. We also present the algorithms of PriServ, a DHT-based P2P privacy service which supports this model and prevents data privacy violation. We show, in a performance evaluation, that PriServ introduces a small overhead.

  3. An efficient query mechanism base on P2P networks

    NASA Astrophysics Data System (ADS)

    Wang, Xiaohua; Mu, Aiqin; Zhao, Defang

    2013-07-01

    How to implement the efficient query is the key problem deployed on P2P networks. This paper analyses the shortage of several query algorithm, and presents a new algorithm DDI, which means distributed searching with double indices. It discusses the popularity of documents and the linking status of the networks, and calculates the availability of the nodes in whole network, determines the route of the query process. It compares the items of time using, the quantity of requests and update information by the emulate experiments. Along with the rapid development of computer network technology, peer-to-peer (referred to as P2P) network research has gradually become mature, and it is widely used in different fields, some large P2P computing project has entered the implementation stage. At present, many more popular software systems such as Gnutella, Freenet, Napster are deployed based on P2P technology. How to achieve effective information query has become one of the key problems of P2P research.

  4. Electron impact ionization of cycloalkanes, aldehydes, and ketones

    SciTech Connect

    Gupta, Dhanoj; Antony, Bobby

    2014-08-07

    The theoretical calculations of electron impact total ionization cross section for cycloalkane, aldehyde, and ketone group molecules are undertaken from ionization threshold to 2 keV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionization contribution method. The results of most of the targets studied compare fairly well with the recent measurements, wherever available and the cross sections for many targets are predicted for the first time. The correlation between the peak of ionization cross sections with number of target electrons and target parameters is also reported. It was found that the cross sections at their maximum depend linearly with the number of target electrons and with other target parameters, confirming the consistency of the values reported here.

  5. Coloring geographical threshold graphs

    SciTech Connect

    Bradonjic, Milan; Percus, Allon; Muller, Tobias

    2008-01-01

    We propose a coloring algorithm for sparse random graphs generated by the geographical threshold graph (GTG) model, a generalization of random geometric graphs (RGG). In a GTG, nodes are distributed in a Euclidean space, and edges are assigned according to a threshold function involving the distance between nodes as well as randomly chosen node weights. The motivation for analyzing this model is that many real networks (e.g., wireless networks, the Internet, etc.) need to be studied by using a 'richer' stochastic model (which in this case includes both a distance between nodes and weights on the nodes). Here, we analyze the GTG coloring algorithm together with the graph's clique number, showing formally that in spite of the differences in structure between GTG and RGG, the asymptotic behavior of the chromatic number is identical: {chi}1n 1n n / 1n n (1 + {omicron}(1)). Finally, we consider the leading corrections to this expression, again using the coloring algorithm and clique number to provide bounds on the chromatic number. We show that the gap between the lower and upper bound is within C 1n n / (1n 1n n){sup 2}, and specify the constant C.

  6. Laser threshold magnetometry

    NASA Astrophysics Data System (ADS)

    Jeske, Jan; Cole, Jared H.; Greentree, Andrew D.

    2016-01-01

    We propose a new type of sensor, which uses diamond containing the optically active nitrogen-vacancy (NV-) centres as a laser medium. The magnetometer can be operated at room-temperature and generates light that can be readily fibre coupled, thereby permitting use in industrial applications and remote sensing. By combining laser pumping with a radio-frequency Rabi-drive field, an external magnetic field changes the fluorescence of the NV- centres. We use this change in fluorescence level to push the laser above threshold, turning it on with an intensity controlled by the external magnetic field, which provides a coherent amplification of the readout signal with very high contrast. This mechanism is qualitatively different from conventional NV--based magnetometers which use fluorescence measurements, based on incoherent photon emission. We term our approach laser threshold magnetometer (LTM). We predict that an NV--based LTM with a volume of 1 mm3 can achieve shot-noise limited dc sensitivity of 1.86 fT /\\sqrt{{{Hz}}} and ac sensitivity of 3.97 fT /\\sqrt{{{Hz}}}.

  7. High Performance Rh2P Electrocatalyst for Efficient Water Splitting.

    PubMed

    Duan, Haohong; Li, Dongguo; Tang, Yan; He, Yang; Fang, Ji Shu; Wang, Rongyue; Lv, Haifeng; Lopes, Pietro P; Paulikas, Arvydas P; Li, Haoyi; Mao, Scott X; Wang, Chong-Min; Markovic, Nenad M; Li, Jun; Stamenkovic, Vojislav R; Li, Yadong

    2017-03-26

    Search for active, stable and cost-efficient electrocataltysts for hydrogen production via water splitting could make substantial impact to the energy technologies that do not rely on fossil fuels. Here we report the synthesis of rhodium phosphide electrocatalyst with low metal loading in the form of nanocubes (NCs) dispersed in high surface area carbon (Rh2P/C) by a facile solvo-thermal approach. The Rh2P/C exhibit remarkable performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) compared to Rh/C and Pt/C catalysts. The atomic structure of the Rh2P NCs was directly observed by annular dark-field scanning transmission electron microscopy (ADF-STEM), which revealed phosphorous-rich outermost atomic layer. Combined experimental and computational studies suggest that surface phosphorous plays crucial role in determining the robust catalyst properties.

  8. Fragrance material review on 2-(p-tolyloxy)ethyl acetate.

    PubMed

    McGinty, D; Letizia, C S; Api, A M

    2012-09-01

    A toxicologic and dermatologic review of 2-(p-tolyloxy)ethyl acetate when used as a fragrance ingredient is presented. 2-(p-tolyloxy)ethyl acetate is a member of the fragrance structural group aryl alkyl alcohol simple acid esters (AAASAE). The AAASAE fragrance ingredients are prepared by reacting an aryl alkyl alcohol with a simple carboxylic acid (a chain of 1-4 carbons) to generate formate, acetate, propionate, butyrate, isobutyrate and carbonate esters. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for 2-(p-tolyloxy)ethyl acetate were evaluated, then summarized, and includes physical properties data. A safety assessment of the entire AAASAE will be published simultaneously with this document. Please refer to Belsito et al. (2012) for an overall assessment of the safe use of this material and all AAASAE in fragrances.

  9. Market Design for a P2P Backup System

    NASA Astrophysics Data System (ADS)

    Seuken, Sven; Charles, Denis; Chickering, Max; Puri, Sidd

    Peer-to-peer (P2P) backup systems are an attractive alternative to server-based systems because the immense costs of large data centers can be saved by using idle resources on millions of private computers instead. This paper presents the design and theoretical analysis of a market for a P2P backup system. While our long-term goal is an open resource exchange market using real money, here we consider a system where monetary transfers are prohibited. A user who wants to backup his data must in return supply some of his resources (storage space, upload and download bandwidth) to the system.We propose a hybrid P2P architecture where all backup data is transferred directly between peers, but a dedicated server coordinates all operations and maintains meta-data. We achieve high reliability guarantees while keeping our data replication factor low by adopting sophisticated erasure coding technology (cf., [2]).

  10. Fuel cell with ionization membrane

    NASA Technical Reports Server (NTRS)

    Hartley, Frank T. (Inventor)

    2007-01-01

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

  11. Faraday effect in Sn2P2S6 crystals.

    PubMed

    Krupych, Oleh; Adamenko, Dmytro; Mys, Oksana; Grabar, Aleksandr; Vlokh, Rostyslav

    2008-11-10

    We have revealed a large Faraday rotation in tin thiohypodiphosphate (Sn(2)P(2)S(6)) crystals, which makes this material promising for magneto-optics. The effective Faraday tensor component and the Verdet constant for the direction of the optic axis have been determined by measuring the pure Faraday rotation in Sn(2)P(2)S(6) crystals with both the single-ray and small-angular polarimetric methods at the normal conditions and a wavelength of 632.8 nm. The effective Verdet constant is found to be equal to 115 rad/T x m.

  12. Mini Magnetospheric Plasma Propulsion (M2P2)

    NASA Technical Reports Server (NTRS)

    Gallagher, Dennis; Winglee, Robert

    2000-01-01

    The M2P2 concept is based on the transfer of momentum from the solar wind to an artificial magnetic field structure like that naturally occurs at all magnetized planets in the Solar System, called the magnetosphere. The objectives of this program include the following: (1) Demonstrate artificial magnetospheric inflation through cold plasma filling in vacuum; (2) Demonstrate deflection of a surrogate solar wind by an artificial magnetosphere in the laboratory vacuum chamber; (3) Compare theoretical calculations for thrust forces with laboratory measurements; (4) Develop flight control algorithms for planning mission specific trajectories; and (5) Develop M2P2 system concept.

  13. The Social Impact of P2P Systems

    NASA Astrophysics Data System (ADS)

    Glorioso, Andrea; Pagallo, Ugo; Ruffo, Giancarlo

    The chapter deals with the social impact of P2P systems in light of a bidirectional connection by which technological developments influence, in a complex and often unpredictable way, the social environment whereas the dynamic evolution of the latter does affect technological progress. From this perspective, the aim is to deepen legal issues, sociological trends, economical aspects, and political dimensions of P2P technology, along with some of its next possible outputs, in order to assess one of the most compelling alternatives to the traditional frame of highly centralized human interaction.

  14. Atmospheric Ionization Measurements

    NASA Astrophysics Data System (ADS)

    Slack, Thomas; Mayes, Riley

    2015-04-01

    The measurement of atmospheric ionization is a largely unexplored science that potentially holds the key to better understanding many different geophysical phenomena through this new and valuable source of data. Through the LaACES program, which is funded by NASA through the Louisiana Space Consortium, students at Loyola University New Orleans have pursued the goal of measuring high altitude ionization for nearly three years, and were the first to successfully collect ionization data at altitudes over 30,000 feet using a scientific weather balloon flown from the NASA Columbia Scientific Ballooning Facility in Palestine, TX. In order to measure atmospheric ionization, the science team uses a lightweight and highly customized sensor known as a Gerdien condenser. Among other branches of science the data is already being used for, such as the study of aerosol pollution levels in the atmosphere, the data may also be useful in meteorology and seismology. Ionization data might provide another variable with which to predict weather or seismic activity more accurately and further in advance. Thomas Slack and Riley Mayes have served as project managers for the experiment, and have extensive knowledge of the experiment from the ground up. LaSPACE Louisiana Space Consortium.

  15. Oscillatory Threshold Logic

    PubMed Central

    Borresen, Jon; Lynch, Stephen

    2012-01-01

    In the 1940s, the first generation of modern computers used vacuum tube oscillators as their principle components, however, with the development of the transistor, such oscillator based computers quickly became obsolete. As the demand for faster and lower power computers continues, transistors are themselves approaching their theoretical limit and emerging technologies must eventually supersede them. With the development of optical oscillators and Josephson junction technology, we are again presented with the possibility of using oscillators as the basic components of computers, and it is possible that the next generation of computers will be composed almost entirely of oscillatory devices. Here, we demonstrate how coupled threshold oscillators may be used to perform binary logic in a manner entirely consistent with modern computer architectures. We describe a variety of computational circuitry and demonstrate working oscillator models of both computation and memory. PMID:23173034

  16. Measurement and analysis of P2P IPTV program resource.

    PubMed

    Wang, Wenxian; Chen, Xingshu; Wang, Haizhou; Zhang, Qi; Wang, Cheng

    2014-01-01

    With the rapid development of P2P technology, P2P IPTV applications have received more and more attention. And program resource distribution is very important to P2P IPTV applications. In order to collect IPTV program resources, a distributed multi-protocol crawler is proposed. And the crawler has collected more than 13 million pieces of information of IPTV programs from 2009 to 2012. In addition, the distribution of IPTV programs is independent and incompact, resulting in chaos of program names, which obstructs searching and organizing programs. Thus, we focus on characteristic analysis of program resources, including the distributions of length of program names, the entropy of the character types, and hierarchy depth of programs. These analyses reveal the disorderly naming conventions of P2P IPTV programs. The analysis results can help to purify and extract useful information from chaotic names for better retrieval and accelerate automatic sorting of program and establishment of IPTV repository. In order to represent popularity of programs and to predict user behavior and popularity of hot programs over a period, we also put forward an analytical model of hot programs.

  17. Measurement and Analysis of P2P IPTV Program Resource

    PubMed Central

    Chen, Xingshu; Wang, Haizhou; Zhang, Qi

    2014-01-01

    With the rapid development of P2P technology, P2P IPTV applications have received more and more attention. And program resource distribution is very important to P2P IPTV applications. In order to collect IPTV program resources, a distributed multi-protocol crawler is proposed. And the crawler has collected more than 13 million pieces of information of IPTV programs from 2009 to 2012. In addition, the distribution of IPTV programs is independent and incompact, resulting in chaos of program names, which obstructs searching and organizing programs. Thus, we focus on characteristic analysis of program resources, including the distributions of length of program names, the entropy of the character types, and hierarchy depth of programs. These analyses reveal the disorderly naming conventions of P2P IPTV programs. The analysis results can help to purify and extract useful information from chaotic names for better retrieval and accelerate automatic sorting of program and establishment of IPTV repository. In order to represent popularity of programs and to predict user behavior and popularity of hot programs over a period, we also put forward an analytical model of hot programs. PMID:24772008

  18. Breit-Pauli energy levels belonging to 2p 4, 2s2p 5, 2p 6, 2p 33ℓ configurations and all E1 transitions among these levels in Mg V

    NASA Astrophysics Data System (ADS)

    Deb, N. C.; Hibbert, A.

    2007-07-01

    We present accurate oscillator strengths, line strengths and radiative rates for 1073 E1 transitions among the 86 levels belonging to 2s 22p 4, 2s2p 5, 2p 6, and 2s 22p 3( 4S o, 2D o, 2P o)3ℓ configurations in Mg V. We have used 1s and 2s Hartree-Fock orbitals, re-optimized 2p on 2p 3( 2D o)3s 3D o and optimized 3s,3p,3d orbitals on real states. Sixteen additional orbitals up to 8d are optimized either as a correction to n = 3 physical orbitals or as a correlation orbital. A very large set of configurations including up to three electron promotions are used to account for all important correlation effects. All of the main five terms in the Breit-Pauli operator (except the orbit-orbit interaction) are included in order to account for the relativistic effects. Small adjustments to the diagonal elements of the Hamiltonian matrix are made to bring the calculated energies within a few cm -1 of the corresponding NIST recommended data wherever available. The calculated oscillator strengths, line strengths, and radiative rates for almost all of the E1 transitions show excellent agreement with the corresponding MCDF results of Fischer. The recent results of Bhatia et al. are found to be consistently higher by 20-45%. The accuracy of the present calculation is considered to be better than the NIST accuracy ratings for various transitions.

  19. Optimising threshold levels for information transmission in binary threshold networks: Independent multiplicative noise on each threshold

    NASA Astrophysics Data System (ADS)

    Zhou, Bingchang; McDonnell, Mark D.

    2015-02-01

    The problem of optimising the threshold levels in multilevel threshold system subject to multiplicative Gaussian and uniform noise is considered. Similar to previous results for additive noise, we find a bifurcation phenomenon in the optimal threshold values, as the noise intensity changes. This occurs when the number of threshold units is greater than one. We also study the optimal thresholds for combined additive and multiplicative Gaussian noise, and find that all threshold levels need to be identical to optimise the system when the additive noise intensity is a constant. However, this identical value is not equal to the signal mean, unlike the case of additive noise. When the multiplicative noise intensity is instead held constant, the optimal threshold levels are not all identical for small additive noise intensity but are all equal to zero for large additive noise intensity. The model and our results are potentially relevant for sensor network design and understanding neurobiological sensory neurons such as in the peripheral auditory system.

  20. Ambient ionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Lebedev, A. T.

    2015-07-01

    Ambient ionization mass spectrometry emerged as a new scientific discipline only about ten years ago. A considerable body of information has been reported since that time. Keeping the sensitivity, performance and informativity of classical mass spectrometry methods, the new approach made it possible to eliminate laborious sample preparation procedures and triggered the development of miniaturized instruments to work directly in the field. The review concerns the theoretical foundations and design of ambient ionization methods. Their advantages and drawbacks, as well as prospects for application in chemistry, biology, medicine, environmetal analysis, etc., are discussed. The bibliography includes 194 references.

  1. Chromosome 2 (2p16) abnormalities in Carney complex tumours

    PubMed Central

    Matyakhina, L; Pack, S; Kirschner, L; Pak, E; Mannan, P; Jaikumar, J; Taymans, S; Sandrini, F; Carney, J; Stratakis, C

    2003-01-01

    Carney complex (CNC) is an autosomal dominant multiple endocrine neoplasia and lentiginosis syndrome characterised by spotty skin pigmentation, cardiac, skin, and breast myxomas, and a variety of endocrine and other tumours. The disease is genetically heterogeneous; two loci have been mapped to chromosomes 17q22–24 (the CNC1 locus) and 2p16 (CNC2). Mutations in the PRKAR1A tumour suppressor gene were recently found in CNC1 mapping kindreds, while the CNC2 and perhaps other genes remain unidentified. Analysis of tumour chromosome rearrangements is a useful tool for uncovering genes with a role in tumorigenesis and/or tumour progression. CGH analysis showed a low level 2p amplification recurrently in four of eight CNC tumours; one tumour showed specific amplification of the 2p16-p23 region only. To define more precisely the 2p amplicon in these and other tumours, we completed the genomic mapping of the CNC2 region, and analysed 46 tumour samples from CNC patients with and without PRKAR1A mutations by fluorescence in situ hybridisation (FISH) using bacterial artificial chromosomes (BACs). Consistent cytogenetic changes of the region were detected in 40 (87%) of the samples analysed. Twenty-four samples (60%) showed amplification of the region represented as homogeneously stained regions (HSRs). The size of the amplicon varied from case to case, and frequently from cell to cell in the same tumour. Three tumours (8%) showed both amplification and deletion of the region in their cells. Thirteen tumours (32%) showed deletions only. These molecular cytogenetic changes included the region that is covered by BACs 400-P-14 and 514-O-11 and, in the genetic map, corresponds to an area flanked by polymorphic markers D2S2251 and D2S2292; other BACs on the centromeric and telomeric end of this region were included in varying degrees. We conclude that cytogenetic changes of the 2p16 chromosomal region that harbours the CNC2 locus are frequently observed in tumours from CNC

  2. Ionizing radiation and life.

    PubMed

    Dartnell, Lewis R

    2011-01-01

    Ionizing radiation is a ubiquitous feature of the Cosmos, from exogenous cosmic rays (CR) to the intrinsic mineral radioactivity of a habitable world, and its influences on the emergence and persistence of life are wide-ranging and profound. Much attention has already been focused on the deleterious effects of ionizing radiation on organisms and the complex molecules of life, but ionizing radiation also performs many crucial functions in the generation of habitable planetary environments and the origins of life. This review surveys the role of CR and mineral radioactivity in star formation, generation of biogenic elements, and the synthesis of organic molecules and driving of prebiotic chemistry. Another major theme is the multiple layers of shielding of planetary surfaces from the flux of cosmic radiation and the various effects on a biosphere of violent but rare astrophysical events such as supernovae and gamma-ray bursts. The influences of CR can also be duplicitous, such as limiting the survival of surface life on Mars while potentially supporting a subsurface biosphere in the ocean of Europa. This review highlights the common thread that ionizing radiation forms between the disparate component disciplines of astrobiology.

  3. Alkali ionization detector

    DOEpatents

    Hrizo, John; Bauerle, James E.; Witkowski, Robert E.

    1982-01-01

    A calibration filament containing a sodium-bearing compound is included in combination with the sensing filament and ion collector plate of a sodium ionization detector to permit periodic generation of sodium atoms for the in-situ calibration of the detector.

  4. Ionizing radiation from tobacco

    SciTech Connect

    Westin, J.B.

    1987-04-24

    Accidents at nuclear power facilities seem inevitably to bring in their wake a great deal of concern on the part of both the lay and medical communities. Relatively little attention, however, is given to what may be the largest single worldwide source of effectively carcinogenic ionizing radiation: tobacco. The risk of cancer deaths from the Chernobyl disaster are tobacco smoke is discussed.

  5. Microchip sonic spray ionization.

    PubMed

    Pól, Jaroslav; Kauppila, Tiina J; Haapala, Markus; Saarela, Ville; Franssila, Sami; Ketola, Raimo A; Kotiaho, Tapio; Kostiainen, Risto

    2007-05-01

    The first microchip version of sonic spray ionization (SSI) as an atmospheric pressure ionization source for mass spectrometry (MS) is presented. The microchip used for SSI has recently been developed in our laboratory, and it has been used before as an atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) source. Now the ionization is achieved simply by applying high (sonic) speed nebulizer gas, without heat, corona discharge, or high voltage. The microchip SSI was applied to the analysis of tetra-N-butylammonium, verapamil, testosterone, angiotensin I, and ibuprofen. The limits of detection were in the range of 15 nM to 4 microM. The technique was found to be highly dependent on the position of the chip toward the mass spectrometer inlet, and on the gas and the sample solution flow rates. The microchip SSI provided dynamic linearity following a pattern similar to that used with electrospray, good quantitative repeatability (RSD=16%), and long-term signal stability.

  6. Learning foraging thresholds for lizards

    SciTech Connect

    Goldberg, L.A.; Hart, W.E.; Wilson, D.B.

    1996-01-12

    This work gives a proof of convergence for a randomized learning algorithm that describes how anoles (lizards found in the Carribean) learn a foraging threshold distance. This model assumes that an anole will pursue a prey if and only if it is within this threshold of the anole`s perch. This learning algorithm was proposed by the biologist Roughgarden and his colleagues. They experimentally confirmed that this algorithm quickly converges to the foraging threshold that is predicted by optimal foraging theory our analysis provides an analytic confirmation that the learning algorithm converses to this optimal foraging threshold with high probability.

  7. Probabilistic Threshold Criterion

    SciTech Connect

    Gresshoff, M; Hrousis, C A

    2010-03-09

    The Probabilistic Shock Threshold Criterion (PSTC) Project at LLNL develops phenomenological criteria for estimating safety or performance margin on high explosive (HE) initiation in the shock initiation regime, creating tools for safety assessment and design of initiation systems and HE trains in general. Until recently, there has been little foundation for probabilistic assessment of HE initiation scenarios. This work attempts to use probabilistic information that is available from both historic and ongoing tests to develop a basis for such assessment. Current PSTC approaches start with the functional form of the James Initiation Criterion as a backbone, and generalize to include varying areas of initiation and provide a probabilistic response based on test data for 1.8 g/cc (Ultrafine) 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and LX-17 (92.5% TATB, 7.5% Kel-F 800 binder). Application of the PSTC methodology is presented investigating the safety and performance of a flying plate detonator and the margin of an Ultrafine TATB booster initiating LX-17.

  8. Supporting seamless mobility for P2P live streaming.

    PubMed

    Kim, Eunsam; Kim, Sangjin; Lee, Choonhwa

    2014-01-01

    With advent of various mobile devices with powerful networking and computing capabilities, the users' demand to enjoy live video streaming services such as IPTV with mobile devices has been increasing rapidly. However, it is challenging to get over the degradation of service quality due to data loss caused by the handover. Although many handover schemes were proposed at protocol layers below the application layer, they inherently suffer from data loss while the network is being disconnected during the handover. We therefore propose an efficient application-layer handover scheme to support seamless mobility for P2P live streaming. By simulation experiments, we show that the P2P live streaming system with our proposed handover scheme can improve the playback continuity significantly compared to that without our scheme.

  9. Supporting Seamless Mobility for P2P Live Streaming

    PubMed Central

    Kim, Eunsam; Kim, Sangjin; Lee, Choonhwa

    2014-01-01

    With advent of various mobile devices with powerful networking and computing capabilities, the users' demand to enjoy live video streaming services such as IPTV with mobile devices has been increasing rapidly. However, it is challenging to get over the degradation of service quality due to data loss caused by the handover. Although many handover schemes were proposed at protocol layers below the application layer, they inherently suffer from data loss while the network is being disconnected during the handover. We therefore propose an efficient application-layer handover scheme to support seamless mobility for P2P live streaming. By simulation experiments, we show that the P2P live streaming system with our proposed handover scheme can improve the playback continuity significantly compared to that without our scheme. PMID:24977171

  10. K2P Potassium Channels, Mysterious and Paradoxically Exciting

    PubMed Central

    Goldstein, Steve A. N.

    2013-01-01

    New evidence reveals that the common electrolyte disorder hypokalemia can induce K2P1 channels that are normally selective for K+ to break the rules and conduct Na+. This defiant behavior leads to paradoxical depolarization of many cells in the heart, increasing the risk for lethal arrhythmia. The new research resolves a mystery uncovered 50 years ago and bestows an array of new riddles. Here, I discuss how K2P1 might achieve this alchemy—through stable residence of the K+ selectivity filter in a Na+-conductive state between its open and C-inactive configurations—and predict that other K+ channels and environmental stimuli will be discovered to produce the same excitatory misconduct. PMID:21868351

  11. Fine Structure of the Upsilon 2p States.

    NASA Astrophysics Data System (ADS)

    Lovelock, Dale Michael John

    1990-01-01

    The Columbia-Stony Brook (CUSB) collaboration has measured the photon spectrum resulting from the decays Upsilon (3S)togamma + hadrons using the CUSB-II BGO calorimeter. The spectrum contains the signal from the electromagnetic transitions Upsilon (3S)togammachi _{b,J=0,1,2} (2P). From this signal the masses of the chi_{b}(2P) states were determined to be 10268.0 +/- 0.8, 10255.4 +/- 0.8, and 10233.9 +/- 1.2 MeV for the J = 2, 1, and 0 states respectively. The ratio of the mass splittings, (M_{chi _{b2}} - M_{chi_{b1}} )/(M_{chi_{b1 }} - M_ {chi_{b0}}) imply that the long range confining piece of the inter-quark potential transforms as a Lorentz scalar.

  12. Extreme ultraviolet ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra

    SciTech Connect

    Buchta, D.; Stienkemeier, F.; Mudrich, M.; Krishnan, S. R.; Moshammer, R.; Brauer, N. B.; Drabbels, M.; O’Keeffe, P.; Coreno, M.; Devetta, M.; Di Fraia, M.; Callegari, C.; Richter, R.; Prince, K. C.; Ullrich, J.

    2013-08-28

    The ionization dynamics of pure He nanodroplets irradiated by Extreme ultraviolet radiation is studied using Velocity-Map Imaging PhotoElectron-PhotoIon COincidence spectroscopy. We present photoelectron energy spectra and angular distributions measured in coincidence with the most abundant ions He{sup +}, He{sub 2}{sup +}, and He{sub 3}{sup +}. Surprisingly, below the autoionization threshold of He droplets, we find indications for multiple excitation and subsequent ionization of the droplets by a Penning-like process. At high photon energies we observe inelastic collisions of photoelectrons with the surrounding He atoms in the droplets.

  13. Aquatic Toxicity of Decontaminating Solutions DS-2/DS-2P

    DTIC Science & Technology

    1994-09-01

    Daphnia magna , fathead minnow, Photobacteriumphosphoreum, and earthworm, 14 SUBJECT TERMS 15, NUMBER OF PAGES Aquatic toxicology Ea.thworm 16 . Daphnia magna ...toxicity of the DS-2 and DS-2P mixtures on Daphnia magna , (water flea), Pimephales promelas (fathead minnow), Eisenia foetida (earthwonm) and...chloroform procedures 151 and proved to be within specifications. 2.1 Dapbnia Assays The Daphnia magna were obtained from Dr. Freida Taub [61 at the

  14. Load Balancing in Structured P2P Networks

    NASA Astrophysics Data System (ADS)

    Zhu, Yingwu

    In this chapter we start by addressing the importance and necessity of load balancing in structured P2P networks, due to three main reasons. First, structured P2P networks assume uniform peer capacities while peer capacities are heterogeneous in deployed P2P networks. Second, resorting to pseudo-uniformity of the hash function used to generate node IDs and data item keys leads to imbalanced overlay address space and item distribution. Lastly, placement of data items cannot be randomized in some applications (e.g., range searching). We then present an overview of load aggregation and dissemination techniques that are required by many load balancing algorithms. Two techniques are discussed including tree structure-based approach and gossip-based approach. They make different tradeoffs between estimate/aggregate accuracy and failure resilience. To address the issue of load imbalance, three main solutions are described: virtual server-based approach, power of two choices, and address-space and item balancing. While different in their designs, they all aim to improve balance on the address space and data item distribution. As a case study, the chapter discusses a virtual server-based load balancing algorithm that strives to ensure fair load distribution among nodes and minimize load balancing cost in bandwidth. Finally, the chapter concludes with future research and a summary.

  15. Uniform Sampling for Directed P2P Networks

    NASA Astrophysics Data System (ADS)

    Hall, Cyrus; Carzaniga, Antonio

    Selecting a random peer with uniform probability across a peer-to-peer (P2P) network is a fundamental function for unstructured search, data replication, and monitoring algorithms. Such uniform sampling is supported by several techniques. However, current techniques suffer from sample bias and limited applicability. In this paper, we present a sampling algorithm that achieves a desired uniformity while making essentially no assumptions about the underlying P2P network. This algorithm, called doubly stochastic converge (DSC), iteratively adjusts the probabilities of crossing each link in the network during a random walk, such that the resulting transition matrix is doubly stochastic. DSC is fully decentralized and is designed to work on both directed and undirected topologies, making it suitable for virtually any P2P network. Our simulations show that DSC converges quickly on a wide variety of topologies, and that the random walks needed for sampling are short for most topologies. In simulation studies with FreePastry, we show that DSC is resilient to high levels of churn, while incurring a minimal sample bias.

  16. Pure P2P mediation system: A mappings discovery approach

    NASA Astrophysics Data System (ADS)

    selma, El yahyaoui El idrissi; Zellou, Ahmed; Idri, Ali

    2015-02-01

    The information integration systems consist in offering a uniform interface to provide access to a set of autonomous and distributed information sources. The most important advantage of this system is that it allows users to specify what they want, rather than thinking about how to get the responses. The works realized in this area have particular leads to two major classes of integration systems: the mediation systems based on the paradigm mediator / adapter and peer to peer systems (P2P). The combination of both systems has led to a third type; is the mediation P2P systems. The P2P systems are large-scale systems, self-organized and distributed. They allow the resource management in a completely decentralized way. However, the integration of structured information sources, heterogeneous and distributed proves to be a complex problem. The objective of this work is to propose an approach to resolve conflicts and establish a mapping between the heterogeneous elements. This approach is based on clustering; the latter is to group similar Peers that share common information in the same subnet. Thus, to facilitate the heterogeneity, we introduced three additional layers of our hierarchy of peers: internal schema, external schema and Schema directory peer. We used linguistic techniques, and precisely the name correspondence technique, that is based on the similarity of names to propose a correspondence.

  17. An Overlapping Structured P2P for REIK Overlay Network

    NASA Astrophysics Data System (ADS)

    Liu, Wenjun; Song, Jingjing; Yu, Jiguo

    REIK is based on a ring which embedded an inverse Kautz digraph, to enable multi-path P2P routing. It has the constant degree and the logarithmic diameter DHT scheme with constant congestion and Byzantine fault tolerance. However, REIK did not consider the interconnection of many independent smaller networks. In this paper, we propose a new approach to build overlay network, OLS-REIK which is an overlapping structured P2P for REIK overlay network. It is a more flexible interconnecting different REIK network. Peers can belong to several rings, allowing this interconnection. By connecting smaller structured overlay networks in an unstructured way, it provides a cost effective alternative to hierarchical structured P2P systems requiring costly merging. Routing of lookup messages is performed as in REIK within one ring, but a peer belonging to several rings forwards the request to the different rings it belongs to. Furthermore a small number of across point is enough to ensure a high exhaustiveness level.

  18. DNA Compaction by Yeast Mitochondrial Protein ABF2p

    SciTech Connect

    Friddle, R W; Klare, J E; Noy, A; Corzett, M; Balhorn, R; Baskin, R J; Martin, S S; Baldwin, E P

    2003-05-09

    We used high resolution Atomic Force Microscopy (AFM) to image compaction of linear and circular DNA by the yeast mitochondrial protein ABF2p , which plays a major role in maintaining mitochondrial DNA. AFM images show that protein binding induces drastic bends in the DNA backbone for both linear and circular DNA. At high concentration of ABF2p DNA collapses into a tight globular structure. We quantified the compaction of linear DNA by measuring the end-to-end distance of the DNA molecule at increasing concentrations of ABF2p. We also derived a polymer statistical mechanics model that gives quantitative description of compaction observed in our experiments. This model shows that a number of sharp bends in the DNA backbone is often sufficient to cause DNA compaction. Comparison of our model with the experimental data showed excellent quantitative correlation and allowed us to determine binding characteristics for ABF2. Our studies indicate that ABF2 compacts DNA through a novel mechanism that involves bending of DNA backbone. We discuss the implications of such a mechanism for mitochondrial DNA maintenance.

  19. The mechano-gated K(2P) channel TREK-1.

    PubMed

    Dedman, Alexandra; Sharif-Naeini, Reza; Folgering, Joost H A; Duprat, Fabrice; Patel, Amanda; Honoré, Eric

    2009-03-01

    The versatility of neuronal electrical activity is largely conditioned by the expression of different structural and functional classes of K+ channels. More than 80 genes encoding the main K+ channel alpha subunits have been identified in the human genome. Alternative splicing, heteromultimeric assembly, post-translational modification and interaction with auxiliary regulatory subunits further increase the molecular and functional diversity of K+ channels. Mammalian two-pore domain K+ channels (K(2P)) make up one class of K+ channels along with the inward rectifiers and the voltage- and/or calcium-dependent K+ channels. Each K(2P) channel subunit is made up of four transmembrane segments and two pore-forming (P) domains, which are arranged in tandem and function as either homo- or heterodimeric channels. This novel structural arrangement is associated with unusual gating properties including "background" or "leak" K+ channel activity, in which the channels show constitutive activity at rest. In this review article, we will focus on the lipid-sensitive mechano-gated K(2P) channel TREK-1 and will emphasize on the polymodal function of this "unconventional" K+ channel.

  20. Life below the threshold.

    PubMed

    Castro, C

    1991-01-01

    This article explains that malnutrition, poor health, and limited educational opportunities plague Philippine children -- especially female children -- from families living below the poverty threshold. Nearly 70% of households in the Philippines do not meet the required daily level of nutritional intake. Because it is often -- and incorrectly -- assumed that women's nutritional requirements are lower than men's, women suffer higher rates of malnutrition and poor health. A 1987 study revealed that 11.7% of all elementary students were underweight and 13.9% had stunted growths. Among elementary-school girls, 17% were malnourished and 40% suffered from anemia (among lactating mothers, more than 1/2 are anemic). A 1988 Program for Decentralized Educational Development study showed that grade VI students learn only about 1/2 of what they are supposed to learn. 30% of the children enrolled in grade school drop out before they reach their senior year. The Department of Education, Culture and Sports estimates that some 2.56 million students dropped out of school in l989. That same year, some 3.7 million children were counted as part of the labor force. In Manila alone, some 60,000 children work the streets, whether doing odd jobs or begging, or turning to crime or prostitution. the article tells the story of a 12 year-old girl named Ging, a 4th grader at a public school and the oldest child in a poor family of 6 children. The undernourished Ging dreams of a good future for her family and sees education as a way out of poverty; unfortunately, her time after school is spend working in the streets or looking after her family. She considers herself luckier than many of the other children working in the streets, since she at least has a family.

  1. Threshold Hypothesis: Fact or Artifact?

    ERIC Educational Resources Information Center

    Karwowski, Maciej; Gralewski, Jacek

    2013-01-01

    The threshold hypothesis (TH) assumes the existence of complex relations between creative abilities and intelligence: linear associations below 120 points of IQ and weaker or lack of associations above the threshold. However, diverse results have been obtained over the last six decades--some confirmed the hypothesis and some rejected it. In this…

  2. The Nature of Psychological Thresholds

    ERIC Educational Resources Information Center

    Rouder, Jeffrey N.; Morey, Richard D.

    2009-01-01

    Following G. T. Fechner (1966), thresholds have been conceptualized as the amount of intensity needed to transition between mental states, such as between a states of unconsciousness and consciousness. With the advent of the theory of signal detection, however, discrete-state theory and the corresponding notion of threshold have been discounted.…

  3. Electron induced inelastic and ionization cross section for plasma modeling

    NASA Astrophysics Data System (ADS)

    Verma, Pankaj; Mahato, Dibyendu; Kaur, Jaspreet; Antony, Bobby

    2016-09-01

    The present paper reports electron impact total inelastic and ionization cross section for silicon, germanium, and tin tetrahalides at energies varying from ionization threshold of the target to 5000 eV. These cross section data over a wide energy domain are very essential to understand the physico-chemical processes involved in various environments such as plasma modeling, semiconductor etching, atmospheric sciences, biological sciences, and radiation physics. However, the cross section data on the above mentioned molecules are scarce. In the present article, we report the computation of total inelastic cross section using spherical complex optical potential formalism and the estimation of ionization cross section through a semi-empirical method. The present ionization cross section result obtained for SiCl4 shows excellent agreement with previous measurements, while other molecules have not yet been investigated experimentally. Present results show more consistent behaviour than previous theoretical estimates. Besides cross sections, we have also studied the correlation of maximum ionization cross section with the square root of the ratio of polarizability to ionization potential for the molecules with known polarizabilities. A linear relation is observed between these quantities. This correlation is used to obtain approximate polarizability volumes for SiBr4, SiI4, GeCl4, GeBr4, and GeI4 molecules.

  4. Ultrafast molecular dynamics of dissociative ionization in OCS probed by soft x-ray synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Ramadhan, Ali; Wales, Benji; Karimi, Reza; Gauthier, Isabelle; MacDonald, Michael; Zuin, Lucia; Sanderson, Joe

    2016-11-01

    Soft x-rays (90-173 eV) from the 3rd generation Canadian Light Source have been used in conjunction with a multi coincidence time and position sensitive detection apparatus to observe the dissociative ionization of OCS. By varying the x-ray energy we can compare dynamics from direct and Auger ionization processes, and access ionization channels which result in two or three body breakup, from 2+ to 4+ ionization states. We make several new observations for the 3+ state such as kinetic energy release limited by photon energy, and using Dalitz plots we can see evidence of timescale effects between the direct and Auger ionization process for the first time. Finally, using Dalitz plots for OCS4+ we observe for the first time that breakup involving an O2+ ion can only proceed from out of equilibrium nuclear arrangement for S(2p) Auger ionization.

  5. Gridded electron reversal ionizer

    NASA Technical Reports Server (NTRS)

    Chutjian, Ara (Inventor)

    1993-01-01

    A gridded electron reversal ionizer forms a three dimensional cloud of zero or near-zero energy electrons in a cavity within a filament structure surrounding a central electrode having holes through which the sample gas, at reduced pressure, enters an elongated reversal volume. The resultant negative ion stream is applied to a mass analyzer. The reduced electron and ion space-charge limitations of this configuration enhances detection sensitivity for material to be detected by electron attachment, such as narcotic and explosive vapors. Positive ions may be generated by generating electrons having a higher energy, sufficient to ionize the target gas and pulsing the grid negative to stop the electron flow and pulsing the extraction aperture positive to draw out the positive ions.

  6. Electrospray Ionization Mass Spectrometry

    SciTech Connect

    Kelly, Ryan T.; Marginean, Ioan; Tang, Keqi

    2014-06-13

    Electrospray Ionization (ESI) is a process whereby gas phase ions are created from molecules in solution. As a solution exits a narrow tube in the presence of a strong electric field, an aerosol of charged droplets are is formed that produces gas phase ions as they it desolvates. ESI-MS comprises the creation of ions by ESI and the determination of their mass to charge ratio (m/z) by MS.

  7. Hysteresis of ionization waves

    SciTech Connect

    Dinklage, A.; Bruhn, B.; Testrich, H.; Wilke, C.

    2008-06-15

    A quasi-logistic, nonlinear model for ionization wave modes is introduced. Modes are due to finite size of the discharge and current feedback. The model consists of competing coupled modes and it incorporates spatial wave amplitude saturation. The hysteresis of wave mode transitions under current variation is reproduced. Sidebands are predicted by the model and found in experimental data. The ad hoc model is equivalent to a general--so-called universal--approach from bifurcation theory.

  8. Ionization energy and active cation vibrations of trans-2-fluorostyrene

    NASA Astrophysics Data System (ADS)

    Wu, Pei Ying; Tzeng, Sheng Yuan; Hsu, Ya Chu; Tzeng, Wen Bih

    2017-02-01

    We applied the two-color resonant two-photon mass-analyzed threshold ionization (MATI) technique to record the cation spectra of trans-2-fluorostyrene by ionizing via six intermediate vibronic levels. The adiabatic ionization energy was determined to be 69 304 ± 5 cm-1. The distinct MATI bands at 67, 124, 242, 355, 737, 806, 833, and 993 cm-1 were assigned to the active cation vibrations related to out-of-plane substituent-sensitive bending vibrations and in-plane ring deformation and bending motions. Many combination vibrations were also observed. Our experimental results suggest that the molecular geometry and vibrational coordinates of the trans-2-fluorostyrene cation in the D0 state resemble those of the neutral species in the S1 state.

  9. Global model including multistep ionizations in helium plasmas

    NASA Astrophysics Data System (ADS)

    Oh, Seung-Ju; Lee, Hyo-Chang; Chung, Chin-Wook

    2016-12-01

    Particle and power balance equations including stepwise ionizations are derived and solved in helium plasmas. In the balance equations, two metastable states (21S1 in singlet and 23S1 triplet) are considered and the followings are obtained. The plasma density linearly increases and the electron temperature is relatively in a constant value against the absorbed power. It is also found that the contribution to multi-step ionization with respect to the single-step ionization is in the range of 8%-23%, as the gas pressure increases from 10 mTorr to 100 mTorr. Compared to the results in the argon plasma, there is little variation in the collisional energy loss per electron-ion pair created (ɛc) with absorbed power and gas pressure due to the small collision cross section and higher inelastic collision threshold energy.

  10. Total and ionization cross sections of electron scattering by fluorocarbons

    NASA Astrophysics Data System (ADS)

    Antony, B. K.; Joshipura, K. N.; Mason, N. J.

    2005-02-01

    Electron impact total cross sections (50-2000 eV) and total ionization cross sections (threshold to 2000 eV) are calculated for typical plasma etching molecules CF4, C2F4, C2F6, C3F8 and CF3I and the CFx (x = 1-3) radicals. The total elastic and inelastic cross sections are determined in the spherical complex potential formalism. The sum of the two gives the total cross section and the total inelastic cross section is used to calculate the total ionization cross sections. The present total and ionization cross sections are found to be consistent with other theories and experimental measurements, where they exist. Our total cross section results for CFx (x = 1-3) radicals presented here are first estimates on these species.

  11. Threshold processes of sodium ion emission from NaAu surface alloy

    NASA Astrophysics Data System (ADS)

    Knat'ko, M. V.; Lapushkin, M. N.

    2015-04-01

    We have studied threshold processes of Na+ ion emission from a semiconductor Na x Au y film formed on the surface of a gold substrate. In contrast to the classical notions of threshold processes involved in the surface ionization of alkali metal ions from heated metal surfaces, the diffusion exchange of atomic species between the surface and volume of the Na x Au y film ensures stable emission of Na+ ions from the substrate in the region of threshold temperatures. A diffusion mechanism of self-regulation of the surface coverage of alkali metal in the Na x Au y film is proposed.

  12. Bayesian estimation of dose thresholds

    NASA Technical Reports Server (NTRS)

    Groer, P. G.; Carnes, B. A.

    2003-01-01

    An example is described of Bayesian estimation of radiation absorbed dose thresholds (subsequently simply referred to as dose thresholds) using a specific parametric model applied to a data set on mice exposed to 60Co gamma rays and fission neutrons. A Weibull based relative risk model with a dose threshold parameter was used to analyse, as an example, lung cancer mortality and determine the posterior density for the threshold dose after single exposures to 60Co gamma rays or fission neutrons from the JANUS reactor at Argonne National Laboratory. The data consisted of survival, censoring times and cause of death information for male B6CF1 unexposed and exposed mice. The 60Co gamma whole-body doses for the two exposed groups were 0.86 and 1.37 Gy. The neutron whole-body doses were 0.19 and 0.38 Gy. Marginal posterior densities for the dose thresholds for neutron and gamma radiation were calculated with numerical integration and found to have quite different shapes. The density of the threshold for 60Co is unimodal with a mode at about 0.50 Gy. The threshold density for fission neutrons declines monotonically from a maximum value at zero with increasing doses. The posterior densities for all other parameters were similar for the two radiation types.

  13. Precision lifetime measurements of the 2p levels in lithium

    SciTech Connect

    Berry, H.G.; Kurtz, C.; Tanner, C.E.

    1995-08-01

    These measurements are motivated by the theoretical challenges posed by lithium. The three-electron lithium atom is one of the simplest atomic systems with which to test atomic structure calculations. Recently, there were several ab initio calculations of the lithium 2s-2p oscillator strengths, which agree to 0.15%. However, the theoretical results differ by 5 sigma from the precise fast-beam-laser lifetime measurement of Gaupp and Andra (Berlin). Hence the need for a new independent and precise measurement. Improvements were added to the fast beam laser techniques developed for cesium in order to measure the lithium 2p state lifetime. Although the technique is similar to that of cesium, the lithium atom presents a few new complications. Since the atom is lighter, it travels more quickly through the interaction and detection regions. Therefore, the 670 nm wavelength requires a dye laser to produce sufficient intensity to populate the excited state. Unfortunately, the intensity of the dye laser is inherently less stable than that of a diode laser. Another complication is that the ion-beam intensity is much more sensitive to fluctuations in the accelerating voltage. Two detectors were added: one to monitor the ion-beam intensity, and the other to monitor the laser power. With the information from the additional detectors, a new data analysis scheme was developed. Sufficient data were taken to evaluate the benefits of the new detectors. No additional work is planned at Argonne for this experiment.

  14. P2P Reputation Management Through Social Networking

    NASA Astrophysics Data System (ADS)

    Despotovic, Zoran

    Reputation systems offer a viable solution to the problem of risk reduction in online communities, in situation in which other mechanism such as litigation or security cannot help. Building on the assumption that its participating entities engage in repeated interactions, a reputation system can either signal what happened in the past or aggregate the past feedback in such a way as to influence the future actions of the concerned entity. In the former case, the concerned entity's behavior is seen as static, while the sent signal is expected to be indicative of the entity's future actions. In the latter case, behavior is dynamic in the sense that the entity can adjust it given the observed feedback, while the purpose of the reputation system is to induce adjustments according to the designer's needs. In this chapter, we discuss these two classes of solutions in detail. In particular, we investigate how they apply to P2P networks, what additional problems and difficulties the P2P environment introduces and what scalable solutions to these problems the current research offers.

  15. Nanocluster ionization energies and work function of aluminum, and their temperature dependence

    SciTech Connect

    Halder, Avik; Kresin, Vitaly V.

    2015-10-28

    Ionization threshold energies of Al{sub n} (n = 32-95) nanoclusters are determined by laser ionization of free neutral metal clusters thermalized to several temperatures in the range from 65 K to 230 K. The photoion yield curves of cold clusters follow a quadratic energy dependence above threshold, in agreement with the Fowler law of surface photoemission. Accurate data collection and analysis procedures make it possible to resolve very small (few parts in a thousand) temperature-induced shifts in the ionization energies. Extrapolation of the data to the bulk limit enables a determination of the thermal shift of the polycrystalline metal work function, found to be in excellent agreement with theoretical prediction based on the influence of thermal expansion. Small clusters display somewhat larger thermal shifts, reflecting their greater susceptibility to thermal expansion. Ionization studies of free size-resolved nanoclusters facilitate understanding of the interplay of surface, electronic, and lattice properties under contamination-free conditions.

  16. Kinetics of the Reactions of F((sup 2)P) and Cl((sup 2)P) with HNO3

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Wells, J. R.; Nicovich, J. M.

    1997-01-01

    The kinetics of the reactions of HNO3 with fluorine (k(sub 1)) and Chlorine (k(sub 2)) atoms have been studied by using a time-resolved long-path laser absorption technique to monitor the appearance of product NO3 radicals following 351-nm pulsed laser photolysis of X2/HNO3/He mixtures (X = F,Cl). Absolute rate coefficients for the F((sup 2)P) + HNO reaction have been determined over the temperature range 260-373 K. Between 260 and 320 K, the data are adequately represented by the Arrhenius expression k(sub 1)(T) = (6.0 +/- 2.6) x 10(exp -12) exp[(40 +/- 120)/T]cu cm/(molecule.s). Between 335 and 373 K, the rate coefficient is found to be (2.0 +/- 0.3) x 10(exp -11)cu cm/(molecule.s) independent of temperature. The observed temperature dependence suggests that reaction proceeds via competing direct abstraction and complex pathways. No NO3 production was observed in the experiments with X equals Cl, thus establishing that k(sub 2)(298 K) is less than 2 x 10(exp -16) cu cm/(molecule.s). The Cl((sup 2)P) + HNO reaction was also investigated by using a pulsed laser photolysis-resonance fluorescence technique to monitor the decay of Cl((sup 2)P). Upper limit values for k(sub 2) obtained from these experiments, in units of 10(exp -16)cu cm/(molecule.s), are 13 at 298 K and 10 at 400 K.

  17. Multiresonant Spectroscopy and the High-Resolution Threshold Photoionization of Combustion Free Radicals

    SciTech Connect

    Edward R. Grant

    2005-09-07

    This report describes the results of a program of research on the thermochemistry, spectroscopy and intramolecular relaxation dynamics of the combustion intermediate, HCO. We prepare this radical from acetaldehyde as a photo-precursor in a differentially pumped laser-ionization source quadrupole mass spectrometer. Using a multiresonant spectroscopic technique established in our laboratory, we select individual rotational states and overcome Franck-Condon barriers associated with neutral-to-cation geometry changes to promote transitions to individual autoionizing series and state-resolved ionization thresholds. Systematic analysis of rotational structure and associated lineshapes provide experimental insight on autoionization dynamics as input for theoretical modeling. Extrapolation of series, combined with direct threshold-photoelectron detection, yield precise ionization potentials that constitute an important contribution to the thermochemical base of information on HCO.

  18. Threshold photodissociation of Cr+2

    NASA Astrophysics Data System (ADS)

    Lessen, D. E.; Asher, R. L.; Brucat, P. J.

    1991-08-01

    A one-photon photodissociation threshold for supersonically cooled Cr+2 is determined to be 2.13 eV. This threshold provides a strict upper limit to the adiabatic binding energy of the ground state of chromium dimer cation if the initial internal energy of the parent ion may be neglected. From the difference in the IPs of chromium atom and dimer, an upper limit to the dissociation of Cr2 is placed at 1.77 eV.

  19. Efficient Plasma Production in Low Background Neutral Pressures with the M2P2 Prototype

    NASA Technical Reports Server (NTRS)

    Ziemba, T.; Euripides, P.; Winglee, R.; Slough, J.; Giersch, L.

    2003-01-01

    Mini-Magnetospheric Plasma Propulsion (M2P2) seeks the creation of a large-scale (10 km radius) magnetic wall or bubble (i.e. a magnetosphere) by the electromagnetic inflation of a small-scale (20 cm radius) dipole magnet. The inflated magnetosphere will intercept the solar wind and thereby provide high-speed propulsion with modest power and fuel requirements due to the gain provided by the ambient medium. Magnetic field inflation is produced by the injection of plasma onto the dipole magnetic field eliminating the need for large mechanical structures and added material weight at launch. For successful inflation of the magnetic bubble a beta near unity must be achieved along the imposed dipole field. This is dependent on the plasma parameters that can be achieved with a plasma source that provide continuous operation at the desired power levels of 1 to 2 kilowatts. Over the last two years we have been developing a laboratory prototype to demonstrate the inflation of the magnetic field under space-like conditions. In this paper we will present some of the latest results from the prototype development at the University of Washington and show that the prototype can produce high ionization efficiencies while operating in near space like neutral background pressures producing electron temperatures of a few tens of electron volts. This allows for operation with propellant expenditures lower than originally estimated.

  20. Modeling of ablation threshold dependence on pulse duration for dielectrics with ultrashort pulsed laser

    NASA Astrophysics Data System (ADS)

    Sun, Mingying; Zhu, Jianqiang; Lin, Zunqi

    2017-01-01

    We present a numerical model of plasma formation in ultrafast laser ablation on the dielectrics surface. Ablation threshold dependence on pulse duration is predicted with the model and the numerical results for water agrees well with the experimental data for pulse duration from 140 fs to 10 ps. Influences of parameters and approximations of photo- and avalanche-ionization on the ablation threshold prediction are analyzed in detail for various pulse lengths. The calculated ablation threshold is strongly dependent on electron collision time for all the pulse durations. The complete photoionization model is preferred for pulses shorter than 1 ps rather than the multiphoton ionization approximations. The transition time of inverse bremsstrahlung absorption needs to be considered when pulses are shorter than 5 ps and it can also ensure the avalanche ionization (AI) coefficient consistent with that in multiple rate equations (MREs) for pulses shorter than 300 fs. The threshold electron density for AI is only crucial for longer pulses. It is reasonable to ignore the recombination loss for pulses shorter than 100 fs. In addition to thermal transport and hydrodynamics, neglecting the threshold density for AI and recombination could also contribute to the disagreements between the numerical and the experimental results for longer pulses.

  1. Threshold models in radiation carcinogenesis

    SciTech Connect

    Hoel, D.G.; Li, P.

    1998-09-01

    Cancer incidence and mortality data from the atomic bomb survivors cohort has been analyzed to allow for the possibility of a threshold dose response. The same dose-response models as used in the original papers were fit to the data. The estimated cancer incidence from the fitted models over-predicted the observed cancer incidence in the lowest exposure group. This is consistent with a threshold or nonlinear dose-response at low-doses. Thresholds were added to the dose-response models and the range of possible thresholds is shown for both solid tumor cancers as well as the different leukemia types. This analysis suggests that the A-bomb cancer incidence data agree more with a threshold or nonlinear dose-response model than a purely linear model although the linear model is statistically equivalent. This observation is not found with the mortality data. For both the incidence data and the mortality data the addition of a threshold term significantly improves the fit to the linear or linear-quadratic dose response for both total leukemias and also for the leukemia subtypes of ALL, AML, and CML.

  2. Two-photon double ionization of the helium atom by ultrashort pulses

    SciTech Connect

    Palacios, Alicia; Horner, Daniel A; Rescigno, Thomas N; McCurdy, C William

    2010-05-14

    Two-photon double ionization of the helium atom was the subject of early experiments at FLASH and will be the subject of future benchmark measurements of the associated electron angular and energy distributions. As the photon energy of a single femtosecond pulse is raised from the threshold for two-photon double ionization at 39.5 eV to beyond the sequential ionization threshold at 54.4 eV, the electron ejection dynamics change from the highly correlated motion associated with nonsequential absorption to the much less correlated sequential ionization process. The signatures of both processes have been predicted in accurate \\textit{ab initio} calculations of the joint angular and energy distributions of the electrons, and those predictions contain some surprises. The dominant terms that contribute to sequential ionization make their presence apparent several eV below that threshold. In two-color pump probe experiments with short pulses whose central frequencies require that the sequential ionization process necessarily dominates, a two-electron interference pattern emerges that depends on the pulse delay and the spin state of the atom.

  3. Calcium: total or ionized?

    PubMed

    Schenck, Patricia A; Chew, Dennis J

    2008-05-01

    Measurement of serum total calcium (tCa) has been relied on for assessment of calcium status, despite the fact that it is the ionized calcium (iCa) fraction that has biologic activity. Serum tCa does not accurately predict iCa status in many clinical conditions. For accurate assessment of iCa status, iCa should be directly measured. Anaerobic measurement of serum iCa under controlled conditions provides the most reliable assessment of calcium status; aerobic measurement of iCa with species-specific pH correction is highly correlated with anaerobic measurements.

  4. Ionization and Positronium Formation in Noble Gases

    NASA Astrophysics Data System (ADS)

    Marler, J. P.; Sullivan, J. P.; Surko, C. M.

    2006-11-01

    This paper reviews key results of our recent study [Marler et al., Phys. Rev. A 71, 022701 (2005)] of direct ionization and positronium formation in the noble gases from the thresholds for these processes to 90 eV. Results for argon and xenon are emphasized. The original study also reports similar results for neon and krypton. The experiment uses a cold, trap-based positron beam and scattering in a strong magnetic field to make absolute cross section measurements. Comparison with a detailed set of previous measurements yields reasonably good absolute agreement. A third, independent analysis was used to resolve the remaining discrepancies to a < 5% level in argon, krypton and xenon. Key aspects of the work, comparison with available theory, and open questions for future research are discussed.

  5. Optical breakdown threshold investigation of 1064 nm laser induced air plasmas

    SciTech Connect

    Thiyagarajan, Magesh; Thompson, Shane

    2012-04-01

    We present the theoretical and experimental measurements and analysis of the optical breakdown threshold for dry air by 1064 nm infrared laser radiation and the significance of the multiphoton and collisional cascade ionization process on the breakdown threshold measurements over pressures range from 10 to 2000 Torr. Theoretical estimates of the breakdown threshold laser intensities and electric fields are obtained using two distinct theories namely multiphoton and collisional cascade ionization theories. The theoretical estimates are validated by experimental measurements and analysis of laser induced breakdown processes in dry air at a wavelength of 1064 nm by focusing 450 mJ max, 6 ns, 75 MW max high-power 1064 nm IR laser radiation onto a 20 {mu}m radius spot size that produces laser intensities up to 3 - 6 TW/cm{sup 2}, sufficient for air ionization over the pressures of interest ranging from 10 to 2000 Torr. Analysis of the measured breakdown threshold laser intensities and electric fields are carried out in relation with classical and quantum theoretical ionization processes, operating pressures. Comparative analysis of the laser air breakdown results at 1064 nm with corresponding results of a shorter laser wavelength (193 nm) [M. Thiyagarajan and J. E. Scharer, IEEE Trans. Plasma Sci. 36, 2512 (2008)] and a longer microwave wavelength (10{sup 8} nm) [A. D. MacDonald, Microwave Breakdown in Gases (Wiley, New York, 1966)]. A universal scaling analysis of the breakdown threshold measurements provided a direct comparison of breakdown threshold values over a wide range of frequencies ranging from microwave to ultraviolet frequencies. Comparison of 1064 nm laser induced effective field intensities for air breakdown measurements with data calculated based on the collisional cascade and multiphoton breakdown theories is used successfully to determine the scaled collisional microwave portion. The measured breakdown threshold of 1064 nm laser intensities are then

  6. Electron Impact Ionization of C_2F_6

    NASA Astrophysics Data System (ADS)

    Iga, Ione; Pereira Sanches, Ivana; Srivastava, Santosh Kumar

    2001-10-01

    Besides CF_4, perfluoroethane, C_2F_6, is also one of the fluorocarbon compounds most frequently used in plasma processing applications. Consequently, the knowledge of the ionization properties of C_2F6 is clearly of interest in order to model the plasma-chemical reactions. Nevertheless, only few partial ionization-cross-section measurements [1,2] for this molecule were reported in the literature. Also, the energy range covered in these studies was very limited (below 120 eV). Recently, we have studied these properties. More specifically, partial ionization cross sections (PICS) for the fragments: C^+, F^+, CF^+, CF_2^+, CF_3^+ and C_2F_5^+, produced by electron impact on C_2F_6, were measured in a single-collision condition from near ionization threshold to 1000 eV. In addition, total ionization cross sections (TICS) are also obtained by summing up the PICS's. The comparison of our measured PICS and derived TICS with available data [1-4] will be presented during the Conference. [1] H. U. Poll, J. Meischner, Contrib. Plasma Phys. 27 (1987) 359. [2] C. Q. Jiao, A Garscadden, P. D. Haaland, Chem. Phys. Lett. 310 (1999) 52. [3] H. Nishimura, W. M. Huo, M. A Ali and Y -K. Kim, J. Chem. Phys. 110 (1999) 3811. [4] L. G. Christophorou and J. K. Olthoff, J. Phys. Chem. Ref. Data 27 (1998) 1 and references therein.

  7. Ionization of highly excited helium atoms in an electric field

    SciTech Connect

    van de Water, W.; Mariani, D.R.; Koch, P.M.

    1984-11-01

    We present detailed measurements of ionization of highly excited triplet helium atoms in a static electric field. The atoms were prepared in states with energy E close to the saddle-point threshold E = -2(F(a.u.))/sup 1/2/. The electric field F was sufficiently strong for the states to be characterized by total spin S and absolute value of the magnetic quantum number M/sub L/. For M/sub L/ = 0 states the experiments measured ionization properties of adiabatic states. In another case, Vertical BarM/sub L/Vertical Bar = 2, they predominantly measured those of diabatic states. In both cases the ionization rate was found to be a highly nonmonotonic function of the field strength. The observations are analyzed in terms of a theory of the helium density of states in an electric field. A companion paper (D. A. Harmin, Phys. Rev. A 30, 2413 (1984)) develops in detail the general theory, which uses quantum defects to parametrize the effect of the core interaction. The agreement between measured and calculated ionization curves is good, indicating that the field ionization of a nonhydrogenic atom can now be understood in a detailed, quantitative, and predictive sense.

  8. Electron-impact dissociation and ionization of NO+ ions

    NASA Astrophysics Data System (ADS)

    Belic, D. S.; Urbain, X.; Cherkani-Hassani, H.; Defrance, P.

    2016-07-01

    Absolute cross sections for electron-impact ionization and dissociation of NO+ ions are reported. Simple ionization to NO2+ ion and production of singly charged N+ and O+ and doubly charged N2+ and O2+ fragments have been investigated. The animated electron-ion crossed-beam method is applied in the energy range from the respective thresholds up to 2.5 keV. The maximum of the simple ionization cross section is found to be (3.49 ± 0.07) × 10-17 cm2 at 135 eV. The total cross sections for N+ and O+ fragments at the maximum are found to be (13.9 ± 1.0) × 10-17 cm2 and (14.0 ± 1.4) × 10-17 cm2, respectively, both at an energy of 85 eV. By performing careful magnetic field scans of the detected signal, contributions of dissociative excitation and dissociative ionization to N+ and O+ production are determined separately. The cross sections for asymmetric dissociative ionization to N2+ and O2+ are found to be over one order of magnitude smaller. Distributions of the kinetic energy release to the fragments are determined for all dissociation processes.

  9. Electron impact ionization of highly charged lithiumlike ions

    SciTech Connect

    Wong, K L

    1992-10-01

    Electron impact ionization cross sections can provide valuable information about the charge-state and power balance of highly charged ions in laboratory and astrophysical plasmas. In the present work, a novel technique based on x-ray measurements has been used to infer the ionization cross section of highly charged lithiumlike ions on the Livermore electron beam ion trap. In particular, a correspondence is established between an observed x ray and an ionization event. The measurements are made at one energy corresponding to approximately 2.3 times the threshold energy for ionization of lithiumlike ions. The technique is applied to the transition metals between Z=22 (titanium, Ti[sup 19+]) and Z=26 (iron, Fe[sup 23+]) and to Z=56 (barium, Ba[sup 53+]). The results for the transition metals, which have an estimated 17-33% uncertainty, are in good overall agreement with a relativistic distorted-wave calculation. However, less good agreement is found for barium, which has a larger uncertainty. Methods for properly accounting for the polarization in the x-ray intensities and for inferring the charge-state abundances from x-ray observations, which were developed for the ionization measurements, as well as an x-ray model that assists in the proper interpretation of the data are also presented.

  10. Fractal dynamics in the ionization of helium Rydberg atoms

    NASA Astrophysics Data System (ADS)

    Xu, Xiulan; Zhang, Yanhui; Cai, Xiangji; Zhao, Guopeng; Kang, Lisha

    2016-11-01

    We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory. By introducing a fractal approach to describe the chaotic dynamical behavior of the ionization, we identify the fractal self-similarity structure of the escape time versus the distribution of the initial launch angles of electrons, and find that the self-similarity region shifts toward larger initial launch angles with a decrease in the scaled energy. We connect the fractal structure of the escape time plot to the escape dynamics of ionized electrons. Of particular note is that the fractal dimensions are sensitively controlled by the scaled energy and magnetic field, and exhibit excellent agreement with the chaotic extent of the ionization systems for both helium and hydrogen Rydberg atoms. It is shown that, besides the electric and magnetic fields, core scattering is a primary factor in the fractal dynamics. Project supported by the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM030).

  11. Energetic Landscape of MDM2-p53 Interactions by Computational Mutagenesis of the MDM2-p53 Interaction.

    PubMed

    Thayer, Kelly M; Beyer, George A

    2016-01-01

    The ubiquitin ligase MDM2, a principle regulator of the tumor suppressor p53, plays an integral role in regulating cellular levels of p53 and thus a prominent role in current cancer research. Computational analysis used MUMBO to rotamerize the MDM2-p53 crystal structure 1YCR to obtain an exhaustive search of point mutations, resulting in the calculation of the ΔΔG comprehensive energy landscape for the p53-bound regulator. The results herein have revealed a set of residues R65-E69 on MDM2 proximal to the p53 hydrophobic binding pocket that exhibited an energetic profile deviating significantly from similar residues elsewhere in the protein. In light of the continued search for novel competitive inhibitors for MDM2, we discuss possible implications of our findings on the drug discovery field.

  12. The cage fragmentation of doubly ionized norbornane: A Born-Oppenheimer molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Knippenberg, S.; Hajgató, B.

    2013-10-01

    Results are reported of Born-Oppenheimer molecular dynamics calculations performed on the singlet dication of norbornane, starting from the neutral ground state geometry. Intramolecular rearrangements and charge dissociation processes, which probably take place in the innermost valence ionization spectrum, are discussed and an analysis by means of natural bond orders and Wiberg bond indices has been performed. The outcome of these simulations and the observed cage fragmentation might explain a tremendous rise of electron-impact (e, 2e) ionization cross sections of norbornane at electron binding energies around the double-ionization threshold.

  13. Electron-Impact Total Ionization Cross Sections of CH and C2H2

    PubMed Central

    Kim, Yong-Ki; Ali, M. Asgar; Rudd, M. Eugene

    1997-01-01

    Electron-impact total ionization cross sections for the CH radical and C2H2 (acetylene) have been calculated using the Binary-Encounter-Bethe (BEB) model. The BEB model combines the Mott cross section and the asymptotic form of the Bethe theory, and has been shown to generate reliable ionization cross sections for a large variety of molecules. The BEB cross sections for CH and C2H2 are in good agreement with the available experimental data from ionization thresholds to hundreds of eV in incident energies. PMID:27805116

  14. Absolute cascade-free cross-sections for the 2S to 2P transition in Zn(+) using electron-energy-loss and merged-beams methods

    NASA Technical Reports Server (NTRS)

    Smith, Steven J.; Man, K.-F.; Chutjian, A.; Mawhorter, R. J.; Williams, I. D.

    1991-01-01

    Absolute cascade-free excitation cross-sections in an ion have been measured for the resonance 2S to 2P transition in Zn(+) using electron-energy-loss and merged electron-ion beams methods. Measurements were carried out at electron energies of below threshold to 6 times threshold. Comparisons are made with 2-, 5-, and 15-state close-coupling and distorted-wave theories. There is good agreement between experiment and the 15-state close-coupling cross-sections over the energy range of the calculations.

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

    NASA Technical Reports Server (NTRS)

    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.

  16. Accurate determination of the first ionization potential of actinides by laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Trautmann, N.

    1994-10-01

    A new method is described for the precise determination of the first ionization potential of elements which are available only in small amounts such as the heavier actinides. It is based on resonance ionization mass spectroscopy (RIMS) in the presence of an external electric field. Extrapolation of the ionization thresholds obtained with different electric field strengths to field strength zero leads directly to the first ionization potential. With samples of 10(exp 12) atoms of Np-237 and Am-243 experimental values for the first ionization potential of neptunium of IP(sub Np) = 6.2655(2) eV and of americium of IP(sub Am) = 5.9738(2) eV were obtained. This technique was also applied to thorium yielding a value of IP(sub Th) = 6.3067(2) eV. In addition the precision of the method was confirmed by the convergences of Rydberg series of americium measured by means of RIMS.

  17. Few-cycle attosecond pulse chirp effects on asymmetries in ionized electron momentum distributions

    SciTech Connect

    Peng Liangyou; Tan Fang; Gong Qihuang; Pronin, Evgeny A.; Starace, Anthony F.

    2009-07-15

    The momentum distributions of electrons ionized from H atoms by chirped few-cycle attosecond pulses are investigated by numerically solving the time-dependent Schroedinger equation. The central carrier frequency of the pulse is chosen to be 25 eV, which is well above the ionization threshold. The asymmetry (or difference) in the yield of electrons ionized along and opposite to the direction of linear laser polarization is found to be very sensitive to the pulse chirp (for pulses with fixed carrier-envelope phase), both for a fixed electron energy and for the energy-integrated yield. In particular, the larger the pulse chirp, the larger the number of times the asymmetry changes sign as a function of ionized electron energy. For a fixed chirp, the ionized electron asymmetry is found to be sensitive also to the carrier-envelope phase of the few-cycle pulse.

  18. Electron Impact Ionization Cross Sections and Rate Coefficients for Single Carbon Freon Molecules

    NASA Astrophysics Data System (ADS)

    Pal, Satyendra; Kumar, Neeraj

    2015-09-01

    Single carbon Freon molecules or chlorofluorocarbons (CFCs) are important industrial material with wide-ranging applications as refrigerant, aerosol propellant and semiconductor etchant, etc. The large-scale industrial consumption is of particular environmental concern because of its potential for ozone destruction in the stratosphere. In the present work, we have extended and generalized the modified Jain-Khare (JK) semi-empirical formalism for the evaluation of the total ionization cross sections corresponding to the formation of the cations in the electron impact ionization of molecules to the electron impact ionization of single carbon freon molecules, viz. CFCl3, CF2Cl2 and CF3Cl. The integral partial and the total ionization cross sections as function of incident electron energy are evaluated in the energy range varying from ionization threshold to 1000 eV. In absence of available differential cross sections, the corresponding derived partial and total ionization cross sections revealed a reasonably good agreement with the experimental and theoretical data, wherever available. In addition to the differential and integral ionization cross sections, we have also calculated the ionization rate coefficients using the evaluated partial ionization cross sections and the Maxwell-Boltzmann distribution as a function of electron temperature/energy. The work is supported by DST, New Delhi, India.

  19. Migration of Dust Particles from Comet 2P Encke

    NASA Technical Reports Server (NTRS)

    Ipatov, S. I.

    2003-01-01

    We investigated the migration of dust particles under the gravitational influence of all planets (except for Pluto), radiation pressure, Poynting-Robertson drag and solar wind drag for Beta equal to 0.002, 0.004, 0.01, 0.05, 0.1, 0.2, and 0.4. For silicate particles such values of Beta correspond to diameters equal to about 200, 100, 40, 9, 4, 2, and 1 microns, respectively. We used the Bulirsh-Stoer method of integration, and the relative error per integration step was taken to be less than lo-'. Initial orbits of the particles were close to the orbit of Comet 2P Encke. We considered initial particles near perihelion (runs denoted as Delta tsub o, = 0), near aphelion (Delta tsub o, = 0.5), and also studied their initial positions when the comet moved for Pa/4 after perihelion passage (such runs are denoted as Delta tsub o, =i 0.25), where Pa is the period of the comet. Variations in time T when perihelion was passed was varied with a step 0.1 day for series 'S' and with a step 1 day for series 'L'. For each Beta we considered N = 101 particles for "S" runs and 150 particles for "L" runs.

  20. Multicast Services over Structured P2P Networks

    NASA Astrophysics Data System (ADS)

    Manzanares-Lopez, Pilar; Malgosa-Sanahuja, Josemaria; Muñoz-Gea, Juan Pedro; Sanchez-Aarnoutse, Juan Carlos

    IP multicast functionality was defined as an efficient method to transmit datagrams to a group of receivers. However, although a lot of research work has been done in this technology, IP multicast has not spread out over the Internet as much as expected, reducing its use for local environments (i.e., LANs). The peer-to-peer networks paradigm can be used to overcome the IP multicast limitations. In this new scenario (called Application Layer Multicast or ALM), the multicast functionality is changed from network to application layer. Although ALM solution can be classified into unstructured and structured solutions, the last ones are the best option to offer multicast services due to the effectiveness in the discovery nodes, their mathematical definition and the totally decentralized management. In this chapter we are going to offer a tutorial of the main structured ALM solutions, but introducing two novelties with respect to related surveys in the past: first, the systematic description of most representative structured ALM solution in OverSim (one of the most popular p2p simulation frameworks). Second, some simulation comparatives between flooding-based and tree-based structured ALM solution are also presented.

  1. Ionization processes in small quasimolecules: He{sub 2}{sup 2+} (He{sup 2+}+ He)

    SciTech Connect

    Ogurtsov, G. N.; Mikoushkin, V. M.; Ovchinnikov, S. Yu.; Macek, J. H.

    2011-09-15

    The energy spectra of electrons ejected in He{sup 2+}-He collisions were measured in the ion energy range 6-30 keV. Theoretical analysis of the ionization mechanisms has been performed on the basis of the advanced adiabatic approximation for one-electron processes and perturbation theory for two-electron processes. The ionization channel 2p{sigma}{sup 2}{yields} 1s{sigma}nd{sigma}{yields} 1s{sigma}{epsilon}d{sigma} has been revealed, which makes a considerable contribution to the ionization cross section in the keV ion energy range.

  2. Ionization Cross Sections and Dissociation Channels of DNA Bases by Electron Collisions

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    Free secondary electrons are the most abundant secondary species in ionizing radiation. Their role in DNA damage, both direct and indirect, is an active area of research. While indirect damage by free radicals, particularly by the hydroxyl radical generated by electron collision with water. is relatively well studied, damage by direct electron collision with DNA is less well understood. Only recently Boudaiffa et al. demonstrated that electrons at energies well below ionization thresholds can induce substantial yields of single- and double-strand breaks in DNA by a resonant, dissociative attachment process. This study attracted renewed interest in electron collisions with DNA, especially in the low energy region. At higher energies ionization becomes important. While Monte Carlo track simulations of radiation damage always include ionization, the probability of dissociative ionization, i.e., simultaneous ionization and dissociation, is ignored. Just like dissociative attachment, dissociative ionization may be an important contributor to double-strand breaks since the radicals and ions produced by dissociative ionization, located in the vicinity of the DNA coil, can readily interact with other parts of the DNA. Using the improved binary-encounter dipole (iBED) formulation, we calculated the ionization cross sections of the four DNA bases, adenine, cytosine, guanine, and thymine, by electrons at energies from threshold to 1 KeV. The present calculation gives cross sections approximately 20% lower than the results by Bemhardt and Paretzke using the Deutsch-Mark and Binary-Encounter-Bethe (BEB) formalisms. The difference is most likely due to the lack of a shielding term in the dipole potential used in the Deutsch-Mark and BEB formalisms. The dissociation channels of ionization for the bases are currently being studied.

  3. Studies in Above- and Below-Threshold Harmonics in Argon with an Infrared Femtosecond Laser

    NASA Astrophysics Data System (ADS)

    Chew, Andrew; Yin, Yanchun; Li, Jie; Ren, Xiaoming; Cunningham, Eric; Wu, Yi; Chang, Zenghu

    2016-05-01

    We investigate and compare the above- and below-threshold harmonics in Argon gas using our recently-developed 1 kHz, two-cycle (11.4 fs), 3mJ, and carrier-envelope-phase(CEP)-stable laser at 1.6 μm. Such ultraviolet pulses can serve as pump or probe for studying dynamics in atoms and molecules. Unlike high harmonics with photon energy well above the ionization potential, the mechanism for generating harmonics near the ionization threshold is still under intense investigation. Previous work by Chini et al. on below-threshold harmonics was done using a 0.8 μm few-cycle Ti:Sapphire spectrally-broadened source with energy up to 300 μJ. It has been predicted by theory that free-free transitions dominate the below threshold harmonic generation as the laser wavelength increase from near infrared to mid-infrared. We are therefore interested in investigating how using a longer wavelength laser might lead to changes to the behavior of below-threshold harmonics when we vary various parameters. We report the π-periodity CEP dependence and ellipticity dependence of the above- and below-threshold harmonics. This material was based on work supported by National Science Foundation (1068604), Army Research Office (W911NF-14-1-0383), Air Force Office of Scientific Research (FA9550-15-1-0037) and the DARPA PULSE program by a Grant from AMRDEC (W31P4Q1310017).

  4. Multiphoton ionization of Uracil

    NASA Astrophysics Data System (ADS)

    Prieto, Eladio; Martinez, Denhi; Guerrero, Alfonso; Alvarez, Ignacio; Cisneros, Carmen

    2016-05-01

    Multiphoton ionization and dissociation of Uracil using a Reflectron time of flight spectrometer was performed along with radiation from the second harmonic of a Nd:YAG laser. Uracil is one of the four nitrogen bases that belong to RNA. The last years special interest has been concentrated on the study of the effects under UV radiation in nucleic acids1 and also in the role that this molecule could have played in the origin and development of life on our planet.2 The MPI mass spectra show that the presence and intensity of the resulting ions strongly depend on the density power. The identification of the ions in the mass spectra is presented. The results are compared with those obtained in other laboratories under different experimental conditions and some of them show partial agreement.3 The present work was supported by CONACYT-Mexico Grant 165410 and DGAPA UNAM Grant IN101215 and IN102613.

  5. Ionized cluster beam deposition

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, A. R.

    1983-01-01

    Ionized Cluster Beam (ICB) deposition, a new technique originated by Takagi of Kyoto University in Japan, offers a number of unique capabilities for thin film metallization as well as for deposition of active semiconductor materials. ICB allows average energy per deposited atom to be controlled and involves impact kinetics which result in high diffusion energies of atoms on the growth surface. To a greater degree than in other techniques, ICB involves quantitative process parameters which can be utilized to strongly control the characteristics of films being deposited. In the ICB deposition process, material to be deposited is vaporized into a vacuum chamber from a confinement crucible at high temperature. Crucible nozzle configuration and operating temperature are such that emerging vapor undergoes supercondensation following adiabatic expansion through the nozzle.

  6. Acid sensitive background potassium channels K2P3.1 and K2P9.1 undergo rapid dynamin-dependent endocytosis

    PubMed Central

    Mant, Alexandra; Williams, Sarah E; O'Kelly, Ita

    2013-01-01

    Acid-sensitive, two-pore domain potassium channels, K2P3.1 and K2P9.1, are implicated in cardiac and nervous tissue responses to hormones, neurotransmitters and drugs. K2P3.1 and K2P9.1 leak potassium from the cell at rest and directly impact membrane potential. Hence altering channel number on the cell surface drives changes in cellular electrical properties. The rate of K2P3.1 and K2P9.1 delivery to and recovery from the plasma membrane determines both channel number at the cell surface and potassium leak from cells. This study examines the endocytosis of K2P3.1 and K2P9.1. Plasma membrane biotinylation was used to follow the fate of internalized GFP-tagged rat K2P3.1 and K2P9.1 transiently expressed in HeLa cells. Confocal fluorescence images were analyzed using Imaris software, which revealed that both channels are endocytosed by a dynamin-dependent mechanism and over the course of 60 min, move progressively toward the nucleus. Endogenous endocytosis of human K2P3.1 and K2P9.1 was examined in the lung carcinoma cell line, A549. Endogenous channels are endocytosed over a similar time-scale to the channels expressed transiently in HeLa cells. These findings both validate the use of recombinant systems and identify an endogenous model system in which K2P3.1 and K2P9.1 trafficking can be further studied. PMID:23807092

  7. Acid sensitive background potassium channels K2P3.1 and K2P9.1 undergo rapid dynamin-dependent endocytosis.

    PubMed

    Mant, Alexandra; Williams, Sarah; O'Kelly, Ita

    2013-01-01

    Acid-sensitive, two-pore domain potassium channels, K(2P)3.1 and K(2P)9.1, are implicated in cardiac and nervous tissue responses to hormones, neurotransmitters and drugs. K(2P)3.1 and K(2P)9.1 leak potassium from the cell at rest and directly impact membrane potential. Hence altering channel number on the cell surface drives changes in cellular electrical properties. The rate of K(2P)3.1 and K(2P)9.1 delivery to and recovery from the plasma membrane determines both channel number at the cell surface and potassium leak from cells. This study examines the endocytosis of K(2P)3.1 and K(2P)9.1. Plasma membrane biotinylation was used to follow the fate of internalized GFP-tagged rat K(2P)3.1 and K(2P)9.1 transiently expressed in HeLa cells. Confocal fluorescence images were analyzed using Imaris software, which revealed that both channels are endocytosed by a dynamin-dependent mechanism and over the course of 60 min, move progressively toward the nucleus. Endogenous endocytosis of human K(2P)3.1 and K(2P)9.1 was examined in the lung carcinoma cell line, A549. Endogenous channels are endocytosed over a similar time-scale to the channels expressed transiently in HeLa cells. These findings both validate the use of recombinant systems and identify an endogenous model system in which K(2P)3.1 and K(2P)9.1 trafficking can be further studied.

  8. The casein kinases Yck1p and Yck2p act in the secretory pathway, in part, by regulating the Rab exchange factor Sec2p

    PubMed Central

    Stalder, Danièle; Novick, Peter J.

    2016-01-01

    Sec2p is a guanine nucleotide exchange factor that activates Sec4p, the final Rab GTPase of the yeast secretory pathway. Sec2p is recruited to secretory vesicles by the upstream Rab Ypt32p acting in concert with phosphatidylinositol-4-phosphate (PI(4)P). Sec2p also binds to the Sec4p effector Sec15p, yet Ypt32p and Sec15p compete against each other for binding to Sec2p. We report here that the redundant casein kinases Yck1p and Yck2p phosphorylate sites within the Ypt32p/Sec15p binding region and in doing so promote binding to Sec15p and inhibit binding to Ypt32p. We show that Yck2p binds to the autoinhibitory domain of Sec2p, adjacent to the PI(4)P binding site, and that addition of PI(4)P inhibits Sec2p phosphorylation by Yck2p. Loss of Yck1p and Yck2p function leads to accumulation of an intracellular pool of the secreted glucanase Bgl2p, as well as to accumulation of Golgi-related structures in the cytoplasm. We propose that Sec2p is phosphorylated after it has been recruited to secretory vesicles and the level of PI(4)P has been reduced. This promotes Sec2p function by stimulating its interaction with Sec15p. Finally, Sec2p is dephosphorylated very late in the exocytic reaction to facilitate recycling. PMID:26700316

  9. Thresholds in chemical respiratory sensitisation.

    PubMed

    Cochrane, Stella A; Arts, Josje H E; Ehnes, Colin; Hindle, Stuart; Hollnagel, Heli M; Poole, Alan; Suto, Hidenori; Kimber, Ian

    2015-07-03

    There is a continuing interest in determining whether it is possible to identify thresholds for chemical allergy. Here allergic sensitisation of the respiratory tract by chemicals is considered in this context. This is an important occupational health problem, being associated with rhinitis and asthma, and in addition provides toxicologists and risk assessors with a number of challenges. In common with all forms of allergic disease chemical respiratory allergy develops in two phases. In the first (induction) phase exposure to a chemical allergen (by an appropriate route of exposure) causes immunological priming and sensitisation of the respiratory tract. The second (elicitation) phase is triggered if a sensitised subject is exposed subsequently to the same chemical allergen via inhalation. A secondary immune response will be provoked in the respiratory tract resulting in inflammation and the signs and symptoms of a respiratory hypersensitivity reaction. In this article attention has focused on the identification of threshold values during the acquisition of sensitisation. Current mechanistic understanding of allergy is such that it can be assumed that the development of sensitisation (and also the elicitation of an allergic reaction) is a threshold phenomenon; there will be levels of exposure below which sensitisation will not be acquired. That is, all immune responses, including allergic sensitisation, have threshold requirement for the availability of antigen/allergen, below which a response will fail to develop. The issue addressed here is whether there are methods available or clinical/epidemiological data that permit the identification of such thresholds. This document reviews briefly relevant human studies of occupational asthma, and experimental models that have been developed (or are being developed) for the identification and characterisation of chemical respiratory allergens. The main conclusion drawn is that although there is evidence that the

  10. On computational Gestalt detection thresholds.

    PubMed

    Grompone von Gioi, Rafael; Jakubowicz, Jérémie

    2009-01-01

    The aim of this paper is to show some recent developments of computational Gestalt theory, as pioneered by Desolneux, Moisan and Morel. The new results allow to predict much more accurately the detection thresholds. This step is unavoidable if one wants to analyze visual detection thresholds in the light of computational Gestalt theory. The paper first recalls the main elements of computational Gestalt theory. It points out a precision issue in this theory, essentially due to the use of discrete probability distributions. It then proposes to overcome this issue by using continuous probability distributions and illustrates it on the meaningful alignment detector of Desolneux et al.

  11. Low Threshold Quantum Dot Lasers.

    PubMed

    Iyer, Veena Hariharan; Mahadevu, Rekha; Pandey, Anshu

    2016-04-07

    Semiconductor quantum dots have replaced conventional inorganic phosphors in numerous applications. Despite their overall successes as emitters, their impact as laser materials has been severely limited. Eliciting stimulated emission from quantum dots requires excitation by intense short pulses of light typically generated using other lasers. In this Letter, we develop a new class of quantum dots that exhibit gain under conditions of extremely low levels of continuous wave illumination. We observe thresholds as low as 74 mW/cm(2) in lasers made from these materials. Due to their strong optical absorption as well as low lasing threshold, these materials could possibly convert light from diffuse, polychromatic sources into a laser beam.

  12. Comparison of self-injection thresholds in He and N2 and role of self-focusing in LWFA

    NASA Astrophysics Data System (ADS)

    Palla, D.; Baffigi, F.; Brandi, F.; Fulgentini, L.; Koester, P.; Labate, L.; Londrillo, P.; Gizzi, L. A.

    2016-09-01

    We present an experimental study of laser-plasma acceleration in which the injected charge was measured at self-injection threshold for He and N2. We use numerical particle-in-cell simulation to unfold the role of ionization in the self-injection process and to reconstruct the local electrons density from the atomic density and the ionization degree. Comparison of measured and calculated self-injection thresholds yields the dependence of injected charge upon the electron density and sheds light on the possible role of the picosecond pedestal of femtosecond laser pulses in setting the initial charge state of the plasma.

  13. Spot detection from MODIS imagery using 2P-CFAR

    NASA Astrophysics Data System (ADS)

    Ding, Xianwen; Li, Xiaofeng

    2015-12-01

    Oil spills are one of the major environmental concerns, especially in the coastal zones of the ocean. Satellite remote sensing imagery has proved to be a useful tool for monitoring oil spills in the marine environment. With its two daily acquisitions and the possibility to obtain near-real-time data free of charge, the Moderate Resolution Imaging Spectroradiometer (MODIS) shows interesting potential as such a cost-effective supplementary tool. Several researches on oil spill detection in MODIS imagery has been carried out for the past few years. Basically, oil spills were manually detected from MODIS imagery [1,2]. The disadvantage of the manual detection method is inefficient and subjective. Shi et al. proposed an oil spill detection method from MODIS imagery by using fuzzy cluster and texture feature extraction [3]. It works in an automatic manner and does not require any priori knowledge of occurrence or the spectral attributes of spills. But its efficiency in very near shore regions is limited. Chen and Zhao detected oil spills from the oil-water contrast ratio image by using a thresholding method [4].They found that the oil-water contrast ratio can be enhanced by replacing the original image with the ratio image of two different band ones in 400-800 nm. To obtain the oil-water contrast ratio image from the MODIS imagery, they selected the oil spill area and the background sea area and then calculated the mean radiance or emissivity value in those areas. By doing so, the automation and the accuracy of the method were reduced. Adamo et al. [5] and Kudryavtsev et al. [6] proposed physical methods for oil spill detection from MODIS imagery acquired in sunglint conditions. These two methods take imaging geometry into consideration and have the aid of other models or functions such as the Cox and Munk (1954) model [7],the CMOD4 model [8,9], the ECMWF (European Centre for Medium-Range Weather Forecasts) atmospheric model, and the transfer function, which increase the

  14. Threshold Concepts and Pedagogic Representation

    ERIC Educational Resources Information Center

    Meyer, Jan H. F.

    2016-01-01

    Purpose: The purpose of this paper is to present a brief exposure to the development of the threshold concepts framework (TCF), the intention being to illuminate for interested readers a broader landscape of research activity than that perhaps conveyed by the individual contributions to this special edition. Design/Methodology/Approach: There is…

  15. Temperature dependent ablation threshold in silicon using ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Thorstensen, Jostein; Erik Foss, Sean

    2012-11-01

    We have experimentally investigated the ablation threshold in silicon as a function of temperature when applying ultrashort laser pulses at three wavelengths. By varying the temperature of a silicon substrate from room temperature to 320 °C, we observe that the ablation threshold for a 3 ps pulse using a wavelength of 1030 nm drops from 0.43 J/cm2 to 0.24 J/cm2, a reduction of 43%. For a wavelength of 515 nm, the ablation threshold drops from 0.22 J/cm2 to 0.15 J/cm2, a reduction of 35%. The observed ablation threshold for pulses at 343 nm remains constant with temperature, at 0.10 J/cm2. These results indicate that substrate heating is a useful technique for lowering the ablation threshold in industrial silicon processing using ultrashort laser pulses in the IR or visible wavelength range. In order to investigate and explain the observed trends, we apply the two-temperature model, a thermodynamic model for investigation of the interaction between silicon and ultrashort laser pulses. Applying the two-temperature model implies thermal equilibrium between optical and acoustic phonons. On the time scales encountered herein, this need not be the case. However, as discussed in the article, the two-temperature model provides valuable insight into the physical processes governing the interaction between the laser light and the silicon. The simulations indicate that ablation occurs when the number density of excited electrons reaches the critical electron density, while the lattice remains well below vaporization temperature. The simulated laser fluence required to reach critical electron density is also found to be temperature dependent. The dominant contributor to increased electron density is, in the majority of the investigated cases, the linear absorption coefficient. Two-photon absorption and impact ionization also generate carriers, but to a lesser extent. As the linear absorption coefficient is temperature dependent, we find that the simulated reduction in

  16. Resonant enhanced multiphoton ionization studies of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Dixit, S. N.; Levin, D.; Mckoy, V.

    1987-01-01

    In resonant enhanced multiphoton ionization (REMPI), an atom absorbs several photons making a transition to a resonant intermediate state and subsequently ionizing out of it. With currently available tunable narrow-band lasers, the extreme sensitivity of REMPI to the specific arrangement of levels can be used to selectively probe minute amounts of a single species (atom) in a host of background material. Determination of the number density of atoms from the observed REMPI signal requires a knowledge of the multiphoton ionization cross sections. The REMPI of atomic oxygen was investigated through various excitation schemes that are feasible with available light sources. Using quantum defect theory (QDT) to estimate the various atomic parameters, the REMPI dynamics in atomic oxygen were studied incorporating the effects of saturation and a.c. Stark shifts. Results are presented for REMPI probabilities for excitation through various 2p(3) (4S sup o) np(3)P and 2p(3) (4S sup o) nf(3)F levels.

  17. Multiphoton inner-shell ionization of the carbon atom

    NASA Astrophysics Data System (ADS)

    Rey, H. F.; van der Hart, H. W.

    2015-07-01

    We apply time-dependent R -matrix theory to study inner-shell ionization of C atoms in ultrashort high-frequency light fields with a photon energy between 170 and 245 eV. At an intensity of 1017 W /cm2, ionization is dominated by single-photon emission of a 2 ℓ electron, with two-photon emission of a 1 s electron accounting for about 2-3% of all emission processes, and two-photon emission of 2 ℓ contributing about 0.5-1%. Three-photon emission of a 1 s electron is estimated to contribute about 0.01-0.03%. Around a photon energy of 225 eV, two-photon emission of a 1 s electron, leaving C+ in either 1 s 2 s 2 p3 or 1 s 2 p4 , is resonantly enhanced by intermediate 1 s 2 s22 p3 states. The results demonstrate the capability of time-dependent R -matrix theory to describe inner-shell ionization processes including rearrangement of the outer electrons.

  18. Energy and charge transfer in ionized argon coated water clusters.

    PubMed

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

    2013-12-07

    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 (H2O)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 (H2O)(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 (H2O)(n)H2(2+) and (H2O)(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.

  19. Energy and charge transfer in ionized argon coated water clusters

    SciTech Connect

    Kočišek, J. E-mail: michal.farnik@jh-inst.cas.cz Lengyel, J.; Fárník, M. E-mail: michal.farnik@jh-inst.cas.cz; Slavíček, P. E-mail: michal.farnik@jh-inst.cas.cz

    2013-12-07

    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{sub 2}O){sub 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{sup +} and water occurs above the threshold; at higher electron energies above ∼28 eV, an excitonic transfer process between Ar{sup +}* and water opens leading to new products Ar{sub n}H{sup +} and (H{sub 2}O){sub n}H{sup +}. 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{sub 2}O){sub n}H{sub 2}{sup 2+} and (H{sub 2}O){sub n}{sup 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.

  20. High pressure xenon ionization detector

    DOEpatents

    Markey, J.K.

    1989-11-14

    A method is provided for detecting ionization comprising allowing particles that cause ionization to contact high pressure xenon maintained at or near its critical point and measuring the amount of ionization. An apparatus is provided for detecting ionization, the apparatus comprising a vessel containing a ionizable medium, the vessel having an inlet to allow high pressure ionizable medium to enter the vessel, a means to permit particles that cause ionization of the medium to enter the vessel, an anode, a cathode, a grid and a plurality of annular field shaping rings, the field shaping rings being electrically isolated from one another, the anode, cathode, grid and field shaping rings being electrically isolated from one another in order to form an electric field between the cathode and the anode, the electric field originating at the anode and terminating at the cathode, the grid being disposed between the cathode and the anode, the field shaping rings being disposed between the cathode and the grid, the improvement comprising the medium being xenon and the vessel being maintained at a pressure of 50 to 70 atmospheres and a temperature of 0 to 30 C. 2 figs.

  1. High pressure xenon ionization detector

    DOEpatents

    Markey, John K.

    1989-01-01

    A method is provided for detecting ionization comprising allowing particles that cause ionization to contact high pressure xenon maintained at or near its critical point and measuring the amount of ionization. An apparatus is provided for detecting ionization, the apparatus comprising a vessel containing a ionizable medium, the vessel having an inlet to allow high pressure ionizable medium to enter the vessel, a means to permit particles that cause ionization of the medium to enter the vessel, an anode, a cathode, a grid and a plurality of annular field shaping rings, the field shaping rings being electrically isolated from one another, the anode, cathode, grid and field shaping rings being electrically isolated from one another in order to form an electric field between the cathode and the anode, the electric field originating at the anode and terminating at the cathode, the grid being disposed between the cathode and the anode, the field shaping rings being disposed between the cathode and the grid, the improvement comprising the medium being xenon and the vessel being maintained at a pressure of 50 to 70 atmospheres and a temperature of 0.degree. to 30.degree. C.

  2. Iron ionization and recombination rates and ionization equilibrium

    NASA Technical Reports Server (NTRS)

    Arnaud, M.; Raymond, J.

    1992-01-01

    In the past few years important progress has been made on the knowledge of ionization and recombination rates of iron, an astrophysically abundant heavy element and a major impurity in laboratory fusion devices. We make a critical review of the existing data on ionization and dielectronic recombination and present new computations of radiative recombination rate coefficients of Fe(+14) through Fe(+25) using the photoionization cross sections of Clark et al. (1986). We provide analytical fits to the recommended data (direct ionization and excitation-autoionization cross sections; radiative and dielectronic recombination rate coefficients). Finally we determine the iron ionic fractions at ionization equilibrium and compare them with previous computations as well as with observational data.

  3. Cosmic ray studies with a gas Cherenkov counter in association with an ionization spectrometer

    NASA Technical Reports Server (NTRS)

    Balasubrahmanyan, V. K.; Ormes, J. F.; Arens, J. F.; Siohan, F.; Yodh, G. B.; Simon, M.; Spiegelhauer, H.

    1980-01-01

    The results from a balloon-borne gas Cherenkov counter (threshold 16.5 GeV/nucleon) and an ionization spectrometer are presented. The gas Cherenkov counter provides an absolute energy distribution for the response of the calorimeter for 5 or = Z 26 nuclei of cosmic rays. The contribution of scintillation to the gas Cherenkov pulse height was obtained by independently selecting particles below the gas Cherenkov threshold using the ionization spectrometer. Energy spectra were derived by minimizing the chi squared between Monte Carlo simulted data and flight data. Best fit power laws, dN/dE = AE-gamma, were determined for C, N, O, Ne, Mg, and Si. The power laws, all consistent with E (-2.7) are not good fits to the data. A better fit is obtained using the spectrum derived from the spectrometer. The data from the ionization calorimeter and the gas Cherenkov are thus completely self-consistent.

  4. Optical ionization detector

    DOEpatents

    Wuest, Craig R.; Lowry, Mark E.

    1994-01-01

    An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium.

  5. Optical ionization detector

    DOEpatents

    Wuest, C.R.; Lowry, M.E.

    1994-03-29

    An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium. 3 figures.

  6. Microwave reflectometer ionization sensor

    NASA Technical Reports Server (NTRS)

    Seals, Joseph; Fordham, Jeffrey A.; Pauley, Robert G.; Simonutti, Mario D.

    1993-01-01

    The development of the Microwave Reflectometer Ionization Sensor (MRIS) Instrument for use on the Aeroassist Flight Experiment (AFE) spacecraft is described. The instrument contract was terminated, due to cancellation of the AFE program, subsequent to testing of an engineering development model. The MRIS, a four-frequency reflectometer, was designed for the detection and location of critical electron density levels in spacecraft reentry plasmas. The instrument would sample the relative magnitude and phase of reflected signals at discrete frequency steps across 4 GHz bandwidths centered at four frequencies: 20, 44, 95, and 140 GHz. The sampled data would be stored for later processing to calculate the distance from the spacecraft surface to the critical electron densities versus time. Four stepped PM CW transmitter receivers were located behind the thermal protection system of the spacecraft with horn antennas radiating and receiving through an insulating tile. Techniques were developed to deal with interference, including multiple reflections and resonance effects, resulting from the antenna configuration and operating environment.

  7. Ionizing radiation promotes protozoan reproduction

    SciTech Connect

    Luckey, T.D.

    1986-11-01

    This experiment was performed to determine whether ionizing radiation is essential for maximum growth rate in a ciliated protozoan. When extraneous ionizing radiation was reduced to 0.15 mrad/day, the reproduction rate of Tetrahymena pyriformis was significantly less (P less than 0.01) than it was at near ambient levels, 0.5 or 1.8 mrad/day. Significantly higher growth rates (P less than 0.01) were obtained when chronic radiation was increased. The data suggest that ionizing radiation is essential for optimum reproduction rate in this organism.

  8. Pulsed helium ionization detection system

    DOEpatents

    Ramsey, R.S.; Todd, R.A.

    1985-04-09

    A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

  9. Pulsed helium ionization detection system

    DOEpatents

    Ramsey, Roswitha S.; Todd, Richard A.

    1987-01-01

    A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

  10. Ionization-based detectors for gas chromatography.

    PubMed

    Poole, Colin F

    2015-11-20

    The gas phase ionization detectors are the most widely used detectors for gas chromatography. The column and makeup gases commonly used in gas chromatography are near perfect insulators. This facilitates the detection of a minute number of charge carriers facilitating the use of ionization mechanisms of low efficiency while providing high sensitivity. The main ionization mechanism discussed in this report are combustion in a hydrogen diffusion flame (flame ionization detector), surface ionization in a plasma (thermionic ionization detector), photon ionization (photoionization detector and pulsed discharge helium ionization detector), attachment of thermal electrons (electron-capture detector), and ionization by collision with metastable helium species (helium ionization detector). The design, response characteristics, response mechanism, and suitability for fast gas chromatography are the main features summarized in this report. Mass spectrometric detection and atomic emission detection, which could be considered as ionization detectors of a more sophisticated and complex design, are not discussed in this report.

  11. Dynamical orientation effects in atomic ionization by impact of protons and positrons

    NASA Astrophysics Data System (ADS)

    Fregenal, Daniel; Barrachina, Raúl; Bernardi, Guillermo; Suárez, Sergio; Fiol, Juan

    2011-10-01

    Recent results in ionization collisions with positrons and protons showed that just above the two-body threshold, for electron velocities close to the final projectile's velocity, the electron-projectile continuum dipole is narrowly oriented along the direction of motion of its centre-of-mass, with the negative charge pointing towards the residual target. Although a forward-backward asymmetry in the vicinity of the two-body threshold has been studied many year ago in ion impact ionization collisions, that was by far a much milder effect that left no fingerprint on the cusp position. Our results show that the phenomena is present for ionization by impact of both protons and positrons. In this communication, through measurements on H+ + He and calculations we analyze in detail this effect that can be linked to a dynamical alignment of the two-body subsystem in the continuum. Recent results in ionization collisions with positrons and protons showed that just above the two-body threshold, for electron velocities close to the final projectile's velocity, the electron-projectile continuum dipole is narrowly oriented along the direction of motion of its centre-of-mass, with the negative charge pointing towards the residual target. Although a forward-backward asymmetry in the vicinity of the two-body threshold has been studied many year ago in ion impact ionization collisions, that was by far a much milder effect that left no fingerprint on the cusp position. Our results show that the phenomena is present for ionization by impact of both protons and positrons. In this communication, through measurements on H+ + He and calculations we analyze in detail this effect that can be linked to a dynamical alignment of the two-body subsystem in the continuum. This work was partially supported by the Consejo Nacional de Investigaciones Cientificas y Tecnicas, Universidad Nacional de Cuyo and Fundacion Balseiro.

  12. Protein Kinase A Is Central for Forward Transport of Two-pore Domain Potassium Channels K2P3.1 and K2P9.1*

    PubMed Central

    Mant, Alexandra; Elliott, David; Eyers, Patrick A.; O'Kelly, Ita M.

    2011-01-01

    Acid-sensitive two-pore domain potassium channels (K2P3.1 and K2P9.1) play key roles in both physiological and pathophysiological mechanisms, the most fundamental of which is control of resting membrane potential of cells in which they are expressed. These background “leak” channels are constitutively active once expressed at the plasma membrane, and hence tight control of their targeting and surface expression is fundamental to the regulation of K+ flux and cell excitability. The chaperone protein, 14-3-3, binds to a critical phosphorylated serine in the channel C termini of K2P3.1 and K2P9.1 (Ser393 and Ser373, respectively) and overcomes retention in the endoplasmic reticulum by βCOP. We sought to identify the kinase responsible for phosphorylation of the terminal serine in human and rat variants of K2P3.1 and K2P9.1. Adopting a bioinformatic approach, three candidate protein kinases were identified: cAMP-dependent protein kinase, ribosomal S6 kinase, and protein kinase C. In vitro phosphorylation assays were utilized to determine the ability of the candidate kinases to phosphorylate the channel C termini. Electrophysiological measurements of human K2P3.1 transiently expressed in HEK293 cells and cell surface assays of GFP-tagged K2P3.1 and K2P9.1 enabled the determination of the functional implications of phosphorylation by specific kinases. All of our findings support the conclusion that cAMP-dependent protein kinase is responsible for the phosphorylation of the terminal serine in both K2P3.1 and K2P9.1. PMID:21357689

  13. Protein kinase A is central for forward transport of two-pore domain potassium channels K2P3.1 and K2P9.1.

    PubMed

    Mant, Alexandra; Elliott, David; Eyers, Patrick A; O'Kelly, Ita M

    2011-04-22

    Acid-sensitive two-pore domain potassium channels (K2P3.1 and K2P9.1) play key roles in both physiological and pathophysiological mechanisms, the most fundamental of which is control of resting membrane potential of cells in which they are expressed. These background "leak" channels are constitutively active once expressed at the plasma membrane, and hence tight control of their targeting and surface expression is fundamental to the regulation of K(+) flux and cell excitability. The chaperone protein, 14-3-3, binds to a critical phosphorylated serine in the channel C termini of K2P3.1 and K2P9.1 (Ser(393) and Ser(373), respectively) and overcomes retention in the endoplasmic reticulum by βCOP. We sought to identify the kinase responsible for phosphorylation of the terminal serine in human and rat variants of K2P3.1 and K2P9.1. Adopting a bioinformatic approach, three candidate protein kinases were identified: cAMP-dependent protein kinase, ribosomal S6 kinase, and protein kinase C. In vitro phosphorylation assays were utilized to determine the ability of the candidate kinases to phosphorylate the channel C termini. Electrophysiological measurements of human K2P3.1 transiently expressed in HEK293 cells and cell surface assays of GFP-tagged K2P3.1 and K2P9.1 enabled the determination of the functional implications of phosphorylation by specific kinases. All of our findings support the conclusion that cAMP-dependent protein kinase is responsible for the phosphorylation of the terminal serine in both K2P3.1 and K2P9.1.

  14. ISODATA: Thresholds for splitting clusters

    NASA Technical Reports Server (NTRS)

    Kan, E. P. F. (Principal Investigator)

    1972-01-01

    The author has identified the following significant results. The parameter AD (average distance) as used in the ISODATA program was critically examined. Thresholds of AD to decide on the splitting of clusters were obtained. For the univariate case, 0.84 was established as a sound choice, after examining several simple, as well as composite, distributions and also after investigating the probability of misclassification when points have to be reassigned to the newly identified clusters. For the multivariate case, the empirical threshold (N-0.16)/square root of N was extrapolated. A final criticism on AD was that AD would lose its effectiveness as a discriminative measure for the present purpose when N was large.

  15. Scaling behavior of threshold epidemics

    NASA Astrophysics Data System (ADS)

    Ben-Naim, E.; Krapivsky, P. L.

    2012-05-01

    We study the classic Susceptible-Infected-Recovered (SIR) model for the spread of an infectious disease. In this stochastic process, there are two competing mechanism: infection and recovery. Susceptible individuals may contract the disease from infected individuals, while infected ones recover from the disease at a constant rate and are never infected again. Our focus is the behavior at the epidemic threshold where the rates of the infection and recovery processes balance. In the infinite population limit, we establish analytically scaling rules for the time-dependent distribution functions that characterize the sizes of the infected and the recovered sub-populations. Using heuristic arguments, we also obtain scaling laws for the size and duration of the epidemic outbreaks as a function of the total population. We perform numerical simulations to verify the scaling predictions and discuss the consequences of these scaling laws for near-threshold epidemic outbreaks.

  16. The excited spin state of Comet 2P/Encke

    NASA Astrophysics Data System (ADS)

    Belton, Michael J. S.; Samarasinha, Nalin H.; Fernández, Yan R.; Meech, Karen J.

    2005-05-01

    Ways to rationalize the different periods (e.g., 15.08 h, Luu and Jewitt, 1990, Icarus 86, 69-81; 11.01 h, Fernández et al., 2004, Icarus, in this issue; Lowry et al., 2003, Lunar Planet. Sci. XXXIV, Abstract 2056) seen in near aphelion R-band light curves of Comet 2P/Encke are explored. We show that the comet is usually active at aphelion and it's observed light curves contain signal from both the nucleus and an unresolved coma. The coma contribution to the observed brightness is generally found to dominate with the nucleus providing from 28 to 87% of the total brightness. The amplitude of the observed variations cannot be explained by the nucleus alone and are due to coma activity. We show that some seven periodicities exist in the observed light curves at various times and that this is likely the result of an active nucleus spinning in an excited spin state. The changing periodicities are probably due to changes in the relative strengths of the active areas. We work out possible excited states based on experience with model light curves and by using an analogy to light curve observations of Comet 1P/Halley for which the spin state has been separately determined from spacecraft observations. There is a possibility of a fully relaxed principal axis spin state (0.538 d -1; P=44.6 h) but, because it provides a poorer fit to the observed periodicities than the best fit excited state together with the absence of a peak near 1.08 d -1 ( 2f) in the frequency spectrum of the Fernández et al. (2000, Icarus 147, 145-160) thermal IR lightcurve, we consider it unlikely. Both SAM and LAM excited states are allowed by the underlying periodicities and additional information is needed to choose between these. Our choice of a low excitation SAM state, i.e., one in which the instantaneous spin axis nutates around the total angular momentum vector in a motion that is characterized by limited angular oscillations around the long axis, is based on Sekanina's (1988, Astron J. 95

  17. Low-energy electron rescattering in laser-induced ionization

    NASA Astrophysics Data System (ADS)

    Becker, W.; Goreslavski, S. P.; Milošević, D. B.; Paulus, G. G.

    2014-10-01

    The low-energy structure (LES) in the energy spectrum of above-threshold ionization of rare-gas atoms is reinvestigated from three different points of view. First, the role of forward rescattering in the completely classical simple-man model (SMM) is considered. Then, the corresponding classical electronic trajectories are retrieved in the quantum-mechanical ionization amplitude derived in the strong-field approximation augmented to allow for rescattering. Third, classical trajectories in the presence of both the laser field and the Coulomb field are scrutinized in order to see how they are related to the LES. It is concluded that the LES is already rooted in the SMM. The Coulomb field enhances the structure so that it can successfully compete with other contributions and become visible in the total spectrum.

  18. Electron- and proton-induced ionization of pyrimidine

    SciTech Connect

    Champion, Christophe; Quinto, Michele; Weck, Philippe F

    2015-03-27

    This present work describes a quantum-mechanically based model of the electron- and proton-induced ionization of isolated pyrimidine molecules. The impact energies range from the target ionization threshold up to ~1 keV for electrons and from 10 keV up to 10 MeV for protons. The cross-section calculations are performed within the 1st Born approximation in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered projectiles are both described by plane waves. The pyrimidine target is described using the Gaussian 09 software package. Furthermore, our theoretical predictions obtained are in good agreement with experimental absolute total cross sections, while large discrepancies are observed between existing semi-empirical models and the present calculations.

  19. Electron- and proton-induced ionization of pyrimidine

    DOE PAGES

    Champion, Christophe; Quinto, Michele; Weck, Philippe F

    2015-03-27

    This present work describes a quantum-mechanically based model of the electron- and proton-induced ionization of isolated pyrimidine molecules. The impact energies range from the target ionization threshold up to ~1 keV for electrons and from 10 keV up to 10 MeV for protons. The cross-section calculations are performed within the 1st Born approximation in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered projectiles are both described by plane waves. The pyrimidine target is described using the Gaussian 09 software package. Furthermore, our theoretical predictions obtained are in good agreement with experimental absolutemore » total cross sections, while large discrepancies are observed between existing semi-empirical models and the present calculations.« less

  20. Roots at the Percolation Threshold

    NASA Astrophysics Data System (ADS)

    Kroener, E.; Ahmed, M. A.; Kaestner, A.; Vontobel, P.; Zarebanadkouki, M.; Carminati, A.

    2014-12-01

    Much of the carbon assimilated by plants during photosynthesis is lost to the soil via rhizodepositions. One component of rhizopdeposition is mucilage, a hydrogel that dramatically alters the soil physical properties. Mucilage was assumed to explain unexpectedly low rhizosphere rewetting rates during irrigation (Carminati et al. 2010) and temporarily water repellency in the rhizosphere after severe drying (Moradi et al. 2012).Here, we present an experimental and theoretical study for the rewetting behaviour of a soil mixed with mucilage, which was used as an analogue of the rhizosphere. Our samples were made of two layers of untreated soils separated by a thin layer (ca. 1 mm) of soil treated with mucilage. We prepared soil columns of varying particle size, mucilage concentration and height of the middle layer above the water table. The dry soil columns were re-wetted by capillary rise from the bottom.The rewetting of the middle layer showed a distinct dual behavior. For mucilage concentrations lower than a certain threshold, water could cross the thin layer almost immediately after rewetting of bulk soil. At slightly higher mucilage concentrations, the thin layer was almost impermeable. The mucilage concentration at the threshold strongly depended on particle size: the smaller the particle size the larger the soil specific surface and the more mucilage was needed to cover the entire particle surface and to induce water repellency.We applied a classic pore network model to simulate the experimental observations. In the model a certain fraction of nodes were randomly disconnected to reproduce the effect of mucilage in temporarily blocking the flow. The percolation model could qualitatively reproduce well the threshold characteristics of the experiments. Our experiments, together with former observations of water dynamics in the rhizosphere, suggest that the rhizosphere is near the percolation threshold, where small variations in mucilage concentration sensitively

  1. New near-threshold mesons

    NASA Astrophysics Data System (ADS)

    Cohen, Thomas D.; Gelman, Boris A.; Nussinov, Shmuel

    2004-01-01

    We show that under a number of rather plausible assumptions QCD spectrum may contain a number of mesons which have not been predicted or observed. Such states will have the quantum numbers of two existing mesons and masses very close to the dissociation threshold into the two mesons. Moreover, at least one of the two mesonic constituents itself must be very close to its dissociation threshold. In particular, one might expect the existence of loosely bound systems of D and D∗sJ(2317); similarly, K and f0(980), K¯ and f0(980), K and a0(980) and K¯ and a0(980) can be bound. The mechanism for binding in these cases is the S-wave kaon exchange. The nearness of one of the constituents to its decay threshold into a kaon plus a remainder, implies that the range of the kaon exchange force becomes abnormally long—significantly longer than 1/mK which greatly aids the binding.

  2. Resonance ionization for analytical spectroscopy

    DOEpatents

    Hurst, George S.; Payne, Marvin G.; Wagner, Edward B.

    1976-01-01

    This invention relates to a method for the sensitive and selective analysis of an atomic or molecular component of a gas. According to this method, the desired neutral component is ionized by one or more resonance photon absorptions, and the resultant ions are measured in a sensitive counter. Numerous energy pathways are described for accomplishing the ionization including the use of one or two tunable pulsed dye lasers.

  3. Ionization oscillations in Hall accelerators

    NASA Astrophysics Data System (ADS)

    Barral, S.; Peradzyński, Z.

    2010-01-01

    The underlying mechanism of low-frequency oscillations in Hall accelerators is investigated theoretically. It is shown that relaxation oscillations arise from a competition between avalanche ionization and the advective transport of the working gas. The model derived recovers the slow progression and fast recession of the ionization front. Analytical approximations of the shape of current pulses and of the oscillation frequency are provided for the case of large amplitude oscillations.

  4. Altered Expression of Two-Pore Domain Potassium (K2P) Channels in Cancer

    PubMed Central

    Williams, Sarah; Bateman, Andrew; O'Kelly, Ita

    2013-01-01

    Potassium channels have become a focus in cancer biology as they play roles in cell behaviours associated with cancer progression, including proliferation, migration and apoptosis. Two-pore domain (K2P) potassium channels are background channels which enable the leak of potassium ions from cells. As these channels are open at rest they have a profound effect on cellular membrane potential and subsequently the electrical activity and behaviour of cells in which they are expressed. The K2P family of channels has 15 mammalian members and already 4 members of this family (K2P2.1, K2P3.1, K2P9.1, K2P5.1) have been implicated in cancer. Here we examine the expression of all 15 members of the K2P family of channels in a range of cancer types. This was achieved using the online cancer microarray database, Oncomine (www.oncomine.org). Each gene was examined across 20 cancer types, comparing mRNA expression in cancer to normal tissue. This analysis revealed all but 3 K2P family members (K2P4.1, K2P16.1, K2P18.1) show altered expression in cancer. Overexpression of K2P channels was observed in a range of cancers including breast, leukaemia and lung while more cancers (brain, colorectal, gastrointestinal, kidney, lung, melanoma, oesophageal) showed underexpression of one or more channels. K2P1.1, K2P3.1, K2P12.1, were overexpressed in a range of cancers. While K2P1.1, K2P3.1, K2P5.1, K2P6.1, K2P7.1 and K2P10.1 showed significant underexpression across the cancer types examined. This analysis supports the view that specific K2P channels may play a role in cancer biology. Their altered expression together with their ability to impact the function of other ion channels and their sensitivity to environmental stimuli (pO2, pH, glucose, stretch) makes understanding the role these channels play in cancer of key importance. PMID:24116006

  5. Altered expression of two-pore domain potassium (K2P) channels in cancer.

    PubMed

    Williams, Sarah; Bateman, Andrew; O'Kelly, Ita

    2013-01-01

    Potassium channels have become a focus in cancer biology as they play roles in cell behaviours associated with cancer progression, including proliferation, migration and apoptosis. Two-pore domain (K2P) potassium channels are background channels which enable the leak of potassium ions from cells. As these channels are open at rest they have a profound effect on cellular membrane potential and subsequently the electrical activity and behaviour of cells in which they are expressed. The K2P family of channels has 15 mammalian members and already 4 members of this family (K2P2.1, K2P3.1, K2P9.1, K2P5.1) have been implicated in cancer. Here we examine the expression of all 15 members of the K2P family of channels in a range of cancer types. This was achieved using the online cancer microarray database, Oncomine (www.oncomine.org). Each gene was examined across 20 cancer types, comparing mRNA expression in cancer to normal tissue. This analysis revealed all but 3 K2P family members (K2P4.1, K2P16.1, K2P18.1) show altered expression in cancer. Overexpression of K2P channels was observed in a range of cancers including breast, leukaemia and lung while more cancers (brain, colorectal, gastrointestinal, kidney, lung, melanoma, oesophageal) showed underexpression of one or more channels. K2P1.1, K2P3.1, K2P12.1, were overexpressed in a range of cancers. While K2P1.1, K2P3.1, K2P5.1, K2P6.1, K2P7.1 and K2P10.1 showed significant underexpression across the cancer types examined. This analysis supports the view that specific K2P channels may play a role in cancer biology. Their altered expression together with their ability to impact the function of other ion channels and their sensitivity to environmental stimuli (pO2, pH, glucose, stretch) makes understanding the role these channels play in cancer of key importance.

  6. Synchrotron threshold photoelectron photoion coincidence spectroscopy of radicals produced in a pyrolysis source: The methyl radical

    NASA Astrophysics Data System (ADS)

    Zhu, Yupeng; Wu, Xiangkun; Tang, Xiaofeng; Wen, Zuoying; Liu, Fuyi; Zhou, Xiaoguo; Zhang, Weijun

    2016-11-01

    We present here a flash pyrolysis source coupled with a threshold photoelectron photoion coincidence (TPEPICO) spectrometer and vacuum ultraviolet synchrotron radiation to investigate the spectroscopy and photochemistry of free radicals. The radicals are produced from pyrolysis in a heated silicon carbide tube, and the TPEPICO scheme provides a strategy to obtain pure spectra of the radicals without contamination from other byproducts. As a representative example, the methyl radical was studied, and its threshold photoelectron spectrum shows a series of umbrella vibrational transitions. The adiabatic ionization energy of the methyl radical was determined to be 9.84 ± 0.01 eV.

  7. Laser ionization and spectroscopy of Cu in superfluid helium nanodroplets

    PubMed Central

    Lindebner, Friedrich; Kautsch, Andreas; Koch, Markus; Ernst, Wolfgang E.

    2014-01-01

    Mass and optical spectroscopic methods are used for the analysis of copper (Cu) atoms and clusters doped to helium nanodroplets (HeN). A two-color resonant two-photon ionization scheme is applied to study the Cu 2P1/2,3/2∘←2S1/2 ground state transition. The absorption is strongly broadened for Cu atoms submerged inside helium nanodroplets and a comparison with computed literature values is provided. An observed ejection of the dopant from the droplet is triggered upon excitation, populating energetically lower states. The formation of Cun clusters up to Cu7 inside helium nanodroplets was observed by means of electron impact ionization mass spectroscopy. PMID:25844053

  8. Bedding material affects mechanical thresholds, heat thresholds and texture preference

    PubMed Central

    Moehring, Francie; O’Hara, Crystal L.; Stucky, Cheryl L.

    2015-01-01

    It has long been known that the bedding type animals are housed on can affect breeding behavior and cage environment. Yet little is known about its effects on evoked behavior responses or non-reflexive behaviors. C57BL/6 mice were housed for two weeks on one of five bedding types: Aspen Sani Chips® (standard bedding for our institute), ALPHA-Dri®, Cellu-Dri™, Pure-o’Cel™ or TEK-Fresh. Mice housed on Aspen exhibited the lowest (most sensitive) mechanical thresholds while those on TEK-Fresh exhibited 3-fold higher thresholds. While bedding type had no effect on responses to punctate or dynamic light touch stimuli, TEK-Fresh housed animals exhibited greater responsiveness in a noxious needle assay, than those housed on the other bedding types. Heat sensitivity was also affected by bedding as animals housed on Aspen exhibited the shortest (most sensitive) latencies to withdrawal whereas those housed on TEK-Fresh had the longest (least sensitive) latencies to response. Slight differences between bedding types were also seen in a moderate cold temperature preference assay. A modified tactile conditioned place preference chamber assay revealed that animals preferred TEK-Fresh to Aspen bedding. Bedding type had no effect in a non-reflexive wheel running assay. In both acute (two day) and chronic (5 week) inflammation induced by injection of Complete Freund’s Adjuvant in the hindpaw, mechanical thresholds were reduced in all groups regardless of bedding type, but TEK-Fresh and Pure-o’Cel™ groups exhibited a greater dynamic range between controls and inflamed cohorts than Aspen housed mice. PMID:26456764

  9. Photo-ionization and residual electron effects in guided streamers

    SciTech Connect

    Wu, S.; Lu, X. Liu, D.; Yang, Y.; Pan, Y.; Ostrikov, K.

    2014-10-15

    Complementary experiments and numerical modeling reveal the important role of photo-ionization in the guided streamer propagation in helium-air gas mixtures. It is shown that the minimum electron concentration ∼10{sup 8 }cm{sup −3} is required for the regular, repeated propagation of the plasma bullets, while the streamers propagate in the stochastic mode below this threshold. The stochastic-to-regular mode transition is related to the higher background electron density in front of the propagating streamers. These findings help improving control of guided streamer propagation in applications from health care to nanotechnology and improve understanding of generic pre-breakdown phenomena.

  10. Second Breakdown in the Presence of Intense Ionizing Radiation

    DTIC Science & Technology

    1974-12-20

    pulses having an amplitude Juat sufficient for melt formation , had a width of a few micrometers. Attempts were made to show the temporal and spatial...threshold of melt spot formation should appear somewhat as illustrated in Figure 17b. 1%, l 6. Temperature Measurements During Pulse Testing a...ana io.n.iix »T "■""• "•-■■—J l K_««l,^«,m ■^ The role of intense pulses of ionizing radiation pntbeis^ond breakdovra transition is investigated

  11. Zero-Net-Charge Air Ionizer

    NASA Technical Reports Server (NTRS)

    Woods, W. R., Jr.

    1985-01-01

    Instrument monitors air supplied by air ionizer and regulates ionizer to ensure net charge neutral. High-impedance electrometer and nulling control amplifier regulate output of air ionizer. Primarily intended to furnish ionized air having no net charge, instrument adaptable to generating air with positive or negative net charge is so desired. Useful where integrated circuit chips are manufactured, inspected, tested or assembled.

  12. Nuclear Recoil Cross Sections from Time-dependent Studies of Two-Photon Double Ionization of Helium

    SciTech Connect

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

    2009-12-21

    We examine the sensitivity of nuclear recoil cross sections produced by two-photon double ionization of helium to the underlying triple differential cross sections (TDCS) used in their computation. We show that this sensitivity is greatest in the energy region just below the threshold for sequential double ionization. Accurate TDCS, extracted from non-perturbative solutions of the time-dependent Schroedinger equation, are used here in new computations of the nuclear recoil cross section.

  13. HF Accelerated Electron Fluxes, Spectra, and Ionization

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert C.; Jensen, Joseph B.

    2015-10-01

    Wave particle interactions, an essential aspect of laboratory, terrestrial, and astrophysical plasmas, have been studied for decades by transmitting high power HF radio waves into Earth's weakly ionized space plasma, to use it as a laboratory without walls. Application to HF electron acceleration remains an active area of research (Gurevich in Usp Fizicheskikh Nauk 177(11):1145-1177, 2007) today. HF electron acceleration studies began when plasma line observations proved (Carlson et al. in J Atmos Terr Phys 44:1089-1100, 1982) that high power HF radio wave-excited processes accelerated electrons not to ~eV, but instead to -100 times thermal energy (10 s of eV), as a consequence of inelastic collision effects on electron transport. Gurevich et al (J Atmos Terr Phys 47:1057-1070, 1985) quantified the theory of this transport effect. Merging experiment with theory in plasma physics and aeronomy, enabled prediction (Carlson in Adv Space Res 13:1015-1024, 1993) of creating artificial ionospheres once ~GW HF effective radiated power could be achieved. Eventual confirmation of this prediction (Pedersen et al. in Geophys Res Lett 36:L18107, 2009; Pedersen et al. in Geophys Res Lett 37:L02106, 2010; Blagoveshchenskaya et al. in Ann Geophys 27:131-145, 2009) sparked renewed interest in optical inversion to estimate electron spectra in terrestrial (Hysell et al. in J Geophys Res Space Phys 119:2038-2045, 2014) and planetary (Simon et al. in Ann Geophys 29:187-195, 2011) atmospheres. Here we present our unpublished optical data, which combined with our modeling, lead to conclusions that should meaningfully improve future estimates of the spectrum of HF accelerated electron fluxes. Photometric imaging data can significantly improve detection of emissions near ionization threshold, and confirm depth of penetration of accelerated electrons many km below the excitation altitude. Comparing observed to modeled emission altitude shows future experiments need electron density profiles

  14. Relativistic calculations of the nonresonant two-photon ionization of neutral atoms

    NASA Astrophysics Data System (ADS)

    Hofbrucker, J.; Volotka, A. V.; Fritzsche, S.

    2016-12-01

    The nonresonant, two-photon, one-electron ionization of neutral atoms is studied theoretically in the framework of relativistic second-order perturbation theory and independent particle approximation. In particular, the importance of relativistic and screening effects in the total two-photon ionization cross section is investigated. Detailed computations have been carried out for the K -shell ionization of neutral Ne, Ge, Xe, and U atoms. The relativistic effects significantly decrease the total cross section; for the case of U, for example, they reduce the total cross section by a factor of two. Moreover, we have found that the account for the screening effects of the remaining electrons leads to occurrence of an unexpected minimum in the total cross section at the total photon energies equal to the ionization threshold; for the case of Ne, for example, the cross section drops there by a factor of three.

  15. Threshold for plasma phase transition of aluminum single crystal induced by hypervelocity impact

    SciTech Connect

    Ju, Yuanyuan; Zhang, Qingming

    2015-12-15

    Molecular dynamics method is used to study the threshold for plasma phase transition of aluminum single crystal induced by hypervelocity impact. Two effective simulation methods, piston-driven method and multi-scale shock technique, are used to simulate the shock wave. The simulation results from the two methods agree well with the experimental data, indicating that the shock wave velocity is linearly dependent on the particle velocity. The atom is considered to be ionized if the increase of its internal energy is larger than the first ionization energy. The critical impact velocity for plasma phase transition is about 13.0 km/s, corresponding to the threshold of pressure and temperature which is about 220 GPa and 11.0 × 10{sup 3 }K on the shock Hugoniot, respectively.

  16. Development of high damage threshold optics for petawatt-class short-pulse lasers

    SciTech Connect

    Stuart, B.C.; Perry, M.D.; Boyd, R.D.

    1995-02-22

    The authors report laser-induced damage threshold measurements on pure and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations, {tau}, ranging from 140 fs to 1 ns. Damage thresholds of gold coatings are limited to 500 mJ/cm{sup 2} in the subpicosecond range for 1053-nm pulses. In dielectrics, qualitative differences in the morphology of damage and a departure from the diffusion-dominated {tau}1/2 scaling indicate that damage results from plasma formation and ablation for {tau}{le}10 ps and from conventional melting and boiling for {tau}>50 ps. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulsewidth and wavelength scaling of experimental results.

  17. Observation of the Forbidden Magnetic Dipole Transition 6{sup 2}P{sub ½} --> 7{sup 2}P{sub ½} in Atomic Thallium

    DOE R&D Accomplishments Database

    Chu, S.

    1976-10-01

    A measurement of the 6{sup 2}P{sub ½} --> 7{sup 2}P{sub ½} forbidden magnetic dipole matrix element in atomic thallium is described. A pulsed, linearly polarized dye laser tuned to the transition frequency is used to excite the thallium vapor from the 6{sup 2}P{sub ½} ground state to the 7{sup 2}P{sub ½} excited state. Interference between the magnetic dipole M1 amplitude and a static electric field induced E1 amplitude results in an atomic polarization of the 7{sup 2}P{sub ½} state, and the subsequent circular polarization of 535 nm fluorescence. The circular polarization is seen to be proportional to / as expected, and measured for several transitions between hyperfine levels of the 6{sup 2}P{sub ½} and 7{sup 2}P{sub ½} states. The result is = -(2.11 +- 0.30) x 10{sup -5} parallel bar e parallel bar dirac constant/2mc, in agreement with theory.

  18. Androstadienone odor thresholds in adolescents.

    PubMed

    Hummel, Thomas; Krone, Franziska; Lundström, Johan N; Bartsch, Oliver

    2005-03-01

    A sex-related difference in olfactory sensitivity to androstenone has been reported to occur during adolescence. More males than females exhibited anosmia to androstenone, or an increase in androstenone threshold with age. The current study addressed the question whether similar, sexually dimorphic effects of aging over puberty can also be found for androstadienone. A total of 102 subjects participated (36 females, 66 males). Similar to previous investigations, subjects were divided into a group of 47 individuals with a mean age of 13.3 years, defined as pre/peri-pubertal, and a group of 55 subjects with a mean age of 17.1 years, defined as post-pubertal. All subjects underwent tests for verbal abilities, general olfactory function, and measurements of androstadienone thresholds. The study provided the following major results: (1) Male subjects exhibited higher androstadienone sensitivity in the pre/peri-pubertal group as compared to the post-pubertal group. This difference was not observed in female subjects. Correspondingly, a negative correlation between age and androstadienone sensitivity was found for male subjects, but not for female subjects. (2) In contrast to this sex-specific change of the androstadienone odor threshold, verbal skills and odor identification abilities increased with age in all subjects regardless of their sex. In conclusion, the present observations confirm previous research on sex-differentiated effects of aging during puberty on sensitivity towards odorous steroids. While the underlying causes are unknown, it may be hypothesized that the decreased sensitivity could result from the increased endogenous levels of androstadienone in male subjects. Future studies should include both steroid and non-steroid odorants to further explore these age-related changes.

  19. Thresholds for impaired species recovery

    PubMed Central

    Hutchings, Jeffrey A.

    2015-01-01

    Studies on small and declining populations dominate research in conservation biology. This emphasis reflects two overarching frameworks: the small-population paradigm focuses on correlates of increased extinction probability; the declining-population paradigm directs attention to the causes and consequences of depletion. Neither, however, particularly informs research on the determinants, rate or uncertainty of population increase. By contrast, Allee effects (positive associations between population size and realized per capita population growth rate, rrealized, a metric of average individual fitness) offer a theoretical and empirical basis for identifying numerical and temporal thresholds at which recovery is unlikely or uncertain. Following a critique of studies on Allee effects, I quantify population-size minima and subsequent trajectories of marine fishes that have and have not recovered following threat mitigation. The data suggest that threat amelioration, albeit necessary, can be insufficient to effect recovery for populations depleted to less than 10% of maximum abundance (Nmax), especially when they remain depleted for lengthy periods of time. Comparing terrestrial and aquatic vertebrates, life-history analyses suggest that population-size thresholds for impaired recovery are likely to be comparatively low for marine fishes but high for marine mammals. Articulation of a ‘recovering population paradigm’ would seem warranted. It might stimulate concerted efforts to identify generic impaired recovery thresholds across species. It might also serve to reduce the confusion of terminology, and the conflation of causes and consequences with patterns currently evident in the literature on Allee effects, thus strengthening communication among researchers and enhancing the practical utility of recovery-oriented research to conservation practitioners and resource managers. PMID:26213739

  20. New superhindered polydentate polyphosphine ligands P(CH2CH2P(t)Bu2)3, PhP(CH2CH2P(t)Bu2)2, P(CH2CH2CH2P(t)Bu2)3, and their ruthenium(II) chloride complexes.

    PubMed

    Gilbert-Wilson, Ryan; Field, Leslie D; Bhadbhade, Mohan M

    2012-03-05

    The synthesis and characterization of the extremely hindered phosphine ligands, P(CH(2)CH(2)P(t)Bu(2))(3) (P(2)P(3)(tBu), 1), PhP(CH(2)CH(2)P(t)Bu(2))(2) (PhP(2)P(2)(tBu), 2), and P(CH(2)CH(2)CH(2)P(t)Bu(2))(3) (P(3)P(3)(tBu), 3) are reported, along with the synthesis and characterization of ruthenium chloro complexes RuCl(2)(P(2)P(3)(tBu)) (4), RuCl(2)(PhP(2)P(2)(tBu)) (5), and RuCl(2)(P(3)P(3)(tBu)) (6). The bulky P(2)P(3)(tBu) (1) and P(3)P(3)(tBu) (3) ligands are the most sterically encumbered PP(3)-type ligands so far synthesized, and in all cases, only three phosphorus donors are able to bind to the metal center. Complexes RuCl(2)(PhP(2)P(2)(tBu)) (5) and RuCl(2)(P(3)P(3)(tBu)) (6) were characterized by crystallography. Low temperature solution and solid state (31)P{(1)H} NMR were used to demonstrate that the structure of RuCl(2)(P(2)P(3)(tBu)) (4) is probably analogous to that of RuCl(2)(PhP(2)P(2)(tBu)) (5) which had been structurally characterized.

  1. The final stages of spliceosome maturation require Spp2p that can interact with the DEAH box protein Prp2p and promote step 1 of splicing.

    PubMed Central

    Roy, J; Kim, K; Maddock, J R; Anthony, J G; Woolford, J L

    1995-01-01

    Pre-mRNA processing occurs by assembly of splicing factors on the substrate to form the spliceosome followed by two consecutive RNA cleavage-ligation reactions. The Prp2 protein hydrolyzes ATP and is required for the first reaction (Yean SL, Lin RJ, 1991, Mol Cell Biol 11:5571-5577; Kim SH, Smith J, Claude A, Lin RJ, 1992, EMBO J 11:2319-2326). The Saccharomyces cerevisiae SPP2 gene was previously identified as a high-copy suppressor of temperature-sensitive prp2 mutants (Last RL, Maddock JR, Woolford JL Jr, 1987, Genetics 117:619-631). We have characterized the function of Spp2p in vivo and in vitro. Spp2p is an essential protein required for the first RNA cleavage reaction in vivo. Depletion of Spp2p from yeast cells results in accumulation of unspliced pre-mRNAs. A temperature-sensitive spp2-1 mutant accumulates pre-mRNAs in vivo and is unable to undergo the first splicing reaction in vitro. However, spliceosomal complexes are assembled in extracts prepared from the mutant. We show that Spp2p function is required after spliceosome assembly but prior to the first reaction. Spp2p associates with the spliceosome before the first RNA cleavage reaction and is likely to be released from the spliceosome following ATP hydrolysis by Prp2p. The Prp2 and Spp2 proteins are capable of physically interacting with each other. These results suggest that Spp2p interacts with Prp2p in the spliceosome prior to the first cleavage-ligation reaction. Spp2p is the first protein that has been found to interact with a DEAD/H box splicing factor. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 9 PMID:7493316

  2. Ultra-low threshold polariton condensation

    NASA Astrophysics Data System (ADS)

    Steger, Mark; Fluegel, Brian; Alberi, Kirstin; Snoke, David W.; Pfeiffer, Loren N.; West, Ken; Mascarenhas, Angelo

    2017-03-01

    We demonstrate condensation of microcavity polaritons with a very sharp threshold occuring at two orders of magnitude lower pump intensity than previous demonstrations of condensation. The long cavity-lifetime and trapping and pumping geometries are crucial to the realization of this low threshold. Polariton condensation, or "polariton lasing" has long been proposed as a promising source of coherent light at lower threshold than traditional lasing, and these results suggest methods to bring this threshold even lower.

  3. Ultra-low threshold polariton condensation.

    PubMed

    Steger, Mark; Fluegel, Brian; Alberi, Kirstin; Snoke, David W; Pfeiffer, Loren N; West, Ken; Mascarenhas, Angelo

    2017-03-15

    We demonstrate the condensation of microcavity polaritons with a very sharp threshold occurring at a two orders of magnitude pump intensity lower than previous demonstrations of condensation. The long cavity lifetime and trapping and pumping geometries are crucial to the realization of this low threshold. Polariton condensation, or "polariton lasing" has long been proposed as a promising source of coherent light at a lower threshold than traditional lasing, and these results indicate some considerations for optimizing designs for lower thresholds.

  4. Forbidden line emission from highly ionized atoms in tokamak plasmas

    NASA Technical Reports Server (NTRS)

    Feldman, U.; Doschek, G. A.; Bhatia, A. K.

    1982-01-01

    Considerable interest in the observation of forbidden spectral lines from highly ionized atoms in tokamak plasmas is related to the significance of such observations for plasma diagnostic applications. Atomic data for the elements Ti Cr, Mn, Fe, Ni, and Kr have been published by Feldman et al. (1980) and Bhatia et al. (1980). The present investigation is concerned with collisional excitation rate coefficients and radiative decay rates, which are interpolated for ions of elements between calcium, and krypton and for levels of the 2s2 2pk, 2s 2p(k+1), and 2p(k+2) configurations, and for the O I, N I, C I, B I, and Be I isoelectronic sequences. The provided interpolated atomic data can be employed to calculate level populations and relative line intensities for ions of the considered sequences, taking into account levels of the stated configurations. Important plasma diagnostic information provided by the forbidden lines includes the ion temperature

  5. Calculation of Collisional Cross Sections for the 2P3/2 - 2P1/2 Transition in Alkali-Noble Gas Systems

    DTIC Science & Technology

    2010-03-01

    collisional cross sections given input potentials of a system may provide a partial answer to this question in systems where collisions play a major...CALCULATION OF COLLISIONAL CROSS SECTIONS FOR THE 2P3/2 → 2P1/2 TRANSITION IN ALKALI-NOBLE GAS SYSTEMS THESIS Sam Butler, Captain, USAF AFIT/GAP/ENP...States Air Force, Department of Defense, or the United States Government. AFIT/GAP/ENP/10-M04 CALCULATION OF COLLISIONAL CROSS SECTIONS FOR THE 2P3/2

  6. Parabolic versus spherical partial cross sections for photoionization excitation of He near threshold

    SciTech Connect

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

    2006-09-15

    Spherical and parabolic partial cross sections and asymmetry parameters, defined in the ejected electron frame, are presented for photoionization excitation of the helium atom at 0.1 eV above its double ionization threshold. A quantitative law giving the dominant spherical partial wave l{sub dom} for each excitation level n is obtained. The parabolic partial cross sections are shown to satisfy the same approximate selection rules as the related Rydberg series of doubly excited states (K,T){sub n}{sup A}. The analysis of radial and angular correlations reveals the close relationship between double excitation, ionization excitation, and double ionization. Opposite to a widespread belief, the observed value of the asymmetry parameter is shown to result from the interplay of radial correlations and symmetry constraints, irrespective of angular correlations. Finally, the measurement of parabolic partial cross sections is proposed as a challenge to experimentalists.

  7. Quasimolecular electron promotion beyond the 1 s σ and 2 p π channels in slow collisions of H e2 + and He

    NASA Astrophysics Data System (ADS)

    Schmidt, L. Ph. H.; Schöffler, M.; Goihl, C.; Jahnke, T.; Schmidt-Böcking, H.; Dörner, R.

    2016-11-01

    The electron emission pattern of transfer ionization in collisions of H e2 + with He was investigated for impact velocities between 0.53 a.u. and 0.77 a.u. (7 keV/u-15 keV/u) employing recoil-ion momentum spectroscopy. This process is known to be dominated by the promotion of the 2 p π quasimolecular orbital into the continuum which results in banana-shaped areas of high electron momentum densities in the collision plane extending from the target to the projectile in velocity space. Asymmetries are explained by a coherent superposition of the 1 s σ channel of quasimolecular promotion with the 2 p π channel. Here we report on additional contributions from channels of higher angular momentum which emerge at the smaller impact velocities. They show up as highly structured electron emission patterns in the plane perpendicular to the direction of impact.

  8. Compositional threshold for Nuclear Waste Glass Durability

    SciTech Connect

    Kruger, Albert A.; Farooqi, Rahmatullah; Hrma, Pavel R.

    2013-04-24

    Within the composition space of glasses, a distinct threshold appears to exist that separates "good" glasses, i.e., those which are sufficiently durable, from "bad" glasses of a low durability. The objective of our research is to clarify the origin of this threshold by exploring the relationship between glass composition, glass structure and chemical durability around the threshold region.

  9. Threshold Concepts in Finance: Student Perspectives

    ERIC Educational Resources Information Center

    Hoadley, Susan; Kyng, Tim; Tickle, Leonie; Wood, Leigh N.

    2015-01-01

    Finance threshold concepts are the essential conceptual knowledge that underpin well-developed financial capabilities and are central to the mastery of finance. In this paper we investigate threshold concepts in finance from the point of view of students, by establishing the extent to which students are aware of threshold concepts identified by…

  10. RAYLEIGH-TAYLOR INSTABILITY IN PARTIALLY IONIZED COMPRESSIBLE PLASMAS

    SciTech Connect

    Diaz, A. J.; Ballester, J. L. E-mail: roberto.soler@wis.kuleuven.be

    2012-07-20

    We study the modification of the classical criterion for the linear onset and growing rate of the Rayleigh-Taylor instability (RTI) in a partially ionized plasma in the two-fluid description. The plasma is composed of a neutral fluid and an electron-ion fluid, coupled by means of particle collisions. The governing linear equations and appropriate boundary conditions, including gravitational terms, are derived and applied to the case of the RTI in a single interface between two partially ionized plasmas. The limits of collisionless, no gravity, and incompressible fluids are checked before addressing the general case. We find that both compressibility and ion-neutral collisions lower the linear growth rate, but do not affect the critical threshold of the onset of the RTI. The configuration is always unstable when a lighter plasma is below a heavier plasma regardless the value of the magnetic field strength, the ionization degree, and the ion-neutral collision frequency. However, ion-neutral collisions have a strong impact on the RTI growth rate, which can be decreased by an order of magnitude compared to the value in the collisionless case. Ion-neutral collisions are necessary to accurately describe the evolution of the RTI in partially ionized plasmas such as prominences. The timescale for the development of the instability is much longer than in the classical incompressible fully ionized case. This result may explain the existence of prominence fine structures with life times of the order of 30 minutes. The timescales derived from the classical theory are about one order of magnitude shorter and incompatible with the observed life times.

  11. X(3872), IG(JPC) = 0+(1++), as the χc1(2P) charmonium

    NASA Astrophysics Data System (ADS)

    Achasov, N. N.; Rogozina, E. V.

    2015-09-01

    Contrary to almost standard opinion that the X(3872) resonance is the D∗0D¯0 + c.c. molecule or the qcq¯c¯ four-quark state, we discuss the scenario where the X(3872) resonance is the cc¯ = χc1(2P) charmonium which “sits on” the D∗0D¯0 threshold. We explain the shift of the mass of the X(3872) resonance with respect to the prediction of a potential model for the mass of the χc1(2P) charmonium by the contribution of the virtual D∗D¯ + c.c. intermediate states into the self energy of the X(3872) resonance. This allows us to estimate the coupling constant of the X(7872) resonance with the D∗0D¯0 channel, the branching ratio of the X(3872) → D∗0D¯0 + c.c. decay, and the branching ratio of the X(3872) decay into all non-D∗0D¯0 + c.c. states. We predict a significant number of unknown decays of X(3872) via two gluon: X(3872) →gluon gluon →hadrons. We suggest a physically clear program of experimental researches for verification of our assumption.

  12. Single ionization of molecular iodine

    NASA Astrophysics Data System (ADS)

    Smith, Dale L.; Tagliamonti, Vincent; Dragan, James; Gibson, George N.

    2017-01-01

    We performed a study of the single ionization of iodine, I2 over a range of wavelengths. Single ionization of I2 is unexpectedly found to have a contribution from inner molecular orbitals involving the 5 s electrons. The I+I+ dissociation channel was recorded through velocity map imaging, and the kinetic-energy release of each channel was determined with two-dimensional fitting of the images. Most of the measured kinetic-energy data were inconsistent with ionization to the X , A , and B states of I2 + , implying ionization from deeper orbitals. A pump-probe Fourier transform technique was used to look for modulation at the X - and A -state vibrational frequencies to see if they were intermediate states in a two-step process. X - and A -state modulation was seen only for kinetic-energy releases below 0.2 eV, consistent with dissociation through the B state. From these results and intensity-, polarization-, and wavelength-dependent experiments we found no evidence of bond softening, electron rescattering, or photon mediation through the X or A states to higher-energy single-ionization channels.

  13. Ionization energies of aqueous nucleic acids: photoelectron spectroscopy of pyrimidine nucleosides and ab initio calculations.

    PubMed

    Slavícek, Petr; Winter, Bernd; Faubel, Manfred; Bradforth, Stephen E; Jungwirth, Pavel

    2009-05-13

    Vertical ionization energies of the nucleosides cytidine and deoxythymidine in water, the lowest ones amounting in both cases to 8.3 eV, are obtained from photoelectron spectroscopy measurements in aqueous microjets. Ab initio calculations employing a nonequilibrium polarizable continuum model quantitatively reproduce the experimental spectra and provide molecular interpretation of the individual peaks of the photoelectron spectrum, showing also that lowest ionization originates from the base. Comparison of calculated vertical ionization potentials of pyrimidine bases, nucleosides, and nucleotides in water and in the gas phase underlines the dramatic effect of bulk hydration on the electronic structure. In the gas phase, the presence of sugar and, in particular, of phosphate has a strong effect on the energetics of ionization of the base. Upon bulk hydration, the ionization potential of the base in contrast becomes rather insensitive to the presence of the sugar and phosphate, which indicates a remarkable screening ability of the aqueous solvent. Accurate aqueous-phase vertical ionization potentials provide a significant improvement to the corrected gas-phase values used in the literature and represent important information in assessing the threshold energies for photooxidation and oxidation free energies of solvent-exposed DNA components. Likewise, such energetic data should allow improved assessment of delocalization and charge-hopping mechanisms in DNA ionized by radiation.

  14. STORAGE RING CROSS-SECTION MEASUREMENTS FOR ELECTRON IMPACT SINGLE AND DOUBLE IONIZATION OF Fe{sup 9+} AND SINGLE IONIZATION OF Fe{sup 10+}

    SciTech Connect

    Hahn, M.; Novotny, O.; Savin, D. W.; Becker, A.; Grieser, M.; Krantz, C.; Wolf, A.; Lestinsky, M.; Repnow, R.; Mueller, A.; Schippers, S.; Spruck, K.

    2012-11-20

    We have measured electron impact ionization from the ground state of Fe{sup 9+} and Fe{sup 10+} over the relative electron-ion collision energy ranges 200-1900 eV and 250-1800 eV, respectively. The ions were confined in an ion storage ring long enough for essentially all metastable levels to radiatively relax to the ground state. For single ionization, we find a number of discrepancies between the existing theoretical cross sections and our results. The calculations appear to neglect some excitation-autoionization (EA) channels, particularly from n = 3 to n' excitations, which are important near threshold, and those from n = 2 {yields} 3 excitations, which contribute at about 650 eV. Conversely, at higher energies the calculations appear to overestimate the importance of EA channels due to excitation into levels where n {>=} 4. The resulting experimental rate coefficients agree with the most recent theory for Fe{sup 9+} to within 16% and for Fe{sup 10+} to within 19% at temperatures where these ions are predicted to form in collisional ionization equilibrium. We have also measured double ionization of Fe{sup 9+} forming Fe{sup 11+} in the energy range 450-3000 eV and found that although there is an appreciable cross section for direct double ionization, the dominant mechanism appears to be through direct ionization of an inner shell electron producing an excited state that subsequently stabilizes through autoionization.

  15. A Novel P2P traffic Prediction Algorithm Based on Hybrid Model

    NASA Astrophysics Data System (ADS)

    Zhi-jie, Han; Ru-chuan, Wang; Xiao-yang, Duan

    The increasing P2P network traffic on the Internet has leaded to the problem of network congestion. In the consequence of the diversification of the P2P traffic and protocol, research on the management of P2P traffic has had many problems needed to resolve. P2P traffic Prediction is kernel problem in the P2P traffic management. Based on the P2P traffic characters, this thesis present a P2P traffic model, gived a traffic prediction algorithm bases on wavelet-analysis, and proved the accuracy of the algorithm. Simulation has experiment figures that the algorithm a high prediction precision and superior real-time performance.

  16. Positron-impact ionization, positronium formation, and electronic excitation cross sections for diatomic molecules

    SciTech Connect

    Marler, J. P.; Surko, C. M.

    2005-12-15

    Absolute measurements are presented for the positron-impact cross sections for positronium formation, direct ionization, and total ionization of the diatomic molecules N{sub 2}, CO, and O{sub 2}, in the range of energies from threshold to 90 eV. Cross sections for the electronic excitation of the a {sup 1}{pi} and a{sup '} {sup 1}{sigma} state in N{sub 2} and the A {sup 1}{pi} state in CO near threshold are also presented. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. In O{sub 2}, a feature previously seen in the total ionization cross section is observed in both the positronium formation and total ionization cross sections. The possible origin of this feature and its relationship to positron-induced dissociation is discussed. In N{sub 2}, the near-threshold electronic excitation cross section is larger than that for positronium formation. This likely explains the relatively high efficiency of this molecule when used for buffer-gas positron trapping.

  17. Threshold temperature optical fibre sensors

    NASA Astrophysics Data System (ADS)

    Stasiewicz, K. A.; Musial, J. E.

    2016-12-01

    This paper presents a new approach to manufacture a threshold temperature sensor based on a biconical optical fibre taper. The presented sensor employs the influence of variable state of concentration of some isotropic materials like wax or paraffin. Application of the above- mentioned materials is an attempt to prove that there is a possibility to obtain a low-cost, repeatable and smart sensor working as an in-line element. Optical fibre taper was obtained from a standard single mode fibre (SMF28®) by using a low pressure gas burner technique. The diameter of the manufactured tapers was 6.0 ± 0.5 μm with the length of elongation equal to 30.50 ± 0.16 mm. The applied technology allowed to produce tapers with the losses of 0.183 ± 0.015 dB. Application of materials with different temperature transition points made it possible to obtain the threshold work at the temperatures connected directly with their conversion temperature. External materials at the temperatures above their melting points do not influence the propagation losses. For each of them two types of the protection area and position of the optical fibre taper were applied.

  18. Computational gestalts and perception thresholds.

    PubMed

    Desolneux, Agnès; Moisan, Lionel; Morel, Jean-Michel

    2003-01-01

    In 1923, Max Wertheimer proposed a research programme and method in visual perception. He conjectured the existence of a small set of geometric grouping laws governing the perceptual synthesis of phenomenal objects, or "gestalt" from the atomic retina input. In this paper, we review this set of geometric grouping laws, using the works of Metzger, Kanizsa and their schools. In continuation, we explain why the Gestalt theory research programme can be translated into a Computer Vision programme. This translation is not straightforward, since Gestalt theory never addressed two fundamental matters: image sampling and image information measurements. Using these advances, we shall show that gestalt grouping laws can be translated into quantitative laws allowing the automatic computation of gestalts in digital images. From the psychophysical viewpoint, a main issue is raised: the computer vision gestalt detection methods deliver predictable perception thresholds. Thus, we are set in a position where we can build artificial images and check whether some kind of agreement can be found between the computationally predicted thresholds and the psychophysical ones. We describe and discuss two preliminary sets of experiments, where we compared the gestalt detection performance of several subjects with the predictable detection curve. In our opinion, the results of this experimental comparison support the idea of a much more systematic interaction between computational predictions in Computer Vision and psychophysical experiments.

  19. Threshold-avoiding proteomics pipeline.

    PubMed

    Suits, Frank; Hoekman, Berend; Rosenling, Therese; Bischoff, Rainer; Horvatovich, Peter

    2011-10-15

    We present a new proteomics analysis pipeline focused on maximizing the dynamic range of detected molecules in liquid chromatography-mass spectrometry (LC-MS) data and accurately quantifying low-abundance peaks to identify those with biological relevance. Although there has been much work to improve the quality of data derived from LC-MS instruments, the goal of this study was to extend the dynamic range of analyzed compounds by making full use of the information available within each data set and across multiple related chromatograms in an experiment. Our aim was to distinguish low-abundance signal peaks from noise by noting their coherent behavior across multiple data sets, and central to this is the need to delay the culling of noise peaks until the final peak-matching stage of the pipeline, when peaks from a single sample appear in the context of all others. The application of thresholds that might discard signal peaks early is thereby avoided, hence the name TAPP: threshold-avoiding proteomics pipeline. TAPP focuses on quantitative low-level processing of raw LC-MS data and includes novel preprocessing, peak detection, time alignment, and cluster-based matching. We demonstrate the performance of TAPP on biologically relevant sample data consisting of porcine cerebrospinal fluid spiked over a wide range of concentrations with horse heart cytochrome c.

  20. Ensemble Monte Carlo calculation of the hole initiated impact ionization rate in bulk GaAs and silicon using a k-dependent, numerical transition rate formulation

    NASA Technical Reports Server (NTRS)

    Oguzman, Ismail H.; Wang, Yang; Kolnik, Jan; Brennan, Kevin F.

    1995-01-01

    The hole initiated impact ionization rate in bulk silicon and GaAs is calculated using a numerical formulation of the impact ionization transition rate incorporated into an ensemble Monte Carlo simulation. The transition rate is calculated from Fermi's golden rule using a two-body screened Coulomb interaction including a wavevector dependent dielectric function. It is found that the effective threshold for hole initiated ionization is relatively soft in both materials, that the split-off band dominates the ionization process in GaAs. and that no clear dominance by any one band is observed in silicon, though the rate out of the light hole band is greatest.

  1. Investigation of the threshold intensity versus gas pressure in the breakdown of helium by 248 nm laser radiation

    NASA Astrophysics Data System (ADS)

    Gamal, Yosr E. E.-D.; Abdellatif, Galila

    2014-10-01

    An investigation of the unexpectedly strong dependence of the threshold intensity on the gas pressure in the experimental study on the breakdown of He by short laser wavelength (Turcu et al., in Opt Commun, 134:66-68, 1997) is presented. A modified electron cascade model is applied (Evans and Gamal, in J Phys D Appl Phys, 13:1447-1458, 1980). Computations revealed reasonable agreement between the calculated thresholds and the measured ones. Moreover, the calculated electron energy distribution function and its parameters proved that multiphoton ionization of ground and excited atoms is the main source for the seed electrons, which contributes to the breakdown of helium. The effect of diffusion losses over pressures <1,000 Torr elucidated the origin of the strong dependence of the threshold intensity on the gas pressure. Collisional ionization dominates only at high pressures. No evidence for recombination losses is observed for pressures up to 3,000 Torr.

  2. N-glycosylation-dependent control of functional expression of background potassium channels K2P3.1 and K2P9.1.

    PubMed

    Mant, Alexandra; Williams, Sarah; Roncoroni, Laura; Lowry, Eleanor; Johnson, Daniel; O'Kelly, Ita

    2013-02-01

    Two-pore domain potassium (K(2P)) channels play fundamental roles in cellular processes by enabling a constitutive leak of potassium from cells in which they are expressed, thus influencing cellular membrane potential and activity. Hence, regulation of these channels is of critical importance to cellular function. A key regulatory mechanism of K(2P) channels is the control of their cell surface expression. Membrane protein delivery to and retrieval from the cell surface is controlled by their passage through the secretory and endocytic pathways, and post-translational modifications regulate their progression through these pathways. All but one of the K(2P) channels possess consensus N-linked glycosylation sites, and here we demonstrate that the conserved putative N-glycosylation site in K(2P)3.1 and K(2P)9.1 is a glycan acceptor site. Patch clamp analysis revealed that disruption of channel glycosylation reduced K(2P)3.1 current, and flow cytometry was instrumental in attributing this to a decreased number of channels on the cell surface. Similar findings were observed when cells were cultured in reduced glucose concentrations. Disruption of N-linked glycosylation has less of an effect on K(2P)9.1, with a small reduction in number of channels on the surface observed, but no functional implications detected. Because nonglycosylated channels appear to pass through the secretory pathway in a manner comparable with glycosylated channels, the evidence presented here suggests that the decreased number of nonglycosylated K(2P)3.1 channels on the cell surface may be due to their decreased stability.

  3. N-Glycosylation-dependent Control of Functional Expression of Background Potassium Channels K2P3.1 and K2P9.1*

    PubMed Central

    Mant, Alexandra; Williams, Sarah; Roncoroni, Laura; Lowry, Eleanor; Johnson, Daniel; O'Kelly, Ita

    2013-01-01

    Two-pore domain potassium (K2P) channels play fundamental roles in cellular processes by enabling a constitutive leak of potassium from cells in which they are expressed, thus influencing cellular membrane potential and activity. Hence, regulation of these channels is of critical importance to cellular function. A key regulatory mechanism of K2P channels is the control of their cell surface expression. Membrane protein delivery to and retrieval from the cell surface is controlled by their passage through the secretory and endocytic pathways, and post-translational modifications regulate their progression through these pathways. All but one of the K2P channels possess consensus N-linked glycosylation sites, and here we demonstrate that the conserved putative N-glycosylation site in K2P3.1 and K2P9.1 is a glycan acceptor site. Patch clamp analysis revealed that disruption of channel glycosylation reduced K2P3.1 current, and flow cytometry was instrumental in attributing this to a decreased number of channels on the cell surface. Similar findings were observed when cells were cultured in reduced glucose concentrations. Disruption of N-linked glycosylation has less of an effect on K2P9.1, with a small reduction in number of channels on the surface observed, but no functional implications detected. Because nonglycosylated channels appear to pass through the secretory pathway in a manner comparable with glycosylated channels, the evidence presented here suggests that the decreased number of nonglycosylated K2P3.1 channels on the cell surface may be due to their decreased stability. PMID:23250752

  4. Charge segregation in weakly ionized microgels

    NASA Astrophysics Data System (ADS)

    Hyatt, John S.; Douglas, Alison M.; Stanley, Chris; Do, Changwoo; Barker, Thomas H.; Fernández-Nieves, Alberto

    2017-01-01

    We investigate microgels synthesized from N -isopropylacrylamide (NIPAM) copolymerized with a large mol% of acrylic acid, finding that when the acid groups are partially ionized at high temperatures, competition between ion-induced swelling and hydrophobic deswelling of poly(NIPAM) chains results in microphase separation. In cross-linked microgels, this manifests as a dramatic decrease in the ratio between the radius of gyration and the hydrodynamic radius to ˜0.2 , indicating that almost all the mass of the microgel is concentrated near the particle center. We also observe a concurrent decrease of the polymer network length scale via small-angle neutron scattering, confirming the presence of a dense, deswollen core surrounded by a diffuse, charged periphery. We compare these results to those obtained for a system of charged ultralow-cross-linked microgels; the form factor shows a distinct peak at high q when the temperature exceeds a threshold value. We successfully fit the form factor to theory developed to describe scattering from weakly charged gels in poor solvents, and we tie this behavior to charge segregation in the case of the cross-linked microgels.

  5. Ionizing radiation effects on silicon test structures

    SciTech Connect

    Kraner, H.W.; Beuttenmuller, R.; Chen, W.; Kierstead, J.A.; Li, Z.; Zhang, Y.; Dou, L.; Fretwurst, E.; Lindstroem, G.

    1993-12-01

    The effects of {sup 60}Co gamma irradiation on MOSCAPS and special junction diode detectors have been studied. The capacitors were used to ellicit the charge accumulation and anneal in two types of thermally grown oxides representative of those used in routine detector processing. Ion implanted, oxide passivated junction detectors having 0.25 and 1 cm{sup 2} areas and perimeter to area ratios of 1 (a square), 2 and 5 were designed and constructed to amplify the ionizing effects expected to largely affect junction edges through changes in fixed oxide charges. Detectors were exposed to over 4 Mrad and showed clear increases in leakage current in proportion to the junction edge length. Annealing schedules were determined to provide a continuous response to incremental irradiations and subsequent room temperature anneals of leakage current. Besides an increase in gate threshold, little effect on the C(V) response was found. PISCES simulation of the edge fields using different fixed oxide charge revealed regions of very high lateral fields near the junction edges for fixed charges in the 2 {times} 10{sup 12}/cm{sup 2} range expected from the capacitor studies which could be responsible for the observed leakage currents.

  6. Threshold phenomena in soft matter

    NASA Astrophysics Data System (ADS)

    Huang, Zhibin

    Although two different fields are covered, this thesis is mainly focused on some threshold behaviors in both liquid crystal field and fluid dynamic systems. A method of rubbed polyimide is used to obtain pretilt. Sufficiently strong rubbing of a polyimide (SE-1211) results in a large polar pretilt of liquid crystal director with respect to the homeotropic orientation. There exists a threshold rubbing strength required to induce nonzero pretilt. For the homologous liquid crystal series alkyl-cyanobyphenyl, we found that the threshold rubbing strength is a monotonic function of the number of methylene units. A dual easy axis model is then used to explain the results. Freedericksz transition measurements have been used to determine the quadratical and quartic coefficients associated with the molecules' tilt with respect to the layer normal in surface-induced smectic layers in the nematic phase above the smectic-A-nematic phase transition temperature. Both the quadratic and quartic coefficients are consistent with the scaling relationship as predicted in theory, and their ratio is approximately constant. A Rayleigh-Taylor instability experiment is performed by using a magnetic field gradient to draw down a low density but highly paramagnetic fluid below a more dense fluid in a Hele-Shaw cell. When turning off the magnetic field, the RT instability occurs in situ and the growth of the most unstable wavevector is measured as a function of time. The wavelength of the RT instability along with the growth rate was measured as a function of capillary number (which is related to the density difference and interfacial tension between two fluids). A theory for the instability that permits different viscosities for two immiscible fluids was developed, and good agreement was found with the experimental results. The technique of magnetic levitation promises to broaden significantly the accessible parameter space of gravitational interfacial instability experiments. A method is

  7. Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols

    SciTech Connect

    Koh, Christine J.; Liu, Chen-Lin; Harmon, Christopher W.; Strasser, Daniel; Golan, Amir; Kostko, Oleg; Chambreau, Steven D.; Vaghjiani, Ghanshyam L.; Leone, Stephen R.

    2011-04-20

    Isolated ion pairs of a conventional ionic liquid, 1-Ethyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide ([Emim+][Tf2N–]), and a reactive hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Dicyanamide ([Bmim+][Dca–]), are generated by vaporizing ionic liquid submicrometer aerosol particles for the first time; the vaporized species are investigated by dissociative ionization with tunable vacuum ultraviolet (VUV) light, exhibiting clear intact cations, Emim+ and Bmim+, presumably originating from intact ion pairs. Mass spectra of ion pair vapor from an effusive source of the hypergolic ionic liquid show substantial reactive decomposition due to the internal energy of the molecules emanating from the source. Also, hotoionization efficiency curves in the near threshold ionization region of isolated ion pairs of [Emim+][Tf2N] ionic liquid vapor are compared for an aerosol source and an effusive source, revealing changes in the appearance energy due to the amount of internal energy in the ion pairs. The aerosol source has a shift to higher threshold energy (~0.3 eV), attributed to reduced internal energy of the isolated ion pairs. Lastly, the method of ionic liquid submicrometer aerosol particle vaporization, for reactive ionic liquids such as hypergolic species, is a convenient, thermally “cooler” source of isolated intact ion pairs in the gas phase compared to effusive sources.

  8. Soft ionization of thermally evaporated hypergolic ionic liquid aerosols

    SciTech Connect

    University of California; ERC, Incorporated, Edwards Air Force Base; Air Force Research Laboratory, Edwards Air Force Base; National Synchrotron Radiation Research Center; Institute of Chemistry, Hebrew University; Koh, Christine J.; Liu, Chen-Lin; Harmon, Christopher W.; Strasser, Daniel; Golan, Amir; Kostko, Oleg; Chambreau, Steven D.; Vaghjiani, Ghanshyam L.; Leone, Stephen R.

    2011-07-19

    Isolated ion pairs of a conventional ionic liquid, 1-Ethyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide ([Emim+][Tf2N?]), and a reactive hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Dicyanamide ([Bmim+][Dca?]), are generated by vaporizing ionic liquid submicron aerosol particles for the first time; the vaporized species are investigated by dissociative ionization with tunable vacuum ultraviolet (VUV) light, exhibiting clear intact cations, Emim+ and Bmim+, presumably originating from intact ion pairs. Mass spectra of ion pair vapor from an effusive source of the hypergolic ionic liquid show substantial reactive decomposition due to the internal energy of the molecules emanating from the source. Photoionization efficiency curves in the near threshold ionization region of isolated ion pairs of [Emim+][Tf2N?]ionic liquid vapor are compared for an aerosol source and an effusive source, revealing changes in the appearance energy due to the amount of internal energy in the ion pairs. The aerosol source has a shift to higher threshold energy (~;;0.3 eV), attributed to reduced internal energy of the isolated ion pairs. The method of ionic liquid submicron aerosol particle vaporization, for reactive ionic liquids such as hypergolic species, is a convenient, thermally ?cooler? source of isolated intact ion pairs in the gas phase compared to effusive sources.

  9. Epidemic thresholds for bipartite networks

    NASA Astrophysics Data System (ADS)

    Hernández, D. G.; Risau-Gusman, S.

    2013-11-01

    It is well known that sexually transmitted diseases (STD) spread across a network of human sexual contacts. This network is most often bipartite, as most STD are transmitted between men and women. Even though network models in epidemiology have quite a long history now, there are few general results about bipartite networks. One of them is the simple dependence, predicted using the mean field approximation, between the epidemic threshold and the average and variance of the degree distribution of the network. Here we show that going beyond this approximation can lead to qualitatively different results that are supported by numerical simulations. One of the new features, that can be relevant for applications, is the existence of a critical value for the infectivity of each population, below which no epidemics can arise, regardless of the value of the infectivity of the other population.

  10. Sulfur vacancies in photorefractive Sn{sub 2}P{sub 2}S{sub 6} crystals

    SciTech Connect

    Golden, E. M.; Giles, N. C.; Basun, S. A.; Grabar, A. A.; Stoika, I. M.; Evans, D. R.; Halliburton, L. E.

    2014-12-28

    A photoinduced electron paramagnetic resonance (EPR) spectrum in single crystals of Sn{sub 2}P{sub 2}S{sub 6} (SPS) is assigned to an electron trapped at a sulfur vacancy. These vacancies are unintentionally present in undoped SPS crystals and are expected to play an important role in the photorefractive behavior of the material. Nonparamagnetic sulfur vacancies are formed during the initial growth of the crystal. Subsequent illumination below 100 K with 442 nm laser light easily converts these vacancies to EPR-active defects. The resulting S = 1/2 spectrum shows well-resolved and nearly isotropic hyperfine interactions with two P ions and two Sn ions. Partially resolved interactions with four additional neighboring Sn ions are also observed. Principal values of the g matrix are 1.9700, 1.8946, and 1.9006, with the corresponding principal axes along the a, b, and c directions in the crystal. The isotropic parts of the two primary {sup 31}P hyperfine interactions are 19.5 and 32.6 MHz and the isotropic parts of the two primary Sn hyperfine interactions are 860 and 1320 MHz (the latter values are each an average for {sup 117}Sn and {sup 119}Sn). These hyperfine results suggest that singly ionized sulfur vacancies have a diffuse wave function in SPS crystals, and thus are shallow donors. Before illumination, sulfur vacancies are in the doubly ionized charge state because of compensation by unidentified acceptors. They then trap an electron during illumination. The EPR spectrum from the sulfur vacancy is destroyed when a crystal is heated above 120 K in the dark and reappears when the crystal is illuminated again at low temperature.

  11. Relative brightness of the O{sup +}({sup 2} D-{sup 2} P) doublets in low-energy aurorae

    SciTech Connect

    Whiter, D. K.; Lanchester, B. S.; Gustavsson, B.; Jallo, N. I. B.; Jokiaho, O.; Dahlgren, H.; Ivchenko, N.

    2014-12-10

    The ratio of the emission line doublets from O{sup +} at 732.0 nm (I {sub 732}) and 733.0 nm (I {sub 733}) has been measured in auroral conditions of low-energy electron precipitation from Svalbard (78.°20 north, 15.°83 east). Accurate determination of R = I {sub 732}/I {sub 733} provides a powerful method for separating the density of the O{sup +} {sup 2} P{sub 1} {sub /2,3} {sub /2}{sup o} levels in modeling of the emissions from the doublets. A total of 383 spectra were included from the winter of 2003-2004. The value obtained is R = I {sub 732}/I {sub 733} = 1.38 ± 0.02, which is higher than theoretical values for thermal equilibrium in fully ionized plasma, but is lower than reported measurements by other authors in similar auroral conditions. The continuity equations for the densities of the two levels are solved for different conditions, in order to estimate the possible variations of R. The results suggest that the production of ions in the two levels from O ({sup 3} P {sub 1}) and O ({sup 3} P {sub 2}) does not follow the statistical weights, unlike astrophysical calculations for plasmas in nebulae. The physics of auroral impact ionization may account for this difference, and therefore for the raised value of R. In addition, the auroral solution of the densities of the ions, and thus of the value of R, is sensitive to the temperature of the neutral atmosphere. Although the present work is a statistical study, it shows that it is necessary to determine whether there are significant variations in the ratio resulting from non-equilibrium conditions, from auroral energy deposition, large electric fields, and changes in temperature and composition.

  12. Ionization energies of argon clusters: A combined experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Echt, O.; Fiegele, T.; Rümmele, M.; Probst, M.; Matt-Leubner, S.; Urban, J.; Mach, P.; Leszczynski, J.; Scheier, P.; Märk, T. D.

    2005-08-01

    We have measured appearance energies of Arn+,n⩽30, by electron impact of gas phase clusters. Quantum-chemical calculations have been performed to determine the adiabatic and vertical ionization energies of argon clusters up to n =4 and 6, respectively. The experimental appearance energy of the dimer ion approaches, under suitable cluster source conditions, the adiabatic ionization energy. The agreement with values obtained by photoionization and threshold photoelectron-photoion coincidence (TPEPICO) spectra demonstrates that autoionizing Rydberg states are accessible by electron impact. Appearance energies of larger clusters, though, exceed the TPEPICO values by about 0.5 eV.

  13. Level-crossing enhancement of the microwave ionization of highly excited hydrogen atoms

    SciTech Connect

    Bayfield, J.E.; Luie, S.Y.

    1993-05-01

    For quasi one-dimensional atoms, we have observed oscillatory ionization probability as a function of microwave field strength, well below the threshold for classical chaos. This occurs within the microwave/Kepler frequency ratio rage 0.45-0.56. A Landau-Zener model modified to include ionizations of one quasienergy eigenstate can fit the data, there are Stuckelberg oscillations arising from occurring during the rise and fall of pulse. Varying the principal quantum number of the atom reveals a large degree of classical scaling, indicating that the quasienergy states involved are largely semiclassical. Observable changes in the data can result from a 0.2% change in microwave frequency.

  14. Advances Toward Inner-Shell Photo-Ionization X-Ray Lasing at 45 (Angstrom)

    SciTech Connect

    Moon, S J; Weber, F A; Celliers, P M; Eder, D C

    2002-07-18

    The inner-shell photo-ionization (ISPI) scheme requires photon energies at least high enough to photo-ionize the K-shell. {approx}286 eV, in the case of carbon. As a consequence of the higher cross-section, the inner-shell are selectively knocked out, leaving a hole state 1s2s{sup 2}2p{sup 2} in the singly charged carbon ion. This generates a population inversion to the radiatively connected state 1s{sup 2}2s{sup 2}2p in C+, leading to gain on the 1s-2p transition at 45 {angstrom}. The resonant character of the lasing transition in the single ionization state intrinsically allows much higher quantum efficiency compared to other schemes. Competing processes that deplete the population inversion include auto-ionization, Auger decay, and in particular collisional ionization of the outer-shell electrons by electrons generated during photo-ionization. These competing processes rapidly quench the gain. Consequently, the pump method must be capable of populating the inversion at a rate faster than the competing processes. This can be achieved by an ultra-fast, high intensity laser that is able to generate an ultra-fast, bright x-ray source. With current advances in the development of high-power, ultra-short pulse lasers it is possible to realize fast x-ray sources based that can deliver powerful pulses of light in the multiple hundred terawatt regime and beyond. They will discuss in greater detail concept, target design and a series of x-ray spectroscopy investigations they have conducted in order to optimize the absorber/x-ray converter--filter package.

  15. Report on the workshop on new directions in soft x-ray near-threshold phenomena

    SciTech Connect

    Lindle, D.W.; Perera, R.C.C.

    1988-07-01

    The ''Workshop on New Directions in Soft X-Ray Near-Threshold Phenomena'' was held at the Asilomar Conference Center in Pacific Grove, CA on March 1--4, 1987. It was attended by 59 scientists from 8 countries, representing 27 institutions. Major funding for the meeting was donated by L-Division of the Lawrence Livermore National Laboratory, who hosted and organized two previous workshops on photoabsorption and scattering in the soft x-ray energy range. Additional funding was provided by the User's Group of the Advanced Light Source. The Workshop, as its name suggests, emphasized physical phenomena in atoms, molecules, and solids near inner-shell thresholds. Of particular interest were threshold ionization, post-collisional interaction, resonant photoemission and fluorescence, and multi-electron effects such as shake-up and shake-off. In these areas and others, special consideration was given to presenting recent discoveries and potential ''new directions'' for future work.

  16. Spa2p Interacts with Cell Polarity Proteins and Signaling Components Involved in Yeast Cell Morphogenesis

    PubMed Central

    Sheu, Yi-Jun; Santos, Beatriz; Fortin, Nathalie; Costigan, Christine; Snyder, Michael

    1998-01-01

    The yeast protein Spa2p localizes to growth sites and is important for polarized morphogenesis during budding, mating, and pseudohyphal growth. To better understand the role of Spa2p in polarized growth, we analyzed regions of the protein important for its function and proteins that interact with Spa2p. Spa2p interacts with Pea2p and Bud6p (Aip3p) as determined by the two-hybrid system; all of these proteins exhibit similar localization patterns, and spa2Δ, pea2Δ, and bud6Δ mutants display similar phenotypes, suggesting that these three proteins are involved in the same biological processes. Coimmunoprecipitation experiments demonstrate that Spa2p and Pea2p are tightly associated with each other in vivo. Velocity sedimentation experiments suggest that a significant portion of Spa2p, Pea2p, and Bud6p cosediment, raising the possibility that these proteins form a large, 12S multiprotein complex. Bud6p has been shown previously to interact with actin, suggesting that the 12S complex functions to regulate the actin cytoskeleton. Deletion analysis revealed that multiple regions of Spa2p are involved in its localization to growth sites. One of the regions involved in Spa2p stability and localization interacts with Pea2p; this region contains a conserved domain, SHD-II. Although a portion of Spa2p is sufficient for localization of itself and Pea2p to growth sites, only the full-length protein is capable of complementing spa2 mutant defects, suggesting that other regions are required for Spa2p function. By using the two-hybrid system, Spa2p and Bud6p were also found to interact with components of two mitogen-activated protein kinase (MAPK) pathways important for polarized cell growth. Spa2p interacts with Ste11p (MAPK kinase [MEK] kinase) and Ste7p (MEK) of the mating signaling pathway as well as with the MEKs Mkk1p and Mkk2p of the Slt2p (Mpk1p) MAPK pathway; for both Mkk1p and Ste7p, the Spa2p-interacting region was mapped to the N-terminal putative regulatory domain

  17. Electroencephalographic responses to ionizing radiation.

    PubMed

    GARCIA, J; BUCHWALD, N A; BACH-Y-RITA, G; FEDER, B H; KOELLING, R A

    1963-04-19

    Electroencephalographic recordings made from chronically implanted cortical electrodes indicate that ionizing radiation has an immediate effect upon brain wave patterns. X-rays delivered at the rate of 0.2 roentgen per second produce an arousal effect resembling that which occurs as a result of stimulation through peripheral receptor systems.

  18. Ionization Cooling for Muon Experiments

    SciTech Connect

    Alexahin, Y.; Neuffer, D.; Prebys, E.

    2014-09-18

    Possible application for muon experiments such as mu2e is discussed of the initial part of the ionization cooling channel originally developed for muon collider. It is shown that with the FNAL Booster as the proton driver the mu2e sensitivity can be increased by two orders of magnitude compared to the presently considered experiment.

  19. Ionization Potentials for Isoelectronic Series.

    ERIC Educational Resources Information Center

    Agmon, Noam

    1988-01-01

    Presents a quantitative treatment of ionization potentials of isoelectronic atoms. By looking at the single-electron view of calculating the total energy of an atom, trends in the screening and effective quantum number parameters are examined. Approaches the question of determining electron affinities. (CW)

  20. Embracing thresholds for better environmental management

    PubMed Central

    Kelly, Ryan P.; Erickson, Ashley L.; Mease, Lindley A.; Battista, Willow; Kittinger, John N.; Fujita, Rod

    2015-01-01

    Three decades of study have revealed dozens of examples in which natural systems have crossed biophysical thresholds (‘tipping points’)—nonlinear changes in ecosystem structure and function—as a result of human-induced stressors, dramatically altering ecosystem function and services. Environmental management that avoids such thresholds could prevent severe social, economic and environmental impacts. Here, we review management measures implemented in ecological systems that have thresholds. Using Ostrom's social–ecological systems framework, we analysed key biophysical and institutional factors associated with 51 social–ecological systems and associated management regimes, and related these to management success defined by ecological outcomes. We categorized cases as instances of prospective or retrospective management, based upon whether management aimed to avoid a threshold or to restore systems that have crossed a threshold. We find that smaller systems are more amenable to threshold-based management, that routine monitoring is associated with successful avoidance of thresholds and recovery after thresholds have been crossed, and that success is associated with the explicit threshold-based management. These findings are powerful evidence for the policy relevance of information on ecological thresholds across a wide range of ecosystems.

  1. Proton and Electron Threshold Energy Measurements for Extravehicular Activity Space Suits. Chapter 2

    NASA Technical Reports Server (NTRS)

    Moyers, M. F.; Nelson, G. D.; Saganti, P. B.

    2003-01-01

    Construction of ISS will require more than 1000 hours of EVA. Outside of ISS during EVA, astronauts and cosmonauts are likely to be exposed to a large fluence of electrons and protons. Development of radiation protection guidelines requires the determination of the minimum energy of electrons and protons that penetrate the suits at various locations. Measurements of the water-equivalent thickness of both US. and Russian EVA suits were obtained by performing CT scans. Specific regions of interest of the suits were further evaluated using a differential range shift technique. This technique involved measuring thickness ionization curves for 6-MeV electron and 155-MeV proton beams with ionization chambers using a constant source-to-detector distance. The thicknesses were obtained by stacking polystyrene slabs immediately upstream of the detector. The thicknesses of the 50% ionizations relative to the maximum ionizations were determined. The detectors were then placed within the suit and the stack thickness adjusted until the 50% ionization was reestablished. The difference in thickness between the 50% thicknesses was then used with standard range-energy tables to determine the threshold energy for penetration. This report provides a detailed description of the experimental arrangement and results.

  2. Therapeutic targeting of two-pore-domain potassium (K(2P)) channels in the cardiovascular system.

    PubMed

    Wiedmann, Felix; Schmidt, Constanze; Lugenbiel, Patrick; Staudacher, Ingo; Rahm, Ann-Kathrin; Seyler, Claudia; Schweizer, Patrick A; Katus, Hugo A; Thomas, Dierk

    2016-05-01

    The improvement of treatment strategies in cardiovascular medicine is an ongoing process that requires constant optimization. The ability of a therapeutic intervention to prevent cardiovascular pathology largely depends on its capacity to suppress the underlying mechanisms. Attenuation or reversal of disease-specific pathways has emerged as a promising paradigm, providing a mechanistic rationale for patient-tailored therapy. Two-pore-domain K(+) (K(2P)) channels conduct outward K(+) currents that stabilize the resting membrane potential and facilitate action potential repolarization. K(2P) expression in the cardiovascular system and polymodal K2P current regulation suggest functional significance and potential therapeutic roles of the channels. Recent work has focused primarily on K(2P)1.1 [tandem of pore domains in a weak inwardly rectifying K(+) channel (TWIK)-1], K(2P)2.1 [TWIK-related K(+) channel (TREK)-1], and K(2P)3.1 [TWIK-related acid-sensitive K(+) channel (TASK)-1] channels and their role in heart and vessels. K(2P) currents have been implicated in atrial and ventricular arrhythmogenesis and in setting the vascular tone. Furthermore, the association of genetic alterations in K(2P)3.1 channels with atrial fibrillation, cardiac conduction disorders and pulmonary arterial hypertension demonstrates the relevance of the channels in cardiovascular disease. The function, regulation and clinical significance of cardiovascular K(2P) channels are summarized in the present review, and therapeutic options are emphasized.

  3. SUMOylation silences heterodimeric TASK potassium channels containing K2P1 subunits in cerebellar granule neurons.

    PubMed

    Plant, Leigh D; Zuniga, Leandro; Araki, Dan; Marks, Jeremy D; Goldstein, Steve A N

    2012-11-20

    The standing outward K(+) current (IKso) governs the response of cerebellar granule neurons to natural and medicinal stimuli including volatile anesthetics. We showed that SUMOylation silenced half of IKso at the surface of cerebellar granule neurons because the underlying channels were heterodimeric assemblies of K2P1, a subunit subject to SUMOylation, and the TASK (two-P domain, acid-sensitive K(+)) channel subunits K2P3 or K2P9. The heterodimeric channels comprised the acid-sensitive portion of IKso and mediated its response to halothane. We anticipate that SUMOylation also influences sensation and homeostatic mechanisms in mammals through TASK channels formed with K2P1.

  4. The excitation and collisional deactivation of metastable N/2P/ atoms in auroras

    NASA Technical Reports Server (NTRS)

    Zipf, E. C.; Espy, P. J.; Boyle, C. F.

    1980-01-01

    The concentration and altitude distribution of metastable N(2P) atoms was measured in a diffuse IBC II(+) auroral arc. The dominant N(2P) source is shown to be the dissociative excitation of N2 by electron impact with a minor contribution from the dissociative recombination of N2(+) ions. The possibility that an ion-molecule process involving atomic oxygen and vibrationally excited N2(+) ions is a significant N(2P) source is examined. Values for the proportional yield of N(+), N(2P), N(2D), and N(4S) atoms from electron-impact dissociation of N2 under optically thick conditions are given.

  5. Recent progress of below-threshold harmonic generation

    NASA Astrophysics Data System (ADS)

    Xiong, Wei-Hao; Peng, Liang-You; Gong, Qihuang

    2017-02-01

    The harmonics generated from the interaction of a strong laser field with atoms and molecules in the gas phase can be applied as coherent light sources and detecting techniques for structures and dynamics in matter. In the last three decades, the most prevailing experimental and theoretical studies have been focused on the high-order harmonic generation due to its applications in attosecond science. However, low-order harmonics near the ionization threshold of the target have been less explored, partially because the spectrum in this region is more complicated from both the theoretical and experimental point of view. After several pioneering investigations in the mid 1990s, near threshold harmonics (NTHs) begun to draw a great attention again because of the development of high repetition rate cavity enhanced harmonics about 10 years ago. Very recently, NTHs have attracted a lot of experimental and theoretical studies due to their potential applications as light sources and complicated mechanisms. In this topical review, we will summarize the progress of NTHs, including the early and recent experimental measurements in atoms and molecules, as well as the relevant theoretical explorations of these harmonics.

  6. Thresholds for Cenozoic bipolar glaciation.

    PubMed

    Deconto, Robert M; Pollard, David; Wilson, Paul A; Pälike, Heiko; Lear, Caroline H; Pagani, Mark

    2008-10-02

    The long-standing view of Earth's Cenozoic glacial history calls for the first continental-scale glaciation of Antarctica in the earliest Oligocene epoch ( approximately 33.6 million years ago), followed by the onset of northern-hemispheric glacial cycles in the late Pliocene epoch, about 31 million years later. The pivotal early Oligocene event is characterized by a rapid shift of 1.5 parts per thousand in deep-sea benthic oxygen-isotope values (Oi-1) within a few hundred thousand years, reflecting a combination of terrestrial ice growth and deep-sea cooling. The apparent absence of contemporaneous cooling in deep-sea Mg/Ca records, however, has been argued to reflect the growth of more ice than can be accommodated on Antarctica; this, combined with new evidence of continental cooling and ice-rafted debris in the Northern Hemisphere during this period, raises the possibility that Oi-1 represents a precursory bipolar glaciation. Here we test this hypothesis using an isotope-capable global climate/ice-sheet model that accommodates both the long-term decline of Cenozoic atmospheric CO(2) levels and the effects of orbital forcing. We show that the CO(2) threshold below which glaciation occurs in the Northern Hemisphere ( approximately 280 p.p.m.v.) is much lower than that for Antarctica ( approximately 750 p.p.m.v.). Therefore, the growth of ice sheets in the Northern Hemisphere immediately following Antarctic glaciation would have required rapid CO(2) drawdown within the Oi-1 timeframe, to levels lower than those estimated by geochemical proxies and carbon-cycle models. Instead of bipolar glaciation, we find that Oi-1 is best explained by Antarctic glaciation alone, combined with deep-sea cooling of up to 4 degrees C and Antarctic ice that is less isotopically depleted (-30 to -35 per thousand) than previously suggested. Proxy CO(2) estimates remain above our model's northern-hemispheric glaciation threshold of approximately 280 p.p.m.v. until approximately 25 Myr

  7. Wavelength dependence of femtosecond laser-induced damage threshold of optical materials

    SciTech Connect

    Gallais, L. Douti, D.-B.; Commandré, M.; Batavičiūtė, G.; Pupka, E.; Ščiuka, M.; Smalakys, L.; Sirutkaitis, V.; Melninkaitis, A.

    2015-06-14

    An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented. The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes. Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to 310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system. Semi-conductors and dielectrics materials, in bulk or thin film forms, in a range of bandgap from 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon energy. A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the photon energy. The calculated damage fluence threshold is found to be consistent with experimental results. From these results, the relative importance of the ionization processes can be derived depending on material properties and irradiation conditions. Moreover, the observed damage morphologies can be described within the framework of the model by taking into account the dynamics of energy deposition with one dimensional propagation simulations in the excited material and thermodynamical considerations.

  8. Following electron impact excitations of single Os, Pt, Hg, Pb and Po atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, M.; Aydeniz, D.

    2016-03-01

    L shell ionization cross section and Li subshells ionization cross sections of Os, Pt, Hg, Pb, Po atoms calculated. For each atom, ten different electron impacty energy values Eoi used. Calculations carried out by using nonrelativistic Lotz equation in Matlab. Ionization cross section values obtained for Eoi values in the energy range of ELi ≤Eoi≤4ELi for each atom. Starting allmost from Eoi = ELi (i = 1,2,3) values of the each subshell ionization threshold energy, ionization cross section are increasing rapidly with Eoi. For a fixed Eoi = 3. ELi values, while Z increases from Z = 76 to Z = 84, ionization cross section are decrease. These results help to understand some results which obtained from other electron-sigle atom impact studies on σLi subshells.

  9. Clinical Application of Ambient Ionization Mass Spectrometry

    PubMed Central

    Li, Li-Hua; Hsieh, Hua-Yi; Hsu, Cheng-Chih

    2017-01-01

    Ambient ionization allows mass spectrometry analysis directly on the sample surface under atmospheric pressure with almost zero sample pretreatment. Since the development of desorption electrospray ionization (DESI) in 2004, many other ambient ionization techniques were developed. Due to their simplicity and low operation cost, rapid and on-site clinical mass spectrometry analysis becomes real. In this review, we will highlight some of the most widely used ambient ionization mass spectrometry approaches and their applications in clinical study. PMID:28337399

  10. Carvedilol targets human K2P3.1 (TASK1) K+ leak channels

    PubMed Central

    Staudacher, K; Staudacher, I; Ficker, E; Seyler, C; Gierten, J; Kisselbach, J; Rahm, A-K; Trappe, K; Schweizer, PA; Becker, R; Katus, HA; Thomas, D

    2011-01-01

    BACKGROUND AND PURPOSE Human K2P3.1 (TASK1) channels represent potential targets for pharmacological management of atrial fibrillation. K2P channels control excitability by stabilizing membrane potential and by expediting repolarization. In the heart, inhibition of K2P currents by class III antiarrhythmic drugs results in action potential prolongation and suppression of electrical automaticity. Carvedilol exerts antiarrhythmic activity and suppresses atrial fibrillation following cardiac surgery or cardioversion. The objective of this study was to investigate acute effects of carvedilol on human K2P3.1 (hK2P3.1) channels. EXPERIMENTAL APPROACH Two-electrode voltage clamp and whole-cell patch clamp electrophysiology was used to record hK2P3.1 currents from Xenopus oocytes, Chinese hamster ovary (CHO) cells and human pulmonary artery smooth muscle cells (hPASMC). KEY RESULTS Carvedilol concentration-dependently inhibited hK2P3.1 currents in Xenopus oocytes (IC50= 3.8 µM) and in mammalian CHO cells (IC50= 0.83 µM). In addition, carvedilol sensitivity of native IK2P3.1 was demonstrated in hPASMC. Channels were blocked in open and closed states in frequency-dependent fashion, resulting in resting membrane potential depolarization by 7.7 mV. Carvedilol shifted the current–voltage (I–V) relationship by −6.9 mV towards hyperpolarized potentials. Open rectification, characteristic of K2P currents, was not affected. CONCLUSIONS AND IMPLICATIONS The antiarrhythmic drug carvedilol targets hK2P3.1 background channels. We propose that cardiac hK2P3.1 current blockade may suppress electrical automaticity, prolong atrial refractoriness and contribute to the class III antiarrhythmic action in patients treated with the drug. PMID:21410455

  11. Optimizing Systems of Threshold Detection Sensors

    DTIC Science & Technology

    2008-03-01

    mean of the "no event" distribution, we use mathematical nonlinear programming techniques to determine appropriate individual thresholds to maximize...decreases in all thresholds (less than five to ten percent) result in modest nonlinear percentage increases in detection performance (again, less than ten...level. In this thesis, we develop a model using nonlinear mathematical programming techniques to determine appropriate individual thresholds at

  12. Required thermal thresholds during transport of animals.

    PubMed

    Schrama, J W; van der Hel, W; Gorssen, J; Henken, A M; Verstegen, M W; Noordhuizen, J P

    1996-09-01

    Conditions (total complex of stressors) during the transport of animals vary strongly between and within transports. Adverse climatic conditions are stressors that animals have to face during transport. The thermoregulation of animals id discussed with respect to threshold values for optimal climatic conditions. These thermal thresholds depend on animal related factors and environmental conditions. The specific impact of transport conditions, such as food and water deprivation, high stocking density, high humidity and high air velocity, on thermal thresholds are described.

  13. GHRS Side 2 Threshold Adjustment - 4

    NASA Astrophysics Data System (ADS)

    Skapik, Joe

    1994-01-01

    This test will determine the optimal, non-standard discriminator thresholds for the few anomalous channels on HRS detector 2. A 15 second flat field observation followed by a 210 second dark count is performed at each of 10 discriminator threshold values for each detector. The result of the test will be the optimal threshold values to be entered into the PDB. Edited 4/30/91 to add comments to disable/re-enable cross-talk tables.

  14. GHRS Side 1 Threshold Adjustment - 4

    NASA Astrophysics Data System (ADS)

    Skapik, Joe

    1994-01-01

    This test will determine the optimal, non-standard discriminator thresholds for the few anomalous channels on HRS detector 1. A 15 second flat field observation followed by a 210 second dark count is performed at each of 10 discriminator threshold values for each detector. The result of the test will be the optimal threshold values to be entered into the PDB. Edited 4/30/91 to add comments to disable/re-enable cross-talk tables.

  15. 29 CFR 1926.53 - Ionizing radiation.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 8 2014-07-01 2014-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor... § 1926.53 Ionizing radiation. (a) In construction and related activities involving the use of sources of ionizing radiation, the pertinent provisions of the Nuclear Regulatory Commission's Standards...

  16. 29 CFR 1926.53 - Ionizing radiation.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 8 2011-07-01 2011-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor... § 1926.53 Ionizing radiation. (a) In construction and related activities involving the use of sources of ionizing radiation, the pertinent provisions of the Nuclear Regulatory Commission's Standards...

  17. 29 CFR 1926.53 - Ionizing radiation.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 8 2010-07-01 2010-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor... § 1926.53 Ionizing radiation. (a) In construction and related activities involving the use of sources of ionizing radiation, the pertinent provisions of the Nuclear Regulatory Commission's Standards...

  18. 29 CFR 1926.53 - Ionizing radiation.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 8 2013-07-01 2013-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor... § 1926.53 Ionizing radiation. (a) In construction and related activities involving the use of sources of ionizing radiation, the pertinent provisions of the Nuclear Regulatory Commission's Standards...

  19. 29 CFR 1926.53 - Ionizing radiation.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 8 2012-07-01 2012-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor... § 1926.53 Ionizing radiation. (a) In construction and related activities involving the use of sources of ionizing radiation, the pertinent provisions of the Nuclear Regulatory Commission's Standards...

  20. Automatic threshold selection using histogram quantization

    NASA Astrophysics Data System (ADS)

    Wang, Yue; Adali, Tulay; Lo, Shih-Chung B.

    1997-04-01

    An automatic threshold selection method is proposed for biomedical image analysis based on a histogram coding scheme. The threshold values can be determined based on the well-known Lloyd-Max scalar quantization rule, which is optimal in the sense of achieving minimum mean-square-error distortion. An iterative self-organizing learning rule is derived to determine the threshold levels. The rule does not require any prior information about the histogram, hence is fully automatic. Experimental results show that this new approach is easy to implement yet is highly efficient, robust with respect to noise, and yields reliable estimates of the threshold levels.

  1. A study of FM threshold extension techniques

    NASA Technical Reports Server (NTRS)

    Arndt, G. D.; Loch, F. J.

    1972-01-01

    The characteristics of three postdetection threshold extension techniques are evaluated with respect to the ability of such techniques to improve the performance of a phase lock loop demodulator. These techniques include impulse-noise elimination, signal correlation for the detection of impulse noise, and delta modulation signal processing. Experimental results from signal to noise ratio data and bit error rate data indicate that a 2- to 3-decibel threshold extension is readily achievable by using the various techniques. This threshold improvement is in addition to the threshold extension that is usually achieved through the use of a phase lock loop demodulator.

  2. Percolation Threshold in Polycarbonate Nanocomposites

    NASA Astrophysics Data System (ADS)

    Ahuja, Suresh

    2014-03-01

    Nanocomposites have unique mechanical, electrical, magnetic, optical and thermal properties. Many methods could be applied to prepare polymer-inorganic nanocomposites, such as sol-gel processing, in-situ polymerization, particle in-situ formation, blending, and radiation synthesis. The analytical composite models that have been put forth include Voigt and Reuss bounds, Polymer nanocomposites offer the possibility of substantial improvements in material properties such as shear and bulk modulus, yield strength, toughness, film scratch resistance, optical properties, electrical conductivity, gas and solvent transport, with only very small amounts of nanoparticles Experimental results are compared against composite models of Hashin and Shtrikman bounds, Halpin-Tsai model, Cox model, and various Mori and Tanaka models. Examples of numerical modeling are molecular dynamics modeling and finite element modeling of reduced modulus and hardness that takes into account the modulus of the components and the effect of the interface between the hard filler and relatively soft polymer, polycarbonate. Higher nanoparticle concentration results in poor dispersion and adhesion to polymer matrix which results in lower modulus and hardness and departure from the existing composite models. As the level of silica increases beyond a threshold level, aggregates form which results in weakening of the structure. Polymer silica interface is found to be weak as silica is non-interacting promoting interfacial slip at silica-matrix junctions. Our experimental results compare favorably with those of nanocomposites of polyesters where the effect of nanoclay on composite hardness and modulus depended on dispersion of nanoclay in polyester.

  3. Exhaustive Thresholds and Resistance Checkpoints

    NASA Technical Reports Server (NTRS)

    Easton, Charles; Khuzadi, Mbuyi

    2008-01-01

    Once deployed, all intricate systems that operate for a long time (such as an airplane or chemical processing plant) experience degraded performance during operational lifetime. These can result from losses of integrity in subsystems and parts that generally do not materially impact the operation of the vehicle (e.g., the light behind the button that opens the sliding door of the minivan). Or it can result from loss of more critical parts or subsystems. Such losses need to be handled quickly in order to avoid loss of personnel, mission, or part of the system itself. In order to manage degraded systems, knowledge of its potential problem areas and the means by which these problems are detected should be developed during the initial development of the system. Once determined, a web of sensors is employed and their outputs are monitored with other system parameters while the system is in preparation or operation. Just gathering the data is only part of the story. The interpretation of the data itself and the response of the system must be carefully developed as well to avoid a mishap. Typically, systems use a test-threshold-response paradigm to process potential system faults. However, such processing sub-systems can suffer from errors and oversights of a consistent type, causing system aberrant behavior instead of expected system and recovery operations. In our study, we developed a complete checklist for determining the completeness of a fault system and its robustness to common processing and response difficulties.

  4. Roots at the percolation threshold.

    PubMed

    Kroener, Eva; Ahmed, Mutez Ali; Carminati, Andrea

    2015-04-01

    The rhizosphere is the layer of soil around the roots where complex and dynamic interactions between plants and soil affect the capacity of plants to take up water. The physical properties of the rhizosphere are affected by mucilage, a gel exuded by roots. Mucilage can absorb large volumes of water, but it becomes hydrophobic after drying. We use a percolation model to describe the rewetting of dry rhizosphere. We find that at a critical mucilage concentration the rhizosphere becomes impermeable. The critical mucilage concentration depends on the radius of the soil particle size. Capillary rise experiments with neutron radiography prove that for concentrations below the critical mucilage concentration water could easily cross the rhizosphere, while above the critical concentration water could no longer percolate through it. Our studies, together with former observations of water dynamics in the rhizosphere, suggest that the rhizosphere is near the percolation threshold, where small variations in mucilage concentration sensitively alter the soil hydraulic conductivity. Is mucilage exudation a plant mechanism to efficiently control the rhizosphere conductivity and the access to water?

  5. Roots at the percolation threshold

    NASA Astrophysics Data System (ADS)

    Kroener, Eva; Ahmed, Mutez Ali; Carminati, Andrea

    2015-04-01

    The rhizosphere is the layer of soil around the roots where complex and dynamic interactions between plants and soil affect the capacity of plants to take up water. The physical properties of the rhizosphere are affected by mucilage, a gel exuded by roots. Mucilage can absorb large volumes of water, but it becomes hydrophobic after drying. We use a percolation model to describe the rewetting of dry rhizosphere. We find that at a critical mucilage concentration the rhizosphere becomes impermeable. The critical mucilage concentration depends on the radius of the soil particle size. Capillary rise experiments with neutron radiography prove that for concentrations below the critical mucilage concentration water could easily cross the rhizosphere, while above the critical concentration water could no longer percolate through it. Our studies, together with former observations of water dynamics in the rhizosphere, suggest that the rhizosphere is near the percolation threshold, where small variations in mucilage concentration sensitively alter the soil hydraulic conductivity. Is mucilage exudation a plant mechanism to efficiently control the rhizosphere conductivity and the access to water?

  6. Electron-Impact Ionization and Dissociative Ionization of Biomolecules

    NASA Technical Reports Server (NTRS)

    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.

  7. Threshold-photoelectron spectroscopic study of methyl-substituted hydrazine compounds.

    PubMed

    Boulanger, Anne-Marie; Rennie, Emma E; Holland, David M P; Shaw, David A; Mayer, Paul M

    2006-07-13

    The valence shell electronic structures of methylhydrazine (CH(3)NHNH(2)), 1,1-dimethylhydrazine ((CH(3))(2)NNH(2)) and tetramethylhydrazine ((CH(3))(4)N(2)) have been studied by recording threshold and conventional (kinetic energy resolved) photoelectron spectra. Ab initio calculations have been performed on ammonia and the three methyl substituted hydrazines, with the structures being optimized at the B3-LYP/6-31+G(d) level of theory. The ionization energies of the valence molecular orbitals were calculated using the Green's function method, allowing the photoelectron bands to be assigned to specific molecular orbitals. The ground-state adiabatic and vertical ionization energies, as determined from the threshold photoelectron spectra, were IE(a) = 8.02 +/- 0.16 eV and IE(v) = 9.36 +/- 0.02 eV for methylhydrazine, IE(a) = 7.78 +/- 0.16 eV and IE(v) = 8.86 +/- 0.01 eV for 1,1-dimethylhydrazine and IE(a) = 7.26 +/- 0.16 eV and IE(v) = 8.38 +/- 0.01 eV for tetramethylhydrazine. Due to the large geometry change that occurs upon ionization, these IE(a) values are all higher than the true thresholds. New features have been observed in the inner valence region and these have been compared with similar structure in the spectrum of hydrazine. The effect of resonant autoionization on the threshold photoelectron yield is discussed. New heats of formation (Delta(f)H) are proposed for the three hydrazines on the basis of G3 calculations: 107, 94, and 95 kJ/mol for methylhydrazine, 1,1-dimethyhydrazine and tetramethylhydrazine, respectively. The previously reported Delta(f)H for tetramethylhydrazine is shown to be erroneous.

  8. Electron Impact Ionization cross sections and rate coefficients for α-tetra hydro furfuryl alcohol

    NASA Astrophysics Data System (ADS)

    Kumar, Neeraj; Pal, Satyendra

    2013-09-01

    α - tetrahydrofurfuryl alcohol (THFA; C5H10O2) is an aromatic compound having the molecular structure similar to that of 2-deoxy-D-ribose (deoxyribose). This molecule has attracted enormous interest in the field of research because its electron charge cloud possesses a quite significant spatial extent (dipole polarizability, α = 70.18 au) and has a relatively strong permanent dipole moment (μ ~ 2D). In the present work, we have extended and generalized the modified Jain-Khare semi-empirical formalism for the evaluation of the total ionization cross sections corresponding to the formation of the cations in the electron impact ionization of molecules to the electron impact ionization of α-tetrahydrofurfuryl alcohol (THFA; C5H10O2) , in the energy range varying from ionization threshold to 1000 eV. The evaluated cross sections revealed a reasonably good agreement with the experimental and theoretical data, wherever available. We have also calculated the ionization rate coefficients as a function of electron energy, using the evaluated total ionization cross sections and the Maxwell-Boltzmann distribution.

  9. Electron-impact-ionization dynamics of five C2 to C4 perfluorocarbons

    NASA Astrophysics Data System (ADS)

    Bull, James N.; Bart, Mark; Vallance, Claire; Harland, Peter W.

    2013-12-01

    Perfluorocarbons (PFCs) are man-made compounds whose ion physics exhibit complex interplays between statistical and nonstatistical fragmentation and intramolecular rearrangement processes. One probe of such processes is the energy-dependent electron-impact-ionization cross section. Partial electron-impact-ionization cross sections are reported for the fragments arising from five C2 to C4 PFCs, namely, C2F6, C3F8, C3F6, CF2=CF-CF=CF2, and CF3-C≡C-CF3, over the energy range from threshold to ˜210 eV. Care was taken to maximize ion collection efficiency and to minimize discrimination against ions produced with high kinetic-energy release, and the measured cross sections have been calibrated using independent absolute total (gross) ionization efficiency curves measured previously in the same laboratory with an instrument that was designed to essentially have unit detection efficiency. Total ionization cross sections have also been modeled using the binary-encounter Bethe model, and the shortcomings of the model when applied to perfluorinated compounds are discussed. Analysis of the mass spectral fragmentation patterns in combination with ab initio energetics suggests that nonstatistical dissociative ionization processes play a significant role in the fragmentation dynamics of saturated PFCs. In contrast, unsaturated PFCs exhibit long-lived parent ions, which tend to undergo a higher degree of statistical dissociation following ionization, involving considerable intramolecular rearrangement.

  10. Development of CDMS-II Surface Event Rejection Techniques and Their Extensions to Lower Energy Thresholds

    NASA Astrophysics Data System (ADS)

    Hofer, Thomas James

    2014-10-01

    The CDMS-II phase of the Cryogenic Dark Matter Search, a dark matter direct-detection experiment, was operated at the Soudan Underground Laboratory from 2003 to 2008. The full payload consisted of 30 ZIP detectors, totaling approximately 1.1 kg of Si and 4.8 kg of Ge, operated at temperatures of 50 mK. The ZIP detectors read out both ionization and phonon pulses from scatters within the crystals; channel segmentation and analysis of pulse timing parameters allowed effective fiducialization of the crystal volumes and background rejection sufficient to set world-leading limits at the times of their publications. A full re-analysis of the CDMS-II data was motivated by an improvement in the event reconstruction algorithms which improved the resolution of ionization energy and timing information. The Ge data were re-analyzed using three distinct background-rejection techniques; the Si data from runs 125--128 were analyzed for the first time using the most successful of the techniques from the Ge re-analysis. The results of these analyses prompted a novel "mid-threshold" analysis, wherein energy thresholds were lowered but background rejection using phonon timing information was still maintained. This technique proved to have significant discrimination power, maintaining adequate signal acceptance and minimizing background leakage. The primary background for CDMS-II analyses comes from surface events, whose poor ionization collection make them difficult to distinguish from true nuclear recoil events. The novel detector technology of SuperCDMS, the successor to CDMS-II, uses interleaved electrodes to achieve full ionization collection for events occurring at the top and bottom detector surfaces. This, along with dual-sided ionization and phonon instrumentation, allows for excellent fiducialization and relegates the surface-event rejection techniques of CDMS-II to a secondary level of background discrimination. Current and future SuperCDMS results hold great promise for

  11. 29 CFR 1917.22 - Hazardous cargo 2 (See § 1917.2(p)).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 7 2010-07-01 2010-07-01 false Hazardous cargo 2 (See § 1917.2(p)). 1917.22 Section 1917.22 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION... § 1917.2(p)). 2 The Department of Transportation and the United States Coast Guard apply...

  12. 29 CFR 1917.22 - Hazardous cargo 2 (See § 1917.2(p)).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 7 2012-07-01 2012-07-01 false Hazardous cargo 2 (See § 1917.2(p)). 1917.22 Section 1917.22 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION... § 1917.2(p)). 2 The Department of Transportation and the United States Coast Guard apply...

  13. 29 CFR 1917.22 - Hazardous cargo 2 (See § 1917.2(p)).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 7 2011-07-01 2011-07-01 false Hazardous cargo 2 (See § 1917.2(p)). 1917.22 Section 1917.22 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION... § 1917.2(p)). 2 The Department of Transportation and the United States Coast Guard apply...

  14. 29 CFR 1917.22 - Hazardous cargo 2 (See § 1917.2(p)).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 7 2013-07-01 2013-07-01 false Hazardous cargo 2 (See § 1917.2(p)). 1917.22 Section 1917.22 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION... § 1917.2(p)). 2 The Department of Transportation and the United States Coast Guard apply...

  15. 29 CFR 1917.22 - Hazardous cargo 2 (See § 1917.2(p)).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 7 2014-07-01 2014-07-01 false Hazardous cargo 2 (See § 1917.2(p)). 1917.22 Section 1917.22 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION... § 1917.2(p)). 2 The Department of Transportation and the United States Coast Guard apply...

  16. Pseudogene CYP4Z2P 3′UTR promotes angiogenesis in breast cancer

    SciTech Connect

    Zheng, Lufeng; Li, Xiaoman; Gu, Yi; Ma, Yihua; Xi, Tao

    2014-10-24

    Highlights: • A new critical role of pseudogene CYP4Z2P 3′UTR in breast cancer is proposed. • We examine the level of pseudogene CYP4Z2P 3′UTR in breast cancer tissues. • The functions of CYP4Z2P 3′UTR and mechanism were studied. • The mechanism provides new insights for the breast cancer progression. - Abstract: Pseudogenes have long been marked as “false” genes, which are similar with real genes but have no apparent function. The 3′UTR is well-known to regulate gene expression post-transcriptionally. Our recent evidence, however, indicates novel functional roles of pseudogene CYP4Z2P 3′UTR (Z2P-UTR). We found that ectopic expression of Z2P-UTR in breast cancer cells significantly increased the expression of VEGF-A without affecting cell proliferation in vitro. Meanwhile, conditioned medium (CM) from Z2P-UTR overexpression cells enhanced proliferation, migration and tube formation of HUVEC, and promoted angiogenesis in ex vivo models. Also, CM increased the expression of VEGFR2 in HUVEC. Our data suggest that Z2P-UTR can promote breast cancer angiogenesis partly via paracrine pathway of VEGF-A/VEGFR2.

  17. Deactivation of Ni2P/SiO2 catalyst in hydrodechlorination of chlorobenzene

    NASA Astrophysics Data System (ADS)

    Chen, Jixiang; Ci, Donghui; Yang, Qing; Li, Kelun

    2014-11-01

    The deactivation of the Ni2P/SiO2 catalyst in the hydrodechlorination of chlorobenzene was studied. To better illuminate the reasons for the deactivation, the effect of HCl on the structure and activity of Ni2P/SiO2 was investigated. For comparison, the deactivation of the Ni/SiO2 catalyst was also involved. It was found that the Ni2P particles possessed good resistance to HCl poison and to sintering, which is ascribed to the electron-deficiency of Niδ+(0 < δ < 1) site in Ni2P. Acted as the Lewis and Brönsted acid site, the Niδ+ site and the Psbnd OH group on Ni2P/SiO2 catalyzed the formation of the carbonaceous deposit that was difficultly eliminated by hydrogenation. The carbonaceous deposit covered the active sites and might also induce a decrease in the Ni2P crystallinity, subsequently leading to the Ni2P/SiO2 deactivation. Different from Ni2P/SiO2, Ni/SiO2 was mainly deactivated by the chlorine poison and the sintering of nickel crystallites.

  18. Shock wave structure for a fully ionized plasma

    SciTech Connect

    Masser, Thomas O; Wohibier, John G; Lowrie, Robert B

    2009-01-01

    We study the structure of planar shock waves in a two-temperature model of a fully ionized plasma that includes electron heat conduction and energy exchange between electrons and ions. For steady flow in a reference frame moving with the shock, the model reduces to an autonomous system of ordinary differential equations which can be numerically integrated. A phase space analysis of the ODEs provides additional insight into the structure of the solutions. For example, below a threshold mach number the model produces fully dispersed shocks; while above another threshold mach number, the solutions contain embedded hydrodynamic shocks. Between these two threshold values, the appearance of embedded shocks depends on the electron diffusivity and the electron-ion coupling term. We also find that the ion temperature may continue to increase after the shock and reaches a maximum near the isothermal sonic point. We summarize the methodology for solving for two-temperature shocks, and show results for several values of shock strength and material parameters to quantify the shock structure and explore the range of possible solutions. Such solutions may be used to verify hydrodynamic codes that use similar plasma physics models.

  19. The collisional drift mode in a partially ionized plasma. [in the F region

    NASA Technical Reports Server (NTRS)

    Hudson, M. K.; Kennel, C. F.

    1974-01-01

    The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

  20. Vertical ionization drift velocities and range type spread F in the evening equatorial ionosphere

    SciTech Connect

    Abdu, M.A.; de Medeiros, R.T.; Bittencourt, J.A.; Batista, I.S.

    1983-01-01

    Range type spread F indices in the post sunset hours, determined from ionograms, are compared with F layer vertical velocities, also deduced from ionograms, for a period of one year, over the magnetic equatorial station Fortaleza (geographic coordinates: 4/sup 0/S, 38/sup 0/W; dip latitude: 1.8/sup 0/S), Brazil. Besides good correlation between the two parameters, the results suggest the presence of a certain threshold value for the vertical ionization velocity and a corresponding threshold height for the base of the evening F layer, as one of the necessary conditions for the occurrence of spread F irregularities valid for southern solstice (summer) and equinoctial months. The nature of the possible variabilities in the amplitude of the initial perturbation in the ionization (seeding mechanism), which is another prerequisite for the generation of irregularities, is discussed briefly.

  1. A Low-Noise Germanium Ionization Spectrometer for Low-Background Science

    SciTech Connect

    Aalseth, Craig E.; Colaresi, Jim; Collar, Juan I.; Fast, James E.; Hossbach, Todd W.; Orrell, John L.; Overman, Cory T.; Scholz, Bjorn; Vandevender, Brent A.; Yocum, K. Michael

    2016-12-01

    Recent progress on the development of very low energy threshold high purity germanium ionization spectrometers has produced an instrument of 1.2 kg mass and excellent noise performance. The detector was installed in a low-background cryostat intended for use in a low mass, WIMP dark matter direct detection search. The integrated detector and low background cryostat achieved noise performance of 98 eV full-width half-maximum of an input electronic pulse generator peak and gamma-ray energy resolution of 1.9 keV full-width half-maximum at the 60Co gamma-ray energy of 1332 keV. This Transaction reports the thermal characterization of the low-background cryostat, specifications of the newly prepared 1.2 kg p-type point contact germanium detector, and the ionization spectroscopy – energy resolution and energy threshold – performance of the integrated system.

  2. Cosmic ray studies with a gas Cerenkov counter in association with an ionization spectrometer

    NASA Technical Reports Server (NTRS)

    Balasubrahmanyan, V. K.; Ormes, J. F.; Arens, J. F.; Siohan, F.; Simon, M.; Spiegelhauer, H.; Yodh, G. B.

    1980-01-01

    The results from a balloon-borne gas Cerenkov counter (threshold 16.5 GeV/nuc) and an ionization spectrometer are presented. The gas Cerenkov counter provides an absolute energy calibration for the response of the calorimeter for the Z range of 5-26 nuclei of cosmic rays. The contribution of scintillation to the gas Cerenkov pulse height has been obtained by independently selecting particles below the gas Cerenkov threshold using the ionization spectrometer. Energy spectra were derived by minimizing the chi-squared between a Monte Carlo simulated data and flight data. Best fit power laws were determined for C, N, O, Ne, Mg, and Si. The power laws, all consistent with E exp-2.7, are not good fits to the data. A better fit is obtained using the spectrum derived from the spectrometer.

  3. Magnetic circular dichroism in the ion yield of polarized chromium atoms at the 2p edge

    SciTech Connect

    Pruemper, G.; Viefhaus, J.; Becker, U.; Kroeger, S.; Mueller, R.; Zimmermann, P.; Martins, M.

    2003-09-01

    The effect of magnetic dichroism in the partial and total ion yield of chromium, i.e., the absorption of polarized chromium vapor was observed in the gas phase. The measurements were performed at the 2p edge and at photon energies above the 2p edge. The structure of the dichroism at the 2p edge can be understood by including the coupling of the 2p hole with the 3d and 4s shells. Our experimental results for the dichroism at the 2p edge are similar to results of solid-state experiments. Implications for the sum rules used as a standard tool to calculate the spin and orbital momentum are discussed.

  4. An anti-attack model based on complex network theory in P2P networks

    NASA Astrophysics Data System (ADS)

    Peng, Hao; Lu, Songnian; Zhao, Dandan; Zhang, Aixin; Li, Jianhua

    2012-04-01

    Complex network theory is a useful way to study many real systems. In this paper, an anti-attack model based on complex network theory is introduced. The mechanism of this model is based on a dynamic compensation process and a reverse percolation process in P2P networks. The main purpose of the paper is: (i) a dynamic compensation process can turn an attacked P2P network into a power-law (PL) network with exponential cutoff; (ii) a local healing process can restore the maximum degree of peers in an attacked P2P network to a normal level; (iii) a restoring process based on reverse percolation theory connects the fragmentary peers of an attacked P2P network together into a giant connected component. In this way, the model based on complex network theory can be effectively utilized for anti-attack and protection purposes in P2P networks.

  5. Fuzzy-rule-based Adaptive Resource Control for Information Sharing in P2P Networks

    NASA Astrophysics Data System (ADS)

    Wu, Zhengping; Wu, Hao

    With more and more peer-to-peer (P2P) technologies available for online collaboration and information sharing, people can launch more and more collaborative work in online social networks with friends, colleagues, and even strangers. Without face-to-face interactions, the question of who can be trusted and then share information with becomes a big concern of a user in these online social networks. This paper introduces an adaptive control service using fuzzy logic in preference definition for P2P information sharing control, and designs a novel decision-making mechanism using formal fuzzy rules and reasoning mechanisms adjusting P2P information sharing status following individual users' preferences. Applications of this adaptive control service into different information sharing environments show that this service can provide a convenient and accurate P2P information sharing control for individual users in P2P networks.

  6. Above threshold dissociation in HD+ using frequency chirped laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Liu, Zheng-Tang; Cong, Shu-Lin

    2011-06-01

    We have theoretically studied the dynamics of above threshold dissociation (ATD) in molecular ions HD+ using frequency chirped femtosecond laser pulses from numerical solutions of the time-dependent Schrödinger equation by using the three-dimensional time-dependent quantum wave packet method. Energy-dependent distributions of ATD fragments are analyzed by an asymptotic-flow expression in momentum space. Linearly positive and negative frequency chirped laser pulses are adopted. It is found that varying frequency chirped parameters can change branching ratios of the 1sσ g and 2pσ u dissociations channels. The concept of a light-induced potential is used to interpret the ATD process. The angular resolved energy distributions of the photofragments are also illustrated.

  7. Kinetics of an oxygen - iodine active medium with iodine atoms optically pumped on the 2P1/2 - 2P3/2 transition

    NASA Astrophysics Data System (ADS)

    Zagidullin, M. V.; Malyshev, M. S.; Azyazov, V. N.

    2015-08-01

    The kinetics of the processes occurring in an O2 - I2 - He - H2O gas flow in which photodissociation of molecular iodine at a wavelength close to 500 nm and excitation of atomic iodine on the 2P1/2 - 2P3/2 transition by narrow-band radiation near 1315 nm are implemented successively has been analysed. It is shown that implementation of these processes allows one to form an oxygen - iodine medium with a high degree of dissociation of molecular iodine and a relative content of singlet oxygen O2(a1Δ) exceeding 10%. Having formed a supersonic gas flow with a temperature ~100 K from this medium, one can reach a small-signal gain of about 10-2 cm-1 on the 2P1/2 - 2P3/2 transition in iodine atoms. The specific power per unit flow cross section in the oxygen - iodine laser with this active medium may reach ~100 W cm-2.

  8. Precision lifetime measurements of Cs 6p 2P1/2 and 6p 2P3/2 levels by single-photon counting

    NASA Astrophysics Data System (ADS)

    Young, L.; Hill, W. T., III; Sibener, S. J.; Price, Stephen D.; Tanner, C. E.; Wieman, C. E.; Leone, Stephen R.

    1994-09-01

    Time-correlated single-photon counting is used to measure the lifetimes of the 6p 2P1/2 and 6p 2P3/2 levels in atomic Cs with accuracies ~=0.2-0.3 %. A high-repetition-rate, femtosecond, self-mode-locked Ti:sapphire laser is used to excite Cs produced in a well-collimated atomic beam. The time interval between the excitation pulse and the arrival of a fluorescence photon is measured repetitively until the desired statistics are obtained. The lifetime results are 34.75(7) and 30.41(10) ns for the 6p 2P1/2 and 6p 2P3/2 levels, respectively. These lifetimes fall between those extracted from ab initio many-body perturbation-theory calculations by Blundell, Johnson, and Sapirstein [Phys. Rev. A 43, 3407 (1991)] and V. A. Dzuba et al. [Phys. Lett. A 142, 373 (1989)] and are in all cases within 0.9% of the calculated values. The measurement errors are dominated by systematic effects, and methods to alleviate these and to approach an accuracy of 0.1% are discussed. The technique is a viable alternative to the fast-beam laser approach for measuring lifetimes with extreme accuracy.

  9. Ionizing radiation and cancer prevention.

    PubMed Central

    Hoel, D G

    1995-01-01

    Ionizing radiation long has been recognized as a cause of cancer. Among environmental cancer risks, radiation is unique in the variety of organs and tissues that it can affect. Numerous epidemiological studies with good dosimetry provide the basis for cancer risk estimation, including quantitative information derived from observed dose-response relationships. The amount of cancer attributable to ionizing radiation is difficult to estimate, but numbers such as 1 to 3% have been suggested. Some radiation-induced cancers attributable to naturally occurring exposures, such as cosmic and terrestrial radiation, are not preventable. The major natural radiation exposure, radon, can often be reduced, especially in the home, but not entirely eliminated. Medical use of radiation constitutes the other main category of exposure; because of the importance of its benefits to one's health, the appropriate prevention strategy is to simply work to minimize exposures. PMID:8741791

  10. Low-density ionization behavior

    SciTech Connect

    Baker, G.A. Jr.

    1995-04-01

    As part of a continuing study of the physics of matter under extreme conditions, I give some results on matter at extremely low density. In particular I compare a quantum mechanical calculation of the pressure for atomic hydrogen with the corresponding pressure given by Thomas-Fermi theory. (This calculation differs from the ``confined atom`` approximation in a physically significant way.) Since Thomas-Fermi theory in some sense, represents the case of infinite nuclear charge, these cases should represent extremes. Comparison is also made with Saha theory, which considers ionization from a chemical point of view, but is weak on excited-state effects. In this theory, the pressure undergoes rapid variation as electron ionization levels are passed. This effect is in contrast to the smooth behavior of the Thomas-Fermi fixed temperature, complete ionization occurs in the low density limit, I study the case where the temperature goes appropriately to zero with the density. Although considerable modification is required, Saha theory is closer to the actual results for this case than is Thomas-Fermi theory.

  11. Theory of dissociative tunneling ionization

    NASA Astrophysics Data System (ADS)

    Svensmark, Jens; Tolstikhin, Oleg I.; Madsen, Lars Bojer

    2016-05-01

    We present a theoretical study of the dissociative tunneling ionization process. Analytic expressions for the nuclear kinetic energy distribution of the ionization rates are derived. A particularly simple expression for the spectrum is found by using the Born-Oppenheimer (BO) approximation in conjunction with the reflection principle. These spectra are compared to exact non-BO ab initio spectra obtained through model calculations with a quantum mechanical treatment of both the electronic and nuclear degrees of freedom. In the regime where the BO approximation is applicable, imaging of the BO nuclear wave function is demonstrated to be possible through reverse use of the reflection principle, when accounting appropriately for the electronic ionization rate. A qualitative difference between the exact and BO wave functions in the asymptotic region of large electronic distances is shown. Additionally, the behavior of the wave function across the turning line is seen to be reminiscent of light refraction. For weak fields, where the BO approximation does not apply, the weak-field asymptotic theory describes the spectrum accurately.

  12. Kinetic-Energy Distribution of D(2p) Atoms from Analysis of the D Lyman-Alpha Line Profile

    NASA Technical Reports Server (NTRS)

    Ciocca, M.; Ajello, Joseph M.; Liu, Xianming; Maki, Justin

    1997-01-01

    The kinetic-energy distribution of D(2p) atoms resulting from electron-impact dissociation of D2 has been measured. A high-resolution vacuum ultraviolet spectrometer was employed for the first measurement of the D Lyman-alpha (D L(alpha)) emission line profiles at 20- and 100-eV excitation energies. Analysis of the deconvoluted line profile of D L(alpha) at 100 eV reveals the existence of a narrow line central peak of 29+/-2 mA full width at half maximum and a broad pedestal wing structure about 190 mA wide. The wings of the line can be used to determine the fast atom distribution. The wings of D L(alpha) arise from dissociative excitation of a series of doubly excited states that cross the Franck-Condon region between 23 and 40 eV. The fast atom distribution at 100-eV electron impact energy spans the energy range from 1 to 10 eV with a peak value near 6 eV. Slow D(2p) atoms characterized by a distribution function with peak energy near 100 meV produce the central peak profile, which is nearly independent of the impact energy. The deconvoluted line profiles of the central peak at 20 eV for dissociative excitation of D2 and H2 are fitted with an analytical function for use in calibration of space flight instrumentation equipped with a D/H absorption cell. The kinetic-energy and line profile results are compared to similar measurements for H2. The absolute cross sections for the line center (slow atoms) and wings (fast atoms) and total emission line profile were measured from threshold to 400 eV. Analytical model coefficients are given for the energy dependence of the measured slow atom cross section.

  13. Photon Energy Deposition in Strong-Field Single Ionization of Multielectron Molecules.

    PubMed

    Zhang, Wenbin; Li, Zhichao; Lu, Peifen; Gong, Xiaochun; Song, Qiying; Ji, Qinying; Lin, Kang; Ma, Junyang; He, Feng; Zeng, Heping; Wu, Jian

    2016-09-02

    Molecules exposed to strong laser fields may coherently absorb multiple photons and deposit the energy into electrons and nuclei, triggering the succeeding dynamics as the primary stage of the light-molecule interaction. We experimentally explore the electron-nuclear sharing of the absorbed photon energy in above-threshold multiphoton single ionization of multielectron molecules. Using CO as a prototype, vibrational and orbital resolved electron-nuclear sharing of the photon energy is observed. Different from the simplest one- or two-electron systems, the participation of the multiple orbitals and the coupling of various electronic states in the strong-field ionization and dissociation processes alter the photon energy deposition dynamics of the multielectron molecule. The population of numerous vibrational states of the molecular cation as the energy reservoir in the ionization process plays an important role in photon energy sharing between the emitted electron and the nuclear fragments.

  14. Ionization of 4,4'-bis(phenylethynyl) anthracene by electron impact.

    PubMed

    Kukhta, A V; Kukhta, I N; Zavilopulo, A N; Agafonova, A S; Shpenik, O B

    2009-01-01

    Ionization of a 4,4'-bis(phenylethynyl)anthracene (C(30)H(18), BPEA) molecule is studied for the first time at different energies of bombarding electrons in crossed electron and molecular beams. The relative cross-section of single ionization of a BPEA molecule in the energy range of 5-55 eV is measured. The ionization potential, E(I) = 7.62 +/- 0.2 eV, is determined using the threshold region of C(30)H(18)(+) ion yield energy dependence. A scheme of the BPEA molecule fragmentation is proposed. Experimental results are in reasonable accordance with calculations made in the framework of the density functional theory.

  15. Multislice theory of fast electron scattering incorporating atomic inner-shell ionization.

    PubMed

    Dwyer, C

    2005-09-01

    It is demonstrated how atomic inner-shell ionization can be incorporated into a multislice theory of fast electron scattering. The resulting theory therefore accounts for both inelastic scattering due to inner-shell ionization and dynamical elastic scattering. The theory uses a description of the ionization process based on the angular momentum representation for both the initial and final states of the atomic electron. For energy losses near threshold, only a small number of independent states of the ejected atomic electron need to be considered, reducing demands on computing time, and eliminating the need for tabulated inelastic scattering factors. The theory is used to investigate the influence of the collection aperture size on the spatial origin of the silicon K-shell EELS signal generated by a STEM probe. The validity of a so-called local approximation is also considered.

  16. Polarization phenomena in multiphoton ionization of atoms.

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.

    1973-01-01

    The theory of multiphoton ionization for an atomic system of arbitrary complexity is developed using a density matrix formalism. An expression is obtained which determines the differential N-photon ionization cross section as a function of the polarization states of the target atom and the incident radiation. The parameters which characterize the photo-electron angular distribution are related to the general reduced matrix elements for the N-photon transition. Two-photon ionization of unpolarized atoms is treated as an illustration of the use of the theory. The dependence of the multiphoton ionization cross section on the polarization state of the incident radiation, which has been observed in two- and three-photon ionization of Cs, is accounted for by the theory. Finally, the photoelectron spin polarization produced by the multiphoton ionization of unpolarized atoms, like the analogous polarization resulting from single-photon ionization, is found to depend on the circular polarization of the incident radiation.

  17. Polarization phenomena in multiphoton ionization of atoms

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.

    1973-01-01

    The theory of multiphoton ionization for an atomic system of arbitrary complexity is developed using a density matrix formalism. An expression is obtained which determines the differential N-photon ionization cross section as a function of the polarization states of the target atom and the incident radiation. The parameters which characterize the photoelectron angular distribution are related to the general reduced matrix elements for the N-photon transition. Two-photon ionization of unpolarized atoms is treated as an illustration of the use of the theory. The dependence of the multiphoton ionization cross section on the polarization state of the incident radiation, which has been observed in two- and three-photon ionization of Cs, is accounted for by the theory. Finally, the photoelectron spin polarization produced by the multiphoton ionization of unpolarized atoms, like the analogous polarization resulting from single-photon ionization, is found to depend on the circular polarization of the incident radiation.

  18. Threshold Concepts, Systems and Learning for Sustainability

    ERIC Educational Resources Information Center

    Sandri, Orana Jade

    2013-01-01

    This paper presents a framework for understanding the role that systems theory might play in education for sustainability (EfS). It offers a sketch and critique of Land and Meyer's notion of a "threshold concept", to argue that seeing systems as a threshold concept for sustainability is useful for understanding the processes of…

  19. 24 CFR 954.104 - Performance thresholds.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 24 Housing and Urban Development 4 2011-04-01 2011-04-01 false Performance thresholds. 954.104... DEVELOPMENT INDIAN HOME PROGRAM Applying for Assistance § 954.104 Performance thresholds. Applicants must have... HOME program must have performed adequately. In cases of previously documented deficient...

  20. 40 CFR 98.221 - Reporting threshold.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Reporting threshold. 98.221 Section 98.221 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Nitric Acid Production § 98.221 Reporting threshold. You must report...

  1. 40 CFR 98.251 - Reporting threshold.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Reporting threshold. 98.251 Section 98.251 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Petroleum Refineries § 98.251 Reporting threshold. You must report...

  2. Applying Threshold Concepts to Finance Education

    ERIC Educational Resources Information Center

    Hoadley, Susan; Wood, Leigh N.; Tickle, Leonie; Kyng, Tim

    2016-01-01

    Purpose: The purpose of this paper is to investigate and identify threshold concepts that are the essential conceptual content of finance programmes. Design/Methodology/Approach: Conducted in three stages with finance academics and students, the study uses threshold concepts as both a theoretical framework and a research methodology. Findings: The…

  3. 40 CFR 98.421 - Reporting threshold.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 21 2014-07-01 2014-07-01 false Reporting threshold. 98.421 Section 98.421 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Suppliers of Carbon Dioxide § 98.421 Reporting threshold. Any supplier...

  4. 40 CFR 98.421 - Reporting threshold.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 22 2013-07-01 2013-07-01 false Reporting threshold. 98.421 Section 98.421 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Suppliers of Carbon Dioxide § 98.421 Reporting threshold. Any supplier...

  5. 40 CFR 98.81 - Reporting threshold.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 22 2013-07-01 2013-07-01 false Reporting threshold. 98.81 Section 98.81 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Cement Production § 98.81 Reporting threshold. You must report...

  6. 40 CFR 98.51 - Reporting threshold.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 22 2013-07-01 2013-07-01 false Reporting threshold. 98.51 Section 98.51 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Adipic Acid Production § 98.51 Reporting threshold. You must report...

  7. 40 CFR 98.421 - Reporting threshold.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Reporting threshold. 98.421 Section 98.421 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Suppliers of Carbon Dioxide § 98.421 Reporting threshold. Any supplier...

  8. Detectability thresholds of general modular graphs

    NASA Astrophysics Data System (ADS)

    Kawamoto, Tatsuro; Kabashima, Yoshiyuki

    2017-01-01

    We investigate the detectability thresholds of various modular structures in the stochastic block model. Our analysis reveals how the detectability threshold is related to the details of the modular pattern, including the hierarchy of the clusters. We show that certain planted structures are impossible to infer regardless of their fuzziness.

  9. Thresholds for odor and nasal pungency.

    PubMed

    Cometto-Muñiz, J E; Cain, W S

    1990-11-01

    Detection thresholds were measured repeatedly for 11 chemicals in normosmic and anosmic subjects. The stimuli comprised the first eight members of the series of n-aliphatic alcohols, phenyl ethyl alcohol, pyridine, and menthol. Results showed that anosmics could detect, via pungency, all but phenyl ethyl alcohol reliably. In the aliphatic series, both odor and pungency thresholds declined with chain length in a way that implied dependence of both in part on phase distribution in the mucosa. Odor thresholds, however, declined more rapidly than pungency thresholds: the ratio of anosmics threshold/normosmics threshold increased from 23 for methanol to 10,000 for 1-octanol. The outcome of a scaling experiment employing normosmic subjects indicated that, with the exception of methanol and ethanol, pungency arose when perceived intensity reached a narrowly tuned criterion level. When thresholds were expressed as percentages of saturated vapor, an index of thermodynamic activity, thereby accounting for differences in solubility and in phase distribution in the mucosa among the various stimuli, both odor and pungency thresholds depicted a striking constancy across stimuli.

  10. 40 CFR 98.471 - Reporting threshold.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 21 2014-07-01 2014-07-01 false Reporting threshold. 98.471 Section 98.471 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Injection of Carbon Dioxide § 98.471 Reporting threshold. (a) You...

  11. 40 CFR 98.471 - Reporting threshold.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 22 2012-07-01 2012-07-01 false Reporting threshold. 98.471 Section 98.471 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Injection of Carbon Dioxide § 98.471 Reporting threshold. (a) You...

  12. 40 CFR 98.471 - Reporting threshold.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 21 2011-07-01 2011-07-01 false Reporting threshold. 98.471 Section 98.471 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Injection of Carbon Dioxide § 98.471 Reporting threshold. (a) You...

  13. 40 CFR 98.471 - Reporting threshold.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 22 2013-07-01 2013-07-01 false Reporting threshold. 98.471 Section 98.471 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Injection of Carbon Dioxide § 98.471 Reporting threshold. (a) You...

  14. Network Motif Basis of Threshold Responses

    EPA Science Inventory

    There has been a long-running debate over the existence of thresholds for adverse effects. The difficulty stems from two fundamental challenges: (i) statistical analysis by itself cannot prove the existence of a threshold, i.e., a dose below which there is no effect; and (ii) the...

  15. 40 CFR 98.341 - Reporting threshold.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 22 2012-07-01 2012-07-01 false Reporting threshold. 98.341 Section 98.341 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Municipal Solid Waste Landfills § 98.341 Reporting threshold. You...

  16. 40 CFR 98.341 - Reporting threshold.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Reporting threshold. 98.341 Section 98.341 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Municipal Solid Waste Landfills § 98.341 Reporting threshold. You...

  17. 40 CFR 98.341 - Reporting threshold.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 21 2014-07-01 2014-07-01 false Reporting threshold. 98.341 Section 98.341 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Municipal Solid Waste Landfills § 98.341 Reporting threshold. You...

  18. 40 CFR 98.341 - Reporting threshold.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 21 2011-07-01 2011-07-01 false Reporting threshold. 98.341 Section 98.341 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Municipal Solid Waste Landfills § 98.341 Reporting threshold. You...

  19. 40 CFR 98.341 - Reporting threshold.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 22 2013-07-01 2013-07-01 false Reporting threshold. 98.341 Section 98.341 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Municipal Solid Waste Landfills § 98.341 Reporting threshold. You...

  20. Intelligence and Creativity: Over the Threshold Together?

    ERIC Educational Resources Information Center

    Welter, Marisete Maria; Jaarsveld, Saskia; van Leeuwen, Cees; Lachmann, Thomas

    2016-01-01

    Threshold theory predicts a positive correlation between IQ and creativity scores up to an IQ level of 120 and no correlation above this threshold. Primary school children were tested at beginning (N = 98) and ending (N = 70) of the school year. Participants performed the standard progressive matrices (SPM) and the Test of Creative…