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

PubMed

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

2016-08-01

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

Enhancement of ionization efficiency of mass spectrometric analysis from non-electrospray ionization friendly solvents with conventional and novel ionization techniques.

PubMed

Jiang, Ping; Lucy, Charles A

2015-10-15

Electrospray ionization mass spectrometry (ESI-MS) has significantly impacted the analysis of complex biological and petroleum samples. However ESI-MS has limited ionization efficiency for samples in low dielectric and low polarity solvents. Addition of a make-up solvent through a T union or electrospray solvent through continuous flow extractive desorption electrospray ionization (CF-EDESI) enable ionization of analytes in non-ESI friendly solvents. A conventional make-up solvent addition setup was used and a CF-EDESI source was built for ionization of nitrogen-containing standards in hexane or hexane/isopropanol. Factors affecting the performance of both sources have been investigated and optimized. Both the make-up solvent addition and CF-EDESI improve the ionization efficiency for heteroatom compounds in non-ESI friendly solvents. Make-up solvent addition provides higher ionization efficiency than CF-EDESI. Neither the make-up solvent addition nor the CF-EDESI eliminates ionization suppression of nitrogen-containing compounds caused by compounds of the same chemical class. Copyright © 2015 Elsevier B.V. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2006-12-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

High-Sensitivity Ionization Trace-Species Detector

NASA Technical Reports Server (NTRS)

Bernius, Mark T.; Chutjian, Ara

1990-01-01

Features include high ion-extraction efficiency, compactness, and light weight. Improved version of previous ionization detector features in-line geometry that enables extraction of almost every ion from region of formation. Focusing electrodes arranged and shaped into compact system of space-charge-limited reversal electron optics and ion-extraction optics. Provides controllability of ionizing electron energies, greater efficiency of ionization, and nearly 100 percent ion-collection efficiency.

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

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

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

2012-07-02

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

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

NASA Astrophysics Data System (ADS)

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

2014-04-01

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

A New Electrospray Aerosol Generator with High Particle Transmission Efficiency

PubMed Central

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

2012-01-01

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

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

PubMed

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

2008-02-28

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

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

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

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

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

Control of nitromethane photoionization efficiency with shaped femtosecond pulses.

PubMed

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

2011-04-21

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

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

NASA Astrophysics Data System (ADS)

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

2015-08-01

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

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

PubMed Central

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

2010-01-01

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

A 200 W Hall thruster with hollow indented anode

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Sun, Hezhi; Wei, Liqiu; Li, Peng; Su, Hongbo; Peng, Wuji; Yu, Daren

2017-10-01

A hollow indented anode is proposed for increasing the neutral gas density in a discharge channel, in order to improve the performance of the thruster. The experimental results show that a hollow indented anode structure can effectively improve the performance, compared to a hollow straight anode under similar operating conditions, in terms of thrust, propellant utilization, ionization rate, and anode efficiency. Furthermore, simulations show that the indented anode can effectively increase the neutral gas density in a discharge channel and on the centerline of the channel, compared to a hollow straight anode. In addition, it can increase the ionization rate in the channel and the pre-ionization in the anode. Therefore, the hollow indented anode could be considered as an important design idea for improving thruster performance.

On the Ionization and Ion Transmission Efficiencies of Different ESI-MS Interfaces

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

Cox, Jonathan T.; Marginean, Ioan; Smith, Richard D.

2014-09-30

It is well known that the achievable sensitivity of electrospray ionization mass spectrometry (ESI-MS) is largely determined by the ionization efficiency in the ESI source and ion transmission efficiency through the ESI-MS interface. In this report we systematically study the ion transmission and ionization efficiencies in different ESI-MS interface configurations. The configurations under investigation include a single emitter/single inlet capillary, single emitter/multi-inlet capillary, and a subambient pressure ionization with nanoelectrospray (SPIN) MS interfaces with a single emitter and an emitter array, respectively. We present an effective method to evaluate the overall ion utilization efficiency of an ESI-MS interface by measuringmore » the total gas phase ion current transmitted through the interface and correlating it to the observed ion abundance measured in the corresponding mass spectrum. Our experimental results suggest that the overall ion utilization efficiency in the SPIN-MS interface configurations is better than that in the inlet capillary based ESI-MS interface configurations.« less

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

NASA Astrophysics Data System (ADS)

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

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

Laser resonance ionization spectroscopy of antimony

NASA Astrophysics Data System (ADS)

Li, R.; Lassen, J.; Ruczkowski, J.; Teigelhöfer, A.; Bricault, P.

2017-02-01

The resonant ionization laser ion source is an element selective, efficient and versatile ion source to generate radioactive ion beams at on-line mass separator facilities. For some elements with complex atomic structures and incomplete spectroscopic data, laser spectroscopic investigations are required for ionization scheme development. Laser resonance ionization spectroscopy using Ti:Sa lasers has been performed on antimony (Sb) at TRIUMF's off-line laser ion source test stand. Laser light of 230.217 nm (vacuum wavelength) as the first excitation step and light from a frequency-doubled Nd:YVO4 laser (532 nm) as the nonresonant ionization step allowed to search for suitable second excitation steps by continuous wavelength scans from 720 nm to 920 nm across the wavelength tuning range of a grating-tuned Ti:Sa laser. Upon the identification of efficient SES, the third excitation steps for resonance ionization were investigated by laser scans across Rydberg states, the ionization potential and autoionizing states. One Rydberg state and six AI states were found to be well suitable for efficient resonance ionization.

Improved efficiency of selective photoionization of palladium isotopes via autoionizing Rydberg states

NASA Astrophysics Data System (ADS)

Locke, Clayton R.; Kobayashi, Tohru; Midorikawa, Katsumi

2017-01-01

Odd-mass-selective ionization of palladium for purposes of resource recycling and management of long-lived fission products can be achieved by exploiting transition selection rules in a well-established three-step excitation process. In this conventional scheme, circularly polarized lasers of the same handedness excite isotopes via two intermediate 2D5/2 core states, and a third laser is then used for ionization via autoionizing Rydberg states. We propose an alternative excitation scheme via intermediate 2D3/2 core states before the autoionizing Rydberg state, improving ionization efficiency by over 130 times. We confirm high selectivity and measure odd-mass isotopes of >99.7(3)% of the total ionized product. We have identified and measured the relative ionization efficiency of the series of Rydberg states that converge to upper ionization limit of the 4 d 9(2D3/2) level, and identify the most efficient excitation is via the Rydberg state at 67668.18(10) cm-1.

Comparison of direct and alternating current vacuum ultraviolet lamps in atmospheric pressure photoionization.

PubMed

Vaikkinen, Anu; Haapala, Markus; Kersten, Hendrik; Benter, Thorsten; Kostiainen, Risto; Kauppila, Tiina J

2012-02-07

A direct current induced vacuum ultraviolet (dc-VUV) krypton discharge lamp and an alternating current, radio frequency (rf) induced VUV lamp that are essentially similar to lamps in commercial atmospheric pressure photoionization (APPI) ion sources were compared. The emission distributions along the diameter of the lamp exit window were measured, and they showed that the beam of the rf lamp is much wider than that of the dc lamp. Thus, the rf lamp has larger efficient ionization area, and it also emits more photons than the dc lamp. The ionization efficiencies of the lamps were compared using identical spray geometries with both lamps in microchip APPI mass spectrometry (μAPPI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). A comprehensive view on the ionization was gained by studying six different μAPPI solvent compositions, five DAPPI spray solvents, and completely solvent-free DAPPI. The observed reactant ions for each solvent composition were very similar with both lamps except for toluene, which showed a higher amount of solvent originating oxidation products with the rf lamp than with the dc lamp in μAPPI. Moreover, the same analyte ions were detected with both lamps, and thus, the ionization mechanisms with both lamps are similar. The rf lamp showed a higher ionization efficiency than the dc lamp in all experiments. The difference between the lamp ionization efficiencies was greatest when high ionization energy (IE) solvent compositions (IEs above 10 eV), i.e., hexane, methanol, and methanol/water, (1:1 v:v) were used. The higher ionization efficiency of the rf lamp is likely due to the larger area of high intensity light emission, and the resulting larger efficient ionization area and higher amount of photons emitted. These result in higher solvent reactant ion production, which in turn enables more efficient analyte ion production. © 2012 American Chemical Society

On the Ionization and Ion Transmission Efficiencies of Different ESI-MS Interfaces

PubMed Central

Cox, Jonathan T.; Marginean, Ioan; Smith, Richard D.; Tang, Keqi

2014-01-01

The achievable sensitivity of electrospray ionization mass spectrometry (ESI-MS) is largely determined by the ionization efficiency in the ESI source and ion transmission efficiency through the ESI-MS interface. These performance characteristics are difficult to evaluate and compare across multiple platforms as it is difficult to correlate electrical current measurements to actual analyte ions reaching the detector of a mass spectrometer. We present an effective method to evaluate the overall ion utilization efficiency of an ESI-MS interface by measuring the total gas phase ion current transmitted through the interface and correlating it to the observed ion abundance measured in the corresponding mass spectrum. Using this method we systematically studied the ion transmission and ionization efficiencies of different ESI-MS interface configurations, including a single emitter/single inlet capillary, single emitter/multi-inlet capillary, and a subambient pressure ionization with nanoelectrospray (SPIN) MS interface with a single emitter and an emitter array, respectively. Our experimental results indicate that the overall ion utilization efficiency of SPIN-MS interface configurations exceeds that of the inlet capillary-based ESI-MS interface configurations. PMID:25267087

On the ionization and ion transmission efficiencies of different ESI-MS interfaces.

PubMed

Cox, Jonathan T; Marginean, Ioan; Smith, Richard D; Tang, Keqi

2015-01-01

The achievable sensitivity of electrospray ionization mass spectrometry (ESI-MS) is largely determined by the ionization efficiency in the ESI source and ion transmission efficiency through the ESI-MS interface. These performance characteristics are difficult to evaluate and compare across multiple platforms as it is difficult to correlate electrical current measurements to actual analyte ions reaching the detector of a mass spectrometer. We present an effective method to evaluate the overall ion utilization efficiency of an ESI-MS interface by measuring the total gas-phase ion current transmitted through the interface and correlating it to the observed ion abundance measured in the corresponding mass spectrum. Using this method, we systematically studied the ion transmission and ionization efficiencies of different ESI-MS interface configurations, including a single emitter/single inlet capillary, single emitter/multi-inlet capillary, and a subambient pressure ionization with nanoelectrospray (SPIN) MS interface with a single emitter and an emitter array, respectively. Our experimental results indicate that the overall ion utilization efficiency of SPIN-MS interface configurations exceeds that of the inlet capillary-based ESI-MS interface configurations.

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

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

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

2008-09-01

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

LTC1877 High Efficiency Regulator Total Ionizing Dose Test Report

NASA Technical Reports Server (NTRS)

Oldham, Timothy; Pellish, Jonathan; Boutte, Alvin

2012-01-01

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

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

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

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

2015-08-03

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

Development Status of the Helicon Hall Thruster

DTIC Science & Technology

2009-09-15

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

Diagnostic studies of ion beam formation in inductively coupled plasma

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

Jacobs, Jenee L.

2015-01-01

This dissertation describes a variety of studies focused on the plasma and the ion beam in inductively coupled plasma mass spectrometry (ICP-MS). The ability to use ICP-MS for measurements of trace elements in samples requires the analytes to be efficiently ionized. Updated ionization efficiency tables are discussed for ionization temperatures of 6500 K and 7000 K with an electron density of 1 x 10 15 cm -3. These values are reflective of the current operating parameters of ICP-MS instruments. Calculations are also discussed for doubly charged (M 2+) ion formation, neutral metal oxide (MO) ionization, and metal oxide (MO +)more » ion dissociation for similar plasma temperature values. Ionization efficiency results for neutral MO molecules in the ICP have not been reported previously.« less

A Corona Discharge Initiated Electrochemical Electrospray Ionization Technique

PubMed Central

Lloyd, John R.; Hess, Sonja

2009-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-08-01

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

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

NASA Astrophysics Data System (ADS)

Popczun, Nicholas James

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

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

PubMed

Feng, Dan; Xia, Yan

2018-07-19

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

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

PubMed

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

2018-05-01

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

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

PubMed

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

2018-04-01

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

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

PubMed

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

2012-10-16

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

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

DOE PAGES

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

2016-12-05

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

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

PubMed Central

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

2014-01-01

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

Single electron dynamics in a Hall thruster electromagnetic field profile

NASA Astrophysics Data System (ADS)

Marini, Samuel; Pakter, Renato

2017-05-01

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

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

DOE PAGES

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

2016-12-02

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

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

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

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

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

A comparative study of disinfection efficiency and regrowth control of microorganism in secondary wastewater effluent using UV, ozone, and ionizing irradiation process.

PubMed

Lee, O-Mi; Kim, Hyun Young; Park, Wooshin; Kim, Tae-Hun; Yu, Seungho

2015-09-15

Ionizing radiation technology was suggested as an alternative method to disinfection processes, such as chlorine, UV, and ozone. Although many studies have demonstrated the effectiveness of irradiation technology for microbial disinfection, there has been a lack of information on comparison studies of disinfection techniques and a regrowth of each treatment. In the present study, an ionizing radiation was investigated to inactivate microorganisms and to determine the critical dose to prevent the regrowth. As a result, it was observed that the disinfection efficiency using ionizing radiation was not affected by the seasonal changes of wastewater characteristics, such as temperature and turbidity. In terms of bacterial regrowth after disinfection, the ionizing radiation showed a significant resistance of regrowth, whereas, on-site UV treatment is influenced by the suspended solid, temperature, or precipitation. The electric power consumption was also compared for the economic feasibility of each technique at a given value of disinfection efficiency of 90% (1-log), showing 0.12, 36.80, and 96.53 Wh/(L/day) for ionizing radiation, ozone, and UV, respectively. The ionizing radiation requires two or three orders of magnitude lower power consumption than UV and ozone. Consequently, ionizing radiation can be applied as an effective and economical alternative technique to other conventional disinfection processes. Copyright © 2015 Elsevier B.V. All rights reserved.

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

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

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

2016-08-15

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

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

PubMed

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

2016-08-02

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

Effect of external applied electric field on the silicon solar cell's thermodynamic efficiency

NASA Astrophysics Data System (ADS)

Zieba Falama, R.; Mibaile, Justin; Guemene Dountio, E.; Djongyang, Noël; Doka, Serge Y.; Kofane, Timoleon C.

2017-03-01

This paper presents a possible solution to improve the efficiency of photovoltaic solar cells. An external electric field is applied on a silicon photovoltaic solar cell, inducing band-trap ionization of charge carriers. Output current is then monitored and the thermodynamic efficiency is calculated. Results show on the one hand a significant increase in efficiency for a certain margin of applied electric field, and on the another hand the instabilities of efficiency. A simple approach is then suggested for the implementation of these results. An efficiency of 67% has been reached for an applied electric of 1586 V/Cm.

Efficient and robust photo-ionization loading of beryllium ions

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

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

PubMed

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

2017-06-01

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

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

PubMed

Stolee, Jessica A; Vertes, Akos

2013-04-02

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

Ion Voltage Diagnostics in the Far-Field Plume of a High-Specific Impulse Hall Thruster

NASA Technical Reports Server (NTRS)

Hofer, Richard R.; Haas, James M.; Gallimore, Alec D.

2003-01-01

The effects of the magnetic field and discharge voltage on the far-field plume of the NASA 173Mv2 laboratory-model Hall thruster were investigated. A cylindrical Langmuir probe was used to measure the plasma potential and a retarding potential analyzer was employed to measure the ion voltage distribution. The plasma potential was affected by relatively small changes in the external magnetic field, which suggested a means to control the plasma surrounding the thruster. As the discharge voltage increased, the ion voltage distribution showed that the acceleration efficiency increased and the dispersion efficiency decreased. This implied that the ionization zone was growing axially and moving closer to the anode, which could have affected thruster efficiency and lifetime due to higher wall losses. However, wall losses may have been reduced by improved focusing efficiency since the total efficiency increased and the plume divergence decreased with discharge voltage.

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

PubMed

Yang, Guang; Wang, Jianlong

2018-05-01

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

Metabolomics relative quantitation with mass spectrometry using chemical derivatization and isotope labeling

DOE PAGES

O'Maille, Grace; Go, Eden P.; Hoang, Linh; ...

2008-01-01

Comprehensive detection and quantitation of metabolites from a biological source constitute the major challenges of current metabolomics research. Two chemical derivatization methodologies, butylation and amination, were applied to human serum for ionization enhancement of a broad spectrum of metabolite classes, including steroids and amino acids. LC-ESI-MS analysis of the derivatized serum samples provided a significant signal elevation across the total ion chromatogram to over a 100-fold increase in ionization efficiency. It was also demonstrated that derivatization combined with isotopically labeled reagents facilitated the relative quantitation of derivatized metabolites from individual as well as pooled samples.

Diode-laser-based RIMS measurements of strontium-90

NASA Astrophysics Data System (ADS)

Bushaw, B. A.; Cannon, B. D.

1998-12-01

Double- and triple-resonance excitation schemes for the ionization of strontium are presented. Use of single-mode diode lasers for the resonance excitations provides a high degree of optical isotopic selectivity: with double-resonance, selectivity of >104 for 90Sr against the stable Sr isotopes has been demonstrated. Measurement of lineshapes and stable isotope shifts in the triple-resonance process indicate that optical selectivity should increase to ˜109. When combined with mass spectrometer selectivity this is sufficient for measurement of 90Sr at background environmental levels. Additionally, autoionizing resonances have been investigated for improving ionization efficiency with lower power lasers.

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

PubMed

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

2017-03-31

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

Low- and high-LET radiation drives clonal expansion of lung progenitor cells in vivo

PubMed Central

Farin, Alicia M.; Manzo, Nicholas D.; Kirsch, David G.; Stripp, Barry R.

2015-01-01

Abundant populations of epithelial progenitor cells maintain the epithelium along the proximal-to-distal axis of the airway. Exposure of lung tissue to ionizing radiation leads to tissue remodeling and potential cancer initiation or progression. However, little is known about the effects of ionizing radiation on airway epithelial progenitor cells. We hypothesized that ionizing radiation exposure will alter the behavior of airway epithelial progenitor cells in a radiation dose- and quality-dependent manner. To address this hypothesis, we cultured primary airway epithelial cells isolated from mice exposed to various doses of 320 kVp X-ray or 600 MeV/nucleon 56Fe ions in a 3D epithelial-fibroblast co-culture system. Colony-forming efficiency of the airway epithelial progenitor cells was assessed at culture day 14. In vivo clonogenic and proliferative potentials of airway epithelial progenitor cells were measured after exposure to ionizing radiation by lineage tracing and IdU incorporation. Exposure to both X-rays and 56Fe resulted in a dose dependent decrease in the ability of epithelial progenitors to form colonies in vitro. In vivo evidence for increased clonogenic expansion of epithelial progenitors was observed after exposure to both X-rays and 56Fe. Interestingly, we found no significant increase in the epithelial proliferative index, indicating that ionizing radiation does not promote increased turnover of the airway epithelium. Therefore, we propose a model in which radiation induces a dose-dependent decrease in the pool of available progenitor cells, leaving fewer progenitors able to maintain the airway long-term. This work provides novel insights into the effects of ionizing radiation exposure on airway epithelial progenitor cell behavior. PMID:25564721

Heating of the solar chromosphere by ionization pumping

NASA Technical Reports Server (NTRS)

Lindsey, C. A.

1981-01-01

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

Ionization Efficiency of Doubly Charged Ions Formed from Polyprotic Acids in Electrospray Negative Mode

NASA Astrophysics Data System (ADS)

Liigand, Piia; Kaupmees, Karl; Kruve, Anneli

2016-07-01

The ability of polyprotic acids to give doubly charged ions in negative mode electrospray was studied and related to physicochemical properties of the acids via linear discriminant analysis (LDA). It was discovered that the compound has to be strongly acidic (low p K a1 and p K a2) and to have high hydrophobicity (log P ow) to become multiply charged. Ability to give multiply charged ions in ESI/MS cannot be directly predicted from the solution phase acidities. Therefore, for the first time, a quantitative model to predict the charge state of the analyte in ESI/MS is proposed and validated for small anions. Also, a model to predict ionization efficiencies of these analytes was developed. Results indicate that acidity of the analyte, its octanol-water partition coefficient, and charge delocalization are important factors that influence ionization efficiencies as well as charge states of the analytes. The pH of the solvent was also found to be an important factor influencing the ionization efficiency of doubly charged ions.

Response of GaAs charge storage devices to transient ionizing radiation

NASA Astrophysics Data System (ADS)

Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

Characterization of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source for mass spectrometry.

PubMed

Forbes, Thomas P; Dixon, R Brent; Muddiman, David C; Degertekin, F Levent; Fedorov, Andrei G

2009-09-01

An initial investigation into the effects of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source is reported to gain understanding of ionization mechanisms and to improve analyte ionization efficiency and operation stability. In RF-only mode, AMUSE ejects, on average, an equal number of slightly positive and slightly negative charged droplets due to random charge fluctuations, providing inefficient analyte ionization. Charge separation at the nozzle orifice is achieved by the application of an external electric field. By bringing the counter electrode close to the nozzle array, strong electric fields can be applied at relatively low DC potentials. It has been demonstrated, through a number of electrode/electrical potential configurations, that increasing charge separation leads to improvement in signal abundance, signal-to-noise ratio, and signal stability.

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

PubMed

Aghaei, Maryam; Lindner, Helmut; Bogaerts, Annemie

2016-08-16

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

Efficient pre-ionization by direct X-B mode conversion in VEST

NASA Astrophysics Data System (ADS)

Jo, JongGab; Lee, H. Y.; Kim, S. C.; Kim, S. H.; An, Y. H.; Hwang, Y. S.

2017-01-01

Pre-ionization experiments with pure toroidal field have been carried out in VEST (Versatile Experiment Spherical Torus) to investigate the feasibility of direct XB mode conversion from perpendicular LFS (Low Field Side) injection for efficient pre-ionization. Pre-ionization plasmas are studied by measuring the electron density and temperature profiles with respect to microwave power and toroidal field strength, and 2D full wave cold plasma simulation using the COMSOL Multiphysics is performed for the comparison. It is experimentally figured out that exceeding the threshold microwave power (>3 kW), the parametric decay and localized collisional heating is observed near the UHR (Upper Hybrid Resonance), and the efficient XB mode conversion can be achieved in both short density scale length (Ln) and magnetic scale length (LB) region positioned at outboard and inboard sides, respectively. From the 2D full wave simulations, the reflection and tunneling of X-wave near the R-cutoff layer according to the measured electron density profiles are analyzed with electric field polarization and power flow. Threshold electric field and wave power density for parametric decay are evaluated at least more than 4.8 × 104 V/m and 100 W/cm2, respectively. This study shows that efficient pre-ionization schemes using direct XB mode conversion can be realized by considering the key factors such as Ln, LB, and transmitted wave power at the UHR. Application to Ohmic start-up experiment is carried out to confirm the effect of the pre-ionization schemes on tokamak plasma start-up in VEST.

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

NASA Technical Reports Server (NTRS)

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

2014-01-01

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

Recombination in liquid-filled ionization chambers beyond the Boag limit

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

Brualla-González, L.; Roselló, J.

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

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

PubMed

Salazar, Gary; Ognibene, Ted

2013-01-01

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

Quantum Phenomena in High Energy Density Plasmas

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

Murnane, Margaret; Kapteyn, Henry

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

The ionization efficiency of aluminum and iron at meteoric velocities

NASA Astrophysics Data System (ADS)

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

2018-07-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-03-01

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

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

PubMed

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

2005-01-01

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

1-(3-aminopropyl)-3-butylimidazolium bromide for carboxyl group derivatization: potential applications in high sensitivity peptide identification by mass spectrometry.

PubMed

Qiao, Xiaoqiang; Zhou, Yuan; Hou, Chunyan; Zhang, Xiaodan; Yang, Kaiguang; Zhang, Lihua; Zhang, Yukui

2013-03-01

The cationic reagent 1-(3-aminopropyl)-3-butylimidazolium bromide (BAPI) was exploited for the derivatization of carboxyl groups on peptides. Nearly 100% derivatization efficiency was achieved with the synthetic peptide RVYVHPI (RI-7). Furthermore, the peptide derivative was stable in a 0.1% TFA/water solution or a 0.1% (v/v) TFA/acetonitrile/water solution for at least one week. The effect of BAPI derivatization on the ionization of the peptide RI-7 was further investigated, and the detection sensitivity was improved >42-fold via matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), thus outperforming the commercial piperazine derivatization approach. Moreover, the charge states of the peptide were largely increased via BAPI derivatization by electrospray ionization (ESI) MS. The results indicate the potential merits of BAPI derivatization for high sensitivity peptide analysis by MS.

Characterization of Charge Separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) Ion Source for Mass Spectrometry

PubMed Central

Forbes, Thomas P.; Dixon, R. Brent; Muddiman, David C.; Degertekin, F. Levent; Fedorov, Andrei G.

2009-01-01

An initial investigation into the effects of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source is reported in order to gain understanding of ionization mechanisms and to improve analyte ionization efficiency and operation stability. In RF-only mode, AMUSE ejects on average, an equal number of slightly positive and slightly negative charged droplets due to random charge fluctuations, providing inefficient analyte ionization. Charge separation at the nozzle orifice is achieved by the application of an external electric field. By bringing the counter electrode close to the nozzle array, strong electric fields can be applied at relatively low DC potentials. It has been demonstrated, through a number of electrode/electrical potential configurations that increasing charge separation leads to improvement in signal abundance, signal-to-noise ratio, and signal stability. PMID:19525123

Composite glycerol/graphite/aromatic acid matrices for thin-layer chromatography/matrix-assisted laser desorption/ionization mass spectrometry of heterocyclic compounds.

PubMed

Esparza, Cesar; Borisov, R S; Varlamov, A V; Zaikin, V G

2016-10-28

New composite matrices have been suggested for the analysis of mixtures of different synthetic organic compounds (N-containing heterocycles and erectile dysfunction drugs) by thin layer chromatography/matrix-assisted laser desorption ionization time-of-flight mass spectrometry (TLC/MALDI-TOF). Different mixtures of classical MALDI matrices and graphite particles dispersed in glycerol were used for the registration of MALDI mass spectra directly from TLC plates after analytes separation. In most of cases, the mass spectra possessed [M+H] + ions; however, for some analytes only [M+Na] + and [M+K] + ions were observed. These ions have been used to generate visualized TLC chromatograms. The described approach increases the desorption/ionization efficiencies of analytes separated by TLC, prevent spot blurring, simplifies and decrease time for sample preparation. Copyright © 2016 Elsevier B.V. All rights reserved.

Hole-transport material variation in fully vacuum deposited perovskite solar cells

NASA Astrophysics Data System (ADS)

Polander, Lauren E.; Pahner, Paul; Schwarze, Martin; Saalfrank, Matthias; Koerner, Christian; Leo, Karl

2014-08-01

This work addresses the effect of energy level alignment between the hole-transporting material and the active layer in vacuum deposited, planar-heterojunction CH3NH3PbIx-3Clx perovskite solar cells. Through a series of hole-transport materials, with conductivity values set using controlled p-doping of the layer, we correlate their ionization potentials with the open-circuit voltage of the device. With ionization potentials beyond 5.3 eV, a substantial decrease in both current density and voltage is observed, which highlights the delicate energetic balance between driving force for hole-extraction and maximizing the photovoltage. In contrast, when an optimal ionization potential match is found, the open-circuit voltage can be maximized, leading to power conversion efficiencies of up to 10.9%. These values are obtained with hole-transport materials that differ from the commonly used Spiro-MeO-TAD and correspond to a 40% performance increase versus this reference.

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

PubMed

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

2016-04-01

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

Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures

DOE PAGES

Cox, Jonathan T.; Marginean, Ioan; Kelly, Ryan T.; ...

2014-03-28

Arrays of chemically etched emitters with individualized sheath gas capillaries have been developed to enhance electrospray ionization (ESI) at subambient pressures. By including an emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, ionization and transmission efficiency can be maximized allowing for increased sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses at conventional ESI-mass spectrometry (MS) interface by placing the emitter in the first vacuum region of the instrument. To facilitate stable electrospray currents in such conditions we have developed an improved emitter array with individualized sheath gas around each emitter. The utilitymore » of the new emitter arrays for generating stable multi-electrosprays at subambient pressures was probed by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared between single emitter/SPIN-MS and multi-emitter/SPIN-MS configurations using an equimolar solution of 9 peptides. An increase in sensitivity correlative to the number of emitters in the array was observed.« less

Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures

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

Cox, Jonathan T.; Marginean, Ioan; Kelly, Ryan T.

Arrays of chemically etched emitters with individualized sheath gas capillaries have been developed to enhance electrospray ionization (ESI) at subambient pressures. By including an emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, ionization and transmission efficiency can be maximized allowing for increased sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses at conventional ESI-mass spectrometry (MS) interface by placing the emitter in the first vacuum region of the instrument. To facilitate stable electrospray currents in such conditions we have developed an improved emitter array with individualized sheath gas around each emitter. The utilitymore » of the new emitter arrays for generating stable multi-electrosprays at subambient pressures was probed by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared between single emitter/SPIN-MS and multi-emitter/SPIN-MS configurations using an equimolar solution of 9 peptides. An increase in sensitivity correlative to the number of emitters in the array was observed.« less

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

NASA Astrophysics Data System (ADS)

Venkatraman, Pitchaikannu; Sureka, Chandrasekaran Senbagavadivoo

2017-11-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-11-01

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

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

NASA Technical Reports Server (NTRS)

Skinner, C. H.

1980-01-01

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

Design for gas chromatography-corona discharge-ion mobility spectrometry.

PubMed

Jafari, Mohammad T; Saraji, Mohammad; Sherafatmand, Hossein

2012-11-20

A corona discharge ionization-ion mobility spectrometry (CD-IMS) with a novel sample inlet system was designed and constructed as a detector for capillary gas chromatography. In this design, a hollow needle was used instead of a solid needle which is commonly used for corona discharge creation, helping us to have direct axial interfacing for GC-IMS. The capillary column was passed through the needle, resulting in a reaction of effluents with reactant ions on the upstream side of the corona discharge ionization source. Using this sample introduction design, higher ionization efficiency was achieved relative to the entrance direction through the side of the drift tube. In addition, the volume of the ionization region was reduced to minimize the resistance time of compounds in the ionization source, increasing chromatographic resolution of the instrument. The effects of various parameters such as drift gas flow, makeup gas flow, and column tip position inside the needle were investigated. The designed instrument was exhaustively validated in terms of sensitivity, resolution, and reproducibility by analyzing the standard solutions of methyl isobutyl ketone, heptanone, nonanone, and acetophenone as the test compounds. The results obtained by CD-IMS detector were compared with those of the flame ionization detector, which revealed the capability of the proposed GC-IMS for two-dimensional separation (based on the retention time and drift time information) and identification of an analyte in complex matrixes.

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

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

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

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

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

How Wolf-Rayet winds are driven by starlight and spectral lines

NASA Astrophysics Data System (ADS)

Onifer, Andrew Joseph, III

Finding the cause of the enormous increase in the mass- loss rate of a Wolf-Rayet (W-R) star, as compared to its O star progenitor, has remained a challenge for many years. This thesis explores the hypothesis that line driving causes the large observed W-R mass-loss rates. Frequency redistribution can cause the photons to filter into gaps in the line spectrum, reducing the efficiency of line driving. Therefore, the role that frequency redistribution plays in lowering the predicted mass-loss rate is explored, both via simple two-domain idealizations of the line list and via a real W-R line list. A simple analytic theory, called the Statistical Sobolev Rosseland (SSR) theory, is developed that calculates the local efficiency of line driving in a completely redistributing wind. In the process a conceptual language is developed to explain the key issues in W-R wind line driving. The results are that with no redistribution, the reduction in radius, and corresponding increase in temperature, of an O star as it evolves into a W-R star causes roughly a six-fold increase in the mass-loss rate. However, with large amounts of redistribution, the efficiency of the wind drops greatly in the presence of spectral gaps. In the most extreme case of SSR, the mass- loss rate drops by a factor of up to an order of magnitude relative to the gray value. To avoid this it is necessary to fill the gaps in the spectrum, and the effect that ionization stratification has in filling the gaps globally over the wind is explored. It is found that with the current line list ionization changes can only fill the gaps sufficiently to cause about a factor of two increase over the SSR value. The conclusion is that in order for line driving to explain the mass-loss rates of W-R winds, more opacity needs to be discovered to fill the gaps, either locally, or globally over a realistic range of ionization strata.

Applicability of post-ionization theory to laser-assisted field evaporation of magnetite

DOE PAGES

Schreiber, Daniel K.; Chiaramonti, Ann N.; Gordon, Lyle M.; ...

2014-12-15

Analysis of the mean Fe ion charge state from laser-assisted field evaporation of magnetite (Fe3O4) reveals unexpected trends as a function of laser pulse energy that break from conventional post-ionization theory for metals. For Fe ions evaporated from magnetite, the effects of post-ionization are partially offset by the increased prevalence of direct evaporation into higher charge states with increasing laser pulse energy. Therefore the final charge state is related to both the field strength and the laser pulse energy, despite those variables themselves being intertwined when analyzing at a constant detection rate. Comparison of data collected at different base temperaturesmore » also show that the increased prevalence of Fe2+ at higher laser energies is possibly not a direct thermal effect. Conversely, the ratio of 16O+:16O2+ is well-correlated with field strength and unaffected by laser pulse energy on its own, making it a better overall indicator of the field evaporation conditions than the mean Fe charge state. Plotting the normalized field strength versus laser pulse energy also elucidates a non-linear dependence, in agreement with previous observations on semiconductors, that suggests a field-dependent laser absorption efficiency. Together these observations demonstrate that the field evaporation process for laser-pulsed oxides exhibits fundamental differences from metallic specimens that cannot be completely explained by post-ionization theory. Further theoretical studies, combined with detailed analytical observations, are required to understand fully the field evaporation process of non-metallic samples.« less

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

PubMed

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

2011-12-15

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

On the SIMS Ionization Probability of Organic Molecules.

PubMed

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

2017-06-01

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

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

PubMed

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

2014-06-01

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

Mode transition induced by the magnetic field gradient in Hall thrusters

NASA Astrophysics Data System (ADS)

Han, Liang; Wei, Liqiu; Yu, Daren

2016-09-01

A mode transition phenomenon was found in Hall thrusters, which was induced by the increase of the magnetic field gradient. In the transition process, we observed experimentally that there have been obvious changes in the oscillation, the mean value of the discharge current, the thrust, the anode efficiency, and the plume pattern. The shifting and compression of the high magnetic field causes the electron density in the discharge channel to decrease and the ionization zone to move towards the exit plane. This also corresponds to a low atom density in the discharge channel, resulting in a loss of stability of the ionization at a high magnetic field gradient, which presents the transition of the discharge mode.

Controlled surface oxidation of multi-layered graphene anode to increase hole injection efficiency in organic electronic devices

NASA Astrophysics Data System (ADS)

Han, Tae-Hee; Kwon, Sung-Joo; Seo, Hong-Kyu; Lee, Tae-Woo

2016-03-01

Ultraviolet ozone (UVO) surface treatment of graphene changes its sp2-hybridized carbons to sp3-bonded carbons, and introduces oxygen-containing components. Oxidized graphene has a finite energy band gap, so UVO modification of the surface of a four-layered graphene anode increases its surface ionization potential up to ∼5.2 eV and improves the hole injection efficiency (η) in organic electronic devices by reducing the energy barrier between the graphene anode and overlying organic layers. By controlling the conditions of the UVO treatment, the electrical properties of the graphene can be tuned to improve η. This controlled surface modification of the graphene will provide a way to achieve efficient and stable flexible displays and solid-state lighting.

Calculation of multiphoton ionization processes

NASA Technical Reports Server (NTRS)

Chang, T. N.; Poe, R. T.

1976-01-01

We propose an accurate and efficient procedure in the calculation of multiphoton ionization processes. In addition to the calculational advantage, this procedure also enables us to study the relative contributions of the resonant and nonresonant intermediate states.

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

NASA Astrophysics Data System (ADS)

Karadag, Burak; Cho, Shinatora; Funaki, Ikkoh

2018-04-01

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

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

PubMed Central

Jing, Linhong; Nash, John J.

2009-01-01

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

Direct Analyses of Secondary Metabolites by Mass Spectrometry Imaging (MSI) from Sunflower (Helianthus annuus L.) Trichomes.

PubMed

Brentan Silva, Denise; Aschenbrenner, Anna-Katharina; Lopes, Norberto Peporine; Spring, Otmar

2017-05-10

Helianthus annuus (sunflower) displays non-glandular trichomes (NGT), capitate glandular trichomes (CGT), and linear glandular trichomes (LGT), which reveal different chemical compositions and locations in different plant tissues. With matrix-assisted laser desorption/ionization (MALDI) and laser desorption/ionization (LDI) mass spectrometry imaging (MSI) techniques, efficient methods were developed to analyze the tissue distribution of secondary metabolites (flavonoids and sesquiterpenes) and proteins inside of trichomes. Herein, we analyzed sesquiterpene lactones, present in CGT, from leaf transversal sections using the matrix 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA) (mixture 1:1) with sodium ions added to increase the ionization in positive ion mode. The results observed for sesquiterpenes and polymethoxylated flavones from LGT were similar. However, upon desiccation, LGT changed their shape in the ionization source, complicating analyses by MSI mainly after matrix application. An alternative method could be applied to LGT regions by employing LDI (without matrix) in negative ion mode. The polymethoxylated flavones were easily ionized by LDI, producing images with higher resolution, but the sesquiterpenes were not observed in spectra. Thus, the application and viability of MALDI imaging for the analyses of protein and secondary metabolites inside trichomes were confirmed, highlighting the importance of optimization parameters.

Laser stripping of hydrogen atoms by direct ionization

DOE PAGES

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

2015-05-08

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

Laser stripping of hydrogen atoms by direct ionization

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

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

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

OH radicals generated by DC corona discharge for improving the pulsed discharge desulfuration efficiency.

PubMed

Li, Jie; Li, Guo-feng; Wu, Yan; Wang, Ning-hui; Huang, Qiu-nan

2004-01-01

Positive DC corona discharge is formed with needle-plate electrode configuration, in which the water vapor is ejected though the needle points. The purpose is to increase the numbers of the water-based radicals, ionize the water molecule and improve the desulfuration efficiency of pulsed corona reactor. The water ions were determined by four stages molecular beam mass spectrometer and diagnose the water-based radicals by emission spectrograph. A conclusion on formation of ions and radicals with DC corona discharges can be drawn.

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

PubMed

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

2016-05-20

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

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

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

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

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

Alton, G.D.; Williams, C.

1995-12-31

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

The study of ionization by electron impact of a substance simulating spent nuclear fuel components

NASA Astrophysics Data System (ADS)

Antonov, N. N.; Bochkarev, E. I.; Gavrikov, A. V.; Samokhin, A. A.; Smirnov, V. P.

2015-11-01

Plasma sources of model substances are necessary to solve problems associated with development of the spent nuclear fuel (SNF) plasma separation method. Lead was chosen to simulate kinetic and dynamic properties of the heavy SNF components. In this paper we present the results of a study of a lead vapor discharge with a lead concentration of 1012-1013 cm-3. Ionization was carried out by an electron beam (with energy of up to 500 eV per electron) inside a centimeter gap between planar electrodes. The discharge was numerically modeled using the hydrodynamic and single-particle approximation. Current-voltage characteristics and single ionization efficiency were obtained as functions of the vapors concentration and thermoelectric current. An ion current of hundreds of microamperes at the ionization efficiency near tenths of a percent was experimentally obtained. These results are in good agreement with our model.

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

PubMed

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

2008-12-15

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

Electrospray Ionization Efficiency Is Dependent on Different Molecular Descriptors with Respect to Solvent pH and Instrumental Configuration

PubMed Central

Kiontke, Andreas; Oliveira-Birkmeier, Ariana; Opitz, Andreas

2016-01-01

Over the past decades, electrospray ionization for mass spectrometry (ESI-MS) has become one of the most commonly employed techniques in analytical chemistry, mainly due to its broad applicability to polar and semipolar compounds and the superior selectivity which is achieved in combination with high resolution separation techniques. However, responsiveness of an analytical method also determines its suitability for the quantitation of chemical compounds; and in electrospray ionization for mass spectrometry, it can vary significantly among different analytes with identical solution concentrations. Therefore, we investigated the ESI-response behavior of 56 nitrogen-containing compounds including aromatic amines and pyridines, two compound classes of high importance to both, synthetic organic chemistry as well as to pharmaceutical sciences. These compounds are increasingly analyzed employing ESI mass spectrometry detection due to their polar, basic character. Signal intensities of the peaks from the protonated molecular ion (MH+) were acquired under different conditions and related to compound properties such as basicity, polarity, volatility and molecular size exploring their quantitative impact on ionization efficiency. As a result, we found that though solution basicity of a compound is the main factor initially determining the ESI response of the protonated molecular ion, other factors such as polarity and vaporability become more important under acidic solvent conditions and may nearly outweigh the importance of basicity under these conditions. Moreover, we show that different molecular descriptors may become important when using different types of instruments for such investigations, a fact not detailed so far in the available literature. PMID:27907110

Note: a novel vacuum ultraviolet light source assembly with aluminum-coated electrodes for enhancing the ionization efficiency of photoionization mass spectrometry.

PubMed

Zhu, Zhixiang; Wang, Jian; Qiu, Keqing; Liu, Chengyuan; Qi, Fei; Pan, Yang

2014-04-01

A novel vacuum ultraviolet (VUV) light source assembly (VUVLSA) for enhancing the ionization efficiency of photoionization mass spectrometer has been described. The VUVLSA composes of a Krypton lamp and a pair of disk electrodes with circular center cavities. The two interior surfaces that face the photoionization region were aluminum-coated. VUV light can be reflected back and forth in the photoionization region between the electrodes, thus the photoionization efficiency can be greatly enhanced. The performances of two different shaped electrodes, the coated double flat electrodes (DFE), and double conical electrodes, were studied. We showed that the signal amplification of coated DFE is around 4 times higher than that of uncoated electrodes without VUV light reflection. The relationship between the pressure of ionization chamber and mass signal enhancement has also been studied.

Time-dependent Cooling in Photoionized Plasma

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

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

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

High efficiency carrier multiplication in PbSe nanocrystals: implications for solar energy conversion.

PubMed

Schaller, R D; Klimov, V I

2004-05-07

We demonstrate for the first time that impact ionization (II) (the inverse of Auger recombination) occurs with very high efficiency in semiconductor nanocrystals (NCs). Interband optical excitation of PbSe NCs at low pump intensities, for which less than one exciton is initially generated per NC on average, results in the formation of two or more excitons (carrier multiplication) when pump photon energies are more than 3 times the NC band gap energy. The generation of multiexcitons from a single photon absorption event is observed to take place on an ultrafast (picosecond) time scale and occurs with up to 100% efficiency depending upon the excess energy of the absorbed photon. Efficient II in NCs can be used to considerably increase the power conversion efficiency of NC-based solar cells.

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

PubMed

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

2016-06-01

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

Resonance-modulated wavelength scaling of high-order-harmonic generation from H2+

NASA Astrophysics Data System (ADS)

Wang, Baoning; He, Lixin; Wang, Feng; Yuan, Hua; Zhu, Xiaosong; Lan, Pengfei; Lu, Peixiang

2018-01-01

Wavelength scaling of high-order harmonic generation (HHG) in a non-Born-Oppenheimer treatment of H2+ is investigated by numerical simulations of the time-dependent Schrödinger equation. The results show that the decrease in the wavelength-dependent HHG yield is reduced compared to that in the fixed-nucleus approximation. This slower wavelength scaling is related to the charge-resonance-enhanced ionization effect, which considerably increases the ionization rate at longer driving laser wavelengths due to the relatively larger nuclear separation. In addition, we find an oscillation structure in the wavelength scaling of HHG from H2+. Upon decreasing the laser intensity or increasing the nuclear mass, the oscillation structure will shift towards a longer wavelength of the laser pulse. These results permit the generation of an efficient harmonic spectrum in the midinfrared regime by manipulating the nuclear dynamics of molecules.

Assessing the role of Hartree-Fock exchange, correlation energy and long range corrections in evaluating ionization potential, and electron affinity in density functional theory.

PubMed

Vikramaditya, Talapunur; Lin, Shiang-Tai

2017-06-05

Accurate determination of ionization potentials (IPs), electron affinities (EAs), fundamental gaps (FGs), and HOMO, LUMO energy levels of organic molecules play an important role in modeling and predicting the efficiencies of organic photovoltaics, OLEDs etc. In this work, we investigate the effects of Hartree Fock (HF) Exchange, correlation energy, and long range corrections in predicting IP and EA in Hybrid Functionals. We observe increase in percentage of HF exchange results in increase of IPs and decrease in EAs. Contrary to the general expectations inclusion of both HF exchange and correlation energy (from the second order perturbation theory MP2) leads to poor prediction. Range separated Hybrid Functionals are found to be more reliable among various DFT Functionals investigated. DFT Functionals predict accurate IPs whereas post HF methods predict accurate EAs. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Power matching between plasma generation and electrostatic acceleration in helicon electrostatic thruster

NASA Astrophysics Data System (ADS)

Ichihara, D.; Nakagawa, Y.; Uchigashima, A.; Iwakawa, A.; Sasoh, A.; Yamazaki, T.

2017-10-01

The effects of a radio-frequency (RF) power on the ion generation and electrostatic acceleration in a helicon electrostatic thruster were investigated with a constant discharge voltage of 300 V using argon as the working gas at a flow rate either of 0.5 Aeq (Ampere equivalent) or 1.0 Aeq. A RF power that was even smaller than a direct-current (DC) discharge power enhanced the ionization of the working gas, thereby both the ion beam current and energy were increased. However, an excessively high RF power input resulted in their saturation, leading to an unfavorable increase in an ionization cost with doubly charged ion production being accompanied. From the tradeoff between the ion production by the RF power and the electrostatic acceleration made by the direct current discharge power, the thrust efficiency has a maximum value at an optimal RF to DC discharge power ratio of 0.6 - 1.0.

High efficiency photoionization detector

DOEpatents

Anderson, David F.

1984-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2008-07-01

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

Lif Spectroscopy of ThF and the Preparation of ThF^{+} for the Jila eEDM Experiment

NASA Astrophysics Data System (ADS)

Ng, Kia Boon; Zhou, Yan; Gresh, Dan; Cairncross, William; Roussy, Tanya; Shagam, Yuval; Cheng, Lan; Ye, Jun; Cornell, Eric

2017-06-01

ThF^{+} is a promising candidate for a second-generation molecular ion-based measurement of the permanent electric dipole moment of the electron (eEDM). Compared to the current HfF^{+} eEDM experiment, ThF^{+} has several advantages: (i) the eEDM-sensitive ^{3}Δ_1 electronic state is the ground state, which facilitates a long measurement coherence time; (ii) its effective electric field (38 GV/cm) is 50% larger than that of HfF+, which promises a direct increase of the eEDM sensitivity; and (iii) the ionization energy of neutral ThF is lower than its dissociation energy, which introduces a greater flexibility for rotational state-selective photoionization via core-nonpenetrating Rydberg states. We use laser-induced fluorescence (LIF) spectroscopy to find suitable intermediate states required for the state selective ionization process. We present the results of our LIF spectroscopy of ThF, and our current progress on efficient ThF ionization and on ThF^{+} dissociation.

Intense laser pulse propagation in ionizing gases

NASA Astrophysics Data System (ADS)

Bian, Zhigang

2003-10-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-05-01

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

Boosting the power conversion efficiency of perovskite solar cells using self-organized polymeric hole extraction layers with high work function.

PubMed

Lim, Kyung-Geun; Kim, Hak-Beom; Jeong, Jaeki; Kim, Hobeom; Kim, Jin Young; Lee, Tae-Woo

2014-10-08

A self-organized hole extraction layer (SOHEL) with high work function (WF) is designed for energy level alignment with the ionization potential level of CH3 NH3 PbI3 . The SOHEL increases the built-in potential, photocurrent, and power conversion efficiency (PCE) of CH3 NH3 PbI3 perovskite solar cells. Thus, interface engineering of the positive electrode of solution-processed planar heterojunction solar cells using a high-WF SOHEL is a very effective way to achieve high device efficiency (PCE = 11.7% on glass). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

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

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

2016-02-15

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

HV discharge acceleration by sequences of UV laser filaments with visible and near-infrared pulses

NASA Astrophysics Data System (ADS)

Schubert, Elise; Rastegari, Ali; Feng, Chengyong; Mongin, Denis; Kamer, Brian; Kasparian, Jérôme; Wolf, Jean-Pierre; Arissian, Ladan; Diels, Jean-Claude

2017-12-01

We investigate the triggering and guiding of DC high-voltage discharges over a distance of 37 cm by filaments produced by ultraviolet (266 nm) laser pulses of 200 ps duration. The latter reduce the breakdown electric field by half and allow up to 80% discharge probability in an electric field of 920 kV m–1. This high efficiency is not further increased by adding nanosecond pulses in the Joule range at 532 and at 1064 nm. However, the latter statistically increases the guiding length, thereby accelerating the discharge by a factor of 2. This effect is due both to photodetachment and to the heating of the plasma channel, that increases the efficiency of avalanche ionization and reduces electron attachment and recombination.

Picoelectrospray Ionization Mass Spectrometry Using Narrow-bore Chemically Etched Emitters

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

Marginean, Ioan; Tang, Keqi; Smith, Richard D.

2014-01-01

Electrospray ionization mass spectrometry (ESI-MS) at flow rates below ~10 nL/min has been only sporadically explored due to difficulty in reproducibly fabricating emitters that can operate at lower flow rates. Here we demonstrate narrow orifice chemically etched emitters for stable electrospray at flow rates as low as 400 pL/min. Depending on the analyte concentration, we observe two types of MS signal response as a function of flow rate. At low concentrations, an optimum flow rate is observed slightly above 1 nL/min, while the signal decreases monotonically with decreasing flow rates at higher concentrations. In spite of lower MS signal, themore » ion utilization efficiency increases exponentially with decreasing flow rate in all cases. No unimolecular response was observed within this flow rate range during the analysis of an equimolar mixture of peptides, indicating that ionization efficiency is an analyte-dependent characteristic in given experimental conditions. While little to no gain in signal-to-noise was achieved at ultralow flow rates for concentration-limited analyses, experiments consuming the same amount of analyte suggest that mass-limited analyses will benefit strongly from the use of low flow rates and avoiding unnecessary sample dilution. By operating under optimal conditions, consumption of just 500 zmol of sample yielded signal-to-noise ratios ~10 for some peptides. These findings have important implications for the analysis of trace biological samples.« less

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

NASA Astrophysics Data System (ADS)

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

2003-01-01

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

High efficiency photoionization detector

DOEpatents

Anderson, D.F.

1984-01-31

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

Mass analyzer ``MASHA'' high temperature target and plasma ion source

NASA Astrophysics Data System (ADS)

Semchenkov, A. G.; Rassadov, D. N.; Bekhterev, V. V.; Bystrov, V. A.; Chizov, A. Yu.; Dmitriev, S. N.; Efremov, A. A.; Guljaev, A. V.; Kozulin, E. M.; Oganessian, Yu. Ts.; Starodub, G. Ya.; Voskresensky, V. M.; Bogomolov, S. L.; Paschenko, S. V.; Zelenak, A.; Tikhonov, V. I.

2004-05-01

A new separator and mass analyzer of super heavy atoms (MASHA) has been created at the FLNR JINR Dubna to separate and measure masses of nuclei and molecules with precision better than 10-3. First experiments with the FEBIAD plasma ion source have been done and give an efficiency of ionization of up to 20% for Kr with a low flow test leak (6 particle μA). We suppose a magnetic field optimization, using the additional electrode (einzel lens type) in the extracting system, and an improving of the vacuum conditions in order to increase the ion source efficiency.

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

PubMed

Fedorov, M; Poluektov, N

2000-02-28

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

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

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

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

1987-01-01

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

The absorption of energetic electrons by molecular hydrogen gas

NASA Technical Reports Server (NTRS)

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

1975-01-01

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

Electron energy deposition in N2 gas

NASA Technical Reports Server (NTRS)

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

1988-01-01

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

Direct olive oil analysis by mass spectrometry: A comparison of different ambient ionization methods.

PubMed

Lara-Ortega, Felipe J; Beneito-Cambra, Miriam; Robles-Molina, José; García-Reyes, Juan F; Gilbert-López, Bienvenida; Molina-Díaz, Antonio

2018-04-01

Analytical methods based on ambient ionization mass spectrometry (AIMS) combine the classic outstanding performance of mass spectrometry in terms of sensitivity and selectivity along with convenient features related to the lack of sample workup required. In this work, the performance of different mass spectrometry-based methods has been assessed for the direct analyses of virgin olive oil for quality purposes. Two sets of experiments have been setup: (1) direct analysis of untreated olive oil using AIMS methods such as Low-Temperature Plasma Mass Spectrometry (LTP-MS) or paper spray mass spectrometry (PS-MS); or alternatively (2) the use of atmospheric pressure ionization (API) mass spectrometry by direct infusion of a diluted sample through either atmospheric pressure chemical ionization (APCI) or electrospray (ESI) ionization sources. The second strategy involved a minimum sample work-up consisting of a simple olive oil dilution (from 1:10 to 1:1000) with appropriate solvents, which originated critical carry over effects in ESI, making unreliable its use in routine; thus, ESI required the use of a liquid-liquid extraction to shift the measurement towards a specific part of the composition of the edible oil (i.e. polyphenol rich fraction or lipid/fatty acid profile). On the other hand, LTP-MS enabled direct undiluted mass analysis of olive oil. The use of PS-MS provided additional advantages such as an extended ionization coverage/molecular weight range (compared to LTP-MS) and the possibility to increase the ionization efficiency towards nonpolar compounds such as squalene through the formation of Ag + adducts with carbon-carbon double bounds, an attractive feature to discriminate between oils with different degree of unsaturation. Copyright © 2017 Elsevier B.V. All rights reserved.

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

PubMed

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

2016-11-01

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

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

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

Alton, G.D.; Williams, C.

1996-04-01

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

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

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

Alton, G.D.; Williams, C.

1996-03-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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

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

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

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

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

DOE PAGES

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

2017-03-20

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

Action-FRET of a Gaseous Protein

NASA Astrophysics Data System (ADS)

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

2017-01-01

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

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

PubMed

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

2014-05-16

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

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.

High-order harmonic generation in a capillary discharge

DOEpatents

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

2010-06-01

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

MALDI TOF Imaging of Latent Fingerprints a Novel Biosignature Tool

DTIC Science & Technology

2010-04-23

old man have been lightly coated with ointment containing tocopherol and imprinted on stainless-steal MALDI plate. Application of low-concentrated... tocopherol allows efficient laser ionization without use of matrixes or additional treatment of the fingerprint. The result of the MS imaging scan...resolution and contrast. Interestingly, MS method optimized for molecular peak and main fragments of tocopherol (395 m/z) gave signal increase of over

New Insights into the Mechanism Underlying the Synergistic Action of Ionizing Radiation With Platinum Chemotherapeutic Drugs: The Role of Low-Energy Electrons

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

Rezaee, Mohammad, E-mail: Mohammad.Rezaee@USherbrooke.ca; Hunting, Darel John; Sanche, Léon

Purpose: To investigate the efficiencies of platinum chemotherapeutic drugs (Pt-drugs) in the sensitization of DNA to the direct effects of ionizing radiation and to determine the role of low-energy electrons (LEEs) in this process. Methods and Materials: Complexes of supercoiled plasmid DNA covalently bound to either cisplatin, carboplatin, or oxaliplatin were prepared in different molar ratios. Solid films of DNA and DNA modified by Pt-drugs were irradiated with either 10-KeV or 10-eV electrons. Damages to DNA were quantified by gel electrophoresis, and the yields for damage formation were obtained from exposure–response curves. Results: The presence of an average of 2more » Pt-drug–DNA adducts (Pt-adducts) in 3199-bp plasmid DNA increases the probability of a double-strand break by factors of 3.1, 2.5, and 2.4 for carboplatin, cisplatin, and oxaliplatin, respectively. Electrons with energies of 10 eV and 10 KeV interact with Pt-adducts to preferentially enhance the formation of cluster lesions. The maximum increase in radiosensitivity per Pt-adduct is found at ratios up to 3.1 × 10{sup −4} Pt-adducts per nucleotide, which is equivalent to an average of 2 adducts per plasmid. Carboplatin and oxaliplatin show higher efficiencies than cisplatin in the radiosensitization of DNA. Because carboplatin and cisplatin give rise to identical reactive species that attach to DNA, carboplatin must be considered as a better radiosensitizer for equal numbers of Pt-adducts. Conclusion: Platinum chemotherapeutic drugs preferentially enhance the formation of cluster damage to DNA induced by the direct effect of ionizing radiation, and LEEs are the main species responsible for such an enhancement via the formation of electron resonances.« less

New insights into the mechanism underlying the synergistic action of ionizing radiation with platinum chemotherapeutic drugs: the role of low-energy electrons.

PubMed

Rezaee, Mohammad; Hunting, Darel John; Sanche, Léon

2013-11-15

To investigate the efficiencies of platinum chemotherapeutic drugs (Pt-drugs) in the sensitization of DNA to the direct effects of ionizing radiation and to determine the role of low-energy electrons (LEEs) in this process. Complexes of supercoiled plasmid DNA covalently bound to either cisplatin, carboplatin, or oxaliplatin were prepared in different molar ratios. Solid films of DNA and DNA modified by Pt-drugs were irradiated with either 10-KeV or 10-eV electrons. Damages to DNA were quantified by gel electrophoresis, and the yields for damage formation were obtained from exposure-response curves. The presence of an average of 2 Pt-drug-DNA adducts (Pt-adducts) in 3199-bp plasmid DNA increases the probability of a double-strand break by factors of 3.1, 2.5, and 2.4 for carboplatin, cisplatin, and oxaliplatin, respectively. Electrons with energies of 10 eV and 10 KeV interact with Pt-adducts to preferentially enhance the formation of cluster lesions. The maximum increase in radiosensitivity per Pt-adduct is found at ratios up to 3.1×10(-4) Pt-adducts per nucleotide, which is equivalent to an average of 2 adducts per plasmid. Carboplatin and oxaliplatin show higher efficiencies than cisplatin in the radiosensitization of DNA. Because carboplatin and cisplatin give rise to identical reactive species that attach to DNA, carboplatin must be considered as a better radiosensitizer for equal numbers of Pt-adducts. Platinum chemotherapeutic drugs preferentially enhance the formation of cluster damage to DNA induced by the direct effect of ionizing radiation, and LEEs are the main species responsible for such an enhancement via the formation of electron resonances. Copyright © 2013 Elsevier Inc. All rights reserved.

New Insights into the Mechanism Underlying the Synergistic Action of Ionizing Radiation with Platinum Chemotherapeutic Drugs: The Role of Low-Energy Electrons

PubMed Central

Rezaee, Mohammad; Hunting, Darel John; Sanche, Léon

2013-01-01

Purpose To investigate the efficiencies of platinum chemotherapeutic drugs (Pt-drugs) in the sensitization of DNA to the direct effects of ionizing radiation and to determine the role of low-energy electrons (LEEs) in this process. Methods and Materials Complexes of supercoiled plasmid DNA covalently bound to either cisplatin, carboplatin or oxaliplatin were prepared in different molar ratios. Solid films of DNA and DNA modified by Pt-drugs were irradiated with either 10-KeV or 10-eV electrons. DNA damages were quantified by gel electrophoresis, and the yields for damage formation were obtained from exposure-response curves. Results The presence of an average of two Pt-adducts in 3199-bp plasmid DNA increases the probability of a double-strand break by factors of 3.1, 2.5 and 2.4 for carboplatin, cisplatin and oxaliplatin, respectively. Electrons with energies of 10-eV and 10-KeV interact with Pt-adducts to preferentially enhance the formation of cluster lesions. The maximum increase in radiosensitivity per Pt-adduct is found at ratios up to 3.1 × 10−4 Pt-adducts per nucleotide which is equivalent to an average of two adducts per plasmid. Carboplatin and oxaliplatin show higher efficiencies than cisplatin in the radiosensitization of DNA. Since carboplatin and cisplatin give rise to identical reactive species which attach to DNA, carboplatin must be considered as a better radiosensitizers for equal number of Pt-adducts. Conclusion Pt-drugs preferentially enhance the formation of cluster damage to DNA induced by the direct effect of ionizing radiation and LEEs are the main species responsible for such an enhancement via the formation of electron resonances. PMID:23910707

Statistical thermodynamic foundation for photovoltaic and photothermal conversion. IV. Solar cells with larger-than-unity quantum efficiency revisited

NASA Astrophysics Data System (ADS)

Badescu, Viorel; Landsberg, Peter T.; De Vos, Alexis; Desoete, Bart

2001-02-01

A detailed balance solar energy conversion model offering a single treatment of both photovoltaic and photothermal conversion is expounded. It includes a heat rejection mechanism. The effect of multiple impact ionizations on the solar cell efficiency is reconsidered by including the constraints dictated by the first law of thermodynamics (which already exist in the model) and it improves of course the solar cell efficiency. However the upper bound efficiencies previously derived are too optimistic as they do not take into consideration the necessary increase in solar cell temperature. The cell efficiency operating under unconcentrated radiation is a few percent lower than in the ideal case (i.e., with perfect cooling). Wider band gap materials are recommended for those applications where the cell cooling is not effective. The best operation of naturally ventilated cells is under unconcentrated or slightly concentrated solar radiation. Increasing the (forced) ventilation rate allows an increase of the optimum concentration ratio. Additional effects such as the radiation reflectance and radiative pair recombination efficiency are also considered. A sort of threshold minimum band gap depending on the last effect is emphasized: materials with band gaps narrower than this threshold are characterized by very low cell efficiency.

Optimizing the ionization and energy absorption of laser-irradiated clusters

NASA Astrophysics Data System (ADS)

Kundu, M.; Bauer, D.

2008-03-01

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

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

DOE PAGES

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

2016-10-15

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

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

PubMed

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

2014-11-15

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

Sensitive electrospray mass spectrometry analysis of one-bead-one-compound peptide libraries labeled by quaternary ammonium salts.

PubMed

Bąchor, Remigiusz; Cydzik, Marzena; Rudowska, Magdalena; Kluczyk, Alicja; Stefanowicz, Piotr; Szewczuk, Zbigniew

2012-08-01

A rapid and straightforward method for high-throughput analysis of single resin beads from one-bead-one-compound combinatorial libraries with high resolution electrospray ionization tandem mass spectrometry (HR ESI-MS/MS) is presented. The application of an efficient method of peptide derivatization by quaternary ammonium salts (QAS) formation increases ionization efficiency and reduces the detection limit, allowing analysis of trace amounts of compounds by ESI-MS. Peptides, synthesized on solid support, contain a new cleavable linker composed of a Peg spacer (9-aza-3,6,12,15-tetraoxa-10-on-heptadecanoic acid), lysine with ɛ-amino group marked by the N,N,N-triethylglycine salt, and methionine, which makes possible the selective cleavage by cyanogen bromide. Even a small portion of peptides derivatized by QAS cleaved from a single resin bead is sufficient for sequencing by HR ESI-MS/MS experiments. The developed strategy was applied to a small training library of α chymotrypsin substrates. The obtained results confirm the applicability of the proposed method in combinatorial chemistry.

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

NASA Technical Reports Server (NTRS)

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

1987-01-01

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

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

NASA Technical Reports Server (NTRS)

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

1991-01-01

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

Extreme ionization of Xe clusters driven by ultraintense laser fields

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

Heidenreich, Andreas; Last, Isidore; Jortner, Joshua

We applied theoretical models and molecular dynamics simulations to explore extreme multielectron ionization in Xe{sub n} clusters (n=2-2171, initial cluster radius R{sub 0}=2.16-31.0 A ring ) driven by ultraintense infrared Gaussian laser fields (peak intensity I{sub M}=10{sup 15}-10{sup 20} W cm{sup -2}, temporal pulse length {tau}=10-100 fs, and frequency {nu}=0.35 fs{sup -1}). Cluster compound ionization was described by three processes of inner ionization, nanoplasma formation, and outer ionization. Inner ionization gives rise to high ionization levels (with the formation of (Xe{sup q+}){sub n} with q=2-36), which are amenable to experimental observation. The cluster size and laser intensity dependence of themore » inner ionization levels are induced by a superposition of barrier suppression ionization (BSI) and electron impact ionization (EII). The BSI was induced by a composite field involving the laser field and an inner field of the ions and electrons, which manifests ignition enhancement and screening retardation effects. EII was treated using experimental cross sections, with a proper account of sequential impact ionization. At the highest intensities (I{sub M}=10{sup 18}-10{sup 20} W cm{sup -2}) inner ionization is dominated by BSI. At lower intensities (I{sub M}=10{sup 15}-10{sup 16} W cm{sup -2}), where the nanoplasma is persistent, the EII contribution to the inner ionization yield is substantial. It increases with increasing the cluster size, exerts a marked effect on the increase of the (Xe{sup q+}){sub n} ionization level, is most pronounced in the cluster center, and manifests a marked increase with increasing the pulse length (i.e., becoming the dominant ionization channel (56%) for Xe{sub 2171} at {tau}=100 fs). The EII yield and the ionization level enhancement decrease with increasing the laser intensity. The pulse length dependence of the EII yield at I{sub M}=10{sup 15}-10{sup 16} W cm{sup -2} establishes an ultraintense laser pulse length control mechanism of extreme ionization products.« less

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

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

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

1998-10-05

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

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

PubMed

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

2016-02-28

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

Photoionized Mixing Layer Models of the Diffuse Ionized Gas

NASA Astrophysics Data System (ADS)

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

2009-04-01

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

Matrix effects on secondary ion emission from a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide

NASA Astrophysics Data System (ADS)

Souda, Ryutaro

2009-06-01

The ionization mechanism of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry in the temperature range of 15-300 K. Analyses of 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide ([emim][Tf2N]) deposited on a Ni(111) substrate revealed that the [emim]+ and [Tf2N]- yields increase together with the Ni+ yield at monolayer coverage; no such increase was observed for the films deposited on a D2O spacer layer. Results indicated that the [emim][Tf2N] molecule is not perfectly ionized; the Ni(111) surface accepts (for [emim]+) or donates (for [Tf2N]-) an electron with higher efficiency than the counterion because of the metal band effect. This phenomenon might be induced by electrostatic interactions between the separated cation and anion during sputtering. It is also suggested that the sputtered Ni atom can be ionized nonadiabatically by the formation of a quasimolecule with adspecies. The multilayer of [emim][Tf2N] deposited at 15 K has a porous structure, resembling that of polar molecules, because of nonionic intermolecular interactions. The phase transition is identifiable, together with the morphological change in the crystalline film, from temperature evolutions of the secondary ion yields.

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

PubMed Central

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

2009-01-01

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

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

PubMed

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

2007-04-01

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

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

PubMed Central

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

2013-01-01

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

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

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

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

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

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

DOE PAGES

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

2015-05-08

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

An evaluation of krypton propellant in Hall thrusters

NASA Astrophysics Data System (ADS)

Linnell, Jesse Allen

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

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

PubMed

Chernetsova, Elena S; Morlock, Gertrud E

2011-01-01

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

A Numerical Simulation of the Energy Conversion Process in Microwave Rocket

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

Shibata, Teppei; Oda, Yasuhisa; Komurasaki, Kimiya

2008-04-28

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

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

PubMed Central

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

2017-01-01

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

A review of nanoelectrospray ionization applications for drug metabolism and pharmacokinetics.

PubMed

Wickremsinhe, Enaksha R; Singh, Gurkeerat; Ackermann, Bradley L; Gillespie, Todd A; Chaudhary, Ajai K

2006-12-01

Although traditionally reserved for proteomic analysis, nanoESI has found increased use for small molecule applications related to drug metabolism/pharmacokinetics (DMPK). NanoESI, which refers to ESI performed at flow rates in the range of 200 to 1000 nL/min using smaller diameter emitters (10 to 100 microm id), produces smaller droplets than conventional ESI resulting in more efficient ionization. Benefits include greater sensitivity, enhanced dynamic range, and a reduced competition for ionization. These advantages may now be harnessed largely due to the introduction of a commercial system for automated nanoESI infusion. This development in turn has allowed ADME (absorption, distribution, metabolism, and excretion) scientists to consider novel approaches to mass spectrometric analysis without direct LC interfacing. While it is freely acknowledged that nanoESI infusion is not likely to supplant LC-MS as the primary analytical platform for ADME, nanoESI infusion has been successfully applied to both quantitative (bioanalysis) and qualitative (metabolite identification) applications. This review summarizes published applications of this technology and offers a perspective on where it fits best into the DMPK laboratory.

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

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

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

2014-12-15

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

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

PubMed Central

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

2010-01-01

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

Resonantly enhanced method for generation of tunable, coherent vacuum ultraviolet radiation

DOEpatents

Glownia, James H.; Sander, Robert K.

1985-01-01

Carbon Monoxide vapor is used to generate coherent, tunable vacuum ultraviolet radiation by third-harmonic generation using a single tunable dye laser. The presence of a nearby electronic level resonantly enhances the nonlinear susceptibility of this molecule allowing efficient generation of the vuv light at modest pump laser intensities, thereby reducing the importance of a six-photon multiple-photon ionization process which is also resonantly enhanced by the same electronic level but to higher order. By choosing the pump radiation wavelength to be of shorter wavelength than individual vibronic levels used to extend tunability stepwise from 154.4 to 124.6 nm, and the intensity to be low enough, multiple-photon ionization can be eliminated. Excitation spectra of the third-harmonic emission output exhibit shifts to shorter wavelength and broadening with increasing CO pressure due to phase matching effects. Increasing the carbon monoxide pressure, therefore, allows the substantial filling in of gaps arising from the stepwise tuning thereby providing almost continuous tunability over the quoted range of wavelength emitted.

Resonantly enhanced method for generation of tunable, coherent vacuum-ultraviolet radiation

DOEpatents

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

1982-06-29

Carbon Monoxide vapor is used to generate coherent, tunable vacuum ultraviolet radiation by third-harmonic generation using a single tunable dye laser. The presence of a nearby electronic level resonantly enhances the nonlinear susceptibility of this molecule allowing efficient generation of the vuv light at modest pump laser intensities, thereby reducing the importance of a six-photon multiple-photon ionization process which is also resonantly enhanced by the same electronic level but no higher order. By choosing the pump radiation wavelength to be of shorter wavelength than individual vibronic levels used to extend tunability stepwise from 154.4 to 124.6 nm, and the intensity to be low enough, multiple-photon ionization can be eliminated. Excitation spectra of the third-harmonic emission output exhibit shifts to shorter wavelength and broadening with increasing CO pressure due to phase matching effects. Increasing the carbon monoxide pressure, therefore, allows the substantial filling in of gaps arising from the stepwise tuning thereby providing almost continuous tunability over the quoted range of wavelength emitted.

Simulation of double stage hall thruster with double-peaked magnetic field

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Li, Peng; Sun, Hezhi; Wei, Liqiu; Xu, Yu; Peng, Wuji; Su, Hongbo; Li, Hong; Yu, Daren

2017-07-01

This study adopts double permanent magnetic rings and four permanent magnetic rings to form two symmetrical magnetic peaks and two asymmetrical magnetic peaks in the channel of a Hall thruster, and uses a 2D-3V PIC-MCC model to analyze the influence of magnetic strength on the discharge characteristic and performance of Hall thrusters with an intermediate electrode and double-peaked magnetic field. As opposed to the two symmetrical magnetic peaks formed by double permanent magnetic rings, increasing the magnetic peak value deep within the channel can cause propellant ionization to occur; with the increase in the magnetic peak deep in the channel, the propellant utilization, thrust, and anode efficiency of the thruster are significantly improved. Double-peaked magnetic field can realize separate control of ionization and acceleration in a Hall thruster, and provide technical means for further improving thruster performance. Contribution to the Topical Issue "Physics of Ion Beam Sources", edited by Holger Kersten and Horst Neumann.

Effects of sub-bandgap illumination on electrical properties and detector performances of CdZnTe:In

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

Xu, Lingyan; Jie, Wanqi, E-mail: jwq@nwpu.edu.cn; Zha, Gangqiang, E-mail: zha-gq@hotmail.com

2014-06-09

The effects of sub-bandgap illumination on electrical properties of CdZnTe:In crystals and spectroscopic performances of the fabricated detectors were discussed. The excitation process of charge carriers through thermal and optical transitions at the deep trap could be described by the modified Shockley-Read-Hall model. The ionization probability of the deep donor shows an increase under illumination, which should be responsible for the variation of electrical properties within CdZnTe bulk materials with infrared (IR) irradiation. By applying Ohm's law, diffusion model and interfacial layer-thermionic-diffusion theory, we obtain the decrease of bulk resistivity and the increase of space charge density in the illuminatedmore » crystals. Moreover, the illumination induced ionization will further contribute to improving carrier transport property and charge collection efficiency. Consequently, the application of IR irradiation in the standard working environment is of great significance to improve the spectroscopic characteristics of CdZnTe radiation detectors.« less

Advanced PIC-MCC simulation for the investigation of step-ionization effect in intermediate-pressure capacitively coupled plasmas

NASA Astrophysics Data System (ADS)

Kim, Jin Seok; Hur, Min Young; Kim, Chang Ho; Kim, Ho Jun; Lee, Hae June

2018-03-01

A two-dimensional parallelized particle-in-cell simulation has been developed to simulate a capacitively coupled plasma reactor. The parallelization using graphics processing units is applied to resolve the heavy computational load. It is found that the step-ionization plays an important role in the intermediate gas pressure of a few Torr. Without the step-ionization, the average electron density decreases while the effective electron temperature increases with the increase of gas pressure at a fixed power. With the step-ionization, however, the average electron density increases while the effective electron temperature decreases with the increase of gas pressure. The cases with the step-ionization agree well with the tendency of experimental measurement. The electron energy distribution functions show that the population of electrons having intermediate energy from 4.2 to 12 eV is relaxed by the step-ionization. Also, it was observed that the power consumption by the electrons is increasing with the increase of gas pressure by the step-ionization process, while the power consumption by the ions decreases with the increase of gas pressure.

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

PubMed Central

2009-01-01

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

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

PubMed

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

2012-10-08

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

Novel Laser Ignition Technique Using Dual-Pulse Pre-Ionization

NASA Astrophysics Data System (ADS)

Dumitrache, Ciprian

Recent advances in the development of compact high power laser sources and fiber optic delivery of giant pulses have generated a renewed interest in laser ignition. The non-intrusive nature of laser ignition gives it a set of unique characteristics over the well-established capacitive discharge devices (or spark plugs) that are currently used as ignition sources in engines. Overall, the use of laser ignition has been shown to have a positive impact on engine operation leading to a reduction in NOx emission, fuel saving and an increased operational envelope of current engines. Conventionally, laser ignition is achieved by tightly focusing a high-power q-switched laser pulse until the optical intensity at the focus is high enough to breakdown the gas molecules. This leads to the formation of a spark that serves as the ignition source in engines. However, there are certain disadvantages associated with this ignition method. This ionization approach is energetically inefficient as the medium is transparent to the laser radiation until the laser intensity is high enough to cause gas breakdown. As a consequence, very high energies are required for ignition (about an order of magnitude higher energy than capacitive plugs at stoichiometric conditions). Additionally, the fluid flow induced during the plasma recombination generates high vorticity leading to high rates of flame stretching. In this work, we are addressing some of the aforementioned disadvantages of laser ignition by developing a novel approach based on a dual-pulse pre-ionization scheme. The new technique works by decoupling the effect of the two ionization mechanisms governing plasma formation: multiphoton ionization (MPI) and electron avalanche ionization (EAI). An UV nanosecond pulse (lambda = 266 nm) is used to generate initial ionization through MPI. This is followed by an overlapped NIR nanosecond pulse (lambda = 1064 nm) that adds energy into the pre-ionized mixture into a controlled manner until the gas temperature is suitable for combustion (T=2000-3000 K). This technique is demonstrated by attempting ignition of various mixtures of propane-air and it is shown to have distinct advantages when compared to the classical approach: lower ignition energy for given stoichiometry than conventional laser ignition ( 20% lower), extension of the lean limit ( 15% leaner) and improvement in combustion efficiency. Moreover, it is demonstrated that careful alignment of the two pulses influences the fluid dynamics of the early flame kernel growth. This finding has a number of implications for practical uses as it demonstrates that the flame kernel dynamics can be tailored using various combinations of laser pulses and opens the door for implementing such a technique to applications such as: flame holding and flame stabilization in high speed flow combustors (such as ramjet and scramjet engines), reducing flame stretching in highly turbulent combustion devices and increasing combustion efficiency for stationary natural gas engines. As such, the work presented in this dissertation should be of interest to a broad audience including those interested in combustion research, engine operation, chemically reacting flows, plasma dynamics and laser diagnostics.

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

NASA Astrophysics Data System (ADS)

Koh, Daegene; Wise, John H.

2018-03-01

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

Laser resonance ionization spectroscopy on lutetium for the MEDICIS project

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

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

DOE PAGES

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

2014-09-15

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

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

USDA-ARS?s Scientific Manuscript database

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

High-efficiency generation of pulsed Lyman-α radiation by resonant laser wave mixing in low pressure Kr-Ar mixture.

PubMed

Saito, Norihito; Oishi, Yu; Miyazaki, Koji; Okamura, Kotaro; Nakamura, Jumpei; Louchev, Oleg A; Iwasaki, Masahiko; Wada, Satoshi

2016-04-04

We report an experimental generation of ns pulsed 121.568 nm Lyman-α radiation by the resonant nonlinear four-wave mixing of 212.556 nm and 845.015 nm radiation pulses providing a high conversion efficiency 1.7x10^-3 with the output pulse energy 3.6 μJ achieved using a low pressure Kr-Ar mixture. Theoretical analysis shows that this efficiency is achieved due to the advantage of using (i) the high input laser intensities in combination with (ii) the low gas pressure allowing us to avoid the onset of full-scale discharge in the laser focus. In particular, under our experimental conditions the main mechanism of photoionization caused by the resonant 2-photon 212.556 nm radiation excitation of Kr atoms followed by the 1-photon ionization leads to ≈17% loss of Kr atoms and efficiency loss only by the end of the pulse. The energy of free electrons, generated by 212.556 nm radiation via (2 + 1)-photon ionization and accelerated mainly by 845.015 nm radiation, remains during the pulse below the level sufficient for the onset of full-scale discharge by the electron avalanche. Our analysis also suggests that ≈30-fold increase of 845.015 nm pulse energy can allow one to scale up the L-α radiation pulse energy towards the level of ≈100 μJ.

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

PubMed

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

2017-11-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

Mobility Peak Tailing Reduction in a Differential Mobility Analyzer (DMA) Coupled with a Mass Spectrometer and Several Ionization Sources

NASA Astrophysics Data System (ADS)

Amo-Gonzalez, Mario; Fernandez de la Mora, Juan

2017-08-01

The differential mobility analyzer (DMA) is a narrow-band linear ion mobility filter operating at atmospheric pressure. It combines in series with a quadrupole mass spectrometer (Q-MS) for mobility/mass analysis, greatly reducing chemical noise in selected ion monitoring. However, the large flow rate of drift gas ( 1000 L/min) required by DMAs complicates the achievement of high gas purity. Additionally, the symmetry of the drying counterflow gas at the interface of many commercial MS instruments, is degraded by the lateral motion of the drift gas at the DMA entrance slit. As a result, DMA mobility peaks often exhibit tails due to the attachment of impurity vapors, either (1) to the reagent ion within the separation cell, or (2) to the analyte of interest in the ionization region. In order to greatly increase the noise-suppression capacity of the DMA, we describe various vapor-removal schemes and measure the resulting increase in the tailing ratio, ( TR = signal at the peak maximum over signal two half-widths away from this maximum). Here we develop a low-outgassing DMA circuit connected to a mass spectrometer, and test it with three ionization sources (APCI, Desolvating-nano ESI, and Desolvating low flow SESI). While prior TR values were in the range 100-1000, the three new sources achieve TR 105. The SESI source has been optimized for maximum sensitivity, delivering an unprecedented gain for TNT of 190 counts/fg, equivalent to an ionization efficiency of one out of 140 neutral molecules.

Was Star Formation Suppressed in High-Redshift Minihalos?

NASA Astrophysics Data System (ADS)

Haiman, Zoltán; Bryan, Greg L.

2006-10-01

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

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

PubMed

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

2014-04-01

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

Study of Conical Pulsed Inductive Thruster with Multiple Modes of Operation

NASA Technical Reports Server (NTRS)

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

2008-01-01

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

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

PubMed

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

2011-10-15

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

Silver-gold alloy nanoparticles as tunable substrates for systematic control of ion-desorption efficiency and heat transfer in surface-assisted laser desorption/ionization.

PubMed

Lai, Samuel Kin-Man; Cheng, Yu-Hong; Tang, Ho-Wai; Ng, Kwan-Ming

2017-08-09

Systematically controlling heat transfer in the surface-assisted laser desorption/ionization (SALDI) process and thus enhancing the analytical performance of SALDI-MS remains a challenging task. In the current study, by tuning the metal contents of Ag-Au alloy nanoparticle substrates (AgNPs, Ag55Au45NPs, Ag15Au85NPs and AuNPs, ∅: ∼2.0 nm), it was found that both SALDI ion-desorption efficiency and heat transfer can be controlled in a wide range of laser fluence (21.3 mJ cm -2 to 125.9 mJ cm -2 ). It was discovered that ion detection sensitivity can be enhanced at any laser fluence by tuning up the Ag content of the alloy nanoparticle, whereas the extent of ion fragmentation can be reduced by tuning up the Au content. The enhancement effect of Ag content on ion desorption was found to be attributable to the increase in laser absorption efficiency (at 355 nm) with Ag content. Tuning the laser absorption efficiency by changing the metal composition was also effective in controlling the heat transfer from the NPs to the analytes. The laser-induced heating of Ag-rich alloy NPs could be balanced or even overridden by increasing the Au content of NPs, resulting in the reduction of the fragmentation of analytes. In the correlation of experimental measurement with molecular dynamics simulation, the effect of metal composition on the dynamics of the ion desorption process was also elucidated. Upon increasing the Ag content, it was also found that phase transition temperatures, such as melting, vaporization and phase explosion temperature, of NPs could be reduced. This further enhanced the desorption of analyte ions via phase-transition-driven desorption processes. The significant cooling effect on the analyte ions observed at high laser fluence was also determined to be originated from the phase explosion of the NPs. This study revealed that the development of alloy nanoparticles as SALDI substrates can constitute an effective means for the systematic control of ion-desorption efficiency and the extent of heat transfer, which could potentially enhance the analytical performance of SALDI-MS.

A Versatile Integrated Ambient Ionization Source Platform.

PubMed

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

2018-04-30

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

A Versatile Integrated Ambient Ionization Source Platform

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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

PubMed

Allan, Guy; Delerue, Christophe

2011-09-27

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

Autophagic cell death induced by reactive oxygen species is involved in hyperthermic sensitization to ionizing radiation in human hepatocellular carcinoma cells.

PubMed

Yuan, Guang-Jin; Deng, Jun-Jian; Cao, De-Dong; Shi, Lei; Chen, Xin; Lei, Jin-Ju; Xu, Xi-Ming

2017-08-14

To investigate whether autophagic cell death is involved in hyperthermic sensitization to ionizing radiation in human hepatocellular carcinoma cells, and to explore the underlying mechanism. Human hepatocellular carcinoma cells were treated with hyperthermia and ionizing radiation. MTT and clonogenic assays were performed to determine cell survival. Cell autophagy was detected using acridine orange staining and flow cytometric analysis, and the expression of autophagy-associated proteins, LC3 and p62, was determined by Western blot analysis. Intracellular reactive oxygen species (ROS) were quantified using the fluorescent probe DCFH-DA. Treatment with hyperthermia and ionizing radiation significantly decreased cell viability and surviving fraction as compared with hyperthermia or ionizing radiation alone. Cell autophagy was significantly increased after ionizing radiation combined with hyperthermia treatment, as evidenced by increased formation of acidic vesicular organelles, increased expression of LC3II and decreased expression of p62. Intracellular ROS were also increased after combined treatment with hyperthermia and ionizing radiation. Pretreatment with N-acetylcysteine, an ROS scavenger, markedly inhibited the cytotoxicity and cell autophagy induced by hyperthermia and ionizing radiation. Autophagic cell death is involved in hyperthermic sensitization of cancer cells to ionizing radiation, and its induction may be due to the increased intracellular ROS.

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

PubMed

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

2009-11-20

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

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

NASA Astrophysics Data System (ADS)

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

2016-07-01

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

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

NASA Astrophysics Data System (ADS)

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

2013-06-01

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

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

NASA Astrophysics Data System (ADS)

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

2007-10-01

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

Palladium modified porous silicon as multi-functional MALDI chip for serum peptide detection.

PubMed

Li, Xiao; Chen, Xiaoming; Tan, Jie; Liang, Xiao; Wu, Jianmin

2017-02-14

Interest in using mesoporous materials for peptidomic research has increased recently. The present study reports a new type of matrix assisted laser desorption/ionization (MALDI) plate derived from electrochemically etched porous silicon (PSi) whose surface was modified with palladium nanoparticles (PdNPs). Owing to the well-tailored pore size and the molecular filtration effect of the PSi, peptides in serum samples can be selectively captured and enriched in the pore channel, thereby eliminating the interference from large proteins in subsequent MALDI-MS detection. On the other hand, the PdNPs with localized surface plasmon resonance (LSPR) effect can help to enhance the efficiency of energy absorption in the UV region. Meanwhile, the charge separation effect between the PSi semiconductor and PdNPs also can be applied to promote the accumulation of positive charges on PdNPs, resulting in an improvement in laser desorption/ionization (LDI) efficiency under positive linear detection mode. The interplay among these unique properties of PSi and PdNPs can synergistically increase the overall sensitivity in serum peptide detection. Using this technology, serum sample can be directly detected on the PSi-PdNPs chip without complicated pretreatment process. Therefore, a high fidelity serum peptide fingerprint can be acquired in a high throughput way. With the assistance of statistical analysis, colorectal cancer patients and healthy people can be accurately distinguished based on the serum peptide fingerprints.

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

PubMed

Santa, Tomofumi

2011-01-01

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

Doping of AlxGa1-xN

NASA Astrophysics Data System (ADS)

Stampfl, C.; Van de Walle, Chris G.

1998-01-01

N-type AlxGa1-xN exhibits a dramatic decrease in the free-carrier concentration for x⩾0.40. Based on first-principles calculations, we propose that two effects are responsible for this behavior: (i) in the case of doping with oxygen (the most common unintentional donor), a DX transition occurs, which converts the shallow donor into a deep level; and (ii) compensation by the cation vacancy (VGa or VAl), a triple acceptor, increases with alloy composition x. For p-type doping, the calculations indicate that the doping efficiency decreases due to compensation by the nitrogen vacancy. In addition, an increase in the acceptor ionization energy is found with increasing x.

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

DOEpatents

Levy, Donald J.; Berman, Samuel M.

1988-01-01

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

Micro Corona Ionizer as an Ozone Source for Bacterial Cell Lysis

NASA Astrophysics Data System (ADS)

Lee, Eun-Hee; Lim, Hyun Jeong; Chua, Beelee; Son, Ahjeong

2015-04-01

DNA extraction is a critical process of DNA assays including polymerase chain reaction (PCR), microarrays, molecular cloning, and DNA hybridization which has been well established and can be implemented by commercial kits. DNA extraction involves cell lysis, precipitation, and purification through the combination of physical and chemical processes. Cell lysis is essential to high DNA recovery yield which can be achieved via a variety of physical, chemical, and enzymatic methods. However, these methods were originally developed for bioassays that were labor intensive, time consuming, and vulnerable to contamination and inhibition. Here, we proposed to employ a micro corona ionizer as an ozone source to lyse bacterial cells. Ozone has been well known and used as a disinfectant which allows cell lysis and DNA extraction. Previously, we have shown that a micro corona ionizer is capable of generating a significant amount of ozone. In this study, we employed the micro corona ionizer for the bacterial cell lysis which consists of a 50 μm diameter cantilever wire as the discharge cathode and a 50 μm thick copper foil as anode. Applied voltages varied from 1900 to 2200 V with corresponding corona currents from 16 to 28 μA. The resultant ozone (concentration > 0.14 ppm) generated from the micro corona ionizer was bubbled into the sample via a miniature pump. We demonstrated the cell lysis of Pseudomonas putida as the target bacterium using the micro corona ionizer. At a flow rate of 38 ml/min and applied corona voltage of 2000 V, 98.5 ± 0.2% lysis (normalized to sonication result) was achieved after 10 min. In comparison, untreated and air-treated samples showed normalized % lysis of 11.9 ± 2.4 and 36.1 ± 1.7%, respectively. We also showed that the cell lysis efficiency could be significantly increased by increasing the flow rate and the applied corona voltage. By comparing the experimental results for continuous and pulsed treatment, we verified that the percentage of lysis is primarily determined by the total ozone treatment time.

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

USGS Publications Warehouse

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

1990-01-01

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

Efficient Ionization Investigation for Flow Control and Energy Extraction

NASA Technical Reports Server (NTRS)

Schneider, Steven J.; Kamhawi, Hani; Blankson, Isaiah M.

2009-01-01

Nonequilibrium ionization of air by nonthermal means is explored for hypersonic vehicle applications. The method selected for evaluation generates a weakly ionized plasma using pulsed nanosecond, high-voltage discharges sustained by a lower dc voltage. These discharges promise to provide a means of energizing and sustaining electrons in the air while maintaining a nearly constant ion/neutral molecule temperature. This paper explores the use of short approx.5 nsec, high-voltage approx.12 to 22 kV, repetitive (40 to 100 kHz) discharges in generating a weakly ionized gas sustained by a 1 kV dc voltage in dry air at pressures from 10 to 80 torr. Demonstrated lifetimes of the sustainer discharge current approx.10 to 25 msec are over three orders of magnitude longer than the 5 nsec pulse that generates the electrons. This life is adequate for many high speed flows, enabling the possibility of exploiting weakly ionized plasma phenomena in flow-fields such as those in hypersonic inlets, combustors, and nozzles. Results to date are obtained in a volume of plasma between electrodes in a bell jar. The buildup and decay of the visible emission from the pulser excited air is photographed on an ICCD camera with nanosecond resolution and the time constants for visible emission decay are observed to be between 10 to 15 nsec decreasing as pressure increases. The application of the sustainer voltage does not change the visible emission decay time constant. Energy consumption as indicated by power output from the power supplies is 194 to 669 W depending on pulse repetition rate.

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

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

Siegfried, M.

2015-10-14

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

First results on Ge resonant laser photoionization in hollow cathode lamp

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

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

2016-02-15

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

Increase in Efficiency of Use of Pedestrian Radiation Portal Monitors

NASA Astrophysics Data System (ADS)

Solovev, D. B.; Merkusheva, A. E.

2017-11-01

Most international airports in the world use radiation portal monitors (RPM) for primary radiation control organization. During the exploitation pedestrian radiation portal monitors operators (in the Russian Federation it is a special subdivision of customs officials) have certain problems related to the search of an ionizing radiation source causing the alarm signal of a radiation monitor. Radiation portal monitors at standard (factory) settings have to find out the illegal moving of the radioisotopes moved by physical persons passing through a controlled zone and having a steady radiation by the gamma or neutron channel. The problem is that recently the number of the ownerships who underwent treatment or medical diagnostics with the use of radio pharmaceuticals considerably increased, i.e,. ownerships represent such an ionizing radiation source. The operator of the radiation portal monitor has to define very quickly whether the ownership is a violator (takes unsolved radioisotopes illegally) or is just a patient of the clinic who underwent treatment/diagnostics with the use of radio pharmaceuticals. The research showing the radioisotopes which are most often used in the medical purposes are given in article, it is offered to use the new software developed by the authors allowing the operator of the radiation portal monitor to define the location of the ownership which has such ionizing radiation source by the activity of radiation similar to the radiation from radio pharmaceuticals.

Temperature dependence of thermal positive ion production from sodium bromide molecules incident upon a glowing rhenium surface

NASA Astrophysics Data System (ADS)

Kawano, Hiroyuki; Kenpō, Tsutomu

1984-08-01

Emission current of Na+ ions produced from NaBr molecules impinging with a flux of 6.55×1013 molecules cm-2 s-1 upon a heated polycrystalline rhenium surface in the residual gas pressure of about 2×10-7 Torr was measured as a function of surface temperature (T) in the range of about 900-2100 K, thereby indicating that the sticking probability of NaBr to the surface is virtually unity and that the ionization efficiency ( β+) is ˜1 and 0.23 for T≂1100-1500 and 1800-2100 K, respectively. These results are explained reasonably by our previous theory that the degree (γ) of dissociation of incident molecules generally depends upon the ionization coefficient (α+) and hence upon the effective work function (φ+) for the positive ionization unless α+ is much smaller than unity. The value of φ+ was 5.45-5.51 eV for T≳1800 K, below which φ+ gradually increased up to ˜6.8 eV according to a decrease in T. By this increase both β+ and γ were kept at virtually unity even at a low temperature down to about 1100 K, at which they began to decrease sharply with a reduction in T because φ+ had already turned to a decrease at about 1200 K.

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

PubMed

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

2012-01-17

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

Materials, properties, and applications of nitrogen-doped organic semiconductors

NASA Astrophysics Data System (ADS)

Chan, Calvin Kar-Fai

As organic semiconducting materials draw increasing attention for many promising applications, including efficient organic light-emitting diodes (OLEDs), large-area organic photovoltaic (OPV) cells, and flexible organic thin-film transistors (OTFTs), chemical doping of organic materials is emerging as an important technique for overcoming performance deficiencies and material limitations of intrinsic organic films. Although p-doping has been amply demonstrated, molecular n-type doping has been difficult to study because of the inherent instability of easily oxidized n-dopants. In this work, the facile use of two low ionization energy (IE) small molecules that are suitable for n-doping a wide range of organic electronic materials is demonstrated. Cobaltocene (CoCp2) and its derivative, decamethylcobaltocene ( CoCp*2 ), were found to have fairly low IEs for organic compounds. Co-deposition of the n-dopants with different host molecules results in pronounced shifts of the Fermi-level towards unoccupied molecular states, indicating a significant increase in electron concentration. The Fermi-level shifts, measured with ultra-violet photoemission spectroscopy (UPS), are correlated with excess carrier densities using a model based on Fermi-Dirac (F-D) statistics and a Gaussian distributed density of states. The calculated electron densities suggest full dopant ionization at low concentrations, and diminished efficiency at high donor concentrations. The concentration of incorporated dopants is examined by chemical composition analysis of doped films using X-ray photoemission spectroscopy (XPS). Atomic concentration depth profiling determined by Rutherford backscattering (RBS) suggests that the incorporation of CoCp2 and CoCp*2 is well-controlled and the dopants are minimally diffusive. Organic films n-doped using CoCp2 and CoCp*2 show several orders of magnitude increase in current density resulting from both enhanced electron injection and increased electron conductivity in the bulk. Increases in the bulk conductivity suggest both improved electron mobility and higher electron concentrations. These findings are applied with previous work on p-doping to fabricate organic p-i-n homojunction devices that exhibit strong rectification and large built-in potentials. Heterojunction OPVs using undoped CuPc and n-doped C60 display significant increases in open-circuit voltage (Voc), short-circuit current (Isc), fill-factor (FF), and efficiency.

N2 Dissociation In The Mesosphere Due To Secondary Electrons During A Solar Proton Event: The Effect On Atomic Nitrogen and Nitric Oxide

NASA Astrophysics Data System (ADS)

Verronen, P. T.; Shematovich, V. I.; Bisikalo, D. V.; Turunen, E.; Ulich, Th.

Solar proton events have an effect on the middle atmospheric odd nitrogen chem- istry. During a solar proton event high energy protons enter Earth's middle atmosphere where they ionize ambient gas. Ionization leads to production of atomic nitrogen, and further to production of nitric oxide, through ion chemistry. In addition, ionization processes produce secondary electrons that, if possessing 9.76 eV or more energy, dissociate N2 providing an additional source of atomic nitrogen. We have calculated mesospheric N2 dissociation rate due to secondary electrons dur- ing a solar proton event. Further, we have studied the effect on atomic nitrogen and nitric oxide at altitudes between 50 and 90 km. It was found that N2 is efficiently dis- sociated in the lower mesosphere by secondary electrons, with rates up to 103 cm-3 s-1 at 50 km. Thus, secondary electrons significantly add to odd nitrogen produc- tion. As a result of N2 dissociation, atomic nitrogen is greatly enhanced in both N(4S) and N(2D) states by 259% and 1220% maximum increases at 50 km, respectively. This further leads to a maximum increase of 16.5% in NO concentration at 61 km via chemical reactions. In our study a Monte Carlo model was used to calculate the total ionization rate and secondary electrons flux due to precipitating protons. These where then used as input to a detailed ion and neutral chemistry model and a steady-state solution was calcu- lated for two cases: With and without N2 dissociation due to secondary electrons.

Efficiency of plasma actuator ionization in shock wave modification in a rarefied supersonic flow over a flat plate

NASA Astrophysics Data System (ADS)

Joussot, Romain; Lago, Viviana; Parisse, Jean-Denis

2014-12-01

This paper describes experimental and numerical investigations focused on the shock wave modification, induced by a dc glow discharge, of a Mach 2 flow under rarefied regime. The model under investigation is a flat plate equipped with a plasma actuator composed of two electrodes. The glow discharge is generated by applying a negative potential to the upstream electrode, enabling the creation of a weakly ionized plasma. The natural flow (i.e. without the plasma) exhibits a thick laminar boundary layer and a shock wave with a hyperbolic shape. Images of the flow obtained with an ICCD camera revealed that the plasma discharge induces an increase in the shock wave angle. Thermal effects (volumetric, and at the surface) and plasma effects (ionization, and thermal non-equilibrium) are the most relevant processes explaining the observed modifications. The effect induced by the heating of the flat plate surface is studied experimentally by replacing the upstream electrode by a heating element, and numerically by modifying the thermal boundary condition of the model surface. The results show that for a similar temperature distribution over the plate surface, modifications induced by the heating element are lower than those produced by the plasma. This difference shows that other effects than purely thermal effects are involved with the plasma actuator. Measurements of the electron density with a Langmuir probe highlight the fact that the ionization degree plays an important role into the modification of the flow. The gas properties, especially the isentropic exponent, are indeed modified by the plasma above the actuator and upstream the flat plate. This leads to a local modification of the flow conditions, inducing an increase in the shock wave angle.

Asymmetric soft-error resistant memory

NASA Technical Reports Server (NTRS)

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

1991-01-01

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

Degradation of fluoroquinolone antibiotics during ionizing radiation treatment and assessment of antibacterial activity, toxicity and biodegradability of the products

NASA Astrophysics Data System (ADS)

Tegze, Anna; Sági, Gyuri; Kovács, Krisztina; Homlok, Renáta; Tóth, Tünde; Mohácsi-Farkas, Csilla; Wojnárovits, László; Takács, Erzsébet

2018-06-01

This work aimed at investigating the ionizing radiation induced degradation of two fluoroquinolone antibiotics: norfloxacin and ciprofloxacin. At 0.1 mmol dm-3 concentration a low dose, 2 kGy was sufficient to degrade the initial molecules. However, despite of the high removal efficiency the degrees of both the mineralization and the oxidation were low, ∼10% and ∼25%, respectively. (The difference between the results obtained in norfloxacin and ciprofloxacin solutions was not statistically significant.) Broth microdilution tests carried out on Staphylococcus aureus evidenced removal of antibacterial activity in samples irradiated with 2 kGy. Acute toxicity determined on Vibrio fischeri bacteria showed increased toxicity at low doses indicating that the early degradation products were more toxic than the initial molecules. The results of biodegradation experiments performed in activated sludge have shown that the degradation products have become available to the metabolic processes of the microorganisms.

Optimal control of the strong-field ionization of silver clusters in helium droplets

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

Truong, N. X.; Goede, S.; Przystawik, A.

Optimal control techniques combined with femtosecond laser pulse shaping are applied to steer and enhance the strong-field induced emission of highly charged atomic ions from silver clusters embedded in helium nanodroplets. With light fields shaped in amplitude and phase we observe a substantial increase of the Ag{sup q+} yield for q>10 when compared to bandwidth-limited and optimally stretched pulses. A remarkably simple double-pulse structure, containing a low-intensity prepulse and a stronger main pulse, turns out to produce the highest atomic charge states up to Ag{sup 20+}. A negative chirp during the main pulse hints at dynamic frequency locking to themore » cluster plasmon. A numerical optimal control study on pure silver clusters with a nanoplasma model converges to a similar pulse structure and corroborates that the optimal light field adapts to the resonant excitation of cluster surface plasmons for efficient ionization.« less

Coulomb-driven energy boost of heavy ions for laser-plasma acceleration.

PubMed

Braenzel, J; Andreev, A A; Platonov, K; Klingsporn, M; Ehrentraut, L; Sandner, W; Schnürer, M

2015-03-27

An unprecedented increase of kinetic energy of laser accelerated heavy ions is demonstrated. Ultrathin gold foils have been irradiated by an ultrashort laser pulse at a peak intensity of 8×10^{19}  W/  cm^{2}. Highly charged gold ions with kinetic energies up to >200  MeV and a bandwidth limited energy distribution have been reached by using 1.3 J laser energy on target. 1D and 2D particle in cell simulations show how a spatial dependence on the ion's ionization leads to an enhancement of the accelerating electrical field. Our theoretical model considers a spatial distribution of the ionization inside the thin target, leading to a field enhancement for the heavy ions by Coulomb explosion. It is capable of explaining the energy boost of highly charged ions, enabling a higher efficiency for the laser-driven heavy ion acceleration.

Ionizing Organic Compound Based Nanocomposites for Efficient Gamma-Ray Sensor

NASA Technical Reports Server (NTRS)

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

2017-01-01

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

Efficient G0W0 using localized basis sets: a benchmark for molecules

NASA Astrophysics Data System (ADS)

Koval, Petr; Per Ljungberg, Mathias; Sanchez-Portal, Daniel

Electronic structure calculations within Hedin's GW approximation are becoming increasingly accessible to the community. In particular, as it has been shown earlier and we confirm by calculations using our MBPT_LCAO package, the computational cost of the so-called G0W0 can be made comparable to the cost of a regular Hartree-Fock calculation. In this work, we study the performance of our new implementation of G0W0 to reproduce the ionization potentials of all 117 closed-shell molecules belonging to the G2/97 test set, using a pseudo-potential starting point provided by the popular density-functional package SIESTA. Moreover, the ionization potentials and electron affinities of a set of 24 acceptor molecules are compared to experiment and to reference all-electron calculations. PK: Guipuzcoa Fellow; PK,ML,DSP: Deutsche Forschungsgemeinschaft (SFB1083); PK,DSP: MINECO MAT2013-46593-C6-2-P.

Multiphoton laser ionization for energy conversion in barium vapor

NASA Astrophysics Data System (ADS)

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

2013-03-01

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

The galaxy NGC 1566 - Distribution and kinematics of the ionized gas

NASA Astrophysics Data System (ADS)

Comte, G.; Duquennoy, A.

1982-10-01

H-alpha narrowband observations are the basis of a study of ionized hydrogen in the large spiral galaxy NGC 1566 which has yielded a catalog of 418 H II regions covering the main body of the galaxy, supplemented by 59 positions and estimated H-alpha luminosities for regions located in the pseudo-outer ring where no H-alpha plate is available. A discussion of luminosity function, diameter distribution and spiral structure notes evidence for a double two-armed spiral pattern. The plane of the galaxy appears warped, and the efficiency of the two different spiral patterns in star formation is different. A preliminary radial velocity field is determined from three interferograms in H-alpha light, and is found to be acceptably fitted by a simple bulge-plus-disk dynamical model in which the apparent disk mass-to-light ratio sharply increases from center to edge.

High Resolution Separations and Improved Ion Production and Transmission in Metabolomics

PubMed Central

Metz, Thomas O.; Page, Jason S.; Baker, Erin S.; Tang, Keqi; Ding, Jie; Shen, Yufeng; Smith, Richard D.

2008-01-01

The goal of metabolomics analyses is the detection and quantitation of as many sample components as reasonably possible in order to identify compounds or “features” that can be used to characterize the samples under study. When utilizing electrospray ionization to produce ions for analysis by mass spectrometry (MS), it is important that metabolome sample constituents be efficiently separated prior to ion production, in order to minimize ionization suppression and thereby extend the dynamic range of the measurement, as well as the coverage of the metabolome. Similarly, optimization of the MS inlet and interface can lead to increased measurement sensitivity. This perspective review will focus on the role of high resolution liquid chromatography (LC) separations in conjunction with improved ion production and transmission for LC-MS-based metabolomics. Additional emphasis will be placed on the compromise between metabolome coverage and sample analysis throughput. PMID:19255623

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

PubMed

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

2006-11-10

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

Modeling weakly-ionized plasmas in magnetic field: A new computationally-efficient approach

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

Parent, Bernard, E-mail: parent@pusan.ac.kr; Macheret, Sergey O.; Shneider, Mikhail N.

2015-11-01

Despite its success at simulating accurately both non-neutral and quasi-neutral weakly-ionized plasmas, the drift-diffusion model has been observed to be a particularly stiff set of equations. Recently, it was demonstrated that the stiffness of the system could be relieved by rewriting the equations such that the potential is obtained from Ohm's law rather than Gauss's law while adding some source terms to the ion transport equation to ensure that Gauss's law is satisfied in non-neutral regions. Although the latter was applicable to multicomponent and multidimensional plasmas, it could not be used for plasmas in which the magnetic field was significant.more » This paper hence proposes a new computationally-efficient set of electron and ion transport equations that can be used not only for a plasma with multiple types of positive and negative ions, but also for a plasma in magnetic field. Because the proposed set of equations is obtained from the same physical model as the conventional drift-diffusion equations without introducing new assumptions or simplifications, it results in the same exact solution when the grid is refined sufficiently while being more computationally efficient: not only is the proposed approach considerably less stiff and hence requires fewer iterations to reach convergence but it yields a converged solution that exhibits a significantly higher resolution. The combined faster convergence and higher resolution is shown to result in a hundredfold increase in computational efficiency for some typical steady and unsteady plasma problems including non-neutral cathode and anode sheaths as well as quasi-neutral regions.« less

Variation of the external quantum efficiency with temperature and current density in red, blue, and deep ultraviolet light-emitting diodes

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

Park, Jun Hyuk; Lee, Jong Won; Kim, Dong Yeong

The temperature-dependent external quantum efficiencies (EQEs) were investigated for a 620 nm AlGaInP red light-emitting diodes (LEDs), a 450 nm GaInN blue LED, and a 285 nm AlGaN deep-ultraviolet (DUV) LED. We observed distinct differences in the variation of the EQE with temperature and current density for the three types of LEDs. Whereas the EQE of the AlGaInP red LED increases as temperature decreases below room temperature, the EQEs of GaInN blue and AlGaN DUV LEDs decrease for the same change in temperature in a low-current density regime. The free carrier concentration, as determined from the dopant ionization energy, shows a strong material-system-specificmore » dependence, leading to different degrees of asymmetry in carrier concentration for the three types of LEDs. We attribute the EQE variation of the red, blue, and DUV LEDs to the different degrees of asymmetry in carrier concentration, which can be exacerbated at cryogenic temperatures. As for the EQE variation with temperature in a high-current density regime, the efficiency droop for the AlGaInP red and GaInN blue LEDs becomes more apparent as temperature decreases, due to the deterioration of the asymmetry in carrier concentration. However, the EQE of the AlGaN DUV LED initially decreases, then reaches an EQE minimum point, and then increases again due to the field-ionization of acceptors by the Poole-Frenkel effect. The results elucidate that carrier transport phenomena allow for the understanding of the droop phenomenon across different material systems, temperatures, and current densities.« less

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

PubMed

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

2016-07-01

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

Eu2+-Doped Sr2B2-2xSi2+3xAl2-xN8+x: A Boron-Containing Orange-Emitting Nitridosilicate with Interesting Composition-Dependent Photoluminescence Properties.

PubMed

Ten Kate, Otmar M; Xie, Rong-Jun; Wang, Chun-Yun; Funahashi, Shiro; Hirosaki, Naoto

2016-11-07

Novel Sr 2-y Eu y B 2-2x Si 2+3x Al 2-x N 8+x phosphors were investigated as a function of the boron and aluminum over silicon ratio and as a function of the Eu 2+ concentration. Samples were prepared via solid-state reaction synthesis by carefully controlling the synthesis conditions and composition. At high boron and aluminum content, that is, x = 0, a Eu 2+ 5d-4f emission is observed of which the maximum shifts from 595 nm for low Eu concentrations (y = 0.005) toward 623 nm for high Eu concentrations (y = 0.5). The samples can be excited by UV or blue light up to ∼475 nm. Substitution of [B 2 Al] 9+ units by [Si 3 N] 9+ units, increasing x up to 0.15, greatly improves the luminescence efficiency up to 46% and shows a very large redshift of the excitation bands with ∼100 nm, while the emission band shifts with ∼10 nm. The shifts are attributed to the lowering of the 5d level as a result of the decreased Eu-N distance upon substitution. Temperature-dependent measurements show that the Eu 2+ 5d-4f emission is largely thermally quenched at room temperature for x = 0 due to thermal ionization toward the conduction band, explaining the low luminescence efficiency. The lowering of the 5d level at larger values of x reduces the thermal ionization and consequently increases the thermal stability and quantum efficiency, resulting in strongly luminescent blue-to-orange conversion phosphors that are interesting for light-emitting diode applications.

Physical Conditions in Shocked Interstellar Gas Interacting with the Supernova Remnant IC 443

NASA Astrophysics Data System (ADS)

Ritchey, Adam M.; Federman, Steven Robert; Jenkins, Edward B.; Caprioli, Damiano; Wallerstein, George

2018-06-01

We present the results of a detailed investigation into the physical conditions in interstellar material interacting with the supernova remnant IC 443. Our analysis is based on an examination of high-resolution HST/STIS spectra of two stars probing predominantly neutral gas located both ahead of and behind the supernova shock front. The pre-shock neutral gas is characterized by densities and temperatures typical of diffuse interstellar clouds, while the post-shock material exhibits a range of more extreme physical conditions, including high temperatures (>104 K) in some cases, which may require a sudden heating event to explain. The ionization level is enhanced in the high-temperature post-shock material, which could be the result of enhanced radiation from shocks or from an increase in cosmic-ray ionization. The gas-phase abundances of refractory elements are also enhanced in the high-pressure gas, suggesting efficient destruction of dust grains by shock sputtering. Observations of highly-ionized species at very high velocity indicate a post-shock temperature of 107 K for the hot X-ray emitting plasma of the remnant’s interior, in agreement with studies of thermal X-ray emission from IC 443.

Short communication: Identification of subclinical cow mastitis pathogens in milk by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

PubMed

Barreiro, J R; Ferreira, C R; Sanvido, G B; Kostrzewa, M; Maier, T; Wegemann, B; Böttcher, V; Eberlin, M N; dos Santos, M V

2010-12-01

Subclinical mastitis is a common and easily disseminated disease in dairy herds. Its routine diagnosis via bacterial culture and biochemical identification is a difficult and time-consuming process. In this work, we show that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) allows bacterial identification with high confidence and speed (1 d for bacterial growth and analysis). With the use of MALDI-TOF MS, 33 bacterial culture isolates from milk of different dairy cows from several farms were analyzed, and the results were compared with those obtained by classical biochemical methods. This proof-of-concept case demonstrates the reliability of MALDI-TOF MS bacterial identification, and its increased selectivity as illustrated by the additional identification of coagulase-negative Staphylococcus species and mixed bacterial cultures. Matrix-assisted laser desorption-ionization mass spectrometry considerably accelerates the diagnosis of mastitis pathogens, especially in cases of subclinical mastitis. More immediate and efficient animal management strategies for mastitis and milk quality control in the dairy industry can therefore be applied. Copyright © 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2016-05-01

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

Modeling photoionization of aqueous DNA and its components.

PubMed

Pluhařová, Eva; Slavíček, Petr; Jungwirth, Pavel

2015-05-19

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

Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation

NASA Astrophysics Data System (ADS)

Crowe, I. F.; Papachristodoulou, N.; Halsall, M. P.; Hylton, N. P.; Hulko, O.; Knights, A. P.; Yang, P.; Gwilliam, R. M.; Shah, M.; Kenyon, A. J.

2013-01-01

We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb-centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth.

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

NASA Astrophysics Data System (ADS)

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

2004-09-01

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

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

PubMed

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

2006-01-01

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

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

PubMed Central

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

2016-01-01

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

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

PubMed

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

2014-01-15

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

Capillary electrophoresis electrospray ionization mass spectrometry interface

DOEpatents

Smith, Richard D.; Severs, Joanne C.

1999-01-01

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

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

PubMed

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

2009-10-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

The SPES surface ionization source

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

The effects of surgery and anesthesia on blood magnesium and calcium concentrations in canine and feline patients.

PubMed

Brainard, Benjamin M; Campbell, Vicki L; Drobatz, Kenneth J; Perkowski, Sandra Z

2007-03-01

To demonstrate the effect of anesthesia and surgery on serum ionized magnesium and ionized calcium concentrations in clinical canine and feline patients. 37 client-owned dogs, ASA PS I-III and 10 client-owned cats, ASA PS I, all receiving anesthesia for elective or emergent surgery at a Veterinary Teaching Hospital. Plasma ionized and serum total magnesium, and plasma ionized calcium were measured prior to and after a group-standardized anesthetic protocol. Regardless of pre-operative medication (hydromorphone or butorphanol), anesthetic induction (thiopental or lidocaine/hydromorphone/diazepam (LHD) and propofol combination), or type of surgical procedure (peripheral surgery or laparotomy), post-operative plasma ionized calcium concentration decreased in all groups of dogs, while post-operative plasma ionized magnesium increased in all groups, although the changes were not always significant. The dogs who were induced with an LHD and propofol technique had a greater increase in ionized magnesium (0.36 +/- 0.07 to 0.42 +/- 0.07 mmol L(-1)) than the group in which anesthesia was induced with thiopental (0.41 +/- 0.07 to 0.42 +/- 0.07 mmol L(-1), p = 0.009). The cats showed similar changes in ionized magnesium and ionized calcium, and also had a significant increase in serum total magnesium (2.17 +/- 0.20 to 2.31 +/- 0.25 mg dL(-1), p = 0.009) CONCLUSIONS, CLINICAL RELEVANCE: A post-operative decrease in ionized calcium was demonstrated in healthy animals, as well as an increase in ionized or total magnesium after various anesthetic protocols and surgeries. These changes, while statistically significant, do not appear to be clinically significant, as values remained within reference ranges at all times.

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

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

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

2015-06-27

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

Metal Cationization Extractive Electrospray Ionization Mass Spectrometry of Compounds Containing Multiple Oxygens

NASA Astrophysics Data System (ADS)

Swanson, Kenneth D.; Spencer, Sandra E.; Glish, Gary L.

2017-06-01

Extractive electrospray ionization is an ambient ionization technique that allows real-time sampling of liquid samples, including organic aerosols. Similar to electrospray ionization, the composition of the electrospray solvent used in extractive electrospray ionization can easily be altered to form metal cationized molecules during ionization simply by adding a metal salt to the electrospray solvent. An increase in sensitivity is observed for some molecules that are lithium, sodium, or silver cationized compared with the protonated molecule formed in extractive electrospray ionization with an acid additive. Tandem mass spectrometry of metal cationized molecules can also significantly improve the ability to identify a compound. Tandem mass spectrometry of lithium and silver cationized molecules can result in an increase in the number and uniqueness of dissociation pathways relative to [M + H]+. These results highlight the potential for extractive electrospray ionization with metal cationization in analyzing complex aerosol mixtures. [Figure not available: see fulltext.

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

PubMed

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

2016-09-01

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

Improving the efficiency of x-ray lasers

NASA Astrophysics Data System (ADS)

Tallents, Gregory J.; Zeitoun, Philippe; Behjat, A.; Demir, A.; Holden, M.; Krishnan, J.; Lewis, Ciaran L. S.; MacPhee, Andrew G.; Warwick, P. J.; Nantel, Marc; Jamelot, Gerard; Rus, Bedrich; Jaegle, Pierre; Klisnick, Annie; Goedtkindt, P.; Carillon, Antoine; Fill, Ernst E.; Li, Yuelin; Pretzler, Georg; Schloegl, Dieter; Steingruber, Juergen; Neely, David; Norreys, Peter A.; Key, Michael H.; Zhang, Jie; Pert, Geoffrey J.; Healy, S. B.; Plowes, J. A.

1995-09-01

Current successful approaches for achieving soft x-ray lasing typically require pumping laser pulses of duration approximately ns and energy approximately kJ (collisionally pumped schemes) or approximately ps pulses and powers of approximately several TW (recombination-pumped schemes). For applications, it is important to improve the efficiency of soft x-ray lasers and so reduce the required power of pumping lasers. The effect of pre- pulse on neon-like collisionally pumped lasers has been investigated using the LULI laser (Ecole Polytechnique, France). A small pre-pulse level approximately 10-3 of the main pulse energy was found to increase the J equals 0 minus 1 neon-like zinc laser output at 21 nm by an order-of-magnitude with a comparable increase in efficiency. A double pumping laser pulse on neon-like yttrium lasing output at 15 nm obtained with the VULCAN laser (Rutherford Appleton Laboratory, England) was also found to increase the x-ray lasing efficiency. With adiabatically cooled recombination lasing, it is shown that approximately 2 ps pulses are optimum for achieving the desired ionization balance for lasing output. The possibility of achieving recombination lasing at short wavelengths on lithium-like ions with longer pulse lasers has been investigated using the ASTERIX laser (Max-Planck Quantenoptik, Germany). These results are presented and interpreted to provide possible directions for improving the efficiency of x-ray lasers.

Synergistic effect of ozonation and ionizing radiation for PVA decomposition.

PubMed

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

2015-08-01

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

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

DOEpatents

Denton, M. Bonner; Sperline, Roger P.

2015-09-15

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

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

DOEpatents

Denton, M. Bonner; Sperline, Roger P

2014-02-18

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

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

DOE PAGES

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

2014-04-23

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

Electrically driven plasmon-exciton coupled random lasing in ZnO metal-semiconductor-metal devices

NASA Astrophysics Data System (ADS)

Suja, Mohammad; Debnath, Bishwajit; Bashar, Sunayna B.; Su, Longxing; Lake, Roger; Liu, Jianlin

2018-05-01

Electrically driven plasmon-exciton coupled random lasing is demonstrated by incorporating Ag nanoparticles on Cu-doped ZnO metal-semiconductor-metal (MSM) devices. Both photoluminescence and electroluminescence studies show that emission efficiencies have been enhanced significantly due to coupling between ZnO excitons and Ag surface plasmons. With the incorporation of Ag nanoparticles on ZnO MSM structures, internal quantum efficiency up to 6 times is demonstrated. Threshold current for lasing is decreased by as much as 30% while the output power is increased up to 350% at an injection current of 40 mA. A numerical simulation study reveals that hole carriers are generated in the ZnO MSM devices from impact ionization processes for subsequent plasmon-exciton coupled lasing.

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

DTIC Science & Technology

2007-07-06

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

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

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

NASA Technical Reports Server (NTRS)

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

1976-01-01

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

Electron-muon ranger: performance in the MICE muon beam

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

Enhanced production of low energy electrons by alpha particle impact

PubMed Central

Kim, Hong-Keun; Titze, Jasmin; Schöffler, Markus; Trinter, Florian; Waitz, Markus; Voigtsberger, Jörg; Sann, Hendrik; Meckel, Moritz; Stuck, Christian; Lenz, Ute; Odenweller, Matthias; Neumann, Nadine; Schössler, Sven; Ullmann-Pfleger, Klaus; Ulrich, Birte; Fraga, Rui Costa; Petridis, Nikos; Metz, Daniel; Jung, Annika; Grisenti, Robert; Czasch, Achim; Jagutzki, Ottmar; Schmidt, Lothar; Jahnke, Till; Schmidt-Böcking, Horst; Dörner, Reinhard

2011-01-01

Radiation damage to living tissue stems not only from primary ionizing particles but to a substantial fraction from the dissociative attachment of secondary electrons with energies below the ionization threshold. We show that the emission yield of those low energy electrons increases dramatically in ion–atom collisions depending on whether or not the target atoms are isolated or embedded in an environment. Only when the atom that has been ionized and excited by the primary particle impact is in immediate proximity of another atom is a fragmentation route known as interatomic Coulombic decay (ICD) enabled. This leads to the emission of a low energy electron. Over the past decade ICD was explored in several experiments following photoionization. Most recent results show its observation even in water clusters. Here we show the quantitative role of ICD for the production of low energy electrons by ion impact, thus approaching a scenario closer to that of radiation damage by alpha particles: We choose ion energies on the maximum of the Bragg peak where energy is most efficiently deposited in tissue. We compare the electron production after colliding He+ ions on isolated Ne atoms and on Ne dimers (Ne2). In the latter case the Ne atom impacted is surrounded by a most simple environment already opening ICD as a deexcitation channel. As a consequence, we find a dramatically enhanced low energy electron yield. The results suggest that ICD may have a significant influence on cell survival after exposure to ionizing radiation. PMID:21730184

Indirect dark matter signatures in the cosmic dark ages. II. Ionization, heating, and photon production from arbitrary energy injections

NASA Astrophysics Data System (ADS)

Slatyer, Tracy R.

2016-01-01

Any injection of electromagnetically interacting particles during the cosmic dark ages will lead to increased ionization, heating, production of Lyman-α photons and distortions to the energy spectrum of the cosmic microwave background, with potentially observable consequences. In this paper we describe numerical results for the low-energy electrons and photons produced by the cooling of particles injected at energies from keV to multi-TeV scales, at arbitrary injection redshifts (but focusing on the post-recombination epoch). We use these data, combined with existing calculations modeling the cooling of these low-energy particles, to estimate the resulting contributions to ionization, excitation and heating of the gas, and production of low-energy photons below the threshold for excitation and ionization. We compute corrected deposition-efficiency curves for annihilating dark matter, and demonstrate how to compute equivalent curves for arbitrary energy-injection histories. These calculations provide the necessary inputs for the limits on dark matter annihilation presented in the accompanying paper I, but also have potential applications in the context of dark matter decay or deexcitation, decay of other metastable species, or similar energy injections from new physics. We make our full results publicly available at http://nebel.rc.fas.harvard.edu/epsilon, to facilitate further independent studies. In particular, we provide the full low-energy electron and photon spectra, to allow matching onto more detailed codes that describe the cooling of such particles at low energies.

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

PubMed

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

2017-09-05

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

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

Zeta potential response of human erythrocyte membranes to the modulators of Gardos channel activity under low rate β-radiation.

PubMed

Zhirnov, V V; Iakovenko, I N; Voitsitskiy, V M; Khyzhnyak, S V; Zubrikova-Chugainova, O G; Gorobetz, V A

2015-12-01

Study of human erythrocyte DP response under modification by activators and blockers of the functional state of Ca2+-dependent K+ channels under low rate β-radiation. Erythrocytes were isolated from the donor blood. The zeta potential was computed from the value of the cell electrophoretic mobility. The investigated drugs preliminary introduced in cellular suspensions, and then aliquote of 90Sr(NO3)2 solution to get the final activity concentration of 44,4kBq⋅l-1. The radioisotope radiation of 90Sr/90Y (RR, 15 μGy⋅h-1) increases an absolute value of erythrocyte membranes DP (DPab), and its action is reversible. It specifies the effect is mediated by non-ionizing part of the RR. Dibutyril-cAMP dose-independent increases DPab of erythrocyte membranes in the concentration range of 1-100 мкМ, but RR does not amplify this effect. Anaprilin increases dose-independent DPab in concentrations 10 and 100 μМ. The effect of maximal concentration of anaprilin (100 μМ) decreases by RR. Clotrimazol increases DPab of erythrocyte membranes in the concentration range of 0,1-10 μМ relatively control, while its maximal concentration - decreases, and the minimal level does not reliably influence on this index The action of сlotrimazol on DP in concentrations of 10-100 μМ is abolished by RR, and is not changed in the range of 0,1-1,0 μМ. Nitrendipine raises DPab of erythrocyte membranes in all of range of concentrations, and RR amplifies the effect of the drug. 1. There is a threshold of the biological action on cells for the ionizing component of radioisotope radiation determined by efficiency of operation their antioxidant system.2. At dose rates below a threshold, the action of ionizing radiation is mediated by its non-ionizing component, and is reversible, and therefore is determined only in the field of radiation. V. V. Zhirnov, I. N. Iakovenko, V.M. Voitsitskiy, S. V. Khyzhnyak, О. G. Zubrikova-Chugainova, V.A. Gorobetz.

Conformational relaxation and water penetration coupled to ionization of internal groups in proteins.

PubMed

Damjanović, Ana; Brooks, Bernard R; García-Moreno, Bertrand

2011-04-28

Molecular dynamics simulations were used to examine the effects of ionization of internal groups on the structures of eighteen variants of staphylococcal nuclease (SNase) with internal Lys, Asp, or Glu. In most cases the RMSD values of internal ionizable side chains were larger when the ionizable moieties were charged than when they were neutral. Calculations of solvent-accessible surface area showed that the internal ionizable side chains were buried in the protein interior when they were neutral and moved toward crevices and toward the protein-water interface when they were charged. The only exceptions are Lys-36, Lys-62, and Lys-103, which remained buried even after charging. With the exception of Lys-38, the number of internal water molecules surrounding the ionizable group increased upon charging: the average number of water oxygen atoms within the first hydration shell increased by 1.7 for Lys residues, by 5.2 for Asp residues, and by 3.2 for Glu residues. The polarity of the microenvironment of the ionizable group also increased when the groups were charged: the average number of polar atoms of any kind within the first hydration shell increased by 2.7 for Lys residues, by 4.8 for Asp residues, and by 4.0 for Glu residues. An unexpected correlation was observed between the absolute value of the shifts in pK(a) values measured experimentally, and several parameters of structural relaxation: the net difference in the polarity of the microenvironment of the charged and neutral forms of the ionizable groups, the net difference in hydration of the charged and neutral forms of the ionizable groups, and the difference in RMSD values of the charged and neutral forms of the ionizable groups. The effects of ionization of internal groups on the conformation of the backbone were noticeable but mostly small and localized to the area immediately next to the internal ionizable moiety. Some variants did exhibit local unfolding.

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

PubMed

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

2015-09-21

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

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

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

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

1989-07-27

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

A Physical Model for the Evolving Ultraviolet Luminosity Function of High Redshift Galaxies and their Contribution to the Cosmic Reionization

NASA Astrophysics Data System (ADS)

Cai, Zhen-Yi; Lapi, Andrea; Bressan, Alessandro; De Zotti, Gianfranco; Negrello, Mattia; Danese, Luigi

2014-04-01

We present a physical model for the evolution of the ultraviolet (UV) luminosity function of high-redshift galaxies, taking into account in a self-consistent way their chemical evolution and the associated evolution of dust extinction. Dust extinction is found to increase fast with halo mass. A strong correlation between dust attenuation and halo/stellar mass for UV selected high-z galaxies is thus predicted. The model yields good fits of the UV and Lyman-α (Lyα) line luminosity functions at all redshifts at which they have been measured. The weak observed evolution of both luminosity functions between z = 2 and z = 6 is explained as the combined effect of the negative evolution of the halo mass function; of the increase with redshift of the star formation efficiency due to the faster gas cooling; and of dust extinction, differential with halo mass. The slope of the faint end of the UV luminosity function is found to steepen with increasing redshift, implying that low luminosity galaxies increasingly dominate the contribution to the UV background at higher and higher redshifts. The observed range of the UV luminosities at high z implies a minimum halo mass capable of hosting active star formation M crit <~ 109.8 M ⊙, which is consistent with the constraints from hydrodynamical simulations. From fits of Lyα line luminosity functions, plus data on the luminosity dependence of extinction, and from the measured ratios of non-ionizing UV to Lyman-continuum flux density for samples of z ~= 3 Lyman break galaxies and Lyα emitters, we derive a simple relationship between the escape fraction of ionizing photons and the star formation rate. It implies that the escape fraction is larger for low-mass galaxies, which are almost dust-free and have lower gas column densities. Galaxies already represented in the UV luminosity function (M UV <~ -18) can keep the universe fully ionized up to z ~= 6. This is consistent with (uncertain) data pointing to a rapid drop of the ionization degree above z ~= 6, such as indications of a decrease of the comoving emission rate of ionizing photons at z ~= 6, a decrease of sizes of quasar near zones, and a possible decline of the Lyα transmission through the intergalactic medium at z > 6. On the other hand, the electron scattering optical depth, τes, inferred from cosmic microwave background (CMB) experiments favor an ionization degree close to unity up to z ~= 9-10. Consistency with CMB data can be achieved if M crit ~= 108.5 M ⊙, implying that the UV luminosity functions extend to M UV ~= -13, although the corresponding τes is still on the low side of CMB-based estimates.

Protonation enhancement by dichloromethane doping in low-pressure photoionization

PubMed Central

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

2016-01-01

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

Protonation enhancement by dichloromethane doping in low-pressure photoionization.

PubMed

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

2016-12-01

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

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

PubMed

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

2018-03-20

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

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-11-01

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

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

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

Beck, Sara; Turner, Jean; Lacy, John

2015-11-20

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

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

PubMed

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

2014-08-01

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

THz field engineering in two-color femtosecond filaments using chirped and delayed laser pulses

NASA Astrophysics Data System (ADS)

Nguyen, A.; González de Alaiza Martínez, P.; Thiele, I.; Skupin, S.; Bergé, L.

2018-03-01

We numerically study the influence of chirping and delaying several ionizing two-color light pulses in order to engineer terahertz (THz) wave generation in air. By means of comprehensive 3D simulations, it is shown that two chirped pulses can increase the THz yield when they are separated by a suitable time delay for the same laser energy in focused propagation geometry. To interpret these results, the local current theory is revisited and we propose an easy, accessible all-optical criterion that predicts the laser-to-THz conversion efficiencies given any input laser spectrum. In the filamentation regime, numerical simulations display evidence that a chirped pulse is able to produce more THz radiation due to propagation effects, which maintain the two colors of the laser field more efficiently coupled over long distances. A large delay between two pulses promotes multi-peaked THz spectra as well as conversion efficiencies above 10‑4.

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

DOE PAGES

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

2016-08-30

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

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

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

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

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

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

PubMed

Silina, Yuliya E; Volmer, Dietrich A

2013-12-07

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

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

PubMed

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

2007-01-01

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

Surface cleaning techniques and efficient B-field profiles for lithium ion sources on extraction ion diodes

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

Cuneo, M.E.; Menge, P.R.; Hanson, D.L.

Application of ion beams to Inertial Confinement Fusion requires efficient production, transport and focusing of an intense, low microdivergence beam of an appropriate range ion. At Sandia, the authors are studying the production of lithium ion beams in extraction applied-B ion diodes on the SABRE accelerator (5 MV, 250 kA). Evidence on both SABRE (1 TW) and PBFA-II (20 TW) indicates that the lithium beam turns off and is replaced by a beam of mostly protons and carbon, possibly due to electron thermal and stimulated desorption of hydrocarbon surface contamination with subsequent avalanche ionization. Turn-off of the lithium beam ismore » accompanied by rapid impedance collapse. Surface cleaning techniques are being developed to reduce beam contamination, increase the total lithium energy and reduce the rate of diode impedance collapse. Application of surface cleaning techniques has increased the production of lithium from passive LiF sources by a factor of 2. Improved diode electric and magnetic field profiles have increased the diode efficiency and production of lithium by a factor of 5, without surface cleaning. Work is ongoing to combine these two advances which are discussed here.« less

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

NASA Astrophysics Data System (ADS)

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

2018-06-01

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

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

PubMed

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

2017-05-29

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

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

PubMed

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

2014-03-01

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

Fundamental mechanisms of laser damage of dielectric crystals by ultrashort pulse: ionization dynamics for the Keldysh model

NASA Astrophysics Data System (ADS)

Gruzdev, Vitaly

2014-12-01

Laser-induced ionization is a major process that initiates and drives the initial stages of laser-induced damage (LID) of high-quality transparent solids. The ionization and its contribution to LID are characterized in terms of the time-dependent ionization rate and conduction-band electron density. Considering femtosecond pulses of various durations (from 35 to 706 fs) and variable peak irradiances (from 0.01 to 60 TW/cm2), we use a single-rate equation to simulate time variations of conduction-band electron density and rates of the photoionization and impact ionization. The photoionization rate is evaluated with the Keldysh equation. At low irradiance, the electron density and total ionization rate demonstrate power scaling characteristic of multiphoton ionization. With the increase of irradiance, there is observed a saturation of the photoionization rate due to photoionization suppression by the Keldysh-type singularity during the increase in the number of simultaneously absorbed photons by 1. A striking result is that the saturation is followed by a stepwise transition from the ionization regime which is completely dominated by the photoionization to a regime totally dominated by the impact ionization. The transition results in the increase of the electron density by a few orders of magnitude induced by a variation of peak laser irradiance by about 15% to 20%. The physical effects that are involved are discussed.

Internal energy deposition with silicon nanoparticle-assisted laser desorption/ionization (SPALDI) mass spectrometry

NASA Astrophysics Data System (ADS)

Dagan, Shai; Hua, Yimin; Boday, Dylan J.; Somogyi, Arpad; Wysocki, Ronald J.; Wysocki, Vicki H.

2009-06-01

The use of silicon nanoparticles for laser desorption/ionization (LDI) is a new appealing matrix-less approach for the selective and sensitive mass spectrometry of small molecules in MALDI instruments. Chemically modified silicon nanoparticles (30 nm) were previously found to require very low laser fluence in order to induce efficient LDI, which raised the question of internal energy deposition processes in that system. Here we report a comparative study of internal energy deposition from silicon nanoparticles to previously explored benzylpyridinium (BP) model compounds during LDI experiments. The internal energy deposition in silicon nanoparticle-assisted laser desorption/ionization (SPALDI) with different fluorinated linear chain modifiers (decyl, hexyl and propyl) was compared to LDI from untreated silicon nanoparticles and from the organic matrix, [alpha]-cyano-4-hydroxycinnamic acid (CHCA). The energy deposition to internal vibrational modes was evaluated by molecular ion survival curves and indicated that the ions produced by SPALDI have an internal energy threshold of 2.8-3.7 eV. This is slightly lower than the internal energy induced using the organic CHCA matrix, with similar molecular survival curves as previously reported for LDI off silicon nanowires. However, the internal energy associated with desorption/ionization from the silicon nanoparticles is significantly lower than that reported for desorption/ionization on silicon (DIOS). The measured survival yields in SPALDI gradually decrease with increasing laser fluence, contrary to reported results for silicon nanowires. The effect of modification of the silicon particle surface with semifluorinated linear chain silanes, including fluorinated decyl (C10), fluorinated hexyl (C6) and fluorinated propyl (C3) was explored too. The internal energy deposited increased with a decrease in the length of the modifier alkyl chain. Unmodified silicon particles exhibited the highest analyte internal energy deposition. These findings may suggest a role of the modifier as a moderator in the energy dissipation and relaxation process. The relatively low internal energy content of SPALDI-produced ions indicates that this is a "soft" desorption technique, with potential advantages in the analysis of labile compounds.

Energy dependence of effective electron mass and laser-induced ionization of wide band-gap solids

NASA Astrophysics Data System (ADS)

Gruzdev, V. E.

2008-10-01

Most of the traditional theoretical models of laser-induced ionization were developed under the assumption of constant effective electron mass or weak dependence of the effective mass on electron energy. Those assumptions exclude from consideration all the effects resulting from significant increase of the effective mass with increasing of electron energy in real the conduction band. Promotion of electrons to the states with high effective mass can be done either via laserinduced electron oscillations or via electron-particle collisions. Increase of the effective mass during laser-material interactions can result in specific regimes of ionization. Performing a simple qualitative analysis by comparison of the constant-mass approximation vs realistic dependences of the effective mass on electron energy, we demonstrate that the traditional ionization models provide reliable estimation of the ionization rate in a very limited domain of laser intensity and wavelength. By taking into account increase of the effective mass with electron energy, we demonstrate that special regimes of high-intensity photo-ionization are possible depending on laser and material parameters. Qualitative analysis of the energy dependence of the effective mass also leads to conclusion that the avalanche ionization can be stopped by the effect of electron trapping in the states with large values of the effective mass.

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

PubMed

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

2013-03-19

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

Electron ionization and dissociation of aliphatic amino acids

NASA Astrophysics Data System (ADS)

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

2012-09-01

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

Electron-Muon Ranger: Performance in the MICE muon beam

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

Adams, D.

2015-12-16

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

A theoretical analysis of vacuum arc thruster performance

NASA Technical Reports Server (NTRS)

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

2001-01-01

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

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

PubMed

Kruve, Anneli; Kaupmees, Karl

2017-05-02

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

Experimental and analytical investigation of a modified ring cusp NSTAR engine

NASA Technical Reports Server (NTRS)

Sengupta, Anita

2005-01-01

A series of experimental measurements on a modified laboratory NSTAR engine were used to validate a zero dimensional analytical discharge performance model of a ring cusp ion thruster. The model predicts the discharge performance of a ring cusp NSTAR thruster as a function the magnetic field configuration, thruster geometry, and throttle level. Analytical formalisms for electron and ion confinement are used to predict the ionization efficiency for a given thruster design. Explicit determination of discharge loss and volume averaged plasma parameters are also obtained. The model was used to predict the performance of the nominal and modified three and four ring cusp 30-cm ion thruster configurations operating at the full power (2.3 kW) NSTAR throttle level. Experimental measurements of the modified engine configuration discharge loss compare well with the predicted value for propellant utilizations from 80 to 95%. The theory, as validated by experiment, indicates that increasing the magnetic strength of the minimum closed reduces maxwellian electron diffusion and electrostatically confines the ion population and subsequent loss to the anode wall. The theory also indicates that increasing the cusp strength and minimizing the cusp area improves primary electron confinement increasing the probability of an ionization collision prior to loss at the cusp.

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

NASA Astrophysics Data System (ADS)

Miller, Michelle

2018-01-01

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

Cellular Response to Ionizing Radiation: A MicroRNA Story

PubMed Central

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

2012-01-01

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

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

NASA Astrophysics Data System (ADS)

Stude, Joan; Wieser, Martin; Barabash, Stas

2016-10-01

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

Resonance Ionization Mass Spectrometry System for Measurement of Environmental Samples

NASA Astrophysics Data System (ADS)

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

2002-10-01

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

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

PubMed

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

2003-01-01

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

Evidence for impact ionization in vanadium dioxide

DOE PAGES

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

2016-10-17

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

Comparison of free radicals formation induced by cold atmospheric plasma, ultrasound, and ionizing radiation.

PubMed

Rehman, Mati Ur; Jawaid, Paras; Uchiyama, Hidefumi; Kondo, Takashi

2016-09-01

Plasma medicine is increasingly recognized interdisciplinary field combining engineering, physics, biochemistry and life sciences. Plasma is classified into two categories based on the temperature applied, namely "thermal" and "non-thermal" (i.e., cold atmospheric plasma). Non-thermal or cold atmospheric plasma (CAP) is produced by applying high voltage electric field at low pressures and power. The chemical effects of cold atmospheric plasma in aqueous solution are attributed to high voltage discharge and gas flow, which is transported rapidly on the liquid surface. The argon-cold atmospheric plasma (Ar-CAP) induces efficient reactive oxygen species (ROS) in aqueous solutions without thermal decomposition. Their formation has been confirmed by electron paramagnetic resonance (EPR) spin trapping, which is reviewed here. The similarities and differences between the plasma chemistry, sonochemistry, and radiation chemistry are explained. Further, the evidence for free radical formation in the liquid phase and their role in the biological effects induced by cold atmospheric plasma, ultrasound and ionizing radiation are discussed. Copyright © 2016 Elsevier Inc. All rights reserved.

Quantitative mass spectrometry methods for pharmaceutical analysis

PubMed Central

Loos, Glenn; Van Schepdael, Ann

2016-01-01

Quantitative pharmaceutical analysis is nowadays frequently executed using mass spectrometry. Electrospray ionization coupled to a (hybrid) triple quadrupole mass spectrometer is generally used in combination with solid-phase extraction and liquid chromatography. Furthermore, isotopically labelled standards are often used to correct for ion suppression. The challenges in producing sensitive but reliable quantitative data depend on the instrumentation, sample preparation and hyphenated techniques. In this contribution, different approaches to enhance the ionization efficiencies using modified source geometries and improved ion guidance are provided. Furthermore, possibilities to minimize, assess and correct for matrix interferences caused by co-eluting substances are described. With the focus on pharmaceuticals in the environment and bioanalysis, different separation techniques, trends in liquid chromatography and sample preparation methods to minimize matrix effects and increase sensitivity are discussed. Although highly sensitive methods are generally aimed for to provide automated multi-residue analysis, (less sensitive) miniaturized set-ups have a great potential due to their ability for in-field usage. This article is part of the themed issue ‘Quantitative mass spectrometry’. PMID:27644982

Dissolution and ionization of sodium superoxide in sodium–oxygen batteries

PubMed Central

Kim, Jinsoo; Park, Hyeokjun; Lee, Byungju; Seong, Won Mo; Lim, Hee-Dae; Bae, Youngjoon; Kim, Haegyeom; Kim, Won Keun; Ryu, Kyoung Han; Kang, Kisuk

2016-01-01

With the demand for high-energy-storage devices, the rechargeable metal–oxygen battery has attracted attention recently. Sodium–oxygen batteries have been regarded as the most promising candidates because of their lower-charge overpotential compared with that of lithium–oxygen system. However, conflicting observations with different discharge products have inhibited the understanding of precise reactions in the battery. Here we demonstrate that the competition between the electrochemical and chemical reactions in sodium–oxygen batteries leads to the dissolution and ionization of sodium superoxide, liberating superoxide anion and triggering the formation of sodium peroxide dihydrate (Na2O2·2H2O). On the formation of Na2O2·2H2O, the charge overpotential of sodium–oxygen cells significantly increases. This verification addresses the origin of conflicting discharge products and overpotentials observed in sodium–oxygen systems. Our proposed model provides guidelines to help direct the reactions in sodium–oxygen batteries to achieve high efficiency and rechargeability. PMID:26892931

Dissolution and ionization of sodium superoxide in sodium-oxygen batteries.

PubMed

Kim, Jinsoo; Park, Hyeokjun; Lee, Byungju; Seong, Won Mo; Lim, Hee-Dae; Bae, Youngjoon; Kim, Haegyeom; Kim, Won Keun; Ryu, Kyoung Han; Kang, Kisuk

2016-02-19

With the demand for high-energy-storage devices, the rechargeable metal-oxygen battery has attracted attention recently. Sodium-oxygen batteries have been regarded as the most promising candidates because of their lower-charge overpotential compared with that of lithium-oxygen system. However, conflicting observations with different discharge products have inhibited the understanding of precise reactions in the battery. Here we demonstrate that the competition between the electrochemical and chemical reactions in sodium-oxygen batteries leads to the dissolution and ionization of sodium superoxide, liberating superoxide anion and triggering the formation of sodium peroxide dihydrate (Na2O2·2H2O). On the formation of Na2O2·2H2O, the charge overpotential of sodium-oxygen cells significantly increases. This verification addresses the origin of conflicting discharge products and overpotentials observed in sodium-oxygen systems. Our proposed model provides guidelines to help direct the reactions in sodium-oxygen batteries to achieve high efficiency and rechargeability.

Quaternary ammonium isobaric tag for a relative and absolute quantification of peptides.

PubMed

Setner, Bartosz; Stefanowicz, Piotr; Szewczuk, Zbigniew

2018-02-01

Isobaric labeling quantification of peptides has become a method of choice for mass spectrometry-based proteomics studies. However, despite of wide variety of commercially available isobaric tags, none of the currently available methods offers significant improvement of sensitivity of detection during MS experiment. Recently, many strategies were applied to increase the ionization efficiency of peptides involving chemical modifications introducing quaternary ammonium fixed charge. Here, we present a novel quaternary ammonium-based isobaric tag for relative and absolute quantification of peptides (QAS-iTRAQ 2-plex). Upon collisional activation, the new stable benzylic-type cationic reporter ion is liberated from the tag. Deuterium atoms were used to offset the differential masses of a reporter group. We tested the applicability of QAS-iTRAQ 2-plex reagent on a series of model peptides as well as bovine serum albumin tryptic digest. Obtained results suggest usefulness of this isobaric ionization tag for relative and absolute quantification of peptides. Copyright © 2017 John Wiley & Sons, Ltd.

MPI_XSTAR: MPI-based Parallelization of the XSTAR Photoionization Program

NASA Astrophysics Data System (ADS)

Danehkar, Ashkbiz; Nowak, Michael A.; Lee, Julia C.; Smith, Randall K.

2018-02-01

We describe a program for the parallel implementation of multiple runs of XSTAR, a photoionization code that is used to predict the physical properties of an ionized gas from its emission and/or absorption lines. The parallelization program, called MPI_XSTAR, has been developed and implemented in the C++ language by using the Message Passing Interface (MPI) protocol, a conventional standard of parallel computing. We have benchmarked parallel multiprocessing executions of XSTAR, using MPI_XSTAR, against a serial execution of XSTAR, in terms of the parallelization speedup and the computing resource efficiency. Our experience indicates that the parallel execution runs significantly faster than the serial execution, however, the efficiency in terms of the computing resource usage decreases with increasing the number of processors used in the parallel computing.

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

PubMed Central

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

2014-01-01

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

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

NASA Astrophysics Data System (ADS)

Suzuki, Yohichi; Seki, Kazuhiko

2018-03-01

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

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

PubMed

Sekimoto, Kanako; Sakai, Mami; Takayama, Mitsuo

2012-06-01

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

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

PubMed

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

2015-06-21

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

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

PubMed

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

2016-03-01

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

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

NASA Astrophysics Data System (ADS)

Wu, Pei Ying; Tzeng, Wen Bih

2015-10-01

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

Effects of ionizing radiation in ginkgo and guarana [rapid communication

NASA Astrophysics Data System (ADS)

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

2005-07-01

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

Plasma catalytic reforming of methane

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

Bromberg, L.; Cohn, D.R.; Rabinovich, A.

1998-08-01

Thermal plasma technology can be efficiently used in the production of hydrogen and hydrogen-rich gases from methane and a variety of fuels. This paper describes progress in plasma reforming experiments and calculations of high temperature conversion of methane using heterogeneous processes. The thermal plasma is a highly energetic state of matter that is characterized by extremely high temperatures (several thousand degrees Celsius) and high degree of dissociation and substantial degree of ionization. The high temperatures accelerate the reactions involved in the reforming process. Hydrogen-rich gas (50% H{sub 2}, 17% CO and 33% N{sub 2}, for partial oxidation/water shifting) can bemore » efficiently made in compact plasma reformers. Experiments have been carried out in a small device (2--3 kW) and without the use of efficient heat regeneration. For partial oxidation/water shifting, it was determined that the specific energy consumption in the plasma reforming processes is 16 MJ/kg H{sub 2} with high conversion efficiencies. Larger plasmatrons, better reactor thermal insulation, efficient heat regeneration and improved plasma catalysis could also play a major role in specific energy consumption reduction and increasing the methane conversion. A system has been demonstrated for hydrogen production with low CO content ({approximately} 1.5%) with power densities of {approximately} 30 kW (H{sub 2} HHV)/liter of reactor, or {approximately} 10 m{sup 3}/hr H{sub 2} per liter of reactor. Power density should further increase with increased power and improved design.« less

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

PubMed

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

2000-05-01

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

Electroless plating of silver nanoparticles on porous silicon for laser desorption/ionization mass spectrometry

NASA Astrophysics Data System (ADS)

Yan, Hong; Xu, Ning; Huang, Wen-Yi; Han, Huan-Mei; Xiao, Shou-Jun

2009-03-01

An improved DIOS (desorption ionization on porous silicon) method for laser desorption/ionization mass spectrometry (LDI MS) by electroless plating of silver nanoparticles (AgNPs) on porous silicon (PSi) was developed. By addition of 4-aminothiophenol (4-ATP) into the AgNO3 plating solution, the plating speed can be slowed down and simultaneously 4-ATP self-assembled monolayers (SAMs) on AgNPs (4-ATP/AgNPs) were formed. Both AgNPs and 4-ATP/AgNPs coated PSi substrates present much higher stability, sensitivity and reproducibility for LDI MS than the un-treated porous silicon ones. Their shelf life in air was tested for several weeks to a month and their mass spectra still displayed the same high quality and sensitivity as the freshly prepared ones. And more 4-ATP SAMs partly play a role of matrix to increase the ionization efficiency. A small organic molecule of tetrapyridinporphyrin (TPyP), oligomers of polyethylene glycol (PEG 400 and 2300), and a peptide of oxytocin were used as examples to demonstrate the feasibility of the silver-plated PSi as a matrix-free-like method for LDI MS. This approach can obtain limits of detection to femtomoles for TPyP, subpicomoles for oxytocin, and picomoles for PEG 400 and 2300, comparable to the traditional matrix method and much better than the DIOS method. It simplifies the sample preparation as a matrix-free-like method without addition of matrix molecules and homogenizes the sample spread over the spot for better and more even mass signals.

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

PubMed

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

2017-02-03

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

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

NASA Astrophysics Data System (ADS)

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

2013-08-01

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

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

PubMed

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

2013-08-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-01-01

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

Increased upstream ionization due to formation of a double layer.

PubMed

Thakur, S Chakraborty; Harvey, Z; Biloiu, I A; Hansen, A; Hardin, R A; Przybysz, W S; Scime, E E

2009-01-23

We report observations that confirm a theoretical prediction that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The theoretical model argues that the increased ionization is needed to balance the difference in diffusive losses upstream and downstream of the expansion region. In our expanding helicon source experiments, we find that the upstream plasma density increases sharply at the same antenna frequency at which the double layer appears.

Changes in the specific migration characteristics of packaging-food simulant combinations caused by ionizing radiation: Effect of food simulant

NASA Astrophysics Data System (ADS)

Zygoura, Panagiota D.; Paleologos, Evangelos K.; Kontominas, Michael G.

2011-08-01

The primary objective of the present study was to evaluate the extent to which the affinity of the surrounding medium for the migrant, as well as the packaging material, affects the specific migration characteristics of the latter. For this purpose, migration tests were conducted with vinylidene chloride copolymer (PVDC/PVC) in contact with the EU specified solvents simulating all food types: namely, distilled water, 3% w/v acetic acid, 10% v/v ethanol and isooctane. Migration testing was carried out at 40 °C for 10 days for the aqueous simulants, and at 20 °C for 2 days for the fatty food simulant (EC, 1997; EEC, 1993). In addition, food-grade saran film was subjected to ionizing radiation treatment with a [60Co] source at doses equal to 5, 15 and 25 kGy. Acetyl tributyl citrate (ATBC) plasticizer levels were monitored as a function of time for untreated, as well as gamma-irradiated packaging material, with a secondary objective to investigate the effect of ionizing radiation on polymer/migrant/surrounding medium interactions. Depending on the food simulant, determination of the analyte was performed by either direct gas chromatographic analysis, or surfactant (Triton X-114) mediated extraction followed by gas chromatographic-flame ionization detection (GC-FID). ATBC concentrations determined in aqueous and fatty food simulants were 0.216-0.497 and 5.0-5.9 mg/L, respectively. Therefore, the most efficient extracting medium of plasticizers in vinyl chloride copolymers is the non-polar isooctane. Moreover, an extremely high rate of ATBC migration into isooctane during the early stages of contact was observed. The above observation verifies the aggressiveness of isooctane towards plastic packaging materials. Amongst the aqueous food simulants tested, the 10% ethanol solution demonstrated the highest migration levels. Gamma-irradiation enhanced ATBC migration; specific migration levels increased with increasing contact time and radiation dose. This was expected, since ATBC did not undergo chemical decomposition upon irradiation up to 25 kGy. Finally, specific migration decreased proportionally with increasing polarity of the food-simulating solvent.

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

PubMed

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

2014-12-01

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

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

NASA Astrophysics Data System (ADS)

Zou, Yunlong; Holmes, Russell

2015-03-01

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

Novel methods for matter interferometry with nanosized objects

NASA Astrophysics Data System (ADS)

Arndt, Markus

2005-05-01

We discuss the current status and prospects for novel experimental methods for coherence^1,2 and decoherence^3 experiments with large molecules. Quantum interferometry with nanosized objects is interesting for the exploration of the quantum-classical transition. The same experimental setup is also promising for metrology applications and molecular nanolithography. Our coherence experiments with macromolecules employ a Talbot-Lau interferometer. We discuss some modifications to this scheme, which are required to extend it to particles with masses in excess of several thousand mass units. In particular, the detection in all previous interference experiments with large clusters and molecules, was based on either laser ionization^1 (e.g. Fullerenes) or electron impact ionization^2 (e.g. Porphyrins etc.). However, most ionization schemes run into efficiency limits when the mass and complexity of the target particle increases. Here we present experimental results for an interference detector which is truly scalable, i.e. one which will even improve with increasing particle size and complexity. ``Mechanically magnified fluorescence imaging'' (MMFI), combines the high spatial resolution, which is intrinsic to Talbot Lau interferometry with the high detection efficiency of fluorophores adsorbed onto a substrate. In the Talbot Lau setup a molecular interference pattern is revealed by scanning the 3^rd grating across the molecular beam^1. The number of transmitted molecules is a function of the relative position between the mask and the molecular density pattern. Both the particle interference pattern and the mechanical mask structure may be far smaller than any optical resolution limit. After mechanical magnification by an arbitrary factor, in our case a factor 5000, the interference pattern can still be inspected in fluorescence microscopy. The fluorescent molecules are collected on a surface which is scanned collinearly and synchronously behind the 3rd grating. The resulting image of the interference pattern is by far large enough to be easily seen by the unaided eye. High contrast interference fringes could be recorded with dyes molecules. ^1B. Brezger et al. , Phys. Rev. Lett. 88, 100404 (2002). ^2L. Hackermüller et al. Phys. Rev. Lett 91, 90408 (2003). ^3L. Hackermüller et al. Nature 427, 711 (2004).

Determination of multislice computed tomography dose index (CTDI) using optically stimulated luminescence technology.

PubMed

Ruan, Chun; Yukihara, Eduardo G; Clouse, William J; Gasparian, Patricia B R; Ahmad, Salahuddin

2010-07-01

The extensive use of multislice computed tomography (MSCT) and the associated increase in patient dose calls for an accurate dose evaluation technique. Optically stimulated luminescence (OSL) dosimetry provides a potential solution to the arising concerns over patient dose. This study was intended to evaluate the feasibility and accuracy of OSL dosimeter systems in the diagnostic CT x-ray beam energy range. MSCT dose profiles were measured by irradiating OSL strips placed inside the extended PMMA head and body phantoms at different scan conditions by varying kVp settings (100, 120, and 140 kVp) and collimated beam widths (5, 10, 20, and 40 mm). All scans in this study were performed using a GE Lightspeed VCT scanner in axial mode. The exposed strips were then read out using a custom-made OSL strip reader and corrected with field-specific conversion factors. Based on the corrected OSL dose profile, the CTDI(450-OSL) and CTDI(l00-OSL) were evaluated. CTDI(100-IC) was also obtained using a 100 mm long pencil ionization chamber for accuracy verification. CTDI(100-efficiency) can be further evaluated by calculating the ratio of CTDI(100-OSL) and CTDI(450-OSL), which was compared to results from previous studies as well. The OSL detectors were found to have good sensitivity and dose response over a wide range of diagnostic CT x-ray beam energy viz. the primary beam and the scatter tail section of the dose profile. The differences between CTDI100 values obtained using the OSL strips and those obtained with 100 mm long pencil ionization chamber were < +/- 5% for all scan conditions, indicating good accuracy of the OSL system. It was also found that the CTDI(100-efficiency) did not significantly change as the beam width increased and tube voltage changed. The average CTDI(100-efficiency) at the center of the head and body phantoms were 72.6% and 56.2%, respectively. The corresponding values for the periphery of the head and body phantoms were 85.0% and 81.7%. These results agreed very well with previous results from the literature using other detection techniques or Monte Carlo simulations. The LED-based OSL system can be an accurate alternative device for CT dose evaluations. CTDI100 measurement with the use of a 100 mm pencil ionization chamber substantially underestimates the CTDIinfinity value even with 5 mm collimated beam width. The established complete set of CTDI(100-efficiency) correction factors for various scan parameters allows for accurately estimating CTDIinfinity with the current use of pencil chamber and dose phantoms. Combined with the simple calibration, it gives this work great potential to be used not only in routine clinical quality assurance checks but also as a promising tool for patient organ dose assessment.

The Effects of Ionizing Radiation on the Oral Cavity.

PubMed

de Barros da Cunha, Sandra Ribeiro; Ramos, Pedro Augusto Mendes; Nesrallah, Ana Cristina Aló; Parahyba, Cláudia Joffily; Fregnani, Eduardo Rodrigues; Aranha, Ana Cecília Corrêa

2015-08-01

The aim of this study is to present a literature review on the effects of the ionizing radiation from radiotherapy treatment on dental tissues. Among the effects of increasing global life expectancy and longevity of the teeth in the oral cavity, increasing rates of neoplastic diseases have been observed. One of the important treatment modalities for head and neck neoplastic diseases is radiotherapy, which uses ionizing radiation as the main mechanism of action. Therefore, it is essential for dentists to be aware of the changes in oral and dental tissues caused by ionizing radiation, and to develop treatment and prevention strategies. In general, there is still controversy about the effects of ionizing radiation on dental structures. However, qualitative and quantitative changes in saliva and oral microbiota, presence of oral mucositis and radiation-related caries are expected, as they represent the well-known side effects of treatment with ionizing radiation. Points that still remain unclear are the effects of radiotherapy on enamel and dentin, and on their mechanisms of bonding to contemporary adhesive materials. Ionizing radiation has shown important interaction with organic tissues, since more deleterious effects have been shown on the oral mucosa, salivary glands and dentin, than on enamel. With the increasing number of patients with cancer seeking dental treatment before and after head and neck radiotherapy, it is important for dentists to be aware of the effects of ionizing radiation on the oral cavity.

Effect of Lipophilicity and Drug Ionization on Permeation Across Porcine Sublingual Mucosa.

PubMed

Goswami, Tarun; Li, Xiaoling; Jasti, Bhaskara R

2017-01-01

Sublingual route is one of the oldest alternative routes studied for the administration of drugs. However, the effect of physical-chemical properties on drug permeation via this route has not been systemically investigated. The objective of this study was to determine the effect of two key physicochemical properties, lipophilicity and ionization, on the transport of drugs across porcine sublingual mucosa. A series of β-blockers were used to study the effect of lipophilicity on drug permeation across the sublingual mucosa, while nimesulide (pKa 6.5) was used as a model drug to study the effect of degree of ionization on sublingual mucosa permeation of ionized and unionized species. Permeation of β-blockers increased linearly with an increase in the lipophilicity for the range of compounds studied. The permeability of nimesulide across sublingual mucosa decreased with an increase of pH. The flux of ionized and unionized forms of nimesulide was determined to delineate the contribution of ionized and unionized species to the total flux. At low pH, the apparent flux was primarily contributed by unionized species; however, when the pH is increased beyond its pKa, the primary contributor to the apparent flux, nimesulide, is ionized species. The contribution of each species to the apparent flux was shown to be determined by the thermodynamic activity of ionized or unionized species. This study identified the roles of lipophilicity and thermodynamic activity in drug permeation across the sublingual mucosa. The findings can help guide the design of sublingual drug delivery systems with optimal pH and solubility.

PHD TUTORIAL: A complete numerical approach to electron hydrogen collisions

NASA Astrophysics Data System (ADS)

Bartlett, Philip L.

2006-11-01

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

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

NASA Astrophysics Data System (ADS)

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

2000-07-01

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

Theoretical and observational determinations of the ionization coefficient of meteors

NASA Astrophysics Data System (ADS)

Jones, William

1997-07-01

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

Double ionization of nitrogen molecules in orthogonal two-color femtosecond laser fields

NASA Astrophysics Data System (ADS)

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

2018-04-01

Double ionization of nitrogen molecules in orthogonally polarized two-color femtosecond laser fields is investigated by varying the relative intensity between the fundamental wave (FW) and its second harmonic (SH) components. The yield ratios of the double ionization channels, i.e., the non-dissociative {{{{N}}}2}2+ and Coulomb exploded (N+, N+), to the singly charged N2 + channel exhibit distinct dependences on the relative strength between the FW and SH fields. As the intensity ratio of SH to FW increases, the yield ratio of (N+, N+)/N2 + gradually increases, while the ratio of {{{{N}}}2}2+/N2 + first descends and then increases constituting a valley shape which is similar to the behavior of Ar2+/Ar+ observed in the same experimental condition. Based on the classical trajectory simulations, we found that the different characteristics of the two doubly ionized channels stem from two mechanisms, i.e., the {{{{N}}}2}2+ is mostly accessed by the (e, 2e) impact ionization while the recollision-induced excitation with subsequent ionization plays an important role in producing the (N+, N+) channel.

Particle-in-cell simulations of the critical ionization velocity effect in finite size clouds

NASA Technical Reports Server (NTRS)

Moghaddam-Taaheri, E.; Lu, G.; Goertz, C. K.; Nishikawa, K. - I.

1994-01-01

The critical ionization velocity (CIV) mechanism in a finite size cloud is studied with a series of electrostatic particle-in-cell simulations. It is observed that an initial seed ionization, produced by non-CIV mechanisms, generates a cross-field ion beam which excites a modified beam-plasma instability (MBPI) with frequency in the range of the lower hybrid frequency. The excited waves accelerate electrons along the magnetic field up to the ion drift energy that exceeds the ionization energy of the neutral atoms. The heated electrons in turn enhance the ion beam by electron-neutral impact ionization, which establishes a positive feedback loop in maintaining the CIV process. It is also found that the efficiency of the CIV mechanism depends on the finite size of the gas cloud in the following ways: (1) Along the ambient magnetic field the finite size of the cloud, L (sub parallel), restricts the growth of the fastest growing mode, with a wavelength lambda (sub m parallel), of the MBPI. The parallel electron heating at wave saturation scales approximately as (L (sub parallel)/lambda (sub m parallel)) (exp 1/2); (2) Momentum coupling between the cloud and the ambient plasma via the Alfven waves occurs as a result of the finite size of the cloud in the direction perpendicular to both the ambient magnetic field and the neutral drift. This reduces exponentially with time the relative drift between the ambient plasma and the neutrals. The timescale is inversely proportional to the Alfven velocity. (3) The transvers e charge separation field across the cloud was found to result in the modulation of the beam velocity which reduces the parallel heating of electrons and increases the transverse acceleration of electrons. (4) Some energetic electrons are lost from the cloud along the magnetic field at a rate characterized by the acoustic velocity, instead of the electron thermal velocity. The loss of energetic electrons from the cloud seems to be larger in the direction of plasma drift relative to the neutrals, where the loss rate is characterized by the neutral drift velocity. It is also shown that a factor of 4 increase in the ambient plasma density, increases the CIV ionization yield by almost 2 orders of magnitude at the end of a typical run. It is concluded that a larger ambient plasma density can result in a larger CIV yield because of (1) larger seed ion production by non-CIV mechanisms, (2) smaller Alfven velocity and hence weak momentum coupling, and (3) smaller ratio of the ion beam density to the ambient ion density, and therefore a weaker modulation of the beam velocity. The simulation results are used to interpret various chemical release experiments in space.

Reversal electron attachment ionizer for detection of trace species

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

Reversal electron attachment ionizer for detection of trace species

NASA Technical Reports Server (NTRS)

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

1989-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

Compressing turbulence and sudden viscous dissipation with compression-dependent ionization state

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

Davidovits, Seth; Fisch, Nathaniel J.

Turbulent plasma flow, amplified by rapid three-dimensional compression, can be suddenly dissipated under continuing compression. Furthermore, this effect relies on the sensitivity of the plasma viscosity to the temperature, μ ~ T 5 / 2 . The plasma viscosity is also sensitive to the plasma ionization state. Here, we show that the sudden dissipation phenomenon may be prevented when the plasma ionization state increases during compression, and we demonstrate the regime of net viscosity dependence on compression where sudden dissipation is guaranteed. In addition, it is shown that, compared to cases with no ionization, ionization during compression is associated withmore » larger increases in turbulent energy and can make the difference between growing and decreasing turbulent energy.« less

Compressing turbulence and sudden viscous dissipation with compression-dependent ionization state

DOE PAGES

Davidovits, Seth; Fisch, Nathaniel J.

2016-11-14

Turbulent plasma flow, amplified by rapid three-dimensional compression, can be suddenly dissipated under continuing compression. Furthermore, this effect relies on the sensitivity of the plasma viscosity to the temperature, μ ~ T 5 / 2 . The plasma viscosity is also sensitive to the plasma ionization state. Here, we show that the sudden dissipation phenomenon may be prevented when the plasma ionization state increases during compression, and we demonstrate the regime of net viscosity dependence on compression where sudden dissipation is guaranteed. In addition, it is shown that, compared to cases with no ionization, ionization during compression is associated withmore » larger increases in turbulent energy and can make the difference between growing and decreasing turbulent energy.« less

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

PubMed

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

2011-07-01

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

Kinetic analysis of competition between aerosol particle removal and generation by ionization air purifiers.

PubMed

Alshawa, Ahmad; Russell, Ashley R; Nizkorodov, Sergey A

2007-04-01

Ionization air purifiers are increasingly used to remove aerosol particles from indoor air. However, certain ionization air purifiers also emit ozone. Reactions between the emitted ozone and unsaturated volatile organic compounds (VOC) commonly found in indoor air produce additional respirable aerosol particles in the ultrafine (<0.1 microm) and fine (<2.5 microm) size domains. A simple kinetic model is used to analyze the competition between the removal and generation of particulate matter by ionization air purifiers under conditions of a typical residential building. This model predicts that certain widely used ionization air purifiers may actually increase the mass concentration of fine and ultrafine particulates in the presence of common unsaturated VOC, such as limonene contained in many household cleaning products. This prediction is supported by an explicit observation of ultrafine particle nucleation events caused by the addition of D-limonene to a ventilated office room equipped with a common ionization air purifier.

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

Aydinol, M., E-mail: aydinolm@dicle.edu.tr; Aydeniz, D., E-mail: daydeniz@hotmail.com

L shell ionization cross section and {sub Li} subshells ionization cross sections of Os, Pt, Hg, Pb, Po atoms calculated. For each atom, ten different electron impacty energy values E{sub oi} used. Calculations carried out by using nonrelativistic Lotz equation in Matlab. Ionization cross section values obtained for Eoi values in the energy range of E{sub Li} ≤E{sub oi}≤4E{sub Li} for each atom. Starting allmost from E{sub oi} = E{sub Li} (i = 1,2,3) values of the each subshell ionization threshold energy, ionization cross section are increasing rapidly with E{sub oi}. For a fixed E{sub oi} = 3. E{sub Li}more » 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 σ{sub Li} subshells.« less

Ion energies in high power impulse magnetron sputtering with and without localized ionization zones

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

Yang, Yuchen; Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720; Tanaka, Koichi

2015-03-23

High speed imaging of high power impulse magnetron sputtering discharges has revealed that ionization is localized in moving ionization zones but localization disappears at high currents for high yield targets. This offers an opportunity to study the effect ionization zones have on ion energies. We measure that ions have generally higher energies when ionization zones are present, supporting the concept that these zones are associated with moving potential humps. We propose that the disappearance of ionization zones is caused by an increased supply of atoms from the target which cools electrons and reduces depletion of atoms to be ionized.

Robe Development for Electrical Conductivity Analysis in an Electron Gun Produced Helium Plasma

NASA Technical Reports Server (NTRS)

Bragg-Sitton, Shannon M.; Bitteker, Leo; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

The use of magnetohydrodynamic (MHD) power conversion systems, potentially coupled with a fission power source, is currently being investigated as a driver for an advanced propulsion system, such as a plasma thruster. The efficiency of a MHD generator is strongly dependent on the electrical conductivity of the fluid that passes through the generator; power density increases as fluid conductivity increases. Although traditional MHD flows depend on thermal ionization to enhance the electrical conductivity, ionization due to nuclear interactions may achieve a comparable or improved conductivity enhancement while avoiding many of the limitations inherent to thermal ionization. Calculations suggest that nuclear-enhanced electrical conductivity increases as the neutron flux increases; conductivity of pure He-3 greater than 10 mho/m may be achievable if exposed to a flux greater than 10(exp 12) neutrons/cm2/s.) However, this remains to be demonstrated experimentally. An experimental facility has been constructed at the Propulsion Research Center at the NASA Marshall Space Flight Center, using helium as the test fluid. High energy electrons will be used to simulate the effects of neutron-induced ionization of helium gas to produce a plasma. These experiments will be focused on diagnosis of the plasma in a virtually static system; results will be applied to future tests with a MHD system. Initial experiments will utilize a 50 keV electron gun that can operate at up to a current of 200 micro A. Spreading the electron beam over a four inch diameter window results in an electron flux of 1.5x 10(exp 13) e/sq cm/s. The equivalent neutron flux that would produce the same ionization fraction in helium is 1x10(exp 12) n/sq cm/s. Experiments will simulate the neutron generated plasma modeled by Bitteker, which takes into account the products of thermal neutron absorption in He-3, and includes various ion species in estimating the conductivity of the resulting plasma. Several different probes will be designed and implemented to verify the plasma kinetics model. System parameters and estimated operating ranges are summarized. The predicted ionization fraction, electron density, and conductivity levels are provided in for an equivalent neutron flux of 1x10(exp 12) n/cm2/s. Understanding the complex plasma kinetics throughout a MHD channel is necessary to design an optimal power conversion system for space propulsion applications. The proposed experiments seek to fully characterize the helium plasma and to determine the reliability of each measurement technique, such that they may be applied to more advanced MHD studies. The expected value of each plasma parameter determined from theoretical models will be verified experimentally by several independent techniques to determine the most reliable method of obtaining each parameter. The results of these experiments will be presented in the final paper.

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

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

Ahedo, Eduardo; Navarro-Cavalle, Jaume

2013-04-15

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

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

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

PubMed Central

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

2016-01-01

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

Degradation kinetics and mechanism of penicillin G in aqueous matrices by ionizing radiation

NASA Astrophysics Data System (ADS)

Chu, Libing; Zhuang, Shuting; Wang, Jianlong

2018-04-01

The gamma radiation induced-degradation of a β-lactam antibiotic, penicillin G was investigated in aqueous solution. Special attention was paid to the effects of the organic substances such as peptone and glucose on penicillin G degradation, which can be found in the wastewater of the factories producing antibiotics. Results showed that gamma radiation was effective to degrade and deactivate penicillin G in pure water. With the initial concentrations of 0.27 mM, 1.34 mM and 2.68 mM, a complete removal of penicillin G could be achieved at the adsorbed doses of 2.5 kGy, 10 kGy and 20 kGy, respectively. Penicilloic acid from the β-lactam ring cleavage and a series of fragment compounds such as thiazolidine and penicillic acid were identified during gamma irradiation-induced degradation of penicillin G. Addition of Fe2+ was efficient to enhance the mineralization. The TOC removal efficiency of penicillin G was 21.7% using gamma irradiation alone at 10 kGy, which increased to 56.4% with 1.0 mM Fe2+ addition. The gamma radiation-induced degradation of penicillin G was inhibited in the presence of peptone and glucose and the inhibitive effect increased with increasing their concentrations. The rate constant, k of the pseudo first-order kinetics decreased by 74% and 64% in the presence of 1.0 g/L of peptone and glucose, respectively, and by 96% and 89% in the presence of 10 g/L of peptone and glucose, respectively. The ratio of k/k0 was increased by 1.3 times with H2O2 addition and by 3 times with Fe2+ addition, in the presence of 10 g/L of glucose. Adding Fe2+ was effective to improve the ionizing radiation induced degradation of penicillin G antibiotic in the glucose-containing wastewater.

Efficiency Analysis of a High-Specific Impulse Hall Thruster

NASA Technical Reports Server (NTRS)

Jacobson, David (Technical Monitor); Hofer, Richard R.; Gallimore, Alec D.

2004-01-01

Performance and plasma measurements of the high-specific impulse NASA-173Mv2 Hall thruster were analyzed using a phenomenological performance model that accounts for a partially-ionized plasma containing multiply-charged ions. Between discharge voltages of 300 to 900 V, the results showed that although the net decrease of efficiency due to multiply-charged ions was only 1.5 to 3.0 percent, the effects of multiply-charged ions on the ion and electron currents could not be neglected. Between 300 to 900 V, the increase of the discharge current was attributed to the increasing fraction of multiply-charged ions, while the maximum deviation of the electron current from its average value was only +5/-14 percent. These findings revealed how efficient operation at high-specific impulse was enabled through the regulation of the electron current with the applied magnetic field. Between 300 to 900 V, the voltage utilization ranged from 89 to 97 percent, the mass utilization from 86 to 90 percent, and the current utilization from 77 to 81 percent. Therefore, the anode efficiency was largely determined by the current utilization. The electron Hall parameter was nearly constant with voltage, decreasing from an average of 210 at 300 V to an average of 160 between 400 to 900 V. These results confirmed our claim that efficient operation can be achieved only over a limited range of Hall parameters.

Prebreakdown characteristics of weakly ionized liquid and gaseous media in the strongly nonuniform electric field

NASA Astrophysics Data System (ADS)

Apfelbaum, M. S.; Syrovatka, R. A.; Vladimirov, V. I.

2018-01-01

A theoretical model of electrohydrodynamic prebreakdown phenomena in slightly ionized (weakly conductive) media is proposed. The electric high voltage conduction of weakly conductive liquids and slightly ionized gases in intense electric fields using this model is considered. The formula for the calculations of volt-ampere characteristics under high voltage spherical capacitor field is analytically obtained. The experimental corona discharge volt-ampere characteristics of air are presented. It was found that the size of the ionization region in the case of corona discharge in air increases monotonically with increasing discharge voltage.

Theory of void formation in dusty plasmas

NASA Astrophysics Data System (ADS)

Hu, Zuquan; Chen, Yinhua; Zheng, Xiang; Huang, Feng; Shi, Gei-fen; Yu, M. Y.

2009-06-01

A fluid theory of void formation in dusty plasmas taking into account ionization is proposed. It is shown that if the ionization rate is larger than a threshold, an initial steady-state dust-density distribution can evolve into a stable distribution containing a void. As the ionization rate is further increased, the time required for void formation decreases. The void size first increases, but then decreases. However, for still larger ionization rates, the dusty region of the plasma becomes ringlike, including the convection term in dust momentum equation. The results are in agreement with existing experiments and theories.

A Double-Blind Placebo-Controlled Crossover Trial of Intravenous Magnesium Sulfate for Foscarnet-Induced Ionized Hypocalcemia and Hypomagnesemia in Patients with AIDS and Cytomegalovirus Infection

PubMed Central

Huycke, Mark M.; Naguib, M. Tarek; Stroemmel, Mathias M.; Blick, Kenneth; Monti, Katherine; Martin-Munley, Sarah; Kaufman, Chris

2000-01-01

Foscarnet (trisodium phosphonoformate hexahydrate) is an antiviral agent used to treat cytomegalovirus disease in immunocompromised patients. One common side effect is acute ionized hypocalcemia and hypomagnesemia following intravenous administration. Foscarnet-induced ionized hypomagnesemia might contribute to ionized hypocalcemia by impairing excretion of preformed parathyroid hormone (PTH) or by producing target organ resistance. Prevention of ionized hypomagnesemia following foscarnet administration could blunt the development of ionized hypocalcemia. To determine whether intravenous magnesium ameliorates the decline in ionized calcium and/or magnesium following foscarnet infusions, MgSO4 at doses of 1, 2, and 3 g was administered in a double-blind, placebo-controlled, randomized, crossover trial to 12 patients with AIDS and cytomegalovirus disease. Overall, increasing doses of MgSO4 reduced or eliminated foscarnet-induced acute ionized hypomagnesemia. Supplementation, however, had no discernible effect on foscarnet-induced ionized hypocalcemia despite significant increases in serum PTH levels. No dose-related, clinically significant adverse events were found, suggesting that intravenous supplementation with up to 3 g of MgSO4 was safe in this chronically ill population. Since parenteral MgSO4 did not alter foscarnet-induced ionized hypocalcemia or symptoms associated with foscarnet, routine intravenous supplementation for patients with normal serum magnesium levels is not recommended during treatment with foscarnet. PMID:10898688

The study of the effects of ionizing and non-ionizing radiations on birth weight of newborns to exposed mothers.

PubMed

Mortazavi, S M J; Shirazi, K R; Mortazavi, G

2013-01-01

Life evolved in an environment filled with a wide variety of ionizing and non-ionizing radiation. It was previously reported that medical exposures to pregnant women increases the risk of low birth weight. This study intends to investigate the relationship between exposure to ionizing and non-ionizing radiation and the risk of low birth weight. One thousand two hundred mothers with their first-term labor (vaginal or cesarean) whose newborns' history had been registered in neonates' screening program in Shiraz were interviewed and surveyed. Data collection was performed by the assessment of mother's history of radiography before and during pregnancy, physical examination of the mother for height and weight and weighing and examining the newborn for any diagnosis of disease and anomalies. There were no statistical significant differences between the mean weight of newborns whose mothers had been exposed to some common sources of ionizing and non-ionizing radiations such as dental or non dental radiographies, mobile phone, cordless phone and cathode ray tube (CRT) and those of non-exposed mothers. The findings of this study cast doubt on previous reports, which indicated that exposure to ionizing radiation during pregnancy increased the risk of low birth weight.

The study of the effects of ionizing and non-ionizing radiations on birth weight of newborns to exposed mothers

PubMed Central

Mortazavi, S. M. J.; Shirazi, K. R.; Mortazavi, G.

2013-01-01

Objectives: Life evolved in an environment filled with a wide variety of ionizing and non-ionizing radiation. It was previously reported that medical exposures to pregnant women increases the risk of low birth weight. This study intends to investigate the relationship between exposure to ionizing and non-ionizing radiation and the risk of low birth weight. Materials and Methods: One thousand two hundred mothers with their first-term labor (vaginal or cesarean) whose newborns’ history had been registered in neonates’ screening program in Shiraz were interviewed and surveyed. Data collection was performed by the assessment of mother's history of radiography before and during pregnancy, physical examination of the mother for height and weight and weighing and examining the newborn for any diagnosis of disease and anomalies. Results: There were no statistical significant differences between the mean weight of newborns whose mothers had been exposed to some common sources of ionizing and non-ionizing radiations such as dental or non dental radiographies, mobile phone, cordless phone and cathode ray tube (CRT) and those of non-exposed mothers. Conclusions: The findings of this study cast doubt on previous reports, which indicated that exposure to ionizing radiation during pregnancy increased the risk of low birth weight. PMID:23633865

Influence of renormalization shielding on the electron-impact ionization process in dense partially ionized plasmas

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

Song, Mi-Young; Yoon, Jung-Sik; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr

2015-04-15

The renormalization shielding effects on the electron-impact ionization of hydrogen atom are investigated in dense partially ionized plasmas. The effective projectile-target interaction Hamiltonian and the semiclassical trajectory method are employed to obtain the transition amplitude as well as the ionization probability as functions of the impact parameter, the collision energy, and the renormalization parameter. It is found that the renormalization shielding effect suppresses the transition amplitude for the electron-impact ionization process in dense partially ionized plasmas. It is also found that the renormalization effect suppresses the differential ionization cross section in the peak impact parameter region. In addition, it ismore » found that the influence of renormalization shielding on the ionization cross section decreases with an increase of the relative collision energy. The variations of the renormalization shielding effects on the electron-impact ionization cross section are also discussed.« less

Identification of Fatty Acids, Phospholipids, and Their Oxidation Products Using Matrix-Assisted Laser Desorption Ionization Mass Spectrometry and Electrospray Ionization Mass Spectrometry

ERIC Educational Resources Information Center

Harmon, Christopher W.; Mang, Stephen A.; Greaves, John; Finlayson-Pitts, Barbara J.

2010-01-01

Electrospray ionization mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) have found increasing application in the analysis of biological samples. Using these techniques to solve problems in analytical chemistry should be an essential component of the training of undergraduate chemists. We…

Soft Argon-Propane Dielectric Barrier Discharge Ionization.

PubMed

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

2018-03-06

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

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

PubMed

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

2017-08-01

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

Quantum mechanical calculations related to ionization and charge transfer in DNA

NASA Astrophysics Data System (ADS)

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

2012-07-01

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

Ionizing spectra of stars that lose their envelope through interaction with a binary companion: role of metallicity

NASA Astrophysics Data System (ADS)

Götberg, Y.; de Mink, S. E.; Groh, J. H.

2017-11-01

Understanding ionizing fluxes of stellar populations is crucial for various astrophysical problems including the epoch of reionization. Short-lived massive stars are generally considered as the main stellar sources. We examine the potential role of less massive stars that lose their envelope through interaction with a binary companion. Here, we focus on the role of metallicity (Z). For this purpose we used the evolutionary code MESA and created tailored atmosphere models with the radiative transfer code CMFGEN. We show that typical progenitors, with initial masses of 12 M⊙, produce hot and compact stars ( 4 M⊙, 60-80 kK, 1 R⊙). These stripped stars copiously produce ionizing photons, emitting 60-85% and 30-60% of their energy as HI and HeI ionizing radiation, for Z = 0.0001-0.02, respectively. Their output is comparable to what massive stars emit during their Wolf-Rayet phase, if we account for their longer lifetimes and the favorable slope of the initial mass function. Their relative importance for reionization may be further favored since they emit their photons with a time delay ( 20 Myr after birth in our fiducial model). This allows time for the dispersal of the birth clouds, allowing the ionizing photons to escape into the intergalactic medium. At low Z, we find that Roche stripping fails to fully remove the H-rich envelope, because of the reduced opacity in the subsurface layers. This is in sharp contrast with the assumption of complete stripping that is made in rapid population synthesis simulations, which are widely used to simulate the binary progenitors of supernovae and gravitational waves. Finally, we discuss the urgency to increase the observed sample of stripped stars to test these models and we discuss how our predictions can help to design efficient observational campaigns.

Towards a full reference library of MS(n) spectra. Testing of a library containing 3126 MS2 spectra of 1743 compounds.

PubMed

Milman, Boris L

2005-01-01

A library consisting of 3766 MS(n) spectra of 1743 compounds, including 3126 MS2 spectra acquired mainly using ion trap (IT) and triple-quadrupole (QqQ) instruments, was composed of numerous collections/sources. Ionization techniques were mainly electrospray ionization and also atmospheric pressure chemical ionization and chemical ionization. The library was tested for the performance in identification of unknowns, and in this context this work is believed to be the largest of all known tests of product-ion mass spectral libraries. The MS2 spectra of the same compounds from different collections were in turn divided into spectra of 'unknown' and reference compounds. For each particular compound, library searches were performed resulting in selection by taking into account the best matches for each spectral collection/source. Within each collection/source, replicate MS2 spectra differed in the collision energy used. Overall, there were up to 950 search results giving the best match factors and their ranks in corresponding hit lists. In general, the correct answers were obtained as the 1st rank in up to 60% of the search results when retrieved with (on average) 2.2 'unknown' and 6.2 reference replicates per compound. With two or more replicates of both 'unknown' and reference spectra (the average numbers of replicates were 4.0 and 7.8, respectively), the fraction of correct answers in the 1st rank increased to 77%. This value is close to the performance of established electron ionization mass spectra libraries (up to 79%) found by other workers. The hypothesis that MS2 spectra better match reference spectra acquired using the same type of tandem mass spectrometer (IT or QqQ) was neither strongly proved nor rejected here. The present work shows that MS2 spectral libraries containing sufficiently numerous different entries for each compound are sufficiently efficient for identification of unknowns and suitable for use with different tandem mass spectrometers. 2005 John Wiley & Sons, Ltd.

Understanding the links between composition, polyhedral distortion, and luminescence properties in green-emitting β-Si 6–zAl zO zN 8–z:Eu 2+ phosphors

DOE PAGES

Cozzan, Clayton; Laurita, Geneva; Gaultois, Michael W.; ...

2017-09-21

Inorganic phosphor materials play a crucial role in the creation of white light from blue and near-UV solid-state light-emitting diodes. Understanding the intricacies of the phosphor structure is key for setting the stage for improved, more efficient functionality. Average structure and coordination environment analysis of the robust and efficient green-emitting phosphor, β-SiAlON:Eu 2+ (β-Si 6–zAl zO zN 8–zEu 0.009), is combined here with a range of property measurements to elucidate the role of Al content ( z) in luminescence properties, including the red shift of emission and the thermal quenching of luminescence as a function of increasing Al content z.more » Average structure techniques reveal changes in polyhedral distortion with increasing z for the 9-coordinate Eu site in β-SiAlON:Eu 2+. X-ray absorption near edge structure (XANES) is used to confirm that the majority of the activator Eu is in the Eu 2+ state, exhibiting the symmetry-allowed and efficient 4f 75d 0 → 4f 65d 1 transitions. As a result, room temperature and temperature-dependent luminescence indicate a curious increase in thermal stability with increasing z over a small range due to an increasing barrier for thermal ionization, which is correlated to an increase in the quantum yield of the phosphor.« less

Understanding the links between composition, polyhedral distortion, and luminescence properties in green-emitting β-Si 6–zAl zO zN 8–z:Eu 2+ phosphors

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

Cozzan, Clayton; Laurita, Geneva; Gaultois, Michael W.

Inorganic phosphor materials play a crucial role in the creation of white light from blue and near-UV solid-state light-emitting diodes. Understanding the intricacies of the phosphor structure is key for setting the stage for improved, more efficient functionality. Average structure and coordination environment analysis of the robust and efficient green-emitting phosphor, β-SiAlON:Eu 2+ (β-Si 6–zAl zO zN 8–zEu 0.009), is combined here with a range of property measurements to elucidate the role of Al content ( z) in luminescence properties, including the red shift of emission and the thermal quenching of luminescence as a function of increasing Al content z.more » Average structure techniques reveal changes in polyhedral distortion with increasing z for the 9-coordinate Eu site in β-SiAlON:Eu 2+. X-ray absorption near edge structure (XANES) is used to confirm that the majority of the activator Eu is in the Eu 2+ state, exhibiting the symmetry-allowed and efficient 4f 75d 0 → 4f 65d 1 transitions. As a result, room temperature and temperature-dependent luminescence indicate a curious increase in thermal stability with increasing z over a small range due to an increasing barrier for thermal ionization, which is correlated to an increase in the quantum yield of the phosphor.« less

Sampling and analyte enrichment strategies for ambient mass spectrometry.

PubMed

Li, Xianjiang; Ma, Wen; Li, Hongmei; Ai, Wanpeng; Bai, Yu; Liu, Huwei

2018-01-01

Ambient mass spectrometry provides great convenience for fast screening, and has showed promising potential in analytical chemistry. However, its relatively low sensitivity seriously restricts its practical utility in trace compound analysis. In this review, we summarize the sampling and analyte enrichment strategies coupled with nine modes of representative ambient mass spectrometry (desorption electrospray ionization, paper vhspray ionization, wooden-tip spray ionization, probe electrospray ionization, coated blade spray ionization, direct analysis in real time, desorption corona beam ionization, dielectric barrier discharge ionization, and atmospheric-pressure solids analysis probe) that have dramatically increased the detection sensitivity. We believe that these advances will promote routine use of ambient mass spectrometry. Graphical abstract Scheme of sampling stretagies for ambient mass spectrometry.

Organic solar cells based on high dielectric constant materials: An approach to increase efficiency

NASA Astrophysics Data System (ADS)

Hamam, Khalil Jumah Tawfiq

The efficiency of organic solar cells still lags behind inorganic solar cells due to their low dielectric constant which results in a weakly screened columbic attraction between the photogenerated electron-hole system, therefore the probability of charge separating is low. Having an organic material with a high dielectric constant could be the solution to get separated charges or at least weakly bounded electron-hole pairs. Therefore, high dielectric constant materials have been investigated and studied by measuring modified metal-phthalocyanine (MePc) and polyaniline in pellets and thin films. The dielectric constant was investigated as a function of temperature and frequency in the range of 20Hz to1MHz. For MePc we found that the high dielectric constant was an extrinsic property due to water absorption and the formation of hydronuim ion allowed by the ionization of the functional groups such as sulphonated and carboxylic groups. The dielectric constant was high at low frequencies and decreasing as the frequency increase. Investigated materials were applied in fabricated bilayer heterojunction organic solar cells. The application of these materials in an organic solar cells show a significant stability under room conditions rather than improvement in their efficiency.

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

DOE PAGES

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

2016-10-13

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a widely adopted, versatile technique, especially in high-throughput analysis and imaging. However, matrix-dependent selectivity of analytes is often a severe limitation. In this work, a mixture of organic 2,5-dihydroxybenzoic acid and inorganic Fe 3O 4 nanoparticles is developed as a binary MALDI matrix to alleviate the well-known issue of triacylglycerol (TG) ion suppression by phosphatidylcholine (PC). In application to lipid standards and maize seed cross-sections, the binary matrix not only dramatically reduced the ion suppression of TG, but also efficiently desorbed and ionized a wide variety of lipids such as cationic PC, anionicmore » phosphatidylethanolamine (PE) and phosphatidylinositol (PI), and neutral digalactosyldiacylglycerol (DGDG). The binary matrix was also very efficient for large polysaccharides, which were not detected by either of the individual matrices. As a result, the usefulness of the binary matrix is demonstrated in MS imaging of maize seed sections, successfully visualizing diverse medium-size molecules and acquiring high-quality MS/MS spectra for these compounds.« less

Preliminary Spectroscopic Measurements for a Gallium Electromagnetic (GEM) Thruster

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Burton, Rodney L.; Glumac, Nick G.; Polzin, Kurt A.

2007-01-01

As a propellant option for electromagnetic thrusters, liquid ,gallium appears to have several advantages relative to other propellants. The merits of using gallium in an electromagnetic thruster (EMT) are discussed and estimates of discharge current levels and mass flow rates yielding efficient operation are given. The gallium atomic weight of 70 predicts high efficiency in the 1500-2000 s specific impulse range, making it ideal for higher-thrust, near-Earth missions. A spatially and temporally broad spectroscopic survey in the 220-520 nm range is used to determine which species are present in the plasma and estimate electron temperature. The spectra show that neutral, singly, and doubly ionized gallium species are present in a 20 J, 1.8 kA (peak) are discharge. With graphite present on the insulator to facilitate breakdown, singly and doubly ionized carbon atoms are also present, and emission is observed from molecular carbon (CZ) radicals. A determination of the electron temperature was attempted using relative emission line data, and while the spatially and temporally averaged, spectra don't fit well to single temperatures, the data and presence of doubly ionized gallium are consistent with distributions in the 1-3 eV range.

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

PubMed

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

2017-12-05

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

Effects of the magnetic field gradient on the wall power deposition of Hall thrusters

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Li, Peng; Zhang, Xu; Wei, Liqiu; Sun, Hezhi; Peng, Wuji; Yu, Daren

2017-04-01

The effect of the magnetic field gradient in the discharge channel of a Hall thruster on the ionization of the neutral gas and power deposition on the wall is studied through adopting the 2D-3V particle-in-cell (PIC) and Monte Carlo collisions (MCC) model. The research shows that by gradually increasing the magnetic field gradient while keeping the maximum magnetic intensity at the channel exit and the anode position unchanged, the ionization region moves towards the channel exit and then a second ionization region appears near the anode region. Meanwhile, power deposition on the walls decreases initially and then increases. To avoid power deposition on the walls produced by electrons and ions which are ionized in the second ionization region, the anode position is moved towards the channel exit as the magnetic field gradient is increased; when the anode position remains at the zero magnetic field position, power deposition on the walls decreases, which can effectively reduce the temperature and thermal load of the discharge channel.

Taurine Protects Mouse Spermatocytes from Ionizing Radiation-Induced Damage Through Activation of Nrf2/HO-1 Signaling.

PubMed

Yang, Wenjun; Huang, Jinfeng; Xiao, Bang; Liu, Yan; Zhu, Yiqing; Wang, Fang; Sun, Shuhan

2017-01-01

The increasing prevalence of ionizing radiation exposure has inevitably raised public concern over the potential detrimental effects of ionizing radiation on male reproductive system function. The detection of drug candidates to prevent reproductive system from damage caused by ionizing radiation is urgent. We aimed to investigate the protective role of taurine on the injury of mouse spermatocyte-derived cells (GC-2) subjected to ionizing radiation. mouse spermatocytes (GC-2 cells) were exposed to ionizing radiation with or without treatment of Taurine. The effect of ionizing radiation and Taurine treatment on GC-2 cells were evaluated by cell viability assay (CCK8), cell cycle and apoptosis. The relative protein abundance change was determined by Western blotting. The siRNA was used to explore whether Nrf2 signaling was involved in the cytoprotection of Taurine. Taurine significantly inhibited the decrease of cell viability, percentage of apoptotic cells and cell cycle arrest induced by ionizing radiation. Western blot analysis showed that taurine significantly limited the ionizing radiation-induced down-regulation of CyclinB1 and CDK1, and suppressed activation of Fas/FasL system pathway. In addition, taurine treatment significantly increased the expression of Nrf2 and HO-1 in GC-2 cells exposed to ionizing radiation, two components in antioxidant pathway. The above cytoprotection of Taurine was blocked by siNrf2. Our results demonstrate that taurine has the potential to effectively protect GC-2 cells from ionizing radiation- triggered damage via upregulation of Nrf2/HO-1 signaling. © 2017 The Author(s). Published by S. Karger AG, Basel.

Avalanche multiplication and impact ionization in amorphous selenium photoconductive target

NASA Astrophysics Data System (ADS)

Park, Wug-Dong; Tanioka, Kenkichi

2014-03-01

The avalanche multiplication factor and the hole ionization coefficient in the amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) target depend on the electric field. The phenomenon of avalanche multiplication and impact ionization in the 0.4-µm-thick a-Se HARP target is investigated. The hot carrier energy in the 0.4-µm-thick a-Se HARP target increases linearly as the target voltage increases. The energy relaxation length of hot carriers in the a-Se photoconductor of the 0.4-µm-thick HARP target saturates as the electric field increases. The average energy Eav of a hot carrier and the energy relaxation length λE in the a-Se photoconductor of the 0.4-µm-thick HARP target at 1 × 108 V/m were 0.25 eV and 2.5 nm, respectively. In addition, the hole ionization coefficient β and the avalanche multiplication factor M are derived as a function of the electric field, the average energy of a hot carrier, and the impact ionization energy. The experimental hole ionization coefficient β and the avalanche multiplication factor M in the 0.4-µm-thick a-Se HARP target agree with the theoretical results.

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

NASA Astrophysics Data System (ADS)

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

2016-02-01

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

Interatomic Coulombic decay cascades in multiply excited neon clusters

PubMed Central

Nagaya, K.; Iablonskyi, D.; Golubev, N. V.; Matsunami, K.; Fukuzawa, H.; Motomura, K.; Nishiyama, T.; Sakai, T.; Tachibana, T.; Mondal, S.; Wada, S.; Prince, K. C.; Callegari, C.; Miron, C.; Saito, N.; Yabashi, M.; Demekhin, Ph. V.; Cederbaum, L. S.; Kuleff, A. I.; Yao, M.; Ueda, K.

2016-01-01

In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold. However on tuning the laser to the lowest resonant transition, the system becomes multiply excited, and more efficient, indirect ionization pathways become operative. These mechanisms are known as interatomic Coulombic decay (ICD), where one of the species de-excites to its ground state, transferring its energy to ionize another excited species. Here we show that on tuning to a higher resonant transition, a previously unknown type of interatomic Coulombic decay, intra-Rydberg ICD occurs. In it, de-excitation of an atom to a close-lying Rydberg state leads to electron emission from another neighbouring Rydberg atom. Moreover, systems multiply excited to higher Rydberg states will decay by a cascade of such processes, producing even more ions. The intra-Rydberg ICD and cascades are expected to be ubiquitous in weakly-bound systems exposed to high-intensity resonant radiation. PMID:27917867

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

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

Samulyak, Roman

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

Spontaneous Charge Separation and Sublimation Processes are Ubiquitous in Nature and in Ionization Processes in Mass Spectrometry

NASA Astrophysics Data System (ADS)

Trimpin, Sarah; Lu, I.-Chung; Rauschenbach, Stephan; Hoang, Khoa; Wang, Beixi; Chubatyi, Nicholas D.; Zhang, Wen-Jing; Inutan, Ellen D.; Pophristic, Milan; Sidorenko, Alexander; McEwen, Charles N.

2018-02-01

Ionization processes have been discovered by which small and large as well as volatile and nonvolatile compounds are converted to gas-phase ions when associated with a matrix and exposed to sub-atmospheric pressure. Here, we discuss experiments further defining these simple and unexpected processes. Charge separation is found to be a common process for small molecule chemicals, solids and liquids, passed through an inlet tube from a higher to a lower pressure region, with and without heat applied. This charge separation process produces positively- and negatively-charged particles with widely different efficiencies depending on the compound and its physical state. Circumstantial evidence is presented suggesting that in the new ionization process, charged particles carry analyte into the gas phase, and desolvation of these particles produce the bare ions similar to electrospray ionization, except that solid particles appear likely to be involved. This mechanistic proposition is in agreement with previous theoretical work related to ion emission from ice.

Dustbuster: a New Generation Impact-ionization Time-of-flight Mass Spectrometer for in situ Analysis of Cosmic Dust

NASA Astrophysics Data System (ADS)

Austin, D. E.; Ahrens, T. J.; Beauchamp, J. L.

2000-10-01

We have developed and tested a small impact-ionization time-of-flight mass spectrometer for analysis of cosmic dust, suitable for use on deep space missions. This mass spectrometer, named Dustbuster, incorporates a large target area and a reflectron, simultaneously optimizing mass resolution, sensitivity, and collection efficiency. Dust particles hitting the 65-cm2 target plate are partially ionized. The resulting ions are accelerated through a modified reflectron that focuses the ions in space and time to produce high-resolution spectra. The instrument, shown below, measures 10 x 10 x 20 cm, has a mass of 500 g, and consumes little power. Laser desorption ionization of metal and mineral samples (embedded in the impact plate) simulates particle impacts for instrument performance tests. Mass resolution in these experiments is near 200, permitting resolution of isotopes. The mass spectrometer can be combined with other instrument components to determine dust particle trajectories and sizes. This project was funded by NASA's Planetary Instrument Definition and Development Program.

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

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

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

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

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

NASA Astrophysics Data System (ADS)

Louchev, Oleg A.; Saito, Norihito; Oishi, Yu; Miyazaki, Koji; Okamura, Kotaro; Nakamura, Jumpei; Iwasaki, Masahiko; Wada, Satoshi

2016-09-01

We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α ) radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i) multi-photon ionization, (ii) step-wise (2+1)-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii) laser-induced avalanche ionization produced by generated free electrons. Developed expressions validated by order of magnitude estimations and available experimental data allow us to identify the area for the operation under high input laser intensities avoiding the onset of full-scale discharge, loss of efficiency and inhibition of generated L-α radiation. Calculations made reveal an opportunity for scaling up the output energy of the experimentally generated pulsed L-α radiation without significant enhancement of photoionization.

High efficiency direct detection of ions from resonance ionization of sputtered atoms

DOEpatents

Gruen, Dieter M.; Pellin, Michael J.; Young, Charles E.

1986-01-01

A method and apparatus are provided for trace and other quantitative analysis with high efficiency of a component in a sample, with the analysis involving the removal by ion or other bombardment of a small quantity of ion and neutral atom groups from the sample, the conversion of selected neutral atom groups to photoions by laser initiated resonance ionization spectroscopy, the selective deflection of the photoions for separation from original ion group emanating from the sample, and the detection of the photoions as a measure of the quantity of the component. In some embodiments, the original ion group is accelerated prior to the RIS step for separation purposes. Noise and other interference are reduced by shielding the detector from primary and secondary ions and deflecting the photoions sufficiently to avoid the primary and secondary ions.

High efficiency direct detection of ions from resonance ionization of sputtered atoms

DOEpatents

Gruen, D.M.; Pellin, M.J.; Young, C.E.

1985-01-16

A method and apparatus are provided for trace and other quantitative analysis with high efficiency of a component in a sample, with the analysis involving the removal by ion or other bombardment of a small quantity of ion and neutral atom groups from the sample, the conversion of selected neutral atom groups to photoions by laser initiated resonance ionization spectroscopy, the selective deflection of the photoions for separation from original ion group emanating from the sample, and the detection of the photoions as a measure of the quantity of the component. In some embodiments, the original ion group is accelerated prior to the RIS step for separation purposes. Noise and other interference are reduced by shielding the detector from primary and secondary ions and deflecting the photoions sufficiently to avoid the primary and secondary ions.

Creating space plasma from the ground

NASA Astrophysics Data System (ADS)

Carlson, H. C.; Djuth, F. T.; Zhang, L. D.

2017-01-01

We have performed an experiment to compare as directly as realizable the ionization production rate by HF radio wave energy versus by solar EUV. We take advantage of the commonality that ionization production by both ground-based high-power HF radio waves and by solar EUV is driven by primary and secondary suprathermal electrons near and above 20 eV. Incoherent scatter radar (ISR) plasma-line amplitudes are used as a measure of suprathermal electron fluxes for ISR wavelengths near those for 430 MHz and are indeed a clean measure of such for those fluxes sufficiently weak to have negligible self-damping. We present data from an HF heating experiment on November 2015 at Arecibo, which even more directly confirm the only prior midlatitude estimate, of order 10% efficiency for conversion of HF energy to ionospheric ionization. We note the theoretical maximum possible is 1/3, while 1% or less reduces the question to near practical irrelevance. Our measurements explicitly confirm the prediction that radio-frequency production of artificial ionospheres can be practicable, even at midlatitudes. Furthermore, that this midlatitude efficiency is comparable to efficiencies measured at high latitudes (which include enhancements unique to high latitudes including magnetic zenith effect, gyrofrequency multiples, and double resonances) requires reexamination of current theoretical thinking about soft-electron acceleration processes in weakly magnetized plasmas. The implications are that electron acceleration by any of a variety of processes may be a fundamental underpinning to energy redistribution in space plasmas.

Calculation of H2-He Flow with Nonequilibrium Ionization and Radiation: an Interim Report

NASA Technical Reports Server (NTRS)

Furudate, Michiko; Chang, Keun-Shik

2005-01-01

The nonequilibrium ionization process in hydrogen-helium mixture behind a strong shock wave is studied numerically using the detailed ionization rate model developed recently by Park which accounts for emission and absorption of Lyman lines. The study finds that, once the avalanche ionization is started, the Lyman line is self-absorbed. The intensity variation of the radiation at 5145 Angstroms found by Leibowitz in a shock tube experiment can be numerically reproduced by assuming that ionization behind the shock wave prior to the onset of avalanche ionization is 1.3%. Because 1.3% initial ionization is highly unlikely, Leibowitz s experimental data is deemed questionable. By varying the initial electron density value in the calculation, the calculated ionization equilibration time is shown to increase approximately as inverse square-root of the initial electron density value. The true ionization equilibration time is most likely much longer than the value found by Leibowitz.

Formation of Pyrylium from Aromatic Systems with a Helium:Oxygen Flowing Atmospheric Pressure Afterglow (FAPA) Plasma Source

NASA Astrophysics Data System (ADS)

Badal, Sunil P.; Ratcliff, Tyree D.; You, Yi; Breneman, Curt M.; Shelley, Jacob T.

2017-06-01

The effects of oxygen addition on a helium-based flowing atmospheric pressure afterglow (FAPA) ionization source are explored. Small amounts of oxygen doped into the helium discharge gas resulted in an increase in abundance of protonated water clusters by at least three times. A corresponding increase in protonated analyte signal was also observed for small polar analytes, such as methanol and acetone. Meanwhile, most other reagent ions (e.g., O2 +·, NO+, etc.) significantly decrease in abundance with even 0.1% v/v oxygen in the discharge gas. Interestingly, when analytes that contained aromatic constituents were subjected to a He:O2-FAPA, a unique (M + 3)+ ion resulted, while molecular or protonated molecular ions were rarely detected. Exact-mass measurements revealed that these (M + 3)+ ions correspond to (M - CH + O)+, with the most likely structure being pyrylium. Presence of pyrylium-based ions was further confirmed by tandem mass spectrometry of the (M + 3)+ ion compared with that of a commercially available salt. Lastly, rapid and efficient production of pyrylium in the gas phase was used to convert benzene into pyridine. Though this pyrylium-formation reaction has not been shown before, the reaction is rapid and efficient. Potential reactant species, which could lead to pyrylium formation, were determined from reagent-ion mass spectra. Thermodynamic evaluation of reaction pathways was aided by calculation of the formation enthalpy for pyrylium, which was found to be 689.8 kJ/mol. Based on these results, we propose that this reaction is initiated by ionized ozone (O3 +·), proceeds similarly to ozonolysis, and results in the neutral loss of the stable CHO2 · radical. [Figure not available: see fulltext.

Formation of Pyrylium from Aromatic Systems with a Helium:Oxygen Flowing Atmospheric Pressure Afterglow (FAPA) Plasma Source.

PubMed

Badal, Sunil P; Ratcliff, Tyree D; You, Yi; Breneman, Curt M; Shelley, Jacob T

2017-06-01

The effects of oxygen addition on a helium-based flowing atmospheric pressure afterglow (FAPA) ionization source are explored. Small amounts of oxygen doped into the helium discharge gas resulted in an increase in abundance of protonated water clusters by at least three times. A corresponding increase in protonated analyte signal was also observed for small polar analytes, such as methanol and acetone. Meanwhile, most other reagent ions (e.g., O 2 +· , NO + , etc.) significantly decrease in abundance with even 0.1% v/v oxygen in the discharge gas. Interestingly, when analytes that contained aromatic constituents were subjected to a He:O 2 -FAPA, a unique (M + 3) + ion resulted, while molecular or protonated molecular ions were rarely detected. Exact-mass measurements revealed that these (M + 3) + ions correspond to (M - CH + O) + , with the most likely structure being pyrylium. Presence of pyrylium-based ions was further confirmed by tandem mass spectrometry of the (M + 3) + ion compared with that of a commercially available salt. Lastly, rapid and efficient production of pyrylium in the gas phase was used to convert benzene into pyridine. Though this pyrylium-formation reaction has not been shown before, the reaction is rapid and efficient. Potential reactant species, which could lead to pyrylium formation, were determined from reagent-ion mass spectra. Thermodynamic evaluation of reaction pathways was aided by calculation of the formation enthalpy for pyrylium, which was found to be 689.8 kJ/mol. Based on these results, we propose that this reaction is initiated by ionized ozone (O 3 +· ), proceeds similarly to ozonolysis, and results in the neutral loss of the stable CHO 2 · radical. Graphical Abstract ᅟ.

Numerical simulation and analysis of electromagnetic-wave absorption of a plasma slab created by a direct-current discharge with gridded anode

NASA Astrophysics Data System (ADS)

Yuan, Chengxun; Tian, Ruihuan; Eliseev, S. I.; Bekasov, V. S.; Bogdanov, E. A.; Kudryavtsev, A. A.; Zhou, Zhongxiang

2018-03-01

In this paper, we present investigation of a direct-current discharge with a gridded anode from the point of view of using it as a means of creating plasma coating that could efficiently absorb incident electromagnetic (EM) waves. A single discharge cell consists of two parallel plates, one of which (anode) is gridded. Electrons emitted from the cathode surface are accelerated in the short interelectrode gap and are injected into the post-anode space, where they lose acquired energy on ionization and create plasma. Numerical simulations were used to investigate the discharge structure and obtain spatial distributions of plasma density in the post-anode space. The numerical model of the discharge was based on a simple hybrid approach which takes into account non-local ionization by fast electrons streaming from the cathode sheath. Specially formulated transparency boundary conditions allowed performing simulations in 1D. Simulations were carried out in air at pressures of 10 Torr and higher. Analysis of the discharge structure and discharge formation is presented. It is shown that using cathode materials with lower secondary emission coefficients can allow increasing the thickness of plasma slabs for the same discharge current, which can potentially enhance EM wave absorption. Spatial distributions of electron density obtained during simulations were used to calculate attenuation of an incident EM wave propagating perpendicularly to the plasma slab boundary. It is shown that plasma created by means of a DC discharge with a gridded anode can efficiently absorb EM waves in the low frequency range (6-40 GHz). Increasing gas pressure results in a broader range of wave frequencies (up to 500 GHz) where a considerable attenuation is observed.

Electron-Atom Ionization Calculations using Propagating Exterior Complex Scaling

NASA Astrophysics Data System (ADS)

Bartlett, Philip

2007-10-01

The exterior complex scaling method (Science 286 (1999) 2474), pioneered by Rescigno, McCurdy and coworkers, provided highly accurate ab initio solutions for electron-hydrogen collisions by directly solving the time-independent Schr"odinger equation in coordinate space. An extension of this method, propagating exterior complex scaling (PECS), was developed by Bartlett and Stelbovics (J. Phys. B 37 (2004) L69, J. Phys. B 39 (2006) R379) and has been demonstrated to provide computationally efficient and accurate calculations of ionization and scattering cross sections over a large range of energies below, above and near the ionization threshold. An overview of the PECS method for three-body collisions and the computational advantages of its propagation and iterative coupling techniques will be presented along with results of: (1) near-threshold ionization of electron-hydrogen collisions and the Wannier threshold laws, (2) scattering cross section resonances below the ionization threshold, and (3) total and differential cross sections for electron collisions with excited targets and hydrogenic ions from low through to high energies. Recently, the PECS method has been extended to solve four-body collisions using time-independent methods in coordinate space and has initially been applied to the s-wave model for electron-helium collisions. A description of the extensions made to the PECS method to facilitate these significantly more computationally demanding calculations will be given, and results will be presented for elastic, single-excitation, double-excitation, single-ionization and double-ionization collisions.

Counting Molecules by Desorption Ionization and Mass Spectrometry/Mass Spectrometry.

ERIC Educational Resources Information Center

Cooks, R. G.; Busch, K. L.

1982-01-01

Discusses two newer methods in mass spectrometry and shows how they can increase signal and signal-to-noise ratios, respectively. The first method, desorption ionization (DI), increases sensitivity while the second method, mass spectrometry/mass spectrometry (MS/MS), increases specificity. Together, the two methods offer improved analytical…

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

NASA Astrophysics Data System (ADS)

Karras, Gabriel; Lockyer, Nicholas P.

2014-05-01

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

Effects of gas temperature on NO(x) removal by dielectric barrier discharge.

PubMed

Wang, Tao; Sun, Bao-Min; Xiao, Hai-Ping

2013-01-01

The purpose of this investigation is to discuss the effect of gas temperature on NO(x) removal by dielectric barrier discharge. The Boltzmann equation was used to analyse the electron distribution function in the reactor, and experiments were conducted to find out the effects of different temperatures. The calculation results show that, with a rise in the temperature, E/N increases, increasing the ionization rate. When the ratio of electric field strength to total gas density (E/N) rises from 50 to 150 Td, the ionization rate and electron mean energy increase by 2.0 x 10(5) and 2.3, respectively. The experiments show that in the NO/N2 system, when the temperature increases to 1 30 degrees C and the applied voltage is 11.1 kV, the discharge power is 44.7 W, which is higher than the discharge power of 35.4 W found at 25 degrees C; in the NO/O2/N2 system, an increase in the temperature increases the decomposition of active O3 species, producing a negative effect on NO oxidation; in the NO/O2/N2/C2H4 system, when the temperature increases, the quantity of active species HO2 increases and the NO removal reaction rate increases, reflecting an obvious improvement in the NO removal; and in the NO/O2/N2/C2H4/H2O system, at 25 degrees C, 90 degrees C, and 130 degrees C, when the energy density is 239.7 J L(-1), the NO removal efficiencies are 52.8%, 66.4%, and 71.0%, respectively.

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

NASA Astrophysics Data System (ADS)

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

2014-02-01

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

Non-random distribution of DNA double-strand breaks induced by particle irradiation

NASA Technical Reports Server (NTRS)

Lobrich, M.; Cooper, P. K.; Rydberg, B.; Chatterjee, A. (Principal Investigator)

1996-01-01

Induction of DNA double-strand breaks (dsbs) in mammalian cells is dependent on the spatial distribution of energy deposition from the ionizing radiation. For high LET particle radiations the primary ionization sites occur in a correlated manner along the track of the particles, while for X-rays these sites are much more randomly distributed throughout the volume of the cell. It can therefore be expected that the distribution of dsbs linearly along the DNA molecule also varies with the type of radiation and the ionization density. Using pulsed-field gel and conventional gel techniques, we measured the size distribution of DNA molecules from irradiated human fibroblasts in the total range of 0.1 kbp-10 Mbp for X-rays and high LET particles (N ions, 97 keV/microns and Fe ions, 150 keV/microns). On a mega base pair scale we applied conventional pulsed-field gel electrophoresis techniques such as measurement of the fraction of DNA released from the well (FAR) and measurement of breakage within a specific NotI restriction fragment (hybridization assay). The induction rate for widely spaced breaks was found to decrease with LET. However, when the entire distribution of radiation-induced fragments was analysed, we detected an excess of fragments with sizes below about 200 kbp for the particles compared with X-irradiation. X-rays are thus more effective than high LET radiations in producing large DNA fragments but less effective in the production of smaller fragments. We determined the total induction rate of dsbs for the three radiations based on a quantitative analysis of all the measured radiation-induced fragments and found that the high LET particles were more efficient than X-rays at inducing dsbs, indicating an increasing total efficiency with LET. Conventional assays that are based only on the measurement of large fragments are therefore misleading when determining total dsb induction rates of high LET particles. The possible biological significance of this non-randomness for dsb induction is discussed.

Solar EUV Irradiance Measurements by the Auto-Calibrating EUV Spectrometers (SolACES) Aboard the International Space Station (ISS)

NASA Astrophysics Data System (ADS)

Schmidtke, G.; Nikutowski, B.; Jacobi, C.; Brunner, R.; Erhardt, C.; Knecht, S.; Scherle, J.; Schlagenhauf, J.

2014-05-01

SolACES is part of the ESA SOLAR ISS mission that started aboard the shuttle mission STS-122 on 7 February 2008. The instrument has recorded solar extreme ultraviolet (EUV) irradiance from 16 to 150 nm during the extended solar activity minimum and the beginning solar cycle 24 with rising solar activity and increasingly changing spectral composition. The SOLAR mission has been extended from a period of 18 months to > 8 years until the end of 2016. SolACES is operating three grazing incidence planar grating spectrometers and two three-current ionization chambers. The latter ones are considered as primary radiometric detector standards. Re-filling the ionization chambers with three different gases repeatedly and using overlapping band-pass filters, the absolute EUV fluxes are derived in these spectral intervals. This way the serious problem of continuing efficiency changes in space-borne instrumentation is overcome during the mission. Evaluating the three currents of the ionization chambers, the overlapping spectral ranges of the spectrometers and of the filters plus inter-comparing the results from the EUV photon absorption in the gases with different absorption cross sections, there are manifold instrumental possibilities to cross-check the results providing a high degree of reliability to the spectral irradiance derived. During the mission a very strong up-and-down variability of the spectrometric efficiency by orders of magnitude is observed. One of the effects involved is channeltron degradation. However, there are still open questions on other effects contributing to these changes. A survey of the measurements carried out and first results of the solar spectral irradiance (SSI) data are presented. Inter-comparison with EUV data from other space missions shows good agreement such that the international effort has started to elaborate a complete set of EUV-SSI data taking into account all data available from 2008 to 2013.

Determination of short chain carboxylic acids in vegetable oils and fats using ion exclusion chromatography electrospray ionization mass spectrometry.

PubMed

Viidanoja, Jyrki

2015-02-27

A new method for quantification of short chain C1-C6 carboxylic acids in vegetable oils and fats by employing Liquid Chromatography Mass Spectrometry (LC-MS) has been developed. The method requires minor sample preparation and applies non-conventional Electrospray Ionization (ESI) liquid phase chemistry. Samples are first dissolved in chloroform and then extracted using water that has been spiked with stable isotope labeled internal standards that are used for signal normalization and absolute quantification of selected acids. The analytes are separated using Ion Exclusion Chromatography (IEC) and detected with Electrospray Ionization Mass Spectrometry (ESI-MS) as deprotonated molecules. Prior to ionization the eluent that contains hydrochloric acid is modified post-column to ensure good ionization efficiency of the analytes. The averaged within run precision and between run precision were generally lower than 8%. The accuracy was between 85 and 115% for most of the analytes. The Lower Limit of Quantification (LLOQ) ranged from 0.006 to 7mg/kg. It is shown that this method offers good selectivity in cases where UV detection fails to produce reliable results. Copyright © 2015 Elsevier B.V. All rights reserved.

Theoretical considerations on the optogalvanic detection of laser induced fluorescence in atmospheric pressure atomizers

NASA Astrophysics Data System (ADS)

Omenetto, N.; Smith, B. W.; Winefordner, J. D.

1989-01-01

Several theoretical considerations are given on the potential and practical capabilities of a detector of fluorescence radiation whose operating principle is based on a multi-step excitation-ionization scheme involving the fluorescence photons as the first excitation step. This detection technique, which was first proposed by MATVEEVet al. [ Zh. Anal Khim.34, 846 (1979)], combines two independent atomizers, one analytical cell for the excitation of the sample fluorescence and one cell, filled with pure analyte atomic vapor, acting as the ionization detector. One laser beam excites the analyte fluorescence in the analytical cell and one (or two) laser beams are used to ionize the excited atoms in the detector. Several different causes of signal and noise are evaluated, together with a discussion on possible analytical atom reservoirs (flames, furnaces) and laser sources which could be used with this approach. For properly devised conditions, i.e. optical saturation of the fluorescence and unity ionization efficiency, detection limits well below pg/ml in solution and well below femtograms as absolute amounts in furnaces can be predicted. However, scattering problems, which are absent in a conventional laser-enhanced ionization set-up, may be important in this approach.

Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization.

PubMed

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

2016-08-07

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

Röntgen spheres around active stars

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Simultaneous ESI-APCI+ ionization and fragmentation pathways for nine benzodiazepines and zolpidem using single quadrupole LC-MS.

PubMed

Galaon, Toma; Vacaresteanu, Catalina; Anghel, Dan-Florin; David, Victor

2014-05-01

Nine important 1,4-benzodiazepines and zolpidem were characterized by liquid chromatography-mass spectrometry using a multimode ionization source able to generate ions using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and a single quadrupole mass analyzer. An optimum chromatographic separation was applied for all target compounds in less than 8 minutes using a Zorbax Eclipse Plus column (100 × 4.6 mm, 3.5 µm) kept at 35°C and a 0.3% HCOOH/ACN/IPA (61:34:5) mobile phase pumped at 1 ml/min. Optimization of LC-MS method generated low limit of quantitation (LOQ) values situated in the range 0.3-20.5 ng/ml. Comparison between differences in method sensitivity, under specified chromatographic conditions, when using ESI-only, APCI-only, and simultaneous ESI-APCI ionization with such a multimode source was discussed. Mixed ESI-APCI(+) mode proved to be the most sensitive ionization generating an average 35% detector response increase compared to ESI-only ionization and 350% detector response increase with respect to APCI-only ionization. Characterization of the nine benzodiazepines and zolpidem concerning their MS fragmentation pathway following 'in-source' collision-induced dissociation is discussed in detail and some general trends regarding these fragmentations are set. Copyright © 2013 John Wiley & Sons, Ltd.

Attosecond-recollision-controlled selective fragmentation of polyatomic molecules.

PubMed

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

2012-12-14

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

Total and dissociative photoionization cross sections of N2 from threshold to 107 eV

NASA Technical Reports Server (NTRS)

Samson, James A. R.; Masuoka, T.; Pareek, P. N.; Angel, G. C.

1986-01-01

The absolute cross sections for the production of N(+) and N2(+) were measured from the dissociative ionization threshold of 115 A. In addition, the absolute photoabsorption and photoionization cross sections were tabulated between 114 and 796 A. The ionization efficiencies were also given at several discrete wave lengths between 660 and 790 A. The production of N(+) fragment ions are discussed in terms of the doubly excited N2(+) states with binding energies in the range of 24 to 44 eV.

Total and dissociative photoionization cross sections of N2 from threshold to 107 eV

NASA Technical Reports Server (NTRS)

Samson, James A. R.; Masuoka, T.; Pareek, P. N.; Angel, G. C.

1987-01-01

The absolute cross sections for the production of N(+) and N2(+) have been measured from the dissociative ionization threshold to 115 A. In addition, the absolute photoabsorption and photoionization cross sections are tabulated between 114 and 796 A. The ionization efficiencies are also given at several discrete wavelengths between 660 and 790 A. The production of N(+) fragment ions are discussed in terms of the doubly excited N2(+) states with binding energies in the range 24 to 44 eV.

Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi.

PubMed

Dadachova, Ekaterina; Bryan, Ruth A; Huang, Xianchun; Moadel, Tiffany; Schweitzer, Andrew D; Aisen, Philip; Nosanchuk, Joshua D; Casadevall, Arturo

2007-05-23

Melanin pigments are ubiquitous in nature. Melanized microorganisms are often the dominating species in certain extreme environments, such as soils contaminated with radionuclides, suggesting that the presence of melanin is beneficial in their life cycle. We hypothesized that ionizing radiation could change the electronic properties of melanin and might enhance the growth of melanized microorganisms. Ionizing irradiation changed the electron spin resonance (ESR) signal of melanin, consistent with changes in electronic structure. Irradiated melanin manifested a 4-fold increase in its capacity to reduce NADH relative to non-irradiated melanin. HPLC analysis of melanin from fungi grown on different substrates revealed chemical complexity, dependence of melanin composition on the growth substrate and possible influence of melanin composition on its interaction with ionizing radiation. XTT/MTT assays showed increased metabolic activity of melanized C. neoformans cells relative to non-melanized cells, and exposure to ionizing radiation enhanced the electron-transfer properties of melanin in melanized cells. Melanized Wangiella dermatitidis and Cryptococcus neoformans cells exposed to ionizing radiation approximately 500 times higher than background grew significantly faster as indicated by higher CFUs, more dry weight biomass and 3-fold greater incorporation of (14)C-acetate than non-irradiated melanized cells or irradiated albino mutants. In addition, radiation enhanced the growth of melanized Cladosporium sphaerospermum cells under limited nutrients conditions. Exposure of melanin to ionizing radiation, and possibly other forms of electromagnetic radiation, changes its electronic properties. Melanized fungal cells manifested increased growth relative to non-melanized cells after exposure to ionizing radiation, raising intriguing questions about a potential role for melanin in energy capture and utilization.

Matrix-assisted laser-desorption/ionization mass spectrometric imaging of olanzapine in a single hair using esculetin as a matrix.

PubMed

Wang, Hang; Wang, Ying; Wang, Ge; Hong, Lizhi

2017-07-15

Matrix-assisted laser desorption/ionization-mass spectrometric imaging (MALDI-MSI) for the analysis of intact hair is a powerful tool for monitoring changes in drug consumption. The embedding of a low drug concentration in the hydrophobic hair matrix makes it difficult to extract and detect, and requires an improved method to increase detection sensitivity. In this study, an MSI method using MALDI-Fourier transform ion cyclotron resonance was developed for direct identification and imaging of olanzapine in hair samples using the positive ion mode. Following decontamination, scalp hair samples from an olanzapine user were scraped from the proximal to the distal end three times, and 5mm hair sections were fixed onto an Indium-Tin-Oxide (ITO)-coated microscopic glass slide. Esculetin (6,7-dihydroxy-2H-chromen-2-one) was used as a new hydrophobic matrix to increase the affinity, extraction and ionization efficiency of olanzapine in the hair samples. The spatial distribution of olanzapine was observed using five single hairs from the same drug user. This matrix improves the affinity of olanzapine in hair for molecular imaging with mass spectrometry. This method may provide a detection power for olanzapine to the nanogram level per 5mm hair. Time course changes in the MSI results were also compared with quantitative HPLC-MS/MS for each 5mm segment of single hair shafts selected from the MALDI target. MALDI imaging intensities in single hairs showed good semi-quantitative correlation with the results from conventional HPLC-MS/MS. MALDI-MSI is suitable for monitoring drug intake with a high time resolution. Copyright © 2017 Elsevier B.V. All rights reserved.

Miniature Dual-Corona Ionizer for Bipolar Charging of Aerosol

PubMed Central

Qi, Chaolong; Kulkarni, Pramod

2015-01-01

A corona-based bipolar charger has been developed for use in compact, field-portable mobility size spectrometers. The charger employs an aerosol flow cavity exposed to two corona ionizers producing ions of opposite polarity. Each corona ionizer houses two electrodes in parallel needle-mesh configuration and is operated at the same magnitude of corona current. Experimental measurement of detailed charge distribution of near-monodisperse particles of different diameter in the submicrometer size range showed that the charger is capable of producing well-defined, consistent bipolar charge distributions for flow rates up to 1.5 L/min and aerosol concentration up to 107 per cm3. For particles with preexisting charge of +1, 0, and −1, the measured charge distributions agreed well with the theoretical distributions within the range of experimental and theoretical uncertainties. The transmission efficiency of the charger was measured to be 80% for 10 nm particles (at 0.3 L/min and 5 μA corona current) and increased with increasing diameter beyond this size. Measurement of uncharged fractions at various combinations of positive and negative corona currents showed the charger performance to be insensitive to fluctuations in corona current. Ion concentrations under positive and negative unipolar operation were estimated to be 8.2 × 107 and 3.37 × 108 cm−3 for positive and negative ions; the n·t product value under positive corona operation was independently estimated to be 8.5 × 105 s/cm3. The ion concentration estimates indicate the charger to be capable of “neutralizing” typical atmospheric and industrial aerosols in most measurement applications. The miniature size, simple and robust operation makes the charger suitable for portable mobility spectrometers. PMID:26512158

Miniature Dual-Corona Ionizer for Bipolar Charging of Aerosol.

PubMed

Qi, Chaolong; Kulkarni, Pramod

2013-01-01

A corona-based bipolar charger has been developed for use in compact, field-portable mobility size spectrometers. The charger employs an aerosol flow cavity exposed to two corona ionizers producing ions of opposite polarity. Each corona ionizer houses two electrodes in parallel needle-mesh configuration and is operated at the same magnitude of corona current. Experimental measurement of detailed charge distribution of near-monodisperse particles of different diameter in the submicrometer size range showed that the charger is capable of producing well-defined, consistent bipolar charge distributions for flow rates up to 1.5 L/min and aerosol concentration up to 10 7 per cm 3 . For particles with preexisting charge of +1, 0, and -1, the measured charge distributions agreed well with the theoretical distributions within the range of experimental and theoretical uncertainties. The transmission efficiency of the charger was measured to be 80% for 10 nm particles (at 0.3 L/min and 5 μ A corona current) and increased with increasing diameter beyond this size. Measurement of uncharged fractions at various combinations of positive and negative corona currents showed the charger performance to be insensitive to fluctuations in corona current. Ion concentrations under positive and negative unipolar operation were estimated to be 8.2 × 10 7 and 3.37 × 10 8 cm -3 for positive and negative ions; the n · t product value under positive corona operation was independently estimated to be 8.5 × 10 5 s/cm 3 . The ion concentration estimates indicate the charger to be capable of "neutralizing" typical atmospheric and industrial aerosols in most measurement applications. The miniature size, simple and robust operation makes the charger suitable for portable mobility spectrometers.

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

PubMed

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

2018-02-20

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

Coupled electronic and atomic effects on defect evolution in silicon carbide under ion irradiation

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

Zhang, Yanwen; Xue, Haizhou; Zarkadoula, Eva

Understanding energy dissipation processes in electronic/atomic subsystems and subsequent non-equilibrium defect evolution is a long-standing challenge in materials science. In the intermediate energy regime, energetic particles simultaneously deposit a significant amount of energy to both electronic and atomic subsystems of silicon carbide (SiC). Here we show that defect evolution in SiC closely depends on the electronic-to-nuclear energy loss ratio (S e/S n), nuclear stopping powers ( dE/dx nucl), electronic stopping powers ( dE/dx ele), and the temporal and spatial coupling of electronic and atomic subsystem for energy dissipation. The integrated experiments and simulations reveal that: (1) increasing S e/S nmore » slows damage accumulation; (2) the transient temperatures during the ionization-induced thermal spike increase with dE/dx ele, which causes efficient damage annealing along the ion trajectory; and (3) for more condensed displacement damage within the thermal spike, damage production is suppressed due to the coupled electronic and atomic dynamics. Ionization effects are expected to be more significant in materials with covalent/ionic bonding involving predominantly well-localized electrons. Here, insights into the complex electronic and atomic correlations may pave the way to better control and predict SiC response to extreme energy deposition« less

Gallium Electromagnetic (GEM) Thruster Performance Measurements

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Burton, Rodney L.; Polzin, K. A.

2009-01-01

Discharge current, terminal voltage, and mass bit measurements are performed on a coaxial gallium electromagnetic thruster at discharge currents in the range of 7-23 kA. It is found that the mass bit varies quadratically with the discharge current which yields a constant exhaust velocity of 20 km/s. Increasing the electrode radius ratio of the thruster from to 2.6 to 3.4 increases the thruster efficiency from 21% to 30%. When operating with a central gallium anode, macroparticles are ejected at all energy levels tested. A central gallium cathode ejects macroparticles when the current density exceeds 3.7 10(exp 8) A/square m . A spatially and temporally broad spectroscopic survey in the 220-520 nm range is used to determine which species are present in the plasma. The spectra show that neutral, singly, and doubly ionized gallium species are present in the discharge, as well as annular electrode species at higher energy levels. Axial Langmuir triple probe measurements yield electron temperatures in the range of 0.8-3.8 eV and electron densities in the range of 8 x 10(exp )20 to 1.6 x 10(exp 21) m(exp -3) . Triple probe measurements suggest an exhaust plume with a divergence angle of 9 , and a completely doubly ionized plasma at the ablating thruster cathode.

Advanced water remediation from ofloxacin by ionizing radiation

NASA Astrophysics Data System (ADS)

Esposito, Biagio R.; Capobianco, Massimo L.; Martelli, Alessandro; Navacchia, Maria Luisa; Pretali, Luca; Saracino, Michela; Zanelli, Alberto; Emmi, Salvatore S.

2017-12-01

The performances of remediation processes initiated by ionizing radiation on ofloxacin are investigated in ambient conditions. The effectiveness of the decomposition of ofloxacin has been assessed both by γ-rays and electron beam in various aqueous solutions differentiated by the dissolved gases (Air or oxygen saturated) and H2O2. By HPLC it is shown that ofloxacin is removed according to a first order process vs. dose in any system. O2 accelerates the decomposition rate, while H2O2 does not seem to enhance any oxidation effect. The simultaneous oxidative-reductive treatment (no additive) demonstrated to have better mineralizing performances than the fully oxidative one (H2O2 present). Mineralization by γ results to be more efficient than by EB. The Total Organic Carbon decrease was investigated in dependence of dose and of the •OH production rate. The latter parameter was changed over 7 orders of magnitude by controlling dose rate and/or by adding H2O2. A steep increase of acidity remarks the phases of fluorine-carbon bond break.

Identification of Lasso Peptide Topologies Using Native Nanoelectrospray Ionization-Trapped Ion Mobility Spectrometry-Mass Spectrometry.

PubMed

Dit Fouque, Kevin Jeanne; Moreno, Javier; Hegemann, Julian D; Zirah, Séverine; Rebuffat, Sylvie; Fernandez-Lima, Francisco

2018-04-17

Lasso peptides are a fascinating class of bioactive ribosomal natural products characterized by a mechanically interlocked topology. In contrast to their branched-cyclic forms, lasso peptides have higher stability and have become a scaffold for drug development. However, the identification and separation of lasso peptides from their unthreaded topoisomers (branched-cyclic peptides) is analytically challenging since the higher stability is based solely on differences in their tertiary structures. In the present work, a fast and effective workflow is proposed for the separation and identification of lasso from branched cyclic peptides based on differences in their mobility space under native nanoelectrospray ionization-trapped ion mobility spectrometry-mass spectrometry (nESI-TIMS-MS). The high mobility resolving power ( R) of TIMS resulted in the separation of lasso and branched-cyclic topoisomers ( R up to 250, 150 needed on average). The advantages of alkali metalation reagents (e.g., Na, K, and Cs salts) as a way to increase the analytical power of TIMS is demonstrated for topoisomers with similar mobilities as protonated species, efficiently turning the metal ion adduction into additional separation dimensions.

Particle in cell/Monte Carlo collision analysis of the problem of identification of impurities in the gas by the plasma electron spectroscopy method

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

Kusoglu Sarikaya, C.; Rafatov, I., E-mail: rafatov@metu.edu.tr; Kudryavtsev, A. A.

2016-06-15

The work deals with the Particle in Cell/Monte Carlo Collision (PIC/MCC) analysis of the problem of detection and identification of impurities in the nonlocal plasma of gas discharge using the Plasma Electron Spectroscopy (PLES) method. For this purpose, 1d3v PIC/MCC code for numerical simulation of glow discharge with nonlocal electron energy distribution function is developed. The elastic, excitation, and ionization collisions between electron-neutral pairs and isotropic scattering and charge exchange collisions between ion-neutral pairs and Penning ionizations are taken into account. Applicability of the numerical code is verified under the Radio-Frequency capacitively coupled discharge conditions. The efficiency of the codemore » is increased by its parallelization using Open Message Passing Interface. As a demonstration of the PLES method, parallel PIC/MCC code is applied to the direct current glow discharge in helium doped with a small amount of argon. Numerical results are consistent with the theoretical analysis of formation of nonlocal EEDF and existing experimental data.« less

Use of GaN as a Scintillating Ionizing Radiation Detector

NASA Astrophysics Data System (ADS)

Wensman, Johnathan; Guardala, Noel; Mathur, Veerendra; Alasagas, Leslie; Vanhoy, Jeffrey; Statham, John; Marron, Daniel; Millett, Marshall; Marsh, Jarrod; Currie, John; Price, Jack

2017-09-01

Gallium nitride (GaN) is a III/V direct bandgap semiconductor which has been used in light emitting diodes (LEDs) since the 1990s. Currently, due to a potential for increased efficiency, GaN is being investigated as a replacement for silicon in power electronics finding potential uses ranging from data centers to electric vehicles. In addition to LEDs and power electronics though, doped GaN can be used as a gamma insensitive fast neutron detector due to the direct band-gap, light propagation properties, and response to ionizing radiations. Investigation of GaN as a semiconductor scintillator for use in a radiation detection system involves mapping the response function of the detector crystal over a range of photon and neutron energies, and measurements of light generation in the GaN crystal due to proton, alpha, and nitrogen projectiles. In this presentation we discuss the measurements made to date, and plausible interpretations of the response functions. This work funded in part by the Naval Surface Warfare Center, Carderock Division In-house Laboratory Independent Research program.

Protons are one of the limiting factors in determining sensitivity of nano surface-assisted (+)-mode LDI MS analyses.

PubMed

Cho, Eunji; Ahn, Miri; Kim, Young Hwan; Kim, Jongwon; Kim, Sunghwan

2013-10-01

A proton source employing a nanostructured gold surface for use in (+)-mode laser desorption ionization mass spectrometry (LDI-MS) was evaluated. Analysis of perdeuterated polyaromatic hydrocarbon compound dissolved in regular toluene, perdeuterated toluene, and deuterated methanol all showed that protonated ions were generated irregardless of solvent system. Therefore, it was concluded that residual water on the surface of the LDI plate was the major source of protons. The fact that residual water remaining after vacuum drying was the source of protons suggests that protons may be the limiting reagent in the LDI process and that overall ionization efficiency can be improved by incorporating an additional proton source. When extra proton sources, such as thiolate compounds and/or citric acid, were added to a nanostructured gold surface, the protonated signal abundance increased. These data show that protons are one of the limiting components in (+)-mode LDI MS analyses employing nanostructured gold surfaces. Therefore, it has been suggested that additional efforts are required to identify compounds that can act as proton donors without generating peaks that interfere with mass spectral interpretation.

Femtosecond response of polyatomic molecules to ultra-intense hard X-rays.

PubMed

Rudenko, A; Inhester, L; Hanasaki, K; Li, X; Robatjazi, S J; Erk, B; Boll, R; Toyota, K; Hao, Y; Vendrell, O; Bomme, C; Savelyev, E; Rudek, B; Foucar, L; Southworth, S H; Lehmann, C S; Kraessig, B; Marchenko, T; Simon, M; Ueda, K; Ferguson, K R; Bucher, M; Gorkhover, T; Carron, S; Alonso-Mori, R; Koglin, J E; Correa, J; Williams, G J; Boutet, S; Young, L; Bostedt, C; Son, S-K; Santra, R; Rolles, D

2017-06-01

X-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions. Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 10 20 watts per square centimetre). However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption, which in a heteronuclear molecular system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge. In serial femtosecond crystallography of biological objects-an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure-the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects and has been suggested as a way of phasing the diffraction data. On the basis of experiments using either soft or less-intense hard X-rays, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 10 20 watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is considerably enhanced compared to that of an individual heavy atom with the same absorption cross-section. This enhancement is driven by ultrafast charge transfer within the molecule, which refills the core holes that are created in the heavy atom, providing further targets for inner-shell ionization and resulting in the emission of more than 50 electrons during the X-ray pulse. Our results demonstrate that efficient modelling of X-ray-driven processes in complex systems at ultrahigh intensities is feasible.

Femtosecond response of polyatomic molecules to ultra-intense hard X-rays

DOE PAGES

Rudenko, A.; Inhester, L.; Hanasaki, K.; ...

2017-05-31

We report x-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions. Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 10 20 watts per square centimetre). However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption, which in a heteronuclear molecularmore » system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge. In serial femtosecond crystallography of biological objects—an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure—the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects and has been suggested as a way of phasing the diffraction data. On the basis of experiments using either soft or less-intense hard X-rays, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 10 20 watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is considerably enhanced compared to that of an individual heavy atom with the same absorption cross-section. This enhancement is driven by ultrafast charge transfer within the molecule, which refills the core holes that are created in the heavy atom, providing further targets for inner-shell ionization and resulting in the emission of more than 50 electrons during the X-ray pulse. Fnally, our results demonstrate that efficient modelling of X-ray-driven processes in complex systems at ultrahigh intensities is feasible.« less

Femtosecond response of polyatomic molecules to ultra-intense hard X-rays

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

Rudenko, A.; Inhester, L.; Hanasaki, K.

We report x-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions. Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 10 20 watts per square centimetre). However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption, which in a heteronuclear molecularmore » system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge. In serial femtosecond crystallography of biological objects—an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure—the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects and has been suggested as a way of phasing the diffraction data. On the basis of experiments using either soft or less-intense hard X-rays, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 10 20 watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is considerably enhanced compared to that of an individual heavy atom with the same absorption cross-section. This enhancement is driven by ultrafast charge transfer within the molecule, which refills the core holes that are created in the heavy atom, providing further targets for inner-shell ionization and resulting in the emission of more than 50 electrons during the X-ray pulse. Fnally, our results demonstrate that efficient modelling of X-ray-driven processes in complex systems at ultrahigh intensities is feasible.« less

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

PubMed

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

2016-03-22

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

Effect of a finite ionization rate on the radiative heating of outer planet atmospheric entry probes

NASA Technical Reports Server (NTRS)

Nelson, H. F.

1981-01-01

The influence of finite rate ionization in the inviscid gas just behind the stagnation shock wave on the radiation heating of probes entering the hydrogen helium atmospere of the major planets was investigated. At the present time, there is disagreement as to whether the radiative flux increases or decreases relative to its equilibrium value when finite rate ionization is considered. Leibowitz and Kuo content that the finite rate ionization in the hydrogen gas just behind the shock wave reduces the radiative flux to the probe, whereas Tiwari and Szema predict that it increases the radiative flux. The radiation modeling used in the calculations of both pairs of these investigators was reviewed. It is concluded that finite rate ionization in the inviscid region of the shock layer should reduce the cold wall radiative heating below the values predicted by equilibrium chemistry assumptions.

Ionizing radiation exposures in treatments of solid neoplasms are not associated with subsequent increased risks of chronic lymphocytic leukemia.

PubMed

Radivoyevitch, Tomas; Sachs, Rainer K; Gale, Robert Peter; Smith, Mitchell R; Hill, Brian T

2016-04-01

Exposure to ionizing radiation is not thought to cause chronic lymphocytic leukemia (CLL). Challenging this notion are recent data suggesting CLL incidence may be increased by radiation exposure from the atomic bombs (after many decades), uranium mining and nuclear power facility accidents. To assess the effects of therapeutic ionizing radiation for the treatment of solid neoplasms we studied CLL risks in data from the Surveillance, Epidemiology, and End Results (SEER) Program. Specifically, we compared the risks of developing CLL in persons with a 1(st) non-hematologic cancer treated with or without ionizing radiation. We controlled for early detection effects on CLL risk induced by surveillance after 1(st) cancer diagnoses by forming all-time cumulative CLL relative risks (RR). We estimate such CLL RR to be 1.20 (95% confidence interval, 1.17, 1.23) for persons whose 1(st) cancer was not treated with ionizing radiation and 1.00 (0.96, 1.05) for persons whose 1(st) cancer was treated with ionizing radiations. These results imply that diagnosis of a solid neoplasm is associated with an increased risk of developing CLL only in persons whose 1(st) cancer was not treated with radiation therapy. Copyright © 2016 Elsevier Ltd. All rights reserved.

Possible modification of the cooling index of interstellar helium pickup ions by electron impact ionization in the inner heliosphere

NASA Astrophysics Data System (ADS)

Chen, Jun Hong; Bochsler, Peter; Möbius, Eberhard; Gloeckler, George

2014-09-01

Interstellar neutrals penetrating into the inner heliosphere are ionized by photoionization, charge exchange with solar wind ions, and electron impact ionization. These processes comprise the first step in the evolution of interstellar pickup ion (PUI) distributions. Typically, PUI distributions have been described in terms of velocity distribution functions that cool adiabatically under solar wind expansion, with a cooling index of 3/2. Recently, the cooling index has been determined experimentally in observations of He PUI distributions with Advanced Composition Explorer (ACE)/Solar Wind Ion Composition Spectrometer and found to vary substantially over the solar cycle. The experimental determination of the cooling index depends on the knowledge of the ionization rates and their spatial variation. Usually, ionization rates increase with 1/r2 as neutral particles approach the Sun, which is not exactly true for electron impact ionization, because the electron temperature increases with decreasing distance from the Sun due to the complexity of its distributions and different radial gradients in temperature. This different dependence on distance may become important in the study of the evolution of PUI distributions and is suspected as one of the potential reasons for the observed variation of the cooling index. Therefore, we investigate in this paper the impact of electron ionization on the variability of the cooling index. We find that the deviation of the electron ionization rate from the canonical 1/r2 behavior of other ionization processes plays only a minor role.

Apollo-Soyuz light-flash observations. [ionizing radiation effects measurement

NASA Technical Reports Server (NTRS)

Budinger, T. F.; Tobias, C. A.; Huesman, R. H.; Upham, F. T.; Wieskamp, T. F.; Hoffman, R. A.

1977-01-01

While dark adapted, two Apollo-Soyuz astronauts saw eighty-two light flash events during a complete 51 deg orbit which passed near the north magnetic pole and through the South Atlantic Anomaly. The frequency of events at the polar parts of the orbit is 25 times that noted in equatorial latitudes and no increased frequency was noted in the South Atlantic Anomaly at the 225-km altitude. The expected flux of heavy particles at the northern and southern points is 1-2/min per eye, and the efficiency for seeing high Z-high energy (HZE) particles which were below the Cerenkov threshold is 50%.

ULTRAVIOLET PHOTON-INDUCED SYNTHESIS AND TRAPPING OF H{sub 2}O{sub 2} AND O{sub 3} IN POROUS WATER ICE FILMS IN THE PRESENCE OF AMBIENT O{sub 2}: IMPLICATIONS FOR EXTRATERRESTRIAL ICE

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

Shi, J.; Raut, U.; Kim, J.-H.

2011-09-01

The mass uptake of ambient oxygen in nanoporous ice is enhanced by irradiation with 193 nm photons, due to conversion of O{sub 2} into H{sub 2}O{sub 2} and O{sub 3}, with an efficiency that increases with decreasing temperature. These findings show a new way to form H{sub 2}O{sub 2} and O{sub 3} on icy surfaces in the outer solar system at depths much larger than are accessible by typical ionizing radiation, with possible astrobiological implications.

Efficient Energy Conversion by Grafting Nanochannels with End-charged Stimuli-responsive Polyelectrolyte Brush

NASA Astrophysics Data System (ADS)

Chen, Guang; Das, Siddhartha

2017-11-01

Polyelectrolyte (PE) brushes have aroused increasing attention in applications in energy conversion and chemical sensing due to the environmentally-responsive and designable nature. PE brushes are charged polymer chains densely grafted on solid-liquid interfaces. By designing copolymeric systems, one can localize the ionizable sites at the brush tip in order to get end-charged PE brushes. Such brushes demonstrate anomalous shrinking/swelling behaviors with tunable environmental parameters such as pH and salt concentration. In this study, we probe the conformation and electrostatics of such PE brush systems with various size, grafting density and charge distribution, and exploit the electrochemomechanical energy conversion capabilities of nanochannels grafted with such PE brush systems. Our results indicate that the presence of the end-charged PE brush layer can massively enhance the streaming potential mediated energy conversion efficiency, and the improvement is more significant in strongly ionic solution.

Copper cladding on polymer surfaces by ionization-assisted deposition

NASA Astrophysics Data System (ADS)

Kohno, Tomoki; Tanaka, Kuniaki; Usui, Hiroaki

2018-03-01

Copper thin films were prepared on poly(ethylene terephthalate) (PET) and polyimide (PI) substrates by an ionization-assisted vapor deposition method. The films had a polycrystalline structure, and their crystallite size decreased with increasing ion acceleration voltage V a. Ion acceleration was effective in reducing the surface roughness of the films. Cross-sectional transmission electron microscopy revealed that the copper/polymer interface showed increased corrugation with increasing V a. The increase in V a also induced the chemical modification of polymer chains of the PET substrate, but the PI substrate underwent smaller modification after ion bombardment. Most importantly, the adhesion strength between the copper film and the PET substrate increased with increasing V a. It was concluded that ionization-assisted deposition is a promising technique for preparing metal clad layers on flexible polymer substrates.

(E)-Propyl α-Cyano-4-Hydroxyl Cinnamylate: A High Sensitive and Salt Tolerant Matrix for Intact Protein Profiling by MALDI Mass Spectrometry

NASA Astrophysics Data System (ADS)

Wang, Sheng; Xiao, Zhaohui; Xiao, Chunsheng; Wang, Huixin; Wang, Bing; Li, Ying; Chen, Xuesi; Guo, Xinhua

2016-04-01

Low-abundance samples and salt interference are always of great challenges for the practical protein profiling by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Herein, a series of carboxyl-esterified derivatives of α-cyano-4-hydroxycinnamic acid (CHCA) were synthesized and evaluated as matrices for MALDI-MS analysis of protein. Among them, (E)-propyl α-cyano-4-hydroxyl cinnamylate (CHCA-C3) was found to exhibit excellent assay performance for intact proteins by improving the detection sensitivity 10 folds compared with the traditional matrices [i.e., super2,5-dihydroxybenzoic acid (superDHB), sinapic acid (SA), and CHCA]. In addition, CHCA-C3 was shown to have high tolerance to salts, the ion signal of myoglobin was readily detected even in the presence of urea (8 M), NH4HCO3 (2 M), and KH2PO4 (500 mM), meanwhile sample washability was robust. These achievements were mainly attributed to improved ablation ability and increased hydrophobicity or affinity of CHCA-C3 to proteins in comparison with hydrophilic matrixes, leading to more efficient ionization of analyte. Furthermore, direct analysis of proteins from crude egg white demonstrated that CHCA-C3 was a highly efficient matrix for the analysis of low-abundance proteins in complex biological samples. These outstanding performances indicate the tremendous potential use of CHCA-C3 in protein profiling by MALDI-MS.

Removal of nonylphenol from industrial sludge by using an electron beam

NASA Astrophysics Data System (ADS)

Choi, Jang-Seung; Park, Jun-Hyun; Kim, Yuri; Kim, JinKyu; Jung, SeungTae; Han, Bumsoo; Alkhuraiji, Turki S.

2016-09-01

Endocrine disrupting chemicals (EDCs) and potential EDCs are mostly man-made, found in various materials such as pesticides, additives or contaminants in food, and personal care products. EDCs have been suspected to be associated with altered reproductive function in males and females increased incidence of breast cancer, abnormal growth patterns and neuro-developmental delays in children and changes in immune function. A number of processes were investigated regarding their potential for removing of endocrine disrupters. Those processes are ferric chloride coagulation, powdered activated carbon, magnetic ion exchange combined with microfiltration or ultrafiltration, as well as nanofiltration, and reverse osmosis. They show some good removal of EDCs in aqueous solution, but do not show good efficiency when EDCs are in sludge. High energy ionizing radiation has the ability to remove the EDCs with a very high degree of reliability and in a clean and efficient manner. The ionizing radiation interacts with EDCs both directly and indirectly. Direct interaction takes place with EDCs, and the structure of EDCs is destroyed or changed. During indirect interaction, radiolysis products of water result in the formation of highly reactive intermediates which then react with the target molecules, culminating in structural changes. For confirmation of radiation reduction of EDCs in industrial sludge, a pilot scale experiment up to 50 kGy of electron beam was conducted with samples from the textile dyeing industries. The experimental result showed over a 90% reduction of nonylphenol (NP) at absorbed doses of around 10 kGy.

Direct characterization of commercial lecithins by easy ambient sonic-spray ionization mass spectrometry.

PubMed

Fernandes, Gabriel D; Alberici, Rosana M; Pereira, Gustavo G; Cabral, Elaine C; Eberlin, Marcos N; Barrera-Arellano, Daniel

2012-12-01

Commercial lecithins are composed mainly of phospholipids and triacylglycerols. The analysis of the commercial lecithins, including their fraction of phospholipids, normally involves laborious and expensive protocols. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) is shown to be an efficient technique for the analysis of lipids. Samples of commercial lecithins including standards, refined, deoiled and modified soy lecithin were tested. Characteristic profiles of phosphatidylcholines and triacylglycerols are detected by EASI(+)-MS, whereas EASI(-)-MS provided phosphatidylethanolamines, glycophospholipids and free fatty acids profiles. Acetylated lecithins also displayed characteristic acetylated derivatives. EASI-MS data was also compared to MALDI-MS, and found to display richer compositional information. The industrial process applied to lecithin fabrication was also characterised via typical EASI-MS profiles. EASI-MS both in its positive and negative ion modes offers a direct, fast and efficient technique able to characterise commercial lecithin. Copyright © 2012 Elsevier Ltd. All rights reserved.

Determination of hexabromocyclododecane by flowing atmospheric pressure afterglow mass spectrometry.

PubMed

Smoluch, Marek; Silberring, Jerzy; Reszke, Edward; Kuc, Joanna; Grochowalski, Adam

2014-10-01

The first application of a flowing atmospheric-pressure afterglow ion source for mass spectrometry (FAPA-MS) for the chemical characterization and determination of hexabromocyclododecane (HBCD) is presented. The samples of technical HBCD and expanded polystyrene foam (EPS) containing HBCD as a flame retardant were prepared by dissolving the appropriate solids in dichloromethane. The ionization of HBCD was achieved with a prototype FAPA source. The ions were detected in the negative-ion mode. The ions corresponding to a deprotonated HBCD species (m/z 640.7) as well as chlorine (m/z 676.8), nitrite (m/z 687.8) and nitric (m/z 703.8) adducts were observed in the spectra. The observed isotope pattern is characteristic for a compound containing six bromine atoms. This technique is an effective approach to detect HBCD, which is efficiently ionized in a liquid phase, resulting in high detection efficiency and sensitivity. Copyright © 2014 Elsevier B.V. All rights reserved.

Dependence of optimal initial density on laser parameters for multi-keV x-ray radiators generated by nanosecond laser-produced underdense plasma

NASA Astrophysics Data System (ADS)

Tu, Shao-yong; Yuan, Yong-teng; Hu, Guang-yue; Miao, Wen-yong; Zhao, Bin; Zheng, Jian; Jiang, Shao-en; Ding, Yong-kun

2016-01-01

Efficient multi-keV x-ray sources can be produced using nanosecond laser pulse-heated middle-Z underdense plasmas generated using gas or foam. Previous experimental results show that an optimal initial target density exists for efficient multi-keV x-ray emission at which the laser ionization wave is supersonic. Here we explore the influence of the laser intensity and the pulse duration on this optimal initial target density via a one-dimensional radiation hydrodynamic simulation. The simulation shows that the optimal initial density is sensitive to both the laser intensity and the pulse duration. However, the speed of the supersonic ionization wave at the end of the laser irradiation is always maintained at 1.5 to 1.7 times that of the ion acoustic wave under the optimal initial density conditions.

Efficient Enrichment and Analysis of Vicinal-Diol-Containing Flavonoid Molecules Using Boronic-Acid-Functionalized Particles and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry.

PubMed

Kim, Eunjin; Kang, Hyunook; Choi, Insung; Song, Jihyeon; Mok, Hyejung; Jung, Woong; Yeo, Woon-Seok

2018-05-09

Detection and quantitation of flavonoids are relatively difficult compared to those of other small-molecule analytes because flavonoids undergo rapid metabolic processes, resulting in their elimination from the body. Here, we report an efficient enrichment method for facilitating the analysis of vicinal-diol-containing flavonoid molecules using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In our strategy, boronic-acid-functionalized polyacrylamide particles were used, where boronic acids bound to vicinal diols to form boronate monoesters at basic pH. This complex remained intact during the enrichment processes, and the vicinal-diol-containing flavonoids were easily separated by centrifugation and subsequent acidic treatments. The selectivity and limit of detection of our strategy were confirmed by mass spectrometry analysis, and the validity was assessed by performing the detection and quantitation of quercetin in mouse organs.

On plate graphite supported sample processing for simultaneous lipid and protein identification by matrix assisted laser desorption ionization mass spectrometry.

PubMed

Calvano, Cosima Damiana; van der Werf, Inez Dorothé; Sabbatini, Luigia; Palmisano, Francesco

2015-05-01

The simultaneous identification of lipids and proteins by matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) after direct on-plate processing of micro-samples supported on colloidal graphite is demonstrated. Taking advantages of large surface area and thermal conductivity, graphite provided an ideal substrate for on-plate proteolysis and lipid extraction. Indeed proteins could be efficiently digested on-plate within 15 min, providing sequence coverages comparable to those obtained by conventional in-solution overnight digestion. Interestingly, detection of hydrophilic phosphorylated peptides could be easily achieved without any further enrichment step. Furthermore, lipids could be simultaneously extracted/identified without any additional treatment/processing step as demonstrated for model complex samples such as milk and egg. The present approach is simple, efficient, of large applicability and offers great promise for protein and lipid identification in very small samples. Copyright © 2015 Elsevier B.V. All rights reserved.

Thermophysics Characterization of Multiply Ionized Air Plasma Absorption of Laser Radiation

NASA Technical Reports Server (NTRS)

Wang, Ten-See; Rhodes, Robert; Turner, Jim (Technical Monitor)

2002-01-01

The impact of multiple ionization of air plasma on the inverse Bremsstrahlung absorption of laser radiation is investigated for air breathing laser propulsion. Thermochemical properties of multiply ionized air plasma species are computed for temperatures up to 200,000 deg K, using hydrogenic approximation of the electronic partition function; And those for neutral air molecules are also updated for temperatures up to 50,000 deg K, using available literature data. Three formulas for absorption are calculated and a general formula is recommended for multiple ionization absorption calculation. The plasma composition required for absorption calculation is obtained by increasing the degree of ionization sequentially, up to quadruple ionization, with a series of thermal equilibrium computations. The calculated second ionization absorption coefficient agrees reasonably well with that of available data. The importance of multiple ionization modeling is demonstrated with the finding that area under the quadruple ionization curve of absorption is found to be twice that of single ionization. The effort of this work is beneficial to the computational plasma aerodynamics modeling of laser lightcraft performance.

Modeling VLF signal modulation during solar flares with GEANT4 Monte Carlo simulation, a simple chemical model and LWPC

NASA Astrophysics Data System (ADS)

Palit, Sourav; Chakrabarti, Sandip Kumar; Pal, Sujay; Basak, Tamal

Extra ionization by X-rays during solar flares affects VLF signal propagation through D-region ionosphere. Ionization produced in the lower ionosphere due to X-ray spectra of solar flares are simulated with an efficient detector simulation program, GEANT4. The balancing between the ionization and loss processes, causing the lower ionosphere to settle back to its undisturbed state is handled with a simple chemical model consisting of four broad species of ion densities. Using the electron densities, modified VLF signal amplitude is then computed with LWPC code. VLF signal along NWC (Australia) to IERC/ICSP (India) propagation path is examined during a M and a X-type solar flares and observational deviations are compared with simulated results. The agreement is found to be excellent.

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

Driving Turbulence and Triggering Star Formation by Ionizing Radiation

NASA Astrophysics Data System (ADS)

Gritschneder, Matthias; Naab, Thorsten; Walch, Stefanie; Burkert, Andreas; Heitsch, Fabian

2009-03-01

We present high-resolution simulations on the impact of ionizing radiation of massive O stars on the surrounding turbulent interstellar medium (ISM). The simulations are performed with the newly developed software iVINE which combines ionization with smoothed particle hydrodynamics (SPH) and gravitational forces. We show that radiation from hot stars penetrates the ISM, efficiently heats cold low-density gas and amplifies overdensities seeded by the initial turbulence. The formation of observed pillar-like structures in star-forming regions (e.g. in M16) can be explained by this scenario. At the tip of the pillars gravitational collapse can be induced, eventually leading to the formation of low-mass stars. Detailed analysis of the evolution of the turbulence spectra shows that UV radiation of O stars indeed provides an excellent mechanism to sustain and even drive turbulence in the parental molecular cloud.

Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi

PubMed Central

Dadachova, Ekaterina; Bryan, Ruth A.; Huang, Xianchun; Moadel, Tiffany; Schweitzer, Andrew D.; Aisen, Philip; Nosanchuk, Joshua D.; Casadevall, Arturo

2007-01-01

Background Melanin pigments are ubiquitous in nature. Melanized microorganisms are often the dominating species in certain extreme environments, such as soils contaminated with radionuclides, suggesting that the presence of melanin is beneficial in their life cycle. We hypothesized that ionizing radiation could change the electronic properties of melanin and might enhance the growth of melanized microorganisms. Methodology/Principal Findings Ionizing irradiation changed the electron spin resonance (ESR) signal of melanin, consistent with changes in electronic structure. Irradiated melanin manifested a 4-fold increase in its capacity to reduce NADH relative to non-irradiated melanin. HPLC analysis of melanin from fungi grown on different substrates revealed chemical complexity, dependence of melanin composition on the growth substrate and possible influence of melanin composition on its interaction with ionizing radiation. XTT/MTT assays showed increased metabolic activity of melanized C. neoformans cells relative to non-melanized cells, and exposure to ionizing radiation enhanced the electron-transfer properties of melanin in melanized cells. Melanized Wangiella dermatitidis and Cryptococcus neoformans cells exposed to ionizing radiation approximately 500 times higher than background grew significantly faster as indicated by higher CFUs, more dry weight biomass and 3-fold greater incorporation of 14C-acetate than non-irradiated melanized cells or irradiated albino mutants. In addition, radiation enhanced the growth of melanized Cladosporium sphaerospermum cells under limited nutrients conditions. Conclusions/Significance Exposure of melanin to ionizing radiation, and possibly other forms of electromagnetic radiation, changes its electronic properties. Melanized fungal cells manifested increased growth relative to non-melanized cells after exposure to ionizing radiation, raising intriguing questions about a potential role for melanin in energy capture and utilization. PMID:17520016

SPECTROSOCPIC STUDIES OF IONIZATION IN A HOLLOW-CATHODE DISCHARGE

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

Mitchell, K.B.

1961-08-01

The influence of carrier gas, carrier gas pressure, cathode geometry, and discharge current on the ionization of metal atoms in a hollow-cathode discharge was studied in some detail. Most of these studies were raade with an iron hollowcathode discharge. A measure of ionization was obtained from the intensity ratio of a line of the second to a line of the first spectrum. In general, this ratio was found to increase with carrier gas pressure and discharge current. This ratio also increased with increasing cathode bcre diameter but decreased with increasing bcre length. This ratio for iron was greatly affected bymore » the use of different inert carrier gases. Of the five common inert gases used, xenon produced the largest value for this ratio and argon produced the smallest. The results of these studies indicated this may be a new method for distinguishing between lines emitted by the neutral atom and lines of the singly ionized atom. (auth)« less

The shape and size distribution of H II regions near the percolation transition

NASA Astrophysics Data System (ADS)

Bag, Satadru; Mondal, Rajesh; Sarkar, Prakash; Bharadwaj, Somnath; Sahni, Varun

2018-06-01

Using Shapefinders, which are ratios of Minkowski functionals, we study the morphology of neutral hydrogen (H I) density fields, simulated using seminumerical technique (inside-out), at various stages of reionization. Accompanying the Shapefinders, we also employ the `largest cluster statistic' (LCS), originally proposed in Klypin & Shandarin, to study the percolation in both neutral and ionized hydrogen. We find that the largest ionized region is percolating below the neutral fraction x_{H I}≲ 0.728 (or equivalently z ≲ 9). The study of Shapefinders reveals that the largest ionized region starts to become highly filamentary with non-trivial topology near the percolation transition. During the percolation transition, the first two Shapefinders - `thickness' (T) and `breadth' (B) - of the largest ionized region do not vary much, while the third Shapefinder - `length' (L) - abruptly increases. Consequently, the largest ionized region tends to be highly filamentary and topologically quite complex. The product of the first two Shapefinders, T × B, provides a measure of the `cross-section' of a filament-like ionized region. We find that, near percolation, the value of T × B for the largest ionized region remains stable at ˜7 Mpc2 (in comoving scale) while its length increases with time. Interestingly, all large ionized regions have similar cross-sections. However, their length shows a power-law dependence on their volume, L ∝ V0.72, at the onset of percolation.

Comments on potential health effects of MRI-induced DNA lesions: quality is more important to consider than quantity

PubMed Central

Hill, M.A.; O'Neill, P.; McKenna, W.G.

2016-01-01

Magnetic resonance imaging (MRI) is increasingly being used in cardiology to detect heart disease and guide therapy. It is mooted to be a safer alternative to imaging techniques, such as computed tomography (CT) or coronary angiographic imaging. However, there has recently been an increased interest in the potential long-term health risks of MRI, especially in the light of the controversy resulting from a small number of research studies reporting an increase in DNA damage following exposure, with calls to limit its use and avoid unnecessary examination, according to the precautionary principle. Overall the published data are somewhat limited and inconsistent; the ability of MRI to produce DNA lesions has yet to be robustly demonstrated and future experiments should be carefully designed to optimize sensitivity and benchmarked to validate and assess reproducibility. The majority of the current studies have focussed on the initial induction of DNA damage, and this has led to comparisons between the reported induction of γH2AX and implied double-strand break (DSB) yields produced following MRI with induction by imaging techniques using ionizing radiation. However, γH2AX is not only a marker of classical double-ended DSB, but also a marker of stalled replication forks and in certain circumstances stalled DNA transcription. Additionally, ionizing radiation is efficient at producing complex DNA damage, unique to ionizing radiation, with an associated reduction in repairability. Even if the fields associated with MRI are capable of producing DNA damage, the lesions produced will in general be simple, similar to those produced by endogenous processes. It is therefore inappropriate to try and infer cancer risk by simply comparing the yields of γH2AX foci or DNA lesions potentially produced by MRI to those produced by a given exposure of ionizing radiation, which will generally be more biologically effective and have a greater probability of leading to long-term health effects. As a result, it is important to concentrate on more relevant downstream end points (e.g. chromosome aberration production), along with potential mechanisms by which MRI may lead to DNA lesions. This could potentially involve a perturbation in homeostasis of oxidative stress, modifying the background rate of endogenous DNA damage induction. In summary, what the field needs at the moment is more research and less fear mongering. PMID:27550664

The ionizing effect of low-energy cosmic rays from a class II object on its protoplanetary disc

NASA Astrophysics Data System (ADS)

Rodgers-Lee, D.; Taylor, A. M.; Ray, T. P.; Downes, T. P.

2017-11-01

We investigate the ionizing effect of low-energy cosmic rays (CRs) from a young star on its protoplanetary disc (PPD). We consider specifically the effect of ∼3 GeV protons injected at the inner edge of the PPD. An increase in the ionization fraction as a result of these CRs could allow the magnetorotational instability to operate in otherwise magnetically dead regions of the disc. For the typical values assumed we find an ionization rate of ζCR ∼ 10-17 s-1 at 1 au. The transport equation is solved by treating the propagation of the CRs as diffusive. We find for increasing diffusion coefficients the CRs penetrate further in the PPD, while varying the mass density profile of the disc is found to have little effect. We investigate the effect of an energy spectrum of CRs. The influence of a disc wind is examined by including an advective term. For advective wind speeds between 1 and 100 km s-1 diffusion dominates at all radii considered here (out to 10 au) for reasonable diffusion coefficients. Overall, we find that low-energy CRs can significantly ionize the mid-plane of PPDs out to ∼1 au. By increasing the luminosity or energy of the CRs, within plausible limits, their radial influence could increase to ∼2 au at the mid-plane but it remains challenging to significantly ionize the mid-plane further out.

The MOSDEF Survey: Direct Observational Constraints on the Ionizing Photon Production Efficiency, ξ ion, at z ∼ 2

NASA Astrophysics Data System (ADS)

Shivaei, Irene; Reddy, Naveen A.; Siana, Brian; Shapley, Alice E.; Kriek, Mariska; Mobasher, Bahram; Freeman, William R.; Sanders, Ryan L.; Coil, Alison L.; Price, Sedona H.; Fetherolf, Tara; Azadi, Mojegan; Leung, Gene; Zick, Tom

2018-03-01

We combine Hα and Hβ spectroscopic measurements and UV photometry for a sample of 673 galaxies from the MOSDEF survey to constrain hydrogen-ionizing photon production efficiencies ({ξ }ion}) at z = 1.4–2.6. We find < {log}({ξ }ion}/[{{{s}}}-1/{erg} {{{s}}}-1 {Hz}}-1])> = 25.06 (25.34), assuming the Calzetti (SMC) curve for the UV dust correction and a scatter of 0.28 dex in the {ξ }ion} distribution. After accounting for observational uncertainties and variations in dust attenuation, we conclude that the remaining scatter in {ξ }ion} is likely dominated by galaxy-to-galaxy variations in stellar populations, including the slope and upper-mass cutoff of the initial mass function, stellar metallicity, star formation burstiness, and stellar evolution (e.g., single/binary star evolution). Moreover, {ξ }ion} is elevated in galaxies with high ionization states (high [O III]/[O II]) and low oxygen abundances (low [N II]/Hα and high [O III]/Hβ) in the ionized ISM. However, {ξ }ion} does not correlate with the offset from the z ∼ 0 star-forming locus in the BPT diagram, suggesting no change in the hardness of the ionizing radiation accompanying the offset from the z ∼ 0 sequence. We also find that galaxies with blue UV spectral slopes (< β > =-2.1) have {ξ }ion} elevated by a factor of ∼2 relative to the average {ξ }ion} of the sample (< β > =-1.4). If these blue galaxies are similar to those at z > 6, our results suggest that a lower Lyman-continuum escape fraction is required for galaxies to maintain reionization, compared to the canonical {ξ }ion} predictions from stellar population models. Furthermore, we demonstrate that even with robustly dust-corrected Hα, the UV dust attenuation can cause on average a ∼0.3 dex systematic uncertainty in {ξ }ion} calculations.

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

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

Nilsen, Joseph

2015-12-16

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

Renormalization shielding effect on the Wannier-ridge mode for double-electron continua in partially ionized dense hydrogen plasmas

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

Lee, Myoung-Jae; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr; Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590

2016-01-15

The influence of renormalization shielding on the Wannier threshold law for the double-electron escapes by the electron-impact ionization is investigated in partially ionized dense plasmas. The renormalized electron charge and Wannier exponent are obtained by considering the equation of motion in the Wannier-ridge including the renormalization shielding effect. It is found that the renormalization shielding effect reduces the magnitude of effective electron charge, especially, within the Bohr radius in partially ionized dense plasmas. The maximum position of the renormalized electron charge approaches to the center of the target atom with an increase of the renormalization parameter. In addition, the Wanniermore » exponent increases with an increase of the renormalization parameter. The variations of the renormalized electron charge and Wannier exponent due to the renormalization shielding effect are also discussed.« less

Nuclear-Recoil Energy Scale in CDMS II Silicon Dark-Matter Detectors

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

Agnese, R.; et al.

The Cryogenic Dark Matter Search (CDMS II) experiment aims to detect dark matter particles that elastically scatter from nuclei in semiconductor detectors. The resulting nuclear-recoil energy depositions are detected by ionization and phonon sensors. Neutrons produce a similar spectrum of low-energy nuclear recoils in such detectors, while most other backgrounds produce electron recoils. The absolute energy scale for nuclear recoils is necessary to interpret results correctly. The energy scale can be determined in CDMS II silicon detectors using neutrons incident from a broad-spectrummore » $$^{252}$$Cf source, taking advantage of a prominent resonance in the neutron elastic scattering cross section of silicon at a recoil (neutron) energy near 20 (182) keV. Results indicate that the phonon collection efficiency for nuclear recoils is $$4.8^{+0.7}_{-0.9}$$% lower than for electron recoils of the same energy. Comparisons of the ionization signals for nuclear recoils to those measured previously by other groups at higher electric fields indicate that the ionization collection efficiency for CDMS II silicon detectors operated at $$\\sim$$4 V/cm is consistent with 100% for nuclear recoils below 20 keV and gradually decreases for larger energies to $$\\sim$$75% at 100 keV. The impact of these measurements on previously published CDMS II silicon results is small.« less

Top-down approach for the direct characterization of low molecular weight heparins using LC-FT-MS.

PubMed

Li, Lingyun; Zhang, Fuming; Zaia, Joseph; Linhardt, Robert J

2012-10-16

Low molecular heparins (LMWHs) are structurally complex, heterogeneous, polydisperse, and highly negatively charged mixtures of polysaccharides. The direct characterization of LMWH is a major challenge for currently available analytical technologies. Electrospray ionization (ESI) liquid chromatography-mass spectrometry (LC-MS) is a powerful tool for the characterization complex biological samples in the fields of proteomics, metabolomics, and glycomics. LC-MS has been applied to the analysis of heparin oligosaccharides, separated by size exclusion, reversed phase ion-pairing chromatography, and chip-based amide hydrophilic interaction chromatography (HILIC). However, there have been limited applications of ESI-LC-MS for the direct characterization of intact LMWHs (top-down analysis) due to their structural complexity, low ionization efficiency, and sulfate loss. Here we present a simple and reliable HILIC-Fourier transform (FT)-ESI-MS platform to characterize and compare two currently marketed LMWH products using the top-down approach requiring no special sample preparation steps. This HILIC system relies on cross-linked diol rather than amide chemistry, affording highly resolved chromatographic separations using a relatively high percentage of acetonitrile in the mobile phase, resulting in stable and high efficiency ionization. Bioinformatics software (GlycReSoft 1.0) was used to automatically assign structures within 5-ppm mass accuracy.

Constraining the sensitivity of iodide adduct chemical ionization mass spectrometry to multifunctional organic molecules using the collision limit and thermodynamic stability of iodide ion adducts

DOE PAGES

Lopez-Hilfiker, Felipe D.; Iyer, Siddarth; Mohr, Claudia; ...

2016-04-06

The sensitivity of a chemical ionization mass spectrometer (ions formed per number density of analytes) is fundamentally limited by the collision frequency between reagent ions and analytes, known as the collision limit, the ion–molecule reaction time, and the transmission efficiency of product ions to the detector. We use the response of a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) to N 2O 5, known to react with iodide at the collision limit, to constrain the combined effects of ion–molecule reaction time, which is strongly influenced by mixing and ion losses in the ion–molecule reaction drift tube. A mass spectrometric voltage scanningmore » procedure elucidates the relative binding energies of the ion adducts, which influence the transmission efficiency of molecular ions through the electric fields within the vacuum chamber. Together, this information provides a critical constraint on the sensitivity of a ToF-CIMS towards a wide suite of routinely detected multifunctional organic molecules for which no calibration standards exist. Lastly, we describe the scanning procedure and collision limit determination, and we show results from the application of these constraints to the measurement of organic aerosol composition at two different field locations.« less

Investigation of Recombination Processes In A Magnetized Plasma

NASA Technical Reports Server (NTRS)

Chavers, Greg; Chang-Diaz, Franklin; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

Interplanetary travel requires propulsion systems that can provide high specific impulse (Isp), while also having sufficient thrust to rapidly accelerate large payloads. One such propulsion system is the Variable Specific Impulse Magneto-plasma Rocket (VASIMR), which creates, heats, and exhausts plasma to provide variable thrust and Isp, optimally meeting the mission requirements. A large fraction of the energy to create the plasma is frozen in the exhaust in the form of ionization energy. This loss mechanism is common to all electromagnetic plasma thrusters and has an impact on their efficiency. When the device operates at high Isp, where the exhaust kinetic energy is high compared to the ionization energy, the frozen flow component is of little consequence; however, at low Isp, the effect of the frozen flow may be important. If some of this energy could be recovered through recombination processes, and re-injected as neutral kinetic energy, the efficiency of VASIMR, in its low Isp/high thrust mode may be improved. In this operating regime, the ionization energy is a large portion of the total plasma energy. An experiment is being conducted to investigate the possibility of recovering some of the energy used to create the plasma. This presentation will cover the progress and status of the experiment involving surface recombination of the plasma.

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

NASA Astrophysics Data System (ADS)

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

2016-10-01

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

Dynamics of the CRRES barium releases in the magnetosphere

NASA Technical Reports Server (NTRS)

Fuselier, S. A.; Mende, S. B.; Geller, S. P.; Miller, M.; Hoffman, R. A.; Wygant, J. R.; Pongratz, M.; Meredith, N. P.; Anderson, R. R.

1994-01-01

The Combined Release and Radiation Effects Satellite (CRRES) G-2, G-3, and G-4 ionized and neutral barium cloud positions are triangulated from ground-based optical data. From the time history of the ionized cloud motion perpendicular to the magnetic field, the late time coupling of the ionized cloud with the collisionless ambient plasma in the magnetosphere is investigated for each of the releases. The coupling of the ionized clouds with the ambient medium is quantitatively consistent with predictions from theory in that the coupling time increases with increasing distance from the Earth. Quantitative comparison with simple theory for the couping time also yields reasonable agreement. Other effects not predicted by the theory are discussed in the context of the observations.

Plasma density enhancement in atmospheric-pressure dielectric-barrier discharges by high-voltage nanosecond pulse in the pulse-on period: a PIC simulation

NASA Astrophysics Data System (ADS)

Sang, Chaofeng; Sun, Jizhong; Wang, Dezhen

2010-02-01

A particle-in-cell (PIC) plus Monte Carlo collision simulation is employed to investigate how a sustainable atmospheric pressure single dielectric-barrier discharge responds to a high-voltage nanosecond pulse (HVNP) further applied to the metal electrode. The results show that the HVNP can significantly increase the plasma density in the pulse-on period. The ion-induced secondary electrons can give rise to avalanche ionization in the positive sheath, which widens the discharge region and enhances the plasma density drastically. However, the plasma density stops increasing as the applied pulse lasts over certain time; therefore, lengthening the pulse duration alone cannot improve the discharge efficiency further. Physical reasons for these phenomena are then discussed.

Experimental investigation of the ionization mechanisms of uranium in thermal ionization mass spectrometry in the presence of carbon

NASA Astrophysics Data System (ADS)

Kraiem, M.; Mayer, K.; Gouder, T.; Seibert, A.; Wiss, T.; Thiele, H.; Hiernaut, J.-P.

2010-01-01

Thermal ionization mass spectrometry (TIMS) is a well established instrumental technique for providing accurate and precise isotope ratio measurements of elements with reasonably low first ionization potential. In nuclear safeguards and in environmental research, it is often required to measure the isotope ratios in small samples of uranium. Empirical studies had shown that the ionization yield of uranium and plutonium in a TIMS ion source can be significantly increased in the presence of a carbon source. But, even though carbon appeared crucial in providing high ionization yields, processes taking place on the ionization surface were still not well understood. This paper describes the experimental results obtained from an extended study on the evaporation and ionization mechanisms of uranium occurring on a rhenium mass spectrometry filament in the presence of carbon. Solid state reactions were investigated using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Additionally, vaporization measurements were performed with a modified-Knudsen cell mass spectrometer for providing information on the neutral uranium species in the vapor phase. Upon heating, under vacuum, the uranyl nitrate sample was found to turn into a uranium carbide compound, independent of the type of carbon used as ionization enhancer. With further heating, uranium carbide leads to formation of single charged uranium metal ions and a small amount of uranium carbide ions. The results are relevant for a thorough understanding of the ion source chemistry of a uranyl nitrate sample under reducing conditions. The significant increase in ionization yield described by many authors on the basis of empirical results can be now fully explained and understood.

Hybrid quadrupole mass filter/quadrupole ion trap/time-of-flight-mass spectrometer for infrared multiple photon dissociation spectroscopy of mass-selected ions

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

Gulyuz, Kerim; Stedwell, Corey N.; Wang Da

2011-05-15

We present a laboratory-constructed mass spectrometer optimized for recording infrared multiple photon dissociation (IRMPD) spectra of mass-selected ions using a benchtop tunable infrared optical parametric oscillator/amplifier (OPO/A). The instrument is equipped with two ionization sources, an electrospray ionization source, as well as an electron ionization source for troubleshooting. This hybrid mass spectrometer is composed of a quadrupole mass filter for mass selection, a reduced pressure ({approx}10{sup -5} Torr) quadrupole ion trap (QIT) for OPO irradiation, and a reflectron time-of-flight drift tube for detecting the remaining precursor and photofragment ions. A helium gas pulse is introduced into the QIT to temporarilymore » increase the pressure and hence enhance the trapping efficiency of axially injected ions. After a brief pump-down delay, the compact ion cloud is subjected to the focused output from the continuous wave OPO. In a recent study, we implemented this setup in the study of protonated tryptophan, TrpH{sup +}, as well as collision-induced dissociation products of this protonated amino acid [W. K. Mino, Jr., K. Gulyuz, D. Wang, C. N. Stedwell, and N. C. Polfer, J. Phys. Chem. Lett. 2, 299 (2011)]. Here, we give a more detailed account on the figures of merit of such IRMPD experiments. The appreciable photodissociation yields in these measurements demonstrate that IRMPD spectroscopy of covalently bound ions can be routinely carried out using benchtop OPO setups.« less

Schinus terebinthifolius scale-up countercurrent chromatography (Part I): High performance countercurrent chromatography fractionation of triterpene acids with off-line detection using atmospheric pressure chemical ionization mass spectrometry.

PubMed

Vieira, Mariana Neves; Costa, Fernanda das Neves; Leitão, Gilda Guimarães; Garrard, Ian; Hewitson, Peter; Ignatova, Svetlana; Winterhalter, Peter; Jerz, Gerold

2015-04-10

'Countercurrent chromatography' (CCC) is an ideal technique for the recovery, purification and isolation of bioactive natural products, due to the liquid nature of the stationary phase, process predictability and the possibility of scale-up from analytical to preparative scale. In this work, a method developed for the fractionation of Schinus terebinthifolius Raddi berries dichloromethane extract was thoroughly optimized to achieve maximal throughput with minimal solvent and time consumption per gram of processed crude extract, using analytical, semi-preparative and preparative 'high performance countercurrent chromatography' (HPCCC) instruments. The method using the biphasic solvent system composed of n-heptane-ethyl acetate-methanol-water (6:1:6:1, v/v/v/v) was volumetrically scaled up to increase sample throughput up to 120 times, while maintaining separation efficiency and time. As a fast and specific detection alternative, the fractions collected from the CCC-separations were injected to an 'atmospheric pressure chemical ionization mass-spectrometer' (APCI-MS/MS) and reconstituted molecular weight MS-chromatograms of the APCI-ionizable compounds from S. terebinthifolius were obtained. This procedure led to the direct isolation of tirucallane type triterpenes such as masticadienonic and 3β-masticadienolic acids. Also oleanonic and moronic acids have been identified for the first time in the species. In summary, this approach can be used for other CCC scale-up processes, enabling MS-target-guided isolation procedures. Copyright © 2015 Elsevier B.V. All rights reserved.

Inhibition of APOBEC3G activity impedes double-stranded DNA repair.

PubMed

Prabhu, Ponnandy; Shandilya, Shivender M D; Britan-Rosich, Elena; Nagler, Adi; Schiffer, Celia A; Kotler, Moshe

2016-01-01

The cellular cytidine deaminase APOBEC3G (A3G) was first described as an anti-HIV-1 restriction factor, acting by directly deaminating reverse transcripts of the viral genome. HIV-1 Vif neutralizes the activity of A3G, primarily by mediating degradation of A3G to establish effective infection in host target cells. Lymphoma cells, which express high amounts of A3G, can restrict Vif-deficient HIV-1. Interestingly, these cells are more stable in the face of treatments that result in double-stranded DNA damage, such as ionizing radiation and chemotherapies. Previously, we showed that the Vif-derived peptide (Vif25-39) efficiently inhibits A3G deamination, and increases the sensitivity of lymphoma cells to ionizing radiation. In the current study, we show that additional peptides derived from Vif, A3G, and APOBEC3F, which contain the LYYF motif, inhibit deamination activity. Each residue in the Vif25-39 sequence moderately contributes to the inhibitory effect, whereas replacing a single residue in the LYYF motif completely abrogates inhibition of deamination. Treatment of A3G-expressing lymphoma cells exposed to ionizing radiation with the new inhibitory peptides reduces double-strand break repair after irradiation. Incubation of cultured irradiated lymphoma cells with peptides that inhibit double-strand break repair halts their propagation. These results suggest that A3G may be a potential therapeutic target that is amenable to peptide and peptidomimetic inhibition. © 2015 FEBS.

Investigation of theoretical efficiency limit of hot carriers solar cells with a bulk indium nitride absorber

NASA Astrophysics Data System (ADS)

Aliberti, P.; Feng, Y.; Takeda, Y.; Shrestha, S. K.; Green, M. A.; Conibeer, G.

2010-11-01

Theoretical efficiencies of a hot carrier solar cell considering indium nitride as the absorber material have been calculated in this work. In a hot carrier solar cell highly energetic carriers are extracted from the device before thermalisation, allowing higher efficiencies in comparison to conventional solar cells. Previous reports on efficiency calculations approached the problem using two different theoretical frameworks, the particle conservation (PC) model or the impact ionization model, which are only valid in particular extreme conditions. In addition an ideal absorber material with the approximation of parabolic bands has always been considered in the past. Such assumptions give an overestimation of the efficiency limits and results can only be considered indicative. In this report the real properties of wurtzite bulk InN absorber have been taken into account for the calculation, including the actual dispersion relation and absorbance. A new hybrid model that considers particle balance and energy balance at the same time has been implemented. Effects of actual impact ionization (II) and Auger recombination (AR) lifetimes have been included in the calculations for the first time, considering the real InN band structure and thermalisation rates. It has been observed that II-AR mechanisms are useful for cell operation in particular conditions, allowing energy redistribution of hot carriers. A maximum efficiency of 43.6% has been found for 1000 suns, assuming thermalisation constants of 100 ps and ideal blackbody absorption. This value of efficiency is considerably lower than values previously calculated adopting PC or II-AR models.

Development of the MICROMEGAS detector for measuring the energy spectrum of alpha particles by using a 241Am source

NASA Astrophysics Data System (ADS)

Kim, Do Yoon; Ham, Cheolmin; Shin, Jae Won; Park, Tae-Sun; Hong, Seung-Woo; Andriamonje, Samuel; Kadi, Yacine; Tenreiro, Claudio

2016-05-01

We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting a particles emitted from an 241Am standard source. The voltage applied to the ionization region of the detector is optimized for stable operation at room temperature and atmospheric pressure. The energy of a particles from the 241Am source can be varied by changing the flight path of the a particle from the 241Am source. The channel numbers of the experimentally-measured pulse peak positions for different energies of the a particles are associated with the energies deposited by the alpha particles in the ionization region of the detector as calculated by using GEANT4 simulations; thus, the energy calibration of the MICROMEGAS detector for a particles is done. For the energy calibration, the thickness of the ionization region is adjusted so that a particles may completely stop in the ionization region and their kinetic energies are fully deposited in the region. The efficiency of our MICROMEGAS detector for a particles under the present conditions is found to be ~97.3%.

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Is electrospray emission really due to columbic forces?

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

Aliotta, Francesco, E-mail: aliotta@ipcf.cnr.it; Ponterio, Rosina C.; Salvato, Gabriele

2014-09-15

Electrospray ionization (ESI) is a widely adopted soft ionization method for mass spectroscopy (MS). In spite of the undeniable success of the technique, its mechanisms are difficult to be analytically modelled because the process is characterized by non-equilibrium conditions. The common belief is that the formation of gas-phase ions takes place at the apex of the Taylor cone via electrophoretic charging. The charge balance implies that a conversion of electrons to ions should occur at the metal-liquid interface of the injector needle. We have detected that the above description is based on unproved assumptions which are not consistent with themore » correct evaluation of the problem. The comparison between experiments performed under the usual geometry and observations obtained under symmetric field configurations suggests that the emitted droplets cannot be significantly charged or, at least, that any possible ionization mechanism is so poorly efficient to ensure that columbic forces cannot play a major role in jet formation, even in cases where the liquid consists of a solution of ionic species. Further work is required to clearly understand how ionization occurs in ESI-MS.« less

Experimental Determination of the Ionization Energies of MoSe 2, WS 2, and MoS 2 on SiO 2 Using Photoemission Electron Microscopy

DOE PAGES

Keyshar, Kunttal; Berg, Morgann; Zhang, Xiang; ...

2017-07-19

Here, the values of the ionization energies of transition metal dichalcogenides (TMDs) are needed to assess their potential usefulness in semiconductor heterojunctions for high-performance optoelectronics. Here, we report on the systematic determination of ionization energies for three prototypical TMD monolayers (MoSe 2, WS 2, and MoS 2) on SiO 2 using photoemission electron microscopy with deep ultraviolet illumination. The ionization energy displays a progressive decrease from MoS 2, to WS 2, to MoSe 2, in agreement with predictions of density functional theory calculations. Combined with the measured energy positions of the valence band edge at the Brillouin zone center, wemore » deduce that, in the absence of interlayer coupling, a vertical heterojunction comprising any of the three TMD monolayers would form a staggered (type-II) band alignment. This band alignment could give rise to long-lived interlayer excitons that are potentially useful for valleytronics or efficient electron–hole separation in photovoltaics.« less

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

NASA Astrophysics Data System (ADS)

Tachikawa, Hiroto; Takada, Tomoya

2013-03-01

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

The effect of surface charge, negative and bipolar ionization on the deposition of airborne bacteria.

PubMed

Meschke, S; Smith, B D; Yost, M; Miksch, R R; Gefter, P; Gehlke, S; Halpin, H A

2009-04-01

A series of experiments were conducted to evaluate the effect of surface charge and air ionization on the deposition of airborne bacteria. The interaction between surface electrostatic potential and the deposition of airborne bacteria in an indoor environment was investigated using settle plates charged with electric potentials of 0, +/-2.5kV and +/-5kV. Results showed that bacterial deposition on the plates increased proportionally with increased potential to over twice the gravitational sedimentation rate at +5kV. Experiments were repeated under similar conditions in the presence of either negative or bipolar air ionization. Bipolar air ionization resulted in reduction of bacterial deposition onto the charged surfaces to levels nearly equal to gravitational sedimentation. In contrast, diffusion charging appears to have occurred during negative air ionization, resulting in an even greater deposition onto the oppositely charged surface than observed without ionization. Static charges on fomitic surfaces may attract bacteria resulting in deposition in excess of that expected by gravitational sedimentation or simple diffusion. Implementation of bipolar ionization may result in reduction of bacterial deposition. Fomitic surfaces are important vehicles for the transmission of infectious organisms. This study has demonstrated a simple strategy for minimizing charge related deposition of bacteria on surfaces.

State-resolved three-dimensional electron-momentum correlation in nonsequential double ionization of benzene

NASA Astrophysics Data System (ADS)

Winney, Alexander H.; Lin, Yun Fei; Lee, Suk Kyoung; Adhikari, Pradip; Li, Wen

2016-03-01

We report state-resolved electron-momentum correlation measurement of strong-field nonsequential double ionization in benzene. With a novel coincidence detection apparatus, highly efficient triple coincidence (electron-electron dication) and quadruple coincidence (electron-electron-cation-cation) are used to resolve the final ionic states and to characterize three-dimensional (3D) electron-momentum correlation. The primary states associated with dissociative and nondissociative dications are assigned. A 3D momentum anticorrelation is observed for the electrons in coincidence with dissociative benzene dication states whereas such a correlation is absent for nondissociative dication states.

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

NASA Technical Reports Server (NTRS)

Jones, H. P.

1982-01-01

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

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

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

Ghosh, Aryya; Vaval, Nayana, E-mail: np.vaval@ncl.res.in; Pal, Sourav

2015-07-14

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

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

PubMed

Abdul-Aziz, Karolin Kamel; Tuorkey, M J

2010-04-02

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

Solvent jet desorption capillary photoionization-mass spectrometry.

PubMed

Haapala, Markus; Teppo, Jaakko; Ollikainen, Elisa; Kiiski, Iiro; Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

2015-03-17

A new ambient mass spectrometry method, solvent jet desorption capillary photoionization (DCPI), is described. The method uses a solvent jet generated by a coaxial nebulizer operated at ambient conditions with nitrogen as nebulizer gas. The solvent jet is directed onto a sample surface, from which analytes are extracted into the solvent and ejected from the surface in secondary droplets formed in collisions between the jet and the sample surface. The secondary droplets are directed into the heated capillary photoionization (CPI) device, where the droplets are vaporized and the gaseous analytes are ionized by 10 eV photons generated by a vacuum ultraviolet (VUV) krypton discharge lamp. As the CPI device is directly connected to the extended capillary inlet of the MS, high ion transfer efficiency to the vacuum of MS is achieved. The solvent jet DCPI provides several advantages: high sensitivity for nonpolar and polar compounds with limit of detection down to low fmol levels, capability of analyzing small and large molecules, and good spatial resolution (250 μm). Two ionization mechanisms are involved in DCPI: atmospheric pressure photoionization, capable of ionizing polar and nonpolar compounds, and solvent assisted inlet ionization capable of ionizing larger molecules like peptides. The feasibility of DCPI was successfully tested in the analysis of polar and nonpolar compounds in sage leaves and chili pepper.

A Systems Approach to Evaluating Ionizing Radiation: Six Focus Areas to Improve Quality, Efficiency, and Patient Safety

PubMed Central

Mower, Laura; Bushe, Chris

2015-01-01

Abstract: Ionizing radiation is an essential component of the care process. However, providers and patients may not be fully aware of the risks involved, the level of ionizing radiation delivered with various procedures, or the potential for harm through incidental overexposure or cumulative dose. Recent high-profile incidents demonstrating the devastating short-term consequences of radiation overexposure have drawn attention to these risks, but applicable solutions are lacking. Although various recommendations and guidelines have been proposed, organizational variability challenges providers to identify their own practical solutions. To identify potential failure modes and develop solutions to preserve patient safety within a large, national healthcare system, we assembled a multidisciplinary team to conduct a comprehensive analysis of practices surrounding the delivery of ionizing radiation. Workgroups were developed to analyze existing culture, processes, and technology to identify deficiencies and propose solutions. Six focus areas were identified: competency and certification; equipment; monitoring and auditing; education; clinical pathways; and communication and marketing. This manuscript summarizes this comprehensive, multidisciplinary, and systemic analysis of risk and provides examples to illustrate how these focus areas can be used to improve the use of ionizing radiation. The proposed solutions, once fully implemented, may advance patient safety and care. PMID:26042626

Interfacing Capillary-Based Separations to Mass Spectrometry Using Desorption Electrospray Ionization

PubMed Central

Barbula, Griffin K.; Safi, Samir; Chingin, Konstantin; Perry, Richard H.; Zare, Richard N.

2014-01-01

The powerful hybrid analysis method of capillary-based separations followed by mass spectrometric analysis gives substantial chemical identity and structural information. It is usually carried out using electrospray ionization. However, the salts and detergents used in the mobile phase for electrokinetic separations suppress ionization efficiencies and contaminate the inlet of the mass spectrometer. This report describes a new method that uses desorption electrospray ionization (DESI) to overcome these limitations. Effluent from capillary columns is deposited on a rotating Teflon disk that is covered with paper. As the surface rotates, the temporal separation of the eluting analytes (i.e., the electropherogram) is spatially encoded on the surface. Then, using DESI, surface-deposited analytes are preferentially ionized, reducing the effects of ion suppression and inlet contamination on signal. With the use of this novel approach, two capillary-based separations were performed: a mixture of the rhodamine dyes at milligram/milliliter levels in a 10 mM sodium borate solution was separated by capillary electrophoresis, and a mixture of three cardiac drugs at milligram/milliliter levels in a 12.5 mM sodium borate and 12.5 mM sodium dodecyl sulfate solution was separated by micellar electrokinetic chromatography. In both experiments, the negative effects of detergents and salts on the MS analyses were minimized. PMID:21319740

CHEMICAL ANALYSIS OF A DIFFUSE CLOUD ALONG A LINE OF SIGHT TOWARD W51: MOLECULAR FRACTION AND COSMIC-RAY IONIZATION RATE

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

Indriolo, Nick; Neufeld, D. A.; Gerin, M.

2012-10-20

Absorption lines from the molecules OH{sup +}, H{sub 2}O{sup +}, and H{sup +} {sub 3} have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. Together, OH{sup +} and H{sub 2}O{sup +} are used to determine the molecular hydrogen fraction in the outskirts of the observed cloud, as well as the cosmic-ray ionization rate of atomic hydrogen. H{sup +} {sub 3} is used to infer the cosmic-ray ionization rate of H{sub 2} in the molecular interior ofmore » the cloud, which we find to be {zeta}{sub 2} = (4.8 {+-} 3.4) Multiplication-Sign 10{sup -16} s{sup -1}. Combining the results from all three species we find an efficiency factor-defined as the ratio of the formation rate of OH{sup +} to the cosmic-ray ionization rate of H-of {epsilon} = 0.07 {+-} 0.04, much lower than predicted by chemical models. This is an important step in the future use of OH{sup +} and H{sub 2}O{sup +} on their own as tracers of the cosmic-ray ionization rate.« less

Degradation spectra and ionization yields of electrons in gases

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

Inokuti, M.; Douthat, D.A.; Rau, A.R.P.

1975-01-01

Progress in the microscopic theory of electron degradation in gases by Platzman, Fano, and co-workers is outlined. The theory consists of (1) the cataloging of all major inelastic-collision cross sections for electrons (including secondary-electron energy distribution in a single ionizing collision) and (2) the evaluation of cumulative consequences of individual electron collisions for the electrons themselves as well as for target molecules. For assessing the data consistency and reliability and extrapolating the data to the unexplored ranges of variables (such as electron energy), a series of plots devised by Platzman are very powerful. Electron degradation spectra were obtained through numericalmore » solution of the Spencer--Fano equation for all electron energies down to the first ionization thresholds for a few examples such as He and Ne. The systematics of the solutions resulted in the recognition of approximate scaling properties of the degradation spectra for different initial electron energies and pointed to new methods of more efficient treatment. Systematics of the ionization yields and their energy dependence on the initial electron energy were also recognized. Finally, the Spencer--Fano equation for the degradation spectra and the Fowler equation for the ionization and other yields are tightly linked with each other by a set of variational principles. (52 references, 7 figures) (DLC)« less

Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization

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

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

2016-08-07

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

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

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

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

NASA Astrophysics Data System (ADS)

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

2000-08-01

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

Upstream ionization instability associated with a current-free double layer.

PubMed

Aanesland, A; Charles, C; Lieberman, M A; Boswell, R W

2006-08-18

A low frequency instability has been observed using various electrostatic probes in a low-pressure expanding helicon plasma. The instability is associated with the presence of a current-free double layer (DL). The frequency of the instability increases linearly with the potential drop of the DL, and simultaneous measurements show their coexistence. A theory for an upstream ionization instability has been developed, which shows that electrons accelerated through the DL increase the ionization upstream and are responsible for the observed instability. The theory is in good agreement with the experimental results.

Radiation exposure and lung disease in today's nuclear world.

PubMed

Deas, Steven D; Huprikar, Nikhil; Skabelund, Andrew

2017-03-01

Ionizing radiation poses important health risks. The per capita annual dose rate has increased in the United States and there is increasing concern for the risks posed by low-dose occupational exposure among workers in nuclear industries and healthcare. Recent nuclear accidents and concern for terrorism have heightened concern for catastrophic, high-dose ionizing radiation exposure. This review will highlight recent research into the risks to lung health posed by ionizing radiation exposure and into potential treatments. Angiotensin-converting enzyme inhibitors and some antioxidants have shown promise as mitigators, to decrease pneumonitis and fibrosis when given after exposure. Studies of survivors of nuclear catastrophes have shown increased risk for lung cancer, especially in nonsmokers. There is evidence for increased lung cancer risk in industrial radiation workers, especially those who process plutonium and may inhale radioactive particles. There does not seem to be an increased risk of lung cancer in healthcare workers who perform fluoroscopic procedures. High-dose ionizing radiation exposure causes pneumonitis and fibrosis, and more research is needed to develop mitigators to improve outcomes in nuclear catastrophes. Long-term, low-dose occupational radiation may increase lung cancer risk. More research to better define this risk could lead to improved safety protocols and screening programs.

Observation of increased space-charge limited thermionic electron emission current by neutral gas ionization in a weakly-ionized deuterium plasma

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

Hollmann, E. M.; Yu, J. H.; Doerner, R. P.

2015-09-14

The thermionic electron emission current emitted from a laser-produced hot spot on a tungsten target in weakly-ionized deuterium plasma is measured. It is found to be one to two orders of magnitude larger than expected for bipolar space charge limited thermionic emission current assuming an unperturbed background plasma. This difference is attributed to the plasma being modified by ionization of background neutrals by the emitted electrons. This result indicates that the allowable level of emitted thermionic electron current can be significantly enhanced in weakly-ionized plasmas due to the presence of large neutral densities.

Size-dependent error of the density functional theory ionization potential in vacuum and solution

DOE PAGES

Sosa Vazquez, Xochitl A.; Isborn, Christine M.

2015-12-22

Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potentialmore » for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. As a result, in vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.« less

Size-dependent error of the density functional theory ionization potential in vacuum and solution

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

Sosa Vazquez, Xochitl A.; Isborn, Christine M., E-mail: cisborn@ucmerced.edu

2015-12-28

Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potentialmore » for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. In vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.« less

Enhancement of carvedilol solubility by solid dispersion technique using cyclodextrins, water soluble polymers and hydroxyl acid.

PubMed

Yuvaraja, K; Khanam, Jasmina

2014-08-05

Aim of the present work is to enhance aqueous solubility of carvedilol (CV) by solid dispersion technique using wide variety of carriers such as: β-cyclodextrin (βCD), hydroxypropyl-β-cyclodextrin (HPβCD), tartaric acid (TA), polyvinyl pyrrolidone K-30 (PVP K-30) and poloxamer-407 (PLX-407). Various products of 'CV-solid dispersion' had been studied extensively in various pH conditions to check enhancement of solubility and dissolution characteristics of carvedilol. Any physical change upon interaction between CV and carriers was confirmed by instrumental analysis: XRD, DSC, FTIR and SEM. Negative change of Gibb's free energy and complexation constants (Kc, 75-240M(-1), for cyclodextrins and 1111-20,365M(-1), for PVP K-30 and PLX-407) were the evidence of stable nature of the binding between CV and carriers. 'Solubility enhancement factor' of ionized-CV was found high enough (340 times) with HPβCD in presence of TA. TA increases the binding efficiency of cyclodextrin and changing the pH of microenvironment in dissolution medium. In addition, ionization process was used to increase the apparent intrinsic solubility of drug. In vitro, dissolution time of CV was remarkably reduced in the solid dispersion system compared to that of pure drug. This may be attributed to increased wettability, dispersing ability and transformation of crystalline state of drug to amorphous one. Copyright © 2014 Elsevier B.V. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

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

NASA Astrophysics Data System (ADS)

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

2011-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Atmospheric Gaseous Plasma with Large Dimensions

NASA Astrophysics Data System (ADS)

Korenev, Sergey

2012-10-01

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

How does ionizing radiation escape from galaxies?

NASA Astrophysics Data System (ADS)

Orlitova, Ivana

2016-10-01

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

Internuclear separation dependent ionization of the valence orbitals of I2 by strong laser fields.

PubMed

Chen, H; Tagliamonti, V; Gibson, G N

2012-11-09

Using a pump-dump-probe technique and Fourier-transform spectroscopy, we study the internuclear separation R dependence and relative strength of the ionization rates of the π and σ electrons of I2, whose valence orbitals are σ(g)(2)π(u)(4)π(g)(4)σ(u)(0). We find that ionization of the highest occupied molecular orbital (HOMO)-2 (σ(g)) has a strong dependence on R while the HOMO and HOMO-1 do not. Surprisingly, the ionization rate of the HOMO-2 exceeds the combined ionization rate of the less bound orbitals and this branching ratio increases with R. Since our technique produces target molecules that are highly aligned with the laser polarization, the σ orbitals will be preferentially ionized and undergo enhanced ionization at larger R compared to the π orbitals. Nevertheless, it is highly unusual that an inner orbital provides the dominant strong field ionization pathway in a small molecule.

Internuclear Separation Dependent Ionization of the Valence Orbitals of I2 by Strong Laser Fields

NASA Astrophysics Data System (ADS)

Chen, H.; Tagliamonti, V.; Gibson, G. N.

2012-11-01

Using a pump-dump-probe technique and Fourier-transform spectroscopy, we study the internuclear separation R dependence and relative strength of the ionization rates of the π and σ electrons of I2, whose valence orbitals are σg2πu4πg4σu0. We find that ionization of the highest occupied molecular orbital (HOMO)-2 (σg) has a strong dependence on R while the HOMO and HOMO-1 do not. Surprisingly, the ionization rate of the HOMO-2 exceeds the combined ionization rate of the less bound orbitals and this branching ratio increases with R. Since our technique produces target molecules that are highly aligned with the laser polarization, the σ orbitals will be preferentially ionized and undergo enhanced ionization at larger R compared to the π orbitals. Nevertheless, it is highly unusual that an inner orbital provides the dominant strong field ionization pathway in a small molecule.

The effect of shallow vs. deep level doping on the performance of thermoelectric materials

NASA Astrophysics Data System (ADS)

Song, Qichen; Zhou, Jiawei; Meroueh, Laureen; Broido, David; Ren, Zhifeng; Chen, Gang

2016-12-01

It is well known that the efficiency of a good thermoelectric material should be optimized with respect to doping concentration. However, much less attention has been paid to the optimization of the dopant's energy level. Thermoelectric materials doped with shallow levels may experience a dramatic reduction in their figures of merit at high temperatures due to the excitation of minority carriers that reduces the Seebeck coefficient and increases bipolar heat conduction. Doping with deep level impurities can delay the excitation of minority carriers as it requires a higher temperature to ionize all dopants. We find through modeling that, depending on the material type and temperature range of operation, different impurity levels (shallow or deep) will be desired to optimize the efficiency of a thermoelectric material. For different materials, we further clarify where the most preferable position of the impurity level within the bandgap falls. Our research provides insight on why different dopants often affect thermoelectric transport properties differently and directions in searching for the most appropriate dopants for a thermoelectric material in order to maximize the device efficiency.

Diamond Pixel Detectors

NASA Astrophysics Data System (ADS)

Adam, W.; Berdermann, E.; Bergonzo, P.; Bertuccio, G.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Doroshenko, J.; Dulinski, W.; van Eijk, B.; Fallou, A.; Fizzotti, F.; Foster, J.; Foulon, F.; Friedl, M.; Gan, K. K.; Gheeraert, E.; Gobbi, B.; Grim, G. P.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Kass, R.; Koeth, T.; Krammer, M.; Lander, R.; Logiudice, A.; Lu, R.; mac Lynne, L.; Manfredotti, C.; Meier, D.; Mishina, M.; Moroni, L.; Oh, A.; Pan, L. S.; Pernicka, M.; Perera, L.; Pirollo, S.; Plano, R.; Procario, M.; Riester, J. L.; Roe, S.; Rott, C.; Rousseau, L.; Rudge, A.; Russ, J.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R. J.; Tesarek, R.; Trischuk, W.; Tromson, D.; Vittone, E.; Wedenig, R.; Weilhammer, P.; White, C.; Zeuner, W.; Zoeller, M.

2001-06-01

Diamond based pixel detectors are a promising radiation-hard technology for use at the LHC. We present first results on a CMS diamond pixel sensor. With a threshold setting of 2000 electrons, an average pixel efficiency of 78% was obtained for normally incident minimum ionizing particles.

Removal of viable bioaerosol particles with a low-efficiency HVAC filter enhanced by continuous emission of unipolar air ions.

PubMed

Huang, R; Agranovski, I; Pyankov, O; Grinshpun, S

2008-04-01

Continuous emission of unipolar ions has been shown to improve the performance of respirators and stationary filters challenged with non-biological particles. In this study, we investigated the ion-induced enhancement effect while challenging a low-efficiency heating, ventilation and air-conditioning (HVAC) filter with viable bacterial cells, bacterial and fungal spores, and viruses. The aerosol concentration was measured in real time. Samples were also collected with a bioaerosol sampler for viable microbial analysis. The removal efficiency of the filter was determined, respectively, with and without an ion emitter. The ionization was found to significantly enhance the filter efficiency in removing viable biological particles from the airflow. For example, when challenged with viable bacteria, the filter efficiency increased as much as four- to fivefold. For viable fungal spores, the ion-induced enhancement improved the efficiency by a factor of approximately 2. When testing with virus-carrying liquid droplets, the original removal efficiency provided by the filter was rather low: 9.09 +/- 4.84%. While the ion emission increased collection about fourfold, the efficiency did not reach 75-100% observed with bacteria and fungi. These findings, together with our previously published results for non-biological particles, demonstrate the feasibility of a new approach for reducing aerosol particles in HVAC systems used for indoor air quality control. Recirculated air in HVAC systems used for indoor air quality control in buildings often contains considerable number of viable bioaerosol particles because of limited efficiency of the filters installed in these systems. In the present study, we investigated - using aerosolized bacterial cells, bacterial and fungal spores, and virus-carrying particles - a novel idea of enhancing the performance of a low-efficiency HVAC filter utilizing continuous emission of unipolar ions in the filter vicinity. The findings described in this paper, together with our previously published results for non-biological particles, demonstrate the feasibility of the newly developed approach.

Mass spectrometry imaging for visualizing organic analytes in food.

PubMed

Handberg, Eric; Chingin, Konstantin; Wang, Nannan; Dai, Ximo; Chen, Huanwen

2015-01-01

The demand for rapid chemical imaging of food products steadily increases. Mass spectrometry (MS) is featured by excellent molecular specificity of analysis and is, therefore, a very attractive method for chemical profiling. MS for food imaging has increased significantly over the past decade, aided by the emergence of various ambient ionization techniques that allow direct and rapid analysis in ambient environment. In this article, the current status of food imaging with MSI is reviewed. The described approaches include matrix-assisted laser desorption/ionization (MALDI), but emphasize desorption atmospheric pressure photoionization (DAPPI), electrospray-assisted laser desorption/ionization (ELDI), probe electrospray ionization (PESI), surface desorption atmospheric pressure chemical ionization (SDAPCI), and laser ablation flowing atmospheric pressure afterglow (LA-FAPA). The methods are compared with regard to spatial resolution; analysis speed and time; limit of detection; and technical aspects. The performance of each method is illustrated with the description of a related application. Specific requirements in food imaging are discussed. © 2014 Wiley Periodicals, Inc.

Resveratrol sensitization of DU145 prostate cancer cells to ionizing radiation is associated to ceramide increase.

PubMed

Scarlatti, Francesca; Sala, Giusy; Ricci, Clara; Maioli, Claudio; Milani, Franco; Minella, Marco; Botturi, Marco; Ghidoni, Riccardo

2007-08-08

Radiotherapy is an established therapeutic modality for prostate cancer. Since it is well known that radiotherapy is limited due to its severe toxicity towards normal cells at high dose and minimal effect at low dose, the search for biological compounds that increase the sensitivity of tumors cells to radiation may improve the efficacy of therapy. Resveratrol, a natural antioxidant, was shown to inhibit carcinogenesis in animal models, and to block the process of tumor initiation and progression. The purpose of this study was to examine whether or not resveratrol can sensitize DU145, an androgen-independent human prostate cancer cell line, to ionizing radiation. We report here that DU145 cells are resistant to ionizing radiation-induced cell death, but pretreatment with resveratrol significantly enhances cell death. Resveratrol acts synergistically with ionizing radiation to inhibit cell survival in vitro. Resveratrol also potentiates ionizing radiation-induced ceramide accumulation, by promoting its de novo biosynthesis. This confirms ceramide as an effective mediator of the anticancer potential induced by resveratrol.

Ion Densities in the Nightside Ionosphere of Mars: Effects of Electron Impact Ionization

NASA Astrophysics Data System (ADS)

Girazian, Z.; Mahaffy, P.; Lillis, R. J.; Benna, M.; Elrod, M.; Fowler, C. M.; Mitchell, D. L.

2017-11-01

We use observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to show how superthermal electron fluxes and crustal magnetic fields affect ion densities in the nightside ionosphere of Mars. We find that due to electron impact ionization, high electron fluxes significantly increase the CO2+, O+, and O2+ densities below 200 km but only modestly increase the NO+ density. High electron fluxes also produce distinct peaks in the CO2+, O+, and O2+ altitude profiles. We also find that superthermal electron fluxes are smaller near strong crustal magnetic fields. Consequently, nightside ion densities are also smaller near strong crustal fields because they decay without being replenished by electron impact ionization. Furthermore, the NO+/O2+ ratio is enhanced near strong crustal fields because, in the absence of electron impact ionization, O2+ is converted into NO+ and not replenished. Our results show that electron impact ionization is a significant source of CO2+, O+, and O2+ in the nightside ionosphere of Mars.

Free radical production by high energy shock waves--comparison with ionizing irradiation.

PubMed

Morgan, T R; Laudone, V P; Heston, W D; Zeitz, L; Fair, W R

1988-01-01

Fricke chemical dosimetry is used as an indirect measure of the free radical production of ionizing irradiation. We adapted the Fricke ferrous sulfate radiation dosimeter to examine the chemical effects of high energy shock waves. Significant free radical production was documented. The reaction was dose dependent, predictably increased by acoustic impedance, but curvilinear. A thousand shocks at 18 kilovolts induced the same free radical oxidation as 1100 rad cobalt-60 gamma ionizing irradiation, increasing to 2900 rad in the presence of an air-fluid zone of acoustic impedance. The biological effect of these free radicals was compared to that of cobalt-60 ionizing irradiation by measuring the affect on Chinese hamster cells by clonogenic assay. While cobalt-60 irradiation produced a marked decrease in clonogenic survivors, little effect was noted with high energy shock waves. This suggested that the chemical effects produced by shock waves were either absent or attenuated in the cells, or were inherently less toxic than those of ionizing irradiation.

Instantaneous characterization of vegetable oils via TAG and FFA profiles by easy ambient sonic-spray ionization mass spectrometry.

PubMed

Simas, Rosineide C; Catharino, Rodrigo R; Cunha, Ildenize B S; Cabral, Elaine C; Barrera-Arellano, Daniel; Eberlin, Marcos N; Alberici, Rosana M

2010-04-01

A fast and reliable method is presented for the analysis of vegetable oils. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) is shown to efficiently desorb and ionize the main oil constituents from an inert surface under ambient conditions and to provide comprehensive triacylglyceride (TAG) and free fatty acid (FFA) profiles detected mainly as either [TAG + Na](+) or [FFA-H](-) ions. EASI(+/-)-MS analysis is simple, easily implemented, requires just a tiny droplet of the oil and is performed without any pre-separation or chemical manipulation. It also causes no fragmentation of TAG ions hence diacylglyceride (DAG) and monoacylglyceride (MAG) profiles and contents can also be measured. The EASI(+/-)-MS profiles of TAG and FFA permit authentication and quality control and can be used, for instance, to access levels of adulteration, acidity, oxidation or hydrolysis of vegetable oils in general.

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

Keyshar, Kunttal; Berg, Morgann; Zhang, Xiang

Here, the values of the ionization energies of transition metal dichalcogenides (TMDs) are needed to assess their potential usefulness in semiconductor heterojunctions for high-performance optoelectronics. Here, we report on the systematic determination of ionization energies for three prototypical TMD monolayers (MoSe 2, WS 2, and MoS 2) on SiO 2 using photoemission electron microscopy with deep ultraviolet illumination. The ionization energy displays a progressive decrease from MoS 2, to WS 2, to MoSe 2, in agreement with predictions of density functional theory calculations. Combined with the measured energy positions of the valence band edge at the Brillouin zone center, wemore » deduce that, in the absence of interlayer coupling, a vertical heterojunction comprising any of the three TMD monolayers would form a staggered (type-II) band alignment. This band alignment could give rise to long-lived interlayer excitons that are potentially useful for valleytronics or efficient electron–hole separation in photovoltaics.« less

Recent progress in microchip electrophoresis-mass spectrometry.

PubMed

Kitagawa, Fumihiko; Otsuka, Koji

2011-06-25

This review highlights the methodological and instrumental developments in microchip electrophoresis (MCE)-mass spectrometry (MS) from 1997. In MCE-MS, the development of ionization interface is one of the most important issues to realize highly sensitive detection and high separation efficiency. Among several interfaces, electrospray ionization (ESI) has been mainly employed to MCE-MS since a simple structure of the ESI interface is suitable for coupling with the microchips. Although the number of publications is still limited, laser desorption ionization (LDI) interface has also been developed for MCE-MS. The characteristics of the ESI and LDI interfaces applied to the electrophoresis microchips are presented in this review. The scope of applications in MCE-MS covers mainly biogenic compounds such as bioactive amines, peptides, tryptic digests and proteins. This review provides a comprehensive table listing the applications in MCE-MS. Copyright © 2010 Elsevier B.V. All rights reserved.