Sample records for negatively charged molecules

  1. Nonequilibrium charge-Kondo transport through negative-U molecules Jens Koch,1,2 Eran Sela,3 Yuval Oreg,3 and Felix von Oppen2

    E-print Network

    von Oppen, Felix

    Nonequilibrium charge-Kondo transport through negative-U molecules Jens Koch,1,2 Eran Sela,3 Yuval-temperature transport through molecules with effectively negative charging energy U exhibits a charge- Kondo effect. We to demonstrate the intimate relation between nonequilibrium transport in the spin-Kondo and charge-Kondo regimes

  2. Exotic negative molecules in AMS

    NASA Astrophysics Data System (ADS)

    Golser, Robin; Gnaser, Hubert; Kutschera, Walter; Priller, Alfred; Steier, Peter; Wallner, Anton

    2007-06-01

    "The techniques and equipment developed for AMS studies are well suited for identifying exotic negative ions". With this sentence begins a pioneering paper by Roy Middleton and Jeff Klein (M&K) on small doubly-charged negative carbon clusters [Nucl. Instr. and Meth. B 123 (1997) 532]. M&K were the first to utilize Accelerator Mass Spectrometry to prove the existence of these clusters and a number of other exotic molecules. We review M&K's efforts and show how their work is being continued at other laboratories. The latest developments are: (1) the discovery of long-lived molecular hydrogen anions H2-,D2- and (2) the unambiguous identification of the smallest doubly-charged negative molecule (LiF 3) 2-. In particular we show new experimental data for D3-, and for (LiF 3) 2-, and we try to answer the question why M&K's search for this di-anion was unsuccessful.

  3. Small and reproducible isotope effects during methylation with trimethylsulfonium hydroxide (TMSH): a convenient derivatization method for isotope analysis of negatively charged molecules.

    PubMed

    Reinnicke, Sandra; Bernstein, Anat; Elsner, Martin

    2010-03-01

    Negatively charged analytes must be derivatized prior to gas chromatography-isotope ratio mass spectrometry (GC-IRMS), with stringent control of isotope fractionation. Current methods require offline sample preparation. This study tests for the first time trimethylsulfonium hydroxide (TMSH) as online methylation agent prior to isotope analysis, addressing the herbicides bentazone and MCPA. Fully automated derivatization was achieved in a temperature-programmable GC injector, where reactants were injected into a packed liner, solvents were removed by split flow, and subsequent flash heating triggered the derivatization, thereby transferring derivatives onto the chromatographic column. Stoichiometric addition of TMSH resulted in complete conversion giving accurate and reproducible nitrogen isotope values of bentazone. In contrast, reproducible carbon isotope analysis required TMSH in > or = 250-fold excess. Contrary to expectations, delta(13)C values became more negative at smaller TMSH excess. This indicates that elevated methyl group concentrations in the pore space of the injection liner facilitated close-to-equilibrium rather than kinetic isotope fractionation resulting in reproducible derivatization conditions. delta(13)C results under these conditions compared favorably with liquid chromatography-IRMS: low standard deviations (0.3 per thousand for GC-IRMS, 0.1 per thousand for LC-IRMS) and a comparable offset of 1 per thousand compared to elemental analyzer-IRMS demonstrate that both methods represent expedient ways for online isotope analysis of anionic target compounds. PMID:20143836

  4. Interaction Between Equally Charged Membrane Surfaces Mediated by Positively and Negatively Charged Macro-Ions

    Microsoft Academic Search

    Šárka Perutková; Mojca Frank; Klemen Bohinc; Goran Bobojevi?; Jasna Zelko; Blaž Rozman; Veronika Kralj-Igli?; Aleš Igli?

    2010-01-01

    In biological systems, charged membrane surfaces are surrounded by charged molecules such as electrolyte ions and proteins.\\u000a Our recent experiments in the systems of giant phospholipid vesicles indicated that some of the blood plasma proteins (macro-ions)\\u000a may promote adhesion between equally charged membrane surfaces. In this work, theory was put forward to describe an IgG antibody-mediated\\u000a attractive interaction between negatively

  5. Charging of dust grains in a plasma with negative ions

    SciTech Connect

    Kim, Su-Hyun; Merlino, Robert L. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)

    2006-05-15

    The effect of negative ions on the charging of dust particles in a plasma is investigated experimentally. A plasma containing a very low percentage of electrons is formed in a single-ended Q machine when SF{sub 6} is admitted into the vacuum system. The relatively cold Q machine electrons (T{sub e}{approx_equal}0.2 eV) readily attach to SF{sub 6} molecules to form SF{sub 6}{sup -} negative ions. Calculations of the dust charge indicate that for electrons, negative ions, and positive ions of comparable temperatures, the charge (or surface potential) of the dust can be positive if the positive ion mass is smaller than the negative ion mass and if {epsilon}, the ratio of the electron to positive ion density, is sufficiently small. The Q machine plasma is operated with K{sup +} positive ions (mass 39 amu) and SF{sub 6}{sup -} negative ions (mass 146 amu), and also utilizes a rotating cylinder to dispense dust into the plasma column. Analysis of the current-voltage characteristics of a Langmuir probe in the dusty plasma shows evidence for the reduction in the (magnitude) of the negative dust charge and the transition to positively charged dust as the relative concentration of the residual electrons is reduced. Some remarks are offered concerning experiments that could become possible in a dusty plasma with positive grains.

  6. Negative ion\\/molecule reactions in a negative corona discharge

    Microsoft Academic Search

    V. Kotasek

    1981-01-01

    An atmospheric pressure negative corona discharge (point to plane) coupled to a quadrupole mass spectrometer was used to study negative ion\\/molecular chemistry. It was shown that neutral intermediates, mainly 03, N02 and N0, are produced by high energy electron dissociation of air constituents in a very narrow volume close to the point electrode. The neutrals are transported by air flow

  7. Charge loss in gas-phase multiply negatively charged oligonucleotides.

    PubMed

    Anusiewicz, Iwona; Berdys-Kochanska, Joanna; Czaplewski, Cezary; Sobczyk, Monika; Daranowski, Emma M; Skurski, Piotr; Simons, Jack

    2005-01-13

    In an attempt to shed light on the mechanism by which gaseous samples of negatively charged oligonucleotides undergo extremely slow (i.e., over 1-1000 s) charge loss, we have carried out molecular dynamics simulations on an oligonucleotide anion, T(5)(3-), containing five thymine, deoxyribose, and phosphate units in which the first, third, and fifth phosphates are negatively charged. The study is aimed at determining the rate at which an electron is detached from such a trianion by way of an internal Coulomb repulsion induced event. In this process, the intrinsic 5.0-5.1 eV electron binding strength of each phosphate site is reduced by the repulsive Coulomb potentials of the other two negative sites. As geometrical fluctuations cause the distances among the three negative phosphate sites to change, this causes the Coulomb repulsion energies at these sites to fluctuate. Once the Coulomb potential at any phosphate site exceeds ca. 5 eV, the electron on that site is able to undergo autodetachment. Although such an electron must tunnel through a barrier to escape, it is shown that the tunneling rate is not the rate-limiting step in electron loss; instead, it is the rate at which geometrical fluctuations cause the Coulomb potentials to exceed 5 eV that determines the rate of electron loss. Because these rates are extremely slow, special techniques had to be introduced to allow results of dynamics simulations on more flexible models of T(5)(3-) to be extrapolated to predict the behavior of the actual T(5)(3-). PMID:16839113

  8. Charging of dust grains in a plasma with negative ions Su-Hyun Kim and Robert L. Merlinoa

    E-print Network

    Merlino, Robert L.

    Charging of dust grains in a plasma with negative ions Su-Hyun Kim and Robert L. Merlinoa; accepted 21 April 2006; published online 26 May 2006 The effect of negative ions on the charging of dust machine electrons Te 0.2 eV readily attach to SF6 molecules to form SF6 - negative ions. Calculations

  9. Probing charge transport through individual molecules on silicon surfaces

    NASA Astrophysics Data System (ADS)

    Hersam, Mark

    2005-03-01

    The ultra-high vacuum (UHV) scanning tunneling microscope (STM) allows individual molecules to be imaged, addressed, and manipulated on semiconducting surfaces with atomic resolution. In particular, this paper considers three different molecules on the Si(100) surface: styrene, cyclopentene, and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). In all cases, room temperature STM current-voltage characteristics on individual molecules mounted on degenerately n-type Si(100) show multiple negative differential resistance (NDR) events at negative sample bias. On the other hand, at positive sample bias, the current-voltage characteristics do not show NDR, although a discontinuity in the differential conductance is observed. When the Si(100) substrate is changed to degenerate p-type doping, multiple NDR events are observed at positive sample bias while the discontinuity in the differential conductance occurs at negative sample bias. These empirical observations can be qualitatively explained by considering the energy band diagram for a semiconductor-molecule-metal junction [1]. More sophisticated nonequilibrium Green's function theoretical treatments also confirm the experimental data [2]. This paper will also describe recent efforts to characterize the temperature dependence of charge transport through molecule-semiconductor junctions using cryogenic UHV STM at temperatures between 10 K and 300 K [3]. In addition, using multi-step feedback controlled lithography [4], heteromolecular nanostructures consisting of both styrene and TEMPO molecules have been fabricated on hydrogen passivated Si(100). Atomic-scale characterization of these structures will be discussed in the context of silicon-based molecular electronics. [1] N. P. Guisinger, M. E. Greene, R. Basu, A. S. Baluch, and M. C. Hersam, Nano Letters, 4, 55 (2004). [2] T. Rakshit, G.-C. Liang, A. W. Ghosh, and S. Datta, Nano Letters, 4, 1803 (2004). [3] E. T. Foley, N. L. Yoder, N. P. Guisinger, and M. C. Hersam, Rev. Sci. Instrum., 75, 5280 (2004). [4] R. Basu, N. P. Guisinger, M. E. Greene, and M. C. Hersam, Appl. Phys. Lett., 85, 2619 (2004).

  10. Iodide uptake by negatively charged clay interlayers?

    PubMed

    Miller, Andrew; Kruichak, Jessica; Mills, Melissa; Wang, Yifeng

    2015-09-01

    Understanding iodide interactions with clay minerals is critical to quantifying risk associated with nuclear waste disposal. Current thought assumes that iodide does not interact directly with clay minerals due to electrical repulsion between the iodide and the negatively charged clay layers. However, a growing body of work indicates a weak interaction between iodide and clays. The goal of this contribution is to report a conceptual model for iodide interaction with clays by considering clay mineral structures and emergent behaviors of chemical species in confined spaces. To approach the problem, a suite of clay minerals was used with varying degrees of isomorphic substitution, chemical composition, and mineral structure. Iodide uptake experiments were completed with each of these minerals in a range of swamping electrolyte identities (NaCl, NaBr, KCl) and concentrations. Iodide uptake behaviors form distinct trends with cation exchange capacity and mineral structure. These trends change substantially with electrolyte composition and concentration, but do not appear to be affected by solution pH. The experimental results suggest that iodide may directly interact with clays by forming ion-pairs (e.g., NaI(aq)) which may concentrate within the interlayer space as well as the thin areas surrounding the clay particle where water behavior is more structured relative to bulk water. Ion pairing and iodide concentration in these zones is probably driven by the reduced dielectric constant of water in confined space and by the relatively high polarizability of the iodide species. PMID:26057987

  11. Recovery of small dye molecules from aqueous solutions using charged ultrafiltration membranes.

    PubMed

    Chen, Xiuwen; Zhao, Yiru; Moutinho, Jennifer; Shao, Jiahui; Zydney, Andrew L; He, Yiliang

    2015-03-01

    Recovery of reactive dyes from effluent streams is a growing environmental challenge. In this study, various charged regenerated cellulose (RC) ultrafiltration (UF) membranes were prepared and tested for removal of three model reactive dyes (reactive red ED-2B, reactive brilliant yellow K-6G, and reactive brilliant blue KN-R). Data were obtained with charged UF membranes having different spacer arm lengths between the base cellulose and the charge functionality. The effects of charge density of the dye molecules, ionic strength of the feed solution, spacer arm length of charged membranes and filtrate flux were studied. Results indicated that dye retention was greatest with the most negatively charged dye molecule. Higher rejection was also observed in low ionic strength solutions. Results were consistent with model calculations based on the partitioning of a charged sphere into a charged cylindrical pore. The membranes with longer spacer arm length had higher rejection coefficients, consistent with the greater negative charge on these membranes. This study confirms that charged UF membranes can effectively recover small reactive dye molecules at low pressures (below 100 kPa) under appropriate solution conditions due to the strong electrostatic repulsion from the membrane pores. PMID:25463218

  12. On charge transfer in the adsorbed molecules-graphene monolayer-SiC substrate system

    SciTech Connect

    Davydov, S. Yu., E-mail: sergei_davydov@mail.ru [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation)

    2011-05-15

    A step-by-step consideration of charge transfer in the molecule-single-layer graphene-SiC substrate system is presented. At the first step, a simple model of the density of states of a single graphene monolayer adsorbed on silicon carbide (the graphene-SiC system) is suggested, which allows the calculation of the corresponding occupation numbers of graphene atoms. It is shown that the graphene monolayer accumulates a negative charge. At the second step, the graphene-SiC system is considered as a substrate that adsorbs molecules with a high electron affinity. The charge of these molecules as a function of their surface concentration is calculated. It is shown that, in the case of a monolayer coating, the negative surface charge density of molecules in the molecule-graphene monolayer-SiC substrate system is considerably higher than the surface charge density transferring from the SiC substrate to the graphene layer. This suggests that it is possible to neutralize the excess charge in the graphene layer via adsorption of proper particles on the layer.

  13. Micro injector sample delivery system for charged molecules

    DOEpatents

    Davidson, James C. (Livermore, CA); Balch, Joseph W. (Livermore, CA)

    1999-11-09

    A micro injector sample delivery system for charged molecules. The injector is used for collecting and delivering controlled amounts of charged molecule samples for subsequent analysis. The injector delivery system can be scaled to large numbers (>96) for sample delivery to massively parallel high throughput analysis systems. The essence of the injector system is an electric field controllable loading tip including a section of porous material. By applying the appropriate polarity bias potential to the injector tip, charged molecules will migrate into porous material, and by reversing the polarity bias potential the molecules are ejected or forced away from the tip. The invention has application for uptake of charged biological molecules (e.g. proteins, nucleic acids, polymers, etc.) for delivery to analytical systems, and can be used in automated sample delivery systems.

  14. Net Electric Charge on Photopigment Molecules and Frog Retinal Receptor Disk Membrane Structure

    PubMed Central

    Blasie, J. K.

    1972-01-01

    The photopigment molecules in frog retinal receptor disk membranes protude some 50-65% of their molecular diameter (?42 A) into the aqueous surface layer of the disk membrane, depending on whether the photopigment is bleached, while the remainder is embedded in the lipid core of the membrane. In order to determine whether the presumably polar groups covering this surface protruding into the aqueous phase possessed net electric charge, we collected X-ray diffraction data from the photopigment molecules in wet pellets of oriented disk membranes as a function of the pH and ionic strength of the sedimentation medium. The Fourier analysis applied to this data provided average nearest neighbor separations for the photopigment molecules for their planar arrangement in the disk membranes. Changes in the average separation of photopigment molecule nearest neighbors as a function of pH, ionic strength, and photopigment bleaching indicated that photopigment molecules possess negative net electric charge, that this net electric charge occurs in the aqueous surface layer of the disk membrane, and that this net charge is reduced on photopigment bleaching. This polar portion of the photopigment molecule may thereby determine the location of the photopigment molecules relative to the lipid core and other photopigment molecules in the disk membrane. In addition, the orientation (dichroism) of the photopigment relative to an axis normal to the plane of the disk membrane and the bleaching-dependent “sinking” of the photopigment molecule into the lipid core of the disk membrane may be accounted for. PMID:4536691

  15. Relative Amounts of Positive or Negative Charge in Lightning Flashes

    Microsoft Academic Search

    F. J. Anderson; G. D. Freier

    1974-01-01

    A simplified model of the thunderstorm is used to calculate energy changes during the lightning process. The calculations show why considerably more positive charge can be released during a flash and why one might expect only a small fraction of the negative charge to be released in a similar flash. Although Berger [1967] found fewer flashes of lightning bringing positive

  16. Control of charge migration in molecules by ultrashort laser pulses

    E-print Network

    Nikolay V. Golubev; Alexander I. Kuleff

    2015-02-19

    Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme for control of the charge migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and an amine moieties that simple pulses can be used for stopping the charge-migration oscillations and localizing the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.

  17. Control of charge migration in molecules by ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Golubev, Nikolay V.; Kuleff, Alexander I.

    2015-05-01

    Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme to control the charge-migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and amine moieties that simple pulses can be used to stop the charge-migration oscillations and localize the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.

  18. Gram-negative bacterial sensors for eukaryotic signal molecules.

    PubMed

    Lesouhaitier, Olivier; Veron, Wilfried; Chapalain, Annelise; Madi, Amar; Blier, Anne-Sophie; Dagorn, Audrey; Connil, Nathalie; Chevalier, Sylvie; Orange, Nicole; Feuilloley, Marc

    2009-01-01

    Ample evidence exists showing that eukaryotic signal molecules synthesized and released by the host can activate the virulence of opportunistic pathogens. The sensitivity of prokaryotes to host signal molecules requires the presence of bacterial sensors. These prokaryotic sensors, or receptors, have a double function: stereospecific recognition in a complex environment and transduction of the message in order to initiate bacterial physiological modifications. As messengers are generally unable to freely cross the bacterial membrane, they require either the presence of sensors anchored in the membrane or transporters allowing direct recognition inside the bacterial cytoplasm. Since the discovery of quorum sensing, it was established that the production of virulence factors by bacteria is tightly growth-phase regulated. It is now obvious that expression of bacterial virulence is also controlled by detection of the eukaryotic messengers released in the micro-environment as endocrine or neuro-endocrine modulators. In the presence of host physiological stress many eukaryotic factors are released and detected by Gram-negative bacteria which in return rapidly adapt their physiology. For instance, Pseudomonas aeruginosa can bind elements of the host immune system such as interferon-? and dynorphin and then through quorum sensing circuitry enhance its virulence. Escherichia coli sensitivity to the neurohormones of the catecholamines family appears relayed by a recently identified bacterial adrenergic receptor. In the present review, we will describe the mechanisms by which various eukaryotic signal molecules produced by host may activate Gram-negative bacteria virulence. Particular attention will be paid to Pseudomonas, a genus whose representative species, P. aeruginosa, is a common opportunistic pathogen. The discussion will be particularly focused on the pivotal role played by these new types of pathogen sensors from the sensing to the transduction mechanism involved in virulence factors regulation. Finally, we will discuss the consequence of the impact of host signal molecules on commensally or opportunistic pathogens associated with different human tissue. PMID:22399982

  19. Electrostatic plasma lens for focusing negatively charged particle beams

    SciTech Connect

    Goncharov, A. A.; Dobrovolskiy, A. M.; Dunets, S. M. [Institute of Physics NAS of Ukraine, Kiev 03028, Ave. Nauki 46 (Ukraine); Litovko, I. V. [Institute for Nuclear Research NAS of Ukraine, Kiev 03650, pr. Nauki 47 (Ukraine); Gushenets, V. I.; Oks, E. M. [High-Current Electronics Institute SB of RAS, Tomsk (Russian Federation)

    2012-02-15

    We describe the current status of ongoing research and development of the electrostatic plasma lens for focusing and manipulating intense negatively charged particle beams, electrons, and negative ions. The physical principle of this kind of plasma lens is based on magnetic isolation electrons providing creation of a dynamical positive space charge cloud in shortly restricted volume propagating beam. Here, the new results of experimental investigations and computer simulations of wide-aperture, intense electron beam focusing by plasma lens with positive space charge cloud produced due to the cylindrical anode layer accelerator creating a positive ion stream towards an axis system is presented.

  20. Negatively charged liposomes show potent adjuvant activity when simply admixed with protein antigens.

    PubMed

    Yanasarn, Nijaporn; Sloat, Brian R; Cui, Zhengrong

    2011-08-01

    Liposomes have been investigated extensively as a vaccine delivery system. Herein the adjuvant activities of liposomes with different net surface charges (neutral, positive, or negative) were evaluated when admixed with protein antigens, ovalbumin (OVA, pI = 4.7), Bacillus anthracis protective antigen protein (PA, pI = 5.6), or cationized OVA (cOVA). Mice immunized subcutaneously with OVA admixed with different liposomes generated different antibody responses. Interestingly, OVA admixed with net negatively charged liposomes prepared with DOPA was as immunogenic as OVA admixed with positively charged liposomes prepared with DOTAP. Immunization of mice with the anthrax PA protein admixed with the net negatively charged DOPA liposomes also induced a strong and functional anti-PA antibody response. When the cationized OVA was used as a model antigen, liposomes with net neutral, negative, or positive charges showed comparable adjuvant activities. Immunization of mice with the OVA admixed with DOPA liposomes also induced OVA-specific CD8(+) cytotoxic T lymphocyte responses and significantly delayed the growth of OVA-expressing B16-OVA tumors in mice. However, not all net negatively charged liposomes showed a strong adjuvant activity. The adjuvant activity of the negatively charged liposomes may be related to the liposome's ability (i) to upregulate the expression of molecules related to the activation and maturation of antigen-presenting cells and (ii) to slightly facilitate the uptake of the antigens by antigen-presenting cells. Simply admixing certain negatively charged liposomes with certain protein antigens of interest may represent a novel platform for vaccine development. PMID:21615153

  1. Negatively charged liposomes show potent adjuvant activity when simply admixed with protein antigens

    PubMed Central

    Yanasarn, Nijaporn; Sloat, Brian R.; Cui, Zhengrong

    2011-01-01

    Liposomes have been investigated extensively as a vaccine delivery system. Herein the adjuvant activities of liposomes with different net surface charges (neutral, positive, or negative) were evaluated when admixed with protein antigens, ovalbumin (OVA, pI = 4.7), Bacillus anthracis protective antigen protein (PA, pI = 5.6), or cationized OVA (cOVA). Mice immunized subcutaneously with OVA admixed with different liposomes generated different antibody responses. Interestingly, OVA admixed with net negatively charged liposomes prepared with DOPA was as immunogenic as OVA admixed with positively charged liposomes prepared with DOTAP. Immunization of mice with the anthrax PA protein admixed with the net negatively charged DOPA liposomes also induced a strong and functional anti-PA antibody response. When the cationized OVA was used as a model antigen, liposomes with net neutral, negative, or positive charges showed comparable adjuvant activities. Immunization of mice with the OVA admixed with DOPA liposomes also induced OVA-specific CD8+ cytotoxic T lymphocyte responses and significantly delayed the growth of OVA-expressing B16-OVA tumors in mice. However, not all net negatively charged liposomes showed a strong adjuvant activity. The adjuvant activity of the negatively charged liposomes may be related to the liposome’s ability (i) to up-regulate the expression of molecules related to the activation and maturation of antigen-presenting cells and (ii) to slightly facilitate the uptake of the antigens by antigen-presenting cells. Simply admixing certain negatively charged liposomes with certain protein antigens of interest may represent a novel platform for vaccine development. PMID:21615153

  2. Mean field theory of charged dendrimer molecules.

    PubMed

    Lewis, Thomas; Pryamitsyn, Victor; Ganesan, Venkat

    2011-11-28

    Using self-consistent field theory (SCFT), we study the conformational properties of polyelectrolyte dendrimers. We compare results for three different models of charge distributions on the polyelectrolytes: (1) a smeared, quenched charge distribution characteristic of strong polyelectrolytes; (2) a smeared, annealed charge distribution characteristic of weak polyelectrolytes; and (3) an implicit counterion model with Debye-Huckel interactions between the charged groups. Our results indicate that an explicit treatment of counterions is crucial for the accurate characterization of the conformations of polyelectrolyte dendrimers. In comparing the quenched and annealed models of charge distributions, annealed dendrimers were observed to modulate their charges in response to the density of polymer monomers, counterions, and salt ions. Such phenomena is not accommodated within the quenched model of dendrimers and is shown to lead to significant differences between the predictions of quenched and annealed model of dendrimers. In this regard, our results indicate that the average dissociated charge ? inside the dendrimer serves as a useful parameter to map the effects of different parametric conditions and models onto each other. We also present comparisons to the scaling results proposed to explain the behavior of polyelectrolyte dendrimers. Inspired by the trends indicated by our results, we develop a strong segregation theory model whose predictions are shown to be in very good agreement with the numerical SCFT calculations. PMID:22128954

  3. Electrostatic Power Generation from Negatively Charged, Simulated Lunar Regolith

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.; King, Glen C.; Kim, Hyun-Jung; Park, Yeonjoon

    2010-01-01

    Research was conducted to develop an electrostatic power generator for future lunar missions that facilitate the utilization of lunar resources. The lunar surface is known to be negatively charged from the constant bombardment of electrons and protons from the solar wind. The resulting negative electrostatic charge on the dust particles, in the lunar vacuum, causes them to repel each other minimizing the potential. The result is a layer of suspended dust about one meter above the lunar surface. This phenomenon was observed by both Clementine and Surveyor spacecrafts. During the Apollo 17 lunar landing, the charged dust was a major hindrance, as it was attracted to the astronauts' spacesuits, equipment, and the lunar buggies. The dust accumulated on the spacesuits caused reduced visibility for the astronauts, and was unavoidably transported inside the spacecraft where it caused breathing irritation [1]. In the lunar vacuum, the maximum charge on the particles can be extremely high. An article in the journal "Nature", titled "Moon too static for astronauts?" (Feb 2, 2007) estimates that the lunar surface is charged with up to several thousand volts [2]. The electrostatic power generator was devised to alleviate the hazardous effects of negatively charged lunar soil by neutralizing the charged particles through capacitive coupling and thereby simultaneously harnessing power through electric charging [3]. The amount of power generated or collected is dependent on the areal coverage of the device and hovering speed over the lunar soil surface. A thin-film array of capacitors can be continuously charged and sequentially discharged using a time-differentiated trigger discharge process to produce a pulse train of discharge for DC mode output. By controlling the pulse interval, the DC mode power can be modulated for powering devices and equipment. In conjunction with a power storage system, the electrostatic power generator can be a power source for a lunar rover or other systems. The negatively charged lunar soil would also be neutralized mitigating some of the adverse effects resulting from lunar dust.

  4. Maximizing ion current by space-charge neutralization using negative ions and dust particles

    E-print Network

    Maximizing ion current by space-charge neutralization using negative ions and dust particles A. Space-charge neutralization with high-mass negative ions or negatively charged dust particles seems ions. Several space-charge neutralization schemes that employ heavy negatively charged particles

  5. Gating capacitive field-effect sensors by the charge of nanoparticle/molecule hybrids.

    PubMed

    Poghossian, Arshak; Bäcker, Matthias; Mayer, Dirk; Schöning, Michael J

    2015-01-21

    The semiconductor field-effect platform is a powerful tool for chemical and biological sensing with direct electrical readout. In this work, the field-effect capacitive electrolyte-insulator-semiconductor (EIS) structure - the simplest field-effect (bio-)chemical sensor - modified with citrate-capped gold nanoparticles (AuNPs) has been applied for a label-free electrostatic detection of charged molecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in AuNP/molecule inorganic/organic hybrids induced by the molecular adsorption or binding events. The feasibility of the proposed detection scheme has been exemplarily demonstrated by realizing capacitive EIS sensors consisting of an Al-p-Si-SiO2-silane-AuNP structure for the label-free detection of positively charged cytochrome c and poly-d-lysine molecules as well as for monitoring the layer-by-layer formation of polyelectrolyte multilayers of poly(allylamine hydrochloride)/poly(sodium 4-styrene sulfonate), representing typical model examples of detecting small proteins and macromolecules and the consecutive adsorption of positively/negatively charged polyelectrolytes, respectively. For comparison, EIS sensors without AuNPs have been investigated, too. The adsorption of molecules on the surface of AuNPs has been verified via the X-ray photoelectron spectroscopy method. In addition, a theoretical model of the functioning of the capacitive field-effect EIS sensor functionalized with AuNP/charged-molecule hybrids has been discussed. PMID:25470772

  6. Positive/negative ion velocity mapping apparatus for electron-molecule reactions

    SciTech Connect

    Wu Bin; Xia Lei; Li Hongkai; Zeng Xianjin; Tian Shanxi [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2012-01-15

    In molecular dissociative ionization by electron collisions and dissociative electron attachment to molecule, the respective positively and negatively charged fragments are the important products. A compact ion velocity mapping apparatus is developed for the angular distribution measurements of the positive or negative fragments produced in the electron-molecule reactions. This apparatus consists of a pulsed electron gun, a set of ion velocity mapping optic lenses, a two-dimensional position detector including two pieces of micro-channel plates, and a phosphor screen, and a charge-coupled-device camera for data acquisition. The positive and negative ion detections can be simply realized by changing the voltage polarity of ion optics and detector. Velocity sliced images can be directly recorded using a narrow voltage pulse applied on the rear micro-channel plate. The efficient performance of this system is evaluated by measuring the angular distribution of O{sup -} from the electron attachments to NO at 7.3 and 8.3 eV and O{sup +} from the electron collision with CO at 40.0 eV.

  7. Charging of dust particles in a negative ion plasma

    NASA Astrophysics Data System (ADS)

    Merlino, Robert

    Positively charges nanoparticles have been detected during sounding rocket flights in the nighttime polar mesosphere. Simultaneous measurements of the plasma densities indicated the presence of few electrons and significant numbers of heavy negative ions. Model calculations show that dust particles immersed in such a plasma can acquire a positive charge if the relative density of the heavy negative ions is sufficiently large. We have performed laboratory experiments in a Q machine plasma to study the effect of the presence of heavy negative ions on the charging of micron-sized hollow glass microspheres. The plasma consists of singly-charged potassium ions and electrons. SF6 is added to the plasma, which readily attaches electrons to form essentially a positive ion (mass 39 amu)/negative ion (mass 146 amu) plasma. When the relative concentration of the remaining free electrons is reduced to less than 1 part per thousand, conditions are formed which favor the formation of positive dust. Results of Langmuir probe measurements are presented which indicate that the glass microspheres dispersed into this plasma acquire a positive charge.

  8. Increased negatively charged nitrogen-vacancy centers in fluorinated diamond

    SciTech Connect

    Cui, Shanying; Hu, Evelyn L. [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)] [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

    2013-07-29

    We investigated the effect of fluorine-terminated diamond surface on the charged state of shallow nitrogen vacancy defect centers (NVs). Fluorination is achieved with CF{sub 4} plasma, and the surface chemistry is confirmed with x-ray photoemission spectroscopy. Photoluminescence of these ensemble NVs reveals that fluorine-treated surfaces lead to a higher and more stable negatively charged nitrogen vacancy (NV{sup ?}) population than oxygen-terminated surfaces. NV{sup ?} population is estimated by the ratio of negative to neutral charged NV zero-phonon lines. Surface chemistry control of NV{sup ?} density is an important step towards improving the optical and spin properties of NVs for quantum information processing and magnetic sensing.

  9. Charge Transport in Azobenzene-Based Single-Molecule Junctions

    NASA Astrophysics Data System (ADS)

    Garcia-Lekue, Aran; Kim, Youngsang; Sysoiev, Dmytro; Frederiksen, Thomas; Groth, Ulrich; Scheer, Elke

    2013-03-01

    The azobenzene class of molecules has become an archetype of molecular photoswitch research, due to their simple structure and the significant difference of the electronic system between their cis and trans isomers. However, a detailed understanding of the charge transport for the two isomers, when embedded in a junction with electrodes is still lacking. In order to clarify this issue, we investigate charge transport properties through single Azobenzene-ThioMethyl (AzoTM) molecules in a mechanically controlled break junction (MCBJ) system at 4.2 K. Single-molecule conductance, I-V characteristics, and IETS spectra of molecular junctions are measured and compared with first-principles transport calculations. Our studies elucidate the origin of a slightly higher conductance of junctions with cis isomer and demonstrate that IETS spectra of cis and trans forms show distinct vibrational fingerprints that can be used for identifying the isomer.

  10. Single molecule detection using charge-coupled device array technology

    SciTech Connect

    Denton, M.B.

    1992-07-29

    A technique for the detection of single fluorescent chromophores in a flowing stream is under development. This capability is an integral facet of a rapid DNA sequencing scheme currently being developed by Los Alamos National Laboratory. In previous investigations, the detection sensitivity was limited by the background Raman emission from the water solvent. A detection scheme based on a novel mode of operating a Charge-Coupled Device (CCD) is being developed which should greatly enhance the discrimination between fluorescence from a single molecule and the background Raman scattering from the solvent. Register shifts between rows in the CCD are synchronized with the sample flow velocity so that fluorescence from a single molecule is collected in a single moving charge packet occupying an area approaching that of a single pixel while the background is spread evenly among a large number of pixels. Feasibility calculations indicate that single molecule detection should be achieved with an excellent signal-to-noise ratio.

  11. Charge Transport in Azobenzene-Based Single-Molecule Junctions

    NASA Astrophysics Data System (ADS)

    Kim, Youngsang; Garcia-Lekue, Aran; Sysoiev, Dmytro; Frederiksen, Thomas; Groth, Ulrich; Scheer, Elke

    2012-11-01

    Azobenzene-derivative molecules change their conformation as a result of a cis-trans transition when exposed to ultraviolet or visible light irradiation and this is expected to induce a significant variation in the conductance of molecular devices. Despite extensive investigations carried out on this type of molecule, a detailed understanding of the charge transport for the two isomers is still lacking. We report a combined experimental and theoretical analysis of electron transport through azobenzene-derivative single-molecule break junctions with Au electrodes. Current-voltage and inelastic electron tunneling spectroscopy (IETS) measurements performed at 4.2 K are interpreted based on first-principles calculations of electron transmission and IETS spectra. This qualitative study unravels the origin of a slightly higher conductance of junctions with the cis isomer and demonstrates that IETS spectra of cis and trans forms show distinct vibrational fingerprints that can be used for identifying the isomer.

  12. Negative thermal expansion induced by intermetallic charge transfer

    NASA Astrophysics Data System (ADS)

    Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

    2015-06-01

    Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu3Fe4O12 and LaCu3Fe4?xMnxO12, as well as in Bi or Ni substituted BiNiO3. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding ?70 × 10?6 K?1 near room temperature, in the temperature range which can be controlled by substitution.

  13. Charge exchange of a polar molecule at its cation

    SciTech Connect

    Buslov, E. Yu., E-mail: buslov@phys.vsu.ru; Zon, B. A., E-mail: zon@niif.vsu.ru [Voronezh State University (Russian Federation)

    2011-01-15

    The Landau-Herring method is used to derive an analytic expression for the one-electron exchange interaction of a polar molecule with its positively charged ion, induced by a {sigma}-electron. Analogously to the classical Van der Pole method, the exchange interaction potential is averaged over the rotational states of colliding particles. The resonant charge-transfer cross section is calculated, and the effect of the dipole moments of the core on the cross section is analyzed. It is shown that allowance for the dependence of the exchange potential on the orientation of the dipole moments relative to the molecular axis may change the dependence of the cross section on the velocity of colliding particles, which is typical of the resonant charge exchange, from the resonance to the quasi-resonance dependence.

  14. A Charge Pump that Generates Negative High Voltage with Variable Voltage , Eugene Ivanova,

    E-print Network

    Ayers, Joseph

    A Charge Pump that Generates Negative High Voltage with Variable Voltage Gain Jun Zhaob, , Eugene, Massachusetts 02115, U.S.A. Abstract A cross-coupled structure based charge pump that generates negative high. The proposed negative charge pump is designed to deliver 40 uA with a wide supply range from 2.5V to 5.5V using

  15. New stable multiply charged negative atomic ions in linearly polarized superintense laser fields

    E-print Network

    Kais, Sabre

    New stable multiply charged negative atomic ions in linearly polarized superintense laser fields Qi doubly-negatively-charged atomic ion in the gas phase, only one electron can be added to a free atom superintense laser field one can stabilize multiply charged negative atomic ions in the gas phase. We present

  16. Charge Loss in Gas-Phase Multiply Negatively Charged Oligonucleotides Iwona Anusiewicz,,, Joanna Berdys-Kochanska,, Cezary Czaplewski, Monika Sobczyk,,

    E-print Network

    Simons, Jack

    Charge Loss in Gas-Phase Multiply Negatively Charged Oligonucleotides Iwona Anusiewicz,,,§ Joanna. Introduction A. Review of Experimental Findings on Negative Oli- goucleotides. In recent gas-phase experiments1 on small mul- tiply charged single-strand oligonucleotides,2 the Parks group has observed very slow (e

  17. Partial Atomic Charge Derivation of small molecule Partial atomic charge is very crucial for computing physical, chemical and biological

    E-print Network

    Jayaram, Bhyravabotla

    Partial Atomic Charge Derivation of small molecule Partial atomic charge is very crucial for computing physical, chemical and biological properties, and reactivity of molecules. Through the information of the atomic charge in a given species, it is possible to predict the stability, solvation energetics

  18. Negatively charged nanoparticles produced by splashing of water

    NASA Astrophysics Data System (ADS)

    Tammet, H.; Hõrrak, U.; Kulmala, M.

    2009-01-01

    The production of splashing-generated balloelectric intermediate ions was studied by means of mobility spectrometry in the atmosphere during the rain and in a laboratory experiment simulating the heavy rain. The partial neutralization of intermediate ions with cluster ions generated by beta rays suppressed the space charge of intermediate ions but preserved the shape of the mobility distribution. The balloelectric ions produced from the waterworks water of high TDS (Total Dissolved Solids) had about the same mobilities as the ions produced from the rainwater of low TDS. This suggests that the balloelectric ions can be considered as singly charged water nanoparticles. By different measurements, the diameter mode of these particles was 2.2-2.7 nm, which is close to the diameter of 2.5 nm of the Chaplin's 280-molecule magic icosahedron superclusters. The measurements can be explained by a hypothesis that the pressure of saturated vapor over the nanoparticle surface is suppressed by a number of magnitudes due to the internal structure of the particles near the size of 2.5 nm. The records of the concentration bursts of balloelectric ions in the atmosphere are formally similar to the records of the nucleation bursts but they cannot be qualified as nucleation bursts because the particles are not growing but shrinking.

  19. Negatively charged nanoparticles produced by splashing of water

    NASA Astrophysics Data System (ADS)

    Tammet, H.; Hõrrak, U.; Kulmala, M.

    2008-09-01

    The production of splashing-generated balloelectric intermediate ions was studied by means of mobility spectrometry in the atmosphere during the rain and in a laboratory experiment simulating the heavy rain. The partial neutralization of intermediate ions with cluster ions generated by beta rays suppressed the space charge of intermediate ions but preserved the shape of the mobility distribution. The balloelectric ions produced from the waterworks water of high TDS (Total Dissolved Solids) had about the same mobilities as the ions produced from the rainwater of low TDS. This suggests that the balloelectric ions can be considered as singly charged water nanodroplets. By different measurements, the diameter mode of these droplets was 2.2 2.7 nm, which is close to the diameter of 2.5 nm of the Chaplin's 280-molecule magic icosahedron superclusters. The measurements can be explained by a hypothesis that the pressure of saturated vapor over the nanodroplet surface is suppressed by a number of magnitudes due to the internal structure of the droplets near the size of 2.5 nm. The records of the concentration bursts of balloelectric ions in the atmosphere are formally similar to the records of the nucleation bursts but they cannot be qualified as nucleation bursts because the particles are not growing but shrinking.

  20. Thermodynamic Evidence for Negative Charge Stabilization by a Catalytic Metal Ion within an RNA Active Site

    E-print Network

    Herschlag, Dan

    Thermodynamic Evidence for Negative Charge Stabilization by a Catalytic Metal Ion within an RNA models generally hinge upon the assumption that the metal ions stabilize negative charge buildup along evidence that this metal ion interaction facilitates the forward reaction by stabilization of negative

  1. Forces Between Protein Molecules in Solution Arising from Fluctuations in Proton Charge and Configuration

    E-print Network

    Forces Between Protein Molecules in Solution Arising from Fluctuations in Proton Charge AND SHUMAKER 863 FORCES BETWEEN PROTEIN MOLECULES IN SOLUTION ARISING FROM FLUCTUATIONS IN PROTON CHARGE, NEW HAVEN, CONNECTICUT Communicated July 23, 1952 The forces between protein molecules in solution

  2. Heparosan based negatively charged nanocarrier for rapid intracellular drug delivery.

    PubMed

    Chen, Jing-Xiao; Liu, Wen; Zhang, Miao; Chen, Jing-Hua

    2014-10-01

    In this study, a heparosan-DOX conjugate (HDC) was designed and prepared by covalently linking heparosan with anticancer drug doxorubicin (DOX) via "Schiff" base. Due to the amphiphilic nature, the HDC could self-assemble into nanoparticles in aqueous solution of pH 7.4. In spite of the surface charge of HDC nanoparticles was negative, HDC could achieve intracellular delivery of DOX efficiently. Cellular uptake study revealed the endocytosis pathway of heparosan based nanocarrier includes clathrin-mediated endocytosis and macropinocytosis, and the process of endocytosis is energy dependent. This meant the HDC would reach endosomes and behave pH-sensitive DOX release profile due to the inherent property of "Schiff" base. The cytotoxicity assay and flow cytometry analysis demonstrated the cellular uptake of HDC was faster than that of free DOX, showing improved efficacy within short co-incubation period. Furthermore, the HDC nanoparticles were stable in culture medium containing 10% FBS, indicating promising application for drug delivery. PMID:25089505

  3. Negatively charged polymers protect antinuclear antibody against inactivation by acylating agents.

    PubMed

    Samokhin, G P; Mongayt, D A; Iakoubov, L Z; Levchenko, T S; Torchilin, V P

    2001-05-15

    For many practical applications, monoclonal antibodies must be chemically modified without any significant loss in their immunoreactivity. In some situations, however, the amino acid residue crucial for antibody activity may be highly reactive toward the modifying agent, which results in antibody inactivation. The method to prevent inactivation of a modification-sensitive antinuclear monoclonal antibody by acylating agents was developed. The method is based on the hypothesis that a highly reactive amino group exists within, or in the vicinity of, the binding site of the antibody, providing crucial interaction with negatively charged moieties of DNA. It has been shown that negatively charged polymers, such as dextran sulfate or heparin, may provide temporary protection, presumably interacting noncovalently with this amino group and thus masking it. The protecting molecule can be removed later by chromatography on a protein A column, thus regenerating modified but not inactivated antibody in the free form for use in subsequent applications. In particular, we have modified antibody 2C5 with a chelating agent, diethylenetriaminepentaacetic acid (DTPA) without the loss of activity. Modified antibody was labeled with radioactive isotope, (111)In, via chelation by antibody-attached DTPA. The labeled antibody was shown to demonstrate the same specificity of binding to nucleosomes as the nonmodified antibody, so it may be used in immunoscintigraphy or biodistribution studies. The method might be useful for the modification of other modification-sensitive antibodies with other acylating chemicals, such as crosslinking agents or biotin derivatives. PMID:11355857

  4. Negative differential conductance and super-Poissonian shot noise in single-molecule magnet junctions

    PubMed Central

    Xue, Hai-Bin; Liang, Jiu-Qing; Liu, Wu-Ming

    2015-01-01

    Molecular spintroinic device based on a single-molecule magnet is one of the ultimate goals of semiconductor nanofabrication technologies. It is thus necessary to understand the electron transport properties of a single-molecule magnet junction. Here we study the negative differential conductance and super-Poissonian shot noise properties of electron transport through a single-molecule magnet weakly coupled to two electrodes with either one or both of them being ferromagnetic. We predict that the negative differential conductance and super-Poissonian shot noise, which can be tuned by a gate voltage, depend sensitively on the spin polarization of the source and drain electrodes. In particular, the shot noise in the negative differential conductance region can be enhanced or decreased originating from the different formation mechanisms of negative differential conductance. The effective competition between fast and slow transport channels is responsible for the observed negative differential conductance and super-Poissonian shot noise. In addition, we further discuss the skewness and kurtosis properties of transport current in the super-Poissonian shot noise regions. Our findings suggest a tunable negative differential conductance molecular device, and the predicted properties of high-order current cumulants are very interesting for a better understanding of electron transport through single-molecule magnet junctions. PMID:25736094

  5. The meteorology of negative cloud-to-ground lightning strokes with large charge moment changes: Implications

    E-print Network

    Cummer, Steven A.

    The meteorology of negative cloud-to-ground lightning strokes with large charge moment changes. [1] This study examined the meteorological characteristics of precipitation systems that produced 38, and W. A. Lyons (2013), The meteorology of negative cloud-to- ground lightning strokes with large charge

  6. Adsorbed anthranilic acid molecules cause charge reversal of nonionic micelles.

    PubMed

    Verma, Gunjan; Aswal, V K; Kulshreshtha, S K; Hassan, P A; Kaler, Eric W

    2008-02-01

    The effect of anthranilic acid, an aromatic amino acid, on the structural characteristics of nonionic micelles of Triton X-100 at different pH values was investigated by light scattering and small-angle neutron scattering (SANS) measurements. The scattered light intensity decreases as pH is increased or decreased on either side of the isoelectric point (IEP = 3.4) of the amino acid. Analysis of the SANS data using a sticky hard-sphere model shows that the micelles are oblate ellipsoids with an axial ratio of approximately 2.3. No significant change could be observed in the size of the micelles with a change in the pH, while the stickiness parameter (tau), which is related to the interaction potential (u(0)) increases on either side of the IEP. As tau increases, u(o) becomes less negative, indicating a decrease in the attractive interaction between nonionic micelles. This can be explained in terms of the changes in the surface charge of the micelles resulting from a shift in the acid-base equilibrium of the adsorbed amino acid. The variation of the intermicellar interaction as calculated from the stickiness parameter is consistent with the picture of reversal of charge of amino acids with pH. This is further supported by the observed variation of the cloud point of the solutions at different pH values. The change in the interparticle interaction is also reflected in the diffusion coefficient of the micelles measured by dynamic light scattering. PMID:18186653

  7. Net negative charge in low-temperature SiO 2 gate dielectric layers

    Microsoft Academic Search

    A. Boogaard; A. Y. Kovalgin; R. A. M. Wolters

    2009-01-01

    SiO2 gate dielectric layers (4–60nm) were grown (0.6nm\\/min) by plasma-enhanced chemical vapor deposition (PECVD) in strongly diluted silane plasmas at low substrate temperatures. In contrast to the well-accepted positive charge for thermally grown silicon dioxide, the net oxide charge was negative and a function of layer thickness. Our experiments suggested that the negative charge was created due to unavoidable oxidation

  8. A new method for enhancing the production of the negatively charged helium dimer He 2-

    NASA Astrophysics Data System (ADS)

    Søgaard, J.; Hazell, I.; Bjerre, N.; Andersen, T.

    1995-08-01

    The production of the negatively charged helium dimer He 2- can be enhanced by nearly an order of magnitude by utilizing laser excited alkali metal as charge-exchange material for fast He 2+ ions. The enhancement can be attributed to both steps in the charge-exchange reactions converting He 2+ via He 2 (a 3?u+) to He 2-( 4? g) .

  9. PRODUCTION OF NEGATIVE HEAVY ION BEAMS BY CHARGE EXCHANGE IN METAL VAPOUR

    E-print Network

    Paris-Sud XI, Université de

    1471 PRODUCTION OF NEGATIVE HEAVY ION BEAMS BY CHARGE EXCHANGE IN METAL VAPOUR J. HEINEMEIER and P and acceleration of negative heavy ion beams in a tandem accelerator. 03BCA intensities of 20 keV beams.of Li-, Be-separator sources. We found that this is the case even for a number of negative ions (Li-, Bé , B-, Na-, AI-, Câ

  10. Ion beam driven ion-acoustic waves in a plasma cylinder with negatively charged dust grains

    NASA Astrophysics Data System (ADS)

    Sharma, Suresh C.; Sharma, Kavita; Walia, Ritu

    2012-07-01

    An ion beam propagating through a magnetized potassium plasma cylinder having negatively charged dust grains drives electrostatic ion-acoustic waves to instability via Cerenkov interaction. The phase velocity of sound wave increases with the relative density of negatively charged dust grains. The unstable wave frequencies and the growth rate increase, with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales as one-third power of the beam density. The real part of frequency of the unstable mode increases with the beam energy and scales as almost the one-half power of the beam energy.

  11. Ion beam driven ion-acoustic waves in a plasma cylinder with negatively charged dust grains

    SciTech Connect

    Sharma, Suresh C.; Walia, Ritu [Department of Physics, Maharaja Agrasen Institute of Technology, PSP Area Plot No.-1, Sector-22, Rohini, Delhi 110 086 (India); Sharma, Kavita [Department of Physics, Bhagwan Parshuram Institute of Technology, Sector-17, Rohini, New Delhi 110 089 (India)

    2012-07-15

    An ion beam propagating through a magnetized potassium plasma cylinder having negatively charged dust grains drives electrostatic ion-acoustic waves to instability via Cerenkov interaction. The phase velocity of sound wave increases with the relative density of negatively charged dust grains. The unstable wave frequencies and the growth rate increase, with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales as one-third power of the beam density. The real part of frequency of the unstable mode increases with the beam energy and scales as almost the one-half power of the beam energy.

  12. Aberration of a negative ion beam caused by space charge effect

    SciTech Connect

    Miyamoto, K. [Naruto University of Education, 748 Nakashima, Takashima, Naruto-cho, Naruto-shi, Tokushima 772-8502 (Japan); Wada, S.; Hatayama, A. [Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)

    2010-02-15

    Aberrations are inevitable when the charged particle beams are extracted, accelerated, transmitted, and focused with electrostatic and magnetic fields. In this study, we investigate the aberration of a negative ion accelerator for a neutral beam injector theoretically, especially the spherical aberration caused by the negative ion beam expansion due to the space charge effect. The negative ion current density profiles with the spherical aberration are compared with those without the spherical aberration. It is found that the negative ion current density profiles in a log scale are tailed due to the spherical aberration.

  13. Surfactin-Triggered Small Vesicle Formation of Negatively Charged Membranes: A Novel Membrane-Lysis Mechanism

    PubMed Central

    Buchoux, Sébastien; Lai-Kee-Him, Joséphine; Garnier, Marie; Tsan, Pascale; Besson, Françoise; Brisson, Alain; Dufourc, Erick J.

    2008-01-01

    The molecular mode of action of the lipopeptide SF with zwitterionic and negatively charged model membranes has been investigated with solid-state NMR, light scattering, and electron microscopy. It has been found that this acidic lipopeptide (negatively charged) induces a strong destabilization of negatively charged micrometer-scale liposomes, leading to the formation of small unilamellar vesicles of a few 10s of nanometers. This transformation is detected for very low doses of SF (Ri = 200) and is complete for Ri = 50. The phenomenon has been observed for several membrane mixtures containing phosphatidylglycerol or phosphatidylserine. The vesicularization is not observed when the lipid negative charges are neutralized and a cholesterol-like effect is then evidenced, i.e., increase of gel membrane dynamics and decrease of fluid membrane microfluidity. The mechanism for small vesicle formation thus appears to be linked to severe changes in membrane curvature and could be described by a two-step action: 1), peptide insertion into membranes because of favorable van der Waals forces between the rather rigid cyclic and lipophilic part of SF and lipid chains and 2), electrostatic repulsion between like charges borne by lipid headgroups and the negatively charged SF amino acids. This might provide the basis for a novel mode of action of negatively charged lipopeptides. PMID:18515378

  14. An electrochemical model of the transport of charged molecules through the capillary glycocalyx.

    PubMed Central

    Stace, T M; Damiano, E R

    2001-01-01

    An electrochemical theory of the glycocalyx surface layer on capillary endothelial cells is developed as a model to study the electrochemical dynamics of anionic molecular transport within capillaries. Combining a constitutive relationship for electrochemical transport, derived from Fick's and Ohm's laws, with the conservation of mass and Gauss's law from electrostatics, a system of three nonlinear, coupled, second-order, partial, integro-differential equations is obtained for the concentrations of the diffusing anionic molecules and the cations and anions in the blood. With the exception of small departures from electroneutrality that arise locally near the apical region of the glycocalyx, the model assumes that cations in the blood counterbalance the fixed negative charges bound to the macromolecular matrix of the glycocalyx in equilibrium. In the presence of anionic molecular tracers injected into the capillary lumen, the model predicts the size- and charge-dependent electrophoretic mobility of ions and tracers within the layer. In particular, the model predicts that anionic molecules are excluded from the glycocalyx at equilibrium and that the extent of this exclusion, which increases with increasing tracer and/or glycocalyx electronegativity, is a fundamental determinant of anionic molecular transport through the layer. The model equations were integrated numerically using a Crank-Nicolson finite-difference scheme and Newton-Raphson iteration. When the concentration of the anionic molecular tracer is small compared with the concentration of ions in the blood, a linearized version of the model can be obtained and solved as an eigenvalue problem. The results of the linear and nonlinear models were found to be in good agreement for this physiologically important case. Furthermore, if the fixed-charge density of the glycocalyx is of the order of the concentration of ions in the blood, or larger, or if the magnitude of the anionic molecular valence is large, a closed-form asymptotic solution for the diffusion time can be obtained from the eigenvalue problem that compares favorably with the numerical solution. In either case, if leakage of anionic molecules out of the capillary occurs, diffusion time is seen to vary exponentially with anionic valence and in inverse proportion to the steady-state anionic tracer concentration in the layer relative to the lumen. These findings suggest several methods for obtaining an estimate of the glycocalyx fixed-charge density in vivo. PMID:11259282

  15. Calculating Henry?s Constants of Charged Molecules Using SPARC

    EPA Science Inventory

    SPARC Performs Automated Reasoning in Chemistry is a computer program designed to model physical and chemical properties of molecules solely based on thier chemical structure. SPARC uses a toolbox of mechanistic perturbation models to model intermolecular interactions. SPARC has ...

  16. Charge Density and Correlation Study of Atoms and Molecules by High-Energy Electron Scattering

    Microsoft Academic Search

    Yuheng Zhang

    1989-01-01

    Energy resolved differential scattering cross sections of high energy electrons and small molecules were measured during the course of this study. The coherent X-ray scattering form factors, which can be derived from the electron scattering experiments, are directly related to the charge density distributions of the target molecules. The difference between the data and the calculations based on the independent

  17. Forth-back oscillated charge carrier motion in dynamically disordered hexathienocoronene molecules: a theoretical study.

    PubMed

    Navamani, K; Senthilkumar, K

    2015-07-21

    Electronic structure calculations were performed to investigate the charge transport properties of hexathienocoronene (HTC) based molecules. The effective displacement of the charge carrier along the ?-orbital of nearby molecules is calculated by monitoring the forth and back oscillations of the charge carrier through kinetic Monte Carlo simulation. The charge transport parameters such as charge transfer rate, mobility, hopping conductivity, localized charge density, time average effective mass and degeneracy pressure are calculated and used to study the charge transport mechanism in the studied molecules. The existence of degeneracy levels facilitates the charge transfer and is analyzed through degeneracy pressure. Theoretical results show that the site energy difference in the dynamically disordered system controls the forth-back oscillation of charge carrier and facilitates the unidirectional charge transport mechanism along the sequential localized sites. The ethyl substituted HTC has good hole and electron hopping conductivity of 415 and 894 S cm(-1), respectively, whereas unsubstituted HTC has the small hole mobility of 0.06 cm(2) V(-1) s(-1) which is due to large average effective mass of 1.42 × 10(-28) kg. PMID:26080732

  18. Energy distribution extraction of negative charges responsible for positive bias temperature instability

    NASA Astrophysics Data System (ADS)

    Ren, Shang-Qing; Yang, Hong; Wang, Wen-Wu; Tang, Bo; Tang, Zhao-Yun; Wang, Xiao-Lei; Xu, Hao; Luo, Wei-Chun; Zhao, Chao; Yan, Jiang; Chen, Da-Peng; Ye, Tian-Chun

    2015-07-01

    A new method is proposed to extract the energy distribution of negative charges, which results from electron trapping by traps in the gate stack of nMOSFET during positive bias temperature instability (PBTI) stress based on the recovery measurement. In our case, the extracted energy distribution of negative charges shows an obvious dependence on energy, and the energy level of the largest energy density of negative charges is 0.01 eV above the conduction band of silicon. The charge energy distribution below that energy level shows strong dependence on the stress voltage. Project supported by the National Science & Technology Major Projects of the Ministry of Science and Technology of China (Grant No. 2009ZX02035) and the National Natural Science Foundation of China (Grant Nos. 61176091 and 61306129).

  19. Polarized Protein-Specific Charges from Atoms-in-Molecule Electron Density Partitioning

    PubMed Central

    2013-01-01

    Atomic partial charges for use in traditional force fields for biomolecular simulation are often fit to the electrostatic potentials of small molecules and, hence, neglect large-scale electronic polarization. On the other hand, recent advances in atoms-in-molecule charge derivation schemes show promise for use in flexible force fields but are limited in size by the underlying quantum mechanical calculation of the electron density. Here, we implement the density derived electrostatic and chemical charges method in the linear-scaling density functional theory code ONETEP. Our implementation allows the straightforward derivation of partial atomic charges for systems comprising thousands of atoms, including entire proteins. We demonstrate that the derived charges are chemically intuitive, reproduce ab initio electrostatic potentials of proteins and are transferable between closely related systems. Simulated NMR data derived from molecular dynamics of three proteins using force fields based on the ONETEP charges are in good agreement with experiment. PMID:23894231

  20. Interactions of PAMAM dendrimers with negatively charged model biomembranes.

    PubMed

    Yanez Arteta, Marianna; Ainalem, Marie-Louise; Porcar, Lionel; Martel, Anne; Coker, Helena; Lundberg, Dan; Chang, Debby P; Soltwedel, Olaf; Barker, Robert; Nylander, Tommy

    2014-11-13

    We have investigated the interactions between cationic poly(amidoamine) (PAMAM) dendrimers of generation 4 (G4), a potential gene transfection vector, with net-anionic model biomembranes composed of different ratios of zwitterionic phosphocholine (PC) and anionic phospho-L-serine (PS) phospholipids. Two types of model membranes were used: solid-supported bilayers, prepared with lipids carrying palmitoyl-oleoyl (PO) and diphytanoyl (DPh) acyl chains, and free-standing bilayers, formed at the interface between two aqueous droplets in oil (droplet interface bilayers, DIBs) using the DPh-based lipids. G4 dendrimers were found to translocate through POPC:POPS bilayers deposited on silica surfaces. The charge density of the bilayer affects translocation, which is reduced when the ionic strength increases. This shows that the dendrimer-bilayer interactions are largely controlled by their electrostatic attraction. The structure of the solid-supported bilayers remains intact upon translocation of the dendrimer. However, the amount of lipids in the bilayer decreases and dendrimer/lipid aggregates are formed in bulk solution, which can be deposited on the interfacial layers upon dilution of the system with dendrimer-free solvent. Electrophysiology measurements on DIBs confirm that G4 dendrimers cross the lipid membranes containing PS, which then become more permeable to ions. The obtained results have implications for PAMAM dendrimers as delivery vehicles to cells. PMID:25310456

  1. Periodic Charging of Individual Molecules Coupled to the Motion of an Atomic Force Microscopy Tip.

    PubMed

    Koci?, N; Weiderer, P; Keller, S; Decurtins, S; Liu, S-X; Repp, J

    2015-07-01

    Individual molecules at the edges of self-assembled islands grown on Ag(111) can be deliberately switched in their charge state with the electric field from a scanning-probe tip. Close to the threshold voltage for a charge state transition, periodic switching of the charge is directly driven by the cantilever motion in frequency-modulated atomic force microscopy (AFM), as can be deduced from the signature in the measured frequency shift. In this regime, the integrated frequency shift yields the tip-sample force that is due to a single additional electron. Further, the signature of the dynamic charging response provides information on the electronic coupling of the molecule to the substrate. In analogy to previous experiments on quantum dots, this may also be used in the future to access excited state properties of single molecules from AFM experiments. PMID:26039575

  2. Water freezes differently on positively and negatively charged surfaces of pyroelectric materials.

    PubMed

    Ehre, David; Lavert, Etay; Lahav, Meir; Lubomirsky, Igor

    2010-02-01

    Although ice melts and water freezes under equilibrium conditions at 0 degrees C, water can be supercooled under homogeneous conditions in a clean environment down to -40 degrees C without freezing. The influence of the electric field on the freezing temperature of supercooled water (electrofreezing) is of topical importance in the living and inanimate worlds. We report that positively charged surfaces of pyroelectric LiTaO3 crystals and SrTiO3 thin films promote ice nucleation, whereas the same surfaces when negatively charged reduce the freezing temperature. Accordingly, droplets of water cooled down on a negatively charged LiTaO3 surface and remaining liquid at -11 degrees C freeze immediately when this surface is heated to -8 degrees C, as a result of the replacement of the negative surface charge by a positive one. Furthermore, powder x-ray diffraction studies demonstrated that the freezing on the positively charged surface starts at the solid/water interface, whereas on a negatively charged surface, ice nucleation starts at the air/water interface. PMID:20133568

  3. Dust acoustic solitary wave with variable dust charge: Role of negative ions

    SciTech Connect

    Ghosh, Samiran [Government College of Engineering and Textile Technology, 4, Cantonment Road, Berhampore, Murshidabad 742101 West Bengal (India)

    2005-09-15

    The role of negative ions on small but finite amplitude dust acoustic solitary wave including the effects of high and low charging rates of dust grains compared to the dust oscillation frequency in electronegative dusty plasma is investigated. In the case of high charging rate, the solitary wave is governed by Korteweg-de Vries (KdV) equation, but in the case of low charging rate, it is governed by KdV equation with a linear damping term. Numerical investigations reveal that in both cases dust acoustic soliton sharpens (flatens) and soliton width decreases (increases) with the increase of negative-ion number density (temperature). Also, the negative ions reduce the damping rate.

  4. Cell proliferation and cell sheet detachment from the positively and negatively charged nanocomposite hydrogels.

    PubMed

    Liu, Dan; Wang, Tao; Liu, Xinxing; Tong, Zhen

    2014-01-01

    The charged nanocomposite hydrogels (NC gels) were synthesized by copolymerization of positively or negatively chargeable monomer with N-isopropylacrylamide (NIPAm) in the aqueous suspension of hectorite clay. The ionic NC gels preserved the thermo-responsibility with the phase-transition temperature below 37°C. The L929 cell proliferation was sensitive to charge polarity and charge density. As compared to the PNIPAm NC gel, the cationic NC gels with <5?mol % of 2-(dimethylamino)ethyl methacrylate (DMAEMA) showed improved cell proliferation, whereas the cells grew slowly on the gels with negatively charged 2-acrylamido-2-methylpropane sulfonic acid (AMPSNa). By lowering temperature, rapid cell sheet detachment was observed from the surface of ionic NC gels with 1?mol % of ionizable monomers. However, lager amount of AMPSNa or DMAEMA did not support rapid cell sheet detachment, probably owing to the adverse swelling effects and/or enhanced electrostatic attraction. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 58-65, 2014. PMID:23640767

  5. Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He*– and He2*–

    PubMed Central

    2014-01-01

    Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium. PMID:25068008

  6. Increasing the Space Charge Limit and Other Effects of Cesium Seeding in Hydrogen Negative Ion Sources

    SciTech Connect

    Bacal, M.; Bruneteau, J.; Raridon, R.J.; Whealton, J.H.

    1999-09-06

    The role of cesium seeding in increasing the negative ion current in volume sources is described. By a reduction in the local plasma potential the current of extracted electrons is vastly reduced. As a result, cesium increases the fraction of the transverse space charge limit available to the ions by as much as a factor of three. In addition, cesium can increase the total space charge limit by injection of Cs+ into the presheath-a newly recognized phenomenon consistent with experimental measurements and determined from application of a Double-Vlasov model for negative ion extraction.

  7. Bionic design for surface optimization combining hydrophilic and negative charged biological macromolecules.

    PubMed

    Ran, Fen; Song, Haiming; Niu, Xiaoqin; Yang, Aimei; Nie, Shengqiang; Wang, Lingren; Li, Jie; Sun, Shudong; Zhao, Changsheng

    2014-06-01

    While polyethersulfone (PES) membrane represents a promising option for blood purification, the blood compatibility must be dramatically enhanced to meet today's ever-increasing demands for many emerging application. In this study, we report a bionic design for optimization and development of a modified PES membrane combining hydrophilic and negative charged biological macromolecules on its surface. The hydrophilic and ionic charged biological macromolecules sulfonated poly(styrene)-b-poly(methyl methacrylate)-b-poly-(styrene) (PSSMSS) and poly(vinyl pyrrolidone)-b-poly(methyl methacrylate)-b-poly-(vinyl pyrrolidone) were synthesized via reversible addition-fragmentation chain transfer polymerization and used together to modify PES membranes by blending method. A hydrophilic membrane surface with negative charged surface coating was obtained, imitating the hydrophilic and negatively charged structure feature of heparin. The modified PES membranes showed suppressed platelet adhesion, and a prolonged blood clotting time, and thereby improved blood compatibility. In addition, the blood clotting time of the modified membranes increased with the blended PSSMSS amounts increment, indicating that both the hydrophilic and negative charged groups play important roles in improving the blood compatibility of PES membranes. PMID:24680810

  8. Calcium-dependent binding of uteroglobin (PCB-BP\\/CCSP) to negatively charged phospholipid liposomes

    Microsoft Academic Search

    Magnus Nord; Jan-Åke Gustafsson; Johan Lund

    1995-01-01

    To investigate interactions between the polychlorinated biphenyl-binding protein uteroglobin and phospholipids, we used a liposome-pelletting assay. PCB-BP\\/uteroglobin bound to liposomes made from negatively charged phospholipids (PtdSer and PtdIns) in the presence of 5 mM calcium. No binding to liposomes made from phospholipids without net charge (PtdChol and PtdEtn) was observed, nor could we detect binding in the absence of calcium

  9. Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer

    Microsoft Academic Search

    Masaki Azuma; Wei-Tin Chen; Hayato Seki; Michal Czapski; Smirnova Olga; Kengo Oka; Masaichiro Mizumaki; Tetsu Watanuki; Naoki Ishimatsu; Naomi Kawamura; Shintaro Ishiwata; Matthew G. Tucker; Yuichi Shimakawa; J. Paul Attfield

    2011-01-01

    The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion <-10-4 K-1 over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO3 shows a 2.6% volume reduction

  10. Space Charge Compensation in the Linac4 Low Energy Beam Transport Line with Negative Hydrogen Ions

    E-print Network

    Valerio-Lizarraga, C; Leon-Monzon, I; Lettry, J; Midttun, O; Scrivens, R

    2014-01-01

    The space charge effect of low energy, unbunched ion beams can be compensated by the trapping of ions or electrons into the beam potential. This has been studied for the 45 keV negative hydrogen ion beam in the CERN Linac4 Low Energy Beam Tranport (LEBT) using the package IBSimu1, which allows the space charge calculation of the particle trajectories. The results of the beam simulations will be compared to emittance measurements of an H- beam at the CERN Linac4 3 MeV test stand, where the injection of hydrogen gas directly into the beam transport region has been used to modify the space charge compensation degree.

  11. Gas-phase ion-molecule reactions of doubly charged fullerenes with oxygen

    Microsoft Academic Search

    James J. Stry; James F. Garvey

    1993-01-01

    The gas-phase ion-molecule chemistry of doubly charged fullerene cations (C[sub n][sup 2+] where n = 46, 48, ..., 60 and 70) with neutral oxygen molecules were investigated using a triple quadrupole mass spectrometer. In this paper, we report additions to the fullerene cage structure which result in the formation of C[sub n]O[sup 2+], C[sub n]O[sub 2][sup 2+], and C[sub n]O[sub

  12. Terminal Supraparticle Assemblies from Similarly Charged Protein Molecules and Nanoparticles

    PubMed Central

    Park, Jai Il; Nguyen, Trung Dac; de Queirós Silveira, Gleiciani; Bahng, Joong Hwan; Srivastava, Sudhanshu; Sun, Kai; Zhao, Gongpu; Zhang, Peijun; Glotzer, Sharon C.; Kotov, Nicholas A.

    2015-01-01

    Self-assembly of proteins and inorganic nanoparticles into terminal assemblies makes possible a large family of uniformly sized hybrid colloids. These particles can be compared in terms of utility, versatility and multifunctionality to other known types of terminal assemblies. They are simple to make and offer theoretical tools for designing their structure and function. To demonstrate such assemblies, we combine cadmium telluride nanoparticles with cytochrome C protein and observe spontaneous formation of spherical supraparticles with a narrow size distribution. Such self-limiting behaviour originates from the competition between electrostatic repulsion and non-covalent attractive interactions. Experimental variation of supraparticle diameters for several assembly conditions matches predictions obtained in simulations. Similar to micelles, supraparticles can incorporate other biological components as exemplified by incorporation of nitrate reductase. Tight packing of nanoscale components enables effective charge and exciton transport in supraparticles as demonstrated by enzymatic nitrate reduction initiated by light absorption in the nanoparticle. PMID:24845400

  13. Terminal supraparticle assemblies from similarly charged protein molecules and nanoparticles

    NASA Astrophysics Data System (ADS)

    Park, Jai Il; Nguyen, Trung Dac; de Queirós Silveira, Gleiciani; Bahng, Joong Hwan; Srivastava, Sudhanshu; Zhao, Gongpu; Sun, Kai; Zhang, Peijun; Glotzer, Sharon C.; Kotov, Nicholas A.

    2014-05-01

    Self-assembly of proteins and inorganic nanoparticles into terminal assemblies makes possible a large family of uniformly sized hybrid colloids. These particles can be compared in terms of utility, versatility and multifunctionality to other known types of terminal assemblies. They are simple to make and offer theoretical tools for designing their structure and function. To demonstrate such assemblies, we combine cadmium telluride nanoparticles with cytochrome C protein and observe spontaneous formation of spherical supraparticles with a narrow size distribution. Such self-limiting behaviour originates from the competition between electrostatic repulsion and non-covalent attractive interactions. Experimental variation of supraparticle diameters for several assembly conditions matches predictions obtained in simulations. Similar to micelles, supraparticles can incorporate other biological components as exemplified by incorporation of nitrate reductase. Tight packing of nanoscale components enables effective charge and exciton transport in supraparticles and bionic combination of properties as demonstrated by enzymatic nitrate reduction initiated by light absorption in the nanoparticle.

  14. Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes

    NASA Astrophysics Data System (ADS)

    Dell, Emma J.; Capozzi, Brian; Xia, Jianlong; Venkataraman, Latha; Campos, Luis M.

    2015-03-01

    To develop advanced materials for electronic devices, it is of utmost importance to design organic building blocks with tunable functionality and to study their properties at the molecular level. For organic electronic and photovoltaic applications, the ability to vary the nature of charge carriers and so create either electron donors or acceptors is critical. Here we demonstrate that charge carriers in single-molecule junctions can be tuned within a family of molecules that contain electron-deficient thiophene-1,1-dioxide (TDO) building blocks. Oligomers of TDO were designed to increase electron affinity and maintain delocalized frontier orbitals while significantly decreasing the transport gap. Through thermopower measurements we show that the dominant charge carriers change from holes to electrons as the number of TDO units is increased. This results in a unique system in which the charge carrier depends on the backbone length, and provides a new means to tune p- and n-type transport in organic materials.

  15. Dust negative ion acoustic shock waves in a dusty multi-ion plasma with positive dust charging current

    Microsoft Academic Search

    S. S. Duha

    2009-01-01

    Recent analysis of Mamun et al. [ Phys. Lett. A 373, 2355 (2009)], who considered electrons, light positive ions, heavy negative ions, and extremely massive (few micron size) charge fluctuating dust, has been extended by positive dust charging current, i.e., considering the charging currents for positively charged dust grains. A dusty multi-ion plasma system consisting of electrons, light positive ions,

  16. Negative dispersion of birefringence of smectic liquid crystal-polymer composite: dependence on the constituent molecules and temperature.

    PubMed

    Yang, Seungbin; Lee, Hyojin; Lee, Ji-Hoon

    2015-02-01

    We investigated the dependence of the negative dispersion of birefringence of smectic liquid crystal-polymer composites on the constituent molecules and temperature. The dispersion of birefringence was significantly varied from positive dispersion to negative dispersion by the change of the relative fraction of the constituent monomers. For the temperature dependence of the dispersion, a composite with more fraction of monomers located at the inter-layer space showed a wider temperature range of the negative dispersion of birefringence. PMID:25836114

  17. Cytochrome c decelerates channel kinetics of negatively charged gramicidin due to electrostatic interaction

    Microsoft Academic Search

    Tatiana I. Rokitskaya; Elena A. Kotova; Yuri N. Antonenko

    2003-01-01

    The effect of cytochrome c on the kinetic properties of ion channels formed by O-pyromellitylgramicidin (OPg), the negatively charged analogue of gramicidin A (gA), in bilayer lipid membranes was studied by the method of sensitized photoinactivation. The addition of cytochrome c to both sides of the membrane caused substantial deceleration of the photoinactivation kinetics of OPg channels which expose three

  18. Bound state properties and photodetachment of the negatively charged hydrogen ions

    NASA Astrophysics Data System (ADS)

    Frolov, Alexei M.

    2015-05-01

    Absorption of infrared and visible radiation from stellar emission spectra by the negatively charged hydrogen ions H- is considered. The explicit formula for the photodetachment cross-section of the negatively charged hydrogen ion(s) is derived. Photodetachemnt cross-sections of the {?}H-, {3}H- (or T-), {2}H- (or D-) and {1}H- ions are determined to high accuracy and for a large number of photo-electron momenta/energies. We introduce criteria which can be used to evaluate the overall quality of highly accurate wave functions of the hydrogen ion(s). One of these criteria is based on highly accurate calculations of the lowest order QED corrections in the negatively charged hydrogen ions, including {1}H- (protium), {2}H- (deuterium), {3}H- (tritium) and model ion with the infinitely heavy nucleus {?}H-. An effective approach has been developed to calculate three-body integrals with the Bessel functions of different orders. Some preliminary evaluations of the phototdetachment cross-sections of the negatively charged hydrogen ions are performed. Inverse bremsstrahlung in the field of the neutral hydrogen atom is briefly discussed.

  19. New results on catalyzed big bang nucleosynthesis with a long-lived negatively charged massive particle

    Microsoft Academic Search

    Motohiko Kusakabe; Toshitaka Kajino; Takashi Yoshida; Grant J. Mathews

    2010-01-01

    It has been proposed that the apparent discrepancies between the inferred primordial abundances of ⁶Li and ⁷Li and the predictions of big bang nucleosynthesis (BBN) can be resolved by the existence of a negatively charged massive unstable supersymmetric particle (X⁻) during the BBN epoch. Here, we present new BBN calculations with an X⁻ particle utilizing an improved nuclear reaction network

  20. New results on catalyzed big bang nucleosynthesis with a long-lived negatively charged massive particle

    Microsoft Academic Search

    Motohiko Kusakabe; Toshitaka Kajino; Takashi Yoshida; Grant J. Mathews

    2010-01-01

    It has been proposed that the apparent discrepancies between the inferred primordial abundances of Li6 and Li7 and the predictions of big bang nucleosynthesis (BBN) can be resolved by the existence of a negatively charged massive unstable supersymmetric particle (X-) during the BBN epoch. Here, we present new BBN calculations with an X- particle utilizing an improved nuclear reaction network

  1. First-Principles Studies of Charge Separation in Single-Molecule Heterojunctions

    NASA Astrophysics Data System (ADS)

    Darancet, Pierre; Doak, Peter; Neaton, Jeffrey

    2010-03-01

    Single-molecule heterojunctions, consisting of donor and acceptor moieties linked by covalent bonds and coupled to metal electrodes, provide an interesting model system for understanding processes fundamental to organic solar cells, such as light absorption and charge separation. However, how the covalent contact with metallic leads influence these processes -- and metal-molecule interface electronic structure -- remains largely unknown. Using density functional theory and many-body perturbation theory, we discuss the influence of the metal contacts and binding groups on junction electronic level alignment for small asymmetric molecules containing covalently-linked moieties based on thiophene, durene and tetrafluoro-, dinitrile-, and metoxy-benzene. Implications for photocurrent and rectification are discussed.

  2. Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

    SciTech Connect

    Zanni, Martin T.

    1999-12-17

    This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents.

  3. Comparison of the binding stoichiometries of positively charged DNA-binding drugs using positive and negative ion electrospray ionization mass spectrometry

    Microsoft Academic Search

    Rajesh Gupta; Jennifer L. Beck; Stephen F. Ralph; Margaret M. Sheil; Janice R. Aldrich-Wright

    2004-01-01

    Positive and negative ion electrospray ionization (ESI) mass spectra of complexes of positively charged small molecules (distamycin,\\u000a Hoechst 33258, [Ru(phen)2dpq]Cl2 and [Ru(phen)2dpqC]Cl2) have been compared. [Ru(phen)2dpq]Cl2 and [Ru(phen)2dpqC]Cl2 bind to DNA by intercalation. Negative ion ESI mass spectra of mixtures of [Ru(phen)2dpq]Cl2 or [Ru(phen)2dpqC]Cl2 with DNA showed ions from DNA-ligand complexes consistent with solution studies. In contrast, only ions from

  4. Properties of clusters in the gas phase. V - Complexes of neutral molecules onto negative ions

    NASA Technical Reports Server (NTRS)

    Keesee, R. G.; Lee, N.; Castleman, A. W., Jr.

    1980-01-01

    Ion-molecules association reactions of the form A(-)(B)n-1 + B = A(-)(B)n were studied over a range of temperatures in the gas phase using high pressure mass spectrometry. Enthalpy and entropy changes were determined for the stepwise clustering reactions of (1) sulfur dioxide onto Cl(-), I(-), and NO2(-) with n ranging from one to three or four, and onto SO2(-) and SO3(-) with n equal to one; and (2) carbon dioxide onto Cl(-), I(-), NO2(-), CO3(-), and SO3(-) with n equal to one. From these data and earlier hydration results, the order of the magnitude of the enthalpy changes on the association of the first neutral for a series of negative ions was found to parallel the gas-phase basicity of those anions.

  5. The effects of electric fields on charged molecules and particles in individual microenvironments

    Microsoft Academic Search

    K. S. Jamieson; H. M. ApSimon; S. S. Jamieson; J. N. B. Bell; M. G. Yost

    2007-01-01

    Measurements of small air ion concentrations, electrostatic potential and AC electric field strengths were taken in an office setting to investigate the link between electric fields and charged molecule and particle concentrations in individual microenvironments. The results obtained indicate that the electromagnetic environments individuals can be exposed to whilst indoors can often bear little resemblance to those experienced outdoors in

  6. Single molecule detection using charge-coupled device array technology. Technical progress report

    SciTech Connect

    Denton, M.B.

    1992-07-29

    A technique for the detection of single fluorescent chromophores in a flowing stream is under development. This capability is an integral facet of a rapid DNA sequencing scheme currently being developed by Los Alamos National Laboratory. In previous investigations, the detection sensitivity was limited by the background Raman emission from the water solvent. A detection scheme based on a novel mode of operating a Charge-Coupled Device (CCD) is being developed which should greatly enhance the discrimination between fluorescence from a single molecule and the background Raman scattering from the solvent. Register shifts between rows in the CCD are synchronized with the sample flow velocity so that fluorescence from a single molecule is collected in a single moving charge packet occupying an area approaching that of a single pixel while the background is spread evenly among a large number of pixels. Feasibility calculations indicate that single molecule detection should be achieved with an excellent signal-to-noise ratio.

  7. Negative Ion CID Fragmentation of O-linked Oligosaccharide Aldoses—Charge Induced and Charge Remote Fragmentation

    NASA Astrophysics Data System (ADS)

    Doohan, Roisin A.; Hayes, Catherine A.; Harhen, Brendan; Karlsson, Niclas Göran

    2011-06-01

    Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O-linked oligosaccharides. It was found that fragmentation of the [M - H]- ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M - H]- ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M - 2H]2- ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the 0,2A-fragmentation. LC-MS also showed that O-linked aldoses existed as interchangeable ?/? pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.

  8. Charge moment change and lightning-driven electric fields associated with negative sprites and halos

    NASA Astrophysics Data System (ADS)

    Li, Jingbo; Cummer, Steven; Lu, Gaopeng; Zigoneanu, Lucian

    2012-09-01

    Sprites are structured high altitude optical emissions produced by lightning-driven electric fields. Both strong positive and negative cloud to ground flashes (CGs) are capable of initiating sprites. However, reported sprites are almost exclusively produced by +CGs. The very limited number of negative polarity sprites makes it difficult to reveal their morphologies and mechanisms. Since 2008, we have operated low light cameras at 5 locations in the United States to detect lightning-driven transient luminous events (TLEs). At Duke University, two pairs of magnetic sensors simultaneously record lightning-radiated magnetic fields. During 4 years of observations, the low light cameras collectively captured 1651 sprite events. Among them, 6 were produced by -CG lightning, which was confirmed by both the National Lightning Detection Network (NLDN) and magnetic field measurements. All of these negative sprites show similar features in their morphology, lightning source current, and lightning-driven ambient electric fields. They all initiate within a few ms from their parent lightning discharges and always are accompanied by sprite halos. Compared to positive sprites, the downward streamers in negative sprites terminate at higher altitudes, about 55-60 km. The extracted source current of their parent lightning discharges is very impulsive and produces at least 450 C km charge moment change in 0.5 ms or less. Unlike most +CG strokes, essentially no continuing current follows these -CGs. Thus the uniformity of negative sprite morphology appears to reflect the uniformity of the characteristics of high charge transfer negative strokes. Numerical simulation shows these impulsive source currents produce very high (>2 Ek, where Ek is the local air breakdown field) but short-lived electric fields at halo altitudes between 70 km and 90 km. At streamer termination altitudes, the inferred background electric field is 0.2-0.3 Ek, which is close to but below the critical field (0.4 Ek) for negative streamer propagation. The simulations also show that the timescale of the lightning source current has a significant impact on the high altitude electric fields and thus the sprite initiation and morphology. With the same amount of charge transfer, a more impulsive current source produces a higher electric field of shorter duration at halo and sprite altitudes. The short timescales may explain why a larger threshold of total charge moment change is required to initiate negative sprites than short-delayed positive sprites, whose parent lightning source current is usually less impulsive.

  9. Degranulating Stimuli Decrease the Negative Surface Charge and Increase the Adhesiveness of Human Neutrophils

    PubMed Central

    Gallin, John I.

    1980-01-01

    Chemotactic factors decrease the negative surface charge of neutrophils (polymorphonuclear leukocytes [PMN]) and this has been speculated to be important in PMN margination and aggregation in vivo. PMN adherence and aggregation are also enhanced by degranulation of lysosomal enzymes. To further assess the possible relationship between degranulation, surface charge, adherence, and aggregation, human peripheral blood PMN (isolated by Hypaque-Ficoll and dextran sedimentation) were exposed to the secretagogues ionophore A23187, phorbol myristate acetate, concanavalin A, and chemotactic factors (partially purified C5a or the synthetic peptide f-met-leu-phe) plus cytochalasin B. Surface charge was measured in a cytopherometer. After incubation of PMN with secretagogues, PMN surface charge was decreased to a greater extent than incubation of PMN with chemotactic factors. The decreased surface charge induced by f-met-leu-phe plus cytochalasin B required both extracellular calcium and magnesium. The ionophore A23187-induced surface charge changes were dependent on extracellular calcium but not magnesium whereas the phorbol myristate acetate effect was only partially dependent on Ca++ and Mg++. The surface charge changes induced by secretagogues were related to both the amount of lysozyme released and to the increased adhesiveness of cells to plastic surfaces. These observations indicate exocytosis of lysosomal granule contents is associated with decreases in neutrophil surface charge, and there appears to be a correlation between decreases in surface charge and facilitation of neutrophil aggregation and adhesiveness. However, a causal relationship between these events has not been established, and the relationship may be simply temporal. PMID:6243307

  10. Observations of negatively-charged particles near Saturn's Main Rings during Saturn Orbit Insertion

    NASA Astrophysics Data System (ADS)

    Jones, G. H.; Coates, A. J.

    2014-04-01

    On arrival at Saturn on 1 July 2004, the Cassini spacecraft passed to the north of Saturn's main rings, providing unique observations of the unusual plasma environment associated with them. The Cassini Plasma Spectrometer (CAPS) electron spectrometer (ELS) obtained in situ observations of electrons [1], whilst positive ions, primarily of oxygen, were observed by CAPS ion mass spectrometer (IMS) [2] and the Ion and Neutral Mass Spectrometer (INMS) [3]. Here, we present an extended analysis of the CAPS-ELS dataset, which reveals previously unreported signatures of several negatively-charged species in the vicinity of the main rings. These are interpreted as negative ions, as observed in other contexts in the Saturnian system, and charged dust. Also present is a magnetic field-aligned beam of electrons. We discuss the significance of these features for our understanding of the ring ionosphere and for the dust environment out of the equatorial plane.

  11. Annihilation, bound state properties and photodetachment of the positronium negatively charged ion

    NASA Astrophysics Data System (ADS)

    Frolov, Alexei M.

    2015-04-01

    Bound state properties of the negatively charged Ps- ion (or e-e+e-) are discussed. The expectation values of operators which correspond to these properties have been determined with the use of the highly accurate wave functions constructed for this ion. Our best variational energy obtained for the Ps- ion is E = -0.2620050 7023298 0107770 40051 a.u. Annihilation of the electron-positron pair(s) in the negatively charged Ps- ion (or e-e+e-) is considered in detail. By using accurate values for a number annihilation rates ?n?, where n = 1, 2, 3, 4 and 5, we evaluated the half-life ?a of the Ps- ion against positron annihilation (?a = 1/? ? 4.793584140 × 10-10 s). Photodetachment of the Ps- ion is considered in the long-range, asymptotic approximation. The overall accuracy of our photodetachment cross-section of the Ps- ion is very good for such a simple approximation.

  12. Polylysine decelerates kinetics of negatively charged gramicidin channels as shown by sensitized photoinactivation

    Microsoft Academic Search

    Andrey V Krylov; Yuri N Antonenko; Elena A Kotova; Tatiana I Rokitskaya; Alexander A Yaroslavov

    1998-01-01

    Effect of a cationic polymer, poly(l-lysine), on the kinetic properties of ionic channels formed by neutral gramicidin A (gA) and its negatively charged analogue O-pyromellitylgramicidin (OPg) in a bilayer lipid membrane is studied using a method of sensitized photoinactivation. This newly developed method is based on the analysis of transmembrane current transients induced by a flash in the presence of

  13. Photoelectron spectroscopy of color centers in negatively charged cesium iodide nanocrystals

    Microsoft Academic Search

    Harry W. Sarkas; Linda H. Kidder; Kit H. Bowen

    1995-01-01

    We present the photoelectron spectra of negatively charged cesium iodide nanocrystals recorded using 2.540 eV photons. The species examined were produced using an inert gas condensation cluster ion source, and they ranged in size from (CsI)?n=13 to nanocrystal anions comprised of 330 atoms. Nanocrystals showing two distinct types of photoemission behavior were observed. For (CsI)?n=13 and (CsI)?n=36?165, a plot of

  14. Surface modification of poly(ether sulfone) membrane with a synthesized negatively charged copolymer.

    PubMed

    Zou, Wen; Qin, Hui; Shi, Wenbin; Sun, Shudong; Zhao, Changsheng

    2014-11-18

    In this study, we provide a new method to modify poly(ether sulfone) (PES) membrane with good biocompatibility, for which diazotized PES (PES-N2(+)) membrane is covalently coated by a negatively charged copolymer of sodium sulfonated poly(styrene-alt-maleic anhydride) (NaSPS-MA). First, aminated PES (PES-NH2) is synthesized by nitro reduction reaction of nitro-PES (PES-NO2), and then blends with pristine PES to prepare PES/PES-NH2 membrane; then the membrane is treated with NaNO2 aqueous solution at acid condition; after surface diazo reaction, surface positively charged PES/PES-N2(+) membrane is prepared. Second, poly(styrene-alt-maleic anhydride) (PS-alt-MA) is synthesized, then sulfonated and treated by sodium hydroxide solution to obtain sodium sulfonated (PS-alt-MA) (NaSPS-MA). Finally, the negatively charged NaSPS-MA copolymer is coated onto the surface positively charged PES/PES-N2(+) membrane via electrostatic interaction; after UV-cross-linking, the linkage between the PES-N2(+) and NaSPS-MA changes to a covalent bond. The surface-modified PES membrane is characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) analyses, and surface zeta potential analyses. The modified membrane exhibits good hemocompatibility and cytocompatibility, and the improved biocompatibility might have resulted from the existence of the hydrophilic groups (sodium carboxylate (-COONa) and sodium sulfonate (-SO3Na)). Moreover, the stability of the modified membrane is also investigated. The results indicated that the modified PES membrane using negatively charged copolymers had a lot of potential in blood purification fields and bioartificial liver supports for a long time. PMID:25347292

  15. Quantum interference and electron correlation in charge transport through triangular quantum dot molecules.

    PubMed

    Chen, Chih-Chieh; Chang, Yia-chung; Kuo, David M T

    2015-03-01

    We study the charge transport properties of triangular quantum dot molecules (TQDMs) connected to metallic electrodes, taking into account all correlation functions and relevant charging states. The quantum interference (QI) effect of TQDMs resulting from electron coherent tunneling between quantum dots is revealed and well interpreted by the long distance coherent tunneling mechanism. The spectra of electrical conductance of TQDMs with charge filling from one to six electrons clearly depict the many-body and topological effects. The calculated charge stability diagram for conductance and total occupation numbers matches well with the recent experimental measurements. We also demonstrate that the destructive QI effect on the tunneling current of TQDMs is robust with respect to temperature variation, making the single electron QI transistor feasible at higher temperatures. PMID:25660124

  16. Metal-molecule contacts and charge transport across monomolecular layers: measurement and theory.

    PubMed

    Kushmerick, J G; Holt, D B; Yang, J C; Naciri, J; Moore, M H; Shashidhar, R

    2002-08-19

    Charge transport studies across molecular length scales under symmetric and asymmetric metal-molecule contact conditions using a simple crossed-wire tunnel junction technique are presented. It is demonstrated that oligo(phenylene ethynylene), a conjugated organic molecule, acts like a molecular wire under symmetric contact conditions, but exhibits characteristics of a molecular diode when the connections are asymmetric. To understand this behavior, we have calculated current-voltage (I-V) characteristics using extended Huckel theory coupled with a Green's function approach. The experimentally observed I-V characteristics are in excellent qualitative agreement with the theory. PMID:12190491

  17. Ultrafast charge rearrangement and nuclear dynamics upon inner-shell multiple ionization of small polyatomic molecules.

    PubMed

    Erk, B; Rolles, D; Foucar, L; Rudek, B; Epp, S W; Cryle, M; Bostedt, C; Schorb, S; Bozek, J; Rouzee, A; Hundertmark, A; Marchenko, T; Simon, M; Filsinger, F; Christensen, L; De, S; Trippel, S; Küpper, J; Stapelfeldt, H; Wada, S; Ueda, K; Swiggers, M; Messerschmidt, M; Schröter, C D; Moshammer, R; Schlichting, I; Ullrich, J; Rudenko, A

    2013-02-01

    Ionization and fragmentation of methylselenol (CH(3)SeH) molecules by intense (>10(17) W/cm(2)) 5 fs x-ray pulses (??=2 keV) are studied by coincident ion momentum spectroscopy. We contrast the measured charge state distribution with data on atomic Kr, determine kinetic energies of resulting ionic fragments, and compare them to the outcome of a Coulomb explosion model. We find signatures of ultrafast charge redistribution from the inner-shell ionized Se atom to its molecular partners, and observe significant displacement of the atomic constituents in the course of multiple ionization. PMID:23414017

  18. Solvent-tuned intramolecular charge-recombination rates in a conjugated donor-acceptor molecule

    NASA Technical Reports Server (NTRS)

    Khundkar, Lutfur R.; Stiegman, A. E.; Perry, Joseph W.

    1990-01-01

    The nonradiative charge-recombination rates from the charge-transfer state of a new conjugated donor-acceptor molecule (p-cyano-p-prime-methylthiodiphenylacetylene) can be tuned over almost an order of magnitude by varying the polarity of the solvent. These measurements of intramolecular recombination show a turnover of rates as a function of emission energy, consistent with the 'normal' and 'inverted' behavior of Marcus theory. Steady-state spectra and time-resolved measurements make it possible to quantitatively compare thermal and optical electron-transfer rates as a function of driving force and demonstrate their correspondence.

  19. Solution, surface, and single molecule platforms for the study of DNA-mediated charge transport

    PubMed Central

    Muren, Natalie B.; Olmon, Eric D.; Barton, Jacqueline K.

    2012-01-01

    The structural core of DNA, a continuous stack of aromatic heterocycles, the base pairs, which extends down the helical axis, gives rise to the fascinating electronic properties of this molecule that is so critical for life. Our laboratory and others have developed diverse experimental platforms to investigate the capacity of DNA to conduct charge, termed DNA-mediated charge transport (DNA CT). Here, we present an overview of DNA CT experiments in solution, on surfaces, and with single molecules that collectively provide a broad and consistent perspective on the essential characteristics of this chemistry. DNA CT can proceed over long molecular distances but is remarkably sensitive to perturbations in base pair stacking. We discuss how this foundation, built with data from diverse platforms, can be used both to inform a mechanistic description of DNA CT and to inspire the next platforms for its study: living organisms and molecular electronics. PMID:22850865

  20. Morphological reasoning for the enhanced charge carrier mobility of a hole transport molecule in polystyrene

    Microsoft Academic Search

    Ferdous Khan; Ah-Mee Hor; P. R. Sundararajan

    2004-01-01

    Pai and coworkers have reported that the charge carrier mobility of the hole trans- port molecule N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) is higher with polystyrene (PS) as the host polymer, in comparison to bisphenol A polycar- bonate (PC) as the binder. It was proposed that the enhanced interaction of TPD with PC and the effect of the carbonyl dipole are responsible for such

  1. Gas-phase ion-molecule reactions of doubly charged fullerenes with oxygen

    SciTech Connect

    Stry, J.J.; Garvey, J.F. (State Univ. of New York, Buffalo (United States))

    1993-07-29

    The gas-phase ion-molecule chemistry of doubly charged fullerene cations (C[sub n][sup 2+] where n = 46, 48, ..., 60 and 70) with neutral oxygen molecules were investigated using a triple quadrupole mass spectrometer. In this paper, we report additions to the fullerene cage structure which result in the formation of C[sub n]O[sup 2+], C[sub n]O[sub 2][sup 2+], and C[sub n]O[sub 3][sup 2+] product ions from the C[sub n][sup 2+] reagent ion. In addition, we also report charge-transfer reactions resulting in the production of C[sub n][sup +] and O[sub 2][sup +] ions, as well as reactive charge-transfer reactions generating C[sub n]O[sup +] and O[sub 3][sup +]. All of these processes are a result of low energy ion-molecule collisions (0.1 - 49 eV[sub lab]). The normalized intensity of the fullerence products exhibit little dependence on size of fullerence clusters examined. However, the reactivities of the fullerenes are found to be highly dependent on the collision energy and the oxygen pressure within the collision cell. 42 refs., 4 figs.

  2. Long-range charge transport in single G-quadruplex DNA molecules

    NASA Astrophysics Data System (ADS)

    Livshits, Gideon I.; Stern, Avigail; Rotem, Dvir; Borovok, Natalia; Eidelshtein, Gennady; Migliore, Agostino; Penzo, Erika; Wind, Shalom J.; di Felice, Rosa; Skourtis, Spiros S.; Cuevas, Juan Carlos; Gurevich, Leonid; Kotlyar, Alexander B.; Porath, Danny

    2014-12-01

    DNA and DNA-based polymers are of interest in molecular electronics because of their versatile and programmable structures. However, transport measurements have produced a range of seemingly contradictory results due to differences in the measured molecules and experimental set-ups, and transporting significant current through individual DNA-based molecules remains a considerable challenge. Here, we report reproducible charge transport in guanine-quadruplex (G4) DNA molecules adsorbed on a mica substrate. Currents ranging from tens of picoamperes to more than 100?pA were measured in the G4-DNA over distances ranging from tens of nanometres to more than 100?nm. Our experimental results, combined with theoretical modelling, suggest that transport occurs via a thermally activated long-range hopping between multi-tetrad segments of DNA. These results could re-ignite interest in DNA-based wires and devices, and in the use of such systems in the development of programmable circuits.

  3. Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer.

    PubMed

    Azuma, Masaki; Chen, Wei-tin; Seki, Hayato; Czapski, Michal; Olga, Smirnova; Oka, Kengo; Mizumaki, Masaichiro; Watanuki, Tetsu; Ishimatsu, Naoki; Kawamura, Naomi; Ishiwata, Shintaro; Tucker, Matthew G; Shimakawa, Yuichi; Attfield, J Paul

    2011-01-01

    The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion <-10(-4) K(-1) over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO(3) shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low- and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi(0.95)La(0.05)NiO(3) is -137×10(-6) K(-1) and a value of -82×10(-6) K(-1) is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders. PMID:21673668

  4. Anisotropic charge transport in large single crystals of ?-conjugated organic molecules.

    PubMed

    Hourani, Wael; Rahimi, Khosrow; Botiz, Ioan; Koch, Felix Peter Vinzenz; Reiter, Günter; Lienerth, Peter; Heiser, Thomas; Bubendorff, Jean-Luc; Simon, Laurent

    2014-05-01

    The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of ?-? stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the ?-? stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility. PMID:24658783

  5. Photoinduced charge separation in an organic donor-acceptor hybrid molecule.

    PubMed

    Marchanka, Aliaksandr; Maier, Stefan K; Höger, Sigurd; van Gastel, Maurice

    2011-11-24

    Photoinduced charge separation in blends of organic materials of different electronic affinity and in organic donor-acceptor hybrids is a process of increasing importance for biological and artificial energy conversion and photovoltaics. Organic polymer solar cells are composed of an electron donor and an electron acceptor between which an electron transfer occurs after excitation by sunlight. Charge separation results in the formation of donor cation radicals and acceptor anion radicals. Here, we present our studies on a donor-acceptor hybrid molecule composed of a phenylene-bithiophene macrocycle used as a donor and a perylene bisimide acceptor. Using continuous wave EPR and modern pulsed EPR methodology in combination with light excitation, intermolecular as well as intramolecular charge separation has been observed. Light-induced charge separation observed upon selective excitation of either one of the chromophores indicates that both LUMO-based and HOMO-based electron transfer from donor to acceptor takes place. These experimental findings are corroborated by DFT calculations in which the HOMO of the donor-acceptor hybrid molecule is found at the phenylene-bithiophene macrocycle and the LUMO at the perylene bisimide. PMID:22004191

  6. The inclusive-exclusive connection and the neutron negative central charge density.

    SciTech Connect

    Miller, G. A.; Arrington, J.; Physics; Univ. of Washington

    2009-10-01

    We find an interpretation of the recent finding that the central charge density of the neutron is negative by using models of generalized parton distributions at zero skewness to relate the behavior of deep inelastic scattering quark distributions, evaluated at high x, to the transverse charge density evaluated at small distances. The key physical input of these models is the Drell-Yan-West relation We find that the d quarks dominate the neutron structure function for large values of Bjorken x, where the large longitudinal momentum of the struck quark has a significant impact on determining the center-of-momentum of the system, and thus the 'center' of the nucleon in the transverse position plane.

  7. Negative isotope effect for charge transport in acenes and derivatives--a theoretical conclusion.

    PubMed

    Jiang, Yuqian; Peng, Qian; Geng, Hua; Ma, He; Shuai, Zhigang

    2015-02-01

    The isotope effect (IE) on charge transport in polyacenes was proposed in 1970 to judge the transport mechanism. However, there had not been a definitive answer for more than 40 years as to whether such an IE is positive or negative, both theoretically and experimentally, because either theory was too approximate or the experimental estimate was too rough to make a judgment. Employing the quantum nuclear tunneling model for organic semiconductors, we investigate the IE on both hole and electron transport for acenes and their derivatives. We show that both (13)C-substitution and deuteration lead to a negative IE. By introducing phenyl, chlorine, or alkyl side-chains into acenes, the IE becomes more remarkable, especially for hole transport. The vibrational relaxation processes involving in-plane bending of ring or alkyl side-chain motions are found to be responsible for the IE. PMID:25521587

  8. Optical spectra and intensities of graphene magnetic dot bound to a negatively charged Coulomb impurity

    SciTech Connect

    Lee, C. M., E-mail: mesimon-hk@yahoo.com.hk, E-mail: apkschan@cityu.edu.hk; Chan, K. S., E-mail: mesimon-hk@yahoo.com.hk, E-mail: apkschan@cityu.edu.hk [Department of Physics and Materials Science and Center for Functional Photonics, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Shenzhen Research Institute, City University of Hong Kong, Shenzhen (China)

    2014-07-28

    Employing numerical diagonalization, we study the optical properties of an electron in a monolayer-graphene magnetic dot bound to an off-center negatively charged Coulomb impurity based on the massless Dirac-Weyl model. Numerical results show that, since the electron-hole symmetry is broken by the Coulomb potential, the optical absorption spectra of the magnetic dot in the presence of a Coulomb impurity are different between the electron states and the hole states. Effects of both the magnetic field and the dot size on the absorption coefficient are presented as functions of the incident photon energies.

  9. Localization accuracy in single molecule microscopy using electron-multiplying charge-coupled device cameras.

    PubMed

    Chao, Jerry; Ward, E Sally; Ober, Raimund J

    2012-03-15

    The electron-multiplying charge-coupled device (EMCCD) is a popular technology for imaging under extremely low light conditions. It has become widely used, for example, in single molecule microscopy experiments where few photons can be detected from the individual molecules of interest. Despite its important role in low light microscopy, however, little has been done in the way of determining how accurately parameters of interest (e.g., location of a single molecule) can be estimated from an image that it produces. Here, we develop the theory for calculating the Fisher information matrix, and hence the Cramer-Rao lower bound-based limit of the accuracy, for estimating parameters from an EMCCD image. An EMCCD operates by amplifying a weak signal that would otherwise be drowned out by the detector's readout noise as in the case of a conventional charge-coupled device (CCD). The signal amplification is a stochastic electron multiplication process, and is modeled here as a geometrically multiplied branching process. In developing our theory, we also introduce a "noise coefficient" which enables the comparison of the Fisher information of different data models via a scalar quantity. This coefficient importantly allows the selection of the best detector (e.g., EMCCD or CCD), based on factors such as the signal level, and regardless of the specific estimation problem at hand. We apply our theory to the problem of localizing a single molecule, and compare the calculated limits of the localization accuracy with the standard deviations of maximum likelihood location estimates obtained from simulated images of a single molecule. PMID:24379939

  10. Localization accuracy in single molecule microscopy using electron-multiplying charge-coupled device cameras

    PubMed Central

    Chao, Jerry; Ward, E. Sally; Ober, Raimund J.

    2012-01-01

    The electron-multiplying charge-coupled device (EMCCD) is a popular technology for imaging under extremely low light conditions. It has become widely used, for example, in single molecule microscopy experiments where few photons can be detected from the individual molecules of interest. Despite its important role in low light microscopy, however, little has been done in the way of determining how accurately parameters of interest (e.g., location of a single molecule) can be estimated from an image that it produces. Here, we develop the theory for calculating the Fisher information matrix, and hence the Cramer-Rao lower bound-based limit of the accuracy, for estimating parameters from an EMCCD image. An EMCCD operates by amplifying a weak signal that would otherwise be drowned out by the detector’s readout noise as in the case of a conventional charge-coupled device (CCD). The signal amplification is a stochastic electron multiplication process, and is modeled here as a geometrically multiplied branching process. In developing our theory, we also introduce a “noise coefficient” which enables the comparison of the Fisher information of different data models via a scalar quantity. This coefficient importantly allows the selection of the best detector (e.g., EMCCD or CCD), based on factors such as the signal level, and regardless of the specific estimation problem at hand. We apply our theory to the problem of localizing a single molecule, and compare the calculated limits of the localization accuracy with the standard deviations of maximum likelihood location estimates obtained from simulated images of a single molecule. PMID:24379939

  11. Excitation of Kelvin Helmholtz instability by an ion beam in a plasma with negatively charged dust grains

    NASA Astrophysics Data System (ADS)

    Rani, Kavita; Sharma, Suresh C.

    2015-02-01

    An ion beam propagating through a magnetized dusty plasma drives Kelvin Helmholtz Instability (KHI) via Cerenkov interaction. The frequency of the unstable wave increases with the relative density of negatively charged dust grains. It is observed that the beam has stabilizing effect on the growth rate of KHI for low shear parameter, but for high shear parameter, the instability is destabilized with relative density of negatively charged dust grains.

  12. Imaging charge and energy transfer in molecules using free-electron lasers

    NASA Astrophysics Data System (ADS)

    Rudenko, Artem

    2014-05-01

    Charge and energy transfer reactions drive numerous important processes in physics, chemistry and biology, with applications ranging from X-ray astrophysics to artificial photosynthesis and molecular electronics. Experimentally, the central goal in studies of transfer phenomena is to trace the spatial localization of charge at a given time. Because of their element and site sensitivity, ultrafast X-rays provide a promising tool to address this goal. In this talk I will discuss several experiments where free-electron lasers were employed to study charge and energy transfer dynamics in fragmenting molecules. In a first example, we used intense, 70 femtosecond 1.5 keV pulses from the Linac Coherent Light Source (LCLS) to study distance dependence of electron transfer in laser-dissociated methyl iodide molecules. Inducing well-localized positive charge on the heavy iodine atom, we observe signature of electron transition from the separated methyl group up to the distances of 35 atomic units. In a complementary experiment, we studied charge exchange between two partners in a dissociating molecular iodine employing a pump-probe arrangement with two identical 90 eV pulses from the Free-Electron LASer in Hamburg (FLASH). In both cases, the effective spatial range of the electron transfer can be reasonably described by a classical over-the-barrier model developed for ion-atom collisions. Finally, I will discuss a time-resolved measurement on non-local relaxation mechanism based on a long-range energy transfer, the so-called interatomic Coulombic decay. This work was supported by Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy and by the Kansas NSF ``First Award'' program.

  13. Dok-3, a Novel Adapter Molecule Involved in the Negative Regulation of Immunoreceptor Signaling

    Microsoft Academic Search

    SERGE LEMAY; DOMINIQUE DAVIDSON; SYLVAIN LATOUR; A. Veillette

    2000-01-01

    Adapters are typically viewed as molecules coordinating the recruitment of positive effectors of cell signaling. Herein, we report the identification of Dok-3, a novel adapter molecule belonging to the Dok family. Our studies show that Dok-3 is highly expressed in several hemopoietic cell types, including B cells and macro- phages. It undergoes rapid tyrosine phosphorylation in response to immunoreceptor-mediated cellular

  14. Annihilation, bound state properties and photodetachment of the positronium negatively charged ion

    E-print Network

    Frolov, Alexei M

    2015-01-01

    Bound state properties of the negatively charged Ps$^{-}$ ion (or $e^{-} e^{+} e^{-}$) are discussed. The expectation values of operators which correspond to these properties have been determined with the use of the highly accurate wave functions constructed for this ion. Our best variational energy obtained for the Ps$^{-}$ ion is $E$ = -0.2620050 7023298 0107770 40035 $a.u.$ Annihilation of the electron-positron pair(s) in the negatively charged Ps$^{-}$ ion (or $e^{-} e^{+} e^{-}$) is considered in detail. The overall life-time of the Ps$^{-}$ ion against positron annihilation $\\tau_a = \\frac{1}{\\Gamma} \\approx 4.793584140 \\cdot 10^{-10}$ $sec$ is determined together with a number of different annihilation rates $\\Gamma_{n \\gamma}$, where $n$ = 1, 2, 3, 4 and 5. Photodetachment of the Ps$^{-}$ ion is considered in the long-range, asymptotic approximation. The overall accuracy of the photodetachment cross-section of the Ps$^{-}$ ion is very good for such a simple approximation.

  15. Manipulating the charge state and conductance of a single molecule on a semiconductor surface by electrostatic gating

    NASA Astrophysics Data System (ADS)

    Martinez-Blanco, Jesus; Nacci, Christophe; Erwin, Steven C.; Kanisawa, Kiyoshi; Locane, Elina; Thomas, Mark; von Oppen, Felix; Brouwer, Piet; Foelsch, Stefan

    2015-03-01

    We studied the charge state and tunneling conductance of single phthalocyanine molecules adsorbed on InAs(111)A using scanning tunneling microscopy (STM) at 5 K. On the InAs(111)A surface, native +1 charged indium adatoms can be repositioned by the STM tip using atom manipulation. This allows us to electrostatically gate an individual adsorbed molecule by placing charged adatoms nearby or, alternatively, by repositioning the molecule within the electrostatic potential landscape created by an STM-engineered adatom corral. By stepwise increasing the gating potential, the molecular charge state can be tuned from neutral to -1, as well as to bistable intermediate states. We find that the molecule changes its orientational conformation when the charge state is switched. Scanning tunneling spectroscopy measurements reveal that the conductance gap of the single-molecule tunneling junction can be precisely controlled by the electrostatic gating. We discuss the observed gating-dependent single-molecule tunneling conductance in terms of charge transport through a gated quantum dot. Granted by the German Research Foundation (FO 362/4-1; SFB 658).

  16. The Negatively Charged Regions of Lactoferrin Binding Protein B, an Adaptation against Anti-Microbial Peptides

    PubMed Central

    Morgenthau, Ari; Beddek, Amanda; Schryvers, Anthony B.

    2014-01-01

    Lactoferrin binding protein B (LbpB) is a bi-lobed membrane bound lipoprotein that is part of the lactoferrin receptor complex in a variety of Gram-negative pathogens. Despite high sequence diversity among LbpBs from various strains and species, a cluster of negatively charged amino acids is invariably present in the protein’s C-terminal lobe in all species except Moraxella bovis. The function of LbpB in iron acquisition has yet to be experimentally demonstrated, whereas in vitro studies have shown that LbpB confers protection against lactoferricin, a short cationic antimicrobial peptide released from the N- terminus of lactoferrin. In this study we demonstrate that the negatively charged regions can be removed from the Neisseria meningitidis LbpB without compromising stability, and this results in the inability of LbpB to protect against the bactericidal effects of lactoferricin. The release of LbpB from the cell surface by the autotransporter NalP reduces the protection against lactoferricin in the in vitro killing assay, attributed to removal of LbpB during washing steps, but is unlikely to have a similar impact in vivo. The protective effect of the negatively charged polysaccharide capsule in the killing assay was less than the protection conferred by LbpB, suggesting that LbpB plays a major role in protection against cationic antimicrobial peptides in vivo. The selective release of LbpB by NalP has been proposed to be a mechanism for evading the adaptive immune response, by reducing the antibody binding to the cell surface, but may also provide insights into the primary function of LbpB in vivo. Although TbpB and LbpB have been shown to be major targets of the human immune response, the selective release of LbpB suggests that unlike TbpB, LbpB may not be essential for iron acquisition, but important for protection against cationic antimicrobial peptides. PMID:24465982

  17. Electronic spectroscopy of molecules in superfluid helium nanodroplets: an excellent sensor for intramolecular charge redistribution.

    PubMed

    Pentlehner, D; Riechers, R; Vdovin, A; Pötzl, G M; Slenczka, A

    2011-06-30

    Electronic spectra of molecules doped into superfluid (4)He nanodroplets reveal important details of the microsolvation in superfluid helium. The vibrational fine structure in the electronic spectra of phthalocyanine derivatives and pyrromethene dye molecules doped into superfluid helium droplets have been investigated. Together with previous studies on anthracene derivatives [J. Chem. Phys.2010, 133, 114505] and 3-hydroxyflavone [J. Chem. Phys.2009, 131, 194307], the line shapes vary between two limiting cases, namely, sharp Lorentzians and nonresolved vibrational fine structure. All different spectral signatures are initiated by the same effect, namely, the change of the electron density distribution initiated by the electronic excitation. This change can be quantified by the difference of the electrostatic moments of the molecule in the electronic ground state and the corresponding Franck-Condon point in the excited state. According to the experimental data, electronic spectroscopy suffers from drastic line broadening when accompanied by significant changes of the charge distribution, in particular, changes of the dipole moment. Vice versa, the vibrational fine structure in electronic spectra of molecules doped into helium droplets is highly sensitive to changes of the electron density distribution. PMID:21615111

  18. Negative Electron Binding Energies Observed in a Triply Charged Anion: Photoelectron Spectroscopy of 1-Hydroxy-3, 6, 8-Pyrene-Trisulfonate

    SciTech Connect

    Yang, Jie; Xing, Xiaopeng; Wang, Xue B.; Wang, Lai S.; Sergeeva, Alina P.; Boldyrev, Alexander I.

    2008-03-07

    We report the observation of negative electron binding energies in a triply charged anion, 1-hydroxy-3,6,8-pyrene-trisulfonate (HPTS3–). Low-temperature photoelectron spectra were obtained for HPTS3– at several photon energies, revealing three detachment features below 0 electron binding energy. The HPTS3– trianion was measured to possess a negative electron binding of -0.66 eV. Despite the relatively high excess energy stored in HPTS3–, it was observed to be a long-lived anion due to its high repulsive Coulomb barrier (~3.3 eV), which prevents spontaneous electron emission. Theoretical calculations were carried out, which confirmed the negative electron binding energies observed. The calculations further showed that the highest occupied molecular orbital in HPTS3– is an anti-bonding ? orbital on the pyrene rings, followed by lone pair electrons in the peripheral –SO3– groups. Negative electron binding energy is a unique feature of multiply-charged anions due to the presence of the repulsive Coulomb barrier. Such metastable species may be good models to study electron-electron and vibronic interactions in complex molecules.

  19. Linear free energy relationships for metal-ligand complexation: Bidentate binding to negatively-charged oxygen donor atoms

    NASA Astrophysics Data System (ADS)

    Carbonaro, Richard F.; Atalay, Yasemin B.; Di Toro, Dominic M.

    2011-05-01

    Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log KML = ?OO( ?O log KHL,1 + ?O log KHL,2) where KML is the metal-ligand stability constant for a 1:1 complex, KHL,1 and KHL,2 are the proton-ligand stability constants (the ligand p Ka values), and ?O is the Irving-Rossotti slope. The parameter ?OO is metal specific and has slightly different values for five and six membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, ?-hydroxycarboxylic acids, and ?-ketocarboxylic acids, a modification of the LFER where log KHL,2 is set equal to zero is required. The chemical interpretation of ?OO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log KML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log KML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems.

  20. New effects of a long-lived negatively charged massive particle on big bang nucleosynthesis

    SciTech Connect

    Kusakabe, Motohiko [School of Liberal Arts and Science, Korea Aerospace University, Goyang 412-791, Korea and Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Kim, K. S. [School of Liberal Arts and Science, Korea Aerospace University, Goyang 412-791 (Korea, Republic of); Cheoun, Myung-Ki [Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Kajino, Toshitaka [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan and Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Kino, Yasushi [Department of Chemistry, Tohoku University, Sendai 980-8578 (Japan); Mathews, Grant J. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan and Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)

    2014-05-02

    Primordial {sup 7}Li abundance inferred from observations of metal-poor stars is a factor of about 3 lower than the theoretical value of standard big bang nucleosynthesis (BBN) model. One of the solutions to the Li problem is {sup 7}Be destruction during the BBN epoch caused by a long-lived negatively charged massive particle, X{sup ?}. The particle can bind to nuclei, and X-bound nuclei (X-nuclei) can experience new reactions. The radiative X{sup ?} capture by {sup 7}Be nuclei followed by proton capture of the bound state of {sup 7}Be and X{sup ?} ({sup 7}Be{sub x}) is a possible {sup 7}Be destruction reaction. Since the primordial abundance of {sup 7}Li originates mainly from {sup 7}Li produced via the electron capture of {sup 7}Be after BBN, the {sup 7}Be destruction provides a solution to the {sup 7}Li problem. We suggest a new route of {sup 7}Be{sub x} formation, that is the {sup 7}Be charge exchange at the reaction of {sup 7}Be{sup 3+} ion and X{sup ?}. The formation rate depends on the ionization fraction of {sup 7}Be{sup 3+} ion, the charge exchange cross section of {sup 7}Be{sup 3+}, and the probability that excited states {sup 7}Be{sub x}* produced at the charge exchange are converted to the ground state. We find that this reaction can be equally important as or more important than ordinary radiative recombination of {sup 7}Be and X{sup ?}. The effect of this new route is shown in a nuclear reaction network calculation.

  1. Inelastic scattering effects on single molecule spectroscopy: Consequences for Negative Differential Resistance

    Microsoft Academic Search

    Jason Pitters; Robert Wolkow

    2006-01-01

    The adsorption of styrene and cyclopentene on Si(100) has been studied with scanning tunneling microscopy and spectroscopy. Blinking of molecules in images and irregularities in current-voltage spectra and in current-time traces are analyzed. It is also shown that NDR-like features in IV spectra of both styrene and cyclopentene molecules are not consistently present. Such erratic behavior cannot be accounted for

  2. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS2.

    PubMed

    Zhou, Changjie; Yang, Weihuang; Zhu, Huili

    2015-06-01

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS2 upon adsorption of various gas molecules (H2, O2, H2O, NH3, NO, NO2, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS2 with a low degree of charge transfer and accept charge from the monolayer, except for NH3, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS2 are not significantly altered upon adsorption of H2, H2O, NH3, and CO, whereas the lowest unoccupied molecular orbitals of O2, NO, and NO2 are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS2. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS2. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides. PMID:26049513

  3. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS2

    NASA Astrophysics Data System (ADS)

    Zhou, Changjie; Yang, Weihuang; Zhu, Huili

    2015-06-01

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS2 upon adsorption of various gas molecules (H2, O2, H2O, NH3, NO, NO2, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS2 with a low degree of charge transfer and accept charge from the monolayer, except for NH3, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS2 are not significantly altered upon adsorption of H2, H2O, NH3, and CO, whereas the lowest unoccupied molecular orbitals of O2, NO, and NO2 are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS2. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS2. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides.

  4. Polymerization on the rocks: negatively-charged alpha-amino acids

    NASA Technical Reports Server (NTRS)

    Hill, A. R. Jr; Bohler, C.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

    1998-01-01

    Oligomers of the negatively-charged amino acids, glutamic acid, aspartic acid, and O-phospho-L-serine are adsorbed by hydroxylapatite and illite with affinities that increase with oligomer length. In the case of oligo-glutamic acids adsorbed on hydroxylapatite, addition of an extra residue results in an approximately four-fold increase in the strength of adsorption. Oligomers much longer than the 7-mer are retained tenaciously by the mineral. Repeated incubation of short oligo-glutamic acids adsorbed on hydroxylapatite or illite with activated monomer leads to the accumulation of oligomers at least 45 units long. The corresponding reactions of aspartic acid and O-phospho-L-serine on hydroxylapatite are less effective in generating long oligomers, while illite fails to accumulate substantial amounts of long oligomers of aspartic acid or of O-phospho-L-serine.

  5. Negatively charged nitrogen-vacancy centers in a 5 nm thin 12C diamond film.

    PubMed

    Ohashi, K; Rosskopf, T; Watanabe, H; Loretz, M; Tao, Y; Hauert, R; Tomizawa, S; Ishikawa, T; Ishi-Hayase, J; Shikata, S; Degen, C L; Itoh, K M

    2013-10-01

    We report successful introduction of negatively charged nitrogen-vacancy (NV(-)) centers in a 5 nm thin, isotopically enriched ([(12)C] = 99.99%) diamond layer by CVD. The present method allows for the formation of NV(-) in such a thin layer even when the surface is terminated by hydrogen atoms. NV(-) centers are found to have spin coherence times of between T2 ~ 10-100 ?s at room temperature. Changing the surface termination to oxygen or fluorine leads to a slight increase in the NV(-) density, but not to any significant change in T2. The minimum detectable magnetic field estimated by this T2 is 3 nT after 100 s of averaging, which would be sufficient for the detection of nuclear magnetic fields exerted by a single proton. We demonstrate the suitability for nanoscale NMR by measuring the fluctuating field from ~10(4) proton nuclei placed on top of the 5 nm diamond film. PMID:24020334

  6. Exploration of Porphyrin-based Semiconductors for Negative Charge Transport Applications Using Synthetic, Spectroscopic, Potentiometric, Magnetic Resonance, and Computational Methods

    NASA Astrophysics Data System (ADS)

    Rawson, Jeffrey Scott

    Organic pi-conjugated materials are emerging as commercially relevant components in electronic applications that include transistors, light-emitting diodes, and solar cells. One requirement common to all of these functions is an aptitude for accepting and transmitting charges. It is generally agreed that the development of organic semiconductors that favor electrons as the majority carriers (n-type) lags behind the advances in hole transporting (p-type) materials. This shortcoming suggests that the design space for n-type materials is not yet well explored, presenting researchers with the opportunity to develop unconventional architectures. In this regard, it is worth noting that discrete molecular materials are demonstrating the potential to usurp the preeminent positions that pi-conjugated polymers have held in these areas of organic electronics research. This dissertation describes how an extraordinary class of molecules, meso-to-meso ethyne-bridged porphyrin arrays, has been bent to these new uses. Chapter one describes vis-NIR spectroscopic and magnetic resonance measurements revealing that these porphyrin arrays possess a remarkable aptitude for the delocalization of negative charge. In fact, the miniscule electron-lattice interactions exhibited in these rigid molecules allow them to host the most vast electron-polarons ever observed in a pi-conjugated material. Chapter two describes the development of an ethyne-bridged porphyrin-isoindigo hybrid chromophore that can take the place of fullerene derivatives in the conventional thin film solar cell architecture. Particularly noteworthy is the key role played by the 5,15-bis(heptafluoropropyl)porphyrin building block in the engineering of a chromophore that, gram for gram, is twice as absorptive as poly(3-hexyl)thiophene, exhibits a lower energy absorption onset than this polymer, and yet possesses a photoexcited singlet state sufficiently energetic to transfer a hole to this polymer. Chapter three describes synthetic efforts that expand the repertoire of readily available meso-heptafluoropropyl porphyrin building blocks. The findings suggest that the remaining challenges to the exploitation of these pigments will be overcome by a sufficiently firm grasp of their subtle electronic structures, and a willingness to eschew the customary strategies of chromophore assembly.

  7. Graphene field effect transistor as a probe of electronic structure and charge transfer at organic molecule-graphene interfaces.

    PubMed

    Cervenka, Jiri; Budi, Akin; Dontschuk, Nikolai; Stacey, Alastair; Tadich, Anton; Rietwyk, Kevin J; Schenk, Alex; Edmonds, Mark T; Yin, Yuefeng; Medhekar, Nikhil; Kalbac, Martin; Pakes, Chris I

    2015-01-28

    The electronic structure of physisorbed molecules containing aromatic nitrogen heterocycles (triazine and melamine) on graphene is studied using a combination of electronic transport, X-ray photoemission spectroscopy and density functional theory calculations. The interfacial electronic structure and charge transfer of weakly coupled molecules on graphene is found to be governed by work function differences, molecular dipole moments and polarization effects. We demonstrate that molecular depolarization plays a significant role in these charge transfer mechanisms even at submonolayer coverage, particularly for molecules which possess strong dipoles. Electronic transport measurements show a reduction of graphene conductivity and charge carrier mobility upon the adsorption of the physisorbed molecules. This effect is attributed to the formation of additional electron scattering sites in graphene by the molecules and local molecular electric fields. Our results show that adsorbed molecules containing polar functional groups on graphene exhibit different coverage behaviour to nonpolar molecules. These effects open up a range of new opportunities for recognition of different molecules on graphene-based sensor devices. PMID:25502349

  8. First Experimental Evidence of Dopamine Interactions with Negatively Charged Model Biomembranes

    PubMed Central

    2013-01-01

    Dopamine is essential for receptor-related signal transduction in mammalian central and peripheral nervous systems. Weak interactions between the neurotransmitter and neuronal membranes have been suggested to modulate synaptic transmission; however, binding forces between dopamine and neuronal membranes have not yet been quantitatively described. Herein, for the first time, we have explained the nature of dopamine interactions with model lipid membranes assembled from neutral 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), negatively charged 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), and the mixture of these two lipids using isothermal titration calorimetry and differential scanning calorimetry. Dopamine binding to anionic membranes is a thermodynamically favored process with negative enthalpy and positive entropy, quantitatively described by the mole ratio partition coefficient, K. K increases with membrane charge to reach its maximal value, 705.4 ± 60.4 M–1, for membrane composed from pure DMPG. The contribution of hydrophobic effects to the binding process is expressed by the intrinsic partition coefficient, K0. The value of K0 = 74.7 ± 6.4 M–1 for dopamine/DMPG interactions clearly indicates that hydrophobic effects are 10 times weaker than electrostatic forces in this system. The presence of dopamine decreases the main transition temperature of DMPG, but no similar effect has been observed for DMPC. Basing on these results, we propose a simple electrostatic model of dopamine interactions with anionic membranes with the hydrophobic contribution expressed by K0. We suggest that dopamine interacts superficially with phospholipid membranes without penetrating into the bilayer hydrocarbon core. The model is physiologically important, since neuronal membranes contain a large (even 20%) fraction of anionic lipids. PMID:23662798

  9. From Self-Assembly to Charge Transport with Single Molecules - An Electrochemical Approach

    NASA Astrophysics Data System (ADS)

    Han, Bo; Li, Zhihai; Li, Chen; Pobelov, Ilya; Su, Guijin; Aguilar-Sanchez, Rocio; Wandlowski, Thomas

    Structure formation and self-assembly of physisorbed and chemisorbed organic monolayers will be described on electrified solid-liquid interfaces employing in-situ scanning tunneling microscopy (STM) and surface-enhanced infrared spectroscopy (SEIRAS) in combination with electrochemical techniques. We present first a case study on self-assembly by directional hydrogen bonding and its interplay with the electrode potential choosing aromatic carboxylic acids, with an emphasis on 1,3,5-benzene-tricarboxylic acid (TMA). Structure and electrical characteristics of chemisorbed organic monolayers involving the formation of covalent bonds with the substrate surface will be discussed for a series of 4-methyl-4'-(n-mercaptoalkyl)biphenyls on Au(111) electrodes. In an attempt to explore single molecule properties, such as charge transport and redox-mediated tunneling, we subsequently introduce an STM-based technique to construct symmetric and asymmetric metal/(single) molecule/metal junctions. Employing ?,?-alkanedithiols and redox-active derivatives of viologens we demonstrate novel transport and single molecule electrochemical studies, which bear unique novel perspectives for fundamental as well as applied investigations.

  10. Photodriven electron transfer in triad molecules: a two-step charge recombination reaction

    SciTech Connect

    Gust, D.; Moore, T.A.; Makings, L.R.; Liddell, P.A.; Nemeth, G.A.; Moore, A.L.

    1986-12-10

    Excitation of carotenoid-porphyrin-quinone (C-P-Q) triad molecules initiates a two-step electron transfer to yield a final charge separated state of the form C/sup .+/-P-Q/sup .-/. This state has a very long lifetime in solution (10/sup -7/-10/sup -6/ s), and the nature of the ultimate charge recombination reaction has not previously been investigated. Nanosecond transient absorption spectroscopic studies have been performed on a series of such triad molecules wherein the nature of the linkages joining the porphyrin to the quinone and/or carotenoid moieties is varied systematically. The results reveal that charge recombination in C/sup .+/-P-Q/sup .-/ does not occur in a single step but rather via an unusual two-step electron transfer involving an intermediate C-P/sup .+/-Q/sup .-/ species. The temperature dependence is consistent with the formation of C-P/sup .+/-Q/sup .-/ via a thermally activated process, and measurements over the range 221-296 K yield ..delta..H double dagger = 2.7 kcal/mol and ..delta..S double dagger = -20 cal/(deg x mol). The transient absorption measurements also reveal that the quantum yield of the C/sup .+/-P-Q/sup .-/ state is a function of three electron transfer rate constants and that it can therefore be maximized by controlling the ratios of these rate constants to one another and to the rates of other pathways which depopulate the relevant excited states.

  11. Positive and negative ion formation in deep-core excited molecules: S 1s excitation in dimethyl sulfoxide.

    PubMed

    Coutinho, L H; Gardenghi, D J; Schlachter, A S; de Souza, G G B; Stolte, W C

    2014-01-14

    The photo-fragmentation of the dimethyl sulfoxide (DMSO) molecule was studied using synchrotron radiation and a magnetic mass spectrometer. The total cationic yield spectrum was recorded in the photon energy region around the sulfur K edge. The sulfur composition of the highest occupied molecular orbital's and lowest unoccupied molecular orbital's in the DMSO molecule has been obtained using both ab initio and density functional theory methods. Partial cation and anion-yield measurements were obtained in the same energy range. An intense resonance is observed at 2475.4 eV. Sulfur atomic ions present a richer structure around this resonant feature, as compared to other fragment ions. The yield curves are similar for most of the other ionic species, which we interpret as due to cascade Auger processes leading to multiply charged species which then undergo Coulomb explosion. The anions S(-), C(-), and O(-) are observed for the first time in deep-core-level excitation of DMSO. PMID:24437884

  12. The role of symmetry and charge delocalization in two-dimensional molecules conjugated molecules for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Galvin, Mary

    2008-03-01

    Our group is investigating whether star molecules offer any advantage over linear polymers when used as the active layer in light-emitting diodes (LEDs), organic transistors (OFETs) or in photovoltaics (PVs). Specifically, we are investigating the role of architecture, synthesizing some novel molecules that contain a central tetra substituted phenyl ring. These molecules have a tendency to pi-pi stack, further delocalizing the carriers. The synthetic strategy used to prepare these molecules is versatile so that the four arms in the molecules do not have to be identical. The placement of differing arms also affords the opportunity to study the effect of symmetry on the properties of these molecules. The HOMO and LUMO levels can be changed via the type and placement of arms. Recent results obtained with these materials and their applications in photovoltaics and light-emitting diodes will be described.

  13. Mapping charge to function relationships of the DNA mimic protein Ocr 

    E-print Network

    Kanwar, Nisha

    2014-06-28

    This thesis investigates the functional consequences of neutralising the negative charges on the bacteriophage T7 antirestriction protein ocr. The ocr molecule is a small highly negatively charged, protein homodimer that ...

  14. Excitation of dust acoustic waves by an ion beam in a plasma cylinder with negatively charged dust grains

    NASA Astrophysics Data System (ADS)

    Sharma, Suresh C.; Kaur, Daljeet; Gahlot, Ajay; Sharma, Jyotsna

    2014-10-01

    An ion beam propagating through a plasma cylinder having negatively charged dust grains drives a low frequency electrostatic dust acoustic wave (DAW) to instability via Cerenkov interaction. The unstable wave frequencies and the growth rate increase with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales to the one-third power of the beam density. The real part of the frequency of the unstable mode increases with the beam energy and scales to almost one-half power of the beam energy. The phase velocity, frequency, and wavelength results of the unstable mode are in compliance with the experimental observations.

  15. Excitation of dust acoustic waves by an ion beam in a plasma cylinder with negatively charged dust grains

    SciTech Connect

    Sharma, Suresh C. [Department of Applied Physics, Delhi Technological University (DTU), Shahbad Daulatpur, Bawana Road, Delhi-42 (India); Kaur, Daljeet [Department of Physics, Guru Teg Bahadur Institute of Technology, Rajouri Garden, New Delhi (India); Gahlot, Ajay [Department of Physics, Maharaja Surajmal Institute of Technology, Janakpuri, New Delhi (India); Sharma, Jyotsna [Department of Physics, KIIT College of Engineering, Bhondsi Gurgaon 122102 (India)

    2014-10-15

    An ion beam propagating through a plasma cylinder having negatively charged dust grains drives a low frequency electrostatic dust acoustic wave (DAW) to instability via Cerenkov interaction. The unstable wave frequencies and the growth rate increase with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales to the one-third power of the beam density. The real part of the frequency of the unstable mode increases with the beam energy and scales to almost one-half power of the beam energy. The phase velocity, frequency, and wavelength results of the unstable mode are in compliance with the experimental observations.

  16. Molecular-scale quantitative charge density measurement of biological molecule by frequency modulation atomic force microscopy in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Umeda, Kenichi; Kobayashi, Kei; Oyabu, Noriaki; Matsushige, Kazumi; Yamada, Hirofumi

    2015-07-01

    Surface charge distributions on biological molecules in aqueous solutions are essential for the interactions between biomolecules, such as DNA condensation, antibody–antigen interactions, and enzyme reactions. There has been a significant demand for a molecular-scale charge density measurement technique for better understanding such interactions. In this paper, we present the local electric double layer (EDL) force measurements on DNA molecules in aqueous solutions using frequency modulation atomic force microscopy (FM-AFM) with a three-dimensional force mapping technique. The EDL forces measured in a 100 mM KCl solution well agreed with the theoretical EDL forces calculated using reasonable parameters, suggesting that FM-AFM can be used for molecular-scale quantitative charge density measurements on biological molecules especially in a highly concentrated electrolyte.

  17. Molecular-scale quantitative charge density measurement of biological molecule by frequency modulation atomic force microscopy in aqueous solutions.

    PubMed

    Umeda, Kenichi; Kobayashi, Kei; Oyabu, Noriaki; Matsushige, Kazumi; Yamada, Hirofumi

    2015-07-17

    Surface charge distributions on biological molecules in aqueous solutions are essential for the interactions between biomolecules, such as DNA condensation, antibody-antigen interactions, and enzyme reactions. There has been a significant demand for a molecular-scale charge density measurement technique for better understanding such interactions. In this paper, we present the local electric double layer (EDL) force measurements on DNA molecules in aqueous solutions using frequency modulation atomic force microscopy (FM-AFM) with a three-dimensional force mapping technique. The EDL forces measured in a 100 mM KCl solution well agreed with the theoretical EDL forces calculated using reasonable parameters, suggesting that FM-AFM can be used for molecular-scale quantitative charge density measurements on biological molecules especially in a highly concentrated electrolyte. PMID:26120025

  18. Highly Efficient Bioinspired Molecular Ru Water Oxidation Catalysts with Negatively Charged Backbone Ligands.

    PubMed

    Duan, Lele; Wang, Lei; Li, Fusheng; Li, Fei; Sun, Licheng

    2015-07-21

    The oxygen evolving complex (OEC) of the natural photosynthesis system II (PSII) oxidizes water to produce oxygen and reducing equivalents (protons and electrons). The oxygen released from PSII provides the oxygen source of our atmosphere; the reducing equivalents are used to reduce carbon dioxide to organic products, which support almost all organisms on the Earth planet. The first photosynthetic organisms able to split water were proposed to be cyanobacteria-like ones appearing ca. 2.5 billion years ago. Since then, nature has chosen a sustainable way by using solar energy to develop itself. Inspired by nature, human beings started to mimic the functions of the natural photosynthesis system and proposed the concept of artificial photosynthesis (AP) with the view to creating energy-sustainable societies and reducing the impact on the Earth environments. Water oxidation is a highly energy demanding reaction and essential to produce reducing equivalents for fuel production, and thereby effective water oxidation catalysts (WOCs) are required to catalyze water oxidation and reduce the energy loss. X-ray crystallographic studies on PSII have revealed that the OEC consists of a Mn4CaO5 cluster surrounded by oxygen rich ligands, such as oxyl, oxo, and carboxylate ligands. These negatively charged, oxygen rich ligands strongly stabilize the high valent states of the Mn cluster and play vital roles in effective water oxidation catalysis with low overpotential. This Account describes our endeavors to design effective Ru WOCs with low overpotential, large turnover number, and high turnover frequency by introducing negatively charged ligands, such as carboxylate. Negatively charged ligands stabilized the high valent states of Ru catalysts, as evidenced by the low oxidation potentials. Meanwhile, the oxygen production rates of our Ru catalysts were improved dramatically as well. Thanks to the strong electron donation ability of carboxylate containing ligands, a seven-coordinate Ru(IV) species was isolated as a reaction intermediate, shedding light on the reaction mechanisms of Ru-catalyzed water oxidation chemistry. Auxiliary ligands have dramatic effects on the water oxidation catalysis in terms of the reactivity and the reaction mechanism. For instance, Ru-bda (H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) water oxidation catalysts catalyze Ce(IV)-driven water oxidation extremely fast via the radical coupling of two Ru(V)?O species, while Ru-pda (H2pda = 1,10-phenanthroline-2,9-dicarboxylic acid) water oxidation catalysts catalyze the same reaction slowly via water nucleophilic attack on a Ru(V)?O species. With a number of active Ru catalysts in hands, light driven water oxidation was accomplished using catalysts with low catalytic onset potentials. The structures of molecular catalysts could be readily tailored to introduce additional functional groups, which favors the fabrication of state-of-the-art Ru-based water oxidation devices, such as electrochemical water oxidation anodes and photo-electrochemical anodes. The development of efficient water oxidation catalysts has led to a step forward in the sustainable energy system. PMID:26131964

  19. Big-Bang Nucleosynthesis Reactions Catalyzed by a Long-Lived Negatively Charged Leptonic Particle

    E-print Network

    Masayasu Kamimura; Yasushi Kino; Emiko Hiyama

    2009-06-13

    An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a long-lived negatively-charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau. The reactions studied here includes, i) 4He-transfer reactions such as (4He X)+d --> 6Li+X, ii) radiative capture reactions such as (7Be X)+ p --> (8B X) + gamma, iii) three-body breakup reactions such as (7Li X)+ p --> 4He+4He+X, iv) charge-exchange reactions such as (p X)+4He -->(4He X) +p, and v) neutron induced reactions such as (8Be X)+ n -->9Be+X, where (A X) denotes a Coulombic bound state of a nucleus A and X^-. In recent papers it has been claimed that some of the catalyzed BBN reactions have significantly large cross sections so as to markedly change the abundances of some elements, not only giving a solution to the 6Li-7Li problem (calculated underproduction of 6Li by a factor of 1000 and overproduction of 7Li+7Be by a factor of nearly 3) but also imposing strong restrictions on the lifetime and the primordial abundance of X^-. However, most of the calculations of these reaction cross sections in the literature were performed assuming too naive models or approximations that are unsuitable for the complicated low-energy nuclear reactions. We use a high-accuracy few-body calculational method developed by the authors, and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

  20. Control of charge trapping in a novel photorefractive composite consisting of a bifunctional molecule based on TPD

    Microsoft Academic Search

    Henk J. Bolink; C. Arts; Victor V. Krasnikov; George G. Malliaras; Georges Hadziioannou

    1996-01-01

    A novel photorefractive polymer is presented, based on a bifunctional molecule which is a derivative of the well known charge transport molecule N,N'-diphenyl-N,N'-bis(3- methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD). In this material the low intrinsic tap density causes the rather low value for the gain coefficient as well as the 90 degree phase shift between the refractive index grating and the illumination pattern. The

  1. Single-molecule conductance of a chemically modified, ?-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ

    PubMed Central

    García, Raúl; Herranz, M Ángeles; González, M Teresa; Bollinger, Gabino Rubio; Bürkle, Marius; Zotti, Linda A; Asai, Yoshihiro; Pauly, Fabian; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-01-01

    Summary We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a ?-extended tetrathiafulvalene (exTTF) group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10?7 G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species. PMID:26199662

  2. N-(1-Naphthyl) Ethylenediamine Dinitrate: A New Matrix for Negative Ion MALDI-TOF MS Analysis of Small Molecules

    NASA Astrophysics Data System (ADS)

    Chen, Rui; Chen, Suming; Xiong, Caiqiao; Ding, Xunlei; Wu, Chih-Che; Chang, Huan-Cheng; Xiong, Shaoxiang; Nie, Zongxiu

    2012-09-01

    An organic salt, N-(1-naphthyl) ethylenediamine dinitrate (NEDN), with rationally designed properties of a strong UV absorbing chromophore, hydrogen binding and nitrate anion donors, has been employed as a matrix to analyze small molecules ( m/z < 1000) such as oligosaccharides, peptides, metabolites and explosives using negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Compared with conventional matrixes such as ?-cyano-4-hydroxycinnamic acid (CCA) and 2,5-dihydroxybenzoic acid (DHB), NEDN provides a significant improvement in detection sensitivity and yields very few matrix-associated fragment and cluster ions interfering with MS analysis. For low-molecular-weight saccharides, the lowest detection limit achieved ranges from 500 amol to 5 pmol, depending on the molecular weight and the structure of the analytes. Additionally, the mass spectra in the lower mass range ( m/z < 200) consist of only nitrate and nitric acid cluster ions, making the matrix particularly useful for structural identification of oligosaccharides by post-source decay (PSD) MALDI-MS. Such a characteristic is illustrated by using maltoheptaose as a model system. This work demonstrates that NEDN is a novel negative ion-mode matrix for MALDI-MS analysis of small molecules with nitrate anion attachment.

  3. New RGD-peptide amphiphile mixtures containing a negatively charged diluent.

    PubMed

    Castelletto, Valeria; Gouveia, Ricardo M; Connon, Che J; Hamley, Ian W

    2013-01-01

    Here, we studied the self-assembly of two peptide amphiphiles, C16-Gly-Gly-Gly-Arg-Gly-Asp (PA 1: C16-GGG-RGD) and C16-Gly-Gly-Gly-Arg-Gly-Asp-Ser (PA 2: C16-GGG-RGDS). We showed that PA 1 and PA 2 self-assemble into nanotapes with an internal bilayer structure. C16 chains were highly interdigitated within the nanotape cores, while the peptide blocks formed water-exposed 13-sheets too. PA 1 nanotapes were characterized by one spacing distribution, corresponding to a more regular internal structure than that of PA 2 nanotapes, which presented two different spacing distributions. We showed that it is possible to obtain homogeneous nanotapes in water by co-assembling PA 1 or PA 2 with the negatively charged diluent C,16-Glu-Thr-Thr-Glu-Ser (PA 3: C16-ETTES). The homogeneous tapes formed by PA 1-PA 3 or PA 2-PA 3 mixtures presented a structure similar to that observed for the corresponding pure PA 1 or PA 2 nanotapes. The mixed nanotapes, which were able to form a stabilized matrix containing homogeneously distributed cell adhesive RGD groups, represent promising materials for designing new cell adhesion substrates. PMID:24611289

  4. Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

    NASA Astrophysics Data System (ADS)

    Wan, Yimao; Bullock, James; Cuevas, Andres

    2015-05-01

    This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta2O5) underneath plasma enhanced chemical vapour deposited silicon nitride (SiNx). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta2O5 and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 ?.cm and n-type 1.0 ?.cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm2 and 68 fA/cm2 are measured on 150 ?/sq boron-diffused p+ and 120 ?/sq phosphorus-diffused n+ c-Si, respectively. Capacitance-voltage measurements reveal a negative fixed insulator charge density of -1.8 × 1012 cm-2 for the Ta2O5 film and -1.0 × 1012 cm-2 for the Ta2O5/SiNx stack. The Ta2O5/SiNx stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.

  5. Radiation transport codes for potential applications related to radiobiology and radiotherapy using protons, neutrons, and negatively charged pions

    NASA Technical Reports Server (NTRS)

    Armstrong, T. W.

    1972-01-01

    Several Monte Carlo radiation transport computer codes are used to predict quantities of interest in the fields of radiotherapy and radiobiology. The calculational methods are described and comparisions of calculated and experimental results are presented for dose distributions produced by protons, neutrons, and negatively charged pions. Comparisons of calculated and experimental cell survival probabilities are also presented.

  6. Influence of charge on encapsulation and release behavior of small molecules in self-assembled layer-by-layer microcapsules.

    PubMed

    Mandapalli, Praveen K; Labala, Suman; Vanamala, Deekshith; Koranglekar, Manali P; Sakimalla, Lakshmi A; Venuganti, Venkata Vamsi K

    2014-12-01

    The objective of this study is to investigate the influence of charge of model small molecules on their encapsulation and release behavior in layer-by-layer microcapsules (LbL-MC). Poly(styrene sulfonate) and poly(ethylene imine) were sequentially adsorbed on calcium carbonate sacrificial templates to prepare LbL-MC. Model molecules with varying charge, anionic - ascorbic acid, cationic - imatinib mesylate (IM) and neutral - 5-fluorouracil were encapsulated in LbL-MC. Free and encapsulated LbL-MC were characterized using zetasizer, FTIR spectroscope and differential scanning calorimeter. The influence of IM-loaded LbL-MC on cell viability was studied in B16F10 murine melanoma cells. Furthermore, biodistribution of IM-loaded LbL-MC with and without PEGylation was studied in BALB/c mice. Results showed spherical LbL-MC of 3.0 ± 0.4 ?m diameter. Encapsulation efficiency of LbL-MC increased linearly (R(2 )= 0.89-0.99) with the increase in solute concentration. Increase in pH from 2 to 6 increased the encapsulation of charged molecules in LbL-MC. Charged molecules showed greater encapsulation efficiency in LbL-MC compared with neutral molecule. In vitro release kinetics showed Fickian and non-Fickian diffusion of small molecules, depending on the nature of molecular interactions with LbL-MC. At 50 ?M concentration, free IM showed significantly (p < 0.05) more cytotoxicity compared with IM-loaded LbL-MC. Biodistribution studies showed that PEGylation of LbL-MC decreased the liver and spleen uptake of IM-encapsulated LbL-MC. In conclusion, LbL-MC can be developed as a potential carrier for small molecules depending on their physical and chemical properties. PMID:24328418

  7. Carrier control via charge transfer at the topological-insulator/organic-molecule interface

    NASA Astrophysics Data System (ADS)

    Tanigaki, Katsumi; Tanabe, Yoichi; Kuynh, Khuong; Urata, Takahiro; Nouchi, Ryo; Heguri, Satoshi; Shimotani, Hidekazu; AIMR, Tohoku University Collaboration; Department of Pysics, Graduate School of Science, Tohoku University Collaboration; Osaka Prefecture University Collaboration

    2013-03-01

    A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications. A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications. Osaka Prefecture University

  8. Spectroscopic investigations on the binding of Methylene Blue and Nile Blue to negatively charged gold nanorods

    NASA Astrophysics Data System (ADS)

    Shrivastava, R.; Jain, B.; Das, K.

    2012-08-01

    The effect of longitudinal surface plasmon (l-SP) electric field of gold nanorods (AuNRs) on the optical (absorption and fluorescence) properties of two dyes Methylene Blue (MB) and Nile Blue (NB) has been studied by tuning and detuning the l-SP band with the absorption maxima of the dyes. Binding between dyes and nanorods were established by electrostatic interaction by making the nanorods negatively charged after coating them with polystyrene sulfonate (PSS). The absorption spectra of the dye-nanorod complex showed two prominent absorption bands in the 550-700 nm regions. For the detuned condition these changes are attributed to the nanorod induced aggregation of the dyes. However for the tuned condition, with increasing dye concentration the energy gap between the bands were observed to increase and then saturate. This is attributed to resonance coupling between the l-SP of the nanorod with the dye absorption. Although the fluorescence intensity of the dyes in the presence of increasing amount of AuNRs were observed to be quenched their lifetimes were observed to increase. Both the radiative (kr) and nonradiative (knr) rates of the dyes decreases in the presence of AuNRs. The magnitude of decrease for kr is much higher than knr, which is attributed to the formation of the non-fluorescent dimeric species. The increase in the fluorescence lifetime is attributed to the suppression of the excited state nonradiative pathways of these dyes adsorbed on the surface of the AuNRs. In addition, the changes of kr and knr were observed to be greater for the tuned condition.

  9. Small-molecule inhibitors of gram-negative lipoprotein trafficking discovered by phenotypic screening.

    PubMed

    McLeod, Sarah M; Fleming, Paul R; MacCormack, Kathleen; McLaughlin, Robert E; Whiteaker, James D; Narita, Shin-Ichiro; Mori, Makiko; Tokuda, Hajime; Miller, Alita A

    2015-03-01

    In Gram-negative bacteria, lipoproteins are transported to the outer membrane by the Lol system. In this process, lipoproteins are released from the inner membrane by the ABC transporter LolCDE and passed to LolA, a diffusible periplasmic molecular chaperone. Lipoproteins are then transferred to the outer membrane receptor protein, LolB, for insertion in the outer membrane. Here we describe the discovery and characterization of novel pyridineimidazole compounds that inhibit this process. Escherichia coli mutants resistant to the pyridineimidazoles show no cross-resistance to other classes of antibiotics and map to either the LolC or LolE protein of the LolCDE transporter complex. The pyridineimidazoles were shown to inhibit the LolA-dependent release of the lipoprotein Lpp from E. coli spheroplasts. These results combined with bacterial cytological profiling are consistent with LolCDE-mediated disruption of lipoprotein targeting to the outer membrane as the mode of action of these pyridineimidazoles. The pyridineimidazoles are the first reported inhibitors of the LolCDE complex, a target which has never been exploited for therapeutic intervention. These compounds open the door to further interrogation of the outer membrane lipoprotein transport pathway as a target for antimicrobial therapy. PMID:25583975

  10. Charge Enhancement of Single-Stranded DNA in Negative Electrospray Ionization Using the Supercharging Reagent Meta-nitrobenzyl Alcohol

    NASA Astrophysics Data System (ADS)

    Brahim, Bessem; Alves, Sandra; Cole, Richard B.; Tabet, Jean-Claude

    2013-12-01

    Charge enhancement of single-stranded oligonucleotide ions in negative ESI mode is investigated. The employed reagent, meta-nitrobenzyl alcohol (m-NBA), was found to improve total signal intensity (Itot), increase the highest observed charge states (zhigh), and raise the average charge states (zavg) of all tested oligonucleotides analyzed in negative ESI. To quantify these increases, signal enhancement ratios (SER1%) and charge enhancement coefficients (CEC1%) were introduced. The SER1%, (defined as the quotient of total oligonucleotide ion abundances with 1 % m-NBA divided by total oligonucleotide abundance without m-NBA) was found to be greater than unity for every oligonucleotide tested. The CEC1% values (defined as the average charge state in the presence of 1 % m-NBA minus the average charge state in the absence of m-NBA) were found to be uniformly positive. Upon close inspection, the degree of charge enhancement for longer oligonucleotides was found to be dependent upon thymine density (i.e., the number and the location of phospho-thymidine units). A correlation between the charge enhancement induced by the presence of m-NBA and the apparent gas-phase acidity (largely determined by the sequence of thymine units but also by the presence of protons on other nucleobases) of multiply deprotonated oligonucleotide species, was thus established. Ammonium cations appeared to be directly involved in the m-NBA supercharging mechanism, and their role seems to be consistent with previously postulated ESI mechanisms describing desorption/ionization of single-stranded DNA into the gas phase.

  11. Charge enhancement of single-stranded DNA in negative electrospray ionization using the supercharging reagent meta-nitrobenzyl alcohol.

    PubMed

    Brahim, Bessem; Alves, Sandra; Cole, Richard B; Tabet, Jean-Claude

    2013-12-01

    Charge enhancement of single-stranded oligonucleotide ions in negative ESI mode is investigated. The employed reagent, meta-nitrobenzyl alcohol (m-NBA), was found to improve total signal intensity (Itot), increase the highest observed charge states (zhigh), and raise the average charge states (zavg) of all tested oligonucleotides analyzed in negative ESI. To quantify these increases, signal enhancement ratios (SER1%) and charge enhancement coefficients (CEC1%) were introduced. The SER1%, (defined as the quotient of total oligonucleotide ion abundances with 1% m-NBA divided by total oligonucleotide abundance without m-NBA) was found to be greater than unity for every oligonucleotide tested. The CEC1% values (defined as the average charge state in the presence of 1% m-NBA minus the average charge state in the absence of m-NBA) were found to be uniformly positive. Upon close inspection, the degree of charge enhancement for longer oligonucleotides was found to be dependent upon thymine density (i.e., the number and the location of phospho-thymidine units). A correlation between the charge enhancement induced by the presence of m-NBA and the apparent gas-phase acidity (largely determined by the sequence of thymine units but also by the presence of protons on other nucleobases) of multiply deprotonated oligonucleotide species, was thus established. Ammonium cations appeared to be directly involved in the m-NBA supercharging mechanism, and their role seems to be consistent with previously postulated ESI mechanisms describing desorption/ionization of single-stranded DNA into the gas phase. PMID:24030289

  12. Role of negatively charged ions in plasma on the growth and field emission properties of spherical carbon nanotube tip

    SciTech Connect

    Tewari, Aarti; Walia, Ritu; Sharma, Suresh C. [Department of Physics, Maharaja Agrasen Institute of Technology, Sector-22, Rohini, Delhi-110086 (India)

    2012-01-15

    The role of negatively charged ions in plasma on growth (without catalyst) and field emission properties of spherical carbon nanotube (CNT) tip has been theoretically investigated. A theoretical model of charge neutrality, including the kinetics of electrons, negatively and positively charged ions, neutral atoms, and the energy balance of various species has been developed. Numerical calculations of the spherical CNT tip radius for different relative density of negatively charged ions {epsilon}{sub r}(=n{sub SF{sub 6{sup -}}}/n{sub C{sup +}}, where n{sub SF{sub 6{sup -}}} and n{sub C}{sup +} are the equilibrium densities of sulphur hexafluoride and carbon ions, respectively) have been carried out for the typical glow discharge plasma parameters. It is found that the spherical CNT tip radius decreases with {epsilon}{sub r} and hence the field emission of electrons from the spherical CNT tip increases. Some of our theoretical results are in accordance with the existing experimental observations.

  13. Nearly Perfect Spin Filter, Spin Valve and Negative Differential Resistance Effects in a Fe4-based Single-molecule Junction

    PubMed Central

    Zu, Fengxia; Liu, Zuli; Yao, Kailun; Gao, Guoying; Fu, Huahua; Zhu, Sicong; Ni, Yun; Peng, Li

    2014-01-01

    The spin-polarized transport in a single-molecule magnet Fe4 sandwiched between two gold electrodes is studied, using nonequilibrium Green's functions in combination with the density-functional theory. We predict that the device possesses spin filter effect (SFE), spin valve effect (SVE), and negative differential resistance (NDR) behavior. Moreover, we also find that the appropriate chemical ligand, coupling the single molecule to leads, is a key factor for manipulating spin-dependent transport. The device containing the methyl ligand behaves as a nearly perfect spin filter with efficiency approaching 100%, and the transport is dominated by transmission through the Fe4 metal center. However, in the case of phenyl ligand, the spin filter effect seems to be reduced, but the spin valve effect is significantly enhanced with a large magnetoresistance ratio, reaching 1800%. This may be attributed to the blocking effect of the phenyl ligands in mediating transport. Our findings suggest that such a multifunctional molecular device, possessing SVE, NDR and high SFE simultaneously, would be an excellent candidate for spintronics of molecular devices. PMID:24787446

  14. Reflectance-based optically detected resonance studies of neutral and negatively charged donors in GaAsAlxGa1xAs quantum wells

    E-print Network

    Dzyubenko, Alexander

    Reflectance-based optically detected resonance studies of neutral and negatively charged donors-based optically detected resonance ODR study of neutral and negatively charged donors in GaAs/AlxGa1 xAs quantum-well structures. The intensity of the e1h1(1s) excitonic reflectance feature was modulated by resonant absorption

  15. Validity of Saha's equation of thermal ionization for negatively charged spherical particles in complex plasmas in thermal equilibrium

    SciTech Connect

    Sodha, M. S.; Mishra, S. K. [DST Project, Department of Education Building, Lucknow University, Lucknow 226 007 (India)

    2011-04-15

    The authors have discussed the validity of Saha's equation for the charging of negatively charged spherical particles in a complex plasma in thermal equilibrium, even when the tunneling of the electrons, through the potential energy barrier surrounding the particle is considered. It is seen that the validity requires the probability of tunneling of an electron through the potential energy barrier surrounding the particle to be independent of the direction (inside to outside and vice versa) or in other words the Born's approximation should be valid.

  16. Reflectance-based optically detected resonance studies of negatively charged donors in GaAs\\/AlGaAs quantum wells

    Microsoft Academic Search

    A. Petrou; G. Kioseoglou; H. D. Cheong; T. Yeo; H. A. Nickel; B. D. McCombe; A. Yu. Sivachenko; A. B. Dzyubenko; W. Schaff

    2000-01-01

    We have carried out a reflectance-based optically detected resonance (RODR) study of negatively charged donors (D^-) in an n-type modulation doped GaAs\\/AlGaAs multiple quantum well structure. Changes in the reflectance intensity of the e_1h1 excitonic feature were induced by a monochromatic far infrared (FIR) laser beam under resonant conditions. Resonance was achieved by applying an external magnetic field (0-15 T)

  17. Spatially Extended Kondo State in Magnetic Molecules Induced by Interfacial Charge Transfer

    E-print Network

    Perera, U. G. E.

    An extensive redistribution of spin density in TBrPP-Co molecules adsorbed on a Cu(111) surface is investigated by monitoring Kondo resonances at different locations on single molecules. Remarkably, the width of the Kondo ...

  18. Charge-transfer complex formation in gelation: the role of solvent molecules with different electron-donating capacities.

    PubMed

    Basak, Shibaji; Bhattacharya, Sumantra; Datta, Ayan; Banerjee, Arindam

    2014-05-01

    A naphthalenediimide (NDI)-based synthetic peptide molecule forms gels in a particular solvent mixture (chloroform/aromatic hydrocarbon, 4:1) through charge-transfer (CT) complex formation; this is evident from the corresponding absorbance and fluorescence spectra at room temperature. Various aromatic hydrocarbon based solvents, including benzene, toluene, xylene (ortho, meta and para) and mesitylene, have been used for the formation of the CT complex. The role of different solvent molecules with varying electron-donation capacities in the formation of CT complexes has been established through spectroscopic and computational studies. PMID:24677404

  19. Negative ion production in small angle scattering of highly charged ions from the (0001) surface of highly oriented pyrolytic graphite

    SciTech Connect

    Reaves, M.; Kessel, Q.C.; Pollack, E.; Smith, W.W. [Department of Physics and The Institute of Materials Science, The University of Connecticut, Storrs, Connecticut 06269 (United States); Briere, M.A.; Schneider, D.H. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

    1997-02-01

    Highly charged N, O, F, and S ions, chosen for their electron affinities, were extracted from the Lawrence Livermore National Laboratory{close_quote}s EBIT II. After collimation, these ions struck a target of highly oriented pyrolytic graphite (HOPG) at an incident angle of 1.0 degree. Those ions scattered by 2.35 degrees (1.35 degree with respect to the surface) were charge state analyzed and the predominant charge state fractions were determined. As might be expected, there is a tendency for the fraction of negative ions to increase with increasing electron affinity; however, the negative ion yield is also strongly dependent on the ion velocity. For example, for sulfur the negative ion yields measured range from 0.13 to 0.23 of the scattered ions while for fluorine the range was 0.35 to 0.40. A pronounced velocity dependence found for the S{sup {minus}} ions is described well by a Saha-Langmuir-type equation. {copyright} {ital 1997 American Institute of Physics.}

  20. Mobilities of negative and positive charge carriers injected from metal electrodes into liquid benzene

    Microsoft Academic Search

    G. Kleinheins

    1970-01-01

    The influence of dissolved water on the electric current between metal electrodes in liquid benzene can be interpreted by assuming an injection of charge carriers, the mobility of which depends linearly on water content. This injection can be demonstrated by a drift method, which allows the determination of the mobility and polarity of the charge carriers in question. It will

  1. Spatial distribution of the charged particles and potentials during beam extraction in a negative-ion source

    SciTech Connect

    Tsumori, K.; Nakano, H.; Kisaki, M.; Ikeda, K.; Nagaoka, K.; Osakabe, M.; Takeiri, Y.; Kaneko, O.; Shibuya, M.; Asano, E.; Kondo, T.; Sato, M.; Komada, S.; Sekiguchi, H. [National Institute for Fusion Science, 322-1 Oroshi Toki-city, Figu 509-5292 (Japan); Kameyama, N.; Fukuyama, T.; Wada, S.; Hatayama, A. [Keio University, 3-14-1 Hiyoshi, Kouhoku-ku, Yokohama 223-8522 (Japan)

    2012-02-15

    We report on the characteristics of the electronegative plasma in a large-scale hydrogen negative ion (H{sup -}) source. The measurement has been made with a time-resolved Langmuir probe installed in the beam extraction region. The H{sup -} density is monitored with a cavity ring-down system to identify the electrons in the negative charges. The electron-saturation current decreases rapidly after starting to seed Cs, and ion-ion plasma is observed in the extraction region. The H{sup -} density steps down during the beam extraction and the electron density jumps up correspondingly. The time integral of the decreasing H{sup -} charge density agrees well with the electron charge collected with the probe. The agreement of the charges is interpreted to indicate that the H{sup -} density decreasing at the beam extraction is compensated by the electrons diffusing from the driver region. In the plasmas with very low electron density, the pre-sheath of the extraction field penetrates deeply inside the plasmas. That is because the shielding length in those plasmas is longer than that in the usual electron-ion plasmas, and furthermore the electrons are suppressed to diffuse to the extraction region due to the strong magnetic field.

  2. Charge recombination in organic small-molecule solar cells by Jiye Lee.

    E-print Network

    Lee, Jiye

    2008-01-01

    To enhance the power conversion efficiency in organic solar cells, charge recombination loss needs to be minimized. First, we perform transient absorption spectroscopy to study the charge recombination dynamics of thin ...

  3. On the Charge and Molecule Based Summations of Solvent Electrostatic Potentials and the Validity of Electrostatic Linear Response in Water

    Microsoft Academic Search

    C. Satheesan Babu; Pei-Kun Yang; Carmay Lim

    2002-01-01

    Solvent-induced electrostatic potentials and field components at thesolute sites of model Na+q–Cs-q molecules were computed bysumming over either solvent charges (q-summation) or solventmolecular centers (M-summation) from molecular dynamics simulations.These were compared with values obtained by solving Poisson equation withthe dielectric boundary defined by Reff = (Ratom+Rgmax )\\/2.q-summation using cut-offs that are = 10 Å generallyunderestimates or overestimates the magnitude of

  4. Understanding the charge-transfer state and singlet exciton emission from solution-processed small-molecule organic solar cells.

    PubMed

    Ran, Niva A; Kuik, Martijn; Love, John A; Proctor, Christopher M; Nagao, Ikuhiro; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2014-11-19

    Electroluminescence (EL) from the charge-transfer state and singlet excitons is observed at low applied voltages from high-performing small-molecule bulk-heterojunction solar cells. Singlet emission from the blends emerges upon altering the processing conditions, such as thermal annealing and processing with a solvent additive, and correlates with improved photovoltaic performance. Low-temperature EL measurements are utilized to access the physics behind the singlet emission. PMID:25212949

  5. 7Be charge exchange between 7Be3+ ion and exotic long-lived negatively charged massive particle in big bang nucleosynthesis

    E-print Network

    Motohiko Kusakabe; K. S. Kim; Myung-Ki Cheoun; Toshitaka Kajino; Yasushi Kino

    2013-07-29

    The existence of an exotic long-lived negatively charged massive particle, i.e., X-, during big bang nucleosynthesis can affect primordial light element abundances. Especially, the final abundance of 7Li, mainly originating from the electron capture of 7Be, has been suggested to reduce by the 7Be destruction via the radiative X- capture of 7Be followed by the radiative proton capture of the bound state of 7Be and X- (7BeX). We suggest a new route of 7BeX formation, that is the 7Be charge exchange at the reaction of 7Be3+ ion and X-. The formation rate depends on the number fraction of 7Be3+ ion, the charge exchange cross section of 7Be3+, and the probability that produced excited states 7BeX* are converted to the ground state. We estimate respective quantities affecting the 7BeX formation rate, and find that this reaction pathway can be more important than ordinary radiative recombination of 7Be and X-. The effect of the charge exchange reaction is then shown in a latest nuclear reaction network calculation. Quantum physical model calculations for related reactions are needed to precisely estimate the efficiency of this pathway in future.

  6. Propagation of charge-neutral beams in space - Modifications when negative ions are present

    NASA Technical Reports Server (NTRS)

    Winglee, R. M.; Pritchett, P. L.

    1987-01-01

    Two-dimensional (three velocity component) electrostatic simulations are used to investigate the properties of a charge-neutral beam consisting of H(+), H(-), and electrons which will be used in the Beams on Rockets (BEAR) experiment to be launched in late 1987 or early 1988. For cross-field injection and beam densities much greater than the ambient plasma density, the beam splits into two approximately charge-neutral beams: a H(+)-e(-) beam that propagates down the field lines and a H(+)-H(-) beam that propagates at nearly the initial beam velocity on time scales less than the ion gyroperiod. Because of this splitting, space-charge oscillations are induced in the H(+)-H(-) component, which lead to its breakup. At lower beam densities, particularly when the beam electron density is less than about the density of the ambient plasma, the ambient plasma response reduces the space-charge fields as the beam splits and the space-charge oscillations are suppressed.

  7. Charge transport in C60-based dumbbell-type molecules: mechanically induced switching between two distinct conductance states.

    PubMed

    Moreno-García, Pavel; La Rosa, Andrea; Kolivoška, Viliam; Bermejo, Daniel; Hong, Wenjing; Yoshida, Koji; Baghernejad, Masoud; Filippone, Salvatore; Broekmann, Peter; Wandlowski, Thomas; Martín, Nazario

    2015-02-18

    Single molecule charge transport characteristics of buckminsterfullerene-capped symmetric fluorene-based dumbbell-type compound 1 were investigated by scanning tunneling microscopy break junction (STM-BJ), current sensing atomic force microscopy break junction (CS-AFM-BJ), and mechanically controlled break junction (MCBJ) techniques, under ambient conditions. We also show that compound 1 is able to form highly organized defect-free surface adlayers, allowing the molecules on the surface to be addressed specifically. Two distinct single molecule conductance states (called high G(H)(1) and low G(L)(1)) were observed, depending on the pressure exerted by the probe on the junction, thus allowing molecule 1 to function as a mechanically driven molecular switch. These two distinct conductance states were attributed to the electron tunneling through the buckminsterfullerene anchoring group and fully extended molecule 1, respectively. The assignment of conductance features to these configurations was further confirmed by control experiments with asymmetrically designed buckminsterfullerene derivative 2 as well as pristine buckminsterfullerene 3, both lacking the G(L) feature. PMID:25651069

  8. Investigation of N-acyl homoserine lactone (AHL) molecule production in Gram-negative bacteria isolated from cooling tower water and biofilm samples.

    PubMed

    Haslan, Ezgi; Kimiran-Erdem, Ayten

    2013-09-01

    In this study, 99 Gram-negative rod bacteria were isolated from cooling tower water, and biofilm samples were examined for cell-to-cell signaling systems, N-acyl homoserine lactone (AHL) signal molecule types, and biofilm formation capacity. Four of 39 (10 %) strains isolated from water samples and 14 of 60 (23 %) strains isolated from biofilm samples were found to be producing a variety of AHL signal molecules. It was determined that the AHL signal molecule production ability and the biofilm formation capacity of sessile bacteria is higher than planktonic bacteria, and there was a statistically significant difference between the AHL signal molecule production of these two groups (p < 0.05). In addition, it was found that bacteria belonging to the same species isolated from cooling tower water and biofilm samples produced different types of AHL signal molecules and that there were different types of AHL signal molecules in an AHL extract of bacteria. In the present study, it was observed that different isolates of the same strains did not produce the same AHLs or did not produce AHL molecules, and bacteria known as AHL producers did not produce AHL. These findings suggest that detection of signal molecules in bacteria isolated from cooling towers may contribute to prevention of biofilm formation, elimination of communication among bacteria in water systems, and blockage of quorum-sensing controlled virulence of these bacteria. PMID:23250628

  9. Negatively Charged Nitrogen-Vacancy Centers in a 5 nm Thin 12 Diamond Film

    E-print Network

    Leonardo, Degiorgi

    , isotopically enriched ([12 C] = 99.99%) diamond layer by CVD. The present method allows for the formation of NVNegatively Charged Nitrogen-Vacancy Centers in a 5 nm Thin 12 C Diamond Film K. Ohashi, T. Rosskopf,# C. L. Degen, and K. M. Itoh*, School of Fundamental Science and Technology, Keio University

  10. Negative Compressibility and Charge Partitioning Between Graphene and MoS2 Two-Dimensional Electron Gases

    NASA Astrophysics Data System (ADS)

    Tolsma, John; Larentis, Stefano; Tutuc, Emanuel; MacDonald, Allan

    2014-03-01

    Electron-electron interactions often have opposite influences on thermodynamic properties of electrons in graphene compared to conventional two-dimensional electron gases (2DEGs), for example by lowering charge and spin-susceptibilities in the graphene case and enhancing them in the ordinary 2DEG case. In ordinary 2DEGs the charge susceptibility diverges at a finite carrier density, below which the compressibility becomes negative. We theoretically explore the influence of this qualitative difference on how charge is partitioned between a MoS2 and a graphene sheet 2DEG when they act as a compound capacitor electrode. Our theory is based on a random phase approximation for charge fluctuations in the 2DEGS and the coupling constant formulation for the ground state energy. We find that in the ideal case the MoS2 2DEG carrier density jumps immediately to a finite value when it is initially populated and discuss how this effect is moderated by disorder. Work supported by the Welch Foundation grant TBF1473 and the DOE Division of Materials Sciences Engineering grant DE-FG03-02ER45958.

  11. Insights into the mechanisms of electromediated gene delivery and application to the loading of giant vesicles with negatively charged macromolecules

    E-print Network

    Thomas Portet; Cyril Favard; Justin Teissié; David S. Dean; Marie-Pierre Rols

    2011-02-03

    We present experimental results regarding the electrotransfer of plasmid DNA into phosphatidylcholine giant unilamellar vesicles (GUVs). Our observations indicate that a direct entry is the predominant mechanism of electrotransfer. A quantitative analysis of the DNA concentration increments inside the GUVs is also performed, and we find that our experimental data are very well described by a simple theoretical model in which DNA entry is mostly driven by electrophoresis. Our theoretical framework allows for the prediction of the amount of transfered DNA as a function of the electric field parameters, and thus paves the way towards a novel method for encapsulating with high efficiency not only DNA, but any negatively charged macromolecule into GUVs.

  12. Fluctuating charge force fields: recent developments and applications from small molecules to macromolecular biological systems

    Microsoft Academic Search

    Sandeep Patel; Charles L. Brooks III

    2006-01-01

    The past decade has seen intense development of what are anticipated to be the next generation of classical force fields to be used in computational statistical mechanical approaches to studying a broad class of physical and biological systems. Among the several approaches being actively pursued currently is the fluctuating charge (or equivalently charge equilibration or electronegativity equalization) method. Within this

  13. A comparison of approximate techniques for the determination of potential energy surfaces of ion-molecule charge transfer systems

    NASA Astrophysics Data System (ADS)

    Diaz, B. Ramiro; Wahnon, P.; Sidis, V.

    1992-11-01

    The (HO2)+ molecular ion is used to experiment two approximate procedures which aim at reducing the computation effort that is needed for the determination of potential energy surfaces of ion-molecule charge transfer systems. The two procedures involve configuration interaction (CI) calculations of moderate sizes and are based on diagonal corrections of the electronic Hamiltonian matrix in a basis of projected-valence bond (PVB) configuration-state functions (CSF). The PVB-CSF's used in practice correspond to a full valence CI for each ionic or neutral partner as well as single excitations accounting for polarization and electron transfer. The diagonal corrections are of two sorts: (i) if insufficiently large orbital expansion bases are used they remove the relative ion-molecule basis set superposition error; (ii) if asymptotic energy levels of the involved neutrals or ions in their ground or valence excited states are misplaced they properly adjust these levels. When applied to (HO2)+ using a minimal or an extended orbital basis set expansion the proposed approaches yield concording results. The results also agree with the effective model potential (EMP) data of Grimbert et al. [Chem. Phys. 124, 187 (1988)] which have proved successful in the description of the H++O2 charge transfer dynamics. Comparison with fragmentary results from MRD-CI calculations by Vazquez et al. [Mol. Phys. 59, 291 (1986)] and Schneider et al. [Chem. Phys. 128, 311 (1988)] is somewhat mitigated. The method should be particularly useful for bulky ion-molecule systems.

  14. Computational modeling of chemical reactions and interstitial growth and remodeling involving charged solutes and solid-bound molecules.

    PubMed

    Ateshian, Gerard A; Nims, Robert J; Maas, Steve; Weiss, Jeffrey A

    2014-10-01

    Mechanobiological processes are rooted in mechanics and chemistry, and such processes may be modeled in a framework that couples their governing equations starting from fundamental principles. In many biological applications, the reactants and products of chemical reactions may be electrically charged, and these charge effects may produce driving forces and constraints that significantly influence outcomes. In this study, a novel formulation and computational implementation are presented for modeling chemical reactions in biological tissues that involve charged solutes and solid-bound molecules within a deformable porous hydrated solid matrix, coupling mechanics with chemistry while accounting for electric charges. The deposition or removal of solid-bound molecules contributes to the growth and remodeling of the solid matrix; in particular, volumetric growth may be driven by Donnan osmotic swelling, resulting from charged molecular species fixed to the solid matrix. This formulation incorporates the state of strain as a state variable in the production rate of chemical reactions, explicitly tying chemistry with mechanics for the purpose of modeling mechanobiology. To achieve these objectives, this treatment identifies the specific theoretical and computational challenges faced in modeling complex systems of interacting neutral and charged constituents while accommodating any number of simultaneous reactions where reactants and products may be modeled explicitly or implicitly. Several finite element verification problems are shown to agree with closed-form analytical solutions. An illustrative tissue engineering analysis demonstrates tissue growth and swelling resulting from the deposition of chondroitin sulfate, a charged solid-bound molecular species. This implementation is released in the open-source program FEBio ( www.febio.org ). The availability of this framework may be particularly beneficial to optimizing tissue engineering culture systems by examining the influence of nutrient availability on the evolution of inhomogeneous tissue composition and mechanical properties, the evolution of construct dimensions with growth, the influence of solute and solid matrix electric charge on the transport of cytokines, the influence of binding kinetics on transport, the influence of loading on binding kinetics, and the differential growth response to dynamically loaded versus free-swelling culture conditions. PMID:24558059

  15. The influence of the fixed negative charges on mechanical and electrical behaviors of articular cartilage under unconfined compression.

    PubMed

    Sun, D D; Guo, X E; Likhitpanichkul, M; Lai, W M; Mow, V C

    2004-02-01

    Unconfined compression test has been frequently used to study the mechanical behaviors of articular cartilage, both theoretically and experimentally. It has also been used in explant and gel-cell-complex studies in tissue engineering. In biphasic and poroelastic theories, the effect of charges fixed on the proteoglycan macromolecules in articular cartilage is embodied in the apparent compressive Young's modulus and the apparent Poisson's ratio of the tissue, and the fluid pressure is considered to be the portion above the osmotic pressure. In order to understand how proteoglycan fixed charges might affect the mechanical behaviors of articular cartilage, and in order to predict the osmotic pressure and electric fields inside the tissue in this experimental configuration, it is necessary to use a model that explicitly takes into account the charged nature of the tissue and the flow of ions within its porous interstices. In this paper, we used a finite element model based on the triphasic theory to study how fixed charges in the porous-permeable soft tissue can modulate its mechanical and electrochemical responses under a step displacement in unconfined compression. The results from finite element calculations showed that: 1) A charged tissue always supports a larger load than an uncharged tissue of the same intrinsic elastic moduli. 2) The apparent Young's modulus (the ratio of the equilibrium axial stress to the axial strain) is always greater than the intrinsic Young's modulus of an uncharged tissue. 3) The apparent Poisson's ratio (the negative ratio of the lateral strain to the axial strain) is always larger than the intrinsic Poisson's ratio of an uncharged tissue. 4) Load support derives from three sources: intrinsic matrix stiffness, hydraulic pressure and osmotic pressure. Under the unconfined compression, the Donnan osmotic pressure can constitute between 13%-22% of the total load support at equilibrium. 5) During the stress-relaxation process following the initial instant of loading, the diffusion potential (due to the gradient of the fixed charge density and the associated gradient of ion concentrations) and the streaming potential (due to fluid convection) compete against each other. Within the physiological range of material parameters, the polarity of the electric potential depends on both the mechanical properties and the fixed charge density (FCD) of the tissue. For softer tissues, the diffusion effects dominate the electromechanical response, while for stiffer tissues, the streaming potential dominates this response. 6) Fixed charges do not affect the instantaneous strain field relative to the initial equilibrium state. However, there is a sudden increase in the fluid pressure above the initial equilibrium osmotic pressure. These new findings are relevant and necessary for the understanding of cartilage mechanics, cartilage biosynthesis, electromechanical signal transduction by chondrocytes, and tissue engineering. PMID:15171124

  16. Direct visual evidence for chemical mechanism of SERRS of the S-complex of pyrimidine molecule adsorbed on silver nanoparticle via charge transfer.

    PubMed

    Zhang, Xin; Wang, Peijie; Sheng, Shaoxiang; Zhang, Lisheng; Fang, Yan

    2014-01-01

    In this paper, the S-complex of pyrimidine molecule absorbed on silver clusters was employed as a model molecule to study the enhancement mechanism in surface-enhanced resonance Raman scattering (SERRS). We described the chemical enhancement of SERRS through charge transfer (CT) from Ag20 to pyrimidine on resonance excitation, and electromagnetic enhancement through intracluster charge redistribution (CR) on the electronic intracluster collective oscillation excitation. It is shown that SERRS process of the pyrimidine molecule absorbed on silver clusters with different incident wavelength are dominated by different enhancement mechanisms. Both experimental and theoretical works have been performed to understand the CT process in SERRS. PMID:24287052

  17. Westward cross-field motion of negative charge filament activated by gradient-curvature proton drift: A cause of the westward traveling surge

    SciTech Connect

    Yamamoto, T.

    1988-07-01

    The cross-field interactive dynamics of two azimuthally elongated filaments of negative and positive charge excess which are close to each other is numerically studied. The negative charge filament is assumed to exist in the premidnight sector the plasmasheet, causing a discrete aurora at high latitude in the ionosphere. The positive charge filament responsible for a diffuse aurora is assumed to be caused by injection of the ring current energetic protons and located equatorward of the negative charge filament. In our simulation model using two-fluid approximation, the energetic protons execute the gradient and curvature (westward) drifts in the addition to the E x B drift and the electron motion is approximated by the E x B drift. The spatial and temporal development of the charge filaments is numerically followed in a perpendicular plane to the magnetic field. The simulation results show that the gradient and curvature drift of the positive charge carriers (energetic protons) can significantly increase the westward front-velocity of the negative charge filament is found to be on the order of a kilometer per second as geomagnetically projected on the ionosphere. It is then suggested that this physical process can be a cause of the westward traveling surge. copyright American Geophysical Union 1988

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

    E-print Network

    Interference effects in double ionization of spatially aligned hydrogen molecules by fast highly asymmetry is attributed to interference effects, analogous to Young's two-slit experiment, arising from scattering model based on two center interference. DOI: 10.1103/PhysRevA.70.042702 PACS number(s): 34.50.Gb I

  19. Long-range charge transport in single G-quadruplex DNA molecules

    E-print Network

    Simon, Emmanuel

    . For such purposes, double- stranded (ds) DNA has been considered a natural electrical conduit3,4 or template5 DNA derivative (250 nm), biotin-avidin (BA)­G4-DNA, as shown schematically in Fig. 1a. This is both have a deleterious effect on electrical transport through the molecules8,33 . Electrostatic force

  20. Single and double charge transfer of He(2+) ions with molecules at near-thermal energies

    NASA Technical Reports Server (NTRS)

    Tosh, R. E.; Johnsen, R.

    1993-01-01

    Rate coefficients were measured for charge-transfer reactions of He(2+) ions with H2, N2, O2, CO, CO2, and H2O. The experiments were carried out using a selected-ion drift-tube mass spectrometer. Total rate coefficients are found to be very large and are generally close to the limiting Langevin capture rate coefficients or the corresponding ADO-model (Su and Bowers, 1973) coefficients. The product-ion spectra indicate that both single and double charge transfer and possibly transfer ionization occur in these reactions.

  1. Regulation of K+ Flow by a Ring of Negative Charges in the Outer Pore of BKCa Channels. Part I

    PubMed Central

    Haug, Trude; Sigg, Daniel; Ciani, Sergio; Toro, Ligia; Stefani, Enrico; Olcese, Riccardo

    2004-01-01

    The pore region of the majority of K+ channels contains the highly conserved GYGD sequence, known as the K+ channel signature sequence, where the GYG is critical for K+ selectivity (Heginbotham, L., T. Abramson, and R. MacKinnon. 1992. Science. 258:1152–1155). Exchanging the aspartate residue with asparagine in this sequence abolishes ionic conductance of the Shaker K+ channel (D447N) (Hurst, R.S., L. Toro, and E. Stefani. 1996. FEBS Lett. 388:59–65). In contrast, we found that the corresponding mutation (D292N) in the pore forming ? subunit (hSlo) of the voltage- and Ca2+-activated K+ channel (BKCa, MaxiK) did not prevent conduction but reduced single channel conductance. We have investigated the role of outer pore negative charges in ion conduction (this paper) and channel gating (Haug, T., R. Olcese, T. Ligia, and E. Stefani. 2004. J. Gen Physiol. 124:185–197). In symmetrical 120 mM [K+], the D292N mutation reduced the outward single channel conductance by ?40% and nearly abolished inward K+ flow (outward rectification). This rectification was partially relieved by increasing the external K+ concentration to 700 mM. Small inward currents were resolved by introducing an additional mutation (R207Q) that greatly increases the open probability of the channel. A four-state multi-ion pore model that incorporates the effects of surface charge was used to simulate the essential properties of channel conduction. The conduction properties of the mutant channel (D292N) could be predicted by a simple ?8.5-fold reduction of the surface charge density without altering any other parameter. These results indicate that the aspartate residue in the BKCa pore plays a key role in conduction and suggest that the pore structure is not affected by the mutation. We speculate that the negative charge strongly accumulates K+ in the outer vestibule close to the selectivity filter, thus increasing the rate of ion entry into the pore. PMID:15277578

  2. Fast calculation of ?-electron charge densities in organic molecules: Non-condensed compounds

    Microsoft Academic Search

    Ivan P. Bangov; Kimito Funatsu; Carlos A. Del Carpio; Shin-ichi Sasaki

    1995-01-01

    A novel approach to fast computation of ?-electron charges in non-condensed conjugated systems is described. The conjugated parts of the molecular structure are regarded as formed of simple rings (annulenes) and chains (polyenes) and their molecular orbital (MO) energies and eigenvectors are given with simple analytical expressions. The nature of the different atoms within the structure are further characterized by

  3. PHYSICAL REVIEW B 86, 115417 (2012) Pseudoparticle approach for charge-transferring molecule-surface collisions

    E-print Network

    Fehske, Holger

    2012-01-01

    to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both percent to the secondary electron emission. DOI: 10.1103/PhysRevB.86.115417 PACS number(s): 34.35.+a, 34 of surface reactions is of fundamental interest. It represents a quantum impurity problem where a finite many

  4. Diagnosis of negative hydrogen ions and rovibrational distribution of H 2 molecule in non-thermal plasmas

    Microsoft Academic Search

    W. G. Wang; Y. Xu; X. F. Yang; A. M. Zhu; Z. W. Liu; X. Liu

    2008-01-01

    .  Rovibrational excited hydrogen molecule plays an important role for the \\u000a production of H- ions. The correlation between H- ion density and \\u000a rovibrational distribution of H2 molecules has been investigated in \\u000a dielectric barrier discharge hydrogen plasmas via optical emission \\u000a spectrometry and molecular beam mass spectrometry. The relative vibrational \\u000a distribution of molecular hydrogen in the electronic ground state has been \\u000a determined by

  5. Integrating high electrical conductivity and photocatalytic activity in cotton fabric by cationizing for enriched coating of negatively charged graphene oxide.

    PubMed

    Sahito, Iftikhar Ali; Sun, Kyung Chul; Arbab, Alvira Ayoub; Qadir, Muhammad Bilal; Jeong, Sung Hoon

    2015-10-01

    Electroconductive textiles have attended tremendous focus recently and researchers are making efforts to increase conductivity of e-textiles, in order to increase the use of such flexible and low cost textile materials. In this study, surface conductivity and photo catalytic activity of standard cotton fabric (SCF) was enhanced by modifying its surface charge, from negative to positive, using Bovine Serum Albumin (BSA) as a cationic agent, to convert it into cationised cotton fabric (CCF). Then, both types of fabrics were dip coated with a simple dip and dry technique for the adsorption of negatively charged graphene oxide (GO) sheets onto its surface. This resulted in 67.74% higher loading amount of GO on the CCF making self-assembly. Finally, this coating was chemically converted by vapor reduction using hydrazine hydrate to reduced graphene oxide (rGO) for restoration of a high electrical conductivity at the fabric surface. Our results revealed that with such high loading of GO, the surface resistance of CCF was only 40?/sq as compared to 510?/sq of the SCF and a 66% higher photo catalytic activity was also achieved through cationization for improved GO coating. Graphene coated SCF and CCF were characterized using FE-SEM, FTIR, Raman, UV-vis, WAXD, EDX and XPS spectroscopy to ascertain successful reduction of GO to rGO. The effect of BSA treatment on adsorption of cotton fabric was studied using drop shape analyzer to measure contact angle and for thermal and mechanical resistance, the fabric was tested for TGA and tensile strength, respectively. rGO coated fabric also showed slightly improved thermal stability yet a minor loss of strength was observed. The high flexibility, photocatalytic activity and excellent conductivity of this fabric suggests that it can be used as an electrode material for various applications. PMID:26076630

  6. Quantum effects in electron emission from and accretion on negatively charged spherical particles in a complex plasma

    SciTech Connect

    Mishra, S. K. [Institute for Plasma Research, Gandhinagar (India); Sodha, M. S.; Misra, Shikha [DST Project, Department of Education Building, University of Lucknow, Lucknow-226007 (India)

    2012-07-15

    The authors have investigated the electron emissions (thermionic, electric field, photoelectric, and light induced field) from and electron accretion on a charged particle in a complex plasma, on the basis of a three region electrical potential model in and around a charged spherical particle in a complex plasma, characterized by Debye shielding. A continuous variation of the transmission coefficient across the surface of a particle (corresponding to emission and accretion) with the radial electron energy {epsilon}{sub r} has been obtained. It is seen that the numerical values of the emission and accretion transmission coefficients [D({epsilon}{sub r})] are almost the same. This is the necessary and sufficient condition for the validity of Saha's equation for thermal equilibrium of a system of dust and electrons. This is in contrast to the earlier condition, which limited the range of validity of Saha's equation to the range of the applicability of Born approximation. It is seen that D({epsilon}{sub r}) increases with increasing {epsilon}{sub r}, increasing negative electric potential on the surface, decreasing radius, and deceasing Debye length. The electron currents, corresponding to thermionic, electric field, photoelectric and light induced field emission increase with increasing surface potential; this fact may have significant repercussions in complex plasma kinetics. Since numerically D({epsilon}{sub r}) is significantly different from unity in the range of {epsilon}{sub r} of interest, it is necessary to take into account the D({epsilon}{sub r})-{epsilon}{sub r} dependence in complex plasma theory.

  7. Comparison of positively and negatively charged achiral co-monomers added to cyclodextrin monolith: improved chiral separations in capillary electrochromatography.

    PubMed

    Lu, Yang; Shamsi, Shahab A

    2014-10-01

    Cyclodextrins (CDs) and their derivatives have been one of the most popular and successful chiral additives used in electrokinetic chromatography because of the presence of multiple chiral centers, which leads to multiple chiral interactions. However, there has been relatively less published work on the use of CDs as monolithic media for capillary electrochromatography (CEC). The goal of this study was to show how the addition of achiral co-monomer to a polymerizable CD such as glycidyl methacrylate ?-cyclodextrin (GMA/?-CD) can affect the enantioselective separations in monolithic CEC. To achieve this goal, polymeric monoliths columns were prepared by co-polymerizing GMA/?-CD with cationic or anionic achiral co-monomers [(2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and vinyl benzyltrimethyl-ammonium (VBTA)] in the presence of conventional crosslinker (ethylene dimethacrylate) and ternary porogen system including butanediol, propanol and water. A total of 34 negatively charged compounds, 30 positively charged compounds and 33 neutral compounds were screened to compare the enantioresolution capability on the GMA/?-CD, GMA/?-CD-VBTA and GMA/?-CD-AMPS monolithic columns. PMID:24108813

  8. Exciton formation as a rate limiting step for charge recombination in disordered organic molecules or polymers

    SciTech Connect

    Preezant, Yevgeni; Tessler, Nir [Department of Electrical Engineering, Microelecronic and Nanoelectronic Centers, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

    2011-01-01

    The exciton formation (direct charge recombination) is studied and quantified as a function of material physical-properties such as the exciton binding energy, the exciton lifetime, and the mechanism causing the electronic disorder. By using a model that is an extension of a charge transport model [Y. Preezant and N. Tessler, Phys. Rev. B 74, 235202 (2006)] we are able to compare the direct exciton formation rate with the one predicted by the Langevin model. Using reasonable material parameters we find that in many cases the overall balance between free charge carrier and excitons is significantly affected by the exciton formation rate with its values being significantly low compared to the Langevin rate. We also find that in order to describe the complete recombination process it is important to introduce an intermediate state which we term exciton-precursor. This is in contrast to the common practice of using the Langevin model which embeds the assumption that the exciton formation rate is negligibly fast. The relations found between the physical-properties and the recombination rate can explain why certain materials exhibit Langevin rate while others exhibit significantly suppressed rates. This would eventually lead to the design of new materials better suited for either photocells or light-emitting diodes.

  9. Structural influences on charge carrier dynamics for small-molecule organic photovoltaics

    SciTech Connect

    Wang, Zhiping, E-mail: wang-zhiping@aist.go.jp; Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji [Research Center for Photovoltaic Technologies, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan); Miyadera, Tetsuhiko, E-mail: tetsuhiko-miyadera@aist.go.jp [Research Center for Photovoltaic Technologies, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan); JST-PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, 332-0012 Saitama (Japan); Saeki, Akinori; Seki, Shu [Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, 565-0871 Suita, Osaka (Japan); Zhou, Ying [Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan)

    2014-07-07

    We investigated the structural influences on the charge carrier dynamics in zinc phthalocyanine/fullerene (ZnPc/C{sub 60}) photovoltaic cells by introducing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2,5-bis(4-biphenylyl)-bithiophene (BP2T) between indium tin oxide and ZnPc layers. ZnPc films can be tuned to be round, long fiber-like, and short fiber-like structure, respectively. Time-resolved microwave conductivity measurements reveal that charge carrier lifetime in ZnPc/C{sub 60} bilayer films is considerably affected by the intra-grain properties. Transient photocurrent of ZnPc single films indicated that the charge carriers can transport for a longer distance in the long fiber-like grains than that in the round grains, due to the greatly lessened grain boundaries. By carefully controlling the structure of ZnPc films, the short-circuit current and fill factor of a ZnPc/C{sub 60} heterojunction solar cell with BP2T are significantly improved and the power conversion efficiency is increased to 2.6%, which is 120% larger than the conventional cell without BP2T.

  10. Calculations for charge transfer and ionization in heavy-particle collisions from water molecules

    NASA Astrophysics Data System (ADS)

    Kirchner, T.; Murakami, M.; Horbatsch, M.; Lüdde, H. J.

    2012-11-01

    A recently introduced method for the description of bare ion-molecule collisions is extended to deal with intermediate-energy He+-H2O collisions, in which both the projectile electron and the target electrons are allowed to undergo transitions. All initially populated orbitals are propagated simultaneously using the same effective single-particle Hamiltonian to ensure their orthogonality at all times. The asymptotic solutions are combined to form many-electron transition probabilities on the level of single determinantal wave functions, thereby respecting the Pauli principle. It is shown that this analysis has interesting consequences for capture, loss, and ionization channels.

  11. Electronegativities in situ, bond hardnesses, and charge-transfer components of bond energies from the topological theory of atoms in molecules

    SciTech Connect

    Cioslowski, J.; Mixon, S.T. (Florida State Univ., Tallahassee (United States))

    1993-02-10

    Rigorous definitions for electronegativities of atoms and functional groups in molecules, bond hardnesses, and the charge-transfer components of the bond energies are proposed. The definitions rely upon values of total energies and their derivatives calculated for molecules composed of fragments with a controlled degree of charge transfer. Such calculations, in which the atomic or fragment charges are obtained with the help of the topological theory of atoms in molecules, are easily accomplished by adding appropriate Lagrange multiplier terms to the electronic Hamiltonian. Numerical examples that are given for 23 different systems indicate that the bond hardnesses are mostly transferable, but because of the electric field generated by the molecular environment the electronegativity differences are not. 27 refs., 1 fig., 1 tab.

  12. A new method to study Li-ion cell safety: laser beam initiated reactions on both charged negative and positive electrodes

    NASA Astrophysics Data System (ADS)

    Pérès, J. P.; Perton, F.; Audry, C.; Biensan, Ph; de Guibert, A.; Blanc, G.; Broussely, M.

    The improvement of Li-ion batteries safety in abuse use is one of the key issues for their establishment in future hybrid or electrical vehicles. Such a challenge requires a perfect understanding of phenomena which could occur in abuse situation. A new technique for a better understanding of Li-ion cell safety has been so investigated. Reactions between electrolyte and charged electrodes (positive and negative just recovered from dismantled charged 4/5A cells) have been initiated by a laser beam, having a monitored intensity and time pulse. From such a device, a strong and controlled heating can be generated, in a very short time scale, on a defined electrode surface area. This localized heating, which is supposed to be similar to that could occur from a cell internal short-circuit, is able to initiate "self-propagation reactions" on charged negative and positive electrodes. This new technique has allowed a ranking of charged electrodes in terms of "self-propagation ability". This range of new data has been compared to results obtained from classical thermal characterization methods (DSC, DTA) and results obtained from normalized abuse tests. Global charged negative and positive electrodes degradation mechanisms have been proposed in good agreement with the whole results. The safety of a done Li-ion cell seems mainly related to active negative and positive active materials, but also to other components of the electrodes, and especially additive carbons and aluminum collector of the positive side.

  13. Vibrational relaxation in H/sub 2/ molecules by wall collisions: applications to negative ion source processes

    SciTech Connect

    Karo, A.M.; Hiskes, J.R.; Hardy, R.J.

    1984-10-01

    In the volume of a hydrogen discharge, H/sub 2/ molecules, excited to high vibrational levels (v'' > 6), are formed either by fast-electron collisions or from H/sub 2//sup +/ ions that are accelerated across the discharge-wall potential that undergo Auger neutralization prior to impact with the discharge chamber wall. We have used computer molecular dynamics to study the de-excitation and re-excitation of vibrationally-excited H/sub 2/ molecules undergoing repeated wall collisions. The initial translational energies range from thermal to 100 eV and the initial vibrational states range from v'' = 2 to v'' = 12. The average loss or gain of vibrational, rotational, translational, and total molecular energies and the survival rates of the molecules have been evaluated. At thermal energies vibrational de-excitation is the predominant process, and a consistent picture emerges of rapid energy redistribution into all the molecular degrees of freedom and a slower rate of loss of total molecular energy to the wall. At higher translational energies (1 to 100 eV) a substantial fraction of the molecules survive with large (v'' > 6) vibrational energy. This vibrational population provides a contribution to the total excited vibrational population comparable to that from the fast-electron collision process.

  14. Negative regulation of TLR9-mediated IFN  induction by a small-molecule, synthetic TLR7 ligand

    Microsoft Academic Search

    Jason D. Marshall; Darren S. Heeke; Marianne L. Gesner; Brian Livingston; Gary Van Nest

    2007-01-01

    Toll-like receptors (TLRs) are a family of molecules that function as sensors for the detec- tion of foreign pathogens through the recognition of nonvariable microbial motifs. Although numer- ous studies have focused on singular TLRs, less attention has been focused on how simultaneous signaling of multiple TLRs may result in counter- regulation of the effects of each. Here, we examine

  15. First results from a double Vlasov model for negative ion extraction from volume sources - the possibility of an enhanced transverse space charge limit

    SciTech Connect

    Whealton, J.H.; Olsen, D.K.; Raridon, R.J.

    1997-12-01

    A new negative ion source extraction model has been formulated and implemented which explicitly considers the motion of positive ions and the volume generation of negative ions. It is found that (1) for high-beam currents, the beam current is limited by a transverse space charge limit, meaning that an increase in negative ion density at the extraction sheath will result in a lower beam current (this result is universally observed at high beam currents); (2) there is a saddle point with a potential barrier preventing the most volume produced negative ions from being extracted (the combination of 1 and 2 indicates that most of the negative ions being created do not find their way into the beam); (3) introduction of cesium may cause, most importantly, an increase in the transverse space charge limit (there is an abundance of experimental data supporting this effect); (4) cesium may also result in an increase in the fraction of volume produced negative ions which are extracted; (5) cesium may also result in a reduction of extracted electrons by dint of a less negative bias on the plasma electrode with respect to the adjacent plasma, thus allowing the transverse space charge limit budget to be taken up wholly by the ions. (The combination of 3-5 represents the way an actual increase in the beam current can be achieved); (6) a strong ion time scale sheath instability due to violation of Bohm criteria produces an anomalous ion temperature that increases with beam current routinely seen in experiments; and (7) introduction of cesium may result in a reduction in this instability. These insights may lead to improvements in volume negative ion sources, and the most important finding of an increased space charge limit has apparently been verified experimentally by reinterpretation of the findings of Bacal, Allison and Leung.

  16. Adsorption and transport of charged vs. neutral hydrophobic molecules at the membrane of murine erythroleukemia (MEL) cells.

    PubMed

    Zeng, Jia; Eckenrode, Heather M; Dai, Hai-Lung; Wilhelm, Michael J

    2015-03-01

    The adsorption and transport of hydrophobic molecules at the membrane surface of pre- and post-DMSO induced differentiated murine erythroleukemia (MEL) cells were examined by time- and wavelength-resolved second harmonic light scattering. Two medium (<600 Da) hydrophobic molecules, cationic malachite green (MG) and neutral bromocresol purple (BCP), were investigated. While it was observed that the MG cation adsorbs onto the surface of the MEL cell, neutral BCP does not. It is suggested that an electrostatic interaction between the opposite charges of the cation and the MEL cell surface is the primary driving force for adsorption. Comparisons of adsorption density and free energy, measured at different pH and cell morphology, indicate that the interaction is predominantly through sialic acid carboxyl groups. MG cation adsorption densities have been determined as (0.6±0.3)×10(6) ?m(-2) on the surface of undifferentiated MEL cells, and (1.8±0.5)×10(7) ?m(-2) on differentiated MEL cells, while the deduced adsorption free energies are effectively identical (ca. -10.9±0.1 and -10.8±0.1 kcal mol(-1), respectively). The measured MG densities indicate that the total number of surface carboxyl groups is largely conserved following differentiation, and therefore the density of carboxylic groups is much larger on the differentiated cell surface than the undifferentiated one. Finally, in contrast to synthetic liposomes and bacterial membranes, surface adsorbed MG cations are unable to traverse the MEL cell membrane. PMID:25660095

  17. Charge competition with oxygen molecules determines the growth of gold particles on doped CaO films.

    PubMed

    Cui, Yi; Huang, Kai; Nilius, Niklas; Freund, Hans-Joachim

    2013-01-01

    The influence of gas-phase oxygen on the growth of Au nanoparticles on Mo-doped CaO films has been investigated by means of low temperature scanning tunnelling microscopy and X-ray photoelectron spectroscopy. Whereas at ideal vacuum conditions, only 2D Au islands develop on the oxide surface, the fraction of 3D deposits increases with increasing O2 pressure until they become the dominant species in 106 mbar oxygen. The morphology crossover arises from changes in the interfacial electron flow between Mo donors in the CaO lattice and different ad-species on the oxide surface. In the absence of 02 molecules, the donor electrons are predominately transferred to the Au ad-atoms, which consequently experience enhanced binding to the oxide surface and agglomerate into 2D islands. In an oxygen atmosphere, on the other hand, a substantial fraction of the excess electrons is trapped by adsorbed O2 molecules, while the Au atoms remain neutral and assemble into tall 3D particles that are typical for non-doped oxides. Our experiments demonstrate how the competition for charge between different adsorbates governs the physical and chemical properties of doped oxides, so widely used in heterogeneous catalysis. PMID:24015581

  18. Using light-switching molecules to modulate charge mobility in a quantum dot array

    NASA Astrophysics Data System (ADS)

    Chu, Iek-Heng; Trinastic, Jonathan; Wang, Lin-Wang; Cheng, Hai-Ping

    2014-03-01

    We have studied the electron hopping in a two-CdSe quantum dot (QD) system linked by an azobenzene-derived light-switching molecule. This system can be considered as a prototype of a QD supercrystal. Following the computational strategies given in our recent work [I.-H. Chu et al., J. Phys. Chem. C 115, 21409 (2011), 10.1021/jp206526s], we have investigated the effects of molecular attachment, molecular isomer (trans and cis), and QD size on the electron hopping rate using Marcus theory. Our results indicate that molecular attachment has a large impact on the system for both isomers. In the most energetically favorable attachment, the cis isomer provides significantly greater coupling between the two QDs and hence the electron hopping rate is greater compared to the trans isomer. As a result, the carrier mobility of the QD array in the low carrier density, weak external electric-field regime is several orders of magnitude higher in the cis compared to the trans configuration. This demonstration of mobility modulation using QDs and azobenzene could lead to an alternative type of switching device.

  19. Dissociative electron attachment to the highly reactive difluoromethylene molecule-importance of CF2 for negative ion formation in fluorocarbon plasmas

    NASA Astrophysics Data System (ADS)

    Graupner, K.; Field, T. A.; Mayhew, C. A.

    2010-08-01

    Dissociative electron attachment to the highly reactive difluoromethylene molecule, CF2, produced in a C3F6/He microwave plasma and stepwise via the fast atom reaction CF3I+H?CF3+HI and CF3+H?CF2+HF, has been investigated. The upper limit for the cross section of formation of F- via dissociative electron attachment to CF2 is estimated to be 5×10-4 Å2. This value is four orders of magnitude smaller than the cross section previously predicted from scattering calculations. It is concluded that difluoromethylene plays a negligible role in negative ion formation in fluorocarbon plasmas.

  20. Unconventional charge distribution in the planar wheel-type M©B6H6(-/0/+) (M = Mn, Fe and Co): central M with negative charges and peripheral boron ring with positive charges.

    PubMed

    Hou, Jianhua; Duan, Qian; Qin, Jieming; Shen, Xiande; Zhao, Jianxun; Liang, Qingcheng; Jiang, Dayong; Gao, Shang

    2015-04-21

    Planar wheel-type D6h M©B6H6(-/0/+) (M = Mn, Fe and Co for anion, neutral and cation, respectively.) clusters with a planar hexacoordinate transition-metal at the center of the boron ring were designed and investigated by density functional theory. These planar clusters are chemically stable as a result of their large binding energy, vertical ionization potential, and vertical electron affinity. The detailed natural population and molecular orbital analyses suggest that not only does the M atom donate electrons to the boron ring for participation in the ?-delocalized bonding, but also the boron ring donates electrons back to the M atom for the formation of the ?-delocalized bonding, which leads to a strong aromaticity and unconventional charge distribution, i.e., the M atom is negatively charged, while the boron ring is positively charged. This study may open a new area in coordination chemistry for planar hexacoordinate transition metals and we expect further experimental exploration of their synthesis and potential applications. PMID:25830384

  1. The major histocompatibility complex class I protein HLA-C plays a crucial role as an inhibitory molecule capable of sending dominant negative signals to both natural killer (NK) cells and

    E-print Network

    as an inhibitory molecule capable of sending dominant negative signals to both natural killer (NK) cells and cytotoxic T lymphocytes (CTL) via binding to killer cell Ig-like receptors (KIR). Recently HLA-C has been

  2. Effect of negatively charged cellulose nanofibers on the dispersion of hydroxyapatite nanoparticles for scaffolds in bone tissue engineering.

    PubMed

    Park, Minsung; Lee, Dajung; Shin, Sungchul; Hyun, Jinho

    2015-06-01

    Nanofibrous 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)-oxidized bacterial cellulose (TOBC) was used as a dispersant of hydroxyapatite (HA) nanoparticles in aqueous solution. The surfaces of TOBC nanofibers were negatively charged after the reaction with the TEMPO/NaBr/NaClO system at pH 10 and room temperature. HA nanoparticles were simply adsorbed on the TOBC nanofibers (HA-TOBC) and dispersed well in DI water. The well-dispersed HA-TOBC colloidal solution formed a hydrogel after the addition of gelatin, followed by crosslinking with glutaraldehyde (HA-TOBC-Gel). The chemical modification of the fiber surfaces and the colloidal stability of the dispersion solution confirmed TOBC as a promising HA dispersant. Both the Young's modulus and maximum tensile stress increased as the amount of gelatin increased due to the increased crosslinking of gelatin. In addition, the well-dispersed HA produced a denser scaffold structure resulting in the increase of the Young's modulus and maximum tensile stress. The well-developed porous structures of the HA-TOBC-Gel composites were incubated with Calvarial osteoblasts. The HA-TOBC-Gel significantly improved cell proliferation as well as cell differentiation confirming the material as a potential candidate for use in bone tissue engineering scaffolds. PMID:25910635

  3. Negatively and positively charged excitons in GaAs/AlxGa1 xAs quantum wells Gleb Finkelstein, Hadas Shtrikman, and Israel Bar-Joseph

    E-print Network

    Finkelstein, Gleb

    gas smoothly transforms into a negatively charged exciton and not into a neutral exciton. The Zeeman . These considerations lead to the choice of a two-dimensional electron gas 2DEG near the metal-insulator transition smoothly transforms into X at the insulating state and not to an exciton. On the other hand, the Zeeman

  4. The KelvinHelmholtz instability in a plasma with negatively charged dust Q. Z. Luo, N. D'Angelo, and R. L. Merlinoa)

    E-print Network

    Merlino, Robert L.

    PVSI instability in a dusty plasma by D'Angelo and Song5 follows closely the earlier work of D'Angelo1The Kelvin­Helmholtz instability in a plasma with negatively charged dust Q. Z. Luo, N. D­Helmholtz parallel velocity shear instability is investigated experimentally in a magnetized cesium plasma. The dust

  5. The reactions of the molecular nitrogen doubly charged ion with neutral molecules of relevance to planetary ionospheres

    NASA Astrophysics Data System (ADS)

    Ricketts, Claire Louise

    Diatomic dications (e.g. C02+) have been known to exist for several decades and are believed to be important components of energised media. Molecular dications possess significant internal energy due to the Coulombic repulsion of their two positive charges, meaning that many possible reaction channels are available to dications in a collision with a neutral molecule. Modellers have recently predicted that N22+ is present in the ionosphere of Earth and Titan as well as the dications C>22+ and 02+ in the ionosphere of Earth and CC>22+ in the ionosphere of Mars. These recent predictions, of dications in planetary ionospheres, imply that dications, and processes involving dication-neutral collisions, may have more significance than previously thought in the upper atmospheres of planets. Therefore this thesis describes a study of the reactions between N2 dications and neutrals, potentially of relevance to the ionosphere of Earth and Titan. A position sensitive coincidence (PSCO) time-of flight (TOF) mass spectrometer is used to probe the reactivity, energetics and dynamics of the bimolecular reactions of N22 . Dication-neutrals reactions often result in a pair of singly charged ions. The PSCO experiment is used to collect these pairs of singly-charged ions in coincidence. From the position-sensitive data we extract the velocity vectors of the product ions, and if the reaction of interest involves the formation of a third, undetected, neutral species, its velocity can be determined via conservation of momentum. The electron transfer reactions between dications and neutrals have been well rationalized 2+ previously, so only the electron transfer reactions of N2 with Ne and NO are discussed in this thesis. This thesis concentrates on probing the less well rationalized, bond- forming reactions between dications and neutrals. The bond-forming reactions of N22+ with O2, CO2, H2O, C2H2, CH4, H2 and Ar have been investigated and discussed. Several new bond-forming reactions mechanisms are derived for example, the bond-forming reactions of N22+ with O2 proceed via a 'long' lived complex which dissociates via loss of a neutral and then charge separation, a mechanism which is also operating for one of the bond-forming reactions of N2 with CO2 and N2 with H2O. Additional bond-forming reactions are detected for N22+ with CO2 and H2O, which proceed via shorter lived collision complexes. The reactions of N22+ with C2H2, CH4, H2 and Ar all proceed via a variety of mechanisms involving short-lived collision complexes or H and electron stripping.

  6. Measurement of the Charge Number Per Adsorbed Molecule and Packing Densities of Self-Assembled Long-Chain Monolayers of Thiols

    E-print Network

    Dutcher, John

    and packing densities in self-assembled monolayers (SAMs) of octadecanethiol (C18SH), a representative long determination of the composition, quality, and coverage of self-assembled monolayers (SAMs) is tremendouslyMeasurement of the Charge Number Per Adsorbed Molecule and Packing Densities of Self-Assembled Long

  7. Formation of negative ions in the interstellar medium by dissociative electron attachment to the H2CN molecule

    NASA Astrophysics Data System (ADS)

    Kokoouline, Viatcheslav; Fonseca Dos Santos, Samantha; Douguet, Nicolas; Orel, Ann

    2013-05-01

    The methylene amidogen radical (H2CN) was first discovered, in 1962 by Cochran et al ., and since then it has received considerable attention from both experimentalists and theoreticians. It is considered an important intermediate in the combustion of nitramine propellants and proposed to play a role in extraterrestrial atmospheres. It was detected in interstellar clouds in 1994, and its dissociative electron attachment (DEA) process may be responsible for the formation of the CN- and the H- negative ions: e-+H2CN --> CN- + H2; e-+H2CN --> H- + HCN. We report here the results of our ab initio quantum chemical studies of the geometrical and electronic structure of the methylene amidogen and and its negative ion H2CN- in the theoretical of DEA in H2CN. The scattering calculations are carried out using the complex Kohn variational method. The nuclear dynamics, including dissociation, will later be treated using the MCTDH code with a three-dimensional potential energy surface, in which the distance of CN is kept frozen. The methylene amidogen radical (H2CN) was first discovered, in 1962 by Cochran et al ., and since then it has received considerable attention from both experimentalists and theoreticians. It is considered an important intermediate in the combustion of nitramine propellants and proposed to play a role in extraterrestrial atmospheres. It was detected in interstellar clouds in 1994, and its dissociative electron attachment (DEA) process may be responsible for the formation of the CN- and the H- negative ions: e-+H2CN --> CN- + H2; e-+H2CN --> H- + HCN. We report here the results of our ab initio quantum chemical studies of the geometrical and electronic structure of the methylene amidogen and and its negative ion H2CN- in the theoretical of DEA in H2CN. The scattering calculations are carried out using the complex Kohn variational method. The nuclear dynamics, including dissociation, will later be treated using the MCTDH code with a three-dimensional potential energy surface, in which the distance of CN is kept frozen. This work is supported by the DOE Office of Basic Energy Science and the National Science Foundation, Grant No's PHY-11-60611 and PHY-10-68785.

  8. Charged clusters in liquid helium

    NASA Astrophysics Data System (ADS)

    Dyugaev, A. M.; Grigor'ev, P. D.; Lebedeva, E. V.

    2010-03-01

    The appropriateness of the experimental study of charged clusters in liquid helium has been supported. The interaction potential of negative ions (electron bubbles) with inert clusters formed by Ne, Ar, Kr, and Xe atoms or H2 and N2 molecules has been found. Small clusters levitate at a distance of 13-16 Å above the negative ion. The scalings laws for the properties of charged inert clusters have been discovered and grounded; the number of quantum levels and states of such clusters has been determined. The mobility measurement of charged clusters may provide a new technique of probing the properties of impurity nanoparticles in helium.

  9. Chemical bonding in hypervalent molecules. The dominance of ionic bonding and negative hyperconjugation over d-orbital participation

    SciTech Connect

    Reed, A.E.; von Rague Schleyer, P. (Universitaet Erlangen-Nuernberg (Germany, F.R.))

    1990-02-14

    Does sulfur form six covalent bonds in CH{sub 3}SO{sub 2}Cl, F{sub 3}S{triple bond}N or carbon or phosphorus five bonds in F{sub 3}C=O{sup {minus}}, F{sub 3}P=O After a brief history of the viewpoints on hypervalent bonding and a comparison of analysis methods (with CH{sub 3}SO{sub 2}Cl as example), natural population and natural bond orbital analysis is applied to a series of 32-valence-electron species of X{sub 3}XY type (CF{sub 4}, F{sub 3}NO, O{sub 3}ClF, O{sub 3}PS{sup 3{minus}}, F{sub 3}SN, etc.). The {sigma}-bonding in these systems is found to be significantly ionic, and the strongly polar {sigma}*{sub AX} orbitals are found to be more effective electron acceptors than the extra-valence d{sub {pi}} (A) orbitals. By generalizing our discussion to n-coordinate 8n-valence-electron species (HF{sub 2}{sup {minus}}, BF{sub 3}, ClO{sub 4}{sup {minus}}, F{sub 4}SO, F{sub 5}TeO{sup {minus}}, IF{sub 6}{sup +}, OXeF{sub 6}, etc.) and their reduced analogues that have one or more lone pairs on the central atom (SF{sub 4}, IF{sub 6}{sup {minus}}, ClF{sub 3}, etc.), we provide a classification of hypervalent (and many nonhypervalent) molecules. The simple, qualitative bonding concepts for hypervalent molecules developed here supercede the inaccurate and misleading dsp{sup 3} and d{sup 2}sp{sup 3} models that are still in widespread use.

  10. Positronium ions and molecules

    NASA Technical Reports Server (NTRS)

    Ho, Y. K.

    1990-01-01

    Recent theoretical studies on positronium ions and molecules are discussed. A positronium ion is a three particle system consisting of two electrons in singlet spin state, and a positron. Recent studies include calculations of its binding energy, positron annihilation rate, and investigations of its doubly excited resonant states. A positronium molecule is a four body system consisting of two positrons and two electrons in an overall singlet spin state. The recent calculations of its binding energy against the dissociation into two positronium atoms, and studies of auto-detaching states in positronium molecules are discussed. These auto-dissociating states, which are believed to be part of the Rydberg series as a result of a positron attaching to a negatively charged positronium ion, Ps-, would appear as resonances in Ps-Ps scattering.

  11. Excitation of atoms and molecules in collisions with highly charged ions. Progress report, January 1, 1990--December 1, 1992

    SciTech Connect

    Watson, R.L.

    1993-01-01

    A study of the double ionization of He by high-energy N{sup 7+} ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N{sub 2}, O{sub 2}, and CO molecular ions produced in collisions with 97-MeV Ar{sup 14+} ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO{sup 2+} and CO{sup 3+} from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO{sup 1+} and CO{sup 2+} molecular ions, and the branching ratios for the most prominent charge division channels of CO{sup 2+} through CO{sup 7+} were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

  12. Excitation of atoms and molecules in collisions with highly charged ions. [Cyclotron Inst. , Texas A M Univ. , College Station, Texas

    SciTech Connect

    Watson, R.L.

    1993-01-01

    A study of the double ionization of He by high-energy N[sup 7+] ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N[sub 2], O[sub 2], and CO molecular ions produced in collisions with 97-MeV Ar[sup 14+] ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO[sup 2+] and CO[sup 3+] from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO[sup 1+] and CO[sup 2+] molecular ions, and the branching ratios for the most prominent charge division channels of CO[sup 2+] through CO[sup 7+] were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

  13. Structural requirements for charged lipid molecules to directly increase or suppress K+ channel activity in smooth muscle cells. Effects of fatty acids, lysophosphatidate, acyl coenzyme A and sphingosine

    Microsoft Academic Search

    Steven Petrou; Richard W. Ordway; James A. Hamilton; John V. Walsh; Joshua J. Singer

    1994-01-01

    We determined the structural features necessary for fatty acids to exert their action on K+ channels of gastric smooth muscle cells. Examination of the effects of a variety of synthetic and naturally occurring lipid compounds on K+ channel activity in cell-attached and excised membrane patches revealed that negatively charged analogs of medium to long chain fatty acids (but not short

  14. Structural requirements for charged lipid molecules to directly increase or suppress K+ channel activity in smooth muscle cells. Effects of fatty acids, lysophosphatidate, acyl coenzyme A and sphingosine

    PubMed Central

    1994-01-01

    We determined the structural features necessary for fatty acids to exert their action on K+ channels of gastric smooth muscle cells. Examination of the effects of a variety of synthetic and naturally occurring lipid compounds on K+ channel activity in cell-attached and excised membrane patches revealed that negatively charged analogs of medium to long chain fatty acids (but not short chain analogs) as well as certain other negatively charged lipids activate the channels. In contrast, positively charged, medium to long chain analogs suppress activity, and neutral analogs are without effect. The key requirements for effective compounds seem to be a sufficiently hydrophobic domain and the presence of a charged group. Furthermore, those negatively charged compounds unable to "flip" across the bilayer are effective only when applied at the cytosolic surface of the membrane, suggesting that the site of fatty acid action is also located there. Finally, because some of the effective compounds, for example, the fatty acids themselves, lysophosphatidate, acyl Coenzyme A, and sphingosine, are naturally occurring substances and can be liberated by agonist- activated or metabolic enzymes, they may act as second messengers targeting ion channels. PMID:8195783

  15. A New Class of Quorum Quenching Molecules from Staphylococcus Species Affects Communication and Growth of Gram-Negative Bacteria

    PubMed Central

    Chu, Ya-Yun; Nega, Mulugeta; Wölfle, Martina; Plener, Laure; Grond, Stephanie; Jung, Kirsten; Götz, Friedrich

    2013-01-01

    The knowledge that many pathogens rely on cell-to-cell communication mechanisms known as quorum sensing, opens a new disease control strategy: quorum quenching. Here we report on one of the rare examples where Gram-positive bacteria, the ‘Staphylococcus intermedius group’ of zoonotic pathogens, excrete two compounds in millimolar concentrations that suppress the quorum sensing signaling and inhibit the growth of a broad spectrum of Gram-negative beta- and gamma-proteobacteria. These compounds were isolated from Staphylococcus delphini. They represent a new class of quorum quenchers with the chemical formula N-[2-(1H-indol-3-yl)ethyl]-urea and N-(2-phenethyl)-urea, which we named yayurea A and B, respectively. In vitro studies with the N-acyl homoserine lactone (AHL) responding receptor LuxN of V. harveyi indicated that both compounds caused opposite effects on phosphorylation to those caused by AHL. This explains the quorum quenching activity. Staphylococcal strains producing yayurea A and B clearly benefit from an increased competitiveness in a mixed community. PMID:24098134

  16. Reflectance-based optically detected resonance studies of neutral and negatively charged donors in GaAs\\/AlxGa1-xAs quantum wells

    Microsoft Academic Search

    G. Kioseoglou; H. D. Cheong; T. Yeo; H. A. Nickel; A. Petrou; B. D. McCombe; A. Yu. Sivachenko; A. B. Dzyubenko; W. Schaff

    2000-01-01

    We report a reflectance-based optically detected resonance (ODR) study of neutral and negatively charged donors in GaAs\\/AlxGa1-xAs quantum-well structures. The intensity of the e1h1(1s) excitonic reflectance feature was modulated by resonant absorption of a monochromatic far-infrared (FIR) laser beam. An externally applied magnetic field was used to bring the internal transitions among various impurity states in resonance with the FIR

  17. Direct correlation of the crystal structure of proteins with the maximum positive and negative charge states of gaseous protein ions produced by electrospray ionization

    Microsoft Academic Search

    Halan Prakash; Shyamalava Mazumdar

    2005-01-01

    Electrospray mass spectrometric studies in native folded forms of several proteins in aqueous solution have been performed\\u000a in the positive and negative ion modes. The mass spectra of the proteins show peaks corresponding to multiple charge states\\u000a of the gaseous protein ions. The results have been analyzed using the known crystal structures of these proteins. Crystal\\u000a structure analysis shows that

  18. Electrophoretic deposition of TiO 2 and composite TiO 2–MnO 2 films using benzoic acid and phenolic molecules as charging additives

    Microsoft Academic Search

    K. Wu; Y. Wang; I. Zhitomirsky

    2010-01-01

    Electrophoretic deposition (EPD) method has been developed for the fabrication of TiO2 and MnO2 films. Benzoic acid and phenolic molecules, such as 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, gallic acid, salicylic acid and salicylic acid sodium salt were investigated as charging additives for the EPD of TiO2 and MnO2 particles. The deposition yield has been studied as a function of the additive

  19. Quantum theory of atoms in molecules/charge-charge flux-dipole flux models for fundamental vibrational intensity changes on H-bond formation of water and hydrogen fluoride

    SciTech Connect

    Silva, Arnaldo F.; Richter, Wagner E.; Bruns, Roy E., E-mail: bruns@iqm.unicamp.br [Instituto de Química, Universidade Estadual de Campinas, CP 6154, Campinas, CEP 13083-970, SP (Brazil); Terrabuio, Luiz A.; Haiduke, Roberto L. A. [Departamento de Química e Física Molecular, Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400, CP 780, 13560-970 São Carlos, SP (Brazil)] [Departamento de Química e Física Molecular, Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400, CP 780, 13560-970 São Carlos, SP (Brazil)

    2014-02-28

    The Quantum Theory of Atoms In Molecules/Charge-Charge Flux-Dipole Flux (QTAIM/CCFDF) model has been used to investigate the electronic structure variations associated with intensity changes on dimerization for the vibrations of the water and hydrogen fluoride dimers as well as in the water-hydrogen fluoride complex. QCISD/cc-pVTZ wave functions applied in the QTAIM/CCFDF model accurately provide the fundamental band intensities of water and its dimer predicting symmetric and antisymmetric stretching intensity increases for the donor unit of 159 and 47 km mol{sup ?1} on H-bond formation compared with the experimental values of 141 and 53 km mol{sup ?1}. The symmetric stretching of the proton donor water in the dimer has intensity contributions parallel and perpendicular to its C{sub 2v} axis. The largest calculated increase of 107 km mol{sup ?1} is perpendicular to this axis and owes to equilibrium atomic charge displacements on vibration. Charge flux decreases occurring parallel and perpendicular to this axis result in 42 and 40 km mol{sup ?1} total intensity increases for the symmetric and antisymmetric stretches, respectively. These decreases in charge flux result in intensity enhancements because of the interaction contributions to the intensities between charge flux and the other quantities. Even though dipole flux contributions are much smaller than the charge and charge flux ones in both monomer and dimer water they are important for calculating the total intensity values for their stretching vibrations since the charge-charge flux interaction term cancels the charge and charge flux contributions. The QTAIM/CCFDF hydrogen-bonded stretching intensity strengthening of 321 km mol{sup ?1} on HF dimerization and 592 km mol{sup ?1} on HF:H{sub 2}O complexation can essentially be explained by charge, charge flux and their interaction cross term. Atomic contributions to the intensities are also calculated. The bridge hydrogen atomic contributions alone explain 145, 237, and 574 km mol{sup ?1} of the H-bond stretching intensity enhancements for the water and HF dimers and their heterodimer compared with total increments of 149, 321, and 592 km mol{sup ?1}, respectively.

  20. Design of an electrolyte composition for stable and rapid charging-discharging of a graphite negative electrode in a bis(fluorosulfonyl)imide-based ionic liquid

    NASA Astrophysics Data System (ADS)

    Matsui, Yukiko; Yamagata, Masaki; Murakami, Satoshi; Saito, Yasuteru; Higashizaki, Tetsuya; Ishiko, Eriko; Kono, Michiyuki; Ishikawa, Masashi

    2015-04-01

    We evaluate the effects of lithium salt on the charge-discharge performance of a graphite negative electrode in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) ionic liquid-based electrolytes. Although the graphite negative electrode exhibits good cyclability and rate capability in both 0.43 mol dm-3 LiFSI/EMImFSI and LiTFSI/EMImFSI (TFSI- = bis(trifluoromethylsulfonyl)imide) at room temperature, only the LiFSI/EMImFSI system enables the graphite electrode to be operated with sufficient discharge capacity at the low temperature of 0 °C, even though there is no noticeable difference in ionic conductivity, compared with LiTFSI/EMImFSI. Furthermore, a clear difference in the low-temperature behaviors of the two cells composed of EMImFSI with a high-concentration of lithium salts is observed. Additionally, charge-discharge operation of the graphite electrode at C-rate of over 5.0 can be achieved using of the high-concentration LiFSI/EMImFSI electrolyte. Considering the low-temperature characteristics in both high-concentration electrolytes, the stable and rapid charge-discharge operation in the high-concentration LiFSI/EMImFSI is presumably attributed to a suitable electrode/electrolyte interface with low resistivity. These results suggest that optimization of the electrolyte composition can realize safe and high-performance lithium-ion batteries that utilize ionic liquid-based electrolytes.

  1. Peptide signal molecules and bacteriocins in Gram-negative bacteria: a genome-wide in silico screening for peptides containing a double-glycine leader sequence and their cognate transporters

    Microsoft Academic Search

    G. Dirix; P. Monsieurs; B. Dombrecht; R. Daniels; K. Marchal; J. Vanderleyden; J. Michiels

    2004-01-01

    Quorum sensing (QS) in Gram-negative bacteria is generally assumed to be mediated by N-acyl-homoserine lactone molecules while Gram-positive bacteria make use of signaling peptides. We analyzed the occurrence in Gram-negative bacteria of peptides and transporters that are involved in quorum sensing in Gram-positive bacteria. Many class II bacteriocins and inducing factors produced by lactic acid bacteria (LAB) and competence stimulating

  2. Charge-sensitive fluorescent nanosensors created from nanodiamonds.

    PubMed

    Petrakova, V; Rehor, I; Stursa, J; Ledvina, M; Nesladek, M; Cigler, P

    2015-08-01

    We show that fluorescent nanodiamonds (FNDs) are among the few types of nanosensors that enable direct optical reading of noncovalent molecular events. The unique sensing mechanism is based on switching between the negatively charged and neutral states of NV centers which is induced by the interaction of the FND surface with charged molecules. PMID:26138745

  3. Role of GCR positive and negative particles in charging the LISA-PF test masses in 2015

    NASA Astrophysics Data System (ADS)

    Grimani, C.; Fabi, M.; Lobo, A. J.; Mateos, I.; Telloni, D.

    2015-05-01

    The LISA Pathfinder (LISA-PF) mission launch is scheduled during the second half of 2015. Galactic and solar ions with energies larger than 100 MeV/n and electrons above 10 MeV penetrate the spacecraft material and charge the gold-platinum test masses. This charging process generates spurious forces that, in some cases, may mimic the effects of genuine gravitational wave signals. A study of the test-mass charging due to galactic cosmic rays (GCRs) down to 1% in composition is reported here. The reliability of the results of this work is mainly limited by our capability to predict the energy spectra of GCRs in 2015. To this purpose, our model is applied to the expected PAMELA experiment proton data for the period January- March 2014 characterized by a positive polarity period and a level of solar modulation similar to those expected at the time of LISA-PF. The PAMELA observations will be available in the next few months. The comparison between our projections and measurements will provide valuable clues on the test-mass charging estimate uncertainty.

  4. Positively and Negatively Charged Ionic Modifications to Cellulose Assessed as Cotton-Based Protease-Lowering and Haemostatic Wound Agents

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent developments in cellulose wound dressings targeted to different stages of wound healing have been based on structural and charge modifications that function to modulate events in the complex inflammatory and hemostatic phases of wound healing. Hemostasis and inflammation comprise two overlapp...

  5. Enhancement of NK Cell Cytotoxicity Induced by Long-Term Living in Negatively Charged-Particle Dominant Indoor Air-Conditions

    PubMed Central

    Nishimura, Yasumitsu; Takahashi, Kazuaki; Mase, Akinori; Kotani, Muneo; Ami, Kazuhisa; Maeda, Megumi; Shirahama, Takashi; Lee, Suni; Matsuzaki, Hidenori; Kumagai-Takei, Naoko; Yoshitome, Kei; Otsuki, Takemi

    2015-01-01

    Investigation of house conditions that promote health revealed that negatively charged-particle dominant indoor air-conditions (NCPDIAC) induced immune stimulation. Negatively charged air-conditions were established using a fine charcoal powder on walls and ceilings and utilizing forced negatively charged particles (approximate diameter: 20 nm) dominant in indoor air-conditions created by applying an electric voltage (72 V) between the backside of the walls and the ground. We reported previously that these conditions induced a slight and significant increase of interleukin-2 during a 2.5-h stay and an increase of NK cell cytotoxicity when examining human subjects after a two-week night stay under these conditions. In the present study, seven healthy volunteers had a device installed to create NCPDIAC in the living or sleeping rooms of their own homes. Every three months the volunteers then turned the NCPDIAC device on or off. A total of 16 ON and 13 OFF trials were conducted and their biological effects were analyzed. NK activity increased during ON trials and decreased during OFF trials, although no other adverse effects were found. In addition, there were slight increases of epidermal growth factor (EGF) during ON trials. Furthermore, a comparison of the cytokine status between ON and OFF trials showed that basic immune status was stimulated slightly during ON trials under NCPIADC. Our overall findings indicate that the NCPDIAC device caused activation of NK activity and stimulated immune status, particularly only on NK activity, and therefore could be set in the home or office buildings. PMID:26173062

  6. Local symmetry breaking for negatively charged impurity centers in SrTi{sub 1-x}Mn{sub x}O{sub 3}

    SciTech Connect

    Kvyatkovskii, O. E., E-mail: kvyatkovskii@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

    2011-01-15

    First-principles calculations of the geometry and electronic structure of the impurity center in SrTi{sub 1-x}Mn{sub x}O{sub 3} have been performed. Neutral and negatively charged defects are considered. It is found that the doubly charged impurity center is polar; it has C{sub 4v} symmetry and electronic state {sup 4}B{sub 1} with electron polaron localized at one of the neighboring titanium atoms. It is shown that this state is due to the spontaneous breaking of the defect local symmetry: O{sub h}({sup 4}A{sub 1g}) {yields} D{sub 4h}({sup 4}B{sub 1g}) {yields} C{sub 4{nu}}({sup 4}B{sub 1}).

  7. Crystal structure of Jararacussin-I: The highly negatively charged catalytic interface contributes to macromolecular selectivity in snake venom thrombin-like enzymes

    PubMed Central

    Ullah, A; Souza, T A C B; Zanphorlin, L M; Mariutti, R B; Santana, V S; Murakami, M T; Arni, R K

    2013-01-01

    Snake venom serine proteinases (SVSPs) are hemostatically active toxins that perturb the maintenance and regulation of both the blood coagulation cascade and fibrinolytic feedback system at specific points, and hence, are widely used as tools in pharmacological and clinical diagnosis. The crystal structure of a thrombin-like enzyme (TLE) from Bothrops jararacussu venom (Jararacussin-I) was determined at 2.48 Å resolution. This is the first crystal structure of a TLE and allows structural comparisons with both the Agkistrodon contortrix contortrix Protein C Activator and the Trimeresurus stejnegeri plasminogen activator. Despite the highly conserved overall fold, significant differences in the amino acid compositions and three-dimensional conformations of the loops surrounding the active site significantly alter the molecular topography and charge distribution profile of the catalytic interface. In contrast to other SVSPs, the catalytic interface of Jararacussin-I is highly negatively charged, which contributes to its unique macromolecular selectivity. PMID:23139169

  8. Matrix Assisted Ionization: New Aromatic and Nonaromatic Matrix Compounds Producing Multiply Charged Lipid, Peptide, and Protein Ions in the Positive and Negative Mode Observed Directly from Surfaces

    NASA Astrophysics Data System (ADS)

    Li, Jing; Inutan, Ellen D.; Wang, Beixi; Lietz, Christopher B.; Green, Daniel R.; Manly, Cory D.; Richards, Alicia L.; Marshall, Darrell D.; Lingenfelter, Steven; Ren, Yue; Trimpin, Sarah

    2012-10-01

    Matrix assisted inlet ionization (MAII) is a method in which a matrix:analyte mixture produces mass spectra nearly identical to electrospray ionization without the application of a voltage or the use of a laser as is required in laserspray ionization (LSI), a subset of MAII. In MAII, the sample is introduced by, for example, tapping particles of dried matrix:analyte into the inlet of the mass spectrometer and, therefore, permits the study of conditions pertinent to the formation of multiply charged ions without the need of absorption at a laser wavelength. Crucial for the production of highly charged ions are desolvation conditions to remove matrix molecules from charged matrix:analyte clusters. Important factors affecting desolvation include heat, vacuum, collisions with gases and surfaces, and even radio frequency fields. Other parameters affecting multiply charged ion production is sample preparation, including pH and solvent composition. Here, findings from over 100 compounds found to produce multiply charged analyte ions using MAII with the inlet tube set at 450 °C are presented. Of the compounds tested, many have -OH or -NH2 functionality, but several have neither (e.g., anthracene), nor aromaticity or conjugation. Binary matrices are shown to be applicable for LSI and solvent-free sample preparation can be applied to solubility restricted compounds, and matrix compounds too volatile to allow drying from common solvents. Our findings suggest that the physical properties of the matrix such as its morphology after evaporation of the solvent, its propensity to evaporate/sublime, and its acidity are more important than its structure and functional groups.

  9. Cationic hydrous thorium dioxide colloids – a useful tool for staining negatively charged surface matrices of bacteria for use in energy-filtered transmission electron microscopy

    PubMed Central

    Lünsdorf, Heinrich; Kristen, Ingeborg; Barth, Elke

    2006-01-01

    Background Synthesis of cationic hydrous thorium dioxide colloids (ca. 1.0 to 1.7 nm) has been originally described by Müller [22] and Groot [11] and these have been used by Groot to stain acidic glucosaminoglycans for ultrastructure research of different tissues by conventional transmission electron microscopy. Results Synthesis of colloidal thorium dioxide has been modified and its use as a suitable stain of acidic mucopolysaccharides and other anionic biopolymers from bacteria, either as whole mount preparations or as preembedment labels, is described. The differences in stain behavior relative to commonly used rutheniumred-lysine and Alcian Blue™ electron dense acidic stains has been investigated and its use is exemplified for Pseudomonas aeruginosa adjacent cell wall biopolymers. For the first time thorificated biopolymers, i.e. bacterial outer cell wall layers, have been analysed at the ultrastructural level with electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), leading to excellent contrast and signal strength for these extracellular biopolymers. Conclusion Application of cationic hydrous ThO2 colloids for tracing acidic groups of the bacterial surface and/or EPS has been shown to be rather effective by transmission electron microscopy. Because of its high electron density and its good diffusibility it stains and outlines electro-negative charges within these biopolymers. In combination with ESI, based on integrated energy-filtered electron microscopy (EFTEM) Th-densities and thus negative charge densities can be discriminated from other elemental densities, especially in environmental samples, such as biofilms. PMID:16803626

  10. Rapid determination of aniline metabolites of chlorpropham in potatoes by micellar electrokinetic chromatography using negative-charged mixed micelles and laser-induced fluorescence detection.

    PubMed

    Orejuela, Eva; Silva, Manuel

    2005-08-01

    A rapid, reliable method has been developed for the multi-residue analysis of aniline metabolites of chlorpropham in potato samples. The method involves the precolumn derivatization of aniline metabolites with 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein (DTAF) and their subsequent separation and determination by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection (MEKC-LIF). The optimum procedure includes a derivatization step of the aniline metabolites (3-chloroaniline, 3-chloro-4-hydroxyaniline and 3-chloro-4-methoxyaniline) at 40 degrees C for 40 min and a 5-fold dilution prior to MEKC analysis, which is conducted within about 7 min using negative-charged mixed micelles (SDS/Triton X-100) in the running buffer. Under these conditions, the DTAF-anilines were readily detected at 0.3-3.1 microg/L level with a precision of 4.8-6.4%. These results indicate that negative-charged mixed surfactant MEKC-LIF is useful as a selective, rapid, and sensitive tool for the determination of these anilines and surpasses other electrophoretic alternatives based on the use of fluorescein-isothiocyanate (FITC) as label reagent. Finally, the potato matrix showed no significant effects on the derivatization and determination of these analytes, since the analytical figures of merit for the real samples were similar to those obtained in aqueous solutions, and the average recovery at fortification levels of 10-250 microg/kg was over 97%. PMID:15995980

  11. Sry HMG Box Protein 9-positive (Sox9+) Epithelial Cell Adhesion Molecule-negative (EpCAM?) Biphenotypic Cells Derived from Hepatocytes Are Involved in Mouse Liver Regeneration*

    PubMed Central

    Tanimizu, Naoki; Nishikawa, Yuji; Ichinohe, Norihisa; Akiyama, Haruhiko; Mitaka, Toshihiro

    2014-01-01

    It has been shown that mature hepatocytes compensate tissue damages not only by proliferation and/or hypertrophy but also by conversion into cholangiocyte-like cells. We found that Sry HMG box protein 9-positive (Sox9+) epithelial cell adhesion molecule-negative (EpCAM?) hepatocyte nuclear factor 4?-positive (HNF4?+) biphenotypic cells showing hepatocytic morphology appeared near EpCAM+ ductular structures in the livers of mice fed 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing diet. When Mx1-Cre:ROSA mice, which were injected with poly(I:C) to label mature hepatocytes, were fed with the DDC diet, we found LacZ+Sox9+ cells near ductular structures. Although Sox9+EpCAM? cells adjacent to expanding ducts likely further converted into ductular cells, the incidence was rare. To know the cellular characteristics of Sox9+EpCAM? cells, we isolated them as GFP+EpCAM? cells from DDC-injured livers of Sox9-EGFP mice. Sox9+EpCAM? cells proliferated and could differentiate to functional hepatocytes in vitro. In addition, Sox9+EpCAM? cells formed cysts with a small central lumen in collagen gels containing Matrigel® without expressing EpCAM. These results suggest that Sox9+EpCAM? cells maintaining biphenotypic status can establish cholangiocyte-type polarity. Interestingly, we found that some of the Sox9+ cells surrounded luminal spaces in DDC-injured liver while they expressed HNF4?. Taken together, we consider that in addition to converting to cholangiocyte-like cells, Sox9+EpCAM? cells provide luminal space near expanded ductular structures to prevent deterioration of the injuries and potentially supply new hepatocytes to repair damaged tissues. PMID:24482234

  12. A negative charge in transmembrane segment 1 of domain II of the cockroach sodium channel is critical for channel gating and action of pyrethroid insecticides

    SciTech Connect

    Du Yuzhe; Song Weizhong [Department of Entomology, Neuroscience Program and Genetics Program, Michigan State University, East Lansing, MI 48824 (United States); Groome, James R. [Department of Biological Sciences, Idaho State University, Pocatello, ID 83209 (United States); Nomura, Yoshiko; Luo Ningguang [Department of Entomology, Neuroscience Program and Genetics Program, Michigan State University, East Lansing, MI 48824 (United States); Dong Ke, E-mail: dongk@msu.ed [Department of Entomology, Neuroscience Program and Genetics Program, Michigan State University, East Lansing, MI 48824 (United States)

    2010-08-15

    Voltage-gated sodium channels are the primary target of pyrethroids, an important class of synthetic insecticides. Pyrethroids bind to a distinct receptor site on sodium channels and prolong the open state by inhibiting channel deactivation and inactivation. Recent studies have begun to reveal sodium channel residues important for pyrethroid binding. However, how pyrethroid binding leads to inhibition of sodium channel deactivation and inactivation remains elusive. In this study, we show that a negatively charged aspartic acid residue at position 802 (D802) located in the extracellular end of transmembrane segment 1 of domain II (IIS1) is critical for both the action of pyrethroids and the voltage dependence of channel activation. Charge-reversing or -neutralizing substitutions (K, G, or A) of D802 shifted the voltage dependence of activation in the depolarizing direction and reduced channel sensitivity to deltamethrin, a pyrethroid insecticide. The charge-reversing mutation D802K also accelerated open-state deactivation, which may have counteracted the inhibition of sodium channel deactivation by deltamethrin. In contrast, the D802G substitution slowed open-state deactivation, suggesting an additional mechanism for neutralizing the action of deltamethrin. Importantly, Schild analysis showed that D802 is not involved in pyrethroid binding. Thus, we have identified a sodium channel residue that is critical for regulating the action of pyrethroids on the sodium channel without affecting the receptor site of pyrethroids.

  13. Quantitative Estimation of the Metal-Induced Negative Oxide Charge Density in n-Type Silicon Wafers from Measurements of Frequency-Dependent AC Surface Photovoltage

    NASA Astrophysics Data System (ADS)

    Shimizu, Hirofumi; Shin, Ryuhei; Ikeda, Masanori

    2006-03-01

    A quantitative estimation of metal-induced oxide charge (Qmi) density is performed on the surface of n-type silicon (Si) wafers rinsed with trivalent aluminum (Al)- and iron (Fe)-contaminated RCA alkaline solution by analyzing the frequency-dependent AC surface photovoltage (SPV). Qmi arises from (AlOSi)- or (FeOSi)- networks in native oxide which are responsible for inducing negative oxide charge. On the basis of Munakata and Nishimatsu’s half-sided junction model [C. Munakata and S. Nishimatsu: Jpn. J. Appl. Phys. 25 (1986) 807], the network densities are estimated in depletion and/or weak inversion in which the cutoff frequencies of the frequency-dependent AC SPV curves are defined. It is found that the charge density Qmi increases with the time of exposure to air and it is calculated that about 4% of Al atoms in the native oxide are activated in the form of an (AlOSi)- network for 1 h of exposure. The (FeOSi)- network density is calculated as a function of Fe concentration. As a result, the frequency-dependent AC SPV measurements carried out here enable a successful evaluation of impurity level in a nondestructive and noncontact manner.

  14. Nanoscale charge localization induced by random orientations of organic molecules in hybrid perovskite CH3NH3PbI3.

    PubMed

    Ma, Jie; Wang, Lin-Wang

    2015-01-14

    Perovskite-based solar cells have achieved high solar-energy conversion efficiencies and attracted wide attentions nowadays. Despite the rapid progress in solar-cell devices, many fundamental issues of the hybrid perovskites have not been fully understood. Experimentally, it is well-known that in CH3NH3PbI3 the organic molecules CH3NH3 are randomly orientated at the room temperature, but the impact of the random molecular orientation has not been investigated. Because of the dipole moment of the organic molecule, the random orientation creates a novel system with long-range potential fluctuations unlike alloys or other conventional disordered systems. Using linear scaling ab initio methods, we find that the charge densities of the conduction band minimum and the valence band maximum are localized in nanoscales due to the potential fluctuations. The charge localization causes electron-hole separation and reduces carrier recombination rates, which may contribute to the long carrier lifetime observed in experiments. PMID:25493911

  15. Revised Big Bang Nucleosynthesis with Long-lived, Negatively Charged Massive Particles: Updated Recombination Rates, Primordial 9Be Nucleosynthesis, and Impact of New 6Li Limits

    NASA Astrophysics Data System (ADS)

    Kusakabe, Motohiko; Kim, K. S.; Cheoun, Myung-Ki; Kajino, Toshitaka; Kino, Yasushi; Mathews, Grant. J.

    2014-09-01

    We extensively reanalyze the effects of a long-lived, negatively charged massive particle, X -, on big bang nucleosynthesis (BBN). The BBN model with an X - particle was originally motivated by the discrepancy between the 6, 7Li abundances predicted in the standard BBN model and those inferred from observations of metal-poor stars. In this model, 7Be is destroyed via the recombination with an X - particle followed by radiative proton capture. We calculate precise rates for the radiative recombinations of 7Be, 7Li, 9Be, and 4He with X -. In nonresonant rates, we take into account respective partial waves of scattering states and respective bound states. The finite sizes of nuclear charge distributions cause deviations in wave functions from those of point-charge nuclei. For a heavy X - mass, mX >~ 100 GeV, the d-wave ? 2P transition is most important for 7Li and 7, 9Be, unlike recombination with electrons. Our new nonresonant rate of the 7Be recombination for mX = 1000 GeV is more than six times larger than the existing rate. Moreover, we suggest a new important reaction for 9Be production: the recombination of 7Li and X - followed by deuteron capture. We derive binding energies of X nuclei along with reaction rates and Q values. We then calculate BBN and find that the amount of 7Be destruction depends significantly on the charge distribution of 7Be. Finally, updated constraints on the initial abundance and the lifetime of the X - are derived in the context of revised upper limits to the primordial 6Li abundance. Parameter regions for the solution to the 7Li problem and the primordial 9Be abundances are revised.

  16. REVISED BIG BANG NUCLEOSYNTHESIS WITH LONG-LIVED, NEGATIVELY CHARGED MASSIVE PARTICLES: UPDATED RECOMBINATION RATES, PRIMORDIAL {sup 9}Be NUCLEOSYNTHESIS, AND IMPACT OF NEW {sup 6}Li LIMITS

    SciTech Connect

    Kusakabe, Motohiko; Kim, K. S. [School of Liberal Arts and Science, Korea Aerospace University, Goyang 412-791 (Korea, Republic of); Cheoun, Myung-Ki [Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Kajino, Toshitaka [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Kino, Yasushi [Department of Chemistry, Tohoku University, Sendai 980-8578 (Japan); Mathews, Grant J., E-mail: motohiko@kau.ac.kr, E-mail: kyungsik@kau.ac.kr, E-mail: cheoun@ssu.ac.kr, E-mail: kajino@nao.ac.jp, E-mail: y.k@m.tohoku.ac.jp, E-mail: gmathews@nd.edu [Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)

    2014-09-01

    We extensively reanalyze the effects of a long-lived, negatively charged massive particle, X {sup –}, on big bang nucleosynthesis (BBN). The BBN model with an X {sup –} particle was originally motivated by the discrepancy between the {sup 6,} {sup 7}Li abundances predicted in the standard BBN model and those inferred from observations of metal-poor stars. In this model, {sup 7}Be is destroyed via the recombination with an X {sup –} particle followed by radiative proton capture. We calculate precise rates for the radiative recombinations of {sup 7}Be, {sup 7}Li, {sup 9}Be, and {sup 4}He with X {sup –}. In nonresonant rates, we take into account respective partial waves of scattering states and respective bound states. The finite sizes of nuclear charge distributions cause deviations in wave functions from those of point-charge nuclei. For a heavy X {sup –} mass, m{sub X} ? 100 GeV, the d-wave ? 2P transition is most important for {sup 7}Li and {sup 7,} {sup 9}Be, unlike recombination with electrons. Our new nonresonant rate of the {sup 7}Be recombination for m{sub X} = 1000 GeV is more than six times larger than the existing rate. Moreover, we suggest a new important reaction for {sup 9}Be production: the recombination of {sup 7}Li and X {sup –} followed by deuteron capture. We derive binding energies of X nuclei along with reaction rates and Q values. We then calculate BBN and find that the amount of {sup 7}Be destruction depends significantly on the charge distribution of {sup 7}Be. Finally, updated constraints on the initial abundance and the lifetime of the X {sup –} are derived in the context of revised upper limits to the primordial {sup 6}Li abundance. Parameter regions for the solution to the {sup 7}Li problem and the primordial {sup 9}Be abundances are revised.

  17. Basic vapor exposure for tuning the charge state distribution of proteins in negative electrospray ionization: elucidation of mechanisms by fluorescence spectroscopy.

    PubMed

    Girod, Marion; Antoine, Rodolphe; Dugourd, Philippe; Love, Craig; Mordehai, Alex; Stafford, George

    2012-07-01

    Manipulation for simplifying or increasing the observed charge state distributions of proteins can be highly desirable in mass spectrometry experiments. In the present work, we implemented a vapor introduction technique to an Agilent Jet Stream ESI (Agilent Technologies, Santa Clara, CA, USA) source. An apparatus was designed to allow for the enrichment of the nitrogen sheath gas with basic vapors. An optical setup, using laser-induced fluorescence and a pH-chromic dye, permits the pH profiling of the droplets as they evaporate in the electrospray plume. Mechanisms of pH droplet modification and its effect on the protein charging phenomenon are elucidated. An important finding is that the enrichment with basic vapors of the nitrogen sheath gas, which surrounds the nebulizer spray, leads to an increase in the spray current. This is attributed to an increase in the electrical conductivity of water-amine enriched solvent at the tip exit. Here, the increased current results in a generation of additional electrolytically produced OH(-) ions and a corresponding increase in the pH at the tip exit. Along the electrospray plume, the pH of the droplets increases due to both droplet evaporation and exposure to basic vapors from the seeded sheath gas. The pH evolution in the ESI plume obtained using pure and basic seeded sheath gas was correlated with the evolution of the charge state distribution observed in mass spectra of proteins, in the negative ion mode. Taking advantage of the Agilent Jet Stream source geometry, similar protein charge state distributions and ion intensities obtained with basic initial solutions, can be obtained using native solution conditions by seeding the heated sheath gas with basic vapors. PMID:22565506

  18. ENTHALPIES OF FORMATION OF NEGATIVE IONS MnO , MnO , AND MnO AS DETERMINED BY ION-MOLECULE EQUILIBRIA METHOD

    E-print Network

    Rudnyi, Evgenii B.

    - - ENTHALPIES OF FORMATION OF NEGATIVE IONS MnO , MnO , AND 2 3 - MnO AS DETERMINED BY ION University, Moscow 119899, Russia - - - running title - NEGATIVE IONS MnO , MnO , AND MnO 2 3 4 Admixture been 2 estimated. The use of manganese-containing negative ions to measure the activity of manganese

  19. Kinetic instability of the dust acoustic mode in inhomogeneous, partially magnetized plasma with both positively and negatively charged grains

    SciTech Connect

    Vranjes, J.; Poedts, S. [Centre for Plasma Astrophysics, Celestijnenlaan 200B, 3001 Leuven (Belgium) and Leuven Mathematical Modeling and Computational Science Research Centre (LMCC), Celestijnenlaan 200B, 3001 Leuven (Belgium)

    2010-08-15

    A purely kinetic instability of the dust acoustic mode in inhomogeneous plasmas is discussed. In the presence of a magnetic field, electrons and ions may be magnetized while at the same time dust grains may remain unmagnetized. Although the dynamics of the light species is strongly affected by the magnetic field, the dust acoustic mode may still propagate in practically any direction. The inhomogeneity implies a source of free energy for an instability that develops through the diamagnetic drift effects of the magnetized species. It is shown that this may be a powerful mechanism for the excitation of dust acoustic waves. The analysis presented in the work is also directly applicable to plasmas containing both positive and negative ions and electrons, provided that at least one of the two ion species is unmagnetized.

  20. Kinetic instability of the dust acoustic mode in inhomogeneous, partially magnetized plasma with both positively and negatively charged grains

    NASA Astrophysics Data System (ADS)

    Vranjes, J.; Poedts, S.

    2010-08-01

    A purely kinetic instability of the dust acoustic mode in inhomogeneous plasmas is discussed. In the presence of a magnetic field, electrons and ions may be magnetized while at the same time dust grains may remain unmagnetized. Although the dynamics of the light species is strongly affected by the magnetic field, the dust acoustic mode may still propagate in practically any direction. The inhomogeneity implies a source of free energy for an instability that develops through the diamagnetic drift effects of the magnetized species. It is shown that this may be a powerful mechanism for the excitation of dust acoustic waves. The analysis presented in the work is also directly applicable to plasmas containing both positive and negative ions and electrons, provided that at least one of the two ion species is unmagnetized.

  1. Potential Dependent Alignment and Hydrogen Bonding of Water Molecules at Charged Air/Water and CCl4/Water Interfaces

    E-print Network

    Richmond, Geraldine L.

    vary the interface potential by changing the surface charge density, the ionic strength for the widespread use of surfactants in commercial products such as motor oils, lubricants, detergents, and soaps of surfactants, little is known on a molecular level about how water and surfactants interact at liquid surfaces

  2. PEG-b-PCL copolymer micelles with the ability of pH-controlled negative-to-positive charge reversal for intracellular delivery of doxorubicin.

    PubMed

    Deng, Hongzhang; Liu, Jinjian; Zhao, Xuefei; Zhang, Yuming; Liu, Jianfeng; Xu, Shuxin; Deng, Liandong; Dong, Anjie; Zhang, Jianhua

    2014-11-10

    The application of PEG-b-PCL micelles was dampened by their inherent low drug-loading capability and relatively poor cell uptake efficiency. In this study, a series of novel PEG-b-PCL copolymers methoxy poly(ethylene glycol)-b-poly(?-caprolactone-co-?-dimethyl maleamidic acid -?-caprolactone) (mPEG-b-P(CL-co-DCL)) bearing different amounts of acid-labile ?-carboxylic amides on the polyester moiety were synthesized. The chain structure and chemical composition of copolymers were characterized by (1)H NMR, Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). mPEG-b-P(CL-co-DCL) with critical micellar concentrations (CMCs) of 3.2-6.3 ?g/mL could self-assemble into stable micelles in water with diameters of 100 to 150 nm. Doxorubicin (DOX), a cationic hydrophobic drug, was successfully encapsulated into the polymer micelles, achieving a very high loading content due to electrostatic interaction. Then the stability, charge-conversional behavior, loading and release profiles, cellular uptake and in vitro cytotoxicity of free drug and drug-loaded micelles were evaluated. The ?-carboxylic amides functionalized polymer micelles are negatively charged and stable in neutral solution but quickly become positively charged at pH 6.0, due to the hydrolysis of ?-carboxylic amides in acidic conditions. The pH-triggered negative-to-positive charge reversal not only resulted in a very fast drug release in acidic conditions, but also effectively enhanced the cellular uptake by electrostatic absorptive endocytosis. The MTT assay demonstrated that mPEG-b-P(CL-co-DCL) micelles were biocompatible to HepG2 cells while DOX-loaded micelles showed significant cytotoxicity. In sum, the introduction of acid-labile ?-carboxylic amides on the polyester block in mPEG-b-P(CL-co-DCL) exhibited great potentials for the modifications in the stability in blood circulation, drug solubilization, and release properties, as well as cell internalization and intracellular drug release. PMID:25325531

  3. Negatively Charged Metal Oxide Nanoparticles Interact with the 20S Proteasome and Differentially Modulate Its Biologic Functional Effects

    PubMed Central

    Falaschetti, Christine A.; Paunesku, Tatjana; Kurepa, Jasmina; Nanavati, Dhaval; Chou, Stanley S.; De, Mrinmoy; Song, MinHa; Jang, Jung-tak; Wu, Aiguo; Dravid, Vinayak P.; Cheon, Jinwoo; Smalle, Jan; Woloschak, Gayle E.

    2013-01-01

    The multicatalytic ubiquitin-proteasome system (UPS) carries out proteolysis in a highly orchestrated way and regulates a large number of cellular processes. Deregulation of the UPS in many disorders has been documented. In some cases, e.g. carcinogenesis, elevated proteasome activity has been implicated in disease development, while the etiology of other diseases, e.g. neurodegeneration, includes decreased UPS activity. Therefore, agents that alter proteasome activity could suppress as well as enhance a multitude of diseases. Metal oxide nanoparticles, often developed as diagnostic tools, have not previously been tested as modulators of proteasome activity. Here, several types of metal oxide nanoparticles were found to adsorb to the proteasome and show variable preferential binding for particular proteasome subunits with several peptide binding “hotspots” possible. These interactions depend on the size, charge, and concentration of the nanoparticles and affect proteasome activity in a time-dependent manner. Should metal oxide nanoparticles increase proteasome activity in cells, as they do in vitro, unintended effects related to changes in proteasome function can be expected. PMID:23930940

  4. A Simultaneous Solution to the ^6Li and ^7Li Big Bang Nucleosynthesis Problems from a Long-Lived Negatively-Charged Leptonic Particle

    E-print Network

    Motohiko Kusakabe; Toshitaka Kajino; Richard N. Boyd; Takashi Yoshida; Grant J. Mathews

    2007-11-24

    The $^6$Li abundance observed in metal poor halo stars exhibits a plateau similar to that for $^7$Li suggesting a primordial origin. However, the observed abundance of $^6$Li is a factor of $10^3$ larger and that of $^7$Li is a factor of 3 lower than the abundances predicted in the standard big bang when the baryon-to-photon ratio is fixed by WMAP. Here we show that both of these abundance anomalies can be explained by the existence of a long-lived massive, negatively-charged leptonic particle during nucleosynthesis. Such particles would capture onto the synthesized nuclei thereby reducing the reaction Coulomb barriers and opening new transfer reaction possibilities, and catalyzing a second round of big bang nucleosynthesis. This novel solution to both of the Li problems can be achieved with or without the additional effects of stellar destruction.

  5. Simultaneous solution to the {sup 6}Li and {sup 7}Li big bang nucleosynthesis problems from a long-lived negatively charged leptonic particle

    SciTech Connect

    Kusakabe, Motohiko [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Kajino, Toshitaka [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Department of Astronomical Science, The Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 (Japan); Boyd, Richard N. [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Lawrence Livermore National Laboratory, University of California, Livermore, California 94550 (United States); Yoshida, Takashi [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Mathews, Grant J. [Department of Physics and Center for Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

    2007-12-15

    The {sup 6}Li abundance observed in metal-poor halo stars exhibits a plateau similar to that for {sup 7}Li suggesting a primordial origin. However, the observed abundance of {sup 6}Li is a factor of 10{sup 3} larger and that of {sup 7}Li is a factor of 3 lower than the abundances predicted in the standard big bang when the baryon-to-photon ratio is fixed by Wilkinson microwave anisotropy probe. Here we show that both of these abundance anomalies can be explained by the existence of a long-lived massive, negatively charged leptonic particle during nucleosynthesis. Such particles would capture onto the synthesized nuclei thereby reducing the reaction Coulomb barriers and opening new transfer reaction possibilities, and catalyzing a second round of big bang nucleosynthesis. This novel solution to both of the Li problems can be achieved with or without the additional effects of stellar destruction.

  6. Retinoschisin (RS1) Interacts with Negatively Charged Lipid Bilayers in the presence of Ca2+: An Atomic Force Microscopy Study

    PubMed Central

    Kotova, Svetlana; Vijayasarathy, Camasamudram; Dimitriadis, Emilios K.; Ikonomou, Laertis; Jaffe, Howard; Sieving, Paul A.

    2010-01-01

    Retinoschisin (RS1) is a retina-specific secreted protein encoding a conserved discoidin domain sequence. As an adhesion molecule, RS1 preserves the retinal cell architecture and promotes visual signal transduction. In young males, loss-of-function mutations in the X- linked retinoschisis gene (RS1) cause X-linked retinoschisis, a form of progressive blindness. Neither the structure of RS1 nor the nature of its anchoring and organization on the plasma membranes is fully understood. The discoidin C2 domains of coagulation factors V and VIII are known to interact with extracellular phosphatidylserine (PS). In this study we have used atomic force microscopy (AFM) to study the interactions of murine retinoschisin (Rs1) with supported anionic lipid bilayers in the presence of Ca2+. The bilayers consisting of a single lipid, PS, and mixtures of lipids with or without PS were used. Consistent with previous X-ray diffraction studies, AFM imaging showed two distinct domains in pure PS bilayers when Ca2+ was present. Upon Rs1 adsorption, these PS and PS-containing mixed bilayers underwent fast and extensive reorganization. Protein localization was ascertained by immunolabeling. AFM imaging showed the Rs1 antibody bound exclusively to the calcium-rich ordered phase of the bilayers pointing to the sequestration of Rs1 within those domains. This was further supported by the increased mechanical strength of these domains after Rs1 binding. Besides, changes in bilayer thickness suggested that Rs1 was partially embedded into the bilayer. These findings support a model whereby the Rs1 protein binds to PS in the retinal cell plasma membranes in a calcium-dependent manner. PMID:20677810

  7. Novel negatively charged hybrids. 3. Removal of Pb2+ from aqueous solution using zwitterionic hybrid polymers as adsorbent.

    PubMed

    Liu, Junsheng; Ma, Yue; Zhang, Yaping; Shao, Guoquan

    2010-01-15

    Using zwitterionic hybrid polymers as adsorbent, the adsorption kinetics and isotherm, thermodynamic parameters of Delta G, Delta H and DeltaS for the removal of Pb(2+) from aqueous solution were investigated. It is indicated that the adsorption of Pb(2+) ions on these zwitterionic hybrid polymers followed the Lagergren second-order kinetic model and Freundlich isotherm model, demonstrating that the adsorption process might be Langmuir monolayer adsorption. The negative values of Delta G and the positive values of Delta H evidence that Pb(2+) adsorption on these zwitterionic hybrid polymers is spontaneous and endothermic process in nature. Moreover, the zwitterionic hybrid polymers produced reveal relatively higher desorption efficiency in 2 mol dm(-3) aqueous HNO(3) solution, indicating that they can be recycled in industrial processes. These findings suggest that these zwitterionic hybrid polymers are the promising adsorbents for Pb(2+) removal and can be potentially applied in the separation and recovery of Pb(2+) ions from the waste chemicals and contaminated water of lead-acid rechargeable battery. PMID:19744785

  8. Big-Bang Nucleosynthesis with Negatively-Charged Massive Particles as a Cosmological Solution to the {sup 6}Li and {sup 7}Li Problems

    SciTech Connect

    Kusakabe, Motohiko [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Kajino, Toshitaka [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Department of Astronomical Science, Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 (Japan); Boyd, Richard N. [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Yoshida, Takashi [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Mathews, Grant J. [Department of Physics and Center for Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States)

    2008-05-21

    Observations of metal poor halo stars exhibit a possible plateau of {sup 6}Li abundance as a function of metallicity similar to that for {sup 7}Li, suggesting a big bang origin. However, the inferred primordial abundance of {sup 6}Li is {approx}1000 times larger than that predicted by standard big bang nucleosynthesis (BBN) for the baryon-to-photon ratio inferred from the WMAP data. On the other hand, the inferred {sup 7}Li primordial abundance is about 3 times smaller than the prediction. We study a possible simultaneous solution to both the problems of underproduction of {sup 6}Li and overproduction of {sup 7}Li in BBN. This solution involves a hypothetical massive, negatively-charged leptonic particle that would bind to the light nuclei produced in BBN, but would decay long before it could be detected. Because the particle gets bound to the existing nuclei after the cessation of the usual big bang nuclear reactions, a second longer epoch of nucleosynthesis can occur among X-nuclei which have reduced Coulomb barriers. We numerically carry out a fully dynamical BBN calculation, simultaneously solving the recombination and ionization processes of negatively-charged particles by normal and X-nuclei as well as many possible nuclear reactions among them. We confirm that a reaction in which the hypothetical particle is transferred can occur that greatly enhance the production of {sup 6}Li while a reaction through an atomic excited state of X-nucleus depletes {sup 7}Li. It is confirmed that BBN in the presence of these hypothetical particles, together with or without an event of stellar burning process, can simultaneously solve the two Li abundance problems.

  9. Beneficial effects of activated carbon additives on the performance of negative lead-acid battery electrode for high-rate partial-state-of-charge operation

    NASA Astrophysics Data System (ADS)

    Xiang, Jiayuan; Ding, Ping; Zhang, Hao; Wu, Xianzhang; Chen, Jian; Yang, Yusheng

    2013-11-01

    Experiments are made with negative electrode of 2 V cell and 12 V lead-acid battery doped with typical activated carbon additives. It turns out that the negative electrode containing tens-of-micron-sized carbon particles in NAM exhibits markedly increased HRPSoC cycle life than the one containing carbon particles with much smaller size of several microns or the one containing no activated carbon. The improved performance is mainly attributed to the optimized NAM microstructure and the enhanced electrode reaction kinetics by introducing appropriate activated carbon. The beneficial effects can be briefly summarized from three aspects. First, activated carbon acts as new porous-skeleton builder to increase the porosity and active surface of NAM, and thus facilitates the electrolyte diffusion from surface to inner and provides more sites for crystallization/dissolution of lead sulfate; second, activated carbon plays the role of electrolyte supplier to provide sufficient H2SO4 in the inner of plate when the diffusion of H2SO4 from plate surface cannot keep pace of the electrode reaction; Third, activated carbon acts as capacitive buffer to absorb excess charge current which would otherwise lead to insufficient NAM conversion and hydrogen evolution.

  10. The role of the strictly conserved positively charged residue differs among the Gram-positive, Gram-negative, and chloroplast YidC homologs.

    PubMed

    Chen, Yuanyuan; Soman, Raunak; Shanmugam, Sri Karthika; Kuhn, Andreas; Dalbey, Ross E

    2014-12-19

    Recently, the structure of YidC2 from Bacillus halodurans revealed that the conserved positively charged residue within transmembrane segment one (at position 72) is located in a hydrophilic groove that is embedded in the inner leaflet of the lipid bilayer. The arginine residue was essential for the Bacillus subtilis SpoIIIJ (YidC1) to insert MifM and to complement a SpoIIIJ mutant strain. Here, we investigated the importance of the conserved positively charged residue for the function of the Escherichia coli YidC, Streptococcus mutans YidC2, and the chloroplast Arabidopsis thaliana Alb3. Like the Gram-positive B. subtilis SpoIIIJ, the conserved arginine was required for functioning of the Gram-positive S. mutans YidC2 and was necessary to complement the E. coli YidC depletion strain and to promote insertion of a YidC-dependent membrane protein synthesized with one but not two hydrophobic segments. In contrast, the conserved positively charged residue was not required for the E. coli YidC or the A. thaliana Alb3 to functionally complement the E. coli YidC depletion strain or to promote insertion of YidC-dependent membrane proteins. Our results also show that the C-terminal half of the helical hairpin structure in cytoplasmic loop C1 is important for the activity of YidC because various deletions in the region either eliminate or impair YidC function. The results here underscore the importance of the cytoplasmic hairpin region for YidC and show that the arginine is critical for the tested Gram-positive YidC homolog but is not essential for the tested Gram-negative and chloroplast YidC homologs. PMID:25359772

  11. Adapting SAFT-? perturbation theory to site-based molecular dynamics simulation. III. Molecules with partial charges at bulk phases, confined geometries and interfaces

    NASA Astrophysics Data System (ADS)

    Ghobadi, Ahmadreza F.; Elliott, J. Richard

    2014-09-01

    In Paper I [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 139(23), 234104 (2013)], we showed that how a third-order Weeks-Chandler-Anderson (WCA) Thermodynamic Perturbation Theory and molecular simulation can be integrated to characterize the repulsive and dispersive contributions to the Helmholtz free energy for realistic molecular conformations. To this end, we focused on n-alkanes to develop a theory for fused and soft chains. In Paper II [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 141(2), 024708 (2014)], we adapted the classical Density Functional Theory and studied the microstructure of the realistic molecular fluids in confined geometries and vapor-liquid interfaces. We demonstrated that a detailed consistency between molecular simulation and theory can be achieved for both bulk and inhomogeneous phases. In this paper, we extend the methodology to molecules with partial charges such as carbon dioxide, water, 1-alkanols, nitriles, and ethers. We show that the electrostatic interactions can be captured via an effective association potential in the framework of Statistical Associating Fluid Theory (SAFT). Implementation of the resulting association contribution in assessing the properties of these molecules at confined geometries and interfaces presents satisfactory agreement with molecular simulation and experimental data. For example, the predicted surface tension deviates less than 4% comparing to full potential simulations. Also, the theory, referred to as SAFT-? WCA, is able to reproduce the specific orientation of hydrophilic head and hydrophobic tail of 1-alkanols at the vapor-liquid interface of water.

  12. Extension of the spectral responsivity of the photocurrent in solution-processed small molecule composite via a charge transfer excitation

    NASA Astrophysics Data System (ADS)

    Hernandez-Sosa, Gerardo; Tong, Minghong; Coates, Nelson E.; Valouch, Sebastian; Moses, Daniel

    2011-10-01

    Incorporating [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in solution-processed composites comprising the two small molecular semiconductors 9,10-Diphenylanthracene (DPA) and 5,6,11,12-tetraphenylnaphthacene (Rubrene) extends significantly the onset wavelength of the steady-state photoconductivity from 610 nm in the pristine DPA:Rubrene composite to 900 nm in the DPA:Rubrene:PCBM composite. The experimental data indicate carrier generation in the near IR spectral region arising from inter-molecular charge transfer (IMCT) excitation that potentially could be useful for extending solar radiation light harvesting. Pump/probe photoinduced absorption (PIA) measurements indicate instantaneous carrier generation at sub-band-gap photon energies, confirming the viability of IMCT excitations as the underlying carrier generation mechanism at the near IR spectral region.

  13. Optimization studies of carbon additives to negative active material for the purpose of extending the life of VRLA batteries in high-rate partial-state-of-charge operation

    Microsoft Academic Search

    D. P. Boden; D. V. Loosemore; M. A. Spence; T. D. Wojcinski

    2010-01-01

    The negative plates of lead-acid batteries subjected to partial-state-of-charge (PSOC) operation fail because of the development of an electrically inert film of lead sulfate on their surfaces. It has been found that carbon additives to the negative active material can significantly increase their cycle life in this type of operation. In this paper we show that various types of carbon,

  14. Effects of graphene coating and charge injection on water adsorption of solid surfaces

    NASA Astrophysics Data System (ADS)

    Guo, Yufeng; Guo, Wanlin

    2013-10-01

    The adhesion and cohesion of water molecules on graphene-coated and bare copper and mica substrates under charge injection have been extensively studied by first-principles calculations. Water adsorption on graphene-coated copper surface is weakened by injecting negative charges into the substrate, while enhanced by positive charges. Both negatively and positively charge injecting on graphene-coated mica strengthen the adsorption between water and the surface. While the adhesive and cohesive energies of water adsorption on charged bare copper and mica exhibit similar trends and much stronger response to charge injection. The charge sensitivity of water adsorbing on positively charged surfaces is significantly weakened by the graphene coating layer, mainly due to lower interfacial charge exchange. Our results suggest a viable way to modify water adsorption on a graphene-coated surface and unveil the role of graphene as a passivation layer for the wetting of a charged substrate.The adhesion and cohesion of water molecules on graphene-coated and bare copper and mica substrates under charge injection have been extensively studied by first-principles calculations. Water adsorption on graphene-coated copper surface is weakened by injecting negative charges into the substrate, while enhanced by positive charges. Both negatively and positively charge injecting on graphene-coated mica strengthen the adsorption between water and the surface. While the adhesive and cohesive energies of water adsorption on charged bare copper and mica exhibit similar trends and much stronger response to charge injection. The charge sensitivity of water adsorbing on positively charged surfaces is significantly weakened by the graphene coating layer, mainly due to lower interfacial charge exchange. Our results suggest a viable way to modify water adsorption on a graphene-coated surface and unveil the role of graphene as a passivation layer for the wetting of a charged substrate. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02867d

  15. Ground state initialization in a doubly-charged, vertically-stacked InAs quantum dot molecule

    NASA Astrophysics Data System (ADS)

    Ross, Aaron; Chow, Colin; Sham, Lu; Bracker, Allan; Gammon, Daniel; Steel, Duncan

    2015-03-01

    We report on the rapid optical initialization of a subset of the two-electron ground states of a self-assembled, vertically stacked InAs quantum dot molecule, where the states of the electron are approximately localized to separate quantum dots with very little spatial overlap. Four eigenstates, a singlet and three triplets (S,T0,T+, T-) , arise from the exchange coupling and are identified via bias-dependent photoluminescence measurements. The degeneracy of the triplet states is lifted using an in-plane magnetic field (Voigt geometry). This allows for the determination of the in-plane electron and hole g-factors using differential transmission measurements in the co-tunneling regime (to avoid optical pumping). Three of the four eigenstates (S,T+, T-) can then be initialized with high fidelity using continuous wave (CW) optical pumping. Optical transition degeneracies prohibit simple CW initialization of the T0 state. Efforts towards near-unity initialization of the T0 state via two-photon Raman transitions will be presented. This work represents the first step in demonstrating a two-qubit quantum register based on electron spins in self-assembled quantum dots. This work is supported by NSF, ARO, AFSOR, DARPA, and ONR.

  16. Nonlocal Desorption of Chlorobenzene Molecules from the Si(111)-(7×7) Surface by Charge Injection from the Tip of a Scanning Tunneling Microscope: Remote Control of Atomic Manipulation

    NASA Astrophysics Data System (ADS)

    Sloan, P. A.; Sakulsermsuk, S.; Palmer, R. E.

    2010-07-01

    We report the nonlocal desorption of chlorobenzene molecules from the Si(111)-(7×7) surface by charge injection from the laterally distant tip of a scanning tunneling microscope and demonstrate remote control of the manipulation process by precise selection of the atomic site for injection. Nonlocal desorption decays exponentially as a function of radial distance (decay length ˜100Å) from the injection site. Electron injection at corner-hole and faulted middle adatoms sites couples preferentially to the desorption of distant adsorbate molecules. Molecules on the faulted half of the unit cell desorb with higher probability than those on the unfaulted half.

  17. Theoretical investigation of the stability of highly charged C60 molecules produced with intense near-infrared laser pulses

    NASA Astrophysics Data System (ADS)

    Sahnoun, Riadh; Nakai, Katsunori; Sato, Yukio; Kono, Hirohiko; Fujimura, Yuichi; Tanaka, Motohiko

    2006-11-01

    We theoretically investigated the stability of highly charged C60z + cations produced from C60 with an ultrashort intense laser pulse of ? ˜1800nm. We first calculated the equilibrium structures and vibrational frequencies of C60z + as well as C60. We then calculated key energies relevant to dissociation of C60z +, such as the excess vibrational energy acquired upon sudden tunnel ionization from C60. By comparing the magnitudes of the calculated energies, we found that C60z + cations up to z ˜12 can be produced as a stable or quasistable (microsecond-order lifetime) intact parent cation, in agreement with the recent experimental report by V. R. Bhardwaj et al. [Phys. Rev. Lett. 93, 043001 (2004)] that almost only intact parent C60z + cations up to z =12 are detected by a mass spectrometer. The results of Rice-Ramsperger-Kassel-Marcus calculation suggest that the lifetime of C60z + drastically decreases by ten orders of magnitude as z increases from z =11 to z =13. Using the time-dependent adiabatic state approach, we also investigated the vibrational excitation of C60 and C60z + by an intense near-infrared pulse. The results indicate that large-amplitude vibration with energy of >10eV is induced in the delocalized hg(1)-like mode of C60z +.

  18. Anti-class II antibodies, but not cytotoxic T-lymphocyte antigen 4-immunoglobulin hybrid molecules, prevent rejection of major histocompatibility complex class II-negative myeloma in T-cell receptor-transgenic mice.

    PubMed

    Dembic, Z; Hofgaard, P O; Omholt, H; Bogen, B

    2004-01-01

    We have previously shown that tumour-specific CD4+ T cells protect against subcutaneous injections of major histocompatibility complex (MHC) class II-negative MOPC315 myeloma cells. Here, we have interfered with the immunologic events that lead to successful rejection of MOPC315 challenges in T-cell receptor (TCR)-transgenic mice. The CD4+ T cells have a transgene-encoded TCR specific for a MOPC315 V-region idiotypic (Id) peptide presented on the MHC class II molecule E(d). A side-by-side comparison indicated that DNA-recombination-deficient TCR-transgenic mice were better protected against MOPC315 tumour development than recombination-sufficient counterparts, suggesting that B cells or endogenous TCR chains might facilitate tumour progression in this model. Intraperitoneal injections of E(d)-specific antibodies over a period of initial 24 days, abrogated protection against tumours in both strains of mice. By contrast, injections of anticostimulatory molecules (cytotoxic T-lymphocyte antigen 4-immunoglobulin hybrid molecules) had no effect. The findings demonstrate that tumour rejection depends on the presence of MHC class II molecules, despite the fact that MOPC315 tumour cells themselves do not express them. The results are consistent with the idea that secreted myeloma protein is processed and presented by class II+ antigen-presenting cells to Id-specific naïve CD4+ T cells that become activated and kill the myeloma cells by a bystander mechanism. While Id presentation on class II molecules is absolutely required for tumour rejection, costimulatory CD80/CD86 molecules might be dispensible in this process. PMID:15238083

  19. Disinfection of Escherichia coli Gram negative bacteria using surface modified TiO2: optimization of Ag metallization and depiction of charge transfer mechanism.

    PubMed

    Gomathi Devi, LakshmipathiNaik; Nagaraj, Basavalingaiah

    2014-01-01

    The antibacterial activity of silver deposited TiO2 (Ag-TiO2 ) against Gram negative Escherichia coli bacteria was investigated by varying the Ag metal content from 0.10 to 0.50% on the surface of TiO2 . Ag depositions by the photoreduction method were found to be stable. Surface silver metallization was confirmed by EDAX and XPS studies. Photoluminescence studies show that the charge carrier recombination is less for 0.1% Ag-TiO2 and this catalyst shows superior bactericidal activity under solar light irradiation compared to Sol gel TiO2 (SG-TiO2 ) due to the surface plasmon effect. The energy levels of deposited Ag are dependent on the Ag content and it varies from -4.64 eV to -1.30 eV with respect to the vacuum energy level based on atomic silver to bulk silver deposits. The ability of electron transfer from Ag deposit to O2 depends on the position of the energy levels. The 0.25% and 0.50% Ag depositions showed detrimental effect on bactericidal activity due to the mismatch of energy levels. The effect of the EROS (External generation of the Reactive Oxygen Species by 0.1% Ag-TiO2 ) and IROS (Interior generation of Reactive Oxygen Species within the bacteria) on the bactericidal inactivation is discussed in detail. PMID:24995499

  20. Optical and electrical detection of single-molecule translocation through carbon nanotubes.

    PubMed

    Song, Weisi; Pang, Pei; He, Jin; Lindsay, Stuart

    2013-01-22

    Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as fluorescence was recorded from charged dye molecules translocating through the SWCNT. Fluorescence bursts generally follow ion current peaks with a delay time consistent with diffusion from the end of the SWCNT to the fluorescence collection point. The fluorescence amplitude distribution of the bursts is consistent with single-molecule signals. Thus each peak in the ion current flowing through the SWCNT is associated with the translocation of a single molecule. Ion current peaks (as opposed to blockades) were produced by both positively (Rhodamine 6G) and negatively (Alexa 546) charged molecules, showing that the charge filtering responsible for the current bursts is caused by the molecules themselves. PMID:23248975

  1. CuFe2O4 magnetic nanocrystal clusters as a matrix for the analysis of small molecules by negative-ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

    PubMed

    Lin, Zian; Zheng, Jiangnan; Bian, Wei; Cai, Zongwei

    2015-07-13

    CuFe2O4 magnetic nanocrystal clusters (CuFe2O4 MNCs) were proposed as a new matrix for small molecule analysis by negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the first time. We demonstrated its advantages over conventional organic matrices in the detection of small molecules such as amino acids, peptides, nucleobases, fatty acids, and steroid hormones. A systematic comparison of CuFe2O4 MNCs with different ionization modes revealed that MS spectra obtained for the CuFe2O4 MNC matrix in the negative ion mode was only featured by deprotonated ion peaks with a free matrix background, which was different from the complicated alkali metal adducts produced in the positive ion mode. The developed method was found relatively tolerant to salt contamination and exhibited good reproducibility. A detection limit down to the subpicomolar level was achieved when testosterone was analyzed. In addition, by comparison of the MS spectra obtained from bare Fe3O4 and MFe2O4 MNC (M = Co, Ni, Cu, Zn) matrices, two main factors of MFe2O4 MNC matrices were revealed to play a vital role in assisting the negative ion desorption/ionization (D/I) process: doping transition metals into ferrite nanocrystals favoring laser absorption and energy transfer and a good match between the UV absorption of MFe2O4 MNCs and the excitation of nitrogen laser source facilitating LDI efficiency. This work creates a new branch of application for MFe2O4 MNCs and provides an alternative solution for small molecule analysis. PMID:26086699

  2. Charge Transfer Reactions Induce Born-Oppenheimer Breakdown in Surface Chemistry: Applications of Double Resonance Spectroscopy in Molecule-Surface Scattering

    NASA Astrophysics Data System (ADS)

    Wodtke, Alec M.

    2013-06-01

    Atomic and molecular interactions constitute a many-body quantum problem governed fundamentally only by the Coulomb forces between many electrons and nuclei. While simple to state, computers are simply not fast enough to solve this problem by brute force, except for the simplest examples. Combining the Born-Oppenheimer Approximation (BOA) with Density Functional Theory (DFT), however, allows theoretical simulations of extraordinarily complex chemical systems including molecular interactions at solid metal surfaces, the physical basis of surface chemistry. This lecture describes experiments demonstrating the limits of the BOA/DFT approximation as it relates to molecules interacting with solid metal surfaces. One of the most powerful experimental tools at our disposal is a form of double resonance spectroscopy, which allows us to define the quantum state of the molecule both before and after the collision with the surface, providing a complete picture of the resulting energy conversion processes. With such data, we are able to emphasize quantitative measurements that can be directly compared to first principles theories that go beyond the Born-Oppenheimer approximation. One important outcome of this work is the realization that Born-Oppenheimer breakdown can be induced by simple charge transfer reactions that are common in surface chemistry. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach and A. M. Wodtke Nature {433}(7025), 503-505 (2005) Y. H. Huang, C. T. Rettner, D. J. Auerbach and A. M. Wodtke Science {290}(5489), 111-114 (2000) R. Cooper, I. Rahinov, Z. S. Li, D. Matsiev, D. J. Auerbach and A. M. Wodtke Chemical Science {1}(1), 55-61 (2010) J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach and A. M. Wodtke PCCP {13}(1), 97-99 (2011).

  3. Charge transport in HoxLu1 -xB12 : Separating positive and negative magnetoresistance in metals with magnetic ions

    NASA Astrophysics Data System (ADS)

    Sluchanko, N. E.; Khoroshilov, A. L.; Anisimov, M. A.; Azarevich, A. N.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Krasnorussky, V. N.; Samarin, N. A.; Shitsevalova, N. Yu.; Filippov, V. B.; Levchenko, A. V.; Pristas, G.; Gabani, S.; Flachbart, K.

    2015-06-01

    The magnetoresistance (MR) ? ? /? of the cage-glass compound HoxLu1 -xB12 with various concentrations of magnetic holmium ions (x ?0.5 ) has been studied in detail concurrently with magnetization M (T ) and Hall effect investigations on high-quality single crystals at temperatures 1.9-120 K and in magnetic field up to 80 kOe. The undertaken analysis of ? ? /? allows us to conclude that the large negative magnetoresistance (nMR) observed in the vicinity of the Néel temperature is caused by scattering of charge carriers on magnetic clusters of Ho3 + ions, and that these nanosize regions with antiferromagnetic (AF) exchange inside may be considered as short-range-order AF domains. It was shown that the Yosida relation -? ? /? ˜M2 provides an adequate description of the nMR effect for the case of Langevin-type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3-9 ?B was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution ? ? /? ˜?D2H2 which dominates in HoxLu1 -xB12 in the intermediate temperature range 20-120 K allows us to estimate the drift mobility exponential changes ?D˜T-? with ? =1.3 -1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of HoxLu1 -xB12 where an additional linear positive component was observed and attributed to charge-carrier scattering on the spin density wave (SDW). High-precision measurements of ? ? /? =f (H ,T ) have allowed us also to reconstruct the magnetic H-T phase diagram of Ho0.5Lu0.5B12 and to resolve its magnetic structure as a superposition of 4 f (based on localized moments) and 5 d (based on SDW) components.

  4. Negative-ion implantation

    SciTech Connect

    Ishikawa, Junzo [Kyoto Univ., Yoshida, Kyoto (Japan). Dept. of Electronics

    1995-12-31

    Negative-ion implantation is a promising technique for forthcoming ULSI (more than 256 M bits) fabrication and TFT (for color LCD) fabrication, since the surface charging voltage of insulated electrodes or insulators implanted by negative ions is found to saturate within so few as several volts, no breakdown of insulators would be expected without a charge neutralizer in these fabrication processes. Scatter-less negative-ion implantation into powders is also possible. For this purpose an rf-plasma-sputter type heavy negative-ion source was developed, which can deliver several milliamperes of various kinds of negative ion currents such as boron, phosphor, silicon, carbon, copper, oxygen, etc. A medium current negative-ion implanter with a small version of this type of ion source has been developed.

  5. Low energy positron interactions with biological molecules

    NASA Astrophysics Data System (ADS)

    Wanniarachchi, Indika L.

    Calculations of the positron density distribution which can be used for positrons bound to midsize and larger molecules have been tested for smaller molecules and subsequently applied to investigate the most likely e +e-- annihilation sites for positrons interacting with biological molecules containing C, H, O, and N. In order to allow consideration of positrons bound to extended molecules with regions of different character and no particular symmetry, atom-centered positron basis sets of Gaussian-type functions were developed for positrons bound to molecules containing O, N, C, H, Li, Na, and Be. Testing shows that there is no need to scale the positron basis functions to take into account different effective charges on the atoms in different molecules. Even at the HF level of theory the calculated positron and the contact density of e+LiH system is in qualitative agreement with the most accurate calculation was done in ECG method. Also it has been found that for larger biological molecules such as derivation of formaldehyde can leave out positron basis sets centered on H atoms and still get qualitatively acceptable contact density distribution. According to our results, the electronic and positronic wavefunctions have the most overlap in the regions of most negative electrostatic potential in the parent molecule, and we can expect that a positron bound to the molecule will be more likely to annihilate with one of the electrons in these regions. Also we find that the highest energy occupied electronic orbital often does not make the largest contribution to e+e -- annihilation, and that the energy liberated by subsequent electronic relaxation is sufficient to break the backbone in several places in di-peptides and other organic molecules.

  6. Spatiotemporal dynamics of charged species in the afterglow of plasmas containing negative ions I. D. Kaganovich,* B. N. Ramamurthi, and Demetre J. Economou

    E-print Network

    Economou, Demetre J.

    to electrons during their diffusion towards the walls. The presence of detached electrons results in ``self, the negative ion fronts propagate towards the chamber walls with a nearly constant velocity. The evolution needed for negative ions to reach the wall, and thus influence surface reactions in plasma processing

  7. Negative ions

    Microsoft Academic Search

    H. Massey

    1976-01-01

    Topics covered include: the negative ion of hydrogen; ground states of complex atomic negative ions-theoretical considerations; the electron affinities of the elements; atomic negative ions-excited states-autodetachment, general account; autodetaching states of specific atomic negative ions; molecular negative ions-ground states; excited electronic states of molecular negative ions; modes of formation of negative ions-formation by radiative processes-radiative attachment and polar photodissociation; modes

  8. Negative ions in comets

    NASA Technical Reports Server (NTRS)

    Wekhof, A.

    1981-01-01

    Negative ion sources in comets are identified and cometary plasma effects caused by negative ions are examined. The primary negative ion sources are shown to be: (1) for the inner coma - photodissociation of HCN, electron attachment of OH, and collision with alkalis; (2) in the vicinity of the nucleus - interplanetary dust collisions with the nucleus; and (3) for both the contaminated solar wind region and sporadic discharges in the nonhomogeneous inner coma plasma - dissociative electron attachment and charge inversion during keV positive ion scattering by cometary dust. Negative ion abundance for Halley's Comet has been estimated to be 10 to the -6th - 10 to the -10th of electron densities.

  9. Models for Cometary Comae Containing Negative Ions

    NASA Technical Reports Server (NTRS)

    Cordiner, M. A.; Charnley, S. B.

    2012-01-01

    The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of IP/Halley. The anions O(-), OH(-), C(-), CH(-) and CN(-) have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu [I]. Organic molecular anions such as C4H(-) and C6H(-) are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been fully explored. We present details of our new models for the chemistry of cometary comae that include atomic and molecular anions. We calculate the impact of these anions on the charge balance and examine their importance for cometary coma chemistry.

  10. Negative charge on hydrogen atoms in carbonylmetal hydrides and their acid properties. Induced electrophilicity of hydrogen as a result of reversal of the direction of polarization of a bond under the action of a nucleophile

    SciTech Connect

    Imyanitov, N.S.

    1987-01-01

    The contradiction between the negative charge on hydrogen atoms in carbonylmetal hydrides and their clearly expressed acid properties has been examined. The inconsistency of the interpretation which states that carbonyl hydrides acquire acid properties under the effects of water and similar solvents, while they remain hydrides (e.e., compounds with a nucleophilic hydrogen atom) in nonpolar media and in the gaseous phase, has been demonstrated. A mechanism for the realization of the acid properties of carbonyl hydrides has been proposed. According to this mechanism, the negative charge is displaced from the hydrogen atom to the metal carbonyl group under the action of a base, this results in a change in the direction of polarization of the hydrogen-transition-metal bond (polarization reversal), and the hydrogen atom acquires a positive charge (induced electrophilicity). It has been shown that in the case of the carbonyl-metal hydrides HFe(CO)/sub 4//sup -/, NMn(CO)/sub 5/, HCo(CO)/sub 4/, HCo(CO)/sub 3/P(C/sub 6/H/sub 5/)/sub 3/, HCo(COP)/sub 3/P(OC/sub 6/H/sub 5/)/sub 3/, and HCo(CO)(PF/sub 3/)/sub 3/, the logarithms of the acid dissociation constants are linearly dependent on the electron-acceptor properties of the metal carbonyl group. The key role of the acid properties of carbonylmetal hydrides in the catalysts of carbonylation reactions has been considered. It has been noted that the negative charge on the hydrogen atom is the cause of the reduced dynamic acidity of carbonyl hydrides and their poor solubility in water.

  11. Charge Challenge

    NSDL National Science Digital Library

    University of Kansas

    2006-01-01

    In this activity, learners explore how objects can have positive, negative, or neutral charges, which attract, repel and move between objects. Learners charge various materials and observe their interactions. Winter is an ideal time to perform these experiments (because there is less water vapor in the air); if it is humid, use a hair dryer to dry the objects, surfaces, and air around the work area.

  12. Solvation thermodynamics and heat capacity of polar and charged solutes in water

    SciTech Connect

    Sedlmeier, Felix; Netz, Roland R. [Fachbereich Physik, Freie Universitaet Berlin, 14195 Berlin (Germany)

    2013-03-21

    The solvation thermodynamics and in particular the solvation heat capacity of polar and charged solutes in water is studied using atomistic molecular dynamics simulations. As ionic solutes we consider a F{sup -} and a Na{sup +} ion, as an example for a polar molecule with vanishing net charge we take a SPC/E water molecule. The partial charges of all three solutes are varied in a wide range by a scaling factor. Using a recently introduced method for the accurate determination of the solvation free energy of polar solutes, we determine the free energy, entropy, enthalpy, and heat capacity of the three different solutes as a function of temperature and partial solute charge. We find that the sum of the solvation heat capacities of the Na{sup +} and F{sup -} ions is negative, in agreement with experimental observations, but our results uncover a pronounced difference in the heat capacity between positively and negatively charged groups. While the solvation heat capacity {Delta}C{sub p} stays positive and even increases slightly upon charging the Na{sup +} ion, it decreases upon charging the F{sup -} ion and becomes negative beyond an ion charge of q=-0.3e. On the other hand, the heat capacity of the overall charge-neutral polar solute derived from a SPC/E water molecule is positive for all charge scaling factors considered by us. This means that the heat capacity of a wide class of polar solutes with vanishing net charge is positive. The common ascription of negative heat capacities to polar chemical groups might arise from the neglect of non-additive interaction effects between polar and apolar groups. The reason behind this non-additivity is suggested to be related to the second solvation shell that significantly affects the solvation thermodynamics and due to its large spatial extent induces quite long-ranged interactions between solvated molecular parts and groups.

  13. Improvement of charge injection efficiency in organic-inorganic hybrid solar cells by chemical modification of metal oxides with organic molecules

    Microsoft Academic Search

    Naomi Kudo; Satoshi Honda; Yuta Shimazaki; Hideo Ohkita; Shinzaburo Ito; Hiroaki Benten

    2007-01-01

    The effect of chemical modification of metal oxide surface with dye molecules in organic-inorganic hybrid solid solar cells was studied by using double layered cells consisting of poly(3-hexylthiophene) (P3HT) and a flat layer of dense TiO2. The external quantum efficiency of the chemically modified cell was nearly double that expected from the photosensitizing effect of the dye molecules. The additional

  14. Polysialic acid–neural cell adhesion molecule in brain plasticity: From synapses to integration of new neurons

    Microsoft Academic Search

    Eduardo Gascon; Laszlo Vutskits; Jozsef Zoltan Kiss

    2007-01-01

    Isoforms of the neuronal cell adhesion molecule (NCAM) carrying the linear homopolymer of alpha 2,8-linked sialic acid (polysialic acid, PSA) have emerged as particularly attractive candidates for promoting plasticity in the nervous system. The large negatively charged PSA chain of NCAM is postulated to be a spacer that reduces adhesion forces between cells allowing dynamic changes in membrane contacts. Accumulating

  15. Holding Charge

    NSDL National Science Digital Library

    Eric Muller

    1995-01-01

    In this trick, learners discover how to stick a straw to the palm of their hand, window door, or anywhere using static electricity. This activity introduces learners to negative and positive charges and shows how opposites attract. Note: this trick works best in low humidity (dry air).

  16. Improvement of charge injection efficiency in organic-inorganic hybrid solar cells by chemical modification of metal oxides with organic molecules

    SciTech Connect

    Kudo, Naomi; Honda, Satoshi; Shimazaki, Yuta; Ohkita, Hideo; Ito, Shinzaburo; Benten, Hiroaki [Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510 (Japan); International Innovation Center, Kyoto University, Katsura, Nishikyo, Kyoto 615-8520 (Japan)

    2007-04-30

    The effect of chemical modification of metal oxide surface with dye molecules in organic-inorganic hybrid solid solar cells was studied by using double layered cells consisting of poly(3-hexylthiophene) (P3HT) and a flat layer of dense TiO{sub 2}. The external quantum efficiency of the chemically modified cell was nearly double that expected from the photosensitizing effect of the dye molecules. The additional increase shows that the chemical modification with dye molecules can serve not only as a photosensitizer but mainly as an energy funnel and/or an electronic mediator to significantly improve the electron injection efficiency from P3HT to TiO{sub 2}.

  17. Charge Pairing of Headgroups in Phosphatidylcholine Membranes: A Molecular Dynamics Simulation Study

    Microsoft Academic Search

    Marta Pasenkiewicz-Gierula; Yuji Takaoka; Hiroo Miyagawa; Kunihiro Kitamura; Akihiro Kusumi

    1999-01-01

    Molecular dynamics simulation of the hydrated dimyristoylphosphatidylcholine (DMPC) bilayer membrane in the liquid-crystalline phase was carried out for 5ns to study the interaction among DMPC headgroups in the membrane\\/water interface region. The phosphatidylcholine headgroup contains a positively charged choline group and negatively charged phosphate and carbonyl groups, although it is a neutral molecule as a whole. Our previous study (Pasenkiewicz-Gierula,

  18. Effect of Charged and Nonionic Membrane Additives on Physicochemical Properties and Stability of Niosomes

    Microsoft Academic Search

    Varaporn Buraphacheep Junyaprasert; Veerawat Teeranachaideekul; Tasaneeya Supaperm

    2008-01-01

    The aim of this study was to investigate an influence of different types of membrane additives including negative charge (dicetylphosphate,\\u000a DCP), positive charge (stearylamine, STR) and non-ionic molecule (cholesteryl poly-24-oxyethylene ether, SC24) on the physicochemical\\u000a properties of drug-free and drug-loaded niosomes. Salicylic acid having different proportions of ionized and unionized species\\u000a at different pH was selected as a model drug.

  19. Mighty Molecules

    NSDL National Science Digital Library

    Carlyn Little

    1997-01-01

    In this activity, learners use marshmallows and gum drops to construct seven models of molecules. Learners classify (solid, liquid or gas) and draw diagrams of the molecules. Learners can also create a table showing the chemical formula for each molecule and identify a common use for each chemical. Use this activity to introduce learners to molecules, compounds, and bonds.

  20. Detection of heavy-metal ions using liquid crystal droplet patterns modulated by interaction between negatively charged carboxylate and heavy-metal cations.

    PubMed

    Han, Gyeo-Re; Jang, Chang-Hyun

    2014-10-01

    Herein, we demonstrated a simple, sensitive, and rapid label-free detection method for heavy-metal (HM) ions using liquid crystal (LC) droplet patterns on a solid surface. Stearic-acid-doped LC droplet patterns were spontaneously generated on an n-octyltrichlorosilane (OTS)-treated glass substrate by evaporating a solution of the nematic LC, 4-cyano-4'-pentylbiphenyl (5CB), dissolved in heptane. The optical appearance of the droplet patterns was a dark crossed texture when in contact with air, which represents the homeotropic orientation of the LC. This was caused by the steric interaction between the LC molecules and the alkyl chains of the OTS-treated surface. The dark crossed appearance of the acid-doped LC patterns was maintained after the addition of phosphate buffered saline (PBS) solution (pH 8.1 at 25°C). The deprotonated stearic-acid molecules self-assembled through the LC/aqueous interface, thereby supporting the homeotropic anchoring of 5CB. However, the optical image of the acid-doped LC droplet patterns incubated with PBS containing HM ions appeared bright, indicating a planar orientation of 5CB at the aqueous/LC droplet interface. This dark to bright transition of the LC patterns was caused by HM ions attached to the deprotonated carboxylate moiety, followed by the sequential interruption of the self-assembly of the stearic acid at the LC/aqueous interface. The results showed that the acid-doped LC pattern system not only enabled the highly sensitive detection of HM ions at a sub-nanomolar concentration but it also facilitated rapid detection (<10 min) with simple procedures. PMID:25059128

  1. Negative temperatures and negative dissipation

    Microsoft Academic Search

    Stefan Machlup

    1975-01-01

    Negative absolute temperature, defined in terms of the Boltzmann factor, corresponds to an upside-down energy pyramid. The example of the laser shows population inversion to be accompanied by the switch from absorption to emission, that is, from positive to negative dissipation, from increasing disorder throughout a system to increasing order in a subsystem. Early treatments of the negative-temperature concept are

  2. Charge separation in CO oxidation involving supported gold clusters

    SciTech Connect

    Berry, R. S. [University of Chicago, Department of Chemistry (United States); Smirnov, B. M., E-mail: bmsmirnov@gmail.com [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

    2011-12-15

    The character of the catalytic oxidation of CO by supported gold cluster catalysts is analyzed with emphasis on the unique characteristics of this process. The scheme of this process used here has the reagent CO molecule captured in the interface between the cluster and support, with oxygen molecules or atoms located on the support surface to react with the CO. (Other models have also been presented.) The experimental data indicate that, together with configurational transitions that lead to the CO molecule joining an oxygen atom to form the CO{sub 2} molecule, the charge separation due to capture of the CO molecule by the supported gold cluster is important. The process of release of the CO{sub 2} molecule results in charge exchange; the time for this process is relatively long because of the large distance separating positive and negative charges, a distance exceeding the cluster radius. This provides a high efficiency of the oxidation of CO with this catalyst despite the relatively high activation energy for the configurational transition.

  3. An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster-configuration interaction method: the accuracy of excitation energies and intuitive charge-transfer indices.

    PubMed

    Fukuda, Ryoichi; Ehara, Masahiro

    2014-10-21

    Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2'-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy. PMID:25338878

  4. Tunable magnetoresistance in an asymmetrically coupled single-molecule junction.

    PubMed

    Warner, Ben; El Hallak, Fadi; Prüser, Henning; Sharp, John; Persson, Mats; Fisher, Andrew J; Hirjibehedin, Cyrus F

    2015-03-01

    Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. The scaling of such phenomena down to the single-molecule level may enable novel spintronic devices. Here, we report magnetoresistance in a single-molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications. PMID:25622229

  5. Tunable magnetoresistance in an asymmetrically coupled single-molecule junction

    NASA Astrophysics Data System (ADS)

    Warner, Ben; El Hallak, Fadi; Prüser, Henning; Sharp, John; Persson, Mats; Fisher, Andrew J.; Hirjibehedin, Cyrus F.

    2015-03-01

    Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. The scaling of such phenomena down to the single-molecule level may enable novel spintronic devices. Here, we report magnetoresistance in a single-molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications.

  6. Electronic friction forces on molecules moving near metals

    Microsoft Academic Search

    M. S. Tomassone; A. Widom

    1997-01-01

    It is well known that molecules feel a long-ranged attractive force to metals which arises from the interaction of various molecular charges with their metal-induced ``image charges.'' Here we calculate (in this image charge model) the friction force coefficients for molecules moving near a metal. We consider the cases of ions, polar molecules, and spherical atoms.

  7. Surface modification by negative-ion implantation

    Microsoft Academic Search

    Junzo Ishikawa; Hiroshi Tsuji; Yasuhito Gotoh

    2009-01-01

    We have developed a negative-ion implantation technique for surface modification of materials together with the development of high-intensity negative-ion sources and negative-ion implanters. In the negative-ion implantation, we have the advantage of a nearly “charge-up-free” property for the implanted surface of insulators or insulated materials. The charging voltage on the implanted surface is no greater than plus or minus a

  8. Positivity, negativity, and entanglement

    E-print Network

    Perlmutter, Eric; Rota, Massimiliano

    2015-01-01

    We explore properties of the universal terms in the entanglement entropy and logarithmic negativity in 4d CFTs, aiming to clarify the ways in which they behave like the analogous entanglement measures in quantum mechanics. We show that, unlike entanglement entropy in finite-dimensional systems, the sign of the universal part of entanglement entropy is indeterminate. In particular, if and only if the central charges obey $a>c$, the entanglement across certain classes of entangling surfaces can become arbitrarily negative, depending on the geometry and topology of the surface. The negative contribution is proportional to the product of $a-c$ and the genus of the surface. Similarly, we show that in $a>c$ theories, the logarithmic negativity does not always exceed the entanglement entropy.

  9. Negative Refraction Induced by Möbius Topology

    E-print Network

    Y. N. Fang; Yao Shen; Qing Ai; C. P. Sun

    2015-01-23

    We theoretically show the negative refraction existing in M\\"{o}bius molecules. The negative refractive index is induced by the non-trivial topology of the molecules. With the M\\"{o}bius boundary condition, the effective electromagnetic fields felt by the electron in a M\\"{o}bius ring is spatially inhomogeneous. In this regard, the $D_{N}$ symmetry is broken in M\\"{o}bius molecules and thus the magnetic response is induced through the effective magnetic field. Our findings open up a new architecture for negative refractive index materials based on the non-trivial topology of M\\"{o}bius molecules.

  10. Intermolecular forces between large molecules

    Microsoft Academic Search

    A. T. Amos; R. J. Crispin

    1976-01-01

    The long-range interaction between large molecules with localized electrons is written as the sum of individual interactions between localized charge distributions. Using minimal basis set ab initio Hartree-Fock wavefunctions the parameters needed to compute these interactions are obtained for water, methane and ethane. Interactions between pairs of these molecules are computed for various orientations to demonstrate the complex orientational dependence

  11. Interaction of the Neuropeptide Met-Enkephalin with Zwitterionic and Negatively Charged Bicelles as Viewed by 31P and 2H Solid-State NMR

    PubMed Central

    Marcotte, Isabelle; Dufourc, Erick J.; Ouellet, Marise; Auger, Michèle

    2003-01-01

    The interaction of the neuropeptide methionine-enkephalin (Menk) with bicelles was investigated by solid-state NMR. Bicelles composed of dimyristoylphosphatidylcholine (DMPC) and dicaproylphosphatidylcholine (DCPC) were modified to investigate the effect of the lipid headgroup and electrostatic charges on the association with Menk. A total of 10 mol % of DMPC was replaced by zwitterionic phosphatidylethanolamine (DMPE), anionic phosphatidylglycerol (DMPG), or phosphatidylserine (DMPS). The preparation of DMPE-doped bicelles (Bic/PE) is reported for the first time. The 31P and 2H NMR results revealed changes in the lipid dynamics when Menk interacts with the bicellar systems. 2H NMR experiments showed a disordering effect of Menk on the lipid chains in all the bicelles except Bic/PG, whereas the study of the choline headgroups indicated a decreased order of the lipids only in Bic/PE and Bic/PG. Our results suggest that the insertion depth of Menk into bicelles is modulated by their composition, more specifically by the balance between hydrophobic and electrostatic interactions. Menk would be buried at the lipid polar/apolar interface, the depth of penetration into the hydrophobic membrane core following the scaling Bic > Bic/PE > Bic/PS at the slightly acidic pH used in this study. The peptide would not insert into the bilayer core of Bic/PG and would rather remain at the surface. PMID:12829487

  12. Organization and intramolecular charge-transfer enhancement in tripodal tris[(pyridine-4-yl)phenyl]amine push-pull molecules by intercalation into layered materials bearing acidic functionalities.

    PubMed

    Melánová, Klára; Cvejn, Daniel; Bureš, Filip; Zima, Vít?zslav; Svoboda, Jan; Beneš, Ludvík; Mikysek, Tomáš; Pytela, Old?ich; Knotek, Petr

    2014-07-21

    Two new intercalates of tris[4-(pyridin-4-yl)phenyl]amine (TPPA) with zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate having formulae Zr(HPO4)2·0.21(C33H24N4)·2.5H2O and Zr(HO3SC6H4PO3)(1.3)(C6H5PO3)(0.7)·0.35(C33H24N4)·2.5H2O were prepared and characterized by thermogravimetry, IR spectroscopy, and powder X-ray diffraction. The TPPA molecule has been selected as a model tripodal push-pull system with three peripheral basic centers that may undergo protonation. Their protonation/quaternization afforded HTPPA/MeTPPA molecules with enhanced intramolecular charge-transfer (ICT), which has been documented by electrochemical measurements, UV-Vis spectra and calculated properties such as the HOMO/LUMO levels and the first and second hyperpolarizabilities. Intercalation of TPPA into layered zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate led to its significant organization and protonation as shown by the IR spectra. From the powder X-ray data we can deduce that the TPPA molecules are placed in the interlayer space of both hosts by anchoring two peripheral nitrogen atoms to one host layer and the opposite pyridine-4-yl terminus to the other neighboring host layer. In zirconium 4-sulfophenylphosphonate, the TPPA molecules are oriented perpendicularly, while in zirconium phosphate these molecules are slanted with respect to the layers of the host. On dehydration by heating, the interlayer distance of the intercalate decreases, which indicates a further slanting of the TPPA molecules. It follows from the UV-Vis spectra that TPPA is present in both intercalates in an equilibrium of protonated and non-protonated forms. The described materials represent the first case when a tripodal push-pull system was incorporated into a system with restricted geometry with the aim to influence its optical properties. PMID:24626407

  13. 1,3-Bis(nitroimido)-1,2,3-triazolate anion, the N-nitroimide moiety, and the strategy of alternating positive and negative charges in the design of energetic materials.

    PubMed

    Klapötke, Thomas M; Petermayer, Christian; Piercey, Davin G; Stierstorfer, Jörg

    2012-12-26

    This unique study reports on the 1,3-bis(nitroimido)-1,2,3-triazolate anion. This compound provides unique insight into both academic and practical considerations surrounding high-nitrogen systems. The bonding in this energetic anion can be represented multiple ways, one of which includes a chain of alternating positive/negative charges nine atoms long. The validity of this resonance structure is discussed in terms of experimental, computational, and valence bond results. The prepared materials based on this energetic anion were also characterized chemically (infrared, Raman, NMR, X-ray) and as high explosives in terms of their energetic performances (detonation velocity, pressure, etc.) and sensitivities (impact, friction, electrostatic), and the 1,3-bis(nitroimido)-1,2,3-triazolate anion is found to be very high performing with high thermal stabilities while being quite sensitive to mechanical stimuli. PMID:23190185

  14. Detection of nucleotides in positive-mode electrospray ionization mass spectrometry using multiply-charged cationic ion-pairing reagents

    Microsoft Academic Search

    Edra Dodbiba; Zachary S. Breitbach; Eranda Wanigasekara; Tharanga Payagala; Xiaotong Zhang; Daniel W. Armstrong

    2010-01-01

    Nucleotides are a class of molecules that play an essential role in biological systems. A new method has been developed in\\u000a the detection of nucleotides. These molecules can exist as monomers or constituents of oligomers and polymers. As such, they\\u000a carry from one to several negative charges. In this study, different cationic ion-pairing reagents were used to complex with\\u000a each

  15. The effects of photochemical and mechanical damage on the excited state dynamics of charge-transfer molecular crystals composed of tetracyanobenzene and aromatic donor molecules.

    PubMed

    Dillon, Robert J; Bardeen, Christopher J

    2011-03-10

    Charge-transfer molecular crystals are structurally well-defined systems whose electron transfer dynamics can be studied using time-resolved spectroscopy. In this paper, five 1:1 complexes, consisting of 1,2,4,5-tetracyanobenzene as the electron acceptor and durene, 9-methylanthracene, naphthalene, phenanthrene, and pyrene as electron donors, are studied using time-resolved fluorescence and transient absorption in the diffuse reflectance geometry. Two different sample morphologies were studied: single crystals and powders prepared by pulverizing the crystals and diluting them with barium sulfate microparticles. Fluorescence lifetime and transient absorption measurements performed on the crystals and the powders yielded different results. The crystals typically exhibited long-lived monoexponential fluorescence decays, while the powders had shorter multiexponential decays. Exposure of both types of samples to high laser fluence was also shown to induce faster excited state decay dynamics as observed using fluorescence and diffuse reflectance. In addition to the more rapid decays, these molecular crystals exhibited relatively high photobleaching quantum yields on the order of 10(-4). Previous work that interpreted picosecond decays in the transient absorption as evidence for rapid recombination and charge dissociation should be re-evaluated based on the susceptibility of this class of compounds to mechanical and photochemical damage. PMID:21319859

  16. Negative learning

    Microsoft Academic Search

    Michael Oppenheimer; Brian C. O’Neill; Mort Webster

    2008-01-01

    New technical information may lead to scientific beliefs that diverge over time from the a posteriori right answer. We call this phenomenon, which is particularly problematic in the global change arena, negative learning. Negative\\u000a learning may have affected policy in important cases, including stratospheric ozone depletion, dynamics of the West Antarctic\\u000a ice sheet, and population and energy projections. We simulate

  17. Three chamber negative ion source

    DOEpatents

    Leung, Ka-Ngo (Hercules, CA); Ehlers, Kenneth W. (Alamo, CA); Hiskes, John R. (Livermore, CA)

    1985-01-01

    A negative ion vessel is divided into an excitation chamber, a negative ionization chamber and an extraction chamber by two magnetic filters. Input means introduces neutral molecules into a first chamber where a first electron discharge means vibrationally excites the molecules which migrate to a second chamber. In the second chamber a second electron discharge means ionizes the molecules, producing negative ions which are extracted into or by a third chamber. A first magnetic filter prevents high energy electrons from entering the negative ionization chamber from the excitation chamber. A second magnetic filter prevents high energy electrons from entering the extraction chamber from the negative ionizing chamber. An extraction grid at the end of the negative ion vessel attracts negative ions into the third chamber and accelerates them. Another grid, located adjacent to the extraction grid, carries a small positive voltage in order to inhibit positive ions from migrating into the extraction chamber and contour the plasma potential. Additional electrons can be suppressed from the output flux using ExB forces provided by magnetic field means and the extractor grid electric potential.

  18. Charge transport in nanoscale junctions.

    PubMed

    Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

    2008-09-01

    Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for

  19. Contact de-electrification of electrostatically charged polymers.

    PubMed

    Soh, Siowling; Kwok, Sen Wai; Liu, Helena; Whitesides, George M

    2012-12-12

    The contact electrification of insulating organic polymers is still incompletely understood, in part because multiple fundamental mechanisms may contribute to the movement of charge. This study describes a mechanism previously unreported in the context of contact electrification: that is, "contact de-electrification", a process in which polymers charged to the same polarity discharge on contact. Both positively charged polymeric beads, e.g., polyamide 6/6 (Nylon) and polyoxymethylene (Delrin), and negatively charged polymeric beads, e.g., polytetrafluoroethylene (Teflon) and polyamide-imide (Torlon), discharge when the like-charged beads are brought into contact. The beads (both with charges of ?±20 ?C/m(2), or ?100 charges/?m(2)) discharge on contact regardless of whether they are made of the same material, or of different materials. Discharge is rapid: discharge of flat slabs of like-charged Nylon and Teflon pieces is completed on a single contact (?3 s). The charge lost from the polymers during contact de-electrification transfers onto molecules of gas in the atmosphere. When like-charged polymers are brought into contact, the increase in electric field at the point of contact exceeds the dielectric breakdown strength of the atmosphere and ionizes molecules of the gas; this ionization thus leads to discharge of the polymers. The detection (using a Faraday cup) of charges transferred to the cup by the ionized gas is compatible with the mechanism. Contact de-electrification occurs for different polymers and in atmospheres with different values of dielectric breakdown strength (helium, argon, oxygen, carbon dioxide, nitrogen, and sulfur hexafluoride): the mechanism thus appears to be general. PMID:23153329

  20. Surface state engineering of molecule-molecule interactions.

    PubMed

    Rojas, Geoffrey; Simpson, Scott; Chen, Xumin; Kunkel, Donna A; Nitz, Justin; Xiao, Jie; Dowben, Peter A; Zurek, Eva; Enders, Axel

    2012-04-14

    Engineering the electronic structure of organics through interface manipulation, particularly the interface dipole and the barriers to charge carrier injection, is of essential importance to improve organic devices. This requires the meticulous fabrication of desired organic structures by precisely controlling the interactions between molecules. The well-known principles of organic coordination chemistry cannot be applied without proper consideration of extra molecular hybridization, charge transfer and dipole formation at the interfaces. Here we identify the interplay between energy level alignment, charge transfer, surface dipole and charge pillow effect and show how these effects collectively determine the net force between adsorbed porphyrin 2H-TPP on Cu(111). We show that the forces between supported porphyrins can be altered by controlling the amount of charge transferred across the interface accurately through the relative alignment of molecular electronic levels with respect to the Shockley surface state of the metal substrate, and hence govern the self-assembly of the molecules. PMID:22395096

  1. Interstellar molecules

    NASA Technical Reports Server (NTRS)

    Townes, C. H.

    1976-01-01

    Progress in the discovery and study of interstellar molecules is summarized. The 36 molecular species thus far identified in interstellar space are listed in several groups which include simple hydrides, oxides, and sulfides, various derivatives of ammonia, molecules involving linear carbon chains, cyanides, and molecules related in structure to formaldehyde, alcohols, or ethers. Several free radicals are described, the discovery of molecules in external galaxies is discussed, and possible mechanisms for molecular formation are noted. Methods for examining relative isotopic abundances by measuring molecules in interstellar clouds are outlined, mechanisms for the excitation of interstellar molecules are reviewed, and values are presented for the C-12/C-13 abundance ratio in a number of interstellar clouds. The detection of interstellar masers is discussed along with pumping mechanisms and masing transitions in H2CO, CH, OH, and SiO. The nature of dense interstellar clouds is examined in terms of several simple and complex cloud models, with emphasis on multiple condensation models.

  2. HOVEDOPPGAVE Polarizable force fields for flexible molecules

    E-print Network

    Izaguirre, Jesús A.

    HOVEDOPPGAVE 2004 Polarizable force fields for flexible molecules Kandidatens navn Asbjørn Holt interactions. In this study a force field for flexible water molecules is constructed. To describe the electrostatic properties of the water molecules in this force fields, atomic charges and dipole moments are used

  3. Weakly Charged Cationic Nanoparticles Induce DNA Bending and Strand Separation

    SciTech Connect

    Railsback, Justin [North Carolina State University; Singh, Abhishek [North Carolina State University; Pearce, Ryan [North Carolina State University; McKnight, Timothy E [ORNL; Collazo, Ramon [North Carolina State University; Sitar, Zlatko [ORNL; Yingling, Yaroslava [North Carolina State University; Melechko, Anatoli Vasilievich [ORNL

    2012-01-01

    The understanding of interactions between double stranded (ds) DNA and charged nanoparticles will have a broad bearing on many important applications from drug delivery [ 1 4 ] to DNAtemplated metallization. [ 5 , 6 ] Cationic nanoparticles (NPs) can bind to DNA, a negatively charged molecule, through a combination of electrostatic attraction, groove binding, and intercalation. Such binding events induce changes in the conformation of a DNA strand. In nature, DNA wraps around a cylindrical protein assembly (diameter and height of 6 nm) [ 7 ] with an 220 positive charge, [ 8 ] creating the complex known as chromatin. Wrapping and bending of DNA has also been achieved in the laboratory through the binding of highly charged species such as molecular assemblies, [ 9 , 10 ] cationic dendrimers, [ 11 , 12 ] and nanoparticles. [ 13 15 ] The charge of a nanoparticle plays a crucial role in its ability to induce DNA structural changes. If a nanoparticle has a highly positive surface charge density, the DNA is likely to wrap and bend upon binding to the nanoparticle [ 13 ] (as in the case of chromatin). On the other hand, if a nanoparticle is weakly charged it will not induce dsDNA compaction. [ 9 , 10 , 15 ] Consequently, there is a transition zone from extended to compact DNA conformations which depends on the chemical nature of the nanoparticle and occurs for polycations with charges between 5 and 10. [ 9 ] While the interactions between highly charged NPs and DNA have been extensively studied, the processes that occur within the transition zone are less explored.

  4. Negative hydrogen ion production mechanisms

    NASA Astrophysics Data System (ADS)

    Bacal, M.; Wada, M.

    2015-06-01

    Negative hydrogen/deuterium ions can be formed by processes occurring in the plasma volume and on surfaces facing the plasma. The principal mechanisms leading to the formation of these negative ions are dissociative electron attachment to ro-vibrationally excited hydrogen/deuterium molecules when the reaction takes place in the plasma volume, and the direct electron transfer from the low work function metal surface to the hydrogen/deuterium atoms when formation occurs on the surface. The existing theoretical models and reported experimental results on these two mechanisms are summarized. Performance of the negative hydrogen/deuterium ion sources that emerged from studies of these mechanisms is reviewed. Contemporary negative ion sources do not have negative ion production electrodes of original surface type sources but are operated with caesium with their structures nearly identical to volume production type sources. Reasons for enhanced negative ion current due to caesium addition to these sources are discussed.

  5. Single Molecules

    NSDL National Science Digital Library

    A new molecular science journal, Single Molecules, from Wiley Interscience, "will provide researchers with a broad overview of current methods and techniques, recent applications and shortcomings of present techniques in the field of single molecules." With temporary free access, the journal's latest issue contains a few full-text articles, with more articles being regularly added. This journal is currently calling for papers.

  6. Further characterization by site-directed mutagenesis of the protein-protein interface in the ferredoxin/ferredoxin:NADP+ reductase system from Anabaena: requirement of a negative charge at position 94 in ferredoxin for rapid electron transfer.

    PubMed

    Hurley, J K; Medina, M; Gomez-Moreno, C; Tollin, G

    1994-08-01

    Ferredoxins are small electron transfer proteins found ubiquitously in nature. In green plant photosynthesis, the soluble [2Fe-2S] ferredoxin shuttles electrons from Photosystem I to ferredoxin:NADP+ reductase. In order to define the features of the protein/protein interface required for efficient electron transfer from ferredoxin to ferredoxin:NADP+ reductase, we have made site-directed mutants of the ferredoxin from the cyanobacterium Anabaena 7120 and measured the rate constants for electron transfer to ferredoxin:NADP+ reductase using laser flash photolysis. Previous results from this laboratory identified two residues in ferredoxin that were crucial to electron transfer between these proteins. One such position (F65) was subsequently shown to require an aromatic amino acid, and it was further shown that interprotein electron transfer was rate-limiting in the case of the slowly reacting F65A mutant (Hurley et al., 1993 J. Am. Chem. Soc. 115, 11,698-11,701). The second crucial position (E94) is shown in the present study to require a negative charge in order to maintain wild-type-like electron transfer reactivity toward ferredoxin:NADP+ reductase. Further, we also demonstrate, for the slowly reacting E94Q mutant, that electron transfer is the rate-limiting step in the interprotein interaction. PMID:8037461

  7. Interface trap and oxide charge generation under negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with ultrathin plasma-nitrided SiON gate dielectrics

    SciTech Connect

    Zhu Shiyang; Nakajima, Anri; Ohashi, Takuo; Miyake, Hideharu [Research Center for Nanodevices and Systems, Hiroshima University, 1-4-2 Kagamiyama, Higashi-Hiroshima 739-8527 (Japan); Elpida Memory, Inc., 7-10 Yoshikawa-kogyo-danchi, Higashi-Hiroshima 739-0198 (Japan)

    2005-12-01

    The interface trap generation ({delta}N{sub it}) and fixed oxide charge buildup ({delta}N{sub ot}) under negative bias temperature instability (NBTI) of p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with ultrathin (2 nm) plasma-nitrided SiON gate dielectrics were studied using a modified direct-current-current-voltage method and a conventional subthreshold characteristic measurement. Different stress time dependences were shown for {delta}N{sub it} and {delta}N{sub ot}. At the earlier stress times, {delta}N{sub it} dominates the threshold voltage shift ({delta}V{sub th}) and {delta}N{sub ot} is negligible. With increasing stress time, the rate of increase of {delta}N{sub it} decreases continuously, showing a saturating trend for longer stress times, while {delta}N{sub ot} still has a power-law dependence on stress time so that the relative contribution of {delta}N{sub ot} increases. The thermal activation energy of {delta}N{sub it} and the NBTI lifetime of pMOSFETs, compared at a given stress voltage, are independent of the peak nitrogen concentration of the SiON film. This indicates that plasma nitridation is a more reliable method for incorporating nitrogen in the gate oxide.

  8. Nanoparticle coagulation in fractionally charged and charge fluctuating dusty plasmas

    SciTech Connect

    Nunomura, Shota; Kondo, Michio [Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568 (Japan); Shiratani, Masaharu; Koga, Kazunori; Watanabe, Yukio [Department of Electronics, Graduate School of Information Science and Electrical Engineering, Kyushu University, Fukuoka 819-0395 (Japan)

    2008-08-15

    The kinetics of nanoparticle coagulation has been studied in fractionally charged and charge fluctuating dusty plasmas. The coagulation occurs when the mutual collision frequency among nanoparticles exceeds their charging and decharging/neutralization frequency. Interestingly, the coagulation is suppressed while a fraction (several percent) of nanoparticles are negatively charged in a plasma, in which stochastic charging plays an important role. A model is developed to predict a phase diagram of the coagulation and its suppression.

  9. Negative Messages

    Microsoft Academic Search

    Jurrien Gregor HALFF

    2010-01-01

    Most people think that if we send out a coherent negative message to stakeholders, everything will be fine. But, as Associate Professor Gregor Halff points out, the reality is very different. During a critical situation, there will be more people talking about you than with you.\\u000aHalff shares in this enlightening video that the key to a successful outcome is

  10. Molecule Polarity

    NSDL National Science Digital Library

    The PhET project at the University of Colorado creates "fun, interactive, research-based simulations of physical phenomena." This particular one deals with molecular polarity. When is a molecule polar? Change the electronegativity of atoms in a molecule to see how it affects polarity. This simulation will allow visitors to see how molecules behave in an electric field, and change the bond angle to see how shape affects polarity for real molecules in 3D. The simulation is also paired with teaching tips and user-contirubed Teaching Ideas, lessons using the simulation in context, that can be found near the bottom of the page. The simulation is also available in multiple languages.

  11. Modeling Molecules

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The molecule modeling method known as Multibody Order (N) Dynamics, or MBO(N)D, was developed by Moldyn, Inc. at Goddard Space Flight Center through funding provided by the SBIR program. The software can model the dynamics of molecules through technology which stimulates low-frequency molecular motions and properties, such as movements among a molecule's constituent parts. With MBO(N)D, a molecule is substructured into a set of interconnected rigid and flexible bodies. These bodies replace the computation burden of mapping individual atoms. Moldyn's technology cuts computation time while increasing accuracy. The MBO(N)D technology is available as Insight II 97.0 from Molecular Simulations, Inc. Currently the technology is used to account for forces on spacecraft parts and to perform molecular analyses for pharmaceutical purposes. It permits the solution of molecular dynamics problems on a moderate workstation, as opposed to on a supercomputer.

  12. Monopole-charge instability

    E-print Network

    Horváthy, P A; Rawnsley, J H

    2009-01-01

    For monopoles with nonvanishing Higgs potential it is shown that with respect to "Brand-Neri-Coleman type" variations (a) the stability problem reduces to that of a pure gauge theory on the two-sphere (b) each topological sector admits one, and only one, stable monopole charge, and (c) each unstable monopole admits $2\\sum_{q<0} (2|q|-1)$ negative modes, where the sum goes over all negative eigenvalues $q$ of the non-Abelian charge $Q$. An explicit construction for (i) the unique stable charge (ii) the negative modes and (iii) the spectrum of the Hessian, on the 2-sphere, is then given. The relation to loops in the residual group is explained. The negative modes are tangent to suitable energy-reducing two-spheres. The general theory is illustrated for the little groups U(2), U(3), SU(3)/Z_3 and O(5).

  13. Dasatinib, an orally active small molecule inhibitor of both the src and abl kinases, selectively inhibits growth of basal-type\\/“triple-negative” breast cancer cell lines growing in vitro

    Microsoft Academic Search

    Richard S. Finn; Judy Dering; Charles Ginther; Cindy A. Wilson; Padraic Glaspy; Nishan Tchekmedyian; Dennis J. Slamon

    2007-01-01

    Dasatinib is an orally active small molecule kinase inhibitor of both the src and abl proteins. To evaluate the potential role of dasatinib in breast cancer we used 39 human breast cancer cell lines that have\\u000a been molecular profiled using Agilent Microarrays. They represent both luminal and basal breast cancer subtypes based on the\\u000a relative gene expression of cytokeratin (CK)

  14. Relativistic calculations of the ground state energies and the critical distances for one-electron homonuclear quasi-molecules

    NASA Astrophysics Data System (ADS)

    Mironova, D. V.; Tupitsyn, I. I.; Shabaev, V. M.; Plunien, G.

    2015-03-01

    The ground-state energies of one-electron homonuclear quasi-molecules for the nuclear charge number in the range Z = 1 - 100 at the "chemical" distances R = 2 / Z (in a.u.) are calculated. The calculations are performed for both point- and extended-charge nucleus cases using the Dirac-Fock-Sturm approach with the basis functions constructed from the one-center Dirac-Sturm orbitals. The critical distances Rcr , at which the ground-state level reaches the edge of the negative-energy Dirac continuum, are calculated for homonuclear quasi-molecules in the range: 85 ? Z ? 100 . It is found that in case of U2183+ the critical distance Rcr = 38.42 fm for the point-charge nuclei and Rcr = 34.72 fm for extended nuclei.

  15. Enhanced electron attachment to vibrationally and electronically excited molecules

    NASA Astrophysics Data System (ADS)

    Tav, Cumali

    Electron attachment studies on vibrationally and electronically excited states have been measured. The attachment of electrons to vibrationally excited states of the ground electronic state populated via temperature increase was measured in the mean electron energy range, (?), 0.04 to 4.8 eV, over the temperature range, T, 300 to 700 K and over the total gas number density, Nt, 2.25 to 15.5 × 1019 molecules/cm3. These studies are presented in Part 1 for three technologically important molecules: Methylene Chloride (C2H2Cl2), Boron Trichloride (BCl3), and Trichlorotrifluoroethane (1,1,2-C 2Cl3F3). Electron attachment rate constants, k a((?),T), was measured as a function of mean electron energy in Ar and N2 gases at different temperatures. Using swarm unfolding technique, electron attachment cross sections, ?a(?,T), was measured as a function of electron energy by unfolding ka((?),T) at each temperature. The results of these measurements show that the dissociative electron attachment cross sections increase with the increase of vibrational energies. In the studies an electronically-excited states, the attaching electrons and the excited states of molecules were produced with a single excimer-laser pulse. The excitation of molecules to energies above the ionization potential (IP) caused the population of core-excited Rydberg states (HR). The electrons produced via photoionization were attached to the concomitantly produced highly-excited molecules leading to negative ion formation under the high-pressure environment provided by Ar or N2 gases. In these experiments two different experimental techniques were used: two- electrode arrangement and three-electrode arrangement. The two-electrode arrangement techniques provided information on the lifetimes of the excited molecules as well as estimates of various experimental parameters including the electron attachment rate constant of excited molecules. The other technique, the three- electrode arrangement, provided information about the density of charged species including electrons and negative ions and the estimation of electron attachment rate constant. These results are presented in Part II for three molecules: Benzene (C6H 6), Oxygen (O2), and Dichlorodifluoromethane (CCl2,F2). It was shown that the electron attachment to highly-excited molecules was extremely efficient process leading to enormous electron attachment cross sections, ?a, ~ 10-10 cm2, which were many orders of magnitude larger compared to the cross sections for corresponding ground electronic states.

  16. Negative Mass Propulsion

    NASA Astrophysics Data System (ADS)

    Winterberg, F.

    Schrödinger's analysis of the Dirac equation gives a hint for the existence of negative masses hidden behind positive masses. But their use for propulsion by reducing the inertia of matter for example, in the limit of macroscopic bodied with zero rest mass, depends on a technical solution to free them from their imprisonment by positive masses. It appears that there are basically two ways this might be achieved: 1. By the application of strong electromagnetic or gravitational fields or by high particle energies. 2. By searching for places in the universe where nature has already done this separation, and from where the negative masses can be mined. The first of these two possibilities is for all practical means excluded, because if possible at all, it would depend on electromagnetic or gravitational fields with strength beyond what is technically attainable, or on extremely large likewise not attainable particle energies. With regard to the 2nd possibility, it has been observed that non-baryonic cold dark matter tends to accumulate near the center of galaxies, or places in the universe which have a large gravitational potential well. Because of the equivalence principle of general relativity, the attraction towards the center of a gravitational potential well, produced by a positive mass, is for negative masses the same as for positive masses, and large amounts of negative masses might have over billions of years been trapped in these gravitational potential wells. Now it just happens that the center of the moon is a potential well, not too deep that it cannot be reached by making a tunnel through the moon, not possible for the deeper potential well of the earth, where the temperature and pressure are too high. Making a tunnel through the moon, provided there is a good supply of negative mass, could revolutionize interstellar space flight. A sequence of thermonuclear shape charges would make such tunnel technically feasible.

  17. Collision-Based Ionization: Bridging the Gap between Chemical Ionization and Aerosol Particle Diffusion Charging

    Microsoft Academic Search

    Vinay Premnath; Derek Oberreit; Christopher J. Hogan Jr

    2011-01-01

    In diffusion charging theory, it is assumed that each ion–particle collision leads to the transfer of charge from ion to particle, and that charge transfer will not occur upon collision between a vapor molecule and a charged particle. However, in chemical ionization, charge transfer can occur in two directions—from charge-donating ion to vapor molecule and back from charged vapor molecule

  18. Surface charge modulated aptasensor in a single glass conical nanopore.

    PubMed

    Cai, Sheng-Lin; Cao, Shuo-Hui; Zheng, Yu-Bin; Zhao, Shuang; Yang, Jin-Lei; Li, Yao-Qun

    2015-09-15

    In this work, we have proposed a label-free nanopore-based biosensing strategy for protein detection by performing the DNA-protein interaction inside a single glass conical nanopore. A lysozyme binding aptamer (LBA) was used to functionalize the walls of glass nanopore via siloxane chemistry and negatively charged recognition sites were thus generated. The covalent modification procedures and their recognition towards lysozyme of the single conical nanopore were characterized via ionic current passing through the nanopore membrane, which was measured by recording the current-voltage (I-V) curves in 1mM KCl electrolyte at pH=7.4. With the occurring of recognition event, the negatively charged wall was partially neutralized by the positively charged lysozyme molecules, leading to a sensitive change of the surface charge-dependent current-voltage (I-V) characteristics. Our results not only demonstrate excellent selectivity and sensitivity towards the target protein, but also suggest a route to extend this nanopore-based sensing strategy to the biosensing platform designs of a wide range of proteins based on a charge modulation. PMID:25884732

  19. Biological Molecules

    NSDL National Science Digital Library

    Paul Anderson

    2013-03-12

    Paul Anderson describes the four major biological molecules found in living things. He begins with a brief discussion of polymerization. Dehydration synthesis is used to connect monomers into polymers and hydrolysis breaks them down again. The major characteristics of nucleic acids are described as well as there directionality from 3' to 5' end.

  20. Biosensing: Taking charge of biomolecules

    NASA Astrophysics Data System (ADS)

    Kinsella, Joseph M.; Ivanisevic, Albena

    2007-10-01

    The combination of two scanning probe microscopy techniques has led to a label-free method of detecting charged molecules at the nanoscale and offers a general approach to biosensing with improved resolution, sensitivity and speed.

  1. Examining the Contributions of Lipid Shape and Headgroup Charge on Bilayer Behavior

    Microsoft Academic Search

    Allison Dickey; Roland Faller

    2008-01-01

    To better understand bilayer property dependency on lipid electrostatics and headgroup size, we use atomistic molecular dynamics simulations to study negatively charged and neutral lipid membranes. We compare the negatively charged phosphatidic acid (PA), which at physiological pH and salt concentration has a negative spontaneous curvature, with the negatively charged phosphatidylglycerol (PG) and neutrally charged phosphatidylcholine (PC), both of which

  2. Charge carrier mobility and transmission across the liquid-vapor interface for the dielectric liquid hydrogen

    Microsoft Academic Search

    G. E. Grimm

    1979-01-01

    A radioactive source is used to inject positive and negative charge carriers into the dielectric fluid, liquid hydrogen. The mobility of positive and negative charge carriers is measured. The negative charge carrier mobility is found to be greater than that of the positive charge carrier. Both mobilities are found to be temperature dependent. The radius of the charge carriers is

  3. Moving Molecules!

    NSDL National Science Digital Library

    2014-06-24

    In this activity about molecular diffusion (located on page 2 of the PDF), learners will make predictions and move molecules of iodine through a seemingly solid plastic sandwich bag. The process of diffusion will be visually indicated by a color change when the iodine reacts with starch inside the bag. Information in the resource explains how this activity relates to nanoparticles and research. Related to linked video, DragonflyTV Nano: Nanosilver.

  4. Shake and Make: Charge Recognition

    NSDL National Science Digital Library

    Arizona Science Center

    2012-01-01

    In this activity, learners explore how molecules self-assemble according to forces of attraction and repulsion. Learners investigate how the placement of charge determines the possible structures that molecules can make when they come together. This activity can be performed as a demonstration if purchasing the magnetic pieces is cost prohibitive.

  5. Negative Refraction Induced by M\\"{o}bius Topology

    E-print Network

    Fang, Y N; Ai, Qing; Sun, C P

    2015-01-01

    We theoretically show the negative refraction existing in M\\"{o}bius molecules. The negative refractive index is induced by the non-trivial topology of the molecules. With the M\\"{o}bius boundary condition, the effective electromagnetic fields felt by the electron in a M\\"{o}bius ring is spatially inhomogeneous. In this regard, the $D_{N}$ symmetry is broken in M\\"{o}bius molecules and thus the magnetic response is induced through the effective magnetic field. Our findings open up a new architecture for negative refractive index materials based on the non-trivial topology of M\\"{o}bius molecules.

  6. Charge-transfer-based Gas Sensing Using Atomic-layer MoS2

    PubMed Central

    Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho

    2015-01-01

    Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules. PMID:25623472

  7. Charge-transfer-based Gas Sensing Using Atomic-layer MoS2

    NASA Astrophysics Data System (ADS)

    Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho

    2015-01-01

    Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules.

  8. The large quadrupole of water molecules

    PubMed Central

    Niu, Shuqiang; Tan, Ming-Liang; Ichiye, Toshiko

    2011-01-01

    Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical?molecular mechanical (QM?MM) calculations at the MP2?aug-cc-pVQZ level on a B3LYP?aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM?MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM?MM multipoles is much closer than that from the site models to the potential from the QM?MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment. PMID:21476758

  9. Building Molecules

    NSDL National Science Digital Library

    Rensselaer Polytechnic Institute

    2005-01-01

    This online interactive has three activities in the NanoLab (press the upper right button): Build, Zoom, and Transform. In Build, learners build increasingly complex molecules out of carbon, oxygen, and hydrogen, and is useful for connecting subscripts and the number of atoms, and for introducing 3D molecular structures which are automatically built. Zoom is a "powers of 10" zoom-in ranging from 10,000 kilometers to 1 nanometer. Transform is a simulation of water changing phase from solid to liquid to gas. Through exploration of the site learners form a better understanding of the composition of matter.

  10. Conformational transitions and stop-and-go nanopore transport of single-stranded DNA on charged graphene

    NASA Astrophysics Data System (ADS)

    Shankla, Manish; Aksimentiev, Aleksei

    2014-10-01

    Control over interactions with biomolecules holds the key to applications of graphene in biotechnology. One such application is nanopore sequencing, where a DNA molecule is electrophoretically driven through a graphene nanopore. Here we investigate how interactions of single-stranded DNA and a graphene membrane can be controlled by electrically biasing the membrane. The results of our molecular dynamics simulations suggest that electric charge on graphene can force a DNA homopolymer to adopt a range of strikingly different conformations. The conformational response is sensitive to even very subtle nucleotide modifications, such as DNA methylation. The speed of DNA motion through a graphene nanopore is strongly affected by the graphene charge: a positive charge accelerates the motion, whereas a negative charge arrests it. As a possible application of the effect, we demonstrate stop-and-go transport of DNA controlled by the charge of graphene. Such on-demand transport of DNA is essential for realizing nanopore sequencing.

  11. Electrostatic Charges on Spores of Fungi in Air

    Microsoft Academic Search

    P. H. Gregory

    1957-01-01

    PARTICLES or droplets suspended in air often carry an electrostatic charge. The size and magnitude of the charge depend on how the charge originates (commonly by picking up positive or negative ions from the air). The phenomenon appears to be fundamentally distinct from the characteristic positive or negative charges acquired by particles in colloidal solution1. Buller reported that spores of

  12. Charge-Tunable Silk-Tropoelastin Protein Alloys That Control Neuron Cell Responses

    PubMed Central

    Hu, Xiao; Tang-Schomer, Min D.; Huang, Wenwen; Xia, Xiao-Xia; Weiss, Anthony S.

    2014-01-01

    Tunable protein composites are important for constructing extracellular matrix mimics of human tissues with control of biochemical, structural, and mechanical properties. Molecular interaction mechanisms between silk fibroin protein and recombinant human tropoelastin, based on charge, are utilized to generate a new group of multifunctional protein alloys (mixtures of silk and tropoelastin) with different net charges. These new biomaterials are then utilized as a biomaterial platform to control neuron cell response. With a +38 net charge in water, tropoelastin molecules provide extraordinary elasticity and selective interactions with cell surface integrins. In contrast, negatively charged silk fibroin protein (net charge ?36) provides remarkable toughness and stiffness with morphologic stability in material formats via autoclaving-induced beta-sheet crystal physical crosslinks. The combination of these properties in alloy format extends the versatility of both structural proteins, providing a new biomaterial platform. The alloys with weak positive charges (silk/tropoelastin mass ratio 75/25, net charge around +16) significantly improved the formation of neuronal networks and maintained cell viability of rat cortical neurons after 10 days in vitro. The data point to these protein alloys as an alternative to commonly used poly-L-lysine (PLL) coatings or other charged synthetic polymers, particularly with regard to the versatility of material formats (e.g., gels, sponges, films, fibers). The results also provide a practical example of physically designed protein materials with control of net charge to direct biological outcomes, in this case for neuronal tissue engineering. PMID:25093018

  13. Charged gold nanoparticles in non-polar solvents: 10-min synthesis and 2D self-assembly.

    PubMed

    Martin, Matthew N; Basham, James I; Chando, Paul; Eah, Sang-Kee

    2010-05-18

    We report a fast and highly reproducible chemical synthesis method for colloidal gold nanoparticles which are negatively charged in nonpolar solvents and coated with hydrophobic organic molecules. If a hexane droplet containing charged gold nanoparticles is mixed with a larger toluene droplet, nanoparticles immediately float to the air-toluene interface and form a close-packed monolayer film. After evaporation of the solvent molecules, the monolayer film of nanoparticles can be deposited to any substrate without any limit in size. The synthesis does not require a postsynthesis cleaning step, since the two immiscible liquid phases separate the reaction byproducts from gold nanoparticles and a minimal amount of coating molecules is used. PMID:20392108

  14. Multiply-charged ions and interstellar chemistry.

    PubMed

    Böhme, Diethard Kurt

    2011-11-01

    Gaseous molecules and ions, and even dust grains, can accumulate charge in the interstellar medium (ISM) by harvesting the energy of UV photons, cosmic rays, helium ions and metastable atoms. This Perspective views the various modes of gas-phase formation of multiply-charged cations and the possible impact of their reactions on the chemical and ionization structure of the ISM, in the light of what is still very limited knowledge. Emphasis is given to gas-phase reactions of multiply-charged cations with atoms, molecules and electrons that lead to charge reduction, charge separation and chemical bond formation and these are examined for multiply-charged atoms, small molecules, hydrocarbons, polycyclic aromatic hydrocarbons and fullerenes, primarily as dications but also as a function of charge state. The increased electrostatic interaction due to multiple charge is seen to promote bonding to individual charge sites on large molecules (e.g. fullerenes) and allow ensuing "surface" chemistry under the influence of Coulomb repulsion. The unique ability of multiply charged cations to undergo charge separation reactions, either unimolecular or bimolecular, can feature in the production in the ISM of internally cold, but translationally hot, cations of lower charge state or hot atoms that may provide the driving force for subsequent chemical reactions in what is otherwise an ultracold environment. Available chemical kinetic models that account for the role of multiply-charged ions in the ISM are few and of limited scope and the observation of these ions in the ISM has remained elusive. PMID:21869973

  15. Effect of charge polydispersity and charge residence time on the dynamics of a micellar system.

    PubMed

    Talha, Lamiae; Filali, Mohammed; Azougarh, Abdelhafid; Cipelletti, Luca

    2015-06-01

    We use dynamic light scattering to investigate the effects of charge polydispersity and charge residence time on the dynamics of a micellar system. While in the corresponding uncharged system only one exponential relaxation is observed, two relaxation modes are seen when charging the micelles by adding charged co-surfactant molecules with a long residence time. We attribute the existence of these two relaxation modes to the combined effect of size polydispersity and charge polydispersity, i.e. frozen fluctuations of the number of charges per micelle. Further support to this scenario is provided by control experiments on a similar charged system, but where the charge residence time is short compared to the time scales probed by dynamic light scattering. Here, charge polydispersity is effectively suppressed due to the rapid exchange of charged molecules between micelles and only one single relaxation mode is seen, thereby demonstrating the key role of frozen charge fluctuations in the complex dynamics of our micellar system. PMID:26077446

  16. Human fibrinogen adsorption on positively charged latex particles.

    PubMed

    Zeliszewska, Paulina; Bratek-Skicki, Anna; Adamczyk, Zbigniew; Cie?la, Micha?

    2014-09-23

    Fibrinogen (Fb) adsorption on positively charged latex particles (average diameter of 800 nm) was studied using the microelectrophoretic and the concentration depletion methods based on AFM imaging. Monolayers on latex were adsorbed from diluted bulk solutions at pH 7.4 and an ionic strength in the range of 10(-3) to 0.15 M where fibrinogen molecules exhibited an average negative charge. The electrophoretic mobility of the latex after controlled fibrinogen adsorption was systematically measured. A monotonic decrease in the electrophoretic mobility of fibrinogen-covered latex was observed for all ionic strengths. The results of these experiments were interpreted according to the three-dimensional electrokinetic model. It was also determined using the concentration depletion method that fibrinogen adsorption was irreversible and the maximum coverage was equal to 0.6 mg m(-2) for ionic strength 10(-3) M and 1.3 mg m(-2) for ionic strength 0.15 M. The increase of the maximum coverage was confirmed by theoretical modeling based on the random sequential adsorption approach. Paradoxically, the maximum coverage of fibrinogen on positively charged latex particles was more than two times lower than the maximum coverage obtained for negative latex particles (3.2 mg m(-2)) at pH 7.4 and ionic strength of 0.15 M. This was interpreted as a result of the side-on adsorption of fibrinogen molecules with their negatively charged core attached to the positively charged latex surface. The stability and acid base properties of fibrinogen monolayers on latex were also determined in pH cycling experiments where it was observed that there were no irreversible conformational changes in the fibrinogen monolayers. Additionally, the zeta potential of monolayers was more positive than the zeta potential of fibrinogen in the bulk, which proves a heterogeneous charge distribution. These experimental data reveal a new, side-on adsorption mechanism of fibrinogen on positively charged surfaces and confirmed the decisive role of electrostatic interactions in this process. PMID:25157934

  17. Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids

    NASA Astrophysics Data System (ADS)

    Randel, Jason C.; Niestemski, Francis C.; Botello-Mendez, Andrés R.; Mar, Warren; Ndabashimiye, Georges; Melinte, Sorin; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Butova, Ekaterina D.; Fokin, Andrey A.; Schreiner, Peter R.; Charlier, Jean-Christophe; Manoharan, Hari C.

    2014-09-01

    The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p–n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane–C60 conjugate. By linking both sp3 (diamondoid) and sp2 (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane–C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism.

  18. Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids

    PubMed Central

    Randel, Jason C.; Niestemski, Francis C.; Botello-Mendez, Andrés R.; Mar, Warren; Ndabashimiye, Georges; Melinte, Sorin; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Butova, Ekaterina D.; Fokin, Andrey A.; Schreiner, Peter R.; Charlier, Jean-Christophe; Manoharan, Hari C.

    2014-01-01

    The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p–n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane–C60 conjugate. By linking both sp3 (diamondoid) and sp2 (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane–C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism. PMID:25202942

  19. Negative ions in the ionospheres of planetary bodies without atmospheres

    NASA Technical Reports Server (NTRS)

    Wekhof, A.

    1981-01-01

    It is noted that negative ions may be formed in the ionospheres of Mercury, the moon, and Jupiter's satellites with densities of a few percent of the ionospheric electron density. Negative ions result from three mechanisms at the planetary surface: charge inversion during energetic proton scattering, with simultaneous secondary negative ion emission, and micrometeorite impacts. The density and distribution of negative ions around planetary bodies depends primarily on the negative ion lifetimes determined through photodetachment by solar radiation.

  20. Electronic structure of Fe- vs. Ru-based dye molecules

    SciTech Connect

    Johnson, Phillip S.; Himpsel, F. J. [Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States); Cook, Peter L. [Natural Sciences Department, University of Wisconsin-Superior, Belknap and Catlin, Superior, Wisconsin 54880 (United States); Zegkinoglou, Ioannis [Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States); Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Garcia-Lastra, J. M. [Dpto. Fisica de Materiales, Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Centro de Fisica de Materiales CSIC-UPV-MPC and DIPC, Universidad del Pais Vasco, Av. Tolosa 72, E-20018 San Sebastian (Spain); Department of Physics, Center for Atomic-scale Materials Design, DTU, DK-2800 Kongens Lyngby (Denmark); Rubio, Angel [Dpto. Fisica de Materiales, Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Centro de Fisica de Materiales CSIC-UPV-MPC and DIPC, Universidad del Pais Vasco, Av. Tolosa 72, E-20018 San Sebastian (Spain); Ruther, Rose E. [NSF Center for Sustainable Materials Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA and University of Oregon, Eugene, Oregon 97403-1253 (United States); Hamers, Robert J. [Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706 (United States)

    2013-01-28

    In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold, octahedral N cage, such as tris(bipyridines) and tris(phenanthrolines), exhibit a systematic downward shift of the N 1s-to-{pi}* transition when Ru is replaced by Fe. This shift is explained by an extra transfer of negative charge from the metal to the N ligands in the case of Fe, which reduces the binding energy of the N 1s core level. The C 1s-to-{pi}* transitions show the opposite trend, with an increase in the transition energy when replacing Ru by Fe. Molecules with the metal in a fourfold, planar N cage (porphyrins) exhibit a more complex behavior due to a subtle competition between the crystal field, axial ligands, and the 2+ vs. 3+ oxidation states.

  1. Electronic structure of Fe- vs. Ru-based dye molecules.

    PubMed

    Johnson, Phillip S; Cook, Peter L; Zegkinoglou, Ioannis; García-Lastra, J M; Rubio, Angel; Ruther, Rose E; Hamers, Robert J; Himpsel, F J

    2013-01-28

    In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold, octahedral N cage, such as tris(bipyridines) and tris(phenanthrolines), exhibit a systematic downward shift of the N 1s-to-?* transition when Ru is replaced by Fe. This shift is explained by an extra transfer of negative charge from the metal to the N ligands in the case of Fe, which reduces the binding energy of the N 1s core level. The C 1s-to-?* transitions show the opposite trend, with an increase in the transition energy when replacing Ru by Fe. Molecules with the metal in a fourfold, planar N cage (porphyrins) exhibit a more complex behavior due to a subtle competition between the crystal field, axial ligands, and the 2+ vs. 3+ oxidation states. PMID:23387617

  2. The Forces Between Hydrogen Molecules

    Microsoft Academic Search

    Arthur A. Evett; Henry Margenau

    1953-01-01

    Earlier calculations of the H2-H2 interaction, based on the use of screening-constant functions, seemed to lead to reasonable answers only with the use of a nuclear charge much greater than the correct value for the isolated molecule, Z0=1.166. The present work is a recalculation of the exchange forces for Z=Z0. A small numerical error in the earlier work is eliminated,

  3. CHARGE STABILITY IN LPCVD SILICON NITRIDE FOR SURFACE PASSIVATION OF SILICON SOLAR CELLS

    E-print Network

    of the rear side of conventional cells based on p type material, a dielectric containing negative charge Negatively charged dielectric films are of great interest for application to silicon solar cells, since negatively charged through the injection of electrons from the silicon substrate. High densities of negative

  4. Net charge fluctuations in Au+Au collisions at root s(NN)=130 GeV

    E-print Network

    Adams, J.; Adler, C.; Aggarwal, MM; Ahammed, Z.; Amonett, J.; Anderson, BD; Anderson, M.; Arkhipkin, D.; Averichev, GS; Badyal, SK; Balewski, J.; Barannikova, O.; Barnby, LS; Baudot, J.; Bekele, S.; Belaga, VV; Bellwied, R.; Berger, J.; Bezverkhny, BI; Bhardwaj, S.; Bhaskar, P.; Bhati, AK; Bichsel, H.; Billmeier, A.; Bland, LC; Blyth, CO; Bonner, BE; Botje, M.; Boucham, A.; Brandin, A.; Bravar, A.; Cadman, RV; Cai, XZ; Caines, H.; Sanchez, MCD; Cardenas, A.; Carroll, J.; Castillo, J.; Castro, M.; Cebra, D.; Chaloupka, P.; Chattopadhyay, S.; Chen, HF; Chen, Y.; Chernenko, SP; Cherney, M.; Chikanian, A.; Choi, B.; Christie, W.; Coffin, JP; Cormier, TM; Cramer, JG; Crawford, HJ; Das, D.; Das, S.; Derevschikov, AA; Didenko, L.; Dietel, T.; Dong, X.; Draper, JE; Du, F.; Dubey, AK; Dunin, VB; Dunlop, JC; Majumdar, MRD; Eckardt, V.; Efimov, LG; Emelianov, V.; Elage, JE; Eppley, G.; Erazmus, B.; Fachini, P.; Faine, V.; Faivre, J.; Fatemi, R.; Filimonov, K.; Filip, P.; Finch, E.; Fisyak, Y.; Flierl, D.; Foley, KJ; Fu, J.; Gagliardi, Carl A.; Ganti, MS; Gutierrez, TD; Gagunashvili, N.; Gans, J.; Gaudichet, L.; Germain, M.; Geurts, E.; Ghazikhanian, V.; Ghosh, R.; Gonzalez, JE; Grachov, O.; Grigoriev, V.; Gronstal, S.; Grosnick, D.; Guedon, M.; Guertin, SM; Gupta, A.; Gushin, E.; Hallman, TJ; Hardtke, D.; Harris, JW; Heinz, M.; Henry, TW; Heppelmann, S.; Herston, T.; Hippolyte, B.; Hirsch, A.; Hjort, E.; Hoffmann, GW; Horsley, M.; Huang, HZ; Huang, SL; Humanic, TJ; Igo, G.; Ishihara, A.; Jacobs, P.; Jacobs, WW; Janik, M.; Johnson, I.; Jones, PG; Judd, EG; Kabana, S.; Kaneta, M.; Kaplan, M.; Keane, D.; Kiryluk, J.; Kisiel, A.; Klay, J.; Klein, SR; Klyachko, A.; Koetke, DD; Kolleger, T.; Konstantmov, AS; Kopytine, M.; Kotchenda, L.; Kovalenko, AD; Kramer, M.; Kravtsov, P.; Krueger, K.; Kuhn, C.; Kulikov, AI; Kumar, A.; Kunde, GJ; Kunz, CL; Kutuev, RK; Kuznetsov, AA; Lamont, MAC; Landgraf, JM; Lange, S.; Lansdell, CP; Lasiuk, B.; Laue, F.; Lauret, J.; Lebedev, A.; Lednicky, R.; Leontiev, VM; LeVine, MJ; Li, C.; Li, Q.; Lindenbatim, SJ; Lisa, MA; Liu, E.; Liu, L.; Liu, Z.; Liu, QJ; Ljubicic, T.; Llope, WJ; Long, H.; Longacre, RS; Lopez-Noriega, M.; Love, WA; Ludlam, T.; Lynn, D.; Ma, J.; Ma, YG; Maestro, D.; Mahajan, S.; Mangotra, LK; Mahapatra, DP; Majka, R.; Manweiler, R.; Margetis, S.; Markert, C.; Martin, L.; Marx, J.; Matis, HS; Matulenko, YA; McShane, TS; Meissner, F.; Melnick, Y.; Meschanin, A.; Messer, M.; Miller, ML; Milosevich, Z.; Minaev, NG; Mironov, C.; Mishra, D.; Mitchell, J.; Mohanty, B.; Molnar, L.; Moore, CF; Mora-Corral, MJ; Morozov, V.; de Moura, MM; Munhoz, MG; Nandi, BK; Nayak, SK; Nayak, TK; Nelson, JM; Nevski, P.; Nikitin, VA; Nogach, LV; Norman, B.; Nurushev, SB; Odyniec, G.; Ogawa, A.; Okorokov, V.; Oldenburg, M.; Olson, D.; Paic, G.; Pandey, SU; Pal, SK; Panebratsev, Y.; Panitkin, SY; Pavlinov, AI; Pawlak, T.; Perevoztchikov, V.; Peryt, W.; Petrov, VA; Phatak, SC; Picha, R.; Planinic, M.; Pluta, J.; Porile, N.; Porter, J.; Poskanzer, AM; Potekhin, M.; Potrebenikova, E.; Potukuchi, BVKS; Prindle, D.; Pruneau, C.; Putschke, J.; Rai, G.; Rakness, G.; Raniwala, R.; Raniwala, S.; Ravel, O.; Razin, SV; Reichhold, D.; Reid, JG; Renault, G.; Retiere, F.; Ridiger, A.; Ritter, HG; Roberts, JB; Rogachevski, OV; Romero, JL; Rose, A.; Roy, C.; Ruan, LJ; Rykov, V.; Sahoo, R.; Sakrejda, I.; Salur, S.; Sandweiss, J.; Savin, I.; Schambach, J.; Scharenberg, RP; Schmitz, N.; Schroeder, LS; Schweda, K.; Seger, J.; Seliverstov, D.; Seyboth, P.; Shahaliev, E.; Shao, M.; Sharma, M.; Shestermanov, KE; Shimanskii, SS; Singaraju, RN; Simon, F.; Skoro, G.; Smirnov, N.; Snellings, R.; Sood, G.; Sorensen, P.; Sowinski, J.; Spinka, H. M.; Srivastava, B.; Stanislaus, S.; Stock, R.; Stolpovsky, A.; Strikhanov, M.; Stringfellow, B.; Struck, C.; Suaide, AAP; Sugarbaker, E.; Suite, C.; Sumbera, M.; Surrow, B.; Symons, TJM; de Toledo, AS; Szarwas, P.; Tai, A.; Takahashi, J.; Tang, AH; Thein, D.; Thomas, JH; Tikhomirov, V.; Tokarev, M.; Tonjes, MB; Trentalange, S.; Tribble, Robert E.; Trivedi, MD; Trofimov, V.; Tsai, O.; Ullrich, T.; Underwood, DG; Van Buren, G.; VanderMolen, AM; Vasiliev, AN; Vasiliev, M.; Vigdor, SE; Viyogi, YP; Voloshin, SA; Waggoner, W.; Wang, F.; Wang, G.; Wang, XL; Wang, ZM; Ward, H.; Watson, JW; Wells, R.; Westfall, GD; Whitten, C.; Wieman, H.; Willson, R.; Wissink, SW; Witt, R.; Wood, J.; Wu, J.; Xu, N.; Xu, Z.; Xu, ZZ; Yakutin, AE; Yamamoto, E.; Yang, J.; Yepes, P.; Yurevich, VI; Zanevski, YV; Zborovsky, I.; Zhang, H.; Zhang, HY; Zhang, WM; Zhang, ZP; Zolnierczuk, PA; Zoulkarneev, R.; Zoulkarneeva, J.; Zubarev, AN; STAR Collaboration.

    2003-01-01

    as for identified charged pions, kaons, and protons. The net charge dynamical fluctuations are found to be large and negative providing clear evidence that positive and negative charged p article production is correlated within the pseudorapidity range investigated...

  5. The Origins of Positive and Negative in Electricity

    ERIC Educational Resources Information Center

    Jensen, William B.

    2005-01-01

    Benjamin Franklin first introduced the terms positive and negative into electrical theory in the year 1747. The positive and negative terms originally had nothing to do with inherent electrical charge, but rather indicated which object had an excess of electrical fluid indicating positive, and which had a deficiency, indicating negative.

  6. Electrochromic graphene molecules.

    PubMed

    Ji, Zhiqiang; Doorn, Stephen K; Sykora, Milan

    2015-04-28

    Polyclic aromatic hydrocarbons also called Graphene Molecules (GMs), with chemical composition C132H36(COOH)2 were synthesized in situ on the surface of transparent nanocrystalline indium tin oxide (nc-ITO) electrodes and their electronic structure was studied electrochemically and spectro-electrochemically. Variations in the potential applied onto the nc-ITO/GM electrodes induce only small changes in the observed current, but they produce dramatic changes in the absorption of the GMs, which are associated with their oxidation and reduction. Analysis of the absorption changes using a modified Nernst equation is used to determine standard potentials associated with the individual charge transfer processes. For the GMs prepared here, these were found to be E1,ox(0) = 0.77 ± 0.01 V and E2,ox(0) = 1.24 ± 0.02 V vs NHE for the first and second oxidation and E1,red(0) = -1.50 ± 0.04 V for the first reduction. The charge transfer processes are found to be nonideal. The nonideality factors associated with the oxidation and reduction processes are attributed to strong interactions between the GM redox centers. Under the conditions of potential cycling, GMs show rapid (seconds) color change with high contrast and stability. An electrochromic application is demonstrated wherein the GMs are used as the optically active component. PMID:25768313

  7. Optimizing Persistent Negative Hydrogen Beams from High-Power RF Plasma Sources

    NASA Astrophysics Data System (ADS)

    Stockli, Martin; Han, Baoxi; Murray, Syd; Pennisi, Terry; Piller, Chip; Santana, Manuel; Welton, Robert

    2011-10-01

    High-power RF ion sources produce intense beams of negative H- ions for high-power accelerators using charge-changing injection schemes. The inductively induced RF plasma produces copious amounts of positive ions, electrons, and excited molecules. Energetic electrons rapidly destroy H- ions with their 0.75 eV electron affinity. A ~250 G filter field reflects the energetic electron while the cold electrons, the ions, and the molecules can drift towards the outlet. There slow electrons colliding with highly excited vibrating molecules form H- ions that can be extracted. However, production yields suggest that most negative ions are formed on a conical Mo converter surface, which surrounds the outlet. This appears to be especially true when the surface is covered with a fractional layer of Cs. The persistence of the extracted H-beam suggests that the Cs layer is persistent, likely due to low levels of impurities and hydrogen being to light to sputter Cs atoms from the metallically clean surface. Experimental evidence, data, and simple models will be presented to support our findings.

  8. Optimizing Persistent Negative Hydrogen Beams from High-Power RF Plasma Sources

    NASA Astrophysics Data System (ADS)

    Stockli, Martin; Han, Baoxi; Murray, Syd; Pennisi, Terry; Piller, Chip; Santana, Manuel; Welton, Robert

    2011-10-01

    High-power RF ion sources produce intense beams of negative H- ions for high-power accelerators using charge-changing injection schemes. The inductively induced RF plasma produces copious amounts of positive ions, electrons, and excited molecules. Energetic electrons rapidly destroy H- ions with their 0.75 eV electron affinity. A ~250 G filter field reflects the energetic electron while the cold electrons, the ions, and the molecules can drift towards the outlet. There slow electrons colliding with highly excited vibrating molecules form H- ions that can be extracted. However, production yields suggest that most negative ions are formed on a conical Mo converter surface, which surrounds the outlet. This appears to be especially true when the surface is covered with a fractional layer of Cs. The persistence of the extracted H- beam suggests that the Cs layer is persistent, likely due to low levels of impurities and hydrogen being to light to sputter Cs atoms from the metallically clean surface. Experimental evidence, data, and simple models will be presented to support our findings.

  9. Environment Assisted Quantum Transport in Organic Molecules

    E-print Network

    Gabor Vattay; Istvan Csabai

    2015-02-28

    One of the new discoveries in quantum biology is the role of Environment Assisted Quantum Transport (ENAQT) in excitonic transport processes. In disordered quantum systems transport is most efficient when the environment just destroys quantum interferences responsible for localization, but the coupling does not drive the system to fully classical thermal diffusion yet. This poised realm between the pure quantum and the semi-classical domains has not been considered in other biological transport processes, such as charge transport through organic molecules. Binding in receptor-ligand complexes is assumed to be static as electrons are assumed to be not able to cross the ligand molecule. We show that ENAQT makes cross ligand transport possible and efficient between certain atoms opening the way for the reorganization of the charge distribution on the receptor when the ligand molecule docks. This new effect can potentially change our understanding how receptors work. We demonstrate room temperature ENAQT on the caffeine molecule.

  10. Negative ion source

    DOEpatents

    Delmore, James E. (Idaho Falls, ID)

    1987-01-01

    A method and apparatus for providing a negative ion source accelerates electrons away from a hot filament electron emitter into a region of crossed electric and magnetic fields arranged in a magnetron configuration. During a portion of the resulting cycloidal path, the electron velocity is reduced below its initial value. The electron accelerates as it leaves the surface at a rate of only slightly less than if there were no magnetic field, thereby preventing a charge buildup at the surface of the emitter. As the electron traverses the cycloid, it is decelerated during the second, third, and fourth quadrants, then reeccelerated as it approaches the end of the fourth quadrant to regain its original velocity. The minimum velocity occurs during the fourth quadrant, and corresponds to an electron temperature of 200.degree. to 500.degree. for the electric and magnetic fields commonly encountered in the ion sources of magnetic sector mass spectrometers. An ion source using the above-described thermalized electrons is also disclosed.

  11. Improved negative ion source

    DOEpatents

    Delmore, J.E.

    1984-05-01

    A method and apparatus for providing a negative ion source accelerates electrons away from a hot filament electron emitter into a region of crossed electric and magnetic fields arranged in a magnetron configuration. During a portion of the resulting cycloidal path, the electron velocity is reduced below its initial value. The electron accelerates as it leaves the surface at a rate of only slightly less than if there were no magnetic field, thereby preventing a charge buildup at the surface of the emitter. As the electron traverses the cycloid, it is decelerated during the second, third, and fourth quadrants, then reaccelerated as it approaches the end of the fourth quadrant to regain its original velocity. The minimum velocity occurs during the fourth quadrant, and corresponds to an electron temperature of 200 to 500/sup 0/C for the electric and magnetic fields commonly encountered in the ion sources of magnetic sector mass spectrometers. An ion source using the above-described thermalized electrons is also disclosed.

  12. Single-molecule dynamics in nanofabricated traps

    NASA Astrophysics Data System (ADS)

    Cohen, Adam

    2009-03-01

    The Anti-Brownian Electrokinetic trap (ABEL trap) provides a means to immobilize a single fluorescent molecule in solution, without surface attachment chemistry. The ABEL trap works by tracking the Brownian motion of a single molecule, and applying feedback electric fields to induce an electrokinetic motion that approximately cancels the Brownian motion. We present a new design for the ABEL trap that allows smaller molecules to be trapped and more information to be extracted from the dynamics of a single molecule than was previously possible. In particular, we present strategies for extracting dynamically fluctuating mobilities and diffusion coefficients, as a means to probe dynamic changes in molecular charge and shape. If one trapped molecule is good, many trapped molecules are better. An array of single molecules in solution, each immobilized without surface attachment chemistry, provides an ideal test-bed for single-molecule analyses of intramolecular dynamics and intermolecular interactions. We present a technology for creating such an array, using a fused silica plate with nanofabricated dimples and a removable cover for sealing single molecules within the dimples. With this device one can watch the shape fluctuations of single molecules of DNA or study cooperative interactions in weakly associating protein complexes.

  13. Recovery of tritium from tritiated molecules

    DOEpatents

    Swansiger, W.A.

    1984-10-17

    This invention relates to the recovery of tritium from various tritiated molecules by reaction with uranium. More particularly, the invention relates to the recovery of tritium from tritiated molecules by reaction with uranium wherein the reaction is conducted in a reactor which permits the reaction to occur as a moving front reaction from the point where the tritium enters the reactor charged with uranium down the reactor until the uranium is exhausted.

  14. Charged particle formation by the ionization of air containing sulfur dioxide

    NASA Astrophysics Data System (ADS)

    Nagato, Kenkichi

    2009-08-01

    Experimental investigation of charged particle formation by the ionization of air containing sulfur dioxide (SO2) was performed using a nano-DMA (differential mobility analyzer) and an atmospheric pressure ionization mass spectrometer. A radioactive ion source of 241Am and a negative dc corona discharge were used to ionize SO2/H2O/air mixtures. The results showed that the number of charged particles that formed had increased as H2O concentration increased (ca. 20-3 × 103 ppm) for both ion sources, but also that the number of charged particles produced when using the negative corona discharge was more than two orders of magnitude greater than what was produced using 241Am. During ionization by [alpha]-ray irradiation, SO4-(H2O)n ions predominated coincident with the formation of charged particles. The negative corona discharge produced a more complicated ion mass spectrum, which included ion groups of NO3-, SOx- (x = 2-5) and HSOx- (x = 3-5). The relative abundance of the ion groups varied depending on H2O concentration and ion reaction time. The ions with an HSO4- core surpassed the ions of other groups as H2O concentration increased. The formations of NO3- ions and cluster ions containing HNO3 also were enhanced at higher H2O concentrations. Possible ion-molecule reactions responsible for the observed mass spectra are discussed in detail.

  15. Surface treatment of silica nanoparticles for stable and charge-controlled colloidal silica.

    PubMed

    Kim, Kyoung-Min; Kim, Hye Min; Lee, Won-Jae; Lee, Chang-Woo; Kim, Tae-il; Lee, Jong-Kwon; Jeong, Jayoung; Paek, Seung-Min; Oh, Jae-Min

    2014-01-01

    An attempt was made to control the surface charge of colloidal silica nanoparticles with 20 nm and 100 nm diameters. Untreated silica nanoparticles were determined to be highly negatively charged and have stable hydrodynamic sizes in a wide pH range. To change the surface to a positively charged form, various coating agents, such as amine containing molecules, multivalent metal cation, or amino acids, were used to treat the colloidal silica nanoparticles. Molecules with chelating amine sites were determined to have high affinity with the silica surface to make agglomerations or gel-like networks. Amino acid coatings resulted in relatively stable silica colloids with a modified surface charge. Three amino acid moiety coatings (L-serine, L-histidine, and L-arginine) exhibited surface charge modifying efficacy of L-histidine > L-arginine > L-serine and hydrodynamic size preservation efficacy of L-serine > L-arginine > L-histidine. The time dependent change in L-arginine coated colloidal silica was investigated by measuring the pattern of the backscattered light in a Turbiscan™. The results indicated that both the 20 nm and 100 nm L-arginine coated silica samples were fairly stable in terms of colloidal homogeneity, showing only slight coalescence and sedimentation. PMID:25565824

  16. The effect of phenylglyoxal on contraction and intramembrane charge movement in frog skeletal muscle.

    PubMed Central

    Etter, E F

    1990-01-01

    1. The effects of the arginine-specific protein-modifying reagent, phenylglyoxal, on contraction and intramembrane charge movement were studied in cut single fibres from frog skeletal muscle, using the double-Vaseline-gap voltage clamp technique. 2. The strength-duration curve for pulses which produced microscopically just-detectable contractions was shifted to more positive potentials and longer durations following treatment of fibres with phenylglyoxal. Caffeine-induced contractures were not blocked. 3. The amount of charge moved by large depolarizing pulses from -100 mV holding potential (charge 1) declined during the phenylglyoxal treatment with a single-exponential time course (tau = 7 min). Linear capacitance did not change significantly over the entire experiment. Inhibition of charge movement was predominantly irreversible. 4. Slow bumps (Q gamma) observed in charge movement current transients recorded before phenylglyoxal treatment, using either large test pulses or small steps superimposed on test pulses, were absent from currents recorded after treatment. The current removed by phenylglyoxal contained the bump (Q gamma) and a small fast transient (Q beta). 5. The amount of charge moved by large depolarizing pulses from -100 mV was reduced 20-50% following phenylglyoxal treatment. Charge moved by pulses to potentials more negative than -40 mV was relatively unaffected. The magnitude and voltage range of this inhibitory effect were the same whether the reagent was applied at -100 mV or at 0 mV holding potential. 6. A phenylglyoxal-sensitive component of charge was isolated which had a much steeper voltage dependence than the total charge movement or the charge remaining after treatment. 7. Charge recorded during hyperpolarizing pulses from 0 mV holding potential (charge 2) was reduced very little (less than 5%) at any potential by phenylglyoxal treatments at either 0 or -100 mV. 8. The phenylglyoxal reaction with charge 2 was kinetically different from the reaction with charge 1. 9. The effects of phenylglyoxal on charge 1 and charge 2 both measured in the same fibre were compared. Whether phenylglyoxal was applied at -100 mV, or at 0 mV the results were the same: charge 1 was inhibited much more (25-60%) than charge 2(2-12%). 10. The results presented here indicate that arginyl residues have a functional role in the voltage-sensing mechanism of excitation-contraction coupling and support the hypothesis that the dihydropyridine receptor is the voltage sensor molecule. PMID:2348398

  17. On the dynamics of chemical reactions of negative ions

    E-print Network

    Mikosch, Jochen; Wester, Roland

    2010-01-01

    This review discusses the dynamics of negative ion reactions with neutral molecules in the gas phase. Most anion-molecule reactions proceed via a qualitatively different interaction potential than cationic or neutral reactions. It has been and still is the goal of many experiments to understand these reaction dynamics and the different reaction mechanisms they lead to. We will show how rate coefficients and cross sections for anion-molecule reactions are measured and interpreted to yield information on the underlying dynamics. We will also present more detailed approaches that study either the transient reaction complex or the energy- and angle-resolved scattering of negative ions with neutral molecules. With the help of these different techniques many aspects of anion-molecule reaction dynamics could be unravelled in the last years. However, we are still far from a complete understanding of the complex molecular interplay that is at work during a negative ion reaction.

  18. A combined molecular docking and charge density analysis is a new approach for medicinal research to understand drug-receptor interaction: curcumin-AChE model.

    PubMed

    Renuga Parameswari, A; Rajalakshmi, G; Kumaradhas, P

    2015-01-01

    In the present study, a molecular docking analysis has been performed on diketone form of curcumin molecule with acetylcholinesterase (AChE). The calculated lowest docked energy of curcumin molecule in the active site of AChE is -11.21 kcal/mol; this high negative value indicates that the molecule exhibits large binding affinity towards AChE. When the curcumin molecule present in the active site of AChE, subsequently, its conformation has altered significantly and the molecule adopts a U-shape geometry as it is linear in gas phase (before entering into the active site). This conformational transition facilitates curcumin to form strong interaction with Phe330 of acyl-binding pocket and the choline binding site with indole ring of Trp84 and Asp72. The gas phase and the active site analysis of curcumin allows to understand the conformational geometry, nature of molecular flexibility, charge density redistribution and the variation of electrostatic properties of curcumin in the active site. To obtain the gas phase structure, the curcumin molecule was optimized using Hartree-Fock and density functional methods (B3LYP) with the basis set 6-311G(??). A charge density analysis on both gas phase as well as the molecule lifted from the active site was carried out using Bader's theory of atoms in molecules (AIM). The difference in molecular electrostatic potential between the two forms of curcumin displays the difference in charge distribution. The large dipole moment of curcumin (7.54 D) in the active site reflects the charge redistribution as it is much less in the gas phase (4.34 D). PMID:25446495

  19. Oppositely charged colloids out of equilibrium

    NASA Astrophysics Data System (ADS)

    Vissers, T.

    2010-11-01

    Colloids are particles with a size in the range of a few nanometers up to several micrometers. Similar to atomic and molecular systems, they can form gases, liquids, solids, gels and glasses. Colloids can be used as model systems because, unlike molecules, they are sufficiently large to be studied directly with light microscopy and move sufficiently slow to study their dynamics. In this thesis, we study binary systems of polymethylmethacrylate (PMMA) colloidal particles suspended in low-polar solvent mixtures. Since the ions can still partially dissociate, a surface charge builds up which causes electrostatic interactions between the colloids. By carefully tuning the conditions inside the suspension, we make two kinds of particles oppositely charged. To study our samples, we use Confocal Laser Scanning Microscopy (CLSM). The positively and negatively charged particles can be distinguished by a different fluorescent dye. Colloids constantly experience a random motion resulting from random kicks of surrounding solvent molecules. When the attractions between the oppositely charged particles are weak, the particles can attach and detach many times and explore a lot of possible configurations and the system can reach thermodynamic equilibrium. For example, colloidal ‘ionic’ crystals consisting of thousands to millions of particles can form under the right conditions. When the attractions are strong, the system can become kinetically trapped inside a gel-like state. We observe that when the interactions change again, crystals can even emerge again from this gel-like phase. By using local order parameters, we quantitatively study the crystallization of colloidal particles and identify growth defects inside the crystals. We also study the effect of gravity on the growth of ionic crystals by using a rotating stage. We find that sedimentation can completely inhibit crystal growth and plays an important role in crystallization from the gel-like state. The surface potential and charge are studied by electrophoresis. Here, the velocity of the particles is measured while they are moving in an electric field. Using our real-space CLSM setup, we find that for a single-component system, the charge on the particles decreases with increasing volume fraction. Apart from structures that oppositely charged particles form close to thermodynamic equilibrium, we also study pattern formation when the system is driven out of equilibrium by an electric field. When oppositely charged particles are driven in opposite directions, the collisions between them cause particle of the same kind to form lanes. By combining our CLSM experiments with Brownian dynamics computer simulations, we study the structure and the dynamics of the suspension on the single-particle level. We find that the number of particles in a lane increases continuously with the field strength. By studying the dynamics and fluctuations parallel and perpendicular to the electric field direction, we identify the key mechanism of lane-formation. We show that pattern formation can easily become more complicated when we introduce alternating current (AC) fields. In addition to the formation of lanes parallel to the field-axis, bands of like-charged particles can form perpendicular to it. When the particles are sufficiently mobile, the system can be remixed again by changing the frequency. When AC-fields with higher field strengths are used, we show that complex patterns, including rotating instabilities, can emerge. The results in this thesis yield fundamental insight in electrophoresis, crystallization and pattern formation when systems are driven out of equilibrium. The results on lane- and band-formation can be relevant for the design of electronic ink (e-ink), where electrically driven oppositely charged particles are used to change the image on a piece of electronic paper.

  20. Charge-Swapping Q Balls

    NASA Astrophysics Data System (ADS)

    Copeland, Edmund J.; Saffin, Paul M.; Zhou, Shuang-Yong

    2014-12-01

    Q balls are nontopological solitonic solutions to a wide class of field theories that possess global symmetries. Here we show that in these same theories there also exists a tower of novel composite Q -ball solutions where, within one composite Q ball, positive and negative charges coexist and swap at a frequency lower than the natural frequency of an individual Q ball. These charge-swapping Q balls are constructed by assembling Q balls and anti-Q balls tightly such that their nonlinear cores overlap. We explain why charge-swapping Q balls can form and why they swap charges.

  1. Charge-swapping Q balls.

    PubMed

    Copeland, Edmund J; Saffin, Paul M; Zhou, Shuang-Yong

    2014-12-01

    Q balls are nontopological solitonic solutions to a wide class of field theories that possess global symmetries. Here we show that in these same theories there also exists a tower of novel composite Q-ball solutions where, within one composite Q ball, positive and negative charges coexist and swap at a frequency lower than the natural frequency of an individual Q ball. These charge-swapping Q balls are constructed by assembling Q balls and anti-Q balls tightly such that their nonlinear cores overlap. We explain why charge-swapping Q balls can form and why they swap charges. PMID:25526114

  2. Charge separation in liquids

    NASA Astrophysics Data System (ADS)

    Mikhelashvili, M. S.; Agam, O.

    2004-10-01

    The common theory of reversible charge transfer (RCT) at low donor system excitation power in liquids is examined. The space averaging procedures describing the kinetics of RCT in the liquid space are discussed. The reaction space is presented as a totality of independent subgroups with one excited donor and some group of acceptors effectively interacting only with the donor in the given “subgroup”. We have shown that the theory [3-5] gives questionable results for cation state probability for the usual parameters of this problem. If the acceptor concentration or the charge transfer rate constants are low, then the cation state probability behaves the same in the two theories [3-5] and [7, 8]. The correct account of the donor’s ground state change and charge back transfer in the RCT theory gives the new, not contradictory results, different from the behavior of the results in references [3-5], but near to results of [7, 8]. The molecules motion accelerates the ionization of donors and neutralization of ions. The influence of the motion of neutral and ionized molecules on charge transfer kinetics is different. The Coulomb interaction of ions is taken into account; the effect depends on the space averaging method used. The new approximation in this article in comparison with references [3-6,9] consists in the space averaging procedure of the donor cation state probability, which takes into account the donor’s ground state.

  3. Manipulating transport through a single-molecule junction

    SciTech Connect

    Sotthewes, Kai; Heimbuch, René; Zandvliet, Harold J. W. [Physics of Interfaces and Nanomaterials, MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands)] [Physics of Interfaces and Nanomaterials, MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands)

    2013-12-07

    Molecular Electronics deals with the realization of elementary electronic devices that rely on a single molecule. For electronic applications, the most important property of a single molecule is its conductance. Here we show how the conductance of a single octanethiol molecule can be measured and manipulated by varying the contact's interspace. This mechanical gating of the single molecule junction leads to a variation of the conductance that can be understood in terms of a tunable image charge effect. The image charge effect increases with a decrease of the contact's interspace due to a reduction of the effective potential barrier height of 1.5 meV/pm.

  4. Quantifying reactivity for electrophilic aromatic substitution reactions with Hirshfeld charge.

    PubMed

    Liu, Shubin

    2015-03-26

    An electrophilic aromatic substitution is a process where one atom or group on an aromatic ring is replaced by an incoming electrophile. The reactivity and regioselectivity of this category of reactions is significantly impacted by the group that is already attached to the aromatic ring. Groups promoting substitution at the ortho/para and meta position are called ortho/para and meta directing groups, respectively. Earlier, we have shown that regioselectivity of the electrophilic aromatic substitution is dictated by the nucleophilicity of the substituted aromatic ring, which is proportional to the Hirshfeld charge on the regioselective site. Ortho/para directing groups have the largest negative charge values at the ortho/para positions, whereas meta directing groups often have the largest negative charge value at the meta position. The electron donation or acceptance feature of a substitution group is irrelevant to the regioselectivity. In this contribution, we extend our previous study by quantifying the reactivity for this kind of reactions. To that end, we examine the transition-state structure and activation energy of an identity reaction for a series of monosubstituted-benzene molecules reacting with hydrogen fluoride using BF3 as the catalyst in the gas phase. A total of 18 substitution groups will be considered, nine of which are ortho/para directing and the other nine groups meta directing. From this study, we found that the barrier height of these reactions strongly correlates with the Hirshfeld charge on the regioselective site for both ortho/para and meta directing groups, with the correlation coefficient R(2) both better than 0.96. We also discovered a less accurate correlation between the barrier height and HOMO energy. These results reconfirm the validity and effectiveness of employing the Hirshfeld charge as a reliable descriptor of both reactivity and regioselectivity for this vastly important category of chemical transformations. PMID:25723372

  5. Dust negative ion acoustic shock waves in a dusty multi-ion plasma

    Microsoft Academic Search

    A. A. Mamun; R. A. Cairns; P. K. Shukla

    2009-01-01

    A dusty multi-ion plasma system containing electrons, light positive ions, heavy negative ions, and extremely massive (few micron size) charge fluctuating dust has been considered. The dust negative ion acoustic (DNIA) shock waves, which are associated with negative ion dynamics and dust charge fluctuation, have been investigated by employing the reductive perturbation method. It has been shown that the dust

  6. Take Charge!

    NSDL National Science Digital Library

    Integrated Teaching and Learning Program,

    Students come to understand static electricity by learning about the nature of electric charge, and different methods for charging objects. In a hands-on activity, students induce an electrical charge on various objects, and experiment with electrical repulsion and attraction.

  7. Secondary electron yields from the bombardment of Al 2O 3 by protons, deuterons, alpha-particles and positively charged hydrogen molecules at energies in the range of 10 to 80 MeV

    Microsoft Academic Search

    C. M. Castaneda; L. McGarry; C. Cahill; T. Essert

    1997-01-01

    Measurements of the electron coefficients of Al2O3 surfaces bombarded by protons, deuterons, alphas and single ionized hydrogen molecules are presented. The 76?-cyclotron of the Crocker Nuclear Laboratory of the University of California was used to accelerate those ions in the range of 10 to 80 MeV. The data has been compared to theoretical predictions and to previous experimental work. For

  8. Correlation of charge, hydrophobicity, and structure with antimicrobial activity of S1 and MIRIAM peptides.

    PubMed

    Leptihn, Sebastian; Har, Jia Yi; Wohland, Thorsten; Ding, Jeak Ling

    2010-11-01

    Antimicrobial peptides are key elements of the innate immune system. Many of them interact with membranes of bacteria leading to perturbation of the lipid bilayer and eventually to inactivation of the pathogen. The emergence of multidrug-resistant bacteria has necessitated innovations of new and more powerful classes of antimicrobials. Here we present the in-depth study of an antimicrobial peptide, MIRIAM, derived from Sushi1 (S1), a well-characterized peptide from the horseshoe crab. MIRIAM interacts strongly with negatively charged lipids, forming an ?-helical structure. MIRIAM was found to neutralize LPS and kill Gram-negative bacteria with high efficiency, while not releasing LPS. The promising therapeutic potential of MIRIAM is shown by hemolytic assays, which demonstrate that eukaryotic membranes are unaffected at bactericidal concentrations. Nanoparticle-conjugated MIRIAM used in single-molecule fluorescence and electron microscopy experiments showed that MIRIAM targets bacterial membranes to kill bacteria similarly to parental S1. Furthermore, fragments derived from MIRIAM and S1 provided insights on their molecular mechanisms of action, in particular, the relationships of functional motifs comprised by charge, hydrophobicity, and structure within each peptide. We conclude that the combination of charge, hydrophobicity, and length of the peptide is important. A close interaction of amino acids in a single molecule in a carefully balanced ensemble of sequence position and secondary structure is crucial. PMID:20873868

  9. Negative-ion states

    SciTech Connect

    Compton, R.N.

    1982-01-01

    In this brief review, we discuss some of the properties of atomic and molecular negative ions and their excited states. Experiments involving photon reactions with negative ions and polar dissociation are summarized. 116 references, 14 figures.

  10. Negative ion generator

    DOEpatents

    Stinnett, R.W.

    1984-05-08

    A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions. 8 figs.

  11. Negative ion generator

    DOEpatents

    Stinnett, Regan W. (Albuquerque, NM)

    1984-01-01

    A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions.

  12. Sentential Negation in English

    ERIC Educational Resources Information Center

    Mowarin, Macaulay

    2009-01-01

    This paper undertakes a detailed analysis of sentential negation in the English language with Chomsky's Government-Binding theory of Transformational Grammar as theoretical model. It distinguishes between constituent and sentential negation in English. The essay identifies the exact position of Negation phrase in an English clause structure. It…

  13. State to State and Charged Particle Kinetic Modeling of Time Filtering and Cs Addition

    SciTech Connect

    Capitelli, M.; Gorse, C.; Longo, S. [Chemistry Department, Bari University, Bari (Italy); IMIP-CNR, Sezione Territoriale di Bari, Bari (Italy); Diomede, P.; Pagano, D. [Chemistry Department, Bari University, Bari (Italy)

    2007-08-10

    We present here an account on the progress of kinetic simulation of non equilibrium plasmas in conditions of interest for negative ion production by using the 1D Bari code for hydrogen plasma simulation. The model includes the state to state kinetics of the vibrational level population of hydrogen molecules, plus a PIC/MCC module for the multispecies dynamics of charged particles. In particular we present new results for the modeling of two issues of great interest: the time filtering and the Cs addition via surface coverage.

  14. Valence shell calculations on polyatomic molecules

    Microsoft Academic Search

    D. D. Shillady; F. P. Billingsley; J. E. Bloor

    1971-01-01

    Dipole moments and charge distributions for twenty molecules of widely different types have been calculated using (a) the CNDO\\/2 method and (b) a CNDO\\/2D method in which the orbitals from the CNDO\\/2 method are deorthogonalized by a Löwdin transformation and are then used to calculate the dipole moments in a rigorous manner. A statistical analysis of the results for the

  15. Directly observing the motion of DNA molecules near solid-state nanopores.

    PubMed

    Ando, Genki; Hyun, Changbae; Li, Jiali; Mitsui, Toshiyuki

    2012-11-27

    We investigate the diffusion and the drift motion of ? DNA molecules near solid-state nanopores prior to their translocation through the nanopores using fluorescence microscopy. The radial dependence of the electric field near a nanopore generated by an applied voltage in ionic solution can be estimated quantitatively in 3D by analyzing the motion of negatively charged DNA molecules. We find that the electric field is approximately spherically symmetric around the nanopore under the conditions investigated. In addition, DNA clogging at the nanopore was directly observed. Surprisingly, the probability of the clogging event increases with increasing external bias voltage. We also find that DNA molecules clogging the nanopore reduce the electric field amplitude at the nanopore membrane surface. To better understand these experimental results, analytical method with Ohm's law and computer simulation with Poisson and Nernst-Planck (PNP) equations are used to calculate the electric field near the nanopore. These results are of great interest in both experimental and theoretical considerations of the motion of DNA molecules near voltage-biased nanopores. These findings will also contribute to the development of solid-state nanopore-based DNA sensing devices. PMID:23046052

  16. Gas molecule adsorption in carbon nanotubes and nanotube bundles

    Microsoft Academic Search

    Jijun Zhao; Alper Buldum; Jie Han; Jian Ping Lu

    2002-01-01

    We studied various gas molecules (NO2, O2, NH3, N2, CO2, CH4, H2O, H2, Ar) on single-walled carbon nanotubes (SWNTs) and bundles using first principles methods. The equilibrium position, adsorption energy, charge transfer, and electronic band structures are obtained for different kinds of SWNTs. Most molecules adsorb weakly on SWNTs and can be either charge donors or acceptors to the nanotubes.

  17. Negative-ion formation in the explosives RDX, PETN, and TNT using the Reversal Electron Attachment Detection (READ) technique

    NASA Technical Reports Server (NTRS)

    Chutijian, Ara; Boumsellek, S.; Alajajian, S. H.

    1992-01-01

    In the search for high sensitivity and direct atmospheric sampling of trace species, techniques have been developed such as atmospheric-sampling, glow-discharge ionization (ASGDI), corona discharge, atmospheric pressure ionization (API), electron-capture detection (ECD), and negative-ion chemical ionization (NICI) that are capable of detecting parts-per-billion to parts-per-trillion concentrations of trace species. These techniques are based on positive- or negative-ion formation via charge-transfer to the target, or electron capture under multiple-collision conditions in a Maxwellian distribution of electron energies at the source temperature. One drawback of the high-pressure, corona- or glow-discharge devices is that they are susceptible to interferences either through indistinguishable product masses, or through undesired ion-molecule reactions. The ASGDI technique is relatively immune from such interferences, since at target concentrations of less than 1 ppm the majority of negative ions arises via electron capture rather than through ion-molecule chemistry. A drawback of the conventional ECD, and possibly of the ASGDI, is that they exhibit vanishingly small densities of electrons with energies in the range 0-10 millielectron volts (meV), as can be seen from a typical Maxwellian electron energy distribution function at T = 300 K. Slowing the electrons to these subthermal (less than 10 meV) energies is crucial, since the cross section for attachment of several large classes of molecules is known to increase to values larger than 10(exp -12) sq cm at near-zero electron energies. In the limit of zero energy these cross sections are predicted to diverge as epsilon(exp -1/2), where epsilon is the electron energy. In order to provide a better 'match' between the electron energy distribution function and attachment cross section, a new concept of attachment in an electrostatic mirror was developed. In this scheme, electrons are brought to a momentary halt by reversing their direction with electrostatic fields. At this turning point the electrons have zero or near-zero energy. A beam of target molecules is introduced, and the resultant negative ions extracted. This basic idea has been recently improved to allow for better reversal geometry, higher electron currents, lower backgrounds, and increased negative-ion extraction efficiency. We present herein application of the so-called reversal electron attachment detector (READ) to the study of negative-ion formation in the explosives molecules RDX, PETN, and TNT under single-collision conditions.

  18. Use of a Carbon Filament Lamp to Charge Electroscopes

    Microsoft Academic Search

    R. Whiddington

    1913-01-01

    I FIND that a very convenient way of charging an ordinary gold-leaf electroscope is to rub the charging rod with the glass bulb of a glowing carbon filament lamp. The leaf system becomes negatively charged. It is quite easy to charge a Braun electrostatic voltmeter to several thousand volts in this way.

  19. Surface Potential of Charged Liposomes Determined by Second Harmonic Generation

    E-print Network

    Eisenthal, Kenneth B.

    Articles Surface Potential of Charged Liposomes Determined by Second Harmonic Generation Yan Liu that the surface potential of charged liposomes can be determined by second harmonic generation. The Gouy charge density and the surface potential of liposomes consisting of the negatively charged phospholipid

  20. Thread bonds in molecules

    E-print Network

    Ivlev, B

    2015-01-01

    Unusual chemical bonds are proposed. Each bond is almost covalent but is characterized by the thread of a small radius $\\sim 0.6\\times 10^{-11}$cm, between two nuclei in a molecule. The main electron density is concentrated outside the thread as in a covalent bond. The thread is formed by the electron wave function which has a tendency to be singular on it. The singularity along the thread is cut off by electron "vibrations" due to the interaction with zero point electromagnetic oscillations. The electron energy has its typical value of (1-10)eV. Due to the small tread radius the uncertainty of the electron momentum inside the thread is large resulting in a large electron kinetic energy $\\sim 1 MeV$. This energy is compensated by formation of a potential well due to the reduction of the energy of electromagnetic zero point oscillations. This is similar to formation of a negative van der Waals potential. Thread bonds are stable and cannot be created or destructed in chemical or optical processes.

  1. Vortex charges in high-temperature superconductors.

    PubMed

    Chen, Yan; Wang, Z D; Zhu, Jian-Xin; Ting, C S

    2002-11-18

    Based on a model Hamiltonian with competing antiferromagnetic (AF) and d-wave superconductivity interactions, the vortex charge is investigated by solving the Bogoliubov-de Gennes equations. We found that the vortex charge is negative when a sufficient strength of AF order is induced inside the vortex core; otherwise, it is positive. By tuning the on-site Coulomb repulsion U or the doping parameter delta, a transition between the positive and negative vortex charges may occur. The vortex charge at optimal doping has also been studied as a function of magnetic field. Recent NMR and Hall effect experiments may be understood in terms of the present results. PMID:12443443

  2. Negative-hydrogen-ion sources

    SciTech Connect

    Prelec, K.

    1983-01-01

    There are two main areas of negative hydrogen ion applications: injection into high energy accelerators and production of beams of energetic hydrogen atoms for fusion devices. In both cases, the ease with which the charge state of negative ions can be changed by either single or double electron stripping is the reason that made their application attractive. In tandem accelerators, the final energy of H/sup +/ ions is twice as high as it would correspond to the terminal voltage, in circular accelerators (synchrotrons, storage rings) injection of H/sup +/ ions by full stripping of H/sup -/ ions in a foil inside the ring is not limited by the Liouville's theorem and results in a higher phase space density than achieved by direct H/sup +/ injection. Finally, beams of hydrogen atoms at energies above 100 keV, which will be required for plasma heating and current drive in future fusion devices, can efficiently be produced only by acceleration of negative ions and their subsequent neutralization.

  3. Internal Charging

    NASA Technical Reports Server (NTRS)

    Minow, Joseph I.

    2014-01-01

    (1) High energy (>100keV) electrons penetrate spacecraft walls and accumulate in dielectrics or isolated conductors; (2) Threat environment is energetic electrons with sufficient flux to charge circuit boards, cable insulation, and ungrounded metal faster than charge can dissipate; (3) Accumulating charge density generates electric fields in excess of material breakdown strenght resulting in electrostatic discharge; and (4) System impact is material damage, discharge currents inside of spacecraft Faraday cage on or near critical circuitry, and RF noise.

  4. [Biophysics of single molecules].

    PubMed

    Serdiuk, I N; Deriusheva, E I

    2011-01-01

    The modern methods of research of biological molecules whose application led to the development of a new field of science, biophysics of single molecules, are reviewed. The measurement of the characteristics of single molecules enables one to reveal their individual features, and it is just for this reason that much more information can be obtained from one molecule than from the entire ensample of molecules. The high sensitivity of the methods considered in detail makes it possible to come close to the solution of the basic problem of practical importance, namely, the determination of the nucleotide sequence of a single DNA molecule. PMID:22117447

  5. The Forces Between Neutral Molecules and Metallic Surfaces

    Microsoft Academic Search

    H. Margenau; W. G. Pollard

    1941-01-01

    A general formula is developed for the interaction between a neutral molecule and a metal, and its relation to the image force law is exhibited, (Section III). The latter is shown to be valid only for molecules containing slowly moving charges, such as rigid permanent dipoles. A fairly accurate evaluation of the general formula involving empirical polarizabilities, f values, and

  6. Bacterial resistance control on mineral surfaces of hydroxyapatite and human teeth via surface charge-driven antifouling coatings.

    PubMed

    Venault, Antoine; Yang, Hui-Shan; Chiang, Yen-Che; Lee, Bor-Shuinn; Ruaan, Ruoh-Chyu; Chang, Yung

    2014-03-12

    This works reports a set of new functionalized polyethyleneimine (PEI) polymers, including a neutral PEGylated polymer PEI-g-PEGMA, a negatively charged polymer PEI-g-SA, and a zwitterionic polymer PEI-g-SBMA, and their use as antibiofouling coating agent for human teeth protection. Polymers were synthesized by Michael addition, XPS analysis revealed that each polymer could be efficiently coated onto hydroxyapatite, ceramic material used as a model tooth. Polymers carrying a negative net charge were more efficiently adsorbed, because of the establishment of electrostatic interactions with calcium ions. Protein adsorption tests revealed that two factors were important in the reduction of protein adsorption. Both the surface charge and the surface ability to bind and entrap water molecules had to be considered. PEI-g-SBMA, which zeta potential in PBS solution was negative, was efficient to inhibit the adsorption of BSA, a negative protein. On the other hand, it also resisted the adsorption of lysozyme, a positive protein, because zwitterionic molecules can easily entrap water and provide a very hydrophilic environment. Streptococcus mutans attachment tests performed unveiled that all modified polymers were efficient to resist this type of bacteria responsible for dental carries. Best results were also obtained with PEI-g-SBMA coating. This polymer was also shown to efficiently resist the adsorption of positively charged bacteria (Stenotrophomonas maltophilia). Tests performed on real human tooth showed that PEI-g-SBMA could inhibit up to 70% of bacteria adhesion, which constitutes a major result considering that surface of teeth is very rough, therefore physically promoting the attachment of proteins and bacteria. PMID:24513459

  7. A rocket-borne mass analyzer for charged aerosol particles in the mesosphere

    SciTech Connect

    Knappmiller, Scott; Robertson, Scott; Sternovsky, Zoltan [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80309-0392 (United States); Friedrich, Martin [Institute of Communication Networks and Satellite Communications, Graz University of Technology, A-8010 Graz (Austria)

    2008-10-15

    An electrostatic mass spectrometer for nanometer-sized charged aerosol particles in the mesosphere has been developed and tested. The analyzer is mounted on the forward end of a rocket and has a slit opening for admitting a continuous sample of air that is exhausted through ports at the sides. Within the instrument housing are two sets of four collection plates that are biased with positive and negative voltages for the collection of negative and positive aerosol particles, respectively. Each collection plate spans about an order of magnitude in mass which corresponds to a factor of 2 in radius. The number density of the charge is calculated from the current collected by the plates. The mean free path for molecular collisions in the mesosphere is comparable to the size of the instrument opening; thus, the analyzer performance is modeled by a Monte Carlo computer code that finds the aerosol particles trajectories within the instrument including both the electrostatic force and the forces from collisions of the aerosol particles with air molecules. Mass sensitivity curves obtained using the computer models are near to those obtained in the laboratory using an ion source. The first two flights of the instrument returned data showing the charge number densities of both positive and negative aerosol particles in four mass ranges.

  8. The Forces Between Polyatomic Molecules. I. Long-Range Forces

    Microsoft Academic Search

    H. C. Longuet-Higgins; L. Salem

    1961-01-01

    It is known that the electrostatic long-range forces between two molecules are `locally additive' in the sense that the first-order interaction energy between molecules bearing charges or permanent multipole moments may be written as a double integral over pairs of points, one in each molecule. In this paper we examine the second-order interaction energy, which comprises polarization and dispersion terms,

  9. Investigating electroluminescence excitation by space charge measurements under transient stress in cross linked polyethylene

    Microsoft Academic Search

    N. Hozumi; G. Teyssedre; C. Laurent; K. Fukunaga

    2004-01-01

    Carrier transport in 150 ?m thick XLPE films under ca. 130 kV\\/mm was characterized by both transient space charge and EL measurements. Both positive and negative charges were injected from the electrodes. For relatively short stressing time (order of minutes), the field distribution was not significantly changed due to the evolution of these charges. Injected positive and negative charges propagated

  10. Osmosis at constant volume. Negative pressure

    E-print Network

    Zupanovic, Pasko; Brumen, Milan; Fajmut, Ales; Juretic, Davor

    2009-01-01

    A thermodynamic state of solvent and solution separated with an elastic semipermeable membrane, in the box with a fixed volume, is considered. It is shown that the minimum of the free energy is accompanied by the compression of the solution and tension of the solvent caused by the transfer of solvent molecules into compartment with solution. The tensile state of the solvent is described in terms of negative pressure. It is found that the negative pressure as well as compression pressure is of the order of osmotic pressure given by van't Hoff equation. It is proposed that this mechanism could be responsible for the water uptake in tall trees.

  11. Negative thermal expansion materials

    Microsoft Academic Search

    J. S. O. Evans; T. A. Mary; A. W. Sleight

    1998-01-01

    The recent discovery of negative thermal expansion over an unprecedented temperature range in ZrW2O8 (which contracts continuously on warming from below 2 K to above 1000 K) has stimulated considerable interest in this unusual phenomenon. Negative and low thermal expansion materials have a number of important potential uses in ceramic, optical and electronic applications. We have now found negative thermal

  12. Negative thermal expansion materials

    Microsoft Academic Search

    J. S. O Evans; T. A Mary; A. W Sleight

    1997-01-01

    The recent discovery of negative thermal expansion over an unprecedented temperature range in ZrW2O8 (which contracts continuously on warming from below 2 K to above 1000 K) has stimulated considerable interest in this unusual phenomenon. Negative and low thermal expansion materials have a number of important potential uses in ceramic, optical and electronic applications. We have now found negative thermal

  13. Negative absorption near a magnetized black hole - Black hole masers

    Microsoft Academic Search

    A. N. Aliev; D. V. Galtsov; V. I. Petukhov

    1986-01-01

    The mechanism of the energy extraction from charged particles moving in the vicinity of black holes due to the negative absorption of electromagnetic waves is considered. It is shown that there exist a number of resonant frequencies for which the ring of particles circling in the equatorial plane of Kerr black holes amplifies the incident electromagnetic waves. The negative absorption

  14. Negative absorption near a magnetized black hole: Black hole masers

    Microsoft Academic Search

    A. N. Aliev; D. V. Gal'tsov; V. I. Petukhov

    1986-01-01

    The mechanism of the energy extraction from charged particles moving in the vicinity of black holes due to the negative absorption of electromagnetic waves is considered. It is shown that there exist a number of resonant frequencies for which the ring of particles circling in the equatorial plane of Kerr black holes amplifies the incident electromagnetic waves. The negative absorption

  15. Negative Ion Density Fronts

    SciTech Connect

    Igor Kaganovich

    2000-12-18

    Negative ions tend to stratify in electronegative plasmas with hot electrons (electron temperature Te much larger than ion temperature Ti, Te > Ti ). The boundary separating a plasma containing negative ions, and a plasma, without negative ions, is usually thin, so that the negative ion density falls rapidly to zero-forming a negative ion density front. We review theoretical, experimental and numerical results giving the spatio-temporal evolution of negative ion density fronts during plasma ignition, the steady state, and extinction (afterglow). During plasma ignition, negative ion fronts are the result of the break of smooth plasma density profiles during nonlinear convection. In a steady-state plasma, the fronts are boundary layers with steepening of ion density profiles due to nonlinear convection also. But during plasma extinction, the ion fronts are of a completely different nature. Negative ions diffuse freely in the plasma core (no convection), whereas the negative ion front propagates towards the chamber walls with a nearly constant velocity. The concept of fronts turns out to be very effective in analysis of plasma density profile evolution in strongly non-isothermal plasmas.

  16. Ultra-Cold Molecules

    Microsoft Academic Search

    A. Fioretti; M. Fazzi; M. Mazzoni; T. Ban; C. Gabbanini

    2004-01-01

    In this paper we overview recent results on the formation of translationally cold molecules. While there are some methods relying on direct cooling of molecules, we shall concentrate on the photoassociation technique that starts from laser-cooled atoms. The detection methods for the ultra-cold molecules will be presented together with a report on the trapping techniques. The treatment is mainly focused

  17. The reaction dynamics of alkali dimer molecules and electronically excited alkali atoms with simple molecules

    SciTech Connect

    Hou, H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1995-12-01

    This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O2. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO2 + Na and NaO + NaO. NaO2 products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O2, which is likely a result of a charge transfer from Na2 to the excited state orbital of O2-. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH3 and Na(CH3OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.

  18. Extracted current saturation in negative ion sources

    SciTech Connect

    Mochalskyy, S.; Lifschitz, A. F.; Minea, T. [LPGP, University Paris-Sud 11, bat 210, 15 rue G. Clemenceau-Orsay, F91405 (France)

    2012-06-01

    The extraction of negatively charged particles from a negative ion source is one of the crucial issues in the development of the neutral beam injector system for future experimental reactor ITER. Full 3D electrostatic particle-in-cell Monte Carlo collision code - ONIX [S. Mochalskyy et al., Nucl. Fusion 50, 105011 (2010)] - is used to simulate the hydrogen plasma behaviour and the extracted particle features in the vicinity of the plasma grid, both sides of the aperture. It is found that the contribution to the extracted negative ion current of ions born in the volume is small compared with that of ions created at the plasma grid walls. The parametric study with respect to the rate of negative ions released from the walls shows an optimum rate. Beyond this optimum, a double layer builds-up by the negative ion charge density close to the grid aperture surface reducing thus extraction probability, and therefore the extracted current. The effect of the extraction potential and magnetic field magnitudes on the extraction is also discussed. Results are in good agreement with available experimental data.

  19. Adsorption of organic molecules on silica surface

    Microsoft Academic Search

    Sudam K. Parida; Sukalyan Dash; Sabita Patel; B. K. Mishra

    2006-01-01

    The adsorption behaviour of various organic adsorbates on silica surface is reviewed. Most of the structural information on silica is obtained from IR spectral data and from the characteristics of water present at the silica surface. Silica surface is generally embedded with hydroxy groups and ethereal linkages, and hence considered to have a negative charged surface prone to adsorption of

  20. Halogen bonds in biological molecules Pascal Auffinger

    E-print Network

    Westhof, Eric

    ­10) coupled with ab initio calculations (10) have characterized the geometry of halogen bonds in small and sulfur) atoms or (ii) the delocalized -electrons of peptide bonds or carboxylate or amide groups. Thus-transfer bonds, were attributed to the transfer of negative charge from an oxygen, nitrogen, or sulfur (a Lewis

  1. Charge Storage, Conductivity and Charge Profiles of Insulators as Related to Spacecraft Charging

    NASA Technical Reports Server (NTRS)

    Dennison, J. R.; Swaminathan, Prasanna; Frederickson, A. R.

    2004-01-01

    Dissipation of charges built up near the surface of insulators due to space environment interaction is central to understanding spacecraft charging. Conductivity of insulating materials is key to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination. Conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator, rather than by flow of current across two electrodes around the sample. We have found that conductivity determined from charge storage decay methods is 102 to 104 smaller than values obtained from classical ASTM and IEC methods for a variety of thin film insulating samples. For typical spacecraft charging conditions, classical conductivity predicts decay times on the order of minutes to hours (less than typical orbit periods); however, the higher charge storage conductivities predict decay times on the order of weeks to months leading to accumulation of charge with subsequent orbits. We found experimental evidence that penetration profiles of radiation and light are exceedingly important, and that internal electric fields due to charge profiles and high-field conduction by trapped electrons must be considered for space applications. We have also studied whether the decay constants depend on incident voltage and flux or on internal charge distributions and electric fields; light-activated discharge of surface charge to distinguish among differing charge trapping centers; and radiation-induced conductivity. Our experiments also show that "Malter" electron emission occurs for hours after turning off the electron beam. This Malter emission similar to emission due to negative electron affinity in semiconductors is a result of the prior radiation or optical excitations of valence electrons and their slow drift among traps towards the surface where they are subsequently emitted. This work is supported through funding from the NASA Space Environments and Effects Program.

  2. Negative thermal expansion materials

    NASA Astrophysics Data System (ADS)

    Evans, J. S. O.; Mary, T. A.; Sleight, A. W.

    The recent discovery of negative thermal expansion over an unprecedented temperature range in ZrW 2O 8 (which contracts continuously on warming from below 2 K to above 1000 K) has stimulated considerable interest in this unusual phenomenon. Negative and low thermal expansion materials have a number of important potential uses in ceramic, optical and electronic applications. We have now found negative thermal expansion in a large new family of materials with the general formula A 2(MO 4) 3. Chemical substitution dramatically influences the thermal expansion properties of these materials allowing the production of ceramics with negative, positive or zero coefficients of thermal expansion, with the potential to control other important materials properties such as refractive index and dielectric constant. The mechanism of negative thermal expansion and the phase transitions exhibited by this important new class of low-expansion materials will be discussed.

  3. Negative thermal expansion materials

    NASA Astrophysics Data System (ADS)

    Evans, J. S. O.; Mary, T. A.; Sleight, A. W.

    1998-04-01

    The recent discovery of negative thermal expansion over an unprecedented temperature range in ZrW2O8 (which contracts continuously on warming from below 2 K to above 1000 K) has stimulated considerable interest in this unusual phenomenon. Negative and low thermal expansion materials have a number of important potential uses in ceramic, optical and electronic applications. We have now found negative thermal expansion in a large new family of materials with the general formula A2(MO4)3. Chemical substitution dramatically influences the thermal expansion properties of these materials allowing the production of ceramics with negative, positive or zero coefficients of thermal expansion, with the potential to control other important materials properties such as refractive index and dielectric constant. The mechanism of negative thermal expansion and the phase transitions exhibited by this important new class of low-expansion materials will be discussed.

  4. Dynamic current suppression and gate voltage response in metal-molecule-metal junctions

    E-print Network

    Evans, Jeremy S.

    We critically re-examine conductance in benzenedithiol (BDT)/gold junctions using real-time DFT simulations. Our results indicate a powerful influence of the BDT molecular charge on current, with negative charge suppressing ...

  5. Multipole moments of water molecules in clusters and ice Ih from first principles calculations

    Microsoft Academic Search

    Enrique R. Batista; Sotiris S. Xantheas; Hannes Jónsson

    1999-01-01

    We have calculated molecular multipole moments for water molecules in clusters and in ice Ih by partitioning the charge density obtained from first principles calculations. Various schemes for dividing the electronic charge density among the water molecules were used. They include Bader's zero flux surfaces and Voronoi partitioning schemes. A comparison was also made with an induction model including dipole,

  6. Electrical Conduction in Pure Water - Trapping and Scattering of Positive Protons and Negative Proton Holes

    NASA Astrophysics Data System (ADS)

    Jie, Binbin; Sah, Chihtang

    2015-03-01

    Water has been characterized by hydronium (H3O)1+ and hydroxide (HO)1- ions, which fail to explain the electrical conductivity of even pure water. Experimental formulas of pure water versus temperature (0-100C) have employed 39 empirical parameters to fit 3 measured properties: ion concentration, and electrical conductance of pure water and (H3O)1+ ion. We have shown (4 invited talks, 3 articles in 14 months) that electrical conduction in pure water can be represented by 5 quasi-particles in the many-body water lattice: the mobile positively charged protons p+ and negatively charged proton holes p-, and the 3 charge states of the immobile water molecule as amphoteric protonic trap, V+ = (H3O)1+, V0+/- = (H2O)0+/-, and V- = (HO)1-; and as few as 6 physics parameters: 3 binding energies, 1 protonic density of state, and 2 Coulombic scattering strengths. Protons in water are strongly coupled to the protonic-phonons, oxygen-phonons and protonic-local modes. Impuritons and affinitons may be present in the hexagonal tunnels of the water lattices.

  7. The Interaction of Positively-charged Ions with Nucleic Acid Systems

    NASA Technical Reports Server (NTRS)

    Pollack, Lois

    2003-01-01

    The successful development of extremely low background sample cells for x-ray scattering studies has enabled experiments designed to elucidate some of the fundamental physical interactions involved in macromolecular folding. Microfabrication techniques were used to fabricate low volume (50 micro-liter) sample cells with silicon nitride membranes (sub micron in thickness) as x-ray windows. Scientifically, these studies focus on the interaction of negatively charged nucleic acid systems, RNA and DNA, with their surrounding (positively charged) ion atmospheres. Understanding the structure of the ion atmosphere and its influence on the shape/conformation of the macromolecule will help reveal the underlying physical forces employed by nature in the self-assembly of these important molecules.

  8. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier.

    PubMed

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-01-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based "rocking chair" type battery. PMID:26043147

  9. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier

    PubMed Central

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-01-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery. PMID:26043147

  10. Charging of mirror surfaces in space

    Microsoft Academic Search

    Shu T. Lai

    2005-01-01

    Spacecraft often charge to negative potentials of several kilovolts in eclipse at geosynchronous altitudes. We suggest that optical mirrors at geosynchronous altitudes will charge in sunlight as if in eclipse. Modern mirrors can attain very high reflectance, the reflected light being nearly as intense as the incoming light. With high reflectance, the sunlight photon energy imparted to mirror surfaces is

  11. SPACE-CHARGE SLOWINGDOWN OF ELECTRON AVALANCHES

    Microsoft Academic Search

    Schmidt-Tiedemann

    1959-01-01

    The electric field generated by the positive and negative space charge ; of single electron avalanche moving in a homogeneous electric field is calculated. ; Treating the interaction of the avalanche with its own space charge field as a ; first order perturbation, a growth formula is obtained which differs markedly ; from the common Townsend formula. The theoretical results

  12. Charge ratio of muons from atmospheric neutrinos

    E-print Network

    Stanev, T

    2003-01-01

    We calculate the intensities and angular distributions of positive and negative muons produced by atmospheric neutrinos. We comment on some sources of uncertainty in the charge ratio. We also draw attention to a potentially interesting signature of neutrino oscillations in the muon charge ratio, and we discuss the prospects for its observation (which are not quite within the reach of currently planned magnetized detectors).

  13. Initial adsorption of water molecule on HfC and TaC (0 0 1) surfaces from density-functional study

    NASA Astrophysics Data System (ADS)

    Liu, Dongliang; Deng, Jianguo; Jin, Yongzhong

    2014-01-01

    We investigated the initial adsorption of molecular water on HfC and TaC (0 0 1) surfaces using first-principles density-functional theory. In our investigation, the revised Perdew-Burke-Ernzerhof functional (RPBE) generalized gradient approach (GGA) was used to treat the exchange and correlation potential. We modeled the (0 0 1) surfaces with (?2 × ?2) R45° supercell. Every supercell contains five atomic planes. Our calculations show that the adsorption energies of H2O are low. The energies are -0.44 eV/molecule and -0.65 eV/molecule on HfC and TaC (0 0 1) surfaces, respectively. On both the (0 0 1) surfaces, molecular water prefers to be adsorbed on top of surface metal atom. However, only the oxygen atom of water molecule is bound with surface metal atom. And the plane of water molecule tends to be parallel to the surfaces. Compared with the oxygen and hydrogen atoms of an isolated water molecule, the oxygen and hydrogen atoms in H2O/HfC (0 0 1) and H2O/TaC (0 0 1) have less negative and positive charges, respectively. Our results show that water molecule is adsorbed molecularly on HfC and TaC (0 0 1) surfaces at initial adsorption stage. Moreover, the interaction of water molecule with the (0 0 1) surfaces is weak. Charge density differences and density of states show that Osbnd Ta bond is slightly stronger than Osbnd Hf bond. Due to the strong Osbnd Ta bond, the oxidation resistance of TaC may stronger than HfC in water vapor atmosphere.

  14. Amphiphilic chitosan nanosphere: studies on formation, toxicity, and guest molecule incorporation.

    PubMed

    Yoksan, Rangrong; Chirachanchai, Suwabun

    2008-03-01

    Amphiphilic chitosan developed by conjugating hydrophobic phthalimido groups and hydrophilic poly (ethylene glycol) chains gives a well-dispersed colloidal solution in polar solvents and shows a regular nano-sized spherical structure ( approximately 200 nm) with negatively charged surface (-31.24+/-4.85 mV). An in vivo acute oral toxicity test confirms the non-toxicity of the chitosan nanosphere with LD(50) higher than 2000 mg/kg body weight. A success of incorporating amine molecules into the nanosphere declares that the heterogeneous incorporation system is more effective than the homogeneous ones. The study on guest molecule incorporation using alkylamines and carboxylic acid as models suggests requirements that the guest be hydrophobic and positively charged. TGA study clarifies that the weight loss at 250-300 degrees C relating to the amount of guest incorporation via heterogeneous system is as high as 42.3%, whereas those of homogeneous systems are about 16.86-28.27%. The nanosphere size is significantly changed after guest incorporation, that is, from 200 nm to approximately 500-1000 nm. PMID:18061462

  15. How does Electrophoretic Mobility Reflect Polyelectrolyte Charge?

    NASA Astrophysics Data System (ADS)

    Hoagland, David; Popov, Alexei

    2003-03-01

    To unravel factors that determine effective polyelectrolyte charge, the mobilities of various ionenes were measured by capillary electrophoresis in variable dielectric constant solvents. Ionenes derive charge from regularly spaced, quaternized nitrogens located in the chain backbone; synthetic methods allow direct control of this spacing. The study sheds light on two questions: (1) Does the dimensionless charge density parameter (predicted to collapse trends of dielectric constant, temperature, and charge spacing) accurately capture polyelectrolyte charge? (2) Does counterion condensation explain trends in mobility as the charge density parameter is varied? A negative response is returned for (1), since plotting mobility against dimensionless charge density does not generate a master curve. A less certain response is returned for (2), since mobility does not saturate with increasing dielectric constant but does with decreasing charge spacing. These responses are discussed in terms of preferential chain solvation, specific ion effects, the electrophoretic "relaxation" effect, etc.

  16. The role of potential barrier formation in spacecraft charging

    NASA Technical Reports Server (NTRS)

    Purvis, C. K.

    1983-01-01

    The role of potential barrier formation in spacecraft charging at geosynchronous orbit is discussed. Sudden dramatic shifts in structure potential at eclipse entry and exit, and in response to injections of hot plasma during eclipse do not indicate the magnitude of differential charging. All daylight charging and some long-term eclipse charging is barrier dominated. Shaded or low yield surfaces charge negatively, forming vacuum potential barriers which suppress emission of photoelectrons and secondary electrons, causing the spacecraft to charge negatively. This process, which is configuration and material dependent, limits the magnitude of insulator-negative differential charging to values substantially lower than supposed, and allows the possibility of insulator-positive differential charging. Discharges are less energetic and more localized than supposed. If the spacecraft changes its potential when electrons are emitted in a discharge, then when the structure is driven positive, electron emission should cease.

  17. Effect of Negative Ions on the Conductivity of the Titan Atmosphere

    NASA Technical Reports Server (NTRS)

    Borucki, W. J.; Bakes, E.; Whitten, R. C.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    In an earlier paper, Borucki et al (1987) calculated the electrical conductivity and electrical charge on aerosols in Titan's atmosphere due to the ionization by galactic cosmic rays and electron precipitation from Saturn's magnetosphere. The lower atmosphere was predicted to be substantially more conducting than the atmospheres of Earth and Venus because of the high concentration of free electrons. The prediction of a high conductivity is based on the lack of electrophillic species which form negative ions with low mobility and which reduce the number of free electrons. At that time, no molecular species capable of forming negative ions in concentrations sufficient to perturb the atmospheric conductivity were identified. Recently, E. Bakes and her colleagues have been investigating the formation of nitrogenous macromolecules using quantum mechanical methods. Their calculations indicate that the molecules will be highly electrophillic and are likely to be present in the atmosphere at mixing ratios of order 10(exp -7). This mixing ratio is sufficiently large that a substantial reduction in the conductivity is expected at altitudes below 100 km. Revision of the atmospheric model to accommodate the presence of negative ions and to increase the fidelity of the modeling will be described.

  18. Analysis of Layer Charge, Cation and Anion Exchange Capacities, and Synthesis of Reduced Charge Clays

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Surface charge is one of the most important properties of clay minerals. Surface charge is used in classification of 2:1 phyllosilicates and has a strong influence on properties of clays such as hydration, swelling, cation exchange, and reactions with organic molecules. In this chapter, analytical m...

  19. Duct type charge eliminator

    SciTech Connect

    Masuda, S.

    1984-09-18

    At least one planar type plasma ion source is positioned in a main duct through which charged materials pass in a manner whereby its active surface producing plasma faces the flow channel of charged materials inside the duct. The plasma ion source has at least one dielectric sheet, at least one corona electrode in operative proximity with one surface of the dielectric sheet and at least one planar type exciting electrode affixed to the opposite surface of the dielectric sheet and covering the entire area facing the corona electrode. A high voltage AC power supply energizes the plasma ion source by producing a high AC voltage and being connected to apply the voltage between the corona and the exciting electrode across the dielectric sheet whereby AC surface coronas serving as an active planar type plasma containing copious positive and negative ions are produced by the corona electrode along the one surface of the dielectric sheet and charged materials entering the flow channel inside the duct are bombarded by ions of opposite polarity from the plasma and are rapidly neutralized in charge during passage through the flow channel.

  20. Magnetic negative stiffness dampers

    NASA Astrophysics Data System (ADS)

    Shi, Xiang; Zhu, Songye

    2015-07-01

    This communication presents the design principle and experimental validation of two novel configurations of magnetic negative stiffness dampers (MNSDs), both of which are composed of several permanent magnets arranged in a conductive pipe. The MNSD, as a passive device, efficiently integrates negative stiffness and eddy-current damping in a simple and compact design, in which the negative stiffness behavior depends on the different arrangements of the permanent magnets. When applied to structural vibration control, passive MNSD may achieve a performance comparable with semi-active or active control in some applications. Laboratory experiments of small-scale prototypes successfully verified the proposed MNSD design concept.

  1. Introduction to Negative Numbers

    NSDL National Science Digital Library

    WNET.org

    2006-01-01

    This lesson plan based on a Cyberchase activity, first addresses a common misconception: starting measurement from 1 instead of 0. Then, it introduces negative numbers by extending a number line beyond 0 in the negative (left) direction. It is motivated by the Cyber Squad’s mission to find the captured Cyberchase Council on a particular floor of a tall building as seen in two quicktime videos: “Importance of the Origin" and "Inventing Negative Numbers" (each are cataloged separately). In addition to the learning activity, other support materials are included: handouts, assessments and answer keys.

  2. Negative birefringent polyimide films

    NASA Technical Reports Server (NTRS)

    Harris, Frank W. (Inventor); Cheng, Stephen Z. D. (Inventor)

    1994-01-01

    A negative birefringent film, useful in liquid crystal displays, and a method for controlling the negative birefringence of a polyimide film is disclosed which allows the matching of an application to a targeted amount of birefringence by controlling the degree of in-plane orientation of the polyimide by the selection of functional groups within both the diamine and dianhydride segments of the polyimide which affect the polyimide backbone chain rigidity, linearity, and symmetry. The higher the rigidity, linearity and symmetry of the polyimide backbone, the larger the value of the negative birefringence of the polyimide film.

  3. Charging measurement using SEM embedded energy filter

    NASA Astrophysics Data System (ADS)

    Levitov, F.; Karabekov, A.; Eytan, G.; Golan, G.

    2007-03-01

    Charging phenomena are investigated using a scanning electron microscope (the Applied Materials VeritySEM), equipped with an energy filter. Three types of charging are studied: wafer charging, uniform charging of the field-of-view (FOV), and non-uniform charging of the FOV. Wafer charging occurs when the wafer is charged by some source other than the scanning electron beam. Uniform and non-uniform charging of the FOV occur when a wafer is scanned with a primary electron beam. On insulating materials, the primary electron density, in units of electrons per unit area, governs whether the charging regime is uniform or non-uniform. At low electron density, the charging regime is uniform FOV charging. In this regime, the surface potential increases linearly with FOV size and extraction field, in agreement with calculations based on an electrostatic simulation. At high electron density, the charging regime changes to a non-uniform local charging, varying over adjacent pixels within the FOV. The local field attracts the emitted SE's until a steady state is reached having a local yield of one. In this regime, the FOV charging potential is weakly depend on FOV size, and it can be either positive or negative, depending on the strength of the applied extraction field.

  4. Detection of chiral molecules

    NASA Astrophysics Data System (ADS)

    Patterson, David

    2014-05-01

    Recent years have seen an enormous growth of rich physics performed with cold samples of diatomic molecules, as well as impressive demonstrations of techniques to cool polyatomic molecules containing several (~7) atoms. Here we present progress in our methods to produce cold, dense, slow moving samples of molecules of many (>20) atoms from cryogenic buffer gas cells. The ability to produce cold, slow samples of such molecules opens up a host of potential research paths, including ultra-high precision spectroscopy, searches for changes in fundamental constants, and a rich set of experiments in the complex, low-decoherence Hilbert space spanned by the rotational and hyperfine states of such molecules. As an early demonstration of the rich physics offered in such systems, recent results demonstrating chirality-sensitive microwave spectroscopy of cold molecules will be presented.

  5. Long-Ranged Oppositely Charged Interactions for Designing New Types of Colloidal Clusters

    NASA Astrophysics Data System (ADS)

    Demirörs, Ahmet Faik; Stiefelhagen, Johan C. P.; Vissers, Teun; Smallenburg, Frank; Dijkstra, Marjolein; Imhof, Arnout; van Blaaderen, Alfons

    2015-04-01

    Getting control over the valency of colloids is not trivial and has been a long-desired goal for the colloidal domain. Typically, tuning the preferred number of neighbors for colloidal particles requires directional bonding, as in the case of patchy particles, which is difficult to realize experimentally. Here, we demonstrate a general method for creating the colloidal analogs of molecules and other new regular colloidal clusters without using patchiness or complex bonding schemes (e.g., DNA coating) by using a combination of long-ranged attractive and repulsive interactions between oppositely charged particles that also enable regular clusters of particles not all in close contact. We show that, due to the interplay between their attractions and repulsions, oppositely charged particles dispersed in an intermediate dielectric constant (4 negatively charged large and positively charged small satellite particles, for which the electrostatic properties and interactions can be changed with an electric field. It appears that for sufficiently strong fields the satellite particles can move over the surface of the host particles and polarize the clusters. For even stronger fields, the satellite particles can be completely pulled off, reversing the net charge on the cluster. With computer simulations, we investigate how charged particles distribute on an oppositely charged sphere to minimize their energy and compare the results with the solutions to the well-known Thomson problem. We also use the simulations to explore the dependence of such clusters on Debye screening length ?-1 and the ratio of charges on the particles, showing good agreement with experimental observations.

  6. Single Molecule Conductance of Oligothiophene Derivatives

    NASA Astrophysics Data System (ADS)

    Dell, Emma J.

    This thesis studies the electronic properties of small organic molecules based on the thiophene motif. If we are to build next-generation devices, advanced materials must be designed which possess requisite electronic functionality. Molecules present attractive candidates for these ad- vanced materials since nanoscale devices are particularly sought after. However, selecting a molecule that is suited to a certain electronic function remains a challenge, and characterization of electronic behavior is therefore critical. Single molecule conductance measurements are a powerful tool to determine properties on the nanoscale and, as such, can be used to investigate novel building blocks that may fulfill the design requirements of next-generation devices. Combining these conductance results with strategic chemical synthesis allows for the development of new families of molecules that show attractive properties for future electronic devices. Since thiophene rings are the fruitflies of organic semiconductors on the bulk scale, they present an intriguing starting point for building functional materials on the nanoscale, and therefore form the structural basis of all molecules studied herein. First, the single-molecule conductance of a family of bithiophene derivatives was measured. A broad distribution in the single-molecule conductance of bithiophene was found compared with that of a biphenyl. This increased breadth in the conductance distribution was shown to be explained by the difference in 5-fold symmetry of thiophene rings as compared to the 6-fold symmetry of benzene rings. The reduced symmetry of thiophene rings results in a restriction on the torsion angle space available to these molecules when bound between two metal electrodes in a junction, causing each molecular junction to sample a different set of conformers in the conductance measurements. By contrast, the rotations of biphenyl are essentially unimpeded by junction binding, allowing each molecular junction to sample similar conformers. This work demonstrates that the conductance of bithiophene displays a strong dependence on the conformational fluctuations accessible within a given junction configuration, and that the symmetry of such small molecules can significantly influence their conductance behavior. Next, the single-molecule conductance of a family of oligothiophenes comprising one to six thiophene units was measured. An anomalous behavior was found: the peak of the conductance histogram distribution did not follow a clear exponential decay with increasing number of thiophene units in the chain. The electronic properties of the materials were characterized by optical spectroscopy and electrochemistry to gain an understanding of the factors affecting the conductance of these molecules. Different conformers in the junction were postulated to be a contributing factor to the anomalous trend in the observed conductance as a function of molecule length. Then, the electronic properties of the thiophene-1,1-dioxide unit were investigated. These motifs have become synthetically accessible in the last decade, due to Rozen's unprecedentedly potent oxidizing reagent - HOF?CH 3CN - which has been shown to be powerful yet selective enough to oxidize thiophenes in various environments. The resulting thiophene-1,1-dioxides show great promise for electronic devices. The oxidation chemistry of thiophenes was expanded and tuning of the frontier energy levels was demonstrated through combining electron poor and electron rich units. Finally, charge carriers in single-molecule junctions were shown to be tunable within a family of molecules containing these thiophene-1,1-dioxide (TDO) building blocks. Oligomers of TDO were designed in order to increase electron affinity, maintain delocalized frontier orbitals, while significantly decreasing the transport gap. Through thermopower measurements, the dominant charge carriers were shown to change from holes to electrons as the number of TDO units was increased. This resulted in a unique system in which the charge carrier depends on ba

  7. Deciphering the "chemical" nature of the exotic isotopes of hydrogen by the MC-QTAIM analysis: the positively charged muon and the muonic helium as new members of the periodic table.

    PubMed

    Goli, Mohammad; Shahbazian, Shant

    2014-04-14

    This report is a primarily survey on the chemical nature of some exotic species containing the positively charged muon and the muonic helium, i.e., the negatively charged muon plus helium nucleus, as exotic isotopes of hydrogen, using the newly developed multi-component quantum theory of atoms in molecules (MC-QTAIM) analysis, employing ab initio non-Born-Oppenhiemer wavefunctions. Accordingly, the "atoms in molecules" analysis performed on various asymmetric exotic isotopomers of the hydrogen molecule, recently detected experimentally [Science, 2011, 331, 448], demonstrates that both the exotic isotopes are capable of forming atoms in molecules and retaining the identity of hydrogen atoms. Various derived properties of atomic basins containing the muonic helium cast no doubt that apart from its short life time, it is a heavier isotope of hydrogen while the properties of basins containing the positively charged muon are more remote from those of the orthodox hydrogen basins, capable of appreciable donation of electrons as well as large charge polarization. However, with some tolerance, they may also be categorized as hydrogen basins though with a smaller electronegativity. All in all, the present study also clearly demonstrates that the MC-QTAIM analysis is an efficient approach to decipher the chemical nature of species containing exotic constituents, which are difficult to elucidate by experimental and/or alternative theoretical schemes. PMID:24569859

  8. Gram-Negative Bacteria

    Microsoft Academic Search

    Craig A. Martin

    \\u000a Gram-negative bacteria are responsible for a broad array of infections in both the ambulatory and hospital settings. Urinary\\u000a tract infections, otitis media, pneumonia, abdominal infections, and meningitis are among the common and serious diseases\\u000a caused by these pathogens. Beta-lactams including penicillins, cephalosporins, monobactams, and carbapenems, along with fluoroquinolones\\u000a and aminoglycosides, comprise the most commonly used treatment regimens for gram-negative infections.

  9. No to negative data

    SciTech Connect

    Wiley, H. S.

    2008-04-01

    A frequent criticism in biology is that we don’t publish our negative data. As a result, the literature has become biased towards papers that favor specific hypotheses1. Some scientists have become so concerned about this trend that they have created journals dedicated to publishing negative results (e.g. the Journal of Negative Results in Biomedicine). Personally, I don’t think they should bother. I say this because I believe negative results are not worth publishing. Rest assured that I do not include drug studies that show a lack of effectiveness towards a specific disease or condition. This type of finding is significant in a societal context, not a scientific one, and thus we all have a vested interest in seeing this type of result published. I am talking about a set of experimental results that fail to support a particular hypothesis. The problem with these types of negative results is that they don’t actually advance science. Science is a set of ideas that can be supported by observations. A negative result does not support any specific idea, but only tells you what isn’t right. Well, there are only a small number of potential hypotheses that are correct, but essentially an infinite number of ideas are not correct. I don’t want to waste my time reading a paper about what doesn’t happen, just about those things that do. I can remember a positive result because I can associate it with a specific concept. What do I do with a negative one? It is hard enough to following the current literature. A flood of negative results would make that task all but impossible

  10. Induction Charge Detector with Multiple Sensing Stages

    NASA Technical Reports Server (NTRS)

    Gamero-Castano, Manuel

    2008-01-01

    An induction charge detector with multiple sensing stages has been conceived for use in characterizing sprayed droplets, dust particles, large ionized molecules, and the like. Like related prior single-stage devices, each stage yields a measurement of the electric charge and the time of flight of the particle. In effect, an n-stage sensor yields n independent sets of such measurements from the same particle. The benefit of doing this is to increase the effective signal-to-noise ratio and thereby lower the charge-detection limit and the standard error of the charge measurement.

  11. Amidothionophosphates: Novel Antioxidant Molecules

    Microsoft Academic Search

    Oren Tirosh; Yehoshua Katzhendler; Yechezkel Barenholz; Isaac Ginsburg; Ron Kohen

    1996-01-01

    This work describes the synthesis and characterization of a new family of antioxidants. The molecules have the same active group, but different oil-to-water and octanol-to-water partition coefficients due to different substituents. Three new molecules were synthesized based on the chemical structure of the primary amide attached to a thiophosphate group forming an amidothionophosphate. The amidothionophosphate molecules were exposed to the

  12. Photochemistry of interstellar molecules

    NASA Technical Reports Server (NTRS)

    Stief, L. J.

    1973-01-01

    The role of photochemistry in determining the lifetime of interstellar molecules is considered. The probability of photodecomposition depends on three factors, including the absorption cross section, the quantum yield or probability of dissociation following photon absorption, and the interstellar radiation field. A more detailed discussion of the photochemistry of five molecules is presented, giving attention to carbonyl sulfide, methyl acetylene, nitric oxide, acetylene, and benzene. Lifetimes of interstellar molecules in unobscured regions are in the range from 5 to 100 years. It is concluded that polyatomic molecules can exist only in dense clouds which protect them from the full interstellar radiation field.

  13. Ion-acoustic solitary waves and shocks in a collisional dusty negative-ion plasma.

    PubMed

    Misra, A P; Adhikary, N C; Shukla, P K

    2012-11-01

    We study the effects of ion-dust collisions and ion kinematic viscosities on the linear ion-acoustic instability as well as the nonlinear propagation of small-amplitude solitary waves and shocks (SWS) in a negative-ion plasma with immobile charged dusts. The existence of two linear ion modes, namely the "fast" and "slow" waves, is shown, and their properties are analyzed in the collisional negative-ion plasma. Using the standard reductive perturbation technique, we derive a modified Korteweg-de Vries-Burger (KdVB) equation which describes the evolution of small-amplitude SWS. The profiles of the latter are numerically examined with parameters relevant for laboratory and space plasmas where charged dusts may be positively or negatively charged. It is found that negative-ion plasmas containing positively charged dusts support the propagation of SWS with negative potential. However, the perturbations with both positive and negative potentials may exist when dusts are negatively charged. The results may be useful for the excitation of SWS in laboratory negative-ion plasmas as well as for observation in space plasmas where charged dusts may be positively or negatively charged. PMID:23214895

  14. Absence of discrete spectrum in highly negative ions

    Microsoft Academic Search

    Mary Beth Ruskai

    1982-01-01

    LetHN be the Hamiltonian for the Coulomb system consisting ofN particles of like charge in the field of a fixed point chargeZ. We show that if the particles are bosons, thenHN has no discrete spectrum whenN?N0=cZ2 for some constantc. If the particles are fermions, thenHN is bounded below uniformly inN. These results can be extended to molecules and to other

  15. Oligomerization of Negatively-Charged Amino Acids by Carbonyldiimidazole

    NASA Technical Reports Server (NTRS)

    Hill, Aubrey R., Jr.; Orgel, Leslie E.

    1996-01-01

    The carbonyldiimidazole-induced oligomerizations of aspartic acid, glutamic acid and 0-phospho-serine are amongst the most efficient reported syntheses of biopolymers in aqueous solution. The dependence of the yields of products on the concentrations of reagents, the temperature and the enantiomeric composition of the substrate amino acids are reported. Catalysis by metal ions, particularly by Mg(2+), is described. These reactions do not generate significant amounts of material in the size-range of several tens of residues that are thought to be needed for a polymer to function as a genetic material.

  16. Effect of divalent cation removal on the structure of gram-negative bacterial outer membrane models.

    PubMed

    Clifton, Luke A; Skoda, Maximilian W A; Le Brun, Anton P; Ciesielski, Filip; Kuzmenko, Ivan; Holt, Stephen A; Lakey, Jeremy H

    2015-01-13

    The Gram-negative bacterial outer membrane (GNB-OM) is asymmetric in its lipid composition with a phospholipid-rich inner leaflet and an outer leaflet predominantly composed of lipopolysaccharides (LPS). LPS are polyanionic molecules, with numerous phosphate groups present in the lipid A and core oligosaccharide regions. The repulsive forces due to accumulation of the negative charges are screened and bridged by the divalent cations (Mg(2+) and Ca(2+)) that are known to be crucial for the integrity of the bacterial OM. Indeed, chelation of divalent cations is a well-established method to permeabilize Gram-negative bacteria such as Escherichia coli. Here, we use X-ray and neutron reflectivity (XRR and NR, respectively) techniques to examine the role of calcium ions in the stability of a model GNB-OM. Using XRR we show that Ca(2+) binds to the core region of the rough mutant LPS (RaLPS) films, producing more ordered structures in comparison to divalent cation free monolayers. Using recently developed solid-supported models of the GNB-OM, we study the effect of calcium removal on the asymmetry of DPPC:RaLPS bilayers. We show that without the charge screening effect of divalent cations, the LPS is forced to overcome the thermodynamically unfavorable energy barrier and flip across the hydrophobic bilayer to minimize the repulsive electrostatic forces, resulting in about 20% mixing of LPS and DPPC between the inner and outer bilayer leaflets. These results reveal for the first time the molecular details behind the well-known mechanism of outer membrane stabilization by divalent cations. This confirms the relevance of the asymmetric models for future studies of outer membrane stability and antibiotic penetration. PMID:25489959

  17. Real-time monitoring and manipulation of single bio-molecules in free solution

    SciTech Connect

    Li, Hung-Wing

    2005-08-01

    The observation and manipulation of single biomolecules allow their dynamic behaviors to be studied to provide insight into molecular genetics, biochip assembly, biosensor design, DNA biophysics. In a PDMS/glass microchannel, a nonuniform electroosmotic flow (EOF) was created. By using a scanning confocal fluorescence microscope and total internal-reflection fluorescence microscope (TIRFM), we demonstrated that negatively charged DNA molecules were focused by the nonuniform EOF into a thin layer at the glass surface. This phenomenon was applied to selectively detect target DNA molecules without requiring the separation of excessive probes and can be applied continuously to achieve high throughput. A variable-angle-TIRFM was constructed for imaging single DNA molecule dynamics at a solid/liquid interface. Implications we have are that the measured intensities cannot be used directly to determine the distances of molecules from the surface and the experimental counting results depict the distance-dependent dynamics of molecules near the surface; Molecules at low ionic strengths experience electrostatic repulsion at distances much further away from the surface than the calculated thickness of the electrical double layer. {delta}-DNA was employed as a nanoprobe for different functionalized surfaces to elucidate adsorption in chromatography. The 12-base unpaired ends of this DNA provide exposed purine and pyrimidine groups for adsorption. Patterns of self-assembled monolayers (SAMs) and patterns of metal oxides are generated. By recording the real-time dynamic motion of DNA molecules at the SAMs/aqueous interface, the various parameters governing the retention of an analyte during chromatographic separation can be studied. Even subtle differences among adsorptive forces can be revealed. Dynamic conformational changes of the prosthetic group, flavin adenine dinucleotide (FAD), in flavoprotein NADH peroxidase, in thioredoxin reductase, and in free solution were monitored with TIWM. FAD bound loosely in the proteins changed from the stacked conformation to the unstacked conformation upon laser excitation. FAD in free solution not only underwent conformational changes but also reacted with each other to form a dimer. Direct measurement of the single-molecule enzymatic cleavage rates of ApaI-DNA complex in the presence of various concentrations of MgCl{sub 2} solution is reported. Results suggest that there exists a distribution of ApaI conformations around the restriction site.

  18. Electronic Transport through Self Assembled Thiol Molecules: Effect of Monolayer Order, Dynamics and Temperature

    NASA Technical Reports Server (NTRS)

    Dholakia, Geetha; Fan, Wendy; Meyyappan, M.

    2005-01-01

    We present the charge transport and tunneling conductance of self assembled organic thiol molecules and discuss the influence of order and dynamics in the monolayer on the transport behavior and the effect of temperature. Conjugated thiol molecular wires and organometals such as terpyridine metal complexes provide a new platform for molecular electronic devices and we study their self assembly on Au(111) substrates by the scanning tunneling microscope. Determining the organization of the molecule and the ability to control the nature of its interface with the substrate is important for reliable performance of the molecular electronic devices. By concurrent scanning tunneling microscopy and spectroscopy studies on SAMs formed from oligo (phenelyne ethynelyne) monolayers with and without molecular order, we show that packing and order determine the response of a self assembled monolayer (SAM) to competing interactions. Molecular resolution STM imaging in vacuum shows that the OPES adopt an imcommensurate SAM structure on Au(111) with a rectangular unit cell. Tunneling spectroscopic measurements were performed on the SAM as a function of junction resistance. STS results show that the I-Vs are non linear and asymmetric due to the inherent asymmetry in the molecular structure, with larger currents at negative sample biases. The asymmetry increases with increasing junction resistance due to the asymmetry in the coupling to the leads. This is brought out clearly in the differential conductance, which also shows a gap at the Fermi level. We also studied the effect of order and dynamics in the monolayer on the charge transport and found that competing forces between the electric field, intermolecular interactions, tip-molecule physisorption and substrate-molecule chemisorption impact the transport measurements and its reliability and that the presence of molecular order is very important for reproducible transport measurements. Thus while developing new electronic platforms based on molecules, it is important to have a good control of the molecule-substrate interface, for the devices to perform reliably. While such a control would minimize fluctuations and dynamics in the ensemble, the real challenge is to develop device architectures that are tolerant to fluctuations, since they cannot be totally eliminated in these low dimensional soft systems. Results of temperature dependent STS measurements will also be discussed.

  19. Dust charging effects on test charge potential in a multi-ion dusty plasma

    SciTech Connect

    Ali, S. [National Centre for Physics, Shahdra Valley Road, Islamabad 44000, Pakistan and IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

    2009-11-15

    The Debye-Hueckel and oscillatory wake potentials caused by a test charge are studied in a multi-ion dusty plasma, whose constituents are the Boltzmann distributed electrons and light positive ions, the heavy mobile negative ions, and static but charge fluctuating dust particles. For this purpose, fluid equations are employed to obtain the dielectric constant of the dust-negative-ion acoustic wave involving the negative ions and dust charge fluctuation effects. Theoretical and numerical investigations have revealed the modification in the Debye-Hueckel and wake potentials due to the effects of dust relaxation rate, dust absorption frequency, dust grain radius, and negative ion temperature. The present results should be important to form new materials in the presence of negative ions in laboratory as well as dust coagulation/agglomeration in space dusty plasmas.

  20. Enzymatic DNA molecules

    NASA Technical Reports Server (NTRS)

    Joyce, Gerald F. (Inventor); Breaker, Ronald R. (Inventor)

    1998-01-01

    The present invention discloses deoxyribonucleic acid enzymes--catalytic or enzymatic DNA molecules--capable of cleaving nucleic acid sequences or molecules, particularly RNA, in a site-specific manner, as well as compositions including same. Methods of making and using the disclosed enzymes and compositions are also disclosed.

  1. Molecules in Living Systems

    NSDL National Science Digital Library

    2012-06-19

    This lesson explains the difference between molecules in living systems and inanimate objects. In living systems, atoms and molecules are organized to a much greater degree and provide the structure of the organism. Lipids, carbohydrates, proteins, and nucleic acids are also discussed.

  2. Physicochemical properties of surface charge-modified ZnO nanoparticles with different particle sizes

    PubMed Central

    Kim, Kyoung-Min; Choi, Mun-Hyoung; Lee, Jong-Kwon; Jeong, Jayoung; Kim, Yu-Ri; Kim, Meyoung-Kon; Paek, Seung-Min; Oh, Jae-Min

    2014-01-01

    In this study, four types of standardized ZnO nanoparticles were prepared for assessment of their potential biological risk. Powder-phased ZnO nanoparticles with different particle sizes (20 nm and 100 nm) were coated with citrate or L-serine to induce a negative or positive surface charge, respectively. The four types of coated ZnO nanoparticles were subjected to physicochemical evaluation according to the guidelines published by the Organisation for Economic Cooperation and Development. All four samples had a well crystallized Wurtzite phase, with particle sizes of ?30 nm and ?70 nm after coating with organic molecules. The coating agents were determined to have attached to the ZnO surfaces through either electrostatic interaction or partial coordination bonding. Electrokinetic measurements showed that the surface charges of the ZnO nanoparticles were successfully modified to be negative (about ?40 mV) or positive (about +25 mV). Although all the four types of ZnO nanoparticles showed some agglomeration when suspended in water according to dynamic light scattering analysis, they had clearly distinguishable particle size and surface charge parameters and well defined physicochemical properties. PMID:25565825

  3. Canadian In-Class Question-Charge Distribution

    NSDL National Science Digital Library

    Harrison, David

    In this set of in-class questions, a solid sphere carrying a positive charge is placed next to a negatively charged circular plate. The questions address the topic of charge distribution. All questions are available for download in PDF format.

  4. Raindrop Electrification by the Association of Randomly Charged Cloud Droplets

    Microsoft Academic Search

    Ross Gunn

    1955-01-01

    Light ions generated in the atmosphere by cosmic rays and radioactivity normally diffuse onto cloud droplets and establish a nearly symmetrical Gaussian distribution of positively and negatively charged droplets. When the cloud becomes unstable, these cloud elements grow by association and the charges accumulate to establish a new equilibrium consisting of nearly equal numbers of larger and highly charged positive

  5. Manipulation of silver nanoparticles in a droplet for label-free detection of biological molecules using surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Çulha, Mustafa; Altunbek, Mine; Keskin, Sercan; Saatçi, Deniz

    2011-03-01

    Detection and identification of biomacromolecules is of critical importance in many fields ranging from biotechnology to medicine. Surface-enhanced Raman scattering (SERS) is an emerging technique for the label-free detection and identification of biological molecules and structures with its fingerprinting properties and high sensitivity. However, there are a number of obstacles for its applications for biological macromolecules due to their complexity. In this report, manipulation of microscopic processes in play during the drying of a sessile droplet as a tool to influence the nanoparticle-macromolecule packing, which has dramatic effect on SERS performance, before the SERS acquisition is demonstrated. A process known as the coffee ring phenomenon jams all particles and molecular species to the edges of the droplet during drying. This uncontrolled process has dramatic effects on a SERS experiment, using colloidal metal nanoparticles as substrates, by sweeping everything to the edges and influencing the packing of nanoparticles in the droplet area. A plastic tip was dipped into a drying sample droplet to influence the uncontrolled piling up. A negatively-charged protein, BSA, a positively-charged protein, cytochrom c, and a 20-base long oligonucleotide, were used as model biomacromolecules in this study. While a minimum of one order of magnitude lower concentration improvement in detection limit was observed with negatively-charged biomacromolecules, no significant improvement was observed with positively-charged ones compared to a sample droplet left on the surface without any interference. With the demonstrated approach, picomolar-level biomolecular detection using SERS is possible.

  6. Negative energy waves

    NASA Astrophysics Data System (ADS)

    Lashmore-Davies, C. N.

    2005-04-01

    A brief history of the concept of negative energy waves in fluid and plasma media is given. The theory of microwave tubes is highlighted, where the small signal power theorem was first derived, which led to the interpretation of these devices in terms of the interaction of positive and negative energy waves. Three examples are described to illustrate the use of negative waves in stability problems. The first is concerned with the Kelvin-Helmholtz instability in neutral fluids. The second comes from a kinetic theory of instability in a collisionless shock wave in a magnetized plasma, and the third is concerned with the effect of a resistive wall and plasma flow on the magnetohydrodynamic stability of a magnetically confined plasma. The paper ends with some general conclusions.

  7. Single-molecule identification via electric current noise

    PubMed Central

    Tsutsui, Makusu; Taniguchi, Masateru; Kawai, Tomoji

    2010-01-01

    Label-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms. Molecular fluctuations are a source of noise that often hinders single-molecule identification by obscuring the fine details of molecular identity. In this study, we report molecular identification through direct observation of quantum-fluctuation-induced inelastic noise in single organic molecules. We investigated current fluctuations flowing through a single molecule that is chemically connected to two electrodes. We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling. This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification. PMID:21266988

  8. Current-driven drift wave instability in a collisional dusty negative ion plasma

    NASA Astrophysics Data System (ADS)

    Rosenberg, M.; Rosenberg

    2013-12-01

    The excitation of drift waves by an electron current parallel to the magnetic field is investigated in a nonuniform plasma composed of electrons, positive ions, negative ions, and massive, negatively charged dust. Electrostatic drift waves with frequencies smaller than the ion gyrofrequencies and wavelengths larger than the ion gyroradii are considered. Linear kinetic theory is used, and collisions of charged particles with neutrals are taken into account. The present results may be relevant to laboratory collisional magnetoplasmas containing negative ions and dust.

  9. Electronic spectroscopy of diatomic molecules

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.

    1994-01-01

    This article provides an overview of the principal computational approaches and their accuracy for the study of electronic spectroscopy of diatomic molecules. We include a number of examples from our work that illustrate the range of application. We show how full configuration interaction benchmark calculations were instrumental in improving the understanding of the computational requirements for obtaining accurate results for diatomic spectroscopy. With this understanding it is now possible to compute radiative lifetimes accurate to within 10% for systems involving first- and second-row atoms. We consider the determination of the infrared vibrational transition probabilities for the ground states of SiO and NO, based on a globally accurate dipole moment function. We show how we were able to assign the a(sup "5)II state of CO as the upper state in the recently observed emission bands of CO in an Ar matrix. We next discuss the assignment of the photoelectron detachment spectra of NO and the alkali oxide negative ions. We then present several examples illustrating the state-of-the-art in determining radiative lifetimes for valence-valence and valence-Rydberg transitions. We next compare the molecular spectroscopy of the valence isoelectronic B2, Al2, and AlB molecules. The final examples consider systems involving transition metal atoms, which illustrate the difficulty in describing states with different numbers of d electrons.

  10. Hydration of highly charged ions

    PubMed Central

    Hofer, Thomas S.; Weiss, Alexander K.H.; Randolf, Bernhard R.; Rode, Bernd M.

    2011-01-01

    Based on a series of ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulations, the broad spectrum of structural and dynamical properties of hydrates of trivalent and tetravalent ions is presented, ranging from extreme inertness to immediate hydrolysis. Main group and transition metal ions representative for different parts of the periodic system are treated, as are 2 threefold negatively charged anions. The results show that simple predictions of the properties of the hydrates appear impossible and that an accurate quantum mechanical simulation in cooperation with sophisticated experimental investigations seems the only way to obtain conclusive results. PMID:22298911

  11. The Molecule Pages database.

    PubMed

    Saunders, Brian; Lyon, Stephen; Day, Matthew; Riley, Brenda; Chenette, Emily; Subramaniam, Shankar; Vadivelu, Ilango

    2008-01-01

    The UCSD-Nature Signaling Gateway Molecule Pages (http://www.signaling-gateway.org/molecule) provides essential information on more than 3800 mammalian proteins involved in cellular signaling. The Molecule Pages contain expert-authored and peer-reviewed information based on the published literature, complemented by regularly updated information derived from public data source references and sequence analysis. The expert-authored data includes both a full-text review about the molecule, with citations, and highly structured data for bioinformatics interrogation, including information on protein interactions and states, transitions between states and protein function. The expert-authored pages are anonymously peer reviewed by the Nature Publishing Group. The Molecule Pages data is present in an object-relational database format and is freely accessible to the authors, the reviewers and the public from a web browser that serves as a presentation layer. The Molecule Pages are supported by several applications that along with the database and the interfaces form a multi-tier architecture. The Molecule Pages and the Signaling Gateway are routinely accessed by a very large research community. PMID:17965093

  12. Carbon-negative biofuels

    Microsoft Academic Search

    John A. Mathews

    2008-01-01

    Current Kyoto-based approaches to reducing the earth's greenhouse gas problem involve looking for ways to reduce emissions. But these are palliative at best, and at worst will allow the problem to get out of hand. It is only through sequestration of atmospheric carbon that the problem can be solved. Carbon-negative biofuels represent the first potentially huge assault on the problem,

  13. Negative Transportation in French.

    ERIC Educational Resources Information Center

    Prince, Ellen F.

    There is a class of verbs in French which require that their complement verb be in the indicative. However, if the matrix clause contains a negative or an interrogative, the complement verb is usually in the subjunctive, but sometimes in the indicative. Examples are the verbs "penser" and "croire" in sentences such as: 1) Elle ne croit pas que…

  14. Negative Binomial Experiment

    NSDL National Science Digital Library

    Kyle Siegrist

    This resource consists of a Java applet and descriptive text. The applet illustrates the number of trials needed to get a specified number of successes in Bernoulli trials, in terms of random points on a discrete timeline. The applet illustrates the negative binomial distribution. The number of successes and the probability of success can be varied.

  15. Anthropological objects and negation

    Microsoft Academic Search

    Marie-Jeanne Borel

    1992-01-01

    Ever since Kant, the possibility of having objects of knowledge has been one of the most basic anthropological questions (“what can I know?”). For the logician, the linguist, or the semiologist who studies natural language, negation is one of these objects. However, as an operation and as a symbol, it has the paradoxical property of not being able to be

  16. The Negative Repetition Effect

    ERIC Educational Resources Information Center

    Mulligan, Neil W.; Peterson, Daniel J.

    2013-01-01

    A fundamental property of human memory is that repetition enhances memory. Peterson and Mulligan (2012) recently documented a surprising "negative repetition effect," in which participants who studied a list of cue-target pairs twice recalled fewer targets than a group who studied the pairs only once. Words within a pair rhymed, and…

  17. Negative pressure wound therapy

    Microsoft Academic Search

    MICHAEL KIRBY

    2010-01-01

    D iabetic foot disease is a major global burden. Foot ulcers frequently develop complications and become chronic, representing a considerable challenge as these are typically very difficult to treat. New therapies are needed to address these wounds and there is an increasing focus on negative pressure wound therapy (NPWT). This technique has been shown to accelerate wound healing and although

  18. Negative pressure wound therapy

    Microsoft Academic Search

    Michael Kirby

    2007-01-01

    iabetic foot disease is a major global burden. Foot ulcers frequently develop complications and become chronic, representing a considerable challenge as these are typically very difficult to treat. New therapies are needed to address these wounds and there is an increasing focus on negative pressure wound therapy (NPWT). This technique has been shown to accelerate wound healing and although its

  19. Validation and comparison of nonlinear negative ion extraction theory for two experimental configurations

    E-print Network

    Paris-Sud XI, Université de

    945 Validation and comparison of nonlinear negative ion extraction theory for two experimental of two volume negative ion sources, one being characterized by a large space charge in the extractor the use of low emittance negative ion beams emanating from such sources. The characteristics of the plasma

  20. Negative ion chemistry in Titan's upper atmosphere V. Vuitton a,b,, P. Lavvas b

    E-print Network

    Yelle, Roger V.

    Negative ion chemistry in Titan's upper atmosphere V. Vuitton a,b,Ã, P. Lavvas b , R.V. Yelle b , M the existence of numerous negative ions in Titan's upper atmosphere. The observations at closest approach ($1000 km) show evidence for negatively charged ions up to $10,000 amu/q, as well as two distinct peaks

  1. Of Molecules and Models.

    ERIC Educational Resources Information Center

    Brinner, Bonnie

    1992-01-01

    Presents an activity in which models help students visualize both the DNA process and transcription. After constructing DNA, RNA messenger, and RNA transfer molecules; students model cells, protein synthesis, codons, and RNA movement. (MDH)

  2. Factors controlling hole injection in single conjugated polymer molecules.

    PubMed

    Fradkin, Leonid; Palacios, Rodrigo E; Bolinger, Joshua C; Lee, Kwang-Jik; Lackowski, William M; Barbara, Paul F

    2009-04-23

    New insights on the molecular level details of the recently reported light-assisted injection of positive charge into single conjugated polymer chains are reported. Extensive new fluorescence-voltage single molecule spectroscopy (FV-SMS) measurements were performed on single chains of the archetypical conjugated polymer MEH-PPV embedded in a capacitor device to complement previous studies of the influence of the bias scan rate and optical excitation intensity. The use of a vacuum microscope allowed for the precise control of the device atmosphere, demonstrating the influence of triplet states in the MEH-PPV on the FV-SMS modulation. For identical device conditions, little variation was observed in the rate and yield of charging from molecule to molecule. Through the use of thicker supporting matrices and insulating polymer "blocking layers", it was determined that good electrical contact between the hole transport layers and the single molecules was necessary for charge injection. The results demonstrate the complexity of charge transfer processes at the interface of organic semiconductors and highlight the ability of single molecule methods to advance the understanding of such processes at the nanoscale. PMID:19260669

  3. Apparatus and method of determining molecular weight of large molecules

    SciTech Connect

    Fuerstenau, Stephen (Montrose, CA); Benner, W. Henry (Danville, CA); Madden, Norman (Livermore, CA); Searles, William (Fremont, CA)

    1998-01-01

    A mass spectrometer determines the mass of multiply charged high molecular weight molecules. This spectrometer utilizes an ion detector which is capable of simultaneously measuring the charge z and transit time of a single ion as it passes through the detector. From this transit time, the velocity of the single ion may then be derived, thus providing the mass-to-charge ratio m/z for a single ion which has been accelerated through a known potential. Given z and m/z, the mass m of the single ion can then be calculated. Electrospray ions with masses in excess of 1 MDa and charge numbers greater than 425 e.sup.- are readily detected. The on-axis single ion detection configuration enables a duty cycle of nearly 100% and extends the practical application of electrospray mass spectrometry to the analysis of very large molecules with relatively inexpensive instrumentation.

  4. Entropy and charge in molecular evolution--the case of phosphate.

    PubMed

    Arrhenius, G; Sales, B; Mojzsis, S; Lee, T

    1997-08-21

    Biopoesis, the creation of life, implies molecular evolution from simple components, randomly distributed and in a dilute state, to form highly organized, concentrated systems capable of metabolism, replication and mutation. This chain of events must involve environmental processes that can locally lower entropy in several steps; by specific selection from an indiscriminate mixture, by concentration from dilute solution, and in the case of the mineral-induced processes, by particular effectiveness in ordering and selective reaction, directed toward formation of functional biomolecules. Numerous circumstances provide support for the notion that negatively charged molecules were functionally required and geochemically available for biopoesis. Sulfite ion may have been important in bisulfite complex formation with simple aldehydes, facilitating the initial concentration by sorption of aldehydes in positively charged surface active minerals. Borate ion may have played a similar, albeit less investigated role in forming charged sugar complexes. Among anionic species, oligophosphate ions and charged phosphate esters are likely to have been of even more wide ranging importance, reflected in the continued need for phosphate in a proposed RNA world, and extending its central role to evolved biochemistry. Phosphorylation is shown to result in selective concentration by surface sorption of compounds, otherwise too dilute to support condensation reactions. It provides protection against rapid hydrolysis of sugars and, by selective concentration, induces the oligomerization of aldehydes. As a manifestation of life arisen, phosphate already appears in an organic context in the oldest preserved sedimentary record. PMID:9299295

  5. Entropy and charge in molecular evolution--the case of phosphate

    NASA Technical Reports Server (NTRS)

    Arrhenius, G.; Sales, B.; Mojzsis, S.; Lee, T.; Bada, J. L. (Principal Investigator)

    1997-01-01

    Biopoesis, the creation of life, implies molecular evolution from simple components, randomly distributed and in a dilute state, to form highly organized, concentrated systems capable of metabolism, replication and mutation. This chain of events must involve environmental processes that can locally lower entropy in several steps; by specific selection from an indiscriminate mixture, by concentration from dilute solution, and in the case of the mineral-induced processes, by particular effectiveness in ordering and selective reaction, directed toward formation of functional biomolecules. Numerous circumstances provide support for the notion that negatively charged molecules were functionally required and geochemically available for biopoesis. Sulfite ion may have been important in bisulfite complex formation with simple aldehydes, facilitating the initial concentration by sorption of aldehydes in positively charged surface active minerals. Borate ion may have played a similar, albeit less investigated role in forming charged sugar complexes. Among anionic species, oligophosphate ions and charged phosphate esters are likely to have been of even more wide ranging importance, reflected in the continued need for phosphate in a proposed RNA world, and extending its central role to evolved biochemistry. Phosphorylation is shown to result in selective concentration by surface sorption of compounds, otherwise too dilute to support condensation reactions. It provides protection against rapid hydrolysis of sugars and, by selective concentration, induces the oligomerization of aldehydes. As a manifestation of life arisen, phosphate already appears in an organic context in the oldest preserved sedimentary record.

  6. On the possibility of negative activation energies in bimolecular reactions

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1978-01-01

    The temperature dependence of the rate constants for model reacting systems was studied to understand some recent experimental measurements which imply the existence of negative activation energies. A collision theory model and classical trajectory calculations are used to demonstrate that the reaction probability can vary inversely with collision energy for bimolecular reactions occurring on attractive potential energy surfaces. However, this is not a sufficient condition to ensure that the rate constant has a negative temperature dependence. On the basis of these calculations, it seems unlikely that a true bimolecular reaction between neutral molecules will have a negative activation energy.

  7. Anisotropic negative-ion emission from cluster nanoplasmas

    NASA Astrophysics Data System (ADS)

    Rajeev, R.; Dalui, Malay; Trivikram, T. Madhu; Rishad, K. P. M.; Krishnamurthy, M.

    2015-06-01

    Recent experiments have shown that the enhanced charge transfer by Rydberg excited clusters (ECTREC) reduces the highly charged ions very efficiently to neutral atoms and negative ions with little loss of momentum. Neutral-atom emission is anisotropic with respect to the laser polarization and the anisotropy is larger than that of the ion emission from Coulomb explosion of isolated single clusters. In such a scenario, it is expected that the negative-ion emission (like neutrals) should be anisotropic and have larger propensity along the laser polarization than in the perpendicular direction. Further, it may be anticipated that negative-ion emission is more anisotropic than neutral-atom emission if ECTREC is taken in to account. We demonstrate that the negative-ion emission is anisotropic. Contrary to expectations, the negative-ion emission anisotropy is not more than that of the neutral-atom emission. We show that this can be rationalized if low-energy (about 10 eV) electron collisional detachment of the negative ions is taken into account. Electron collisional detachment depletes the negative-ion yield preferentially along the laser polarization direction and reduces the negative-ion emission anisotropy.

  8. Think (Gram) negative!

    PubMed Central

    2010-01-01

    The increasing prevalence of multiresistant Gram-negative bacteria of the Enterobacteriaceae family in Europe is a worrisome phenomenon. Extended spectrum betalactamase-producing Escherichia coli strains are widespread in the community and are frequently imported into the hospital. Of even more concern is the spread of carbapenem-resistant strains of Klebsiella spp. from regions where they are already endemic. Antibiotic use is a main driver of antibiotic resistance, which again increases broad spectrum antibiotic use, resulting in a vicious circle that is difficult to interrupt. The present commentary highlights important findings of a surveillance study of antimicrobial use and resistance in German ICUs over 8 years with a focus on Gram-negative resistance. PMID:20587087

  9. Ion-molecule reactions and fragmentation patterns in helium nanodroplets.

    PubMed

    Boatwright, Adrian; Jeffs, Jay; Stace, Anthony J

    2007-08-01

    A study has been made of the ion chemistry of a series of small molecules that have been embedded in helium nanodroplets. In most instances, the molecules H2O, SO2, CO2, CH3OH, C2H5OH, C3H7OH, CH3F, and CH3Cl have been allowed to form clusters, and reactivity within these has been initiated through electron impact ionization. For two of the molecules studied, CF2Cl2 and CF3I, reactivity is believed to originate from single molecules embedded in the droplets. Electron impact on the droplets is thought to first create a helium ion, and formation of molecular ions is then assumed to proceed via a charge hopping mechanism that propagates though the droplet and terminates with charge-transfer to a molecule or cluster. The chemistry exhibited by many of the cluster ions and at least one of the single molecular ions is very different from that observed for the same species in isolation. In most cases, reactivity appears to be dominated by high-energy bond breaking processes as opposed to, in the case of the clusters, ion-molecule reactions. Overall, charge-transfer from He+ does not appear to be a "soft" ionization mechanism. PMID:17585742

  10. Single-Molecule Force Spectroscopy of Cartilage Aggrecan Self-Adhesion

    PubMed Central

    Harder, Alexander; Walhorn, Volker; Dierks, Thomas; Fernàndez-Busquets, Xavier; Anselmetti, Dario

    2010-01-01

    We investigated self-adhesion between highly negatively charged aggrecan macromolecules extracted from bovine cartilage extracellular matrix by performing atomic force microscopy (AFM) imaging and single-molecule force spectroscopy (SMFS) in saline solutions. By controlling the density of aggrecan molecules on both the gold substrate and the gold-coated tip surface at submonolayer densities, we were able to detect and quantify the Ca2+-dependent homodimeric interaction between individual aggrecan molecules at the single-molecule level. We found a typical nonlinear sawtooth profile in the AFM force-versus-distance curves with a molecular persistence length of lp = 0.31 ± 0.04 nm. This is attributed to the stepwise dissociation of individual glycosaminoglycan (GAG) side chains in aggrecans, which is very similar to the known force fingerprints of other cell adhesion proteoglycan systems. After studying the GAG-GAG dissociation in a dynamic, loading-rate-dependent manner (dynamic SMFS) and analyzing the data according to the stochastic Bell-Evans model for a thermally activated decay of a metastable state under an external force, we estimated for the single glycan interaction a mean lifetime of ? = 7.9 ± 4.9 s and a reaction bond length of x? = 0.31 ± 0.08 nm. Whereas the x?-value compares well with values from other cell adhesion carbohydrate recognition motifs in evolutionary distant marine sponge proteoglycans, the rather short GAG interaction lifetime reflects high intermolecular dynamics within aggrecan complexes, which may be relevant for the viscoelastic properties of cartilage tissue. PMID:21081100

  11. Think (Gram) negative!

    Microsoft Academic Search

    Benedikt Huttner; Stephan Harbarth

    2010-01-01

    The increasing prevalence of multiresistant Gram-negative bacteria of the Enterobacteriaceae family in Europe is a worrisome\\u000a phenomenon. Extended spectrum betalactamase-producing Escherichia coli strains are widespread in the community and are frequently imported into the hospital. Of even more concern is the spread\\u000a of carbapenem-resistant strains of Klebsiella spp. from regions where they are already endemic. Antibiotic use is a main

  12. Algebra Balance Scales - Negatives

    NSDL National Science Digital Library

    Utah State University

    2009-07-01

    This site provides a virtual balance on which the student can represent (and then solve) simple linear equations with integer answers. Conceptually, positive weights (unit-blocks and x-boxes) push the pans of the scale downward. Negative values are represented by balloons which can be attached to the pans of the scale. The student can then manipulate the weights to solve the equation while simultaneously seeing a visual display of these effects on the equation.

  13. Photoionization of atoms and molecules. [of hydrogen, helium, and xenon

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1976-01-01

    A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

  14. Low-energy-electron induced permanently reactive CO? molecules.

    PubMed

    Davis, Daly; Sajeev, Y

    2014-09-01

    Ab initio quantum chemical studies show that a very weak molecular complexation of CO2 with a dipolar molecule is able to suppress the autoionization of the electron from its transient negative ion states. Since the autoionization is suppressed, the transient negative ion can efficiently relax its geometry to form the reductively activated CO2 moiety. Unlike the reductively activated isolated CO2 molecules, which are deactivated immediately due to their thermodynamic metastability, the reductively activated CO2 moieties of the weak molecular complexes are infinitely long-lived and, hence, permanently reactive. PMID:25023668

  15. Space Charge and Electrical Conduction Properties of Polypropylene Copolymer Films

    NASA Astrophysics Data System (ADS)

    Nakane, Emi; Kaneko, Kazue; Mori, Tatsuo; Mizutani, Teruyoshi; Takino, Hiroshi; Ishioka, Mitsugu

    We investigated the space charge and charging current characteristics in polypropylene copolymer films polymerized with metallocene and Ziegler-Natta catalysts, respectively. Positive and negative homo space charges were observed and their amounts showed maxima at 40 °C. Charge carriers injected from the semiconducting (SC) electrode were dominant at 60 °C. The copolymerization of ethylene enhanced the apparent carrier mobility and the charging current. Evaporated Al electrode showed much less carrier injection than Al plate or SC electrode (mechanically-contacted electrode). Carrier injection from SC electrode was dominant than that from Al plate. These suggest that the space charge formation depends on not only electrode materials but also contact conditions.

  16. Proof that the hydrogen-antihydrogen molecule is unstable.

    PubMed

    Gridnev, D K; Greiner, Carsten

    2005-06-10

    In the framework of nonrelativistic quantum mechanics we derive a necessary condition for four Coulomb charges (m1(+), m2(-), m3(+), m4(-)), where all masses are assumed finite, to form the stable system. The obtained stability condition is physical and is expressed through the required minimal ratio of Jacobi masses. In particular, this provides the rigorous proof that hydrogen-antihydrogen and muonium-antimuonium molecules and hydrogen-positron-muon systems are unstable. It also proves that replacing hydrogen in the hydrogen-antihydrogen molecule with its heavier isotopes does not make the molecule stable. These are the first rigorous results on the instability of these systems. PMID:16090392

  17. Mechanisms of the electron-impact-induced methionine molecule fragmentation

    NASA Astrophysics Data System (ADS)

    Tamuliene, J.; Romanova, L. G.; Vukstich, V. S.; Snegursky, A. V.

    2012-08-01

    The fragmentation of a methionine (C5H11NO2S) molecule by a low-energy electron impact has been studied both experimentally and theoretically. A series of doubly-charged fragment ions have been observed for the first time. The main emphasis has been given to the mechanisms of the initial molecule fragment production. A special attention has been paid to the energy characteristics of the ionic fragment yield. The geometrical parameters of the initial molecule rearrangement have also been analyzed.

  18. Charge distribution in lightning flashes

    NASA Technical Reports Server (NTRS)

    Rustan, P. L.; Uman, M. A.

    1980-01-01

    Four VHF receivers about 10 km apart were used to detect three-dimensional lightning VHF sources during active thunderstorms. A computer implemented algorithm was used to determine the difference in the time of arrival (DTOA) between the VHF pulses. The three-dimensional source locations determined from the DTOA were correlated with ground electric field measurements (0.1 Hz to 1.5 MHz). Four cloud to ground (CG) and three intracloud (IC) flashes, selected randomly, were studied. A point charge model was used to determine the charge being removed during the different phases of CG and IC flashes. It was determined that return strokes lowered between 24.1 and 3.6 coulombs of negative charge to ground from heights between 10.5 and 5.8 km above MSL. The interstroke process after the first return stroke in a CG flash lowered between 3.4 and 0.9 coulombs of negative charge between the heights of 14.2 (near the cloud tops) to heights of 5.8 km (near the beginning of the leader-return stroke process).

  19. Intense negative ion beams and their diagnostics

    NASA Astrophysics Data System (ADS)

    Papadichev, V. A.; Shelkovenko, T. A.

    1990-01-01

    Using negative ions for accelerators and CTR has some peculiarities. High-power beams of fast atoms obtained by charge exchange of negative ions can have advantage over positive ion beams for ICF since they do not experience any deviation, instabilities, and scattering. H- current up to 7 kA in a 100-200-ns pulse with densities up to 200 A/cm2 and a voltage of 0.8 MV were obtained in experiments on magnetically insulated diodes at the Lebedev Physical Institute. The cathode plasma was formed by surface discharge of a dielectric. Diagnostics of high-power H- beams is described, which includes target activation, prompt gamma-ray recording, registration of ion traces on Mylar foils, and others. It was concluded that up to 1 kA/cm2 of H- can be obtained.

  20. Negative transconductance in apertured electron guns

    NASA Astrophysics Data System (ADS)

    Harris, John R.; O'Shea, Patrick G.

    2008-06-01

    Passing an electron beam through an aperture can serve to reduce the beam current or change the transverse beam profile. For a sufficiently intense beam, space charge will drive a radial expansion of the beam, which may cause the current passing through the aperture to decrease even though the current arriving at the aperture is increasing. When a gridded electron gun is used, this may be expressed by stating that the transconductance of the apertured gun is negative. Here, we explain this effect and explore some of the key factors governing when it can occur and influencing its strength.

  1. Negative Transconductance in Apertured Electron Guns

    SciTech Connect

    Harris, J R; O'Shea, P G

    2007-09-21

    Passing an electron beam through an aperture can serve to reduce the beam current or change the transverse beam profile. For a sufficiently intense beam, space charge will drive a radial expansion of the beam, which may cause the current passing through the aperture to increase even though the current arriving at the aperture is decreasing. When a gridded electron gun is used, this may be expressed by stating that the transconductance of the apertured gun is negative. Here we explain this effect, and explore some of the key factors governing when it can occur and influencing its strength.

  2. Charge separation and energy transfer in carotenopyropheophorbide-quinone triads

    SciTech Connect

    Liddell, P.A.; Barrett, D.; Makings, L.R.; Pessiki, P.J.; Gust, D.; Moore, T.A.

    1986-08-20

    In natural photosynthesis membranes, chlorophyll molecules serve as the site of the initial photodriven charge separation. In addition, they play a role in subsequent electron-transfer steps, accept singlet excitation energy from carotenoid antenna molecules, and transfer triplet energy to carotenoid acceptors (thereby preventing sensitized singlet oxygen production and subsequent photodamage to the organism). The authors report herein the synthesis and study of chlorophyll-based carotenopyropheophorbide-quinone triad molecules which mimic all of these natural processes.

  3. Negative ion photoelectron spectroscopy of alkyl peroxides, alkoxides, and group VIII transition metal oxides

    NASA Astrophysics Data System (ADS)

    Ramond, Tanya Michelle

    I employed negative ion photoelectron spectroscopy to investigate the structure and energetics of three groups of anions and their corresponding neutrals: alkyl peroxides ROO-, (R = H, D, CH3, CD3, and CH3CH2); alkoxides RO- (R=CH3, CD3, CH3CH2, CD3CD2, (CH3)2CH, and (CH 3)3C); and Group VIII transition metal oxides XO- and OXO- (X = Ni, Pd, Pt). The peroxides and the alkoxides are of great interest to those who study atmospheric or combustion chemistry, while the metal oxides play an important role in catalysis reactions. However, each of these groups of molecules displays interesting behavior that is itself a motivation for their investigation. The spectra of HOO- and DOO- are relatively straightforward to analyze and understand and provide a good basis from which to compare the larger alkyl peroxides. The ROO- spectra exhibit the normal Franck-Condon behavior leading to clear assignments of the expected vibrational progressions in both the ground and first excited state of the neutral species. Although the molecules increase in size from HOO to CH3CH2OO, many of the spectral characteristics such as electron affinity (EA) and prominence of the O-O stretch vibration do not appreciably change. The EA of HOO is revised, which becomes important as part of a newly revised thermochemistry of HOO and HOOH. The RO- species exhibit an additional layer of complexity. Both the CH3O- and (CH3)3 CO- molecules possess relatively high C3v , symmetry about the CO axis as well as a doubly degenerate ground electronic state of the neutral RO molecule. Both of these elements are expected to produce a Jahn-Teller effect, where in order to break the molecular symmetry and electronic state degeneracy, the Born-Oppenheimer approximation breaks down and nuclear and electronic wavefunctions become coupled. The extent to which Jahn-Teller effects affect the RO molecule photoelectron spectra is discussed. Although the transition metal monoxides are diatomics and thus perhaps presumed to be uncomplicated molecules, they are the most difficult to understand in this thesis and the most difficult to obtain in the laboratory. The d orbitals of the metals are closely spaced together, leading to congested spectra and mixing of the properties of orbitals that complicates analysis and ab initio calculations. Furthermore, the high nuclear charge of the atoms involved leads to non-negligible spin-orbit and other relativistic effects. Perhaps for these reasons there is relatively little information in the literature on these molecules. However, despite the complexities involved, comparison of all three metal molecules has allowed for a consistent interpretation of the spectra. Assignments are made including electron affinities, spin-orbit excited states of both anion and neutral XO molecules, other excited electronic states of anion and neutral, and vibrational frequencies and bond length changes. Analysis of the OXO molecules yields electron affinities, vibrational frequencies, and anion to neutral geometry changes.

  4. Noise reduction in negative-ion quadrupole mass spectrometry

    DOEpatents

    Chastagner, Philippe (3134 Natalie Cir., Augusta, GA 30909-2748)

    1993-01-01

    A quadrupole mass spectrometer (QMS) system having an ion source, quadrupole mass filter, and ion collector/recorder system. A weak, transverse magnetic field and an electron collector are disposed between the quadrupole and ion collector. When operated in negative ion mode, the ion source produces a beam of primarily negatively-charged particles from a sample, including electrons as well as ions. The beam passes through the quadrupole and enters the magnetic field, where the electrons are deflected away from the beam path to the electron collector. The negative ions pass undeflected to the ion collector where they are detected and recorded as a mass spectrum.

  5. Noise reduction in negative-ion quadrupole mass spectrometry

    DOEpatents

    Chastagner, P.

    1993-04-20

    A quadrupole mass spectrometer (QMS) system is described having an ion source, quadrupole mass filter, and ion collector/recorder system. A weak, transverse magnetic field and an electron collector are disposed between the quadrupole and ion collector. When operated in negative ion mode, the ion source produces a beam of primarily negatively-charged particles from a sample, including electrons as well as ions. The beam passes through the quadrupole and enters the magnetic field, where the electrons are deflected away from the beam path to the electron collector. The negative ions pass undeflected to the ion collector where they are detected and recorded as a mass spectrum.

  6. Single-molecule bioelectronics.

    PubMed

    Rosenstein, Jacob K; Lemay, Serge G; Shepard, Kenneth L

    2015-07-01

    Experimental techniques that interface single biomolecules directly with microelectronic systems are increasingly being used in a wide range of powerful applications, from fundamental studies of biomolecules to ultra-sensitive assays. In this study, we review several technologies that can perform electronic measurements of single molecules in solution: ion channels, nanopore sensors, carbon nanotube field-effect transistors, electron tunneling gaps, and redox cycling. We discuss the shared features among these techniques that enable them to resolve individual molecules, and discuss their limitations. Recordings from each of these methods all rely on similar electronic instrumentation, and we discuss the relevant circuit implementations and potential for scaling these single-molecule bioelectronic interfaces to high-throughput arrayed sensing platforms. WIREs Nanomed Nanobiotechnol 2015, 7:475-493. doi: 10.1002/wnan.1323 For further resources related to this article, please visit the WIREs website. PMID:25529538

  7. Photochemistry of interstellar molecules

    NASA Technical Reports Server (NTRS)

    Stief, L. J.

    1971-01-01

    The photochemistry of two diatomic and eight polyatomic molecules is discussed quantitatively. For an interstellar molecule, the lifetime against photodecomposition depends upon the absorption cross section, the quantum yield or probability of dissociation following photon absorption, and the interstellar radiation field. The constant energy density of Habing is used for the unobserved regions of interstellar radiation field, and the field in obscuring clouds is estimated by combining the constant flux with the observed interstellar extinction curve covering the visible and ultraviolet regions. Lifetimes against photodecomposition in the unobscured regions and as a function of increasing optical thickness in obscuring clouds are calculated for the ten species. The results show that, except for CO, all the molecules have comparable lifetimes of less than one hundred years. Thus they can exist only in dense clouds and can never have been exposed to the unobscured radiation. The calculations further show that the lifetimes in clouds of moderate opacity are of the order of one million years.

  8. The influence of space charge shielding on dielectric multipactor

    SciTech Connect

    Chang, C.; Liu, G. Z.; Tang, C. X.; Yan, L. X. [Department of Engineering Physics, Tsinghua University, Beijing, 100084 (China)

    2009-05-15

    A model of space charge influenced by multipactor electrons and plasma has been established. The positive space charge potential/field for vacuum dielectric multipactor is analytically studied. After considering the plasma, the positive space charge field is further shielded, and multipactor saturates at higher surface accumulated field, compared with that for only considering multipactor electrons. The negative space charge potential/field for dielectric breakdown at high pressure is analyzed. It is found that the negative potential can be nonmonotonously varied, forming a minimum potential well.

  9. Radiation-induced charge dynamics in dielectrics

    SciTech Connect

    Labonte, K.

    1982-12-01

    A general physical model is presented for the analysis of charge dynamics in dielectrics exposed to ionizing radiation. Discrete trap levels, recombination between trapped and free carriers, trapping and detrapping events, and the mobility of positive and negative charge carriers are included in the theory. This model is applied to electron beam irradiated Teflon FEP foils and results for various boundary conditions are compared with experimental data from a split Faraday cup arrangement.

  10. Mighty Molecule Models

    NSDL National Science Digital Library

    Greg Rushton

    2008-01-01

    As part of the SMATHematics Project: The Wonder of Science, The Power of Mathematics--a collaborative partnership between Kennesaw State University and two local school districts, fifth graders had the opportunity to puzzle out chemical formulas of propane, methanol, and other important molecules. In addition, they explored properties that characterize certain molecules and then used their newly acquired knowledge of atoms' bonding requirements to help them build three-dimensional molecular models. The effort is succeeding--as you can see by the fifth-grade classroom experience described here.

  11. JCE Featured Molecules

    NSDL National Science Digital Library

    These interactive images are linked to molecular structures or other graphic images from articles in our print Journal. Many articles in the Journal of Chemical Education include molecular structures naturally in a two-dimensional representation. This collection of interactive Chime-based structures are chosen from some of these molecules. While many such Web-based structure collections exist, having the structures in a single location and linked to specific articles in JCE (and vice versa) will benefit both teachers and students. In addition to static images, two fully manipulable versions (Jmol, MDL Chime) of these molecules are available.

  12. Extraction of negative ions from pulsed electronegative capacitively coupled plasmas

    SciTech Connect

    Agarwal, Ankur; Rauf, Shahid; Collins, Ken [Applied Materials Inc., 974 E. Arques Avenue, M/S 81312, Sunnyvale, California 94085 (United States)

    2012-08-01

    Charge buildup during plasma etching of dielectric features can lead to undesirable effects, such as notching, bowing, and twisting. Pulsed plasmas have been suggested as a method to achieve charge-free plasma etching. In particular, electronegative plasmas are attractive as the collapse of the plasma potential during the after-glow period of pulsed capacitively coupled plasmas (CCPs) can allow for extraction of negative ions into the feature. The extraction of negative ions in the after-glow of pulsed CCPs sustained in CF{sub 4} containing gas mixtures is computationally investigated. In this paper, the consequences of pulse frequency and gas chemistry on negative ion flux to the wafer are discussed. A low negative ion flux to the wafer was observed only in the late after-glow period of low pulse frequencies. The negative ion flux was found to significantly increase with the addition of highly electronegative gases (such as thermally attaching Cl{sub 2}) even at a high pulse frequency of 10 kHz. As the production of negative ions during the after-glow diminishes, alternative strategies to enhance the flux were also pursued. The flux of negative ions was found to increase by the addition of a pulsed dc voltage on the top electrode that is 180 Degree-Sign out-of-phase with the rf pulse.

  13. Spontaneous electrical charging of droplets by conventional pipetting

    PubMed Central

    Choi, Dongwhi; Lee, Horim; Im, Do Jin; Kang, In Seok; Lim, Geunbae; Kim, Dong Sung; Kang, Kwan Hyoung

    2013-01-01

    We report that a droplet dispensed from a micropipette almost always has a considerable electrical charge of a magnitude dependent on the constituents of the droplet, on atmospheric humidity and on the coating material of pipette tip. We show that this natural electrification of a droplet originates from the charge separation between a droplet and pipette tip surface by contact with water due to the ionization of surface chemical groups. Charge on a droplet can make it difficult to detach the droplet from the pipette tip, can decrease its surface tension, can affect the chemical characteristics of solutions due to interactions with charged molecules, and can influence the combination and localization of charged bio-molecules; in all cases, the charge may affect results of experiments in which any of these factors is important. Thus, these findings reveal experimental parameters that should be controlled in experiments that use micropipettes. PMID:23784001

  14. Single molecule DNA interaction kinetics of retroviral nucleic acid chaperone proteins

    NASA Astrophysics Data System (ADS)

    Williams, Mark

    2010-03-01

    Retroviral nucleocapsid (NC) proteins are essential for several viral replication processes including specific genomic RNA packaging and reverse transcription. The nucleic acid chaperone activity of NC facilitates the latter process. In this study, we use single molecule biophysical methods to quantify the DNA interactions of wild type and mutant human immunodeficiency virus type 1 (HIV-1) NC and Gag and human T-cell leukemia virus type 1 (HTLV-1) NC. We find that the nucleic acid interaction properties of these proteins differ significantly, with HIV-1 NC showing rapid protein binding kinetics, significant duplex destabilization, and strong DNA aggregation, all properties that are critical components of nucleic acid chaperone activity. In contrast, HTLV-1 NC exhibits significant destabilization activity but extremely slow DNA interaction kinetics and poor aggregating capability, which explains why HTLV-1 NC is a poor nucleic acid chaperone. To understand these results, we developed a new single molecule method for quantifying protein dissociation kinetics, and applied this method to probe the DNA interactions of wild type and mutant HIV-1 and HTLV-1 NC. We find that mutations to aromatic and charged residues strongly alter the proteins' nucleic acid interaction kinetics. Finally, in contrast to HIV-1 NC, HIV-1 Gag, the nucleic acid packaging protein that contains NC as a domain, exhibits relatively slow binding kinetics, which may negatively impact its ability to act as a nucleic acid chaperone.

  15. Electrically charged small soot particles in the exhaust of an aircraft gas-turbine engine combustor: comparison of model and experiment

    NASA Astrophysics Data System (ADS)

    Sorokin, A.; Arnold, F.

    The emission of electrically charged soot particles by an aircraft gas-turbine combustor is investigated using a theoretical model. Particular emphasis is placed on the influence of the fuel sulfur content (FSC). The model considers the production of primary "combustion" electrons and ions in the flame zone and their following interaction with molecular oxygen, sulfur-bearing molecules (e.g. O 2, SO 2, SO 3, etc.) and soot particles. The soot particle size distribution is approximated by two different populations of mono-dispersed large and small soot particles with diameters of 20-30 and 5-7 nm, respectively. The effect of thermal ionization of soot and its interaction with electrons and positive and negative ions is included in the model. The computed positive and negative chemiion (CI) concentrations at the combustor exit and relative fractions of small neutral and charged soot particles were found to be in satisfactory agreement with experimental data. The results show that the FSC indeed may influence the concentration of negative CI at low fuel flow into combustor. Importantly the simulation indicates a very efficient mutual interaction of electrons and ions with soot particles with a large effect on both ion and charged soot particle concentrations. This result may be interpreted as a possible indirect effect of FSC on the growth and size distribution of soot particles.

  16. Negative Ion Excited States

    NASA Astrophysics Data System (ADS)

    Mead, Roy D.

    This dissertation describes high-resolution tunable laser photodetachment studies of both valence and dipole -bound excited states of negative ions. Also discussed is a merged laser-ion beam photodetachment spectrometer. The photodetachment cross section of C(,2)('-) displays many sharp resonances, due to excitation of autodetaching levels of the B('2)(SIGMA)(,u)('+) valence state lying above the onset of the (C(,2) + e) continuum. The positions of approximately 1,000 resonances were measured, allowing the spectroscopic constants of the ground X('2)(SIGMA)(,g)('+) and excited B('2)(SIGMA)(,u)('+) states to be determined, including spin-rotation constants. The previously unobserved A('2)(PI)(,u) state has been characterized by deperturbation analysis. Strong A-X transitions are predicted near 2.5 microns. The widths of C(,2)('-) resonances with v = 6 -10 and J = 1-60 have also been measured, providing autodetachment rates as a function of both rotation and vibration, ranging from 10('8) to 10('11) s('-1). The first conclusive observation of an entirely new class of states, called dipole-bound or dipole-supported states, is discussed for the case of acetaldehyde enolate (vinyl oxide) negative ion. In these novel states, the extra electron is weakly bound ((TURN)5 cm('-1)) in a very diffuse orbital ((TURN)100 (ANGSTROM)) by the dipole moment of the neutral core. Weak electric fields (< 70 V/cm) are found to rapidly detach the dipole-bound electron. These dipole-bound states resemble Rydberg states of neutrals, but differ from Rydbergs in many important respects. They should be present for all neutrals with dipole moments > 2 Debye. The merged laser-ion beam (also known as coaxial -beams) spectrometer has 0.0005 cm('-1) resolution in the visible region, simultaneously achieving very high sensitivity. It employs quadrupole beam deflectors to merge and laser and negative ion beams, and can scan spectra either by scanning the laser frequency or the Doppler shift of the ion beam. Both electrons and neutral photodetachment products are detected. Even very low energy electrons (< 20 meV) are collected and counted, and the collector may be adjusted to collect either all electrons or only low energy electrons as needed.

  17. Supersymmetry in spherical molecules and fullerenes under perpendicular magnetic fields.

    PubMed

    Jakubský, V; Kuru, S; Negro, J; Tristao, S

    2013-04-24

    Methods of supersymmetric quantum mechanics are used to obtain analytical solutions for massless Dirac electrons in spherical molecules, including fullerenes, in the presence of magnetic fields. The solutions for Dirac massive charges are also obtained via the solutions of the Dirac-Weyl equation. PMID:23553418

  18. Supersymmetry in spherical molecules and fullerenes under perpendicular magnetic fields

    NASA Astrophysics Data System (ADS)

    Jakubský, V.; Kuru, ?.; Negro, J.; Tristao, S.

    2013-04-01

    Methods of supersymmetric quantum mechanics are used to obtain analytical solutions for massless Dirac electrons in spherical molecules, including fullerenes, in the presence of magnetic fields. The solutions for Dirac massive charges are also obtained via the solutions of the Dirac-Weyl equation.

  19. Ion-Molecule Reactions in Gas Phase Radiation Chemistry.

    ERIC Educational Resources Information Center

    Willis, Clive

    1981-01-01

    Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)

  20. Direct Conductance Measurement of Single DNA Molecules in Aqueous

    E-print Network

    Zhang, Yanchao

    charge transport, a phenomenon that is associated with oxidative damage of DNA,1-4 on a singleDirect Conductance Measurement of Single DNA Molecules in Aqueous Solution Bingqian Xu, Peiming have studied electron transport in DNA duplexes, covalently bonded to two electrodes in aqueous buffer