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Sample records for gramicidin channel cs

  1. Interactions in cation permeation through the gramicidin channel. Cs, Rb, K, Na, Li, Tl, H, and effects of anion binding.

    PubMed Central

    Eisenman, G; Sandblom, J; Neher, E

    1978-01-01

    As a prototype for binding and interaction in biological Na and K channels, the single channel conductances for Li, Na, K, Rb, Cs, H, and Tl and the membrane potentials for Tl-K mixtures are characterized for gramicidin A over wider concentration rangers than previously and analyzed using an "equilibrium domain" model that assumes a central rate-determining barrier. Peculiarities in the conductance-concentration relationship for TlF, TlNO3, and TlAc suggest that anions bind to Tl-loaded channels, and the theory is extended to allow for this. For concreteness, the selectivity of cation permeation is characterized in terms of individual binding and rate constants of this model, with the conclusions that the strongest site binds Cs greater than Rb greater than K greater than Na greater than Li, while the next strongest binds Na greater than K greater than Li greater than Rb greater than Cs. However, because Schagina, Grinfeldt, and Lev's recent finding of single filing (personal communication) indicates that the channel sites in gramicidin cannot be at equilibrium with the solution, and work in progress with Hägglund and Enos (Biophys. J. 21:26a. [Abstr.]) indicates that the simplest model adequate to account for the observed concentration-dependences of flux-ratio, conductance, I--V characteristic, and permeability has three barriers and four sites, some implications of additional rate-determining barriers at the mouth of the channel are discussed. The results are summarized using phenomenological "experimental" parameters that provide a model-independent way to represent that data concisely and which can be interpreted physically in terms of any desired model. PMID:77689

  2. Gramicidins A, B, and C form structurally equivalent ion channels.

    PubMed Central

    Sawyer, D B; Williams, L P; Whaley, W L; Koeppe, R E; Andersen, O S

    1990-01-01

    The membrane structure of the naturally occurring gramicidins A, B, and C was investigated using circular dichroism (CD) spectroscopy and single-channel recording techniques. All three gramicidins form channels with fairly similar properties (Bamberg, E., K. Noda, E. Gross, and P. Läuger. 1976. Biochim. Biophys. Acta. 419:223-228.). When incorporated into lysophosphatidylcholine micelles, however, the CD spectrum of gramicidin B is different from that of gramicidin A or C (cf. Prasad, K. U., T. L. Trapane, D. Busath, G. Szabo, and D. W. Urry. 1983. Int. J. Pept. Protein Res. 22:341-347.). The structural identity of the channels formed by gramicidin B has, therefore, been uncertain. We find that when gramicidins A and B are incorporated into dipalmitoylphosphatidylcholine vesicles, their CD spectra are fairly similar, suggesting that the two channel structures could be similar. In planar bilayers, gramicidins A, B, and C all form hybrid channels with each other. The properties of the hybrid channels are intermediate to those of the symmetric channels, and the appearance rates of the hybrid channels (relative to the symmetric channels) corresponds to what would be predicted if all three gramicidin molecules were to form structurally equivalent channels. These results allow us to interpret the different behavior of channels formed by the three gramicidins solely on the basis of the amino acid substitution at position 11. PMID:1705449

  3. Theoretical Study of Ion Transport in the Gramicidin a Channel

    NASA Astrophysics Data System (ADS)

    Roux, Benoi T.

    Modern techniques are used to study the permeation process of ions through the gramicidin A channel. The conformation of the gramicidin molecule is investigated experimentally in dimethylsulfoxide/acetone using the techniques of two-dimensional NMR spectroscopy. An empirical energy function is developed from ab initio calculations to represent the interaction of Li^{+}, Na^{+} and K^ {+} ions with the backbone of polypeptides; the parameters are tested in dense systems with free energy simulations. The dynamics of the gramicidin A channel dimer in the absence of water and ions is studied in the harmonic approximation by a vibrational analysis of the atomic motions relative to their equilibrium positions. The behavior of the water molecules in the channel is studied with a molecular dynamics simulation of a fully solvated Gramicidin A dimer embedded in a model membrane. the potential of mean force and the mobility of Na^{+ }, K^{+} and water are calculated in the interior of a gramicidin-like periodic poly (L,D)-alanine beta -helix. The potential of mean force of Na^ {+} ion along the axis of the gramicidin A channel is calculated with a molecular dynamics simulation of a fully solvated Gramicidin A dimer embedded in a model membrane; the gramicidin channel is modeled as a right -handed head-to-head beta-helix dimer. Binding sites are found at the extremities of the channel; no large activation energy barrier is caused by the dehydration process at the entrance of the channel. In the appendices, Statistical Mechanical theories are used to investigate the equilibrium and dynamical properties of the liquid state. A theory of aqueous solutions is used to provide an interpretation for the Born model of ion hydration at the molecular level; the Born radius of hydration is interpreted in terms of the first peak in the solute-solvent radial distribution function. We show that some proposed closures for the RISM equation of Chandler and Andersen possess no solution because

  4. Ion transport in the gramicidin channel: molecular dynamics study of single and double occupancy.

    PubMed Central

    Roux, B; Prod'hom, B; Karplus, M

    1995-01-01

    The structural and thermodynamic factors responsible for the singly and doubly occupied saturation states of the gramicidin channel are investigated with molecular dynamics simulations and free energy perturbation methods. The relative free energy of binding of all of the five common cations Li+, Na+, K+, Rb+, and Cs+ is calculated in the singly and doubly occupied channel and in bulk water. The atomic system, which includes the gramicidin channel, a model membrane made of neutral Lennard-Jones particles and 190 explicit water molecules to form the bulk region, is similar to the one used in previous work to calculate the free energy profile of a Na+ ion along the axis of the channel. In all of the calculations, the ions are positioned in the main binding sites located near the entrances of the channel. The calculations reveal that the doubly occupied state is relatively more favorable for the larger ions. Thermodynamic decomposition is used to show that the origin of the trend observed in the calculations is due to the loss of favorable interactions between the ion and the single file water molecules inside the channel. Small ions are better solvated by the internal water molecules in the singly occupied state than in the doubly occupied state; bigger ions are solvated almost as well in both occupation states. Water-channel interactions play a role in the channel response. The observed trends are related to general thermodynamical properties of electrolyte solutions. Images FIGURE 2 PMID:7538804

  5. Effects of volatile anesthetic on channel structure of gramicidin A.

    PubMed Central

    Tang, Pei; Mandal, Pravat K; Zegarra, Martha

    2002-01-01

    Volatile anesthetic agent, 1-chloro-1,2,2-trifluorocyclobutane (F3), was found to alter gramicidin A channel function by enhancing Na(+) transport (. Biophys. J. 77:739-746). Whether this functional change is associated with structural alternation is evaluated by circular dichroism and nuclear magnetic resonance spectroscopy. The circular dichroism and nuclear magnetic resonance results indicate that at low millimolar concentrations, 1-chloro-1,2,2-trifluorocyclobutane causes minimal changes in gramicidin A channel structure in sodium dodecyl sulfate micelles. All hydrogen bonds between channel backbones are well maintained in the presence of 1-chloro-1,2,2-trifluorocyclobutane, and the channel structure is stable. The finding supports the notion that low affinity drugs such as volatile anesthetics and alcohols can cause significant changes in protein function without necessarily producing associated changes in protein structure. To understand the molecular mechanism of general anesthesia, it is important to recognize that in addition to structural changes, other protein properties, including dynamic characteristics of channel motions, may also be of functional significance. PMID:12202367

  6. Solvent drag across gramicidin channels demonstrated by microelectrodes.

    PubMed Central

    Pohl, P; Saparov, S M

    2000-01-01

    The competition of ion and water fluxes across gramicidin channels was assessed from the concentration distributions of both pore-impermeable and -permeable cations that were simultaneously measured by double-barreled microelectrodes in the immediate vicinity of a planar bilayer. Because water movement across the membrane led to accumulation of solutes on one side of the membrane and depletion on the other, the permeable cation was not only pushed by water across the channel (true solvent drag); it also flowed along its concentration gradient (pseudo-solvent drag). For the demonstration of true solvent drag, a difference between the bulk concentrations on the hypertonic and the hypotonic sides of the membrane was established. It was adjusted to get equal cation concentrations at both membrane/water interfaces. From the sodium and potassium fluxes measured along with membrane conductivity under these conditions, approximately five water molecules were found to be transported simultaneously with one ion through the channel. In diphytanoyl phosphatidylcholine membranes, a single-channel hydraulic permeability coefficient of 1.6 x 10(-14) cm(3) s(-1) was obtained. PMID:10777738

  7. Covalently linked gramicidin channels: effects of linker hydrophobicity and alkaline metals on different stereoisomers.

    PubMed Central

    Armstrong, K M; Quigley, E P; Quigley, P; Crumrine, D S; Cukierman, S

    2001-01-01

    The direct role of the dioxolane group on the gating and single-channel conductance of different stereoisomers of the dioxolane-linked gramicidin A (gA) channels reconstituted in planar lipid bilayers was investigated. Four different covalently linked gA dimers were synthesized. In two of them, the linker was the conventional dioxolane described previously (SS and RR channels). Two gAs were covalently linked with a novel modified dioxolane group containing a retinal attachment (ret-SS and ret-RR gA dimers). These proteins also formed ion channels in lipid bilayers and were selective for monovalent cations. The presence of the bulky and hydrophobic retinal group immobilizes the dioxolane linker in the bilayer core preventing its rotation into the hydrophilic lumen of the pore. In 1 M HCl the gating kinetics of the SS or RR dimers were indistinguishable from their retinal counterparts; the dwell-time distributions of the open and closed states in the SS and ret-SS were basically the same. In particular, the inactivation of the RR was not prevented by the presence of the retinal group. It is concluded that neither the fast closing events in the SS or RR dimers nor the inactivation of the RR are likely to be a functional consequence of the flipping of the dioxolane inside the pore of the channel. On the other hand, the inactivation of the RR dimer was entirely eliminated when alkaline metals (Cs(+) or K(+)) were the permeating cations in the channel. In fact, the open state of the RR channel became extremely stable, and the gating characteristics of both the SS and RR channels were different from what was seen before with permeating protons. As in HCl, the presence of a retinal in the dioxolane linker did not affect the gating behavior of the SS and RR in Cs(+)- or K(+)-containing solutions. Alternative hypotheses concerning the gating of linked gA dimers are discussed. PMID:11259294

  8. Ion transport in a model gramicidin channel. Structure and thermodynamics.

    PubMed Central

    Roux, B; Karplus, M

    1991-01-01

    The potential of mean force for Na+ and K+ ions as a function of position in the interior of a periodic poly(L,D)-alanine model for the gramicidin beta-helix is calculated with a detailed atomic model and realistic interactions. The calculated free energy barriers are 4.5 kcal/mol for Na+ and 1.0 kcal/mol for K+. A decomposition of the free energy demonstrates that the water molecules make a significant contribution to the free energy of activation. There is an increase in entropy at the transition state associated with greater fluctuations. Analysis reveals that the free energy profile of ions in the periodic channel is controlled not by the large interaction energy involving the ion but rather by the weaker water-water, water-peptide and peptide-peptide hydrogen bond interactions. The interior of the channel retains much of the solvation properties of a liquid in its interactions with the cations. Of particular importance is the flexibility of the helix, which permits it to respond to the presence of an ion in a fluidlike manner. The distortion of the helix is local (limited to a few carbonyls) because the structure is too flexible to transmit a perturbation to large distances. The plasticity of the structure (i.e., the property to deform without generating a large energy stress) appears to be an essential factor in the transport of ions, suggesting that a rigid helix model would be inappropriate. Images FIGURE 1 FIGURE 10 PMID:1714305

  9. Evaluation of surface tension and ion occupancy effects on gramicidin A channel lifetime.

    PubMed Central

    Ring, A.; Sandblom, J.

    1988-01-01

    The surface tension of glycerylmonooleate-hexadecane lipid bilayer membranes and the lifetime of gramicidin A channels were measured at various concentrations of the surrounding solutions. For HCl the surface tension is essentially constant at approximately 5 mN/m up to approximately 1 M, whereas the average lifetime increases approximately 40-fold. At higher concentrations the surface tension decreases markedly. For CsCl the surface tension is constant up to about 1 M then increases with salt level. The average lifetime in this case increases about sixfold. In both cases the lifetime levels off and even decreases at higher salt levels. The increase in lifetime observed with ion activity is therefore qualitatively different from, and not explained by, the established dependence of lifetime on membrane properties (Elliot, J.R., D. Needham, J.P. Dilger, and D.A. Haydon. 1983. Biochim. Biophys. Acta. 735:95-103). We have previously proposed that ion occupancy is a determinant of channel stability, and to test this hypothesis the voltage dependence of channel lifetime was measured in asymmetrical solutions. For the case of a potassium chloride solution on one side of the membrane and a hydrogen chloride solution, on the other, the voltage dependence of the lifetime is asymmetrical. The asymmetry is such that when the electrical field is applied in the direction of the chemical gradient for each of the ions, the channel lifetime approaches, at increasing field strengths, that of a symmetrical solution of the respective ion. The voltage dependence of the surface tension, on the other hand, is negligible for the range of voltages used. These results, and the earlier findings that the order of the lifetimes for the alkali cations generally agree with the order of the permeability selectivity of the gramicidin A channel, support the hypothesis that ion occupancy is a major factor determining the lifetime of gramicidin A channels. The effects of multivalent blockers and

  10. Effect of pyrrolidinium based ionic liquid on the channel form of gramicidin in lipid vesicles.

    PubMed

    Singh, Upendra Kumar; Dohare, Neeraj; Mishra, Prabhash; Singh, Prashant; Bohidar, Himadri B; Patel, Rajan

    2015-08-01

    The present work is focused on the interaction between membrane bound gramicidin and 1-butyl-1-methyl-2-oxopyrrolidinium bromide (BMOP) ionic liquid. Ionic liquids (ILs) are solvents that are often liquid at room temperature and composed of organic cation and appropriate anion. The gramicidin peptide forms prototypical ion channels for cations, which have been extensively used to study the organization, dynamics, and function of membrane spanning channels. The interaction was studied by circular dichroism, steady state, time-resolved fluorescence spectroscopy in combination with dynamic surface tension and field emission scanning electron microscopic methods (FESEM). The results obtained from circular dichroism shows that the BMOP interacts with the channel form of gramicidin in lipid vesicle without any considerable effect on its conformation. The Red-edge excitation shift (REES) also supported the above findings. In addition, the fluorescence studies suggested that BMOP makes ground state complex with ion channel, which was further supported by time resolved measurements. Furthermore, dynamic surface tension analysis shows the faster adsorption of BMOP with membrane bound gramicidin at the air-water interface. Additionally, FESEM results indicated that BMOP forms a film around the membrane bound gramicidin at higher concentration. These results are potentially useful to analyze the effect of ionic liquids on the behaviour of membrane proteins.

  11. Gravity dependency of the gramicidin A channel conductivity. A model for gravity perception on the cellular level.

    PubMed

    Schatz, A; Linke-Hommes, A; Neubert, J

    1996-01-01

    Theoretical investigations involving the membrane-solution interface have revealed that the density of the solution varies appreciably within interfacial layers adjacent to charged membrane surfaces. The hypothesis that gravity interacts with this configuration and modifies transport rates across horizontal and vertical membranes differently was supported by initial experiments with gramicidin A channels in phosphatidylserine (PS) membranes in 0.1 M KCl. Channel conductivity was found to be about 1.6 times higher in horizontal membranes than in vertical membranes. Here we present the results of further experiments with gramicidin A channels (incorporated into charged PS- and uncharged phosphatidylcholine (PC) membranes in KCl- and CsCl-solutions) to demonstrate that the hypothesis is more generally applicable. Again, channel conductivity was found to be higher in horizontal PS membranes by a factor of between 1.20 and 1.75 in 0.1 M CsCl. No difference in channel conductivity was found for uncharged PC membranes in 0.1 M KCl and in 0.1 M CsCl. However, for PC membranes in 0.05 M KCl the channel conductivity was significantly higher in horizontal membranes by a factor of between 1.07 and 1.14. These results are consistent with the results of our model calculations of layer density and extension, which showed that the layer formation is enhanced by increasing membrane surface charge and decreasing electrolyte ion concentration. The mechanism of gravity interaction with membrane transport processes via interface reactions might be utilized by biological systems for orientational behaviour in the gravity field, which has been observed even for cellular systems.

  12. Permeation characteristics of gramicidin conformers.

    PubMed Central

    Busath, D; Szabo, G

    1988-01-01

    To investigate the molecular origin of decreased conductance in variant gramicidin channels, we examined the current-voltage (IV) characteristics of single Val1-gramicidin A channels. Unlike standard channels, all variant channels showed pronounced rectification even though bathing solutions were symmetrical. Moreover, channels of lower conductance consistently showed more pronounced rectification. Analysis within the framework of a three-barrier, two-site, single-filing model indicates that the shape of the variant channel IVs could be best explained by an increase in binding affinity near one of the two channel entrances. This conclusion was further tested by characterizing single channel IVs in bi-ionic solutions having different cationic species at each channel entrance. In Cs/Na bi-ionic solutions, reversal potentials of variant channels often differed by a small but significant amount from those of standard channels. When a membrane potential was applied, the ionic currents tended to be reduced more when flowing from the Na+ side than the Cs+ side. These observations support the conclusion that variant channels have increased binding affinity at one end of the channel. Furthermore, H+ currents were increased while Ag+ currents were unaltered for most variant channels exhibiting decreased Na+ or Cs+ currents. The increased H+ conductance argues against long-range coulombic forces as the basis for decreased Na+ or Cs+ conductance while the normal Ag+ conductance suggests that the binding site field strength increases by a change in carbonyl geometry at the channel entrance. PMID:2455549

  13. Spring constants for channel-induced lipid bilayer deformations. Estimates using gramicidin channels.

    PubMed Central

    Lundbaek, J A; Andersen, O S

    1999-01-01

    Hydrophobic interactions between a bilayer and its embedded membrane proteins couple protein conformational changes to changes in the packing of the surrounding lipids. The energetic cost of a protein conformational change therefore includes a contribution from the associated bilayer deformation energy (DeltaGdef0), which provides a mechanism for how membrane protein function depends on the bilayer material properties. Theoretical studies based on an elastic liquid-crystal model of the bilayer deformation show that DeltaGdef0 should be quantifiable by a phenomenological linear spring model, in which the bilayer mechanical characteristics are lumped into a single spring constant. The spring constant scales with the protein radius, meaning that one can use suitable reporter proteins for in situ measurements of the spring constant and thereby evaluate quantitatively the DeltaGdef0 associated with protein conformational changes. Gramicidin channels can be used as such reporter proteins because the channels form by the transmembrane assembly of two nonconducting monomers. The monomerleft arrow over right arrow dimer reaction thus constitutes a well characterized conformational transition, and it should be possible to determine the phenomenological spring constant describing the channel-induced bilayer deformation by examining how DeltaGdef0 varies as a function of a mismatch between the hydrophobic channel length and the unperturbed bilayer thickness. We show this is possible by analyzing experimental studies on the relation between bilayer thickness and gramicidin channel duration. The spring constant in nominally hydrocarbon-free bilayers agrees well with estimates based on a continuum analysis of inclusion-induced bilayer deformations using independently measured material constants. PMID:9929490

  14. Ion-water and ion-polypeptide correlations in a gramicidin-like channel. A molecular dynamics study.

    PubMed Central

    Jordan, P C

    1990-01-01

    This work describes a molecular dynamics study of ion-water and ion-polypeptide correlation in a model gramicidin-like channel (the polyglycine analogue) based upon interaction between polarizable, multipolar groups. The model suggests that the vicinity of the dimer junction and of the ethanolamine tail are regions of unusual flexibility. Cs+ binds weakly in the mouth of the channel: there it coordinates five water molecules and the #11CO group with which it interacts strongly and is ideally aligned. In the channel interior it is generally pentacoordinate; at the dimer junction, because of increased channel flexibility, it again becomes essentially hexacoordinate. The ion is also strongly coupled to the #13 CO but not to either #9 or #15, consistent with 13C NMR data. Water in the channel interior is strikingly different from bulk water; it has a much lower mean dipole moment. This correlates with our observation (which differs from that of previous studies) that water-water angular correlations do not persist within the channel, a result independent of ion occupancy or ionic polarity. In agreement with streaming potential measurements, there are seven single file water molecules associated with Cs+ permeation; one of these is always in direct contact with bulk water. At the mouth of an ion-free channel, there is a pattern of dipole moment alteration among the polar groups. Due to differential interaction with water, exo-carbonyls have unusually large dipole moments whereas those of the endo-carbonyls are low. The computed potential of mean force for CS+ translocation is qualitatively reasonable. However, it only exhibits a weakly articulated binding site and it does not quantitatively account for channel energetics. Correction for membrane polarization reduces, but does not eliminate, these problems. PMID:1705448

  15. Structural restraints and heterogeneous orientation of the gramicidin A channel closed state in lipid bilayers.

    PubMed

    Mo, Y; Cross, T A; Nerdal, W

    2004-05-01

    Although there have been several decades of literature illustrating the opening and closing of the monovalent cation selective gramicidin A channel through single channel conductance, the closed conformation has remained poorly characterized. In sharp contrast, the open-state dimer is one of the highest resolution structures yet characterized in a lipid environment. To shift the open/closed equilibrium dramatically toward the closed state, a lower peptide/lipid molar ratio and, most importantly, long-chain lipids have been used. For the first time, structural evidence for a monomeric state has been observed for the native gramicidin A peptide. Solid-state NMR spectroscopy of single-site (15)N-labeled gramicidin in uniformly aligned bilayers in the L(alpha) phase have been observed. The results suggest a kinked structure with considerable orientational heterogeneity. The C-terminal domain is well structured, has a well-defined orientation in the bilayer, and appears to be in the bilayer interfacial region. On the other hand, the N-terminal domain, although appearing to be well structured and in the hydrophobic core of the bilayer, has a broad range of orientations relative to the bilayer normal. The structure is not just half of the open-state dimer, and neither is the structure restricted to the surface of the bilayer. Consequently, the monomeric or closed state appears to be a hybrid of these two models from the literature.

  16. Time-correlation analysis of simulated water motion in flexible and rigid gramicidin channels.

    PubMed Central

    Chiu, S W; Jakobsson, E; Subramaniam, S; McCammon, J A

    1991-01-01

    Molecular dynamics simulations have been done on a system consisting of the polypeptide membrane channel former gramicidin, plus water molecules in the channel and caps of waters at the two ends of the channel. In the absence of explicit simulation of the surrounding membrane, the helical form of the channel was maintained by artificial restraints on the peptide motion. The characteristic time constant of the artificial restraint was varied to assess the effect of the restraints on the channel structure and water motions. Time-correlation analysis was done on the motions of individual channel waters and on the motions of the center of mass of the channel waters. It is found that individual water molecules confined in the channel execute higher frequency motions than bulk water, for all degrees of channel peptide restraint. The center-of-mass motion of the chain of channel waters (which is the motion that is critical for transmembrane transport, due to the mandatory single filing of water in the channel) does not exhibit these higher frequency motions. The mobility of the water chain is dramatically reduced by holding the channel rigid. Thus permeation through the channel is not like flow through a rigid pipe; rather permeation is facilitated by peptide motion. For the looser restraints we used, the mobility of the water chain was not very much affected by the degree of restraint. Depending on which set of experiments is considered, the computed mobility of our water chain in the flexible channel is four to twenty times too high to account for the experimentally measured resistance of the gramicidin channel to water flow. From this result it appears likely that the peptide motions of an actual gramicidin channel embedded in a lipid membrane may be more restrained than in our flexible channel model, and that these restraints may be a significant modulator of channel permeability. For the completely rigid channel model the "trapping" of the water molecules in

  17. Structural consequences of anesthetic and nonimmobilizer interaction with gramicidin A channels.

    PubMed Central

    Tang, P; Simplaceanu, V; Xu, Y

    1999-01-01

    Although interactions of general anesthetics with soluble proteins have been studied, the specific interactions with membrane bound-proteins that characterize general anesthesia are largely unknown. The structural modulations of anesthetic interactions with synaptic ion channels have not been elucidated. Using gramicidin A as a simplified model for transmembrane ion channels, we have recently demonstrated that a pair of structurally similar volatile anesthetic and nonimmobilizer, 1-chloro-1,2,2-trifluorocyclobutane (F3) and 1,2-dichlorohexafluorocyclobutane (F6), respectively, have distinctly different effects on the channel function. Using high-resolution NMR structural analysis, we show here that neither F3 nor F6 at pharmacologically relevant concentrations can significantly affect the secondary structure of the gramicidin A channel. Although both the anesthetic F3 and the nonimmobilizer F6 can perturb residues at the middle section of the channel deep inside the hydrophobic region in the sodium dodecyl sulfate micelles, only F3, but not F6, can significantly alter the chemical shifts of the tryptophan indole N-H protons near the channel entrances. The results are consistent with the notion that anesthetics cause functional change of the channel by interacting with the amphipathic domains at the peptide-lipid-water interface. PMID:10233053

  18. Theoretical study of the antiparallel double-stranded helical dimer of gramicidin as an ion channel.

    PubMed Central

    Sung, S S; Jordan, P C

    1988-01-01

    Recent experimental studies by Durkin, J. T., O. S. Andersen, F. Heitz, Y. Trudelle, and R. E. Koeppe II (1987. Biophys. J. 51:451a) have suggested that the antiparallel double-stranded helical (APDS) dimer of gramicidin can form a transmembrane cation channel. This article reports a theoretical study that successfully rationalizes the channel properties of the APDS dimer. As in the case of the head-to-head (HH) dimer, the APDS exhibits a high potential energy barrier as anions approach the channel mouth, according for the observation of valence selectivity. The calculated potential energies of cations show two binding sites near the channel mouths, a typical feature of the HH channel. The potential energies of hydrated cations in the APDS are generally higher than those in the HH channel and show a larger pseudoperiodicity and higher barriers, an observation which suggests that the APDS should exhibit lower single channel conductance. PMID:2462929

  19. Gramicidin A channel as a test ground for molecular dynamics force fields.

    PubMed

    Allen, Toby W; Baştuğ, Turgut; Kuyucak, Serdar; Chung, Shin-Ho

    2003-04-01

    We use the well-known structural and functional properties of the gramicidin A channel to test the appropriateness of force fields commonly used in molecular dynamics (MD) simulations of ion channels. For this purpose, the high-resolution structure of the gramicidin A dimer is embedded in a dimyristoylphosphatidylcholine bilayer, and the potential of mean force of a K(+) ion is calculated along the channel axis using the umbrella sampling method. Calculations are performed using two of the most common force fields in MD simulations: CHARMM and GROMACS. Both force fields lead to large central barriers for K(+) ion permeation, that are substantially higher than those deduced from the physiological data by inverse methods. In long MD simulations lasting over 60 ns, several ions are observed to enter the binding site but none of them crossed the channel despite the presence of a large driving field. The present results, taken together with many earlier studies, highlights the shortcomings of the standard force fields used in MD simulations of ion channels and calls for construction of more appropriate force fields for this purpose.

  20. The study of volt-ampere characteristics of ionic channels formed by gramicidin A.

    PubMed

    Passechnik, V I; Flerov, M N; Hianik, T

    1985-02-01

    A method of measurement of the non-linearity coefficient of volt-ampere characteristics of the type i(U) approximately = U(1 + beta U2) has been developed for ionic channels formed by gramicidin A, using the third harmonic of the membrane current. The shape of the volt-ampere characteristics (VA) of ionic channels formed by gramicidin A did not depend on the antibiotic concentration in the membrane. The coefficient beta of non-linearity of VA of membranes modified by gramicidin A depended on electrolyte concentration "c" and it increased proportionally with the lg c from -17 V-2 at 0.03 mol/l KC1 to 8 V-2 at 3.4 mol/l KCl, and it was zero at co = 0.3 - 1 mol/l KCl. Egg lecithin and glycerol monooleate (GMO) membranes differ in their co values. The substitution of K+ for Li+ of the membrane solvent (n-heptane for n-hexadecane) did not influence the value of beta; the same applied for GMO membranes without any solvent. In a number of membranes, spontaneous change of the non-linearity coefficient with time observed after the membrane formation, as well as jumps of the non-linearity coefficient at a practically unchanged membrane conductivity. An analysis of some theoretical models of the ion transport through the channel has shown that, at voltages above 200 mV, these models provide rather small values of beta, or extremely high VA non-linearity.

  1. Immobilization and characterization of the transmembrane ion channel peptide gramicidin in a sol-gel matrix

    NASA Astrophysics Data System (ADS)

    Esquembre, Rocío; Poveda, José Antonio; Mallavia, Ricardo; Mateo, C. Reyes

    2007-05-01

    Immobilization of ion channels requires of a methodology able to retain the physical properties of the lipid bilayer where their activity is performed. However, most of lipid membrane immobilization methods have been observed to alter the structural properties of the bilayers. Use of sol-gel routes seems to be an interesting alternative, although unstable liposomes were obtained when conventional sol-gel methodology was employed for immobilizing. Recently, we have suggested that use of alcohol-free sol-gel routes combined with negatively charged lipids could minimize effects exerted by host matrix on liposome structure, increasing its stability. Here we confirm this assumption by analysing the physical properties of a series of zwitterionic and anionic liposomes entrapped in a sol-gel matrix and we develop a methodology able to retain the physical properties of the lipid bilayer. This methodology has been successfully used to immobilize the transmembrane ion channel peptide gramicidin. Gramicidin was reconstituted in anionic liposomes and its immobilization was confirmed from changes observed in the photophysical properties of the tryptophan residues. Ion channel activity was determined using the fluorescent dye pyrene-1,3,6,8-tetrasulphonic acid (PTSA) and long term stability of the immobilized system was checked from steady-state fluorescence anisotropy measurements.

  2. Conformation of gramicidin A channel in phospholipid vesicles: a 13C and 19F nuclear magnetic resonance study.

    PubMed Central

    Weinstein, S; Wallace, B A; Blout, E R; Morrow, J S; Veatch, W

    1979-01-01

    We have determined the conformation of the channel-forming polypeptide antibiotic gramicidin A in phosphatidylcholine vesicles by using 13C and 19F NMR spectroscopy. The models previously proposed for the conformation of the dimer channel differ in the surface localization of the NH2 and COOH termini. We have incorporated specific 13C and 19F nuclei at both the NH2, and COOH termini of gramicidin and have used 13C and 19F chemical shifts and spin lattice relaxation time measurements to determine the accessibility of these labels to three paramagnetic NMR probes--two in aqueous solution and one attached to the phosphatidylcholine fatty acid chain9 all of our results indicate that the COOH terminus of gramicidin in the channel is located near the surface of the membrane and the NH2 terminus is buried deep within the lipid bilayer. These findings strongly favor an NH2-terminal to NH2-terminal helical dimer as the major conformation for the gramicidin channel in phosphatidylcholine vesicles. PMID:92025

  3. Peroxyl radicals promoted changes in water permeability through gramicidin channels in DPPC and lecithin-PC vesicles.

    PubMed

    Soto, M A; Sotomayor, C P; Lissi, E A

    2003-03-01

    Gramicidin incorporation to DPPC or lecithin-PC large unilamellar vesicles (LUVs) leads to pore formation that, under hyper-osmotic conditions, produces a noticeable increase in the rate of trans-membrane water flow. This pore formation is more efficient in the more fluid lecithin-PC LUVs. Exposure of these vesicles to peroxyl radicals generated in the aerobic thermolysis of 2,2'-azo-bis(2-amidinopropane) (AAPH), changes the physical properties of the bilayer (as sensed employing fluorescent probes), modifies gramicidin molecules (as sensed by the decrease in Trp fluorescence) and notably reduces the transbilayer rate of water outflow. In order to evaluate if this reduced water-transport capacity is due to changes in the membrane due to lipid-peroxidation and/or direct damage to gramicidin channels, results obtained in the oxidable vesicles (lecithin-PC) were compared to those obtained in DPPC vesicles. The data obtained show that most of the water transport efficiency loss can be ascribed to a direct disruption of gramicidin channels by AAPH derived peroxyl radicals.

  4. Noncontact dipole effects on channel permeation. III. Anomalous proton conductance effects in gramicidin

    PubMed Central

    Phillips, LR; Cole, CD; Hendershot, RJ; Cotten, M; Cross, TA; Busath, DD

    1999-01-01

    Proton transport on water wires, of interest for many problems in membrane biology, is analyzed in side-chain analogs of gramicidin A channels. In symmetrical 0.1 N HCl solutions, fluorination of channel Trp(11), Trp-(13), or Trp(15) side chains is found to inhibit proton transport, and replacement of one or more Trps with Phe enhances proton transport, the opposite of the effects on K(+) transport in lecithin bilayers. The current-voltage relations are superlinear, indicating that some membrane field-dependent process is rate limiting. The interfacial dipole effects are usually assumed to affect the rate of cation translocation across the channel. For proton conductance, however, water reorientation after proton translocation is anticipated to be rate limiting. We propose that the findings reported here are most readily interpreted as the result of dipole-dipole interactions between channel waters and polar side chains or lipid headgroups. In particular, if reorientation of the water column begins with the water nearest the channel exit, this hypothesis explains the negative impact of fluorination and the positive impact of headgroup dipole on proton conductance. PMID:20540928

  5. Stochastic theory of ion movement in channels with single-ion occupancy. Application to sodium permeation of gramicidin channels.

    PubMed Central

    Jakobsson, E; Chiu, S W

    1987-01-01

    The electrodiffusion equations were solved for the one-ion channel both by the analytical method due to Levitt and also by Brownian dynamic simulations. For both types of calculations equilibration of ion distribution between the bath and the ends of the channel was assumed. Potential profiles were found that give good fits to published data on Na+ permeation of gramicidin channels. The data were best fit by profiles that have no relative energy maximum at the mouth of the channel. This finding suggests that alignment of waters or channel charged groups inside the channel in response to an ion's approach may provide an energetically favorable situation for entry sufficient to overcome the energy required for removing bulk waters of hydration. An alternative possibility is that the barrier to ion entry is situated outside the region restricted to single-ion occupancy. Replacement of valine with more polar amino acids at the No. 1 location was found to correspond to a deepening of the potential minima near the channel mouths, an increase in height of the central barrier to ion translocation across the channel, and possibly a reduction in the mobility of the ion-water complex in the channel. The Levitt theory was extended to calculate passage times for ions to cross the channel and the blocking effects of ions that entered the channel but didn't cross. These quantities were also calculated by the Brownian dynamics method. PMID:2440492

  6. Density-functional theory study of gramicidin A ion channel geometry and electronic properties.

    PubMed

    Todorović, Milica; Bowler, David R; Gillan, Michael J; Miyazaki, Tsuyoshi

    2013-12-06

    Understanding the mechanisms underlying ion channel function from the atomic-scale requires accurate ab initio modelling as well as careful experiments. Here, we present a density functional theory (DFT) study of the ion channel gramicidin A (gA), whose inner pore conducts only monovalent cations and whose conductance has been shown to depend on the side chains of the amino acids in the channel. We investigate the ground state geometry and electronic properties of the channel in vacuum, focusing on their dependence on the side chains of the amino acids. We find that the side chains affect the ground state geometry, while the electrostatic potential of the pore is independent of the side chains. This study is also in preparation for a full, linear scaling DFT study of gA in a lipid bilayer with surrounding water. We demonstrate that linear scaling DFT methods can accurately model the system with reasonable computational cost. Linear scaling DFT allows ab initio calculations with 10,000-100,000 atoms and beyond, and will be an important new tool for biomolecular simulations.

  7. Molecular mechanism of H+ conduction in the single-file water chain of the gramicidin channel.

    PubMed Central

    Pomès, Régis; Roux, Benoît

    2002-01-01

    The conduction of protons in the hydrogen-bonded chain of water molecules (or "proton wire") embedded in the lumen of gramicidin A is studied with molecular dynamics free energy simulations. The process may be described as a "hop-and-turn" or Grotthuss mechanism involving the chemical exchange (hop) of hydrogen nuclei between hydrogen-bonded water molecules arranged in single file in the lumen of the pore, and the subsequent reorganization (turn) of the hydrogen-bonded network. Accordingly, the conduction cycle is modeled by two complementary steps corresponding respectively to the translocation 1) of an ionic defect (H+) and 2) of a bonding defect along the hydrogen-bonded chain of water molecules in the pore interior. The molecular mechanism and the potential of mean force are analyzed for each of these two translocation steps. It is found that the mobility of protons in gramicidin A is essentially determined by the fine structure and the dynamic fluctuations of the hydrogen-bonded network. The translocation of H+ is mediated by spontaneous (thermal) fluctuations in the relative positions of oxygen atoms in the wire. In this diffusive mechanism, a shallow free-energy well slightly favors the presence of the excess proton near the middle of the channel. In the absence of H+, the water chain adopts either one of two polarized configurations, each of which corresponds to an oriented donor-acceptor hydrogen-bond pattern along the channel axis. Interconversion between these two conformations is an activated process that occurs through the sequential and directional reorientation of water molecules of the wire. The effect of hydrogen-bonding interactions between channel and water on proton translocation is analyzed from a comparison to the results obtained previously in a study of model nonpolar channels, in which such interactions were missing. Hydrogen-bond donation from water to the backbone carbonyl oxygen atoms lining the pore interior has a dual effect: it

  8. Molecular dynamics study of free energy profiles for organic cations in gramicidin A channels.

    PubMed Central

    Hao, Y; Pear, M R; Busath, D D

    1997-01-01

    The free energy profiles for four organic cations in right-handed single-helix gramicidin A dimers were computed by using umbrella sampling molecular dynamics with CHARMM. Ion-water column translocations were facilitated by using a novel "water-tunnel" approach. The overlapping pieces of free energy profile for adjacent windows were selected from three trajectories that differed in initial ion rotation and were aligned by the method of umbrella potential differences. Neglected long-range electrostatic energies from the bulk water and the bilayer were computed with DelPhi and added to the profile. The approach was corroborated for the formamidinium-guanidinium pair by using perturbation dynamics at axial positions 0, 6, 12, and 15 A from the channel center. The barrier to ethylammonium entry was prohibitive at 21 kcal/mol, whereas for methylammonium it was 5.5 kcal/mol, and the profile was quite flat through the channel, roughly consistent with conductance measurements. The profile for formamidinium was very similar to that of methylammonium. Guanidinium had a high entry barrier (deltaF = +8.6 kcal/mol) and a narrow deep central well (deltaF = -2.6 kcal/mol), qualitatively consistent with predictions from voltage-dependent potassium current block measurements. Its deep central well, contrasting with the flat profile for formamidinium, was verified with perturbation dynamics and was correlated with its high propensity to form hydrogen bonds with the channel at the dimer junction (not shared by the other three cations). Analysis of the ensemble average radial forces on the ions demonstrates that all four ions undergo compressive forces in the channel that are at maximum at the center of the monomer and relieved at the dimer junction, illustrating increased flexibility of the channel walls in the center of the channel. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 PMID:9336167

  9. Three-dimensional Poisson-Nernst-Planck theory studies: influence of membrane electrostatics on gramicidin A channel conductance.

    PubMed

    Cárdenas, A E; Coalson, R D; Kurnikova, M G

    2000-07-01

    A recently introduced real-space lattice methodology for solving the three-dimensional Poisson-Nernst-Planck equations is used to compute current-voltage relations for ion permeation through the gramicidin A ion channel embedded in membranes characterized by surface dipoles and/or surface charge. Comparisons to a variety of experimental results, presented herein, have proven largely successful. Strengths and weaknesses of the method are discussed.

  10. Three-dimensional Poisson-Nernst-Planck theory studies: influence of membrane electrostatics on gramicidin A channel conductance.

    PubMed Central

    Cárdenas, A E; Coalson, R D; Kurnikova, M G

    2000-01-01

    A recently introduced real-space lattice methodology for solving the three-dimensional Poisson-Nernst-Planck equations is used to compute current-voltage relations for ion permeation through the gramicidin A ion channel embedded in membranes characterized by surface dipoles and/or surface charge. Comparisons to a variety of experimental results, presented herein, have proven largely successful. Strengths and weaknesses of the method are discussed. PMID:10866939

  11. High-resolution polypeptide structure and dynamics in anisotropic environments: The gramicidin channel

    SciTech Connect

    Cross, T.A.; Lee, K.C.; Ketchem, R.R.; Hu, W.; Lazo, N.D.; Huo, S.

    1994-12-01

    To understand the details of macromolecular function, high-resolution structural and dynamic detail is essential. The polypeptide fold of the gramicidin channel has been effectively modeled for the past 20 years, yet the functional changes in conductance and channel lifetime associated with amino acid substitutions cannot be predicted. To accomplish this goal, high-resolution electrostatic modeling and the precise orientation of all dipoles are required. Furthermore, an enhanced knowledge of the complex molecular environment of this membrane-bound peptide is needed. An aqueous environment is relatively uniform and achiral. The membrane environment is very heterogenous and chiral. A knowledge of the interactions, specific and nonspecific, between peptide and lipid will aid in developing a better understanding of this environment. To accomplish this goal, it is necessary to study the peptide in an extended lipid bilayer, rather than in a vesicular or micellar form. These latter environments are likely to possess increased dynamics, increased water penetration, and distorted interactions between the polypeptide and membrane surface. To perform NMR studies on bilayer bound peptides, solid state NMR methods are required, and for specific site information, isotopic labels are incorporated using solid phase peptide synthesis.

  12. Investigation of polarization effects in the gramicidin A channel from ab initio molecular dynamics simulations.

    PubMed

    Timko, Jeff; Kuyucak, Serdar

    2012-11-28

    Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K(+) ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K(+) ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K(+) ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K(+) ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.

  13. Investigation of polarization effects in the gramicidin A channel from ab initio molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Timko, Jeff; Kuyucak, Serdar

    2012-11-01

    Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K+ ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K+ ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K+ ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K+ ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.

  14. Double-stranded helical twisted beta-sheet channels in crystals of gramicidin S grown in the presence of trifluoroacetic and hydrochloric acids.

    PubMed

    Llamas-Saiz, Antonio L; Grotenbreg, Gijsbert M; Overhand, Mark; van Raaij, Mark J

    2007-03-01

    Gramicidin S is a nonribosomally synthesized cyclic decapeptide antibiotic with twofold symmetry (Val-Orn-Leu-D-Phe-Pro)(2); a natural source is Bacillus brevis. Gramicidin S is active against Gram-positive and some Gram-negative bacteria. However, its haemolytic toxicity in humans limits its use as an antibiotic to certain topical applications. Synthetically obtained gramicidin S was crystallized from a solution containing water, methanol, trifluoroacetic acid and hydrochloric acid. The structure was solved and refined at 0.95 A resolution. The asymmetric unit contains 1.5 molecules of gramicidin S, two trifluoroacetic acid molecules and ten water molecules located and refined in 14 positions. One gramicidin S molecule has an exact twofold-symmetrical conformation; the other deviates from the molecular twofold symmetry. The cyclic peptide adopts an antiparallel beta-sheet secondary structure with two type II' beta-turns. These turns have the residues D-Phe and Pro at positions i + 1 and i + 2, respectively. In the crystals, the gramicidin S molecules line up into double-stranded helical channels that differ from those observed previously. The implications of the supramolecular structure for several models of gramicidin S conformation and assembly in the membrane are discussed.

  15. The Antimicrobial Peptide Gramicidin S Permeabilizes Phospholipid Bilayer Membranes Without Forming Discrete Ion Channels

    PubMed Central

    Ashrafuzzaman, Md.; Andersen, O. S.; McElhaney, R. N.

    2008-01-01

    We examined the permeabilization of lipid bilayers by the β-sheet, cyclic antimicrobial decapeptide gramicidin S (GS) in phospholipid bilayers formed either by mixtures of zwitterionic diphytanoylphosphatidylcholine and anionic diphytanoylphosphatidylglycerol or by single zwitterionic unsaturated phosphatidylcholines having various hydrocarbon chain lengths, with and without cholesterol. In the zwitterionic bilayers formed by the phosphatidylcholines, without or with cholesterol, the peptide concentrations and membrane potentials required to initiate membrane permeabilization vary little as function of bilayer thickness and cholesterol content. In all the systems tested, the GS-induced transient ion conductance events exhibit a broad range of conductances, which are little affected by the bilayer composition or thickness. In the zwitterionic phosphatidylcholine bilayers, the effect of GS does not depend on the polarity of the transmembrane potential; however, in bilayers formed from mixtures of phosphatidylcholines and anionic phospholipids, the polarity of the transmembrane potential becomes important, with the GS-induced conductance events being much more frequent when the GS-containing solution is positive relative to the GS-free solution. Overall, these results suggest that GS does not form discrete, well-defined, channel-like structures in phospholipid bilayers, but rather induces a wide variety of transient, differently sized defects which serve to compromise the bilayer barrier properties for small electrolytes. PMID:18809374

  16. The antimicrobial peptide gramicidin S permeabilizes phospholipid bilayer membranes without forming discrete ion channels.

    PubMed

    Ashrafuzzaman, Md; Andersen, O S; McElhaney, R N

    2008-12-01

    We examined the permeabilization of lipid bilayers by the beta-sheet, cyclic antimicrobial decapeptide gramicidin S (GS) in phospholipid bilayers formed either by mixtures of zwitterionic diphytanoylphosphatidylcholine and anionic diphytanoylphosphatidylglycerol or by single zwitterionic unsaturated phosphatidylcholines having various hydrocarbon chain lengths, with and without cholesterol. In the zwitterionic bilayers formed by the phosphatidylcholines, without or with cholesterol, the peptide concentrations and membrane potentials required to initiate membrane permeabilization vary little as function of bilayer thickness and cholesterol content. In all the systems tested, the GS-induced transient ion conductance events exhibit a broad range of conductances, which are little affected by the bilayer composition or thickness. In the zwitterionic phosphatidylcholine bilayers, the effect of GS does not depend on the polarity of the transmembrane potential; however, in bilayers formed from mixtures of phosphatidylcholines and anionic phospholipids, the polarity of the transmembrane potential becomes important, with the GS-induced conductance events being much more frequent when the GS-containing solution is positive relative to the GS-free solution. Overall, these results suggest that GS does not form discrete, well-defined, channel-like structures in phospholipid bilayers, but rather induces a wide variety of transient, differently sized defects which serve to compromise the bilayer barrier properties for small electrolytes.

  17. Structure of gramicidin A.

    PubMed Central

    Wallace, B A

    1986-01-01

    Gramicidin A, a hydrophobic linear polypeptide, forms channels in phospholipid membranes that are specific for monovalent cations. Nuclear Magnetic Resonance (NMR) spectroscopy provided the first direct physical evidence that the channel conformation in membranes is an amino terminal-to-amino terminal helical dimer, and circular dichroism (CD) spectroscopy has shown the sensitivity of its conformation to different environments and the structural consequences of ion binding. The three-dimensional structure of a gramicidin/cesium complex has been determined by x-ray diffraction of single crystals using single wavelength anomalous scattering for phasing. The left-handed double helix in this crystal form corresponds to one of the intermediates in the process of folding and insertion into membranes. Co-crystals of gramicidin and lipid that appear to have gramicidin in their membrane channel conformation have also been formed and are presently under investigation. Hence, we have used a combination of spectroscopic and diffraction techniques to examine the conformation and functionally-related structural features of gramicidin A. Images FIGURE 7 FIGURE 6 FIGURE 8 FIGURE 9 FIGURE 10 FIGURE 11 FIGURE 12 PMID:2420381

  18. Effect of gating modifier toxins on membrane thickness: implications for toxin effect on gramicidin and mechanosensitive channels.

    PubMed

    Chen, Rong; Chung, Shin-Ho

    2013-02-22

    Various gating modifier toxins partition into membranes and interfere with the gating mechanisms of biological ion channels. For example, GsMTx4 potentiates gramicidin and several bacterial mechanosensitive channels whose gating kinetics are sensitive to mechanical properties of the membrane, whereas binding of HpTx2 shifts the voltage-activity curve of the voltage-gated potassium channel Kv4.2 to the right. The detailed process by which the toxin partitions into membranes has been difficult to probe using molecular dynamics due to the limited time scale accessible. Here we develop a protocol that allows the spontaneous assembly of a polypeptide toxin into membranes in atomistic molecular dynamics simulations of tens of nanoseconds. The protocol is applied to GsMTx4 and HpTx2. Both toxins, released in water at the start of the simulation, spontaneously bind into the lipid bilayer within 50 ns, with their hydrophobic patch penetrated into the bilayer beyond the phosphate groups of the lipids. It is found that the bilayer is about 2 Å thinner upon the binding of a GsMTx4 monomer. Such a thinning effect of GsMTx4 on membranes may explain its potentiation effect on gramicidin and mechanosensitive channels.

  19. Noncontact dipole effects on channel permeation. I. Experiments with (5F-indole)Trp13 gramicidin A channels.

    PubMed

    Busath, D D; Thulin, C D; Hendershot, R W; Phillips, L R; Maughan, P; Cole, C D; Bingham, N C; Morrison, S; Baird, L C; Hendershot, R J; Cotten, M; Cross, T A

    1998-12-01

    Gramicidin A (gA), with four Trp residues per monomer, has an increased conductance compared to its Phe replacement analogs. When the dipole moment of the Trp13 side chain is increased by fluorination at indole position 5 (FgA), the conductance is expected to increase further. gA and FgA conductances to Na+, K+, and H+ were measured in planar diphytanoylphosphatidylcholine (DPhPC) or glycerylmonoolein (GMO) bilayers. In DPhPC bilayers, Na+ and K+ conductances increased upon fluorination, whereas in GMO they decreased. The low ratio in the monoglyceride bilayer was not reversed in GMO-ether bilayers, solvent-inflated or -deflated bilayers, or variable fatty acid chain monoglyceride bilayers. In both GMO and DPhPC bilayers, fluorination decreased conductance to H+ but increased conductance in the mixed solution, 1 M KCl at pH 2.0, where K+ dominates conduction. Eadie-Hofstee plot slopes suggest similar destabilization of K+ binding in both lipids. Channel lifetimes were not affected by fluorination in either lipid. These observations indicate that fluorination does not change the rotameric conformation of the side chain. The expected difference in the rate-limiting step for transport through channels in the two bilayers qualitatively explains all of the above trends.

  20. Noncontact dipole effects on channel permeation. I. Experiments with (5F-indole)Trp13 gramicidin A channels.

    PubMed Central

    Busath, D D; Thulin, C D; Hendershot, R W; Phillips, L R; Maughan, P; Cole, C D; Bingham, N C; Morrison, S; Baird, L C; Hendershot, R J; Cotten, M; Cross, T A

    1998-01-01

    Gramicidin A (gA), with four Trp residues per monomer, has an increased conductance compared to its Phe replacement analogs. When the dipole moment of the Trp13 side chain is increased by fluorination at indole position 5 (FgA), the conductance is expected to increase further. gA and FgA conductances to Na+, K+, and H+ were measured in planar diphytanoylphosphatidylcholine (DPhPC) or glycerylmonoolein (GMO) bilayers. In DPhPC bilayers, Na+ and K+ conductances increased upon fluorination, whereas in GMO they decreased. The low ratio in the monoglyceride bilayer was not reversed in GMO-ether bilayers, solvent-inflated or -deflated bilayers, or variable fatty acid chain monoglyceride bilayers. In both GMO and DPhPC bilayers, fluorination decreased conductance to H+ but increased conductance in the mixed solution, 1 M KCl at pH 2.0, where K+ dominates conduction. Eadie-Hofstee plot slopes suggest similar destabilization of K+ binding in both lipids. Channel lifetimes were not affected by fluorination in either lipid. These observations indicate that fluorination does not change the rotameric conformation of the side chain. The expected difference in the rate-limiting step for transport through channels in the two bilayers qualitatively explains all of the above trends. PMID:9826605

  1. Proton mobilities in water and in different stereoisomers of covalently linked gramicidin A channels.

    PubMed Central

    Cukierman, S

    2000-01-01

    Proton conductivities in bulk solution (lambda(H)) and single-channel proton conductances (g(H)) in two different stereoisomers of the dioxolane-linked gramicidin A channel (the SS and RR dimers) were measured in a wide range of bulk proton concentrations ([H], 0.1-8000 mM). Proton mobilities (micro(H)) in water as well as in the SS and RR dimers were calculated from the conductivity data. In the concentration range of 0.1-2000 mM, a straight line with a slope of 0.75 describes the log (g(H))-log ([H]) relationship in the SS dimer. At [H] > 2000 mM, saturation is followed by a decline in g(H). The g(H)-[H] relationship in the SS dimer is qualitatively similar to the [H] dependence of lambda(H). However, the slope of the straight line in the log(lambda(H))-log([H]) plot is 0.96, indicating that the rate-limiting step for proton conduction through the SS dimer is not the diffusion of protons in bulk solution. The significant difference between the slopes of those linear relationships accounts for the faster decline of micro(H) as a function of [H] in the SS dimer in relation to bulk solution. In the high range of [H], saturation and decline of g(H) in the SS dimer can be accounted for by the significant decrease of micro(H) in bulk solution. At any given [H], g(H) in the RR dimer is significantly smaller than in the SS. Moreover, the g(H)-[H] relationship in the RR stereoisomer is qualitatively different from that in the SS. Between 1 and 50 mM [H], g(H) can be fitted with an adsorption isotherm, suggesting the presence of a proton-binding site inside the pore (pK(a) approximately 2), which limits proton exit from the channel. At 100 mM < [H] < 3000 mM, g(H) increases linearly with [H]. The distinctive shape of the g(H)-[H] relationship in the RR dimer suggests that the channel can be occupied simultaneously by more than one proton. At higher [H], the saturation and decline of g(H) in the RR dimer reflect the properties of micro(H) in bulk solution. In the entire

  2. Conformation states of gramicidin A along the pathway to the formation of channels in model membranes determined by 2D NMR and circular dichroism spectroscopy.

    PubMed

    Abdul-Manan, N; Hinton, J F

    1994-06-07

    Gramicidin A incorporated into SDS (sodium dodecyl sulfate) micelles exists as a right-handed, N-to-N-terminal beta 6.3 helical dimer [Lomize, A. L., Orechov, V. Yu., & Arseniev, A.S. (1992) Bioorg. Khim. 18, 182-189]. In the incorporation procedure to achieve the ion channel state of gramicidin A in SDS micelles, trifluoroethanol (TFE) is used to solubilize the hydrophobic peptide before addition to the aqueous/micelle solution. The conformational transition of gramicidin A to form ion channels in SDS micelles, i.e., in TFE and 10% TFE/water, has been investigated using 2D NMR and CD spectroscopy. In neat TFE, gramicidin A was found to be monomeric and may possibly exist in an equilibrium of rapidly interconverting conformers of at least three different forms believed to be left- and/or right-handed alpha and beta 4.4 helices. It was found that the interconversion between these conformers was slowed down in 55% TFE as evident by the observation of at least three different sets of d alpha N COSY peaks although CD gave a net spectrum similar to that in neat TFE. In 10% TFE gramicidin A spontaneously forms a precipitate. The precipitated species were isolated and solubilized in dioxane where gramicidin conformers undergo very slow interconversion and could be characterized by NMR. At least seven different gramicidin A conformations were found in 10% TFE. Four of thes are the same types of double helices as previously found in ethanol (i.e., a symmetric left-handed parallel beta 5.6 double helix, an unsymmetric left-handed parallel beta 5.6 double helix, a symmetric left-handed antiparallel beta 5.6 double helix, a symmetric right-handed parallel beta 5.6 double helix); the fifth is possibly a symmetric right-handed antiparallel beta 5.6 double helix. There is also evidence for the presence of at least one form of monomeric species. Previous observation on the solvent history dependence in the ease of channel incorporation may be explained by the presence of several

  3. Investigation of Ion Channel Activities of Gramicidin A in the Presence of Ionic Liquids Using Model Cell Membranes.

    PubMed

    Ryu, Hyunil; Lee, Hwankyu; Iwata, Seigo; Choi, Sangbaek; Kim, Moon Ki; Kim, Young-Rok; Maruta, Shinsaku; Kim, Sun Min; Jeon, Tae-Joon

    2015-07-20

    Ionic liquids (ILs) are considered to be green solvents because of their non-volatility. Although ILs are relatively safe in the atmospheric environment, they may be toxic in other environments. Our previous research showed that the cytotoxicity of ILs to biological organisms is attributable to interference with cell membranes by IL insertion. However, the effects of ILs on ion channels, which play important roles in cell homeostasis, have not been comprehensively studied to date. In this work, we studied the interactions between ILs and lipid bilayer membranes with gramicidin A ion channels. We used two methods, namely electrical and fluorescence measurements of ions that permeate the membrane. The lifetimes of channels were increased by all the ILs tested in this work via stabilizing the compressed structure of the lipid bilayer and the rate of ion flux through gA channels was decreased by changing the membrane surface charge. The former effect, which increased the rate of ion flux, was dominant at high salt concentrations, whereas the latter, which decreased the rate of ion flux, was dominant at low salt concentrations. The effects of ILs increased with increasing concentration and alkyl chain length. The experimental results were further studied using molecular dynamics simulations.

  4. Investigation of Ion Channel Activities of Gramicidin A in the Presence of Ionic Liquids Using Model Cell Membranes

    PubMed Central

    Ryu, Hyunil; Lee, Hwankyu; Iwata, Seigo; Choi, Sangbaek; Ki Kim, Moon; Kim, Young-Rok; Maruta, Shinsaku; Min Kim, Sun; Jeon, Tae-Joon

    2015-01-01

    Ionic liquids (ILs) are considered to be green solvents because of their non-volatility. Although ILs are relatively safe in the atmospheric environment, they may be toxic in other environments. Our previous research showed that the cytotoxicity of ILs to biological organisms is attributable to interference with cell membranes by IL insertion. However, the effects of ILs on ion channels, which play important roles in cell homeostasis, have not been comprehensively studied to date. In this work, we studied the interactions between ILs and lipid bilayer membranes with gramicidin A ion channels. We used two methods, namely electrical and fluorescence measurements of ions that permeate the membrane. The lifetimes of channels were increased by all the ILs tested in this work via stabilizing the compressed structure of the lipid bilayer and the rate of ion flux through gA channels was decreased by changing the membrane surface charge. The former effect, which increased the rate of ion flux, was dominant at high salt concentrations, whereas the latter, which decreased the rate of ion flux, was dominant at low salt concentrations. The effects of ILs increased with increasing concentration and alkyl chain length. The experimental results were further studied using molecular dynamics simulations. PMID:26189604

  5. A semi-microscopic Monte Carlo study of permeation energetics in a gramicidin-like channel: the origin of cation selectivity.

    PubMed Central

    Dorman, V; Partenskii, M B; Jordan, P C

    1996-01-01

    The influence of a gramicidin-like channel former on ion free energy barriers is studied using Monte Carlo simulation. The model explicitly describes the ion, the water dipoles, and the peptide carbonyls; the remaining degrees of freedom, bulk electrolyte, non-polar lipid and peptide regions, and electronic (high frequency) permittivity, are treated in continuum terms. Contributions of the channel waters and peptide COs are studied both separately and collectively. We found that if constrained to their original orientations, the COs substantially increase the cationic permeation free energy; with or without water present, CO reorientation is crucial for ion-CO interaction to lower cation free energy barriers; the translocation free energy profiles for potassium-, rubidium-, and cesium-like cations exhibit no broad barriers; the lipid-bound peptide interacts more effectively with anions than cations; anionic translocation free energy profiles exhibit well defined maxima. Using experimental data to estimate transfer free energies of ions and water from bulk electrolyte to a non-polar dielectric (continuum lipid), we found reasonable ion permeation profiles; cations bind and permeate, whereas anions cannot enter the channel. Cation selectivity arises because, for ions of the same size and charge, anions bind hydration water more strongly. PMID:8770192

  6. A lattice relaxation algorithm for three-dimensional Poisson-Nernst-Planck theory with application to ion transport through the gramicidin A channel.

    PubMed Central

    Kurnikova, M G; Coalson, R D; Graf, P; Nitzan, A

    1999-01-01

    A lattice relaxation algorithm is developed to solve the Poisson-Nernst-Planck (PNP) equations for ion transport through arbitrary three-dimensional volumes. Calculations of systems characterized by simple parallel plate and cylindrical pore geometries are presented in order to calibrate the accuracy of the method. A study of ion transport through gramicidin A dimer is carried out within this PNP framework. Good agreement with experimental measurements is obtained. Strengths and weaknesses of the PNP approach are discussed. PMID:9929470

  7. A lattice relaxation algorithm for three-dimensional Poisson-Nernst-Planck theory with application to ion transport through the gramicidin A channel.

    PubMed

    Kurnikova, M G; Coalson, R D; Graf, P; Nitzan, A

    1999-02-01

    A lattice relaxation algorithm is developed to solve the Poisson-Nernst-Planck (PNP) equations for ion transport through arbitrary three-dimensional volumes. Calculations of systems characterized by simple parallel plate and cylindrical pore geometries are presented in order to calibrate the accuracy of the method. A study of ion transport through gramicidin A dimer is carried out within this PNP framework. Good agreement with experimental measurements is obtained. Strengths and weaknesses of the PNP approach are discussed.

  8. Enhanced eryptosis following gramicidin exposure.

    PubMed

    Malik, Abaid; Bissinger, Rosi; Liu, Guoxing; Liu, Guilai; Lang, Florian

    2015-04-23

    The peptide antibiotic and ionophore gramicidin has previously been shown to trigger apoptosis of nucleated cells. In analogy to apoptosis, the suicidal death of erythrocytes or eryptosis involves cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include oxidative stress, increase of cytosolic Ca2+ activity ([Ca2+]i), and ceramide. The present study explored, whether gramicidin triggers eryptosis. To this end phosphatidylserine exposure at the cell surface was estimated from annexin V binding, cell volume from forward scatter, red blood cell distribution width (RDW) from electronic particle counting, reactive oxidant species (ROS) from 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence, [Ca2+]i from Fluo3- and Fluo4 fluorescence, and ceramide abundance from binding of specific antibodies. As a result, a 24 h exposure of human erythrocytes to gramicidin significantly increased the percentage of annexin-V-binding cells (≥1 µg/mL), forward scatter (≥0.5 µg/mL) and hemolysis. Gramicidin enhanced ROS activity, [Ca2+]i and ceramide abundance at the erythrocyte surface. The stimulation of annexin-V-binding by gramicidin was significantly blunted but not abolished by removal of extracellular Ca2+. In conclusion, gramicidin stimulates phospholipid scrambling of the erythrocyte cell membrane, an effect at least partially due to induction of oxidative stress, increase of [Ca2+]i and up-regulation of ceramide abundance. Despite increase of [Ca2+]i, gramicidin increases cell volume and slightly reduces RWD.

  9. Synthesis and characterization of a new biotinylated gramicidin.

    PubMed

    Suarez, E; Emmanuelle, E D; Molle, G; Lazaro, R; Viallefont, P

    1998-09-01

    A new linear gramicidin analog bearing a biotinyl group grafted on C-terminal part was designed to study ligand-receptor interactions. The C-terminal alcohol in the native peptide was first replaced by an amino group. Then the peptide was synthesized on a polystyrene resin functionalized by the 2-chlorotrityl chloride following a biotinylation performed in solution. This new N'-biotinyl-(EDA)15-Gramicidin A was reconstituted in planar lipid bilayers and exhibited channel activities similar to those of natural gramicidin, with unitary conductance value about 30 ps in 1 M KCl. Furthermore this ionophore activity was quenched by addition of streptavidin in the surrounding medium. Our system is an outstanding tool for monitoring ligand-receptor interactions and could be used for designing a new biosensor.

  10. Gramicidin conformational studies with mixed-chain unsaturated phospholipid bilayer systems

    SciTech Connect

    Cox, K.J.; Ho, Cojen; Lombardi, J.V.; Stubbs, C.D. )

    1992-02-04

    The transition of gramicidin from a nonchannel to a channel form was investigated using mixed-chain phosphatidylcholine lipid bilayers. Gramicidin and phospholipids were codispersed, after removal of the solvents chloroform/methanol or trifluoroethanol which resulted in nonchannel and channel conformations, respectively, as confirmed using circular dichroism (CD). The fluorescence emission maxima of the nonchannel form were shifted toward shorter wavelengths by heating at 60C (for 0-12 h), which converted it to a channel form, again as confirmed by CD. The channel form did not respond to heat treatment. Heat treatment also increased the fluorescence anisotropy of the nonchannel gramicidin tryptophans. The rate of transition from the nonchannel to channel conformation was found to be faster is phosphatidylethanolamine was present in combination with phosphatidylcholine compared to phosphatidylcholine alone. Using the fluorescence anisotropy of the membrane lipid probe, 1,6-diphenyl-1,3,5-hexatriene, it was also shown that the motional properties of the surrounding lipid acyl chains differed for the channel and nonchannel gramicidin conformations. The possibility that lipids tending to favor the hexagonal phase (H{sub II}) would enhance the rate of the nonchannel to channel transition was supported by {sup 31}P NMR which revealed the presence of some H{sub II} lipids in the channel preparations. The results of this study suggest that gramicidin may serve as a useful model for similar conformational transitions in other more complex membrane proteins.

  11. Dielectric boundary force and its crucial role in gramicidin

    NASA Astrophysics Data System (ADS)

    Nadler, Boaz; Hollerbach, Uwe; Eisenberg, R. S.

    2003-08-01

    In an electrostatic problem with nonuniform geometry, a charge Q in one region induces surface charges [called dielectric boundary charges (DBC)] at boundaries between different dielectrics. These induced surface charges, in return, exert a force [called dielectric boundary force (DBF)] on the charge Q that induced them. The DBF is often overlooked. It is not present in standard continuum theories of (point) ions in or near membranes and proteins, such as Gouy-Chapman, Debye-Huckel, Poisson-Boltzmann or Poisson-Nernst- Planck. The DBF is important when a charge Q is near dielectric interfaces, for example, when ions permeate through protein channels embedded in biological membranes. In this paper, we define the DBF and calculate it explicitly for a planar dielectric wall and for a tunnel geometry resembling the ionic channel gramicidin. In general, we formulate the DBF in a form useful for continuum theories, namely, as a solution of a partial differential equation with boundary conditions. The DBF plays a crucial role in the permeation of ions through the gramicidin channel. A positive ion in the channel produces a DBF of opposite sign to that of the fixed charge force (FCF) produced by the permanent charge of the gramicidin polypeptide, and so the net force on the positive ion is reduced. A negative ion creates a DBF of the same sign as the FCF and so the net (repulsive) force on the negative ion is increased. Thus, a positive ion can permeate the channel, while a negative ion is excluded from it. In gramicidin, it is this balance between the FCF and DBF that allows only singly charged positive ions to move into and through the channel. The DBF is not directly responsible, however, for selectivity between the alkali metal ions (e.g., Li+, Na+, K+): we prove that the DBF on a mobile spherical ion is independent of the ion’s radius.

  12. Theoretical analysis of hydrophobic matching and membrane-mediated interactions in lipid bilayers containing gramicidin.

    PubMed Central

    Harroun, T A; Heller, W T; Weiss, T M; Yang, L; Huang, H W

    1999-01-01

    We present a quantitative analysis of the effects of hydrophobic matching and membrane-mediated protein-protein interactions exhibited by gramicidin embedded in dimyristoylphosphatidylcholine (DMPC) and dilauroylphosphatidylcholine (DLPC) bilayers (Harroun et al., 1999. Biophys. J. 76:937-945). Incorporating gramicidin, at 1:10 peptide/lipid molar ratio, decreases the phosphate-to-phosphate (PtP) peak separation in the DMPC bilayer from 35.3 A without gramicidin to 32.7 A. In contrast, the same molar ratio of gramicidin in DLPC increases the PtP from 30.8 A to 32.1 A. Concurrently, x-ray in-plane scattering showed that the most probable nearest-neighbor separation between gramicidin channels was 26.8 A in DLPC, but reduced to 23.3 A in DMPC. In this paper we review the idea of hydrophobic matching in which the lipid bilayer deforms to match the hydrophobic surface of the embedded proteins. We use a simple elasticity theory, including thickness compression, tension, and splay terms to describe the membrane deformation. The energy of membrane deformation is compared with the energy cost of hydrophobic mismatch. We discuss the boundary conditions between a gramicidin channel and the lipid bilayer. We used a numerical method to solve the problem of membrane deformation profile in the presence of a high density of gramicidin channels and ran computer simulations of 81 gramicidin channels to find the equilibrium distributions of the channels in the plane of the bilayer. The simulations contain four parameters: bilayer thickness compressibility 1/B, bilayer bending rigidity Kc, the channel-bilayer mismatch Do, and the slope of the interface at the lipid-protein boundary s. B, Kc, and Do were experimentally measured; the only free parameter is s. The value of s is determined by the requirement that the theory produces the experimental values of bilayer thinning by gramicidin and the shift in the peak position of the in-plane scattering due to membrane-mediated channel-channel

  13. Expression of a Cs(+)-resistant guard cell K+ channel confers Cs(+)-resistant, light-induced stomatal opening in transgenic arabidopsis.

    PubMed Central

    Ichida, A M; Pei, Z M; Baizabal-Aguirre, V M; Turner, K J; Schroeder, J I

    1997-01-01

    Inward-rectifying K+ (K+in) channels in the guard cell plasma membrane have been suggested to function as a major pathway for K+ influx into guard cells during stomatal opening. When K+in channels were blocked with external Cs+ in wild-type Arabidopsis guard cells, light-induced stomatal opening was reduced. Transgenic Arabidopsis plants were generated that expressed a mutant of the guard cell K+in channel, KAT1, which shows enhanced resistance to the Cs+ block. Stomata in these transgenic lines opened in the presence of external Cs+. Patch-clamp experiments with transgenic guard cells showed that inward K+(in) currents were blocked less by Cs+ than were K+ currents in controls. These data provide direct evidence that KAT1 functions as a plasma membrane K+ channel in vivo and that K+in channels constitute an important mechanism for light-induced stomatal opening. In addition, biophysical properties of K+in channels in guard cells indicate that components in addition to KAT1 may contribute to the formation of K+in channels in vivo. PMID:9368418

  14. TI-205 nuclear magnetic resonance determination of the thermodynamic parameters for the binding of monovalent cations to gramicidins A and C.

    PubMed Central

    Hinton, J F; Fernandez, J Q; Shungu, D C; Whaley, W L; Koeppe, R E; Millett, F S

    1988-01-01

    Thermodynamic parameters for the binding of the monovalent cations, Li+, Na+, K+, Rb+, Cs+, NH4+, TI+, and Ag+, to gramicidin A and for the binding of TI+ to gramicidin C, incorporated into lysophosphatidylcholine, have been determined using a combination of TI-205 nuclear magnetic resonance spectroscopy and competition binding. The thermodynamic parameters, enthalpy and entropy, are discussed in terms of a process involving the transfer of cations from an aqueous to amide environment. PMID:2462930

  15. Structure and dynamics of ion transport through gramicidin A.

    PubMed Central

    Mackay, D H; Berens, P H; Wilson, K R; Hagler, A T

    1984-01-01

    Molecular dynamics calculations in which all atoms were allowed to move were performed on a water-filled ion channel of the polypeptide dimer gramicidin A (approximately 600 atoms total) in the head-to-head Urry model conformation. Comparisons were made among nine simulations in which four different ions (lithium, sodium, potassium, and cesium) were each placed at two different locations in the channel as well as a reference simulation with only water present. Each simulation lasted for 5 ps and was carried out at approximately 300 K. The structure and dynamics of the peptide and interior waters were found to depend strongly on the ion tested and upon its location along the pore. Speculations on the solution and diffusion of ions in gramicidin are offered based on the observations in our model that smaller ions tended to lie off axis and to distort the positions of the carbonyl oxygens more to achieve proper solvation and that the monomer-monomer junction was more distortable than the center of the monomer. With the potential energy surface used, the unique properties of the linear chain of interior water molecules were found to be important for optimal solvation of the various ions. Strongly correlated motions persisting over 25 A among the waters in the interior single-file column were observed. PMID:6206901

  16. Sedimentation rates measurements in former channels of the upper Rhône river using Chernobyl 137Cs and 134Cs as tracers.

    PubMed

    Rostan, J C; Juget, J; Brun, A M

    1997-01-30

    Former river channels are aquatic ecosystems with a different geomorphology generated by fluvial dynamics more or less linked to the main channel. They present different ecological successions to become terrestrial ecosystems and are thus supposed to have different sedimentation rates. The aim of this paper is to assess this sedimentation rate using radioactive tracer methodology commonly used in lake studies. Chernobyl impacts, expressed in 137Cs concentration and 137Cs/134Cs ratio, were determined in sediment cores. Sites (21) were sampled in the alluvial plain of the Upper Rhône River from 1989 to 1994. The contamination presented a high spatial heterogeneity. The maximum values encountered by site ranged between 34 and 541 Bq/kg of dry matter. The method generally gave good core profiles. Sedimentation rate ranged between 0.14 and 0.70 cm/year for the former meanders and between 0.14 and 2.86 cm/year for the braided channels. The sediment accumulation rates ranged from 0.03 to 0.25 g/cm2 per year and 0.03 to 2.26 g/cm2 per year, respectively. These values are similar to those found for Lake Geneva. The importance of the former channels in relation to the main channel is enhanced by the higher contamination and radionuclides retention. The sediment accumulation rate is related to the organic carbon content in the sediment. A comparison between two former channels with different productivity showed that the the allogenous driven system presents a high organic sediment accumulation rate with a low organic content in the sediment and inversely, a low organic sediment accumulation rate with a high organic carbon content was found for the autogenous drive system.

  17. Gramicidin A: A New Mission for an Old Antibiotic

    PubMed Central

    2015-01-01

    Gramicidin A (GA) is a channel-forming ionophore that renders biological membranes permeable to specific cations which disrupts cellular ionic homeostasis. It is a well-known antibiotic, however it’s potential as a therapeutic agent for cancer has not been widely evaluated. In two recently published studies, we showed that GA treatment is toxic to cell lines and tumor xenografts derived from renal cell carcinoma (RCC), a devastating disease that is highly resistant to conventional therapy. GA was found to possess the qualities of both a cytotoxic drug and a targeted angiogenesis inhibitor, and this combination significantly compromised RCC growth in vitro and in vivo. In this review, we summarize our recent research on GA, discuss the possible mechanisms whereby it exerts its anti-tumor effects, and share our perspectives on the future opportunities and challenges to the use of GA as a new anticancer agent.

  18. Phase equilibria and molecular packing in the N,N-dimethyldodecylamine oxide/gramicidin D/water system studied by 2H nuclear magnetic resonance spectroscopy.

    PubMed Central

    Orädd, G; Lindblom, G; Arvidson, G; Gunnarsson, K

    1995-01-01

    A partial phase diagram of the system N,N-dimethyldodecylamine oxide (DDAO)/water/gramicidin D was determined by 2H-NMR. Both 2H2O and perdeuterated DDAO (DDAO-d31) were studied by solid state NMR techniques. Addition of gramicidin D to the micellar (L1), normal hexagonal (HI) and cubic (I) phases of DDAO induces phase separations, giving two-phase regions, which all contain a lamellar (L alpha) phase. The L alpha phase containing gramicidin is characterized by larger order parameters for DDAO-d31 compared with the corresponding order parameters in the L alpha and HI phases of DDAO-d31/H2O. The L alpha phase may stay in equilibrium with any other phase in the phase diagram. The DDAO exchange between the coexisting phases is slow on the NMR timescale, which is why the recorded NMR spectrum consists of superimposed spectra from the different phases occurring in the sample. Gramicidin D can be solubilized in appreciable quantities only in the lamellar phase of DDAO-d31. Increasing amounts of gramicidin in the liquid crystalline phases result in a continuous increase in the molecular ordering up to about 5 mol% gramicidin, where a plateau is reached. This is consistent with a recent theoretical model describing the influence on the ordering of lipids by a membrane protein with larger hydrophobic thickness than the lipid bilayer. The solvent used for dissolving gramicidin at the incorporation of the peptide in the lipid aggregates has no effect on the 2H-NMR lineshapes of DDAO-d31. It is concluded that gramicidin is solubilized in the L alpha phase and that it always adopts the channel conformation independent of a particular solvent. The channel conformation is also supported by CD studies. In some of the samples, macroscopic orientation of the lipid aggregates is observed. It is concluded that DDAO-d31 in the binary system favors an orientation with the long axis of the hydrocarbon chain perpendicular to the magnetic field, whereas when gramicidin D is present the

  19. Quantum efficiency of opaque CsI photocathodes with channel electron multiplier arrays in the extreme and far ultraviolet

    NASA Technical Reports Server (NTRS)

    Martin, C.; Bowyer, S.

    1982-01-01

    The arrays are overcoated with a CsI photocathode in the VUV. The measurements are part of the development program for the Extreme Ultraviolet Explorer. Monochromatic light from a hollow cathode discharge source passing through a McPherson grazing incidence monochromator is used to illuminate the CsI photocathode. The beam diameter is kept small (approximately 2 mm) to confine it within the individual thickness strips. A bias grid is used to produce a 50-V/mm electric field to guarantee collection of all photoelectrons emitted by the CEMA (channel electron multiplier array) webbing. The CEMAs are operated with a gain of 2-3 x 10 to the 6th and are moderately saturated. A channeltron secondary transfer standard is used to determine the absolute QE in the EUV, whereas an NBS calibrated windowed photodiode is used to measure the FUV absolute QE. It is noted that the CsI gives a factor of 3 increase in the QE in the EUV and a factor of 50-5000 in the FUV.

  20. Quantum efficiency of opaque CsI photocathodes with channel electron multiplier arrays in the extreme and far ultraviolet

    NASA Technical Reports Server (NTRS)

    Martin, C.; Bowyer, S.

    1982-01-01

    The arrays are overcoated with a CsI photocathode in the VUV. The measurements are part of the development program for the Extreme Ultraviolet Explorer. Monochromatic light from a hollow cathode discharge source passing through a McPherson grazing incidence monochromator is used to illuminate the CsI photocathode. The beam diameter is kept small (approximately 2 mm) to confine it within the individual thickness strips. A bias grid is used to produce a 50-V/mm electric field to guarantee collection of all photoelectrons emitted by the CEMA (channel electron multiplier array) webbing. The CEMAs are operated with a gain of 2-3 x 10 to the 6th and are moderately saturated. A channeltron secondary transfer standard is used to determine the absolute QE in the EUV, whereas an NBS calibrated windowed photodiode is used to measure the FUV absolute QE. It is noted that the CsI gives a factor of 3 increase in the QE in the EUV and a factor of 50-5000 in the FUV.

  1. Electronic control of H+ current in a bioprotonic device with Gramicidin A and Alamethicin

    PubMed Central

    Hemmatian, Zahra; Keene, Scott; Josberger, Erik; Miyake, Takeo; Arboleda, Carina; Soto-Rodríguez, Jessica; Baneyx, François; Rolandi, Marco

    2016-01-01

    In biological systems, intercellular communication is mediated by membrane proteins and ion channels that regulate traffic of ions and small molecules across cell membranes. A bioelectronic device with ion channels that control ionic flow across a supported lipid bilayer (SLB) should therefore be ideal for interfacing with biological systems. Here, we demonstrate a biotic–abiotic bioprotonic device with Pd contacts that regulates proton (H+) flow across an SLB incorporating the ion channels Gramicidin A (gA) and Alamethicin (ALM). We model the device characteristics using the Goldman–Hodgkin–Katz (GHK) solution to the Nernst–Planck equation for transport across the membrane. We derive the permeability for an SLB integrating gA and ALM and demonstrate pH control as a function of applied voltage and membrane permeability. This work opens the door to integrating more complex H+ channels at the Pd contact interface to produce responsive biotic–abiotic devices with increased functionality. PMID:27713411

  2. Electronic control of H+ current in a bioprotonic device with Gramicidin A and Alamethicin

    NASA Astrophysics Data System (ADS)

    Hemmatian, Zahra; Keene, Scott; Josberger, Erik; Miyake, Takeo; Arboleda, Carina; Soto-Rodríguez, Jessica; Baneyx, François; Rolandi, Marco

    2016-10-01

    In biological systems, intercellular communication is mediated by membrane proteins and ion channels that regulate traffic of ions and small molecules across cell membranes. A bioelectronic device with ion channels that control ionic flow across a supported lipid bilayer (SLB) should therefore be ideal for interfacing with biological systems. Here, we demonstrate a biotic-abiotic bioprotonic device with Pd contacts that regulates proton (H+) flow across an SLB incorporating the ion channels Gramicidin A (gA) and Alamethicin (ALM). We model the device characteristics using the Goldman-Hodgkin-Katz (GHK) solution to the Nernst-Planck equation for transport across the membrane. We derive the permeability for an SLB integrating gA and ALM and demonstrate pH control as a function of applied voltage and membrane permeability. This work opens the door to integrating more complex H+ channels at the Pd contact interface to produce responsive biotic-abiotic devices with increased functionality.

  3. Heterodimer formation and crystal nucleation of gramicidin D.

    PubMed Central

    Burkhart, B M; Gassman, R M; Langs, D A; Pangborn, W A; Duax, W L

    1998-01-01

    The linear pentadecapeptide antibiotic gramicidin D is a heterogeneous mixture of six components. Precise refinements of three-dimensional structures of naturally occurring gramicidin D in crystals obtained from methanol, ethanol, and n-propanol demonstrate the unexpected presence of stable left-handed antiparallel double-helical heterodimers that vary with the crystallization solvent. The side chains of Trp residues in the three structures exhibit sequence-specific patterns of conformational preference. Tyr substitution for Trp at position 11 appears to favor beta ribbon formation and stabilization of the antiparallel double helix that acts as a template for gramicidin folding and nucleation of different crystal forms. The fact that a minor component in a heterogeneous mixture influences aggregation and crystal nucleation has potential applications to other systems in which anomalous behavior is exhibited by aggregation of apparently homogeneous materials, such as the enigmatic behavior of prion proteins. PMID:9788907

  4. Effect of sub-cooling channel in an ITER 13 T-40 kA Nb 3Sn coil (CS insert) on stability

    NASA Astrophysics Data System (ADS)

    Inaguchi, T.; Hasegawa, M.

    2005-04-01

    This paper analyzes the stability of a center solenoid (CS) insert and describes the effects a sub-cooling channel (central channel) at the center cross section of a cable-in-conduit (CIC) conductor has on stability. First, the calculation results are compared with test results in a center solenoid (CS) insert, and the effectiveness of the calculation is verified. Next, the effects of central channel on stability are examined by comparing the energy margin between a case in which perforations exist between the bundle region and the central channel, such as a CS insert, to allow the fluid to migrate and a case in which perforations are blocked to prevent the coolant from migrating. The following points are clarified: (1) if most of the thermal disturbance is applied to the jacket, the case with perforations is more stable than the case without perforations, thus the central channel contributes to the improvement of stability; (2) if thermal disturbance is applied only to the cable and is produced for about 20 ms, the central channel hardly has any effect on the stability. If the thermal disturbance is produced for about 400 ms, the central channel contributes to the stability; (3) the effect of cooling the bundle region by means of heat conduction through the central channel wall is very small, and it hardly affects the stability at all.

  5. Gramicidin-perforated patch revealed depolarizing effect of GABA in cultured frog melanotrophs

    PubMed Central

    Le Foll, Frank; Castel, Hélène; Soriani, Olivier; Vaudry, Hubert; Cazin, Lionel

    1998-01-01

    In frog pituitary melanotrophs, GABA induces a transient stimulation followed by prolonged inhibition of hormone secretion. This biphasic effect is inconsistent with the elevation of cytosolic calcium and the inhibition of electrical activity also provoked by GABA in single melanotrophs. In the present study, standard patch-clamp configurations and gramicidin-perforated patches were used to investigate the physiological GABAA receptor-mediated response and intracellular chloride concentration ([Cl−]i) in cultured frog melanotrophs. In the gramicidin-perforated patch configuration, 1 μM GABA caused a depolarization associated with an action potential discharge and a slight fall of membrane resistance. In contrast, at a higher concentration (10 μm) GABA elicited a depolarization accompanied by a transient volley of action potentials, followed by a sustained inhibitory plateau and a marked fall of membrane resistance. Isoguvacine mimicked the GABA-evoked responses, indicating a mediation by GABAA receptors. In gramicidin-perforated cells, the depolarizing excitatory effect of 1 μm GABA was converted into a depolarizing inhibitory action when 0.4 μm allopregnanolone was added to the bath solution. After gaining the whole-cell configuration, the amplitude and/or direction of the GABA-evoked current (IGABA) rapidly changed before stabilizing. After stabilization, the reversal potential of IGABA followed the values predicted by the Nernst equation for chloride ions when [Cl−]i was varied. In gramicidin-perforated cells, the steady-state I–V relationships of 10 μm GABA- or isoguvacine-evoked currents yielded reversal potentials of −37.5 ± 1.6 (n= 17) and −38.6 ± 2.0 mV (n= 8), respectively. These values were close to those obtained by using a voltage-ramp protocol in the presence of Na+, K+ and Ca2+ channel blockers. The current evoked by 1 μm GABA also reversed at these potentials. We conclude that, in frog pituitary melanotrophs, chloride is the

  6. High-speed magic angle spinning solid-state 1H nuclear magnetic resonance study of the conformation of gramicidin A in lipid bilayers.

    PubMed Central

    Bouchard, M; Davis, J H; Auger, M

    1995-01-01

    One- and two-dimensional solid-state 1H nuclear magnetic resonance spectra of gramicidin A incorporated in a dimyristoylphosphatidylcholine membrane have been obtained with use of high-speed magic angle spinning. By rotating the sample at 13 kHz, it is possible to observe signals in the 1H spectra between 6.0 and 9.0 ppm attributable to the aromatic protons of the tryptophan residues and the formyl group proton of gramicidin A. Two-dimensional solid-state COSY spectra provided information for the peak assignments. Moreover, changes in the 1H spectra have been observed as a function of the co-solubilization solvent initially used to prepare the samples and therefore as a function of the conformation adopted by gramicidin A. Three organic solvents have been used: trifluoroethanol, a mixture of methanol/chloroform (1:1 v/v), and ethanol. The conformational interconversion of gramicidin A from the double helix conformation to the channel structure for the sample prepared from ethanol was confirmed by following the time evolution of the proton spectra. PMID:8580336

  7. Residues beyond the selectivity filter of the K+ channel kir2.1 regulate permeation and block by external Rb+ and Cs+.

    PubMed

    Thompson, G A; Leyland, M L; Ashmole, I; Sutcliffe, M J; Stanfield, P R

    2000-07-15

    1. Kir2.1 channels are blocked by Rb+ and Cs+ in a voltage-dependent manner, characteristic of many inward rectifier K+ channels. Mutation of Ser165 in the transmembrane domain M2 to Leu (S165L) abolished Rb+ blockage and lowered Cs+ blocking affinity. At negative voltages Rb+ carried large inward currents. 2. A model of the Kir2.1 channel, built by homology with the structure of the Streptomyces lividans K+ channel KcsA, suggested the existence of an intersubunit hydrogen bond between Ser165 and Thr141 in the channel pore-forming P-region that helps stabilise the structure of this region. However, mutations of Thr141 and Ser165 did not produce effects consistent with a hydrogen bond between these residues being essential for blockage. 3. An alternative alignment between the M2 regions of Kir2.1 and KcsA suggested that Ser165 is itself a pore-lining residue, more directly affecting blockage. We were able to replace Ser165 with a variety of polar and non-polar residues, consistent with this residue being pore lining. Some of these changes affected channel blockage. 4. We tested the hypothesis that Asp172 - a residue implicated in channel gating by polyamines - formed an additional selectivity filter by using the triple mutant T141A/S165L/D172N. Large Rb+ and Cs+ currents were measured in this mutant. 5. We propose that both Thr141 and Ser165 are likely to provide binding sites for monovalent blocking cations in wild-type channels. These residues lie beyond the carbonyl oxygen tunnel thought to form the channel selectivity filter, which the blocking cations must therefore traverse.

  8. Anomalous volume change of gramicidin A in ethanol solutions

    NASA Technical Reports Server (NTRS)

    Derechin, M.; Hayashi, D. M.; Jordan, B. E.

    1975-01-01

    Results of studies aimed at clarifying the failure of gramicidin A (GA) to sediment in early experiments are analyzed. In the present work, no sedimentation was observed in pure pentanol or ethanol, while normal sedimentation was observed in ethanol-water mixtures. It is concluded that GA exists in two conformations that differ in volume. Since the apparent specific volume in absolute ethanol sinks to its lowest values on increasing concentration, the GA molecule probably unfolds completely in conditions favorable for dimerization.

  9. CNS sites activated by renal pelvic epithelial sodium channels (ENaCs) in response to hypertonic saline in awake rats.

    PubMed

    Goodwill, Vanessa S; Terrill, Christopher; Hopewood, Ian; Loewy, Arthur D; Knuepfer, Mark M

    2017-05-01

    In some patients, renal nerve denervation has been reported to be an effective treatment for essential hypertension. Considerable evidence suggests that afferent renal nerves (ARN) and sodium balance play important roles in the development and maintenance of high blood pressure. ARN are sensitive to sodium concentrations in the renal pelvis. To better understand the role of ARN, we infused isotonic or hypertonic NaCl (308 or 500mOsm) into the left renal pelvis of conscious rats for two 2hours while recording arterial pressure and heart rate. Subsequently, brain tissue was analyzed for immunohistochemical detection of the protein Fos, a marker for neuronal activation. Fos-immunoreactive neurons were identified in numerous sites in the forebrain and brainstem. These areas included the nucleus tractus solitarius (NTS), the lateral parabrachial nucleus, the paraventricular nucleus of the hypothalamus (PVH) and the supraoptic nucleus (SON). The most effective stimulus was 500mOsm NaCl. Activation of these sites was attenuated or prevented by administration of benzamil (1μM) or amiloride (10μM) into the renal pelvis concomitantly with hypertonic saline. In anesthetized rats, infusion of hypertonic saline but not isotonic saline into the renal pelvis elevated ARN activity and this increase was attenuated by simultaneous infusion of benzamil or amiloride. We propose that renal pelvic epithelial sodium channels (ENaCs) play a role in activation of ARN and, via central visceral afferent circuits, this system modulates fluid volume and peripheral blood pressure. These pathways may contribute to the development of hypertension.

  10. Gramicidin S production by Bacillus brevis in simulated microgravity

    NASA Technical Reports Server (NTRS)

    Fang, A.; Pierson, D. L.; Mishra, S. K.; Koenig, D. W.; Demain, A. L.

    1997-01-01

    In a continuing study of microbial secondary metabolism in simulated microgravity, we have examined gramicidin S (GS) production by Bacillus brevis strain Nagano in NASA High Aspect Rotating Vessels (HARVs), which are designed to simulate some aspects of microgravity. Growth and GS production were found to occur under simulated microgravity. When performance under simulated microgravity was compared with that under normal gravity conditions in the bioreactors, GS production was found to be unaffected by simulated microgravity. The repressive effect of glycerol in flask fermentations was not observed in the HARV. Thus the negative effect of glycerol on specific GS formation is dependent on shear and/or vessel geometry, not gravity.

  11. Gramicidin S production by Bacillus brevis in simulated microgravity

    NASA Technical Reports Server (NTRS)

    Fang, A.; Pierson, D. L.; Mishra, S. K.; Koenig, D. W.; Demain, A. L.

    1997-01-01

    In a continuing study of microbial secondary metabolism in simulated microgravity, we have examined gramicidin S (GS) production by Bacillus brevis strain Nagano in NASA High Aspect Rotating Vessels (HARVs), which are designed to simulate some aspects of microgravity. Growth and GS production were found to occur under simulated microgravity. When performance under simulated microgravity was compared with that under normal gravity conditions in the bioreactors, GS production was found to be unaffected by simulated microgravity. The repressive effect of glycerol in flask fermentations was not observed in the HARV. Thus the negative effect of glycerol on specific GS formation is dependent on shear and/or vessel geometry, not gravity.

  12. Novel gramicidin formulations in cationic lipid as broad-spectrum microbicidal agents

    PubMed Central

    Ragioto, Danielle AMT; Carrasco, Letícia DM; Carmona-Ribeiro, Ana M

    2014-01-01

    Dioctadecyldimethylammonium bromide (DODAB) is an antimicrobial lipid that can be dispersed as large closed bilayers (LV) or bilayer disks (BF). Gramicidin (Gr) is an antimicrobial peptide assembling as channels in membranes and increasing their permeability towards cations. In mammalian cells, DODAB and Gr have the drawbacks of Gram-positive resistance and high toxicity, respectively. In this study, DODAB bilayers incorporating Gr showed good antimicrobial activity and low toxicity. Techniques employed were spectroscopy, photon correlation spectroscopy for sizing and evaluation of the surface potential at the shear plane, turbidimetric detection of dissipation of osmotic gradients in LV/Gr, determination of bacterial cell lysis, and counting of colony-forming units. There was quantitative incorporation of Gr and development of functional channels in LV. Gr increased the bilayer charge density in LV but did not affect the BF charge density, with localization of Gr at the BF borders. DODAB/Gr formulations substantially reduce Gr toxicity against eukaryotic cells and advantageously broaden the antimicrobial activity spectrum, effectively killing Escherichia coli and Staphylococcus aureus bacteria with occurrence of cell lysis. PMID:25061295

  13. Diffusion constant of K+ inside Gramicidin A: A comparative study of four computational methods

    PubMed Central

    Mamonov, Artem B.; Kurnikova, Maria G.; Coalson, Rob D.

    2007-01-01

    The local diffusion constant of K+ inside the Gramicidin A (GA) channel has been calculated using four computational methods based on molecular dynamics (MD) simulations, specifically: Mean Square Displacement (MSD), Velocity Autocorrelation Function (VACF), Second Fluctuation Dissipation Theorem (SFDT) and analysis of the Generalized Langevin Equation for a Harmonic Oscillator (GLE-HO). All methods were first tested and compared for K+ in bulk water—all predicted the correct diffusion constant. Inside GA, MSD and VACF methods were found to be unreliable because they are biased by the systematic force exerted by the membrane-channel system on the ion. SFDT and GLE-HO techniques properly unbias the influence of the systematic force on the diffusion properties and predicted a similar diffusion constant of K+ inside GA, namely, ca. 10 times smaller than in the bulk. It was found that both SFDT and GLE-HO methods require extensive MD sampling on the order of tens of nanoseconds to predict a reliable diffusion constant of K+ inside GA. PMID:16797116

  14. Gramicidin D enhances the antibacterial activity of fluoride.

    PubMed

    Nelson, James W; Zhou, Zhiyuan; Breaker, Ronald R

    2014-07-01

    Fluoride is a toxic anion found in many natural environments. One of the major bacterial defenses against fluoride is the cell envelope, which limits passage of the membrane-impermeant fluoride anion. Accordingly, compounds that enhance the permeability of bacterial membranes to fluoride should also enhance fluoride toxicity. In this study, we demonstrate that the pore-forming antibiotic gramicidin D increases fluoride uptake in Bacillus subtilis and that the antibacterial activity of this compound is potentiated by fluoride. Polymyxin B, another membrane-targeting antibiotic with a different mechanism of action, shows no such improvement. These results, along with previous findings, indicate that certain compounds that destabilize bacterial cell envelopes can enhance the toxicity of fluoride.

  15. The antimicrobial activity of gramicidin A is associated with hydroxyl radical formation.

    PubMed

    Liou, Je-Wen; Hung, Yu-Jiun; Yang, Chin-Hao; Chen, Yi-Cheng

    2015-01-01

    Gramicidin A is an antimicrobial peptide that destroys gram-positive bacteria. The bactericidal mechanism of antimicrobial peptides has been linked to membrane permeation and metabolism disruption as well as interruption of DNA and protein functions. However, the exact bacterial killing mechanism of gramicidin A is not clearly understood. In the present study, we examined the antimicrobial activity of gramicidin A on Staphylococcus aureus using biochemical and biophysical methods, including hydroxyl radical and NAD+/NADH cycling assays, atomic force microscopy, and Fourier transform infrared spectroscopy. Gramicidin A induced membrane permeabilization and changed the composition of the membrane. The morphology of Staphylococcus aureus during gramicidin A destruction was divided into four stages: pore formation, water permeability, bacterial flattening, and lysis. Changes in membrane composition included the destruction of membrane lipids, proteins, and carbohydrates. Most interestingly, we demonstrated that gramicidin A not only caused membrane permeabilization but also induced the formation of hydroxyl radicals, which are a possible end product of the transient depletion of NADH from the tricarboxylic acid cycle. The latter may be the main cause of complete Staphylococcus aureus killing. This new finding may provide insight into the underlying bactericidal mechanism of gA.

  16. The Antimicrobial Activity of Gramicidin A Is Associated with Hydroxyl Radical Formation

    PubMed Central

    Liou, Je-Wen; Hung, Yu-Jiun; Yang, Chin-Hao; Chen, Yi-Cheng

    2015-01-01

    Gramicidin A is an antimicrobial peptide that destroys gram-positive bacteria. The bactericidal mechanism of antimicrobial peptides has been linked to membrane permeation and metabolism disruption as well as interruption of DNA and protein functions. However, the exact bacterial killing mechanism of gramicidin A is not clearly understood. In the present study, we examined the antimicrobial activity of gramicidin A on Staphylococcus aureus using biochemical and biophysical methods, including hydroxyl radical and NAD+/NADH cycling assays, atomic force microscopy, and Fourier transform infrared spectroscopy. Gramicidin A induced membrane permeabilization and changed the composition of the membrane. The morphology of Staphylococcus aureus during gramicidin A destruction was divided into four stages: pore formation, water permeability, bacterial flattening, and lysis. Changes in membrane composition included the destruction of membrane lipids, proteins, and carbohydrates. Most interestingly, we demonstrated that gramicidin A not only caused membrane permeabilization but also induced the formation of hydroxyl radicals, which are a possible end product of the transient depletion of NADH from the tricarboxylic acid cycle. The latter may be the main cause of complete Staphylococcus aureus killing. This new finding may provide insight into the underlying bactericidal mechanism of gA. PMID:25622083

  17. Computational Investigation of the Effect of Lipid Membranes on Ion Permeation in Gramicidin A

    PubMed Central

    Setiadi, Jeffry; Kuyucak, Serdar

    2016-01-01

    Membrane proteins are embedded in a lipid bilayer and interact with the lipid molecules in subtle ways. This can be studied experimentally by examining the effect of different lipid bilayers on the function of membrane proteins. Understanding the causes of the functional effects of lipids is difficult to dissect experimentally but more amenable to a computational approach. Here we perform molecular dynamics simulations and free energy calculations to study the effect of two lipid types (POPC and NODS) on the conductance of the gramicidin A (gA) channel. A larger energy barrier is found for the K+ potential of mean force in gA embedded in POPC compared to that in NODS, which is consistent with the enhanced experimental conductance of cations in gA embedded in NODS. Further analysis of the contributions to the potential energy of K+ reveals that gA and water molecules in gA make similar contributions in both bilayers but there are significant differences between the two bilayers when the lipid molecules and interfacial waters are considered. It is shown that the stronger dipole moments of the POPC head groups create a thicker layer of interfacial waters with better orientation, which ultimately is responsible for the larger energy barrier in the K+ PMF in POPC. PMID:26999229

  18. Sub-nanosecond multi-channel time-to-digital converter for the 2-D position-sensitive neutron detectors at TriCS and AMOR

    NASA Astrophysics Data System (ADS)

    Buehler, Ch.; Greuter, U.; Frey, G.; Zaharko, O.; Koennecke, M.; Schefer, J.; Rasmussen, P.; Schaniel, D.; Clemens, D.; Gabriel, A.; Felsche, J.; Schlumpf, N.

    We have developed an ultra-fast multi-channel time-to-digital converter (mC-TDC). The mC-TDC electronics is used to read out the delay-line-based 2-D detectors of the neutron diffractometer and reflectometer TriCS and AMOR, respectively. The high time resolution of the mC-TDC ( 145 ps) allows the conversion of the position-sensitive detector signals into accurate 2-D scattering coordinates ( 2×2 mm2). The mC-TDC also generates low-jitter time-of-flight signals and incorporates an efficient two-stage pileup-rejection mechanism. Neutron rates exceeding 100000cps can be processed.

  19. Ionic channels in Langmuir-Blodgett films imaged by a scanning tunneling microscope.

    PubMed Central

    Kolomytkin, O V; Golubok, A O; Davydov, D N; Timofeev, V A; Vinogradova, S A; Tipisev SYa

    1991-01-01

    The molecular structure of channels formed by gramicidin A in a lipid membrane was imaged by a scanning tunneling microscope operating in air. The mono- and bimolecular films of lipid with gramicidin A were deposited onto a highly oriented pyrolitic graphite substrate by the Langmuir-Blodgett technique. It has been shown that under high concentration gramicidin A molecules can form in lipid films a quasi-regular, densely packed structure. Single gramicidin A molecules were imaged for the first time as well. The cavity of 0.4 +/- 0.05 nm in halfwidth was found on the scanning tunneling microscopy image of the gramicidin A molecule. The results of direct observation obtained by means of scanning tunneling microscope are in good agreement with the known molecular model of gramicidin A. It was shown that gramicidin A molecules can exist in a lipid monolayer as individual molecules or combined into clusters. The results demonstrate that scanning tunneling microscope can be used for high spatial resolution study of ionic channel structure. Images FIGURE 1 FIGURE 2 FIGURE 4 FIGURE 5 PMID:1712239

  20. Experimental evidence for hydrophobic matching and membrane-mediated interactions in lipid bilayers containing gramicidin.

    PubMed Central

    Harroun, T A; Heller, W T; Weiss, T M; Yang, L; Huang, H W

    1999-01-01

    Hydrophobic matching, in which transmembrane proteins cause the surrounding lipid bilayer to adjust its hydrocarbon thickness to match the length of the hydrophobic surface of the protein, is a commonly accepted idea in membrane biophysics. To test this idea, gramicidin (gD) was embedded in 1, 2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) and 1, 2-myristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers at the peptide/lipid molar ratio of 1:10. Circular dichroism (CD) was measured to ensure that the gramicidin was in the beta6.3 helix form. The bilayer thickness (the phosphate-to-phosphate distance, or PtP) was measured by x-ray lamellar diffraction. In the Lalpha phase near full hydration, PtP is 30.8 A for pure DLPC, 32.1 A for the DLPC/gD mixture, 35.3 A for pure DMPC, and 32.7 A for the DMPC/gD mixture. Gramicidin apparently stretches DLPC and thins DMPC toward a common thickness as expected by hydrophobic matching. Concurrently, gramicidin-gramicidin correlations were measured by x-ray in-plane scattering. In the fluid phase, the gramicidin-gramicidin nearest-neighbor separation is 26.8 A in DLPC, but shortens to 23.3 A in DMPC. These experiments confirm the conjecture that when proteins are embedded in a membrane, hydrophobic matching creates a strain field in the lipid bilayer that in turn gives rise to a membrane-mediated attractive potential between proteins. PMID:9929495

  1. Influence of Hydrophobic Mismatch on Structures and Dynamics of Gramicidin A and Lipid Bilayers

    PubMed Central

    Kim, Taehoon; Lee, Kyu Il; Morris, Phillip; Pastor, Richard W.; Andersen, Olaf S.; Im, Wonpil

    2012-01-01

    Gramicidin A (gA) is a 15-amino-acid antibiotic peptide with an alternating L-D sequence, which forms (dimeric) bilayer-spanning, monovalent cation channels in biological membranes and synthetic bilayers. We performed molecular dynamics simulations of gA dimers and monomers in all-atom, explicit dilauroylphosphatidylcholine (DLPC), dimyristoylphosphatidylcholine (DMPC), dioleoylphosphatidylcholine (DOPC), and 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayers. The variation in acyl chain length among these different phospholipids provides a way to alter gA-bilayer interactions by varying the bilayer hydrophobic thickness, and to determine the influence of hydrophobic mismatch on the structure and dynamics of both gA channels (and monomeric subunits) and the host bilayers. The simulations show that the channel structure varied little with changes in hydrophobic mismatch, and that the lipid bilayer adapts to the bilayer-spanning channel to minimize the exposure of hydrophobic residues. The bilayer thickness, however, did not vary monotonically as a function of radial distance from the channel. In all simulations, there was an initial decrease in thickness within 4–5 Å from the channel, which was followed by an increase in DOPC and POPC or a further decrease in DLPC and DMPC bilayers. The bilayer thickness varied little in the monomer simulations—except one of three independent simulations for DMPC and all three DLPC simulations, where the bilayer thinned to allow a single subunit to form a bilayer-spanning water-permeable pore. The radial dependence of local lipid area and bilayer compressibility is also nonmonotonic in the first shell around gA dimers due to gA-phospholipid interactions and the hydrophobic mismatch. Order parameters, acyl chain dynamics, and diffusion constants also differ between the lipids in the first shell and the bulk. The lipid behaviors in the first shell around gA dimers are more complex than predicted from a simple mismatch

  2. Structure, toxicity and antibiotic activity of gramicidin S and derivatives.

    PubMed

    Swierstra, J; Kapoerchan, V; Knijnenburg, A; van Belkum, A; Overhand, M

    2016-05-01

    Development of new antibiotics is declining whereas antibiotic resistance is rising, heralding a post-antibiotic era. Antimicrobial peptides such as gramicidin S (GS), exclusively topically used due to its hemolytic side-effect, could still be interesting as therapeutic compounds. By modifying the amino-acid composition of GS, we synthesized GS analogues. We now show that derivative VK7 has a lower MIC (7.8-31.2 μg/ml, median 15.6 μg/ml) against strains of multi-drug resistant (MDR) Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa than GS has (3.9-62.5 μg/ml, median 31.3 μg/ml). Low MICs for both VK7 and GS were observed for Staphylococcus aureus and Enterococcus faecium. VK7 showed reduced haemolysis and less lactate dehydrogenase release. All compounds were fully bactericidal at MIC values. Modification of GS enables production of novel derivatives potentially useful for systemic treatment of human infections.

  3. Hydrophobic mismatch in gramicidin A prime /lecithin systems

    SciTech Connect

    Watnick, P.I.; Chan, S.I. ); Dea, P. )

    1990-07-03

    Gramicidin A{prime} (GA{prime}) has been added to three lipid systems of varying hydrophobic thickness: dimyristoyllecithin (DML), dipalmitoyllecithin (DPL), and distearoyllecithin (DSL). The similarity in length between the hydrophobic portion of GA{prime} and the hydrocarbon chains of the lipid bilayers has been studied by using {sup 31}P and {sup 2}H NMR. Hydrophobic mismatch has been found to be most severe in the DML bilayer system and minimal in the case of DSL. In addition, the effects of hydrophobic mismatch on the cooperative properties of the bilayer have been obtained from {sup 2}H NMR relaxation measurements. The results indicate that incorporation of the peptide into the bilayer disrupts the cooperative director fluctuations characteristic of pure multilamellar lipid dispersions. Finally, the GA{prime}/lecithin ratio at which the well-known transformation from bilayer to reverse hexagonal (H{sub II}) phase occurs is shown to depend on the acyl chain length of the phospholipid. A rationale is proposed for this chain length dependence.

  4. A combination of curcumin with either gramicidin or ouabain selectively kills cells that express the multidrug resistance-linked ABCG2 transporter.

    PubMed

    Rao, Divya K; Liu, Haiyan; Ambudkar, Suresh V; Mayer, Michael

    2014-11-07

    This paper introduces a strategy to kill selectively multidrug-resistant cells that express the ABCG2 transporter (also called breast cancer resistance protein, or BCRP). The approach is based on specific stimulation of ATP hydrolysis by ABCG2 transporters with subtoxic doses of curcumin combined with stimulation of ATP hydrolysis by Na(+),K(+)-ATPase with subtoxic doses of gramicidin A or ouabain. After 72 h of incubation with the drug combinations, the resulting overconsumption of ATP by both pathways inhibits the efflux activity of ABCG2 transporters, leads to depletion of intracellular ATP levels below the viability threshold, and kills resistant cells selectively over cells that lack ABCG2 transporters. This strategy, which was also tested on a clinically relevant human breast adenocarcinoma cell line (MCF-7/FLV1), exploits the overexpression of ABCG2 transporters and induces caspase-dependent apoptotic cell death selectively in resistant cells. This work thus introduces a novel strategy to exploit collateral sensitivity (CS) with a combination of two clinically used compounds that individually do not exert CS. Collectively, this work expands the current knowledge on ABCG2-mediated CS and provides a potential strategy for discovery of CS drugs against drug-resistant cancer cells. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

  5. Aggregation of gramicidin A in phospholipid Langmuir-Blodgett monolayers.

    PubMed Central

    Diociaiuti, Marco; Bordi, Federico; Motta, Annelisa; Carosi, Alessandra; Molinari, Agnese; Arancia, Giuseppe; Coluzza, Carlo

    2002-01-01

    The aggregation of Gramicidin A (gA) in dipalmitoylphosphatidylcoline (DPPC) monolayers is investigated by both thermodynamic and structural methods. Compression isotherm analysis and atomic force microscopy (AFM) observations are performed. Our experimental results indicate that gA aggregation does occur in DPPC monolayers even at very low gA concentration (about 8 x 10(-4) mol%). At the low gA concentration limit, the aggregation process seems to be mainly horizontal (i.e., side-by-side, into the monolayer plane), following a fractal pattern growth producing the formation of typical, flat (0.5 nm height) "doughnut" structures, with a diameter of approximately 150 nm. These structures appear to be composed of smaller subunits (about 70 nm diameter) showing the same doughnut structure. At a molar fraction of approximately 3.8 mol%, the big doughnuts start to disaggregate and only small doughnuts appear. Above a gA concentration of approximately 4.4 mol%, all doughnuts (large and small) disappear, and the morphology assumes the appearance of a patchwork of two distinct phases: one that, being very flat, can be associated with a gA-free or gA-poor DPPC phase, and a second one, characterized by a more corrugated surface, associated with a gA-rich DPPC phase. At gA concentration of approximately 5 mol%, a percolation transition in the gA-rich DPPC phase occurs. Thermodynamic data indicate that the maximum of miscibility between gA and DPPC molecules occurs at approximately 28 mol%, suggesting that gA could aggregate in hexamers that are, on average, bound to 16 DPPC molecules. At the same concentration, AFM images show a network of small gA aggregation units of a size compatible with gA hexamers. PMID:12023244

  6. Channel-selective independent sorption and collection of hydrophilic and hydrophobic molecules by Cs2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40] ionic crystal.

    PubMed

    Jiang, Chunjie; Lesbani, Aldes; Kawamoto, Ryosuke; Uchida, Sayaka; Mizuno, Noritaka

    2006-11-08

    An ionic crystal of Cs2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40].4H2O 1a with hydrophilic and hydrophobic channels has been designed and successfully synthesized. The guest-free phase 1b sorbs dichloromethane and water in the hydrophobic and hydrophilic channels, respectively. The rate and equilibrium amount of the dichloromethane sorption into the hydrophobic channel and those of water into the hydrophilic channel were independent of each other. The sorption properties can be applied to the channel-selective sorption and collection of hydrophobic (dichloromethane) and hydrophilic (water) molecules from the mixture.

  7. Comparative studies on primycin and gramicidin induced cation transport changes in human erythrocytes.

    PubMed

    Blaskó, K; Schagina, L V; Malev, V V; Sugár, I P; Györgyi, S

    1984-01-01

    A comparative study of the actions of antibiotics primycin and gramicidin on tracer exchange of red blood cells at steady state salt distribution was carried out. The equilibrium radioactive ion distribution was not achieved at definite concentrations of either antibiotics. A development of Adam's statistical mechanical model for cooperative transitions in membranes are presented to explain the results obtained.

  8. Gramicidin Peptides Alter Global Lipid Compositions and Bilayer Thicknesses of Coexisting Liquid-Ordered and Liquid-Disordered Membrane Domains.

    PubMed

    Hassan-Zadeh, Ebrahim; Hussain, Fazle; Huang, Juyang

    2017-04-04

    Effects of adding 1 mol % of gramicidin-A on the biochemical properties of coexisting liquid-ordered and liquid-disordered (Lo + Ld) membrane domains were investigated. Quaternary giant unilamellar vesicles (GUV) of di18:1PC(DOPC)/di18:0PC(DSPC)/cholesterol/gramicidin-A were prepared using our recently developed damp-film method. The phase boundary of Lo + Ld coexisting region was determined using video fluorescence microscopy. Through fitting Nile Red fluorescence emission spectra, the thermodynamic tie-lines in the Lo + Ld two-phase region were determined. We found that at 1 mol % (i.e., ∼7% of membrane area), gramicidin peptides alter the phase boundary and thermodynamic tie-lines. Gramicidin abolishes the coexisting phases at some lipid compositions but induces phase separation at others. Previous studies of gramicidin emphasize the local perturbation of bilayer thickness adjacent to the protein through the interaction of "hydrophobic mismatch". For the first time, it becomes clear that adding gramicidin produces significant long-range and global effects on the structure of membrane domains: it alters the overall lipid compositions and bilayer thicknesses of coexisting Lo and Ld domains. We also found that gramicidin partitions favorably into the Ld phase. Adding gramicidin decreases cholesterol in the Ld phase and increases cholesterol in the Lo phase. Those compositional changes broaden the bilayer thickness difference between Lo and Ld domains and facilitate preferential partition of gramicidin into thinner Ld domains. Our results demonstrate that membrane proteins play significant roles in determining lipid compositions and bilayer thicknesses of biomembrane domains.

  9. Photosensitizer binding to lipid bilayers as a precondition for the photoinactivation of membrane channels.

    PubMed Central

    Rokitskaya, T I; Block, M; Antonenko, Y N; Kotova, E A; Pohl, P

    2000-01-01

    The photodynamic activity of sulfonated aluminum phthalocyanines (AlPcS(n), 1 gramicidin channels, as revealed by measurements of the electric current across planar lipid bilayers. The increase in the degree of sulfonation of phthalocyanine progressively reduced its affinity for the lipid bilayer as well as its potency of sensitizing gramicidin channel photoinactivation. The portion of photoinactivated gramicidin channels, alpha, increased with rising photosensitizer concentration up to some optimum. The concentration at which alpha was at half-maximum amounted to 80 nM, 30 nM, 200 nM, and 2 microM for AlPcS(1), AlPcS(2), AlPcS(3), and AlPcS(4), respectively. At high concentrations alpha was found to decrease, which was attributed to quenching of reactive oxygen species and self-quenching of the photosensitizer triplet state by its ground state. Fluoride anions were observed to inhibit both AlPcS(n) (2 gramicidin channels. It is concluded that photosensitizer binding to membrane lipids is a prerequisite for the photodynamic inactivation of gramicidin channels. PMID:10777753

  10. Spectroscopic Evidence for Complexing of Acetic Acid with Bovine Serum Albumin, Gramicidin, and Dimethylformamide

    PubMed Central

    Cann, John R.

    1961-01-01

    Acetic acid has a major effect on the absorption spectra of bovine serum albumin, gramicidin, and dimethylformamide in the region, 255 to 200 mμ. Increasing the concentration of acetic acid causes progressively decreasing absorbency accompanied by a large and progressively increasing red shift of the absorption maximum. The decrease in absorbency is interpreted in terms of a reversible complexing of acetic acid with these molecules and the red shift in terms of a non-specific solvent effect. PMID:13876221

  11. Gramicidin-perforated patch recording: GABA response in mammalian neurones with intact intracellular chloride.

    PubMed Central

    Ebihara, S; Shirato, K; Harata, N; Akaike, N

    1995-01-01

    1. By the development of a new perforated patch method using gramicidin, the effects of GABA on neurones dissociated from the rat substantia nigra pars reticulata (SNR) were examined without disturbing the intracellular chloride concentration. 2. Using the patch pipette solution containing gramicidin (100 micrograms ml-1), the access resistance dropped to less than 20 M omega within 40 min after making the gigaohm seal. 3. Under current-clamp conditions, GABA caused a hyperpolarization accompanied by a blockade of spontaneous firing. Under voltage clamp at a holding potential (Vh) of -50 mV, GABA evoked an outward current by way of bicuculline- and picrotoxin-sensitive GABAA receptors. 4. A 10-fold change of extracellular chloride concentration resulted in a 58 mV shift of the reversal potential of GABA-induced outward current (EGABA), indicating that the membrane behaves like a chloride electrode in the presence of GABA. 5. The intracellular chloride activities (aCli), calculated with the Nernst equation using both extracellular chloride activity and EGABA values, ranged from 2.8 to 19.7 mM with a mean value of 9.5 mM. The aCli was not affected either by different pipette solutions or by different holding potentials more hyperpolarized than -40 mV. 6. In the recording from SNR neurones in brain slice using the gramicidin-perforated patch-clamp technique, the inhibitory and excitatory postsynaptic currents were recorded in different current directions and the former was blocked by bicuculline. 7. In conclusion, the gramicidin-perforated patch method will disclose previously unknown aspects of biological responses involving Cl-. PMID:7541464

  12. Equilibrium binding constants for Tl+ with gramicidins A, B and C in a lysophosphatidylcholine environment determined by 205Tl nuclear magnetic resonance spectroscopy.

    PubMed Central

    Hinton, J F; Koeppe, R E; Shungu, D; Whaley, W L; Paczkowski, J A; Millett, F S

    1986-01-01

    Nuclear Magnetic Resonance (NMR) 205Tl spectroscopy has been used to monitor the binding of Tl+ to gramicidins A, B, and C packaged in aqueous dispersions of lysophosphatidylcholine. For 5 mM gramicidin dimer in the presence of 100 mM lysophosphatidylcholine, only approximately 50% or less of the gramicidin appears to be accessible to Tl+. Analysis of the 205Tl chemical shift as a function of Tl+ concentration over the 0.65-50 mM range indicates that only one Tl+ ion can be bound by gramicidin A, B, or C under these experimental conditions. In this system, the Tl+ equilibrium binding constant is 582 +/- 20 M-1 for gramicidin 1949 +/- 100 M-1 for gramicidin B, and 390 +/- 20 M-1 for gramicidin C. Gramicidin B not only binds Tl+ more strongly but it is also in a different conformational state than that of A and C, as shown by Circular Dichroism spectroscopy. The 205Tl NMR technique can now be extended to determinations of binding constants of other cations to gramicidin by competition studies using a 205Tl probe. PMID:2420383

  13. Distinguishing gramicidin D conformers through two-dimensional infrared spectroscopy of vibrational excitons

    NASA Astrophysics Data System (ADS)

    Stevenson, Paul; Tokmakoff, Andrei

    2015-06-01

    Gramicidin D is a short peptide which dimerizes to form helical pores, adopting one of two conformations in the process. These conformations differ primarily in number of residues per turn and the hydrogen-bond registry between rungs of the helix. Using amide I 2D infrared (IR) and FTIR, we have demonstrated that it is possible to distinguish between the different conformers of gramicidin D in solution. We show that the spectra observed for this helical peptide bear no resemblance to the spectra of α- or 310-helices and that while the FTIR spectra appear similar to spectra of β-sheets, 2D IR reveals that the observed resonances arise from vibrational modes unlike those observed in β-sheets. We also present an idealized model which reproduces the experimental data with high fidelity. This model is able to explain the polarization-dependence of the experimental 2D IR data. Using this model, we show the coupling between the rungs of the helix dominates the spectra, and as a consequence of this, the number of residues per turn can greatly influence the amide I spectra of gramicidin D.

  14. Multiple solution conformations and internal rotations of the decapeptide gramicidin S.

    PubMed

    Jones, C R; Kuo, M; Gibbons, W A

    1979-10-25

    The conformations of every C alpha H-C beta H2 moiety of the peptide gramicidin S are reported. Internal rotation occurs, but distinct preferences for one side chain rotamer, greater than 80%, are found for the D-phenylalanine and ornithine residues. Leucine and valine exhibit more extensive averaging while proline is shown to be at least 90% in the Ramachandran B conformation. The data are consistent with the coexistence of many tertiary conformations of gramicidin S; the statistical weights of the twelve major tertiary conformations consistent with the rotamer populations are reported. The relative statistical weights of the tertiary conformers depend upon temperature and solvent. A comparison of the conclusions from this publication and conformations derived by energy minimization procedures is made. Partial agreement was found, but the calculations have not yet predicted the wealth of coexisting tertiary conformations nor accounted for the subtle effects of solvent. It is proposed that a more complete picture of the conformational dynamics of gramicidin S and other peptides will result from calculations which use as a basis the extensive data reported here.

  15. Gramicidin Alters the Lipid Compositions of Liquid-Ordered and Liquid-Disordered Membrane Domains

    NASA Astrophysics Data System (ADS)

    Hassan-Zadeh, Ebrahim; Huang, Juyang

    2012-10-01

    The effects of adding 1 mol % of gramicidin A to the well-known DOPC/DSPC/cholesterol lipid mixtures were investigated. 4-component giant unilamellar vesicles (GUV) were prepared using our recently developed Wet-Film method. The phase boundary of liquid-ordered and liquid-disordered (Lo-Ld) coexisting region was determined using video fluorescence microscopy. We found that if cares were not taken, light-induced domain artifacts could significantly distort the measured phase boundary. After testing several fluorescence dyes, we found that the emission spectrum of Nile Red is quite sensitive to membrane composition. By fitting the Nile Red emission spectra at the phase boundary to the spectra in the Lo-Ld coexisting region, the thermodynamic tie-lines were determined. As an active component of lipid membranes, gramicidin not only partitions favorably into the liquid-disordered (Ld) phase, it also alters the phase boundary and thermodynamic tie-lines. Even at as low as 1 mol %, gramicidin decreases the cholesterol mole fraction of Ld phase and increases the area of Lo phase.

  16. Distinguishing gramicidin D conformers through two-dimensional infrared spectroscopy of vibrational excitons

    PubMed Central

    Tokmakoff, Andrei

    2015-01-01

    Gramicidin D is a short peptide which dimerizes to form helical pores, adopting one of two conformations in the process. These conformations differ primarily in number of residues per turn and the hydrogen-bond registry between rungs of the helix. Using amide I 2D infrared (IR) and FTIR, we have demonstrated that it is possible to distinguish between the different conformers of gramicidin D in solution. We show that the spectra observed for this helical peptide bear no resemblance to the spectra of α- or 310-helices and that while the FTIR spectra appear similar to spectra of β-sheets, 2D IR reveals that the observed resonances arise from vibrational modes unlike those observed in β-sheets. We also present an idealized model which reproduces the experimental data with high fidelity. This model is able to explain the polarization-dependence of the experimental 2D IR data. Using this model, we show the coupling between the rungs of the helix dominates the spectra, and as a consequence of this, the number of residues per turn can greatly influence the amide I spectra of gramicidin D. PMID:26049444

  17. Polarization-modulated FTIR spectroscopy of lipid/gramicidin monolayers at the air/water interface.

    PubMed Central

    Ulrich, W P; Vogel, H

    1999-01-01

    Monolayers of gramicidin A, pure and in mixtures with dimyristoylphosphatidylcholine (DMPC), were studied in situ at the air/H2O and air/D2O interfaces by polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Simulations of the entire set of amide I absorption modes were also performed, using complete parameter sets for different conformations based on published normal mode calculations. The structure of gramicidin A in the DMPC monolayer could clearly be assigned to a beta6.3 helix. Quantitative analysis of the amide I bands revealed that film pressures of up to 25-30 mN/m the helix tilt angle from the vertical in the pure gramicidin A layer exceeded 60 degrees. A marked dependence of the peptide orientation on the applied surface pressure was observed for the mixed lipid-peptide monolayers. At low pressure the helix lay flat on the surface, whereas at high pressures the helix was oriented almost parallel to the surface normal. PMID:10049344

  18. Channels

    NASA Image and Video Library

    2014-04-29

    Two channels are visible in this image from NASA 2001 Mars Odyssey spacecraft . The smaller one near the bottom did not carve as deeply as the larger channel at the top. The channel near the top of the image is near the origin of Mamers Valles.

  19. Formation of ultracold X {sup 1}{Sigma}{sup +}(v{sup ''}=0) NaCs molecules via coupled photoassociation channels

    SciTech Connect

    Zabawa, P.; Wakim, A.; Haruza, M.; Bigelow, N. P.

    2011-12-15

    We report production of ultracold X {sup 1}{Sigma}{sup +}(v{sup ''}=0) NaCs molecules via photoassociation. We utilize a combination of spectroscopic techniques to determine formation pathways and label ground-state samples. Efficient free-bound excitation occurs due to coupling between B {sup 1}{Pi} and neighboring electronic states in the Na 3S+Cs 6P complex. An f-wave shape resonance contributes to formation of a rotationally pure sample of X {sup 1}{Sigma}{sup +}(v{sup ''}=0,J{sup ''}=1) molecules.

  20. Direct coupled-channels deperturbation analysis of the A{sup 1}Σ{sup +} ∼ b{sup 3}Π complex in LiCs with experimental accuracy

    SciTech Connect

    Kowalczyk, P.; Jastrzebski, W.; Szczepkowski, J.

    2015-06-21

    We have carried out the direct deperturbation analysis of about 780 rovibronic term values of the strongly spin-orbit (SO) coupled A{sup 1}Σ{sup +} and b{sup 3}Π states of the {sup 7}Li{sup 133}Cs molecule recorded by polarization labelling spectroscopy technique. The explicit A{sup 1}Σ{sup +} ∼ b{sup 3}Π{sub Ω=0,1,2} coupled-channels treatment allowed us to reproduce 95% experimental term values with a standard deviation of 0.05 cm{sup −1} which is close to the accuracy of the present experiment. The initial potential energy curves (PECs) of the mutually perturbed states and SO matrix elements were ab initio evaluated in the basis of the spin-averaged wave functions. The empirically refined PECs and SO functions, along with the theoretical transition dipole moments, were used to predict energy and radiative properties of the A ∼ b complex for low J levels of both {sup 7}Li{sup 133}Cs and {sup 6}Li{sup 133}Cs isotopologues. The reasonable candidates for the stimulated Raman transitions between initial Feshbach resonance states, the mixed levels of the A ∼ b complex, and absolute ground X{sup 1}Σ{sup +} (v = 0 and J = 0) state were identified.

  1. Reactive Landing of Gramicidin S and Ubiquitin Ions onto Activated Self-Assembled Monolayer Surfaces.

    PubMed

    Laskin, Julia; Hu, Qichi

    2017-03-13

    Using mass-selected ion deposition combined with in situ infrared reflection absorption spectroscopy (IRRAS), we examined the reactive landing of gramicidin S and ubiquitin ions onto activated self-assembled monolayer (SAM) surfaces terminated with N-hydroxysuccinimidyl ester (NHS-SAM) and acyl fluoride (COF-SAM) groups. Doubly protonated gramicidin S, [GS + 2H](2+), and two charge states of ubiquitin, [U + 5H](5+) and [U + 13H](13+), were used as model systems, allowing us to explore the effect of the number of free amino groups and the secondary structure on the efficiency of covalent bond formation between the projectile ion and the surface. For all projectile ions, ion deposition resulted in the depletion of IRRAS bands corresponding to the terminal groups on the SAM and the appearance of several new bands not associated with the deposited species. These new bands were assigned to the C=O stretching vibrations of COOH and COO(-) groups formed on the surface as a result of ion deposition. The presence of these bands was attributed to an alternative reactive landing pathway that competes with covalent bond formation. This pathway with similar yields for both gramicidin S and ubiquitin ions is analogous to the hydrolysis of the NHS ester bond in solution. The covalent bond formation efficiency increased linearly with the number of free amino groups and was found to be lower for the more compact conformation of ubiquitin compared with the fully unfolded conformation. This observation was attributed to the limited availability of amino groups on the surface of the folded conformation. Our results have provided new insights on the efficiency and mechanism of reactive landing of peptides and proteins onto activated SAMs. Graphical Abstract ᅟ.

  2. Reactive Landing of Gramicidin S and Ubiquitin Ions onto Activated Self-Assembled Monolayer Surfaces

    NASA Astrophysics Data System (ADS)

    Laskin, Julia; Hu, Qichi

    2017-03-01

    Using mass-selected ion deposition combined with in situ infrared reflection absorption spectroscopy (IRRAS), we examined the reactive landing of gramicidin S and ubiquitin ions onto activated self-assembled monolayer (SAM) surfaces terminated with N-hydroxysuccinimidyl ester (NHS-SAM) and acyl fluoride (COF-SAM) groups. Doubly protonated gramicidin S, [GS + 2H]2+, and two charge states of ubiquitin, [U + 5H]5+ and [U + 13H]13+, were used as model systems, allowing us to explore the effect of the number of free amino groups and the secondary structure on the efficiency of covalent bond formation between the projectile ion and the surface. For all projectile ions, ion deposition resulted in the depletion of IRRAS bands corresponding to the terminal groups on the SAM and the appearance of several new bands not associated with the deposited species. These new bands were assigned to the C=O stretching vibrations of COOH and COO- groups formed on the surface as a result of ion deposition. The presence of these bands was attributed to an alternative reactive landing pathway that competes with covalent bond formation. This pathway with similar yields for both gramicidin S and ubiquitin ions is analogous to the hydrolysis of the NHS ester bond in solution. The covalent bond formation efficiency increased linearly with the number of free amino groups and was found to be lower for the more compact conformation of ubiquitin compared with the fully unfolded conformation. This observation was attributed to the limited availability of amino groups on the surface of the folded conformation. Our results have provided new insights on the efficiency and mechanism of reactive landing of peptides and proteins onto activated SAMs.

  3. Reactive Landing of Gramicidin S and Ubiquitin Ions onto Activated Self-Assembled Monolayer Surfaces

    NASA Astrophysics Data System (ADS)

    Laskin, Julia; Hu, Qichi

    2017-07-01

    Using mass-selected ion deposition combined with in situ infrared reflection absorption spectroscopy (IRRAS), we examined the reactive landing of gramicidin S and ubiquitin ions onto activated self-assembled monolayer (SAM) surfaces terminated with N-hydroxysuccinimidyl ester (NHS-SAM) and acyl fluoride (COF-SAM) groups. Doubly protonated gramicidin S, [GS + 2H]2+, and two charge states of ubiquitin, [U + 5H]5+ and [U + 13H]13+, were used as model systems, allowing us to explore the effect of the number of free amino groups and the secondary structure on the efficiency of covalent bond formation between the projectile ion and the surface. For all projectile ions, ion deposition resulted in the depletion of IRRAS bands corresponding to the terminal groups on the SAM and the appearance of several new bands not associated with the deposited species. These new bands were assigned to the C=O stretching vibrations of COOH and COO- groups formed on the surface as a result of ion deposition. The presence of these bands was attributed to an alternative reactive landing pathway that competes with covalent bond formation. This pathway with similar yields for both gramicidin S and ubiquitin ions is analogous to the hydrolysis of the NHS ester bond in solution. The covalent bond formation efficiency increased linearly with the number of free amino groups and was found to be lower for the more compact conformation of ubiquitin compared with the fully unfolded conformation. This observation was attributed to the limited availability of amino groups on the surface of the folded conformation. Our results have provided new insights on the efficiency and mechanism of reactive landing of peptides and proteins onto activated SAMs.

  4. Gated Ion Channel-Based Biosensor Device

    NASA Astrophysics Data System (ADS)

    Separovic, Frances; Cornell, Bruce A.

    A biosensor device based on the ion channel gramicidin A (gA) incorporated into a bilayer membrane is described. This generic immunosensing device utilizes gA coupled to an antibody and assembled in a lipid membrane. The membrane is chemically tethered to a gold electrode, which reports on changes in the ionic conduction of the lipid bilayer. Binding of a target molecule in the bathing solution to the antibody causes the gramicidin channels to switch from predominantly conducting dimers to predominantly nonconducting monomers. Conventional a.c. impedance spectroscopy between the gold and a counter electrode in the bathing solution is used to measure changes in the ionic conductivity of the membrane. This approach permits the quantitative detection of a range of target species, including bacteria, proteins, toxins, DNA sequences, and drug molecules.

  5. Conformation of gramicidin A in Triton X-100 micelles from CD and FTIR data: a clean example of antiparallel double β5.6 helix formation.

    PubMed

    Sychev, Sergei V; Barsukov, Leonid I; Ivanov, Vadim T

    2013-07-01

    The linear peptide gramicidin A (gA) forms prototypical ion channels specific for monovalent cations and has been extensively used to study the organization and dynamics of membrane channels. This polymorphic peptide can adopt two different types of structures, the helical dimer β6.3 ('channel state') and the double helical structure with two intertwined monomers. The structure of gA in micelles of detergent Triton X-100 has been studied using CD, Fourier transform infrared, and fluorescence spectroscopy. The results obtained demonstrate that only one thermodynamically stable gA structure, the antiparallel left-handed double helix β5.6, is formed in this membrane-mimetic environment. The position of the tryptophan fluorescence maximum at 332 nm is the same as that in phospholipid membranes. The causative factors governing the double helix formation in the micellar medium are discussed on the basis of known physicochemical properties of Triton X-100. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.

  6. Computer Simulation Studies of Ion Channels at High Temperatures

    NASA Astrophysics Data System (ADS)

    Song, Hyun Deok

    The gramicidin channel is the smallest known biological ion channel, and it exhibits cation selectivity. Recently, Dr. John Cuppoletti's group at the University of Cincinnati showed that the gramicidin channel can function at high temperatures (360 ˜ 380K) with significant currents. This finding may have significant implications for fuel cell technology. In this thesis, we have examined the gramicidin channel at 300K, 330K, and 360K by computer simulation. We have investigated how the temperature affects the current and differences in magnitude of free energy between the two gramicidin forms, the helical dimer (HD) and the double helix (DH). A slight decrease of the free energy barrier inside the gramicidin channel and increased diffusion at high temperatures result in an increase of current. An applied external field of 0.2V/nm along the membrane normal results in directly observable ion transport across the channels at high temperatures for both HD and DH forms. We found that higher temperatures also affect the probability distribution of hydrogen bonds, the bending angle, the distance between dimers, and the size of the pore radius for the helical dimer structure. These findings may be related to the gating of the gramicidin channel. Methanococcus jannaschii (MJ) is a methane-producing thermophile, which was discovered at a depth of 2600m in a Pacific Ocean vent in 1983. It has the ability to thrive at high temperatures and high pressures, which are unfavorable for most life forms. There have been some experiments to study its stability under extreme conditions, but still the origin of the stability of MJ is not exactly known. MJ0305 is the chloride channel protein from the thermophile MJ. After generating a structure of MJ0305 by homology modeling based on the Ecoli ClC templates, we examined the thermal stability, and the network stability from the change of network entropy calculated from the adjacency matrices of the protein. High temperatures increase the

  7. [The safety evaluation of fradiomycin-gramicidin S troches "Meiji" (author's transl)].

    PubMed

    Yokota, M; Odaki, M; Koeda, T; Sato, K; Akiyoshi, M

    1976-09-01

    The troches "Meiji" contain fradiomycin (neomycin), an aminoglycoside antibiotic, and gramicidin S, and are effective against gram-negative and -positive bacteria. In this paper the safety evaluation of the troches is reported. In this study male guinea pigs of Hartley strain were used, and fradiomycin (FRM) and gramicidin S (GRMN) were administered orally for 35 days consecutively except Sunday. The PRYER'S reflex test was carried out with frequency range of 10,000 approximately 15,000 Hz before, during and after the administration. After the last administration the animals underwent vital perfusion with physiological saline and then with Wittmack's fixative. Bilateral temporal bones were removed and fixed in the same fixative for several days. Using a conventional method, serial celloidin horinzontal sections were prepared and stained with hematoxyline-eosine to observe histopathological effect of the medicines on the organs of CORTI. The results were as follows: 1) There were no remarkable differences in the treated animals from the initial states. No animal died at all the doses tested. 2) All of the guinea pigs received 10 and 50 mg/kg of FRM and 4 and 20 mg/kg of GRMN for 35 days indicated positive pinna reflex in the extensive frequency range of 10,000 approximately 15,000 Hz. There was no remarkable damage in the organ of CORTI on histopathological examination. 3) It was concluded from these results that the troches are highly safe.

  8. [Heavy metal cation-induced increase in the antimicrobial activity of gramicidin S. Increased sensitivity of metal-resistant mutants of Escherichia coli B to the antibiotic].

    PubMed

    Kuzovnikova, T A; Fedorov, Iu I

    1990-04-01

    Gramicidin S response of metal resistant mutants of E. coli B and the effect of concentrations of Cu2+, Ag+, Co2+ and Cd2+ on the growth and sensitivity of E. coli B to cationic antibiotics, i.e. gramicidin S2+ and streptomycin2+, were studied. It was shown that the metal-cumulating mutants of E. coli B with two different mechanisms of cross resistance to Cu2+, Cd2+ and Ag+ had higher sensitivity to gramicidin S than the initial wild type strain of E. coli B. It was found that in the threshold or higher doses the salts of Cu, Ag, Co and Cd increased the gramicidin S antimicrobial action on actively metabolizing cells of E. coli B. Analysis of the experimental data as well as the literature ones suggested that the synergic action of gramicidin S and the heavy metals stemmed from an increase in the cationic conductivity of the cytoplasma membrane modified by the metals in the threshold doses which induced an increase in the transport and accumulation of the cations in the bacterial cells by the electric field gradient (with the negative sign inside). Withdrawal of Ca2+ and Mg2+ from the E. coli outer structures into the cytoplasm impaired the barrier properties of the outer membrane and promoted binding of the gramicidin S cations to the liberated anionic groups of the E. coli outer structures and potentiation of the gramicidin S antimicrobial activity as was shown in our experiments.

  9. Channels

    NASA Image and Video Library

    2015-11-20

    Today's VIS image shows a number of unnamed channels located on the northeastern margin of Terra Sabaea. Orbit Number: 61049 Latitude: 33.5036 Longitude: 58.6967 Instrument: VIS Captured: 2015-09-18 12:54 http://photojournal.jpl.nasa.gov/catalog/PIA20097

  10. Inhibiting mild steel corrosion from sulfate-reducing and iron-oxidizing bacteria using gramicidin-S-producing biofilms.

    PubMed

    Zuo, Rongjun; Wood, Thomas K

    2004-11-01

    A gramicidin-S-producing Bacillus brevis 18-3 biofilm was shown to reduce corrosion rates of mild steel by inhibiting both the sulfate-reducing bacterium Desulfosporosinus orientis and the iron-oxidizing bacterium Leptothrix discophora SP-6. When L. discophora SP-6 was introduced along with D. orientis to a non-antimicrobial-producing biofilm control, Paenibacillus polymyxa ATCC 10401, a corrosive synergy was created and mild steel coupons underwent more severe corrosion than when only D. orientis was present, showing a 2.3-fold increase via electrochemical impedance spectroscopy (EIS) and a 1.8-fold difference via mass-loss measurements. However, when a gramicidin-S-producing, protective B. brevis 18-3 biofilm was established on mild steel, the metal coupons were protected against the simultaneous attack of D. orientis and L. discophora SP-6. EIS data showed that the protective B. brevis 18-3 biofilm decreased the corrosion rate about 20-fold compared with the non-gramicidin-producing P. polymyxa ATCC 10401 biofilm control. The mass loss for the protected mild steel coupons was also significantly lower than that for the unprotected ones (4-fold decrease). Scanning electron microscope images corroborated the corrosion inhibition by the gramicidin-S-producing B. brevis biofilm on mild steel by showing that the metal surface remained untarnished, i.e., the polishing grooves were still visible after exposure to the simultaneous attack of the sulfate-reducing bacterium and the iron-oxidizing bacterium.

  11. CS Informativeness Governs CS-US Associability

    PubMed Central

    Ward, Ryan D.; Gallistel, C. R.; Jensen, Greg; Richards, Vanessa L.; Fairhurst, Stephen; Balsam, Peter D

    2012-01-01

    In a conditioning protocol, the onset of the conditioned stimulus (CS) provides information about when to expect reinforcement (the US). There are two sources of information from the CS in a delay conditioning paradigm in which the CS-US interval is fixed. The first depends on the informativeness, the degree to which CS onset reduces the average expected time to onset of the next US. The second depends only on how precisely a subject can represent a fixed-duration interval (the temporal Weber fraction). In three experiments with mice, we tested the differential impact of these two sources of information on rate of acquisition of conditioned responding (CS-US associability). In Experiment 1, we show that associability (the inverse of trials to acquisition) increases in proportion to informativeness. In Experiment 2, we show that fixing the duration of the US-US interval or the CS-US interval or both has no effect on associability. In Experiment 3, we equated the increase in information produced by varying the C̅/T̅ ratio with the increase produced by fixing the duration of the CS-US interval. Associability increased with increased informativeness, but, as in Experiment 2, fixing the CS-US duration had no effect on associability. These results are consistent with the view that CS-US associability depends on the increased rate of reward signaled by CS onset. The results also provide further evidence that conditioned responding is temporally controlled when it emerges. PMID:22468633

  12. Cooperative binding of primycin and gramicidin on erythrocyte membranes. A cation transport study.

    PubMed

    Suga'r, I P; Blaskó, K; Györgyi, S; Shcagina, L V; Malev, V V; Lev, A A

    1989-01-01

    In this paper the authors present a comparative study of the actions of the antibiotics primycin and gramicidin on the erythrocyte membrane permeability. It has been found that both antibiotics have a nonlinear effect on the membrane permeability. Above a threshold antibiotic concentration, which is characteristic of the type of the antibiotic, the cation permeability of the erythrocyte membranes increases sharply. In the range of nonlinearity the transport-kinetic curves level off before achieving the equilibrium radioactive ion distribution between the extra- and intracellular spaces. A stochastic model of the cooperative and aspecific incorporation of antibiotic molecules into the membrane explains the experimental findings. The authors conclude that membrane permeability increases at the places where two or more antibiotic molecules form aggregates in the membrane.

  13. The quantitation of nuclear Overhauser effect methods for total conformational analysis of peptides in solution. Application to gramicidin S.

    PubMed Central

    Jones, C R; Sikakana, C T; Hehir, S; Kuo, M C; Gibbons, W A

    1978-01-01

    The [1H:1H] nuclear Overhauser effects (NOE's) and spin-lattice relaxation times (T1's) are reported for the backbone protons of the decapeptide gramicidin S. Several methods for calculating interproton distances from these measurements are presented. Ratios of interproton distances were obtained from [1H:1H] NOE's and from the combination of [1H:1H]NOE'S and T1 values. Actual proton-proton distances were calculated from these ratios either by using the known distance between two geminal protons or distances derived from scalar coupling constants. The interproton distances calculated for gramicidin S are consistent with a II' beta-turn/antiparallel beta-sheet conformation. PMID:83886

  14. Effect of Polymyxin B, Tyrocidine, Gramicidin D, and Other Antibiotics on the Enzymatic Hydrolysis of Poly-β-Hydroxybutyrate

    PubMed Central

    Merrick, J. M.

    1965-01-01

    Merrick, J. M. (State University of New York, Buffalo). Effect of polymyxin B, tyrocydine, gramicidin D, and other antibiotics on the enzymatic hydrolysis of poly-β-hydroxybutyrate. J. Bacteriol. 90:965–969. 1965.—Previous studies have demonstrated that native poly-β-hydroxybutyrate (PHB) granules isolated from Bacillus megaterium are surrounded by a discrete membranelike structure. Morphological alterations of PHB granules are mainly characterized by membrane fragmentation, and can be correlated with decreased susceptibility of the polymer to enzymatic hydrolysis by soluble factors. In the present investigation, the inhibitory effect of a variety of surface-active and other antibiotics on the enzymatic depolymerization of PHB was examined. The most potent inhibitors were polymyxin B, tyrocidine, and gramicidin D. These polypeptide antibiotics are known to attack other types of membranous structures. The results, therefore, support previous evidence that the membrane or similar constituents of PHB granules are intimately involved in its metabolism. Chlortetracycline was also found to be a potent inhibitor of the depolymerization, but its mechanism of action may be different from the other antibiotics. The polymer-synthesizing enzyme(s), also localized on the granules, is inhibited by tyrocidine and gramicidin D but not by polymyxin B or chlortetracycline. PMID:4284918

  15. Cs(3)Sm(7)Se(12).

    PubMed

    Schneck, Christof; Elbe, Andreas; Schurz, Christian M; Schleid, Thomas

    2012-01-01

    The title compound, tricaesium hepta-samarium(III) dodeca-selenide, is setting a new starting point for realization of the channel structure of the Cs(3)M(7)Se(12) series, now with M = Sm, Gd-Er. This Cs(3)Y(7)Se(12)-type arrangement is structurally based on the Z-type sesquiselenides M(2)Se(3) adopting the Sc(2)S(3) structure. Thus, the structural set-up of Cs(3)Sm(7)Se(12) consists of edge- and vertex-connected [SmSe(6)](9-) octa-hedra [d(Ø)(Sm(3+) - Se(2-)) = 2.931 Å], forming a rock-salt-related network [Sm(7)Se(12)](3-) with channels along [001] that are apt to take up monovalent cations (here Cs(+)) with coordination numbers of 7 + 1 for one and of 6 for the second cation. The latter cation has a trigonal-prismatic coordination and shows half-occupancy, resulting in an impossible short distance [2.394 (4) Å] between symmetrically coupled Cs(+) cations of the same kind. While one Sm atom occupies Wyckoff position 2b with site symmetry ..2/m, all other 11 crystallographically different atoms (namely 2 × Cs, 3 × Sm and 6 × Se) are located at Wyckoff positions 4g with site symmetry ..m.

  16. Lipid-gramicidin interactions: dynamic structure of the boundary lipid by 2D-ELDOR.

    PubMed

    Costa-Filho, Antonio J; Crepeau, Richard H; Borbat, Petr P; Ge, Mingtao; Freed, Jack H

    2003-05-01

    The use of 2D-electron-electron double resonance (2D-ELDOR) for the characterization of the boundary lipid in membrane vesicles of DPPC and gramicidin A' (GA) is reported. We show that 2D-ELDOR, with its enhanced spectral resolution to dynamic structure as compared with continuous-wave electron spin resonance, provides a reliable and useful way of studying lipid-protein interactions. The 2D-ELDOR spectra of the end-chain spin label 16-PC in DPPC/GA vesicles is composed of two components, which are assigned to the bulk lipids (with sharp auto peaks and crosspeaks) and to the boundary lipids (with broad auto peaks). Their distinction is clearest for higher temperatures and higher GA concentrations. The quantitative analysis of these spectra shows relatively faster motions and very low ordering for the end chain of the bulk lipids, whereas the boundary lipids show very high "y-ordering" and slower motions. The y-ordering represents a dynamic bending at the end of the boundary lipid acyl chain, which can then coat the GA molecules. These results are consistent with the previous studies by Ge and Freed (1999) using continuous-wave electron spin resonance, thereby supporting their model for GA aggregation and H(II) phase formation for high GA concentrations. Improved instrumental and simulation methods have been employed.

  17. Antimicrobial peptide gramicidin S is accumulated in granules of producer cells for storage of bacterial phosphagens

    PubMed Central

    Berditsch, Marina; Trapp, Mareike; Afonin, Sergii; Weber, Christian; Misiewicz, Julia; Turkson, Joana; Ulrich, Anne S.

    2017-01-01

    Many antimicrobial peptides are synthesized non-ribosomally in bacteria, but little is known about their subcellular route of biosynthesis, their mode of intracellular accumulation, or their role in the physiology of the producer cells. Here, we present a comprehensive view on the biosynthesis of gramicidin S (GS) in Aneurinibacillus migulanus, having observed a peripheral membrane localization of its synthetases. The peptide gets accumulated in nano-globules, which mature by fusion into larger granules and end up within vacuolar structures. These granules serve as energy storage devices, as they contain GS molecules that are non-covalently attached to alkyl phosphates and protect them from dephosphorylation and premature release of energy. This finding of a fundamentally new type of high-energy phosphate storage mechanism can explain the curious role of GS biosynthesis in the physiology of the bacterial producer cells. The unknown role of the GrsT protein, which is part of the non-ribosomal GS synthetase operon, can thus be assumed to be responsible for the biosynthesis of alkyl phosphates. GS binding to alkyl phosphates may suggest its general affinity to phosphagens such as ATP and GTP, which can represent the important intracellular targets in pathogenic bacteria. PMID:28295017

  18. Therapeutic Potential of Gramicidin S in the Treatment of Root Canal Infections

    PubMed Central

    Berditsch, Marina; Lux, Hannah; Babii, Oleg; Afonin, Sergii; Ulrich, Anne S.

    2016-01-01

    An intrinsic clindamycin-resistant Enterococcus faecalis, the most common single species present in teeth after failed root canal therapy, often possesses acquired tetracycline resistance. In these cases, root canal infections are commonly treated with Ledermix® paste, which contains demeclocycline, or the new alternative endodontic paste Odontopaste, which contains clindamycin; however, these treatments are often ineffective. We studied the killing activity of the cyclic antimicrobial peptide gramicidin S (GS) against planktonic and biofilm cells of tetracycline-resistant clinical isolates of E. faecalis. The high therapeutic potential of GS for the topical treatment of problematic teeth is based on the rapid bactericidal effect toward the biofilm-forming, tetracycline-resistant E. faecalis. GS reduces the cell number of planktonic cells within 20–40 min at a concentration of 40–80 μg/mL. It kills the cells of pre-grown biofilms at concentrations of 100–200 μg/mL, such that no re-growth is possible. The translocation of the peptide into the cell interior and its complexation with intracellular nucleotides, including the alarmon ppGpp, can explain its anti-biofilm effect. The successful treatment of persistently infected root canals of two volunteers confirms the high effectiveness of GS. The broad GS activity towards resistant, biofilm-forming E. faecalis suggests its applications for approval in root canal medication. PMID:27618065

  19. Atomic detail peptide-membrane interactions: molecular dynamics simulation of gramicidin S in a DMPC bilayer.

    PubMed Central

    Mihailescu, D; Smith, J C

    2000-01-01

    Molecular dynamics simulations have been performed of the sequence-symmetric cyclic decapeptide antibiotic gramicidin S (GS), in interaction with a hydrated dimyristoylphosphatidylcholine (DMPC) bilayer, and the results compared with a "control" simulation of the system in the absence of GS. Following experimental evidence, the GS was initially set in a single antiparallel beta-sheet conformation with two Type II' beta-turns in an amphiphilic interaction with the membrane. This conformation and position remained in the 6.5 ns simulation. Main-chain dihedrals are on average approximately 26 degrees from those determined by NMR experiment on GS in dimethylsulfoxide (DMSO) solution. Sequence-symmetric main-chain and side-chain dihedral angle pairs converge to within approximately 5 degrees and approximately 10 degrees, respectively. The area per lipid, lipid tail order parameters, and quadrupole spin-lattice relaxation times of the control simulation are mostly in good agreement with corresponding experiments. The GS has little effect on the membrane dipole potential or water permeability. However, it is found to have a disordering effect (in agreement with experiment) and a fluidifying effect on lipids directly interacting with it, and an ordering effect on those not directly interacting. PMID:11023880

  20. Structural basis for the activation of phenylalanine in the non-ribosomal biosynthesis of gramicidin S.

    PubMed Central

    Conti, E; Stachelhaus, T; Marahiel, M A; Brick, P

    1997-01-01

    The non-ribosomal synthesis of the cyclic peptide antibiotic gramicidin S is accomplished by two large multifunctional enzymes, the peptide synthetases 1 and 2. The enzyme complex contains five conserved subunits of approximately 60 kDa which carry out ATP-dependent activation of specific amino acids and share extensive regions of sequence similarity with adenylating enzymes such as firefly luciferases and acyl-CoA ligases. We have determined the crystal structure of the N-terminal adenylation subunit in a complex with AMP and L-phenylalanine to 1.9 A resolution. The 556 amino acid residue fragment is folded into two domains with the active site situated at their interface. Each domain of the enzyme has a similar topology to the corresponding domain of unliganded firefly luciferase, but a remarkable relative domain rotation of 94 degrees occurs. This conformation places the absolutely conserved Lys517 in a position to form electrostatic interactions with both ligands. The AMP is bound with the phosphate moiety interacting with Lys517 and the hydroxyl groups of the ribose forming hydrogen bonds with Asp413. The phenylalanine substrate binds in a hydrophobic pocket with the carboxylate group interacting with Lys517 and the alpha-amino group with Asp235. The structure reveals the role of the invariant residues within the superfamily of adenylate-forming enzymes and indicates a conserved mechanism of nucleotide binding and substrate activation. PMID:9250661

  1. Shifting the equilibrium mixture of gramicidin double helices toward a single conformation with multivalent cationic salts.

    PubMed Central

    Doyle, D A; Wallace, B A

    1998-01-01

    The conformation of the polypeptide antibiotic gramicidin is greatly influenced by its environment. In methanol, it exists as an equilibrium mixture of four interwound double-helical conformers that differ in their handedness, chain orientation, and alignment. Upon the addition of multivalent cationic salts, there is a shift in the equilibrium to a single conformer, which was monitored in this study by circular dichroism spectroscopy. With increasing concentrations of multivalent cations, both the magnitude of the entire spectrum and the ratio of the 229-nm to the 210-nm peak were increased. The spectral change is not related to the charge on the cation, but appears to be related to the cationic radius, with the maximum change in ellipticity occurring for cations with a radius of approximately 1 A. The effect requires the presence of an anion whose radius is greater than that of a fluoride ion, but is otherwise not a function of anion type. It is postulated that multivalent cations interact with a binding site in one of the conformers, known as species 1 (a left-handed, parallel, no stagger double helix), stabilizing a modified form of this type of structure. PMID:9675165

  2. Gramicidin A Mutants with Antibiotic Activity against Both Gram-Positive and Gram-Negative Bacteria.

    PubMed

    Zerfas, Breanna L; Joo, Yechaan; Gao, Jianmin

    2016-03-17

    Antimicrobial peptides (AMPs) have shown potential as alternatives to traditional antibiotics for fighting infections caused by antibiotic-resistant bacteria. One promising example of this is gramicidin A (gA). In its wild-type sequence, gA is active by permeating the plasma membrane of Gram-positive bacteria. However, gA is toxic to human red blood cells at similar concentrations to those required for it to exert its antimicrobial effects. Installing cationic side chains into gA has been shown to lower its hemolytic activity while maintaining the antimicrobial potency. In this study, we present the synthesis and the antibiotic activity of a new series of gA mutants that display cationic side chains. Specifically, by synthesizing alkylated lysine derivatives through reductive amination, we were able to create a broad selection of structures with varied activities towards Staphylococcus aureus and methicillin-resistant S. aureus (MRSA). Importantly, some of the new mutants were observed to have an unprecedented activity towards important Gram-negative pathogens, including Escherichia coli, Klebsiella pneumoniae and Psuedomonas aeruginosa. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Physical origin of selectivity in ionic channels of biological membranes.

    PubMed Central

    Laio, A; Torre, V

    1999-01-01

    This paper shows that the selectivity properties of monovalent cation channels found in biological membranes can originate simply from geometrical properties of the inner core of the channel without any critical contribution from electrostatic interactions between the permeating ions and charged or polar groups. By using well-known techniques of statistical mechanics, such as the Langevin equations and Kramer theory of reaction rates, a theoretical equation is provided relating the permeability ratio PB/PA between ions A and B to simple physical properties, such as channel geometry, thermodynamics of ion hydration, and electrostatic interactions between the ion and charged (or polar) groups. Diffusive corrections and recrossing rates are also considered and evaluated. It is shown that the selectivity found in usual K+, gramicidin, Na+, cyclic nucleotide gated, and end plate channels can be explained also in the absence of any charged or polar group. If these groups are present, they significantly change the permeability ratio only if the ion at the selectivity filter is in van der Waals contact with them, otherwise these groups simply affect the channel conductance, lowering the free energy barrier of the same amount for the two ions, thus explaining why single channel conductance, as it is experimentally observed, can be very different in channels sharing the same selectivity sequence. The proposed theory also provides an estimate of channel minimum radius for K+, gramicidin, Na+, and cyclic nucleotide gated channels. PMID:9876129

  4. Regulation of Sodium Channel Function by Bilayer Elasticity

    PubMed Central

    Lundbæk, Jens A.; Birn, Pia; Hansen, Anker J.; Søgaard, Rikke; Nielsen, Claus; Girshman, Jeffrey; Bruno, Michael J.; Tape, Sonya E.; Egebjerg, Jan; Greathouse, Denise V.; Mattice, Gwendolyn L.; Koeppe, Roger E.; Andersen, Olaf S.

    2004-01-01

    Membrane proteins are regulated by the lipid bilayer composition. Specific lipid–protein interactions rarely are involved, which suggests that the regulation is due to changes in some general bilayer property (or properties). The hydrophobic coupling between a membrane-spanning protein and the surrounding bilayer means that protein conformational changes may be associated with a reversible, local bilayer deformation. Lipid bilayers are elastic bodies, and the energetic cost of the bilayer deformation contributes to the total energetic cost of the protein conformational change. The energetics and kinetics of the protein conformational changes therefore will be regulated by the bilayer elasticity, which is determined by the lipid composition. This hydrophobic coupling mechanism has been studied extensively in gramicidin channels, where the channel–bilayer hydrophobic interactions link a “conformational” change (the monomer↔dimer transition) to an elastic bilayer deformation. Gramicidin channels thus are regulated by the lipid bilayer elastic properties (thickness, monolayer equilibrium curvature, and compression and bending moduli). To investigate whether this hydrophobic coupling mechanism could be a general mechanism regulating membrane protein function, we examined whether voltage-dependent skeletal-muscle sodium channels, expressed in HEK293 cells, are regulated by bilayer elasticity, as monitored using gramicidin A (gA) channels. Nonphysiological amphiphiles (β-octyl-glucoside, Genapol X-100, Triton X-100, and reduced Triton X-100) that make lipid bilayers less “stiff”, as measured using gA channels, shift the voltage dependence of sodium channel inactivation toward more hyperpolarized potentials. At low amphiphile concentration, the magnitude of the shift is linearly correlated to the change in gA channel lifetime. Cholesterol-depletion, which also reduces bilayer stiffness, causes a similar shift in sodium channel inactivation. These results

  5. Characterisation of the tyrocidine and gramicidin fractions of the tyrothricin complex from Bacillus brevis using liquid chromatography and mass spectrometry

    NASA Astrophysics Data System (ADS)

    Tang, Xue-Jun; Thibault, Pierre; Boyd, Robert K.

    1992-12-01

    The tyrothricin peptide complex, isolated from the fermentation broth of Bacillus brevis, is comprised of a basic fraction of cyclic decapeptides (the tyrocidines) and a neutral fraction composed of linear peptides (the gramicidins). Previously, five cyclic compounds (tyrocidines A-E) had been characterised by classical chemical procedures, and an additional five by M. Barber, D.J. Bell, M.R. Morris, L.W. Tetler, J.J. Monaghan, W.E. Morden, B.W. Bycroft and B.N. Green, Int. J. Mass Spectrom. Ion Processes, 122 (1992) 143-150, who employed tandem mass spectrometric analysis of the crude mixture, together with an interpretative strategy based upon mass shifts related to simple amino acid substitutions. In the present work, initial profiling of the tyrothricin complex, using reverse phase liquid chromatography (HPLC) coupled directly to tandem mass spectrometry via an ionspray interface, showed that the mixture is extremely complex. Semi-preparative HPLC provided 32 fractions, some of which were still mixtures, amenable to analysis by tandem mass spectrometry using the doubly-protonated peptide precursors produced by ionspray ionisation. In this way the 10 previously known tyrocidines were confirmed, and structures of an additional 18 cyclic variants established with only minor uncertainties (e.g. present techniques could not distinguish Ile from Leu). Six linear gramicidins were known previously, and were confirmed in the present work. In addition, three previously unknown variants, of the Val1 -gramicidins A,B and C, were discovered, in which the ethanolamide residue at the C-terminus is replaced by a propanolamide residue.

  6. Improving CS regulations.

    SciTech Connect

    Nesse, R.J.; Scheer, R.M.; Marasco, A.L.; Furey, R.

    1980-10-01

    President Carter issued Executive Order 12044 (3/28/78) that required all Federal agencies to distinguish between significant and insignificant regulations, and to determine whether a regulation will result in major impacts. This study gathered information on the impact of the order and the guidelines on the Office of Conservation and Solar Energy (CS) regulatory practices, investigated problems encountered by the CS staff when implementing the order and guidelines, and recommended solutions to resolve these problems. Major tasks accomplished and discussed are: (1) legislation, Executive Orders, and DOE Memoranda concerning Federal administrative procedures relevant to the development and analysis of regulations within CS reviewed; (2) relevant DOE Orders and Memoranda analyzed and key DOE and CS staff interviewed in order to accurately describe the current CS regulatory process; (3) DOE staff from the Office of the General Counsel, the Office of Policy and Evaluation, the Office of the Environment, and the Office of the Secretary interviewed to explore issues and problems encountered with current CS regulatory practices; (4) the regulatory processes at five other Federal agencies reviewed in order to see how other agencies have approached the regulatory process, dealt with specific regulatory problems, and responded to the Executive Order; and (5) based on the results of the preceding four tasks, recommendations for potential solutions to the CS regulatory problems developed. (MCW)

  7. Models of ionic transport in biological membranes. Raman spectroscopy as a probe of valinomycin, gramicidin A', and rhodopsin conformations.

    PubMed

    Rothschild, K J; Stanley, H E

    1975-05-01

    There is evidence that membrane proteins can serve as the functional units of ionic transport in biological membranes. Laser Raman spectroscopy has been used to probe specific molecular interactions inside two models of transport membrane proteins, valinomycin and gramicidin A. Conformational changes of these molecules, as well as specific interactions with ions, can be detected and may help elucidate how membrane transport proteins such as Na+ minus K+ ATPase and rhodopsin function. Resonance Raman spectroscopy has also been used to study conformational changes and protein-chromophore interactions in rhodopsin, the membrane protein that acts as the primary unit of visual excitation in the eye.

  8. The efficacy and safety of topical polymyxin B, neomycin and gramicidin for treatment of presumed bacterial corneal ulceration

    PubMed Central

    Bosscha, M I; van Dissel, J T; Kuijper, E J; Swart, W; Jager, M J

    2004-01-01

    Aim: To evaluate the clinical efficacy and safety of topical polymyxin B, neomycin, and gramicidin for the treatment of suspected bacterial corneal ulceration at the Leiden University Medical Center. Methods: Patients with a diagnosis of a suspected bacterial corneal ulcer between April 1995 and February 2002 were retrospectively identified and reviewed; clinical and microbiological features and response to therapy were analysed. All patients were treated with Polyspectran eye drops. Results: In total, 91 patients were included in this analysis. Bacteriological cultures of 46 patients (51%) were positive and revealed 51 microorganisms. Staphylococcus aureus (29.4%) and Pseudomonas aeruginosa (23.5%) were the most frequently encountered bacteria. Eighteen patients switched therapy before complete healing of the corneal ulceration, four patients were lost to follow up. Of the 69 patients who completed Polyspectran treatment, re-epithelialisation occurred in 68 patients (99%) and on average took 12.6 (median 8) days. Among 91 patients, there were four perforations and one evisceration. Seven toxic or allergic reactions were reported. Conclusion: This study shows that the combination of polymyxin B, neomycin, and gramicidin is an effective and safe treatment of suspected corneal ulceration. PMID:14693766

  9. Bicarbonate efflux via GABAA receptors depolarizes membrane potential and inhibits two-pore domain potassium channels of astrocytes in rat hippocampal slices

    PubMed Central

    Ma, Bao-Feng; Xie, Min-Jie; Zhou, Min

    2014-01-01

    Increasing evidence indicates the functional expression of ionotropic γ-aminobutyric acid receptor (GABAA-R) in astrocytes. However, it remains controversial in regard to the intracellular Cl− concentration ([Cl−]i) and the functional role of anion-selective GABAA-R in astrocytes. In gramicidin perforated-patch recordings from rat hippocampal CA1 astrocytes, GABA and GABAA-R specific agonist THIP depolarized astrocyte membrane potential (Vm), and the THIP induced currents reversed at the voltages between −75.3 to −78.3 mV, corresponding to a [Cl−]i of 3.1 – 3.9 mM that favors a passive distribution of Cl− anions across astrocyte membrane. Further analysis showed that GABAA-R induced Vm depolarization is ascribed to HCO3− efflux, while a passively distributed Cl− mediates no net flux or influx of Cl-that leads to an unchanged or hyperpolarized Vm. In addition to a rapidly activated GABAA-R current component, GABA and THIP also induced a delayed inward current (DIC) in 63% of astrocytes. The DIC became manifest after agonist withdrawal and enhanced in amplitude with increasing agonist application duration or concentrations. Astrocytic two-pore domain K+ channels (K2Ps), especially TWIK-1, appeared to underlie the DIC, because 1) acidic intracellular pH, as a result of HCO3− efflux, inhibited TWIK-1; 2) the DIC remained in the Cs+ recording solutions that inhibited conventional K+ channels and 3) the DIC was completely inhibited by 1 mM quinine but not by blockers for other cation/anion channels. Altogether, HCO3− efflux through activated GABAA-R depolarizes astrocyte Vm and induces a delayed inhibition of K2Ps K+ channels via intracellular acidification. PMID:22855415

  10. An electron spin resonance study of interactions between gramicidin A' and phosphatidylcholine bilayers.

    PubMed Central

    Ge, M; Freed, J H

    1993-01-01

    The model of microscopic order and macroscopic disorder was used to stimulate electron spin resonance spectra of spin-labeled lipids, 5-PC, 10-PC, and 16-PC in multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) containing gramicidin A' (GA) at temperatures above the gel-to-liquid crystal transition of DPPC. The simulations show that at a lower concentration of GA (i.e., molar ratios of DPPC/GA greater than 3), GA has only a slight effect on the acyl chain dynamics. The rotational diffusion rate around the axis parallel to the long hydrocarbon chain remains unchanged or increases slightly, while the rate around the perpendicular axes decreases slightly. These spectra from DPPC/GA mixtures could only be fit successfully with two or more components consistent with the well-known concept of "boundary lipids," that is, the peptide induces structural inhomogeneity in lipid bilayers. However, the spectra were significantly better fit with additional components that exhibit increased local ordering, implying decreased amplitude of rotational motion, rather than immobilized components with sharply a reduced rotational rate. The largest relative effects occur at the end of the acyl chains, where the average local order parameter St of 16-PC increases from 0.06 for pure lipid to 0.66 for 1:1 DPPC/GA. The inhomogeneity in ordering in DPPC bilayers due to GA decreases with increasing temperature. The hyperfine tensor component Azz increases for 10-PC and 16-PC when GA is incorporated into DPPC bilayers, indicating that water has deeply penetrated into the DPPC bilayers. Simulations of published electron spin resonance spectra of 14-PC in dimyristoylphosphatidylcholine/cytochrome oxidase complexes were also better fit by additional components that were more ordered, rather than immobilized. The average local order parameter in this case is found to increase from 0.11 for pure dimyristoylphosphatidylcholine to 0.61 for a lipid/protein ratio of 50. These spectra and

  11. EXTRAGALACTIC CS SURVEY

    SciTech Connect

    Bayet, E.; Viti, S.; Aladro, R.; MartIn, S.; MartIn-Pintado, J.

    2009-12-10

    We present a coherent and homogeneous multi-line study of the CS molecule in nearby (D < 10 Mpc) galaxies. We include, from the literature, all the available observations from the J = 1-0 to the J = 7-6 transitions toward NGC 253, NGC 1068, IC 342, Henize 2-10, M 82, the Antennae Galaxies, and M 83. We have, for the first time, detected the CS(7-6) line in NGC 253, M 82 (both in the northeast and southwest molecular lobes), NGC 4038, M 83 and tentatively in NGC 1068, IC 342, and Henize 2-10. We use the CS molecule as a tracer of the densest gas component of the interstellar medium in extragalactic star-forming regions, following previous theoretical and observational studies by Bayet et al. In this first paper out of a series, we analyze the CS data sample under both local thermodynamical equilibrium (LTE) and non-LTE (large velocity gradient) approximations. We show that except for M 83 and Overlap (a shifted gas-rich position from the nucleus NGC 4039 in the Antennae Galaxies), the observations in NGC 253, IC 342, M 82-NE, M 82-SW, and NGC 4038 are not well reproduced by a single set of gas component properties and that, at least, two gas components are required. For each gas component, we provide estimates of the corresponding kinetic temperature, total CS column density, and gas density.

  12. Solid-phase peptide synthesis and solid-state NMR spectroscopy of (Ala/sup 3/-/sup 15/N)(Val/sup 1/)gramicidin A

    SciTech Connect

    Fields, G.B.; Fields, C.G.; Petefish, J.; Van Wart, H.E.; Cross, T.A.

    1988-03-01

    (Ala/sup 3-15/N)(Val/sup 1/)Gramicidin A has been prepared by solid-phase peptide synthesis and studied by solid-state /sup 15/N nuclear magnetic resonance spectroscopy. The synthesis of desformyl(Ala/sup 3-15/N)(Val/sup 1/)gramicidin A employed N-hydroxysuccinimide esters of 9-fluorenylmethoxycarbonyl-N/sup ..cap alpha../-amino acids and completely avoided the use of acid. Since deblocking was done with piperidine and the peptide was removed from the resin by treatment with ethanolamine, this synthetic protocol prevented oxidation of the indole rings of this tryptophan-rich peptide and reduced truncations produced by acid hydrolysis. After formylation and purification by anion-exchange and high-pressure liquid chromatography, the peptide was obtained in an overall yield of 30%. Solid-state /sup 15/N nuclear magnetic resonance spectra of this peptide and uniformly labeled (/sup 15/N)gramicidin A' oriented in hydrated lipid bilayers have been obtained, allowing unambiguous assignment of the (/sup 15/N)Ala/sup 3/ resonance in the latter. The solid-state /sup 15/N nuclear magnetic resonance experiments provide evidence that (Val/sup 1/)gramicidin A is rotating about an axis that is perpendicular to the plane of the lipid bilayer and that the N-H axis is nearly parallel with the rotational axis. This study demonstrates that site-specifically labeled (/sup 15/N)gramicidin A analogs prepared by solid-phase peptide synthesis are valuable tools in the study of the solid-state nuclear magnetic resonance spectra of samples in oriented lipid bilayers.

  13. Desformylgramicidin: a model channel with an extremely high water permeability.

    PubMed Central

    Saparov, S M; Antonenko, Y N; Koeppe, R E; Pohl, P

    2000-01-01

    The water conductivity of desformylgramicidin exceeds the permeability of gramicidin A by two orders of magnitude. With respect to its single channel hydraulic permeability coefficient of 1.1.10(-12) cm(3) s(-1), desformylgramicidin may serve as a model for extremely permeable aquaporin water channel proteins (AQP4 and AQPZ). This osmotic permeability exceeds the conductivity that is predicted by the theory of single-file transport. It was derived from the concentration distributions of both pore-impermeable and -permeable cations that were simultaneously measured by double barreled microelectrodes in the immediate vicinity of a planar bilayer. From solvent drag experiments, approximately five water molecules were found to be transported by a single-file process along with one ion through the channel. The single channel proton, potassium, and sodium conductivities were determined to be equal to 17 pS (pH 2.5), 7 and 3 pS, respectively. Under any conditions, the desformyl-channel remains at least 10 times longer in its open state than gramicidin A. PMID:11053127

  14. Sequence inversion and phenylalanine surrogates at the β-turn enhance the antibiotic activity of gramicidin S

    PubMed Central

    Solanas, Concepción; de la Torre, Beatriz G.; Fernández-Reyes, María; Santiveri, Clara M.; Jiménez, M. Ángeles; Rivas, Luis; Jiménez, Ana I.; Andreu, David; Cativiela, Carlos

    2010-01-01

    A series of gramicidin S (GS) analogs have been synthesized where the Phe (i+1) and Pro (i+2) residues of the β-turn have been swapped while the respective chiralities (D-, L-) at each position are preserved, and Phe is replaced by surrogates with aromatic side chains of diverse size, orientation and flexibility. Although most analogs preserve the β-sheet structure, as assessed by NMR, their antibiotic activities turn out to be highly dependent on the bulkiness and spatial arrangement of the aromatic side chain. Significant increases in microbicidal potency against both Gram-positive and Gram-negative pathogens are observed for several analogs, resulting in improved therapeutic profiles. Data indicate that seemingly minor replacements at the GS β-turn can have significant impact on antibiotic activity, highlighting this region as a hot spot for modulating GS plasticity and activity. PMID:20411945

  15. Therapeutic index of gramicidin S is strongly modulated by d-phenylalanine analogues at the β-turn

    PubMed Central

    Solanas, Concepción; de la Torre, Beatriz G.; Fernández-Reyes, María; Santiveri, Clara M.; Jiménez, M. Ángeles; Rivas, Luis; Jiménez, Ana I.; Andreu, David; Cativiela, Carlos

    2009-01-01

    Analogues of the cationic antimicrobial peptide gramicidin S (GS), cyclo(Val-Orn-Leu-d-Phe-Pro)2, with d-Phe residues replaced by different (restricted mobility, mostly) surrogates have been synthesized and used in SAR studies against several pathogenic bacteria. While all d-Phe substitutions are shown by NMR to preserve the overall β-sheet conformation, they entail subtle structural alterations that lead to significant modifications in biological activity. In particular, the analogue incorporating d-Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) shows a modest but significant increase in therapeutic index, mostly due to a sharp decrease in hemolytic effect. The fact that NMR data show a shortened distance between the d-Tic aromatic ring and the Orn δ-amino group may help explain the improved antibiotic profile of this analogue. PMID:19132829

  16. Effect of single base substitutions at glycine-870 codon of gramicidin S synthetase 2 gene on proline activation.

    PubMed

    Tokita, K; Hori, K; Kurotsu, T; Kanda, M; Saito, Y

    1993-10-01

    The mutant gene coding for a proline-activating domain (grs2-pro) was cloned and sequenced from Bacillus brevis Nagano, BII-3 strain, which produces gramicidin S synthetase 2 defective in proline-activation. By comparison of the nucleotide sequence with the wild-type sequence, a single point mutation was found at the 2609th guanine, which was replaced with adenine, resulting in the change of the 870th glycine to glutamic acid. Homology search for the deduced amino acid sequence of grs2-pro gene revealed that the 870th glycine was conserved in adenylate-forming enzymes, and its flanking sequence was highly conserved among the aminoacyl adenylate-forming enzymes, such as antibiotic peptide synthetases: gramicidin S synthetase 1 and 2 (GS1, GS2), tyrocidine synthetase 1 (TS1), and delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS); and other aminoacyl adenylation enzymes: alpha-aminoadipate reductase (LYS2), EntF, and AngR. On the other hand, this flanking sequence was not conserved in the other adenylate-forming enzymes lacking amino acid activation, such as acetyl-CoA synthetase, long-chain acyl-CoA synthetase, luciferase, and 4-coumarate CoA ligase. Single base substitutions at the 870th GGG codon were carried out by oligonucleotide site-directed mutagenesis. Four mutagenized clones were isolated, containing grs2-pro genes which exchange 870-Gly for alanine, valine, arginine, and tryptophan. The translated products from these clones could scarcely catalyze proline-dependent ATP-32PPi exchange reaction. The coil structure of 870-Gly region was lost in the mutants. These results suggest that the 870-Gly residue of grs2-pro protein is essential for aminoacyl-adenylation in the antibiotic peptide synthetase family.

  17. Charge Fluctuations and Boundary Conditions of Biological Ion Channels: Effect on the Ionic Transition Rate

    SciTech Connect

    Tindjong, R.; McClintock, P. V. E.; Luchinsky, D. G.; Kaufman, I.; Eisenberg, R. S.

    2009-04-23

    A self-consistent solution is derived for the Poisson-Nernst-Planck (PNP) equation, valid both inside a biological ion channel and in the adjacent bulk fluid. An iterative procedure is used to match the two solutions together at the channel mouth. Charge fluctuations at the mouth are modeled as shot noise flipping the height of the potential barrier at the selectivity site. The resultant estimates of the conductivity of the ion channel are in good agreement with Gramicidin experimental measurements and they reproduce the observed current saturation with increasing concentration.

  18. Activation of CS2 and CS by ML3 complexes.

    PubMed

    Ariafard, Alireza; Brookes, Nigel J; Stranger, Robert; Yates, Brian F

    2008-09-10

    The aim of this study was to determine the best neutral ML3 metal complexes for activating and cleaving the multiple bonds in CS2 and CS. Current experimental results show that, so far, only one bond in CS2 can be cleaved, and that CS can be activated but the bond is not broken. In the work described in this paper, density functional theory calculations have been used to evaluate the effectiveness of different ML3 complexes to activate the C-S bonds in CS2 and CS, with M = Mo, Re, W, and Ta and L = NH2. These calculations show that the combination of Re and Ta in the L3Re/CS2/TaL3 complex would be the most promising system for the cleavage of both C-S bonds of CS2. The reaction to cleave both C-S bonds is predicted to be exothermic by about 700 kJ mol(-1) and to proceed in an almost barrierless fashion. In addition, we are able to rationalize why the breaking of the C-S bond in CS has not been observed experimentally with M = Mo: this reaction is strongly endothermic. There is a subtle interplay between charge transfer and pi back-donation, and it appears that the Mo-C and Mo-S bonds are not strong enough to compensate for the breaking of the C-S bond. Our results suggest that, instead, CS could be cleaved with ReL3 or, even better, with a combination of ReL3 and TaL3. Molecular orbitals and Mulliken charges have been used to help explain these trends and to make predictions about the most promising systems for future experimental exploration.

  19. The Role of the Dielectric Barrier in Narrow Biological Channels: A Novel Composite Approach to Modeling Single-Channel Currents

    PubMed Central

    Mamonov, Artem B.; Coalson, Rob D.; Nitzan, Abraham; Kurnikova, Maria G.

    2003-01-01

    A composite continuum theory for calculating ion current through a protein channel of known structure is proposed, which incorporates information about the channel dynamics. The approach is utilized to predict current through the Gramicidin A ion channel, a narrow pore in which the applicability of conventional continuum theories is questionable. The proposed approach utilizes a modified version of Poisson-Nernst-Planck (PNP) theory, termed Potential-of-Mean-Force-Poisson-Nernst-Planck theory (PMFPNP), to compute ion currents. As in standard PNP, ion permeation is modeled as a continuum drift-diffusion process in a self-consistent electrostatic potential. In PMFPNP, however, information about the dynamic relaxation of the protein and the surrounding medium is incorporated into the model of ion permeation by including the free energy of inserting a single ion into the channel, i.e., the potential of mean force along the permeation pathway. In this way the dynamic flexibility of the channel environment is approximately accounted for. The PMF profile of the ion along the Gramicidin A channel is obtained by combining an equilibrium molecular dynamics (MD) simulation that samples dynamic protein configurations when an ion resides at a particular location in the channel with a continuum electrostatics calculation of the free energy. The diffusion coefficient of a potassium ion within the channel is also calculated using the MD trajectory. Therefore, except for a reasonable choice of dielectric constants, no direct fitting parameters enter into this model. The results of our study reveal that the channel response to the permeating ion produces significant electrostatic stabilization of the ion inside the channel. The dielectric self-energy of the ion remains essentially unchanged in the course of the MD simulation, indicating that no substantial changes in the protein geometry occur as the ion passes through it. Also, the model accounts for the experimentally observed

  20. High temperature synthesis of two open-framework uranyl silicates with ten-ring channels: Cs{sub 2}(UO{sub 2}){sub 2}Si{sub 8}O{sub 19} and Rb{sub 2}(UO{sub 2}){sub 2}Si{sub 5}O{sub 13}

    SciTech Connect

    Babo, Jean-Marie; Albrecht-Schmitt, Thomas E.

    2013-01-15

    The uranyl silicates Cs{sub 2}(UO{sub 2}){sub 2}Si{sub 8}O{sub 19} and Rb{sub 2}(UO{sub 2}){sub 2}Si{sub 5}O{sub 13} were obtained by mixing stoichiometric amounts of uranium metal, tellurium dioxide, silicon dioxide, and an excess of correspondent alkali metal halide flux. These compounds crystallize in the orthorhombic space groups Pnma and C222 with eight and two units per unit cell, respectively. Their crystal structures are dominated by zippered pentagonal bipyramidal chains of UO{sub 7} and silicates layer that are further connected into 3D frameworks. The cesium compound has silicate double layers while rubidium has a single layer. Six-ring voids and ten-ring channels are found in both compounds. - Graphical abstract: A view of the three-dimensional network structure of Cs{sub 2}(UO{sub 2}){sub 2}Si{sub 8}O{sub 19}. Highlights: Black-Right-Pointing-Pointer Three-dimensional uranium silicates. Black-Right-Pointing-Pointer Analogs of natural uranyl silicate minerals. Black-Right-Pointing-Pointer Complexity and symmetry ambiguity of uranyl silicates.

  1. Solid-state 19F-NMR analysis of 19F-labeled tryptophan in gramicidin A in oriented membranes.

    PubMed Central

    Grage, Stephan L; Wang, Junfeng; Cross, Timothy A; Ulrich, Anne S

    2002-01-01

    The response of membrane-associated peptides toward the lipid environment or other binding partners can be monitored by solid-state NMR of suitably labeled side chains. Tryptophan is a prominent amino acid in transmembrane helices, and its (19)F-labeled analogues are generally biocompatible and cause little structural perturbation. Hence, we use 5F-Trp as a highly sensitive NMR probe to monitor the conformation and dynamics of the indole ring. To establish this (19)F-NMR strategy, gramicidin A was labeled with 5F-Trp in position 13 or 15, whose chi(1)/chi(2) torsion angles are known from previous (2)H-NMR studies. First, the alignment of the (19)F chemical shift anisotropy tensor within the membrane was deduced by lineshape analysis of oriented samples. Next, the three principal axes of the (19)F chemical shift anisotropy tensor were assigned within the molecular frame of the indole ring. Finally, determination of chi(1)/chi(2) for 5F-Trp in the lipid gel phase showed that the side chain alignment differs by up to 20 degrees from its known conformation in the liquid crystalline state. The sensitivity gain of (19)F-NMR and the reduction in the amount of material was at least 10-fold compared with previous (2)H-NMR studies on the same system and 100-fold compared with (15)N-NMR. PMID:12496101

  2. Integrating Internet Tools into Traditional CS Distance Education Students' Attitudes.

    ERIC Educational Resources Information Center

    Gal-Ezer, Judith; Lupo, David

    2002-01-01

    Describes a study conducted on the attitudes of students towards the integration of the Web as a channel of communication and a study tool in traditional distance teaching of Computer Science (CS) at the Open University of Israel. Results of questionnaires show the Web cannot substitute entirely for face-to-face learning. (Author/LRW)

  3. Mentoring and the 6Cs.

    PubMed

    Young, Lorna

    2016-02-10

    As a staff nurse in a rehabilitation unit, I have been involved in patient care initiatives using the 6Cs of nursing: care, compassion, competence, communication, courage and commitment. However, I had not appreciated the benefits of using the 6Cs of nursing in the mentorship role.

  4. Single-Molecule Ion Channel Conformational Dynamics in Living Cells

    NASA Astrophysics Data System (ADS)

    Lu, H. Peter

    2014-03-01

    Stochastic and inhomogeneous conformational changes regulate the function and dynamics of ion channels that are crucial for cell functions, neuronal signaling, and brain functions. Such complexity makes it difficult, if not impossible, to characterize ion channel dynamics using conventional electrical recording alone since that the measurement does not specifically interrogate the associated conformational changes but rather the consequences of the conformational changes. Recently, new technology developments on single-molecule spectroscopy, and especially, the combined approaches of using single ion channel patch-clamp electrical recording and single-molecule fluorescence imaging have provided us the capability of probing ion channel conformational changes simultaneously with the electrical single channel recording. By combining real-time single-molecule fluorescence imaging measurements with real-time single-channel electric current measurements in artificial lipid bilayers and in living cell membranes, we were able to probe single ion-channel-protein conformational changes simultaneously, and thus providing an understanding the dynamics and mechanism of ion-channel proteins at the molecular level. The function-regulating and site-specific conformational changes of ion channels are now measurable under physiological conditions in real-time, one molecule at a time. We will focus our discussion on the new development and results of real-time imaging of the dynamics of gramicidin, colicin, and NMDA receptor ion channels in lipid bilayers and living cells. Our results shed light on new perspectives of the intrinsic interplay of lipid membrane dynamics, solvation dynamics, and the ion channel functions.

  5. Volatile anesthetics inhibit sodium channels without altering bulk lipid bilayer properties

    PubMed Central

    Sanford, R. Lea; Lee, William; Schultz, Margaret F.; Ingólfsson, Helgi I.

    2014-01-01

    Although general anesthetics are clinically important and widely used, their molecular mechanisms of action remain poorly understood. Volatile anesthetics such as isoflurane (ISO) are thought to alter neuronal function by depressing excitatory and facilitating inhibitory neurotransmission through direct interactions with specific protein targets, including voltage-gated sodium channels (Nav). Many anesthetics alter lipid bilayer properties, suggesting that ion channel function might also be altered indirectly through effects on the lipid bilayer. We compared the effects of ISO and of a series of fluorobenzene (FB) model volatile anesthetics on Nav function and lipid bilayer properties. We examined the effects of these agents on Nav in neuronal cells using whole-cell electrophysiology, and on lipid bilayer properties using a gramicidin-based fluorescence assay, which is a functional assay for detecting changes in lipid bilayer properties sensed by a bilayer-spanning ion channel. At clinically relevant concentrations (defined by the minimum alveolar concentration), both the FBs and ISO produced prepulse-dependent inhibition of Nav and shifted the voltage dependence of inactivation toward more hyperpolarized potentials without affecting lipid bilayer properties, as sensed by gramicidin channels. Only at supra-anesthetic (toxic) concentrations did ISO alter lipid bilayer properties. These results suggest that clinically relevant concentrations of volatile anesthetics alter Nav function through direct interactions with the channel protein with little, if any, contribution from changes in bulk lipid bilayer properties. Our findings further suggest that changes in lipid bilayer properties are not involved in clinical anesthesia. PMID:25385786

  6. Three-Dimensional Stress Field around a Membrane Protein: Atomistic and Coarse-Grained Simulation Analysis of Gramicidin A

    PubMed Central

    Yoo, Jejoong; Cui, Qiang

    2013-01-01

    Using both atomistic and coarse-grained (CG) models, we compute the three-dimensional stress field around a gramicidin A (gA) dimer in lipid bilayers that feature different degrees of negative hydrophobic mismatch. The general trends in the computed stress field are similar at the atomistic and CG levels, supporting the use of the CG model for analyzing the mechanical features of protein/lipid/water interfaces. The calculations reveal that the stress field near the protein-lipid interface exhibits a layered structure with both significant repulsive and attractive regions, with the magnitude of the stress reaching 1000 bar in certain regions. Analysis of density profiles and stress field distributions helps highlight the Trp residues at the protein/membrane/water interface as mechanical anchors, suggesting that similar analysis is useful for identifying tension sensors in other membrane proteins, especially membrane proteins involved in mechanosensation. This work fosters a connection between microscopic and continuum mechanics models for proteins in complex environments and makes it possible to test the validity of assumptions commonly made in continuum mechanics models for membrane mediated processes. For example, using the calculated stress field, we estimate the free energy of membrane deformation induced by the hydrophobic mismatch, and the results for regions beyond the annular lipids are in general consistent with relevant experimental data and previous theoretical estimates using elasticity theory. On the other hand, the assumptions of homogeneous material properties for the membrane and a bilayer thickness at the protein/lipid interface being independent of lipid type (e.g., tail length) appear to be oversimplified, highlighting the importance of annular lipids of membrane proteins. Finally, the stress field analysis makes it clear that the effect of even rather severe hydrophobic mismatch propagates to only about two to three lipid layers, thus putting a

  7. Maxwell displacement current allows to study structural changes of gramicidin A in monolayers at the air-water interface.

    PubMed

    Vitovic, Pavol; Weis, Martin; Tomcík, Pavol; Cirák, Július; Hianik, Tibor

    2007-05-01

    We applied methods of measurement Maxwell displacement current (MDC) pressure-area isotherms and dipole potential for analysis of the properties of gramicidin A (gA) and mixed gA/DMPC monolayers at an air-water interface. The MDC method allowed us to observe the kinetics of formation of secondary structure of gA in monolayers at an air-water interface. We showed, that secondary structure starts to form at rather low area per molecule at which gA monolayers are in gaseous state. Changes of the MDC during compression can be attributed to the reorientation of dipole moments in a gA double helix at area 7 nm(2)/molecule, followed by the formation of intertwined double helix of gA. The properties of gA in mixed monolayers depend on the molar fraction of gA/DMPC. At higher molar fractions of gA (around 0.5) the shape of the changes of dipole moment of mixed monolayer was similar to that for pure gA. The analysis of excess free energy in a gel (18( ) degrees C) and in a liquid-crystalline phase (28( ) degrees C) allowed us to show influence of the monolayer structural state on the interaction between gA and the phospholipids. In a gel state and at the gA/DMPC molar ratio below 0.17 the aggregates of gA were formed, while above this molar ratio gA interacts favorably with DMPC. In contrast, for DMPC in a liquid-crystalline state aggregation of gA was observed for all molar fractions studied. The effect of formation ordered structures between gA and DMPC is more pronounced at low temperatures.

  8. Three-dimensional stress field around a membrane protein: atomistic and coarse-grained simulation analysis of gramicidin A.

    PubMed

    Yoo, Jejoong; Cui, Qiang

    2013-01-08

    Using both atomistic and coarse-grained (CG) models, we compute the three-dimensional stress field around a gramicidin A (gA) dimer in lipid bilayers that feature different degrees of negative hydrophobic mismatch. The general trends in the computed stress field are similar at the atomistic and CG levels, supporting the use of the CG model for analyzing the mechanical features of protein/lipid/water interfaces. The calculations reveal that the stress field near the protein-lipid interface exhibits a layered structure with both significant repulsive and attractive regions, with the magnitude of the stress reaching 1000 bar in certain regions. Analysis of density profiles and stress field distributions helps highlight the Trp residues at the protein/membrane/water interface as mechanical anchors, suggesting that similar analysis is useful for identifying tension sensors in other membrane proteins, especially membrane proteins involved in mechanosensation. This work fosters a connection between microscopic and continuum mechanics models for proteins in complex environments and makes it possible to test the validity of assumptions commonly made in continuum mechanics models for membrane mediated processes. For example, using the calculated stress field, we estimate the free energy of membrane deformation induced by the hydrophobic mismatch, and the results for regions beyond the annular lipids are in general consistent with relevant experimental data and previous theoretical estimates using elasticity theory. On the other hand, the assumptions of homogeneous material properties for the membrane and a bilayer thickness at the protein/lipid interface being independent of lipid type (e.g., tail length) appear to be oversimplified, highlighting the importance of annular lipids of membrane proteins. Finally, the stress field analysis makes it clear that the effect of even rather severe hydrophobic mismatch propagates to only about two to three lipid layers, thus putting a

  9. Bandhead Energies in 125Cs

    NASA Astrophysics Data System (ADS)

    Sun, Ji; Hu, Xue-Yuan; Ma, Ying-Jun; Liu, Yun-Zuo; Tetsuro, Komatsubara; Kohei, Furuno; Zhang, Yu-Hu; Zhou, Wen-Ping; Wang, Shou-Yu

    Excited states in 125Cs have been studied with the fusion-evaporation-reaction 116Cd(14N,5n)125Cs at 65 MeV beam energy, using the Nordball-multidetector-system at the Niels-Bohr-Institute in Denmark. The level scheme of 125Cs was extended with the addition of more than 40 new γ-transitions. Moreover, the bandhead excitation energies of the previously known g9/2 and h11/2 bands were unambiguously corrected with plenty of hard evidence.

  10. Structures and isomorphous substitutions in Cs-Mg-beryl and Cs-rich beryllian indialite formed in a flux medium

    NASA Astrophysics Data System (ADS)

    Mikhailov, M. A.; Rozhdestvenskaya, I. V.; Bannova, I. I.

    2012-11-01

    The crystal structures of isostructural compounds — Cs-Mg-beryl (Al1.68Mg0.31Fe0.01)(Be2.68Si0.02Al0.26□0.04)Si6.00O18 · Cs0.07 ( a = 9.2359(9) Å, c = 9.204(1)Å) and the Cs variety of beryllian indialite (Mg1.90Fe0.10)(Be1.02Al1.98)(Al0.30Si5.70)O18 · Na0.02Cs0.16 ( a = 9.598(3) Å, c = 9.284(3) Å) — were refined. These compounds were formed in the Al2Be3Si6O18-Mg,Ca/F,Cl flux system in the presence of cesium chloride. The main structural features of these compounds were determined. It was found that the iso-morphous incorporation of Cs+ cations into anhydrous beryl proceeds according to the simple "vacancy" scheme BeT2 → 2(Cs+) R + □T2, whereas the complex heterovalent substitution 9SiT1 + AlT2 → 9AlT1 + BeT2 + 9(Cs, Na) R is observed in Cs-rich beryllian indialite under anhydrous conditions; i.e., no vacancies are formed in the tetrahedral framework of the latter structure. In Cs-Mg-beryl, an increase in the average bond lengths in the M octahedron and in the interring T2 tetrahedron leads to an increase in the unit-cell parameters a and c. In Cs-rich beryllian indialite, a slight increase in the M-O bond length and a decrease in T2-O bond length cause a slight increase in the parameter a and a decrease in the parameter c. The Cs+ cations are incorporated into the channels of both compounds at the height of the interring M-T2 layer (like K+ cations), whereas the Na+ cation is incorporated inside the Si6O18 ring. The δT1 value suggests that the change in the composition caused by the incorporation of Cs+ cations leads to the incongruent melting of beryllian indialite.

  11. Biophysical properties of the voltage gated proton channel HV1

    PubMed Central

    Musset, Boris; DeCoursey, Thomas

    2012-01-01

    The biophysical properties of the voltage gated proton channel (HV1) are the key elements of its physiological function. The voltage gated proton channel is a unique molecule that in contrast to all other ion channels is exclusively selective for protons. Alone among proton channels, it has voltage and time dependent gating like other “classical” ion channels. HV1 is furthermore a sensor for the pH in the cell and the surrounding media. Its voltage dependence is strictly coupled to the pH gradient across the membrane. This regulation restricts opening of the channel to specific voltages at any given pH gradient, therefore allowing HV1 to perform its physiological task in the tissue it is expressed in. For HV1 there is no known blocker. The most potent channel inhibitor is zinc (Zn2+) which prevents channel opening. An additional characteristic of HV1 is its strong temperature dependence of both gating and conductance. In contrast to single-file water filled pores like the gramicidin channel, HV1 exhibits pronounced deuterium effects and temperature effects on conduction, consistent with a different conduction mechanism than other ion channels. These properties may be explained by the recent identification of an aspartate in the pore of HV1 that is essential to its proton selectivity. PMID:23050239

  12. Timing of the developmental switch in GABA(A) mediated signaling from excitation to inhibition in CA3 rat hippocampus using gramicidin perforated patch and extracellular recordings.

    PubMed

    Tyzio, Roman; Holmes, Gregory L; Ben-Ari, Yehezkiel; Khazipov, Roustem

    2007-01-01

    The timing of the developmental switch in the GABA(A) mediated responses from excitatory to inhibitory was studied in Wistar rat CA3 hippocampal pyramidal cells using gramicidin perforated patch-clamp and extracellular recordings. Gramicidin perforated patch recordings revealed a gradual developmental shift in the reversal potential of synaptic and isoguvacine-induced GABA(A) mediated responses from -55 +/- 4 mV at postnatal days P0-2 to -74 +/- 3 mV at P13-15 with a midpoint of disappearance of the excitatory effects of GABA at around P8. Extracellular recordings in CA3 pyramidal cell layer revealed that the effect of isoguvacine on multiple unit activity (MUA) switched from an increase to a decrease at around P10. The effect of synaptic GABA(A) mediated responses on MUA switched from an increase to a decrease at around P8. It is concluded that the developmental switch in the action of GABA via GABA(A) receptors from excitatory to inhibitory occurs in Wistar rat CA3 pyramidal cells at around P8-10, an age that coincides with the transition from immature to mature hippocampal rhythms. We propose that excitatory GABA contributes to enhanced excitability and ictogenesis in the neonatal rat hippocampus.

  13. The orientation effect of gramicidin A on bicelles and Eu3+ -doped bicelles as studied by solid-state NMR and FT-IR spectroscopy.

    PubMed

    Marcotte, Isabelle; Bélanger, Anne; Auger, Michèle

    2006-02-01

    We have explored the effect of gramicidin A (gA) on bicelle (Bic) orientation in the absence and presence of Eu(3+) by (31)P and (2)H NMR at different DMPC/gA ratios. FT-IR spectroscopy was used to assess the lipid chain ordering and verify the transmembrane peptide conformation. Our results show a time-dependent flipping of the bilayer normal alignment at high temperatures and high proportion of gA. The results are explained by both the diamagnetic susceptibility anisotropy of the beta(6.3) helical peptides and viscosity of the lipid mixture. The concentration effect of gramicidin on Bic/Eu(3+) is compared to that on Eu(3+)-doped DMPC liposomes. The Bic/Eu(3+) system is no longer oriented in the presence of gA and adopts a vesicular morphology while the peptide incorporation induces the formation of ellipsoidal DMPC/Eu(3+) assemblies aligned with their normal parallel to the magnetic field. The difference is explained in terms of lipid chain disorder and size of the bilayers.

  14. Determinants of Water Permeability through Nanoscopic Hydrophilic Channels

    PubMed Central

    Portella, Guillem; de Groot, Bert L.

    2009-01-01

    Naturally occurring pores show a variety of polarities and sizes that are presumably directly linked to their biological function. Many biological channels are selective toward permeants similar or smaller in size than water molecules, and therefore their pores operate in the regime of single-file water pores. Intrinsic factors affecting water permeability through such pores include the channel-membrane match, the structural stability of the channel, the channel geometry and channel-water affinity. We present an extensive molecular dynamics study on the role of the channel geometry and polarity on the water osmotic and diffusive permeability coefficients. We show that the polarity of the naturally occurring peptidic channels is close to optimal for water permeation, and that the water mobility for a wide range of channel polarities is essentially length independent. By systematically varying the geometry and polarity of model hydrophilic pores, based on the fold of gramicidin A, the water density, occupancy, and permeability are studied. Our focus is on the characterization of the transition between different permeation regimes in terms of the structure of water in the pores, the average pore occupancy and the dynamics of the permeating water molecules. We show that a general relationship between osmotic and diffusive water permeability coefficients in the single-file regime accounts for the time averaged pore occupancy, and that the dynamics of the permeating water molecules through narrow non single file channels effectively behaves like independent single-file columns. PMID:19186131

  15. Lysophospholipids modulate channel function by altering the mechanical properties of lipid bilayers

    PubMed Central

    1994-01-01

    Lipid metabolites, free fatty acids and lysophospholipids, modify the function of membrane proteins including ion channels. Such alterations can occur through signal transduction pathways, but may also result from "direct" effects of the metabolite on the protein. To investigate possible mechanisms for such direct effects, we examined the alterations of gramicidin channel function by lysophospholipids (LPLs): lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), lysophosphatidylserine (LPS), and lysophosphatidylinositol (LPI). The experiments were done on planar bilayers formed by diphytanoylphosphatidylcholine in n-decane a system where receptor- mediated effects can be excluded. At aqueous concentrations below the critical micelle concentration (CMC), LPLs can increase the dimerization constant for membrane-bound gramicidin up to 500-fold (at 2 microM). The relative potency increases as a function of the size of the polar head group, but does not seem to vary as a function of head group charge. The increased dimerization constant results primarily from an increase in the rate constant for channel formation, which can increase more than 100-fold (in the presence of LPC and LPI), whereas the channel dissociation rate constant decreases only about fivefold. The LPL effect cannot be ascribed to an increased membrane fluidity, which would give rise to an increased channel dissociation rate constant. The ability of LPC to decrease the channel dissociation rate constant varies as a function of channel length (which is always less than the membrane's equilibrium thickness): as the channel length is decreased, the potency of LPC is increased. LPC has no effect on membrane thickness or the surface tension of monolayers at the air/electrolyte interface. The bilayer-forming glycerolmonooleate does not decrease the channel dissociation rate constant. These results show that LPLs alter gramicidin channel function by altering the membrane deformation energy, and

  16. Lysophospholipids modulate channel function by altering the mechanical properties of lipid bilayers.

    PubMed

    Lundbaek, J A; Andersen, O S

    1994-10-01

    Lipid metabolites, free fatty acids and lysophospholipids, modify the function of membrane proteins including ion channels. Such alterations can occur through signal transduction pathways, but may also result from "direct" effects of the metabolite on the protein. To investigate possible mechanisms for such direct effects, we examined the alterations of gramicidin channel function by lysophospholipids (LPLs): lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), lysophosphatidylserine (LPS), and lysophosphatidylinositol (LPI). The experiments were done on planar bilayers formed by diphytanoylphosphatidylcholine in n-decane a system where receptor-mediated effects can be excluded. At aqueous concentrations below the critical micelle concentration (CMC), LPLs can increase the dimerization constant for membrane-bound gramicidin up to 500-fold (at 2 microM). The relative potency increases as a function of the size of the polar head group, but does not seem to vary as a function of head group charge. The increased dimerization constant results primarily from an increase in the rate constant for channel formation, which can increase more than 100-fold (in the presence of LPC and LPI), whereas the channel dissociation rate constant decreases only about fivefold. The LPL effect cannot be ascribed to an increased membrane fluidity, which would give rise to an increased channel dissociation rate constant. The ability of LPC to decrease the channel dissociation rate constant varies as a function of channel length (which is always less than the membrane's equilibrium thickness): as the channel length is decreased, the potency of LPC is increased. LPC has no effect on membrane thickness or the surface tension of monolayers at the air/electrolyte interface. The bilayer-forming glycerolmonooleate does not decrease the channel dissociation rate constant. These results show that LPLs alter gramicidin channel function by altering the membrane deformation energy, and

  17. Through the channel and around the channel: Validating and comparing microscopic approaches for the evaluation of free energy profiles for ion penetration through ion channels.

    PubMed

    Kato, Mitsunori; Warshel, Arieh

    2005-10-20

    Microscopic calculations of free energy profiles for ion transport through biological ion channels present a very serious challenge to modern simulation approaches. The main problem is due to the major convergence problems associated with the heterogeneous landscape of the electrostatic environment in ion channels and with the need to evaluate the profile associated with the transfer of the ion from bulk water to the channel environment. This problem is compounded by the lack of reliable and relevant benchmarks that can discriminate between alternative approaches. The present study is aimed at reducing the above problems by defining benchmarks that are directly relevant to ion channels and can also give converging results. This is done by constructing a series of models of a truncated gramicidin channel with different numbers of water molecules and by comparing the profiles for going around the channel and through the channel. These discriminating models are then used to validate and compare the adiabatic charging free energy perturbation (FEP) approach combined with an umbrella sampling approach (Warshel, A. J. Phys. Chem. 1982, 86, 2218) and the potential of mean force (PMF) approach used frequently in studies of ion channels. It is found that both approaches work quite well until one moves to the case of the fully solvated channel. In this limit, the PMF approach may give different results for the overall work of going through the channel and around the channel, while the FEP approach gives physically consistent results. The present benchmark also indicates that the weighted histogram analysis method (WHAM) approach does not offer a significant advantage over earlier approaches at least as much as studies of ion channels are concerned. Finally, it is concluded that the FEP approach may be more useful in evaluating the overall barrier for moving ions from water to ion channels and that in some cases it might be beneficial to use the FEP approach for selective

  18. Linear rate-equilibrium relations arising from ion channel-bilayer energetic coupling

    PubMed Central

    Greisen, Per; Lum, Kevin; Ashrafuzzaman, Md.; Greathouse, Denise V.; Andersen, Olaf S.; Lundbæk, Jens A.

    2011-01-01

    Linear rate-equilibrium (RE) relations, also known as linear free energy relations, are widely observed in chemical reactions, including protein folding, enzymatic catalysis, and channel gating. Despite the widespread occurrence of linear RE relations, the principles underlying the linear relation between changes in activation and equilibrium energy in macromolecular reactions remain enigmatic. When examining amphiphile regulation of gramicidin channel gating in lipid bilayers, we noted that the gating process could be described by a linear RE relation with a simple geometric interpretation. This description is possible because the gating process provides a well-understood reaction, in which structural changes in a bilayer-embedded model protein can be studied at the single-molecule level. It is thus possible to obtain quantitative information about the energetics of the reaction transition state and its position on a spatial coordinate. It turns out that the linear RE relation for the gramicidin monomer-dimer reaction can be understood, and the quantitative relation between changes in activation energy and equilibrium energy can be interpreted, by considering the effects of amphiphiles on the changes in bilayer elastic energy associated with channel gating. We are not aware that a similar simple mechanistic explanation of a linear RE relation has been provided for a chemical reaction in a macromolecule. RE relations generally should be useful for examining how amphiphile-induced changes in bilayer properties modulate membrane protein folding and function, and for distinguishing between direct (e.g., due to binding) and indirect (bilayer-mediated) effects. PMID:21768343

  19. CHeCS Commanding Hardware

    NASA Technical Reports Server (NTRS)

    Moore, Jamie

    2010-01-01

    This slide presentation reviews the Crew Health Care System (CHeCS) commanding hardware. It includes information on the hardware status, commanding plan, and command training status with specific information the EV-CPDS 2 and 3, TEPC, MEC, and T2

  20. Seven Cs for Effective Teaching

    ERIC Educational Resources Information Center

    Emdin, Christopher

    2016-01-01

    When faced with students who have learning skills, styles, and backgrounds very different from their own, teachers can promote academic rigor by engaging in reality pedagogy. This approach proposes seven strategies, or Cs: Cogenerative dialogues (in which teachers solicit feedback from a dissimilar group of students); coteaching (in which students…

  1. Reactive barriers for 137Cs retention

    NASA Astrophysics Data System (ADS)

    Krumhansl, James L.; Brady, Patrick V.; Anderson, Howard L.

    2001-02-01

    137Cs was dispersed globally by cold war activities and, more recently, by the Chernobyl accident. Engineered extraction of 137Cs from soils and groundwaters is exceedingly difficult. Because the half-life of 137Cs is only 30.2 years, remediation might be more effective (and less costly) if 137Cs bioavailability could be demonstrably limited for even a few decades by use of a reactive barrier. Essentially permanent isolation must be demonstrated in those few settings where high nuclear level wastes contaminated the environment with 135Cs (half-life 2.3×10 6 years) in addition to 137Cs. Clays are potentially a low-cost barrier to Cs movement, though their long-term effectiveness remains untested. To identify optimal clays for Cs retention, Cs desorption was measured for five common clays: Wyoming Montmorillonite (SWy-1), Georgia Kaolinites (KGa-1 and KGa-2), Fithian Illite (F-Ill), and K-Metabentonite (K-Mbt). Exchange sites were pre-saturated with 0.16 M CsCl for 14 days and readily exchangeable Cs was removed by a series of LiNO 3 and LiCl washes. Washed clays were then placed into dialysis bags and the Cs release to the deionized water outside the bags measured. Release rates from 75 to 139 days for SWy-1, K-Mbt and F-Ill were similar; 0.017% to 0.021% sorbed Cs released per day. Both kaolinites released Cs more rapidly (0.12% to 0.05% of the sorbed Cs per day). In a second set of experiments, clays were Cs-doped for 110 days and subjected to an extreme and prolonged rinsing process. All the clays exhibited some capacity for irreversible Cs uptake. However, the residual loading was greatest on K-Mbt (˜0.33 wt.% Cs). Thus, this clay would be the optimal material for constructing artifical reactive barriers.

  2. Three body dissociation of CS2(2+) subsequent to various S(2p) Auger transitions.

    PubMed

    Saha, K; Banerjee, S B; Bapat, B

    2013-10-28

    Fragmentation kinematics of CS2 following various S(2p) Auger transitions is studied. Employing a combination of electron energy analysis and recoil ion momentum spectroscopy, changes in the dissociation channel yields, as well as the differences in the kinematical parameters for various bands of Auger hole states are presented. The fragmentation mechanism for dissociative channels leading to complete atomization of CS2(2+) molecular ion is studied in detail. We find that CS2(2+) does not retain linear geometry and is bent before undergoing concerted break-up. It is also observed that different geometric configurations of the CS2(2+) precursor result in different kinetic energy release values.

  3. Three body dissociation of CS22+ subsequent to various S(2p) Auger transitions

    NASA Astrophysics Data System (ADS)

    Saha, K.; Banerjee, S. B.; Bapat, B.

    2013-10-01

    Fragmentation kinematics of CS2 following various S(2p) Auger transitions is studied. Employing a combination of electron energy analysis and recoil ion momentum spectroscopy, changes in the dissociation channel yields, as well as the differences in the kinematical parameters for various bands of Auger hole states are presented. The fragmentation mechanism for dissociative channels leading to complete atomization of CS_2^{2+} molecular ion is studied in detail. We find that CS_2^{2+} does not retain linear geometry and is bent before undergoing concerted break-up. It is also observed that different geometric configurations of the CS_2^{2+} precursor result in different kinetic energy release values.

  4. Channel Estimation in DCT-Based OFDM

    PubMed Central

    Wang, Yulin; Zhang, Gengxin; Xie, Zhidong; Hu, Jing

    2014-01-01

    This paper derives the channel estimation of a discrete cosine transform- (DCT-) based orthogonal frequency-division multiplexing (OFDM) system over a frequency-selective multipath fading channel. Channel estimation has been proved to improve system throughput and performance by allowing for coherent demodulation. Pilot-aided methods are traditionally used to learn the channel response. Least square (LS) and mean square error estimators (MMSE) are investigated. We also study a compressed sensing (CS) based channel estimation, which takes the sparse property of wireless channel into account. Simulation results have shown that the CS based channel estimation is expected to have better performance than LS. However MMSE can achieve optimal performance because of prior knowledge of the channel statistic. PMID:24757439

  5. An Electrospray Ionization Mass Spectrometry Study on the "In Vacuo" Hetero-Oligomers Formed by the Antimicrobial Peptides, Surfactin and Gramicidin S

    NASA Astrophysics Data System (ADS)

    Rautenbach, Marina; Vlok, N. Maré; Eyéghé-Bickong, Hans A.; van der Merwe, Marthinus J.; Stander, Marietjie A.

    2017-08-01

    It was previously observed that the lipopeptide surfactants in surfactin (Srf) have an antagonistic action towards the highly potent antimicrobial cyclodecapeptide, gramicidin S (GS). This study reports on some of the molecular aspects of the antagonism as investigated through complementary electrospray ionization mass spectrometry techniques. We were able to detect stable 1:1 and 2:1 hetero-oligomers in a mixture of surfactin and gramicidin S. The noncovalent interaction between GS and Srf, with the proposed equilibrium: GS Srf↔GS+Srf correlated to apparent K d values of 6-9 μM in gas-phase and 1 μM in aqueous solution. The apparent K d values decreased with a longer incubation time and indicated a slow oligomerization equilibrium. Furthermore, the low μM K d app values of GS Srf↔GS+Srf fell within the biological concentration range and related to the 2- to 3-fold increase in [GS] needed for bacterial growth inhibition in the presence of Srf. Competition studies indicated that neither Na+ nor Ca2+ had a major effect on the stability of preformed heterodimers and that GS in fact out-competed Ca2+ and Na+ from Srf. Traveling wave ion mobility mass spectrometry revealed near symmetrical peaks of the heterodimers correlating to a compact dimer conformation that depend on specific interactions. Collision-induced dissociation studies indicated that the peptide interaction is most probably between one Orn residue in GS and the Asp residue, but not the Glu residue in Srf. We propose that flanking hydrophobic residues in both peptides stabilize the antagonistic and inactive peptide hetero-oligomers and shield the specific polar interactions in an aqueous environment.

  6. Ion channels generating complex spikes in cartwheel cells of the dorsal cochlear nucleus.

    PubMed

    Kim, Yuil; Trussell, Laurence O

    2007-02-01

    Cartwheel cells are glycinergic interneurons that modify somatosensory input to the dorsal cochlear nucleus. They are characterized by firing of mixtures of both simple and complex action potentials. To understand what ion channels determine the generation of these two types of spike waveforms, we recorded from cartwheel cells using the gramicidin perforated-patch technique in brain slices of mouse dorsal cochlear nucleus and applied channel-selective blockers. Complex spikes were distinguished by whether they arose directly from a negative membrane potential or later during a long depolarization. Ca(2+) channels and Ca(2+)-dependent K(+) channels were major determinants of complex spikes. Onset complex spikes required T-type and possibly R-type Ca(2+) channels and were shaped by BK and SK K(+) channels. Complex spikes arising later in a depolarization were dependent on P/Q- and L-type Ca(2+) channels as well as BK and SK channels. BK channels also contributed to fast repolarization of simple spikes. Simple spikes featured an afterdepolarization that is probably the trigger for complex spiking and is shaped by T/R-type Ca(2+) and SK channels. Fast spikes were dependent on Na(+) channels; a large persistent Na(+) current may provide a depolarizing drive for spontaneous activity in cartwheel cells. Thus the diverse electrical behavior of cartwheel cells is determined by the interaction of a wide variety of ion channels with a prominent role played by Ca(2+).

  7. CS2SAT Desktop Tool

    SciTech Connect

    2006-03-15

    The Idaho National Laboratory (INL) has developed a Control System Cyber Security Self-Assessment Tool (CS2SAT) desktop tool that provides a repeatable and systematic approach for control system users to assess the cyber security posture of their control system networks. The tool assists users in identifying the cyber security parameters of their systems and then offers security objectives, in the form of requirements, for improving the security of their specific network. Each requirement is linked to a series of associated recommendations for compliance dependent upon the desired level of security protection. Each requirement is supported by links to the original standards document and recommendations are supported by links to whitepapers and other help documents. Package also includes two back-end supporting codes: CS2SAT Requirements Matrix and Control System Security Information System.

  8. ITER CS Intermodule Support Structure

    SciTech Connect

    Myatt, R.; Freudenberg, Kevin D

    2011-01-01

    With five independently driven, bi-polarity power supplies, the modules of the ITER central solenoid (CS) can be energized in aligned or opposing field directions. This sets up the possibility for repelling modules, which indeed occurs, particularly between CS2L and CS3L around the End of Burn (EOB) time point. Light interface compression between these two modules at EOB and wide variations in these coil currents throughout the pulse produce a tendency for relative motion or slip. Ideally, the slip is purely radial as the modules breathe without any accumulative translational motion. In reality, however, asymmetries such as nonuniformity in intermodule friction, lateral loads from a plasma Vertical Disruption Event (VDE), magnetic forces from manufacturing and assembly tolerances, and earthquakes can all contribute to a combination of radial and lateral module motion. This paper presents 2D and 3D, nonlinear, ANSYS models which simulate these various asymmetries and determine the lateral forces which must be carried by the intermodule structure. Summing all of these asymmetric force contributions leads to a design-basis lateral load which is used in the design of various support concepts: the CS-CDR centering rings and a variation, the 2001 FDR baseline radial keys, and interlocking castles structures. Radial key-type intermodule structure interface slip and stresses are tracked through multiple 15 MA scenario current pulses to demonstrate stable motion following the first few cycles. Detractions and benefits of each candidate intermodule structure are discussed, leading to the simplest and most robust configuration which meets the design requirements: match-drilled radial holes and pin-shaped keys.

  9. Observation of thresholds and overlapping resonances below the 10 2P1/2 and 2P3/2 thresholds in the photodetachment of Cs-

    NASA Astrophysics Data System (ADS)

    Lindahl, A. O.; Rohlén, J.; Hultgren, H.; Pegg, D. J.; Walter, C. W.; Hanstorp, D.

    2013-11-01

    A collinear beam apparatus has been used to study photodetachment of Cs-. Partial cross sections were measured using state-selective detection based on a resonance ionization scheme. Several resonances were observed in the Cs(102S), Cs(62F), Cs(62G), and Cs(62H) final-state channels below the Cs(102P3/2) channel opening. A model was developed to account for the interference between overlapping resonances. This model is essentially a generalization of the Fano [U. Fano, Phys. Rev.PHRVAO0031-899X10.1103/PhysRev.124.1866 124, 1866 (1961)] and Shore [B. W. Shore, Phys. Rev.PHRVAO0031-899X10.1103/PhysRev.171.43 171, 43 (1968)] parametrizations for single resonances. Resonance parameters were extracted by fitting the model to the data sets. The openings of the Cs(102S) and Cs(62F) channels, where the polarizabilities of the atomic states are large and positive, showed rapid onsets. In the case of the Cs(62G) and Cs(62H) channels, on the other hand, the photodetachment cross sections increased slowly with energy. For the Cs(62H) channel this is the expected behavior, since it is the result of a large and negative polarizability of the 62H state. In addition, the excitation of the Cs(62H) state with respect to the Cs ground state was found to be 28 356.3(2) cm-1, in agreement with a previous experiment.

  10. Experimental and theoretical studies of the reaction of Rh+ with CS2 in the gas phase: thermochemistry of RhS+ and RhCS+.

    PubMed

    Armentrout, P B; Kretzschmar, Ilona

    2009-10-15

    The gas-phase reactivity of the atomic transition-metal cation rhodium, Rh(+), with CS(2) is investigated using guided-ion-beam mass spectrometry (GIBMS). Endothermic reactions forming RhS(+) and RhCS(+) are observed. Analysis of the kinetic energy dependence of the cross sections for formation of these two products yields the 0 K bond energies of D(0)(Rh(+)-S) = 2.61 +/- 0.12 eV and D(0)(Rh(+)-CS) = 2.66 +/- 0.19 eV. These compare favorably with quantum chemical calculations at the CCSD(T)/Def2TZVPP//B3LYP/Def2TZVPP and CCSD(T)/Def2TZVPP levels of theory, where the former is also used to explore the complete potential energy surface of the reaction. It is found that the reaction initially involves insertion of the rhodium cation into one of the CS bonds of CS(2), followed by metal ligand cleavages to form the two product channels. The formation of ground state RhS(+) products is spin-forbidden, whereas RhCS(+) formation is spin-allowed. Crossing points between the triplet and quintet surfaces are located in the region of the SRh(+)(CS) intermediate, which suggests that coupling between the surfaces is reasonably efficient, consistent with experiment.

  11. Detection of single ion channel activity with carbon nanotubes

    PubMed Central

    Zhou, Weiwei; Wang, Yung Yu; Lim, Tae-Sun; Pham, Ted; Jain, Dheeraj; Burke, Peter J.

    2015-01-01

    Many processes in life are based on ion currents and membrane voltages controlled by a sophisticated and diverse family of membrane proteins (ion channels), which are comparable in size to the most advanced nanoelectronic components currently under development. Here we demonstrate an electrical assay of individual ion channel activity by measuring the dynamic opening and closing of the ion channel nanopores using single-walled carbon nanotubes (SWNTs). Two canonical dynamic ion channels (gramicidin A (gA) and alamethicin) and one static biological nanopore (α-hemolysin (α-HL)) were successfully incorporated into supported lipid bilayers (SLBs, an artificial cell membrane), which in turn were interfaced to the carbon nanotubes through a variety of polymer-cushion surface functionalization schemes. The ion channel current directly charges the quantum capacitance of a single nanotube in a network of purified semiconducting nanotubes. This work forms the foundation for a scalable, massively parallel architecture of 1d nanoelectronic devices interrogating electrophysiology at the single ion channel level. PMID:25778101

  12. Detection of single ion channel activity with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zhou, Weiwei; Wang, Yung Yu; Lim, Tae-Sun; Pham, Ted; Jain, Dheeraj; Burke, Peter J.

    2015-03-01

    Many processes in life are based on ion currents and membrane voltages controlled by a sophisticated and diverse family of membrane proteins (ion channels), which are comparable in size to the most advanced nanoelectronic components currently under development. Here we demonstrate an electrical assay of individual ion channel activity by measuring the dynamic opening and closing of the ion channel nanopores using single-walled carbon nanotubes (SWNTs). Two canonical dynamic ion channels (gramicidin A (gA) and alamethicin) and one static biological nanopore (α-hemolysin (α-HL)) were successfully incorporated into supported lipid bilayers (SLBs, an artificial cell membrane), which in turn were interfaced to the carbon nanotubes through a variety of polymer-cushion surface functionalization schemes. The ion channel current directly charges the quantum capacitance of a single nanotube in a network of purified semiconducting nanotubes. This work forms the foundation for a scalable, massively parallel architecture of 1d nanoelectronic devices interrogating electrophysiology at the single ion channel level.

  13. Distinctly different interactions of anesthetic and nonimmobilizer with transmembrane channel peptides.

    PubMed Central

    Tang, P; Hu, J; Liachenko, S; Xu, Y

    1999-01-01

    Although it plays no clinical role in general anesthesia, gramicidin A, a transmembrane channel peptide, provides an excellent model for studying the specific interaction between volatile anesthetics and membrane proteins at the molecular level. We show here that a pair of structurally similar volatile anesthetic and nonimmobilizer (nonanesthetic), 1-chloro-1,2,2-trifluorocyclobutane (F3) and 1, 2-dichlorohexafluorocyclobutane (F6), respectively, interacts differently with the transmembrane peptide. With 400 microM gramicidin A in a vesicle suspension of 60 mM phosphatidylcholine-phosphatidylglycerol (PC/PG), the intermolecular cross-relaxation rate constants between (19)F of F3 and (1)H in the chemical shift regions for the indole and backbone amide protons were 0.0106 +/- 0.0007 (n = 12) and 0.0105 +/- 0.0014 (n = 8) s(-1), respectively. No cross-relaxation was measurable between (19)F of F6 and protons in these regions. Sodium transport study showed that with 75 microM gramicidin A in a vesicle suspension of 66 mM PC/PG, F3 increased the (23)Na apparent efflux rate constant from 149.7 +/- 7.2 of control (n = 3) to 191.7 +/- 12.2 s(-1) (n = 3), and the apparent influx rate constant from 182.1 +/- 15.4 to 222.8 +/- 21.7 s(-1) (n = 3). In contrast, F6 had no effects on either influx or efflux rate. It is concluded that the ability of general anesthetics to interact with amphipathic residues near the peptide-lipid-water interface and the inability of nonimmobilizer to do the same may represent some characteristics of anesthetic-protein interaction that are of importance to general anesthesia. PMID:10423422

  14. Reactive barriers for {sup 137}Cs retention

    SciTech Connect

    KRUMHANSL,JAMES L.; BRADY,PATRICK V.; ANDERSON,HOWARD L.

    2000-05-19

    {sup 137}Cs was dispersed globally by cold war activities and, more recently, by the Chernobyl accident. Engineered extraction of {sup 137}Cs from soils and groundwaters is exceedingly difficult. Because the half life of {sup 137}Cs is only 30.2 years, remediation might be more effective (and less costly) if {sup 137}Cs bioavailability could be demonstrably limited for even a few decades by use of a reactive barrier. Essentially permanent isolation must be demonstrated in those few settings where high nuclear level wastes contaminated the environment with {sup 135}Cs (half life 2.3x10{sup 6} years) in addition to {sup 137}Cs. Clays are potentially a low-cost barrier to Cs movement, though their long-term effectiveness remains untested. To identify optimal clays for Cs retention Cs resorption was measured for five common clays: Wyoming Montmorillonite (SWy-1), Georgia Kaolinites (KGa-1 and KGa-2), Fithian Illite (F-Ill), and K-Metabentonite (K-Mbt). Exchange sites were pre-saturated with 0.16 M CsCl for 14 days and readily exchangeable Cs was removed by a series of LiNO{sub 3} and LiCl washes. Washed clay were then placed into dialysis bags and the Cs release to the deionized water outside the bags measured. Release rates from 75 to 139 days for SWy-1, K-Mbt and F- 111 were similar; 0.017 to 0.021% sorbed Cs released per day. Both kaolinites released Cs more rapidly (0.12 to 0.05% of the sorbed Cs per day). In a second set of experiments, clays were doped for 110 days and subjected to an extreme and prolonged rinsing process. All the clays exhibited some capacity for irreversible Cs uptake so most soils have some limited ability to act as a natural barrier to Cs migration. However, the residual loading was greatest on K-Mbt ({approximately} 0.33 wt% Cs). Thus, this clay would be the optimal material for constructing artificial reactive barriers.

  15. Neural stem cell proliferation and differentiation in the conductive PEDOT-HA/Cs/Gel scaffold for neural tissue engineering.

    PubMed

    Wang, Shuping; Guan, Shui; Xu, Jianqiang; Li, Wenfang; Ge, Dan; Sun, Changkai; Liu, Tianqing; Ma, Xuehu

    2017-09-12

    Engineering scaffolds with excellent electro-activity is increasingly important in tissue engineering and regenerative medicine. Herein, conductive poly(3,4-ethylenedioxythiophene) doped with hyaluronic acid (PEDOT-HA) nanoparticles were firstly synthesized via chemical oxidant polymerization. A three-dimensional (3D) PEDOT-HA/Cs/Gel scaffold was then developed by introducing PEDOT-HA nanoparticles into a chitosan/gelatin (Cs/Gel) matrix. HA, as a bridge, not only was used as a dopant, but also combined PEDOT into the Cs/Gel via chemical crosslinking. The PEDOT-HA/Cs/Gel scaffold was used as a conductive substrate for neural stem cell (NSC) culture in vitro. The results demonstrated that the PEDOT-HA/Cs/Gel scaffold had excellent biocompatibility for NSC proliferation and differentiation. 3D confocal fluorescence images showed cells attached on the channel surface of Cs/Gel and PEDOT-HA/Cs/Gel scaffolds with a normal neuronal morphology. Compared to the Cs/Gel scaffold, the PEDOT-HA/Cs/Gel scaffold not only promoted NSC proliferation with up-regulated expression of Ki67, but also enhanced NSC differentiation into neurons and astrocytes with up-regulated expression of β tubulin-III and GFAP, respectively. It is expected that this electro-active and bio-active PEDOT-HA/Cs/Gel scaffold will be used as a conductive platform to regulate NSC behavior for neural tissue engineering.

  16. [Assessment of health effects of CS gas].

    PubMed

    Schindel, H J

    1993-07-01

    O-chlorobenzylidene malononitrile (CS) gas or aerosol is by no means a harmless tear-gas, as often is described; in particular, CS is a very effective irritating war gas. The effects of CS on humans are relatively unknown because publications in this respect are mostly on military medical research, partly classified as secret, and brought to the knowledge of a small number of experts only. CS is highly soluble in water, and hence the effects in police water jets are very low. The efficacy of CS-containing water-jetting consists only in the pressure of the jet stream. Medically, in police use, CS is therefore considered to be harmless. Military medical research results, however, show that persons older than 30 years, those under physical strain, and those with hitherto undetected aneurysm are especially at risk.

  17. Label-free study of the function of ion channel protein on a microfluidic optical sensor integrated with artificial cell membrane.

    PubMed

    Li, Zhen; Tang, Yanyan; Zhang, Ling; Wu, Jianmin

    2014-01-21

    A label-free optical sensor was constructed by integrating pH sensing material and supported phospholipid bilayers (SPBs) in a microfluidic chip. The pH sensing material was composed of a double layer structure consisting of chitosan hydrogel and electrochemically etched porous silicon. The pH change in the microchip could induce a reversible swelling of the chitosan hydrogel layer and consequently caused a shift in effective optical thickness (EOT) of the double layer, which could be observed by Fourier transformed reflectometric interference spectroscopy (FT-RIS). After phospholipid bilayers (PLBs) were self-assembled on the sensing layer, the EOT almost remained constant during the cycling of pH from 7.4 to 6.2, indicating the blockage of H(+) translocation by the PLBs. For studying the behavior of ion channel protein, gramicidin A, a typical ion channel protein, was inserted in the SPBs for mimicking the ion transportation function of cell membrane. Due to the H(+) transportation capability of gramicidin A, the optical response to pH change could partially recover. In the presence of Ca(2+), the pore of the ion channel protein was blocked, causing a significant decrease in the EOT response upon pH change. The bio-functionalized microfluidic sensor fabricated in this work will provide a reliable platform for studying the function of ion channel protein, which is an important class of drug targets.

  18. Atomic force microscopy imaging and electrical recording of lipid bilayers supported over microfabricated silicon chip nanopores: lab-on-a-chip system for lipid membranes and ion channels.

    PubMed

    Quist, Arjan P; Chand, Ami; Ramachandran, Srinivasan; Daraio, Chiara; Jin, Sungho; Lal, Ratnesh

    2007-01-30

    We describe a silicon chip-based supported bilayer system to detect the presence of ion channels and their electrical conductance in lipid bilayers. Nanopores were produced in microfabricated silicon membranes by electron beam lithography as well as by using a finely focused ion beam. Thermal oxide was used to shrink pore sizes, if necessary, and to create an insulating surface. The chips with well-defined pores were easily mounted on a double-chamber plastic cell recording system, allowing for controlling the buffer conditions both above and below the window. The double-chamber system allowed using an atomic force microscopy (AFM) tip as one electrode and inserting a platinum wire as the second electrode under the membrane window, to measure electrical current across lipid bilayers that are suspended over the pores. Atomic force imaging, stiffness measurement, and electrical capacitance measurement show the feasibility of supporting lipid bilayers over defined nanopores: a key requirement to use any such technique for structure-function study of ion channels. Online addition of gramicidin, an ion-channel-forming peptide, resulted in electrical current flow across the bilayer, and the I-V curve that was measured using the conducting AFM tip indicates the presence of many conducting gramicidin ion channels.

  19. Microstructure of Cs-implanted zirconia: Role of temperature

    SciTech Connect

    Vincent, L.; Thome, L.; Garrido, F.; Kaitasov, O.; Houdelier, F.

    2008-12-01

    The aim of this study was to identify experimentally the phase which includes cesium in yttria stabilized zirconia (YSZ). The solubility and retention of cesium in YSZ were studied at high temperature (HT). Cesium was ion implanted (at 300 keV) into YSZ at room temperature (RT), 750 deg. C, or 900 deg. C at fluences up to 5x10{sup 16} cm{sup -2}. The temperature dependence of the radiation-induced damage and of the cesium distribution in YSZ single crystals was investigated by Rutherford backscattering spectrometry and ion channeling. Transmission electron microscopy (TEM) studies were performed in order to determine the damage nature and search for a predicted ternary phase of cesium zirconate. Whatever the implantation temperature, the thickness of the damaged layer increases inwards with ion fluence. At RT, amorphization occurs, caused by the high Cs concentration (7 at. %). In situ TEM during postannealing shows recrystallization of cubic zirconia after release of cesium. A high implantation temperature has a significant influence on the nature of radiation defects and on the retained Cs concentration. At HT, dislocation loops and voids are formed but no amorphization is observed whereas polygonization occurs at high fluence. The implanted cesium concentration reaches a saturation value of 1.5 at. % above which Cs can no longer be retained in the matrix and is then released at the surface. At that concentration, cesium forms a solid solution in YSZ; no other phase is formed, neither during irradiation nor after thermal annealing.

  20. Localization of a continuum shape resonance - Photoionization of CS2

    NASA Astrophysics Data System (ADS)

    Kakar, Sandeep; Choi, Heung-Cheun; Poliakoff, E. D.

    1992-10-01

    We report a vibrationally resolved investigation into the 5sigma(u) exp -1 shape-resonant ionization dynamics for CS2 in the range h nu 18-30 eV. The intensity of dispersed fluorescence from CS2(+)(B 2Sigma(u)(+) photoions is measured to obtain partial photoionization cross-section curves for the v = (0,0,0) and (1,0,0) levels of CS2(+)(B 2Sigma(u)(+), as well as the vibrational branching ratio. Our results indicate a shape resonance at hv equal to about 21 eV which is insensitive to changes in the symmetric stretching coordinate. These data are consistent with recent theoretical efforts that predict a shape resonance in the 5sigma(u) - epsilon pi(g) channel. All previous vibrationally resolved data on shape resonances have been obtained for systems whose shape resonances occur in the (epsilon sigma) continuum. The current results are in contrast to behavior observed for other shape resonances, highlighting both their diverse nature and possible extensions of the current measurements.

  1. Microstructure of Cs-implanted zirconia: Role of temperature

    NASA Astrophysics Data System (ADS)

    Vincent, L.; Thomé, L.; Garrido, F.; Kaitasov, O.; Houdelier, F.

    2008-12-01

    The aim of this study was to identify experimentally the phase which includes cesium in yttria stabilized zirconia (YSZ). The solubility and retention of cesium in YSZ were studied at high temperature (HT). Cesium was ion implanted (at 300 keV) into YSZ at room temperature (RT), 750 °C, or 900 °C at fluences up to 5×1016 cm-2. The temperature dependence of the radiation-induced damage and of the cesium distribution in YSZ single crystals was investigated by Rutherford backscattering spectrometry and ion channeling. Transmission electron microscopy (TEM) studies were performed in order to determine the damage nature and search for a predicted ternary phase of cesium zirconate. Whatever the implantation temperature, the thickness of the damaged layer increases inwards with ion fluence. At RT, amorphization occurs, caused by the high Cs concentration (7at.%). In situ TEM during postannealing shows recrystallization of cubic zirconia after release of cesium. A high implantation temperature has a significant influence on the nature of radiation defects and on the retained Cs concentration. At HT, dislocation loops and voids are formed but no amorphization is observed whereas polygonization occurs at high fluence. The implanted cesium concentration reaches a saturation value of 1.5 at. % above which Cs can no longer be retained in the matrix and is then released at the surface. At that concentration, cesium forms a solid solution in YSZ; no other phase is formed, neither during irradiation nor after thermal annealing.

  2. Towards sparse characterisation of on-body ultra-wideband wireless channels.

    PubMed

    Yang, Xiaodong; Ren, Aifeng; Zhang, Zhiya; Ur Rehman, Masood; Abbasi, Qammer Hussain; Alomainy, Akram

    2015-06-01

    With the aim of reducing cost and power consumption of the receiving terminal, compressive sensing (CS) framework is applied to on-body ultra-wideband (UWB) channel estimation. It is demonstrated in this Letter that the sparse on-body UWB channel impulse response recovered by the CS framework fits the original sparse channel well; thus, on-body channel estimation can be achieved using low-speed sampling devices.

  3. Numerical methods for a Poisson-Nernst-Planck-Fermi model of biological ion channels

    NASA Astrophysics Data System (ADS)

    Liu, Jinn-Liang; Eisenberg, Bob

    2015-07-01

    Numerical methods are proposed for an advanced Poisson-Nernst-Planck-Fermi (PNPF) model for studying ion transport through biological ion channels. PNPF contains many more correlations than most models and simulations of channels, because it includes water and calculates dielectric properties consistently as outputs. This model accounts for the steric effect of ions and water molecules with different sizes and interstitial voids, the correlation effect of crowded ions with different valences, and the screening effect of polarized water molecules in an inhomogeneous aqueous electrolyte. The steric energy is shown to be comparable to the electrical energy under physiological conditions, demonstrating the crucial role of the excluded volume of particles and the voids in the natural function of channel proteins. Water is shown to play a critical role in both correlation and steric effects in the model. We extend the classical Scharfetter-Gummel (SG) method for semiconductor devices to include the steric potential for ion channels, which is a fundamental physical property not present in semiconductors. Together with a simplified matched interface and boundary (SMIB) method for treating molecular surfaces and singular charges of channel proteins, the extended SG method is shown to exhibit important features in flow simulations such as optimal convergence, efficient nonlinear iterations, and physical conservation. The generalized SG stability condition shows why the standard discretization (without SG exponential fitting) of NP equations may fail and that divalent Ca2 + may cause more unstable discrete Ca2 + fluxes than that of monovalent Na+. Two different methods—called the SMIB and multiscale methods—are proposed for two different types of channels, namely, the gramicidin A channel and an L-type calcium channel, depending on whether water is allowed to pass through the channel. Numerical methods are first validated with constructed models whose exact solutions are

  4. Numerical methods for a Poisson-Nernst-Planck-Fermi model of biological ion channels.

    PubMed

    Liu, Jinn-Liang; Eisenberg, Bob

    2015-07-01

    Numerical methods are proposed for an advanced Poisson-Nernst-Planck-Fermi (PNPF) model for studying ion transport through biological ion channels. PNPF contains many more correlations than most models and simulations of channels, because it includes water and calculates dielectric properties consistently as outputs. This model accounts for the steric effect of ions and water molecules with different sizes and interstitial voids, the correlation effect of crowded ions with different valences, and the screening effect of polarized water molecules in an inhomogeneous aqueous electrolyte. The steric energy is shown to be comparable to the electrical energy under physiological conditions, demonstrating the crucial role of the excluded volume of particles and the voids in the natural function of channel proteins. Water is shown to play a critical role in both correlation and steric effects in the model. We extend the classical Scharfetter-Gummel (SG) method for semiconductor devices to include the steric potential for ion channels, which is a fundamental physical property not present in semiconductors. Together with a simplified matched interface and boundary (SMIB) method for treating molecular surfaces and singular charges of channel proteins, the extended SG method is shown to exhibit important features in flow simulations such as optimal convergence, efficient nonlinear iterations, and physical conservation. The generalized SG stability condition shows why the standard discretization (without SG exponential fitting) of NP equations may fail and that divalent Ca(2+) may cause more unstable discrete Ca(2+) fluxes than that of monovalent Na(+). Two different methods-called the SMIB and multiscale methods-are proposed for two different types of channels, namely, the gramicidin A channel and an L-type calcium channel, depending on whether water is allowed to pass through the channel. Numerical methods are first validated with constructed models whose exact solutions are

  5. Hydrodynamic model of temperature change in open ionic channels.

    PubMed Central

    Chen, D P; Eisenberg, R S; Jerome, J W; Shu, C W

    1995-01-01

    Most theories of open ionic channels ignore heat generated by current flow, but that heat is known to be significant when analogous currents flow in semiconductors, so a generalization of the Poisson-Nernst-Planck theory of channels, called the hydrodynamic model, is needed. The hydrodynamic theory is a combination of the Poisson and Euler field equations of electrostatics and fluid dynamics, conservation laws that describe diffusive and convective flow of mass, heat, and charge (i.e., current), and their coupling. That is to say, it is a kinetic theory of solute and solvent flow, allowing heat and current flow as well, taking into account density changes, temperature changes, and electrical potential gradients. We integrate the equations with an essentially nonoscillatory shock-capturing numerical scheme previously shown to be stable and accurate. Our calculations show that 1) a significant amount of electrical energy is exchanged with the permeating ions; 2) the local temperature of the ions rises some tens of degrees, and this temperature rise significantly alters for ionic flux in a channel 25 A long, such as gramicidin-A; and 3) a critical parameter, called the saturation velocity, determines whether ionic motion is overdamped (Poisson-Nernst-Planck theory), is an intermediate regime (called the adiabatic approximation in semiconductor theory), or is altogether unrestricted (requiring the full hydrodynamic model). It seems that significant temperature changes are likely to accompany current flow in the open ionic channel. PMID:8599638

  6. Vibrationally resolved cross sections for the photoionization of CS2

    NASA Astrophysics Data System (ADS)

    Stratmann, R. E.; Lucchese, Robert R.

    1994-12-01

    We have performed vibrationally resolved calculations of the excitation of the symmetric stretch in the photoionization of CS2 leading to the X 2Πg, A 2Πu, B 2Σ+u, and C 2Σ+g states of CS+2. Previous theoretical work has determined that the kπg shape resonance in the (5σu)-1 channel consists mainly of a linear combination of low lying virtual d orbitals on sulfur and is thus essentially atomic in nature. This conclusion was primarily based on the shape of the resonant wave function and the insensitivity of the energy of the resonance to bond stretching. Here, we have determined that the energies of the kπ shape resonances located well above threshold and the σ bound states just below threshold are insensitive to bond length. We have also found nearly constant vibrational branching ratios in all channels and polarization components. This is in qualitative agreement with experimental vibrationally resolved cross sections [S. Kakar, H. C. Choi, and E. D. Poliakoff, J. Chem. Phys. 97, 4690 (1992)] which show nearly constant vibrational branching ratios. Our present results indicate that caution must be exercised when using bond length sensitivity as an exclusive means to determine the existence of shape resonances.

  7. Electrostatic calculations for an ion channel. I. Energy and potential profiles and interactions between ions.

    PubMed Central

    Levitt, D G

    1978-01-01

    The electrostatic energy profile of one, two, or three ions in an aqueous channel through a lipid membrane is calculated. It is shown that the previous solution to this problem (based on the assumption that the channel is infinitely long) significantly overestimates the electrostatic energy barrier. For example, for a 3-A radius pore, the energy is 16 kT for the infinite channel and 6.7 kT for an ion in the center of a channel 25 A long. The energy as a function of the position of the ion is also determined. With this energy profile, the rate of crossing the membrane (using the Nernst-Planck equation) was estimated and found to be compatible with the maximum conductance observed for the gramicidin A channel. The total electrostatic energy (as a function of position) required to place two or three ions in the channel is also calculated. The electrostatic interaction is small for two ions at opposite ends of the channel and large for any positioning of the three ions. Finally, the gradient through the channel of an applied potential is calculated. The solution to these problems is based on solving an equivalent problem in which an appropriate surface charge is placed on the boundary between the lipid and aqueous regions. The magnitude of the surface charge is obtained from the numerical solution for a system of coupled integral equations. PMID:656542

  8. Not only enthalpy: large entropy contribution to ion permeation barriers in single-file channels.

    PubMed

    Portella, Guillem; Hub, Jochen S; Vesper, Martin D; de Groot, Bert L

    2008-09-01

    The effect of channel length on the barrier for potassium ion permeation through single-file channels has been studied by means of all-atom molecular dynamics simulations. Using series of peptidic gramicidin-like and simplified ring-structured channels, both embedded in model membranes, we obtained two distinct types of behavior: saturation of the central free energy barriers for peptidic channels and a linear increase in simplified ring-structured channels with increasing channel length. The saturation of the central free energy barrier for the peptidic channels occurs at relatively short lengths, and it is correlated with the desolvation from the bulk water. Remarkably, decomposition of free energy barriers into enthalpic and entropic terms reveals an entropic cost for ion permeation. Furthermore, this entropic cost dominates the ion permeation free energy barrier, since the corresponding free energy contribution is higher than the enthalpic barrier. We conclude that the length dependence of the free energy is enthalpy-dominated, but the entropy is the major contribution to the permeation barrier. The decrease in rotational water motion and the reduction of channel mobility are putative origins for the overall entropic penalty.

  9. Potential value of Cs-137 capsules

    SciTech Connect

    Bloomster, C.H.; Brown, D.R.; Bruno, G.A.; Hazelton, R.F.; Hendrickson, P.L.; Lezberg, A.J.; Tingey, G.L.; Wilfert, G.L.

    1985-04-01

    We determined the value of Cs-137 compared to Co-60 as a source for the irradiation of fruit (apples and cherries), pork and medical supplies. Cs-137, in the WESF capsule form, had a value of approximately $0.40/Ci as a substitute for Co-60 priced at approximately $1.00/Ci. The comparison was based on the available curies emitted from the surface of each capsule. We developed preliminary designs for fourteen irradiation facilities; seven were based on Co-60 and seven were based on Cs-137. These designs provided the basis for estimating capital and operating costs which, in turn, provided the basis for determining the value of Cs-137 relative to Co-60 in these applications. We evaluated the effect of the size of the irradiation facility on the value of Cs-137. The cost of irradiation is low compared to the value of the product. Irradiation of apples for disinfestation costs $.01 to .02 per pound. Irradiation for trichina-safe pork costs $.02 per pound. Irradiation of medical supplies for sterilization costs $.07 to .12 per pound. The cost of the irradiation source, either Co-60 or Cs-137, contributed only a minor amount to the total cost of irradiation, about 5% for the fruit and hog cases and about 20% for the medical supply cases. We analyzed the sensitivity of the irradiation costs and Cs-137 value to several key assumptions.

  10. Memory Is Not Extinguished along with CS Presentation but within a Few Seconds after CS-Offset

    ERIC Educational Resources Information Center

    Perez-Cuesta, Luis Maria; Hepp, Yanil; Pedreira, Maria Eugenia; Maldonado, Hector

    2007-01-01

    Prior work with the crab's contextual memory model showed that CS-US conditioned animals undergoing an unreinforced CS presentation would either reconsolidate or extinguish the CS-US memory, depending on the length of the reexposure to the CS. Either memory process is only triggered once the CS is terminated. Based on these results, the following…

  11. Memory Is Not Extinguished along with CS Presentation but within a Few Seconds after CS-Offset

    ERIC Educational Resources Information Center

    Perez-Cuesta, Luis Maria; Hepp, Yanil; Pedreira, Maria Eugenia; Maldonado, Hector

    2007-01-01

    Prior work with the crab's contextual memory model showed that CS-US conditioned animals undergoing an unreinforced CS presentation would either reconsolidate or extinguish the CS-US memory, depending on the length of the reexposure to the CS. Either memory process is only triggered once the CS is terminated. Based on these results, the following…

  12. Regeneration of Used Frying Palm Oil with Coffee Silverskin (CS), CS Ash (CSA) and Nanoparticles of CS (NCS).

    PubMed

    Ismail, Samir Abd-Elmonem A; El-Anany, Ayman Mohammed; Ali, Rehab Farouk M

    2017-01-01

    The present investigation aimed to evaluate the efficiency of coffee silverskin (CS), CS ash (CSA) and nanoparticles of CS (NCS) in regeneration the quality of used frying palm oil. The adsorbents were mixed individually with used frying palm oil at level 4% (w/v) for 60 min. The properties of CS, CSA and NCS adsorbents were studied using (SEM) scanning electron microscopy technique. Some of physico-chemical characteristics of used frying palm oil (UFPO) and UFPO treated with adsorbents were determined. The results showed that the CS ash particles composed of irregular spherical and semispherical grains with deep cavities. The size of particles of CS ash ranged in diameter from 1.1 to 1.7 µm. The morphology of NCS consisted of cluster-type spherical nanoparticles and flakes. The particle size of NCS varies from 0.9 to 1.7 µm. Purification treatments caused marked (p<0.05) increases in the quality parameters of treated oil compared to untreated oil. The treatment of UFPO with 4% of adsorbents caused significant reductions in the content of free fatty acids ranged from 51.2 to 65.0%. The lowest level of peroxide (2.1 meq/kg) was recorded for UFPO treated with 4% of NCS. The highest reductions (72.8; 70.0%) in p-anisidine value were observed in UFPO treated with 4% of CSA and NCS, respectively. Treatment of UFPO with 4% of CS, CSA and NCS significantly lowered the polar content from 13.9% to 6.3, 4.8 and 3.9%, respectively. The results also indicate that CSA and NCS have nearly the same adsorption efficiency in lowering polymer content of UFPO. Filtration treatment of UFPO with 4% of CS, CSA and NCS markedly lowered the viscosity and colour values of treated UFPO.

  13. Damage of the bacterial cell envelope by antimicrobial peptides gramicidin S and PGLa as revealed by transmission and scanning electron microscopy.

    PubMed

    Hartmann, Mareike; Berditsch, Marina; Hawecker, Jacques; Ardakani, Mohammad Fotouhi; Gerthsen, Dagmar; Ulrich, Anne S

    2010-08-01

    Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the ultrastructural changes in bacteria induced by antimicrobial peptides (AMPs). Both the beta-stranded gramicidin S and the alpha-helical peptidyl-glycylleucine-carboxyamide (PGLa) are cationic amphiphilic AMPs known to interact with bacterial membranes. One representative Gram-negative strain, Escherichia coli ATCC 25922, and one representative Gram-positive strain, Staphylococcus aureus ATCC 25923, were exposed to the AMPs at sub-MICs and supra-MICs in salt-free medium. SEM revealed a shortening and swelling of the E. coli cells, and multiple blisters and bubbles formed on their surface. The S. aureus cells seemed to burst upon AMP exposure, showing open holes and deep craters in their envelope. TEM revealed the formation of intracellular membranous structures in both strains, which is attributed to a lateral expansion of the lipid membrane upon peptide insertion. Also, some morphological alterations in the DNA region were detected for S. aureus. After E. coli was incubated with AMPs in medium with low ionic strength, the cells appeared highly turgid compared to untreated controls. This observation suggests that the AMPs enhance osmosis through the inner membrane, before they eventually cause excessive leakage of the cellular contents. The adverse effect on the osmoregulatory capacity of the bacteria is attributed to the membrane-permeabilizing action of the amphiphilic peptides, even at low (sub-MIC) AMP concentrations. Altogether, the results demonstrate that both TEM and SEM, as well as appropriate sample preparation protocols, are needed to obtain detailed mechanistic insights into peptide function.

  14. Fermentation and Cost-Effective 13C/15N Labeling of the Nonribosomal Peptide Gramicidin S for Nuclear Magnetic Resonance Structure Analysis

    PubMed Central

    Berditsch, Marina; Afonin, Sergii; Steineker, Anna; Orel, Nataliia; Jakovkin, Igor; Weber, Christian

    2015-01-01

    Gramicidin S (GS) is a nonribosomally synthesized decapeptide from Aneurinibacillus migulanus. Its pronounced antibiotic activity is attributed to amphiphilic structure and enables GS interaction with bacterial membranes. Despite its medical use for over 70 years, the peptide-lipid interactions of GS and its molecular mechanism of action are still not fully understood. Therefore, a comprehensive structural analysis of isotope-labeled GS needs to be performed in its biologically relevant membrane-bound state, using advanced solid-state nuclear magnetic resonance (NMR) spectroscopy. Here, we describe an efficient method for producing the uniformly 13C/15N-labeled peptide in a minimal medium supplemented by selected amino acids. As GS is an intracellular product of A. migulanus, we characterized the producer strain DSM 5759 (rough-convex phenotype) and examined its biosynthetic activity in terms of absolute and biomass-dependent peptide accumulation. We found that the addition of either arginine or ornithine increases the yield only at very high supplementing concentrations (1% and 0.4%, respectively) of these expensive 13C/15N-labeled amino acids. The most cost-effective production of 13C/15N-GS, giving up to 90 mg per gram of dry cell weight, was achieved in a minimal medium containing 1% 13C-glycerol and 0.5% 15N-ammonium sulfate, supplemented with only 0.025% of 13C/15N-phenylalanine. The 100% efficiency of labeling is corroborated by mass spectrometry and preliminary solid-state NMR structure analysis of the labeled peptide in the membrane-bound state. PMID:25795666

  15. Fourier transform infrared spectroscopic studies of the interaction of the antimicrobial peptide gramicidin S with lipid micelles and with lipid monolayer and bilayer membranes.

    PubMed

    Lewis, R N; Prenner, E J; Kondejewski, L H; Flach, C R; Mendelsohn, R; Hodges, R S; McElhaney, R N

    1999-11-16

    We have utilized Fourier transform infrared spectroscopy to study the interaction of the antimicrobial peptide gramicidin S (GS) with lipid micelles and with lipid monolayer and bilayer membranes as a function of temperature and of the phase state of the lipid. Since the conformation of GS does not change under the experimental conditions employed in this study, we could utilize the dependence of the frequency of the amide I band of the central beta-sheet region of this peptide on the polarity and hydrogen-bonding potential of its environment to probe GS interaction with and location in these lipid model membrane systems. We find that the GS is completely or partially excluded from the gel states of all of the lipid bilayers examined in this study but strongly partitions into lipid micelles, monolayers, or bilayers in the liquid-crystalline state. Moreover, in general, the penetration of GS into zwitterionic and uncharged lipid bilayer coincides closely with the gel to liquid-crystalline phase transition of the lipid. However, GS begins to penetrate into the gel-state bilayers of anionic phospholipids prior to the actual chain-melting phase transition, while in cationic lipid bilayers, GS does not partition strongly into the liquid-crystalline bilayer until temperatures well above the chain-melting phase transition are reached. In the liquid-crystalline state, the polarity of the environment of GS indicates that this peptide is located primarily at the polar/apolar interfacial region of the bilayer near the glycerol backbone region of the lipid molecule. However, the depth of GS penetration into this interfacial region can vary somewhat depending on the structure and charge of the lipid molecule. In general, GS associates most strongly with and penetrates most deeply into more disordered bilayers with a negative surface charge, although the detailed chemical structure of the lipid molecule and physical organization of the lipid aggregate (micelle versus monolayer

  16. The nature of ion and water barrier crossings in a simulated ion channel.

    PubMed Central

    Chiu, S. W.; Novotny, J. A.; Jakobsson, E.

    1993-01-01

    Using a combination of techniques, including molecular dynamics, time-correlation analysis, stochastic dynamics, and fitting of continuum diffusion theory to electrophysiological data, a characterization is made of thermally driven sodium, water, and D2O motion within the gramicidin A channel. Since the channel contents are constrained to move in a single-file fashion, the motion that corresponds to experimentally measurable rates of permeation of the membrane is the motion of the center of mass of the channel contents. We therefore emphasize channel contents center-of-mass motion in our analysis of molecular dynamics computations. The usual free energy calculation techniques would be of questionable validity when applied to such motion. As an alternative to those techniques, we postulate a periodic sinusoidal free energy profile (related to the periodic structure of the helical channel) and deduce the fluid dynamic diffusion coefficient and the height and spacing of the free energy barriers from the form of the mean-square-deviation function, using stochastic computations. The fluid dynamic friction in each case appears similar to that for aqueous solution. However, the diffusive motions are modulated by a spatially periodic free energy profile with a periodicity characteristic of an L-D pair of amino acids in the gramicidin helix, approximately 1.7 A in the model we use. The barrier height depends on which substance is moving in the channel, but in each case is several times thermal energy. For barriers of this width and height, the motion is intermediate between the low-friction (transition-state) and high-friction (Brownian) limits. Thus, neither of these formalisms that have been used commonly to describe membrane permeation gives an accurate picture of the underlying physical process (although the Brownian description seems closer to correct). The non-Markovian Langevin equation must be solved to describe properly the statistics of the process. The "channel

  17. Cucumber CsBPCs Regulate the Expression of CsABI3 during Seed Germination

    PubMed Central

    Mu, Ying; Liu, Yumei; Bai, Longqiang; Li, Shuzhen; He, Chaoxing; Yan, Yan; Yu, Xianchang; Li, Yansu

    2017-01-01

    Cucumber seeds with shallow dormancy start to germinate in fruit that are harvested late. ABSCISIC ACID INSENSITIVE3 (ABI3), a transcription factor in the abscisic acid (ABA) signaling pathway, is one of the most important regulators in the transition from late embryogenesis to germination. Our analysis found a candidate cis-regulatory motif for cucumber BASIC PENTACYSTEINE (CsBPC) in the promoter of CsABI3. Yeast one-hybrid and chromatin immunoprecipitation (ChIP) assays showed that CsBPCs bound to the promoter of CsABI3. Examination of β-glucuronidase (GUS) activity driven by the CsABI3 promoter in transgenic Arabidopsis thaliana plants overexpressing CsBPCs and a Nicotiana benthamiana (tobacco) luciferase assay indicated that CsBPCs inhibited the expression of CsABI3. Transgenic plants overexpressing CsBPCs were constructed to confirm that CsBPCs participates in the control of seed germination. This study of the cucumber BPC-ABI3 pathway will help to explore and characterize the molecular mechanisms underlying seed germination and will provide necessary information for seed conservation in agriculture and forestry. PMID:28421094

  18. Cucumber CsBPCs Regulate the Expression of CsABI3 during Seed Germination.

    PubMed

    Mu, Ying; Liu, Yumei; Bai, Longqiang; Li, Shuzhen; He, Chaoxing; Yan, Yan; Yu, Xianchang; Li, Yansu

    2017-01-01

    Cucumber seeds with shallow dormancy start to germinate in fruit that are harvested late. ABSCISIC ACID INSENSITIVE3 (ABI3), a transcription factor in the abscisic acid (ABA) signaling pathway, is one of the most important regulators in the transition from late embryogenesis to germination. Our analysis found a candidate cis-regulatory motif for cucumber BASIC PENTACYSTEINE (CsBPC) in the promoter of CsABI3. Yeast one-hybrid and chromatin immunoprecipitation (ChIP) assays showed that CsBPCs bound to the promoter of CsABI3. Examination of β-glucuronidase (GUS) activity driven by the CsABI3 promoter in transgenic Arabidopsis thaliana plants overexpressing CsBPCs and a Nicotiana benthamiana (tobacco) luciferase assay indicated that CsBPCs inhibited the expression of CsABI3. Transgenic plants overexpressing CsBPCs were constructed to confirm that CsBPCs participates in the control of seed germination. This study of the cucumber BPC-ABI3 pathway will help to explore and characterize the molecular mechanisms underlying seed germination and will provide necessary information for seed conservation in agriculture and forestry.

  19. Engineered ion channels as emerging tools for chemical biology.

    PubMed

    Mayer, Michael; Yang, Jerry

    2013-12-17

    Over the last 25 years, researchers have developed exogenously expressed, genetically engineered, semi-synthetic, and entirely synthetic ion channels. These structures have sufficient fidelity to serve as unique tools that can reveal information about living organisms. One of the most exciting success stories is optogenetics: the use of light-gated channels to trigger action potentials in specific neurons combined with studies of the response from networks of cells or entire live animals. Despite this breakthrough, the use of molecularly engineered ion channels for studies of biological systems is still in its infancy. Historically, researchers studied ion channels in the context of their own function in single cells or in multicellular signaling and regulation. Only recently have researchers considered ion channels and pore-forming peptides as responsive tools to report on the chemical and physical changes produced by other biochemical processes and reactions. This emerging class of molecular probes has a number of useful characteristics. For instance, these structures can greatly amplify the signal of chemical changes: the binding of one molecule to a ligand-gated ion channel can result in flux of millions of ions across a cell membrane. In addition, gating occurs on sub-microsecond time scales, resulting in fast response times. Moreover, the signal is complementary to existing techniques because the output is ionic current rather than fluorescence or radioactivity. And finally, ion channels are also localized at the membrane of cells where essential processes such as signaling and regulation take place. This Account highlights examples, mostly from our own work, of uses of ion channels and pore-forming peptides such as gramicidin in chemical biology. We discuss various strategies for preparing synthetically tailored ion channels that range from de novo designed synthetic molecules to genetically engineered or simply exogenously expressed or reconstituted wild

  20. Channel-forming bacterial toxins in biosensing and macromolecule delivery.

    PubMed

    Gurnev, Philip A; Nestorovich, Ekaterina M

    2014-08-21

    To intoxicate cells, pore-forming bacterial toxins are evolved to allow for the transmembrane traffic of different substrates, ranging from small inorganic ions to cell-specific polypeptides. Recent developments in single-channel electrical recordings, X-ray crystallography, protein engineering, and computational methods have generated a large body of knowledge about the basic principles of channel-mediated molecular transport. These discoveries provide a robust framework for expansion of the described principles and methods toward use of biological nanopores in the growing field of nanobiotechnology. This article, written for a special volume on "Intracellular Traffic and Transport of Bacterial Protein Toxins", reviews the current state of applications of pore-forming bacterial toxins in small- and macromolecule-sensing, targeted cancer therapy, and drug delivery. We discuss the electrophysiological studies that explore molecular details of channel-facilitated protein and polymer transport across cellular membranes using both natural and foreign substrates. The review focuses on the structurally and functionally different bacterial toxins: gramicidin A of Bacillus brevis, α-hemolysin of Staphylococcus aureus, and binary toxin of Bacillus anthracis, which have found their "second life" in a variety of developing medical and technological applications.

  1. Channel-Forming Bacterial Toxins in Biosensing and Macromolecule Delivery

    PubMed Central

    Gurnev, Philip A.; Nestorovich, Ekaterina M.

    2014-01-01

    To intoxicate cells, pore-forming bacterial toxins are evolved to allow for the transmembrane traffic of different substrates, ranging from small inorganic ions to cell-specific polypeptides. Recent developments in single-channel electrical recordings, X-ray crystallography, protein engineering, and computational methods have generated a large body of knowledge about the basic principles of channel-mediated molecular transport. These discoveries provide a robust framework for expansion of the described principles and methods toward use of biological nanopores in the growing field of nanobiotechnology. This article, written for a special volume on “Intracellular Traffic and Transport of Bacterial Protein Toxins”, reviews the current state of applications of pore-forming bacterial toxins in small- and macromolecule-sensing, targeted cancer therapy, and drug delivery. We discuss the electrophysiological studies that explore molecular details of channel-facilitated protein and polymer transport across cellular membranes using both natural and foreign substrates. The review focuses on the structurally and functionally different bacterial toxins: gramicidin A of Bacillus brevis, α-hemolysin of Staphylococcus aureus, and binary toxin of Bacillus anthracis, which have found their “second life” in a variety of developing medical and technological applications. PMID:25153255

  2. The "Seven Cs" for Employee Retention.

    ERIC Educational Resources Information Center

    Taguchi, Sherrie Gong

    2001-01-01

    Defines the "Seven Cs," traditional yet effective business fundamentals used to engage employees. Discusses how many companies are leveraging the basics of good employee relations in order to inspire staff productivity and loyalty. (GCP)

  3. The "Seven Cs" for Employee Retention.

    ERIC Educational Resources Information Center

    Taguchi, Sherrie Gong

    2001-01-01

    Defines the "Seven Cs," traditional yet effective business fundamentals used to engage employees. Discusses how many companies are leveraging the basics of good employee relations in order to inspire staff productivity and loyalty. (GCP)

  4. A Venom-derived Neurotoxin, CsTx-1, from the Spider Cupiennius salei Exhibits Cytolytic Activities*

    PubMed Central

    Kuhn-Nentwig, Lucia; Fedorova, Irina M.; Lüscher, Benjamin P.; Kopp, Lukas S.; Trachsel, Christian; Schaller, Johann; Vu, Xuan Lan; Seebeck, Thomas; Streitberger, Kathrin; Nentwig, Wolfgang; Sigel, Erwin; Magazanik, Lev G.

    2012-01-01

    CsTx-1, the main neurotoxic acting peptide in the venom of the spider Cupiennius salei, is composed of 74 amino acid residues, exhibits an inhibitory cysteine knot motif, and is further characterized by its highly cationic charged C terminus. Venom gland cDNA library analysis predicted a prepropeptide structure for CsTx-1 precursor. In the presence of trifluoroethanol, CsTx-1 and the long C-terminal part alone (CT1-long; Gly-45–Lys-74) exhibit an α-helical structure, as determined by CD measurements. CsTx-1 and CT1-long are insecticidal toward Drosophila flies and destroys Escherichia coli SBS 363 cells. CsTx-1 causes a stable and irreversible depolarization of insect larvae muscle cells and frog neuromuscular preparations, which seem to be receptor-independent. Furthermore, this membranolytic activity could be measured for Xenopus oocytes, in which CsTx-1 and CT1-long increase ion permeability non-specifically. These results support our assumption that the membranolytic activities of CsTx-1 are caused by its C-terminal tail, CT1-long. Together, CsTx-1 exhibits two different functions; as a neurotoxin it inhibits L-type Ca2+ channels, and as a membranolytic peptide it destroys a variety of prokaryotic and eukaryotic cell membranes. Such a dualism is discussed as an important new mechanism for the evolution of spider venomous peptides. PMID:22613721

  5. PyCS : Python Curve Shifting

    NASA Astrophysics Data System (ADS)

    Tewes, Malte

    2015-09-01

    PyCS is a software toolbox to estimate time delays between multiple images of strongly lensed quasars, from resolved light curves such as obtained by the COSMOGRAIL monitoring program. The pycs package defines a collection of classes and high level functions, that you can script in a flexible way. PyCS makes it easy to compare different point estimators (including your own) without much code integration. The package heavily depends on numpy, scipy, and matplotlib.

  6. 135Cs activity and 135Cs/137Cs atom ratio in environmental samples before and after the Fukushima Daiichi Nuclear Power Plant accident.

    PubMed

    Yang, Guosheng; Tazoe, Hirofumi; Yamada, Masatoshi

    2016-04-07

    (135)Cs/(137)Cs is a potential tracer for radiocesium source identification. However, due to the challenge to measure (135)Cs, there were no (135)Cs data available for Japanese environmental samples before the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. It was only 3 years after the accident that limited (135)Cs values could be measured in heavily contaminated environmental samples. In the present study, activities of (134)Cs, (135)Cs, and (137)Cs, along with their ratios in 67 soil and plant samples heavily and lightly contaminated by the FDNPP accident were measured by combining γ spectrometry with ICP-MS/MS. The arithmetic means of the (134)Cs/(137)Cs activity ratio (1.033 ± 0.006) and (135)Cs/(137)Cs atom ratio (0.334 ± 0.005) (decay corrected to March 11, 2011), from old leaves of plants collected immediately after the FDNPP accident, were confirmed to represent the FDNPP derived radiocesium signature. Subsequently, for the first time, trace (135)Cs amounts before the FDNPP accident were deduced according to the contribution of global and FDNPP accident-derived fallout. Apart from two soil samples with a tiny global fallout contribution, contributions of global fallout radiocesium in other soil samples were observed to be 0.338%-52.6%. The obtained (135)Cs/(137)Cs database will be useful for its application as a geochemical tracer in the future.

  7. 135Cs activity and 135Cs/137Cs atom ratio in environmental samples before and after the Fukushima Daiichi Nuclear Power Plant accident

    PubMed Central

    Yang, Guosheng; Tazoe, Hirofumi; Yamada, Masatoshi

    2016-01-01

    135Cs/137Cs is a potential tracer for radiocesium source identification. However, due to the challenge to measure 135Cs, there were no 135Cs data available for Japanese environmental samples before the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. It was only 3 years after the accident that limited 135Cs values could be measured in heavily contaminated environmental samples. In the present study, activities of 134Cs, 135Cs, and 137Cs, along with their ratios in 67 soil and plant samples heavily and lightly contaminated by the FDNPP accident were measured by combining γ spectrometry with ICP-MS/MS. The arithmetic means of the 134Cs/137Cs activity ratio (1.033 ± 0.006) and 135Cs/137Cs atom ratio (0.334 ± 0.005) (decay corrected to March 11, 2011), from old leaves of plants collected immediately after the FDNPP accident, were confirmed to represent the FDNPP derived radiocesium signature. Subsequently, for the first time, trace 135Cs amounts before the FDNPP accident were deduced according to the contribution of global and FDNPP accident-derived fallout. Apart from two soil samples with a tiny global fallout contribution, contributions of global fallout radiocesium in other soil samples were observed to be 0.338%–52.6%. The obtained 135Cs/137Cs database will be useful for its application as a geochemical tracer in the future. PMID:27052481

  8. 135Cs activity and 135Cs/137Cs atom ratio in environmental samples before and after the Fukushima Daiichi Nuclear Power Plant accident

    NASA Astrophysics Data System (ADS)

    Yang, Guosheng; Tazoe, Hirofumi; Yamada, Masatoshi

    2016-04-01

    135Cs/137Cs is a potential tracer for radiocesium source identification. However, due to the challenge to measure 135Cs, there were no 135Cs data available for Japanese environmental samples before the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. It was only 3 years after the accident that limited 135Cs values could be measured in heavily contaminated environmental samples. In the present study, activities of 134Cs, 135Cs, and 137Cs, along with their ratios in 67 soil and plant samples heavily and lightly contaminated by the FDNPP accident were measured by combining γ spectrometry with ICP-MS/MS. The arithmetic means of the 134Cs/137Cs activity ratio (1.033 ± 0.006) and 135Cs/137Cs atom ratio (0.334 ± 0.005) (decay corrected to March 11, 2011), from old leaves of plants collected immediately after the FDNPP accident, were confirmed to represent the FDNPP derived radiocesium signature. Subsequently, for the first time, trace 135Cs amounts before the FDNPP accident were deduced according to the contribution of global and FDNPP accident-derived fallout. Apart from two soil samples with a tiny global fallout contribution, contributions of global fallout radiocesium in other soil samples were observed to be 0.338%-52.6%. The obtained 135Cs/137Cs database will be useful for its application as a geochemical tracer in the future.

  9. Fast CsI-phoswich detector

    DOEpatents

    Langenbrunner, James R.

    1996-01-01

    An improved phoswich radiation detector used pure CsI crystal and a fast plastic scintillator and a single photomultiplier tube. The plastic is arranged to receive incident radiation, and that which passed through then strikes the CsI crystal. Scintillation light from both the plastic and CsI crystal are applied to the photomultiplier tube, with the light from the plastic passing through the crystal without absorption therein. Electronics are provided for analyzing the output of the photomultiplier tube to discriminate responses due to the plastic and the CsI crystal, through short gate and long gate integration, to produce results which are indicative of the characteristics of the different types of incident radiation, even in the presence of large amounts of radiation. The phoswich detector has excellent timing resolution. The scintillators of the CsI- phoswich were chosen for their fast risetimes, of about 3 ns for NE102A, and 30 ns for the pure CsI.

  10. Fast CsI-phoswich detector

    DOEpatents

    Langenbrunner, J.R.

    1996-05-07

    An improved phoswich radiation detector used pure CsI crystal and a fast plastic scintillator and a single photomultiplier tube. The plastic is arranged to receive incident radiation, and that which passed through then strikes the CsI crystal. Scintillation light from both the plastic and CsI crystal are applied to the photomultiplier tube, with the light from the plastic passing through the crystal without absorption therein. Electronics are provided for analyzing the output of the photomultiplier tube to discriminate responses due to the plastic and the CsI crystal, through short gate and long gate integration, to produce results which are indicative of the characteristics of the different types of incident radiation, even in the presence of large amounts of radiation. The phoswich detector has excellent timing resolution. The scintillators of the CsI- phoswich were chosen for their fast risetimes, of about 3 ns for NE102A, and 30 ns for the pure CsI. 5 figs.

  11. Cesium leaching from gamma-irradiated CsA and CsX zeolites.

    PubMed

    Lima, Enrique; Ibarra, Ilich A; Lara, Victor; Bosch, Pedro; Bulbulian, Silvia

    2008-12-30

    The present study discusses the effect of gamma-irradiation on Cs+-exchanged X and A zeolites. The incorporation of Cs+ ions into A and X zeolites was performed using three different cesium salts (chloride, nitrate or acetate). Cs+ ions immobilized into the vitrified zeolites by thermal treatment are located in different sites of the zeolite networks. It is found that gamma-irradiation favors cesium retention depending on the cesium precursor salt used in the cationic exchange step.

  12. Scintillation properties of Eu-doped CsCl and CsBr crystals

    NASA Astrophysics Data System (ADS)

    Saeki, Keiichiro; Koshimizu, Masanori; Fujimoto, Yutaka; Yanagida, Takayuki; Okada, Go; Yahaba, Takuma; Tanaka, Hironori; Asai, Keisuke

    2016-11-01

    Eu-doped CsCl and CsBr crystals were grown by the vertical Bridgman-Stockbarger method and the scintillation properties of the crystals were investigated. The radioluminescence (RL) bands of CsCl:Eu were observed at 245-270 nm and 450 nm. The former bands are attributed to Auger-free luminescence, and the latter band is attributed to Eu2+ 5d-4f transitions. CsBr:Eu showed an RL band at 435 nm, and this broad band is attributed to Eu2+ 5d-4f transitions. The scintillation decay-time constants of the slow components for CsCl:Eu and CsBr:Eu were 0.38 and 2.8 μs, respectively. Based on the pulse-height spectra for 662 keV gamma ray from 137Cs, the light yield of CsCl:Eu and CsBr:Eu are estimated to be 1700 and 2500 photons/MeV, respectively.

  13. Distribution of radioactive cesium ((134)Cs plus (137)Cs) in rice fractions during polishing and cooking.

    PubMed

    Hachinohe, Mayumi; Okunishi, Tomoya; Hagiwara, Shoji; Todoriki, Setsuko; Kawamoto, Shinichi; Hamamatsu, Shioka

    2015-03-01

    We investigated the distribution of cesium-134 ((134)Cs) and cesium-137 ((137)Cs) during polishing and cooking of rice to obtain their processing factors (Pf) and food processing retention factors (Fr) to make the information available for an adequate understanding of radioactive Cs dynamics. Polishing brown rice resulted in a decreased radioactive Cs concentration of the polished rice, but the bran and germ (outer layers) exhibited higher concentrations than brown rice. The Pf values for 100% polished rice and outer layers ranged from 0.47 to 0.48 and 6.5 to 7.8, respectively. The Fr values for 100% polished rice and outer layers were 0.43 and 0.58 to 0.60, respectively. The distribution of radioactive Cs in polished rice and outer layers was estimated at approximately 40 and 60%, respectively. On the other hand, cooked rice showed significantly lower levels of radioactive Cs than polished rice, and transfer of radioactive Cs into wash water was observed. The Pf and Fr values for cooked rice were 0.28 and 0.65 to 0.66, respectively. From these results, we can calculate that if the radioactive Cs concentration in brown rice is 100 Bq/kg, the concentrations of Cs in polished rice and cooked rice will be 47 to 48 Bq/kg and 13 Bq/kg, respectively.

  14. Molecular dynamics - potential of mean force calculations as a tool for understanding ion permeation and selectivity in narrow channels.

    PubMed

    Allen, Toby W; Andersen, Olaf S; Roux, Benoit

    2006-12-01

    Ion channels catalyze the permeation of charged molecules across cell membranes and are essential for many vital physiological functions, including nerve and muscle activity. To understand better the mechanisms underlying ion conduction and valence selectivity of narrow ion channels, we have employed free energy techniques to calculate the potential of mean force (PMF) for ion movement through the prototypical gramicidin A channel. Employing modern all-atom molecular dynamics (MD) force fields with umbrella sampling methods that incorporate one hundred 1-2 ns trajectories, we find that it is possible to achieve semi-quantitative agreement with experimental binding and conductance measurements. We also examine the sensitivity of the MD-PMF results to the choice of MD force field and compare PMFs for potassium, calcium and chloride ions to explore the basis for the valence selectivity of this narrow and uncharged ion channel. A large central barrier is observed for both anions and divalent ions, consistent with lack of experimental conductance. Neither anion or divalent cation is seen to be stabilized inside the channel relative to the bulk electrolyte and each leads to large disruptions to the protein and membrane structure when held deep inside the channel. Weak binding of calcium ions outside the channel corresponds to a free energy well that is too shallow to demonstrate channel blocking. Our findings emphasize the success of the MD-PMF approach and the sensitivity of ion energetics to the choice of biomolecular force field.

  15. Potential role of CS2 photooxidation in tropospheric sulfur chemistry

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Chameides, W. L.; Ravishankara, A. R.

    1981-01-01

    Absorption cross section measurements and model calculations indicate that CS2 photooxidation may be an important tropospheric sink for the CS2, giving a lifetime on the order of a week or two. If background CS2 levels are 10-20 pptv, then CS2 photooxidation may be an important global source of OCS as well.

  16. A biokinetic model for {sup 137}Cs

    SciTech Connect

    Melo, D.R.; Lipsztein, J.L.; Oliveira, C.A.N.; Lundgren, D.L.

    1997-08-01

    An improved biokinetic model for {sup 137}Cs in humans was developed based on an analysis of data obtained from individuals internally contaminated during an accident in Goiania, Brazil, and other data. Seventeen children (ten girls and seven boys 1-10 y old), ten adolescents (four females and six males), and thirty adults, (fifteen females and fifteen males) contaminated in the accident in Goiania contributed to this study. {sup 137}Cs retention was determined through periodic measurements in a whole-body counter. In addition to the data on {sup 137}Cs retention from these individuals, data from a study on the metabolism of {sup 137}Cs in immature, adult, and aged Beagle dogs and data from the literature were used in the formulation of the {sup 137}Cs biokinetic model presented. Mathematically, the retention of cesium is described by three exponential terms, and the retention model is based on a step function of body weight. When the ICRP Publication 56 model for cesium was compared to the model suggested in this paper, it was determined that the ICRP model predicts lower effective doses in 5-y-old children and higher effective doses in infants, adolescents, and adults.

  17. The relationship between the binding to and permeabilization of phospholipid bilayer membranes by GS14dK4, a designed analog of the antimicrobial peptide gramicidin S.

    PubMed

    Abraham, Thomas; Marwaha, Seema; Kobewka, Daniel M; Lewis, Ruthven N A H; Prenner, Elmar J; Hodges, Robert S; McElhaney, Ronald N

    2007-09-01

    The cationic beta-sheet cyclic tetradecapeptide cyclo[VKLdKVdYPLKVKLdYP] (GS14dK(4)) is a diastereomeric lysine ring-size analog of the potent naturally occurring antimicrobial peptide gramicidin S (GS) which exhibits enhanced antimicrobial but markedly reduced hemolytic activity compared to GS itself. We have previously studied the binding of GS14dK(4) to various phospholipid bilayer model membranes using isothermal titration calorimetry [Abraham, T. et al. (2005) Biochemistry 44, 2103-2112]. In the present study, we compare the ability of GS14dK(4) to bind to and disrupt these same phospholipid model membranes by employing a fluorescent dye leakage assay to determine the ability of this peptide to permeabilize large unilamellar vesicles. We find that in general, the ability of GS14dK(4) to bind to and to permeabilize phospholipid bilayers of different compositions are not well correlated. In particular, the binding affinity of GS14dK(4) varies markedly with the charge and to some extent with the polar headgroup structure of the phospholipid and with the cholesterol content of the model membrane. Specifically, this peptide binds much more tightly to anionic than to zwitterionic phospholipids and much less tightly to cholesterol-containing than to cholesterol-free model membranes. In addition, the maximum extent of binding of GS14dK(4) can also vary considerably with phospholipid composition in a parallel fashion. In contrast, the ability of this peptide to permeabilize phospholipid vesicles is only weakly dependent on phospholipid charge, polar headgroup structure or cholesterol content. We provide tentative explanations for the observed lack of a correlation between the affinity and extent of GS14dK(4) binding to, and degree of disruption of the structure and integrity of, phospholipid bilayers membranes. We also present evidence that the lack of correlation between these two parameters may be a general phenomenon among antimicrobial peptides. Finally, we

  18. Effects of single d-amino acid substitutions on disruption of β-sheet structure and hydrophobicity in cyclic 14-residue antimicrobial peptide analogs related to gramicidin S

    PubMed Central

    Lee, D.L.; Powers, J.-P.S.; Pflegerl, K.; Vasil, M.L.; Hancock, R.E.W.; Hodges, R.S.

    2005-01-01

    Gramicidin S (GS) is a 10-residue cyclic β-sheet peptide with lytic activity against the membranes of both microbial and human cells, i.e. it possesses little to no biologic specificity for either cell type. Structure–activity studies of de novo-designed 14-residue cyclic peptides based on GS have previously shown that higher specificity against microbial membranes, i.e. a high therapeutic index (TI), can be achieved by the replacement of a single l-amino acid with its corresponding d-enantiomer [Kondejewski, L.H. et al. (1999) J. Biol. Chem. 274, 13181]. The diastereomer with a d-Lys substituted at position 4 caused the greatest improvement in specificity vs. other l to d substitutions within the cyclic 14-residue peptide GS14, through a combination of decreased peptide amphipathicity and disrupted β-sheet structure in aqueous conditions [McInnes, C. et al. (2000) J. Biol. Chem. 275, 14287]. Based on this information, we have created a series of peptide diastereomers substituted only at position 4 by a d- or l-amino acid (Leu, Phe, Tyr, Asn, Lys, and achiral Gly). The amino acids chosen in this study represent a range of hydrophobicities/hydrophilicities as a subset of the 20 naturally occurring amino acids. While the d- and l-substitutions of Leu, Phe, and Tyr all resulted in strong hemolytic activity, the substitutions of hydrophilic d-amino acids d-Lys and d-Asn in GS14 at position 4 resulted in weaker hemolytic activity than in the l-diastereomers, which demonstrated strong hemolysis. All of the l-substitutions also resulted in poor antimicrobial activity and an extremely low TI, while the antimicrobial activity of the d-substituted peptides tended to improve based on the hydrophilicity of the residue. d-Lys was the most polar and most efficacious substitution, resulting in the highest TI. Interestingly, the hydrophobic d-amino acid substitutions had superior antimicrobial activity vs. the l-enantiomers although substitution of a hydrophobic d-amino acid

  19. CS Unplugged and Middle-School Students' Views, Attitudes, and Intentions regarding CS

    ERIC Educational Resources Information Center

    Taub, Rivka; Armoni, Michal; Ben-Ari, Mordechai

    2012-01-01

    Many students hold incorrect ideas and negative attitudes about computer science (CS). In order to address these difficulties, a series of learning activities called Computer Science Unplugged was developed by Tim Bell and his colleagues. These activities expose young people to central concepts in CS in an entertaining way without requiring a…

  20. Magnetic Separation Using HTS Bulk Magnet for Cs-Bearing Fe precipitates

    NASA Astrophysics Data System (ADS)

    Oka, T.; Ichiju, K.; Sasaki, S.; Ogawa, J.; Fukui, S.; Sato, T.; Ooizumi, M.; Yokoyama, K.; Aoki, S.; Ohnishi, N.

    2017-09-01

    A peculiar magnetic separation technique has been examined in order to remove the Cs-bearing Fe precipitates formed of the waste ash from the withdrawn incinerator furnaces in Fukushima. The separation system was constructed in combination with high temperature superconducting bulk magnets which generates the intensive magnetic field over 2 T, which was activated by the pulsed field magnetization process. The separation experiment has been operated with use of the newly-built alternating channel type magnetic separating device, which followed the high-gradient magnetic separation technique. The magnetic stainless steel filters installed in the water channels are magnetized by the applied magnetic fields, and are capable of attracting the precipitates bearing the Fe compound and thin Cs contamination. The experimental results clearly exhibited the positive feasibility of HTS bulk magnets.

  1. Mitochondrial chloride channels: electrophysiological characterization and pH induction of channel pore dilation.

    PubMed

    Misak, Anton; Grman, Marian; Malekova, Lubica; Novotova, Marta; Markova, Jana; Krizanova, Olga; Ondrias, Karol; Tomaskova, Zuzana

    2013-09-01

    Physiological and pathological functions of mitochondria are highly dependent on the properties and regulation of mitochondrial ion channels. There is still no clear understanding of the molecular identity, regulation, and properties of anion mitochondrial channels. The inner membrane anion channel (IMAC) was assumed to be equivalent to mitochondrial centum picosiemens (mCS). However, the different properties of IMAC and mCS channels challenges this opinion. In our study, we characterized the single-channel anion selectivity and pH regulation of chloride channels from purified cardiac mitochondria. We observed that channel conductance decreased in the order: Cl⁻ > Br⁻ > I⁻ > chlorate ≈ formate > acetate, and that gluconate did not permeate under control conditions. The selectivity sequence was Br⁻ ≥ chlorate ≥ I⁻ ≥ Cl⁻ ≥ formate ≈ acetate. Measurement of the concentration dependence of chloride conductance revealed altered channel gating kinetics, which was demonstrated by prolonged mean open time value with increasing chloride concentration. The observed mitochondrial chloride channels were in many respects similar to those of mCS, but not those of IMAC. Surprisingly, we observed that acidic pH increased channel conductance and that an increase of pH from 7.4 to 8.5 reduced it. The gluconate current appeared and gradually increased when pH decreased from pH 7.0 to 5.6. Our results indicate that pH regulates the channel pore diameter in such a way that dilation increases with more acidic pH. We assume this newly observed pH-dependent anion channel property may be involved in pH regulation of anion distribution in different mitochondrial compartments.

  2. Lava Channels

    NASA Image and Video Library

    2013-12-03

    The channels and linear depression in this image captured by NASA 2001 Mars Odyssey spacecraft are located on the western margin of the Elysium Volcanic complex. The channels were created by lava flow.

  3. CS EMISSION NEAR MIR-BUBBLES

    SciTech Connect

    Watson, C.; Devine, Kathryn; Quintanar, N.; Candelaria, T. E-mail: KDevine@collegeofidaho.edu E-mail: tcandela@nmt.edu

    2016-02-10

    We survey 44 young stellar objects located near the edges of mid-IR-identified bubbles in CS (1–0) using the Green Bank Telescope. We detect emission in 18 sources, indicating young protostars that are good candidates for being triggered by the expansion of the bubble. We calculate CS column densities and abundances. Three sources show evidence of infall through non-Gaussian line-shapes. Two of these sources are associated with dark clouds and are promising candidates for further exploration of potential triggered star formation. We obtained on-the-fly maps in CS (1–0) of three sources, showing evidence of significant interactions between the sources and the surrounding environment.

  4. CS Emission Near MIR-bubbles

    NASA Astrophysics Data System (ADS)

    Watson, C.; Devine, Kathryn; Quintanar, N.; Candelaria, T.

    2016-02-01

    We survey 44 young stellar objects located near the edges of mid-IR-identified bubbles in CS (1-0) using the Green Bank Telescope. We detect emission in 18 sources, indicating young protostars that are good candidates for being triggered by the expansion of the bubble. We calculate CS column densities and abundances. Three sources show evidence of infall through non-Gaussian line-shapes. Two of these sources are associated with dark clouds and are promising candidates for further exploration of potential triggered star formation. We obtained on-the-fly maps in CS (1-0) of three sources, showing evidence of significant interactions between the sources and the surrounding environment.

  5. Long haul and high speed network using dual polarization two-band OFDM CS-NRZ-(D)QPSK signal

    NASA Astrophysics Data System (ADS)

    Fazel, Sina; Lourdiane, Mounia; Lepers, Catherine

    2014-09-01

    In this paper, we propose to demonstrate a long haul and high speed network based on a 2 band Orthogonal Frequency Division Multiplexing (OFDM) signal and a Carrier Suppression (CS) Non Return to Zero (NRZ) Differential QPSK non-coherent modulation format. We considered 112 Gbit/s per channel bit rate and multiplexed 32 channels following the 100 GHz WDM ITU grid. We demonstrate a transmission over more than 3000 km with a BER bellow 10-3.

  6. Garan conducts CsPINs Experiment Operations

    NASA Image and Video Library

    2011-04-28

    ISS027-E-017840 (28 April 2011) --- NASA astronaut Ron Garan, Expedition 27 flight engineer, supports the Dynamism of Auxin Efflux Facilitators responsible for Gravity-regulated Growth and Development in Cucumber (CsPINs) experiment in the Kibo laboratory of the International Space Station. CsPINs studies the phenomenon of tropism, i.e., the growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. Specifically focusing on gravity, the new JAXA life science experiment investigates how plants sense gravity as an environmental signal and use it for governing their morphology and growth orientation.

  7. Garan conducts CsPINs Experiment Operations

    NASA Image and Video Library

    2011-04-28

    ISS027-E-017839 (28 April 2011) --- NASA astronaut Ron Garan, Expedition 27 flight engineer, supports the Dynamism of Auxin Efflux Facilitators responsible for Gravity-regulated Growth and Development in Cucumber (CsPINs) experiment in the Kibo laboratory of the International Space Station. CsPINs studies the phenomenon of tropism, i.e., the growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. Specifically focusing on gravity, the new JAXA life science experiment investigates how plants sense gravity as an environmental signal and use it for governing their morphology and growth orientation.

  8. Garan conducts CsPINs Experiment Operations

    NASA Image and Video Library

    2011-04-28

    ISS027-E-017843 (28 April 2011) --- NASA astronaut Ron Garan, Expedition 27 flight engineer, supports the Dynamism of Auxin Efflux Facilitators responsible for Gravity-regulated Growth and Development in Cucumber (CsPINs) experiment in the Kibo laboratory of the International Space Station. CsPINs studies the phenomenon of tropism, i.e., the growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. Specifically focusing on gravity, the new JAXA life science experiment investigates how plants sense gravity as an environmental signal and use it for governing their morphology and growth orientation.

  9. When and how the melittin ion channel exhibits ohmic behavior.

    PubMed

    Becucci, Lucia; Aloisi, Giovanni; Guidelli, Rolando

    2017-02-01

    Melittin exhibits an ohmic behavior in a lipid bilayer having a DOPC distal leaflet and interposed between a 2.25nm tetraethyleneoxy chain tethered to a mercury drop and an aqueous solution. This behavior is induced in a pH6.8 buffer solution of 0.8μg/mL melittin by a pretreatment consisting of series of electrochemical impedance spectroscopy measurements at bias potentials varied by 50mV steps over a transmembrane potential range from about +250 to -250mV. This metastable ohmic behavior remains unchanged for hours, even after acidifying the solution to pH3. The midpoint potential E1/2 between the positive and negative peaks of the resulting cyclic voltammogram is almost coincident with that of the ohmic channels gramicidin and syringopeptin 25A and shifts by the same amount toward more positive potentials with a pH decrease from 6.8 to 3. This common cyclic voltammetry behavior is explained by a tilt of the DOPC polar heads around the channel mouth of these three peptides and is simulated by a modelistic approach. The ohmic behavior of melittin is explained by the persistence of the peptide orientation initially assumed at trans-negative potentials even after application of trans-positive ones, at sufficiently high peptide-to-lipid molar ratios.

  10. Analysis of blocker-labeled channels reveals the dependence of recycling rates of ENaC on the total amount of recycled channels.

    PubMed

    Taruno, Akiyuki; Marunaka, Yoshinori

    2010-01-01

    Trafficking is one of the primary mechanisms of epithelial Na(+) channel (ENaC) regulation. Although it is known that ENaCs are recycled between the apical membrane and the intracellular channel pool, it has been difficult to investigate the recycling of ENaCs; especially endogenously expressed ENaCs. The aim of the present study is to investigate if the recycling rates of ENaCs depend on the total amount of recycled ENaCs. To accomplish this point, we established a novel method to estimate the total amount of recycled ENaCs and the ENaC recycling rates by using a specific blocker (benzamil) of ENaC with a high-affinity for functional label of the channels in recycling. Applying this method, we studied if a decrease in the total amount of ENaCs caused by brefeldin A (5 μg/mL, 1 h) affects respectively the rates of insertion and endocytosis of ENaCs to and from the apical membrane in monolayers of renal epithelial A6 cells. Our observations indicate that: 1) both insertion and endocytosis rates of ENaC increase when the total amount of ENaCs decreases, 2) the increase in the insertion rate is larger than that in the endocytosis rate, and 3) this larger increase in the insertion rate than the endocytosis rate caused by the decrease in the total amount of ENaCs plays an important role in preventing Na(+) transport from drastically diminishing due to a decrease in the total amount of ENaCs. The newly established analysis of blocker-labeled ENaCs in the present study provides a useful tool to investigate the recycling of endogenously expressed ENaCs. Copyright © 2010 S. Karger AG, Basel.

  11. A Low-Noise Transimpedance Amplifier for BLM-Based Ion Channel Recording

    PubMed Central

    Crescentini, Marco; Bennati, Marco; Saha, Shimul Chandra; Ivica, Josip; de Planque, Maurits; Morgan, Hywel; Tartagni, Marco

    2016-01-01

    High-throughput screening (HTS) using ion channel recording is a powerful drug discovery technique in pharmacology. Ion channel recording with planar bilayer lipid membranes (BLM) is scalable and has very high sensitivity. A HTS system based on BLM ion channel recording faces three main challenges: (i) design of scalable microfluidic devices; (ii) design of compact ultra-low-noise transimpedance amplifiers able to detect currents in the pA range with bandwidth >10 kHz; (iii) design of compact, robust and scalable systems that integrate these two elements. This paper presents a low-noise transimpedance amplifier with integrated A/D conversion realized in CMOS 0.35 μm technology. The CMOS amplifier acquires currents in the range ±200 pA and ±20 nA, with 100 kHz bandwidth while dissipating 41 mW. An integrated digital offset compensation loop balances any voltage offsets from Ag/AgCl electrodes. The measured open-input input-referred noise current is as low as 4 fA/√Hz at ±200 pA range. The current amplifier is embedded in an integrated platform, together with a microfluidic device, for current recording from ion channels. Gramicidin-A, α-haemolysin and KcsA potassium channels have been used to prove both the platform and the current-to-digital converter. PMID:27213382

  12. A Low-Noise Transimpedance Amplifier for BLM-Based Ion Channel Recording.

    PubMed

    Crescentini, Marco; Bennati, Marco; Saha, Shimul Chandra; Ivica, Josip; de Planque, Maurits; Morgan, Hywel; Tartagni, Marco

    2016-05-19

    High-throughput screening (HTS) using ion channel recording is a powerful drug discovery technique in pharmacology. Ion channel recording with planar bilayer lipid membranes (BLM) is scalable and has very high sensitivity. A HTS system based on BLM ion channel recording faces three main challenges: (i) design of scalable microfluidic devices; (ii) design of compact ultra-low-noise transimpedance amplifiers able to detect currents in the pA range with bandwidth >10 kHz; (iii) design of compact, robust and scalable systems that integrate these two elements. This paper presents a low-noise transimpedance amplifier with integrated A/D conversion realized in CMOS 0.35 μm technology. The CMOS amplifier acquires currents in the range ±200 pA and ±20 nA, with 100 kHz bandwidth while dissipating 41 mW. An integrated digital offset compensation loop balances any voltage offsets from Ag/AgCl electrodes. The measured open-input input-referred noise current is as low as 4 fA/√Hz at ±200 pA range. The current amplifier is embedded in an integrated platform, together with a microfluidic device, for current recording from ion channels. Gramicidin-A, α-haemolysin and KcsA potassium channels have been used to prove both the platform and the current-to-digital converter.

  13. Tear gasses CN, CR, and CS are potent activators of the human TRPA1 receptor

    SciTech Connect

    Brone, Bert; Peeters, Pieter J.; Marrannes, Roger; Mercken, Marc; Nuydens, Ronny; Meert, Theo; Gijsen, Harrie J.M.

    2008-09-01

    The TRPA1 channel is activated by a number of pungent chemicals, such as allylisothiocyanate, present in mustard oil and thiosulfinates present in garlic. Most of the known activating compounds contain reactive, electrophilic chemical groups, reacting with cysteine residues in the active site of the TRPA1 channel. This covalent modification results in activation of the channel and has been shown to be reversible for several ligands. Commonly used tear gasses CN, CR and CS are also pungent chemicals, and in this study we show that they are extremely potent and selective activators of the human TRPA1 receptor. To our knowledge, these are the most potent TRPA1 agonists known to date. The identification of the molecular target for these tear gasses may open up possibilities to alleviate the effects of tear gasses via treatment with TRPA1 antagonists. In addition these results may contribute to the basic knowledge of the TRPA1 channel that is gaining importance as a pharmacological target.

  14. Near-yrast structure of {sup 142}Cs and {sup 144}Cs

    SciTech Connect

    RzaPca-Urban, T.; Sadowski, M. P.; Genevey, J.; Pinston, J. A.; Urban, W.; Smith, A. G.; Simpson, G. S.; Bail, A.; Mathieu, L.; Serot, O.; Michel-Sendis, F.; Ahmad, I.

    2009-12-15

    Excited states in {sup 142}Cs and {sup 144}Cs, populated in the spontaneous fission of {sup 248}Cm and {sup 252}Cf and in thermal neutron-induced fission of {sup 235}U and {sup 242}Am were studied by means of {gamma} spectroscopy using the EUROGAM2 and Gammasphere multidetector Ge arrays and the LOHENGRIN fission-fragment separator, respectively. In {sup 142}Cs, a band and an isomer with a half-life of T{sub 1/2}=11(3) ns have been identified. Spins and parities have been proposed for excited levels in this nucleus. In {sup 144}Cs excited levels have been observed. A T{sub 1/2}=1.1(1) {mu}s isomer was found with a {gamma} cascade, which probably feeds this isomer. There is also an indication of a nanosecond isomer in {sup 144}Cs. Quasiparticle-rotor model calculations done in this work allowed proton-neutron configurations to be proposed for levels in {sup 142}Cs and {sup 144}Cs.

  15. Influence of a channel-forming peptide on energy barriers to ion permeation, viewed from a continuum dielectric perspective.

    PubMed Central

    Partenskii, M B; Dorman, V; Jordan, P C

    1994-01-01

    The continuum three-dielectric model for an aqueous ion channel pore-forming peptide-membrane system is extended to account for the finite length of the channel. We focus on the electrostatic influence that a channel-forming peptide may exert on energy barriers to ion permeation. The nonlinear dielectric behavior of channel water caused by dielectric saturation in the presence of an ion is explicitly modeled by assigning channel water a mean dielectric constant much less than that of bulk water. An exact solution of the continuum problem is formulated by approximating the dielectric behavior of bulk water, assigning it a dielectric constant of infinity. The validity of this approximation is verified by comparison with a Poisson-Boltzmann description of the electrolyte. The formal equivalence of high ionic strength and high electrolyte dielectric constant is demonstrated. We estimate limits on the reduction of the electrostatic free energy caused by ionic interaction with the channel-forming peptide. We find that even assigning this region an epsilon of 100, its influence is insufficient to lower permeation free energy barriers to values consistent with observed channel conductances. We provide estimates of the effective dielectric constant of this highly polarizable region, by comparing energy barriers computed using the continuum approach with those found from a semi-microscopic analysis of a simplified model of a gramicidin-like charge distribution. Possible ways of improving both models are discussed. PMID:7529581

  16. Magnetoencephalography with a Cs-based high-sensitivity compact atomic magnetometer.

    PubMed

    Sheng, Jingwei; Wan, Shuangai; Sun, Yifan; Dou, Rongshe; Guo, Yuhao; Wei, Kequan; He, Kaiyan; Qin, Jie; Gao, Jia-Hong

    2017-09-01

    In recent years, substantial progress has been made in developing a new generation of magnetoencephalography (MEG) with a spin-exchange relaxation free (SERF)-based atomic magnetometer (AM). An AM employs alkali atoms to detect weak magnetic fields. A compact AM array with high sensitivity is crucial to the design; however, most proposed compact AMs are potassium (K)- or rubidium (Rb)-based with single beam configurations. In the present study, a pump-probe two beam configuration with a Cesium (Cs)-based AM (Cs-AM) is introduced to detect human neuronal magnetic fields. The length of the vapor cell is 4 mm, which can fully satisfy the need of designing a compact sensor array. Compared with state-of-the-art compact AMs, our new Cs-AM has two advantages. First, it can be operated in a SERF regime, requiring much lower heating temperature, which benefits the sensor with a closer distance to scalp due to ease of thermal insulation and less electric heating noise interference. Second, the two-beam configuration in the design can achieve higher sensitivity. It is free of magnetic modulation, which is necessary in one-beam AMs; however, such modulation may cause other interference in multi-channel circumstances. In the frequency band between 10 Hz and 30 Hz, the noise level of the proposed Cs-AM is approximately 10 f T/Hz(1/2), which is comparable with state-of-the-art K- or Rb-based compact AMs. The performance of the Cs-AM was verified by measuring human auditory evoked fields (AEFs) in reference to commercial superconducting quantum interference device (SQUID) channels. By using a Cs-AM, we observed a clear peak in AEFs around 100 ms (M100) with a much larger amplitude compared with that of a SQUID, and the temporal profiles of the two devices were in good agreement. The results indicate the possibility of using the compact Cs-AM for MEG recordings, and the current Cs-AM has the potential to be designed for multi-sensor arrays and gradiometers for future neuroscience

  17. Magnetoencephalography with a Cs-based high-sensitivity compact atomic magnetometer

    NASA Astrophysics Data System (ADS)

    Sheng, Jingwei; Wan, Shuangai; Sun, Yifan; Dou, Rongshe; Guo, Yuhao; Wei, Kequan; He, Kaiyan; Qin, Jie; Gao, Jia-Hong

    2017-09-01

    In recent years, substantial progress has been made in developing a new generation of magnetoencephalography (MEG) with a spin-exchange relaxation free (SERF)-based atomic magnetometer (AM). An AM employs alkali atoms to detect weak magnetic fields. A compact AM array with high sensitivity is crucial to the design; however, most proposed compact AMs are potassium (K)- or rubidium (Rb)-based with single beam configurations. In the present study, a pump-probe two beam configuration with a Cesium (Cs)-based AM (Cs-AM) is introduced to detect human neuronal magnetic fields. The length of the vapor cell is 4 mm, which can fully satisfy the need of designing a compact sensor array. Compared with state-of-the-art compact AMs, our new Cs-AM has two advantages. First, it can be operated in a SERF regime, requiring much lower heating temperature, which benefits the sensor with a closer distance to scalp due to ease of thermal insulation and less electric heating noise interference. Second, the two-beam configuration in the design can achieve higher sensitivity. It is free of magnetic modulation, which is necessary in one-beam AMs; however, such modulation may cause other interference in multi-channel circumstances. In the frequency band between 10 Hz and 30 Hz, the noise level of the proposed Cs-AM is approximately 10 f T/Hz1/2, which is comparable with state-of-the-art K- or Rb-based compact AMs. The performance of the Cs-AM was verified by measuring human auditory evoked fields (AEFs) in reference to commercial superconducting quantum interference device (SQUID) channels. By using a Cs-AM, we observed a clear peak in AEFs around 100 ms (M100) with a much larger amplitude compared with that of a SQUID, and the temporal profiles of the two devices were in good agreement. The results indicate the possibility of using the compact Cs-AM for MEG recordings, and the current Cs-AM has the potential to be designed for multi-sensor arrays and gradiometers for future neuroscience

  18. 135Cs/137Cs isotopic composition of environmental samples across Europe: Environmental transport and source term emission applications

    DOE PAGES

    Snow, Mathew S.; Snyder, Darin C.

    2015-11-02

    135Cs/137Cs isotopic analyses represent an important tool for studying the fate and transport of radiocesium in the environment; in this work the 135Cs/137Cs isotopic composition in environmental samples taken from across Europe is reported. Surface soil and vegetation samples from western Russia, Ukraine, Austria, and Hungary show consistent aged thermal fission product 135Cs/137Cs isotope ratios of 0.58 ± 0.01 (age corrected to 1/1/15), with the exception of one sample of soil-moss from Hungary which shows an elevated 135Cs/137Cs ratio of 1.78 ± 0.12. With the exception of the outlier sample from Hungary, surface soil/vegetation data are in quantitative agreement withmore » values previously reported for soils within the Chernobyl exclusion zone, suggesting that radiocesium at these locations is primarily composed of homogenous airborne deposition from Chernobyl. Seawater samples taken from the Irish Sea show 135Cs/137Cs isotope ratios of 1.22 ± 0.11 (age corrected to 1/1/15), suggesting aged thermal fission product Cs discharged from Sellafield. Furthermore, the differences in 135Cs/137Cs isotope ratios between Sellafield, Chernobyl, and global nuclear weapons testing fallout indicate that 135Cs/137Cs isotope ratios can be utilized to discriminate between and track radiocesium transport from different nuclear production source terms, including major emission sources in Europe.« less

  19. (135)Cs/(137)Cs isotopic composition of environmental samples across Europe: Environmental transport and source term emission applications.

    PubMed

    Snow, Mathew S; Snyder, Darin C

    2016-01-01

    (135)Cs/(137)Cs isotopic analyses represent an important tool for studying the fate and transport of radiocesium in the environment; in this work the (135)Cs/(137)Cs isotopic composition in environmental samples taken from across Europe is reported. Surface soil and vegetation samples from western Russia, Ukraine, Austria, and Hungary show consistent aged thermal fission product (135)Cs/(137)Cs isotope ratios of 0.58 ± 0.01 (age corrected to 1/1/15), with the exception of one sample of soil-moss from Hungary which shows an elevated (135)Cs/(137)Cs ratio of 1.78 ± 0.12. With the exception of the outlier sample from Hungary, surface soil/vegetation data are in quantitative agreement with values previously reported for soils within the Chernobyl exclusion zone, suggesting that radiocesium at these locations is primarily composed of homogenous airborne deposition from Chernobyl. Seawater samples taken from the Irish Sea show (135)Cs/(137)Cs isotope ratios of 1.22 ± 0.11 (age corrected to 1/1/15), suggesting aged thermal fission product Cs discharged from Sellafield. The differences in (135)Cs/(137)Cs isotope ratios between Sellafield, Chernobyl, and global nuclear weapons testing fallout indicate that (135)Cs/(137)Cs isotope ratios can be utilized to discriminate between and track radiocesium transport from different nuclear production source terms, including major emission sources in Europe. Copyright © 2015 Elsevier Ltd. All rights reserved.

  20. TRP Channels

    PubMed Central

    Venkatachalam, Kartik; Montell, Craig

    2011-01-01

    The TRP (Transient Receptor Potential) superfamily of cation channels is remarkable in that it displays greater diversity in activation mechanisms and selectivities than any other group of ion channels. The domain organizations of some TRP proteins are also unusual, as they consist of linked channel and enzyme domains. A unifying theme in this group is that TRP proteins play critical roles in sensory physiology, which include contributions to vision, taste, olfaction, hearing, touch, and thermo- and osmosensation. In addition, TRP channels enable individual cells to sense changes in their local environment. Many TRP channels are activated by a variety of different stimuli and function as signal integrators. The TRP superfamily is divided into seven subfamilies: the five group 1 TRPs (TRPC, TRPV, TRPM, TRPN, and TRPA) and two group 2 subfamilies (TRPP and TRPML). TRP channels are important for human health as mutations in at least four TRP channels underlie disease. PMID:17579562

  1. Transverse-pumped Cs vapor laser

    NASA Astrophysics Data System (ADS)

    Zhdanov, B. V.; Shaffer, M. K.; Sell, J.; Knize, R. J.

    2009-02-01

    Scaling of alkali lasers to higher powers requires combining beams of multiple diode laser pump sources. For longitudinal pumping this can be very complicated if more than four beams are to be combined. In this paper we report a first demonstration of a transversely pumped Cs laser with fifteen laser diode arrays. The LDA pump beams were individually collimated with a beam size of about 1 x 4 cm as measured at a 1 m distance from the diodes. All these beams were incident on a cylindrical lens to be focused and coupled through the side slit of a hollow, cylindrical diffuse reflector which contained the Cs vapor cell. We measured the output power and efficiency of the Cs laser for pump powers up to 200 W at different cell temperatures. Although the values of output power and slope efficiency obtained for this laser system were less than those for a longitudinally pumped alkali laser, these recent results can be significantly improved by using a more optimal laser cavity design. The demonstrated operation of Cs laser with transverse pumping opens new possibilities in power scaling of alkali lasers.

  2. Ceramic Breeder Blanket for ARIES-CS

    SciTech Connect

    Raffray, A.R.; Malang, S.; El-Guebaly, L.; Wang, X.

    2005-05-15

    This paper describes the conceptual design of a ceramic breeder blanket considered as one of the candidate blankets in the first phase of the ARIES-CS study. The blanket is coupled to a Brayton power cycle to avoid the safety concern associated with the possibility of Be/steam reaction in case of accident.

  3. Atmospheric oxidation of carbon disulfide (CS2)

    NASA Astrophysics Data System (ADS)

    Zeng, Zhe; Altarawneh, Mohammednoor; Dlugogorski, Bogdan Z.

    2017-02-01

    This contribution investigates primary steps governing the OH-initiated atmospheric oxidation of CS2. Our approach comprises high-level density functional theory calculation of energies and optimisation of molecular structures as well as RRKM-ME analysis for estimating pressure-dependent reaction rate constants. We find the overall reaction OH + CS2 → OCS + SH too slow to account for the formation of the reported experimental products. The initial reaction of OH with CS2 proceeds to produce an S-adduct, SCS(OH). Species-formation history for the system OH + CS2 indicates that, the S-adduct represents the most plausible product with a barrier-less addition process and a stability amounting to 48.5 kJ/mol, in reference to the separated reactants. This adduct then undergoes a bimolecular reaction with atmospheric O2 yielding OCS and HOSO, rather than dissociating back into its separated reactants. We also find that further atmospheric oxidation of the C-adduct (if formed) yields two of the major experimental products namely OCS and SO2. The kinetic analysis provided in this study explains the atmospheric fate of reduced sulfur species, an important S-bearing group in the global cycle of sulfur.

  4. Properties of CsI and CsI-TMAE photocathodes

    SciTech Connect

    Anderson, D.F.; Kwan, S.; Peskov, V.; Hoeneisen, B.

    1992-06-01

    The importance of heating the CsI or CsI-TMAE photocathodes during preparation, as well as the importance of the gas environment on the quantum efficiency is presented. The dependence of the aging characteristics of these photocathodes on the operating temperature, on the presence of gas, and on the charge amplification of the chamber is also discussed. For CsI photocathodes charges in excess of 2{times}10{sup 14} e{sup {minus}}/mm{sup 2} can be collected with little degradation of performance. A timing resolution of 0.55 ns is also achieved for single photoelectrons suggesting a possible time-of-flight detector.

  5. Surface charge potentiates conduction through the cardiac ryanodine receptor channel

    PubMed Central

    1994-01-01

    Single channel currents through cardiac sarcoplasmic reticulum (SR) Ca2+ release channels were measured in very low levels of current carrier (e.g., 1 mM Ba2+). The hypothesis that surface charge contributes to these anomalously large single channel currents was tested by changing ionic strength and surface charge density. Channel identity and sidedness was pharmacologically determined. At low ionic strength (20 mM Cs+), Cs+ conduction in the lumen-->myoplasm (L-->M) direction was significantly greater than in the reverse direction (301.7 +/- 92.5 vs 59.8 +/- 38 pS, P < 0.001; mean +/- SD, t test). The Cs+ concentration at which conduction reached half saturation was asymmetric (32 vs 222 mM) and voltage independent. At high ionic strength (400 mM Cs+), conduction in both direction saturated at 550 +/- 32 pS. Further, neutralization of carboxyl groups on the lumenal side of the channel significantly reduced conduction (333.0 +/- 22.5 vs 216.2 +/- 24.4 pS, P < 0.002). These results indicate that negative surface charge exists near the lumenal mouth of the channel but outside the electric field of the membrane. In vivo, this surface charge may potentiate conduction by increasing the local Ca2+ concentration and thus act as a preselection filter for this poorly selective channel. PMID:8035165

  6. Local environments for Cs(1) and Cs(2) sites in a perovskite Cs2CoBr4 single crystal with a dominant magnetic type based on the observed spin-lattice relaxation time

    NASA Astrophysics Data System (ADS)

    Lim, Ae Ran; Lim, Kye-Young

    2017-08-01

    The local structure and molecular motion for 133Cs in a Cs2CoBr4 single crystal were examined by using the spin-lattice relaxation time from nuclear magnetic resonance (NMR). The two inequivalent Cs(1) and Cs(2) sites surrounded by Br ions in Cs2CoBr4 were clearly distinguished by using 133Cs NMR spectra. The spin-lattice relaxation times T1 of the Cs(1) and Cs(2) nuclei in Cs2CoBr4 were obtained, and the temperature dependence of the relaxation time for Cs(2) changed more abruptly than that for Cs(1). The T1 values for Cs(1) and Cs(2) ions were used to determine the activation energies for the molecular motions, and the molecular motion of Cs(2) surrounded by nine bromide ions was tighter than that of Cs(1) surrounded by 11 bromide ions.

  7. Monitoring 137Cs and 134Cs at marine coasts in Indonesia between 2011 and 2013.

    PubMed

    Suseno, Heny; Prihatiningsih, Wahyu Retno

    2014-11-15

    Environmental samples (seawater, sediments and biota) were collected along the eastern and western Indonesian coasts between 2011 and 2013 to anticipate the possible impacts of the Fukushima radioactive releases in Indonesia. On the eastern coasts (south and north Sulawesi), the (137)Cs concentrations in the seawater and sediments were 0.12-0.32 Bq m(-3) and 0.10-1.03 Bq kg(-1), respectively. On the western coasts (West Sumatra, Bangka Island, North Java, South Java and Madura island), the (137)Cs concentrations in the seawater and sediments were 0.12-0.66 Bq m(-3) and 0.19-1.64 Bq kg(-1), respectively. In general, the (137)Cs concentrations in the fish from several Indonesian coasts were Cs concentrations in mollusk, crab and prawn were 10.65-38.78, 4.02 and 6.16 mBq kg(-1), respectively. (134)Cs was not detected in the seawater, sediments or biota. Thus, it was concluded that (137)Cs on the eastern and western Indonesian coasts originated from global fallout.

  8. Luminescence of CsPbBr 3-like quantum dots in CsBr single crystals

    NASA Astrophysics Data System (ADS)

    Nikl, M.; Nitsch, K.; Mihóková, E.; Polák, K.; Fabeni, P.; Pazzi, G. P.; Gurioli, M.; Santucci, S.; Phani, R.; Scacco, A.; Somma, F.

    Luminescence and decay kinetics of the Pb 2+ aggregates in CsBr host crystals were measured in the 4-300 K temperature interval and in 10 -10-10 -3 time scale. Their emission properties are similar to those of CsPbBr 3 bulk crystal showing a subnanosecond free exciton emission in the 520-540 nm spectral region and slower trapped exciton emission in the 530-580 nm spectral region. An efficient energy exchange between the free and trapped exciton states is shown by the temperature dependencies of emission spectra. The quantum size effect is demonstrated in the high energy shift and broadening of the absorption and emission spectra and an estimate of the size of the CsPbBr 3-like aggregates is provided. Independent evidence of the presence of the CsPbBr 3 and Cs 4PbBr 6 aggregated phases in the CsBr host was obtained by X-ray structural studies.

  9. Bilayer lipid membranes supported on Teflon filters: a functional environment for ion channels.

    PubMed

    Phung, Thai; Zhang, Yanli; Dunlop, James; Dalziel, Julie

    2011-03-15

    Many ion channel proteins have binding sites for toxins and pharmaceutical drugs and therefore have much promise as the sensing entity in high throughput technologies and biosensor devices. Measurement of ionic conductance changes through ion channels requires a robust biological membrane with sufficient longevity for practical applications. The conventional planar BLM is 100-300 μm in diameter and typically contains fewer than a dozen channels whereas pharmaceutical screening methods in cells use current recordings for many ion channels. We present a new, simple method for the fabrication of a disposable porous-supported bilayer lipid membrane (BLM) ion channel biosensor using hydrated Teflon (polytetrafluoroethylene, PTFE) filter material (pore size 5 μm, filter diameter=1 mm). The lipid layer was monitored for its thickness and mechanical stability by electrical impedance spectroscopy. The results showed membrane capacitances of 1.8±0.2 nF and membrane resistances of 25.9±4.1 GΩ, indicating the formation of lipid bilayers. The current level increased upon addition of the pore-forming peptide gramicidin. Following addition of liposomes containing voltage-gated sodium channels, small macroscopic sodium currents (1-80 pA) could be recorded. By preloading the porous Teflon with sodium channel proteoliposomes, prior to BLM formation, currents of 1-10 nA could be recorded in the presence of the activator veratridine that increased with time, and were inhibited by tetrodotoxin. A lack of rectification suggests that the channels incorporated in both orientations. This work demonstrates that PTFE filters can support BLMs that provide an environment in which ion channels can maintain their functional activity relevant for applications in drug discovery, toxin detection, and odour sensing.

  10. Translocation of (133)Cs administered to Cryptomeria japonica wood.

    PubMed

    Aoki, Dan; Asai, Ryutaro; Tomioka, Rie; Matsushita, Yasuyuki; Asakura, Hiroyuki; Tabuchi, Masao; Fukushima, Kazuhiko

    2017-04-15

    To reveal the in planta behaviour of caesium (Cs), the stable isotope (133)Cs was administered into 3-year-old Cryptomeria japonica seedlings by the application of (133)CsCl aqueous solution to the bark surface. The administered (133)Cs was quantified by ICP-MS measurements, which showed transportation of (133)Cs in an ascending direction in the stem. Distribution of (133)Cs was visualized using freeze-fixed C. japonica woody stem samples and cryo-time-of-flight secondary ion mass spectrometry/scanning electron microscopy (cryo-TOF-SIMS/SEM) analysis. Cryo-TOF-SIMS/SEM visualization suggested that (133)Cs was rapidly transported radially by ray parenchyma cells followed by axial transportation by pith and axial parenchyma cells. Adsorption experiments using powdered C. japonica wood samples and X-ray absorption fine structure (XAFS) analysis suggested that (133)Cs was in the hydrated state following its deposition into tracheid cell walls.

  11. Charging the quantum capacitance of graphene with a single biological ion channel.

    PubMed

    Wang, Yung Yu; Pham, Ted D; Zand, Katayoun; Li, Jinfeng; Burke, Peter J

    2014-05-27

    The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents.

  12. Charging the Quantum Capacitance of Graphene with a Single Biological Ion Channel

    PubMed Central

    2015-01-01

    The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents. PMID:24754625

  13. Communications satellite no. 2 (CS-2)

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The purpose of the Japanese CS-2 satellite is to provide national communications and industrial communications, such as special emergency and remote communications, and to contribute to the development of technology pertaining to communications satellites. Description and operating parameters of the following satellite components are presented: structure, communications system, telemetry/command system, electric power system, attitude and antenna control system, secondary propulsion system, apogee motor, framework, and heat control system.

  14. IR-Improved DGLAP-CS Theory

    DOE PAGES

    Ward, B. F. L.

    2008-01-01

    We show that it is possible to improve the infrared aspects of the standard treatment of the DGLAP-CS evolution theory to take into account a large class of higher-order corrections that significantly improve the precision of the theory for any given level of fixed-order calculation of its respective kernels. We illustrate the size of the effects we resum using the moments of the parton distributions.

  15. End-Pumped 895 nm Cs Laser

    SciTech Connect

    Beach, R J; Krupke, W F; Kanz, V K; Payne, S A; Dubinskii, M A; Merkle, L D

    2004-02-09

    A scientific demonstration of a Cs laser is described in which the measured slope efficiency is as high as 0.59 W/W using a Ti:Sapphire laser as a surrogate diode-pump. In addition to presenting experimental data, a laser energetics model that accurately predicts laser performance is described and used to model a power-scaled, diode-pumped system.

  16. TRP Channels

    NASA Astrophysics Data System (ADS)

    Voets, Thomas; Owsianik, Grzegorz; Nilius, Bernd

    The TRP superfamily represents a highly diverse group of cation-permeable ion channels related to the product of the Drosophila trp (transient receptor potential) gene. The cloning and characterization of members of this cation channel family has experienced a remarkable growth during the last decade, uncovering a wealth of information concerning the role of TRP channels in a variety of cell types, tissues, and species. Initially, TRP channels were mainly considered as phospholipase C (PLC)-dependent and/or store-operated Ca2+-permeable cation channels. More recent research has highlighted the sensitivity of TRP channels to a broad array of chemical and physical stimuli, allowing them to function as dedicated biological sensors involved in processes ranging from vision to taste, tactile sensation, and hearing. Moreover, the tailored selectivity of certain TRP channels enables them to play key roles in the cellular uptake and/or transepithelial transport of Ca2+, Mg2+, and trace metal ions. In this chapter we give a brief overview of the TRP channel superfamily followed by a survey of current knowledge concerning their structure and activation mechanisms.

  17. Coulomb explosion of CS2 molecule under an intense femtosecond laser field

    NASA Astrophysics Data System (ADS)

    Xiao, Wang; Jian, Zhang; Shi-An, Zhang; Zhen-Rong, Sun

    2016-05-01

    We experimentally demonstrate the Coulomb explosion process of CS2 molecule under a near-infrared (800 nm) intense femtosecond laser field by a DC-sliced ion imaging technique. We obtain the DC-sliced images of these fragment ions S+, S2+, CS+, and CS2+ by breaking one C-S bond, and assign their Coulomb explosion channels by considering their kinetic energy release and angular distribution. We also numerically simulate the dissociation dynamics of parent ions by a Coulomb potential approximation, and obtain the time evolution of Coulomb energy and kinetic energy release, which indicates that the dissociation time of parent ions decreases with the increase of the charge number k. These experimental and theoretical results can serve as a useful benchmark for those researchers who work in the related area. Project supported by the National Natural Science Foundation of China (Grant Nos. 51132004 and 11474096), and the Science and Technology Commission of Shanghai Municipality, China (Grant No. 14JC1401500). We acknowledge the support of the NYU-ECNU Institute of Physics at NYU Shanghai, China.

  18. Rippley Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    18 September 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a narrow channel on the upper east flank of the martian volcano, Hadriaca Patera. Because it is located on a volcano, most likely this channel was formed by lava, perhaps as a lava tube at which the thin roof later collapsed. Large ripples of windblown sediment now occur on the channel floor; their crests are generally perpendicular to the channel walls, suggesting that winds blow up and down through this channel.

    Location near: 30.5oS, 266.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Autumn

  19. Rippley Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    18 September 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a narrow channel on the upper east flank of the martian volcano, Hadriaca Patera. Because it is located on a volcano, most likely this channel was formed by lava, perhaps as a lava tube at which the thin roof later collapsed. Large ripples of windblown sediment now occur on the channel floor; their crests are generally perpendicular to the channel walls, suggesting that winds blow up and down through this channel.

    Location near: 30.5oS, 266.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Autumn

  20. Teaching Algorithm Efficiency at CS1 Level: A Different Approach

    NASA Astrophysics Data System (ADS)

    Gal-Ezer, Judith; Vilner, Tamar; Zur, Ela

    2004-09-01

    Realizing the importance of teaching efficiency at early stages of the program of study in computer science (CS) on one hand, and the difficulties encountered when introducing this concept on the other, we advocate a different didactic approach in the introductory CS course (CS1). This paper describes the approach as it is used at the Open University of Israel (OUI).

  1. Teaching Algorithm Efficiency at CS1 Level: A Different Approach

    ERIC Educational Resources Information Center

    Gal-Ezer, Judith; Vilner, Tamar; Zur, Ela

    2004-01-01

    Realizing the importance of teaching efficiency at early stages of the program of study in computer science (CS) on one hand, and the difficulties encountered when introducing this concept on the other, we advocate a different didactic approach in the introductory CS course (CS1). This paper describes the approach as it is used at the Open…

  2. Cesium Platinide Hydride 4Cs 2 Pt-CsH: An Intermetallic Double Salt Featuring Metal Anions

    SciTech Connect

    Smetana, Volodymyr; Mudring, Anja-Verena

    2016-10-24

    With Cs9Pt4H a new representative of ionic compounds featuring metal anions can be added to this rare-membered family. Cs9Pt4H exhibits a complex crystal structure containing Cs+ cations, Pt2- and H- anions. Being a red, transparent compound its band gap is in the visible range of the electromagnetic spectrum and the ionic type of bonding is confirmed by quantum chemical calculations. This cesium platinide hydride can formally be considered as a double salt of the “alloy” cesium–platinum, or better cesium platinide, Cs2Pt, and the salt cesium hydride CsH according to Cs9Pt4H≡4 Cs2Pt∙CsH.

  3. Cesium Platinide Hydride 4Cs2 Pt⋅CsH: An Intermetallic Double Salt Featuring Metal Anions.

    PubMed

    Smetana, Volodymyr; Mudring, Anja-Verena

    2016-11-14

    With Cs9 Pt4 H a new representative of ionic compounds featuring metal anions can be added to this rare-membered family. Cs9 Pt4 H exhibits a complex crystal structure containing Cs(+) cations, Pt(2-) and H(-) anions. Being a red, transparent compound its band gap is in the visible range of the electromagnetic spectrum and the ionic type of bonding is confirmed by quantum chemical calculations. This cesium platinide hydride can formally be considered as a double salt of the "alloy" cesium-platinum, or better cesium platinide, Cs2 Pt, and the salt cesium hydride CsH according to Cs9 Pt4 H≡4 Cs2 Pt⋅CsH.

  4. Pressure-induced metathesis reaction to sequester Cs.

    PubMed

    Im, Junhyuck; Seoung, Donghoon; Lee, Seung Yeop; Blom, Douglas A; Vogt, Thomas; Kao, Chi-Chang; Lee, Yongjae

    2015-01-06

    We report here a pressure-driven metathesis reaction where Ag-exchanged natrolite (Ag16Al16Si24O80·16H2O, Ag-NAT) is pressurized in an aqueous CsI solution, resulting in the exchange of Ag(+) by Cs(+) in the natrolite framework forming Cs16Al16Si24O80·16H2O (Cs-NAT-I) and, above 0.5 GPa, its high-pressure polymorph (Cs-NAT-II). During the initial cation exchange, the precipitation of AgI occurs. Additional pressure and heat at 2 GPa and 160 °C transforms Cs-NAT-II to a pollucite-related, highly dense, and water-free triclinic phase with nominal composition CsAlSi2O6. At ambient temperature after pressure release, the Cs remains sequestered in a now monoclinic pollucite phase at close to 40 wt % and a favorably low Cs leaching rate under back-exchange conditions. This process thus efficiently combines the pressure-driven separation of Cs and I at ambient temperature with the subsequent sequestration of Cs under moderate pressures and temperatures in its preferred waste form suitable for long-term storage at ambient conditions. The zeolite pollucite CsAlSi2O6·H2O has been identified as a potential host material for nuclear waste remediation of anthropogenic (137)Cs due to its chemical and thermal stability, low leaching rate, and the large amount of Cs it can contain. The new water-free pollucite phase we characterize during our process will not display radiolysis of water during longterm storage while maintaining the Cs content and low leaching rate.

  5. Developments towards detection of 135Cs at VERA

    NASA Astrophysics Data System (ADS)

    Lachner, Johannes; Kasberger, Magdalena; Martschini, Martin; Priller, Alfred; Steier, Peter; Golser, Robin

    2015-10-01

    Radioisotopes produced in natural or anthropogenic fission are widely used for tracer studies of environmental processes, in nuclear forensics, and are important for nuclear waste disposal. Besides the well-known 137Cs, the longer-lived sister isotope 135Cs (T1/2 = 2.3 Myr) is also produced, and the combined measurement of the two isotopes would allow for assessment of contaminating sources. The insufficient suppression of the stable isobar 135Ba presently prevents AMS measurements down to expected natural levels of 135Cs/133Cs ≈ 10-11. Via the difference in electron affinities between Cs and Ba further isobar suppression should be achievable after the installation of the Ion-Laser-Interaction System (ILIAS) at VERA. We present a preparatory study on the performance of the 3 MV VERA AMS facility for 135Cs concerning ion formation, transmission and detection. Since the usual Cs sputtering would obscure the 135Cs/133Cs ratio of a sample, Rb sputtering was successfully applied and tested also for various other typical AMS elements. Partial suppression of 135Ba is possible with the extraction of Cs- and negative Cs-fluorides. Cs- currents of several 10 nA were extracted over hours from mg amounts of Cs2SO4 material. The transmission to various charge states was tested with gas (Ar, He) and foil stripping. Experiments showed that no suppression in the detection system is possible at high beam energies with the VERA facility. For this reason, gas stripping to low charge states (2+, 3+) with transmissions up to 30% is favorable to guarantee optimal beam transport to the detector. In the present setup, utilizing a simple Bragg-type detector, the blank 135Cs/133Cs ratios from chemically pure samples are determined by the 135Ba background to a value of (4.0 ± 1.3)·10-9.

  6. Histidine substitution identifies a surface position and confers Cs+ selectivity on a K+ pore.

    PubMed Central

    De Biasi, M; Drewe, J A; Kirsch, G E; Brown, A M

    1993-01-01

    The amino acid located at position 369 is a key determinant of the ion conduction pathway or pore of the voltage-gated K+ channels, Kv2.1 and a chimeric channel, CHM, constructed by replacing the pore region of Kv2.1 with that of Kv3.1. To determine the orientation of residue 369 with respect to the aqueous lumen of the pore, the nonpolar Ile at 369 in Kv2.1 was replaced with a basic His. This substitution produced a Cs(+)-selective channel with Cs+:K+ permeability ratio of 4 compared to 0.1 in the wild type. Block by external tetraethylammonium (TEA) was reduced about 20-fold, while block by internal TEA was unaffected. External protons and Zn2+, that are known to interact with the imidazole ring of His, blocked the mutant channel much more effectively than the wild type channel. The blockade by Zn2+ and protons was voltage-independent, and the proton blockade had a pKa of about 6.5, consistent with the pKa for His in solution. The histidyl-specific reagent diethylpyrocarbonate produced greatly exaggerated blockade of the mutated channel compared to the wild type. The residue at position 369 appears to form part of the binding site for external TEA and to influence the selectivity for monovalent cations. We suggest that the imidazole side-chain of His369 is exposed to the aqueous lumen at a surface position near the external mouth of the pore. PMID:8241404

  7. Chondroitin sulfate (CS) lyases: Structure, function and application in therapeutics.

    PubMed

    Rani, Aruna; Patel, Seema; Goyal, Arun

    2017-01-02

    Glycosaminoglycans (GAGs) such as chondroitin sulfate (CS) are the chief natural polysaccharides which reside in biological tissues mainly in extracellular matrix. These CS along with adhesion molecules and growth factors are involved in central nervous system (CNS) development, cell progression and pathogenesis. The chondroitin lyases are the enzyme that degrade and alter the CS chains and hence modify various signalling pathways involving CS chains. These CS lyases are substrate specific, can precisely manipulate the CS polysaccharides and have various biotechnological, medical and therapeutic applications. These enzymes can be used to produce the unsaturated oligosaccharides, which have immune-modulatory, anti-inflammatory and neuroprotective properties. This review focuses on the major breakthrough of the chondroitin sulfate degrading enzymes, their structures and functioning mechanism. This also provides comprehensive information regarding production, purification, characterization of CS lyases and their major applications, both established as well as emerging ones such as neural development.

  8. Bacterial CS2 Hydrolases from Acidithiobacillus thiooxidans Strains Are Homologous to the Archaeal Catenane CS2 Hydrolase

    PubMed Central

    Smeulders, Marjan J.; Pol, Arjan; Venselaar, Hanka; Barends, Thomas R. M.; Hermans, John; Jetten, Mike S. M.

    2013-01-01

    Carbon disulfide (CS2) and carbonyl sulfide (COS) are important in the global sulfur cycle, and CS2 is used as a solvent in the viscose industry. These compounds can be converted by sulfur-oxidizing bacteria, such as Acidithiobacillus thiooxidans species, to carbon dioxide (CO2) and hydrogen sulfide (H2S), a property used in industrial biofiltration of CS2-polluted airstreams. We report on the mechanism of bacterial CS2 conversion in the extremely acidophilic A. thiooxidans strains S1p and G8. The bacterial CS2 hydrolases were highly abundant. They were purified and found to be homologous to the only other described (archaeal) CS2 hydrolase from Acidianus strain A1-3, which forms a catenane of two interlocked rings. The enzymes cluster in a group of β-carbonic anhydrase (β-CA) homologues that may comprise a subclass of CS2 hydrolases within the β-CA family. Unlike CAs, the CS2 hydrolases did not hydrate CO2 but converted CS2 and COS with H2O to H2S and CO2. The CS2 hydrolases of A. thiooxidans strains G8, 2Bp, Sts 4-3, and BBW1, like the CS2 hydrolase of Acidianus strain A1-3, exist as both octamers and hexadecamers in solution. The CS2 hydrolase of A. thiooxidans strain S1p forms only octamers. Structure models of the A. thiooxidans CS2 hydrolases based on the structure of Acidianus strain A1-3 CS2 hydrolase suggest that the A. thiooxidans strain G8 CS2 hydrolase may also form a catenane. In the A. thiooxidans strain S1p enzyme, two insertions (positions 26 and 27 [PD] and positions 56 to 61 [TPAGGG]) and a nine-amino-acid-longer C-terminal tail may prevent catenane formation. PMID:23836868

  9. Mechanosensitive Channels

    NASA Astrophysics Data System (ADS)

    Martinac, Boris

    Living cells are exposed to a variety of mechanical stimuli acting throughout the biosphere. The range of the stimuli extends from thermal molecular agitation to potentially destructive cell swelling caused by osmotic pressure gradients. Cellular membranes present a major target for these stimuli. To detect mechanical forces acting upon them cell membranes are equipped with mechanosensitive (MS) ion channels. Functioning as molecular mechanoelectrical transducers of mechanical forces into electrical and/or chemical intracellular signals these channels play a critical role in the physiology of mechanotransduction. Studies of prokaryotic MS channels and recent work on MS channels of eukaryotes have significantly increased our understanding of their gating mechanism, physiological functions, and evolutionary origins as well as their role in the pathology of disease.

  10. Channel catfish

    USDA-ARS?s Scientific Manuscript database

    This book chapter provides a comprehensive overview of channel catfish aquaculture. Sections include fish biology; commercial culture; culture facilities; production practices; water quality management; nutrition, feeding and feed formulation; infectious diseases; harvesting and processing; and the...

  11. Spin accumulation in thin Cs salts on contact with optically polarized Cs vapor

    SciTech Connect

    Ishikawa, Kiyoshi

    2011-09-15

    The spin angular momentum accumulates in the Cs nuclei of salt on contact with optically pumped Cs vapor. The spin polarization in stable chloride as well as dissociative hydride indicates that nuclear dipole interaction works in spin transferring with a lesser role of atom exchange. In the solid film, not only the spin buildup but also the decay of enhanced polarization is faster than the thermal recovery rate for the bulk salt. Eliminating the signal of thick salt, we find that the nuclear spin polarization in the chloride film reaches over 100 times the thermal equilibrium.

  12. Spatial distribution of 137Cs in surface soil under different land uses in Chao Phraya watershed: Potential used as sediment source tracing

    NASA Astrophysics Data System (ADS)

    Srisuksawad, K.; porntepkasemsan, B.; Noipow, N.; Omanee, A.; Wiriyakitnateekul, W.; Chouybudha, R.; Srimawong, P.

    2015-05-01

    Sediment fingerprinting techniques involves the discrimination of sediment sources based on differences in source material properties and quantification of the relative contributions from these sources to sediment delivered downstream to the river catchments. Results of the previous study indicated that fallout radionuclides (FRNs); 137Cs and excess 210Pb (210Pbex) are the most suitable radionuclides to be used as sediments sources tracers. This study investigated the spatial distribution of 137Cs in soil under different land uses in Chao Phraya watershed; the most significant watershed in Thailand. Emphasis was placed on discriminating among potential sediment sources including the cultivated (upland crops), pasture field, uncultivated (swamp, forest, and grass field), and channel erosion (stream and river bank). One hundred and twenty four soil samples were collected from all sources and determining for 137Cs. The 137Cs mass activities in pasture areas varied from the limit of detection (LLD) to 1.22±0.05 with the average of 0.64±0.14 Bq kg-1. In cultivated areas the 137Cs mass activities varied from LLD to 1.41±0.04 with the average of 0.38±0.04 Bq kg-1. The 137Cs mass activities were higher in uncultivated areas varied from 0.12±0.03 to 1.73±0.05 with the average of 0.76±0.15 Bq kg-1. The 137Cs mass activities in channel bank varied from LLD to 1.16±0.04 with the average of 0.39±0.05 Bq kg-1.GIS and geospatial interpolations revealed pattern in the spatial concentrations of 137Cs and indicated important differences in its distributions showing the differences behaviour of 137Cs in different land uses.

  13. Red luminescence of CsI crystals

    SciTech Connect

    Smol`skaya, L.P.; Kolesnikova, T.A.

    1995-12-01

    Emission in the red spectral range with the maximum at 670 nm and two decay components <5 ns and 1 {mu}s is found in the cathodoluminescence of CsI crystals excited by a pulsed electron beam with the 5-ns duration. The short component is assigned to the ultrafast luminescence caused by the transitions within the valence band. It is assumed that the microsecond component of the red luminescence is caused by the radiative exciton annihilation at the unstable defects produced by ionizing radiation. 8 refs., 1 fig.

  14. Reactor Configuration Development for ARIES-CS

    SciTech Connect

    Ku LP, the ARIES-CS Team

    2005-09-27

    New compact, quasi-axially symmetric stellarator configurations have been developed as part of the ARIES-CS reactor studies. These new configurations have good plasma confinement and transport properties, including low losses of α particles and good integrity of flux surfaces at high β. We summarize the recent progress by showcasing two attractive classes of configurations — configurations with judiciously chosen rotational transforms to avoid undesirable effects of low order resonances on the flux surface integrity and configurations with very small aspect ratios (∼2.5) that have excellent quasi-axisymmetry and low field ripples.

  15. K2CsSb Cathode Development

    SciTech Connect

    Smedley,J.; Rao, T.; Wang, E.

    2008-10-01

    K{sub 2}CsSb is an attractive photocathode for high current applications. With a quantum efficiency of >4% at 532nm and >10% at 355nm, it is the only cathode to have demonstrated an average current of 35mA in an accelerator environment We describe ongoing cathode development work. for the energy recovery linac being constructed at BNL Several cathodes have been created on both copper and stainless steel substrates, and their spatial uniformity and spectral response have been characterized. Preliminary lifetime measurements have been performed at high average current densities (>1 mA/mm{sup 2}).

  16. Analyzing Feshbach resonances: A Li6-Cs133 case study

    NASA Astrophysics Data System (ADS)

    Pires, R.; Repp, M.; Ulmanis, J.; Kuhnle, E. D.; Weidemüller, M.; Tiecke, T. G.; Greene, Chris H.; Ruzic, Brandon P.; Bohn, John L.; Tiemann, E.

    2014-07-01

    We provide a comprehensive comparison of a coupled channel calculation, the asymptotic bound-state model (ABM), and the multichannel quantum defect theory (MQDT). Quantitative results for 6Li-133Csare presented and compared to previously measured 6Li-133CsFeshbach resonances (FRs) [Repp et al., Phys. Rev. A 87, 010701(R) (2013), 10.1103/PhysRevA.87.010701]. We demonstrate how the accuracy of the ABM can be stepwise improved by including magnetic dipole-dipole interactions and coupling to a nondominant virtual state. We present a MQDT calculation, where magnetic dipole-dipole and second-order spin-orbit interactions are included. A frame transformation formalism is introduced, which allows the assignment of measured FRs with only three parameters. All three models achieve a total rms error of <1G on the observed FRs. We critically compare the different models in view of the accuracy for the description of FRs and the required input parameters for the calculations.

  17. Thermal Beam Spectroscopy of 133 Cs

    NASA Astrophysics Data System (ADS)

    Gerginov, Vladislav; Tanner, Carol E.

    2001-05-01

    We report our progress towards high resolution frequency measurements of the cesium excited states hyperfine structure (HFS). A thermal beam apparatus is used to eliminate the Doppler background and collision effects present in vapor cells. A tubing array expands the beam size without increasing its divergence. The beam is collimated using thin parallel glass plate collimator. The optical detection system and the photo detector amplifier circuit allow measurements of extremely low fluorescence signals. The direct computer based measurement of the photo detector amplifier output assures a good signal linearity and no systematic line shape distortion. The estimations of different broadening effects are based on Cs D2 line HFS measurements. The spectra are fitted with exactly calculated Voigt profiles using a Fortran fitting program based on Levenberg-Marquardt method. The diode laser linewidth is determined from the beat note between two separate laser systems. The natural linewidth of Cs 6 2P3/2 is taken from our precise lifetime measurements. The residual Doppler broadening due to the finite angular beam distribution and optical alignment is estimated from the data. Financial support for this work is provided by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research at the U. S. Department of Energy under contract number DE-FG02-95ER14579.

  18. Antibodies derived from an enterotoxigenic Escherichia coli (ETEC) adhesin tip MEFA (multiepitope fusion antigen) against adherence of nine ETEC adhesins: CFA/I, CS1, CS2, CS3, CS4, CS5, CS6, CS21 and EtpA.

    PubMed

    Nandre, Rahul M; Ruan, Xiaosai; Duan, Qiangde; Sack, David A; Zhang, Weiping

    2016-06-30

    Diarrhea continues to be a leading cause of death in children younger than 5 years in developing countries. Enterotoxigenic Escherichia coli (ETEC) is a leading bacterial cause of children's diarrhea and travelers' diarrhea. ETEC bacteria initiate diarrheal disease by attaching to host receptors at epithelial cells and colonizing in small intestine. Therefore, preventing ETEC attachment has been considered the first line of defense against ETEC diarrhea. However, developing vaccines effectively against ETEC bacterial attachment encounters challenge because ETEC strains produce over 23 immunologically heterogeneous adhesins. In this study, we applied MEFA (multiepitope fusion antigen) approach to integrate epitopes from adhesin tips or adhesive subunits of CFA/I, CS1, CS2, CS3, CS4, CS5, CS6, CS21 and EtpA adhesins and to construct an adhesin tip MEFA peptide. We then examined immunogenicity of this tip MEFA in mouse immunization, and assessed potential application of this tip MEFA for ETEC vaccine development. Data showed that mice intraperitoneally immunized with this adhesin tip MEFA developed IgG antibody responses to all nine ETEC adhesins. Moreover, ETEC and E. coli bacteria expressing these nine adhesins, after incubation with serum of the immunized mice, exhibited significant reduction in attachment to Caco-2 cells. These results indicated that anti-adhesin antibodies induced by this adhesin tip MEFA blocked adherence of the most important ETEC adhesins, suggesting this multivalent tip MEFA may be useful for developing a broadly protective anti-adhesin vaccine against ETEC diarrhea.

  19. Unitary conductance variation in Kir2.1 and in cardiac inward rectifier potassium channels.

    PubMed Central

    Picones, A; Keung, E; Timpe, L C

    2001-01-01

    Kir2.1 (IRK1) is the complementary DNA for a component of a cardiac inwardly rectifying potassium channel. When Kir2.1 is expressed in Xenopus oocytes or human embryonic kidney (HEK) cells (150 mM external KCl), the unitary conductances form a broad distribution, ranging from 2 to 33 pS. Channels with a similarly broad distribution of unitary conductance amplitudes are also observed in recordings from adult mouse cardiac myocytes under similar experimental conditions. In all three cell types channels with conductances smaller, and occasionally larger, than the ~30 pS ones are found in the same patches as the ~30 pS openings, or in patches by themselves. The unitary conductances in patches with a single active channel are stable for the durations of the recordings. Channels of all amplitudes share several biophysical characteristics, including inward rectification, voltage sensitivity of open probability, sensitivity of open probability to external divalent cations, shape of the open channel i-V relation, and Cs(+) block. The only biophysical difference found between large and small conductance channels is that the rate constant for Cs(+) block is reduced for the small-amplitude channels. The unblocking rate constant is similar for channels of different unitary conductances. Apparently there is significant channel-to-channel variation at a site in the outer pore or in the selectivity filter, leading to variability in the rate at which K(+) or Cs(+) enters the channel. PMID:11566776

  20. Unitary conductance variation in Kir2.1 and in cardiac inward rectifier potassium channels.

    PubMed

    Picones, A; Keung, E; Timpe, L C

    2001-10-01

    Kir2.1 (IRK1) is the complementary DNA for a component of a cardiac inwardly rectifying potassium channel. When Kir2.1 is expressed in Xenopus oocytes or human embryonic kidney (HEK) cells (150 mM external KCl), the unitary conductances form a broad distribution, ranging from 2 to 33 pS. Channels with a similarly broad distribution of unitary conductance amplitudes are also observed in recordings from adult mouse cardiac myocytes under similar experimental conditions. In all three cell types channels with conductances smaller, and occasionally larger, than the ~30 pS ones are found in the same patches as the ~30 pS openings, or in patches by themselves. The unitary conductances in patches with a single active channel are stable for the durations of the recordings. Channels of all amplitudes share several biophysical characteristics, including inward rectification, voltage sensitivity of open probability, sensitivity of open probability to external divalent cations, shape of the open channel i-V relation, and Cs(+) block. The only biophysical difference found between large and small conductance channels is that the rate constant for Cs(+) block is reduced for the small-amplitude channels. The unblocking rate constant is similar for channels of different unitary conductances. Apparently there is significant channel-to-channel variation at a site in the outer pore or in the selectivity filter, leading to variability in the rate at which K(+) or Cs(+) enters the channel.

  1. Changing US Attributes After CS-US Pairings Changes CS-Attribute-Assessments: Evidence for CS-US Associations in Attribute Conditioning.

    PubMed

    Förderer, Sabine; Unkelbach, Christian

    2016-03-01

    Attribute Conditioning (AC) refers to people's changed assessments of stimuli's (CSs) attributes due to repeated pairing with stimuli (USs) possessing these attributes; for example, when an athletic person (US) is paired with a neutral person (CS), the neutral person is judged to be more athletic after the pairing. We hypothesize that this AC effect is due to CSs' associations with USs rather than direct associations with attributes. Three experiments test this hypothesis by changing US attributes after CS-US pairings. Experiments 1 and 2 conditioned athleticism by pairing neutral men (CSs) with athletic and non-athletic USs. Post-conditioning, USs' athleticism was reversed, which systematically influenced participants' assessment of CS athleticism. Experiment 3 conditioned athleticism and changed USs' musicality after CS-US pairings. This post-conditioning change affected musicality assessments of CSs but did not influence athleticism-assessments. The results indicate that AC effects are based on an associative CS-US-attribute structure.

  2. Na₄La₂(CO₃)₅ and CsNa₅Ca₅(CO₃)₈: two new carbonates as UV nonlinear optical materials.

    PubMed

    Luo, Min; Wang, GenXiang; Lin, Chensheng; Ye, Ning; Zhou, Yuqiao; Cheng, Wendan

    2014-08-04

    Two nonlinear optical crystal carbonates (Na4La2(CO3)5 and CsNa5Ca5(CO3)8 were successfully synthesized by hydrothermal method, and both of them crystallized in the same noncentrosymmetric hexagonal space group P63mc (No. 186). The structure of Na4La2(CO3)5 consists of a three-dimensional network made up of [CO3] triangles as well as irregular [Na(0.67)La(0.33)O10] and [NaO8] polyhedra. The structure of CsNa5Ca5(CO3)8 can be described as the standing-on-edge [CO3] groups connect the adjacent infinite [CaCO3]∞ layers in the ab plane to construct a framework with four types of channels running parallel to [010]. The Na, Cs, and [Na(0.67)Ca(0.33)] atoms reside in these channels. The measurement of second harmonic generation (SHG) by the method adapted from Kurtz and Perry indicated that Na4La2(CO3)5 and CsNa5Ca5(CO3)8 were phase-matchable in the visible region and exhibited SHG responses of approximately 3 and 1 × KH2PO4 (KDP). Meanwhile, they exhibited wide transparent region with short UV cutoff edge at about 235 and 210 nm, respectively, suggesting that these crystals as NLO materials may have potential applications in the UV region.

  3. Quantum efficiencies of imaging detectors with alkali halide photocathodes. I - Microchannel plates with separate and integral CsI photocathodes

    NASA Technical Reports Server (NTRS)

    Carruthers, George R.

    1987-01-01

    Measurements and comparisons have been made of the quantum efficiencies of microchannel plate (MCP) detectors in the far-UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiences were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are about 15 percent at 1216 A for a CsI-coated MCP compared with 65 percent for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20 percent for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration.

  4. Quantum efficiencies of imaging detectors with alkali halide photocathodes. I - Microchannel plates with separate and integral CsI photocathodes

    NASA Technical Reports Server (NTRS)

    Carruthers, George R.

    1987-01-01

    Measurements and comparisons have been made of the quantum efficiencies of microchannel plate (MCP) detectors in the far-UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiences were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are about 15 percent at 1216 A for a CsI-coated MCP compared with 65 percent for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20 percent for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration.

  5. Efimov Physics in a 6Li-133Cs Atomic Mixture

    NASA Astrophysics Data System (ADS)

    Johansen, Jacob; Feng, Lei; Parker, Colin; Chin, Cheng; Wang, Yujun

    2015-05-01

    We investigate Efimov physics based on three-body recombination in an atomic mixture of 6Li and 133Cs in the vicinity of interspecies Feshbach resonances at 843 and 889 G. This allows us to compare the loss spectra near different resonances and test the universality of Efimov states. Theoretically the Efimov spectrum near 889 G is expected to be similar to that near 843 G, except that the first resonance is absent near the former Feshbach resonance. This is due to the difference in the Cs-Cs scattering length near the two resonances: At 843 G it is negative, whereas at 889 G it is positive. Although it is primarily the Li-Cs interactions that lead to Efimov resonances, the Cs-Cs scattering length is expected to influence the spectrum. This work is supported by NSF and Chicago MRSEC.

  6. Experimental Progress in a 6Li-133Cs Atomic Mixture

    NASA Astrophysics Data System (ADS)

    Feng, Lei; Johansen, Jacob; Parker, Colin; Chin, Cheng

    2015-05-01

    We report experimental progress in a mixture of 6Li and 133Cs. The mass imbalance of this system results in a particular challenge, as gravity has a significant influence on Cs position, but not on Li, separating the two gases at temperatures on the order of 200 nK. We overcome this difficulty using a two color optical dipole trap. We demonstrate mixing of these species below 100 nK in preparation for studies of quantum degenerate mixtures of this system. We further report on progress toward degeneracy and many-body physics measurements in this trap. Finally, we consider Efimov physics in this system, studying the effects of Cs-Cs interaction on the spectrum of LiCsCs trimers by a comparison of Feshbach resonances at 843 and 889 G. This work is supported by NSF and Chicago MRSEC.

  7. On the Formation of Cometary Carbon Disulfide (CS2)

    NASA Astrophysics Data System (ADS)

    Hudson, Reggie L.; Moore, M. H.; Ferrante, R. F.

    2009-09-01

    The formation of cometary CS molecules from carbon disulfide, CS2, was proposed about 20 years before the latter's detection in comet 122P/de Vico by Jackson et al. (2002). However, the origin of CS2 has received little attention from either experimentalists or theorists. As part of our on-going laboratory program to investigate cometary molecules we have examined chemical reactions that lead to CS2 in the solid state. Icy mixtures of known cometary molecules were proton irradiated near 10 K to doses of several eV per molecule. Mid-IR spectroscopy was used as an in situ probe to record both CS2 formation in the ices and the destruction of precursors. We find that the most likely route to cometary CS2 is through OCS by way of the S + CO reaction. - This work was funded by NASA's Planetary Geology and Geophysics and Planetary Atmospheres programs.

  8. On the Formation of Cometary Carbon Disulfide (CS2)

    NASA Technical Reports Server (NTRS)

    Hudson, Reggie; Moore, marla; Ferrante, Robert F.

    2009-01-01

    The formation of cometary CS molecules from carbon disulfide, CS2 , was proposed about 20 years before the latter's detection in comet 122P/de Vico by Jackson et al. (2002). However, the origin of CS2 has received little attention from either experimentalists or theorists. As part of our on-going laboratory program to investigate cometary molecules we have examined chemical reactions that lead to CS2 in the solid state. Icy mixtures of known cometary molecules were proton irradiated near 10 K to doses of several eV per molecule. Mid-IR spectroscopy was used as an in situ probe to record both CS2 formation in the ices and the destruction of precursors. We find that the most likely route to cometary CS2 is through OCS by way of the S + CO reaction.

  9. English Channel

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The cloud covered earthscape of Northern Europe demonstrates the difficulty of photographing this elusive subject from space. The English Channel (51.0N, 1.5E) separating the British Islands from Europe is in the center of the scene. The white cliffs of Dover on the SE coast of the UK, the Thames River estuary and a partial view of the city of London can be seen on the north side of the Channel while the Normandy coast of France is to the south.

  10. English Channel

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The cloud covered earthscape of Northern Europe demonstrates the difficulty of photographing this elusive subject from space. The English Channel (51.0N, 1.5E) separating the British Islands from Europe is in the center of the scene. The white cliffs of Dover on the SE coast of the UK, the Thames River estuary and a partial view of the city of London can be seen on the north side of the Channel while the Normandy coast of France is to the south.

  11. Thermionic work function of /Cs/ZnO

    NASA Technical Reports Server (NTRS)

    Sommer, A. H.; Briere, T. R.

    1976-01-01

    The collector electrode of a thermionic converter requires a material having a low thermionic work function and chemical stability in a Cs atmosphere in the 800-K range. This letter reports that ZnO with an adsorbed Cs film meets these requirements. The work function is approximately 1.3 eV. Various methods of preparing the ZnO film are described as well as an experiment in which Cs was replaced by K.

  12. Comparison of channel assignment techniques for hybrid switching

    NASA Technical Reports Server (NTRS)

    Schwartz, M.; Kraimeche, B.

    1982-01-01

    The performance of four circuit-switched channel assignment strategies for use in a hybrid switch accommodating multiple users is analyzed and compared. Each scheme is associated with a fixed frame movable boundary TDM channel that multiplexes circuit-switched (CS) and packet-switched (PS) traffic. The performance measures used are blocking probability for the circuit-switched traffic and time delay for the packet-switched traffic.

  13. Thermal ionization of Cs Rydberg states

    NASA Astrophysics Data System (ADS)

    Glukhov, I. L.; Ovsiannikov, V. D.

    2009-01-01

    Rates Pnl of photoionization from Rydberg ns-, np-, nd-states of a valence electron in Cs, induced by black-body radiation, were calculated on the basis of the modified Fues model potential method. The numerical data were approximated with a three-term expression which reproduces in a simple analytical form the dependence of Pnl on the ambient temperature T and on the principal quantum number n. The comparison between approximate and exactly calculated values of the thermal ionization rate demonstrates the applicability of the proposed approximation for highly excited states with n from 20 to 100 in a wide temperature range of T from 100 to 10,000 K. We present coefficients of this approximation for the s-, p- and d-series of Rydberg states.

  14. CS-Studio Scan System Parallelization

    SciTech Connect

    Kasemir, Kay; Pearson, Matthew R

    2015-01-01

    For several years, the Control System Studio (CS-Studio) Scan System has successfully automated the operation of beam lines at the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) and Spallation Neutron Source (SNS). As it is applied to additional beam lines, we need to support simultaneous adjustments of temperatures or motor positions. While this can be implemented via virtual motors or similar logic inside the Experimental Physics and Industrial Control System (EPICS) Input/Output Controllers (IOCs), doing so requires a priori knowledge of experimenters requirements. By adding support for the parallel control of multiple process variables (PVs) to the Scan System, we can better support ad hoc automation of experiments that benefit from such simultaneous PV adjustments.

  15. Fractionation of (137)Cs and Pu in natural peatland.

    PubMed

    Mihalík, Ján; Bartusková, Miluše; Hölgye, Zoltán; Ježková, Tereza; Henych, Ondřej

    2014-08-01

    High Cs-137 concentrations in plants growing on peatland inspired us to investigate the quantity of its bioavailable fraction in natural peat. Our investigation aims to: a) estimate the quantity of bioavailable Cs-137 and Pu present in peat, b) verify the similarity of Cs-137 and K-40 behaviours, and c) perform a quantification of Cs-137 and Pu transfer from peat to plants. We analysed the vertical distribution of Cs-137 and Pu isotopes in the peat and their concentrations in plants growing on these places. Bioavailability of radionuclides was investigated by sequential extraction. Sequential analyses revealed that it was the upper layer which contained the majority of Cs-137 in an available form while deeper layers retained Cs-137 in immobile fractions. We can conclude that 18% of all Cs-137 in the peat is still bioavailable. Despite of the low quantity of bioavailable fraction of Cs-137 its transfer factor reached extremely high values. In the case of Pu, 64% of its total amount was associated with fulvic/humic acids which resulted in the high transfer factor from peat to plants. 27 years after the Chernobyl nuclear accident, the significant part of radionuclides deposited in peatland is still bioavailable.

  16. Improved TV-CS Approaches for Inverse Scattering Problem

    PubMed Central

    2015-01-01

    Total Variation and Compressive Sensing (TV-CS) techniques represent a very attractive approach to inverse scattering problems. In fact, if the unknown is piecewise constant and so has a sparse gradient, TV-CS approaches allow us to achieve optimal reconstructions, reducing considerably the number of measurements and enforcing the sparsity on the gradient of the sought unknowns. In this paper, we introduce two different techniques based on TV-CS that exploit in a different manner the concept of gradient in order to improve the solution of the inverse scattering problems obtained by TV-CS approach. Numerical examples are addressed to show the effectiveness of the method. PMID:26495420

  17. A semi-synthetic ion channel platform for detection of phosphatase and protease activity.

    PubMed

    Macrae, Michael X; Blake, Steven; Jiang, Xiayun; Capone, Ricardo; Estes, Daniel J; Mayer, Michael; Yang, Jerry

    2009-11-24

    Sensitive methods to probe the activity of enzymes are important for clinical assays and for elucidating the role of these proteins in complex biochemical networks. This paper describes a semi-synthetic ion channel platform for detecting the activity of two different classes of enzymes with high sensitivity. In the first case, this method uses single ion channel conductance measurements to follow the enzyme-catalyzed hydrolysis of a phosphate group attached to the C-terminus of gramicidin A (gA, an ion channel-forming peptide) in the presence of alkaline phosphatase (AP). Enzymatic hydrolysis of this phosphate group removes negative charges from the entrance of the gA pore, resulting in a product with measurably reduced single ion channel conductance compared to the original gA-phosphate substrate. This technique employs a standard, commercial bilayer setup and takes advantage of the catalytic turnover of enzymes and the amplification characteristics of ion flux through individual gA pores to detect picomolar concentrations of active AP in solution. Furthermore, this technique makes it possible to study the kinetics of an enzyme and provides an estimate for the observed rate constant (k(cat)) and the Michaelis constant (K(M)) by following the conversion of the gA-phosphate substrate to product over time in the presence of different concentrations of AP. In the second case, modification of gA with a substrate for proteolytic cleavage by anthrax lethal factor (LF) afforded a sensitive method for detection of LF activity, illustrating the utility of ion channel-based sensing for detection of a potential biowarfare agent. This ion channel-based platform represents a powerful, novel approach to monitor the activity of femtomoles to picomoles of two different classes of enzymes in solution. Furthermore, this platform has the potential for realizing miniaturized, cost-effective bioanalytical assays that complement currently established assays.

  18. Microhydration of caesium compounds: Cs, CsOH, CsI and Cs₂I₂ complexes with one to three H₂O molecules of nuclear safety interest.

    PubMed

    Sudolská, Mária; Cantrel, Laurent; Cernušák, Ivan

    2014-04-01

    Structure and thermodynamic properties (standard enthalpies of formation and Gibbs free energies) of hydrated caesium species of nuclear safety interest, Cs, CsOH, CsI and its dimer Cs₂I₂, with one up to three water molecules, are calculated to assess their possible existence in severe accident occurring to a pressurized water reactor. The calculations were performed using the coupled cluster theory including single, double and non-iterative triple substitutions (CCSD(T)) in conjunction with the basis sets (ANO-RCC) developed for scalar relativistic calculations. The second-order spin-free Douglas-Kroll-Hess Hamiltonian was used to account for the scalar relativistic effects. Thermodynamic properties obtained by these correlated ab initio calculations (entropies and thermal capacities at constant pressure as a function of temperature) are used in nuclear accident simulations using ASTEC/SOPHAEROS software. Interaction energies, standard enthalpies and Gibbs free energies of successive water molecules addition determine the ordering of the complexes. CsOH forms the most hydrated stable complexes followed by CsI, Cs₂I₂, and Cs. CsOH still exists in steam atmosphere even at quite high temperature, up to around 1100 K.

  19. Phase Transitions in CsSnCl3 and CsPbBr3 An NMR and NQR Study

    NASA Astrophysics Data System (ADS)

    Sharma, Surendra; Weiden, Norbert; Weiss, Alarich

    1991-04-01

    The phase transitions in CsSnCl3 and CsPbBr3 have been studied by X-ray powder diffraction, by 81Br-NQR and by 'H-, 119Sn-, and 113Cs-NMR. At room temperature in air CsSnCl3 forms a hydrate which can be dehydrated to the monoclinic phase II of CsSnCl3. The high temperature phase I has the Perovskite structure, as the X-ray and NMR experiments show. The three phases of CsPbBr3, known from literature, have been corroborated. The results are discussed in the framework of the group ABX3, A = alkalimetal ion, B = IV main group ion, and X = Halogen ion

  20. Using Atmospheric (137)Cs Measurements and Hysplit to Confirm Chernobyl as a Source of (137)Cs in Europe

    DTIC Science & Technology

    2001-10-01

    USING ATMOSPHERIC 137CS MEASUREMENTS AND HYSPLIT TO CONFIRM CHERNOBYL AS A SOURCE OF 137CS IN EUROPE Erik L. Swanberg1 and Steven G. Hoffert2...Veridian Systems1, Autometric2 Sponsored by Defense Threat Reduction Agency Contract No. DTRA01-99-C-0031 ABSTRACT The Chernobyl ...this 137Cs is the ground contaminated by the Chernobyl accident. The PIDC routinely uses HYSPLIT (HYbrid Single-Particle Lagrangian Integrated

  1. The Mechanism Responsible for Extraordinary Cs-ion Selectivity in Crystalline Silicotitanate

    SciTech Connect

    Celestian,A.; Kubicki, J.; Hanson, J.; Clearfield, A.; Parise, J.

    2008-01-01

    Combining information from time-resolved X-ray and neutron scattering with theoretical calculations has revealed the elegant mechanism whereby hydrogen crystalline silicotitanate (H-CST; H2Ti2SiO7{center_dot}1.5H2O) achieves its remarkable ion-exchange selectivity for cesium. Rather than a simple ion-for-ion displacement reaction into favorable sites, which has been suggested by static structural studies of ion-exchanged variants of CST, Cs+ exchange proceeds via a two-step process mediated by conformational changes in the framework. Similar to the case of ion channels in proteins, occupancy of the most favorable site does not occur until the first lever, cooperative repulsive interactions between water and the initial Cs-exchange site, repels a hydrogen lever on the silicotitanate framework. Here we show that these interactions induce a subtle conformational rearrangement in CST that unlocks the preferred Cs site and increases the overall capacity and selectivity for ion exchange.

  2. Correlated electronic structure of Fe in bulk Cs and on a Cs surface

    NASA Astrophysics Data System (ADS)

    Costa, M.; Thunström, P.; Di Marco, I.; Bergman, A.; Klautau, A. B.; Lichtenstein, A. I.; Katsnelson, M. I.; Eriksson, O.

    2013-03-01

    We have investigated the spectral properties of Fe impurities in a Cs host, for both surface and bulk systems, by means of a combination of density functional theory in the local density approximation and dynamical mean-field theory (LDA + DMFT). The effective impurity model arising in LDA + DMFT was solved via two different techniques, i.e., the Hubbard I approximation and the exact diagonalization. It is shown that noticeable differences can be seen in the unoccupied part of the spectrum for different positions of Fe atoms in the host, despite the fact that hybridization between Fe d-states and Cs is low. Our calculations show good agreement with the experimental photoemission spectra reported by Carbone [Carbone, Veronese, Moras, Gardonio, Grazioli, Zhou, Rader, Varykhalov, Krull, Balashov, Mugarza, Gambardella, Lebègue, Eriksson, Katsnelson, and Lichtenstein, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.104.117601 104, 117601 (2010)].

  3. Cesium Accumulation and Growth Characteristics of Rhodococcus erythropolis CS98 and Rhodococcus sp. Strain CS402

    PubMed Central

    Tomioka, Noriko; Uchiyama, Hiroo; Yagi, Osami

    1994-01-01

    Growth and cesium accumulation characteristics of two cesium-accumulating bacteria isolated from soils were investigated. Rhodococcus erythropolis CS98 and Rhodococcus sp. strain CS402 accumulated high levels of cesium (approximately 690 and 380 μmol/g [dry weight] of cells or 92 and 52 mg/g [dry weight] of cells, respectively) after 24 h of incubation in the presence of 0.5 mM cesium. The optimum pH for cesium uptake by both Rhodococcus strains was 8.5. Rubidium and cesium assumed part of the role of potassium in the growth of both Rhodococcus strains. Potassium and rubidium inhibited cesium accumulation by these Rhodococcus strains. It is likely that both Rhodococcus strains accumulated cesium through a potassium transport system. PMID:16349312

  4. Memory is not extinguished along with CS presentation but within a few seconds after CS-offset

    PubMed Central

    Pérez-Cuesta, Luis María; Hepp, Yanil; Pedreira, María Eugenia; Maldonado, Héctor

    2007-01-01

    Prior work with the crab’s contextual memory model showed that CS-US conditioned animals undergoing an unreinforced CS presentation would either reconsolidate or extinguish the CS-US memory, depending on the length of the reexposure to the CS. Either memory process is only triggered once the CS is terminated. Based on these results, the following questions are raised. First, when is extinction memory acquired, if not along extinction training, and how long does it take? Second, can acquisition and consolidation of extinction memory be pharmacologically dissected? Here we address these questions performing three series of experiments: a first one aimed to study systematically the relationship between extinction and increasing periods of unreinforced CS presentations, a second one to determine the time boundaries of the extinction memory acquisition, and the third one to assay the requirement for protein synthesis and NMDA-like receptors of acquisition and consolidation of extinction memory. Our results confirm that it is CS-offset and not the mere retrieval (CS-onset) that triggers acquisition of extinction memory and that it is completed in less than 45 sec after CS-offset. In addition, protein synthesis is required for consolidation but not for acquisition of this memory and, conversely, NMDA-like receptor activity is required for its acquisition but not for its consolidation. Finally, we offer an interpretative scheme of our results and we discuss to what extent it could apply to multitrial extinction. PMID:17272655

  5. CsEuBr3: Crystal structure and its role in the photostimulation of CsBr :Eu2+

    NASA Astrophysics Data System (ADS)

    Hesse, S.; Zimmermann, J.; von Seggern, H.; Ehrenberg, H.; Fuess, H.; Fasel, C.; Riedel, R.

    2006-10-01

    CsBr :Eu2+ has recently been investigated as a photostimulable x-ray storage phosphor with great potential for application in high-resolution image plates. In a recent paper Hackenschmied et al. [J. Appl. Phys. 93, 5109 (2003)] suggested that segregations of CsEuBr3 or Cs4EuBr6 formed within CsBr :Eu2+ during annealing are responsible for an increase in the photostimulated luminescence (PSL) yield. In this work single crystals of CsEuBr3 were prepared by a one step synthesis and identified by x-ray diffraction (XRD) analysis as single phase perovskites. It was concluded that, after preparation, CsEuBr3 degrades in normal atmosphere into at least two phases, one of which is the orthorhombic structure of Cs2EuBr5•10H2O. The XRD powder diffraction pattern of this compound is very similar to that of the segregations observed within CsBr :Eu2+ and reported by Hackenschmied et al. However, the increased PSL yield in CsBr :Eu2+ after annealing cannot be due to the segregations, because the trivalent nature of the europium in the segregations renders them PSL inactive.

  6. The Crystal Structure of Cs 2TiSi 6O 15

    NASA Astrophysics Data System (ADS)

    Grey, I. E.; Roth, R. S.; Balmer, M. L.

    1997-06-01

    Crystals of a new titanosilicate phase, Cs2TiSi6O15, were grown from a cesium vanadate flux. The compound has monoclinic symmetry, space groupC2/c, witha=13.386(5),b=7.423(3),c=15.134(5) Å,β=107.71(3)°,Z=4. The crystal structure was solved using single crystal X-ray data (MoKαradiation) and refined toR(F)=0.039 for 1874 unique reflections. In the structure, isolated titanium-centred octahedra and silica-centred tetrahedra share all corners to form an open framework structure containing large cavities in which the cesium ions are located. Each cavity is bound by three 5-rings, two 6-rings, and two 8-rings. The cavities are linked via the 8-rings into channels parallel to [101]. The cesium ions occur in pairs along the channels, separated by 3.765(2) Å.

  7. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, Victor R.

    1988-01-01

    The geomorphology of Mars is discussed, focusing on the Martian channels. The great flood channels of Mars, the processes of channel erosion, and dendritic channel networks, are examined. The topography of the Channeled Scabland region of the northwestern U.S. is described and compared to the Martian channels. The importance of water in the evolution of the channel systems is considered.

  8. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, Victor R.

    1988-01-01

    The geomorphology of Mars is discussed, focusing on the Martian channels. The great flood channels of Mars, the processes of channel erosion, and dendritic channel networks, are examined. The topography of the Channeled Scabland region of the northwestern U.S. is described and compared to the Martian channels. The importance of water in the evolution of the channel systems is considered.

  9. Channel estimation based on quantized MMP for FDD massive MIMO downlink

    NASA Astrophysics Data System (ADS)

    Guo, Yao-ting; Wang, Bing-he; Qu, Yi; Cai, Hua-jie

    2016-10-01

    In this paper, we consider channel estimation for Massive MIMO systems operating in frequency division duplexing mode. By exploiting the sparsity of propagation paths in Massive MIMO channel, we develop a compressed sensing(CS) based channel estimator which can reduce the pilot overhead. As compared with the conventional least squares (LS) and linear minimum mean square error(LMMSE) estimation, the proposed algorithm is based on the quantized multipath matching pursuit - MMP - reduced the pilot overhead and performs better than other CS algorithms. The simulation results demonstrate the advantage of the proposed algorithm over various existing methods including the LS, LMMSE, CoSaMP and conventional MMP estimators.

  10. Inverted Channels

    NASA Technical Reports Server (NTRS)

    2006-01-01

    23 June 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows sinuous ridges and other landforms exposed by erosion in the Aeolis region of Mars. The ridges in this scene indicate the locations of ancient channels in a fan of sediment deposited in this region. Over time, wind erosion has removed surrounding materials and left the channels, which had been filled by sediment, standing as ridges.

    Location near: 4.5oS, 205.2oW Image width: 2 km (1.2 mi) Illumination from: upper left Season: Southern Autumn

  11. Starburst Channels

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    Translucent carbon dioxide ice covers the polar regions of Mars seasonally. It is warmed and sublimates (evaporates) from below, and escaping gas carves a numerous channel morphologies.

    In this example (figure 1) the channels form a 'starburst' pattern, radiating out into feathery extensions. The center of the pattern is being buried with dust and new darker dust fans ring the outer edges. This may be an example of an expanding morphology, where new channels are formed as the older ones fill and are no longer efficiently channeling the subliming gas out.

    Observation Geometry Image PSP_003443_0980 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 21-Apr-2007. The complete image is centered at -81.8 degrees latitude, 76.2 degrees East longitude. The range to the target site was 247.1 km (154.4 miles). At this distance the image scale is 24.7 cm/pixel (with 1 x 1 binning) so objects 74 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel. The image was taken at a local Mars time of 04:52 PM and the scene is illuminated from the west with a solar incidence angle of 71 degrees, thus the sun was about 19 degrees above the horizon. At a solar longitude of 223.4 degrees, the season on Mars is Northern Autumn.

  12. Starburst Channels

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    Translucent carbon dioxide ice covers the polar regions of Mars seasonally. It is warmed and sublimates (evaporates) from below, and escaping gas carves a numerous channel morphologies.

    In this example (figure 1) the channels form a 'starburst' pattern, radiating out into feathery extensions. The center of the pattern is being buried with dust and new darker dust fans ring the outer edges. This may be an example of an expanding morphology, where new channels are formed as the older ones fill and are no longer efficiently channeling the subliming gas out.

    Observation Geometry Image PSP_003443_0980 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 21-Apr-2007. The complete image is centered at -81.8 degrees latitude, 76.2 degrees East longitude. The range to the target site was 247.1 km (154.4 miles). At this distance the image scale is 24.7 cm/pixel (with 1 x 1 binning) so objects 74 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel. The image was taken at a local Mars time of 04:52 PM and the scene is illuminated from the west with a solar incidence angle of 71 degrees, thus the sun was about 19 degrees above the horizon. At a solar longitude of 223.4 degrees, the season on Mars is Northern Autumn.

  13. Narrating Data Structures: The Role of Context in CS2

    ERIC Educational Resources Information Center

    Yarosh, Svetlana; Guzdial, Mark

    2008-01-01

    Learning computing with respect to the context of its use has been linked in previous reports to student motivation in introductory Computer Science (CS) courses. In this report, we consider the role of context in a second course. We present a case study of a CS2 data structures class that uses a media computation context. In this course, students…

  14. Occasion Setting Is Specific to the CS-US Association

    ERIC Educational Resources Information Center

    Bonardi, Charlotte

    2007-01-01

    In Experiment 1, rats were trained on a discrimination in which one occasion setter, A, signaled that one cue (conditioned stimulus, CS), x, would be followed by one outcome, p (unconditioned stimulus, US), and a second CS, y, by a different outcome, q (x [right arrow] p and y [right arrow] q); a second occasion setter, B signalled the reverse…

  15. Occasion Setting Is Specific to the CS-US Association

    ERIC Educational Resources Information Center

    Bonardi, Charlotte

    2007-01-01

    In Experiment 1, rats were trained on a discrimination in which one occasion setter, A, signaled that one cue (conditioned stimulus, CS), x, would be followed by one outcome, p (unconditioned stimulus, US), and a second CS, y, by a different outcome, q (x [right arrow] p and y [right arrow] q); a second occasion setter, B signalled the reverse…

  16. In Quest of Fame at the 4Cs

    ERIC Educational Resources Information Center

    Livatino, Mel

    2006-01-01

    Mel Livatino had stopped attending Conferences on College Composition and Communication (4Cs), but this year one came to his hometown, so he attended and now reports back. Where once the 4Cs had offered helpful insights into teaching kids how to write, today frivolity and radicalism reign. Professor Livatino's notes paint a very precise, largely…

  17. Narrating Data Structures: The Role of Context in CS2

    ERIC Educational Resources Information Center

    Yarosh, Svetlana; Guzdial, Mark

    2008-01-01

    Learning computing with respect to the context of its use has been linked in previous reports to student motivation in introductory Computer Science (CS) courses. In this report, we consider the role of context in a second course. We present a case study of a CS2 data structures class that uses a media computation context. In this course, students…

  18. Small Column Ion Exchange Testing of Superlig 644 for Removal of 137Cs from Hanford Tank Waste Envelope C (Tank 241-AN-107)

    SciTech Connect

    DE Kurath; DL Blanchard; JR Bontha

    2000-06-28

    The current BNFL Inc. flowsheet for the pretreatment of the Hanford high-level tank wastes includes the use of Superlig{reg_sign} materials for removing {sup 137}Cs from the aqueous fraction of the waste. The Superlig materials applicable to cesium removal include the cesium-selective Superlig 632and Superlig 644. These materials have been developed and supplied by IBC Advanced Technologies, Inc., American Fork, Utah. This report describes the testing of the Superlig 644 ion exchange material in a small dual-column system. The bed volume of the lead column was 18.6 mL (L/D = 7), and the bed volume of the lag column was 15.9 mL (L/D = 6) during the loading phase. The sample processed was approximately 1.6 L of diluted waste ([Na{sup +}] = 4.84 M) from Tank 241-AN-107 (Envelope C). This sample had been previously treated for removal of Sr/transuranic (TRU) values and clarified in a single tube cross-flow filtration unit. All ion exchange process steps were tested, including resin-bed preparation, loading, feed displacement, water rinse, elution, eluant rinse, and resin regeneration. A summary of performance measures for both columns is shown in Table S1. The Cs {lambda} values represent a measure of the effective capacity of the SL-644 resin. The Cs {lambda} of 20 for the lead column is much lower than the estimated 150 obtained by the Savannah River Technology Center during Phase 1A testing. Equilibrium data obtained with batch contacts using the AN-107 Cs IX feed predicts a Cs {lambda} of 183. A Cs {lambda} for the lag column could not be determined due to insufficient breakthrough, but it appeared to work well and removed nearly all of the cesium not removed by the lead column. The low value for the lead column indicates that it did not perform as expected. This may have been due to air or gas in the bed that caused fluid channeling or blinding of the resin. The maximum decontamination factor (DF) for {sup 137}Cs listed in Table S1 is based on {sup 137}Cs

  19. Nonlinear channelizer.

    PubMed

    In, Visarath; Longhini, Patrick; Kho, Andy; Neff, Joseph D; Leung, Daniel; Liu, Norman; Meadows, Brian K; Gordon, Frank; Bulsara, Adi R; Palacios, Antonio

    2012-12-01

    The nonlinear channelizer is an integrated circuit made up of large parallel arrays of analog nonlinear oscillators, which, collectively, serve as a broad-spectrum analyzer with the ability to receive complex signals containing multiple frequencies and instantaneously lock-on or respond to a received signal in a few oscillation cycles. The concept is based on the generation of internal oscillations in coupled nonlinear systems that do not normally oscillate in the absence of coupling. In particular, the system consists of unidirectionally coupled bistable nonlinear elements, where the frequency and other dynamical characteristics of the emergent oscillations depend on the system's internal parameters and the received signal. These properties and characteristics are being employed to develop a system capable of locking onto any arbitrary input radio frequency signal. The system is efficient by eliminating the need for high-speed, high-accuracy analog-to-digital converters, and compact by making use of nonlinear coupled systems to act as a channelizer (frequency binning and channeling), a low noise amplifier, and a frequency down-converter in a single step which, in turn, will reduce the size, weight, power, and cost of the entire communication system. This paper covers the theory, numerical simulations, and some engineering details that validate the concept at the frequency band of 1-4 GHz.

  20. Nonlinear channelizer

    NASA Astrophysics Data System (ADS)

    In, Visarath; Longhini, Patrick; Kho, Andy; Neff, Joseph D.; Leung, Daniel; Liu, Norman; Meadows, Brian K.; Gordon, Frank; Bulsara, Adi R.; Palacios, Antonio

    2012-12-01

    The nonlinear channelizer is an integrated circuit made up of large parallel arrays of analog nonlinear oscillators, which, collectively, serve as a broad-spectrum analyzer with the ability to receive complex signals containing multiple frequencies and instantaneously lock-on or respond to a received signal in a few oscillation cycles. The concept is based on the generation of internal oscillations in coupled nonlinear systems that do not normally oscillate in the absence of coupling. In particular, the system consists of unidirectionally coupled bistable nonlinear elements, where the frequency and other dynamical characteristics of the emergent oscillations depend on the system's internal parameters and the received signal. These properties and characteristics are being employed to develop a system capable of locking onto any arbitrary input radio frequency signal. The system is efficient by eliminating the need for high-speed, high-accuracy analog-to-digital converters, and compact by making use of nonlinear coupled systems to act as a channelizer (frequency binning and channeling), a low noise amplifier, and a frequency down-converter in a single step which, in turn, will reduce the size, weight, power, and cost of the entire communication system. This paper covers the theory, numerical simulations, and some engineering details that validate the concept at the frequency band of 1-4 GHz.

  1. Role of chloride channels in bradykinin-induced guinea pig airway vagal C-fibre activation.

    PubMed

    Lee, Min-Goo; Macglashan, Donald W; Undem, Bradley J

    2005-07-01

    We tested the hypothesis that an ionic current carried by chloride ions contributes to bradykinin (BK)-induced membrane depolarization and activation of vagal afferent C-fibres. In an ex vivo innervated trachea/bronchus preparation, BK (1 microM) consistently produced action potential discharge in vagal afferent C-fibres with receptive fields in the trachea or main stem bronchus. The Ca2+-activated Cl- channel (CLCA) inhibitor, niflumic acid (NFA, 100 microM), significantly reduced BK-induced action potential discharge to 21 +/- 7% of the control BK response. NFA did not inhibit capsaicin-induced or citric-acid-induced action potential discharge in tracheal C-fibres. The inhibitory effect of NFA was mimicked by another CLCA inhibitor, 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB, 100 microM). NFA also inhibited the BK-induced inward current in gramicidin-perforated whole-cell patch-clamp recordings of capsaicin-sensitive jugular ganglion neurones retrogradely labelled from the airways. NFA did not inhibit the BK-induced increase in intracellular free Ca2+. The TRPV1 inhibitor, iodo-resiniferatoxin (1 microM), also partially inhibited BK-induced action potential discharge, and the combination of iodo-resiniferatoxin and NFA virtually abolished the BK-induced action potential discharge. We concluded that in vagal afferent C-fibres, BK evokes membrane depolarization and action potential discharge through the additive effects of TRPV1 and Cl- channel activation.

  2. Is 137Cs Dating Becoming Obsolete in North America?

    NASA Astrophysics Data System (ADS)

    Drexler, J. Z.; Fuller, C.; Salas, A.

    2016-12-01

    Dating of wetland sediments and peat is routinely carried out using 137Cs and 210Pb analysis. Unlike 210Pb, 137Cs is an anthropogenic radionuclide with a history of fallout from nuclear weapons testing. 137Cs is used as a single time marker; its peak is coincident with the height of atmospheric nuclear testing in 1963/4. During its use in the 1970s-90s, 137Cs peaks were usually highly distinct in wetland sediments (e.g., see 137Cs peaks from Louisiana marshes in Feijtel et al., 1988). This enabled its use as a check for dates assigned to a profile by 210Pb and other methods. However, recently, the efficacy of 137Cs dating in North America has deteriorated. In this presentation, we will provide specific examples of 137Cs as well as 210Pb dating in wetland sediments/peats we collected between 2005 and 2015 in Maine, California, Virginia, North Carolina, South Carolina, and Washington. Two main reasons exist for this decline. First, 137Cs activities in our recent cores are 30-40 % of the original activities in 1963/4 due to decay of the original 137Cs in situ (half-life = 30.17 years) and no major new sources. This manifests in lower signal to noise ratio, with some peaks barely recognizable above the noise. Second, 137Cs peaks are much less distinct due to 137Cs migration through time independent of substrate (or sediment) particles. Migration of peaks has resulted in estimated accretion rates being systematically lower or higher than those derived from 210Pb dating. These issues with 137Cs dating have important implications because 137Cs is used with 210Pb dating or even alone to determine rates of recent wetland carbon accumulation. Such rates are required to enter wetland restoration projects into carbon markets and to document IPCC mandated reductions in carbon pollution. Our analysis shows that, although dating by 137Cs alone has always been highly tenuous, now it is especially contraindicated and should be disallowed for the purposes of carbon accounting.

  3. The pore properties of human nociceptor channel TRPA1 evaluated in single channel recordings

    PubMed Central

    Bobkov, Y.V.; Corey, E.A.; Ache, B.W.

    2011-01-01

    TRPA channels detect stimuli of different sensory modalities, including a broad spectrum of chemosensory stimuli, noxious stimuli associated with tissue damage and inflammation, mechanical stimuli, and thermal stimuli. Despite a growing understanding of potential modulators, agonists, and antagonists for these channels, the exact mechanisms of channel regulation and activation remain mostly unknown or controversial and widely debated. Relatively little is also known about the basic biophysical parameters of both native and heterologously expressed TRPA channels. Here we use conventional single channel inside-out and outside-out patch recording from the human TRPA1 channel transiently expressed in human embryonic kidney 293T cells to characterize the selectivity of the channel for inorganic mono-/divalent and organic monovalent cations in the presence of Allylisothiocyanate (AITC). We show the relative permeability of the hTRPA1 channel to inorganic cations to be: Ca2+(5.1)>Ba2+(3.5)>Mg2+(2.8)>NH4+(1.5)>Li+(1.2)>Na+(1.0)≥K+(0.98)≥Rb+(0.98)>Cs+(0.95); and to organic cations: Na+(1.0)≥Dimethylamine(0.99)>Trimethylamine(0.7)>Tetramethylammonium(0.4)>N-methyl-d-glucamine(0.1). Activation of the hTRPA1 channels by AITC appears to recruit the channels to a conformational state with an increased permeability to large organic cations. The pore of the channels in this state can be characterized as dilated by approximately 1–2.5A. These findings provide important insight into the basic fundamental properties and function of TRPA1 channels in general and human TRPA1 channel in particular. PMID:21195050

  4. Do CS-US Pairings Actually Matter? A Within-Subject Comparison of Instructed Fear Conditioning with and without Actual CS-US Pairings

    PubMed Central

    Raes, An K.; De Houwer, Jan; De Schryver, Maarten; Brass, Marcel; Kalisch, Raffael

    2014-01-01

    Previous research showed that instructions about CS-US pairings can lead to fear of the CS even when the pairings are never presented. In the present study, we examined whether the experience of CS-US pairings adds to the effect of instructions by comparing instructed conditioning with and without actual CS-US pairings in a within-subject design. Thirty-two participants saw three fractals as CSs (CS+1, CS+2, CS−) and received electric shocks as USs. Before the start of a so-called training phase, participants were instructed that both CS+1 and CS+2 would be followed by the US, but only CS+1 was actually paired with the US. The absence of the US after CS+2 was explained in such a way that participants would not doubt the instructions about the CS+2-US relation. After the training phase, a test phase was carried out. In this phase, participants expected the US after both CS+s but none of the CS+s was actually paired with the US. During test, self-reported fear was initially higher for CS+1 than for CS+2, which indicates that the experience of actual CS-US pairings adds to instructions about these pairings. On the other hand, the CS+s elicited similar skin conductance responses and US expectancies. Theoretical and clinical implications are discussed. PMID:24465447

  5. Determination of 135Cs by accelerator mass spectrometry

    NASA Astrophysics Data System (ADS)

    MacDonald, C. M.; Charles, C. R. J.; Zhao, X.-L.; Kieser, W. E.; Cornett, R. J.; Litherland, A. E.

    2015-10-01

    The ratio of anthropogenic 135Cs and 137Cs isotopes is characteristic of a uranium fission source. This research evaluates the technique of isotope dilution (yield tracing) for the purpose of quantifying 135Cs by accelerator mass spectrometry with on-line isobar separation. Interferences from Ba, Zn2, and isotopes of equal mass to charge ratios were successfully suppressed. However, some sample crosstalk from source contamination remains. The transmission and di-fluoride ionization efficiencies of Cs isotopes were found to be 8 × 10-3 and 1.7 × 10-7 respectively. This quantification of 135Cs using yield tracing by accelerator mass spectrometry shows promise for future environmental sample analysis once the issues of sample crosstalk and low efficiency can be resolved.

  6. Transformation of Sintered CsPbBr3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBrxI3-x through Halide Exchange.

    PubMed

    Hoffman, Jacob B; Schleper, A Lennart; Kamat, Prashant V

    2016-07-13

    All-inorganic cesium lead halide (CsPbX3, X = Br(-), I(-)) perovskites could potentially provide comparable photovoltaic performance with enhanced stability compared to organic-inorganic lead halide species. However, small-bandgap cubic CsPbI3 has been difficult to study due to challenges forming CsPbI3 in the cubic phase. Here, a low-temperature procedure to form cubic CsPbI3 has been developed through a halide exchange reaction using films of sintered CsPbBr3 nanocrystals. The reaction was found to be strongly dependent upon temperature, featuring an Arrhenius relationship. Additionally, film thickness played a significant role in determining internal film structure at intermediate reaction times. Thin films (50 nm) showed only a small distribution of CsPbBrxI3-x species, while thicker films (350 nm) exhibited much broader distributions. Furthermore, internal film structure was ordered, featuring a compositional gradient within film. Transient absorption spectroscopy showed the influence of halide exchange on the excited state of the material. In thicker films, charge carriers were rapidly transferred to iodide-rich regions near the film surface within the first several picoseconds after excitation. This ultrafast vectorial charge-transfer process illustrates the potential of utilizing compositional gradients to direct charge flow in perovskite-based photovoltaics.

  7. Epithelial Sodium and Chloride Channels and Asthma

    PubMed Central

    Wang, Wen; Ji, Hong-Long

    2015-01-01

    Objective: To focus on the asthmatic pathogenesis and clinical manifestations related to epithelial sodium channel (ENaC)/chlorine ion channel. Data Sources: The data analyzed in this review were the English articles from 1980 to 2015 from journal databases, primarily PubMed and Google Scholar. The terms used in the literature search were: (1) ENaCs; cystic fibrosis (CF) transmembrane conductance regulator (CFTR); asthma/asthmatic, (2) ENaC/sodium salt; CF; asthma/asthmatic, (3) CFTR/chlorine ion channels; asthma/asthmatic, (4) ENaC/sodium channel/scnn1a/scnn1b/scnn1g/scnn1d/amiloride-sensitive/amiloride-inhibtable sodium channels/sodium salt; asthma/asthmatic, lung/pulmonary/respiratory/tracheal/alveolar, and (5) CFTR; CF; asthma/asthmatic (ti). Study Selection: These studies included randomized controlled trials or studies covering asthma pathogenesis and clinical manifestations related to ENaC/chlorine ion channels within the last 25 years (from 1990 to 2015). The data involving chronic obstructive pulmonary disease and CF obtained from individual studies were also reviewed by the authors. Results: Airway surface liquid dehydration can cause airway inflammation and obstruction. ENaC and CFTR are closely related to the airway mucociliary clearance. Ion transporters may play a critical role in pathogenesis of asthmatic exacerbations. Conclusions: Ion channels have been the center of many studies aiming to understand asthmatic pathophysiological mechanisms or to identify therapeutic targets for better control of the disease. PMID:26265620

  8. Differential fear conditioning induces reciprocal changes in the sensory responses of lateral amygdala neurons to the CS(+) and CS(-).

    PubMed

    Collins, D R; Paré, D

    2000-01-01

    In classical fear conditioning, a neutral sensory stimulus (CS) acquires the ability to elicit fear responses after pairing to a noxious unconditioned stimulus (US). As amygdala lesions prevent the acquisition of fear responses and the lateral amygdaloid (LA) nucleus is the main input station of the amygdala for auditory afferents, the effect of auditory fear conditioning on the sensory responsiveness of LA neurons has been examined. Although conditioning was shown to increase CS-evoked LA responses, the specificity of the changes in responsiveness was not tested. Because conditioning might induce nonspecific increases in LA responses to auditory afferents, we re-examined this issue in conscious, head-restrained cats using a differential conditioning paradigm where only one of two tones (CS(+) but not CS(-)) was paired to the US. Differential conditioning increased unit and field responses to the CS(+), whereas responses to the CS(-) decreased. Such changes have never been observed in the amygdala except in cases where the CS(-) had been paired to the US before and fear responses not extinguished. This suggests that fear conditioning is not only accompanied by potentiation of amygdalopetal pathways conveying the CS(+) but also by the depression of sensory inputs unpaired to noxious stimuli.

  9. Cs/CsPbX3 (X = Br, Cl) epitaxial heteronanocrystals with magic-angle stable/metastable grain boundary

    NASA Astrophysics Data System (ADS)

    Zhang, Yumeng; Fan, Baolu; Wu, Wenhui; Fan, Jiyang

    2017-05-01

    Metal-semiconductor heteronanostructures are crucial building blocks of nanoscale electronic and optoelectronic devices. However, the lattice misfit remains a challenge in constructing heteronanostructures. Perovskite nanocrystals are superior candidates for constructing nanodevices owing to excellent optical, ferroelectric, and superconducting properties. We report the epitaxial growth of lattice-matched Cs/CsPbBr3 metal-semiconductor heteronanocrystals in a liquid medium. The well-crystallized ultrathin Cs layers grow epitaxially on the surfaces of colloidal CsPbBr3 nanocrystals, forming heteronanocrystals with interface diameters of several nanometers. Most of them are pseudomorphic with coherent interfaces free from dislocations, and the others exhibit discrete high-angle grain boundaries. The model based on the calculation of the elastic potential energy of the epilayer and analysis of the near-coincidence sites explains well the experimental result. The analysis shows that the excellent lattice match between the metal and the semiconductor ensures the ideal epitaxial-growth of both Cs/CsPbBr3 and Cs/CsPbCl3 heteronanocrystals. Such metal/semiconductor heteronanocrystals pave the way for developing perovskite-based nanodevices.

  10. CsAlSi/sub 5/O/sub 12/: a possible host for /sup 137/Cs immobilization

    SciTech Connect

    Adl, T.; Vance, E.R.

    1982-03-31

    CsAlSi/sub 5/O/sub 12/ exhibits more acid resistance than pollucite (CsAlSi/sub 2/O/sub 6/). At pH values of 1.02 and 1.40, the extraction of Cs from CsAlSi/sub 5/O/sub 12/ at 25/sup 0/C was approximately proportional to the square root of leach time. The Cs extraction at 25/sup 0/C varied as (H/sup +/)/sup 0/ /sup 36/ over the pH range of 1 to 6. Also, the Cs extraction in various brines at 300/sup 0/C/30 MPa was comparable with that for pollucite. CsAlSi/sub 5/O/sub 12/ can be crystallized at about 1000/sup 0/C from calcines if a small amount of CaO is present, but in the absence of such sintering acids, crystallization temperatures of about 1400/sup 0/C are necessary. Compatibility data were also obtained with respect to several other phases with which CsAlSi/sub 5/O/sub 12/ might be expected to coexist in tailored ceramics designed for high-level defense waste.

  11. 137Cs Results and Interpretation of Cesium Soil Data on the Upper Fortymile Wash Alluvial Fan, Amargosa Valley, Nevada.

    NASA Astrophysics Data System (ADS)

    Harrington, C.

    2004-12-01

    Studies using 137Cs were used to produce soil Cs profiles and to use them to determine erosion rates on interchannel divides of the Fortymile Wash alluvial fan over the last 50 years. Sample locations whose 137Cs profiles most resemble the reference-sample (stable surface) profiles are located on interchannel divide areas between distributary channels. These profiles are similar to the reference profiles that have low 137Cs values (in the range of 0.02 to 0.08 pCi/g) in the 3 to 6 cm layers. However, the surface layers (1-3 cm depth) typically have values much less than the reference samples from equivalent depths (range from 0.251 to 0.421 pCi/g). The data indicate that many of these interchannel divide areas have had part of the upper layer removed. Interchannel divide areas have the least likelihood of having been submerged during floods over the last fifty years. Thus, the loss of material from these otherwise stable surfaces appears to be due to eolian processes. Erosion of an interchannel divide area with little evidence of recent water movement is most easily explained by eolian removal. Evidence for wind erosion as the predominant process on the interchannel divide areas includes the lack of new or developing stream channels and the presence of modern coppice dunes near channels on interchannel divides. The presence of nearby Big Dune and other eolian deposits provides strong support for eolian erosion and transport. The amount of material removed from the interchannel divide areas was estimated by comparing the 137Cs value of the upper 3 cm layer to that of the reference value and calculating the thickness of the layer that would have to be removed to obtain the lower value. Applying this method across the interchannel divide sample locations indicates 1 to 2 cm of material has been removed from the interchannel divide surfaces in the last 50 years. This results in erosion rates that range from 0.02 to 0.04 cm/yr. These rates are similar to erosion rates

  12. Epiphytic fruticose lichens as biomonitors for retrospective evaluation of the (134)Cs/(137)Cs ratio in Fukushima fallout.

    PubMed

    Ramzaev, V; Barkovsky, A; Gromov, A; Ivanov, S; Kaduka, M

    2014-12-01

    In 2011-2013, sampling of epiphytic fruticose lichens of the genera Usnea, Bryoria and Alectoria was carried out on Sakhalin and Kuril Islands (the Sakhalin region, Russia) to investigate contamination of these organisms with the Fukushima-derived (134)Cs and (137)Cs. Activities of the radionuclides were determined in all 56 samples of lichens taken for the analysis. After correction for radioactive decay (on 15 March 2011), the activity concentrations ranged from 2.1 Bq kg(-1) (d.w.) to 52 Bq kg(-1) for (134)Cs and from 2.3 Bq kg(-1) to 52 Bq kg(-1) for (137)Cs. Cesium-134 and (137)Cs activities for the whole set of lichens (n = 56) were strongly positively correlated; Spearman's rank correlation coefficient was calculated as 0.991 (P < 0.01). The activity concentrations of (134)Cs and (137)Cs in Usnea lichens from the Sakhalin and Kunashir islands declined with a factor of three in the period from 2011 to 2013. The average biological half-time for both cesium radionuclides in lichens of the genus Usnea is estimated as 1.3 y. The mean of 0.99 ± 0.10 and median of 0.99 were calculated for the decay corrected (134)Cs/(137)Cs activities ratios in the lichens (n = 56). The radionuclides ratio in the lichens did not depend on location of sampling site, species and the time that had passed after the Fukushima accident. The regression analysis has shown the background pre-Fukushima level of (137)Cs of 0.4 ± 0.3 Bq kg(-1), whereas the ratio between the Fukushima-borne (134)Cs and (137)Cs in the lichens was estimated as 1.04. The (134)Cs/(137)Cs activities ratio in lichens from the Sakhalin region is consistent with the ratios reported by others for the heavy contaminated areas on Honshu Island in Japan following the Fukushima accident. The activity concentrations of natural (7)Be in lichens from the Sakhalin region varied between 100 Bq kg(-1) and 600 Bq kg(-1); the activity concentrations did not exhibit temporal variations during a 2y

  13. Dynamic Channel Allocation

    DTIC Science & Technology

    2003-09-01

    7 1 . Fixed Channel Allocation (FCA) ........................................................7 2. Dynamic Channel ...19 7. CSMA/CD-Based Multiple Network Lines .....................................20 8. Hybrid Channel Allocation in Wireless Networks...28 1 . Channel Allocation

  14. Coaxial Measurement of the Translational Distribution of CS Produced in the Laser Photolysis of CS2 at 193nm.

    DTIC Science & Technology

    1983-11-04

    IKasakawi, and R. Bersohn, J. Chemn. Phys. 72, 4058 (1980). *2. M.C. Addison, C.D. Bryne and R.J. Donovan, Chem. Phys. Letters, 64, 57 (1979). *3. J.E...population of CS2 fragments produced in processes: (a). CS2- + hV CS ( Z ,v" ) + S (3p) represented by 0; (b). CS2 + hv CS (X1 Z +,v") + S (1D...0 0 1 1 1 fl l i 0 z 0 - >0 -) p ~m 0 z D:O m l CCD X CA > 0__ -" -’ o- o 0 -0 "C 0 o 00 CL CL 0 0 -." - ’ .:.-:.- "- * -.5

  15. Photoresponse of CsPbBr3 and Cs4PbBr6 Perovskite Single Crystals.

    PubMed

    Cha, Ji-Hyun; Han, Jae Hoon; Yin, Wenping; Park, Cheolwoo; Park, Yongmin; Ahn, Tae Kyu; Cho, Jeong Ho; Jung, Duk-Young

    2017-02-02

    High-quality and millimeter-sized perovskite single crystals of CsPbBr3 and Cs4PbBr6 were prepared in organic solvents and studied for correlation between photocurrent generation and photoluminescence (PL) emission. The CsPbBr3 crystals, which have a 3D perovskite structure, showed a highly sensitive photoresponse and poor PL signal. In contrast, Cs4PbBr6 crystals, which have a 0D perovskite structure, exhibited more than 1 order of magnitude higher PL intensity than CsPbBr3, which generated an ultralow photoresponse under illumination. Their contrasting optoelectrical characteristics were attributed to different exciton binding energies, induced by coordination geometry of the [PbBr6](4-) octahedron sublattices. This work correlated the local structures of lead in the primitive perovskite and its derivatives to PL spectra as well as photoconductivity.

  16. 137Cs in the western South Pacific Ocean.

    PubMed

    Yamada, Masatoshi; Wang, Zhong-Liang

    2007-09-01

    The 137Cs activities were determined for seawater samples from the East Caroline, Coral Sea, New Hebrides, South Fiji and Tasman Sea (two stations) Basins of the western South Pacific Ocean by gamma spectrometry using a low background Ge detector. The 137Cs activities ranged from 1.4 to 2.3 Bq m(-3) over the depth interval 0-250 m and decreased exponentially from the subsurface to 1000 m depth. The distribution profiles of 137Cs activity at these six western South Pacific Ocean stations did not differ from each other significantly. There was a remarkable difference for the vertical profiles of 137Cs activity between the East Caroline Basin station in this study and the GEOSECS (Geochemical Ocean Sections Study) station at the same latitude in the Equatorial Pacific Ocean; the 137Cs inventory over the depth interval 100-1000 m increased from 400+/-30 Bq m(-2) to 560+/-30 Bq m(-2) during the period from 1973 to 1992. The total 137Cs inventories in the western South Pacific Ocean ranged from 850+/-70 Bq m(-2) in the Coral Sea Basin to 1270+/-90 Bq m(-2) in the South Fiji Basin. Higher 137Cs inventories were observed at middle latitude stations in the subtropical gyre than at low latitude stations. The 137Cs inventories were 1.9-4.5 times (2.9+/-0.7 on average) and 1.7-4.3 times (3.1+/-0.7 on average) higher than that of the expected deposition density of atmospheric global fallout at the same latitude and that of the estimated 137Cs deposition density in 10 degrees latitude by 10 degrees longitude grid data obtained by Aoyama et al. [Aoyama M, Hirose K, Igarashi Y. Re-construction and updating our understanding on the global weapons tests 137Cs fallout. J Environ Monit 2006;8:431-438], respectively. The possible processes for higher 137Cs inventories in the western South Pacific Ocean than that of the expected deposition density of atmospheric global fallout may be attributable to the inter-hemisphere dispersion of the atmospheric nuclear weapons testing 137Cs from

  17. Integration of biological ion channels onto optically addressable micro-fluidic electrode arrays for single molecule characterization.

    SciTech Connect

    Brozik, Susan Marie; Frink, Laura J. Douglas; Bachand, George David; Keller, David J.; Patrick, Elizabeth L.; Marshall, Jason A.; Ortiz, Theodore P.; Meyer, Lauren A.; Davis, Ryan W.; Brozik, James A.; Flemming, Jeb Hunter

    2004-12-01

    The challenge of modeling the organization and function of biological membranes on a solid support has received considerable attention in recent years, primarily driven by potential applications in biosensor design. Affinity-based biosensors show great promise for extremely sensitive detection of BW agents and toxins. Receptor molecules have been successfully incorporated into phospholipid bilayers supported on sensing platforms. However, a collective body of data detailing a mechanistic understanding of membrane processes involved in receptor-substrate interactions and the competition between localized perturbations and delocalized responses resulting in reorganization of transmembrane protein structure, has yet to be produced. This report describes a systematic procedure to develop detailed correlation between (recognition-induced) protein restructuring and function of a ligand gated ion channel by combining single molecule fluorescence spectroscopy and single channel current recordings. This document is divided into three sections: (1) reported are the thermodynamics and diffusion properties of gramicidin using single molecule fluorescence imaging and (2) preliminary work on the 5HT{sub 3} serotonin receptor. Thirdly, we describe the design and fabrication of a miniaturized platform using the concepts of these two technologies (spectroscopic and single channel electrochemical techniques) for single molecule analysis, with a longer term goal of using the physical and electronic changes caused by a specific molecular recognition event as a transduction pathway in affinity based biosensors for biotoxin detection.

  18. VSOP/Hv1 proton channels sustain calcium entry, neutrophil migration, and superoxide production by limiting cell depolarization and acidification.

    PubMed

    El Chemaly, Antoun; Okochi, Yoshifumi; Sasaki, Mari; Arnaudeau, Serge; Okamura, Yasushi; Demaurex, Nicolas

    2010-01-18

    Neutrophils kill microbes with reactive oxygen species generated by the NADPH oxidase, an enzyme which moves electrons across membranes. Voltage-gated proton channels (voltage-sensing domain only protein [VSOP]/Hv1) are required for high-level superoxide production by phagocytes, but the mechanism of this effect is not established. We show that neutrophils from VSOP/Hv1-/- mice lack proton currents but have normal electron currents, indicating that these cells have a fully functional oxidase that cannot conduct protons. VSOP/Hv1-/- neutrophils had a more acidic cytosol, were more depolarized, and produced less superoxide and hydrogen peroxide than neutrophils from wild-type mice. Hydrogen peroxide production was rescued by providing an artificial conductance with gramicidin. Loss of VSOP/Hv1 also aborted calcium responses to chemoattractants, increased neutrophil spreading, and decreased neutrophil migration. The migration defect was restored by the addition of a calcium ionophore. Our findings indicate that proton channels extrude the acid and compensate the charge generated by the oxidase, thereby sustaining calcium entry signals that control the adhesion and motility of neutrophils. Loss of proton channels thus aborts superoxide production and causes a severe signaling defect in neutrophils.

  19. VSOP/Hv1 proton channels sustain calcium entry, neutrophil migration, and superoxide production by limiting cell depolarization and acidification

    PubMed Central

    El Chemaly, Antoun; Okochi, Yoshifumi; Sasaki, Mari; Arnaudeau, Serge; Okamura, Yasushi

    2010-01-01

    Neutrophils kill microbes with reactive oxygen species generated by the NADPH oxidase, an enzyme which moves electrons across membranes. Voltage-gated proton channels (voltage-sensing domain only protein [VSOP]/Hv1) are required for high-level superoxide production by phagocytes, but the mechanism of this effect is not established. We show that neutrophils from VSOP/Hv1−/− mice lack proton currents but have normal electron currents, indicating that these cells have a fully functional oxidase that cannot conduct protons. VSOP/Hv1−/− neutrophils had a more acidic cytosol, were more depolarized, and produced less superoxide and hydrogen peroxide than neutrophils from wild-type mice. Hydrogen peroxide production was rescued by providing an artificial conductance with gramicidin. Loss of VSOP/Hv1 also aborted calcium responses to chemoattractants, increased neutrophil spreading, and decreased neutrophil migration. The migration defect was restored by the addition of a calcium ionophore. Our findings indicate that proton channels extrude the acid and compensate the charge generated by the oxidase, thereby sustaining calcium entry signals that control the adhesion and motility of neutrophils. Loss of proton channels thus aborts superoxide production and causes a severe signaling defect in neutrophils. PMID:20026664

  20. Annealing behavior of a Cs2O/Cs2O2)/GaAs(110 surface studied by electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Wu, J. X.; Li, F. Q.; Zhu, J. S.; Ji, M. R.; Ma, M. S.

    2002-09-01

    A Cs2O/Cs2O2 overlayer was prepared by simultaneous oxygen-cesium adsorption on GaAs(110) at room temperature. In situ electron spectroscopy and work function measurements have been used to study the Cs2O/Cs2O2/GaAs surface as a function of annealing temperature. The Cs2O/Cs2O2/GaAs surface exhibits metallic and has a work function value of 0.9 eV. There are Cs-O-Ga, Cs-O-As, As-O, and Ga-O bonds at the interface of Cs2O2/GaAs. Annealing facilitates the interfacial reaction and the minimum of the work function (0.7 eV) was observed after annealing at 540 K. After the decomposition of Cs2O and Cs2O2 at 620 K, the surface dominated by the Cs-O-Ga and Cs-O-As species remains negative electron affinity with a work function value of 1.1 eV. For further annealing, the fast Cs desorption is associated with the decomposition of the Cs-O-Ga and Ca-O-As bonds as well as the evaporations of As2O3 and CsAsO2, forming Ga2O3. copyright 2002 American Vacuum Society.

  1. Plutonium, (137)Cs and uranium isotopes in Mongolian surface soils.

    PubMed

    Hirose, K; Kikawada, Y; Igarashi, Y; Fujiwara, H; Jugder, D; Matsumoto, Y; Oi, T; Nomura, M

    2017-01-01

    Plutonium ((238)Pu and (239,240)Pu), (137)Cs and plutonium activity ratios ((238)Pu/(239,240)Pu) as did uranium isotope ratio ((235)U/(238)U) were measured in surface soil samples collected in southeast Mongolia. The (239,240)Pu and (137)Cs concentrations in Mongolian surface soils (<53 μm of particle size) ranged from 0.42 ± 0.03 to 3.53 ± 0.09 mBq g(-1) and from 11.6 ± 0.7 to 102 ± 1 mBq g(-1), respectively. The (238)Pu/(239,240)Pu activity ratios in the surface soils (0.013-0.06) coincided with that of global fallout. The (235)U/(238)U atom ratios in the surface soil show the natural one. There was a good correlation between the (239,240)Pu and (137)Cs concentrations in the surface soils. We introduce the migration depth to have better understanding of migration behaviors of anthropogenic radionuclides in surface soil. We found a difference of the migration behavior between (239,240)Pu and (137)Cs from (137)Cs/(239,240)Pu - (137)Cs plots for the Mongolian and Tsukuba surface soils; plutonium in surface soil is migrated easier than (137)Cs.

  2. Radioactive Cs capture in the early solar system

    PubMed Central

    Hidaka, Hiroshi; Yoneda, Shigekazu

    2013-01-01

    Barium isotopic compositions of primitive materials in the solar system are generally affected by s- and r-process nucleosynthetic components that hide the contribution of the isotopic excess of 135Ba formed by decay of radioactive 135Cs. However, the Ba isotopic composition of the chemical separates from chondrules in the Sayama CM2 chondrite shows an excess of 135Ba isotopic abundance up to (0.33 ± 0.06)%, which is independent of the isotopic components from s- and r-process nucleosyntheses. The isotopic excesses of 135Ba correlate with the elemental abundance of Ba relative to Cs, providing chemical and isotopic evidence for the existence of the presently extinct radionuclide 135Cs (t1/2 = 2.3 million years) in the early solar system. The estimated abundance of 135Cs/133Cs = (6.8 ± 1.9) × 10−4 is more than double that expected from the uniform production model of the short-lived radioisotopes, suggesting remobilization of Cs including 135Cs in the chondrules of the meteorite parent body. PMID:23435551

  3. The Density Structure of UCHII Regions: CS Observations

    NASA Astrophysics Data System (ADS)

    Butner, H. M.; Lauwers, T. L.

    2000-12-01

    Ultra-compact HII (UCHII) regions are sites of massive star formation. As yet, the physical conditions inside these regions are still poorly known. Submillimeter observations offer one way of probing the gas density and temperature. As part of an extensive study of the chemistry and physical conditions inside UCHII regions, we undertook a project to map several UCHII regions in CS. CS is an abundant molecule, and is an excellent density probe. Using the Submillimeter Telescope Observatory (SMTO), we are mapping ten UCHII regions in detail at a variety of CS transitions, including the CS 5-4, 7-6 and C34S 5-4 and 7-6 lines. The regions chosen also have far-infrared data and submm data available, so we will be able to compare the dust and gas properties. We report the first results of the CS mapping program for CS 5-4 and CS 7-6 lines. We compare our conclusions with other studies of these regions. T. L. Lauwers was supported by the University of Arizona/NASA Space Grant Undergraduate Research Internship Program.

  4. On the Formation of Cometary Carbon Disulfide (CS2)

    NASA Technical Reports Server (NTRS)

    Hudson, Reggie; Moore, Maria; Ferrante, Robert F.

    2010-01-01

    The formation of cometary CS from CS2 was proposed about 20 years before the latter's detection in comet 122P/de Vico by Jackson et al. (2002). However, the origin of CS2 has received little attention from either experimentalists or theorists. As part of our on-going laboratory program to investigate cometary molecules we have examined chemical reactions that lead to CS2 in the solid state. Icy mixtures of known cometary molecules were proton irradiated near 10K to doses of several eV per molecule. Mid-IR spectroscopy was used as an in situ probe to record both CS2 formation in the ices and the destruction of precursors. We find that the most likely route to cometary CS2 is through OCS by way of the S + CO reaction. We also observe the monocyclic molecule OCS2 as an intermediate on the path from OCS to CS2. This work was funded by NASA's Planetary Geology and Geophysics program.

  5. Physics design for ARIES-CS

    SciTech Connect

    Ku, L. P.; Garabedian, P. R.; Lyon, James F; Turnbull, A. D.; Grossman, A.; Mau, T. K.; Zarnstorff, M. C.

    2008-01-01

    Novel stellarator configurations have been developed for ARIES-CS. These configurations are optimized to provide good plasma confinement and flux surface integrity at high beta. Modular coils have been designed for them in which the space needed for the breeding blanket and radiation shielding was specifically targeted such that reactors generating GW electrical powers would require only moderate major radii (<10 m). These configurations are quasi-axially symmetric in the magnetic field topology and have small numbers of field periods (<= 3) and low aspect ratios (<= 6). The baseline design chosen for detailed systems and power plant studies has three field periods, aspect ratio 4.5, and major radius 7.5 m operating at beta similar to 6.5% to yield 1 GW of electric power. The shaping of the plasma accounts for >= 75% of the rotational transform. The effective helical ripples are very small (<0.6% everywhere), and the energy loss of alpha particles is calculated to be <= 5% when operating in high-density regimes. An interesting feature in this configuration is that instead of minimizing all residues in the magnetic spectrum, we preferentially retained a small amount of the nonaxisymmetric mirror field. The presence of this mirror and its associated helical field alters the ripple distribution, resulting in the reduced ripple-trapped loss of alpha particles despite the long connection length in a tokamak-like field structure. Additionally, we discuss two other potentially attractive classes of configurations, both quasi-axisymmetrie: one with only two field periods, very low aspect ratios (similar to 2.5), and less complex coils, and the other with the plasma shaping designed to produce low-shear rotational transform so as to ensure the robustness and integrity of flux surfaces when operating at high beta.

  6. Physics Design for ARIES-CS

    SciTech Connect

    L.P. Ku, P.R. Garabedian, J. Lyon, A. Turnbull, A. Grossman, T.K. Mau, M. Zarnstorff, and the ARIES Team

    2007-10-10

    Novel stellarator configurations have been developed for ARIES-CS. These configurations are optimized to provide good plasma confinement and flux surface integrity at high beta. Modular coils have been designed for them in which the space needed for the breeding blanket and radiation shielding was specifically targeted such that reactors generating GW electrical powers would require only moderate major radii (<10 m). These configurations are quasi-axially symmetric in the magnetic field topology and have small number of field periods (≤3) and low aspect ratios (≤6). The baseline design chosen for detailed systems and power plant studies has 3 field periods, aspect ratio 4.5 and major radius 7.5 m operating at β~6.5% to yield 1 GW electric power. The shaping of the plasma accounts for ≥75% of the rotational transform. The effective helical ripples are very small (< 0.6% everywhere) and the energy loss of alpha particles is calculated to be ≤5% when operating in high density regimes. An interesting feature in this configuration is that instead of minimizing all residues in the magnetic spectrum, we preferentially retained a small amount of the non-axisymmetric mirror field. The presence of this mirror and its associated helical field alters the ripple distribution, resulting in the reduced ripple-trapped loss of alpha particles despite the long connection length in a tokamak-like field structure. Additionally, we discuss two other potentially attractive classes of configurations, both quasi-axisymmetric: one with only two field periods, very low aspect ratios (~2.5), and less complex coils, and the other with the plasma shaping designed to produce low shear rotational transform so as to assure the robustness and integrity of flux surfaces when operating at high β.

  7. Influence of water management and fertilizer application on (137)Cs and (133)Cs uptake in paddy rice fields.

    PubMed

    Wakabayashi, Shokichi; Itoh, Sumio; Kihou, Nobuharu; Matsunami, Hisaya; Hachinohe, Mayumi; Hamamatsu, Shioka; Takahashi, Shigeru

    2016-06-01

    Cesium-137 derived from the Tokyo Electric Power Company's Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident contaminated large areas of agricultural land in Eastern Japan. Previous studies before the accident have indicated that flooding enhances radiocesium uptake in rice fields. We investigated the influence of water management in combination with fertilizers on (137)Cs concentrations in rice plants at two fields in southern Ibaraki Prefecture. Stable Cs ((133)Cs) in the plants was also determined as an analogue for predicting (137)Cs behavior after long-term aging of soil (137)Cs. The experimental periods comprised 3 y starting from 2012 in one field, and 2 y from 2013 in another field. These fields were divided into three water management sections: a long-flooding section without midsummer drainage, and medial-flooding, and short-flooding sections with one- or two-week midsummer drainage and earlier end of flooding than the long-flooding section. Six or four types of fertilizer subsections (most differing only in potassium application) were nested in each water management section. Generally, the long-flooding treatment led to higher (137)Cs and (133)Cs concentrations in both straw and brown rice than medial- and short-flooding treatments, although there were some notable exceptions in the first experimental year at each site. Effects of differing potassium fertilizer treatments were cumulative; the effects on (137)Cs and (133)Cs concentrations in rice plants were not obvious in 2012 and 2013, but in 2014, these concentrations were highest where potassium fertilizer had been absent and lowest where basal dressings of K had been tripled. The relationship between (137)Cs and (133)Cs in rice plants was not correlative in the first experimental year at each site, but correlation became evident in the subsequent year(s). This study demonstrates a novel finding that omitting midsummer drainage and/or delaying drainage during the grain-filling period enhances

  8. Accumulation and transfer of 137Cs and 90Sr in the plants of the forest ecosystem near the Ignalina Nuclear Power Plant.

    PubMed

    Lukšienė, B; Marčiulionienė, D; Gudelienė, I; Schönhofer, F

    2013-02-01

    The radioecological state of the forest ecosystem in the vicinity of the Ignalina Power Plant prior to decommissioning was analysed with specific emphasis on (137)Cs and (90)Sr activity concentrations in plant species growing in two reference sampling sites (Tilze and Grikiniskes). In the period of 1996-2008 the mean contamination of plants with (137)Cs was from 45 to 119 Bq/kg and with (90)Sr - from 3 to 42 Bq/kg. Measured (137)Cs TF values for soil-root transfer mainly ranged between 1.0-1.4, except for Calamagrostis arundinacea which had a TF value of 0.1. On average, the (137)Cs TF value from root to shoot was 1.7 fold higher than for soil to root transfer. (90)Sr TF values (soil-root) were in the range of 1.2-1.8 but for Calluna vulgaris it was 0.2. The mean root to shoot TF value for (90)Sr was 7.7 fold higher. These results indicate the higher (90)Sr bioavailability than that of (137)Cs in the forested area. The Grikiniskes reference site is located nearby the Ignalina NPP, specifically the heated water outlet channel, which results in altered microclimatic conditions. These specific microclimatic conditions result in relationships between (137)Cs TF (soil-root) values and pH, moisture and organic matter content in the soil at Grikiniskes which appear to be different to those at the Tilze reference sampling site.

  9. Dual channel self-oscillating optical magnetometer

    SciTech Connect

    Belfi, J.; Bevilacqua, G.; Biancalana, V.; Dancheva, Y.; Khanbekyan, K.; Moi, L.; Cartaleva, S.

    2009-05-15

    We report on a two-channel magnetometer based on nonlinear magneto-optical rotation in a Cs glass cell with buffer gas. The Cs atoms are optically pumped and probed by free running diode lasers tuned to the D{sub 2} line. A wide frequency modulation of the pump laser is used to produce both synchronous Zeeman optical pumping and hyperfine repumping. The magnetometer works in an unshielded environment, and a spurious signal from distant magnetic sources is rejected by means of differential measurement. In this regime the magnetometer simultaneously gives the magnetic field modulus and the field difference. Rejection of the common-mode noise allows for high-resolution magnetometry with a sensitivity of 2 pT/{radical}(Hz). This sensitivity, in conjunction with long-term stability and a large bandwidth, makes it possible to detect water proton magnetization and its free induction decay in a measurement volume of 5 cm{sup 3}.

  10. Altimeter Products for the Sentinel-6/Jason-CS Mission

    NASA Astrophysics Data System (ADS)

    Scharroo, Remko; Bonekamp, Hans; Ponsard, Christelle; Nogueira Loddo, Carolina

    2015-12-01

    The Sentinel-6 mission will be developed and implemented through a partnership between the EU, ESA, EUMETSAT and NOAA . Its aim is to secure the continuity until 2030+ of critical high precision observations of ocean surface topography beyond Jason-3. The European contribution will be implemented through the combination of the ESA Copernicus Space Component, the EUMETSAT Jason-CS optional programme, and the EU Copernicus programme, for the joint benefits of the meteorological and Copernicus user communities in Europe. NASA and CNES will be supporting partners. The mission will start with the launch of Jason-CS A in 2020, followed by Jason-CS B in 2025.

  11. Scintillation, Afterglow and Thermoluminescence of CsI:Tl,Sm

    NASA Astrophysics Data System (ADS)

    Kappers, L. A.; Bartram, R. H.; Hamilton, D. S.; Lempicki, A.; Brecher, C.; Gaysinskiy, V.; Ovechkina, E. E.; Nagarkar, V. V.

    2010-11-01

    Experiments on co-doped CsI:Tl,Sm suggest that samarium electron traps scavenge electrons from thallium traps and that electrons subsequently released by samarium recombine non-radiatively with trapped holes, thus suppressing afterglow. These experiments support the inference that electrons tunnel freely between samarium ions and are trapped preferentially as substitutional Sm+ near VKA(Tl+) centers where non-radiative recombination is the rate-limiting step. Combined radioluminescence, afterglow and thermoluminescence on single-crystal samples of CsI:Tl and CsI:Tl,Sm, recorded sequentially at adjusted gain settings following low-temperature irradiation, reveal reversible radiation damage as well.

  12. The transfer of {sup 137}Cs from barley to beer

    SciTech Connect

    Proehl, G.; Mueller, H.; Voigt, G.

    1997-01-01

    Beer has been brewed from barley contaminated with {sup 137}Cs as a consequence of the Chernobyl accident. The {sup 137}Cs activity has been measured in all intermediate steps and in the by-products of the production process. About 35 % of the {sup 137}Cs in barley were recovered in beer. Processing factors defined as the concentration ratio of processed and raw products were determined to be 0.61, 3.3, 0.1 and 0.11 for malt, malt germs, spent grains and beer, respectively. 4 refs., 2 tabs.

  13. Anion Permeation in Ca2+-Activated Cl− Channels

    PubMed Central

    Qu, Zhiqiang; Hartzell, H. Criss

    2000-01-01

    Ca2+-activated Cl channels (ClCaCs) are an important class of anion channels that are opened by increases in cytosolic [Ca2+]. Here, we examine the mechanisms of anion permeation through ClCaCs from Xenopus oocytes in excised inside-out and outside-out patches. ClCaCs exhibited moderate selectivity for Cl over Na: PNa/PCl = 0.1. The apparent affinity of ClCaCs for Cl was low: Kd = 73 mM. The channel had an estimated pore diameter >0.6 nm. The relative permeabilities measured under bi-ionic conditions by changes in Erev were as follows: C(CN)3 > SCN > N(CN)2 > ClO4 > I > N3 > Br > Cl > formate > HCO3 > acetate = F > gluconate. The conductance sequence was as follows: N3 > Br > Cl > N(CN)2 > I > SCN > COOH > ClO4 > acetate > HCO3 = C(CN)3 > gluconate. Permeant anions block in a voltage-dependent manner with the following affinities: C(CN)3 > SCN = ClO4 > N(CN)2 > I > N3 > Br > HCO3 > Cl > gluconate > formate > acetate. Although these data suggest that anionic selectivity is determined by ionic hydration energy, other factors contribute, because the energy barrier for permeation is exponentially related to anion hydration energy. ClCaCs exhibit weak anomalous mole fraction behavior, implying that the channel may be a multi-ion pore, but that ions interact weakly in the pore. The affinity of the channel for Ca2+ depended on the permeant anion at low [Ca2+] (100–500 nM). Apparently, occupancy of the pore by a permeant anion increased the affinity of the channel for Ca2+. The current was strongly dependent on pH. Increasing pH on the cytoplasmic side decreased the inward current, whereas increasing pH on the external side decreased the outward current. In both cases, the apparent pKa was voltage-dependent with apparent pKa at 0 mV = ∼9.2. The channel may be blocked by OH− ions, or protons may titrate a site in the pore necessary for ion permeation. These data demonstrate that the permeation properties of ClCaCs are different from those of CFTR or ClC-1, and provide

  14. New type of borophosphate anionic radical in the crystal structure of CsAl2BP6O20

    NASA Astrophysics Data System (ADS)

    Shvanskaya, L. V.; Yakubovich, O. V.; Belik, V. I.

    2016-09-01

    The crystal structure of a new borophosphate CsAl2BP6O20 obtained by spontaneous crystallization in a multicomponent Cs-Cu-B-P-O system is determined by X-ray diffraction ( a = 11.815(2), b = 10.042(2), and c = 26.630(4) Å; space group Pbca, Z = 8, V = 3159.5(10) Å3; R 1 = 0.043). A new type of borophosphate anionic 2D radical characterized by the lowest B: P = 1: 6 ratio and containing P3O10 phosphate groups is found in the compound. A mixed-type anionic framework consisting of vertex-sharing BO4 and PO4 tetrahedra and AlO6 octahedra is distinguished in the structure. Large cesium atoms are located in the channels of the framework. Topological relationships are revealed between the structures of the CsAl3(P3O10)2 and CsAl2BP6O20 phases having different cationic compositions. These compounds can be considered quasi-polytypic phases.

  15. Studies of rotationally inelastic collisions of NaK and NaCs with Ar and He perturbers

    NASA Astrophysics Data System (ADS)

    Jones, J.; Faust, C.; Richter, K.; Wolfe, C. M.; Ashman, S.; Malenda, R. F.; Weiser, P.; Carlus, S.; Fragale, A.; Hickman, A. P.; Huennekens, J.

    2013-05-01

    We report studies of rotationally inelastic collisions of Ar and He atoms with the molecules NaK and NaCs prepared in various ro-vibrational levels of the A1Σ+ electronic state. We use laser induced fluorescence (LIF) and polarization labeling (PL) spectroscopy in a pump-probe, two step excitation process. The pump excites the molecule to a ro-vibrational level (v , J) in the A state. The probe laser is scanned over transitions to the 31 Π state in NaK or the 53 Π state in NaCs. In addition to strong direct lines, we observe weak satellite lines that arise from collision-induced transitions of the A state level (v , J) to (v , J + ΔJ) . The ratio of intensities of the satellite line to the direct line in LIF and PL yields information about population and orientation transfer. Preliminary results show a strong propensity for collisions with ΔJ =even for NaK; the propensity is larger for He than for Ar. Collisions of NaCs with He show a similar propensity, but collisions of NaCs with Ar do not. Theoretical calculations are also underway. For He-NaK, we have completed potential surface calculations using GAMESS and coupled channel scattering calculations of rotational energy transfer and transfer of orientation. Work supported by NSF and XSEDE.

  16. A Kv3-like persistent, outwardly rectifying, Cs+-permeable, K+ current in rat subthalamic nucleus neurones

    PubMed Central

    Wigmore, Mark A; Lacey, Michael G

    2000-01-01

    A persistent outward K+ current (IPO), activated by depolarization from resting potential, has been identified and characterized in rat subthalamic nucleus (SThN) neurones using whole-cell voltage-clamp recording in brain slices.IPO both rapidly activated (τ= 8 ms at +5 mV) and deactivated (τ= 2 ms at −68 mV), while showing little inactivation. Tail current reversal potentials varied with extracellular K+ concentration in a Nernstian manner.Intracellular Cs+ did not alter either IPO amplitude or the voltage dependence of activation, but blocked transient (A-like) outward currents activated by depolarization. When extracellular K+ was replaced with Cs+, IPO tail current reversal potentials were dependent upon the extracellular Cs+ concentration, indicating an ability to conduct Cs+, as well as K+.IPO was blocked by Ba2+ (1 mm), 4-aminopyridine (1 mm) and tetraethylammonium (TEA; 20 mm), with an IC50 for TEA of 0.39 mm.The IPO conductance appeared maximal (38 nS) at around +27 mV, half-maximal at −13 mV, with the threshold for activation at around −38 mV.TEA (1 mm) blocked the action potential after-hyperpolarization and permitted accommodation of action potential firing at frequencies greater than around 200 Hz.We conclude that IPO, which shares many characteristics of currents attributable to Kv3.1 K+ channels, enables high-frequency spike trains in SThN neurones. PMID:10990536

  17. VizieR Online Data Catalog: TW Hya CO (2-1), CN (2-1) and CS (5-4) data cubes (Teague+, 2016)

    NASA Astrophysics Data System (ADS)

    Teague, R.; Guilloteau, S.; Semenov, D.; Henning, T.; Dutrey, A.; Pietu, V.; Birnstiel, T.; Chapillon, E.; Hollenbach, D.; Gorti, U.

    2016-07-01

    The observations were performed using ALMA on May 13, 2015 under excellent weather conditions (Cycle 2, 2013.1.00387.S). The receivers were tuned to cover CO J=(2-1), CS J=(5-4) and all strong hyperfine components of CN N=(2-1) simultaneously. The correlator was configured to deliver very high spectral resolution, with a channel spacing of 15kHz (and an effective velocity resolution of 40m/s) for the CO J=(2-1) and CS J=(5-4) lines, and 30kHz (80m/s) for the CN N=(2-1) transition. (2 data files).

  18. From Nonluminescent Cs4PbX6 (X = Cl, Br, I) Nanocrystals to Highly Luminescent CsPbX3 Nanocrystals: Water-Triggered Transformation through a CsX-Stripping Mechanism.

    PubMed

    Wu, Linzhong; Hu, Huicheng; Xu, Yong; Jiang, Shu; Chen, Min; Zhong, Qixuan; Yang, Di; Liu, Qipeng; Zhao, Yun; Sun, Baoquan; Zhang, Qiao; Yin, Yadong

    2017-09-13

    We report a novel CsX-stripping mechanism that enables the efficient chemical transformation of nonluminescent Cs4PbX6 (X = Cl, Br, I) nanocrystals (NCs) to highly luminescent CsPbX3 NCs. During the transformation, Cs4PbX6 NCs dispersed in a nonpolar solvent are converted into CsPbX3 NCs by stripping CsX through an interfacial reaction with water in a different phase. This process takes advantage of the high solubility of CsX in water as well as the ionic nature and high ion diffusion property of Cs4PbX6 NCs, and produces monodisperse and air-stable CsPbX3 NCs with controllable halide composition, tunable emission wavelength covering the full visible range, narrow emission width, and high photoluminescent quantum yield (up to 75%). An additional advantage is that this is a clean synthesis as Cs4PbX6 NCs are converted into CsPbX3 NCs in the nonpolar phase while the byproduct of CsX is formed in water that could be easily separated from the organic phase. The as-prepared CsPbX3 NCs show enhanced stability against moisture because of the passivated surface. Our finding not only provides a new pathway for the preparation of highly luminescent CsPbX3 NCs but also adds insights into the chemical transformation behavior and stabilization mechanism of these emerging perovskite nanocrystals.

  19. Status and prospect of the Swiss continuous Cs fountain FoCS-2

    NASA Astrophysics Data System (ADS)

    Jallageas, A.; Devenoges, L.; Petersen, M.; Morel, J.; Bernier, L.-G.; Thomann, P.; Südmeyer, T.

    2016-06-01

    The continuous cesium fountain clock FoCS-2 at METAS presents many unique characteristics and challenges in comparison with standard pulsed fountain clocks. For several years FoCS-2 was limited by an unexplained frequency sensitivity on the velocity of the atoms, in the range of 140 • 10-15. Recent experiments allowed us to identify the origin of this problem as undesirable microwave surface currents circulating on the shield of the coaxial cables that feed the microwave cavity. A strong reduction of this effect was obtained by adding microwave absorbing coatings on the coaxial cables and absorbers inside of the vacuum chamber. This breakthrough opens the door to a true metrological validation of the fountain. A series of simulation tools have already been developed and proved their efficiency in the evaluation of some of the uncertainties of the continuous fountain. With these recent improvements, we are confident in the future demonstration of an uncertainty budget at the 10-15 level and below.

  20. Low temperature phase transition and crystal structure of CsMgPO{sub 4}

    SciTech Connect

    Orlova, Maria; Khainakov, Sergey; Michailov, Dmitriy; Perfler, Lukas; Langes, Christoph; Kahlenberg, Volker; Orlova, Albina

    2015-01-15

    CsMgPO{sub 4} doped with radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at temperatures close to ambient conditions (∼−40 °C) was observed. Information about such kind of structural changes is important in order to understand whether it can cause any problem for medical use of this compound. The phase transition has been investigated in detail using synchrotron powder diffraction, Raman spectroscopy and DFT calculations. The structure undergoes a transformation from an orthorhombic modification, space group Pnma (RT phase) to a monoclinic polymorph, space group P2{sub 1}/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2) Å, b=8.95501(1) Å, c=5.50344(2) Å, β=90.68583(1)°, V=472.198(3) Å{sup 3}. CsMgPO{sub 4} belongs to the group of framework compounds and is made up of strictly alternating MgO{sub 4}- and PO{sub 4}-tetrahedra sharing vertices. The cesium counter cations are located in the resulting channel-like cavities. Upon the transformation a combined tilting of the tetrahedra is observed. A comparison with other phase transitions in ABW-type framework compounds is given. - Graphical abstract: Structural behavior of β-tridymite-type phosphate CsMgPO{sub 4}, considered as potential chemical form for radioactive Cs-source has been studied at near ambient temperatures. A phase transition at (∼−40 °C) has been found and investigated. It has been established that the known orthorhombic RT modification, space group Pnma, adopts a monoclinic cell with space group P2{sub 1}/n at low temperatures. In this paper, we present results of structural analysis of changes accompanying this phase transition and discuss its possible impact on the application properties. - Highlights: • β-Tridymite type phosphate CsMgPO{sub 4} undergoes so called translationengleiche phase transition of index 2 at −40 °C. • The structure

  1. Second-order Poisson Nernst-Planck solver for ion channel transport

    PubMed Central

    Zheng, Qiong; Chen, Duan; Wei, Guo-Wei

    2010-01-01

    The Poisson Nernst-Planck (PNP) theory is a simplified continuum model for a wide variety of chemical, physical and biological applications. Its ability of providing quantitative explanation and increasingly qualitative predictions of experimental measurements has earned itself much recognition in the research community. Numerous computational algorithms have been constructed for the solution of the PNP equations. However, in the realistic ion-channel context, no second order convergent PNP algorithm has ever been reported in the literature, due to many numerical obstacles, including discontinuous coefficients, singular charges, geometric singularities, and nonlinear couplings. The present work introduces a number of numerical algorithms to overcome the abovementioned numerical challenges and constructs the first second-order convergent PNP solver in the ion-channel context. First, a Dirichlet to Neumann mapping (DNM) algorithm is designed to alleviate the charge singularity due to the protein structure. Additionally, the matched interface and boundary (MIB) method is reformulated for solving the PNP equations. The MIB method systematically enforces the interface jump conditions and achieves the second order accuracy in the presence of complex geometry and geometric singularities of molecular surfaces. Moreover, two iterative schemes are utilized to deal with the coupled nonlinear equations. Furthermore, extensive and rigorous numerical validations are carried out over a number of geometries, including a sphere, two proteins and an ion channel, to examine the numerical accuracy and convergence order of the present numerical algorithms. Finally, application is considered to a real transmembrane protein, the Gramicidin A channel protein. The performance of the proposed numerical techniques is tested against a number of factors, including mesh sizes, diffusion coefficient profiles, iterative schemes, ion concentrations, and applied voltages. Numerical predictions are

  2. Second-order Poisson Nernst-Planck solver for ion channel transport.

    PubMed

    Zheng, Qiong; Chen, Duan; Wei, Guo-Wei

    2011-06-01

    The Poisson Nernst-Planck (PNP) theory is a simplified continuum model for a wide variety of chemical, physical and biological applications. Its ability of providing quantitative explanation and increasingly qualitative predictions of experimental measurements has earned itself much recognition in the research community. Numerous computational algorithms have been constructed for the solution of the PNP equations. However, in the realistic ion-channel context, no second order convergent PNP algorithm has ever been reported in the literature, due to many numerical obstacles, including discontinuous coefficients, singular charges, geometric singularities, and nonlinear couplings. The present work introduces a number of numerical algorithms to overcome the abovementioned numerical challenges and constructs the first second-order convergent PNP solver in the ion-channel context. First, a Dirichlet to Neumann mapping (DNM) algorithm is designed to alleviate the charge singularity due to the protein structure. Additionally, the matched interface and boundary (MIB) method is reformulated for solving the PNP equations. The MIB method systematically enforces the interface jump conditions and achieves the second order accuracy in the presence of complex geometry and geometric singularities of molecular surfaces. Moreover, two iterative schemes are utilized to deal with the coupled nonlinear equations. Furthermore, extensive and rigorous numerical validations are carried out over a number of geometries, including a sphere, two proteins and an ion channel, to examine the numerical accuracy and convergence order of the present numerical algorithms. Finally, application is considered to a real transmembrane protein, the Gramicidin A channel protein. The performance of the proposed numerical techniques is tested against a number of factors, including mesh sizes, diffusion coefficient profiles, iterative schemes, ion concentrations, and applied voltages. Numerical predictions are

  3. Measurement of |V{sub cs}| with DELPHI experiment

    SciTech Connect

    Golob, Bostjan

    1998-10-19

    Pair production of charged weak bosons W{sup {+-}} at LEP2 collider can be exploited to measure the absolute value of the V{sub cs} element of Cabbibo-Kobayashi-Maskawa matrix. The value can be most accurately extracted from the measured hadronic branching ratio of W{sup {+-}} bosons. An independent method to obtain the |V{sub cs}| value consists of tagging the flavour of primary quarks in jets, produced in W{sup {+-}} decays. Using both methods on the data collected with DELPHI experiment during 1996 and 1997 runs, we obtained |V{sub cs}|=0.99{+-}0.06(stat.){+-}0.04(syst.). Combined result of |V{sub cs}| measurements with four LEP experiments enables a test of CKM matrix unitarity.

  4. Thirsk during CHeCS medical emergency training

    NASA Image and Video Library

    2009-07-02

    ISS020-E-016866 (2 July 2009) --- Canadian Space Agency astronaut Robert Thirsk, Expedition 20 flight engineer, participates in Crew Health Care Systems (CHeCS) medical emergency training in the Destiny laboratory of the International Space Station.

  5. CS in nearby galaxies: Distribution, kinematics, and multilevel studies

    NASA Technical Reports Server (NTRS)

    Mauersberger, R.; Henkel, Christian

    1990-01-01

    As a result of observations at the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-m telescope, maps of the distribution of the J = 2-1 transition of CS toward the galaxies IC 342 and NGC 253 are presented. The distribution of the CS emission from NGC 253 is consistent with the CO 1-0 line. The distribution of the CS emission from IC 342, however, resembles more that seen in the CO 3-2 line. For the first time, the detection of the isotopic substitution C-34S is reported toward an external galaxy: The C-34S 2-1 line has been detected toward NGC 253 and M 82 and the C-34S line has been detected tentatively toward M 82. Also for the first time, extragalactic CS has been observed in the 3-2 (toward NGC 253, IC 342 and M 82) and 5-4 (NGC 253 and IC 342) transitions.

  6. Photoassociation spectroscopy of ultracold highly excited NaCs molecules

    NASA Astrophysics Data System (ADS)

    Jayaseelan, Maitreyi; Haruza, Marek; Bigelow, Nicholas

    2013-05-01

    We report on our spectroscopic investigations of translationally ultracold NaCs molecules. Photoassociation from laser cooled mixtures of ground state sodium and excited cesium atoms creates molecules in excited states detuned from the Na(3s) + Cs(6d) dissociation asymptote. This is an as yet unexplored asymptote for molecule formation. We infer properties of the scattering wave from the PA spectra, and investigate the populated ground states using photoionization and depletion spectroscopy.

  7. Surface adsorption of Cs137 ions on quartz crystals

    USGS Publications Warehouse

    Antkiw, Stephen; Waesche, H.; Senftle, F.

    1954-01-01

    Adsorption tests were made on four large synthetic and three natural quartz crystals to see if surface defects might be detected by subsequent autoradiography techniques. The adsorbent used was radioactive Cs137 in a solution of Cs 137Cl. Natural quartz crystals adsorbed more cesium than the synthetic crystals. Certain surface defects were made evident by this method, but twinning features could not be detected.

  8. /sup 137/Cs radioactive dating of Lake Ontario sediment cores

    SciTech Connect

    Ward, T.E.; Breeden, J.; Komisarcik, K.; Porter, R.; Czuczwa, J.; Kaminski, R.; McVeety, B.D.

    1987-12-01

    The distribution of /sup 137/Cs in sediment cores from Lake Ontario provides estimates of the sediment accumulation rates. Geochronology with /sup 210/Pb dating and distribution of Ambrosia (ragweed) pollen compare well with /sup 137/Cs dating. These methods can determine with precision, changes in sedimentation occurring over the past 100 years or so. Typical sedimentation rates of 0.18-0.36 cm/yr were measured. 16 refs., 3 figs., 2 tabs.

  9. Microbial cleavage of organic C-S bonds

    DOEpatents

    Kilbane, J.J. II.

    1994-10-25

    A microbial process is described for selective cleavage of organic C-S bonds which may be used for reducing the sulfur content of sulfur-containing organic carbonaceous materials. Microorganisms of Rhodococcus rhodochrous and Bacillus sphaericus have been found which have the ability of selective cleavage of organic C-S bonds. Particularly preferred microorganisms are Rhodococcus rhodochrous strain ATCC 53968 and Bacillus sphaericus strain ATCC 53969 and their derivatives.

  10. Microbial cleavage of organic C-S bonds

    DOEpatents

    Kilbane, II, John J.

    1994-01-01

    A microbial process for selective cleavage of organic C--S bonds which may be used for reducing the sulfur content of sulfur-containing organic carbonaceous materials, Microorganisms of Rhodococcus rhodochrous and Bacillus sphaericus have been found which have the ability of selective cleavage of organic C--S bonds. Particularly preferred microorganisms are Rhodococcus rhodochrous strain ATCC 53968 and Bacillus sphaericus strain ATCC 53969 and their derivatives.

  11. Measurement of dissolved Cs-137 in stream water, soil water and groundwater at Headwater Forested Catchment in Fukushima after Fukushima Dai-ichi Nuclear Power Plant Accident

    NASA Astrophysics Data System (ADS)

    Iwagami, Sho; Tsujimura, Maki; Onda, Yuichi; Sakakibara, Koichi; Konuma, Ryohei; Sato, Yutaro

    2016-04-01

    Radiocesium migration from headwater forested catchment is important perception as output from the forest which is also input to the subsequent various land use and downstream rivers after Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. In this study, dissolved Cs-137 concentration of stream water, soil water and groundwater were measured. Observations were conducted at headwater catchment in Yamakiya district, located 35 km northwest of FDNPP from April 2014 to November 2015. Stream water discharge was monitored and stream water samples were taken at main channel and sub channel. Stream water discharge was monitored by combination of parshallflume and v-notch weir. Stream water was sampled manually at steady state condition in 3-4 month interval and also intense few hours interval sampling were conducted during rainfall events using automated water sampler. Around the sub channel, it is found that there is a regularly saturated area at the bottom of the slope, temporary saturated area which saturate during the rainy season in summer and regularly dry area. 6 interval cameras were installed to monitor the changing situation of saturated area. Suction lysimeters were installed at three areas (regularly saturated area, temporary saturated area and dry area) for sampling soil water in depth of 0.1 m and 0.3 m. Boreholes were installed at three points along the sub channel. Three boreholes with depth of 3 m, 5 m and 10 m were installed at temporary saturated area, 20 m upstream of sub channel weir. Another three boreholes with depth of 3 m, 5 m and 10 m were installed at dry area, 40 m upstream of sub channel weir. And a borehole with depth of 20 m was installed at ridge of sub catchment, 52 m upstream of sub channel weir. Groundwater was sampled by electrically powered pump and groundwater level was monitored. Also suction-free lysimeter was installed at temporary saturated area for sampling the near surface subsurface water. Soil water samples were collected

  12. The Transfer of Dissolved Cs-137 from Soil to Plants

    SciTech Connect

    Prorok, V.V.; Melnichenko, L.Yu.; Mason, C.F.V.; Ageyev, V.A.; Ostashko, V.V.

    2006-07-01

    Rapidly maturing plants were grown simultaneously at the same experimental sites under natural conditions at the Chernobyl Exclusion Zone. Roots of the plants were side by side in the soil. During two seasons we selected samples of the plants and of the soils several times every season. Content of Cs-137 in the plant and in the soil solution extracted from the samples of soils was measured. Results of measurements of the samples show that, for the experimental site, Cs-137 content in the plant varies with date of the sample selection. The plant:soil solution Cs-137 concentration ratio depends strongly on the date of selection and also on the type of soil. After analysis of the data we conclude that Cs-137 plant uptake is approximately proportional to the content of dissolved Cs-137 in the soil per unit of volume, and the plant:soil solution Cs-137 concentration ratio for the soil is approximately proportional to the soil moisture. (authors)

  13. Cs + ADC in Rat Brain Decreases Markedly at Death

    PubMed Central

    Goodman, James A.; Ackerman, Joseph J.H.; Neil, Jeffrey J.

    2010-01-01

    Spectroscopic resolution of intracellular and extracellular compartments can be used to probe the kinetic environment of those spaces and the compartment-specific changes that occur following injury. This is important for understanding the biophysical mechanisms that underlie the remarkable diffusion-weighted MRI contrast of injured central nervous system (CNS) tissue. Cesium-133 is a physiologic analog of potassium that is actively taken up by cells and resides primarily in the intracellular space. The 133Cs+ signal can, thus, be exploited to probe the kinetic environment of the intracellular space. Two principal 133Cs+ resonances were observed at 11.74 T. These resonances arise separately from 133Cs+ in brain and temporalis muscle. The apparent diffusion coefficient (ADC) of Cs+ in brain decreased from 1.0 ± 0.2 μm2/ms in healthy tissue to 0.24 ± 0.04 μm2/ms following global ischemia (average ADC ± average uncertainty), while there was no significant change in the ADC of Cs+ in temporalis muscle after injury. This finding underscores the tissue-specific nature of the decrease in ADC that accompanies brain injury. Further, as the Cs+ ADC should reflect water ADC in the intracellular space, these results strongly support the hypothesis that the decrease in water ADC associated with CNS injury arises largely from kinetic changes taking place in the intracellular space. PMID:18098293

  14. Dielectric breakdown during Cs+ sputtering of polyvinyl chloride

    NASA Astrophysics Data System (ADS)

    Wahoud, F.; Guillot, J.; Audinot, J. N.; Bertrand, P.; Delcorte, A.; Migeon, H. N.

    2014-02-01

    Thin films of insulating polymers are sometimes analyzed by secondary ion mass spectrometry (SIMS) or by X-ray photoelectron spectroscopy (XPS) without the use of an electron gun. In this work, both SIMS and XPS have been used to study the chemical and structural modifications due to the charge effect during Cs+ sputtering of a thin film of polyvinyl chloride (PVC). The kinetic energy distribution study shows that at a small primary fluence ˜1015 Cs+ ions/cm2, the dielectric breakdown voltage of the PVC film is reached, i.e. the minimum voltage that causes a portion of an insulator to become electrically conductive. XPS study indicates that the conducting phase created in the PVC film after energetic Cs+ bombardment consists of graphitized carbon and metallic cesium clusters. After the dielectric breakdown of the film, the positive charge, previously accumulated on the surface, is neutralized through the conductive regions, which are created in the insulating film. During Cs+ sputtering of a PVC film, the chemical structure of the analyzed surface is completely modified and some ionic bonds such as CsC and CsCl are also created.

  15. From sneeze to wheeze: what we know about rhinovirus Cs.

    PubMed

    Miller, E Kathryn; Mackay, Ian M

    2013-08-01

    While the discovery of HRV-Cs is recent, there are no indications that they are new viruses, or that they are emerging in real-time. Genetically, HRV-Cs are most closely related to the members of HRV-A and HRV-B but even a small genetic difference can impart encompass significant changes to their clinical impact, complicated by a diverse human background of prior virus exposure and underlying host immune and disease variability. It is well known that HRVs are a major trigger of asthma exacerbations and HRV-Cs are now under investigation for their potential involvement in asthma inception. The newly described HRV-Cs account for a large proportion of HRV-related illness, including common colds and wheezing exacerbations. HRV-Cs are genetically diverse and appear to circulate with seasonal variation, exchanging dominance with HRV-A. Whether HRV-Cs are consistently more pathogenic or "asthmagenic" is unproven. Antigenic diversity complicates passive and active prophylactic interventions (i.e. antibodies or vaccines), so further identification and characterisation of individual types (and their neutralising antigens) is likely to inform future preventive strategies. In the meantime, new antivirals should benefit groups at risk of the most severe disease.

  16. Triplet-singlet conversion in ultracold Cs{sub 2} and production of ground-state molecules

    SciTech Connect

    Bouloufa, Nadia; Aymar, Mireille; Dulieu, Olivier; Pichler, Marin

    2011-02-15

    We propose a process to convert ultracold metastable Cs{sub 2} molecules in their lowest triplet state into (singlet) ground-state molecules in their lowest vibrational levels. Molecules are first pumped into an excited triplet state, and the triplet-singlet conversion is facilitated by a two-step spontaneous decay through the coupled A {sup 1{Sigma}}{sub u}{sup +}-b {sup 3{Pi}}{sub u} states. Using spectroscopic data and accurate quantum chemistry calculations for Cs{sub 2} potential curves and transition dipole moments, we show that this process competes favorably with the single-photon decay back to the lowest triplet state. In addition, we demonstrate that this conversion process represents a loss channel for vibrational cooling of metastable triplet molecules, preventing an efficient optical pumping cycle down to low vibrational levels.

  17. Syntheses, structures, and optical properties of the indium/germanium selenides Cs{sub 4}In{sub 8}GeSe{sub 16}, CsInSe{sub 2}, and CsInGeSe{sub 4}

    SciTech Connect

    Ward, Matthew D.; Pozzi, Eric A.; Van Duyne, Richard P.; Ibers, James A.

    2014-04-01

    The three solid-state indium/germanium selenides Cs{sub 4}In{sub 8}GeSe{sub 16}, CsInSe{sub 2}, and CsInGeSe{sub 4} have been synthesized at 1173 K. The structure of Cs{sub 4}In{sub 8}GeSe{sub 16} is a three-dimensional framework whereas those of CsInSe{sub 2} and CsInGeSe{sub 4} comprise sheets separated by Cs cations. Both Cs{sub 4}In{sub 8}GeSe{sub 16} and CsInGeSe{sub 4} display In/Ge disorder. From optical absorption measurements these compounds have band gaps of 2.20 and 2.32 eV, respectively. All three compounds are charge balanced. - Graphical abstract: Structure of Cs{sub 4}In{sub 8}GeSe{sub 16}. - Highlights: • The solid-state In/Ge selenides Cs{sub 4}In{sub 8}GeSe{sub 16}, CsInSe{sub 2}, and CsInGeSe{sub 4} have been synthesized. • Both Cs{sub 4}In{sub 8}GeSe{sub 16} and CsInGeSe{sub 4} display In/Ge disorder. • Cs{sub 4}In{sub 8}GeSe{sub 16} and CsInGeSe{sub 4} have band gaps of 2.20 eV and 2.32 eV, respectively.

  18. Syntheses, crystal structures, and optical properties of CsBa5Ti2Se9Cl and CsBa2Cl5

    NASA Astrophysics Data System (ADS)

    Mesbah, Adel; Prakash, Jai; Malliakas, Christos D.; Lebègue, Sébastien; Badawi, Michael; Ibers, James A.

    2017-09-01

    The mixed-cation compounds CsBa5Ti2Se9Cl and CsBa2Cl5 were synthesized in the same solid-state reaction at 1173 K. CsBa5Ti2Se9Cl adopts the Cs3CoCl5 structure type in the tetragonal crystal system whereas CsBa2Cl5 crystallizes in the PbU2Se5 structure type in the monoclinic crystal system. The CsBa5Ti2Se9Cl structure displays both Cs/Ba and Se/Cl disorder. From optical absorption measurements CsBa5Ti2Se9Cl is an indirect wide-gap semiconductor. From theoretical calculations CsBa2Cl5 has a large band gap of 6.4 eV.

  19. The distribution of (137)Cs, K, Rb and Cs in plants in a Sphagnum-dominated peatland in eastern central Sweden.

    PubMed

    Vinichuk, M; Johanson, K J; Rydin, H; Rosén, K

    2010-02-01

    We record the distribution of (137)Cs, K, Rb and Cs within individual Sphagnum plants (down to 20cm depth) as well as (137)Cs in vascular plants growing on a peatland in eastern central Sweden. In Calluna vulgaris(137)Cs was mainly located within the green parts, whereas Andromeda polifolia, Eriophorum vaginatum and Vaccinium oxycoccos showed higher (137)Cs activity in roots. Carex rostrata and Menyanthes trifoliata showed variable distribution of (137)Cs within the plants. The patterns of (137)Cs activity concentration distribution as well as K, Rb and Cs concentrations within individual Sphagnum plants were rather similar and were usually highest in the capitula and/or in the subapical segments and lowest in the lower dead segments, which suggests continuous relocation of those elements to the actively growing apical part. The (137)Cs and K showed relatively weak correlations, especially in capitula and living green segments (0-10cm) of the plant (r=0.50). The strongest correlations were revealed between (137)Cs and Rb (r=0.89), and between (137)Cs and stable Cs (r=0.84). This suggests similarities between (137)Cs and Rb in uptake and relocation within the Sphagnum, but that (137)Cs differs from K.

  20. Properties of CsI, CsBr and GaAs thin films grown by pulsed laser deposition

    SciTech Connect

    Brendel, V M; Garnov, S V; Yagafarov, T F; Iskhakova, L D; Ermakov, R P

    2014-09-30

    CsI, CsBr and GaAs thin films have been grown by pulsed laser deposition on glass substrates. The morphology and structure of the films have been studied using X-ray diffraction and scanning electron microscopy. The CsI and CsBr films were identical in stoichiometry to the respective targets and had a polycrystalline structure. Increasing the substrate temperature led to an increase in the density of the films. All the GaAs films differed in stoichiometry from the target. An explanation was proposed for this fact. The present results demonstrate that, when the congruent transport condition is not fulfilled, films identical in stoichiometry to targets can be grown by pulsed laser deposition in the case of materials with a low melting point and thermal conductivity. (interaction of laser radiation with matter)

  1. CsCl Separation From a LiCl-CsCl Mixture by Using a Crystallization Approach

    SciTech Connect

    Jong-Hyeon, Lee; Gyu-Hwan, Oh; Han-Soo, Lee; Sung-Bin, Park; Yoon-Sang, Lee; In-Tae, Kim; Eung-Ho, Kim; Seong-Won, Park

    2008-07-01

    Separation of CsCl and SrCl{sub 2} from LiCl was carried out by using a noble separation technology, the Czochralski crystallization method. It was experimentally confirmed that Cs as well as Sr could be simultaneously separated from a LiCl molten salt by the suggested crystallization process without any kind of additive or adsorption media. The concentrations of Cs and Sr in the LiCl were decreased from 1.53 wt% and 4.18 wt% in the initial salt to a minimum of 114 ppm and 135 ppm in the grown LiCl crystal respectively. The separation mechanism of Cs and Sr is described by the solubility difference of the solutes between the molten and the solid states. It is expected that the total amount of salt waste could be drastically decreased, because most of the LiCl could be recovered for recycling to the electroreduction process. (authors)

  2. Safety and immunogenicity of the malaria candidate vaccines FP9 CS and MVA CS in adult Gambian men.

    PubMed

    Imoukhuede, E B; Berthoud, T; Milligan, P; Bojang, K; Ismaili, J; Keating, S; Nwakanma, D; Keita, S; Njie, F; Sowe, M; Todryk, S; Laidlaw, S M; Skinner, M A; Lang, T; Gilbert, S; Greenwood, B M; Hill, A V S

    2006-10-30

    We assessed the safety and immunogenicity of prime-boost vectors encoding the Plasmodium falciparum circumsporozoite (CS) protein expressed either in the attenuated fowl-pox virus (FP9) or modified vaccinia virus Ankara (MVA). Thirty-two adult Gambians in groups of four to eight received one, two or three doses of FP9 CS and/or MVA CS. No serious adverse event was observed following vaccination. The most immunogenic regimen was two doses of FP9 followed by a single dose of MVA 4 weeks later (an average of 1000 IFN-gamma spot forming units/million PBMCs). This level of effector T-cell responses appears higher than that seen in previously reported studies of CS-based candidate malaria vaccines.

  3. Eukaryotic mechanosensitive channels.

    PubMed

    Arnadóttir, Jóhanna; Chalfie, Martin

    2010-01-01

    Mechanosensitive ion channels are gated directly by physical stimuli and transduce these stimuli into electrical signals. Several criteria must apply for a channel to be considered mechanically gated. Mechanosensitive channels from bacterial systems have met these criteria, but few eukaryotic channels have been confirmed by the same standards. Recent work has suggested or confirmed that diverse types of channels, including TRP channels, K(2P) channels, MscS-like proteins, and DEG/ENaC channels, are mechanically gated. Several studies point to the importance of the plasma membrane for channel gating, but intracellular and/or extracellular structures may also be required.

  4. The third-generation turbocharged engine for the Audi 5000 CS and 5000 CS Quattro

    SciTech Connect

    Stock, D.

    1986-01-01

    In September 1985 the new Audi 5000 CS Quattro was introduced to the American market. This luxurious high performance touring sedan has been equipped with a more advanced turbocharged engine with intercooler and electronic engine management giving improved performance, excellent torque, faster response and better fuel economy. The basic engine is the tried-and-tested Audi 5-cylinder unit. The turbocharged engine's ancillary systems, the electronic ignition control and fuel injection have all been newly developed, carefully optimized and well matched in the special demands of a turbocharged engine. The ignition system controls the engine and fuel injection and delivers analog and digital signals to the car's instrument panel display. The system also has an integrated self-diagnostic function.

  5. Update global budget of 134Cs and 137Cs derived from Fukushima NPP1 accident

    NASA Astrophysics Data System (ADS)

    Aoyama, Michio; Tsumune, Daisuke; Tsubono, Takaki; Misuimi, Kazuhiro; Inomata, Yayoi; Kumamoto, Yuichiro; Hamajima, Yasunori

    2014-05-01

    134Cs and 137Cs, hereafter radiocaesium, were released from the Fukushima NPP1 accident on March 2011 and to evaluate total amount of released radiocaesium is essential to assess impacts of released radiocaesium to iur environment. We however still have wide range of reports about total amount of released radiocaesium after the accident till today. Released radiocasium were injected in the North Pacific Ocean by two major pathways, direct discharge from the accident site and atmospheric pathway to the ocean while there was only atmospheric deposition on land. We summarize estimations of budget of radiocasium based on both observations and model studies for land deposition, deposition on the North Pacific Ocean and inventory in the North Pacific Ocean, an inventory of sediment close to the site. The major portion of released radiocaesium can be believed to be deposited mainly in the western North Pacific Ocean because deposition density at west coast of US continent was only at an order of 100 Bq m-2 while that at close to accident site was MBq m-2. An inventory in the North Pacific Ocean by some of the authors was 15-18 PBq on April-May 2011 by model-observation comparison and that in the mode water in the western North Pacific Ocean based on the observations on January- February 2012 was 6 PBq. The second portion might be on main land Japan and it is rather easy to evaluate total amount of deposited radiocaesium because there are good observation both by direct sampling of soil and aerial survey. A result of integration for land deposition was about 2.5 PBq. The third portion is in the sediment and an inventory in the sediment by observation showed 42 TBq at close to the site while the total inventory of 137Cs in sediments off the Fukushima coast is thus estimated to be the order of 0.1 PBq by a model study by some of the authors. Estimations of direct discharge from the site also still varied much from 3 PBq to 27 PBq. Two larger estimations did the backward

  6. Single Na+ channels activated by veratridine and batrachotoxin

    PubMed Central

    1987-01-01

    Voltage-sensitive Na+ channels from rat skeletal muscle plasma membrane vesicles were inserted into planar lipid bilayers in the presence of either of the alkaloid toxins veratridine (VT) or batrachotoxin (BTX). Both of these toxins are known to cause persistent activation of Na+ channels. With BTX as the channel activator, single channels remain open nearly all the time. Channels activated with VT open and close on a time scale of 1-10 s. Increasing the VT concentration enhances the probability of channel opening, primarily by increasing the rate constant of opening. The kinetics and voltage dependence of channel block by 21-sulfo-11-alpha-hydroxysaxitoxin are identical for VT and BTX, as is the ionic selectivity sequence determined by bi-ionic reversal potential (Na+ approximately Li+ greater than K+ greater than Rb+ greater than Cs+). However, there are striking quantitative differences in open channel conduction for channels in the presence of the two activators. Under symmetrical solution conditions, the single channel conductance for Na+ is about twice as high with BTX as with VT. Furthermore, the symmetrical solution single channel conductances show a different selectivity for BTX (Na+ greater than Li+ greater than K+) than for VT (Na+ greater than K+ greater than Li+). Open channel current-voltage curves in symmetrical Na+ and Li+ are roughly linear, while those in symmetrical K+ are inwardly rectifying. Na+ currents are blocked asymmetrically by K+ with both BTX and VT, but the voltage dependence of K+ block is stronger with BTX than with VT. The results show that the alkaloid neurotoxins not only alter the gating process of the Na+ channel, but also affect the structure of the open channel. We further conclude that the rate-determining step for conduction by Na+ does not occur at the channel's "selectivity filter," where poorly permeating ions like K+ are excluded. PMID:2435846

  7. Purification and characterization of a novel class IIa bacteriocin, piscicocin CS526, from surimi-associated Carnobacterium piscicola CS526.

    PubMed

    Yamazaki, Koji; Suzuki, Minako; Kawai, Yuji; Inoue, Norio; Montville, Thomas J

    2005-01-01

    The bacteriocin piscicocin CS526 was inactivated by proteolytic enzymes, was stable at 100 degrees C for 30 min, had a pH range of 2 to 8, and was active against Enterococcus, Listeria, Pediococcus, and Leuconostoc. The N-terminal sequence was YGNGL, not the YGNGV consensus motif common in class IIa bacteriocins (alternate residues underlined). The molecular mass of piscicocin CS526, which had a bactericidal mode of action, was approximately 4,430 Da.

  8. Purification and Characterization of a Novel Class IIa Bacteriocin, Piscicocin CS526, from Surimi-Associated Carnobacterium piscicola CS526

    PubMed Central

    Yamazaki, Koji; Suzuki, Minako; Kawai, Yuji; Inoue, Norio; Montville, Thomas J.

    2005-01-01

    The bacteriocin piscicocin CS526 was inactivated by proteolytic enzymes, was stable at 100°C for 30 min, had a pH range of 2 to 8, and was active against Enterococcus, Listeria, Pediococcus, and Leuconostoc. The N-terminal sequence was YGNGL, not the YGNGV consensus motif common in class IIa bacteriocins (alternate residues underlined). The molecular mass of piscicocin CS526, which had a bactericidal mode of action, was ∼4,430 Da. PMID:15640235

  9. Correlations between potassium, rubidium and cesium ((133)Cs and (137)Cs) in sporocarps of Suillus variegatus in a Swedish boreal forest.

    PubMed

    Vinichuk, M; Rosén, K; Johanson, K J; Dahlberg, A

    2011-04-01

    An analysis of sporocarps of ectomycorrhizal fungi Suillus variegatus assessed whether cesium ((133)Cs and (137)Cs) uptake was correlated with potassium (K) or rubidium (Rb) uptake. The question was whether intraspecific correlations of Rb, K and (133)Cs mass concentrations with (137)Cs activity concentrations in sporocarps were higher within, rather than among, different fungal species, and if genotypic origin of sporocarps within a population affected uptake and correlation. Sporocarps (n = 51) from a Swedish forest population affected by the fallout after the Chernobyl accident were studied. The concentrations were 31.9 ± 6.79 g kg(-1) for K (mean ± SD, dwt), 0.40 ± 0.09 g kg(-1) for Rb, 8.7 ± 4.36 mg kg(-1) for (133)Cs and 63.7 ± 24.2 kBq kg(-1) for (137)Cs. The mass concentrations of (133)Cs correlated with (137)Cs activity concentrations (r = 0.61). There was correlation between both (133)Cs concentrations (r = 0.75) and (137)Cs activity concentrations (r = 0.44) and Rb, but the (137)Cs/(133)Cs isotopic ratio negatively correlated with Rb concentration. Concentrations of K and Rb were weakly correlated (r = 0.51). The (133)Cs mass concentrations, (137)Cs activity concentrations and (137)Cs/(133)Cs isotopic ratios did not correlate with K concentrations. No differences between, within or, among genotypes in S. variegatus were found. This suggested the relationships between K, Rb, (133)Cs and (137)Cs in sporocarps of S. variegatus is similar to other fungal species. Copyright © 2011 Elsevier Ltd. All rights reserved.

  10. Procedures for precise measurements of (135)Cs/(137)Cs atom ratios in environmental samples at extreme dynamic ranges and ultra-trace levels by thermal ionization mass spectrometry.

    PubMed

    Dunne, James A; Richards, David A; Chen, Hsin-Wei

    2017-11-01

    Determination of (135)Cs/(137)Cs atom ratios has the potential to be a powerful tool for nuclear forensics and monitoring environmental processes. We present optimized chemical separation techniques and thermal ionization mass spectrometry (TIMS) protocols to obtain precise (135)Cs/(137)Cs atom ratios for a range of environmental sample types. We use a combination of double AMP-PAN separation and Sr-spec resin column purification to yield excellent separation from the alkali metals (Rb separation factor > 600), which normally suppress ionization of Cs. A range of emission activators for the ionization of Cs were evaluated and glucose solution yielded the optimal combination of a stable Cs(+) beam, minimal low-temperature polyatomic interferences and improved ionization efficiency. Mass-spectrometric determination of low abundance (135)Cs and (137)Cs is compromised by the presence of a very large (133)Cs(+) beam, which may be scattered and cause significant spectral interferences. These are explored using multi-static Faraday cup - ion counter methods and a range of energy filter settings. The method is evaluated using environmental samples and standards from regions affected by fallout from Chernobyl (IAEA-330) and Fukushima nuclear disasters. Where the intensity of (133)Cs(+) is large relative to (135)Cs(+) and (137)Cs(+) (< 30cps), minor polyatomic interferences need to be considered. In the absence of a standard with (135, 137)Cs/(133)Cs < 1 × 10(-8), we explored the reproducibility of (135)Cs/(137)Cs atom ratios at these high dynamic ranges and extremely low abundance ((137)Cs ≈ 12 fg g(-1)) for sediments from an estuarine setting in SW England, UK. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

  11. The interaction of H 2S and S 2 with Cs and {Cs}/{ZnO} surfaces: photoemission and molecular-orbital studies

    NASA Astrophysics Data System (ADS)

    Rodriguez, JoséA.; Jirsak, Tomas; Chaturvedi, Sanjay; Hrbek, Jan

    1998-06-01

    the surface chemistry of H 2S and S 2 on metallic Cs and {Cs}/{ZnO} surfaces has been investigated using high-resolution synchrotron based photoemission and ab initio self-consistent-field calculations. Metallic Cs is very reactive toward H 2S and S 2 at temperatures between 100 and 300 K. Pure cesium decomposes H 2S to form Cs 2S compounds. After dosing S 2 to Cs, one obtains Cs 2S and Cs 2S 2 m ( m ≥1 ) compounds. The formation of cesium sulfides induces an increase in the intensity of the Cs 3d levels and large negative shifts (0.8-1.3 eV) in their peak positions. Cesium atoms supported on ZnO are in an ionic state (Cs δ+), but they are still able to interact with H 2S and S 2 more strongly than Zn and O sites of the oxide support. A correlation is found between the electron density on the Cs adatoms and their reactivity: Cs atoms supported on Zn sites of the oxide bond S-containing species (H 2S, HS, S 2, S) are stronger than Cs atoms supported on O sites. H 2S dissociates into HS and atomic S upon adsorption on {Cs}/{ZnO} surfaces at 300 K. The HS species decompose at temperatures below 450 K leaving S atoms that are bonded to Cs and Zn. The adsorption of S 2 on {Cs}/{ZnO} surfaces at 300 K leads to the formation of Cs 2S and Cs 2S 2 m ( m ≥ 1) compounds. Cs↔S interactions increase the thermal stability of cesium on the ZnO surface. The poisoning of Cs/Cu/ZnO catalysts is discussed in light of these results and those previously reported for the S 2/Cu/ZnO system.

  12. Role of excited state photoionization in the 852.1 nm Cs laser pumped by Cs-Ar photoassociation

    SciTech Connect

    Hewitt, J. D.; Houlahan, T. J. Jr.; Eden, J. G.; Gallagher, J. E.; Perram, G. P.; Carroll, D. L.; Palla, A. D.; Verdeyen, J. T.

    2013-03-18

    Photoionization of Cs (6p {sup 2}P{sub 3/2}) atoms during the operation of a Cs D{sub 2} line (852.1 nm: 6p {sup 2}P{sub 3/2}{yields}6s {sup 2}S{sub 1/2}) laser, pumped by free{yields}free transitions of thermal Cs-Ar ground state pairs, has been investigated experimentally and computationally. Photoexcitation of Cs vapor/Ar mixtures through the blue satellite of the D{sub 2} transition (peaking at 836.7 nm) selectively populates the {sup 2}P{sub 3/2} upper laser level by the dissociation of the CsAr excited complex. Comparison of laser output energy data, for instantaneous pump powers up to 3 MW, with the predictions of a numerical model sets an upper bound of 8 Multiplication-Sign 10{sup -26} cm{sup 4} W{sup -1} on the Cs (6p {sup 2}P{sub 3/2}) two photon ionization cross-section at 836.7 nm which corresponds to a single photon cross-section of 2.4 Multiplication-Sign 10{sup -19} cm{sup 2} for a peak pump intensity of 3 MW cm{sup -2}.

  13. Proficiency testing with uncertainty evaluation for measuring activities per unit mass of (134)Cs and (137)Cs in brown rice in Japan.

    PubMed

    Furukawa, R; Unno, Y; Miura, T; Yunoki, A; Hachinohe, M; Hamamatsu, S; Itadzu, H; Mizui, M

    2017-08-01

    In Japan, we conducted proficiency testing of activity measurement by using high-purity germanium detectors for (134)Cs and (137)Cs in brown rice grains. Among 176 reported results, 86 % (for (134)Cs) and 93 % (for (137)Cs) of the results satisfied |En| ≦ 1. However, 58 reports for (134)Cs and 51 reports for (137)Cs had some failures in their evaluations of uncertainties. The proficiency testing was effective to improve the ability of uncertainty evaluation. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. Replacement of 137Cs irradiators with x-ray irradiators.

    PubMed

    Dodd, Brian; Vetter, Richard J

    2009-02-01

    Self-shielded 137Cs irradiators have been used for many years to irradiate blood products to prevent graft vs. host disease and to irradiate cells and small animals in research. A report by the National Academy of Sciences recommends that careful consideration be given to replacement of 137Cs irradiators with x-ray irradiators. Several manufacturers and users of x-ray irradiators were contacted to determine costs of replacing and maintaining 137Cs irradiators with x-ray units and to assess users' experience with x-ray irradiators. Purchase costs of x-ray units are similar to 137Cs irradiators, but maintenance costs are significantly higher if annual service contracts are used. Performance of the two irradiator types appears to be equivalent, but in some cases x-ray irradiations may need to be performed in multiple configurations to achieve adequate uniformity in dose. No literature reports were found that evaluated the biological effectiveness of x rays vs. 137Cs gamma rays; therefore, a careful study should be conducted to determine the biological effectiveness of x rays vs. 137Cs gamma rays for biological responses relevant to transfusion medicine and immunological research. Throughput may be problematic for large transfusion medicine programs, and back-up plans may be necessary in case the x-ray unit needs to be taken out of service for extended maintenance. Disposition of a 137Cs irradiator will add to the cost of replacement with an x-ray unit, but disposal may be possible through the U.S. Department of Energy's Off-Site Source Recovery Program.

  15. High-temperature, high-pressure hydrothermal synthesis, crystal structure, and solid-state NMR spectroscopy of Cs2(UO2)(Si2O6) and variable-temperature powder X-ray diffraction study of the hydrate phase Cs2(UO2)(Si2O6) x 0.5H2O.

    PubMed

    Chen, Chih-Shan; Chiang, Ray-Kuang; Kao, Hsien-Ming; Lii, Kwang-Hwa

    2005-05-30

    A new uranium(VI) silicate, Cs2(UO2)(Si2O6), has been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy. It crystallizes in the orthorhombic space group Ibca (No. 73) with a = 15.137(1) A, b = 15.295(1) A, c = 16.401(1) A, and Z = 16. Its structure consists of corrugated achter single chains of silicate tetrahedra extending along the c axis linked together via corner-sharing by UO6 tetragonal bipyramids to form a 3-D framework which delimits 8- and 6-ring channels. The Cs+ cations are located in the channels or at sites between channels. The 29Si and 133Cs MAS NMR spectra are consistent with the crystal structure as determined from X-ray diffraction, and the resonances in the spectra are assigned. Variable-temperature in situ powder X-ray diffraction study of the hydrate Cs2(UO2)(Si2O6) x 0.5H2O indicates that the framework structure is stable up to 800 degrees C and transforms to the structure of the title compound at 900 degrees C. A comparison of related uranyl silicate structures is made.

  16. Low temperature phase transition and crystal structure of CsMgPO4

    NASA Astrophysics Data System (ADS)

    Orlova, Maria; Khainakov, Sergey; Michailov, Dmitriy; Perfler, Lukas; Langes, Christoph; Kahlenberg, Volker; Orlova, Albina

    2015-01-01

    CsMgPO4 doped with radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at temperatures close to ambient conditions (~-40 °C) was observed. Information about such kind of structural changes is important in order to understand whether it can cause any problem for medical use of this compound. The phase transition has been investigated in detail using synchrotron powder diffraction, Raman spectroscopy and DFT calculations. The structure undergoes a transformation from an orthorhombic modification, space group Pnma (RT phase) to a monoclinic polymorph, space group P21/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2) Å, b=8.95501(1) Å, c=5.50344(2) Å, β=90.68583(1)°, V=472.198(3) Å3. CsMgPO4 belongs to the group of framework compounds and is made up of strictly alternating MgO4- and PO4-tetrahedra sharing vertices. The cesium counter cations are located in the resulting channel-like cavities. Upon the transformation a combined tilting of the tetrahedra is observed. A comparison with other phase transitions in ABW-type framework compounds is given.

  17. VUV fluorescence following electron-impact dissociative excitation of CS{sub 2}

    SciTech Connect

    Brotton, S. J.; McConkey, J. W.

    2011-01-15

    Electron-impact dissociation of CS{sub 2} has been studied by observation of the atomic spectral emission features in the range 115-170 nm. Absolute photoemission cross sections are presented over the complete wavelength range for an incident electron energy of 100 eV. As an example, the measured cross section of the strong C i emission at 165.7 nm, which is a prominent feature in many solar and other extraterrestrial spectra, is (1.45{+-}0.19)x10{sup -18} cm{sup 2}. Comparison with earlier cross-sectional measurements suggest that these were too high by a factor of more than three. Excitation functions of the dominant C i (156.1 nm) and S i (147.4 nm) emission lines have been measured for electron-impact energies from threshold to 360 eV. From appearance energy measurements in the near-threshold region, likely fragmentation channels are identified which involve both two-fragment breakup and total fragmentation of the parent CS{sub 2}.

  18. Ephedrine QoS: an antidote to slow, congested, bufferless NoCs.

    PubMed

    Fang, Juan; Yao, Zhicheng; Sui, Xiufeng; Bao, Yungang

    2014-01-01

    Datacenters consolidate diverse applications to improve utilization. However when multiple applications are colocated on such platforms, contention for shared resources like networks-on-chip (NoCs) can degrade the performance of latency-critical online services (high-priority applications). Recently proposed bufferless NoCs (Nychis et al.) have the advantages of requiring less area and power, but they pose challenges in quality-of-service (QoS) support, which usually relies on buffer-based virtual channels (VCs). We propose QBLESS, a QoS-aware bufferless NoC scheme for datacenters. QBLESS consists of two components: a routing mechanism (QBLESS-R) that can substantially reduce flit deflection for high-priority applications and a congestion-control mechanism (QBLESS-CC) that guarantees performance for high-priority applications and improves overall system throughput. We use trace-driven simulation to model a 64-core system, finding that, when compared to BLESS, a previous state-of-the-art bufferless NoC design, QBLESS, improves performance of high-priority applications by an average of 33.2% and reduces network-hops by an average of 42.8%.

  19. Ephedrine QoS: An Antidote to Slow, Congested, Bufferless NoCs

    PubMed Central

    Fang, Juan; Yao, Zhicheng; Sui, Xiufeng; Bao, Yungang

    2014-01-01

    Datacenters consolidate diverse applications to improve utilization. However when multiple applications are colocated on such platforms, contention for shared resources like networks-on-chip (NoCs) can degrade the performance of latency-critical online services (high-priority applications). Recently proposed bufferless NoCs (Nychis et al.) have the advantages of requiring less area and power, but they pose challenges in quality-of-service (QoS) support, which usually relies on buffer-based virtual channels (VCs). We propose QBLESS, a QoS-aware bufferless NoC scheme for datacenters. QBLESS consists of two components: a routing mechanism (QBLESS-R) that can substantially reduce flit deflection for high-priority applications and a congestion-control mechanism (QBLESS-CC) that guarantees performance for high-priority applications and improves overall system throughput. We use trace-driven simulation to model a 64-core system, finding that, when compared to BLESS, a previous state-of-the-art bufferless NoC design, QBLESS, improves performance of high-priority applications by an average of 33.2% and reduces network-hops by an average of 42.8%. PMID:25250386

  20. Resonance-mode electrochemical impedance measurements of silicon dioxide supported lipid bilayer formation and ion channel mediated charge transport.

    PubMed

    Lundgren, Anders; Hedlund, Julia; Andersson, Olof; Brändén, Magnus; Kunze, Angelika; Elwing, Hans; Höök, Fredrik

    2011-10-15

    A single-chip electrochemical method based on impedance measurements in resonance mode has been employed to study lipid monolayer and bilayer formation on hydrophobic alkanethiolate and SiO(2) substrates, respectively. The processes were monitored by temporally resolving changes in interfacial capacitance and resistance, revealing information about the rate of formation, coverage, and defect density (quality) of the layers at saturation. The resonance-based impedance measurements were shown to reveal significant differences in the layer formation process of bilayers made from (i) positively charged lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine (POEPC), (ii) neutral lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) on SiO(2), and (iii) monolayers made from POEPC on hydrophobic alkanethiolate substrates. The observed responses were represented with an equivalent circuit, suggesting that the differences primarily originate from the presence of a conductive aqueous layer between the lipid bilayers and the SiO(2). In addition, by adding the ion channel gramicidin D to bilayers supported on SiO(2), channel-mediated charge transport could be measured with high sensitivity (resolution around 1 pA).

  1. A CsI low-temperature detector for dark matter search

    NASA Astrophysics Data System (ADS)

    Angloher, G.; Dafinei, I.; Gektin, A.; Gironi, L.; Gotti, C.; Gütlein, A.; Hauff, D.; Maino, M.; Nagorny, S. S.; Nisi, S.; Pagnanini, L.; Pattavina, L.; Pessina, G.; Petricca, F.; Pirro, S.; Pröbst, F.; Reindl, F.; Schäffner, K.; Schieck, J.; Seidel, W.; Vasyukov, S.

    2016-11-01

    Cryogenic detectors have a long history of success in the field of rare event searches. In particular scintillating calorimeters are very suitable detectors for this task since two signals are induced by a particle interaction in a scintillating crystal. The thermal signal provides a precise measurement of the deposited energy while the simultaneously measured scintillation light signal yields particle discrimination as the amount of produced scintillation light depends on the nature of the interacting particle. We investigate the calorimetric properties and background rejection capabilities of two large CsI (undoped) crystals (∼122 g each) operated as scintillating calorimeters at milli-Kelvin temperatures. Furthermore, we discuss the feasibility of this detection approach towards a future background-free dark matter experiment based on alkali halide crystals, with active particle discrimination via the two-channel detection.

  2. 30/20 GHz satellite communication experiments using small earth stations in CS project

    NASA Astrophysics Data System (ADS)

    Saruwatari, T.; Uchida, K.; Matsumoto, K.; Iguchi, M.; Ohashi, H.; Isobe, S.

    Design features and the results of preliminary performance tests of small earth terminals (SETs) for the Japanese CS-II 20/30 GHz communications satellites are described. The tests covered 1- and 2-m antennas with 2 W IMPATT transmitters and FET receivers with less than 750 K noise temperature. Delta-M FM SCPC and MCPC data treatment and transmission equipment were used with the vehicle-mounted antennas. Measurements were made of the C/No and bit error rates and the effect of S/N performance on FM transmission. The stations received and transmitted newspaper data for publication and formed links of a computer network. The FM-SCPC link permitted broadcast of 220 channels between a central station and the small antennas. Communication could not be stabilized between small antennas during rainy conditions.

  3. Luminescence and scintillation properties of Tl- and In-doped CsCl crystals

    NASA Astrophysics Data System (ADS)

    Sakai, Takumi; Koshimizu, Masanori; Fujimoto, Yutaka; Nakauchi, Daisuke; Yanagida, Takayuki; Asai, Keisuke

    2017-06-01

    Optical and scintillation properties of CsCl:Tl and CsCl:In single crystals were investigated. Ions Tl+ and In+ were selected as dopants to enhance the light yield of CsCl crystals. Luminescence and scintillation spectra of CsCl:Tl and CsCl:In could be attributed to the relaxed excited state (RES) originating from each dopant ion. The decay-time constants of the fast component had values of 5.4 ns for CsCl:Tl and 2.2 ns for CsCl:In, and can be ascribed to the overlapping of on-center STE and auger-free luminescence (AFL) for CsCl:Tl and only AFL for CsCl:In, respectively. Decay-time constants of the slow component were relatively long (220 ns for CsCl:Tl and 240 ns for CsCl:In), possibly owing to their low energy transfer rate from host to each dopant ion. The light yields of CsCl:1%Tl and CsCl:0.5%Tl were estimated to be 2800 and 2200 photons/MeV, respectively. The light yield of CsCl:0.5%In crystals was estimated to be 2200 photons/MeV. In conclusion, the light yield of pure CsCl (several ten photons/MeV) can be enhanced by doping Tl+ and In+ while maintaining the fast component of the CsCl crystal.

  4. Thiazolidinedione insulin sensitizers alter lipid bilayer properties and voltage-dependent sodium channel function: implications for drug discovery

    PubMed Central

    Herold, Karl F.; Sanford, R. Lea; Greathouse, Denise V.; Hemmings, Hugh C.; Andersen, Olaf S.

    2011-01-01

    The thiazolidinediones (TZDs) are used in the treatment of diabetes mellitus type 2. Their canonical effects are mediated by activation of the peroxisome proliferator–activated receptor γ (PPARγ) transcription factor. In addition to effects mediated by gene activation, the TZDs cause acute, transcription-independent changes in various membrane transport processes, including glucose transport, and they alter the function of a diverse group of membrane proteins, including ion channels. The basis for these off-target effects is unknown, but the TZDs are hydrophobic/amphiphilic and adsorb to the bilayer–water interface, which will alter bilayer properties, meaning that the TZDs may alter membrane protein function by bilayer-mediated mechanisms. We therefore explored whether the TZDs alter lipid bilayer properties sufficiently to be sensed by bilayer-spanning proteins, using gramicidin A (gA) channels as probes. The TZDs altered bilayer elastic properties with potencies that did not correlate with their affinity for PPARγ. At concentrations where they altered gA channel function, they also altered the function of voltage-dependent sodium channels, producing a prepulse-dependent current inhibition and hyperpolarizing shift in the steady-state inactivation curve. The shifts in the inactivation curve produced by the TZDs and other amphiphiles can be superimposed by plotting them as a function of the changes in gA channel lifetimes. The TZDs’ partition coefficients into lipid bilayers were measured using isothermal titration calorimetry. The most potent bilayer modifier, troglitazone, alters bilayer properties at clinically relevant free concentrations; the least potent bilayer modifiers, pioglitazone and rosiglitazone, do not. Unlike other TZDs tested, ciglitazone behaves like a hydrophobic anion and alters the gA monomer–dimer equilibrium by more than one mechanism. Our results provide a possible mechanism for some off-target effects of an important group of

  5. Electron induced surface chemistry at the Cs/sapphire interface

    SciTech Connect

    Zavadil, K.R.; Ing, J.L.

    1996-03-01

    Electron induced etching of sapphire in the presence of Cs has been studied using a variety of surface analytical techniques. We find that this process occurs on both the (0001) and (1{bar 1}02) orientations of sapphire. Monolayer amounts of Al and sub-oxides of Al are thermally desorbed from the surface at temperatures as low as 1000 K when the surface is irradiated with electrons in the presence of Cs. Etching is highly dependent on Cs coverage with the (0001) and (1{bar 1}02) surfaces requiring 2.0{times}10{sup 14} and 3.4{times}10{sup 14} atoms/cm{sup 2} to support etching, respectively. Adsorption profiles demonstrate that these coverages correspond to initial saturation of the surface with Cs. Electron damage of the surface in the absence of Cs also produces desorption of Al and sub-oxides of Al, indicating a possible mechanism for etching. The impact of etching on the surface is to increase the adsorption capacity on the (0001) surface while decreasing both initial adsorption probability and capacity on the (1{bar 1}02) surface. {copyright} {ital 1996 American Institute of Physics.}

  6. Radiation stability of CsBr:Eu needle image plates

    NASA Astrophysics Data System (ADS)

    Batentschuk, M.; Neudert, S.; Weidner, M.; Osvet, A.; Struye, L.; Tahon, J.-P.; Leblans, P.

    2009-10-01

    Needle image plates (NIPs) based on CsBr:Eu are a good alternative to the BaFBr:Eu powder image plates due to their higher sensitivity and improved spatial resolution. The x-ray radiation stability of the NIPs produced by Agfa Gevaert was investigated and it was found that the radiation stability of the optimized NIPs is as high as that of the commercial CsI:Tl single crystals and much higher than reported in literature for the CsBr:Eu NIPs. The dependence of the sensitivity of the NIPs on the accumulated dose was determined for three different types of x-ray irradiation. It is shown that degradation of the sensitivity starts at about 10 Gy and it is the strongest for the most hard x-ray beam. If the energy absorbed by a NIP is taken into account, the degradation does not depend on the hardness of the applied x-ray beam. It is suggested that the main reason for the observed high radiation stability of the CsBr:Eu NIPs is the use of the oxygen-free Eu2+-containing precursor CsEuBr3 for the doping in the manufacturing process.

  7. Radiation stability of CsBr:Eu needle image plates

    SciTech Connect

    Batentschuk, M.; Neudert, S.; Weidner, M.; Osvet, A.; Struye, L.; Tahon, J.-P.; Leblans, P.

    2009-10-15

    Needle image plates (NIPs) based on CsBr:Eu are a good alternative to the BaFBr:Eu powder image plates due to their higher sensitivity and improved spatial resolution. The x-ray radiation stability of the NIPs produced by Agfa Gevaert was investigated and it was found that the radiation stability of the optimized NIPs is as high as that of the commercial CsI:Tl single crystals and much higher than reported in literature for the CsBr:Eu NIPs. The dependence of the sensitivity of the NIPs on the accumulated dose was determined for three different types of x-ray irradiation. It is shown that degradation of the sensitivity starts at about 10 Gy and it is the strongest for the most hard x-ray beam. If the energy absorbed by a NIP is taken into account, the degradation does not depend on the hardness of the applied x-ray beam. It is suggested that the main reason for the observed high radiation stability of the CsBr:Eu NIPs is the use of the oxygen-free Eu{sup 2+}-containing precursor CsEuBr{sub 3} for the doping in the manufacturing process.

  8. Chemistry in circumstellar disks - CS toward HL Tauri

    NASA Technical Reports Server (NTRS)

    Blake, Geoffrey A.; Van Dishoeck, Ewine F.; Sargent, Anneila I.

    1992-01-01

    High spatial and spectral resolution dust continuum and CS line-emission maps of the material immediately surrounding HL Tauri are presented. The 3.06-thermal dust map gives an upper limit to the source size of roughly 200 AU. When combined with previous millimeter continuum measurements, a beta value of 1.2 +/-0.3 is derived along with a disk mass of 0.1 solar mass, in agreement with previous disk radiative transfer models of the IR and submillimeter flux from HL Tau. The low dust emissivity index as compared to particles in the diffuse ISM is best explained by grain growth or composition evolution. The present observations of the CS and CO emission lines forming the molecular cloud surrounding HL Tauri are consistent with the 'canonical' temperatures, densities, and abundances derived in other Taurus cloud cores. In contrast, the CS emission in aperture synthesis maps at 650-AU spatial resolution is most consistent with CS/CO ratios at least 25-50 times lower in the gas immediately surrounding HL Tauri if the CS emission is optically thin. The continuum and spectral line results obtained are strong indicators of conditions thought to be similar to those in the presolar nebula some 4.5 AE ago.

  9. Optimal High-TC Superconductivity in Cs3C60

    NASA Astrophysics Data System (ADS)

    Harshman, Dale; Fiory, Anthony

    The highest superconducting transition temperatures in the (A1-xBx)3C60 superconducting family are seen in the A15 and FCC structural phases of Cs3C60 (optimized under hydrostatic pressure), exhibiting measured values for near-stoichiometric samples of TC0 meas . = 37.8 K and 35.7 K, respectively. It is argued these two Cs-intercalated C60 compounds represent the optimal materials of their respective structures, with superconductivity originating from Coulombic e- h interactions between the C60 molecules, which host the n-type superconductivity, and mediating holes associated with the Cs cations. A variation of the interlayer Coulombic pairing model [Harshman and Fiory, J. Supercond. Nov. Magn. 28 ̲, 2967 (2015), and references therein] is introduced in which TC0 calc . ~ 1 / lζ , where l relates to the mean spacing between interacting charges on surfaces of the C60 molecules, and ζ is the average radial distance between the surface of the C60 molecules and the neighboring Cs cations. For stoichiometric Cs3C60, TC0 calc . = 38.08 K and 35.67 K for the A15 and FCC macrostructures, respectively; the dichotomy is attributable to differences in ζ.

  10. Photoelectron Emission Studies in CsBr at 257 nm

    SciTech Connect

    Maldonado, Juan R.; Liu, Zhi; Sun, Yun; Pianetta, Piero A.; Pease, Fabian W.; /Stanford U., Elect. Eng. Dept. /SLAC, SSRL

    2006-09-28

    CsBr/Cr photocathodes were found [1,2] to meet the requirements of a multi-electron beam lithography system operating with a light energy of 4.8 eV (257nm). The fact that photoemission was observed with a light energy below the reported 7.3 eV band gap for CsBr was not understood. This paper presents experimental results on the presence of intra-band gap absorption sites (IBAS) in CsBr thin film photo electron emitters, and presents a model based on IBAS to explain the observed photoelectron emission behavior at energies below band gap. A fluorescence band centered at 330 nm with a FWHM of about 0.34 eV was observed in CsBr/Cr samples under 257 nm laser illumination which can be attributed to IBAS and agrees well with previously obtained synchrotron photoelectron spectra[1] from the valence band of CsBr films.

  11. CS based confocal microwave imaging algorithm for breast cancer detection.

    PubMed

    Sun, Y P; Zhang, S; Cui, Z; Qu, L L

    2016-04-29

    Based on compressive sensing (CS) technology, a high resolution confocal microwave imaging algorithm is proposed for breast cancer detection. With the exploitation of the spatial sparsity of the target space, the proposed image reconstruction problem is cast within the framework of CS and solved by the sparse constraint optimization. The effectiveness and validity of the proposed CS imaging method is verified by the full wave synthetic data from numerical breast phantom using finite-difference time-domain (FDTD) method. The imaging results have shown that the proposed imaging scheme can improve the imaging quality while significantly reducing the amount of data measurements and collection time when compared to the traditional delay-and-sum imaging algorithm.

  12. Charge exchange between low energy Si ions and Cs adatoms

    NASA Astrophysics Data System (ADS)

    Chen, X.; Sroubek, Z.; Yarmoff, J. A.

    Unexpectedly large yields of positive and negative ions are produced when 2 and 5 keV Si + is singly scattered from Cs adatoms on Al(1 0 0) and Si(1 1 1). This is in contrast with Li +, in which case the ions are almost completely neutralized. The Si + ions likely result from valence electron resonant charge transfer (RCT) enhanced by promotion of the ionization level as it interacts with the Cs 5p level, but incomplete resonance neutralization of the incoming Si + cannot be absolutely excluded. The experimental data are quantitatively compared to the model and values of the microscopic parameters are estimated. Negative Si - ions are produced when the surface work function is very small, presumably by direct RCT to the projectile affinity level as it is bent downward by the image potential and by the dipole formed by the adsorbed Cs.

  13. Atomic sites and stability of Cs+ captured within zeolitic nanocavities

    PubMed Central

    Yoshida, Kaname; Toyoura, Kazuaki; Matsunaga, Katsuyuki; Nakahira, Atsushi; Kurata, Hiroki; Ikuhara, Yumi H.; Sasaki, Yukichi

    2013-01-01

    Zeolites have potential application as ion-exchangers, catalysts and molecular sieves. Zeolites are once again drawing attention in Japan as stable adsorbents and solidification materials of fission products, such as 137Cs+ from damaged nuclear-power plants. Although there is a long history of scientific studies on the crystal structures and ion-exchange properties of zeolites for practical application, there are still open questions, at the atomic-level, on the physical and chemical origins of selective ion-exchange abilities of different cations and detailed atomic structures of exchanged cations inside the nanoscale cavities of zeolites. Here, the precise locations of Cs+ ions captured within A-type zeolite were analyzed using high-resolution electron microscopy. Together with theoretical calculations, the stable positions of absorbed Cs+ ions in the nanocavities are identified, and the bonding environment within the zeolitic framework is revealed to be a key factor that influences the locations of absorbed cations. PMID:23949184

  14. Rate of reaction of OH with CS/sub 2/

    SciTech Connect

    Wine, P.H.; Shah, R.C.; Ravishankara, A.R.

    1980-10-02

    The flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction OH + CS/sub 2/ ..-->.. products (k/sub 1/) over the temperature range 251-363 K. Complicating secondary reactions involving CS/sub 2/ photofragments were eliminated only when the photoflash was filtered by 10 torr cm of CS/sub 2/ and SF/sub 6/ was used as the buffer gas. The rate constant was found to be much slower than previous measurements indicated. Based on our experiments, upper limits for k/sub 1/ (in units of 10/sup -15/ cm/sup 3/ molecule/sup -1/s/sup -1/) are 9.9 at 251 K, 1.5 at 297 K, and 1.6 at 363 K. Our results suggest that the title reaction is unimportant as a source for COS in the atmosphere.

  15. Atomic sites and stability of Cs+ captured within zeolitic nanocavities

    NASA Astrophysics Data System (ADS)

    Yoshida, Kaname; Toyoura, Kazuaki; Matsunaga, Katsuyuki; Nakahira, Atsushi; Kurata, Hiroki; Ikuhara, Yumi H.; Sasaki, Yukichi

    2013-08-01

    Zeolites have potential application as ion-exchangers, catalysts and molecular sieves. Zeolites are once again drawing attention in Japan as stable adsorbents and solidification materials of fission products, such as 137Cs+ from damaged nuclear-power plants. Although there is a long history of scientific studies on the crystal structures and ion-exchange properties of zeolites for practical application, there are still open questions, at the atomic-level, on the physical and chemical origins of selective ion-exchange abilities of different cations and detailed atomic structures of exchanged cations inside the nanoscale cavities of zeolites. Here, the precise locations of Cs+ ions captured within A-type zeolite were analyzed using high-resolution electron microscopy. Together with theoretical calculations, the stable positions of absorbed Cs+ ions in the nanocavities are identified, and the bonding environment within the zeolitic framework is revealed to be a key factor that influences the locations of absorbed cations.

  16. Quasi-freestanding graphene on Ni(111) by Cs intercalation

    NASA Astrophysics Data System (ADS)

    Alattas, M.; Schwingenschlögl, U.

    2016-05-01

    A possible approach to achieve quasi-freestanding graphene on a substrate for technological purpose is the intercalation of alkali metal atoms. Cs intercalation between graphene and Ni(111) therefore is investigated using density functional theory, incorporating van der Waals corrections. It is known that direct contact between graphene and Ni(111) perturbs the Dirac states. We find that Cs intercalation restores the linear dispersion characteristic of Dirac fermions, which agrees with experiments, but the Dirac cone is shifted to lower energy, i.e., the graphene sheet is n-doped. Cs intercalation therefore decouples the graphene sheet from the substrate except for a charge transfer. On the other hand, the spin polarization of Ni(111) does not extend through the intercalated atoms to the graphene sheet, for which we find virtually spin-degeneracy.

  17. Performance verification tests of JT-60SA CS model coil

    NASA Astrophysics Data System (ADS)

    Obana, Tetsuhiro; Murakami, Haruyuki; Takahata, Kazuya; Hamaguchi, Shinji; Chikaraishi, Hirotaka; Mito, Toshiyuki; Imagawa, Shinsaku; Kizu, Kaname; Natsume, Kyohei; Yoshida, Kiyoshi

    2015-11-01

    As a final check of the coil manufacturing method of the JT-60 Super Advanced (JT-60SA) central solenoid (CS), we verified the performance of a CS model coil. The model coil comprised a quad-pancake wound with a Nb3Sn cable-in-conduit conductor. Measurements of the critical current, joint resistance, pressure drop, and magnetic field were conducted in the verification tests. In the critical-current measurement, the critical current of the model coil coincided with the estimation derived from a strain of -0.62% for the Nb3Sn strands. As a result, critical-current degradation caused by the coil manufacturing process was not observed. The results of the performance verification tests indicate that the model coil met the design requirements. Consequently, the manufacturing process of the JT-60SA CS was established.

  18. (BAl12)Cs:mA cluster-assembled solid

    NASA Astrophysics Data System (ADS)

    Ashman, C.; Khanna, S. N.; Liu, Feng; Jena, P.; Kaplan, T.; Mostoller, M.

    1997-06-01

    First-principles calculations on the geometry and stability of AlnBm clusters have been carried out to examine the effect of size, composition, and electronic-shell filling on their relative stability. It is shown that although Al and B are both trivalent, a BAl12 cluster is more stable than an Al13 by 3.4 eV. The enhanced stability is shown to arise due to the relaxation of surface strain in the Al cage when the central Al is replaced by a smaller B atom. Replacement of an additional Al by B to produce B2Al11 results in deformation of the icosahedral BAl12 cage and reduces the stability. The possibility of forming crystals using BAl12 and Cs is examined via total-energy calculations. It is shown that a solid with icosahedral or cuboctahedral BAl12 and Cs and having the CsCl structure is metastable and could be synthesized.

  19. Accumulation of K+ and Cs+ in Tropical Plant Species

    NASA Astrophysics Data System (ADS)

    Velasco, H.; Anjos, R. M.; Zamboni, C. B.; Macario, K. D.; Rizzotto, M.; Cid, A. S.; Medeiros, I. M. A.; Fernández, J.; Rubio, L.; Audicio, P.; Lacerda, T.

    2010-08-01

    Concentrations of K+ and 137Cs+ in tissues of the Citrus aurantifolia were measured both by gamma spectrometry and neutron activation analysis, aiming to understand the behavior of monovalent inorganic cations in plants as well as its capability to store these elements. In contrast to K+, Cs+ ions are not essential elements to plants, what might explain the difference in bioavailability. However, our results have shown that 137Cs+ is positively correlated to 40K+ concentration within tropical plant species, suggesting that these elements might be assimilated in a similar way, and that they pass through the biological cycle together. A simple mathematical model was also proposed to describe the temporal evolution of 40K activity concentration in such tropical woody fruit species. This model exhibited close agreement with the 40K experimental results in the fruit ripening processes of lemon trees.

  20. Quantum Efficiency Enhancement in CsI/Metal Photocathodes

    SciTech Connect

    Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Hess, Wayne P.

    2015-02-01

    High quantum efficiency enhancement is found for hybrid metal-insulator photocathodes consisting of thin films of CsI deposited on Cu(100), Ag(100), Au(111) and Au films irradiated by 266 nm laser pulses. Low work functions (near or below 2 eV) are observed following ultraviolet laser activation. Work functions are reduced by roughly 3 eV from that of clean metal surfaces. We discuss various mechanisms of quantum efficiency enhancement for alkali halide/metal photocathode systems and conclude that the large change in work function, due to Cs accumulation of Cs metal at the metal-alkali halide interface, is the dominant mechanism for quantum efficiency enhancement

  1. Cs-137 concentration in reindeer and its fodder plants.

    PubMed

    Rissanen, K; Rahola, T

    1989-09-01

    Radionuclides, especially the long-lived 137Cs (physical half-life 30 years), are accumulated efficiently in the northern, subarctic, lichen-reindeer-man foodchain. Until the Chernobyl accident the fallout nuclides studied originated from nuclear weapons tests. After this accident some fresh fallout was deposited in Finnish Lapland. Lichens grow very slowly and collect nutrients very efficiently from air, rain and snow. During winter the basic fodder plants for reindeer are lichens and some winter-green plants, shrubs and dry leaves. During the bare-ground season, the reindeer eat various grasses, herbs and leaves etc. Lichens constitute 30-50 per cent of the entire vegetable mass consumed by the reindeer in a year. The highest 137Cs-concentration 2500 Bq/kg dry weight was found in lichen in the middle of the 1960s. In 1985 the concentration had decreased to about 240 Bq/kg dry weight. After the Chernobyl accident the 137Cs-concentration in lichen varied from 200 to 2000 Bq/kg dry weight in Finnish Lapland. In reindeer fodder plant samples collected in the 1980s before the Chernobyl accident the 137Cs-concentration varied from 5 to 970 Bq/kg dry weight. The highest 137Cs-concentration in reindeer meat, about 2500 Bq/kg fresh weight, was found in 1965 and thereafter decreased to about 300 Bq/kg fresh weight in the winter before the Chernobyl accident. After the accident the mean 137Cs-concentration in reindeer meat from the 1986-87 slaughtering period was 720 Bq/kg fresh weight and in 1987-88, 630 Bq/kg fresh weight.

  2. Estimation of average burnup of damaged fuels loaded in Fukushima Dai-ichi reactors by using the {sup 134}Cs/{sup 137}Cs ratio method

    SciTech Connect

    Endo, T.; Sato, S.; Yamamoto, A.

    2012-07-01

    Average burnup of damaged fuels loaded in Fukushima Dai-ichi reactors is estimated, using the {sup 134}Cs/{sup 137}Cs ratio method for measured radioactivities of {sup 134}Cs and {sup 137}Cs in contaminated soils within the range of 100 km from the Fukushima Dai-ichi nuclear power plants. As a result, the measured {sup 134}Cs/{sup 137}Cs ratio from the contaminated soil is 0.996{+-}0.07 as of March 11, 2011. Based on the {sup 134}Cs/{sup 137}Cs ratio method, the estimated burnup of damaged fuels is approximately 17.2{+-}1.5 [GWd/tHM]. It is noted that the numerical results of various calculation codes (SRAC2006/PIJ, SCALE6.0/TRITON, and MVP-BURN) are almost the same evaluation values of {sup 134}Cs/ {sup 137}Cs ratio with same evaluated nuclear data library (ENDF-B/VII.0). The void fraction effect in depletion calculation has a major impact on {sup 134}Cs/{sup 137}Cs ratio compared with the differences between JENDL-4.0 and ENDF-B/VII.0. (authors)

  3. Observation of the Symmetry-Forbidden 5σu→kσu CS2 Transition: A Vibrationally Driven Photoionization Resonance

    NASA Astrophysics Data System (ADS)

    Rathbone, G. J.; Poliakoff, E. D.; Bozek, John D.; Lucchese, R. R.

    2004-04-01

    Vibrationally resolved photoelectron spectroscopy and Schwinger calculations are used to characterize a new resonance phenomenon in the 5σu→kσu photoionization of CS2. This resonant channel is symmetry forbidden, yet is observable because it is activated by the antisymmetric stretching vibration. In addition, we show that a Franck-Condon breakdown occurs even though the energy dependence of the cross section is insensitive to geometry changes, which is unprecedented in photoionization.

  4. A winning combination: the 3Cs of business continuity.

    PubMed

    Glendon, Lee

    2013-01-01

    Contingency planning is a natural part of business life and is used across identified strategic, financial and operational risks. But is it being done well and is it the right approach all of the time? This paper shows how contingency planning forms one layer of a three-line defence termed 'the 3Cs of business continuity': contingency planning; continuity capability; crisis response. Collectively, 'the 3Cs' help organisations deliver a robust response to the risks that can be seen and those that cannot.

  5. Spin-Exchange-Relaxation-Free Magnetometry with Cs Vapor

    DTIC Science & Technology

    2008-03-13

    Larmor precession 6,7. In Ref. 5, sensitivity of 5 pG /Hz was achieved with the cell operating at 190 °C using potassium atoms. Estimates of the...cell containing a droplet of Cs metal, 600 Torr He buffer gas to reduce the rate at which atoms in the central part of the cell diffuse to the cell...broadening of Cs lines by helium 19, we extrapolate the FWHM of the D1 and D2 optical resonances to be =15.7 and 14.1 GHz, respectively. The cell was

  6. Fluorescence polarization studies of autoionization in CS2

    NASA Astrophysics Data System (ADS)

    Poliakoff, E. D.; Dehmer, J. L.; Parr, A. C.; Leroi, G. E.

    1987-03-01

    The fluorescence polarization spectrum of CS2(+) produced by photoionization of CS2 (using synchrotron radiation from the NBS SURF-II electron-storage ring) at excitation wavelengths 875-967 A is investigated experimentally, with a focus on autoionization features. The results of polarization measurements for the A2Pi-X2Pi transition are presented in graphs and compared with spectra simulated using the procedure of Poliakoff et al. (1982); qualitative agreement is obtained, but quantitative discrepancies are noted, especially on the low-wavelength side of the resonance. The spectral assignments of Ogawa and Chang (1970) for the autoionizing Rydberg states are confirmed.

  7. Photoemission from Ag, Cu, and CsI

    SciTech Connect

    Srinivasan-Rao, T.; Fischer, J.; Tsang, T.

    1992-06-01

    Photoemission characteristics of three different cathodes, CsI, Ag film and Cu were investigated. CsI, upon irradiation by 213 nm, 10ps laser pulse yields a quantum efficiency of 4% at O.2[mu]J input energy. The saturation mechanism observed at higher input energies require further investigation. Ag film, upon irradiation by 630 nm, 300 fs laser emit prompt photoelectrons after absorbing 2 photons. There was no evidence of optical damage of the film up to 10[sup 11] W/cm[sup 2]. At low intensities, photoemission from Cu is a simple [nu]-e[sup [minus

  8. The Submillimeter-Wave Spectrum of the CS+ Radical Ion

    NASA Astrophysics Data System (ADS)

    Bailleux, Stéphane; Walters, Adam; Grigorova, Eva; Margulès, Laurent

    2008-05-01

    The submillimeter-wave spectrum of the CS+ radical cation in its ground electronic state (X2Σ+) has been observed for the first time, in a flowing positive column discharge in a CS2-Ar mixture partially cooled with a limited flow of liquid nitrogen. Nine rotational transition frequencies were recorded between 414 and 622 GHz, leading to the determination of accurate molecular constants B0 = 25908.8560(41) MHz, D0 = 41.344(18) kHz, and γ0 = 597.629(41) MHz, which we use to predict transition frequencies up to the terahertz region in order to stimulate new attempts at astronomical detection.

  9. 137Cs in a raised bog in central Sweden.

    PubMed

    Rosén, K; Vinichuk, M; Johanson, K J

    2009-07-01

    The vertical distribution of (137)Cs activity in peat soil profiles and (137)Cs activity concentration in plants of various species was studied in samples collected at two sites on a raised bog in central Sweden. One site (open bog) was in an area with no trees and only a few sparsely growing plant species, while the other (low pine) was less than 100 m from the open bog site and had slowly growing Scots pine, a field layer dominated by some ericaceous plants and ground well-covered by plants. The plant samples were collected in 2004-2007 and were compared with samples collected in 1989 from the same open bog and low pine sites. Ground deposition of (137)Cs in 2005 was similar at both sites, 23,000 Bq m(-2). In the open bog peat profile it seems to be an upward transport of caesium since a clear peak of (137)Cs activity was found in the uppermost 1-4 cm of Sphagnum layers, whereas at the low pine site (137)Cs was mainly found in deeper (10-12 cm) layers. The migration rate was 0.57 cm yr(-1) at the open bog site and the migration centre of (137)Cs was at a depth of 10.7, while the rate at the low pine site was 0.78 cm yr(-1) and the migration centre was at 14.9 cm. Heather (Calluna vulgaris) was the plant species with the highest (137)Cs activity concentrations at both sites, 43.5 k Bq(-1) DM in 1989 decreasing to 20.4 in 2004-2007 on open bog and 22.3 k Bq kg(-1) DM in 1989 decreasing to 11.2 k Bq(-1) DM by the period 2004-2007 on the low pine site. (137)Cs transfer factors in plants varied between 0.88 and 1.35 on the open bog and between 0.48 and 0.69 m(2)kg(-1) DM at the low pine site.

  10. Electronic correlations and magnetic ordering in CsC60

    NASA Astrophysics Data System (ADS)

    Thier, K.-F.; Mehring, M.; Rachdi, F.

    1998-08-01

    We investigate the spin arrangement in the magnetically ordered orthorhombic phase of CsC60 by a comparison of 133Cs NMR data and simulations of a 3D ordered anisotropic antiferromagnet. Consistent results are obtained for two different magnetic ordering vectors. The agreement between simulation and experiment can be further improved by including a substantial amount of magnetic disorder. In addition, the metastable low temperature cubic phase is investigated using 13C NMR. We find a strongly correlated metallic system that transforms to the semiconducting dimer phase at T=140 K.

  11. SorCS1 variants and amyloid precursor protein (APP) are co-transported in neurons but only SorCS1c modulates anterograde APP transport.

    PubMed

    Hermey, Guido; Schmidt, Nadine; Bluhm, Björn; Mensching, Daniel; Ostermann, Kristina; Rupp, Carsten; Kuhl, Dietmar; Kins, Stefan

    2015-10-01

    Processing of amyloid precursor protein (APP) into amyloid-β peptide (Aβ) is crucial for the development of Alzheimer's disease (AD). Because this processing is highly dependent on its intracellular itinerary, altered subcellular targeting of APP is thought to directly affect the degree to which Aβ is generated. The sorting receptor SorCS1 has been genetically linked to AD, but the underlying molecular mechanisms are poorly understood. We analyze two SorCS1 variants; one, SorCS1c, conveys internalization of surface-bound ligands whereas the other, SorCS1b, does not. In agreement with previous studies, we demonstrate co-immunoprecipitation and co-localization of both SorCS1 variants with APP. Our results suggest that SorCS1c and APP are internalized independently, although they mostly share a common post-endocytic pathway. We introduce functional Venus-tagged constructs to study SorCS1b and SorCS1c in living cells. Both variants are transported by fast anterograde axonal transport machinery and about 30% of anterograde APP-positive transport vesicles contain SorCS1. Co-expression of SorCS1b caused no change of APP transport kinetics, but SorCS1c reduced the anterograde transport rate of APP and increased the number of APP-positive stationary vesicles. These data suggest that SorCS1 and APP share trafficking pathways and that SorCS1c can retain APP from insertion into anterograde transport vesicles. Altered APP trafficking is thought to modulate its processing. SorCS1 has been suggested to function in APP trafficking. We analyzed if the two SorCS1 variants, SorCS1b and SorCS1c, tie APP to the cell surface or modify its internalization and intracellular targeting. We observed co-localization and vesicular co-transport of APP and SorCS1, but independent internalization and sorting through a common post-endocytic pathway. Co-expression of one variant, SorCS1c, reduced anterograde APP transport. These data demonstrate that SorCS1 and APP share trafficking pathways and

  12. A parallel finite element simulator for ion transport through three-dimensional ion channel systems.

    PubMed

    Tu, Bin; Chen, Minxin; Xie, Yan; Zhang, Linbo; Eisenberg, Bob; Lu, Benzhuo

    2013-09-15

    A parallel finite element simulator, ichannel, is developed for ion transport through three-dimensional ion channel systems that consist of protein and membrane. The coordinates of heavy atoms of the protein are taken from the Protein Data Bank and the membrane is represented as a slab. The simulator contains two components: a parallel adaptive finite element solver for a set of Poisson-Nernst-Planck (PNP) equations that describe the electrodiffusion process of ion transport, and a mesh generation tool chain for ion channel systems, which is an essential component for the finite element computations. The finite element method has advantages in modeling irregular geometries and complex boundary conditions. We have built a tool chain to get the surface and volume mesh for ion channel systems, which consists of a set of mesh generation tools. The adaptive finite element solver in our simulator is implemented using the parallel adaptive finite element package Parallel Hierarchical Grid (PHG) developed by one of the authors, which provides the capability of doing large scale parallel computations with high parallel efficiency and the flexibility of choosing high order elements to achieve high order accuracy. The simulator is applied to a real transmembrane protein, the gramicidin A (gA) channel protein, to calculate the electrostatic potential, ion concentrations and I - V curve, with which both primitive and transformed PNP equations are studied and their numerical performances are compared. To further validate the method, we also apply the simulator to two other ion channel systems, the voltage dependent anion channel (VDAC) and α-Hemolysin (α-HL). The simulation results agree well with Brownian dynamics (BD) simulation results and experimental results. Moreover, because ionic finite size effects can be included in PNP model now, we also perform simulations using a size-modified PNP (SMPNP) model on VDAC and α-HL. It is shown that the size effects in SMPNP can

  13. The Psychology of Channeling.

    ERIC Educational Resources Information Center

    Corey, Michael A.

    1988-01-01

    Theoretically analyzes phenomenon of channeling from perspective of C. G. Jung's analytic psychology. Hypothesizes that contact with otherworldly spiritual beings claimed by channelers is actually projected contact with contents of channeler's own unconscious mind. Suggests that channelers seek more constructive ways of contacting their…

  14. Patterns and dynamics of Cs-137 soil contamination on the plot scale of the Bryansk Region (Russia): the role of processes, connectivity

    NASA Astrophysics Data System (ADS)

    Linnik, Vitaly; Sokolov, Alexander; Saveliev, Anatoly

    2014-05-01

    parameters, general additive models were used. According to results of modeling using a detailed and a generalized grid it has been found (Linnik, Saveliev et.al., 2007), that in accumulation zones (depressions) 137Cs deposit was lower when Laplace operator was positive (Laplace1>0=915 kBq/m2; Laplace2>0=921 kBq/m2) than in wash-out zones, singled out by negative values of Laplace operator (Laplace1<0=978 kBq/m2; Laplace2<0=979 kBq/m2). The inversion effect revealed in 137Cs deposit distribution could not be accounted for be processes of surface 137Cs wash-off as the chain of depressions was isolated. We found that connectivity of subsurface moving soil moisture saturation was made up by a number of small and shallow channels, covered by litter, they served as 137Cs travel paths at the period of spring wetting in April-May 1986. The total 137Cs output in soluble form from this plot calculated for the two models was 5,9% and 6,4%. References: Linnik V.G., Saveliev A.A., Govorun A.P., Ivanitsky O.M., Sokolov A.V. Spatial Variability and Topographic Factors of 137Cs Soil Contamination at a Field Scale// International Journal of Ecology & Development, 2007, Vol. 8, No.7, p.8-25.

  15. Theoretical evaluation of the radiative lifetimes of LiCs and NaCs in the A1Σ+ state

    NASA Astrophysics Data System (ADS)

    Mabrouk, N.; Berriche, H.

    2017-08-01

    Calculations of the adiabatic potential energy curves and the transition dipole moments between the ground (A1Σ+) and the first excited (A1Σ+) states have been determined for the LiCs and NaCs molecules. The calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Cs+, Li+ and Na+ cores, parameterized l-dependent polarization potentials and full configuration interaction calculations. The potential energy curves and the transition dipole moment are used to estimate the radiative lifetimes of the vibrational levels of the A+Σ+ state using the Franck-Condon (FC) approximation and the approximate sum rule method. The radiative lifetimes associated with the A+Σ+ state are presented here for the first time. These data can help experimentalists to optimize photoassociative formation of ultracold molecules and their longevity in a trap or in an optical lattice.

  16. Spatial and temporal variability in sedimentation rates associated with cutoff channel infill deposits: Ain River, France

    USGS Publications Warehouse

    Piegay, H.; Hupp, C.R.; Citterio, A.; Dufour, S.; Moulin, B.; Walling, D.E.

    2008-01-01

    Floodplain development is associated with lateral accretion along stable channel geometry. Along shifting rivers, the floodplain sedimentation is more complex because of changes in channel position but also cutoff channel presence, which exhibit specific overflow patterns. In this contribution, the spatial and temporal variability of sedimentation rates in cutoff channel infill deposits is related to channel changes of a shifting gravel bed river (Ain River, France). The sedimentation rates estimated from dendrogeomorphic analysis are compared between and within 14 cutoff channel infills. Detailed analyses along a single channel infill are performed to assess changes in the sedimentation rates through time by analyzing activity profiles of the fallout radionuclides 137Cs and unsupported 210Pb. Sedimentation rates are also compared within the channel infills with rates in other plots located in the adjacent floodplain. Sedimentation rates range between 0.65 and 2.4 cm a -1 over a period of 10 to 40 years. The data provide additional information on the role of distance from the bank, overbank flow frequency, and channel geometry in controlling the sedimentation rate. Channel infills, lower than adjacent floodplains, exhibit higher sedimentation rates and convey overbank sediment farther away within the floodplain. Additionally, channel degradation, aggradation, and bank erosion, which reduce or increase the distance between the main channel and the cutoff channel aquatic zone, affect local overbank flow magnitude and frequency and therefore sedimentation rates, thereby creating a complex mosaic of sedimentation zones within the floodplain and along the cutoff channel infills. Last, the dendrogeomorphic and 137Cs approaches are cross validated for estimating the sedimentation rate within a channel infill. Copyright 2008 by the American Geophysical Union.

  17. 135Cs/137Cs isotopic composition of environmental samples across Europe: Environmental transport and source term emission applications

    SciTech Connect

    Snow, Mathew S.; Snyder, Darin C.

    2015-11-02

    135Cs/137Cs isotopic analyses represent an important tool for studying the fate and transport of radiocesium in the environment; in this work the 135Cs/137Cs isotopic composition in environmental samples taken from across Europe is reported. Surface soil and vegetation samples from western Russia, Ukraine, Austria, and Hungary show consistent aged thermal fission product 135Cs/137Cs isotope ratios of 0.58 ± 0.01 (age corrected to 1/1/15), with the exception of one sample of soil-moss from Hungary which shows an elevated 135Cs/137Cs ratio of 1.78 ± 0.12. With the exception of the outlier sample from Hungary, surface soil/vegetation data are in quantitative agreement with values previously reported for soils within the Chernobyl exclusion zone, suggesting that radiocesium at these locations is primarily composed of homogenous airborne deposition from Chernobyl. Seawater samples taken from the Irish Sea show 135Cs/137Cs isotope ratios of 1.22 ± 0.11 (age corrected to 1/1/15), suggesting aged thermal fission product Cs discharged from Sellafield. Furthermore, the differences in 135Cs/137Cs isotope ratios between Sellafield, Chernobyl, and global nuclear weapons testing fallout indicate that 135Cs/137Cs isotope ratios can be utilized to discriminate between and track radiocesium transport from different nuclear production source terms, including major emission sources in Europe.

  18. Terahertz Spectroscopic Probe of Hot Electron and Hole Transfer from Colloidal CsPbBr3 Perovskite Nanocrystals.

    PubMed

    Sarkar, Sohini; Ravi, Vikash Kumar; Banerjee, Sneha; Yettapu, Gurivi Reddy; Markad, Ganesh B; Nag, Angshuman; Mandal, Pankaj

    2017-09-13

    Colloidal all inorganic CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) have emerged to be an excellent material for applications in light emission, photovoltaics, and photocatalysis. Efficient interfacial transfer of photogenerated electrons and holes are essential for a good photovoltaic and photocatalytic material. Using time-resolved terahertz spectroscopy, we have measured the kinetics of photogenerated electron and hole transfer processes in CsPbBr3 NCs in the presence of benzoquinone and phenothiazine molecules as electron and hole acceptors, respectively. Efficient hot electron/hole transfer with a sub-300 fs time scale is the major channel of carrier transfer thus overcomes the problem related to Auger recombination. A secondary transfer of thermalized carriers also takes place with time scales of 20-50 ps for electrons and 137-166 ps for holes. This work suggests that suitable interfaces of CsPbX3 NCs with electron and hole transport layers would harvest hot carriers, increasing the photovoltaic and photocatalytic efficiencies.

  19. The preliminary results of the measurements of environmental levels of 40K and 137Cs in Venezuela

    NASA Astrophysics Data System (ADS)

    LaBrecque, J. J.; Rosales, P. A.; Carias, O.

    1992-02-01

    The study of the beta-particle radioactivity in air and 90Sr in rainwater collected at Instituto Venezolano de Investigaciones Cientificas, IVIC, that began in 1959 in conjunction with the U.S. Atomic Energy Commission was discontinued in 1963. But after the Chernobyl nuclear power plant accident in the USSR, work on the radioactive contamination in Venezuela has been renewed. Initially the measurement of 134Cs and 137Cs in imported foodstuffs, such as milk powders and meats were undertaken, and these have now been extended to measurements of environmental levels of 40K and 137Cs in soils, sea sediments and foodstuffs. The data present herein are the only readily available data on radioactive contamination in the environment in Venezuela since 1963. The measurements were performed with a simple Nal(Tl) detector and two single channel analyzers as well as with a 25% efficient hyper-pure germanium semiconductor coupled to a multichannel analyzer system. Finally, these results can be used as baseline values (environmental background) in case of a nuclear accident in the region, as well as to screen imported foodstuff which is suspected to be contaminated.

  20. Role of Epithelial Sodium Channels and Their Regulators in Hypertension*

    PubMed Central

    Soundararajan, Rama; Pearce, David; Hughey, Rebecca P.; Kleyman, Thomas R.

    2010-01-01

    The kidney has a central role in the regulation of blood pressure, in large part through its role in the regulated reabsorption of filtered Na+. Epithelial Na+ channels (ENaCs) are expressed in the most distal segments of the nephron and are a target of volume regulatory hormones. A variety of factors regulate ENaC activity, including several aldosterone-induced proteins that are present within an ENaC regulatory complex. Proteases also regulate ENaC by cleaving the channel and releasing intrinsic inhibitory tracts. Polymorphisms or mutations within channel subunits or regulatory pathways that enhance channel activity may contribute to an increase in blood pressure in individuals with essential hypertension. PMID:20624922

  1. Synthesis, structural characterization and optical properties of a new cesium aluminum borate, Cs{sub 2}Al{sub 2}B{sub 2}O{sub 7}

    SciTech Connect

    Feng Kai; Yin Wenlong; Yao Jiyong; Wu Yicheng

    2011-12-15

    A new borate, Cs{sub 2}Al{sub 2}B{sub 2}O{sub 7}, was synthesized by solid-state reaction. It crystallizes in the monoclinic space group P2{sub 1}/c with a=6.719(1) A, b=7.121(1) A, c=9.626(3) A, {beta}=115.3(1) Degree-Sign , and Z=2. In the structure, two AlO{sub 4} tetrahedra and two BO{sub 3} planar triangles are connected alternately by corner-sharing to from nearly planar [Al{sub 2}B{sub 2}O{sub 10}] rings, which are further linked via common O1 atom to generate layers in the bc plane. These layers then share the O3 atoms lying on a center of inversion to form a three-dimensional framework with Cs atoms residing in the channels. The IR spectrum confirms the presence of both BO{sub 3} and AlO{sub 4} groups and the UV-vis-IR diffuse reflectance spectrum indicates a band gap of about 4.13(2) eV. - Graphical abstract: A new borate, Cs{sub 2}Al{sub 2}B{sub 2}O{sub 7}, was synthesized. In the structure, BO{sub 3} triangles and AlO{sub 4} tetrahedra are connected to form a three-dimensional framework with Cs{sup +} in the channels. Black-Small-Square Highlights: Black-Right-Pointing-Pointer A new borate Cs{sub 2}Al{sub 2}B{sub 2}O{sub 7} was synthesized and crystals were obtained by flux method. Black-Right-Pointing-Pointer Cs{sub 2}Al{sub 2}B{sub 2}O{sub 7} crystallizes in a new structure type. Black-Right-Pointing-Pointer Two AlO{sub 4} and two BO{sub 3} generate a [Al{sub 2}B{sub 2}O{sub 10}] ring in the structure. Black-Right-Pointing-Pointer Rings are linked to form a three-dimensional framework with Cs{sup +} in the channels. Black-Right-Pointing-Pointer Optical band gap is about 4.13 eV.

  2. Channel nut tool

    DOEpatents

    Olson, Marvin

    2016-01-12

    A method, system, and apparatus for installing channel nuts includes a shank, a handle formed on a first end of a shank, and an end piece with a threaded shaft configured to receive a channel nut formed on the second end of the shaft. The tool can be used to insert or remove a channel nut in a channel framing system and then removed from the channel nut.

  3. Permeation of internal and external monovalent cations through the catfish cone photoreceptor cGMP-gated channel

    PubMed Central

    1995-01-01

    The permeation of monovalent cations through the cGMP-gated channel of catfish cone outer segments was examined by measuring permeability and conductance ratios under biionic conditions. For monovalent cations presented on the cytoplasmic side of the channel, the permeability ratios with respect to extracellular Na followed the sequence NH4 > K > Li > Rb = Na > Cs while the conductance ratios at +50 mV followed the sequence Na approximately NH4 > K > Rb > Li = Cs. These patterns are broadly similar to the amphibian rod channel. The symmetry of the channel was tested by presenting the test ion on the extracellular side and using Na as the common reference ion on the cytoplasmic side. Under these biionic conditions, the permeability ratios with respect to Na at the intracellular side followed the sequence NH4 > Li > K > Na > Rb > Cs while the conductance ratios at +50 mV followed the sequence NH4 > K approximately Na > Rb > Li > Cs. Thus, the channel is asymmetric with respect to external and internal cations. Under symmetrical 120 mM ionic conditions, the single-channel conductance at +50 mV ranged from 58 pS in NH4 to 15 pS for Cs and was in the order NH4 > Na > K > Rb > Cs. Unexpectedly, the single-channel current-voltage relation showed sufficient outward rectification to account for the rectification observed in multichannel patches without invoking voltage dependence in gating. The concentration dependence of the reversal potential for K showed that chloride was impermeant. Anomalous mole fraction behavior was not observed, nor, over a limited concentration range, were multiple dissociation constants. An Eyring rate theory model with a single binding site was sufficient to explain these observations. PMID:8786344

  4. A simple method for activity determination of ¹³⁴Cs and ¹³⁷Cs in foodstuffs using NaI(Tl) scintillation spectrometer.

    PubMed

    Yamada, T; Ishizu, H; Kawada, Y

    2013-11-01

    A simplified peak fitting technique for the analysis of the overlapped pulse-height spectra of (134)Cs and (137)Cs γ-rays obtained with a NaI(Tl) scintillation spectrometer was studied. In this analysis, nearly an upper half of 662 keV (137)Cs peak data was employed for fitting of the Gaussian peak using the least squares algorithm. Consistent results were obtained as compared with the reference value of test samples mixed with (134)Cs and (137)Cs standard solutions. Copyright © 2013 Elsevier Ltd. All rights reserved.

  5. Phase transitions in CsCl-type intemetallic compounds

    SciTech Connect

    Chen, Bai-Hao.

    1990-06-13

    Phase transitions in binary intermetallic compounds with the CsCl-type structure have been studied by a novel combination of high-temperature powder X-ray diffraction and Rietveld Landau theory of symmetry and phase transitions and the Gibbs-Knonvalow equation have been applied to understand the phase behavior of some systems with the CsCl-type structure. The nonstoichiometric compounds RhTi, NbRu, and RuTa with the CsCl-type structure at high temperature undergo thermal symmetry breaking transitions upon cooling. The transitions are first to the AuCu-type tetragonal, and taken to the orthorhombic NbRu-type with Cmmm symmetry. Alloys Ir-Ti which are titanium rich have the CsCl-type structure. This cubic structure transforms to the AuCu-type tetragonal structure and then to the NbRu-type structure with increasing atomic percent iridium. New partial phase diagrams for the composition ranges in near equiatomic MnAu, NbRu, and RuTa are also presented.

  6. Changing CS Features Alters Evaluative Responses in Evaluative Conditioning

    ERIC Educational Resources Information Center

    Unkelbach, Christian; Stahl, Christoph; Forderer, Sabine

    2012-01-01

    Evaluative conditioning (EC) refers to changes in people's evaluative responses toward initially neutral stimuli (CSs) by mere spatial and temporal contiguity with other positive or negative stimuli (USs). We investigate whether changing CS features from conditioning to evaluation also changes people's evaluative response toward these CSs. We used…

  7. Isoform Specificity of Protein Kinase Cs in Synaptic Plasticity

    ERIC Educational Resources Information Center

    Sossin, Wayne S.

    2007-01-01

    Protein kinase Cs (PKCs) are implicated in many forms of synaptic plasticity. However, the specific isoform(s) of PKC that underlie(s) these events are often not known. We have used "Aplysia" as a model system in order to investigate the isoform specificity of PKC actions due to the presence of fewer isoforms and a large number of documented…

  8. Developing a Technology Enhanced CS0 Course for Engineering Students

    ERIC Educational Resources Information Center

    Lokkila, Erno; Kaila, Erkki; Lindén, Rolf; Laakso, Mikko-Jussi; Sutinen, Erkki

    2016-01-01

    The CS0 course in the curriculum typically has the role of introducing students into basic concepts and terminology of computer science. Hence, it is used to form a base on which the subsequent programming courses can build on. However, much of the effort to build better methodologies for courses is spent on introductory programming courses…

  9. A CS1 Pedagogical Approach to Parallel Thinking

    ERIC Educational Resources Information Center

    Rague, Brian William

    2010-01-01

    Almost all collegiate programs in Computer Science offer an introductory course in programming primarily devoted to communicating the foundational principles of software design and development. The ACM designates this introduction to computer programming course for first-year students as CS1, during which methodologies for solving problems within…

  10. CHeCS: International Space Station Medical Hardware Catalog

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The purpose of this catalog is to provide a detailed description of each piece of hardware in the Crew Health Care System (CHeCS), including subpacks associated with the hardware, and to briefly describe the interfaces between the hardware and the ISS. The primary user of this document is the Space Medicine/Medical Operations ISS Biomedical Flight Controllers (ISS BMEs).

  11. Accumulation and distribution of 137Cs in tropical plants

    NASA Astrophysics Data System (ADS)

    Anjos, R. M.; Carvalho, C.; Mosquera, B.; Veiga, R.; Sanches, N.; Bastos, J.; Macario, K.

    2007-02-01

    The accumulation and distribution of 40K and 137Cs in several tropical plant species were studied through measurements of gamma-ray spectra, focusing on establishing the suitability of using radiocesium to trace the plant uptake of nutrients such as potassium.

  12. Narnian Virtues: C.S. Lewis as Character Educator

    ERIC Educational Resources Information Center

    Pike, Mark; Lickona, Thomas; Nesfield, Victoria

    2015-01-01

    This article argues that C.S. Lewis is a highly relevant but largely neglected character educator for 21st century schools characterized by diversity. We make the case for the objective reality of Lewis's Tao, the moral law recognized in the moral precepts of a wide range of cultures and traditions. We show why these universal precepts are…

  13. Fallout 137Cs in reindeer herders in Arctic Norway.

    PubMed

    Skuterud, Lavrans; Thørring, Håvard

    2015-03-03

    Reindeer herders in the Arctic were among the most heavily exposed populations to the global fallout from nuclear weapons testing in the 1950s and 1960s, due to high transfer of radionuclides in the lichens-reindeer-human food chain. Annual studies of (137)Cs in reindeer herders in Kautokeino, Norway, were initiated in 1965 to monitor radiation doses and follow environmental (137)Cs behavior. The (137)Cs concentrations declined from the peak in 1965 with effective half-times of 6-8 years, only interrupted by a temporary doubling in levels from 1986 to 1987 due to the Chernobyl fallout. During the period of 1950-2010 an average herder received an integrated effective dose from incorporated (137)Cs of about 18 mSv. This dose represents an insignificant increase in the risk for developing cancer. Health studies even show a significantly lower cancer incidence among Sámis and reindeer herders in northern Norway compared to other populations in the same area.

  14. A CS1 Pedagogical Approach to Parallel Thinking

    ERIC Educational Resources Information Center

    Rague, Brian William

    2010-01-01

    Almost all collegiate programs in Computer Science offer an introductory course in programming primarily devoted to communicating the foundational principles of software design and development. The ACM designates this introduction to computer programming course for first-year students as CS1, during which methodologies for solving problems within…

  15. Isoform Specificity of Protein Kinase Cs in Synaptic Plasticity

    ERIC Educational Resources Information Center

    Sossin, Wayne S.

    2007-01-01

    Protein kinase Cs (PKCs) are implicated in many forms of synaptic plasticity. However, the specific isoform(s) of PKC that underlie(s) these events are often not known. We have used "Aplysia" as a model system in order to investigate the isoform specificity of PKC actions due to the presence of fewer isoforms and a large number of documented…

  16. Changing CS Features Alters Evaluative Responses in Evaluative Conditioning

    ERIC Educational Resources Information Center

    Unkelbach, Christian; Stahl, Christoph; Forderer, Sabine

    2012-01-01

    Evaluative conditioning (EC) refers to changes in people's evaluative responses toward initially neutral stimuli (CSs) by mere spatial and temporal contiguity with other positive or negative stimuli (USs). We investigate whether changing CS features from conditioning to evaluation also changes people's evaluative response toward these CSs. We used…

  17. Plutonium and Cs-137 in autopsy tissues in Great Britain.

    PubMed

    Popplewell, D S; Ham, G J; Dodd, N J; Shuttler, S D

    1988-03-01

    Tissues removed at autopsy from members of the general public contain significantly higher concentrations of plutonium and 137Cs in west Cumbrians than in people from three other regions of Great Britain. Several autopsy cases from Cumbria showed unusually high values of plutonium. Subsequently it was found that the subjects had been former employees of British Nuclear Fuels.

  18. Measurements of Cs absorption and retention in man

    SciTech Connect

    Henrichs, H.; Paretzke, H.G.; Voigt, G.; Berg, D. )

    1989-10-01

    One of the consequences of the Chernobyl reactor accident in 1986 was a comparatively high contamination of foodstuffs in Southern Federal Republic of Germany. In order to test radioecological models predicting the radiological consequences of such accidents, several thousand measurements were performed to determine Cs body burdens in members of the public. For the interpretation of these data and as a contribution to the improvement of the available database on the biokinetics of Cs isotopes in humans, we followed a small group of volunteers after their consumption of highly contaminated venison. Intakes, excretion rates and total body activities were measured during a period of more than 200 d. The data obtained were evaluated in terms of a compartment model to derive gastrointestinal uptakes, biological half-lives and dose conversion factors. The resulting uptake factors range from 65-90%, the half-lives of the long-term retention from 45 to 200 d. The majority of the resulting dose conversion factors lie below the values recommended by the ICRP, showing that the ICRP model is a reasonable and safe description of the Cs biokinetics in our study group, while the great variability of the results shows that it is not an accurate representation of the individual Cs retention.

  19. CsRAV1 induces sylleptic branching in hybrid poplar.

    PubMed

    Moreno-Cortés, Alicia; Hernández-Verdeja, Tamara; Sánchez-Jiménez, Paloma; González-Melendi, Pablo; Aragoncillo, Cipriano; Allona, Isabel

    2012-04-01

    • Sylleptic branching in trees may increase significantly branch number, leaf area and the general growth of the tree, particularly in its early years. Although this is a very important trait, so far little is known about the genes that control this process. • This article characterizes the Castanea sativa RAV1 gene, homologous to Arabidopsis TEM genes, by analyzing its circadian behavior and examining its winter expression in chestnut stems and buds. Transgenic hybrid poplars over-expressing CsRAV1 or showing RNA interference down-regulated PtaRAV1 and PtaRAV2 expression were produced and analyzed. • Over-expression of the CsRAV1 gene induces the early formation of sylleptic branches in hybrid poplar plantlets during the same growing season in which the lateral buds form. Only minor growth differences and no changes in wood anatomy are produced. • The possibility of generating trees with a greater biomass by manipulating the CsRAV1 gene makes CsRAV1 transgenic plants promising candidates for bioenergy production. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.

  20. Web-CS: Infrastructure for Web-Based Competitions.

    ERIC Educational Resources Information Center

    Aerts, A. T. M.; Bierhoff, P. F. M.; De Bra, P. M. E.

    This paper presents a World Wide Web-based infrastructure for cooperation between many different parties. The infrastructure is designed for Web-based competitions involving an editorial board, designers of assignments or events, evaluators, different organizational layers, and contestants. Web-CS is entirely Web-based: all the communication…

  1. Excitation-transfer collisions in cesium vapor: CS(5d (5/2)) + CS(6s (1/2)) yields CS(5d (3/2)) + CS(6s (1/2))

    SciTech Connect

    Keramati, B.; Masters, M.; Huennekens, J.

    1988-11-01

    The excitation-transfer collision Cs(5D5/2) + Cs(6S) yields CS(5D3/2) + Cs(6S) was studied. The upper 5D5/2 state was excited by a c-w dye laser tuned to the one photon, quadrupole-allowed 6S yields 5D5/2 transition. Since the direct 5D yields 6P fluorescence could not be detected with our apparatus we monitored instead the cascade 6P yields 6S fluorescence. The ratio of 6P 1/2 to 6P3/2 fluorescence contains information on the collisional mixing that takes place in the 5D levels but also includes a significant contribution from mixing in the 6P levels. This latter contribution could effectively be subtracted out using the results of a second experiment in which a tunable cw diode laser was used to pump the 6P3/2 state, and the same fluorescence ratio monitored. The 5D mixing cross section obtained, 70 A, is significantly larger than previous indirect determinations.

  2. Excitation-transfer collisions in cesium vapor: Cs(5D/sub 5/2/)+Cs(6S/sub 1/2/). -->. Cs (5D/sub 3/2/)+ Cs(6S/sub 1/2/)

    SciTech Connect

    Keramati, B.; Masters, M.; Huennekens, J.

    1988-11-01

    We report an experimental investigation of the excitation-transfer collision Cs(5D/sub 5/2/)+Cs(6S)..-->..CS ((5D/sub 3/2/)+Cs(6S). The upper 5D/sub 5/2/ state was excited by a cw dye laser tuned to the one-photon, quadrupole-allowed 6S..-->..5D/sub 5/2/ transition. Since the direct 5D..-->..6P fluorescence could not be detected with our apparatus, we monitored instead the cascade 6P..-->..6S fluorescence. The ratio of 6P/sub 1/2/ to 6P/sub 3/2/ fluorescence contains information on the collisional mixing that takes place in the 5D levels but also includes a significant contribution from mixing in the 6P levels. This latter contribution could effectively be subtracted out using the results of a second experiment in which a tunable cw diode laser was used to pump the 6P/sub 3/2/ state, and the same fluorescence ratio monitored. The 5D mixing cross section we obtain, 70 A/sup 2/, is significantly larger than previous indirect determinations.

  3. Teaching a CS Introductory Course: An Active Approach

    ERIC Educational Resources Information Center

    Moura, Isabel C.; van Hattum-Janssen, Natascha

    2011-01-01

    Computer Science (CS) introductory courses that are offered by the Department of Information Systems at the University of Minho (UM), Portugal, seem to abound in non-motivated students. They are characterized by high failure and withdrawal rates and use mainly deductive teaching approaches. Deductive instruction begins with theories and progresses…

  4. There and Back Again?: The Disappearing Pulsations of CS 1246

    NASA Astrophysics Data System (ADS)

    Vasquez Soto, Alan; Barlow, Brad

    2016-01-01

    Hot subdwarf stars were once main sequence stars, like the sun, that deviated from normal stellar evolution due to binary interactions and evolved into extreme horizontal branch stars. Several of these stars exhibit rapid pulsations driven by iron opacity instabilities. CS 1246 is a rapidly pulsating hot subdwarf discovered in 2009 that is dominated by a single 371 second pulsation. At the time of its discovery, the pulsational amplitude was one of the largest known, making CS 1246 an ideal candidate for follow up studies. Observations in 2013 implied that the pulsational amplitude had decreased significantly. Since then we have continued monitoring the star using the robotic SKYNET telescopes in Chile, in order to further characterize any changes. Our recent observations show that the pulsational amplitude has gone down by a factor of six: CS 1246 is barely a pulsator anymore. The decay in amplitude over time is reminiscent of a damped harmonic oscillator. Here we present six years of photometry for CS 1246 and discuss possible scenarios that might explain its interesting behavior.

  5. Teaching a CS Introductory Course: An Active Approach

    ERIC Educational Resources Information Center

    Moura, Isabel C.; van Hattum-Janssen, Natascha

    2011-01-01

    Computer Science (CS) introductory courses that are offered by the Department of Information Systems at the University of Minho (UM), Portugal, seem to abound in non-motivated students. They are characterized by high failure and withdrawal rates and use mainly deductive teaching approaches. Deductive instruction begins with theories and progresses…

  6. Positively and Negatively Charged Cesium and (C60) m Cs n Cluster Ions.

    PubMed

    Renzler, Michael; Kranabetter, Lorenz; Goulart, Marcelo; Scheier, Paul; Echt, Olof

    2017-05-25

    We report on the formation and ionization of cesium and C60Cs clusters in superfluid helium nanodroplets. Size distributions of positively and negatively charged (C60) m Cs n(±) ions have been measured for m ≤ 7, n ≤ 12. Reproducible intensity anomalies are observed in high-resolution mass spectra. For both charge states, (C60) m Cs3(±) and (C60) m Cs5(±) are particularly abundant, with little dependence on the value of m. Distributions of bare cesium cluster ions also indicate enhanced stability of Cs3(±) and Cs5(±), in agreement with theoretical predictions. These findings contrast with earlier reports on highly Cs-doped cationic fullerene aggregates which showed enhanced stability of C60Cs6 building blocks attributed to charge transfer. The dependence of the (C60) m Cs3(-) anion yield on electron energy shows a resonance that, surprisingly, oscillates in strength as m increases from 1 to 6.

  7. Satellite bands of the RbCs molecule in the range of highly excited states

    NASA Astrophysics Data System (ADS)

    Rakić, Mario; Beuc, Robert; Bouloufa-Maafa, Nadia; Dulieu, Olivier; Vexiau, Romain; Pichler, Goran; Skenderović, Hrvoje

    2016-05-01

    We report on the observation of three RbCs satellite bands in the blue and green ranges of the visible spectrum. Absorption measurements are performed using all-sapphire cell filled with a mixture of Rb and Cs. We compare high resolution absorption spectrum of Rb-Cs vapor mixture with pure Rb and Cs vapor spectra from the literature. After detailed analysis, the new satellite bands of RbCs molecule at 418.3 nm, 468.3, and 527.5 nm are identified. The origin of these bands is discussed by direct comparison with difference potentials derived from quantum chemistry calculations of RbCs potential energy curves. These bands originate from the lower Rydberg states of the RbCs molecule. This study thus provides further insight into photoassociation of lower Rydberg molecular states, approximately between Cs(7s) + Rb(5s) and Cs(6s) + Rb(6p) asymptotes, in ultracold gases.

  8. ¹³⁴Cs and ¹³⁷Cs radioactivity in soil and moss samples of Jeju Island after Fukushima nuclear reactor accident.

    PubMed

    Park, Kyung-Ho; Kang, Tae-Woo; Kim, Won-Jik; Park, Jae Woo

    2013-11-01

    Specific activities of (134)Cs and (137)Cs in surface soil and moss samples were investigated at 12 locations of Jeju Island, Korea. Specific activities of (134)Cs and (137)Cs in the surface soil vary from less than MDA to 17 Bq/kg and from 12 Bq/kg to 109 Bq/kg, respectively. Specific activities of (134)Cs and (137)Cs in moss samples lie in the range 6 Bq/kg-39 Bq/kg and 15 Bq/kg-41 Bq/kg, respectively. The activity ratios (134)Cs/(137)Cs in the soil samples are much less than the reference value of about 1.0, but they are close to 1.0 in the moss samples. Average amount of (137)Cs added to the surface soil after the Fukushima accident is estimated to be 7.8 ± 1.7 Bq/kg. The depth profile of (137)Cs specific activity has a lognormal shape with a peak between 5 cm and 7.5 cm below the ground. For the cored soil sample, (134)Cs was detected up to 3 cm below the ground.

  9. Kup-mediated Cs(+) uptake and Kdp-driven K(+) uptake coordinate to promote cell growth during excess Cs(+) conditions in Escherichia coli.

    PubMed

    Tanudjaja, Ellen; Hoshi, Naomi; Su, Yi-Hsin; Hamamoto, Shin; Uozumi, Nobuyuki

    2017-05-18

    The physiological effects of caesium (Cs) on living cells are poorly understood. Here, we examined the physiological role of Cs(+) on the activity of the potassium transporters in E. coli. In the absence of potassium (K(+)), Kup-mediated Cs(+) uptake partially supported cell growth, however, at a much lower rate than with sufficient K(+). In K(+)-limited medium (0.1 mM), the presence of Cs(+) (up to 25 mM) in the medium enhanced growth as much as control medium containing 1 mM K(+). This effect depended on the maintenance of basal levels of intracellular K(+) by other K(+) uptake transporters. Higher amounts of K(+) (1 mM) in the medium eliminated the positive effect of Cs(+) on growth, and revealed the inhibitory effect of high Cs(+) on the growth of wild-type E. coli. Cells lacking Kdp, TrkG and TrkH but expressing Kup grew less well when Cs(+) was increased in the medium. A kdp mutant contained an increased ratio of Cs(+)/K(+) in the presence of high Cs(+) in the medium and consequently was strongly inhibited in growth. Taken together, under excess Cs(+) conditions Kup-mediated Cs(+) influx sustains cell growth, which is supported by intracellular K(+) supplied by Kdp.

  10. 137Cs activities and 135Cs/137Cs isotopic ratios from soils at Idaho National Laboratory: a case study for contaminant source attribution in the vicinity of nuclear facilities.

    PubMed

    Snow, Mathew S; Snyder, Darin C; Clark, Sue B; Kelley, Morgan; Delmore, James E

    2015-03-03

    Radiometric and mass spectrometric analyses of Cs contamination in the environment can reveal the location of Cs emission sources, release mechanisms, modes of transport, prediction of future contamination migration, and attribution of contamination to specific generator(s) and/or process(es). The Subsurface Disposal Area (SDA) at Idaho National Laboratory (INL) represents a complicated case study for demonstrating the current capabilities and limitations to environmental Cs analyses. (137)Cs distribution patterns, (135)Cs/(137)Cs isotope ratios, known Cs chemistry at this site, and historical records enable narrowing the list of possible emission sources and release events to a single source and event, with the SDA identified as the emission source and flood transport of material from within Pit 9 and Trench 48 as the primary release event. These data combined allow refining the possible number of waste generators from dozens to a single generator, with INL on-site research and reactor programs identified as the most likely waste generator. A discussion on the ultimate limitations to the information that (135)Cs/(137)Cs ratios alone can provide is presented and includes (1) uncertainties in the exact date of the fission event and (2) possibility of mixing between different Cs source terms (including nuclear weapons fallout and a source of interest).

  11. 137 Cs Activities and 135 Cs/ 137 Cs Isotopic Ratios from Soils at Idaho National Laboratory: A Case Study for Contaminant Source Attribution in the Vicinity of Nuclear Facilities

    SciTech Connect

    Snow, Mathew S.; Snyder, Darin C.; Clark, Sue B.; Kelley, Morgan; Delmore, James E.

    2015-03-03

    Radiometric and mass spectrometric analyses of Cs contamination in the environment can reveal the location of Cs emission sources, release mechanisms, modes of transport, prediction of future contamination migration, and attribution of contamination to specific generator(s) and/or process(es). The Subsurface Disposal Area (SDA) at Idaho National Laboratory (INL) represents a complicated case study for demonstrating the current capabilities and limitations to environmental Cs analyses. 137Cs distribution patterns, 135Cs/137Cs isotope ratios, known Cs chemistry at this site, and historical records enable narrowing the list of possible emission sources and release events to a single source and event, with the SDA identified as the emission source and flood transport of material from within Pit 9 and Trench 48 as the primary release event. These data combined allow refining the possible number of waste generators from dozens to a single generator, with INL on-site research and reactor programs identified as the most likely waste generator. A discussion on the ultimate limitations to the information that 135Cs/137Cs ratios alone can provide is presented and includes (1) uncertainties in the exact date of the fission event and (2) possibility of mixing between different Cs source terms (including nuclear weapons fallout and a source of interest).

  12. The ultraviolet detection component based on Te-Cs image intensifier

    NASA Astrophysics Data System (ADS)

    Qian, Yunsheng; Zhou, Xiaoyu; Wu, Yujing; Wang, Yan; Xu, Hua

    2017-05-01

    Ultraviolet detection technology has been widely focused and adopted in the fields of ultraviolet warning and corona detection for its significant value and practical meaning. The component structure of ultraviolet ICMOS, imaging driving and the photon counting algorithm are studied in this paper. Firstly, the one-inch and wide dynamic range CMOS chip with the coupling optical fiber panel is coupled to the ultraviolet image intensifier. The photocathode material in ultraviolet image intensifier is Te-Cs, which contributes to the solar blind characteristic, and the dual micro-channel plates (MCP) structure ensures the sufficient gain to achieve the single photon counting. Then, in consideration of the ultraviolet detection demand, the drive circuit of the CMOS chip is designed and the corresponding program based on Verilog language is written. According to the characteristics of ultraviolet imaging, the histogram equalization method is applied to enhance the ultraviolet image and the connected components labeling way is utilized for the ultraviolet single photon counting. Moreover, one visible light video channel is reserved in the ultraviolet ICOMS camera, which can be used for the fusion of ultraviolet and visible images. Based upon the module, the ultraviolet optical lens and the deep cut-off solar blind filter are adopted to construct the ultraviolet detector. At last, the detection experiment of the single photon signal is carried out, and the test results are given and analyzed.

  13. Surface Functionalization of Nanodiamonds Using the Biomacromolecule Chitosan (CS)

    NASA Astrophysics Data System (ADS)

    Lott, Lewis Q.

    NDs are highly promising drug delivery vehicles (DDVs) due to the materials low cytotoxicity and biocompatibility. The advantage of these materials lies within their tunable surface chemistry and inherent optical properties. Despite the numerous benefits, the use of NDs in biological systems is impeded by their high aggregation propensity in polar liquid medium, a caveat from its rich chemistry. ND particles typically aggregate into much larger groups >200 nm, which are too large for drug delivery applications. In this work, salt assisted attrition milling was utilized to decrease ND aggregates. After 5 hours of milling, dynamic light scattering (DLS) measurements revealed a maximum particle distribution at 127 nm, with significant reduction in the mass fraction of larger particle size distribution from 300-1000nm. The average size of the nanodiamond particles was also shown to increase with an increasing concentration of chitosan (0.25 w/v%; 142nm and 1 w/v%; 825nm). In the modification of nanodiamonds, FTIR was used to examine the chemical composition of the nanodiamonds, both before and after functionalization. FTIR results of the pristine nanodiamonds showed characteristic bands at 3400cm -1 (-OH) 1630 cm-1 (C=O) and 1080 (-C-O). Chitosan exhibited spectral regions of interest at 3350 cm-1 (-OH), 1665 cm-1 (NH2) and 1030 cm-1 (C-O). Successful functionalization of the nanodiamaond surface was confirmed by the appearance of the amide band I at 1664 cm-1 and presence of strong C-O stretching at 1197cm-1 from the chitosan backbone. This is indicative of the covalent binding of NH2 on chitosan with COOH on the ND surface. X-ray diffraction was performed to observe the structure and crystallinity of the NDs and showed crystalline characteristic peaks at 2theta 44° (111), 75° (220), and 91° (113) for the pristine ND. The appearance of an amorphous band at 2theta 22° in the analysis of ND-COOH-CS is indicative of the surface modification of the nanodiamond with

  14. Prescription dose in permanent {sup 131}Cs seed prostate implants

    SciTech Connect

    Yue Ning; Heron, Dwight E.; Komanduri, Krishna; Huq, M. Saiful

    2005-08-15

    Recently, {sup 131}Cs seeds have been introduced for prostate permanent seed implants. This type of seed has a relatively short half-life of 9.7 days and has its most prominent emitted photon energy peaks in the 29-34 keV region. Traditionally, 145 and 125 Gy have been prescribed for {sup 125}I and {sup 103}Pd seed prostate implants, respectively. Since both the half-life and dosimetry characteristics of {sup 131}Cs seed are quite different from those of {sup 125}I and {sup 103}Pd, the appropriate prescription dose for {sup 131}Cs seed prostate implant may well be different. This study was designed to use a linear quadratic radiobiological model to determine an appropriate dose prescription scheme for permanent {sup 131}Cs seed prostate implants. In this model, prostate edema was taken into consideration. Calculations were also performed for tumors of different doubling times and for other related radiobiological parameters of different values. As expected, the derived prescription dose values were dependent on type of tumors and types of edema. However, for prostate cancers in which tumor cells are relatively slow growing and are reported to have a mean potential doubling time of around 40 days, the appropriate prescription dose for permanent {sup 131}Cs seed prostate implants was determined to be: 127{sub -12}{sup +5}Gy if the experiences of {sup 125}I seed implants were followed and 121{sub -3}{sup +0}Gy if the experiences of {sup 103}Pd seed implants were followed.

  15. Microfluidic channel fabrication method

    DOEpatents

    Arnold, Don W.; Schoeniger, Joseph S.; Cardinale, Gregory F.

    2001-01-01

    A new channel structure for microfluidic systems and process for fabricating this structure. In contrast to the conventional practice of fabricating fluid channels as trenches or grooves in a substrate, fluid channels are fabricated as thin walled raised structures on a substrate. Microfluidic devices produced in accordance with the invention are a hybrid assembly generally consisting of three layers: 1) a substrate that can or cannot be an electrical insulator; 2) a middle layer, that is an electrically conducting material and preferably silicon, forms the channel walls whose height defines the channel height, joined to and extending from the substrate; and 3) a top layer, joined to the top of the channels, that forms a cover for the channels. The channels can be defined by photolithographic techniques and are produced by etching away the material around the channel walls.

  16. Low (134)Cs/(137)Cs ratio anomaly in the north-northwest direction from the Fukushima Dai-ichi Nuclear Power Station.

    PubMed

    Kobayashi, Shingo; Shinomiya, Takayuki; Ishikawa, Takahiro; Imaseki, Hitoshi; Iwaoka, Kazuki; Kitamura, Hisashi; Kodaira, Satoshi; Kobayashi, Keisuke; Oikawa, Masakazu; Miyaushiro, Norihiro; Takashima, Yoshio; Uchihori, Yukio

    2017-08-07

    A low (134)Cs/(137)Cs ratio anomaly in the north-northwest (NNW) direction from the Fukushima Dai-ichi Nuclear Power Station (FDNPS) is identified by a new analysis of the (134)Cs/(137)Cs ratio dataset which we had obtained in 2011-2015 by a series of car-borne surveys that employed a germanium gamma-ray spectrometer. We found that the (134)Cs/(137)Cs ratio is slightly lower (0.95, decay-corrected to March 11, 2011) in an area with a length of about 15 km and a width of about 3 km in the NNW direction from the FDNPS than in other directions from the station. Furthermore, the area of this lower (134)Cs/(137)Cs ratio anomaly corresponds to a narrow contamination band that runs NNW from the FDNPS and it is nearly parallel with the major and heaviest contamination band in the west-northwest. The plume trace with a low (134)Cs/(137)Cs ratio previously found by other researchers within the 3-km radius of the FDNPS is in a part of the area with the lower (134)Cs/(137)Cs ratio anomaly that we found. Our result suggests that this lower (134)Cs/(137)Cs ratio anomaly is the area which was contaminated before March 13, 2011 (UTC) in association with the hydrogen explosion of Unit 1 on March 12, 2011 at 06:36 (UTC) and it was less influenced by later subsequent plumes. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. GALAXY EVOLUTION EXPLORER OBSERVATIONS OF CS AND OH EMISSION IN COMET 9P/TEMPEL 1 DURING DEEP IMPACT

    SciTech Connect

    Feldman, Paul D.; McCandliss, Stephan R.; Morgenthaler, Jeffrey P.; Lisse, Carey M.; Weaver, Harold A.; A'Hearn, Michael F.

    2010-03-10

    Galaxy Evolution Explorer (GALEX) observations of comet 9P/Tempel 1 using the near-ultraviolet (NUV) objective grism were made before, during and after the Deep Impact event that occurred on 2005 July 4 at 05:52:03 UT when a 370 kg NASA spacecraft was maneuvered into the path of the comet. The NUV channel provides usable spectral information in a bandpass covering 2000-3400 A with a point source spectral resolving power of R {approx} 100. The primary spectral features in this range include solar continuum scattered from cometary dust and emissions from OH and CS molecular bands centered near 3085 and 2575 A, respectively. In particular, we report the only cometary CS emission detected during this event. The observations allow the evolution of these spectral features to be tracked over the period of the encounter. In general, the NUV emissions observed from Tempel 1 are much fainter than those that have been observed by GALEX from other comets. However, it is possible to derive production rates for the parent molecules of the species detected by GALEX in Tempel 1 and to determine the number of these molecules liberated by the impact. The derived quiescent production rates are Q(H{sub 2}O) = 6.4 x 10{sup 27} molecules s{sup -1} and Q(CS{sub 2}) = 6.7 x 10{sup 24} molecules s{sup -1}, while the impact produced an additional 1.6 x 10{sup 32} H{sub 2}O molecules and 1.3 x 10{sup 29} CS{sub 2} molecules, a similar ratio as in quiescent outgassing.

  18. Channel Properties of Nax Expressed in Neurons

    PubMed Central

    Matsumoto, Masahito; Hiyama, Takeshi Y.; Kuboyama, Kazuya; Suzuki, Ryoko; Fujikawa, Akihiro; Noda, Masaharu

    2015-01-01

    Nax is a sodium-concentration ([Na+])-sensitive Na channel with a gating threshold of ~150 mM for extracellular [Na+] ([Na+]o) in vitro. We previously reported that Nax was preferentially expressed in the glial cells of sensory circumventricular organs including the subfornical organ, and was involved in [Na+] sensing for the control of salt-intake behavior. Although Nax was also suggested to be expressed in the neurons of some brain regions including the amygdala and cerebral cortex, the channel properties of Nax have not yet been adequately characterized in neurons. We herein verified that Nax was expressed in neurons in the lateral amygdala of mice using an antibody that was newly generated against mouse Nax. To investigate the channel properties of Nax expressed in neurons, we established an inducible cell line of Nax using the mouse neuroblastoma cell line, Neuro-2a, which is endogenously devoid of the expression of Nax. Functional analyses of this cell line revealed that the [Na+]-sensitivity of Nax in neuronal cells was similar to that expressed in glial cells. The cation selectivity sequence of the Nax channel in cations was revealed to be Na+ ≈ Li+ > Rb+ > Cs+ for the first time. Furthermore, we demonstrated that Nax bound to postsynaptic density protein 95 (PSD95) through its PSD95/Disc-large/ZO-1 (PDZ)-binding motif at the C-terminus in neurons. The interaction between Nax and PSD95 may be involved in promoting the surface expression of Nax channels because the depletion of endogenous PSD95 resulted in a decrease in Nax at the plasma membrane. These results indicated, for the first time, that Nax functions as a [Na+]-sensitive Na channel in neurons as well as in glial cells. PMID:25961826

  19. The fragmentation dynamics of small Cs(CsI)n+ cluster ions under low-energy multiple collision conditions

    NASA Astrophysics Data System (ADS)

    Herzschuh, Rainer; Drewello, Thomas

    2004-04-01

    The collision-induced dissociations of small caesium iodide cluster ions of the type Cs(CsI)n+ where n=3-7, have been investigated under low-energy multiple collision conditions. The collisions were performed in the rf-only quadrupole of a BEqQ hybrid mass spectrometer. Breakdown graphs of selected parent ions were obtained by varying the laboratory collision energy in the range of 0-400 eV. The fragmentation dynamic established under these conditions provides a link between the well-known decay behaviour occurring unimolecularly and the dissociations following high energy (keV) collisional activation. Of particular interest is the observation that the energy-dependent dissociation pattern supplies support for the occurrence of one-step fission reactions, featuring the evaporation of presumably intact (CsI)n neutrals as opposed to a sequential decay via nCsI losses. The breakdown graphs thus provide a valuable tool to enhance insight into the fragmentation mechanism of these clusters.

  20. Measurement of intrinsic radioactive backgrounds from the 137Cs and U/Th chains in CsI(Tl) crystals

    NASA Astrophysics Data System (ADS)

    Liu, Shu-Kui; Yue, Qian; Lin, Shin-Ted; Li, Yuan-Jing; Tang, Chang-Jian; Wong Tsz-King, Henry; Xing, Hao-Yang; Yang, Chao-Wen; Zhao, Wei; Zhu, Jing-Jun

    2015-04-01

    The inorganic CsI(Tl) crystal scintillator is a candidate anti-compton detector for the China Dark matter Experiment. Studying the intrinsic radiopurity of the CsI(Tl) crystal is an issue of major importance. The timing, energy and spatial correlations, as well as the capability of pulse shape discrimination provide powerful methods for the measurement of intrinsic radiopurities. The experimental design, detector performance and event-selection algorithms are described. A total of 359×3 kg-days data from three prototypes of CsI(Tl) crystals were taken at China Jinping Underground Laboratory (CJPL), which offers a good shielding environment. The contamination levels of internal isotopes from 137Cs, 232Th and 238U series, as well as the upper bounds of 235U series are reported. Identification of the whole α peaks from U/Th decay chains and derivation of those corresponding quenching factors are achieved. Supported by National Natural Science Foundation of China (11275107, 11175099)

  1. Mechanosensitivity of an epithelial Na+ channel in planar lipid bilayers: release from Ca2+ block.

    PubMed Central

    Ismailov, I I; Berdiev, B K; Shlyonsky, V G; Benos, D J

    1997-01-01

    A family of novel epithelial Na+ channels (ENaCs) have recently been cloned from several different tissues. Three homologous subunits (alpha, beta, gamma-ENaCs) from the core conductive unit of Na(+)-selective, amiloride-sensitive channels that are found in epithelia. We here report the results of a study assessing the regulation of alpha,beta,gamma-rENaC by Ca2+ in planar lipid bilayers. Buffering of the bilayer bathing solutions to [Ca2+] < 1 nM increased single-channel open probability by fivefold. Further investigation of this phenomenon revealed that Ca2+ ions produced a voltage-dependent block, affecting open probability but not the unitary conductance of ENaC. Imposing a hydrostatic pressure gradient across bilayers containing alpha,beta,gamma-rENaC markedly reduced the sensitivity of these channels to inhibition by [Ca2+]. Conversely, in the nominal absence of Ca2+, the channels lost their sensitivity to mechanical stimulation. These results suggest that the previously observed mechanical activation of ENaCs reflects a release of the channels from block by Ca2+. Images FIGURE 3 FIGURE 4 PMID:9138565

  2. Experimental quantum channel simulation

    NASA Astrophysics Data System (ADS)

    Lu, He; Liu, Chang; Wang, Dong-Sheng; Chen, Luo-Kan; Li, Zheng-Da; Yao, Xing-Can; Li, Li; Liu, Nai-Le; Peng, Cheng-Zhi; Sanders, Barry C.; Chen, Yu-Ao; Pan, Jian-Wei

    2017-04-01

    Quantum simulation is of great importance in quantum information science. Here, we report an experimental quantum channel simulator imbued with an algorithm for imitating the behavior of a general class of quantum systems. The reported quantum channel simulator consists of four single-qubit gates and one controlled-not gate. All types of quantum channels can be decomposed by the algorithm and implemented on this device. We deploy our system to simulate various quantum channels, such as quantum-noise channels and weak quantum measurement. Our results advance experimental quantum channel simulation, which is integral to the goal of quantum information processing.

  3. Channel estimation scheme based on compressed sensing and parameter estimation for an orthogonal frequency division multiplexing visible light communications system

    NASA Astrophysics Data System (ADS)

    Du, Jie; Deng, Honggui; Qian, Xuewen; Zhang, Chaoyang

    2016-11-01

    In order to mitigate bandwidth attenuation of diffusion link visible light communication systems caused by multipath effects, we present an optical orthogonal frequency division multiplexing channel estimation scheme based on compressed sensing (CS) and estimation of signal parameters via rotational invariance techniques (ESPRIT). First, we derived a parametric channel model. Then, we used ESPRIT to obtain multipath channel parameters. After that, we built a dynamic over-complete dictionary that can be used in CS processing. Finally, we reconstructed the channel response by using a basis pursuit denoising algorithm to equalize the received signal in frequency domain. Compared with traditional schemes, the proposed scheme can improve channel estimation accuracy without increasing dictionary size. A set of computer simulations demonstrated the effectiveness of the proposed scheme.

  4. Measurements and Observations of 134Cs and 137Cs around a Nuclear Power Plant in Busan, South Korea

    NASA Astrophysics Data System (ADS)

    Chong, H. Y.; Park, J. N.; Kim, J. S.

    2015-12-01

    The purpose of this study is to know the change of representative species 134Cs and 137Cs of artificial radionuclides from the nuclear power station nearby for the last five years(2010~2014). The Kori Nuclear Power Plant, nuclear power facility located near Busan, is located in the south-east coast of Korea and about 21km north-east away from the Haeundae and about 25km south away from the Ulsan. An administrative district is Jangan-eup, Gijang-gun, Busan, Korea. A point was selected on the basis of the "Environmental Radiation Monitoring Plan around Nuclear Power Plants" and periodically samples were collected and analyzed. The samples were collected from the soils of the surface in the Wolnae area (NW, 1.7km). The soil samples were analyzed by gamma spectrometer with High Purity Germanium detector (HPGe) of 40% relative efficiency and were measured for 80,000 sec. As a results of soil analysis, 137Cs were detected in samples only selected in March 2013. The activity concentration of 137Cs founded in the soil sample was 0.513±0.052Bq/kg-dry. In the other hands, the concentration of 137Cs in the year 2010, 2011, 2012, and 2014 were below the minimum detectable activity (MDA). 40K, natural radionuclides which is widely present, was detected in the soil samples and other artificial radionuclides were not detected. The result of overall comparison of the environmental radioactivity survey around Kori Nuclear Power Plant for the last five years is that radioactivity levels are within average range. However, it is necessary to continue to carefully observe a fine change in regional or the monthly radiation concentration.

  5. Cholesterol and Ion Channels

    PubMed Central

    Levitan, Irena; Fang, Yun; Rosenhouse-Dantsker, Avia; Romanenko, Victor

    2010-01-01

    A variety of ion channels, including members of all major ion channel families, have been shown to be regulated by changes in the level of membrane cholesterol and partition into cholesterol-rich membrane domains. In general, several types of cholesterol effects have been described. The most common effect is suppression of channel activity by an increase in membrane cholesterol, an effect that was described for several types of inwardly-rectifying K+ channels, voltage-gated K+ channels, Ca+2 sensitive K+ channels, voltage-gated Na+ channels, N-type voltage-gated Ca+2 channels and volume-regulated anion channels. In contrast, several types of ion channels, such as epithelial amiloride-sensitive Na+ channels and Transient Receptor Potential channels, as well as some of the types of inwardly-rectifying and voltage-gated K+ channels were shown to be inhibited by cholesterol depletion. Cholesterol was also shown to alter the kinetic properties and current-voltage dependence of several voltage-gated channels. Finally, maintaining membrane cholesterol level is required for coupling ion channels to signalling cascades. In terms of the mechanisms, three general mechanisms have been proposed: (i) specific interactions between cholesterol and the channel protein, (ii) changes in the physical properties of the membrane bilayer and (iii) maintaining the scaffolds for protein-protein interactions. The goal of this review is to describe systematically the role of cholesterol in regulation of the major types of ion channels and to discuss these effects in the context of the models proposed. PMID:20213557

  6. Hadamard quantum broadcast channels

    NASA Astrophysics Data System (ADS)

    Wang, Qingle; Das, Siddhartha; Wilde, Mark M.

    2017-10-01

    We consider three different communication tasks for quantum broadcast channels, and we determine the capacity region of a Hadamard broadcast channel for these various tasks. We define a Hadamard broadcast channel to be such that the channel from the sender to one of the receivers is entanglement-breaking and the channel from the sender to the other receiver is complementary to this one. As such, this channel is a quantum generalization of a degraded broadcast channel, which is well known in classical information theory. The first communication task we consider is classical communication to both receivers, the second is quantum communication to the stronger receiver and classical communication to other, and the third is entanglement-assisted classical communication to the stronger receiver and unassisted classical communication to the other. The structure of a Hadamard broadcast channel plays a critical role in our analysis: The channel to the weaker receiver can be simulated by performing a measurement channel on the stronger receiver's system, followed by a preparation channel. As such, we can incorporate the classical output of the measurement channel as an auxiliary variable and solve all three of the above capacities for Hadamard broadcast channels, in this way avoiding known difficulties associated with quantum auxiliary variables.

  7. Fading channel simulator

    SciTech Connect

    Argo, P.E.; Fitzgerald, T.J.

    1991-12-31

    This invention relates to high frequency (HF) radio signal propagation through fading channels and, more particularly, to simulation of fading channels in order to characterize HF radio system performance in transmitting and receiving signals through such fading channels. Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

  8. G-protein-coupled inward rectifier potassium channels involved in corticostriatal presynaptic modulation.

    PubMed

    Meneses, David; Mateos, Verónica; Islas, Gustavo; Barral, Jaime

    2015-09-01

    Presynaptic modulation has been associated mainly with calcium channels but recent data suggests that inward rectifier potassium channels (K(IR)) also play a role. In this work we set to characterize the role of presynaptic K(IR) channels in corticostriatal synaptic transmission. We elicited synaptic potentials in striatum by stimulating cortical areas and then determined the synaptic responses of corticostriatal synapsis by using paired pulse ratio (PPR) in the presence and absence of several potassium channel blockers. Unspecific potassium channels blockers Ba(2+) and Cs(+) reduced the PPR, suggesting that these channels are presynaptically located. Further pharmacological characterization showed that application of tertiapin-Q, a specific K(IR)3 channel family blocker, also induced a reduction of PPR, suggesting that K(IR)3 channels are present at corticostriatal terminals. In contrast, exposure to Lq2, a specific K(IR)1.1 inward rectifier potassium channel, did not induce any change in PPR suggesting the absence of these channels in the presynaptic corticostriatal terminals. Our results indicate that K(IR)3 channels are functionally expressed at the corticostriatal synapses, since blockage of these channels result in PPR decrease. Our results also help to explain how synaptic activity may become sensitive to extracellular signals mediated by G-protein coupled receptors. A vast repertoire of receptors may influence neurotransmitter release in an indirect manner through regulation of K(IR)3 channels.

  9. Vaporization Mechanisms of Water-Insoluble Cs in Ash During Thermal Treatment with Calcium Chloride Addition.

    PubMed

    Jiao, Facun; Iwata, Norie; Kinoshita, Norikazu; Kawaguchi, Masato; Asada, Motoyuki; Honda, Maki; Sueki, Keisuke; Ninomiya, Yoshihiko

    2016-12-20

    The vaporization mechanisms of water-insoluble Cs in raw ash and Cs-doped ash during thermal treatment with CaCl2 addition was systematically examined in a lab-scale electrical heating furnace over a temperature range of 500-1500 °C. The results indicate that the water-insoluble Cs in the ash was associated with aluminosilicate as pollucite. Addition of 10% CaCl2 caused the maximum vaporization ratio of Cs in the raw ash to reach approximately 80% at temperatures higher than 1200 °C, whereas approximately 95% of Cs was vaporized at temperatures higher than 1300 °C when 30% CaCl2 was added. The formation of an intermediate compound, CsCaCl3, through the chemical reaction of Cs with CaCl2 was responsible for Cs vaporization by means of the subsequent decomposition of this intermediate upon the increase in temperature. The indirect chlorination of Cs by the gaseous chlorine released from the decomposition of CaCl2 was insignificant. A high CaCl2 content in the resulting annealed products with 30% CaCl2 addition delayed the decomposition of CsCaCl3 and thus lowered the Cs vaporization ratio compared to that with 10% CaCl2 addition at 900-1250 °C. Thermal treatment with CaCl2 addition is a proposed method to remove Cs from Cs-contaminated incineration ash.

  10. The Channel Tunnel

    NASA Image and Video Library

    2006-08-11

    The Channel Tunnel is a 50.5 km-long rail tunnel beneath the English Channel at the Straits of Dover. It connects Dover, Kent in England with Calais, northern France. This image was acquired by NASA Terra spacecraft.

  11. Bayesian sparse channel estimation

    NASA Astrophysics Data System (ADS)

    Chen, Chulong; Zoltowski, Michael D.

    2012-05-01

    In Orthogonal Frequency Division Multiplexing (OFDM) systems, the technique used to estimate and track the time-varying multipath channel is critical to ensure reliable, high data rate communications. It is recognized that wireless channels often exhibit a sparse structure, especially for wideband and ultra-wideband systems. In order to exploit this sparse structure to reduce the number of pilot tones and increase the channel estimation quality, the application of compressed sensing to channel estimation is proposed. In this article, to make the compressed channel estimation more feasible for practical applications, it is investigated from a perspective of Bayesian learning. Under the Bayesian learning framework, the large-scale compressed sensing problem, as well as large time delay for the estimation of the doubly selective channel over multiple consecutive OFDM symbols, can be avoided. Simulation studies show a significant improvement in channel estimation MSE and less computing time compared to the conventional compressed channel estimation techniques.

  12. Ionic Selectivity and Permeation Properties of Human PIEZO1 Channels.

    PubMed

    Gnanasambandam, Radhakrishnan; Bae, Chilman; Gottlieb, Philip A; Sachs, Frederick

    2015-01-01

    Members of the eukaryotic PIEZO family (the human orthologs are noted hPIEZO1 and hPIEZO2) form cation-selective mechanically-gated channels. We characterized the selectivity of human PIEZO1 (hPIEZO1) for alkali ions: K+, Na+, Cs+ and Li+; organic cations: TMA and TEA, and divalents: Ba2+, Ca2+, Mg2+ and Mn2+. All monovalent ions permeated the channel. At a membrane potential of -100 mV, Cs+, Na+ and K+ had chord conductances in the range of 35-55 pS with the exception of Li+, which had a significantly lower conductance of ~ 23 pS. The divalents decreased the single-channel permeability of K+, presumably because the divalents permeated slowly and occupied the open channel for a significant fraction of the time. In cell-attached mode, 90 mM extracellular divalents had a conductance for inward currents carried by the divalents of: 25 pS for Ba2+ and 15 pS for Ca2+ at -80 mV and 10 pS for Mg2+ at -50 mV. The organic cations, TMA and TEA, permeated slowly and attenuated K+ currents much like the divalents. As expected, the channel K+ conductance increased with K+ concentration saturating at ~ 45 pS and the KD of K+ for the channel was 32 mM. Pure divalent ion currents were of lower amplitude than those with alkali ions and the channel opening rate was lower in the presence of divalents than in the presence of monovalents. Exposing cells to the actin disrupting reagent cytochalasin D increased the frequency of openings in cell-attached patches probably by reducing mechanoprotection.

  13. A magnesium-carboxylate framework showing luminescent sensing for CS{sub 2} and nitroaromatic compounds

    SciTech Connect

    Wu, Zhao-Feng; Tan, Bin; Feng, Mei-Ling; Du, Cheng-Feng; Huang, Xiao-Ying

    2015-03-15

    A magnesium metal-organic framework compound, namely [NH{sub 2}(CH{sub 3}){sub 2}][Mg{sub 3}(NDC){sub 2.5}(HCO{sub 2}){sub 2}(DMF){sub 0.75}(H{sub 2}O){sub 0.25}]·1.25DMF·0.75H{sub 2}O (1) (H{sub 2}NDC=1,4-naphthalene dicarboxylic acid, DMF=N,N′-dimethylformamide), has been synthesized in solvothermal conditions and structurally characterized. It features a three-dimensionally anionic framework with aligned channels parallel to the b-axis. Luminescent studies indicated that it showed significant luminescence quenching for carbon disulfide (CS{sub 2}) and nitrobenzene after being activated, at a content of only 3.0 and 0.1 vol% in DMF, respectively. In addition, the activated sample showed sensitive luminescence quenching for 1,3,5-trinitrophenol with a low concentration of 5×10{sup −5} mol/L. - Graphical abstract: Presented is a microporous 3D Mg-MOF, namely, [NH{sub 2}(CH{sub 3}){sub 2}][Mg{sub 3}(NDC){sub 2.5}(HCO{sub 2}){sub 2}(DMF){sub 0.75}(H{sub 2}O){sub 0.25}]·1.25DMF·0.75H{sub 2}O (1) (H{sub 2}NDC=1,4-naphthalene dicarboxylic acid) showing significant luminescence quenching for carbon disulfide and nitrobenzene. - Highlights: • A microporous 3D metal-organic framework based on Mg. • The compound shows significant luminescence quenching for CS{sub 2} and nitrobenzene after activated. • The compound shows sensitive luminescence quenching for 1,3,5-trinitrophenol with a low concentration of 5×10{sup −5} mol/L.

  14. Quasi-Anonymous Channels

    DTIC Science & Technology

    2003-01-01

    QUASI- ANONYMOUS CHANNELS Ira S. Moskowitz Center for High Assurance Computer Systems - Code 5540 Naval Research Laboratory, Washington, DC...Assurance Computer Systems - Code 5540 Naval Research Laboratory, Washington, DC 20375, USA Abstract Although both anonymity and covert...channels are part of the larger topic of information hiding, there also exists an intrinsic linkage between anonymity and covert channels. This linkage

  15. Channel morphology [Chapter 5

    Treesearch

    Jonathan W. Long; Alvin L. Medina; Daniel G. Neary

    2012-01-01

    Channel morphology has become an increasingly important subject for analyzing the health of rivers and associated fish populations, particularly since the popularization of channel classification and assessment methods. Morphological data can help to evaluate the flows of sediment and water that influence aquatic and riparian habitat. Channel classification systems,...

  16. [Effect of soil microflora on 137Cs transition to plants].

    PubMed

    Pareniuk, O Yu; Shavanova, K E; Ilienko, V V; Tytova, L V; Levchuk, S E; Gudkov, I N

    2015-01-01

    The impact of certain types of microorganisms on 137Cs transfer from the substrate into the plant was analyzed in the experiment on artificial mediums. It was found that certain types of microorganisms could either reduce or increase the ratio of 137Cs transfer from the substrate to the plant. It is shown that this property is independent of the localization of the microorganism on the surface of the root, for all the analyzed bacteria belonging to the rhizospheric group. Azotobacter chroococcum UKM B-6003 stimulated the radionuclide transfer to plants up to 1.5 times, while the best bacteria for reducing its accumulation is Burkholderia sp IMER-B1 -53 - 1.3 times in comparison with the control. It was shown that the strain Bacillus megaterium UKM B-5724 from the collection of the Institute of Microbiology and Virology of NASU has a high ability to accumulate radionuclides.

  17. Absorption spectra of shocked liquid CS/sub 2/

    SciTech Connect

    Dallman, J.C.

    1985-01-01

    The importance of shock initiation of high explosives (HE) was understood as early as 1863 when Alfred Nobel introduced the detonator as a means of detonating nitroglycerine. The critical pressure rise times required to achieve shock initiation and steady propagation of detonation are determined by the chemical and mechanical properties of an explosive. Although progress has been made in the understanding of the effects of mechanical properties, the detailed effects of high pressures on chemical reaction mechanisms are still only poorly understood. This paper reports the results of two experiments using CS/sub 2/, which is known to undergo electronic state transitions when shocked to high pressures. The goal of these experiments was to examine the known shock-generated expansion of CS/sub 2/ absorption bands while generating the shocks with a flyer plate system driven by high explosives.

  18. Characteristics of ultra-low-energy Cs + ion beam bombardments

    NASA Astrophysics Data System (ADS)

    Li, Zhanping; Hoshi, Takahiro; Oiwa, Retsu

    2003-01-01

    Shallow arsenic implants and extra-thin film (SiON) are routinely analyzed by modern SIMS under ultra-low-energy Cs + ion beam bombardment, either at oblique (<60°) or glancing (˜80°) incident angle [J. Surf. Anal. 6 (3) (1999) A-3; in: A. Benninghoven, et al. (Eds.), Proceedings of the SIMS XII, Elsevier, Amsterdam, 1999, p. 549]. This article investigates the basic aspects of ultra-low-energy Cs + ion beam bombardment using a delta-doped boron sample (four layers, 5.3 nm per cycle), such as useful yield, depth resolution and changes in sputter rate in the near surface region. Our results indicated that there is a magic incidence angle (˜70°) at which the depth resolution is very poor, and at glancing (˜80°) incident angle the best depth resolution is observed.

  19. CS-based fast ultrasound imaging with improved FISTA algorithm

    NASA Astrophysics Data System (ADS)

    Lin, Jie; He, Yugao; Shi, Guangming; Han, Tingyu

    2015-08-01

    In ultrasound imaging system, the wave emission and data acquisition is time consuming, which can be solved by adopting the plane wave as the transmitted signal, and the compressed sensing (CS) theory for data acquisition and image reconstruction. To overcome the very high computation complexity caused by introducing CS into ultrasound imaging, in this paper, we propose an improvement of the fast iterative shrinkage-thresholding algorithm (FISTA) to achieve the fast reconstruction of the ultrasound imaging, in which a modified setting is done with the parameter of step size for each iteration. Further, the GPU strategy is designed for the proposed algorithm, to guarantee the real time implementation of imaging. The simulation results show that the GPU-based image reconstruction algorithm can achieve the fast ultrasound imaging without damaging the quality of image.

  20. Pretreatment/Radionuclide Separations of Cs/Tc from Supernates

    SciTech Connect

    Thompson, M.C.

    1998-09-01

    Significant improvements have been made in ion exchange and solvent extraction materials and processes available for separation of the radionuclides cesium and technetium from both acid and alkaline waste solutions. New ion exchange materials and solvent extraction reagents are more selective for Cs over sodium and potassium than previous materials. The higher selectivity gives higher Cs capacity and improved separation processes. Technetium removal has been improved by new ion exchange resins, which have either improved capacity or easier elution. Several different crown ethers have been shown to extract pertechnetate ion selectively over other anions. Organic complexants in some waste solutions reduce pertechnetate ion and stabilize the reduced species. Selective oxidation allows conversion to pertechnetate without oxidation of the organic complexants.