Attosecond transient absorption of a bound wave packet coupled to a smooth continuum

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

Dahlström, Jan Marcus; Pabst, Stefan; Lindroth, Eva

Here, we investigate the possibility of using transient absorption of a coherent bound electron wave packet in hydrogen as an attosecond pulse characterization technique. In a recent work, we have shown that photoionization of such a coherent bound electron wave packet opens up for pulse characterization with unprecedented temporal accuracy—independent of the atomic structure—with maximal photoemission at all kinetic energies given a wave packet with zero relative phase. Here, we perform numerical propagation of the time-dependent Schrödinger equation and analytical calculations based on perturbation theory to show that the energy-resolved maximal absorption of photons from the attosecond pulse does not uniquely occur at a zero relative phase of the initial wave packet. Instead, maximal absorption occurs at different relative wave packet phases, distributed as a non-monotonous function with a smoothmore » $$-\\pi /2$$ shift across the central photon energy (given a Fourier-limited Gaussian pulse). Similar results are also found in helium. Our finding is surprising, because it implies that the energy-resolved photoelectrons are not mapped one-to-one with the energy-resolved absorbed photons of the attosecond pulse.« less

Phase-dependent above-barrier ionization of excited-state electrons.

PubMed

Yang, Weifeng; Song, Xiaohong; Chen, Zhangjin

2012-05-21

The carrier-envelope phase (CEP)-dependent above-barrier ionization (ABI) has been investigated in order to probe the bound-state electron dynamics. It is found that when the system is initially prepared in the excited state, the ionization yield asymmetry between left and right sides can occur both in low-energy and high-energy parts of the photoelectron spectra. Moreover, in electron momentum map, a new interference effect along the direction perpendicular to the laser polarization is found. We show that this interference is related to the competition among different excited states. The interference effect is dependent on CEPs of few-cycle probe pulses, which can be used to trace the superposition information and control the electron wave packet of low excited states.

Longitudinal and transverse spin dynamics of donor-bound electrons in fluorine-doped ZnSe: Spin inertia versus Hanle effect

NASA Astrophysics Data System (ADS)

Heisterkamp, F.; Zhukov, E. A.; Greilich, A.; Yakovlev, D. R.; Korenev, V. L.; Pawlis, A.; Bayer, M.

2015-06-01

The spin dynamics of strongly localized donor-bound electrons in fluorine-doped ZnSe epilayers is studied using pump-probe Kerr rotation techniques. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time T1 in a wide range of magnetic fields, temperatures, and pump densities. The T1 time of the donor-bound electron spin of about 1.6 μ s remains nearly constant for external magnetic fields varied from zero up to 2.5 T (Faraday geometry) and in a temperature range 1.8-45 K. These findings impose severe restrictions on possible spin relaxation mechanisms. In our opinion they allow us to rule out scattering between free and donor-bound electrons, jumping of electrons between different donor centers, scattering between phonons and donor-bound electrons, and with less certainty charge fluctuations in the environment of the donors caused by the 1.5 ps pulsed laser excitation.

27 CFR 73.33 - Am I legally bound by a form I sign electronically?

Code of Federal Regulations, 2010 CFR

2010-04-01

... TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE TREASURY (CONTINUED) PROCEDURES AND PRACTICES ELECTRONIC SIGNATURES; ELECTRONIC SUBMISSION OF FORMS Electronic Filing of Documents with TTB § 73.33 Am I legally bound... paper document submitted to satisfy the same reporting requirement. Persons using electronic signatures...

Theoretical derivation of laser-dressed atomic states by using a fractal space

NASA Astrophysics Data System (ADS)

Duchateau, Guillaume

2018-05-01

The derivation of approximate wave functions for an electron submitted to both a Coulomb and a time-dependent laser electric fields, the so-called Coulomb-Volkov (CV) state, is addressed. Despite its derivation for continuum states does not exhibit any particular problem within the framework of the standard theory of quantum mechanics (QM), difficulties arise when considering an initially bound atomic state. Indeed the natural way of translating the unperturbed momentum by the laser vector potential is no longer possible since a bound state does not exhibit a plane wave form explicitly including a momentum. The use of a fractal space permits to naturally define a momentum for a bound wave function. Within this framework, it is shown how the derivation of laser-dressed bound states can be performed. Based on a generalized eikonal approach, a new expression for the laser-dressed states is also derived, fully symmetric relative to the continuum or bound nature of the initial unperturbed wave function. It includes an additional crossed term in the Volkov phase which was not obtained within the standard theory of quantum mechanics. The derivations within this fractal framework have highlighted other possible ways to derive approximate laser-dressed states in QM. After comparing the various obtained wave functions, an application to the prediction of the ionization probability of hydrogen targets by attosecond XUV pulses within the sudden approximation is provided. This approach allows to make predictions in various regimes depending on the laser intensity, going from the non-resonant multiphoton absorption to tunneling and barrier-suppression ionization.

Attosecond transient absorption probing of electronic superpositions of bound states in neon. Detection of quantum beats

DOE PAGES

Beck, Annelise R; Bernhardt, Birgitta; Warrick, Erika R.; ...

2014-11-07

Electronic wavepackets composed of multiple bound excited states of atomic neon lying between 19.6 and 21.5 eV are launched using an isolated attosecond pulse. Individual quantum beats of the wavepacket are detected by perturbing the induced polarization of the medium with a time-delayed few-femtosecond near-infrared (NIR) pulse via coupling the individual states to multiple neighboring levels. All of the initially excited states are monitored simultaneously in the attosecond transient absorption spectrum, revealing Lorentzian to Fano lineshape spectral changes as well as quantum beats. The most prominent beating of the several that were observed was in the spin–orbit split 3d absorptionmore » features, which has a 40 femtosecond period that corresponds to the spin–orbit splitting of 0.1 eV. The few-level models and multilevel calculations confirm that the observed magnitude of oscillation depends strongly on the spectral bandwidth and tuning of the NIR pulse and on the location of possible coupling states.« less

Singularity in the positive Hall coeffcient near pre-onset temperatures in high-Tc superconductors

NASA Astrophysics Data System (ADS)

Vezzoli, G. C.; Chen, M. F.; Craver, F.; Moon, B. M.; Safari, A.; Burke, T.; Stanley, W.

1990-10-01

Hall measurements using continuous extremely slow cooling and reheating rates as well as employing eqiulibrium point-by-point conventional techniques reveals a clear anomally in RH at pre-onset temperatures near Tc in polycrystalline samples Y1Ba2Cu3O7 and Bi2Sr2Ca2Cu3O10. The anomaly has the appearance of a singularity of Dirac-delta function which parallels earlier work on La1-xSrxCuO4. Recent single crystal work on the Bi-containing high-Tc superconductor is in accord with a clearcut anomaly. The singularity is tentatively interpreted to be associated (upon cooling) with initially the removal of positive holes from the hopping conduction system of the normal state such as from the increased concentration of bound virtual excitons due to increased exciton and hole lifetimes at low temperature. Subsequently the formation of Cooper pairs by mediation from these centers (bound-holes) and/or bound excitons) may cause an ionization of these bound virtual excitons thereby re-introducing holes and electrons into the conduction system at Tc.

Electron accommodation dynamics in the DNA base thymine

NASA Astrophysics Data System (ADS)

King, Sarah B.; Stephansen, Anne B.; Yokoi, Yuki; Yandell, Margaret A.; Kunin, Alice; Takayanagi, Toshiyuki; Neumark, Daniel M.

2015-07-01

The dynamics of electron attachment to the DNA base thymine are investigated using femtosecond time-resolved photoelectron imaging of the gas phase iodide-thymine (I-T) complex. An ultraviolet pump pulse ejects an electron from the iodide and prepares an iodine-thymine temporary negative ion that is photodetached with a near-IR probe pulse. The resulting photoelectrons are analyzed with velocity-map imaging. At excitation energies ranging from -120 meV to +90 meV with respect to the vertical detachment energy (VDE) of 4.05 eV for I-T, both the dipole-bound and valence-bound negative ions of thymine are observed. A slightly longer rise time for the valence-bound state than the dipole-bound state suggests that some of the dipole-bound anions convert to valence-bound species. No evidence is seen for a dipole-bound anion of thymine at higher excitation energies, in the range of 0.6 eV above the I-T VDE, which suggests that if the dipole-bound anion acts as a "doorway" to the valence-bound anion, it only does so at excitation energies near the VDE of the complex.

Electron accommodation dynamics in the DNA base thymine.

PubMed

King, Sarah B; Stephansen, Anne B; Yokoi, Yuki; Yandell, Margaret A; Kunin, Alice; Takayanagi, Toshiyuki; Neumark, Daniel M

2015-07-14

The dynamics of electron attachment to the DNA base thymine are investigated using femtosecond time-resolved photoelectron imaging of the gas phase iodide-thymine (I(-)T) complex. An ultraviolet pump pulse ejects an electron from the iodide and prepares an iodine-thymine temporary negative ion that is photodetached with a near-IR probe pulse. The resulting photoelectrons are analyzed with velocity-map imaging. At excitation energies ranging from -120 meV to +90 meV with respect to the vertical detachment energy (VDE) of 4.05 eV for I(-)T, both the dipole-bound and valence-bound negative ions of thymine are observed. A slightly longer rise time for the valence-bound state than the dipole-bound state suggests that some of the dipole-bound anions convert to valence-bound species. No evidence is seen for a dipole-bound anion of thymine at higher excitation energies, in the range of 0.6 eV above the I(-)T VDE, which suggests that if the dipole-bound anion acts as a "doorway" to the valence-bound anion, it only does so at excitation energies near the VDE of the complex.

Electronic excitation of ground state atoms by collision with heavy gas particles

NASA Technical Reports Server (NTRS)

Hansen, C. Frederick

1993-01-01

Most of the important chemical reactions which occur in the very high temperature air produced around space vehicles as they enter the atmosphere were investigated both experimentally and theoretically, to some extent at least. One remaining reaction about which little is known, and which could be quite important at the extremely high temperatures that will be produced by the class of space vehicles now contemplated - such as the AOTV - is the excitation of bound electron states due to collisions between heavy gas particles. Rates of electronic excitation due to free electron collisions are known to be very rapid, but because these collisions quickly equilibrate the free and bound electron energy, the approach to full equilibrium with the heavy particle kinetic energy will depend primarily on the much slower process of bound electron excitation in heavy particle collisions and the subsequent rapid transfer to free electron energy. This may be the dominant mechanism leading to full equilibrium in the gas once the dissociation process has depleted the molecular states so the transfer between molecular vibrational energy and free electron energy is no longer available as a channel for equilibration of free electron and heavy particle kinetic energies. Two mechanisms seem probable in electronic excitation by heavy particle impact. One of these is the collision excitation and deexcitation of higher electronic states which are Rydberg like. A report, entitled 'Semi-Classical Theory of Electronic Excitation Rates', was submitted previously. This presented analytic expressions for the transition probabilities, assuming that the interaction potential is an exponential repulsion with a perturbation ripple due to the dipole-induced dipole effect in the case of neutral-neutral collisions, and to the ion-dipole interaction in the case of ion-neutral collisions. However the above may be, there is little doubt that excitation of ground state species by collision occurs at the point where the initial and final potentials cross, or at least come very close. Therefore, this mechanism would be applicable to the case where a gas is initially at very low temperature suddenly subjected to high energy heavy particle bombardment. This situation would model the measurement of excitation cross section by molecular beam techniques, for example. The purpose is to report values of cross sections and rate coefficients for collision excitation of ground state atoms estimated with the Landau-Zener transition theory and to compare results with measurement of excitation cross sections for a beam of Hydrogen atoms impacting Argon atom targets. Some very dubious approximations are used, and the comparison with measurement is found less than ideal, but results are at least consistent within order of magnitude. The same model is then applied to the case of N-N atom collisions, even though the approximations then become even more doubtful. Still the rate coefficients obtained are at least plausible in both magnitude and functional form, and as far as I am aware these are the only estimates available for such rate coefficients.

Variable frequency iteration MPPT for resonant power converters

DOEpatents

Zhang, Qian; Bataresh, Issa; Chen, Lin

2015-06-30

A method of maximum power point tracking (MPPT) uses an MPPT algorithm to determine a switching frequency for a resonant power converter, including initializing by setting an initial boundary frequency range that is divided into initial frequency sub-ranges bounded by initial frequencies including an initial center frequency and first and second initial bounding frequencies. A first iteration includes measuring initial powers at the initial frequencies to determine a maximum power initial frequency that is used to set a first reduced frequency search range centered or bounded by the maximum power initial frequency including at least a first additional bounding frequency. A second iteration includes calculating first and second center frequencies by averaging adjacent frequent values in the first reduced frequency search range and measuring second power values at the first and second center frequencies. The switching frequency is determined from measured power values including the second power values.

Evidence for weakly bound electrons in non-irradiated alkane crystals: The electrons as a probe of structural differences in crystals.

PubMed

Pietrow, M; Gagoś, M; Misiak, L E; Kornarzyński, K; Szurkowski, J; Rochowski, P; Grzegorczyk, M

2015-02-14

It is generally assumed that weakly bound (trapped) electrons in organic solids come only from radiolytical (or photochemical) processes like ionization caused by an excited positron entering the sample. This paper presents evidence for the presence of these electrons in non-irradiated samples of docosane. This can be due to the triboelectrification process. We argue that these electrons can be located (trapped) either in interlamellar gaps or in spaces made by non-planar conformers. Electrons from the former ones are bound more weakly than electrons from the latter ones. The origin of Vis absorption for the samples is explained. These spectra can be used as a probe indicating differences in the solid structures of hydrocarbons.

First muon acceleration using a radio-frequency accelerator

NASA Astrophysics Data System (ADS)

Bae, S.; Choi, H.; Choi, S.; Fukao, Y.; Futatsukawa, K.; Hasegawa, K.; Iijima, T.; Iinuma, H.; Ishida, K.; Kawamura, N.; Kim, B.; Kitamura, R.; Ko, H. S.; Kondo, Y.; Li, S.; Mibe, T.; Miyake, Y.; Morishita, T.; Nakazawa, Y.; Otani, M.; Razuvaev, G. P.; Saito, N.; Shimomura, K.; Sue, Y.; Won, E.; Yamazaki, T.

2018-05-01

Muons have been accelerated by using a radio-frequency accelerator for the first time. Negative muonium atoms (Mu- ), which are bound states of positive muons (μ+) and two electrons, are generated from μ+'s through the electron capture process in an aluminum degrader. The generated Mu- 's are initially electrostatically accelerated and injected into a radio-frequency quadrupole linac (RFQ). In the RFQ, the Mu- 's are accelerated to 89 keV. The accelerated Mu- 's are identified by momentum measurement and time of flight. This compact muon linac opens the door to various muon accelerator applications including particle physics measurements and the construction of a transmission muon microscope.

Mechanisms for the Reduction of Actinides and Tc(VII) in Geobacter sulfurreducens

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

Lloyd, Jonathan R.

2004-06-01

The mechanism of the reduction of U(VI) and Cr(VI) has now been studied in detail. Cr(VI) is reduced by one-electron transfer reactions to Cr(III), via a cell-bound Cr(V) intermediate identified by EPR spectroscopy. Studies with a cytochrome c7 mutant demonstrate that the electron transfer chain includes this protein which may be the terminal reductase for Cr(VI). Potential mechanisms of inhibition of Cr(III) precipitation, involving complex formation with organic acids commonly used as electron donors for metal reduction in the subsurface have also been identified. We have also initiated a collaboration with computational chemists led by Prof Ian Hillier in Manchester,more » to model metal binding to cytochrome c7, and subsequent electron transfer from the enzyme to the metal quantum mechanically.« less

Evidence for weakly bound electrons in non-irradiated alkane crystals: The electrons as a probe of structural differences in crystals

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

Pietrow, M., E-mail: mrk@kft.umcs.lublin.pl; Misiak, L. E.; Gagoś, M.

2015-02-14

It is generally assumed that weakly bound (trapped) electrons in organic solids come only from radiolytical (or photochemical) processes like ionization caused by an excited positron entering the sample. This paper presents evidence for the presence of these electrons in non-irradiated samples of docosane. This can be due to the triboelectrification process. We argue that these electrons can be located (trapped) either in interlamellar gaps or in spaces made by non-planar conformers. Electrons from the former ones are bound more weakly than electrons from the latter ones. The origin of Vis absorption for the samples is explained. These spectra canmore » be used as a probe indicating differences in the solid structures of hydrocarbons.« less

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

PubMed Central

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

2016-01-01

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

Quasi-four-particle first-order Faddeev-Watson-Lovelace terms in proton-helium scattering

NASA Astrophysics Data System (ADS)

Safarzade, Zohre; Akbarabadi, Farideh Shojaei; Fathi, Reza; Brunger, Michael J.; Bolorizadeh, Mohammad A.

2017-06-01

The Faddeev-Watson-Lovelace equations, which are typically used for solving three-particle scattering problems, are based on the assumption of target having one active electron while the other electrons remain passive during the collision process. So, in the case of protons scattering from helium or helium-like targets, in which there are two bound-state electrons, the passive electron has a static role in the collision channel to be studied. In this work, we intend to assign a dynamic role to all the target electrons, as they are physically active in the collision. By including an active role for the second electron in proton-helium-like collisions, a new form of the Faddeev-Watson-Lovelace integral equations is needed, in which there is no disconnected kernel. We consider the operators and the wave functions associated with the electrons to obey the Pauli exclusion principle, as the electrons are indistinguishable. In addition, a quasi-three-particle collision is assumed in the initial channel, where the electronic cloud is represented as a single identity in the collision.

Exploring Photoinduced Excited State Evolution in Heterobimetallic Ru(II)-Co(III) Complexes.

PubMed

Kuhar, Korina; Fredin, Lisa A; Persson, Petter

2015-06-18

Quantum chemical calculations provide detailed theoretical information concerning key aspects of photoinduced electron and excitation transfer processes in supramolecular donor-acceptor systems, which are particularly relevant to fundamental charge separation in emerging molecular approaches for solar energy conversion. Here we use density functional theory (DFT) calculations to explore the excited state landscape of heterobimetallic Ru-Co systems with varying degrees of interaction between the two metal centers, unbound, weakly bound, and tightly bound systems. The interplay between structural and electronic factors involved in various excited state relaxation processes is examined through full optimizations of multiple charge/spin states of each of the investigated systems. Low-energy relaxed heterobimetallic states of energy transfer and excitation transfer character are characterized in terms of energy, structure, and electronic properties. These findings support the notion of efficient photoinduced charge separation from a Ru(II)-Co(III) ground state, via initial optical excitation of the Ru-center, to low-energy Ru(III)-Co(II) states. The strongly coupled system has significant involvement of the conjugated bridge, qualitatively distinguishing it from the other two weakly coupled systems. Finally, by constructing potential energy surfaces for the three systems where all charge/spin state combinations are projected onto relevant reaction coordinates, excited state decay pathways are explored.

Observation of quantum entanglement between a photon and a single electron spin confined to an InAs quantum dot

NASA Astrophysics Data System (ADS)

Schaibley, John; Burgers, Alex; McCracken, Greg; Duan, Luming; Berman, Paul; Steel, Duncan; Bracker, Allan; Gammon, Daniel; Sham, Lu

2013-03-01

A single electron spin confined to a single InAs quantum dot (QD) can serve as a qubit for quantum information processing. By utilizing the QD's optically excited trion states in the presence of an externally applied magnetic field, the QD spin can be rapidly initialized, manipulated and read out. A key resource for quantum information is the ability to entangle distinct QD spins. One approach relies on intermediate spin-photon entanglement to mediate the entanglement between distant QD spin qubits. We report a demonstration of quantum entanglement between a photon's polarization state and the spin state of a single electron confined to a single QD. Here, the photon is spontaneously emitted from one of the QD's trion states. The emitted photon's polarization along the detection axis is entangled with the resulting spin state of the QD. By performing projective measurements on the photon's polarization state and correlating these measurements with the state of the QD spin in two different bases, we obtain a lower bound on the entanglement fidelity of 0.59 (after background correction). The fidelity bound is limited almost entirely by the timing resolution of our single photon detector. The spin-photon entanglement generation rate is 3 ×103 s-1. Supported by: NSF, MURI, AFOSR, DARPA, ARO.

Crystallographic analysis of the solid-state dewetting of polycrystalline gold film using automated indexing in a transmission electron microscope

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

Jang, S. A.; Lee, H. J.; Oh, Y. J., E-mail: yjoh@hanbat.ac.kr

We analyzed the effect of crystallographic anisotropy on the morphological evolution of a 12-nm-thick gold film during solid-state dewetting at high temperatures using automated indexing tool in a transmission electron microscopy. Dewetting initiated at grain-boundary triple junctions adjacent to large grains resulting from abnormal grain growth driven by (111) texture development. Voids at the junctions developed shapes with faceted edges bounded by low-index crystal planes. The kinetic mobility of the edges varied with the crystal orientation normal to the edges, with a predominance of specific edges with the slowest retraction rates as the annealing time was increased.

Paramagnetic or diamagnetic persistent currents? A topological point of view

NASA Astrophysics Data System (ADS)

Waintal, Xavier

2009-03-01

A persistent current flows at low temperatures in small conducting rings when they are threaded by a magnetic flux. I will discuss the sign of this persistent current (diamagnetic or paramagnetic response) in the special case of N electrons in a one dimensional ring [1]. One dimension is very special in the sense that the sign of the persistent current is entirely controlled by the topology of the system. I will establish lower bounds for the free energy in the presence of arbitrary electron-electron interactions and external potentials. Those bounds are the counterparts of upper bounds derived by Leggett using another topological argument. Rings with odd (even) numbers of polarized electrons are always diamagnetic (paramagnetic). The situation is more interesting with unpolarized electrons where Leggett upper bound breaks down: rings with N=4n exhibit either paramagnetic behavior or a superconductor-like current-phase relation. The topological argument provides a rigorous justification for the phenomenological Huckel rule which states that cyclic molecules with 4n + 2 electrons like benzene are aromatic while those with 4n electrons are not. [4pt] [1] Xavier Waintal, Geneviève Fleury, Kyryl Kazymyrenko, Manuel Houzet, Peter Schmitteckert, and Dietmar Weinmann Phys. Rev. Lett.101, 106804 (2008).

Molecular mechanism and structure of Trigger Factor bound to the translating ribosome

PubMed Central

Merz, Frieder; Boehringer, Daniel; Schaffitzel, Christiane; Preissler, Steffen; Hoffmann, Anja; Maier, Timm; Rutkowska, Anna; Lozza, Jasmin; Ban, Nenad; Bukau, Bernd; Deuerling, Elke

2008-01-01

Ribosome-associated chaperone Trigger Factor (TF) initiates folding of newly synthesized proteins in bacteria. Here, we pinpoint by site-specific crosslinking the sequence of molecular interactions of Escherichia coli TF and nascent chains during translation. Furthermore, we provide the first full-length structure of TF associated with ribosome–nascent chain complexes by using cryo-electron microscopy. In its active state, TF arches over the ribosomal exit tunnel accepting nascent chains in a protective void. The growing nascent chain initially follows a predefined path through the entire interior of TF in an unfolded conformation, and even after folding into a domain it remains accommodated inside the protective cavity of ribosome-bound TF. The adaptability to accept nascent chains of different length and folding states may explain how TF is able to assist co-translational folding of all kinds of nascent polypeptides during ongoing synthesis. Moreover, we suggest a model of how TF's chaperoning function can be coordinated with the co-translational processing and membrane targeting of nascent polypeptides by other ribosome-associated factors. PMID:18497744

Dynamic spin injection into a quantum well coupled to a spin-split bound state

NASA Astrophysics Data System (ADS)

Maslova, N. S.; Rozhansky, I. V.; Mantsevich, V. N.; Arseyev, P. I.; Averkiev, N. S.; Lähderanta, E.

2018-05-01

We present a theoretical analysis of dynamic spin injection due to spin-dependent tunneling between a quantum well (QW) and a bound state split in spin projection due to an exchange interaction or external magnetic field. We focus on the impact of Coulomb correlations at the bound state on spin polarization and sheet density kinetics of the charge carriers in the QW. The theoretical approach is based on kinetic equations for the electron occupation numbers taking into account high order correlation functions for the bound state electrons. It is shown that the on-site Coulomb repulsion leads to an enhanced dynamic spin polarization of the electrons in the QW and a delay in the carriers tunneling into the bound state. The interplay of these two effects leads to nontrivial dependence of the spin polarization degree, which can be probed experimentally using time-resolved photoluminescence experiments. It is demonstrated that the influence of the Coulomb interactions can be controlled by adjusting the relaxation rates. These findings open a new way of studying the Hubbard-like electron interactions experimentally.

Non-College Bound Student Demonstration Project in Electronics and Laser-ElectroOptics--in Cooperation with Area High Schools, the Private Industry Council, and the Business Labor Council. Final Report.

ERIC Educational Resources Information Center

Alfano, Kathleen

A model program was developed to increase the number of noncollege-bound students who were capable of succeeding in electronics and laser/electro-optics technology (LET) vocational training. The target population was noncollege-bound disadvantaged students, at least 60 percent minorities and women who were historically underrepresented in…

Structure of a human cap-dependent 48S translation pre-initiation complex

PubMed Central

Eliseev, Boris; Yeramala, Lahari; Leitner, Alexander; Karuppasamy, Manikandan; Raimondeau, Etienne; Huard, Karine; Alkalaeva, Elena; Aebersold, Ruedi

2018-01-01

Abstract Eukaryotic translation initiation is tightly regulated, requiring a set of conserved initiation factors (eIFs). Translation of a capped mRNA depends on the trimeric eIF4F complex and eIF4B to load the mRNA onto the 43S pre-initiation complex comprising 40S and initiation factors 1, 1A, 2, 3 and 5 as well as initiator-tRNA. Binding of the mRNA is followed by mRNA scanning in the 48S pre-initiation complex, until a start codon is recognised. Here, we use a reconstituted system to prepare human 48S complexes assembled on capped mRNA in the presence of eIF4B and eIF4F. The highly purified h-48S complexes are used for cross-linking/mass spectrometry, revealing the protein interaction network in this complex. We report the electron cryo-microscopy structure of the h-48S complex at 6.3 Å resolution. While the majority of eIF4B and eIF4F appear to be flexible with respect to the ribosome, additional density is detected at the entrance of the 40S mRNA channel which we attribute to the RNA-recognition motif of eIF4B. The eight core subunits of eIF3 are bound at the 40S solvent-exposed side, as well as the subunits eIF3d, eIF3b and eIF3i. elF2 and initiator-tRNA bound to the start codon are present at the 40S intersubunit side. This cryo-EM structure represents a molecular snap-shot revealing the h-48S complex following start codon recognition. PMID:29401259

Bound-free Spectra for Diatomic Molecules

NASA Technical Reports Server (NTRS)

Schwenke, David W.

2012-01-01

It is now recognized that prediction of radiative heating of entering space craft requires explicit treatment of the radiation field from the infrared (IR) to the vacuum ultra violet (VUV). While at low temperatures and longer wavelengths, molecular radiation is well described by bound-bound transitions, in the short wavelength, high temperature regime, bound-free transitions can play an important role. In this work we describe first principles calculations we have carried out for bound-bound and bound-free transitions in N2, O2, C2, CO, CN, NO, and N2+. Compared to bound ]bound transitions, bound-free transitions have several particularities that make them different to deal with. These include more complicated line shapes and a dependence of emission intensity on both bound state diatomic and atomic concentrations. These will be discussed in detail below. The general procedure we used was the same for all species. The first step is to generate potential energy curves, transition moments, and coupling matrix elements by carrying out ab initio electronic structure calculations. These calculations are expensive, and thus approximations need to be made in order to make the calculations tractable. The only practical method we have to carry out these calculations is the internally contracted multi-reference configuration interaction (icMRCI) method as implemented in the program suite Molpro. This is a widely used method for these kinds of calculations, and is capable of generating very accurate results. With this method, we must first of choose which electrons to correlate, the one-electron basis to use, and then how to generate the molecular orbitals.

Ultrafast terahertz snapshots of excitonic Rydberg states and electronic coherence in an organometal halide perovskite

DOE PAGES

Luo, Liang; Men, Long; Liu, Zhaoyu; ...

2017-06-01

How photoexcitations evolve into Coulomb-bound electron and hole pairs, called excitons, and unbound charge carriers is a key cross-cutting issue in photovoltaics and optoelectronics. Until now, the initial quantum dynamics following photoexcitation remains elusive in the hybrid perovskite system. Furthermore we reveal excitonic Rydberg states with distinct formation pathways by observing the multiple resonant, internal quantum transitions using ultrafast terahertz quasi-particle transport. Nonequilibrium emergent states evolve with a complex co-existence of excitons, carriers and phonons, where a delayed buildup of excitons under on- and off-resonant pumping conditions allows us to distinguish between the loss of electronic coherence and hot statemore » cooling processes. The nearly ~1 ps dephasing time, efficient electron scattering with discrete terahertz phonons and intermediate binding energy of ~13.5 meV in perovskites are distinct from conventional photovoltaic semiconductors. In addition to providing implications for coherent energy conversion, these are potentially relevant to the development of light-harvesting and electron-transport devices.« less

Ultrafast terahertz snapshots of excitonic Rydberg states and electronic coherence in an organometal halide perovskite

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

Luo, Liang; Men, Long; Liu, Zhaoyu

How photoexcitations evolve into Coulomb-bound electron and hole pairs, called excitons, and unbound charge carriers is a key cross-cutting issue in photovoltaics and optoelectronics. Until now, the initial quantum dynamics following photoexcitation remains elusive in the hybrid perovskite system. Furthermore we reveal excitonic Rydberg states with distinct formation pathways by observing the multiple resonant, internal quantum transitions using ultrafast terahertz quasi-particle transport. Nonequilibrium emergent states evolve with a complex co-existence of excitons, carriers and phonons, where a delayed buildup of excitons under on- and off-resonant pumping conditions allows us to distinguish between the loss of electronic coherence and hot statemore » cooling processes. The nearly ~1 ps dephasing time, efficient electron scattering with discrete terahertz phonons and intermediate binding energy of ~13.5 meV in perovskites are distinct from conventional photovoltaic semiconductors. In addition to providing implications for coherent energy conversion, these are potentially relevant to the development of light-harvesting and electron-transport devices.« less

Absorption enhancement in type-II coupled quantum rings due to existence of quasi-bound states

NASA Astrophysics Data System (ADS)

Hsieh, Chi-Ti; Lin, Shih-Yen; Chang, Shu-Wei

2018-02-01

The absorption of type-II nanostructures is often weaker than type-I counterpart due to spatially separated electrons and holes. We model the bound-to-continuum absorption of type-II quantum rings (QRs) using a multiband source-radiation approach using the retarded Green function in the cylindrical coordinate system. The selection rules due to the circular symmetry for allowed transitions of absorption are utilized. The bound-tocontinuum absorptions of type-II GaSb coupled and uncoupled QRs embedded in GaAs matrix are compared here. The GaSb QRs act as energy barriers for electrons but potential wells for holes. For the coupled QR structure, the region sandwiched between two QRs forms a potential reservoir of quasi-bound electrons. Electrons in these states, though look like bound ones, would ultimately tunnel out of the reservoir through barriers. Multiband perfectly-matched layers are introduced to model the tunneling of quasi-bound states into open space. Resonance peaks are observed on the absorption spectra of type-II coupled QRs due to the formation of quasi-bound states in conduction bands, but no resonance exist in the uncoupled QR. The tunneling time of these metastable states can be extracted from the resonance and is in the order of ten femtoseconds. Absorption of coupled QRs is significantly enhanced as compared to that of uncoupled ones in certain spectral windows of interest. These features may improve the performance of photon detectors and photovoltaic devices based on type-II semiconductor nanostructures.

Coherent control of the formation of cold heteronuclear molecules by photoassociation

NASA Astrophysics Data System (ADS)

de Lima, Emanuel F.

2017-01-01

We consider the formation of cold diatomic molecules in the electronic ground state by photoassociation of atoms of dissimilar species. A combination of two transition pathways from the free colliding pair of atoms to a bound vibrational level of the electronic molecular ground state is envisioned. The first pathway consists of a pump-dump scheme with two time-delayed laser pulses in the near-infrared frequency domain. The pump pulse drives the transition to a bound vibrational level of an excited electronic state, while the dump pulse transfers the population to a bound vibrational level of the electronic ground state. The second pathway takes advantage of the existing permanent dipole moment and employs a single pulse in the far-infrared domain to drive the transition from the unbound atoms directly to a bound vibrational level in the electronic ground state. We show that this scheme offers the possibility to coherently control the photoassociation yield by manipulating the relative phase and timing of the pulses. The photoassociation mechanism is illustrated for the formation of cold LiCs molecules.

Bound and resonance states of the dipolar anion of hydrogen cyanide: Competition between threshold effects and rotation in an open quantum system

DOE PAGES

Fossez, K.; Michel, N.; Nazarewicz, W.; ...

2015-01-12

In this paper, bound and resonance states of the dipole-bound anion of hydrogen cyanide HCN – are studied using a nonadiabatic pseudopotential method and the Berggren expansion technique involving bound states, decaying resonant states, and nonresonant scattering continuum. We devise an algorithm to identify the resonant states in the complex energy plane. To characterize spatial distributions of electronic wave functions, we introduce the body-fixed density and use it to assign families of resonant states into collective rotational bands. We find that the nonadiabatic coupling of electronic motion to molecular rotation results in a transition from the strong-coupling to weak-coupling regime.more » In the strong-coupling limit, the electron moving in a subthreshold, spatially extended halo state follows the rotational motion of the molecule. Above the ionization threshold, the electron's motion in a resonance state becomes largely decoupled from molecular rotation. Finally, the widths of resonance-band members depend primarily on the electron orbital angular momentum.« less

Quantum Control and Entanglement of Spins in Silicon Carbide

NASA Astrophysics Data System (ADS)

Klimov, Paul

Over the past several decades silicon carbide (SiC) has matured into a versatile material platform for high-power electronics and optoelectronic and micromechanical devices. Recent advances have also established SiC as a promising host for quantum technologies based on the spin of intrinsic defects, with the potential of leveraging existing device fabrication protocols alongside solid-state quantum control. Among these defects are the divacancies and related color centers, which have ground-state electron-spin triplets with coherence times as long as one millisecond and built-in optical interfaces operating near the telecommunication wavelengths. This rapidly developing field has prompted research into the SiC material host to understand how defect-bound electron spins interact with their surrounding nuclear spin bath. Although nuclear spins are a major source of decoherence in color-center spin systems, they are also a valuable resource since they can have coherence times that are orders of magnitude longer than electron spins. In this talk I will discuss our recent efforts to interface defect-bound electron spins in SiC with the nuclear spins of naturally occurring 29Si and 13C isotopic defects. I will discuss how the hyperfine interaction can be used to strongly initialize them, to coherently control them, to read them out, and to produce genuine electron-nuclear ensemble entanglement, all at ambient conditions. These demonstrations motivate further research into spins in SiC for prospective quantum technologies. In collaboration with A. Falk, D. Christle, K. Miao, H. Seo, V. Ivady, A. Gali, G. Galli, and D. D. Awschalom. This research was supported by the AFOSR, the NSF DMR-1306300, and the NSF Materials Research Science and Engineering Center.

Studying electron-PAG interactions using electron-induced fluorescence

NASA Astrophysics Data System (ADS)

Narasimhan, Amrit; Grzeskowiak, Steven; Ostrander, Jonathan; Schad, Jonathon; Rebeyev, Eliran; Neisser, Mark; Ocola, Leonidas E.; Denbeaux, Gregory; Brainard, Robert L.

2016-03-01

In extreme ultraviolet (EUV) lithography, 92 eV photons are used to expose photoresists. Typical EUV resists are organic-based and chemically amplified using photoacid generators (PAGs). Upon exposure, PAGs produce acids which catalyze reactions that result in changes in solubility. In EUV lithography, photo- and secondary electrons (energies of 10- 80 eV) play a large role in PAG acid-production. Several mechanisms for electron-PAG interactions (e.g. electron trapping, and hole-initiated chemistry) have been proposed. The aim of this study is to explore another mechanism - internal excitation - in which a bound PAG electron can be excited by receiving energy from another energetic electron, causing a reaction that produces acid. This paper explores the mechanism of internal excitation through the analogous process of electron-induced fluorescence, in which an electron loses energy by transferring that energy to a molecule and that molecule emits a photon rather than decomposing. We will show and quantify electron-induced fluorescence of several fluorophores in polymer films to mimic resist materials, and use this information to refine our proposed mechanism. Relationships between the molecular structure of fluorophores and fluorescent quantum yield may aid in the development of novel PAGs for EUV lithography.

Electron teleportation via Majorana bound states in a mesoscopic superconductor.

PubMed

Fu, Liang

2010-02-05

Zero-energy Majorana bound states in superconductors have been proposed to be potential building blocks of a topological quantum computer, because quantum information can be encoded nonlocally in the fermion occupation of a pair of spatially separated Majorana bound states. However, despite intensive efforts, nonlocal signatures of Majorana bound states have not been found in charge transport. In this work, we predict a striking nonlocal phase-coherent electron transfer process by virtue of tunneling in and out of a pair of Majorana bound states. This teleportation phenomenon only exists in a mesoscopic superconductor because of an all-important but previously overlooked charging energy. We propose an experimental setup to detect this phenomenon in a superconductor-quantum-spin-Hall-insulator-magnetic-insulator hybrid system.

Photoexcitation circular dichroism in chiral molecules

NASA Astrophysics Data System (ADS)

Beaulieu, S.; Comby, A.; Descamps, D.; Fabre, B.; Garcia, G. A.; Géneaux, R.; Harvey, A. G.; Légaré, F.; Mašín, Z.; Nahon, L.; Ordonez, A. F.; Petit, S.; Pons, B.; Mairesse, Y.; Smirnova, O.; Blanchet, V.

2018-05-01

Chiral effects appear in a wide variety of natural phenomena and are of fundamental importance in science, from particle physics to metamaterials. The standard technique of chiral discrimination—photoabsorption circular dichroism—relies on the magnetic properties of a chiral medium and yields an extremely weak chiral response. Here, we propose and demonstrate an orders of magnitude more sensitive type of circular dichroism in neutral molecules: photoexcitation circular dichroism. This technique does not rely on weak magnetic effects, but takes advantage of the coherent helical motion of bound electrons excited by ultrashort circularly polarized light. It results in an ultrafast chiral response and the efficient excitation of a macroscopic chiral density in an initially isotropic ensemble of randomly oriented chiral molecules. We probe this excitation using linearly polarized laser pulses, without the aid of further chiral interactions. Our time-resolved study of vibronic chiral dynamics opens a way to the efficient initiation, control and monitoring of chiral chemical change in neutral molecules at the level of electrons.

Magnetic tunnel spin injectors for spintronics

NASA Astrophysics Data System (ADS)

Wang, Roger

Research in spin-based electronics, or "spintronics", has a universal goal to develop applications for electron spin in a broad range of electronics and strives to produce low power nanoscale devices. Spin injection into semiconductors is an important initial step in the development of spintronic devices, with the goal to create a highly spin polarized population of electrons inside a semiconductor at room temperature for study, characterization, and manipulation. This dissertation investigates magnetic tunnel spin injectors that aim to meet the spin injection requirements needed for potential spintronic devices. Magnetism and spin are inherently related, and chapter 1 provides an introduction on magnetic tunneling and spintronics. Chapter 2 then describes the fabrication of the spin injector structures studied in this dissertation, and also illustrates the optical spin detection technique that correlates the measured electroluminescence polarization from quantum wells to the electron spin polarization inside the semiconductor. Chapter 3 reports the spin injection from the magnetic tunnel transistor (MTT) spin injector, which is capable of producing highly spin polarized tunneling currents by spin selective scattering in its multilayer structure. The MTT achieves ˜10% lower bound injected spin polarization in GaAs at 1.4 K. Chapter 4 reports the spin injection from CoFe-MgO(100) tunnel spin injectors, where spin dependent tunneling through MgO(100) produces highly spin polarized tunneling currents. These structures achieve lower bound spin polarizations exceeding 50% at 100 K and 30% in GaAs at 290 K. The CoFe-MgO spin injectors also demonstrate excellent thermal stability, maintaining high injection efficiencies even after exposure to temperatures of up to 400 C. Bias voltage and temperature dependent studies on these structures indicate a significant dependence of the electroluminescence polarization on the spin and carrier recombination lifetimes inside the semiconductor. Chapter 5 investigates these spin and carrier lifetime effects on the electroluminescence polarization using time resolved optical techniques. These studies suggest that a peak in the carrier lifetime with temperature is responsible for the nonmonotonic temperature dependence observed in the electroluminescence polarization, and that the initially injected spin polarization from CoFe-MgO spin injectors is a nearly temperature independent ˜70% from 10 K up to room temperature.

The effect of anions on bound acetylcholine in frog sartorius muscle.

PubMed Central

Ceccarelli, B; Molenaar, P C; Oen, B S; Polak, R L; Torri-Tarelli, F; van Kempen, G T

1989-01-01

1. Frog sartorius muscles were treated with an irreversible cholinesterase inhibitor and then incubated in isotonic potassium propionate solution (isotonic KPr). Total and bound, presumably vesicular, acetylcholine (ACh) in the tissue and ACh in the medium were assayed by mass fragmentography, miniature end-plate potentials (MEPPs) were recorded and the end-plates were investigated by electron microscopy. 2. Incubation in isotonic KPr for 30 min stimulated ACh release and concomitantly decreased total and bound ACh. Nerve stimulation for 30 min by trains of impulses (0.1 s trains of 100 Hz, 1 train s-1) in normal-potassium propionate-containing solution had the same effects. 3. When the tissue was incubated in normal-K+ Ringer solution for 3 h, following chemical or electric stimulation, bound ACh recovered to about 75% of the initial value, provided that Cl- ions were present in the medium. In the presence of propionate instead of Cl- ions almost no recovery of bound ACh took place. There was also recovery of bound ACh in the presence of either NO3- or gluconate ions. In NO3- it was the same as in Cl-, but in gluconate it was less than found in Cl- -containing medium. 4. Recovery of total ACh, in contrast to bound ACh, took place even in the presence of propionate ions, showing that extracellular Cl- is not required for the synthesis of ACh. 5. In terminals recovered in normal Ringer solution, many synaptic vesicles were found, but terminals 'recovered' in propionate solution were depleted of vesicles. 6. From these and other results it is concluded that the recycling of synaptic vesicles normally requires the presence of extracellular chloride. Images Fig. 1 Fig. 2 PMID:2789283

Gedanken densities and exact constraints in density functional theory.

PubMed

Perdew, John P; Ruzsinszky, Adrienn; Sun, Jianwei; Burke, Kieron

2014-05-14

Approximations to the exact density functional for the exchange-correlation energy of a many-electron ground state can be constructed by satisfying constraints that are universal, i.e., valid for all electron densities. Gedanken densities are designed for the purpose of this construction, but need not be realistic. The uniform electron gas is an old gedanken density. Here, we propose a spherical two-electron gedanken density in which the dimensionless density gradient can be an arbitrary positive constant wherever the density is non-zero. The Lieb-Oxford lower bound on the exchange energy can be satisfied within a generalized gradient approximation (GGA) by bounding its enhancement factor or simplest GGA exchange-energy density. This enhancement-factor bound is well known to be sufficient, but our gedanken density shows that it is also necessary. The conventional exact exchange-energy density satisfies no such local bound, but energy densities are not unique, and the simplest GGA exchange-energy density is not an approximation to it. We further derive a strongly and optimally tightened bound on the exchange enhancement factor of a two-electron density, which is satisfied by the local density approximation but is violated by all published GGA's or meta-GGA's. Finally, some consequences of the non-uniform density-scaling behavior for the asymptotics of the exchange enhancement factor of a GGA or meta-GGA are given.

Generalization of the Hartree-Fock approach to collision processes

NASA Astrophysics Data System (ADS)

Hahn, Yukap

1997-06-01

The conventional Hartree and Hartree-Fock approaches for bound states are generalized to treat atomic collision processes. All the single-particle orbitals, for both bound and scattering states, are determined simultaneously by requiring full self-consistency. This generalization is achieved by introducing two Ansäauttze: (a) the weak asymptotic boundary condition, which maintains the correct scattering energy and target orbitals with correct number of nodes, and (b) square integrable amputated scattering functions to generate self-consistent field (SCF) potentials for the target orbitals. The exact initial target and final-state asymptotic wave functions are not required and thus need not be specified a priori, as they are determined simultaneously by the SCF iterations. To check the asymptotic behavior of the solution, the theory is applied to elastic electron-hydrogen scattering at low energies. The solution is found to be stable and the weak asymptotic condition is sufficient to produce the correct scattering amplitudes. The SCF potential for the target orbital shows the strong penetration by the projectile electron during the collision, but the exchange term tends to restore the original form. Potential applicabilities of this extension are discussed, including the treatment of ionization and shake-off processes.

Photoinduced Oxidative DNA Damage Revealed by an Agarose Gel Nicking Assay: A Biophysical Chemistry Laboratory Experiment

NASA Astrophysics Data System (ADS)

Shafirovich, Vladimir; Singh, Carolyn; Geacintov, Nicholas E.

2003-11-01

Oxidative damage of DNA molecules associated with electron-transfer reactions is an important phenomenon in living cells, which can lead to mutations and contribute to carcinogenesis and the aging processes. This article describes the design of several simple experiments to explore DNA damage initiated by photoinduced electron-transfer reactions sensitized by the acridine derivative, proflavine (PF). A supercoiled DNA agarose gel nicking assay is employed as a sensitive probe of DNA strand cleavage. A low-cost experimental and computer-interfaced imaging apparatus is described allowing for the digital recording and analysis of the gel electrophoresis results. The first experiment describes the formation of direct strand breaks in double-stranded DNA induced by photoexcitation of the intercalated PF molecules. The second experiment demonstrates that the addition of the well-known electron acceptor, methylviologen, gives rise to a significant enhancement of the photochemical DNA strand cleavage effect. This occurs by an electron transfer step to methylviologen that renders the inital photoinduced charge separation between photoexcited PF and DNA irreversible. The third experiment demonstrates that the action spectrum of the DNA photocleavage matches the absorption spectrum of DNA-bound, intercalated PF molecules, which differs from that of free PF molecules. This result demonstrates that the photoinduced DNA strand cleavage is initiated by intercalated rather than free PF molecules.

Extending Quantum Chemistry of Bound States to Electronic Resonances

NASA Astrophysics Data System (ADS)

Jagau, Thomas-C.; Bravaya, Ksenia B.; Krylov, Anna I.

2017-05-01

Electronic resonances are metastable states with finite lifetime embedded in the ionization or detachment continuum. They are ubiquitous in chemistry, physics, and biology. Resonances play a central role in processes as diverse as DNA radiolysis, plasmonic catalysis, and attosecond spectroscopy. This review describes novel equation-of-motion coupled-cluster (EOM-CC) methods designed to treat resonances and bound states on an equal footing. Built on complex-variable techniques such as complex scaling and complex absorbing potentials that allow resonances to be associated with a single eigenstate of the molecular Hamiltonian rather than several continuum eigenstates, these methods extend electronic-structure tools developed for bound states to electronic resonances. Selected examples emphasize the formal advantages as well as the numerical accuracy of EOM-CC in the treatment of electronic resonances. Connections to experimental observables such as spectra and cross sections, as well as practical aspects of implementing complex-valued approaches, are also discussed.

Resistivity bound for hydrodynamic bad metals

PubMed Central

Lucas, Andrew; Hartnoll, Sean A.

2017-01-01

We obtain a rigorous upper bound on the resistivity ρ of an electron fluid whose electronic mean free path is short compared with the scale of spatial inhomogeneities. When such a hydrodynamic electron fluid supports a nonthermal diffusion process—such as an imbalance mode between different bands—we show that the resistivity bound becomes ρ≲AΓ. The coefficient A is independent of temperature and inhomogeneity lengthscale, and Γ is a microscopic momentum-preserving scattering rate. In this way, we obtain a unified mechanism—without umklapp—for ρ∼T2 in a Fermi liquid and the crossover to ρ∼T in quantum critical regimes. This behavior is widely observed in transition metal oxides, organic metals, pnictides, and heavy fermion compounds and has presented a long-standing challenge to transport theory. Our hydrodynamic bound allows phonon contributions to diffusion constants, including thermal diffusion, to directly affect the electrical resistivity. PMID:29073054

THE IN VITRO DIFFERENTIATION OF MONONUCLEAR PHAGOCYTES

PubMed Central

Cohn, Zanvil A.; Fedorko, Martha E.; Hirsch, James G.

1966-01-01

A combined morphological, autoradiographic, and cytochemical study at the electron microscope level has been directed towards the formation of electron-opaque granules of cultured macrophages. Labeling of the membrane-bound vesicular structures of pinocytic origin was accomplished with colloidal gold. The initial uptake of gold occurred within micropinocytic vesicles. These electron-lucent vesicles subsequently fused with and discharged their contents into larger pinocytic vacuoles. Colloidal gold was homogeneously distributed in the large pinosomes. In contrast, gold was initially deposited in the periphery of preformed dense granules indicating that these structures were also in constant interaction with the external environment. Colloidal gold was not observed within the cisternae of the endoplasmic reticulum nor within the saccules or vesicles of the Golgi apparatus. There were, however, many small, gold-free vesicles, indistinguishable from Golgi vesicles, which were preferentially aligned about and appeared to fuse with the large pinosomes. The intracellular flow of leucine-H3-labeled protein was followed by electron microscopic autoradiography. After a 15 min pulse of labeled amino acid there was initial labeling of the rough endoplasmic reticulum. Subsequently, much of the label appeared in the Golgi complex. At still later time periods the cytoplasmic dense granules contained the majority of the isotope. Acid phosphatase activity was localized to the dense granules and in the majority of cells to the Golgi apparatus. It is suggested that hydrolytic enzymes are initially synthesized in the endoplasmic reticulum and are then transferred to the Golgi apparatus. Here they are packaged into small Golgi vesicles which represent the primary lysosome of macrophages. The Golgi vesicles subsequently fuse with pinosomes, thereby discharging their hydrolases and forming digestive granules or secondary lysosomes. PMID:5931922

Role of Humic-Bound Iron as an Electron Transfer Agent in Dissimilatory Fe(III) Reduction

PubMed Central

Lovley, Derek R.; Blunt-Harris, Elizabeth L.

1999-01-01

The dissimilatory Fe(III) reducer Geobacter metallireducens reduced Fe(III) bound in humic substances, but the concentrations of Fe(III) in a wide range of highly purified humic substances were too low to account for a significant portion of the electron-accepting capacities of the humic substances. Furthermore, once reduced, the iron in humic substances could not transfer electrons to Fe(III) oxide. These results suggest that other electron-accepting moieties in humic substances, such as quinones, are the important electron-accepting and shuttling agents under Fe(III)-reducing conditions. PMID:10473447

Advancing medical device innovation through collaboration and coordination of structured data capture pilots: Report from the Medical Device Epidemiology Network (MDEpiNet) Specific, Measurable, Achievable, Results-Oriented, Time Bound (SMART) Think Tank.

PubMed

Reed, Terrie L; Drozda, Joseph P; Baskin, Kevin M; Tcheng, James; Conway, Karen; Wilson, Natalia; Marinac-Dabic, Danica; Heise, Theodore; Krucoff, Mitchell W

2017-12-01

The Medical Device Epidemiology Network (MDEpiNet) is a public private partnership (PPP) that provides a platform for collaboration on medical device evaluation and depth of expertise for supporting pilots to capture, exchange and use device information for improving device safety and protecting public health. The MDEpiNet SMART Think Tank, held in February, 2013, sought to engage expert stakeholders who were committed to improving the capture of device data, including Unique Device Identification (UDI), in key electronic health information. Prior to the Think Tank there was limited collaboration among stakeholders beyond a few single health care organizations engaged in electronic capture and exchange of device data. The Think Tank resulted in what has become two sustainable multi-stakeholder device data capture initiatives, BUILD and VANGUARD. These initiatives continue to mature within the MDEpiNet PPP structure and are well aligned with the goals outlined in recent FDA-initiated National Medical Device Planning Board and Medical Device Registry Task Force white papers as well as the vision for the National Evaluation System for health Technology.%. Published by Elsevier Inc.

Universal bounds on current fluctuations.

PubMed

Pietzonka, Patrick; Barato, Andre C; Seifert, Udo

2016-05-01

For current fluctuations in nonequilibrium steady states of Markovian processes, we derive four different universal bounds valid beyond the Gaussian regime. Different variants of these bounds apply to either the entropy change or any individual current, e.g., the rate of substrate consumption in a chemical reaction or the electron current in an electronic device. The bounds vary with respect to their degree of universality and tightness. A universal parabolic bound on the generating function of an arbitrary current depends solely on the average entropy production. A second, stronger bound requires knowledge both of the thermodynamic forces that drive the system and of the topology of the network of states. These two bounds are conjectures based on extensive numerics. An exponential bound that depends only on the average entropy production and the average number of transitions per time is rigorously proved. This bound has no obvious relation to the parabolic bound but it is typically tighter further away from equilibrium. An asymptotic bound that depends on the specific transition rates and becomes tight for large fluctuations is also derived. This bound allows for the prediction of the asymptotic growth of the generating function. Even though our results are restricted to networks with a finite number of states, we show that the parabolic bound is also valid for three paradigmatic examples of driven diffusive systems for which the generating function can be calculated using the additivity principle. Our bounds provide a general class of constraints for nonequilibrium systems.

Attosecond delay in the molecular photoionization of asymmetric molecules.

PubMed

Chacón, Alexis; Ruiz, Camilo

2018-02-19

We report theoretical calculations of the delay in photoemission from CO with particular emphasis on the role of the ultrafast electronic bound dynamics. We study the delays in photoionization in the HOMO and HOMO-1 orbitals of the CO molecule by looking into the stereo Wigner time delay technique. That compares the delay in photoemission from electrons emitted to the left and right to extract structural and dynamical information of the ionization process. For this we apply two techniques: The attosecond streak camera and the time of flight technique. Although they should provide the same results we have found large discrepancies of up to 36 in the case of HOMO, while for the HOMO-1 we obtain the same results with the two techniques. We have found that the large time delays observed in the HOMO orbital with the streaking technique are a consequence of the resonant transition triggered by the streaking field. This resonant transition produces a bound electron wavepacket that modifies the measurements of delay in photoionization. As a result of this observation, our technique allows us to reconstruct the bound wavepacket dynamics induced by the streaking field. By measuring the expected value of the electron momentum along the polarization direction after the streaking field has finished, we can recover the relative phase between the complex amplitudes of the HOMO and LUMO orbitals. These theoretical calculations pave the way for the measurement of ultrafast bound-bound electron transitionsand its crucial role for the delay in photoemission observation.

A Proteomic View at the Biochemistry of Syntrophic Butyrate Oxidation in Syntrophomonas wolfei

PubMed Central

Schmidt, Alexander; Müller, Nicolai; Schink, Bernhard; Schleheck, David

2013-01-01

In syntrophic conversion of butyrate to methane and CO2, butyrate is oxidized to acetate by secondary fermenting bacteria such as Syntrophomonas wolfei in close cooperation with methanogenic partner organisms, e.g., Methanospirillum hungatei. This process involves an energetically unfavourable shift of electrons from the level of butyryl-CoA oxidation to the substantially lower redox potential of proton and/or CO2 reduction, in order to transfer these electrons to the methanogenic partner via hydrogen and/or formate. In the present study, all prominent membrane-bound and soluble proteins expressed in S. wolfei specifically during syntrophic growth with butyrate, in comparison to pure-culture growth with crotonate, were examined by one- and two-dimensional gel electrophoresis, and identified by peptide fingerprinting-mass spectrometry. A membrane-bound, externally oriented, quinone-linked formate dehydrogenase complex was expressed at high level specifically during syntrophic butyrate oxidation, comprising a selenocystein-linked catalytic subunit with a membrane-translocation pathway signal (TAT), a membrane-bound iron-sulfur subunit, and a membrane-bound cytochrome. Soluble hydrogenases were expressed at high levels specifically during growth with crotonate. The results were confirmed by native protein gel electrophoresis, by formate dehydrogenase and hydrogenase-activity staining, and by analysis of formate dehydrogenase and hydrogenase activities in intact cells and cell extracts. Furthermore, constitutive expression of a membrane-bound, internally oriented iron-sulfur oxidoreductase (DUF224) was confirmed, together with expression of soluble electron-transfer flavoproteins (EtfAB) and two previously identified butyryl-CoA dehydrogenases. Our findings allow to depict an electron flow scheme for syntrophic butyrate oxidation in S. wolfei. Electrons derived from butyryl-CoA are transferred through a membrane-bound EtfAB:quinone oxidoreductase (DUF224) to a menaquinone cycle and further via a b-type cytochrome to an externally oriented formate dehydrogenase. Hence, an ATP hydrolysis-driven proton-motive force across the cytoplasmatic membrane would provide the energy input for the electron potential shift necessary for formate formation. PMID:23468890

New constraints and prospects for sub-GeV dark matter scattering off electrons in xenon

NASA Astrophysics Data System (ADS)

Essig, Rouven; Volansky, Tomer; Yu, Tien-Tien

2017-08-01

We study in detail sub-GeV dark matter scattering off electrons in xenon, including the expected electron recoil spectra and annual modulation spectra. We derive improved constraints using low-energy XENON10 and XENON100 ionization-only data. For XENON10, in addition to including electron-recoil data corresponding to about 1-3 electrons, we include for the first time events corresponding to about 4-7 electrons. Assuming the scattering is momentum independent (FDM=1 ), this strengthens a previous cross-section bound by almost an order of magnitude for dark matter masses above 50 MeV. The available XENON100 data corresponds to events with about 4-50 electrons, and leads to a constraint that is comparable to the XENON10 bound above 50 MeV for FDM=1 . We demonstrate that a search for an annual modulation signal in upcoming xenon experiments (XENON1T, XENONnT, LZ) could substantially improve the above bounds even in the presence of large backgrounds. We also emphasize that in simple benchmark models of sub-GeV dark matter, the dark matter-electron scattering rate can be as high as one event every ten (two) seconds in the XENON1T (XENONnT or LZ) experiments, without being in conflict with any other known experimental bounds. While there are several sources of backgrounds that can produce single- or few-electron events, a large event rate can be consistent with a dark matter signal and should not be simply written off as purely a detector curiosity. This fact motivates a detailed analysis of the ionization-data ("S2") data, taking into account the expected annual modulation spectrum of the signal rate, as well as the DM-induced electron-recoil spectra, which are another powerful discriminant between signal and background.

Dissociative recombination of O2(+), NO(+) and N2(+)

NASA Technical Reports Server (NTRS)

Guberman, S. L.

1983-01-01

A new L(2) approach for the calculation of the threshold molecular capture width needed for the determination of DR cross sections was developed. The widths are calculated with Fermi's golden rule by substituting Rydberg orbitals for the free electron continuum coulomb orbital. It is shown that the calculated width converges exponentially as the effective principal quantum number of the Rydberg orbital increases. The threshold capture width is then easily obtained. Since atmospheric recombination involves very low energy electrons, the threshold capture widths are essential to the calculation of DR cross sections for the atmospheric species studied here. The approach described makes use of bound state computer codes already in use. A program that collects width matrix elements over CI wavefunctions for the initial and final states is described.

Tunneling spectroscopy of quasiparticle bound states in a spinful Josephson junction.

PubMed

Chang, W; Manucharyan, V E; Jespersen, T S; Nygård, J; Marcus, C M

2013-05-24

The spectrum of a segment of InAs nanowire, confined between two superconducting leads, was measured as function of gate voltage and superconducting phase difference using a third normal-metal tunnel probe. Subgap resonances for odd electron occupancy-interpreted as bound states involving a confined electron and a quasiparticle from the superconducting leads, reminiscent of Yu-Shiba-Rusinov states-evolve into Kondo-related resonances at higher magnetic fields. An additional zero-bias peak of unknown origin is observed to coexist with the quasiparticle bound states.

Exploration of momentum evolution and three-dimensional localization in recombined electron wave packets

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

Zeibel, J. G.; Jones, R. R.

2003-08-01

Picosecond ''half-cycle'' pulses (HCPs) have been used to produce electronic wave packets by recombining photoelectrons with their parent ions. The time-dependent momentum distributions of the bound wave packets are probed using a second HCP and the impulsive momentum retrieval (IMR) method. For a given delay between the initial photoionization event and the HCP recombination, classical trajectory simulations predict pronounced periodic wave packet motion for a restricted range of recombining HCP amplitudes. This motion is characterized by the repeated formation and collapse of a highly localized spike in the three-dimensional electron probability density at a large distance from the nucleus. Ourmore » experiments confirm that oscillatory wave packet motion occurs only for certain recombination ''kick'' strengths. Moreover, the measured time-dependent momentum distributions are consistent with the predicted formation of a highly localized electron packet. We demonstrate a variation of the IMR in which amplitude modulation of the HCP probe field is employed to suppress noise and allow for a more direct recovery of electron momentum from experimental ionization data.« less

Observation of the continuous stern-gerlach effect on an electron bound in an atomic Ion

PubMed

Hermanspahn; Haffner; Kluge; Quint; Stahl; Verdu; Werth

2000-01-17

We report on the first observation of the continuous Stern-Gerlach effect on an electron bound in an atomic ion. The measurement was performed on a single hydrogenlike ion ( 12C5+) in a Penning trap. The measured g factor of the bound electron, g = 2.001 042(2), is in excellent agreement with the theoretical value, confirming the relativistic correction at a level of 0.1%. This proves the possibility of g-factor determinations on atomic ions to high precision by using the continuous Stern-Gerlach effect. The result demonstrates the feasibility of conducting experiments on single heavy highly charged ions to test quantum electrodynamics in the strong electric field of the nucleus.

Finite-nuclear-size contribution to the g factor of a bound electron: Higher-order effects

NASA Astrophysics Data System (ADS)

Karshenboim, Savely G.; Ivanov, Vladimir G.

2018-02-01

A precision comparison of theory and experiments on the g factor of an electron bound in a hydrogenlike ion with a spinless nucleus requires a detailed account of finite-nuclear-size contributions. While the relativistic corrections to the leading finite-size contribution are known, the higher-order effects need an additional consideration. Two results are presented in the paper. One is on the anomalous-magnetic-moment correction to the finite-size effects and the other is due to higher-order effects in Z α m RN . We also present here a method to relate the contributions to the g factor of a bound electron in a hydrogenlike atom to its energy within a nonrelativistic approach.

Architecture of the RNA polymerase II-Mediator core initiation complex.

PubMed

Plaschka, C; Larivière, L; Wenzeck, L; Seizl, M; Hemann, M; Tegunov, D; Petrotchenko, E V; Borchers, C H; Baumeister, W; Herzog, F; Villa, E; Cramer, P

2015-02-19

The conserved co-activator complex Mediator enables regulated transcription initiation by RNA polymerase (Pol) II. Here we reconstitute an active 15-subunit core Mediator (cMed) comprising all essential Mediator subunits from Saccharomyces cerevisiae. The cryo-electron microscopic structure of cMed bound to a core initiation complex was determined at 9.7 Å resolution. cMed binds Pol II around the Rpb4-Rpb7 stalk near the carboxy-terminal domain (CTD). The Mediator head module binds the Pol II dock and the TFIIB ribbon and stabilizes the initiation complex. The Mediator middle module extends to the Pol II foot with a 'plank' that may influence polymerase conformation. The Mediator subunit Med14 forms a 'beam' between the head and middle modules and connects to the tail module that is predicted to bind transcription activators located on upstream DNA. The Mediator 'arm' and 'hook' domains contribute to a 'cradle' that may position the CTD and TFIIH kinase to stimulate Pol II phosphorylation.

Global a priori estimates for the inhomogeneous Landau equation with moderately soft potentials

NASA Astrophysics Data System (ADS)

Cameron, Stephen; Silvestre, Luis; Snelson, Stanley

2018-05-01

We establish a priori upper bounds for solutions to the spatially inhomogeneous Landau equation in the case of moderately soft potentials, with arbitrary initial data, under the assumption that mass, energy and entropy densities stay under control. Our pointwise estimates decay polynomially in the velocity variable. We also show that if the initial data satisfies a Gaussian upper bound, this bound is propagated for all positive times.

Inhomogeneous nuclear spin polarization induced by helicity-modulated optical excitation of fluorine-bound electron spins in ZnSe

NASA Astrophysics Data System (ADS)

Heisterkamp, F.; Greilich, A.; Zhukov, E. A.; Kirstein, E.; Kazimierczuk, T.; Korenev, V. L.; Yugova, I. A.; Yakovlev, D. R.; Pawlis, A.; Bayer, M.

2015-12-01

Optically induced nuclear spin polarization in a fluorine-doped ZnSe epilayer is studied by time-resolved Kerr rotation using resonant excitation of donor-bound excitons. Excitation with helicity-modulated laser pulses results in a transverse nuclear spin polarization, which is detected as a change of the Larmor precession frequency of the donor-bound electron spins. The frequency shift in dependence on the transverse magnetic field exhibits a pronounced dispersion-like shape with resonances at the fields of nuclear magnetic resonance of the constituent zinc and selenium isotopes. It is studied as a function of external parameters, particularly of constant and radio frequency external magnetic fields. The width of the resonance and its shape indicate a strong spatial inhomogeneity of the nuclear spin polarization in the vicinity of a fluorine donor. A mechanism of optically induced nuclear spin polarization is suggested based on the concept of resonant nuclear spin cooling driven by the inhomogeneous Knight field of the donor-bound electron.

Hybrid Theory of Electron-Hydrogenic Systems Elastic Scattering

NASA Technical Reports Server (NTRS)

Bhatia, A. K.

2007-01-01

Accurate electron-hydrogen and electron-hydrogenic cross sections are required to interpret fusion experiments, laboratory plasma physics and properties of the solar and astrophysical plasmas. We have developed a method in which the short-range and long-range correlations can be included at the same time in the scattering equations. The phase shifts have rigorous lower bounds and the scattering lengths have rigorous upper bounds. The phase shifts in the resonance region can be used to calculate very accurately the resonance parameters.

Electron-Transfer Kinetics of Redox Centers Anchored to Metal Surfaces: Weak- versus Strong-Overlap Reaction Pathways.

DTIC Science & Technology

1983-11-01

constants ket are presented for the one-electron electroreduction of various Co1]:I(NH3)5X complexes bound to mercury, platinum, and gold surfaces...electroreduction of various Co^^(NH𔃽)𔃿X complexes bound to mercury, platinum, and gold surfaces via either small inorganic or extended organic ligands X. t...platinum, gold , and copper, to enable values of ke* to be obtained for the one-electron reduction of the surface-Douna_redox center.2.3 These

Coated particles for lithium battery cathodes

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

Singh, Mohit; Eitouni, Hany Basam; Pratt, Russell Clayton

Particles of cathodic materials are coated with polymer to prevent direct contact between the particles and the surrounding electrolyte. The polymers are held in place either by a) growing the polymers from initiators covalently bound to the particle, b) attachment of the already-formed polymers by covalently linking to functional groups attached to the particle, or c) electrostatic interactions resulting from incorporation of cationic or anionic groups in the polymer chain. Carbon or ceramic coatings may first be formed on the surfaces of the particles before the particles are coated with polymer. The polymer coating is both electronically and ionically conductive.

Electron induced surface reactions of (η5-C5H5)Fe(CO)2Mn(CO)5, a potential heterobimetallic precursor for focused electron beam induced deposition (FEBID).

PubMed

Unlu, Ilyas; Spencer, Julie A; Johnson, Kelsea R; Thorman, Rachel M; Ingólfsson, Oddur; McElwee-White, Lisa; Fairbrother, D Howard

2018-03-14

Electron-induced surface reactions of (η 5 -C 5 H 5 )Fe(CO) 2 Mn(CO) 5 were explored in situ under ultra-high vacuum conditions using X-ray photoelectron spectroscopy and mass spectrometry. The initial step involves electron-stimulated decomposition of adsorbed (η 5 -C 5 H 5 )Fe(CO) 2 Mn(CO) 5 molecules, accompanied by the desorption of an average of five CO ligands. A comparison with recent gas phase studies suggests that this precursor decomposition step occurs by a dissociative ionization (DI) process. Further electron irradiation decomposes the residual CO groups and (η 5 -C 5 H 5 , Cp) ligand, in the absence of any ligand desorption. The decomposition of CO ligands leads to Mn oxidation, while electron stimulated Cp decomposition causes all of the associated carbon atoms to be retained in the deposit. The lack of any Fe oxidation is ascribed to either the presence of a protective carbonaceous matrix around the Fe atoms created by the decomposition of the Cp ligand, or to desorption of both CO ligands bound to Fe in the initial decomposition step. The selective oxidation of Mn in the absence of any Fe oxidation suggests that the fate of metal atoms in mixed-metal precursors for focused electron beam induced deposition (FEBID) will be sensitive to the nature and number of ligands in the immediate coordination sphere. In related studies, the composition of deposits created from (η 5 -C 5 H 5 )Fe(CO) 2 Mn(CO) 5 under steady state deposition conditions, representative of those used to create nanostructures in electron microscopes, were measured and found to be qualitatively consistent with predictions from the UHV surface science studies.

Lifetime of a Chemically Bound Helium Compound

NASA Technical Reports Server (NTRS)

Chaban, Galina M.; Lundell, Jan; Gerber, R. Benny; Kwak, Dochan (Technical Monitor)

2001-01-01

The rare-gas atoms are chemically inert, to an extent unique among all elements. This is due to the stable electronic structure of the atoms. Stable molecules with chemically bound rare-gas atoms are, however, known. A first such compound, XePtF6, W2S prepared in 1962 and since then a range of molecules containing radon, xenon and krypton have been obtained. Most recently, a first stable chemically bound compound of argon was prepared, leaving neon and helium as the only elements for which stable chemically bound molecules are not yet known. Electronic structure calculations predict that a metastable species HHeF exists, but significance of the result depends on the unknown lifetime. Here we report quantum dynamics calculations of the lifetime of HHeF, using accurate interactions computed from electronic structure theory. HHeF is shown to disintegrate by tunneling through energy barriers into He + HF and H + He + F the first channel greatly dominating. The lifetime of HHeF is more than 120 picoseconds, that of DHeF is 14 nanoseconds. The relatively long lifetimes are encouraging for the preparation prospects of this first chemically bound helium compound.

Thomson scattering in the average-atom approximation.

PubMed

Johnson, W R; Nilsen, J; Cheng, K T

2012-09-01

The average-atom model is applied to study Thomson scattering of x-rays from warm dense matter with emphasis on scattering by bound electrons. Parameters needed to evaluate the dynamic structure function (chemical potential, average ionic charge, free electron density, bound and continuum wave functions, and occupation numbers) are obtained from the average-atom model. The resulting analysis provides a relatively simple diagnostic for use in connection with x-ray scattering measurements. Applications are given to dense hydrogen, beryllium, aluminum, and titanium plasmas. In the case of titanium, bound states are predicted to modify the spectrum significantly.

Numerical method for N electrons bound to a polar quantum dot with a Coulomb impurity

NASA Astrophysics Data System (ADS)

Yau, J. K.; Lee, C. M.

2003-03-01

A numerical method is proposed to calculate the Frohlich Hamiltonian containing N electrons bound to polar quantum dot with a Coulomb impurity without transformation to the coordination frame of the center of mass and by direct diagonalization. As an example to demonstrate the formalism of this method, the low-lying spectra of three interacting electrons bound to an on-center Coulomb impurity, both for accepter and donor, are calculated and analyzed in a polar quantum dot under a perpendicular magnetic field. Taking polaron effect into account, the physical meaning of the phonon-induced terms, both self-square terms and cross terms of the Hamiltonian are discussed. The calculation can also be applied to systems containing particles with opposite charges, such as excitons.

The role of amino acid electron-donor/acceptor atoms in host-cell binding peptides is associated with their 3D structure and HLA-binding capacity in sterile malarial immunity induction

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

Patarroyo, Manuel E., E-mail: mepatarr@mail.com; Universidad Nacional de Colombia, Bogota; Almonacid, Hannia

Highlights: Black-Right-Pointing-Pointer Fundamental residues located in some HABPs are associated with their 3D structure. Black-Right-Pointing-Pointer Electron-donor atoms present in {beta}-turn, random, distorted {alpha}-helix structures. Black-Right-Pointing-Pointer Electron-donor atoms bound to HLA-DR53. Black-Right-Pointing-Pointer Electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. -- Abstract: Plasmodium falciparum malaria continues being one of the parasitic diseases causing the highest worldwide mortality due to the parasite's multiple evasion mechanisms, such as immunological silence. Membrane and organelle proteins are used during invasion for interactions mediated by high binding ability peptides (HABPs); these have amino acids which establish hydrogen bonds between them in some of theirmore » critical binding residues. Immunisation assays in the Aotus model using HABPs whose critical residues had been modified have revealed a conformational change thereby enabling a protection-inducing response. This has improved fitting within HLA-DR{beta}1{sup Asterisk-Operator} molecules where amino acid electron-donor atoms present in {beta}-turn, random or distorted {alpha}-helix structures preferentially bound to HLA-DR53 molecules, whilst HABPs having amino acid electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. This data has great implications for vaccine development.« less

Observation of an edge coherent mode and poloidal flow in the electron cyclotron wave induced high β{sub p} plasma in QUEST

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

Banerjee, Santanu, E-mail: sbanerje@ipr.res.in; Mishra, K.; Zushi, H.

Fluctuations are measured in the edge and scrape-off layer (SOL) of QUEST using fast visible imaging diagnostic. Electron cyclotron wave injection in the Ohmic plasma features excitation of low frequency coherent fluctuations near the separatrix and enhanced cross-field transport. Plasma shifts from initial high field side limiter bound (inboard limited, IL) towards inboard poloidal null (IPN) configuration with steepening of the density profile at the edge. This may have facilitated the increased edge and SOL fluctuation activities. Observation of the coherent mode, associated plasma flow, and particle out-flux, for the first time in the IPN plasma configuration in a sphericalmore » tokamak may provide further impetus to the edge and SOL turbulence studies in tokamaks.« less

Reactions of molybdenum-sulphur compounds with cyanide: chemical evolution and deactivation of molybdoenzymes.

PubMed

Mitchell, P C; Pygall, C F

1979-08-01

Reactions of molybdenum-sulphur compounds with cyanide are reported which may be relevant to (1) the chemical evolution of molybdoenzymes and (2) deactivation of molybdoenzymes by cyanide. (1) With aqueous cyanide MoS2 gave thio-bridged complex anions [(Mo(CN)6)2(mu-S)]6- and [(Mo(CN)4(mu-S))2]6-. Under prebiotic conditions such complexes could have been formed similarly from molybdenite and may have been precursors of molybdoenzymes. (2) Only those compounds which contained terminal sulphur bound to molybdenum (i.e., Mo = S groups), viz. oxothiomolybdates and the complex [(Mo(mu-S)(S)(Et2NCS2))2], reacted with cyanide; thiocyanate was formed and the molybdenum underwent two-electron reduction. That the cyanolysable sulphur of xanthine oxidase reacts in the same way with cyanide suggests the presence of a Mo = S group which could be a structural feature of the enzyme or could have been formed by initial cyanolysis of a bound persulphide or cysteine residue.

Structural and dynamical properties of recombining ultracold neutral plasma

NASA Astrophysics Data System (ADS)

Tiwari, Sanat Kumar; Shaffer, Nathaniel R.; Baalrud, Scott D.

2017-10-01

An ultracold plasma (UCP) is an evolving collection of free charges and bound charges (Rydberg atoms). Over time, bound species concentration increases due to recombination. We present the structural and dynamical properties of an evolving UCP using classical molecular dynamics simulation. Coulomb collapse is avoided using a repulsive core with the attractive Coulomb potential. The repulsive core size controls the concentration of bound states, as it determines the depth of the potential well between opposite charges. We vary the repulsive core size to emulate the quasi-static state of plasma at different time during the evolution. Binary, chain and ring-like bound states are observed in the simulation carried out at different coupling strengths and repulsive core size. The effect of bound states can be seen as molecular peaks in the radial distribution function (RDF). The thermodynamic properties associated with the free charges can be analyzed from RDF by separating free from bound states. These bound states also change the dynamical properties of the plasma. The electron velocity auto-correlation displays oscillations due to the orbital motion in bound states. These bound states act like a neutral species, damping electron plasmon modes and broadening the ion acoustic mode. This work is supported by AFOSR Grant Number FA9550-16-1-0221. It used computational resources by XSEDE, which is supported by NSF Grant Number ACI-1053575.

Performance bounds on parallel self-initiating discrete-event

NASA Technical Reports Server (NTRS)

Nicol, David M.

1990-01-01

The use is considered of massively parallel architectures to execute discrete-event simulations of what is termed self-initiating models. A logical process in a self-initiating model schedules its own state re-evaluation times, independently of any other logical process, and sends its new state to other logical processes following the re-evaluation. The interest is in the effects of that communication on synchronization. The performance is considered of various synchronization protocols by deriving upper and lower bounds on optimal performance, upper bounds on Time Warp's performance, and lower bounds on the performance of a new conservative protocol. The analysis of Time Warp includes the overhead costs of state-saving and rollback. The analysis points out sufficient conditions for the conservative protocol to outperform Time Warp. The analysis also quantifies the sensitivity of performance to message fan-out, lookahead ability, and the probability distributions underlying the simulation.

Neutrino Photoproduction on the Electron of a Hydrogen-Like Atom

NASA Astrophysics Data System (ADS)

Skobelev, V. V.

2017-10-01

The process of interaction of a photon with the bound electron of a hydrogen-like atom with creation of a neutrino pair γ +{(Ze)}^{\\ast \\ast}\\to \\overline{νν}+{(Ze)}^{\\ast } is considered here for the first time. This process can take place with and without a change in the energy of the pair relative to the energy of the "initial" photon due to atomic transitions. It is shown that in the case when the system of atoms is located in an equilibrium radiation field with temperature T << m e this process can be neglected in comparison with spontaneous emission of the hydrogen-like atom {(Ze)}^{\\ast}\\to (Ze)+ν\\overline{ν} , despite the smaller power of the expansion parameter ( Zα) < < 1, α = e 2/ ℏc ≈ 1/137 in the expressions for the cross sections and probabilities. Calculations have been performed for the first time using the density matrix, introduced in the previous paper, of the electron in the field of the nucleus in the leading approximation in (Zα).

Ligand Electron Density Shape Recognition Using 3D Zernike Descriptors

NASA Astrophysics Data System (ADS)

Gunasekaran, Prasad; Grandison, Scott; Cowtan, Kevin; Mak, Lora; Lawson, David M.; Morris, Richard J.

We present a novel approach to crystallographic ligand density interpretation based on Zernike shape descriptors. Electron density for a bound ligand is expanded in an orthogonal polynomial series (3D Zernike polynomials) and the coefficients from this expansion are employed to construct rotation-invariant descriptors. These descriptors can be compared highly efficiently against large databases of descriptors computed from other molecules. In this manuscript we describe this process and show initial results from an electron density interpretation study on a dataset containing over a hundred OMIT maps. We could identify the correct ligand as the first hit in about 30 % of the cases, within the top five in a further 30 % of the cases, and giving rise to an 80 % probability of getting the correct ligand within the top ten matches. In all but a few examples, the top hit was highly similar to the correct ligand in both shape and chemistry. Further extensions and intrinsic limitations of the method are discussed.

The FEM-R-Matrix Approach: Use of Mixed Finite Element and Gaussian Basis Sets for Electron Molecule Collisions

NASA Technical Reports Server (NTRS)

Thuemmel, Helmar T.; Huo, Winifred M.; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

For the calculation of electron molecule collision cross sections R-matrix methods automatically take advantage of the division of configuration space into an inner region (I) bounded by radius tau b, where the scattered electron is within the molecular charge cloud and the system is described by an correlated Configuration Interaction (CI) treatment in close analogy to bound state calculations, and an outer region (II) where the scattered electron moves in the long-range multipole potential of the target and efficient analytic methods can be used for solving the asymptotic Schroedinger equation plus boundary conditions.

New constraints and prospects for sub-GeV dark matter scattering off electrons in xenon

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

Essig, Rouven; Volansky, Tomer; Yu, Tien-Tien

2017-08-30

We study in detail sub-GeV dark matter scattering off electrons in xenon, including the expected electron recoil spectra and annual modulation spectra. We derive improved constraints using low-energy XENON10 and XENON100 ionization-only data. For XENON10, in addition to including electron-recoil data corresponding to about 1–3 electrons, we include for the first time events corresponding to about 4–7 electrons. Assuming the scattering is momentum independent (F DM = 1 ), this strengthens a previous cross-section bound by almost an order of magnitude for dark matter masses above 50 MeV. The available XENON100 data corresponds to events with about 4–50 electrons, andmore » leads to a constraint that is comparable to the XENON10 bound above 50 MeV for F DM = 1 . We demonstrate that a search for an annual modulation signal in upcoming xenon experiments (XENON1T, XENONnT, LZ) could substantially improve the above bounds even in the presence of large backgrounds. We also emphasize that in simple benchmark models of sub-GeV dark matter, the dark matter-electron scattering rate can be as high as one event every ten (two) seconds in the XENON1T (XENONnT or LZ) experiments, without being in conflict with any other known experimental bounds. While there are several sources of backgrounds that can produce single- or few-electron events, a large event rate can be consistent with a dark matter signal and should not be simply written off as purely a detector curiosity. This fact motivates a detailed analysis of the ionization-data (“S2”) data, taking into account the expected annual modulation spectrum of the signal rate, as well as the DM-induced electron-recoil spectra, which are another powerful discriminant between signal and background.« less

Spin Measurements of an Electron Bound to a Single Phosphorous Donor in Silicon

NASA Astrophysics Data System (ADS)

Luhman, D. R.; Nguyen, K.; Tracy, L. A.; Carr, S. M.; Borchardt, J.; Bishop, N. C.; Ten Eyck, G. A.; Pluym, T.; Wendt, J.; Carroll, M. S.; Lilly, M. P.

2014-03-01

The spin of an electron bound to a single donor implanted in silicon is potentially useful for quantum information processing. We report on our efforts to measure and manipulate the spin of an electron bound to a single P donor in silicon. A low number of P donors are implanted using a self-aligned process into a silicon substrate in close proximity to a single-electron-transistor (SET) defined by lithographically patterned polysilicon gates. The SET is used to sense the occupancy of the electron on the donor and for spin read-out. An adjacent transmission line allows the application of microwave pulses to rotate the spin of the electron. We will present data from various experiments designed to exploit these capabilities. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. The work was supported by Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.

Bound state and localization of excitation in many-body open systems

NASA Astrophysics Data System (ADS)

Cui, H. T.; Shen, H. Z.; Hou, S. C.; Yi, X. X.

2018-04-01

We study the exact bound state and time evolution for single excitations in one-dimensional X X Z spin chains within a non-Markovian reservoir. For the bound state, a common feature is the localization of single excitations, which means the spontaneous emission of excitations into the reservoir is prohibited. Exceptionally, the pseudo-bound state can be found, for which the single excitation has a finite probability of emission into the reservoir. In addition, a critical energy scale for bound states is also identified, below which only one bound state exists, and it is also the pseudo-bound state. The effect of quasirandom disorder in the spin chain is also discussed; such disorder induces the single excitation to locate at some spin sites. Furthermore, to display the effect of bound state and disorder on the preservation of quantum information, the time evolution of single excitations in spin chains is studied exactly. An interesting observation is that the excitation can stay at its initial location with high probability only when the bound state and disorder coexist. In contrast, when either one of them is absent, the information of the initial state can be erased completely or becomes mixed. This finding shows that the combination of bound state and disorder can provide an ideal mechanism for quantum memory.

Temperature Regulation of Endogenous Gibberellin Activity and Development of Tulipa gesneriana L. 1

PubMed Central

Aung, L. H.; De Hertogh, A. A.; Staby, G.

1969-01-01

The changes in the contents of free and bound gibberellin-like activity (GA) of Tulipa gesneriana L. cv. Ralph during development under 2 temperature conditions were studied. The results show that the content of free GA of bulbs grown at 18° increased by 67% over the initial level during development. The bound GA showed a slight initial increase and was followed by a rapid decrease. In contrast, bulbs treated at 13° showed a marked decline in free GA and a 2-fold increase in the content of bound GA. However, after the transfer of these bulbs from 13° to 18° the free GA increased to the initial level while the bound GA decreased to a low level. The rate of floral shoot and root development and time of flowering were accelerated at 18° as compared to 13°. From the data obtained, it was suggested that a temperature-sensitive interconversion mechanism between free and bound GA exists in tulip bulbs and that there is apparent synthesis or transformation of these phytohormones during development of the bulbs. PMID:16657075

Multipactor saturation in parallel-plate waveguides

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

Sorolla, E.; Mattes, M.

2012-07-15

The saturation stage of a multipactor discharge is considered of interest, since it can guide towards a criterion to assess the multipactor onset. The electron cloud under multipactor regime within a parallel-plate waveguide is modeled by a thin continuous distribution of charge and the equations of motion are calculated taking into account the space charge effects. The saturation is identified by the interaction of the electron cloud with its image charge. The stability of the electron population growth is analyzed and two mechanisms of saturation to explain the steady-state multipactor for voltages near above the threshold onset are identified. Themore » impact energy in the collision against the metal plates decreases during the electron population growth due to the attraction of the electron sheet on the image through the initial plate. When this growth remains stable till the impact energy reaches the first cross-over point, the electron surface density tends to a constant value. When the stability is broken before reaching the first cross-over point the surface charge density oscillates chaotically bounded within a certain range. In this case, an expression to calculate the maximum electron surface charge density is found whose predictions agree with the simulations when the voltage is not too high.« less

X-ray Thomson Scattering in Warm Dense Matter without the Chihara Decomposition.

PubMed

Baczewski, A D; Shulenburger, L; Desjarlais, M P; Hansen, S B; Magyar, R J

2016-03-18

X-ray Thomson scattering is an important experimental technique used to measure the temperature, ionization state, structure, and density of warm dense matter (WDM). The fundamental property probed in these experiments is the electronic dynamic structure factor. In most models, this is decomposed into three terms [J. Chihara, J. Phys. F 17, 295 (1987)] representing the response of tightly bound, loosely bound, and free electrons. Accompanying this decomposition is the classification of electrons as either bound or free, which is useful for gapped and cold systems but becomes increasingly questionable as temperatures and pressures increase into the WDM regime. In this work we provide unambiguous first principles calculations of the dynamic structure factor of warm dense beryllium, independent of the Chihara form, by treating bound and free states under a single formalism. The computational approach is real-time finite-temperature time-dependent density functional theory (TDDFT) being applied here for the first time to WDM. We compare results from TDDFT to Chihara-based calculations for experimentally relevant conditions in shock-compressed beryllium.

Bound-Electron Nonlinearity Beyond the Ionization Threshold.

PubMed

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

2018-05-04

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

Bound-Electron Nonlinearity Beyond the Ionization Threshold

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

Isolation and Characterization of Methanophenazine and Function of Phenazines in Membrane-Bound Electron Transport of Methanosarcina mazei Gö1

PubMed Central

Abken, Hans-Jörg; Tietze, Mario; Brodersen, Jens; Bäumer, Sebastian; Beifuss, Uwe; Deppenmeier, Uwe

1998-01-01

A hydrophobic, redox-active component with a molecular mass of 538 Da was isolated from lyophilized membranes of Methanosarcina mazei Gö1 by extraction with isooctane. After purification on a high-performance liquid chromatography column, the chemical structure was analyzed by mass spectroscopy and nuclear magnetic resonance studies. The component was called methanophenazine and represents a 2-hydroxyphenazine derivative which is connected via an ether bridge to a polyisoprenoid side chain. Since methanophenazine was almost insoluble in aqueous buffers, water-soluble phenazine derivatives were tested for their ability to interact with membrane-bound enzymes involved in electron transport and energy conservation. The purified F420H2 dehydrogenase from M. mazei Gö1 showed highest activity with 2-hydroxyphenazine and 2-bromophenazine as electron acceptors when F420H2 was added. Phenazine-1-carboxylic acid and phenazine proved to be less effective. The Km values for 2-hydroxyphenazine and phenazine were 35 and 250 μM, respectively. 2-Hydroxyphenazine was also reduced by molecular hydrogen catalyzed by an F420-nonreactive hydrogenase which is present in washed membrane preparations. Furthermore, the membrane-bound heterodisulfide reductase was able to use reduced 2-hydroxyphenazine as an electron donor for the reduction of CoB-S-S-CoM. Considering all these results, it is reasonable to assume that methanophenazine plays an important role in vivo in membrane-bound electron transport of M. mazei Gö1. PMID:9555882

Electron-impact dissociation of molecular hydrogen into neutral fragments

NASA Astrophysics Data System (ADS)

Scarlett, Liam H.; Tapley, Jonathan K.; Fursa, Dmitry V.; Zammit, Mark C.; Savage, Jeremy S.; Bray, Igor

2018-02-01

We present convergent close-coupling calculations of electron-impact dissociation of the ground state of molecular hydrogen into neutral fragments over the range of impact energies from 6 to 300 eV. The calculations account for dissociative excitation, excitation radiative decay dissociation, and predissociation through all bound electronic triplet states, and singlet states up to the D' 1 Π u state. An estimate is given for the contribution from the remaining bound electronic singlet states. Our results are in agreement with the recommended data of Yoon et al. [J. Phys. Chem. Ref. Data 37, 913 (2008)] in the low (6-12 eV) and high (60-70 eV) energy regions, but somewhat lower at the intermediate energies.

Scattering of fast electrons by vapour-atoms and by solid-atoms - A comparison

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

Joshipura, K.N.; Mohanan, S.

1988-08-01

A comparative theoretical study has been done on the scattering of fast electrons by free (vapour) atoms and bound (solid) atoms, in particular, the alkali atoms, Al and Cu. The Born differential cross-sections (DCS), calculated with the static plus polarization electron-atom potential, are found in general, to be larger for free atoms that for bound atoms, at least at small angles of scattering. For Rb and Cs the two DCS tend to merge at very large angles only. The sample incident energies chosen are 400 eV and above.

Timely binding of IHF and Fis to DARS2 regulates ATP–DnaA production and replication initiation

PubMed Central

Kasho, Kazutoshi; Fujimitsu, Kazuyuki; Matoba, Toshihiro; Oshima, Taku; Katayama, Tsutomu

2014-01-01

In Escherichia coli, the ATP-bound form of DnaA (ATP–DnaA) promotes replication initiation. During replication, the bound ATP is hydrolyzed to ADP to yield the ADP-bound form (ADP–DnaA), which is inactive for initiation. The chromosomal site DARS2 facilitates the regeneration of ATP–DnaA by catalyzing nucleotide exchange between free ATP and ADP bound to DnaA. However, the regulatory mechanisms governing this exchange reaction are unclear. Here, using in vitro reconstituted experiments, we show that two nucleoid-associated proteins, IHF and Fis, bind site-specifically to DARS2 to activate coordinately the exchange reaction. The regenerated ATP–DnaA was fully active in replication initiation and underwent DnaA–ATP hydrolysis. ADP–DnaA formed heteromultimeric complexes with IHF and Fis on DARS2, and underwent nucleotide dissociation more efficiently than ATP–DnaA. Consistently, mutant analyses demonstrated that specific binding of IHF and Fis to DARS2 stimulates the formation of ATP–DnaA production, thereby promoting timely initiation. Moreover, we show that IHF–DARS2 binding is temporally regulated during the cell cycle, whereas Fis only binds to DARS2 in exponentially growing cells. These results elucidate the regulation of ATP–DnaA and replication initiation in coordination with the cell cycle and growth phase. PMID:25378325

A Priori Bound on the Velocity in Axially Symmetric Navier-Stokes Equations

NASA Astrophysics Data System (ADS)

Lei, Zhen; Navas, Esteban A.; Zhang, Qi S.

2016-01-01

Let v be the velocity of Leray-Hopf solutions to the axially symmetric three-dimensional Navier-Stokes equations. Under suitable conditions for initial values, we prove the following a priori bound |v(x, t)| ≤ C |ln r|^{1/2}/r^2, qquad 0 < r ≤ 1/2, where r is the distance from x to the z axis, and C is a constant depending only on the initial value. This provides a pointwise upper bound (worst case scenario) for possible singularities, while the recent papers (Chiun-Chuan et al., Commun PDE 34(1-3):203-232, 2009; Koch et al., Acta Math 203(1):83-105, 2009) gave a lower bound. The gap is polynomial order 1 modulo a half log term.

Bound-bound transitions in the emission spectra of Ba+-He excimer

NASA Astrophysics Data System (ADS)

Moroshkin, P.; Kono, K.

2016-05-01

We present an experimental and theoretical study of the emission and absorption spectra of the Ba+ ions and Ba+*He excimer quasimolecules in the cryogenic Ba-He plasma. We observe several spectral features in the emission spectrum, which we assign to the electronic transitions between bound states of the excimer correlating to the 6 2P3 /2 and 5 2D3 /2 ,5 /2 states of Ba+. The resulting Ba+(5 2DJ) He is a metastable electronically excited complex with orbital angular momentum L =2 , thus expanding the family of known metal-helium quasimolecules. It might be suitable for high-resolution spectroscopic studies and for the search for new polyatomic exciplex structures.

Optical transitions in two-dimensional topological insulators with point defects

NASA Astrophysics Data System (ADS)

Sablikov, Vladimir A.; Sukhanov, Aleksei A.

2016-12-01

Nontrivial properties of electronic states in topological insulators are inherent not only to the surface and boundary states, but to bound states localized at structure defects as well. We clarify how the unusual properties of the defect-induced bound states are manifested in optical absorption spectra in two-dimensional topological insulators. The calculations are carried out for defects with short-range potential. We find that the defects give rise to the appearance of specific features in the absorption spectrum, which are an inherent property of topological insulators. They have the form of two or three absorption peaks that are due to intracenter transitions between electron-like and hole-like bound states.

Experimental observation of multiphoton Thomson scattering

NASA Astrophysics Data System (ADS)

Yan, Wenchao; Golovin, Grigory; Fruhling, Colton; Haden, Daniel; Zhang, Ping; Zhang, Jun; Zhao, Baozhen; Liu, Cheng; Chen, Shouyuan; Banerjee, Sudeep; Umstadter, Donald

2016-10-01

With the advent of high-power lasers, several multiphoton processes have been reported involving electrons in strong fields. For electrons that were initially bound to atoms, both multiphoton ionization and scattering have been reported. However, for free electrons, only low-order harmonic generation has been observed until now. This limitation stems from past difficulty in achieving the required ultra-high-field strengths in scattering experiments. Highly relativistic laser intensities are required to reach the multiphoton regime of Thomson scattering, and generate high harmonics from free electrons. The scaling parameter is the normalized vector potential (a0). Previous experiments have observed phenomena in the weakly relativistic case (a0 >> 1). In ultra-intense fields (a0 >>1), the anomalous electron trajectory is predicted to produce a spectrum characterized by the merging of multiple high-order harmonic generation into a continuum. This may be viewed as the multiphoton Thomson scattering regime analogous to the wiggler of a synchrotron. Thus, the light produced reflects the electrons behavior in an ultra-intense lase field. We discuss the first experiments in the highly relativistic case (a0 15). This material is based upon work supported by NSF No. PHY-153700; US DOE, Office of Science, BES, # DE-FG02-05ER15663; AFOSR # FA9550-11-1-0157; and DHS DNDO # HSHQDC-13-C-B0036.

Benchmark calculations of excess electrons in water cluster cavities: balancing the addition of atom-centered diffuse functions versus floating diffuse functions.

PubMed

Zhang, Changzhe; Bu, Yuxiang

2016-09-14

Diffuse functions have been proved to be especially crucial for the accurate characterization of excess electrons which are usually bound weakly in intermolecular zones far away from the nuclei. To examine the effects of diffuse functions on the nature of the cavity-shaped excess electrons in water cluster surroundings, both the HOMO and LUMO distributions, vertical detachment energies (VDEs) and visible absorption spectra of two selected (H2O)24(-) isomers are investigated in the present work. Two main types of diffuse functions are considered in calculations including the Pople-style atom-centered diffuse functions and the ghost-atom-based floating diffuse functions. It is found that augmentation of atom-centered diffuse functions contributes to a better description of the HOMO (corresponding to the VDE convergence), in agreement with previous studies, but also leads to unreasonable diffuse characters of the LUMO with significant red-shifts in the visible spectra, which is against the conventional point of view that the more the diffuse functions, the better the results. The issue of designing extra floating functions for excess electrons has also been systematically discussed, which indicates that the floating diffuse functions are necessary not only for reducing the computational cost but also for improving both the HOMO and LUMO accuracy. Thus, the basis sets with a combination of partial atom-centered diffuse functions and floating diffuse functions are recommended for a reliable description of the weakly bound electrons. This work presents an efficient way for characterizing the electronic properties of weakly bound electrons accurately by balancing the addition of atom-centered diffuse functions and floating diffuse functions and also by balancing the computational cost and accuracy of the calculated results, and thus is very useful in the relevant calculations of various solvated electron systems and weakly bound anionic systems.

Potential for EMU Fabric Damage by Electron Beam and Molten Metal During Space Welding for the International Space Welding Experiment

NASA Technical Reports Server (NTRS)

Fragomeni, James M.

1998-01-01

As a consequence of preparations concerning the International Space Welding Experiment (ISWE), studies were performed to better understand the effect of molten metal contact and electron beam impingement with various fabrics for space suit applications. The question arose as to what would occur if the electron beam from the Ukrainian Universal Hand Tool (UHT) designed for welding in space were to impinge upon a piece of Nextel AF-62 ceramic cloth designed to withstand temperatures up to 1427 C. The expectation was that the electron beam would lay down a static charge pattern with no damage to the ceramic fabric. The electron beam is capable of spraying the fabric with enough negative charge to repel further electrons from the fabric before significant heating occurs. The static charge pattern would deflect any further charge accumulation except for a small initial amount of leakage to the grounded surface of the welder. However, when studies were made of the effect of the electron beam on the insulating ceramic fabric it was surprisingly found that the electron beam did indeed burn through the ceramic fabric. It was also found that the shorter electron beam standoff distances had longer burnthrough times than did some greater electron beam standoff distances. A possible explanation for the longer burnthrough times for the small electron beam standoff distance would be outgassing of the fabric which caused the electron beam hand-tool to cycle on and off to provide some protection for the cathodes. The electron beam hand tool was observed to cycle off at the short standoff distance of two inches likely due to vapors being outgassed. During the electron beam welding process there is an electron leakage, or current leakage, flow from the fabric. A static charge pattern is initially laid down by the electron beam current flow. The static charge makes up the current leakage flow which initially slightly heats up the fabric. The initially laid down surface charge leaks a small amount of current. The rate at which the current charge leaks from the fabric controls how fast the fabric heats up. As the ceramic fabric is heated it begins to outgass primarily from contamination/impurities atoms or molecules on and below the fabric surface. The contaminant gases ionize to create extra charge carriers and multiply a current of electrons. The emitted gas which ionized in the electron leakage flow promotes further leakage. Thus, the small leakage of charge from the fabric surface is enhanced by outgassing. When the electron beam current makes up the lost current, the incoming electrons heat the fabric and further enhance the outgassing. The additional leakage promotes additional heating up of the ceramic fabric. The electrons bound to the ceramic fabric surface leak off more and more as the surface gets hotter promoting even greater leakage. The additional electrons that result also gain energy in the field and produce further electrons. Eventually the process becomes unstable and accelerates to the point where a hole is burned through the fabric.

Can even-order laser harmonics exhibited by Bohmian trajectories in symmetric potentials be observed?

PubMed

Peatross, J; Johansen, J

2014-01-13

Strong-field laser-atom interactions provide extreme conditions that may be useful for investigating the de Broglie-Bohm quantum interpretation. Bohmian trajectories representing bound electrons in individual atoms exhibit both even and odd harmonic motion when subjected to a strong external laser field. The phases of the even harmonics depend on the random initial positions of the trajectories within the wave function, making the even harmonics incoherent. In contrast, the phases of odd harmonics remain for the most part coherent regardless of initial position. Under the conjecture that a Bohmian point particle plays the role of emitter, this suggests an experiment to determine whether both even and odd harmonics are produced at the atomic level. Estimates suggest that incoherent emission of even harmonics may be detectable out the side of an intense laser focus interacting with a large number of atoms.

Reduction of Fe(III) colloids by Shewanella putrefaciens: A kinetic model

NASA Astrophysics Data System (ADS)

Bonneville, Steeve; Behrends, Thilo; van Cappellen, Philippe; Hyacinthe, Christelle; Röling, Wilfred F. M.

2006-12-01

A kinetic model for the microbial reduction of Fe(III) oxyhydroxide colloids in the presence of excess electron donor is presented. The model assumes a two-step mechanism: (1) attachment of Fe(III) colloids to the cell surface and (2) reduction of Fe(III) centers at the surface of attached colloids. The validity of the model is tested using Shewanella putrefaciens and nanohematite as model dissimilatory iron reducing bacteria and Fe(III) colloidal particles, respectively. Attachment of nanohematite to the bacteria is formally described by a Langmuir isotherm. Initial iron reduction rates are shown to correlate linearly with the relative coverage of the cell surface by nanohematite particles, hence supporting a direct electron transfer from membrane-bound reductases to mineral particles attached to the cells. Using internally consistent parameter values for the maximum attachment capacity of Fe(III) colloids to the cells, Mmax, the attachment constant, KP, and the first-order Fe(III) reduction rate constant, k, the model reproduces the initial reduction rates of a variety of fine-grained Fe(III) oxyhydroxides by S. putrefaciens. The model explains the observed dependency of the apparent Fe(III) half-saturation constant, Km∗, on the solid to cell ratio, and it predicts that initial iron reduction rates exhibit saturation with respect to both the cell density and the abundance of the Fe(III) oxyhydroxide substrate.

Upward Bound Math-Science: Program Description and Interim Impact Estimates

ERIC Educational Resources Information Center

Olsen, Robert; Seftor, Neil; Silva, Tim; Myers, David; DesRoches, David; Young, Julie

2007-01-01

To help address continuing disparities in academic achievement and under-representation of disadvantaged groups in math and science majors and careers, the U.S. Department of Education (ED) established a math and science initiative in 1990 within Upward Bound, a federal grant program known as Upward Bound Math-Science (UBMS) designed to provide…

VhuD Facilitates Electron Flow from H2 or Formate to Heterodisulfide Reductase in Methanococcus maripaludis

PubMed Central

Costa, Kyle C.; Lie, Thomas J.; Xia, Qin

2013-01-01

Flavin-based electron bifurcation has recently been characterized as an essential energy conservation mechanism that is utilized by hydrogenotrophic methanogenic Archaea to generate low-potential electrons in an ATP-independent manner. Electron bifurcation likely takes place at the flavin associated with the α subunit of heterodisulfide reductase (HdrA). In Methanococcus maripaludis the electrons for this reaction come from either formate or H2 via formate dehydrogenase (Fdh) or Hdr-associated hydrogenase (Vhu). However, how these enzymes bind to HdrA to deliver electrons is unknown. Here, we present evidence that the δ subunit of hydrogenase (VhuD) is central to the interaction of both enzymes with HdrA. When M. maripaludis is grown under conditions where both Fdh and Vhu are expressed, these enzymes compete for binding to VhuD, which in turn binds to HdrA. Under these conditions, both enzymes are fully functional and are bound to VhuD in substoichiometric quantities. We also show that Fdh copurifies specifically with VhuD in the absence of other hydrogenase subunits. Surprisingly, in the absence of Vhu, growth on hydrogen still occurs; we show that this involves F420-reducing hydrogenase. The data presented here represent an initial characterization of specific protein interactions centered on Hdr in a hydrogenotrophic methanogen that utilizes multiple electron donors for growth. PMID:24039260

Timely binding of IHF and Fis to DARS2 regulates ATP-DnaA production and replication initiation.

PubMed

Kasho, Kazutoshi; Fujimitsu, Kazuyuki; Matoba, Toshihiro; Oshima, Taku; Katayama, Tsutomu

2014-12-01

In Escherichia coli, the ATP-bound form of DnaA (ATP-DnaA) promotes replication initiation. During replication, the bound ATP is hydrolyzed to ADP to yield the ADP-bound form (ADP-DnaA), which is inactive for initiation. The chromosomal site DARS2 facilitates the regeneration of ATP-DnaA by catalyzing nucleotide exchange between free ATP and ADP bound to DnaA. However, the regulatory mechanisms governing this exchange reaction are unclear. Here, using in vitro reconstituted experiments, we show that two nucleoid-associated proteins, IHF and Fis, bind site-specifically to DARS2 to activate coordinately the exchange reaction. The regenerated ATP-DnaA was fully active in replication initiation and underwent DnaA-ATP hydrolysis. ADP-DnaA formed heteromultimeric complexes with IHF and Fis on DARS2, and underwent nucleotide dissociation more efficiently than ATP-DnaA. Consistently, mutant analyses demonstrated that specific binding of IHF and Fis to DARS2 stimulates the formation of ATP-DnaA production, thereby promoting timely initiation. Moreover, we show that IHF-DARS2 binding is temporally regulated during the cell cycle, whereas Fis only binds to DARS2 in exponentially growing cells. These results elucidate the regulation of ATP-DnaA and replication initiation in coordination with the cell cycle and growth phase. © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

Hydrated electrons react with high specificity with cisplatin bound to single-stranded DNA.

PubMed

Behmand, B; Cloutier, P; Girouard, S; Wagner, J R; Sanche, L; Hunting, D J

2013-12-19

Short oligonucleotides TTTTTGTGTTT and TTTTTTTGTTT in solution with and without cisplatin (cisPt) bound to the guanine bases were irradiated with γ-rays at doses varying from 0 to 2500 Gy. To determine the effect of hydrated electrons from water radiolysis on the oligonucleotides, we quenched (•)OH radicals with ethylenediaminetetraacetic acid (EDTA) and displaced oxygen, which reacts with hydrated electrons, by bubbling the solution with wet nitrogen. DNA strand breaks and platinum detachment were quantified by gel electrophoresis. Our results demonstrate that hydrated electrons react almost exclusively at the position of the cisPt adduct, where they induce cisPt detachment from one or both guanines in the oligonucleotide. Given the high yield of hydrated electrons in irradiated tissues, this reaction may be an important step in the mechanism of radiosensitization of DNA by cisPt.

The Aharonov-Bohm effect and Tonomura et al. experiments: Rigorous results

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

Ballesteros, Miguel; Weder, Ricardo

The Aharonov-Bohm effect is a fundamental issue in physics. It describes the physically important electromagnetic quantities in quantum mechanics. Its experimental verification constitutes a test of the theory of quantum mechanics itself. The remarkable experiments of Tonomura et al. ['Observation of Aharonov-Bohm effect by electron holography', Phys. Rev. Lett 48, 1443 (1982) and 'Evidence for Aharonov-Bohm effect with magnetic field completely shielded from electron wave', Phys. Rev. Lett 56, 792 (1986)] are widely considered as the only experimental evidence of the physical existence of the Aharonov-Bohm effect. Here we give the first rigorous proof that the classical ansatz of Aharonovmore » and Bohm of 1959 ['Significance of electromagnetic potentials in the quantum theory', Phys. Rev. 115, 485 (1959)], that was tested by Tonomura et al., is a good approximation to the exact solution to the Schroedinger equation. This also proves that the electron, that is, represented by the exact solution, is not accelerated, in agreement with the recent experiment of Caprez et al. in 2007 ['Macroscopic test of the Aharonov-Bohm effect', Phys. Rev. Lett. 99, 210401 (2007)], that shows that the results of the Tonomura et al. experiments can not be explained by the action of a force. Under the assumption that the incoming free electron is a Gaussian wave packet, we estimate the exact solution to the Schroedinger equation for all times. We provide a rigorous, quantitative error bound for the difference in norm between the exact solution and the Aharonov-Bohm Ansatz. Our bound is uniform in time. We also prove that on the Gaussian asymptotic state the scattering operator is given by a constant phase shift, up to a quantitative error bound that we provide. Our results show that for intermediate size electron wave packets, smaller than the ones used in the Tonomura et al. experiments, quantum mechanics predicts the results observed by Tonomura et al. with an error bound smaller than 10{sup -99}. It would be quite interesting to perform experiments with electron wave packets of intermediate size. Furthermore, we provide a physical interpretation of our error bound.« less

Modelling fragmentations of aminoacids after resonant electron attachment: quantum evidence of possible direct -OH detachment

NASA Astrophysics Data System (ADS)

Panosetti, C.; Baccarelli, I.; Sebastianelli, F.; Gianturco, F. A.

2010-10-01

We investigate some aspects of the radiation damage mechanisms in biomolecules, focusing on the modelling of resonant fragmentation caused by the attachment of low-energy electrons (LEEs) initially ejected by biological tissues when exposed to ionizing radiation. Scattering equations are formulated within a symmetry-adapted, single-center expansion of both continuum and bound electrons, and the interaction forces are obtained from a combination of ab initio calculations and a nonempirical model of exchange and correlation effects developped in our group. We present total elastic scattering cross-sections and resonance features obtained for the equilibrium geometries of glycine, alanine, proline and valine. Our results at those geometries of the target molecules are briefly shown to qualitatively explain some of the fragmentation patterns obtained in experiments. We further carry out a one-dimensional (1D) modeling for the dynamics of intramolecular energy transfers mediated by the vibrational activation of selected bonds: our calculations indicate that resonant electron attachment to glycine can trigger direct, dissociative evolution of the complex into (Gly-OH)- and -OH losses, while they also find that the same process does not occur via a direct, 1D dissociative path in the larger aminoacids of the present study.

Knowledge management for the protection of information in electronic medical records.

PubMed

Lea, Nathan; Hailes, Stephen; Austin, Tony; Kalra, Dipak

2008-01-01

This paper describes foundational work investigating the protection requirements of sensitive medical information, which is being stored more routinely in repository systems for electronic medical records. These systems have increasingly powerful sharing capabilities at the point of clinical care, in medical research and for clinical and managerial audit. The potential for sharing raises concerns about the protection of individual patient privacy and challenges the duty of confidentiality by which medical practitioners are ethically and legally bound. By analysing the protection requirements and discussing the need to apply policy-based controls to discrete items of medical information in a record, this paper suggests that this is a problem for which existing privacy management solutions are not sufficient or appropriate to the protection requirements. It proposes that a knowledge management approach is required and it introduces a new framework based on the knowledge management techniques now being used to manage electronic medical record data. The background, existing work in this area, initial investigation methods, results to date and discussion are presented, and the paper is concluded with the authors' comments on the ramifications of the work.

Ab initio study of the ground and excited electronic states of the methyl radical

PubMed Central

Zanchet, A.; Bañares, L.; Senent, M. L.; García-Vela, A.

2016-01-01

The ground and some excited electronic states of the methyl radical have been characterized by means of highly correlated ab intio techniques. The specific excited states investigated are those involved in the dissociation of the radical, namely the 3s and 3pz Rydberg states, and the A1 and B1 valence states crossing them, respectively. The C-H dissociative coordinate and the HCH bending angle were considered in order to generate the first two-dimensional ab initio representation of the potential surfaces of the above electronic states of CH3, along with the nonadiabatic couplings between them. Spectroscopic constants and frequencies calculated for the ground and bound excited states agree well with most of the available experimental data. Implications of the shape of the excited potential surfaces and couplings for the dissociation pathways of CH3 are discussed in the light of recent experimental results for dissociation from low-lying vibrational states of CH3. Based on the ab initio data some predictions are made regarding methyl photodissociation from higher initial vibrational states. PMID:27892569

Thomson scattering from a three-component plasma.

PubMed

Johnson, W R; Nilsen, J

2014-02-01

A model for a three-component plasma consisting of two distinct ionic species and electrons is developed and applied to study x-ray Thomson scattering. Ions of a specific type are assumed to be identical and are treated in the average-atom approximation. Given the plasma temperature and density, the model predicts mass densities, effective ionic charges, and cell volumes for each ionic type, together with the plasma chemical potential and free-electron density. Additionally, the average-atom treatment of individual ions provides a quantum-mechanical description of bound and continuum electrons. The model is used to obtain parameters needed to determine the dynamic structure factors for x-ray Thomson scattering from a three-component plasma. The contribution from inelastic scattering by free electrons is evaluated in the random-phase approximation. The contribution from inelastic scattering by bound electrons is evaluated using the bound-state and scattering wave functions obtained from the average-atom calculations. Finally, the partial static structure factors for elastic scattering by ions are evaluated using a two-component version of the Ornstein-Zernike equations with hypernetted chain closure, in which electron-ion interactions are accounted for using screened ion-ion interaction potentials. The model is used to predict the x-ray Thomson scattering spectrum from a CH plasma and the resulting spectrum is compared with experimental results obtained by Feltcher et al. [Phys. Plasmas 20, 056316 (2013)].

Active penetration of Trypanosoma cruzi into host cells: historical considerations and current concepts

PubMed Central

de Souza, Wanderley; de Carvalho, Tecia M. Ulisses

2013-01-01

In the present short review, we analyze past experiments that addressed the interactions of intracellular pathogenic protozoa (Trypanosoma cruzi, Toxoplasma gondii, and Plasmodium) with host cells and the initial use of the term active penetration to indicate that a protozoan “crossed the host cell membrane, penetrating into the cytoplasm.” However, the subsequent use of transmission electron microscopy showed that, for all of the protozoans and cell types examined, endocytosis, classically defined as involving the formation of a membrane-bound vacuole, took place during the interaction process. As a consequence, the recently penetrated parasites are always within a vacuole, designated the parasitophorous vacuole (PV). PMID:23355838

A dipole-bound dianion

NASA Astrophysics Data System (ADS)

Skurski, Piotr; Simons, Jack

2000-04-01

The possibility of binding two electrons by the dipole potential of a molecule was examined earlier by us using model potentials. That study suggested that large dipole moments μ=qR and large charge separation distances R (or equivalently large charges q) would be required to achieve binding two electrons. For example, even with a charge q=1.5 a.u. which might be achieved using di- or tri-valent cations, a dipole moment exceeding 15.922 D is needed. The presence of inner-shell electrons even further increases the value of μ that is required because the dipole-bound electrons' orbital must be orthogonal to and excluded from such inner shells. In the present work, we discuss our efforts to find a real molecule that can actually bind two electrons to a single dipole site. Numerical results are presented for the mono- and dianions of a double 5-member carbon ring system substituted with a Ca atom and three superhalogen -PF5 groups. The dianion of this molecule is found to be geometrically stable and to have a vertical electron detachment energy of ca. 0.8 eV. Its two excess electrons occupy the same fully symmetric a1 molecular orbital localized at the electropositive Ca end of the neutral system as is routinely observed in dipole-bound monoanions. Although our final candidate is chemically unusual, it is hoped that our predictions about it will encourage others to search for more synthetically tractable alternatives.

Thermodynamic models for bounding pressurant mass requirements of cryogenic tanks

NASA Technical Reports Server (NTRS)

Vandresar, Neil T.; Haberbusch, Mark S.

1994-01-01

Thermodynamic models have been formulated to predict lower and upper bounds for the mass of pressurant gas required to pressurize a cryogenic tank and then expel liquid from the tank. Limiting conditions are based on either thermal equilibrium or zero energy exchange between the pressurant gas and initial tank contents. The models are independent of gravity level and allow specification of autogenous or non-condensible pressurants. Partial liquid fill levels may be specified for initial and final conditions. Model predictions are shown to successfully bound results from limited normal-gravity tests with condensable and non-condensable pressurant gases. Representative maximum collapse factor maps are presented for liquid hydrogen to show the effects of initial and final fill level on the range of pressurant gas requirements. Maximum collapse factors occur for partial expulsions with large final liquid fill fractions.

Critical screening in the one- and two-electron Yukawa atoms

NASA Astrophysics Data System (ADS)

Montgomery, H. E.; Sen, K. D.; Katriel, Jacob

2018-02-01

The one- and two-electron Yukawa atoms, also referred to as the Debye-Hückel or screened Coulomb atoms, have been topics of considerable interest both for intrinsic reasons and because of their relevance to terrestrial and astrophysical plasmas. At sufficiently high screening the one-electron Yukawa atom ceases to be bound. Some calculations appeared to suggest that as the screening increases in the ground state of the two-electron Yukawa atom (in which both the one-particle attraction and the interparticle repulsion are screened) the two electrons are detached simultaneously, at the same screening constant at which the one-electron atom becomes unbound. Our results rule this scenario out, offering an alternative that is not less interesting. In particular, it is found that for Z <1 a mild amount of screening actually increases the binding energy of the second electron. At the nuclear charge Zc≈0.911028 ... , at which the bare Coulomb two-electron atom becomes unbound, and even over a range of lower nuclear charges, an appropriate amount of screening gives rise to a bound two-electron system.

Electron scattering from high-momentum neutrons in deuterium

NASA Astrophysics Data System (ADS)

Klimenko, A. V.; Kuhn, S. E.; Butuceanu, C.; Egiyan, K. S.; Griffioen, K. A.; Adams, G.; Ambrozewicz, P.; Anghinolfi, M.; Asryan, G.; Avakian, H.; Bagdasaryan, H.; Baillie, N.; Ball, J. P.; Baltzell, N. A.; Barrow, S.; Batourine, V.; Battaglieri, M.; Bedlinskiy, I.; Bektasoglu, M.; Bellis, M.; Benmouna, N.; Biselli, A. S.; Bouchigny, S.; Boiarinov, S.; Bradford, R.; Branford, D.; Brooks, W. K.; Bültmann, S.; Burkert, V. D.; Calarco, J. R.; Careccia, S. L.; Carman, D. S.; Cazes, A.; Chen, S.; Cole, P. L.; Coltharp, P.; Cords, D.; Corvisiero, P.; Crabb, D.; Cummings, J. P.; Dashyan, N. B.; Devita, R.; Sanctis, E. De; Degtyarenko, P. V.; Denizli, H.; Dennis, L.; Dharmawardane, K. V.; Djalali, C.; Dodge, G. E.; Donnelly, J.; Doughty, D.; Dugger, M.; Dytman, S.; Dzyubak, O. P.; Egiyan, H.; Elouadrhiri, L.; Eugenio, P.; Fatemi, R.; Fedotov, G.; Fersch, R. G.; Feuerbach, R. J.; Funsten, H.; Garçon, M.; Gavalian, G.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Goetz, J. T.; Gonenc, A.; Gordon, C. I. O.; Gothe, R. W.; Guidal, M.; Guillo, M.; Guler, N.; Guo, L.; Gyurjyan, V.; Hadjidakis, C.; Hakobyan, R. S.; Hardie, J.; Hersman, F. W.; Hicks, K.; Hleiqawi, I.; Holtrop, M.; Hyde-Wright, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Ito, M. M.; Jenkins, D.; Jo, H. S.; Joo, K.; Juengst, H. G.; Kellie, J. D.; Khandaker, M.; Kim, W.; Klein, A.; Klein, F. J.; Kossov, M.; Kramer, L. H.; Kubarovsky, V.; Kuhn, J.; Kuleshov, S. V.; Lachniet, J.; Laget, J. M.; Langheinrich, J.; Lawrence, D.; Li, Ji; Livingston, K.; McAleer, S.; McKinnon, B.; McNabb, J. W. C.; Mecking, B. A.; Mehrabyan, S.; Melone, J. J.; Mestayer, M. D.; Meyer, C. A.; Mibe, T.; Mikhailov, K.; Minehart, R.; Mirazita, M.; Miskimen, R.; Mokeev, V.; Morand, L.; Morrow, S. A.; Mueller, J.; Mutchler, G. S.; Nadel-Turonski, P.; Napolitano, J.; Nasseripour, R.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Niczyporuk, B. B.; Niyazov, R. A.; Nozar, M.; O'Rielly, G. V.; Osipenko, M.; Ostrovidov, A. I.; Park, K.; Pasyuk, E.; Paterson, C.; Pierce, J.; Pivnyuk, N.; Pocanic, D.; Pogorelko, O.; Pozdniakov, S.; Preedom, B. M.; Price, J. W.; Prok, Y.; Protopopescu, D.; Raue, B. A.; Riccardi, G.; Ricco, G.; Ripani, M.; Ritchie, B. G.; Ronchetti, F.; Rosner, G.; Rossi, P.; Sabatié, F.; Salgado, C.; Santoro, J. P.; Sapunenko, V.; Schumacher, R. A.; Serov, V. S.; Sharabian, Y. G.; Skabelin, A. V.; Smith, E. S.; Smith, L. C.; Sober, D. I.; Stavinsky, A.; Stepanyan, S. S.; Stepanyan, S.; Stokes, B. E.; Stoler, P.; Strauch, S.; Taiuti, M.; Tedeschi, D. J.; Thoma, U.; Tkabladze, A.; Tkachenko, S.; Todor, L.; Tur, C.; Ungaro, M.; Vineyard, M. F.; Vlassov, A. V.; Weinstein, L. B.; Weygand, D. P.; Williams, M.; Wolin, E.; Wood, M. H.; Yegneswaran, A.; Zana, L.; Zhang, J.; Zhao, B.

2006-03-01

We report results from an experiment measuring the semiinclusive reaction H2(e,e'ps) in which the proton ps is moving at a large angle relative to the momentum transfer. If we assume that the proton was a spectator to the reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred. This method, known as spectator tagging, can be used to study electron scattering from high-momentum (off-shell) neutrons in deuterium. The data were taken with a 5.765 GeV electron beam on a deuterium target in Jefferson Laboratory's Hall B, using the CEBAF large acceptance spectrometer. A reduced cross section was extracted for different values of final state missing mass W*, backward proton momentum p→s, and momentum transfer Q2. The data are compared to a simple plane wave impulse approximation (PWIA) spectator model. A strong enhancement in the data observed at transverse kinematics is not reproduced by the PWIA model. This enhancement can likely be associated with the contribution of final state interactions (FSI) that were not incorporated into the model. Within the framework of the simple spectator model, a “bound neutron structure function” F2neff was extracted as a function of W* and the scaling variable x* at extreme backward kinematics, where the effects of FSI appear to be smaller. For ps>0.4GeV/c, where the neutron is far off-shell, the model overestimates the value of F2neff in the region of x* between 0.25 and 0.6. A dependence of the bound neutron structure function on the neutron's “off-shell-ness” is one possible effect that can cause the observed deviation.

Ab initio based study of the ArO- photoelectron spectra: Selectivity of spin-orbit transitions

NASA Astrophysics Data System (ADS)

Buchachenko, A. A.; Jakowski, Jacek; Chałasiński, Grzegorz; Szczȩśniak, M. M.; Cybulski, S. M.

2000-04-01

A combined ab initio atoms-in-molecule approach was implemented to model the photoelectron spectra of the ArO- anion. The lowest adiabatic states of Σ and Π symmetry of ArO and ArO- were investigated using the fourth-order Møller-Plessett perturbation theory including bond functions. The total energies were dissected into electrostatic, exchange, induction, and dispersion components. The complex of Ar with atomic oxygen is only weakly bound, primarily by dispersion interaction. The Π state possesses a deeper minimum (Re=3.4Å,De=380μEh) than the Σ state (Re=3.8Å,De=220μEh). In contrast, the anion complex is fairly strongly bound, primarily by ion-induced dipole induction forces, and the Σ state possesses a deeper minimum at shorter interatomic distances (Re=3.02Å,De=3600μEh) than the Π state (Re=3.35Å,De=2400μEh). The Σ-Π splittings in both systems are mainly due to differences in the exchange repulsion terms. Atoms-in-molecule models were used to account for the spin-orbit interaction, and to generate adiabatic relativistic potentials and wave functions. Collisional properties, diffusion, and mobility coefficients of O and O- in Ar, and absolute total Ar+O scattering cross sections, were calculated and found to agree well with the available experimental data. The photoelectron spectra were simulated within vibronic model, and were found in excellent agreement with the experimental measurements. The bimodal electron kinetic energy distribution was shown to stem from the strong selectivity of spin-orbit transitions, which split into two dense groups, depending on the initial electronic state of the anion. The latter feature cannot be described without explicit consideration of electronic intensity factor.

Population kinetics on K alpha lines of partially ionized Cl atoms.

PubMed

Kawamura, Tohru; Nishimura, Hiroaki; Koike, Fumihiro; Ochi, Yoshihiro; Matsui, Ryoji; Miao, Wen Yong; Okihara, Shinichiro; Sakabe, Shuji; Uschmann, Ingo; Förster, Eckhart; Mima, Kunioki

2002-07-01

A population kinetics code was developed to analyze K alpha emission from partially ionized chlorine atoms in hydrocarbon plasmas. Atomic processes are solved under collisional-radiative equilibrium for two-temperature plasmas. It is shown that the fast electrons dominantly contribute to ionize the K-shell bound electrons (i.e., inner-shell ionization) and the cold electrons to the outer-shell bound ones. Ratios of K alpha lines of partially ionized atoms are presented as a function of cold-electron temperature. The model was validated by observation of the K alpha lines from a chlorinated plastic target irradiated with 1 TW Ti:sapphire laser pulses at 1.5 x 10(17) W/cm(2), inferring a plasma temperature of about 100 eV on the target surface.

Visualizing polynucleotide polymerase machines at work

PubMed Central

Steitz, Thomas A

2006-01-01

The structures of T7 RNA polymerase (T7 RNAP) captured in the initiation and elongation phases of transcription, that of φ29 DNA polymerase bound to a primer protein and those of the multisubunit RNAPs bound to initiating factors provide insights into how these proteins can initiate RNA synthesis and synthesize 6–10 nucleotides while remaining bound to the site of initiation. Structural insight into the translocation of the product transcript and the separation of the downstream duplex DNA is provided by the structures of the four states of nucleotide incorporation. Single molecule and biochemical studies show a distribution of primer terminus positions that is altered by the binding of NTP and PPi ligands. This article reviews the insights that imaging the structure of polynucleotide polymerases at different steps of the polymerization reaction has provided on the mechanisms of the polymerization reaction. Movies are shown that allow the direct visualization of the conformational changes that the polymerases undergo during the different steps of polymerization. PMID:16900098

A recurrent neural network for nonlinear optimization with a continuously differentiable objective function and bound constraints.

PubMed

Liang, X B; Wang, J

2000-01-01

This paper presents a continuous-time recurrent neural-network model for nonlinear optimization with any continuously differentiable objective function and bound constraints. Quadratic optimization with bound constraints is a special problem which can be solved by the recurrent neural network. The proposed recurrent neural network has the following characteristics. 1) It is regular in the sense that any optimum of the objective function with bound constraints is also an equilibrium point of the neural network. If the objective function to be minimized is convex, then the recurrent neural network is complete in the sense that the set of optima of the function with bound constraints coincides with the set of equilibria of the neural network. 2) The recurrent neural network is primal and quasiconvergent in the sense that its trajectory cannot escape from the feasible region and will converge to the set of equilibria of the neural network for any initial point in the feasible bound region. 3) The recurrent neural network has an attractivity property in the sense that its trajectory will eventually converge to the feasible region for any initial states even at outside of the bounded feasible region. 4) For minimizing any strictly convex quadratic objective function subject to bound constraints, the recurrent neural network is globally exponentially stable for almost any positive network parameters. Simulation results are given to demonstrate the convergence and performance of the proposed recurrent neural network for nonlinear optimization with bound constraints.

Estimation of Free Radical Ionization Energies by the Kinetic Method and the Relationship between the Kinetic Method and the Hammett Equation.

PubMed

Chen, G; Wong, P; Cooks, R G

1997-09-01

Substituted 1,2-diphenylethanes undergo competitive dissociations upon electron ionization (EI) to generate substituted benzyl cation and benzyl radical pairs. Application of the kinetic method to the previous reported EI mass spectra of these covalently bound precursor ions (data are taken from McLafferty et al. J. Am. Chem. Soc. 1970, 92, 6867)) is used to estimate the ionization energies of substituted benzyl free radicals. A correlation is observed between the Hammett σ constant of the substituents and the kinetic method parameter, ln(k(x)/k(H)), where k(x) is the rate of fragmentation to give the substituted product ion and k(H) is the rate to give the benzyl ion itself. Systems involving weakly bound cluster ions, including proton-bound dimers of meta- and para-substituted pyridines and meta- and para-substituted anilines, and electron-bound dimers of meta- and para-substituted nitrobenzenes, also show good correlations between the kinetic method parameter and the Hammett σ constant.

Hydrated Electrons React with High Specificity with Cisplatin Bound to Single-Stranded DNA

PubMed Central

Behmand, B.; Cloutier, P.; Girouard, S.; Wagner, J. R.; Sanche, L.; Hunting, D. J.

2015-01-01

Short oligonucleotides TTTTTGTGTTT and TTTTTTTGTTT in solution with and without cisplatin (cisPt) bound to the guanine bases were irradiated with γ-rays at doses varying from 0 to 2500 Gy. To determine the effect of hydrated electrons from water radiolysis on the oligonucleotides, we quenched •OH radicals with ethylenediaminetetraacetic acid (EDTA) and displaced oxygen, which reacts with hydrated electrons, by bubbling the solution with wet nitrogen. DNA strand breaks and platinum detachment were quantified by gel electrophoresis. Our results demonstrate that hydrated electrons react almost exclusively at the position of the cisPt adduct, where they induce cisPt detachment from one or both guanines in the oligonucleotide. Given the high yield of hydrated electrons in irradiated tissues, this reaction may be an important step in the mechanism of radiosensitization of DNA by cisPt. PMID:24205952

Localization behavior at bound Bi complex states in GaA s 1 - x B i x

DOE PAGES

Alberi, K.; Christian, T. M.; Fluegel, B.; ...

2017-07-01

While bismuth-related states are known to localize carriers in GaAs 1-xBi x alloys, the localization behavior of distinct Bi pair, triplet and cluster states bound above the valence band is less well understood. We probe localization at three different Bi complex states in dilute GaAs 1-xBi x alloys using magneto-photoluminescence and time-resolved photoluminescence spectroscopy. The mass of electrons Coulomb-bound to holes trapped at Bi pair states is found to increase relative to the average electron mass in the alloy. This increase is attributed to enhanced local compressive strain in the immediate vicinity of the pairs. The dependence of energy transfermore » between these states on composition is also explored.« less

An improved error bound for linear complementarity problems for B-matrices.

PubMed

Gao, Lei; Li, Chaoqian

2017-01-01

A new error bound for the linear complementarity problem when the matrix involved is a B -matrix is presented, which improves the corresponding result in (Li et al. in Electron. J. Linear Algebra 31(1):476-484, 2016). In addition some sufficient conditions such that the new bound is sharper than that in (García-Esnaola and Peña in Appl. Math. Lett. 22(7):1071-1075, 2009) are provided.

The application of quasi-steady approximation in atomic kinetics in simulation of hohlraum radiation drive

NASA Astrophysics Data System (ADS)

Ren, Guoli; Pei, Wenbing; Lan, Ke; Li, Xin; Hohlraum Physics Team

2014-10-01

In current routine 2D simulation of hohlraum physics, we adopt the principal-quantum-number (n-level) average atom model (AAM) in NLTE plasma description. The more sophisticated atomic kinetics description is better choice, but the in-line calculation consumes much more resource. By distinguishing the much more fast bound-bound atomic processes from the relative slow bound-free atomic processes, we found a method to built up a bound electron distribution (n-level or nl-level) using in-line n-level calculated plasma condition (such as temperature, density, average ionization degree). We name this method ``quasi-steady approximation.'' Using this method and the plasma condition calculated under n-level, we re-build the nl-level bound electron distribution (Pnl), and acquire a new hohlraum radiative drive by post-processing. Comparison with the n-level post-processed hohlraum drive shows that we get an almost identical radiation flux but with more-detailed frequency-dependant structures. Also we use this method in the benchmark gold sphere experiment, the constructed nl-level radiation drive resembles the experimental results and DCA results, while the n-level raditation does not.

To acquire more detailed radiation drive by use of ``quasi-steady'' approximation in atomic kinetics

NASA Astrophysics Data System (ADS)

Ren, Guoli; Pei, Wenbing; Lan, Ke; Gu, Peijun; Li, Xin

2012-10-01

In current routine 2D simulation of hohlraum physics, we adopt the principal-quantum- number(n-level) average atom model(AAM) in NLTE plasma description. However, the detailed experimental frequency-dependant radiative drive differs from our n-level simulated drive, which reminds us the need of a more detailed atomic kinetics description. The orbital-quantum- number(nl-level) average atom model is a natural consideration, however the nl-level in-line calculation needs much more computational resource. By distinguishing the rapid bound-bound atomic processes from the relative slow bound-free atomic processes, we found a method to build up a more detailed bound electron distribution(nl-level even nlm-level) using in-line n-level calculated plasma conditions(temperature, density, and average ionization degree). We name this method ``quasi-steady approximation'' in atomic kinetics. Using this method, we re-build the nl-level bound electron distribution (Pnl), and acquire a new hohlraum radiative drive by post-processing. Comparison with the n-level post-processed hohlraum drive shows that we get an almost identical radiation flux but with more fine frequency-denpending spectrum structure which appears only in nl-level transition with same n number(n=0) .

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

Sun, Jianwei; Yang, Zenghui; Peng, Haowei

The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin densitymore » approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound.« less

Strong solutions for an incompressible Navier-Stokes/Allen-Cahn system with different densities

NASA Astrophysics Data System (ADS)

Li, Yinghua; Huang, Mingxia

2018-06-01

In this paper, we investigate a coupled Navier-Stokes/Allen-Cahn system describing a diffuse interface model for two-phase flow of viscous incompressible fluids with different densities in a bounded domain Ω \\subset R^N(N=2,3). We prove the existence and uniqueness of local strong solutions to the initial boundary value problem when the initial density function ρ _0 has a positive lower bound.

RefleX: X-ray absorption and reflection in active galactic nuclei for arbitrary geometries

NASA Astrophysics Data System (ADS)

Paltani, S.; Ricci, C.

2017-11-01

Reprocessed X-ray radiation carries important information about the structure and physical characteristics of the material surrounding the supermassive black hole (SMBH) in active galactic nuclei (AGN). We report here on a newly developed simulation platform, RefleX, which allows to reproduce absorption and reflection by quasi-arbitrary geometries. We show here the reliability of our approach by comparing the results of our simulations with existing spectral models such as pexrav, MYTorus and BNTorus. RefleX implements both Compton scattering on free electrons and Rayleigh scattering and Compton scattering on bound electrons. We show the effect of bound-electron corrections on a torus geometry simulated like in MYTorus. We release with this paper the RefleX executable, as well as RXTorus, a model that assumes absorption and reflection from a torus with a varying ratio of the minor to major axis of the torus. To allow major flexibility RXTorus is also distributed in three components: absorbed primary emission, scattered radiation and fluorescent lines. RXTorus is provided for different values of the abundance, and with (atomic configuration) or without (free-electron configuration) taking into account Rayleigh scattering and bound electrons. We apply the RXTorus model in both configurations on the XMM-Newton and NuSTAR spectrum of the Compton-thick AGN NGC 424 and find that the models are able to reproduce very well the observations, but that the assumption on the bound or free state of the electrons has significant consequences on the fit parameters. RefleX executable, user manual and example models are available at http://www.astro.unige.ch/reflex. A copy of the RefleX executable is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A31

Precision Measurement of the Electron's Electric Dipole Moment Using Trapped Molecular Ions

NASA Astrophysics Data System (ADS)

Cairncross, William B.; Gresh, Daniel N.; Grau, Matt; Cossel, Kevin C.; Roussy, Tanya S.; Ni, Yiqi; Zhou, Yan; Ye, Jun; Cornell, Eric A.

2017-10-01

We describe the first precision measurement of the electron's electric dipole moment (de) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on 180Hf 19F+ in its metastable 3Δ1 electronic state, we obtain de=(0.9 ±7. 7stat±1. 7syst)×10-29 e cm , resulting in an upper bound of |de|<1.3 ×10-28 e cm (90% confidence). Our result provides independent confirmation of the current upper bound of |de|<9.4 ×10-29 e cm [J. Baron et al., New J. Phys. 19, 073029 (2017), 10.1088/1367-2630/aa708e], and offers the potential to improve on this limit in the near future.

DAMPE electron-positron excess in leptophilic Z' model

NASA Astrophysics Data System (ADS)

Ghorbani, Karim; Ghorbani, Parsa Hossein

2018-05-01

Recently the DArk Matter Particle Explorer (DAMPE) has reported an excess in the electron-positron flux of the cosmic rays which is interpreted as a dark matter particle with the mass about 1.5 TeV. We come up with a leptophilic Z' scenario including a Dirac fermion dark matter candidate which beside explaining the observed DAMPE excess, is able to pass various experimental/observational constraints including the relic density value from the WMAP/Planck, the invisible Higgs decay bound at the LHC, the LEP bounds in electron-positron scattering, the muon anomalous magnetic moment constraint, Fermi-LAT data, and finally the direct detection experiment limits from the XENON1t/LUX. By computing the electron-positron flux produced from a dark matter with the mass about 1.5 TeV we show that the model predicts the peak observed by the DAMPE.

Sites of electron transfer to membrane-bound copper and hydroperoxide-induced damage in the respiratory chain of Escherichia coli.

PubMed

Rodríguez-Montelongo, L; Farías, R N; Massa, E M

1995-10-20

Previous studies in Escherichia coli as a model system for peroxide toxicity (L. Rodríguez-Montelongo, L. C. De la Cruz-Rodríguez, R. N. Farías, and E. M. Massa, 1993, Biochim. Biophys. Acta 1144, 77-84) have shown that electron flow through the respiratory chain supports a membrane-associated Cu(II)/Cu(I) redox cycle involved in irreversible impairment of the respiratory system by tert-butyl hydroperoxide (t-BOOH). In this paper, E. coli mutants deficient in specific respiratory chain components have been used to determine the sites of copper reduction and the targets inactivated by t-BOOH. Two sites of electron transfer to membrane-bound copper were identified: one in the region between NADH and ubiquinone supported by NADH as electron donor and another localized between ubiquinone and the cytochromes supported by electrons coming from NADH, succinate, or D-lactate. Electron flow through the former site in the presence of t-BOOH led to inactivation of NADH dehydrogenase II, whereas electron flow through the latter site in the presence of the hydroperoxide led to damage of ubiquinone. In agreement with the above in vitro results with isolated membranes, copper-dependent inactivation of NADH dehydrogenase and ubiquinone was demonstrated in E. coli cells exposed to t-BOOH. It is proposed that the t-BOOH-induced damage is a consequence of t-butylalkoxy radical generation through a Fenton-type reaction mediated by redox cycling of membrane-bound copper at those two loci of the respiratory chain.

A Cryo-Electron Microscopy Study Identifies the Complete H16.V5 Epitope and Reveals Global Conformational Changes Initiated by Binding of the Neutralizing Antibody Fragment

PubMed Central

Lee, Hyunwook; Brendle, Sarah A.; Bywaters, Stephanie M.; Guan, Jian; Ashley, Robert E.; Yoder, Joshua D.; Makhov, Alexander M.; Conway, James F.; Christensen, Neil D.

2014-01-01

ABSTRACT Human papillomavirus 16 (HPV16) is a worldwide health threat and an etiologic agent of cervical cancer. To understand the antigenic properties of HPV16, we pursued a structural study to elucidate HPV capsids and antibody interactions. The cryo-electron microscopy (cryo-EM) structures of a mature HPV16 particle and an altered capsid particle were solved individually and as complexes with fragment of antibody (Fab) from the neutralizing antibody H16.V5. Fitted crystal structures provided a pseudoatomic model of the virus-Fab complex, which identified a precise footprint of H16.V5, including previously unrecognized residues. The altered-capsid–Fab complex map showed that binding of the Fab induced significant conformational changes that were not seen in the altered-capsid structure alone. These changes included more ordered surface loops, consolidated so-called “invading-arm” structures, and tighter intercapsomeric connections at the capsid floor. The H16.V5 Fab preferentially bound hexavalent capsomers likely with a stabilizing effect that directly correlated with the number of bound Fabs. Additional cryo-EM reconstructions of the virus-Fab complex for different incubation times and structural analysis provide a model for a hyperstabilization of the capsomer by H16.V5 Fab and showed that the Fab distinguishes subtle differences between antigenic sites. IMPORTANCE Our analysis of the cryo-EM reconstructions of the HPV16 capsids and virus-Fab complexes has identified the entire HPV.V5 conformational epitope and demonstrated a detailed neutralization mechanism of this clinically important monoclonal antibody against HPV16. The Fab bound and ordered the apical loops of HPV16. This conformational change was transmitted to the lower region of the capsomer, resulting in enhanced intercapsomeric interactions evidenced by the more ordered capsid floor and “invading-arm” structures. This study advances the understanding of the neutralization mechanism used by H16.V5. PMID:25392224

Biogeochemical stability and reactions of iron-organic carbon complexes

NASA Astrophysics Data System (ADS)

Yang, Y.; Adhikari, D.; Zhao, Q.; Dunham-Cheatham, S.; Das, K.; Mejia, J.; Huang, R.; Wang, X.; Poulson, S.; Tang, Y.; Obrist, D.; Roden, E. E.

2017-12-01

Our core hypothesis is that the degradation rate of soil organic carbon (OC) is governed by the amount of iron (Fe)-bound OC, and the ability of microbial communities to utilize OC as an energy source and electron shuttle for Fe reduction that in turn stimulates reductive release of Fe-bound labile dissolved OC. This hypothesis is being systematically evaluated using model Fe-OC complexes, natural soils, and microcosm system. We found that hematite-bound aliphatic C was more resistant to reduction release, although hematite preferred to sorb more aromatic C. Resistance to reductive release represents a new mechanism that aliphatic soil OC was stabilized by association with Fe oxide. In other studies, pyrogenic OC was found to facilitate the reduction of hematite, by enhancing extracellular electron transport and sorbing Fe(II). For ferrihydrite-OC co-precipitates, the reduction of Fe and release of OC was closely governed by the C/Fe ratio in the system. Based on the XPS, XANES and XAFS analysis, the transformation of Fe speciation was heterogeneous, depending on the conformation and composition of Fe-OC complexes. For natural soils, we investigated the quantity, characteristics, and reactivity of Fe-bound OC in soils collected from 14 forests in the United States. Fe-bound OC contributed up to 57.8% of total OC in the forest soils. Under the anaerobic conditions, the reduction of Fe was positively correlated to the electron accepting capacity of OC. Our findings highlight the closely coupled dynamics of Fe and OC, with broad implications on the turnover of OC and biogeochemical cycles of Fe.

Nanowire electron scattering spectroscopy

NASA Technical Reports Server (NTRS)

Hunt, Brian D. (Inventor); Bronikowski, Michael (Inventor); Wong, Eric W. (Inventor); von Allmen, Paul (Inventor); Oyafuso, Fabiano A. (Inventor)

2009-01-01

Methods and devices for spectroscopic identification of molecules using nanoscale wires are disclosed. According to one of the methods, nanoscale wires are provided, electrons are injected into the nanoscale wire; and inelastic electron scattering is measured via excitation of low-lying vibrational energy levels of molecules bound to the nanoscale wire.

Preliminary analysis of coronal electron content measurements from spacecraft Helios A around first solar occultation

NASA Technical Reports Server (NTRS)

Edenhofer, P.; Esposito, P. B.; Martin, W. L.; Zygielbaum, A. I.; Hansen, R. T.; Hansen, S. F.; Lueneburg, E.

1977-01-01

Steady-state and dynamical features of the electron density distribution in the solar corona emerge from a preliminary analysis of Helios A electron content measurements. There are strong indications that correlations can be established with earth-bound K-coronagraph measurements.

Photodissociation of HCN and HNC isomers in the 7-10 eV energy range

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

Chenel, Aurelie; Roncero, Octavio, E-mail: octavio.roncero@csic.es; Aguado, Alfredo

2016-04-14

The ultraviolet photoabsorption spectra of the HCN and HNC isomers have been simulated in the 7-10 eV photon energy range. For this purpose, the three-dimensional adiabatic potential energy surfaces of the 7 lowest electronic states, and the corresponding transition dipole moments, have been calculated, at multireference configuration interaction level. The spectra are calculated with a quantum wave packet method on these adiabatic potential energy surfaces. The spectra for the 3 lower excited states, the dissociative electronic states, correspond essentially to predissociation peaks, most of them through tunneling on the same adiabatic state. The 3 higher electronic states are bound, hereaftermore » electronic bound states, and their spectra consist of delta lines, in the adiabatic approximation. The radiative lifetime towards the ground electronic states of these bound states has been calculated, being longer than 10 ns in all cases, much longer that the characteristic predissociation lifetimes. The spectra of HCN is compared with the available experimental and previous theoretical simulations, while in the case of HNC there are no previous studies to our knowledge. The spectrum for HNC is considerably more intense than that of HCN in the 7-10 eV photon energy range, which points to a higher photodissociation rate for HNC, compared to HCN, in astrophysical environments illuminated by ultraviolet radiation.« less

Electron transfer flavoprotein domain II orientation monitored using double electron-electron resonance between an enzymatically reduced, native FAD cofactor, and spin labels

PubMed Central

Swanson, Michael A; Kathirvelu, Velavan; Majtan, Tomas; Frerman, Frank E; Eaton, Gareth R; Eaton, Sandra S

2011-01-01

Human electron transfer flavoprotein (ETF) is a soluble mitochondrial heterodimeric flavoprotein that links fatty acid β-oxidation to the main respiratory chain. The crystal structure of human ETF bound to medium chain acyl-CoA dehydrogenase indicates that the flavin adenine dinucleotide (FAD) domain (αII) is mobile, which permits more rapid electron transfer with donors and acceptors by providing closer access to the flavin and allows ETF to accept electrons from at least 10 different flavoprotein dehydrogenases. Sequence homology is high and low-angle X-ray scattering is identical for Paracoccus denitrificans (P. denitrificans) and human ETF. To characterize the orientations of the αII domain of P. denitrificans ETF, distances between enzymatically reduced FAD and spin labels in the three structural domains were measured by double electron-electron resonance (DEER) at X- and Q-bands. An FAD to spin label distance of 2.8 ± 0.15 nm for the label in the FAD-containing αII domain (A210C) agreed with estimates from the crystal structure (3.0 nm), molecular dynamics simulations (2.7 nm), and rotamer library analysis (2.8 nm). Distances between the reduced FAD and labels in αI (A43C) were between 4.0 and 4.5 ± 0.35 nm and for βIII (A111C) the distance was 4.3 ± 0.15 nm. These values were intermediate between estimates from the crystal structure of P. denitrificans ETF and a homology model based on substrate-bound human ETF. These distances suggest that the αII domain adopts orientations in solution that are intermediate between those which are observed in the crystal structures of free ETF (closed) and ETF bound to a dehydrogenase (open). PMID:21308847

Structures of riboswitch RNA reaction states by mix-and-inject XFEL serial crystallography

NASA Astrophysics Data System (ADS)

Stagno, J. R.; Liu, Y.; Bhandari, Y. R.; Conrad, C. E.; Panja, S.; Swain, M.; Fan, L.; Nelson, G.; Li, C.; Wendel, D. R.; White, T. A.; Coe, J. D.; Wiedorn, M. O.; Knoska, J.; Oberthuer, D.; Tuckey, R. A.; Yu, P.; Dyba, M.; Tarasov, S. G.; Weierstall, U.; Grant, T. D.; Schwieters, C. D.; Zhang, J.; Ferré-D'Amaré, A. R.; Fromme, P.; Draper, D. E.; Liang, M.; Hunter, M. S.; Boutet, S.; Tan, K.; Zuo, X.; Ji, X.; Barty, A.; Zatsepin, N. A.; Chapman, H. N.; Spence, J. C. H.; Woodson, S. A.; Wang, Y.-X.

2017-01-01

Riboswitches are structural RNA elements that are generally located in the 5‧ untranslated region of messenger RNA. During regulation of gene expression, ligand binding to the aptamer domain of a riboswitch triggers a signal to the downstream expression platform. A complete understanding of the structural basis of this mechanism requires the ability to study structural changes over time. Here we use femtosecond X-ray free electron laser (XFEL) pulses to obtain structural measurements from crystals so small that diffusion of a ligand can be timed to initiate a reaction before diffraction. We demonstrate this approach by determining four structures of the adenine riboswitch aptamer domain during the course of a reaction, involving two unbound apo structures, one ligand-bound intermediate, and the final ligand-bound conformation. These structures support a reaction mechanism model with at least four states and illustrate the structural basis of signal transmission. The three-way junction and the P1 switch helix of the two apo conformers are notably different from those in the ligand-bound conformation. Our time-resolved crystallographic measurements with a 10-second delay captured the structure of an intermediate with changes in the binding pocket that accommodate the ligand. With at least a 10-minute delay, the RNA molecules were fully converted to the ligand-bound state, in which the substantial conformational changes resulted in conversion of the space group. Such notable changes in crystallo highlight the important opportunities that micro- and nanocrystals may offer in these and similar time-resolved diffraction studies. Together, these results demonstrate the potential of ‘mix-and-inject’ time-resolved serial crystallography to study biochemically important interactions between biomacromolecules and ligands, including those that involve large conformational changes.

Structures of riboswitch RNA reaction states by mix-and-inject XFEL serial crystallography

PubMed Central

Stagno, J. R.; Liu, Y.; Bhandari, Y. R.; Conrad, C. E.; Panja, S.; Swain, M.; Fan, L.; Nelson, G.; Li, C.; Wendel, D. R.; White, T. A.; Coe, J. D.; Wiedorn, M. O.; Knoska, J.; Oberthuer, D.; Tuckey, R. A.; Yu, P.; Dyba, M.; Tarasov, S. G.; Weierstall, U.; Grant, T. D.; Schwieters, C. D.; Zhang, J.; Ferré-D’Amaré, A. R.; Fromme, P.; Draper, D. E.; Liang, M.; Hunter, M. S.; Boutet, S.; Tan, K.; Zuo, X.; Ji, X.; Barty, A.; Zatsepin, N. A.; Chapman, H. N.; Spence, J. C. H.; Woodson, S. A.; Wang, Y.-X.

2017-01-01

Riboswitches are structural RNA elements that are generally located in the 5′ untranslated region of messenger RNA. During regulation of gene expression, ligand binding to the aptamer domain of a riboswitch triggers a signal to the downstream expression platform1–3. A complete understanding of the structural basis of this mechanism requires the ability to study structural changes over time4. Here we use femtosecond X-ray free electron laser (XFEL) pulses5,6 to obtain structural measurements from crystals so small that diffusion of a ligand can be timed to initiate a reaction before diffraction. We demonstrate this approach by determining four structures of the adenine riboswitch aptamer domain during the course of a reaction, involving two unbound apo structures, one ligand-bound intermediate, and the final ligand-bound conformation. These structures support a reaction mechanism model with at least four states and illustrate the structural basis of signal transmission. The three-way junction and the P1 switch helix of the two apo conformers are notably different from those in the ligand-bound conformation. Our time-resolved crystallographic measurements with a 10-second delay captured the structure of an intermediate with changes in the binding pocket that accommodate the ligand. With at least a 10-minute delay, the RNA molecules were fully converted to the ligand-bound state, in which the substantial conformational changes resulted in conversion of the space group. Such notable changes in crystallo highlight the important opportunities that micro- and nanocrystals may offer in these and similar time-resolved diffraction studies. Together, these results demonstrate the potential of ‘mix-and-inject’ time-resolved serial crystallography to study biochemically important interactions between biomacromolecules and ligands, including those that involve large conformational changes. PMID:27841871

The Impacts of Upward Bound Math-Science on Postsecondary Outcomes 7-9 Years after Scheduled High School Graduation: Final Report

ERIC Educational Resources Information Center

Seftor, Neil S.; Calcagno, Juan Carlos

2010-01-01

This final report updates the report "Upward Bound Math-Science: Program Description and Interim Impact Estimates" published in 2007 (Olsen et al. 2007). The 2007 interim report contained descriptive findings from a survey of Upward Bound Math-Science (UBMS) grantees from the late 1990s at the time of the study's initiation and impact estimates…

Spectral methods for study of the G-protein-coupled receptor rhodopsin. II. Magnetic resonance methods

NASA Astrophysics Data System (ADS)

Struts, A. V.; Barmasov, A. V.; Brown, M. F.

2016-02-01

This article continues our review of spectroscopic studies of G-protein-coupled receptors. Magnetic resonance methods including electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) provide specific structural and dynamical data for the protein in conjunction with optical methods (vibrational, electronic spectroscopy) as discussed in the accompanying article. An additional advantage is the opportunity to explore the receptor proteins in the natural membrane lipid environment. Solid-state 2H and 13C NMR methods yield information about both the local structure and dynamics of the cofactor bound to the protein and its light-induced changes. Complementary site-directed spin-labeling studies monitor the structural alterations over larger distances and correspondingly longer time scales. A multiscale reaction mechanism describes how local changes of the retinal cofactor unlock the receptor to initiate large-scale conformational changes of rhodopsin. Activation of the G-protein-coupled receptor involves an ensemble of conformational substates within the rhodopsin manifold that characterize the dynamically active receptor.

Electron Microscope Study of Sporulation and Parasporal Crystal Formation in Bacillus thuringiensis

PubMed Central

Bechtel, Donald B.; Bulla, Lee A.

1976-01-01

A comprehensive ultrastructural analysis of sporulation and parasporal crystal development is described for Bacillus thuringiensis. The insecticidal crystal of B. thuringiensis is initiated at the start of engulfment and is nearly complete by the time the exosporium forms. The crystal and a heretofore unobserved ovoid inclusion develop without any clear association with the forespore septum, exosporium, or mesosomes. These observations contradict previous hypotheses that the crystal is synthesized on the forespore membrane, exosporium, or mesosomes. Formation of forespore septa involves densely staining, double-membrane-bound, vesicular mesosomes that have a bridged appearance. Forespore engulfment is subpolar and also involves mesosomes. Upon completion of engulfment the following cytoplasmic changes occur: decrease in electron density of the incipient forespore membrane; loss of bridged appearance of incipient forespore membrane; change in stainability of incipient forespore, forespore, and mother cell cytoplasms; and alteration in staining quality of plasma membrane. These changes are involved in the conversion of the incipient forespore into a forespore and reflect “commitment” to sporulation. Images PMID:182671

Coseismic and initial postseismic deformation from the 2004 Parkfield, California, earthquake, observed by global positioning system, electronic distance meter, creepmeters, and borehole strainmeters

USGS Publications Warehouse

Langbein, J.; Murray, J.R.; Snyder, H.A.

2006-01-01

Global Positioning System (GPS), electronic distance meter, creepmeter, and strainmeter measurements spanning the M 6.0 Parkfield, California, earthquake are examined. Using these data from 100 sec through 9 months following the main-shock, the Omori's law, with rate inversely related to time, l/t p and p ranging between 0.7 and 1.3, characterizes the time-dependent deformation during the post-seismic period; these results are consistent with creep models for elastic solids. With an accurate function of postseismic response, the coseismic displacements can be estimated from the high-rate, 1-min sampling GPS; and the coseismic displacements are approximately 75% of those estimated from the daily solutions. Consequently, fault-slip models using daily solutions overestimate coseismic slip. In addition, at 2 months and at 8 months following the mainshock, postseismic displacements are modeled as slip on the San Andreas fault with a lower bound on the moment exceeding that of the coseismic moment.

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

Nilsson, A.; LaRue, J.; Öberg, H.

Here, we describe how the unique temporal and spectral characteristics of X-ray free-electron lasers (XFEL) can be utilized to follow chemical transformations in heterogeneous catalysis in real time. We highlight the systematic study of CO oxidation on Ru(0 0 0 1), which we initiate either using a femtosecond pulse from an optical laser or by activating only the oxygen atoms using a THz pulse. We find that CO is promoted into an entropy-controlled precursor state prior to desorbing when the surface is heated in the absence of oxygen, whereas in the presence of oxygen, CO desorbs directly into the gasmore » phase. We monitor the activation of atomic oxygen explicitly by the reduced split between bonding and antibonding orbitals as the oxygen comes out of the strongly bound hollow position. Applying these novel XFEL techniques to the full oxidation reaction resulted in the surprising observation of a significant fraction of the reactants at the transition state through the electronic signature of the new bond formation.« less

Topological triplon modes and bound states in a Shastry-Sutherland magnet

NASA Astrophysics Data System (ADS)

McClarty, P. A.; Krüger, F.; Guidi, T.; Parker, S. F.; Refson, K.; Parker, A. W.; Prabhakaran, D.; Coldea, R.

2017-08-01

The twin discoveries of the quantum Hall effect, in the 1980s, and of topological band insulators, in the 2000s, were landmarks in physics that enriched our view of the electronic properties of solids. In a nutshell, these discoveries have taught us that quantum mechanical wavefunctions in crystalline solids may carry nontrivial topological invariants which have ramifications for the observable physics. One of the side effects of the recent topological insulator revolution has been that such physics is much more widespread than was appreciated ten years ago. For example, while topological insulators were originally studied in the context of electron wavefunctions, recent work has initiated a hunt for topological insulators in bosonic systems: in photonic crystals, in the vibrational modes of crystals, and in the excitations of ordered magnets. Using inelastic neutron scattering along with theoretical calculations, we demonstrate that, in a weak magnetic field, the dimerized quantum magnet SrCu2(BO3)2 is a bosonic topological insulator with topologically protected chiral edge modes of triplon excitations.

Catalysis in real time using x-ray lasers

DOE PAGES

Nilsson, A.; LaRue, J.; Öberg, H.; ...

2017-02-14

Here, we describe how the unique temporal and spectral characteristics of X-ray free-electron lasers (XFEL) can be utilized to follow chemical transformations in heterogeneous catalysis in real time. We highlight the systematic study of CO oxidation on Ru(0 0 0 1), which we initiate either using a femtosecond pulse from an optical laser or by activating only the oxygen atoms using a THz pulse. We find that CO is promoted into an entropy-controlled precursor state prior to desorbing when the surface is heated in the absence of oxygen, whereas in the presence of oxygen, CO desorbs directly into the gasmore » phase. We monitor the activation of atomic oxygen explicitly by the reduced split between bonding and antibonding orbitals as the oxygen comes out of the strongly bound hollow position. Applying these novel XFEL techniques to the full oxidation reaction resulted in the surprising observation of a significant fraction of the reactants at the transition state through the electronic signature of the new bond formation.« less

Communication: Near-locality of exchange and correlation density functionals for 1- and 2-electron systems

NASA Astrophysics Data System (ADS)

Sun, Jianwei; Perdew, John P.; Yang, Zenghui; Peng, Haowei

2016-05-01

The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin density approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound.

Quantum speed limit for arbitrary initial states

PubMed Central

Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Cao, Jun-Peng; Fan, Heng

2014-01-01

The minimal time a system needs to evolve from an initial state to its one orthogonal state is defined as the quantum speed limit time, which can be used to characterize the maximal speed of evolution of a quantum system. This is a fundamental question of quantum physics. We investigate the generic bound on the minimal evolution time of the open dynamical quantum system. This quantum speed limit time is applicable to both mixed and pure initial states. We then apply this result to the damped Jaynes-Cummings model and the Ohimc-like dephasing model starting from a general time-evolution state. The bound of this time-dependent state at any point in time can be found. For the damped Jaynes-Cummings model, when the system starts from the excited state, the corresponding bound first decreases and then increases in the Markovian dynamics. While in the non-Markovian regime, the speed limit time shows an interesting periodic oscillatory behavior. For the case of Ohimc-like dephasing model, this bound would be gradually trapped to a fixed value. In addition, the roles of the relativistic effects on the speed limit time for the observer in non-inertial frames are discussed. PMID:24809395

An accurate and linear-scaling method for calculating charge-transfer excitation energies and diabatic couplings

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

Pavanello, Michele; Van Voorhis, Troy; Visscher, Lucas

2013-02-07

Quantum-mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this goal for those charge transfer excitations that take place between non-covalently bound molecules. In particular, we present a method that scales linearly with the number of non-covalently bound molecules in the system and is based on a two-pronged approach: The molecular electronic structure of broken-symmetry charge-localized states is obtained with the frozen density embedding formulation of subsystem density-functional theory; subsequently, in a post-SCF calculation, the full-electron Hamiltonian and overlapmore » matrix elements among the charge-localized states are evaluated with an algorithm which takes full advantage of the subsystem DFT density partitioning technique. The method is benchmarked against coupled-cluster calculations and achieves chemical accuracy for the systems considered for intermolecular separations ranging from hydrogen-bond distances to tens of Angstroms. Numerical examples are provided for molecular clusters comprised of up to 56 non-covalently bound molecules.« less

An accurate and linear-scaling method for calculating charge-transfer excitation energies and diabatic couplings.

PubMed

Pavanello, Michele; Van Voorhis, Troy; Visscher, Lucas; Neugebauer, Johannes

2013-02-07

Quantum-mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this goal for those charge transfer excitations that take place between non-covalently bound molecules. In particular, we present a method that scales linearly with the number of non-covalently bound molecules in the system and is based on a two-pronged approach: The molecular electronic structure of broken-symmetry charge-localized states is obtained with the frozen density embedding formulation of subsystem density-functional theory; subsequently, in a post-SCF calculation, the full-electron Hamiltonian and overlap matrix elements among the charge-localized states are evaluated with an algorithm which takes full advantage of the subsystem DFT density partitioning technique. The method is benchmarked against coupled-cluster calculations and achieves chemical accuracy for the systems considered for intermolecular separations ranging from hydrogen-bond distances to tens of Ångstroms. Numerical examples are provided for molecular clusters comprised of up to 56 non-covalently bound molecules.

Evidence for a positron bound state on the surface of a topological insulator

NASA Astrophysics Data System (ADS)

Shastry, K.; Weiss, A. H.; Barbiellini, B.; Assaf, B. A.; Lim, Z. H.; Joglekar, P. V.; Heiman, D.

2015-06-01

We describe experiments aimed at probing the sticking of positrons to the surfaces of topological insulators using the Positron Annihilation induced Auger Electron Spectrometer (PAES). A magnetically guided beam was used to deposit positrons at the surface of Bi2Te2Se sample at energy of ∼2eV. Peaks observed in the energy spectra and intensities of electrons emitted as a result of positron annihilation showed peaks at energies corresponding to Auger peaks in Bi, Teand Se providing clear evidence of Auger emission associated with the annihilation of positrons in a surface bound state. Theoretical estimates of the binding energy of this state are compared with estimates obtained by measuring the incident beam energy threshold for secondary electron emission and the temperature dependence positronium(Ps) emission. The experiments provide strong evidence for the existence of a positron bound state at the surface of Bi2Te2Se and indicate the practicality of using positron annihilation to selectively probe the critically important top most layer of topological insulator system.

Charged excitons in a dilute two-dimensional electron gas in a high magnetic field

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

Wojs, Arkadiusz; Institute of Physics, Wroclaw University of Technology, Wroclaw 50-370,; Quinn, John J.

2000-08-15

A theory of charged excitons X{sup -} in a dilute two-dimensional (2D) electron gas in a high-magnetic field is presented. In contrast to previous calculations, three bound X{sup -} states (one singlet and two triplets) are found in a narrow and symmetric GaAs quantum well. The singlet and a ''bright'' triplet are the two optically active states observed in experiments. The bright triplet has the binding energy of about 1 meV, smaller than the singlet and a ''dark'' triplet. The interaction of bound X{sup -}'s with a dilute 2D electron gas is investigated using exact diagonalization techniques. It is foundmore » that the short-range character of the e-X{sup -} interactions effectively isolates bound X{sup -} states from a dilute e-h plasma. This results in the insensitivity of the photoluminescence spectrum to the filling factor {nu}, and a rapid decrease of the oscillator strength of the dark triplet X{sup -} as a function of {nu}{sup -1}. (c) 2000 The American Physical Society.« less

Invariant criteria for bound states, degree of ionization, and plasma phase transition

NASA Technical Reports Server (NTRS)

Girardeau, M. D.

1990-01-01

Basis invariant characterizations of bound states and bound fraction of a partially ionized hydrogen plasma are given in terms of properties of the spectrum of eigenvalues and eigenfunctions of the equilibrium quantum statistical one-proton-one-electron reduced density matrix. It is suggested that these can be used to place theories of a proposed plasma-ionization phase transition on a firm foundation. This general approach may be relevant to cosmological questions such as the quark deconfinement-confinement transition.

Substrate specificity and interferences of a direct-electron-transfer-based glucose biosensor.

PubMed

Felice, Alfons K G; Sygmund, Christoph; Harreither, Wolfgang; Kittl, Roman; Gorton, Lo; Ludwig, Roland

2013-05-01

Electrochemical sensors for glucose monitoring employ different signal transduction strategies for electron transfer from the biorecognition element to the electrode surface. We present a biosensor that employs direct electron transfer and evaluate its response to various interfering substances known to affect glucose biosensors. The enzyme cellobiose dehydrogenase (CDH) was adsorbed on the surface of a carbon working electrode and covalently bound by cross linking. The response of CDH-modified electrodes to glucose and possible interfering compounds was measured by flow-injection analysis, linear sweep, and chronoamperometry. Chronoamperometry showed initial swelling/wetting of the electrode. After stabilization, the signal was stable and a sensitivity of 0.21 µA mM-1 cm-2 was obtained. To investigate the influence of the interfering substances on the biorecognition element, the simplest possible sensor architecture was used. The biosensor showed little (<5% signal deviation) or no response to various reported electroactive or otherwise interfering substances. Direct electron transfer from the biorecognition element to the electrode is a new principle applied to glucose biosensors, which can be operated at a low polarization potential of -100 mV versus silver/silver chloride. The reduction of interferences by electrochemically active substances is an attractive feature of this promising technology for the development of continuous glucose biosensors. © 2013 Diabetes Technology Society.

Flowing afterglow studies of the electron recombination of protonated cyanides (RCN)H+ and their proton-bound dimer ions (RCN)2H+ where R is H, CH3, and CH3CH2

NASA Astrophysics Data System (ADS)

McLain, J. L.; Molek, C. D.; , D. Osborne, Jr.; Adams, N. G.

2009-05-01

A study has been made of the electron-ion dissociative recombination of the protonated cyanides (RCNH+, R = H, CH3, C2H5) and their proton-bound dimers (RCN)2H+ at 300 K. This has been accomplished with the flowing afterglow technique using an electrostatic Langmuir probe to determine the electron density decay along the flow tube. For the protonated species, the recombination coefficients, [alpha]e(cm3 s-1), are (3.6 +/- 0.5) × 10-7, (3.4 +/- 0.5) × 10-7, (4.6 +/- 0.7) × 10-7 for R = H, CH3, C2H5, respectively. For the proton-bound dimers, the [alpha]e are substantially greater being (2.4 +/- 0.4) × 10-6, (2.8 +/- 0.4) × 10-6, (2.3 +/- 0.3) × 10-6 for R = H, CH3, C2H5, respectively. Fitting of the electron density decay data to a simple model has shown that the rate coefficients for the three-body association of RCNH+ with RCN are very large being (2.0 +/- 0.5) × 10-26 cm6 s-1. The significance of these data to the Titan ionosphere is discussed.

Auger mediated positron sticking on graphene and highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

Chirayath, V. A.; Chrysler, M.; McDonald, A.; Lim, Z.; Shastry, K.; Gladen, R.; Fairchild, A.; Koymen, A.; Weiss, A.

Positron annihilation induced Auger electron spectroscopy (PAES) measurements on 6-8 layers graphene grown on polycrystalline copper and the measurements on a highly oriented pyrolytic graphite (HOPG) sample have indicated the presence of a bound surface state for positrons. Measurements carried out with positrons of kinetic energies lower than the electron work function for graphene or HOPG have shown emission of low energy electrons possible only through the Auger mediated positron sticking (AMPS) process. In this process the positron makes a transition from a positive energy scattering state to a bound surface state. The transition energy is coupled to a valence electron which may then have enough energy to get ejected from the sample surface. The positrons which are bound to surface state are highly localized in a direction perpendicular to surface and delocalized parallel to it which makes this process highly surface sensitive and can thus be used for characterizing graphene or graphite surfaces for open volume defects and surface impurities. The measurements have also shown an extremely large low energy tail for the C KVV Auger transition at 263eV indicative of another physical process for low energy emission. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

Amplified stimulated emission in the NaK(D-X) band by high power copper vapor laser pumping

NASA Astrophysics Data System (ADS)

Dinev, S. G.; Hadjicristov, G. B.; Marazov, O.

1991-04-01

Using a 10 W copper vapor laser we have studied a stimulated emission at 520-570 nm in the D-X electronic transition of the NaK heteronuclear molecule. The influence of the cavity configuration on the bound-bound stimulated lines is considered.

Amplified stimulated emission in the NaK( D→ X) band by high power copper vapor laser pumping

NASA Astrophysics Data System (ADS)

Dinev, S. G.; Hadjichristov, G. B.; Marazov, O.

1991-04-01

Using a 10 W copper vapor laser we have studied a stimulated emission at 520 570 nm in the D→ X electronic transition of the NaK heteronuclear molecule. The influence of the cavity configuration on the bound-bound stimulated lines is considered.

Noisy metrology: a saturable lower bound on quantum Fisher information

NASA Astrophysics Data System (ADS)

Yousefjani, R.; Salimi, S.; Khorashad, A. S.

2017-06-01

In order to provide a guaranteed precision and a more accurate judgement about the true value of the Cramér-Rao bound and its scaling behavior, an upper bound (equivalently a lower bound on the quantum Fisher information) for precision of estimation is introduced. Unlike the bounds previously introduced in the literature, the upper bound is saturable and yields a practical instruction to estimate the parameter through preparing the optimal initial state and optimal measurement. The bound is based on the underling dynamics, and its calculation is straightforward and requires only the matrix representation of the quantum maps responsible for encoding the parameter. This allows us to apply the bound to open quantum systems whose dynamics are described by either semigroup or non-semigroup maps. Reliability and efficiency of the method to predict the ultimate precision limit are demonstrated by three main examples.

Resolving the Spatial Structures of Bound Hole States in Black Phosphorus.

PubMed

Qiu, Zhizhan; Fang, Hanyan; Carvalho, Alexandra; Rodin, A S; Liu, Yanpeng; Tan, Sherman J R; Telychko, Mykola; Lv, Pin; Su, Jie; Wang, Yewu; Castro Neto, A H; Lu, Jiong

2017-11-08

Understanding the local electronic properties of individual defects and dopants in black phosphorus (BP) is of great importance for both fundamental research and technological applications. Here, we employ low-temperature scanning tunnelling microscope (LT-STM) to probe the local electronic structures of single acceptors in BP. We demonstrate that the charge state of individual acceptors can be reversibly switched by controlling the tip-induced band bending. In addition, acceptor-related resonance features in the tunnelling spectra can be attributed to the formation of Rydberg-like bound hole states. The spatial mapping of the quantum bound states shows two distinct shapes evolving from an extended ellipse shape for the 1s ground state to a dumbbell shape for the 2p x excited state. The wave functions of bound hole states can be well-described using the hydrogen-like model with anisotropic effective mass, corroborated by our theoretical calculations. Our findings not only provide new insight into the many-body interactions around single dopants in this anisotropic two-dimensional material but also pave the way to the design of novel quantum devices.

Application of the N-quantum approximation to the proton radius problem

NASA Astrophysics Data System (ADS)

Cowen, Steven

This thesis is organized into three parts: 1. Introduction and bound state calculations of electronic and muonic hydrogen, 2. Bound states in motion, and 3.Treatment of soft photons. In the first part, we apply the N-Quantum Approximation (NQA) to electronic and muonic hydrogen and search for any new corrections to energy levels that could account for the 0.31 meV discrepancy of the proton radius problem. We derive a bound state equation and compare our numerical solutions and wave functions to those of the Dirac equation. We find NQA Lamb shift diagrams and calculate the associated energy shift contributions. We do not find any new corrections large enough to account for the discrepancy. In part 2, we discuss the effects of motion on bound states using the NQA. We find classical Lorentz contraction of the lowest order NQA wave function. Finally, in part 3, we develop a clothing transformation for interacting fields in order to produce the correct asymptotic limits. We find the clothing eliminates a trilinear interacting Hamiltonian term and produces a quadrilinear soft photon interaction term.

Collisional-radiative nonequilibrium in partially ionized atomic nitrogen

NASA Technical Reports Server (NTRS)

Kunc, J. A.; Soon, W. H.

1989-01-01

A nonlinear collisional-radiative model for determination of nonequilibrium production of electrons, excited atoms, and bound-bound, dielectronic and continuum line intensities in stationary partially ionized atomic nitrogen is presented. Populations of 14 atomic levels and line intensities are calculated in plasma with T(e) = 8000-15,000 K and N(t) = 10 to the 12th - 10 to the 18th/cu cm. Transport of radiation is included by coupling the rate equations of production of the electrons and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions.

Searching for the rules that govern hadron construction

DOE PAGES

Shepherd, Matthew R.; Dudek, Jozef J.; Mitchell, Ryan E.

2016-06-22

Just as quantum electrodynamics describes how electrons are bound in atoms by the electromagnetic force, mediated by the exchange of photons, quantum chromodynamics (QCD) describes how quarks are bound inside hadrons by the strong force, mediated by the exchange of gluons. QCD seems to allow hadrons constructed from increasingly many quarks to exist, just as atoms with increasing numbers of electrons exist, yet such complex constructions seemed, until recently, not to be present in nature. In this paper, we describe advances in the spectroscopy of mesons that are refining our understanding of the rules for predicting hadron structure from QCD.

Cathodoluminescence of stacking fault bound excitons for local probing of the exciton diffusion length in single GaN nanowires

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

Nogues, Gilles, E-mail: gilles.nogues@neel.cnrs.fr; Den Hertog, Martien; Inst. NEEL, CNRS, F-38042 Grenoble

We perform correlated studies of individual GaN nanowires in scanning electron microscopy combined to low temperature cathodoluminescence, microphotoluminescence, and scanning transmission electron microscopy. We show that some nanowires exhibit well localized regions emitting light at the energy of a stacking fault bound exciton (3.42 eV) and are able to observe the presence of a single stacking fault in these regions. Precise measurements of the cathodoluminescence signal in the vicinity of the stacking fault give access to the exciton diffusion length near this location.

VizieR Online Data Catalog: Thermodynamic quantities of molecular hydrogen (Popovas+, 2016)

NASA Astrophysics Data System (ADS)

Popovas, A.; Jorgensen, U. G.

2016-07-01

New partition functions for equilibrium, normal, and ortho and para hydrogen are calculated and thermodynamic quantities are reported for the temperature range 1-20000K. Our results are compared to previous estimates in the literature. The calculations are not limited to the ground electronic state, but include all bound and quasi-bound levels of excited electronic states. Dunham coefficients of these states of H2 are also reported. Reported internal partition functions and thermodynamic quantities in the present work are shown to be more accurate than previously available data. (4 data files).

Human spire interacts with the barbed end of the actin filament.

PubMed

Ito, Takuto; Narita, Akihiro; Hirayama, Tasuku; Taki, Masayasu; Iyoshi, Shohei; Yamamoto, Yukio; Maéda, Yuichiro; Oda, Toshiro

2011-04-22

Spire is an actin nucleator that initiates actin polymerization at a specific place in the cell. Similar to the Arp2/3 complex, spire was initially considered to bind to the pointed end of the actin filament when it generates a new actin filament. Subsequently, spire was reported to be associated with the barbed end (B-end); thus, there is still no consensus regarding the end with which spire interacts. Here, we report direct evidence that spire binds to the B-end of the actin filament, under conditions where spire accelerates actin polymerization. Using electron microscopy, we visualized the location of spire bound to the filament by gold nanoparticle labeling of the histidine-tagged spire, and the polarity of the actin filament was determined by image analysis. In addition, our results suggest that multiple spires, linked through one gold nanoparticle, enhance the acceleration of actin polymerization. The B-end binding of spire provides the basis for understanding its functional mechanism in the cell. Copyright © 2011 Elsevier Ltd. All rights reserved.

Transverse Space-Charge Field-Induced Plasma Dynamics for Ultraintense Electron-Beam Characterization

NASA Astrophysics Data System (ADS)

Tarkeshian, R.; Vay, J. L.; Lehe, R.; Schroeder, C. B.; Esarey, E. H.; Feurer, T.; Leemans, W. P.

2018-04-01

Similarly to laser or x-ray beams, the interaction of sufficiently intense particle beams with neutral gases will result in the creation of plasma. In contrast to photon-based ionization, the strong unipolar field of a particle beam can generate a plasma where the electron population receives a large initial momentum kick and escapes, leaving behind unshielded ions. Measuring the properties of the ensuing Coulomb exploding ions—such as their kinetic energy distribution, yield, and spatial distribution—can provide information about the peak electric fields that are achieved in the electron beams. Particle-in-cell simulations and analytical models are presented for high-brightness electron beams of a few femtoseconds or even hundreds of attoseconds, and transverse beam sizes on the micron scale, as generated by today's free electron lasers. Different density regimes for the utilization as a potential diagnostics are explored, and the fundamental differences in plasma dynamical behavior for e-beam or photon-based ionization are highlighted. By measuring the dynamics of field-induced ions for different gas and beam densities, a lower bound on the beam charge density can be obtained in a single shot and in a noninvasive way. The exponential dependency of the ionization yield on the beam properties can provide unprecedented spatial and temporal resolution, at the submicrometer and subfemtosecond scales, respectively, offering a practical and powerful approach to characterizing beams from accelerators at the frontiers of performance.

Precision Measurement of the Electron's Electric Dipole Moment Using Trapped Molecular Ions.

PubMed

Cairncross, William B; Gresh, Daniel N; Grau, Matt; Cossel, Kevin C; Roussy, Tanya S; Ni, Yiqi; Zhou, Yan; Ye, Jun; Cornell, Eric A

2017-10-13

We describe the first precision measurement of the electron's electric dipole moment (d_{e}) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on ^{180}Hf^{19}F^{+} in its metastable ^{3}Δ_{1} electronic state, we obtain d_{e}=(0.9±7.7_{stat}±1.7_{syst})×10^{-29}  e cm, resulting in an upper bound of |d_{e}|<1.3×10^{-28}  e cm (90% confidence). Our result provides independent confirmation of the current upper bound of |d_{e}|<9.4×10^{-29}  e cm [J. Baron et al., New J. Phys. 19, 073029 (2017)NJOPFM1367-263010.1088/1367-2630/aa708e], and offers the potential to improve on this limit in the near future.

Prediction and observation of tin and silver plasmas with index of refraction greater than one in the soft x-ray range.

PubMed

Filevich, Jorge; Grava, Jonathan; Purvis, Mike; Marconi, Mario C; Rocca, Jorge J; Nilsen, Joseph; Dunn, James; Johnson, Walter R

2006-07-01

We present the calculated prediction and the experimental confirmation that doubly ionized Ag and Sn plasmas can have an index of refraction greater than one for soft x-ray wavelengths. Interferometry experiments conducted using a capillary discharge soft x-ray laser operating at a wavelength of confirm that in few times ionized laser-created plasmas of these elements the anomalous dispersion from bound electrons can dominate the free electron contribution, making the index of refraction greater than one. The results confirm that bound electrons can strongly influence the index of refraction of numerous plasmas over a broad range of soft x-ray wavelengths confirming recent observations. The understanding of index of refraction at short wavelengths will become even more essential during the next decade as x-ray free electron lasers will become available to probe a wider variety of plasmas at higher densities and shorter wavelengths.

Experimental Potential Energy Curve for the 43 Π Electronic State of NaCs

NASA Astrophysics Data System (ADS)

Steely, Andrew; Cooper, Hannah; Zain, Hareem; Whipp, Ciara; Faust, Carl; Kortyna, Andrew; Huennekens, John

2017-04-01

We present results from experimental studies of the 43 Π electronic state of the NaCs molecule. This electronic state is interesting in that its potential energy curve likely exhibits a double minimum. As a result, interference effects are observed in the resolved bound-free fluorescence spectra. The optical-optical double resonance method was used to obtain Doppler-free excitation spectra for the 43 Π state. This dataset of measured level energies was expanded largely by observing fluorescence from levels populated by collisions. To aid in level assignments, simulations of resolved bound-free fluorescence spectra were calculated using the BCONT program (R. J. Le Roy, University of Waterloo). Spectroscopic constants were determined to summarize data belonging to inner well, outer well, and above barrier regions of the electronic state. Current work focuses on using the IPA method to construct an experimental potential energy curve. Work supported by NSF and Susquehanna University.

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

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

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

2014-12-28

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

Binding of two-electron metastable states in semiconductor quantum dots under a magnetic field

NASA Astrophysics Data System (ADS)

Garagiola, Mariano; Pont, Federico M.; Osenda, Omar

2018-04-01

Applying a strong enough magnetic field results in the binding of few-electron resonant states. The mechanism was proposed many years ago but its verification in laboratory conditions is far more recent. In this work we study the binding of two-electron resonant states. The electrons are confined in a cylindrical quantum dot which is embedded in a semiconductor wire. The geometry considered is similar to the one used in actual experimental setups. The low-energy two-electron spectrum is calculated numerically from an effective-mass approximation Hamiltonian modelling the system. Methods for binding threshold calculations in systems with one and two electrons are thoroughly studied; in particular, we use quantum information quantities to assess when the strong lateral confinement approximation can be used to obtain reliable low-energy spectra. For simplicity, only cases without bound states in the absence of an external field are considered. Under these conditions, the binding threshold for the one-electron case is given by the lowest Landau energy level. Moreover, the energy of the one-electron bounded resonance can be used to obtain the two-electron binding threshold. It is shown that for realistic values of the two-electron model parameters it is feasible to bind resonances with field strengths of a few tens of tesla.

Strong-field dissociation of CS2+ via a pump/dump-like mechanism

NASA Astrophysics Data System (ADS)

Severt, T.; Zohrabi, M.; Betsch, K. J.; Ablikim, U.; Jochim, Bethany; Carnes, K. D.; Zeng, S.; Esry, B. D.; Ben-Itzhak, I.; Uhlíková, T.

2014-05-01

Laser-induced dissociation of the quasi-bound electronic ground state of CS2+ is investigated in intense laser pulses (<55 fs, <1016 W/cm2). Photodissociation is observed to be the dominant dissociation pathway; however, a more curious feature in the kinetic energy release spectrum suggests no significant energy gain from the initial states. We propose a pump/dump-like mechanism to explain this observed feature. Contrary to the conventional pump/dump control scheme, this process occurs within a single laser pulse, where the time delay is caused by the molecular structure. The process begins when the vibrational wavepacket in the electronic ground state of CS2+ is pumped into the electronic first excited state's continuum by a single photon. After a period of stretching at an energy above the potential barrier, the emission of a second photon is stimulated by the same laser pulse, most likely at the Condon point. Supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, Grants DE-FG02-86ER13491 and DE-FG02-09ER16115. TU supported by GACR and MetaCentrum.

Unmatter Plasma revisited

NASA Astrophysics Data System (ADS)

Smarandache, Florentin

2017-10-01

Unmmatter Plasma is a novel form of plasma, exclusively made of matter and its antimatter counterpart. The electron-positron beam plasma was generated in the laboratory in the beginning of 2015. This experimental fact shows that unmatter, a new form of matter that is formed by matter and antimatter bind together (mathematically predicted since 2004) really exists. That is the electron-positron plasma experiment of 2015 is the experimentum crucis verifying the mathematically predicted unmatter. Unmatter is formed by combinations of matter and antimatter that bind together, or by long-range mixture of matter and antimatter forming a weakly-coupled phase. Binding and bound state means that the interaction is sufficiently strong to tie together the particles of a system, therefore hindering them from becoming free. For example, a usual liquid is a bound state of molecules, while a gas is an un-bounded where the molecules can move freely in successive collisions.

Internal structure of acceptor-bound excitons in wide-band-gap wurtzite semiconductors

NASA Astrophysics Data System (ADS)

Gil, Bernard; Bigenwald, Pierre; Paskov, Plamen P.; Monemar, Bo

2010-02-01

We describe the internal structure of acceptor-bound excitons in wurtzite semiconductors. Our approach consists in first constructing, in the context of angular momentum algebra, the wave functions of the two-hole system that fulfill Pauli’s exclusion’s principle. Second, we construct the acceptor-bound exciton states by adding the electron states in a similar manner that two-hole states are constructed. We discuss the optical selection rules for the acceptor-bound exciton recombination. Finally, we compare our theory with experimental data for CdS and GaN. In the specific case of CdS for which much experimental information is available, we demonstrate that, compared with cubic semiconductors, the sign of the short-range hole-exchange interaction is reversed and more than one order of magnitude larger. The whole set of data is interpreted in the context of a large value of the short-range hole-exchange interaction Ξ0=3.4±0.2meV . This value dictates the splitting between the ground-state line I1 and the other transitions. The values we find for the electron-hole spin-exchange interaction and of the crystal-field splitting of the two-hole state are, respectively, -0.4±0.1 and 0.2±0.1meV . In the case of GaN, the experimental data for the acceptor-bound excitons in the case of Mg and Zn acceptors, show more than one bound-exciton line. We discuss a possible assignment of these states.

Improved Limits on Axionlike-Particle-Mediated P, T-Violating Interactions between Electrons and Nucleons from Electric Dipole Moments of Atoms and Molecules.

PubMed

Stadnik, Y V; Dzuba, V A; Flambaum, V V

2018-01-05

In the presence of P, T-violating interactions, the exchange of axionlike particles between electrons and nucleons in atoms and molecules induces electric dipole moments (EDMs) of atoms and molecules. We perform calculations of such axion-exchange-induced atomic EDMs using the relativistic Hartree-Fock-Dirac method including electron core polarization corrections. We present analytical estimates to explain the dependence of these induced atomic EDMs on the axion mass and atomic parameters. From the experimental bounds on the EDMs of atoms and molecules, including ^{133}Cs, ^{205}Tl, ^{129}Xe, ^{199}Hg, ^{171}Yb^{19}F, ^{180}Hf^{19}F^{+}, and ^{232}Th^{16}O, we constrain the P, T-violating scalar-pseudoscalar nucleon-electron and electron-electron interactions mediated by a generic axionlike particle of arbitrary mass. Our limits improve on existing laboratory bounds from other experiments by many orders of magnitude for m_{a}≳10^{-2}  eV. We also place constraints on CP violation in certain types of relaxion models.

Stabilizing photoassociated Cs2 molecules by optimal control

NASA Astrophysics Data System (ADS)

Zhang, Wei; Xie, Ting; Huang, Yin; Wang, Gao-Ren; Cong, Shu-Lin

2013-01-01

We demonstrate theoretically that photoassociated molecules can be stabilized to deeply bound states. This process is achieved by transferring the population from the outer well to the inner well using the optimal control theory, the Cs2 molecule is taken as an example. Numerical calculations show that weakly bound molecules formed in the outer well by a pump pulse can be compressed to the inner well via a vibrational level of the ground electronic state as an intermediary by an additionally optimized laser pulse. The positively chirped pulse can enhance the population of the target state. With a transform-limited dump pulse, nearly all the photoassociated molecules in the inner well of the excited electronic state can be transferred to the deeply vibrational level of the ground electronic state.

On the validity of the Arrhenius equation for electron attachment rate coefficients.

PubMed

Fabrikant, Ilya I; Hotop, Hartmut

2008-03-28

The validity of the Arrhenius equation for dissociative electron attachment rate coefficients is investigated. A general analysis allows us to obtain estimates of the upper temperature bound for the range of validity of the Arrhenius equation in the endothermic case and both lower and upper bounds in the exothermic case with a reaction barrier. The results of the general discussion are illustrated by numerical examples whereby the rate coefficient, as a function of temperature for dissociative electron attachment, is calculated using the resonance R-matrix theory. In the endothermic case, the activation energy in the Arrhenius equation is close to the threshold energy, whereas in the case of exothermic reactions with an intermediate barrier, the activation energy is found to be substantially lower than the barrier height.

Tuning the properties of conjugated polyelectrolytes and application in a biosensor platform

DOEpatents

Chen, Liaohai

2004-05-18

The present invention provides a method of detecting a biological agent including contacting a sample with a sensor including a polymer system capable of having an alterable measurable property from the group of luminescence, anisotropy, redox potential and uv/vis absorption, the polymer system including an ionic conjugated polymer and an electronically inert polyelectrolyte having a biological agent recognition element bound thereto, the electronically inert polyelectrolyte adapted for undergoing a conformational structural change upon exposure to a biological agent having affinity for binding to the recognition element bound to the electronically inert polyelectrolyte, and, detecting the detectable change in the alterable measurable property. A chemical moiety being the reaction product of (i) a polyelectrolyte monomer and (ii) a biological agent recognition element-substituted polyelectrolyte monomer is also provided.

Universality classes of order parameters composed of many-body bound states

DOE PAGES

Tsvelik, A. M.

2016-11-28

This theoretical paper discusses microscopic models giving rise to special types of order in which conduction electrons are bound together with localized spins to create composite order parameters. It is shown that composite order is related to the formation of a spin liquid with gapped excitations carrying quantum numbers which are a fraction of those of electron. These spin liquids are special in the sense that their formation necessarily involves spin degrees of freedom of both the conduction and the localized electrons and can be characterized by nonlocal order parameters. A detailed description of such spin liquid states is presentedmore » with a special care given to a demonstration of their robustness against local perturbations preserving the Lie group symmetry and the translational invariance.« less

Further characterization of ribosome binding to thylakoid membranes. [Pisum sativum

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

Hurewitz, J.; Jagendorf, A.T.

1987-05-01

Previous work indicated more polysomes bound to pea (Pisum sativum cv Progress No. 9) thylakoids in light than in the dark, in vivo. With isolated intact chloroplasts incubated in darkness, addition of MgATP had no effect but 24 to 74% more RNA was thylakoid-bound at pH 8.3 than at pH 7. Thus, the major effect of light on ribosome-binding in vivo may be due to higher stroma pH. In isolated pea chloroplasts, initiation inhibitors (pactamycin and kanamycin) decreased the extent of RNA binding, and elongation inhibitors (lincomycin and streptomycin) increased it. Thus, cycling of ribosomes is controlled by translation, initiation,more » and termination. Bound RNA accounted for 19 to 24% of the total chloroplast RNA and the incorporation of (/sup 3/H)leucine into thylakoids was proportional to the amount of this bound RNA. These data support the concept that stroma ribosomes are recruited into thylakoid polysomes, which are active in synthesizing thylakoid proteins.« less

Final Report Program Plan for Search and Rescue Electronics Alerting and Locating System

DOT National Transportation Integrated Search

1974-02-01

This study investigates the requirements that exist for electronic devices for alerting and locating distress incidents and presents a plan for acquiring an adequate capability. Data are provided that bound the problem. Possible alternatives are exam...

Time-resolved photoelectron spectroscopy of IR-driven electron dynamics in a charge transfer model system.

PubMed

Falge, Mirjam; Fröbel, Friedrich Georg; Engel, Volker; Gräfe, Stefanie

2017-08-02

If the adiabatic approximation is valid, electrons smoothly adapt to molecular geometry changes. In contrast, as a characteristic of diabatic dynamics, the electron density does not follow the nuclear motion. Recently, we have shown that the asymmetry in time-resolved photoelectron spectra serves as a tool to distinguish between these dynamics [Falge et al., J. Phys. Chem. Lett., 2012, 3, 2617]. Here, we investigate the influence of an additional, moderately intense infrared (IR) laser field, as often applied in attosecond time-resolved experiments, on such asymmetries. This is done using a simple model for coupled electronic-nuclear motion. We calculate time-resolved photoelectron spectra and their asymmetries and demonstrate that the spectra directly map the bound electron-nuclear dynamics. From the asymmetries, we can trace the IR field-induced population transfer and both the field-driven and intrinsic (non-)adiabatic dynamics. This holds true when considering superposition states accompanied by electronic coherences. The latter are observable in the asymmetries for sufficiently short XUV pulses to coherently probe the coupled states. It is thus documented that the asymmetry is a measure for phases in bound electron wave packets and non-adiabatic dynamics.

Structure Functions of Bound Neutrons

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

Sebastian Kuhn

2005-04-01

We describe an experiment measuring electron scattering on a neutron bound in deuterium with coincident detection of a fast, backward-going spectator proton. Our data map out the relative importance of the pure PWIA spectator mechanism and final state interactions in various kinematic regions, and give a first glimpse of the modification of the structure function of a bound neutron as a function of its off-shell mass. We also discuss a new experimental program to study the structure of a free neutron by extending the same technique to much lower spectator momenta.

On the relation between Marcus theory and ultrafast spectroscopy of solvation kinetics

NASA Astrophysics Data System (ADS)

Roy, Santanu; Galib, Mirza; Schenter, Gregory K.; Mundy, Christopher J.

2018-01-01

The phenomena of solvent exchange control the process of solvating ions, protons, and charged molecules. Building upon our extension of Marcus' philosophy of electron transfer, we provide a new perspective of ultrafast solvent exchange mechanism around ions measurable by two-dimensional infrared (2DIR) spectroscopy. In this theory, solvent rearrangement drives an ion-bound water to an activated state of higher coordination number, triggering ion-water separation that leads to the solvent-bound state of the water molecule. This ion-bound to solvent-bound transition rate for a BF4--water system is computed using ab initio molecular dynamics and Marcus theory, and is found to be in excellent agreement with the 2DIR measurement.

Heme-bound nitroxyl, hydroxylamine, and ammonia ligands as intermediates in the reaction cycle of cytochrome c nitrite reductase: a theoretical study.

PubMed

Bykov, Dmytro; Plog, Matthias; Neese, Frank

2014-01-01

In this article, we consider, in detail, the second half-cycle of the six-electron nitrite reduction mechanism catalyzed by cytochrome c nitrite reductase. In total, three electrons and four protons must be provided to reach the final product, ammonia, starting from the HNO intermediate. According to our results, the first event in this half-cycle is the reduction of the HNO intermediate, which is accomplished by two PCET reactions. Two isomeric radical intermediates, HNOH(•) and H2NO(•), are formed. Both intermediates are readily transformed into hydroxylamine, most likely through intramolecular proton transfer from either Arg114 or His277. An extra proton must enter the active site of the enzyme to initiate heterolytic cleavage of the N-O bond. As a result of N-O bond cleavage, the H2N(+) intermediate is formed. The latter readily picks up an electron, forming H2N(+•), which in turn reacts with Tyr218. Interestingly, evidence for Tyr218 activity was provided by the mutational studies of Lukat (Biochemistry 47:2080, 2008), but this has never been observed in the initial stages of the overall reduction process. According to our results, an intramolecular reaction with Tyr218 in the final step of the nitrite reduction process leads directly to the final product, ammonia. Dissociation of the final product proceeds concomitantly with a change in spin state, which was also observed in the resonance Raman investigations of Martins et al. (J Phys Chem B 114:5563, 2010).

Comparable Stocks, Boundedly Rational Stock Markets and IPO Entry Rates

PubMed Central

Chok, Jay; Qian, Jifeng

2013-01-01

In this study, we examine how initial public offerings (IPO) entry rates are affected when stock markets are boundedly rational and IPO firms infer information from their counterparts in the market. We hypothesize a curvilinear relationship between the number of comparable stocks and initial public offerings (IPO) entry rates into the NASDAQ Stock Exchange. Furthermore, we argue that trading volume and changes in stock returns partially mediates the relationship between the number of comparable stocks and IPO entry rates. The statistical evidence provides strong support for the hypotheses. PMID:23690924

Comparable stocks, boundedly rational stock markets and IPO entry rates.

PubMed

Chok, Jay; Qian, Jifeng

2013-01-01

In this study, we examine how initial public offerings (IPO) entry rates are affected when stock markets are boundedly rational and IPO firms infer information from their counterparts in the market. We hypothesize a curvilinear relationship between the number of comparable stocks and initial public offerings (IPO) entry rates into the NASDAQ Stock Exchange. Furthermore, we argue that trading volume and changes in stock returns partially mediates the relationship between the number of comparable stocks and IPO entry rates. The statistical evidence provides strong support for the hypotheses.

Distinctive Spectral Features of Exciton and Excimer States in the Ultrafast Electronic Deactivation of the Adenine Dinucleotide

NASA Astrophysics Data System (ADS)

Stuhldreier, Mayra C.; Röttger, Katharina; Temps, Friedrich

We report the observation by transient absorption spectroscopy of distinctive spectro-temporal signatures of delocalized exciton versus relaxed, weakly bound excimer states in the ultrafast electronic deactivation after UV photoexcitation of the adenine dinucleotide.

Structure and Dynamics of the Membrane-Bound Cytochrome P450 2C9

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

Cojocaru, Vlad; Balali-Mood, Kia; Sansom, Mark S.

The microsomal, membrane-bound, human cytochrome P450 (CYP) 2C9 is a liver-specific monooxygenase essential for drug metabolism. CYPs require electron transfer from the membrane-bound CYP reductase (CPR) for catalysis. The structural details and functional relevance of the CYP-membrane interaction are not understood. From multiple coarse grained molecular simulations started with arbitrary configurations of protein-membrane complexes, we found two predominant orientations of CYP2C9 in the membrane, both consistent with experiments and conserved in atomic-resolution simulations. The dynamics of membrane-bound and soluble CYP2C9 revealed correlations between opening and closing of different tunnels from the enzyme’s buried active site. The membrane facilitated the openingmore » of a tunnel leading into it by stabilizing the open state of an internal aromatic gate. Other tunnels opened selectively in the simulations of product-bound CYP2C9. We propose that the membrane promotes binding of liposoluble substrates by stabilizing protein conformations with an open access tunnel and provide evidence for selective substrate access and product release routes in mammalian CYPs. The models derived here are suitable for extension to incorporate other CYPs for oligomerization studies or the CYP reductase for studies of the electron transfer mechanism, whereas the modeling procedure is generally applicable to study proteins anchored in the bilayer by a single transmembrane helix.« less

Phonon coupling in optical transitions for singlet-triplet pairs of bound excitons in semiconductors

NASA Astrophysics Data System (ADS)

Pistol, M. E.; Monemar, B.

1986-05-01

A model is presented for the observed strong difference in selection rules for coupling of phonons in the one-phonon sideband of optical spectra related to bound excitons in semiconductors. The present treatment is specialized to the case of a closely spaced pair of singlet-triplet character as the lowest electronic states, as is common for bound excitons associated with neutral complexes in materials like GaP and Si. The optical transition for the singlet bound-exciton state is found to couple strongly only to symmetric A1 modes. The triplet state has a similar coupling strength to A1 modes, but in addition strong contributions are found for replicas corresponding to high-density-of-states phonons TAX, LAX, and TOX. This can be explained by a treatment of particle-phonon coupling beyond the ordinary adiabatic approximation. A weak mixing between the singlet and triplet states is mediated by the phonon coupling, as described in first-order perturbation theory. The model derived in this work, for such phonon-induced mixing of closely spaced electronic states, is shown to explain the observed phonon coupling for several bound-exciton systems of singlet-triplet character in GaP. In addition, the observed oscillator strength of the forbidden triplet state may be explained as partly derived from phonon-induced mixing with the singlet state, which has a much larger oscillator strength.

Searching for dark absorption with direct detection experiments

DOE PAGES

Bloch, Itay M.; Essig, Rouven; Tobioka, Kohsaku; ...

2017-06-16

We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB formore » silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.« less

Searching for dark absorption with direct detection experiments

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

Bloch, Itay M.; Essig, Rouven; Tobioka, Kohsaku

We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB formore » silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.« less

The Development and Study of Surface Bound Ruthenium Organometallic Complexes

NASA Astrophysics Data System (ADS)

Abbott, Geoffrey Reuben

The focus of this project has been on the use of mono-diimine ruthenium organometallic complexes, of the general structure [H(Ru)(CO)(L)2(L') 2][PF6] (L=PPh3, DPPENE and L'=Bpy, DcBpy, MBpyC, Phen, AminoPhen) bound to surfaces as luminescent probes. Both biological and inorganic/organic hybrid surfaces have been studied. The complexes were characterized both bound and unbound using standard analytical techniques such as NMR, IR and X-ray crystallography, as well as through several photophysical methods as well. Initially the study focused on how the photophyscial properties of the complexes were affected by incorporation into biological membranes. It was found that by conjugating the probes to a more rigid cholesterol moiety that luminescence was conserved, compared to conjugation with a far more flexible lipid moiety, where luminescence was either lost or reduced. Both the cholesterol and lipid conjugates were able to insert into a lipid membrane, and in the more rigid environment some of the lipid conjugates regained some of their luminescence, but often blue shifted and reduced, depending on the conjugation site. Silica Polyamine Composites (SPCs) were a hybrid material developed in the Rosenberg Lab as useful metal separation materials, that could be easily modified, and had several benefits over current commercially available polymers, or inorganic materials. These SPCs also provided an opportunity for the development of a heterogeneous platform for luminescent complexes as either catalysts or sensors. Upon binding of the luminescent Ru complexes to the surface no loss, or major change in luminescence was seen, however, when bound to the rigid surface a significant increase in excited state lifetime was measured. It is likely that through binding and interacting with the surface that the complexes lost non-radiative decay pathways, resulting in the increase in lifetime, however, these interactions do not seem to affect the energy level of the MLCT band in a large way. With a better understanding of the effects of surface binding on the complexes, the study turned to possible applications, as either sensors or catalysts. Recently the bound complexes have been found to be very useful as toxic metal sensors, as the free amines left on the surface could bind toxic metal ions in close proximity leading to either a quenching or enhancement of the luminescence of the complexes, depending on the metal ion. This process was determined to be a static process, requiring the toxic metal to remain bound to the surface in order to affect the luminescence of the Ru complex. The quenching is thought to be due to a metal-centered electron-transfer reaction, in which the excited-state electron is transferred from the Ru to the toxic metal, but relaxes back to the Ru center. The enhancement of luminescence is due to the external heavy-atom effect, in which heavier atoms mixes MLCT singlet state with the triplet state through spin-orbit coupling.

Mineralogical transformations controlling acid mine drainage chemistry

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

Peretyazhko, Tetyana; Zachara, John M.; Boily, Jean F.

2009-05-30

The role of Fe(III) minerals in controlling acid mine drainage (AMD) chemistry was studied using samples from two AMD sites [Gum Boot (GB) and Fridays-2 (FR)] located in northern Pennsylvania. Chemical extractions, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were used to identify and characterize Fe(III) phases. The mineralogical analysis revealed that schwertmannite and goethite were the principal Fe(III) phases in the sediments. Schwertmannite transformation occurred at the GB site where poorly-crystallized goethite rich in surface-bound sulfate was initially formed. In contrast, no schwertmannite transformation occurred at the FR site. The goethite in GBmore » sediments had spherical morphology due to preservation of schwertmannite structure by adsorbed sulfate. Results of chemical extractions showed that poorly-crystallized goethite was subject to further crystallization accompanied by sulfate desorption. Changes in sulfate speciation preceded its desorption, with a conversion of bidentate- to monodentate-bound sulfate surface complexes. Laboratory sediment incubation experiments were conducted to evaluate the effect of mineral transformation on water chemistry. Incubation experiments were carried out with schwertmannite-containing sediments and AMD waters with different pH and chemical composition. The pH decreased to 1.9-2.2 in all suspensions and the concentrations of dissolved Fe and S increased significantly. Regardless of differences in the initial water composition, pH, Fe and S were similar in suspensions of the same sediment. XRD measurements revealed that schwertmannite transformed into goethite in GB and FR sediments during laboratory incubation. The incubation experiment demonstrated that schwertmannite transformation controlled AMD water chemistry during “closed system” laboratory contact.« less

Electron transfer flavoprotein domain II orientation monitored using double electron-electron resonance between an enzymatically reduced, native FAD cofactor, and spin labels.

PubMed

Swanson, Michael A; Kathirvelu, Velavan; Majtan, Tomas; Frerman, Frank E; Eaton, Gareth R; Eaton, Sandra S

2011-03-01

Human electron transfer flavoprotein (ETF) is a soluble mitochondrial heterodimeric flavoprotein that links fatty acid β-oxidation to the main respiratory chain. The crystal structure of human ETF bound to medium chain acyl-CoA dehydrogenase indicates that the flavin adenine dinucleotide (FAD) domain (αII) is mobile, which permits more rapid electron transfer with donors and acceptors by providing closer access to the flavin and allows ETF to accept electrons from at least 10 different flavoprotein dehydrogenases. Sequence homology is high and low-angle X-ray scattering is identical for Paracoccus denitrificans (P. denitrificans) and human ETF. To characterize the orientations of the αII domain of P. denitrificans ETF, distances between enzymatically reduced FAD and spin labels in the three structural domains were measured by double electron-electron resonance (DEER) at X- and Q-bands. An FAD to spin label distance of 2.8 ± 0.15 nm for the label in the FAD-containing αII domain (A210C) agreed with estimates from the crystal structure (3.0 nm), molecular dynamics simulations (2.7 nm), and rotamer library analysis (2.8 nm). Distances between the reduced FAD and labels in αI (A43C) were between 4.0 and 4.5 ± 0.35 nm and for βIII (A111C) the distance was 4.3 ± 0.15 nm. These values were intermediate between estimates from the crystal structure of P. denitrificans ETF and a homology model based on substrate-bound human ETF. These distances suggest that the αII domain adopts orientations in solution that are intermediate between those which are observed in the crystal structures of free ETF (closed) and ETF bound to a dehydrogenase (open). Copyright © 2011 The Protein Society.

Two-electron states of a group-V donor in silicon from atomistic full configuration interactions

NASA Astrophysics Data System (ADS)

Tankasala, Archana; Salfi, Joseph; Bocquel, Juanita; Voisin, Benoit; Usman, Muhammad; Klimeck, Gerhard; Simmons, Michelle Y.; Hollenberg, Lloyd C. L.; Rogge, Sven; Rahman, Rajib

2018-05-01

Two-electron states bound to donors in silicon are important for both two-qubit gates and spin readout. We present a full configuration interaction technique in the atomistic tight-binding basis to capture multielectron exchange and correlation effects taking into account the full band structure of silicon and the atomic-scale granularity of a nanoscale device. Excited s -like states of A1 symmetry are found to strongly influence the charging energy of a negative donor center. We apply the technique on subsurface dopants subjected to gate electric fields and show that bound triplet states appear in the spectrum as a result of decreased charging energy. The exchange energy, obtained for the two-electron states in various confinement regimes, may enable engineering electrical control of spins in donor-dot hybrid qubits.

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

Krasnenko, V.; Boltrushko, V.; Hizhnyakov, V.

Chemically bound states of benzene molecules with graphene are studied both analytically and numerically. The states are formed by switching off intrabonds of π-electrons in C{sub 6} rings to interbonds. A number of different undistorted and distorted structures are established both with aligned and with transversal mutual orientation of benzene and graphene. The vibronic interactions causing distortions of bound states are found, by using a combination of analytical and numerical considerations. This allows one to determine all electronic transitions of π-electrons without explicit numerical calculations of excited states, to find the conical intersections of potentials, and to show that themore » mechanism of distortions is the pseudo-Jahn-Teller effect. It is found that the aligned distorted benzene molecule placed between two graphene sheets makes a chemical bond with both of them, which may be used for fastening of graphene sheets together.« less

Hydrogenic impurity bound polaron in an anisotropic quantum dot

NASA Astrophysics Data System (ADS)

Chen, Shi-Hua

2018-01-01

The effect of the electron-phonon interaction on an electron bound to a hydrogenic impurity in a three-dimensional (3D) anisotropic quantum dot (QD) is studied theoretically. We use the Landau-Pekar variational approach to calculate the binding energy of ground state (GS) and first-excited state (ES) with considering electron-phonon interaction. The expressions of the GS and ES energies under investigation depict a rich variety of dependent relationship with the variational parameters in three different limiting cases. Numerical calculations were performed for ZnSe QDs with different confinement lengths in the xy-plane and the z-direction, respectively. It is illustrated that binding energies of impurity polarons corresponding to each level are larger in small QDs. Furthermore, the contribution to binding energy from phonon is about 15% of the total binding energy.

Polaron pair mediated triplet generation in polymer/fullerene blends

PubMed Central

Dimitrov, Stoichko D.; Wheeler, Scot; Niedzialek, Dorota; Schroeder, Bob C.; Utzat, Hendrik; Frost, Jarvist M.; Yao, Jizhong; Gillett, Alexander; Tuladhar, Pabitra S.; McCulloch, Iain; Nelson, Jenny; Durrant, James R.

2015-01-01

Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields. PMID:25735188

Order, criticality, and excitations in the extended Falicov-Kimball model.

PubMed

Ejima, S; Kaneko, T; Ohta, Y; Fehske, H

2014-01-17

Using exact numerical techniques, we investigate the nature of excitonic (electron-hole) bound states and the development of exciton coherence in the one-dimensional half-filled extended Falicov-Kimball model. The ground-state phase diagram of the model exhibits, besides band-insulator and staggered orbital ordered phases, an excitonic insulator (EI) with power-law correlations. The criticality of the EI state shows up in the von Neumann entropy. The anomalous spectral function and condensation amplitude provide the binding energy and coherence length of the electron-hole pairs which, on their part, point towards a Coulomb interaction driven crossover from BCS-like electron-hole pairing fluctuations to tightly bound excitons. We show that while a mass imbalance between electrons and holes does not affect the location of the BCS-BEC crossover regime, it favors staggered orbital ordering to the disadvantage of the EI. Within the Bose-Einstein condensation (BEC) regime, the quasiparticle dispersion develops a flat valence-band top, in accord with the experimental finding for Ta2NiSe5.

Thermal Destruction Of CB Contaminants Bound On Building ...

EPA Pesticide Factsheets

Symposium Paper An experimental and theoretical program has been initiated by the U.S. EPA to investigate issues of chemical/biological agent destruction in incineration systems when the agent in question is bound on common porous building interior materials. This program includes 3-dimensional computational fluid dynamics modeling with matrix-bound agent destruction kinetics, bench-scale experiments to determine agent destruction kinetics while bound on various matrices, and pilot-scale experiments to scale-up the bench-scale experiments to a more practical scale. Finally, model predictions are made to predict agent destruction and combustion conditions in two full-scale incineration systems that are typical of modern combustor design.

Precipitation in Ni-Si during electron and ion irradiation

NASA Astrophysics Data System (ADS)

Lucas, G. E.; Zama, T.; Ishino, S.

1986-11-01

This study was undertaken to further investigate how the nature of the irradiation condition affects precipitation in a dilute Ni-Si system. Transmission electron microscopy (TEM) discs of a solution annealed Ni alloy containing 5 at% Si were irradiated with 400 keV Ar + ions, 200 keV He + ions and 1 MeV electrons at average displacement rates in the range 2 × 10 -5dpa/s to 2 × 10 -3dpa/s at temperatures in the range 25°C to 450°C. Samples irradiated with electrons were observed in situ in an HVEM, while ion irradiated specimens were examined in a TEM after irradiation. Precipitation of Ni 3Si was detected by the appearance of superlattice spots in the electron diffraction patterns. It was found that as the mass of the irradiating species increased, the lower bound temperature at which Ni 3Si precipitation was first observed increased. For electron irradiation, the lower bound temperature at 2 × 10 -3dpa/s was ˜125°C, whereas for 400 keV Ar + irradiation at a similar average displacement rate the lower boundary was approximately 325°C. This suggests that cascade disordering competes with radiation induced solute segregation.

DYNAMICS OF TIDALLY CAPTURED PLANETS IN THE GALACTIC CENTER

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

Trani, Alessandro A.; Bressan, Alessandro; Mapelli, Michela

2016-11-01

Recent observations suggest ongoing planet formation in the innermost parsec of the Galactic center. The supermassive black hole (SMBH) might strip planets or planetary embryos from their parent star, bringing them close enough to be tidally disrupted. Photoevaporation by the ultraviolet field of young stars, combined with ongoing tidal disruption, could enhance the near-infrared luminosity of such starless planets, making their detection possible even with current facilities. In this paper, we investigate the chance of planet tidal captures by means of high-accuracy N -body simulations exploiting Mikkola's algorithmic regularization. We consider both planets lying in the clockwise (CW) disk andmore » planets initially bound to the S-stars. We show that tidally captured planets remain on orbits close to those of their parent star. Moreover, the semimajor axis of the planetary orbit can be predicted by simple analytic assumptions in the case of prograde orbits. We find that starless planets that were initially bound to CW disk stars have mild eccentricities and tend to remain in the CW disk. However, we speculate that angular momentum diffusion and scattering by other young stars in the CW disk might bring starless planets into orbits with low angular momentum. In contrast, planets initially bound to S-stars are captured by the SMBH on highly eccentric orbits, matching the orbital properties of the clouds G1 and G2. Our predictions apply not only to planets but also to low-mass stars initially bound to the S-stars and tidally captured by the SMBH.« less

Two-electron oxidation of deoxyguanosine by a Ru(III) complex without involving oxygen molecules through disproportionation.

PubMed

Choi, Sunhee; Ryu, DaWeon; DellaRocca, Joseph G; Wolf, Matthew W; Bogart, Justin A

2011-07-18

Among the many mechanisms for the oxidation of guanine derivatives (G) assisted by transition metals, Ru(III) and Pt(IV) metal ions share basically the same principle. Both Ru(III)- and Pt(IV)-bound G have highly positively polarized C8-H's that are susceptible to deprotonation by OH(-), and both undergo two-electron redox reactions. The main difference is that, unlike Pt(IV), Ru(III) is thought to require O(2) to undergo such a reaction. In this study, however, we report that [Ru(III)(NH(3))(5)(dGuo)] (dGuo = deoxyguanosine) yields cyclic-5'-O-C8-dGuo (a two-electron G oxidized product, cyclic-dGuo) without O(2). In the presence of O(2), 8-oxo-dGuo and cyclic-dGuo were observed. Both [Ru(II)(NH(3))(5)(dGuo)] and cyclic-dGuo were produced from [Ru(III)(NH(3))(5)(dGuo)] accelerated by [OH(-)]. We propose that [Ru(III)(NH(3))(5)(dGuo)] disproportionates to [Ru(II)(NH(3))(5)(dGuo)] and [Ru(IV)(NH(3))(4)(NH(2)(-))(dGuo)], followed by a 5'-OH attack on C8 in [Ru(IV)(NH(3))(4)(NH(2)(-))(dGuo)] to initiate an intramolecular two-electron transfer from dGuo to Ru(IV), generating cyclic-dGuo and Ru(II) without involving O(2).

On the relation between Marcus theory and ultrafast spectroscopy of solvation kinetics

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

Roy, Santanu; Galib, Mirza; Schenter, Gregory K.

The phenomena of solvent exchange control the process of solvating ions, protons, and charged molecules. Building upon our extension of Marcus’ philosophy of electron transfer, here we provide a new perspective of ultrafast solvent exchange mechanism around ions measurable by two-dimensional infrared (2DIR) spectroscopy. In this theory, solvent rearrangement drives an ion-bound water to an activated state of higher coordination number, triggering ion-water separation that leads to the solvent-bound state of the water molecule. This ion-bound to solvent-bound transition rate for a BF 4 --water system is then computed using ab initio molecular dynamics and Marcus theory, and is foundmore » to be in excellent agreement with the 2DIR measurement.« less

On the relation between Marcus theory and ultrafast spectroscopy of solvation kinetics

DOE PAGES

Roy, Santanu; Galib, Mirza; Schenter, Gregory K.; ...

2017-12-24

The phenomena of solvent exchange control the process of solvating ions, protons, and charged molecules. Building upon our extension of Marcus’ philosophy of electron transfer, here we provide a new perspective of ultrafast solvent exchange mechanism around ions measurable by two-dimensional infrared (2DIR) spectroscopy. In this theory, solvent rearrangement drives an ion-bound water to an activated state of higher coordination number, triggering ion-water separation that leads to the solvent-bound state of the water molecule. This ion-bound to solvent-bound transition rate for a BF 4 --water system is then computed using ab initio molecular dynamics and Marcus theory, and is foundmore » to be in excellent agreement with the 2DIR measurement.« less

On the relation between Marcus theory and ultrafast spectroscopy of solvation kinetics

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

Roy, Santanu; Galib, Mirza; Schenter, Gregory K.

The phenomena of solvent exchange control the process of solvating ions, protons, and charged molecules. Building upon our extension of Marcus’ philosophy of electron transfer, we provide a new perspective of ultrafast solvent exchange mechanism around ions measurable by two-dimensional infrared (2DIR) spectroscopy. In this theory, solvent rearrangement drives an ion-bound water to an activated state of higher coordination number, triggering ion-water separation that leads to the solvent-bound state of the water molecule. This ion-bound to solvent-bound transition rate for a BF4- water system is computed using ab initio molecular dynamics and Marcus theory, and is found to be inmore » excellent agreement with the 2DIR measurement.« less

Electronic structure of the metal center in the Cd(2+), Zn(2+), and Cu(2+) substituted forms of KDO8P synthase: implications for catalysis.

PubMed

Kona, Fathima; Tao, Peng; Martin, Philip; Xu, Xingjue; Gatti, Domenico L

2009-04-28

Aquifex aeolicus 3-deoxy-d-manno-octulosonate 8-phosphate synthase (KDO8PS) is active with a variety of different divalent metal ions bound in the active site. The Cd(2+), Zn(2+), and Cu(2+) substituted enzymes display similar values of k(cat) and similar dependence of K(m)(PEP) and K(m)(A5P) on both substrate and product concentrations. However, the flux-control coefficients for some of the catalytically relevant reaction steps are different in the presence of Zn(2+) or Cu(2+), suggesting that the type of metal bound in the active site affects the behavior of the enzyme in vivo. The type of metal also affects the rate of product release in the crystal environment. For example, the crystal structure of the Cu(2+) enzyme incubated with phosphoenolpyruvate (PEP) and arabinose 5-phosphate (A5P) shows the formed product, 3-deoxy-d-manno-octulosonate 8-phosphate (KDO8P), still bound in the active site in its linear conformation. This observation completes our structural studies of the condensation reaction, which altogether have provided high-resolution structures for the reactants, the intermediate, and the product bound forms of KDO8PS. The crystal structures of the Cd(2+), Zn(2+), and Cu(2+) substituted enzymes show four residues (Cys-11, His-185, Glu-222, and Asp-233) and a water molecule as possible metal ligands. Combined quantum mechanics/molecular mechanics (QM/MM) geometry optimizations reveal that the metal centers have a delocalized electronic structure, and that their true geometry is square pyramidal for Cd(2+) and Zn(2+) and distorted octahedral or distorted tetrahedral for Cu(2+). These geometries are different from those obtained by QM optimization in the gas phase (tetrahedral for Cd(2+) and Zn(2+), distorted tetrahedral for Cu(2+)) and may represent conformations of the metal center that minimize the reorganization energy between the substrate-bound and product-bound states. The QM/MM calculations also show that when only PEP is bound to the enzyme the electronic structure of the metal center is optimized to prevent a wasteful reaction of PEP with water.

The elusive role of Nb_Li bound polaron energy in hopping charge transport in Fe : LiNbO₃.

PubMed

Guilbert, Laurent; Vittadello, Laura; Bazzan, Marco; Mhaouech, Imed; Messerschmidt, Simon; Imlau, M

2018-02-06

Charge transport due to small polarons hopping among defective (bound polarons) and regular (free polarons) sites is shown to depend in a non-trivial way from the value of the stabilization energy provided by the lattice distortion surrounding the charge carriers. This energy, normally not directly accessible for bound polarons by spectroscopic techniques, is here determined by a combination of experimental and numerical methods for the important case of small electron polarons bound to \\mathrm{Nb}_{\\mathrm{Li}} defects in the prototype ferroelectric oxide lithium niobate. Our findings provide an estimation of the \\mathrm{Nb}_{\\mathrm{Li}} polaron stabilization energy E_{GP}=\\unit[(0.75\\pm0.05)]{eV} and point out that in lithium niobate both free and bound polarons contributes to charge transport already at room temperature, explaining the fast decays of the light-induced bound polaron population observed by transient absorption spectroscopy. © 2018 IOP Publishing Ltd.

37 CFR 10.85 - Representing a client within the bounds of the law.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 37 Patents, Trademarks, and Copyrights 1 2010-07-01 2010-07-01 false Representing a client within... OFFICE Patent and Trademark Office Code of Professional Responsibility § 10.85 Representing a client within the bounds of the law. (a) In representation of a client, a practitioner shall not: (1) Initiate...

Rabi oscillations in the dissociative continuum: Rotation and alignment effects

NASA Astrophysics Data System (ADS)

Granucci, Giovanni; Magnier, Sylvie; Persico, Maurizio

2002-01-01

We have simulated a set of experiments in which Rabi oscillations are induced in bound-free and free-free transitions of a diatomic molecule. Dissociative vibrational states belonging to different electronic terms are involved. We show analytically and confirm computationally that a simple relationship exists between the one-dimensional dynamics of a molecule with fixed orientation with respect to the polarization of the radiation field and the three-dimensional dynamics of a rotating system. It is demonstrated that sufficiently short laser pulses can induce oscillations in the probabilities of two coupled electronic states, and in the yields of the respective dissociation products, as functions of the radiation intensity. As a result of molecular rotation the oscillations are damped but not washed out. The initial thermal distribution on several rotational levels has a negligible effect on the photodissociation yields and other experimentally relevant quantities. Since the molecule undergoes a strong alignment along the polarization axis of the laser field, the ejection of atoms and ions is anisotropic. We have chosen the well known diatomic ion Na2+ as a convenient example.

Quantification of ionic transport within thermally-activated batteries using electron probe micro-analysis

DOE PAGES

Humplik, Thomas; Stirrup, Emily K.; Grillet, Anne M.; ...

2016-04-30

The transient transport of electrolytes in thermally-activated batteries is studied in this paper using electron probe micro-analysis (EPMA), demonstrating the robust capability of EPMA as a useful tool for studying and quantifying mass transport within porous materials, particularly in difficult environments where classical flow measurements are challenging. By tracking the mobility of bromine and potassium ions from the electrolyte stored within the separator into the lithium silicon anode and iron disulfide cathode, we are able to quantify the transport mechanisms and physical properties of the electrodes including permeability and tortuosity. Due to the micron to submicron scale porous structure ofmore » the initially dry anode, a fast capillary pressure driven flow is observed into the anode from which we are able to set a lower bound on the permeability of 10 -1 mDarcy. The transport into the cathode is diffusion-limited because the cathode originally contained some electrolyte before activation. Finally, using a transient one-dimensional diffusion model, we estimate the tortuosity of the cathode electrode to be 2.8 ± 0.8.« less

Spread of entanglement and causality

NASA Astrophysics Data System (ADS)

Casini, Horacio; Liu, Hong; Mezei, Márk

2016-07-01

We investigate causality constraints on the time evolution of entanglement entropy after a global quench in relativistic theories. We first provide a general proof that the so-called tsunami velocity is bounded by the speed of light. We then generalize the free particle streaming model of [1] to general dimensions and to an arbitrary entanglement pattern of the initial state. In more than two spacetime dimensions the spread of entanglement in these models is highly sensitive to the initial entanglement pattern, but we are able to prove an upper bound on the normalized rate of growth of entanglement entropy, and hence the tsunami velocity. The bound is smaller than what one gets for quenches in holographic theories, which highlights the importance of interactions in the spread of entanglement in many-body systems. We propose an interacting model which we believe provides an upper bound on the spread of entanglement for interacting relativistic theories. In two spacetime dimensions with multiple intervals, this model and its variations are able to reproduce intricate results exhibited by holographic theories for a significant part of the parameter space. For higher dimensions, the model bounds the tsunami velocity at the speed of light. Finally, we construct a geometric model for entanglement propagation based on a tensor network construction for global quenches.

Measurement of the spectra of low energy electrons resulting from Auger transitions induced by the annihilation of low energy positrons implanted at The Ag (100) surface

NASA Astrophysics Data System (ADS)

Shastry, Karthik; Joglekar, Prasad; Weiss, A. H.; Fazleev, N. G.

2013-04-01

A few percent of positrons bound to a solid surface annihilate with core electrons resulting in highly excited atoms containing core holes. These core holes may be filled in an auto-ionizing process in which a less tightly bound electron drops into the hole and the energy difference transferred to an outgoing "Auger electron." Because the core holes are created by annihilation and not impact it is possible to use very low energy positron beams to obtain annihilation induced Auger signals. The Auger signals so obtained have little or none of the large impact induced secondary electron background that interferes with measurements of the low energy Auger spectra obtained using the much higher incident energies necessary when using electron or photon beams. Here we present the results of measurements of the energy spectrum of low energy electrons emitted as a result of Positron Annihilation Induce Auger Electron Emission [1] from a clean Ag (100) surface. The measurements were performed using the University of Texas Arlington Time of Flight Positron Annihilation induced Auger Electron Spectrometer (T-O-F-PAES) System [2]. A strong double peak was observed at ˜35eV corresponding to the N2VV and N3VV Auger transitions in agreement with previous PAES studies [3].

Upper bounds on the photon mass

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

Accioly, Antonio; Group of Field Theory from First Principles, Sao Paulo State University; Instituto de Fisica Teorica

2010-09-15

The effects of a nonzero photon rest mass can be incorporated into electromagnetism in a simple way using the Proca equations. In this vein, two interesting implications regarding the possible existence of a massive photon in nature, i.e., tiny alterations in the known values of both the anomalous magnetic moment of the electron and the gravitational deflection of electromagnetic radiation, are utilized to set upper limits on its mass. The bounds obtained are not as stringent as those recently found; nonetheless, they are comparable to other existing bounds and bring new elements to the issue of restricting the photon mass.

Glycine receptor mechanism illuminated by electron cryo-microscopy

PubMed Central

Du, Juan; Lü, Wei; Wu, Shenping; Cheng, Yifan; Gouaux, Eric

2015-01-01

Summary The strychnine-sensitive glycine receptor (GlyR) mediates inhibitory synaptic transmission in the spinal cord and brainstem and is linked to neurological disorders including autism and hyperekplexia. Understanding of molecular mechanisms and pharmacology of GlyRs has been hindered by a dearth of high-resolution structures. Here we report electron cryo-microscopy structures of the α1 GlyR with strychnine, glycine, or glycine/ivermectin. Strychnine arrests the receptor in an antagonist-bound, closed ion channel state, glycine stabilizes the receptor in an agonist-bound open channel state, and the glycine/ivermectin complex adopts a potentially desensitized or partially open state. Relative to the glycine-bound state, strychnine expands the agonist-binding pocket via outward movement of the C loop, promotes rearrangement of the extracellular and transmembrane domain ‘wrist’ interface, and leads to rotation of the transmembrane domain toward the pore axis, occluding the ion conduction pathway. These structures illuminate GlyR mechanism and define a rubric to interpret structures of Cys-loop receptors. PMID:26344198

Glycine receptor mechanism elucidated by electron cryo-microscopy.

PubMed

Du, Juan; Lü, Wei; Wu, Shenping; Cheng, Yifan; Gouaux, Eric

2015-10-08

The strychnine-sensitive glycine receptor (GlyR) mediates inhibitory synaptic transmission in the spinal cord and brainstem and is linked to neurological disorders, including autism and hyperekplexia. Understanding of molecular mechanisms and pharmacology of glycine receptors has been hindered by a lack of high-resolution structures. Here we report electron cryo-microscopy structures of the zebrafish α1 GlyR with strychnine, glycine, or glycine and ivermectin (glycine/ivermectin). Strychnine arrests the receptor in an antagonist-bound closed ion channel state, glycine stabilizes the receptor in an agonist-bound open channel state, and the glycine/ivermectin complex adopts a potentially desensitized or partially open state. Relative to the glycine-bound state, strychnine expands the agonist-binding pocket via outward movement of the C loop, promotes rearrangement of the extracellular and transmembrane domain 'wrist' interface, and leads to rotation of the transmembrane domain towards the pore axis, occluding the ion conduction pathway. These structures illuminate the GlyR mechanism and define a rubric to interpret structures of Cys-loop receptors.

Effects of Shape and Strain Distribution of Quantum Dots on Optical Transition in the Quantum Dot Infrared Photodetectors

PubMed Central

2008-01-01

We present a systemic theoretical study of the electronic properties of the quantum dots inserted in quantum dot infrared photodetectors (QDIPs). The strain distribution of three different shaped quantum dots (QDs) with a same ratio of the base to the vertical aspect is calculated by using the short-range valence-force-field (VFF) approach. The calculated results show that the hydrostatic strain ɛHvaries little with change of the shape, while the biaxial strain ɛBchanges a lot for different shapes of QDs. The recursion method is used to calculate the energy levels of the bound states in QDs. Compared with the strain, the shape plays a key role in the difference of electronic bound energy levels. The numerical results show that the deference of bound energy levels of lenslike InAs QD matches well with the experimental results. Moreover, the pyramid-shaped QD has the greatest difference from the measured experimental data. PMID:20596318

Magneto-optical properties and recombination dynamics of isoelectronic bound excitons in ZnO

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

Chen, S. L.; Chen, W. M.; Buyanova, I. A.

2014-02-21

Magneto-optical and time-resolved photoluminescence (PL) spectroscopies are employed to evaluate electronic structure of a bound exciton (BX) responsible for the 3.364 eV line (labeled as I{sub 1}{sup *}) in bulk ZnO. From time-resolved PL spectroscopy, I{sub 1}{sup *} is concluded to originate from the exciton ground state. Based on performed magneto-PL studies, the g-factors of the involved electron and hole are determined as being g{sub e} = 1.98 and g{sub h}{sup ∥}(g{sub h}{sup ⊥}) = 1.2(1.62), respectively. These values are nearly identical to the reported g-factors for the I{sup *} line in ZnO (Phys. Rev. B 86, 235205 (2012)), which proves thatmore » I{sub 1}{sup *} should have a similar origin as I{sup *} and should arise from an exciton bound to an isoelectronic center with a hole-attractive potential.« less

Time- and angle-resolved photoemission spectroscopy of hydrated electrons near a liquid water surface.

PubMed

Yamamoto, Yo-ichi; Suzuki, Yoshi-Ichi; Tomasello, Gaia; Horio, Takuya; Karashima, Shutaro; Mitríc, Roland; Suzuki, Toshinori

2014-05-09

We present time- and angle-resolved photoemission spectroscopy of trapped electrons near liquid surfaces. Photoemission from the ground state of a hydrated electron at 260 nm is found to be isotropic, while anisotropic photoemission is observed for the excited states of 1,4-diazabicyclo[2,2,2]octane and I- in aqueous solutions. Our results indicate that surface and subsurface species create hydrated electrons in the bulk side. No signature of a surface-bound electron has been observed.

Convergence of the Full Compressible Navier-Stokes-Maxwell System to the Incompressible Magnetohydrodynamic Equations in a Bounded Domain II: Global Existence Case

NASA Astrophysics Data System (ADS)

Fan, Jishan; Li, Fucai; Nakamura, Gen

2018-06-01

In this paper we continue our study on the establishment of uniform estimates of strong solutions with respect to the Mach number and the dielectric constant to the full compressible Navier-Stokes-Maxwell system in a bounded domain Ω \\subset R^3. In Fan et al. (Kinet Relat Models 9:443-453, 2016), the uniform estimates have been obtained for large initial data in a short time interval. Here we shall show that the uniform estimates exist globally if the initial data are small. Based on these uniform estimates, we obtain the convergence of the full compressible Navier-Stokes-Maxwell system to the incompressible magnetohydrodynamic equations for well-prepared initial data.

Decipher the mechanisms of protein conformational changes induced by nucleotide binding through free-energy landscape analysis: ATP binding to Hsp70.

PubMed

Nicolaï, Adrien; Delarue, Patrice; Senet, Patrick

2013-01-01

ATP regulates the function of many proteins in the cell by transducing its binding and hydrolysis energies into protein conformational changes by mechanisms which are challenging to identify at the atomic scale. Based on molecular dynamics (MD) simulations, a method is proposed to analyze the structural changes induced by ATP binding to a protein by computing the effective free-energy landscape (FEL) of a subset of its coordinates along its amino-acid sequence. The method is applied to characterize the mechanism by which the binding of ATP to the nucleotide-binding domain (NBD) of Hsp70 propagates a signal to its substrate-binding domain (SBD). Unbiased MD simulations were performed for Hsp70-DnaK chaperone in nucleotide-free, ADP-bound and ATP-bound states. The simulations revealed that the SBD does not interact with the NBD for DnaK in its nucleotide-free and ADP-bound states whereas the docking of the SBD was found in the ATP-bound state. The docked state induced by ATP binding found in MD is an intermediate state between the initial nucleotide-free and final ATP-bound states of Hsp70. The analysis of the FEL projected along the amino-acid sequence permitted to identify a subset of 27 protein internal coordinates corresponding to a network of 91 key residues involved in the conformational change induced by ATP binding. Among the 91 residues, 26 are identified for the first time, whereas the others were shown relevant for the allosteric communication of Hsp70 s in several experiments and bioinformatics analysis. The FEL analysis revealed also the origin of the ATP-induced structural modifications of the SBD recently measured by Electron Paramagnetic Resonance. The pathway between the nucleotide-free and the intermediate state of DnaK was extracted by applying principal component analysis to the subset of internal coordinates describing the transition. The methodology proposed is general and could be applied to analyze allosteric communication in other proteins.

Decipher the Mechanisms of Protein Conformational Changes Induced by Nucleotide Binding through Free-Energy Landscape Analysis: ATP Binding to Hsp70

PubMed Central

Nicolaï, Adrien; Delarue, Patrice; Senet, Patrick

2013-01-01

ATP regulates the function of many proteins in the cell by transducing its binding and hydrolysis energies into protein conformational changes by mechanisms which are challenging to identify at the atomic scale. Based on molecular dynamics (MD) simulations, a method is proposed to analyze the structural changes induced by ATP binding to a protein by computing the effective free-energy landscape (FEL) of a subset of its coordinates along its amino-acid sequence. The method is applied to characterize the mechanism by which the binding of ATP to the nucleotide-binding domain (NBD) of Hsp70 propagates a signal to its substrate-binding domain (SBD). Unbiased MD simulations were performed for Hsp70-DnaK chaperone in nucleotide-free, ADP-bound and ATP-bound states. The simulations revealed that the SBD does not interact with the NBD for DnaK in its nucleotide-free and ADP-bound states whereas the docking of the SBD was found in the ATP-bound state. The docked state induced by ATP binding found in MD is an intermediate state between the initial nucleotide-free and final ATP-bound states of Hsp70. The analysis of the FEL projected along the amino-acid sequence permitted to identify a subset of 27 protein internal coordinates corresponding to a network of 91 key residues involved in the conformational change induced by ATP binding. Among the 91 residues, 26 are identified for the first time, whereas the others were shown relevant for the allosteric communication of Hsp70 s in several experiments and bioinformatics analysis. The FEL analysis revealed also the origin of the ATP-induced structural modifications of the SBD recently measured by Electron Paramagnetic Resonance. The pathway between the nucleotide-free and the intermediate state of DnaK was extracted by applying principal component analysis to the subset of internal coordinates describing the transition. The methodology proposed is general and could be applied to analyze allosteric communication in other proteins. PMID:24348227

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

Alberi, K.; Christian, T. M.; Fluegel, B.

While bismuth-related states are known to localize carriers in GaAs 1-xBi x alloys, the localization behavior of distinct Bi pair, triplet and cluster states bound above the valence band is less well understood. We probe localization at three different Bi complex states in dilute GaAs 1-xBi x alloys using magneto-photoluminescence and time-resolved photoluminescence spectroscopy. The mass of electrons Coulomb-bound to holes trapped at Bi pair states is found to increase relative to the average electron mass in the alloy. This increase is attributed to enhanced local compressive strain in the immediate vicinity of the pairs. The dependence of energy transfermore » between these states on composition is also explored.« less

Designed Long‐Lived Emission from CdSe Quantum Dots through Reversible Electronic Energy Transfer with a Surface‐Bound Chromophore

PubMed Central

La Rosa, Marcello; Denisov, Sergey A.

2018-01-01

Abstract The size‐tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface‐bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self‐assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer. PMID:29383800

Free-bound electron exchange contribution to l-split atomic structure in dense plasmas

NASA Astrophysics Data System (ADS)

Bennadji, K.; Rosmej, F.; Lisitsa, V. S.

2013-11-01

An analytical expression for the exchange energy between the bound electron in hydrogen-like ions and the free electrons of plasma is proposed. Two limiting cases are identified: 1) the low temperature limit where the energy depends linearly on density and on the ion charge as 1/Z2 but does not depend on the temperature itself, 2) the high temperature limit where the energy depends on temperature as 1/T but does not depend on the ion charge. These two regimes are separated by a characteristic temperature (T∗ = 4Z2Ry) which is a universal parameter depending only on the charge Z of the ions. We presented numerical results for aluminum: the exchange energy contributes about 15% to the total plasma energy and can reach an order of 10-4 of the total transition energy. Comparison to the Local-density Approximation (Kohn-Sham) exchange energy shows a good agreement.

Highly Charged Rydberg Ions from the Coulomb Explosion of Clusters

NASA Astrophysics Data System (ADS)

Komar, D.; Kazak, L.; Almassarani, M.; Meiwes-Broer, K.-H.; Tiggesbäumker, J.

2018-03-01

Ion emission from a nanoplasma produced in the interaction of intense optical laser pulses with argon clusters is studied resolving simultaneously charge states and recoil energies. By applying appropriate static electric fields we observe that a significant fraction of the ions Arq + (q =1 - 7 ) has electrons with binding energies lower than 150 meV; i.e., nRyd≥15 levels are populated. Charge state changes observed on a μ s time scale can be attributed to electron emission due to autoionizing Rydberg states, indicating that high-ℓ Rydberg levels are populated as well. The experiments support theoretical predictions that a significant fraction of delocalized electrons, which are bound with hundreds of eV to the nanoplasma after the laser exposure, fill up meV bound ion states in the adiabatic expansion. We expect the process to be relevant for the long-term evolution of expanding laser-induced dense plasmas in general.

First direct detection limits on sub-GeV dark matter from XENON10.

PubMed

Essig, Rouven; Manalaysay, Aaron; Mardon, Jeremy; Sorensen, Peter; Volansky, Tomer

2012-07-13

The first direct detection limits on dark matter in the MeV to GeV mass range are presented, using XENON10 data. Such light dark matter can scatter with electrons, causing ionization of atoms in a detector target material and leading to single- or few-electron events. We use 15  kg day of data acquired in 2006 to set limits on the dark-matter-electron scattering cross section. The strongest bound is obtained at 100 MeV where σ(e)<3×10(-38)  cm2 at 90% C.L., while dark-matter masses between 20 MeV and 1 GeV are bounded by σ(e)<10(-37)  cm2 at 90% C.L. This analysis provides a first proof of principle that direct detection experiments can be sensitive to dark-matter candidates with masses well below the GeV scale.

Spin noise spectroscopy of donor-bound electrons in ZnO

NASA Astrophysics Data System (ADS)

Horn, H.; Balocchi, A.; Marie, X.; Bakin, A.; Waag, A.; Oestreich, M.; Hübner, J.

2013-01-01

We investigate the intrinsic spin dynamics of electrons bound to Al impurities in bulk ZnO by optical spin noise spectroscopy. Spin noise spectroscopy enables us to investigate the longitudinal and transverse spin relaxation time with respect to nuclear and external magnetic fields in a single spectrum. On one hand, the spin dynamic is dominated by the intrinsic hyperfine interaction with the nuclear spins of the naturally occurring 67Zn isotope. We measure a typical spin dephasing time of 23 ns, in agreement with the expected theoretical values. On the other hand, we measure a third, very high spin dephasing rate which is attributed to a high defect density of the investigated ZnO material. Measurements of the spin dynamics under the influence of transverse as well as longitudinal external magnetic fields unambiguously reveal the intriguing connections of the electron spin with its nuclear and structural environment.

Estimating rate constants from single ion channel currents when the initial distribution is known.

PubMed

The, Yu-Kai; Fernandez, Jacqueline; Popa, M Oana; Lerche, Holger; Timmer, Jens

2005-06-01

Single ion channel currents can be analysed by hidden or aggregated Markov models. A classical result from Fredkin et al. (Proceedings of the Berkeley conference in honor of Jerzy Neyman and Jack Kiefer, vol I, pp 269-289, 1985) states that the maximum number of identifiable parameters is bounded by 2n(o)n(c), where n(o) and n(c) denote the number of open and closed states, respectively. We show that this bound can be overcome when the probabilities of the initial distribution are known and the data consist of several sweeps.

Radiative double electron capture in collisions of fully-stripped fluorine ions with thin carbon foils

NASA Astrophysics Data System (ADS)

Elkafrawy, Tamer Mohammad Samy

Radiative double electron capture (RDEC) is a one-step process in ion-atom collisions occurring when two target electrons are captured to a bound state of the projectile simultaneously with the emission of a single photon. The emitted photon has approximately double the energy of the photon emitted due to radiative electron capture (REC), which occurs when a target electron is captured to a projectile bound state with simultaneous emission of a photon. REC and RDEC can be treated as time-reversed photoionization (PI) and double photoionization (DPI), respectively, if loosely-bound target electrons are captured. This concept can be formulated with the principle of detailed balance, in which the processes of our interest can be described in terms of their time-reversed ones. Fully-stripped ions were used as projectiles in the performed RDEC experiments, providing a recipient system free of electron-related Coulomb fields. This allows the target electrons to be transferred without interaction with any of the projectile electrons, enabling accurate investigation of the electron-electron interaction in the vicinity of electromagnetic field. In this dissertation, RDEC was investigated during the collision of fully-stripped fluorine ions with a thin carbon foil and the results are compared with the recent experimental and theoretical studies. In the current work, x rays associated with projectile charge-changing by single and double electron capture and no charge change by F9+ ions were observed and compared with recent work for O8+ ions and with theory. Both the F 9+ and O8+ ions had energies in the ˜MeV/u range. REC, in turn, was investigated as a means to compare with the theoretical predictions of the RDEC/REC cross section ratio. The most significant background processes including various mechanisms of x-ray emission that may interfere with the energy region of interest are addressed in detail. This enables isolation of the contributions of REC and RDEC from the entire continuous spectrum of x-ray emission or at least ensures that the background processes have negligible contribution to the energy range of interest. Special emphasis is given to showing how the data analysis was carried out by the subtraction of the x rays due to contamination lines.

Estimating inelastic heavy-particle - hydrogen collision data. II. Simplified model for ionic collisions and application to barium-hydrogen ionic collisions

NASA Astrophysics Data System (ADS)

Belyaev, Andrey K.; Yakovleva, Svetlana A.

2017-12-01

Aims: A simplified model is derived for estimating rate coefficients for inelastic processes in low-energy collisions of heavy particles with hydrogen, in particular, the rate coefficients with high and moderate values. Such processes are important for non-local thermodynamic equilibrium modeling of cool stellar atmospheres. Methods: The derived method is based on the asymptotic approach for electronic structure calculations and the Landau-Zener model for nonadiabatic transition probability determination. Results: It is found that the rate coefficients are expressed via statistical probabilities and reduced rate coefficients. It is shown that the reduced rate coefficients for neutralization and ion-pair formation processes depend on single electronic bound energies of an atomic particle, while the reduced rate coefficients for excitation and de-excitation processes depend on two electronic bound energies. The reduced rate coefficients are calculated and tabulated as functions of electronic bound energies. The derived model is applied to barium-hydrogen ionic collisions. For the first time, rate coefficients are evaluated for inelastic processes in Ba+ + H and Ba2+ + H- collisions for all transitions between the states from the ground and up to and including the ionic state. Tables with calculated data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A33

Estimating inelastic heavy-particle-hydrogen collision data. I. Simplified model and application to potassium-hydrogen collisions

NASA Astrophysics Data System (ADS)

Belyaev, Andrey K.; Yakovleva, Svetlana A.

2017-10-01

Aims: We derive a simplified model for estimating atomic data on inelastic processes in low-energy collisions of heavy-particles with hydrogen, in particular for the inelastic processes with high and moderate rate coefficients. It is known that these processes are important for non-LTE modeling of cool stellar atmospheres. Methods: Rate coefficients are evaluated using a derived method, which is a simplified version of a recently proposed approach based on the asymptotic method for electronic structure calculations and the Landau-Zener model for nonadiabatic transition probability determination. Results: The rate coefficients are found to be expressed via statistical probabilities and reduced rate coefficients. It turns out that the reduced rate coefficients for mutual neutralization and ion-pair formation processes depend on single electronic bound energies of an atom, while the reduced rate coefficients for excitation and de-excitation processes depend on two electronic bound energies. The reduced rate coefficients are calculated and tabulated as functions of electronic bound energies. The derived model is applied to potassium-hydrogen collisions. For the first time, rate coefficients are evaluated for inelastic processes in K+H and K++H- collisions for all transitions from ground states up to and including ionic states. Tables with calculated data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A147

A Truly Bookless Library

ERIC Educational Resources Information Center

Kolowich, Steve

2011-01-01

The difference between the University of Texas at San Antonio's Applied Engineering and Technology Library and other science-focused libraries is not that its on-site collection is also available electronically. It is that its on-site collection is only available electronically. The idea of libraries with no bound books has been a recurring theme…

Metastable Bound States of Two-Dimensional Magnetoexcitons in the Lowest Landau Levels Approximation

NASA Astrophysics Data System (ADS)

Moskalenko, S. A.; Khadzhi, P. I.; Podlesny, I. V.; Dumanov, E. V.; Liberman, M. A.; Zubac, I. A.

2017-12-01

The possible existence of the two-dimensional bimagnetoexcitons and metastable bound states formed by two magnetoexcitons with opposite in-plane wave vectors k and -k has been studied. Magnetoexcitons taking part in the formation of molecules look as two electric dipoles with the arms oriented in-plane perpendicular to the respective wave vectors and with the length of the arms d=k(l_0)^2, where l_0 is the magnetic length. Two antiparallel dipoles moving with equal, yet antiparallel, wave vectors have the possibility of moving with equal probability in any direction of the plane, which is determined by the trial wave function of relative motion φ_n(|k|), depending on modulus k. The magnetoexcitons are composed of electrons and holes situated on the lowest Landau levels with the cyclotron energies greater than the binding energy of the 2D Wannier-Mott exciton. The description has been made in Landau gauge. The spin states of two electrons have been chosen in the form of antisymmetric or symmetric combinations with parameter η=+/-1. The effective spins of two heavy holes have been combined in the same resultant spinor states as the spin of the electrons. Because the projections of the both spinor states with η=+/-1 are equal to zero, the influence of the Zeeman splitting effect vanishes. In the case of trial wave function, the maximal density of the magnetoexcitons in the momentum space is concentrated on the in-plane ring. In the approximation of the lowest Landau levels, when the influence of the excited Landau levels is neglected, stable bound states of bimagnetoexcitons do not exist for both spin orientations. Instead, in the case of α=0.5 and η=1, a deep metastable bound state with the activation barrier comparable with two magnetoexciton ionization potentials 2I_l has been revealed. In the case of η=-1 and α=3.4, only a shallow metastable bound state can appear.

Semilocal density functional obeying a strongly tightened bound for exchange

PubMed Central

Sun, Jianwei; Perdew, John P.; Ruzsinszky, Adrienn

2015-01-01

Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb–Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic “meta-GGA made very simple” (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew–Burke–Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules. PMID:25561554

Semilocal density functional obeying a strongly tightened bound for exchange.

PubMed

Sun, Jianwei; Perdew, John P; Ruzsinszky, Adrienn

2015-01-20

Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb-Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic "meta-GGA made very simple" (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew-Burke-Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules.

Chemotaxis with logistic source

NASA Astrophysics Data System (ADS)

Winkler, Michael

2008-12-01

We consider the chemotaxis system in a smooth bounded domain , where [chi]>0 and g generalizes the logistic function g(u)=Au-bu[alpha] with [alpha]>1, A[greater-or-equal, slanted]0 and b>0. A concept of very weak solutions is introduced, and global existence of such solutions for any nonnegative initial data u0[set membership, variant]L1([Omega]) is proved under the assumption that . Moreover, boundedness properties of the constructed solutions are studied. Inter alia, it is shown that if b is sufficiently large and u0[set membership, variant]L[infinity]([Omega]) has small norm in L[gamma]([Omega]) for some then the solution is globally bounded. Finally, in the case that additionally holds, a bounded set in L[infinity]([Omega]) can be found which eventually attracts very weak solutions emanating from arbitrary L1 initial data. The paper closes with numerical experiments that illustrate some of the theoretically established results.

Structural changes of bacteriophage [phi]29 upon DNA packaging and release

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

Xiang, Y.; Morais, M.C.; Battisti, A.J.

2008-04-24

Cryo-electron microscopy three-dimensional reconstructions have been made of mature and of emptied bacteriophage {phi}29 particles without making symmetry assumptions. Comparisons of these structures with each other and with the {phi}29 prohead indicate how conformational changes might initiate successive steps of assembly and infection. The 12 adsorption capable 'appendages' were found to have a structure homologous to the bacteriophage P22 tailspikes. Two of the appendages are extended radially outwards, away from the long axis of the virus, whereas the others are around and parallel to the phage axis. The appendage orientations are correlated with the symmetry-mismatched positions of the five-fold relatedmore » head fibers, suggesting a mechanism for partial cell wall digestion upon rotation of the head about the tail when initiating infection. The narrow end of the head-tail connector is expanded in the mature virus. Gene product 3, bound to the 5-foot ends of the genome, appears to be positioned within the expanded connector, which may potentiate the release of DNA-packaging machine components, creating a binding site for attachment of the tail.« less

Ultrafast exciton migration in an HJ-aggregate: Potential surfaces and quantum dynamics

NASA Astrophysics Data System (ADS)

Binder, Robert; Polkehn, Matthias; Ma, Tianji; Burghardt, Irene

2017-01-01

Quantum dynamical and electronic structure calculations are combined to investigate the mechanism of exciton migration in an oligothiophene HJ aggregate, i.e., a combination of oligomer chains (J-type aggregates) and stacked aggregates of such chains (H-type aggregates). To this end, a Frenkel exciton model is parametrized by a recently introduced procedure [Binder et al., J. Chem. Phys. 141, 014101 (2014)] which uses oligomer excited-state calculations to perform an exact, point-wise mapping of coupled potential energy surfaces to an effective Frenkel model. Based upon this parametrization, the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method is employed to investigate ultrafast dynamics of exciton transfer in a small, asymmetric HJ aggregate model composed of 30 sites and 30 active modes. For a partially delocalized initial condition, it is shown that a torsional defect confines the trapped initial exciton, and planarization induces an ultrafast resonant transition between an HJ-aggregated segment and a covalently bound "dangling chain" end. This model is a minimal realization of experimentally investigated mixed systems exhibiting ultrafast exciton transfer between aggregated, highly planarized chains and neighboring disordered segments.

Analysis of Radiation Effects in Silicon using Kinetic Monte Carlo Methods

DOE PAGES

Hehr, Brian Douglas

2014-11-25

The transient degradation of semiconductor device performance under irradiation has long been an issue of concern. Neutron irradiation can instigate the formation of quasi-stable defect structures, thereby introducing new energy levels into the bandgap that alter carrier lifetimes and give rise to such phenomena as gain degradation in bipolar junction transistors. Normally, the initial defect formation phase is followed by a recovery phase in which defect-defect or defect-dopant interactions modify the characteristics of the damaged structure. A kinetic Monte Carlo (KMC) code has been developed to model both thermal and carrier injection annealing of initial defect structures in semiconductor materials.more » The code is employed to investigate annealing in electron-irradiated, p-type silicon as well as the recovery of base current in silicon transistors bombarded with neutrons at the Los Alamos Neutron Science Center (LANSCE) “Blue Room” facility. Our results reveal that KMC calculations agree well with these experiments once adjustments are made, within the appropriate uncertainty bounds, to some of the sensitive defect parameters.« less

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

NASA Astrophysics Data System (ADS)

Skourtis, Spiros S.; Prytkova, Tatiana; Beratan, David N.

2007-12-01

This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH--containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH-, upon photo-excitation of FADH- with 350-450 nm light. We compute the lowest singlet excited states of FADH- in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH- that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron-acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH--thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green's function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH- causes a π→π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH--to-dimer electronic coupling, thus inducing rapid electron transfer.

Time-resolved radiation chemistry: Dynamics of electron attachment to uracil following UV excitation of iodide-uracil complexes

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

King, Sarah B.; Yandell, Margaret A.; Stephansen, Anne B.

Electron attachment to uracil was investigated by applying time-resolved photoelectron imaging to iodide-uracil (I{sup –}U) complexes. In these studies, an ultraviolet pump pulse initiated charge transfer from the iodide to the uracil, and the resulting dynamics of the uracil temporary negative ion were probed. Five different excitation energies were used, 4.00 eV, 4.07 eV, 4.14 eV, 4.21 eV, and 4.66 eV. At the four lowest excitation energies, which lie near the vertical detachment energy of the I{sup –}U complex (4.11 eV), signatures of both the dipole bound (DB) as well as the valence bound (VB) anion of uracil were observed.more » In contrast, only the VB anion was observed at 4.66 eV, in agreement with previous experiments in this higher energy range. The early-time dynamics of both states were highly excitation energy dependent. The rise time of the DB anion signal was ∼250 fs at 4.00 eV and 4.07 eV, ∼120 fs at 4.14 eV and cross-correlation limited at 4.21 eV. The VB anion rise time also changed with excitation energy, ranging from 200 to 300 fs for excitation energies 4.00–4.21 eV, to a cross-correlation limited time at 4.66 eV. The results suggest that the DB state acts as a “doorway” state to the VB anion at 4.00–4.21 eV, while direct attachment to the VB anion occurs at 4.66 eV.« less

Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110)

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

Mu, Rentao; Dahal, Arjun; Wang, Zhi-Tao

Adsorption and photodesorption of weakly-bound carbon monoxide, CO, from reduced and hydroxylated rutile TiO2(110) (r- and h- TiO2(110)) at sub-monolayer coverages is studied with atomically-resolved scanning tunneling microscopy (STM) along with ensemble-averaged temperature-programmed desorption (TPD) and angle-resolved photon-stimulated desorption (PSD) at low temperatures ( 50 K). STM data weighted by the concentration of each kind of adsorption sites on r-TiO2(110) give an adsorption probability which is the highest for the bridging oxygen vacancies (VO) and very low for the Ti5c sites closest to VO. Occupancy of the remaining Ti5c sites with CO is significant, but smaller than for VO. Themore » probability distribution for the different adsorption sites corresponds to a very small difference in CO adsorption energies: < 0.02 eV. We also find that UV irradiation stimulates both diffusion and desorption of CO at low temperature. CO photodesorbs primarily from the vacancies with a bi-modal angular distribution. In addition to a major, normal to the surface component, there is a broader cosine component indicating scattering from the surface which likely also leads to photo-stimulated diffusion. Hydroxylation of VO’s does not significantly change the CO PSD yield and angular distribution, indicating that not atomic but rather electronic surface defects are involved in the site-specific PSD process. We suggest that photodesorption can be initiated by recombination of photo-generated holes with excess unpaired electrons localized near the surface point-defect (either VO or bridging hydroxyl), leading to the surface atoms rearrangement and ejection of the weakly-bound CO molecules.« less

Electron transfer in the complex of membrane-bound human cytochrome P450 3A4 with the flavin domain of P450BM-3: the effect of oligomerization of the heme protein and intermittent modulation of the spin equilibrium†

PubMed Central

Davydov, Dmitri R.; Sineva, Elena V.; Sistla, Srinivas; Davydova, Nadezhda Y.; Frank, Daniel J.; Sligar, Stephen G.; Halpert, James R.

2009-01-01

We studied the kinetics of NADPH-dependent reduction of human CYP3A4 incorporated into Nanodiscs (CYP3A4-ND) and proteoliposomes in order to probe the effect of P450 oligomerization on its reduction. The flavin domain of cytochrome P450-BM3 (BMR) was used as a model electron donor partner. Unlike CYP3A4 oligomers, where only 50% of the enzyme was shown to be reducible by BMR, CYP3A4-ND could be reduced almost completely. High reducibility was also observed in proteoliposomes with a high lipid-to-protein ratio (L/P=910), where the oligomerization equilibrium is displaced towards monomers. In contrast, the reducibililty in proteoliposomes with L/P=76 did not exceed 55 ± 6%. The effect of the surface density of CYP3A4 in proteoliposomes on the oligomerization equilibrium was confirmed with a FRET-based assay employing a cysteine-depleted mutant labeled on Cys-468 with BODIPY iodoacetamide. These results confirm a pivotal role of CYP3A4 oligomerization in its functional heterogeneity. Furthermore, the investigation of the initial phase of the kinetics of CYP3A4 reduction showed that the addition of NADPH causes a rapid low-to-high spin transition in the CYP3A4-BMR complex, which is followed by a partial slower reversal. This observation reveals a mechanism whereby the CYP3A4 spin equilibrium is modulated by the redox state of the bound flavoprotein. PMID:20026040

Electron emission from surfaces resulting from low energy positron bombardment

NASA Astrophysics Data System (ADS)

Mukherjee, Saurabh

Measurements of the secondary electron energy spectra resulting from very low energy positron bombardment of a polycrystalline Au and Cu (100) surfaces are presented that provide evidence for a single step transition from an unbound scattering state to an image potential bound state. The primary positron energy threshold for secondary electron emission and energy cutoff of the positron induced secondary electron energy peak are consistent with an Auger like process in which an incident positron make a transition from a scattering state to a surface-image potential bound while transferring all of the energy difference to an outgoing secondary electron. We term this process: the Auger mediated quantum sticking effect (AQSE). The intensities of the positron induced secondary electron peak are used to estimate the probability of this process as a function of incident positron energy. Positron annihilation induced Auger spectra (PAES) of Cu and Au are presented that are free of all primary beam induced secondary electron background. This background was eliminated by setting the positron beam energy below AQSE threshold. The background free PAES spectra obtained include the first measurements of the low energy tail of CVV Auger transitions all the way down to zero kinetic energy. The integrated intensity of this tail is several times larger than Auger peak itself which provides strong evidence for multi-electron Auger processes.

Atomistic model for excitons: Capturing Strongly Bound Excitons in Monolayer Transition-Metal Dichalcogenides

NASA Astrophysics Data System (ADS)

Tseng, Frank; Simsek, Ergun; Gunlycke, Daniel

2015-03-01

Monolayer transition-metal dichalcogenides form a direct bandgap predicted in the visible regime making them attractive host materials for various electronic and optoelectronic applications. Due to a weak dielectric screening in these materials, strongly bound electron-hole pairs or excitons have binding energies up to at least several hundred meV's. While the conventional wisdom is to think of excitons as hydrogen-like quasi-particles, we show that the hydrogen model breaks down for these experimentally observed strongly bound, room-temperature excitons. To capture these non-hydrogen-like photo-excitations, we introduce an atomistic model for excitons that predicts both bright excitons and dark excitons, and their broken degeneracy in these two-dimensional materials. For strongly bound exciton states, the lattice potential significantly distorts the envelope wave functions, which affects predicted exciton peak energies. The combination of large binding energies and non-degeneracy of exciton states in monolayer transition metal dichalogendies may furthermore be exploited in room temperature applications where prolonged exciton lifetimes are necessary. This work has been funded by the Office of Naval Research (ONR), directly and through the Naval Research Laboratory (NRL). F.T and E.S acknowledge support from NRL through the NRC Research Associateship Program and ONR Summer Faculty Program, respectively.

A Comparison of the Bounded Derivative and the Normal Mode Initialization Methods Using Real Data

NASA Technical Reports Server (NTRS)

Semazzi, F. H. M.; Navon, I. M.

1985-01-01

Browning et al. (1980) proposed an initialization method called the bounded derivative method (BDI). They used analytical data to test the new method. Kasahara (1982) theoretically demonstrated the equivalence between BDI and the well known nonlinear normal mode initialization method (NMI). The purposes of this study are the extension of the application of BDI to real data and comparison with NMI. The unbalanced initial state (UBD) is data of January, 1979 OOZ which were interpolated from the adjacent sigma levels of the GLAS GCM to the 300 mb surface. The global barotropic model described by Takacs and Balgovind (1983) is used. Orographic forcing is explicitly included in the model. Many comparisons are performed between various quantities. However, we only present a comparison of the time evolution at two grid points A(50 S, 90 E) and B(10 S, 20 E) which represent low and middle latitude locations. To facilitate a more complete comparison an initialization experiment based on the classical balance equation (CBE) was also included.

Quantum Dynamical Applications of Salem's Theorem

NASA Astrophysics Data System (ADS)

Damanik, David; Del Rio, Rafael

2009-07-01

We consider the survival probability of a state that evolves according to the Schrödinger dynamics generated by a self-adjoint operator H. We deduce from a classical result of Salem that upper bounds for the Hausdorff dimension of a set supporting the spectral measure associated with the initial state imply lower bounds on a subsequence of time scales for the survival probability. This general phenomenon is illustrated with applications to the Fibonacci operator and the critical almost Mathieu operator. In particular, this gives the first quantitative dynamical bound for the critical almost Mathieu operator.

Polystyrene bound oxidovanadium(IV) and dioxidovanadium(V) complexes of histamine derived ligand for the oxidation of methyl phenyl sulfide, diphenyl sulfide and benzoin.

PubMed

Maurya, Mannar R; Arya, Aarti; Kumar, Amit; Pessoa, João Costa

2009-03-28

Ligand Hsal-his (I) derived from salicylaldehyde and histamine has been covalently bound to chloromethylated polystyrene cross-linked with 5% divinylbenzene. Upon treatment with [VO(acac)(2)] in DMF, the polystyrene-bound ligand (abbreviated as PS-Hsal-his, II) gave the stable polystyrene-bound oxidovanadium(iv) complex PS-[V(IV)O(sal-his)(acac)] , which upon oxidation yielded the dioxidovanadium(v) PS-[V(V)O(2)(sal-his)] complex. The corresponding non polymer-bound complexes [V(IV)O(sal-his)(acac)] and [V(V)O(2)(sal-his)] have also been obtained. These complexes have been characterised by IR, electronic, (51)V NMR and EPR spectral studies, and thermal as well as scanning electron micrograph studies. Complexes and have been used as a catalyst for the oxidation of methyl phenyl sulfide, diphenyl sulfide and benzoin with 30% H(2)O(2) as oxidant. Under the optimised reaction conditions, a maximum of 93.8% conversion of methyl phenyl sulfide with 63.7% selectivity towards methyl phenyl sulfoxide and 36.3% towards methyl phenyl sulfone has been achieved in 2 h with 2 . Under similar conditions, diphenyl sulfide gave 83.4% conversion where selectivity of reaction products varied in the order: diphenyl sulfoxide (71.8%) > diphenyl sulfone (28.2%). A maximum of 91.2% conversion of benzoin has been achieved within 6 h, and the selectivities of reaction products are: methylbenzoate (37.0%) > benzil (30.5%) > benzaldehyde-dimethylacetal (22.5%) > benzoic acid (8.1%). The PS-bound complex, 1 exhibits very comparable catalytic potential. These polymer-anchored heterogeneous catalysts do not leach during catalytic action, are recyclable and show higher catalytic activity and turnover frequency than the corresponding non polymer-bound complexes. EPR and (51)V NMR spectroscopy was used to characterise methanolic solutions of 3 and 4 and to identify species formed upon addition of H(2)O(2) and/or acid and/or methyl phenyl sulfide.

Structure and function of NADPH-cytochrome P450 reductase and nitric oxide synthase reductase domain

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

Iyanagi, Takashi

2005-12-09

NADPH-cytochrome P450 reductase (CPR) and the nitric oxide synthase (NOS) reductase domains are members of the FAD-FMN family of proteins. The FAD accepts two reducing equivalents from NADPH (dehydrogenase flavin) and FMN acts as a one-electron carrier (flavodoxin-type flavin) for the transfer from NADPH to the heme protein, in which the FMNH {sup {center_dot}}/FMNH{sub 2} couple donates electrons to cytochrome P450 at constant oxidation-reduction potential. Although the interflavin electron transfer between FAD and FMN is not strictly regulated in CPR, electron transfer is activated in neuronal NOS reductase domain upon binding calmodulin (CaM), in which the CaM-bound activated form canmore » function by a similar mechanism to that of CPR. The oxygenated form and spin state of substrate-bound cytochrome P450 in perfused rat liver are also discussed in terms of stepwise one-electron transfer from CPR. This review provides a historical perspective of the microsomal mixed-function oxidases including CPR and P450. In addition, a new model for the redox-linked conformational changes during the catalytic cycle for both CPR and NOS reductase domain is also discussed.« less

Highly accurate bound state calculations of the two-center molecular ions by using the universal variational expansion for three-body systems

NASA Astrophysics Data System (ADS)

Frolov, Alexei M.

2018-03-01

The universal variational expansion for the non-relativistic three-body systems is explicitly constructed. This universal expansion can be used to perform highly accurate numerical computations of the bound state spectra in various three-body systems, including Coulomb three-body systems with arbitrary particle masses and electric charges. Our main interest is related to the adiabatic three-body systems which contain one bound electron and two heavy nuclei of hydrogen isotopes: the protium p, deuterium d and tritium t. We also consider the analogous (model) hydrogen ion ∞H2+ with the two infinitely heavy nuclei.

Kinetic balance and variational bounds failure in the solution of the Dirac equation in a finite Gaussian basis set

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.; Faegri, Knut, Jr.

1990-01-01

The paper investigates bounds failure in calculations using Gaussian basis sets for the solution of the one-electron Dirac equation for the 2p1/2 state of Hg(79+). It is shown that bounds failure indicates inadequacies in the basis set, both in terms of the exponent range and the number of functions. It is also shown that overrepresentation of the small component space may lead to unphysical results. It is concluded that it is important to use matched large and small component basis sets with an adequate size and exponent range.

Structure of the protein core of translation initiation factor 2 in apo, GTP-bound and GDP-bound forms

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

Simonetti, Angelita; Marzi, Stefano; Fabbretti, Attilio

2013-06-01

The crystal structures of the eubacterial translation initiation factor 2 in apo form and with bound GDP and GTP reveal conformational changes upon nucleotide binding and hydrolysis, notably of the catalytically important histidine in the switch II region. Translation initiation factor 2 (IF2) is involved in the early steps of bacterial protein synthesis. It promotes the stabilization of the initiator tRNA on the 30S initiation complex (IC) and triggers GTP hydrolysis upon ribosomal subunit joining. While the structure of an archaeal homologue (a/eIF5B) is known, there are significant sequence and functional differences in eubacterial IF2, while the trimeric eukaryotic IF2more » is completely unrelated. Here, the crystal structure of the apo IF2 protein core from Thermus thermophilus has been determined by MAD phasing and the structures of GTP and GDP complexes were also obtained. The IF2–GTP complex was trapped by soaking with GTP in the cryoprotectant. The structures revealed conformational changes of the protein upon nucleotide binding, in particular in the P-loop region, which extend to the functionally relevant switch II region. The latter carries a catalytically important and conserved histidine residue which is observed in different conformations in the GTP and GDP complexes. Overall, this work provides the first crystal structure of a eubacterial IF2 and suggests that activation of GTP hydrolysis may occur by a conformational repositioning of the histidine residue.« less

Hda, a novel DnaA-related protein, regulates the replication cycle in Escherichia coli

PubMed Central

Kato, Jun-ichi; Katayama, Tsutomu

2001-01-01

The bacterial DnaA protein binds to the chromosomal origin of replication to trigger a series of initiation reactions, which leads to the loading of DNA polymerase III. In Escherichia coli, once this polymerase initiates DNA synthesis, ATP bound to DnaA is efficiently hydrolyzed to yield the ADP-bound inactivated form. This negative regulation of DnaA, which occurs through interaction with the β-subunit sliding clamp configuration of the polymerase, functions in the temporal blocking of re-initiation. Here we show that the novel DnaA-related protein, Hda, from E.coli is essential for this regulatory inactivation of DnaA in vitro and in vivo. Our results indicate that the hda gene is required to prevent over-initiation of chromosomal replication and for cell viability. Hda belongs to the chaperone-like ATPase family, AAA+, as do DnaA and certain eukaryotic proteins essential for the initiation of DNA replication. We propose that the once-per-cell-cycle rule of replication depends on the timely interaction of AAA+ proteins that comprise the apparatus regulating the activity of the initiator of replication. PMID:11483528

Hda, a novel DnaA-related protein, regulates the replication cycle in Escherichia coli.

PubMed

Kato , J; Katayama, T

2001-08-01

The bacterial DnaA protein binds to the chromosomal origin of replication to trigger a series of initiation reactions, which leads to the loading of DNA polymerase III. In Escherichia coli, once this polymerase initiates DNA synthesis, ATP bound to DnaA is efficiently hydrolyzed to yield the ADP-bound inactivated form. This negative regulation of DnaA, which occurs through interaction with the beta-subunit sliding clamp configuration of the polymerase, functions in the temporal blocking of re-initiation. Here we show that the novel DnaA-related protein, Hda, from E.coli is essential for this regulatory inactivation of DnaA in vitro and in vivo. Our results indicate that the hda gene is required to prevent over-initiation of chromosomal replication and for cell viability. Hda belongs to the chaperone-like ATPase family, AAA(+), as do DnaA and certain eukaryotic proteins essential for the initiation of DNA replication. We propose that the once-per-cell-cycle rule of replication depends on the timely interaction of AAA(+) proteins that comprise the apparatus regulating the activity of the initiator of replication.

High-energy electrons from the muon decay in orbit: Radiative corrections

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

Szafron, Robert; Czarnecki, Andrzej

2015-12-07

We determine the Ο(α) correction to the energy spectrum of electrons produced in the decay of muons bound in atoms. We focus on the high-energy end of the spectrum that constitutes a background for the muon-electron conversion and will be precisely measured by the upcoming experiments Mu2e and COMET. As a result, the correction suppresses the background by about 20%.

Improved Limits on Axionlike-Particle-Mediated P , T -Violating Interactions between Electrons and Nucleons from Electric Dipole Moments of Atoms and Molecules

NASA Astrophysics Data System (ADS)

Stadnik, Y. V.; Dzuba, V. A.; Flambaum, V. V.

2018-01-01

In the presence of P , T -violating interactions, the exchange of axionlike particles between electrons and nucleons in atoms and molecules induces electric dipole moments (EDMs) of atoms and molecules. We perform calculations of such axion-exchange-induced atomic EDMs using the relativistic Hartree-Fock-Dirac method including electron core polarization corrections. We present analytical estimates to explain the dependence of these induced atomic EDMs on the axion mass and atomic parameters. From the experimental bounds on the EDMs of atoms and molecules, including Cs 133 , Tl 205 , Xe 129 , Hg 199 , Yb 171 F 19 , Hf 180 F+ 19 , and Th 232 O 16 , we constrain the P , T -violating scalar-pseudoscalar nucleon-electron and electron-electron interactions mediated by a generic axionlike particle of arbitrary mass. Our limits improve on existing laboratory bounds from other experiments by many orders of magnitude for ma≳10-2 eV . We also place constraints on C P violation in certain types of relaxion models.

Donor states in inverse opals

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

Mahan, G. D.

We calculate the binding energy of an electron bound to a donor in a semiconductor inverse opal. Inverse opals have two kinds of cavities, which we call octahedral and tetrahedral, according to their group symmetry. We put the donor in the center of each of these two cavities and obtain the binding energy. The binding energies become very large when the inverse opal is made from templates with small spheres. For spheres less than 50 nm in diameter, the donor binding can increase to several times its unconfined value. Then electrons become tightly bound to the donor and are unlikelymore » to be thermally activated to the semiconductor conduction band. This conclusion suggests that inverse opals will be poor conductors.« less

Quantum theory of atoms in molecules: results for the SR-ZORA Hamiltonian.

PubMed

Anderson, James S M; Ayers, Paul W

2011-11-17

The quantum theory of atoms in molecules (QTAIM) is generalized to include relativistic effects using the popular scalar-relativistic zeroth-order regular approximation (SR-ZORA). It is usually assumed that the definition of the atom as a volume bounded by a zero-flux surface of the electron density is closely linked to the form of the kinetic energy, so it is somewhat surprising that the atoms corresponding to the relativistic kinetic-energy operator in the SR-ZORA Hamiltonian are also bounded by zero-flux surfaces. The SR-ZORA Hamiltonian should be sufficient for qualitative descriptions of molecular electronic structure across the periodic table, which suggests that QTAIM-based analysis can be useful for molecules and solids containing heavy atoms.

Localization of massless Dirac particles via spatial modulations of the Fermi velocity

NASA Astrophysics Data System (ADS)

Downing, C. A.; Portnoi, M. E.

2017-08-01

The electrons found in Dirac materials are notorious for being difficult to manipulate due to the Klein phenomenon and absence of backscattering. Here we investigate how spatial modulations of the Fermi velocity in two-dimensional Dirac materials can give rise to localization effects, with either full (zero-dimensional) confinement or partial (one-dimensional) confinement possible depending on the geometry of the velocity modulation. We present several exactly solvable models illustrating the nature of the bound states which arise, revealing how the gradient of the Fermi velocity is crucial for determining fundamental properties of the bound states such as the zero-point energy. We discuss the implications for guiding electronic waves in few-mode waveguides formed by Fermi velocity modulation.

ESR and X-ray Structure Investigations on the Binding and Mechanism of Inhibition of the Native State of Myeloperoxidase with Low Molecular Weight Fragments

DOE PAGES

Chavali, Balagopalakrishna; Masquelin, Thierry; Nilges, Mark J.; ...

2015-05-19

As an early visitor to the injured loci, neutrophil-derived human Myeloperoxidase (hMPO) offers an attractive protein target to modulate the inflammation of the host tissue through suitable inhibitors. We describe a novel methodology of using low temperature ESR spectroscopy (6 K) and FAST™ technology to screen a diverse series of small molecules that inhibit the peroxidase function through reversible binding to the native state of MPO. Also, our initial efforts to profile molecules on the inhibition of MPO-initiated nitration of the Apo-A1 peptide (AEYHAKATEHL) assay showed several potent (with sub-micro molar IC50s) but spurious inhibitors that either do not bindmore » to the heme pocket in the enzyme or retain high (>50 %) anti oxidant potential. Such molecules when taken forward for X-ray did not yield inhibitor-bound co-crystals. We then used ESR to confirm direct binding to the native state enzyme, by measuring the binding-induced shift in the electronic parameter g to rank order the molecules. Molecules with a higher rank order—those with g-shift R relative ≥15—yielded well-formed protein-bound crystals (n = 33 structures). The co-crystal structure with the LSN217331 inhibitor reveals that the chlorophenyl group projects away from the heme along the edges of the Phe366 and Phe407 side chain phenyl rings thereby sterically restricting the access to the heme by the substrates like H 2O 2. Both ESR and antioxidant screens were used to derive the mechanism of action (reversibility, competitive substrate inhibition, and percent antioxidant potential). In conclusion, our results point to a viable path forward to target the native state of MPO to tame local inflammation.« less

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

Chavali, Balagopalakrishna; Masquelin, Thierry; Nilges, Mark J.

As an early visitor to the injured loci, neutrophil-derived human Myeloperoxidase (hMPO) offers an attractive protein target to modulate the inflammation of the host tissue through suitable inhibitors. We describe a novel methodology of using low temperature ESR spectroscopy (6 K) and FAST™ technology to screen a diverse series of small molecules that inhibit the peroxidase function through reversible binding to the native state of MPO. Also, our initial efforts to profile molecules on the inhibition of MPO-initiated nitration of the Apo-A1 peptide (AEYHAKATEHL) assay showed several potent (with sub-micro molar IC50s) but spurious inhibitors that either do not bindmore » to the heme pocket in the enzyme or retain high (>50 %) anti oxidant potential. Such molecules when taken forward for X-ray did not yield inhibitor-bound co-crystals. We then used ESR to confirm direct binding to the native state enzyme, by measuring the binding-induced shift in the electronic parameter g to rank order the molecules. Molecules with a higher rank order—those with g-shift R relative ≥15—yielded well-formed protein-bound crystals (n = 33 structures). The co-crystal structure with the LSN217331 inhibitor reveals that the chlorophenyl group projects away from the heme along the edges of the Phe366 and Phe407 side chain phenyl rings thereby sterically restricting the access to the heme by the substrates like H 2O 2. Both ESR and antioxidant screens were used to derive the mechanism of action (reversibility, competitive substrate inhibition, and percent antioxidant potential). In conclusion, our results point to a viable path forward to target the native state of MPO to tame local inflammation.« less

One-step detection of pathogens and cancer biomarkers by the naked eye based on aggregation of immunomagnetic beads

NASA Astrophysics Data System (ADS)

Chen, Yiping; Xianyu, Yunlei; Sun, Jiashu; Niu, Yajing; Wang, Yu; Jiang, Xingyu

2015-12-01

This report shows that immunomagnetic beads (IMBs) can act as the optical readout for assays, in addition to serving as the carrier for purification/separation. Under the influence of an external magnet, IMBs are attracted to coat one side of a test tube. IMBs specifically bound to targets can form a narrow brown stripe, whereas free IMBs will form a diffuse, yellow coating on the side of the test tube. Target analytes can aggregate initially dispersed IMBs in a sample concentration-dependent manner, yielding a color change from yellow to brown that can be seen with the naked eye. This assay combines the convenience of a lateral flow assay, allowing a one-step assay to finish within 15 min, with the sensitivity of an enzyme-linked immonosorbent assay.This report shows that immunomagnetic beads (IMBs) can act as the optical readout for assays, in addition to serving as the carrier for purification/separation. Under the influence of an external magnet, IMBs are attracted to coat one side of a test tube. IMBs specifically bound to targets can form a narrow brown stripe, whereas free IMBs will form a diffuse, yellow coating on the side of the test tube. Target analytes can aggregate initially dispersed IMBs in a sample concentration-dependent manner, yielding a color change from yellow to brown that can be seen with the naked eye. This assay combines the convenience of a lateral flow assay, allowing a one-step assay to finish within 15 min, with the sensitivity of an enzyme-linked immonosorbent assay. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07044a

Cosmological singularity theorems and splitting theorems for N-Bakry-Émery spacetimes

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

Woolgar, Eric, E-mail: ewoolgar@ualberta.ca; Wylie, William, E-mail: wwylie@syr.edu

We study Lorentzian manifolds with a weight function such that the N-Bakry-Émery tensor is bounded below. Such spacetimes arise in the physics of scalar-tensor gravitation theories, including Brans-Dicke theory, theories with Kaluza-Klein dimensional reduction, and low-energy approximations to string theory. In the “pure Bakry-Émery” N = ∞ case with f uniformly bounded above and initial data suitably bounded, cosmological-type singularity theorems are known, as are splitting theorems which determine the geometry of timelike geodesically complete spacetimes for which the bound on the initial data is borderline violated. We extend these results in a number of ways. We are able tomore » extend the singularity theorems to finite N-values N ∈ (n, ∞) and N ∈ (−∞, 1]. In the N ∈ (n, ∞) case, no bound on f is required, while for N ∈ (−∞, 1] and N = ∞, we are able to replace the boundedness of f by a weaker condition on the integral of f along future-inextendible timelike geodesics. The splitting theorems extend similarly, but when N = 1, the splitting is only that of a warped product for all cases considered. A similar limited loss of rigidity has been observed in a prior work on the N-Bakry-Émery curvature in Riemannian signature when N = 1 and appears to be a general feature.« less

Cosmological singularity theorems and splitting theorems for N-Bakry-Émery spacetimes

NASA Astrophysics Data System (ADS)

Woolgar, Eric; Wylie, William

2016-02-01

We study Lorentzian manifolds with a weight function such that the N-Bakry-Émery tensor is bounded below. Such spacetimes arise in the physics of scalar-tensor gravitation theories, including Brans-Dicke theory, theories with Kaluza-Klein dimensional reduction, and low-energy approximations to string theory. In the "pure Bakry-Émery" N = ∞ case with f uniformly bounded above and initial data suitably bounded, cosmological-type singularity theorems are known, as are splitting theorems which determine the geometry of timelike geodesically complete spacetimes for which the bound on the initial data is borderline violated. We extend these results in a number of ways. We are able to extend the singularity theorems to finite N-values N ∈ (n, ∞) and N ∈ (-∞, 1]. In the N ∈ (n, ∞) case, no bound on f is required, while for N ∈ (-∞, 1] and N = ∞, we are able to replace the boundedness of f by a weaker condition on the integral of f along future-inextendible timelike geodesics. The splitting theorems extend similarly, but when N = 1, the splitting is only that of a warped product for all cases considered. A similar limited loss of rigidity has been observed in a prior work on the N-Bakry-Émery curvature in Riemannian signature when N = 1 and appears to be a general feature.

Ab initio calculations of potential energy curves of Hg/sub 2/ and TlHg

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

Celestino, K.C.; Ermler, W.C.

1984-08-15

Potential energy curves for electronic states of Hg/sub 2/ and TlHg are presented and analyzed. They are derived using large scale configuration interaction procedures for the valence electrons, with the core electrons represented by ab initio relativistic effective potentials. The effect of spin-orbit coupling are investigated for the low-lying excimer states. It is determined that neither system possesses strongly bound electronic states for which transitions to the repulsive ground states are optically allowed.

Direct and Indirect Electron Emission from the Green Fluorescent Protein Chromophore

NASA Astrophysics Data System (ADS)

Toker, Y.; Rahbek, D. B.; Klærke, B.; Bochenkova, A. V.; Andersen, L. H.

2012-09-01

Photoelectron spectra of the deprotonated green fluorescent protein chromophore have been measured in the gas phase at several wavelengths within and beyond the S0-S1 photoabsorption band of the molecule. The vertical detachment energy (VDE) was determined to be 2.68±0.1eV. The data show that the first electronically excited state is bound in the Franck-Condon region, and that electron emission proceeds through an indirect (resonant) electron-emission channel within the corresponding absorption band.

Vlasov-Maxwell and Vlasov-Poisson equations as models of a one-dimensional electron plasma

NASA Technical Reports Server (NTRS)

Klimas, A. J.; Cooper, J.

1983-01-01

The Vlasov-Maxwell and Vlasov-Poisson systems of equations for a one-dimensional electron plasma are defined and discussed. A method for transforming a solution of one system which is periodic over a bounded or unbounded spatial interval to a similar solution of the other is constructed.

Binding the Electronic Book: Design Features for Bibliophiles

ERIC Educational Resources Information Center

Ruecker, Stan; Uszkalo, Kirsten C.

2007-01-01

This paper proposes a design for the electronic book based on discussions with frequent book readers. We adopted a conceptual framework for this project consisting of a spectrum of possible designs, with the conventional bound book at one difference pole, and the laptop computer at the other; the design activity then consisted of appropriately…

Effect of Ligand Exchange on the Photoluminescence Properties of Cu-Doped Zn-In-Se Quantum Dots

NASA Astrophysics Data System (ADS)

Dong, Xiaofei; Xu, Jianping; Yang, Hui; Zhang, Xiaosong; Mo, Zhaojun; Shi, Shaobo; Li, Lan; Yin, Shougen

2018-04-01

The surface-bound ligands of a semiconductor nanocrystal can affect its electron transition behavior. We investigate the photoluminescence (PL) properties of Cu-doped Zn-In-Se quantum dots (QDs) through the exchange of oleylamine with 6-mercaptohexanol (MCH). Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies, and mass spectrometry reveal that the short-chain MCH molecules are bound to the QD surface. The emission peaks remain unchanged after ligand exchange, and the PL quantum yield is reduced from 49% to 38%. The effects of particle size and defect type on the change in PL behavior upon ligand substitution are excluded through high-resolution transmission electron microscopy, UV-Vis absorption, and PL spectroscopies. The origin of the decreased PL intensity is associated with increased ligand density and the stronger ligand electron-donating abilities of MCH-capped QDs that induce an increase in the nonradiative transition probability. A lower PL quenching transition temperature is observed for MCH-capped QDs and is associated with increasing electron-acoustic phonon coupling due to the lower melting temperature of MCH.

Ab Initio Electronic Structure Calculation of [4Fe-3S] Cluster of Hydrogenase as Dihydrogen Dissociation/Production Catalyst

NASA Astrophysics Data System (ADS)

Kim, Jaehyun; Kang, Jiyoung; Nishigami, Hiroshi; Kino, Hiori; Tateno, Masaru

2018-03-01

Hydrogenases catalyze both the dissociation and production of dihydrogen (H2). Most hydrogenases are inactivated rapidly and reactivated slowly (in vitro), in the presence of dioxygen (O2) and H2, respectively. However, membrane-bound [NiFe] hydrogenases (MBHs) sustain their activity even together with O2, which is termed "O2 tolerance". In previous experimental analyses, an MBH was shown to include a hydroxyl ion (OH-) bound to an Fe of the super-oxidized [4Fe-3S]5+ cluster in the proximity of the [NiFe] catalytic cluster. In this study, the functional role of the OH- in the O2 tolerance was investigated by ab initio electronic structure calculation of the [4Fe-3S] proximal cluster. The analysis revealed that the OH- significantly altered the electronic structure, thereby inducing the delocalization of the lowest unoccupied molecular orbital (LUMO) toward the [NiFe] catalytic cluster, which may intermediate the electron transfer between the catalytic and proximal clusters. This can promote the O2-tolerant catalytic cycle in the hydrogenase reaction.

Cell-secreted flavins bound to membrane cytochromes dictate electron transfer reactions to surfaces with diverse charge and pH.

PubMed

Okamoto, Akihiro; Kalathil, Shafeer; Deng, Xiao; Hashimoto, Kazuhito; Nakamura, Ryuhei; Nealson, Kenneth H

2014-07-11

The variety of solid surfaces to and from which microbes can deliver electrons by extracellular electron transport (EET) processes via outer-membrane c-type cytochromes (OM c-Cyts) expands the importance of microbial respiration in natural environments and industrial applications. Here, we demonstrate that the bifurcated EET pathway of OM c-Cyts sustains the diversity of the EET surface in Shewanella oneidensis MR-1 via specific binding with cell-secreted flavin mononucleotide (FMN) and riboflavin (RF). Microbial current production and whole-cell differential pulse voltammetry revealed that RF and FMN enhance EET as bound cofactors in a similar manner. Conversely, FMN and RF were clearly differentiated in the EET enhancement by gene-deletion of OM c-Cyts and the dependency of the electrode potential and pH. These results indicate that RF and FMN have specific binding sites in OM c-Cyts and highlight the potential roles of these flavin-cytochrome complexes in controlling the rate of electron transfer to surfaces with diverse potential and pH.

Interlayer excitons in a bulk van der Waals semiconductor.

PubMed

Arora, Ashish; Drüppel, Matthias; Schmidt, Robert; Deilmann, Thorsten; Schneider, Robert; Molas, Maciej R; Marauhn, Philipp; Michaelis de Vasconcellos, Steffen; Potemski, Marek; Rohlfing, Michael; Bratschitsch, Rudolf

2017-09-21

Bound electron-hole pairs called excitons govern the electronic and optical response of many organic and inorganic semiconductors. Excitons with spatially displaced wave functions of electrons and holes (interlayer excitons) are important for Bose-Einstein condensation, superfluidity, dissipationless current flow, and the light-induced exciton spin Hall effect. Here we report on the discovery of interlayer excitons in a bulk van der Waals semiconductor. They form due to strong localization and spin-valley coupling of charge carriers. By combining high-field magneto-reflectance experiments and ab initio calculations for 2H-MoTe 2 , we explain their salient features: the positive sign of the g-factor and the large diamagnetic shift. Our investigations solve the long-standing puzzle of positive g-factors in transition metal dichalcogenides, and pave the way for studying collective phenomena in these materials at elevated temperatures.Excitons, quasi-particles of bound electron-hole pairs, are at the core of the optoelectronic properties of layered transition metal dichalcogenides. Here, the authors unveil the presence of interlayer excitons in bulk van der Waals semiconductors, arising from strong localization and spin-valley coupling of charge carriers.

Search for a hidden strange baryon-meson bound state from ϕ production in a nuclear medium

NASA Astrophysics Data System (ADS)

Gao, Haiyan; Huang, Hongxia; Liu, Tianbo; Ping, Jialun; Wang, Fan; Zhao, Zhiwen

2017-05-01

We investigate the hidden strange light baryon-meson system. With the resonating-group method, two bound states, η'-N and ϕ -N , are found in the quark delocalization color screening model. Focusing on the ϕ -N bound state around 1950 MeV, we obtain the total decay width of about 4 MeV by calculating the phase shifts in the resonance scattering processes. To study the feasibility of an experimental search for the ϕ -N bound state, we perform a Monte Carlo simulation of the bound state production with an electron beam and a gold target. In the simulation, we use the CLAS12 detector with the Forward Tagger and the BONUS12 detector in Hall B at Jefferson Lab. Both the signal and the background channels are estimated. We demonstrate that the signal events can be separated from the background with some momentum cuts. Therefore it is feasible to experimentally search for the ϕ -N bound state through the near threshold ϕ meson production from heavy nuclei.

Structure of the apoptosome: mechanistic insights into activation of an initiator caspase from Drosophila

PubMed Central

Pang, Yuxuan; Bai, Xiao-chen; Yan, Chuangye; Hao, Qi; Chen, Zheqin; Wang, Jia-Wei

2015-01-01

Apoptosis is executed by a cascade of caspase activation. The autocatalytic activation of an initiator caspase, exemplified by caspase-9 in mammals or its ortholog, Dronc, in fruit flies, is facilitated by a multimeric adaptor complex known as the apoptosome. The underlying mechanism by which caspase-9 or Dronc is activated by the apoptosome remains unknown. Here we report the electron cryomicroscopic (cryo-EM) structure of the intact apoptosome from Drosophila melanogaster at 4.0 Å resolution. Analysis of the Drosophila apoptosome, which comprises 16 molecules of the Dark protein (Apaf-1 ortholog), reveals molecular determinants that support the assembly of the 2.5-MDa complex. In the absence of dATP or ATP, Dronc zymogen potently induces formation of the Dark apoptosome, within which Dronc is efficiently activated. At 4.1 Å resolution, the cryo-EM structure of the Dark apoptosome bound to the caspase recruitment domain (CARD) of Dronc (Dronc-CARD) reveals two stacked rings of Dronc-CARD that are sandwiched between two octameric rings of the Dark protein. The specific interactions between Dronc-CARD and both the CARD and the WD40 repeats of a nearby Dark protomer are indispensable for Dronc activation. These findings reveal important mechanistic insights into the activation of initiator caspase by the apoptosome. PMID:25644603

Full-potential multiple scattering theory with space-filling cells for bound and continuum states.

PubMed

Hatada, Keisuke; Hayakawa, Kuniko; Benfatto, Maurizio; Natoli, Calogero R

2010-05-12

We present a rigorous derivation of a real-space full-potential multiple scattering theory (FP-MST) that is free from the drawbacks that up to now have impaired its development (in particular the need to expand cell shape functions in spherical harmonics and rectangular matrices), valid both for continuum and bound states, under conditions for space partitioning that are not excessively restrictive and easily implemented. In this connection we give a new scheme to generate local basis functions for the truncated potential cells that is simple, fast, efficient, valid for any shape of the cell and reduces to the minimum the number of spherical harmonics in the expansion of the scattering wavefunction. The method also avoids the need for saturating 'internal sums' due to the re-expansion of the spherical Hankel functions around another point in space (usually another cell center). Thus this approach provides a straightforward extension of MST in the muffin-tin (MT) approximation, with only one truncation parameter given by the classical relation l(max) = kR(b), where k is the electron wavevector (either in the excited or ground state of the system under consideration) and R(b) is the radius of the bounding sphere of the scattering cell. Moreover, the scattering path operator of the theory can be found in terms of an absolutely convergent procedure in the l(max) --> ∞ limit. Consequently, this feature provides a firm ground for the use of FP-MST as a viable method for electronic structure calculations and makes possible the computation of x-ray spectroscopies, notably photo-electron diffraction, absorption and anomalous scattering among others, with the ease and versatility of the corresponding MT theory. Some numerical applications of the theory are presented, both for continuum and bound states.

A Hidden Transhydrogen Activity of a FMN-Bound Diaphorase under Anaerobic Conditions

DTIC Science & Technology

2016-05-04

RESEARCH ARTICLE A Hidden Transhydrogen Activity of a FMN- Bound Diaphorase under Anaerobic Conditions John Collins1, Ting Zhang1, Scott Huston1... metabolic pathways for facilitating the electron transfer from one molecule to another in redox reactions. Transhy- drogenase plays an important role in...March 2, 2016 Accepted: April 20, 2016 Published: May 4, 2016 Copyright: © 2016 Collins et al. This is an open access article distributed under the

Pair-Wise and Many-Body Dispersive Interactions Coupled to an Optimally Tuned Range-Separated Hybrid Functional.

PubMed

Agrawal, Piyush; Tkatchenko, Alexandre; Kronik, Leeor

2013-08-13

We propose a nonempirical, pair-wise or many-body dispersion-corrected, optimally tuned range-separated hybrid functional. This functional retains the advantages of the optimal-tuning approach in the prediction of the electronic structure. At the same time, it gains accuracy in the prediction of binding energies for dispersively bound systems, as demonstrated on the S22 and S66 benchmark sets of weakly bound dimers.

An apparatus for studying electrical breakdown in liquid helium at 0.4 K and testing electrode materials for the neutron electric dipole moment experiment at the Spallation Neutron Source

NASA Astrophysics Data System (ADS)

Ito, T. M.; Ramsey, J. C.; Yao, W.; Beck, D. H.; Cianciolo, V.; Clayton, S. M.; Crawford, C.; Currie, S. A.; Filippone, B. W.; Griffith, W. C.; Makela, M.; Schmid, R.; Seidel, G. M.; Tang, Z.; Wagner, D.; Wei, W.; Williamson, S. E.

2016-04-01

We have constructed an apparatus to study DC electrical breakdown in liquid helium at temperatures as low as 0.4 K and at pressures between the saturated vapor pressure and ˜600 Torr. The apparatus can house a set of electrodes that are 12 cm in diameter with a gap of 1-2 cm between them, and a potential up to ±50 kV can be applied to each electrode. Initial results demonstrated that it is possible to apply fields exceeding 100 kV/cm in a 1 cm gap between two electropolished stainless steel electrodes 12 cm in diameter for a wide range of pressures at 0.4 K. We also measured the current between two electrodes. Our initial results, I < 1 pA at 45 kV, correspond to a lower bound on the effective volume resistivity of liquid helium of ρV > 5 × 1018 Ω cm. This lower bound is 5 times larger than the bound previously measured. We report the design, construction, and operational experience of the apparatus, as well as initial results.

An apparatus for studying electrical breakdown in liquid helium at 0.4 K and testing electrode materials for the neutron electric dipole moment experiment at the Spallation Neutron Source.

PubMed

Ito, T M; Ramsey, J C; Yao, W; Beck, D H; Cianciolo, V; Clayton, S M; Crawford, C; Currie, S A; Filippone, B W; Griffith, W C; Makela, M; Schmid, R; Seidel, G M; Tang, Z; Wagner, D; Wei, W; Williamson, S E

2016-04-01

We have constructed an apparatus to study DC electrical breakdown in liquid helium at temperatures as low as 0.4 K and at pressures between the saturated vapor pressure and ∼600 Torr. The apparatus can house a set of electrodes that are 12 cm in diameter with a gap of 1-2 cm between them, and a potential up to ±50 kV can be applied to each electrode. Initial results demonstrated that it is possible to apply fields exceeding 100 kV/cm in a 1 cm gap between two electropolished stainless steel electrodes 12 cm in diameter for a wide range of pressures at 0.4 K. We also measured the current between two electrodes. Our initial results, I < 1 pA at 45 kV, correspond to a lower bound on the effective volume resistivity of liquid helium of ρV > 5 × 10(18) Ω cm. This lower bound is 5 times larger than the bound previously measured. We report the design, construction, and operational experience of the apparatus, as well as initial results.

Mechanism of resonant electron emission from the deprotonated GFP chromophore and its biomimetics.

PubMed

Bochenkova, Anastasia V; Mooney, Ciarán R S; Parkes, Michael A; Woodhouse, Joanne L; Zhang, Lijuan; Lewin, Ross; Ward, John M; Hailes, Helen C; Andersen, Lars H; Fielding, Helen H

2017-04-01

The Green Fluorescent Protein (GFP), which is widely used in bioimaging, is known to undergo light-induced redox transformations. Electron transfer is thought to occur resonantly through excited states of its chromophore; however, a detailed understanding of the electron gateway states of the chromophore is still missing. Here, we use photoelectron spectroscopy and high-level quantum chemistry calculations to show that following UV excitation, the ultrafast electron dynamics in the chromophore anion proceeds via an excited shape resonance strongly coupled to the open continuum. The impact of this state is found across the entire 355-315 nm excitation range, from above the first bound-bound transition to below the opening of higher-lying continua. By disentangling the electron dynamics in the photodetachment channels, we provide an important reference for the adiabatic position of the electron gateway state, which is located at 348 nm, and discover the source of the curiously large widths of the photoelectron spectra that have been reported in the literature. By introducing chemical modifications to the GFP chromophore, we show that the detachment threshold and the position of the gateway state, and hence the underlying excited-state dynamics, can be changed systematically. This enables a fine tuning of the intrinsic electron emission properties of the GFP chromophore and has significant implications for its function, suggesting that the biomimetic GFP chromophores are more stable to photooxidation.

Resonant interatomic Coulombic decay in HeNe: Electron angular emission distributions

NASA Astrophysics Data System (ADS)

Mhamdi, A.; Trinter, F.; Rauch, C.; Weller, M.; Rist, J.; Waitz, M.; Siebert, J.; Metz, D.; Janke, C.; Kastirke, G.; Wiegandt, F.; Bauer, T.; Tia, M.; Cunha de Miranda, B.; Pitzer, M.; Sann, H.; Schiwietz, G.; Schöffler, M.; Simon, M.; Gokhberg, K.; Dörner, R.; Jahnke, T.; Demekhin, Ph. Â. V.

2018-05-01

We present a joint experimental and theoretical study of resonant interatomic Coulombic decay (RICD) in HeNe employing high resolution cold target recoil ion momentum spectroscopy and ab initio electronic structure and nuclear dynamics calculations. In particular, laboratory- and molecular-frame angular emission distributions of RICD electrons are examined in detail. The exciting-photon energy-dependent anisotropy parameter β (ω ) , measured for decay events that populate bound HeNe+ ions, is in agreement with the calculations performed for the ground ionic state X2Σ1/2 + . A contribution from the a2Π3 /2 final ionic state is found to be negligible. For the He +Ne+ fragmentation channel, the observed laboratory-frame angular distribution of RICD electrons is explained by a slow homogeneous dissociation of bound vibrational levels of the final ionic state A2Π1 /2 into vibrational continua of the lower lying states X2Σ1/2 + and a2Π3 /2 . Our calculations predict that the angular distributions of RICD electrons in the body-fixed dipole plane provide direct access to the electronic character (i.e., symmetry) of intermediate vibronic resonances. However, because of the very slow dissociation of the A2Π1 /2 state, the molecular-frame angular distributions of RICD electrons in the He +Ne+ fragmentation channel are inaccessible to our coincidence experiment.

Wait for It: Post-supernova Winds Driven by Delayed Radioactive Decays

NASA Astrophysics Data System (ADS)

Shen, Ken J.; Schwab, Josiah

2017-01-01

In most astrophysical situations, the radioactive decay of {}56{Ni} to {}56{Co} occurs via electron capture with a fixed half-life of 6.1 days. However, this decay rate is significantly slowed when the nuclei are fully ionized because K-shell electrons are unavailable for capture. In this paper, we explore the effect of these delayed decays on white dwarfs (WDs) that may survive Type Ia and Type Iax supernovae (SNe Ia and SNe Iax). The energy released by the delayed radioactive decays of {}56{Ni} and {}56{Co} drives a persistent wind from the surviving WD’s surface that contributes to the late-time appearance of these SNe after emission from the bulk of the SN ejecta has faded. We use the stellar evolution code MESA to calculate the hydrodynamic evolution and resulting light curves of these winds. Our post-SN Ia models conflict with late-time observations of SN 2011fe, but uncertainties in our initial conditions prevent us from ruling out the existence of surviving WD donors. Much better agreement with observations is achieved with our models of post-SN Iax bound remnants, providing evidence that these explosions are due to deflagrations in accreting WDs that fail to completely unbind the WDs. Future radiative transfer calculations and wind models utilizing simulations of explosions for more accurate initial conditions will extend our study of radioactively powered winds from post-SN surviving WDs and enable their use as powerful discriminants among the various SN Ia and SN Iax progenitor scenarios.

Stabilization of very rare tautomers of uracil by an excess electron.

PubMed

Bachorz, Rafał A; Rak, Janusz; Gutowski, Maciej

2005-05-21

We characterized valence-type and dipole-bound anionic states of uracil using various electronic structure methods. We found that the most stable anion is related to neither the canonical 2,4-dioxo nor a rare imino-hydroxy tautomer. Instead, it is related to an imino-oxo tautomer, in which the N1H proton is transferred to the C5 atom. This valence anion is characterized by an electron vertical detachment energy (VDE) of 1267 meV and it is adiabatically stable with respect to the canonical neutral by 3.93 kcal mol(-1). It is also more stable by 2.32 and 5.10 kcal mol(-1) than the dipole-bound and valence anion, respectively, of the canonical tautomer. The VDE values for the former and the latter are 73 and 506 meV, respectively. Another, anionic, low-lying imino-oxo tautomer with a VDE of 2499 meV has a proton transferred from N3H to C5. It is less stable than the neutral canonical tautomer by 1.38 kcal mol(-1). The mechanism of formation of anionic tautomers with the carbon C5 protonated may involve intermolecular proton transfer or dissociative electron attachment to the canonical neutral tautomer followed by a barrier-free attachment of a hydrogen atom to C5. The six-member ring structure of anionic tautomers with carbon atoms protonated might be unstable upon an excess electron detachment. Indeed, the neutral systems resulting from electron detachment from anionic tautomers with carbon atoms protonated evolve along barrier-free decomposition pathways to a linear or a bicyclo structure, which might be viewed as lesions to RNA. Within the PCM hydration model, the low-lying valence anions become adiabatically bound with respect to the canonical neutral and the two most stable tautomers have carbon atoms protonated.

Quantifying the cellular uptake of semiconductor quantum dot nanoparticles by analytical electron microscopy.

PubMed

Hondow, Nicole; Brown, M Rowan; Starborg, Tobias; Monteith, Alexander G; Brydson, Rik; Summers, Huw D; Rees, Paul; Brown, Andy

2016-02-01

Semiconductor quantum dot nanoparticles are in demand as optical biomarkers yet the cellular uptake process is not fully understood; quantification of numbers and the fate of internalized particles are still to be achieved. We have focussed on the characterization of cellular uptake of quantum dots using a combination of analytical electron microscopies because of the spatial resolution available to examine uptake at the nanoparticle level, using both imaging to locate particles and spectroscopy to confirm identity. In this study, commercially available quantum dots, CdSe/ZnS core/shell particles coated in peptides to target cellular uptake by endocytosis, have been investigated in terms of the agglomeration state in typical cell culture media, the traverse of particle agglomerates across U-2 OS cell membranes during endocytosis, the merging of endosomal vesicles during incubation of cells and in the correlation of imaging flow cytometry and transmission electron microscopy to measure the final nanoparticle dose internalized by the U-2 OS cells. We show that a combination of analytical transmission electron microscopy and serial block face scanning electron microscopy can provide a comprehensive description of the internalization of an initial exposure dose of nanoparticles by an endocytically active cell population and how the internalized, membrane bound nanoparticle load is processed by the cells. We present a stochastic model of an endosome merging process and show that this provides a data-driven modelling framework for the prediction of cellular uptake of engineered nanoparticles in general. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Anarchy with linear and bilinear interactions

NASA Astrophysics Data System (ADS)

Da Rold, Leandro

2017-10-01

Composite Higgs models with anarchic partial compositeness require a scale of new physics O(10-100) TeV, with the bounds being dominated by the dipole moments and ɛ K . The presence of anarchic bilinear interactions can change this picture. We show a solution to the SM flavor puzzle where the electron and the Right-handed quarks of the first generation have negligible linear interactions, and the bilinear interactions account for most of their masses, whereas the other chiral fermions follow a similar pattern to anarchic partial compositeness. We compute the bounds from flavor and CP violation and show that neutron and electron dipole moments, as well as ɛ K and μ → eγ, are compatible with a new physics scale below the TeV. Δ F = 2 operators involving Left-handed quarks and Δ F = 1 operators with d L give the most stringent bounds in this scenario. Their Wilson coefficients have the same origin as in anarchic partial compositeness, requiring the masses of the new states to be larger than O(6-7) TeV.

Imaginary-frequency polarizability and van der Waals force constants of two-electron atoms, with rigorous bounds

NASA Technical Reports Server (NTRS)

Glover, R. M.; Weinhold, F.

1977-01-01

Variational functionals of Braunn and Rebane (1972) for the imagery-frequency polarizability (IFP) have been generalized by the method of Gramian inequalities to give rigorous upper and lower bounds, valid even when the true (but unknown) unperturbed wavefunction must be represented by a variational approximation. Using these formulas in conjunction with flexible variational trial functions, tight error bounds are computed for the IFP and the associated two- and three-body van der Waals interaction constants of the ground 1(1S) and metastable 2(1,3S) states of He and Li(+). These bounds generally establish the ground-state properties to within a fraction of a per cent and metastable properties to within a few per cent, permitting a comparative assessment of competing theoretical methods at this level of accuracy. Unlike previous 'error bounds' for these properties, the present results have a completely a priori theoretical character, with no empirical input data.

Benzonitrile: Electron affinity, excited states, and anion solvation

NASA Astrophysics Data System (ADS)

Dixon, Andrew R.; Khuseynov, Dmitry; Sanov, Andrei

2015-10-01

We report a negative-ion photoelectron imaging study of benzonitrile and several of its hydrated, oxygenated, and homo-molecularly solvated cluster anions. The photodetachment from the unsolvated benzonitrile anion to the X ˜ 1 A 1 state of the neutral peaks at 58 ± 5 meV. This value is assigned as the vertical detachment energy (VDE) of the valence anion and the upper bound of adiabatic electron affinity (EA) of benzonitrile. The EA of the lowest excited electronic state of benzonitrile, a ˜ 3 A 1 , is determined as 3.41 ± 0.01 eV, corresponding to a 3.35 eV lower bound for the singlet-triplet splitting. The next excited state, the open-shell singlet A ˜ 1 A 1 , is found about an electron-volt above the triplet, with a VDE of 4.45 ± 0.01 eV. These results are in good agreement with ab initio calculations for neutral benzonitrile and its valence anion but do not preclude the existence of a dipole-bound state of similar energy and geometry. The step-wise and cumulative solvation energies of benzonitrile anions by several types of species were determined, including homo-molecular solvation by benzonitrile, hydration by 1-3 waters, oxygenation by 1-3 oxygen molecules, and mixed solvation by various combinations of O2, H2O, and benzonitrile. The plausible structures of the dimer anion of benzonitrile were examined using density functional theory and compared to the experimental observations. It is predicted that the dimer anion favors a stacked geometry capitalizing on the π-π interactions between the two partially charged benzonitrile moieties.

Evolution of jets driven by relativistic radiation hydrodynamics as Long and Low Luminosity GRBs

NASA Astrophysics Data System (ADS)

Rivera-Paleo, F. J.; Guzmán, F. S.

2018-06-01

We present numerical simulations of jets modeled with Relativistic Radiation Hydrodynamics (RRH), that evolve across two environments: i) a stratified surrounding medium and ii) a 16TI progenitor model. We consider opacities consistent with various processes of interaction between the fluid and radiation, specifically, free-free, bound-free, bound-bound and electron scattering. We explore various initial conditions, with different radiation energy densities of the beam in hydrodynamical and radiation pressure dominated scenarios, considering only highly-relativistic jets. In order to investigate the impact of the radiation field on the evolution of the jets, we compare our results with purely hydrodynamical jets. Comparing among jets driven by RRH, we find that radiation pressure dominated jets propagate slightly faster than gas pressure dominated ones. Finally, we construct the luminosity Light Curves (LCs) associated with the two cases. The construction of LCs uses the fluxes of the radiation field which is fully coupled to the hydrodynamics equations during the evolution. The main properties of the jets propagating on the stratified surrounding medium are that the LCs show the same order of magnitude as the gamma-ray luminosity of typical Long Gamma-Ray Bursts 1050 - 1054erg/s and the difference between the radiation and gas temperatures is of nearly one order of magnitude. The properties of jets breaking out from the progenitor star model are that the LCs are of the order of magnitude of low-luminosity GRBs 1046 - 1049 erg/s, and in this scenario the difference between the gas and radiation temperature is of four orders of magnitude, which is a case far from thermal equilibrium.

Connecting nitrogenase intermediates with the kinetic scheme for N2 reduction by a relaxation protocol and identification of the N2 binding state

PubMed Central

Lukoyanov, Dmitriy; Barney, Brett M.; Dean, Dennis R.; Seefeldt, Lance C.; Hoffman, Brian M.

2007-01-01

A major obstacle to understanding the reduction of N2 to NH3 by nitrogenase has been the impossibility of synchronizing electron delivery to the MoFe protein for generation of specific enzymatic intermediates. When an intermediate is trapped without synchronous electron delivery, the number of electrons, n, it has accumulated is unknown. Consequently, the intermediate is untethered from kinetic schemes for reduction, which are indexed by n. We show that a trapped intermediate itself provides a “synchronously prepared” initial state, and its relaxation to the resting state at 253 K, conditions that prevent electron delivery to MoFe protein, can be analyzed to reveal n and the nature of the relaxation reactions. The approach is applied to the “H+/H− intermediate” (A) that appears during turnover both in the presence and absence of N2 substrate. A exhibits an S = ½ EPR signal from the active-site iron–molybdenum cofactor (FeMo-co) to which are bound at least two hydrides/protons. A undergoes two-step relaxation to the resting state (C): A → B → C, where B has an S = 3/2 FeMo-co. Both steps show large solvent kinetic isotope effects: KIE ≈ 3–4 (85% D2O). In the context of the Lowe–Thorneley kinetic scheme for N2 reduction, these results provide powerful evidence that H2 is formed in both relaxation steps, that A is the catalytically central state that is activated for N2 binding by the accumulation of n = 4 electrons, and that B has accumulated n = 2 electrons. PMID:17251348

Light-induced protoporphyrin release from erythrocytes in erythropoietic protoporphyria.

PubMed Central

Sandberg, S; Brun, A

1982-01-01

The photohemolysis of normal erythrocytes incubated with protoporphyrin is reduced in the presence of albumin. When globin is added to normal erythrocytes loaded with protoporphyrin, protoporphyrin is bound to globin. During irradiation protoporphyrin moves from globin to the erythrocyte membrane and photohemolysis is initiated. Erythrocytes in patients with erythropoietic protoporphyria contain large amounts of protoporphyrin bound to hemoglobin. Upon irradiation of these cells in the absence of albumin, 40% of protoporphyrin and 80% of hemoglobin is released after 240 kJ/m2. The released protoporphyrin is hemoglobin bound. In contrast, when albumin is present only 8% of hemoglobin is released whereas protoporphyrin is released to 76%. The released protoporphyrin is albumin bound. A hypothesis for the release of erythrocyte protoporphyrin in erythropoietic protoporphyria without simultaneous hemolysis is proposed. Upon irradiation protoporphyrin photodamages its binding sites on hemoglobin, moves through the plasma membrane, and is bound to albumin in plasma. PMID:7107898

Spin noise spectroscopy of ZnO

NASA Astrophysics Data System (ADS)

Horn, H.; Berski, F.; Balocchi, A.; Marie, X.; Mansur-Al-Suleiman, M.; Bakin, A.; Waag, A.; Hübner, J.; Oestreich, M.

2013-12-01

We investigate the thermal equilibrium dynamics of electron spins bound to donors in nanoporous ZnO by optical spin noise spectroscopy. The spin noise spectra reveal two noise contributions: A weak spin noise signal from undisturbed localized donor electrons with a dephasing time of 24 ns due to hyperfine interaction and a strong spin noise signal with a spin dephasing time of 5 ns which we attribute to localized donor electrons which interact with lattice defects.

Investigating molecule-semiconductor interfaces with nonlinear spectroscopies

NASA Astrophysics Data System (ADS)

Giokas, Paul George

Knowledge of electronic structures and transport mechanisms at molecule-semiconductor interfaces is motivated by their ubiquity in photoelectrochemical cells. In this dissertation, optical spectroscopies are used uncover the influence of electronic coupling, coherent vibrational motion, and molecular geometry, and other factors on dynamics initiated by light absorption at such interfaces. These are explored for a family of ruthenium bipyridyl chromophores bound to titanium dioxide. Transient absorption measurements show molecular singlet state electron injection in 100 fs or less. Resonance Raman intensity analysis suggests the electronic excitations possess very little charge transfer character. The connections drawn in this work between molecular structure and photophysical behavior contribute to the general understanding of photoelectrochemical cells. Knowledge of binding geometry in nanocrystalline films is challenged by heterogeneity of semiconductor surfaces. Polarized resonance Raman spectroscopy is used to characterize the ruthenium chromophore family on single crystal titanium dioxide . Chromophores display a broad distribution of molecular geometries at the interface, with increased variation in binding angle due to the presence of a methylene bridge, as well as additional phosphonate anchors. This result implies multiple binding configurations for chromophores which incorporate multiple phosphonate ligands, and indicates the need for careful consideration when developing surface-assembled chromophore-catalyst cells. Electron transfer transitions occurring on the 100 fs time scale challenge conventional second-order approximations made when modeling these reactions. A fourth-order perturbative model which includes the relationship between coincident electron transfer and nuclear relaxation processes is presented. Insights provided by the model are illustrated for a two-level donor molecule. The presented fourth-order rate formula constitutes a rigorous and intuitive framework for understanding sub-picosecond photoinduced electron transfer dynamics. Charge transfer systems fit by this model include catechol-sensitized titanium dioxide nanoparticles and a closely-related molecular complex. These systems exhibit vibrational coherence coincident with back-electron transfer in the first picosecond after excitation, which suggests that intramolecular nuclear motion strongly influences the electronic transfer process and plays an important role in the dynamics of interfacial systems following light absorption.

Probing solid catalysts under operating conditions: electrons or X-rays?

PubMed

Thomas, John Meurig; Hernandez-Garrido, Juan-Carlos

2009-01-01

Seeing is believing: In light of recent advances, the pros and cons of using electrons and X-rays for in situ studies of catalysts are analyzed: by using X-rays the structure of bound reactants at steady state are obtained from extended X-ray adsorption fine structure spectroscopy (EXAFS) data (see graph), thereby affording mechanistic insights.

Assessing and Evaluating Department of Defense Efforts to Inform, Influence, and Persuade: Work Example

DTIC Science & Technology

2017-01-01

reviewing and refining their initial objectives to ensure that these objectives are SMART: specific, measurable, achievable, relevant, and time -bound...should not conflate exposure and effectiveness where messaging is concerned, and they should aim to capture trends over time . Assessors should use...specific, measurable, achievable, relevant, and time -bound TAA target audience analysis TCO transnational criminal organization UN United Nations VEO

Analysis of cyanide in whole blood of dosed cathartids

USGS Publications Warehouse

Krynitsky, A.J.; Wiemeyer, Stanley N.; Hill, E.F.; Carpenter, J.W.

1986-01-01

A gas-liquid chromatographic method was modified to quantify both unmetabolized ('free') and metabolized ('bound', i.e., thiocyanates) cyanides. The methods for both are efficient and sensitive to 0.05 ppm. Repeated freezing and thawing of whole blood from treated cathartids caused an initial increase in free cyanide concentrations, followed by a gradual decline to a plateau. Bound cyanide concentrations declined after repeated freezing and thawing.

Optically Based Rapid Screening Method for Proven Optimal Treatment Strategies Before Treatment Begins

DTIC Science & Technology

2015-08-01

lifetime ( t2 ) corresponds to protein- bound NADH (23). Conversely, protein-bound FAD corre- sponds to the short lifetime, whereas free FAD corresponds...single photon counting (TCSPC) electronics (SPC-150, Becker and Hickl). TCSPC uses a fast detector PMT to measure the time between a laser pulse and... Becker and Hickl). A binning of nine surrounding pixels was used. Then, the fluorescence lifetime components were computed for each pixel by deconvolving

Stabilization and control of Majorana bound states with elongated skyrmions

DOE PAGES

Güngördü, Utkan; Sandhoefner, Shane; Kovalev, Alexey A.

2018-03-16

We show that elongated magnetic skyrmions can host Majorana bound states in a proximity-coupled two-dimensional electron gas sandwiched between a chiral magnet and an s-wave superconductor. Our proposal requires stable skyrmions with unit topological charge, which can be realized in a wide range of multilayer magnets, and it allows quantum information transfer by using standard methods in spintronics via skyrmion motion. Finally, we also show how braiding operations can be realized in our proposal.

Protonation-dependent conformational dynamics of the multidrug transporter EmrE

PubMed Central

Dastvan, Reza; Mishra, Smriti; Meiler, Jens; Mchaourab, Hassane S.

2016-01-01

The small multidrug transporter from Escherichia coli, EmrE, couples the energetically uphill extrusion of hydrophobic cations out of the cell to the transport of two protons down their electrochemical gradient. Although principal mechanistic elements of proton/substrate antiport have been described, the structural record is limited to the conformation of the substrate-bound state, which has been shown to undergo isoenergetic alternating access. A central but missing link in the structure/mechanism relationship is a description of the proton-bound state, which is an obligatory intermediate in the transport cycle. Here we report a systematic spin labeling and double electron electron resonance (DEER) study that uncovers the conformational changes of EmrE subsequent to protonation of critical acidic residues in the context of a global description of ligand-induced structural rearrangements. We find that protonation of E14 leads to extensive rotation and tilt of transmembrane helices 1–3 in conjunction with repacking of loops, conformational changes that alter the coordination of the bound substrate and modulate its access to the binding site from the lipid bilayer. The transport model that emerges from our data posits a proton-bound, but occluded, resting state. Substrate binding from the inner leaflet of the bilayer releases the protons and triggers alternating access between inward- and outward-facing conformations of the substrate-loaded transporter, thus enabling antiport without dissipation of the proton gradient. PMID:26787875

Designed Long-Lived Emission from CdSe Quantum Dots through Reversible Electronic Energy Transfer with a Surface-Bound Chromophore.

PubMed

La Rosa, Marcello; Denisov, Sergey A; Jonusauskas, Gediminas; McClenaghan, Nathan D; Credi, Alberto

2018-03-12

The size-tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface-bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self-assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Complex Correlation Kohn-T Method of Calculating Total and Elastic Cross Sections. Part 1; Electron-Hydrogen Elastic Scattering

NASA Technical Reports Server (NTRS)

Bhatia, A. K.; Temkin, A.; Fisher, Richard R. (Technical Monitor)

2001-01-01

We report on the first part of a study of electron-hydrogen scattering, using a method which allows for the ab initio calculation of total and elastic cross sections at higher energies. In its general form the method uses complex 'radial' correlation functions, in a (Kohn) T-matrix formalism. The titled method, abbreviated Complex Correlation Kohn T (CCKT) method, is reviewed, in the context of electron-hydrogen scattering, including the derivation of the equation for the (complex) scattering function, and the extraction of the scattering information from the latter. The calculation reported here is restricted to S-waves in the elastic region, where the correlation functions can be taken, without loss of generality, to be real. Phase shifts are calculated using Hylleraas-type correlation functions with up to 95 terms. Results are rigorous lower bounds; they are in general agreement with those of Schwartz, but they are more accurate and outside his error bounds at a couple of energies,

Mesoscopic structure formation in condensed matter due to vacuum fluctuations

NASA Astrophysics Data System (ADS)

Sen, Siddhartha; Gupta, Kumar S.; Coey, J. M. D.

2015-10-01

An observable influence of zero-point fluctuations of the vacuum electromagnetic field on bound electrons is well known in the hydrogen atom, where it produces the Lamb shift. Here, we adapt an approach used to explain the Lamb shift in terms of a slight expansion of the orbits due to interaction with the zero-point field and apply it to assemblies of N electrons that are modeled as independent atomically bound two-level systems. The effect is to stabilize a collective ground-state energy, which leads to a prediction of novel effects at room temperature for quasi-two-dimensional systems over a range of parameters in the model, namely, N , the two-level excitation energy ℏ ω and the ionization energy ℏ ω +ɛ . Some mesoscopic systems where these effects may be observable include water sheaths on protein or DNA, surfaces of gaseous nanobubbles, and the magnetic response of inhomogeneous, electronically dilute oxides. No such effects are envisaged for uniform three-dimensional systems.

Energy conservation by oxidation of formate to carbon dioxide and hydrogen via a sodium ion current in a hyperthermophilic archaeon

PubMed Central

Lim, Jae Kyu; Mayer, Florian; Kang, Sung Gyun; Müller, Volker

2014-01-01

Thermococcus onnurineus NA1 is known to grow by the anaerobic oxidation of formate to CO2 and H2, a reaction that operates near thermodynamic equilibrium. Here we demonstrate that this reaction is coupled to ATP synthesis by a transmembrane ion current. Formate oxidation leads to H+ translocation across the cytoplasmic membrane that then drives Na+ translocation. The ion-translocating electron transfer system is rather simple, consisting of only a formate dehydrogenase module, a membrane-bound hydrogenase module, and a multisubunit Na+/H+ antiporter module. The electrochemical Na+ gradient established then drives ATP synthesis. These data give a mechanistic explanation for chemiosmotic energy conservation coupled to formate oxidation to CO2 and H2. Because it is discussed that the membrane-bound hydrogenase with the Na+/H+ antiporter module are ancestors of complex I of mitochondrial and bacterial electron transport these data also shed light on the evolution of ion transport in complex I-like electron transport chains. PMID:25049407

Energy conservation by oxidation of formate to carbon dioxide and hydrogen via a sodium ion current in a hyperthermophilic archaeon.

PubMed

Lim, Jae Kyu; Mayer, Florian; Kang, Sung Gyun; Müller, Volker

2014-08-05

Thermococcus onnurineus NA1 is known to grow by the anaerobic oxidation of formate to CO2 and H2, a reaction that operates near thermodynamic equilibrium. Here we demonstrate that this reaction is coupled to ATP synthesis by a transmembrane ion current. Formate oxidation leads to H(+) translocation across the cytoplasmic membrane that then drives Na(+) translocation. The ion-translocating electron transfer system is rather simple, consisting of only a formate dehydrogenase module, a membrane-bound hydrogenase module, and a multisubunit Na(+)/H(+) antiporter module. The electrochemical Na(+) gradient established then drives ATP synthesis. These data give a mechanistic explanation for chemiosmotic energy conservation coupled to formate oxidation to CO2 and H2. Because it is discussed that the membrane-bound hydrogenase with the Na(+)/H(+) antiporter module are ancestors of complex I of mitochondrial and bacterial electron transport these data also shed light on the evolution of ion transport in complex I-like electron transport chains.

Graphene quantum blisters: A tunable system to confine charge carriers

NASA Astrophysics Data System (ADS)

Abdullah, H. M.; Van der Donck, M.; Bahlouli, H.; Peeters, F. M.; Van Duppen, B.

2018-05-01

Due to Klein tunneling, electrostatic confinement of electrons in graphene is not possible. This hinders the use of graphene for quantum dot applications. Only through quasi-bound states with finite lifetime has one achieved to confine charge carriers. Here, we propose that bilayer graphene with a local region of decoupled graphene layers is able to generate bound states under the application of an electrostatic gate. The discrete energy levels in such a quantum blister correspond to localized electron and hole states in the top and bottom layers. We find that this layer localization and the energy spectrum itself are tunable by a global electrostatic gate and that the latter also coincides with the electronic modes in a graphene disk. Curiously, states with energy close to the continuum exist primarily in the classically forbidden region outside the domain defining the blister. The results are robust against variations in size and shape of the blister which shows that it is a versatile system to achieve tunable electrostatic confinement in graphene.

Atomic Resolution Cryo-EM Structure of β-Galactosidase.

PubMed

Bartesaghi, Alberto; Aguerrebere, Cecilia; Falconieri, Veronica; Banerjee, Soojay; Earl, Lesley A; Zhu, Xing; Grigorieff, Nikolaus; Milne, Jacqueline L S; Sapiro, Guillermo; Wu, Xiongwu; Subramaniam, Sriram

2018-05-10

The advent of direct electron detectors has enabled the routine use of single-particle cryo-electron microscopy (EM) approaches to determine structures of a variety of protein complexes at near-atomic resolution. Here, we report the development of methods to account for local variations in defocus and beam-induced drift, and the implementation of a data-driven dose compensation scheme that significantly improves the extraction of high-resolution information recorded during exposure of the specimen to the electron beam. These advances enable determination of a cryo-EM density map for β-galactosidase bound to the inhibitor phenylethyl β-D-thiogalactopyranoside where the ordered regions are resolved at a level of detail seen in X-ray maps at ∼ 1.5 Å resolution. Using this density map in conjunction with constrained molecular dynamics simulations provides a measure of the local flexibility of the non-covalently bound inhibitor and offers further opportunities for structure-guided inhibitor design. Published by Elsevier Ltd.

Two-color ionization injection using a plasma beatwave accelerator

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

Schroeder, C. B.; Benedetti, C.; Esarey, E.

Two-color laser ionization injection is a method to generate ultra-low emittance (sub-100 nm transverse normalized emittance) beams in a laser-driven plasma accelerator. A plasma beatwave accelerator is proposed to drive the plasma wave for ionization injection, where the beating of the lasers effectively produces a train of long-wavelength pulses. The plasma beatwave accelerator excites a large amplitude plasma wave with low peak laser electric fields, leaving atomically-bound electrons with low ionization potential. A short-wavelength, low-amplitude ionization injection laser pulse (with a small ponderomotive force and large peak electric field) is used to ionize the remaining bound electrons at a wakemore » phase suitable for trapping, generating an ultra-low emittance electron beam that is accelerated in the plasma wave. Using a plasma beatwave accelerator for wakefield excitation, compared to short-pulse wakefield excitation, allows for a lower amplitude injection laser pulse and, hence, a lower emittance beam may be generated.« less

Two-color ionization injection using a plasma beatwave accelerator

DOE PAGES

Schroeder, C. B.; Benedetti, C.; Esarey, E.; ...

2018-01-10

Two-color laser ionization injection is a method to generate ultra-low emittance (sub-100 nm transverse normalized emittance) beams in a laser-driven plasma accelerator. A plasma beatwave accelerator is proposed to drive the plasma wave for ionization injection, where the beating of the lasers effectively produces a train of long-wavelength pulses. The plasma beatwave accelerator excites a large amplitude plasma wave with low peak laser electric fields, leaving atomically-bound electrons with low ionization potential. A short-wavelength, low-amplitude ionization injection laser pulse (with a small ponderomotive force and large peak electric field) is used to ionize the remaining bound electrons at a wakemore » phase suitable for trapping, generating an ultra-low emittance electron beam that is accelerated in the plasma wave. Using a plasma beatwave accelerator for wakefield excitation, compared to short-pulse wakefield excitation, allows for a lower amplitude injection laser pulse and, hence, a lower emittance beam may be generated.« less

Magnetic hard gap due to bound magnetic polarons in the localized regime.

PubMed

Rimal, Gaurab; Tang, Jinke

2017-02-08

We investigate the low temperature electron transport properties of manganese doped lead sulfide films. The system shows variable range hopping at low temperatures that crosses over into an activation regime at even lower temperatures. This crossover is destroyed by an applied magnetic field which suggests a magnetic origin of the hard gap, associated with bound magnetic polarons. Even though the gap forms around the superconducting transition temperature of lead, we do not find evidence of this being due to insulator-superconductor transition. Comparison with undoped PbS films, which do not show the activated transport behavior, suggests that bound magnetic polarons create the hard gap in the system that can be closed by magnetic fields.

Free-standing leaping experiments with a power-autonomous elastic-spined quadruped

NASA Astrophysics Data System (ADS)

Pusey, Jason L.; Duperret, Jeffrey M.; Haynes, G. Clark; Knopf, Ryan; Koditschek, Daniel E.

2013-05-01

We document initial experiments with Canid, a freestanding, power-autonomous quadrupedal robot equipped with a parallel actuated elastic spine. Research into robotic bounding and galloping platforms holds scientific and engineering interest because it can both probe biological hypotheses regarding bounding and galloping mammals and also provide the engineering community with a new class of agile, efficient and rapidly-locomoting legged robots. We detail the design features of Canid that promote our goals of agile operation in a relatively cheap, conventionally prototyped, commercial off-the-shelf actuated platform. We introduce new measurement methodology aimed at capturing our robot's "body energy" during real time operation as a means of quantifying its potential for agile behavior. Finally, we present joint motor, inertial and motion capture data taken from Canid's initial leaps into highly energetic regimes exhibiting large accelerations that illustrate the use of this measure and suggest its future potential as a platform for developing efficient, stable, hence useful bounding gaits.

Superconductivity versus bound-state formation in a two-band superconductor with small Fermi energy: Applications to Fe pnictides/chalcogenides and doped SrTiO3

NASA Astrophysics Data System (ADS)

Chubukov, Andrey V.; Eremin, Ilya; Efremov, Dmitri V.

2016-05-01

We analyze the interplay between superconductivity and the formation of bound pairs of fermions (BCS-BEC crossover) in a 2D model of interacting fermions with small Fermi energy EF and weak attractive interaction, which extends to energies well above EF. The 2D case is special because a two-particle bound state forms at arbitrary weak interaction, and already at weak coupling, one has to distinguish between the bound-state formation and superconductivity. We briefly review the situation in the one-band model and then consider two different two-band models: one with one hole band and one electron band and another with two hole or two electron bands. In each case, we obtain the bound-state energy 2 E0 for two fermions in a vacuum and solve the set of coupled equations for the pairing gaps and the chemical potentials to obtain the onset temperature of the pairing Tins and the quasiparticle dispersion at T =0 . We then compute the superfluid stiffness ρs(T =0 ) and obtain the actual Tc. For definiteness, we set EF in one band to be near zero and consider different ratios of E0 and EF in the other band. We show that at EF≫E0 , the behavior of both two-band models is BCS-like in the sense that Tc≈Tins≪EF and Δ ˜Tc . At EF≪E0 , the two models behave differently: in the model with two hole/two electron bands, Tins˜E0/lnE/0EF , Δ ˜(E0EF) 1 /2 , and Tc˜EF , like in the one-band model. In between Tins and Tc, the system displays a preformed pair behavior. In the model with one hole and one electron bands, Tc remains of order Tins, and both remain finite at EF=0 and of the order of E0. The preformed pair behavior still does exist in this model because Tc is numerically smaller than Tins. For both models, we reexpress Tins in terms of the fully renormalized two-particle scattering amplitude by extending to the two-band case (the method pioneered by Gorkov and Melik-Barkhudarov back in 1961). We apply our results for the model with a hole and an electron band to Fe pnictides and Fe chalcogenides in which a superconducting gap has been detected on the bands that do not cross the Fermi level, and to FeSe, in which the superconducting gap is comparable to the Fermi energy. We apply the results for the model with two electron bands to Nb-doped SrTiO3 and argue that our theory explains the rapid increase of Tc when both bands start crossing the Fermi level.

Peptide π-Electron Conjugates: Organic Electronics for Biology?

PubMed

Ardoña, Herdeline Ann M; Tovar, John D

2015-12-16

Highly ordered arrays of π-conjugated molecules are often viewed as a prerequisite for effective charge-transporting materials. Studies involving these materials have traditionally focused on organic electronic devices, with more recent emphasis on biological systems. In order to facilitate the transition to biological environments, biomolecules that can promote hierarchical ordering and water solubility are often covalently appended to the π-electron unit. This review highlights recent work on π-conjugated systems bound to peptide moieties that exhibit self-assembly and aims to provide an overview on the development and emerging applications of peptide-based supramolecular π-electron systems.

Spacecraft Observations and Analytic Theory of Crescent-Shaped Electron Distributions in Asymmetric Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Egedal, J.; Le, A.; Daughton, W.; Wetherton, B.; Cassak, P. A.; Chen, L.-J.; Lavraud, B.; Torbert, R. B.; Dorelli, J.; Gershman, D. J.; Avanov, L. A.

2016-10-01

Supported by a kinetic simulation, we derive an exclusion energy parameter EX providing a lower kinetic energy bound for an electron to cross from one inflow region to the other during magnetic reconnection. As by a Maxwell demon, only high-energy electrons are permitted to cross the inner reconnection region, setting the electron distribution function observed along the low-density side separatrix during asymmetric reconnection. The analytic model accounts for the two distinct flavors of crescent-shaped electron distributions observed by spacecraft in a thin boundary layer along the low-density separatrix.

Spacecraft Observations and Analytic Theory of Crescent-Shaped Electron Distributions in Asymmetric Magnetic Reconnection

NASA Technical Reports Server (NTRS)

Egedal, J.; Le, A.; Daughton, W.; Wetherton, B.; Cassak, P.A.; Chen, L.-J.; Lavraud, B.; Trobert, Roy; Dorelli, J.; Gershman, D. J.;

Live-cell analysis of endogenous GFP-RPB1 uncovers rapid turnover of initiating and promoter-paused RNA Polymerase II.

PubMed

Steurer, Barbara; Janssens, Roel C; Geverts, Bart; Geijer, Marit E; Wienholz, Franziska; Theil, Arjan F; Chang, Jiang; Dealy, Shannon; Pothof, Joris; van Cappellen, Wiggert A; Houtsmuller, Adriaan B; Marteijn, Jurgen A

2018-05-08

Initiation and promoter-proximal pausing are key regulatory steps of RNA Polymerase II (Pol II) transcription. To study the in vivo dynamics of endogenous Pol II during these steps, we generated fully functional GFP-RPB1 knockin cells. GFP-RPB1 photobleaching combined with computational modeling revealed four kinetically distinct Pol II fractions and showed that on average 7% of Pol II are freely diffusing, while 10% are chromatin-bound for 2.4 seconds during initiation, and 23% are promoter-paused for only 42 seconds. This unexpectedly high turnover of Pol II at promoters is most likely caused by premature termination of initiating and promoter-paused Pol II and is in sharp contrast to the 23 minutes that elongating Pol II resides on chromatin. Our live-cell-imaging approach provides insights into Pol II dynamics and suggests that the continuous release and reinitiation of promoter-bound Pol II is an important component of transcriptional regulation. Copyright © 2018 the Author(s). Published by PNAS.

Optical identification of sulfur vacancies: Bound excitons at the edges of monolayer tungsten disulfide

PubMed Central

Carozo, Victor; Wang, Yuanxi; Fujisawa, Kazunori; Carvalho, Bruno R.; McCreary, Amber; Feng, Simin; Lin, Zhong; Zhou, Chanjing; Perea-López, Néstor; Elías, Ana Laura; Kabius, Bernd; Crespi, Vincent H.; Terrones, Mauricio

2017-01-01

Defects play a significant role in tailoring the optical properties of two-dimensional materials. Optical signatures of defect-bound excitons are important tools to probe defective regions and thus interrogate the optical quality of as-grown semiconducting monolayer materials. We have performed a systematic study of defect-bound excitons using photoluminescence (PL) spectroscopy combined with atomically resolved scanning electron microscopy and first-principles calculations. Spatially resolved PL spectroscopy at low temperatures revealed bound excitons that were present only on the edges of monolayer tungsten disulfide and not in the interior. Optical pumping of the bound excitons was sublinear, confirming their bound nature. Atomic-resolution images reveal that the areal density of monosulfur vacancies is much larger near the edges (0.92 ± 0.45 nm−2) than in the interior (0.33 ± 0.11 nm−2). Temperature-dependent PL measurements found a thermal activation energy of ~36 meV; surprisingly, this is much smaller than the bound-exciton binding energy of ~300 meV. We show that this apparent inconsistency is related to a thermal dissociation of the bound exciton that liberates the neutral excitons from negatively charged point defects. First-principles calculations confirm that sulfur monovacancies introduce midgap states that host optical transitions with finite matrix elements, with emission energies ranging from 200 to 400 meV below the neutral-exciton emission line. These results demonstrate that bound-exciton emission induced by monosulfur vacancies is concentrated near the edges of as-grown monolayer tungsten disulfide. PMID:28508048

A Multidimensional View of Personal Health Systems for Underserved Populations

PubMed Central

Botts, Nathan E; Burkhard, Richard J

2010-01-01

The advent of electronic personal health records (PHR) provides a major opportunity to encourage positive health management practices, such as chronic disease management. Yet, to date there has been little attention toward the use of PHRs where advanced health information services are perhaps most needed, namely, in underserved communities. Drawing upon research conducted with safety net providers and patients, the authors propose a multi-level analytical framework for guiding actions aimed at fostering PHR adoption and utilization. The authors first outline distinctive user and technical requirements that need to be considered. Next, they assess organizational requirements necessary to implement PHRs within health systems bound by limited resources. Finally, the authors analyze the overriding health care policy context that can facilitate or thwart such efforts. The conclusion notes that heightened national attention toward health information technology and reform provides a significant opportunity for initiatives whose goal is to increase widepread access to PHRs. PMID:20685644

Revisiting the Supramolecular Organization of Photosystem II in Chlamydomonas reinhardtii*

PubMed Central

Tokutsu, Ryutaro; Kato, Nobuyasu; Bui, Khanh Huy; Ishikawa, Takashi; Minagawa, Jun

2012-01-01

Photosystem II (PSII) is a multiprotein complex that splits water and initiates electron transfer in photosynthesis. The central part of PSII, the PSII core, is surrounded by light-harvesting complex II proteins (LHCIIs). In higher plants, two or three LHCII trimers are seen on each side of the PSII core whereas only one is seen in the corresponding positions in Chlamydomonas reinhardtii, probably due to the absence of CP24, a minor monomeric LHCII. Here, we re-examined the supramolecular organization of the C. reinhardtii PSII-LHCII supercomplex by determining the effect of different solubilizing detergents. When we solubilized the thylakoid membranes with n-dodecyl-β-d-maltoside (β-DM) or n-dodecyl-α-d-maltoside (α-DM) and subjected them to gel filtration, we observed a clear difference in molecular mass. The α-DM-solubilized PSII-LHCII supercomplex bound twice more LHCII than the β-DM-solubilized supercomplex and retained higher oxygen-evolving activity. Single-particle image analysis from electron micrographs of the α-DM-solubilized and negatively stained supercomplex revealed that the PSII-LHCII supercomplex had a novel supramolecular organization, with three LHCII trimers attached to each side of the core. PMID:22801422

Light-induced covalent immobilization of monolayers of magnetic nanoparticles on hydrogen-terminated silicon.

PubMed

Leem, Gyu; Zhang, Shishan; Jamison, Andrew C; Galstyan, Eduard; Rusakova, Irene; Lorenz, Bernd; Litvinov, Dmitri; Lee, T Randall

2010-10-01

Specifically tailored ω-alkenyl-1-carboxylic acids were synthesized for use as surfactants in the single-step preparation of manganese ferrite (MnFe2O4) nanoparticles (NPs). Monodisperse manganese ferrite NPs terminated with ω-alkenyl moieties were prepared via a one-pot reaction at high temperature without the need of ligand exchange. Using this approach, simple adjustment of the rate of heating allowed precise tuning of the size of the nanoparticles, which were characterized in bulk form by transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD). These surfactant-coated magnetic nanoparticles were then deposited onto hydrogen-terminated silicon(111) wafers and covalently anchored to the surface by UV-initiated covalent bonding. Analysis by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) confirmed that the UV treatment led to covalent immobilization of the NPs on the silicon surface with a consistent packing density across the surface. The magnetic properties of the stable, surface-bound nanoparticle arrays were characterized using a superconducting quantum interference device (SQUID) magnetometer. The materials and methods described here are being developed for use in bit-patterned ultrahigh density magnetic recording media and nanoscale biomagnetic sensing.

Many-body effects in valleytronics: direct measurement of valley lifetimes in single-layer MoS2.

PubMed

Mai, Cong; Barrette, Andrew; Yu, Yifei; Semenov, Yuriy G; Kim, Ki Wook; Cao, Linyou; Gundogdu, Kenan

2014-01-08

Single layer MoS2 is an ideal material for the emerging field of "valleytronics" in which charge carrier momentum can be finely controlled by optical excitation. This system is also known to exhibit strong many-body interactions as observed by tightly bound excitons and trions. Here we report direct measurements of valley relaxation dynamics in single layer MoS2, by using ultrafast transient absorption spectroscopy. Our results show that strong Coulomb interactions significantly impact valley population dynamics. Initial excitation by circularly polarized light creates electron-hole pairs within the K-valley. These excitons coherently couple to dark intervalley excitonic states, which facilitate fast electron valley depolarization. Hole valley relaxation is delayed up to about 10 ps due to nondegeneracy of the valence band spin states. Intervalley biexciton formation reveals the hole valley relaxation dynamics. We observe that biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors. These measurements provide significant insight into valley specific processes in 2D semiconductors. Hence they could be used to suggest routes to design semiconducting materials that enable control of valley polarization.

The Surface Chemistry of Metal Chalcogenide Nanocrystals

NASA Astrophysics Data System (ADS)

Anderson, Nicholas Charles

The surface chemistry of metal chalcogenide nanocrystals is explored through several interrelated analytical investigations. After a brief discussion of the nanocrystal history and applications, molecular orbital theory is used to describe the electronic properties of semiconductors, and how these materials behave on the nanoscale. Quantum confinement plays a major role in dictating the optical properties of metal chalcogenide nanocrystals, however surface states also have an equally significant contribution to the electronic properties of nanocrystals due to the high surface area to volume ratio of nanoscale semiconductors. Controlling surface chemistry is essential to functionalizing these materials for biological imaging and photovoltaic device applications. To better understand the surface chemistry of semiconducting nanocrystals, three competing surface chemistry models are presented: 1.) The TOPO model, 2.) the Non-stoichiometric model, and 3.) the Neutral Fragment model. Both the non-stoichiometric and neutral fragment models accurately describe the behavior of metal chalcogenide nanocrystals. These models rely on the covalent bond classification system, which divides ligands into three classes: 1.) X-type, 1-electron donating ligands that balance charge with excess metal at the nanocrystal surface, 2.) L-type, 2-electron donors that bind metal sites, and 3.) Z-type, 2-electron acceptors that bind chalcogenide sites. Each of these ligand classes is explored in detail to better understand the surface chemistry of metal chalcogenide nanocrystals. First, chloride-terminated, tri-n-butylphosphine (Bu 3P) bound CdSe nanocrystals were prepared by cleaving carboxylate ligands from CdSe nanocrystals with chlorotrimethylsilane in Bu3P solution. 1H and 31P{1H} nuclear magnetic resonance spectra of the isolated nanocrystals allowed assignment of distinct signals from several free and bound species, including surface-bound Bu3P and [Bu3P-H]+[Cl]- ligands as well as a Bu3P complex of cadmium chloride. Nuclear magnetic resonance spectroscopy supports complete cleavage of the X-type carboxylate ligands. Combined with measurements of the Se:Cd:Cl ratio using Rutherford backscattering spectrometry, these studies support a structural model of nanocrystals where chloride ligands terminate the crystal lattice by balancing the charges of excess Cd2+ ions. The adsorption of dative phosphine ligands leads to nanocrystals who's solubility is afforded by reversibly bound and readily exchanged L-type ligands, e.g. primary amines and phosphines. The other halides (Br and I) can also be used to prepare Bu 3P-bound, halide-terminated CdSe nanocrystals, however these nanocrystals are not soluble after exchange. The change in binding affinity of Bu 3P over the halide series is briefly discussed. Next, we report a series of L-type ligand exchanges using Bu3P-bound, chloride-terminated CdSe nanocrystals with several Lewis bases, including aromatic, cyclic, and non-cyclic sulfides, and ethers; primary, secondary, and tertiary amines and phosphines; tertiary phosphine chalcogenides; primary alcohols, isocyanides, and isothiocyanides. Using 31P nuclear magnetic resonance spectroscopy, we establish a relative binding affinity for these ligands that reflects electronic considerations but is dominated primarily by steric interactions, as determined by comparing binding affinity to Tolmann cone angles. We also used chloride-terminated CdSe nanocrystals to explore the reactivity of ionic salts at nanocrystal surfaces. These salts, particularly [Bu3P-H]+[Cl]-, bind nanocrystals surfaces as L-type ligands, making them soluble in polar solvents such as acetonitrile. This information should provide insight for rational ligand design for future applications involving metal chalcogenide nanocrystals. The strongest ligand, primary n-alkylamine, rapidly displace the Bu3P from halide-terminated CdSe nanocrystals, leading to amine-bound nanocrystals with higher dative ligand coverages and greatly increased photoluminescence quantum yields. The importance of ligand coverage to both the UV-visible absorption and photoluminescence spectra are discussed. (Abstract shortened by UMI.).

Notes on Barkas-Andersen effect

NASA Astrophysics Data System (ADS)

Sigmund, Peter; Schinner, Andreas

2014-10-01

Stimulated by recent statements in the literature on electronic stopping of heavy ions in matter, we try to clarify some central theoretical aspects of the Barkas-Andersen effect, about which there does not seem to be unanimous agreement in the community. We address the role of inner versus outer target shells, of projectile screening by bound electrons, the interference between Lindhard's description and perturbation theory, as well as the equivalence between a single-electron versus Fermi-gas description of the effect.

Quasi-bound states in strained graphene

NASA Astrophysics Data System (ADS)

Bahamon, Dario; Qi, Zenan; Park, Harold; Pareira, Vitor; Campbell, David

In this work, we explore the possibility of manipulating electronic states in graphene nanostructures by mechanical means. Specifically, we use molecular dynamics and tight-binding models to access the electronic and transport properties of strained graphene nanobubbles and graphene kirigami. We establish that low energy electrons can be confined in the arms of the kirigami and within the nanobubbles; under different load conditions the coupling between confined states and continuous states is modified creating different conductance line-shapes.

Ionization-potential depression and other dense plasma statistical property studies - Application to spectroscopic diagnostics.

NASA Astrophysics Data System (ADS)

Calisti, Annette; Ferri, Sandrine; Mossé, Caroline; Talin, Bernard

2017-02-01

The radiative properties of an emitter surrounded by a plasma, are modified through various mechanisms. For instance the line shapes emitted by bound-bound transitions are broadened and carry useful information for plasma diagnostics. Depending on plasma conditions the electrons occupying the upper quantum levels of radiators no longer exist as they belong to the plasma free electron population. All the charges present in the radiator environment contribute to the lowering of the energy required to free an electron in the fundamental state. This mechanism is known as ionization potential depression (IPD). The knowledge of IPD is useful as it affects both the radiative properties of the various ionic states and their populations. Its evaluation deals with highly complex n-body coupled systems, involving particles with different dynamics and attractive ion-electron forces. A classical molecular dynamics (MD) code, the BinGo-TCP code, has been recently developed to simulate neutral multi-component (various charge state ions and electrons) plasma accounting for all the charge correlations. In the present work, results on IPD and other dense plasma statistical properties obtained using the BinGo-TCP code are presented. The study focuses on aluminum plasmas for different densities and several temperatures in order to explore different plasma coupling conditions.

Distinguishing Majorana bound states from localized Andreev bound states by interferometry

NASA Astrophysics Data System (ADS)

Hell, Michael; Flensberg, Karsten; Leijnse, Martin

2018-04-01

Experimental evidence for Majorana bound states (MBSs) is so far mainly based on the robustness of a zero-bias conductance peak. However, similar features can also arise due to Andreev bound states (ABSs) localized at the end of an island. We show that these two scenarios can be distinguished by an interferometry experiment based on embedding a Coulomb-blockaded island into an Aharonov-Bohm ring. For two ABSs, when the ground state is nearly degenerate, cotunneling can change the state of the island, and interference is suppressed. By contrast, for two MBSs the ground state is nondegenerate, and cotunneling has to preserve the island state, which leads to h /e -periodic conductance oscillations with magnetic flux. Such interference setups can be realized with semiconducting nanowires or two-dimensional electron gases with proximity-induced superconductivity and may also be a useful spectroscopic tool for parity-flip mechanisms.

Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex.

PubMed

Lennox, J Christian; Dempsey, Jillian L

2017-11-22

A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru 3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pK a units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.

Calculations of the Auger deexcitation rate of dtμ within the muonic quasimolecule (dtμ)dee

NASA Astrophysics Data System (ADS)

Armour, E. A. G.; Lewis, D. M.; Hara, S.

1992-12-01

A key process in muon-catalyzed fusion is the deexcitation of dtμ within the resonant muonic quasimolecule (dtμ)dee, by emission of an Auger electron. The dtμ in the quasimolecule is initially in a weakly bound excited state with J=1 and v=1. Calculations are carried out of the rate of the dominant transition to the state with J=0 and v=1. Use is made of the dipole matrix element obtained for this transition by Scrinzi and Szalewicz [Phys. Rev. A 39, 2855 (1989)]. Full account is taken of the molecular nature of the quasimolecule. The continuum electronic wave functions for the Auger electron for all four contributing symmetries, i.e., Σ+g, Σ+u, Πu, and Πg, are first obtained by a two-center Coulomb calculation and a static-exchange calculation, extended to include dipole polarization. Comparison is then made with the results of a calculation in which the Σ+μ and Πu wave functions are obtained as in a previous paper by Armour and Lewis [J. Phys. B 23, L25 (1990)] and the Σ+g and Πg wave functions are obtained by the Kohn method. There are significant differences between the contributions from the individual symmetries, but the overall values for the deexcitation rate are all of the same order of magnitude as the results of earlier calculations.

Fate of phenanthrene and mineralization of its non-extractable residues in an oxic soil.

PubMed

Wang, Yongfeng; Xu, Jun; Shan, Jun; Ma, Yini; Ji, Rong

2017-05-01

The fate of organic pollutants in the environment, especially the formation and stability of non-extractable (i.e., bound) residues (NERs) determines their environmental risk. Using 14 C-tracers, we studied the fate of the carcinogen phenanthrene in active or sterilized oxic loamy soil in the absence and presence of the geophagous earthworm Metaphire guillelmi and characterized the NERs derived from phenanthrene. After incubation of 14 C-phenanthrene in active soil for 28 days, 40 ± 3.1% of the initial amount was mineralized and 70.1 ± 1.9% was converted to NERs. Most of the NERs (>92%) were bound to soil humin. Silylation of the humin-bound residues released 45.3 ± 5.3% of these residues, which indicated that they were physically entrapped, whereas the remainder of the residues were chemically bound or biogenic. By contrast, in sterilized soil, only 43.4 ± 12.6% of the phenanthrene was converted to NERs and all of these residues were completely released upon silylation, which underlines the essential role of microbial activity in NER formation. The presence of M. guillelmi in active soil significantly inhibited phenanthrene mineralization (24.4 ± 2.6% mineralized), but NER formation was not significantly affected. Only a small amount of phenanthrene-derived residues (1.9-5.3% of the initial amount) accumulated in the earthworm body. When humin-bound residues were mixed with fresh soil, 33.9% (humin recovered from active soils) and 12.4% (humin recovered from sterilized soils) of the residues were mineralized after 75 days of incubation, respectively, which indicated a high bioavailability of NERs, albeit lower than the initial addition of phenanthrene. Our results indicated that many phenanthrene-derived NERs, especially those physically entrapped, are still bioavailable and may pose a toxic threat to soil organisms. Copyright © 2017 Elsevier Ltd. All rights reserved.

Cisplatin Radiosensitization of DNA Irradiated with 2-20 eV Electrons: Role of Transient Anions.

PubMed

Bao, Qianhong; Chen, Yunfeng; Zheng, Yi; Sanche, Léon

2014-06-20

Platinum chemotherapeutic agents, such as cisplatin ( cis -diamminedichloroplatinum(II)), can act as radiosensitizers when bound covalently to nuclear DNA in cancer cells. This radiosensitization is largely due to an increase in DNA damage induced by low-energy secondary electrons, produced in large quantities by high-energy radiation. We report the yields of single- and double-strand breaks (SSB and DSB) and interduplex cross-links (CL) induced by electrons of 1.6-19.6 eV (i.e., the yield functions) incident on 5 monolayer (ML) films of cisplatin-DNA complexes. These yield functions are compared with those previously recorded with 5 ML films of unmodified plasmid DNA. Binding of five cisplatin molecules to plasmid DNA (3197 base pairs) enhances SSB, DSB, and CL by factors varying, from 1.2 to 2.8, 1.4 to 3.5, and 1.2 to 2.7, respectively, depending on electron energy. All yield functions exhibit structures around 5 and 10 eV that can be attributed to enhancement of bond scission, via the initial formation of core-excited resonances associated with π → π * transitions of the bases. This increase in damage is interpreted as arising from a modification of the parameters of the corresponding transient anions already present in nonmodified DNA, particularly those influencing molecular dissociation. Two additional resonances, specific to cisplatin-modified DNA, are formed at 13.6 and 17.6 eV in the yield function of SSB. Furthermore, cisplatin binding causes the induction of DSB by electrons of 1.6-3.6 eV, i.e., in an energy region where a DSB cannot be produced by a single electron in pure DNA. Breaking two bonds with a subexcitation-energy electron is tentatively explained by a charge delocalization mechanism, where a single electron occupies simultaneously two σ * bonds linking the Pt atom to guanine bases on opposite strands.

Cisplatin Radiosensitization of DNA Irradiated with 2–20 eV Electrons: Role of Transient Anions

PubMed Central

Bao, Qianhong; Chen, Yunfeng; Zheng, Yi; Sanche, Léon

2015-01-01

Platinum chemotherapeutic agents, such as cisplatin (cis-diamminedichloroplatinum(II)), can act as radiosensitizers when bound covalently to nuclear DNA in cancer cells. This radiosensitization is largely due to an increase in DNA damage induced by low-energy secondary electrons, produced in large quantities by high-energy radiation. We report the yields of single- and double-strand breaks (SSB and DSB) and interduplex cross-links (CL) induced by electrons of 1.6–19.6 eV (i.e., the yield functions) incident on 5 monolayer (ML) films of cisplatin–DNA complexes. These yield functions are compared with those previously recorded with 5 ML films of unmodified plasmid DNA. Binding of five cisplatin molecules to plasmid DNA (3197 base pairs) enhances SSB, DSB, and CL by factors varying, from 1.2 to 2.8, 1.4 to 3.5, and 1.2 to 2.7, respectively, depending on electron energy. All yield functions exhibit structures around 5 and 10 eV that can be attributed to enhancement of bond scission, via the initial formation of core-excited resonances associated with π → π* transitions of the bases. This increase in damage is interpreted as arising from a modification of the parameters of the corresponding transient anions already present in nonmodified DNA, particularly those influencing molecular dissociation. Two additional resonances, specific to cisplatin-modified DNA, are formed at 13.6 and 17.6 eV in the yield function of SSB. Furthermore, cisplatin binding causes the induction of DSB by electrons of 1.6–3.6 eV, i.e., in an energy region where a DSB cannot be produced by a single electron in pure DNA. Breaking two bonds with a subexcitation-energy electron is tentatively explained by a charge delocalization mechanism, where a single electron occupies simultaneously two σ* bonds linking the Pt atom to guanine bases on opposite strands. PMID:26793285

Calculating Rayleigh scattering amplitudes from 100 eV to 10 MeV. [100 eV to 10 MeV

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

Parker, J.C.; Reynaud, G.W.; Botto, D.J.

1979-05-01

An attempt is made to explain how to calculate the contribution to elastic photon-atom scattering due to Rayleigh scattering (the scattering off bound electrons) in the photon energy range 100 eV less than or equal to W less than or equal to 10 MeV. All intermediate calculations are described, including the calculation of the potential, bound state wave functions, matrix elements, and final cross sections. 12 references. (JFP)

Unbound states in quantum heterostructures

PubMed Central

Bastard, G

2006-01-01

We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron – hole states. The part played by Auger scattering in Quantum Dots is also discussed.

Calculation of the Energy-Band Structure of the Kronig-Penney Model Using the Nearly-Free and Tightly-Bound-Electron Approximations

ERIC Educational Resources Information Center

Wetsel, Grover C., Jr.

1978-01-01

Calculates the energy-band structure of noninteracting electrons in a one-dimensional crystal using exact and approximate methods for a rectangular-well atomic potential. A comparison of the two solutions as a function of potential-well depth and ratio of lattice spacing to well width is presented. (Author/GA)

Excessive distribution of quantum entanglement

NASA Astrophysics Data System (ADS)

Zuppardo, Margherita; Krisnanda, Tanjung; Paterek, Tomasz; Bandyopadhyay, Somshubhro; Banerjee, Anindita; Deb, Prasenjit; Halder, Saronath; Modi, Kavan; Paternostro, Mauro

2016-01-01

We classify entanglement distribution protocols based on whether or not entanglement gain is observed with respect to communicated and initial entanglement. We call a protocol nonexcessive if the gain of entanglement is bounded by the communicated entanglement and excessive if it violates this bound. We present examples of excessive protocols that achieve significant gain, independently of the presence of the initial and (or) communicated entanglement. We show that, for certain entanglement measures, excessive entanglement distribution is possible even with pure states, which sheds light on the possibility of formulating a unifying approach to quantifiers of quantum correlations. We point out a "catalytic" effect, where a protocol is turned into an excessive one by sending an intermediate particle (which does not change the initial entanglement) in advance of the designated carrier. Finally, we analyze the protocols in noisy scenarios and show that, under suitable conditions, excessive distribution may be the only way to achieve entanglement gain.

Dynamic-Stark-effect-induced coherent mixture of virtual paths in laser-dressed helium: energetic electron impact excitation

NASA Astrophysics Data System (ADS)

Agueny, Hicham; Makhoute, Abdelkader; Dubois, Alain

2017-06-01

We theoretically investigate quantum virtual path interference caused by the dynamic Stark effect in bound-bound electronic transitions. The effect is studied in an intermediate resonant region and in connection with the energetic electron impact excitation of a helium atom embedded in a weak low-frequency laser field. The process under investigation is dealt with via a Born-Floquet approach. Numerical calculations show a resonant feature in laser-assisted cross sections. The latter is found to be sensitive to the intensity of the laser field dressing. We show that this feature is a signature of quantum beats which result from the coherent mixture of different quantum virtual pathways, and that excitation may follow in order to end up with a common final channel. This mixture arises from the dynamic Stark effect, which produces a set of avoided crossings in laser-dressed states. The effect allows one to coherently control quantum virtual path interference by varying the intensity of the laser field dressing. Our findings suggest that the combination of an energetic electron and a weak laser field is a useful tool for the coherent control of nonadiabatic transitions in an intermediate resonant region.

Vibronic transitions in the alkali-metal (Li, Na, K, Rb) - alkaline-earth-metal (Ca, Sr) series: A systematic analysis of de-excitation mechanisms based on the graphical mapping of Frank-Condon integrals

NASA Astrophysics Data System (ADS)

Pototschnig, Johann V.; Meyer, Ralf; Hauser, Andreas W.; Ernst, Wolfgang E.

2017-02-01

Research on ultracold molecules has seen a growing interest recently in the context of high-resolution spectroscopy and quantum computation. After forming weakly bound molecules from atoms in cold collisions, the preparation of molecules in low vibrational levels of the ground state is experimentally challenging, and typically achieved by population transfer using excited electronic states. Accurate potential energy surfaces are needed for a correct description of processes such as the coherent de-excitation from the highest and therefore weakly bound vibrational levels in the electronic ground state via couplings to electronically excited states. This paper is dedicated to the vibrational analysis of potentially relevant electronically excited states in the alkali-metal (Li, Na, K, Rb)- alkaline-earth metal (Ca,Sr) diatomic series. Graphical maps of Frank-Condon overlap integrals are presented for all molecules of the group. By comparison to overlap graphics produced for idealized potential surfaces, we judge the usability of the selected states for future experiments on laser-enhanced molecular formation from mixtures of quantum degenerate gases.

Charge renormalization at the large-D limit for N-electron atoms and weakly bound systems

NASA Astrophysics Data System (ADS)

Kais, S.; Bleil, R.

1995-05-01

We develop a systematic way to determine an effective nuclear charge ZRD such that the Hartree-Fock results will be significantly closer to the exact energies by utilizing the analytically known large-D limit energies. This method yields an expansion for the effective nuclear charge in powers of (1/D), which we have evaluated to the first order. This first order approximation to the desired effective nuclear charge has been applied to two-electron atoms with Z=2-20, and weakly bound systems such as H-. The errors for the two-electron atoms when compared with exact results were reduced from ˜0.2% for Z=2 to ˜0.002% for large Z. Although usual Hartree-Fock calculations for H- show this to be unstable, our results reduce the percent error of the Hartree-Fock energy from 7.6% to 1.86% and predicts the anion to be stable. For N-electron atoms (N=3-18, Z=3-28), using only the zeroth order approximation for the effective charge significantly reduces the error of Hartree-Fock calculations and recovers more than 80% of the correlation energy.

Global Passivity in Microscopic Thermodynamics

NASA Astrophysics Data System (ADS)

Uzdin, Raam; Rahav, Saar

2018-04-01

The main thread that links classical thermodynamics and the thermodynamics of small quantum systems is the celebrated Clausius inequality form of the second law. However, its application to small quantum systems suffers from two cardinal problems. (i) The Clausius inequality does not hold when the system and environment are initially correlated—a commonly encountered scenario in microscopic setups. (ii) In some other cases, the Clausius inequality does not provide any useful information (e.g., in dephasing scenarios). We address these deficiencies by developing the notion of global passivity and employing it as a tool for deriving thermodynamic inequalities on observables. For initially uncorrelated thermal environments the global passivity framework recovers the Clausius inequality. More generally, global passivity provides an extension of the Clausius inequality that holds even in the presences of strong initial system-environment correlations. Crucially, the present framework provides additional thermodynamic bounds on expectation values. To illustrate the role of the additional bounds, we use them to detect unaccounted heat leaks and weak feedback operations ("Maxwell demons") that the Clausius inequality cannot detect. In addition, it is shown that global passivity can put practical upper and lower bounds on the buildup of system-environment correlations for dephasing interactions. Our findings are highly relevant for experiments in various systems such as ion traps, superconducting circuits, atoms in optical cavities, and more.

An apparatus for studying electrical breakdown in liquid helium at 0.4 K and testing electrode materials for the neutron electric dipole moment experiment at the Spallation Neutron Source

DOE PAGES

Ito, T. M.; Ramsey, J. C.; Yao, W.; ...

2016-04-25

In this study, we have constructed an apparatus to study DC electrical breakdown in liquid helium at temperatures as low as 0.4 K and at pressures between the saturated vapor pressure and ~600 Torr. The apparatus can house a set of electrodes that are 12 cm in diameter with a gap of 1–2 cm between them, and a potential up to ±50 kV can be applied to each electrode. Initial results demonstrated that it is possible to apply fields exceeding 100 kV/cm in a 1 cm gap between two electropolished stainless steel electrodes 12 cm in diameter for a widemore » range of pressures at 0.4 K. We also measured the current between two electrodes. Our initial results, I < 1 pA at 45 kV, correspond to a lower bound on the effective volume resistivity of liquid helium of ρ V > 5 × 10 18 Ω cm. This lower bound is 5 times larger than the bound previously measured. Finally, we report the design, construction, and operational experience of the apparatus, as well as initial results« less

Local conditions for the generalized covariant entropy bound

NASA Astrophysics Data System (ADS)

Gao, Sijie; Lemos, José P.

2005-04-01

A set of sufficient conditions for the generalized covariant entropy bound given by Strominger and Thompson is as follows: Suppose that the entropy of matter can be described by an entropy current sa. Let ka be any null vector along L and s≡-kasa. Then the generalized bound can be derived from the following conditions: (i) s'≤2πTabkakb, where s'=ka∇as and Tab is the stress-energy tensor; (ii) on the initial 2-surface B, s(0)≤-1/4θ(0), where θ is the expansion of ka. We prove that condition (ii) alone can be used to divide a spacetime into two regions: The generalized entropy bound holds for all light sheets residing in the region where s<-1/4θ and fails for those in the region where s>-1/4θ. We check the validity of these conditions in FRW flat universe and a scalar field spacetime. Some apparent violations of the entropy bounds in the two spacetimes are discussed. These holographic bounds are important in the formulation of the holographic principle.

Membrane-bound oxygen reductases of the anaerobic sulfate-reducing Desulfovibrio vulgaris Hildenborough: roles in oxygen defence and electron link with periplasmic hydrogen oxidation.

PubMed

Ramel, F; Amrani, A; Pieulle, L; Lamrabet, O; Voordouw, G; Seddiki, N; Brèthes, D; Company, M; Dolla, A; Brasseur, G

2013-12-01

Cytoplasmic membranes of the strictly anaerobic sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough contain two terminal oxygen reductases, a bd quinol oxidase and a cc(b/o)o3 cytochrome oxidase (Cox). Viability assays pointed out that single Δbd, Δcox and double ΔbdΔcox deletion mutant strains were more sensitive to oxygen exposure than the WT strain, showing the involvement of these oxygen reductases in the detoxification of oxygen. The Δcox strain was slightly more sensitive than the Δbd strain, pointing to the importance of the cc(b/o)o3 cytochrome oxidase in oxygen protection. Decreased O2 reduction rates were measured in mutant cells and membranes using lactate, NADH, ubiquinol and menadiol as substrates. The affinity for oxygen measured with the bd quinol oxidase (Km, 300 nM) was higher than that of the cc(b/o)o3 cytochrome oxidase (Km, 620 nM). The total membrane activity of the bd quinol oxidase was higher than that of the cytochrome oxidase activity in line with the higher expression of the bd oxidase genes. In addition, analysis of the ΔbdΔcox mutant strain indicated the presence of at least one O2-scavenging membrane-bound system able to reduce O2 with menaquinol as electron donor with an O2 affinity that was two orders of magnitude lower than that of the bd quinol oxidase. The lower O2 reductase activity in mutant cells with hydrogen as electron donor and the use of specific inhibitors indicated an electron transfer link between periplasmic H2 oxidation and membrane-bound oxygen reduction via the menaquinol pool. This linkage is crucial in defence of the strictly anaerobic bacterium Desulfovibrio against oxygen stress.

Kinetic and Spectral Properties of Isovaleryl-CoA Dehydrogenase and Interaction with Ligands

PubMed Central

Mohsen, Al-Walid A.; Vockley, Jerry

2014-01-01

Isovaleryl-CoA dehydrogenase (IVD) catalyzes the conversion of isovaleryl-CoA to 3-methylcrotonyl-CoA and the transfer of electrons to the electron transfer flavoprotein (ETF). Recombinant human IVD purifies with bound CoA-persulfide. A modified purification protocol was developed to isolate IVD without bound CoA-persulfide and to protect the protein thiols from oxidation. The CoA-persulfide-free IVD specific activity was 112.5 µmol porcine ETF•min−1•mg−1, which was ~20-fold higher than that of its CoA-persulfide bound form. The Km and catalytic efficiency (kcat/Km) for isovaleryl-CoA were 1.0 µM and 4.3 × 106•M−1•sec−1 per monomer, respectively, and its Km for ETF was 2.0 µM. Anaerobic titration of isovaleryl-CoA into an IVD solution resulted in a stable blue complex with increased absorbance at 310 nm, decreased absorbance at 373 and 447 nm, and the appearance of the charge transfer complex band at 584 nm. The apparent dissociation constant (KD app) determined spectrally for isovaleryl-CoA was 0.54 µM. Isovaleryl-CoA, acetoacetyl-CoA, methylenecyclopropylacetyl-CoA, and ETF induced CD spectral changes at the 250–500 nm region while isobutyryl-CoA did not, suggesting conformational changes occur at the flavin ring that are ligand specific. Replacement of the IVD Trp166 with a Phe did not block IVD interaction with ETF, indicating that its indole ring is not essential for electron transfer to ETF. A twelve amino acid synthetic peptide that matches the sequence of the ETF docking peptide competitively inhibited the enzyme reaction when ETF was used as the electron acceptor with a Ki of 1.5 mM. PMID:25450250

Riboflavin Is an Active Redox Cofactor in the Na+-pumping NADH:Quinone Oxidoreductase (Na+-NQR) from Vibrio cholerae*

PubMed Central

Juárez, Oscar; Nilges, Mark J.; Gillespie, Portia; Cotton, Jennifer; Barquera, Blanca

2008-01-01

Here we present new evidence that riboflavin is present as one of four flavins in Na+-NQR. In particular, we present conclusive evidence that the source of the neutral radical is not one of the FMNs and that riboflavin is the center that gives rise to the neutral flavosemiquinone. The riboflavin is a bona fide redox cofactor and is likely to be the last redox carrier of the enzyme, from which electrons are donated to quinone. We have constructed a double mutant that lacks both covalently bound FMN cofactors (NqrB-T236Y/NqrC-T225Y) and have studied this mutant together with the two single mutants (NqrB-T236Y and NqrC-T225Y) and a mutant that lacks the noncovalently bound FAD in NqrF (NqrF-S246A). The double mutant contains riboflavin and FAD in a 0.6:1 ratio, as the only flavins in the enzyme; noncovalently bound flavins were detected. In the oxidized form, the double mutant exhibits an EPR signal consistent with a neutral flavosemiquinone radical, which is abolished on reduction of the enzyme. The same radical can be observed in the FAD deletion mutant. Furthermore, when the oxidized enzyme reacts with ubiquinol (the reduced form of the usual electron acceptor) in a process that reverses the physiological direction of the electron flow, a single kinetic phase is observed. The kinetic difference spectrum of this process is consistent with one-electron reduction of a neutral flavosemiquinone. The presence of riboflavin in the role of a redox cofactor is thus far unique to Na+-NQR. PMID:18832377

Generation of hydroxyl radical in isolated pea root cell wall, and the role of cell wall-bound peroxidase, Mn-SOD and phenolics in their production.

PubMed

Kukavica, Biljana; Mojovic, Milos; Vuccinic, Zeljko; Maksimovic, Vuk; Takahama, Umeo; Jovanovic, Sonja Veljovic

2009-02-01

The hydroxyl radical produced in the apoplast has been demonstrated to facilitate cell wall loosening during cell elongation. Cell wall-bound peroxidases (PODs) have been implicated in hydroxyl radical formation. For this mechanism, the apoplast or cell walls should contain the electron donors for (i) H(2)O(2) formation from dioxygen; and (ii) the POD-catalyzed reduction of H(2)O(2) to the hydroxyl radical. The aim of the work was to identify the electron donors in these reactions. In this report, hydroxyl radical (.OH) generation in the cell wall isolated from pea roots was detected in the absence of any exogenous reductants, suggesting that the plant cell wall possesses the capacity to generate .OH in situ. Distinct POD and Mn-superoxide dismutase (Mn-SOD) isoforms different from other cellular isoforms were shown by native gel electropho-resis to be preferably bound to the cell walls. Electron paramagnetic resonance (EPR) spectroscopy of cell wall isolates containing the spin-trapping reagent, 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO), was used for detection of and differentiation between .OH and the superoxide radical (O(2)(-).). The data obtained using POD inhibitors confirmed that tightly bound cell wall PODs are involved in DEPMPO/OH adduct formation. A decrease in DEPMPO/OH adduct formation in the presence of H(2)O(2) scavengers demonstrated that this hydroxyl radical was derived from H(2)O(2). During the generation of .OH, the concentration of quinhydrone structures (as detected by EPR spectroscopy) increased, suggesting that the H(2)O(2) required for the formation of .OH in isolated cell walls is produced during the reduction of O(2) by hydroxycinnamic acids. Cell wall isolates in which the proteins have been denaturated (including the endogenous POD and SOD) did not produce .OH. Addition of exogenous H(2)O(2) again induced the production of .OH, and these were shown to originate from the Fenton reaction with tightly bound metal ions. However, the appearance of the DEPMPO/OOH adduct could also be observed, due to the production of O(2)(-). when endogenous SOD has been inactivated. Also, O(2)(-). was converted to .OH in an in vitro horseradish peroxidase (HRP)/H(2)O(2) system to which exogenous SOD has been added. Taken together with the discovery of the cell wall-bound Mn-SOD isoform, these results support the role of such a cell wall-bound SOD in the formation of .OH jointly with the cell wall-bound POD. According to the above findings, it seems that the hydroxycinnamic acids from the cell wall, acting as reductants, contribute to the formation of H(2)O(2) in the presence of O(2) in an autocatalytic manner, and that POD and Mn-SOD coupled together generate .OH from such H(2)O(2).

Light-driven enzymatic catalysis of DNA repair: a review of recent biophysical studies on photolyase.

PubMed

Weber, Stefan

2005-02-25

More than 50 years ago, initial experiments on enzymatic photorepair of ultraviolet (UV)-damaged DNA were reported [Proc. Natl. Acad. Sci. U. S. A. 35 (1949) 73]. Soon after this discovery, it was recognized that one enzyme, photolyase, is able to repair UV-induced DNA lesions by effectively reversing their formation using blue light. The enzymatic process named DNA photoreactivation depends on a non-covalently bound cofactor, flavin adenine dinucleotide (FAD). Flavins are ubiquitous redox-active catalysts in one- and two-electron transfer reactions of numerous biological processes. However, in the case of photolyase, not only the ground-state redox properties of the FAD cofactor are exploited but also, and perhaps more importantly, its excited-state properties. In the catalytically active, fully reduced redox form, the FAD absorbs in the blue and near-UV ranges of visible light. Although there is no direct experimental evidence, it appears generally accepted that starting from the excited singlet state, the chromophore initiates a reductive cleavage of the two major DNA photodamages, cyclobutane pyrimidine dimers and (6-4) photoproducts, by short-distance electron transfer to the DNA lesion. Back electron transfer from the repaired DNA segment is believed to eventually restore the initial redox states of the cofactor and the DNA nucleobases, resulting in an overall reaction with net-zero exchanged electrons. Thus, the entire process represents a true catalytic cycle. Many biochemical and biophysical studies have been carried out to unravel the fundamentals of this unique mode of action. The work has culminated in the elucidation of the three-dimensional structure of the enzyme in 1995 that revealed remarkable details, such as the FAD-cofactor arrangement in an unusual U-shaped configuration. With the crystal structure of the enzyme at hand, research on photolyases did not come to an end but, for good reason, intensified: the geometrical structure of the enzyme alone is not sufficient to fully understand the enzyme's action on UV-damaged DNA. Much effort has therefore been invested to learn more about, for example, the geometry of the enzyme-substrate complex, and the mechanism and pathways of intra-enzyme and enzyme <-->DNA electron transfer. Many of the key results from biochemical and molecular biology characterizations of the enzyme or the enzyme-substrate complex have been summarized in a number of reviews. Complementary to these articles, this review focuses on recent biophysical studies of photoreactivation comprising work performed from the early 1990s until the present.

Magnetic field enhancement of organic photovoltaic cells performance.

PubMed

Oviedo-Casado, S; Urbina, A; Prior, J

2017-06-27

Charge separation is a critical process for achieving high efficiencies in organic photovoltaic cells. The initial tightly bound excitonic electron-hole pair has to dissociate fast enough in order to avoid photocurrent generation and thus power conversion efficiency loss via geminate recombination. Such process takes place assisted by transitional states that lie between the initial exciton and the free charge state. Due to spin conservation rules these intermediate charge transfer states typically have singlet character. Here we propose a donor-acceptor model for a generic organic photovoltaic cell in which the process of charge separation is modulated by a magnetic field which tunes the energy levels. The impact of a magnetic field is to intensify the generation of charge transfer states with triplet character via inter-system crossing. As the ground state of the system has singlet character, triplet states are recombination-protected, thus leading to a higher probability of successful charge separation. Using the open quantum systems formalism we demonstrate that the population of triplet charge transfer states grows in the presence of a magnetic field, and discuss the impact on carrier population and hence photocurrent, highlighting its potential as a tool for research on charge transfer kinetics in this complex systems.

Cdc6-Induced Conformational Changes in ORC Bound to Origin DNA Revealed by Cryo-Electron Microscopy

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

Sun J.; Li H.; Kawakami, H.

2012-03-07

The eukaryotic origin recognition complex (ORC) interacts with and remodels origins of DNA replication prior to initiation in S phase. Here, we report a single-particle cryo-EM-derived structure of the supramolecular assembly comprising Saccharomyces cerevisiae ORC, the replication initiation factor Cdc6, and double-stranded ARS1 origin DNA in the presence of ATP{gamma}S. The six subunits of ORC are arranged as Orc1:Orc4:Orc5:Orc2:Orc3, with Orc6 binding to Orc2. Cdc6 binding changes the conformation of ORC, in particular reorienting the Orc1 N-terminal BAH domain. Segmentation of the 3D map of ORC-Cdc6 on DNA and docking with the crystal structure of the homologous archaeal Orc1/Cdc6 proteinmore » suggest an origin DNA binding model in which the DNA tracks along the interior surface of the crescent-like ORC. Thus, ORC bends and wraps the DNA. This model is consistent with the observation that binding of a single Cdc6 extends the ORC footprint on origin DNA from both ends.« less

Spectroscopy of Photovoltaic Materials: Charge-Transfer Complexes and Titanium Dioxide

NASA Astrophysics Data System (ADS)

Dillon, Robert John

The successful function of photovoltaic (PV) and photocatalytic (PC) systems centers primarily on the creation and photophysics of charge separated electron-hole pairs. The pathway leading to separate carriers varies by material; organic materials typically require multiple events to charge separate, whereas inorganic semiconductors can directly produce free carriers. In this study, time-resolved spectroscopy is used to provide insight into two such systems: 1) organic charge-transfer (CT) complexes, where electrons and holes are tightly bound to each other, and 2) Au-TiO2 core-shell nanostructures, where free carriers are directly generated. 1) CT complexes are structurally well defined systems consisting of donor molecules, characterized by having low ionization potentials, and acceptor molecules, characterized by having high electron affinities. Charge-transfer is the excitation of an electron from the HOMO of a donor material directly into the LUMO of the acceptor material, leading to an electron and hole separated across the donor:acceptor interface. The energy of the CT transition is often less than that of the bandgaps of donor and acceptor materials individually, sparking much interest if PV systems can utilize the CT band to generate free carriers from low energy photons. In this work we examine the complexes formed between acceptors tetracyanobenzene (TCNB) and tetracyanoquinodimethane (TCNQ) with several aromatic donors. We find excitation of the charge-transfer band of these systems leads to strongly bound electron-hole pairs that exclusively undergo recombination to the ground state. In the case of the TCNB complexes, our initial studies were flummoxed by the samples' generally low threshold for photo and mechanical damage. As our results conflicted with previous literature, a significant portion of this study was spent quantifying the photodegradation process. 2) Unlike the previous system, free carriers are directly photogenerated in TiO2, and the prime consideration is avoiding loss due to recombination of the electron and hole. In this study, four samples of core-shell Au-TiO 2 nanostructures are analyzed for their photocatalytic activity and spectroscopic properties. The samples were made with increasingly crystalline TiO2 shells. The more crystalline samples had higher photocatalytic activities, attributed to longer carrier lifetimes. The observed photophysics of these samples vary with excitation wavelength and detection method used. We find the time-resolved photoluminescence correlates with the samples' photocatalytic activities only when high energy, excitation wavelength less than or equal to 300 nm is used, while transient absorption experiments show no correlation regardless of excitation source. The results imply that photoexcitation with high energy photons can generate both reactive surface sites and photoluminescent surface sites in parallel. Both types of sites then undergo similar electron-hole recombination processes that depend on the crystallinity of the TiO2 shell. Surface sites created by low energy photons, as well as bulk TiO2 carrier dynamics that are probed by transient absorption, do not appear to be sensitive to the same dynamics that determine chemical reactivity.

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2013-05-28

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Magnetophotoluminescence de dyades d'azote uniques dans le gallium arsenide

NASA Astrophysics Data System (ADS)

Ouellet-Plamondon, Clauderic

On the goal to achieve an efficient quantum light source, there are many possibilities ranging from lasers to quantum dots. One of those candiate is to use a single nitrogen dyad in GaAs. This nanostructure is composed of two nitrogen atoms in nearest neigbors subsituting for two arsenic atoms. Since both of those atoms have the same valence, the combined effet of the electronegativity and the small size of the nitrogen atoms form a potential well which attracts an electron. A hole is then bound to the electron via coulomb interaction, creating a bound exciton at the dyad from which the luminescence can be studied. In this work, we present an experimental study of the fine structure of the emission from single nitrogen dyads. The photoluminescence measurements are realised using a high resolution confocal microscope and under a magnetic field of up to 7 T. The spatial resolution combined with the sample's surface density of nitrogen dyads allows studying the properties of individual dyads. Since the C2v symmetry of the dyad lifts the degeneracy of the excitonic levels without magnetic field, four or five transitions are observed, depending on the orientation of the dyad with respect to the observation axis. Using a Hamiltonian taking into account the exchange interaction, the local crystal field and the Zeeman effect, the energie of excitonic states as well as their transition probabilites are modelised. This model reproduce the linear polarization of the emmited photons and is used to determine a range of acceptable value for the g-factor of the bound electron as well as the isotropic and anisotropic factors of the interaction of the weakly-bound hole with the magnetic field. Furthermore, from the diamagnetic shift, the radius of the wavefunction of the electron is evalutated at 16.2 °A, confirming that it is strongly localized to the dyad. Of all the dyads studied, a certain number of them had an emission strickingly different from the ones usually observed. In a first case, the environment perturbed the excitonic states making only the two states at higher energy observable. In a second case, an additional depolarised transition is observed at lower energy. We show that this transition is associated to a charged exciton, indicating for the first time that these nanotructures can bind multiple charges like their larger epitaxial and colloidal counterpart. This work gives a better comprehension of excitons bound to a nitrogen dyad and opens the way to many applications.

The role of electron transfer in DNA building blocks: Evaluation of strand breaks and their implications

NASA Astrophysics Data System (ADS)

Almeida, Diogo Alexandre Fialho de

Radiation-induced damage to biological systems, both direct and indirect processes, has increasingly come under scrutiny by the international scientific community due to recent findings that electrons are a very effective agent in damaging DNA/RNA. Indeed, much remains to be discovered regarding the exact physico-chemical processes that occur in the nascent stages of DNA/RNA damage by incident radiation. However, it is also known that electrons do not exist freely in the physiological medium, but rather solvated and/or pre-solvated states. This leads to the need for new techniques that can better explore the damaging role of "bound" electrons to DNA/RNA. The work presented in this thesis consists on the study of electron transfer in collisions of atomic species with molecules of biological relevance. In order to study these processes, two experimental setups were used. One setup consists of a crossed beam experiment where a neutral potassium beam is created and made to collide with an effusive molecular target beam. The anionic products that stem from electron transfer in potassium atom to the molecular target collisions are then extracted and time-of-flight (TOF) mass analysed. In the second setup a beam of anionic species is formed and made to collide with a molecular target. Collisions with three different anionic beams were performed (H-, O- and OH-), as well as with different simple organic molecules, by measuring the positive and negative ion fragmentation patterns with a quadrupole mass spectrometer (QMS). A comparison between these two collisional systems can greatly help to understand the underlying mechanisms of the electron transfer processes. Finally, studies of potassium collisions with sugar surrogates D-Ribose and THF were performed. These studies show very different fragmentation patterns from DEA, although in the case of THF, it is suggested that the initially accessed states are the same as in DEA. With these studies was also possible to show for the first time collision induced site and bond selectivity breaking, where the electron is transferred into a given state of the acceptor molecule and the resulting fragmentation pathways are exclusive to the initial anionic state. Furthermore, the role of the potassium cation post collisionwas explored and indeed its presence is suggested to induce at least partial suppression of auto-detachment. The implications that ensue from this degradation are analysed in the light of the obtained fragmentation patterns.

Distinct properties of the triplet pair state from singlet fission

DOE PAGES

Trinh, M. Tuan; Pinkard, Andrew; Pun, Andrew B.; ...

2017-07-14

Singlet fission, the conversion of a singlet exciton (S 1) to two triplets (2 × T 1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1(TT). Despite extensive research, the nature of the 1(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of themore » S 1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1(TT)→S n and S 1→S n' transitions; S n and S n' likely come from the antisymmetric and symmetric linear combinations, respectively, of the S 2 state localized on each pentacene unit in the dimer molecule. The 1(TT)→S n transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1(TT) state also shows chemical reactivity that is distinctively different from that of an individual T 1 state. Using an electron-accepting iron oxide molecular cluster [Fe 8O 4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T 1 in pentacene but not from the tightly bound 1(TT) state. Thus, reducing intertriplet electronic coupling in 1(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.« less

Distinct properties of the triplet pair state from singlet fission.

PubMed

Trinh, M Tuan; Pinkard, Andrew; Pun, Andrew B; Sanders, Samuel N; Kumarasamy, Elango; Sfeir, Matthew Y; Campos, Luis M; Roy, Xavier; Zhu, X-Y

2017-07-01

Singlet fission, the conversion of a singlet exciton (S 1 ) to two triplets (2 × T 1 ), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1 (TT). Despite extensive research, the nature of the 1 (TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1 (TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of the S 1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1 (TT)→S n and S 1 →S n' transitions; S n and S n' likely come from the antisymmetric and symmetric linear combinations, respectively, of the S 2 state localized on each pentacene unit in the dimer molecule. The 1 (TT)→S n transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1 (TT) state also shows chemical reactivity that is distinctively different from that of an individual T 1 state. Using an electron-accepting iron oxide molecular cluster [Fe 8 O 4 ] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T 1 in pentacene but not from the tightly bound 1 (TT) state. Thus, reducing intertriplet electronic coupling in 1 (TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.

Oxygen control of nif gene expression in Klebsiella pneumoniae depends on NifL reduction at the cytoplasmic membrane by electrons derived from the reduced quinone pool.

PubMed

Grabbe, Roman; Schmitz, Ruth A

2003-04-01

In Klebsiella pneumoniae, the flavoprotein, NifL regulates NifA mediated transcriptional activation of the N2-fixation (nif) genes in response to molecular O2 and ammonium. We investigated the influence of membrane-bound oxidoreductases on nif-regulation by biochemical analysis of purified NifL and by monitoring NifA-mediated expression of nifH'-'lacZ reporter fusions in different mutant backgrounds. NifL-bound FAD-cofactor was reduced by NADH only in the presence of a redox-mediator or inside-out vesicles derived from anaerobically grown K. pneumoniae cells, indicating that in vivo NifL is reduced by electrons derived from membrane-bound oxidoreductases of the anaerobic respiratory chain. This mechanism is further supported by three lines of evidence: First, K. pneumoniae strains carrying null mutations of fdnG or nuoCD showed significantly reduced nif-induction under derepressing conditions, indicating that NifL inhibition of NifA was not relieved in the absence of formate dehydrogenase-N or NADH:ubiquinone oxidoreductase. The same effect was observed in a heterologous Escherichia coli system carrying a ndh null allele (coding for NADH dehydrogenaseII). Second, studying nif-induction in K. pneumoniae revealed that during anaerobic growth in glycerol, under nitrogen-limitation, the presence of the terminal electron acceptor nitrate resulted in a significant decrease of nif-induction. The final line of evidence is that reduced quinone derivatives, dimethylnaphthoquinol and menadiol, are able to transfer electrons to the FAD-moiety of purified NifL. On the basis of these data, we postulate that under anaerobic and nitrogen-limited conditions, NifL inhibition of NifA activity is relieved by reduction of the FAD-cofactor by electrons derived from the reduced quinone pool, generated by anaerobic respiration, that favours membrane association of NifL. We further hypothesize that the quinol/quinone ratio is important for providing the signal to NifL.

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

Trinh, M. Tuan; Pinkard, Andrew; Pun, Andrew B.

Singlet fission, the conversion of a singlet exciton (S 1) to two triplets (2 × T 1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1(TT). Despite extensive research, the nature of the 1(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of themore » S 1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1(TT)→S n and S 1→S n' transitions; S n and S n' likely come from the antisymmetric and symmetric linear combinations, respectively, of the S 2 state localized on each pentacene unit in the dimer molecule. The 1(TT)→S n transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1(TT) state also shows chemical reactivity that is distinctively different from that of an individual T 1 state. Using an electron-accepting iron oxide molecular cluster [Fe 8O 4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T 1 in pentacene but not from the tightly bound 1(TT) state. Thus, reducing intertriplet electronic coupling in 1(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.« less

Distinct properties of the triplet pair state from singlet fission

PubMed Central

Trinh, M. Tuan; Pinkard, Andrew; Pun, Andrew B.; Sanders, Samuel N.; Kumarasamy, Elango; Sfeir, Matthew Y.; Campos, Luis M.; Roy, Xavier; Zhu, X.-Y.

2017-01-01

Singlet fission, the conversion of a singlet exciton (S1) to two triplets (2 × T1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1(TT). Despite extensive research, the nature of the 1(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of the S1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1(TT)→Sn and S1→Sn′ transitions; Sn and Sn′ likely come from the antisymmetric and symmetric linear combinations, respectively, of the S2 state localized on each pentacene unit in the dimer molecule. The 1(TT)→Sn transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1(TT) state also shows chemical reactivity that is distinctively different from that of an individual T1 state. Using an electron-accepting iron oxide molecular cluster [Fe8O4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T1 in pentacene but not from the tightly bound 1(TT) state. Thus, reducing intertriplet electronic coupling in 1(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission. PMID:28740866

Derivation of the density functional theory from the cluster expansion.

PubMed

Hsu, J Y

2003-09-26

The density functional theory is derived from a cluster expansion by truncating the higher-order correlations in one and only one term in the kinetic energy. The formulation allows self-consistent calculation of the exchange correlation effect without imposing additional assumptions to generalize the local density approximation. The pair correlation is described as a two-body collision of bound-state electrons, and modifies the electron- electron interaction energy as well as the kinetic energy. The theory admits excited states, and has no self-interaction energy.

Laser modified processes: bremsstrahlung and inelastic photon atom scattering

NASA Astrophysics Data System (ADS)

Budriga, Olimpia; Dondera, Mihai; Florescu, Viorica

2007-08-01

We consider the influence of a low-frequency monochromatic external electromagnetic field (the laser) on two basic atomic processes: electron Coulomb bremsstrahlung and inelastic photon scattering on an electron bound in the ground state of a hydrogenic atom. We briefly describe the approximations adopted and illustrate in figures how the laser parameters modify the shape of the differential cross-sections and extend the energy domain for emitted electrons, due to simultaneous absorption or emission of a large number (hundreds) of laser photons.

Exotic lepton searches via bound state production at the LHC

NASA Astrophysics Data System (ADS)

Barrie, Neil D.; Kobakhidze, Archil; Liang, Shelley; Talia, Matthew; Wu, Lei

2018-06-01

Heavy long-lived multi-charged leptons (MCLs) are predicted by various new physics models. These hypothetical MCLs can form bound states, due to their high electric charges and long life times. In this work, we propose a novel strategy of searching for MCLs through their bound state productions and decays. By utilising LHC-8 TeV data in searching for resonances in the diphoton channel, we exclude the masses of isospin singlet heavy leptons with electric charge | q | ≥ 6 (in units of electron charge) lower than ∼1.2 TeV, which are much stronger than the corresponding 8 TeV LHC bounds from analysing the high ionisation and the long time-of-flight of MCLs. By utilising the current 13 TeV LHC diphoton channel measurements the bound can further exclude MCL masses up to ∼1.6 TeV for | q | ≥ 6. Also, we demonstrate that the conventional LHC limits from searching for MCLs produced via Drell-Yan processes can be enhanced by including the contribution of photon fusion processes.

Bound and continuum energy distributions of nuclear fragments resulting from tunneling ionization of molecules

NASA Astrophysics Data System (ADS)

Svensmark, Jens; Tolstikhin, Oleg I.; Madsen, Lars Bojer

2018-03-01

We present the theory of tunneling ionization of molecules with both electronic and nuclear motion treated quantum mechanically. The theory provides partial rates for ionization into the different final states of the molecular ion, including both bound vibrational and dissociative channels. The exact results obtained for a one-dimensional model of H2 and D2 are compared with two approximate approaches, the weak-field asymptotic theory and the Born-Oppenheimer approximation. The validity ranges and compatibility of the approaches are identified formally and illustrated by the calculations. The results quantify that at typical field strengths considered in strong-field physics, it is several orders of magnitude more likely to ionize into bound vibrational ionic channels than into the dissociative channel.

The spectrum of darkonium in the Sun

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

Kouvaris, Chris; Langæble, Kasper; Nielsen, Niklas Grønlund

Dark matter that gets captured in the Sun may form positronium-like bound states if it self-interacts via light dark photons. In this case, dark matter can either annihilate to dark photons or recombine in bound states which subsequently also decay to dark photons. The fraction of the dark photons that leave the Sun without decaying to Standard Model particles have a characteristic energy spectrum which is a mixture of the direct annihilation process, the decays of ortho- and para- bound states and the recombination process. The ultimate decay of these dark photons to positron-electron pairs (via kinetic mixing) outside themore » Sun creates a distinct signal that can either identify or set strict constraints on dark photon models.« less

Pd-Catalyzed N-Arylation of Secondary Acyclic Amides: Catalyst Development, Scope, and Computational Study

PubMed Central

Hicks, Jacqueline D.; Hyde, Alan M.; Cuezva, Alberto Martinez; Buchwald, Stephen L.

2009-01-01

We report the efficient N-arylation of acyclic secondary amides and related nucleophiles with aryl nonaflates, triflates, and chlorides. This method allows for easy variation of the aromatic component in tertiary aryl amides. A new biaryl phosphine with P-bound 3,5-(bis)trifluoromethylphenyl groups was found to be uniquely effective for this amidation. The critical aspects of the ligand were explored through synthetic, mechanistic, and computational studies. Systematic variation of the ligand revealed the importance of (1) a methoxy group on the aromatic carbon of the “top ring” ortho to the phosphorus and (2) two highly electron-withdrawing P-bound 3,5-(bis)trifluoromethylphenyl groups. Computational studies suggest the electron-deficient nature of the ligand is important in facilitating amide binding to the LPd(II)(Ph)(X) intermediate. PMID:19886610

Influences of temperature and impurity on excited state of bound polaron in the parabolic quantum dots

NASA Astrophysics Data System (ADS)

Xiao, Jing-Lin

2014-06-01

On the condition of strong electron-LO phonon coupling in parabolic quantum dot (QD), the first excited state energy, the excitation energy and the transition frequency between the first excited and the ground states of the bound polaron are calculated by using the linear combination operator and the unitary transformation methods. The variation of the above quantities with the temperature, the Coulombic impurity potential and the QD confinement strength are studied in detail. We find that (1) These physical quantities will increase with increasing temperature. (2) They are increasing functions of the confinement strength due to the existence of the Coulombic impurity potential between the electron and the hydrogen-like impurity. (3) We obtain three ways of tuning them via controlling the temperature, the Coulombic impurity potential and the confinement strength.

Components of polarization-transfer to a bound proton in a deuteron measured by quasi-elastic electron scattering

NASA Astrophysics Data System (ADS)

Izraeli, D.; Yaron, I.; Schlimme, B. S.; Achenbach, P.; Arenhövel, H.; Ashkenazi, A.; Beričič, J.; Böhm, R.; Bosnar, D.; Cohen, E. O.; Distler, M. O.; Esser, A.; Friščić, I.; Gilman, R.; Korover, I.; Lichtenstadt, J.; Mardor, I.; Merkel, H.; Middleton, D. G.; Mihovilovič, M.; Müller, U.; Olivenboim, M.; Piasetzky, E.; Pochodzalla, J.; Ron, G.; Schoth, M.; Schulz, F.; Sfienti, C.; Širca, S.; Štajner, S.; Strauch, S.; Thiel, M.; Tyukin, A.; Weber, A.; A1 Collaboration

2018-06-01

We report the first measurements of the transverse (Px and Py) and longitudinal (Pz) components of the polarization transfer to a bound proton in the deuteron via the 2H (e → ,e‧ p →) reaction, over a wide range of missing momentum. A precise determination of the electron beam polarization reduces the systematic uncertainties on the individual components to a level that enables a detailed comparison to a state-of-the-art calculation of the deuteron using free-proton electromagnetic form factors. We observe very good agreement between the measured and the calculated Px /Pz ratios, but deviations of the individual components. Our results cannot be explained by medium modified electromagnetic form factors. They point to an incomplete description of the nuclear reaction mechanism in the calculation.

Creation of Rydberg Polarons in a Bose Gas

NASA Astrophysics Data System (ADS)

Camargo, F.; Schmidt, R.; Whalen, J. D.; Ding, R.; Woehl, G.; Yoshida, S.; Burgdörfer, J.; Dunning, F. B.; Sadeghpour, H. R.; Demler, E.; Killian, T. C.

2018-02-01

We report spectroscopic observation of Rydberg polarons in an atomic Bose gas. Polarons are created by excitation of Rydberg atoms as impurities in a strontium Bose-Einstein condensate. They are distinguished from previously studied polarons by macroscopic occupation of bound molecular states that arise from scattering of the weakly bound Rydberg electron from ground-state atoms. The absence of a p -wave resonance in the low-energy electron-atom scattering in Sr introduces a universal behavior in the Rydberg spectral line shape and in scaling of the spectral width (narrowing) with the Rydberg principal quantum number, n . Spectral features are described with a functional determinant approach (FDA) that solves an extended Fröhlich Hamiltonian for a mobile impurity in a Bose gas. Excited states of polyatomic Rydberg molecules (trimers, tetrameters, and pentamers) are experimentally resolved and accurately reproduced with a FDA.

Appearance of Membrane-bound Iron-Sulfur Centers and the Photosystem I Reaction Center during Greening of Barley Leaves 1

PubMed Central

Baltimore, Barbara G.; Malkin, Richard

1977-01-01

Dark-grown barley (Hordeum vulgare) etioplasts were examined for their content of membrane-bound iron-sulfur centers by electron paramagnetic resonance spectroscopy at 15K. They were found to contain the high potential iron-sulfur center characterized (in the reduced state) by an electron paramagnetic resonance g value of 1.89 (the “Rieske” center) but did not contain any low potential iron-sulfur centers. Per mole of cytochrome f, dark-grown etioplasts and fully developed chloroplasts had the same content of the Rieske center. During greening of etioplasts under continuous light, low potential bound iron-sulfur centers appear. In addition, the photosystem I reaction center, as measured by the photooxidation of P700 at 15K, also became functional; during greening the appearance of a photoreducible low potential iron-sulfur center paralleled the appearance of P700 photoactivity. These findings indicate the close association of the low potential iron-sulfur centers with the photosystem I reaction center; they also support the concept that the development of stable charge separation in the photosystem I reaction center requires, in addition to P700, a low potential iron-sulfur center. PMID:16660048

The membrane-bound [NiFe]-hydrogenase (Ech) from Methanosarcina barkeri: unusual properties of the iron-sulphur clusters.

PubMed

Kurkin, Sergei; Meuer, Jörn; Koch, Jürgen; Hedderich, Reiner; Albracht, Simon P J

2002-12-01

The purified membrane-bound [NiFe]-hydrogenase from Methanosarcina barkeri was studied with electron paramagnetic resonance (EPR) focusing on the properties of the iron-sulphur clusters. The EPR spectra showed signals from three different [4Fe-4S] clusters. Two of the clusters could be reduced under 101 kPa of H2, whereas the third cluster was only partially reduced. Magnetic interaction of one of the clusters with an unpaired electron localized on the Ni-Fe site indicated that this was the proximal cluster as found in all [NiFe]-hydrogenases. Hence, this cluster was assigned to be located in the EchC subunit. The other two clusters could therefore be assigned to be bound to the EchF subunit, which has two conserved four-Cys motifs for the binding of a [4Fe-4S] cluster. Redox titrations at different pH values demonstrated that the proximal cluster and one of the clusters in the EchF subunit had a pH-dependent midpoint potential. The possible relevance of these properties for the function of this proton-pumping [NiFe]-hydrogenase is discussed.

The mechanism of high-T(sub c) superconductivity due to bound hole mediators: Relationship to ferroelectricity

NASA Technical Reports Server (NTRS)

Vezzoli, G. C.; Stanley, William

1990-01-01

The mediation by bound holes creating Cooper pairing in high T(sub c) superconductors has its origin in charge transfer excitations on the multivalence cation (virtual excitions) and in bound excitions or polarizations associated with the oxygen 2p electrons. These phenomena are produced and/or enhanced by a high internal electric field which is itself created by virtue of the unique crystal structures and polyhedral building blocks of high T(sub c) materials. The polarizations which can create oxygen holes (in addition to excitions) may be due to simply the internal electric field or to polaronic and electron-deficient bond behavior. This gives rise to two energy-dependent oxygen bands near the Fermi level. The magnitude and direction of the internal electric fields were calculated for Y1Ba2Cu3O(7-delta) (1-2-3) and show strong z-direction fields at the Cu(2), O2, and O3 sites and an even stronger -z direction field at the O4 site. The field calculations also show why electrical conductivity in the 1-2-3 material is essentially in the base plane of the CuO5 pyramid (the CuO2 plane).

Hydrodynamic & Transport Properties of Dirac Materials in the Quantum Limit

NASA Astrophysics Data System (ADS)

Gochan, Matthew; Bedell, Kevin

Dirac materials are a versatile class of materials in which an abundance of unique physical phenomena can be observed. Such materials are found in all dimensions, with the shared property that their low-energy fermionic excitations behave as massless Dirac fermions and are therefore governed by the Dirac equation. The most popular Dirac material, its two dimensional version in graphene, is the focus of this work. We seek a deeper understanding of the interactions in the quantum limit within graphene. Specifically, we derive hydrodynamic and transport properties, such as the conductivity, viscosity, and spin diffusion, in the low temperature regime where electron-electron scattering is dominant. To conclude, we look at the so-called universal lower bound conjectured by the anti-de Sitter/conformal field theory (AdS/CFT) correspondence for the ratio of shear viscosity to entropy density ratio. The lower bound, given by η / s >= ℏ / (4 πkB) , is supposedly obeyed by all quantum fluids. This leads us to ask whether or not graphene can be considered a quantum fluid and perhaps a ''nearly perfect fluid''(NPF) if this is the case, is it possible to find a violation of this bound at low temperatures.

Spacecraft Observations and Analytic Theory of Crescent-Shaped Electron Distributions in Asymmetric Magnetic Reconnection

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

Egedal, J.; Le, A.; Daughton, W.

Supported by a kinetic simulation, we derive in this paper an exclusion energy parametermore » $${\\mathcal{E}}_{X}$$ providing a lower kinetic energy bound for an electron to cross from one inflow region to the other during magnetic reconnection. As by a Maxwell demon, only high-energy electrons are permitted to cross the inner reconnection region, setting the electron distribution function observed along the low-density side separatrix during asymmetric reconnection. Finally, the analytic model accounts for the two distinct flavors of crescent-shaped electron distributions observed by spacecraft in a thin boundary layer along the low-density separatrix.« less

Spacecraft Observations and Analytic Theory of Crescent-Shaped Electron Distributions in Asymmetric Magnetic Reconnection

DOE PAGES

Egedal, J.; Le, A.; Daughton, W.; ...

2016-10-24

Supported by a kinetic simulation, we derive in this paper an exclusion energy parametermore » $${\\mathcal{E}}_{X}$$ providing a lower kinetic energy bound for an electron to cross from one inflow region to the other during magnetic reconnection. As by a Maxwell demon, only high-energy electrons are permitted to cross the inner reconnection region, setting the electron distribution function observed along the low-density side separatrix during asymmetric reconnection. Finally, the analytic model accounts for the two distinct flavors of crescent-shaped electron distributions observed by spacecraft in a thin boundary layer along the low-density separatrix.« less

Efficient traffic grooming in SONET/WDM BLSR Networks

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

Awwal, A S; Billah, A B; Wang, B

2004-04-02

In this paper, we study traffic grooming in SONET/WDM BLSR networks under the uniform all-to-all traffic model with an objective to reduce total network costs (wavelength and electronic multiplexing costs), in particular, to minimize the number of ADMs while using the optimal number of wavelengths. We derive a new tighter lower bound for the number of wavelengths when the number of nodes is a multiple of 4. We show that this lower bound is achievable. All previous ADM lower bounds except perhaps that in were derived under the assumption that the magnitude of the traffic streams (r) is one unitmore » (r = 1) with respect to the wavelength capacity granularity g. We then derive new, more general and tighter lower bounds for the number of ADMs subject to that the optimal number of wavelengths is used, and propose heuristic algorithms (circle construction algorithm and circle grooming algorithm) that try to minimize the number of ADMs while using the optimal number of wavelengths in BLSR networks. Both the bounds and algorithms are applicable to any value of r and for different wavelength granularity g. Performance evaluation shows that wherever applicable, our lower bounds are at least as good as existing bounds and are much tighter than existing ones in many cases. Our proposed heuristic grooming algorithms perform very well with traffic streams of larger magnitude. The resulting number of ADMs required is very close to the corresponding lower bounds derived in this paper.« less

Dominant Majorana bound energy and critical current enhancement in ferromagnetic-superconducting topological insulator

NASA Astrophysics Data System (ADS)

Khezerlou, Maryam; Goudarzi, Hadi; Asgarifar, Samin

2017-03-01

Among the potential applications of topological insulators, we theoretically study the coexistence of proximity-induced ferromagnetic and superconducting orders in the surface states of a 3-dimensional topological insulator. The superconducting electron-hole excitations can be significantly affected by the magnetic order induced by a ferromagnet. In one hand, the surface state of the topological insulator, protected by the time-reversal symmetry, creates a spin-triplet and, on the other hand, magnetic order causes to renormalize the effective superconducting gap. We find Majorana mode energy along the ferromagnet/superconductor interface to sensitively depend on the magnitude of magnetization m zfs from superconductor region, and its slope around perpendicular incidence is steep with very low dependency on m zfs . The superconducting effective gap is renormalized by a factor η( m zfs ), and Andreev bound state in ferromagnet-superconductor/ferromagnet/ferromagnet-superconductor (FS/F/FS) Josephson junction is more sensitive to the magnitude of magnetizations of FS and F regions. In particular, we show that the presence of m zfs has a noticeable impact on the gap opening in Andreev bound state, which occurs in finite angle of incidence. This directly results in zero-energy Andreev state being dominant. By introducing the proper form of corresponding Dirac spinors for FS electron-hole states, we find that via the inclusion of m zfs , the Josephson supercurrent is enhanced and exhibits almost abrupt crossover curve, featuring the dominant zero-energy Majorana bound states.

Stability analysis of spectral methods for hyperbolic initial-boundary value systems

NASA Technical Reports Server (NTRS)

Gottlieb, D.; Lustman, L.; Tadmor, E.

1986-01-01

A constant coefficient hyperbolic system in one space variable, with zero initial data is discussed. Dissipative boundary conditions are imposed at the two points x = + or - 1. This problem is discretized by a spectral approximation in space. Sufficient conditions under which the spectral numerical solution is stable are demonstrated - moreover, these conditions have to be checked only for scalar equations. The stability theorems take the form of explicit bounds for the norm of the solution in terms of the boundary data. The dependence of these bounds on N, the number of points in the domain (or equivalently the degree of the polynomials involved), is investigated for a class of standard spectral methods, including Chebyshev and Legendre collocations.

The Escherichia coli cAMP receptor protein bound at a single target can activate transcription initiation at divergent promoters: a systematic study that exploits new promoter probe plasmids.

PubMed Central

El-Robh, Mohamed Samir; Busby, Stephen J W

2002-01-01

We report the first detailed quantitative study of divergent promoters dependent on the Escherichia coli cAMP receptor protein (CRP), a factor known to activate transcription initiation at target promoters by making direct interactions with the RNA polymerase holoenzyme. In this work, we show that CRP bound at a single target site is able to activate transcription at two divergently organized promoters. Experiments using promoter probe plasmids, designed to study divergent promoters in vivo and in vitro, show that the divergent promoters function independently. Further in vitro experiments show that two holo RNA polymerase molecules cannot be accommodated simultaneously at the divergent promoters. PMID:12350222

Shewanella oneidensis cytochrome c nitrite reductase (ccNiR) does not disproportionate hydroxylamine to ammonia and nitrite, despite a strongly favorable driving force.

PubMed

Youngblut, Matthew; Pauly, Daniel J; Stein, Natalia; Walters, Daniel; Conrad, John A; Moran, Graham R; Bennett, Brian; Pacheco, A Andrew

2014-04-08

Cytochrome c nitrite reductase (ccNiR) from Shewanella oneidensis, which catalyzes the six-electron reduction of nitrite to ammonia in vivo, was shown to oxidize hydroxylamine in the presence of large quantities of this substrate, yielding nitrite as the sole free nitrogenous product. UV-visible stopped-flow and rapid-freeze-quench electron paramagnetic resonance data, along with product analysis, showed that the equilibrium between hydroxylamine and nitrite is fairly rapidly established in the presence of high initial concentrations of hydroxylamine, despite said equilibrium lying far to the left. By contrast, reduction of hydroxylamine to ammonia did not occur, even though disproportionation of hydroxylamine to yield both nitrite and ammonia is strongly thermodynamically favored. This suggests a kinetic barrier to the ccNiR-catalyzed reduction of hydroxylamine to ammonia. A mechanism for hydroxylamine reduction is proposed in which the hydroxide group is first protonated and released as water, leaving what is formally an NH2(+) moiety bound at the heme active site. This species could be a metastable intermediate or a transition state but in either case would exist only if it were stabilized by the donation of electrons from the ccNiR heme pool into the empty nitrogen p orbital. In this scenario, ccNiR does not catalyze disproportionation because the electron-donating hydroxylamine does not poise the enzyme at a sufficiently low potential to stabilize the putative dehydrated hydroxylamine; presumably, a stronger reductant is required for this.

Efficiency bounds for nonequilibrium heat engines

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

Mehta, Pankaj; Polkovnikov, Anatoli, E-mail: asp@bu.edu

2013-05-15

We analyze the efficiency of thermal engines (either quantum or classical) working with a single heat reservoir like an atmosphere. The engine first gets an energy intake, which can be done in an arbitrary nonequilibrium way e.g. combustion of fuel. Then the engine performs the work and returns to the initial state. We distinguish two general classes of engines where the working body first equilibrates within itself and then performs the work (ergodic engine) or when it performs the work before equilibrating (non-ergodic engine). We show that in both cases the second law of thermodynamics limits their efficiency. For ergodicmore » engines we find a rigorous upper bound for the efficiency, which is strictly smaller than the equivalent Carnot efficiency. I.e. the Carnot efficiency can be never achieved in single reservoir heat engines. For non-ergodic engines the efficiency can be higher and can exceed the equilibrium Carnot bound. By extending the fundamental thermodynamic relation to nonequilibrium processes, we find a rigorous thermodynamic bound for the efficiency of both ergodic and non-ergodic engines and show that it is given by the relative entropy of the nonequilibrium and initial equilibrium distributions. These results suggest a new general strategy for designing more efficient engines. We illustrate our ideas by using simple examples. -- Highlights: ► Derived efficiency bounds for heat engines working with a single reservoir. ► Analyzed both ergodic and non-ergodic engines. ► Showed that non-ergodic engines can be more efficient. ► Extended fundamental thermodynamic relation to arbitrary nonequilibrium processes.« less

Molecular design of light-harvesting photosensitizers: effect of varied linker conjugation on interfacial electron transfer

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

Jiang, Jianbing; Swierk, John R.; Hedstrom, Svante

2016-06-30

Here, interfacial electron transfer dynamics of a series of photosensitizers bound to TiO 2 via linkers of varying conjugation strength are explored by spectroscopic and computational techniques. Injection and recombination depend on the extent of conjugation in the linker, where the LUMO delocalization determines the injection dynamics but both the HOMO and HOMO–1 are involved in recombination.

Adrenoleukodystrophy. Electron microscopic findings.

PubMed

Powell, H; Tindall, R; Schultz, P; Paa, D; O'Brien, J; Lampert, P

1975-04-01

Ultrastructural and neurochemical studies were done on three male patients with adrenoleukodystrophy. In each case, the affected white matter contained enlarged glial cells filled with pathognomic intracytoplasmic inclusions consisting of electron-lucent spicules bounded by 25-Angstrom wide membranes. Similar inclusions were present in adrenocortical cells. These findings and a review of 47 reported cases indicate that adrenoleukodystrophy is a storage disorder caused by a sex-linked recessive error of metabolism.

Measurement of the beta+ and orbital electron-capture decay rates in fully ionized, hydrogenlike, and heliumlike 140Pr ions.

PubMed

Litvinov, Yu A; Bosch, F; Geissel, H; Kurcewicz, J; Patyk, Z; Winckler, N; Batist, L; Beckert, K; Boutin, D; Brandau, C; Chen, L; Dimopoulou, C; Fabian, B; Faestermann, T; Fragner, A; Grigorenko, L; Haettner, E; Hess, S; Kienle, P; Knöbel, R; Kozhuharov, C; Litvinov, S A; Maier, L; Mazzocco, M; Montes, F; Münzenberg, G; Musumarra, A; Nociforo, C; Nolden, F; Pfützner, M; Plass, W R; Prochazka, A; Reda, R; Reuschl, R; Scheidenberger, C; Steck, M; Stöhlker, T; Torilov, S; Trassinelli, M; Sun, B; Weick, H; Winkler, M

2007-12-31

We report on the first measurement of the beta+ and orbital electron-capture decay rates of 140Pr nuclei with the simplest electron configurations: bare nuclei, hydrogenlike, and heliumlike ions. The measured electron-capture decay constant of hydrogenlike 140Pr58+ ions is about 50% larger than that of heliumlike 140Pr57+ ions. Moreover, 140Pr ions with one bound electron decay faster than neutral 140Pr0+ atoms with 59 electrons. To explain this peculiar observation one has to take into account the conservation of the total angular momentum, since only particular spin orientations of the nucleus and of the captured electron can contribute to the allowed decay.

Polymeric capsule-cushioned leukocyte cell membrane vesicles as a biomimetic delivery platform

NASA Astrophysics Data System (ADS)

Gao, Changyong; Wu, Zhiguang; Lin, Zhihua; Lin, Xiankun; He, Qiang

2016-02-01

We report a biomimetic delivery of microsized capsule-cushioned leukocyte membrane vesicles (CLMVs) through the conversion of freshly reassembled leukocyte membrane vesicles (LMVs), including membrane lipids and membrane-bound proteins onto the surface of layer-by-layer assembled polymeric multilayer microcapsules. The leukocyte membrane coating was verified by using electron microscopy, a quartz crystal microbalance, dynamic light scattering, and confocal laser scanning microscopy. The resulting CLMVs have the ability to effectively evade clearance by the immune system and thus prolong the circulation time in mice. Moreover, we also show that the right-side-out leukocyte membrane coating can distinctly improve the accumulation of capsules in tumor sites through the molecular recognition of membrane-bound proteins of CLMVs with those of tumor cells in vitro and in vivo. The natural cell membrane camouflaged polymeric multilayer capsules with the immunosuppressive and tumor-recognition functionalities of natural leukocytes provide a new biomimetic delivery platform for disease therapy.We report a biomimetic delivery of microsized capsule-cushioned leukocyte membrane vesicles (CLMVs) through the conversion of freshly reassembled leukocyte membrane vesicles (LMVs), including membrane lipids and membrane-bound proteins onto the surface of layer-by-layer assembled polymeric multilayer microcapsules. The leukocyte membrane coating was verified by using electron microscopy, a quartz crystal microbalance, dynamic light scattering, and confocal laser scanning microscopy. The resulting CLMVs have the ability to effectively evade clearance by the immune system and thus prolong the circulation time in mice. Moreover, we also show that the right-side-out leukocyte membrane coating can distinctly improve the accumulation of capsules in tumor sites through the molecular recognition of membrane-bound proteins of CLMVs with those of tumor cells in vitro and in vivo. The natural cell membrane camouflaged polymeric multilayer capsules with the immunosuppressive and tumor-recognition functionalities of natural leukocytes provide a new biomimetic delivery platform for disease therapy. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08407e

Tunable Electron-Electron Interactions in LaAlO 3 / SrTiO 3 Nanostructures

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

Cheng, Guanglei; Tomczyk, Michelle; Tacla, Alexandre B.

The interface between the two complex oxides LaAlO 3 and SrTiO 3 has remarkable properties that can be locally reconfigured between conducting and insulating states using a conductive atomic force microscope. Prior investigations of “sketched” quantum dot devices revealed a phase in which electrons form pairs, implying a strongly attractive electron-electron interaction. Here, we show that these devices with strong electron-electron interactions can exhibit a gate-tunable transition from a pair-tunneling regime to a single-electron (Andreev bound state) tunneling regime where the interactions become repulsive. The electron-electron interaction sign change is associated with a Lifshitz transition where the d xz andmore » d yz bands start to become occupied. This electronically tunable electron-electron interaction, combined with the nanoscale reconfigurability of this system, provides an interesting starting point towards solid-state quantum simulation.« less

Tunable Electron-Electron Interactions in LaAlO 3 / SrTiO 3 Nanostructures

DOE PAGES

Cheng, Guanglei; Tomczyk, Michelle; Tacla, Alexandre B.; ...

2016-12-01

The interface between the two complex oxides LaAlO 3 and SrTiO 3 has remarkable properties that can be locally reconfigured between conducting and insulating states using a conductive atomic force microscope. Prior investigations of “sketched” quantum dot devices revealed a phase in which electrons form pairs, implying a strongly attractive electron-electron interaction. Here, we show that these devices with strong electron-electron interactions can exhibit a gate-tunable transition from a pair-tunneling regime to a single-electron (Andreev bound state) tunneling regime where the interactions become repulsive. The electron-electron interaction sign change is associated with a Lifshitz transition where the d xz andmore » d yz bands start to become occupied. This electronically tunable electron-electron interaction, combined with the nanoscale reconfigurability of this system, provides an interesting starting point towards solid-state quantum simulation.« less

Development and Application of Pyrolysis Gas Chromatography/Mass Spectrometry for the Analysis of Bound Trinitrotoluene Residues in Soil

USGS Publications Warehouse

Weiss, J.M.; Mckay, A.J.; Derito, C.; Watanabe, C.; Thorn, K.A.; Madsen, E.L.

2004-01-01

TNT (trinitrotoluene) is a contaminant of global environmental significance, yet determining its environmental fate has posed longstanding challenges. To date, only differential extraction-based approaches have been able to determine the presence of covalently bound, reduced forms of TNT in field soils. Here, we employed thermal elution, pyrolysis, and gas chromatography/mass spectrometry (GC/MS) to distinguish between covalently bound and noncovalently bound reduced forms of TNT in soil. Model soil organic matter-based matrixes were used to develop an assay in which noncovalently bound (monomeric) aminodinitrotoluene (ADNT) and diaminonitrotoluene (DANT) were desorbed from the matrix and analyzed at a lower temperature than covalently bound forms of these same compounds. A thermal desorption technique, evolved gas analysis, was initially employed to differentiate between covalently bound and added 15N-labeled monomeric compounds. A refined thermal elution procedure, termed "double-shot analysis" (DSA), allowed a sample to be sequentially analyzed in two phases. In phase 1, all of an added 15N-labeled monomeric contaminant was eluted from the sample at relatively low temperature. In phase 2 during high-temperature pyrolysis, the remaining covalently bound contaminants were detected. DSA analysis of soil from the Louisiana Army Ammunition Plant (LAAP; ???5000 ppm TNT) revealed the presence of DANT, ADNT, and TNT. After scrutinizing the DSA data and comparing them to results from solvent-extracted and base/acid-hydrolyzed LAAP soil, we concluded that the TNT was a noncovalently bound "carryover" from phase 1. Thus, the pyrolysis-GC/MS technique successfully defined covalently bound pools of ADNT and DANT in the field soil sample.

The structural changes of T7 RNA polymerase from transcription initiation to elongation

PubMed Central

Steitz, Thomas A

2010-01-01

Summary The structures of T7 RNA polymerase (T7 RNAP) captured in the initiation and elongation phases of transcription, as well as an intermediate stage provide insights into how this RNA polymerase protein can initiate RNA synthesis and synthesize 7 to 10 nucleotides of RNA while remaining bound to the DNA promoter site. Recently, the structures of T7 RNAP bound to it promoter DNA along with either a 7 nucleotide or 8 nucleotide transcript show an elongated product site resulting from a 40° or 45° rotation of the promoter and domain that binds it. The different functional properties of the initiation and elongation phases of transcription are illuminated from structures of the initiation and elongation complexes. Structural insights into the translocation of the product transcript of RNAP, its separation of the downstream duplex DNA and its removal of the transcript from the heteroduplex are provided by the structures of several states of nucleotide incorporation. A conformational change in the “fingers” domain that results from the binding or dissociation of incoming NTP or PPi appears to be associated with the state of translocation of T7 RNAP. PMID:19811903

NASA's explorer school and spaceward bound programs: Insights into two education programs designed to heighten public support for space science initiatives

USGS Publications Warehouse

Allner, Matthew; McKay, Christopher P; Coe, Liza; Rask, Jon; Paradise, Jim; Wynne, J. Judson

2010-01-01

IntroductionNASA has played an influential role in bringing the enthusiasm of space science to schools across the United States since the 1980s. The evolution of this public outreach has led to a variety of NASA funded education programs designed to promote student interest in science, technology, engineering, math, and geography (STEM-G) careers.PurposeThis paper investigates the educational outreach initiatives, structure, and impact of two of NASA's largest educational programs: the NASA Explorer School (NES) and NASA Spaceward Bound programs.ResultsSince its induction in 2003 the NES program has networked and provided resources to over 300 schools across the United States. Future directions include further development of mentor schools for each new NES school selected, while also developing a longitudinal student tracking system for NES students to monitor their future involvement in STEM-G careers. The Spaceward Bound program, now in its third year of teacher outreach, is looking to further expand its teacher network and scientific collaboration efforts, while building on its teacher mentorship framework.

Membrane-bound amylopullulanase is essential for starch metabolism of Sulfolobus acidocaldarius DSM639.

PubMed

Choi, Kyoung-Hwa; Cha, Jaeho

2015-09-01

Sulfolobus acidocaldarius DSM639 produced an acid-resistant membrane-bound amylopullulanase (Apu) during growth on starch as a sole carbon and energy source. The physiological role of Apu in starch metabolism was investigated by the growth and starch degradation pattern of apu disruption mutant as well as biochemical properties of recombinant Apu. The Δapu mutant lost the ability to grow in minimal medium in the presence of starch, and the amylolytic activity observed in the membrane fraction of the wild-type strain was not detected in the Δapu mutant when the cells were grown in YT medium. The purified membrane-bound Apu initially hydrolyzed starch, amylopectin, and pullulan into various sizes of maltooligosaccharides, and then produced glucose, maltose, and maltotriose in the end, indicating Apu is a typical endo-acting glycoside hydrolase family 57 (GH57) amylopullulanase. The maltose and maltotriose observed in the culture medium during the exponential and stationary phase growth indicates that Apu is the essential enzyme to initially hydrolyze the starch into small maltooligosaccharides to be transported into the cell.

High-Resolution Two-Dimensional Optical Spectroscopy of Electron Spins

NASA Astrophysics Data System (ADS)

Salewski, M.; Poltavtsev, S. V.; Yugova, I. A.; Karczewski, G.; Wiater, M.; Wojtowicz, T.; Yakovlev, D. R.; Akimov, I. A.; Meier, T.; Bayer, M.

2017-07-01

Multidimensional coherent optical spectroscopy is one of the most powerful tools for investigating complex quantum mechanical systems. While it was conceived decades ago in magnetic resonance spectroscopy using microwaves and radio waves, it has recently been extended into the visible and UV spectral range. However, resolving MHz energy splittings with ultrashort laser pulses still remains a challenge. Here, we analyze two-dimensional Fourier spectra for resonant optical excitation of resident electrons to localized trions or donor-bound excitons in semiconductor nanostructures subject to a transverse magnetic field. Particular attention is devoted to Raman coherence spectra, which allow one to accurately evaluate tiny splittings of the electron ground state and to determine the relaxation times in the electron spin ensemble. A stimulated steplike Raman process induced by a sequence of two laser pulses creates a coherent superposition of the ground-state doublet which can be retrieved only optically because of selective excitation of the same subensemble with a third pulse. This provides the unique opportunity to distinguish between different complexes that are closely spaced in energy in an ensemble. The related experimental demonstration is based on photon-echo measurements in an n -type CdTe /(Cd ,Mg )Te quantum-well structure detected by a heterodyne technique. The difference in the sub-μ eV range between the Zeeman splittings of donor-bound electrons and electrons localized at potential fluctuations can be resolved even though the homogeneous linewidth of the optical transitions is larger by 2 orders of magnitude.

Direct observation of sequential oxidations of a titania-bound molecular proxy catalyst generated through illumination of molecular sensitizers

NASA Astrophysics Data System (ADS)

Chen, Hsiang-Yun; Ardo, Shane

2018-01-01

Natural photosynthesis uses the energy in sunlight to oxidize or reduce reaction centres multiple times, therefore preparing each reaction centre for a multiple-electron-transfer reaction that will ultimately generate stable reaction products. This process relies on multiple chromophores per reaction centre to quickly generate the active state of the reaction centre and to outcompete deleterious charge recombination. Using a similar design principle, we report spectroscopic evidence for the generation of a twice-oxidized TiO2-bound molecular proxy catalyst after low-intensity visible-light excitation of co-anchored molecular Ru(II)-polypyridyl dyes. Electron transfer from an excited dye to TiO2 generated a Ru(III) state that subsequently and repeatedly reacted with neighbouring Ru(II) dyes via self-exchange electron transfer to ultimately oxidize a distant co-anchored proxy catalyst before charge recombination. The largest yield for twice-oxidized proxy catalysts occurred when they were present at low coverage, suggesting that large dye/electrocatalyst ratios are also desired in dye-sensitized photoelectrochemical cells.

Bound and resonance states of positronic copper atoms

NASA Astrophysics Data System (ADS)

Yamashita, Takuma; Umair, Muhammad; Kino, Yasushi

2017-10-01

We report a theoretical calculation for the bound and S-wave resonance states of the positronic copper atom (e+Cu). A positron is a positively charged particle; therefore, a positronic atom has an attractive correlation between the positron and electron. A Gaussian expansion method is adopted to directly describe this correlation as well as the strong repulsive interaction with the nucleus. The correlation between the positron and electron is much more important than that between electrons in an analogous system of Cu-, although the formation of a positronium (Ps) in e+Cu is not expressed in the ground state structure explicitly. Resonance states are calculated with a complex scaling method and identified above the first excited state of the copper atom. Resonance states below Ps (n = 2) + Cu+ classified to a dipole series show agreement with a simple analytical law. Comparison of the resonance energies and widths of e+Cu with those of e+K, of which the potential energy of the host atom resembles that of e+Cu, reveals that the positions of the resonance for the e+Cu dipole series deviate equally from those of e+K.

Isotope dependence of the Zeeman effect in lithium-like calcium

PubMed Central

Köhler, Florian; Blaum, Klaus; Block, Michael; Chenmarev, Stanislav; Eliseev, Sergey; Glazov, Dmitry A.; Goncharov, Mikhail; Hou, Jiamin; Kracke, Anke; Nesterenko, Dmitri A.; Novikov, Yuri N.; Quint, Wolfgang; Minaya Ramirez, Enrique; Shabaev, Vladimir M.; Sturm, Sven; Volotka, Andrey V.; Werth, Günter

2016-01-01

The magnetic moment μ of a bound electron, generally expressed by the g-factor μ=−g μB s ħ−1 with μB the Bohr magneton and s the electron's spin, can be calculated by bound-state quantum electrodynamics (BS-QED) to very high precision. The recent ultra-precise experiment on hydrogen-like silicon determined this value to eleven significant digits, and thus allowed to rigorously probe the validity of BS-QED. Yet, the investigation of one of the most interesting contribution to the g-factor, the relativistic interaction between electron and nucleus, is limited by our knowledge of BS-QED effects. By comparing the g-factors of two isotopes, it is possible to cancel most of these contributions and sensitively probe nuclear effects. Here, we present calculations and experiments on the isotope dependence of the Zeeman effect in lithium-like calcium ions. The good agreement between the theoretical predicted recoil contribution and the high-precision g-factor measurements paves the way for a new generation of BS-QED tests. PMID:26776466

On the formation of anions: frequency-, angle-, and time-resolved photoelectron imaging of the menadione radical anion† †Electronic supplementary information (ESI) available: A summary of the ground-state geometries and molecular orbitals from the ab initio calculations; fitted residuals from the FA-PI simulation; plots of all spectra included in the frequency-resolved two-dimensional figure; and example time-resolved PE spectra from the 3.10 + 1.55 eV pump-probe experiments. See DOI: 10.1039/c4sc03491k Click here for additional data file.

PubMed Central

Bull, James N.; West, Christopher W.

2015-01-01

Frequency-, angle-, and time-resolved photoelectron imaging of gas-phase menadione (vitamin K3) radical anions was used to show that quasi-bound resonances of the anion can act as efficient doorway states to produce metastable ground electronic state anions on a sub-picosecond timescale. Several anion resonances have been experimentally observed and identified with the assistance of ab initio calculations, and ground state anion recovery was observed across the first 3 eV above threshold. Time-resolved measurements revealed the mechanism of electronic ground state anion formation, which first involves a cascade of very fast internal conversion processes to a bound electronic state that, in turn, decays by slower internal conversion to the ground state. Autodetachment processes from populated resonances are inefficient compared with electronic relaxation through internal conversion. The mechanistic understanding gained provides insight into the formation of radical anions in biological and astrochemical systems. PMID:29560245

Runaway electron dynamics in tokamak plasmas with high impurity content

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

Martín-Solís, J. R., E-mail: solis@fis.uc3m.es; Loarte, A.; Lehnen, M.

2015-09-15

The dynamics of high energy runaway electrons is analyzed for plasmas with high impurity content. It is shown that modified collision terms are required in order to account for the collisions of the relativistic runaway electrons with partially stripped impurity ions, including the effect of the collisions with free and bound electrons, as well as the scattering by the full nuclear and the electron-shielded ion charge. The effect of the impurities on the avalanche runaway growth rate is discussed. The results are applied, for illustration, to the interpretation of the runaway electron behavior during disruptions, where large amounts of impuritiesmore » are expected, particularly during disruption mitigation by massive gas injection. The consequences for the electron synchrotron radiation losses and the resulting runaway electron dynamics are also analyzed.« less

Compton spectra of atoms at high x-ray intensity

NASA Astrophysics Data System (ADS)

Son, Sang-Kil; Geffert, Otfried; Santra, Robin

2017-03-01

Compton scattering is the nonresonant inelastic scattering of an x-ray photon by an electron and has been used to probe the electron momentum distribution in gas-phase and condensed-matter samples. In the low x-ray intensity regime, Compton scattering from atoms dominantly comes from bound electrons in neutral atoms, neglecting contributions from bound electrons in ions and free (ionized) electrons. In contrast, in the high x-ray intensity regime, the sample experiences severe ionization via x-ray multiphoton multiple ionization dynamics. Thus, it becomes necessary to take into account all the contributions to the Compton scattering signal when atoms are exposed to high-intensity x-ray pulses provided by x-ray free-electron lasers (XFELs). In this paper, we investigate the Compton spectra of atoms at high x-ray intensity, using an extension of the integrated x-ray atomic physics toolkit, xatom. As the x-ray fluence increases, there is a significant contribution from ionized electrons to the Compton spectra, which gives rise to strong deviations from the Compton spectra of neutral atoms. The present study provides not only understanding of the fundamental XFEL-matter interaction but also crucial information for single-particle imaging experiments, where Compton scattering is no longer negligible. , which features invited work from the best early-career researchers working within the scope of J. Phys. B. This project is part of the Journal of Physics series’ 50th anniversary celebrations in 2017. Sang-Kil Son was selected by the Editorial Board of J. Phys. B as an Emerging Leader.

Expression and Purification of a Matrix Metalloprotease Transmembrane Domain in Escherichia coli.

PubMed

Galea, Charles A

2017-01-01

Membrane tethered matrix metalloproteases are bound to the plasma membrane by a glycosylphosphatidylinositol-anchor or a transmembrane domain. To date, most studies of membrane-bound matrix metalloprotease have focused on the globular catalytic and protein-protein interaction domains of these enzymes. However, the transmembrane domains have been poorly studied even though they are known to mediate intracellular signaling via interaction with various cellular proteins. The expression and purification of the transmembrane domain of these proteins can be challenging due to their hydrophobic nature. In this chapter we describe the purification of a transmembrane domain for a membrane-bound matrix metalloprotease expressed in E. coli and its initial characterization by NMR spectroscopy.

Few-body model approach to the bound states of helium-like exotic three-body systems

NASA Astrophysics Data System (ADS)

Khan, Md A.

2016-10-01

In this paper, calculated energies of the lowest bound S-state of Coulomb three-body systems containing an electron (e —), a negatively charged muon (μ—) and a nucleus (NZ+) of charge number Z are reported. The 3-body relative wave function in the resulting Schrödinger equation is expanded in the complete set of hyperspherical harmonics (HH). Use of the orthonormality of HH leads to an infinite set of coupled differential equations (CDE) which are solved numerically to get the energy E.

Global boundedness of solutions to a two-species chemotaxis system

NASA Astrophysics Data System (ADS)

Zhang, Qingshan; Li, Yuxiang

2015-02-01

In this paper, we consider the chemotaxis system of two species which are attracted by the same signal substance under homogeneous Neumann boundary conditions in a smooth bounded domain . We prove that if the nonnegative initial data and for some r > n, the system possesses a unique global uniformly bounded solution under some conditions on the chemotaxis sensitivity functions χ 1( w), χ 2( w) and the logistic growth coefficients μ 1, μ 2.

Delta-Complete Analysis for Bounded Reachability of Hybrid Systems

DTIC Science & Technology

2014-07-16

framework makes bounded reachability of hybrid systems a much more mathematically tractable problem and show that our practical implementation can handle...step i in the hybrid trajectory to an appropriate discrete mode in H , and make sure that the flow, jump, inv, init conditions are satisfied...trajectories start with some initial state satisfying initq(x0) for some q. In each step, it follows flowq(xi,xti, t) and makes a continuous flow from xi to x t

Quantum speed limit constraints on a nanoscale autonomous refrigerator

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Chiranjib; Misra, Avijit; Bhattacharya, Samyadeb; Pati, Arun Kumar

2018-06-01

Quantum speed limit, furnishing a lower bound on the required time for the evolution of a quantum system through the state space, imposes an ultimate natural limitation to the dynamics of physical devices. Quantum absorption refrigerators, however, have attracted a great deal of attention in the past few years. In this paper, we discuss the effects of quantum speed limit on the performance of a quantum absorption refrigerator. In particular, we show that there exists a tradeoff relation between the steady cooling rate of the refrigerator and the minimum time taken to reach the steady state. Based on this, we define a figure of merit called "bounding second order cooling rate" and show that this scales linearly with the unitary interaction strength among the constituent qubits. We also study the increase of bounding second-order cooling rate with the thermalization strength. We subsequently demonstrate that coherence in the initial three qubit system can significantly increase the bounding second-order cooling rate. We study the efficiency of the refrigerator at maximum bounding second-order cooling rate and, in a limiting case, we show that the efficiency at maximum bounding second-order cooling rate is given by a simple formula resembling the Curzon-Ahlborn relation.

Sensors closeness test based on an improved [0, 1] bounded Mahalanobis distance Δ{sup 2}

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

Masnan, Maz Jamilah, E-mail: mazjamilah@unimap.edu.my; Mahat, Nor Idayu, E-mail: noridayu@uum.edu.my; Shakaff, Ali Yeon Md, E-mail: aliyeon@unimap.edu.my

2015-12-11

Mahalanobis distance Δ{sup 2} values are commonly in the range of 0 to +∞ where higher values represent greater distance between class means or points. The increase in Mahalanobis distance is unbounded as the distance multiply. To certain extend, the unbounded distance values pose difficulties in the evaluation and decision for instance in the sensors closeness test. This paper proposes an approach to [0, 1] bounded Mahalanobis distance Δ{sup 2} that enable researcher to easily perform sensors closeness test. The experimental data of four different types of rice based on three different electronic nose sensors namely InSniff, PEN3, and Cyranose320more » were analyzed and sensor closeness test seems successfully performed within the [0, 1] bound.« less

Acid generation mechanism in anion-bound chemically amplified resists used for extreme ultraviolet lithography

NASA Astrophysics Data System (ADS)

Komuro, Yoshitaka; Yamamoto, Hiroki; Kobayashi, Kazuo; Utsumi, Yoshiyuki; Ohomori, Katsumi; Kozawa, Takahiro

2014-11-01

Extreme ultraviolet (EUV) lithography is the most promising candidate for the high-volume production of semiconductor devices with half-pitches of sub-10 nm. An anion-bound polymer (ABP), in which the anion part of onium salts is polymerized, has attracted much attention from the viewpoint of the control of acid diffusion. In this study, the acid generation mechanism in ABP films was investigated using electron (pulse), γ, and EUV radiolyses. On the basis of experimental results, the acid generation mechanism in anion-bound chemically amplified resists was proposed. The major path for proton generation in the absence of effective proton sources is considered to be the reaction of phenyl radicals with diphenylsulfide radical cations that are produced through hole transfer to the decomposition products of onium salts.

Structure and symmetry inform gating principles of ionotropic glutamate receptors.

PubMed

Zhu, Shujia; Gouaux, Eric

2017-01-01

Ionotropic glutamate receptors (iGluRs) transduce signals derived from release of the excitatory neurotransmitter glutamate from pre-synaptic neurons into excitation of post-synaptic neurons on a millisecond time-scale. In recent years, the elucidation of full-length iGluR structures of NMDA, AMPA and kainate receptors by X-ray crystallography and single particle cryo-electron microscopy has greatly enhanced our understanding of the interrelationships between receptor architecture and gating mechanism. Here we briefly review full-length iGluR structures and discuss the similarities and differences between NMDA receptors and non-NMDA iGluRs. We focus on distinct conformations, including ligand-free, agonist-bound active, agonist-bound desensitized and antagonist-bound conformations as well as modulator and auxiliary protein-bound states. These findings provide insights into structure-based mechanisms of iGluR gating and modulation which together shape the amplitude and time course of the excitatory postsynaptic potential. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'. Copyright © 2016 Elsevier Ltd. All rights reserved.

Shooting quasiparticles from Andreev bound states in a superconducting constriction

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

Riwar, R.-P.; Houzet, M.; Meyer, J. S.

2014-12-15

A few-channel superconducting constriction provides a set of discrete Andreev bound states that may be populated with quasiparticles. Motivated by recent experimental research, we study the processes in an a.c. driven constriction whereby a quasiparticle is promoted to the delocalized states outside the superconducting gap and flies away. We distinguish two processes of this kind. In the process of ionization, a quasiparticle present in the Andreev bound state is transferred to the delocalized states leaving the constriction. The refill process involves two quasiparticles: one flies away while another one appears in the Andreev bound state. We notice an interesting asymmetrymore » of these processes. The electron-like quasiparticles are predominantly emitted to one side of the constriction while the hole-like ones are emitted to the other side. This produces a charge imbalance of accumulated quasiparticles, that is opposite on opposite sides of the junction. The imbalance may be detected with a tunnel contact to a normal metal lead.« less

Crystallization of the Na+-translocating NADH:quinone oxidoreductase from Vibrio cholerae

PubMed Central

Casutt, Marco S.; Wendelspiess, Severin; Steuber, Julia; Fritz, Günter

2010-01-01

The Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from the human pathogen Vibrio cholerae couples the exergonic oxidation of NADH by membrane-bound quinone to Na+ translocation across the membrane. Na+-NQR consists of six different subunits (NqrA–NqrF) and contains a [2Fe–2S] cluster, a noncovalently bound FAD, a noncovalently bound riboflavin, two covalently bound FMNs and potentially Q8 as cofactors. Initial crystallization of the entire Na+-NQR complex was achieved by the sitting-drop method using a nanolitre dispenser. Optimization of the crystallization conditions yielded flat yellow-coloured crystals with dimensions of up to 200 × 80 × 20 µm. The crystals diffracted to 4.0 Å resolution and belonged to space group P21, with unit-cell parameters a = 94, b = 146, c = 105 Å, α = γ = 90, β = 111°. PMID:21139223

Structural mechanism of JH delivery in hemolymph by JHBP of silkworm, Bombyx mori

PubMed Central

Suzuki, Rintaro; Fujimoto, Zui; Shiotsuki, Takahiro; Tsuchiya, Wataru; Momma, Mitsuru; Tase, Akira; Miyazawa, Mitsuhiro; Yamazaki, Toshimasa

2011-01-01

Juvenile hormone (JH) plays crucial roles in many aspects of the insect life. All the JH actions are initiated by transport of JH in the hemolymph as a complex with JH-binding protein (JHBP) to target tissues. Here, we report structural mechanism of JH delivery by JHBP based upon the crystal and solution structures of apo and JH-bound JHBP. In solution, apo-JHBP exists in equilibrium of multiple conformations with different orientations of the gate helix for the hormone-binding pocket ranging from closed to open forms. JH-binding to the gate-open form results in the fully closed JHBP-JH complex structure where the bound JH is completely buried inside the protein. JH-bound JHBP opens the gate helix to release the bound hormone likely by sensing the less polar environment at the membrane surface of target cells. This is the first report that provides structural insight into JH signaling. PMID:22355650

Upper bound of abutment scour in laboratory and field data

USGS Publications Warehouse

Benedict, Stephen

2016-01-01

The U.S. Geological Survey, in cooperation with the South Carolina Department of Transportation, conducted a field investigation of abutment scour in South Carolina and used those data to develop envelope curves that define the upper bound of abutment scour. To expand on this previous work, an additional cooperative investigation was initiated to combine the South Carolina data with abutment scour data from other sources and evaluate upper bound patterns with this larger data set. To facilitate this analysis, 446 laboratory and 331 field measurements of abutment scour were compiled into a digital database. This extensive database was used to evaluate the South Carolina abutment scour envelope curves and to develop additional envelope curves that reflected the upper bound of abutment scour depth for the laboratory and field data. The envelope curves provide simple but useful supplementary tools for assessing the potential maximum abutment scour depth in the field setting.

A Novel Electrophototrophic Bacterium Rhodopseudomonas palustris Strain RP2, Exhibits Hydrocarbonoclastic Potential in Anaerobic Environments

PubMed Central

Venkidusamy, Krishnaveni; Megharaj, Mallavarapu

2016-01-01

An electrophototrophic, hydrocarbonoclastic bacterium Rhodopseudomonas palustris stain RP2 was isolated from the anodic biofilms of hydrocarbon fed microbial electrochemical remediation systems (MERS). Salient properties of the strain RP2 were direct electrode respiration, dissimilatory metal oxide reduction, spore formation, anaerobic nitrate reduction, free living diazotrophy and the ability to degrade n-alkane components of petroleum hydrocarbons (PH) in anoxic, photic environments. In acetate fed microbial electrochemical cells, a maximum current density of 305 ± 10 mA/m2 (1000Ω) was generated (power density 131.65 ± 10 mW/m2) by strain RP2 with a coulombic efficiency of 46.7 ± 1.3%. Cyclic voltammetry studies showed that anaerobically grown cells of strain RP2 is electrochemically active and likely to transfer electrons extracellularly to solid electron acceptors through membrane bound compounds, however, aerobically grown cells lacked the electrochemical activity. The ability of strain RP2 to produce current (maximum current density 21 ± 3 mA/m2; power density 720 ± 7 μW/m2, 1000 Ω) using PH as a sole energy source was also examined using an initial concentration of 800 mg l-1 of diesel range hydrocarbons (C9-C36) with a concomitant removal of 47.4 ± 2.7% hydrocarbons in MERS. Here, we also report the first study that shows an initial evidence for the existence of a hydrocarbonoclastic behavior in the strain RP2 when grown in different electron accepting and illuminated conditions (anaerobic and MERS degradation). Such observations reveal the importance of photoorganotrophic growth in the utilization of hydrocarbons from contaminated environments. Identification of such novel petrochemical hydrocarbon degrading electricigens, not only expands the knowledge on the range of bacteria known for the hydrocarbon bioremediation but also shows a biotechnological potential that goes well beyond its applications to MERS. PMID:27462307

Biofuel Cells Select for Microbial Consortia That Self-Mediate Electron Transfer

PubMed Central

Rabaey, Korneel; Boon, Nico; Siciliano, Steven D.; Verhaege, Marc; Verstraete, Willy

2004-01-01

Microbial fuel cells hold great promise as a sustainable biotechnological solution to future energy needs. Current efforts to improve the efficiency of such fuel cells are limited by the lack of knowledge about the microbial ecology of these systems. The purposes of this study were (i) to elucidate whether a bacterial community, either suspended or attached to an electrode, can evolve in a microbial fuel cell to bring about higher power output, and (ii) to identify species responsible for the electricity generation. Enrichment by repeated transfer of a bacterial consortium harvested from the anode compartment of a biofuel cell in which glucose was used increased the output from an initial level of 0.6 W m−2 of electrode surface to a maximal level of 4.31 W m−2 (664 mV, 30.9 mA) when plain graphite electrodes were used. This result was obtained with an average loading rate of 1 g of glucose liter−1 day−1 and corresponded to 81% efficiency for electron transfer from glucose to electricity. Cyclic voltammetry indicated that the enhanced microbial consortium had either membrane-bound or excreted redox components that were not initially detected in the community. Dominant species of the enhanced culture were identified by denaturing gradient gel electrophoresis and culturing. The community consisted mainly of facultative anaerobic bacteria, such as Alcaligenes faecalis and Enterococcus gallinarum, which are capable of hydrogen production. Pseudomonas aeruginosa and other Pseudomonas species were also isolated. For several isolates, electrochemical activity was mainly due to excreted redox mediators, and one of these mediators, pyocyanin produced by P. aeruginosa, could be characterized. Overall, the enrichment procedure, irrespective of whether only attached or suspended bacteria were examined, selected for organisms capable of mediating the electron transfer either by direct bacterial transfer or by excretion of redox components. PMID:15345423

High precision hyperfine measurements in Bismuth challenge bound-state strong-field QED

NASA Astrophysics Data System (ADS)

Ullmann, Johannes; Andelkovic, Zoran; Brandau, Carsten; Dax, Andreas; Geithner, Wolfgang; Geppert, Christopher; Gorges, Christian; Hammen, Michael; Hannen, Volker; Kaufmann, Simon; König, Kristian; Litvinov, Yuri A.; Lochmann, Matthias; Maaß, Bernhard; Meisner, Johann; Murböck, Tobias; Sánchez, Rodolfo; Schmidt, Matthias; Schmidt, Stefan; Steck, Markus; Stöhlker, Thomas; Thompson, Richard C.; Trageser, Christian; Vollbrecht, Jonas; Weinheimer, Christian; Nörtershäuser, Wilfried

2017-05-01

Electrons bound in highly charged heavy ions such as hydrogen-like bismuth 209Bi82+ experience electromagnetic fields that are a million times stronger than in light atoms. Measuring the wavelength of light emitted and absorbed by these ions is therefore a sensitive testing ground for quantum electrodynamical (QED) effects and especially the electron-nucleus interaction under such extreme conditions. However, insufficient knowledge of the nuclear structure has prevented a rigorous test of strong-field QED. Here we present a measurement of the so-called specific difference between the hyperfine splittings in hydrogen-like and lithium-like bismuth 209Bi82+,80+ with a precision that is improved by more than an order of magnitude. Even though this quantity is believed to be largely insensitive to nuclear structure and therefore the most decisive test of QED in the strong magnetic field regime, we find a 7-σ discrepancy compared with the theoretical prediction.

High precision hyperfine measurements in Bismuth challenge bound-state strong-field QED.

PubMed

Ullmann, Johannes; Andelkovic, Zoran; Brandau, Carsten; Dax, Andreas; Geithner, Wolfgang; Geppert, Christopher; Gorges, Christian; Hammen, Michael; Hannen, Volker; Kaufmann, Simon; König, Kristian; Litvinov, Yuri A; Lochmann, Matthias; Maaß, Bernhard; Meisner, Johann; Murböck, Tobias; Sánchez, Rodolfo; Schmidt, Matthias; Schmidt, Stefan; Steck, Markus; Stöhlker, Thomas; Thompson, Richard C; Trageser, Christian; Vollbrecht, Jonas; Weinheimer, Christian; Nörtershäuser, Wilfried

2017-05-16

Electrons bound in highly charged heavy ions such as hydrogen-like bismuth 209 Bi 82+ experience electromagnetic fields that are a million times stronger than in light atoms. Measuring the wavelength of light emitted and absorbed by these ions is therefore a sensitive testing ground for quantum electrodynamical (QED) effects and especially the electron-nucleus interaction under such extreme conditions. However, insufficient knowledge of the nuclear structure has prevented a rigorous test of strong-field QED. Here we present a measurement of the so-called specific difference between the hyperfine splittings in hydrogen-like and lithium-like bismuth 209 Bi 82+,80+ with a precision that is improved by more than an order of magnitude. Even though this quantity is believed to be largely insensitive to nuclear structure and therefore the most decisive test of QED in the strong magnetic field regime, we find a 7-σ discrepancy compared with the theoretical prediction.

The application of quasi-steady approximation in atomic kinetics in simulation of hohlraum radiation drive

NASA Astrophysics Data System (ADS)

Ren, Guoli; Pei, Wenbing; Lan, Ke; Gu, Peijun; Li, Xin; Institute of Applied Physics; Computional Mathematics Team

2011-10-01

In current routine 2D simulation of hohlraum physics, we adopt the principal-quantum- number(n-level) average atom model(AAM). However, the experimental frequency-dependant radiative drive differs from our n-level simulated drive, which reminds us the need of a more detailed atomic kinetics description. The orbital-quantum-number(nl-level) AAM is a natural consideration but the in-line calculation consumes much more resources. We use a new method to built up a nl-level bound electron distribution using in-line n-level calculated plasma condition (such as temperature, density, average ionization degree). We name this method ``quasi-steady approximation.'' Using the re-built nl-level bound electron distribution (Pnl) , we acquire a new hohlraum radiative drive by post-processing. Comparison with the n-level post-processed hohlraum drive shows that we get an almost identical radiation flux but with more-detailed frequency-dependant structures.

Efficient Auger Charge-Transfer Processes in ZnO

NASA Astrophysics Data System (ADS)

Stehr, J. E.; Chen, S. L.; Svensson, B. G.; Buyanova, I. A.; Chen, W. M.

2018-05-01

Photoluminescence and magneto-optical measurements are performed on a line peaking at 3.354 eV (labeled as NBX) in electron-irradiated ZnO. Even though the energy position of the NBX line is close to that for bound excitons in ZnO, it has distinctively different magneto-optical properties. Photoelectron paramagnetic resonance measurements reveal a connection and a charge-transfer process involving NBX and Fe and Al centers. The experimental results are explained within a model which assumes that the NBX is a neutral donor bound exciton at a defect center located near a Fe impurity and an Auger-type charge-transfer process occurs between NBX and Fe3 + . While the NBX dissociates, its hole is captured by an excited state of Fe3 + and the released energy is transferred to the NBX electron, which is excited to the conduction band and subsequently trapped by a substitutional AlZn shallow donor.

Interconversion between Free Charges and Bound Excitons in 2D Hybrid Lead Halide Perovskites.

PubMed

Gélvez-Rueda, María C; Hutter, Eline M; Cao, Duyen H; Renaud, Nicolas; Stoumpos, Constantinos C; Hupp, Joseph T; Savenije, Tom J; Kanatzidis, Mercouri G; Grozema, Ferdinand C

2017-11-30

The optoelectronic properties of hybrid perovskites can be easily tailored by varying their components. Specifically, mixing the common short organic cation (methylammonium (MA)) with a larger one (e.g., butyl ammonium (BA)) results in 2-dimensional perovskites with varying thicknesses of inorganic layers separated by the large organic cation. In both of these applications, a detailed understanding of the dissociation and recombination of electron-hole pairs is of prime importance. In this work, we give a clear experimental demonstration of the interconversion between bound excitons and free charges as a function of temperature by combining microwave conductivity techniques with photoluminescence measurements. We demonstrate that the exciton binding energy varies strongly (between 80 and 370 meV) with the thickness of the inorganic layers. Additionally, we show that the mobility of charges increases with the layer thickness, in agreement with calculated effective masses from electronic structure calculations.

Picosecond absorption studies of photoinduced charge separation in polyelectrolyte bound aromatic chromophores

NASA Astrophysics Data System (ADS)

Shand, M. A.; Rodgers, M. A. J.; Webber, S. E.

1991-02-01

Picosecond absorption studies of photoinduced electron transfer between aromatic chromophores bound to polymethacrylic acid (P) and methylviologen (MV 2+ have been carried out in aqueous solution. The diphenylanthracene copolymer/viologen system at pH 2.8 shows the corresponding redox products DPA + rad and MV + rad arising from the singlet state of DPA with a forward rate constant of electron transfer of 2.6 × 10 9 s -1. At pH 9.0 the quenching of the S 1 state of DPA occurs with no charge separated products being observed. The pyrene copolymer shows no evidence of charge separated products at any pH in the range 2.8-9.0. It is proposed that the differences in the radical pair kinetics arise from differences in the degree of binding of the ground state complexes formed by the donor and acceptor species.

Theoretical study of transition-metal ions bound to benzene

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R.

1992-01-01

Theoretical binding energies are reported for all first-row and selected second-row transition metal ions (M+) bound to benzene. The calculations employ basis sets of at least double-zeta plus polarization quality and account for electron correlation using the modified coupled-pair functional method. While the bending is predominantly electrostatic, the binding energies are significantly increased by electron correlation, because the donation from the metal d orbitals to the benzene pi* orbitals is not well described at the self-consistent-field level. The uncertainties in the computed binding energies are estimated to be about 5 kcal/mol. Although the calculated and experimental binding energies generally agree to within their combined uncertainties, it is likely that the true binding energies lie in the lower portion of the experimental range. This is supported by the very good agreement between the theoretical and recent experimental binding energies for AgC6H6(+).

The widetilde{A}←widetilde{X} ABSORPTION SPECTRUM OF 2-NITROOXYBUTYL PEROXY RADICAL

NASA Astrophysics Data System (ADS)

Eddingsaas, Nathan; Takematsu, Kana; Okumura, Mitchio

2009-06-01

The nitrate radical is an important atmospheric oxidant in the nighttime sky. Nitrate radicals react by addition to alkenes, and in the presence of oxygen form nitrooxyalkyl peroxy radicals. The peroxy radical formed from the reaction of 2-butene, nitrate radical, and oxygen was detected by cavity ringdown spectroscopy (CRDS) via its widetilde{A}←widetilde{X} electronic absorption spectrum. The widetilde{A}←widetilde{X} electronic transition is a bound-bound transition with enough structure to distinguish between different peroxy radicals as well as different conformers of the same peroxy radical. Two conformers of the nitrooxybutyl peroxy radical have been observed; the absorption features are red shifted from the same absorption features of sec-butyl peroxy radical. Calculations on the structure of nitrooxyalkyl peroxy radicals and general trends of the position of the widetilde{A}←widetilde{X} absorption transitions have also been performed and compared to those of unsubstituted peroxy radicals.

Exchange and relaxation effects in low-energy radiationless transitions

NASA Technical Reports Server (NTRS)

Chen, M. H.; Crasemann, B.; Aoyagi, M.; Mark, H.

1978-01-01

The effect on low-energy atomic inner-shell Coster-Kronig and super Coster-Kronig transitions that is produced by relaxation and by exchange between the continuum electron and bound electrons was examined and illustrated by specific calculations for transitions that deexcite the 3p vacancy state of Zn. Taking exchange and relaxation into account is found to reduce, but not to eliminate, the discrepancies between theoretical rates and measurements.

On the Q-dependence of the lowest-order QED corrections and other properties of the ground 11S-states in the two-electron ions

NASA Astrophysics Data System (ADS)

Frolov, Alexei M.

2015-10-01

Formulas and expectation values which are need to determine the lowest-order QED corrections (∼α3) and corresponding recoil (or finite mass) corrections in the two-electron helium-like ions are presented. Other important properties of the two-electron ions are also determined to high accuracy, including the expectation values of the quasi-singular Vinti operator and < reN-2> and < ree-2> expectation values. Elastic scattering of fast electrons by the two-electron ions in the Born approximation is considered. Interpolation formulas are derived for the bound state properties of the two-electron ions as the function of the nuclear electric charge Q.

Ground and excited states of CaSH through electron propagator calculations

NASA Astrophysics Data System (ADS)

Ortiz, J. V.

1990-05-01

Electron propagator calculations of electron affinities of CaSH + produce ground and excited state energies at the optimized, C s minimum of the neutral ground state and at a C ∞v geometry. Feynman-Dyson amplitudes (FDAs) describe the distribution of the least bound electron in various states. The neutral ground state differs from the cation by the occupation of a one-electron state dominated by Ca s functions. Described by FDAs with Ca-S π pseudosymmetry, corresponding excited states have unpaired electrons in orbitals displaying interference between Ca p and d functions. Above these lies a σ pseudosymmetry FDA with principal contributions from Ca d functions. Two FDAs with σ pseudosymmetry follow. Higher excited states exhibit considerable delocalization onto S.

Suppression of electron spin relaxation in Mn-doped GaAs.

PubMed

Astakhov, G V; Dzhioev, R I; Kavokin, K V; Korenev, V L; Lazarev, M V; Tkachuk, M N; Kusrayev, Yu G; Kiessling, T; Ossau, W; Molenkamp, L W

2008-08-15

We report a surprisingly long spin relaxation time of electrons in Mn-doped p-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter, the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.

Suppression of Electron Spin Relaxation in Mn-Doped GaAs

NASA Astrophysics Data System (ADS)

Astakhov, G. V.; Dzhioev, R. I.; Kavokin, K. V.; Korenev, V. L.; Lazarev, M. V.; Tkachuk, M. N.; Kusrayev, Yu. G.; Kiessling, T.; Ossau, W.; Molenkamp, L. W.

2008-08-01

We report a surprisingly long spin relaxation time of electrons in Mn-doped p-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter, the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.

Internal transitions of neutral (X) and negatively charged (X(-)) magneto-excitons investigated by optically detected resonance (ODR) spectroscopy

NASA Astrophysics Data System (ADS)

Nickel, Hans Andreas

Optically detected resonance (ODR) spectroscopy, an experimental technique combining spectroscopy in the far-infrared and visible regimes of the spectrum, has been applied to non-intentionally- and modulation-doped, quasi-2D GaAs/AlGaAs heterostructures at low temperatures and high magnetic fields to study internal transitions of neutral (X) and negatively charged (X--) magneto-excitons. In quasi-2D GaAs/AlGaAs heterostructures with a low density of free carriers, such as undoped multiple-quantum-wells, the ground state of optical excitations is the neutral exciton. This hydrogenic system was studied by far-infrared ODR spectroscopy, and internal excitonic transitions (IETs) 1s → np+/- from the ground state (1s) to excited states (np+/-) were found. Three samples of different well widths were studied systematically, and the behavior of the observed transitions as a function of the sample well-width was as expected. A predicted consequence of an inherent symmetry to the system was verified experimentally for the first time by the simultaneous observation of IETs and electron and hole cyclotron resonance in one sample in one experiment. In addition, it was also found, that the observability of IETs is destroyed as soon as there is a sign of X---recombination in the photoluminescence spectrum. In quantum wells with a small number of excess electrons the ground state of the system under optical excitation is the negatively charged exciton, X--. This mobile system of a hole binding two electrons differs significantly in certain aspects from its immobile impurity analogue, the negatively charged donor ion D-- . The mobility of the charged complex is tied to a hidden symmetry of magnetic translations, which leads to a new selection rule, that forbids X-- bound-to-bound transitions, in contrast to the D -- system, in which these transitions are dominant. In this dissertation, several samples that show X-- recombination in photoluminescence measurements were studied with ODR spectroscopy, and internal singlet and triplet bound-to-continuum transitions were observed for the first time. The experimental results were found to agree well with theoretical numerical calculations. Furthermore, the theoretical predictions were verified: no bound-to-bound X-- internal transition was observed.

Theoretical and computational studies of excitons in conjugated polymers

NASA Astrophysics Data System (ADS)

Barford, William; Bursill, Robert J.; Smith, Richard W.

2002-09-01

We present a theoretical and computational analysis of excitons in conjugated polymers. We use a tight-binding model of π-conjugated electrons, with 1/r interactions for large r. In both the weak-coupling limit (defined by W>>U) and the strong-coupling limit (defined by W<

Formation of nitro-PAHs from the heterogeneous reaction of ambient particle-bound PAHs with N2O5/NO3/NO2

PubMed Central

Zimmermann, Kathryn; Jariyasopit, Narumol; Massey Simonich, Staci L.; Tao, Shu; Atkinson, Roger; Arey, Janet

2014-01-01

Reactions of ambient particles collected from four sites within the Los Angeles, CA air basin and Beijing, China with a mixture of N2O5, NO2, and NO3 radicals were studied in an environmental chamber at ambient pressure and temperature. Exposures in the chamber system resulted in the degradation of particle-bound PAHs and formation of molecular weight (mw) 247 nitropyrenes (NPYs) and nitrofluoranthenes (NFLs), mw 273 nitrotriphenylenes (NTPs), nitrobenz[a]anthracenes (NBaAs), and nitrochrysene (NCHR), and mw 297 nitrobenzo[a]pyrene (NBaP). The distinct isomer distributions resulting from exposure of filter-adsorbed deuterated fluoranthene to N2O5/NO3/NO2 and that collected from the chamber gas-phase suggest that formation of NFLs in ambient particles did not occur by NO3 radical-initiated reaction, but from reaction of N2O5, presumably subsequent to its surface adsorption. Accordingly, isomers known to result from gas-phase radical-initiated reactions of parent PAHs, such as 2-NFL and 2- and 4-NPY, were not enhanced from the exposure of ambient particulate matter to N2O5/NO3/NO2. The reactivity of ambient particles toward nitration by N2O5/NO3/NO2, defined by relative 1-NPY formation, varied significantly, with the relative amounts of freshly emitted particles versus aged particles (particles that had undergone atmospheric chemical processing) affecting the reactivity of particle-bound PAHs toward heterogeneous nitration. Analyses of unexposed ambient samples suggested that, in nighttime samples where NO3 radical-initiated chemistry had occurred, heterogeneous formation of 1-NPY on ambient particles may have contributed to the ambient 1-NPY concentrations at downwind receptor sites. These results, together with observations that 2-NFL is consistently the dominant particle-bound nitro-PAH measured in ambient atmospheres, suggest that for PAHs that exist in both the gas- and particle-phase, the heterogeneous formation of particle-bound nitro-PAHs is a minor formation route compared to gas-phase formation. PMID:23865889

Linking Thermodynamics to Pollutant Reduction Kinetics by Fe2+ Bound to Iron Oxides.

PubMed

Stewart, Sydney M; Hofstetter, Thomas B; Joshi, Prachi; Gorski, Christopher A

2018-05-15

Numerous studies have reported that pollutant reduction rates by ferrous iron (Fe 2+ ) are substantially enhanced in the presence of an iron (oxyhydr)oxide mineral. Developing a thermodynamic framework to explain this phenomenon has been historically difficult due to challenges in quantifying reduction potential ( E H ) values for oxide-bound Fe 2+ species. Recently, our group demonstrated that E H values for hematite- and goethite-bound Fe 2+ can be accurately calculated using Gibbs free energy of formation values. Here, we tested if calculated E H values for oxide-bound Fe 2+ could be used to develop a free energy relationship capable of describing variations in reduction rate constants of substituted nitrobenzenes, a class of model pollutants that contain reducible aromatic nitro groups, using data collected here and compiled from the literature. All the data could be described by a single linear relationship between the logarithms of the surface-area-normalized rate constant ( k SA ) values and E H and pH values [log( k SA ) = - E H /0.059 V - pH + 3.42]. This framework provides mechanistic insights into how the thermodynamic favorability of electron transfer from oxide-bound Fe 2+ relates to redox reaction kinetics.

Mitochondrial rhodanese: membrane-bound and complexed activity.

PubMed

Ogata, K; Volini, M

1990-05-15

We have proposed that phosphorylated and dephosphorylated forms of the mitochondrial sulfurtransferase, rhodanese, function as converter enzymes that interact with membrane-bound iron-sulfur centers of the electron transport chain to modulate the rate of mitochondrial respiration (Ogata, K., Dai, X., and Volini, M. (1989) J. Biol. Chem. 204, 2718-2725). In the present studies, we have explored some structural aspects of the mitochondrial rhodanese system. By sequential extraction of lysed mitochondria with phosphate buffer and phosphate buffer containing 20 mM cholate, we have shown that 30% of the rhodanese activity of bovine liver is membrane-bound. Resolution of cholate extracts on Sephadex G-100 indicates that part of the bound rhodanese is complexed with other mitochondrial proteins. Tests with the complex show that it forms iron-sulfur centers when incubated with the rhodanese sulfur-donor substrate thiosulfate, iron ions, and a reducing agent. Experiments on the rhodanese activity of rat liver mitochondria give similar results. Taken together, the findings indicate that liver rhodanese is in part bound to the mitochondrial membrane as a component of a multiprotein complex that forms iron-sulfur centers. The findings are consistent with the role we propose for rhodanese in the modulation of mitochondrial respiratory activity.

On the Error of the Dixon Plot for Estimating the Inhibition Constant between Enzyme and Inhibitor

ERIC Educational Resources Information Center

Fukushima, Yoshihiro; Ushimaru, Makoto; Takahara, Satoshi

2002-01-01

In textbook treatments of enzyme inhibition kinetics, adjustment of the initial inhibitor concentration for inhibitor bound to enzyme is often neglected. For example, in graphical plots such as the Dixon plot for estimation of an inhibition constant, the initial concentration of inhibitor is usually plotted instead of the true inhibitor…

Computational experience with a parallel algorithm for tetrangle inequality bound smoothing.

PubMed

Rajan, K; Deo, N

1999-09-01

Determining molecular structure from interatomic distances is an important and challenging problem. Given a molecule with n atoms, lower and upper bounds on interatomic distances can usually be obtained only for a small subset of the 2(n(n-1)) atom pairs, using NMR. Given the bounds so obtained on the distances between some of the atom pairs, it is often useful to compute tighter bounds on all the 2(n(n-1)) pairwise distances. This process is referred to as bound smoothing. The initial lower and upper bounds for the pairwise distances not measured are usually assumed to be 0 and infinity. One method for bound smoothing is to use the limits imposed by the triangle inequality. The distance bounds so obtained can often be tightened further by applying the tetrangle inequality--the limits imposed on the six pairwise distances among a set of four atoms (instead of three for the triangle inequalities). The tetrangle inequality is expressed by the Cayley-Menger determinants. For every quadruple of atoms, each pass of the tetrangle inequality bound smoothing procedure finds upper and lower limits on each of the six distances in the quadruple. Applying the tetrangle inequalities to each of the (4n) quadruples requires O(n4) time. Here, we propose a parallel algorithm for bound smoothing employing the tetrangle inequality. Each pass of our algorithm requires O(n3 log n) time on a REW PRAM (Concurrent Read Exclusive Write Parallel Random Access Machine) with O(log(n)n) processors. An implementation of this parallel algorithm on the Intel Paragon XP/S and its performance are also discussed.

CO2 Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane.

PubMed

Khadka, Nimesh; Dean, Dennis R; Smith, Dayle; Hoffman, Brian M; Raugei, Simone; Seefeldt, Lance C

2016-09-06

The reduction of N2 to NH3 by Mo-dependent nitrogenase at its active-site metal cluster FeMo-cofactor utilizes reductive elimination of Fe-bound hydrides with obligatory loss of H2 to activate the enzyme for binding/reduction of N2. Earlier work showed that wild-type nitrogenase and a nitrogenase with amino acid substitutions in the MoFe protein near FeMo-cofactor can catalytically reduce CO2 by two or eight electrons/protons to carbon monoxide (CO) and methane (CH4) at low rates. Here, it is demonstrated that nitrogenase preferentially reduces CO2 by two electrons/protons to formate (HCOO(-)) at rates >10 times higher than rates of CO2 reduction to CO and CH4. Quantum mechanical calculations on the doubly reduced FeMo-cofactor with a Fe-bound hydride and S-bound proton (E2(2H) state) favor a direct reaction of CO2 with the hydride ("direct hydride transfer" reaction pathway), with facile hydride transfer to CO2 yielding formate. In contrast, a significant barrier is observed for reaction of Fe-bound CO2 with the hydride ("associative" reaction pathway), which leads to CO and CH4. Remarkably, in the direct hydride transfer pathway, the Fe-H behaves as a hydridic hydrogen, whereas in the associative pathway it acts as a protic hydrogen. MoFe proteins with amino acid substitutions near FeMo-cofactor (α-70(Val→Ala), α-195(His→Gln)) are found to significantly alter the distribution of products between formate and CO/CH4.

DnaA protein DNA-binding domain binds to Hda protein to promote inter-AAA+ domain interaction involved in regulatory inactivation of DnaA.

PubMed

Keyamura, Kenji; Katayama, Tsutomu

2011-08-19

Chromosomal replication is initiated from the replication origin oriC in Escherichia coli by the active ATP-bound form of DnaA protein. The regulatory inactivation of DnaA (RIDA) system, a complex of the ADP-bound Hda and the DNA-loaded replicase clamp, represses extra initiations by facilitating DnaA-bound ATP hydrolysis, yielding the inactive ADP-bound form of DnaA. However, the mechanisms involved in promoting the DnaA-Hda interaction have not been determined except for the involvement of an interaction between the AAA+ domains of the two. This study revealed that DnaA Leu-422 and Pro-423 residues within DnaA domain IV, including a typical DNA-binding HTH motif, are specifically required for RIDA-dependent ATP hydrolysis in vitro and that these residues support efficient interaction with the DNA-loaded clamp·Hda complex and with Hda in vitro. Consistently, substitutions of these residues caused accumulation of ATP-bound DnaA in vivo and oriC-dependent inhibition of cell growth. Leu-422 plays a more important role in these activities than Pro-423. By contrast, neither of these residues is crucial for DNA replication from oriC, although they are highly conserved in DnaA orthologues. Structural analysis of a DnaA·Hda complex model suggested that these residues make contact with residues in the vicinity of the Hda AAA+ sensor I that participates in formation of a nucleotide-interacting surface. Together, the results show that functional DnaA-Hda interactions require a second interaction site within DnaA domain IV in addition to the AAA+ domain and suggest that these interactions are crucial for the formation of RIDA complexes that are active for DnaA-ATP hydrolysis.

DnaA Protein DNA-binding Domain Binds to Hda Protein to Promote Inter-AAA+ Domain Interaction Involved in Regulatory Inactivation of DnaA*

PubMed Central

Keyamura, Kenji; Katayama, Tsutomu

2011-01-01

Chromosomal replication is initiated from the replication origin oriC in Escherichia coli by the active ATP-bound form of DnaA protein. The regulatory inactivation of DnaA (RIDA) system, a complex of the ADP-bound Hda and the DNA-loaded replicase clamp, represses extra initiations by facilitating DnaA-bound ATP hydrolysis, yielding the inactive ADP-bound form of DnaA. However, the mechanisms involved in promoting the DnaA-Hda interaction have not been determined except for the involvement of an interaction between the AAA+ domains of the two. This study revealed that DnaA Leu-422 and Pro-423 residues within DnaA domain IV, including a typical DNA-binding HTH motif, are specifically required for RIDA-dependent ATP hydrolysis in vitro and that these residues support efficient interaction with the DNA-loaded clamp·Hda complex and with Hda in vitro. Consistently, substitutions of these residues caused accumulation of ATP-bound DnaA in vivo and oriC-dependent inhibition of cell growth. Leu-422 plays a more important role in these activities than Pro-423. By contrast, neither of these residues is crucial for DNA replication from oriC, although they are highly conserved in DnaA orthologues. Structural analysis of a DnaA·Hda complex model suggested that these residues make contact with residues in the vicinity of the Hda AAA+ sensor I that participates in formation of a nucleotide-interacting surface. Together, the results show that functional DnaA-Hda interactions require a second interaction site within DnaA domain IV in addition to the AAA+ domain and suggest that these interactions are crucial for the formation of RIDA complexes that are active for DnaA-ATP hydrolysis. PMID:21708944

On the Singular Incompressible Limit of Inviscid Compressible Fluids

NASA Astrophysics Data System (ADS)

Secchi, P.

We consider the Euler equations of barotropic inviscid compressible fluids in a bounded domain. It is well known that, as the Mach number goes to zero, the compressible flows approximate the solution of the equations of motion of inviscid, incompressible fluids. In this paper we discuss, for the boundary case, the different kinds of convergence under various assumptions on the data, in particular the weak convergence in the case of uniformly bounded initial data and the strong convergence in the norm of the data space.

Blow-up of solutions to a quasilinear wave equation for high initial energy

NASA Astrophysics Data System (ADS)

Li, Fang; Liu, Fang

2018-05-01

This paper deals with blow-up solutions to a nonlinear hyperbolic equation with variable exponent of nonlinearities. By constructing a new control function and using energy inequalities, the authors obtain the lower bound estimate of the L2 norm of the solution. Furthermore, the concavity arguments are used to prove the nonexistence of solutions; at the same time, an estimate of the upper bound of blow-up time is also obtained. This result extends and improves those of [1,2].

Resonant polarization transfer from electron spins to nuclear spins-or to muon spins-in semiconductors

NASA Astrophysics Data System (ADS)

Henstra, A.; Wenckebach, W. Th.

1991-02-01

A review is given of newly developed pulsed Electron Spin Resonance (ESR) methods for dynamic polarization of nuclear spins. The application of two of these methods, Nuclear Orientation Via Electron spin Locking (NOVEL) and the Integrated Solid Effect (ISE), for the polarization of nuclear spins in semiconductors is discussed in more detail. It is proposed to use these methods to study the ESR spectrum of unpaired electrons in the vicinity of muons that are bound in a solid. Thus, ESR would be observed with a sensitivity which is enhanced by about ten orders of magnitude compared to conventional ESR.

FAST TRACK COMMUNICATION: Attosecond correlation dynamics during electron tunnelling from molecules

NASA Astrophysics Data System (ADS)

Walters, Zachary B.; Smirnova, Olga

2010-08-01

In this communication, we present an analytical theory of strong-field ionization of molecules, which takes into account the rearrangement of multiple interacting electrons during the ionization process. We show that such rearrangement offers an alternative pathway to the ionization of orbitals more deeply bound than the highest occupied molecular orbital. This pathway is not subject to the full exponential suppression characteristic of direct tunnel ionization from the deeper orbitals. The departing electron produces an 'attosecond correlation pulse' which controls the rearrangement during the tunnelling process. The shape and duration of this pulse are determined by the electronic structure of the relevant states, molecular orientation and laser parameters.

[Research of the surface oxide film on anodizing Ni-Cr porcelain alloy].

PubMed

Zhu, Song; Sun, Hong-Chen; Zhang, Jing-Wei; Li, Zong-Hui

2006-08-01

To study the shape, thickness and oxide percentage of major metal element of oxide film on Ni-Cr porcelain alloy after anodizing pretreatment. 10 samples were made and divided into 2 groups at random. Then after surface pretreatment, the oxide films of two samples of each group were analyzed using electronic scanning microscope. The rest 3 samples were measured by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Lightly selective solution appeared because the different component parts of the alloy have dissimilar electrode, whose dissolve velocity were quite unlike. The sample's metal surface expanded, so the mechanical interlocking of porcelain and metal increased bond strength. The thickness of oxide film was 1.72 times of the control samples. The oxide percentage of major metal elements such as Cr, Ni and Mo were higher, especially Cr. It initially involved the formation of a thin oxide bound to the alloy and second, the ability of the formed oxide to saturate the porcelain, completing the chemical bond of porcelain to metal. The method of anodizing Ni-Cr porcelain alloy can easily control the forming of oxide film which was thin and its surface pattern was uniform. It is repeated and a good method of surface pretreatment before firing cycle.

Association Mechanisms of Unsaturated C2 Hydrocarbons with Their Cations: Acetylene and Ethylene

NASA Technical Reports Server (NTRS)

Bera, Partha P.; Head-Gordon, Martin; Lee, Timothy J.

2013-01-01

The ion-molecule association mechanism of acetylene and ethylene with their cations is investigated by ab initio quantum chemical methods to understand the structures, association energies, and the vibrational and electronic spectra of the products. Stable puckered cyclic isomers are found as the result of first forming less stable linear and bridge isomers. The puckered cyclic complexes are calculated to be strongly bound, by 87, 35 and 56 kcal/mol for acetylene-acetylene cation, ethylene-ethylene cation and acetylene-ethylene cation, respectively. These stable complexes may be intermediates that participate in further association reactions. There are no association barriers, and no significant inter-conversion barriers, so the initial linear and bridge encounter complexes are unlikely to be observable. However, the energy gap between the bridged and cyclic puckered isomers greatly differs from complex to complex: it is 44 kcal/mol in C4H4 +, but only 6 kcal/mol in C4H8 +. The accurate CCSD(T) calculations summarized above are also compared against less computationally expensive MP2 and density functional theory (DFT) calculations for structures, relative energies, and vibrational spectra. Calculated vibrational spectra are compared against available experiments for cyclobutadiene cation. Electronic spectra are also calculated using time-dependent DFT.

Calculation of photoionization differential cross sections using complex Gauss-type orbitals.

PubMed

Matsuzaki, Rei; Yabushita, Satoshi

2017-09-05

Accurate theoretical calculation of photoelectron angular distributions for general molecules is becoming an important tool to image various chemical reactions in real time. We show in this article that not only photoionization total cross sections but also photoelectron angular distributions can be accurately calculated using complex Gauss-type orbital (cGTO) basis functions. Our method can be easily combined with existing quantum chemistry techniques including electron correlation effects, and applied to various molecules. The so-called two-potential formula is applied to represent the transition dipole moment from an initial bound state to a final continuum state in the molecular coordinate frame. The two required continuum functions, the zeroth-order final continuum state and the first-order wave function induced by the photon field, have been variationally obtained using the complex basis function method with a mixture of appropriate cGTOs and conventional real Gauss-type orbitals (GTOs) to represent the continuum orbitals as well as the remaining bound orbitals. The complex orbital exponents of the cGTOs are optimized by fitting to the outgoing Coulomb functions. The efficiency of the current method is demonstrated through the calculations of the asymmetry parameters and molecular-frame photoelectron angular distributions of H2+ and H2 . In the calculations of H2 , the static exchange and random phase approximations are employed, and the dependence of the results on the basis functions is discussed. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Investigating ozone-induced decomposition of surface-bound permethrin for conditions in aircraft cabins.

PubMed

Coleman, B K; Wells, J R; Nazaroff, W W

2010-02-01

The reaction of ozone with permethrin can potentially form phosgene. Published evidence on ozone levels and permethrin surface concentrations in aircraft cabins indicated that significant phosgene formation might occur in this setting. A derivatization technique was developed to detect phosgene with a lower limit of detection of 2 ppb. Chamber experiments were conducted with permethrin-coated materials (glass, carpet, seat fabric, and plastic) exposed to ozone under cabin-relevant conditions (150 ppb O(3), 4.5/h air exchange rate, <1% relative humidity, 1700 ng/cm(2) of permethrin). Phosgene was not detected in these experiments. Reaction of ozone with permethrin appears to be hindered by the electron-withdrawing chlorine atoms adjacent to the double bond in permethrin. Experimental results indicate that the upper limit on the reaction probability of ozone with surface-bound permethrin is approximately 10(-7). Extrapolation by means of material-balance modeling indicates that the upper limit on the phosgene level in aircraft cabins resulting from this chemistry is approximately 1 microg/m(3) or approximately 0.3 ppb. It was thus determined that phosgene formation, if it occurs in aircraft cabins, is not likely to exceed relevant, health-based phosgene exposure guidelines. Phosgene formation from ozone-initiated oxidation of permethrin in the aircraft cabin environment, if it occurs, is estimated to generate levels below the California Office of Environmental Health Hazard Assessment acute reference exposure level of 4 microg/m(3) or approximately 1 ppb.

Multi-Orbital contributions in High Harmonic Generation

NASA Astrophysics Data System (ADS)

Guehr, Markus

2009-05-01

The high harmonic spectrum generated from atoms or molecules in a strong laser field contains information about the electronic structure of the generation medium. In the high harmonic generation (HHG) process, a free electron wave packet tunnel-ionizes from the molecular orbital in a strong laser field. After being accelerated by the laser electric field, the free electron wave packet coherently recombines to the orbital from which is was initially ionized, thereby emitting the harmonic spectrum. Interferences between the free electron wave packet and the molecular orbital will shape the spectrum in a characteristic way. These interferences have been used to tomographically image the highest occupied molecular orbital (HOMO) of N2 [1]. Molecular electronic states energetically below the HOMO should contribute to laser-driven high harmonic generation (HHG), but this behavior has not been observed previously. We have observed evidence of HHG from multiple orbitals in aligned N2 [2]. The tunneling ionization (and therefore the harmonic generation) is most efficient if the orbital has a large extension in the direction of the harmonic generation polarization. The HOMO with its σg symmetry therefore dominates the harmonic spectrum if the molecular axis is parallel to the harmonic generation polarization, the lower bound πu HOMO-1 dominates in the perpendicular case. The HOMO contributions appear as a regular plateau with a cutoff in the HHG spectrum. In contrast, the HOMO-1 signal is strongly peaked in the cutoff region. We explain this by semi-classical simulations of the recombination process that show constructive interferences between the HOMO-1 and the recombining wave packet in the cutoff region. The ability to monitor several orbitals opens the route to imaging coherent superpositions of electronic orbitals. [1] J. Itatani et al., Nature 432, 867 (2004)[2] B. K. McFarland, J. P. Farrell, P. H. Bucksbaum and M. Gühr, Science 322, 1232 (2008)

Selenite reduction by the thioredoxin system: kinetics and identification of protein-bound selenide.

PubMed

Tamura, Takashi; Sato, Kumi; Komori, Kentaro; Imai, Takeshi; Kuwahara, Mitsuhiko; Okugochi, Takahiro; Mihara, Hisaaki; Esaki, Nobuyoshi; Inagaki, Kenji

2011-01-01

Selenite (SeO(3)(2-)) assimilation into a bacterial selenoprotein depends on thioredoxin (trx) reductase in Esherichia coli, but the molecular mechanism has not been elucidated. The mineral-oil overlay method made it possible to carry out anaerobic enzyme assay, which demonstrated an initial lag-phase followed by time-dependent steady NADPH consumption with a positive cooperativity toward selenite and trx. SDS-PAGE/autoradiography using (75)Se-labeled selenite as substrate revealed the formation of trx-bound selenium in the reaction mixture. The protein-bound selenium has metabolic significance in being stabilized in the divalent state, and it also produced the selenopersulfide (-S-SeH) form by the catalysis of E. coli trx reductase (TrxB).

An upper bound on the second order asymptotic expansion for the quantum communication cost of state redistribution

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

Datta, Nilanjana, E-mail: n.datta@statslab.cam.ac.uk; Hsieh, Min-Hsiu, E-mail: Min-Hsiu.Hsieh@uts.edu.au; Oppenheim, Jonathan, E-mail: j.oppenheim@ucl.ac.uk

State redistribution is the protocol in which given an arbitrary tripartite quantum state, with two of the subsystems initially being with Alice and one being with Bob, the goal is for Alice to send one of her subsystems to Bob, possibly with the help of prior shared entanglement. We derive an upper bound on the second order asymptotic expansion for the quantum communication cost of achieving state redistribution with a given finite accuracy. In proving our result, we also obtain an upper bound on the quantum communication cost of this protocol in the one-shot setting, by using the protocol ofmore » coherent state merging as a primitive.« less

Resource Constrained Planning of Multiple Projects with Separable Activities

NASA Astrophysics Data System (ADS)

Fujii, Susumu; Morita, Hiroshi; Kanawa, Takuya

In this study we consider a resource constrained planning problem of multiple projects with separable activities. This problem provides a plan to process the activities considering a resource availability with time window. We propose a solution algorithm based on the branch and bound method to obtain the optimal solution minimizing the completion time of all projects. We develop three methods for improvement of computational efficiency, that is, to obtain initial solution with minimum slack time rule, to estimate lower bound considering both time and resource constraints and to introduce an equivalence relation for bounding operation. The effectiveness of the proposed methods is demonstrated by numerical examples. Especially as the number of planning projects increases, the average computational time and the number of searched nodes are reduced.

Initation of pitting corrosion in martensitic stainless steels. [17-4PH; 13-8Mo; Custom 450

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

Cieslak, W.R.; Semarge, R.E.; Bovard, F.S.

1986-01-01

The form of localized corrosion known as pitting often initiates preferentially at microstructural inhomogeneities. The pit initiation resistance, therefore, is controlled by the characteristics of the initiation sites, rather than by the bulk material composition. This investigation correlates the pit initiation resistance, as measured by critical pitting potentials, with preferred pit initiation sites for 3 martensitic stainless steels. Pit initiation sites are determined by secondary electron (SE) and backscattered electron (BSE) imaging and energy dispersive and wavelength dispersive spectrometries (EDS and WDS) with a scalling electron microscope (SEM) and an electron probe microanalyzer (EPMA).

Impact of a star formation efficiency profile on the evolution of open clusters

NASA Astrophysics Data System (ADS)

Shukirgaliyev, B.; Parmentier, G.; Berczik, P.; Just, A.

2017-09-01

Aims: We study the effect of the instantaneous expulsion of residual star-forming gas on star clusters in which the residual gas has a density profile that is shallower than that of the embedded cluster. This configuration is expected if star formation proceeds with a given star-formation efficiency per free-fall time in a centrally concentrated molecular gas clump. Methods: We performed direct N-body simulations whose initial conditions were generated by the program "mkhalo" from the package "falcON", adapted for our models. Our model clusters initially had a Plummer profile and are in virial equilibrium with the gravitational potential of the cluster-forming clump. The residual gas contribution was computed based on a local-density driven clustered star formation model. Our simulations included mass loss by stellar evolution and the tidal field of a host galaxy. Results: We find that a star cluster with a minimum global star formation efficiency (SFE) of 15 percent is able to survive instantaneous gas expulsion and to produce a bound cluster. Its violent relaxation lasts no longer than 20 Myr, independently of its global SFE and initial stellar mass. At the end of violent relaxation, the bound fractions of the surviving clusters with the same global SFEs are similar, regardless of their initial stellar mass. Their subsequent lifetime in the gravitational field of the Galaxy depends on their bound stellar masses. Conclusions: We therefore conclude that the critical SFE needed to produce a bound cluster is 15 percent, which is roughly half the earlier estimates of 33 percent. Thus we have improved the survival likelihood of young clusters after instantaneous gas expulsion. Young clusters can now survive instantaneous gas expulsion with a global SFEs as low as the SFEs observed for embedded clusters in the solar neighborhood (15-30 percent). The reason is that the star cluster density profile is steeper than that of the residual gas. However, in terms of the effective SFE, measured by the virial ratio of the cluster at gas expulsion, our results are in agreement with previous studies.

Structural analysis of the PSD-95 cluster by electron tomography and CEMOVIS: a proposal for the application of the genetically encoded metallothionein tag.

PubMed

Hirabayashi, Ai; Fukunaga, Yuko; Miyazawa, Atsuo

2014-06-01

Postsynaptic density-95 (PSD-95) accumulates at excitatory postsynapses and plays important roles in the clustering and anchoring of numerous proteins at the PSD. However, a detailed ultrastructural analysis of clusters exclusively consisting of PSD-95 has never been performed. Here, we employed a genetically encoded tag, three tandem repeats of metallothionein (3MT), to study the structure of PSD-95 clusters in cells by electron tomography and cryo-electron microscopy of vitreous sections. We also performed conventional transmission electron microscopy (TEM). Cultured hippocampal neurons expressing a fusion protein of PSD-95 coupled to 3MT (PDS-95-3MT) were incubated with CdCl2 to result in the formation of Cd-bound PSD-95-3MT. Two types of electron-dense deposits composed of Cd-bound PSD-95-3MT were observed in these cells by TEM, as reported previously. Electron tomography revealed the presence of membrane-shaped structures representing PSD-95 clusters at the PSD and an ellipsoidal structure located in the non-synaptic cytoplasm. By TEM, the PSD-95 clusters appeared to be composed of a number of dense cores. In frozen hydrated sections, these dense cores were also found beneath the postsynaptic membrane. Taken together, our findings suggest that dense cores of PSD-95 aggregate to form the larger clusters present in the PSD and the non-synaptic cytoplasm. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

A new concept in laser-assisted chemistry - The electronic-field representation

NASA Technical Reports Server (NTRS)

George, T. F.; Zimmerman, I. H.; Yuan, J.-M.; Laing, J. R.; Devries, P. L.

1977-01-01

Electronic-field representation is proposed as a technique for laser-assisted chemistry. Specifically, it is shown that several field-assisted chemical processes can be described in terms of mixed matter-field quantum states and their associated energies. The technique may be used to analyze the effects exerted by an intense laser on both bound and unbound molecular systems, and to investigate other field-induced effects including multiphoton processes, emission, and photodissociation.

An Externalized Polypeptide Partitions between Two Distinct Sites on Genome-Released Poliovirus Particles ▿

PubMed Central

Lin, Jun; Cheng, Naiqian; Chow, Marie; Filman, David J.; Steven, Alasdair C.; Hogle, James M.; Belnap, David M.

2011-01-01

During cell entry, native poliovirus (160S) converts to a cell-entry intermediate (135S) particle, resulting in the externalization of capsid proteins VP4 and the amino terminus of VP1 (residues 1 to 53). Externalization of these entities is followed by release of the RNA genome (uncoating), leaving an empty (80S) particle. The antigen-binding fragment (Fab) of a monospecific peptide 1 (P1) antibody, which was raised against a peptide corresponding to amino-terminal residues 24 to 40 of VP1, was utilized to track the location of the amino terminus of VP1 in the 135S and 80S states of poliovirus particles via cryogenic electron microscopy (cryo-EM) and three-dimensional image reconstruction. On 135S, P1 Fabs bind to a prominent feature on the external surface known as the “propeller tip.” In contrast, our initial 80S-P1 reconstruction showed P1 Fabs also binding to a second site, at least 50 Å distant, at the icosahedral 2-fold axes. Further analysis showed that the overall population of 80S-P1 particles consisted of three kinds of capsids: those with P1 Fabs bound only at the propeller tips, P1 Fabs bound only at the 2-fold axes, or P1 Fabs simultaneously bound at both positions. Our results indicate that, in 80S particles, a significant fraction of VP1 can deviate from icosahedral symmetry. Hence, this portion of VP1 does not change conformation synchronously when switching from the 135S state. These conclusions are compatible with previous observations of multiple conformations of the 80S state and suggest that movement of the amino terminus of VP1 has a role in uncoating. Similar deviations from icosahedral symmetry may be biologically significant during other viral transitions. PMID:21775460

In Situ Transmission Electron Microscopy Study of Electron Beam-Induced Transformations in Colloidal Cesium Lead Halide Perovskite Nanocrystals.

PubMed

Dang, Zhiya; Shamsi, Javad; Palazon, Francisco; Imran, Muhammad; Akkerman, Quinten A; Park, Sungwook; Bertoni, Giovanni; Prato, Mirko; Brescia, Rosaria; Manna, Liberato

2017-02-28

An increasing number of studies have recently reported the rapid degradation of hybrid and all-inorganic lead halide perovskite nanocrystals under electron beam irradiation in the transmission electron microscope, with the formation of nanometer size, high contrast particles. The nature of these nanoparticles and the involved transformations in the perovskite nanocrystals are still a matter of debate. Herein, we have studied the effects of high energy (80/200 keV) electron irradiation on colloidal cesium lead bromide (CsPbBr 3 ) nanocrystals with different shapes and sizes, especially 3 nm thick nanosheets, a morphology that facilitated the analysis of the various ongoing processes. Our results show that the CsPbBr 3 nanocrystals undergo a radiolysis process, with electron stimulated desorption of a fraction of bromine atoms and the reduction of a fraction of Pb 2+ ions to Pb 0 . Subsequently Pb 0 atoms diffuse and aggregate, giving rise to the high contrast particles, as previously reported by various groups. The diffusion is facilitated by both high temperature and electron beam irradiation. The early stage Pb nanoparticles are epitaxially bound to the parent CsPbBr 3 lattice, and evolve into nonepitaxially bound Pb crystals upon further irradiation, leading to local amorphization and consequent dismantling of the CsPbBr 3 lattice. The comparison among CsPbBr 3 nanocrystals with various shapes and sizes evidences that the damage is particularly pronounced at the corners and edges of the surface, due to a lower diffusion barrier for Pb 0 on the surface than inside the crystal and the presence of a larger fraction of under-coordinated atoms.

Origin of poor doping efficiency in solution processed organic semiconductors.

PubMed

Jha, Ajay; Duan, Hong-Guang; Tiwari, Vandana; Thorwart, Michael; Miller, R J Dwayne

2018-05-21

Doping is an extremely important process where intentional insertion of impurities in semiconductors controls their electronic properties. In organic semiconductors, one of the convenient, but inefficient, ways of doping is the spin casting of a precursor mixture of components in solution, followed by solvent evaporation. Active control over this process holds the key to significant improvements over current poor doping efficiencies. Yet, an optimized control can only come from a detailed understanding of electronic interactions responsible for the low doping efficiencies. Here, we use two-dimensional nonlinear optical spectroscopy to examine these interactions in the course of the doping process by probing the solution mixture of doped organic semiconductors. A dopant accepts an electron from the semiconductor and the two ions form a duplex of interacting charges known as ion-pair complexes. Well-resolved off-diagonal peaks in the two-dimensional spectra clearly demonstrate the electronic connectivity among the ions in solution. This electronic interaction represents a well resolved electrostatically bound state, as opposed to a random distribution of ions. We developed a theoretical model to recover the experimental data, which reveals an unexpectedly strong electronic coupling of ∼250 cm -1 with an intermolecular distance of ∼4.5 Å between ions in solution, which is approximately the expected distance in processed films. The fact that this relationship persists from solution to the processed film gives direct evidence that Coulomb interactions are retained from the precursor solution to the processed films. This memory effect renders the charge carriers equally bound also in the film and, hence, results in poor doping efficiencies. This new insight will help pave the way towards rational tailoring of the electronic interactions to improve doping efficiencies in processed organic semiconductor thin films.

Oxidation of the FAD cofactor to the 8-formyl-derivative in human electron-transferring flavoprotein

PubMed Central

Augustin, Peter; Toplak, Marina; Fuchs, Katharina; Gerstmann, Eva Christine; Prassl, Ruth; Winkler, Andreas; Macheroux, Peter

2018-01-01

The heterodimeric human (h) electron-transferring flavoprotein (ETF) transfers electrons from at least 13 different flavin dehydrogenases to the mitochondrial respiratory chain through a non-covalently bound FAD cofactor. Here, we describe the discovery of an irreversible and pH-dependent oxidation of the 8α-methyl group to 8-formyl-FAD (8f-FAD), which represents a unique chemical modification of a flavin cofactor in the human flavoproteome. Furthermore, a set of hETF variants revealed that several conserved amino acid residues in the FAD-binding pocket of electron-transferring flavoproteins are required for the conversion to the formyl group. Two of the variants generated in our study, namely αR249C and αT266M, cause glutaric aciduria type II, a severe inherited disease. Both of the variants showed impaired formation of 8f-FAD shedding new light on the potential molecular cause of disease development. Interestingly, the conversion of FAD to 8f-FAD yields a very stable flavin semiquinone that exhibited slightly lower rates of electron transfer in an artificial assay system than hETF containing FAD. In contrast, the formation of 8f-FAD enhanced the affinity to human dimethylglycine dehydrogenase 5-fold, indicating that formation of 8f-FAD modulates the interaction of hETF with client enzymes in the mitochondrial matrix. Thus, we hypothesize that the FAD cofactor bound to hETF is subject to oxidation in the alkaline (pH 8) environment of the mitochondrial matrix, which may modulate electron transport between client dehydrogenases and the respiratory chain. This discovery challenges the current concepts of electron transfer processes in mitochondria. PMID:29301933

Emergent low-energy bound states in the two-orbital Hubbard model

DOE PAGES

Nunez-Fernandez, Y.; Kotliar, G.; Hallberg, K.

2018-03-30

A repulsive Coulomb interaction between electrons in different orbitals in correlated materials can give rise to bound quasiparticle states. We study the nonhybridized two-orbital Hubbard model with intra- (inter)orbital interaction U (U 12) and different bandwidths using an improved dynamical mean-field theory numerical technique which leads to reliable spectra on the real energy axis directly at zero temperature. We find that a finite density of states at the Fermi energy in one band is correlated with the emergence of well-defined quasiparticle states at excited energies Δ = U - U 12 in the other band. These excitations are interband holon-doublonmore » bound states. At the symmetric point U = U 12, the quasiparticle peaks are located at the Fermi energy, leading to a simultaneous and continuous Mott transition settling a long-standing controversy.« less

Temporal analysis of nonresonant two-photon coherent control involving bound and dissociative molecular states

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

Su Jing; Chen Shaohao; Jaron-Becker, Agnieszka

We theoretically study the control of two-photon excitation to bound and dissociative states in a molecule induced by trains of laser pulses, which are equivalent to certain sets of spectral phase modulated pulses. To this end, we solve the time-dependent Schroedinger equation for the interaction of molecular model systems with an external intense laser field. Our numerical results for the temporal evolution of the population in the excited states show that, in the case of an excited dissociative state, control schemes, previously validated for the atomic case, fail due to the coupling of electronic and nuclear motion. In contrast, formore » excitation to bound states the two-photon excitation probability is controlled via the time delay and the carrier-envelope phase difference between two consecutive pulses in the train.« less

Emergent low-energy bound states in the two-orbital Hubbard model

NASA Astrophysics Data System (ADS)

Núñez-Fernández, Y.; Kotliar, G.; Hallberg, K.

2018-03-01

A repulsive Coulomb interaction between electrons in different orbitals in correlated materials can give rise to bound quasiparticle states. We study the nonhybridized two-orbital Hubbard model with intra- (inter)orbital interaction U (U12) and different bandwidths using an improved dynamical mean-field theory numerical technique which leads to reliable spectra on the real energy axis directly at zero temperature. We find that a finite density of states at the Fermi energy in one band is correlated with the emergence of well-defined quasiparticle states at excited energies Δ =U -U12 in the other band. These excitations are interband holon-doublon bound states. At the symmetric point U =U12 , the quasiparticle peaks are located at the Fermi energy, leading to a simultaneous and continuous Mott transition settling a long-standing controversy.

Ab initio theoretical study of dipole-bound anions of molecular complexes: (HF)3- and (HF)4- anions

NASA Astrophysics Data System (ADS)

Ramaekers, Riet; Smith, Dayle M. A.; Smets, Johan; Adamowicz, Ludwik

1997-12-01

Ab initio calculations have been performed to determine structures and vertical electron detachment energy (VDE) of the hydrogen fluoride trimer and tetramer anions, (HF)3- and (HF)4-. In these systems the excess electron is bound by the dipole field of the complex. It was determined that, unlike the neutral complexes which prefer the cyclic structures, the equilibrium geometries of the anions have "zig-zag" shapes. For both complexes the predicted VDEs are positive [210 meV and 363 meV for (HF)3- and (HF)4-, respectively], indicating that the anions are stable systems with respect to the vertical electron detachment. These results were obtained at the coupled-cluster level of theory with single, double and triple excitations [CCSD(T) method; the triple-excitation contribution in this method is calculated approximately using the perturbation approach] with the anion geometries obtained using the second-order Møller-Plesset perturbation theory (MP2) method. The same approach was also used to determine the adiabatic electron affinities (AEA) of (HF)3 and (HF)4. In addition to the electronic contribution, we also calculated the contributions (using the harmonic approximation) resulting from different zero-point vibration energies of the neutral and anionic clusters. The calculations predicted that while the AEA of (HF)3 is positive (44 meV), the AEA for (HF)4 is marginally negative (-16 meV). This suggests that the (HF)3- anion should be a stable system, while the (HF)4- is probably metastable.

Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study.

PubMed

Kobyłecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

2008-01-28

The propensity of four representative conformations of 2(')-deoxyadenosine-5(')-monophosphate (5(')-dAMPH) to bind an excess electron has been studied at the B3LYP6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5(')-dAMPH form adiabatically stable anions. The type of an anionic 5(')-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4(')-C5(') bond. The adiabatic electron affinity of the a_south-syn anion is 1.19 eV, while its vertical detachment energy is 1.89 eV. Our results are compared with the photoelectron spectrum (PES) of 5(')-dAMPH(-) measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding.

Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study

NASA Astrophysics Data System (ADS)

Kobyłecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

2008-01-01

The propensity of four representative conformations of 2'-deoxyadenosine-5'-monophosphate (5'-dAMPH) to bind an excess electron has been studied at the B3LYP /6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5'-dAMPH form adiabatically stable anions. The type of an anionic 5'-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4'-C5' bond. The adiabatic electron affinity of the a&barbelow;south-syn anion is 1.19eV, while its vertical detachment energy is 1.89eV. Our results are compared with the photoelectron spectrum (PES) of 5'-dAMPH- measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding.

Kinetic and spectral properties of isovaleryl-CoA dehydrogenase and interaction with ligands.

PubMed

Mohsen, Al-Walid A; Vockley, Jerry

2015-01-01

Isovaleryl-CoA dehydrogenase (IVD) catalyzes the conversion of isovaleryl-CoA to 3-methylcrotonyl-CoA and the transfer of electrons to the electron transfer flavoprotein (ETF). Recombinant human IVD purifies with bound CoA-persulfide. A modified purification protocol was developed to isolate IVD without bound CoA-persulfide and to protect the protein thiols from oxidation. The CoA-persulfide-free IVD specific activity was 112.5 μmol porcine ETF min(-)(1) mg(-)(1), which was ∼20-fold higher than that of its CoA-persulfide bound form. The Km and catalytic efficiency (kcat/Km) for isovaleryl-CoA were 1.0 μM and 4.3 × 10(6) M(-1) s(-1) per monomer, respectively, and its Km for ETF was 2.0 μM. Anaerobic titration of isovaleryl-CoA into an IVD solution resulted in a stable blue complex with increased absorbance at 310 nm, decreased absorbance at 373 and 447 nm, and the appearance of the charge transfer complex band at 584 nm. The apparent dissociation constant (KDapp) determined spectrally for isovaleryl-CoA was 0.54 μM. Isovaleryl-CoA, acetoacetyl-CoA, methylenecyclopropyl-acetyl-CoA, and ETF induced CD spectral changes at the 250-500 nm region while isobutyryl-CoA did not, suggesting conformational changes occur at the flavin ring that are ligand specific. Replacement of the IVD Trp166 with a Phe did not block IVD interaction with ETF, indicating that its indole ring is not essential for electron transfer to ETF. A twelve amino acid synthetic peptide that matches the sequence of the ETF docking peptide competitively inhibited the enzyme reaction when ETF was used as the electron acceptor with a Ki of 1.5 mM. Copyright © 2014 Elsevier B.V. and Société française de biochimie et biologie Moléculaire (SFBBM). All rights reserved.

Adhesion of the clay minerals montmorillonite, kaolinite, and attapulgite reduces respiration of Histoplasma capsulatum.

PubMed Central

Lavie, S; Stotzky, G

1986-01-01

The respiration of three phenotypes of Histoplasma capsulatum, the causal agent of histoplasmosis in humans, was markedly reduced by low concentrations of montmorillonite but was reduced less by even higher concentrations of kaolinite or attapulgite (palygorskite). The reduction in respiration followed a pattern that suggested saturation-type kinetics: an initial sharp reduction that occurred with low concentrations of clay (0.01 to 0.5% [wt/vol]), followed by a more gradual reduction with higher concentrations (1 to 8%). Increases in viscosity (which could impair the movement of O2) caused by the clays were not responsible for the reduction in respiration, and the clays did not interfere with the availability of nutrients. Scanning electron microscopy after extensive washing showed that the clay particles were tightly bound to the hyphae, suggesting that the clays reduced the rate of respiration of H. capsulatum by adhering to the mycelial surface and, thereby, interfered with the movement of nutrients, metabolites, and gases across the mycelial wall. Images PMID:3954340

Adhesion of the clay minerals montmorillonite, kaolinite, and attapulgite reduces respiration of Histoplasma capsulatum.

PubMed

Lavie, S; Stotzky, G

1986-01-01

The respiration of three phenotypes of Histoplasma capsulatum, the causal agent of histoplasmosis in humans, was markedly reduced by low concentrations of montmorillonite but was reduced less by even higher concentrations of kaolinite or attapulgite (palygorskite). The reduction in respiration followed a pattern that suggested saturation-type kinetics: an initial sharp reduction that occurred with low concentrations of clay (0.01 to 0.5% [wt/vol]), followed by a more gradual reduction with higher concentrations (1 to 8%). Increases in viscosity (which could impair the movement of O2) caused by the clays were not responsible for the reduction in respiration, and the clays did not interfere with the availability of nutrients. Scanning electron microscopy after extensive washing showed that the clay particles were tightly bound to the hyphae, suggesting that the clays reduced the rate of respiration of H. capsulatum by adhering to the mycelial surface and, thereby, interfered with the movement of nutrients, metabolites, and gases across the mycelial wall.

Quantum Mechanical Calculations of Free Energy and Open-Circuit Voltage in Lattice Modeled Organic Photovoltaic Devices

NASA Astrophysics Data System (ADS)

Lankevich, Vladimir; Bittner, Eric

In organic photovoltaic devices (OPVs), initially bound electron and hole can take many different paths to dissociate and become free charge carriers. This leads to the increase in their density of states and therefore increase in the entropy of the system. Accurate description of the energy barriers that charges have to overcome, therefore requires calculation of the free energy. Free energy of an OPV is directly related to its open-circuit voltage and depends only on few important parameters such as average life-time of a charge-transfer state, average energy of the charge-transfer state and energetic disorder in the system. We extend these ideas to the quantum mechanical simulations of the dissociation in the lattice modeled bulk-heterojunction system. We observe average excitonic and free energies that agree with theoretical predictions and the number of experimental results from previous studies. We study effects of the energy disorder and importance of the dimensionality and morphology in materials such as polymer-fullerene blends.

Characterization of Glutaredoxin Fe-S Cluster-Binding Interactions Using Circular Dichroism Spectroscopy.

PubMed

Albetel, Angela-Nadia; Outten, Caryn E

2018-01-01

Monothiol glutaredoxins (Grxs) with a conserved Cys-Gly-Phe-Ser (CGFS) active site are iron-sulfur (Fe-S) cluster-binding proteins that interact with a variety of partner proteins and perform crucial roles in iron metabolism including Fe-S cluster transfer, Fe-S cluster repair, and iron signaling. Various analytical and spectroscopic methods are currently being used to monitor and characterize glutaredoxin Fe-S cluster-dependent interactions at the molecular level. The electronic, magnetic, and vibrational properties of the protein-bound Fe-S cluster provide a convenient handle to probe the structure, function, and coordination chemistry of Grx complexes. However, some limitations arise from sample preparation requirements, complexity of individual techniques, or the necessity for combining multiple methods in order to achieve a complete investigation. In this chapter, we focus on the use of UV-visible circular dichroism spectroscopy as a fast and simple initial approach for investigating glutaredoxin Fe-S cluster-dependent interactions. © 2018 Elsevier Inc. All rights reserved.

A non-ideal MHD model for structure formation

NASA Astrophysics Data System (ADS)

Karmakar, Pralay Kumar; Sarma, Pankaj

2018-02-01

The evolutionary initiation dynamics of triggered planetary structure formation is indeed a complex process yet to be well understood. We herein develop a theoretical classical model to see the gravitational fragmentation kinetics of the viscoelastic non-ideal magneto-hydro-dynamic (MHD) fabric. The inhomogeneous planetary disk is primarily composed of heavier dust grains (strongly correlated) together with relatively lighter electrons, ions and neutrals (weakly correlated) in a mean-fluidic approximation. A normal harmonic mode analysis results in a quadratic dispersion relation of a unique shape. It is demonstrated that the growth rate of the MHD fluctuations (magnetosonic) contributing to the planet formation rate, apart from the wave vector and its projection orientation, has a pure explicit dependency on the viscoelastic parameters. The analysis specifically shows that the effective generalized viscosity (χ) , viscoelastic relaxation time (τm) , and K-orientation (θ) play as destabilizing agencies against the non-local gravitational disk collapse. The relevancy is briefly indicated in the real astronomical context of bounded planetary structure formation and evolution.

Long-Lived Correlated Triplet Pairs in a π-Stacked Crystalline Pentacene Derivative.

PubMed

Folie, Brendan D; Haber, Jonah B; Refaely-Abramson, Sivan; Neaton, Jeffrey B; Ginsberg, Naomi S

2018-02-14

Singlet fission is the spin-conserving process by which a singlet exciton splits into two triplet excitons. Singlet fission occurs via a correlated triplet pair intermediate, but direct evidence of this state has been scant, and in films of TIPS-pentacene, a small molecule organic semiconductor, even the rate of fission has been unclear. We use polarization-resolved transient absorption microscopy on individual crystalline domains of TIPS-pentacene to establish the fission rate and demonstrate that the initially created triplets remain bound for a surprisingly long time, hundreds of picoseconds, before separating. Furthermore, using a broadband probe, we show that it is possible to determine absorbance spectra of individual excited species in a crystalline solid. We find that triplet interactions perturb the absorbance, and provide evidence that triplet interaction and binding could be caused by the π-stacked geometry. Elucidating the relationship between the lattice structure and the electronic structure and dynamics has important implications for the creation of photovoltaic devices that aim to boost efficiency via singlet fission.

The beginning of kinesin's force-generating cycle visualized at 9-Å resolution

PubMed Central

Sindelar, Charles V.; Downing, Kenneth H.

2007-01-01

We have used cryo-electron microscopy of kinesin-decorated microtubules to resolve the structure of the motor protein kinesin's crucial nucleotide response elements, switch I and the switch II helix, in kinesin's poorly understood nucleotide-free state. Both of the switch elements undergo conformational change relative to the microtubule-free state. The changes in switch I suggest a role for it in “ejecting” adenosine diphosphate when kinesin initially binds to the microtubule. The switch II helix has an N-terminal extension, apparently stabilized by conserved microtubule contacts, implying a microtubule activation mechanism that could convey the state of the bound nucleotide to kinesin's putative force-delivering element (the “neck linker”). In deriving this structure, we have adapted an image-processing technique, single-particle reconstruction, for analyzing decorated microtubules. The resulting reconstruction visualizes the asymmetric seam present in native, 13-protofilament microtubules, and this method will provide an avenue to higher-resolution characterization of a variety of microtubule- binding proteins, as well as the microtubule itself. PMID:17470637

Two photon excitation of atomic oxygen

NASA Technical Reports Server (NTRS)

Pindzola, M. S.

1977-01-01

A standard perturbation expansion in the atom-radiation field interaction is used to calculate the two photon excitation cross section for 1s(2) 2s(2) 2p(4) p3 to 1s(2) 2s(2) 2p(3) (s4) 3p p3 transition in atomic oxygen. The summation over bound and continuum intermediate states is handled by solving the equivalent inhomogeneous differential equation. Exact summation results differ by a factor of 2 from a rough estimate obtained by limiting the intermediate state summation to one bound state. Higher order electron correlation effects are also examined.

Out-of-Bounds Hydrodynamics in Anisotropic Dirac Fluids

NASA Astrophysics Data System (ADS)

Link, Julia M.; Narozhny, Boris N.; Kiselev, Egor I.; Schmalian, Jörg

2018-05-01

We study hydrodynamic transport in two-dimensional, interacting electronic systems with merging Dirac points at charge neutrality. The dispersion along one crystallographic direction is Dirac-like, while it is Newtonian-like in the orthogonal direction. As a result, the electrical conductivity is metallic in one and insulating in the other direction. The shear viscosity tensor contains six independent components, which can be probed by measuring an anisotropic thermal flow. One of the viscosity components vanishes at zero temperature leading to a generalization of the previously conjectured lower bound for the shear viscosity to entropy density ratio.

Plasmon effects in light scalar and pseudo-scalar emission from a supernova.

NASA Astrophysics Data System (ADS)

Altherr, T.

1991-05-01

The emission of light scalars and pseudo-scalars (axion-like particles) coupled to the chromo/electric field from a QCD/AED plasma at high temperature and very high density is studied in detail. The calculation is then applied to the SN 1987A event for which new bounds on the Peccei-Quinn symmetry breaking scale fa are derived, fa ⪆ 3×109GeV in presence of a quark-gluon core and fa ⪆ 107GeV, which is the same bound as the one obtained from red giant stars, by considering axion emission from the electron gas.

Observation of Excited Quadrupole-Bound States in Cold Anions

NASA Astrophysics Data System (ADS)

Zhu, Guo-Zhu; Liu, Yuan; Wang, Lai-Sheng

2017-07-01

We report the first observation of an excited quadrupole-bound state (QBS) in an anion. High-resolution photoelectron imaging of cryogenically cooled 4-cyanophenoxide (4 CP- ) anions yields an electron detachment threshold of 24 927 cm-1 . The photodetachment spectrum reveals a resonant transition 20 cm-1 below the detachment threshold, which is attributed to an excited QBS of 4 CP- because neutral 4CP has a large quadrupole moment with a negligible dipole moment. The QBS is confirmed by observation of seventeen above-threshold resonances due to autodetachment from vibrational levels of the QBS.

Relativistic many-body bound systems: electromagnetic properties. Monograph report

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

Danos, M.; Gillet, V.

1977-04-01

The formulae for the calculation of the electron scattering form factors, and of the static magnetic dipole and electric quadrupole moments, of relativistic many-body bound systems are derived. The framework, given in NBS Monograph 147, is relativistic quantum field theory in the Schrodinger picture; the physical particles, i.e., the solutions of the interacting fields, are given as linear combinations of the solutions of the free fields, called the parton fields. The parton--photon interaction is taken as given by minimal coupling. In addition, the contribution of the photon--vector meson vertex of the vector dominance model is derived.

Generation of short electron bunches by a laser pulse crossing a sharp boundary of inhomogeneous plasma

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

Kuznetsov, S. V., E-mail: svk-IVTAN@yandex.ru

The formation of short electron bunches during the passage of a laser pulse of relativistic intensity through a sharp boundary of semi-bounded plasma has been analytically studied. It is shown in one-dimensional geometry that one physical mechanism that is responsible for the generation of electron bunches is their self-injection into the wake field of a laser pulse, which occurs due to the mixing of electrons during the action of the laser pulse on plasma. Simple analytic relationships are obtained that can be used for estimating the length and charge of an electron bunch and the spread of electron energies inmore » the bunch. The results of the analytical investigation are confirmed by data from numerical simulations.« less

Co-integrating plasmonics with Si3N4 photonics towards a generic CMOS compatible PIC platform for high-sensitivity multi-channel biosensors: the H2020 PlasmoFab approach (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tsiokos, Dimitris M.; Dabos, George; Ketzaki, Dimitra; Weeber, Jean-Claude; Markey, Laurent; Dereux, Alain; Giesecke, Anna Lena; Porschatis, Caroline; Chmielak, Bartos; Wahlbrink, Thorsten; Rochracher, Karl; Pleros, Nikos

2017-05-01

Silicon photonics meet most fabrication requirements of standard CMOS process lines encompassing the photonics-electronics consolidation vision. Despite this remarkable progress, further miniaturization of PICs for common integration with electronics and for increasing PIC functional density is bounded by the inherent diffraction limit of light imposed by optical waveguides. Instead, Surface Plasmon Polariton (SPP) waveguides can guide light at sub-wavelength scales at the metal surface providing unique light-matter interaction properties, exploiting at the same time their metallic nature to naturally integrate with electronics in high-performance ASPICs. In this article, we demonstrate the main goals of the recently introduced H2020 project PlasmoFab towards addressing the ever increasing needs for low energy, small size and high performance mass manufactured PICs by developing a revolutionary yet CMOS-compatible fabrication platform for seamless co-integration of plasmonics with photonic and supporting electronic. We demonstrate recent advances on the hosting SiN photonic hosting platform reporting on low-loss passive SiN waveguide and Grating Coupler circuits for both the TM and TE polarization states. We also present experimental results of plasmonic gold thin-film and hybrid slot waveguide configurations that can allow for high-sensitivity sensing, providing also the ongoing activities towards replacing gold with Cu, Al or TiN metal in order to yield the same functionality over a CMOS metallic structure. Finally, the first experimental results on the co-integrated SiN+plasmonic platform are demonstrated, concluding to an initial theoretical performance analysis of the CMOS plasmo-photonic biosensor that has the potential to allow for sensitivities beyond 150000nm/RIU.

Ultracold neutral plasmas

NASA Astrophysics Data System (ADS)

Lyon, M.; Rolston, S. L.

2017-01-01

By photoionizing samples of laser-cooled atoms with laser light tuned just above the ionization limit, plasmas can be created with electron and ion temperatures below 10 K. These ultracold neutral plasmas have extended the temperature bounds of plasma physics by two orders of magnitude. Table-top experiments, using many of the tools from atomic physics, allow for the study of plasma phenomena in this new regime with independent control over the density and temperature of the plasma through the excitation process. Characteristic of these systems is an inhomogeneous density profile, inherited from the density distribution of the laser-cooled neutral atom sample. Most work has dealt with unconfined plasmas in vacuum, which expand outward at velocities of order 100 m/s, governed by electron pressure, and with lifetimes of order 100 μs, limited by stray electric fields. Using detection of charged particles and optical detection techniques, a wide variety of properties and phenomena have been observed, including expansion dynamics, collective excitations in both the electrons and ions, and collisional properties. Through three-body recombination collisions, the plasmas rapidly form Rydberg atoms, and clouds of cold Rydberg atoms have been observed to spontaneously avalanche ionize to form plasmas. Of particular interest is the possibility of the formation of strongly coupled plasmas, where Coulomb forces dominate thermal motion and correlations become important. The strongest impediment to strong coupling is disorder-induced heating, a process in which Coulomb energy from an initially disordered sample is converted into thermal energy. This restricts electrons to a weakly coupled regime and leaves the ions barely within the strongly coupled regime. This review will give an overview of the field of ultracold neutral plasmas, from its inception in 1999 to current work, including efforts to increase strong coupling and effects on plasma properties due to strong coupling.

Plasma Relaxation and Topological Aspects in Electron Magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, Bhimsen

2016-10-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient and turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve therefore in the same way as potential vorticity lines in 2D hydrodynamics.

Plasma relaxation and topological aspects in electron magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, B. K.

2016-07-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient α turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve, therefore, in the same way as potential vorticity lines in 2D hydrodynamics.

Electron momentum density and Compton profile by a semi-empirical approach

NASA Astrophysics Data System (ADS)

Aguiar, Julio C.; Mitnik, Darío; Di Rocco, Héctor O.

2015-08-01

Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi-Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron-electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects. We tested the approach for all metals with Z=3-50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments.

The Cauchy Problem in Local Spaces for the Complex Ginzburg-Landau EquationII. Contraction Methods

NASA Astrophysics Data System (ADS)

Ginibre, J.; Velo, G.

We continue the study of the initial value problem for the complex Ginzburg-Landau equation (with a > 0, b > 0, g>= 0) in initiated in a previous paper [I]. We treat the case where the initial data and the solutions belong to local uniform spaces, more precisely to spaces of functions satisfying local regularity conditions and uniform bounds in local norms, but no decay conditions (or arbitrarily weak decay conditions) at infinity in . In [I] we used compactness methods and an extended version of recent local estimates [3] and proved in particular the existence of solutions globally defined in time with local regularity of the initial data corresponding to the spaces Lr for r>= 2 or H1. Here we treat the same problem by contraction methods. This allows us in particular to prove that the solutions obtained in [I] are unique under suitable subcriticality conditions, and to obtain for them additional regularity properties and uniform bounds. The method extends some of those previously applied to the nonlinear heat equation in global spaces to the framework of local uniform spaces.

Survival of pq -superstrings in field theory simulations

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

Lizarraga, Joanes; Urrestilla, Jon, E-mail: joanes.lizarraga@ehu.eus, E-mail: jon.urrestilla@ehu.eus

2016-04-01

We perform large-scale field theoretical simulations in expanding universe to characterize a network of strings that can form composed bound states. The network consists of two copies of Abelian Higgs strings (which we label p and q , respectively) coupled via a potential term to give pq bound states. The simulations are performed using two different kinds of initial conditions: the first one with a network of p - and q -strings, and the second one with a network of q - and pq -strings. This way, we start from two opposite situations: one with no initial pq -strings, andmore » one with a large initial number of pq -strings. We find that in both cases the system scales, and in both cases the system prefers to have a low fraction of pq -strings. This is somewhat surprising in the case for the second type of conditions, showing that the unzipping mechanism is very efficient. We also find hints that both initial conditions tend to asymptote to a common configuration, though we would need a larger dynamical range to confirm it. The average velocities of the different types of strings in the network have also been explored for the first time.« less

Fluoride-Mediated Capture of a Noncovalent Bound State of a Reversible Covalent Enzyme Inhibitor: X-ray Crystallographic Analysis of an Exceptionally Potent [alpha]-Ketoheterocycle Inhibitor of Fatty Acid Amide Hydrolase

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

Mileni, Mauro; Garfunkle, Joie; Ezzili, Cyrine

2011-11-02

Two cocrystal X-ray structures of the exceptionally potent {alpha}-ketoheterocycle inhibitor 1 (K{sub i} = 290 pM) bound to a humanized variant of rat fatty acid amide hydrolase (FAAH) are disclosed, representing noncovalently and covalently bound states of the same inhibitor with the enzyme. Key to securing the structure of the noncovalently bound state of the inhibitor was the inclusion of fluoride ion in the crystallization conditions that is proposed to bind the oxyanion hole precluding inhibitor covalent adduct formation with stabilization of the tetrahedral hemiketal. This permitted the opportunity to detect important noncovalent interactions stabilizing the binding of the inhibitormore » within the FAAH active site independent of the covalent reaction. Remarkably, noncovalently bound 1 in the presence of fluoride appears to capture the active site in the same 'in action' state with the three catalytic residues Ser241-Ser217-Lys142 occupying essentially identical positions observed in the covalently bound structure of 1, suggesting that this technique of introducing fluoride may have important applications in structural studies beyond inhibiting substrate or inhibitor oxyanion hole binding. Key insights to emerge from the studies include the observations that noncovalently bound 1 binds in its ketone (not gem diol) form, that the terminal phenyl group in the acyl side chain of the inhibitor serves as the key anchoring interaction overriding the intricate polar interactions in the cytosolic port, and that the role of the central activating heterocycle is dominated by its intrinsic electron-withdrawing properties. These two structures are also briefly compared with five X-ray structures of {alpha}-ketoheterocycle-based inhibitors bound to FAAH recently disclosed.« less

Non-LTE Equation of State for ICF simulations

NASA Astrophysics Data System (ADS)

Klapisch, Marcel; Bar-Shalom, Avraham; Colombant, Denis

2002-11-01

SCROLL is a collisional radiative model able to deal with complex spectra[1]. It is used to generate opacity/emissivity databases [2] compatible with the hydrocode FAST[3] for all elements of interest in the simulation of ICF targets, including high-Z. It is now modified to yield tables of EOS data for FAST, in the whole range of interest (T=1 to 25000eV, rho=10-6 to 100g/cc). SCROLL contributes the electronic -free and bound- part of the EOS, replacing Busquet's model of an ionization temperature. Ionization energies include contributions of all excited states. Energies and Z* go smoothly to the high density regime, where a "jellium" model is assumed. The free electrons are self consistent with the bound electrons. Examples of runs will be shown. Supported by USDOE through a contract with the Naval Research Laboratory. [1] A. Bar-Shalom, J. Oreg, and M. Klapisch, J. Quant. Spectrosc. Radiat. Transfer 65, 43 (2000). [2] A. Bar-shalom, M. Klapisch, J. Oreg, and D. Colombant, Bull. Am. Phys. Soc. 46, 295 (2001). [3] J. H. Gardner, A. J. Schmitt, J. P. Dahlburg, et al, Phys. Plasmas 5, 1935 (1998).

Alcohol dehydrogenase of acetic acid bacteria: structure, mode of action, and applications in biotechnology.

PubMed

Yakushi, Toshiharu; Matsushita, Kazunobu

2010-05-01

Pyrroquinoline quinone-dependent alcohol dehydrogenase (PQQ-ADH) of acetic acid bacteria is a membrane-bound enzyme involved in the acetic acid fermentation by oxidizing ethanol to acetaldehyde coupling with reduction of membranous ubiquinone (Q), which is, in turn, re-oxidized by ubiquinol oxidase, reducing oxygen to water. PQQ-ADHs seem to have co-evolved with the organisms fitting to their own habitats. The enzyme consists of three subunits and has a pyrroloquinoline quinone, 4 heme c moieties, and a tightly bound Q as the electron transfer mediators. Biochemical, genetic, and electrochemical studies have revealed the unique properties of PQQ-ADH since it was purified in 1978. The enzyme is unique to have ubiquinol oxidation activity in addition to Q reduction. This mini-review focuses on the molecular properties of PQQ-ADH, such as the roles of the subunits and the cofactors, particularly in intramolecular electron transport of the enzyme from ethanol to Q. Also, we summarize biotechnological applications of PQQ-ADH as to enantiospecific oxidations for production of the valuable chemicals and bioelectrocatalysis for sensors and fuel cells using indirect and direct electron transfer technologies and discuss unsolved issues and future prospects related to this elaborate enzyme.

Isotope effects on the optical spectra of semiconductors

NASA Astrophysics Data System (ADS)

Cardona, Manuel; Thewalt, M. L. W.

2005-10-01

Since the end of the cold war, macroscopic amounts of separated stable isotopes of most elements have been available “off the shelf” at affordable prices. Using these materials, single crystals of many semiconductors have been grown and the dependence of their physical properties on isotopic composition has been investigated. The most conspicuous effects observed have to do with the dependence of phonon frequencies and linewidths on isotopic composition. These affect the electronic properties of solids through the mechanism of electron-phonon interaction, in particular, in the corresponding optical excitation spectra and energy gaps. This review contains a brief introduction to the history, availability, and characterization of stable isotopes, including their many applications in science and technology. It is followed by a concise discussion of the effects of isotopic composition on the vibrational spectra, including the influence of average isotopic masses and isotopic disorder on the phonons. The final sections deal with the effects of electron-phonon interaction on energy gaps, the concomitant effects on the luminescence spectra of free and bound excitons, with particular emphasis on silicon, and the effects of isotopic composition of the host material on the optical transitions between the bound states of hydrogenic impurities.

Autoionization following nanoplasma formation in atomic and molecular clusters

NASA Astrophysics Data System (ADS)

Schütte, Bernd; Lahl, Jan; Oelze, Tim; Krikunova, Maria; Vrakking, Marc J. J.; Rouzée, Arnaud

2016-05-01

Nanoplasmas resulting from the ionization of nano-scale particles by intense laser pulses are typically described by quasiclassical models, where electron emission is understood to take place via thermal processes. Recently, we discovered that, following the interaction of intense near-infrared (NIR) laser pulses with molecular oxygen clusters, electron emission from nanoplasmas can also occur from atomic bound states via autoionization [Schütte et al., Phys. Rev. Lett. 114, 123002 (2015)]. Here we extend these studies and demonstrate that the formation and decay of doubly-excited atoms and ions is a very common phenomenon in nanoplasmas. We report on the observation of autoionization involving spin-orbit excited states in molecular oxygen and carbon dioxide clusters as well as in atomic krypton and xenon clusters ionized by intense NIR pulses, for which we find clear bound-state signatures in the electron kinetic energy spectra. By applying terahertz (THz) streaking, we show that the observed autoionization processes take place on a picosecond to nanosecond timescale after the interaction of the NIR laser pulse with the clusters. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.

Finite-time and fixed-time leader-following consensus for multi-agent systems with discontinuous inherent dynamics

NASA Astrophysics Data System (ADS)

Ning, Boda; Jin, Jiong; Zheng, Jinchuan; Man, Zhihong

2018-06-01

This paper is concerned with finite-time and fixed-time consensus of multi-agent systems in a leader-following framework. Different from conventional leader-following tracking approaches where inherent dynamics satisfying the Lipschitz continuous condition is required, a more generalised case is investigated: discontinuous inherent dynamics. By nonsmooth techniques, a nonlinear protocol is first proposed to achieve the finite-time leader-following consensus. Then, based on fixed-time stability strategies, the fixed-time leader-following consensus problem is solved. An upper bound of settling time is obtained by using a new protocol, and such a bound is independent of initial states, thereby providing additional options for designers in practical scenarios where initial conditions are unavailable. Finally, numerical simulations are provided to demonstrate the effectiveness of the theoretical results.

Uncertainty relation in Schwarzschild spacetime

NASA Astrophysics Data System (ADS)

Feng, Jun; Zhang, Yao-Zhong; Gould, Mark D.; Fan, Heng

2015-04-01

We explore the entropic uncertainty relation in the curved background outside a Schwarzschild black hole, and find that Hawking radiation introduces a nontrivial modification on the uncertainty bound for particular observer, therefore it could be witnessed by proper uncertainty game experimentally. We first investigate an uncertainty game between a free falling observer and his static partner holding a quantum memory initially entangled with the quantum system to be measured. Due to the information loss from Hawking decoherence, we find an inevitable increase of the uncertainty on the outcome of measurements in the view of static observer, which is dependent on the mass of the black hole, the distance of observer from event horizon, and the mode frequency of quantum memory. To illustrate the generality of this paradigm, we relate the entropic uncertainty bound with other uncertainty probe, e.g., time-energy uncertainty. In an alternative game between two static players, we show that quantum information of qubit can be transferred to quantum memory through a bath of fluctuating quantum fields outside the black hole. For a particular choice of initial state, we show that the Hawking decoherence cannot counteract entanglement generation after the dynamical evolution of system, which triggers an effectively reduced uncertainty bound that violates the intrinsic limit -log2 ⁡ c. Numerically estimation for a proper choice of initial state shows that our result is comparable with possible real experiments. Finally, a discussion on the black hole firewall paradox in the context of entropic uncertainty relation is given.

Growth of Iron(III)-Reducing Bacteria on Clay Minerals as the Sole Electron Acceptor and Comparison of Growth Yields on a Variety of Oxidized Iron Forms†

PubMed Central

Kostka, Joel E.; Dalton, Dava D.; Skelton, Hayley; Dollhopf, Sherry; Stucki, Joseph W.

2002-01-01

Smectite clay minerals are abundant in soils and sediments worldwide and are typically rich in Fe. While recent investigations have shown that the structural Fe(III) bound in clay minerals is reduced by microorganisms, previous studies have not tested growth with clay minerals as the sole electron acceptor. Here we have demonstrated that a pure culture of Shewanella oneidensis strain MR-1 as well as enrichment cultures of Fe(III)-reducing bacteria from rice paddy soil and subsurface sediments are capable of conserving energy for growth with the structural Fe(III) bound in smectite clay as the sole electron acceptor. Pure cultures of S. oneidensis were used for more detailed growth rate and yield experiments on various solid- and soluble-phase electron acceptors [smectite, Fe(III) oxyhydroxide FeOOH, Fe(III) citrate, and oxygen] in the same minimal medium. Growth was assessed as direct cell counts or as an increase in cell carbon (measured as particulate organic carbon). Cell counts showed that similar growth of S. oneidensis (108 cells ml−1) occurred with smectitic Fe(III) and on other Fe forms [amorphous Fe(III) oxyhydroxide, and Fe citrate] or oxygen as the electron acceptor. In contrast, cell yields of S. oneidensis measured as the increase in cell carbon were similar on all Fe forms tested while yields on oxygen were five times higher, in agreement with thermodynamic predictions. Over a range of particle loadings (0.5 to 4 g liter−1), the increase in cell number was highly correlated to the amount of structural Fe in smectite reduced. From phylogenetic analysis of the complete 16S rRNA gene sequences, a predominance of clones retrieved from the clay mineral-reducing enrichment cultures were most closely related to the low-G+C gram-positive members of the Bacteria (Clostridium and Desulfitobacterium) and the δ-Proteobacteria (members of the Geobacteraceae). Results indicate that growth with smectitic Fe(III) is similar in magnitude to that with Fe(III) oxide minerals and is dependent upon the mineral surface area available. Iron(III) bound in clay minerals should be considered an important electron acceptor supporting the growth of bacteria in soils or sedimentary environments. PMID:12450850

Hepatitis-C-virus-like internal ribosome entry sites displace eIF3 to gain access to the 40S subunit

NASA Astrophysics Data System (ADS)

Hashem, Yaser; Des Georges, Amedee; Dhote, Vidya; Langlois, Robert; Liao, Hstau Y.; Grassucci, Robert A.; Pestova, Tatyana V.; Hellen, Christopher U. T.; Frank, Joachim

2013-11-01

Hepatitis C virus (HCV) and classical swine fever virus (CSFV) messenger RNAs contain related (HCV-like) internal ribosome entry sites (IRESs) that promote 5'-end independent initiation of translation, requiring only a subset of the eukaryotic initiation factors (eIFs) needed for canonical initiation on cellular mRNAs. Initiation on HCV-like IRESs relies on their specific interaction with the 40S subunit, which places the initiation codon into the P site, where it directly base-pairs with eIF2-bound initiator methionyl transfer RNA to form a 48S initiation complex. However, all HCV-like IRESs also specifically interact with eIF3 (refs 2, 5, 6, 7, 9, 10, 11, 12), but the role of this interaction in IRES-mediated initiation has remained unknown. During canonical initiation, eIF3 binds to the 40S subunit as a component of the 43S pre-initiation complex, and comparison of the ribosomal positions of eIF3 and the HCV IRES revealed that they overlap, so that their rearrangement would be required for formation of ribosomal complexes containing both components. Here we present a cryo-electron microscopy reconstruction of a 40S ribosomal complex containing eIF3 and the CSFV IRES. Remarkably, although the position and interactions of the CSFV IRES with the 40S subunit in this complex are similar to those of the HCV IRES in the 40S-IRES binary complex, eIF3 is completely displaced from its ribosomal position in the 43S complex, and instead interacts through its ribosome-binding surface exclusively with the apical region of domain III of the IRES. Our results suggest a role for the specific interaction of HCV-like IRESs with eIF3 in preventing ribosomal association of eIF3, which could serve two purposes: relieving the competition between the IRES and eIF3 for a common binding site on the 40S subunit, and reducing formation of 43S complexes, thereby favouring translation of viral mRNAs.