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Sample records for deep core-level photoexcitation

  1. Dynamics deep from the core

    PubMed Central

    Carbone, F.

    2015-01-01

    In van der Veen et al., [Struct. Dyn. 2, 024302 (2015)], femtosecond and nanosecond electron energy loss spectroscopy of deep core-levels are demonstrated. These results pave the way to the investigation of materials and molecules with combined energy, time, and spatial resolution in a transmission electron microscope. Furthermore, the authors elucidate the role of the electron phonon coupling in the band-gap renormalization that takes place in graphite upon photo-excitation. PMID:26798787

  2. Trends in adsorbate induced core level shifts

    NASA Astrophysics Data System (ADS)

    Nilsson, Viktor; Van den Bossche, Maxime; Hellman, Anders; Grönbeck, Henrik

    2015-10-01

    Photoelectron core level spectroscopy is commonly used to monitor atomic and molecular adsorption on metal surfaces. As changes in the electron binding energies are convoluted measures with different origins, calculations are often used to facilitate the decoding of experimental signatures. The interpretation could in this sense benefit from knowledge on trends in surface core level shifts for different metals and adsorbates. Here, density functional theory calculations have been used to systematically evaluate core level shifts for (111) and (100) surfaces of 3d, 4d, and 5d transition metals upon CO, H, O and S adsorption. The results reveal trends and several non-intuitive cases. Moreover, the difficulties correlating core level shifts with charging and d-band shifts are underlined.

  3. Core level shifts of intercalated graphene

    NASA Astrophysics Data System (ADS)

    Schröder, Ulrike A.; Petrović, Marin; Gerber, Timm; Martínez-Galera, Antonio J.; Grånäs, Elin; Arman, Mohammad A.; Herbig, Charlotte; Schnadt, Joachim; Kralj, Marko; Knudsen, Jan; Michely, Thomas

    2017-03-01

    Through intercalation of metals and gases the Dirac cone of graphene on Ir(111) can be shifted with respect to the Fermi level without becoming destroyed by strong hybridization. Here, we use x-ray photoelectron spectroscopy to measure the C 1s core level shift (CLS) of graphene in contact with a number of structurally well-defined intercalation layers (O, H, Eu, and Cs). By analysis of our own and additional literature data for decoupled graphene, the C 1s CLS is found to be a non-monotonic function of the doping level. For small doping levels the shifts are well described by a rigid band model. However, at larger doping levels, a second effect comes into play which is proportional to the transferred charge and counteracts the rigid band shift. Moreover, not only the position, but also the C 1s peak shape displays a unique evolution as a function of doping level. Our conclusions are supported by intercalation experiments with Li, with which, due to the absence of phase separation, the doping level of graphene can be continuously tuned.

  4. Core-level photoabsorption characterization of diamond and carbon films

    SciTech Connect

    Terminello, L.J.; Carlisle, J.A.; Sutherland, D.G.

    1996-12-31

    We have used synchrotron radiation core-level photoabsorption to characterize the electronic structure and morphology of carbon thin-films and determined the relative ratio of sp2 vs. sp3 bonding. The diamond, diamond-like, and carbon films characterized were prepared by a variety of methods including sputtering, CVD, microwave plasma CVD, and laser ablation. We have also measured these films using Raman spectroscopy and have found that in cases where the domain size of the crystallites in the carbon films was nanoscopic (less than 100 nm), Raman spectroscopy gave indeterminate results. In these cases, as well as with larger crystallite size films, core-level photoabsorption was able to unambiguously identify the bonding in the film. We will present photoabsorption data obtained from these materials. These experiments and prospects for other experiments that can identify the unique electronic properties and bonding of such novel thin films will be discussed.

  5. Core-level binding-energy shifts for the metallic elements

    NASA Astrophysics Data System (ADS)

    Johansson, Börje; Mårtensson, Nils

    1980-05-01

    chromium relative to the dns2 configuration in vanadium and manganese. When the core-level shift is referred to, the dns2 (or dn+1s) atomic configuration for all the elements in a transition series, a quite regular behavior of the shift is found. However, some structure can still be observed originating from a change of screening within the d band from a bonding to an antibonding type as one proceeds through the series. For elements beyond the coin metals the screening of a core hole is performed by p electrons, which provide a less effective screening mechanism than the d electrons for the transition metals. The coin metals are intermediate cases, partly due to a dominating s-electron screening and partly due to d-electron bonding in the initial state. The effect of the electron-density redistribution between the free atom and the solid on the core-level shift is particularly striking in the case of the rare-earth elements Pr-Sm and Tb-Tm. Here the remarkable situation is that a deep core electron is less bound in the atom than in the solid. Also for the actinides the electronic redistribution upon condensation gives rise to pronounced effects on the core-level shifts. Further, it is shown that the measured 6p32 binding energy in metallic uranium provides a clear demonstration of the occupation of the 5f level in this metal. The present treatment of the core-level shift for bulk metallic atoms can easily be generalized to surface atoms. From an empirical relation for the surface energy a simple expression for the shift of the surface core-level relative to the bulk can be derived. For the earlier transition metals, it is found that the core electrons are more bound at the surface than in the bulk, while for the heavier ones the opposite situation exists. This change of sign of the surface shift depends on the bonding-antibonding division of the d band. To illustrate how the present approach can be applied to alloy systems, a treatment of core-level shifts for rare

  6. Collinear scattering of photoexcited carriers in graphene

    NASA Astrophysics Data System (ADS)

    Trushin, Maxim

    2016-11-01

    We propose an explicitly solvable model for collinear scattering of photoexcited carriers in intrinsic graphene irradiated by monochromatic light. We find that the collinear scattering rate is directly proportional to the photocarrier energy and derive an analytic expression for the corresponding relaxation time. The result agrees with the recent numerical prediction [Nat. Commun. 7, 11617 (2016), 10.1038/ncomms11617] and is able to describe the photocarrier evolution at low energies, where scattering on optical phonons is strongly suppressed.

  7. Quantum Mechanics in Biology: Photoexcitations in DNA

    NASA Astrophysics Data System (ADS)

    Bittner, Eric R.; Czader, Arkadiusz

    We consider here the theoretical and quantum chemical description of the photoexcitated states in DNA duplexes. We discuss the motivation and limitations of an exciton model and use this as the starting point for more detailed excited state quantum chemical evaluations. In particular, we focus upon the role of interbase proton transfer between Watson/Crick pairs in localizing an excitation and then quenching it through intersystem crossing and charge transfer.

  8. Efficient terahertz modulator based on photoexcited graphene

    NASA Astrophysics Data System (ADS)

    Fu, Maixia; Wang, Xinke; Wang, Sen; Xie, Zhenwei; Feng, Shengfei; Sun, Wenfeng; Ye, Jiasheng; Han, Peng; Zhang, Yan

    2017-04-01

    An efficient terahertz (THz) modulator consisting of a single-layer graphene on a silicon substrate has been investigated using an external 450 nm continuous-wave laser with a low photoexcitation power. Upon photoexcitation, both transmission and reflection are measured using a THz time-domain spectroscopy. The experimental results show that the modulation depth of the transmission can reach 74% for the proposed modulator under external photoexcitation. The difference between the transmission through the sample and bare silicon substrate can reach a maximal value of 49.3% with a pump power of 420 mW, which indicates that the modulation effect of graphene is dominant with minimal contribution from the silicon substrate. The analyses of the strong attenuation of the transmitted THz waves reveals that an enhanced absorption of the THz wave takes place, which is shown to be rooted in the increase of the doping level in graphene, the accumulation of the photo-induced carrier at the interface of the graphene and silicon substrate, as well as the scattering between carriers, phonons and defects. The results of this study imply promising applications for the development of high-performance THz modulators and absorbers.

  9. Alkaline Earth Core Level Photoemission Spectroscopy of High-Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Vasquez, R.

    1993-01-01

    This paper examines photoemission measurements of the alkaline Earth core levels of high-temperature superconductors and related materials, models that seek to explain the large negative shifts observed relative to the corresponding alkaline Earth metals, and the effect of lattice site disorder on the core level spectra and the presence or absence of intrinsic surface peaks.

  10. The surface core level shift for lithium at the surface of lithium borate

    NASA Astrophysics Data System (ADS)

    Wooten, David; Ketsman, I.; Xiao, Jie; Losovyj, Ya. B.; Petrosky, J.; McClory, J.; Burak, Ya. V.; Adamiv, V. T.; Dowben, P. A.

    2010-01-01

    The shallow Li 1s core level exhibits a surface-to-bulk core level shift for the stoichiometric Li 2B 4O 7(1 1 0) surface. Angle-resolved photoemission spectroscopy was used to indentify Li 1s bulk and surface core level components at binding energies -56.5±0.4 and -53.7±0.5 eV, respectively. We find photoemission evidence for surface states of Li 2B 4O 7(1 1 0) that exist in the gap of the projected bulk density of states. The existence of surface states is consistent with the large surface-to-bulk core level shift for the Li 1s core.

  11. A first-principles core-level XPS study on the boron impurities in germanium crystal

    SciTech Connect

    Yamauchi, Jun; Yoshimoto, Yoshihide; Suwa, Yuji

    2013-12-04

    We systematically investigated the x-ray photoelectron spectroscopy (XPS) core-level shifts and formation energies of boron defects in germanium crystals and compared the results to those in silicon crystals. Both for XPS core-level shifts and formation energies, relationship between defects in Si and Ge is roughly linear. From the similarity in the formation energy, it is expected that the exotic clusters like icosahedral B12 exist in Ge as well as in Si.

  12. A first-principles core-level XPS study on the boron impurities in germanium crystal

    NASA Astrophysics Data System (ADS)

    Yamauchi, Jun; Yoshimoto, Yoshihide; Suwa, Yuji

    2013-12-01

    We systematically investigated the x-ray photoelectron spectroscopy (XPS) core-level shifts and formation energies of boron defects in germanium crystals and compared the results to those in silicon crystals. Both for XPS core-level shifts and formation energies, relationship between defects in Si and Ge is roughly linear. From the similarity in the formation energy, it is expected that the exotic clusters like icosahedral B12 exist in Ge as well as in Si.

  13. Dynamics of photoexcited carrier relaxation and recombination in CdTe/CdS thin films

    SciTech Connect

    Levi, D.H.; Fluegel, B.D.; Ahrenkiel, R.K.

    1996-05-01

    Efficiency-limiting defects in photovoltaic devices are readily probed by time-resolved spectroscopy. This paper presents the first direct optical measurements of the relaxation and recombination pathways of photoexcited carriers in the CdS window layer of CdTe/CdS polycrystalline thin films. Femtosecond time-resolved pump/probe measurements indicate the possible existence of a two-phase CdS/CdSTe layer, rather than a continuously graded alloy layer at the CdTe/CdS interface. Complementary time-resolved photoluminescence (PL) measurements show that the photoexcited carriers are rapidly captured by deep-level defects. The temporal and density-dependent properties of the photoluminescence prove that the large Stokes shift of the PL relative to the band edge is due to strong phonon coupling to deep-level defects in CdS. The authors suggest that modifications in the CdS processing may enhance carrier collection efficiency in the blue spectral region.

  14. An easy-to-implement filter for separating photo-excited signals from topography in scanning tunneling microscopy.

    PubMed

    Wang, Kangkang; Rosenmann, Daniel; Holt, Martin; Winarski, Robert; Hla, Saw-Wai; Rose, Volker

    2013-06-01

    In order to achieve elemental and chemical sensitivity in scanning tunneling microscopy (STM), synchrotron x-rays have been applied to excite core-level electrons during tunneling. The x-ray photo-excitations result in tip currents that are superimposed onto conventional tunneling currents. While carrying important physical information, the varying x-ray induced currents can destabilize the feedback loop causing it to be unable to maintain a constant tunneling current, sometimes even causing the tip to retract fully or crash. In this paper, we report on an easy-to-implement filter circuit that can separate the x-ray induced currents from conventional tunneling currents, thereby allowing simultaneous measurements of topography and chemical contrasts. The filter and the schematic presented here can also be applied to other variants of light-assisted STM such as laser STM.

  15. An easy-to-implement filter for separating photo-excited signals from topography in scanning tunneling microscopy

    SciTech Connect

    Wang Kangkang; Rosenmann, Daniel; Holt, Martin; Winarski, Robert; Hla, Saw-Wai; Rose, Volker

    2013-06-15

    In order to achieve elemental and chemical sensitivity in scanning tunneling microscopy (STM), synchrotron x-rays have been applied to excite core-level electrons during tunneling. The x-ray photo-excitations result in tip currents that are superimposed onto conventional tunneling currents. While carrying important physical information, the varying x-ray induced currents can destabilize the feedback loop causing it to be unable to maintain a constant tunneling current, sometimes even causing the tip to retract fully or crash. In this paper, we report on an easy-to-implement filter circuit that can separate the x-ray induced currents from conventional tunneling currents, thereby allowing simultaneous measurements of topography and chemical contrasts. The filter and the schematic presented here can also be applied to other variants of light-assisted STM such as laser STM.

  16. Observation of suppressed terahertz absorption in photoexcited graphene

    NASA Astrophysics Data System (ADS)

    Frenzel, A. J.; Lui, C. H.; Fang, W.; Nair, N. L.; Herring, P. K.; Jarillo-Herrero, P.; Kong, J.; Gedik, N.

    2013-03-01

    When light is absorbed by a semiconductor, photoexcited charge carriers enhance the absorption of far-infrared radiation due to intraband transitions. We observe the opposite behavior in monolayer graphene, a zero-gap semiconductor with linear dispersion. By using time domain terahertz (THz) spectroscopy in conjunction with optical pump excitation, we observe a reduced absorption of THz radiation in photoexcited graphene. The measured spectral shape of the differential optical conductivity exhibits non-Drude behavior. We discuss several possible mechanisms that contribute to the observed low-frequency non-equilibrium optical response of graphene.

  17. Enhancement of Paramagnetic Relaxation by Photoexcited Gold Nanorods

    PubMed Central

    Wen, Tao; Wamer, Wayne G.; Subczynski, Witold K.; Hou, Shuai; Wu, Xiaochun; Yin, Jun-Jie

    2016-01-01

    Electron spin resonance (ESR) spectroscopy was used to investigate the switchable, light-dependent effects of gold nanorods (GNRs) on paramagnetic properties of nitroxide spin probes. The photoexcited GNRs enhanced the spin-spin and spin-lattice relaxations of nitroxide spin probes. It was shown that molecular oxygen plays the key role in this process. Our results demonstrate that ESR is a powerful tool for investigating the events following photoexcitation of GNRs. The novel light-controlled effects observed for GNRs on paramagnetic properties and activities of surrounding molecules have a number of significant applications where oxygen sensing and oxygen activity is important. PMID:27071507

  18. Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

    SciTech Connect

    Menchero, Jose Gabriel

    1997-05-01

    In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.

  19. Femtomagnetism in graphene induced by core level excitation of organic adsorbates

    PubMed Central

    Ravikumar, Abhilash; Baby, Anu; Lin, He; Brivio, Gian Paolo; Fratesi, Guido

    2016-01-01

    We predict the induction or suppression of magnetism in the valence shell of physisorbed and chemisorbed organic molecules on graphene occurring on the femtosecond time scale as a result of core level excitations. For physisorbed molecules, where the interaction with graphene is dominated by van der Waals forces and the system is non-magnetic in the ground state, numerical simulations based on density functional theory show that the valence electrons relax towards a spin polarized configuration upon excitation of a core-level electron. The magnetism depends on efficient electron transfer from graphene on the femtosecond time scale. On the other hand, when graphene is covalently functionalized, the system is magnetic in the ground state showing two spin dependent mid gap states localized around the adsorption site. At variance with the physisorbed case upon core-level excitation, the LUMO of the molecule and the mid gap states of graphene hybridize and the relaxed valence shell is not magnetic anymore. PMID:27089847

  20. Detection of subsurface core-level shifts in Si 2p core-level photoemission from Si(111)-(1x1):As

    SciTech Connect

    Paggel, J.J.; Hasselblatt, M.; Horn, K.

    1997-04-01

    The (7 x 7) reconstruction of the Si(111) surface arises from a lowering energy through the reduction of the number of dangling bonds. This reconstruction can be removed by the adsorption of atoms such as hydrogen which saturate the dangling bonds, or by the incorporation of atoms, such as arsenic which, because of the additional electron it possesses, can form three bonds and a nonreactive lone pair orbital from the remaining two electrons. Core and valence level photoemission and ion scattering data have shown that the As atoms replace the top silicon atoms. Previous core level spectra were interpreted in terms of a bulk and a single surface doublet. The authors present results demonstrate that the core level spectrum contains two more lines. The authors assign these to subsurface silicon layers which also experience changes in the charge distribution when a silicon atom is replaced by an arsenic atom. Subsurface core level shifts are not unexpected since the modifications of the electronic structure and/or of photohole screening are likely to decay into the bulk and not just to affect the top-most substrate atoms. The detection of subsurface components suggests that the adsorption of arsenic leads to charge flow also in the second double layer of the Si(111) surface. In view of the difference in atomic radius between As and Si, it was suggested that the (1 x 1): As surface is strained. The presence of charge rearrangement up to the second double layer implies that the atomic coordinates also exhibit deviations from their ideal Si(111) counterparts, which might be detected through a LEED I/V or photoelectron diffraction analysis.

  1. Ultrafast X-ray Auger probing of photoexcited molecular dynamics

    DOE PAGES

    McFarland, B. K.; Farrell, J. P.; Miyabe, S.; ...

    2014-06-23

    Here, molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation—X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towardsmore » high kinetic energies, resulting from a particular C–O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.« less

  2. Ultrafast X-ray Auger probing of photoexcited molecular dynamics

    SciTech Connect

    McFarland, B. K.; Farrell, J. P.; Miyabe, S.; Tarantelli, F.; Aguilar, A.; Berrah, N.; Bostedt, C.; Bozek, J. D.; Bucksbaum, P. H.; Castagna, J. C.; Coffee, R. N.; Cryan, J. P.; Fang, L.; Feifel, R.; Gaffney, K. J.; Glownia, J. M.; Martinez, T. J.; Mucke, M.; Murphy, B.; Natan, A.; Osipov, T.; Petrović, V. S.; Schorb, S.; Schultz, Th.; Spector, L. S.; Swiggers, M.; Tenney, I.; Wang, S.; White, J. L.; White, W.; Gühr, M.

    2014-06-23

    Here, molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation—X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towards high kinetic energies, resulting from a particular C–O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.

  3. Modeling Shallow Core-Level Transitions in the Reflectance Spectra of Gallium-Containing Semiconductors

    NASA Astrophysics Data System (ADS)

    Stoute, Nicholas; Aspnes, David

    2012-02-01

    The electronic structure of covalent materials is typically approached by band theory. However, shallow core level transitions may be better modeled by an atomic-scale approach. We investigate shallow d-core level reflectance spectra in terms of a local atomic-multiplet theory, a novel application of a theory typically used for higher-energy transitions on more ionic type material systems. We examine specifically structure in reflectance spectra of GaP, GaAs, GaSb, GaSe, and GaAs1-xPx due to transitions that originate from Ga3d core levels and occur in the 20 to 25 eV range. We model these spectra as a Ga^+3 closed-shell ion whose transitions are influenced by perturbations on 3d hole-4p electron final states. These are specifically spin-orbit effects on the hole and electron, and a crystal-field effect on the hole, attributed to surrounding bond charges and positive ligand anions. Empirical radial-strength parameters were obtained by least-squares fitting. General trends with respect to anion electronegativity are consistent with expectations. In addition to the spin-orbit interaction, crystal-field effects play a significant role in breaking the degeneracy of the d levels, and consequently are necessary to understand shallow 3d core level spectra.

  4. Absolute Binding Energies of Core Levels in Solids from First Principles

    NASA Astrophysics Data System (ADS)

    Ozaki, Taisuke; Lee, Chi-Cheng

    2017-01-01

    A general method is presented to calculate absolute binding energies of core levels in metals and insulators, based on a penalty functional and an exact Coulomb cutoff method in the framework of density functional theory. The spurious interaction of core holes between supercells is avoided by the exact Coulomb cutoff method, while the variational penalty functional enables us to treat multiple splittings due to chemical shift, spin-orbit coupling, and exchange interaction on equal footing, both of which are not accessible by previous methods. It is demonstrated that the absolute binding energies of core levels for both metals and insulators are calculated by the proposed method in a mean absolute (relative) error of 0.4 eV (0.16%) for eight cases compared to experimental values measured with x-ray photoemission spectroscopy within a generalized gradient approximation to the exchange-correlation functional.

  5. Separation of distinct photoexcitation species in femtosecond transient absorption microscopy

    SciTech Connect

    Xiao, Kai; Ma, Ying -Zhong; Simpson, Mary Jane; Doughty, Benjamin; Yang, Bing

    2016-02-03

    Femtosecond transient absorption microscopy is a novel chemical imaging capability with simultaneous high spatial and temporal resolution. Although several powerful data analysis approaches have been developed and successfully applied to separate distinct chemical species in such images, the application of such analysis to distinguish different photoexcited species is rare. In this paper, we demonstrate a combined approach based on phasor and linear decomposition analysis on a microscopic level that allows us to separate the contributions of both the excitons and free charge carriers in the observed transient absorption response of a composite organometallic lead halide perovskite film. We found spatial regions where the transient absorption response was predominately a result of excitons and others where it was predominately due to charge carriers, and regions consisting of signals from both contributors. Lastly, quantitative decomposition of the transient absorption response curves further enabled us to reveal the relative contribution of each photoexcitation to the measured response at spatially resolved locations in the film.

  6. Symmetry rules in magnetic core-level photoelectron spectroscopy from epitaxial ferromagnetic ultrathin films

    NASA Astrophysics Data System (ADS)

    Schellenberg, R.; Meinert, H.; Perez, A.; Kisker, E.

    2001-09-01

    For two x-ray incidence directions onto an epitaxial FeNi(001) film, one to the left and a second one to the right side of the symmetry plane spanned by the magnetization direction and the photoelectron wave vector, we have measured distributions of the emission-angle dependence with respect to the crystallographic axes of the Fe 2p3/2 core-level photoelectron intensity asymmetry occurring upon magnetization reversal. The two angular distributions transform into each other when the signs of the magnetization and of the photoelectron emission angle are inverted, in accordance with the conservation of parity.

  7. Direct Measurement of Core-Level Relaxation Dynamics on a Surface-Adsorbate System

    NASA Astrophysics Data System (ADS)

    Miaja-Avila, L.; Saathoff, G.; Mathias, S.; Yin, J.; La-O-Vorakiat, C.; Bauer, M.; Aeschlimann, M.; Murnane, M. M.; Kapteyn, H. C.

    2008-07-01

    The coupling between electronic states in a surface-adsorbate system is fundamental to the understanding of many surface interactions. In this Letter, we present the first direct time-resolved observations of the lifetime of core-excited states of an atom adsorbed onto a surface. By comparing laser-assisted photoemission from a substrate with a delayed Auger decay process from an adsorbate, we measure the lifetime of the 4d-1 core level of xenon on Pt(111) to be 7.1±1.1fs. This result opens up time-domain measurements of surface dynamics where energy-resolved measurements may provide incomplete information.

  8. Photoemission core-level shifts reveal the thiolate-Au(111) interface

    SciTech Connect

    Groenbeck, Henrik; Odelius, Michael

    2010-08-15

    The nature of the thiolate/Au(111) interface is a long-standing puzzle. It has been suggested that thiolates drive surface reconstruction, however, a consensus regarding the adsorption configuration is missing. Herein, the density-functional theory is used to evaluate surface core-level shifts (SCLSs) for methyl thiolates on Au(111) assuming a representative set of different surface reconstructions. The SCLSs are found to provide sensitive fingerprints of the anchoring configuration, and it is only thiolate adsorption in the form of MeS-Au-SMe complexes that can be reconciled with experimental data.

  9. Modeling photoexcited reactions of simple molecules in solution

    NASA Astrophysics Data System (ADS)

    Zhang, Jing

    Photoexcited iodine in rare gas systems offer a paradigm for understanding excited state condensed phase chemistry. Solvent induced nonadiabaticity plays an important role in the dynamics of these systems and modifies electronic structure by introducing off-diagonal coupling elements to our electronic Hamiltonian matrix. A semi-empirical electronic structure method, diatomics-in-molecules (DIM), together with its extension designed for ionic systems, diatomics-in-ionic-systems (DIIS), is applied to dynamical studies of photoexcited iodine in Ar and Xe rare gas systems. Mixed quantum-classical molecular dynamics implemented using a surface hopping algorithm is employed in a trajectory study which successfully describes the nonadiabatic nature of these systems. First we looked into the photoexcited I2 in its manifold of covalent states in solid Ar, focusing on the cage-bound but otherwise dissociative potential curves. Cage motions disturb the electronic structure and influence the coupling between electronic states to a large extent due to the large-scale intramolecular motion associated with stretching of the I2 bond resulting from double-photon excitation. Dynamical simulation with a surface hopping algorithm describes the cage-bound state photoexcitation dynamics which has only been simulated by other groups using classical methods that do not allow for nonadiabatic electronic transitions. A characteristic recursion time of the cage-bound state motion is found though our simulation which matches the experimental results, and our simulated pump-probe signals successfully reproduce the experimental spectrum. Finally we apply our potential model and surface hopping dynamical calculation method to the charge transfer complex Xe+2I- in xenon clusters. The states of this system are accessed at much higher energy than the covalent states. Charge transfer occurs between atoms and requires a significantly more complex potential energy model for which we use an extension

  10. Photoexcited riboflavin induces oxidative damage to human serum albumin

    NASA Astrophysics Data System (ADS)

    Hirakawa, Kazutaka; Yoshioka, Takuto

    2015-08-01

    Photoexcited riboflavin induced damage of human serum albumin (HSA), a water soluble protein, resulting in the diminishment of fluorescence from the tryptophan residue. Because riboflavin hardly photosensitized singlet oxygen generation and sodium azide, a singlet oxygen quencher, did not inhibit protein damage, electron transfer-mediated oxidation of HSA was speculated. Fluorescence lifetime of riboflavin was not affected by HSA, suggesting that the excited triplet state of riboflavin is responsible for protein damage through electron transfer. In addition, the preventive effect of xanthone derivatives, triplet quenchers, on photosensitized protein damage could be evaluated using this photosensitized reaction system of riboflavin and HSA.

  11. Photoexcitation dynamics in thin films of insulated molecular wires

    NASA Astrophysics Data System (ADS)

    Chang, M. H.; Frampton, M. J.; Anderson, H. L.; Herz, L. M.

    2006-12-01

    A study is presented on how encapsulation of conjugated polymer chains affects the motion of photoexcitations and the formation of interchain aggregates in solid films. It is shown that threading of a poly(diphenylene vinylene) backbone inside insulating cyclodextrins (rotaxination) and/or complexation of the chains with poly(ethylene oxide) are effective means of preventing the diffusion of excitons to nonradiative defect sites. Ultrafast time-resolved photoluminescence data reveal that excitation transfer between encapsulated chains is still possible and, for the case of rotaxination, is likely to be facilitated through close packing of end groups belonging to adjacent chains.

  12. Quanty for core level spectroscopy - excitons, resonances and band excitations in time and frequency domain

    NASA Astrophysics Data System (ADS)

    Haverkort, Maurits W.

    2016-05-01

    Depending on the material and edge under consideration, core level spectra manifest themselves as local excitons with multiplets, edge singularities, resonances, or the local projected density of states. Both extremes, i.e., local excitons and non-interacting delocalized excitations are theoretically well under control. Describing the intermediate regime, where local many body interactions and band-formation are equally important is a challenge. Here we discuss how Quanty, a versatile quantum many body script language, can be used to calculate a variety of different core level spectroscopy types on solids and molecules, both in the frequency as well as the time domain. The flexible nature of Quanty allows one to choose different approximations for different edges and materials. For example, using a newly developed method merging ideas from density renormalization group and quantum chemistry [1-3], Quanty can calculate excitons, resonances and band-excitations in x-ray absorption, photoemission, x-ray emission, fluorescence yield, non-resonant inelastic x-ray scattering, resonant inelastic x-ray scattering and many more spectroscopy types. Quanty can be obtained from: http://www.quanty.org.

  13. Core level excitations—A fingerprint of structural and electronic properties of epitaxial silicene

    SciTech Connect

    Friedlein, R. Fleurence, A.; Aoyagi, K.; Yamada-Takamura, Y.; Jong, M. P. de; Van Bui, H.; Wiggers, F. B.; Yoshimoto, S.; Koitaya, T.; Shimizu, S.; Noritake, H.; Mukai, K.; Yoshinobu, J.

    2014-05-14

    From the analysis of high-resolution Si 2p photoelectron and near-edge x-ray absorption fine structure (NEXAFS) spectra, we show that core level excitations of epitaxial silicene on ZrB{sub 2}(0001) thin films are characteristically different from those of sp{sup 3}-hybridized silicon. In particular, it is revealed that the lower Si 2p binding energies and the low onset in the NEXAFS spectra as well as the occurrence of satellite features in the core level spectra are attributed to the screening by low-energy valence electrons and interband transitions between π bands, respectively. The analysis of observed Si 2p intensities related to chemically distinct Si atoms indicates the presence of at least one previously unidentified component. The presence of this component suggests that the observation of stress-related stripe domains in scanning tunnelling microscopy images is intrinsically linked to the relaxation of Si atoms away from energetically unfavourable positions.

  14. Core-level photoemission from nanocluster-matrix composites: Au clusters in amorphous carbon

    NASA Astrophysics Data System (ADS)

    Calliari, L.; Minati, L.; Speranza, G.; Paris, A.; Baranov, A.; Fanchenko, S.

    2014-09-01

    We investigate a system consisting of Au nano-clusters and amorphous carbon (a-C) via core-level photoemission. While the ability of photoemission to characterize nano-sized metal clusters is well-known, still some issues deserve investigation. For example, the well-established dominance of final-state relaxation effects in core-level spectra from nano-clusters necessarily involves a crucial role of the cluster dielectric-environment. To the best of our knowledge however, a thorough discussion on this point is lacking. We thus intend to investigate dielectric-environment effects by considering several configurations for Au clusters, i.e. supported and embedded, with the latter obtained either by depositing a-C on top of supported clusters or by co-depositing a-C and Au. We analyze the Au4 f spectrum from clusters accounting for both cluster size and cluster location with respect to the a-C matrix. We show that spectral changes caused by a-C deposition are entirely explained in terms of changes in the cluster dielectric environment. Moreover, we prove that supported clusters are in a well-characterized dielectric environment, while embedded clusters are not. This is because embedded clusters, whatever the method of production, are spatially distributed over the matrix surface-region which is characterized by rapid fluctuations in the dielectric constant.

  15. Photoexcited quantum dots for killing multidrug-resistant bacteria.

    PubMed

    Courtney, Colleen M; Goodman, Samuel M; McDaniel, Jessica A; Madinger, Nancy E; Chatterjee, Anushree; Nagpal, Prashant

    2016-05-01

    Multidrug-resistant bacterial infections are an ever-growing threat because of the shrinking arsenal of efficacious antibiotics. Metal nanoparticles can induce cell death, yet the toxicity effect is typically nonspecific. Here, we show that photoexcited quantum dots (QDs) can kill a wide range of multidrug-resistant bacterial clinical isolates, including methicillin-resistant Staphylococcus aureus, carbapenem-resistant Escherichia coli, and extended-spectrum β-lactamase-producing Klebsiella pneumoniae and Salmonella typhimurium. The killing effect is independent of material and controlled by the redox potentials of the photogenerated charge carriers, which selectively alter the cellular redox state. We also show that the QDs can be tailored to kill 92% of bacterial cells in a monoculture, and in a co-culture of E. coli and HEK 293T cells, while leaving the mammalian cells intact, or to increase bacterial proliferation. Photoexcited QDs could be used in the study of the effect of redox states on living systems, and lead to clinical phototherapy for the treatment of infections.

  16. Photoexcited quantum dots for killing multidrug-resistant bacteria

    NASA Astrophysics Data System (ADS)

    Courtney, Colleen M.; Goodman, Samuel M.; McDaniel, Jessica A.; Madinger, Nancy E.; Chatterjee, Anushree; Nagpal, Prashant

    2016-05-01

    Multidrug-resistant bacterial infections are an ever-growing threat because of the shrinking arsenal of efficacious antibiotics. Metal nanoparticles can induce cell death, yet the toxicity effect is typically nonspecific. Here, we show that photoexcited quantum dots (QDs) can kill a wide range of multidrug-resistant bacterial clinical isolates, including methicillin-resistant Staphylococcus aureus, carbapenem-resistant Escherichia coli, and extended-spectrum β-lactamase-producing Klebsiella pneumoniae and Salmonella typhimurium. The killing effect is independent of material and controlled by the redox potentials of the photogenerated charge carriers, which selectively alter the cellular redox state. We also show that the QDs can be tailored to kill 92% of bacterial cells in a monoculture, and in a co-culture of E. coli and HEK 293T cells, while leaving the mammalian cells intact, or to increase bacterial proliferation. Photoexcited QDs could be used in the study of the effect of redox states on living systems, and lead to clinical phototherapy for the treatment of infections.

  17. Separation of distinct photoexcitation species in femtosecond transient absorption microscopy

    DOE PAGES

    Xiao, Kai; Ma, Ying -Zhong; Simpson, Mary Jane; ...

    2016-02-03

    Femtosecond transient absorption microscopy is a novel chemical imaging capability with simultaneous high spatial and temporal resolution. Although several powerful data analysis approaches have been developed and successfully applied to separate distinct chemical species in such images, the application of such analysis to distinguish different photoexcited species is rare. In this paper, we demonstrate a combined approach based on phasor and linear decomposition analysis on a microscopic level that allows us to separate the contributions of both the excitons and free charge carriers in the observed transient absorption response of a composite organometallic lead halide perovskite film. We found spatialmore » regions where the transient absorption response was predominately a result of excitons and others where it was predominately due to charge carriers, and regions consisting of signals from both contributors. Lastly, quantitative decomposition of the transient absorption response curves further enabled us to reveal the relative contribution of each photoexcitation to the measured response at spatially resolved locations in the film.« less

  18. Control of lasing from a highly photoexcited semiconductor microcavity

    NASA Astrophysics Data System (ADS)

    Hsu, Feng-Kuo

    Technological advances in the fabrication of optical cavities and crystal growth have enabled the studies on macroscopic quantum states and emergent nonequilibrium phenomena of light-matter hybrids in condensed matter. Optical excitations in a semiconductor microcavity can result in a coupled electron-hole-photon (e-h-gamma) system, in which various many-body physics can be studied by varying particle densities and particle-particle interactions. Recently there have been reports of phenomena analogous to Bose-Einstein condensates or superfluids for exciton-polaritons in a microcavity. An exciton-polariton is a quasiparticle resulting from strong coupling between the cavity light field and the exciton (e-h pair) transition, and typically is only stable at a low density ( 10 11 to 1012 cm-2 or less). At a higher density, it has been theoretically predicted that pairing of electrons and holes can result in a BCS-like state at cryogenic temperatures, which can produce cooperative radiation known as superradiance. In this work, we explore cooperative phenomena caused by e-h correlation and many-body effect in a highly photoexcited microcavity at room temperature. High-density e-h plasmas in a photoexcited microcavity are studied under the following conditions: (1) the sample is photoexcited GaAs-based microcavity with large detuning between the band gap Eg of quantum well and cavity resonance to prevent carriers from radiative loss, (2) the density of e-h pairs is high enough to build long-range correlation with the assistance of cavity light field. The Fermi level of electron-hole pairs is about 80 meV above Eg, and (3) the e-h correlation is stabilized through thermal management, which includes modulating the excitation pulse laser temporally and spatially to reduce the heating and carrier diffusion effect. We have observed ultrafast (sub-10 picoseconds) spin-polarized lasing with sizable energy shifts and linewidth broadenings as pump flux is increased. With

  19. Exciton and core-level electron confinement effects in transparent ZnO thin films

    PubMed Central

    Mosquera, Adolfo A.; Horwat, David; Rashkovskiy, Alexandr; Kovalev, Anatoly; Miska, Patrice; Wainstein, Dmitry; Albella, Jose M.; Endrino, Jose L.

    2013-01-01

    The excitonic light emission of ZnO films have been investigated by means of photoluminescence measurements in ultraviolet-visible region. Exciton confinement effects have been observed in thin ZnO coatings with thickness below 20 nm. This is enhanced by a rise of the intensity and a blue shift of the photoluminescence peak after extraction of the adsorbed species upon annealing in air. It is found experimentally that the free exciton energy (determined by the photoluminescence peak) is inversely proportional to the square of the thickness while core-level binding energy is inversely proportional to the thickness. These findings correlate very well with the theory of kinetic and potential confinements.

  20. Physics of the Be(10{bar 1} 0) Surface Core Level Spectrum

    SciTech Connect

    Lizzit, S.; Pohl, K. |; Baraldi, A.; Comelli, G.; Fritzsche, V.; Plummer, E.W. |; Stumpf, R.; Hofmann, P. ||

    1998-10-01

    Photoelectron diffraction has been utilized to confirm the theoretical prediction that the surface core level shifts observed for Be(10{bar 1}0) have been improperly assigned. The original assignment based upon the relative intensity of the shifted components was intuitively obvious: the peak with the largest shift of {minus}0.7 eV with respect to the bulk was associated with the surface plane, the next peak shifted by {minus}0.5 eV stems from the second layer, and the third peak at {minus}0.22 eV from the third and fourth layers. First-principles theory and our experimental data show that the largest shift is associated with the second plane, not the first plane. {copyright} {ital 1998} {ital The American Physical Society }

  1. Er/Si (111) interface intermixing investigation using core level photoemission

    SciTech Connect

    Haderbache, L.; Wetzel, P.; Pirri, C.; Peruchetti, J.C.; Bolmont, D.; Gewinner, G. )

    1990-07-23

    We present in this letter Si 2{ital p} core level photoemission measurements on the Er/Si (111) interface formed at room temperature. These spectroscopic data are compared with those measured on amorphous silicide films for various Er concentrations grown by coevaporation of Er and Si species at room temperature under ultrahigh vacuum conditions. This study reveals a strong interaction between Er and the Si (111) substrate even at very low coverage. A mixed interface is observed with silicide formation up to 6 monolayers of deposited metal which corresponds to the onset of erbium metal overgrowth. The Er concentration in the interfacial silicide is found to increase as a function of the deposited Er thickness. A model for the interface is proposed and discussed.

  2. Direct measurement of core-level relaxation dynamics on a surface- adsorbate system

    NASA Astrophysics Data System (ADS)

    Yin, Jing; Miaja-Avila, Luis; Saathoff, Guido; La-O-Vorakiat, Chan; Murnane, Margaret; Kapteyn, Henry; Mathias, Stefan; Aeschlimann, Martin; Bauer, Michael

    2008-03-01

    Electronic coupling between an adsorbate and the surface on which it resides is fundamental to the understanding of many surface interactions. However, the interaction of highly-excited adsorbate states is an area that has been explored only indirectly to-date. In this work, we present the first direct time-resolved observations of the lifetime of core-excited states of an atom adsorbed onto a surface. By implementing laser-assisted Auger decay on an adsorbate/surface system, we directly measure the lifetime of the 4d-1 core level of Xenon on Pt(111) to be 7.1 ± 1.1 fs. This result opens up time domain measurements of highly-excited state dynamics in materials systems where, because of complex interactions, energy-resolved measurements provide incomplete information.

  3. Direct measurement of core-level relaxation dynamics on a surface- adsorbate system

    NASA Astrophysics Data System (ADS)

    Yin, Jing; Miaja-Avila, Luis; Saathoff, Guido; La-O-Vorakiat, Chan; Murnane, Margaret; Kapteyn, Henry; Mathias, Stefan; Aeschlimann, Martin; Bauer, Michael

    2008-05-01

    Electronic coupling between an adsorbate and the surface on which it resides is fundamental to the understanding of many surface interactions. However, the interaction of highly-excited adsorbate states is an area that has been explored only indirectly to-date. In this work, we present the first direct time-resolved observations of the lifetime of core-excited states of an atom adsorbed onto a surface. By implementing laser-assisted Auger decay on an adsorbate/surface system, we directly measure the lifetime of the 4d-1 core level of Xenon on Pt(111) to be 7.1 ± 1.1 fs. This result opens up time domain measurements of highly-excited state dynamics in materials systems where, because of complex interactions, energy-resolved measurements provide incomplete information.

  4. Carrier confinement and bond softening in photoexcited bismuth films

    NASA Astrophysics Data System (ADS)

    Shin, Taeho; Wolfson, Johanna W.; Teitelbaum, Samuel W.; Kandyla, Maria; Nelson, Keith A.

    2015-11-01

    Femtosecond pump-probe spectroscopy of bismuth thin films has revealed strong dependencies of reflectivity and phonon frequency on film thickness in the range of 25 -40 nm . The reflectivity variations are ascribed to distinct electronic structures originating from strongly varying electronic temperatures and proximity of the film thickness to the optical penetration depth of visible light. The phonon frequency is redshifted by an amount that increases with decreasing film thickness under the same excitation fluence, indicating carrier density-dependent bond softening that increases due to suppressed diffusion of carriers away from the photoexcited region in thin films. The results have significant implications for nonthermal melting of bismuth as well as lattice heating due to inelastic electron-phonon scattering.

  5. Defect-induced supercollision cooling of photoexcited carriers in graphene.

    PubMed

    Alencar, Thonimar V; Silva, Mychel G; Malard, Leandro M; de Paula, Ana M

    2014-10-08

    Defects play a fundamental role in the energy relaxation of hot photoexcited carriers in graphene, thus a complete understanding of these processes are vital for improving the development of graphene devices. Recently, it has been theoretically predicted and experimentally demonstrated that defect-assisted acoustic phonon supercollision, the collision between a carrier and both an acoustic phonon and a defect, is an important energy relaxation process for carriers with excess energy below the optical phonon emission. Here, we studied samples with defects optically generated in a controlled manner to experimentally probe the supercollision model as a function of the defect density. We present pump and probe transient absorption measurements showing that the decay time decreases as the density of defect increases as predicted by the supercollision model.

  6. Spectral Weight Transfer and the Role of Photoexcitation in PCMO

    NASA Astrophysics Data System (ADS)

    McGill, S. A.; Miller, R. I.; Torrens, O. N.; Kikkawa, J. M.; Mamchik, A.; Chen, I.-Wei

    2004-03-01

    We have performed static white light reflectivity measurements on Pr_0.67Ca_0.33MnO3 from T = 35 K to room temperature and magnetic fields up to 7 Tesla to measure spectral weight transfer in the optical and mid-IR ranges. Here we compare our results with pump-probe transient reflectivity obtained for similar conditions of temperature, magnetic field, and photoexcitation. We use these data to assess the contribution of lattice heating to the transient signals. Finally, we have observed long-lived changes in the DC reflectivity spectrum after controlled exposures to pulsed excitation. We discuss these effects in terms of the destruction and creation of the B = 0 T, low-temperature, charge-ordered insulating state and the subsequent implications for the material's magnetic order.

  7. Photoexcited Carrier Dynamics of Cu2S Thin Films.

    PubMed

    Riha, Shannon C; Schaller, Richard D; Gosztola, David J; Wiederrecht, Gary P; Martinson, Alex B F

    2014-11-20

    Copper sulfide is a simple binary material with promising attributes for low-cost thin film photovoltaics. However, stable Cu2S-based device efficiencies approaching 10% free from cadmium have yet to be realized. In this Letter, transient absorption spectroscopy is used to investigate the dynamics of the photoexcited state of isolated Cu2S thin films prepared by atomic layer deposition or vapor-based cation exchange of ZnS. While a number of variables including film thickness, carrier concentration, surface oxidation, and grain boundary passivation were examined, grain structure alone was found to correlate with longer lifetimes. A map of excited state dynamics is deduced from the spectral evolution from 300 fs to 300 μs. Revealing the effects of grain morphology on the photophysical properties of Cu2S is a crucial step toward reaching high efficiencies in operationally stable Cu2S thin film photovoltaics.

  8. Near-field spectroscopy of graphene during ultrafast photoexcitation

    NASA Astrophysics Data System (ADS)

    Wagner, Martin; Fei, Zhe; McLeod, Alexander; Rodin, Aleksandr; Bao, Wenzhong; Zhang, Lingfeng; Zhao, Zeng; Iwinski, Eric; Thiemens, Mark; Fogler, Michael; Castro-Neto, Antonio; Lau, Chunning; Keilmann, Fritz; Basov, Dimitri

    2013-03-01

    Recently, impressive progress in nanoplasmonics of graphene using near-field spectroscopy and imaging has been reported [Z. Fei et al., Nano Lett. 11, 4701 (2011); Z. Fei et al., Nature 487, 82 (2012)]. However, these studies of the interaction of the graphene plasmon with the SiO2 substrate surface phonon were time-independent. Here we combine imaging and material characterization on the nano scale with ultrafast sub-picosecond time resolution and present optical pump broadband mid-infrared probe spectroscopy of graphene. We discuss the optical pump induced changes of the coupled plasmon-phonon modes with respect to carrier density and time-dependence. The difference between ultrafast photoexcitation and conventional electrostatic doping via the field effect is analyzed and compared with modeling.

  9. Low-temperature galvanomagnetic studies of nominally undoped germanium subjected to intrinsic photoexcitation

    SciTech Connect

    Bannaya, V. F.

    2015-09-15

    The results of studying the heating of charge carriers by an electric field in nominally undoped Ge (with impurity concentrations of (N{sub a} + N{sub g}) ≤ 5 × 10{sup 13} cm{sup –3}) subjected to interband illumination are reported. It is necessary in this situation to take into account two types of free charge carriers. In the case of such generation, the relation between the concentrations of electrons and holes depends to a large extent on the value of the electric field since this field differently affects the recombination coefficients of charge carriers and gives rise to new effects. The results of experimental studies of the conductivity σ and the Hall constant R{sub H} in n-Ge and p-Ge at T = 4.2 K and at different intensities of intrinsic photoexcitation are reported. A model of interband recombination, which takes into account deep-level impurity centers, is suggested for explanation of the results.

  10. Calculation of core-level excitation in some MAX-phase compounds

    NASA Astrophysics Data System (ADS)

    Wang, Liaoyuan; Rulis, Paul; Ching, W. Y.

    2013-07-01

    We report first-principles spectroscopic calculation of core level excitations in five MAX-phase compounds. The spectra of Ti-K edges in Ti2AlC and Ti2AlN, C-K edge in Ti2AlC, N-K edge in Ti2AlN, and Nb-K edge in Nb2AlC are calculated and found to be in good agreement with reported experimental measurements. Based on this agreement, the Al-K and Al-L3 edges in the same five phases plus the Cr-K and C-K edges in Cr2AlC and the C-K edge in Nb2AlC are calculated as theoretical predictions. We further analyze the anisotropy in the calculated spectra to gain additional insights on the structure-properties relationships in these MAX-phase compounds. These results are further discussed in the context of the local atomic environments of the M, A, and X elements in MAX-phase compounds and in relation to their fundamental electronic structures.

  11. Atomic signatures of local environment from core-level spectroscopy in β -Ga2O3

    NASA Astrophysics Data System (ADS)

    Cocchi, Caterina; Zschiesche, Hannes; Nabok, Dmitrii; Mogilatenko, Anna; Albrecht, Martin; Galazka, Zbigniew; Kirmse, Holm; Draxl, Claudia; Koch, Christoph T.

    2016-08-01

    We present a joint theoretical and experimental study on core-level excitations from the oxygen K edge of β -Ga2O3 . A detailed analysis of the electronic structure reveals the importance of O-Ga hybridization effects in the conduction region. The spectrum from O 1 s core electrons is dominated by excitonic effects, which overall redshift the absorption onset by 0.5 eV, and significantly redistribute the intensity to lower energies. Analysis of the spectra obtained within many-body perturbation theory reveals atomic fingerprints of the inequivalent O atoms. From the comparison of energy-loss near-edge fine-structure (ELNES) spectra computed with respect to different crystal planes, with measurements recorded under the corresponding diffraction conditions, we show how the spectral contributions of specific O atoms can be enhanced while quenching others. These results suggest ELNES, combined with ab initio many-body theory, as a very powerful technique to characterize complex systems, with sensitivity to individual atomic species and to their local environment.

  12. Core level electron binding energies of realgar (As{sub 4}S{sub 4})

    SciTech Connect

    Pratt, A.R.; Nesbitt, H.W.

    2000-04-01

    XPS broad scans and high-resolution narrow-region spectra were collected from fresh realgar (As{sub 4}S{sub 4}) surfaces to measure core level S and As binding energies. Reasonably accurate As and S concentrations were determined from XPS broad scans using peak areas and manufacturer supplied sensitivity factors. High resolution S(2p) and As(3d) narrow region spectra were comprised of photoelectron emissions indicative of As and S in intermediate oxidation states akin to binding energies of As and S polymeric species. S(2p) spectra were interpreted using only S contributions expected from the bulk mineral matrix and showed that S was not greatly affected by surface state phenomena. This was attributed to breakage of intermolecular van der Waals bonds rather than covalent interatomic bonds. As(3d) spectra were found to contain two contributions one from As atoms in As{sub 4}S{sub 4} molecules in the bulk mineral matrix and another possibly from As atoms in molecules situated at the surface.

  13. Pressure-induced crossing of the core levels in 5 d metals

    NASA Astrophysics Data System (ADS)

    Tal, Alexey A.; Katsnelson, Mikhail I.; Ekholm, Marcus; Jönsson, H. Johan M.; Dubrovinsky, Leonid; Dubrovinskaia, Natalia; Abrikosov, Igor A.

    2016-05-01

    A pressure-induced interaction between core electrons, the core-level crossing (CLC) transition, has been observed in hcp Os at P ≈400 GPa [L. Dubrovinsky et al., Nature (London) 525, 226 (2015)], 10.1038/nature14681. By carrying out a systematic theoretical study for all metals of the 5 d series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at ≈1500 GPa , at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements.

  14. Reversible and irreversible structural transformations of nanocomponents of molecular layers by resonance photoexcitation or heating

    NASA Astrophysics Data System (ADS)

    Kaliteevskaya, Elena N.; Krutyakova, Valentina P.; Razumova, Tatyana K.; Starovoytov, Anton A.

    2010-09-01

    The reversible and irreversible structural transformations of monomolecular and associated nanocomponents of a polymethine dye layer by photoexcitation or heating are studied experimentally. The photo- and thermodestruction yields of the layers are investigated.

  15. Photoexcited energy transfer in a weakly coupled dimer

    SciTech Connect

    Hernandez, Laura Alfonso; Nelson, Tammie; Tretiak, Sergei; Fernandez-Alberti, Sebastian

    2015-01-08

    Nonadiabatic excited-state molecular dynamics (NA-ESMD) simulations have been performed in order to study the time-dependent exciton localization during energy transfer between two chromophore units of the weakly coupled anthracene dimer dithia-anthracenophane (DTA). Simulations are done at both low temperature (10 K) and room temperature (300 K). The initial photoexcitation creates an exciton which is primarily localized on a single monomer unit. Subsequently, the exciton experiences an ultrafast energy transfer becoming localized on either one monomer unit or the other, whereas delocalization between both monomers never occurs. In half of the trajectories, the electronic transition density becomes completely localized on the same monomer as the initial excitation, while in the other half, it becomes completely localized on the opposite monomer. In this article, we present an analysis of the energy transfer dynamics and the effect of thermally induced geometry distortions on the exciton localization. Finally, simulated fluorescence anisotropy decay curves for both DTA and the monomer unit dimethyl anthracene (DMA) are compared. As a result, our analysis reveals that changes in the transition density localization caused by energy transfer between two monomers in DTA is not the only source of depolarization and exciton relaxation within a single DTA monomer unit can also cause reorientation of the transition dipole.

  16. Two-Step Photoexcitation Mechanism in Amorphous Se

    NASA Astrophysics Data System (ADS)

    Berashevich, J.; Mishchenko, A.; Reznik, A.

    2014-04-01

    The first-principles simulations are applied to study a photoinduced metastability in amorphous selenium and contribution of the valence-alteration pair (VAP) defects in this process. The VAP defect is confirmed to be the equilibrium defect; it minimizes the destabilizing interaction induced by disorientation of the lone-pair (LP) electrons along the Se chains, and, thus, relieves tension in a system. The photoexcitation involves the LP electrons, and it is proposed to be described by two coexisting processes, namely, single- and double-electron excitations. Both processes are found to induce the defect states in the band gap and cause experimentally observed photodarkening; however, only double-electron excitation is capable of triggering bond rearrangement and structural transformation. Lattice relaxation, which follows bond rearrangement, occurs with characteristic energy of -0.9±0.3 eV. It is found to promote formation of energetically favorable VAP defects and to trigger the ringlike to helixlike transformations, thus, ultimately stimulating the photoinduced crystallization. The photoinduced crystallization is directly simulated in a system characterized by increased crystalline order.

  17. Photoexcited energy transfer in a weakly coupled dimer

    DOE PAGES

    Hernandez, Laura Alfonso; Nelson, Tammie; Tretiak, Sergei; ...

    2015-01-08

    Nonadiabatic excited-state molecular dynamics (NA-ESMD) simulations have been performed in order to study the time-dependent exciton localization during energy transfer between two chromophore units of the weakly coupled anthracene dimer dithia-anthracenophane (DTA). Simulations are done at both low temperature (10 K) and room temperature (300 K). The initial photoexcitation creates an exciton which is primarily localized on a single monomer unit. Subsequently, the exciton experiences an ultrafast energy transfer becoming localized on either one monomer unit or the other, whereas delocalization between both monomers never occurs. In half of the trajectories, the electronic transition density becomes completely localized on themore » same monomer as the initial excitation, while in the other half, it becomes completely localized on the opposite monomer. In this article, we present an analysis of the energy transfer dynamics and the effect of thermally induced geometry distortions on the exciton localization. Finally, simulated fluorescence anisotropy decay curves for both DTA and the monomer unit dimethyl anthracene (DMA) are compared. As a result, our analysis reveals that changes in the transition density localization caused by energy transfer between two monomers in DTA is not the only source of depolarization and exciton relaxation within a single DTA monomer unit can also cause reorientation of the transition dipole.« less

  18. Competing ultrafast energy relaxation pathways in photoexcited graphene.

    PubMed

    Jensen, S A; Mics, Z; Ivanov, I; Varol, H S; Turchinovich, D; Koppens, F H L; Bonn, M; Tielrooij, K J

    2014-10-08

    For most optoelectronic applications of graphene, a thorough understanding of the processes that govern energy relaxation of photoexcited carriers is essential. The ultrafast energy relaxation in graphene occurs through two competing pathways: carrier-carrier scattering, creating an elevated carrier temperature, and optical phonon emission. At present, it is not clear what determines the dominating relaxation pathway. Here we reach a unifying picture of the ultrafast energy relaxation by investigating the terahertz photoconductivity, while varying the Fermi energy, photon energy and fluence over a wide range. We find that sufficiently low fluence (≲4 μJ/cm(2)) in conjunction with sufficiently high Fermi energy (≳0.1 eV) gives rise to energy relaxation that is dominated by carrier-carrier scattering, which leads to efficient carrier heating. Upon increasing the fluence or decreasing the Fermi energy, the carrier heating efficiency decreases, presumably due to energy relaxation that becomes increasingly dominated by phonon emission. Carrier heating through carrier-carrier scattering accounts for the negative photoconductivity for doped graphene observed at terahertz frequencies. We present a simple model that reproduces the data for a wide range of Fermi levels and excitation energies and allows us to qualitatively assess how the branching ratio between the two distinct relaxation pathways depends on excitation fluence and Fermi energy.

  19. Gamma Spectra Resulting From the Annihilation of Positrons with Electrons in Single, Selected Core Levels of Cu, Ag and Au

    SciTech Connect

    Kim, S; Eshed, A; Goktepeli, S; Sterne, P A; Koymen, A R; Chen, W C; Weiss, A H

    2005-07-25

    The {gamma}-ray energy spectra due to positron annihilation with the 3p core-level of Cu, the 4p core-level of Ag, and 5p core level of Au were obtained separately from the total annihilation spectrum by measuring the energies of {gamma}-rays time coincident with Auger electrons emitted as a result of filling the core-hole left by annihilation. The results of these measurements are compared to the total annihilation spectra and with LDA based theoretical calculations. A comparison of area normalized momentum distributions with the individual cores extracted from the Doppler measurements shows good qualitative agreement, however, in all three spectra, the calculated values of the momentum density appears to fall below the measured values as the momentum increases. The discrepancies between theory and experiment are well outside the statistical uncertainties of the experiment and become more pronounced with increasing Z going down the column from Cu to Ag to Au. The comparison with the experimental results clearly indicates that the calculations are not predicting the correct ratio of high momentum to low momentum spectral weight and suggest the need to improve the treatment of many body electron-positron correlation effects in annihilation as they pertain to core levels.

  20. Kinetics of photoconductivity in ZnSe crystals upon photoexcitation of deep centers

    SciTech Connect

    Bruk, L.I.; Gorya, O.S.; Korotkov, V.A.

    1995-10-01

    It has long been known that investigation of the spectral characteristics of photoconductivity (PC) in wide-band-gap semiconductors does not provide full information on the position of photosensitive centers in the forbidden band. The broad spectrum of intrinsic and impurity PC consists of several overlapping bands. In the long-wavelength region, impurity photoeffect is superimposed over the falling-off spectrum of intrinsic PC. In addition, measurements of steady-state PC are incapable of revealing photoinsensitive recombination and trapping centers. Those levels that were not excited prior to illumination of the semiconductor may provide no contribution to PC and may appear either photoinsensitive or indistinguishable from dominant channels of recombination and trapping on other centers. Preliminary excitation may alter the state of these levels to such a degree that they will show up as a spike in the PC relaxation curve. In this paper, we report kinetic studies of the PC and the effective cross section for photon capture (CSPC) in the photosensitivity range of zinc selenide single crystals containing trace impurities.

  1. Photo-excitation of carotenoids causes cytotoxicity via singlet oxygen production

    SciTech Connect

    Yoshii, Hiroshi; Yoshii, Yukie; Asai, Tatsuya; Furukawa, Takako; Takaichi, Shinichi; Fujibayashi, Yasuhisa

    2012-01-06

    Highlights: Black-Right-Pointing-Pointer Some photo-excited carotenoids have photosensitizing ability. Black-Right-Pointing-Pointer They are able to produce ROS. Black-Right-Pointing-Pointer Photo-excited fucoxanthin can produce singlet oxygen through energy transfer. -- Abstract: Carotenoids, natural pigments widely distributed in algae and plants, have a conjugated double bond system. Their excitation energies are correlated with conjugation length. We hypothesized that carotenoids whose energy states are above the singlet excited state of oxygen (singlet oxygen) would possess photosensitizing properties. Here, we demonstrated that human skin melanoma (A375) cells are damaged through the photo-excitation of several carotenoids (neoxanthin, fucoxanthin and siphonaxanthin). In contrast, photo-excitation of carotenoids that possess energy states below that of singlet oxygen, such as {beta}-carotene, lutein, loroxanthin and violaxanthin, did not enhance cell death. Production of reactive oxygen species (ROS) by photo-excited fucoxanthin or neoxanthin was confirmed using a reporter assay for ROS production with HeLa Hyper cells, which express a fluorescent indicator protein for intracellular ROS. Fucoxanthin and neoxanthin also showed high cellular penetration and retention. Electron spin resonance spectra using 2,2,6,6-tetramethil-4-piperidone as a singlet oxygen trapping agent demonstrated that singlet oxygen was produced via energy transfer from photo-excited fucoxanthin to oxygen molecules. These results suggest that carotenoids such as fucoxanthin, which are capable of singlet oxygen production through photo-excitation and show good penetration and retention in target cells, are useful as photosensitizers in photodynamic therapy for skin disease.

  2. Effects of non-local exchange on core level shifts for gas-phase and adsorbed molecules

    NASA Astrophysics Data System (ADS)

    Van den Bossche, M.; Martin, N. M.; Gustafson, J.; Hakanoglu, C.; Weaver, J. F.; Lundgren, E.; Grönbeck, H.

    2014-07-01

    Density functional theory calculations are often used to interpret experimental shifts in core level binding energies. Calculations based on gradient-corrected (GC) exchange-correlation functionals are known to reproduce measured core level shifts (CLS) of isolated molecules and metal surfaces with reasonable accuracy. In the present study, we discuss a series of examples where the shifts calculated within a GC-functional significantly deviate from the experimental values, namely the CLS of C 1s in ethyl trifluoroacetate, Pd 3d in PdO and the O 1s shift for CO adsorbed on PdO(101). The deviations are traced to effects of the electronic self-interaction error with GC-functionals and substantially better agreements between calculated and measured CLS are obtained when a fraction of exact exchange is used in the exchange-correlation functional.

  3. The S(2p) Core Level Binding Energies for Alternative Adsorption Sites and the Example of Thiol Self Assembly

    NASA Astrophysics Data System (ADS)

    Jia, Juanjuan; Esaulov, Vladimir; Kara, Abdelkader

    2015-03-01

    Results of an investigation of the characteristics of thiol SAMs obtained by vacuum evaporative adsorption, useful for reactive substrates, are presented along with core level binding energy (BE) calculations. Thiol ended SAMs of 1,4-benzenedimethanethiol (BDMT) are obtained by evaporation on Au. They display an unconventional BE structure at about 161 eV, which is close to a known BE of an S atom on Au. S(2p) core level BE calculations for molecules chemisorbed on hollow, bridge and atop sites are reported and suggest that the 161 eV peak is indeed due to an alternative adsorption site, which can be associated to an atop configuration. This must therefore not be confused with atomic sulfur and dissociation processes with S-C bond scission. Work partially supported by the U.S. Department of Energy Basic Energy Science under Contract No DE-FG02-11ER16243.

  4. An Ultraviolet X-Ray Laser Source for Core Level Spectroscopy and Dynamics of Metal Cluster/Ceramic Chemistry

    DTIC Science & Technology

    2007-11-02

    TYPE AND DATES COVERED Final Rpnnrt. 3/1/97 - 5/31/98 4. TITLE AND SUBTITLE An Ultraviolet X-ray Laser Source for Core Level Spectroscopy and...DISTRIBUTION CODE 13. ABSTRACT (Maximum 200 words) A99B0722 A titanium sapphire ultrafast laser system was procured and merged with a high repetition rate...pulsed valve to produce higher harmonic light output in a rare gas jet. The ultrafast laser system consists of a seed laser , a regenerative amplifier

  5. Predicting core level binding energies shifts: Suitability of the projector augmented wave approach as implemented in VASP.

    PubMed

    Pueyo Bellafont, Noèlia; Viñes, Francesc; Hieringer, Wolfgang; Illas, Francesc

    2017-03-30

    Here, we assess the accuracy of various approaches implemented in Vienna ab initio simulation package code to estimate core-level binding energy shifts (ΔBEs) using a projector augmented wave method to treat core electrons. The performance of the Perdew-Burke-Ernzerhof (PBE) and the Tao-Perdew-Staroverov-Scuseria (TPSS) exchange-correlation density functionals is examined on a dataset of 68 molecules containing B→F atoms in diverse chemical environments, accounting for 185 different 1s core level binding energy shifts, for which both experimental gas-phase X-ray photoemission (XPS) data and accurate all electron ΔBEs are available. Four procedures to calculate core-level shifts are investigated. Janak-Slater transition state approach yields mean absolute errors of 0.37 (0.21) eV at PBE (TPSS) level, similar to highly accurate all electron ΔSCF approaches using same functionals, and close to XPS experimental accuracy of 0.1 eV. The study supports the use of these procedures to assign ΔBEs of molecular moieties on material surfaces of interest in surface science, nanotechnology, and heterogeneous catalysis. © 2017 Wiley Periodicals, Inc.

  6. Slow deactivation channels in UV-photoexcited adenine DNA.

    PubMed

    Chen, Xuebo; Fang, Weihai; Wang, Haobin

    2014-03-07

    The molecular mechanism for removing the excess energy in DNA bases is responsible for the high photostability of DNA and is thus the subject of intense theoretical/computational investigation. To understand why the excited state decay of the stacked bases is significantly longer than that of the monomers, we carried out electronic structure calculations on an adenine monomer and an aqueous (dA)5 oligonucleotide employing the CASPT2//CASSCF and CASPT2//CASSCF/AMBER levels of theory. The newly-found bright excited state pair Sstack1((1)ππ*) and Sstack2((1)ππ*) of d(A)5, originated from base stacking, is of intra-base charge transfer nature and occurs in different stacked bases with charge transfer along opposite directions. Two slow deactivation channels of d(A)5 were proposed as a result of the sizable barriers along the relaxation paths starting from the FC point of the Sstack1((1)ππ*) state. The SN1P((1)nπ*) state of d(A)5 serves as an intermediate state in one relaxation channel, to which a nonadiabatic decay from the Sstack1((1)ππ*) state occurs in an energy degeneracy region. A relatively high barrier in this state is found and attributed to the steric hindrance of the DNA environment due to the large NH2 group twisting, which gives a weak and red-shifted fluorescence. Another direct relaxation channel, induced by the C2-H2 bond twisting motion, is found to go through a conical intersection between the Sstack1((1)ππ*) and the ground state. The barrier found here enables fluorescence from the Sstack1((1)ππ*) state and may explain the bright state emission observed in the fluorescence upconversion measurements. The inter-molecular SCT((1)ππ*) state may be involved in the slow relaxation process of the photoexcited adenine oligomers through efficient internal conversion to the intra-base Sstack1((1)ππ*) state.

  7. A Model for Nonlinear Photoexcitation of Molecular Hydrogen in Space

    NASA Astrophysics Data System (ADS)

    Glownia, J. H.; Sorokin, P. P.

    2000-05-01

    A model for nonlinear photoexcitation of H2 molecules in tenuous clouds near bright stars (e.g. PDRs or PNe) is presented. In the model, H atoms and H2 molecules coexist in a cold neutral cloud surrounding an H II region represented by a conventional Strömgren sphere. An intense band of Ly-α radiation is produced by H++ e- recombination and frequency redistribution occuring in the H II region. Due to elastic scattering by H atoms, the Ly-α radiation slowly diffuses outward through the neutral cloud, its photon density becoming enormously enhanced in the process. This provides the basic pumping field required for the nonlinear effects to be described. Via resonant inverse Raman scattering (IRS), the intense Ly-α radiation field induces strong nonlinear absorption of VUV continuum starlight by orthohydrogen molecules in X0, J''=1 around three ''primary'' frequencies (B9-0P1, B6-0P1, and B3-0R1), the primary IRS terminal levels (X5, J''=1), (X4, J''=1), and (X3, J''=1) simultaneously becoming strongly populated. (Parahydrogen absorbs via IRS on B3-0R0.) Via either Ly-α -pumped, spontaneous resonant Raman scattering, or secondary IRS processes, molecules in the primary IRS terminal levels are selectively redistributed into higher-lying X-state levels such as (X10, J''=5), (X13, J''=5), and (X14, J''=1). A thin shell (thickness ~ 10,000 km) of H2 molecules populating select vibrationally excited X-state levels thus surrounds the Strömgren sphere. >From a handful of the populated high-lying X-state levels, there occur strong resonances with Ly-α . Intense Ly-α radiation can thus induce broadband stimulated Raman scattering (SRS) to occur on these transitions, generating broadband IR Stokes-wave light on strong transitions to EF-state levels. An SRS process would occur as part of a 2n-wave parametric oscillation (SRS-PO) process, with light at additional frequencies being generated on strong transitions ultimately returning molecules to the X-state level from

  8. Measurement of excited layer thickness in highly photo-excited GaAs

    NASA Astrophysics Data System (ADS)

    Liang, Lingliang; Tian, Jinshou; Wang, Tao; Wu, Shengli; Li, Fuli; Gao, Guilong

    2016-10-01

    Highly photo-excited layer thickness in GaAs is measured using a pump probe arrangement. A normally incident pump illumination spatially modulated by a mask will induce a corresponding refractive index change distribution in the depth direction due to edge scattering and attenuation absorption effect, which can deflect the probe beam passing through this excited region. Maximum deflection of the probe beam will be limited by the thickness of excited layer, and thus can also be employed to measure the thickness of the photo-excited layer of the material. Theoretical calculation confirms the experimental results. This method can find its application in measurements of photo-excited layer thickness of many kinds of materials and be significant to study the characteristics of materials in laser machining, grating and waveguide fabricating.

  9. Observation of perturbed 3snp double photoexcited Ryberg series of beryllium atoms

    SciTech Connect

    Yoshida, Fumiko; Matsuoka, Leo; Osaki, Hiroyuki; Kikkawa, Satoshi; Fukushima, Yu; Hasegawa, Shuichi; Nagata, Tetsuo; Azuma, Yoshiro; Obara, Satoshi

    2006-04-15

    We observed the 3snp autoionizing Rydberg series of the Be atom in order to investigate the double-photoexcitation processes in two-s-electron systems. We employed synchrotron radiation to photoexcite the Be atoms and measured the generated Be{sup +} photoions by the time-of-flight method. The 3snp (n=3-9) photoexcitation resonance peaks with interloper state of 3p4s that converges to Be{sup +}(3p) threshold were observed. We derived the resonance parameters of 3snp series from a fitting procedure and obtained the Fano parameter q, energy position E{sub 0}, and resonance width {gamma}. These parameters are in good agreement with theoretical values. In the vicinity of the 3s5p state these experimental results clearly revealed the influence of the interloper 3p4s state, and the comparison with the numerical calculations indicates that more detailed calculations might be required to fully explain this phenomenon.

  10. Influence of photoexcitation on hopping conduction in neutron-transmutation-doped GaAs

    SciTech Connect

    Satoh, M.; Kawahara, H.; Kuriyama, K.; Kawakubo, T.; Yoneda, K.; Kimura, I.

    1988-02-15

    The nature of the tunneling-assisted hopping conduction in neutron-transmutation-doped GaAs has been studied under photoexcitation with a photon energy of 1.32 eV. It is found that the dopants activated by annealing around 400 /sup 0/C provide the electrons to the defect levels originating the hopping conduction even when under photoexcitation. The hopping conduction under photoexcitation is affected by quenching in photoconductance below 120 K concerned with the main electron trap (EL2) and/or the As antisite defect (As/sub Ga/) induced by the neutron irradiation. The photoconductance of the samples with a lower radiation damage, As/sub Ga/less than or equal to1 x 10/sup 18/ cm/sup -3/, consists of the coexistence of the hopping and band conductions.

  11. Theoretical and experimental study of kinetics of photoexcited carriers in wide band gap semiconductors

    NASA Astrophysics Data System (ADS)

    Shishehchi, Sara; Rudin, Sergey; Garrett, Gregory; Wraback, Michael; Bellotti, Enrico

    2013-03-01

    We present a theoretical and experimental study of the subpicosecond kinetics of photo-excited carriers in the wide band gap semiconductors GaN and ZnO. In the theoretical model, interaction with a photo-excitation laser pulse is treated coherently and a generalized Monte Carlo simulation is used to account for scattering and dephasing. The scattering mechanisms included are carrier interactions with polar optical phonons and acoustic phonons, and carrier-carrier Coulomb interactions. For comparison, experimental time-resolved photoluminescence studies on GaN and ZnO samples are performed over a range of temperatures and excitation powers.

  12. Instantaneous band gap collapse in photoexcited monoclinic VO2 due to photocarrier doping.

    PubMed

    Wegkamp, Daniel; Herzog, Marc; Xian, Lede; Gatti, Matteo; Cudazzo, Pierluigi; McGahan, Christina L; Marvel, Robert E; Haglund, Richard F; Rubio, Angel; Wolf, Martin; Stähler, Julia

    2014-11-21

    Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic VO2 quasi-instantaneously into a metal. Thereby, we exclude an 80 fs structural bottleneck for the photoinduced electronic phase transition of VO2. First-principles many-body perturbation theory calculations reveal a high sensitivity of the VO2 band gap to variations of the dynamically screened Coulomb interaction, supporting a fully electronically driven isostructural insulator-to-metal transition. We thus conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V 3d valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occurred.

  13. Probing core-electron orbitals by scanning transmission electron microscopy and measuring the delocalization of core-level excitations

    NASA Astrophysics Data System (ADS)

    Jeong, Jong Seok; Odlyzko, Michael L.; Xu, Peng; Jalan, Bharat; Mkhoyan, K. Andre

    2016-04-01

    By recording low-noise energy-dispersive x-ray spectroscopy maps from crystalline specimens using aberration-corrected scanning transmission electron microscopy, it is possible to probe core-level electron orbitals in real space. Both the 1 s and 2 p orbitals of Sr and Ti atoms in SrTi O3 are probed, and their projected excitation potentials are determined. This paper also demonstrates experimental measurement of the electronic excitation impact parameter and the delocalization of an excitation due to Coulombic beam-orbital interaction.

  14. Molecular dynamics study of the weakly solvent dependent relaxation dynamics following chlorine dioxide photoexcitation

    NASA Astrophysics Data System (ADS)

    Brooksby, Craig; Prezhdo, Oleg V.; Reid, Philip J.

    2003-11-01

    The solvation dynamics following photoexcitation of chlorine dioxide (OClO) in different solvents are investigated by classical molecular dynamics. Following previous work on the aqueous response to OClO photoexcitation [J. Chem. Phys. 118, 4563 (2003)], the present study considers the response of chloroform and cyclohexane; these three liquids present unique solvent environments that differ significantly in both polarity and structure. The study is designed to ascertain the origin of the solvent-invariant homogeneous linewidth associated with OClO photoexcitation and to confirm, at the molecular level, whether the relaxation dynamics are similar across dissimilar solvents due to chance or a common relaxation origin. The results obtained here are used to predict the time scale of solvent-induced optical dephasing, and excellent agreement with experiment is observed for all solvents. Analysis demonstrates that the solvation dynamics of OClO are dominated by short-ranged mechanical solute-solvent interactions regardless of the identity and electrostatic properties of the solvent. Low-frequency translational motions dominate the coupling spectrum, and virtually no contribution to energy gap relaxation is achieved through intramolecular solvent motions. The invariant homogeneous linewidth is attributed to the similarity in the primary response of all solvents to OClO photoexcitation.

  15. Photoexcited breathers in conjugated polyenes: an excited-state molecular dynamics study.

    PubMed

    Tretiak, S; Saxena, A; Martin, R L; Bishop, A R

    2003-03-04

    pi-conjugated polymers have become an important class of materials for electronic devices. Design of these devices requires understanding such processes as photochemical reactions, spatial dynamics of photoexcitations, and energy and charge transport, which in turn involve complex coupled electron-vibrational dynamics. Here we study nonlinear photoexcitation dynamics in the polyene oligomers by using a quantum-chemical method suitable for the simulation of excited-state molecular dynamics in extended molecular systems with sizes up to hundreds of atoms. The method is based on the adiabatic propagation of the ground-state and transition single-electron density matrices along the trajectory. The simulations reveal formation of a self-localized vibronic excitation ("breather" or multiquanta bound state) with a typical period of 34 fs and allows us to identify specific slow and fast nuclear motions strongly coupled to the electronic degrees of freedom. The effect of chain imperfections and chemical defects on the dynamics is also investigated. A complementary two-dimensional analysis of corresponding transition density matrices provides an efficient way to monitor time-dependent real-space localization of the photoexcitation by identifying the underlying changes in charge densities and bond orders. Possible correlated electronic and vibrational spectroscopic signatures of photoexcited breathers are predicted, and generalizations to energy localization in complex macromolecules are discussed.

  16. Evidence of the nature of core-level photoemission satellites using angle-resolved photoemission extended fine structure

    SciTech Connect

    Moler, E.J.; Kellar, S.A.; Huff, W.R.A.

    1997-04-01

    The authors present a unique method of experimentally determining the angular momentum and intrinsic/extrinsic origin of core-level photoemission satellites by examining the satellite diffraction pattern in the Angle Resolved Photoemission Extended Fine Structure (ARPEFS) mode. They show for the first time that satellite peaks not associated with chemically differentiated atomic species display an ARPEFS intensity oscillation. They present ARPEFS data for the carbon 1s from ({radical}3x{radical}3)R30 CO/Cu(111) and p2mg(2xl)CO/Ni(110), nitrogen 1s from c(2x2) N{sub 2}/Ni(100), cobalt 1s from p(1x1)Co/Cu(100), and nickel 3p from clean nickel (111). The satellite peaks and tails of the Doniach-Sunjic line shapes in all cases exhibit ARPEFS curves which indicate an angular momentum identical to the main peak and are of an intrinsic nature.

  17. On sulfur core level binding energies in thiol self-assembly and alternative adsorption sites: An experimental and theoretical study

    SciTech Connect

    Jia, Juanjuan; Kara, Abdelkader E-mail: vladimir.esaulov@u-psud.fr; Pasquali, Luca; Bendounan, Azzedine; Sirotti, Fausto; Esaulov, Vladimir A. E-mail: vladimir.esaulov@u-psud.fr

    2015-09-14

    Characteristic core level binding energies (CLBEs) are regularly used to infer the modes of molecular adsorption: orientation, organization, and dissociation processes. Here, we focus on a largely debated situation regarding CLBEs in the case of chalcogen atom bearing molecules. For a thiol, this concerns the case when the CLBE of a thiolate sulfur at an adsorption site can be interpreted alternatively as due to atomic adsorption of a S atom, resulting from dissociation. Results of an investigation of the characteristics of thiol self-assembled monolayers (SAMs) obtained by vacuum evaporative adsorption are presented along with core level binding energy calculations. Thiol ended SAMs of 1,4-benzenedimethanethiol (BDMT) obtained by evaporation on Au display an unconventional CLBE structure at about 161.25 eV, which is close to a known CLBE of a S atom on Au. Adsorption and CLBE calculations for sulfur atoms and BDMT molecules are reported and allow delineating trends as a function of chemisorption on hollow, bridge, and atop sites and including the presence of adatoms. These calculations suggest that the 161.25 eV peak is due to an alternative adsorption site, which could be associated to an atop configuration. Therefore, this may be an alternative interpretation, different from the one involving the adsorption of atomic sulfur resulting from the dissociation process of the S–C bond. Calculated differences in S(2p) CLBEs for free BDMT molecules, SH group sulfur on top of the SAM, and disulfide are also reported to clarify possible errors in assignments.

  18. Photoexcited Carrier Dynamics of In2S3 Thin Films.

    PubMed

    McCarthy, Robert F; Schaller, Richard D; Gosztola, David J; Wiederrecht, Gary P; Martinson, Alex B F

    2015-07-02

    Indium sulfide (In2S3) is a promising absorber base for substitutionally doped intermediate band photovoltaics (IBPV); however, the dynamics of charge carriers traversing the electronic density of states that determine the optical and electronic response of thin films under stimuli have yet to be explored. The kinetics of photophysical processes in In2S3 grown by oxygen-free atomic layer deposition are deduced from photoconductivity, photoluminescence (PL), and transient absorption spectroscopy. We develop a map of excited-state dynamics for polycrystalline thin films including a secondary conduction band ∼2.1 eV above the first, plus sulfur vacancy and indium interstitial defect levels resulting in long-lived (∼100 ns) transients. Band-edge recombination produces PL and stimulated emission, which both intensify and red-shift as deposition temperature and grain size increase. The effect of rapid conduction band electron relaxation (<30 ps) and deep defect levels on IBPV employing In2S3-based absorbers is finally considered.

  19. Dynamical Evolution of Anisotropic Response in Black Phosphorus under Ultrafast Photoexcitation.

    PubMed

    Ge, Shaofeng; Li, Chaokai; Zhang, Zhiming; Zhang, Chenglong; Zhang, Yudao; Qiu, Jun; Wang, Qinsheng; Liu, Junku; Jia, Shuang; Feng, Ji; Sun, Dong

    2015-07-08

    Black phosphorus has recently emerged as a promising material for high-performance electronic and optoelectronic device for its high mobility, tunable mid-infrared bandgap, and anisotropic electronic properties. Dynamical evolution of photoexcited carriers and the induced transient change of electronic properties are critical for materials' high-field performance but remain to be explored for black phosphorus. In this work, we perform angle-resolved transient reflection spectroscopy to study the dynamical evolution of anisotropic properties of black phosphorus under photoexcitation. We find that the anisotropy of reflectivity is enhanced in the pump-induced quasi-equilibrium state, suggesting an extraordinary enhancement of the anisotropy in dynamical conductivity in hot carrier dominated regime. These results raise attractive possibilities of creating high-field, angle-sensitive electronic, optoelectronic, and remote sensing devices exploiting the dynamical electronic anisotropy with black phosphorus.

  20. The new high field photoexcitation muon spectrometer at the ISIS pulsed neutron and muon source.

    PubMed

    Yokoyama, K; Lord, J S; Murahari, P; Wang, K; Dunstan, D J; Waller, S P; McPhail, D J; Hillier, A D; Henson, J; Harper, M R; Heathcote, P; Drew, A J

    2016-12-01

    A high power pulsed laser system has been installed on the high magnetic field muon spectrometer (HiFi) at the International Science Information Service pulsed neutron and muon source, situated at the STFC Rutherford Appleton Laboratory in the UK. The upgrade enables one to perform light-pump muon-probe experiments under a high magnetic field, which opens new applications of muon spin spectroscopy. In this report we give an overview of the principle of the HiFi laser system and describe the newly developed techniques and devices that enable precisely controlled photoexcitation of samples in the muon instrument. A demonstration experiment illustrates the potential of this unique combination of the photoexcited system and avoided level crossing technique.

  1. Hot carrier and hot phonon coupling during ultrafast relaxation of photoexcited electrons in graphene

    SciTech Connect

    Iglesias, J. M.; Martín, M. J.; Pascual, E.; Rengel, R.

    2016-01-25

    We study, by means of a Monte Carlo simulator, the hot phonon effect on the relaxation dynamics in photoexcited graphene and its quantitative impact as compared with considering an equilibrium phonon distribution. Our multi-particle approach indicates that neglecting the hot phonon effect significantly underestimates the relaxation times in photoexcited graphene. The hot phonon effect is more important for a higher energy of the excitation pulse and photocarrier densities between 1 and 3 × 10{sup 12 }cm{sup −2}. Acoustic intervalley phonons play a non-negligible role, and emitted phonons with wavelengths limited up by a maximum (determined by the carrier concentration) induce a slower carrier cooling rate. Intrinsic phonon heating is damped in graphene on a substrate due to the additional cooling pathways, with the hot phonon effect showing a strong inverse dependence with the carrier density.

  2. Nanosecond time-scale semiconductor photoexcitations probed by a scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Gallagher, Mark J.; Ruskell, Todd G.; Chen, Dong; Sarid, Dror; Jenkinson, Howard

    1994-01-01

    The high-frequency response of scanning tunneling microscopy of a semiconductor is demonstrated by using the beat frequencies of the longitudinal modes of a HeNe laser at the tunneling junction. We present a comparison of the slow and fast optical response of photoexcited charge carriers in the layered structure semiconductors n-type MoS2 and p-type WSe2 using this method.

  3. Plasma mechanism of terahertz photomixing in high-electron mobility transistor under interband photoexcitation

    NASA Astrophysics Data System (ADS)

    Ryzhii, V.; Khmyrova, I.; Satou, A.; Vaccaro, P. O.; Aida, T.; Shur, M.

    2002-11-01

    We show that modulated near-infrared radiation can generate terahertz plasma oscillations in the channel of a high-electron mobility transistor. This effect is associated with a temporarily periodic injection of the electrons photoexcited by modulated near-infrared radiation into the transistor channel. The excitation of the plasma oscillations has the resonant character. It results in the pertinent excitation of the electric current in the external circuit that can be used for generation of terahertz electromagnetic radiation.

  4. Terahertz and Microwave Devices Based on the Photo-Excited Low Dimensional Electronic System

    DTIC Science & Technology

    2015-03-11

    condition that is realized by photo-exciting the system with electromagnetic waves in the microwave and THz parts of the radiation spectrum, in the...electron system. This research aimed to advance the understanding of such radiation -induced phenomena in the two-dimensional electron system, while helping...exciting a high mobility low dimensional electron system. This research aimed to advance the understanding of such radiation -induced phenomena in the two

  5. Ultrafast Scanning Tunneling Microscopy Using a Photoexcited Low-Temperature-Grown GaAs Tip

    SciTech Connect

    Donati, G.P.; Rodriguez, G.; Taylor, A.J.

    1999-05-21

    The authors report ultrafast scanning tunneling microscopy using a low-temperature-grown GaAs tip photoexcited by 100-fs, 800-nm pulses. They use this tip to detect picosecond transients on a coplanar stripline and demonstrate a temporal resolution of 1.7 ps. A dependence of the transient signal upon spatial position of the tip is revealed, indicating that the signal arises from areas on the sample smaller than {approximately}20nm.

  6. Core-level positive-ion and negative-ion fragmentation of gaseous and condensed HCCl3 using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Lu, K. T.; Chen, J. M.; Lee, J. M.; Haw, S. C.; Liang, Y. C.; Deng, M. J.

    2011-07-01

    We investigated the dissociation dynamics of positive-ion and negative-ion fragments of gaseous and condensed HCCl3 following photoexcitation of Cl 2p electrons to various resonances. Based on ab initio calculations at levels HF/cc-pVTZ and QCISD/6-311G*, the first doublet structures in Cl L-edge x-ray absorption spectrum of HCCl3 are assigned to transitions from the Cl (2P3/2,1/2) initial states to the 10a1* orbitals. The Cl 2p → 10a1* excitation of HCCl3 induces a significant enhancement of the Cl+ desorption yield in the condensed phase and a small increase in the HCCl+ yield in the gaseous phase. Based on the resonant photoemission of condensed HCCl3, excitations of Cl 2p electrons to valence orbitals decay predominantly via spectator Auger transitions. The kinetic energy distributions of Cl+ ion via the Cl 2p → 10a1* excitation are shifted to higher energy ˜0.2 eV and ˜0.1 eV relative to those via the Cl 2p → 10e* excitation and Cl 2p → shape resonance excitation, respectively. The enhancement of the yields of ionic fragments at specific core-excited resonance states is assisted by a strongly repulsive surface that is directly related to the spectator electrons localized in the antibonding orbitals. The Cl- anion is significantly reinforced in the vicinity of Cl 2p ionization threshold of gaseous HCCl3, mediated by photoelectron recapture through post-collision interaction.

  7. Electrochemical immobilization of Fluorescent labelled probe molecules on a FTO surface for affinity detection based on photo-excited current

    NASA Astrophysics Data System (ADS)

    Haruyama, Tetsuya; Wakabayashi, Ryo; Cho, Takeshi; Matsuyama, Sho-taro

    2011-10-01

    Photo-excited current can be generated at a molecular interface between a photo-excited molecules and a semi-conductive material in appropriate condition. The system has been recognized for promoting photo-energy devices such as an organic dye sensitized solar-cell. The photo-current generated reactions are totally dependent on the interfacial energy reactions, which are in a highly fluctuated interfacial environment. The authors investigated the photo-excited current reaction to develop a smart affinity detection method. However, in order to perform both an affinity reaction and a photo-excited current reaction at a molecular interface, ordered fabrications of the functional (affinity, photo-excitation, etc.) molecules layer on a semi-conductive surface is required. In the present research, we would like to present the fabrication and functional performance of photo-excited current-based affinity assay device and its application for detection of endocrine disrupting chemicals. On the FTO surface, fluorescent pigment labelled affinity peptide was immobilized through the EC tag (electrochemical-tag) method. The modified FTO produced a current when it was irradiated with diode laser light. However, the photo current decreased drastically when estrogen (ES) coexisted in the reaction solution. In this case, immobilized affinity probe molecules formed a complex with ES and estrogen receptor (ER). The result strongly suggests that the photo-excited current transduction between probe molecule-labelled cyanine pigment and the FTO surface was partly inhibited by a complex that formed at the affinity oligo-peptide region in a probe molecule on the FTO electrode. The bound bulky complex may act as an impediment to perform smooth transduction of photo-excited current in the molecular interface. The present system is new type of photo-reaction-based analysis. This system can be used to perform simple high-sensitive homogeneous assays.

  8. Photoexcitation of K-shell and L-shell Hollow Beryllium

    SciTech Connect

    Hasegawa, Shuichi; Yoshida, Fumiko; Matsuoka, Leo; Koike, Fumihiro; Fritzsche, Stephan; Obara, Satoshi; Azuma, Yoshiro; Nagata, Tetsuo

    2006-07-14

    We have observed K-shell and L-shell hollow beryllium atoms (2s{sup 2}2p3s and 1s3s{sup 2}3p) created by photoexcitation using synchrotron radiation. Resonance shapes were fitted to the Fano profile and the parameters were deduced. A Dirac-Fock calculation was performed to identify the configuration of the peaks and to predict other hollow atomic peaks. The results of the calculation were in good agreement with the experimental data. The comparison of the transition strength has revealed that the three-electron photoexcitation to the 1s3s{sup 2}3p configuration is stronger than the two-electron photoexcitation to the 2s{sup 2}2p3s configuration. This is attributed to the large overlap between the 2s orbital of the ground state (1s{sup 2}2s{sup 2}) with the 3s orbital of the L-shell hollow state (1s3s{sup 2}3p)

  9. Photoexcitation of adsorbates on metal surfaces: One-step or three-step

    SciTech Connect

    Petek, Hrvoje

    2012-09-07

    In this essay we discuss the light-matter interactions at molecule-covered metal surfaces that initiate surface photochemistry. The hot-electron mechanism for surface photochemistry, whereby the absorption of light by a metal surface creates an electron-hole pair, and the hot electron scatters through an unoccupied resonance of adsorbate to initiate nuclear dynamics leading to photochemistry, has become widely accepted. Yet, ultrafast spectroscopic measurements of molecule-surface electronic structure and photoexcitation dynamics provide scant support for the hot electron mechanism. Instead, in most cases the adsorbate resonances are excited through photoinduced substrate-to-adsorbate charge transfer. Based on recent studies of the role of coherence in adsorbate photoexcitation, as measured by the optical phase and momentum resolved two-photon photoemission measurements, we examine critically the hot electron mechanism, and propose an alternative description based on direct charge transfer of electrons from the substrate to adsorbate. The advantage of this more quantum mechanically rigorous description is that it informs how material properties of the substrate and adsorbate, as well as their interaction, influence the frequency dependent probability of photoexcitation and ultimately how light can be used to probe and control surface femtochemistry.

  10. Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements.

    PubMed

    Hada, Masaki; Norimatsu, Katsura; Tanaka, Sei Ichi; Keskin, Sercan; Tsuruta, Tetsuya; Igarashi, Kyushiro; Ishikawa, Tadahiko; Kayanuma, Yosuke; Miller, R J Dwayne; Onda, Ken; Sasagawa, Takao; Koshihara, Shin-Ya; Nakamura, Kazutaka G

    2016-07-14

    The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

  11. Large-amplitude chirped coherent phonons in tellurium mediated by ultrafast photoexcited carrier diffusion

    NASA Astrophysics Data System (ADS)

    Kamaraju, N.; Kumar, Sunil; Anija, M.; Sood, A. K.

    2010-11-01

    We report femtosecond time-resolved reflectivity measurements of coherent phonons in tellurium performed over a wide range of temperatures (3-296 K) and pump-laser intensities. A totally symmetric A1 coherent phonon at 3.6 THz responsible for the oscillations in the reflectivity data is observed to be strongly positively chirped (i.e., phonon time period decreases at longer pump-probe delay times) with increasing photoexcited carrier density, more so at lower temperatures. We show that the temperature dependence of the coherent phonon frequency is anomalous (i.e, increasing with increasing temperature) at high photoexcited carrier density due to electron-phonon interaction. At the highest photoexcited carrier density of ˜1.4×1021cm-3 and the sample temperature of 3 K, the lattice displacement of the coherent phonon mode is estimated to be as high as ˜0.24Å . Numerical simulations based on coupled effects of optical absorption and carrier diffusion reveal that the diffusion of carriers dominates the nonoscillatory electronic part of the time-resolved reflectivity. Finally, using the pump-probe experiments at low carrier density of 6×1018cm-3 , we separate the phonon anharmonicity to obtain the electron-phonon coupling contribution to the phonon frequency and linewidth.

  12. Multiple regimes of carrier cooling in photoexcited graphene probed by time-resolved terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Frenzel, A. J.; Gabor, N. M.; Herring, P. K.; Fang, W.; Kong, J.; Jarillo-Herrero, P.; Gedik, N.

    2013-03-01

    Energy relaxation and cooling of photoexcited charge carriers in graphene has recently attracted significant attention due to possible hot carrier effects, large quantum efficiencies, and photovoltaic applications. However, the details of these processes remain poorly understood, with many conflicting interpretations reported. Here we use time-resolved terahertz spectroscopy to explore multiple relaxation and cooling regimes in graphene in order to elucidate the fundamental physical processes which occur upon photoexcitation of charge carriers. We observe a novel negative terahertz photoconductivity that results from the unique linear dispersion and allows us to measure the electron temperature with ultrafast time resolution. Additionally, we present measurements of the relaxation dynamics over a wide range of excitation fluence. By varying the pump photon energy, we demonstrate that cooling dynamics of photoexcited carriers depend on the amount of energy deposited in the graphene system by the pump pulse, not the number of absorbed photons. The data suggest that fundamentally different regimes are encountered for different excitation fluences. These results may provide a unifying framework for reconciling various measurements of energy relaxation and cooling in graphene.

  13. Core-level Photoemission Study for Cuprates with a Dynamical Mean-Field Approach Considering Realistic Crystal Structure

    NASA Astrophysics Data System (ADS)

    Hariki, Atsushi; Uozumi, Takayuki

    2013-03-01

    Recently, remarkable experimental progress reveals some characteristic spectral features in the 2p3/2main line of Cu 2p core-level X-ray photoemission spectra (XPS). The structures show strong material dependence and drastic changes for electron or hole doping. Van Veenendaal et al., pointed out that the main line shape is strongly affected by the so-called nonlocal screening which is accompanied by a formation of a Zhang-Rice singlet (ZRS) in the XPS final state. On the other hand, Taguchi et al., shows these features are reproduced by introducing an phenomenological extended impurity model. We consider that this topic on 2pXPS of cuprates still remain controversial. In this study, we propose another approach based on the dynamical mean field theory(DMFT) considering the realistic crystal structure. Many-particle effects including the ZRS is appropriately embedded in the hybridization function of a single impurity Anderson model through the DMFT self-consistent cycle. Our approach reproduces experimental results and shows that the Cu 2p3/2 main line is closely related with the quasi-particle structure near the Fermi energy.

  14. Ab initio study of 2p core-level x-ray photoemission spectra in ferromagnetic transition metals

    NASA Astrophysics Data System (ADS)

    Takahashi, Manabu; Igarashi, Jun-Ichi

    2012-02-01

    We study the 2p core-level x-ray photoemission spectra in ferromagnetic transition metals, Fe, Co, and Ni using a recently developed ab initio method. The excited final states are set up by distributing electrons on the one-electron states calculated under the fully screened potential in the presence of the core hole. We evaluate the overlap between these excited states and the ground state by using one-electron wave functions, and obtain the spectral curves as a function of binding energy. The calculated spectra reproduce well the observed spectra displaying interesting dependence on the element and on the spin of the removed core electron. The origin of the spectral shapes is elucidated in terms of the one-electron states screening the core hole. The magnetic splitting of the threshold energy is also estimated by using the coherent potential approximation within the fully screened potential approximation. It decreases more rapidly than the local spin moment with moving from Fe to Ni. It is estimated to be almost zero for Ni despite the definite local moment about 0.6μB, in agreement with the experiment.

  15. Skin-depth lattice strain, core-level trap depression and valence charge polarization of Al surfaces

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Bo, Maolin; Liu, Yonghui; Guo, Yongling; Wang, Haibin; Yue, Jian; Huang, Yongli

    2016-01-01

    Clarifying the origin for surface core-level shift (SCLS) and gaining quantitative information regarding the coordination-resolved local strain, binding energy (BE) shift and cohesive energy change have been a challenge. Here, we show that a combination of the bond order-length-strength (BOLS) premise, X-ray photoelectron spectroscopy (XPS) and the ab initio density functional theory (DFT) calculations of aluminum (Al) 2p3/2 energy shift of Al surfaces has enabled us to derive such information, namely, (i) the 2p3/2 energy of an isolated Al atom (72.146 ± 0.003eV) and its bulk shift (0.499 eV); (ii) the skin lattice contracts by up to 12.5% and the BE density increases by 70%; and (iii) the cohesive energy drops up to 38%. It is affirmed that the shorter and stronger bonds between under-coordinated atoms provide a perturbation to the Hamiltonian and hence lead to the local strain, quantum entrapment and valence charge polarization. Findings should help in understanding the phenomena of surface pre-melting and skin-high elasticity, in general.

  16. Ce Core-Level Spectroscopy, and Magnetic and Electrical Transport Properties of Lightly Ce-Doped YCoO3

    NASA Astrophysics Data System (ADS)

    Kobayashi, Yoshihiko; Koike, Tsuyoshi; Okawa, Mario; Takayanagi, Ryohei; Takei, Shohei; Minohara, Makoto; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Yasui, Akira; Ikenaga, Eiji; Saitoh, Tomohiko; Asai, Kichizo

    2016-11-01

    We have investigated the Ce and Co core level spectroscopy, and the magnetic and electrical transport properties of lightly Ce-doped YCoO3. We have successfully synthesized single-phase Y1-xCexCoO3 for 0.0 ≤ x ≤ 0.1 by the sol-gel method. Hard X-ray photoelectron and X-ray absorption spectroscopy experiments reveal that the introduced Ce ions are tetravalent, which is considered to be the first case of electron doping into bulk trivalent Co oxides with perovskite RECoO3 (RE: rare-earth element or Y) caused by RE site substitution. The magnitude of the effective magnetic moment peff obtained from the temperature dependence of magnetic susceptibility χ(T) at higher temperatures is close to that for high-spin Co2+ introduced by the Ce doping, implying that the electrons doped into the Co site induce Co2+ with a high-spin state. For x = 0.1, ferromagnetic ordering is observed below about 7 K. Electrical transport properties such as resistivity and thermoelectric power show that negative electron-like carriers are introduced by Ce substitution.

  17. Charge transfer dynamics between photoexcited CdS nanorods and mononuclear Ru water-oxidation catalysts.

    PubMed

    Tseng, Huan-Wei; Wilker, Molly B; Damrauer, Niels H; Dukovic, Gordana

    2013-03-06

    We describe the charge transfer interactions between photoexcited CdS nanorods and mononuclear water oxidation catalysts derived from the [Ru(bpy)(tpy)Cl](+) parent structure. Upon excitation, hole transfer from CdS oxidizes the catalyst (Ru(2+) → Ru(3+)) on a 100 ps to 1 ns timescale. This is followed by 10-100 ns electron transfer (ET) that reduces the Ru(3+) center. The relatively slow ET dynamics may provide opportunities for the accumulation of multiple holes at the catalyst, which is necessary for water oxidation.

  18. Neutral dissociation of hydrogen following photoexcitation of HCl at the chlorine K edge

    SciTech Connect

    Hansen, D.L.; Arrasate, M.E.; Martin, R.; Vanderford, B.; Lindle, D.W.; Cotter, J.; Neill, P.; Fisher, G.R.; Perera, R.C.; Leung, K.T.; Levin, J.C.; Sellin, I.A.; Simon, M.; Simon, M.; Uehara, Y.; Whitfield, S.B.

    1998-04-01

    Time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K edge ({approximately}2.8keV) using monochromatic synchrotron radiation. At the lowest resonant excitation to the 6{sigma}{sup {asterisk}} antibonding orbital, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cl{sup n+} ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very short lifetimes (1 fs). {copyright} {ital 1998} {ital The American Physical Society}

  19. Observation of standing waves of electron-hole sound in a photoexcited semiconductor.

    PubMed

    Padmanabhan, P; Young, S M; Henstridge, M; Bhowmick, S; Bhattacharya, P K; Merlin, R

    2014-07-11

    Three-dimensional multicomponent plasmas composed of species with very different masses support a new branch of charge-density fluctuations known as acoustic plasmons. Here, we report on an ultrafast optical method to generate and probe coherent states of acoustic plasmons in a slab of GaAs, which relies on strong photoexcitation to create a large population of light electrons and heavy holes. Consistent with the random-phase-approximation theory, the data reveal standing plasma waves confined to these slabs, similar to those of conventional sound but with associated velocities that are significantly larger.

  20. X-ray resonant photoexcitation: linewidths and energies of Kα transitions in highly charged Fe ions.

    PubMed

    Rudolph, J K; Bernitt, S; Epp, S W; Steinbrügge, R; Beilmann, C; Brown, G V; Eberle, S; Graf, A; Harman, Z; Hell, N; Leutenegger, M; Müller, A; Schlage, K; Wille, H-C; Yavaş, H; Ullrich, J; Crespo López-Urrutia, J R

    2013-09-06

    Photoabsorption by and fluorescence of the Kα transitions in highly charged iron ions are essential mechanisms for x-ray radiation transfer in astrophysical environments. We study photoabsorption due to the main Kα transitions in highly charged iron ions from heliumlike to fluorinelike (Fe24+ to Fe17+) using monochromatic x rays around 6.6 keV at the PETRA III synchrotron photon source. Natural linewidths were determined with hitherto unattained accuracy. The observed transitions are of particular interest for the understanding of photoexcited plasmas found in x-ray binary stars and active galactic nuclei.

  1. Method And Apparatus For Examining A Tissue Using The Spectral Wing Emission Therefrom Induced By Visible To Infrared Photoexcitation.

    DOEpatents

    Alfano, Robert R.; Demos, Stavros G.; Zhang, Gang

    2003-12-16

    Method and an apparatus for examining a tissue using the spectral wing emission therefrom induced by visible to infrared photoexcitation. In one aspect, the method is used to characterize the condition of a tissue sample and comprises the steps of (a) photoexciting the tissue sample with substantially monochromatic light having a wavelength of at least 600 nm; and (b) using the resultant far red and near infrared spectral wing emission (SW) emitted from the tissue sample to characterize the condition of the tissue sample. In one embodiment, the substantially monochromatic photoexciting light is a continuous beam of light, and the resultant steady-state far red and near infrared SW emission from the tissue sample is used to characterize the condition of the tissue sample. In another embodiment, the substantially monochromatic photoexciting light is a light pulse, and the resultant time-resolved far red and near infrared SW emission emitted from the tissue sample is used to characterize the condition of the tissue sample. In still another embodiment, the substantially monochromatic photoexciting light is a polarized light pulse, and the parallel and perpendicular components of the resultant polarized time-resolved SW emission emitted from the tissue sample are used to characterize the condition of the tissue sample.

  2. Catalyst-free activation of peroxides under visible LED light irradiation through photoexcitation pathway.

    PubMed

    Gao, Yaowen; Li, Yixi; Yao, Linyu; Li, Simiao; Liu, Jin; Zhang, Hui

    2017-05-05

    Catalysts are known to activate peroxides to generate active radicals (i.e., hydroxyl radical (OH) and sulfate radical (SO4(-))) under certain conditions, but the activation of peroxides in the absence of catalysts under visible light irradiation has been rarely reported. This work demonstrates a catalyst-free activation of peroxides for the generation of OH and/or SO4(-) through photoexcited electron transfer from organic dyes to peroxides under visible LED light irradiation, where Rhodamine B (RhB) and Eosin Y (EY) were selected as model dyes. The formation of OH and/or SO4(-) in the reactions and the electron transfer from the excited dyes to peroxides were validated via electron paramagnetic resonance (EPR), photoluminescence (PL) spectra and cyclic voltammetry (CV). The performance of the peroxide/dye/Vis process was demonstrated to be altered depending on the target substrate. Meanwhile, the peroxide/dye/Vis process was effective for simultaneous decolorization of dyes and production of active radicals under neutral even or basic conditions. The findings of this study clarified a novel photoexcitation pathway for catalyst-free activation of peroxides under visible light irradiation, which could avoid the secondary metal ion (dissolved or leached) pollution from the metal-based catalysts and expand the application range of the peroxide-based catalytic process.

  3. Theoretical and experimental study of dynamics of photoexcited carriers in GaN

    NASA Astrophysics Data System (ADS)

    Shishehchi, Sara; Rudin, Sergey; Garrett, Gregory A.; Wraback, Michael; Bellotti, Enrico

    2013-12-01

    We present a theoretical and experimental study of the sub-picosecond dynamics of photo-excited carriers in GaN. In the theoretical model, interaction with an external ultrafast laser pulse is treated coherently and to account for the scattering mechanisms and dephasing processes, a generalized Monte-Carlo simulation is used. The scattering mechanisms included are carrier interactions with polar optical phonons and acoustic phonons, and carrier-carrier Coulomb interactions. We study the effect of different scattering mechanisms on the carrier densities. In the case that the excitation energy satisfies the threshold for polar optical scattering, phonon contribution is the dominant process in relaxing the system, otherwise, carrier-carrier mechanism is dominant. Furthermore, we present the temperature and pulse power dependent normalized luminescence intensity. The results are presented over a range of temperatures, electric field, and excitation energy of the laser pulse. For comparison, we also report the experimental time-resolved photoluminescence studies on GaN samples. There is a good agreement between the simulation and experiment in normalized luminescence intensity results. Therefore, we show that we can explain the dynamics of the photo-excited carriers in GaN by including only carrier-carrier and carrier-phonon interactions and a relatively simple two-band electronic structure model.

  4. The photoexcited triplet state as a probe of chromophore-protein interaction in myoglobin.

    PubMed Central

    Angiolillo, P J; Vanderkooi, J M

    1998-01-01

    The photoexcited metastable triplet state of Mg(2+)-mesoporphyrin IX (MgMPIX) or Mg(2+)-protoporphyrin IX (MgPPIX) located in the heme pocket of horse myoglobin (Mb) was investigated by optical and electron paramagnetic resonance (EPR) spectroscopy, and its properties were compared with the model complexes, MgMPIX, MgPPIX, and Mg2+ etioporphyrin I (MgETIOI), in noncoordinating and coordinating organic glasses. Zero-field splitting parameters, line shape, and Jahn-Teller distortion in the temperature range of 3.8-110 K are discussed in terms of porphyrin-protein interactions. The triplet line shapes for MgMPIXMb and MGPPIXMb show no temperature-dependent spectral line shape changes suggestive of Jahn-Teller dynamics, and it is concluded that the energy splitting is >> 150 cm-1, suggesting symmetry breaking from the anisotropy of intermal electric fields of the protein, and consistent with previous predictions (Geissinger et al. 1995. J. Phys. Chem. 99:16527-16529). Both MgMPIXMb and MgPPIXMb demonstrate electron spin polarization at low temperature, and from the polarization pattern it can be concluded that intersystem crossing occurs predominantly into in-plane spin sublevels of the triplet state. The splitting in the Q0.0 absorption band and the temperature dependence and splitting of the photoexcited triplet state of myoglobin in which the iron was replaced by Mg2+ are interpreted in terms of effects produced by electric field asymmetry in the heme pocket. PMID:9726951

  5. Theoretical and experimental study of dynamics of photoexcited carriers in GaN

    SciTech Connect

    Shishehchi, Sara; Bellotti, Enrico; Rudin, Sergey; Garrett, Gregory A.; Wraback, Michael

    2013-12-21

    We present a theoretical and experimental study of the sub-picosecond dynamics of photo-excited carriers in GaN. In the theoretical model, interaction with an external ultrafast laser pulse is treated coherently and to account for the scattering mechanisms and dephasing processes, a generalized Monte-Carlo simulation is used. The scattering mechanisms included are carrier interactions with polar optical phonons and acoustic phonons, and carrier-carrier Coulomb interactions. We study the effect of different scattering mechanisms on the carrier densities. In the case that the excitation energy satisfies the threshold for polar optical scattering, phonon contribution is the dominant process in relaxing the system, otherwise, carrier-carrier mechanism is dominant. Furthermore, we present the temperature and pulse power dependent normalized luminescence intensity. The results are presented over a range of temperatures, electric field, and excitation energy of the laser pulse. For comparison, we also report the experimental time-resolved photoluminescence studies on GaN samples. There is a good agreement between the simulation and experiment in normalized luminescence intensity results. Therefore, we show that we can explain the dynamics of the photo-excited carriers in GaN by including only carrier-carrier and carrier-phonon interactions and a relatively simple two-band electronic structure model.

  6. Interactions between photoexcited NIR emitting CdHgTe quantum dots and graphene oxide

    NASA Astrophysics Data System (ADS)

    Jagtap, Amardeep M.; Varade, Vaibhav; Konkena, Bharathi; Ramesh, K. P.; Chatterjee, Abhijit; Banerjee, Arup; Pendyala, Naresh Babu; Koteswara Rao, K. S. R.

    2016-02-01

    Hydrothermally grown mercury cadmium telluride quantum dots (CdHgTe QDs) are decorated on graphene oxide (GO) sheets through physisorption. The structural change of GO through partial reduction of oxygen functional groups is observed with X-ray photoelectron spectroscopy in GO-QDs composites. Raman spectroscopy provides relatively a small change (˜1.1 times) in D/G ratio of band intensity and red shift in G band from 1606 cm-1 to 1594 cm-1 in GO-CdHgTe QDs (2.6 nm) composites, which indicates structural modification of GO network. Steady state and time resolved photoluminescence (PL) spectroscopy shows the electronic interactions between photoexcited near infrared emitting CdHgTe QDs and GO. Another interesting observation is PL quenching in the presence of GO, and it is quite effective in the case of smaller size QDs (2.6 nm) compared to the larger size QDs (4.2 nm). Thus, the observed PL quenching is attributed to the photogenerated electron transfer from QDs to GO. The photoexcited electron transfer rate decreases from 2.2 × 109 to 1.5 × 108 s-1 with increasing particle size from 2.6 to 4.2 nm. Photoconductivity measurements on QDs-GO composite devices show nearly 3 fold increase in the current density under photo-illumination, which is a promising aspect for solar energy conversion and other optoelectronic applications.

  7. Pentacene appended to a TEMPO stable free radical: the effect of magnetic exchange coupling on photoexcited pentacene.

    PubMed

    Chernick, Erin T; Casillas, Rubén; Zirzlmeier, Johannes; Gardner, Daniel M; Gruber, Marco; Kropp, Henning; Meyer, Karsten; Wasielewski, Michael R; Guldi, Dirk M; Tykwinski, Rik R

    2015-01-21

    Understanding the fundamental spin dynamics of photoexcited pentacene derivatives is important in order to maximize their potential for optoelectronic applications. Herein, we report on the synthesis of two pentacene derivatives that are functionalized with the [(2,2,6,6-tetramethylpiperidin-1-yl)oxy] (TEMPO) stable free radical. The presence of TEMPO does not quench the pentacene singlet excited state, but does quench the photoexcited triplet excited state as a function of TEMPO-to-pentacene distance. Time-resolved electron paramagnetic resonance experiments confirm that triplet quenching is accompanied by electron spin polarization transfer from the pentacene excited state to the TEMPO doublet state in the weak coupling regime.

  8. On the pathway of photoexcited electrons: probing photon-to-electron and photon-to-phonon conversions in silicon by ATR-IR.

    PubMed

    Karabudak, Engin; Yüce, Emre; Schlautmann, Stefan; Hansen, Ole; Mul, Guido; Gardeniers, Han J G E

    2012-08-21

    Photoexcitation and charge carrier thermalization inside semiconductor photocatalysts are two important steps in solar fuel production. Here, photoexcitation and charge carrier thermalization in a silicon wafer are for the first time probed by a novel, yet simple and user-friendly Attenuated Total Reflectance Infrared spectroscopy (ATR-IR) system.

  9. Electronic Charges and Electric Potential at LaAlO3/SrTiO3 Interfaces Studied by Core-Level Photoemission Spectroscopy

    SciTech Connect

    Hwang, Harold

    2011-08-19

    We studied LaAlO{sub 3}/SrTiO{sub 3} interfaces for varying LaAlO{sub 3} thickness by core-level photoemission spectroscopy. In Ti 2p spectra for conducting 'n-type' interfaces, Ti{sup 3+} signals appeared, which were absent for insulating 'p-type' interfaces. The Ti{sup 3+} signals increased with LaAlO{sub 3} thickness, but started well below the critical thickness of 4 unit cells for metallic transport. Core-level shifts with LaAlO{sub 3} thickness were much smaller than predicted by the polar catastrophe model. We attribute these observations to surface defects/adsorbates providing charges to the interface even below the critical thickness.

  10. Spin-Orbit Effects in Spin-Resolved L2,3 Core Level Photoemission of 3d Ferromagnetic Thin Films

    SciTech Connect

    Komesu, T; Waddill, G D; Yu, S W; Butterfield, M; Tobin, J G

    2007-10-02

    We present spin-resolved 2p core level photoemission for the 3d transition metal films of Fe and Co grown on Cu(100). We observe clear spin asymmetry in the main 2p core level photoemission peaks of Fe and Co films consistent with trends in the bulk magnetic moments. The spin polarization can be strongly enhanced, by variation of the experimental geometry, when the photoemission is undertaken with circularly polarized light, indicating that spin-orbit interaction can have a profound in spin polarized photoemission. Further spin polarized photoemission studies using variable circularly polarized light at high photon energies, high flux are indicated, underscoring the value of synchrotron measurements at facilities with increased beam stability.

  11. Study on dynamics of photoexcited charge injection and trapping in CdS quantum dots sensitized TiO{sub 2} nanowire array film electrodes

    SciTech Connect

    Pang, Shan; Cheng, Ke; Yuan, Zhanqiang; Xu, Suyun; Cheng, Gang; Du, Zuliang

    2014-05-19

    The photoexcited electrons transfer dynamics of the CdS quantum dots (QDs) deposited in TiO{sub 2} nanowire array films are studied using surface photovoltage (SPV) and transient photovoltage (TPV) techniques. By comparing the SPV results with different thicknesses of QDs layers, we can separate the dynamic characteristics of photoexcited electrons injection and trapping. It is found that the TPV signals of photoexcited electrons trapped in the CdS QDs occur at timescales of about 2 × 10{sup −8} s, which is faster than that of the photoexcited electrons injected from CdS into TiO{sub 2}. More than 90 nm of the thickness of the CdS QDs layer will seriously affect the photoexcited electrons transfer and injection.

  12. Observation of core-level binding energy shifts between (100) surface and bulk atoms of epitaxial CuInSe{sub 2}

    SciTech Connect

    Nelson, A.J.; Berry, G.; Rockett, A.

    1997-04-01

    Core-level and valence band photoemission from semiconductors has been shown to exhibit binding energy differences between surface atoms and bulk atoms, thus allowing one to unambiguously distinguish between the two atomic positions. Quite clearly, surface atoms experience a potential different from the bulk due to the lower coordination number - a characteristic feature of any surface is the incomplete atomic coordination. Theoretical accounts of this phenomena are well documented in the literature for III-V and II-VI semiconductors. However, surface state energies corresponding to the equilibrium geometry of (100) and (111) surfaces of Cu-based ternary chalcopyrite semiconductors have not been calculated or experimental determined. These compounds are generating great interest for optoelectronic and photovoltaic applications, and are an isoelectronic analog of the II-VI binary compound semiconductors. Surface core-level binding energy shifts depend on the surface cohesive energies, and surface cohesive energies are related to surface structure. For ternary compound semiconductor surfaces, such as CuInSe{sub 2}, one has the possibility of variations in surface stoichiometry. Applying standard thermodynamical calculations which consider the number of individual surface atoms and their respective chemical potentials should allow one to qualitatively determine the magnitude of surface core-level shifts and, consequently, surface state energies.

  13. Detecting the Photoexcited Carrier Distribution Across GaAs/Transition Metal Oxide Interfaces by Coherent Longitudinal Acoustic Phonons.

    PubMed

    Pollock, Kevin L; Doan, Hoang Q; Rustagi, Avinash; Stanton, Christopher J; Cuk, Tanja

    2017-03-02

    A prominent architecture for solar energy conversion layers diverse materials, such as traditional semiconductors (Si, III-V) and transition metal oxides (TMOs), into a monolithic device. The efficiency with which photoexcited carriers cross each layer is critical to device performance and dependent on the electronic properties of a heterojunction. Here, by time-resolved changes in the reflectivity after excitation of an n-GaAs/p-GaAs/TMO (Co3O4, IrO2) device, we detect a photoexcited carrier distribution specific to the p-GaAs/TMO interface through its coupling to phonons in both materials. The photoexcited carriers generate two coherent longitudinal acoustic phonons (CLAPs) traveling in opposite directions, one into the TMO and the other into the p-GaAs. This is the first time a CLAP is reported to originate at a semiconductor/TMO heterojunction. Therefore, these experiments seed future modeling of the built-in electric fields, the internal Fermi level, and the photoexcited carrier density of semiconductor/TMO interfaces within multilayered heterostructures.

  14. Role of photoexcited nitrogen dioxide chemistry on ozone formation and emission control strategy over the Pearl River Delta, China

    EPA Science Inventory

    A new hydroxyl radical formation pathway via photo-excited nitrogen dioxide chemistry is incorporated into a chemistry-only box model as well as a 3D air quality model to examine its potential role on ozone formation and emission control strategy over the Pearl River Delta region...

  15. Photoexcitation of electron wave packets in quantum spin Hall edge states: Effects of chiral anomaly from a localized electric pulse

    NASA Astrophysics Data System (ADS)

    Dolcini, Fabrizio; Iotti, Rita Claudia; Montorsi, Arianna; Rossi, Fausto

    2016-10-01

    We show that, when a spatially localized electric pulse is applied at the edge of a quantum spin Hall system, electron wave packets of the helical states can be photoexcited by purely intrabranch electrical transitions, without invoking the bulk states or the magnetic Zeeman coupling. In particular, as long as the electric pulse remains applied, the photoexcited densities lose their character of right and left movers, whereas after the ending of the pulse they propagate in opposite directions without dispersion, i.e., maintaining their space profile unaltered. Notably we find that, while the momentum distribution of the photoexcited wave packets depends on the temperature T and the chemical potential μ of the initial equilibrium state and displays a nonlinear behavior on the amplitude of the applied pulse, in the mesoscopic regime the space profile of the wave packets is independent of T and μ . Instead, it depends purely on the applied electric pulse, in a linear manner, as a signature of the chiral anomaly characterizing massless Dirac electrons. We also discuss how the photoexcited wave packets can be tailored with the electric pulse parameters, for both low and finite frequencies.

  16. Transient reflectance of photoexcited Cd{sub 3}As{sub 2}

    SciTech Connect

    Weber, C. P. Berggren, Bryan S.; Arushanov, Ernest; Nateprov, Alex; Hosseini, Tahereh; Kouklin, Nikolai

    2015-06-08

    We report ultrafast transient-grating measurements of crystals of the three-dimensional Dirac semimetal cadmium arsenide, Cd{sub 3}As{sub 2}, at both room temperature and 80 K. After photoexcitation with 1.5-eV photons, charge-carriers relax by two processes, one of duration 500 fs and the other of duration 3.1 ps. By measuring the complex phase of the change in reflectance, we determine that the faster signal corresponds to a decrease in absorption, and the slower signal to a decrease in the light's phase velocity, at the probe energy. We attribute these signals to electrons' filling of phase space, first near the photon energy and later at lower energy. We attribute their decay to cooling by rapid emission of optical phonons, then slower emission of acoustic phonons. We also present evidence that both the electrons and the lattice are strongly heated.

  17. First-Principles Calculation of Femtosecond Symmetry-Breaking Atomic Forces in Photoexcited Bismuth

    NASA Astrophysics Data System (ADS)

    Murray, Éamonn D.; Fahy, Stephen

    2015-02-01

    We present a first-principles method for the calculation of the polarization-dependent atomic forces resulting from optical excitation in a solid. We calculate the induced force driving the Eg phonon mode in bismuth immediately after absorption of polarized light. When radiation with polarization perpendicular to the c axis is absorbed, the photoexcited charge density breaks the threefold rotational symmetry, leading to an atomic force component perpendicular to the axis. We calculate the initial excited electronic distribution as a function of photon energy and polarization and find the resulting atomic force components parallel and perpendicular to the axis. The magnitude of the calculated force is in excellent agreement with that derived from recent measurements of the amplitude of Eg atomic motion and the decay time of several femtoseconds for the driving force.

  18. Non-Band-Gap Photoexcitation of Hydroxylated TiO2.

    PubMed

    Zhang, Yu; Payne, Daniel T; Pang, Chi L; Fielding, Helen H; Thornton, Geoff

    2015-09-03

    The photochemistry of TiO2 has been studied intensively since it was discovered that TiO2 can act as a photocatalyst. Nevertheless, it has proven difficult to establish the detailed charge-transfer processes involved, partly because the excited states involved are difficult to study. Here we present evidence of the existence of hydroxyl-induced excited states in the conduction band region. Using two-photon photoemission, we show that stepwise photoexcitation from filled band gap states lying 0.8 eV below the Fermi level of rutile TiO2(110) excites hydroxyl-induced states 2.73 eV above the Fermi level that has an onset energy of ∼3.1 eV. The onset is shifted to lower energy by the coadsorption of molecular water, which suggests a means of tuning the energy of the excited state.

  19. Highly efficient terahertz wave modulators by photo-excitation of organics/silicon bilayers

    SciTech Connect

    Yoo, Hyung Keun; Kang, Chul; Hwang, In-Wook; Yoon, Youngwoon; Lee, Kiejin; Kee, Chul-Sik; Lee, Joong Wook

    2014-07-07

    Using hybrid bilayer systems comprising a molecular organic semiconductor and silicon, we achieve optically controllable active terahertz (THz) modulators that exhibit extremely high modulation efficiencies. A modulation efficiency of 98% is achieved from thermally annealed C{sub 60}/silicon bilayers, due to the rapid photo-induced electron transfer from the excited states of the silicon onto the C{sub 60} layer. Furthermore, we demonstrate the broadband modulation of THz waves. The cut-off condition of the system that is determined by the formation of efficient charge separation by the photo-excitation is highly variable, changing the system from insulating to metallic. The phenomenon enables an extremely high modulation bandwidth and rates of electromagnetic waves of interest. The realization of near-perfect modulation efficiency in THz frequencies opens up the possibilities of utilizing active modulators for THz spectroscopy and communications.

  20. A Static Picture of the Relaxation and Intersystem Crossing Mechanisms of Photoexcited 2-Thiouracil

    PubMed Central

    2015-01-01

    Accurate excited-state quantum chemical calculations on 2-thiouracil, employing large active spaces and up to quadruple-ζ quality basis sets in multistate complete active space perturbation theory calculations, are reported. The results suggest that the main relaxation path for 2-thiouracil after photoexcitation should be S2 → S1 → T2 → T1, and that this relaxation occurs on a subpicosecond time scale. There are two deactivation pathways from the initially excited bright S2 state to S1, one of which is nearly barrierless and should promote ultrafast internal conversion. After relaxation to the S1 minimum, small singlet–triplet energy gaps and spin–orbit couplings of about 130 cm–1 are expected to facilitate intersystem crossing to T2, from where very fast internal conversion to T1 occurs. An important finding is that 2-thiouracil shows strong pyramidalization at the carbon atom of the thiocarbonyl group in several excited states. PMID:26284285

  1. Ultrafast lattice response of photoexcited thin films studied by X-ray diffraction

    PubMed Central

    Herzog, Marc; Bojahr, André; Leitenberger, Wolfram; Hertwig, Andreas; Bargheer, Matias

    2014-01-01

    Using ultrafast X-ray diffraction, we study the coherent picosecond lattice dynamics of photoexcited thin films in the two limiting cases, where the photoinduced stress profile decays on a length scale larger and smaller than the film thickness. We solve a unifying analytical model of the strain propagation for acoustic impedance-matched opaque films on a semi-infinite transparent substrate, showing that the lattice dynamics essentially depend on two parameters: One for the spatial profile and one for the amplitude of the strain. We illustrate the results by comparison with high-quality ultrafast X-ray diffraction data of SrRuO3 films on SrTiO3 substrates. PMID:26798784

  2. Photo-ionization and photo-excitation of curcumin investigated by laser flash photolysis.

    PubMed

    Qian, Tingting; Kun, Li; Gao, Bo; Zhu, Rongrong; Wu, Xianzheng; Wang, Shilong

    2013-12-01

    Curcumin (Cur) has putative antitumor properties. In the current study, we examined photophysical and photochemical properties of Cur using laser flash photolysis. The results demonstrated that Cur could be photo-ionized at 355 nm laser pulse to produce radical cation (Cur(+)) and solvated electron e(sol)(-) in 7:3 ethanol-water mixtures. The quantum yield of Cur photo-ionization and the ratio of photo-ionization to photo-excitation were also determined. Cur(+) could be transferred into neutral radical of Cur (Cur) via deprotonation with the pKa 4.13. The excited singlet of Cur ((1)Cur* could be transferred into excited triplet ((3)Cur*, which could be quenched by oxygen to produce singlet oxygen (1)O2*. Reaction of (3)Cur* with tryptophan was confirmed. The results encourage developing curcumin as a photosensitive antitumor agent.

  3. Magnetic-field cycling instrumentation for dynamic nuclear polarization-nuclear magnetic resonance using photoexcited triplets.

    PubMed

    Kagawa, Akinori; Negoro, Makoto; Takeda, Kazuyuki; Kitagawa, Masahiro

    2009-04-01

    To advance static solid-state NMR with hyperpolarized nuclear spins, a system has been developed enabling dynamic nuclear polarization (DNP) using electron spins in the photoexcited triplet state with X-band microwave apparatus, followed by static solid-state nuclear magnetic resonance (NMR) experiments using the polarized nuclear-spin system with a goniometer. In order to perform the DNP and NMR procedures in different magnetic fields, the DNP system and the NMR system are spatially separated, between which the sample can be shuttled while its orientation is controlled in a reproducible fashion. We demonstrate that the system developed in this work is operational for solid-state NMR with hyperpolarized nuclear-spin systems in static organic materials, and also discuss the application of our system.

  4. Femtosecond and continuous-wave photoexcitations of thiophene-based conjugated polymers

    NASA Astrophysics Data System (ADS)

    Luzzati, Silva; Botta, Chiara; Romanoni, Mariachiara; Comoretto, Davide; Tubino, Riccardo; Nisoli, Mauro; Cybo-Ottone, Alessandro; De Silvestri, Sandro

    1993-12-01

    We present an extensive photoinduced absorption study of alkyl substituted poly (2,5- thienylenevinylene)s in both the solid state and in solution. The optical and conformational properties of the samples are monitored with UV-Vis absorption and emission, IR absorption and Raman scattering. Three photoinduced states are detected under steady state condition which display lifetimes of the order of 100 ms in the solid state. The two low-energy bands are assigned to bipolarons, while a third band peaked near the band edge has a different origin. In solution very lone-lived photoexcitated states are observed and they are assumed to recombine via a solvent-assisted photo-doping mechanism.

  5. Ultrafast Relaxation Dynamics of Photoexcited Zinc-Porphyrin: Electronic-Vibrational Coupling

    SciTech Connect

    Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

    2016-08-02

    Cyclic tetrapyrroles are the active core of compounds with crucial roles in living systems, such as hemoglobin and chlorophyll, and in technology as photocatalysts and light absorbers for solar energy conversion. Zinc-tetraphenylporphyrin (Zn-TPP) is a prototypical cyclic tetrapyrrole that has been intensely studied in past decades. Because of its importance for photochemical processes the optical properties are of particular interest, and, accordingly, numerous studies have focused on light absorption and excited-state dynamics of Zn-TPP. Relaxation after photoexcitation in the Soret band involves internal conversion that is preceded by an ultrafast process. This relaxation process has been observed by several groups. Until now, it has not been established if it involves a higher lying ”dark” state or vibrational relaxation in the excited S2 state. Here we combine high time resolution electronic and vibrational spectroscopy to show that this process constitutes vibrational relaxation in the anharmonic 2 potential.

  6. Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

    NASA Technical Reports Server (NTRS)

    Levine, B. F.; Zussman, A.; Gunapala, S. D.; Asom, M. T.; Kuo, J. M.; Hobson, W. S.

    1992-01-01

    We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n- and p-doped QWIPs, as well as intersubband transitions based on photoexcitation from bound-to-bound, bound-to-quasi-continuum, and bound-to-continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path; net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

  7. Shape transformation and relaxation dynamics of photoexcited TiO2/Ag nanocomposites.

    PubMed

    Kim, Mee Rahn; Ah, Chil Seong; Shin, Dongha; Lee, Sang Kyung; Lee, Wan In; Jang, Du-Jeon

    2008-06-01

    The laser-induced sintering of TiO2 nanoparticles into larger nanospheres is accelerated by adsorbed silver particles. For the same weight fraction of silver, silver nanoparticles of 5 nm in diameter modify TiO2 nanoparticles more effectively than those of 1.5 nm do, suggesting that the photocatalysis of TiO2 nanoparticles as well as their stability is highly dependent on the sizes, the shapes, and the distribution of adsorbed metal nanoparticles. The photoexcited electrons of TiO2 nanoparticles are quenched at trap sites and surface states by transfer to the conduction band of silver, implying that the presence of adsorbed silver nanoparticles enhances the photocatalytic effect of TiO2.

  8. Anomalous Above-Gap Photoexcitations and Optical Signatures of Localized Charge Puddles in Monolayer Molybdenum Disulfide.

    PubMed

    Borys, Nicholas J; Barnard, Edward S; Gao, Shiyuan; Yao, Kaiyuan; Bao, Wei; Buyanin, Alexander; Zhang, Yingjie; Tongay, Sefaattin; Ko, Changhyun; Suh, Joonki; Weber-Bargioni, Alexander; Wu, Junqiao; Yang, Li; Schuck, P James

    2017-02-28

    Broadband optoelectronics such as artificial light harvesting technologies necessitate efficient and, ideally, tunable coupling of excited states over a wide range of energies. In monolayer MoS2, a prototypical two-dimensional layered semiconductor, the excited state manifold spans the visible electromagnetic spectrum and is comprised of an interconnected network of excitonic and free-carrier excitations. Here, photoluminescence excitation spectroscopy is used to reveal the energetic and spatial dependence of broadband excited state coupling to the ground-state luminescent excitons of monolayer MoS2. Photoexcitation of the direct band gap excitons is found to strengthen with increasing energy, demonstrating that interexcitonic coupling across the Brillouin zone is more efficient than previously reported, and thus bolstering the import and appeal of these materials for broadband optoelectronic applications. Narrow excitation resonances that are superimposed on the broadband photoexcitation spectrum are identified and coincide with the energetic positions of the higher-energy excitons and the electronic band gap as predicted by first-principles calculations. Identification of such features outlines a facile route to measure the optical and electronic band gaps and thus the exciton binding energy in the more sophisticated device architectures that are necessary for untangling the rich many-body phenomena and complex photophysics of these layered semiconductors. In as-grown materials, the excited states exhibit microscopic spatial variations that are characteristic of local carrier density fluctuations, similar to charge puddling phenomena in graphene. Such variations likely arise from substrate inhomogeneity and demonstrate the possibility to use substrate patterning to tune local carrier density and dynamically control excited states for designer optoelectronics.

  9. Structural origin of Si-2p core-level shifts from Si(100)-c[4x2] surface: A spectral x-ray photoelectron diffraction study

    SciTech Connect

    Chen, X.; Tonner, B.P.; Denlinger, J.

    1997-04-01

    The authors have performed angle-resolved x-ray photoelectron diffraction (XPD) from a Si(100)-c(4x2) surface to study the structural origin of Si-2p core-level shifts. In the experiment, the highly resolved surface Si-2p core-level spectra were measured as a fine grid of hemisphere and photon energies, using the SpectroMicroscopy Facility {open_quotes}ultraESCA{close_quotes} instrument. By carefully decomposing the spectra into several surface peaks, the authors are able to obtain surface-atom resolved XPD patterns. Using a multiple scattering analysis, they derived a detailed atomic model for the Si(100)-c(4x2) surface. In this model, the asymmetric dimers were found tilted by 11.5 plus/minus 2.0 degrees with bond length of 2.32 plus/minus 0.05{angstrom}. By matching model XPD patterns to experiment, the authors can identify which atoms in the reconstructed surface are responsible for specific photoemission lines in the 2p spectrum.

  10. Visualization of Photoexcited Carrier Responses in a Solar Cell Using Optical Pump—Terahertz Emission Probe Technique

    NASA Astrophysics Data System (ADS)

    Nakanishi, Hidetoshi; Ito, Akira; Takayama, Kazuhisa; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi

    2016-05-01

    We observed photoexcited carrier responses in solar cells excited by femtosecond laser pulses with spatial and temporal resolution using an optical pump-terahertz emission probe technique. We visualized the ultrafast local variation of the intensity of terahertz emission from a polycrystalline silicon solar cell using this technique and clearly observed the change in signals between a grain boundary and the inside of a grain in the solar cell. Further, the time evolution of the pump-probe signals of the polycrystalline and monocrystalline silicon solar cells was observed, and the relaxation times of photoexcited carriers in the emitter layers of crystalline silicon solar cells were estimated using this technique. The estimated relaxation time was consistent with the lifetime of the Auger recombination process that was dominant in heavily doped silicon used as an emitter layer for the silicon solar cells, which is difficult to obtain with photoluminescence method commonly used for the evaluation of solar cells.

  11. Ultrafast Terahertz Probe of Transient Evolution of Charged and Neutral Phase of Photoexcited Electron-hole Gas in Monolayer Semiconductor

    NASA Astrophysics Data System (ADS)

    Liu, Xuefeng; Ji, Qingqing; Gao, Zhihan; Ge, Shaofeng; Qiu, Jun; Liu, Zhongfan; Zhang, Yanfeng; Sun, Dong

    2015-03-01

    We investigate the dynamical formation of excitons from photoexcited electron-hole plasma and its subsequent decay dynamics in monolayer MoS2 grown by chemical vapor deposition using ultrafast pump and terahertz probe spectroscopy under temperature down to 78 K. The observed transient THz transmission can be fit with two decay components: a fast component with decay lifetime of 20 ps, which is attributed to exciton life time including the exciton formation and subsequent intraexciton relaxation; a slow component with extremely long decay lifetime of several ns which is attributed to long live dark exciton or localized exciton state. Further temperature and pump fluence dependent studies of the two decay components verify the above relaxation dynamics. The measured time resolved evolution of photoexcited carriers provides new opportunities in developing novel optoelectronic and excitonic devices based on monolayer transition-metal dichalcogenides.

  12. Characteristics of terahertz wave modulation using wavelength-selective photoexcitation in pentacene/Si and TIPS pentacene/Si bilayers

    NASA Astrophysics Data System (ADS)

    Yoo, Hyung Keun; Kang, Chul; Kee, Chul-Sik; Hwang, In-Wook; Lee, Joong Wook

    2016-11-01

    We demonstrate the characteristics of the optical control of terahertz (THz) wave transmission in photoexcited bilayers of pentacene/Si and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene)/Si. The modulation efficiency is influenced significantly by the photoexcitation wavelength of the optical beams. Lower optical absorption of organic materials leads to higher modulation efficiency because the photocarriers excited on Si with a higher diffusion rate and mobility are far more instrumental in increasing the modulation than the excitons generated on the organic layers. Securing a sufficient depth for carrier diffusion on organic layers is also important for increasing the THz modulation efficiency. These findings may be useful for designing highly efficient and spectrally controllable THz wave modulators.

  13. EXAFS studies on the structure of photoexcited cyclopentadienylnickelnitrosyl(C{sub 5}H{sub 5}NiNO)

    SciTech Connect

    Chen, L.X.; Bowman, M.K.; Montano, A.; Norris, J.R. |

    1993-05-01

    The structures of C{sub 5}H{sub 5}NiNO in a reversible photochemical reaction were studied via EXAFS, FTIR, and optical absorption spectroscopies. A photoexcited intermediate with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was generated upon irradiation using 365 mn light at 20K in a 3-methylpentane solution. The reverse reaction was induced by irradiation with 310 mn light. The EXAFS data analysis has shown a 0.12 {Angstrom} elongation of the Ni-N bond and the bending, of Ni-N-0 in the photoexcited intermediate. Several ZINDO calculations were conducted based on the structures obtained from the EXAFS spectroscopy. These calculations reproduced the changes in the optical spectra and the intramolecular electron transfer in C{sub 5}H{sub 5}NiNO.

  14. EXAFS studies on the structure of photoexcited cyclopentadienylnickelnitrosyl(C[sub 5]H[sub 5]NiNO)

    SciTech Connect

    Chen, L.X.; Bowman, M.K.; Montano, A. ); Norris, J.R. Chicago Univ., IL . Dept. of Chemistry)

    1993-01-01

    The structures of C[sub 5]H[sub 5]NiNO in a reversible photochemical reaction were studied via EXAFS, FTIR, and optical absorption spectroscopies. A photoexcited intermediate with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was generated upon irradiation using 365 mn light at 20K in a 3-methylpentane solution. The reverse reaction was induced by irradiation with 310 mn light. The EXAFS data analysis has shown a 0.12 [Angstrom] elongation of the Ni-N bond and the bending, of Ni-N-0 in the photoexcited intermediate. Several ZINDO calculations were conducted based on the structures obtained from the EXAFS spectroscopy. These calculations reproduced the changes in the optical spectra and the intramolecular electron transfer in C[sub 5]H[sub 5]NiNO.

  15. Quenching of photoexcited states of the proteins chromophores and introduced into the protein macromolecules fluorescent probes by heavy metal ions

    NASA Astrophysics Data System (ADS)

    Melnikov, A. G.; Dyachuk, O. A.; Melnikov, G. V.

    2015-03-01

    We have studied the processes of quenching of photoexcited states of fluorescent probes and quenching of the fluorescence of the chromophores of human serum albumin (HSA) by heavy metal ions (HM): cations Tl+, Pb2+, Cu2+, Cd2+, and the anion of iodine (I-). We used the dye from xanthene series - eosin as a fluorescent probe. By quenching of the fluorescence of protein chromophores we found an influence of HM on the structure of proteins, resulting in a shift of the peak of the fluorescence of HSA tryptophanyl. This can be explained by proteins denaturation under the influence of heavy metals and penetration of water into the inner environment of HSA tryptophan. It was established that the constant of the quenching of the probe phosphorescence is much higher than the fluorescence, which is explained by significantly longer lifetime of the photoexcited states of fluorescent probes in the triplet state than in the singlet.

  16. Core-level spectra and binding energies of transition metal nitrides by non-destructive x-ray photoelectron spectroscopy through capping layers

    NASA Astrophysics Data System (ADS)

    Greczynski, G.; Primetzhofer, D.; Lu, J.; Hultman, L.

    2017-02-01

    We present the first measurements of x-ray photoelectron spectroscopy (XPS) core level binding energies (BE:s) for the widely-applicable group IVb-VIb polycrystalline transition metal nitrides (TMN's) TiN, VN, CrN, ZrN, NbN, MoN, HfN, TaN, and WN as well as AlN and SiN, which are common components in the TMN-based alloy systems. Nitride thin film samples were grown at 400 °C by reactive dc magnetron sputtering from elemental targets in Ar/N2 atmosphere. For XPS measurements, layers are either (i) Ar+ ion-etched to remove surface oxides resulting from the air exposure during sample transfer from the growth chamber into the XPS system, or (ii) in situ capped with a few nm thick Cr or W overlayers in the deposition system prior to air-exposure and loading into the XPS instrument. Film elemental composition and phase content is thoroughly characterized with time-of-flight elastic recoil detection analysis (ToF-E ERDA), Rutherford backscattering spectrometry (RBS), and x-ray diffraction. High energy resolution core level XPS spectra acquired with monochromatic Al Kα radiation on the ISO-calibrated instrument reveal that even mild etching conditions result in the formation of a nitrogen-deficient surface layer that substantially affects the extracted binding energy values. These spectra-modifying effects of Ar+ ion bombardment increase with increasing the metal atom mass due to an increasing nitrogen-to-metal sputter yield ratio. The superior quality of the XPS spectra obtained in a non-destructive way from capped TMN films is evident from that numerous metal peaks, including Ti 2p, V 2p, Zr 3d, and Hf 4f, exhibit pronounced satellite features, in agreement with previously published spectra from layers grown and analyzed in situ. In addition, the N/metal concentration ratios are found to be 25-90% higher than those obtained from the corresponding ion-etched surfaces, and in most cases agree very well with the RBS and ToF-E ERDA values. The N 1 s BE:s extracted from

  17. Deep Earthquakes.

    ERIC Educational Resources Information Center

    Frohlich, Cliff

    1989-01-01

    Summarizes research to find the nature of deep earthquakes occurring hundreds of kilometers down in the earth's mantle. Describes further research problems in this area. Presents several illustrations and four references. (YP)

  18. Delayed fluorescence spectra of intact leaves photoexcited by sunlight measured with a multichannel Fourier-transform chemiluminescence spectrometer

    NASA Astrophysics Data System (ADS)

    Akita, Saeka; Yano, Ayako; Ishii, Hiroshi; Satoh, Chikahiro; Akai, Nobuyuki; Nakata, Munetaka

    2013-06-01

    Delayed fluorescence spectra of intact leaves of Green pak choi (Brassica rapa var. chinensis) were measured with a multichannel Fourier-transform chemiluminescence spectrometer, which we developed recently. The intact samples, photoexcited by sunlight without artificial light sources, showed delayed fluorescence around 740 nm with a lifetime of ˜6 s. The observed spectra were deconvoluted into two Gaussian bands: the delayed fluorescence from photosystem II and photosystem I complexes. Their relative intensities depended on the chlorophyll concentration, but their wavelengths were unchanged.

  19. X-ray absorption structural study of a reversible, photoexcited charge-transfer state

    SciTech Connect

    Chen, L.X.; Bowman, M.K.; Norris, J.R. Univ. of Chicago, IL ); Montano, P.A. )

    1993-05-19

    Electron-transfer reactions can be accompanied by significant nuclear movements. Nuclear motion appears to be especially vital to the reversible, photoinduced charge-transfer chemistry of cyclopentadienylnickel nitrosyl (C[sub 5]H[sub 5]NiNO). Although extended X-ray absorption fine structure (EXAFS) spectroscopy has recorded photoinduced changes in the ligation of myoglobins, similar X-ray studies of electron-transfer chemistry have not been reported. Here we examine reversible, photoinduced structural changes in C[sub 5]H[sub 5]NiNO by EXAFS and propose a mechanism for the electron-transfer chemistry. This work demonstrates that EXAFS can measure distance changes accompanying photoinduced electron transfer to provide new details of the geometry of photoexcited state and suggests that electron transfer occurs in the transient, optically excited states of C[sub 5]H[sub 5]NiNO and C[sub 5]H[sub 5]NiNO[sup CT] as dictated by NO movement that produces either C[sub 5]H[sub 5]NiNO[sup CT] or C[sub 5]H[sub 5]NiNO[sup GS]. 14 refs., 2 figs.

  20. Ultrafast Relaxation Dynamics of Photoexcited Zinc-Porphyrin: Electronic-Vibrational Coupling

    DOE PAGES

    Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

    2016-08-02

    Cyclic tetrapyrroles are the active core of compounds with crucial roles in living systems, such as hemoglobin and chlorophyll, and in technology as photocatalysts and light absorbers for solar energy conversion. Zinc-tetraphenylporphyrin (Zn-TPP) is a prototypical cyclic tetrapyrrole that has been intensely studied in past decades. Because of its importance for photochemical processes the optical properties are of particular interest, and, accordingly, numerous studies have focused on light absorption and excited-state dynamics of Zn-TPP. Relaxation after photoexcitation in the Soret band involves internal conversion that is preceded by an ultrafast process. This relaxation process has been observed by several groups.more » Until now, it has not been established if it involves a higher lying ”dark” state or vibrational relaxation in the excited S2 state. Here we combine high time resolution electronic and vibrational spectroscopy to show that this process constitutes vibrational relaxation in the anharmonic 2 potential.« less

  1. Amoeba-inspired nanoarchitectonic computing: solving intractable computational problems using nanoscale photoexcitation transfer dynamics.

    PubMed

    Aono, Masashi; Naruse, Makoto; Kim, Song-Ju; Wakabayashi, Masamitsu; Hori, Hirokazu; Ohtsu, Motoichi; Hara, Masahiko

    2013-06-18

    Biologically inspired computing devices and architectures are expected to overcome the limitations of conventional technologies in terms of solving computationally demanding problems, adapting to complex environments, reducing energy consumption, and so on. We previously demonstrated that a primitive single-celled amoeba (a plasmodial slime mold), which exhibits complex spatiotemporal oscillatory dynamics and sophisticated computing capabilities, can be used to search for a solution to a very hard combinatorial optimization problem. We successfully extracted the essential spatiotemporal dynamics by which the amoeba solves the problem. This amoeba-inspired computing paradigm can be implemented by various physical systems that exhibit suitable spatiotemporal dynamics resembling the amoeba's problem-solving process. In this Article, we demonstrate that photoexcitation transfer phenomena in certain quantum nanostructures mediated by optical near-field interactions generate the amoebalike spatiotemporal dynamics and can be used to solve the satisfiability problem (SAT), which is the problem of judging whether a given logical proposition (a Boolean formula) is self-consistent. SAT is related to diverse application problems in artificial intelligence, information security, and bioinformatics and is a crucially important nondeterministic polynomial time (NP)-complete problem, which is believed to become intractable for conventional digital computers when the problem size increases. We show that our amoeba-inspired computing paradigm dramatically outperforms a conventional stochastic search method. These results indicate the potential for developing highly versatile nanoarchitectonic computers that realize powerful solution searching with low energy consumption.

  2. Spatially Resolved Photoexcited Charge-Carrier Dynamics in Phase-Engineered Monolayer MoS2

    DOE PAGES

    Yamaguchi, Hisato; Blancon, Jean-Christophe; Kappera, Rajesh; ...

    2014-12-18

    A fundamental understanding of the intrinsic optoelectronic properties of atomically thin transition metal dichalcogenides (TMDs) is crucial for its integration into high performance semiconductor devices. We investigate the transport properties of chemical vapor deposition (CVD) grown monolayer molybdenum disulfide (MoS2) under photo-excitation using correlated scanning photocurrent microscopy and photoluminescence imaging. We examined the effect of local phase transformation underneath the metal electrodes on the generation of photocurrent across the channel length with diffraction-limited spatial resolution. While maximum photocurrent generation occurs at the Schottky contacts of semiconducting (2H-phase) MoS2, after the metallic phase transformation (1T-phase), the photocurrent peak is observed towardsmore » the center of the device channel, suggesting a strong reduction of native Schottky barriers. Analysis using the bias and position dependence of the photocurrent indicates that the Schottky barrier heights are few meV for 1T- and ~200 meV for 2H-contacted devices. We also demonstrate that a reduction of native Schottky barriers in a 1T device enhances the photo responsivity by more than one order of magnitude, a crucial parameter in achieving high performance optoelectronic devices. The obtained results pave a pathway for the fundamental understanding of intrinsic optoelectronic properties of atomically thin TMDs where Ohmic contacts are necessary for achieving high efficiency devices with low power consumption.« less

  3. Ultrafast reflectance of photoexcited Weyl and Dirac semimetals TaAs and ZrSiS

    NASA Astrophysics Data System (ADS)

    Weber, Christopher; Berggren, Bryan; Dani, Keshav; Ali, Mazhar; Parkin, Stuart; Schoop, Leslie; Lotsch, Bettina; Zhao, Lingxiao; Chen, Genfu

    We report ultrafast pump-probe and transient-grating (TG) measurements of the Weyl semimetal TaAs and the Dirac line-node semimetal ZrSiS, and contrast these results with prior measurements on the Dirac semimetal Cd3As2. After absorption of photons from the pump pulse, we monitor the samples' recovery to equilibrium by measuring the change in reflectance of a time-delayed probe pulse. For TaAs, the reflectance recovers in just 1.2 ps, significantly faster than the 3.1 ps measured in Cd3As2. This rapid recovery appears not to change when temperature is varied from 300 K to 8 K, when a magnetic field of order 0.3 T is applied, or when the excitation fluence is increased by a factor of 20. TG measurements allow us to assign the changes in reflectance to changes in either the dispersive (real) or absorptive (imaginary) parts of the index of refraction. Intriguingly, and in contrast to Cd3As2, the initial change in reflectance is caused by an abrupt reduction in the dispersive part, followed by a slower reduction in the absorptive part. For ZrSiS, the recovery after photoexcitation is even faster, at 0.3 ps. We will discuss the implications of these findings for carrier dynamics in topological semimetals.

  4. Semiclassical molecular dynamics simulations of intramolecular proton transfer in photoexcited 2-(2'-hydroxyphenyl)-oxazole

    NASA Astrophysics Data System (ADS)

    Guallar, Victor; Batista, Victor S.; Miller, William H.

    2000-12-01

    A full-dimensional excited state potential energy surface is constructed, and the proton transfer dynamics associated with the keto-enolic tautomerization reaction in photoexcited 2-(2'-hydroxyphenyl)-oxazole is simulated according to an approximate version of the semiclassical initial value representation method introduced by Miller and co-workers [V. Guallar, V. S. Batista, and W. H. Miller, J. Chem. Phys. 110, 9922 (1999)]. The full-dimensional potential energy surface is developed according to an ab initio reaction surface model obtained at the CIS level of quantum chemistry. Proton transfer is found to be substantially affected by isotopic substitution, and significantly coupled to the internal oxazole-hydroxyphenyl in-the-plane bending mode. The nascent tautomer is found to be stabilized primarily through vibrational energy redistribution into all of the remaining in-the-plane vibrational modes. The accuracy of the methodology is verified by reducing the dimensionality of the system and comparing our semiclassical results with full quantum mechanical calculations.

  5. Nonequilibrium dynamics of photoexcited electrons in graphene: Collinear scattering, Auger processes, and the impact of screening

    NASA Astrophysics Data System (ADS)

    Tomadin, Andrea; Brida, Daniele; Cerullo, Giulio; Ferrari, Andrea C.; Polini, Marco

    2013-07-01

    We present a combined analytical and numerical study of the early stages (sub-100-fs) of the nonequilibrium dynamics of photoexcited electrons in graphene. We employ the semiclassical Boltzmann equation with a collision integral that includes contributions from electron-electron (e-e) and electron-optical phonon interactions. Taking advantage of circular symmetry and employing the massless Dirac fermion (MDF) Hamiltonian, we are able to perform an essentially analytical study of the e-e contribution to the collision integral. This allows us to take particular care of subtle collinear scattering processes—processes in which incoming and outgoing momenta of the scattering particles lie on the same line—including carrier multiplication (CM) and Auger recombination (AR). These processes have a vanishing phase space for two-dimensional MDF bare bands. However, we argue that electron-lifetime effects, seen in experiments based on angle-resolved photoemission spectroscopy, provide a natural pathway to regularize this pathology, yielding a finite contribution due to CM and AR to the Coulomb collision integral. Finally, we discuss in detail the role of physics beyond the Fermi golden rule by including screening in the matrix element of the Coulomb interaction at the level of the random phase approximation (RPA), focusing in particular on the consequences of various approximations including static RPA screening, which maximizes the impact of CM and AR processes, and dynamical RPA screening, which completely suppresses them.

  6. Photoexcitation and Photochemical Stability of Organic Photovoltaic Materials from First Principles

    NASA Astrophysics Data System (ADS)

    Sai, Na; Leung, Kevin

    2013-03-01

    The development of high efficiency organic photovoltaics (OPV) has recently become enabled by the synthesis of new conjugated polymers with low band gap that allow light absorption over a broader range of the spectrum. Stability of these new polymers, a key requirement for commercialization, has not yet received sufficient attention. Here, we report first-principles theoretical modeling of photo-induced degradation of OPV polymers carried out using ab-initio density functional theory (DFT). We report photooxidation routes and reaction products for reactive species including superoxide oxygen anions and hydroxyl groups interacting with the standard workhorse OPV polymer, poly(3-hexyl-thiophene) (P3HT). We discuss theoretical issues and challenges affecting the modeling such reactions in OPV polymers. We also discuss the application of theoretical methods to low-band-gap polymers, and in particular, the effect of the chemical substitution on the photoexcitation properties of these new polymers. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Deparment of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. This work is supported by the Energy Frontier Research Center funded by the U.S. DOE Office of Basic Energy Sciences under Award number DE-SC0001091.

  7. Photoexcited State Molecular Structures in Solution Studied by Pump-Probe XAFS

    NASA Astrophysics Data System (ADS)

    Chen, Lin

    2002-03-01

    The photoexcitation causes displacement of electron densities within or among molecules, which consequently leads to nuclear movements. Such nuclear displacements often occur in transient states with short lifetimes. Knowing transient molecular structures during photochemical reactions is important for understanding fundamental aspects of solar energy conversion and storage. Fast x-ray techniques provide direct probes for these transient structures. Using x-ray pulses from the Advanced Photon Source at Argonne, a laser pulse pump, x-ray pulse probe XAFS technique has been developed to capture transient molecular structures in disordered media with nanosecond time resolution. We have carried out several pump-probe XAFS measurements on 1)identifying a transient molecular structure of the photodissociation product of nickel-tetraphenylporphyrin with piperidine axial ligands (NiTPP-L2); 2)determination of the MLCT state structure of Bis(2,9-dimethyl-1,10-phenanthroline) Copper(I) [Cu(I)(dmp)2]+, and 3) triplet state molecular structures of metalloporphyrins. These studies not only prove the feasibility of the technique, but also gain structural information that otherwise will not be available. Future studies include probing transient structures in electron donor-acceptor complexes and optical polarization selected XAFS (OPS-XAFS) using the same technique with a 100-ps time resolution. This work is supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U. S. Department of Energy, under contract W-31-109-Eng-38.

  8. Distinguishing between plasmon-induced and photoexcited carriers in a device geometry

    PubMed Central

    Zheng, Bob Y.; Zhao, Hangqi; Manjavacas, Alejandro; McClain, Michael; Nordlander, Peter; Halas, Naomi J.

    2015-01-01

    The use of surface plasmons, charge density oscillations of conduction electrons of metallic nanostructures, to boost the efficiency of light-harvesting devices through increased light-matter interactions could drastically alter how sunlight is converted into electricity or fuels. These excitations can decay directly into energetic electron–hole pairs, useful for photocurrent generation or photocatalysis. However, the mechanisms behind plasmonic carrier generation remain poorly understood. Here we use nanowire-based hot-carrier devices on a wide-bandgap semiconductor to show that plasmonic carrier generation is proportional to internal field-intensity enhancement and occurs independently of bulk absorption. We also show that plasmon-induced hot electrons have higher energies than carriers generated by direct excitation and that reducing the barrier height allows for the collection of carriers from plasmons and direct photoexcitation. Our results provide a route to increasing the efficiency of plasmonic hot-carrier devices, which could lead to more efficient devices for converting sunlight into usable energy. PMID:26165521

  9. Alterations of transmembrane currents in frog atrial heart muscle induced by photoexcited gymnochrome A purified from the crinoid, Gymnochrinus richeri.

    PubMed

    Sauviat, M P; Benoit, A G; Debitus, C; Pouny, I; Laurent, D

    2001-08-01

    The effects of gymnochrome A were tested on the electrical activity of the frog atrial heart muscle. Gymnochrome A (1-5 microM) did not alter the resting potential. Gymnochrome A (5 microM) slowed the initial depolarizing phase of the spontaneously beating action potential. Under voltage-clamp conditions gymnochrome A (5 microM) did not affect the electrical constant of the membrane and the kinetic parameters of the peak Na+ current (INa) recorded in the Ringer solution containing tetraethylammonium (2 mM) and Cd2+ (1 mM) but shifted the membrane potential at which the current both activated and reached its maximal value toward more negative membrane potentials. It did not alter the reversal potential for INa, indicating that the selectivity of the Na+ channels had not changed. These observations suggest that gymnochrome A binds to the membrane and shifts the activation of INa on the voltage axis by modifying the free negative fixed charges present at the membrane surface rather than by occupying a specific site on the Na+ channel. Photoexcited gymnochrome A transiently triggered an early outward current which lengthened the time-to-peak of INa and decreased its amplitude. In addition, photoexcited gymnochrome A blocked the background K+ current. This is, to our knowledge, the first time that such effects are reported on the cardiac muscle. These observations suggest that the photoexcitation of gymnochrome produces physico-chemical effects which lead to intracellular changes. Further experiments are required to determine their nature.

  10. Photoexcited electron and hole dynamics in semiconductor quantum dots: phonon-induced relaxation, dephasing, multiple exciton generation and recombination

    NASA Astrophysics Data System (ADS)

    Hyeon-Deuk, Kim; Prezhdo, Oleg V.

    2012-09-01

    Photoexcited dynamics of electrons and holes in semiconductor quantum dots (QD), including phonon-induced relaxation, multiple exciton generation, fission and recombination (MEG, MEF and MER), were simulated by combining ab initio time-dependent density functional theory and non-adiabatic molecular dynamics. These nonequilibrium phenomena govern the optical properties and photoexcited dynamics of QDs, determining the branching between electronic processes and thermal energy losses. Our approach accounts for QD size and shape as well as defects, core-shell distribution, surface ligands and charge trapping, which significantly influence the properties of photoexcited QDs. The method creates an explicit time-domain representation of photoinduced processes and describes various kinetic regimes owing to the non-perturbative treatment of quantum dynamics. QDs of different sizes and materials, with and without ligands, are considered. The simulations provide direct evidence that the high-frequency ligand modes on the QD surface play a pivotal role in the electron-phonon relaxation, MEG, MEF and MER. The insights reported here suggest novel routes for controlling the photoinduced processes in semiconductor QDs and lead to new design principles for increasing the efficiencies of photovoltaic devices.

  11. Ultrafast relaxation dynamics of photoexcited Dirac fermions in the three-dimensional Dirac semimetal C d3A s2

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Ge, Shaofeng; Liu, Xuefeng; Lu, Hong; Li, Caizhen; Lai, Jiawei; Zhao, Chuan; Liao, Zhimin; Jia, Shuang; Sun, Dong

    2017-01-01

    Three-dimensional (3D) Dirac semimetals that can be seen as 3D analogues of graphene have attracted enormous interest in research recently. In order to apply these ultra-high-mobility materials in future electronic/optoelectronic devices, it is crucial to understand the relaxation dynamics of photoexcited carriers and their coupling with lattice. In this paper, we report ultrafast transient reflection measurements of the photoexcited carrier dynamics in cadmium arsenide (C d3A s2 ), which is one of the most stable Dirac semimetals that have been confirmed experimentally. By using the low-energy probe photon of 0.3 eV, we probed the dynamics of the photoexcited carriers that are Dirac-Fermi-like approaching the Dirac point. We systematically studied the transient reflection on bulk and nanoplate samples that have different doping intensities by tuning the probe wavelength, pump power, and lattice temperature and find that the dynamical evolution of carrier distributions can be retrieved qualitatively by using a two-temperature model. This result is very similar to that of graphene, but the carrier cooling through the optical phonon couplings is slower and lasts over larger electron temperature range because the optical phonon energies in C d3A s2 are much lower than those in graphene.

  12. sp2/sp3 hybridization ratio in amorphous carbon from C 1s core-level shifts: X-ray photoelectron spectroscopy and first-principles calculation

    NASA Astrophysics Data System (ADS)

    Haerle, Rainer; Riedo, Elisa; Pasquarello, Alfredo; Baldereschi, Alfonso

    2002-01-01

    Using a combined experimental and theoretical approach, we address C 1s core-level shifts in amorphous carbon. Experimental results are obtained by x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) on thin-film samples of different atomic density, obtained by a pulsed-laser deposition growth process. The XPS spectra are deconvoluted into two contributions, which are attributed to sp2- and sp3-hybridized atoms, respectively, separated by 0.9 eV, independent of atomic density. The sp3 hybridization content extracted from XPS is consistent with the atomic density derived from the plasmon energy in the EELS spectrum. In our theoretical study, we generate several periodic model structures of amorphous carbon of different densities applying two schemes of increasing accuracy in sequence. We first use a molecular-dynamics approach, based on an environmental-dependent tight-binding Hamiltonian to quench the systems from the liquid phase. The final model structures are then obtained by further atomic relaxation using a first-principles pseudopotential plane-wave approach within density-functional theory. Within the latter framework, we also calculate carbon 1s core-level shifts for our disordered model structures. We find that the shifts associated to threefold- and fourfold- coordinated carbon atoms give rise to two distinct peaks separated by about 1.0 eV, independent of density, in close agreement with experimental observations. This provides strong support for decomposing the XPS spectra into two peaks resulting from sp2- and sp3-hybridized atoms. Core-hole relaxations effects account for about 30% of the calculated shifts.

  13. Li induced effects in the core level and π-band electronic structure of graphene grown on C-face SiC

    SciTech Connect

    Johansson, Leif I. Xia, Chao; Virojanadara, Chariya

    2015-11-15

    Studies of the effects induced in the electronic structure after Li deposition, and subsequent heating, on graphene samples prepared on C-face SiC are reported. The as prepared graphene samples are essentially undoped, but after Li deposition, the Dirac point shifts down to 1.2 eV below the Fermi level due to electron doping. The shape of the C 1s level also indicates a doping concentration of around 10{sup 14 }cm{sup −2} after Li deposition, when compared with recent calculated results of core level spectra of graphene. The C 1s, Si 2p, and Li 1s core level results show little intercalation directly after deposition but that most of the Li has intercalated after heating at 280 °C. Heating at higher temperatures leads to desorption of Li from the sample, and at 1030 °C, Li can no longer be detected on the sample. The single π-band observable from multilayer C-face graphene samples in conventional angle resolved photoelectron spectroscopy is reasonably sharp both on the initially prepared sample and after Li deposition. After heating at 280 °C, the π-band appears more diffuse and possibly split. The Dirac point becomes located at 0.4 eV below the Fermi level, which indicates occurrence of a significant reduction in the electron doping concentration. Constant energy photoelectron distribution patterns extracted from the as prepared graphene C-face sample and also after Li deposition and heating at 280 °C look very similar to earlier calculated distribution patterns for monolayer graphene.

  14. Deep learning.

    PubMed

    LeCun, Yann; Bengio, Yoshua; Hinton, Geoffrey

    2015-05-28

    Deep learning allows computational models that are composed of multiple processing layers to learn representations of data with multiple levels of abstraction. These methods have dramatically improved the state-of-the-art in speech recognition, visual object recognition, object detection and many other domains such as drug discovery and genomics. Deep learning discovers intricate structure in large data sets by using the backpropagation algorithm to indicate how a machine should change its internal parameters that are used to compute the representation in each layer from the representation in the previous layer. Deep convolutional nets have brought about breakthroughs in processing images, video, speech and audio, whereas recurrent nets have shone light on sequential data such as text and speech.

  15. Deep learning

    NASA Astrophysics Data System (ADS)

    Lecun, Yann; Bengio, Yoshua; Hinton, Geoffrey

    2015-05-01

    Deep learning allows computational models that are composed of multiple processing layers to learn representations of data with multiple levels of abstraction. These methods have dramatically improved the state-of-the-art in speech recognition, visual object recognition, object detection and many other domains such as drug discovery and genomics. Deep learning discovers intricate structure in large data sets by using the backpropagation algorithm to indicate how a machine should change its internal parameters that are used to compute the representation in each layer from the representation in the previous layer. Deep convolutional nets have brought about breakthroughs in processing images, video, speech and audio, whereas recurrent nets have shone light on sequential data such as text and speech.

  16. Deep earthquakes

    SciTech Connect

    Frohlich, C.

    1989-01-01

    Earthquakes are often recorded at depths as great as 650 kilometers or more. These deep events mark regions where plates of the earth's surface are consumed in the mantle. But the earthquakes themselves present a conundrum: the high pressures and temperatures at such depths should keep rock from fracturing suddenly and generating a tremor. This paper reviews the research on this problem. Almost all deep earthquakes conform to the pattern described by Wadati, namely, they generally occur at the edge of a deep ocean and define an inclined zone extending from near the surface to a depth of 600 kilometers of more, known as the Wadati-Benioff zone. Several scenarios are described that were proposed to explain the fracturing and slipping of rocks at this depth.

  17. Relaxation dynamics of photoexcited resorcinol: internal conversion versus H atom tunnelling.

    PubMed

    Young, Jamie D; Staniforth, Michael; Chatterley, Adam S; Paterson, Martin J; Roberts, Gareth M; Stavros, Vasilios G

    2014-01-14

    The excited state dynamics of resorcinol (1,3-dihydroxybenzene) following UV excitation at a range of pump wavelengths, 278 ≥ λ ≥ 255 nm, have been investigated using a combination of time-resolved velocity map ion imaging and ultrafast time-resolved ion yield measurements coupled with complementary ab initio calculations. After excitation to the 1(1)ππ* state we extract a timescale, τ1, for excited state relaxation that decreases as a function of excitation energy from 2.70 ns to ~120 ps. This is assigned to competing relaxation mechanisms. Tunnelling beneath the 1(1)ππ*/(1)πσ* conical intersection, followed by coupling onto the dissociative (1)πσ* state, yields H atoms born with high kinetic energy (~5000 cm(-1)). This mechanism is in competition with an internal conversion process that is able to transfer population from the photoexcited 1(1)ππ* state back to a vibrationally excited ground state, S0*. When exciting between 264-260 nm a second decay component, τ2, is observed and we put forth several possible explanations as to the origins of τ2, including conformer specific dynamics. Excitation with 237 nm light (above the 1(1)ππ*/(1)πσ* conical intersection) yields high kinetic energy H atoms (~11,000 cm(-1)) produced in ~260 fs, in line with a mechanism involving ultrafast coupling between the 1(1)ππ* (or 2(1)ππ*) and (1)πσ* state followed by dissociation. The results presented highlight the profound effect the presence of additional functional groups, and more specifically the precise location of the functional groups, can have on the excited state dynamics of model heteroaromatic systems following UV excitation.

  18. Relaxation pathways of photoexcited iodide-methanol clusters: a computational investigation.

    PubMed

    Mak, Chun C; Peslherbe, Gilles H

    2014-06-26

    Upon photoexcitation of iodide-methanol clusters, I(-)(CH3OH)n, to a charge-transfer-to-solvent (CTTS) excited state, extensive relaxation was found to occur, accompanied by a convoluted modulation of the stability of the excited electron, which ultimately decreases substantially. In order to develop a molecular-level understanding of the relaxation processes of CTTS excited I(-)(CH3OH)n, high-level quantum chemical calculations are first used to investigate the ground, excited, and ionized states of I(-)(CH3OH)n (n = 2). Because of the relatively small size of I(-)(CH3OH)2, it was possible to characterize the contributions of solvent-solvent interactions to the stability of the CTTS excited cluster relative to dissociation into methanol, iodine, and a free electron, which exhibits a substantial dependence on the cluster geometric configuration. Ab initio molecular dynamics simulations of CTTS excited I(-)(CH3OH)3 are then performed to shed some light onto the nature of the relaxation pathways involved in the modulation of the stability of the excited electron in larger clusters. Simulation results suggest that separation of I and (CH3OH)3(-) accompanied by solvent reorganization in the latter can initially stabilize the excited electron, while gradual cluster fragmentation to I, (CH3OH)2(-), and CH3OH ultimately destabilizes it. This work shows, for the first time, that the inability of small CTTS excited I(-)(CH3OH)n to retain a solvated electron may be attributed to the limited hydrogen-bonding capacity of CH3OH, which increases the propensity for fragmentation to smaller clusters with lower excess-electron binding energies, and highlights the critical role of intricate molecular interactions in the electron solvation process.

  19. Photoexcited Surface Frustrated Lewis Pairs for Heterogeneous Photocatalytic CO2 Reduction.

    PubMed

    Ghuman, Kulbir Kaur; Hoch, Laura B; Szymanski, Paul; Loh, Joel Y Y; Kherani, Nazir P; El-Sayed, Mostafa A; Ozin, Geoffrey A; Singh, Chandra Veer

    2016-02-03

    In this study we investigated, theoretically and experimentally, the unique photoactive behavior of pristine and defected indium oxide surfaces providing fundamental insights into their excited state properties as well as an explanation for the experimentally observed enhanced activity of defected indium oxide surfaces for the gas-phase reverse water gas shift reaction, CO2 + H2 + hν→ CO + H2O in the light compared to the dark. To this end, a detailed excited-state study of pristine and defected forms of indium oxide (In2O3, In2O3-x, In2O3(OH)y and In2O3-x(OH)y) surfaces was performed using time dependent density functional theory (TDDFT) calculations, the results of which were supported experimentally by transient absorption spectroscopy and photoconductivity measurements. It was found that the surface frustrated Lewis pairs (FLPs) created by a Lewis acidic coordinately unsaturated surface indium site proximal to an oxygen vacancy and a Lewis basic surface hydroxide site in In2O3-x(OH)y become more acidic and basic and hence more active in the ES compared to the GS. This provides a theoretical mechanism responsible for the enhanced activity and reduced activation energy of the photochemical reverse water gas shift reaction observed experimentally for In2O3-x(OH)y compared to the thermochemical reaction. This fundamental insight into the role of photoexcited surface FLPs for catalytic CO2 reduction could lead to improved photocatalysts for solar fuel production.

  20. Unraveling the mechanisms of nonradiative deactivation in model peptides following photoexcitation of a phenylalanine residue.

    PubMed

    Mališ, Momir; Loquais, Yohan; Gloaguen, Eric; Biswal, Himansu S; Piuzzi, François; Tardivel, Benjamin; Brenner, Valérie; Broquier, Michel; Jouvet, Christophe; Mons, Michel; Došlić, Nađa; Ljubić, Ivan

    2012-12-19

    The mechanisms of nonradiative deactivation of a phenylalanine residue after near-UV photoexcitation have been investigated in an isolated peptide chain model (N-acetylphenylalaninylamide, NAPA) both experimentally and theoretically. Lifetime measurements at the origin of the first ππ* state of jet-cooled NAPA molecules have shown that (i) among the three most stable conformers of the molecule, the folded conformer NAPA B is ∼50-times shorter lived than the extended major conformer NAPA A and (ii) this lifetime is virtually insensitive to deuteration at the NH(2) and NH sites. Concurrent time-dependent density functional theory (TDDFT) based nonadiabatic dynamics simulations in the full dimensionality, carried out for the NAPA B conformer, provided direct insights on novel classes of ultrafast deactivation mechanisms, proceeding through several conical intersections and leading in fine to the ground state. These mechanisms are found to be triggered either (i) by a stretch of the N(Phe)H bond, which leads to an H-transfer to the ring, or (ii) by specific backbone amide distortions. The potential energy surfaces of the NAPA conformers along these critical pathways have been characterized more accurately using the coupled cluster doubles (CC2) method and shown to exhibit barriers that can be overcome with moderate excess energies. These results analyzed in the light of the experimental findings enabled us to assign the short lifetime of NAPA B conformer to a number of easily accessible exit channels from the initial ππ* surface, most importantly the one involving a transfer of electronic excitation to an nπ* surface, induced by distortions of the backbone peptide bond.

  1. Deep Trouble.

    ERIC Educational Resources Information Center

    Popke, Michael

    2002-01-01

    Discusses how the safety-related ruling by the National Federation of State High School Associations to eliminate the option of using 18-inch starting platforms in pools less than 4 feet deep may affect operators of swimming pools and the swim teams who use them. (EV)

  2. Deep Fish.

    PubMed

    Ishaq, Omer; Sadanandan, Sajith Kecheril; Wählby, Carolina

    2017-01-01

    Zebrafish ( Danio rerio) is an important vertebrate model organism in biomedical research, especially suitable for morphological screening due to its transparent body during early development. Deep learning has emerged as a dominant paradigm for data analysis and found a number of applications in computer vision and image analysis. Here we demonstrate the potential of a deep learning approach for accurate high-throughput classification of whole-body zebrafish deformations in multifish microwell plates. Deep learning uses the raw image data as an input, without the need of expert knowledge for feature design or optimization of the segmentation parameters. We trained the deep learning classifier on as few as 84 images (before data augmentation) and achieved a classification accuracy of 92.8% on an unseen test data set that is comparable to the previous state of the art (95%) based on user-specified segmentation and deformation metrics. Ablation studies by digitally removing whole fish or parts of the fish from the images revealed that the classifier learned discriminative features from the image foreground, and we observed that the deformations of the head region, rather than the visually apparent bent tail, were more important for good classification performance.

  3. Deep Lysimeter

    DOEpatents

    Hubbell, Joel M.; Sisson, James B.

    2004-06-01

    A deep lysimeter including a hollow vessel having a chamber, a fill conduit extending into the chamber through apertures, a semi-permeable member mounted on the vessel and in fluid communication with the fill conduit, and a line connection for retrieving the lysimeter.

  4. Charge-Separation Kinetics of Photoexcited Oxygen Vacancies in ZnO Nanowire Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Lu, Ming-Pei; Chen, Chieh-Wei; Lu, Ming-Yen

    2016-11-01

    Photoinduced atomic structural transitions of negative-U defects: neutral oxygen vacancies (VO 0 ), accompanied by lattice relaxation, can form ionized 1 + and 2 + vacancy defects in ZnO materials, giving rise to an optoelectronic phenomenon named "persistent photoconductivity," thereby limiting the applications of ZnO materials in optoelectronic fields. Nevertheless, very little is known about the kinetics of the separation-recombination interactions between an electron and an ionized oxygen vacancy, constituting a photoexcited charge pair, in nanoscale ZnO material systems, especially when considering the effect of electric fields. In this report, we describe the charge-separation kinetics of photoexcited VO 0 defects in ZnO nanowire (NW) field-effect transistor (FET) systems, examined through modulation of the surface electric field of the ZnO NW. We apply oxygen plasma treatment to tailor the doping concentration within the ZnO NWs with the goal of modulating the electric field within their surface space-charge layers. X-ray photoelectron spectroscopy and low-frequency current-noise spectroscopy are applied to identify the change in the density of oxygen-vacancy defects near the NW surface after oxygen plasma treatment. A model describing the initial stage of the photoconductance responses associated with the formation of the photoinduced ionized 1 + state of the oxygen-vacancy defects (VO + ) in the fully depleted ZnO NW FETs in the low-photoconductance regime upon UV excitation is proposed to extract the charge-separation probabilities of the photoexcited electron/VO + pair. Accordingly, the charge-separation probability increases from approximately 0.0012 to 0.042 upon increasing the electric field at the NW surface from approximately 7.5 ×106 to 5.0 ×107 V m-1 . Moreover, we employ modified Braun empirical theory to model the effect of the electric field on the charge-separation behavior of photoexcited electron/VO + pairs in ZnO NWs, obtaining a

  5. SO2 photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

    PubMed Central

    Hattori, Shohei; Schmidt, Johan A.; Johnson, Matthew S.; Danielache, Sebastian O.; Yamada, Akinori; Ueno, Yuichiro; Yoshida, Naohiro

    2013-01-01

    Natural climate variation, such as that caused by volcanoes, is the basis for identifying anthropogenic climate change. However, knowledge of the history of volcanic activity is inadequate, particularly concerning the explosivity of specific events. Some material is deposited in ice cores, but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions. Stable sulfur isotope abundances contain additional information, and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass-independent anomalies in sulfur isotopes in glacial sulfate. We describe a mechanism, photoexcitation of SO2, that links the two, yielding a useful metric of the explosivity of historic volcanic events. A plume model of S(IV) to S(VI) conversion was constructed including photochemistry, entrainment of background air, and sulfate deposition. Isotopologue-specific photoexcitation rates were calculated based on the UV absorption cross-sections of 32SO2, 33SO2, 34SO2, and 36SO2 from 250 to 320 nm. The model shows that UV photoexcitation is enhanced with altitude, whereas mass-dependent oxidation, such as SO2 + OH, is suppressed by in situ plume chemistry, allowing the production and preservation of a mass-independent sulfur isotope anomaly in the sulfate product. The model accounts for the amplitude, phases, and time development of Δ33S/δ34S and Δ36S/Δ33S found in glacial samples. We are able to identify the process controlling mass-independent sulfur isotope anomalies in the modern atmosphere. This mechanism is the basis of identifying the magnitude of historic volcanic events. PMID:23417298

  6. SO2 photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism.

    PubMed

    Hattori, Shohei; Schmidt, Johan A; Johnson, Matthew S; Danielache, Sebastian O; Yamada, Akinori; Ueno, Yuichiro; Yoshida, Naohiro

    2013-10-29

    Natural climate variation, such as that caused by volcanoes, is the basis for identifying anthropogenic climate change. However, knowledge of the history of volcanic activity is inadequate, particularly concerning the explosivity of specific events. Some material is deposited in ice cores, but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions. Stable sulfur isotope abundances contain additional information, and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass-independent anomalies in sulfur isotopes in glacial sulfate. We describe a mechanism, photoexcitation of SO2, that links the two, yielding a useful metric of the explosivity of historic volcanic events. A plume model of S(IV) to S(VI) conversion was constructed including photochemistry, entrainment of background air, and sulfate deposition. Isotopologue-specific photoexcitation rates were calculated based on the UV absorption cross-sections of (32)SO2, (33)SO2, (34)SO2, and (36)SO2 from 250 to 320 nm. The model shows that UV photoexcitation is enhanced with altitude, whereas mass-dependent oxidation, such as SO2 + OH, is suppressed by in situ plume chemistry, allowing the production and preservation of a mass-independent sulfur isotope anomaly in the sulfate product. The model accounts for the amplitude, phases, and time development of Δ(33)S/δ(34)S and Δ(36)S/Δ(33)S found in glacial samples. We are able to identify the process controlling mass-independent sulfur isotope anomalies in the modern atmosphere. This mechanism is the basis of identifying the magnitude of historic volcanic events.

  7. Conformational changes in photoexcited (R)-(+)-1,1'-bi-2-naphthol studied by time-resolved circular dichroism.

    PubMed

    Niezborala, Claire; Hache, François

    2008-09-24

    Conformational changes following photoexcitation of ( R)-(+)-1,1'-bi-2-naphthol are studied with a time-resolved circular dichroism (CD) experiment. Two wavelengths are investigated. For lambda = 237 nm, we observe a bleaching of the ground-state absorption and a transient CD structure. Thanks to a coupled-oscillator calculation, we can attribute this effect to a decrease of the dihedral angle. For lambda = 245 nm, excited-state absorption and CD are observed. All these effects are solvent-dependent. In particular, it is shown that dynamics is slower in a protic solvent, which is attributed to hydrogen-bonding of the hydroxy groups with the solvent.

  8. Ultrafast, correlated multidimensional shell dynamics of neon matrices after photoexcitation of an NO impurity: An MCTDH approach

    NASA Astrophysics Data System (ADS)

    Uranga-Piña, L.; Meier, C.; Rubayo-Soneira, J.

    2012-08-01

    Photoexcitation of NO embedded in rare gas matrices triggers a shock-wave like radial perturbation of the surrounding rare gas atoms. In this Letter, we present quantum dynamical studies of this process, based on a radial shell model. The high-dimensional quantum dynamics is preformed with the multi-configuration time dependent Hartree (MCTDH) method. By comparison with time-dependent Hartree (TDH) results, we study the effects of dynamical correlations. Their inclusion modifies the high-dimensional wavefunction, however, mean values are well described within the TDH ansatz. Finally, pump-probe signals are simulated and shown to lead to small but measurable effects when including the correlations.

  9. Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers

    SciTech Connect

    Cotoros, Ingrid A.

    2008-12-01

    The field of spintronics offers perspectives for seamless integration of coupled and inter-tunable electrical and magnetic properties in a single device. For integration of the spin degree of freedom with current electronic technology, new semiconductors are needed that show electrically-tunable magnetic properties at room temperature and above. Dilute magnetic semiconductors derived from III-V compounds, like GaMnAs and InMnAs, show coupled and tunable magnetic, transport, and optical properties, due to the fact that their ferromagnetism is hole-mediated. These unconventional materials are ideal systems for manipulating the magnetic order by changing the carrier polarization, population density, and energy band distribution of the complementary subsystem of holes. This is the main theme we cover in this thesis. In particular, we develop a unique setup by use of ultraviolet pump, near-infrared probe femtosecond laser pulses, that allows for magneto-optical Kerr effect (MOKE) spectroscopy experiments. We photo-excite transient carriers in our samples, and measure the induced transient magnetization dynamics. One set of experiments performed allowed us to observe for the first time enhancement of the ferromagnetic order in GaMnAs, on an ultrafast time scale of hundreds of picoseconds. The corresponding transient increase of Curie temperature (Tc, the temperature above which a ferromagnetic material loses its permanent magnetism) of about 1 K for our experimental conditions is a very promising result for potential spintronics applications, especially since it is seconded by observation of an ultrafast ferromagnetic to paramagnetic phase transition above Tc. In a different set of experiments, we "write" the magnetization in a particular orientation in the sample plane. Using an ultrafast scheme, we alter the distribution of holes in the system and detect signatures of the particular memory state in the subsequent magnetization dynamics, with unprecedented hundreds of

  10. The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C{sub 60} derivative PCBM

    SciTech Connect

    Brumboiu, Iulia Emilia Eriksson, Olle; Brena, Barbara; Ericsson, Leif; Hansson, Rickard; Moons, Ellen

    2015-02-07

    Fullerenes have been a main focus of scientific research since their discovery due to the interesting possible applications in various fields like organic photovoltaics (OPVs). In particular, the derivative [6,6]-phenyl-C{sub 60}-butyric acid methyl ester (PCBM) is currently one of the most popular choices due to its higher solubility in organic solvents compared to unsubstituted C{sub 60}. One of the central issues in the field of OPVs is device stability, since modules undergo deterioration (losses in efficiency, open circuit voltage, and short circuit current) during operation. In the case of fullerenes, several possibilities have been proposed, including dimerization, oxidation, and impurity related deterioration. We have studied by means of density functional theory the possibility of oxygen adsorption on the C{sub 60} molecular moiety of PCBM. The aim is to provide guidelines for near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) measurements which can probe the presence of atomic or molecular oxygen on the fullerene cage. By analysing several configurations of PCBM with one or more adsorbed oxygen atoms, we show that a joint core level XPS and O1s NEXAFS investigation could be effectively used not only to confirm oxygen adsorption but also to pinpoint the bonding configuration and the nature of the adsorbate.

  11. Exploring large O 1s and N 1s core level shifts due to intermolecular hydrogen bond formation in organic molecules

    NASA Astrophysics Data System (ADS)

    Garcia-Gil, S.; Arnau, A.; Garcia-Lekue, A.

    2013-07-01

    Core level shifts (CLSs) induced by intermolecular hydrogen bond (H-bond) formation are studied with a recent implementation based on density functional theory using pseudopotentials and localized atomic orbitals, as applied to the SIESTA code. By calculating different CLSs for a set of representative simple systems containing O and/or N atoms as proton donors and/or acceptors, we are able to determine the role of the core hole screening, from the difference of CLS values calculated in the final and initial state approximations. Our calculations show that CLSs are dominated by electrostatic effects, and that the final magnitude of the CLSs, which are positive (higher binding energy) for the proton acceptor and negative for the proton donor, can be larger than 1 eV for strong H-bonds. We also find that core hole screening contribution to final CLS absolute values is always negative, thus being responsible for the difference in the magnitude of the CLS of the proton donor and proton acceptor.

  12. The evolution of Ga and As core levels in the formation of Fe/GaAs (001):A high resolution soft x-ray photoelectron spectroscopic study

    SciTech Connect

    Thompson, Jamie; Neal, James; Shen, Tiehan; Morton, Simon; Tobin, James; Waddill, George Dan; Matthew, Jim; Greig, Denis; Hopkinson, Mark

    2008-07-14

    A high resolution soft x-ray photoelectron spectroscopic study of Ga and As 3d core levels has been conducted for Fe/GaAs (001) as a function of Fe thickness. This work has provided unambiguous evidence of substrate disrupting chemical reactions induced by the Fe overlayer--a quantitative analysis of the acquired spectra indicates significantly differing behavior of Ga and As during Fe growth, and our observations have been compared with existing theoretical models. Our results demonstrate that the outdiffusing Ga and As remain largely confined to the interface region, forming a thin intermixed layer. Whereas at low coverages Fe has little influence on the underlying GaAs substrate, the onset of substrate disruption when the Fe thickness reaches 3.5 Angstrom results in major changes in the energy distribution curves (EDCs) of both As and Ga 3d cores. Our quantitative analysis suggests the presence of two additional As environments of metallic character: one bound to the interfacial region and another which, as confirmed by in situ oxidation experiments, surface segregates and persists over a wide range of overlayer thickness. Analysis of the corresponding Ga 3d EDCs found not two, but three additional environments--also metallic in nature. Two of the three are interface resident whereas the third undergoes outdiffusion at low Fe coverages. Based on the variations of the integrated intensities of each component, we present a schematic of the proposed chemical makeup of the Fe/GaAs (001) system.

  13. The evolution of Ga and As core levels in the formation of Fe/GaAs (001): A high resolution soft x-ray photoelectron spectroscopic study

    SciTech Connect

    Thompson, Jamie D. W.; Neal, James R.; Shen, Tiehan H.; Morton, Simon A.; Tobin, James G.; Dan Waddill, G.; Matthew, Jim A. D.; Greig, Denis; Hopkinson, Mark

    2008-07-15

    A high resolution soft x-ray photoelectron spectroscopic study of Ga and As 3d core levels has been conducted for Fe/GaAs (001) as a function of Fe thickness. This work has provided unambiguous evidence of substrate disrupting chemical reactions induced by the Fe overlayer--a quantitative analysis of the acquired spectra indicates significantly differing behavior of Ga and As during Fe growth, and our observations have been compared with existing theoretical models. Our results demonstrate that the outdiffusing Ga and As remain largely confined to the interface region, forming a thin intermixed layer. Whereas at low coverages Fe has little influence on the underlying GaAs substrate, the onset of substrate disruption when the Fe thickness reaches 3.5 A results in major changes in the energy distribution curves (EDCs) of both As and Ga 3d cores. Our quantitative analysis suggests the presence of two additional As environments of metallic character: one bound to the interfacial region and another which, as confirmed by in situ oxidation experiments, surface segregates and persists over a wide range of overlayer thickness. Analysis of the corresponding Ga 3d EDCs found not two, but three additional environments--also metallic in nature. Two of the three are interface resident whereas the third undergoes outdiffusion at low Fe coverages. Based on the variations of the integrated intensities of each component, we present a schematic of the proposed chemical makeup of the Fe/GaAs (001) system.

  14. Layer-by-layer resolved core-level shifts in CaF2 and SrF2 on Si(111): Theory and experiment

    NASA Astrophysics Data System (ADS)

    Rotenberg, Eli; Denlinger, J. D.; Leskovar, M.; Hessinger, U.; Olmstead, Marjorie A.

    1994-10-01

    Using x-ray-photoelectron spectroscopy and Auger-electron spectroscopy, we have resolved surface, bulk, and interface Ca and F core-level emission in thin films (3-8 triple layers) of CaF2 and SrF2 on Si(111). We confirmed these assignments using x-ray-photoelectron diffraction (XPD) and surface modification. XPD was also used to identify the growth modes of the films as being either laminar or layer plus islands; in the latter case we have resolved buried and uncovered interface F and Ca/Sr emission. We compare the observed energy differences between surface, bulk, and interface emission to theoretical estimates of the extra-atomic contributions to emission energies. We find excellent agreement considering only the Madelung (electrostatic) potentials for the initial-state contribution and polarization response for the final-state contribution, including the effect of tetragonal strain. Small discrepancies for emission from metal atoms bonded to the Si substrate are interpreted in terms of chemical shifts.

  15. Synthesis Dependent Core Level Binding Energy Shift in the Oxidation State of Platinum Coated on Ceria–Titania and its Effect on Catalytic Decomposition of Methanol

    SciTech Connect

    Karakoti, A. S.; King, Jessica; Vincent, Abhilash; Seal, Sudipta

    2010-11-20

    Synergistic interaction of catalyst and support has attracted the interest of the catalytic community for several decades. The decomposition/oxidation of alcohols for the production of hydrogen as a source of fuel requires such support catalyst interaction. Recent studies have suggested the active role of oxide based supports on the catalytic ability of noble metals such as gold, platinum and palladium. Herein, we report the effect of synthesis technique on the catalytic activity of platinum coated on mixed ceria-titania support system. Wet impregnation technique followed by calcination was compared with the chemical reduction of platinum during the coating over oxide support. Methanol decomposition studied using an in-house built catalytic reactor coupled to a mass spectrometer showed that catalyst prepared by thermal reduction of platinum demonstrated better catalytic ability than the catalyst prepared by chemical reduction of platinum. Transmission electron microscopy revealed that the size of both platinum and ceria-titania particles remained unchanged, while the X-ray photoelectron spectroscopy (XPS) revealed that the oxidation state of platinum was modified by different coating procedures. A shift in the core level binding energy of the Pt 4f towards lower binding energy was observed with chemical reduction. Based on the XPS data it was found that platinum (on ceria-titania supports) in mixed oxidation state outperformed the Pt in reduced metallic state. Results from catalysis and in situ Fourier transform infra red spectroscopy are presented and discussed.

  16. UVA-visible photo-excitation of guanine radical cations produces sugar radicals in DNA and model structures

    PubMed Central

    Adhikary, Amitava; Malkhasian, Aramice Y. S.; Collins, Sean; Koppen, Jessica; Becker, David; Sevilla, Michael D.

    2005-01-01

    This work presents evidence that photo-excitation of guanine radical cations results in high yields of deoxyribose sugar radicals in DNA, guanine deoxyribonucleosides and deoxyribonucleotides. In dsDNA at low temperatures, formation of C1′• is observed from photo-excitation of G•+ in the 310–480 nm range with no C1′• formation observed ≥520 nm. Illumination of guanine radical cations in 2′dG, 3′-dGMP and 5′-dGMP in aqueous LiCl glasses at 143 K is found to result in remarkably high yields (∼85–95%) of sugar radicals, namely C1′•, C3′• and C5′•. The amount of each of the sugar radicals formed varies dramatically with compound structure and temperature of illumination. Radical assignments were confirmed using selective deuteration at C5′ or C3′ in 2′-dG and at C8 in all the guanine nucleosides/tides. Studies of the effect of temperature, pH, and wavelength of excitation provide important information about the mechanism of formation of these sugar radicals. Time-dependent density functional theory calculations verify that specific excited states in G•+ show considerable hole delocalization into the sugar structure, in accord with our proposed mechanism of action, namely deprotonation from the sugar moiety of the excited molecular radical cation. PMID:16204456

  17. A two-step photoexcitation system for photocatalytic water splitting into hydrogen and oxygen under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Abe, Ryu

    2011-10-01

    The developments of water-splitting systems that can efficiently use visible light have been a major challenge for many years in order to realize efficient conversion of solar light. We have developed a new type of photocatalysis system that can split water into H2 and O2 under visible light irradiation, which was inspired by the two-step photoexcitation (Zscheme) mechanism of natural photosynthesis in green plants. In this system, the water splitting reaction is broken up into two stages: one for H2 evolution and the other for O2 evolution; these are combined by using a shuttle redox couple (Red/Ox) in the solution. The introduction of a Z-scheme mechanism reduces the energy required to drive each photocatalysis process, extending the usable wavelengths significantly (~460 nm for H2 evolution and ~600 nm for O2evolution) from that in conventional water splitting systems (~460 nm) based on one-step photoexcitation in single semiconductor material.

  18. Observation of photoexcitation of Fe-oxide grown on TiO2(100) by visible light irradiation

    NASA Astrophysics Data System (ADS)

    Kawauchi, Taizo; Nagatsuka, Naoki; Fukutani, Katsuyuki

    2016-12-01

    Electronic excitation of materials is of fundamental and technological importance and interest in terms of photoinduced phase transition, photovoltaics, and photocatalysis. In the present study, photoexcitation of Fe2 O 3 epitaxially grown on rutile TiO2(100) was investigated with conversion electron Mössbauer spectroscopy (CEMS) under dominantly visible-light irradiation. 57Fe was deposited on the substrate at a substrate temperature of 973 K, and the resulting film was characterized by RHEED and XPS. After deposition of Fe on TiO2(100), it was found that Fe was oxidized to Fe 3+, and the structure was analyzed to be the rhombohedral phase of Fe2 O 3. While the CEMS spectrum without light irradiation showed a quadrupole splitting of 0.80 mm/s with an isomer shift of +0.25 mm/s, an additional component with a quadrupole splitting of 0.85 and an isomer shift of +0.67 mm/s was observed under light irradiation. The latter component corresponds to a reduced state of Fe at the octahedral site surrounded by oxygen atoms. The lifetime of this photoexcited state is discussed.

  19. Femtosecond transient infrared and stimulated Raman spectroscopy shed light on the relaxation mechanisms of photo-excited peridinin

    NASA Astrophysics Data System (ADS)

    Di Donato, Mariangela; Ragnoni, Elena; Lapini, Andrea; Foggi, Paolo; Hiller, Roger G.; Righini, Roberto

    2015-06-01

    By means of one- and two-dimensional transient infrared spectroscopy and femtosecond stimulated Raman spectroscopy, we investigated the excited state dynamics of peridinin, a carbonyl carotenoid occurring in natural light harvesting complexes. The presence of singly and doubly excited states, as well as of an intramolecular charge transfer (ICT) state, makes the behavior of carbonyl carotenoids in the excited state very complex. In this work, we investigated by time resolved spectroscopy the relaxation of photo-excited peridinin in solvents of different polarities and as a function of the excitation wavelength. Our experimental results show that a characteristic pattern of one- and two-dimensional infrared bands in the C=C stretching region allows monitoring the relaxation pathway. In polar solvents, moderate distortions of the molecular geometry cause a variation of the single/double carbon bond character, so that the partially ionic ICT state is largely stabilized by the solvent reorganization. After vertical photoexcitation at 400 nm of the S2 state, the off-equilibrium population moves to the S1 state with ca. 175 fs time constant; from there, in less than 5 ps, the non-Franck Condon ICT state is reached, and finally, the ground state is recovered in 70 ps. That the relevant excited state dynamics takes place far from the Franck Condon region is demonstrated by its noticeable dependence on the excitation wavelength.

  20. Femtosecond transient infrared and stimulated Raman spectroscopy shed light on the relaxation mechanisms of photo-excited peridinin.

    PubMed

    Di Donato, Mariangela; Ragnoni, Elena; Lapini, Andrea; Foggi, Paolo; Hiller, Roger G; Righini, Roberto

    2015-06-07

    By means of one- and two-dimensional transient infrared spectroscopy and femtosecond stimulated Raman spectroscopy, we investigated the excited state dynamics of peridinin, a carbonyl carotenoid occurring in natural light harvesting complexes. The presence of singly and doubly excited states, as well as of an intramolecular charge transfer (ICT) state, makes the behavior of carbonyl carotenoids in the excited state very complex. In this work, we investigated by time resolved spectroscopy the relaxation of photo-excited peridinin in solvents of different polarities and as a function of the excitation wavelength. Our experimental results show that a characteristic pattern of one- and two-dimensional infrared bands in the C=C stretching region allows monitoring the relaxation pathway. In polar solvents, moderate distortions of the molecular geometry cause a variation of the single/double carbon bond character, so that the partially ionic ICT state is largely stabilized by the solvent reorganization. After vertical photoexcitation at 400 nm of the S2 state, the off-equilibrium population moves to the S1 state with ca. 175 fs time constant; from there, in less than 5 ps, the non-Franck Condon ICT state is reached, and finally, the ground state is recovered in 70 ps. That the relevant excited state dynamics takes place far from the Franck Condon region is demonstrated by its noticeable dependence on the excitation wavelength.

  1. Equilibration kinetics in isolated and membrane-bound photosynthetic reaction centers upon illumination: a method to determine the photoexcitation rate.

    PubMed

    Manzo, Anthony J; Goushcha, Alexander O; Barabash, Yuri M; Kharkyanen, Valery N; Scott, Gary W

    2009-07-01

    Kinetics of electron transfer, following variation of actinic light intensity, for photosynthetic reaction centers (RCs) of purple bacteria (isolated and membrane-bound) were analyzed by measuring absorbance changes in the primary photoelectron donor absorption band at 865 nm. The bleaching of the primary photoelectron donor absorption band in RCs, following a sudden increase of illumination from the dark to an actinic light intensity of I(exp), obeys a simple exponential law with the rate constant alphaI(exp) + k(rec), in which alpha is a parameter relating the light intensity, measured in mW/cm(2), to a corresponding theoretical rate in units of reciprocal seconds, and k(rec) is the effective rate constant of the charge recombination in the photosynthetic RCs. In this work, a method for determining the alpha parameter value is developed and experimentally verified for isolated and membrane-bound RCs, allowing for rigorous modeling of RC macromolecule dynamics under varied photoexcitation conditions. Such modeling is necessary for RCs due to alterations of the forward photoexcitation rates and relaxation rates caused by illumination history and intramolecular structural dynamics effects. It is demonstrated that the classical Bouguer-Lambert-Beer formalism can be applied for the samples with relatively low scattering, which is not necessarily the case with strongly scattering media or high light intensity excitation.

  2. Deep smarts.

    PubMed

    Leonard, Dorothy; Swap, Walter

    2004-09-01

    When a person sizes up a complex situation and rapidly comes to a decision that proves to be not just good but brilliant, you think, "That was smart." After you watch him do this a few times, you realize you're in the presence of something special. It's not raw brainpower, though that helps. It's not emotional intelligence, either, though that, too, is often involved. It's deep smarts. Deep smarts are not philosophical--they're not"wisdom" in that sense, but they're as close to wisdom as business gets. You see them in the manager who understands when and how to move into a new international market, in the executive who knows just what kind of talk to give when her organization is in crisis, in the technician who can track a product failure back to an interaction between independently produced elements. These are people whose knowledge would be hard to purchase on the open market. Their insight is based on know-how more than on know-what; it comprises a system view as well as expertise in individual areas. Because deep smarts are experienced based and often context specific, they can't be produced overnight or readily imported into an organization. It takes years for an individual to develop them--and no time at all for an organization to lose them when a valued veteran walks out the door. They can be taught, however, with the right techniques. Drawing on their forthcoming book Deep Smarts, Dorothy Leonard and Walter Swap say the best way to transfer such expertise to novices--and, on a larger scale, to make individual knowledge institutional--isn't through PowerPoint slides, a Web site of best practices, online training, project reports, or lectures. Rather, the sage needs to teach the neophyte individually how to draw wisdom from experience. Companies have to be willing to dedicate time and effort to such extensive training, but the investment more than pays for itself.

  3. Deep blast

    NASA Astrophysics Data System (ADS)

    From southern New Mexico to the Great Slave Lake of Canada, scientists from the United States and Canada recently detonated 10 underground chemical explosions to generate a clearer picture of the Earth's crust and upper mantle. Called Project Deep Probe, the experiment is designed to see through the crust and into the upper mantle to a depth of 300 miles.In the United States, Earth scientists from Rice University, Purdue University, and the University of Oregon are participating in the project. “Researchers hope to get a picture of the upper mantle beneath the Rocky Mountains and the Colorado Plateau, to understand the role the mantle played in formation and uplift,” says Alan Levander of Rice. To enhance that “picture,” 750 portable seismographs were placed along a roughly north-south line extending from Crownpoint, New Mexico to Edmonton, Alberta. The seismic recordings will be used to enhance weak seismic waves that penetrated the upper mantle.

  4. The requisite electronic structure theory to describe photoexcited nonadiabatic dynamics: nonadiabatic derivative couplings and diabatic electronic couplings.

    PubMed

    Subotnik, Joseph E; Alguire, Ethan C; Ou, Qi; Landry, Brian R; Fatehi, Shervin

    2015-05-19

    Electronically photoexcited dynamics are complicated because there are so many different relaxation pathways: fluorescence, phosphorescence, radiationless decay, electon transfer, etc. In practice, to model photoexcited systems is a very difficult enterprise, requiring accurate and very efficient tools in both electronic structure theory and nonadiabatic chemical dynamics. Moreover, these theoretical tools are not traditional tools. On the one hand, the electronic structure tools involve couplings between electonic states (rather than typical single state energies and gradients). On the other hand, the dynamics tools involve propagating nuclei on multiple potential energy surfaces (rather than the usual ground state dynamics). In this Account, we review recent developments in electronic structure theory as directly applicable for modeling photoexcited systems. In particular, we focus on how one may evaluate the couplings between two different electronic states. These couplings come in two flavors. If we order states energetically, the resulting adiabatic states are coupled via derivative couplings. Derivative couplings capture how electronic wave functions change as a function of nuclear geometry and can usually be calculated with straightforward tools from analytic gradient theory. One nuance arises, however, in the context of time-dependent density functional theory (TD-DFT): how do we evaluate derivative couplings between TD-DFT excited states (which are tricky, because no wave function is available)? This conundrum was recently solved, and we review the solution below. We also discuss the solution to a second, pesky problem of origin dependence, whereby the derivative couplings do not (strictly) satisfy translation variance, which can lead to a lack of momentum conservation. Apart from adiabatic states, if we order states according to their electronic character, the resulting diabatic states are coupled via electronic or diabatic couplings. The couplings

  5. Manifestation of screening effects and A-O covalency in the core level spectra of A site elements in the ABO3 structure of Ca1-xSrxRuO3

    NASA Astrophysics Data System (ADS)

    Singh, Ravi Shankar; Maiti, Kalobaran

    2007-08-01

    We investigate the evolution of Ca2p and Sr3d core level spectra in Ca1-xSrxRuO3 using photoemission spectroscopy. Core level spectra in this system exhibit multiple features and unusual evolution with the composition and temperatures. Analysis of the core level spectra in conjunction with the band structure results indicates final state effects due to different core hole screening channels. Such screening in the photoemission final states can be attributed to the large A-O covalency in these systems. Changes in the core level spectra with temperature and composition suggest significant modification in A-O (A=Ca/Sr) covalency in Ca-dominated samples, which gradually reduces with the increase in Sr content and becomes insignificant in SrRuO3 . This study thus provides a direct evidence of cation-oxygen covalency and its evolution with temperature, which may be useful in understanding the unusual ground state properties of these materials.

  6. Overlapping resonances interference-induced transparency: the S0 → S2/S1 photoexcitation spectrum of pyrazine.

    PubMed

    Grinev, Timur; Shapiro, Moshe; Brumer, Paul

    2012-09-07

    The phenomenon of "overlapping resonances interference-induced transparency" (ORIT) is introduced and studied in detail for the S(0) → S(2)/S(1) photoexcitation of cold pyrazine (C(4)H(4)N(2)). In ORIT, a molecule becomes transparent at specific wavelengths due to interferences between envelopes of spectral lines displaying overlapping resonances. An example is the S(2) ↔ S(1) internal conversion in pyrazine where destructive interference between overlapping resonances causes the S(0) → S(2)/S(1) light absorption to disappear at certain wavelengths. ORIT may be of practical importance in multi-component mixtures where it would allow for the selective excitation of some molecules in preference to others. Interference-induced cross section enhancement is also shown.

  7. Relaxation Dynamics in Photoexcited Chiral Molecules Studied by Time-Resolved Photoelectron Circular Dichroism: Toward Chiral Femtochemistry

    PubMed Central

    2016-01-01

    Unravelling the main initial dynamics responsible for chiral recognition is a key step in the understanding of many biological processes. However, this challenging task requires a sensitive enantiospecific probe to investigate molecular dynamics on their natural femtosecond time scale. Here we show that, in the gas phase, the ultrafast relaxation dynamics of photoexcited chiral molecules can be tracked by recording time-resolved photoelectron circular dichroism (TR-PECD) resulting from the photoionization by a circularly polarized probe pulse. A large forward–backward asymmetry along the probe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump–probe delay reveals ultrafast dynamics that are inaccessible in the angle-integrated photoelectron spectrum or via the usual electron emission anisotropy parameter (β). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamics in chiral systems. PMID:27786493

  8. Photoexcitation and ionization in carbon dioxide - Theoretical studies in the separated-channel static-exchange approximation

    NASA Technical Reports Server (NTRS)

    Padial, N.; Csanak, G.; Mckoy, B. V.; Langhoff, P. W.

    1981-01-01

    Vertical-electronic static-exchange photoexcitation and ionization cross sections are reported which provide a first approximation to the complete dipole spectrum of CO2. Separated-channel static-exchange calculations of vertical-electronic transition energies and oscillator strengths, and Stieltjes-Chebyshev moment methods were used in the development. Detailed comparisons were made of the static-exchange excitation and ionization spectra with photoabsorption, electron-impact excitation, and quantum-defect estimates of discrete transition energies and intensities, and with partial-channel photoionization cross sections obtained from fluorescence measurements and from tunable-source and (e, 2e) photoelectron spectroscopy. Results show that the separate-channel static-exchange approximation is generally satisfactory in CO2.

  9. Indirect IUE observation of O VI from photoexcited fluorescence lines of Fe II, present in the spectrum of RR Telescopii

    NASA Technical Reports Server (NTRS)

    Johansson, Sveneric

    1988-01-01

    A new, highly excited level of Fe II at 13.7 eV has been established by means of six lines in the laboratory spectrum below 2000 A. Confirming transitions appear in the infrared region. Four of the ultraviolet lines coincide with previously unidentified lines in the IUE spectrum of RR Tel reported by Penston et al. in 1983. One of the remaining UV lines coincides with the resonance line of O VI at 1032 A, outside the range of the IUE. This suggests that the new FE II level is selectively photoexcited by O VI in RR Tel, resulting in the strong fluorescence lines observed. This case of a Bowen mechanism provides an indirect observation of O VI, important for diagnostics of, e.g., symbiotic stars.

  10. Model of the photoexcitation processes of a two-level molecule coherently coupled to an optical antenna.

    PubMed

    Nakatani, Masatoshi; Nobuhiro, Atsushi; Yokoshi, Nobuhiko; Ishihara, Hajime

    2013-06-07

    We theoretically investigate photoexcitation processes of a two-level molecular system coherently coupled with an antenna system having a significant dissipation. The auxiliary antenna enables the whole system to exhibit anomalous optical effects by controlling the coupling with the molecule. For example, in the weak excitation regime, the quantum interference yields a distinctive energy transparency through the antenna, which drastically reduces the energy dissipation. On the other hand, in the strong excitation regime, a population inversion of the two-level molecule appears due to the nonlinear effect. Both phenomena can be explained by regarding the antenna and molecule as one quantum-mechanically coupled system. Such an approach drives further research to exploit the full potential of the coupled systems.

  11. Zero-field magnetic resonance of the photo-excited triplet state of pentacene at room temperature

    NASA Astrophysics Data System (ADS)

    Yang, Tran-Chin; Sloop, David J.; Weissman, S. I.; Lin, Tien-Sung

    2000-12-01

    The pulsed EPR free induction decay (FID) signals of the photo-excited pentacene triplet state are reported for three mixed crystals at room temperature: pentacene-h14 in p-terphenyl, pentacene-h14 in benzoic acid, and pentacene-d14 in p-terphenyl. The recorded FID signals have relatively long decay times of about four microseconds, presumably due to the reduced hyperfine interactions in the zero magnetic field. The time domain FID signals transform to spectral components typically narrower than 500 kHz, allowing us to determine the pentacene triplet zero field splitting parameters to better accuracy than previously reported. Further, a new experimental technique using the high speed magnetic field jumping capability enables us to examine the anisotropic hyperfine and quadrupole interactions.

  12. A photoexcited switchable perfect metamaterial absorber/reflector with polarization-independent and wide-angle for terahertz waves

    NASA Astrophysics Data System (ADS)

    Cheng, Yongzhi; Gong, Rongzhou; Zhao, Jingcheng

    2016-12-01

    We present a photoexcited switchable perfect metamaterial absorber/reflector for terahertz waves. The switchable absorber/reflector is based on a cross-shaped structure (CSS) integrated semiconductor photoconductive silicon (Si). The electric response property of the photoconductive Si can be easily modified through a pump optical beam. The conductivity of Si pads filled in the gap of CSS is tuned efficiently through the incident pump optical beam with different power, resulting in the modulation of absorption magnitude from 0 to 100% at the fixed operation frequency. Thus, the switch ability of the perfect absorber/reflector can be easily realized. Furthermore, the proposed design is polarization insensitive and operated well at wide incidence angles for both TE and TM waves.

  13. Time-dependent transition density matrix for visualizing charge-transfer excitations in photoexcited organic donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Li, Yonghui; Ullrich, Carsten

    2013-03-01

    The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. This work is supported by NSF Grant DMR-1005651

  14. Deep breathing after surgery

    MedlinePlus

    ... page: //medlineplus.gov/ency/patientinstructions/000440.htm Deep breathing after surgery To use the sharing features on ... way to do so is by doing deep breathing exercises. Deep breathing keeps your lungs well-inflated ...

  15. Preventing Deep Vein Thrombosis

    MedlinePlus

    ... Education & Events Advocacy For Patients About ACOG Preventing Deep Vein Thrombosis Home For Patients Search FAQs Preventing ... Vein Thrombosis FAQ174, August 2011 PDF Format Preventing Deep Vein Thrombosis Women's Health What is deep vein ...

  16. Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

    NASA Astrophysics Data System (ADS)

    Lucovsky, Gerry; Wu, Kun; Pappas, Brian; Whitten, Jerry

    2013-04-01

    Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9>=n>3, and (TiO2)x(HfO2)1-x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii} local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding

  17. H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

    PubMed Central

    Silva, R.; Gichuhi, W. K.; Huang, C.; Doyle, M. B.; Kislov, V. V.; Mebel, A. M.; Suits, A. G.

    2008-01-01

    We present an experimental investigation of the UV photochemistry of diacetylene under collisionless conditions. The H loss channel is studied using DC slice ion imaging with two-color reduced-Doppler detection at 243 nm and 212 nm. The photochemistry is further studied deep in the vacuum UV, that is, at Lyman-alpha (121.6 nm). Translational energy distributions for the H + C4H product arising from dissociation of C4H2 after excitation at 243, 212, and 121.6 nm show an isotropic angular distribution and characteristic translational energy profile suggesting statistical dissociation from the ground state or possibly from a low-lying triplet state. From these distributions, a two-photon dissociation process is inferred at 243 nm and 212 nm, whereas at 121.6 nm, a one-photon dissociation process prevails. The results are interpreted with the aid of ab initio calculations on the reaction pathways and statistical calculations of the dissociation rates and product branching. In a second series of experiments, nanosecond time-resolved phototionization measurements yield a direct determination of the lifetime of metastable triplet diacetylene under collisionless conditions, as well as its dependence on excitation energy. The observed submicrosecond lifetimes suggest that reactions of metastable diacetylene are likely to be less important in Titan's atmosphere than previously believed. PMID:18697925

  18. Terahertz dielectric response of photoexcited carriers in Si revealed via single-shot optical-pump and terahertz-probe spectroscopy

    SciTech Connect

    Minami, Yasuo; Horiuchi, Kohei; Masuda, Kaisei; Takeda, Jun; Katayama, Ikufumi

    2015-10-26

    We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay time between the pump and THz pulses, thereby sufficiently extending the time interval between the pump pulses. As a result, we can accurately measure the dielectric properties of materials, while avoiding artifacts in the response caused by the accumulation of long-lived photoexcited carriers. Using our single-shot scheme, the transmittance of a Si plate was measured in the range of 0.5–2.5 THz with different pump fluences. Based on a Drude model analysis, the optically induced complex dielectric constant, plasma frequency, and damping rate in the THz region were quantitatively evaluated.

  19. Moving solvated electrons with light: Nonadiabatic mixed quantum/classical molecular dynamics simulations of the relocalization of photoexcited solvated electrons in tetrahydrofuran (THF)

    SciTech Connect

    Bedard-Hearn, Michael J.; Larsen, Ross E.; Schwartz, Benjamin J.

    2006-11-21

    Motivated by recent ultrafast spectroscopic experiments [Martini et al., Science 293, 462 (2001)], which suggest that photoexcited solvated electrons in tetrahydrofuran (THF) can relocalize (that is, return to equilibrium in solvent cavities far from where they started), we performed a series of nonequilibrium, nonadiabatic, mixed quantum/classical molecular dynamics simulations that mimic one-photon excitation of the THF-solvated electron. We find that as photoexcited THF-solvated electrons relax to their ground states either by continuous mixing from the excited state or via nonadiabatic transitions, {approx}30% of them relocalize into cavities that can be over 1 nm away from where they originated, in close agreement with the experiments. A detailed investigation shows that the ability of excited THF-solvated electrons to undergo photoinduced relocalization stems from the existence of preexisting cavity traps that are an intrinsic part of the structure of liquid THF. This explains why solvated electrons can undergo photoinduced relocalization in solvents like THF but not in solvents like water, which lack the preexisting traps necessary to stabilize the excited electron in other places in the fluid. We also find that even when they do not ultimately relocalize, photoexcited solvated electrons in THF temporarily visit other sites in the fluid, explaining why the photoexcitation of THF-solvated electrons is so efficient at promoting recombination with nearby scavengers. Overall, our study shows that the defining characteristic of a liquid that permits the photoassisted relocalization of solvated electrons is the existence of nascent cavities that are attractive to an excess electron; we propose that other such liquids can be found from classical computer simulations or neutron diffraction experiments.

  20. Time Evolution of Charge Carriers & Phonons after Photo-Excitation by an Ultra-Short Light Pulse in Bulk Germanium

    NASA Astrophysics Data System (ADS)

    Fahy, Stephen; Murphy-Armando, Felipe; Trigo, Mariano; Savic, Ivana; Murray, Eamonn; Reis, David

    We have calculated the time-evolution of carriers and generated phonons in Ge after ultrafast photo-excitation above the direct band-gap. The relevant electron-phonon and anharmonic phonon scattering rates are obtained from first-principles electronic structure calculations. Measurements of the x-ray diffuse scattering after excitation near the L point in the Brillouin zone find a relatively slow (5 ps, compared to the typical electron-phonon energy relaxation of the Gamma-L phonon) increase of the phonon population. We find this is due to emission caused by the scattering of electrons between the Delta and L valleys, after the initial depopulation of the Gamma valley. The relative slowness of this process is due to a combination of causes: (i) the finite time for the initial depopulation of the conduction Gamma valley; (ii) the associated electron-phonon coupling is relatively weaker (compared to Gamma-L, Gamma-Delta and Delta-Delta couplings) ; (iii) the TA associated phonon has a long lifetime and (iv) the depopulation of the Delta valley suppresses the phonon emission. Supported by Science Foundation Ireland, Grant 12/1A/1601.

  1. Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy.

    PubMed

    Santomauro, Fabio G; Grilj, Jakob; Mewes, Lars; Nedelcu, Georgian; Yakunin, Sergii; Rossi, Thomas; Capano, Gloria; Al Haddad, André; Budarz, James; Kinschel, Dominik; Ferreira, Dario S; Rossi, Giacomo; Gutierrez Tovar, Mario; Grolimund, Daniel; Samson, Valerie; Nachtegaal, Maarten; Smolentsev, Grigory; Kovalenko, Maksym V; Chergui, Majed

    2017-07-01

    We report on an element-selective study of the fate of charge carriers in photoexcited inorganic CsPbBr3 and CsPb(ClBr)3 perovskite nanocrystals in toluene solutions using time-resolved X-ray absorption spectroscopy with 80 ps time resolution. Probing the Br K-edge, the Pb L3-edge, and the Cs L2-edge, we find that holes in the valence band are localized at Br atoms, forming small polarons, while electrons appear as delocalized in the conduction band. No signature of either electronic or structural changes is observed at the Cs L2-edge. The results at the Br and Pb edges suggest the existence of a weakly localized exciton, while the absence of signatures at the Cs edge indicates that the Cs(+) cation plays no role in the charge transport, at least beyond 80 ps. This first, time-resolved element-specific study of perovskites helps understand the rather modest charge carrier mobilities in these materials.

  2. Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy

    PubMed Central

    Santomauro, Fabio G.; Grilj, Jakob; Mewes, Lars; Nedelcu, Georgian; Yakunin, Sergii; Rossi, Thomas; Capano, Gloria; Al Haddad, André; Budarz, James; Kinschel, Dominik; Ferreira, Dario S.; Rossi, Giacomo; Gutierrez Tovar, Mario; Grolimund, Daniel; Samson, Valerie; Nachtegaal, Maarten; Smolentsev, Grigory; Kovalenko, Maksym V.; Chergui, Majed

    2016-01-01

    We report on an element-selective study of the fate of charge carriers in photoexcited inorganic CsPbBr3 and CsPb(ClBr)3 perovskite nanocrystals in toluene solutions using time-resolved X-ray absorption spectroscopy with 80 ps time resolution. Probing the Br K-edge, the Pb L3-edge, and the Cs L2-edge, we find that holes in the valence band are localized at Br atoms, forming small polarons, while electrons appear as delocalized in the conduction band. No signature of either electronic or structural changes is observed at the Cs L2-edge. The results at the Br and Pb edges suggest the existence of a weakly localized exciton, while the absence of signatures at the Cs edge indicates that the Cs+ cation plays no role in the charge transport, at least beyond 80 ps. This first, time-resolved element-specific study of perovskites helps understand the rather modest charge carrier mobilities in these materials. PMID:28083541

  3. SWCNT Photocatalyst for Hydrogen Production from Water upon Photoexcitation of (8, 3) SWCNT at 680-nm Light

    NASA Astrophysics Data System (ADS)

    Murakami, Noritake; Tango, Yuto; Miyake, Hideaki; Tajima, Tomoyuki; Nishina, Yuta; Kurashige, Wataru; Negishi, Yuichi; Takaguchi, Yutaka

    2017-03-01

    Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100 meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QY = 0.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT.

  4. Spatially Resolved Photoexcited Charge-Carrier Dynamics in Phase-Engineered Monolayer MoS2

    SciTech Connect

    Yamaguchi, Hisato; Blancon, Jean-Christophe; Kappera, Rajesh; Lei, Sidong; Najmaei, Sina; Mangum, Benjamin D.; Gupta, Gautam; Ajayan, Pulickel M.; Lou, Jun; Chhowalla, Manish; Crochet, Jared J.; Mohite, Aditya D.

    2014-12-18

    A fundamental understanding of the intrinsic optoelectronic properties of atomically thin transition metal dichalcogenides (TMDs) is crucial for its integration into high performance semiconductor devices. We investigate the transport properties of chemical vapor deposition (CVD) grown monolayer molybdenum disulfide (MoS2) under photo-excitation using correlated scanning photocurrent microscopy and photoluminescence imaging. We examined the effect of local phase transformation underneath the metal electrodes on the generation of photocurrent across the channel length with diffraction-limited spatial resolution. While maximum photocurrent generation occurs at the Schottky contacts of semiconducting (2H-phase) MoS2, after the metallic phase transformation (1T-phase), the photocurrent peak is observed towards the center of the device channel, suggesting a strong reduction of native Schottky barriers. Analysis using the bias and position dependence of the photocurrent indicates that the Schottky barrier heights are few meV for 1T- and ~200 meV for 2H-contacted devices. We also demonstrate that a reduction of native Schottky barriers in a 1T device enhances the photo responsivity by more than one order of magnitude, a crucial parameter in achieving high performance optoelectronic devices. The obtained results pave a pathway for the fundamental understanding of intrinsic optoelectronic properties of atomically thin TMDs where Ohmic contacts are necessary for achieving high efficiency devices with low power consumption.

  5. Manipulation of an Innate Escape Response in Drosophila: Photoexcitation of acj6 Neurons Induces the Escape Response

    PubMed Central

    Manoli, Devanand S.; Zhang, Feng; Deisseroth, Karl; Baker, Bruce S.; Scott, Matthew P.

    2009-01-01

    Background The genetic analysis of behavior in Drosophila melanogaster has linked genes controlling neuronal connectivity and physiology to specific neuronal circuits underlying a variety of innate behaviors. We investigated the circuitry underlying the adult startle response, using photoexcitation of neurons that produce the abnormal chemosensory jump 6 (acj6) transcription factor. This transcription factor has previously been shown to play a role in neuronal pathfinding and neurotransmitter modality, but the role of acj6 neurons in the adult startle response was largely unknown. Principal Findings We show that the activity of these neurons is necessary for a wild-type startle response and that excitation is sufficient to generate a synthetic escape response. Further, we show that this synthetic response is still sensitive to the dose of acj6 suggesting that that acj6 mutation alters neuronal activity as well as connectivity and neurotransmitter production. Results/Significance These results extend the understanding of the role of acj6 and of the adult startle response in general. They also demonstrate the usefulness of activity-dependent characterization of neuronal circuits underlying innate behaviors in Drosophila, and the utility of integrating genetic analysis into modern circuit analysis techniques. PMID:19340304

  6. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

    2016-02-01

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

  7. (2)H-decoupling-accelerated (1)H spin diffusion in dynamic nuclear polarization with photoexcited triplet electrons.

    PubMed

    Negoro, M; Nakayama, K; Tateishi, K; Kagawa, A; Takeda, K; Kitagawa, M

    2010-10-21

    In dynamic nuclear polarization (DNP) experiments applied to organic solids for creating nonequilibrium, high (1)H spin polarization, an efficient buildup of (1)H polarization is attained by partially deuterating the material of interest with an appropriate (1)H concentration. In such a dilute (1)H spin system, it is shown that the (1)H spin diffusion rate and thereby the buildup efficiency of (1)H polarization can further be enhanced by continually applying radiofrequency irradiation for deuterium decoupling during the DNP process. As experimentally confirmed in this work, the electron spin polarization of the photoexcited triplet state is mainly transferred only to those (1)H spins, which are in the vicinity of the electron spins, and (1)H spin diffusion transports the localized (1)H polarization over the whole sample volume. The (1)H spin diffusion coefficients are estimated from DNP repetition interval dependence of the initial buildup rate of (1)H polarization, and the result indicates that the spin diffusion coefficient is enhanced by a factor of 2 compared to that without (2)H decoupling.

  8. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    PubMed Central

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

    2016-01-01

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems. PMID:26915398

  9. SWCNT Photocatalyst for Hydrogen Production from Water upon Photoexcitation of (8, 3) SWCNT at 680-nm Light

    PubMed Central

    Murakami, Noritake; Tango, Yuto; Miyake, Hideaki; Tajima, Tomoyuki; Nishina, Yuta; Kurashige, Wataru; Negishi, Yuichi; Takaguchi, Yutaka

    2017-01-01

    Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100 meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QY = 0.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT. PMID:28262708

  10. A photoexcited broadband switchable metamaterial absorber with polarization-insensitive and wide-angle absorption for terahertz waves

    NASA Astrophysics Data System (ADS)

    Cheng, Yongzhi; Gong, Rongzhou; Cheng, Zhengze

    2016-02-01

    We present a design and numerical study of a polarization-insensitive and wide-angle photoexcited broadband switchable metamaterial absorber (MMA) in the terahertz (THz) regime. The switchable MMA comprises a periodic array of dielectric substrate sandwiched with metallic four-splits-ring resonator (FSRR) structure and continuous metallic film. Filling the gap between the SRRs with a photoconductive semiconductor (silicon, Si), leading to easy modification of its electromagnetic (EM) response through a pump beam. The conductivity of photoconductive Si pads filled in the gap of SRRs can be tuned efficiently by external pump power. This results in the modulation of absorption magnitude with a modulation depth of 62.2%, and a broadband switch of absorption peak frequencies varying from 0.82 to 0.51 THz. Further numerical simulations demonstrate that the switchable MMA has the merit of polarization-insensitive and wide-angle absorption. The realization of broadband redshift tunable MMA offers opportunities to mature semiconductor technologies and potential applications in active THz modulator and switcher.

  11. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    DOE PAGES

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; ...

    2016-02-26

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiatedmore » at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.« less

  12. SWCNT Photocatalyst for Hydrogen Production from Water upon Photoexcitation of (8, 3) SWCNT at 680-nm Light.

    PubMed

    Murakami, Noritake; Tango, Yuto; Miyake, Hideaki; Tajima, Tomoyuki; Nishina, Yuta; Kurashige, Wataru; Negishi, Yuichi; Takaguchi, Yutaka

    2017-03-06

    Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100 meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QY = 0.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT.

  13. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy.

    PubMed

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J; Jung, Il Woong; Walko, Donald A; Dufresne, Eric M; Jeong, Jaewoo; Samant, Mahesh G; Parkin, Stuart S P; Freeland, John W; Evans, Paul G; Wen, Haidan

    2016-02-26

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

  14. Photoexcited Nuclear Dynamics with Ab Initio Electronic Structure Theory: Is TD-DFT Ready For the Challenge?

    NASA Astrophysics Data System (ADS)

    Subotnik, Joseph

    In this talk, I will give a broad overview of our work in nonadiabatic dynamics, i.e. the dynamics of strongly coupled nuclear-electronic motion whereby the relaxation of a photo-excited electron leads to the heating up of phonons. I will briefly discuss how to model such nuclear motion beyond mean field theory. Armed with the proper framework, I will then focus on how to calculate one flavor of electron-phonon couplings, known as derivative couplings in the chemical literature. Derivative couplings are the matrix elements that couple adiabatic electronic states within the Born-Oppenheimer treatment, and I will show that these matrix elements show spurious poles using formal (frequency-independent) time-dependent density functional theory. To correct this TD-DFT failure, a simple approximation will be proposed and evaluated. Finally, time permitting, I will show some ab initio calculations whereby one can use TD-DFT derivative couplings to study electronic relaxation through a conical intersection.

  15. Experimental and theoretical study of hydroxyquinolines: hydroxyl group position dependent dipole moment and charge-separation in the photoexcited state leading to fluorescence

    NASA Astrophysics Data System (ADS)

    Singh Mehata, Mohan; Singh, Ajay K.; Sinha, Ravindra Kumar

    2016-12-01

    Optical absorption and fluorescence (FL) spectra of 2-, 6-, 7-, 8-hydroxyquinolines (2-,6-,7- and 8-HQs) have been measured at room temperature in the wide range of solvents of different polarities, dielectric constant and refractive index. The ground state dipole moment (µ g) and excited state dipole moment (µ e) of 2-, 6-, 7- and 8-HQs were obtained using solvatochromic shift (SS) methods and microscopic solvent polarity parameters (MSPP). Change in the dipole moment (Δµ) between the ground and photo-excited states was estimated from SS and MSPP methods. DFT and TDDFT based theoretical calculations were performed for the ground and excited states dipole moments, and for vertical transitions. A significant enhancement in the excited state dipole moment was observed following photo-excitation. The large value of Δµ clearly indicates to the charge-separation in the photo-excited states, which in turn depends on the position of the hydroxyl group in the ring.

  16. Probing the photoexcited states of rhodium corroles by time-resolved Q-band EPR. Observation of strong spin-orbit coupling effects.

    PubMed

    Rozenshtein, V; Wagnert, L; Berg, A; Stavitski, E; Berthold, T; Kothe, G; Saltsman, I; Gross, Z; Levanon, H

    2008-06-19

    The photoexcited states of two 5,10,15-tris(pentafluorophenyl)corroles (tpfc), hosting Rh(III) in their core, namely Rh(pyr)(PPh 3)(tpfc) and Rh(PPh 3)(tpfc), have been studied by time-resolved electron paramagnetic resonance (TREPR) combined with pulsed laser excitation. Using the transient nutation technique, the spin polarized spectra are assigned to photoexcited triplet states. The spectral widths observed for the two Rh(III) corroles crucially depend on the axial ligands at the Rh(III) metal ion. In case of Rh(PPh 3)(tpfc), the TREPR spectra are found to extend over 200 mT, which exceeds the spectral width of non-transition-metal corroles by more than a factor of 3. Moreover, the EPR lines of the Rh(III) corroles are less symmetric than those of the non-transition-metal corrroles. The peculiarities in the TREPR spectra of the Rh(III) corroles can be rationalized in terms of strong spin-orbit coupling (SOC) associated with the transition-metal character of the Rh(III) ion. It is assumed that SOC in the photoexcited Rh(III) corroles effectively admixes metal centered (3)dd-states to the corrole centered (3)pipi*-states detected in the TREPR experiments. This admixture leads to an increased zero-field splitting and a large g-tensor anisotropy as manifested by the excited Rh(III) corroles.

  17. Experimental and theoretical study of hydroxyquinolines: hydroxyl group position dependent dipole moment and charge-separation in the photoexcited state leading to fluorescence.

    PubMed

    Mehata, Mohan Singh; Singh, Ajay K; Sinha, Ravindra Kumar

    2016-11-17

    Optical absorption and fluorescence (FL) spectra of 2-, 6-, 7-, 8-hydroxyquinolines (2-,6-,7- and 8-HQs) have been measured at room temperature in the wide range of solvents of different polarities, dielectric constant and refractive index. The ground state dipole moment (µ g) and excited state dipole moment (µ e) of 2-, 6-, 7- and 8-HQs were obtained using solvatochromic shift (SS) methods and microscopic solvent polarity parameters (MSPP). Change in the dipole moment (Δµ) between the ground and photo-excited states was estimated from SS and MSPP methods. DFT and TDDFT based theoretical calculations were performed for the ground and excited states dipole moments, and for vertical transitions. A significant enhancement in the excited state dipole moment was observed following photo-excitation. The large value of Δµ clearly indicates to the charge-separation in the photo-excited states, which in turn depends on the position of the hydroxyl group in the ring.

  18. Tuning Hole and Electron Transfer from Photo-excited CdSe Quantum Dot to Phenol Derivatives: Effect of Electron Donating and Withdrawing Moiety.

    PubMed

    Ghosh, Hirendra Nath; Debnath, Tushar; Sebastian, Deepa; Maiti, Sourav

    2017-03-27

    Charge transfer processes from photo-excited CdSe QDs to phenol derivatives with electron donating (4-methoxy) and electron withdrawing (4-nitro) moiety have been demonstrated by using steady state and time-resolved emission and femto-second transient absorption spectroscopy. Steady state and time-resolved emission studies suggest that in presence of both 4-nitro phenol (4NP) and 4-methoxy phenol (4MP) CdSe QDs luminescence gets quenched. Stern-Volmer analysis suggests both static and dynamic mechanisms are active for both the QD/phenol composites. Cyclic volatmetric analysis recommends that photo-excited CdSe QDs can donate electron to 4NP and hole to 4MP. To reconfirm both electron and hole transfer mechanism CdSe/CdS quasi type-II and CdSe/CdTe type-II core-shell NC were synthesized and the photoluminescence quenching were monitored in absence and in presence of both 4NP and 4MP where systematically hole and electron transfer were restricted. Our studies suggest that indeed electron and hole transfer take place from photo-excited CdSe to 4NP and 4MP respectively. To monitor the charge transfer dynamics in both the systems in early time scale, we have employed femtosecond transient absorption (TA) spectroscopic techniques. Both electron and hole transfer and charge recombination dynamics have been discussed and effect of electron donating and withdrawing group has been demonstrated.

  19. Deep vein thrombosis - discharge

    MedlinePlus

    ... this page: //medlineplus.gov/ency/patientinstructions/000027.htm Deep vein thrombosis - discharge To use the sharing features ... page, please enable JavaScript. You were treated for deep vein thrombosis ( DVT ). This is a condition in ...

  20. Taoism and Deep Ecology.

    ERIC Educational Resources Information Center

    Sylvan, Richard; Bennett, David

    1988-01-01

    Contrasted are the philosophies of Deep Ecology and ancient Chinese. Discusses the cosmology, morality, lifestyle, views of power, politics, and environmental philosophies of each. Concludes that Deep Ecology could gain much from Taoism. (CW)

  1. Deep Space Telecommunications

    NASA Technical Reports Server (NTRS)

    Kuiper, T. B. H.; Resch, G. M.

    2000-01-01

    The increasing load on NASA's deep Space Network, the new capabilities for deep space missions inherent in a next-generation radio telescope, and the potential of new telescope technology for reducing construction and operation costs suggest a natural marriage between radio astronomy and deep space telecommunications in developing advanced radio telescope concepts.

  2. Deep Web video

    SciTech Connect

    None Available

    2009-06-01

    To make the web work better for science, OSTI has developed state-of-the-art technologies and services including a deep web search capability. The deep web includes content in searchable databases available to web users but not accessible by popular search engines, such as Google. This video provides an introduction to the deep web search engine.

  3. Deep Web video

    ScienceCinema

    None Available

    2016-07-12

    To make the web work better for science, OSTI has developed state-of-the-art technologies and services including a deep web search capability. The deep web includes content in searchable databases available to web users but not accessible by popular search engines, such as Google. This video provides an introduction to the deep web search engine.

  4. Mechanism of photoexcited precession of magnetization in (Ga,Mn)As on the basis of time-resolved spectroscopy

    NASA Astrophysics Data System (ADS)

    Matsuda, T.; Munekata, H.

    2016-02-01

    In order to investigate the mechanism of photoexcited precession of magnetization in ferromagnetic G a1 -xM nxAs , magneto-optical (MO) and differential reflectivity (Δ R /R ; DR) temporal profiles are studied at relatively long (picosecond to nanosecond) and ultrashort (1 ps or less) time scales for samples with different Mn content (x =0.01 -0.11 ) . As to the oscillatory MO profiles observed in the long time scale, simulation based on the Landau-Lifshitz-Gilbert equation combined with two different MO effects confirms photoinducement of the perpendicular anisotropy component Δ Heff ,⊥ . As for the profiles observed in the ultrashort time scale, they are consistently explained in terms of the dynamics of photogenerated carriers, but not by the sudden reduction in magnetization (the ultrafast demagnetization). In light of these experimental results and analyses, a mechanism that accounts for the photoinduced Δ Heff ,⊥ is addressed: namely, photoionizationlike excitation of M n2 + , M n2 ++h ν →M n2 +,*=M n3++e- . That such excitation tips magnetic anisotropy toward the out-of-plane direction through the inducement of orbital angular momentum and the gradient ∂ (M n2 +,* )/∂ z is discussed. The validity of the proposed mechanism is examined by estimating the efficiency of excitation on the basis of the Lambert-Beer law and the experimental Δ Heff ,⊥ values, through which an efficiency of 1-10 ppm with a nominal optical cross section of around 5 ×10-12m2 is obtained.

  5. Probing the Electronic Structure of a Photoexcited Solar Cell Dye with Transient X-ray Absorption Spectroscopy

    SciTech Connect

    Van Kuiken, Benjamin E.; Huse, Nils; Cho, Hana; Strader, Matthew L.; Lynch, Michael S.; Schoenlein, Robert W.; Khalil, Munira

    2012-06-21

    This study uses transient X-ray absorption (XA) spectroscopy and timedependent density functional theory (TD-DFT) to directly visualize the charge density around the metal atom and the surrounding ligands following an ultrafast metal-to-ligand charge-transfer (MLCT) process in the widely used RuII solar cell dye, Ru(dcbpy)2(NCS)2 (termed N3). We measure the Ru L-edge XA spectra of the singlet ground (1A1) and the transient triplet (3MLCT) excited state of N34 and perform TD-DFT calculations of 2p core-level excitations, which identify a unique spectral signature of the electron density on the NCS ligands. We find that the Ru 2p, Ru eg, and NCS orbitals are stabilized by 2.0, 1.0, and 0.6 eV, respectively, in the transient 3MLCT state of the dye. These results highlight the role of the NCS ligands in governing the oxidation state of the Ru center.

  6. The photoexcitation of crystalline ice and amorphous solid water: A molecular dynamics study of outcomes at 11 K and 125 K

    SciTech Connect

    Crouse, J.; Loock, H.-P. Cann, N. M.

    2015-07-21

    Photoexcitation of crystalline ice Ih and amorphous solid water at 7-9 eV is examined using molecular dynamics simulations and a fully flexible water model. The probabilities of photofragment desorption, trapping, and recombination are examined for crystalline ice at 11 K and at 125 K and for amorphous solid water at 11 K. For 11 K crystalline ice, a fully rigid water model is also employed for comparison. The kinetic energy of desorbed H atoms and the distance travelled by trapped fragments are correlated to the location and the local environment of the photoexcited water molecule. In all cases, H atom desorption is found to be the most likely outcome in the top bilayer while trapping of all photofragments is most probable deeper in the solid where the likelihood for recombination of the fragments into H{sub 2}O molecules also rises. Trajectory analysis indicates that the local hydrogen bonding network in amorphous solid water is more easily distorted by a photodissociation event compared to crystalline ice. Also, simulations indicate that desorption of OH radicals and H{sub 2}O molecules are more probable in amorphous solid water. The kinetic energy distributions for desorbed H atoms show a peak at high energy in crystalline ice, arising from photoexcited water molecules in the top monolayer. This peak is less pronounced in amorphous solid water. H atoms that are trapped may be displaced by up to ∼10 water cages, but migrate on average 3 water cages. Trapped OH fragments tend to stay near the original solvent cage.

  7. Photoexcitations in Polyacetylene.

    DTIC Science & Technology

    1981-11-11

    recombination luminescence; (CH) X interband absorption edge; excitation energies ; Stokes shift; temperature 0....dependence; isomerization; phototransport...turns on sharply for excitation S energies greater than 2.k5e ; irLivin., as S;takes shift of 0.15eV. Studies of the temperature Ulependence kT 7K) -ci...Philadelphia, PA 19104 INov ~e!f M 81 Reproduction in whole or in part is permitted for any purpose of the United States Government Approved for public

  8. Identification of Deep Earthquakes

    DTIC Science & Technology

    2010-09-01

    develop a ground truth dataset of earthquakes at both normal crustal depths and earthquakes from subduction zones , below the overlying crust. Many...deep earthquakes (depths between about 50 and 300 km). These deep earthquakes are known to occur in the Asia-India continental collision zone ...and/or NIL, as these stations are within a few hundred km of the zone where deep earthquakes are known to occur. To date we have selected about 300

  9. Deep Water Ocean Acoustics

    DTIC Science & Technology

    2016-04-30

    OASIS, INC. 1 Report No. QSR-14C0172-Ocean Acoustics-043016 Quarterly Progress Report Technical and Financial Deep Water Ocean Acoustics...understanding of the impact of the ocean and seafloor environmental variability on deep- water (long-range) ocean acoustic propagation and to...improve our understanding. During the past few years, the physics effects studied have been three-dimensional propagation on global scales, deep water

  10. Deep Water Ocean Acoustics

    DTIC Science & Technology

    2015-10-19

    OASIS, INC. 1 Report No. QSR-14C0172-Ocean Acoustics-093015 Quarterly Progress Report Technical and Financial Deep Water Ocean Acoustics...number. 1. REPORT DATE OCT 2015 2. REPORT TYPE 3. DATES COVERED 01-07-2015 to 30-09-2015 4. TITLE AND SUBTITLE Deep Water Ocean Acoustics...understanding of the impact of the ocean and seafloor environmental variability on deep- water (long-range) ocean acoustic propagation and to develop

  11. The deep space network

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Presented is Deep Space Network (DSN) progress in flight project support, tracking and data acquisition (TDA) research and technology, network engineering, hardware and software implementation, and operations.

  12. Deep Space Communication

    NASA Technical Reports Server (NTRS)

    Manshadi, Farzin

    2012-01-01

    ITU defines deep space as the volume of Space at distances from the Earth equal to, or greater than, 2 106 km. Deep Space Spacecraft have to travel tens of millions of km from Earth to reach the nearest object in deep space. Spacecraft mass and power are precious. Large ground-based antennas and very high power transmitters are needed to overcome large space loss and spacecraft's small antennas and low power transmitters. Navigation is complex and highly dependent on measurements from the Earth. Every deep space mission is unique and therefore very costly to develop.

  13. The deep space network

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Summaries are given of Deep Space Network progress in flight project support, tracking and data acquisition research and technology, network engineering, hardware and software implementation, and operations.

  14. A deep reef in deep trouble

    USGS Publications Warehouse

    Menza, Charles; Kendall, M.; Rogers, C.; Miller, J.

    2007-01-01

    The well-documented degradation of shallower reefs which are often closer to land and more vulnerable to pollution, sewage and other human-related stressors has led to the suggestion that deeper, more remote offshore reefs could possibly serve as sources of coral and fish larvae to replenish the shallower reefs. Yet, the distribution, status, and ecological roles of deep (>30 m) Caribbean reefs are not well known. In this report, an observation of a deep reef which has undergone a recent extensive loss of coral cover is presented. In stark contrast to the typical pattern of coral loss in shallow reefs, the deeper corals were most affected. This report is the first description of such a pattern of coral loss on a deep reef.

  15. Characterization of a deep-level compensation ratio through picosecond four-wave mixing on a transient reflection grating

    NASA Astrophysics Data System (ADS)

    Kadys, A.; Delaye, Ph; Roosen, G.; Jarasiunas, K.

    2007-09-01

    We demonstrate a novel application of a time-resolved four-wave mixing technique for the determination of a deep-level compensation ratio in a semi-insulating crystal. The approach is based on photoexcitation of carriers from deep impurity levels, formation of a space-charge electric field in deep traps, and monitoring dynamics of photorefractive, free- carrier and absorption gratings by light diffraction. The analysis of anisotropic diffraction features on the reflection grating provided requirements for crystal orientation in order to discriminate contribution of amplitude grating from the photorefractive phase grating, both being related to deep-trap occupation. Contributions of these optical nonlinearities were studied experimentally in (0 0 1)-oriented GaAs wafers by using a transient reflection grating configuration with a very small grating period (150 nm). Comparison of the reflection grating picosecond kinetics and its diffraction efficiency with modeling curves allowed us to ascribe the slow decay component to amplitude grating in recharged deep traps and determine their compensation ratio. The proposed technique allowed the determination of the compensation ratio of a deep EL2 donor, equal to 0.6 ± 0.05 in the given GaAs crystal.

  16. A study of angle-resolved photoemission extended fine structure as applied to the Ni 3p, Cu 3s, and Cu 3p core levels of the respective clean (111) surfaces

    SciTech Connect

    Huff, W.R.A.; Moler, E.J.; Kellar, S.A.

    1997-04-01

    The first non-s initial state angle-resolved photoemission extended fine structure (ARPEFS) study of clean surfaces for the purpose of further understanding the technique is reported. The surface structure sensitivity of ARPEFS applied to clean surfaces and to arbitrary initial states is studied using normal photoemission data taken from the Ni 3p core levels of a Ni(111) single crystal and the Cu 3s and the Cu 3p core-levels of a Cu(111) single crystal. The Fourier transforms of these clean surface data are dominated by backscattering. Unlike the s initial state data, the p initial state data show a peak in the Fourier transform corresponding to in-plane scattering from the six nearest-neighbors to the emitter. Evidence was seen for single-scattering events from in the same plane as the emitters and double-scattering events. Using a newly developed, multiple-scattering calculation program, ARPEFS data from clean surfaces and from p initial states can be modeled to high precision. Although there are many layers of emitters when measuring photoemission from a clean surface, test calculations show that the ARPEFS signal is dominated by photoemission from atoms in the first two crystal layers. Thus, ARPEFS applied to clean surfaces is sensitive to surface reconstruction. The known contraction of the first two Cu(111) layers is confirmed. The best-fit calculation for clean Ni(111) indicates an expansion of the first two layers. To better understand the ARPEFS technique, the authors studied s and non-s initial state photoemission from clean metal surfaces.

  17. Hubble Deep Fields

    NASA Astrophysics Data System (ADS)

    Ferguson, H.; Murdin, P.

    2000-11-01

    The Hubble Deep Fields are two small areas of the sky that were carefully selected for deep observations by the HUBBLE SPACE TELESCOPE (HST). They represent the deepest optical observations to date and reveal galaxies as faint as V=30, 4 billion times fainter than can be seen with the unaided eye....

  18. Deep sea waste disposal

    SciTech Connect

    Kester, D.R.; Burt, W.V.; Capuzzo, J.M.; Park, P.K.; Ketchum, B.W.; Duedall, I.W.

    1985-01-01

    The book presents papers on the marine disposal of wastes. Topics considered include incineration at sea, the modelling and biological effects of industrial wastes, microbial studies of ocean dumping, deep-sea mining wastes, the chemical analysis of ferromanganese nodules, and economic aspects of deep-sea disposal.

  19. Deep-diving dinosaurs

    NASA Astrophysics Data System (ADS)

    Hayman, John

    2012-08-01

    Dysbaric bone necrosis demonstrated in ichthyosaurs may be the result of prolonged deep diving rather than rapid ascent to escape predators. The bone lesions show structural and anatomical similarity to those that may occur in human divers and in the deep diving sperm whale, Physeter macrocephalus.

  20. The Deep Space Network

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Deep Space Network progress in flight project support, tracking and data acquisition, research and technology, network engineering, hardware and software implementation, and operations is cited. Topics covered include: tracking and ground based navigation; spacecraft/ground communication; station control and operations technology; ground communications; and deep space stations.

  1. The deep space network

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The progress is reported of Deep Space Network (DSN) research in the following areas: (1) flight project support, (2) spacecraft/ground communications, (3) station control and operations technology, (4) network control and processing, and (5) deep space stations. A description of the DSN functions and facilities is included.

  2. Deep Impact Spots Quarry

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Sixty-nine days before it gets up-close-and-personal with a comet, NASA's Deep Impact spacecraft successfully photographed its quarry, comet Tempel 1, at a distance of 39.7 million miles. The image, taken on April 25, 2005, is the first of many comet portraits Deep Impact will take leading up to its historic comet encounter on July 4.

  3. Deep venous thrombosis

    MedlinePlus

    ... ncbi.nlm.nih.gov/pubmed/22315257 . Kline JA. Pulmonary embolism and deep vein thrombosis. In: Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice . 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 88. ... Instructions Deep vein thrombosis - discharge ...

  4. New achievements on relaxation dynamics of atoms and molecules photoexcited in the tender x-ray domain at synchrotron SOLEIL

    NASA Astrophysics Data System (ADS)

    Piancastelli, M. N.; Guillemin, R.; Marchenko, T.; Journel, L.; Travnikova, O.; Marin, T.; Goldsztejn, G.; Cunha de Miranda, B.; Ismail, I.; Simon, M.

    2017-02-01

    The so-called ‘tender’ x-ray domain, from 2 to 13 keV, has recently become available for atomic and molecular studies at the French synchrotron SOLEIL with state-of-the-art photon and electron energy resolution. We investigated a wealth of new phenomena by means of photoelectron and Auger spectroscopy and electron–ion coincidence techniques. The list includes recoil due to the photoelectron’s momentum, ultrafast nuclear motion on the femto- and sub-femtosecond time scale, double-core-hole studies, electron recapture effects, exotic Auger decay pathways, deep-edge molecular-frame photoelectron angular distribution studies, and core-hole localization/delocalization phenomena for deep-core vacancies. We demonstrate that the newly accessible extended photon energy range does not simply allow studying more systems with deeper core edges, but opens a totally new horizon in what concerns electron and nuclear dynamics of deep-core-excited and core-ionized isolated species.

  5. Deep learning in bioinformatics.

    PubMed

    Min, Seonwoo; Lee, Byunghan; Yoon, Sungroh

    2016-07-29

    In the era of big data, transformation of biomedical big data into valuable knowledge has been one of the most important challenges in bioinformatics. Deep learning has advanced rapidly since the early 2000s and now demonstrates state-of-the-art performance in various fields. Accordingly, application of deep learning in bioinformatics to gain insight from data has been emphasized in both academia and industry. Here, we review deep learning in bioinformatics, presenting examples of current research. To provide a useful and comprehensive perspective, we categorize research both by the bioinformatics domain (i.e. omics, biomedical imaging, biomedical signal processing) and deep learning architecture (i.e. deep neural networks, convolutional neural networks, recurrent neural networks, emergent architectures) and present brief descriptions of each study. Additionally, we discuss theoretical and practical issues of deep learning in bioinformatics and suggest future research directions. We believe that this review will provide valuable insights and serve as a starting point for researchers to apply deep learning approaches in their bioinformatics studies.

  6. Deep subsurface microbial processes

    USGS Publications Warehouse

    Lovley, D.R.; Chapelle, F.H.

    1995-01-01

    Information on the microbiology of the deep subsurface is necessary in order to understand the factors controlling the rate and extent of the microbially catalyzed redox reactions that influence the geophysical properties of these environments. Furthermore, there is an increasing threat that deep aquifers, an important drinking water resource, may be contaminated by man's activities, and there is a need to predict the extent to which microbial activity may remediate such contamination. Metabolically active microorganisms can be recovered from a diversity of deep subsurface environments. The available evidence suggests that these microorganisms are responsible for catalyzing the oxidation of organic matter coupled to a variety of electron acceptors just as microorganisms do in surface sediments, but at much slower rates. The technical difficulties in aseptically sampling deep subsurface sediments and the fact that microbial processes in laboratory incubations of deep subsurface material often do not mimic in situ processes frequently necessitate that microbial activity in the deep subsurface be inferred through nonmicrobiological analyses of ground water. These approaches include measurements of dissolved H2, which can predict the predominant microbially catalyzed redox reactions in aquifers, as well as geochemical and groundwater flow modeling, which can be used to estimate the rates of microbial processes. Microorganisms recovered from the deep subsurface have the potential to affect the fate of toxic organics and inorganic contaminants in groundwater. Microbial activity also greatly influences 1 the chemistry of many pristine groundwaters and contributes to such phenomena as porosity development in carbonate aquifers, accumulation of undesirably high concentrations of dissolved iron, and production of methane and hydrogen sulfide. Although the last decade has seen a dramatic increase in interest in deep subsurface microbiology, in comparison with the study of

  7. Photo-excitation of adenine cation radical [A•+] in the near UV-vis region produces sugar radicals in Adenosine and in its nucleotides

    PubMed Central

    Adhikary, Amitava; Khanduri, Deepti; Kumar, Anil; Sevilla, Michael D.

    2011-01-01

    In this study, we report the formation of ribose sugar radicals in high yields (85 – 100%) via photo-excitation of adenine cation radical (A•+) in Ado and its ribonucleotides. Photo-excitation of A•+ at low temperatures in homogenous aqueous glassy samples of Ado, 2′-AMP, 3′-AMP and 5′-AMP forms sugar radicals predominantly at C5′- and also at C3′-sites. The C5′• and C3′• sugar radicals were identified employing Ado deuterated at specific carbon sites: C1′, C2′, and at C5′. Phosphate substitution is found to deactivate sugar radical formation at the site of substitution. Thus, in 5′-AMP, C3′• is observed to be the main radical formed via photo-excitation at ca. 143 K whereas in 3′-AMP, C5′• is the only species found. These results were supported by results obtained employing 5′-AMP with specific deuteration at C5′-site (i.e., 5′,5′-D,D-5′-AMP). Moreover, contrary to the C5′• observed in 3′-dAMP, we find that C5′• in 3′-AMP shows a clear pH dependent conformational change as evidenced by a large increase in the C4′ β–hyperfine coupling on increasing the pH from 6 to 9. Calculations performed employing DFT (B3LYP/6-31G*) for C5′• in 3′-AMP show that the two conformations of C5′• result from strong hydrogen bond formation between the O5′-H and the 3′-phosphate dianion at higher pHs. Employing time-dependent density functional theory [TD-DFT, B3LYP/6-31G(d)] we show that in the excited state, the hole transfers to the sugar moiety and has significant hole localization at the C5′-site in a number of allowed transitions. This hole localization is proposed to lead to the formation of the neutral C5′-radical (C5′•) via deprotonation. PMID:19367991

  8. The deep space network

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Progress is reported in flight project support, tracking and data acquisition research and technology, network engineering, hardware and software implementation, and operations. The functions and facilities of the Deep Space Network are emphasized.

  9. Nurturing Deep Connections.

    ERIC Educational Resources Information Center

    Kessler, Rachael

    2002-01-01

    Argues that the missing ingredient in school reform is soul, that is, deep connections among students, teachers, and administrators. Discusses five principles of leadership with soul: Personalize, pacing, permission, protection, and paradox. (PKP)

  10. The deep space network

    NASA Technical Reports Server (NTRS)

    1980-01-01

    The functions and facilities of the Deep Space Network are considered. Progress in flight project support, tracking and data acquisition research and technology, network engineering, hardware and software implementation, and operations is reported.

  11. Deep Vein Thrombosis

    MedlinePlus

    ... vein swells, the condition is called thrombophlebitis. A deep vein thrombosis can break loose and cause a serious problem in the lung, called a pulmonary embolism. Sitting still for a long time can make ...

  12. The deep space network

    NASA Technical Reports Server (NTRS)

    1977-01-01

    The facilities, programming system, and monitor and control system for the deep space network are described. Ongoing planetary and interplanetary flight projects are reviewed, along with tracking and ground-based navigation, communications, and network and facility engineering.

  13. Deep Vein Thrombosis (DVT)

    MedlinePlus

    ... helps reduce the chances that your blood will pool and clot. You should wear these stockings during ... Make lifestyle changes. Lose weight and quit smoking. Obesity and smoking increase your risk of deep vein ...

  14. The Deep Space Network

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Progress on the Deep Space Network (DSN) supporting research and technology, advanced development, engineering and implementation, and DSN operations is presented. The functions and facilities of the DSN are described.

  15. The deep space network

    NASA Technical Reports Server (NTRS)

    1979-01-01

    A report is given of the Deep Space Networks progress in (1) flight project support, (2) tracking and data acquisition research and technology, (3) network engineering, (4) hardware and software implementation, and (5) operations.

  16. The Deep Space Network

    NASA Technical Reports Server (NTRS)

    1977-01-01

    The various systems and subsystems are discussed for the Deep Space Network (DSN). A description of the DSN is presented along with mission support, program planning, facility engineering, implementation and operations.

  17. The deep space network

    NASA Technical Reports Server (NTRS)

    1977-01-01

    A Deep Space Network progress report is presented dealing with in flight project support, tracking and data acquisition research and technology, network engineering, hardware and software implementation, and operations.

  18. The deep space network

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The objectives, functions, and organization of the Deep Space Network are summarized along with deep space station, ground communication, and network operations control capabilities. Mission support of ongoing planetary/interplanetary flight projects is discussed with emphasis on Viking orbiter radio frequency compatibility tests, the Pioneer Venus orbiter mission, and Helios-1 mission status and operations. Progress is also reported in tracking and data acquisition research and technology, network engineering, hardware and software implementation, and operations.

  19. Exploration for deep coal

    SciTech Connect

    2008-12-15

    The most important factor in safe mining is the quality of the roof. The article explains how the Rosebud Mining Co. conducts drilling and exploration in 11 deep coal mine throughout Pennsylvania and Ohio. Rosebud uses two Atlas Copco CS10 core drilling rigs mounted on 4-wheel drive trucks. The article first appeared in Atlas Copco's in-house magazine, Deep Hole Driller. 3 photos.

  20. Diagnosing Deep Venous Thrombosis

    PubMed Central

    Doyle, D. Lynn

    1992-01-01

    Patients often present with unexplained lower limb pain and swelling. It is important to exclude deep venous thrombosis in the diagnosis because of the threat of sudden death. Simple clinical diagnosis is unacceptable, and noninvasive tests should be used initially. Serial testing detects proximal extension of isolated calf thrombi. Multiple diagnostic modalities are employed to diagnose a new deep venous thrombosis in patients with postphlebitic syndrome. PMID:21221369

  1. The Deep Space Network

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The objectives, functions, and organization, of the Deep Space Network are summarized. Deep Space stations, ground communications, and network operations control capabilities are described. The network is designed for two-way communications with unmanned spacecraft traveling approximately 1600 km from earth to the farthest planets in the solar system. It has provided tracking and data acquisition support for the following projects: Ranger, Surveyor, Mariner, Pioneer, Apollo, Helios, Viking, and the Lunar Orbiter.

  2. New insight into the potential energy landscape and relaxation pathways of photoexcited aniline from CASSCF and XMCQDPT2 electronic structure calculations.

    PubMed

    Sala, Matthieu; Kirkby, Oliver M; Guérin, Stéphane; Fielding, Helen H

    2014-02-21

    There have been a number of recent experimental investigations of the nonadiabatic relaxation dynamics of aniline following excitation to the first three singlet excited states, 1(1)ππ*, 1(1)π3s/πσ* and 2(1)ππ*. Motivated by differences between the interpretations of experimental observations, we have employed CASSCF and XMCQDPT2 calculations to explore the potential energy landscape and relaxation pathways of photoexcited aniline. We find a new prefulvene-like MECI connecting the 1(1)ππ* state with the GS in which the carbon-atom carrying the amino group is distorted out-of-plane. This suggests that excitation above the 1(1)π3s/πσ* vertical excitation energy could be followed by electronic relaxation from the 1(1)ππ* state to the ground-electronic state through this MECI. We find a MECI connecting the 1(1)π3s/πσ* and 1(1)ππ* states close to the local minimum on 1(1)π3s/πσ* which suggests that photoexcitation to the 1(1)π3s/πσ* state could be followed by relaxation to the 1(1)ππ* state and to the dissociative component of the 1(1)π3s/πσ* state. We also find evidence for a new pathway from the 2(1)ππ* state to the ground electronic state that is likely to pass through a three-state conical intersection involving the 2(1)ππ*, 1(1)π3s/πσ* and 1(1)ππ* states.

  3. Real-time propagation time-dependent density functional theory study on the ring-opening transformation of the photoexcited crystalline benzene

    NASA Astrophysics Data System (ADS)

    Tateyama, Yoshitaka; Oyama, Norihisa; Ohno, Takahisa; Miyamoto, Yoshiyuki

    2006-03-01

    Mechanism of the ring-opening transformation in the photoexcited crystalline benzene is investigated on the femtosecond scale by a computational method based on the real-time propagation (RTP) time-dependent density functional theory (TDDFT). The excited-state dynamics of the benzene molecule is also examined not only for the distinction between the intrinsic properties of molecule and the intermolecular interaction but for the first validation using the vibration frequencies for the RTP-TDDFT approach. It is found that the vibration frequencies of the excited and ground states in the molecule are well reproduced. This demonstrates that the present method of time evolution using the Suzuki-Trotter-type split operator technique starting with the Franck-Condon state approximated by the occupation change of the Kohn-Sham orbitals is adequately accurate. For the crystalline benzene, we carried out the RTP-TDDFT simulations for two typical pressures. At both pressures, large swing of the C-H bonds and subsequent twist of the carbon ring occurs, leading to tetrahedral (sp3-like) C-H bonding. The ν4 and ν16 out-of-plane vibration modes of the benzene molecule are found mostly responsible for these motions, which is different from the mechanism proposed for the thermal ring-opening transformation occurring at higher pressure. Comparing the results between different pressures, we conclude that a certain increase of the intermolecular interaction is necessary to make seeds of the ring opening (e.g., radical site formation and breaking of the molecular character) even with the photoexcitation, while the hydrogen migration to fix them requires more free volume, which is consistent with the experimental observation that the transformation substantially proceeds on the decompression.

  4. Core-level electronic structure of solid-phase glycine, glycyl-glycine, diglycyl-glycine, and polyglycine: X-ray photoemission analysis and Hartree-Fock calculations of their zwitterions.

    PubMed

    Chatterjee, Avisek; Zhao, Liyan; Zhang, Lei; Pradhan, Debabrata; Zhou, Xiaojing; Leung, K T

    2008-09-14

    X-ray photoelectron spectroscopy (XPS) has been used to investigate the core-level electronic structures of glycine (G) and its peptides, including glycyl-glycine (GG), diglycyl-glycine (GGG), and polyglycine (poly-G), in their powder forms. Increasing the number of G units in the peptides does not change the locations of the respective C 1s, N 1s, and O 1s features corresponding to different functional groups: -COO(-), -NH(3)(+), >CH(2), and -CONH-. The electronic structures of the zwitterions of these molecules have been calculated as isolated molecules and as molecules in an aqueous environment under the periodic boundary conditions by quantum-mechanical and molecular mechanics methods. In the case of glycine zwitterion, the binding energies of the C 1s, N 1s, and O 1s XPS features are found to be in reasonable accord with the respective orbital energies obtained by Hartree-Fock self-consistent-field calculations, within the context of Koopmans' approximation. However, considerably worse agreement in the binding energies is found for the larger zwitterions (with the specific conformations considered in this work), indicating the need for higher-level calculations. The present work shows that optimizing the zwitterion in an aqueous environment under the periodic boundary conditions by molecular mechanics could be a very cost-effective approach for calculating the electronic structures of large, complex biomolecular systems.

  5. Calculating core-level excitations and X-ray absorption spectra of medium-sized closed-shell molecules with the algebraic-diagrammatic construction scheme for the polarization propagator.

    PubMed

    Wenzel, Jan; Wormit, Michael; Dreuw, Andreas

    2014-10-05

    Core-level excitations are generated by absorption of high-energy radiation such as X-rays. To describe these energetically high-lying excited states theoretically, we have implemented a variant of the algebraic-diagrammatic construction scheme of second-order ADC(2) by applying the core-valence separation (CVS) approximation to the ADC(2) working equations. Besides excitation energies, the CVS-ADC(2) method also provides access to properties of core-excited states, thereby allowing for the calculation of X-ray absorption spectra. To demonstrate the potential of our implementation of CVS-ADC(2), we have chosen medium-sized molecules as examples that have either biological importance or find application in organic electronics. The calculated results of CVS-ADC(2) are compared with standard TD-DFT/B3LYP values and experimental data. In particular, the extended variant, CVS-ADC(2)-x, provides the most accurate results, and the agreement between the calculated values and experiment is remarkable.

  6. Deep space laser communications

    NASA Astrophysics Data System (ADS)

    Biswas, Abhijit; Kovalik, Joseph M.; Srinivasan, Meera; Shaw, Matthew; Piazzolla, Sabino; Wright, Malcolm W.; Farr, William H.

    2016-03-01

    A number of laser communication link demonstrations from near Earth distances extending out to lunar ranges have been remarkably successful, demonstrating the augmented channel capacity that is accessible with the use of lasers for communications. The next hurdle on the path to extending laser communication and its benefits throughout the solar system and beyond is to demonstrate deep-space laser communication links. In this paper, concepts and technology development being advanced at the Jet Propulsion Laboratory (JPL) in order to enable deep-space link demonstrations to ranges of approximately 3 AU in the next decade, will be discussed.

  7. DEEP UNDERGROUND NEUTRINO EXPERIMENT

    SciTech Connect

    Wilson, Robert J.

    2016-03-03

    The Deep Underground Neutrino Experiment (DUNE) collaboration will perform an experiment centered on accelerator-based long-baseline neutrino studies along with nucleon decay and topics in neutrino astrophysics. It will consist of a modular 40-kt (fiducial) mass liquid argon TPC detector located deep underground at the Sanford Underground Research Facility in South Dakota and a high-resolution near detector at Fermilab in Illinois. This conguration provides a 1300-km baseline in a megawatt-scale neutrino beam provided by the Fermilab- hosted international Long-Baseline Neutrino Facility.

  8. The deep penetrating nevus.

    PubMed

    Strazzula, Lauren; Senna, Maryanne Makredes; Yasuda, Mariko; Belazarian, Leah

    2014-12-01

    The deep penetrating nevus (DPN), also known as the plexiform spindle cell nevus, is a pigmented lesion that commonly arises on the head and neck in the first few decades of life. Histopathologically, the DPN is wedge-shaped and contains melanocytes that exhibit deep infiltration into the dermis. Given these features, DPN may clinically and histopathologically mimic malignant melanoma, sparking confusion about the appropriate evaluation and management of these lesions. The goal of this review is to summarize the clinical and histopathological features of DPN and to discuss diagnostic and treatment strategies for dermatologists.

  9. Deduction of the chemical state and the electronic structure of Nd{sub 2}Fe{sub 14}B compound from X-ray photoelectron spectroscopy core-level and valence-band spectra

    SciTech Connect

    Wang, Jing; Liang, Le; Zhang, Lanting E-mail: lmsun@sjtu.edu.cn; Sun, Limin E-mail: lmsun@sjtu.edu.cn; Hirano, Shinichi

    2014-10-28

    Characterization of chemical state and electronic structure of the technologically important Nd{sub 2}Fe{sub 14}B compound is attractive for understanding the physical nature of its excellent magnetic properties. X-ray photoelectron spectroscopy (XPS) study of such rare-earth compound is important and also challenging due to the easy oxidation of surface and small photoelectron cross-sections of rare-earth 4f electrons and B 2p electrons, etc. Here, we reported an investigation based on XPS spectra of Nd{sub 2}Fe{sub 14}B compound as a function of Ar ion sputtering time. The chemical state of Fe and that of B in Nd{sub 2}Fe{sub 14}B compound can be clearly determined to be 0 and −3, respectively. The Nd in Nd{sub 2}Fe{sub 14}B compound is found to have the chemical state of close to +3 instead of +3 as compared with the Nd in Nd{sub 2}O{sub 3}. In addition, by comparing the valence-band spectrum of Nd{sub 2}Fe{sub 14}B compound to that of the pure Fe, the contributions from Nd, Fe, and B to the valence-band structure of Nd{sub 2}Fe{sub 14}B compound is made more clear. The B 2p states and B 2s states are identified to be at ∼11.2 eV and ∼24.6 eV, respectively, which is reported for the first time. The contribution from Nd 4f states can be identified both in XPS core-level spectrum and XPS valence-band spectrum. Although Nd 4f states partially hybridize with Fe 3d states, Nd 4f states are mainly localized in Nd{sub 2}Fe{sub 14}B compound.

  10. Reading Knee-Deep

    ERIC Educational Resources Information Center

    Jewett, Pamela

    2007-01-01

    Freire told his audience at a seminar at the University of Massachusetts, "You need to read knee-deep in texts, for deeper than surface meanings, and you need to know the words to be able to do it" (quoted in Cleary, 2003). In a children's literature class, fifteen teachers and I traveled along a path that moved us toward reading…

  11. The Deep Space Network

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Work accomplished on the Deep Space Network (DSN) was described, including the following topics: supporting research and technology, advanced development and engineering, system implementation, and DSN operations pertaining to mission-independent or multiple-mission development as well as to support of flight projects.

  12. [Deep vein thrombosis prophylaxis.

    PubMed

    Sandoval-Chagoya, Gloria Alejandra; Laniado-Laborín, Rafael

    2013-01-01

    Background: despite the proven effectiveness of preventive therapy for deep vein thrombosis, a significant proportion of patients at risk for thromboembolism do not receive prophylaxis during hospitalization. Our objective was to determine the adherence to thrombosis prophylaxis guidelines in a general hospital as a quality control strategy. Methods: a random audit of clinical charts was conducted at the Tijuana General Hospital, Baja California, Mexico, to determine the degree of adherence to deep vein thrombosis prophylaxis guidelines. The instrument used was the Caprini's checklist for thrombosis risk assessment in adult patients. Results: the sample included 300 patient charts; 182 (60.7 %) were surgical patients and 118 were medical patients. Forty six patients (15.3 %) received deep vein thrombosis pharmacologic prophylaxis; 27.1 % of medical patients received deep vein thrombosis prophylaxis versus 8.3 % of surgical patients (p < 0.0001). Conclusions: our results show that adherence to DVT prophylaxis at our hospital is extremely low. Only 15.3 % of our patients at risk received treatment, and even patients with very high risk received treatment in less than 25 % of the cases. We have implemented strategies to increase compliance with clinical guidelines.

  13. Teaching for Deep Learning

    ERIC Educational Resources Information Center

    Smith, Tracy Wilson; Colby, Susan A.

    2007-01-01

    The authors have been engaged in research focused on students' depth of learning as well as teachers' efforts to foster deep learning. Findings from a study examining the teaching practices and student learning outcomes of sixty-four teachers in seventeen different states (Smith et al. 2005) indicated that most of the learning in these classrooms…

  14. Dynamical mechanism of charge separation by photoexcited generation of proton-electron pairs in organic molecular systems. A nonadiabatic electron wavepacket dynamics study

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kentaro; Takatsuka, Kazuo

    2016-08-01

    In this perspective article, we review, along with presenting new results, a series of our theoretical analyses on the excited-state mechanism of charge separation (proton-electron pair creation) relevant to the photoinduced water-splitting reaction (2H2O → 4H+ + 4e- + O2) in organic and biological systems, which quite often includes Mn clusters in various molecular configurations. The present mechanism is conceived to be universal in the triggering process of the photoexcited water splitting dynamics. In other words, any Mn-based catalytic charge separation is quite likely to be initiated according to this mechanism. As computationally tractable yet realistic models, we examine a series of systems generally expressed as X-Mn-OH2⋯A, where X = (OH, Ca(OH)3) and A = (N-methylformamidine, guanidine, imidazole or ammonia cluster) in terms of the theory of nonadiabatic electron wavepacket dynamics. We first find both an electron and a proton are simultaneously transferred to the acceptors through conical intersections upon photoexcitation. In this mechanism, the electron takes different pathways from that of the proton and reaches the densely lying Rydberg-like states of the acceptors in the end, thereby inducing charge separation. Therefore the presence of the Rydberg-like diffused unoccupied states as an electron acceptor is critical for this reaction to proceed. We also have found another crucial nonadiabatic process that deteriorates the efficiency of charge separation by rendering the created pair of proton and electron back to the originally donor site through the states of d-d band originated from Mn atom. Repetition of this process gradually annihilates the created pair of proton and electron in a way different from the usual charge recombination process. We address this dynamics by means of our proposed path-branching representation. The dynamical roles of a doped Ca atom are also uncovered, which are relevant to controlling the pathways of electron

  15. Deep depth undex simulator

    SciTech Connect

    Higginbotham, R. R.; Malakhoff, A.

    1985-01-29

    A deep depth underwater simulator is illustrated for determining the dual effects of nuclear type underwater explosion shockwaves and hydrostatic pressures on a test vessel while simulating, hydrostatically, that the test vessel is located at deep depths. The test vessel is positioned within a specially designed pressure vessel followed by pressurizing a fluid contained between the test and pressure vessels. The pressure vessel, with the test vessel suspended therein, is then placed in a body of water at a relatively shallow depth, and an explosive charge is detonated at a predetermined distance from the pressure vessel. The resulting shockwave is transmitted through the pressure vessel wall so that the shockwave impinging on the test vessel is representative of nuclear type explosive shockwaves transmitted to an underwater structure at great depths.

  16. Deep gluteal syndrome

    PubMed Central

    Martin, Hal David; Reddy, Manoj; Gómez-Hoyos, Juan

    2015-01-01

    Deep gluteal syndrome describes the presence of pain in the buttock caused from non-discogenic and extrapelvic entrapment of the sciatic nerve. Several structures can be involved in sciatic nerve entrapment within the gluteal space. A comprehensive history and physical examination can orientate the specific site where the sciatic nerve is entrapped, as well as several radiological signs that support the suspected diagnosis. Failure to identify the cause of pain in a timely manner can increase pain perception, and affect mental control, patient hope and consequently quality of life. This review presents a comprehensive approach to the patient with deep gluteal syndrome in order to improve the understanding of posterior hip anatomy, nerve kinematics, clinical manifestations, imaging findings, differential diagnosis and treatment considerations. PMID:27011826

  17. Project DEEP STEAM

    NASA Astrophysics Data System (ADS)

    Aeschliman, D. P.; Clay, R. G.; Donaldson, A. B.; Eisenhawer, S. W.; Fox, R. L.; Johnson, D. R.; Mulac, A. J.

    1982-01-01

    The objective of Project DEEP STEAM is to develop the technology to economically produce heavy oils from deep reservoirs. The tasks included in this project are the development of thermally efficient delivery systems and downhole steam generation systems. During the period January 1-March 31, 1981, effort has continued on a low pressure combustion downhole generator (Rocketdyne), and on two high pressure designs (Foster-Miller Associates, Sandia National Laboratories). The Sandia design was prepared for deployment in the Wilmington Field at Long Beach, California. Progress continued on the Min-Stress II packer concept at L'Garde, Inc., and on the extruded metal packer at Foster-Miller. Initial bare string field data are reported on the insulated tubular test at Lloydminster, Saskatchewan, Canada.

  18. Deep Water Ocean Acoustics

    DTIC Science & Technology

    2015-07-17

    under-ice scattering , bathymetric diffraction and the application of the ocean acoustic Parabolic Equation to infrasound. 2. Tasks a. Task 1...QSR-14C0172-Ocean Acoustics -063015 Figure 10. Estimated reflection coefficient as a function of frequency by taking the difference of downgoing and...OASIS, INC. 1 Report No. QSR-14C0172-Ocean Acoustics -063015 Quarterly Progress Report Technical and Financial Deep Water Ocean Acoustics

  19. Deep Brain Stimulation

    PubMed Central

    Chen, X.L.; Xiong, Y.Y.; Xu, G.L.; Liu, X.F.

    2013-01-01

    Deep brain stimulation (DBS) has provided remarkable therapeutic benefits for people with a variety of neurological disorders. Despite the uncertainty of the precise mechanisms underlying its efficacy, DBS is clinically effective in improving motor function of essential tremor, Parkinson's disease and primary dystonia and in relieving obsessive-compulsive disorder. Recently, this surgical technique has continued to expand to other numerous neurological diseases with encouraging results. This review highlighted the current and potential future clinical applications of DBS. PMID:25187779

  20. Deep Water Formation

    NASA Technical Reports Server (NTRS)

    Killworth, P. D.

    1984-01-01

    Some simple arguments on plumes of dense water and filling boxes were given. What determines the time for a large-scale environment to be modified by the injection of dense water at its edge is the mass flux, not the buoyancy flux. However, it is the denser buoyancy flux, when there are several competing plumes (e.g., the Mediterranean outflow versus the Denmark Strait outflow) that determines which plume will provide the bottom water for that ocean basin. It was noted that the obvious laboratory experiment (rotate a pie-shaped annulus, and heat/cool it on the surface) had never been performed. Thus, to some extent our belief that deep convection is somehow automatic at high latitudes to close off some ill-defined meridional circulation has never been tested. A summary of deep convection was given. The two fundamental formation mechanisms were shown. Of the two, it is open-ocean convection which forms the water which supplies the Denmark Strait overflow -- in all likelihood, as formation in the Greenland Sea remains stubbornly unobserved. But it is the slope convection which finally creates North Atlantic deep water, following the Denmark Strait overspill.

  1. I. Excitonic Phase Diagram in Silicon: Evidence for Two Condensed Phases. I. Motion of Photoexcited Carriers in GALLIUM-ARSENIDE/ALUMINUM(X)GALLIUM(1-X)ARSENIDE Multiple Quantum Wells-Anomalous Confinement at High Densities.

    NASA Astrophysics Data System (ADS)

    Smith, Leigh Morris

    This thesis describes work on the thermodynamics and transport properties of photoexcited carriers in bulk and two-dimensional semiconductors. Two major topics are addressed. I. Photoluminescence experiments of excitons in unstressed silicon are presented which indicate the existence of a new non-degenerate condensed phase of plasma. This new liquid has a density one-tenth that of the ground state electron-hole liquid and is observed both above and below the liquid-gas critical point (~24.5K). A new phase diagram of excitons in silicon is presented which includes these two condensed plasmas. Consistent with the Gibbs phase rule, a triple point at 18.5 K is inferred from the luminescence data as the only temperature where the exciton gas, condensed plasma (CP) and electron-hole liquid (EHL) coexist. The low density condensed plasma persists up to a second critical point at 45 +/- 5K, above which the photoexcited carriers are observed to continuously decay into a partially ionized excitonic gas. II. We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 μm spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n = 2 times 10^{11}cm ^{-2} is found to depend upon excitation level, possibly indicating defect-limited diffusion or phonon-wind effects. Above this density the spatial profiles exhibit two distinct components with widely differing diffusivities. This remarkable behavior may be understood with consideration of the interactions of non-equilibrium phonons with the photoexcited carriers. We postulate that the slowly diffusing component represents carriers which are "thermally confined" to a phonon hot spot, while the rapidly moving component is driven by the flux of non-equilibrium phonons away from the excitation region.

  2. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-02-01

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  3. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr₀.₇Ca₀.₃MnO₃.

    PubMed

    Zhou, S Y; Langner, M C; Zhu, Y; Chuang, Y-D; Rini, M; Glover, T E; Hertlein, M P; Gonzalez, A G Cruz; Tahir, N; Tomioka, Y; Tokura, Y; Hussain, Z; Schoenlein, R W

    2014-02-13

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr₀.₇Ca₀.₃MnO₃ following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  4. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    SciTech Connect

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y. -D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-01-16

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  5. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    PubMed Central

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-01-01

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering. PMID:24522173

  6. Tuning optical absorption and photoexcited recombination dynamics in La1-xSrxFeO3-δ through A-site substitution and oxygen vacancies

    NASA Astrophysics Data System (ADS)

    Smolin, Sergey; Scafetta, Mark; Choquette, Amber; Sfeir, Matthew; Baxter, Jason; May, Steven

    We study optical absorption and recombination dynamics in La1-xSrxFeO3-δ thin films, uncovering the effects of tuning nominal Fe valence via A-site substitution and oxygen stoichiometry. Variable angle spectroscopic ellipsometry was used to measure static optical properties, revealing a linear increase in absorption coefficient at 1.25 eV and a red-shifting of the optical absorption edge with increasing Sr fraction. The absorption spectra can be similarly tuned through the introduction of oxygen vacancies, indicating the critical role that nominal Fe valence plays in optical absorption. Dynamic optoelectronic properties were studied with ultrafast transient reflectance spectroscopy, revealing similar nanosecond photoexcited carrier lifetimes for oxygen deficient and stoichiometric films with the same nominal Fe valence. These results demonstrate that while the static optical absorption is strongly dependent on Fe valence tuned through cation or anion stoichiometry, oxygen vacancies do not appear to play a significantly detrimental role in the recombination kinetics. Nsf: ECCS-1201957, MRI DMR-0922929, MRI DMR-1040166. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

  7. Rationalizing long-lived photo-excited carriers in photocatalyst (La5Ti2CuS5O7) in terms of one-dimensional carrier transport

    NASA Astrophysics Data System (ADS)

    Suzuki, Yohichi; Singh, Rupashree Balia; Matsuzaki, Hiroyuki; Furube, Akihiro; Ma, Guijun; Hisatomi, Takashi; Domen, Kazunari; Seki, Kazuhiko

    2016-09-01

    The semiconductor La5Ti2CuS5O7 (LTC) is a potential photocatalyst capable of operating under visible light irradiation and behaves both as a photocathode and anode when embedded onto metal layers. Time-resolved diffuse reflectance (TRDR) measurements were carried out on LTC powder and LTC deposited on Au as the back contact using the particle-transfer method. Results of TRDR measurements of powdered LTC indicated the existence of long-lived photo-excited carriers, and suggested the existence of a mechanism for preventing carrier loss in LTC. Prior research has reported that LTC has a rod-shaped crystal structure and that electrons and holes are transported through different, spatially separated channels. Based on this, we introduced a one-dimensional carrier transport model. By analyzing TRDR data, we extracted material parameters such as the diffusion coefficient of LTC. Theoretical results indicated that a micron-sized LTC particle would be preferable if carriers trapped at the top-surface do contribute to photocatalytic gas generation.

  8. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    SciTech Connect

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, II Woong; Walko, Donald A.; Dufresne, Eric M.; Jaewoo, Jeong; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

    2016-02-26

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

  9. Dissociation of deep-core-excited CH{sub 3}Cl

    SciTech Connect

    Hansen, D.L.; Martin, R.; Vanderford, B.

    1997-04-01

    Using x-rays from B.L. 9.3.1, a space-focused time-of-flight (TOF) was used to study photofragmentation of CH{sub 3}Cl following excitation in the neighborhood of the Cl K-shell threshold ({approximately} 2.8 keV). Multi-ion coincidence measurements were used to search for selective dissociation of specific bonds in the molecule. Such selectivity has been observed for excitation near outer-core-level thresholds (e.g., Cl 2p), but this is the first study in deep core levels, where very-short core-hole lifetimes and Auger cascade effects may influence fragmentation. Both high-resolution time-of-flight spectroscopy and multi-coincidence photoelectron-photoion-photoion (PE-PIPICO), as well as photoelectron-photoion-photoion-photoion (PE3PICO) measurements were performed. Dramatic changes in the line shapes for different fragment ions are observed as a function of the excitation energy, and are attributed to selective dissociation of the CH{sub 3}Cl molecule along the C-Cl bond. In addition, pronounced angular distributions of the ejected ions are observed on resonance.

  10. The deep subterranean biosphere

    NASA Astrophysics Data System (ADS)

    Pedersen, Karsten

    1993-08-01

    The main purpose with this review is to summarise present research on the microbiology of deep subterranean environments, deeper than 50-100 m. Included are mainly studies where drilling, excavation, core sampling and ground water sampling have been made for research. Studies done in environments penetrated for commercial purposes, such as water wells, mining, oil recovery etc., have been dismissed because of the obvious risk for contamination during the penetration. Different measures that can be applied to reduce the risk of microbial contamination of sampled specimens by the access operations are discussed. The requirement for reliable estimations of the present microbial biomass, its activity and diversity in subterranean ecosystems, is fundamental. An array of different methods to achieve this goal are presented. The depth limit for subterranean life is suggested to be set by temperature, provided there is energy available for microbial life. If so, it should be possible to enrich thermophilic bacteria from deep hot ground waters which also has been done. There are only a few sites where the subterranean microbiology has been studied in multidisiplinary programs including chemistry and geology. The two most extensively published sites are the sediments of the Atlantic coastal plain of South Carolina, USA, studied in a subsurface program, initiated and sponsored by the U.S. Department of Energy, and crystalline bed-rock in Sweden studied in a program concerning the safety of future underground repositories for nuclear waste. This review presents an array of independent reports suggesting that microbial life is widespread at depth in the crust of earth—the deep subterranean biosphere. The obvious consequences is that microbes may be involved in many subterranean geochemical processes, such as diagenesis, weathering, precipitation, and in oxidation or reduction reactions of metals, carbon, nitrogen and sulfur—just as they are in most terranean environments.

  11. Deep Space Positioning System

    NASA Technical Reports Server (NTRS)

    Vaughan, Andrew T. (Inventor); Riedel, Joseph E. (Inventor)

    2016-01-01

    A single, compact, lower power deep space positioning system (DPS) configured to determine a location of a spacecraft anywhere in the solar system, and provide state information relative to Earth, Sun, or any remote object. For example, the DPS includes a first camera and, possibly, a second camera configured to capture a plurality of navigation images to determine a state of a spacecraft in a solar system. The second camera is located behind, or adjacent to, a secondary reflector of a first camera in a body of a telescope.

  12. Deep shadow occulter

    NASA Technical Reports Server (NTRS)

    Cash, Webster (Inventor)

    2010-01-01

    Methods and apparatus are disclosed for occulting light. The occulter shape suppresses diffraction at any given size or angle and is practical to build because it can be made binary to avoid scatter. Binary structures may be fully opaque or fully transmitting at specific points. The diffraction suppression is spectrally broad so that it may be used with incoherent white light. An occulter may also include substantially opaque inner portion and an at least partially transparent outer portion. Such occulters may be used on the ground to create a deep shadow in a short distance, or may be used in space to suppress starlight and reveal exoplanets.

  13. Fluorescence Excitation Function Produced Through Photoexcitation of the Rydberg States b, cn, and o3 of N2 in the 80-100 nm Region

    NASA Astrophysics Data System (ADS)

    Wu, R. C.; Judge, D. L.; Singh, T. S.; Mu, X. L.; Nee, J. B.; Chiang, S. Y.; Fung, H. S.

    2006-12-01

    Fluorescence excitation functions produced through photoexcitation of N2 using synchrotron radiation in the spectral region between 80 and 100 nm have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 115-320 nm and 300-700 nm region, respectively. The peaks in the VUV Fluorescence excitation functions are found to correspond to excitation of absorption transitions from the ground electronic state to the Rydberg states of b, cn (with n= 4-9), and o3 of N2. The relative fluorescence production cross sections for the observed peaks are determined. No fluorescence has been produced through excitation of the most dominating absorption features of the b-X transition except the (1,0), (5,0), and (6,0) bands, in excellent agreement with the recent lifetime measurements [1] and theoretical calculations [2]. In addition, fluorescence peaks correlate with the long vibrational progression of the c4 (v = 0-7) has also been observed. Weak fluorescence excitation peaks are also found to correlate with the excitation of the (1,0), (2,0), and (3,0) bands of the o3 VX transition. The present results provide important information for further unraveling of complicated and intriguing interactions among the excited electronic states of N2. Furthermore, solar photon excitation of N2 leading to the production of c4(0) may provide useful data required for evaluation and analysis of dayglow models of the c4(0) issue of the Earth's atmosphere [3]. Detailed results will be presented. This research is based on work supported by NSF grant ATM-0096761. [1] Sprengers, J. P., W. Ubachs, and K. G. H. Baldwin, J. Chem. Phys., 122, 144301 (2005). [2] Lewis, B. R., S. T. Gibson, W. Zhang, H. Lefebvre-Brion, and J.-M. Robbe, J. Chem. Phys., 122, 144302 (2005). [3] e.g., Meier, R. R., Space Sci. Rev., 58, 1 (1991).

  14. Distributed Episodic Exploratory Planning (DEEP)

    DTIC Science & Technology

    2012-04-01

    and numbers representing case identifiers, it showed the memory usage to be extremely minimal. 3.2.2.2. Latent Semantic Analysis (LSA) The DEEP team...faced a challenge in preparing historical StarCraft log files for storage in a DEEP-friendly case-base. Latent semantic analysis (LSA) is a...the document. (Using Latent Semantic Analysis to Improve Information Retrieval, 1988) The challenge for DEEP was to convert a continuous APPROVED FOR

  15. Deep drawing of uranium metal

    SciTech Connect

    Jackson, R J; Lundberg, M R

    1987-01-19

    A procedure was developed to fabricate uranium forming blanks with high ''draw-ability'' so that cup shapes could be easily and uniformly deep drawn. The overall procedure involved a posttreatment to develop optimum mechanical and structural properties in the deep-drawn cups. The fabrication sequence is casting high-purity logs, pucking cast logs, cross-rolling pucks to forming blanks, annealing and outgassing forming blanks, cold deep drawing to hemispherical shapes, and stress relieving, outgassing, and annealing deep-drawn parts to restore ductility and impart dimensional stability. The fabrication development and the resulting fabrication procedure are discussed in detail. The mechanical properties and microstructural properties are discussed.

  16. Deep learning for image classification

    NASA Astrophysics Data System (ADS)

    McCoppin, Ryan; Rizki, Mateen

    2014-06-01

    This paper provides an overview of deep learning and introduces the several subfields of deep learning including a specific tutorial of convolutional neural networks. Traditional methods for learning image features are compared to deep learning techniques. In addition, we present our preliminary classification results, our basic implementation of a convolutional restricted Boltzmann machine on the Mixed National Institute of Standards and Technology database (MNIST), and we explain how to use deep learning networks to assist in our development of a robust gender classification system.

  17. Deep frequency modulation interferometry.

    PubMed

    Gerberding, Oliver

    2015-06-01

    Laser interferometry with pm/Hz precision and multi-fringe dynamic range at low frequencies is a core technology to measure the motion of various objects (test masses) in space and ground based experiments for gravitational wave detection and geodesy. Even though available interferometer schemes are well understood, their construction remains complex, often involving, for example, the need to build quasi-monolithic optical benches with dozens of components. In recent years techniques have been investigated that aim to reduce this complexity by combining phase modulation techniques with sophisticated digital readout algorithms. This article presents a new scheme that uses strong laser frequency modulations in combination with the deep phase modulation readout algorithm to construct simpler and easily scalable interferometers.

  18. Neptune's deep atmosphere revealed

    SciTech Connect

    de Pater, I. ); Atreya, S.K. ); Romani, P.N.

    1989-08-01

    The brightness temperature of Uranus at 20 cm is 260 {plus minus} 10K, while for Neptune it is 318 {plus minus} 16K. Since NH{sub 3} is the dominant absorber at this wavelength the authors have modeled the microwave spectra of Neptune based upon an assumed deep gaseous mixing ratio of NH{sub 3} and subsequent loss into clouds. The difference between the two brightness temperatures implies that the NH{sub 3} mixing ratio below the level of cloud formation on Neptune compared to Uranus is lower by nearly 2 order of magnitude. An alternative explanation is that the 20 cm radiation from Neptune is a combination of thermal plus synchrotron emission as proposed by de Pater and Goertz (1989).

  19. Deep, zonal subequatorial currents.

    PubMed

    Talley, L D; Johnson, G C

    1994-02-25

    Large-scale, westward-extending tongues of warm (Pacific) and cold (Atlantic) water are found between 2000 and 3000 meters both north and south of the equator in the Pacific and Atlantic oceans. They are centered at 5 degrees to 8 degrees north and 10 degrees to 15 degrees south (Pacific) and 5 degrees to 8 degrees north and 15 degrees to 20 degrees south (Atlantic). They are separated in both oceans by a contrasting eastward-extending tongue, centered at about 1 degrees to 2 degrees south, in agreement with previous helium isotope observations (Pacific). Thus, the indicated deep tropical westward flows north and south of the equator and eastward flow near the equator may result from more general forcing than the hydrothermal forcing previously hypothesized.

  20. Method of deep drilling

    DOEpatents

    Colgate, Stirling A.

    1984-01-01

    Deep drilling is facilitated by the following steps practiced separately or in any combination: (1) Periodically and sequentially fracturing zones adjacent the bottom of the bore hole with a thixotropic fastsetting fluid that is accepted into the fracture to overstress the zone, such fracturing and injection being periodic as a function of the progression of the drill. (2) Casing the bore hole with ductile, pre-annealed casing sections, each of which is run down through the previously set casing and swaged in situ to a diameter large enough to allow the next section to run down through it. (3) Drilling the bore hole using a drill string of a low density alloy and a high density drilling mud so that the drill string is partially floated.

  1. Modeling ocean deep convection

    NASA Astrophysics Data System (ADS)

    Canuto, V. M.; Howard, A.; Hogan, P.; Cheng, Y.; Dubovikov, M. S.; Montenegro, L. M.

    The goal of this study is to assess models for Deep Convection with special emphasis on their use in coarse resolution ocean general circulation models. A model for deep convection must contain both vertical transport and lateral advection by mesoscale eddies generated by baroclinic instabilities. The first process operates mostly in the initial phases while the second dominates the final stages. Here, the emphasis is on models for vertical mixing. When mesoscales are not resolved, they are treated with the Gent and McWilliams parameterization. The model results are tested against the measurements of Lavender, Davis and Owens, 2002 (LDO) in the Labrador Sea. Specifically, we shall inquire whether the models are able to reproduce the region of " deepest convection," which we shall refer to as DC (mixed layer depths 800-1300 m). The region where it was measured by Lavender et al. (2002) will be referred to as the LDO region. The main results of this study can be summarized as follows. 3° × 3° resolution. A GFDL-type OGCM with the GISS vertical mixing model predicts DC in the LDO region where the vertical heat diffusivity is found to be 10 m 2 s -1, a value that is quite close to the one suggested by heuristic studies. No parameter was changed from the original GISS model. However, the GISS model also predicts some DC in a region to the east of the LDO region. 3° × 3° resolution. A GFDL-type OGCM with the KPP model (everything else being the same) does not predict DC in the LDO region where the vertical heat diffusivity is found to be 0.5 × 10 -4 m 2 s -1 which is the background value. The KPP model yields DC only to the east of the LDO region. 1° × 1° resolution. In this case, a MY2.5 mixing scheme predicts DC in the LDO region. However, it also predicts DC to the west, north and south of it, where it is not observed. The behavior of the KPP and MY models are somewhat anti-symmetric. The MY models yield too low a mixing in stably stratified flows since they

  2. The Capodimonte Deep Field

    NASA Astrophysics Data System (ADS)

    2001-04-01

    A Window towards the Distant Universe Summary The Osservatorio Astronomico Capodimonte Deep Field (OACDF) is a multi-colour imaging survey project that is opening a new window towards the distant universe. It is conducted with the ESO Wide Field Imager (WFI) , a 67-million pixel advanced camera attached to the MPG/ESO 2.2-m telescope at the La Silla Observatory (Chile). As a pilot project at the Osservatorio Astronomico di Capodimonte (OAC) [1], the OACDF aims at providing a large photometric database for deep extragalactic studies, with important by-products for galactic and planetary research. Moreover, it also serves to gather experience in the proper and efficient handling of very large data sets, preparing for the arrival of the VLT Survey Telescope (VST) with the 1 x 1 degree 2 OmegaCam facility. PR Photo 15a/01 : Colour composite of the OACDF2 field . PR Photo 15b/01 : Interacting galaxies in the OACDF2 field. PR Photo 15c/01 : Spiral galaxy and nebulous object in the OACDF2 field. PR Photo 15d/01 : A galaxy cluster in the OACDF2 field. PR Photo 15e/01 : Another galaxy cluster in the OACDF2 field. PR Photo 15f/01 : An elliptical galaxy in the OACDF2 field. The Capodimonte Deep Field ESO PR Photo 15a/01 ESO PR Photo 15a/01 [Preview - JPEG: 400 x 426 pix - 73k] [Normal - JPEG: 800 x 851 pix - 736k] [Hi-Res - JPEG: 3000 x 3190 pix - 7.3M] Caption : This three-colour image of about 1/4 of the Capodimonte Deep Field (OACDF) was obtained with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the la Silla Observatory. It covers "OACDF Subfield no. 2 (OACDF2)" with an area of about 35 x 32 arcmin 2 (about the size of the full moon), and it is one of the "deepest" wide-field images ever obtained. Technical information about this photo is available below. With the comparatively few large telescopes available in the world, it is not possible to study the Universe to its outmost limits in all directions. Instead, astronomers try to obtain the most detailed

  3. Deep space network energy program

    NASA Technical Reports Server (NTRS)

    Friesema, S. E.

    1980-01-01

    If the Deep Space Network is to exist in a cost effective and reliable manner in the next decade, the problems presented by international energy cost increases and energy availability must be addressed. The Deep Space Network Energy Program was established to implement solutions compatible with the ongoing development of the total network.

  4. Context and Deep Learning Design

    ERIC Educational Resources Information Center

    Boyle, Tom; Ravenscroft, Andrew

    2012-01-01

    Conceptual clarification is essential if we are to establish a stable and deep discipline of technology enhanced learning. The technology is alluring; this can distract from deep design in a surface rush to exploit the affordances of the new technology. We need a basis for design, and a conceptual unit of organization, that are applicable across…

  5. Deep sulfur cycle

    NASA Astrophysics Data System (ADS)

    Shimizu, N.; Mandeville, C. W.

    2009-12-01

    Geochemical cycle of sulfur in near-surface reservoirs has been a subject of intense studies for decades. It has been shown that sulfur isotopic compositions of sedimentary sulfides and sulfates record interactions of the atmosphere, hydrosphere, biosphere and lithosphere, with δ34S of sedimentary sulfides continuously decreasing from 0‰ toward present-day values of ~-30 to -40‰ over the Phanerozoic (e.g., Canfield, 2004). It has also been shown that microbial reduction of the present-day seawater sulfate (δ34S=+21‰) results in large shifts in isotopic compositions of secondary pyrites in altered oceanic crust (to δ34S=-70‰: Rouxel et al., 2009). How much of these near surface isotopic variations survive during deep geochemical cycle of sulfur interacting with the mantle infinite reservoir with δ34S=0‰? Could extent of their survival be used as a tracer of processes and dynamics involved in deep geochemical cycle? As a first step toward answering these questions, δ34S was determined in-situ using a Cameca IMS 1280 ion microprobe at Woods Hole Oceanographic Institution in materials representing various domains of deep geochemical cycle. They include pyrites in altered MORB as potential subducting materials and pyrites in UHP eclogites as samples that have experienced subduction zone processes, and mantle-derived melts are represented by olivine-hosted melt inclusions in MORB and those in IAB, and undegassed submarine OIB glasses. Salient features of the results include: (1) pyrites in altered MORB (with O. Rouxel; from ODP site 801 and ODP Hole 1301B) range from -70 to +19‰, (2) pyrites in UHP eclogites from the Western Gneiss Region, Norway (with B. Hacker and A. Kylander-Clark) show a limited overall range from -3.4 to + 2.8‰ among five samples, with one of them covering almost the entire range, indicating limited scale lengths of isotopic equilibration during subduction, (3) olivine-hosted melt inclusions in arc basalts from Galunggung (-2

  6. Deep Learning the Universe

    NASA Astrophysics Data System (ADS)

    Singh, Shiwangi; Bard, Deborah

    2017-01-01

    Weak gravitational lensing is an effective tool to map the structure of matter in the universe, and has been used for more than ten years as a probe of the nature of dark energy. Beyond the well-established two-point summary statistics, attention is now turning to methods that use the full statistical information available in the lensing observables, through analysis of the reconstructed shear field. This offers an opportunity to take advantage of powerful deep learning methods for image analysis. We present two early studies that demonstrate that deep learning can be used to characterise features in weak lensing convergence maps, and to identify the underlying cosmological model that produced them.We developed an unsupervised Denoising Convolutional Autoencoder model in order to learn an abstract representation directly from our data. This model uses a convolution-deconvolution architecture, which is fed with input data (corrupted with binomial noise to prevent over-fitting). Our model effectively trains itself to minimize the mean-squared error between the input and the output using gradient descent, resulting in a model which, theoretically, is broad enough to tackle other similarly structured problems. Using this model we were able to successfully reconstruct simulated convergence maps and identify the structures in them. We also determined which structures had the highest “importance” - i.e. which structures were most typical of the data. We note that the structures that had the highest importance in our reconstruction were around high mass concentrations, but were highly non-Gaussian.We also developed a supervised Convolutional Neural Network (CNN) for classification of weak lensing convergence maps from two different simulated theoretical models. The CNN uses a softmax classifier which minimizes a binary cross-entropy loss between the estimated distribution and true distribution. In other words, given an unseen convergence map the trained CNN determines

  7. Spin Polarization of Rb and Cs np ^{2}P_{3/2} (n=5, 6) Atoms by Circularly Polarized Photoexcitation of a Transient Diatomic Molecule.

    PubMed

    Mironov, A E; Hewitt, J D; Eden, J G

    2017-03-17

    We report the selective population of Rb or Cs np ^{2}P_{3/2} (n=5, 6; F=4, 5) hyperfine states by the photodissociation of a transient, alkali-rare gas diatomic molecule. Circularly polarized (σ^{-}), amplified spontaneous emission (ASE) on the D_{2} line of Rb or Cs (780.0 and 852.1 nm, respectively) is generated when Rb-Xe or Cs-Xe ground state collision pairs are photoexcited by a σ^{+}-polarized optical field having a wavelength within the D_{2} blue satellite continuum, associated with the B^{2}Σ_{1/2}^{+}←X^{2}Σ_{1/2}^{+} (free←free) transition of the diatomic molecule. The degree of spin polarization of Cs (6p ^{2}P_{3/2}), specifically, is found to be dependent on the interatomic distance (R) at which the excited complex is born, a result attributed to the structure of the B^{2}Σ_{1/2}^{+} state. For Cs-Xe atomic pairs, tuning the wavelength of the optical field from 843 to 848 nm varies the degree of circular polarization of the ASE from 63% to almost unity because of the perturbation, in the 5≤R≤6  Å interval, of the ^{2}Σ_{1/2}^{+} potential by a dσ molecular orbital associated with a higher ^{2}Λ electronic state. Monitoring only the Cs 6p ^{2}P_{3/2} spin polarization reveals a previously unobserved interaction of CsXe (B^{2}Σ_{1/2}^{+}) with the lowest vibrational levels of a ^{2}Λ state derived from Cs (5d)+Xe. By inserting a molecular intermediate into the alkali atom excitation mechanism, these experiments realize electronic spin polarization through populating no more than two np ^{2}P_{3/2} hyperfine states, and demonstrate a sensitive spectroscopic probe of R-dependent state-state interactions and their impact on interatomic potentials.

  8. Etude experimentale de la photoexcitation des colorants de type anthracene, azobenzene et thioindigo dans des matrices de cristaux liquides nematiques et smectiques

    NASA Astrophysics Data System (ADS)

    Saad, Bendaoud

    Nous avons étudié le comportement de différents colorants (tétracène et azobenzènes AZD3, DR1 et D2) dans des matrices de cristaux liquides (E7 et 5CB). Les résultats obtenus ont montré que la réorientation optique des molécules de cristaux liquides se produit à des intensités extrêmement faibles (~1 μW/cm 2). Nous avons attribué cet effet à l'interaction entre les molécules des colorants photoexcitées et celles des cristaux liquides hôtes. Ces interactions se produisent lorsque les molécules dichroïques exçitées transitent entre des états triplets intermédiaires tout en conduisant à la génération d'un nouveau moment optique géant, responsable de la réorientation des molécules. Le changement de la forme de la molécule du colorant, dû à l'isomérisation Trans-Cis , est à l'origine de la création de ce moment. Ce qui distingue notre réorientation moléculaire de celle obtenue sur d'autres systèmes hôtes-dopants est que les molécules sont repoussées du champ électrique de la lumière. Par ailleurs, cette réorientation est accompagnée d'une diffusion anisotrope des molécules excitées. Nous avons aussi étudié le cristal liquide PhBz rendu ferroélectrique en le dopant par des molécules thioindigos. En exploitant l'augmentation de la polarisation spontanée due à la photoisomérisation du colorant, nous avons pu réaliser un hologramme dynamique contrôlable par un champ optique assisté par une tension statique.

  9. Deep atomic force microscopy

    SciTech Connect

    Barnard, H.; Drake, B.; Randall, C.; Hansma, P. K.

    2013-12-15

    The Atomic Force Microscope (AFM) possesses several desirable imaging features including the ability to produce height profiles as well as two-dimensional images, in fluid or air, at high resolution. AFM has been used to study a vast selection of samples on the scale of angstroms to micrometers. However, current AFMs cannot access samples with vertical topography of the order of 100 μm or greater. Research efforts have produced AFM scanners capable of vertical motion greater than 100 μm, but commercially available probe tip lengths are still typically less than 10 μm high. Even the longest probe tips are below 100 μm and even at this range are problematic. In this paper, we present a method to hand-fabricate “Deep AFM” probes with tips of the order of 100 μm and longer so that AFM can be used to image samples with large scale vertical topography, such as fractured bone samples.

  10. Operation Deep Sweep

    NASA Astrophysics Data System (ADS)

    Bell, Peter M.

    Fifty scientists and a crew of 18 have embarked on a 64,000 km odyssey to explore the Pacific from pole to pole—the most ambitious program in the history of the marine geology branch of the U.S. Geological Survey (USGS). Called Operation Deep Sweep, the 1-year cruise will search areas above the Arctic Circle, off of Alaska, to McMurdo Sound in Antarctica. The 63-m, 1,300-tonne research vessel Samuel P. Lee sailed from its home port of Redwood City, Calif., to San Francisco to begin the first leg of the lengthy journey.According to USGS officials and the cosponsoring Circum-Pacific Council for Energy and Mineral Resources of the American Association of Petroleum Geologists, the cruise will ultimately involve 150 scientists, some of them representing Germany, France, Australia, and New Zealand. David Howell, branch chief of Pacific Marine Geology for the USGS, said the voyage of the Lee was “the most far reaching and of the longest duration” ever attempted by his unit. He said the cruise would string together a large number of scientific experiments spanning the Pacific. Howell likened the voyage to the Lewis and Clark Expedition of 1803-1806 (which explored Louisiana and the western United States) because “we're going into unknown territory and into regions not studied except in the most cursory manner.”

  11. Deep learning for computational chemistry.

    PubMed

    Goh, Garrett B; Hodas, Nathan O; Vishnu, Abhinav

    2017-03-08

    The rise and fall of artificial neural networks is well documented in the scientific literature of both computer science and computational chemistry. Yet almost two decades later, we are now seeing a resurgence of interest in deep learning, a machine learning algorithm based on multilayer neural networks. Within the last few years, we have seen the transformative impact of deep learning in many domains, particularly in speech recognition and computer vision, to the extent that the majority of expert practitioners in those field are now regularly eschewing prior established models in favor of deep learning models. In this review, we provide an introductory overview into the theory of deep neural networks and their unique properties that distinguish them from traditional machine learning algorithms used in cheminformatics. By providing an overview of the variety of emerging applications of deep neural networks, we highlight its ubiquity and broad applicability to a wide range of challenges in the field, including quantitative structure activity relationship, virtual screening, protein structure prediction, quantum chemistry, materials design, and property prediction. In reviewing the performance of deep neural networks, we observed a consistent outperformance against non-neural networks state-of-the-art models across disparate research topics, and deep neural network-based models often exceeded the "glass ceiling" expectations of their respective tasks. Coupled with the maturity of GPU-accelerated computing for training deep neural networks and the exponential growth of chemical data on which to train these networks on, we anticipate that deep learning algorithms will be a valuable tool for computational chemistry. © 2017 Wiley Periodicals, Inc.

  12. Microbial Life in the Deep Subsurface: Deep, Hot and Radioactive

    NASA Technical Reports Server (NTRS)

    DeStefano, Andrea L.; Ford, Jill C.; Winsor, Seana K.; Allen, Carlton C.; Miller, Judith; McNamara, Karen M.; Gibson, Everett K., Jr.

    2000-01-01

    Recent studies, motivated in part by the search for extraterrestrial life, continue to expand the recognized limits of Earth's biosphere. This work explored evidence for life a high-temperature, radioactive environment in the deep subsurface.

  13. Deep Learning in Drug Discovery.

    PubMed

    Gawehn, Erik; Hiss, Jan A; Schneider, Gisbert

    2016-01-01

    Artificial neural networks had their first heyday in molecular informatics and drug discovery approximately two decades ago. Currently, we are witnessing renewed interest in adapting advanced neural network architectures for pharmaceutical research by borrowing from the field of "deep learning". Compared with some of the other life sciences, their application in drug discovery is still limited. Here, we provide an overview of this emerging field of molecular informatics, present the basic concepts of prominent deep learning methods and offer motivation to explore these techniques for their usefulness in computer-assisted drug discovery and design. We specifically emphasize deep neural networks, restricted Boltzmann machine networks and convolutional networks.

  14. Deep UV LEDs

    NASA Astrophysics Data System (ADS)

    Han, Jung; Amano, Hiroshi; Schowalter, Leo

    2014-06-01

    Deep ultraviolet (DUV) photons interact strongly with a broad range of chemical and biological molecules; compact DUV light sources could enable a wide range of applications in chemi/bio-sensing, sterilization, agriculture, and industrial curing. The much shorter wavelength also results in useful characteristics related to optical diffraction (for lithography) and scattering (non-line-of-sight communication). The family of III-N (AlGaInN) compound semiconductors offers a tunable energy gap from infrared to DUV. While InGaN-based blue light emitters have been the primary focus for the obvious application of solid state lighting, there is a growing interest in the development of efficient UV and DUV light-emitting devices. In the past few years we have witnessed an increasing investment from both government and industry sectors to further the state of DUV light-emitting devices. The contributions in Semiconductor Science and Technology 's special issue on DUV devices provide an up-to-date snapshot covering many relevant topics in this field. Given the expected importance of bulk AlN substrate in DUV technology, we are pleased to include a review article by Hartmann et al on the growth of AlN bulk crystal by physical vapour transport. The issue of polarization field within the deep ultraviolet LEDs is examined in the article by Braut et al. Several commercial companies provide useful updates in their development of DUV emitters, including Nichia (Fujioka et al ), Nitride Semiconductors (Muramoto et al ) and Sensor Electronic Technology (Shatalov et al ). We believe these articles will provide an excellent overview of the state of technology. The growth of AlGaN heterostructures by molecular beam epitaxy, in contrast to the common organo-metallic vapour phase epitaxy, is discussed by Ivanov et al. Since hexagonal boron nitride (BN) has received much attention as both a UV and a two-dimensional electronic material, we believe it serves readers well to include the

  15. Deep Space Telecommunications Systems Engineering

    NASA Technical Reports Server (NTRS)

    Yuen, J. H. (Editor)

    1982-01-01

    Descriptive and analytical information useful for the optimal design, specification, and performance evaluation of deep space telecommunications systems is presented. Telemetry, tracking, and command systems, receiver design, spacecraft antennas, frequency selection, interference, and modulation techniques are addressed.

  16. NEW APPROACHES: Deep inelastic scattering

    NASA Astrophysics Data System (ADS)

    Allday, J.

    1998-01-01

    Feynman diagrams can be used to explain deep inelastic scattering, but it must be remembered that the emission and absorption of a photon are not independent events - the underlying field is important.

  17. What Is Deep Vein Thrombosis?

    MedlinePlus

    ... deep vein of the leg can break off, travel to the lungs, and block blood flow. Rate This Content: NEXT >> Updated: October 28, 2011 Twitter Facebook YouTube Google+ SITE INDEX ACCESSIBILITY PRIVACY STATEMENT FOIA NO FEAR ACT ...

  18. Goldstone Deep Space Communication Complex

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Three 34m (110 ft.) diameter Beam Waveguide antennas located at the Goldstone Deep Space Communications Complex, situated in the Mojave Desert in California. This is one of three complexes which comprise NASA's Deep Space Network (DSN). The DSN provides radio communications for all of NASA's interplanetary spacecraft and is also utilized for radio astronomy and radar observations of the solar system and the universe.

  19. Hot, deep origin of petroleum: deep basin evidence and application

    USGS Publications Warehouse

    Price, Leigh C.

    1978-01-01

    Use of the model of a hot deep origin of oil places rigid constraints on the migration and entrapment of crude oil. Specifically, oil originating from depth migrates vertically up faults and is emplaced in traps at shallower depths. Review of petroleum-producing basins worldwide shows oil occurrence in these basins conforms to the restraints of and therefore supports the hypothesis. Most of the world's oil is found in the very deepest sedimentary basins, and production over or adjacent to the deep basin is cut by or directly updip from faults dipping into the basin deep. Generally the greater the fault throw the greater the reserves. Fault-block highs next to deep sedimentary troughs are the best target areas by the present concept. Traps along major basin-forming faults are quite prospective. The structural style of a basin governs the distribution, types, and amounts of hydrocarbons expected and hence the exploration strategy. Production in delta depocenters (Niger) is in structures cut by or updip from major growth faults, and structures not associated with such faults are barren. Production in block fault basins is on horsts next to deep sedimentary troughs (Sirte, North Sea). In basins whose sediment thickness, structure and geologic history are known to a moderate degree, the main oil occurrences can be specifically predicted by analysis of fault systems and possible hydrocarbon migration routes. Use of the concept permits the identification of significant targets which have either been downgraded or ignored in the past, such as production in or just updip from thrust belts, stratigraphic traps over the deep basin associated with major faulting, production over the basin deep, and regional stratigraphic trapping updip from established production along major fault zones.

  20. Sulfur mass-independent fractionation during photolysis and photoexcitation of SO2 and CS2 and implications to the source reactions for Archean sulfur isotope anomaly

    NASA Astrophysics Data System (ADS)

    Ono, S.; Whitehill, A. R.; Oduro, H. D.

    2012-12-01

    produces large positive anomaly in both Δ33S and Δ36S (up to 100 ‰) even in optically thin conditions, suggesting quantum dynamic origin of the S-MIF. Brown polymer material produced under photolysis and photoexciation of CS2 also yield S-MIF but isotope patterns are different from those of SO2 photochemistry and different from Archean pattern. If SO2 photolysis and photoexcitation are the main source of Archean S-MIF, the different Δ36S/Δ33S values can be linked to the different magnitude of contributions from SO2 photolysis and photoexciation. For example, increased contribution of photoexciation band is expected under a thick organic haze layer that attenuates high energy UV and chemically traps excited state SO2.

  1. A Deep ALMA Image of the Hubble Ultra Deep Field

    NASA Astrophysics Data System (ADS)

    Dunlop, J. S.

    2016-12-01

    Although primarily designed as a high-resolution imaging spectrometer at submillimetre/millimetre wavelengths, the Atacama Large Millimeter/submillimeter Array (ALMA) has a vital role to play in producing the key deep, unconfused, submillimetre/millimetre continuum surveys required to bridge the current gap in our understanding of visible and dust-obscured star formation in the young Universe. The first such survey has now been completed, comprising a mosaic of 45 ALMA pointings at a wavelength of 1.3 mm, covering the Hubble Ultra Deep Field (HUDF). This deep, homogeneous ALMA survey, combined with the wealth of existing data in the HUDF, has already provided new clarity on the nature of dusty star-forming galaxies, and the relative evolution of dust-obscured and unobscured star formation over cosmic time.

  2. Deep RNNs for video denoising

    NASA Astrophysics Data System (ADS)

    Chen, Xinyuan; Song, Li; Yang, Xiaokang

    2016-09-01

    Video denoising can be described as the problem of mapping from a specific length of noisy frames to clean one. We propose a deep architecture based on Recurrent Neural Network (RNN) for video denoising. The model learns a patch-based end-to-end mapping between the clean and noisy video sequences. It takes the corrupted video sequences as the input and outputs the clean one. Our deep network, which we refer to as deep Recurrent Neural Networks (deep RNNs or DRNNs), stacks RNN layers where each layer receives the hidden state of the previous layer as input. Experiment shows (i) the recurrent architecture through temporal domain extracts motion information and does favor to video denoising, and (ii) deep architecture have large enough capacity for expressing mapping relation between corrupted videos as input and clean videos as output, furthermore, (iii) the model has generality to learned different mappings from videos corrupted by different types of noise (e.g., Poisson-Gaussian noise). By training on large video databases, we are able to compete with some existing video denoising methods.

  3. Deep Learning and Bayesian Methods

    NASA Astrophysics Data System (ADS)

    Prosper, Harrison B.

    2017-03-01

    A revolution is underway in which deep neural networks are routinely used to solve diffcult problems such as face recognition and natural language understanding. Particle physicists have taken notice and have started to deploy these methods, achieving results that suggest a potentially significant shift in how data might be analyzed in the not too distant future. We discuss a few recent developments in the application of deep neural networks and then indulge in speculation about how such methods might be used to automate certain aspects of data analysis in particle physics. Next, the connection to Bayesian methods is discussed and the paper ends with thoughts on a significant practical issue, namely, how, from a Bayesian perspective, one might optimize the construction of deep neural networks.

  4. Deep Impact Network Experiment (DINET)

    NASA Technical Reports Server (NTRS)

    Burleigh, Scott

    2008-01-01

    DINET is a technology development experiment intended to increase the technical readiness of JPL s implementation of DTN protocols - "ION". The objective is to advance ION in flight and ground SW to TRL 8, with code of sufficient quality that future flight projects can easily use it at low risk. DINET is to be implemented on the Deep Impact flyby spacecraft. DINET operations will be performed in late 2008 during the Deep Impact spacecraft team "stand down" after EPOCH operations and before the start of development for DIXI operations.

  5. Stimulation Technologies for Deep Well Completions

    SciTech Connect

    2003-09-30

    The Department of Energy (DOE) is sponsoring the Deep Trek Program targeted at improving the economics of drilling and completing deep gas wells. Under the DOE program, Pinnacle Technologies is conducting a study to evaluate the stimulation of deep wells. The objective of the project is to assess U.S. deep well drilling & stimulation activity, review rock mechanics & fracture growth in deep, high pressure/temperature wells and evaluate stimulation technology in several key deep plays. An assessment of historical deep gas well drilling activity and forecast of future trends was completed during the first six months of the project; this segment of the project was covered in Technical Project Report No. 1. The second progress report covers the next six months of the project during which efforts were primarily split between summarizing rock mechanics and fracture growth in deep reservoirs and contacting operators about case studies of deep gas well stimulation.

  6. STIMULATION TECHNOLOGIES FOR DEEP WELL COMPLETIONS

    SciTech Connect

    Stephen Wolhart

    2003-06-01

    The Department of Energy (DOE) is sponsoring a Deep Trek Program targeted at improving the economics of drilling and completing deep gas wells. Under the DOE program, Pinnacle Technologies is conducting a project to evaluate the stimulation of deep wells. The objective of the project is to assess U.S. deep well drilling & stimulation activity, review rock mechanics & fracture growth in deep, high pressure/temperature wells and evaluate stimulation technology in several key deep plays. Phase 1 was recently completed and consisted of assessing deep gas well drilling activity (1995-2007) and an industry survey on deep gas well stimulation practices by region. Of the 29,000 oil, gas and dry holes drilled in 2002, about 300 were drilled in the deep well; 25% were dry, 50% were high temperature/high pressure completions and 25% were simply deep completions. South Texas has about 30% of these wells, Oklahoma 20%, Gulf of Mexico Shelf 15% and the Gulf Coast about 15%. The Rockies represent only 2% of deep drilling. Of the 60 operators who drill deep and HTHP wells, the top 20 drill almost 80% of the wells. Six operators drill half the U.S. deep wells. Deep drilling peaked at 425 wells in 1998 and fell to 250 in 1999. Drilling is expected to rise through 2004 after which drilling should cycle down as overall drilling declines.

  7. Electrochemical Machining Removes Deep Obstructions

    NASA Technical Reports Server (NTRS)

    Catania, Mark J.

    1987-01-01

    Electrochemical machining (ECM) is effective way of removing obstructing material between two deep holes supposed to intersect but do not because of misalignment of drilling tools. ECM makes it possible to rework costly castings otherwise scrapped. Method fast even for tough or hard alloys and complicated three-dimensional shapes.

  8. A Deep-Sea Simulation.

    ERIC Educational Resources Information Center

    Montes, Georgia E.

    1997-01-01

    Describes an activity that simulates exploration techniques used in deep-sea explorations and teaches students how this technology can be used to take a closer look inside volcanoes, inspect hazardous waste sites such as nuclear reactors, and explore other environments dangerous to humans. (DDR)

  9. Keeping It Simple and Deep.

    ERIC Educational Resources Information Center

    Strong, Richard; Silver, Harvey; Perini, Matthew

    1999-01-01

    Like today's educators, Japanese haiku poets were caught between standards (like courtly love) and everyday realities. From this tension, they created a remarkable poetic form. Three examples from teachers' professional development work apply simple-and-deep principles to listening tasks, an assessment "deal," and curricular-standards…

  10. Ploughing the deep sea floor.

    PubMed

    Puig, Pere; Canals, Miquel; Company, Joan B; Martín, Jacobo; Amblas, David; Lastras, Galderic; Palanques, Albert

    2012-09-13

    Bottom trawling is a non-selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor. The direct impact of this technique on fish populations and benthic communities has received much attention, but trawling can also modify the physical properties of seafloor sediments, water–sediment chemical exchanges and sediment fluxes. Most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments, however, where the capacity of trawling to modify the seafloor morphology coexists with high-energy natural processes driving sediment erosion, transport and deposition. Here we show that on upper continental slopes, the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales. We found that trawling-induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time, reducing its original complexity as shown by high-resolution seafloor relief maps. Our results suggest that in recent decades, following the industrialization of fishing fleets, bottom trawling has become an important driver of deep seascape evolution. Given the global dimension of this type of fishery, we anticipate that the morphology of the upper continental slope in many parts of the world’s oceans could be altered by intensive bottom trawling, producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land.

  11. Digging Deeper: The Deep Web.

    ERIC Educational Resources Information Center

    Turner, Laura

    2001-01-01

    Focuses on the Deep Web, defined as Web content in searchable databases of the type that can be found only by direct query. Discusses the problems of indexing; inability to find information not indexed in the search engine's database; and metasearch engines. Describes 10 sites created to access online databases or directly search them. Lists ways…

  12. Lessons from Earth's Deep Time

    ERIC Educational Resources Information Center

    Soreghan, G. S.

    2005-01-01

    Earth is a repository of data on climatic changes from its deep-time history. Article discusses the collection and study of these data to predict future climatic changes, the need to create national study centers for the purpose, and the necessary cooperation between different branches of science in climatic research.

  13. C5′- and C3′-sugar radicals produced via photo-excitation of one-electron oxidized adenine in 2′-deoxyadenosine and its derivatives

    PubMed Central

    Adhikary, Amitava; Becker, David; Collins, Sean; Koppen, Jessica; Sevilla, Michael D.

    2006-01-01

    We report that photo-excitation of one-electron-oxidized adenine [A(-H)•] in dAdo and its 2′-deoxyribonucleotides leads to formation of deoxyribose sugar radicals in remarkably high yields. Illumination of A(-H)• in dAdo, 3′-dAMP and 5′-dAMP in aqueous glasses at 143 K leads to 80-100% conversion to sugar radicals at C5′ and C3′. The position of the phosphate in 5′- and 3′-dAMP is observed to deactivate radical formation at the site of substitution. In addition, the pH has a crucial influence on the site of sugar radical formation; e.g. at pH ∼5, photo-excitation of A(-H)• in dAdo at 143 K produces mainly C5′• whereas only C3′• is observed at high pH ∼12. 13C substitution at C5′ in dAdo yields 13C anisotropic couplings of (28, 28, 84) G whose isotropic component 46.7 G identifies formation of the near planar C5′•. A β-13C 16 G isotropic coupling from C3′• is also found. These results are found to be in accord with theoretically calculated 13C couplings at C5′ [DFT, B3LYP, 6-31(G) level] for C5′• and C3′•. Calculations using time-dependent density functional theory [TD-DFT B3LYP, 6-31G(d)] confirm that transitions in the near UV and visible induce hole transfer from the base radical to the sugar group leading to sugar radical formation. PMID:16537838

  14. A strategy to increase the efficiency of the dye-sensitized TiO2 solar cells operated by photoexcitation of dye-to-TiO2 charge-transfer bands.

    PubMed

    Tae, Eunju Lee; Lee, Seung Hwan; Lee, Jae Kwan; Yoo, Su San; Kang, Eun Ju; Yoon, Kyung Byung

    2005-12-01

    Dye-sensitized nanoporous TiO2 solar cells (DSSCs) can be classified into two types, namely, Type-I and Type-II. Type-I DSSCs are the DSSCs in which electrons are injected from the adsorbed dyes by photoexcitation of the dyes followed by electron injection from the excited dyes to TiO2 (pathway A). Type-II DSSCs are the DSSCs in which electrons are injected not only by pathway A but also by direct one-step electron injection from the dyes to TiO2 by photoexcitation of the dye-to-TiO2 charge-transfer (DTCT) bands (pathway B). The DSSCs employing catechol (Cat) or its derivatives as the sensitizers have been the typical examples of Type-II DSSCs. However, their solar energy-to-electricity conversion efficiencies (eta) have never exceeded 0.7%, and the external quantum efficiencies (EQE) at the absorption maximums of the DTCT bands have never exceeded 10%. We found that the attachment of electron-donating compounds such as (pyridin-4-yl)vinyl and (quinolin-4-yl)vinyl, respectively, to Cat (designated as Cat-v-P and Cat-v-Q, respectively) leads to 2- and 2.7-fold increases, respectively, in eta, driven by large increases in short circuit current (Jsc). The EQE increased from 8.5 to 30% at 400 nm upon changing from Cat to Cat-v-P, at which only the DTCT band absorbs. In the case of the Cat-v-Q-sensitized DSSC, even the eta obtained by exciting only the DTCT band was higher than 1%. Interestingly, the illumination of only the DTCT band resulted in the increase of fill factor from 62.6% to 72.3%. This paper provides for the first time an insight into the strategy to increase the eta values of Type-II DSSCs.

  15. Stimulation Technologies for Deep Well Completions

    SciTech Connect

    Stephen Wolhart

    2005-06-30

    The Department of Energy (DOE) is sponsoring the Deep Trek Program targeted at improving the economics of drilling and completing deep gas wells. Under the DOE program, Pinnacle Technologies conducted a study to evaluate the stimulation of deep wells. The objective of the project was to review U.S. deep well drilling and stimulation activity, review rock mechanics and fracture growth in deep, high-pressure/temperature wells and evaluate stimulation technology in several key deep plays. This report documents results from this project.

  16. DeepSurveyCam--A Deep Ocean Optical Mapping System.

    PubMed

    Kwasnitschka, Tom; Köser, Kevin; Sticklus, Jan; Rothenbeck, Marcel; Weiß, Tim; Wenzlaff, Emanuel; Schoening, Timm; Triebe, Lars; Steinführer, Anja; Devey, Colin; Greinert, Jens

    2016-01-28

    Underwater photogrammetry and in particular systematic visual surveys of the deep sea are by far less developed than similar techniques on land or in space. The main challenges are the rough conditions with extremely high pressure, the accessibility of target areas (container and ship deployment of robust sensors, then diving for hours to the ocean floor), and the limitations of localization technologies (no GPS). The absence of natural light complicates energy budget considerations for deep diving flash-equipped drones. Refraction effects influence geometric image formation considerations with respect to field of view and focus, while attenuation and scattering degrade the radiometric image quality and limit the effective visibility. As an improvement on the stated issues, we present an AUV-based optical system intended for autonomous visual mapping of large areas of the seafloor (square kilometers) in up to 6000 m water depth. We compare it to existing systems and discuss tradeoffs such as resolution vs. mapped area and show results from a recent deployment with 90,000 mapped square meters of deep ocean floor.

  17. DeepSurveyCam—A Deep Ocean Optical Mapping System

    PubMed Central

    Kwasnitschka, Tom; Köser, Kevin; Sticklus, Jan; Rothenbeck, Marcel; Weiß, Tim; Wenzlaff, Emanuel; Schoening, Timm; Triebe, Lars; Steinführer, Anja; Devey, Colin; Greinert, Jens

    2016-01-01

    Underwater photogrammetry and in particular systematic visual surveys of the deep sea are by far less developed than similar techniques on land or in space. The main challenges are the rough conditions with extremely high pressure, the accessibility of target areas (container and ship deployment of robust sensors, then diving for hours to the ocean floor), and the limitations of localization technologies (no GPS). The absence of natural light complicates energy budget considerations for deep diving flash-equipped drones. Refraction effects influence geometric image formation considerations with respect to field of view and focus, while attenuation and scattering degrade the radiometric image quality and limit the effective visibility. As an improvement on the stated issues, we present an AUV-based optical system intended for autonomous visual mapping of large areas of the seafloor (square kilometers) in up to 6000 m water depth. We compare it to existing systems and discuss tradeoffs such as resolution vs. mapped area and show results from a recent deployment with 90,000 mapped square meters of deep ocean floor. PMID:26828495

  18. Deep Space 1 in Cleanroom

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Deep Space 1 was launched in October 1998 as part of NASA's New Millennium Program, which is managed by JPL for NASA's Office of Space Science, Washington, DC. The California Institute of Technology in Pasadena manages JPL for NASA. Deep Space 1 used a unique ion drive propulsion system. Unlike the fireworks of most chemical rockets using solid or liquid fuels, the ion drive emits only an eerie blue glow as ionized (electrically charged) atoms of xenon are pushed out of the engine. Xenon is the same gas found in photo flash tubes and many lighthouse bulbs. The almost imperceptible thrust from the system is equivalent to the pressure exerted by a sheet of paper held in the palm of your hand. The ion engine is very slow to pick up speed, but over the long haul it can deliver 10 times as much thrust per pound of fuel as more traditional rockets. Previous ion propulsion systems, like those found on some communications satellites, were not used as the main engines, but only to keep the satellites on track. Deep Space 1 is the first spacecraft to use this important technology as its primary means of propulsion. The importance of ion propulsion is its great efficiency,' says Dr. Marc Rayman, project manager for Deep Space 1. 'It uses very little propellant, and that means it weighs less so it can use a less expensive launch vehicle and ultimately go much faster than other spacecraft. This opens the solar system to many future exciting missions which otherwise would have been unaffordable or even impossible,' added Dr. Rayman. The ion particles travel out at about 68,000 miles per hour. However, Deep Space 1 doesn't move that fast in the other direction, because it is much heavier than the ion particles. By the end of the mission, the ion engine will have changed the spacecraft's speed by about 6,800 mph (over 11,000 kph). The technology is so efficient that it only consumes about 3.5 ounces (100 g) of xenon per day, taking about four days to expend just one pound (0.4 kg

  19. Eco-Philosophy and Deep Ecology.

    ERIC Educational Resources Information Center

    Skolimowski, Henryk

    1988-01-01

    Criticizes the Deep Ecology Movement as a new ecological world view. Discusses the limits of this philosophy including its views of destiny, evolution and cosmology. Concludes that although its intentions are admirable, Deep Ecology leaves too much unanswered. (CW)

  20. Weighing the deep continental biosphere.

    PubMed

    McMahon, Sean; Parnell, John

    2014-01-01

    There is abundant evidence for widespread microbial activity in deep continental fractures and aquifers, with important implications for biogeochemical cycling on Earth and the habitability of other planetary bodies. Whitman et al. (P Natl Acad Sci USA, 95, 1998, 6578) estimated a continental subsurface biomass on the order of 10(16) -10(17) g C. We reassess this value in the light of more recent data including over 100 microbial population density measurements from groundwater around the world. Making conservative assumptions about cell carbon content and the ratio of attached and free-living microorganisms, we find that the evidence continues to support a deep continental biomass estimate of 10(16) -10(17) g C, or 2-19% of Earth's total biomass.

  1. Deep learning for computational biology.

    PubMed

    Angermueller, Christof; Pärnamaa, Tanel; Parts, Leopold; Stegle, Oliver

    2016-07-29

    Technological advances in genomics and imaging have led to an explosion of molecular and cellular profiling data from large numbers of samples. This rapid increase in biological data dimension and acquisition rate is challenging conventional analysis strategies. Modern machine learning methods, such as deep learning, promise to leverage very large data sets for finding hidden structure within them, and for making accurate predictions. In this review, we discuss applications of this new breed of analysis approaches in regulatory genomics and cellular imaging. We provide background of what deep learning is, and the settings in which it can be successfully applied to derive biological insights. In addition to presenting specific applications and providing tips for practical use, we also highlight possible pitfalls and limitations to guide computational biologists when and how to make the most use of this new technology.

  2. Correction of deep overbite in adults.

    PubMed

    Nanda, R

    1997-01-01

    Deep overbite is one of the most common features of adult malocclusions. Treatment of deep overbites involves a careful diagnosis, treatment plan, and mechanics plan. Pure intrusion of upper or lower incisors alone or in combination with flaring and extrusion of posterior teeth are common methods to correct deep overbites. This article describes appliance systems and biomechanical considerations necessary for intrusion of incisors.

  3. The Deep Structure of the Paragraph.

    ERIC Educational Resources Information Center

    Woodson, Linda

    Paragraphs, as well as sentences, can be spoken of as having a deep and a surface structure. The amount of deep structure of the paragraph that is mapped onto the surface paragraph is related to the mode of discourse in which the paragraph is found: the deep structure in scientific paragraphs is relatively uncomplicated with few assumptions made;…

  4. Tropical deep convective cloud morphology

    NASA Astrophysics Data System (ADS)

    Igel, Matthew R.

    A cloud-object partitioning algorithm is developed. It takes contiguous CloudSat cloudy regions and identifies various length scales of deep convective clouds from a tropical, oceanic subset of data. The methodology identifies a level above which anvil characteristics become important by analyzing the cloud object shape. Below this level in what is termed the pedestal region, convective cores are identified based on reflectivity maxima. Identifying these regions allows for the assessment of length scales of the anvil and pedestal of the deep convective clouds. Cloud objects are also appended with certain environmental quantities from the ECMWF reanalysis. Simple geospatial and temporal assessments show that the cloud object technique agrees with standard observations of local frequency of deep-convective cloudiness. Additionally, the nature of cloud volume scale populations is investigated. Deep convection is seen to exhibit power-law scaling. It is suggested that this scaling has implications for the continuous, scale invariant, and random nature of the physics controlling tropical deep convection and therefore on the potentially unphysical nature of contemporary convective parameterizations. Deep-convective clouds over tropical oceans play important roles in Earth's climate system. The response of tropical, deep convective clouds to sea surface temperatures (SSTs) is investigated using this new data set. Several previously proposed feedbacks are examined: the FAT hypothesis, the Iris hypothesis, and the Thermostat hypothesis. When the data are analyzed per cloud object, each hypothesis is broadly found to correctly predict cloud behavior in nature, although it appears that the FAT hypothesis needs a slight modification to allow for cooling cloud top temperatures with increasing SSTs. A new response that shows that the base temperature of deep convective anvils remains approximately constant with increasing SSTs is introduced. These cloud-climate feedbacks are

  5. EHR Big Data Deep Phenotyping

    PubMed Central

    Lenert, L.; Lopez-Campos, G.

    2014-01-01

    Summary Objectives Given the quickening speed of discovery of variant disease drivers from combined patient genotype and phenotype data, the objective is to provide methodology using big data technology to support the definition of deep phenotypes in medical records. Methods As the vast stores of genomic information increase with next generation sequencing, the importance of deep phenotyping increases. The growth of genomic data and adoption of Electronic Health Records (EHR) in medicine provides a unique opportunity to integrate phenotype and genotype data into medical records. The method by which collections of clinical findings and other health related data are leveraged to form meaningful phenotypes is an active area of research. Longitudinal data stored in EHRs provide a wealth of information that can be used to construct phenotypes of patients. We focus on a practical problem around data integration for deep phenotype identification within EHR data. The use of big data approaches are described that enable scalable markup of EHR events that can be used for semantic and temporal similarity analysis to support the identification of phenotype and genotype relationships. Conclusions Stead and colleagues’ 2005 concept of using light standards to increase the productivity of software systems by riding on the wave of hardware/processing power is described as a harbinger for designing future healthcare systems. The big data solution, using flexible markup, provides a route to improved utilization of processing power for organizing patient records in genotype and phenotype research. PMID:25123744

  6. Deep Learning for Health Informatics.

    PubMed

    Ravi, Daniele; Wong, Charence; Deligianni, Fani; Berthelot, Melissa; Andreu-Perez, Javier; Lo, Benny; Yang, Guang-Zhong

    2017-01-01

    With a massive influx of multimodality data, the role of data analytics in health informatics has grown rapidly in the last decade. This has also prompted increasing interests in the generation of analytical, data driven models based on machine learning in health informatics. Deep learning, a technique with its foundation in artificial neural networks, is emerging in recent years as a powerful tool for machine learning, promising to reshape the future of artificial intelligence. Rapid improvements in computational power, fast data storage, and parallelization have also contributed to the rapid uptake of the technology in addition to its predictive power and ability to generate automatically optimized high-level features and semantic interpretation from the input data. This article presents a comprehensive up-to-date review of research employing deep learning in health informatics, providing a critical analysis of the relative merit, and potential pitfalls of the technique as well as its future outlook. The paper mainly focuses on key applications of deep learning in the fields of translational bioinformatics, medical imaging, pervasive sensing, medical informatics, and public health.

  7. Core-level excitation and fragmentation of chlorine dioxide

    NASA Astrophysics Data System (ADS)

    Flesch, R.; Plenge, J.; Rühl, E.

    2006-03-01

    Inner-shell excitation and fragmentation of chlorine dioxide (OClO) in the Cl 2p- and O 1s-excitation regime is reported. The electronic structure of the element-selectively excited radical is studied by X-ray absorption and total cation yields. A comparison of both approaches allows us to estimate the absolute photoionization cross-section and the ionization yield near the Cl 2p- and O 1s-absorption edges. The latter quantity is characteristically enhanced in core-ionization continua. We observe below both core-absorption edges intense core-to-valence-transitions. These are assigned in comparison with related work on core-excited sulfur dioxide. These results give clear evidence that the highest molecular orbital of OClO is half-filled. High-resolution spectra recorded in the Cl 2p-regime show evidence for Rydberg transitions. The extrapolation of the term values of the low-lying Rydberg states allows us to derive the Cl 2p-ionization energy of OClO. Fragmentation of core-excited OClO is reported. Photoelectron-photoion-coincidence (PEPICO) spectra are recorded, indicating that singly and doubly charged fragments are formed. Fission of the doubly and multiply charged OClO leads to singly charged fragments. These are measured by photoion-photoion-coincidence (PIPICO) spectra, where characteristic changes in intensity of the fission channels in the Cl 2p- and O 1s-continuum are observed.

  8. Electronic core level microanalyses and microcopies in multipurpose apparatus.

    PubMed

    Cazaux, J; Gramari, D; Jbara, O; Mouze, D; Nassiopoulos, A; Thomas, X

    1989-03-01

    Using an instrument equipped with two electron guns, an electron analyzer, and a Si(Li) diode detector, we developed microanalytical techniques based on inner-shell electron excitations by incident electrons and X-rays, that is, electron energy-loss spectroscopy (EELS) in the reflection mode; electron probe microanalysis (EPMA) and X-ray appearance potential spectroscopy (XAPS); electron-induced Auger electron spectroscopy (e-AES); X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS); X-ray induced AES (XAES), X-ray fluorescence analysis (XRF), and scanning X-ray radiography (SXR). The corresponding characteristic images (including X-ray microradiography and X-ray photoelectron microscopy) were obtained in the scanning mode. The principle of the apparatus is described. Each spectroscopy and microscopy is illustrated by an example. Their performance and limits are discussed.

  9. Deep water recycling through time

    PubMed Central

    Magni, Valentina; Bouilhol, Pierre; van Hunen, Jeroen

    2014-01-01

    We investigate the dehydration processes in subduction zones and their implications for the water cycle throughout Earth's history. We use a numerical tool that combines thermo-mechanical models with a thermodynamic database to examine slab dehydration for present-day and early Earth settings and its consequences for the deep water recycling. We investigate the reactions responsible for releasing water from the crust and the hydrated lithospheric mantle and how they change with subduction velocity (vs), slab age (a) and mantle temperature (Tm). Our results show that faster slabs dehydrate over a wide area: they start dehydrating shallower and they carry water deeper into the mantle. We parameterize the amount of water that can be carried deep into the mantle, W (×105 kg/m2), as a function of vs (cm/yr), a (Myrs), and Tm (°C):. We generally observe that a 1) 100°C increase in the mantle temperature, or 2) ∼15 Myr decrease of plate age, or 3) decrease in subduction velocity of ∼2 cm/yr all have the same effect on the amount of water retained in the slab at depth, corresponding to a decrease of ∼2.2×105 kg/m2 of H2O. We estimate that for present-day conditions ∼26% of the global influx water, or 7×108 Tg/Myr of H2O, is recycled into the mantle. Using a realistic distribution of subduction parameters, we illustrate that deep water recycling might still be possible in early Earth conditions, although its efficiency would generally decrease. Indeed, 0.5–3.7 × 108 Tg/Myr of H2O could still be recycled in the mantle at 2.8 Ga. Key Points Deep water recycling might be possible even in early Earth conditions We provide a scaling law to estimate the amount of H2O flux deep into the mantle Subduction velocity has a a major control on the crustal dehydration pattern PMID:26321881

  10. Dual-wavelength excited photoluminescence spectroscopy of deep-level hole traps in Ga(In)NP

    SciTech Connect

    Dagnelund, D.; Huang, Y. Q.; Buyanova, I. A.; Chen, W. M.; Tu, C. W.; Yonezu, H.

    2015-01-07

    By employing photoluminescence (PL) spectroscopy under dual-wavelength optical excitation, we uncover the presence of deep-level hole traps in Ga(In)NP alloys grown by molecular beam epitaxy (MBE). The energy level positions of the traps are determined to be at 0.56 eV and 0.78 eV above the top of the valance band. We show that photo-excitation of the holes from the traps, by a secondary light source with a photon energy below the bandgap energy, can lead to a strong enhancement (up to 25%) of the PL emissions from the alloys under a primary optical excitation above the bandgap energy. We further demonstrate that the same hole traps can be found in various MBE-grown Ga(In)NP alloys, regardless of their growth temperatures, chemical compositions, and strain. The extent of the PL enhancement induced by the hole de-trapping is shown to vary between different alloys, however, likely reflecting their different trap concentrations. The absence of theses traps in the GaNP alloy grown by vapor phase epitaxy suggests that their incorporation could be associated with a contaminant accompanied by the N plasma source employed in the MBE growth, possibly a Cu impurity.

  11. Deep Spitzer/IRAC Imaging of the Subaru Deep Field

    NASA Astrophysics Data System (ADS)

    Jiang, Linhua; Egami, Eiichi; Cohen, Seth; Fan, Xiaohui; Ly, Chun; Mechtley, Matthew; Windhorst, Rogier

    2013-10-01

    The last decade saw great progress in our understanding of the distant Universe as a number of objects at z > 6 were discovered. The Subaru Deep Field (SDF) project has played an important role on study of high-z galaxies. The SDF is unique: it covers a large area of 850 sq arcmin; it has extremely deep optical images in a series of broad and narrow bands; it has the largest sample of spectroscopically-confirmed galaxies known at z >= 6, including ~100 Lyman alpha emitters (LAEs) and ~50 Lyman break galaxies (LBGs). Here we propose to carry out deep IRAC imaging observations of the central 75% of the SDF. The proposed observations together with those from our previous Spitzer programs will reach a depth of ~10 hours, and enable the first complete census of physical properties and stellar populations of spectroscopically-confirmed galaxies at the end of cosmic reionization. IRAC data is the key to measure stellar masses and constrain stellar populations in high-z galaxies. From SED modeling with secure redshifts, we will characterize the physical properties of these galaxies, and trace their mass assembly and star formation history. In particular, it allows us, for the first time, to study stellar populations in a large sample of z >=6 LAEs. We will also address some critical questions, such as whether LAEs and LBGs represent physically different galaxy populations. All these will help us to understand the earliest galaxy formation and evolution, and better constrain the galaxy contribution to reionization. The IRAC data will also cover 10,000 emission-line selected galaxies at z < 1.5, 50,000 UV and mass selected LBGs at 1.5 < z < 3, and more than 5,000 LBGs at 3 < z < 6. It will have a legacy value for SDF-related programs.

  12. Deep water recycling through time.

    PubMed

    Magni, Valentina; Bouilhol, Pierre; van Hunen, Jeroen

    2014-11-01

    We investigate the dehydration processes in subduction zones and their implications for the water cycle throughout Earth's history. We use a numerical tool that combines thermo-mechanical models with a thermodynamic database to examine slab dehydration for present-day and early Earth settings and its consequences for the deep water recycling. We investigate the reactions responsible for releasing water from the crust and the hydrated lithospheric mantle and how they change with subduction velocity (vs ), slab age (a) and mantle temperature (Tm). Our results show that faster slabs dehydrate over a wide area: they start dehydrating shallower and they carry water deeper into the mantle. We parameterize the amount of water that can be carried deep into the mantle, W (×10(5) kg/m(2)), as a function of vs (cm/yr), a (Myrs), and Tm (°C):[Formula: see text]. We generally observe that a 1) 100°C increase in the mantle temperature, or 2) ∼15 Myr decrease of plate age, or 3) decrease in subduction velocity of ∼2 cm/yr all have the same effect on the amount of water retained in the slab at depth, corresponding to a decrease of ∼2.2×10(5) kg/m(2) of H2O. We estimate that for present-day conditions ∼26% of the global influx water, or 7×10(8) Tg/Myr of H2O, is recycled into the mantle. Using a realistic distribution of subduction parameters, we illustrate that deep water recycling might still be possible in early Earth conditions, although its efficiency would generally decrease. Indeed, 0.5-3.7 × 10(8) Tg/Myr of H2O could still be recycled in the mantle at 2.8 Ga.

  13. The deep Ionian Basin revisited

    NASA Astrophysics Data System (ADS)

    Tugend, Julie; Chamot-Rooke, Nicolas; Arsenikos, Stavros; Frizon de Lamotte, Dominique; Blanpied, Christian

    2016-04-01

    The deep Eastern Mediterranean Basins (Ionian and Herodotus) are characterized by thick sedimentary sequences overlying an extremely thinned basement evidenced from different geophysical methods. Yet, the nature of the crust (continental or oceanic) and the timing of the extreme crustal and lithosphere thinning in the different sub-basins remain highly controversial, casting doubts on the tectonic setting related to the formation of this segment of the North Gondwana paleo-margin. We focus on the Ionian Basin located at the western termination of the Eastern Mediterranean with the aim of identifying, characterizing and mapping the deepest sedimentary sequences. We present tentative age correlations relying on calibrations and observations from the surrounding margins and basins (Malta shelf and Escarpment, Cyrenaica margin, Sirte Basin, Apulian Platform). Two-ship deep refraction seismic data (Expanding Spread Profiles from the PASIPHAE cruise) combined with reprocessed reflection data (from the ARCHIMEDE survey) enabled us to present a homogeneous seismic stratigraphy across the basin and to investigate the velocity structure of its basement. Based on our results, and on a review of geological and geophysical observations, we suggest an Upper Triassic-Early Dogger age for the formation of the deep Ionian Basin. The nature of the underlying basement remains uncertain, both highly-thinned continental and slow-spreading type oceanic crust being compatible with the available constraints. The narrow size and relatively short-lived evolution of the Ionian Basin lead us to suggest that it is more likely the remnant of an immature oceanic basin than of a stable oceanic domain. Eventually, upscaling these results at the scale of the Eastern Mediterranean Basins highlights the complex interaction observed between two propagating oceans: The Central Atlantic and Neo-Tethys.

  14. Advanced deep sea diving equipment

    NASA Technical Reports Server (NTRS)

    Danesi, W. A.

    1972-01-01

    Design requirements are generated for a deep sea heavy duty diving system to equip salvage divers with equipment and tools that permit work of the same quality and in times approaching that done on the surface. The system consists of a helmet, a recirculator for removing carbon dioxide, and the diver's dress. The diver controls the inlet flow by the recirculatory control valve and is able to change closed cycle operation to open cycle if malfunction occurs. Proper function of the scrubber in the recirculator minimizes temperature and humidity effects as it filters the returning air.

  15. Deep endometriosis of the colon.

    PubMed

    Ropacka-Lesiak, Mariola; Świder-Musielak, Joanna; Wójcicka, Małgorzata; Łyczywek, Anna; Skrzypek, Maciej; Waliszewski, Wojciech

    2013-01-01

    The article presents a case of deep intestinal endometriosis in a 27-year-old woman who complained of dysmenorrhea and infertility. The diagnostic process included ultrasonography as well as colonoscopy, barium enema and CT imaging. Because of the presence of two distant changes which involved nearly the full thickness of the rectal wall and the major part of its circumference, the decision to perform an anterior rectal resection with a simultaneous retroperitoneal colorectostomy was made. The Knight technique was implemented. The surgery involved the anterior rectal resection, the transverse rectal stump closure by use of a stapling device (TA50), and the creation of colorectal circular anastomosis with the CEEA 31 stapler.

  16. Deep Ocean Hydrazine Decomposition Testing

    DTIC Science & Technology

    1976-01-01

    therefore of the form shown in Table A-1, where all data but those for the load cell are averaged over the time period ( Tn - Tn - d =l:lTn-1· Table A·1...SECURITY CLASSIFICATIOII OF THIS PAGE (1󈧏., D .,o £nto,.cO REPORT DOCUklEHTATIOH PAGE READ INSTRUC’nONS BEFORE COIIPLETIJIIG FORM II. REPORT IIUMBER r...GOVT ACCESSION NO 3. RECIPIENT’S CATALOG NUMBER NUC TP 495 .. TITLE (_, d SuOWio) 5 . TYPE OF REPORT 6 PERIOD COVERED DEEP OCEAN HYDRAZINE Final

  17. Segmental neurofibromatosis with deep schwannoma

    PubMed Central

    Smith, Wallace A.; Buhalog, Brittany A.; Fiala, Katherine H.

    2016-01-01

    An elderly patient presented with two clusters of asymptomatic fleshy and pedunculated papules. Biopsy of the papules was consistent with neurofibromas. Decades prior she had undergone a surgery for the excision of a large schwannoma. Given her lack of other neurofibromatosis findings, the patient was diagnosed with multisegmental neurofibromatosis (multi-SN) with deep schwannoma, a possible new phenotype of SN. Because this entity may be associated with internal malignancy, it is important to screen and educate these patients as well as to provide regular follow-up. PMID:27990385

  18. Mössbauer investigation of the photoexcited spin states and crystal structure analysis of the spin-crossover dinuclear complex [{Fe(bt)(NCS)(2)}(2)bpym] (bt=2,2'-bithiazoline, bpym=2,2'-bipyrimidine).

    PubMed

    Gaspar, Ana B; Ksenofontov, Vadim; Reiman, Sergey; Gütlich, Philipp; Thompson, Amber L; Goeta, Andrés E; Muñoz, M Carmen; Real, José A

    2006-12-13

    The crystal structure of the complex [{Fe(bt)(NCS)(2)}(2)bpym] (1) (bt=2,2'-bithiazoline, bpym=2,2'-bipyrimidine) has been solved at 293, 240, 175 and 30 K. At all four temperatures the crystal remains in the P space group with a=8.7601(17), b=9.450(2), c=12.089(3) A, alpha=72.77(2), beta=79.150(19), gamma=66.392(18) degrees , V=873.1(4) Angstrom(3) (data for 293 K structure). The structure consists of centrosymmetric dinuclear units in which each iron(II) atom is coordinated by two NCS(-) ions in the cis position and two nitrogen atoms of the bridging bpym ligand, with the remaining positions occupied by the peripheral bt ligand. The iron atom is in a severely distorted octahedral FeN(6) environment. The average Fe--N bond length of 2.15(9) Angstrom indicates that compound 1 is in the high-spin state (HS-HS) at 293 K. Crystal structure determinations at 240, 175 and 30 K gave a cell comparable to that seen at 293 K, but reduced in volume. At 30 K, the average Fe--N distance is 1.958(4) Angstrom, showing that the structure is clearly low spin (LS-LS). At 175 K the average Fe--N bond length of 2.052(11) Angstrom suggests that there is an intermediate phase. Mössbauer investigations of the light-induced excited spin state trapping (LIESST) effect (lambda=514 nm, 25 mW cm(-2)) in 1 (4.2 K, H(ext)=50 kOe) show that the excited spin states correspond to the HS-HS and HS-LS pairs. The dynamics of the relaxation of the photoexcited states studied at 4.2 K and H(ext)=50 kOe demonstrate that HS-HS pairs revert with time to both HS-LS and LS-LS configurations. The HS-LS photoexcited pairs relax with time back to the ground LS-LS configuration. Complex [{Fe(0.15)Zn(0.85)(bt)(NCS)(2)}(2)bpym] (2) exhibits a continuous spin transition centred around 158 K in contrast to the two-step transition observed for 1. The different spin-crossover behaviour observed for 2 is due to the decrease of cooperativity (intermolecular interactions) imposed by the matrix of Zn(II) ions. This

  19. Deep pulverization along active faults ?

    NASA Astrophysics Data System (ADS)

    Doan, M.

    2013-12-01

    Pulverization is a intensive damage observed along some active faults. Rarely found in the field, it has been associated with dynamic damage produced by large earthquakes. Pulverization has been so far only described at the ground surface, consistent with the high frequency tensile loading expected for earthquake occurring along bimaterial faults. However, we discuss here a series of hints suggesting that pulverization is expected also several hundred of meters deep. In the deep well drilled within Nojima fault after the 1995 Kobe earthquake, thin sections reveal non localized damage, with microfractured pervading a sample, but with little shear disturbing the initial microstructure. In the SAFOD borehole drilled near Parkfield, Wiersberg and Erzinger (2008) made gas monitoring while drilling found large amount of H2 gas in the sandstone west to the fault. They attribute this high H2 concentration to mechanochemical origin, in accordance with some example of diffuse microfracturing found in thin sections from cores of SAFOD phase 3 and from geophysical data from logs. High strain rate experiments in both dry (Yuan et al, 2011) and wet samples (Forquin et al, 2010) show that even under confining pressures of several tens of megapascals, diffuse damage similar to pulverization is possible. This could explain the occurrence of pulverization at depth.

  20. Density functionals from deep learning

    NASA Astrophysics Data System (ADS)

    McMahon, Jeffrey

    Density-functional theory is a formally exact description of a many-body quantum system in terms of its density; in practice, however, approximations to the universal density functional (DF) are necessary. Machine learning has recently been proposed as a novel approach to discover such a DF (or components of it). Conventional machine learning algorithms, however, are limited in their ability to process data in their raw form, leading to invariance and/or sensitivity issues. In this presentation, an alternative approach based on deep learning will be demonstrated. Deep learning allows computational models that are capable of discovering intricate structure in large and/or high-dimensional data sets with multiple levels of abstraction, and do not suffer from the aforementioned issues. Results from the application of this approach to the prediction of the kinetic-energy DF of noninteracting electrons will be presented. Using theoretical results from computer science, a connection between the underlying model and the theorems of Hohenberg and Kohn will also be suggested.

  1. Deep Space 1 Technology Demonstrator

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The completely assembled Deep Space 1 (DS-1) technology demonstrator spacecraft. The DS-1 spacecraft incorporates a number of advanced technology concepts in its mission, but none so 'high profile' as its Ion propulsion system. The name itself evokes visions of Star Trek and science fiction fantasy, although the idea actually dates from the 1950s. However, unlike the 'Warp Drive' propulsion system that zings the fictional starship Enterprise across the cosmos in minutes, the almost imperceptible thrust from the ion propulsion system is equivalent to the pressure exerted by a sheet of paper held in the palm of your hand. The ion engine is very slow to pick up speed, but over the long haul it can deliver 10 times as much thrust per pound of fuel as more traditional rockets. Unlike the fireworks of most chemical rockets using solid or liquid fuels, the ion drive emits only an eerie blue glow as ionized (electrically charged) atoms of xenon are pushed out of the engine. Xenon is the same gas found in photo flash tubes and many lighthouse bulbs. Deep Space 1 was launched in October 1998 as part of NASA's New Millennium Program, which is managed by JPL for NASA's Office of Space Science, Washington, DC. The California Institute of Technology in Pasadena manages JPL for NASA.

  2. Exploring life's limits: Deep geobiochemistry

    NASA Astrophysics Data System (ADS)

    Cox, A. D.

    2014-12-01

    N-dimensional chemical space on Earth and beyond produces diverse habitats for microbial activity. Hydrothermal environments cover a wide range of habitable space up to and including life's known limits and provide a window into deep geological, geochemical, and biological processes. Hydrothermal water compositions, as sampled from and measured in terrestrial hot springs on Earth's surface, vary in chemical constituent speciation and concentrations over orders of magnitude in a plethora of geochemical parameters with biological significance, including hydronium ion, sulfide, iron, zinc, magnesium, manganese, and molybdenum. Proteins provide a link between geochemistry and microbial activity by catalyzing chemical reactions. Proteins extracted and identified by tandem mass spectrometry from 13 hot spring sediments and biofilms - covering pH values from 2-9 and diverse geochemical compositions - function as efflux transporters, permeases, electron transporters, and others, suggesting that these processes were present in the environment and occurring at the time of sampling. Metalloenzymes have been identified, including the iron protein rubrerythrin, thought to be involved in oxidative stress protection in anaerobic bacteria and archaea, as well as proteins involved in macronutrient processing (carbon, phosphorus, nitrogen, and sulfur). The melding of biochemistry with geochemistry shows potential for quantifying microbial activity in deep environments by demonstrating the presence - and as techniques improve, relative abundances - of reaction-catalyzing enzymes. Moreover, using hot spring sources and their outflow channels as chemical and biological models of geologic time helps decipher the origin and co-evolution of life and geochemistry.

  3. Geologic studies of deep natural gas resources

    USGS Publications Warehouse

    Dyman, T. S.; Kuuskraa, V.A.

    2001-01-01

    In 1995, the USGS estimated a mean resource of 114 trillion cubic feet of undiscovered technically recoverable natural gas in plays deeper than 15,000 feet/4,572 meters in onshore regions of the United States. This volume summarizes major conclusions of ongoing work. Chapters A and B address the areal extent of drilling and distribution of deep basins in the U.S. Chapter C summarizes distribution of deep sedimentary basins and potential for deep gas in the former Soviet Union. Chapters D and E are geochemical papers addressing source-rock issues and deep gas generation. Chapter F develops a probabilistic method for subdividing gas resources into depth slices, and chapter G analyzes the relative uncertainty of estimates of deep gas in plays in the Gulf Coast Region. Chapter H evaluates the mechanism of hydrogenation of deep, high-rank spent kerogen by water, with subsequent generation of methane-rich HC gas.

  4. The deep space network, volume 13

    NASA Technical Reports Server (NTRS)

    1973-01-01

    The objectives, functions, and organization of the Deep Space Network are summarized. The deep space instrumentation facility, the ground communications facility, and the network control system are described. Other areas reported include: Helios Mission support, DSN support of the Mariner Mars 1971 extended mission, Mariner Venus/Mercury 1973 mission support, Viking mission support, radio science, tracking and ground-based navigation, network control and data processing, and deep space stations.

  5. Dynamics of the Q2Π1u(1 ) state studied from the isotope effect on the cross sections for the formation of the 2 p atom pair in the photoexcitation of H2 and D2

    NASA Astrophysics Data System (ADS)

    Hosaka, Kouichi; Shiino, Kennichi; Nakanishi, Yuko; Odagiri, Takeshi; Kitajima, Masashi; Kouchi, Noriyuki

    2016-06-01

    The absolute values of the cross section for formation of a 2 p atom pair in the photoexcitation of H2 and D2 are measured against the incident photon energy in the range of doubly excited states by means of the coincidence detection of two Lyman-α photons. The cross-section curves are explained only by the contribution of the doubly excited Q2Π1u(1 ) state. The isotope effect on the oscillator strengths of 2 p +2 p pair formation for H2 and D2 from the Q2Π1u(1 ) state is almost the same as that on the oscillator strengths of 2 s +2 p pair formation from the Q2Π1u(1 ) state obtained by our group [T. Odagiri et al., Phys. Rev. A 84, 053401 (2011), 10.1103/PhysRevA.84.053401]. This channel independence indicates that both isotope effects are dominated by the early dynamics of the Q2Π1u(1 ) state, before reaching the branching point into 2 p +2 p pair formation and 2 s +2 p pair formation.

  6. Deep Ultrasound Enhancements Final Report

    SciTech Connect

    Quarry, M; Thomas, G; Ward, W; Gardner, D

    2006-05-01

    This study involves collaboration between Los Alamos National Laboratory and Lawrence Livermore National Laboratory to enhance and optimize LANL's ultrasonic inspection capabilities for production. Deep-penetrating ultrasonic testing enhancement studies will extend the current capabilities, which only look for disbonds. Current ultrasonic methods in production use 15-20 MHz to inspect for disbonds. The enhanced capabilities use 5 MHz to penetrate to the back surface and image the back surface for any flaws. The enhanced capabilities for back surface inspection use transducers and squirter modifications that can be incorporated into the existing production system. In a production setup the current 15-20 MHz transducer and squirter would perform a bond inspection, followed by a deep inspection that would be performed by simply swapping out the 5 MHz transducer and squirter. Surrogate samples were manufactured of beryllium and bismuth to perform the ultrasonic enhancement studies. The samples were used to simulate flaws on the back surface and study ultrasound's ability to image them. The ultrasonic technique was optimized by performing experiments with these samples and analyzing transducer performance in detecting flaws in the surrogate. Beam patterns were also studied experimentally using a steel ball reflector to measure beam patterns, focal points, and sensitivities to better understand the relationship between design and performance. Many transducers were evaluated including transducers from LANL's production system, LLNL, and other commercially available transducers. Squirter design was also analyzed while performing experiments Flat-bottom holes and ball-mill defects of various sizes were introduced into the samples for experimentation. Flaws depths were varied from .020'' to 0.060'', and diameters varied from 0.0625'' to 0.187''. The smallest defect, .020'' depth and 0.0625'', was detected. Ultrasonic amplitude features produced better images than time

  7. Stimulation Technologies for Deep Well Completions

    SciTech Connect

    2004-03-31

    The Department of Energy (DOE) is sponsoring the Deep Trek Program targeted at improving the economics of drilling and completing deep gas wells. Under the DOE program, Pinnacle Technologies is conducting a study to evaluate the stimulation of deep wells. The objective of the project is to assess U.S. deep well drilling and stimulation activity, review rock mechanics and fracture growth in deep, high-pressure/temperature wells and evaluate stimulation technology in several key deep plays. An assessment of historical deep gas well drilling activity and forecast of future trends was completed during the first six months of the project; this segment of the project was covered in Technical Progress Report No. 1. During the next six months, efforts were primarily split between summarizing rock mechanics and fracture growth in deep reservoirs and contacting operators about case studies of deep gas well stimulation as documented in Technical Progress Report No. 2. This report details work done with Anadarko and ChevronTexaco in the Table Rock Field in Wyoming.

  8. Deep subspace mapping in hyperspectral imaging

    NASA Astrophysics Data System (ADS)

    Wadströmer, Niclas; Gustafsson, David; Perersson, Henrik; Bergström, David

    2016-10-01

    We propose a novel Deep learning approach using autoencoders to map spectral bands to a space of lower dimensionality while preserving the information that makes it possible to discriminate different materials. Deep learning is a relatively new pattern recognition approach which has given promising result in many applications. In Deep learning a hierarchical representation of increasing level of abstraction of the features is learned. Autoencoder is an important unsupervised technique frequently used in Deep learning for extracting important properties of the data. The learned latent representation is a non-linear mapping of the original data which potentially preserve the discrimination capacity.

  9. The deep ocean under climate change.

    PubMed

    Levin, Lisa A; Le Bris, Nadine

    2015-11-13

    The deep ocean absorbs vast amounts of heat and carbon dioxide, providing a critical buffer to climate change but exposing vulnerable ecosystems to combined stresses of warming, ocean acidification, deoxygenation, and altered food inputs. Resulting changes may threaten biodiversity and compromise key ocean services that maintain a healthy planet and human livelihoods. There exist large gaps in understanding of the physical and ecological feedbacks that will occur. Explicit recognition of deep-ocean climate mitigation and inclusion in adaptation planning by the United Nations Framework Convention on Climate Change (UNFCCC) could help to expand deep-ocean research and observation and to protect the integrity and functions of deep-ocean ecosystems.

  10. Flyby Delivers Multiple Deep Jupiter Probes

    NASA Technical Reports Server (NTRS)

    Spilker, T. R.; Hubbard, W. B.; Ingersoll, A. P.

    2001-01-01

    In situ probes are the most reliable means for sampling composition and conditions deep in giant planet atmospheres. While exceeding its baseline mission, the Galileo probe entered a distinctly non-representative region of Jupiter (a 'hot spot') and apparently did not measure the full deep abundances of such important species as H2O and H2S, whose measured abundances were still increasing at the deepest datum. Multiple deep (approx. 100 bar) in situ probes minimize the hot spot risk, and address spatial variations and deep constituent abundances. Additional information is contained in the original extended abstract.

  11. Deep learning in neural networks: an overview.

    PubMed

    Schmidhuber, Jürgen

    2015-01-01

    In recent years, deep artificial neural networks (including recurrent ones) have won numerous contests in pattern recognition and machine learning. This historical survey compactly summarizes relevant work, much of it from the previous millennium. Shallow and Deep Learners are distinguished by the depth of their credit assignment paths, which are chains of possibly learnable, causal links between actions and effects. I review deep supervised learning (also recapitulating the history of backpropagation), unsupervised learning, reinforcement learning & evolutionary computation, and indirect search for short programs encoding deep and large networks.

  12. Deep Circulation in the South China Sea

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaolong; Zhao, Wei; Xu, Xiaobiao; Tian, Jiwei; Zhou, Chun

    2016-04-01

    The South China Sea (SCS) is the largest marginal sea of the northwest Pacific. The deep circulation in the SCS is investigated on the basis of the Hybrid Coordinate Ocean Model (HYCOM). All the experiments show reasonable agreement with observation from mooring arrays. Analysis of these results provides a detailed spatial structure and temporal variability of the deep circulation in the SCS. The major features of the SCS deep circulation are basin-scale cyclonic gyre and concentrated deep western boundary current (DWBC). The transport of the DWBC is ~2 Sv at 16.5°N with a width of ~53 km. As flowing southwestward, the DWBC becomes weaker with a wider range. Deep upwelling in the SCS is estimated of 0.19 to 1.15 m d-1 with the strongest area around the DWBC. The model results reveal the existence of 80 to 120 days oscillation in the deep northeastern circulation and the DWBC, which are also the areas with large eddy kinetic energy. This seasonal oscillation is northwestward with a velocity amplitude of ~1.0~1.5 cm s-1. The distribution of mixing parameters in the deep SCS plays a role in both spatial structure and volume transport of the deep circulation. Compared with the north shelf of the SCS with the Luzon Strait, deep circulation in the SCS is more sensitive to the large vertical mixing parameters of the Zhongsha Island Chain area.

  13. Deep space communication - Past, present, and future

    NASA Technical Reports Server (NTRS)

    Posner, E. C.; Stevens, R.

    1984-01-01

    This paper reviews the progress made in deep space communication from its beginnings until now, describes the development and applications of NASA's Deep Space Network, and indicates directions for the future. Limiting factors in deep space communication are examined using the upcoming Voyager encounter with Uranus, centered on the downlink telemetry from spacecraft to earth, as an example. A link calculation for Voyager at Uranus over Australia is exhibited. Seven basic deep space communication functions are discussed, and technical aspects of spacecraft communication equipment, ground antennas, and ground electronics and processing are considered.

  14. The deep ocean under climate change

    NASA Astrophysics Data System (ADS)

    Levin, Lisa A.; Le Bris, Nadine

    2015-11-01

    The deep ocean absorbs vast amounts of heat and carbon dioxide, providing a critical buffer to climate change but exposing vulnerable ecosystems to combined stresses of warming, ocean acidification, deoxygenation, and altered food inputs. Resulting changes may threaten biodiversity and compromise key ocean services that maintain a healthy planet and human livelihoods. There exist large gaps in understanding of the physical and ecological feedbacks that will occur. Explicit recognition of deep-ocean climate mitigation and inclusion in adaptation planning by the United Nations Framework Convention on Climate Change (UNFCCC) could help to expand deep-ocean research and observation and to protect the integrity and functions of deep-ocean ecosystems.

  15. Deep Brain Stimulation: Expanding Applications

    PubMed Central

    TEKRIWAL, Anand; BALTUCH, Gordon

    2015-01-01

    For over two decades, deep brain stimulation (DBS) has shown significant efficacy in treatment for refractory cases of dyskinesia, specifically in cases of Parkinson's disease and dystonia. DBS offers potential alleviation from symptoms through a well-tolerated procedure that allows personalized modulation of targeted neuroanatomical regions and related circuitries. For clinicians contending with how to provide patients with meaningful alleviation from often debilitating intractable disorders, DBSs titratability and reversibility make it an attractive treatment option for indications ranging from traumatic brain injury to progressive epileptic supra-synchrony. The expansion of our collective knowledge of pathologic brain circuitries, as well as advances in imaging capabilities, electrophysiology techniques, and material sciences have contributed to the expanding application of DBS. This review will examine the potential efficacy of DBS for neurologic and psychiatric disorders currently under clinical investigation and will summarize findings from recent animal models. PMID:26466888

  16. Deep Borehole Disposal Safety Analysis.

    SciTech Connect

    Freeze, Geoffrey A.; Stein, Emily; Price, Laura L.; MacKinnon, Robert J.; Tillman, Jack Bruce

    2016-10-01

    This report presents a preliminary safety analysis for the deep borehole disposal (DBD) concept, using a safety case framework. A safety case is an integrated collection of qualitative and quantitative arguments, evidence, and analyses that substantiate the safety, and the level of confidence in the safety, of a geologic repository. This safety case framework for DBD follows the outline of the elements of a safety case, and identifies the types of information that will be required to satisfy these elements. At this very preliminary phase of development, the DBD safety case focuses on the generic feasibility of the DBD concept. It is based on potential system designs, waste forms, engineering, and geologic conditions; however, no specific site or regulatory framework exists. It will progress to a site-specific safety case as the DBD concept advances into a site-specific phase, progressing through consent-based site selection and site investigation and characterization.

  17. Mechanisms of deep brain stimulation

    PubMed Central

    Cheng, Jennifer J.; Eskandar, Emad N.

    2015-01-01

    Deep brain stimulation (DBS) is widely used for the treatment of movement disorders including Parkinson's disease, essential tremor, and dystonia and, to a lesser extent, certain treatment-resistant neuropsychiatric disorders including obsessive-compulsive disorder. Rather than a single unifying mechanism, DBS likely acts via several, nonexclusive mechanisms including local and network-wide electrical and neurochemical effects of stimulation, modulation of oscillatory activity, synaptic plasticity, and, potentially, neuroprotection and neurogenesis. These different mechanisms vary in importance depending on the condition being treated and the target being stimulated. Here we review each of these in turn and illustrate how an understanding of these mechanisms is inspiring next-generation approaches to DBS. PMID:26510756

  18. Deep epistasis in human metabolism

    NASA Astrophysics Data System (ADS)

    Imielinski, Marcin; Belta, Calin

    2010-06-01

    We extend and apply a method that we have developed for deriving high-order epistatic relationships in large biochemical networks to a published genome-scale model of human metabolism. In our analysis we compute 33 328 reaction sets whose knockout synergistically disables one or more of 43 important metabolic functions. We also design minimal knockouts that remove flux through fumarase, an enzyme that has previously been shown to play an important role in human cancer. Most of these knockout sets employ more than eight mutually buffering reactions, spanning multiple cellular compartments and metabolic subsystems. These reaction sets suggest that human metabolic pathways possess a striking degree of parallelism, inducing "deep" epistasis between diversely annotated genes. Our results prompt specific chemical and genetic perturbation follow-up experiments that could be used to query in vivo pathway redundancy. They also suggest directions for future statistical studies of epistasis in genetic variation data sets.

  19. Automatic pump for deep wells

    SciTech Connect

    Brown, K.D.

    1981-11-24

    An automatic pump for deep wells comprises a long stroke reciprocating pump having its piston normally in its bottom position and an automatic control dependent upon the collection of a predetermined amount of liquid in the pump cylinder above the piston for actuating the piston to pump the liquid into a production line. The automatic control includes an electric motor driven hydraulic pump and a reservoir of hydraulic fluid which is actuated upon filling of the reciprocating pump chamber to supply hydraulic fluid to a closed chamber below the piston and force the piston upwardly to discharge liquid from the pump cylinder. Gas collected in the top of the pump cylinder results in low starting current and a saving of energy. The hydraulic pump is reversed automatically upon completion of the pumping stroke of the piston.

  20. Looking Up from the Deep

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Click on the image for Looking Up from the Deep (QTVR)

    Not long after conducting extensive investigations of tilted martian rock layers along its path, NASA's Spirit rover prepared to resume the trek to the top of the 'Columbia Hills' in June. This panorama, nicknamed 'Sunset Ridge,' shows the terrain that lay ahead of the rover on Spirit's 519th martian day, or sol (June 19, 2005). On the left is the summit of 'Husband Hill,' Spirit's objective at that time.

    This mosaic of images is an approximate true-color rendering of snapshots taken by the rover's panoramic camera using 750-, 530-, and 430-nanometer filters. Spirit took these images at approximately 3 p.m. local true solar time in Gusev Crater on Mars. The rover then continued to climb throughout July, making numerous scientific investigations of martian rocks along the way.

  1. Superficial versus deep dry needling.

    PubMed

    Baldry, Peter

    2002-08-01

    Ninety percent of my patients with myofascial trigger point (MTrP) pain have this alone and are treated with superficial dry needling. Approximately 10% have concomitant MTrP pain and nerve root compression pain. These are treated with deep dry needling. SUPERFICIAL DRY NEEDLING (SDN): The activated and sensitised nociceptors of a MTrP cause it to be so exquisitely tender that firm pressure applied to it gives rise to a flexion withdrawal reflex (jump sign) and in some cases the utterance of an expletive (shout sign). The optimum strength of SDN at a MTrP site is the minimum necessary to abolish these two reactions. With respect to this patients are divided into strong, average and weak responders. The responsiveness of each individual is determined by trial and error. It is my practice to insert a needle (0.3mm x 30mm) into the tissues immediately overlying the MTrP to a depth of 5-10 mm and to leave it in situ long enough for the two reactions to be abolished. For an average reactor this is about 30secs. For a weak reactor it is several minutes. And for a strong reactor the insertion of the needle and its immediate withdrawal is all that is required. Following treatment muscle stretching exercises should be carried out, and any steps taken to eliminate factors that might lead to the reactivation of the MTrPs. DEEP DRY NEEDLING (DDN): This in my practice is only used either when primary MTrP activity causes shortening of muscle sufficient enough to bring about compression of nerve roots. Or when there is nerve compression pain usually from spondylosis or disc prolapse and the secondary development of MTrP activity. Unlike SDN, DDN is a painful procedure and one which gives rise to much post-treatment soreness.

  2. Deep brain stimulation: postoperative issues.

    PubMed

    Deuschl, Günther; Herzog, Jan; Kleiner-Fisman, Galit; Kubu, Cynthia; Lozano, Andres M; Lyons, Kelly E; Rodriguez-Oroz, Maria C; Tamma, Filippo; Tröster, Alexander I; Vitek, Jerrold L; Volkmann, Jens; Voon, Valerie

    2006-06-01

    Numerous factors need to be taken into account when managing a patient with Parkinson's disease (PD) after deep brain stimulation (DBS). Questions such as when to begin programming, how to conduct a programming screen, how to assess the effects of programming, and how to titrate stimulation and medication for each of the targeted sites need to be addressed. Follow-up care should be determined, including patient adjustments of stimulation, timing of follow-up visits and telephone contact with the patient, and stimulation and medication conditions during the follow-up assessments. A management plan for problems that can arise after DBS such as weight gain, dyskinesia, axial symptoms, speech dysfunction, muscle contractions, paresthesia, eyelid, ocular and visual disturbances, and behavioral and cognitive problems should be developed. Long-term complications such as infection or erosion, loss of effect, intermittent stimulation, tolerance, and pain or discomfort can develop and need to be managed. Other factors that need consideration are social and job-related factors, development of dementia, general medical issues, and lifestyle changes. This report from the Consensus on Deep Brain Stimulation for Parkinson's Disease, a project commissioned by the Congress of Neurological Surgeons and the Movement Disorder Society, outlines answers to a series of questions developed to address all aspects of DBS postoperative management and decision-making with a systematic overview of the literature (until mid-2004) and by the expert opinion of the authors. The report has been endorsed by the Scientific Issues Committee of the Movement Disorder Society and the American Society of Stereotactic and Functional Neurosurgery.

  3. A deep ALMA image of the Hubble Ultra Deep Field

    NASA Astrophysics Data System (ADS)

    Dunlop, J. S.; McLure, R. J.; Biggs, A. D.; Geach, J. E.; Michałowski, M. J.; Ivison, R. J.; Rujopakarn, W.; van Kampen, E.; Kirkpatrick, A.; Pope, A.; Scott, D.; Swinbank, A. M.; Targett, T. A.; Aretxaga, I.; Austermann, J. E.; Best, P. N.; Bruce, V. A.; Chapin, E. L.; Charlot, S.; Cirasuolo, M.; Coppin, K.; Ellis, R. S.; Finkelstein, S. L.; Hayward, C. C.; Hughes, D. H.; Ibar, E.; Jagannathan, P.; Khochfar, S.; Koprowski, M. P.; Narayanan, D.; Nyland, K.; Papovich, C.; Peacock, J. A.; Rieke, G. H.; Robertson, B.; Vernstrom, T.; Werf, P. P. van der; Wilson, G. W.; Yun, M.

    2017-04-01

    We present the results of the first, deep Atacama Large Millimeter Array (ALMA) imaging covering the full ≃4.5 arcmin2 of the Hubble Ultra Deep Field (HUDF) imaged with Wide Field Camera 3/IR on HST. Using a 45-pointing mosaic, we have obtained a homogeneous 1.3-mm image reaching σ1.3 ≃ 35 μJy, at a resolution of ≃0.7 arcsec. From an initial list of ≃50 > 3.5σ peaks, a rigorous analysis confirms 16 sources with S1.3 > 120 μJy. All of these have secure galaxy counterparts with robust redshifts ( = 2.15). Due to the unparalleled supporting data, the physical properties of the ALMA sources are well constrained, including their stellar masses (M*) and UV+FIR star formation rates (SFR). Our results show that stellar mass is the best predictor of SFR in the high-redshift Universe; indeed at z ≥ 2 our ALMA sample contains seven of the nine galaxies in the HUDF with M* ≥ 2 × 1010 M⊙, and we detect only one galaxy at z > 3.5, reflecting the rapid drop-off of high-mass galaxies with increasing redshift. The detections, coupled with stacking, allow us to probe the redshift/mass distribution of the 1.3-mm background down to S1.3 ≃ 10 μJy. We find strong evidence for a steep star-forming 'main sequence' at z ≃ 2, with SFR ∝M* and a mean specific SFR ≃ 2.2 Gyr-1. Moreover, we find that ≃85 per cent of total star formation at z ≃ 2 is enshrouded in dust, with ≃65 per cent of all star formation at this epoch occurring in high-mass galaxies (M* > 2 × 1010 M⊙), for which the average obscured:unobscured SF ratio is ≃200. Finally, we revisit the cosmic evolution of SFR density; we find this peaks at z ≃ 2.5, and that the star-forming Universe transits from primarily unobscured to primarily obscured at z ≃ 4.

  4. Relating to Nature: Deep Ecology or Ecofeminism?

    ERIC Educational Resources Information Center

    Mathews, Freya

    1994-01-01

    This essay begins with an examination of the metaphysical axioms of deep ecology. It is argued that the axioms generate a fundamental dilemma for deep ecologists and that in attempting to resolve this dilemma, it is necessary to draw on an ethical perspective more akin to that found in ecofeminist literature. (LZ)

  5. Observed deep energetic eddies by seamount wake.

    PubMed

    Chen, Gengxin; Wang, Dongxiao; Dong, Changming; Zu, Tingting; Xue, Huijie; Shu, Yeqiang; Chu, Xiaoqing; Qi, Yiquan; Chen, Hui

    2015-11-30

    Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

  6. Temperature Impacts on Deep-Sea Biodiversity

    NASA Astrophysics Data System (ADS)

    Yasuhara, M.; Danovaro, R.

    2015-12-01

    Temperature is considered to be a fundamental factor controlling biodiversity in marine ecosystems, but precisely what role temperature plays in modulating diversity is still not clear. The deep ocean, lacking light and in situ photosynthetic primary production, is an ideal model system to test the effects of temperature changes on biodiversity. Here we synthesize current knowledge on temperature-diversity relationships in the deep sea. Our results from both present and past deep-sea assemblages suggest that, when a wide range of deep-sea bottom-water temperatures is considered, a unimodal relationship exists between temperature and diversity (that may be right skewed). It is possible that temperature is important only when at relatively high and low levels but does not play a major role in the intermediate temperature range. Possible mechanisms explaining the temperature-biodiversity relationship include the physiological-tolerance hypothesis, the metabolic hypothesis, island biogeography theory, or some combination of these. The possible unimodal relationship discussed here may allow us to identify tipping points at which on-going global change and deep-water warming may increase or decrease deep-sea biodiversity. Predicted changes in deep-sea temperatures due to human-induced climate change may have more adverse consequences than expected considering the sensitivity of deep-sea ecosystems to temperature changes.

  7. Observed deep energetic eddies by seamount wake

    NASA Astrophysics Data System (ADS)

    Chen, Gengxin; Wang, Dongxiao; Dong, Changming; Zu, Tingting; Xue, Huijie; Shu, Yeqiang; Chu, Xiaoqing; Qi, Yiquan; Chen, Hui

    2015-11-01

    Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

  8. Temperature impacts on deep-sea biodiversity.

    PubMed

    Yasuhara, Moriaki; Danovaro, Roberto

    2016-05-01

    Temperature is considered to be a fundamental factor controlling biodiversity in marine ecosystems, but precisely what role temperature plays in modulating diversity is still not clear. The deep ocean, lacking light and in situ photosynthetic primary production, is an ideal model system to test the effects of temperature changes on biodiversity. Here we synthesize current knowledge on temperature-diversity relationships in the deep sea. Our results from both present and past deep-sea assemblages suggest that, when a wide range of deep-sea bottom-water temperatures is considered, a unimodal relationship exists between temperature and diversity (that may be right skewed). It is possible that temperature is important only when at relatively high and low levels but does not play a major role in the intermediate temperature range. Possible mechanisms explaining the temperature-biodiversity relationship include the physiological-tolerance hypothesis, the metabolic hypothesis, island biogeography theory, or some combination of these. The possible unimodal relationship discussed here may allow us to identify tipping points at which on-going global change and deep-water warming may increase or decrease deep-sea biodiversity. Predicted changes in deep-sea temperatures due to human-induced climate change may have more adverse consequences than expected considering the sensitivity of deep-sea ecosystems to temperature changes.

  9. Observed deep energetic eddies by seamount wake

    PubMed Central

    Chen, Gengxin; Wang, Dongxiao; Dong, Changming; Zu, Tingting; Xue, Huijie; Shu, Yeqiang; Chu, Xiaoqing; Qi, Yiquan; Chen, Hui

    2015-01-01

    Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport. PMID:26617343

  10. Microplastic pollution in deep-sea sediments.

    PubMed

    Van Cauwenberghe, Lisbeth; Vanreusel, Ann; Mees, Jan; Janssen, Colin R

    2013-11-01

    Microplastics are small plastic particles (<1 mm) originating from the degradation of larger plastic debris. These microplastics have been accumulating in the marine environment for decades and have been detected throughout the water column and in sublittoral and beach sediments worldwide. However, up to now, it has never been established whether microplastic presence in sediments is limited to accumulation hot spots such as the continental shelf, or whether they are also present in deep-sea sediments. Here we show, for the first time ever, that microplastics have indeed reached the most remote of marine environments: the deep sea. We found plastic particles sized in the micrometre range in deep-sea sediments collected at four locations representing different deep-sea habitats ranging in depth from 1100 to 5000 m. Our results demonstrate that microplastic pollution has spread throughout the world's seas and oceans, into the remote and largely unknown deep sea.

  11. Deep learning for neuroimaging: a validation study.

    PubMed

    Plis, Sergey M; Hjelm, Devon R; Salakhutdinov, Ruslan; Allen, Elena A; Bockholt, Henry J; Long, Jeffrey D; Johnson, Hans J; Paulsen, Jane S; Turner, Jessica A; Calhoun, Vince D

    2014-01-01

    Deep learning methods have recently made notable advances in the tasks of classification and representation learning. These tasks are important for brain imaging and neuroscience discovery, making the methods attractive for porting to a neuroimager's toolbox. Success of these methods is, in part, explained by the flexibility of deep learning models. However, this flexibility makes the process of porting to new areas a difficult parameter optimization problem. In this work we demonstrate our results (and feasible parameter ranges) in application of deep learning methods to structural and functional brain imaging data. These methods include deep belief networks and their building block the restricted Boltzmann machine. We also describe a novel constraint-based approach to visualizing high dimensional data. We use it to analyze the effect of parameter choices on data transformations. Our results show that deep learning methods are able to learn physiologically important representations and detect latent relations in neuroimaging data.

  12. Deep Carbon Cycling in the Deep Hydrosphere: Abiotic Organic Synthesis and Biogeochemical Cycling

    NASA Astrophysics Data System (ADS)

    Sherwood Lollar, B.; Sutcliffe, C. N.; Ballentine, C. J.; Warr, O.; Li, L.; Ono, S.; Wang, D. T.

    2014-12-01

    Research into the deep carbon cycle has expanded our understanding of the depth and extent of abiotic organic synthesis in the deep Earth beyond the hydrothermal vents of the deep ocean floor, and of the role of reduced gases in supporting deep subsurface microbial communities. Most recently, this research has expanded our understanding not only of the deep biosphere but the deep hydrosphere - identifying for the first time the extreme antiquity (millions to billions of years residence time) of deep saline fracture waters in the world's oldest rocks. Energy-rich saline fracture waters in the Precambrian crust that makes up more than 70% of the Earth's continental lithosphereprovide important constraints on our understanding of the extent of the crust that is habitable, on the time scales of hydrogeologic isolation (and conversely mixing) of fluids relevant to the deep carbon cycle, and on the geochemistry of substrates that sustain both abiotic organic synthesis and biogeochemical cycles driven by microbial communities. Ultimately the chemistry and hydrogeology of the deep hydrosphere will help define the limits for life in the subsurface and the boundary between the biotic-abiotic fringe. Using a variety of novel techniques including noble gas analysis, clumped isotopologues of methane, and compound specific isotope analysis of CHNOS, this research is addressing questions about the distribution of deep saline fluids in Precambrian rocks worldwide, the degree of interconnectedness of these potential biomes, the habitability of these fluids, and the biogeographic diversity of this new realm of the deep hydrosphere.

  13. Orientation selective deep brain stimulation

    NASA Astrophysics Data System (ADS)

    Lehto, Lauri J.; Slopsema, Julia P.; Johnson, Matthew D.; Shatillo, Artem; Teplitzky, Benjamin A.; Utecht, Lynn; Adriany, Gregor; Mangia, Silvia; Sierra, Alejandra; Low, Walter C.; Gröhn, Olli; Michaeli, Shalom

    2017-02-01

    Objective. Target selectivity of deep brain stimulation (DBS) therapy is critical, as the precise locus and pattern of the stimulation dictates the degree to which desired treatment responses are achieved and adverse side effects are avoided. There is a clear clinical need to improve DBS technology beyond currently available stimulation steering and shaping approaches. We introduce orientation selective neural stimulation as a concept to increase the specificity of target selection in DBS. Approach. This concept, which involves orienting the electric field along an axonal pathway, was tested in the corpus callosum of the rat brain by freely controlling the direction of the electric field on a plane using a three-electrode bundle, and monitoring the response of the neurons using functional magnetic resonance imaging (fMRI). Computational models were developed to further analyze axonal excitability for varied electric field orientation. Main results. Our results demonstrated that the strongest fMRI response was observed when the electric field was oriented parallel to the axons, while almost no response was detected with the perpendicular orientation of the electric field relative to the primary fiber tract. These results were confirmed by computational models of the experimental paradigm quantifying the activation of radially distributed axons while varying the primary direction of the electric field. Significance. The described strategies identify a new course for selective neuromodulation paradigms in DBS based on axonal fiber orientation.

  14. Deep Brain Stimulation for Obesity

    PubMed Central

    Sussman, Eric S; Zhang, Michael; Pendharkar, Arjun V; Azagury, Dan E; Bohon, Cara; Halpern, Casey H

    2015-01-01

    Obesity is now the third leading cause of preventable death in the US, accounting for 216,000 deaths annually and nearly 100 billion dollars in health care costs. Despite advancements in bariatric surgery, substantial weight regain and recurrence of the associated metabolic syndrome still occurs in almost 20-35% of patients over the long-term, necessitating the development of novel therapies. Our continually expanding knowledge of the neuroanatomic and neuropsychiatric underpinnings of obesity has led to increased interest in neuromodulation as a new treatment for obesity refractory to current medical, behavioral, and surgical therapies. Recent clinical trials of deep brain stimulation (DBS) in chronic cluster headache, Alzheimer’s disease, and depression and obsessive-compulsive disorder have demonstrated the safety and efficacy of targeting the hypothalamus and reward circuitry of the brain with electrical stimulation, and thus provide the basis for a neuromodulatory approach to treatment-refractory obesity. In this study, we review the literature implicating these targets for DBS in the neural circuitry of obesity. We will also briefly review ethical considerations for such an intervention, and discuss genetic secondary-obesity syndromes that may also benefit from DBS. In short, we hope to provide the scientific foundation to justify trials of DBS for the treatment of obesity targeting these specific regions of the brain. PMID:26180683

  15. Ice Nucleation in Deep Convection

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Ackerman, Andrew; Stevens, David; Gore, Warren J. (Technical Monitor)

    2001-01-01

    The processes controlling production of ice crystals in deep, rapidly ascending convective columns are poorly understood due to the difficulties involved with either modeling or in situ sampling of these violent clouds. A large number of ice crystals are no doubt generated when droplets freeze at about -40 C. However, at higher levels, these crystals are likely depleted due to precipitation and detrainment. As the ice surface area decreases, the relative humidity can increase well above ice saturation, resulting in bursts of ice nucleation. We will present simulations of these processes using a large-eddy simulation model with detailed microphysics. Size bins are included for aerosols, liquid droplets, ice crystals, and mixed-phase (ice/liquid) hydrometers. Microphysical processes simulated include droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. We are focusing on the importance of ice nucleation events in the upper part of the cloud at temperatures below -40 C. We will show that the ultimate evolution of the cloud in this region (and the anvil produced by the convection) is sensitive to these ice nucleation events, and hence to the composition of upper tropospheric aerosols that get entrained into the convective column.

  16. Coring in deep hardrock formations

    SciTech Connect

    Drumheller, D.S.

    1988-08-01

    The United States Department of Energy is involved in a variety of scientific and engineering feasibility studies requiring extensive drilling in hard crystalline rock. In many cases well depths extend from 6000 to 20,000 feet in high-temperature, granitic formations. Examples of such projects are the Hot Dry Rock well system at Fenton Hill, New Mexico and the planned exploratory magma well near Mammoth Lakes, California. In addition to these programs, there is also continuing interest in supporting programs to reduce drilling costs associated with the production of geothermal energy from underground sources such as the Geysers area near San Francisco, California. The overall progression in these efforts is to drill deeper holes in higher temperature, harder formations. In conjunction with this trend is a desire to improve the capability to recover geological information. Spot coring and continuous coring are important elements in this effort. It is the purpose of this report to examine the current methods used to obtain core from deep wells and to suggest projects which will improve existing capabilities. 28 refs., 8 figs., 2 tabs.

  17. Phylogenomics reveals deep molluscan relationships

    PubMed Central

    Kocot, Kevin M.; Cannon, Johanna T.; Todt, Christiane; Citarella, Mathew R.; Kohn, Andrea B.; Meyer, Achim; Santos, Scott R.; Schander, Christoffer; Moroz, Leonid L.; Lieb, Bernhard; Halanych, Kenneth M.

    2014-01-01

    Evolutionary relationships among the eight major lineages of Mollusca have remained unresolved despite their diversity and importance. Previous investigations of molluscan phylogeny, based primarily on nuclear ribosomal gene sequences1–3 or morphological data4, have been unsuccessful at elucidating these relationships. Recently, phylogenomic studies using dozens to hundreds of genes have greatly improved our understanding of deep animal relationships5. However, limited genomic resources spanning molluscan diversity has prevented use of a phylogenomic approach. Here we use transcriptome and genome data from all major lineages (except Monoplacophora) and recover a well-supported topology for Mollusca. Our results strongly support the Aculifera hypothesis placing Polyplacophora (chitons) in a clade with a monophyletic Aplacophora (worm-like molluscs). Additionally, within Conchifera, a sister-taxon relationship between Gastropoda and Bivalvia is supported. This grouping has received little consideration and contains most (>95%) molluscan species. Thus we propose the node-based name Pleistomollusca. In light of these results, we examined the evolution of morphological characters and found support for advanced cephalization and shells as possibly having multiple origins within Mollusca. PMID:21892190

  18. Deep brain stimulation for dystonia.

    PubMed

    Vidailhet, Marie; Jutras, Marie-France; Grabli, David; Roze, Emmanuel

    2013-09-01

    The few controlled studies that have been carried out have shown that bilateral internal globus pallidum stimulation is a safe and long-term effective treatment for hyperkinetic disorders. However, most recent published data on deep brain stimulation (DBS) for dystonia, applied to different targets and patients, are still mainly from uncontrolled case reports (especially for secondary dystonia). This precludes clear determination of the efficacy of this procedure and the choice of the 'good' target for the 'good' patient. We performed a literature analysis on DBS for dystonia according to the expected outcome. We separated those with good evidence of favourable outcome from those with less predictable outcome. In the former group, we review the main results for primary dystonia (generalised/focal) and highlight recent data on myoclonus-dystonia and tardive dystonia (as they share, with primary dystonia, a marked beneficial effect from pallidal stimulation with good risk/benefit ratio). In the latter group, poor or variable results have been obtained for secondary dystonia (with a focus on heredodegenerative and metabolic disorders). From this overview, the main results and limits for each subgroup of patients that may help in the selection of dystonic patients who will benefit from DBS are discussed.

  19. Deep and shallow inelastic scattering

    SciTech Connect

    Ray, Heather

    2015-05-15

    In this session we focused on the higher energy deep and shallow inelastic particle interactions, DIS and SIS. DIS interactions occur when the energy of the incident particle beam is so large that the beam is able to penetrate the nucleons inside of the target nuclei. These interactions occur at the smallest level possible, that of the quark-gluon, or parton, level. SIS interactions occur in an intermediate energy range, just below the energy required for DIS interactions. The DIS cross section formula contains structure functions that describe our understanding of the underlying parton structure of nature. The full description of DIS interactions requires three structure functions: two may be measured in charged lepton or neutrino scattering, but one can only be extracted from neutrino DIS data. There are reasons to expect that the impact of nuclear effects could be different for neutrinos engaging in the DIS interaction, vs those felt by leptons. In fact, fits by the nCTEQ collaboration have found that the neutrino-Fe structure functions appear to differ from those extracted from lepton scattering data [1]. To better understand the global picture of DIS and SIS, we chose a three-pronged attack that examined recent experimental results, data fits, and latest theory predictions. Experimental results from neutrino and lepton scattering, as well as collider experiments, were presented.

  20. [Deep brain stimulation and neuroethics].

    PubMed

    Katayama, Yoichi; Fukaya, Chikashi

    2009-01-01

    The use of deep brain stimulation (DBS) for mental disorders has been discussed in Japan from the viewpoint of ethical problems. Trials of experimental therapies require a basis of sound scientific rationale. New standard therapy emerges from such trials through detailed analysis of the outcome and side effects. Long-suffering patients with intractable symptoms may desperately seek an experimental therapy even though it has not yet been accepted as standard therapy. The ethical committee of each institution evaluates the level of scientific rationale and the expected level of benefits on the bias of the reported data, and decides whether the patients can receive the experimental therapy. However, the use of DBS for mental disorders is not based on sound scientific rational, since the disease mechanisms involved are far from understood. The data reported from the previous trials are insufficient for assuring the satisfactory results for mental disoder patients. Most institutions in Japan do not accept such levels of scientific rationale and expected benefits. Furthermore, from the cultural perspective, strong skepticism exists in Japan with regard to surgical interventions for mental disorders. Such an attitude is unexpectedly in harmony with many of the subjects currently discussed in the field of neuroethics. For example, who has the right to control DBS? How does someone decide the level of control of mental function by DBS? These questions are related to the discussion on how human society is formed and how the ethics are decided by considering both scientific rationale and human society.

  1. Looking Deep with Infrared Eyes

    NASA Astrophysics Data System (ADS)

    2006-07-01

    Today, British astronomers are releasing the first data from the largest and most sensitive survey of the heavens in infrared light to the ESO user community. The UKIRT Infrared Deep Sky Survey (UKIDSS) has completed the first of seven years of data collection, studying objects that are too faint to see at visible wavelengths, such as very distant or very cool objects. New data on young galaxies is already challenging current thinking on galaxy formation, revealing galaxies that are massive at a much earlier stage of development than expected. These first science results already show how powerful the full survey will be at finding rare objects that hold vital clues to how stars and galaxies in our Universe formed. UKIDSS will make an atlas of large areas of the sky in the infrared. The data become available to the entire ESO user community immediately after they are entered into the archive [2]. Release to the world follows 18 months after each release to ESO. "Astronomers across Europe will jump on these exciting new data. We are moving into new territory - our survey is both wide and deep, so we are mapping huge volumes of space. That's how we will locate rare objects - the very nearest and smallest stars, and young galaxies at the edge of the universe," said Andy Lawrence from the University of Edinburgh, UKIDSS Principal Investigator. The UKIDSS data are collected by the United Kingdom Infrared Telescope [3] situated near the summit of Mauna Kea in Hawaii using the Wide Field Camera (WFCAM) built by the United Kingdom Astronomy Technology Centre (UKATC) in Edinburgh. WFCAM is the most powerful infrared imager in the world, generating enormous amounts of data - 150 gigabytes per night (equivalent to more than 200 CDs) - and approximately 10.5 Terabytes in total so far (or 15,000 CDs). Mark Casali, now at ESO, was the Project Scientist in charge of the WFCAM instrument construction at the UKATC. "WFCAM was a bold technological undertaking," said Mark Casali

  2. Effect of number of stack on the thermal escape and non-radiative and radiative recombinations of photoexcited carriers in strain-balanced InGaAs/GaAsP multiple quantum-well-inserted solar cells

    SciTech Connect

    Aihara, Taketo; Fukuyama, Atsuhiko; Ikari, Tetsuo; Suzuki, Hidetoshi; Fujii, Hiromasa; Nakano, Yoshiaki; Sugiyama, Masakazu

    2015-02-28

    Three non-destructive methodologies, namely, surface photovoltage (SPV), photoluminescence, and piezoelectric photothermal (PPT) spectroscopies, were adopted to detect the thermal carrier escape from quantum well (QW) and radiative and non-radiative carrier recombinations, respectively, in strain-balanced InGaAs/GaAsP multiple-quantum-well (MQW)-inserted GaAs p-i-n solar cell structure samples. Although the optical absorbance signal intensity was proportional to the number of QW stack, the signal intensities of the SPV and PPT methods decreased at high number of stack. To explain the temperature dependency of these signal intensities, we proposed a model that considers the three carrier dynamics: the thermal escape from the QW, and the non-radiative and radiative carrier recombinations within the QW. From the fitting procedures, it was estimated that the activation energies of the thermal escape ΔE{sub barr} and non-radiative recombination ΔE{sub NR} were 68 and 29 meV, respectively, for a 30-stacked MQW sample. The estimated ΔE{sub barr} value agreed well with the difference between the first electron subband and the top of the potential barrier in the conduction band. We found that ΔE{sub barr} remained constant at approximately 70 meV even with increasing QW stack number. However, the ΔE{sub NR} value monotonically increased with the increase in the number of stack. Since this implies that non-radiative recombination becomes improbable as the number of stack increases, we found that the radiative recombination probability for electrons photoexcited within the QW increased at a large number of QW stack. Additional processes of escaping and recapturing of carriers at neighboring QW were discussed. As a result, the combination of the three non-destructive methodologies provided us new insights for optimizing the MQW components to further improve the cell performance.

  3. 2. Deep Creek Road, old bridge at campground entrance. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Deep Creek Road, old bridge at campground entrance. - Great Smoky Mountains National Park Roads & Bridges, Deep Creek Road, Between Park Boundary near Bryson City & Deep Creek Campground, Gatlinburg, Sevier County, TN

  4. 1. Deep Creek Road, picnic pavilion Great Smoky Mountains ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Deep Creek Road, picnic pavilion - Great Smoky Mountains National Park Roads & Bridges, Deep Creek Road, Between Park Boundary near Bryson City & Deep Creek Campground, Gatlinburg, Sevier County, TN

  5. The JPL roadmap for Deep Space navigation

    NASA Technical Reports Server (NTRS)

    Martin-Mur, Tomas J.; Abraham, Douglas S.; Berry, David; Bhaskaran, Shyam; Cesarone, Robert J.; Wood, Lincoln

    2006-01-01

    This paper reviews the tentative set of deep space missions that will be supported by NASA's Deep Space Mission System in the next twenty-five years, and extracts the driving set of navigation capabilities that these missions will require. There will be many challenges including the support of new mission navigation approaches such as formation flying and rendezvous in deep space, low-energy and low-thrust orbit transfers, precise landing and ascent vehicles, and autonomous navigation. Innovative strategies and approaches will be needed to develop and field advanced navigation capabilities.

  6. Earthquakes induced by deep penetrating bombing?

    NASA Astrophysics Data System (ADS)

    Balassanian, Serguei Y.

    2005-11-01

    The data of M≥5 earthquakes occurred in one year before and after 4 deep penetrating bombs in the region within 500 km and 1 000 km from the shooting site are presented. The 4 bombs are those happened in 1999 Kosovo of Yugoslavia, the 1991 Baghdad of Iraq, the 2001 Tora Bora of Afghanistan, and the 2003 Kirkuk of Iraq, respectively. The data indicate that the deep penetrating bombs may have remotely triggered some earthquakes. The deep penetrating bombs in seismically active regions should be forbidden.

  7. Comet Dust After Deep Impact

    NASA Technical Reports Server (NTRS)

    Wooden, Diane H.; Harker, David E.; Woodward, Charles E.

    2006-01-01

    When the Deep Impact Mission hit Jupiter Family comet 9P/Tempel 1, an ejecta crater was formed and an pocket of volatile gases and ices from 10-30 m below the surface was exposed (A Hearn et aI. 2005). This resulted in a gas geyser that persisted for a few hours (Sugita et al, 2005). The gas geyser pushed dust grains into the coma (Sugita et a1. 2005), as well as ice grains (Schulz et al. 2006). The smaller of the dust grains were submicron in radii (0-25.3 micron), and were primarily composed of highly refractory minerals including amorphous (non-graphitic) carbon, and silicate minerals including amorphous (disordered) olivine (Fe,Mg)2SiO4 and pyroxene (Fe,Mg)SiO3 and crystalline Mg-rich olivine. The smaller grains moved faster, as expected from the size-dependent velocity law produced by gas-drag on grains. The mineralogy evolved with time: progressively larger grains persisted in the near nuclear region, having been imparted with slower velocities, and the mineralogies of these larger grains appeared simpler and without crystals. The smaller 0.2-0.3 micron grains reached the coma in about 1.5 hours (1 arc sec = 740 km), were more diverse in mineralogy than the larger grains and contained crystals, and appeared to travel through the coma together. No smaller grains appeared at larger coma distances later (with slower velocities), implying that if grain fragmentation occurred, it happened within the gas acceleration zone. These results of the high spatial resolution spectroscopy (GEMINI+Michelle: Harker et 4. 2005, 2006; Subaru+COMICS: Sugita et al. 2005) revealed that the grains released from the interior were different from the nominally active areas of this comet by their: (a) crystalline content, (b) smaller size, (c) more diverse mineralogy. The temporal changes in the spectra, recorded by GEMIM+Michelle every 7 minutes, indicated that the dust mineralogy is inhomogeneous and, unexpectedly, the portion of the size distribution dominated by smaller grains has

  8. Microkeratome assisted deep lamellar keratoprosthesis

    PubMed Central

    Shimmura, S; Miyashita, H; Uchino, Y; Taguchi, T; Kobayashi, H; Shimazaki, J; Tanaka, J; Tsubota, K

    2006-01-01

    Aims To establish a keratoprosthesis (Kpro) surgical technique that maintains an intact superficial corneal layer. Methods A manual microkeratome (Moria LSK‐1) was used to create a 130 μm flap of approximately 10 mm diameter in the right eye of Japanese white rabbits. The stoma beneath the flap area was dissected before the removal of a 5.0 mm stromal disc. A 5.0 mm collagen I immobilised poly(vinyl alcohol) (COL‐PVA) disc was placed on the exposed posterior stroma close to Descemet's membrane. The flap was repositioned and fixed using 10‐0 nylon sutures, which were removed 2 days following surgery. The corneas were followed clinically by slit lamp microscopy and photographs. Rabbits were sacrificed after 6 months, and the transplanted corneas were examined histologically by haematoxylin and eosin staining and immunohistochemistry against vimentin and α‐smooth muscle actin (α‐SMA). Results The transplanted COL‐PVA discs remained transparent throughout the study, with no complications related to the flap or overlying epithelium. The interface between COL‐PVA and Descemet's membrane remained clear without signs of opacification caused by scarring or cellular deposition. Pathology revealed the intact COL‐PVA polymer in the posterior stroma, with minimal cellular infiltration along the anterior and posterior interfaces. Immunohistology shows vimentin and α‐SMA staining at levels comparable to lamellar keratoplasty control. Conclusions Microkeratome assisted deep lamellar keratoprosthesis may be a safe technique for the transplantation of artificial hydrogels for therapeutic purposes. PMID:16597665

  9. NATURAL GAS RESOURCES IN DEEP SEDIMENTARY BASINS

    SciTech Connect

    Thaddeus S. Dyman; Troy Cook; Robert A. Crovelli; Allison A. Henry; Timothy C. Hester; Ronald C. Johnson; Michael D. Lewan; Vito F. Nuccio; James W. Schmoker; Dennis B. Riggin; Christopher J. Schenk

    2002-02-05

    From a geological perspective, deep natural gas resources are generally defined as resources occurring in reservoirs at or below 15,000 feet, whereas ultra-deep gas occurs below 25,000 feet. From an operational point of view, ''deep'' is often thought of in a relative sense based on the geologic and engineering knowledge of gas (and oil) resources in a particular area. Deep gas can be found in either conventionally-trapped or unconventional basin-center accumulations that are essentially large single fields having spatial dimensions often exceeding those of conventional fields. Exploration for deep conventional and unconventional basin-center natural gas resources deserves special attention because these resources are widespread and occur in diverse geologic environments. In 1995, the U.S. Geological Survey estimated that 939 TCF of technically recoverable natural gas remained to be discovered or was part of reserve appreciation from known fields in the onshore areas and State waters of the United. Of this USGS resource, nearly 114 trillion cubic feet (Tcf) of technically-recoverable gas remains to be discovered from deep sedimentary basins. Worldwide estimates of deep gas are also high. The U.S. Geological Survey World Petroleum Assessment 2000 Project recently estimated a world mean undiscovered conventional gas resource outside the U.S. of 844 Tcf below 4.5 km (about 15,000 feet). Less is known about the origins of deep gas than about the origins of gas at shallower depths because fewer wells have been drilled into the deeper portions of many basins. Some of the many factors contributing to the origin of deep gas include the thermal stability of methane, the role of water and non-hydrocarbon gases in natural gas generation, porosity loss with increasing thermal maturity, the kinetics of deep gas generation, thermal cracking of oil to gas, and source rock potential based on thermal maturity and kerogen type. Recent experimental simulations using laboratory

  10. The Deep Space Network. [tracking and communication functions and facilities

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The objectives, functions, and organization of the Deep Space Network are summarized. The Deep Space Instrumentation Facility, the Ground Communications Facility, and the Network Control System are described.

  11. High detectivity solar-blind high-temperature deep-ultraviolet photodetector based on multi-layered (l00) facet-oriented β-Ga₂O₃ nanobelts.

    PubMed

    Zou, Rujia; Zhang, Zhenyu; Liu, Qian; Hu, Junqing; Sang, Liwen; Liao, Meiyong; Zhang, Wenjun

    2014-05-14

    Fabrication of a high-temperature deep-ultraviolet photodetector working in the solar-blind spectrum range (190-280 nm) is a challenge due to the degradation in the dark current and photoresponse properties. Herein, β-Ga2O3 multi-layered nanobelts with (l00) facet-oriented were synthesized, and were demonstrated for the first time to possess excellent mechanical, electrical properties and stability at a high temperature inside a TEM studies. As-fabricated DUV solar-blind photodetectors using (l00) facet-oriented β-Ga2O3 multi-layered nanobelts demonstrated enhanced photodetective performances, that is, high sensitivity, high signal-to-noise ratio, high spectral selectivity, high speed, and high stability, importantly, at a temperature as high as 433 K, which are comparable to other reported semiconducting nanomaterial photodetectors. In particular, the characteristics of the photoresponsivity of the β-Ga2O3 nanobelt devices include a high photoexcited current (>21 nA), an ultralow dark current (below the detection limit of 10(-14) A), a fast time response (<0.3 s), a high R(λ) (≈851 A/W), and a high EQE (~4.2 × 10(3)). The present fabricated facet-oriented β-Ga2O3 multi-layered nanobelt based devices will find practical applications in photodetectors or optical switches for high-temperature environment.

  12. Habitat Demonstration Unit - Deep Space Habitat Configuration

    NASA Video Gallery

    This animated video shows the process of transporting, assembling and testing the Habitat Demonstration Unit - Deep Space Habitat (HDU DSH) configuration, which will be deployed during the 2011 Des...

  13. Semantic Antinomies and Deep Structure Analysis

    ERIC Educational Resources Information Center

    Zuber, Ryszard

    1975-01-01

    This article discusses constructions known as semantic antinomies, that is, the paradoxical results of false presuppositions, and how they can be dealt with by means of deep structure analysis. See FL 508 186 for availability. (CLK)

  14. How Is Deep Vein Thrombosis Diagnosed?

    MedlinePlus

    ... Vein Thrombosis Diagnosed? Your doctor will diagnose deep vein thrombosis (DVT) based on your medical history, a physical exam, and test results. He or she will identify your risk factors and rule out other causes of your symptoms. ...

  15. Deep Space Atomic Clock Ticks Toward Success

    NASA Video Gallery

    Dr. Todd Ely, principal investigator for NASA's Deep Space Atomic Clock at the Jet Propulsion Laboratory in Pasadena, Calif., spotlights the paradigm-busting innovations now in development to revol...

  16. The Deep Space Atomic Clock Mission

    NASA Technical Reports Server (NTRS)

    Ely, Todd A.; Koch, Timothy; Kuang, Da; Lee, Karen; Murphy, David; Prestage, John; Tjoelker, Robert; Seubert, Jill

    2012-01-01

    The Deep Space Atomic Clock (DSAC) mission will demonstrate the space flight performance of a small, low-mass, high-stability mercury-ion atomic clock with long term stability and accuracy on par with that of the Deep Space Network. The timing stability introduced by DSAC allows for a 1-Way radiometric tracking paradigm for deep space navigation, with benefits including increased tracking via utilization of the DSN's Multiple Spacecraft Per Aperture (MSPA) capability and full ground station-spacecraft view periods, more accurate radio occultation signals, decreased single-frequency measurement noise, and the possibility for fully autonomous on-board navigation. Specific examples of navigation and radio science benefits to deep space missions are highlighted through simulations of Mars orbiter and Europa flyby missions. Additionally, this paper provides an overview of the mercury-ion trap technology behind DSAC, details of and options for the upcoming 2015/2016 space demonstration, and expected on-orbit clock performance.

  17. Toolkits and Libraries for Deep Learning.

    PubMed

    Erickson, Bradley J; Korfiatis, Panagiotis; Akkus, Zeynettin; Kline, Timothy; Philbrick, Kenneth

    2017-03-17

    Deep learning is an important new area of machine learning which encompasses a wide range of neural network architectures designed to complete various tasks. In the medical imaging domain, example tasks include organ segmentation, lesion detection, and tumor classification. The most popular network architecture for deep learning for images is the convolutional neural network (CNN). Whereas traditional machine learning requires determination and calculation of features from which the algorithm learns, deep learning approaches learn the important features as well as the proper weighting of those features to make predictions for new data. In this paper, we will describe some of the libraries and tools that are available to aid in the construction and efficient execution of deep learning as applied to medical images.

  18. Applications of Deep Learning in Biomedicine.

    PubMed

    Mamoshina, Polina; Vieira, Armando; Putin, Evgeny; Zhavoronkov, Alex

    2016-05-02

    Increases in throughput and installed base of biomedical research equipment led to a massive accumulation of -omics data known to be highly variable, high-dimensional, and sourced from multiple often incompatible data platforms. While this data may be useful for biomarker identification and drug discovery, the bulk of it remains underutilized. Deep neural networks (DNNs) are efficient algorithms based on the use of compositional layers of neurons, with advantages well matched to the challenges -omics data presents. While achieving state-of-the-art results and even surpassing human accuracy in many challenging tasks, the adoption of deep learning in biomedicine has been comparatively slow. Here, we discuss key features of deep learning that may give this approach an edge over other machine learning methods. We then consider limitations and review a number of applications of deep learning in biomedical studies demonstrating proof of concept and practical utility.

  19. Future Plans for NASA's Deep Space Network

    NASA Technical Reports Server (NTRS)

    Deutsch, Leslie J.; Preston, Robert A.; Geldzahler, Barry J.

    2008-01-01

    This slide presentation reviews the importance of NASA's Deep Space Network (DSN) to space exploration, and future planned improvements to the communication capabilities that the network allows, in terms of precision, and communication power.

  20. Colonization of the deep sea by fishes

    PubMed Central

    Priede, I G; Froese, R

    2013-01-01

    Analysis of maximum depth of occurrence of 11 952 marine fish species shows a global decrease in species number (N) with depth (x; m): log10N = −0·000422x + 3·610000 (r2 = 0·948). The rate of decrease is close to global estimates for change in pelagic and benthic biomass with depth (−0·000430), indicating that species richness of fishes may be limited by food energy availability in the deep sea. The slopes for the Classes Myxini (−0·000488) and Actinopterygii (−0·000413) follow this trend but Chondrichthyes decrease more rapidly (−0·000731) implying deficiency in ability to colonize the deep sea. Maximum depths attained are 2743, 4156 and 8370 m for Myxini, Chondrichthyes and Actinopterygii, respectively. Endemic species occur in abundance at 7–7800 m depth in hadal trenches but appear to be absent from the deepest parts of the oceans, >9000 m deep. There have been six global oceanic anoxic events (OAE) since the origin of the major fish taxa in the Devonian c. 400 million years ago (mya). Colonization of the deep sea has taken place largely since the most recent OAE in the Cretaceous 94 mya when the Atlantic Ocean opened up. Patterns of global oceanic circulation oxygenating the deep ocean basins became established coinciding with a period of teleost diversification and appearance of the Acanthopterygii. Within the Actinopterygii, there is a trend for greater invasion of the deep sea by the lower taxa in accordance with the Andriashev paradigm. Here, 31 deep-sea families of Actinopterygii were identified with mean maximum depth >1000 m and with >10 species. Those with most of their constituent species living shallower than 1000 m are proposed as invasive, with extinctions in the deep being continuously balanced by export of species from shallow seas. Specialized families with most species deeper than 1000 m are termed deep-sea endemics in this study; these appear to persist in the deep by virtue of global distribution enabling

  1. Colonization of the deep sea by fishes.

    PubMed

    Priede, I G; Froese, R

    2013-12-01

    Analysis of maximum depth of occurrence of 11 952 marine fish species shows a global decrease in species number (N) with depth (x; m): log10 N = -0·000422x + 3·610000 (r(2)  = 0·948). The rate of decrease is close to global estimates for change in pelagic and benthic biomass with depth (-0·000430), indicating that species richness of fishes may be limited by food energy availability in the deep sea. The slopes for the Classes Myxini (-0·000488) and Actinopterygii (-0·000413) follow this trend but Chondrichthyes decrease more rapidly (-0·000731) implying deficiency in ability to colonize the deep sea. Maximum depths attained are 2743, 4156 and 8370 m for Myxini, Chondrichthyes and Actinopterygii, respectively. Endemic species occur in abundance at 7-7800 m depth in hadal trenches but appear to be absent from the deepest parts of the oceans, >9000 m deep. There have been six global oceanic anoxic events (OAE) since the origin of the major fish taxa in the Devonian c. 400 million years ago (mya). Colonization of the deep sea has taken place largely since the most recent OAE in the Cretaceous 94 mya when the Atlantic Ocean opened up. Patterns of global oceanic circulation oxygenating the deep ocean basins became established coinciding with a period of teleost diversification and appearance of the Acanthopterygii. Within the Actinopterygii, there is a trend for greater invasion of the deep sea by the lower taxa in accordance with the Andriashev paradigm. Here, 31 deep-sea families of Actinopterygii were identified with mean maximum depth >1000 m and with >10 species. Those with most of their constituent species living shallower than 1000 m are proposed as invasive, with extinctions in the deep being continuously balanced by export of species from shallow seas. Specialized families with most species deeper than 1000 m are termed deep-sea endemics in this study; these appear to persist in the deep by virtue of global distribution enabling recovery

  2. Methanogenesis in the hot and deep: implication for the deep biosphere

    NASA Astrophysics Data System (ADS)

    Takai, K.; Nakamura, K.; Toki, T.; Tsunogai, U.

    2008-12-01

    Microbial methanogenesis in the deep-sea and deep subseafloor is a key process in the carbon cycle of Earth. Hyperthermophilic methanogens are important primary producers in the deep, hot ecosystem and may represent the most ancient type of life flourishing in the early Earth. Nevertheless, the biogeochemical function and impact of methanogens in deep sea and deep subseafloor are poorly understood, in part because it is difficult to replicate the high temperatures and hydrostatic pressures in the laboratory. We develop a new technique for cultivation of chemolithoautotrophs under high hydrostatic pressures. Using this technique, growth, survival and methane production of a newly isolated, hyperthermophilic methanogen Methanopyrus kandleri strain 116 are characterized under high temperatures and hydrostatic pressures. The results renewed the previous record of upper temperature limit (UTL) for life and the stable carbon isotopic fractionation of the microbiological methane production. These new findings are of great implication for the limits of life and function in the deep biosphere.

  3. Life Support for Deep Space and Mars

    NASA Technical Reports Server (NTRS)

    Jones, Harry W.; Hodgson, Edward W.; Kliss, Mark H.

    2014-01-01

    How should life support for deep space be developed? The International Space Station (ISS) life support system is the operational result of many decades of research and development. Long duration deep space missions such as Mars have been expected to use matured and upgraded versions of ISS life support. Deep space life support must use the knowledge base incorporated in ISS but it must also meet much more difficult requirements. The primary new requirement is that life support in deep space must be considerably more reliable than on ISS or anywhere in the Earth-Moon system, where emergency resupply and a quick return are possible. Due to the great distance from Earth and the long duration of deep space missions, if life support systems fail, the traditional approaches for emergency supply of oxygen and water, emergency supply of parts, and crew return to Earth or escape to a safe haven are likely infeasible. The Orbital Replacement Unit (ORU) maintenance approach used by ISS is unsuitable for deep space with ORU's as large and complex as those originally provided in ISS designs because it minimizes opportunities for commonality of spares, requires replacement of many functional parts with each failure, and results in substantial launch mass and volume penalties. It has become impractical even for ISS after the shuttle era, resulting in the need for ad hoc repair activity at lower assembly levels with consequent crew time penalties and extended repair timelines. Less complex, more robust technical approaches may be needed to meet the difficult deep space requirements for reliability, maintainability, and reparability. Developing an entirely new life support system would neglect what has been achieved. The suggested approach is use the ISS life support technologies as a platform to build on and to continue to improve ISS subsystems while also developing new subsystems where needed to meet deep space requirements.

  4. Low Gravity Issues of Deep Space Refueling

    NASA Technical Reports Server (NTRS)

    Chato, David J.

    2005-01-01

    This paper discusses the technologies required to develop deep space refueling of cryogenic propellants and low cost flight experiments to develop them. Key technologies include long term storage, pressure control, mass gauging, liquid acquisition, and fluid transfer. Prior flight experiments used to mature technologies are discussed. A plan is presented to systematically study the deep space refueling problem and devise low-cost experiments to further mature technologies and prepare for full scale flight demonstrations.

  5. Deep Water Ambient Noise and Mode Processing

    DTIC Science & Technology

    2014-09-30

    Deep Water Ambient Noise and Mode Processing Kathleen E. Wage George Mason University Electrical and Computer Engineering Department 4400...specific objectives of the project are: 1) to characterize the ambient noise in the PhilSea data set using spectral analysis and to compare the results...to those for other deep water data sets; 2) to analyze the acoustic modes in the ambient noise and moored source data sets acquired in the PhilSea

  6. Deep circulations under simple classes of stratification

    NASA Technical Reports Server (NTRS)

    Salby, Murry L.

    1989-01-01

    Deep circulations where the motion field is vertically aligned over one or more scale heights are studied under barotropic and equivalent barotropic stratifications. The study uses two-dimensional equations reduced from the three-dimensional primitive equations in spherical geometry. A mapping is established between the full primitive equations and general shallow water behavior and the correspondence between variables describing deep atmospheric motion and those of shallow water behavior is established.

  7. Microbial life in the deep terrestrial subsurface

    SciTech Connect

    Fliermans, C.B.; Balkwill, D.L.; Beeman, R.E.

    1988-12-31

    The distribution and function of microorganisms is a vital issue in microbial ecology. The US Department of Energy`s Program, ``Microbiology of the Deep Subsurface,`` concentrates on establishing fundamental scientific information about organisms at depth, and the use of these organisms for remediation of contaminants in deep vadose zone and groundwater environments. This investigation effectively extends the Biosphere hundreds of meters into the Geosphere and has implications to a variety of subsurface activities.

  8. Helios mission support. [Deep Space Network

    NASA Technical Reports Server (NTRS)

    Goodwin, P. S.; Rockwell, G. M.

    1978-01-01

    Activities of the Deep Space Network Operations organization in support of the Helios Project from 15 October 1977 through 15 December 1977 are described. Topics covered include: (1) Mark 3 data subsystem testing at the conjoint Deep Space Stations (DSS) 42/43 (Canberra, Australia); (2) MDS implementation at DSS 61/63 (Madrid, Spain); (3) Radio Science update, and (4) other mission-related activities.

  9. Long Range Acoustic Communication in Deep Water

    DTIC Science & Technology

    2013-09-30

    ocean is challenging due to the substantial propagation loss, multipath delay spread , and channel variability. Analysis of deep-water data collected...were exploited. In addition, a robust algorithm (double differentially coded spread spectrum) was demonstrated recently using the LRAC10 data [10...Spray gliders with a commercial acoustic modem for data retrieval from subsurface moorings and seafloor systems installed with a similar modem in deep

  10. Information sources for deep sky astronomy

    NASA Astrophysics Data System (ADS)

    Brazell, O.

    1998-04-01

    With the increasing availability of computer systems and with more information becoming available through magazines and books, amateur astronomers now have access to a wide variety of material on non-stellar deep sky objects. The purpose of this paper is to explore some of the sources of information open to deep sky astronomers and to clarify the nature of the plethora of designations used to describe non-stellar astronomical objects.

  11. DEEP VADOSE ZONE TREATABILITY TEST PLAN

    SciTech Connect

    GB CHRONISTER; MJ TRUEX

    2009-07-02

    {sm_bullet} Treatability test plan published in 2008 {sm_bullet} Outlines technology treatability activities for evaluating application of in situ technologies and surface barriers to deep vadose zone contamination (technetium and uranium) {sm_bullet} Key elements - Desiccation testing - Testing of gas-delivered reactants for in situ treatment of uranium - Evaluating surface barrier application to deep vadose zone - Evaluating in situ grouting and soil flushing

  12. The deep space network, volume 6

    NASA Technical Reports Server (NTRS)

    1971-01-01

    Progress on Deep Space Network (DSN) supporting research and technology is presented, together with advanced development and engineering, implementation, and DSN operations of flight projects. The DSN is described. Interplanetary and planetary flight projects and radio science experiments are discussed. Tracking and navigational accuracy analysis, communications systems and elements research, and supporting research are considered. Development of the ground communications and deep space instrumentation facilities is also presented. Network allocation schedules and angle tracking and test development are included.

  13. The deep space network, volume 18. [Deep Space Instrumentation Facility, Ground Communication Facility, and Network Control System

    NASA Technical Reports Server (NTRS)

    1973-01-01

    The objectives, functions, and organization of the Deep Space Network are summarized. The Deep Space Instrumentation Facility, the Ground Communications Facility, and the Network Control System are described.

  14. Deep endometriosis: definition, pathogenesis, and clinical management.

    PubMed

    Vercellini, Paolo; Frontino, Giada; Pietropaolo, Giuliana; Gattei, Umberto; Daguati, Raffaella; Crosignani, Pier Giorgio

    2004-05-01

    "Deep endometriosis" includes rectovaginal lesions as well as infiltrative forms that involve vital structures such as bowel, ureters, and bladder. The available evidence suggests the same pathogenesis for deep infiltrating vesical and rectovaginal endometriosis (i.e., intraperitoneal seeding of regurgitated endometrial cells, which collect and implant in the most dependent portions of the peritoneal cavity and the anterior and posterior cul-de-sac, and trigger an inflammatory process leading to adhesion of contiguous organs with creation of false peritoneal bottoms). According to anatomic, surgical, and pathologic findings, deep endometriotic lesions seem to originate intraperitoneally rather than extraperitoneally. Also the lateral asymmetry in the occurrence of ureteral endometriosis is compatible with the menstrual reflux theory and with the anatomic differences of the left and right hemipelvis. Peritoneal, ovarian, and deep endometriosis may be diverse manifestations of a disease with a single origin (i.e., regurgitated endometrium). Based on different pathogenetic hypotheses, several schemes have been proposed to classify deep endometriosis, but further data are needed to demonstrate their validity and reliability. Drugs induce temporary quiescence of active deep lesions and may be useful in selected circumstances. Progestins should be considered as first-line medical treatment for temporary pain relief. However, in most cases of severely infiltrating disease, surgery is the final solution. Great importance must be given to complete and balanced counseling, as awareness of the real possibilities of different treatments will enhance the patient's collaboration.

  15. Sub-types of deep dyslexia: a case study of central deep dyslexia.

    PubMed

    Dickerson, J; Johnson, H

    2004-02-01

    A case study is reported of a female patient (JAH), who following a left middle cerebral artery infarct, presented with the cardinal symptoms of deep dyslexia and deep dysphasia (semantic errors when reading and repeating words aloud, respectively). Detailed assessment revealed impaired performance across modalities for many tasks, but particularly those tasks that depend on an intact store of semantic knowledge. Her acquired dyslexia is best characterised as deep dyslexia of a central sub-type.

  16. Deep Logic Networks: Inserting and Extracting Knowledge From Deep Belief Networks.

    PubMed

    Tran, Son N; d'Avila Garcez, Artur S

    2016-11-08

    Developments in deep learning have seen the use of layerwise unsupervised learning combined with supervised learning for fine-tuning. With this layerwise approach, a deep network can be seen as a more modular system that lends itself well to learning representations. In this paper, we investigate whether such modularity can be useful to the insertion of background knowledge into deep networks, whether it can improve learning performance when it is available, and to the extraction of knowledge from trained deep networks, and whether it can offer a better understanding of the representations learned by such networks. To this end, we use a simple symbolic language--a set of logical rules that we call confidence rules--and show that it is suitable for the representation of quantitative reasoning in deep networks. We show by knowledge extraction that confidence rules can offer a low-cost representation for layerwise networks (or restricted Boltzmann machines). We also show that layerwise extraction can produce an improvement in the accuracy of deep belief networks. Furthermore, the proposed symbolic characterization of deep networks provides a novel method for the insertion of prior knowledge and training of deep networks. With the use of this method, a deep neural-symbolic system is proposed and evaluated, with the experimental results indicating that modularity through the use of confidence rules and knowledge insertion can be beneficial to network performance.

  17. Spin Polarization of Rb and Cs n p P2 3/2 (n =5 , 6) Atoms by Circularly Polarized Photoexcitation of a Transient Diatomic Molecule

    NASA Astrophysics Data System (ADS)

    Mironov, A. E.; Hewitt, J. D.; Eden, J. G.

    2017-03-01

    We report the selective population of Rb or Cs n p P2 3/2 (n =5 , 6; F =4 , 5) hyperfine states by the photodissociation of a transient, alkali-rare gas diatomic molecule. Circularly polarized (σ-), amplified spontaneous emission (ASE) on the D2 line of Rb or Cs (780.0 and 852.1 nm, respectively) is generated when Rb-Xe or Cs-Xe ground state collision pairs are photoexcited by a σ+-polarized optical field having a wavelength within the D2 blue satellite continuum, associated with the B Σ2 1/2 +←X Σ2 1/2 + (free←free ) transition of the diatomic molecule. The degree of spin polarization of Cs (6 p P3/2 2 ), specifically, is found to be dependent on the interatomic distance (R ) at which the excited complex is born, a result attributed to the structure of the B Σ2 1/2 + state. For Cs-Xe atomic pairs, tuning the wavelength of the optical field from 843 to 848 nm varies the degree of circular polarization of the ASE from 63% to almost unity because of the perturbation, in the 5 ≤R ≤6 Å interval, of the Σ2 1/2 + potential by a d σ molecular orbital associated with a higher Λ 2 electronic state. Monitoring only the Cs 6 p P3/2 2 spin polarization reveals a previously unobserved interaction of CsXe (B Σ2 1/2 + ) with the lowest vibrational levels of a Λ 2 state derived from Cs (5 d )+Xe . By inserting a molecular intermediate into the alkali atom excitation mechanism, these experiments realize electronic spin polarization through populating no more than two n p P2 3/2 hyperfine states, and demonstrate a sensitive spectroscopic

  18. Ultra Deep Wave Equation Imaging and Illumination

    SciTech Connect

    Alexander M. Popovici; Sergey Fomel; Paul Sava; Sean Crawley; Yining Li; Cristian Lupascu

    2006-09-30

    In this project we developed and tested a novel technology, designed to enhance seismic resolution and imaging of ultra-deep complex geologic structures by using state-of-the-art wave-equation depth migration and wave-equation velocity model building technology for deeper data penetration and recovery, steeper dip and ultra-deep structure imaging, accurate velocity estimation for imaging and pore pressure prediction and accurate illumination and amplitude processing for extending the AVO prediction window. Ultra-deep wave-equation imaging provides greater resolution and accuracy under complex geologic structures where energy multipathing occurs, than what can be accomplished today with standard imaging technology. The objective of the research effort was to examine the feasibility of imaging ultra-deep structures onshore and offshore, by using (1) wave-equation migration, (2) angle-gathers velocity model building, and (3) wave-equation illumination and amplitude compensation. The effort consisted of answering critical technical questions that determine the feasibility of the proposed methodology, testing the theory on synthetic data, and finally applying the technology for imaging ultra-deep real data. Some of the questions answered by this research addressed: (1) the handling of true amplitudes in the downward continuation and imaging algorithm and the preservation of the amplitude with offset or amplitude with angle information required for AVO studies, (2) the effect of several imaging conditions on amplitudes, (3) non-elastic attenuation and approaches for recovering the amplitude and frequency, (4) the effect of aperture and illumination on imaging steep dips and on discriminating the velocities in the ultra-deep structures. All these effects were incorporated in the final imaging step of a real data set acquired specifically to address ultra-deep imaging issues, with large offsets (12,500 m) and long recording time (20 s).

  19. Mass extinctions in the deep sea

    NASA Technical Reports Server (NTRS)

    Thomas, E.

    1988-01-01

    The character of mass extinctions can be assessed by studying extinction patterns of organisms, the fabric of the extinction, and assessing the environmental niche and mode of life of survivors. Deep-sea benthic foraminifera have been listed as little affected by the Cretaceous-Tertiary (K-T) mass extinction, but very few quantitative data are available. New data on deep-sea Late Maestrichtian-Eocene benthic foraminifera from Maud Rise (Antractica) indicate that about 10 percent of the species living at depths of 2000 to 2500 m had last appearances within 1 my of the Cretaceous-Tertiary (K-T) boundary, versus about 25 percent of species at 1000 to 1500 m. Many survivors from the Cretaceous became extinct in a period of global deep-sea benthic foraminiferal extinction at the end of the Paleocene, a time otherwise marked by very few extinctions. Preliminary conclusions suggest that the deep oceanic environment is essentially decoupled from the shallow marine and terrestrial environment, and that even major disturbances of one of these will not greatly affect the other. This gives deep-sea benthic faunas a good opportunity to recolonize shallow environments from greater depths and vice versa after massive extinctions. The decoupling means that data on deep-sea benthic boundary was caused by the environmental effects of asteriod impact or excessive volcanism. The benthic foraminiferal data strongly suggest, however, that the environmental results were strongest at the Earth's surface, and that there was no major disturbance of the deep ocean; this pattern might result both from excessive volcanism and from an impact on land.

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

    SciTech Connect

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

    2014-01-14

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

  1. Unraveling ultrafast dynamics in photoexcited aniline.

    PubMed

    Roberts, Gareth M; Williams, Craig A; Young, Jamie D; Ullrich, Susanne; Paterson, Martin J; Stavros, Vasilios G

    2012-08-01

    A combination of ultrafast time-resolved velocity map imaging (TR-VMI) methods and complete active space self-consistent field (CASSCF) ab initio calculations are implemented to investigate the electronic excited-state dynamics in aniline (aminobenzene), with a perspective for modeling (1)πσ* mediated dynamics along the amino moiety in the purine derived DNA bases. This synergy between experiment and theory has enabled a comprehensive picture of the photochemical pathways/conical intersections (CIs), which govern the dynamics in aniline, to be established over a wide range of excitation wavelengths. TR-VMI studies following excitation to the lowest-lying (1)ππ* state (1(1)ππ*) with a broadband femtosecond laser pulse, centered at wavelengths longer than 250 nm (4.97 eV), do not generate any measurable signature for (1)πσ* driven N-H bond fission on the amino group. Between wavelengths of 250 and >240 nm (<5.17 eV), coupling from 1(1)ππ* onto the (1)πσ* state at a 1(1)ππ*/(1)πσ* CI facilitates ultrafast nonadiabatic N-H bond fission through a (1)πσ*/S(0) CI in <1 ps, a notion supported by CASSCF results. For excitation to the higher lying 2(1)ππ* state, calculations reveal a near barrierless pathway for CI coupling between the 2(1)ππ* and 1(1)ππ* states, enabling the excited-state population to evolve through a rapid sequential 2(1)ππ* → 1(1)ππ* → (1)πσ* → N-H fission mechanism, which we observe to take place in 155 ± 30 fs at 240 nm. We also postulate that an analogous cascade of CI couplings facilitates N-H bond scission along the (1)πσ* state in 170 ± 20 fs, following 200 nm (6.21 eV) excitation to the 3(1)ππ* surface. Particularly illuminating is the fact that a number of the CASSCF calculated CI geometries in aniline bear an exceptional resemblance with previously calculated CIs and potential energy profiles along the amino moiety in guanine, strongly suggesting that the results here may act as an excellent grounding for better understanding (1)πσ* driven dynamics in this ubiquitous genetic building block.

  2. (Photoexcited charge pair escape and recombination)

    SciTech Connect

    Braun, C.L.

    1990-01-01

    Progress in four research areas on this project are summarized under the following topics: (1) Geminate charge pair recombination in hexane; (2) Fast current measurements resulting from excitation of charge transfer (CT) states; (3) Measurement of the dipole moment of excited states by DC conductivity; and (4) Charge separation at macroscopic interfaces between electron donor and acceptor solids. In a final section, personnel who have contributed to the project during the past budget period are described.

  3. Extracting hot carriers from photoexcited semiconductor nanocrystals

    SciTech Connect

    Zhu, Xiaoyang

    2014-12-10

    This research program addresses a fundamental question related to the use of nanomaterials in solar energy -- namely, whether semiconductor nanocrystals (NCs) can help surpass the efficiency limits, the so-called “Shockley-Queisser” limit, in conventional solar cells. In these cells, absorption of photons with energies above the semiconductor bandgap generates “hot” charge carriers that quickly “cool” to the band edges before they can be utilized to do work; this sets the solar cell efficiency at a limit of ~31%. If instead, all of the energy of the hot carriers could be captured, solar-to-electric power conversion efficiencies could be increased, theoretically, to as high as 66%. A potential route to capture this energy is to utilize semiconductor nanocrystals. In these materials, the quasi-continuous conduction and valence bands of the bulk semiconductor become discretized due to confinement of the charge carriers. Consequently, the energy spacing between the electronic levels can be much larger than the highest phonon frequency of the lattice, creating a “phonon bottleneck” wherein hot-carrier relaxation is possible via slower multiphonon emission. For example, hot-electron lifetimes as long as ~1 ns have been observed in NCs grown by molecular beam epitaxy. In colloidal NCs, long lifetimes have been demonstrated through careful design of the nanocrystal interfaces. Due to their ability to slow electronic relaxation, semiconductor NCs can in principle enable extraction of hot carriers before they cool to the band edges, leading to more efficient solar cells.

  4. 47 CFR 32.2424 - Submarine & deep sea cable.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Submarine & deep sea cable. 32.2424 Section 32... Submarine & deep sea cable. (a) This account shall include the original cost of submarine cable and deep sea... defined below, are to be maintained for nonmetallic submarine and deep sea cable and metallic...

  5. 47 CFR 32.2424 - Submarine & deep sea cable.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 2 2014-10-01 2014-10-01 false Submarine & deep sea cable. 32.2424 Section 32... Submarine & deep sea cable. (a) This account shall include the original cost of submarine cable and deep sea... defined below, are to be maintained for nonmetallic submarine and deep sea cable and metallic...

  6. 47 CFR 32.2424 - Submarine & deep sea cable.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 2 2013-10-01 2013-10-01 false Submarine & deep sea cable. 32.2424 Section 32... Submarine & deep sea cable. (a) This account shall include the original cost of submarine cable and deep sea... defined below, are to be maintained for nonmetallic submarine and deep sea cable and metallic...

  7. 47 CFR 32.2424 - Submarine & deep sea cable.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 2 2012-10-01 2012-10-01 false Submarine & deep sea cable. 32.2424 Section 32... Submarine & deep sea cable. (a) This account shall include the original cost of submarine cable and deep sea... defined below, are to be maintained for nonmetallic submarine and deep sea cable and metallic...

  8. 47 CFR 32.2424 - Submarine & deep sea cable.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 2 2011-10-01 2011-10-01 false Submarine & deep sea cable. 32.2424 Section 32... Submarine & deep sea cable. (a) This account shall include the original cost of submarine cable and deep sea... defined below, are to be maintained for nonmetallic submarine and deep sea cable and metallic...

  9. Global sampling of the photochemical reaction paths of bromoform by ultrafast deep-UV through near-IR transient absorption and ab initio multiconfigurational calculations

    NASA Astrophysics Data System (ADS)

    Pal, S. K.; Mereshchenko, A. S.; Butaeva, E. V.; El-Khoury, P. Z.; Tarnovsky, A. N.

    2013-03-01

    Ultrafast deep-ultraviolet through near infrared (210-950 nm) transient absorption spectroscopy complemented by ab initio multiconfigurational calculations offers a global description of the photochemical reaction pathways of bromoform following 255-nm excitation in methylcyclohexane and acetonitrile solutions. Photoexcitation of CHBr3 leads to the ground-state iso-CHBr3 product in a large quantum yield (˜35%), formed through two different mechanisms: concerted excited-state isomerization and cage-induced isomerization through the recombination of the nascent radical pair. These two processes take place on different time scales of tens of femtoseconds and several picoseconds, respectively. The novel ultrafast direct isomerization pathway proposed herein is consistent with the occurrence of a conical intersection between the first excited singlet state of CHBr3 and the ground electronic state of iso-CHBr3. Complete active space self-consistent field calculations characterize this singularity in the vicinity of a second order saddle point on the ground state which connects the two isomer forms. For cage-induced isomerization, both the formation of the nascent radical pair and its subsequent collapse into ground-state iso-CHBr3 are directly monitored through the deep-ultraviolet absorption signatures of the radical species. In both mechanisms, the optically active (i.e., those with largest Franck-Condon factors) C-Br-Br bending and Br-Br stretching modes of ground-state iso-CHBr3 have the largest projection on the reaction coordinate, enabling us to trace the structural changes accompanying vibrational relaxation of the non-equilibrated isomers through transient absorption dynamics. The iso-CHBr3 photoproduct is stable in methylcyclohexane, but undergoes either facile thermal isomerization to the parent CHBr3 structure through a cyclic transition state stabilized by the polar acetonitrile medium (˜300-ps lifetime), and hydrolysis in the presence of water.

  10. Development of deep eutectic solvents applied in extraction and separation.

    PubMed

    Li, Xiaoxia; Row, Kyung Ho

    2016-09-01

    Deep eutectic solvents, as an alternative to ionic liquids, have greener credentials than ionic liquids, and have attracted considerable attention in related chemical research. Deep eutectic solvents have attracted increasing attention in chemistry for the extraction and separation of various target compounds from natural products. This review highlights the preparation of deep eutectic solvents, unique properties of deep eutectic solvents, and synthesis of deep-eutectic-solvent-based materials. On the other hand, application in the extraction and separation of deep eutectic solvents is also included in this report. In this paper, the available data and references in this field are reviewed to summarize the applications and developments of deep eutectic solvents. Based on the development of deep eutectic solvents, an exploitation of new deep eutectic solvents and deep eutectic solvents-based materials is expected to diversify into extraction and separation.

  11. The Deep Space Network. An instrument for radio navigation of deep space probes

    NASA Technical Reports Server (NTRS)

    Renzetti, N. A.; Jordan, J. F.; Berman, A. L.; Wackley, J. A.; Yunck, T. P.

    1982-01-01

    The Deep Space Network (DSN) network configurations used to generate the navigation observables and the basic process of deep space spacecraft navigation, from data generation through flight path determination and correction are described. Special emphasis is placed on the DSN Systems which generate the navigation data: the DSN Tracking and VLBI Systems. In addition, auxiliary navigational support functions are described.

  12. The Deep Space Network: A Radio Communications Instrument for Deep Space Exploration

    NASA Technical Reports Server (NTRS)

    Renzetti, N. A.; Stelzried, C. T.; Noreen, G. K.; Slobin, S. D.; Petty, S. M.; Trowbridge, D. L.; Donnelly, H.; Kinman, P. W.; Armstrong, J. W.; Burow, N. A.

    1983-01-01

    The primary purpose of the Deep Space Network (DSN) is to serve as a communications instrument for deep space exploration, providing communications between the spacecraft and the ground facilities. The uplink communications channel provides instructions or commands to the spacecraft. The downlink communications channel provides command verification and spacecraft engineering and science instrument payload data.

  13. Climate Influence on Deep Sea Populations

    PubMed Central

    Company, Joan B.; Puig, Pere; Sardà, Francesc; Palanques, Albert; Latasa, Mikel; Scharek, Renate

    2008-01-01

    Dynamics of biological processes on the deep-sea floor are traditionally thought to be controlled by vertical sinking of particles from the euphotic zone at a seasonal scale. However, little is known about the influence of lateral particle transport from continental margins to deep-sea ecosystems. To address this question, we report here how the formation of dense shelf waters and their subsequent downslope cascade, a climate induced phenomenon, affects the population of the deep-sea shrimp Aristeus antennatus. We found evidence that strong currents associated with intense cascading events correlates with the disappearance of this species from its fishing grounds, producing a temporary fishery collapse. Despite this initial negative effect, landings increase between 3 and 5 years after these major events, preceded by an increase of juveniles. The transport of particulate organic matter associated with cascading appears to enhance the recruitment of this deep-sea living resource, apparently mitigating the general trend of overexploitation. Because cascade of dense water from continental shelves is a global phenomenon, we anticipate that its influence on deep-sea ecosystems and fisheries worldwide should be larger than previously thought. PMID:18197243

  14. Training Deep Spiking Neural Networks Using Backpropagation

    PubMed Central

    Lee, Jun Haeng; Delbruck, Tobi; Pfeiffer, Michael

    2016-01-01

    Deep spiking neural networks (SNNs) hold the potential for improving the latency and energy efficiency of deep neural networks through data-driven event-based computation. However, training such networks is difficult due to the non-differentiable nature of spike events. In this paper, we introduce a novel technique, which treats the membrane potentials of spiking neurons as differentiable signals, where discontinuities at spike times are considered as noise. This enables an error backpropagation mechanism for deep SNNs that follows the same principles as in conventional deep networks, but works directly on spike signals and membrane potentials. Compared with previous methods relying on indirect training and conversion, our technique has the potential to capture the statistics of spikes more precisely. We evaluate the proposed framework on artificially generated events from the original MNIST handwritten digit benchmark, and also on the N-MNIST benchmark recorded with an event-based dynamic vision sensor, in which the proposed method reduces the error rate by a factor of more than three compared to the best previous SNN, and also achieves a higher accuracy than a conventional convolutional neural network (CNN) trained and tested on the same data. We demonstrate in the context of the MNIST task that thanks to their event-driven operation, deep SNNs (both fully connected and convolutional) trained with our method achieve accuracy equivalent with conventional neural networks. In the N-MNIST example, equivalent accuracy is achieved with about five times fewer computational operations. PMID:27877107

  15. Deep-Plane Lipoabdominoplasty in East Asians

    PubMed Central

    Jang, Jun-Young; Hong, Yoon Gi; Sim, Hyung Bo; Sun, Sang Hoon

    2016-01-01

    Background The objective of this study was to develop a new surgical technique by combining traditional abdominoplasty with liposuction. This combination of operations permits simpler and more accurate management of various abdominal deformities. In lipoabdominoplasty, the combination of techniques is of paramount concern. Herein, we introduce a new combination of liposuction and abdominoplasty using deep-plane flap sliding to maximize the benefits of both techniques. Methods Deep-plane lipoabdominoplasty was performed in 143 patients between January 2007 and May 2014. We applied extensive liposuction on the entire abdomen followed by a sliding flap through the deep plane after repairing the diastasis recti. The abdominal wound closure was completed with repair of Scarpa's fascia. Results The average amount of liposuction aspirate was 1,400 mL (700–3,100 mL), and the size of the average excised skin ellipse was 21.78×12.81 cm (from 15×10 to 25×15 cm). There were no major complications such as deep-vein thrombosis or pulmonary embolism. We encountered 22 cases of minor complications: one wound infection, one case of skin necrosis, two cases of undercorrection, nine hypertrophic scars, and nine seromas. These complications were solved by conservative management or simple revision. Conclusions The use of deep-plane lipoabdominoplasty can correct abdominal deformities more effectively and with fewer complications than traditional abdominoplasty. PMID:27462568

  16. Preface: Deep Slab and Mantle Dynamics

    NASA Astrophysics Data System (ADS)

    Suetsugu, Daisuke; Bina, Craig R.; Inoue, Toru; Wiens, Douglas A.

    2010-11-01

    We are pleased to publish this special issue of the journal Physics of the Earth and Planetary Interiors entitled "Deep Slab and Mantle Dynamics". This issue is an outgrowth of the international symposium "Deep Slab and Mantle Dynamics", which was held on February 25-27, 2009, in Kyoto, Japan. This symposium was organized by the "Stagnant Slab Project" (SSP) research group to present the results of the 5-year project and to facilitate intensive discussion with well-known international researchers in related fields. The SSP and the symposium were supported by a Grant-in-Aid for Scientific Research (16075101) from the Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government. In the symposium, key issues discussed by participants included: transportation of water into the deep mantle and its role in slab-related dynamics; observational and experimental constraints on deep slab properties and the slab environment; modeling of slab stagnation to constrain its mechanisms in comparison with observational and experimental data; observational, experimental and modeling constraints on the fate of stagnant slabs; eventual accumulation of stagnant slabs on the core-mantle boundary and its geodynamic implications. This special issue is a collection of papers presented in the symposium and other papers related to the subject of the symposium. The collected papers provide an overview of the wide range of multidisciplinary studies of mantle dynamics, particularly in the context of subduction, stagnation, and the fate of deep slabs.

  17. Biology of deep-water chondrichthyans: Introduction

    NASA Astrophysics Data System (ADS)

    Cotton, C. F.; Grubbs, R. D.

    2015-05-01

    Approximately half of the known chondrichthyans (sharks, skates, rays, and chimaeras), 575 of 1207 species (47.6%, Table 1), live in the deep ocean (below 200 m), yet little is known of the biology or life histories of most of these fishes (Kyne and Simpfendorfer, 2007). The limited information available for deep-water chondrichthyans is compounded by their rarity, as well as the prevalent uncertainty in the alpha taxonomy of deep-water species. Many species are known only from the type materials, which are generally limited to nondestructive sampling, e.g., morphometrics, imaging (X-ray, MRI, CT scanning). Thus, research has been hindered by a lack of specimens available for investigation that requires destructive sampling or live specimens (e.g., life history, diet, telemetry). The need for more research and dissemination of information about deep-water chondrichthyans has become imperative as fisheries worldwide continue to expand into deeper waters and exploit deep-water stocks, usually in the absence of data required for appropriate management (Morato et al., 2006; Kyne and Simpfendorfer, 2010).

  18. Climate influence on deep sea populations.

    PubMed

    Company, Joan B; Puig, Pere; Sardà, Francesc; Palanques, Albert; Latasa, Mikel; Scharek, Renate

    2008-01-16

    Dynamics of biological processes on the deep-sea floor are traditionally thought to be controlled by vertical sinking of particles from the euphotic zone at a seasonal scale. However, little is known about the influence of lateral particle transport from continental margins to deep-sea ecosystems. To address this question, we report here how the formation of dense shelf waters and their subsequent downslope cascade, a climate induced phenomenon, affects the population of the deep-sea shrimp Aristeus antennatus. We found evidence that strong currents associated with intense cascading events correlates with the disappearance of this species from its fishing grounds, producing a temporary fishery collapse. Despite this initial negative effect, landings increase between 3 and 5 years after these major events, preceded by an increase of juveniles. The transport of particulate organic matter associated with cascading appears to enhance the recruitment of this deep-sea living resource, apparently mitigating the general trend of overexploitation. Because cascade of dense water from continental shelves is a global phenomenon, we anticipate that its influence on deep-sea ecosystems and fisheries worldwide should be larger than previously thought.

  19. Training Deep Spiking Neural Networks Using Backpropagation.

    PubMed

    Lee, Jun Haeng; Delbruck, Tobi; Pfeiffer, Michael

    2016-01-01

    Deep spiking neural networks (SNNs) hold the potential for improving the latency and energy efficiency of deep neural networks through data-driven event-based computation. However, training such networks is difficult due to the non-differentiable nature of spike events. In this paper, we introduce a novel technique, which treats the membrane potentials of spiking neurons as differentiable signals, where discontinuities at spike times are considered as noise. This enables an error backpropagation mechanism for deep SNNs that follows the same principles as in conventional deep networks, but works directly on spike signals and membrane potentials. Compared with previous methods relying on indirect training and conversion, our technique has the potential to capture the statistics of spikes more precisely. We evaluate the proposed framework on artificially generated events from the original MNIST handwritten digit benchmark, and also on the N-MNIST benchmark recorded with an event-based dynamic vision sensor, in which the proposed method reduces the error rate by a factor of more than three compared to the best previous SNN, and also achieves a higher accuracy than a conventional convolutional neural network (CNN) trained and tested on the same data. We demonstrate in the context of the MNIST task that thanks to their event-driven operation, deep SNNs (both fully connected and convolutional) trained with our method achieve accuracy equivalent with conventional neural networks. In the N-MNIST example, equivalent accuracy is achieved with about five times fewer computational operations.

  20. Linking Deep Earth and Surface Processes

    NASA Astrophysics Data System (ADS)

    Cloetingh, Sierd; Willett, Sean D.

    2013-01-01

    One of the important developments in Earth science over the past decade has been recognition of the significance of linking deep Earth dynamic processes with surface and near-surface geologic processes [e.g., Braun, 2010]. Deep Earth research, encompassing fields such as seismology and mantle geodynamics, has traditionally operated distinctly from fields focusing on dynamics of the Earth's surface, such as sedimentology and geomorphology. However, these endeavors have in common the study of Earth's topography and the prediction of changes in its surface. Observables from surface studies, such as basin stratigraphy, geomorphology of landscapes, changes in surface elevation, and changes in sea level, provide some of the principal constraints on geodynamic and tectonic models. Conversely, deep geodynamic processes give rise to the topography, erosion, and sediment generation that are the basis of surface geology. Surface manifestations of deep geodynamic processes have significant societal impact by creating natural hazards, such as earthquakes and mass movements, and controlling the distribution of natural resources such as fossil fuels or geothermal energy. The relevance of research conducted in both the deep Earth and surface regimes is thus enhanced through a focus on their interaction.

  1. In Brief: Deep-sea observatory

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2008-11-01

    The first deep-sea ocean observatory offshore of the continental United States has begun operating in the waters off central California. The remotely operated Monterey Accelerated Research System (MARS) will allow scientists to monitor the deep sea continuously. Among the first devices to be hooked up to the observatory are instruments to monitor earthquakes, videotape deep-sea animals, and study the effects of acidification on seafloor animals. ``Some day we may look back at the first packets of data streaming in from the MARS observatory as the equivalent of those first words spoken by Alexander Graham Bell: `Watson, come here, I need you!','' commented Marcia McNutt, president and CEO of the Monterey Bay Aquarium Research Institute, which coordinated construction of the observatory. For more information, see http://www.mbari.org/news/news_releases/2008/mars-live/mars-live.html.

  2. Deep-Ocean Measurements of Tsunami Waves

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander B.; Eblé, Marie C.

    2015-12-01

    Deep-ocean tsunami measurements play a major role in understanding the physics of tsunami wave generation and propagation, and in improving the effectiveness of tsunami warning systems. This paper provides an overview of the history of tsunami recording in the open ocean from the earliest days, approximately 50 years ago, to the present day. Modern tsunami monitoring systems such as the self-contained Deep-ocean Assessment and Reporting of Tsunamis and innovative cabled sensing networks, including, but not limited to, the Japanese bottom cable projects and the NEPTUNE-Canada geophysical bottom observatory, are highlighted. The specific peculiarities of seafloor longwave observations in the deep ocean are discussed and compared with observations recorded in coastal regions. Tsunami detection in bottom pressure observations is exemplified through analysis of distant (22,000 km from the source) records of the 2004 Sumatra tsunami in the northeastern Pacific.

  3. Measurement of light scattering in deep sea

    NASA Astrophysics Data System (ADS)

    Maragos, N.; Balasi, K.; Domvoglou, T.; Kiskiras, I.; Lenis, D.; Maniatis, M.; Stavropoulos, G.

    2016-04-01

    The deep-sea neutrino telescope in the Mediterranean Sea, being prepared by the KM3NET collaboration, will contain thousands of optical sensors to readout. The accurate knowledge of the optical properties of deep-sea water is of great importance for the neutrino event reconstruction process. In this study we describe our progress in designing an experimental setup and studying a method to measure the parameters describing the absorption and scattering characteristics of deep-sea water. Three PMTs will be used to measure in situ the scattered light emitted from six laser diodes in three different wavelengths covering the Cherenkov radiation spectrum. The technique for the evaluation of the parameters is based on Monte Carlo simulations and our results show that we are able to determine these parameters with satisfying precision.

  4. Excess plutonium disposition: The deep borehole option

    SciTech Connect

    Ferguson, K.L.

    1994-08-09

    This report reviews the current status of technologies required for the disposition of plutonium in Very Deep Holes (VDH). It is in response to a recent National Academy of Sciences (NAS) report which addressed the management of excess weapons plutonium and recommended three approaches to the ultimate disposition of excess plutonium: (1) fabrication and use as a fuel in existing or modified reactors in a once-through cycle, (2) vitrification with high-level radioactive waste for repository disposition, (3) burial in deep boreholes. As indicated in the NAS report, substantial effort would be required to address the broad range of issues related to deep bore-hole emplacement. Subjects reviewed in this report include geology and hydrology, design and engineering, safety and licensing, policy decisions that can impact the viability of the concept, and applicable international programs. Key technical areas that would require attention should decisions be made to further develop the borehole emplacement option are identified.

  5. New proppant for deep hydraulic fracturing

    SciTech Connect

    Underdown, D.R.; Das, K.

    1982-01-01

    Much work has been done in the development and evaluation of various materials for use as proppants for hydraulic fracturing. Sand is most often used as a frac proppant in shallow wells. Deep wells having high closure stresses require a proppant such as sintered bauxite which will not crush under such adverse conditions. Proppants such as ceramic and zirconium oxide beads and resin coated sand have been developed for deep hydraulic fracturing; however, use of these materials has been limited. A new frac proppant has been developed which exhibits the properties necessary for use in deep hydraulic fracturing. This frac proppant is produced by precuring a specially modified phenol-formaldehyde resin onto sand. The new frac proppant maintains conductivity and resists crushing, similar to that of sintered bauxite at high closure stress. 11 references.

  6. Interpretable Deep Models for ICU Outcome Prediction

    PubMed Central

    Che, Zhengping; Purushotham, Sanjay; Khemani, Robinder; Liu, Yan

    2016-01-01

    Exponential surge in health care data, such as longitudinal data from electronic health records (EHR), sensor data from intensive care unit (ICU), etc., is providing new opportunities to discover meaningful data-driven characteristics and patterns ofdiseases. Recently, deep learning models have been employedfor many computational phenotyping and healthcare prediction tasks to achieve state-of-the-art performance. However, deep models lack interpretability which is crucial for wide adoption in medical research and clinical decision-making. In this paper, we introduce a simple yet powerful knowledge-distillation approach called interpretable mimic learning, which uses gradient boosting trees to learn interpretable models and at the same time achieves strong prediction performance as deep learning models. Experiment results on Pediatric ICU dataset for acute lung injury (ALI) show that our proposed method not only outperforms state-of-the-art approaches for morality and ventilator free days prediction tasks but can also provide interpretable models to clinicians. PMID:28269832

  7. The South China Sea Deep: Introduction

    NASA Astrophysics Data System (ADS)

    Wang, Pinxian; Li, Qianyu; Dai, Minhan

    2015-12-01

    The South China Sea (SCS) has increasingly become a global focus in ocean research and hydrocarbon explorations. Over the last two decades, at least 17 international cruises including two ODP/IODP expeditions were conducted in the SCS, and more than 2000 exploratory wells were drilled (Wang et al., 2014a). While its sedimentary basins on the continental shelf and slope are explored for offshore resources, the deep basin below 3500 m in depth that overlies the basaltic oceanic crust preserves the key to understanding their formation and development. In order to better understand the life history and functional system of the marginal sea, a major research program "Deep Sea Processes and Evolution of the South China Sea", or "The South China Sea Deep" for short, was launched in January 2011 by the National Natural Science Foundation (NSFC) of China. This venture represents the first ever large-scale basic-research program in ocean science in the country (Wang, 2012).

  8. Microbial survival in deep space environment.

    NASA Technical Reports Server (NTRS)

    Silverman, G. J.

    1971-01-01

    Review of the knowledge available on the extent to which microorganisms (mainly microbial spores, vegetative cells, and fungi) are capable of surviving the environment of deep space, based on recent simulation experiments of deep space. A description of the experimental procedures used is followed by a discussion of deep space ecology, the behavior of microorganisms in ultrahigh vacuum, and factors influencing microbial survival. It is concluded that, so far, simulation experiments have proved far less lethal to microorganisms than to other forms of life. There are, however, wide gaps in the knowledge available, and no accurate predictions can as yet be made on the degree of lethality that might be incurred by a microbial population on a given mission. Therefore, sterilization of spacecraft surfaces is deemed necessary if induced panspermia (i.e., interplanetary life propagation) is to be avoided.

  9. Deep Learning in Medical Image Analysis.

    PubMed

    Shen, Dinggang; Wu, Guorong; Suk, Heung-Il

    2017-03-09

    This review covers computer-assisted analysis of images in the field of medical imaging. Recent advances in machine learning, especially with regard to deep learning, are helping to identify, classify, and quantify patterns in medical images. At the core of these advances is the ability to exploit hierarchical feature representations learned solely from data, instead of features designed by hand according to domain-specific knowledge. Deep learning is rapidly becoming the state of the art, leading to enhanced performance in various medical applications. We introduce the fundamentals of deep learning methods and review their successes in image registration, detection of anatomical and cellular structures, tissue segmentation, computer-aided disease diagnosis and prognosis, and so on. We conclude by discussing research issues and suggesting future directions for further improvement. Expected final online publication date for the Annual Review of Biomedical Engineering Volume 19 is June 4, 2017. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

  10. Strategic Technologies for Deep Space Transport

    NASA Technical Reports Server (NTRS)

    Litchford, Ronald J.

    2016-01-01

    Deep space transportation capability for science and exploration is fundamentally limited by available propulsion technologies. Traditional chemical systems are performance plateaued and require enormous Initial Mass in Low Earth Orbit (IMLEO) whereas solar electric propulsion systems are power limited and unable to execute rapid transits. Nuclear based propulsion and alternative energetic methods, on the other hand, represent potential avenues, perhaps the only viable avenues, to high specific power space transport evincing reduced trip time, reduced IMLEO, and expanded deep space reach. Here, key deep space transport mission capability objectives are reviewed in relation to STMD technology portfolio needs, and the advanced propulsion technology solution landscape is examined including open questions, technical challenges, and developmental prospects. Options for potential future investment across the full compliment of STMD programs are presented based on an informed awareness of complimentary activities in industry, academia, OGAs, and NASA mission directorates.

  11. Spaceport operations for deep space missions

    NASA Technical Reports Server (NTRS)

    Holt, Alan C.

    1990-01-01

    Space Station Freedom is designed with the capability to cost-effectively evolve into a transportation node which can support manned lunar and Mars missions. To extend a permanent human presence to the outer planets (moon outposts) and to nearby star systems, additional orbiting space infrastructure and great advances in propulsion system and other technologies will be required. To identify primary operations and management requirements for these deep space missions, an interstellar design concept was developed and analyzed. The assembly, test, servicing, logistics resupply, and increment management techniques anticipated for lunar and Mars missions appear to provide a pattern which can be extended in an analogous manner to deep space missions. A long range, space infrastructure development plan (encompassing deep space missions) coupled with energetic, breakthrough level propulsion research should be initiated now to assist in making the best budget and schedule decisions.

  12. Disposition of plutonium in deep boreholes

    SciTech Connect

    Halsey, W.G.; Jardine, L.J.; Walter, C.E.

    1995-05-01

    Substantial inventories of excess plutonium are expected to result from dismantlement of U.S. and Russian nuclear weapons. Disposition of this material should be a high priority in both countries. A variety of disposition options are under consideration. One option is to place the plutonium either directly or in an immobilized form at the bottom of a deep borehole that is then sealed. Deep-borehole disposition involves placing plutonium several kilometers deep into old, stable, rock formations that have negligible free water present. Containment assurance is based on the presence of ancient groundwater indicating lack of migration and communication with the biosphere. Recovery would be extremely difficult (costly) and impossible to accomplish clandestinely.

  13. Autonomous, Retrievable, Deep Sea Microbial Fuel Cell

    NASA Astrophysics Data System (ADS)

    Richter, K.

    2014-12-01

    Microbial fuel cells (MFCs) work by providing bacteria in anaerobic sediments with an electron acceptor (anode) that stimulates metabolism of organic matter. The buried anode is connected via control circuitry to a cathode exposed to oxygen in the overlying water. During metabolism, bacteria release hydrogen ions into the sediment and transfer electrons extra-cellularly to the anode, which eventually reduce dissolved oxygen at the cathode, forming water. The open circuit voltage is approximately 0.8 v. The voltage between electrodes is operationally kept at 0.4 v with a potentiastat. The current is chiefly limited by the rate of microbial metabolism at the anode. The Office of Naval Research has encouraged development of microbial fuel cells in the marine environment at a number of academic and naval institutions. Earlier work in shallow sediments of San Diego Bay showed that the most important environmental parameters that control fuel cell power output in San Diego Bay were total organic carbon in the sediment and seasonal water temperature. Current MFC work at SPAWAR includes extension of microbial fuel cell tests to the deep sea environment (>1000 m) and, in parallel, testing microbial fuel cells in the laboratory under deep sea conditions. One question we are asking is whether MFC power output from deep water sediments repressurized and chilled in the laboratory comparable to those measured in situ. If yes, mapping the power potential of deep sea sediments may be made much easier, requiring sediment grabs and lab tests rather than deployment and retrieval of fuel cells. Another question we are asking is whether in situ temperature and total organic carbon in the deep sea sediment can predict MFC power. If yes, then we can make use of the large collection of publicly available, deep sea oceanographic measurements to make these predictions, foregoing expensive work at sea. These regressions will be compared to those derived from shallow water measurements.

  14. The study of deep-sea cephalopods.

    PubMed

    Hoving, Henk-Jan T; Perez, Jose Angel A; Bolstad, Kathrin S R; Braid, Heather E; Evans, Aaron B; Fuchs, Dirk; Judkins, Heather; Kelly, Jesse T; Marian, José E A R; Nakajima, Ryuta; Piatkowski, Uwe; Reid, Amanda; Vecchione, Michael; Xavier, José C C

    2014-01-01

    "Deep-sea" cephalopods are here defined as cephalopods that spend a significant part of their life cycles outside the euphotic zone. In this chapter, the state of knowledge in several aspects of deep-sea cephalopod research are summarized, including information sources for these animals, diversity and general biogeography and life cycles, including reproduction. Recommendations are made for addressing some of the remaining knowledge deficiencies using a variety of traditional and more recently developed methods. The types of oceanic gear that are suitable for collecting cephalopod specimens and images are reviewed. Many groups of deep-sea cephalopods require taxonomic reviews, ideally based on both morphological and molecular characters. Museum collections play a vital role in these revisions, and novel (molecular) techniques may facilitate new use of old museum specimens. Fundamental life-cycle parameters remain unknown for many species; techniques developed for neritic species that could potentially be applied to deep-sea cephalopods are discussed. Reproductive tactics and strategies in deep-sea cephalopods are very diverse and call for comparative evolutionary and experimental studies, but even in the twenty-first century, mature individuals are still unknown for many species. New insights into diet and trophic position have begun to reveal a more diverse range of feeding strategies than the typically voracious predatory lifestyle known for many cephalopods. Regular standardized deep-sea cephalopod surveys are necessary to provide insight into temporal changes in oceanic cephalopod populations and to forecast, verify and monitor the impacts of global marine changes and human impacts on these populations.

  15. 'War on terrorism' and deep culture.

    PubMed

    Barbara, Joanna Santa

    2003-01-01

    This article examines the reasons underlying the massive reaction to the terrorist attacks of 11 September 2001 compared with the lack of response to the many thousands of preventable deaths elsewhere daily. It is suggested that the explanation is the 'deep culture' of the United States based on the myth of the frontiersman. The world is divided into winners and losers, good and bad; non-US citizens are of less value as human beings. The only response allowed by this deep culture is striking back at 'the enemy'. The difficulties with this response are discussed and non-violent alternatives considered.

  16. Deep Space 1 is prepared for launch

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Workers in the Payload Hazardous Servicing Facility check out Deep Space 1 to prepare it for launch aboard a Boeing Delta 7326 rocket in October. The first flight in NASA's New Millennium Program, Deep Space 1 is designed to validate 12 new technologies for scientific space missions of the next century. Onboard experiments include an ion propulsion engine and software that tracks celestial bodies so the spacecraft can make its own navigation decisions without the intervention of ground controllers. Most of its mission objectives will be completed within the first two months. A near-Earth asteroid, 1992 KD, has also been selected for a possible flyby.

  17. Deep Space 1 is prepared for launch

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Workers in the Payload Hazardous Servicing Facility remove a solar panel from Deep Space 1 as part of the preparations for launch aboard a Boeing Delta 7326 rocket in October. The first flight in NASA's New Millennium Program, Deep Space 1 is designed to validate 12 new technologies for scientific space missions of the next century. Onboard experiments include an ion propulsion engine and software that tracks celestial bodies so the spacecraft can make its own navigation decisions without the intervention of ground controllers. Most of its mission objectives will be completed within the first two months. A near- Earth asteroid, 1992 KD, has also been selected for a possible flyby.

  18. Deep Space 1 is prepared for launch

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Workers in the Payload Hazardous Servicing Facility check equipment on Deep Space 1 to prepare it for launch aboard a Boeing Delta 7326 rocket in October. The first flight in NASA's New Millennium Program, Deep Space 1 is designed to validate 12 new technologies for scientific space missions of the next century. Onboard experiments include an ion propulsion engine and software that tracks celestial bodies so the spacecraft can make its own navigation decisions without the intervention of ground controllers. Most of its mission objectives will be completed within the first two months. A near-Earth asteroid, 1992 KD, has also been selected for a possible flyby.

  19. Pallidotomy after chronic deep brain stimulation.

    PubMed

    Bulluss, Kristian J; Pereira, Erlick A; Joint, Carole; Aziz, Tipu Z

    2013-11-01

    Recent publications have demonstrated that deep brain stimulation for Parkinson's disease still exerts beneficial effects on tremor, rigidity, and bradykinesia for up to 10 years after implantation of the stimulator. However with the progression of Parkinson's disease, features such as cognitive decline or "freezing" become prominent, and the presence of an implanted and functioning deep brain stimulator can impose a profound burden of care on the clinical team and family. The authors describe their experience in treating 4 patients who underwent removal of the implanted device due to either progressive dementia requiring full-time nursing or due to infection, and who subsequently underwent a unilateral pallidotomy.

  20. Deep Space 1 is prepared for launch

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Workers in the Payload Hazardous Servicing Facility test equipment on Deep Space 1 to prepare it for launch aboard a Boeing Delta 7326 rocket in October. The first flight in NASA's New Millennium Program, Deep Space 1 is designed to validate 12 new technologies for scientific space missions of the next century. Onboard experiments include an ion propulsion engine and software that tracks celestial bodies so the spacecraft can make its own navigation decisions without the intervention of ground controllers. Most of its mission objectives will be completed within the first two months. A near-Earth asteroid, 1992 KD, has also been selected for a possible flyby.

  1. Experimental investigation of deep sea riser interaction

    SciTech Connect

    Huse, E.

    1996-12-31

    In future deep sea field developments the drag force and corresponding static deflections of the risers due to current can become quite large. The prevention of mechanical contact (collision) between the risers will need more careful evaluation than in moderate water depths. The paper describes a series of model experiments in a Norwegian fjord to determine criteria for on-set of collisions between the risers of a deep sea TLP. The current was modeled using the natural tidal current in the fjord. Results from the tests are summarized and used for verification of numerical calculations of collision criteria.

  2. Deep Space 1 is prepared for launch

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Workers in the Payload Hazardous Servicing Facility prepare Deep Space 1 for launch aboard a Boeing Delta 7326 rocket in October. The first flight in NASA's New Millennium Program, Deep Space 1 is designed to validate 12 new technologies for scientific space missions of the next century. Onboard experiments include an ion propulsion engine and software that tracks celestial bodies so the spacecraft can make its own navigation decisions without the intervention of ground controllers. Most of its mission objectives will be completed within the first two months. A near- Earth asteroid, 1992 KD, has also been selected for a possible flyby.

  3. Deep Horizons - Implications of the deep carbon cycle for life, energy, and the environment (Invited)

    NASA Astrophysics Data System (ADS)

    Sherwood Lollar, B.; Ballentine, C. J.; Shock, E.

    2010-12-01

    B. Sherwood Lollar1, C.J. Ballentine2, E. Shock3 1Dept. of Geology, University of Toronto, Toronto, Ontario, Canada M5S 3B1 email bslollar@chem.utoronto.ca 2School of Earth, Atmospheric & Environ. Sci., Univ. of Manchester, UK M13 9PL 3School of Earth & Space Exploration, Arizona State Univ., Tempe, AZ 85287-1404 While well-developed models exist regarding surface biogeochemical carbon cycles on short-, medium- and long-term scales over geologic time, major unknowns persist concerning the deep carbon cycle, including the pathways and flux of carbon exchange between the surface and deep interior of the planet; the nature of microbial life in the Earth's deep subsurface; and the implications of the deep carbon cycle for energy resources and the environment. Major research questions include: What is the distribution, form and abundance of carbon in the deep crust and mantle? What is the nature of deep carbon flux and the timescale and mechanisms of recycling? Do the lower crust and mantle contribute biologically available carbon to the shallow subsurface and surface? To what extent does the deep carbon cycle support microbial ecosystems in the deep marine and/or deep terrestrial biosphere? What is the volume and depth of the Earth's habitable zone and what are the implications of this for the search for life on other planets and moons? What is the role of the deep carbon cycle in sustaining abiotic organic synthesis and what potential contribution might such chemical organic synthesis have made to the origin of life and the sustainability of deep microbial ecosystems? How does our understanding of the deep carbon cycle impact on emerging global issues such as climate change, energy and carbon sequestration? While fundamental to our understanding of the origin and evolution of life and the planet - these questions are also relevant to the major practical challenges facing science and society as we struggle with the implications of still increasing fossil fuel

  4. The deep Madden Field, a super-deep Madison gas reservoir, Wind River Basin, Wyoming

    SciTech Connect

    Moore, C.H.; Hawkins, C.

    1996-12-31

    Madison dolomites form the reservoir of a super deep, potential giant sour gas field developed on the Madden Anticline immediately in front of the Owl Creek Thrust along the northern rim of the Wind River Basin, central Wyoming. The Madison reservoir dolomites are presently buried to some 25,000 feet at Madden Field and exhibit porosity in excess of 15%. An equivalent dolomitized Madison sequence is exposed in outcrop only 5 miles to the north on the hanging wall of the Owl Creek thrust at Lysite Mountain. Preliminary comparative stratigraphic, geochemical and petrologic data, between outcrop and available cores and logs at Deep Madden suggests: (1) early, sea level-controlled, evaporite-related dolomitization of the reservoir and outcrop prior to significant burial; (2) both outcrop and deep reservoir dolomites underwent significant recrystallization during a common burial history until their connection was severed during Laramide faulting in the Eocene; (3) While the dolomite reservoir at Madden suffered additional diagenesis during an additional 7-10 thousand feet of burial, the pore systems between outcrop and deep reservoir are remarkably similar. The two existing deep Madison wells at Madden are on stream, with a third deep Madison well currently drilling. The sequence stratigraphic framework and the diagenetic history of the Madison strongly suggests that outcrops and surface cores of the Madison in the Owl Creek Mountains will be useful in further development and detailed reservoir modeling of the Madden Deep Field.

  5. The deep Madden Field, a super-deep Madison gas reservoir, Wind River Basin, Wyoming

    SciTech Connect

    Moore, C.H. ); Hawkins, C. )

    1996-01-01

    Madison dolomites form the reservoir of a super deep, potential giant sour gas field developed on the Madden Anticline immediately in front of the Owl Creek Thrust along the northern rim of the Wind River Basin, central Wyoming. The Madison reservoir dolomites are presently buried to some 25,000 feet at Madden Field and exhibit porosity in excess of 15%. An equivalent dolomitized Madison sequence is exposed in outcrop only 5 miles to the north on the hanging wall of the Owl Creek thrust at Lysite Mountain. Preliminary comparative stratigraphic, geochemical and petrologic data, between outcrop and available cores and logs at Deep Madden suggests: (1) early, sea level-controlled, evaporite-related dolomitization of the reservoir and outcrop prior to significant burial; (2) both outcrop and deep reservoir dolomites underwent significant recrystallization during a common burial history until their connection was severed during Laramide faulting in the Eocene; (3) While the dolomite reservoir at Madden suffered additional diagenesis during an additional 7-10 thousand feet of burial, the pore systems between outcrop and deep reservoir are remarkably similar. The two existing deep Madison wells at Madden are on stream, with a third deep Madison well currently drilling. The sequence stratigraphic framework and the diagenetic history of the Madison strongly suggests that outcrops and surface cores of the Madison in the Owl Creek Mountains will be useful in further development and detailed reservoir modeling of the Madden Deep Field.

  6. DeepPicker: A deep learning approach for fully automated particle picking in cryo-EM.

    PubMed

    Wang, Feng; Gong, Huichao; Liu, Gaochao; Li, Meijing; Yan, Chuangye; Xia, Tian; Li, Xueming; Zeng, Jianyang

    2016-09-01

    Particle picking is a time-consuming step in single-particle analysis and often requires significant interventions from users, which has become a bottleneck for future automated electron cryo-microscopy (cryo-EM). Here we report a deep learning framework, called DeepPicker, to address this problem and fill the current gaps toward a fully automated cryo-EM pipeline. DeepPicker employs a novel cross-molecule training strategy to capture common features of particles from previously-analyzed micrographs, and thus does not require any human intervention during particle picking. Tests on the recently-published cryo-EM data of three complexes have demonstrated that our deep learning based scheme can successfully accomplish the human-level particle picking process and identify a sufficient number of particles that are comparable to those picked manually by human experts. These results indicate that DeepPicker can provide a practically useful tool to significantly reduce the time and manual effort spent in single-particle analysis and thus greatly facilitate high-resolution cryo-EM structure determination. DeepPicker is released as an open-source program, which can be downloaded from https://github.com/nejyeah/DeepPicker-python.

  7. Design and Analysis of Deep Drawing Process on angular Deep Drawing Dies for Different Anisotropic Materials

    NASA Astrophysics Data System (ADS)

    Venkateshwar Reddy, P.; Janaki Ramulu, Perumalla; Sandhya Madhuri, G.; Govardhan, Dasari; Ram Prasad, P. V. S.

    2016-09-01

    Deep drawing process is a significant metal forming process used in the sheet metal forming operations. From this process, complex shapes can be manufactured with fewer defects. Deep drawing process has different effectible process parameters from which an optimum level of parameters can be identified so that an efficient final product with required mechanical properties will be obtained. The present work is to evaluate the formability of different metal sheets using deep drawing process. In which effects of different sheets and die/blank holder angle on deep drawing process observed for sheet metal of 0.8mm of SS304 and Brass and 0.9 mm of Al. The experiments were performed by designing the deep drawing tools such as die, blank holder, and punch. In addition, the numerical simulations are performed for deep drawing of cylindrical cups using three levels of previously mentioned. Punch forces and dome heights are evaluated for all the conditions. From this work, the formability for different metal sheets is observed for angular geometries of deep drawing tools. Moreover, it is observed that strain formation is more for the brass sheet and stress is more for aluminium sheets.

  8. Deep drilling; Probing beneath the earth's surface

    SciTech Connect

    Rosen, J.250

    1991-06-01

    This paper reports on boreholes from 4.5 to greater than 10 kilometers deep that are pushing back the boundaries of earth science as they yield information that is used to refine seismic surveys, chart the evolution of sedimentary basins and shield volcanos, and uncover important clues on the origin and migration of mantle-derived water and gas.

  9. Parity violation in deep inelastic scattering

    SciTech Connect

    Souder, P.

    1994-04-01

    AA beam of polarized electrons at CEBAF with an energy of 8 GeV or more will be useful for performing precision measurements of parity violation in deep inelastic scattering. Possible applications include precision tests of the Standard Model, model-independent measurements of parton distribution functions, and studies of quark correlations.

  10. Nonlinear Deep Kernel Learning for Image Annotation.

    PubMed

    Jiu, Mingyuan; Sahbi, Hichem

    2017-02-08

    Multiple kernel learning (MKL) is a widely used technique for kernel design. Its principle consists in learning, for a given support vector classifier, the most suitable convex (or sparse) linear combination of standard elementary kernels. However, these combinations are shallow and often powerless to capture the actual similarity between highly semantic data, especially for challenging classification tasks such as image annotation. In this paper, we redefine multiple kernels using deep multi-layer networks. In this new contribution, a deep multiple kernel is recursively defined as a multi-layered combination of nonlinear activation functions, each one involves a combination of several elementary or intermediate kernels, and results into a positive semi-definite deep kernel. We propose four different frameworks in order to learn the weights of these networks: supervised, unsupervised, kernel-based semisupervised and Laplacian-based semi-supervised. When plugged into support vector machines (SVMs), the resulting deep kernel networks show clear gain, compared to several shallow kernels for the task of image annotation. Extensive experiments and analysis on the challenging ImageCLEF photo annotation benchmark, the COREL5k database and the Banana dataset validate the effectiveness of the proposed method.

  11. Regulatory issues for deep borehole plutonium disposition

    SciTech Connect

    Halsey, W.G.

    1995-03-01

    As a result of recent changes throughout the world, a substantial inventory of excess separated plutonium is expected to result from dismantlement of US nuclear weapons. The safe and secure management and eventual disposition of this plutonium, and of a similar inventory in Russia, is a high priority. A variety of options (both interim and permanent) are under consideration to manage this material. The permanent solutions can be categorized into two broad groups: direct disposal and utilization. The deep borehole disposition concept involves placing excess plutonium deep into old stable rock formations with little free water present. Issues of concern include the regulatory, statutory and policy status of such a facility, the availability of sites with desirable characteristics and the technologies required for drilling deep holes, characterizing them, emplacing excess plutonium and sealing the holes. This white paper discusses the regulatory issues. Regulatory issues concerning construction, operation and decommissioning of the surface facility do not appear to be controversial, with existing regulations providing adequate coverage. It is in the areas of siting, licensing and long term environmental protection that current regulations may be inappropriate. This is because many current regulations are by intent or by default specific to waste forms, facilities or missions significantly different from deep borehole disposition of excess weapons usable fissile material. It is expected that custom regulations can be evolved in the context of this mission.

  12. Neurological long term consequences of deep diving.

    PubMed Central

    Todnem, K; Nyland, H; Skeidsvoll, H; Svihus, R; Rinck, P; Kambestad, B K; Riise, T; Aarli, J A

    1991-01-01

    Forty commercial saturation divers, mean age 34.9 (range 24-49) years, were examined one to seven years after their last deep dive (190-500 metres of seawater). Four had by then lost their divers' licence because of neurological problems. Twenty seven (68%) had been selected by neurological examination and electroencephalography before the deep dives. The control group consisted of 100 men, mean age 34.0 (range 22-48) years. The divers reported significantly more symptoms from the nervous system. Concentration difficulties and paraesthesia in feet and hands were common. They had more abnormal neurological findings by neurological examination compatible with dysfunction in the lumbar spinal cord or roots. They also had a larger proportion of abnormal electroencephalograms than the controls. The neurological symptoms and findings were highly significantly correlated with exposure to deep diving (depth included), but even more significantly correlated to air and saturation diving and prevalence of decompression sickness. Visual evoked potentials, brainstem auditory evoked potentials, and magnetic resonance imaging of the brain did not show more abnormal findings in the divers. Four (10%) divers had had episodes of cerebral dysfunction during or after the dives; two had had seizures, one had had transitory cerebral ischaemia and one had had transitory global amnesia. It is concluded that deep diving may have a long term effect on the nervous system of the divers. PMID:2025592

  13. Launching a Projectile into Deep Space

    ERIC Educational Resources Information Center

    Maruszewski, Richard F., Jr.

    2004-01-01

    As part of the discussion about Newton's work in a history of mathematics course, one of the presentations calculated the amount of energy necessary to send a projectile into deep space. Afterwards, the students asked for a recalculation with two changes: First the launch under study consisted of a single stage, but the students desired to…

  14. Citizenship as the Practice of Deep Ecology.

    ERIC Educational Resources Information Center

    Chamberlin, Charles

    1997-01-01

    Defines the educational practice of deep ecology as utilizing a social action framework to teach students how to take action on behalf of the communities of flora, fauna, and people. Discusses the theories that form the basis for this movement and specifically addresses how this can be applied to citizenship education. (MJP)

  15. Advanced transponders for deep space applications

    NASA Technical Reports Server (NTRS)

    Nguyen, Tien M.; Kayalar, Selahattin; Yeh, Hen-Geul; Kyriacou, Charles

    1993-01-01

    Three architectures for advanced deep space transponders are proposed. The architectures possess various digital techniques such as fast Fourier transform (FFT), digital phase-locked loop (PLL), and digital sideband aided carrier detection with analog or digital turn-around ranging. Preliminary results on the design and conceptual implementation are presented. Modifications to the command detector unit (CDU) are also presented.

  16. Pressure studies of deep levels in semiconductors

    SciTech Connect

    Samara, G.A.

    1989-01-01

    The effects of pressure on the energetics and kinetics of electron emission and capture processes by several important deep levels in Si are discussed. The results yield the first quantitative measures of the breathing mode lattice relaxations accompanying these processes. 2 refs., 1 fig.

  17. A Study of Detrainment from Deep Convection

    NASA Astrophysics Data System (ADS)

    Glenn, I. B.; Krueger, S. K.

    2014-12-01

    Uncertainty in the results of Global Climate Model simulations has been attributed to errors and simplifications in how parameterizations of convection coarsely represent the processes of entrainment, detrainment, and mixing between convective clouds and their environment. Using simulations of convection we studied these processes at a resolution high enough to explicitly resolve them. Two of several recently developed analysis techniques that allow insight into these processes at their appropriate scale are an Eulerian method of directly measuring entrainment and detrainment, and a Lagrangian method that uses particle trajectories to map convective mass flux over height and a cloud variable of interest. The authors of the Eulerian technique used it to show that the dynamics of shells of cold, humid air that surround shallow convective updrafts have important effects on the properties of air entrained and detrained from the updrafts. There is some evidence for the existence of such shells around deep convective updrafts as well, and that detrainment is more important than entrainment in determining the ultimate effect of the deep convection on the large scale environment. We present results from analyzing a simulation of deep convection through the Eulerian method as well as using Lagrangian particle trajectories to illustrate the role of the shell in the process of detrainment and mixing between deep convection and its environment.

  18. Deep Impurity States in Gallium Arsenide.

    DTIC Science & Technology

    1981-10-01

    determinations using a level to conduction band) and the capture rates mercury Schottky barrier. mercry chotky arrer.(fr m conduction band to deep level) as a...heating. The luminescence is dispersed through a grating spectrometer and detected with a cooled lead- sulphide photoconduc- tor. An important feature in the

  19. Deep inelastic scattering near the Coulomb barrier

    SciTech Connect

    Gehring, J.; Back, B.; Chan, K.

    1995-08-01

    Deep inelastic scattering was recently observed in heavy ion reactions at incident energies near and below the Coulomb barrier. Traditional models of this process are based on frictional forces and are designed to predict the features of deep inelastic processes at energies above the barrier. They cannot be applied at energies below the barrier where the nuclear overlap is small and friction is negligible. The presence of deep inelastic scattering at these energies requires a different explanation. The first observation of deep inelastic scattering near the barrier was in the systems {sup 124,112}Sn + {sup 58,64}Ni by Wolfs et al. We previously extended these measurements to the system {sup 136}Xe + {sup 64}Ni and currently measured the system {sup 124}Xe + {sup 58}Ni. We obtained better statistics, better mass and energy resolution, and more complete angular coverage in the Xe + Ni measurements. The cross sections and angular distributions are similar in all of the Sn + Ni and Xe + Ni systems. The data are currently being analyzed and compared with new theoretical calculations. They will be part of the thesis of J. Gehring.

  20. Modeling deep convection in the Greenland Sea

    NASA Technical Reports Server (NTRS)

    Hakkinen, S.; Mellor, G. L.; Kantha, L. H.

    1992-01-01

    The development of deep convective events in the high-latitude ocean is studied using a three-dimensional, coupled ice-ocean model. Oceanic mixing is described according to the level 2.5 turbulence closure scheme in which convection occurs in a continuous way, i.e., convective adjustment is not invoked. The model is forced by strong winds and surface cooling. Strong upwelling at the multilyear ice edge and consequent entrainment of warm Atlantic waters into the mixed layer is produced by winds parallel to the ice edge. Concomitant cooling drives deep convection and produces chimneylike structures. Inclusion of a barotropic mean flow over topography to the model provides important preconditioning and selects the location of deep convection. The most efficient preconditioning occurs at locations where the flow ascends a slope. In a stratified environment similar to the Greenland Sea with a 12 m/s wind the model simulations show that localized deep convection takes place after about 10 days to depths of 1000 m.