Science.gov

Sample records for projectile electronic structure

  1. Effects of the projectile electronic structure on stopping parameters for nickel

    NASA Astrophysics Data System (ADS)

    Damache, S.; Ouichaoui, S.; Moussa, D.; Dib, A.

    2006-08-01

    The stopping powers of nickel foils for 1H+, 2H+ and 4He2+ ions have been accurately measured over the energy range E ≈ (0.166-2.725) MeV/amu. The data were compared to those reported in the literature and to values derived by the SRIM-2003 code. They were analysed in the framework of the modified Bethe-Bloch theory to extract the target mean excitation and ionisation potential, I, and the Barkas effect parameter, b. The values derived from the proton and the alpha particle data are {I = (311.11 ± 2.61) eV, b = 1.38 ± 0.01} and {I = (276.12 ± 2.84) eV, b = 1.58 ± 0.01}, respectively. They thus show opposite variations of the I and b parameters as the projectile charge increases, presumably due only to the incident ions electronic structure. Besides, the reduced stopping power data for incident deuterons show to be fully consistent with those for protons indicating no effect of the projectile isotopic structure on the target stopping parameters. These results are discussed in comparison with ones reported in the literature.

  2. Effects of the projectile electronic structure on Bethe-Bloch stopping parameters for Ag

    NASA Astrophysics Data System (ADS)

    Moussa, D.; Damache, S.; Ouichaoui, S.

    2010-06-01

    Energy losses of protons and alpha particles in silver have been accurately measured under the same experimental conditions over the velocity range E=(0.192-2.595) MeV/amu using the transmission method. Deduced S(E) stopping powers are compared to most accurate ones from the literature, to values generated by the SRIM-2008 computer code and to ICRU-49 compilation. They were analyzed in the framework of modified Bethe-Bloch theory for extracting Ag target mean excitation and ionization potential, I, and Barkas effect parameter, b. Values of ( 466±5) eV and 1.20±0.01 for these two parameters were inferred from the proton S(E) data while the alpha particle data yielded values of (438±4) eV and 1.38±0.01, respectively. The ( I, b) stopping parameters thus exhibit opposite variations as the projectile charge increases, similarly as we have found previously for nickel [6]. This can be ascribed only to an effect of the projectile electronic structure at low velocities. The obtained results are discussed in comparison to previous ones reported in the literature.

  3. Multielectron transitions resulting from interactions between target and projectile electrons in ionizing collisions

    SciTech Connect

    Manson, S.T. ); DuBois, R.D. )

    1992-12-01

    Interactions between target and projectile electrons leading to ionization of one of the collision partners and simultaneous excitation of the other are investigated for fast clothed-particle--clothed-particle collisions. For H-atom impact, the first Born approximation is used to demonstrate that the low-energy-electron emission is dominated by electron-electron rather than by electron-nucleus interaction processes. For a broad class of structured particle collision systems, the electron-electron interaction is shown to play an important, non-neglibible, role. Doubly differential cross sections for energetic H-He collisions illustrate this point.

  4. 73. DETAIL OF 'A' FRAME STRUCTURE LOOKING NORTH SHOWING PROJECTILE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    73. DETAIL OF 'A' FRAME STRUCTURE LOOKING NORTH SHOWING PROJECTILE CAR, CAMERA TOWER, CANTILEVERED WALKWAYS AND ELECTRICAL GEAR, August 17, 1948. (Original photograph in possession of Dave Willis, San Diego, California.) - Variable Angle Launcher Complex, Variable Angle Launcher, CA State Highway 39 at Morris Reservior, Azusa, Los Angeles County, CA

  5. Atomic Physics with Accelerators: Projectile Electron Spectroscopy (APAPES)

    NASA Astrophysics Data System (ADS)

    Madesis, I.; Dimitriou, A.; Laoutaris, A.; Lagoyannis, A.; Axiotis, M.; Mertzimekis, T.; Andrianis, M.; Harissopulos, S.; Benis, E. P.; Sulik, B.; Valastyán, I.; Zouros, T. J. M.

    2015-01-01

    The new research initiative APAPES (http://apapes.physics.uoc.gr/) has already established a new experimental station with a beam line dedicated for atomic collisions physics research, at the 5 MV TANDEM accelerator of the National Research Centre "Demokritos" in Athens, Greece. A complete zero-degree Auger projectile spectroscopy (ZAPS) apparatus has been put together to perform high resolution studies of electrons emitted in ion-atom collisions. A single stage hemispherical spectrometer with a 2-dimensional Position Sensitive Detector (PSD) combined with a doubly-differentially pumped gas target will be used to perform a systematic isoelectronic investigation of K-Auger spectra emitted from collisions of preexcited and ground state He-like ions with gas targets using novel techniques. Our intention is to provide a more thorough understanding of cascade feeding of the 1s2s2p 4P metastable states produced by electron capture in collisions of He-like ions with gas targets and further elucidate their role in the non-statistical production of excited three-electron 1s2s2p states by electron capture, recently a field of conflicting interpretations awaiting further resolution. At the moment, the apparatus is being completed and the spectrometer will soon be fully operational. Here we present the project progress and the recent high resolution spectrum obtained in collisions of 12 MeV C4+ on a Neon gas target.

  6. Damage tolerance of composite sandwich structures subjected to projectile impact. [of low velocity foreign object

    NASA Technical Reports Server (NTRS)

    Sharma, A. V.

    1979-01-01

    An experimental investigation was conducted to evaluate the effect of low velocity projectile impact on the strength carrying ability of secondary aerospace structural components fabricated with graphite/epoxy composite materials. The preload and the impact energy combinations necessary to cause catastrophic failure were determined. Those specimens that survived the projectile impact were evaluated for the residual strength.

  7. On the universal scaling in the electronic stopping cross section for heavy ion projectiles

    NASA Astrophysics Data System (ADS)

    Cabrera-Trujillo, R.; Martínez-Flores, C.; Trujillo-López, L. N.; Serkovic-Loli, L. N.

    2016-02-01

    Energy deposition of heavy ions when penetrating a material is of crucial importance in determining the damage to materials with implications in areas such as material science, plasma physics, radiotherapy and dosimetry. Due to the N-body electron problem, it has been thought that the electronic stopping cross section is unique for a given projectile-target combination and differs from system to system. In this work, we show that within the Bethe theory, there is a universal scaling when the electronic stopping cross sections and projectile kinetic energy are scaled properly in terms of the target mean excitation energy, ?, for all projectile-target combinations. We show that the scaling is given by ? as a function of ?, thus showing the importance of the characterization of the mean excitation energy. The scaling law expresses a systematic and universal behavior among complex projectile-target systems in the energy deposition, characterized by the minimum momentum transfer during the slowing down process. We provide an analytic expression for the universal scaling law for the stopping cross section of any projectile-target combination valid at high collision energies. Finally, we verify the universal scaling law by comparison to atomic and molecular experimental data available in the literature. We expect our findings will motivate further experimental work to verify our universal scaling for more complex systems in the absence of experimental data.

  8. Fraunhofer-type diffraction patterns of matter-wave scattering of projectiles: Electron transfer in energetic ion-atom collisions

    NASA Astrophysics Data System (ADS)

    Agueny, Hicham

    2015-07-01

    We present results for single and double electron captures in intermediate energies H+ and 2H+ projectiles colliding with a helium target. The processes under investigations are treated using a nonperturbative semiclassical approach in combination with Eikonal approximation to calculate the scattering differential cross sections. The latter reveals pronounced minima and maxima in the scattering angles, in excellent agreement with the recent experimental data. It turns out that the present structure depends strongly on the projectile energy and shows only slight variations with different capture channels. The observed structure demonstrates the analogy of atomic de Broglie's matter-wave scattering with λd B=1.3 -3.2 ×10-3 a.u. and Fraunhofer-type diffraction of light waves.

  9. Projectile charge state effects on electron emission in transfer ionization processes

    NASA Astrophysics Data System (ADS)

    Zhang, R. T.; Zhu, X. L.; Feng, W. T.; Guo, D. L.; Gao, Y.; Qian, D. B.; Li, B.; Yan, S. C.; Xu, S.; Zhang, P.; Ma, X.

    2015-07-01

    Electron emissions in transfer ionization processes were studied for 75 keV u-1 He2+, and 80 keV u-1 Ne8+on He collisions, using the well-developed reaction microscope techniques. Momentum distributions in the scattering plane, doubly differential distributions as a function of longitudinal momentum and emission angles of the ejected electrons were obtained. An apparent enhancement of electrons distributed around the projectile in the scattering plane was found for the Ne8+ incident case. Furthermore, we report the ratio of doubly differential distributions at the emission angle of 0° between these two transfer ionization processes, in which an abrupt rise is found at and above the electron capture to the continuum peak. This rise qualitatively agrees with the prediction within the framework of Dettmann’s theory. We conclude that this kind of enhancement was caused by the charge state effect of the projectile.

  10. Evidence of strong projectile-target-core interaction in single ionization of neon by electron impact

    SciTech Connect

    Yan, S.; Zhang, P.; Xu, S.; Ma, X.; Zhang, S. F.; Zhu, X. L.; Feng, W. T.; Liu, H. P.

    2010-11-15

    The momentum distributions of recoil ions were measured in the single ionization of neon by electron impact at incident energies between 80 and 2300 eV. It was found that there are a noticeable number of recoil ions carrying large momenta, and the relative contributions of these ions becomes more pronounced with the further decrease of incident electron energy. These observed behaviors indicate that there is a strong projectile-target-core interaction in the single-ionization reaction. By comparing our results with those of electron-neon elastic scattering, we concluded that the elastic scattering of the projectile electron on the target core plays an important role at low and intermediate collision energies.

  11. Role of elastic projectile-electron scattering in double ionization of helium by fast proton impact

    NASA Astrophysics Data System (ADS)

    Schulz, M.; Ciappina, M. F.; Kirchner, T.; Fischer, D.; Moshammer, R.; Ullrich, J.

    2009-04-01

    We present a systematic study of atomic four-body fragmentation dynamics. To this end we have measured a variety of multiple differential double ionization cross sections for 6 MeV p+He collisions. The data are compared to a first-order calculation with correlated electrons and to a simulation representing a second-order process, with some experimental results seemingly in favor of the first, others in agreement with the second approach. This apparent conflict can be resolved by accounting for elastic scattering between the projectile and one electron already promoted to the continuum through electron-electron correlation in the first-order process.

  12. Absolute cross sections for projectile electron loss accompanied by target multiple ionization in collisions of He+ with noble gases

    NASA Astrophysics Data System (ADS)

    Santos, A. C. F.; Sigaud, G. M.; Melo, W. S.; Sant'Anna, M. M.; Montenegro, E. C.

    2011-02-01

    Absolute cross sections for projectile electron loss accompanied by target multiple ionization in collisions between He+ ions and noble gases have been measured for energies between 1.0 and 3.5 MeV. The data have been compared with other absolute cross sections that exist in the literature for the same projectile, and with calculations for the screening mode (nucleus-electron interaction) using both perturbative (plane-wave Born approximation (PWBA)) and non-perturbative (extended classical-impulse free-collision model, sudden approximation and coupled-channel method) approaches, and for the antiscreening mode (electron-electron interaction) within the PWBA. The energy dependence of the average number of active electrons for the antiscreening has been described by means of a simple function, which is 'universal' for noble gases but projectile dependent. A previously developed method has been employed to obtain the number of active electrons for each target subshell in the high-velocity regime.

  13. Differential studies and projectile charge effects in ionization of molecular nitrogen by positron and electron impact

    NASA Astrophysics Data System (ADS)

    de Lucio, O. G.; DuBois, R. D.

    2016-03-01

    Singly, doubly, and triply differential information, obtained from coincidence measurements, are presented for 250-eV positron- and electron-impact ionization of molecular nitrogen. Comparisons of these data as functions of energy loss, scattering, and emission angles illustrate differences associated with the sign of the projectile charge. Via a deconvolution and normalization procedure, the triply differential data are converted to absolute cross sections. By fitting the triply differential cross sections for single ionization with simple functions, the intensities, directions, and peak to background intensities of the binary peaks plus the ratio of recoil to binary interactions are compared for positron and electron impact. Formulas for the binary and recoil intensities plus for the orientation of the binary peak as a function of momentum transfer are extracted from the data. Differences in the relative amount of fragmentation as a function of energy loss are also observed.

  14. A new method to measure the velocity dependence of electronic stopping for low velocity hydrogen projectiles

    NASA Astrophysics Data System (ADS)

    Semrad, D.; Golser, R.; Steinbauer, E.

    1994-12-01

    We propose a new method by which the velocity dependence of the electronic stopping cross section for low energy projectiles can be determined accurately. The measurement is done in backscattering geometry and needs a high resolution detector; we intend to use an existing time-of-flight assembly with a resolution of {T}/{ΔT} ≈ 500 . The basic idea is that corrections due to plural and multiple scattering can be avoided by using protons and deuterons of equal energy, since they follow the same multiple scattering distribution. Using the Monte-Carlo code TRBS, we have simulated the energy spectra of 7 keV protons and 7 keV deuterons backscattered from 6.7 μg/cm 2 Cu. Our evaluation procedure applied to the simulated spectra yields good agreement with the input data.

  15. Role of projectile charge state in convoy electron emission by fast protons colliding with LiF(0 0 1)

    NASA Astrophysics Data System (ADS)

    Aldazabal, I.; Gravielle, M. S.; Miraglia, J. E.; Arnau, A.; Ponce, V. H.

    2005-05-01

    Target ionization and projectile ionization differential cross sections are used to calculate the electron emission spectra by fast proton impact on ionic crystal surfaces under grazing incidence conditions. Both bare protons and neutral hydrogen species are considered. We use a planar potential approach to determine the projectile trajectory that later on allows us to calculate the charge state fractions. We show that, although the fraction of protons is significantly higher, the contribution from neutral hydrogen ionization has to be considered. The energy and angular dependence of the spectra is analyzed.

  16. The EMET railgun projectile

    SciTech Connect

    Burton, R.L.; Witherspoon, F.D.; Goldstein, S.A. )

    1991-01-01

    This paper reports on the EMET projectile which uses joule heating to accelerate the projectile in a railgun with a predominantly electrothermal driving force. The structure is designed to conduct armature current within a thin annular band around the shank of the large L/D dumbbell-shaped projectile. Current is initiated by a fuse located around the shank, and an impedance of 8 m{Omega} is achieved, compared to the 1-2 m{Omega} observed for EM guns. A supersonic nozzle in the projectile tail section expands and cools the armature plasma to raise its resistivity, prevent secondary arcs and provide additional accelerating thrust. Experimental data is presented for 9.5 mm diameter, 5 gm projectiles, accelerated to nearly 600 m/sec at 55 kA in a 0.9 m railgun. The armature remains confined in the projectile structure, and 75% of the acceleration is provided electrothermally.

  17. Electron correlations in single-electron capture into any state of fast projectiles from heliumlike atomic systems

    NASA Astrophysics Data System (ADS)

    Mančev, Ivan; Milojević, Nenad; Belkić, Dževad

    2013-11-01

    State-selective and total single-electron capture cross sections in fast collisions of a bare projectile with a heliumlike target are examined in the four-body formalism. A special emphasis is given to a proper inclusion of dynamic electron-electron correlation effects. For this purpose, the post form of the four-body boundary-corrected first Born approximation (CB1-4B) is utilized. With regard to our related previous study, where the prior version has been considered, in the present work an extensive analytical study of the post-transition amplitude for electron capture into the arbitrary final states nflfmf of the projectile is carried out. The post-transition amplitude for single charge exchange encompassing symmetric and asymmetric collisions is derived in terms of five-dimensional integrals over real variables. The dielectronic interaction V12=1/r12≡1/|r⃗1-r⃗2| explicitly appears in the perturbation potential Vf of the post-transition probability amplitude Tif+, such that the CB1-4B method can provide information about the relative significance of the dynamic interelectron correlation in the collisions under study. An illustrative computation is performed involving state-selective and total single capture cross sections for the p-He collisions at intermediate and high impact energies. The so-called post-prior discrepancy, which plagues almost all the existing distorted wave approximations, is presently shown to be practically nonexistent in the CB1-4B method. The validity of our findings is critically assessed in comparisons with the available experimental data for both state-selective and total cross sections summed over all the discrete energy levels of the hydrogenlike atom formed with the projectile. Overall, excellent performance of the CB1-4B method is recorded, thus robustly establishing this formalism as the leading first-order description of high-energy single charge exchange, which is a collision of paramount theoretical and practical

  18. Stability analyses of the mass abrasive projectile high-speed penetrating into concrete target. Part II: Structural stability analyses

    NASA Astrophysics Data System (ADS)

    Wu, Hao; Chen, Xiao-Wei; Fang, Qin; He, Li-Lin

    2014-12-01

    The initial oblique and attacking angles as well as the asymmetrical nose abrasion may lead to bending or even fracture of a projectile, and the penetration efficiency decreases distinctly. The structural stability of a high-speed projectile non-normally penetrating into concrete and the parametric influences involved are analyzed with the mass abrasion taken into account. By considering the symmetrical or asymmetrical nose abrasion as well as the initial oblique and attacking angles, both the axial and the transverse drag forces acting on the projectile are derived. Based on the ideal elastic-plastic yield criterion, an approach is proposed for predicting the limit striking velocity (LSV) that is the highest velocity at which no yielding failure has occurred and the projectile can still maintain its integral structural stability. Furthermore, some particular penetration scenarios are separately discussed in detail. Based on the engineering model for the mass loss and nose-blunting of ogive-nose projectiles established in Part I of this study, the above approach is validated by several high-speed penetration tests. The analysis on parametric influences indicates that the LSV is reduced with an increase in the asymmetrical nose abrasion, the length-diameter-ratio, and the concrete strength, as well as the oblique and attacking angles. Also, the LSV raises with an increase in the initial caliber-radius-head (CRH) and the dimensionless cartridge thickness of a projectile.

  19. Projectiles Impact Assessment of Aircraft Wing Structures with Real Dynamic Load

    NASA Astrophysics Data System (ADS)

    Han, Lu; Han, Qing; Wang, Changlin

    2015-07-01

    This paper presents an analysis to achieve the impact damage of the wing structure under real dynamic load. MPCCI tools are utilized to convert wing aerodynamic load into structural Finite Element Method (FEM) node load. The ANSYS/LS-DYNA code is also used to simulate the dynamic loading effects of the wing structure hit by several projectiles, including both active damage mechanism and common damage mechanism. In addition, structural node force on the leading edge and the midline is compared to the aerodynamic load separately. Furthermore, the statistical analysis of the penetrating size and the stress concentration around the damage holes indicates that under the same load situation, the structural damage efficiency of active damage mechanism is significantly higher than the one of common damage mechanism.

  20. Small caliber guided projectile

    DOEpatents

    Jones, James F.; Kast, Brian A.; Kniskern, Marc W.; Rose, Scott E.; Rohrer, Brandon R.; Woods, James W.; Greene, Ronald W.

    2010-08-24

    A non-spinning projectile that is self-guided to a laser designated target and is configured to be fired from a small caliber smooth bore gun barrel has an optical sensor mounted in the nose of the projectile, a counterbalancing mass portion near the fore end of the projectile and a hollow tapered body mounted aft of the counterbalancing mass. Stabilizing strakes are mounted to and extend outward from the tapered body with control fins located at the aft end of the strakes. Guidance and control electronics and electromagnetic actuators for operating the control fins are located within the tapered body section. Output from the optical sensor is processed by the guidance and control electronics to produce command signals for the electromagnetic actuators. A guidance control algorithm incorporating non-proportional, "bang-bang" control is used to steer the projectile to the target.

  1. Projectile stopping system

    DOEpatents

    Karr, T.J.; Pittenger, L.C.

    1996-11-26

    A projectile interceptor launches a projectile catcher into the path of a projectile. In one embodiment, signals indicative of the path of a projectile are received by the projectile interceptor. A flinger mechanism has a projectile catcher releasably attached thereto, such that the projectile catcher can be released and launched from the flinger mechanism. A controller connected to the flinger mechanism uses the signals indicative of the path of the projectile to determine the launch parameters of the projectile catcher. The controller directs the flinger mechanism to release the projectile catcher such that the projectile catcher is launched into the path of the projectile and intercepts the projectile. 13 figs.

  2. Projectile stopping system

    DOEpatents

    Karr, Thomas J.; Pittenger, Lee C.

    1996-01-01

    A projectile interceptor launches a projectile catcher into the path of a projectile. In one embodiment, signals indicative of the path of a projectile are received by the projectile interceptor. A flinger mechanism has a projectile catcher releasably attached thereto, such that the projectile catcher can be released and launched from the flinger mechanism. A controller connected to the flinger mechanism uses the signals indicative of the path of the projectile to determine the launch parameters of the projectile catcher. The controller directs the flinger mechanism to release the projectile catcher such that the projectile catcher is launched into the path of the projectile and intercepts the projectile.

  3. Projectile energy and atomic number dependence of electron capture from pair production in relativistic heavy ion collisions

    NASA Astrophysics Data System (ADS)

    Belkacem, A.; Gould, Harvey; Feinberg, B.; Bossingham, R.; Meyerhof, W. E.

    1994-10-01

    We report the first measurement of the energy dependence of electron capture from electron-positron pair production in relativistic heavy ion collisions. For a La57+ beam incident on Au, Ag, and Cu targets at energies of 0.405, 0.956, and 1.3 GeV/u we find that the cross sections for capture from pair production and the free pair production process increase with increasing collision energy at similar rates. Combining with uranium data reported previously gives a projectile atomic number dependence for 0.956 GeV/u ions on a Au target of Z6.54+/-0.65p for capture from pair production and Z1.53+/-0.80p for the free pair production process.

  4. Prevention of breakdown behind railgun projectiles

    DOEpatents

    Hawke, Ronald S.

    1992-01-01

    An electromagnetic railgun accelerator system, for accelerating projectiles (14, 15, 114, 214, 314, 414) by a plasma arc (3), introduces a breakdown inhibiting gas into the railgun chamber (26) behind the accelerating projectile (14). The breakdown inhibiting gas, which absorbs electrons, is a halide or a halide compound such as fluorine or SF.sub.6. The gas is introduced between the railgun rails (12) after the projectile (14) has passed through inlets (16) in the rails (12) or the projectile (114); by coating the rails (12) or the projectile (15) with a material (28) which releases the gas after the projectile (14) passes over it; by fabricating the rails (12) or the projectile (15) or insulators out of a material which releases the gas into the portions of the chamber (26) through which the projectile has travelled. The projectile (214, 314, 414) may have a cavity (232, 332, 432) at its rear to control the release of ablation products (4).

  5. Prevention of breakdown behind railgun projectiles

    DOEpatents

    Hawke, Ronald S.

    1992-01-01

    An electromagnetic railgun accelerator system, for accelerating projectiles (14, 15, 114, 214, 314, 444) by a plasma arc (3), introduces a breakdown inhibiting gas into the railgun chamber (26) behind the accelerating projectile (14). The breakdown inhibiting gas, which absorbs electrons, is a halide or a halide compound such as fluorine or SF.sub.6. The gas is introduced between the railgun rails (12) after the projectile (14) has passed through inlets (16) in the rails (12) or the projectile (114); by coating the rails (12) or the projectile (15) with a material (28) which releases the gas after the projectile (14 ) passes over it; by fabricating the rails (12) or the projectile (15) or insulators out of a material which releases the gas into the portions of the chamber (26) through which the projectile has travelled. The projectile (214, 314, 414) may have a cavity (232, 332, 432) at its rear to control the release of ablation products (4).

  6. Prevention of breakdown behind railgun projectiles

    DOEpatents

    Hawke, R.S.

    1992-10-13

    An electromagnetic railgun accelerator system, for accelerating projectiles by a plasma arc, introduces a breakdown inhibiting gas into the railgun chamber behind the accelerating projectile. The breakdown inhibiting gas, which absorbs electrons, is a halide or a halide compound such as fluorine or SF[sub 6]. The gas is introduced between the railgun rails after the projectile has passed through inlets in the rails or the projectile; by coating the rails or the projectile with a material which releases the gas after the projectile passes over it; by fabricating the rails or the projectile or insulators out of a material which releases the gas into the portions of the chamber through which the projectile has travelled. The projectile may have a cavity at its rear to control the release of ablation products. 12 figs.

  7. Prevention of breakdown behind railgun projectiles

    DOEpatents

    Hawke, R.S.

    1992-09-01

    An electromagnetic railgun accelerator system, for accelerating projectiles by a plasma arc, introduces a breakdown inhibiting gas into the railgun chamber behind the accelerating projectile. The breakdown inhibiting gas, which absorbs electrons, is a halide or a halide compound such as fluorine or SF[sub 6]. The gas is introduced between the railgun rails after the projectile has passed through inlets in the rails or the projectile; by coating the rails or the projectile with a material which releases the gas after the projectile passes over it; by fabricating the rails or the projectile or insulators out of a material which releases the gas into the portions of the chamber through which the projectile has travelled. The projectile may have a cavity at its rear to control the release of ablation products. 12 figs.

  8. Prevention of breakdown behind railgun projectiles

    SciTech Connect

    Hawke, R.S.

    1989-04-20

    An electromagnetic railgun accelerator system, for accelerating projectiles by a plasma arc, introduces a breakdown inhibiting gas into the railgun chamber behind the accelerating projectile. The breakdown inhibiting gas, which absorbs electrons, is a halide or a halide compound such as fluorine or SF{sub 6}. The gas is introduced between the railgun rails after the projectile has passed through inlets in the rails or the projectile; by coating the rails or the projectile with a material which releases the gas after the projectile passes over it; by fabricating the rails or the projectile or insulators out of a material which releases the gas into the portions of the chamber through which the projectile has traveled. The projectile may have a cavity at its rear to control the release of ablation products. 9 figs.

  9. High-resolution study of electron capture by 72- and 52-MeV 3He projectiles from targets of high atomic number

    NASA Astrophysics Data System (ADS)

    Katayama, I.; Ikegami, H.; Ogawa, H.; Haruyama, Y.; Tozaki, M.; Aoki, A.; Fukuzawa, F.; Yoshida, K.; Sugai, I.

    1996-01-01

    An electron capture at the cyclotron energy has been explored by using a high-resolution magnetic spectrograph. The K-shell electron capture from heavy elements (V, Cr, Cu, Ge, Nb, Ag, and Sn) by 3He2+ projectiles at 52 and 72 MeV was measured. The dependence of the cross sections on the atomic number of the target obtained at these two energies are compared with current electron-capture theories.

  10. Projectile-generating explosive access tool

    SciTech Connect

    Jakaboski, Juan-Carlos; Hughs, Chance G; Todd, Steven N

    2013-06-11

    A method for generating a projectile using an explosive device that can generate a projectile from the opposite side of a wall from the side where the explosive device is detonated. The projectile can be generated without breaching the wall of the structure or container. The device can optionally open an aperture in a solid wall of a structure or a container and form a high-kinetic-energy projectile from the portion of the wall removed to create the aperture.

  11. A model for debris clouds produced by impact of hypervelocity projectiles on multiplate structures

    NASA Astrophysics Data System (ADS)

    Zhang, Qingming; Long, Renrong; Huang, Fenglei; Chen, Li; Fu, Yuesheng

    2008-11-01

    Hypervelocity impact of spherical and cylindrical projectiles on multipate shields at velocities between 4 and 6km/s was investigated experimentally. A model was developed to describe the motion of the debris clouds generated. Good agreement was obtained between the experimental and simulation results. The model is capable of predicting damage induced by the impact and can be applied to the optimization and design of multiplate shields.

  12. Stopping power: Effect of the projectile deceleration

    SciTech Connect

    Kompaneets, Roman Ivlev, Alexei V.; Morfill, Gregor E.

    2014-11-15

    The stopping force is the force exerted on the projectile by its wake. Since the wake does not instantly adjust to the projectile velocity, the stopping force should be affected by the projectile deceleration caused by the stopping force itself. We address this effect by deriving the corresponding correction to the stopping force in the cold plasma approximation. By using the derived expression, we estimate that if the projectile is an ion passing through an electron-proton plasma, the correction is small when the stopping force is due to the plasma electrons, but can be significant when the stopping force is due to the protons.

  13. Projectile-generating explosive access tool

    DOEpatents

    Jakaboski, Juan-Carlos; Todd, Steven N.

    2011-10-18

    An explosive device that can generate a projectile from the opposite side of a wall from the side where the explosive device is detonated. The projectile can be generated without breaching the wall of the structure or container. The device can optionally open an aperture in a solid wall of a structure or a container and form a high-kinetic-energy projectile from the portion of the wall removed to create the aperture.

  14. Osmium-isotope Evidence for a Projectile Component in Impact-melt Rocks, Chesapeake Bay Impact Structure, Virginia, USA

    NASA Astrophysics Data System (ADS)

    Lee, S.; Horton, J. W.; Walker, R. J.

    2004-12-01

    The late Eocene Chesapeake Bay impact structure (CBIS) is preserved beneath post-impact sediments on the Atlantic margin of Virginia. This 85-km-diameter complex crater formed on the continental shelf of a passive margin in a layered target consisting of ocean water, Cretaceous and Tertiary sediments (mainly siliciclastic), and crystalline basement rocks. The basement rocks include Neoproterozoic granitoids and felsite as well as gneiss of undetermined age. In May, 2004, the USGS drilled an 823-m test hole in the central uplift of the CBIS at Cape Charles, Va., providing drill cuttings and limited core. The core from 744 to 823 m depth contains crystalline-clast breccia and brecciated gneiss that are distinct from sediment-clast breccias recovered from coreholes in the annular trough of the CBIS. Rocks interpreted to be impact-melt clasts and dikes in the crystalline-clast breccia were sampled for analyses of osmium (Os) concentrations and 187Os/188Os ratios to test for evidence of the projectile. These analyses were conducted on samples from a dike (aphanitic to partly hyaline, ST2440.8C) within a gneissic block, from a block of holocrystalline mafic rock (aphanitic, ST2453.3C), and from a flow-laminated bomb (aphanitic to partly hyaline, ST2570.0C). The Os concentrations and 187Os/188Os ratios for samples ST2440.8C, ST2453.3C and ST2570.0C are 0.928, 0.711 and 0.312 ppb, and 0.15205, 0.15545 and 0.22345, respectively. These values are much higher (Os) or lower (187Os/188Os) than those reported for rocks of the upper continental crust, suggesting a significant contribution of osmium from the projectile in these impact-melt rocks. Moreover, a strong negative correlation between 187Os/188Os and Os for these samples suggests that it may be possible to use mixing curves to calculate the proportions of projectile and target-rock components. Our results from the CBIS contrast with those from the Chicxulub crater, where there is little or no evidence for the

  15. Projectile Motion Details.

    ERIC Educational Resources Information Center

    Schnick, Jeffrey W.

    1994-01-01

    Presents an exercise that attempts to correct for the common discrepancies between theoretical and experimental predictions concerning projectile motion using a spring-loaded projectile ball launcher. Includes common correction factors for student use. (MVL)

  16. Determination of the solid angle and response function of a hemispherical spectrograph with injection lens for Auger electrons emitted from long lived projectile states

    SciTech Connect

    Doukas, S.; Madesis, I.; Dimitriou, A.; Zouros, T. J. M.; Laoutaris, A.; Benis, E. P.

    2015-04-15

    We present SIMION 8.1 Monte Carlo type simulations of the response function and detection solid angle for long lived Auger states (lifetime τ ∼ 10{sup −9} − 10{sup −5} s) recorded by a hemispherical spectrograph with injection lens and position sensitive detector used for high resolution Auger spectroscopy of ion beams. Also included in these simulations for the first time are kinematic effects particular to Auger emission from fast moving projectile ions such as line broadening and solid angle limitations allowing for a more accurate and realistic line shape modeling. Our results are found to be in excellent agreement with measured electron line shapes of both long lived 1s2s2p{sup 4}P and prompt Auger projectile states formed by electron capture in collisions of 25.3 MeV F{sup 7+} with H{sub 2} and 12.0 MeV C{sup 4+} with Ne recorded at 0{sup ∘} to the beam direction. These results are important for the accurate evaluation of the 1s2s2p {sup 4}P/{sup 2}P ratio of K-Auger cross sections whose observed non-statistical production by electron capture into He-like ions, recently a field of interesting interpretations, awaits further resolution.

  17. Superconducting Magnetic Projectile Launcher

    NASA Technical Reports Server (NTRS)

    Jan, Darrell L.; Lawson, Daniel D.

    1991-01-01

    Proposed projectile launcher exploits Meissner effect to transfer much of kinetic energy of relatively massive superconducting plunger to smaller projectile, accelerating projectile to high speed. Because it operates with magnetic fields, launcher not limited by gas-expansion thermodynamics. Plunger energized mechanically and/or chemically, avoiding need for large electrical power supplies and energy-storage systems. Potential applications include launching of projectiles for military purposes and for scientific and industrial tests of hypervelocity impacts.

  18. Strong asymmetry of the electron-loss-to-continuum cusp of multielectron U28 + projectiles in near-relativistic collisions with gaseous targets

    NASA Astrophysics Data System (ADS)

    Hillenbrand, P.-M.; Hagmann, S.; Monti, J. M.; Rivarola, R. D.; Blumenhagen, K.-H.; Brandau, C.; Chen, W.; DuBois, R. D.; Gumberidze, A.; Guo, D. L.; Lestinsky, M.; Litvinov, Yu. A.; Müller, A.; Schippers, S.; Spillmann, U.; Trotsenko, S.; Weber, G.; Stöhlker, Th.

    2016-04-01

    The process of electron-loss to the continuum (ELC) has been studied for the collision systems U28 ++H2 at a collision energy of 50 MeV/u, U28 ++N2 at 30 MeV/u, and U28 ++Xe at 50 MeV/u. The energy distributions of cusp electrons emitted at an angle of 0∘ with respect to the projectile beam were measured using a magnetic forward-angle electron spectrometer. For these collision systems far from equilibrium charge state, a significantly asymmetric cusp shape is observed. The experimental results are compared to calculations based on first-order perturbation theory, which predict an almost symmetric cusp shape. Some possible reasons for this discrepancy are discussed.

  19. Investigations of nuclear structure and nuclear reactions induced by complex projectiles

    SciTech Connect

    Sarantites, D.G.

    1990-01-01

    This report discusses research in the following areas: nuclear structure; fusion reactions near and below the barrier; incomplete fusion and fragmentation reactions; and instrumentation and analysis. (LSP).

  20. Projectile development for railguns using hypervelocity preacceleration

    NASA Astrophysics Data System (ADS)

    Susoeff, A. R.; Hawke, R. S.; Ang, J. A.; Asay, J. R.; Hall, C. A.; Konrad, C. H.; Sauve, G. L.

    1992-03-01

    The STARFIRE Project is a joint Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL) effort to achieve hypervelocity projectile launches up to 15 km/s. The apparatus used to achieve this goal is a three stage acceleration system made up of a two-stage light-gas gun (2SLGG) coupled to a railgun. The 2SLGG is used as a preaccelerator capable of injecting 2 gram projectiles at velocities of 6 km/s or more. Projectiles used in this environment are subject to many conditions. Some of these which effect projectile design include acceleration loading, structural response, barrel condition and alignment. Development of a projectile to satisfy the programmatic requirements is underway. This report covers the evolution of design and fabrication for railgun projectiles from previous experimentation at LLNL to the replenished plasma armature and projectile now used on STARFIRE. Projectile design, development and fabrication methods which use off-the-shelf materials and standard techniques to meet the operational criteria of the experimental program are discussed in this paper. Initial work involving the design and fabrication of skirted projectiles, which are expected to further reduce interaction phenomena between the plasma armature and railgun barrel, is also described.

  1. Projectile development for railguns using hypervelocity preacceleration

    SciTech Connect

    Susoeff, A.R.; Hawke, R.S.; Sauve, G.L.; Konrad, C.H.; Hickman, R.J.

    1991-02-01

    The STARFIRE Project is a joint Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL) effort to achieve hypervelocity projectile launches up to 15 km/s. The apparatus used to achieve this goal is a three stage acceleration system made up of a two-stage light-gas gun (2SLGG) is used as a preaccelerator capable of injecting 2 gram projectiles at velocities of 6 km/s or more. Projectiles used in this environment are subject to many conditions. Some of these which effect projectile design include: acceleration loading, structural response, barrel condition and alignment. Development of a projectile to satisfy the programmatic requirements is underway. This report covers the evolution of design and fabrication for railgun projectiles from previous experience at LLNL to the replenished plasma armature and projectile now used on STARFIRE. Projectile design, development and fabrication methods which use off-the-shelf materials and standard techniques to meet the operational criteria of the experimental program are discussed in this paper. Initial work involving the design and fabrication of skirted projectiles, which are expected to further reduce interaction phenomena between the plasma armature and railgun barrel, is also described.

  2. Projectile development for railguns using hypervelocity preacceleration

    SciTech Connect

    Susoeff, A.R.; Hawke, R.S. ); Ang, J.A.; Asay, J.R.; Hall, C.A.; Konrad, C.H. ); Sauve, G.L. . Rocky Flats Plant); Hickman, R.J. )

    1992-03-20

    The STARFIRE Project is a joint Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL) effort to achieve hypervelocity projectile launches up to 15 km/s. The apparatus used to achieve this goal is a three stage acceleration system made up of a two-stage light-gas gun (2SLGG) coupled to a railgun. The 2SLGG is used as a preaccelerator capable of injecting 2 gram projectiles at velocities of 6 km/s or more. Projectiles used in this environment are subject to many conditions. Some of these which effect projectile design include: acceleration loading, structural response, barrel condition and alignment. Development of a projectile to satisfy the programmatic requirements is underway. This report covers the evolution of design and fabrication for railgun projectiles from previous experiment at LLNL to the replenished plasma armature and projectile now used on STARFIRE. Projectile design, development and fabrication methods which use off-the-shelf materials and standard techniques to meet the operational criteria of the experimental program are discussed in this paper. Initial work involving the design and fabrication of skirted projectiles, which are expected to further reduce interaction phenomena between the plasma armature and railgun barrel, is also described.

  3. Investigations of nuclear structure and nuclear reactions induced by complex projectiles

    SciTech Connect

    Sarantites, D.G.

    1991-01-01

    The research program of our group touches five areas of nuclear physics: (1) Nuclear structure studies at high spin; (2) Studies at the interface between structure and reactions; (3) Production and study of hot nuclei; (4) Incomplete fusion and fragmentation reactions; and (5) Development and use of novel techniques and instrumentation in the above areas of research. The papers from these areas are discussed in this report.

  4. Three-phase hypervelocity projectile launcher

    DOEpatents

    Fugelso, L. Erik; Langner, Gerald C.; Burns, Kerry L.; Albright, James N.

    1994-01-01

    A hypervelocity projectile launcher for use in perforating borehole casings provides improved penetration into the surrounding rock structure. The launcher includes a first cylinder of explosive material that defines an axial air-filled cavity, a second cylinder of explosive material defining an axial frustum-shaped cavity abutting and axially aligned with the first cylinder. A pliant washer is located between and axially aligned with the first and second cylinders. The frustum shaped cavity is lined with a metal liner effective to form a projectile when the first and second cylinders are detonated. The washer forms a unique intermediate projectile in advance of the liner projectile and enables the liner projectile to further penetrate into and fracture the adjacent rock structure.

  5. Electron Structure of Francium

    NASA Astrophysics Data System (ADS)

    Koufos, Alexander

    2012-02-01

    This talk presents the first calculations of the electronic structure of francium for the bcc, fcc and hcp structures, using the Augmented Plane Wave (APW) method in its muffin-tin and linearized general potential forms. Both the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA), were used to calculate the electronic structure and total energy of francium (Fr). The GGA and LDA both found the total energy of the hcp structure slightly below that of the fcc and bcc structure, respectively. This is in agreement with similar results for the other alkali metals using the same methodology. The equilibrium lattice constant, bulk modulus and superconductivity parameters were calculated. We found that under pressures, in the range of 1-5 GPa, Fr could be a superconductor at a critical temperature of about 4K.

  6. Electron-impact ionization of neon at low projectile energy: an internormalized experiment and theory for a complex target.

    PubMed

    Pflüger, Thomas; Zatsarinny, Oleg; Bartschat, Klaus; Senftleben, Arne; Ren, Xueguang; Ullrich, Joachim; Dorn, Alexander

    2013-04-12

    As a fundamental test for state-of-the-art theoretical approaches, we have studied the single ionization (2p) of neon at a projectile energy of 100 eV. The experimental data were acquired using an advanced reaction microscope that benefits from high efficiency and a large solid-angle acceptance of almost 4π. We put special emphasis on the ability to measure internormalized triple-differential cross sections over a large part of the phase space. The data are compared to predictions from a second-order hybrid distorted-wave plus R-matrix model and a fully nonperturbative B-spline R-matrix (BSR) with pseudostates approach. For a target of this complexity and the low-energy regime, unprecedented agreement between experiment and the BSR model is found. This represents a significant step forward in the investigation of complex targets. PMID:25167263

  7. A Gas-Actuated Projectile Launcher for High-Energy Impact Testing of Structures

    NASA Technical Reports Server (NTRS)

    Ambur, Damodar R.; Jaunky, Navin; Lawson, Robin E.; Knight, Norman F., Jr.; Lyle, Karen H.

    1999-01-01

    A gas-act,uated penetration device has been developed for high-energy impact testing of structures. The high-energy impact. t,estiiig is for experimental simulation of uncontained engine failures. The non-linear transient finite element, code LS-DYNA3D has been used in the numerical simula.tions of a titanium rectangular blade with a.n aluminum target, plate. Threshold velocities for different combinations of pitch and yaw angles of the impactor were obtained for the impactor-target, t8est configuration in the numerica.1 simulations. Complet,e penet,ration of the target plate was also simulat,ed numerically. Finally, limited comparison of analytical and experimental results is presented for complete penetration of the target by the impactor.

  8. Teaching Projectile Motion

    ERIC Educational Resources Information Center

    Summers, M. K.

    1977-01-01

    Described is a novel approach to the teaching of projectile motion of sixth form level. Students are asked to use an analogue circuit to observe projectile motion and to graph the experimental results. Using knowledge of basic dynamics, students are asked to explain the shape of the curves theoretically. (Author/MA)

  9. Hybrid armature projectile

    DOEpatents

    Hawke, R.S.; Asay, J.R.; Hall, C.A.; Konrad, C.H.; Sauve, G.L.; Shahinpoor, M.; Susoeff, A.R.

    1993-03-02

    A projectile for a railgun that uses a hybrid armature and provides a seed block around part of the outer surface of the projectile to seed the hybrid plasma brush. In addition, the hybrid armature is continuously vaporized to replenish plasma in a plasma armature to provide a tandem armature and provides a unique ridge and groove to reduce plasma blowby.

  10. Hybrid armature projectile

    DOEpatents

    Hawke, Ronald S.; Asay, James R.; Hall, Clint A.; Konrad, Carl H.; Sauve, Gerald L.; Shahinpoor, Mohsen; Susoeff, Allan R.

    1993-01-01

    A projectile for a railgun that uses a hybrid armature and provides a seed block around part of the outer surface of the projectile to seed the hybrid plasma brush. In addition, the hybrid armature is continuously vaporized to replenish plasma in a plasma armature to provide a tandem armature and provides a unique ridge and groove to reduce plasama blowby.

  11. Projectile Motion Revisited.

    ERIC Educational Resources Information Center

    Lucie, Pierre

    1979-01-01

    Analyzes projectile motion using symmetry and simple geometry. Deduces the direction of velocity at any point, range, time of flight, maximum height, safety parabola, and maximum range for a projectile launched upon a plane inclined at any angle with respect to the horizontal. (Author/GA)

  12. Coincidence studies of diffraction structures in binary encounter electron spectra

    SciTech Connect

    Liao, C.; Hagmann, S.; Richard, P.

    1994-12-31

    The authors have measured binary encounter electron (BEe) production in collisions of 0.3 MeV/u Cu{sup q+} (q=4,12) projectiles on H{sub 2} targets from 0 to 70 degrees with respect to the beam direction. Prominent features are the appearance of the BEe peak splitting and a very strong forward peaked angular distribution which are attributed to the diffractive scattering of the quasifree target electrons in the short range potential of the projectile. Using electron-projectile final charge state coincidence techniques, different collision reaction channels can be separated. Measurements of this type are being pursued.

  13. A Projectile Motion Bullseye.

    ERIC Educational Resources Information Center

    Lamb, William G.

    1985-01-01

    Explains a projectile motion experiment involving a bow and arrow. Procedures to measure "muzzle" velocity, bow elastic potential energy, range, flight time, wind resistance, and masses are considered. (DH)

  14. Ablative shielding for hypervelocity projectiles

    NASA Technical Reports Server (NTRS)

    Rucker, Michelle A. (Inventor)

    1993-01-01

    A hypervelocity projectile shield which includes a hollow semi-flexible housing fabricated from a plastic like, or otherwise transparent membrane which is filled with a fluid (gas or liquid) is presented. The housing has a inlet valve, similar to that on a tire or basketball, to introduce an ablating fluid into the housing. The housing is attached by a Velcro mount or double-sided adhesive tape to the outside surface of a structure to be protected. The housings are arrayed in a side-by-side relationship for complete coverage of the surface to be protected. In use, when a hypervelocity projectile penetrates the outer wall of a housing it is broken up and then the projectile is ablated as it travels through the fluid, much like a meteorite 'burns up' as it enters the earth's atmosphere, and the housing is deflated. The deflated housing can be easily spotted for replacement, even from a distance. Replacement is then accomplished by simply pulling a deflated housing off the structure and installing a new housing.

  15. Hypervelocity projectile design and fabrication

    SciTech Connect

    Ang, J.A.; Konrad, C.H.; Hall, C.A.; Susoeff, A.R.; Hawke, R.S.; Sauve, G.L.; Vasey, A.R.; Gosling, S.M.; Hickman, R.J.

    1990-12-31

    The projectile is the easiest element of a railgun system to modify. The projectile design can also play a major role in the successful operation of a railgun. This paper presents the design and fabrication techniques that have been used to increase the strength of the projectiles used in the STARFIRE Project. In addition, various diagnostics that have been used to guide our projectile development and monitor projectile integrity are reviewed. 10 refs.

  16. Hign-speed penetration of projectile with cavitator into sand

    NASA Astrophysics Data System (ADS)

    Daurskikh, Anna; Veldanov, Vladislav

    2011-06-01

    Cavitators are used in underwater projectiles design to form a cavern in which projectile could move with no or significantly reduced drag. An investigation of possible application of this structural element for penetration into porous media was conducted. High-speed impact of a conical-shaped head projectile with cavitator was studied in terms of its influence on penetration capacity and projectile stability in sand for impact velocity about 1500 m/s. Cavitators were manufactured of steel with different strength moduli, and thus two penetration regimes (with eroding/non-eroding cavitator) were compared. Numerical simulations showing wave propagation in target and projectile were performed in AUTODYN with Johnson-Cook model for projectile and granular model for sand.

  17. More on Projectile Motion.

    ERIC Educational Resources Information Center

    Molina, M. I.

    2000-01-01

    Mathematically explains why the range of a projectile is most insensitive to aiming errors when the initial angle is close to 45 degrees, whereas other observables such as maximum height or flight time are most insensitive for near-vertical launching conditions. (WRM)

  18. Projectiles and Aerodynamic Forces.

    ERIC Educational Resources Information Center

    Armstrong, H. L.

    1984-01-01

    Discusses the air resistance on projectiles, examining (in separate sections) air resistance less than gravity and air resistance greater than gravity. Also considers an approximation in which a trajectory is divided into two parts, the first part neglecting gravity and the second part neglecting the air resistance. (JN)

  19. Flight dynamics of a spinning projectile descending on a parachute

    SciTech Connect

    Benedetti, G.A.

    1989-02-01

    During the past twenty years Sandia National Laboratories and the US Army have vertically gun launched numerous 155mm and eight-inch diameter flight test projectiles. These projectiles are subsequently recovered using an on-board parachute recovery system which is attached to the forward case structure of the projectile. There have been at least five attempts to describe, through analytical and numerical simulations, the translational and rotational motions of a spinning projectile descending on a parachute. However, none of these investigations have correctly described the large nutational motion of the projectile since all of them overlooked the fundamental mechanism which causes these angular motions. Numerical simulations as well as a closed form analytical solution show conclusively that the Magnus moment is responsible for the large nutational motion of the projectile. That is, when the center of pressure for the Magnus force is aft of the center of mass for the projectile, the Magnus moment causes an unstable (or large) nutational motion which always tends to turn the spinning projectile upside down while it is descending on the parachute. Conversely, when the center of mass for the projectile is aft of the center of pressure for the Magnus force, the Magnus moment stabilizes the nutational motion tending to always point the base of the spinning projectile down. The results of this work are utilized to render projectile parachute recovery systems more reliable and to explain what initially may appear to be strange gyrodynamic behavior of a spinning projectile descending on a parachute. 14 refs., 20 figs.

  20. Projectile development for railguns using hypervelocity preacceleration. Revision 1

    SciTech Connect

    Susoeff, A.R.; Hawke, R.S.; Ang, J.A.; Asay, J.R.; Hall, C.A.; Konrad, C.H.; Sauve, G.L.; Hickman, R.J.

    1992-03-20

    The STARFIRE Project is a joint Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL) effort to achieve hypervelocity projectile launches up to 15 km/s. The apparatus used to achieve this goal is a three stage acceleration system made up of a two-stage light-gas gun (2SLGG) coupled to a railgun. The 2SLGG is used as a preaccelerator capable of injecting 2 gram projectiles at velocities of 6 km/s or more. Projectiles used in this environment are subject to many conditions. Some of these which effect projectile design include: acceleration loading, structural response, barrel condition and alignment. Development of a projectile to satisfy the programmatic requirements is underway. This report covers the evolution of design and fabrication for railgun projectiles from previous experiment at LLNL to the replenished plasma armature and projectile now used on STARFIRE. Projectile design, development and fabrication methods which use off-the-shelf materials and standard techniques to meet the operational criteria of the experimental program are discussed in this paper. Initial work involving the design and fabrication of skirted projectiles, which are expected to further reduce interaction phenomena between the plasma armature and railgun barrel, is also described.

  1. Electronics for Piezoelectric Smart Structures

    NASA Technical Reports Server (NTRS)

    Warkentin, D. J.; Tani, J.

    1997-01-01

    This paper briefly presents work addressing some of the basic considerations for the electronic components used in smart structures incorporating piezoelectric elements. After general remarks on the application of piezoelectric elements to the problem of structural vibration control, three main topics are described. Work to date on the development of techniques for embedding electronic components within structural parts is presented, followed by a description of the power flow and dissipation requirements of those components. Finally current work on the development of electronic circuits for use in an 'active wall' for acoustic noise is introduced.

  2. Subcaliber discarding sabot airgun projectiles.

    PubMed

    Frank, Matthias; Schönekeß, Holger; Herbst, Jörg; Staats, Hans-Georg; Ekkernkamp, Axel; Nguyen, Thanh Tien; Bockholdt, Britta

    2014-03-01

    Medical literature abounds with reports on injuries and fatalities caused by airgun projectiles. While round balls or diabolo pellets have been the standard projectiles for airguns for decades, today, there are a large number of different airgun projectiles available. A very uncommon--and until now unique--discarding sabot airgun projectile (Sussex Sabo Bullet) was introduced into the market in the 1980s. The projectile, available in 0.177 (4.5 mm) and 0.22 (5.5 mm) caliber, consists of a plastic sabot cup surrounding a subcaliber copper-coated lead projectile in typical bullet shape. Following the typical principle of a discarding sabot projectile, the lightweight sabot is supposed to quickly loose velocity and to fall to the ground downrange while the bullet continues on target. These sabot-loaded projectiles are of special forensic interest due to their non-traceability and ballistic parameters. Therefore, it is the aim of this work to investigate the ballistic performance of these sabot airgun projectiles by high-speed video analyses and by measurement of the kinetic parameters of the projectile parts by a transient recording system as well as observing their physical features after being fired. While the sabot principle worked properly in high-energy airguns (E > 17 J), separation of the core projectile from the sabot cup was also observed when discharged in low-energy airguns (E < 7.5 J). While the velocity of the discarded Sussex Sabo core projectile was very close to the velocity of a diabolo-type reference projectile (RWS Meisterkugel), energy density was up to 60 % higher. To conclude, this work is the first study to demonstrate the regular function of this uncommon type of airgun projectile. PMID:24263305

  3. Skirted projectiles for railguns

    DOEpatents

    Hawke, R.S.; Susoeff, A.R.

    1994-01-04

    A single skirt projectile (20) having an insulating skirt (22) at its rear, or a dual trailing skirt projectile (30, 40, 50, 60) having an insulating skirt (32, 42, 52, 62) succeeded by an arc extinguishing skirt (34, 44, 54, 64), is accelerated by a railgun accelerator 10 having a pair of parallel conducting rails (1a, 1b) which are separated by insulating wall spacers (11). The insulating skirt (22, 32, 42, 52, 62) includes a plasma channel (38). The arc extinguishing skirt (34, 44, 54, 64) interrupts the conduction that occurs in the insulating skirt channel (38) by blocking the plasma arc (3) from conducting current from rail to rail (1a, 1b) at the rear of the projectile (30, 40, 50, 60). The arc extinguishing skirt may be comprised of two plates (36a, 36b) which form a horseshoe wherein the plates are parallel to the rails (1a, b); a chisel-shape design; cross-shaped, or it may be a cylindrical (64). The length of the insulating skirt channel is selected such that there is sufficient plasma in the channel to enable adequate current conduction between the rails (1a, 1b).

  4. Skirted projectiles for railguns

    DOEpatents

    Hawke, Ronald S.; Susoeff, Allan R.

    1994-01-01

    A single skirt projectile (20) having an insulating skirt (22) at its rear, or a dual trailing skirt projectile (30, 40, 50, 60) having an insulating skirt (32, 42, 52, 62) succeeded by an arc extinguishing skirt (34, 44, 54, 64), is accelerated by a railgun accelerator 10 having a pair of parallel conducting rails (1a, 1b) which are separated by insulating wall spacers (11). The insulating skirt (22, 32, 42, 52, 62) includes a plasma channel (38). The arc extinguishing skirt (34, 44, 54, 64) interrupts the conduction that occurs in the insulating skirt channel (38) by blocking the plasma arc (3) from conducting current from rail to rail (1a, 1b) at the rear of the projectile (30, 40, 50, 60). The arc extinguishing skirt may be comprised of two plates (36a, 36b) which form a horseshoe wherein the plates are parallel to the rails (1a, b); a chisel-shape design; cross-shaped, or it may be a cylindrical (64). The length of the insulating skirt channel is selected such that there is sufficient plasma in the channel to enable adequate current conduction between the rails (1a, 1b).

  5. Microcraters formed in glass by projectiles of various densities

    NASA Technical Reports Server (NTRS)

    Vedder, J. F.; Mandeville, J.-C.

    1974-01-01

    An experiment was conducted investigating the effect of projectile density on the structure and size of craters in soda lime glass and fused quartz. The projectiles were spheres of polystyrene-divinylbenzene (PS-DVB), aluminum, and iron with velocities between 0.5 and 15 km/sec and diameters between 0.4 and 5 microns. The projectile densities spanned the range expected for primary and secondary particles of micrometer size at the lunar surface, and the velocities spanned the lower range of micrometeoroid velocities and the upper range of secondary projectile velocities. There are changes in crater morphology as the impact velocity increases, and the transitions occur at lower velocities for the projectiles of higher density. The sequence of morphological features of the craters found for PS-DVB impacting soda lime glass for increasing impact velocity, described in a previous work (Mandeville and Vedder, 1971), also occurs in fused quartz and in both targets with the more dense aluminum and iron projectiles. Each transition in morphology occurs at impact velocities generating a certain pressure in the target. High density projectiles require a lower velocity than low-density projectiles to generate a given shock pressure.

  6. Theoretical electronic structure of structurally modified graphene

    NASA Astrophysics Data System (ADS)

    Dvorak, Marc David

    Graphene has emerged as a promising replacement for silicon in next-generation electronics and optoelectronic devices. If graphene is to be used in semiconductor devices, however, it must acquire an electronic band gap. Numerous approaches have been proposed to control the band gap of graphene, including the periodic patterning of defects. However, the mechanism for band gap opening and the associated physics in graphene patterned with defects remain unclear. Using both analytic theory and first-principles calculations, we show that periodic patterning of defects on graphene can open a large and tunable band gap, induce strong absorption peaks at optical wavelengths, and host a giant band gap quantum spin Hall phase. First, a geometric rule is analytically derived for the arrangements of defects that open a band gap in graphene, with one ninth of all possible patterns opening a band gap. Next, we perform ab-initio density functional calculations to compare the effects of structural vacancies, hexagonal BN dopants, and passivants on the electronic structure of graphene. Qualitatively, these three types of structural defects behave the same, with only slight differences in their resulting band structures. By adjusting the shape of structural defects, we show how to move the Dirac cones in reciprocal space in accordance with the tight-binding model for the anisotropic honeycomb lattice, while the fundamental mechanism for band gap opening remains the same. To quantitatively predict the band gap and optical properties of these materials, we employ many-body perturbation theory with Green's functions (GW/Bethe-Salpeter equation) to directly include electron-electron and electron-hole interactions. Structurally modified graphene shows a strong renormalization of the fundamental band gap over single particle descriptions, and a strong electron-hole interaction as indicated by strong exciton binding energies (> 0.5 eV). Finally, we show that structurally modified graphene

  7. Investigations of nuclear structure and nuclear reactions induced by complex projectiles. Progress report, September 1, 1991--August 31, 1992

    SciTech Connect

    Sarantites, D.G.

    1992-12-01

    The research program described touches five areas of nuclear physics: nuclear structure studies at high spin (hyperdeformation in the mass A {approx_equal} 182 region, structure of {sup 182}Hg and {sup 182}Au at high spin, a highly deformed band in {sup 136}Pm and the anomalous h{sub 11/2} proton crossing in the A{approximately}135 superdeformed region), studies at the interface between structure and reactions (population of entry states in heavy-ion fusion reactions, nuclear structure effects in proton evaporation spectra, nuclear structure- dependent entry state population by total spectroscopy, entrance channel effects in fusion near the barrier, lifetimes of subbarrier {alpha} particles by the atomic clock method), production and study of hot nuclei (the statistical model evaporation code EVAP, statistical emission of deuterons and tritons from highly excited compound nuclei, heavy-fragment emission as a probe of the thermal properties of highly excited compound nuclei, use of incoming-wave boundary condition transmission coefficients in the statistical model: implications in the particle evaporation spectra, study of transparency in the optical model), reaction mechanism studies (binary character of highly dissipative {sup 209}Bi + {sup 136}Xe collisions at E/A=28.2 MeV), and development and use of novel techniques and instrumentation in these areas of research (including a 4{pi} channel selection device, a novel x-ray detector, and a simple channel-selecting detector).

  8. Investigations of nuclear structure and nuclear reactions induced by complex projectiles. [Dept. of Chemistry, Washington Univ. , St. Louis, Mo

    SciTech Connect

    Sarantites, D.G.

    1992-01-01

    The research program described touches five areas of nuclear physics: nuclear structure studies at high spin (hyperdeformation in the mass A [approx equal] 182 region, structure of [sup 182]Hg and [sup 182]Au at high spin, a highly deformed band in [sup 136]Pm and the anomalous h[sub 11/2] proton crossing in the A[approximately]135 superdeformed region), studies at the interface between structure and reactions (population of entry states in heavy-ion fusion reactions, nuclear structure effects in proton evaporation spectra, nuclear structure- dependent entry state population by total spectroscopy, entrance channel effects in fusion near the barrier, lifetimes of subbarrier [alpha] particles by the atomic clock method), production and study of hot nuclei (the statistical model evaporation code EVAP, statistical emission of deuterons and tritons from highly excited compound nuclei, heavy-fragment emission as a probe of the thermal properties of highly excited compound nuclei, use of incoming-wave boundary condition transmission coefficients in the statistical model: implications in the particle evaporation spectra, study of transparency in the optical model), reaction mechanism studies (binary character of highly dissipative [sup 209]Bi + [sup 136]Xe collisions at E/A=28.2 MeV), and development and use of novel techniques and instrumentation in these areas of research (including a 4[pi] channel selection device, a novel x-ray detector, and a simple channel-selecting detector).

  9. Electronic structure and correlation effects in actinides

    SciTech Connect

    Albers, R.C.

    1998-12-01

    This report consists of the vugraphs given at a conference on electronic structure. Topics discussed are electronic structure, f-bonding, crystal structure, and crystal structure stability of the actinides and how they are inter-related.

  10. Ballistic projectile trajectory determining system

    DOEpatents

    Karr, T.J.

    1997-05-20

    A computer controlled system determines the three-dimensional trajectory of a ballistic projectile. To initialize the system, predictions of state parameters for a ballistic projectile are received at an estimator. The estimator uses the predictions of the state parameters to estimate first trajectory characteristics of the ballistic projectile. A single stationary monocular sensor then observes the actual first trajectory characteristics of the ballistic projectile. A comparator generates an error value related to the predicted state parameters by comparing the estimated first trajectory characteristics of the ballistic projectile with the observed first trajectory characteristics of the ballistic projectile. If the error value is equal to or greater than a selected limit, the predictions of the state parameters are adjusted. New estimates for the trajectory characteristics of the ballistic projectile are made and are then compared with actual observed trajectory characteristics. This process is repeated until the error value is less than the selected limit. Once the error value is less than the selected limit, a calculator calculates trajectory characteristics such a the origin and destination of the ballistic projectile. 8 figs.

  11. Ballistic projectile trajectory determining system

    DOEpatents

    Karr, Thomas J.

    1997-01-01

    A computer controlled system determines the three-dimensional trajectory of a ballistic projectile. To initialize the system, predictions of state parameters for a ballistic projectile are received at an estimator. The estimator uses the predictions of the state parameters to estimate first trajectory characteristics of the ballistic projectile. A single stationary monocular sensor then observes the actual first trajectory characteristics of the ballistic projectile. A comparator generates an error value related to the predicted state parameters by comparing the estimated first trajectory characteristics of the ballistic projectile with the observed first trajectory characteristics of the ballistic projectile. If the error value is equal to or greater than a selected limit, the predictions of the state parameters are adjusted. New estimates for the trajectory characteristics of the ballistic projectile are made and are then compared with actual observed trajectory characteristics. This process is repeated until the error value is less than the selected limit. Once the error value is less than the selected limit, a calculator calculates trajectory characteristics such a the origin and destination of the ballistic projectile.

  12. Electron Scattering and Nuclear Structure

    ERIC Educational Resources Information Center

    Trower, W. P.; Ficenec, J. R.

    1971-01-01

    Presents information about the nucleus gained by studies of electron scattering. Discusses what can be implied about the shape of the charge distribution, the nucleus positions, the vibrational modes of the nucleus, the momentum of the nucleus, and the granularity and core structures of the nucleus. (DS)

  13. Electronic Structure Principles and Aromaticity

    ERIC Educational Resources Information Center

    Chattaraj, P. K.; Sarkar, U.; Roy, D. R.

    2007-01-01

    The relationship between aromaticity and stability in molecules on the basis of quantities such as hardness and electrophilicity is explored. The findings reveal that aromatic molecules are less energetic, harder, less polarizable, and less electrophilic as compared to antiaromatic molecules, as expected from the electronic structure principles.

  14. Intact capture of hypervelocity projectiles.

    PubMed

    Tsou, P

    1990-01-01

    The ability to capture projectiles intact at hypervelocities opens new applications in science and technology that would either not be possible or would be very costly by other means. This capability has been demonstrated in the laboratory for aluminum projectiles of 1.6 mm diameter, captured at 6 km/s, in one unmelted piece, and retaining up to 95% of the original mass. Furthermore, capture was accomplished passively using microcellular underdense polymer foam. Another advantage of capturing projectiles in an underdense medium is the ability of such a medium to preserve a record of the projectile's original velocity components of speed and direction. A survey of these experimental results is described in terms of a dozen parameters which characterize the amount of capture and the effect on the projectile due to different capture media. PMID:11538362

  15. Double-peak structures in transmission of H2+ ions through conical multicapillaries in a polymer: Projectile-energy dependence

    NASA Astrophysics Data System (ADS)

    Liu, S. D.; Wang, Y. Y.; Zhao, Y. T.; Zhou, X. M.; Cheng, R.; Lei, Y.; Sun, Y. B.; Ren, J. R.; Duan, J. L.; Liu, J.; Xu, H. S.; Xiao, G. Q.

    2015-01-01

    Transmission experiments of 7 -200 keV H2+ ions through conical multicapillaries with inlet or outlet diameters of 4/2 μ m and a length of 30 μ m etched in a PC polymer are reported. The yield of the transmitted particles as a function of the capillary tilt angle was measured. The results show that for 200 keV H2+ ions the guiding effect disappears but a focusing effect is obtained with a density enhancement factor of 3.5. For 7 -50 keV H2+ ions their transmitted particle curves exhibit a pair of shoulder peaks on the left- and right-hand side of the center angle 0∘. As the ion energy increases, the shoulder-peak structure is found to vanish leaving one peak at 0∘.

  16. Electronic structure of black sodalite

    NASA Astrophysics Data System (ADS)

    Sankey, Otto F.; Demkov, Alexander A.; Lenosky, Thomas

    1998-06-01

    The electronic structure of black sodalite, Na8(AlSiO4)6, is determined in the local-spin-density approximation (LSDA). This structure has six Na atoms to compensate the six Al atoms, leaving two excess Na atoms. A band-gap electronic state is induced in the wide oxide gap by the excess sodium, and has ``particle in a box'' behavior. Magnetic orderings of these gap states are studied. Analytic models show that an antiferromagnetic ordering is lowest in energy in the LSDA. A self-consistent LSDA calculation shows the system to change from a metal to an antiferromagnetic insulator when spin orderings are allowed. Hopping and Hubbard-U parameters are estimated, and the many-body correlated Hubbard model is solved using a constrained path Monte Carlo technique, which again predicts the system to be antiferromagnetic with a Tc of order 50 K.

  17. Electronic structure of Calcium hexaborides

    SciTech Connect

    Lee, Byounghak; Wang, Lin-Wang

    2005-06-15

    We present a theoretical study of crystal and electronic structures of CaB6 within a screened-exchange local density approximation (sX-LDA). Our ab initio total energy calculations show that CaB6 is a semiconductor with a gap of >1.2 eV, in agreement with recent experimental observations. We show a very sensitive band gap dependence on the crystal internal parameter, which might partially explain the scatter of previous theoretical results. Our calculation demonstrates that it is essential to study this system simultaneously for both crystal structures and electronic properties, and that the sX-LDA provides an ideal method for this problem.

  18. Experimental and numerical study on fragmentation of steel projectiles

    NASA Astrophysics Data System (ADS)

    Råkvaag, K. G.; Børvik, T.; Hopperstad, O. S.; Westermann, I.

    2012-08-01

    A previous experimental study on penetration and perforation of circular Weldox 460E target plates with varying thicknesses struck by blunt-nose projectiles revealed that fragmentation of the projectile occurred if the target thickness or impact velocity exceeded a certain value. Thus, numerical simulations that do not account for fragmentation during impact can underestimate the perforation resistance of protective structures. Previous numerical studies have focused primarily on the target plate behaviour. This study considers the behaviour of the projectile and its possible fragmentation during impact. Hardened steel projectiles were launched at varying velocities in a series of Taylor tests. The impact events were captured using a high-speed camera. Fractography of the fragmented projectiles showed that there are several fracture mechanisms present during the fragmentation process. Tensile tests of the projectile material revealed that the hardened material has considerable variations in yield stress and fracture stress and strain. In the finite element model, the stress-strain behaviour from tensile tests was used to model the projectile material with solid elements and the modified Johnson-Cook constitutive relation. Numerical simulations incorporating the variations in material properties are capable of reproducing the experimental fracture patterns, albeit the predicted fragmentation velocities are too low.

  19. Structural Dynamics of Electronic Systems

    NASA Astrophysics Data System (ADS)

    Suhir, E.

    2013-03-01

    The published work on analytical ("mathematical") and computer-aided, primarily finite-element-analysis (FEA) based, predictive modeling of the dynamic response of electronic systems to shocks and vibrations is reviewed. While understanding the physics of and the ability to predict the response of an electronic structure to dynamic loading has been always of significant importance in military, avionic, aeronautic, automotive and maritime electronics, during the last decade this problem has become especially important also in commercial, and, particularly, in portable electronics in connection with accelerated testing of various surface mount technology (SMT) systems on the board level. The emphasis of the review is on the nonlinear shock-excited vibrations of flexible printed circuit boards (PCBs) experiencing shock loading applied to their support contours during drop tests. At the end of the review we provide, as a suitable and useful illustration, the exact solution to a highly nonlinear problem of the dynamic response of a "flexible-and-heavy" PCB to an impact load applied to its support contour during drop testing.

  20. Air-Powered Projectile Launcher

    NASA Technical Reports Server (NTRS)

    Andrews, T.; Bjorklund, R. A.; Elliott, D. G.; Jones, L. K.

    1987-01-01

    Air-powered launcher fires plastic projectiles without using explosive propellants. Does not generate high temperatures. Launcher developed for combat training for U.S. Army. With reservoir pressurized, air launcher ready to fire. When pilot valve opened, sleeve (main valve) moves to rear. Projectile rapidly propelled through barrel, pushed by air from reservoir. Potential applications in seismic measurements, avalanche control, and testing impact resistance of windshields on vehicles.

  1. Electronic structure of graphite oxide

    NASA Astrophysics Data System (ADS)

    Jeong, Hae Kyung; Yang, Cheolsoo; Kim, Bong Soo; Kim, Ki-Jeong

    2011-03-01

    We have investigated the electronic structure of graphite oxide by photoelectron spectroscopy at the Pohang Accelerator Laboratory, Korea. The typical sp 2 hybridization states found in graphite were also seen in graphite oxide. However, the π state disappeared near the Fermi level because of bonding between the π and oxygen-related states originating from graphite oxide, indicating electron transfer from graphite to oxygen and resulting in a downward shift of the highest occupied molecular orbital (HOMO) state to higher binding energies. The band gap opening increased to about 1.8 eV, and additional oxygen-related peaks were observed at 8.5 and 27 eV. This research was supported by the Basic Science Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2010-0004592), and partly by the MEST (2009-0087138). Experiments at the PLS were supported in part by POSTECH and MEST.

  2. Electronic instrumentation for smart structures

    NASA Astrophysics Data System (ADS)

    Blanar, George J.

    1995-04-01

    The requirements of electronic instrumentation for smart structures are similar to those of data acquisition systems at our national particle physics laboratories. Modern high energy and heavy ion physics experiments may have tens of thousands of channels of data sources producing data that must be converted to digital form, compacted, stored and interpreted. In parallel, multiple sensors distributed in and around smart structures generate either binary or analog signals that are voltage, charge, or time like in their information content. In all cases, they must be transmitted, converted and preserved into a unified digital format for real-time processing. This paper will review the current status of practical large scale electronic measurement systems with special attention to architectures and physical organization. Brief surveys of the current state of the art will include preamplifiers and amplifiers, comparators and discriminators, voltage or charge analog-to-digital converters, time internal meters or time-to-digital converters, and finally, counting or scalar systems. The paper will conclude by integrating all of these ideas in a concept for an all-digital readout of a smart structure using the latest techniques used in physics research today.

  3. Initiation of Gaseous Detonation by Conical Projectiles

    NASA Astrophysics Data System (ADS)

    Verreault, Jimmy

    qualitatively well with the experimental results for relatively blunt projectiles (cone half-angle larger than 35°) and low mixture pressures (lower than 100 kPa). The trend of the critical Damköhler number calculated along the projectile cone surface was similar to that of the experimental results for slender cones (cone half-angles lower 35°) and high mixture pressures (higher than 100 kPa). Steady 2D simulations of reacting flows over finite wedges using the method of characteristics with a one-step Arrhenius chemical reaction model reproduced the three regimes observed for direct initiation of a detonation: the subcritical, critical and supercritical regimes. It is shown that in order for a 2D wedge to be equivalent to the problem of blast initiation of a detonation (which is the essence of the Lee-Vasiljev model), the Mach number normal to the oblique shock needs to be greater than 50 and the wedge angle has to be smaller than 30°. Simulations of reacting flows over semi-infinite wedges and cones were validated with CFD results. Excellent agreement was reached between the angle of overdriven oblique detonations obtained from the simulations and those from a polar analysis. For wedge or cone angles equal or lower than the minimum angle for which an oblique detonation is attached (according to the polar analysis), a Chapman-Jouguet oblique detonation was initiated. In the conical configuration, the curvature around the cone axis allowed an oblique detonation to be self-sustained at an angle less than without the curvature effect. At larger activation energies, the initiation process of an oblique detonation wave at the tip of a semi-infinite wedge or cone was identified. Unsteady 2D computational simulations were also conducted and showed the cellular structure of an oblique detonation wave. Instabilities in the form of transverse shock waves along the oblique detonation front arise for large activation energies.

  4. Projectile penetration into ballistic gelatin.

    PubMed

    Swain, M V; Kieser, D C; Shah, S; Kieser, J A

    2014-01-01

    Ballistic gelatin is frequently used as a model for soft biological tissues that experience projectile impact. In this paper we investigate the response of a number of gelatin materials to the penetration of spherical steel projectiles (7 to 11mm diameter) with a range of lower impacting velocities (<120m/s). The results of sphere penetration depth versus projectile velocity are found to be linear for all systems above a certain threshold velocity required for initiating penetration. The data for a specific material impacted with different diameter spheres were able to be condensed to a single curve when the penetration depth was normalised by the projectile diameter. When the results are compared with a number of predictive relationships available in the literature, it is found that over the range of projectiles and compositions used, the results fit a simple relationship that takes into account the projectile diameter, the threshold velocity for penetration into the gelatin and a value of the shear modulus of the gelatin estimated from the threshold velocity for penetration. The normalised depth is found to fit the elastic Froude number when this is modified to allow for a threshold impact velocity. The normalised penetration data are found to best fit this modified elastic Froude number with a slope of 1/2 instead of 1/3 as suggested by Akers and Belmonte (2006). Possible explanations for this difference are discussed. PMID:24184862

  5. Fusion and direct reactions for strongly and weakly bound projectiles

    NASA Astrophysics Data System (ADS)

    Hugi, M.; Lang, J.; Müller, R.; Ungricht, E.; Bodek, K.; Jarczyk, L.; Kamys, B.; Magiera, A.; Strzałkowski, A.; Willim, G.

    1981-09-01

    The interaction of 6Li, 9Be and 12C projectiles with a 28Si target was investigated by measuring the angular distributions of the elastically scattered projectiles and of the emitted protons, deuterons and α-particles. The experiment was performed in order to deduce direct and compound nucleus process contributions to the total reaction cross section and to study the influence of the projectile structure on the relative importance of these two mechanisms. Optical model parameters and therefore the total reaction cross section are strongly influenced by the binding energy of the projectile. The parameters of the Glas-Mosel model describing the fusion reaction vary smoothly with the atomic number. In the system 9Be + 28Si around 50% of all reactions are direct processes even at energies near the Coulomb barrier, whereas in the other systems the direct part amounts to 15 % ( 12C) and 30 % ( 6Li) only.

  6. Electronic structure of lithium amide

    NASA Astrophysics Data System (ADS)

    Kamakura, N.; Takeda, Y.; Saitoh, Y.; Yamagami, H.; Tsubota, M.; Paik, B.; Ichikawa, T.; Kojima, Y.; Muro, T.; Kato, Y.; Kinoshita, T.

    2011-01-01

    The electronic structure of the insulator lithium amide (LiNH2), which is a lightweight complex hydride being considered as a high-capacity hydrogen storage material, is investigated by N 1s soft x-ray emission spectroscopy (XES) and absorption spectroscopy (XAS). The XES and XAS spectra show a band gap between the valence and conduction bands. The valence band in the XES spectrum consists of three peaks, which extend up to ~-8 eV from the valence band top. The band calculation within the local-density approximation (LDA) for LiNH2shows energetically separated three peaks in the occupied N 2p partial density of states (pDOS) and the band gap. The energy distribution of three peaks in the XES spectrum agrees with that in the calculated pDOS except for the peak at the highest binding energy, which is attributed to the strongly hybridized state between N 2p and H 1s. The XES experiment has clarified that the strongly hybridized state with H 1s in LiNH2is located at binding energy higher than that of the LDA calculation, while the overall feature of the electronic structure of LiNH2experimentally obtained by XES and XAS is consistent with the calculated result.

  7. Fragmentation of hypervelocity aluminum projectiles on fabrics

    NASA Astrophysics Data System (ADS)

    Rudolph, Martin; Schäfer, Frank; Destefanis, Roberto; Faraud, Moreno; Lambert, Michel

    2012-07-01

    This paper presents work performed for a study investigating the ability of different flexible materials to induce fragmentation of a hypervelocity projectile. Samples were chosen to represent a wide range of industrially available types of flexible materials like ceramic, aramid and carbon fabrics as well as a thin metallic mesh. Impact conditions and areal density were kept constant for all targets. Betacloth and multi-layer insulation (B-MLI) are mounted onto the targets to account for thermal system engineering requirements. All tests were performed using the Space light-gas gun facility (SLGG) of the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI. Projectiles were aluminum spheres with 5 mm diameter impacting at approximately 6.3 km/s. Fragmentation was evaluated using a witness plate behind the target. An aramid and a ceramic fabric lead the ranking of fabrics with the best projectile fragmentation and debris cloud dispersion performance. A comparison with an equal-density rigid aluminum plate is presented. The work presented can be applied to optimize the micrometeoroid and space debris (MM/SD) shielding structure of inflatable modules.

  8. a Study of Ricochet Phenomenon for Inclined Impact of Projectile

    NASA Astrophysics Data System (ADS)

    Jo, Jong-Hyun; Lee, Young-Shin

    In this study, the numerical simulation using AUTODYN-3D program was investigated for trajectory prediction for inclined impacts of projectiles. The penetration and perforation of polycarbonate(PC) plate by 7.62 mm projectile was investigated numerically. The characteristic structure of the projectile's trajectory in the PC plates was studied. Two combined failure criteria were used in the target plate, and the target plate was modeled with the properties of polycarbonate for simulating the ricochet phenomenon. The numerical analyses were used to study the effect of the angle of inclination on the trajectory and kinetic energy of the projectile. The dynamic deformation behaviors tests of PC were compared with numerical simulation results which can be used for predictive purpose. Ricochet phenomenon for angles of inclination of 0° ≤ θ ≤ 20° in the analysis. The projectile perforated the plate for θ > 30°, thus defined a failure envelope for numerical configuration. The numerical analyses was used to study the effect under the projectile impact velocity on the depth of penetration(DOP).

  9. Projectile Motion Without Trigonometric Functions

    NASA Astrophysics Data System (ADS)

    Mohazzabi, Pirooz; Kohneh, Zahra A.

    2005-02-01

    In this paper we provide a treatment of projectile motion that is accessible to students who are unfamiliar with trigonometry but do have a minimal knowledge of elementary algebra and know the Pythagorean theorem. In this approach, we view the initial velocity of the projectile as being a combination of a vertical part (component) v0V and a horizontal component v0H (see Fig. 1). This is in contrast to the usual approach of taking the initial speed v0 and the launch angle as being given. We let the initial position be the origin and neglect air drag. Assuming that the constant acceleration kinematics equations are known, we may write vH = v0H, and the horizontal distance traveled is x = v0H t, where t is the elapsed time. We also have vV = v0V - gt, where g is the magnitude of the acceleration due to gravity. And the vertical displacement is y = v0V t - ½ gt2. These equations may be used to find the location and velocity of the projectile at any time t. We can also find the equation of the path of the projectile by combining Eq. [1(b)] and Eq. [2(b)] to get y = -(g/2v0H2)x2 + (v0V/v0H) x, which is the equation of a concave-down parabola.

  10. Multiple impacts of dusty projectiles

    NASA Astrophysics Data System (ADS)

    Kothe, Stefan; Güttler, Carsten; Blum, Jurgen

    In the context of early stages of planetesimal formation we performed laboratory and drop tower experiments to study multiple impacts of small dust-aggregate projectiles into solid sintered dust targets. Both collision partners consisted of 1.5 µm monodisperse spherical SiO2 monomers with volume filling factors of 0.15 (projectiles) and 0.35 (targets), respectively. The fragile projectiles were accelerated by a solenoid accelerator with a linear projectile magazine, which enabled us to perform 25 impacts within 4.5 s of microgravity time in the Bremen drop tower. We measured the mass-accretion efficiency for different impact velocities between 3 and 5 m s-1 , using an analytical balance and imaging methods. Furthermore, we observed random collisions among small dust aggregates with sizes around 1 mm and collision velocities of the order of 0.25 m s-1 and used them to improve the dust-aggregate collision model of Güttler et al. (2010). u

  11. Electronic structure of herbicides: Atrazine and bromoxynil

    NASA Astrophysics Data System (ADS)

    Novak, Igor; Kovač, Branka

    2011-06-01

    The electronic structures of herbicides atrazine and bromoxynil have been investigated by UV photoelectron spectroscopy (UPS), quantum chemical calculations and comparison with X-ray diffraction, molecular docking and molecular dynamics studies. Their electronic and molecular structures are discussed in the context of their biological activity. This is the first report which correlates the molecular mechanism of biological activity of these herbicides with their experimentally determined electronic and molecular structures.

  12. Having Fun with a 3-D Projectile

    ERIC Educational Resources Information Center

    Lammi, Matthew; Greenhalgh, Scott

    2011-01-01

    The use of projectiles is a concept familiar to most students, whether it is a classic slingshot, bow and arrow, or even a spit wad through a straw. Perhaps the last thing a teacher wants is more projectiles in the classroom. However, the concept of projectiles is relevant to most students and may provide a means of bringing more authenticity into…

  13. Precision Measurement of the Hyperfine Structure of Laser-Cooled Radioactive {sup 7}Be{sup +} Ions Produced by Projectile Fragmentation

    SciTech Connect

    Okada, K.; Wada, M.; Nakamura, T.; Takamine, A.; Schury, P.; Ishida, Y.; Sonoda, T.; Kanai, Y.; Kojima, T. M.; Lioubimov, V.; Ogawa, M.; Yamazaki, Y.; Yoshida, A.; Kubo, T.; Katayama, I.; Ohtani, S.; Wollnik, H.; Schuessler, H. A.

    2008-11-21

    The ground state hyperfine splitting of {sup 7}Be{sup +} has been measured by laser-microwave double-resonance spectroscopy in the online rf trap of RIKEN's slow RI-beam facility. Be ions produced by projectile fragmentation of {sup 13}C at {approx_equal}1 GeV were thermalized in a rf ion guide gas cell and subsequently laser cooled in the ion trap to {approx_equal}1 {mu}eV. This 10{sup 15}-fold reduction of the kinetic energy allows precision spectroscopy of these ions. A magnetic hfs constant of A=-742.772 28(43) MHz was measured for {sup 7}Be{sup +}, from which a nuclear magnetic moment of {mu}{sub I}=-1.399 28(2){mu}{sub N} was deduced.

  14. Nano-hillock formation in diamond-like carbon induced by swift heavy projectiles in the electronic stopping regime: Experiments and atomistic simulations

    NASA Astrophysics Data System (ADS)

    Schwen, D.; Bringa, E.; Krauser, J.; Weidinger, A.; Trautmann, C.; Hofsäss, H.

    2012-09-01

    The formation of surface hillocks in diamond-like carbon is studied experimentally and by means of large-scale molecular dynamics simulations with 5 × 106 atoms combined with a thermal spike model. The irradiation experiments with swift heavy ions cover a large electronic stopping range between ˜12 and 72 keV/nm. Both experiments and simulations show that beyond a stopping power threshold, the hillock height increases linearly with the electronic stopping, and agree extremely well assuming an efficiency of approximately 20% in the transfer of electronic energy to the lattice. The simulations also show a transition of sp3 to sp2 bonding along the tracks with the hillocks containing almost no sp3 contribution.

  15. Nano-hillock formation in diamond-like carbon induced by swift heavy projectiles in the electronic stopping regime: Experiments and atomistic simulations

    SciTech Connect

    Schwen, D.; Bringa, E.; Krauser, J.; Weidinger, A.; Trautmann, C.; Hofsaess, H.

    2012-09-10

    The formation of surface hillocks in diamond-like carbon is studied experimentally and by means of large-scale molecular dynamics simulations with 5 Multiplication-Sign 10{sup 6} atoms combined with a thermal spike model. The irradiation experiments with swift heavy ions cover a large electronic stopping range between {approx}12 and 72 keV/nm. Both experiments and simulations show that beyond a stopping power threshold, the hillock height increases linearly with the electronic stopping, and agree extremely well assuming an efficiency of approximately 20% in the transfer of electronic energy to the lattice. The simulations also show a transition of sp{sup 3} to sp{sup 2} bonding along the tracks with the hillocks containing almost no sp{sup 3} contribution.

  16. Four-body charge transfer processes in collisions of bare projectile ions with helium atoms

    NASA Astrophysics Data System (ADS)

    Jana, S.; Mandal, C. R.; Purkait, M.

    2015-02-01

    Single-electron capture by a bare ion from a helium atom at intermediate and high energies in the framework of four-body distorted wave (DW-4B) approximation in both prior and post form has been considered. In the entrance channel, the initial bound state wave function is distorted by the incoming projectile ion, and the corresponding distortion is related to the Coulomb continuum states of the active electron and the residual target ion in the field of the projectile ion respectively. Continuum states of the active electron and the projectile ion in the field of the residual target ion are also included in the exit channel. It may be mentioned that the effect of dynamic electron correlation is explicitly taken into account through the complete perturbation potential. The total single-electron capture cross sections are obtained by summing over all contributions up to n = 3 shells and sub-shells respectively. In addition, the differential cross sections for alpha particle-helium collision are calculated at impact energies of 60, 150, 300, 450, and 630 keV amu-1, respectively. The cross sections exhibit a monotonically decreasing angular dependence, with clear peak structures around 0.1 to 0.2 mrad being found at low impact energies. The current theoretical results, both in prior and post forms of the transition amplitude for symmetric and asymmetric collision, are compared with the available theoretical and experimental results. Current computed results have been found to be satisfactory in comparison with other theoretical and experimental findings.

  17. Electronic correlation contributions to structural energies

    NASA Astrophysics Data System (ADS)

    Haydock, Roger

    2015-03-01

    The recursion method is used to calculate electronic excitation spectra including electron-electron interactions within the Hubbard model. The effects of correlation on structural energies are then obtained from these spectra and applied to stacking faults. http://arxiv.org/abs/1405.2288 Supported by the Richmond F. Snyder Fund and Gifts.

  18. Electronic structure of lithium tetraborate

    NASA Astrophysics Data System (ADS)

    Wooten, David J.

    Due to many of its attributes, Li2B4O7 provides a possible material for incorporation as either a primary or companion material in future solid state neutron detectors. There is however a lack of fundamental characterization information regarding this useful material, particularly its electronic configuration. To address this, an investigation of Li2B4O7(110) and Li2B 4O7(100) was undertaken, utilizing photoemission and inverse photoemission spectroscopic techniques. The measured band gap depended on crystallographic direction with the band gaps ranging from 8.9+/-0.5 eV to 10.1+/-0.5 eV. The measurement yielded a density of states that qualitatively agreed with the theoretical results from model bulk band structure calculations for Li2B4O7; albeit with a larger band gap than predicted, but consistent with the known deficiencies of Local Density Approximation and Density Functional Theory calculations. The occupied states of both surfaces were extremely flat; to the degree that resolving periodic dispersion of the occupied states was inconclusive, within the resolution of the system. However, both surfaces demonstrated clear periodic dispersion within the empty states very close to theoretical Brillouin zone values. These attributes also translated to a lighter charge carrier effective mass in the unoccupied states. Of the two surfaces, Li2B4O 7(110) yielded the more consistent values in orthogonal directions for energy states. The presence of a bulk band gap surface state and image potential state in Li2B4O7(110) was indicative of a defect-free surface. The absence of both in the more polar, more dielectric Li2B4O7(100) was attributed to the presence of defects determined to be O vacancies. The results from Li2B 4O7(110) were indicative of a more stable surface than Li 2B4O7(100). In addition, Li 1s bulk and surface core level components were determined at the binding energies of -56.5+0.4 and -53.7+0.5 eV. Resonance features were observed along the [001

  19. Deformation and Melting of Iron-Rich Projectiles in Hypervelocity MEMIN Cratering Experiments

    NASA Astrophysics Data System (ADS)

    Kenkmann, T.; Ebert, M.; Trullenque, G.; Deutsch, A.; Hecht, L.; Salge, T.; Schäfer, F.; Thoma, K.

    2013-09-01

    We conducted 23-54 kJ impact experiments using projectiles composed of steel and iron meteorite Campo del Cielo to study the structural changes that occur upon impact in these projectiles. Extensive melting is largely the result of plastic deformation.

  20. Electron tomography of dislocation structures

    SciTech Connect

    Liu, G.S.; House, S.D.; Kacher, J.; Tanaka, M.; Higashida, K.; Robertson, I.M.

    2014-01-15

    Recent developments in the application of electron tomography for characterizing microstructures in crystalline solids are described. The underlying principles for electron tomography are presented in the context of typical challenges in adapting the technique to crystalline systems and in using diffraction contrast imaging conditions. Methods for overcoming the limitations associated with the angular range, the number of acquired images, and uniformity of image contrast are introduced. In addition, a method for incorporating the real space coordinate system into the tomogram is presented. As the approach emphasizes development of experimental solutions to the challenges, the solutions developed and implemented are presented in the form of examples.

  1. Wind-influenced projectile motion

    NASA Astrophysics Data System (ADS)

    Bernardo, Reginald Christian; Perico Esguerra, Jose; Day Vallejos, Jazmine; Jerard Canda, Jeff

    2015-03-01

    We solved the wind-influenced projectile motion problem with the same initial and final heights and obtained exact analytical expressions for the shape of the trajectory, range, maximum height, time of flight, time of ascent, and time of descent with the help of the Lambert W function. It turns out that the range and maximum horizontal displacement are not always equal. When launched at a critical angle, the projectile will return to its starting position. It turns out that a launch angle of 90° maximizes the time of flight, time of ascent, time of descent, and maximum height and that the launch angle corresponding to maximum range can be obtained by solving a transcendental equation. Finally, we expressed in a parametric equation the locus of points corresponding to maximum heights for projectiles launched from the ground with the same initial speed in all directions. We used the results to estimate how much a moderate wind can modify a golf ball’s range and suggested other possible applications.

  2. [The dynamics of projectile wounding. Concepts in ballistic injuries].

    PubMed

    Houdelette, P

    1998-04-01

    Analysis of the structure and terminal ballistic behavior of bullets provides a better understanding of their wounding power. The studies of ballistics specialists serve as a base. The concept of "scientific shot" remains an intellectual approach to a random phenomenon. Wound ballistic studies examine the behavior of projectiles in vivo or in a simulation medium. War events, in which projectiles do not meet requirements of international conventions, sport or hunting accidents, urban violence may confront the surgeon with various types of ballistic pathologies. The appropriate saying of Lindsey that the surgeons has to treat a wound and not a weapon should not justify etiologic ignorance. PMID:9768076

  3. Electron gun controlled smart structure

    DOEpatents

    Martin, Jeffrey W.; Main, John Alan; Redmond, James M.; Henson, Tammy D.; Watson, Robert D.

    2001-01-01

    Disclosed is a method and system for actively controlling the shape of a sheet of electroactive material; the system comprising: one or more electrodes attached to the frontside of the electroactive sheet; a charged particle generator, disposed so as to direct a beam of charged particles (e.g. electrons) onto the electrode; a conductive substrate attached to the backside of the sheet; and a power supply electrically connected to the conductive substrate; whereby the sheet changes its shape in response to an electric field created across the sheet by an accumulation of electric charge within the electrode(s), relative to a potential applied to the conductive substrate. Use of multiple electrodes distributed across on the frontside ensures a uniform distribution of the charge with a single point of e-beam incidence, thereby greatly simplifying the beam scanning algorithm and raster control electronics, and reducing the problems associated with "blooming". By placing a distribution of electrodes over the front surface of a piezoelectric film (or other electroactive material), this arrangement enables improved control over the distribution of surface electric charges (e.g. electrons) by creating uniform (and possibly different) charge distributions within each individual electrode. Removal or deposition of net electric charge can be affected by controlling the secondary electron yield through manipulation of the backside electric potential with the power supply. The system can be used for actively controlling the shape of space-based deployable optics, such as adaptive mirrors and inflatable antennae.

  4. Modern toxic antipersonnel projectiles.

    PubMed

    Gaillard, Yvan; Regenstreif, Philippe; Fanton, Laurent

    2014-12-01

    In the spring of 1944, Kurt von Gottberg, the SS police chief in Minsk, was shot and injured by 2 Soviet agents. Although he was only slightly injured, he died 6 hours later. The bullets were hollow and contained a crystalline white powder. They were 4-g bullets, semi-jacketed in cupronickel, containing 28 mg of aconitine. They were later known as akonitinnitratgeschosse. The Sipo (the Nazi security police) then ordered a trial with a 9-mm Parabellum cartridge containing Ditran, an anticholinergic drug with hallucinogenic properties causing intense mental confusion. In later years, QNB was used and given the NATO code BZ (3-quinuclidinyl-benzylate). It was proven that Saddam Hussein had this weapon (agent 15) manufactured and used it against the Kurds. Serbian forces used the same type of weapon in the Bosnian conflict, particularly in Srebrenica.The authors go on to list the Cold War toxic weapons developed by the KGB and the Warsaw pact countries for the discreet elimination of dissidents and proindependence leaders who had taken refuge in the West. These weapons include PSZh-13 launchers, the Troika electronic sequential pistol, and the ingenious 4-S110T captive piston system designed by the engineer Stechkin. Disguised as a cigarette case, it could fire a silent charge of potassium cyanide. This rogues gallery also includes the umbrella rigged to inject a pellet of ricin (or another phytalbumin of similar toxicity, such as abrin or crotin) that was used to assassinate the Bulgarian writer and journalist Georgi Markov on September 7, 1978, in London.During the autopsy, the discovery of a bullet burst into 4 or 5 parts has to make at once suspecting the use of a toxic substance. Toxicological analysis has to look for first and foremost aconitine, cyanide, suxamethonium, Ditran, BZ, or one of the toxic phytalbumins. The use of such complex weapons has to make suspect a powerful organization: army, secret service, terrorism. The existence of the Russian UDAR spray

  5. Structural change of graphite during electron irradiation

    SciTech Connect

    Koike, J. . Dept. of Mechanical Engineering); Pedraza, D.F. )

    1992-01-01

    Highly oriented pyrolytic graphite was irradiated at room temperature with 300-keV electrons. High resolution transmission electron microscopy and electron energy loss spectroscopy were employed to study the structure of electron-irradiated graphite. Results consistently indicated absence of long-range order periodicity in the basal plane, and loose retention of the c-axis periodicity. Structure was modeled based on a mixture of sixfold and non-sixfold atom rings. Formation of non-sixfold atom rings was related to the observed buckling and discontinuity of the original graphite basal plane.

  6. Structural change of graphite during electron irradiation

    SciTech Connect

    Koike, J.; Pedraza, D.F.

    1992-12-31

    Highly oriented pyrolytic graphite was irradiated at room temperature with 300-keV electrons. High resolution transmission electron microscopy and electron energy loss spectroscopy were employed to study the structure of electron-irradiated graphite. Results consistently indicated absence of long-range order periodicity in the basal plane, and loose retention of the c-axis periodicity. Structure was modeled based on a mixture of sixfold and non-sixfold atom rings. Formation of non-sixfold atom rings was related to the observed buckling and discontinuity of the original graphite basal plane.

  7. About zitterbewegung and electron structure

    NASA Astrophysics Data System (ADS)

    Rodrigues, Waldyr A.; Vaz, Jayme; Recami, Erasmo; Salesi, Giovanni

    1993-12-01

    We start from the spinning electron model by Barut and Zanghi, which has been recently translated into the Clifford algebra language. We ``complete'' such a translation, first of all, by expressing in the Clifford formalism a particular Barut-Zanghi (BZ) solution, which refers (at the classical limit) to an ``internal'' helical motion with a time-like speed (and is here shown to originate from the superposition of positive and negative frequency solutions of the Dirac equation). Then, we show how to construct solutions of the Dirac equation describing helical motions with light-like speed, which meet very well the standard interpretation of the velocity operator in the Dirac equation theory (and agree with the solution proposed by Hestenes, on the basis - however - of ad-hoc assumptions that are unnecessary in the present approach). The above results appear to support the conjecture that the zitterbewegung motion (a helical motion, at the classical limit) is responsible for the electron spin.

  8. 22. VAL, VIEW OF PROJECTILE LOADING DECK LOOKING NORTHEAST TOWARD ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    22. VAL, VIEW OF PROJECTILE LOADING DECK LOOKING NORTHEAST TOWARD TOP OF CONCRETE 'A' FRAME STRUCTURE SHOWING DRIVE CABLES, DRIVE GEAR, BOTTOM OF CAMERA TOWER AND 'CROWS NEST' CONTROL ROOM. - Variable Angle Launcher Complex, Variable Angle Launcher, CA State Highway 39 at Morris Reservior, Azusa, Los Angeles County, CA

  9. Electronic structure of metallic glasses

    SciTech Connect

    Oelhafen, P.; Lapka, R.; Gubler, U.; Krieg, J.; DasGupta, A.; Guentherodt, H.J.; Mizoguchi, T.; Hague, C.; Kuebler, J.; Nagel, S.R.

    1981-01-01

    This paper is organized in six sections and deals with (1) the glassy transition metal alloys, their d-band structure, the d-band shifts on alloying and their relation to the alloy heat of formation (..delta..H) and the glass forming ability, (2) the glass to crystal phase transition viewed by valence band spectroscopy, (3) band structure calculations, (4) metallic glasses prepared by laser glazing, (5) glassy normal metal alloys, and (6) glassy hydrides.

  10. Structural physiology based on electron crystallography

    PubMed Central

    Fujiyoshi, Yoshinori

    2011-01-01

    There are many questions in brain science, which are extremely interesting but very difficult to answer. For example, how do education and other experiences during human development influence the ability and personality of the adult? The molecular mechanisms underlying such phenomena are still totally unclear. However, technological and instrumental advancements of electron microscopy have facilitated comprehension of the structures of biological components, cells, and organelles. Electron crystallography is especially good for studying the structure and function of membrane proteins, which are key molecules of signal transduction in neural and other cells. Electron crystallography is now an established technique to analyze the structures of membrane proteins in lipid bilayers, which are close to their natural biological environment. By utilizing cryo-electron microscopes with helium cooled specimen stages, which were developed through a personal motivation to understand functions of neural systems from a structural point of view, structures of membrane proteins were analyzed at a resolution higher than 3 Å. This review has four objectives. First, it is intended to introduce the new research field of structural physiology. Second, it introduces some of the personal struggles, which were involved in developing the cryo-electron microscope. Third, it discusses some of the technology for the structural analysis of membrane proteins based on cryo-electron microscopy. Finally, it reviews structural and functional analyses of membrane proteins. PMID:21416541

  11. Electron-phonon renormalization of the electronic structure of diamond

    NASA Astrophysics Data System (ADS)

    Giustino, Feliciano; Louie, Steven G.; Cohen, Marvin L.

    2011-03-01

    The calculation of band structures from first-principles has reached a high level of accuracy. Calculations combining density-functional theory with many-body perturbation theory often are in good agreement with measurements by photoemission, tunneling, and other spectroscopic probes. While significant efforts have been devoted to improving the description of electron-electron interactions in these calculations, the effect of lattice vibrations has largely been overlooked so far. In this work we study from first principles the electron-phonon renormalization of the band gap of diamond. The calculated temperature dependence of the gap and the broadening of the absorption edge are in excellent agreement with spectroscopic ellipsometry data. Interestingly we find a gap renormalization due to zero-point vibrations as large as 0.6 eV. We discuss the implications of our findings for the electronic structure of other carbon-based bulk materials and nanostructures.

  12. Sequential injection gas guns for accelerating projectiles

    DOEpatents

    Lacy, Jeffrey M.; Chu, Henry S.; Novascone, Stephen R.

    2011-11-15

    Gas guns and methods for accelerating projectiles through such gas guns are described. More particularly, gas guns having a first injection port located proximate a breech end of a barrel and a second injection port located longitudinally between the first injection port and a muzzle end of the barrel are described. Additionally, modular gas guns that include a plurality of modules are described, wherein each module may include a barrel segment having one or more longitudinally spaced injection ports. Also, methods of accelerating a projectile through a gas gun, such as injecting a first pressurized gas into a barrel through a first injection port to accelerate the projectile and propel the projectile down the barrel past a second injection port and injecting a second pressurized gas into the barrel through the second injection port after passage of the projectile and to further accelerate the projectile are described.

  13. Instructional Approach to Molecular Electronic Structure Theory

    ERIC Educational Resources Information Center

    Dykstra, Clifford E.; Schaefer, Henry F.

    1977-01-01

    Describes a graduate quantum mechanics projects in which students write a computer program that performs ab initio calculations on the electronic structure of a simple molecule. Theoretical potential energy curves are produced. (MLH)

  14. Computational Chemistry Using Modern Electronic Structure Methods

    ERIC Educational Resources Information Center

    Bell, Stephen; Dines, Trevor J.; Chowdhry, Babur Z.; Withnall, Robert

    2007-01-01

    Various modern electronic structure methods are now days used to teach computational chemistry to undergraduate students. Such quantum calculations can now be easily used even for large size molecules.

  15. Electronic structure and photophysical properties of polyimides

    SciTech Connect

    LaFemina, J.P.; Kafafi, S.A.

    1992-04-01

    The quantum mechanical AM1 and CNDO/S3 models were used to examine the effect of isoelectronic substitutions on the conformation, electronic structure, and optical absorption spectra for a series of aromatic polyimides. An analysis of the geometric changes at the substitution site and its effect on the electronic structure allowed for the prediction of changes in the ICT band of the optical absorption spectra.

  16. MCSNA: Experimental Benchmarking of Pu Electronic Structure

    SciTech Connect

    Tobin, J G

    2007-01-29

    The objective of this work is to develop and/or apply advanced diagnostics to the understanding of aging of Pu. Advanced characterization techniques such as photoelectron and x-ray absorption spectroscopy will provide fundamental data on the electronic structure of Pu phases. These data are crucial for the validation of the electronic structure methods. The fundamental goal of this project is to narrow the parameter space for the theoretical modeling of Pu aging. The short-term goal is to perform experiments to validate electronic structure calculations of Pu. The long-term goal is to determine the effects of aging upon the electronic structure of Pu. Many of the input parameters for aging models are not directly measurable. These parameters will need to be calculated or estimated. Thus a First Principles-Approach Theory is needed, but it is unclear what terms are important in the Hamiltonian. (H{Psi} = E{Psi}) Therefore, experimental data concerning the 5f electronic structure are needed, to determine which terms in the Hamiltonian are important. The data obtained in this task are crucial for reducing the uncertainty of Task LL-01-developed models and predictions. The data impact the validation of electronic structure methods, the calculation of defect properties, the evaluation of helium diffusion, and the validation of void nucleation models. The importance of these activities increases if difficulties develop with the accelerating aging alloy approach.

  17. Projectile Motion Gets the Hose

    NASA Astrophysics Data System (ADS)

    Goff, John Eric; Liyanage, Chinthaka

    2011-10-01

    Students take a weekly quiz in our introductory physics course. During the week in which material focused on projectile motion, we not-so-subtly suggested what problem the students would see on the quiz. The quiz problem was an almost exact replica of a homework problem we worked through in the class preceding the quiz. The goal of the problem is to find the launch speed if the final horizontal and vertical positions and launch angle are given. Figure 1 shows a schematic of the trajectory.

  18. REDUCED ENERGY CONSUMPTION THROUGH PROJECTILE BASED EXCAVATION

    SciTech Connect

    Mark Machina

    2002-01-09

    The Projectile Based Excavation (ProjEX) program has as its goal, the reduction of energy required for production mining and secondary breakage through the use of a projectile based excavation system. It depends on the development of a low cost family of projectiles that will penetrate and break up different types of ore/rock and a low cost electric launch system. The electric launch system will eliminate the need for high cost propellant considered for similar concepts in the past. This document reports on the progress made in the program during the past quarter. It reports on projectile development experiments and the development of the electric launch system design.

  19. REDUCED ENERGY CONSUMPTION THROUGH PROJECTILE BASED EXCAVATION

    SciTech Connect

    Mark Machina

    2002-10-12

    The Projectile Based Excavation (ProjEX) program has as its goal, the reduction of energy required for production mining and secondary breakage through the use of a projectile based excavation system. It depends on the development of a low cost family of projectiles that will penetrate and break up different types of ore/rock and a low cost electric launch system. The electric launch system will eliminate the need for high cost propellant investigated for similar concepts in the past. This document reports on the progress made in the program during the past quarter. It reports on projectile development and the development of the electric launch system design.

  20. Impact response of graphite-epoxy flat laminates using projectiles that simulate aircraft engine encounters

    NASA Technical Reports Server (NTRS)

    Preston, J. L., Jr.; Cook, T. S.

    1975-01-01

    An investigation of the response of a graphite-epoxy material to foreign object impact was made by impacting spherical projectiles of gelatin, ice, and steel normally on flat panels. The observed damage was classified as transverse (stress wave delamination and cracking), penetrative, or structural (gross failure): the minimum, or threshold, velocity to cause each class of damage was established as a function of projectile characteristics. Steel projectiles had the lowest transverse damage threshold, followed by gelatin and ice. Making use of the threshold velocities and assuming that the normal component of velocity produces the damage in nonnormal impacts, a set of impact angles and velocities was established for each projectile material which would result in damage to composite fan blades. Analysis of the operating parameters of a typical turbine fan blade shows that small steel projectiles are most likely to cause delamination and penetration damage to unprotected graphite-epoxy composite fan blades.

  1. Foil support structure for large electron guns

    SciTech Connect

    Brucker, J.P.; Rose, E.A.

    1993-08-01

    This paper describes a novel support structure for a vacuum diode used to pump a gaseous laser with an electron beam. Conventional support structures are designed to hold a foil flat and rigid. This new structure takes advantage of the significantly greater strength of metals in pure tension, utilizing curved shapes for both foil and support structure. The shape of the foil is comparable to the skin of a balloon, and the shape of the support structures is comparable to the cables of a suspension bridge. This design allows a significant reduction in foil thickness and support structure mass, resulting in a lower electron-beam loss between diode and laser gas. In addition, the foil is pre-formed in the support structure at pressures higher than operating pressure. Therefore, the foil is operated far from the yield point. Increased reliability is anticipated.

  2. Electronic structure calculations in arbitrary electrostatic environments

    NASA Astrophysics Data System (ADS)

    Watson, Mark A.; Rappoport, Dmitrij; Lee, Elizabeth M. Y.; Olivares-Amaya, Roberto; Aspuru-Guzik, Alán

    2012-01-01

    Modeling of electronic structure of molecules in electrostatic environments is of considerable relevance for surface-enhanced spectroscopy and molecular electronics. We have developed and implemented a novel approach to the molecular electronic structure in arbitrary electrostatic environments that is compatible with standard quantum chemical methods and can be applied to medium-sized and large molecules. The scheme denoted CheESE (chemistry in electrostatic environments) is based on the description of molecular electronic structure subject to a boundary condition on the system/environment interface. Thus, it is particularly suited to study molecules on metallic surfaces. The proposed model is capable of describing both electrostatic effects near nanostructured metallic surfaces and image-charge effects. We present an implementation of the CheESE model as a library module and show example applications to neutral and negatively charged molecules.

  3. The Electronic Structure of Amorphous Carbon Nanodots.

    PubMed

    Margraf, Johannes T; Strauss, Volker; Guldi, Dirk M; Clark, Timothy

    2015-06-18

    We have studied hydrogen-passivated amorphous carbon nanostructures with semiempirical molecular orbital theory in order to provide an understanding of the factors that affect their electronic properties. Amorphous structures were first constructed using periodic calculations in a melt/quench protocol. Pure periodic amorphous carbon structures and their counterparts doped with nitrogen and/or oxygen feature large electronic band gaps. Surprisingly, descriptors such as the elemental composition and the number of sp(3)-atoms only influence the electronic structure weakly. Instead, the exact topology of the sp(2)-network in terms of effective conjugation defines the band gap. Amorphous carbon nanodots of different structures and sizes were cut out of the periodic structures. Our calculations predict the occurrence of localized electronic surface states, which give rise to interesting effects such as amphoteric reactivity and predicted optical band gaps in the near-UV/visible range. Optical and electronic gaps display a dependence on particle size similar to that of inorganic colloidal quantum dots. PMID:25731776

  4. Aerodynamic flail for a spinning projectile

    DOEpatents

    Cole, James K.

    1990-05-01

    A flail is provided which reduces the spin of a projectile in a recovery system which includes a parachute, a cable connected to the parachute, a swivel, and means for connecting the swivel to the projectile. The flail includes a plurality of flexible filaments and a rotor for attaching the filaments to the front end of the projectile. The rotor is located radially with respect to the spinning axis of the projectile. In one embodiment, the projectile includes a first nose cone section housing a deployable spin damping assembly; a second nose cone section, housing a deployable parachute assembly; a shell section, supporting the first and second nose cone sections during flight of the projectile; a mechanism for releasing the first nose cone section from the second cone section; and a mechanism for releasing the second nose cone section from the shell section. In operation of this embodiment, the deployable spin damping assembly deploys during flight of the projectile when the mechanism for releasing the first nose cone section from the second nose cone section are actuated. Then, upon actuation of the mechanism for releasing the second nose cone section from the shell section, two things happen: the spin damping assembly separates from the projectile; and the deployable parachute assembly is deployed.

  5. Aerodynamic flail for a spinning projectile

    DOEpatents

    Cole, James K.

    1990-01-01

    A flail is provided which reduces the spin of a projectile in a recovery system which includes a parachute, a cable connected to the parachute, a swivel, and means for connecting the swivel to the projectile. The flail includes a plurality of flexible filaments and a rotor for attaching the filaments to the front end of the projectile. The rotor is located radially with respect to the spinning axis of the projectile. In one embodiment, the projectile includes a first nose cone section housing a deployable spin damping assembly; a second nose cone section, housing a deployable parachute assembly; a shell section, supporting the first and second nose cone sections during flight of the projectile; a mechanism for releasing the first nose cone section from the second cone section; and a mechanism for releasing the second nose cone section from the shell section. In operation of this embodiment, the deployable spin damping assembly deploys during flight of the projectile when the mechanism for releasing the first nose cone section from the second nose cone section are actuated. Then, upon actuation of the mechanism for releasing the second nose cone section from the shell section, two things happen: the spin damping assembly separates from the projectile; and the deployable parachute assembly is deployed.

  6. Graphical Method for Determining Projectile Trajectory

    ERIC Educational Resources Information Center

    Moore, J. C.; Baker, J. C.; Franzel, L.; McMahon, D.; Songer, D.

    2010-01-01

    We present a nontrigonometric graphical method for predicting the trajectory of a projectile when the angle and initial velocity are known. Students enrolled in a general education conceptual physics course typically have weak backgrounds in trigonometry, making inaccessible the standard analytical calculation of projectile range. Furthermore,…

  7. REDUCED ENERGY CONSUMPTION THROUGH PROJECTILE BASED EXCAVATION

    SciTech Connect

    Unknown

    2001-10-12

    The hypothesis to be tested is that the addition of steel or other synthetic fiber and/or high strength, low cost aggregate to strong grouts or concrete will result in a projectile of sufficient strength to produce cracking and spall enough to make its use cost effective for mining. Based on experiments conducted to date, no conclusions can yet be reached. Results of the experiments conducted suggest that reinforcement of a concrete projectile can yield performance that portends cost effective projectile based excavation. It is recognized that the projectile is but one component of the matrix. The electric launch system to be developed in the next phase of the program is the other factor that weighs heavily in the cost effectiveness equation. At this point, however, emerging low cost options for the projectile are very promising.

  8. Structure and Dynamics with Ultrafast Electron Microscopes

    NASA Astrophysics Data System (ADS)

    Siwick, Bradley

    In this talk I will describe how combining ultrafast lasers and electron microscopes in novel ways makes it possible to directly `watch' the time-evolving structure of condensed matter, both at the level of atomic-scale structural rearrangements in the unit cell and at the level of a material's nano- microstructure. First, I will briefly describe my group's efforts to develop ultrafast electron diffraction using radio- frequency compressed electron pulses in the 100keV range, a system that rivals the capabilities of xray free electron lasers for diffraction experiments. I will give several examples of the new kinds of information that can be gleaned from such experiments. In vanadium dioxide we have mapped the detailed reorganization of the unit cell during the much debated insulator-metal transition. In particular, we have been able to identify and separate lattice structural changes from valence charge density redistribution in the material on the ultrafast timescale. In doing so we uncovered a previously unreported optically accessible phase/state of vanadium dioxide that has monoclinic crystallography like the insulator, but electronic structure and properties that are more like the rutile metal. We have also combined these dynamic structural measurements with broadband ultrafast spectroscopy to make detailed connections between structure and properties for the photoinduced insulator to metal transition. Second, I will show how dynamic transmission electron microscopy (DTEM) can be used to make direct, real space images of nano-microstructural evolution during laser-induced crystallization of amorphous semiconductors at unprecedented spatio-temporal resolution. This is a remarkably complex process that involves several distinct modes of crystal growth and the development of intricate microstructural patterns on the nanosecond to ten microsecond timescales all of which can be imaged directly with DTEM.

  9. Non-invasive timing of gas gun projectiles with light detection and ranging

    NASA Astrophysics Data System (ADS)

    Goodwin, P. M.; Bartram, B. D.; Gibson, L. L.; Wu, M.; Dattelbaum, D. M.

    2014-05-01

    We have developed a Light Detection and Ranging (LIDAR) diagnostic to track the position of a projectile inside of a gas gun launch tube in real-time. This capability permits the generation of precisely timed trigger pulses useful for triggering high-latency diagnostics such as a flash lamp-pumped laser. An initial feasibility test was performed using a 72 mm bore diameter single-stage gas gun routinely used for dynamic research at Los Alamos. A 655 nm pulsed diode laser operating at a pulse repetition rate of 100 kHz was used to interrogate the position of the moving projectile in real-time. The position of the projectile in the gun barrel was tracked over a distance of ~ 3 meters prior to impact. The position record showed that the projectile moved at a velocity of 489 m/s prior to impacting the target. This velocity was in good agreement with independent measurements of the projectile velocity by photon Doppler velocimetry and timing of the passage of the projectile through optical marker beams positioned at the muzzle of the gun. The time-to-amplitude conversion electronics used enable the LIDAR data to be processed in real-time to generate trigger pulses at preset separations between the projectile and target.

  10. Electronic structure of disordered conjugated polymers: Polythiophenes

    SciTech Connect

    Vukmirovic, Nenad; Wang, Lin-Wang

    2008-11-26

    Electronic structure of disordered semiconducting conjugated polymers was studied. Atomic structure was found from a classical molecular dynamics simulation and the charge patching method was used to calculate the electronic structure with the accuracy similar to the one of density functional theory in local density approximation. The total density of states, the local density of states at different points in the system and the wavefunctions of several states around the gap were calculated in the case of poly(3-hexylthiophene) (P3HT) and polythiophene (PT) systems to gain insight into the origin of disorder in the system, the degree of carrier localization and the role of chain interactions. The results indicated that disorder in the electronic structure of alkyl substituted polythiophenes comes from disorder in the conformation of individualchains, while in the case of polythiophene there is an additional contribution due to disorder in the electronic coupling between the chains. Each of the first several wavefunctions in the conduction and valence band of P3HT is localized over several rings of a single chain. It was shown that the localization can be caused in principle both by ring torsions and chain bending, however the effect of ring torsions is much stronger. PT wavefunctions are more complicated due to larger interchain electronic coupling and are not necessarily localized on a single chain.

  11. Defect Induced Electronic Structure of Uranofullerene

    PubMed Central

    Dai, Xing; Cheng, Cheng; Zhang, Wei; Xin, Minsi; Huai, Ping; Zhang, Ruiqin; Wang, Zhigang

    2013-01-01

    The interaction between the inner atoms/cluster and the outer fullerene cage is the source of various novel properties of endohedral metallofullerenes. Herein, we introduce an adatom-type spin polarization defect on the surface of a typical endohedral stable U2@C60 to predict the associated structure and electronic properties of U2@C61 based on the density functional theory method. We found that defect induces obvious changes in the electronic structure of this metallofullerene. More interestingly, the ground state of U2@C61 is nonet spin in contrast to the septet of U2@C60. Electronic structure analysis shows that the inner U atoms and the C ad-atom on the surface of the cage contribute together to this spin state, which is brought about by a ferromagnetic coupling between the spin of the unpaired electrons of the U atoms and the C ad-atom. This discovery may provide a possible approach to adapt the electronic structure properties of endohedral metallofullerenes. PMID:23439318

  12. Membrane protein structure determination by electron crystallography

    PubMed Central

    Ubarretxena-Belandia, Iban; Stokes, David L.

    2012-01-01

    During the past year, electron crystallography of membrane proteins has provided structural insights into the mechanism of several different transporters and into their interactions with lipid molecules within the bilayer. From a technical perspective there have been important advances in high-throughput screening of crystallization trials and in automated imaging of membrane crystals with the electron microscope. There have also been key developments in software, and in molecular replacement and phase extension methods designed to facilitate the process of structure determination. PMID:22572457

  13. The Electronic Structure of Heavy Element Complexes

    SciTech Connect

    Bursten, Bruce E.

    2000-07-25

    The area of study is the bonding in heavy element complexes, and the application of more sophisticated electronic structure theories. Progress is recounted in several areas: (a) technological advances and current methodologies - Relativistic effects are extremely important in gaining an understanding of the electronic structure of compounds of the actinides, transactinides, and other heavy elements. Therefore, a major part of the continual benchmarking was the proper inclusion of the appropriate relativistic effects for the properties under study. (b) specific applications - These include organoactinide sandwich complexes, CO activation by actinide atoms, and theoretical studies of molecules of the transactinide elements. Finally, specific directions in proposed research are described.

  14. Ionization of water molecules by fast charged projectiles

    SciTech Connect

    Dubois, A.; Carniato, S.; Fainstein, P. D.; Hansen, J. P.

    2011-07-15

    Single-ionization cross sections of water molecules colliding with fast protons are calculated from lowest-order perturbation theory by taking all electrons and molecular orientations consistently into account. Explicit analytical formulas based on the peaking approximation are obtained for differential ionization cross sections with the partial contribution from the various electron orbitals accounted for. The results, which are in very good agreement with total and partial cross sections at high electron and projectile energies, display a strong variation on molecular orientation and molecular orbitals.

  15. The influence of projectile ion induced chemistry on surface pattern formation

    NASA Astrophysics Data System (ADS)

    Karmakar, Prasanta; Satpati, Biswarup

    2016-07-01

    We report the critical role of projectile induced chemical inhomogeneity on surface nanostructure formation. Experimental inconsistency is common for low energy ion beam induced nanostructure formation in the presence of uncontrolled and complex contamination. To explore the precise role of contamination on such structure formation during low energy ion bombardment, a simple and clean experimental study is performed by selecting mono-element semiconductors as the target and chemically inert or reactive ion beams as the projectile as well as the source of controlled contamination. It is shown by Atomic Force Microscopy, Cross-sectional Transmission Electron Microscopy, and Electron Energy Loss Spectroscopy measurements that bombardment of nitrogen-like reactive ions on Silicon and Germanium surfaces forms a chemical compound at impact zones. Continuous bombardment of the same ions generates surface instability due to unequal sputtering and non-uniform re-arrangement of the elemental atom and compound. This instability leads to ripple formation during ion bombardment. For Argon-like chemically inert ion bombardment, the chemical inhomogeneity induced boost is absent; as a result, no ripples are observed in the same ion energy and fluence.

  16. Electronic structure in the crossover regimes in lower dimensional structures

    NASA Astrophysics Data System (ADS)

    Batabyal, R.; Dev, B. N.

    2014-11-01

    Modern growth and fabrication techniques can produce lower dimensional structures in the crossover regimes. Such structures in the crossover regimes can provide tunability of various properties of materials. For example, a zero-dimensional (0-D) structure (quantum dot) evolving towards a 3-D structure (bulk) shows electronic structure, which is neither 0-D-like, nor 3-D-like in the dimensional crossover regime. Within the crossover regime the electronic density of states (DOS) at Fermi level (Ef) keeps on changing as the size of the system changes. DOS at Ef determines many properties of materials, such as electronic specific heat, spin susceptibility, etc. Such properties can be tuned by controlling the size of the system in the crossover regimes. Keeping the importance of DOS at Ef in mind, we determine their values and other details of electronic structure of lower dimensional structures, in the 0-D to 1-D, 1-D to 2-D, 2-D to 3-D, 0-D to 2-D, 0-D to 3-D and 1-D to 3-D crossover regimes, in a simple free electron model. We compare our results with analytical theory and experimental results, wherever available. We also present some results obtained by scanning tunneling spectroscopy measurements on Ag islands on Si(1 1 1) substrates evolving from a 0-D to a 2-D structure. This simple model is quite useful in understanding lower dimensional structures in the crossover regimes and, in general, in nanoscale science. Fabrication of such structures would provide control on materials properties.

  17. Cavity dynamics and particle alignment in the wake of a supersonic projectile penetrating a dusty plasma

    SciTech Connect

    Arp, O.; Caliebe, D.; Piel, A.

    2011-06-15

    The penetration of a projectile into a strongly coupled dusty plasma was studied in a radio-frequency discharge under microgravity conditions. A supersonic projectile produces an elongated dust-free cavity in its wake. The dynamics of the cavity is analyzed and compared with Langevin dynamics simulations. Besides a three-dimensional Mach cone structure, the simulation shows that the cavity dynamics can be subdivided into three phases: An opening phase with fixed time scale, a closing phase, whose duration is affected by the projectile speed and, finally, a phase of particle realignment in the target cloud, which persists for a long time after the closure of the cavity.

  18. Structure refinement from precession electron diffraction data.

    PubMed

    Palatinus, Lukáš; Jacob, Damien; Cuvillier, Priscille; Klementová, Mariana; Sinkler, Wharton; Marks, Laurence D

    2013-03-01

    Electron diffraction is a unique tool for analysing the crystal structures of very small crystals. In particular, precession electron diffraction has been shown to be a useful method for ab initio structure solution. In this work it is demonstrated that precession electron diffraction data can also be successfully used for structure refinement, if the dynamical theory of diffraction is used for the calculation of diffracted intensities. The method is demonstrated on data from three materials - silicon, orthopyroxene (Mg,Fe)(2)Si(2)O(6) and gallium-indium tin oxide (Ga,In)(4)Sn(2)O(10). In particular, it is shown that atomic occupancies of mixed crystallographic sites can be refined to an accuracy approaching X-ray or neutron diffraction methods. In comparison with conventional electron diffraction data, the refinement against precession diffraction data yields significantly lower figures of merit, higher accuracy of refined parameters, much broader radii of convergence, especially for the thickness and orientation of the sample, and significantly reduced correlations between the structure parameters. The full dynamical refinement is compared with refinement using kinematical and two-beam approximations, and is shown to be superior to the latter two. PMID:23403968

  19. Projectile channeling in chain bundle dusty plasma liquids: Wave excitation and projectile-wave interaction

    SciTech Connect

    Chang, Mei-Chu; Tseng, Yu-Ping; I, Lin

    2011-03-15

    The microscopic channeling dynamics of projectiles in subexcitable chain bundle dusty plasma liquids consisting of long chains of negatively charged dusts suspended in low pressure glow discharges is investigated experimentally using fast video-microscopy. The long distance channeling of the projectile in the channel formed by the surrounding dust chain bundles and the excitation of a narrow wake associated with the elliptical motions of the background dusts are demonstrated. In the high projectile speed regime, the drag force due to wake wave excitation increases with the decreasing projectile speed. The excited wave then leads the slowed down projectile after the projectile speed is decreased below the resonant speed of wave excitation. The wave-projectile interaction causes the increasing projectile drag below the resonant speed and the subsequent oscillation around a descending average level, until the projectile settles down to the equilibrium point. Long distance projectile surfing through the resonant crest trapping by the externally excited large amplitude solitary wave is also demonstrated.

  20. Electronic structure engineering of various structural phases of phosphorene.

    PubMed

    Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K

    2016-07-21

    We report the tailoring of the electronic structures of various structural phases of phosphorene (α-P, β-P, γ-P and δ-P) based homo- and hetero-bilayers through in-plane mechanical strains, vertical pressure and transverse electric field by employing density functional theory. In-plane biaxial strains have considerably modified the electronic bandgap of both homo- and hetero-bilayers while vertical pressure induces metallization in the considered structures. The γ-P homo-bilayer structure showed the highest ultimate tensile strength (UTS ∼ 6.21 GPa) upon in-plane stretching. Upon application of a transverse electric field, the variation in the bandgap of hetero-bilayers was found to be strongly dependent on the polarity of the applied field which is attributed to the counterbalance between the external electric field and the internal field induced by different structural phases and heterogeneity in the arrangements of atoms of each surface of the hetero-bilayer system. Our results demonstrate that the electronic structures of the considered hetero- and homo-bilayers of phosphorene could be modified by biaxial strain, pressure and electric field to achieve the desired properties for future nano-electronic devices. PMID:27334095

  1. Projectile dynamics at low barrel pressures

    NASA Astrophysics Data System (ADS)

    Chankaev, S. K.; Yakovlev, V. Ya.

    2007-11-01

    A mathematical model for a projectile shot at low pressures in the space behind the projectile space is developed. The pressure rise is limited because of the nonsimultaneity of propellant ignition and combustion and the discharge of the propellant combustion products through the gap between the projectile and the walls of the gun barrel. The kinetic characteristics of flame propagation over the propellant particles are determined. A comparison of calculation and experimental data is performed. The calculation results are used in designing 2A85 self-propelled launchers and upgrading 2A30 self-propelled launchers.

  2. Effects of barrel joints on hypervelocity projectiles

    SciTech Connect

    Shahinpoor, M.; Asay, J.R.; Dixon, W.R.; Hawke, R.S.

    1987-01-01

    Development of new hypervelocity launchers is necessary for equation of state (EOS) studies at high impact velocities. The requirements for barrel joint alignment and concentricity at high velocities place severe constraints on fabrication and assembly procedures; small steps or longitudinal direction changes at joints may cause major damage to precision projectiles. Research has been initiated to identify the technical limits of fabrication and assembly tolerances for hypervelocity gun barrels. Numerical and experimental studies have evaluated projectile performance at velocities of 6 to 15 km/s and have identified failure modes for Lexan projectiles with thin metal facings.

  3. Electronic structure and electron momentum density in TiSi

    NASA Astrophysics Data System (ADS)

    Ghaleb, A. M.; Mohammad, F. M.; Sahariya, Jagrati; Sharma, Mukesh; Ahuja, B. L.

    2013-03-01

    We report the electron momentum density in titanium monosilicide using 241Am Compton spectrometer. Experimental Compton profile has been compared with the theoretical profiles computed using linear combination of atomic orbitals (LCAO). The energy bands, density of states and Fermi surface structures of TiSi are reported using the LCAO and the full potential linearized augmented plane wave methods. Theoretical anisotropies in directional Compton profiles are interpreted in terms of energy bands. To confirm the conducting behavior, we also report the real space analysis of experimental Compton profile of TiSi.

  4. Electronic structure of bacterial surface protein layers

    SciTech Connect

    Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L.

    2008-01-15

    We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer (S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

  5. Electronic structures of carbon nanotube peopods

    NASA Astrophysics Data System (ADS)

    Kuk, Young

    2003-03-01

    Carbon nanotubes have been successfully used for nanometer-sized devices such as diodes and transistors. These discrete devices utilize the spatially varying electronic structures of processed nanotubes by creating defect junctions or introducing substitutional or interstitial dopants. It was recently found that adsorption or insertion of molecules inside or outside of a nanotube modifies the electronic structure as observed with a low-temperature scanning tunneling microscope (LTSTM). We report a method to form spatial variation of the electronic structure by inserting various molecules such as fullerenes, metallo-fullerenes, metals or insulators. The results suggest that one can synthesize this band gap-engineered 1-dimensional wire by self-assembly instead of epitaxial growth. We propose a new type of device structure made by this processing technology. 1. J. Lee, H.J. Kim, G. Kim, Y.-W. Son, J. Ihm, S.J. Kahng, H. Kato, Z.W. Wang, T. Okazaki, H. Shinohara, and Y. Kuk, Nature, 415, 1005 (2002)

  6. Electronic structure theory: Applications and geometrical aspects

    NASA Astrophysics Data System (ADS)

    Coh, Sinisa

    This thesis contains several applications of the first-principles electronic-structure theory with special emphasis in parts of the thesis on the geometrical aspects of the theory. We start by reviewing the basics of the first-principles electronic-structure methods which are then used throughout the thesis. The first application of these methods is on the analysis of the stability and lattice dynamics of alpha- and beta-cristobalite phases of SiO2. We also map the complete low-energy landscape connecting these two structures and give implications on the phase transition in this compound. Next we study a family of Pbnm perovskites that are promising candidates for silicon-compatible high-K dielectrics. We calculate their structure and dielectric response, and compare with experimental results where available. The third application of these methods is to the large isosymmetric reorientation of oxygen octahedra rotation axes in epitaxially strained perovskites. We explain the origin of the peculiar energy landscape topology as a function of epitaxial strain. In the part of the thesis devoted to the geometrical aspects of electronic structure theory, we begin by extending the concept of electronic polarization to a Chern insulators. These insulators are characterized by a non-zero off-diagonal sigma_xy conductivity tensor component, quantized in units of e 2/h. Finally we discuss another geometrical quantity, the Chern-Simons orbital magnetoelectric coupling. We present a first-principles based calculation of this quantity in several compounds, and motivated by recent developments in the theory of topological insulators, we speculate about the existence of "large-theta materials," in which this kind of coupling could be unusually large.

  7. Electromagnetic theta gun and tubular projectiles

    SciTech Connect

    Burgess, T.J.; Cnare, E.C.; Oberkampf, W.L.; Beard, S.G.; Cowan, M.

    1980-12-01

    Unlike the better known rail gun, the theta gun applies the propelling force along the length of its projectile. This is shown to allow much greater acceleration of high fineness ratio projectiles for a given barrel pressure, allowing much shorter barrels for military applications. A computer code which simulates performance of the theta gun is described and experimental results from a few simple, low energy experiments show close agreement with code predictions. Trajectories and aerodynamic heating for three candidate military projectiles are calculated for vertical and horizontal atmospheric launches where initial velocity is as high as 3 km/s. The calculations indicate that in some cases a thin layer of heatshield (ablator) will be required to control projectile heating.

  8. Hypervelocity High Speed Projectile Imagery and Video

    NASA Technical Reports Server (NTRS)

    Henderson, Donald J.

    2009-01-01

    This DVD contains video showing the results of hypervelocity impact. One is showing a projectile impact on a Kevlar wrapped Aluminum bottle containing 3000 psi gaseous oxygen. One video show animations of a two stage light gas gun.

  9. REDUCED ENERGY CONSUMPTION THROUGH PROJECTILE BASED EXCAVATION

    SciTech Connect

    Mark Machina

    2003-06-06

    The Projectile Based Excavation (ProjEX) program has as its goal, the reduction of energy required for production mining and secondary breakage through the use of a projectile based excavation system. It depends on the development of a low cost family of projectiles that will penetrate and break up different types of ore/rock and a low cost electric launch system. The electric launch system will eliminate the need for high cost propellant considered for similar concepts in the past. This document reports on the program findings through the first two phases. It presents projectile design and experiment data and the preliminary design for electric launch system. Advanced Power Technologies, Inc., now BAE SYSTEMS Advanced Technologies, Inc., was forced to withdraw from the program with the loss of one of our principal mining partners, however, the experiments conducted suggest that the approach is feasible and can be made cost effective.

  10. Electronic structure of oxygen functionalized graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Simbeck, Adam; Gu, Deyang; Kharche, Neerav; Nayak, Saroj

    2013-03-01

    We investigate the electronic and magnetic properties of armchair graphene nanoribbons whose edges are passivated by oxygen. Using a first-principles density functional approach and the many-body GW method we find that oxygen-passivation results in a rich geometrical environment which in turn determines the electronic and magnetic properties of the ribbon. For planar systems we report magnetic ground states whose electronic structure depends upon the magnetic coupling between edges. For non-planar ribbons we report a nonmagnetic ground state with a band gap that decreases as a function of increasing ribbon width. Our results will be discussed in light of previous experimental and computational studies. Interconnect Focus Center (MARCO program), State of New York, NSF IGERT program, Grant no. 0333314, and computing resources of the Computationial Center for Nanotechnology Innovation (CCNI), RPI

  11. Probing Structural and Electronic Dynamics with Ultrafast Electron Microscopy

    SciTech Connect

    Plemmons, DA; Suri, PK; Flannigan, DJ

    2015-05-12

    In this Perspective, we provide an overview,of the field of ultrafast electron microscopy (UEM). We begin by briefly discussing the emergence of methods for probing ultrafast structural dynamics and the information that can be obtained. Distinctions are drawn between the two main types a probes for femtosecond (fs) dynamics fast electrons and X-ray photons and emphasis is placed on hour the nature of charged particles is exploited in ultrafast electron-based' experiments:. Following this, we describe the versatility enabled by the ease with which electron trajectories and velocities can be manipulated with transmission electron microscopy (TEM): hardware configurations, and we emphasize how this is translated to the ability to measure scattering intensities in real, reciprocal, and energy space from presurveyed and selected rianoscale volumes. Owing to decades of ongoing research and development into TEM instrumentation combined with advances in specimen holder technology, comprehensive experiments can be conducted on a wide range of materials in various phases via in situ methods. Next, we describe the basic operating concepts, of UEM, and we emphasize that its development has led to extension of several of the formidable capabilities of TEM into the fs domain, dins increasing the accessible temporal parameter spade by several orders of magnitude. We then divide UEM studies into those conducted in real (imaging), reciprocal (diffraction), and energy (spectroscopy) spate. We begin each of these sections by providing a brief description of the basic operating principles and the types of information that can be gathered followed by descriptions of how these approaches are applied in UM, the type of specimen parameter space that can be probed, and an example of the types of dynamics that can be resolved. We conclude with an Outlook section, wherein we share our perspective on some future directions of the field pertaining to continued instrument development and

  12. Graphical Method for Determining Projectile Trajectory

    NASA Astrophysics Data System (ADS)

    Moore, J. C.; Baker, J. C.; Franzel, L.; McMahon, D.; Songer, D.

    2010-12-01

    We present a nontrigonometric graphical method for predicting the trajectory of a projectile when the angle and initial velocity are known. Students enrolled in a general education conceptual physics course typically have weak backgrounds in trigonometry, making inaccessible the standard analytical calculation of projectile range. Furthermore, research shows that standard instructional techniques fail to confront student misconceptions about motion in a gravitational field.1-4 We have designed a guided inquiry-based lesson that specifically addresses these misconceptions with minimal mathematics.

  13. Elastic scattering with weakly bound projectiles

    SciTech Connect

    Figueira, J. M.; Abriola, D.; Arazi, A.; Capurro, O. A.; Marti, G. V.; Martinez Heinmann, D.; Pacheco, A. J.; Testoni, J. E.; Barbara, E. de; Fernandez Niello, J. O.; Padron, I.; Gomes, P. R. S.; Lubian, J.

    2007-02-12

    Possible effects of the break-up channel on the elastic scattering threshold anomaly has been investigated. We used the weakly bound 6,7Li nuclei, which is known to undergo break-up, as projectiles in order to study the elastic scattering on a 27Al target. In this contribution we present preliminary results of these experiments, which were analyzed in terms of the Optical Model and compared with other elastic scattering data using weakly bound nuclei as projectile.

  14. Electronic Structure of Iridium Clusters on Graphene

    NASA Astrophysics Data System (ADS)

    Barker, Bradford A.; Bradley, Aaron J.; Ugeda, Miguel M.; Coh, Sinisa; Zettl, Alex; Crommie, Michael F.; Cohen, Marvin L.; Louie, Steven G.

    2015-03-01

    Graphene was predicted to exhibit non-trivial Z2 topology, but its exceedingly weak spin-orbit coupling prevented this from being observed. Previous theoretical work has proposed enhancing the spin-orbit coupling strength by depositing individual adatoms adsorbed onto the surface of graphene. We show experimental evidence that the iridium adatoms cluster, with a cluster size of at least two atoms. We investigate through theoretical calculations the orientation of the iridium dimers on graphene, contrast the electronic structure of iridium dimers with iridium monomers, and compare the theoretical iridium dimer electronic structure calculations with the experimental results determined via scanning tunneling spectroscopy. This work was supported by NSF Grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility.

  15. Electronic structure of the multivacancies in Si

    NASA Astrophysics Data System (ADS)

    Ren, Shang Yuan; Mao, Deqiang; Li, Mingfu

    A complete set of equations for determining the energy levels and the wavefunctions with different symmetries of electronic states of several well-known multivacancies in Si is given using the Koster-Slater Green's function method. By using an empirical tight binding Hamiltonian for the band structure of the host and the central-cell perturbation approximation for the defect, only the on-site and the off-site Green's functions of the host and their derivatives with respect to energy E appear in these equations. The electronic structure of the ideal multivacancies, especially the divacancy, are investigated and compared with known experimental results and previous qualitative analyses. Some misunderstandings of the experimental results are analyzed. The wavefunctions of some multivacancy states are accurately evaluated and compared with the EPR and ENDOR data for the first time.

  16. Electronic structure tuning of diamondoids through functionalization

    NASA Astrophysics Data System (ADS)

    Rander, Torbjörn; Staiger, Matthias; Richter, Robert; Zimmermann, Tobias; Landt, Lasse; Wolter, David; Dahl, Jeremy E.; Carlson, Robert M. K.; Tkachenko, Boryslav A.; Fokina, Natalie A.; Schreiner, Peter R.; Möller, Thomas; Bostedt, Christoph

    2013-01-01

    We investigated the changes in electronic structures induced by chemical functionalization of the five smallest diamondoids using valence photoelectron spectroscopy. Through the variation of three parameters, namely functional group (thiol, hydroxy, and amino), host cluster size (adamantane, diamantane, triamantane, [121]tetramantane, and [1(2,3)4]pentamantane), and functionalization site (apical and medial) we are able to determine to what degree these affect the electronic structures of the overall systems. We show that unlike, for example, in the case of halobenzenes, the ionization potential does not show a linear dependence on the electronegativity of the functional group. Instead, a linear correlation exists between the HOMO-1 ionization potential and the functional group electronegativity. This is due to localization of the HOMO on the functional group and the HOMO-1 on the diamondoid cage. Density functional theory supports our interpretations.

  17. Structural and electronic properties of sodium nanoclusters

    NASA Astrophysics Data System (ADS)

    Perez, Luis A.; Reyes-Nava, Juan A.; Garzon, Ignacio L.

    2006-03-01

    Recent advances on mass selection of sodium nanoclusters and their characterization by photoemission electron spectroscopy [1] have given useful data for a variety of clusters sizes. These data may lead to assignments of the relevant structures by comparing the measured photoelectron spectra (PES) with the electronic density of states (DOS) obtained from DFT calculations. In this work, the lowest energy structures modeled by the many-body Gupta potential, are obtained by using molecular dynamics simulations for Nan (n= 178, 204, 271, 298-300, 309). DFT calculations were then performed for neutral, positively- and negatively-charged Nan clusters. A comparison between the DOS of clusters of the same size but different charge will be presented, as well as between the available experimental PES and the theoretical obtained DOS.[1] H. Haberland, T. Hippler, J. Donges, O. Kostko, M. Schmidt, B. von Issendorff, Phys. Rev. Lett. 94, 035701 (2005).

  18. Structural and electronic properties of thallium compounds

    NASA Astrophysics Data System (ADS)

    Paliwal, Neetu; Srivastava, Vipul

    2016-05-01

    The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA has been used to calculate structural and electronic properties of thallium pnictides TlX (X=Sb, Bi) at high pressure. As a function of volume, the total energy is evaluated. Apart from this, the lattice parameter (a0), bulk modulus (B0), band structure (BS) and density of states (DOS) are calculated. From energy band diagram we observed metallic behaviour in TlSb and TlBi compounds. The values of equilibrium lattice constants and bulk modulus are agreed well with the available data.

  19. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  20. Polycrystalline graphene with single crystalline electronic structure.

    PubMed

    Brown, Lola; Lochocki, Edward B; Avila, José; Kim, Cheol-Joo; Ogawa, Yui; Havener, Robin W; Kim, Dong-Ki; Monkman, Eric J; Shai, Daniel E; Wei, Haofei I; Levendorf, Mark P; Asensio, María; Shen, Kyle M; Park, Jiwoong

    2014-10-01

    We report the scalable growth of aligned graphene and hexagonal boron nitride on commercial copper foils, where each film originates from multiple nucleations yet exhibits a single orientation. Thorough characterization of our graphene reveals uniform crystallographic and electronic structures on length scales ranging from nanometers to tens of centimeters. As we demonstrate with artificial twisted graphene bilayers, these inexpensive and versatile films are ideal building blocks for large-scale layered heterostructures with angle-tunable optoelectronic properties. PMID:25207847

  1. Smart electronics and MEMS for aerospace structures

    NASA Astrophysics Data System (ADS)

    Varadan, Vijay K.; Varadan, Vasundara V.

    1995-09-01

    In this paper, smart electronics and MEMS are employed to sense and control the drag in aircraft structures. The sensors are fabricated with interdigital transducers printed on a piezoelectric polymer. They in turn are mounted onto an ultra thin Penn State's novel RF antenna (Patent field). The sensor are designed to measure both pressure and shear of the fluid flow on aerospace structures. The wave form measurements may be monitored at a remote location either at the cockpit or elsewhere via the antennas in the sensors and an outside antenna. The integrated MEMS actuators which comprise of cantilever-, diaphram- and microbridge-based MEMS with suitable smart electronics etched onto the structure are controlled by the built-in antennas through feedback and feedforward control architecture. The integration of such materials and smart electronics into the skin of airfoil is ideal for sensing and controlling drag. The basic idea of this concept involves detection of the point of transition from laminar to turbulent flow and transmitting acoustical energy into the boundary layer so that the low energy fluid particles accelerate in the transverse direction and mix with the high energy flow outside of the boundary layer. 3D microriblets can be fabricated using stereo lithography and UV curable conducting polymers. The control of drag using these active microriblets are outlined.

  2. Investigations of nuclear structure and nuclear reactions induced by complex projectiles. Progress report for the period September 1, 1992--August 31, 1993

    SciTech Connect

    Sarantites, D.G.

    1993-09-06

    This is a progress report on activities of the Washington University group in nuclear reaction studies for the period Sept 1, 1992 to Aug 31, 1993. This group has a research program which touches five areas of nuclear physics: nuclear structure studies at high spin; studies at the interface between structure and reactions; production and study of hot nuclei; reaction mechanism studies; development and use of novel techniques and instrumentation in the above areas of research. Specific activities of the group include in part: superdeformation in {sup 82}Sr; structure of and identical bands in {sup 182}Hg and {sup 178}Pt; a highly deformed band in {sup 136}Pm; particle decay of the {sup 164}Yb compound nucleus; fusion reactions; proton evaporation; two-proton decay of {sup 12}O; modeling and theoretical studies; excited {sup 16}O disassembly into four alpha particles; {sup 209}Bi + {sup 136}Xe collisions at 28.2 MeV/amu; and development work on 4{pi} solid angle gamma detectors, and x-ray detectors.

  3. Thermal transfer structures coupling electronics card(s) to coolant-cooled structure(s)

    DOEpatents

    David, Milnes P; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Parida, Pritish R; Schmidt, Roger R

    2014-12-16

    Cooling apparatuses and coolant-cooled electronic systems are provided which include thermal transfer structures configured to engage with a spring force one or more electronics cards with docking of the electronics card(s) within a respective socket(s) of the electronic system. A thermal transfer structure of the cooling apparatus includes a thermal spreader having a first thermal conduction surface, and a thermally conductive spring assembly coupled to the conduction surface of the thermal spreader and positioned and configured to reside between and physically couple a first surface of an electronics card to the first surface of the thermal spreader with docking of the electronics card within a socket of the electronic system. The thermal transfer structure is, in one embodiment, metallurgically bonded to a coolant-cooled structure and facilitates transfer of heat from the electronics card to coolant flowing through the coolant-cooled structure.

  4. Electronic structure theory of the superheavy elements

    NASA Astrophysics Data System (ADS)

    Eliav, Ephraim; Fritzsche, Stephan; Kaldor, Uzi

    2015-12-01

    High-accuracy calculations of atomic properties of the superheavy elements (SHE) up to element 122 are reviewed. The properties discussed include ionization potentials, electron affinities and excitation energies, which are associated with the spectroscopic and chemical behavior of these elements, and are therefore of considerable interest. Accurate predictions of these quantities require high-order inclusion of relativity and electron correlation, as well as large, converged basis sets. The Dirac-Coulomb-Breit Hamiltonian, which includes all terms up to second order in the fine-structure constant α, serves as the framework for the treatment; higher-order Lamb shift terms are considered in some selected cases. Electron correlation is treated by either the multiconfiguration self-consistent-field approach or by Fock-space coupled cluster theory. The latter is enhanced by the intermediate Hamiltonian scheme, allowing the use of larger model (P) spaces. The quality of the calculations is assessed by applying the same methods to lighter homologs of the SHEs and comparing with available experimental information. Very good agreement is obtained, within a few hundredths of an eV, and similar accuracy is expected for the SHEs. Many of the properties predicted for the SHEs differ significantly from what may be expected by straightforward extrapolation of lighter homologs, demonstrating that the structure and chemistry of SHEs are strongly affected by relativity. The major scientific challenge of the calculations is to find the electronic structure and basic atomic properties of the SHE and assign its proper place in the periodic table. Significant recent developments include joint experimental-computational studies of the excitation spectrum of Fm and the ionization energy of Lr, with excellent agreement of experiment and theory, auguring well for the future of research in the field.

  5. Resolving Presynaptic Structure by Electron Tomography

    PubMed Central

    Perkins, Guy A.; Jackson, Dakota R.; Spirou, George A.

    2016-01-01

    A key goal in neurobiology is to generate a theoretical framework that merges structural, physiological and molecular explanations of brain function. These categories of explanation do not advance in synchrony; advances in one category define new experiments in other categories. For example, the synapse was defined physiologically and biochemically before it was visualized using electron microscopy. Indeed, the original descriptions of synapses in the 1950s were lent credence by the presence of spherical vesicles in presynaptic terminals that were considered to be the substrate for quantal neurotransmission. In the last few decades, our understanding of synaptic function has again been driven by physiological and molecular techniques. The key molecular players for synaptic vesicle structure, mobility and fusion were identified and applications of the patch clamp technique permitted physiological estimation of neurotransmitter release and receptor properties. These advances demand higher resolution structural images of synapses. During the 1990s a second renaissance in cell biology driven by EM was fueled by improved techniques for electron tomography (ET) with the ability to compute virtual images with nm resolution between image planes. Over the last fifteen years, ET has been applied to the presynaptic terminal with special attention to the active zone and organelles of the nerve terminal. In this review, we first summarize the technical improvements that have led to a resurgence in utilization of ET and then we summarize new insights gained by the application of ET to reveal the high-resolution structure of the nerve terminal. PMID:25683026

  6. Resolving presynaptic structure by electron tomography.

    PubMed

    Perkins, Guy A; Jackson, Dakota R; Spirou, George A

    2015-05-01

    A key goal in neurobiology is to generate a theoretical framework that merges structural, physiological, and molecular explanations of brain function. These categories of explanation do not advance in synchrony; advances in one category define new experiments in other categories. For example, the synapse was defined physiologically and biochemically before it was visualized using electron microscopy. Indeed, the original descriptions of synapses in the 1950s were lent credence by the presence of spherical vesicles in presynaptic terminals that were considered to be the substrate for quantal neurotransmission. In the last few decades, our understanding of synaptic function has again been driven by physiological and molecular techniques. The key molecular players for synaptic vesicle structure, mobility and fusion were identified and applications of the patch clamp technique permitted physiological estimation of neurotransmitter release and receptor properties. These advances demand higher resolution structural images of synapses. During the 1990s a second renaissance in cell biology driven by EM was fueled by improved techniques for electron tomography (ET) with the ability to compute virtual images with nm resolution between image planes. Over the last 15 years, ET has been applied to the presynaptic terminal with special attention to the active zone and organelles of the nerve terminal. In this review, we first summarize the technical improvements that have led to a resurgence in utilization of ET and then we summarize new insights gained by the application of ET to reveal the high-resolution structure of the nerve terminal. PMID:25683026

  7. Electronic structure theory of weakly interacting bilayers

    NASA Astrophysics Data System (ADS)

    Fang, Shiang; Kaxiras, Efthimios

    2016-06-01

    We derive electronic structure models for weakly interacting bilayers such as graphene-graphene and graphene-hexagonal boron nitride, based on density functional theory calculations followed by Wannier transformation of electronic states. These transferable interlayer coupling models can be applied to investigate the physics of bilayers with arbitrary translations and twists. The functional form, in addition to the dependence on the distance, includes the angular dependence that results from higher angular momentum components in the Wannier pz orbitals. We demonstrate the capabilities of the method by applying it to a rotated graphene bilayer, which produces the analytically predicted renormalization of the Fermi velocity, Van Hove singularities in the density of states, and moiré pattern of the electronic localization at small twist angles. We further extend the theory to obtain the effective couplings by integrating out neighboring layers. This approach is instrumental for the design of van der Walls heterostructures with desirable electronic features and transport properties and for the derivation of low-energy theories for graphene stacks, including proximity effects from other layers.

  8. Spin Structure Functions from Electron Scattering

    SciTech Connect

    Seonho Choi

    2012-09-01

    The spin structure of the nucleon can play a key testing ground for Quantum Chromo-Dynamics (QCD) at wide kinematic ranges from smaller to large four momentum transfer Q{sup 2}. The pioneering experiments have confirmed several QCD sum rules at high Q{sup 2} where a perturbative picture holds. For a full understanding of QCD at various scales, various measurements were made at intermediate and small Q{sup 2} region and their interpretation would be a challenging task due to the non-perturbative nature. Jefferson Lab has been one of the major experimental facilities for the spin structure with its polarized electron beams and various polarized targets. A few QCD sum rules have been compared with the measured spin structure functions g{sub 1}(x, Q{sup 2}) and g{sub 2}(x, Q{sup 2}) at low Q{sup 2} and surprising results have been obtained for the spin polarizabilities, {gamma}{sub 0} and {delta}{sub LT} . As for the proton spin structure functions, the lack of data for g{sub 2}(x,Q{sup 2}) structure functions has been complemented with a new experiment at Jefferson Lab, SANE. The results from SANE will provide a better picture of the proton spin structure at a wide kinematic range in x and Q{sup 2}.

  9. Extraordinary electronic properties in uncommon structure types

    NASA Astrophysics Data System (ADS)

    Ali, Mazhar Nawaz

    In this thesis I present the results of explorations into several uncommon structure types. In Chapter 1 I go through the underlying idea of how we search for new compounds with exotic properties in solid state chemistry. The ideas of exploring uncommon structure types, building up from the simple to the complex, using chemical intuition and thinking by analogy are discussed. Also, the history and basic concepts of superconductivity, Dirac semimetals, and magnetoresistance are briefly reviewed. In chapter 2, the 1s-InTaS2 structural family is introduced along with the discovery of a new member of the family, Ag0:79VS2; the synthesis, structure, and physical properties of two different polymorphs of the material are detailed. Also in this chapter, we report the observation of superconductivity in another 1s structure, PbTaSe2. This material is especially interesting due to it being very heavy (resulting in very strong spin orbit coulping (SOC)), layered, and noncentrosymmetric. Electronic structure calculations reveal the presence of a bulk 3D Dirac cone (very similar to graphene) that is gapped by SOC originating from the hexagonal Pb layer. In Chapter 3 we show the re-investigation of the crystal structure of the 3D Dirac semimetal, Cd3As2. It is found to be centrosymmetric, rather than noncentrosymmetric, and as such all bands are spin degenerate and there is a 4-fold degenerate bulk Dirac point at the Fermi level, making Cd3As2 a 3D electronic analog to graphene. Also, for the first time, scanning tunneling microscopy experiments identify a 2x2 surface reconstruction in what we identify as the (112) cleavage plane of single crystals; needle crystals grow with a [110] long axis direction. Lastly, in chapter 4 we report the discovery of "titanic" (sadly dubbed ⪉rge, nonsaturating" by Nature editors and given the acronym XMR) magnetoresistance (MR) in the non-magnetic, noncentrosymmetric, layered transition metal dichalcogenide WTe2; over 13 million% at 0.53 K in

  10. Pu electronic structure and photoelectron spectroscopy

    SciTech Connect

    Joyce, John J; Durakiewicz, Tomasz; Graham, Kevin S; Bauer, Eric D; Moore, David P; Mitchell, Jeremy N; Kennison, John A; Martin, Richard L; Roy, Lindsay E; Scuseria, G. E.

    2010-01-01

    The electronic structure of PuCoGa{sub 5}, Pu metal, and PuO{sub 2} is explored using photoelectron spectroscopy. Ground state electronic properties are inferred from temperature dependent photoemission near the Fermi energy for Pu metal. Angle-resolved photoemission details the energy vs. crystaJ momentum landscape near the Fermi energy for PuCoGa{sub 5} which shows significant dispersion in the quasiparticle peak near the Fermi energy. For the Mott insulators AnO{sub 2}(An = U, Pu) the photoemission results are compared against hybrid functional calculations and the model prediction of a cross over from ionic to covalent bonding is found to be reasonable.

  11. Electronic Structure of B12 coenzymes

    NASA Astrophysics Data System (ADS)

    Ouyang, Lizhi; Ching, W. Y.; Randaccio, Lucio

    2001-06-01

    We have carried out an ab-initio local density functional calculations of the two most important B12 coenzymes, adoensyl-cobalamin (Ado-Cbl) and methyl-cobalamin (Me-Cbl). The crystal structures were determined by accurate X-ray synchrotron radiation measurements. Both crystals have space group P2121 with four molecules, or about 800 atoms, per unit cell. Our electronic structure calculation is based on one full molecule including the side chains. Results are analyzed in terms of atom and orbital resolved partial density of states (PDOS), Mulliken effective charges and bond orders. The PDOS analysis shows that the Co complexes of both B12 coenzymes had a HOMO/LUMO gap of about 1.5 eV. The Co-C bond order in Me-Cbl is smaller than that in Ado-Cbl. This appears to be in contradiction with the measured bond dissociated energies. However, this could also indicate the importance of the effects of solvents, which were not included in the calculation. We are investigating whether the effect of the solvents could dramatically modify the electronic structures of Ado-Cbl and Me-Cbl.

  12. Electronic Structure of Buried Interfaces - Oral Presentation

    SciTech Connect

    Porter, Zachary

    2015-08-25

    In the electronics behind computer memory storage, the speed and size are dictated by the performance of permanent magnets inside devices called read heads. Complicated magnets made of stacked layers of thin films can be engineered to have properties that yield more energy storage and faster switching times compared to conventional iron or cobalt magnets. The reason is that magnetism is a result of subtle interactions amongst electrons; just how neurons come together on large scales to make cat brains and dog brains, ensembles of electrons interact and become ferromagnets and paramagnets. These interactions make magnets too difficult to study in their entirety, so I focus on the interfaces between layers, which are responsible for the coupling materials physicists hope to exploit to produce next-generation magnets. This project, I study a transition metal oxide material called LSCO, Lanthanum Cobaltite, which can be a paramagnet or a ferromagnet depending on how you tweak the electronic structure. It exhibits an exciting behavior: its sum is greater than the sum of its parts. When another similar material called a LSMO, Lanthanum Manganite, is grown on top of it, their interface has a different type of magnetism from the LSCO or the LSMO! I hope to explain this by demonstrating differently charged ions in the interface. The typical method for quantifying this is x-ray absorption, but all conventional techniques look at every layer simultaneously, averaging the interfaces and the LSCO layers that we want to characterize separately. Instead, I must use a new reflectivity technique, which tracks the intensity of reflected x-rays at different angles, at energies near the absorption peaks of certain elements, to track changes in the electronic structure of the material. The samples were grown by collaborators at the Takamura group at U.C. Davis and probed with this “resonant reflectivity” technique on Beamline 2-1 at the Stanford Synchrotron Radiation Lightsource

  13. Electronic and magnetic structures of chain structured iron selenide compounds

    NASA Astrophysics Data System (ADS)

    Li, Wei; Setty, Chandan; Chen, X. H.; Hu, Jiangping

    2014-08-01

    Electronic and magnetic structures of iron selenide compounds Ce2O2FeSe2 (2212*) and BaFe2Se3 (123*) are studied by the first-principles calculations. We find that while all these compounds are composed of one-dimensional (1D) Fe chain (or ladder) structures, their electronic structures are not close to be quasi-1D. The magnetic exchange couplings between two nearest-neighbor (NN) chains in 2212* and between two NN two-leg-ladders in 123* are both antiferromagnetic (AFM), which is consistent with the presence of significant third NN AFM coupling, a common feature shared in other iron-chalcogenides, FeTe (11*) and K y Fe2- x Se2 (122*). In magnetic ground states, each Fe chain of 2212* is ferromagnetic and each two-leg ladder of 123* form a block-AFM structure. We suggest that all magnetic structures in iron-selenide compounds can be unified into an extended J 1- J 2- J 3 model. Spin-wave excitations of the model are calculated and can be tested by future experiments on these two systems.

  14. Electronic structure and optical properties of resin

    NASA Astrophysics Data System (ADS)

    Rao, Zhi-Fan; Zhou, Rong-Feng

    2013-03-01

    We used the density of functional theory (DFT) to study the electronic structure and density of states of resin by ab initio calculation. The results show the band gap of resin is 1.7 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The results of optical properties show the reflectivity is low, and the refractive index is 1.7 in visible light range. The highest absorption coefficient peak is in 490 nm and the value is 75,000.

  15. Lattice Boltzmann Model for Electronic Structure Simulations

    NASA Astrophysics Data System (ADS)

    Mendoza, M.; Herrmann, H. J.; Succi, S.

    2015-09-01

    Recently, a new connection between density functional theory and kinetic theory has been proposed. In particular, it was shown that the Kohn-Sham (KS) equations can be reformulated as a macroscopic limit of the steady-state solution of a suitable single-particle kinetic equation. By using a discrete version of this new formalism, the exchange and correlation energies of simple atoms and the geometrical configuration of the methane molecule were calculated accurately. Here, we discuss the main ideas behind the lattice kinetic approach to electronic structure computations, offer some considerations for prospective extensions, and also show additional numerical results, namely the geometrical configuration of the water molecule.

  16. Surface structure and electronic properties of materials

    NASA Technical Reports Server (NTRS)

    Siekhaus, W. J.; Somorjai, G. A.

    1975-01-01

    A surface potential model is developed to explain dopant effects on chemical vapor deposition. Auger analysis of the interaction between allotropic forms of carbon and silicon films has shown Si-C formation for all forms by glassy carbon. LEED intensity measurements have been used to determine the mean square displacement of surface atoms of silicon single crystals, and electron loss spectroscopy has shown the effect of structure and impurities on surface states located within the band gap. A thin film of Al has been used to enhance film crystallinity at low temperature.

  17. Electronic structure of cobalt nanocrystals suspended inliquid

    SciTech Connect

    Liu, Hongjian; Guo, Jinghua; Yin, Yadong; Augustsson, Andreas; Dong, Chungli; Nordgren, Joseph; Chang, Chinglin; Alivisatos, Paul; Thornton, Geoff; Ogletree, D. Frank; Requejo, Felix G.; de Groot, Frank; Salmeron, Miquel

    2007-07-16

    The electronic structure of cobalt nanocrystals suspended in liquid as a function of size has been investigated using in-situ x-ray absorption and emission spectroscopy. A sharp absorption peak associated with the ligand molecules is found that increases in intensity upon reducing the nanocrystal size. X-ray Raman features due to d-d and to charge-transfer excitations of ligand molecules are identified. The study reveals the local symmetry of the surface of {var_epsilon}-Co phase nanocrystals, which originates from a dynamic interaction between Co nanocrystals and surfactant + solvent molecules.

  18. Pepper spray projectile/disperser for countering hostage and barricade situations

    NASA Astrophysics Data System (ADS)

    Kelly, Roy

    1997-01-01

    An improved less-than-lethal projectile for use in hostage, barricade and tactical assault situations has been developed. The projectile is launched from a standoff position and disperse the incapacitating agent oleoresin capsicum in the form of atomized droplets. A literature search followed by an experimental study were conducted of the mechanism of barrier defeat for various shaped projectiles against the targets of interest in this work: window glass, plasterboard and plywood. Some of the trade- offs between velocity, standoff, projectile shape and size, penetration, and residual energy were quantified. Analysis of the ballistic trajectory and recoil, together with calculations of he amount of pepper spray needed to incapacitate the occupants of a typical barricaded structure, indicated the suitability of using a fin stabilized projectile fired from a conventional 37 mm riot control gas gun. Two projectile designs were considered, manufactured and tested. The results of static tests to simulate target impact, together with live firing trials against a variety of targets, showed that rear ejection of the atomized spray was more reproducible and effective than nose ejection. The performance characteristics of the finalized design were investigated in trials using the standard barrier for testing barrier penetrating tear gas agents as defined by the National Institute of Justice.

  19. The CECAM Electronic Structure Library: community-driven development of software libraries for electronic structure simulations

    NASA Astrophysics Data System (ADS)

    Oliveira, Micael

    The CECAM Electronic Structure Library (ESL) is a community-driven effort to segregate shared pieces of software as libraries that could be contributed and used by the community. Besides allowing to share the burden of developing and maintaining complex pieces of software, these can also become a target for re-coding by software engineers as hardware evolves, ensuring that electronic structure codes remain at the forefront of HPC trends. In a series of workshops hosted at the CECAM HQ in Lausanne, the tools and infrastructure for the project were prepared, and the first contributions were included and made available online (http://esl.cecam.org). In this talk I will present the different aspects and aims of the ESL and how these can be useful for the electronic structure community.

  20. Analysis of boron carbides' electronic structure

    NASA Technical Reports Server (NTRS)

    Howard, Iris A.; Beckel, Charles L.

    1986-01-01

    The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

  1. Electron beam coupling to a metamaterial structure

    SciTech Connect

    French, David M.; Shiffler, Don; Cartwright, Keith

    2013-08-15

    Microwave metamaterials have shown promise in numerous applications, ranging from strip lines and antennas to metamaterial-based electron beam driven devices. In general, metamaterials allow microwave designers to obtain electromagnetic characteristics not typically available in nature. High Power Microwave (HPM) sources have in the past drawn inspiration from work done in the conventional microwave source community. In this article, the use of metamaterials in an HPM application is considered by using an effective medium model to determine the coupling of an electron beam to a metamaterial structure in a geometry similar to that of a dielectric Cerenkov maser. Use of the effective medium model allows for the analysis of a wide range of parameter space, including the “mu-negative,”“epsilon-negative,” and “double negative” regimes of the metamaterial. The physics of such a system are modeled analytically and by utilizing the particle-in-cell code ICEPIC. For this geometry and effective medium representation, optimum coupling of the electron beam to the metamaterial, and thus the optimum microwave or RF production, occurs in the epsilon negative regime of the metamaterial. Given that HPM tubes have been proposed that utilize a metamaterial, this model provides a rapid method of characterizing a source geometry that can be used to quickly understand the basic physics of such an HPM device.

  2. Experimental Benchmarking of Pu Electronic Structure

    SciTech Connect

    Tobin, J G; Moore, K T; Chung, B W; Wall, M A; Schwartz, A J; Ebbinghaus, B B; Butterfield, M T; Teslich, Jr., N E; Bliss, R A; Morton, S A; Yu, S W; Komesu, T; Waddill, G D; der Laan, G v; Kutepov, A L

    2005-10-13

    The standard method to determine the band structure of a condensed phase material is to (1) obtain a single crystal with a well defined surface and (2) map the bands with angle resolved photoelectron spectroscopy (occupied or valence bands) and inverse photoelectron spectroscopy (unoccupied or conduction bands). Unfortunately, in the case of Pu, the single crystals of Pu are either nonexistent, very small and/or having poorly defined surfaces. Furthermore, effects such as electron correlation and a large spin-orbit splitting in the 5f states have further complicated the situation. Thus, we have embarked upon the utilization of unorthodox electron spectroscopies, to circumvent the problems caused by the absence of large single crystals of Pu with well-defined surfaces. Our approach includes the techniques of resonant photoelectron spectroscopy [1], x-ray absorption spectroscopy [1,2,3,4], electron energy loss spectroscopy [2,3,4], Fano Effect measurements [5], and Bremstrahlung Isochromat Spectroscopy [6], including the utilization of micro-focused beams to probe single-crystallite regions of polycrystalline Pu samples. [2,3,6

  3. Towards scalable electronic structure calculations for alloys

    SciTech Connect

    Stocks, G.M.; Nicholson, D.M.C.; Wang, Y.; Shelton, W.A.; Szotek, Z.; Temmermann, W.M.

    1994-06-01

    A new approach to calculating the properties of large systems within the local density approximation (LDA) that offers the promise of scalability on massively parallel supercomputers is outlined. The electronic structure problem is formulated in real space using multiple scattering theory. The standard LDA algorithm is divided into two parts. Firstly, finding the self-consistent field (SCF) electron density, Secondly, calculating the energy corresponding to the SCF density. We show, at least for metals and alloys, that the former problem is easily solved using real space methods. For the second we take advantage of the variational properties of a generalized Harris-Foulkes free energy functional, a new conduction band Fermi function, and a fictitious finite electron temperature that again allow us to use real-space methods. Using a compute-node {R_arrow} atom equivalence the new method is naturally highly parallel and leads to O(N) scaling where N is the number of atoms making up the system. We show scaling data gathered on the Intel XP/S 35 Paragon for systems up to 512-atoms/simulation cell. To demonstrate that we can achieve metallurgical-precision, we apply the new method to the calculation the energies of disordered CuO{sub 0.5}Zn{sub 0.5} alloys using a large random sample.

  4. Electronic structure of rare-earth hexaborides

    NASA Astrophysics Data System (ADS)

    Kimura, S.; Nanba, T.; Tomikawa, M.; Kunii, S.; Kasuya, T.

    1992-11-01

    Reflectivity spectra of all rare-earth hexaboride RB6 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Y) single crystals have been measured systematically in the energy region from 1 meV to 40 eV at 300 K in order to investigate the electronic state and the contribution of the 4f electron to the band structure. The analysis of the optical conductivity and the loss-function spectra, which were derived from the Kramers-Kronig transformation of the reflectivity spectra, allowed us to make clear the origin of the peak structure in the spectrum due to the various interband transitions. The origins of the main peaks in the spectrum were assigned to the interband transitions from the bonding to the antibonding bands of the boron 2s and 2p states and to the rare-earth 5d state. The intra-atomic transition from the 4f and the 5p to the 5d(t2g) states in the rare-earth ion was also observed.

  5. Structure and navigation for electronic publishing

    NASA Astrophysics Data System (ADS)

    Tillinghast, John; Beretta, Giordano B.

    1998-01-01

    The sudden explosion of the World Wide Web as a new publication medium has given a dramatic boost to the electronic publishing industry, which previously was a limited market centered around CD-ROMs and on-line databases. While the phenomenon has parallels to the advent of the tabloid press in the middle of last century, the electronic nature of the medium brings with it the typical characteristic of 4th wave media, namely the acceleration in its propagation speed and the volume of information. Consequently, e-publications are even flatter than print media; Shakespeare's Romeo and Juliet share the same computer screen with a home-made plagiarized copy of Deep Throat. The most touted tool for locating useful information on the World Wide Web is the search engine. However, due to the medium's flatness, sought information is drowned in a sea of useless information. A better solution is to build tools that allow authors to structure information so that it can easily be navigated. We experimented with the use of ontologies as a tool to formulate structures for information about a specific topic, so that related concepts are placed in adjacent locations and can easily be navigated using simple and ergonomic user models. We describe our effort in building a World Wide Web based photo album that is shared among a small network of people.

  6. Electronic Structure and Bonding in Complex Biomolecule

    NASA Astrophysics Data System (ADS)

    Ouyang, Lizhi

    2005-03-01

    For over a century vitamin B12 and its enzyme cofactor derivates have persistently attracted research efforts for their vital biological role, unique Co-C bonding, rich red-ox chemistry, and recently their candidacies as drug delivery vehicles etc. However, our understanding of this complex metalorganic molecule's efficient enzyme activated catalytic power is still controversial. We have for the first time calculated the electronic structure, Mulliken effective charge and bonding of a whole Vitamin B12 molecule without any structural simplification by first- principles approaches based on density functional theory using structures determined by high resolution X-ray diffraction. A partial density of states analysis shows excellent agreement with X-ray absorption data and has been used successfully to interpret measured optical absorption spectra. Mulliken bonding analysis of B12 and its derivatives reveal noticeable correlations between the two axial ligands which could be exploited by the enzyme to control the catalytic process. Our calculated X-ray near edge structure of B12 and its derivates using Slater's transition state theory are also in good agreement with experiments. The same approach has been applied to other B12 derivatives, ferrocene peptides, and recently DNA molecules.

  7. Multigrid Methods in Electronic Structure Calculations

    NASA Astrophysics Data System (ADS)

    Briggs, Emil

    1996-03-01

    Multigrid techniques have become the method of choice for a broad range of computational problems. Their use in electronic structure calculations introduces a new set of issues when compared to traditional plane wave approaches. We have developed a set of techniques that address these issues and permit multigrid algorithms to be applied to the electronic structure problem in an efficient manner. In our approach the Kohn-Sham equations are discretized on a real-space mesh using a compact representation of the Hamiltonian. The resulting equations are solved directly on the mesh using multigrid iterations. This produces rapid convergence rates even for ill-conditioned systems with large length and/or energy scales. The method has been applied to both periodic and non-periodic systems containing over 400 atoms and the results are in very good agreement with both theory and experiment. Example applications include a vacancy in diamond, an isolated C60 molecule, and a 64-atom cell of GaN with the Ga d-electrons in valence which required a 250 Ry cutoff. A particular strength of a real-space multigrid approach is its ready adaptability to massively parallel computer architectures. The compact representation of the Hamiltonian is especially well suited to such machines. Tests on the Cray-T3D have shown nearly linear scaling of the execution time up to the maximum number of processors (512). The MPP implementation has been used for studies of a large Amyloid Beta Peptide (C_146O_45N_42H_210) found in the brains of Alzheimers disease patients. Further applications of the multigrid method will also be described. (in collaboration D. J. Sullivan and J. Bernholc)

  8. Electronic and structural properties of metallic microclusters

    SciTech Connect

    Maiti, A.

    1992-04-01

    The first part of this thesis presents a first-order pseudopotential calculation at T=O of the total energy of small sodium clusters of size N<800. The calculation is based on a local-pseudopotential scheme and local-density correlation and exchange. A temperature-size (T-N) phase-diagram is then derived using the T=O results and Lindemann`s criterion for melting. The phase-diagram contains three regions of stability: (1) a liquid (jellium) phase at temperatures above the melting line T{sub M}(N) where cluster-stability occurs at electronic magic numbers: (2) a phase related to complete geometrical shells of body-centered-cubic structure at temperatures below the melting line; and (3) a close-packed structure at very low temperatures and sufficiently large N. The melting line drops to T{sub M}(N)=O for N<65, where electronic magic numbers are stable even at T=O. The phase diagram reduces asymptotically to the known phases of sodium as N{yields}{infinity}, including the known martensitic transformation at T{approximately}5 K. The second and the last part of this thesis consists of a study of small-cluster many-body systems by means of an on-site ``local`` chemical potential which allows the continuous variation of local electron-density. This method yields a criterion to distinguish particular features of a small cluster that are likely to survive in the large-N thermodynamic limit from those discontinuities that arise only from finite-size effects.

  9. Electronic and structural properties of metallic microclusters

    SciTech Connect

    Maiti, A.

    1992-04-01

    The first part of this thesis presents a first-order pseudopotential calculation at T=O of the total energy of small sodium clusters of size N<800. The calculation is based on a local-pseudopotential scheme and local-density correlation and exchange. A temperature-size (T-N) phase-diagram is then derived using the T=O results and Lindemann's criterion for melting. The phase-diagram contains three regions of stability: (1) a liquid (jellium) phase at temperatures above the melting line T{sub M}(N) where cluster-stability occurs at electronic magic numbers: (2) a phase related to complete geometrical shells of body-centered-cubic structure at temperatures below the melting line; and (3) a close-packed structure at very low temperatures and sufficiently large N. The melting line drops to T{sub M}(N)=O for N<65, where electronic magic numbers are stable even at T=O. The phase diagram reduces asymptotically to the known phases of sodium as N{yields}{infinity}, including the known martensitic transformation at T{approximately}5 K. The second and the last part of this thesis consists of a study of small-cluster many-body systems by means of an on-site local'' chemical potential which allows the continuous variation of local electron-density. This method yields a criterion to distinguish particular features of a small cluster that are likely to survive in the large-N thermodynamic limit from those discontinuities that arise only from finite-size effects.

  10. Flight trajectory simulation of fluid payload projectiles

    SciTech Connect

    Vaughn, H.R.; Wolfe, W.P.; Oberkampf, W.L.

    1985-01-01

    A flight trajectory simulation method has been developed for calculating the six degree of freedom motion of fluid filled projectiles. Numerically calculated internal fluid moments and experimentally known aerodynamic forces and moments are coupled to the projectile motion. Comparisons of predicted results with flight test data of an M483 155mm artillery projectile with a highly viscous payload confirm the accuracy of the simulation. This simulation clearly shows that the flight instability is due to the growth of the nutation component of angular motion caused by the viscous effects of the fluid payload. This simulation procedure, when used in conjunction with the previously developed method for calculating internal fluid moments, allows the designer to examine the effects of various liquid payloads and container geometries on the dynamic behavior of flight vehicles.

  11. Ocular injuries due to projectile impacts.

    PubMed

    Scott, W R; Lloyd, W C; Benedict, J V; Meredith, R

    2000-01-01

    An animal model has been developed using enucleated porcine eyes to evaluate ocular trauma. The eyes were pressurized to approximately 18 mmHg and mounted in a container with a 10% gelatin mixture. The corneas of sixteen pressurized eyes were impacted by a blunt metal projectile (mass of 2.6 gm, 3.5 gm or 45.5 gm) at velocities of 4.0 to 38.1 m/s. The impacted eyes were evaluated by an ophthalmologist. A numerical classification scheme was used to categorize the severity of the ocular injury. A chi-squared test indicates that the injury level is associated with the kinetic energy (KE) and not the momentum of the projectile. The enucleated eyes began to experience lens dislocations when the KE of the projectile was approximately 0.75 Nm, and retinal injuries when the KE was approximately 1.20 Nm. PMID:11558084

  12. Additional Crime Scenes for Projectile Motion Unit

    NASA Astrophysics Data System (ADS)

    Fullerton, Dan; Bonner, David

    2011-12-01

    Building students' ability to transfer physics fundamentals to real-world applications establishes a deeper understanding of underlying concepts while enhancing student interest. Forensic science offers a great opportunity for students to apply physics to highly engaging, real-world contexts. Integrating these opportunities into inquiry-based problem solving in a team environment provides a terrific backdrop for fostering communication, analysis, and critical thinking skills. One such activity, inspired jointly by the museum exhibit "CSI: The Experience"2 and David Bonner's TPT article "Increasing Student Engagement and Enthusiasm: A Projectile Motion Crime Scene,"3 provides students with three different crime scenes, each requiring an analysis of projectile motion. In this lesson students socially engage in higher-order analysis of two-dimensional projectile motion problems by collecting information from 3-D scale models and collaborating with one another on its interpretation, in addition to diagramming and mathematical analysis typical to problem solving in physics.

  13. Electronic structure of Ca, Sr, and Ba under pressure.

    NASA Technical Reports Server (NTRS)

    Animalu, A. O. E.; Heine, V.; Vasvari, B.

    1967-01-01

    Electronic band structure calculations phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure

  14. Reversible Hydrogen Storage Materials – Structure, Chemistry, and Electronic Structure

    SciTech Connect

    Robertson, Ian M.; Johnson, Duane D.

    2014-06-21

    To understand the processes involved in the uptake and release of hydrogen from candidate light-weight metal hydride storage systems, a combination of materials characterization techniques and first principle calculation methods have been employed. In addition to conventional microstructural characterization in the transmission electron microscope, which provides projected information about the through thickness microstructure, electron tomography methods were employed to determine the three-dimensional spatial distribution of catalyst species for select systems both before and after dehydrogenation. Catalyst species identification as well as compositional analysis of the storage material before and after hydrogen charging and discharging was performed using a combination of energy dispersive spectroscopy, EDS, and electron energy loss spectroscopy, EELS. The characterization effort was coupled with first-principles, electronic-structure and thermodynamic techniques to predict and assess meta-stable and stable phases, reaction pathways, and thermodynamic and kinetic barriers. Systems studied included:NaAlH4, CaH2/CaB6 and Ca(BH4)2, MgH2/MgB2, Ni-Catalyzed Magnesium Hydride, TiH2-Catalyzed Magnesium Hydride, LiBH4, Aluminum-based systems and Aluminum

  15. Meso-scale hypervelocity cratering experiments (MEMIN project): Characterization of projectile material

    NASA Astrophysics Data System (ADS)

    Domke, Isabelle; Deutsch, Alex; Hecht, Lutz; Kenkmann, Thomas; Berndt, Jasper

    2010-05-01

    The DFG-funded "MEMIN" (multidisciplinary experimental and modelling impact crater research network) research group is aimed at a better understanding of the impact cratering process by combining (i) numerical modelling of crater formation, (ii) investigation of terrestrial craters and (iii) meso-scale hypervelocity impact experiments using the large two-stage light gas gun at the Ernst-Mach-Institute (EMI; Efringen-Kirchen, Germany). In the framework of MEMIN, 1 cm-sized projectiles of the steel SAE 4130 (mass of 4.1 g) have been fired with a velocity of ~ 5.3 km s-1 onto blocks of Seeberger sandstone (size 100 x 100 x 50 cm, grain size 169+/-8 μm; porosity 12-20 vol.%). One goal of MEMIN is to document, analyze, and understand the fate of the projectile and its distribution between crater and ejecta; hence, the use of well-analyzed projectile material is mandatory. For this purpose, we use optical, and electron microscopy, electron microprobe (WWU, and MfN), and LA-ICP-MS microanalysis (WWU). Currently we evaluate which steel or iron meteorite is adequate for the intended use. Important properties of a projectile are (i) textural and chemical homogeneity, (ii) clear chemical distinction to the target sandstone, (iii) presence of elements such as Co, Ni, Cr, PGE that as "meteoritic component" are used in terrestrial craters to trace projectile matter, and characterize the type of the projectile (i.e., meteorite group), and finally (iv) mechanical properties that guarantee stability during sphere production, launch and flight. Strong chemical differences to the target material and geochemical homogeneity of the projectile will allow detection of small volumes of projectile matter by high spatial resolution in-situ analysis with the LA-ICP-MS. Steel SAE 4130 is heterogeneous at the 100-µm scale and has low trace element contents. In future, we plan the use of the alloyed heat treatable steel D290-1 as projectile as its texture is quite homogenous at the scale of

  16. Numerical simulations of gun-launched kinetic energy projectiles subjected to asymmetric projectile base pressure

    SciTech Connect

    Rabern, D.A.

    1991-12-31

    Three-dimensional numerical simulations were performed to determine the effect of an asymmetric base pressure on kinetic energy projectiles during launch. A matrix of simulations was performed in two separate launch environments. One launch environment represented a severe lateral load environment, while the other represented a nonsevere lateral load environment based on the gun tube straightness. The orientation of the asymmetric pressure field, its duration, the projectile`s initial position, and the tube straightness were altered to determine the effects of each parameter. The pressure asymmetry translates down the launch tube to exit parameters and is washed out by tube profile. Results from the matrix of simulations are presented.

  17. Multilevel domain decomposition for electronic structure calculations

    SciTech Connect

    Barrault, M. . E-mail: maxime.barrault@edf.fr; Cances, E. . E-mail: cances@cermics.enpc.fr; Hager, W.W. . E-mail: hager@math.ufl.edu; Le Bris, C. . E-mail: lebris@cermics.enpc.fr

    2007-03-01

    We introduce a new multilevel domain decomposition method (MDD) for electronic structure calculations within semi-empirical and density functional theory (DFT) frameworks. This method iterates between local fine solvers and global coarse solvers, in the spirit of domain decomposition methods. Using this approach, calculations have been successfully performed on several linear polymer chains containing up to 40,000 atoms and 200,000 atomic orbitals. Both the computational cost and the memory requirement scale linearly with the number of atoms. Additional speed-up can easily be obtained by parallelization. We show that this domain decomposition method outperforms the density matrix minimization (DMM) method for poor initial guesses. Our method provides an efficient preconditioner for DMM and other linear scaling methods, variational in nature, such as the orbital minimization (OM) procedure.

  18. Electronic structures of reconstructed zigzag silicene nanoribbons

    SciTech Connect

    Ding, Yi E-mail: wangyanli-04@tsinghua.org.cn; Wang, Yanli E-mail: wangyanli-04@tsinghua.org.cn

    2014-02-24

    Edge states and magnetism are crucial for spintronic applications of nanoribbons. Here, using first-principles calculations, we explore structural stabilities and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with Klein and pentagon-heptagon reconstructions. Comparing to unreconstructed zigzag edges, deformed bare pentagon-heptagon ones are favored under H-poor conditions, while H-rich surroundings stabilize di-hydrogenated Klein edges. These Klein edges have analogous magnetism to zigzag ones, which also possess the electric-field-induced half-metallicity of nanoribbons. Moreover, diverse magnetic states can be achieved by asymmetric Klein and zigzag edges into ZSiNRs, which could be transformed from antiferromagnetic-semiconductors to bipolar spin-gapless-semiconductors and ferromagnetic-metals depending on edge hydrogenations.

  19. Electronic Structure Calculations of Highly Charged Ions

    NASA Astrophysics Data System (ADS)

    Bromley, Steve; Ziolkowski, Marcin; Marler, Joan

    2016-05-01

    Exotic systems like Highly Charged Ions (HCIs) are attracting more attention based on their properties and possible interactions. Abundance of HCIs in the solar wind and their interaction with the upper atmosphere puts them in the attention of astro- and atmospheric physicists. Also, their unique properties originating in the high charge make them an excellent candidate for precision measurements and the next generation of atomic clocks. For a better understanding of the dynamics of processes involving HCIs a combined theoretical and experimental effort is needed to study their basic properties and interactions. Both theory and experiment need to be combined due to the extreme nature of these systems. We present preliminary insight into electronic structure of light HCIs, their interactions with neutral atoms and dynamics of charge transfer processes.

  20. Electron Liquids in Semiconductor Quantum Structures

    SciTech Connect

    Aron Pinczuk

    2009-05-25

    The groups led by Stormer and Pinczuk have focused this project on goals that seek the elucidation of novel many-particle effects that emerge in two-dimensional electron systems (2DES) as the result from fundamental quantum interactions. This experimental research is conducted under extreme conditions of temperature and magnetic field. From the materials point of view, the ultra-high mobility systems in GaAs/AlGaAs quantum structures continue to be at the forefront of this research. The newcomer materials are based on graphene, a single atomic layer of graphite. The graphene research is attracting enormous attention from many communities involved in condensed matter research. The investigated many-particle phenomena include the integer and fractional quantum Hall effect, composite fermions, and Dirac fermions, and a diverse group of electron solid and liquid crystal phases. The Stormer group performed magneto-transport experiments and far-infrared spectroscopy, while the Pinczuk group explores manifestations of such phases in optical spectra.

  1. Dynamic effects of interaction of composite projectiles with targets

    NASA Astrophysics Data System (ADS)

    Zakharov, V. M.

    2016-01-01

    The process of high-speed impact of projectiles against targets of finite thickness is experimentally investigated. Medium-hard steel plates are used as targets. The objective of this research is to carry out a comparative analysis of dynamic effects of interaction of various types of projectiles with targets, such as characteristics of destruction of the target, the state of the projectile behind the target, and particularities of the after-penetration stream of fragments after the target has been pierced. The projectiles are made of composites on the basis of tungsten carbide obtained by caking and the SHS-technology. To compare effectiveness of composite projectiles steel projectiles are used. Their effectiveness was estimated in terms of the ballistic limit. High density projectiles obtained by means of the SHS-technology are shown to produce results comparable in terms of the ballistic limit with high-strength projectiles that contain tungsten received by caking.

  2. Speed, acceleration, chameleons and cherry pit projectiles

    NASA Astrophysics Data System (ADS)

    Planinsic, Gorazd; Likar, Andrej

    2012-01-01

    The paper describes the mechanics of cherry pit projectiles and ends with showing the similarity between cherry pit launching and chameleon tongue projecting mechanisms. The whole story is written as an investigation, following steps that resemble those typically taken by scientists and can therefore serve as an illustration of scientific reasoning and how scientific knowledge is built.

  3. Ballistics projectile image analysis for firearm identification.

    PubMed

    Li, Dongguang

    2006-10-01

    This paper is based upon the observation that, when a bullet is fired, it creates characteristic markings on the cartridge case and projectile. From these markings, over 30 different features can be distinguished, which, in combination, produce a "fingerprint" for a firearm. By analyzing features within such a set of firearm fingerprints, it will be possible to identify not only the type and model of a firearm, but also each and every individual weapon just as effectively as human fingerprint identification. A new analytic system based on the fast Fourier transform for identifying projectile specimens by the line-scan imaging technique is proposed in this paper. This paper develops optical, photonic, and mechanical techniques to map the topography of the surfaces of forensic projectiles for the purpose of identification. Experiments discussed in this paper are performed on images acquired from 16 various weapons. Experimental results show that the proposed system can be used for firearm identification efficiently and precisely through digitizing and analyzing the fired projectiles specimens. PMID:17022254

  4. An Inexpensive Mechanical Model for Projectile Motion

    ERIC Educational Resources Information Center

    Kagan, David

    2011-01-01

    As experienced physicists, we see the beauty and simplicity of projectile motion. It is merely the superposition of uniform linear motion along the direction of the initial velocity vector and the downward motion due to the constant acceleration of gravity. We see the kinematic equations as just the mathematical machinery to perform the…

  5. Speed, Acceleration, Chameleons and Cherry Pit Projectiles

    ERIC Educational Resources Information Center

    Planinsic, Gorazd; Likar, Andrej

    2012-01-01

    The paper describes the mechanics of cherry pit projectiles and ends with showing the similarity between cherry pit launching and chameleon tongue projecting mechanisms. The whole story is written as an investigation, following steps that resemble those typically taken by scientists and can therefore serve as an illustration of scientific…

  6. Developing Impact Marking Projectiles Using Triboluminescent Materials

    NASA Astrophysics Data System (ADS)

    Hollerman, William; Fontenot, Ross; Broussard, Brady; Goedeke, Shawn; Guidry, Corey

    2011-06-01

    In 1888, Wiedemann and Schmidt defined triboluminescence as the emission of light produced by mechanical action. In 1999, Sage and Geddes patented a design for a sensor capable of discerning the locations of impacts. Their design involved embedding a sensor inside a material coated with a triboluminescent crystal. Using this idea, the authors have been investigating the triboluminescent properties of several materials (like ZnS:Mn) for their possible use as the active element in ballistic projectiles. These new and improved rounds would be very useful because triboluminescence would mark the landing point of the projectile. This light would be ``cold'' in the sense it was not generated as a result of burning gunpowder or similar pyrotechnics. This light emission would also have a relatively short duration compared to other new projectiles, which generate long-term phosphorescence when two chemicals are mixed at impact (chemiluminescence). This presentation will give a status report in our efforts to develop practical impact marking ballistic projectiles using a triboluminescent charge.

  7. High School Students' Understanding of Projectile Motion Concepts

    ERIC Educational Resources Information Center

    Dilber, Refik; Karaman, Ibrahim; Duzgun, Bahattin

    2009-01-01

    The aim of this study was to investigate the effectiveness of conceptual change-based instruction and traditionally designed physics instruction on students' understanding of projectile motion concepts. Misconceptions related to projectile motion concepts were determined by related literature on this subject. Accordingly, the Projectile Motion…

  8. Stability analyses of the mass abrasive projectile high-speed penetrating into concrete target. Part I: Engineering model for the mass loss and nose-blunting of ogive-nosed projectiles

    NASA Astrophysics Data System (ADS)

    Wu, Hao; Chen, Xiao-Wei; He, Li-Lin; Fang, Qin

    2014-12-01

    The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator, obviously reducing the penetration efficiency of penetrator. Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface, an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile. A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile. The critical value V {0/c} of the initial striking velocity is formulated, and the mass loss of projectile tends to increase weakly nonlinearly with I/ N when V 0 < V {0/c}, whilst the mass loss is proportional to the initial kinetic energy of projectile when V 0 < V {0/c}. The theoretical prediction of V {0/c} is further confirmed to be very close to the experimental value of 1.0 km/s based on 11 sets of different penetration tests. Also the validity of the proposed expressions of mass loss and nose-blunting coefficients of a projectile are verified by the tests. Therefore, a theoretical basis is for the empirical conclusions drawn in previous publications. Regarding the completely empirical determinations of the mass loss and nose-blunting coefficients given in previous papers, the present analysis reveals its physical characteristic and also guarantees its prediction accuracy. The engineering model established in the present paper forms the basis for further discussions on the structural stability and the terminal ballistic stability of ogive-nosed projectiles high-speed penetrating into concrete targets, which will respectively be elaborated in Part II and Part III of the present study.

  9. RESCU: A real space electronic structure method

    NASA Astrophysics Data System (ADS)

    Michaud-Rioux, Vincent; Zhang, Lei; Guo, Hong

    2016-02-01

    In this work we present RESCU, a powerful MATLAB-based Kohn-Sham density functional theory (KS-DFT) solver. We demonstrate that RESCU can compute the electronic structure properties of systems comprising many thousands of atoms using modest computer resources, e.g. 16 to 256 cores. Its computational efficiency is achieved from exploiting four routes. First, we use numerical atomic orbital (NAO) techniques to efficiently generate a good quality initial subspace which is crucially required by Chebyshev filtering methods. Second, we exploit the fact that only a subspace spanning the occupied Kohn-Sham states is required, and solving accurately the KS equation using eigensolvers can generally be avoided. Third, by judiciously analyzing and optimizing various parts of the procedure in RESCU, we delay the O (N3) scaling to large N, and our tests show that RESCU scales consistently as O (N2.3) from a few hundred atoms to more than 5000 atoms when using a real space grid discretization. The scaling is better or comparable in a NAO basis up to the 14,000 atoms level. Fourth, we exploit various numerical algorithms and, in particular, we introduce a partial Rayleigh-Ritz algorithm to achieve efficiency gains for systems comprising more than 10,000 electrons. We demonstrate the power of RESCU in solving KS-DFT problems using many examples running on 16, 64 and/or 256 cores: a 5832 Si atoms supercell; a 8788 Al atoms supercell; a 5324 Cu atoms supercell and a small DNA molecule submerged in 1713 water molecules for a total 5399 atoms. The KS-DFT is entirely converged in a few hours in all cases. Our results suggest that the RESCU method has reached a milestone of solving thousands of atoms by KS-DFT on a modest computer cluster.

  10. The electronic structure of hard materials

    NASA Astrophysics Data System (ADS)

    Winarski, Robert Paul

    This research dissertation involves an experimental as well as a theoretical examination of the electronic structure of hard materials. The materials that are presented in this dissertation cover a wide class of materials, consisting of transition metal borides, irradiated polymer films, theoretically predicted superhard semiconductors, doped intermetallic alloys, and transition metal carbides. The borides are traditionally used in high temperature, hard coating applications, such as rocket nozzle linings, extreme wear surfaces, and corrosion coatings. Measurements of the borides appear to show that the bonding in these hard materials is primarily between the boron atoms in these systems. Also of note are the remarkably short interatomic distances between the boron atoms and between the boron and metal atoms in these materials. Irradiated polymer films are being developed for electronic applications, in the hopes that circuits can be developed that can benefit from the high thermal stability, dielectric properties, and mechanical properties provided by these materials. C3N4 is a theoretically predicted superhard material, and some of the first soft x-ray emission measurements of well-characterized samples of this compound are discussed in this work. Intermetallic alloys, in particular Ni3Al, are rather hard, but brittle metallic alloys. It has been found that the addition of boron atoms, in rather low concentrations, can increase the ductility of these alloys, allowing them to be utilized in a wider variety of applications. Measurements of this system have examined a question regarding the positioning of the boron atoms in the structures of this alloy. Finally, the transition metal carbides are used extensively as coatings in industrial applications such as cutting and grinding tools, and polishing compounds. Measurements of these materials suggest that the high degree of covalency between the metal and carbon atoms is primarily responsible for the hardness of

  11. Impact Features and Projectile Residues in Aerogel Exposed on Mir

    NASA Astrophysics Data System (ADS)

    Hörz, F.; Zolensky, M. E.; Bernhard, R. P.; See, T. H.; Warren, J. L.

    2000-10-01

    Approximately 0.63 m 2 of SiO 2-based aerogel (0.02 g cm -3) was exposed for 18 months on the Mir Station to capture hypervelocity particles from both man-made and natural sources. Optical inspection revealed two major classes of hypervelocity impact features in the aerogel: (1) long, carrot-shaped tracks, well known from laboratory impact experiments, that exhibit a depth- ( t) to-diameter ( D) relationship of t/ D>10, typically 20-30, and (2) shallow pits ( t/ D<10; typically 1-3) that have no laboratory analog. Blunt-nosed, yet deep ( t/ D=5-10), cylindrically shaped cavities suggest the existence of transitional morphologies between these tracks and pits. All tracks contain projectile residues that are unmelted, while pits rarely contain even traces of projectile material. These and other observations suggest that slender tracks form at lower impact velocities than the shallow pits. In addition, we observed that the measured track-length does not systematically correlate with the size of the projectile residue. This renders the reconstruction of encounter velocity and/or projectile mass from measured track dimensions not feasible at present. Recovery of particles from individual tracks is time-consuming, yet readily accomplished by operators familiar with the handling of individual, micrometer-sized particles. Compositional analyses by SEM-EDS identified a variety of man-made and natural particles. A few natural particles were embedded in epoxy, microtomed, and analyzed by TEM. All were polymineralic aggregates that contained olivine exhibiting sharp electron-diffraction spots, and suggesting that the materials had experienced only minimal shock-deformation, if any. One natural particle contained olivine, augite, diopside, troilite, chromite/magnetite, and hercynite, the latter existing as pristine, undeformed octahedral crystals. The olivine in two of the particles were Fo 60-70 and Fo 39-53, and thus, more equilibrated than olivines in most stratospheric

  12. Method of and apparatus for accelerating a projectile

    DOEpatents

    Goldstein, Yeshayahu S. A.; Tidman, Derek A.

    1986-01-01

    A projectile is accelerated along a confined path by supplying a pulsed high pressure, high velocity plasma jet to the rear of the projectile as the projectile traverses the path. The jet enters the confined path at a non-zero angle relative to the projectile path. The pulse is derived from a dielectric capillary tube having an interior wall from which plasma forming material is ablated in response to a discharge voltage. The projectile can be accelerated in response to the kinetic energy in the plasma jet or in response to a pressure increase of gases in the confined path resulting from the heat added to the gases by the plasma.

  13. Apparatus and method for the acceleration of projectiles to hypervelocities

    DOEpatents

    Hertzberg, Abraham; Bruckner, Adam P.; Bogdanoff, David W.

    1990-01-01

    A projectile is initially accelerated to a supersonic velocity and then injected into a launch tube filled with a gaseous propellant. The projectile outer surface and launch tube inner surface form a ramjet having a diffuser, a combustion chamber and a nozzle. A catalytic coated flame holder projecting from the projectile ignites the gaseous propellant in the combustion chamber thereby accelerating the projectile in a subsonic combustion mode zone. The projectile then enters an overdriven detonation wave launch tube zone wherein further projectile acceleration is achieved by a formed, controlled overdriven detonation wave capable of igniting the gaseous propellant in the combustion chamber. Ultrahigh velocity projectile accelerations are achieved in a launch tube layered detonation zone having an inner sleeve filled with hydrogen gas. An explosive, which is disposed in the annular zone between the inner sleeve and the launch tube, explodes responsive to an impinging shock wave emanating from the diffuser of the accelerating projectile thereby forcing the inner sleeve inward and imparting an acceleration to the projectile. For applications wherein solid or liquid high explosives are employed, the explosion thereof forces the inner sleeve inward, forming a throat behind the projectile. This throat chokes flow behind, thereby imparting an acceleration to the projectile.

  14. Study of critical ricochet angle for conical nose shape projectiles

    NASA Astrophysics Data System (ADS)

    Murali, Vijayalakshmi; Law, Manish G.; Naik, Smita D.

    2012-09-01

    The purpose of this research is to formulate a generic analytical model to assess the phenomena of water ricochet for a conical nose shaped projectile. A theoretical model is analyzed to study the critical angle of conical nose shaped projectile entering in water and is extended for different mediums as normal sand and mercury. Numerical Simulation has been carried out to find the effect of tip angle of the conical nose shaped projectile on the critical angle. Critical angle is defined as that angle of impact of the projectile above which ricochet will occur. This angle is obtained by balancing the momentums acting on the projectile at the time of impact on the basis of Newtonian theory. Major factors affecting critical angle are impact velocity, impact angle, density of the projectile and the target. An attempt has been made to study the effect of longitudinal spin of the projectile on the critical angle.

  15. Shallow-angle water entry of ballistic projectiles

    NASA Astrophysics Data System (ADS)

    Truscott, Tadd T.; Gomez, Jason T.; Beal, David N.; Techet, Alexandra H.

    2008-11-01

    The water-entry of ballistic projectiles is investigated using high-speed digital imaging. Projectiles enter the water at shallow angles to the free surface, 5^o-15^o, without ricochet at Mach numbers between 0.3 and 2.0. Projectile dynamics, critical entry angle, and cavity growth are discussed. Geometric modifications to a projectile allow it to travel large distances underwater assuming a sufficiently large air-cavity is formed after impact, which dramatically decreases drag on the projectile. Results show that successful water-entry occurs for projectiles with modified tip geometries at Mach numbers ranging from 0.3 to 2; these projectile modifications include tip geometry and material properties. A theoretical cavity model compares well with the experimental data and will be discussed for a range of experimental conditions.

  16. Graph-based linear scaling electronic structure theory

    NASA Astrophysics Data System (ADS)

    Niklasson, Anders M. N.; Mniszewski, Susan M.; Negre, Christian F. A.; Cawkwell, Marc J.; Swart, Pieter J.; Mohd-Yusof, Jamal; Germann, Timothy C.; Wall, Michael E.; Bock, Nicolas; Rubensson, Emanuel H.; Djidjev, Hristo

    2016-06-01

    We show how graph theory can be combined with quantum theory to calculate the electronic structure of large complex systems. The graph formalism is general and applicable to a broad range of electronic structure methods and materials, including challenging systems such as biomolecules. The methodology combines well-controlled accuracy, low computational cost, and natural low-communication parallelism. This combination addresses substantial shortcomings of linear scaling electronic structure theory, in particular with respect to quantum-based molecular dynamics simulations.

  17. Probing Actinide Electronic Structure through Pu Cluster Calculations

    DOE PAGESBeta

    Ryzhkov, Mickhail V.; Mirmelstein, Alexei; Yu, Sung-Woo; Chung, Brandon W.; Tobin, James G.

    2013-02-26

    The calculations for the electronic structure of clusters of plutonium have been performed, within the framework of the relativistic discrete-variational method. Moreover, these theoretical results and those calculated earlier for related systems have been compared to spectroscopic data produced in the experimental investigations of bulk systems, including photoelectron spectroscopy. Observation of the changes in the Pu electronic structure as a function of size provides powerful insight for aspects of bulk Pu electronic structure.

  18. Graph-based linear scaling electronic structure theory.

    PubMed

    Niklasson, Anders M N; Mniszewski, Susan M; Negre, Christian F A; Cawkwell, Marc J; Swart, Pieter J; Mohd-Yusof, Jamal; Germann, Timothy C; Wall, Michael E; Bock, Nicolas; Rubensson, Emanuel H; Djidjev, Hristo

    2016-06-21

    We show how graph theory can be combined with quantum theory to calculate the electronic structure of large complex systems. The graph formalism is general and applicable to a broad range of electronic structure methods and materials, including challenging systems such as biomolecules. The methodology combines well-controlled accuracy, low computational cost, and natural low-communication parallelism. This combination addresses substantial shortcomings of linear scaling electronic structure theory, in particular with respect to quantum-based molecular dynamics simulations. PMID:27334148

  19. An experimental, metallurgical and modelling analysis of silver and copper explosively formed projectiles (EFPs)

    NASA Astrophysics Data System (ADS)

    MacMahon, J.; Church, P.; Cullis, I.; Findlay, S.; Hart, A.; Wickenden, M.

    2003-09-01

    This paper describes an experimental, metallurgical and modelling study into the structure and properties of silver and copper explosively fonned projectiles. The project started with the conditioning, processing and characterisation of the non-shocked silver and copper materials. Here, the material constants were derived for the Goldthorpe path-dependant constitutive model[1]. For the purposes of this study the warhead designs produced some conservative EFP projectiles. These were designed using the indigenous Eulerian hydrocode GRIM. Due to the ductile nature of both silver and copper, care was taken with respect to the equation of state, in particular with the temperature supplied to the constitutive models. The EFP projectiles were then experimentally recovered using soft-capturing techniques[2]. The comparison of the code predictions with the experimental radiography results was very good, suggesting that there could not be large material phase changes or significant changes to the microstructure of the material due to the explosively applied shock. Finally, the sectioning and metallurgical analysis of the recovered projectiles showed that although there were some variations in both grain size, microstructure and material hardness throughoutlacross the sectioned projectiles, these were not significant.

  20. An Inexpensive Mechanical Model for Projectile Motion

    NASA Astrophysics Data System (ADS)

    Kagan, David

    2011-05-01

    As experienced physicists, we see the beauty and simplicity of projectile motion. It is merely the superposition of uniform linear motion along the direction of the initial velocity vector and the downward motion due to the constant acceleration of gravity. We see the kinematic equations as just the mathematical machinery to perform the calculations. What do our students see? Likely, most see no deeper than the operational understanding needed to use the kinematic equations. Described below is a device (shown in Fig. 1) that illustrates the physicist's view of projectile motion. It can be used as a classroom demonstration or as a project for your students, and it costs less than three dollars to make.

  1. Modeling projectile impact onto prestressed ceramic targets

    NASA Astrophysics Data System (ADS)

    Holmquist, T. J.; Johnson, G. R.

    2003-09-01

    This work presents computed results for the responses of ceramic targets, with and without prestress, subjected to projectile impact. Also presented is a computational technique to include prestress. Ceramic materials have been considered for armor applications for many years because of their high strength and low density. Many researchers have demonstrated that providing confinement enhances the ballistic performance of ceramic targets. More recently, prestressing the ceramic is being considered as an additional enhancement technique. This work investigates the effect of prestressing the ceramic for both thin and thick target configurations subjected to projectile impact. In all cases the targets with ceramic prestress provided enhanced ballistic performance. The computed results indicate that prestressed ceramic reduces and/or delays failure, resulting in improved ceramic performance and ballistic efficiency.

  2. The aerodynamics of some guided projectiles

    NASA Technical Reports Server (NTRS)

    Spearman, M. L.

    1984-01-01

    Some characteristic projectile shapes are considered with various added components intended to provide lift, stability, and control. The intent of the additions is to provide some means for altering the normal ballistic flight path of a projectile for various purposes such as: achieving greater accuracy at the impact point, selecting alternate impact points, extending range, improved evasion, and so on. The configurations presented illustrate the effects of a flare, wings, and tails for providing stability and lift, and the effects of aft-tails, a close-coupled flap, and all-moving forward wings for control. The relative merits of the various configurations, all of which provided for flight path alterations, are discussed.

  3. The aerodynamics of some guided projectiles

    NASA Technical Reports Server (NTRS)

    Spearman, M. L.

    1984-01-01

    Some characteristic projectile shapes are considered with various added components intended to provide lift, stability, and control. The intent of the additions is to provide some means for altering the normal ballistic flight path of a projectile for various purposes such as: achieving greater accuracy at the impact point, selecting alternate impact points, extending range, improved evasion, and so on. The configurations presented illustrate the effects of a flare, wings, and tails for providing stability and lift, and the effects of aft-tails, a close-coupled flap, and all-moving forward wings for control. The relative merits of the various configurations, all of which provided for flight path alterations are discussed.

  4. Projectile Density Effects on Shield Performance

    NASA Technical Reports Server (NTRS)

    Christiansen, Eric L.; Lear, Dana; Lyons, Frankel; Davis, Alan

    2009-01-01

    In the past, the orbital debris environment was modeled as consisting entirely of aluminum particles. As a consequence, most of the impact test database on spacecraft micro-meteoroid and orbital debris (MMOD) shields, and the resulting ballistic limit equations used to predict shielding performance, has been based on using aluminum projectiles. Recently, data has been collected from returned spacecraft materials and other sources that indicate higher and lower density components of orbital debris also exist. New orbital debris environment models such as ORDEM2008 provide predictions of the fraction of orbital debris in various density bins (high = 7.9 g/cu cm, medium = 2.8 g/cu cm, and low = 0.9-1.1 g/cu cm). This paper describes impact tests to assess the effects of projectile density on the performance capabilities of typical MMOD shields. Updates to shield ballistic limit equations are provided based on results of tests and analysis.

  5. Projectile compositions and modal frequencies on the chemistry of micrometeoroids LDEF experiment

    NASA Technical Reports Server (NTRS)

    Bernhard, Ronald P.; See, Thomas H.; Hoerz, Friedrich

    1993-01-01

    The Chemistry of Micrometeoroids Experiment (LDEF instrument A0187-1) exposed witness plates of high-purity gold (greater than 99.99 percent Au) and commercial aluminum (greater than 99 percent Al) with the objective of analyzing the residues of cosmic-dust and orbital-debris particles associated with hypervelocity impact craters. The gold substrates were located approximately 8 deg off LDEF's trailing edge (Bay A03), while the aluminum surfaces resided in Bay A11, approximately 52 deg from LDEF's leading edge. SEM-EDX techniques were employed to analyze the residues associated with 199 impacts on the gold and 415 impacts on the aluminum surfaces. The residues that could be analyzed represent natural or man-made materials. The natural particles dominate at all particle sizes less than 5 micron. It is possible to subdivide both particle populations into subclasses. Chondritic compositions dominate the natural impactors (71 percent), followed by monomineralic, mafic-silicate compositions (26 percent), and by Fe-Ni rich sulfides (approximately 3 percent). Approximately 30 percent of all craters on the gold collectors were caused by man-made debris such as aluminum, paint flakes, and other disintegrated, structural and electronic components. Equations-of-state and associated calculations of shock stresses for typical LDEF impacts into the gold and aluminum substrates suggest that substantial vaporization may have occurred during many of the impacts and is the reason why approximately 50 percent of all craters did not contain sufficient residue to permit analysis by the SEM-EDX technique. After converting the crater diameters into projectile sizes using encounter speeds typical for the trailing-edge and forward-facing (Row 11) directions, and accounting for normalized exposure conditions of the CME collectors, we derived the absolute and relative fluxes of specific projectile classes. The natural impactors encounter all LDEF pointing directions with comparable, modal

  6. Energy loss of hydrogen projectiles in gases

    SciTech Connect

    Schiefermueller, A.; Golser, R.; Stohl, R.; Semrad, D. )

    1993-12-01

    The stopping cross sections of H[sub 2], D[sub 2], He, and Ne for hydrogen projectiles in the energy range 3--20 keV per nucleon have been measured by time of flight. We compare our experimental result to the sum of the individual contributions due to excitation and ionization of the target and of the projectile, respectively, and due to charge exchange, using published cross-section data. Satisfactory agreement is found only for the He target and only at moderate projectile velocities, whereas for H[sub 2] and D[sub 2] the calculated values are about 30% too low. A Monte Carlo program allows us to simulate the measured time-of-flight spectra and to explain minor trends in the experimental data: for increased Ne gas pressure, an increased specific energy loss has been found that can be traced to different regions of impact parameters selected in our transmission geometry. This also explains, in part, the increased specific energy loss for deuterons compared to protons of equal velocity that is most evident for Ne. In contrast, a decrease of the specific energy loss with increasing pressure for He may be explained by impurities in the target gas. If we correct for the effect of impurities, the stopping cross section of He at 4 keV per nucleon is slightly smaller (0.60[times]10[sup [minus]15] eV cm[sup 2]) than published earlier (0.72[times]10[sup [minus]15] eV cm[sup 2]) and depends on the 3.8th power of projectile velocity.

  7. A hypervelocity projectile launcher for well perforation

    SciTech Connect

    Albright, J.N.; Fugelso, L.E.; Lagner, G.C.; Burns, K.L.

    1989-01-01

    Current oil well perforation techniques use low- to medium-velocity gun launchers for completing wells in soft rock. Shaped-charge jets are normally used in harder, more competent rock. A device to create a much higher velocity projectile was designed. This launcher will provide an alternative technique to be used when the conventional devices do not yield the maximum well performance. It is an adaptation of the axial cavity in a high explosive (HE) annulus design, with the axial cavity being filled with a low density foam material. Two configurations were tested; both had an HE annulus filled with organic foam, one had a projectile. Comparison of the two shots was made. A time sequence of Image Intensifier Camera photographs and sequential, orthogonal flash x-ray radiographs provided information on the propagation of the foam fragments, the first shock wave disturbance, the projectile motion and deformation, and the direct shock wave transmission from the main HE charge. DYNA2D calculations were made to assist in the experimental interpretation. 25 refs., 9 figs.

  8. Improvements to a model of projectile fragmentation

    NASA Astrophysics Data System (ADS)

    Mallik, S.; Chaudhuri, G.; Das Gupta, S.

    2011-11-01

    In a recent paper [Phys. Rev. CPRVCAN0556-281310.1103/PhysRevC.83.044612 83, 044612 (2011)] we proposed a model for calculating cross sections of various reaction products which arise from disintegration of projectile-like fragments resulting from heavy-ion collisions at intermediate or higher energy. The model has three parts: (1) abrasion, (2) disintegration of the hot abraded projectile-like fragment (PLF) into nucleons and primary composites using a model of equilibrium statistical mechanics, and (3) possible evaporation of hot primary composites. It was assumed that the PLF resulting from abrasion has one temperature T. Data suggested that, while just one value of T seemed adequate for most cross-section calculations, a single value failed when dealing with very peripheral collisions. We have now introduced a variable T=T(b) where b is the impact parameter of the collision. We argue that there are data which not only show that T must be a function of b but, in addition, also point to an approximate value of T for a given b. We propose a very simple formula: T(b)=D0+D1[As(b)/A0] where As(b) is the mass of the abraded PLF and A0 is the mass of the projectile; D0 and D1 are constants. Using this model we compute cross sections for several collisions and compare with data.

  9. Spin alignment of excited projectiles due to target spin-flip interactions

    NASA Astrophysics Data System (ADS)

    Charity, R. J.; Elson, J. M.; Manfredi, J.; Shane, R.; Sobotka, L. G.; Chajecki, Z.; Coupland, D.; Iwasaki, H.; Kilburn, M.; Lee, Jenny; Lynch, W. G.; Sanetullaev, A.; Tsang, M. B.; Winkelbauer, J.; Youngs, M.; Marley, S. T.; Shetty, D. V.; Wuosmaa, A. H.

    2015-02-01

    The sequential breakup of E /A =65.5 -MeV7Be and E /A =36.6 -MeV6Li projectiles excited through inelastic interactions with 9Be target nuclei has been studied. For events where the target nucleus remained in its ground state, significant alignment of the excited projectile's spin axis parallel or antiparallel to the beam direction was observed. This unusual spin alignment was found to be largely independent of the projectile's scattering angle and it was deduced that the target nucleus has a significant probability of changing its spin orientation during the interaction. It is proposed that the unusual spin alignment is a consequence of the molecular structure of the 9Be nucleus.

  10. Dramatic changes in electronic structure revealed by fractionally charged nuclei

    SciTech Connect

    Cohen, Aron J.; Mori-Sánchez, Paula

    2014-01-28

    Discontinuous changes in the electronic structure upon infinitesimal changes to the Hamiltonian are demonstrated. These are revealed in one and two electron molecular systems by full configuration interaction (FCI) calculations when the realm of the nuclear charge is extended to be fractional. FCI electron densities in these systems show dramatic changes in real space and illustrate the transfer, hopping, and removal of electrons. This is due to the particle nature of electrons seen in stretched systems and is a manifestation of an energy derivative discontinuity at constant number of electrons. Dramatic errors of density functional theory densities are seen in real space as this physics is missing from currently used approximations. The movements of electrons in these simple systems encapsulate those in real physical processes, from chemical reactions to electron transport and pose a great challenge for the development of new electronic structure methods.

  11. Forensic and clinical issues in the use of frangible projectile.

    PubMed

    Komenda, Jan; Hejna, Petr; Rydlo, Martin; Novák, Miroslav; Krajsa, Jan; Racek, František; Rejtar, Pavel; Jedlička, Luděk

    2013-08-01

    Frangible projectiles for firearms, which break apart on impact, are mainly used by law enforcement agencies for training purposes, but can also be used for police interventions. Apart from the usual absence of lead in the projectiles, the main advantage of using frangible projectiles is the reduced risk of ricochet after impact with a hard target. This article describes the design and function of frangible projectiles, and describes gunshot wounds caused by ultra-frangible projectiles which fragment after penetration of soft tissues. Shooting experiments performed by the authors confirmed that differences in the geometry and technology of frangible projectiles can significantly modify their wounding effects. Some frangible projectiles have minimal wounding effects because they remain compact after penetration of soft tissues, comparable to standard fully jacketed projectiles. However, a number of ultra-frangible projectiles disintegrate into very small fragments after impact with a soft tissue substitute. In shooting experiments, we found that the terminal behavior of selected ultra-frangible projectiles was similar in a block of ballistic gel and the soft tissues of the hind leg of a pig, except that the degree of disintegration was less in the gel. PMID:23910864

  12. On the forces produced by oblique projectile impact

    SciTech Connect

    Yew, C.H.

    1995-12-31

    A mathematical model for calculating the force produced by projectile impact on terrestrial target was developed based on assumptions that (1) the projectile was rigid, and (2) the target material near the nose section was displaced normally to the nose surface by the penetrating projectile. The assumption suggested that the crater or tunnel produced by the penetrating projectile was similar to that produced by a series of dynamic spherical cavity expansions initiated at the nose tip, and the growth rate of cavities was restricted by the nose shape of the projectile and its penetrating velocity vector. The model allowed the calculation of pressure against the penetrating projectile by taking the inertia and the resistant pressure of the moving soil into consideration. The effect of projectile obliquity on pressure distribution on the nose section of projectile could also be calculated by relating the angle of attack and the angle of incidence to the rate of local radius change of the expanding cavity. Using this model, the time history of force vector exerted on the projectile as well as the corresponding trajectory of penetration were calculated. For a small angle of incidence, the calculated axial and lateral forces exerted on the nose of projectile showed a reasonable agreement with those measured from reverse ballistic impact tests. It was demonstrated that the magnitude of forces depended upon the impact velocity, the shape of projectile`s nose section, and the relative density between the projectile and the target material. There were no quantitative measurement of forces when the angle of incidence was large i.e., a shallow impact. For this case, the calculated forces were compared and discussed with the results from similitude analysis.

  13. Electronic band structure and photoemission: A review and projection

    SciTech Connect

    Falicov, L.M.

    1987-09-01

    A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types: ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations; surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby; and many-body calculations, which go beyond average-field approximations and consider dynamic rearrangement effects caused by electron-electron correlations during the photoemission process. 44 refs.

  14. Spatial and electron structure of substituted gold clusters

    NASA Astrophysics Data System (ADS)

    Yarzhemsky, V. G.; Kazaryan, M. A.; Bulychev, N. A.; Dyakov, Y. A.; Kosheleva, O. K.; Chen, C. H.

    2015-12-01

    The structure of intermetallic clusters Au12M (M=Hf, Ta, W, Re, Os) and features of their interaction with electron donors and acceptor atoms, i.e. H and F, were investigated making use computer calculation based of density functional theory. In was found that metal clusters with effective electron number equal to 18 have more symmetrical shape then that with a number of electrons differing from 18. The interaction of gold nanoparticles with silica was modeled by attachment of SiO4H groups and the connection of the electronic structure with electronic transitions in spaser is discussed.

  15. Target and Projectile: Material Effects on Crater Excavation and Growth

    NASA Technical Reports Server (NTRS)

    Anderson, J. L. B.; Burleson, T.; Cintala, Mark J.

    2010-01-01

    Scaling relationships allow the initial conditions of an impact to be related to the excavation flow and final crater size and have proven useful in understanding the various processes that lead to the formation of a planetary-scale crater. In addition, they can be examined and tested through laboratory experiments in which the initial conditions of the impact are known and ejecta kinematics and final crater morphometry are measured directly. Current scaling relationships are based on a point-source assumption and treat the target material as a continuous medium; however, in planetary-scale impacts, this may not always be the case. Fragments buried in a megaregolith, for instance, could easily approach or exceed the dimensions of the impactor; rubble-pile asteroids could present similar, if not greater, structural complexity. Experiments allow exploration into the effects of target material properties and projectile deformation style on crater excavation and dimensions. This contribution examines two of these properties: (1) the deformation style of the projectile, ductile (aluminum) or brittle (soda-lime glass) and (2) the grain size of the target material, 0.5-1 mm vs. 1-3 mm sand.

  16. Numerical simulations of gun-launched kinetic energy projectiles subjected to asymmetric projectile base pressure

    SciTech Connect

    Rabern, D.A.

    1991-01-01

    Three-dimensional numerical simulations were performed to determine the effect of an asymmetric base pressure on kinetic energy projectiles during launch. A matrix of simulations was performed in two separate launch environments. One launch environment represented a severe lateral load environment, while the other represented a nonsevere lateral load environment based on the gun tube straightness. The orientation of the asymmetric pressure field, its duration, the projectile's initial position, and the tube straightness were altered to determine the effects of each parameter. The pressure asymmetry translates down the launch tube to exit parameters and is washed out by tube profile. Results from the matrix of simulations are presented.

  17. Molecular dynamics simulations of sputtering of Langmuir-Blodgett multilayers by keV C60 projectiles

    PubMed Central

    Paruch, R.; Rzeznik, L.; Czerwinski, B.; Garrison, B. J.; Winograd, N.; Postawa, Z.

    2009-01-01

    Coarse-grained molecular dynamics computer simulations are applied to investigate fundamental processes induced by an impact of keV C60 projectile at an organic overlayer composed of long, well-organized linear molecules. The energy transfer pathways, sputtering yields, and the damage induced in the irradiated system, represented by a Langmuir-Blodgett (LB) multilayers composed from molecules of bariated arachidic acid, are investigated as a function of the kinetic energy and impact angle of the projectile and the thickness of the organic system. In particular, the unique challenges of depth profiling through a LB film vs. a more isotropic solid are discussed. The results indicate that the trajectories of projectile fragments and, consequently, the primary energy can be channeled by the geometrical structure of the overlayer. Although, a similar process is known from sputtering of single crystals by atomic projectiles, it has not been anticipated to occur during C60 bombardment due to the large size of the projectile. An open and ordered molecular structure of LB films is responsible for such behavior. Both the extent of damage and the efficiency of sputtering depend on the kinetic energy, the impact angle, and the layer thickness. The results indicate that the best depth profiling conditions can be achieved with low-energy cluster projectiles irradiating the organic overlayer at large off-normal angles. PMID:20174461

  18. Lightweight Exoatmospheric Projectile (LEAP) test program. Supplemental environmental assessment

    NASA Astrophysics Data System (ADS)

    1992-06-01

    The proposed action is to modify previously planned Lightweight Exoatmospheric Projectile (LEAP) Test Program activities (LEAP EA, July 1991, Ref 32) at White Sands Missile Range (WSMR), New Mexico; Kwajalein Missile Range (KMR), U.S. Army Kwajalein Atoll (USAKA); and Wake Island. The proposed action includes modifications of flight trajectories for LEAP flights 3, 5, and 6. Two additional flights, LEAP-X and LEAP-7 have been added to the program. LEAP-X is a single rocket test flight from KMR and LEAP-7 is a two-rocket test flight from KMR and Wake Island. Component/assembly ground tests will take place at Orbital Sciences Corporation (OSC), Space Data Division (SDD), Chandler, Arizona; Phillips Laboratory, Edwards Air Force Base, California; Rocketdyne Division of Rockwell International; Boeing Aerospace and Electronics, Kent, Washington; Hughes Aircraft Corporation, Missile Systems Group, Canoga Park California; Aerojet, Sacramento, California; and Thiokol Corporation, Elkton, Maryland.

  19. Computational studies of projectile melt in impact with typical whipple shields

    SciTech Connect

    Rhoades, C.E. Jr.; Alme, M.L.

    1994-12-01

    Protecting space-based structures against the impact of orbital debris is an important problem of current interest. This paper presents scaling results based on simulations with the CALE computer program of aluminum projectile impacting typical aluminum Whipple shields at speeds of 6 to 14 km/s. The objective was to determine the extent of projectile and shield material melting. The approach was to perform a matrix of computer simulations varying the impact speed from 6 to 14 km/s and varying the areal density of the shield from 5 percent to 80 percent of the centerline areal density of the projectile. The projectile radius was fixed at 9.5 mm (mass = 1.27 grams). The melt state of the projectile material and the shield material was assessed after release of the initial shock. The post-release specific energy in the projectile and in the shield was compared with the enthalpy of incipient melt and the enthalpy of complete melt provided in the Hultgren Tables. Material with specific energy greater than the enthalpy of complete melt was assumed to be fully melted. Material with specific energy greater than the enthalpy of incipient melt but less than that of complete melt was assumed to be partially solid and partially melted mixed phase material with no strength. Material with specific energy less than the enthalpy of incipient melt was assumed to be in a solid state with strength. It is likely that this solid material is in a highly fragmented state as a result of the initial shock.

  20. Railgun using plasma initiation separated from the projectile

    SciTech Connect

    Katsuki, S.; Akiyama, H.; Yamada, T.; Eguchi, N.; Maeda, S.; Sato, K.N.

    1993-12-01

    Preacceleration of a projectile is quite important to reduce the erosion of the bore surface in a railgun. Gas guns, electrothermal guns and other railguns have been used to preaccelerate the projectile. Here, the new method using Plasma Initiation Separated from the Projectile (PISP method) is proposed, and its effectiveness is confirmed experimentally. A thin copper is placed near the edge of the railgun, which explodes and forms a plasma that has a fast flow velocity due to the Lorentz force. This fast flowing plasma collides with the projectile which obtains an initial velocity mainly by the momentum transfer. Since the current increases while only the plasma is accelerated, the driving force of the projectile just after the collision of the plasma with the projectile is large. In other words, the PISP method works as an inductive energy storage circuit with an opening switch.

  1. Design and fabrication of projectiles for round bore railguns

    SciTech Connect

    Susoeff, A.R.; Hawke, R.S.

    1985-03-07

    A hypervelocity railgun system which operates in a vacuum and uses a gas gun injector to pre-accelerate the projectiles required that the projectile seal operate over wide pressure and velocity ranges. In our case, the helium gas gun injector operated at up to 35 MPa (5 ksi) while the railgun, using a plasma arc armature, operated at up to 150 MPa (22 ksi). In addition to gas and arc sealing, it was necessary that a metal fuse be attached to the rear of the projectile in order to electrically commutate the rails upon entry to the railgun. This paper discusses procedures and techniques in the design and fabrication of projectiles for a round bore railgun. It is divided into three sections: (1) machining the projectile; (2) fuse fabrication; and (3) assembly of the projectile/fuse package.

  2. Design and testing of high-pressure railguns and projectiles

    SciTech Connect

    Peterson, D.R.; Fowler, C.M.

    1984-03-01

    The results of high-pressure tests of four railgun designs and four projectile types are presented. All tests were conducted at the Los Alamos explosive magnetic-flux compression facility in Ancho Canyon. The data suggest that the high-strength projectiles have lower resistance to acceleration than the lowstrength projectiles, which expand against the bore during acceleration. The railguns were powered by explosive magneticflux compression generators. Calculations to predict railgun and power supply performance were performed by Kerrisk.

  3. Design and testing of high-pressure railguns and projectiles

    SciTech Connect

    Peterson, D.R.; Fowler, C.M.; Cummings, C.E.; Kerrisk, J.F.; Parker, J.V.; Marsh, S.P.; Adams, D.F.

    1983-01-01

    The results of high-pressure tests of four railgun designs and four projectile types are presented. All tests were conducted at the Los Alamos explosive magnetic-flux compression facility in Ancho Canyon. The data suggest that the high-strength projectiles have lower resistance to acceleration than the low-strength projectiles, which expand against the bore during acceleration. The railguns were powered by explosive magnetic-flux compression generators. Calculations to predict railgun and power supply performance were performed.

  4. Ionization of small molecules induced by H+, H e+ , and N+ projectiles: Comparison of experiment with quantum and classical calculations

    NASA Astrophysics Data System (ADS)

    Kovács, S. T. S.; Herczku, P.; Juhász, Z.; Sarkadi, L.; Gulyás, L.; Sulik, B.

    2016-07-01

    We report the energy and angular distribution of ejected electrons from C H4 and H2O molecules impacted by 1 MeV H+, H e+ , and 650 keV N+ ions. Spectra were measured at different observation angles, from 2 to 2000 eV. The obtained absolute double-differential electron-emission cross sections (DDCSs) were compared with the results of classical trajectory Monte Carlo (CTMC) and continuum distorted wave, eikonal initial state (CDW-EIS) calculations. For the bare H+ projectile both theories show remarkable agreement with the experiment at all observed angles and energies. The CTMC results are in similarly good agreement with the DDCS spectra obtained for impact by dressed H e+ and N+ ions, where screening effects and electron loss from the projectile gain importance. The CDW-EIS calculations slightly overestimate the electron loss for 1 MeV H e+ impact, and overestimate both the target and projectile ionization at low emitted electron energies for 650 keV N+ impact. The contribution of multiple electron scattering by the projectile and target centers (Fermi shuttle) dominates the N+-impact spectra at higher electron energies, and it is well reproduced by the nonperturbative CTMC calculations. The contributions of different processes in medium-velocity collisions of dressed ions with molecules are determined.

  5. Penetration into limestone targets with ogive-nose steel projectiles

    SciTech Connect

    Frew, D.J.; Green, M.L.; Forrestal, M.J.; Hanchak, S.J.

    1996-12-01

    We conducted depth of penetration experiments into limestone targets with 3.0 caliber-radius-head, 4340 Rc 45 steel projectiles. Powder guns launched two projectiles with length-to-diameter ratios of ten to striking velocities between 0.4 and 1.5 km/s. Projectiles had diameters and masses of 12.7 mm, 0. 117 kg and 25.4 mm, 0.610 kg. Based on data sets with these two projectile scales, we proposed an empirical penetration equation that described the target by its density and an empirical strength constant determined from penetration depth versus striking velocity data.

  6. Prediction of projectile ricochet behavior after water impact.

    PubMed

    Baillargeon, Yves; Bergeron, Guy

    2012-11-01

    Although not very common, forensic investigation related to projectile ricochet on water can be required when undesirable collateral damage occurs. Predicting the ricochet behavior of a projectile is challenging owing to numerous parameters involved: impact velocity, incident angle, projectile stability, angular velocity, etc. Ricochet characteristics of different projectiles (K50 BMG, 0.5-cal Ball M2, 0.5-cal AP-T C44, 7.62-mm Ball C21, and 5.56-mm Ball C77) were studied in a pool. The results are presented to assess projectile velocity after ricochet, ricochet angle, and projectile azimuth angle based on impact velocity or incident angle for each projectile type. The azimuth ranges show the highest variability at low postricochet velocity. The critical ricochet angles were ranging from 15 to 30°. The average ricochet angles for all projectiles were pretty close for all projectiles at 2.5 and 10° incident angles for the range of velocities studied. PMID:22536929

  7. Design and testing of high-pressure railguns and projectiles

    NASA Technical Reports Server (NTRS)

    Peterson, D. R.; Fowler, C. M.; Cummings, C. E.; Kerrisk, J. F.; Parker, J. V.; Marsh, S. P.; Adams, D. F.

    1984-01-01

    Attention is given to the results of high-pressure tests involving four railgun designs and four projectile types. Explosive magnetic-flux compression generators were employed to power the railguns. On the basis of the experimental data, it appears that the high-strength projectiles have lower resistance to acceleration than low-strength projectiles, which expand against the bore during acceleration. While confined in the bore, polycarbonate projectiles can be subjected to pressures as high as 1.3 GPa without shattering. In multishot railguns, it is important to prevent an accumulation of sooty material from the plasma armature in railgun seams.

  8. Design and testing of high-pressure railguns and projectiles

    NASA Astrophysics Data System (ADS)

    Peterson, D. R.; Fowler, C. M.; Cummings, C. E.; Kerrisk, J. F.; Parker, J. V.; Marsh, S. P.; Adams, D. F.

    1984-03-01

    Attention is given to the results of high-pressure tests involving four railgun designs and four projectile types. Explosive magnetic-flux compression generators were employed to power the railguns. On the basis of the experimental data, it appears that the high-strength projectiles have lower resistance to acceleration than low-strength projectiles, which expand against the bore during acceleration. While confined in the bore, polycarbonate projectiles can be subjected to pressures as high as 1.3 GPa without shattering. In multishot railguns, it is important to prevent an accumulation of sooty material from the plasma armature in railgun seams.

  9. Electric rail gun projectile acceleration to high velocity

    NASA Technical Reports Server (NTRS)

    Bauer, D. P.; Mccormick, T. J.; Barber, J. P.

    1982-01-01

    Electric rail accelerators are being investigated for application in electric propulsion systems. Several electric propulsion applications require that the rail accelerator be capable of launching projectiles at velocities above 10 km/s. An experimental program was conducted to develop rail accelerator technology for high velocity projectile launch. Several 6 mm bore, 3 m long rail accelerators were fabricated. Projectiles with a mass of 0.2 g were accelerated by plasmas, carrying currents up to 150 kA. Experimental design and results are described. Results indicate that the accelerator performed as predicted for a fraction of the total projectile acceleration. The disparity between predicted and measured results are discussed.

  10. Approximate analysis of balloting motion of railgun projectiles. Technical report

    SciTech Connect

    Chu, S.H.

    1991-07-01

    This is the final of three reports dealing with the in-bore balloting motion of a projectile fired from an electromagnetic railgun. Knowledge of projectile in-bore motion is important to its design and the design of the railgun. It is a complicated problem since many parameters are involved and it is not easy to determine the interacting relationships between them. To make the problem easier to understand it was analyzed on several levels. Beginning from the basic simple model which computed only the axial motion, more complicated models were introduced in upper levels that included the more significant lateral forces and gun tube vibration effects. This report deals with the approximate analysis of balloting motion. This model considers the effects of the propulsion force, the friction force of the projectile package (projectile and armature), air resistance, gravity, the elastic forces, and the projectile/barrel clearance. To simplify the modeling, a plane motion configuration is assumed. Though the projectile is moving with a varying yaw angle, the axes of the barrel and the projectile package, and the projectile center of gravity are always considered in a plane containing the centerlines of the rails. Equations of motion are derived and solved. A sample computation is performed and the results plotted to give a clearer understanding of projectile in-bore motion.

  11. Continuous measurements of in-bore projectile velocity

    SciTech Connect

    Asay, J.R.; Konrad, C.H.; Hall, C.A.; Shahinpoor, M.; Hickman, R.

    1988-01-01

    The application of velocity interferometry to the continuous measurement of in-bore projectile velocity in a small-bore three-stage railgun is described. These measurements are useful for determining projectile acceleration and for evaluating gun performance. The launcher employed in these studies consists of a two-stage light gas gun used to inject projectiles into a railgun for additional acceleration. Results obtained for projectile velocities to 7.4 km/s with the two-stage injector are reported and potential improvements for railgun applications are discussed. 12 refs., 7 figs.

  12. Continuous measurements of in-bore projectile velocity

    SciTech Connect

    Asay, J.R.; Konrad, C.H.; Hall, C.A. ); Shahinpoor, M. . Dept. of Mechanical Engineering); Hickman, R. )

    1989-01-01

    The application of velocity interferometry to the continuous measurement of in-bore projectile velocity in a small-bore three-stage railgun is described. These measurements are useful for determining projectile acceleration and for evaluating gun performance. The launcher employed in these studies consists of a two-stage light gas gun used to inject projectiles into a railgun for additional acceleration. Results obtained for projectile velocities to 7.4 km/s with the two-stage injector are reported and potential improvements for railgun applications are discussed.

  13. Microcraters formed in glass by low density projectiles

    NASA Technical Reports Server (NTRS)

    Mandeville, J.-C.; Vedder, J. F.

    1971-01-01

    Microcraters were produced in soda-lime glass by the impact of low density projectiles of polystyrene with masses between 0.7 and 62 picograms and velocities between 2 and 14 kilometers per second. The morphology of the craters depends on the velocity and angle of incidence of the projectiles. The transitions in morphology of the craters formed by polystyrene spheres occur at higher velocities than they do for more dense projectiles. For oblique impact, the craters are elongated and shallow with the spallation threshold occuring at higher velocity. For normal incidence, the total displaced mass of the target material per unit of projectile kinetic energy increases slowly with the energy.

  14. Syntheses and electronic structures of decamethylmetallocenes

    SciTech Connect

    Robbins, J.L.

    1981-04-01

    The synthesis of decamethylmanganocene ((eta-C/sub 5/(CH/sub 3/)/sub 5/)/sub 2/Mn or (Me/sub 5/Cp)/sub 2/Mn)) is described. Magnetic susceptibility and electron paramagnetic resonance (EPR) studies show that (Me/sub 5/Cp)/sub 2/Mn is a low-spin, 17-electron compound with an orbitally degenerate, /sup 2/E/sub 2g/ (e/sub 2g//sup 3/ a/sub 1g//sup 2/) ground state. An x-ray crystallographic study of (Me/sub 5/Cp)/sub 2/Mn shows that it is a monomeric, D/sub 5d/ decamethylmetallocene with metal to ring carbon distances that are about 0.3 A shorter than those determined for high-spin manganocenes. The syntheses of new (Me/sub 5/Cp)/sub 2/M (M = Mg,V,Cr,Co, and Ni) and ((Me/sub 5/Cp)/sub 2/M)PF/sub 6/ (M = Cr,Co, and Ni) compounds are described. In addition, a preparative route to a novel, dicationic decamethylmetallocene, ((Me/sub 5/Cp)/sub 2/Ni)(PF/sub 6/)/sub 2/ is reported. Infrared, nuclear magnetic resonance, magnetic susceptibility, and/or x-ray crystallographic studies indicate that all the above compounds are D/sub 5d/ or D/sub 5h/ decamethylmetallocenes with low-spin electronic configurations. Cyclic voltammetry studies verify the reversibility and the one-electron nature of the (Me/sub 5/Cp)/sub 2/M ..-->.. ((Me/sub 5/Cp)/sub 2/M)/sup +/ (M = Cr,Mn,Fe,Co,Ni), ((Me/sub 5/Cp)/sub 2/Mn)/sup -/ ..-->.. (Me/sub 5/Cp)/sub 2/Mn and ((Me/sub 5/Cp)/sub 2/Ni)/sup +/ ..-->.. (Me/sub 5/Cp)/sub 2/Ni)/sup 2 +/ redox reactions. These studies reveal that the neutral decamethylmetallocenes are much more easily oxidized than their metallocene counterparts. This result attests to the electron-donating properties of the ten substituent methyl groups. Proton and carbon-13 NMR data are reported for the diamagnetic Mg(II), Mn(I), Fe(II), Co(III), and Ni(IV) decamethylmetallocenes and for ((Me/sub 5/Cp)/sub 2/V(CO)/sub 2/)/sup +/. The uv-visible absorption spectra of the 15-, 18- and 20- electron decamethylmetallocenes are also reported.

  15. Structural phase transition and electronic properties of NdBi

    SciTech Connect

    Sahu, Ashvini K.; Patiya, Jagdish; Sanyal, Sankar P.

    2015-06-24

    The structural and electronic properties of NdBi from an electronic structure calculation have been presented. The calculation is performed using self-consistent tight binding linear muffin tin orbital (TB-LMTO) method within the local density approximation (LDA). The calculated equilibrium structural parameters are in good agreement with the available experimental results. It is found that this compound shows metallic behavior under ambient condition and undergoes a structural phase transition from the NaCl structure to the CsCl structure at the pressure 20.1 GPa. The electronic structures of NdBi under pressure are investigated. It is found that NdBi have metallization and the hybridizations of atoms in NdBi under pressure become stronger.

  16. Electron Precipitation Associated with Small-Scale Auroral Structures

    NASA Astrophysics Data System (ADS)

    Michell, R.; Samara, M.; Grubbs, G. A., II; Hampton, D. L.; Bonnell, J. W.; Ogasawara, K.

    2014-12-01

    We present results from the Ground-to-Rocket Electrons Electrodynamics Correlative Experiment (GREECE) sounding rocket mission, where we combined high-resolution ground-based auroral imaging with high time-resolution precipitating electron measurements. The GREECE payload successfully launched from Poker Flat, Alaska on 03 March 2014 and reached an apogee of approximately 335 km. The narrow field-of-view auroral imaging was taken from Venetie, AK, which is directly under apogee. This enabled the small-scale auroral features at the magnetic footpoint of the rocket payload to be imaged in detail. The electron precipitation was measured with the Acute Precipitating Electron Spectrometer (APES) onboard the payload. Features in the electron data are matched up with their corresponding auroral structures and boundaries, enabling measurement of the exact electron distributions responsible for the specific small-scale auroral features. These electron distributions will then be used to infer what the potential electron acceleration processes were.

  17. Electronic structure and stability of some silicon compounds

    NASA Astrophysics Data System (ADS)

    Novak, Igor; Abu-Izneid, Tareq; Kovač, Branka

    2010-05-01

    The electronic structures of N,1,3-tris(1,1-dimethylethyl)-cyclodisilazan-2-amine ( I) and 2,3,5,5-tetrakis(trimethylsilyl)cyclopentadiene ( II) have been investigated by HeI and HeII UV photoelectron spectroscopy (UPS) and quantum chemical calculations. We discuss the influence of substituent effects on their electronic structure and thermodynamic stability. Our study shows that trimethylsilyl substituents have strong influence on the electronic structure of cyclopentadiene via inductive effect. Their influence on thermodynamic stability is also pronounced. In substituted cyclodisilazanes hyperconjugative influence of alkylsilyl groups was shown to cause relative thermodynamic stabilization of the cyclodisilazane system.

  18. Electronic Structure Contributions to Reactivity in Xanthine Oxidase Family Enzymes

    PubMed Central

    Stein, Benjamin W.; Kirk, Martin L.

    2016-01-01

    We review the xanthine oxidase (XO) family of pyranopterin molybdenum enzymes with a specific emphasis on electronic structure contributions to reactivity. In addition to xanthine and aldehyde oxidoreductases, which catalyze the 2-electron oxidation of aromatic heterocycles and aldehyde substrates, this mini-review highlights recent work on the closely related carbon monoxide dehydrogenase (CODH) that catalyzes the oxidation of CO using a unique Mo-Cu heterobimetallic active site. A primary focus of this mini-review relates to how spectroscopy and computational methods have been used to develop an understanding of critical relationships between geometric structure, electronic structure, and catalytic function. PMID:25425163

  19. Spectral differences in real-space electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Jordan, D. K.; Mazziotti, D. A.

    2004-01-01

    Real-space grids for electronic structure calculations are efficient because the potential is diagonal while the second derivative in the kinetic energy may be sparsely evaluated with finite differences or finite elements. In applications to vibrational problems in chemical physics a family of methods known as spectral differences has improved finite differences by several orders of magnitude. In this paper the use of spectral differences for electronic structure is studied. Spectral differences are implemented in two electronic structure programs PARSEC and HARES which currently employ finite differences. Applications to silicon clusters and lattices indicate that spectral differences achieve the same accuracy as finite differences with less computational work.

  20. Kinetic effects on robustness of electron magnetohydrodynamic structures

    SciTech Connect

    Hata, M.; Sakagami, H.; Das, A.

    2013-04-15

    Following recent remarkable progress in the development of high-power short-pulse lasers, exploration is ongoing into hitherto unknown phenomena at fast time scales of electrons, the understanding of which is becoming crucial. For a simplified description of such phenomena, the Electron Magnetohydrodynamics (EMHDs) fluid description is often adopted. For the possibility of electron transport in high-density plasma, exact solutions of the EMHD model in the form of electron vortex currents, together with their associated magnetic fields, have been considered. However, the fluid EMHD model does not incorporate kinetic effects. Here, the finite Larmor radius effects owing to a finite electron temperature on the robustness of the exact EMHD structures are investigated using two-dimensional particle-in-cell simulations. It is found that larger EMHD vortex structures can sustain themselves for long periods, even in high temperature plasma; however, sustaining structures at higher temperatures tends to be difficult. With increasing temperature, electrons with finite Larmor radii become disengaged from the localized region. It is also shown that structures localized in smaller regions are more difficult to sustain. A quantitative criterion in terms of the structure size and Larmor radius has been established by simulations over a wide range of parameters. Finally, we conclude that a structure, larger than about eight times the typical Larmor radius at r=R, could form and exist even under the effects of finite electron temperature.

  1. Recent advances in electronic structure theory

    NASA Astrophysics Data System (ADS)

    Piecuch, Piotr; Kowalski, Karol; Pimienta, Ian S. O.; McGuire, Michael J.

    The recently developed new approach to the many-electron correlation problem in atoms and molecules, termed the method of moments of coupled-cluster (CC) equations (MMCC), is reviewed. The ground-state MMCC formalism and its extension to excited electronic states via the equation-of-motion coupled-cluster (EOMCC) approach are discussed. The main principle of all MMCC methods is that of the non-iterative energy corrections which, when added to the ground- and excited-state energies obtained in the standard CC calculations, such as CCSD or EOMCCSD, recover the exact, full configuration interaction (CI) energies. Three types of the MMCC approximations are reviewed in detail: (i) the CI-corrected MMCC methods, which can be applied to ground and excited states; (ii) the renormalized and completely renormalized CC methods for ground states; and (iii) the quasi-variational MMCC approaches for the ground-state problem, including the quadratic MMCC models. It is demonstrated that the MMCC formalism provides a new theoretical framework for designing 'black-box' CC approaches that lead to an excellent description of entire potential energy surfaces of ground- and excited-state molecular systems with an ease of use of the standard single-reference methods. The completely renormalized (CR) CCSD(T) and CCSD(TQ) methods and their quadratic and excited-state MMCC analogues remove the failing of the standard CCSD, CCSD(T), EOMCCSD and similar methods at larger internuclear separations and for states that normally require a genuine multireference description. All theoretical ideas are illustrated by numerical examples involving bond breaking, excited vibrational states, reactive potential energy surfaces and difficult cases of excited electronic states. The description of the existing and well-established variants of the MMCC theory, such as CR-CCSD(T), is augmented by the discussion of future prospects and potentially useful recent developments, including the extension of the black

  2. Penetration of projectiles into granular targets

    NASA Astrophysics Data System (ADS)

    Ruiz-Suárez, J. C.

    2013-06-01

    Energetic collisions of subatomic particles with fixed or moving targets have been very valuable to penetrate into the mysteries of nature. But the mysteries are quite intriguing when projectiles and targets are macroscopically immense. We know that countless debris wandering in space impacted (and still do) large asteroids, moons and planets; and that millions of craters on their surfaces are traces of such collisions. By classifying and studying the morphology of such craters, geologists and astrophysicists obtain important clues to understand the origin and evolution of the Solar System. This review surveys knowledge about crater phenomena in the planetary science context, avoiding detailed descriptions already found in excellent papers on the subject. Then, it examines the most important results reported in the literature related to impact and penetration phenomena in granular targets obtained by doing simple experiments. The main goal is to discern whether both schools, one that takes into account the right ingredients (planetary bodies and very high energies) but cannot physically reproduce the collisions, and the other that easily carries out the collisions but uses laboratory ingredients (small projectiles and low energies), can arrive at a synergistic intersection point.

  3. Powder metallurgy process for manufacturing core projectile

    NASA Astrophysics Data System (ADS)

    Akbar, Taufik; Setyowati, Vuri Ayu; Widyastuti

    2013-09-01

    Bullets are part of the defense equipment which the development is very rapid. There are a variety of forms but the bullet Lead is a metal that has always been used for applications projectiles. Lead core constituent materials are combined with antimony. In this research will be conducted by making the material for the core projectile with Tin Lead. The addition of Tin will increase the stiffness of Lead which is soft in nature. The Lead Tin composition variation was given in 10% weight of Sn. The manufacturing process using powder metallurgy using temperature and holding time variations of sintering at 100, 150, and 200°C for 1,2, and 3 hours. XRD samples will be tested to determine the form and phase morphology was observed using SEM-EDX. These results revealed that Pb-10%wtSn Composite which is sintered in temperature 200°C for 3 hours has the greatest density, 10.695 g/cm3 as well as the smallest porosity, 2.2%. In agreement with theoretical analysis that increasing higher temperature and longer holding time give decrease in porosity level due to activation energy which further promotes grain growth. Moreover, there is no intermetallic phase formation as well as no oxide found on composites.

  4. Jetting during vertical impacts of spherical projectiles

    NASA Astrophysics Data System (ADS)

    Johnson, B. C.; Bowling, T. J.; Melosh, H. J.

    2014-08-01

    The extreme pressures reached during jetting, a process by which material is squirted out from the contact point of two colliding objects, causes melting and vaporization at low impact velocities. Jetting is a major source of melting in shocked porous material, a potential source of tektites, a possible origin of chondrules, and even a conceivable origin of the Moon. Here, in an attempt to quantify the importance of jetting, we present numerical simulation of jetting during the vertical impacts of spherical projectiles on both flat and curved targets. We find that impacts on curved targets result in more jetted material but that higher impact velocities result in less jetted material. For an aluminum impactor striking a flat Al target at 2 km/s we find that 3.4% of a projectile mass is jetted while 8.3% is jetted for an impact between two equal sized Al spheres. Our results indicate that the theory of jetting during the collision of thin plates can be used to predict the conditions when jetting will occur. However, we find current analytic models do not make accurate predictions of the amount of jetted mass. Our work indicates that the amount of jetted mass is independent of model resolution as long as some jetted material is resolved. This is the result of lower velocity material dominating the mass of the jet.

  5. Penetration of projectiles into granular targets.

    PubMed

    Ruiz-Suárez, J C

    2013-06-01

    Energetic collisions of subatomic particles with fixed or moving targets have been very valuable to penetrate into the mysteries of nature. But the mysteries are quite intriguing when projectiles and targets are macroscopically immense. We know that countless debris wandering in space impacted (and still do) large asteroids, moons and planets; and that millions of craters on their surfaces are traces of such collisions. By classifying and studying the morphology of such craters, geologists and astrophysicists obtain important clues to understand the origin and evolution of the Solar System. This review surveys knowledge about crater phenomena in the planetary science context, avoiding detailed descriptions already found in excellent papers on the subject. Then, it examines the most important results reported in the literature related to impact and penetration phenomena in granular targets obtained by doing simple experiments. The main goal is to discern whether both schools, one that takes into account the right ingredients (planetary bodies and very high energies) but cannot physically reproduce the collisions, and the other that easily carries out the collisions but uses laboratory ingredients (small projectiles and low energies), can arrive at a synergistic intersection point. PMID:23660625

  6. Fundamental Aerodynamic Investigations for Development of Arrow-Stabilized Projectiles

    NASA Technical Reports Server (NTRS)

    Kurzweg, Hermann

    1947-01-01

    The numerous patent applications on arrow-stabilized projectiles indicate that the idea of projectiles without spin is not new, but has appeared in various proposals throughout the last decades. As far as projectiles for subsonic speeds are concerned, suitable shapes have been developed for sometime, for example, numerous grenades. Most of the patent applications, though, are not practicable particularly for projectiles with supersonic speed. This is because the inventor usually does not have any knowledge of aerodynamic flow around the projectile nor any particular understanding of the practical solution. The lack of wind tunnels for the development of projectiles made it necessary to use firing tests for development. These are obviously extremely tedious or expensive and lead almost always to failures. The often expressed opinion that arrow-stabilized projectiles cannot fly supersonically can be traced to this condition. That this is not the case has been shown for the first time by Roechling on long projectiles with foldable fins. Since no aerodynamic investigations were made for the development of these projectiles, only tedious series of firing tests with systematic variation of the fins could lead to satisfactory results. These particular projectiles though have a disadvantage which lies in the nature cf foldable fins. They occasionally do not open uniformly in flight, thus causing unsymmetry in flow and greater scatter. The junctions of fins and body are very bad aerodynamically and increase the drag. It must be possible to develop high-performance arrow-stabilized projectiles based on the aerodynamic research conducted during the last few years at Peenemuende and new construction ideas. Thus the final shape, ready for operational use, could be developed in the wind tunnel without loss of expensive time in firing tests. The principle of arrow-stabilized performance has been applied to a large number of caliburs which were stabilized by various means Most

  7. Electronic-structure calculation for metals by local optimization

    SciTech Connect

    Woodward, C.; Min, B.I.; Benedek, R.; Garner, J.

    1989-03-15

    Recent work by Car and Parrinello has generated considerable interest in the calculation of electronic structure by nonlinear optimization. The technique introduced by these authors, dynamical simulated annealing, is designed for problems that involve energy barriers. When local optimization suffices to determine the energy minimum, more direct methods are available. In this paper we apply the algorithm suggested by Williams and Soler to calculate the electronic structure of metals, using a plane-wave expansion for the electronic orbitals and an electron-ion pseudopotential of the Kleinman-Bylander form. Radial pseudopotentials were taken from the compilation of Bachelet, Hamann, and Schlueter. Calculations are performed to optimize the electronic structure (i) with fixed atomic configuration, or (ii) with the atomic volume being optimized simultaneously. It is found that the dual optimization (ii) converges in essentially the same number of steps as the static lattice optimization (i). Numerical results are presented for Li, K, Al, and simple-cubic P.

  8. Modeling Polymorphic Molecular Crystals with Electronic Structure Theory.

    PubMed

    Beran, Gregory J O

    2016-05-11

    Interest in molecular crystals has grown thanks to their relevance to pharmaceuticals, organic semiconductor materials, foods, and many other applications. Electronic structure methods have become an increasingly important tool for modeling molecular crystals and polymorphism. This article reviews electronic structure techniques used to model molecular crystals, including periodic density functional theory, periodic second-order Møller-Plesset perturbation theory, fragment-based electronic structure methods, and diffusion Monte Carlo. It also discusses the use of these models for predicting a variety of crystal properties that are relevant to the study of polymorphism, including lattice energies, structures, crystal structure prediction, polymorphism, phase diagrams, vibrational spectroscopies, and nuclear magnetic resonance spectroscopy. Finally, tools for analyzing crystal structures and intermolecular interactions are briefly discussed. PMID:27008426

  9. Electron structure: Shape, size, and generalized parton distributions in QED

    NASA Astrophysics Data System (ADS)

    Miller, Gerald A.

    2014-12-01

    The shape of the electron is studied using lowest-order perturbation theory. Quantities used to probe the structure of the proton—form factors, generalized parton distributions, transverse densities, Wigner distributions and the angular momentum content—are computed for the electron-photon component of the electron wave function. The influence of longitudinally polarized photons, demanded by the need for infrared regularization via a nonzero photon mass, is included. The appropriate value of the photon mass depends on experimental conditions, and consequently the size of the electron (as defined by the slope of its Dirac form factor) bound in a hydrogen atom is found to be about four times larger than when the electron is in a continuum scattering state. The shape of the electron, as determined from the transverse density and generalized parton distributions, is shown not to be round, and the continuum electron is shown to be far less round than the bound electron. An electron distribution function (analogous to the quark distribution function) is defined, and that of the bound electron is shown to be suppressed compared to that of the continuum electron. If the relative transverse momentum of the virtual electron and photon is large compared with the electron mass, the virtual electron and photon each carry nearly the total angular momentum of the physical electron (1 /2 ), with the orbital angular momentum being nearly (-1 /2 ). Including the nonzero photon mass leads to the suppression of end-point contributions to form factors. Implications for proton structure and color transparency are discussed.

  10. Basis functions for electronic structure calculations on spheres.

    PubMed

    Gill, Peter M W; Loos, Pierre-François; Agboola, Davids

    2014-12-28

    We introduce a new basis function (the spherical Gaussian) for electronic structure calculations on spheres of any dimension D. We find general expressions for the one- and two-electron integrals and propose an efficient computational algorithm incorporating the Cauchy-Schwarz bound. Using numerical calculations for the D = 2 case, we show that spherical Gaussians are more efficient than spherical harmonics when the electrons are strongly localized. PMID:25554128

  11. Electron Diffraction Determination of Nanoscale Structures

    SciTech Connect

    Parks, Joel H

    2013-03-01

    Dominant research results on adsorption on gold clusters are reviewed, including adsorption of H{sub 2}O and O{sub 2} on gold cluster cations and anions, kinetics of CO adsorption to middle sized gold cluster cations, adsorption of CO on Au{sub n}{sup +} with induced changes in structure, and H{sub 2}O enhancement of CO adsorption.

  12. Linear Scaling Electronic Structure Methods with Periodic Boundary Conditions

    SciTech Connect

    Gustavo E. Scuseria

    2008-02-08

    The methodological development and computational implementation of linear scaling quantum chemistry methods for the accurate calculation of electronic structure and properties of periodic systems (solids, surfaces, and polymers) and their application to chemical problems of DOE relevance.

  13. Revealing the hidden correlated electronic structure of strained graphene

    NASA Astrophysics Data System (ADS)

    Craco, L.; Selli, D.; Seifert, G.; Leoni, S.

    2015-05-01

    We explore the effect of isotropic strain on the electronic structure of graphene. It is shown that the interplay between one-particle band narrowing and sizable multiorbital Coulomb interactions induces a transition from a Dirac-liquid semimetal to an orbital selective metal characterized by narrow π -orbital Kondo clouds and abrupt downshift of σ* states. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain the reshaped electronic structure of graphene nanobubbles probed in scanning tunneling microscopy. Our proposal is a key step in understanding the intricate and interdependent changes in orbital and electronic degrees of freedom of strained materials with hexagonal lattice structure.

  14. Secondary electron emission from surfaces with small structure

    NASA Astrophysics Data System (ADS)

    Dzhanoev, A. R.; Spahn, F.; Yaroshenko, V.; Lühr, H.; Schmidt, J.

    2015-09-01

    It is found that for objects possessing small surface structures with differing radii of curvature the secondary electron emission (SEE) yield may be significantly higher than for objects with smooth surfaces of the same material. The effect is highly pronounced for surface structures of nanometer scale, often providing a more than 100 % increase of the SEE yield. The results also show that the SEE yield from surfaces with structure does not show a universal dependence on the energy of the primary, incident electrons as it is found for flat surfaces in experiments. We derive conditions for the applicability of the conventional formulation of SEE using the simplifying assumption of universal dependence. Our analysis provides a basis for studying low-energy electron emission from nanometer structured surfaces under a penetrating electron beam important in many technological applications.

  15. Stacking dependent electronic structures of transition metal dichalcogenides heterobilayer

    NASA Astrophysics Data System (ADS)

    Lee, Yea-Lee; Park, Cheol-Hwan; Ihm, Jisoon

    The systematic study of the electronic structures and optical properties of the transition metal dichalcogenides (TMD) heterobilayers can significantly improve the designing of new electronic and optoelectronic devices. Here, we theoretically study the electronic structures and optical properties of TMD heterobilayers using the first-principles methods. The band structures of TMD heterobilayer are shown to be determined by the band alignments of the each layer, the weak interlayer interactions, and angle dependent stacking patterns. The photoluminescence spectra are investigated using the calculated band structures, and the optical absorption spectra are examined by the GW approximations including the electron-hole interaction through the solution of the Bethe-Salpeter equation. It is expected that the weak interlayer interaction gives rise to the substantial interlayer optical transition which will be corresponding to the interlayer exciton.

  16. Projectile charge dependence of ionization and dissociation of CO in fast collisions

    NASA Astrophysics Data System (ADS)

    Krishnamurthi, Vidhya; Ben-Itzhak, I.; Carnes, K. D.

    1997-02-01

    Experiments have been carried out to study how changes in the interaction strength (defined as q/vb) of a fast ion-molecule colision affect the ionization and dissociation of the molecular target, in this case CO. The coincidence time-of-flight technique was used for collisions at fixed velocity (energy of 1 MeV/amu). The interaction strength was changed by varying the charge of the projectile ion. The cross sections for single and multiple ionization of CO increase rapidly for small q, approximately as q2n (where n is the number of ionized electrons), and more slowly for larger values of q. A rather simple theoretical model based on the independent electron approximation and perturbation theory is in good agreement with the data [1]. The dissociation patterns of the transient COQ+ molecular ions also exhibit a dependence on the projectile charge which is qualitatively explained by the same model.

  17. Electronic structure of carbon-boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Sanginés-Mendoza, Raúl; Martinez, Edgar

    2013-03-01

    Structures of carbon and boron nitride nanotubes (CNTs, BNNTs) are quite similar, conversely, electronic properties are radically different from each other. Carbon nanotubes, whose electronic properties can be either metallic or semiconducting depending on their chiral structure, boron nitride nanotubes are always semiconductors with bandgaps over 4 eV. We have looked to hybrid systems, to predict a new kind of nanostructures with novel electronic properties. In this way, we explore the electronic properties of C-BN nanotubes. In particular, we studied the electronic structure of armchair C-BN nanotubes. The calculations were performed using the pseudopotential LCAO method with a Generalized Gradient Approximation for the exchange-correlation energy functional. The band structure of most of these systems have semiconductor character with an indirect gap smaller than its analogous BNNTs. In addition, the most prominent feature of these systems is the existence of flat bands both at the valence band top and at the conduction band minimum. Such flat bands results in sharp and narrow peaks on the total density of states. The behavior of these flat bands mainly indicates that electrons are largely localized. Thus, a detailed analysis on the electronic band structure shows that hybridization between those orbitals on the interfaces is responsible to exhibit localization effects on the hybrid systems.This research was supported by Conacyt under Grant No. 133022.

  18. Corrected Launch Speed for a Projectile Motion Laboratory

    ERIC Educational Resources Information Center

    Sanders, Justin M.; Boleman, Michael W.

    2013-01-01

    At our university, students in introductory physics classes perform a laboratory exercise to measure the range of a projectile fired at an assigned angle. A set of photogates is used to determine the initial velocity of the projectile (the launch velocity). We noticed a systematic deviation between the experimentally measured range and the range…

  19. Electron beam enhanced surface modification for making highly resolved structures

    DOEpatents

    Pitts, John R.

    1986-01-01

    A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

  20. Electron beam enhanced surface modification for making highly resolved structures

    DOEpatents

    Pitts, J.R.

    1984-10-10

    A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

  1. New Insight into Carbon Nanotube Electronic Structure Selectivity

    SciTech Connect

    Sumpter, Bobby G; Meunier, Vincent; Jiang, Deen

    2009-01-01

    The fundamental role of aryl diazonium salts for post synthesis selectivity of carbon nanotubes is investigated using extensive electronic structure calculations. The resulting understanding for diazonium salt based selective separation of conducting and semiconducting carbon nanotubes shows how the primary contributions come from the interplay between the intrinsic electronic structure of the carbon nanotubes and that of the anion of the salt. We demonstrate how the electronic transport properties change upon the formation of charge transfer complexes and upon their conversion into covalently attached functional groups. Our results are found to correlate well with experiments and provide for the first time an atomistic description for diazonium salt based chemical separation of carbon nanotubes

  2. Improving Boundary Conditions for Electronic Structure Calculations

    NASA Astrophysics Data System (ADS)

    Benesh, G. A.; Haydock, Roger

    Boundary conditions imposed on a local system joined to a much larger substrate system routinely introduce unphysical reflections that affect the calculation of electronic properties such as energies, charge densities, and densities of states. These problems persist in atomic cluster, slab, and supercell calculations alike. However, wave functions in real, physical systems do not reflect at artificial boundaries. Instead, they carry current smoothly across the surface separating the local system from the underlying medium. Haydock and Nex have derived a non-reflecting boundary condition that works well for discrete systems [Phys. Rev. B 75, 205121 (2006)]. Solutions satisfying their maximal breaking of time-reversal symmetry (MBTS) boundary condition carry current away from the boundary at a maximal rate--in much the same way as exact wave functions in physical systems. The MBTS approach has now been extended to studies employing continuous basis functions. In model systems, MBTS boundary conditions work well for calculating wave functions, eigenenergies, and densities of states. Results are reported for an Al(001) surface. Comparisons are made with slab calculations, embedding calculations, and experiment.

  3. MATERIALS WITH COMPLEX ELECTRONIC/ATOMIC STRUCTURES

    SciTech Connect

    D. M. PARKIN; L. CHEN; ET AL

    2000-09-01

    We explored both experimentally and theoretically the behavior of materials at stresses close to their theoretical strength. This involves the preparation of ultra fine scale structures by a variety of fabrication methods. In the past year work has concentrated on wire drawing of in situ composites such as Cu-Ag and Cu-Nb. Materials were also fabricated by melting alloys in glass and drawing them into filaments at high temperatures by a method known as Taylor wire technique. Cu-Ag microwires have been drawn by this technique to produce wires 10 {micro}m in diameter that consist of nanoscale grains of supersaturated solid solution. Organogels formed from novel organic gelators containing cholesterol tethered to squaraine dyes or trans-stilbene derivatives have been studied from several different perspectives. The two types of molecules are active toward several organic liquids, gelling in some cases at w/w percentages as low as 0.1. While relatively robust, acroscopically dry gels are formed in several cases, studies with a variety of probes indicate that much of the solvent may exist in domains that are essentially liquid-like in terms of their microenvironment. The gels have been imaged by atomic force microscopy and conventional and fluorescence microscopy, monitoring both the gelator fluorescence in the case of the stilbene-cholesterol gels and, the fluorescence of solutes dissolved in the solvent. Remarkably, our findings show that several of the gels are composed of similarly appearing fibrous structures visible at the nano-, micro-, and macroscale.

  4. Structural properties of amorphous silicon produced by electron irradiation

    SciTech Connect

    Yamasaki, J.; Takeda, S.

    1999-07-01

    The structural properties of the amorphous Si (a-Si), which was created from crystalline silicon by 2 MeV electron irradiation at low temperatures about 25 K, are examined in detail by means of transmission electron microscopy and transmission electron diffraction. The peak positions in the radial distribution function (RDF) of the a-Si correspond well to those of a-Si fabricated by other techniques. The electron-irradiation-induced a-Si returns to crystalline Si after annealing at 550 C.

  5. Hemispherical Analyser with 2-D PSD for Zero-degree Auger Projectile Spectroscopy

    NASA Astrophysics Data System (ADS)

    Benis, E. P.; Zouros, T. J. M.; Aliabadi, H.; Richard, P.

    Details of a new high gain zero-degree Auger projectile electron spectrograph using a hemispherical analyser and a 2-dimensional position sensitive detector (PSD) with multichannel plates and a resistive anode encoder are presented. A four-element lens mounted at the entrance of the analyser, provides a virtual slit for the incoming electrons by focusing them while at the same time decelerating them to improve their energy resolution. Electrons enter through an aperture at a position R0 which is displaced (along the energy dispersion axis) with respect to the commonly used central entrance position at 1/2 (R1+R2). The analyser has an acceptance energy range of 20% and an energy resolution of 0.9%. An ion-optics trajectory simulation indicates improved focusing properties for this off-center position thus avoiding the need for cumbersome fringing field correction schemes. Test measurements of high resolution projectile Auger spectra produced in 21.7 MeV collisions of F8+ and F7+ projectiles with H2 and He are presented.

  6. Graphene Oxide: Synthesis, Characterization, Electronic Structure, and Applications

    NASA Astrophysics Data System (ADS)

    Stewart, Derek A.; Mkhoyan, K. Andre

    While graphite oxide was first identified in 1855 [1, 2], the recent discovery of stable graphene sheets has led to renewed interest in the chemical structure and potential applications of graphene oxide sheets. These structures have several physical properties that could aid in the large scale development of a graphene electronics industry. Depending on the degree of oxidization, graphene oxide layers can be either semiconducting or insulating and provide an important complement to metallic graphene layers. In addition, the electronic and optical properties of these films can be controlled by the selective removal or addition of oxygen. For example, selective oxidationof graphene sheets could lead to electronic circuit fabrication on the scale of a single atomic layer. Graphene oxide is also dispersible in water and other solvents and this provides a facile route for graphene deposition on a wide range of substrates for macroelectronics applications. Although graphite oxide has been known for roughly 150 years, key questions remain in regards to its chemical structure, electronic properties, and fabrication. Answering these issues has taken on special urgency with the development of graphene electronics. In this chapter, we will provide an overview of the field with special focus on synthesis, characterization, and first principles analysis of bonding and electronic structures. Finally, we will also address some of the most promising applications for graphene oxide in electronics and other industries.

  7. Nano-structured electron transporting materials for perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Hefei; Huang, Ziru; Wei, Shiyuan; Zheng, Lingling; Xiao, Lixin; Gong, Qihuang

    2016-03-01

    Organic-inorganic hybrid perovskite solar cells have been developing rapidly in the past several years, and their power conversion efficiency has reached over 20%, nearing that of polycrystalline silicon solar cells. Because the diffusion length of the hole in perovskites is longer than that of the electron, the performance of the device can be improved by using an electron transporting layer, e.g., TiO2, ZnO and TiO2/Al2O3. Nano-structured electron transporting materials facilitate not only electron collection but also morphology control of the perovskites. The properties, morphology and preparation methods of perovskites are reviewed in the present article. A comprehensive understanding of the relationship between the structure and property will benefit the precise control of the electron transporting process and thus further improve the performance of perovskite solar cells.

  8. Nano-structured electron transporting materials for perovskite solar cells.

    PubMed

    Liu, Hefei; Huang, Ziru; Wei, Shiyuan; Zheng, Lingling; Xiao, Lixin; Gong, Qihuang

    2016-03-17

    Organic-inorganic hybrid perovskite solar cells have been developing rapidly in the past several years, and their power conversion efficiency has reached over 20%, nearing that of polycrystalline silicon solar cells. Because the diffusion length of the hole in perovskites is longer than that of the electron, the performance of the device can be improved by using an electron transporting layer, e.g., TiO2, ZnO and TiO2/Al2O3. Nano-structured electron transporting materials facilitate not only electron collection but also morphology control of the perovskites. The properties, morphology and preparation methods of perovskites are reviewed in the present article. A comprehensive understanding of the relationship between the structure and property will benefit the precise control of the electron transporting process and thus further improve the performance of perovskite solar cells. PMID:26457406

  9. Electronic spectra of structurally deformed lutein.

    PubMed

    Macernis, Mindaugas; Sulskus, Juozas; Duffy, Christopher D P; Ruban, Alexander V; Valkunas, Leonas

    2012-10-11

    Quantum chemical calculations have been employed for the investigation of the lowest excited electronic states of lutein, with particular reference to its function within light harvesting antenna complexes of higher plants. Through comparative analysis obtained by using different methods based on gas-phase calculations of the spectra, it was determined that variations in the lengths of the long C-C valence bonds and the dihedral angles of the polyene chain are the dominant factors in determining the spectral properties of Lut 1 and Lut 2 corresponding to the deformed lutein molecules taken from crystallographic data of the major pigment-protein complex of photosystem II. By MNDO-CAS-CI method, it was determined that the two singlet B(u) states of lutein (nominally 1B(u)(-)* and 1B(u)(+)) arise as a result of mixing of the canonical 1B(u)(-) and 1B(u)(+) states of the all-trans polyene due to the presence of the ending rings in lutein. The 1B(u)(-)* state of lutein is optically allowed, while the 1B(u)(-) of a pure all-trans polyene chain is optically forbidden. As demonstrated, the B(u) states are much more sensitive to minor distortions of the conjugated chain due to mixing of the canonical states, resulting in states of poorly defined particle-hole symmetry. Conversely, the A(g) states are relatively robust with respect to geometric distortion, and their respective inversion and particle-hole symmetries remain relatively well-defined. PMID:22974387

  10. Electronic structure of a graphene superlattice with massive Dirac fermions

    SciTech Connect

    Lima, Jonas R. F.

    2015-02-28

    We study the electronic and transport properties of a graphene-based superlattice theoretically by using an effective Dirac equation. The superlattice consists of a periodic potential applied on a single-layer graphene deposited on a substrate that opens an energy gap of 2Δ in its electronic structure. We find that extra Dirac points appear in the electronic band structure under certain conditions, so it is possible to close the gap between the conduction and valence minibands. We show that the energy gap E{sub g} can be tuned in the range 0 ≤ E{sub g} ≤ 2Δ by changing the periodic potential. We analyze the low energy electronic structure around the contact points and find that the effective Fermi velocity in very anisotropic and depends on the energy gap. We show that the extra Dirac points obtained here behave differently compared to previously studied systems.

  11. Electronic, Thermal and Structural Properties of Graphene Oxide Frameworks

    SciTech Connect

    Zhu, Pan; Sumpter, Bobby G; Meunier, V.

    2013-01-01

    We report a theoretical study of the electronic, thermal, and structural properties of a series of graphene oxide frameworks (GOFs) using first-principles calculations based on density functional theory. The molecular structure of GOFs is systematically studied by varying the nature and concentration of linear boronic acid pillars and the thermal stability is assessed using ab initio molecular dynamics. The results demonstrate that GOFs are thermally stable up to 550 K and that electronic properties, such as their band gap, can be modified controllably by an appropriate choice of pillaring unit and pillar concentration. The tunability of the electronic structure using non-chemical means, e.g., mechanical strain, is also quantified. Overall, this class of materials is predicted to offer highly tunable materials electronic properties ranging from metallic to semiconducting.

  12. Electronic, Thermal, and Structural Properties of Graphene Oxide Frameworks

    SciTech Connect

    Zhu, Pan; Sumpter, Bobby G; Meunier, V.

    2013-01-01

    We report a theoretical study of the electronic, thermal, and structural properties of a series of graphene oxide frameworks (GOFs) using first-principles calculations based on density functional theory. The molecular structure of GOFs is systematically studied by varying the nature and concentration of linear boronic acid pillars, and the thermal stability is assessed using ab initio molecular dynamics. The results demonstrate that GOFs are thermally stable up to 550 K and that electronic properties, such as their band gap, can be modified controllably by an appropriate choice of pillaring unit and pillar concentration. The tunability of the electronic structure using nonchemical means, e.g., mechanical strain, is also quantified. Overall, this class of materials is predicted to offer highly tunable materials electronic properties ranging from metallic to semiconducting.

  13. Electron-electron interactions in fast neutral-neutral collisions

    SciTech Connect

    DuBois, R.D. ); Manson, S.T. . Dept. of Physics and Astronomy)

    1992-11-01

    Differential electron emission is studied for 50--500 keV H[sup +] and H atom impact on helium. Using the first Born formulation, it is shown that projectile electron-target electron interactions are expected to dominate the differential cross sections for low energy target electron emission induced by fast neutral projectile impact on any target. Measurements of the 15[degrees] electron emission were made in order to investigate this prediction. For low impact energies, a constant ratio between the hydrogen atom and proton impact cross sections was found for emitted electron velocities less than half the projectile velocity, V[sub p] But as the collision energy increased, for electron velocities less than 0.25 V[sub p], the cross section ratio increased as the emitted electron velocity decreased. This is interpreted as a signature of projectile electron-target electron interactions becoming dominant for distant collisions between neutral particles.

  14. Electron-electron interactions in fast neutral-neutral collisions

    SciTech Connect

    DuBois, R.D.; Manson, S.T.

    1992-11-01

    Differential electron emission is studied for 50--500 keV H{sup +} and H atom impact on helium. Using the first Born formulation, it is shown that projectile electron-target electron interactions are expected to dominate the differential cross sections for low energy target electron emission induced by fast neutral projectile impact on any target. Measurements of the 15{degrees} electron emission were made in order to investigate this prediction. For low impact energies, a constant ratio between the hydrogen atom and proton impact cross sections was found for emitted electron velocities less than half the projectile velocity, V{sub p} But as the collision energy increased, for electron velocities less than 0.25 V{sub p}, the cross section ratio increased as the emitted electron velocity decreased. This is interpreted as a signature of projectile electron-target electron interactions becoming dominant for distant collisions between neutral particles.

  15. Projectile impact Hugoniot parameters for selected materials

    SciTech Connect

    Vigil, M G

    1989-08-01

    The Rankine Hugoniot equation relating the conversion of momentum across a shock front and the empirical relationship for shock velocity as a function of particle velocity are used to calculate the impact pressures for selected materials. The shock velocity and particle velocities are then calculated as a function of impact pressures. The calculated data are graphically presented sets of three figures for the selected materials as follows: Impact pressure as a function of impact velocity, impact pressure as a function of particle velocity, impact pressure as a function of shock velocity. Given the projectile impact velocity and material Hugoniot information, this graphical representation of the data allows for a fast approximation of the impact pressure particle velocity, and shock velocity in the target material. 9 refs., 1 fig., 3 tabs.

  16. Turbulent Flow Past Projectiles: A Computational Investigation

    NASA Astrophysics Data System (ADS)

    Mehmedagic, Igbal; Carlucci, Donald; Buckley, Liam; Carlucci, Pasquale; Thangam, Siva

    2010-11-01

    Projectiles with free spinning bases are often used for smart munitions to provide effective control, stability and terminal guidance. Computational investigations are performed for flow past cylinders aligned along their axis where a base freely spins while attached to and separated at various distances from a non-spinning fore-body. The energy spectrum is modified to incorporate the effects of swirl and rotation using a parametric characterization of the model coefficients. An efficient finite-volume algorithm is used to solve the time-averaged equations of motion and energy along with the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation. Computations are performed for both rigid cylinders as well as cylinders with free-spinning bases. Experimental data for a range of spin rates and free stream flow conditions obtained from subsonic wind tunnel with sting-mounted spinning cylinders is used for validating the computational findings.

  17. Electronic correlation in magnetic contributions to structural energies

    NASA Astrophysics Data System (ADS)

    Haydock, Roger

    For interacting electrons the density of transitions [see http://arxiv.org/abs/1405.2288] replaces the density of states in calculations of structural energies. Extending previous work on paramagnetic metals, this approach is applied to correlation effects on the structural stability of magnetic transition metals. Supported by the H. V. Snyder Gift to the University of Oregon.

  18. ESTIMATION OF ELECTRON AFFINITY BASED ON STRUCTURE ACTIVITY RELATIONSHIPS

    EPA Science Inventory

    Electron affinity for a wide range of organic molecules was calculated from molecular structure using the chemical reactivity models developed in SPARC. hese models are based on fundamental chemical structure theory applied to the prediction of chemical reactivities for organic m...

  19. Electronic properties in a quantum well structure of Weyl semimetal

    NASA Astrophysics Data System (ADS)

    You, Wen-Long; Wang, Xue-Feng; Oleś, Andrzej M.; Zhou, Jiao-Jiao

    2016-04-01

    We investigate the confined states and transport of three-dimensional Weyl electrons around a one-dimensional external rectangular electrostatic potential. The confined states with finite transverse wave vector exist at energies higher than the half well depth or lower than the half barrier height. The rectangular potential appears completely transparent to the normal incident electrons but not otherwise. The tunneling transmission coefficient is sensitive to their incident angle and shows resonant peaks when their energy coincides with the confined spectra. In addition, for the electrons in the conduction (valence) band through a potential barrier (well), the transmission spectrum has a gap of width increasing with the incident angle. Interestingly, the electron linear zero-temperature conductance over the potential can approach zero when the Fermi energy is aligned to the top and bottom energies of the potential, when only electron beams normal to the potential interfaces can pass through. The considered structure can be used to collimate the Weyl electron beams.

  20. A NASTRAN investigation of simulated projectile damage effects on a UH-1B tail boom model

    NASA Technical Reports Server (NTRS)

    Futterer, A. T.

    1980-01-01

    A NASTRAN model of a UH-1B tail boom that had been designed for another project was used to investigate the effect on structural integrity of simulated projectile damage. Elements representing skin, and sections of stringers, longerons and bulkheads were systematically deleted to represent projectile damage. The structure was loaded in a manner to represent the flight loads that would be imposed on the tail boom at a 130 knot cruise. The deflection of four points on the rear of the tail boom relative to the position of these points for the unloaded, undamaged condition of the tail boom was used as a measure of the loss of structural rigidity. The same procedure was then used with the material properties of the aluminum alloys replaced with the material properties of T300/5208 high strength graphite/epoxy fibrous composite material, (0, + or - 45, 90)s for the skin and (0, + or - 45)s for the longerons, stringers, and bulk heads.

  1. Electron vortex magnetic holes: A nonlinear coherent plasma structure

    NASA Astrophysics Data System (ADS)

    Haynes, Christopher T.; Burgess, David; Camporeale, Enrico; Sundberg, Torbjorn

    2015-01-01

    We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

  2. Electron vortex magnetic holes: A nonlinear coherent plasma structure

    SciTech Connect

    Haynes, Christopher T. Burgess, David; Sundberg, Torbjorn; Camporeale, Enrico

    2015-01-15

    We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

  3. Engineering the Electronic Band Structure for Multiband Solar Cells

    SciTech Connect

    Lopez, N.; Reichertz, L.A.; Yu, K.M.; Campman, K.; Walukiewicz, W.

    2010-07-12

    Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

  4. Role of interface band structure on hot electron transport

    NASA Astrophysics Data System (ADS)

    Garramone, John J.

    Knowledge of electron transport through materials and interfaces is fundamentally and technologically important. For example, metal interconnects within integrated circuits suffer increasingly from electromigration and signal delay due to an increase in resistance from grain boundary and sidewall scattering since their dimensions are becoming shorter than the electron mean free path. Additionally, all semiconductor based devices require the transport of electrons through materials and interfaces where scattering and parallel momentum conservation are important. In this thesis, the inelastic and elastic scattering of hot electrons are studied in nanometer thick copper, silver and gold films deposited on silicon substrates. Hot electrons are electron with energy greater than kBT above the Fermi level (EF). This work was performed utilizing ballistic electron emission microscopy (BEEM) which is a three terminal scanning tunneling microscopy (STM) technique that measures the percentage of hot electrons transmitted across a Schottky barrier interface. Hot electron attenuation lengths of the metals were extracted by measuring the BEEM current as a function of metal overlayer thickness for both hot electron and hot hole injection at 80 K and under ultra high vacuum. The inelastic and elastic scattering lengths were extracted by fitting the energetic dependence of the measured attenuation lengths to a Fermi liquid based model. A sharp increase in the attenuation length is observed at low injection energies, just above the Schottky barrier height, only for metals on Si(001) substrates. In contrast, the attenuation length measured on Si(111) substrates shows a sharp decrease. These results indicate that interface band structure and parallel momentum conservation have significant impact upon the transport of hot electrons across non epitaxial metal-semiconductor interfaces. In addition, they help to separate effects upon hot electron transport that are inherent to the metal

  5. Advanced Accelerating Structures and Their Interaction with Electron Beams

    SciTech Connect

    Gai Wei

    2009-01-22

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  6. Advanced accelerating structures and their interaction with electron beams.

    SciTech Connect

    Gai, W.; High Energy Physics

    2008-01-01

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  7. Goeppert-Mayer Award Recipient: Electron Scattering and Nucleon Structure

    NASA Astrophysics Data System (ADS)

    Beise, Elizabeth

    1998-04-01

    Electron scattering from hydrogen and light nuclear targets has long been recognized as one of the best tools for understanding the electromagnetic structure of protons, neutrons and few-nucleon systems. In the last decade, considerable progress has been made in the field through advances in polarized beams and polarized targets. Improvements in polarized electron sources has made it feasible to also study the structure of the nucleon through parity-violating electron scattering, where the nucleon's neutral weak structure is probed. In this talk, a summary of the present experimental status of the nucleon's electroweak structure will be presented, with an emphasis on recent results from the MIT-Bates and Jefferson Laboratories.

  8. Membrane protein structures without crystals, by single particle electron cryomicroscopy

    PubMed Central

    Vinothkumar, Kutti R

    2015-01-01

    It is an exciting period in membrane protein structural biology with a number of medically important protein structures determined at a rapid pace. However, two major hurdles still remain in the structural biology of membrane proteins. One is the inability to obtain large amounts of protein for crystallization and the other is the failure to get well-diffracting crystals. With single particle electron cryomicroscopy, both these problems can be overcome and high-resolution structures of membrane proteins and other labile protein complexes can be obtained with very little protein and without the need for crystals. In this review, I highlight recent advances in electron microscopy, detectors and software, which have allowed determination of medium to high-resolution structures of membrane proteins and complexes that have been difficult to study by other structural biological techniques. PMID:26435463

  9. Parallel adaptive mesh refinement for electronic structure calculations

    SciTech Connect

    Kohn, S.; Weare, J.; Ong, E.; Baden, S.

    1996-12-01

    We have applied structured adaptive mesh refinement techniques to the solution of the LDA equations for electronic structure calculations. Local spatial refinement concentrates memory resources and numerical effort where it is most needed, near the atomic centers and in regions of rapidly varying charge density. The structured grid representation enables us to employ efficient iterative solver techniques such as conjugate gradients with multigrid preconditioning. We have parallelized our solver using an object-oriented adaptive mesh refinement framework.

  10. Electronic Structure and Phase Stability of PdPt Nanoparticles.

    PubMed

    Ishimoto, Takayoshi; Koyama, Michihisa

    2016-03-01

    To understand the origin of the physicochemical nature of bimetallic PdPt nanoparticles, we theoretically investigated the phase stability and electronic structure employing the PdPt nanoparticles models consisting of 711 atoms (ca. 3 nm). For the Pd-Pt core-shell nanoparticle, the PdPt solid-solution phase was found to be a thermodynamically stable phase in the nanoparticle as the result of difference in surface energy of Pd and Pt nanoparticles and configurational entropy effect, while it is well known that the Pd and Pt are the immiscible combination in the bulk phase. The electronic structure of nanoparticles is conducted to find that the electron transfer occurs locally within surface and subsurface layers. In addition, the electron transfer from Pd to Pt at the interfacial layers in core-shell nanoparticles is observed, which leads to unique geometrical and electronic structure changes. Our results show a clue for the tunability of the electronic structure of nanoparticles by controlling the arrangement in the nanoparticles. PMID:26862885

  11. Supernumerary rainbows in the angular distribution of scattered projectiles for grazing collisions of fast atoms with a LiF(001) surface.

    PubMed

    Schüller, A; Winter, H

    2008-03-01

    Fast atoms with keV energies are scattered under a grazing angle of incidence from a clean and flat LiF(001) surface. For scattering along low index azimuthal directions within the surface plane ("axial surface channeling") we observe pronounced peak structures in the angular distributions for scattered projectiles that are attributed to "supernumerary rainbows." This phenomenon can be understood in the framework of quantum scattering only and is observed here up to projectile energies of 20 keV. We demonstrate that the interaction potential and, in particular, its corrugation for fast atomic projectiles at surfaces can be derived with a high accuracy. PMID:18352749

  12. Structure of a Bacterial Cell Surface Decaheme Electron Conduit

    SciTech Connect

    Clarke, Thomas A.; Edwards, Marcus; Gates, Andrew J.; Hall, Andrea; White, Gaye; Bradley, Justin; Reardon, Catherine L.; Shi, Liang; Beliaev, Alex S.; Marshall, Matthew J.; Wang, Zheming; Watmough, Nicholas; Fredrickson, Jim K.; Zachara, John M.; Butt, Julea N.; Richardson, David J.

    2011-05-23

    Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves deca-heme cytochromes that are located on the bacterial cell surface at the termini of trans-outermembrane (OM) electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular inter-cytochrome electron exchange along ‘nanowire’ appendages. We present a 3.2 Å crystal structure of one of these deca-heme cytochromes, MtrF, that allows the spatial organization of the ten hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65 Å octa-heme chain transects the length of the protein and is bisected by a planar 45 Å tetra-heme chain that connects two extended Greek key split β-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g. minerals), soluble substrates (e.g. flavins) and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface.

  13. Structure and electronic properties of (+)-catechin: aqueous solvent effects.

    PubMed

    Bentz, Erika N; Pomilio, Alicia B; Lobayan, Rosana M

    2014-02-01

    We report a study of the structure of (+)-catechin, which belongs to the family of the flavan-3-ols-one of the five most widely distributed phenolic groups. The biological activities and pharmaceutical utility of these compounds are related to antioxidant activity due to their ability to scavenge free radicals. A breakthrough in the study of the conformational space of this compound, so far absent in the literature, is presented herein. A detailed analysis of the electronic distribution, charge delocalization effects, and stereoelectronic effects is presented following application of the theory of atoms in molecules (AIM) and natural bond orbital analysis. The stability order, and the effects of electron delocalization in the structures were analyzed in depth. The molecular electrostatic potential (MEP) was also obtained, assessing changes in the electronic distribution in aqueous solution, the effects of the solvent on the intrinsic electronic properties, and molecular geometry. The effect of the aqueous solvent on MEP was also quantified, and rationalized by charge delocalization mechanisms, relating them to structural changes and topological properties of the electronic charge density. To further analyze the effects of the aqueous solvent, as well as investigating the molecular and structural properties of these compounds in a biological environment, the polarizabilities for all conformers characterized were also calculated. All results were interpreted on the basis of our accumulated knowledge on (4α→6", 2α→O→1")-phenylflavans in previous reports, thus enriching and deepening the analysis of both types of structure. PMID:24526380

  14. Electronic structure of Fe-based amorphous alloys studied using electron-energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, H. J.; Gu, X. J.; Poon, S. J.; Shiflet, G. J.

    2008-01-01

    The local atomic electronic structures of Fe-Mo-C-B metallic glasses are investigated using electron energy-loss spectroscopy (EELS). The fracture behavior of this Fe-based amorphous alloy system undergoes the transition from being ductile to exhibiting brittleness when alloyed with Cr or Er atoms. In addition, the glass-forming ability is also enhanced. This plastic-to-brittle transition is suggested to correlate with the change of local atomic short-range order or bonding configurations. Therefore, the bonding configuration of Fe-Mo-C-B-Er(Cr) amorphous alloys is investigated by studying the electronic structure of Fe and C atoms using electron energy-loss spectroscopy. It is shown that the normalized EELS white line intensities of Fe-L2,3 edges decrease slightly with an increasing amount of Er additions, while no noticeable difference is obtained with Cr additions. As for the C K edge, a prominent change of edge shape is observed for both alloy systems, where the first peak corresponding to a 1s→1π* transition increases with increasing Er and Cr additions. Accordingly, it is concluded that changes in the local atomic and electronic structure occur around Fe and C atoms when Er and Cr are introduced into the alloys. Furthermore, it is pointed out that the formation of Er-C and Cr-C carbide like local order inferred from the observed C K edge spectra can provide a plausible explanation for the plastic-to-brittle transition observed in these Fe-based amorphous alloys. In spite of the complexity of electronic and atomic structure in this multicomponent Fe-based metallic glass system, this study could serve as a starting point for providing a qualitative interpretation between electronic structure and plasticity in the Fe-Mo-C-B amorphous alloy system. Complimentary techniques, such as x-ray diffraction and high-resolution transmission electron microscope are also employed, providing a more complete structural characterization.

  15. The Electronic Structure of Single-Layer Graphene

    NASA Astrophysics Data System (ADS)

    Siegel, David Alan

    Single-layer graphene has been widely researched in recent years due to its perceived technological applicability and its scientific importance as a unique model system with relativistic Dirac Fermions. Because of its unique geometric and electronic structure, the properties of graphene can be tuned or manipulated in several ways. This tunability is important for technological applications in its own right, and it also allows us to study the fundamental properties of Dirac Fermions, including unique many-body interactions and the nature of the quasiparticles at half-filling. This thesis is a detailed examination of the electronic and structural properties of graphene, studied with angle-resolved photoemission spectroscopy (ARPES) and other surface science techniques like low-energy electron microscopy and diffraction. This thesis is organized as follows. Chapter 1 gives an introduction to the electronic and structural properties of single-layer graphene. It provides a brief historical overview of major theoretical and experimental milestones and sets the stage for the important theoretical and experimental questions that this thesis addresses. Chapters 2 and 3 describe the experimental setup. Chapter 2 discusses the experimental techniques used in this thesis with particular focus on the mechanics of ARPES. Chapter 3 discusses the different graphene growth techniques that were used to create our sample with particular focus on our characterization of epitaxial graphene on SiC(0001). Chapters 4 and 5 form the meat of this thesis: they provide a thorough discussion of the electronic properties of graphene as studied by ARPES. Chapter 4 describes how various perturbations can result in the manipulation of the bare electronic band structure, including the deposition of atomic or molecular species on top of an epitaxial graphene sheet as well as the interactions between graphene and its substrate. Chapter 5 describes the many-body physics in single-layer graphene. It

  16. Veterinary Forensics: Firearms and Investigation of Projectile Injury.

    PubMed

    Bradley-Siemens, N; Brower, A I

    2016-09-01

    Projectile injury represents an estimated 14% of reported animal cruelty cases in the United States. Cases involving projectiles are complicated by gross similarities to other common types of injury, including bite wounds and motor vehicle injuries, by weapons and ammunition not commonly recognized or understood by veterinary medical professionals, and by required expertise beyond that employed in routine postmortem examination. This review describes the common types of projectile injuries encountered within the United States, as well as firearms and ammunition associated with this form of injury. The 3 stages of ballistics-internal, external, and terminal-and wounding capacity are discussed. A general understanding of firearms, ammunition, and ballistics is necessary before pursuing forensic projectile cases. The forensic necropsy is described, including gunshot wound examination, projectile trajectories, different imaging procedures, collection and storage of projectile evidence, and potential advanced techniques for gunpowder analysis. This review presents aspects of projectile injury investigation that must be considered in tandem with standard postmortem practices and procedures to ensure reliable conclusions are reached for medicolegal as well as diagnostic purposes. PMID:27312366

  17. Delivering a projectile component to the vestan regolith

    NASA Astrophysics Data System (ADS)

    Daly, R. Terik; Schultz, Peter H.

    2016-01-01

    Dark material on Vesta may consist of carbonaceous chondrite-like material delivered by impact events. This study uses hypervelocity impact experiments to assess the viability of the impact delivery hypothesis. Experiments reveal that impact events deliver significant fractions of the projectile to the target during impacts at average vestan speeds. Hence, dark material can plausibly be delivered to Vesta by impacts, with the projectile component accumulating in the regolith with time. Projectile retention is sensitive to impact angle, ranging from 7% for 30° impacts (measured from horizontal) to 72% for vertical impacts. Averaged over the probability distribution of impact angles, 17% of the projectile's mass remains in or near the crater. Projectile-contaminated breccias largely remain inside the crater for vertical impacts. In oblique impacts, projectile-contaminated pieces concentrate downrange beyond the crater rim. Based on experiments, projectile delivery is expected for typical vestan impact conditions, not only for extraordinary events such as low-probability and very low-speed (e.g., <2 km s-1) impacts. These experiments indicate that other (non-dark) impactors contaminate the vestan regolith. Regolith-laden bodies in environments with similar impact speeds also may accrete significant amounts of foreign debris.

  18. Enhancement of electron mobility in asymmetric coupled quantum well structures

    SciTech Connect

    Das, S.; Nayak, R. K.; Sahu, T. Panda, A. K.

    2014-02-21

    We study the low temperature multisubband electron mobility in a structurally asymmetric GaAs/Al{sub x}Ga{sub 1-x}As delta doped double quantum well. We calculate the subband energy levels and wave functions through selfconsistent solution of the coupled Schrodinger equation and Poisson's equation. We consider ionized impurity scattering, interface roughness scattering, and alloy disorder scattering to calculate the electron mobility. The screening of the scattering potentials is obtained by using static dielectric response function formalism within the random phase approximation. We analyze, for the first time, the effect of asymmetric structure parameters on the enhancement of multisubband electron mobility through intersubband interactions. We show that the asymmetric variation of well width, doping concentration, and spacer width considerably influences the interplay of scattering mechanisms on mobility. Our results of asymmetry induced enhancement of electron mobility can be utilized for low temperature device applications.

  19. Electronic structure of the silicon vacancy color center in diamond.

    PubMed

    Hepp, Christian; Müller, Tina; Waselowski, Victor; Becker, Jonas N; Pingault, Benjamin; Sternschulte, Hadwig; Steinmüller-Nethl, Doris; Gali, Adam; Maze, Jeronimo R; Atatüre, Mete; Becher, Christoph

    2014-01-24

    The negatively charged silicon vacancy (SiV) color center in diamond has recently proven its suitability for bright and stable single photon emission. However, its electronic structure so far has remained elusive. We here explore the electronic structure by exposing single SiV defects to a magnetic field where the Zeeman effect lifts the degeneracy of magnetic sublevels. The similar responses of single centers and a SiV ensemble in a low strain reference sample prove our ability to fabricate almost perfect single SiVs, revealing the true nature of the defect's electronic properties. We model the electronic states using a group-theoretical approach yielding a good agreement with the experimental observations. Furthermore, the model correctly predicts polarization measurements on single SiV centers and explains recently discovered spin selective excitation of SiV defects. PMID:24484153

  20. Electron Energy Loss Spectroscopy of a Chiral Plasmonic Structure

    NASA Astrophysics Data System (ADS)

    Paterson, G. W.; Karimullah, A.; Williamson, SDR; Kadodwala, M.; MacLaren, D. A.

    2015-10-01

    A detailed analysis of the plasmonic excitations within a nanopatterned gold chiral biosensor element, measured by scanning transmission electron microscopy electron energy loss spectroscopy, is presented. We discuss aspects of data acquisition, processing, analysis and simulation. The localised surface plasmonic resonance modes in the structure are extracted using non-negative matrix factorisation and we use simulations to correlate notable deviations from the idealised spectrum to nanometric fabrication imperfections. The methodology presented has wide applicability to a variety of metamaterials.

  1. Electron Crystallography – The Waking Beauty of Structural Biology

    PubMed Central

    Pope, Christopher R; Unger, Vinzenz M

    2012-01-01

    Since its debut in the mid 70ties, electron crystallography has been a valuable alternative in the structure determination of biological macromolecules. Its reliance on single- or double-layered two-dimensionally ordered arrays and the ability to obtain structural information from small and disordered crystals make this approach particularly useful for the study of membrane proteins in a lipid bilayer environment. Despite its unique advantages, technological hurdles have kept electron crystallography from reaching its full potential. Addressing the issues, recent initiatives developed high-throughput pipelines for crystallization and screening. Adding progress in automating data collection, image analysis and phase extension methods, electron crystallography is poised to raise its profile and may lead the way in exploring the structural biology of macromolecular complexes. PMID:22525160

  2. Structural and electronic properties of dense liquid and amorphous nitrogen

    SciTech Connect

    Boates, B; Bonev, S A

    2011-02-11

    We present first-principles calculations of the structural and electronic properties of liquid nitrogen in the pressure-temperature range of 0-200 GPa and 2000-6000 K. The molecular-polymerization and molecular-atomic liquid phase boundaries have been mapped over this region. We find the polymeric liquid to be metallic, similar to what has been reported for the higher-temperature atomic fluid. An explanation of the electronic properties is given based on the structure and bonding character of the transformed liquids. We discuss the structural and bonding differences between the polymeric liquid and insulating solid cubic-gauche nitrogen to explain the differences in their electronic properties. Furthermore, we discuss the mechanism responsible for charge transport in polymeric nitrogen systems to explain the conductivity of the polymeric fluid and the semi-conducting nature of low-temperature amorphous nitrogen.

  3. The electronic structure of diodes probed under bias

    NASA Astrophysics Data System (ADS)

    Glans, Per-Anders; Guo, Jinghua; Park, Jeong; Gabor, Somorjai

    2009-03-01

    Chemists have known for decades that when metal nano-particles are affixed to a catalytically inactive oxide surface, the catalytic turnover rate of the array is more than 10 times that of a metal surface alone. However, the mechanism behind the effect is not clear. To understand the catalytic activity of the interface between the metal nano-structures and the oxide substrate, we have investigated the electronic structure of Pt and Pd doped diodes on a TiO2 substrate. The devices were put under bias during the measurements in an attempt to reproduce the potential differences found over the diode when used as a catalyst. This is challenging for electron based measuring techniques, but using photon-in, photon-out techniques we have successfully probed the electronic structure of Pt and Pd doped diodes under bias. The results from soft x-ray absorption and emission will be presented.

  4. Atomic and electronic structure of exfoliated black phosphorus

    SciTech Connect

    Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok; Wentzcovitch, Renata M.; Mkhoyan, K. Andre; Low, Tony; Robbins, Matthew C.; Haratipour, Nazila; Koester, Steven J.

    2015-11-15

    Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO{sub 3} or H{sub 3}PO{sub 3} during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.

  5. Corrected Launch Speed for a Projectile Motion Laboratory

    NASA Astrophysics Data System (ADS)

    Sanders, Justin M.; Boleman, Michael W.

    2013-09-01

    At our university, students in introductory physics classes perform a laboratory exercise to measure the range of a projectile fired at an assigned angle. A set of photogates is used to determine the initial velocity of the projectile (the launch velocity). We noticed a systematic deviation between the experimentally measured range and the range calculated using the speed as determined by the photogates. In this paper, we will discuss the origin of this systematic error and derive a simple formula to correct it. In particular, we find that the launch speed given by our instrument is significantly different from the actual launch speed of our projectile.

  6. Penetration of granular projectiles into a water target.

    PubMed

    González-Gutiérrez, Jorge; Carrillo-Estrada, J L; Ruiz-Suárez, J C

    2014-01-01

    The penetration of low-speed projectiles into a water target has been studied in the last several years to understand the physics behind the formation and collapse of cavities. In such studies, the projectiles employed were solid bodies or liquid drops. Here we report similar impact experiments using granular projectiles, with the aim to investigate how the morphology of the cavities is determined by the balance between the dynamic pressure exerted by the fluid and the cohesive strength of the impactors. From the results we present and discuss in this manuscript, we speculate on the dynamics of meteorite disintegration in the atmosphere of our planet. PMID:25342448

  7. Microcraters formed in glass by low density projectiles

    NASA Technical Reports Server (NTRS)

    Mandeville, J.-C.; Vedder, J. F.

    1971-01-01

    Microcraters were produced in soda-lime glass by the impact of low density projectiles of polystyrene (p = 1.06 g/cu cm) with masses between 0.7 and 62 picograms and velocities between 2 and 14 km/s. The morphology of the craters depended on the velocity and the angle of incidence of the projectiles and these are discussed in detail. It was found that the transitions in morphology of the craters formed by polystyrene spheres occurred at higher velocities than they did for more dense projectiles.

  8. Penetration of Granular Projectiles into a Water Target

    PubMed Central

    González-Gutiérrez, Jorge; Carrillo-Estrada, J. L.; Ruiz-Suárez, J. C.

    2014-01-01

    The penetration of low-speed projectiles into a water target has been studied in the last several years to understand the physics behind the formation and collapse of cavities. In such studies, the projectiles employed were solid bodies or liquid drops. Here we report similar impact experiments using granular projectiles, with the aim to investigate how the morphology of the cavities is determined by the balance between the dynamic pressure exerted by the fluid and the cohesive strength of the impactors. From the results we present and discuss in this manuscript, we speculate on the dynamics of meteorite disintegration in the atmosphere of our planet. PMID:25342448

  9. Dynamic impact analysis of the M1 105mm projectile

    SciTech Connect

    Walls, J.C.; Webb, D.S.

    1993-06-01

    Evaluation of the effects of {open_quotes}rough-handling{close_quotes}-induced stresses in the nose region of a 105mm artillery projectile was performed to determine if these stresses could have contributed to the premature explosion of a projectile during a Desert Shield training mission of the 101st Army Airborne in Saudi Arabia. The rough-handling evaluations were simulated by dynamic impact analysis. It was concluded that the combined residual stress and dynamic impact-induced stress would not be of sufficient magnitude to cause cracking of the projectile in the nose region.

  10. Dynamic impact analysis of the M1 105mm projectile

    SciTech Connect

    Walls, J.C.; Webb, D.S.

    1993-06-01

    Evaluation of the effects of [open quotes]rough-handling[close quotes]-induced stresses in the nose region of a 105mm artillery projectile was performed to determine if these stresses could have contributed to the premature explosion of a projectile during a Desert Shield training mission of the 101st Army Airborne in Saudi Arabia. The rough-handling evaluations were simulated by dynamic impact analysis. It was concluded that the combined residual stress and dynamic impact-induced stress would not be of sufficient magnitude to cause cracking of the projectile in the nose region.

  11. Heterogeneous electron transfer at nanoscopic electrodes: importance of electronic structures and electric double layers.

    PubMed

    Chen, Shengli; Liu, Yuwen; Chen, Junxiang

    2014-08-01

    Heterogeneous electron-transfer (ET) processes at solid electrodes play key roles in molecular electronics and electrochemical energy conversion and sensing. Electrode nanosization and/or nanostructurization are among the major current strategies for performance promotion in these fields. Besides, nano-sized/structured electrodes offer great opportunities to characterize electrochemical structures and processes with high spatial and temporal resolution. This review presents recent insights into the nanoscopic size and structure effects of electrodes and electrode materials on heterogeneous ET kinetics, by emphasizing the importance of the electric double-layer (EDL) at the electrode/electrolyte interface and the electronic structure of electrode materials. It is shown, by general conceptual analysis and recent example demonstrations of representative electrode systems including electrodes of nanometer sizes and gaps and of nanomaterials such as sp(2) hybridized nanocarbons and semiconductor quantum dots, how the heterogeneous ET kinetics, the electronic structures of electrodes, the EDL structures at the electrode/electrolyte interface and the nanoscopic electrode sizes and structures may be related. PMID:24871071

  12. Theoretical studies of the electronic structure of small metal clusters

    NASA Technical Reports Server (NTRS)

    Jordan, K. D.

    1982-01-01

    Theoretical studies of the electronic structure of metal clusters, in particular clusters of Group IIA and IIB atoms were conducted. Early in the project it became clear that electron correlation involving d orbitals plays a more important role in the binding of these clusters than had been previously anticipated. This necessitated that computer codes for calculating two electron integrals and for constructing the resulting CI Hamiltonions be replaced with newer, more efficient procedures. Program modification, interfacing and testing were performed. Results of both plans are reported.

  13. Electronic structure of spatially aligned graphene nanoribbons on Au(788).

    PubMed

    Linden, S; Zhong, D; Timmer, A; Aghdassi, N; Franke, J H; Zhang, H; Feng, X; Müllen, K; Fuchs, H; Chi, L; Zacharias, H

    2012-05-25

    We report on a bottom-up approach of the selective and precise growth of subnanometer wide straight and chevron-type armchair nanoribbons (GNRs) on a stepped Au(788) surface using different specific molecular precursors. This process creates spatially well-aligned GNRs, as characterized by STM. High-resolution direct and inverse photoemission spectroscopy of occupied and unoccupied states allows the determination of the energetic position and momentum dispersion of electronic states revealing the existence of band gaps of several electron volts for straight 7-armchair, 13-armchair, and chevron-type GNRs in the electronic structure. PMID:23003288

  14. Super instruction architecture of petascale electronic structure software: the story

    NASA Astrophysics Data System (ADS)

    Lotrich, V. F.; Ponton, J. M.; Perera, A. S.; Deumens, E.; Bartlett, R. J.; Sanders, B. A.

    2010-11-01

    Theoretical methods in chemistry lead to algorithms for the computation of electronic energies and other properties of electronic wave functions that require large numbers of floating point operations and involve large data sets. Thus, computational chemists are very interested in using massively parallel computer systems and in particular the new petascale systems. In this paper we discuss a new programming paradigm that was developed at the Quantum Theory Project to construct electronic structure software that can scale to large numbers of cores of the order of 100,000 and beyond to solve problems in materials engineering relevant to the problems facing society today.

  15. Banded Electron Structure Formation in the Inner Magnetosphere

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    Banded electron structures in energy-time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce-averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making open pass around the Earth do not have time to develop this feature. The separation of high-energy bands from the injection population due to the preferential advection of the gradient-curvature drift creates spikes in the energy distribution, which overlap to form a series of bands in the energy spectrograms. The lowest band is the bulk of the injected population in the sub-key energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the development of their distribution function is examined and discussed.

  16. Comparison of electronic structure between monolayer silicenes on Ag (111)

    NASA Astrophysics Data System (ADS)

    Chun-Liang, Lin; Ryuichi, Arafune; Maki, Kawai; Noriaki, Takagi

    2015-08-01

    The electronic structures of monolayer silicenes (4 × 4 and ) grown on Ag (111) surface are studied by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. While both phases have similar electronic structures around the Fermi level, significant differences are observed in the higher energy unoccupied states. The DFT calculations show that the contributions of Si 3pz orbitals to the unoccupied states are different because of their different buckled configurations. Project supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) through Grants-in-Aid for Scientific Research (Grant Nos. 24241040 and 25110008) and the World Premier International Research Center Initiative (WPI), MEXT, Japan.

  17. Structural and luminescent properties of electron-irradiated silicon

    SciTech Connect

    Sobolev, N. A.; Loshachenko, A. S.; Aruev, P. N.; Kalyadin, A. E.; Shek, E. I.; Zabrodskiy, V. V.; Shtel'makh, K. F.; Vdovin, V. I.; Xiang, Luelue; Yang, Deren

    2014-02-21

    Structural defects induced by electron irradiation of p-Cz-Si wafers were identified. The influence of the annealing conditions in a chlorine-containing atmosphere on the structural and luminescent properties of the samples was examined. Light-emitting diodes based on electron-irradiated and high-temperature-annealed wafers were fabricated by a vapour-phase epitaxy technique and their luminescence properties were studied. A high-intensity dislocation-related D1 line was observed at 1.6 μm in the room-temperature electroluminescence spectrum.

  18. Chemistry and Electronic Structure of Iron-Based Superconductors

    SciTech Connect

    Safa-Sefat, Athena; Singh, David J

    2011-01-01

    The solid state provides a richly varied fabric for intertwining chemical bonding, electronic structure, and magnetism. The discovery of superconductivity in iron pnictides and chalcogenides has revealed new aspects of this interplay, especially involving magnetism and superconductivity. Moreover, it has challenged prior thinking about high-temperature superconductivity by providing a set of materials that differ in many crucial aspects from the previously known cuprate superconductors. Here we review some of what is known about the superconductivity and its interplay with magnetism, chemistry, and electronic structure in Fe-based superconductors.

  19. Orientation-dependent C-60 electronic structures revealed byphotoemission spectroscopy

    SciTech Connect

    Brouet, V.; Yang, W.L.; Zhou, X.J.; Choi, H.J.; Louie, S.G.; Cohen, M.L.; Goldoni, A.; Parmigiani, F.; Hussain, Z.; Shen, Z.X.

    2008-01-17

    We observe, with angle-resolved photoemission, a dramaticchange in the electronic structure of two C60 monolayers, deposited,respectively, on Ag (111) and (100) substrates, and similarly doped withpotassium to half filling of the C60 lowest unoccupied molecular orbital.The Fermi surface symmetry, the bandwidth, and the curvature of thedispersion at gamma point are different. Orient ations of the C60molecules on the two substrates are known to be the main structuraldifference between the two monolayers, and we present new band-structurecalculations for some of these orientations. We conclude thatorientations play a key role in the electronic structure offullerides.

  20. The electronic structure and chemical bonding of vitamin B12

    NASA Astrophysics Data System (ADS)

    Kurmaev, E. Z.; Moewes, A.; Ouyang, L.; Randaccio, L.; Rulis, P.; Ching, W. Y.; Bach, M.; Neumann, M.

    2003-05-01

    The electronic structure and chemical bonding of vitamin B12 (cyanocobalamin) and B12-derivative (methylcobalamin) are studied by means of X-ray emission (XES) and photoelectron (XPS) spectroscopy. The obtained results are compared with ab initio electronic structure calculations using the orthogonalized linear combination of the atomic orbital method (OLCAO). We show that the chemical bonding in vitamin B12 is characterized by the strong Co-C bond and relatively weak axial Co-N bond. It is further confirmed that the Co-C bond in cyanocobalamin is stronger than that of methylcobalamin resulting in their different biological activity.

  1. Comparison of less lethal 40 mm sponge projectile and the 37 mm projectile for injury assessment on human thorax

    NASA Astrophysics Data System (ADS)

    Nsiampa, N.; Robbe, C.; Oukara, A.; Papy, A.

    2012-08-01

    Since there is an increasing interest in avoiding human body injury in diverse situations like crowd control or peacekeeping missions, less lethal ammunition are more and more used. In this study we focus only on kinetic energy non-lethal (KENLW) projectiles. Their desired effects on human body are the temporary incapacitation through blunt trauma. There are different types of KENLW projectiles ranging from rigid to deformable projectiles. Unfortunately, the effects of such projectiles are not really well known as it is difficult to measure the force transmitted to the human body or the related deformation. Because the potential of injury excludes human living tests, tests are performed on cadavers, animals or human tissue surrogates. Besides these tests, numerical simulations are more and more used to gain more understanding, to assess or to predict the effects of this kind of projectile on human body. In this paper a comparison based on the viscous criterion between the 37 mm rigid projectile and the 40 mm sponge projectile was made.

  2. High charge short electron bunches for wakefield accelerator structures development.

    SciTech Connect

    Conde, M. E.

    1998-09-25

    The Argonne Wakefield Accelerator group develops accelerating structures based on dielectric loaded waveguides. We use high charge short electron bunches to excite wakefields in dielectric loaded structures, and a second (low charge) beam to probe the wakefields left behind by the drive beam. We report measurements of beam parameters and also initial results of the dielectric loaded accelerating structures. We have studied acceleration of the probe beam in these structures and we have also made measurements on the RF pulses that are generated by the drive beam. Single drive bunches, as well as multiple bunches separated by an integer number of RF periods have been used to generate the accelerating wakefields.

  3. New quinternary selenides: Syntheses, characterizations, and electronic structure calculations

    SciTech Connect

    Chung, Ming-Yan; Lee, Chi-Shen

    2013-06-01

    Five quinternary selenides, Sr₂.₆₃Y₀.₃₇Ge₀.₆₃Sb₂.₃₇Se₈ (I), Sr₂.₆₃La₀.₃₇Ge₀.₆₃Sb₂.₃₇Se₈ (II), Sr₂.₇₁La₀.₂₉Sn₀.₇₇Bi₂.₂₃Se₈ (III), Ba₂.₆₇ La₀.₃₃ Sn₀.₆₇Sb₂.₃₃Se₈ (IV), and Ba₂.₆₇ La₀.₃₃Sn₀.₆₇Bi₂.₃₃Se₈ (V), were synthesized by solid-state reaction in fused silica tubes. These compounds are isostructural and crystallize in the Sr₃GeSb₂Se₈ structural-type, which belongs to the orthorhombic space group Pnma (no. 62). Three structural units, 1[MSe₃], 1[M₄Se₁₀] (M=Tt, Pn) and M´ (M´=groups II and III element), comprise the entire one-dimensional structure, separated by M´. Measurements of electronic resistivity and diffused reflectance suggest that IV and V have semiconducting properties. Electronic structure calculations confirm the site preferences of Sr/La element discovered by crystal structure refinement. - Graphical abstract: Quinternary selenides Ae₂.₆₇M₀.₃₃Tt₀.₆₇Pn₂.₃₃Se₈ (Ae, M, Tt, Pn=Sr/Ba, Y/La, Ge/Sn, Sb/Bi) were synthesized and their site preferences were characterized by single-crystal X-ray diffraction and electronic structure calculation. Highlights: • Five new quinternary selenides were synthesized and characterized. • Structural units, 1[MSe₃] and 1[M₄Se₁₀] (M=Tt, Pn), construct the one-dimensional structure. • Calculations of electronic structure confirm site preference of Sr/La sites.

  4. Electronic structure and electron correlation in weakly confining spherical quantum dot potentials

    NASA Astrophysics Data System (ADS)

    Kimani, Peter Borgia Ndungu

    The electronic structure and electron correlations in weakly confining spherical quantum dots potentials are investigated. Following a common practice, the investigation starts with the restricted Hartree-Fock (HF) approximation. Then electron correlation is added in steps in a series of approximations based on the single particle Green's function approach: (i) Second-order Green function (GF) (ii) 2ph-Tamm-Dancoff approximation (TDA) and (iii) an extended version thereof (XTDA) which introduces ground-state correlation into the TDA. The study includes as well Hartree-Fock V (N-1) potential approximation in which framework the Hartree-Fock virtual orbitals are calculated in the field of the N-1 electrons as opposed to the regular but unphysical N-electron field Hartree-Fock calculation of virtual orbitals. For contrast and comparison, the same approximation techniques are applied to few-electron closed-shell atoms and few-electron negative ions for which pertinent data is readily available. The results for the weakly confining spherical quantum dot potentials and the standard atomic systems exhibit fundamental similarities as well as significant differences. For the most part the results of these calculations are in favor of application of HF, GF, and TDA techniques in the modeling of three-dimensional weakly confining quantum dot potentials. The observed differences emphasize the significance of confinement and electronic features unique to quantum dots such as the increased binding of electrons with higher angular momentum and the modified shell filling sequences.

  5. Chiral phosphorus nanotubes: structure, bonding, and electronic properties.

    PubMed

    Fernández-Escamilla, H N; Quijano-Briones, J J; Tlahuice-Flores, A

    2016-05-14

    The study of black phosphorus nanotubes (PNTs) had been devoted to zigzag and armchair structures, with no consideration of chiral structures to date. In this communication, we studied the structural and electronic (band structure) properties of chiral nanotubes using a periodic plane wave-pseudopotential approach. We found that some chiral nanotubes display similar bandgaps and binding energies per atom (BEA) as armchair PNTs and Born-Oppenheimer molecular dynamics (BOMD) calculations attest their thermal stability. Interestingly, we determined that the bandgap is tuned by varying the PNTs chirality and it is not related to their diameters. This feature can be exploited in optical and electronic applications wherein a direct and sizable bandgap is required. PMID:27094567

  6. Free electron laser-driven ultrafast rearrangement of the electronic structure in Ti

    PubMed Central

    Principi, E.; Giangrisostomi, E.; Cucini, R.; Bencivenga, F.; Battistoni, A.; Gessini, A.; Mincigrucci, R.; Saito, M.; Di Fonzo, S.; D'Amico, F.; Di Cicco, A.; Gunnella, R.; Filipponi, A.; Giglia, A.; Nannarone, S.; Masciovecchio, C.

    2015-01-01

    High-energy density extreme ultraviolet radiation delivered by the FERMI seeded free-electron laser has been used to create an exotic nonequilibrium state of matter in a titanium sample characterized by a highly excited electron subsystem at temperatures in excess of 10 eV and a cold solid-density ion lattice. The obtained transient state has been investigated through ultrafast absorption spectroscopy across the Ti M2,3-edge revealing a drastic rearrangement of the sample electronic structure around the Fermi level occurring on a time scale of about 100 fs. PMID:26798835

  7. Hartree-Fock electronic structure calculations for free atoms and immersed atoms in an electron gas

    NASA Astrophysics Data System (ADS)

    Walsh, Kenneth Charles

    Electronic structure calculations for free and immersed atoms are performed in the context of unrestricted Hartree-Fock Theory. Spherical symmetry is broken, lifting degeneracies in electronic configurations involving the magnetic quantum number mℓ. Basis sets, produced from density functional theory, are then explored for completeness. Comparison to spectroscopic data is done by a configurational interaction of the appropriate L and S symmetry. Finally, a perturbation technique by Lowdin is used to couple the bound atomic states to a neutral, uniform background electronic gas (jellium).

  8. Perforation of woven fabric by spherical projectiles

    SciTech Connect

    Shim, V.P.W.; Tan, V.B.C.; Tay, T.E.

    1995-12-31

    Rectangular specimens of Twaron{reg_sign} fabric, clamped on two opposite sides, are subjected to impact perforation by 9.5 mm diameter spherical steel projectiles at speeds ranging from 140 m/s to 420 m/s. This plain woven fabric, comprising PPTA (poly-paraphenylene terepthalamide) fibers, is commonly employed in flexible an-nor applications. Its perforation response is examined in terms of residual velocity, energy absorbed and resulting deformation patterns. The existence of a critical or transition impact velocity, beyond which there is a significant reduction in energy absorbed by perforation, is observed. Differences in creasing and deformation induced in specimens are also demarcated by this transition impact velocity. Effects of difference in boundary conditions (clamped and free) on yarn breakage are also noted. A numerical model, based on an initially orthogonal network of pin-jointed bars interconnected at nodes, is formulated to simulate the fabric. Fiber yam mechanical properties are represented via a three-element spring-dashpot model which encapsulates viscoelastic behavior and fiber failure. Numerical results exhibit good correlation with experimental observations in terms of prediction of threshold perforation velocity, energy absorbed, occurrence of a transition critical velocity and fabric deformation characteristics.

  9. 22. Emplacement no. 1 showing well for projectile hoist at ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    22. Emplacement no. 1 showing well for projectile hoist at right. at left is passage toward the shot gallery. View looking northwest - Fort Wadsworth Battery Romeyn B. Ayers, South side of Ayers Road, Staten Island, Rosebank, Richmond County, NY

  10. Penetration analysis of projectile with inclined concrete target

    NASA Astrophysics Data System (ADS)

    Kim, S. B.; Kim, H. W.; Yoo, Y. H.

    2015-09-01

    This paper presents numerical analysis result of projectile penetration with concrete target. We applied dynamic material properties of 4340 steels, aluminium and explosive for projectile body. Dynamic material properties were measured with static tensile testing machine and Hopkinson pressure bar tests. Moreover, we used three concrete damage models included in LS-DYNA 3D, such as SOIL_CONCRETE, CSCM (cap model with smooth interaction) and CONCRETE_DAMAGE (K&C concrete) models. Strain rate effect for concrete material is important to predict the fracture deformation and shape of concrete, and penetration depth for projectiles. CONCRETE_DAMAGE model with strain rate effect also applied to penetration analysis. Analysis result with CSCM model shows good agreement with penetration experimental data. The projectile trace and fracture shapes of concrete target were compared with experimental data.

  11. 32. VAL, DETAIL SHOWING LOADING PLATFORM, PROJECTILE LOADING CAR, LAUNCHER ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    32. VAL, DETAIL SHOWING LOADING PLATFORM, PROJECTILE LOADING CAR, LAUNCHER SLAB AND UNDERSIDE OF LAUNCHER BRIDGE LOOKING SOUTHWEST. - Variable Angle Launcher Complex, Variable Angle Launcher, CA State Highway 39 at Morris Reservior, Azusa, Los Angeles County, CA

  12. Oblique Perforation of Thick Metallic Plates by Rigid Projectiles

    NASA Astrophysics Data System (ADS)

    Chen, Xiaowei; Li, Qingming; Fan, Saucheong

    2006-08-01

    Oblique perforation of thick metallic plates by rigid projectiles with various nose shapes is studied in this paper. Two perforation mechanisms, i.e., the hole enlargement for a sharp projectile nose and the plugging formation for a blunt projectile nose, are considered in the proposed analytical model. It is shown that the perforation of a thick plate is dominated by several non-dimensional numbers, i.e., the impact function, the geometry function of projectile, the non-dimensional thickness of target and the impact obliquity. Explicit formulae are obtained to predict the ballistic limit, residual velocity and directional change for the oblique perforation of thick metallic plates. The proposed model is able to predict the critical condition for the occurrence of ricochet. The proposed model is validated by comparing the predictions with other existing models and independent experimental data.

  13. Electron-Phonon Renormalization of Electronic Band Structures of C Allotropes and BN Polymorphs

    NASA Astrophysics Data System (ADS)

    Tutchton, Roxanne M.; Marchbanks, Christopher; Wu, Zhigang

    The effect of lattice vibration on electronic band structures has been mostly neglected in first-principles calculations because the electron-phonon (e-ph) renormalization of quasi-particle energies is often small (< 100 meV). However, in certain materials, such as diamond, the electron-phonon coupling reduces the band gap by nearly 0.5 eV, which is comparable to the many-body corrections of the electronic band structures calculated using the density functional theory (DFT). In this work, we compared two implementations of the Allen-Heine-Cardona theory in the EPW code and the ABINIT package respectively. Our computations of Si and diamond demonstrate that the ABINIT implementation converges much faster. Using this method, the e-ph renormalizations of electronic structures of three C allotropes (diamond, graphite, graphene) and four BN polymorphs (zincblend, wurtzite, mono-layer, and layered-hexagonal) were calculated. Our results suggest that (1) all of the zero-point renormalizations of band gaps in these materials, except for graphene, are larger than 100 meV, and (2) there are large variations in e-ph renormalization of band gaps due to differences in crystal structure. This work was supported by a U.S. DOE Early Career Award (Grant No. DE-SC0006433). Computations were carried out at the Golden Energy Computing Organization at CSM and the National Energy Research Scientific Computing Center (NERSC).

  14. Electronic structure of hydrogenated diamond: Microscopical insight into surface conductivity

    NASA Astrophysics Data System (ADS)

    Iacobucci, S.; Alippi, Paola; Calvani, P.; Girolami, M.; Offi, F.; Petaccia, L.; Trucchi, D. M.

    2016-07-01

    We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a p -type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the Γ -X direction with an average hole effective mass of (0.43 ±0.02 ) m0 , where m0 is the bare electron mass; a second flatter band, with an effective mass of (2.2 ±0.9 ) m0 , proves that a hole gas confined in the topmost layers is responsible for the conductivity of the (2 ×1 ) hydrogen-terminated diamond (100 ) surface.

  15. Geometric and electronic structures of potassium-adsorbed rubrene complexes

    SciTech Connect

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-06-28

    The geometric and electronic structures of potassium-adsorbed rubrene complexes are studied in this article. It is found that the potassium-rubrene (K{sub 1}RUB) complexes inherit the main symmetry characteristics from their pristine counterparts and are thus classified into D{sub 2}- and C{sub 2h}-like complexes according to the relative orientations of the four phenyl side groups. The geometric structures of K{sub 1}RUB are governed by two general effects on the total energy: Deformation of the carbon frame of the pristine rubrene increases the total energy, while proximity of the potassium ion to the phenyl ligands decreases the energy. Under these general rules, the structures of D{sub 2}- and C{sub 2h}-like K{sub 1}RUB, however, exhibit their respective peculiarities. These peculiarities can be illustrated by their energy profiles of equilibrium structures. For the potassium adsorption-sites, the D{sub 2}-like complexes show minimum-energy basins, whereas the C{sub 2h}-like ones have single-point minimum-energies. If the potassium atom ever has the energy to diffuse from the minimum-energy site, the potassium diffusion path on the D{sub 2}-like complexes is most likely along the backbone in contrast to the C{sub 2h}-like ones. Although the electronic structures of the minimum-energy structures of D{sub 2}- and C{sub 2h}-like K{sub 1}RUB are very alike, decompositions of their total spectra reveal insights into the electronic structures. First, the spectral shapes are mainly determined by the facts that, in comparison with the backbone carbons, the phenyl carbons have more uniform chemical environments and far less contributions to the electronic structures around the valence-band edge. Second, the electron dissociated from the potassium atom mainly remains on the backbone and has little effects on the electronic structures of the phenyl groups. Third, the two phenyls on the same side of the backbone as the potassium atom have more similar chemical environments

  16. Geometric and electronic structures of potassium-adsorbed rubrene complexes

    NASA Astrophysics Data System (ADS)

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-06-01

    The geometric and electronic structures of potassium-adsorbed rubrene complexes are studied in this article. It is found that the potassium-rubrene (K1RUB) complexes inherit the main symmetry characteristics from their pristine counterparts and are thus classified into D2- and C2h-like complexes according to the relative orientations of the four phenyl side groups. The geometric structures of K1RUB are governed by two general effects on the total energy: Deformation of the carbon frame of the pristine rubrene increases the total energy, while proximity of the potassium ion to the phenyl ligands decreases the energy. Under these general rules, the structures of D2- and C2h-like K1RUB, however, exhibit their respective peculiarities. These peculiarities can be illustrated by their energy profiles of equilibrium structures. For the potassium adsorption-sites, the D2-like complexes show minimum-energy basins, whereas the C2h-like ones have single-point minimum-energies. If the potassium atom ever has the energy to diffuse from the minimum-energy site, the potassium diffusion path on the D2-like complexes is most likely along the backbone in contrast to the C2h-like ones. Although the electronic structures of the minimum-energy structures of D2- and C2h-like K1RUB are very alike, decompositions of their total spectra reveal insights into the electronic structures. First, the spectral shapes are mainly determined by the facts that, in comparison with the backbone carbons, the phenyl carbons have more uniform chemical environments and far less contributions to the electronic structures around the valence-band edge. Second, the electron dissociated from the potassium atom mainly remains on the backbone and has little effects on the electronic structures of the phenyl groups. Third, the two phenyls on the same side of the backbone as the potassium atom have more similar chemical environments than the other two on the opposite side, which leads to the largely enhanced

  17. Electronic Structure and Properties of Organic Bulk-Heterojunction Interfaces.

    PubMed

    Street, Robert A

    2016-05-01

    The electronic structure and physical mechanisms of carrier generation and transport in the organic bulk heterojunction are reviewed. The electronic structure describes the bands and band-tail states, the band alignment at the bulk-heterojunction interface, and the overall density-of-states model. The different electronic character of excitons and mobile charge is discussed, the former being highly molecular and the latter more delocalized. Dissociation of the exciton via the charge-transfer (CT) states is attributed to weak binding of the CT state arising from charge delocalization. Carrier transport and charge collection is strongly influenced by the presence of localized band-tail states. Recombination is attributed primarily to transitions from mobile carriers to band-tail or deep trap states. PMID:26603977

  18. Surface crystallography and electronic structure of potassium yttrium tungstate

    SciTech Connect

    Atuchin, V. V.; Pokrovsky, L. D.; Khyzhun, O. Yu.; Sinelnichenko, A. K.; Ramana, C. V.

    2008-08-01

    Structural and electronic characteristics of KY(WO{sub 4}){sub 2} (KYW) (010) crystal surfaces have been studied using reflection high-energy electron diffraction (RHEED) and x-ray photoelectron spectroscopy (XPS). The results indicate that the crystal structure and chemical composition of the mechanically polished pristine surface is stoichiometrically well maintained as expected for KYW crystals. Combined measurements of RHEED and XPS as a function of 1.5 keV Ar{sup +} ion irradiation of the KYW (010) surfaces indicate amorphization, partial loss of potassium atoms, and partial transformation of chemical valence state of tungsten from W{sup 6+} to a lower valence state, W{sup 0} state predominantly, which induces electronic states at the top of valence band.

  19. Projectile-power-compressed magnetic-field pulse generator

    SciTech Connect

    Barlett, R.H.; Takemori, H.T.; Chase, J.B.

    1983-03-17

    Design considerations and experimental results are presented of a compressed magnetic field pulsed energy source. A 100-mm-diameter, gun-fired projectile of approx. 2MJ kinetic energy was the input energy source. An initial magnetic field was trapped and compressed by the projectile. With a shorted load, a magajoule in a nanohenry was the design goal, i.e., 50 percent energy transformation from kinetic to magnetic. Five percent conversion was the highest recorded before gauge failure.

  20. Highlighting material structure with transmission electron diffraction correlation coefficient maps.

    PubMed

    Kiss, Ákos K; Rauch, Edgar F; Lábár, János L

    2016-04-01

    Correlation coefficient maps are constructed by computing the differences between neighboring diffraction patterns collected in a transmission electron microscope in scanning mode. The maps are shown to highlight material structural features like grain boundaries, second phase particles or dislocations. The inclination of the inner crystal interfaces are directly deduced from the resulting contrast. PMID:26866276

  1. Flat pack interconnection structure simplifies modular electronic assemblies

    NASA Technical Reports Server (NTRS)

    Katzin, L.

    1967-01-01

    Flat pack interconnection structure composed of stick modules simplifies modular electronic assemblies by allowing a single axis mother board. Two of the wiring planes are located in the stick module, which is the lower level of assembly, with the third wiring plane in the mother board.

  2. The electronic structure of grain boundaries in Nb

    SciTech Connect

    Sowa, E.C.; Gonis, A. ); Zhang, X.G. )

    1990-11-01

    We present first-principles calculations of the electronic structure of Nb grain boundaries. These are the first such calculations for a bcc metal using the real-space multiple-scattering theory (RSMST). Local densities of states near a {Sigma}5 twist grain boundary are compared to those for bulk Nb. 5 refs., 1 fig.

  3. The electronic structure of heavy fermions: Narrow temperature independent bands

    SciTech Connect

    Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B.

    1996-08-01

    The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.

  4. Electron Heat Flux in Pressure Balance Structures at Ulysses

    NASA Technical Reports Server (NTRS)

    Yamauchi, Yohei; Suess, Steven T.; Sakurai, Takashi; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Pressure balance structures (PBSs) are a common feature in the high-latitude solar wind near solar minimum. Rom previous studies, PBSs are believed to be remnants of coronal plumes and be related to network activity such as magnetic reconnection in the photosphere. We investigated the magnetic structures of the PBSs, applying a minimum variance analysis to Ulysses/Magnetometer data. At 2001 AGU Spring meeting, we reported that PBSs have structures like current sheets or plasmoids, and suggested that they are associated with network activity at the base of polar plumes. In this paper, we have analyzed high-energy electron data at Ulysses/SWOOPS to see whether bi-directional electron flow exists and confirm the conclusions more precisely. As a result, although most events show a typical flux directed away from the Sun, we have obtained evidence that some PBSs show bi-directional electron flux and others show an isotropic distribution of electron pitch angles. The evidence shows that plasmoids are flowing away from the Sun, changing their flow direction dynamically in a way not caused by Alfven waves. From this, we have concluded that PBSs are generated due to network activity at the base of polar plumes and their magnetic structures axe current sheets or plasmoids.

  5. Controlling electron-phonon scattering with metamaterial plasmonic structures

    NASA Astrophysics Data System (ADS)

    Kempa, Krzysztof; Wu, Xueyuan; Kong, Jiantao; Broido, David

    Electron-plasmon scattering can be faster than electron-phonon scattering. While in metals plasmons occur in the UV range, phonons dominate behavior at much lower frequencies (far IR range), and this typically decouples these phenomena. In metamaterial plasmonic structures, however, plasma effects can be tuned down to the far IR range, allowing for their interference with phonons. It was recently shown, that such interference can protect hot electron energy induced in a solar cell, from dissipation into heat. In this work we explore the possibility of using such an effect to control the electron-phonon interaction and transport in semiconductors. We demonstrate, that this could lead to a novel path to enhancing the electrical and thermal conductivities and the thermoelectric figure of merit.

  6. Correlative Light Electron Microscopy: Connecting Synaptic Structure and Function.

    PubMed

    Begemann, Isabell; Galic, Milos

    2016-01-01

    Many core paradigms of contemporary neuroscience are based on information obtained by electron or light microscopy. Intriguingly, these two imaging techniques are often viewed as complementary, yet separate entities. Recent technological advancements in microscopy techniques, labeling tools, and fixation or preparation procedures have fueled the development of a series of hybrid approaches that allow correlating functional fluorescence microscopy data and ultrastructural information from electron micrographs from a singular biological event. As correlative light electron microscopy (CLEM) approaches become increasingly accessible, long-standing neurobiological questions regarding structure-function relation are being revisited. In this review, we will survey what developments in electron and light microscopy have spurred the advent of correlative approaches, highlight the most relevant CLEM techniques that are currently available, and discuss its potential and limitations with respect to neuronal and synapse-specific applications. PMID:27601992

  7. Correlative Light Electron Microscopy: Connecting Synaptic Structure and Function

    PubMed Central

    Begemann, Isabell; Galic, Milos

    2016-01-01

    Many core paradigms of contemporary neuroscience are based on information obtained by electron or light microscopy. Intriguingly, these two imaging techniques are often viewed as complementary, yet separate entities. Recent technological advancements in microscopy techniques, labeling tools, and fixation or preparation procedures have fueled the development of a series of hybrid approaches that allow correlating functional fluorescence microscopy data and ultrastructural information from electron micrographs from a singular biological event. As correlative light electron microscopy (CLEM) approaches become increasingly accessible, long-standing neurobiological questions regarding structure-function relation are being revisited. In this review, we will survey what developments in electron and light microscopy have spurred the advent of correlative approaches, highlight the most relevant CLEM techniques that are currently available, and discuss its potential and limitations with respect to neuronal and synapse-specific applications. PMID:27601992

  8. Electronic Structure of Crystalline 4He at High Pressures

    SciTech Connect

    Mao, Ho Kwang; Shirley, Eric L.; Ding, Yang; Eng, Peter; Cai, Yong Q.; Chow, Paul; Xiao, Yuming; Jinfu Shu, A=Kao, Chi-Chang; Hemley, Russell J.; Kao, Chichang; Mao, Wendy L.; /Stanford U., Geo. Environ. Sci. /SLAC

    2011-01-10

    Using inelastic X-ray scattering techniques, we have succeeded in probing the high-pressure electronic structure of helium crystal at 300 K which has the widest known electronic energy bandgap of all materials, that was previously inaccessible to measurements due to the extreme energy and pressure range. We observed rich electron excitation spectrum, including a cut-off edge above 23 eV, a sharp exciton peak showing linear volume dependence, and a series of excitations and continuum at 26 to 45 eV. We determined electronic dispersion along the {Gamma}-M direction over two Brillouin zones, and provided a quantitative picture of the helium exciton beyond the simplified Wannier-Frenkel description.

  9. Effect of Structural Relaxation on the Electronic Structure of Graphene on Hexagonal Boron Nitride.

    PubMed

    Slotman, G J; van Wijk, M M; Zhao, Pei-Liang; Fasolino, A; Katsnelson, M I; Yuan, Shengjun

    2015-10-30

    We performed calculations of electronic, optical, and transport properties of graphene on hexagonal boron nitride with realistic moiré patterns. The latter are produced by structural relaxation using a fully atomistic model. This relaxation turns out to be crucially important for electronic properties. We describe experimentally observed features such as additional Dirac points and the "Hofstadter butterfly" structure of energy levels in a magnetic field. We find that the electronic structure is sensitive to many-body renormalization of the local energy gap. PMID:26565485

  10. Effect of Structural Relaxation on the Electronic Structure of Graphene on Hexagonal Boron Nitride

    NASA Astrophysics Data System (ADS)

    Slotman, G. J.; van Wijk, M. M.; Zhao, Pei-Liang; Fasolino, A.; Katsnelson, M. I.; Yuan, Shengjun

    2015-10-01

    We performed calculations of electronic, optical, and transport properties of graphene on hexagonal boron nitride with realistic moiré patterns. The latter are produced by structural relaxation using a fully atomistic model. This relaxation turns out to be crucially important for electronic properties. We describe experimentally observed features such as additional Dirac points and the "Hofstadter butterfly" structure of energy levels in a magnetic field. We find that the electronic structure is sensitive to many-body renormalization of the local energy gap.

  11. Response of simulated propellants and explosives to projectile impact

    SciTech Connect

    Yuan, W.

    1990-11-01

    This dissertation deals with experimental, analytical and numerical investigations into the response of two types of simulated propellants and explosives, known as Propergol, to projectile impact. The targets consisted of a polymeric mixture composed of potassium chloride, plaster of Paris and a polyurethane binder. Following the determination of the constitutive behavior of Propergol, experiments were conducted to study their penetration, perforation and fragmentation by projectiles. Both pneumatic and powder guns were employed in the tests, perfragmentation by projectiles. Both pneumatic and powder guns were employed in the tests, permitting impact velocities ranging from 40 to 1100 m/s, for flat- and conically-tipped as well as armor-piercing projectiles. The specimens include monolithic, composite and constrained Propergol circular disks and cylinders of 140 mm diameter with thicknesses ranging from 9 to 90 mm. Penetration tests were also conducted on model warheads loaded with the simulant material. Ballistic limit velocities for various target/projectile combinations were determined. Damage modes, such as cracking and fragmentation, were examined using experimental evidence including high-speed film data and microscopic photographs. Two types of fragments, Propergol clusters and crystalline particles, were recognized, and their size distributions were found to fit exponential functions. The dependent of fragment number and volume on initial projectile velocity was also studied. 103 refs., 172 figs., 19 tabs.

  12. Orientation estimation algorithm applied to high-spin projectiles

    NASA Astrophysics Data System (ADS)

    Long, D. F.; Lin, J.; Zhang, X. M.; Li, J.

    2014-06-01

    High-spin projectiles are low cost military weapons. Accurate orientation information is critical to the performance of the high-spin projectiles control system. However, orientation estimators have not been well translated from flight vehicles since they are too expensive, lack launch robustness, do not fit within the allotted space, or are too application specific. This paper presents an orientation estimation algorithm specific for these projectiles. The orientation estimator uses an integrated filter to combine feedback from a three-axis magnetometer, two single-axis gyros and a GPS receiver. As a new feature of this algorithm, the magnetometer feedback estimates roll angular rate of projectile. The algorithm also incorporates online sensor error parameter estimation performed simultaneously with the projectile attitude estimation. The second part of the paper deals with the verification of the proposed orientation algorithm through numerical simulation and experimental tests. Simulations and experiments demonstrate that the orientation estimator can effectively estimate the attitude of high-spin projectiles. Moreover, online sensor calibration significantly enhances the estimation performance of the algorithm.

  13. Writing Electron Dot Structures: Abstract of Issue 9905M

    NASA Astrophysics Data System (ADS)

    Magnell, Kenneth R.

    1999-10-01

    Writing Electron Dot Structures is a computer program for Mac OS that provides drill with feedback for students learning to write electron dot structures. While designed for students in the first year of college general chemistry it may also be used by high school chemistry students. A systematic method similar to that found in many general chemistry texts is employed:

    1. determine the number of valence shell electrons,
    2. select the central atom,
    3. construct a skeleton,
    4. add electrons to complete octets,
    5. examine the structure for resonance forms.
    During the construction of a structure, the student has the option of quitting, selecting another formula, or returning to a previous step. If an incorrect number of electrons is entered the student may not proceed until the correct number is entered. The symbol entered for the central atom must follow accepted upper/lower case practice, and entry of the correct symbol must be accomplished before proceeding to the next step. A periodic table is accessible and feedback provides assistance for these steps. Construction of the skeleton begins with the placement of the central atom. Atoms can be added, moved, or removed. Prompts and feedback keep the student informed of progress and problems. A correct skeleton is required before proceeding to the next step. Completion of the structure begins with the addition of electron pairs to form the required bonds. Remaining electrons are added to complete the formation of multiple bonds, assure compliance with the octet rule, and form expanded octets. Resonance forms are made by moving or removing and replacing electron pairs in the existing skeleton. Prompts and feedback guide the student through this process. A running tally of bond pairs, unshared pairs, octets, electrons used, and electrons remaining is provided during this step. Structural and Electronic Investigations of Complex Intermetallic Compounds

    SciTech Connect

    Ko, Hyunjin

    2008-01-01

    In solid state chemistry, numerous investigations have been attempted to address the relationships between chemical structure and physical properties. Such questions include: (1) How can we understand the driving forces of the atomic arrangements in complex solids that exhibit interesting chemical and physical properties? (2) How do different elements distribute themselves in a solid-state structure? (3) Can we develop a chemical understanding to predict the effects of valence electron concentration on the structures and magnetic ordering of systems by both experimental and theoretical means? Although these issues are relevant to various compound classes, intermetallic compounds are especially interesting and well suited for a joint experimental and theoretical effort. For intermetallic compounds, the questions listed above are difficult to answer since many of the constituent atoms simply do not crystallize in the same manner as in their separate, elemental structures. Also, theoretical studies suggest that the energy differences between various structural alternatives are small. For example, Al and Ga both belong in the same group on the Periodic Table of Elements and share many similar chemical properties. Al crystallizes in the fcc lattice with 4 atoms per unit cell and Ga crystallizes in an orthorhombic unit cell lattice with 8 atoms per unit cell, which are both fairly simple structures (Figure 1). However, when combined with Mn, which itself has a very complex cubic crystal structure with 58 atoms per unit cell, the resulting intermetallic compounds crystallize in a completely different fashion. At the 1:1 stoichiometry, MnAl forms a very simple tetragonal lattice with two atoms per primitive unit cell, while MnGa crystallizes in a complicated rhombohedral unit cell with 26 atoms within the primitive unit cell. The mechanisms influencing the arrangements of atoms in numerous crystal structures have been studied theoretically by calculating electronic

  14. The solar maximum satellite capture cell: Impact features and orbital debris and micrometeoritic projectile materials

    NASA Technical Reports Server (NTRS)

    Mckay, D. S.; Rietmeijer, F. J. M.; Schramm, L. S.; Barrett, R. A.; Zook, H. A.; Blanford, G. E.

    1986-01-01

    The physical properties of impact features observed in the Solar Max main electronics box (MEB) thermal blanket generally suggest an origin by hypervelocity impact. The chemistry of micrometeorite material suggests that a wide variety of projectile materials have survived impact with retention of varying degrees of pristinity. Impact features that contain only spacecraft paint particles are on average smaller than impact features caused by micrometeorite impacts. In case both types of materials co-occur, it is belevied that the impact feature, generally a penetration hole, was caused by a micrometeorite projectile. The typically smaller paint particles were able to penetrate though the hole in the first layer and deposit in the spray pattern on the second layer. It is suggested that paint particles have arrived with a wide range of velocities relative to the Solar Max satellite. Orbiting paint particles are an important fraction of materials in the near-Earth environment. In general, the data from the Solar Max studies are a good calibration for the design of capture cells to be flown in space and on board Space Station. The data also suggest that development of multiple layer capture cells in which the projectile may retain a large degree of pristinity is a feasible goal.

  15. Electronics speckle interferometry applications for NDE of spacecraft structural components

    NASA Astrophysics Data System (ADS)

    Rao, M. V.; Samuel, R.; Ananthan, A.; Dasgupta, S.; Nair, P. S.

    2008-09-01

    The spacecraft components viz., central cylinder, deck plates, solar panel substrates, antenna reflectors are made of aluminium/composite honeycomb sandwich construction. Detection of these defects spacecraft structural components is important to assess the integrity of the spacecraft structure. Electronic Speckle Interferometry (ESI) techniques identify the defects as anomalous regions in the interferometric fringe patterns of the specklegram while the component is suitably stressed to give rise to differential displacement/strain around the defective region. Calibration studies, different phase shifting methods associated with ESI and the development of a prototype Twin Head ESSI System (THESSIS) and its use for the NDE of a typical satellite structural component are presented.

  16. Electronically induced structure transformations in graphite & silver, studied using ultrafast electron crystallography

    NASA Astrophysics Data System (ADS)

    Raman, Ramani K.

    Electronically induced structure transformations are a unique class of phenomena in which material transformation can be effected by impulsive excitation of the electronic system, often resulting in exotic structural phases and transformation pathways inaccessible to thermodynamic channels. Using ultrafast electron crystallography (UEC), we have directly observed such photodinduced atomic dynamics in two systems - graphite and silver nanocrystals (Ag NC) that appear to be driven by the strong coupling between the laser excitation and lattice perturbations in the form of strongly coupled optical phonons and laser induced electron redistribution. In graphite, structural changes resulting from photoexcitation with p-polarized, near-IR, femtosecond laser pulses are observed to lead to the nonthermal creation of a transient state with sp3 like bonding characteristics. At laser fluences approaching, but below the damage threshold, the average inter-layer spacing contracts along with creation of new inter-layer distances at ≈ 2 A while the lattice is only moderately heated. The advantage of using electrons (which carry a charge) as a probe is demonstrated, as it reveals the transformation to be driven by a hitherto unobserved surface dipole field, observed here via a Coulomb refraction shift of the scattered electrons within the sub-surface region. Ab initio density functional theory calculations are employed to relate these structural changes to a nonthermal heating of the electrons, followed by a photoinduced charge separation causing a compressive Coulomb stress. To quantify the role and dynamics of electrons emitted from photoexcited surfaces, a novel 'point-projection method' is introduced, capable of directly imaging the spatiotemporal evolution of such photoemitted electron bunches. The method is shown to provide sufficient sensitivity to image electron bunches (as small as 1010 e/cm3) and permit quantitative investigation of the electron emission from

  17. Electronic Structure Studies of Silicon Carbide Cationic Nanoclusters

    NASA Astrophysics Data System (ADS)

    Pradhan, Prachi

    2005-03-01

    As a continuation of our studies on the high stabilities and associated electronic structure properties of Si8C2 to Si14C2 and Si20Cn (n=3-6) clusters,^1 we report here detailed ab initio electronic and geometric structure studies of small SimCn^+ (1< m, n < 4) cationic clusters. The theoretical formalism used is the local density approximation (LDA) to density functional theory (DFT) and the Gaussian03 suite of programs^2 with an all electron 6-311++G** basis set has been used. Complete geometry optimizations of different possible structures have been carried out. The stability of the clusters varies with the ratio of the number of silicon to carbon atoms in the cluster. In contrast to the neutral clusters,^3 cationic clusters appear to prefer more open structures. Results will be presented for binding energies, relative energies, fragmentation energies, vibrational frequencies, and adiabatic ionization potentials^3 for the optimized clusters. Detailed comparisons with published data in the literature will also be presented. * Work supported, in part, by the Welch Foundation, Houston, Texas (Grant No. Y-1525) ^1M. N. Huda and A. K. Ray, Phys. Rev. A (R) 69, 011201 (2004); Eur. Phys. J. D 31, 63 (2004). ^2 Gaussian03, Revision A.1, M. J. Frisch et al., Gaussian Inc., Pittsburgh, PA , 2003. ^3 P. Pradhan and A. K. Ray, J. Mol. Structure (Theochem), in press.

  18. Ultrafast Structural Dynamics of Tertiary Amines upon Electronic Excitation

    NASA Astrophysics Data System (ADS)

    Cheng, Xinxin; Minitti, Michael P.; Deb, Sanghamitra; Zhang, Yao; Budarz, James; Weber, Peter M.

    2011-06-01

    The structural response of several tertiary amines to electronic excitation has been investigated using Rydberg Fingerprint Spectroscopy. The 3p Rydberg states are reached by excitation with a 5.93 eV photon while 3s states are populated by electronic relaxation from 3p state. We observe binding energy shifts on ultrafast time scales in all peaks that reflect the structural change of the molecular ion cores. The shifts are in the range of 15 meV to 30 meV, within time scales of less than 500 fs, depending on the specific molecular systems and the nature of the electronic state. In cases where the p states are spectrally separate, the trends of the energy shifts are different for the p_z and p_x_y Rydberg states whereas the p_z and s states are similar. This suggests that the response of the Rydberg states to structural displacements depends on the symmetry. Very fast binding energy shifts, observed on sub-picosecond time scales, are attributed to the structural adjustment from a pyramidal to a planar structure upon Rydberg excitation. The quantitative values of the binding energy shifts can also be affected by laser chirp, which we model using simulations.

  19. Defective graphene and nanoribbons: electronic, magnetic and structural properties

    NASA Astrophysics Data System (ADS)

    Guerra, Thiago; Azevedo, Sérgio; Machado, Marcelo

    2016-03-01

    We make use of first-principles calculations, based on the density functional theory (DFT), to investigate the alterations at the structural, energetic, electronic and magnetic properties of graphene and zigzag graphene nanoribbons (ZGNRs) due to the inclusion of different types of line and punctual defects. For the graphene it is found that the inclusion of defects breaks the translational symmetry of the crystal with drastic changes at its electronic structure, going from semimetallic to semiconductor and metallic. Regarding the magnetic properties, no magnetization is observed for the defective graphene. We also show that the inclusion of defects at ZGNRs is a good way to create and control pronounced peaks at the Fermi level. Furthermore, defective ZGNRs structures show magnetic moment by supercell up to 2.0 μ B . For the non defective ZGNRs is observed a switch of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferrimagnetic and ferromagnetic configurations.

  1. Characterization of electronic structure of periodically strained graphene

    SciTech Connect

    Aslani, Marjan; Garner, C. Michael Nishi, Yoshio; Kumar, Suhas; Nordlund, Dennis; Pianetta, Piero

    2015-11-02

    We induced periodic biaxial tensile strain in polycrystalline graphene by wrapping it over a substrate with repeating pillar-like structures with a periodicity of 600 nm. Using Raman spectroscopy, we determined to have introduced biaxial strains in graphene in the range of 0.4% to 0.7%. Its band structure was characterized using photoemission from valance bands, shifts in the secondary electron emission, and x-ray absorption from the carbon 1s levels to the unoccupied graphene conduction bands. It was observed that relative to unstrained graphene, strained graphene had a higher work function and higher density of states in the valence and conduction bands. We measured the conductivity of the strained and unstrained graphene in response to a gate voltage and correlated the changes in their behavior to the changes in the electronic structure. From these sets of data, we propose a simple band diagram representing graphene with periodic biaxial strain.

  2. Correlation of Local Structure and Electronic Properties of Glass Materials

    NASA Astrophysics Data System (ADS)

    Lordi, Vincenzo; Adelstein, Nicole

    2015-03-01

    Wide band gap glasses such as silica and its derivatives are typically considered insulators. However, electronic transport in glasses can be important for certain applications, such as when used as the host material for a scintillator radiation detector. Here we explore the relationship between local structure in glass materials and the corresponding electronic properties of carrier transport and charge trapping. We present a novel analysis that decomposes the distribution of localized band tail states in terms of specific local structural features in the glass. Comparison of the structure-related transport properties of different glass compositions is given, using silica and sodium silicate as prototypes. Prepared by LLNL under Contract DE-AC52-07NA27344.

  3. Characterization of electronic structure of periodically strained graphene

    SciTech Connect

    Aslani, Marjan; Garner, C. Michael; Kumar, Suhas; Nordlund, Dennis; Pianetta, Piero; Nishi, Yoshio

    2015-11-03

    We induced periodic biaxial tensile strain in polycrystalline graphene by wrapping it over a substrate with repeating pillar-like structures with a periodicity of 600 nm. Using Raman spectroscopy, we determined to have introduced biaxial strains in graphene in the range of 0.4% to 0.7%. Its band structure was characterized using photoemission from valance bands, shifts in the secondary electron emission, and x-ray absorption from the carbon 1s levels to the unoccupied graphene conduction bands. It was observed that relative to unstrained graphene, strained graphene had a higher work function and higher density of states in the valence and conduction bands. Furthermore, we measured the conductivity of the strained and unstrained graphene in response to a gate voltage and correlated the changes in their behavior to the changes in the electronic structure. From these sets of data, we propose a simple band diagram representing graphene with periodic biaxial strain.

  4. Dynamics of formation of K-hole fractions of sulfur projectiles inside a carbon foil

    SciTech Connect

    Braziewicz, J.; Majewska, U.; Slabkowska, K.; Polasik, M.; Fijal, I.; Jaskola, M.; Korman, A.; Czarnacki, W.; Chojnacki, S.; Kretschmer, W.

    2004-06-01

    The K{alpha} and K{beta} satellite and hypersatellite x-ray lines emitted by highly ionized sulfur projectiles passing with energies from 65 MeV up to 122 MeV through carbon foils of thickness of 15-210 {mu}g cm{sup -2} have been recorded using a Si(Li) detector. The additional hypersatellite Ky{sup h} peak proves that for such high energies of the sulfur ions very high subshells (4p and 5p) could be occupied. In order to study the dynamics of formation of K-shell vacancy fractions of sulfur projectiles passing through a carbon foil the dependence of sulfur K x-ray production cross sections on foil thickness has been examined separately for each recorded line using the three component model. For each projectile energy the values of K-shell hole production cross sections and K-shell electron capture cross sections (both common for all recorded x-ray lines in the case of each projectile energy) have been fitted, as well as the specific values (for each recorded x-ray line) of K-shell hole filling cross sections, which are directly connected with average lifetimes of appropriate states of sulfur ions. The obtained ''experimental'' values of K-shell vacancy production cross sections are much higher than the theoretical predictions. This suggests that apart from the ionization process the excitation from K shell into higher shells is responsible for a production of K-shell vacancies, which has been confirmed by recent classical trajectory Monte Carlo calculations.

  5. Electronic structure and crystal phase stability of palladium hydrides

    SciTech Connect

    Houari, Abdesalem; Matar, Samir F.; Eyert, Volker

    2014-11-07

    The results of electronic structure calculations for a variety of palladium hydrides are presented. The calculations are based on density functional theory and used different local and semilocal approximations. The thermodynamic stability of all structures as well as the electronic and chemical bonding properties are addressed. For the monohydride, taking into account the zero-point energy is important to identify the octahedral Pd-H arrangement with its larger voids and, hence, softer hydrogen vibrational modes as favorable over the tetrahedral arrangement as found in the zincblende and wurtzite structures. Stabilization of the rocksalt structure is due to strong bonding of the 4d and 1s orbitals, which form a characteristic split-off band separated from the main d-band group. Increased filling of the formerly pure d states of the metal causes strong reduction of the density of states at the Fermi energy, which undermines possible long-range ferromagnetic order otherwise favored by strong magnetovolume effects. For the dihydride, octahedral Pd-H arrangement as realized, e.g., in the pyrite structure turns out to be unstable against tetrahedral arrangement as found in the fluorite structure. Yet, from both heat of formation and chemical bonding considerations, the dihydride turns out to be less favorable than the monohydride. Finally, the vacancy ordered defect phase Pd{sub 3}H{sub 4} follows the general trend of favoring the octahedral arrangement of the rocksalt structure for Pd:H ratios less or equal to one.

  6. Electronic structures of Ascaris trypsin inhibitor in solution

    NASA Astrophysics Data System (ADS)

    Zheng, Haoping

    2003-11-01

    The electronic structures of Ascaris trypsin inhibitor in solution are obtained by the first-principles, all-electron, ab initio calculation using the self-consistent cluster-embedding (SCCE) method. The inhibitor, made up of 62 amino acid residues with 912 atoms, has two three-dimensional solution structures: 1ata and 1atb. The calculated ground-state energy of structure 1atb is lower than that of structure 1ata by 6.12 eV. The active sites are determined and explained: only structure 1atb has a N terminal at residue ARG+31. This shows that the structure 1atb is the stable and active form of the inhibitor, which is in agreement with the experimental results. The calculation reveals that some parts of the inhibitor can be easily changed while the inhibitor’s biological activity may be kept. This kind of information may be helpful in fighting viruses such as AIDS, SARS, and flu, since these viruses have higher variability. The calculation offers an independent theoretical estimate of the precision of structure determination.

  7. Mapping the Electronic States of One Dimensional Peapod Structures

    NASA Astrophysics Data System (ADS)

    Hornbaker, D. J.

    2003-03-01

    A key issue of potential technological importance is how the electronic properties of single wall carbon nanotubes are altered by their interactions with other molecules. We address this question by examining the properties of carbon heterostructures formed by the encapsulation of C_60 molecules within the hollow interiors of single wall nanotubes.^1 We study the properties of these novel macromolecules (dubbed 'peapods') using a low temperature, ultra-high vacuum scanning tunneling microscope (STM). Our experiments reveal that while no discernable change in the atomic structure of the encapsulating nanotubes is evident, the presence of interior C_60 molecules can dramatically affect the electronic structure of the nanotube cage. Constant current STM images of peapods display pronounced spatial modulation of the electronic density at sample biases greater than 1V, with a periodicity consistent with the intermolecular spacing of close-packed C_60 molecules inside the nanotube. This effect has been observed on peapods displaying both semiconducting and metallic densities of states. Coincident with this modulation is the appearance of characteristic features in the electronic band structure measured via tunneling spectroscopy. Theoretical modeling^2,3 indicates these features arise from coupling between the valence states of the encapsulated fullerenes, leading to the formation of a hybrid electronic band. Our experiments demonstrate that encapsulation of molecules is a viable route for selectively altering the electronic properties of carbon nanotubes. ^1B.W. Smith and D.E. Luzzi, Chem. Phys. Lett. 321, 169 (2000). ^2D.J. Hornbaker et al. Science 295, 828 (2002). ^3C. Kane et al. Phys. Rev. B (submitted).

  8. Shigella flexneri Spa15 Crystal Structure Verified in Solution by Double Electron Electron Resonance

    PubMed Central

    Lillington, James E.D.; Lovett, Janet E.; Johnson, Steven; Roversi, Pietro; Timmel, Christiane R.; Lea, Susan M.

    2011-01-01

    Shigella flexneri Spa15 is a chaperone of the type 3 secretion system, which binds a number of effectors to ensure their stabilization prior to secretion. One of these effectors is IpgB1, a mimic of the human Ras-like Rho guanosine triphosphatase RhoG. In this study, Spa15 alone and in complex with IpgB1 has been studied by double electron electron resonance, an experiment that gives distance information showing the spacial separation of attached spin labels. This distance is explained by determining the crystal structure of the spin-labeled Spa15 where labels are seen to be buried in hydrophobic pockets. The double electron electron resonance experiment on the Spa15 complex with IpgB1 shows that IpgB1 does not bind Spa15 in the same way as is seen in the homologous Salmonella sp. chaperone:effector complex InvB:SipA. PMID:21075116

  9. Toward the origin of exciton electronic structure in phycobiliproteins

    NASA Astrophysics Data System (ADS)

    Womick, Jordan M.; Miller, Stephen A.; Moran, Andrew M.

    2010-07-01

    Femtosecond laser spectroscopies are used to examine the electronic structures of two proteins found in the phycobilisome antenna of cyanobacteria, allophycocyanin (APC) and C-phycocyanin (CPC). The wave function composition involving the pairs of phycocyanobilin pigments (i.e., dimers) found in both proteins is the primary focus of this investigation. Despite their similar geometries, earlier experimental studies conducted in our laboratory and elsewhere observe clear signatures of exciton electronic structure in APC but not CPC. This issue is further investigated here using new experiments. Transient grating (TG) experiments employing broadband quasicontinuum probe pulses find a redshift in the signal spectrum of APC, which is almost twice that of CPC. Dynamics in the TG signal spectra suggest that the sub-100 fs dynamics in APC and CPC are respectively dominated by internal conversion and nuclear relaxation. A specialized technique, intraband electronic coherence spectroscopy (IECS), photoexcites electronic and nuclear coherences with nearly full suppression of signals corresponding to electronic populations. The main conclusion drawn by IECS is that dephasing of intraband electronic coherences in APC occurs in less than 25 fs. This result rules out correlated pigment fluctuations as the mechanism enabling exciton formation in APC and leads us to propose that the large Franck-Condon factors of APC promote wave function delocalization in the vibronic basis. For illustration, we compute the Hamiltonian matrix elements involving the electronic origin of the α84 pigment and the first excited vibronic level of the β84 pigment associated with a hydrogen out-of-plane wagging mode at 800 cm-1. For this pair of vibronic states, the -51 cm-1 coupling is larger than the 40 cm-1 energy gap, thereby making wave function delocalization a feasible prospect. By contrast, CPC possesses no pair of vibronic levels for which the intermolecular coupling is larger than the energy

  10. Antistiction technique using elastomer contact structure in woven electronic textiles

    NASA Astrophysics Data System (ADS)

    Yamashita, Takahiro; Takamatsu, Seiichi; Miyake, Koji; Itoh, Toshihiro

    2014-01-01

    In this paper, we present an antistiction technique using an elastomer contact structure in woven electronic textiles (e-textiles). A coating of poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) in the form of a solid conductive film on a hemispherical silicone elastomer structure is employed in creating an electrical circuit embedded into the fabric of a woven e-textile, where the contact structure reduces the contact area and capillary force generated by the moisture in air between weft and warp ribbons. Stiction occurs between a weft and a warp without the contact structure under an RH of 80%, and the detachment of the stuck ribbon requires a delamination load of about 0.2 N. On the other hand, in the case of contact between the contact structure and the ribbon coated with plain PEDOT:PSS, stiction does not occur as the relative humidity increases from 20 to 80%.

  11. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    SciTech Connect

    Antonowicz, J. Pietnoczka, A.; Pękała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-28

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  12. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    NASA Astrophysics Data System (ADS)

    Antonowicz, J.; Pietnoczka, A.; Pekała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-01

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  13. Multi-million atom electronic structure calculations for quantum dots

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined

  14. Electronic and magnetic structures of CeTe2

    NASA Astrophysics Data System (ADS)

    Shim, J. H.; Youn, S. J.; Park, Min Sik; Min, B. I.

    2005-05-01

    We have investigated electronic structures of CeTe2 to explore the correlation between the magnetic, charge density wave, and superconducting phases by using the local spin density approximation (LSDA) and LSDA +U (U =on-site Coulomb interaction) methods. We have found that the contribution near EF from Ce 4f states is negligible, suggesting that Ce 4f electrons are not the superconducting carriers. The total energy calculation indicates that the ABBA-type antiferromagnetic configuration is the most stable, while the stability is weakened by pressure. We have discussed the possible superconducting mechanism in the magnetic phase of CeTe1.82.

  15. The surface electronic structure of silicon terminated (100) diamond

    NASA Astrophysics Data System (ADS)

    Schenk, A. K.; Tadich, A.; Sear, M. J.; Qi, D.; Wee, A. T. S.; Stacey, A.; Pakes, C. I.

    2016-07-01

    A combination of synchrotron-based x-ray spectroscopy and contact potential difference measurements have been used to examine the electronic structure of the (3 × 1) silicon terminated (100) diamond surface under ultra high vacuum conditions. An occupied surface state which sits 1.75 eV below the valence band maximum has been identified, and indications of mid-gap unoccupied surface states have been found. Additionally, the pristine silicon terminated surface is shown to possess a negative electron affinity of ‑0.86 ± 0.1 eV.

  16. Electronic structure basis for the extraordinary magnetoresistance in WTe2.

    PubMed

    Pletikosić, I; Ali, Mazhar N; Fedorov, A V; Cava, R J; Valla, T

    2014-11-21

    The electronic structure basis of the extremely large magnetoresistance in layered nonmagnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at low temperatures, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. A change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior of the magnetoresistance in WTe2 was identified. PMID:25479512

  17. Electronic Structure Basis for the Extraordinary Magnetoresistance in WTe2

    NASA Astrophysics Data System (ADS)

    Pletikosić, I.; Ali, Mazhar N.; Fedorov, A. V.; Cava, R. J.; Valla, T.

    2014-11-01

    The electronic structure basis of the extremely large magnetoresistance in layered nonmagnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at low temperatures, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. A change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior of the magnetoresistance in WTe2 was identified.

  18. Grid-based electronic structure calculations: The tensor decomposition approach

    NASA Astrophysics Data System (ADS)

    Rakhuba, M. V.; Oseledets, I. V.

    2016-05-01

    We present a fully grid-based approach for solving Hartree-Fock and all-electron Kohn-Sham equations based on low-rank approximation of three-dimensional electron orbitals. Due to the low-rank structure the total complexity of the algorithm depends linearly with respect to the one-dimensional grid size. Linear complexity allows for the usage of fine grids, e.g. 81923 and, thus, cheap extrapolation procedure. We test the proposed approach on closed-shell atoms up to the argon, several molecules and clusters of hydrogen atoms. All tests show systematical convergence with the required accuracy.

  19. The surface electronic structure of silicon terminated (100) diamond.

    PubMed

    Schenk, A K; Tadich, A; Sear, M J; Qi, D; Wee, A T S; Stacey, A; Pakes, C I

    2016-07-01

    A combination of synchrotron-based x-ray spectroscopy and contact potential difference measurements have been used to examine the electronic structure of the (3 × 1) silicon terminated (100) diamond surface under ultra high vacuum conditions. An occupied surface state which sits 1.75 eV below the valence band maximum has been identified, and indications of mid-gap unoccupied surface states have been found. Additionally, the pristine silicon terminated surface is shown to possess a negative electron affinity of -0.86 ± 0.1 eV. PMID:27211214

  20. Structure and dynamics in two-electron atoms

    NASA Astrophysics Data System (ADS)

    Shuman, Edward Somerville

    In this dissertation, I present experimental studies of two-electron atoms. I have been primarily concerned with the effects of external perturbations on dielectronic recombination (DR). Specifically I have examined dielectronic recombination in the presence of electric, microwave, and combined electric and magnetic fields. These measurements illustrate that any external perturbation must have a coupling in excess of the autoionization rate to affect the DR rate. I have also studied the structure of two-electron atoms using microwave resonance techniques. In particular I present experiments which provide new insight into the core polarization model and which provide techniques for measuring both bound and autoionizing energy levels with microwaves.

  1. Dual-phase steel structure visualized by extremely slow electrons.

    PubMed

    Mikmeková, Šárka; Yamada, Katsumi; Noro, Hisato

    2015-12-01

    Mechanical properties of complex steels are affected by their multi-phase structure. Scanning electron microscopy (SEM) is routinely used for characterizing dual-phase (DP) steels, although the identification of steel constituents is not straightforward. In fact, there are several ways of enabling the ferrite-martensite segmentation by SEM, and a wide range of electron energies can be utilized. This study demonstrates the phase identification of DP steels at high, low and extremely low landing energies of the primary electrons from tens of keV to tens of eV. Visualization of the specimen surface at very low landing energies has been achieved by inserting an earthed detector between the pole piece and the negatively biased specimen. This 'cathode lens mode' enables the use of the full energy range up to the primary electron energies. It has been found that extremely slow electrons (<100 eV) are exceptionally suitable for separation of the martensite from the ferrite matrix due to high surface sensitivity, enabling visualization of very fine features. Moreover, the channelling contrast is significantly suppressed at the landing energy of tens of eV of the primary electrons, which enables separation of the phases clearly even in the images acquired at low magnification. The contrast between the phases at tens of eV can be explained by the different thickness of native oxide covering the martensite and the ferrite phase. PMID:26497974

  2. Real-time feedback from iterative electronic structure calculations.

    PubMed

    Vaucher, Alain C; Haag, Moritz P; Reiher, Markus

    2016-04-01

    Real-time feedback from iterative electronic structure calculations requires to mediate between the inherently unpredictable execution times of the iterative algorithm used and the necessity to provide data in fixed and short time intervals for real-time rendering. We introduce the concept of a mediator as a component able to deal with infrequent and unpredictable reference data to generate reliable feedback. In the context of real-time quantum chemistry, the mediator takes the form of a surrogate potential that has the same local shape as the first-principles potential and can be evaluated efficiently to deliver atomic forces as real-time feedback. The surrogate potential is updated continuously by electronic structure calculations and guarantees to provide a reliable response to the operator for any molecular structure. To demonstrate the application of iterative electronic structure methods in real-time reactivity exploration, we implement self-consistent semiempirical methods as the data source and apply the surrogate-potential mediator to deliver reliable real-time feedback. © 2015 Wiley Periodicals, Inc. PMID:26678030

  3. Compressed Sensing Electron Tomography for Determining Biological Structure.

    PubMed

    Guay, Matthew D; Czaja, Wojciech; Aronova, Maria A; Leapman, Richard D

    2016-01-01

    There has been growing interest in applying compressed sensing (CS) theory and practice to reconstruct 3D volumes at the nanoscale from electron tomography datasets of inorganic materials, based on known sparsity in the structure of interest. Here we explore the application of CS for visualizing the 3D structure of biological specimens from tomographic tilt series acquired in the scanning transmission electron microscope (STEM). CS-ET reconstructions match or outperform commonly used alternative methods in full and undersampled tomogram recovery, but with less significant performance gains than observed for the imaging of inorganic materials. We propose that this disparity stems from the increased structural complexity of biological systems, as supported by theoretical CS sampling considerations and numerical results in simulated phantom datasets. A detailed analysis of the efficacy of CS-ET for undersampled recovery is therefore complicated by the structure of the object being imaged. The numerical nonlinear decoding process of CS shares strong connections with popular regularized least-squares methods, and the use of such numerical recovery techniques for mitigating artifacts and denoising in reconstructions of fully sampled datasets remains advantageous. This article provides a link to the software that has been developed for CS-ET reconstruction of electron tomographic data sets. PMID:27291259

  4. Compressed Sensing Electron Tomography for Determining Biological Structure

    PubMed Central

    Guay, Matthew D.; Czaja, Wojciech; Aronova, Maria A.; Leapman, Richard D.

    2016-01-01

    There has been growing interest in applying compressed sensing (CS) theory and practice to reconstruct 3D volumes at the nanoscale from electron tomography datasets of inorganic materials, based on known sparsity in the structure of interest. Here we explore the application of CS for visualizing the 3D structure of biological specimens from tomographic tilt series acquired in the scanning transmission electron microscope (STEM). CS-ET reconstructions match or outperform commonly used alternative methods in full and undersampled tomogram recovery, but with less significant performance gains than observed for the imaging of inorganic materials. We propose that this disparity stems from the increased structural complexity of biological systems, as supported by theoretical CS sampling considerations and numerical results in simulated phantom datasets. A detailed analysis of the efficacy of CS-ET for undersampled recovery is therefore complicated by the structure of the object being imaged. The numerical nonlinear decoding process of CS shares strong connections with popular regularized least-squares methods, and the use of such numerical recovery techniques for mitigating artifacts and denoising in reconstructions of fully sampled datasets remains advantageous. This article provides a link to the software that has been developed for CS-ET reconstruction of electron tomographic data sets. PMID:27291259

  5. Electronic structure and insulating gap in epitaxial VO2 polymorphs

    DOE PAGESBeta

    Lee, Shinbuhm; Meyer, Tricia L.; Sohn, Changhee; Lee, Donghwa; Nichols, John A.; Lee, Dongkyu; Seo, Sung Seok Ambrose; Freeland, John W.; Noh, Tae Won; Lee, Ho Nyung

    2015-12-24

    Here, determining the origin of the insulating gap in the monoclinic VO2(M1) is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating VO2(A) and VO2(B) thin films to better understand the insulating phase of VO2. As these A and B phases do not undergo a structural transition upon thermal cycling, we comparatively study the origin of the gap opening in the insulating VO2 phases. By x-ray absorption and optical spectroscopy, we findmore » that the shift of unoccupied t2g orbitals away from the Fermi level is a common feature, which plays an important role for the insulating behavior in VO2 polymorphs. The distinct splitting of the half-filled t2g orbital is observed only in the M1 phase, widening the bandgap up to ~0.6 eV. Our approach of comparing all three insulating VO2 phases provides insight into a better understanding of the electronic structure and the origin of the insulating gap in VO2.« less

  6. Oligothiophene wires: impact of torsional conformation on the electronic structure.

    PubMed

    Kislitsyn, D A; Taber, B N; Gervasi, C F; Zhang, L; Mannsfeld, S C B; Prell, J S; Briseno, A L; Nazin, G V

    2016-02-14

    Charge transport in polymer- and oligomer-based semiconductor materials depends strongly on the structural ordering of the constituent molecules. Variations in molecular conformations influence the electronic structures of polymers and oligomers, and thus impact their charge-transport properties. In this study, we used Scanning Tunneling Microscopy and Spectroscopy (STM/STS) to investigate the electronic structures of different alkyl-substituted oligothiophenes displaying varied torsional conformations on the Au(111) surface. STM imaging showed that on Au(111), oligothiophenes self-assemble into chain-like structures, binding to each other via interdigitated alkyl ligands. The molecules adopted distinct planar conformations with alkyl ligands forming cis- or trans- mutual orientations. For each molecule, by using STS mapping, we identify a progression of particle-in-a-box-like states corresponding to the LUMO, LUMO+1 and LUMO+2 orbitals. Analysis of STS data revealed very similar unoccupied molecular orbital energies for different possible molecular conformations. By using density functional theory calculations, we show that the lack of variation in molecular orbital energies among the different oligothiophene conformers implies that the effect of the Au-oligothiophene interaction on molecular orbital energies is nearly identical for all studied torsional conformations. Our results suggest that cis-trans torsional disorder may not be a significant source of electronic disorder and charge carrier trapping in organic semiconductor devices based on oligothiophenes. PMID:26804474

  7. Compressed Sensing Electron Tomography for Determining Biological Structure

    NASA Astrophysics Data System (ADS)

    Guay, Matthew D.; Czaja, Wojciech; Aronova, Maria A.; Leapman, Richard D.

    2016-06-01

    There has been growing interest in applying compressed sensing (CS) theory and practice to reconstruct 3D volumes at the nanoscale from electron tomography datasets of inorganic materials, based on known sparsity in the structure of interest. Here we explore the application of CS for visualizing the 3D structure of biological specimens from tomographic tilt series acquired in the scanning transmission electron microscope (STEM). CS-ET reconstructions match or outperform commonly used alternative methods in full and undersampled tomogram recovery, but with less significant performance gains than observed for the imaging of inorganic materials. We propose that this disparity stems from the increased structural complexity of biological systems, as supported by theoretical CS sampling considerations and numerical results in simulated phantom datasets. A detailed analysis of the efficacy of CS-ET for undersampled recovery is therefore complicated by the structure of the object being imaged. The numerical nonlinear decoding process of CS shares strong connections with popular regularized least-squares methods, and the use of such numerical recovery techniques for mitigating artifacts and denoising in reconstructions of fully sampled datasets remains advantageous. This article provides a link to the software that has been developed for CS-ET reconstruction of electron tomographic data sets.

  8. Geometric, electronic, and magnetic structure of FexOy+ clusters

    NASA Astrophysics Data System (ADS)

    Logemann, R.; de Wijs, G. A.; Katsnelson, M. I.; Kirilyuk, A.

    2015-10-01

    Correlation between geometry, electronic structure, and magnetism of solids is both intriguing and elusive. This is particularly strongly manifested in small clusters, where a vast number of unusual structures appear. Here, we employ density functional theory in combination with a genetic search algorithm GGA +U and a hybrid functional to determine the structure of gas phase FexOy+/0 clusters. For FexOy+ cation clusters we also calculate the corresponding vibration spectra and compare them with experiments. We successfully identify Fe3O4+ , Fe4O5+ , Fe4O6+ , Fe5O7+ and propose structures for Fe6O8+ . Within the triangular geometric structure of Fe3O4+ , a noncollinear, ferrimagnetic, and ferromagnetic state are comparable in energy. Fe4O5+ and Fe4O6+ are ferrimagnetic with a residual magnetic moment of 1 μB due to ionization. Fe5O7+ is ferrimagnetic due to the odd number of Fe atoms. We compare the electronic structure with bulk magnetite and find Fe4O5+ , Fe4O6+ , Fe6O8+ to be mixed valence clusters. In contrast, in Fe3O4+ and Fe5O7+ , all Fe are found to be trivalent.

  9. Electronic structure of germanium selenide investigated using ultra-violet photo-electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Mishra, P.; Lohani, H.; Kundu, A. K.; Patel, R.; Solanki, G. K.; Menon, Krishnakumar S. R.; Sekhar, B. R.

    2015-07-01

    The valence band electronic structure of GeSe single crystals has been investigated using angle resolved photoemission spectroscopy (ARPES) and x-ray photoelectron spectroscopy. The experimentally observed bands from ARPES, match qualitatively with our LDA-based band structure calculations along the Γ-Z, Γ-Y and Γ-T symmetry directions. The valence band maximum occurs nearly midway along the Γ-Z direction, at a binding energy of -0.5 eV, substantiating the indirect band gap of GeSe. Non-dispersive features associated with surface states and indirect transitions have been observed. The difference in hybridization of Se and Ge 4p orbitals leads to the variation of dispersion along the three symmetry directions. The predominance of the Se 4pz orbitals, evidenced from theoretical calculations, may be the cause for highly dispersive bands along the Γ-T direction. Detailed electronic structure analysis reveals the significance of the cation-anion 4p orbitals hybridization in the valence band dispersion of IV-VI semiconductors. This is the first comprehensive report of the electronic structure of a GeSe single crystal using ARPES in conjugation with theoretical band structure analysis.

  10. Electronic structure of the unoccupied electron energy states in FeSe1-xTex

    NASA Astrophysics Data System (ADS)

    Mishra, Pramita; Lohani, Himanshu; Maniraj, M.; Nayak, Jayita; Zargar, R. A.; Awana, V. P. S.; Barman, Sudipta Roy; Sekhar, Biju Raja

    2015-10-01

    Inverse photoemission spectroscopic (IPES) measurements along with LDA based band structure calculations have been used to investigate the unoccupied electronic structure of FeSe1-xTex system. The observed doping and temperature dependent pseudogap in this system is found to be linked to the change in the chalcogen height in their geometric structure. The depletion in spectral weight from the near EF states at low temperature in IPES has been correlated with the enhancement of the 3z2-r2 orbitals in the photoemission spectroscopy (PES). The Coulomb correlation energy U, estimated from the combined PES and IPES spectra, signifies the enhancement in electron correlations in FeSe1-xTex, with doping. The formation of pseudogap in PES and IPES confirms the importance of correlations in the 11 family of Fe superconductors.

  11. DFT investigation on the electronic structure of Faujasite

    SciTech Connect

    Popeneciu, Horea; Calborean, Adrian; Tudoran, Cristian; Buimaga-Iarinca, Luiza

    2013-11-13

    We report here first-principle pseudopotential DFT calculations to investigate relevant aspects of the electronic structure of zeolites based FAU. Fundamental molecular issues of the band-gap and electronic population analysis were reviewed under GGA/RPBE level of theory, corroborated with a DZP basis set and Troullier-Martins norm conserving pseudo-potentials. The atom-projected density of states and the analysis of HOMO-LUMO frontier orbitals at Gamma point were performed. Their electronic transfers are discussed through the alignment and relative positions of orbitals in order to determine the way that the molecule interacts with adsorbed molecules and other practical applications. Mulliken population analysis was employed for describing atomic charge distribution in the chosen systems.

  12. Anomalous electronic structure and magnetoresistance in TaAs2

    PubMed Central

    Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

    2016-01-01

    The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions. PMID:27271852

  13. DFT investigation on the electronic structure of Faujasite

    NASA Astrophysics Data System (ADS)

    Popeneciu, Horea; Calborean, Adrian; Tudoran, Cristian; Buimaga-Iarinca, Luiza

    2013-11-01

    We report here first-principle pseudopotential DFT calculations to investigate relevant aspects of the electronic structure of zeolites based FAU. Fundamental molecular issues of the band-gap and electronic population analysis were reviewed under GGA/RPBE level of theory, corroborated with a DZP basis set and Troullier-Martins norm conserving pseudo-potentials. The atom-projected density of states and the analysis of HOMO-LUMO frontier orbitals at Gamma point were performed. Their electronic transfers are discussed through the alignment and relative positions of orbitals in order to determine the way that the molecule interacts with adsorbed molecules and other practical applications. Mulliken population analysis was employed for describing atomic charge distribution in the chosen systems.

  14. Anomalous electronic structure and magnetoresistance in TaAs2.

    PubMed

    Luo, Yongkang; McDonald, R D; Rosa, P F S; Scott, B; Wakeham, N; Ghimire, N J; Bauer, E D; Thompson, J D; Ronning, F

    2016-01-01

    The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions. PMID:27271852

  15. Anomalous electronic structure and magnetoresistance in TaAs2

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

    2016-06-01

    The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.

  16. Electronic Structure of Crystalline 4He at High Pressure

    SciTech Connect

    Mao, H.K.; Cai, Y.; Shirley, E.L.; Ding, Y.; Eng, P.; Chow, P.; Xiao, Y.; Shu, J.; Hemley, R.J.; Kao, C.C.; Mao, W.L.

    2010-10-29

    Using inelastic x-ray scattering techniques, we have succeeded in probing the high-pressure electronic structure of helium at 300 K. Helium has the widest known valence-conduction band gap of all materials a property whose high-pressure response has been inaccessible to direct measurements. We observed a rich electron excitation spectrum, including a cutoff edge above 23 eV, a sharp exciton peak showing linear volume dependence, and a series of excitations and continuum at 26 to 45 eV. We determined the electronic dispersion along the {Gamma}-M direction over two Brillouin zones, and provided a quantitative picture of the helium exciton beyond the simplified Wannier-Frenkel description.

  17. Linear Multigrid Techniques in Self-consistent Electronic Structure Calculations

    SciTech Connect

    Fattebert, J-L

    2000-05-23

    Ab initio DFT electronic structure calculations involve an iterative process to solve the Kohn-Sham equations for an Hamiltonian depending on the electronic density. We discretize these equations on a grid by finite differences. Trial eigenfunctions are improved at each step of the algorithm using multigrid techniques to efficiently reduce the error at all length scale, until self-consistency is achieved. In this paper we focus on an iterative eigensolver based on the idea of inexact inverse iteration, using multigrid as a preconditioner. We also discuss how this technique can be used for electrons described by general non-orthogonal wave functions, and how that leads to a linear scaling with the system size for the computational cost of the most expensive parts of the algorithm.

  18. Spatially Resolved Electronic Structures of Atomically Precise Armchair Graphene Nanoribbons

    NASA Astrophysics Data System (ADS)

    Huang, Han; Wei, Dacheng; Sun, Jiatao; Wong, Swee Liang; Feng, Yuan Ping; Neto, A. H. Castro; Wee, Andrew Thye Shen

    2012-12-01

    Graphene has attracted much interest in both academia and industry. The challenge of making it semiconducting is crucial for applications in electronic devices. A promising approach is to reduce its physical size down to the nanometer scale. Here, we present the surface-assisted bottom-up fabrication of atomically precise armchair graphene nanoribbons (AGNRs) with predefined widths, namely 7-, 14- and 21-AGNRs, on Ag(111) as well as their spatially resolved width-dependent electronic structures. STM/STS measurements reveal their associated electron scattering patterns and the energy gaps over 1 eV. The mechanism to form such AGNRs is addressed based on the observed intermediate products. Our results provide new insights into the local properties of AGNRs, and have implications for the understanding of their electrical properties and potential applications.

  19. Anomalous electronic structure and magnetoresistance in TaAs2

    DOE PAGESBeta

    Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

    2016-01-01

    We report that the change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. In conclusion, density functional calculations find that TaAs2 is a new topological semimetal [Z2 invariant (0;111)] withoutmore » Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.« less

  20. Spatially Resolved Electronic Structures of Atomically Precise Armchair Graphene Nanoribbons

    PubMed Central

    Huang, Han; Wei, Dacheng; Sun, Jiatao; Wong, Swee Liang; Feng, Yuan Ping; Neto, A. H. Castro; Wee, Andrew Thye Shen

    2012-01-01

    Graphene has attracted much interest in both academia and industry. The challenge of making it semiconducting is crucial for applications in electronic devices. A promising approach is to reduce its physical size down to the nanometer scale. Here, we present the surface-assisted bottom-up fabrication of atomically precise armchair graphene nanoribbons (AGNRs) with predefined widths, namely 7-, 14- and 21-AGNRs, on Ag(111) as well as their spatially resolved width-dependent electronic structures. STM/STS measurements reveal their associated electron scattering patterns and the energy gaps over 1 eV. The mechanism to form such AGNRs is addressed based on the observed intermediate products. Our results provide new insights into the local properties of AGNRs, and have implications for the understanding of their electrical properties and potential applications. PMID:23248746

  1. Structural stability and electronic properties of small gold clusters induced by 3p electron atoms

    NASA Astrophysics Data System (ADS)

    Zhang, Meng; Yang, Su-Bin; Feng, Xiao-Juan; Zhao, Li-Xia; Zhang, Hong-Yu; Luo, You-Hua

    2013-01-01

    The geometries and electronic properties of gold clusters doped with atoms containing 3 p valence electrons (MAu n ; M = Al, Si, P, S, Cl; n = 2-8) have been systematically investigated using density functional theory (DFT) at the PBE/LANL2DZ level. A number of low-energy isomers are identified for neutral MAu n clusters. It is found that doping with different 3 p impurity atoms can drastically influence the geometrical structures, relative stabilities, electronic properties, and growth-pattern behaviors of gold clusters, which is very different from the case of 3 d transition-metal impurity doped Au n clusters. Partially filled 3 p electron impurities can stabilize Au clusters. In particular, SiAu4 cluster with T d symmetry have been found to have highly stable geometries and electronic structures with binding energies of 2.43 eV per atom (0.96 eV higher than pristine Au5 clusters), large HOMO-LUMO gaps (2.17 eV), and vertical ionization potentials of 8.68 eV. Using scalar relativistic molecular dynamics at T = 300 K, we show that the T d symmetry structure of SiAu4 is stable. The frontier molecular orbitals (HOMO and LUMO) and the partial densities of states (PDOS) show that strong hybridization occurs between the atomic orbitals of Si and Au atoms, resulting in strong Si-Au bonding. In addition, the vertical ionization potential, the vertical electron affinity, and charge transfers of MAu n clusters have also been analyzed. Our results are in good agreement with available experimental data.

  2. Electronic structure and chemical bonding in PuO2

    NASA Astrophysics Data System (ADS)

    Teterin, Yu. A.; Maslakov, K. I.; Teterin, A. Yu.; Ivanov, K. E.; Ryzhkov, M. V.; Petrov, V. G.; Enina, D. A.; Kalmykov, St. N.

    2013-06-01

    Quantitative analysis of the x-ray photoelectron spectra structure in the binding energy (BE) range of 0 eV-˜35 eV for plutonium dioxide (PuO2) valence electrons was done. The BEs and structure of the core electronic shells (35 eV-1250 eV BE), as well as the relativistic discrete variation calculation results for the finite fragments of the PuO2 lattice and the data of other authors, were taken into account. The experimental data show that the many-body effects and the multiplet splitting contribute to the spectral structure much less than the outer (0 eV-˜15 eV) and the inner (˜15 eV-˜35 eV) valence molecular orbitals (OVMO and IVMO, respectively). The filled Pu 5f electronic states were shown to form in the PuO2 valence band. The Pu 6p electrons participate in the formation of both the IVMO and the OVMO (bands). The filled Pu 6p3/2 and the O 2s electronic shells were found to take maximum part in the IVMO formation. The MO composition and the sequence order in the BE range of 0 eV-˜35 eV in PuO2 were established. The experimental and theoretical data allowed a quantitative MO scheme for PuO2, which is fundamental for understanding both the chemical bond nature in plutonium dioxide and the interpretation of other x-ray spectra of PuO2.

  3. Electronic structure and optic absorption of phosphorene under strain

    NASA Astrophysics Data System (ADS)

    Duan, Houjian; Yang, Mou; Wang, Ruiqiang

    2016-07-01

    We studied the electronic structure and optic absorption of phosphorene (monolayer of black phosphorus) under strain. Strain was found to be a powerful tool for the band structure engineering. The in-plane strain in armchair or zigzag direction changes the effective mass components along both directions, while the vertical strain only has significant effect on the effective mass in the armchair direction. The band gap is narrowed by compressive in-plane strain and tensile vertical strain. Under certain strain configurations, the gap is closed and the energy band evolves to the semi-Dirac type: the dispersion is linear in the armchair direction and is gapless quadratic in the zigzag direction. The band-edge optic absorption is completely polarized along the armchair direction, and the polarization rate is reduced when the photon energy increases. Strain not only changes the absorption edge (the smallest photon energy for electron transition), but also the absorption polarization.

  4. Observation of Electronic Structure Minima in High-Harmonic Generation

    SciTech Connect

    Woerner, Hans Jakob; Villeneuve, D. M.; Niikura, Hiromichi; Bertrand, Julien B.; Corkum, P. B.

    2009-03-13

    We report detailed measurements of the high-harmonic spectra generated from argon atoms. The spectra exhibit a deep minimum that is shown to be independent of the laser intensity, and is thus a clear measure of the electronic structure of the atom. We show that exact field-free continuum wave functions reproduce the minimum, but plane wave and Coulomb wave functions do not. This remarkable observation suggests that electronic structure can be accurately determined in high-harmonic experiments despite the presence of the strong laser field. Our results clarify the relation between high-harmonic generation and photoelectron spectroscopy. The use of exact continuum functions also resolves the ambiguity associated with the choice of the dispersion relation.

  5. Molecular structures of porphyrin-quinone models for electron transfer

    SciTech Connect

    Fajer, J.; Barkigia, K.M.; Melamed, D.; Sweet, R.M.; Kurreck, H.; Gersdorff, J. von; Plato, M.; Rohland, H.C.; Elger, G.; Moebius, K.

    1996-08-15

    Synthetic porphyrin-quinone complexes are commonly used to mimic electron transport in photosynthetic reaction centers and to probe the effects of energetics, distances, and relative orientations on rates of electron transfer between donor-acceptor couples. The structures of two such models have been determined by X-ray diffraction. The redox pairs consist of a zinc porphyrin covalently linked to benzoquinone in cis and trans configurations via a cyclohexanediyl bridge. The crystallographic studies were undertaken to provide a structural foundation for the extensive body of experimental and theoretical results that exists for these compounds in both the ground and photoinduced charge-separated states. The results validate conclusions reached from theoretical calculations, EPR and two-dimensional NMR results for these states. 15 refs., 6 figs., 2 tabs.

  6. Atomic and electronic structure of Ni-Nb metallic glasses

    SciTech Connect

    Yuan, C. C.; Yang, Y.-F. Xi, X. K.

    2013-12-07

    Solid state {sup 93}Nb nuclear magnetic resonance spectroscopy has been employed to investigate the atomic and electronic structures in Ni-Nb based metallic glass (MG) model system. {sup 93}Nb nuclear magnetic resonance (NMR) isotropic metallic shift of Ni{sub 60}Nb{sub 35}Sn{sub 5} has been found to be ∼100 ppm lower than that of Ni{sub 60}Nb{sub 35}Zr{sub 5} MG, which is correlated with their intrinsic fracture toughness. The evolution of {sup 93}Nb NMR isotropic metallic shifts upon alloying is clearly an electronic origin, as revealed by both local hyperfine fields analysis and first-principle computations. This preliminary result indicates that, in addition to geometrical considerations, atomic form factors should be taken into a description of atomic structures for better understanding the mechanical behaviors of MGs.

  7. On the Electronic Structure of Cocaine and its Metabolites

    NASA Astrophysics Data System (ADS)

    Rincón, David A.; Dias Soeiro Cordeiro, Maria Natália; Mosquera, Ricardo A.

    2009-11-01

    This work aims at describing the electronic features of cocaine and how they are modified by the different substituents present in its metabolites. The QTAIM analysis of B3LYP and MP2 electron densities obtained with the 6-311++G** 6d basis set for cocaine and its principal metabolites indicates: (i) its positive charge is shared among the amino hydrogen, those of the methylamino group, and all of the hydrogens attached to the bicycle structure; (ii) the zwitterionic structure of benzoylecgonine can be described as two partial charges of 0.63 au, the negative one shared by the oxygens of the carboxylate group, whereas the positive charge is distributed among all the hydrogens that bear the positive charge in cocaine; (iii) its hydrogen bond is strengthened in the derivatives without benzoyloxy group and is also slightly strengthened as the size of the alkyl ester group at position 2 increases.

  8. A Synchrotron Investigation Of The Electronic Structure Of Lanthanide Zirconates

    NASA Astrophysics Data System (ADS)

    Clements, Richard; Kennedy, Brendan; Ling, Christopher; Stampfl, Anton P. J.

    2010-03-01

    abstract- The lanthanide zirconates are of interest for use in inert matrix fuels and nuclear wasteforms. For use in these applications, the material's structure must be resistant to radiation damage and its thermal, thermodynamic and mechanical properties must be known. The rare earth zirconates are interesting model systems to explore such problems. In such materials the f-electrons may play a localized valence decisive role in determining their thermo-mechanical properties. We have undertaken a synthesis of the full range of the lanthanide zirconate series using solid state techniques. We have performed X-ray photoemission spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES) with synchrotron radiation on a selection of the series, in conjunction with a density functional theory (DFT) determination of the electronic structure. -

  9. Strongly correlated electron materials. I. Theory of the quasiparticle structure

    SciTech Connect

    Lopez-Aguilar, F.; Costa-Quintana, J.; Puig-Puig, L. )

    1993-07-01

    In this paper we give a method for analyzing the renormalized electronic structure of the Hubbard systems. The first step is the determination of effective interactions from the random-phase approximation (RPA) and from an extended RPA (ERPA) that introduces vertex effects within the bubble polarization. The second step is the determination of the density of states deduced from the spectral functions. Its analysis leads us to conclude that these systems can exhibit three types of resonances in their electronic structures: the lower-, middle-, and upper-energy resonances. Furthermore, we analyze the conditions for which there is only one type of resonance and the causes that lead to the disappearance of the heavy-fermion state. We finally introduce the RPA and ERPA effective interactions within the strong-coupling theory and we give the conditions for obtaining coupling and superconductivity.

  10. Electronic Structure and Geometries of Small Compound Metal Clusters

    SciTech Connect

    1999-04-14

    During the tenure of the DOE grant DE-FG05-87EI145316 we have concentrated on equilibrium geometries, stability, and the electronic structure of transition metal-carbon clusters (met-cars), clusters designed to mimic the chemistry of atoms, and reactivity of homo-nuclear metal clusters and ions with various reactant molecules. It is difficult to describe all the research the authors have accomplished as they have published 38 papers. In this report, they outline briefly the salient features of their work on the following topics: (1) Designer Clusters: Building Blocks for a New Class of Solids; (2) Atomic Structure, Stability, and Electronic Properties of Metallo-Carbohedrenes; (3) Reactivity of Metal Clusters with H{sub 2} and NO; and (4) Anomalous Spectroscopy of Li{sub 4} Clusters.

  11. Electronic Structure of Silicon Nanowires Matrix from Ab Initio Calculations.

    PubMed

    Monastyrskii, Liubomyr S; Boyko, Yaroslav V; Sokolovskii, Bogdan S; Potashnyk, Vasylyna Ya

    2016-12-01

    An investigation of the model of porous silicon in the form of periodic set of silicon nanowires has been carried out. The electronic energy structure was studied using a first-principle band method-the method of pseudopotentials (ultrasoft potentials in the basis of plane waves) and linearized mode of the method of combined pseudopotentials. Due to the use of hybrid exchange-correlation potentials (B3LYP), the quantitative agreement of the calculated value of band gap in the bulk material with experimental data is achieved. The obtained results show that passivation of dangling bonds with hydrogen atoms leads to substantial transformation of electronic energy structure. At complete passivation of the dangling silicon bonds by hydrogen atoms, the band gap value takes the magnitude which substantially exceeds that for bulk silicon. The incomplete passivation gives rise to opposite effect when the band gap value decreases down the semimetallic range. PMID:26768147

  12. Structure and Process of Infrared Hot Electron Transistor Arrays

    PubMed Central

    Fu, Richard

    2012-01-01

    An infrared hot-electron transistor (IHET) 5 × 8 array with a common base configuration that allows two-terminal readout integration was investigated and fabricated for the first time. The IHET structure provides a maximum factor of six in improvement in the photocurrent to dark current ratio compared to the basic quantum well infrared photodetector (QWIP), and hence it improved the array S/N ratio by the same factor. The study also showed for the first time that there is no electrical cross-talk among individual detectors, even though they share the same emitter and base contacts. Thus, the IHET structure is compatible with existing electronic readout circuits for photoconductors in producing sensitive focal plane arrays. PMID:22778655

  13. Elongation method for electronic structure calculations of random DNA sequences.

    PubMed

    Orimoto, Yuuichi; Liu, Kai; Aoki, Yuriko

    2015-10-30

    We applied ab initio order-N elongation (ELG) method to calculate electronic structures of various deoxyribonucleic acid (DNA) models. We aim to test potential application of the method for building a database of DNA electronic structures. The ELG method mimics polymerization reactions on a computer and meets the requirements for linear scaling computational efficiency and high accuracy, even for huge systems. As a benchmark test, we applied the method for calculations of various types of random sequenced A- and B-type DNA models with and without counterions. In each case, the ELG method maintained high accuracy with small errors in energy on the order of 10(-8) hartree/atom compared with conventional calculations. We demonstrate that the ELG method can provide valuable information such as stabilization energies and local densities of states for each DNA sequence. In addition, we discuss the "restarting" feature of the ELG method for constructing a database that exhaustively covers DNA species. PMID:26337429

  14. Quantum mirages formed by coherent projection of electronic structure

    PubMed

    Manoharan; Lutz; Eigler

    2000-02-01

    Image projection relies on classical wave mechanics and the use of natural or engineered structures such as lenses or resonant cavities. Well-known examples include the bending of light to create mirages in the atmosphere, and the focusing of sound by whispering galleries. However, the observation of analogous phenomena in condensed matter systems is a more recent development, facilitated by advances in nanofabrication. Here we report the projection of the electronic structure surrounding a magnetic Co atom to a remote location on the surface of a Cu crystal; electron partial waves scattered from the real Co atom are coherently refocused to form a spectral image or 'quantum mirage'. The focusing device is an elliptical quantum corral, assembled on the Cu surface. The corral acts as a quantum mechanical resonator, while the two-dimensional Cu surface-state electrons form the projection medium. When placed on the surface, Co atoms display a distinctive spectroscopic signature, known as the many-particle Kondo resonance, which arises from their magnetic moment. By positioning a Co atom at one focus of the ellipse, we detect a strong Kondo signature not only at the atom, but also at the empty focus. This behaviour contrasts with the usual spatially-decreasing response of an electron gas to a localized perturbation. PMID:10676952

  15. Atomistic simulations of divacancy defects in armchair graphene nanoribbons: Stability, electronic structure, and electron transport properties

    NASA Astrophysics Data System (ADS)

    Zhao, Jun; Zeng, Hui; Wei, Jianwei; Li, Biao; Xu, Dahai

    2014-01-01

    Using the first principles calculations associated with nonequilibrium Green's function, we have studied the electronic structures and quantum transport properties of defective armchair graphene nanoribbon (AGNR) in the presence of divacancy defects. The triple pentagon-triple heptagon (555-777) defect in the defective AGNR is energetically more favorable than the pentagon-octagon-pentagon (5-8-5) defect. Our calculated results reveal that both 5-8-5-like defect and 555-777-like defect in AGNR could improve the electron transport. It is anticipated that defective AGNRs can exhibit large range variations in transport behaviors, which are strongly dependent on the distributions of the divacancy defect.

  16. Electronic Structure of NiPdP Amorphous Metals

    NASA Astrophysics Data System (ADS)

    Swihart, J. C.; Nicholson, D. M. C.; Shelton, W. A.; Wang, Y.

    1996-03-01

    The understanding of the structure, properties and required cooling rates for bulk amorphous alloys is hindered by the the large number of constituents in the typical alloy. One of the compositionally simplest systems that can be cast into bulk specimens is Ni_0.4Pd_0.4P_0.2. Furthermore, the thoroughly studied structure of amorphous Ni_0.8P_0.2 provides a useful starting point for its investigation. We use the locally selfconsistent multiple scattering (LSMS) method to determine the electronic structure, mass density, and energy as Pd is substituted at random for Ni in the Ni_0.8P_0.2 amorphous structure. Work supported by Laboratory Directors Research Development program at Oak Ridge National Laboratory, Division of Materials Science, and the Mathematical Information and Computational Science Division of the Office of Computational Technology Research, US DOE under subcontract DEAC05-84OR21400 with Lockheed-Martin Energy Systems, Inc.

  17. Final Technical Report: Electronic Structure Workshop (ES13)

    SciTech Connect

    Zhang, Shiwei

    2015-02-26

    The 25th Annual Workshop on Recent Developments in Electronic Structure Methods (ES2013) was successfully held at the College of William & Mary in Williamsburg VA on June 11-14, 2013. The workshop website is at http://es13.wm.edu/ , which contains updated information on the workshop and a permanent archive of the scientific contents. DOE's continued support has been instrumental to the success of the workshop.

  18. Electronic and chemical structure of metal-silicon interfaces

    NASA Technical Reports Server (NTRS)

    Grunthaner, P. J.; Grunthaner, F. J.

    1984-01-01

    This paper reviews our current understanding of the near-noble metal silicides and the interfaces formed with Si(100). Using X-ray photoemission spectroscopy, we compare the chemical composition and electronic structure of the room temperature metal-silicon and reacted silicide-silicon interfaces. The relationship between the interfacial chemistry and the Schottky barrier heights for this class of metals on silicon is explored.

  19. Structure and electronic properties of nanodiamond and its fluorination effect

    NASA Astrophysics Data System (ADS)

    Takai, Kazuyuki; Kogane, Kenta; Touhara, Hidekazu; Hattori, Yoshiyuki

    2015-03-01

    Fluorination of nano-sized diamond (ND) is expected not only to stabilize the surface structure, but also to introduce functional groups on the surface, the conduction carriers, and so on. In this study, we evaluate the structure and magnetic properties of ND and fluorinated ND (FND) in order to consider the change in the electronic state and the surface structure by fluorination. Fluorination of ND was carried out by the direct reaction between gaseous fluorine (1 atm) and commercially available detonation diamond at 623 - 873 K. X-ray Diffraction study reveals the structural stability of core part of ND during fluorination. X-ray photoemission spectroscopy exhibits F1s peak at the lower binding energy region than that for physisorbed molecular fluorine, indicating the formation of the chemical bonding between C and F in the sample. The Electron Paramagnetic Resonance results suggest that fluorination induces not only changes in the surface structure but also relaxation of defects in the core part.

  20. Electronic Structure Studies of Amorphous Hydrogenated Boron Carbide

    NASA Astrophysics Data System (ADS)

    Sky Driver, M.; Sandstrom, Joseph; Boyko, Teak; Moewes, Alexander; Caruso, Anthony

    2010-03-01

    Boron carbide is a technologically relevant material with importance in voltaic transduction. However, the local physical, chemical and electronic structure of low temperature deposited thin films of amorphous boron carbide is far from understood, hindering its progress in application. X-ray absorption and emission spectroscopies (XAS/XES) were applied to thin films of B4C and B5C:Hx to study the near Fermi edge structure; the films were prepared by RF magnetron sputtering and plasma enhanced chemical vapor deposition (PECVD) and were thermally treated after deposition from 400 to 800 C. XES spectra indicate a physical structure transition from amorphous to nanocrystalline at 700 C, a much lower temperature than expected from traditional physical vapor deposition or flash annealing temperatures reported. These structural differences are of significant interest to transport measurements and will be discussed as a correlation. Further, x-ray and ultraviolet photoemission were also collected as a compliment to XES/XAS and will be discussed in the context of understanding the local intra vs. intermolecular electronic structure of these boron-rich molecular based solids.

  1. On the filamentary structure of energetic electrons during flares

    NASA Astrophysics Data System (ADS)

    Drake, J.; Swisdak, M.; Shay, M.

    2007-12-01

    Simulations and analytic arguments are presented that demonstrate that magnetic reconnection in the tenuous high temperature corona does not occur as a single large-scale x-line. Rather the narrow current layers that form at x-lines form secondary magnetic islands at small spatial scales. An electron acceleration model based on the interaction of particles with many contracting islands has been developed. A consequence of particle acceleration in any multi-island system is that energetic particles are released in narrow streams with characteristic widths of the order of the electron skin depth. This is because electrons are released from islands as they reconnect with the macro-scale field of the corona or magnetosphere. The characteristic width of the released energetic electron streams correspond to the width of the reconnection dissipation region. Thus, energetic electrons do not propagate away from the reconnection site in the corona as a single large-scale front but as a filamentary web. As a result, the return current problem is transformed: the narrow filaments of energetic particles propagate parallel to the magnetic field as kinetic Alfven waves with propagation speeds comparable to the thermal velocity of the energetic particles. Simple estimates suggest that the conversion of particle to kinetic Alfven wave energy is efficient so that the wave and particle energy propagates together as a radiation front from the corona toward the solar surface. The structure and dynamics of this radiation front are being explored.

  2. Atomic structures and electronic properties of phosphorene grain boundaries

    NASA Astrophysics Data System (ADS)

    Guo, Yu; Zhou, Si; Zhang, Junfeng; Bai, Yizhen; Zhao, Jijun

    2016-06-01

    Grain boundary (GB) is one main type of defects in two-dimensional (2D) crystals, and has significant impact on the physical properties of 2D materials. Phosphorene, a recently synthesized 2D semiconductor, possesses a puckered honeycomb lattice and outstanding electronic properties. It is very interesting to know the possible GBs present in this novel material, and how their properties differ from those in the other 2D materials. Based on first-principles calculations, we explore the atomic structure, thermodynamic stability, and electronic properties of phosphorene GBs. A total of 19 GBs are predicted and found to be energetically stable with formation energies much lower than those in graphene. These GBs do not severely affect the electronic properties of phosphorene: the band gap of perfect phosphorene is preserved, and the electron mobilities are only moderately reduced in these defective systems. Our theoretical results provide vital guidance for experimental tailoring the electronic properties of phosphorene as well as the device applications using phosphorene materials.

  3. Phosphorene Nanoribbons: Electronic Structure and Electric Field Modulation

    NASA Astrophysics Data System (ADS)

    Soleimanikahnoj, Sina; Knezevic, Irena

    Phosphorene, a newcomer among the 2D van der Waals materials, has attracted the attention of many scientists due to its promising electronic properties. Monolayer phosphorene has a direct band gap of 2 eV located at the Gamma point of the Brillouin zone. Increasing the number of layers reduces the bandgap due to the van der Waals interaction. The direct nature of the bandgap makes phosphorene particularly favorable for electronic transport and optoelectronic applications. While multilayer phosphorene sheets have been studied, the electronic properties of their 1D counterparts are still unexplored. An accurate tight-binding model was recently proposed for multilayer phosphorene nanoribbons. Employing this model along with the non-equilibrium Green's function method, we calculate the band structure and electronic properties of phosphorene nanoribbons. We show that, depending on the edge termination, phosphorene nanoribbons can be metallic or semiconducting. Our analysis also shows that the electronic properties of phosphorene nanoribbons are highly tunable by in-plane and out-of-plane electric fields. In metallic ribbons, the conductance can be switched off by a threshold electric field, similar to field effect devices. Support by the NSF through the University of Wisconsin MRSEC Seed (NSF Award DMR-1121288).

  4. Electronic structure and shearing in nanolaminated ternary carbides

    NASA Astrophysics Data System (ADS)

    Music, Denis; Sun, Zhimei; Voevodin, Andrey A.; Schneider, Jochen M.

    2006-07-01

    We have studied shearing in M 2AlC phases (M=Sc,Y,La,Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W) using ab initio calculations. We propose that these phases can be classified into two groups based on the valence electron concentration induced changes in C 44. One group comprises M=V B and VIB, where the C 44 values are approximately 170 GPa and independent of the corresponding MC. The other group includes M=IIIB and IVB, where the C 44 shows a linear dependency with the corresponding MC. This may be understood based on the electronic structure: shear resistant bands are filled in M 2AlC phases with M=V B and VIB, while they are not completely filled when M=IIIB and IVB. This notion is also consistent with our stress-strain analysis. These valence electron concentration induced changes in shear behaviour were compared to previously published valence electron concentration induced changes in compression behaviour [Z. Sun, D. Music, R. Ahuja, S. Li, J.M. Schneider, Phys. Rev. B 70 (2004) 092102]. These classification proposals exhibit identical critical valence electron concentration values for the group boundary. However, the physical mechanisms are not identical: the classification proposal for the bulk modulus is based on MC-A coupling, while shearing is based on MC-MC coupling.

  5. Electronic Structure Studies of Silicon Carbide Anionic Nanoclusters

    NASA Astrophysics Data System (ADS)

    Pradhan, Prachi

    2005-03-01

    As a continuation of our studies on the high stabilities and electronic structure properties of Si8C2 to Si14C2 clusters and Si60Cn (n=3-6) clusters,^1 we report here ab initio studies of small SimCn^- (1< m, n < 4) anionic clusters. The theoretical formalism used is the local density approximation (LDA) to density functional theory (DFT) and the Gaussian03 suite of programs^2 with an all electron 6-311++G** basis set has been used. Complete geometry optimizations of different possible structures have been carried out. Carbon-rich and silicon rich species show distinctly different patterns with respect to the vertical detachment energies. For carbon-rich aggregates, the VDE's show an even odd alternation, similar to that of the carbon anions. We present results on binding energies, relative energies, fragmentation energies, vertical detachment energies, vibrational frequencies, and adiabatic electron affinities^3 for the optimized clusters. Detailed comparisons with published data in the literature will also be presented. * Work supported, in part, by the Welch Foundation, Houston, Texas (Grant No. Y-1525). ^1M. N. Huda and A. K. Ray, Phys. Rev. A (R) 69, 011201 (2004); Eur. Phys. J. D 31, 63 (2004). ^2 Gaussian03, Revision A.1, M. J. Frisch et al., Gaussian Inc., Pittsburgh, PA , 2003. ^3 P. Pradhan and A. K. Ray, J. Mol. Structure (Theochem), in press.

  6. Structural basis of interprotein electron transfer in bacterial sulfite oxidation

    PubMed Central

    McGrath, Aaron P; Laming, Elise L; Casas Garcia, G Patricia; Kvansakul, Marc; Guss, J Mitchell; Trewhella, Jill; Calmes, Benoit; Bernhardt, Paul V; Kappler, Ulrike; Maher, Megan J

    2015-01-01

    Interprotein electron transfer underpins the essential processes of life and relies on the formation of specific, yet transient protein-protein interactions. In biological systems, the detoxification of sulfite is catalyzed by the sulfite-oxidizing enzymes (SOEs), which interact with an electron acceptor for catalytic turnover. Here, we report the structural and functional analyses of the SOE SorT from Sinorhizobium meliloti and its cognate electron acceptor SorU. Kinetic and thermodynamic analyses of the SorT/SorU interaction show the complex is dynamic in solution, and that the proteins interact with Kd = 13.5 ± 0.8 μM. The crystal structures of the oxidized SorT and SorU, both in isolation and in complex, reveal the interface to be remarkably electrostatic, with an unusually large number of direct hydrogen bonding interactions. The assembly of the complex is accompanied by an adjustment in the structure of SorU, and conformational sampling provides a mechanism for dissociation of the SorT/SorU assembly. DOI: http://dx.doi.org/10.7554/eLife.09066.001 PMID:26687009

  7. Structural basis of interprotein electron transfer in bacterial sulfite oxidation.

    PubMed

    McGrath, Aaron P; Laming, Elise L; Casas Garcia, G Patricia; Kvansakul, Marc; Guss, J Mitchell; Trewhella, Jill; Calmes, Benoit; Bernhardt, Paul V; Hanson, Graeme R; Kappler, Ulrike; Maher, Megan J

    2015-01-01

    Interprotein electron transfer underpins the essential processes of life and relies on the formation of specific, yet transient protein-protein interactions. In biological systems, the detoxification of sulfite is catalyzed by the sulfite-oxidizing enzymes (SOEs), which interact with an electron acceptor for catalytic turnover. Here, we report the structural and functional analyses of the SOE SorT from Sinorhizobium meliloti and its cognate electron acceptor SorU. Kinetic and thermodynamic analyses of the SorT/SorU interaction show the complex is dynamic in solution, and that the proteins interact with Kd = 13.5 ± 0.8 μM. The crystal structures of the oxidized SorT and SorU, both in isolation and in complex, reveal the interface to be remarkably electrostatic, with an unusually large number of direct hydrogen bonding interactions. The assembly of the complex is accompanied by an adjustment in the structure of SorU, and conformational sampling provides a mechanism for dissociation of the SorT/SorU assembly. PMID:26687009

  8. Transmission electron microscopy in molecular structural biology: A historical survey.

    PubMed

    Harris, J Robin

    2015-09-01

    In this personal, historic account of macromolecular transmission electron microscopy (TEM), published data from the 1940s through to recent times is surveyed, within the context of the remarkable progress that has been achieved during this time period. The evolution of present day molecular structural biology is described in relation to the associated biological disciplines. The contribution of numerous electron microscope pioneers to the development of the subject is discussed. The principal techniques for TEM specimen preparation, thin sectioning, metal shadowing, negative staining and plunge-freezing (vitrification) of thin aqueous samples are described, with a selection of published images to emphasise the virtues of each method. The development of digital image analysis and 3D reconstruction is described in detail as applied to electron crystallography and reconstructions from helical structures, 2D membrane crystals as well as single particle 3D reconstruction of icosahedral viruses and macromolecules. The on-going development of new software, algorithms and approaches is highlighted before specific examples of the historical progress of the structural biology of proteins and viruses are presented. PMID:25475529

  9. Tritium projectiles for fueling magnetic fusion plasmas

    SciTech Connect

    Fisher, P.W.; Gouge, M.J.

    1995-12-31

    As part of the International Thermonuclear Engineering Reactor (ITER) plasma fueling development program, Oak Ridge National Laboratory (ORNL) has fabricated a pellet (cylindrical projectile of frozen hydrogenic gas at a temperature in the range 6--16 K) injection system to test the mechanical and thermal properties of extruded tritium, a radioactive isotope of hydrogen. This repeating, single-stage, pneumatic injector, called the Tritium-Proof-of-Principle Phase 2 (TPOP-2) Pellet Injector, has a piston-driven mechanical extruder and is designed to extrude and accelerate hydrogenic pellets sized for the ITER device. The TPOP-2 program has the following development goals: evaluate the feasibility of extruding tritium and deuterium-tritium (D-T) mixtures for use in future pellet injection systems; determine the mechanical and thermal properties of tritium and D-T extrusions; integrate, test, and evaluate the extruder in a repeating, single-stage light gas gun that is sized for the ITER application (pellet diameter {approximately} 7 to 8 mm); evaluate options for recycling propellant and extruder exhaust gas; evaluate operability and reliability of ITER prototypical fueling systems in an environment of significant tritium inventory that requires secondary and room containment systems. In initial tests with deuterium feed at ORNL, up to 13 pellets have been extruded at rates up to 1 Hz and accelerated to speeds of 1.0 to 1.1 km/s, using hydrogen propellant gas at a supply pressure of 65 bar. The pellets, typically 7.4 mm in diameter and up to 11 mm in length, are the largest cryogenic pellets produced by the fusion program to date. These pellets represent about a 11% density perturbation to ITER. Hydrogenic pellets will be used in ITER to sustain the fusion power in the plasma core and may be crucial in reducing first-wall tritium inventories by a process called isotopic fueling in which tritium-rich pellets fuel the burning plasma core and deuterium gas fuels the edge.

  10. Dependence of debris cloud formation on projectile shape

    NASA Astrophysics Data System (ADS)

    Konrad, C. H.; Chhabildas, L. C.; Boslough, M. B.; Piekutowski, A. J.; Poormon, K. L.; Mullin, S. A.; Littlefield, D. L.

    1994-07-01

    A two-stage lights-gas gun has been used to impact thin zinc bumpers by zinc projectiles over the velocity range of 2.4 km/s to 6.7 km/s to determine the propagation characteristics of the impact generated debris. Constant-mass projectiles in the form of spheres, discs, cylinders, and rods were used in these studies. Radiographic techniques were employed to record the debris cloud generated upon impact and the dynamic formation of the resulting rupture in an aluminum backing plate resulting from the loading of the debris cloud. The characteristics of the debris cloud generated upon impact is found to depend on the projectile shape. The data indicate that the debris front velocity is independent of the shape of the projectile, whereas the debris lateral/radial velocity is strongly dependent on projectile geometry. Spherical impactors generate the most radially dispersed debris cloud while the normal plate impactors result in column-like debris. It has been observed that the debris generated by the impact of thin plates on a thin bumper shield is considerably more damaging to a backwall than the debris generated by an equivalent-mass sphere.

  11. Injury risk assessment of non-lethal projectile head impacts.

    PubMed

    Oukara, Amar; Nsiampa, Nestor; Robbe, Cyril; Papy, Alexandre

    2014-01-01

    Kinetic energy non-lethal projectiles are used to impart sufficient effect onto a person in order to deter uncivil or hazardous behavior with a low probability of permanent injury. Since their first use, real cases indicate that the injuries inflicted by such projectiles may be irreversible and sometimes lead to death, especially for the head impacts. Given the high velocities and the low masses involved in such impacts, the assessment approaches proposed in automotive crash tests and sports may not be appropriate. Therefore, there is a need of a specific approach to assess the lethality of these projectiles. In this framework, some recent research data referred in this article as "force wall approach" suggest the use of three lesional thresholds (unconsciousness, meningeal damages and bone damages) that depend on the intracranial pressure. Three corresponding critical impact forces are determined for a reference projectile. Based on the principle that equal rigid wall maximal impact forces will produce equal damage on the head, these limits can be determined for any other projectile. In order to validate the consistence of this innovative method, it is necessary to compare the results with other existing assessment methods. This paper proposes a comparison between the "force wall approach" and two different head models. The first one is a numerical model (Strasbourg University Finite Element Head Model-SUFEHM) from Strasbourg University; the second one is a mechanical surrogate (Ballistics Load Sensing Headform-BLSH) from Biokinetics. PMID:25400712

  12. Injury Risk Assessment of Non-Lethal Projectile Head Impacts

    PubMed Central

    Oukara, Amar; Nsiampa, Nestor; Robbe, Cyril; Papy, Alexandre

    2014-01-01

    Kinetic energy non-lethal projectiles are used to impart sufficient effect onto a person in order to deter uncivil or hazardous behavior with a low probability of permanent injury. Since their first use, real cases indicate that the injuries inflicted by such projectiles may be irreversible and sometimes lead to death, especially for the head impacts. Given the high velocities and the low masses involved in such impacts, the assessment approaches proposed in automotive crash tests and sports may not be appropriate. Therefore, there is a need of a specific approach to assess the lethality of these projectiles. In this framework, some recent research data referred in this article as “force wall approach” suggest the use of three lesional thresholds (unconsciousness, meningeal damages and bone damages) that depend on the intracranial pressure. Three corresponding critical impact forces are determined for a reference projectile. Based on the principle that equal rigid wall maximal impact forces will produce equal damage on the head, these limits can be determined for any other projectile. In order to validate the consistence of this innovative method, it is necessary to compare the results with other existing assessment methods. This paper proposes a comparison between the “force wall approach” and two different head models. The first one is a numerical model (Strasbourg University Finite Element Head Model-SUFEHM) from Strasbourg University; the second one is a mechanical surrogate (Ballistics Load Sensing Headform-BLSH) from Biokinetics. PMID:25400712

  13. Dependence of debris cloud formation on projectile shape

    SciTech Connect

    Konrad, C.H.; Chhabildas, L.C.; Boslough, M.B.; Piekutowski, A.J.; Poormon, K.L.; Mullin, S.A.; Littlefield, D.L.

    1993-07-01

    A two-stage light-gas gun has been used to impact thin zinc bumpers by zinc projectiles over the velocity range of 2.4 km/s to 6.7 km/s to determine the propagation characteristics of the impact generated debris. Constant-mass projectiles in the form of spheres, discs, cylinders and rods were used in these studies. Radiographic techniques were employed to record the debris cloud generated upon impact and the dynamic formation of the resulting rupture in an aluminum backing plate resulting from the loading of the debris cloud. The characteristics of the debris cloud generated upon impact is found to depend on the projectile shape. The data indicate that the debris front velocity is independent of the shape of the projectile, whereas the debris lateral/radial velocity is strongly dependent on projectile geometry. Spherical impactors generate the most radially dispersed debris cloud while the normal plate impactors result in column-like debris. It has been observed that the debris generated by the impact of thin plates on a thin bumper shield is considerably more damaging to a backwall than the debris generated by an equivalent-mass sphere.

  14. Interdependence of spin structure, anion height and electronic structure of BaFe2As2

    NASA Astrophysics Data System (ADS)

    Sen, Smritijit; Ghosh, Haranath

    2016-05-01

    Superconducting as well as other electronic properties of Fe-based superconductors are quite sensitive to the structural parameters specially, on anion height which is intimately related to zAs, the fractional z co-ordinate of As atom. Due to presence of strong magnetic fluctuation in these Fe-based superconductors, optimized structural parameters (lattice parameters a, b, c) including zAs using density functional theory (DFT) under generalized gradient approximation (GGA) does not match experimental values accurately. In this work, we show that the optimized value of zAs is strongly influenced by the spin structures in the orthorhombic phase of BaFe2As2 system. We take all possible spin structures for the orthorhombic BaFe2As2 system and then optimize zAs. Using these optimized structures we calculate electronic structures like density of states, band structures etc., for each spin configurations. From these studies we show that the electronic structure, orbital order which is responsible for structural as well as related to nematic transition, are significantly influenced by the spin structures.

  15. Measurement of electronic structure at nanoscale solid-solid interfaces by surface-sensitive electron spectroscopy

    SciTech Connect

    Wang, H.-Q.; Henrich, Victor E.; Altman, Eric I.

    2008-01-07

    We explore the use of electron spectroscopy that samples the near-surface region of a crystal to study the electronic structure at the buried interfaces between two dissimilar transition-metal oxides. The interface is probed by comparing experimental ultraviolet photoelectron spectra to model spectra and by taking sequential differences between the experimental spectra as one oxide is grown on another. Using (100) Fe{sub 3}O{sub 4}-NiO and Fe{sub 3}O{sub 4}-CoO interfaces grown by molecular beam epitaxy, we show that there is a much higher density of electronic states at the Fe{sub 3}O{sub 4}-CoO interface than at the Fe{sub 3}O{sub 4}-NiO interface. The origin of this difference is discussed.

  16. Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

    SciTech Connect

    Zhou, X.J.

    2010-04-30

    In addition to the record high superconducting transition temperature (T{sub c}), high temperature cuprate superconductors are characterized by their unusual superconducting properties below T{sub c}, and anomalous normal state properties above T{sub c}. In the superconducting state, although it has long been realized that superconductivity still involves Cooper pairs, as in the traditional BCS theory, the experimentally determined d-wave pairing is different from the usual s-wave pairing found in conventional superconductors. The identification of the pairing mechanism in cuprate superconductors remains an outstanding issue. The normal state properties, particularly in the underdoped region, have been found to be at odd with conventional metals which is usually described by Fermi liquid theory; instead, the normal state at optimal doping fits better with the marginal Fermi liquid phenomenology. Most notable is the observation of the pseudogap state in the underdoped region above T{sub c}. As in other strongly correlated electrons systems, these unusual properties stem from the interplay between electronic, magnetic, lattice and orbital degrees of freedom. Understanding the microscopic process involved in these materials and the interaction of electrons with other entities is essential to understand the mechanism of high temperature superconductivity. Since the discovery of high-T{sub c} superconductivity in cuprates, angle-resolved photoemission spectroscopy (ARPES) has provided key experimental insights in revealing the electronic structure of high temperature superconductors. These include, among others, the earliest identification of dispersion and a large Fermi surface, an anisotropic superconducting gap suggestive of a d-wave order parameter, and an observation of the pseudogap in underdoped samples. In the mean time, this technique itself has experienced a dramatic improvement in its energy and momentum resolutions, leading to a series of new discoveries not

  17. Refractory metals in molten salts: Theory and simulation of geometry, electronic structure, and electron transport

    NASA Astrophysics Data System (ADS)

    Koslowski, Thorsten

    2000-12-01

    In this work, we present a theoretical and numerical study of the microscopic and electronic structure of solutions of refractory metal halides in alkali halide melts, [NbCl5]x[KCl]1-x and [TaCl5]x[KCl]1-x with 0⩽x⩽0.5. The geometry of the melts is described by ensembles of charged hard spheres, the electronic structure is modeled by a tight-binding Hamiltonian, which is extended by a reaction field to describe the diabatic energy profile of the electronic self-exchange in many-orbital mixed-valence systems. Despite its simplicity, the model leads to the formation of distorted octahedral [NbCl6]- and [TaCl6]- clusters, as evident both from the inspection of the simulation geometries and from the analysis of the partial pair distribution functions. Even in the presence of the strong potential energy fluctuations characteristic of ionic liquids, the octahedral structure is manifest in the density of states in a t2g-eg splitting of the conduction band. The Hamiltonian that describes mixed-valence systems is solved self-consistently. Using an attractive Hubbard parameter of 1.5 eV, we show that the numerical results can be interpreted by Marcus' theory of outer-sphere electron transfer reactions with a reorganization energy of 2.2 eV, an electronic coupling parameter of 0.12 eV, and an activation energy of 0.42 eV. Both anion-d metal cation and intervalence charge transfer excitations contribute to the optical absorption spectrum, the latter leads to a pronounced polaron absorption peak. These findings are compared to recent experimental results.

  18. Modeling and simulation of electronic structure, material interface and random doping in nano electronic devices.

    PubMed

    Chen, Duan; Wei, Guo-Wei

    2010-06-20

    The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano scale. By optimization of the energy functional, we derive consistently-coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I-V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical convergence

  19. Modeling and simulation of electronic structure, material interface and random doping in nano electronic devices

    PubMed Central

    Chen, Duan; Wei, Guo-Wei

    2010-01-01

    The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano scale. By optimization of the energy functional, we derive consistently-coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I-V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical convergence

  20. Phase effect in the energy loss of hydrogen projectiles in zinc targets

    SciTech Connect

    Arnau, A.; Bauer, P.; Kastner, F.; Salin, A.; Ponce, V.H.; Fainstein, P.D.; Echenique, P.M.

    1994-03-01

    We present an experimental and theoretical study of the phase effect in the energy loss of fast hydrogen beams colliding with gas and solid zinc targets. The experiments show a maximum phase effect of 50% around 50 keV/u, the energy loss per atom in the solid target being smaller than in the gas target. An extensive theoretical study of all the processes contributing to the energy loss in the two phases shows that the experimental findings can be explained primarily by the screening of the projectile field by the valence electrons in the solid.

  1. Software abstractions and computational issues in parallel structure adaptive mesh methods for electronic structure calculations

    SciTech Connect

    Kohn, S.; Weare, J.; Ong, E.; Baden, S.

    1997-05-01

    We have applied structured adaptive mesh refinement techniques to the solution of the LDA equations for electronic structure calculations. Local spatial refinement concentrates memory resources and numerical effort where it is most needed, near the atomic centers and in regions of rapidly varying charge density. The structured grid representation enables us to employ efficient iterative solver techniques such as conjugate gradient with FAC multigrid preconditioning. We have parallelized our solver using an object- oriented adaptive mesh refinement framework.

  2. Atomic and electronic structures of an extremely fragile liquid

    PubMed Central

    Kohara, Shinji; Akola, Jaakko; Patrikeev, Leonid; Ropo, Matti; Ohara, Koji; Itou, Masayoshi; Fujiwara, Akihiko; Yahiro, Jumpei; Okada, Junpei T.; Ishikawa, Takehiko; Mizuno, Akitoshi; Masuno, Atsunobu; Watanabe, Yasuhiro; Usuki, Takeshi

    2014-01-01

    The structure of high-temperature liquids is an important topic for understanding the fragility of liquids. Here we report the structure of a high-temperature non-glass-forming oxide liquid, ZrO2, at an atomistic and electronic level. The Bhatia–Thornton number–number structure factor of ZrO2 does not show a first sharp diffraction peak. The atomic structure comprises ZrO5, ZrO6 and ZrO7 polyhedra with a significant contribution of edge sharing of oxygen in addition to corner sharing. The variety of large oxygen coordination and polyhedral connections with short Zr–O bond lifetimes, induced by the relatively large ionic radius of zirconium, disturbs the evolution of intermediate-range ordering, which leads to a reduced electronic band gap and increased delocalization in the ionic Zr–O bonding. The details of the chemical bonding explain the extremely low viscosity of the liquid and the absence of a first sharp diffraction peak, and indicate that liquid ZrO2 is an extremely fragile liquid. PMID:25520236

  3. Impact of lattice distortion and electron doping on α-MoO3 electronic structure

    PubMed Central

    Huang, Peng-Ru; He, Yao; Cao, Chao; Lu, Zheng-Hong

    2014-01-01

    Band structure of transition metal oxides plays a critical role in many applications such as photo-catalysis, photovoltaics, and electroluminescent devices. In this work we report findings that the band structure of MoO3 can be significantly altered by a distortion in the octahedral coordination structure. We discovered that, in addition to epitaxial type of structural strain, chemical force such as hydrogen inclusion can also cause extended lattice distortion. The lattice distortion in hydrogenated MoO3 led to a significant reduction of the energy gap, overshadowing the Moss-Burstein effect of band filling. Charge doping simulations revealed that filling of conduction band drives the lattice distortion. This suggests that any charge transfer or n-type electron doping could lead to lattice distortion and consequentially a reduction in energy gap. PMID:25410814

  4. A new parametrizable model of molecular electronic structure

    NASA Astrophysics Data System (ADS)

    Laikov, Dimitri N.

    2011-10-01

    A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good dipole polarizabilities and improved intermolecular potentials with dispersion terms. The molecular integrals include up to three-center one-electron and two-center two-electron terms, all in simple analytical forms. A method to extract the effective one-electron Hamiltonian of nonlocal-exchange Kohn-Sham theory from the coupled-cluster one-electron density matrix is designed and used to get its matrix representation in a molecule-intrinsic minimal basis as an input to the parametrization procedure - making a direct link to the correlated wavefunction theory. The model has been trained for 15 elements (H, Li-F, Na-Cl, 720 parameters) on a set of 5581 molecules (including ions, transition states, and weakly bound complexes) whose first- and second-order properties were computed by the coupled-cluster theory as a reference, and a good agreement is seen. The model looks promising for the study of large molecular systems, it is believed to be an important step forward from the traditional semiempirical models towards higher accuracy at nearly as low a computational cost.

  5. A new parametrizable model of molecular electronic structure.

    PubMed

    Laikov, Dimitri N

    2011-10-01

    A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good dipole polarizabilities and improved intermolecular potentials with dispersion terms. The molecular integrals include up to three-center one-electron and two-center two-electron terms, all in simple analytical forms. A method to extract the effective one-electron Hamiltonian of nonlocal-exchange Kohn-Sham theory from the coupled-cluster one-electron density matrix is designed and used to get its matrix representation in a molecule-intrinsic minimal basis as an input to the parametrization procedure--making a direct link to the correlated wavefunction theory. The model has been trained for 15 elements (H, Li-F, Na-Cl, 720 parameters) on a set of 5581 molecules (including ions, transition states, and weakly bound complexes) whose first- and second-order properties were computed by the coupled-cluster theory as a reference, and a good agreement is seen. The model looks promising for the study of large molecular systems, it is believed to be an important step forward from the traditional semiempirical models towards higher accuracy at nearly as low a computational cost. PMID:21992295

  6. The structure and electronic properties of hexagonal Fe2Si

    NASA Astrophysics Data System (ADS)

    Tang, Chi Pui; Tam, Kuan Vai; Xiong, Shi Jie; Cao, Jie; Zhang, Xiaoping

    2016-06-01

    On the basis of first principle calculations, we show that a hexagonal structure of Fe2Si is a ferromagnetic crystal. The result of the phonon spectra indicates that it is a stable structure. Such material exhibits a spin-polarized and half-metal-like band structure. From the calculations of generalized gradient approximation, metallic and semiconducting behaviors are observed with a direct and nearly 0 eV band gap in various spin channels. The densities of states in the vicinity of the Fermi level is mainly contributed from the d-electrons of Fe. We calculate the reflection spectrum of Fe2Si, which has minima at 275nm and 3300nm with reflectance of 0.27 and 0.49, respectively. Such results may provide a reference for the search of hexagonal Fe2Si in experiments. With this band characteristic, the material may be applied in the field of novel spintronics devices.

  7. Electronic structure of SrRuO{sub 3}

    SciTech Connect

    Fujioka, K.; Okamoto, J.; Mizokawa, T.; Fujimori, A.; Hase, I.; Abbate, M.; Lin, H.J.; Chen, C.T.; Takeda, Y.; Takano, M.

    1997-09-01

    We have measured photoemission and oxygen 1s x-ray absorption spectra of the ferromagnetic metal SrRuO{sub 3} and compared them with a first-principles band-structure calculation. The overall distribution of Ru 4d and O 2p spectral weight is in good agreement with that predicted by the band-structure calculation. However, the observed spectral line shape of the Ru 4d band is spread over a wide energy range and the emission intensity at the Fermi level is weakened compared to the band-structure calculation. This implies the importance of electron correlation in the Ru oxide. {copyright} {ital 1997} {ital The American Physical Society}

  8. Model for the hyperfine structure of electronically excited KCs molecules

    NASA Astrophysics Data System (ADS)

    Orbán, A.; Vexiau, R.; Krieglsteiner, O.; Nägerl, H.-C.; Dulieu, O.; Crubellier, A.; Bouloufa-Maafa, N.

    2015-09-01

    A model for determining the hyperfine structure of the excited electronic states of diatomic bialkali heteronuclear molecules is formulated from the atomic hyperfine interactions and is applied to the case of bosonic 39KCs and fermionic 40KCs molecules. The hyperfine structure of the potential-energy curves of the states correlated to the K (4 s 2S1 /2) +Cs (6 p 2P1 /2 ,3 /2) dissociation limits is described in terms of different coupling schemes depending on the internuclear distance R . These results provide a step in the calculation of the hyperfine structure of rovibrational levels of these excited molecular states in the perspective of the identification of efficient paths for creating ultracold ground-state KCs molecules.

  9. Perforation of HY-100 steel plates with long rod projectiles

    SciTech Connect

    Hanchak, S.J.; Altman, B.S.; Forrestal, M.J.

    1993-07-01

    The authors conducted perforation experiments with 4340 steel, rod projectiles and HY-100 steel, target plates at striking velocities between 80 and 370 m/s. Projectiles were machined to nominally 30-mm-diameter and 281-mm-length so they could be launched from a 30-mm-powder gun without sabots. The target plates were rigidly clamped at 305-mm diameter and had a nominal thickness of 10.2 mm. In addition to measuring striking and residual projectile velocities, they obtained back surface framing camera data that showed clearly the plate deformation and plug ejection process. An Imacon 792 camera provided up to 20 frames per experiment with an interframe time duration of 10 {mu}s. The modeling work is in progress, but they present a beam model that exhibits the features observed in the experiments.

  10. Influence of the projectiles' material in a coilgun

    NASA Astrophysics Data System (ADS)

    Hinaje, Melika; Netter, Denis

    2006-09-01

    A simple model of an electromagnetic launcher is introduced in this paper. The proposed model is an electrical one and is suitable for undergraduate students. The work consists of establishing an electrical model whose resolution gives the induced current and the speed of the projectile at a given inductor current and material projectile. In this manner by changing the material of the projectile we can deduce which one is the best. Then, a simple experiment illustrating the principles of a coilgun is described and some test results are given. Therefore, students learn electromagnetic phenomena through an electrical model which is simpler to study than a magnetic one. They have to solve a system of differential equations of the second order using numerical method. And finally, their theoretical study of the coilgun leads to an experimental bench.

  11. Using Tracker as a pedagogical tool for understanding projectile motion

    NASA Astrophysics Data System (ADS)

    Wee, Loo Kang; Chew, Charles; Hwee Goh, Giam; Tan, Samuel; Lee, Tat Leong

    2012-07-01

    This article reports on the use of Tracker as a pedagogical tool in the effective learning and teaching of projectile motion in physics. When a computer model building learning process is supported and driven by video analysis data, this free Open Source Physics tool can provide opportunities for students to engage in active enquiry-based learning. We discuss the pedagogical use of Tracker to address some common misconceptions concerning projectile motion by allowing students to test their hypothesis by juxtaposing their mental models against the analysis of real-life videos. Initial research findings suggest that allowing learners to relate abstract physics concepts to real life through coupling computer modelling with traditional video analysis could be an innovative and effective way to learn projectile motion.

  12. Semiempirical electronic structure calculation on Ca and Pb apatites

    NASA Astrophysics Data System (ADS)

    Matos, Maria; Terra, Joice; Ellis, D. E.

    A systematic study is made on the electronic structure of stoichiometric calcium and lead apatites, using the tight binding extended Hückel method (eHT). The aim is to investigate the applicability of the semiempirical theory to study this family of compounds. A10(BO4)6X2 (A = Ca, Pb) apatites, differing by substitutions in the BO4 tetrahedral unit (B = P, As, and V) and X-channel ion (X = OH, Cl), are considered. The calculations show that eHT is suitable to describe basic properties especially concerning trends with atomic substitution and geometry changes. Band structure, Mulliken charge distribution, and bond orders are in good agreement with results of ab initio density functional theory (DFT) found in the literature. Large variations in the optical gap due to vanadium and lead substitutions are newly found. Changes in the anion X-channel affect the optical gap, which is in close agreement with DFT results. Analysis involving subnets are performed to determine the role of halogenic orbitals in the electronic structure of chloroapatites, showing evidence of covalent Cl bonding. It was also found that Pb=OH bonding in hydroxy-vanadinite Pb10(VO4)6(OH)2, recently synthesized, is weaker than that of Ca=OH in vanadate Ca10(VO4)6(OH)2. Arsenium is found to be more weakely bound to the O-tetrahedron than phosphorous, although Ca=O bond is increased with the substitution. We investigate, in addition, the electronic structure of a model system Ca10(AsO4)6(OH)2, obtained from direct As substitution in the vanadate Ca10(VO4)6(OH)2.

  13. Electronic structure of LaPt2Si2

    NASA Astrophysics Data System (ADS)

    Hase, I.; Yanagisawa, T.

    2013-01-01

    Iron-pnictide superconductor (Ba, K)Fe2As2 has the ThCr2Si2-type crystal structure. On the other hand, recently found arsenide superconductor SrPt2As2 has the CaBe2Ge2-type structure, which is a different polymorphic form of the ThCr2Si2-type structure. LaPt2Si2 shows superconductivity with Tc = 2.2 K and the above-shown two different crystal structures have been reported previously. In this paper we have calculated the electronic structure of LaPt2Si2 from first-principles. From the total energy calculation, we show that the CaBe2Ge2-type structure is more stable in this compound. The density of states at the Fermi level (D(EF)) mainly consists of Pt1-d orbitals, while the Pt2-d orbitals contribute to D(EF) only half of Pt1-d orbitals. In contrast to iron-pnictide system, the total density of states at the Fermi level does not depend so much on the distortion of the PtX4 tetrahedra and/or the height of the X atom from the two-dimensional Pt plane. The calculated electronic specific heat coefficient is 7.0 mJ/mol K2 for LaPt2Si2, which is comparable with that of SrPt2As2, but larger than the experimental value 4 mJ/mol K2.

  14. Electron microscopic examination of wastewater biofilm formation and structural components.

    PubMed Central

    Eighmy, T T; Maratea, D; Bishop, P L

    1983-01-01

    This research documents in situ wastewater biofilm formation, structure, and physiochemical properties as revealed by scanning and transmission electron microscopy. Cationized ferritin was used to label anionic sites of the biofilm glycocalyx for viewing in thin section. Wastewater biofilm formation paralleled the processes involved in marine biofilm formation. Scanning electron microscopy revealed a dramatic increase in cell colonization and growth over a 144-h period. Constituents included a variety of actively dividing morphological types. Many of the colonizing bacteria were flagellated. Filaments were seen after primary colonization of the surface. Transmission electron microscopy revealed a dominant gram-negative cell wall structure in the biofilm constituents. At least three types of glycocalyces were observed. The predominant glycocalyx possessed interstices and was densely labeled with cationized ferritin. Two of the glycocalyces appeared to mediate biofilm adhesion to the substratum. The results suggest that the predominant glycocalyx of this thin wastewater biofilm serves, in part, to: (i) enclose the bacteria in a matrix and anchor the biofilm to the substratum and (ii) provide an extensive surface area with polyanionic properties. Images PMID:6881965

  15. Low energy electrons and swift ion track structure in PADC

    NASA Astrophysics Data System (ADS)

    Fromm, Michel; Quinto, Michele A.; Weck, Philippe F.; Champion, Christophe

    2015-10-01

    The current work aims at providing an accurate description of the ion track-structure in poly-allyl dyglycol carbonate (PADC) by using an up-to-date Monte-Carlo code-called TILDA-V (a French acronym for Transport d'Ions Lourds Dans l'Aqua & Vivo). In this simulation the ion track-structure in PADC is mainly described in terms of ejected electrons with a particular attention done to the Low Energy Electrons (LEEs). After a brief reminder of the most important channels through which LEEs are prone to break a chemical bond, we will report on the simulated energetic distributions of LEEs along an ion track in PADC for particular incident energies located on both sides of the Bragg-peak position. Finally, based on the rare data dealing with LEEs interaction with polymers or organic molecules, we will emphasise the role played by the LEEs in the formation of a latent track in PADC, and more particularly the one played by the sub-ionization electrons.

  16. Metallic carbon nanotubes with metal contacts: electronic structure and transport

    NASA Astrophysics Data System (ADS)

    Zienert, A.; Schuster, J.; Gessner, T.

    2014-10-01

    We study quasi-ballistic electron transport in metallic (6,0) carbon nanotubes (CNTs) of variable length in contact with Al, Cu, Pd, Pt, Ag, and Au electrodes by using the non-equilibrium Green's function formalism in combination with either density functional theory or self-consistent extended Hückel theory. We find good agreement between both. Visualizing the local device density of states of the systems gives a descriptive link between electronic structure and transport properties. In comparison with bare finite and infinite tubes, we show that the electronic structure of short metallic CNTs is strongly modified by the presence of the metallic electrodes, which leads to pronounced size effects in the conductance. The mean conductances and linear response currents allow a ranking of the metals regarding their ability to form low-Ohmic contacts with the nanotube: Ag≲ Au\\lt Cu\\ll Pt≈ Pd\\ll Al. These findings are contrasted with similar trends in contact distance, binding energy, calculated work function of the metal surfaces, and various results from literature.

  17. The Electronic Structure of Transition Metal Coated Fullerenes

    NASA Astrophysics Data System (ADS)

    Patton, David C.; Pederson, Mark R.; Kaxiras, Efthimios

    1998-03-01

    Clusters composed of fullerene molecules with an outer shell of transition metal atoms in the composition C_60M_62 (M being a transition metal) have been produced with laser vaporisation techniques(F. Tast, N. Malinowski, S. Frank, M. Heinebrodt, I.M.L. Billas, and T. P. Martin, Z. Phys D 40), 351 (1997).. We have studied several of these very large systems with a parallel version of the all-electron NRLMOL cluster code. Optimized geometries of the metal encased fullerenes C_60Ti_62 and C_60V_62 are presented along with their HOMO-LUMO gaps, electron affinities, ionization energies, and cohesive energies. We compare the stability of these clusters to relaxed met-car structures (e.g. Ti_8C_12) and to relaxed rocksalt metal-carbide fragments (TiC)n with n=8 and 32. In addition to metal-coated fullerenes we consider the possibility of a trilayered structure consisting of a small shell of metal atoms enclosed by a metal coated fullerene. The nature of bonding in these systems is analyzed by studying the electronic charge distributions.

  18. Structural Fingerprinting of Nanocrystals in the Transmission Electron Microscope

    NASA Astrophysics Data System (ADS)

    Rouvimov, Sergei; Plachinda, Pavel; Moeck, Peter

    2010-03-01

    Three novel strategies for the structurally identification of nanocrystals in a transmission electron microscope are presented. Either a single high-resolution transmission electron microscopy image [1] or a single precession electron diffractogram (PED) [2] may be employed. PEDs from fine-grained crystal powders may also be utilized. Automation of the former two strategies is in progress and shall lead to statistically significant results on ensembles of nanocrystals. Open-access databases such as the Crystallography Open Database which provides more than 81,500 crystal structure data sets [3] or its mainly inorganic and educational subsets [4] may be utilized. [1] http://www.scientificjournals.org/journals 2007/j/of/dissertation.htm [2] P. Moeck and S. Rouvimov, in: {Drugs and the Pharmaceutical Sciences}, Vol. 191, 2009, 270-313 [3] http://cod.ibt.lt, http://www.crystallography.net, http://cod.ensicaen.fr, http://nanocrystallography.org, http://nanocrystallography.net, http://journals.iucr.org/j/issues/2009/04/00/kk5039/kk5039.pdf [4] http://nanocrystallography.research.pdx.edu/CIF-searchable

  19. Multiscale approach to the electronic structure of doped semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Sinai, Ofer; Hofmann, Oliver T.; Rinke, Patrick; Scheffler, Matthias; Heimel, Georg; Kronik, Leeor

    2015-02-01

    The inclusion of the global effects of semiconductor doping poses a unique challenge for first-principles simulations, because the typically low concentration of dopants renders an explicit treatment intractable. Furthermore, the width of the space-charge region (SCR) at charged surfaces often exceeds realistic supercell dimensions. Here, we present a multiscale technique that fully addresses these difficulties. It is based on the introduction of a charged sheet, mimicking the SCR-related field, along with free charge which mimics the bulk charge reservoir, such that the system is neutral overall. These augment a slab comprising "pseudoatoms" possessing a fractional nuclear charge matching the bulk doping concentration. Self-consistency is reached by imposing charge conservation and Fermi level equilibration between the bulk, treated semiclassically, and the electronic states of the slab, which are treated quantum-mechanically. The method, called CREST—the charge-reservoir electrostatic sheet technique—can be used with standard electronic structure codes. We validate CREST using a simple tight-binding model, which allows for comparison of its results with calculations encompassing the full SCR explicitly. Specifically, we show that CREST successfully predicts scenarios spanning the range from no to full Fermi level pinning. We then employ it with density functional theory, obtaining insight into the doping dependence of the electronic structures of the metallic "clean-cleaved" Si(111) surface and its semiconducting (2 ×1 ) reconstructions.

  20. Low energy electrons and swift ion track structure in PADC

    SciTech Connect

    Fromm, Michel; Quinto, Michele A.; Weck, Philippe F.; Champion, Christophe

    2015-05-27

    The current work aims at providing an accurate description of the ion track-structure in poly-allyl dyglycol carbonate (PADC) by using an up-to-date Monte-Carlo code-called TILDA-V (a French acronym for Transport d’Ions Lourds Dans l’Aqua & Vivo). In this simulation the ion track-structure in PADC is mainly described in terms of ejected electrons with a particular attention done to the Low Energy Electrons (LEEs). After a brief reminder of the most important channels through which LEEs are prone to break a chemical bond, we will report on the simulated energetic distributions of LEEs along an ion track in PADC for particular incident energies located on both sides of the Bragg-peak position. Lastly, based on the rare data dealing with LEEs interaction with polymers or organic molecules, we will emphasise the role played by the LEEs in the formation of a latent track in PADC, and more particularly the one played by the sub-ionization electrons.

  1. Low energy electrons and swift ion track structure in PADC

    DOE PAGESBeta

    Fromm, Michel; Quinto, Michele A.; Weck, Philippe F.; Champion, Christophe

    2015-05-27

    The current work aims at providing an accurate description of the ion track-structure in poly-allyl dyglycol carbonate (PADC) by using an up-to-date Monte-Carlo code-called TILDA-V (a French acronym for Transport d’Ions Lourds Dans l’Aqua & Vivo). In this simulation the ion track-structure in PADC is mainly described in terms of ejected electrons with a particular attention done to the Low Energy Electrons (LEEs). After a brief reminder of the most important channels through which LEEs are prone to break a chemical bond, we will report on the simulated energetic distributions of LEEs along an ion track in PADC for particularmore » incident energies located on both sides of the Bragg-peak position. Lastly, based on the rare data dealing with LEEs interaction with polymers or organic molecules, we will emphasise the role played by the LEEs in the formation of a latent track in PADC, and more particularly the one played by the sub-ionization electrons.« less

  2. Electronic Properties of Semiconductor Quantum-Ring Structures

    NASA Astrophysics Data System (ADS)

    Pacheco, Mónica; Fuster, Gonzalo; Barticevic, Zdenka

    2002-03-01

    Motivated by the interesting electronic properties exhibited by these nanorings when they are threaded by a magnetic field, we studied a new semiconductor structure formed by two coupled rings which are concentrically disposed. In order to calculate the two-ring electronic spectrum it is assumed that the in-plane electronic-potential of each ring is generated by a rotation, around the ring axis, of a one-dimensional parabolic potential centered to a distance ρ=ρo of the ring center. The potential of the two-rings system is then assumed as a superposition of a potential for each ring with their minimum at different radii and being truncated in the intersection point. In this way a potential barrier is formed in between the rings. We solve the in-plane problem by expanding the corresponding envelope function as a linear combination of solutions of isolated rings. We have made a detailed study about the influence of the characteristic confinement-parameters of each rings, and of the barrier strength, on the electronic energy spectrum of the system. A uniform magnetic field is applied along the common ring axis and we explore the effects on the Aharonov-Bohm-type oscillations in the energy levels caused by the particular geometry of two coupled quantum-rings.

  3. Electronic tagging and population structure of Atlantic bluefin tuna.

    PubMed

    Block, Barbara A; Teo, Steven L H; Walli, Andreas; Boustany, Andre; Stokesbury, Michael J W; Farwell, Charles J; Weng, Kevin C; Dewar, Heidi; Williams, Thomas D

    2005-04-28

    Electronic tags that archive or transmit stored data to satellites have advanced the mapping of habitats used by highly migratory fish in pelagic ecosystems. Here we report on the electronic tagging of 772 Atlantic bluefin tuna in the western Atlantic Ocean in an effort to identify population structure. Reporting electronic tags provided accurate location data that show the extensive migrations of individual fish (n = 330). Geoposition data delineate two populations, one using spawning grounds in the Gulf of Mexico and another from the Mediterranean Sea. Transatlantic movements of western-tagged bluefin tuna reveal site fidelity to known spawning areas in the Mediterranean Sea. Bluefin tuna that occupy western spawning grounds move to central and eastern Atlantic foraging grounds. Our results are consistent with two populations of bluefin tuna with distinct spawning areas that overlap on North Atlantic foraging grounds. Electronic tagging locations, when combined with US pelagic longline observer and logbook catch data, identify hot spots for spawning bluefin tuna in the northern slope waters of the Gulf of Mexico. Restrictions on the time and area where longlining occurs would reduce incidental catch mortalities on western spawning grounds. PMID:15858572

  4. Structural phase transition and electronic properties in samarium chalcogenides

    NASA Astrophysics Data System (ADS)

    Panwar, Y. S.; Aynyas, Mahendra; Pataiya, J.; Sanyal, Sankar P.

    2016-05-01

    The electronic structure and high pressure properties of samarium monochalcogenides SmS, SmSe and SmTe have been reported by using tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). The total energy as a function of volume is evaluated. It is found that these monochalcogenides are stable in NaCl-type structure under ambient pressure. We predict a structural phase transition from NaCl-type (B1-phase) structure to CsCl-type (B2-type) structure for these compounds. Phase transition pressures were found to be 1.7, 4.4 and 6.6 GPa, for SmS, SmSe and SmTe respectively. Apart from this, the lattice parameter (a0), bulk modulus (B0), band structure (BS) and density of states (DOS) are calculated. From energy band diagram we observed that these compounds exhibit metallic character. The calculated values of equilibrium lattice parameter and phase transition pressure are in general good agreement with available data.

  5. Projectile transverse motion and stability in electromagnetic induction launchers

    SciTech Connect

    Shokair, I.R.

    1993-12-31

    The transverse motion of a projectile in an electromagnetic induction launcher is considered. The equations of motion for translation and rotation are derived assuming a rigid projectile and a flyway restoring force per unit length that is proportional to the local displacement. Linearized transverse forces and torques due to energized coils are derived for displaced or tilted armature elements based on a first order perturbation method. The resulting equations of motion for a rigid projectile composed of multiple elements in a multi-coil launcher are analyzed as a coupled oscillator system of equations and a simple linear stability condition is derived. The equations of motion are incorporated into the 2-D Slingshot circuit code and numerical solutions for the transverse motion are obtained. For a launcher with a 10 cm bore radius with a 40 cm long solid armature, we find that stability is achieved with a restoring force (per unit length) constant of k {approx} 1 {times} 10{sup 8} N/m{sup 2}. For k = 1.5 {times} 10{sup 8} N/m{sup 2} and sample coil misalignment modeled as a sine wave of 1 mm amplitude at wavelengths of one or two meters, the projectile displacement grows to a maximum of 4 mm. This growth is due to resonance between the natural frequency of the projectile transverse motion and the coil displacement wavelength. This resonance does not persist because of the changing axial velocity. Random coil displacement is also found to cause roughly the same projectile displacement. For the maximum displacement a rough estimate of the transverse pressure is 50 bars. Results for a wound armature with uniform current density throughout show very similar displacements.

  6. Energetics, bonding mechanism and electronic structure of metal/ceramic interfaces

    SciTech Connect

    Freeman, A.J.

    1993-01-01

    Progress are reported on: electronic structure of PdO, PtO, and AgO (band structure calculations); ab initio calculations of electronic structure of TiO{sub 2}(110) surface; and electronic structure of VO{sub 2} and TiO{sub 2} thin films and multilayers. (DLC)

  7. Electronic structure of graphene oxide and reduced graphene oxide monolayers

    SciTech Connect

    Sutar, D. S.; Singh, Gulbagh; Divakar Botcha, V.

    2012-09-03

    Graphene oxide (GO) monolayers obtained by Langmuir Blodgett route and suitably treated to obtain reduced graphene oxide (RGO) monolayers were studied by photoelectron spectroscopy. Upon reduction of GO to form RGO C1s x-ray photoelectron spectra showed increase in graphitic carbon content, while ultraviolet photoelectron spectra showed increase in intensity corresponding to C2p-{pi} electrons ({approx}3.5 eV). X-ray excited Auger transitions C(KVV) and plasmon energy loss of C1s photoelectrons have been analyzed to elucidate the valence band structure. The effective number of ({pi}+{sigma}) electrons as obtained from energy loss spectra was found to increase by {approx}28% on reduction of GO.

  8. Cryo electron microscopy to determine the structure of macromolecular complexes.

    PubMed

    Carroni, Marta; Saibil, Helen R

    2016-02-15

    Cryo-electron microscopy (cryo-EM) is a structural molecular and cellular biology technique that has experienced major advances in recent years. Technological developments in image recording as well as in processing software make it possible to obtain three-dimensional reconstructions of macromolecular assemblies at near-atomic resolution that were formerly obtained only by X-ray crystallography or NMR spectroscopy. In parallel, cryo-electron tomography has also benefitted from these technological advances, so that visualization of irregular complexes, organelles or whole cells with their molecular machines in situ has reached subnanometre resolution. Cryo-EM can therefore address a broad range of biological questions. The aim of this review is to provide a brief overview of the principles and current state of the cryo-EM field. PMID:26638773

  9. The electronic structure of free aluminum clusters: Metallicity and plasmons

    SciTech Connect

    Andersson, Tomas; Zhang Chaofan; Svensson, Svante; Maartensson, Nils; Bjoerneholm, Olle; Tchaplyguine, Maxim

    2012-05-28

    The electronic structure of free aluminum clusters with {approx}3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms.

  10. The electronic structure of free aluminum clusters: Metallicity and plasmons

    NASA Astrophysics Data System (ADS)

    Andersson, Tomas; Zhang, Chaofan; Tchaplyguine, Maxim; Svensson, Svante; Mârtensson, Nils; Björneholm, Olle

    2012-05-01

    The electronic structure of free aluminum clusters with ˜3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms.

  11. Topological Signatures in the Electronic Structure of Graphene Spirals

    PubMed Central

    Avdoshenko, Stas M.; Koskinen, Pekka; Sevinçli, Haldun; Popov, Alexey A.; Rocha, Claudia G.

    2013-01-01

    Topology is familiar mostly from mathematics, but also natural sciences have found its concepts useful. Those concepts have been used to explain several natural phenomena in biology and physics, and they are particularly relevant for the electronic structure description of topological insulators and graphene systems. Here, we introduce topologically distinct graphene forms - graphene spirals - and employ density-functional theory to investigate their geometric and electronic properties. We found that the spiral topology gives rise to an intrinsic Rashba spin-orbit splitting. Through a Hamiltonian constrained by space curvature, graphene spirals have topologically protected states due to time-reversal symmetry. In addition, we argue that the synthesis of such graphene spirals is feasible and can be achieved through advanced bottom-up experimental routes that we indicate in this work. PMID:23568379

  12. Effect of helium on the electronic structure of palladium tritide

    SciTech Connect

    Gupta, R.P.; Gupta, M.

    1998-12-31

    Tritium is usually stored in the form of a metal tritide since it is safe to handle in this form, easily recoverable, and further large quantities of tritium can be stored. However, since tritium is radioactive it decays into {sup 3}He and an electron. Helium recoil energy in this reaction is very small, and not enough to create defects. The authors have performed ab-initio electronic structure calculations that show that in PdT, a considerable amount of {sup 3}He can be accommodated at the octahedral interstitial sites where it is produced. Their calculations also show that the presence of {sup 3}He results in an overall enhancement in the strength of the metal-tritium bonding that leads to the lowering of the plateau pressure. They also find that there is a weakening of the metal-metal bonds due to the repulsive interaction with {sup 3}He.

  13. Cluster calculations of the electronic structure of copper oxide superconductors

    SciTech Connect

    Wang Yujuin.

    1990-01-01

    A semiempirical INDO model suitable for examination of the transition metal complexes is used to study the electronic structure of various clusters representing the La-Sr-Cu-O and Nd-Ce-Cu-O types of the high-{Tc} superconductors. The clusters are stabilized by embedding in an appropriate Madelung field. The results show a convergent picture independent of the cluster sizes. In the undoped clusters, all copper sites have a {approximately} d{sup 9} configuration with one unpaired spin coupled antiferromagnetically to the spin of adjacent Cu sites. Fitting the resulting energies to the Heisenberg spin Hamiltonian, the superexchange J values obtained were in excellent agreement with experiments. The hole carriers are mainly of planar O character, while the electron carriers are of Cu character.

  14. Structural and electronic properties of GaAsBi

    NASA Astrophysics Data System (ADS)

    Achour, H.; Louhibi, S.; Amrani, B.; Tebboune, A.; Sekkal, N.

    2008-08-01

    The structural and electronic properties of the GaAs 1- xBi x ternary alloy are investigated by means of two first principles and full potential methods, the linear augmented plane waves (FPLAPW) method and a recent version of the full potential linear muffin-tin orbitals method (FPLMTO) which enables an accurate treatment of the interstitial regions. In particular, we have found that the maximal GaBi mole fraction x for which GaBi xAs 1- x remains a semiconductor is probably around x=0.5. The electronic properties of (GaAs) m/(GaBi) n quantum well superlattices (SLs) have also been calculated and it is found that such SLs are semiconductors when m is larger or equal to n.

  15. Electronic structure basis for the extraordinary magnetoresistance in WTe2

    DOE PAGESBeta

    Pletikosić, I.; Ali, Mazhar N.; Fedorov, A. V.; Cava, R. J.; Valla, T.

    2014-11-19

    The electronic structure basis of the extremely large magnetoresistance in layered non-magnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at the Fermi level, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic, quasi one-dimensional Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. As a result, a change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior ofmore » the magnetoresistance in WTe₂ was identified.« less

  16. Electronic Structures of Clusters of Hydrogen Vacancies on Graphene

    PubMed Central

    Wu, Bi-Ru; Yang, Chih-Kai

    2015-01-01

    Hydrogen vacancies in graphane are products of incomplete hydrogenation of graphene. The missing H atoms can alter the electronic structure of graphane and therefore tune the electronic, magnetic, and optical properties of the composite. We systematically studied a variety of well-separated clusters of hydrogen vacancies in graphane, including the geometrical shapes of triangles, parallelograms, hexagons, and rectangles, by first-principles density functional calculation. The results indicate that energy levels caused by the missing H are generated in the broad band gap of pure graphane. All triangular clusters of H vacancies are magnetic, the larger the triangle the higher the magnetic moment. The defect levels introduced by the missing H in triangular and parallelogram clusters are spin-polarized and can find application in optical transition. Parallelograms and open-ended rectangles are antiferromagnetic and can be used for nanoscale registration of digital information. PMID:26468677

  17. Electronic structure of benzene adsorbed on Ni and Cu surfaces

    SciTech Connect

    Weinelt, M.; Nilsson, A.; Wassdahl, N.

    1997-04-01

    Benzene has for a long time served as a prototype adsorption system of large molecules. It adsorbs with the molecular plane parallel to the surface. The bonding of benzene to a transition metal is typically viewed to involve the {pi} system. Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the adsorption strength is reflected in the electronic structure of the adsorbate-substrate complex. The authors have used X-ray Emission (XE) and X-ray Absorption (XA) spectroscopies to selectively study the electronic states localized on the adsorbed benzene molecule. Using XES the occupied states can be studies and with XAS the unoccupied states. The authors have used beamline 8.0 and the Swedish endstation equipped with a grazing incidence x-ray spectrometer and a partial yield absorption detector. The resolution in the XES and XAS were 0.5 eV and 0.05 eV, respectively.

  18. Tailoring the Electronic Structure of Gold Chains on Vicinal Silicon

    NASA Astrophysics Data System (ADS)

    Crain, Jason; Altmann, Kyle; Bromberger, Christian; Erwin, Steven; Kirakosian, Armen; McChesney, Jessica; Lin, Jia-Ling; Himpsel, Franz

    2003-03-01

    Surface states on silicon provide a unique opportunity to study one-dimensional electron systems. By growing chains of gold atoms on vicinal silicon surfaces we demonstrate the capability of engineering one-dimensional metallic states with varying inter-chain spacing and electron count. Using high-resolution angle-resolved photoemission we map the band structures and Fermi surfaces for these atomic chains. The resulting metallic bands exhibit novel properties including the formation of two half-filled metallic bands in place of a single semiconducting band and the formation of a fractionally filled band. From the Fermi surfaces we calculate the one-dimensional versus two-dimensional coupling strengths and demonstrate that their ratio can be tuned from 12:1 to >70:1 by increasing the chain spacing via the miscut angle. [1] [1] J. N. Crain et al., submitted.

  19. Definition of lethality thresholds for KE less-lethal projectiles

    NASA Astrophysics Data System (ADS)

    Cuadros, Jaime H.

    1997-01-01

    The interest in the definition and application of the lethality threshold for KE less-lethal projectiles has increased in the last few years, as the demand for proper use of these weapons has increased from the public at large and the law enforcement community. Experiments have been performed and reported utilizing commercially available projectiles in 12 ga., 37 mm against an anthropomorphic dummy and damage criteria developed by the automobile industry. The utility of the method is discussed and future trends are presented.

  20. Projectile general motion in a vacuum and a spreadsheet simulation

    NASA Astrophysics Data System (ADS)

    Benacka, Jan

    2015-01-01

    This paper gives the solution and analysis of projectile motion in a vacuum if the launch and impact heights are not equal. Formulas for the maximum horizontal range and the corresponding angle are derived. An Excel application that simulates the motion is also presented, and the result of an experiment in which 38 secondary school students developed the application and investigated the system is given. A questionnaire survey was carried out to find out whether the students found the lessons interesting, learned new skills and wanted to model projectile motion in the air as an example of more realistic motion. The results are discussed.