High-pressure combustor exhaust emissions with improved air-atomizing and conventional pressure-atomizing fuel nozzles

NASA Technical Reports Server (NTRS)

Ingebo, R. D.; Norgren, C. T.

1973-01-01

A high-pressure combustor segment 0.456 meter (18 in.) long with a maximum cross section of 0.153 by 0.305 meter (6 by 12 in.) was tested with specially designed air-atomizing and conventional pressure-atomizing fuel nozzles at inlet-air temperatures of 340 to 755 k (610 deg to 1360 R), reference velocities of 12.4 to 26.1 meters per second (41 to 86 ft/sec), and fuel-air ratios of 0.008 to 0.020. Increasing inlet-air pressure from 4 to 20 atmospheres generally increased smoke number and nitric oxide, but decreased carbon monoxide and unburned hydrocarbon concentrations with air-atomizing and pressure-atomizing nozzles. Emission indexes for carbon monoxide and unburned hydrocarbons were lower at 4, 10, and 20 atmospheres, and nitric oxide emission indexes were lower at 10 and 20 atmospheres with air-atomizing than with pressure-atomizing nozzles.

Atomic fountain clock with very high frequency stability employing a pulse-tube-cryocooled sapphire oscillator.

PubMed

Takamizawa, Akifumi; Yanagimachi, Shinya; Tanabe, Takehiko; Hagimoto, Ken; Hirano, Iku; Watabe, Ken-ichi; Ikegami, Takeshi; Hartnett, John G

2014-09-01

The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber.

Upgrading of petroleum oil feedstocks using alkali metals and hydrocarbons

DOEpatents

Gordon, John Howard

2014-09-09

A method of upgrading an oil feedstock by removing heteroatoms and/or one or more heavy metals from the oil feedstock composition. This method reacts the oil feedstock with an alkali metal and an upgradant hydrocarbon. The alkali metal reacts with a portion of the heteroatoms and/or one or more heavy metals to form an inorganic phase separable from the organic oil feedstock material. The upgradant hydrocarbon bonds to the oil feedstock material and increases the number of carbon atoms in the product. This increase in the number of carbon atoms of the product increases the energy value of the resulting oil feedstock.

Improved atom number with a dual color magneto—optical trap

NASA Astrophysics Data System (ADS)

Cao, Qiang; Luo, Xin-Yu; Gao, Kui-Yi; Wang, Xiao-Rui; Chen, Dong-Min; Wang, Ru-Quan

2012-04-01

We demonstrate a novel dual color magneto—optical trap (MOT), which uses two sets of overlapping laser beams to cool and trap 87Rb atoms. The volume of cold cloud in the dual color MOT is strongly dependent on the frequency difference of the laser beams and can be significantly larger than that in the normal MOT with single frequency MOT beams. Our experiment shows that the dual color MOT has the same loading rate as the normal MOT, but much longer loading time, leading to threefold increase in the number of trapped atoms. This indicates that the larger number is caused by reduced light induced loss. The dual color MOT is very useful in experiments where both high vacuum level and large atom number are required, such as single chamber quantum memory and Bose—Einstein condensation (BEC) experiments. Compared to the popular dark spontaneous-force optical trap (dark SPOT) technique, our approach is technically simpler and more suitable to low power laser systems.

Impact of Pb content on the physical parameters of Se-Te-Pb system

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

Anjali,; Sharma, Raman; Thakur, Nagesh

2015-05-15

In the present study, we have investigated the impact of Pb content on the physical parameters in Se-Te-Pb system via average coordination number, constraints, the fraction of floppy modes, cross-linking density, lone pairs electrons, heat of atomization, mean bond energy, cohesive energy and electronegativity. The bulk samples have been prepared by using melt quenching technique. X-ray diffraction pattern of various samples indicates the amorphous nature of investigated glassy alloys. It is observed that average coordination number, average number of constraints and cross-linking density increase with Pb content. However, lone-pair electrons, floppy modes, average heat of atomization, cohesive energy and meanmore » bond energy are found to decrease with Pb atomic percentage.« less

The abundances of solar accelerated nuclei from carbon to iron.

NASA Technical Reports Server (NTRS)

Mogro-Campero, A.; Simpson, J. A.

1972-01-01

Revised observation periods and new data are found to confirm previous evidence that the overabundance of solar-flare nuclei with respect to solar photospheric and coronal abundances increases with increasing atomic number. It is also verified that enhancements can vary from flare to flare and that this variability is large enough to explain the differences observed by various investigators regarding the magnitude of solar-flare high-Z particle enhancements. Additional evidence for a two-stage solar acceleration mechanism is obtained. It is shown that the galactic cosmic-ray source composition displays a similar overabundance as a function of atomic number.

Geometric Electron Models.

ERIC Educational Resources Information Center

Nika, G. Gerald; Parameswaran, R.

1997-01-01

Describes a visual approach for explaining the filling of electrons in the shells, subshells, and orbitals of the chemical elements. Enables students to apply the principles of atomic electron configuration while using manipulatives to model the building up of electron configurations as the atomic numbers of elements increase on the periodic…

Environment-Assisted Speed-up of the Field Evolution in Cavity Quantum Electrodynamics

DOE PAGES

Cimmarusti, A. D.; Yan, Z.; Patterson, B. D.; ...

2015-06-11

We measure the quantum speed of the state evolution of the field in a weakly-driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment assisted speed-up is realized: the quantum speed of the state re-population in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms).

Electrodeposition of Isolated Platinum Atoms and Clusters on Bismuth-Characterization and Electrocatalysis.

PubMed

Zhou, Min; Dick, Jeffrey E; Bard, Allen J

2017-12-06

We describe a method for the electrodeposition of an isolated single Pt atom or small cluster, up to 9 atoms, on a bismuth ultramicroelectrode (UME). This deposition was immediately followed by electrochemical characterization via the hydrogen evolution reaction (HER) that occurs readily on the electrodeposited Pt but not on Bi. The observed voltammetric current plateau, even for a single atom, which behaves as an electrode, allows the estimation of deposit size. Pt was plated from solutions of femtomolar PtCl 6 2- , which allowed precise control of the arrival of ions and thus the plating rate on the Bi UME, to one ion every few seconds. This allowed the atom-by-atom fabrication of isolated platinum deposits, ranging from single atoms to 9-atom clusters. The limiting currents in voltammetry gave the size and number of atoms of the clusters. Given the stochasticity of the plating process, we show that the number of atoms plated over a given time (10 and 20 s) follows a Poisson distribution. Taking the potential at a certain current density as a measure of the relative rate of the HER, we found that the potential shifted positively as the size increased, with single atoms showing the largest overpotentials compared to bulk Pt.

Investigation of the impact of high liquid viscosity on jet atomization in crossflow via high-fidelity simulations

NASA Astrophysics Data System (ADS)

Li, Xiaoyi; Gao, Hui; Soteriou, Marios C.

2017-08-01

Atomization of extremely high viscosity liquid can be of interest for many applications in aerospace, automotive, pharmaceutical, and food industries. While detailed atomization measurements usually face grand challenges, high-fidelity numerical simulations offer the advantage to comprehensively explore the atomization details. In this work, a previously validated high-fidelity first-principle simulation code HiMIST is utilized to simulate high-viscosity liquid jet atomization in crossflow. The code is used to perform a parametric study of the atomization process in a wide range of Ohnesorge numbers (Oh = 0.004-2) and Weber numbers (We = 10-160). Direct comparisons between the present study and previously published low-viscosity jet in crossflow results are performed. The effects of viscous damping and slowing on jet penetration, liquid surface instabilities, ligament formation/breakup, and subsequent droplet formation are investigated. Complex variations in near-field and far-field jet penetrations with increasing Oh at different We are observed and linked with the underlying jet deformation and breakup physics. Transition in breakup regimes and increase in droplet size with increasing Oh are observed, mostly consistent with the literature reports. The detailed simulations elucidate a distinctive edge-ligament-breakup dominated process with long surviving ligaments for the higher Oh cases, as opposed to a two-stage edge-stripping/column-fracture process for the lower Oh counterparts. The trend of decreasing column deflection with increasing We is reversed as Oh increases. A predominantly unimodal droplet size distribution is predicted at higher Oh, in contrast to the bimodal distribution at lower Oh. It has been found that both Rayleigh-Taylor and Kelvin-Helmholtz linear stability theories cannot be easily applied to interpret the distinct edge breakup process and further study of the underlying physics is needed.

Photon Counting as a Probe of Superfluidity in a Two-Band Bose-Hubbard System Coupled to a Cavity Field

NASA Astrophysics Data System (ADS)

Rajaram, Sara; Trivedi, Nandini

2013-12-01

We show that photon number measurement can be used to detect superfluidity for a two-band Bose-Hubbard model coupled to a cavity field. The atom-photon coupling induces transitions between the two internal atomic levels and results in entangled polaritonic states. In the presence of a cavity field, we find different photon numbers in the Mott-insulating versus superfluid phases, providing a method of distinguishing the atomic phases by photon counting. Furthermore, we examine the dynamics of the photon field after a rapid quench to zero atomic hopping by increasing the well depth. We find a robust correlation between the field’s quench dynamics and the initial superfluid order parameter, thereby providing a novel and accurate method of determining the order parameter.

Directional detector of gamma rays

DOEpatents

Cox, Samson A.; Levert, Francis E.

1979-01-01

A directional detector of gamma rays comprises a strip of an electrical cuctor of high atomic number backed with a strip of a second electrical conductor of low atomic number. These elements are enclosed within an electrical conductor that establishes an electrical ground, maintains a vacuum enclosure and screens out low-energy gamma rays. The detector exhibits a directional sensitivity marked by an increased output in the favored direction by a factor of ten over the output in the unfavored direction.

Electrochemical oxygen reduction behavior of selectively deposited platinum atoms on gold nanoparticles.

PubMed

Sarkar, A; Kerr, J B; Cairns, E J

2013-07-22

Carbon-supported Pt@Au "core-shell" nanoparticles with varying surface concentration of platinum atoms have been synthesized using a novel redox-mediated synthesis approach. The synthesis technique allows for a selective deposition of platinum atoms on the surface of prefabricated gold nanoparticles. Energy dispersive spectroscopic analyses in a scanning electron microscope reveal that the platinum to gold atomic ratios are close to the nominal values, validating the synthesis scheme. X-ray diffraction data indicate an un-alloyed structure. The platinum to gold surface atomic ratio determined from cyclic voltammetry and copper under-potential deposition experiments reveal good agreement with the calculated values at low platinum concentration. However, there is an increase in non-uniformity in the deposition process upon increasing the platinum concentration. Koutecky-Levich analysis of the samples indicates a transition of the total number of electrons transferred (n) in the electrochemical oxygen reduction reaction from two to four electrons upon increasing the surface concentration of platinum atoms. Furthermore, the data indicate that isolated platinum atoms can reduce molecular oxygen but via a two-electron route. Moreover, successful four-electron reduction of molecular oxygen requires clusters of platinum atoms. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Irradiation of DNA loaded with platinum containing molecules by fast atomic ions C(6+) and Fe(26+).

PubMed

Usami, N; Kobayashi, K; Furusawa, Y; Frohlich, H; Lacombe, S; Sech, C Le

2007-09-01

In order to study the role of the Linear Energy Transfer (LET) of fast atomic ions in platinum-DNA complexes inducing breaks, DNA Plasmids were irradiated by C(6+) and Fe(26+) ions. DNA Plasmids (pBR322) loaded with different amounts of platinum contained in a terpyridine-platinum molecule (PtTC) were irradiated by C(6+) ions and Fe(26+) ions. The LET values ranged between 13.4 keV/microm and 550 keV/microm. In some experiments, dimethyl sulfoxide (DMSO) was added. In all experiments, a significant increase in DNA strand breaks was observed when platinum was present. The yield of breaks induced per Gray decreased when the LET increased. The yield of single and double strand breaks per plasmid per track increased with the LET, indicating that the number of DNA breaks per Gray was related to the number of tracks through the medium. These findings show that more DNA breaks are induced by atomic ions when platinum is present. This effect increases for low LET heavy atoms. As DSB induction may induce cell death, these results could open new perspectives with the association of hadrontherapy and chemotherapy. Thus the therapeutic index might be improved by loading the tumour with platinum salts.

Effect on magnetic properties of germanium encapsulated C60 fullerene

NASA Astrophysics Data System (ADS)

Umran, Nibras Mossa; Kumar, Ranjan

2013-02-01

Structural and electronic properties of Gen(n = 1-4) doped C60 fullerene are investigated with ab initio density functional theory calculations by using an efficient computer code, known as SIESTA. The pseudopotentials are constructed using a Trouiller-Martins scheme, to describe the interaction of valence electrons with the atomic cores. In endohedral doped embedding of more germanium atoms complexes we have seen that complexes are stable and thereafter cage break down. We have also investigated that binding energy, electronic affinity increases and magnetic moment oscillating behavior as the number of semiconductor atoms in C60 fullerene goes on increasing.

Mean excitation energies for molecular ions

NASA Astrophysics Data System (ADS)

Jensen, Phillip W. K.; Sauer, Stephan P. A.; Oddershede, Jens; Sabin, John R.

2017-03-01

The essential material constant that determines the bulk of the stopping power of high energy projectiles, the mean excitation energy, is calculated for a range of smaller molecular ions using the RPA method. It is demonstrated that the mean excitation energy of both molecules and atoms increase with ionic charge. However, while the mean excitation energies of atoms also increase with atomic number, the opposite is the case for mean excitation energies for molecules and molecular ions. The origin of these effects is explained by considering the spectral representation of the excited state contributing to the mean excitation energy.

Tunnel ionization of highly excited atoms in a noncoherent laser radiation field

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

Krainov, V.P.; Todirashku, S.S.

1982-10-01

A theory is developed of the ionization of highly excited atomic states by a low-frequency field of noncoherent laser radiation with a large number of modes. Analytic formulas are obtained for the probability of the tunnel ionization in such a field. An analysis is made of the case of the hydrogen atom when the parabolic quantum numbers are sufficiently good in the low-frequency limit, as well as of the case of highly excited states of complex atoms when these states are characterized by a definite orbital momentum and parity. It is concluded that the statistical factor representing the ratio ofmore » the probability in a stochastic field to the probability in a monochromatic field decreases, compared with the case of a short-range potential, if the ''Coulomb tail'' is included. It is shown that at a given field intensity the statistical factor decreases on increase in the principal quantum number of the state being ionized.« less

Structural, electronic and vibrational properties of GexCy (x+y=2-5) nanoclusters: A B3LYP-DFT study

NASA Astrophysics Data System (ADS)

Goswami, Sohini; Saha, Sushmita; Yadav, R. K.

2015-11-01

An ab-initio study of the stability, structural and electronic properties has been made for 84 germanium carbide nanoclusters, GexCy (x+y=2-5). The configuration possessing the maximum value of final binding energy (FBE), among the various configurations corresponding to a fixed x+y=n value, is named as the most stable structure. The vibrational and optical properties have been investigated only for the most stable structures. A B3LYP-DFT/6-311G(3df) method has been employed to optimize fully the geometries of the nanoclusters. The binding energies (BE), highest-occupied and lowest-unoccupied molecular orbital (HOMO-LUMO) gaps have been obtained for all the clusters and the bond lengths have been reported for the most stable clusters. We have considered the zero point energy (ZPE) corrections. The adiabatic and vertical ionization potentials (IPs) and electron affinities (EAs), charge on atoms, dipole moments, vibrational frequencies, infrared intensities (IR Int.), relative infrared intensities (Rel. IR Int.) and Raman scattering activities have also been investigated for the most stable structures. The configurations containing the carbon atoms in majority are seen to be the most stable structures. The strong C-C bond has important role in stabilizing the clusters. For the clusters containing one germanium atom and all the other as carbon atoms, the BE increases monotonically with the number of the carbon atoms. The HOMO-LUMO gap, IPs and EAs fluctuates with increase in the number of atoms. The nanoclusters containing even number of carbon atoms have large HOMO-LUMO gaps and IPs, whereas the nanoclusters containing even number of carbon atoms have small EAs. In general, the adiabatic IP (EA) is smaller (greater) than the vertical IP (EA). The optical absorption spectrum or electron energy loss spectrum (EELS) is unique for every cluster, and may be used to characterize a specific cluster. All the predicted physical quantities are in good agreement with the experimental data wherever available. The growth of these most stable structures should be possible in the experiments.

Atom counting in HAADF STEM using a statistical model-based approach: methodology, possibilities, and inherent limitations.

PubMed

De Backer, A; Martinez, G T; Rosenauer, A; Van Aert, S

2013-11-01

In the present paper, a statistical model-based method to count the number of atoms of monotype crystalline nanostructures from high resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images is discussed in detail together with a thorough study on the possibilities and inherent limitations. In order to count the number of atoms, it is assumed that the total scattered intensity scales with the number of atoms per atom column. These intensities are quantitatively determined using model-based statistical parameter estimation theory. The distribution describing the probability that intensity values are generated by atomic columns containing a specific number of atoms is inferred on the basis of the experimental scattered intensities. Finally, the number of atoms per atom column is quantified using this estimated probability distribution. The number of atom columns available in the observed STEM image, the number of components in the estimated probability distribution, the width of the components of the probability distribution, and the typical shape of a criterion to assess the number of components in the probability distribution directly affect the accuracy and precision with which the number of atoms in a particular atom column can be estimated. It is shown that single atom sensitivity is feasible taking the latter aspects into consideration. © 2013 Elsevier B.V. All rights reserved.

Stability and electronic properties of Gex(BN)y monolayers

NASA Astrophysics Data System (ADS)

Freitas, A.; Machado, L. D.; Tromer, R. M.; Bezerra, C. G.; Azevedo, S.

2017-10-01

In this work, we employ ab initio simulations to propose a new class of monolayers with stoichiometry Gex(BN)y . These monolayers belong to a family of 2D materials combining B, N and group IV atoms, such as BxCyNz and SixByNz . We calculated the formation energy for ten atomic arrangements, and found that it increases when the number of Bsbnd Ge and Nsbnd Ge bonds increases, and decreases when the number of Bsbnd N and Gesbnd Ge bonds increases. We found that the lowest energy monolayer presented a Ge2 BN stoichiometry, and maximized the number of Bsbnd N and Gesbnd Ge bonds. This structure also presented mixed sp2 and sp3 bonds and out-of-plane buckling. Moreover, it remained stable in our ab initio molecular dynamics simulations carried out at T = 300 K. The calculated electronic properties revealed that Gex(BN)y monolayers might present conductor or semiconductor behavior, with band gaps ranging from 0.0 to 0.74 eV, depending on atomic arrangement. Tunable values of band gap can be useful in applications. In optoelectronics, for instance, this property might be employed to control absorbed light wavelengths. Our calculations add a new class of monolayers to the increasing library of 2D materials.

Rydberg interaction induced enhanced excitation in thermal atomic vapor.

PubMed

Kara, Dushmanta; Bhowmick, Arup; Mohapatra, Ashok K

2018-03-27

We present the experimental demonstration of interaction induced enhancement in Rydberg excitation or Rydberg anti-blockade in thermal atomic vapor. We have used optical heterodyne detection technique to measure Rydberg population due to two-photon excitation to the Rydberg state. The anti-blockade peak which doesn't satisfy the two-photon resonant condition is observed along with the usual two-photon resonant peak which can't be explained using the model with non-interacting three-level atomic system. A model involving two interacting atoms is formulated for thermal atomic vapor using the dressed states of three-level atomic system to explain the experimental observations. A non-linear dependence of vapor density is observed for the anti-blockade peak which also increases with increase in principal quantum number of the Rydberg state. A good agreement is found between the experimental observations and the proposed interacting model. Our result implies possible applications towards quantum logic gates using Rydberg anti-blockade in thermal atomic vapor.

Ultra-cold 4He atom beams

NASA Astrophysics Data System (ADS)

Mulders, N.; Wyatt, A. F. G.

1994-02-01

It has been shown that it is possible to create ultra-cold 4He atom beams, using a metal film heater covered with a superfluid helium film. The transient behaviour of the atom pulse can be improved significantly by shaping of the heater pulse. The leading edge of more energetic atoms can be suppressed nearly completely, leaving a core of mono-energetic atoms. The maximum number of atoms in the pulse is determined by the amount of helium in the superfluid film on the heater. This seriously limits the ranges of pulse width and energy over which this beam source can be operated. However, these can be increased significantly by using porous gold smoke heaters.

Photoelectrochemical cells including chalcogenophosphate photoelectrodes

NASA Technical Reports Server (NTRS)

Reichman, B.; Byvik, C. E. (Inventor)

1984-01-01

Photoelectrochemical cells employing chalcogenophosphate (MPX3) photoelectrodes are described where M is selected from the group of transition metal series of elements beginning with scandium (atomic number 21) through germanium (atomic number 32) yttrium (atomic number 39) through antimony (atomic number 51) and lanthanum (atomic number 57) through polonium (atomic number 84); P is phosphorus; and X is selected from the chalogenide series consisting of sulfur, selenium, and tellurium. These compounds have bandgaps in the desirable range from 2.0 eV to 2.2 eV for the photoelectrolysis of water and are stable when used as photoelectrodes for the same.

Shock wave loading of a magnetic guide

NASA Astrophysics Data System (ADS)

Kindt, L.

2011-10-01

The atom laser has long been a holy grail within atom physics and with the creation of an atom laser we hope to bring a similar revolution in to the field of atom optics. With the creation of the Bose-Einstein Condensate (BEC) in 1995 the path to an atom laser was initiated. An atom laser is continues source of BEC. In a Bose condensate all the atoms occupy the same quantum state and can be described by the same wave function and phase. With an atom laser the De Broglie wavelength of atoms can be much smaller than the wavelength of light. Due to the ultimate control over the atoms the atom laser is very interesting for atom optics, lithography, metrology, etching and deposition of atoms on a surface. All previous atom lasers have been created from atoms coupled out from an existing Bose-Einstein Condensate. There are different approaches but common to them all is that the duration of the output of the atom laser is limited by the size of the initial BEC and they all have a low flux. This leaves the quest to build a continuous high flux atom laser. An alternative approach to a continuous BEC beam is to channel a continuous ultra cold atomic beam into a magnetic guide and then cool this beam down to degeneracy. Cooling down a continuous beam of atoms faces three large problems: The collision rate has to be large enough for effective rethermalization, since evaporative cooling in 2D is not as effective as in 3D and a large thermal conductivity due to atoms with a high angular momentum causes heating downstream in the guide. We have built a 4 meter magnetic guide that is placed on a downward slope with a magnetic barrier in the end. In the guide we load packets of ultra cold rubidium atoms with a frequency rate large enough for the packets to merge together to form a continuous atomic beam. The atomic beam is supersonic and when the beam reaches the end barrier it will return and collide with itself. The collisions lowers the velocity of the beam into subsonic velocities and a shock wave is created between the two velocity regions. In order to conserve number of particle, momentum and enthalpy the density of the atomic beam passing through the shock wave must increase. We have build such a shock wave in an atomic beam and observed the density increase due to this. As an extra feature having a subsonic beam on a downward slope adds an extra density increase due to gravitational compression. Loading ultra cold atoms into a 3D trap from the dense subsonic beam overcomes the problem with 2D cooling and thermal conductivity. This was done and evaporative cooling was applied creating an unprecedented large number rubidium BEC.

Adelphi-Goddard emulsified fuel project. [using water/oil emulsions

NASA Technical Reports Server (NTRS)

1977-01-01

Thermal efficiency and particle emissions were studied using water/oil emulsions. These studies were done using number 2 and number 6 fuel oil. The number 6 oil had a sulfur content greater than one percent and experiments were conducted to remove the sulfur dioxide from the stack gases. Test findings include: (1) emulsion effected a reduction in soot at a low excess air levels; (2) a steam atomizing system will produce a water/oil emulsion. The fuel in the study was emulsified in the steam atomization process, hence, pre-emulsification did not yield a dramatic reduction in soot or an increase in thermal efficiency.

Principles determining the structure of high-pressure forms of metals: The structures of cesium(IV) and cesium(V)

PubMed Central

Pauling, Linus

1989-01-01

Consideration of the relation between bond length and bond number and the average atomic volume for different ways of packing atoms leads to the conclusion that the average ligancy of atoms in a metal should increase when a phase change occurs on increasing the pressure. Minimum volume for each value of the ligancy results from triangular coordination polyhedra (with triangular faces), such as the icosahedron and the Friauf polyhedron. Electron transfer may permit atoms of an element to assume different ligancies. Application of these principles to Cs(IV) and Cs(V), which were previously assigned structures with ligancy 8 and 6, respectively, has led to the assignment to Cs(IV) of a primitive cubic unit cell with a = 16.11 Å and with about 122 atoms in the cube and to Cs(V) of a primitive cubic unit cell resembling that of Mg32(Al,Zn)49, with a = 16.97 Å and with 162 atoms in the cube. PMID:16578839

The influence of cavitation in the breakup of liquid free jets

NASA Astrophysics Data System (ADS)

Bode, Juergen

1991-03-01

The interaction between a diesel injection nozzle flow and the atomizing jet was investigated over a wide range of Reynolds numbers. If the pressure gradient towards the centerline of the injection nozzle, generated by the curved streamlines, becomes too large, cavitation occurs at the inlet corner. The cavitation region grows in length and boundary surface with increasing Reynolds number. The instability of the reentry flow causes unsteady fluctuations of the cavitation which influences the breakup of the liquid jet, whereby liquid films are generated which take off from the jet. Cavitation amplifies the mechanism of the atomization, based on the interaction between the jet and surrounding gas. The influence of the cavitation on the atomization is restricted to the region directly behind the nozzle exit. The injection pressure and the temperature of the gas hardly affect the atomization. The jet angle depends mainly on the density of the surrounding gas.

Steady-state entanglement in levitated optomechanical systems coupled to a higher order excited atomic ensemble

NASA Astrophysics Data System (ADS)

Chen, Aixi; Nie, Wenjie; Li, Ling; Zeng, Wei; Liao, Qinghong; Xiao, Xianbo

2017-11-01

We investigate the steady-state entanglement in an optomechanical system with a levitated dielectric nanosphere and a higher order excited atomic ensemble. The single nanosphere is trapped by an external harmonic dipole trap and coupled to the single-mode cavity field by the effective optomechanical coupling, which depends on the steady-state position of the nanosphere. We show that the steady-state optomechanical entanglement can be generated via the effective optomechanical interaction between the mechanical motion and the cavity mode. Further, these exist an optimal effective cavity detuning that maximizes the optomechanical entanglement. We also analyze in detail the influences of the excitation number of atoms, the radius of the nanosphere and the thermal noise strength on the steady-state optomechanical entanglement. It is found that the steady-state entanglement can be enhanced by increasing the excitation number of atoms and the radius of the nanosphere.

The Hyperfine Structure of the Ground State in the Muonic Helium Atoms

NASA Astrophysics Data System (ADS)

Aznabayev, D. T.; Bekbaev, A. K.; Korobov, V. I.

2018-05-01

Non-relativistic ionization energies 3He2+μ-e- and 4He2+μ-e- of helium-muonic atoms are calculated for ground states. The calculations are based on the variational method of the exponential expansion. Convergence of the variational energies is studied by an increasing of a number of the basis functions N. This allows to claim that the obtained energy values have 26 significant digits for ground states. With the obtained results we calculate hyperfine splitting of the muonic helium atoms.

Heavy Atom Vibrational Modes and Low-Energy Vibrational Autodetachment in Nitromethane Anions

NASA Astrophysics Data System (ADS)

Thompson, Michael C.; Baraban, Joshua H.; Stanton, John F.; Weber, J. Mathias

2015-06-01

We use Ar predissociation and vibrational autodetachment below 2100 wn to obtain vibrational spectra of the low-energy modes of nitromethane anion. We interpret the spectra using anharmonic calculations, which reveal strong mode coupling and Fermi resonances. Not surprisingly, the number of evaporated Ar atoms varies with photon energy, and we follow the propensity of evaporating two versus one Ar atoms as photon energy increases. The photodetachment spectrum is discussed in the context of threshold effects and the importance of hot bands.

Drop size distribution and air velocity measurements in air assist swirl atomizer sprays

NASA Technical Reports Server (NTRS)

Mao, C.-P.; Oechsle, V.; Chigier, N.

1987-01-01

Detailed measurements of mean drop size (SMD) and size distribution parameters have been made using a Fraunhofer diffraction particle sizing instrument in a series of sprays generated by an air assist swirl atomizer. Thirty-six different combinations of fuel and air mass flow rates were examined with liquid flow rates up to 14 lbm/hr and atomizing air flow rates up to 10 lbm/hr. Linear relationships were found between SMD and liquid to air mass flow rate ratios. SMD increased with distance downstream along the center line and also with radial distance from the axis. Increase in obscuration with distance downstream was due to an increase in number density of particles as the result of deceleration of drops and an increase in the exposed path length of the laser beam. Velocity components of the atomizing air flow field measured by a laser anemometer show swirling jet air flow fields with solid body rotation in the core and free vortex flow in the outer regions.

Dynamical preparation of Einstein-Podolsky-Rosen entanglement in two-well Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Opanchuk, B.; He, Q. Y.; Reid, M. D.; Drummond, P. D.

2012-08-01

We propose to generate Einstein-Podolsky-Rosen (EPR) entanglement between groups of atoms in a two-well Bose-Einstein condensate using a dynamical process similar to that employed in quantum optics. A local nonlinear S-wave scattering interaction has the effect of creating spin squeezing at each well, while a tunneling coupling, analogous to a beam splitter in optics, introduces an interference between these fields that causes interwell entanglement. We consider two internal modes at each well so that the entanglement can be detected by measuring a reduction in the variances of the sums of local Schwinger spin observables. As is typical of continuous variable (CV) entanglement, the entanglement is predicted to increase with atom number. It becomes sufficiently strong at higher numbers of atoms so that the EPR paradox and steering nonlocality can be realized. The entanglement is predicted using an analytical approach and, for larger atom numbers, using stochastic simulations based on a truncated Wigner function approximation. We find generally that strong tunneling is favorable, and that entanglement persists and is even enhanced in the presence of realistic nonlinear losses.

Semiclassical approach to atomic decoherence by gravitational waves

NASA Astrophysics Data System (ADS)

Quiñones, D. A.; Varcoe, B. T. H.

2018-01-01

A new heuristic model of interaction of an atomic system with a gravitational wave (GW) is proposed. In it, the GW alters the local electromagnetic field of the atomic nucleus, as perceived by the electron, changing the state of the system. The spectral decomposition of the wave function is calculated, from which the energy is obtained. The results suggest a shift in the difference of the atomic energy levels, which will induce a small detuning to a resonant transition. The detuning increases with the quantum numbers of the levels, making the effect more prominent for Rydberg states. We performed calculations on the Rabi oscillations of atomic transitions, estimating how they would vary as a result of the proposed effect.

Influence of average ion energy and atomic oxygen flux per Si atom on the formation of silicon oxide permeation barrier coatings on PET

NASA Astrophysics Data System (ADS)

Mitschker, F.; Wißing, J.; Hoppe, Ch; de los Arcos, T.; Grundmeier, G.; Awakowicz, P.

2018-04-01

The respective effect of average incorporated ion energy and impinging atomic oxygen flux on the deposition of silicon oxide (SiO x ) barrier coatings for polymers is studied in a microwave driven low pressure discharge with additional variable RF bias. Under consideration of plasma parameters, bias voltage, film density, chemical composition and particle fluxes, both are determined relative to the effective flux of Si atoms contributing to film growth. Subsequently, a correlation with barrier performance and chemical structure is achieved by measuring the oxygen transmission rate (OTR) and by performing x-ray photoelectron spectroscopy. It is observed that an increase in incorporated energy to 160 eV per deposited Si atom result in an enhanced cross-linking of the SiO x network and, therefore, an improved barrier performance by almost two orders of magnitude. Furthermore, independently increasing the number of oxygen atoms to 10 500 per deposited Si atom also lead to a comparable barrier improvement by an enhanced cross-linking.

Exciton-dominated dielectric function of atomically thin MoS 2 films

DOE PAGES

Yu, Yiling; Yu, Yifei; Cai, Yongqing; ...

2015-11-24

We systematically measure the dielectric function of atomically thin MoS 2 films with different layer numbers and demonstrate that excitonic effects play a dominant role in the dielectric function when the films are less than 5–7 layers thick. The dielectric function shows an anomalous dependence on the layer number. It decreases with the layer number increasing when the films are less than 5–7 layers thick but turns to increase with the layer number for thicker films. We show that this is because the excitonic effect is very strong in the thin MoS 2 films and its contribution to the dielectricmore » function may dominate over the contribution of the band structure. We also extract the value of layer-dependent exciton binding energy and Bohr radius in the films by fitting the experimental results with an intuitive model. The dominance of excitonic effects is in stark contrast with what reported at conventional materials whose dielectric functions are usually dictated by band structures. Lastly, the knowledge of the dielectric function may enable capabilities to engineer the light-matter interactions of atomically thin MoS 2 films for the development of novel photonic devices, such as metamaterials, waveguides, light absorbers, and light emitters.« less

Atomic weights of the elements--Review 2000 (IUPAC Technical Report)

USGS Publications Warehouse

de Laeter, John R.; Böhlke, John Karl; De Bièvre, P.; Hidaka, H.; Peiser, H.S.; Rosman, K.J.R.; Taylor, P.D.P.

2003-01-01

A consistent set of internationally accepted atomic weights has long been an essential aim of the scientific community because of the relevance of these values to science and technology, as well as to trade and commerce subject to ethical, legal, and international standards. The standard atomic weights of the elements are regularly evaluated, recommended, and published in updated tables by the Commission on Atomic Weights and Isotopic Abundances (CAWIA) of the International Union of Pure and Applied Chemistry (IUPAC). These values are invariably associated with carefully evaluated uncertainties. Atomic weights were originally determined by mass ratio measurements coupled with an understanding of chemical stoichiometry, but are now based almost exclusively on knowledge of the isotopic composition (derived from isotope-abundance ratio measurements) and the atomic masses of the isotopes of the elements. Atomic weights and atomic masses are now scaled to a numerical value of exactly 12 for the mass of the carbon isotope of mass number 12. Technological advances in mass spectrometry and nuclear-reaction energies have enabled atomic masses to be determined with a relative uncertainty of better than 1 ×10−7 . Isotope abundances for an increasing number of elements can be measured to better than 1 ×10−3 . The excellent precision of such measurements led to the discovery that many elements, in different specimens, display significant variations in their isotope-abundance ratios, caused by a variety of natural and industrial physicochemical processes. While such variations increasingly place a constraint on the uncertainties with which some standard atomic weights can be stated, they provide numerous opportunities for investigating a range of important phenomena in physical, chemical, cosmological, biological, and industrial processes. This review reflects the current and increasing interest of science in the measured differences between source-specific and even sample-specific atomic weights. These relative comparisons can often be made with a smaller uncertainty than is achieved in the best calibrated “absolute ” (=SI-traceable) atomic-weight determinations. Accurate determinations of the atomic weights of certain elements also influence the values of fundamental constants such as the Avogadro, Faraday, and universal gas constants. This review is in two parts: the first summarizes the development of the science of atomic-weight determinations during the 20th century; the second summarizes the changes and variations that have been recognized in the values and uncertainties of atomic weights, on an element-by-element basis, in the latter part of the 20th century.

Atomic level structural modulation during the structural relaxation and its effect on magnetic properties of Fe81Si4B10P4Cu1 nanocrystalline alloy

NASA Astrophysics Data System (ADS)

Cao, C. C.; Zhu, L.; Meng, Y.; Zhai, X. B.; Wang, Y. G.

2018-06-01

The evolution of local structure and defects in the Fe81Si4B10P4Cu1 amorphous alloy during the structural relaxation has been investigated by Mössbauer spectroscopy, positron annihilation lifetime spectroscopy and transmission electron microscopy to explore their effects on magnetic properties of the nanocrystalline. The atomic rearrangements at the early stage of the structural relaxation cause the density increase of the amorphous matrix, but the subsequent atomic rearrangements contribute to the transformation of Fe3B-like atomic arrangements to FeB-like ones with the temperature increasing. As the structural relaxation processes, the released Fe atoms both from Fe3B- and Fe3P-like atomic arrangements result in the formation of new Fe clusters and the increase of Fe-Fe coordination number in the existing Fe clusters and the nucleation sites for α-Fe gradually increase, both of which promote the crystallization. However, the homogeneity of amorphous matrix will be finally destroyed under excessive relaxation temperature, which coarsens nanograins during the crystallization instead. Therefore, soft magnetic properties of the Fe81Si4B10P4Cu1 nanocrystalline alloy can be improved by pre-annealing the amorphous precursor at an appropriate temperature due to the atomic level structural optimization.

Positive column of a glow discharge in neon with charged dust grains (a review)

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

Polyakov, D. N., E-mail: cryolab@ihed.ras.ru; Shumova, V. V.; Vasilyak, L. M.

The effect of charged micron-size dust grains (microparticles) on the electric parameters of the positive column of a low-pressure dc glow discharge in neon has been studied experimentally and numerically. Numerical analysis is carried out in the diffusion-drift approximation with allowance for the interaction of dust grains with metastable neon atoms. In a discharge with a dust grain cloud, the longitudinal electric field increases. As the number density of dust grains in an axisymmetric cylindrical dust cloud rises, the growth of the electric field saturates. It is shown that the contribution of metastable atoms to ionization is higher in amore » discharge with dust grains, in spite of the quenching of metastable atoms on dust grains. The processes of charging of dust grains and the dust cloud are considered. As the number density of dust grains rises, their charge decreases, while the space charge of the dust cloud increases. The results obtained can be used in plasma technologies involving microparticles.« less

Magneto-optical trap for thulium atoms

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

Sukachev, D.; Sokolov, A.; Chebakov, K.

2010-07-15

Thulium atoms are trapped in a magneto-optical trap using a strong transition at 410 nm with a small branching ratio. We trap up to 7x10{sup 4} atoms at a temperature of 0.8(2) mK after deceleration in a 40-cm-long Zeeman slower. Optical leaks from the cooling cycle influence the lifetime of atoms in the magneto-optical trap which varies between 0.3 and 1.5 s in our experiments. The lower limit for the leaking rate from the upper cooling level is measured to be 22(6) s{sup -1}. The repumping laser transferring the atomic population out of the F=3 hyperfine ground-state sublevel gives amore » 30% increase for the lifetime and the number of atoms in the trap.« less

Large-scale quantum transport calculations for electronic devices with over ten thousand atoms

NASA Astrophysics Data System (ADS)

Lu, Wenchang; Lu, Yan; Xiao, Zhongcan; Hodak, Miro; Briggs, Emil; Bernholc, Jerry

The non-equilibrium Green's function method (NEGF) has been implemented in our massively parallel DFT software, the real space multigrid (RMG) code suite. Our implementation employs multi-level parallelization strategies and fully utilizes both multi-core CPUs and GPU accelerators. Since the cost of the calculations increases dramatically with the number of orbitals, an optimal basis set is crucial for including a large number of atoms in the ``active device'' part of the simulations. In our implementation, the localized orbitals are separately optimized for each principal layer of the device region, in order to obtain an accurate and optimal basis set. As a large example, we calculated the transmission characteristics of a Si nanowire p-n junction. The nanowire is along (110) direction in order to minimize the number dangling bonds that are saturated by H atoms. Its diameter is 3 nm. The length of 24 nm is necessary because of the long-range screening length in Si. Our calculations clearly show the I-V characteristics of a diode, i.e., the current increases exponentially with forward bias and is near zero with backward bias. Other examples will also be presented, including three-terminal transistors and large sensor structures.

The Nonlinear Jaynes-Cummings Model for the Multiphoton Transition

NASA Astrophysics Data System (ADS)

Liu, Xiao-Jing; Lu, Jing-Bin; Zhang, Si-Qi; Liu, Ji-Ping; Li, Hong; Liang, Yu; Ma, Ji; Weng, Yi-Jiao; Zhang, Qi-Rui; Liu, Han; Zhang, Xiao-Ru; Wu, Xiang-Yao

2018-01-01

With the nonlinear Jaynes-Cummings model, we have studied the atom and light field quantum entanglement of multiphoton transition in nonlinear medium, and researched the effect of the transition photon number N and the nonlinear coefficient χ on the quantum entanglement degrees. We have given the quantum entanglement degrees curves with time evolution, we find when the transition photon number N increases, the entanglement degrees oscillation get faster. When the nonlinear coefficient α > 0, the entanglement degrees oscillation get quickly, the nonlinear term is disadvantage of the atom and light field entanglement, and when the nonlinear coefficient α < 0, the entanglement degrees oscillation get slow, the nonlinear term is advantage of the atom and light field entanglement. These results will have been used in the quantum communication and quantum information.

Energy dependence of radiation interaction parameters of some organic compounds

NASA Astrophysics Data System (ADS)

Singh, Mohinder; Tondon, Akash; Sandhu, B. S.; Singh, Bhajan

2018-04-01

Gamma rays interact with a material through photoelectric absorption, Compton scattering, Rayleigh scattering and Pair production in the intermediate energy range. The probability of occurrence of a particular type of process depends on the energy of incident gamma rays, atomic number of the material, scattering angle and geometrical conditions. Various radiological parameters for organic compounds, namely ethylene glycol (C2H6O2), propylene glycol (C3H8O2), glycerin (C3H8O3), isoamyl alcohol (C5H12O), butanone (C4H8O), acetophenone (C8H8O2), cyclohexanone (C6H10O), furfural (C5H4O2), benzaldehyde (C7H6O), cinnamaldehyde (C9H8O), glutaraldehyde (C5H8O2), aniline (C6H7N), benzyl amine (C6H7N), nitrobenzene (C6H5NO2), ethyl benzene (C8H10), ethyl formate (C3H6O2) and water (H2O) are presented at 81, 122, 356 and 511 keV energies employing NaI(Tl) scintillation detector in narrow-beam transmission geometry. The radiation interaction parameters such as mass attenuation, molar extinction and mass energy absorption coefficients, half value layer, total atomic and effective electronic cross-sections and CT number have been evaluated for these organic compounds. The general trend of values of mass attenuation coefficients, half value layer, molar extinction coefficients, total atomic and effective electronic cross-sections and mass energy absorption coefficients shows a decrease with increase in incident gamma photon energy. The values of CT number are found to increases linearly with increase of effective atomic number (Zeff). The variation in CT number around Zeff ≈ 3.3 shows the peak like structure with respect to water and the correlation between CT number and linear attenuation coefficient is about 0.99. Appropriate equations are fitted to these experimentally determined parameters for the organic compounds at incident photon energy ranging from 81 keV to 511 keV used in the present study. Experimental values are compared with the theoretical data obtained using WinXcom software package, and are found in good agreement.

Preparation of Ultracold Atom Clouds at the Shot Noise Level.

PubMed

Gajdacz, M; Hilliard, A J; Kristensen, M A; Pedersen, P L; Klempt, C; Arlt, J J; Sherson, J F

2016-08-12

We prepare number stabilized ultracold atom clouds through the real-time analysis of nondestructive images and the application of feedback. In our experiments, the atom number N∼10^{6} is determined by high precision Faraday imaging with uncertainty ΔN below the shot noise level, i.e., ΔN

Related Structure Characters and Stability of Structural Defects in a Metallic Glass

PubMed Central

Niu, Xiaofeng; Feng, Shidong; Pan, Shaopeng

2018-01-01

Structural defects were investigated by a recently proposed structural parameter, quasi-nearest atom (QNA), in a modeled Zr50Cu50 metallic glass through molecular dynamics simulations. More QNAs around an atom usually means that more defects are located near the atom. Structural analysis reveals that the spatial distribution of the numbers of QNAs displays to be clearly heterogeneous. Furthermore, QNA is closely correlated with cluster connections, especially four-atom cluster connections. Atoms with larger coordination numbers usually have less QNAs. When two atoms have the same coordination number, the atom with larger five-fold symmetry has less QNAs. The number of QNAs around an atom changes rather frequently and the change of QNAs might be correlated with the fast relaxation metallic glasses. PMID:29565298

Factors driving stable growth of He clusters in W: first-principles study

NASA Astrophysics Data System (ADS)

Feng, Y. J.; Xin, T. Y.; Xu, Q.; Wang, Y. X.

2018-07-01

The evolution of helium (He) bubbles is responsible for the surface morphology variation and subsequent degradation of the properties of plasma-facing materials (PFMs) in nuclear fusion reactors. These severe problems unquestionably trace back to the behavior of He in PFMs, which is closely associated with the interaction between He and the matrix. In this paper, we decomposed the binding energy of the He cluster into three parts, those from W–W, W–He, and He–He interactions, using density functional theory. As a result, we clearly identified the main factors that determine a steplike decrease in the binding energy with increasing number of He atoms, which explains the process of self-trapping and athermal vacancy generation during He cluster growth in the PFM tungsten. The three interactions were found to synergetically shape the features of the steplike decrease in the binding energy. Fairly strong He–He repulsive forces at a short distance, which stem from antibonding states between He atoms, need to be released when additional He atoms are continuously bonded to the He cluster. This causes the steplike feature in the binding energy. The bonding states between W and He atoms in principle facilitate the decreasing trend of the binding energy. The decrease in binding energy with increasing number of He atoms implies that He clusters can grow stably.

Fine structure of the K X-ray absorption spectra of titanium in some hydrides, borides, and silicides (in Russian)

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

Vainshtein, �. E.; Zhurakovskii, E. A.

1959-08-01

X-ray spectral analyses confirmed the hypothesis on the metal-like state of hydrogen in tithnium hydrides. Experiments with titunium borides and silicides indicate the special character and degree of the 3d--level participation in the metallic'' bond between the atoms of various complexes. The structure of metalloid elements becomes more complicated with an increase in the specific number of boron and silicon atoms and the bond between the atoms tends to become covalent. (R.V.J.)

Effective atomic numbers of some tissue substitutes by different methods: A comparative study.

PubMed

Singh, Vishwanath P; Badiger, N M

2014-01-01

Effective atomic numbers of some human organ tissue substitutes such as polyethylene terephthalate, red articulation wax, paraffin 1, paraffin 2, bolus, pitch, polyphenylene sulfide, polysulfone, polyvinylchloride, and modeling clay have been calculated by four different methods like Auto-Zeff, direct, interpolation, and power law. It was found that the effective atomic numbers computed by Auto-Zeff, direct and interpolation methods were in good agreement for intermediate energy region (0.1 MeV < E < 5 MeV) where the Compton interaction dominates. A large difference in effective atomic numbers by direct method and Auto-Zeff was observed in photo-electric and pair-production regions. Effective atomic numbers computed by power law were found to be close to direct method in photo-electric absorption region. The Auto-Zeff, direct and interpolation methods were found to be in good agreement for computation of effective atomic numbers in intermediate energy region (100 keV < E < 10 MeV). The direct method was found to be appropriate method for computation of effective atomic numbers in photo-electric region (10 keV < E < 100 keV). The tissue equivalence of the tissue substitutes is possible to represent by any method for computation of effective atomic number mentioned in the present study. An accurate estimation of Rayleigh scattering is required to eliminate effect of molecular, chemical, or crystalline environment of the atom for estimation of gamma interaction parameters.

Effective atomic numbers of some tissue substitutes by different methods: A comparative study

PubMed Central

Singh, Vishwanath P.; Badiger, N. M.

2014-01-01

Effective atomic numbers of some human organ tissue substitutes such as polyethylene terephthalate, red articulation wax, paraffin 1, paraffin 2, bolus, pitch, polyphenylene sulfide, polysulfone, polyvinylchloride, and modeling clay have been calculated by four different methods like Auto-Zeff, direct, interpolation, and power law. It was found that the effective atomic numbers computed by Auto-Zeff, direct and interpolation methods were in good agreement for intermediate energy region (0.1 MeV < E < 5 MeV) where the Compton interaction dominates. A large difference in effective atomic numbers by direct method and Auto-Zeff was observed in photo-electric and pair-production regions. Effective atomic numbers computed by power law were found to be close to direct method in photo-electric absorption region. The Auto-Zeff, direct and interpolation methods were found to be in good agreement for computation of effective atomic numbers in intermediate energy region (100 keV < E < 10 MeV). The direct method was found to be appropriate method for computation of effective atomic numbers in photo-electric region (10 keV < E < 100 keV). The tissue equivalence of the tissue substitutes is possible to represent by any method for computation of effective atomic number mentioned in the present study. An accurate estimation of Rayleigh scattering is required to eliminate effect of molecular, chemical, or crystalline environment of the atom for estimation of gamma interaction parameters. PMID:24600169

Sulphurisation of homohopanoids: Effects on carbon number distribution, speciation, and 22 S/22 R epimer ratios

NASA Astrophysics Data System (ADS)

Köster, Jürgen; Van Kaam-Peters, Heidy M. E.; Koopmans, Martin P.; De Leeuw, Jan W.; Sinninghe Damsté, Jaap S.

1997-06-01

Sulphurisation has been recognised as the most important diagenetic pathway acting on hopanoids in the organic-rich limestones, marlstone, and dolomite investigated. The qualitative and quantitative analysis of free and S-bound hopanoid moieties revealed that the incorporation of sulphur has a major impact on the carbon number distribution, the speciation and on the 22 S/(22S+22 R) ratio of the hopanoids. C 35 carbon skeletons are preferentially preserved by sulphur incorporation at the end of the side chain. Hopanoid sulphides, with the sulphur atom attached to one carbon atom of ring D or E and to one carbon atom of the side chain (condensed-type), are predominantly formed from precursors with a partially degraded side chain. In all samples the degree of sulphurisation of hopanoids increases with increasing carbon number. The carbon skeleton speciation changes with maturation in favour of hopanoid thiophenes, which are evidently the most stable hopanoid sulphur compounds, and hopanes. Hopanes are mainly formed via a sulphurisation/desulphurisation pathway and increase in concentration with maturity. Their original carbon number distribution is strongly shifted towards the lower homologues. With increasing maturity only a slight dominance of the C 35 members emerges. The most abundant series of condensed-type hopanoid sulphides have a 22R homohopane carbon skeleton that is not isomerised during maturation. The generation of hopanes from these condensed-type hopanoid sulphides during maturation leads to 22 S/(22S+22 R) ratios which increase with carbon number (e.g., from about 0.2 for C 31 to 0.5 for C 35 homologues). Data acquired from the sedimentary rock samples are supported by those obtained from artificial maturation experiments of a limestone by hydrous pyrolysis at different temperatures. The data show that generally accepted molecular maturation parameters have to be applied with caution.

Homoepitaxial growth of non-polar AlN crystals using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Leathersich, Jeff; Suvarna, Puneet; Tungare, Mihir; Shahedipour-Sandvik, F. (Shadi)

2013-11-01

Homoepitaxial growth of AlN on (11-20) a-plane and (1-100) m-plane under varying deposition temperatures and aluminum to nitrogen flux ratios was carried out using molecular dynamics (MD) simulations with a Tersoff based interatomic potential. The results indicate that much thicker overgrown films are obtained on m-plane as compared to the a-plane, for the same temperature, N:Al flux, and number of precursor atoms. Crystallinity of the depositions improves as the temperature is increased above 1000 K, accompanied with a better stoichiometry due to increased adatom mobility. Improvement in crystal quality with a N:Al ratio greater than 1 is seen because N atoms desorb more easily than Al atoms. Increasing the N:Al ratio too high limits Al adatom mobility as well as causes site blocking for Al atoms and degrades the deposition quality. The optimum value for N:Al flux ratio was found to be between 1.2 and 1.8 for the deposition temperatures tested based on crystallinity and stoichiometry.

Core-dependent and ligand-dependent relativistic corrections to the nuclear magnetic shieldings in MH4-n Y n (n = 0-4; M = Si, Ge, Sn, and Y = H, F, Cl, Br, I) model compounds.

PubMed

Maldonado, Alejandro F; Aucar, Gustavo A; Melo, Juan I

2014-09-01

The nuclear magnetic shieldings of Si, Ge, and Sn in MH(4-n) Y(n) (M = Si, Ge, Sn; Y = F, Cl, Br, I and n = 1-4) molecular systems are highly influenced by the substitution of one or more hydrogens by heavy-halogen atoms. We applied the linear response elimination of small components (LRESC) formalism to calculate those shieldings and learn whether including only a few of the leading relativistic correction terms is sufficient to be able to quantitatively reproduce the full relativistic value. It was observed that the nuclear magnetic shieldings change as the number of heavy halogen substituents and their weights vary, and the pattern of σ(M) generally does not exhibit the normal halogen dependence (NHD) behavior that can be seen in similar molecular systems containing carbon atoms. We also analyzed each relativistic correction afforded by the LRESC method and split them in two: core-dependent and ligand-dependent contributions; we then looked for the electronic mechanisms involved in the different relativistic effects and in the total relativistic value. Based on this analysis, we were able to study the electronic mechanism involved in a recently proposed relativistic effect, the "heavy atom effect on vicinal heavy atom" (HAVHA), in more detail. We found that the main electronic mechanism is the spin-orbit or σ p (T(3)) correction, although other corrections such as σ p (S(1)) and σ p (S(3)) are also important. Finally, we analyzed proton magnetic shieldings and found that, for molecules containing Sn as the central atom, σ(H) decreases as the number of heavy halogen substituents (of the same type: either F, Cl, or Br) increases, albeit at different rates for different halogens. σ(H) only increase as the number of halogen substituents increases if the halogen is iodine.

Autocorrelation descriptor improvements for QSAR: 2DA_Sign and 3DA_Sign

NASA Astrophysics Data System (ADS)

Sliwoski, Gregory; Mendenhall, Jeffrey; Meiler, Jens

2016-03-01

Quantitative structure-activity relationship (QSAR) is a branch of computer aided drug discovery that relates chemical structures to biological activity. Two well established and related QSAR descriptors are two- and three-dimensional autocorrelation (2DA and 3DA). These descriptors encode the relative position of atoms or atom properties by calculating the separation between atom pairs in terms of number of bonds (2DA) or Euclidean distance (3DA). The sums of all values computed for a given small molecule are collected in a histogram. Atom properties can be added with a coefficient that is the product of atom properties for each pair. This procedure can lead to information loss when signed atom properties are considered such as partial charge. For example, the product of two positive charges is indistinguishable from the product of two equivalent negative charges. In this paper, we present variations of 2DA and 3DA called 2DA_Sign and 3DA_Sign that avoid information loss by splitting unique sign pairs into individual histograms. We evaluate these variations with models trained on nine datasets spanning a range of drug target classes. Both 2DA_Sign and 3DA_Sign significantly increase model performance across all datasets when compared with traditional 2DA and 3DA. Lastly, we find that limiting 3DA_Sign to maximum atom pair distances of 6 Å instead of 12 Å further increases model performance, suggesting that conformational flexibility may hinder performance with longer 3DA descriptors. Consistent with this finding, limiting the number of bonds in 2DA_Sign from 11 to 5 fails to improve performance.

Comparison of rescue and relief activities within 72 hours of the atomic bombings in Hiroshima and Nagasaki.

PubMed

Matsunari, Yuko; Yoshimoto, Nao

2013-12-01

To clarify the factors and reasons for the differences in the outcomes of rescue and relief efforts in Hiroshima and Nagasaki, mainly focusing on the numbers of rescue/relief staffs and casualties in the period within 72 hours of the atomic bombings in August 1945. By retrieving the data and information from the records and reports concerning the disasters in the two cities, together with other publications as to the damages by the atomic bombings and subsequent rescue-relief activities, and restoration activities. It seems that there was less damage in Nagasaki, where a stronger atomic bomb was used than in Hiroshima. There were crucial geographic factors that led to the different effects in terms of the numbers of victims; however, systematic organization and mobilization of rescue and relief staffs, maintenance of functional transportation, and advanced medical knowledge and public warning with regard to disaster all may have contributed to a lower death toll and increase in survivors in Nagasaki.

Determination of the number density of excited and ground Zn atoms during rf magnetron sputtering of ZnO target

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

Maaloul, L.; Gangwar, R. K.; Stafford, L., E-mail: luc.stafford@umontreal.ca

2015-07-15

A combination of optical absorption spectroscopy (OAS) and optical emission spectroscopy measurements was used to monitor the number density of Zn atoms in excited 4s4p ({sup 3}P{sub 2} and {sup 3}P{sub 0}) metastable states as well as in ground 4s{sup 2} ({sup 1}S{sub 0}) state in a 5 mTorr Ar radio-frequency (RF) magnetron sputtering plasma used for the deposition of ZnO-based thin films. OAS measurements revealed an increase by about one order of magnitude of Zn {sup 3}P{sub 2} and {sup 3}P{sub 0} metastable atoms by varying the self-bias voltage on the ZnO target from −115 to −300 V. Over themore » whole range of experimental conditions investigated, the triplet-to-singlet metastable density ratio was 5 ± 1, which matches the statistical weight ratio of these states in Boltzmann equilibrium. Construction of a Boltzmann plot using all Zn I emission lines in the 200–500 nm revealed a constant excitation temperature of 0.33 ± 0.04 eV. In combination with measured populations of Zn {sup 3}P{sub 2} and {sup 3}P{sub 0} metastable atoms, this temperature was used to extrapolate the absolute number density of ground state Zn atoms. The results were found to be in excellent agreement with those obtained previously by actinometry on Zn atoms using Ar as the actinometer gas [L. Maaloul and L. Stafford, J. Vac. Sci. Technol., A 31, 061306 (2013)]. This set of data was then correlated to spectroscopic ellipsometry measurements of the deposition rate of Zn atoms on a Si substrate positioned at 12 cm away from the ZnO target. The deposition rate scaled linearly with the number density of Zn atoms. In sharp contrast with previous studies on RF magnetron sputtering of Cu targets, these findings indicate that metastable atoms play a negligible role on the plasma deposition dynamics of Zn-based coatings.« less

Molecular dynamics simulation of melting of 2D glassy monatomic system

NASA Astrophysics Data System (ADS)

Nhu Tranh, Duong Thi; Van Hoang, Vo; Thu Hanh, Tran Thi

2018-01-01

The melting of two-dimensional (2D) glassy monatomic systems is studied using the molecular dynamics simulation with Lennard-Jones-Gauss interaction potential. The temperature dependence of various structural and dynamical properties of the systems during heating is analyzed and discussed via the radial distribution functions, the coordination number distributions, the ring statistics, the mobility of atoms and their clustering. Atomic mechanism of melting is also analyzed via tendency to increase mobility and breaking clusters of atoms upon heating. We found that melting of a 2D glass does not follow any theory of the melting of 2D crystals proposed in the past. The melting exhibits a homogeneous nature, i.e. liquid-like atoms occur homogeneously throughout the system and melting proceeds further leading to the formation of an entire liquid phase. In addition, we found a defined transition temperature region in which structural and dynamical properties of systems strongly change with increasing temperature.

Thin film deposition using rarefied gas jet

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2017-01-01

The rarefied gas jet of aluminium is studied at Mach number Ma =(U_j /√{ kbTj / m }) in the range .01

Shallow doping effect of ZnO treatment using atomic layer deposition process on p-type In0.53Ga0.47As

NASA Astrophysics Data System (ADS)

Lee, Changmin; An, Youngseo; Choi, Sungho; Kim, Hyoungsub

2018-06-01

The number of atomic layer deposition (ALD) cycles for ZnO treatment was changed to study its merits and demerits as a passivation layer prior to the deposition of a HfO2 film on a p-type In0.53Ga0.47As substrate. Even a few cycles of ZnO ALD treatment was effective in improving the capacitance–voltage (C–V) characteristics by suppressing strong Fermi-level pinning, which occurred because of a high interface state density near the lower half of the In0.53Ga0.47As band gap. Increases in the number of ZnO ALD cycles induced an increase in the minimum capacitance and response of minority carriers at higher frequencies in the inversion region of the C–V characteristics. According to various temperature- and frequency-dependent C–V analyses, these changes were explained by the shallow p-type doping effect of Zn atoms in the In0.53Ga0.47As substrate. As a disadvantage, ZnO ALD treatment caused a slight increase in the dielectric leakage current.

Strengthened PAN-based carbon fibers obtained by slow heating rate carbonization.

PubMed

Kim, Min-A; Jang, Dawon; Tejima, Syogo; Cruz-Silva, Rodolfo; Joh, Han-Ik; Kim, Hwan Chul; Lee, Sungho; Endo, Morinobu

2016-03-23

Large efforts have been made over the last 40 years to increase the mechanical strength of polyacrylonitrile (PAN)-based carbon fibers (CFs) using a variety of chemical or physical protocols. In this paper, we report a new method to increase CFs mechanical strength using a slow heating rate during the carbonization process. This new approach increases both the carbon sp(3) bonding and the number of nitrogen atoms with quaternary bonding in the hexagonal carbon network. Theoretical calculations support a crosslinking model promoted by the interstitial carbon atoms located in the graphitic interlayer spaces. The improvement in mechanical performance by a controlled crosslinking between the carbon hexagonal layers of the PAN based CFs is a new concept that can contribute further in the tailoring of CFs performance based on the understanding of their microstructure down to the atomic scale.

STIR-Physics: Cold Atoms and Nanocrystals in Tapered Nanofiber and High-Q Resonator Potentials

DTIC Science & Technology

2016-11-02

STIR- Physics : Cold Atoms and Nanocrystals in Tapered Nanofiber and High-Q Resonator Potentials We worked on a tapered fiber in cold atomic cloud...reviewed journals: Number of Papers published in non peer-reviewed journals: Final Report: STIR- Physics : Cold Atoms and Nanocrystals in Tapered Nanofiber...other than abstracts): Number of Peer-Reviewed Conference Proceeding publications (other than abstracts): Books Number of Manuscripts: 0.00Number of

Empirical model of atomic nitrogen in the upper thermosphere

NASA Technical Reports Server (NTRS)

Engebretson, M. J.; Mauersberger, K.; Kayser, D. C.; Potter, W. E.; Nier, A. O.

1977-01-01

Atomic nitrogen number densities in the upper thermosphere measured by the open source neutral mass spectrometer (OSS) on Atmosphere Explorer-C during 1974 and part of 1975 have been used to construct a global empirical model at an altitude of 375 km based on a spherical harmonic expansion. The most evident features of the model are large diurnal and seasonal variations of atomic nitrogen and only a moderate and latitude-dependent density increase during periods of geomagnetic activity. Maximum and minimum N number densities at 375 km for periods of low solar activity are 3.6 x 10 to the 6th/cu cm at 1500 LST (local solar time) and low latitude in the summer hemisphere and 1.5 x 10 to the 5th/cu cm at 0200 LST at mid-latitudes in the winter hemisphere.

Atomic structure of water/Au, Ag, Cu and Pt atomic junctions.

PubMed

Li, Yu; Kaneko, Satoshi; Fujii, Shintaro; Nishino, Tomoaki; Kiguchi, Manabu

2017-02-08

Much progress has been made in understanding the transport properties of atomic-scale conductors. We prepared atomic-scale metal contacts of Cu, Ag, Au and Pt using a mechanically controllable break junction method at 10 K in a cryogenic vacuum. Water molecules were exposed to the metal atomic contacts and the effect of molecular adsorption was investigated by electronic conductance measurements. Statistical analysis of the electronic conductance showed that the water molecule(s) interacted with the surface of the inert Au contact and the reactive Cu ant Pt contacts, where molecular adsorption decreased the electronic conductance. A clear conductance signature of water adsorption was not apparent at the Ag contact. Detailed analysis of the conductance behaviour during a contact-stretching process indicated that metal atomic wires were formed for the Au and Pt contacts. The formation of an Au atomic wire consisting of low coordination number atoms leads to increased reactivity of the inert Au surface towards the adsorption of water.

Enhanced Kinetics of Electrochemical Hydrogen Uptake and Release by Palladium Powders Modified by Electrochemical Atomic Layer Deposition

DOE PAGES

Benson, David M.; Tsang, Chu F.; Sugar, Joshua Daniel; ...

2017-04-28

One method for the formation of nanofilms of materials, is Electrochemical atomic layer deposition (E-ALD), one atomic layer at a time. It uses the galvanic exchange of a less noble metal, deposited using underpotential deposition (UPD), to produce an atomic layer of a more noble element by reduction of its ions. This process is referred to as surface limited redox replacement and can be repeated in a cycle to grow thicker deposits. Previously, we performed it on nanoparticles and planar substrates. In the present report, E-ALD is applied for coating a submicron-sized powder substrate, making use of a new flowmore » cell design. E-ALD is used to coat a Pd powder substrate with different thicknesses of Rh by exchanging it for Cu UPD. Furthermore, cyclic voltammetry and X-ray photoelectron spectroscopy indicate an increasing Rh coverage with increasing numbers of deposition cycles performed, in a manner consistent with the atomic layer deposition (ALD) mechanism. Cyclic voltammetry also indicated increased kinetics of H sorption and desorption in and out of the Pd powder with Rh present, relative to unmodified Pd.« less

Combustor exhaust-emissions and blowout-limits with diesel number 2 and Jet A fuels utilizing air-atomizing and pressure-atomizing nozzles

NASA Technical Reports Server (NTRS)

Ingebo, R. D.; Norgren, C. T.

1975-01-01

The effect of fuel properties on exhaust emissions and blowout limits of a high-pressure combustor segment is evaluated using a splash-groove air-atomizing fuel injector and a pressure-atomizing simplex fuel nozzle to burn both diesel number 2 and Jet A fuels. Exhaust emissions and blowout data are obtained and compared on the basis of the aromatic content and volatility of the two fuels. Exhaust smoke number and emission indices for oxides of nitrogen, carbon monoxide, and unburned hydrocarbons are determined for comparison. As compared to the pressure-atomizing nozzle, the air-atomizing nozzle is found to reduce nitrogen oxides by 20%, smoke number by 30%, carbon monoxide by 70%, and unburned hydrocarbons by 50% when used with diesel number 2 fuel. The higher concentration of aromatics and lower volatility of diesel number 2 fuel as compared to Jet A fuel appears to have the most detrimental effect on exhaust emissions. Smoke number and unburned hydrocarbons are twice as high with diesel number 2 as with Jet A fuel.

Progress towards a cesium atomic fountain clock

NASA Astrophysics Data System (ADS)

Klipstein, William M.; Raithel, Georg A.; Rolston, Steven L.; Phillips, William D.; Ekstrom, Christopher R.

1997-04-01

We have been developing a fountain of laser--cooled cesium atoms for use as an atomic clock. Our design largely follows that of the fountain built at LPTF in Paris. In our fountain, chirp--slowed atoms are first collected in a Magneto--Optic Trap (MOT) and then cooled to a few μK in optical molasses. The cooled atoms are then launched vertically into a "moving molasses" by shifting the frequencies of the vertical cooling beams. The atoms then travel through a microwave cavity tuned to the 9.2 GHz cesium hyperfine frequency for a first Ramsey pulse. After roughly 0.5 seconds of free flight under the influence of gravity, the atoms fall back through the microwave cavity and into an optical state--detection region which detects the number of atoms making the F=3 arrow F=4 transition. The increased Ramsey interaction time improves the short--time precision as compared to traditional atomic beam experiments, while many systematic shifts which limit the accuracy of an atomic beam clock are reduced by the low atomic velocity and the retrace of the atomic trajectory through the microwave cavity. We will discuss the progress towards a working fountain being assembled in our laboratory.

Analysis of the relationship between lung cancer drug response level and atom connectivity dynamics based on trimmed Delaunay triangulation

NASA Astrophysics Data System (ADS)

Zou, Bin; Wang, Debby D.; Ma, Lichun; Chen, Lijiang; Yan, Hong

2016-05-01

Epidermal growth factor receptor (EGFR) mutation is a pathogenic factor of non-small cell lung cancer (NSCLC). Tyrosine kinase inhibitors (TKIs), such as gefitinib, are widely used in NSCLC treatment. In this work, we investigated the relationship between the number of EGFR residues connected with gefitinib and the response level for each EGFR mutation type. Three-dimensional trimmed Delaunay triangulation was applied to construct connections between EGFR residues and gefitinib atoms. Through molecular dynamics (MD) simulations, we discovered that when the number of EGFR residues connected with gefitinib increases, the response level of the corresponding EGFR mutation tends to descend.

Combustor exhaust-emissions and blowout-limits with diesel number 2 and jet A fuels utilizing air-atomizing and pressure atomizing nozzles

NASA Technical Reports Server (NTRS)

Ingebo, R. D.; Norgren, C. T.

1975-01-01

Experimental tests with diesel number 2 and Jet A fuels were conducted in a combustor segment to obtain comparative data on exhaust emissions and blowout limits. An air-atomizing nozzle was used to inject the fuels. Tests were also made with diesel number 2 fuel using a pressure-atomizing nozzle to determine the effectiveness of the air-atomizing nozzle in reducing exhaust emissions. Test conditions included fuel-air ratios of 0.008 to 0.018, inlet-air total pressures and temperatures of 41 to 203 newtons per square centimeter and 477 to 811 K, respectively, and a reference velocity of 21.3 meters per second. Smoke number and unburned hydrocarbons were twice as high with diesel number 2 as with Jet A fuel. This was attributed to diesel number 2 having a higher concentration of aromatics and lower volatility than Jet A fuel. Oxides of nitrogen, carbon monoxide, and blowout limits were approximately the same for the two fuels. The air-atomizing nozzle, as compared with the pressure-atomizing nozzle, reduced oxides-of-nitrogen by 20 percent, smoke number by 30 percent, carbon monoxide by 70 percent, and unburned hydrocarbons by 50 percent when used with diesel number 2 fuel.

Transfer of a weakly bound electron in collisions of Rydberg atoms with neutral particles. II. Ion-pair formation and resonant quenching of the Rb(nl) and Ne(nl) States by Ca, Sr, and Ba atoms

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

Narits, A. A.; Mironchuk, E. S.; Lebedev, V. S., E-mail: vlebedev@sci.lebedev.ru

2013-10-15

Electron-transfer processes are studied in thermal collisions of Rydberg atoms with alkaline-earth Ca(4s{sup 2}), Sr(5s{sup 2}), and Ba(6s{sup 2}) atoms capable of forming negative ions with a weakly bound outermost p-electron. We consider the ion-pair formation and resonant quenching of highly excited atomic states caused by transitions between Rydberg covalent and ionic terms of a quasi-molecule produced in collisions of particles. The contributions of these reaction channels to the total depopulation cross section of Rydberg states of Rb(nl) and Ne(nl) atoms as functions of the principal quantum number n are compared for selectively excited nl-levels with l Much-Less-Than n andmore » for states with large orbital quantum numbers l = n - 1, n - 2. It is shown that the contribution from resonant quenching dominates at small values of n, and the ion-pair formation process begins to dominate with increasing n. The values and positions of the maxima of cross sections for both processes strongly depend on the electron affinity of an alkaline-earth atom and on the orbital angular momentum l of a highly excited atom. It is shown that in the case of Rydberg atoms in states with large l {approx} n - 1, the rate constants of ion-pair formation and collisional quenching are considerably lower than those for nl-levels with l Much-Less-Than n.« less

Description of atomic burials in compact globular proteins by Fermi-Dirac probability distributions.

PubMed

Gomes, Antonio L C; de Rezende, Júlia R; Pereira de Araújo, Antônio F; Shakhnovich, Eugene I

2007-02-01

We perform a statistical analysis of atomic distributions as a function of the distance R from the molecular geometrical center in a nonredundant set of compact globular proteins. The number of atoms increases quadratically for small R, indicating a constant average density inside the core, reaches a maximum at a size-dependent distance R(max), and falls rapidly for larger R. The empirical curves turn out to be consistent with the volume increase of spherical concentric solid shells and a Fermi-Dirac distribution in which the distance R plays the role of an effective atomic energy epsilon(R) = R. The effective chemical potential mu governing the distribution increases with the number of residues, reflecting the size of the protein globule, while the temperature parameter beta decreases. Interestingly, betamu is not as strongly dependent on protein size and appears to be tuned to maintain approximately half of the atoms in the high density interior and the other half in the exterior region of rapidly decreasing density. A normalized size-independent distribution was obtained for the atomic probability as a function of the reduced distance, r = R/R(g), where R(g) is the radius of gyration. The global normalized Fermi distribution, F(r), can be reasonably decomposed in Fermi-like subdistributions for different atomic types tau, F(tau)(r), with Sigma(tau)F(tau)(r) = F(r), which depend on two additional parameters mu(tau) and h(tau). The chemical potential mu(tau) affects a scaling prefactor and depends on the overall frequency of the corresponding atomic type, while the maximum position of the subdistribution is determined by h(tau), which appears in a type-dependent atomic effective energy, epsilon(tau)(r) = h(tau)r, and is strongly correlated to available hydrophobicity scales. Better adjustments are obtained when the effective energy is not assumed to be necessarily linear, or epsilon(tau)*(r) = h(tau)*r(alpha,), in which case a correlation with hydrophobicity scales is found for the product alpha(tau)h(tau)*. These results indicate that compact globular proteins are consistent with a thermodynamic system governed by hydrophobic-like energy functions, with reduced distances from the geometrical center, reflecting atomic burials, and provide a conceptual framework for the eventual prediction from sequence of a few parameters from which whole atomic probability distributions and potentials of mean force can be reconstructed. Copyright 2006 Wiley-Liss, Inc.

Atomization of Impinging Droplets on Superheated Superhydrophobic Surfaces

NASA Astrophysics Data System (ADS)

Emerson, Preston; Crockett, Julie; Maynes, Daniel

2017-11-01

Water droplets impinging smooth superheated surfaces may be characterized by dynamic vapor bubbles rising to the surface, popping, and causing a spray of tiny droplets to erupt from the droplet. This spray is called secondary atomization. Here, atomization is quantified experimentally for water droplets impinging superheated superhydrophobic surfaces. Smooth hydrophobic and superhydrophobic surfaces with varying rib and post microstructuring were explored. Each surface was placed on an aluminum heating block, and impingement events were captured with a high speed camera at 3000 fps. For consistency among tests, all events were normalized by the maximum atomization found over a range of temperatures on a smooth hydrophobic surface. An estimate of the level of atomization during an impingement event was created by quantifying the volume of fluid present in the atomization spray. Droplet diameter and Weber number were held constant, and atomization was found for a range of temperatures through the lifetime of the impinging droplet. The Leidenfrost temperature was also determined and defined to be the lowest temperature at which atomization ceases to occur. Both atomization and Leidenfrost temperature increase with decreasing pitch (distance between microstructures).

Strengthened PAN-based carbon fibers obtained by slow heating rate carbonization

PubMed Central

Kim, Min-A; Jang, Dawon; Tejima, Syogo; Cruz-Silva, Rodolfo; Joh, Han-Ik; Kim, Hwan Chul; Lee, Sungho; Endo, Morinobu

2016-01-01

Large efforts have been made over the last 40 years to increase the mechanical strength of polyacrylonitrile (PAN)-based carbon fibers (CFs) using a variety of chemical or physical protocols. In this paper, we report a new method to increase CFs mechanical strength using a slow heating rate during the carbonization process. This new approach increases both the carbon sp3 bonding and the number of nitrogen atoms with quaternary bonding in the hexagonal carbon network. Theoretical calculations support a crosslinking model promoted by the interstitial carbon atoms located in the graphitic interlayer spaces. The improvement in mechanical performance by a controlled crosslinking between the carbon hexagonal layers of the PAN based CFs is a new concept that can contribute further in the tailoring of CFs performance based on the understanding of their microstructure down to the atomic scale. PMID:27004752

Effective atomic numbers and electron densities of bioactive glasses for photon interaction

NASA Astrophysics Data System (ADS)

Shantappa, Anil; Hanagodimath, S. M.

2015-08-01

This work was carried out to study the nature of mass attenuation coefficient of bioactive glasses for gamma rays. Bioactive glasses are a group of synthetic silica-based bioactive materials with unique bone bonding properties. In the present study, we have calculated the effective atomic number, electron density for photon interaction of some selected bioactive glasses viz., SiO2-Na2O, SiO2-Na2O-CaO and SiO2-Na2O-P2O5 in the energy range 1 keV to 100 MeV. We have also computed the single valued effective atomic number by using XMuDat program. It is observed that variation in effective atomic number (ZPI, eff) depends also upon the weight fractions of selected bioactive glasses and range of atomic numbers of the elements. The results shown here on effective atomic number, electron density will be more useful in the medical dosimetry for the calculation of absorbed dose and dose rate.

Mechanical and thermodynamic properties of AlX (X = N, P, As) compounds

NASA Astrophysics Data System (ADS)

Xu, Lifang; Bu, Wei

2017-09-01

The Vickers hardness of various AlX (X = N, P, As) compound polymorphs were calculated with the bond resistance model. Thermodynamic properties, such as vibrational entropy, constant volume specific heat and Debye temperatures, were calculated using phonon dispersion relations and phonon density of states (DOS). The calculated values are in good agreement with the previous experimental and theoretical data. For the same structure of AlX (X = N, P, As) compounds, their hardness and Debye temperatures both decrease with the X atomic number. The wurtzite (wz) and zincblende (zb) structures of the same compounds AlX share an almost identical hardness, but have different Debye temperatures. The difference between wz and zb structures increases as the atomic number of X increases. The thermodynamic properties reveal that the constant volume specific heat approaches the Dulong-Petit rule at high temperatures.

Flat panel X-ray detector with reduced internal scattering for improved attenuation accuracy and dynamic range

DOEpatents

Smith, Peter D [Santa Fe, NM; Claytor, Thomas N [White Rock, NM; Berry, Phillip C [Albuquerque, NM; Hills, Charles R [Los Alamos, NM

2010-10-12

An x-ray detector is disclosed that has had all unnecessary material removed from the x-ray beam path, and all of the remaining material in the beam path made as light and as low in atomic number as possible. The resulting detector is essentially transparent to x-rays and, thus, has greatly reduced internal scatter. The result of this is that x-ray attenuation data measured for the object under examination are much more accurate and have an increased dynamic range. The benefits of this improvement are that beam hardening corrections can be made accurately, that computed tomography reconstructions can be used for quantitative determination of material properties including density and atomic number, and that lower exposures may be possible as a result of the increased dynamic range.

Quantification of evaporation induced error in atom probe tomography using molecular dynamics simulation.

PubMed

Chen, Shu Jian; Yao, Xupei; Zheng, Changxi; Duan, Wen Hui

2017-11-01

Non-equilibrium molecular dynamics was used to simulate the dynamics of atoms at the atom probe surface and five objective functions were used to quantify errors. The results suggested that before ionization, thermal vibration and collision caused the atoms to displace up to 1Å and 25Å respectively. The average atom displacements were found to vary between 0.2 and 0.5Å. About 9 to 17% of the atoms were affected by collision. Due to the effects of collision and ion-ion repulsion, the back-calculated positions were on average 0.3-0.5Å different from the pre-ionized positions of the atoms when the number of ions generated per pulse was minimal. This difference could increase up to 8-10Å when 1.5ion/nm 2 were evaporated per pulse. On the basis of the results, surface ion density was considered an important factor that needed to be controlled to minimize error in the evaporation process. Copyright © 2017. Published by Elsevier B.V.

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

Benson, David M.; Tsang, Chu F.; Sugar, Joshua Daniel

One method for the formation of nanofilms of materials, is Electrochemical atomic layer deposition (E-ALD), one atomic layer at a time. It uses the galvanic exchange of a less noble metal, deposited using underpotential deposition (UPD), to produce an atomic layer of a more noble element by reduction of its ions. This process is referred to as surface limited redox replacement and can be repeated in a cycle to grow thicker deposits. Previously, we performed it on nanoparticles and planar substrates. In the present report, E-ALD is applied for coating a submicron-sized powder substrate, making use of a new flowmore » cell design. E-ALD is used to coat a Pd powder substrate with different thicknesses of Rh by exchanging it for Cu UPD. Furthermore, cyclic voltammetry and X-ray photoelectron spectroscopy indicate an increasing Rh coverage with increasing numbers of deposition cycles performed, in a manner consistent with the atomic layer deposition (ALD) mechanism. Cyclic voltammetry also indicated increased kinetics of H sorption and desorption in and out of the Pd powder with Rh present, relative to unmodified Pd.« less

Defect-suppressed atomic crystals in an optical lattice.

PubMed

Rabl, P; Daley, A J; Fedichev, P O; Cirac, J I; Zoller, P

2003-09-12

We present a coherent filtering scheme which dramatically reduces the site occupation number defects for atoms in an optical lattice by transferring a chosen number of atoms to a different internal state via adiabatic passage. With the addition of superlattices it is possible to engineer states with a specific number of atoms per site (atomic crystals), which are required for quantum computation and the realization of models from condensed matter physics, including doping and spatial patterns. The same techniques can be used to measure two-body spatial correlation functions.

Observation of oxide particles below the apparent oxygen solubility limit in tantalum

NASA Technical Reports Server (NTRS)

Stecura, S.

1973-01-01

The apparent solubility of oxygen in polycrystalline tantalum as determined by the X-ray diffraction lattice parameter technique is about 1.63 atomic percent at 820 C. However, oxide particles were identified in samples containing as low as 0.5 atomic percent of oxygen. These oxide particles were present at the grain boundaries and within the grains. The number of oxide particles increased with increasing oxygen concentration in tantalum. The presence of oxide particles suggests that the true solubility of oxygen in the polycrystalline tantalum metal is probably significantly lower than that reported in the literature.

Searching for the rules that govern hadron construction

DOE PAGES

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

2016-06-22

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

Optical Properties and Microstructure of Barium Titanate Thin Film (BaTiO3) for Solar Cell Applications

NASA Astrophysics Data System (ADS)

Setyadi, A. U. L. S.; Iriani, Y.; Nurosyid, F.

2018-03-01

Barium Titanate thin films were prepared with variations in the number of layers and variation of the solution on a Quartz substrate using the sol-gel method with spin coating technique, at rotation speed 3000 rpm for 30 seconds. The first solution was made with heated and the second with stirred and heated. In this experiment, BaTiO3 were heated at 900°C for 2 hours. The characterization of optical properties was performed by UV-Vis spectrometer and microstructural characterization was performed by X-Ray Diffraction (XRD). Variation of layers number affects the intensity of the diffraction peaks. The more layers of the intensity are also greater. The variation of solution making process affects the intensity of diffraction peak. The process of making the solution with stirred and heated has greater intensity than the process of solution by simply heating it. When stirred at the same time heated to produce atoms diffuses more easily with other atoms so the bonds between atoms are more orderly and strong. The process of making the solution in the heated is larger in the crystallite size of than preparation of solution by stirred and heated. The stirred which the solution is produced influences the appearance of the size of the crystal. Variation number of layers influences the absorbance value of layer. The absorbance increases with increasing number of layers. The absorbance of the sample was made with heated the higher than with stirred and heated.

Change of Energy of the Cubic Subnanocluster of Iron Under Influence of Interstitial and Substitutional Atoms.

PubMed

Nedolya, Anatoliy V; Bondarenko, Natalya V

2016-12-01

Energy change of an iron face-centred cubic subnanocluster was evaluated using molecular mechanics method depending on the position of a carbon interstitial atom and substitutional atoms of nickel. Calculations of all possible positions of impurity atoms show that the energy change of the system are discrete and at certain positions of the atoms are close to continuous.In terms of energy, when all impurity atoms are on the same edge of an atomic cluster, their positions are more advantageous. The presence of nickel atoms on the edge of a cubic cluster resulted in decrease of potential barrier for a carbon atom and decrease in energy in the whole cluster. A similar drift of a carbon atom from central octahedral interstitial site to the surface in the direction <011> occurred under the influence of surface factors.Such configuration corresponds to decreasing symmetry and increasing the number of possible energy states of a subnanocluster, and it corresponds to the condition of spontaneous crystallization process in an isolated system.Taking into account accidental positions of the nickel atom in the iron cluster, such behaviour of the carbon atom can explain the mechanism of growth of a new phase and formation of new clusters in the presence of other kind of atoms because of surface influence.

Glenn T. Seaborg - Contributions to Advancing Science

Science.gov Websites

. Documents: The First Weighing of Plutonium (Atomic Number 94); DOE Technical Report; September 1967 The New Element Americium (Atomic Number 95); DOE Technical Report; January 1948 The New Element Curium (Atomic Number 96); DOE Technical Report; January 1948 Frontiers of Chemistry for Americium and Curium; DOE

Optimization of Monte Carlo dose calculations: The interface problem

NASA Astrophysics Data System (ADS)

Soudentas, Edward

1998-05-01

High energy photon beams are widely used for radiation treatment of deep-seated tumors. The human body contains many types of interfaces between dissimilar materials that affect dose distribution in radiation therapy. Experimentally, significant radiation dose perturbations has been observed at such interfaces. The EGS4 Monte Carlo code was used to calculate dose perturbations at boundaries between dissimilar materials (such as bone/water) for 60Co and 6 MeV linear accelerator beams using a UNIX workstation. A simple test of the reliability of a random number generator was also developed. A systematic study of the adjustable parameters in EGS4 was performed in order to minimize calculational artifacts at boundaries. Calculations of dose perturbations at boundaries between different materials showed that there is a 12% increase in dose at water/bone interface, and a 44% increase in dose at water/copper interface. with the increase mainly due to electrons produced in water and backscattered from the high atomic number material. The dependence of the dose increase on the atomic number was also investigated. The clinically important case of using two parallel opposed beams for radiation therapy was investigated where increased doses at boundaries has been observed. The Monte Carlo calculations can provide accurate dosimetry data under conditions of electronic non-equilibrium at tissue interfaces.

EXAFS Study of Halato-Telechelic Polymers End-Capped With Group IVb Metal Carboxylates at Room and Low Temperatures

NASA Astrophysics Data System (ADS)

Vlaic, G.; Navarra, G.; Regnard, J.-R.; Williams, C. E.; Jérôme, R.

1995-05-01

The EXAFS analysis at 300, 70 and 5 K has shown that the thermal disorder is very low in a carboxylato telechelic polybutadiene neutralized with an increasing excess of Zr isopropoxide. Two types of Zr-O bonds in the first shell account for the experimental data. The Zr-O distances and number of oxygen neighbours in the two subshells are found to be independent of temperature in the investigated range. The proportion of Zr in the samples has no effect on the total number of oxygen atoms around Zr, in contrast to their relative distribution in the two subshells. The number of Zr atoms increases in the second shell with the total amount of this metal. Upon increasing degree of neutralization from 200 to 600%, the static disorder increases together with a strong reduction of the dynamic part of the Debye-Waller (DW) factor. At a high degree of neutralization (> 400%), the DW factor for the Zr-Zr bond is largely independent of temperature. These observations agree with formation of Zr polynuclear microdomains, the size and rigidity of which increase with the Zr content, in good agreement with the profound changes previously reported in the viscoelastic properties of these materials.

Influence of ball milling on atomic structure and magnetic properties of Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} glassy alloy

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

Taghvaei, Amir Hossein, E-mail: Amirtaghvaei@gmail.com; Department of Materials Science and Engineering, Shiraz University of Technology, Shiraz; Stoica, Mihai

2014-06-01

The influence of ball milling on the atomic structure and magnetic properties of the Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} metallic glass with a high thermal stability and excellent soft magnetic properties has been investigated. After 14 h of milling, the obtained powders were found to consist mainly of an amorphous phase and a small fraction of the (Co,Fe){sub 21}Ta{sub 2}B{sub 6} nanocrystals. The changes in the reduced pair correlation functions suggest noticeable changes in the atomic structure of the amorphous upon ball milling. Furthermore, it has been shown that milling is accompanied by introduction of compressive and dilatational sites inmore » the glassy phase and increasing the fluctuation of the atomic-level hydrostatic stress without affecting the coordination number of the nearest neighbors. Ball milling has decreased the thermal stability and significantly affected the magnetic properties through increasing the saturation magnetization, Curie temperature of the amorphous phase and coercivity. - Highlights: • Ball milling affected the atomic structure of Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} metallic glass. • Mechanically-induced crystallization started after 4 h milling. • Milling increased the fluctuation of the atomic-level hydrostatic stress in glass. • Ball milling influenced the thermal stability and magnetic properties.« less

HYDROLYSIS OF HALOACETONITRILES: LINEAR FREE ENERGY RELATIONSHIP, KINETICS AND PRODUCTS. (R825362)

EPA Science Inventory

Abstract

The hydrolysis rates of mono-, di- and trihaloacetonitriles were studied in aqueous buffer solutions at different pH. The stability of haloacetonitriles decreases and the hydrolysis rate increases with increasing pH and number of halogen atoms in the molecule:...

High Fidelity Simulation of Atomization in Diesel Engine Sprays

DTIC Science & Technology

2015-09-01

ARL-RP-0555 ● SEP 2015 US Army Research Laboratory High Fidelity Simulation of Atomization in Diesel Engine Sprays by L Bravo...ARL-RP-0555 ● SEP 2015 US Army Research Laboratory High Fidelity Simulation of Atomization in Diesel Engine Sprays by L...Simulation of Atomization in Diesel Engine Sprays 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) L Bravo, CB Ivey, D

Forecasting Periodic Trends: A Semester-Long Team Exercise for Nonscience Majors

ERIC Educational Resources Information Center

Tierney, John

2008-01-01

Team learning is an effective means of teaching that can contribute toward increased student interest. This article describes a team learning exercise developed for a course for nonscience majors. Students are randomly assigned numbers (atomic numbers) the first day of class. Each student builds a portfolio of information for their element. In the…

Cooperative single-photon subradiant states in a three-dimensional atomic array

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

Jen, H.H., E-mail: sappyjen@gmail.com

2016-11-15

We propose a complete superradiant and subradiant states that can be manipulated and prepared in a three-dimensional atomic array. These subradiant states can be realized by absorbing a single photon and imprinting the spatially-dependent phases on the atomic system. We find that the collective decay rates and associated cooperative Lamb shifts are highly dependent on the phases we manage to imprint, and the subradiant state of long lifetime can be found for various lattice spacings and atom numbers. We also investigate both optically thin and thick atomic arrays, which can serve for systematic studies of super- and sub-radiance. Our proposal offers an alternative schememore » for quantum memory of light in a three-dimensional array of two-level atoms, which is applicable and potentially advantageous in quantum information processing. - Highlights: • Cooperative single-photon subradiant states in a three-dimensional atomic array. • Subradiant state manipulation via spatially-increasing phase imprinting. • Quantum storage of light in the subradiant state in two-level atoms.« less

Atomic Mass and Nuclear Binding Energy for I-131 (Iodine)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume A `Nuclei with Z = 1 - 54' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms'. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope I-131 (Iodine, atomic number Z = 53, mass number A = 131).

Atomic Mass and Nuclear Binding Energy for F-22 (Fluorine)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume A `Nuclei with Z = 1 - 54' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms'. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope F-22 (Fluorine, atomic number Z = 9, mass number A = 22).

Control of Wave Propagation and Effect of Kerr Nonlinearity on Group Index

NASA Astrophysics Data System (ADS)

Hazrat, Ali; Ziauddin; Iftikhar, Ahmed

2013-07-01

We use four-level atomic system and control the wave propagation via forbidden decay rate. The Raman gain process becomes dominant on electromagnetically induced transparency (EIT) medium by increasing the forbidden decay rate via increasing the number of atoms [G.S. Agarwal and T.N. Dey, Phys. Rev. A 74 (2006) 043805 and K. Harada, T. Kanbashi, and M. Mitsunaga, Phys. Rev. A 73 (2006) 013803]. The behavior of wave propagation is dramatically changed from normal (subluminal) to anomalous (superluminal) dispersion by increasing the forbidden decay rate. The system can also give a control over the group velocity of the light propagating through the medium via Kerr field.

Effective atomic numbers and electron densities of bioactive glasses for photon interaction

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

Shantappa, Anil, E-mail: anilmalipatil@yahoo.co.in; Hanagodimath, S. M., E-mail: smhmath@rediffmail.com

2015-08-28

This work was carried out to study the nature of mass attenuation coefficient of bioactive glasses for gamma rays. Bioactive glasses are a group of synthetic silica-based bioactive materials with unique bone bonding properties. In the present study, we have calculated the effective atomic number, electron density for photon interaction of some selected bioactive glasses viz., SiO{sub 2}-Na{sub 2}O, SiO{sub 2}-Na{sub 2}O-CaO and SiO{sub 2}-Na{sub 2}O-P{sub 2}O{sub 5} in the energy range 1 keV to 100 MeV. We have also computed the single valued effective atomic number by using XMuDat program. It is observed that variation in effective atomic number (Z{submore » PI,} {sub eff}) depends also upon the weight fractions of selected bioactive glasses and range of atomic numbers of the elements. The results shown here on effective atomic number, electron density will be more useful in the medical dosimetry for the calculation of absorbed dose and dose rate.« less

C60 as a Faraday cage

NASA Astrophysics Data System (ADS)

Delaney, P.; Greer, J. C.

2004-01-01

Endohedral fullerenes have been proposed for a number of technological uses, for example, as a nanoscale switch, memory bit and as qubits for quantum computation. For these technology applications, it is important to know the ease with which the endohedral atom can be manipulated using an applied electric field. We find that the Buckminsterfullerene (C60) acts effectively as a small Faraday cage, with only 25% of the field penetrating the interior of the molecule. Thus influencing the atom is difficult, but as a qubit the endohedral atom should be well shielded from environmental electrical noise. We also predict how the field penetration should increase with the fullerene radius.

Generalized charge-screening in relativistic Thomas–Fermi model

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

Akbari-Moghanjoughi, M.

In this paper, we study the charge shielding within the relativistic Thomas-Fermi model for a wide range of electron number-densities and the atomic-number of screened ions. A generalized energy-density relation is obtained using the force-balance equation and taking into account the Chandrasekhar's relativistic electron degeneracy pressure. By numerically solving a second-order nonlinear differential equation, the Thomas-Fermi screening length is investigated, and the results are compared for three distinct regimes of the solid-density, warm-dense-matter, and white-dwarfs (WDs). It is revealed that our nonlinear screening theory is compatible with the exponentially decaying Thomas-Fermi-type shielding predicted by the linear response theory. Moreover, themore » variation of relative Thomas-Fermi screening length shows that extremely dense quantum electron fluids are relatively poor charge shielders. Calculation of the total number of screening electrons around a nucleus shows that there is a position of maximum number of screening localized electrons around the screened nucleus, which moves closer to the point-like nucleus by increase in the plasma number density but is unaffected due to increase in the atomic-number value. It is discovered that the total number of screening electrons, (N{sub s}∝r{sub TF}{sup 3}/r{sub d}{sup 3} where r{sub TF} and r{sub d} are the Thomas-Fermi and interparticle distance, respectively) has a distinct limit for extremely dense plasmas such as WD-cores and neutron star crusts, which is unique for all given values of the atomic-number. This is equal to saying that in an ultrarelativistic degeneracy limit of electron-ion plasma, the screening length couples with the system dimensionality and the plasma becomes spherically self-similar. Current analysis can provide useful information on the effects of relativistic correction to the charge screening for a wide range of plasma density, such as the inertial-confined plasmas and compact stellar objects.« less

The formation of periodic micro/nano structured on stainless steel by femtosecond laser irradiation

NASA Astrophysics Data System (ADS)

Yao, Caizhen; Gao, Wei; Ye, Yayun; Jiang, Yong; Xu, Shizhen; Yuan, Xiaodong

2017-07-01

Stainless steel surface was irradiated by linear polarized laser (800 nm, 35 fs, 4 Hz and 0.7 J/cm2) with different pulse numbers. Environmental scanning electron microscope (ESEM/EDS) was used for detailed morphology, microstructure and composition studies. The wettability of irradiated steel surface was tested by Interface Tensiometer JC-2000X and compared with untreated stainless steel. Results showed that micro/nanostripes with different periods were formed. The period increased with the increasing pulse numbers from 450 nm for 90 pulses to 500 nm for 180 pulses. The orientation of those stripes was parallel with the laser beam polarization. Nanoparticles were observed on those periodic structures. EDS indicated that the atomic ratio of Cr increased and the atomic ratios of Fe and Ni decreased after laser irradiation, which may enhance the corrosion resistance due to the Cr-rich layer. The prepared structure exhibited hydrophobic property without further treatment. The formation mechanism of micro/nanoperiodic structures was also explored.

Phonon localization transition in relaxor ferroelectric PZN-5%PT

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

Manley, Michael E.; Christianson, Andrew D.; Abernathy, Douglas L.

Relaxor ferroelectric behavior occurs in many disordered ferroelectric materials but is not well understood at the atomic level. Recent experiments and theoretical arguments indicate that Anderson localization of phonons instigates relaxor behavior by driving the formation of polar nanoregions (PNRs). Here, we use inelastic neutron scattering to observe phonon localization in relaxor ferroelectric PZN-5%PT (0.95[Pb(Zn 1/3 Nb 2/3)O 3]–0.05PbTiO 3) and detect additional features of the localization process. In the lead, up to phonon localization on cooling, the local resonant modes that drive phonon localization increase in number. The increase in resonant scattering centers is attributed to a known increasemore » in the number of locally off centered Pb atoms on cooling. The transition to phonon localization occurs when these random scattering centers increase to a concentration where the Ioffe-Regel criterion is satisfied for localizing the phonon. Finally, we also model the effects of damped mode coupling on the observed phonons and phonon localization structure.« less

Phonon localization transition in relaxor ferroelectric PZN-5%PT

DOE PAGES

Manley, Michael E.; Christianson, Andrew D.; Abernathy, Douglas L.; ...

2017-03-27

Relaxor ferroelectric behavior occurs in many disordered ferroelectric materials but is not well understood at the atomic level. Recent experiments and theoretical arguments indicate that Anderson localization of phonons instigates relaxor behavior by driving the formation of polar nanoregions (PNRs). Here, we use inelastic neutron scattering to observe phonon localization in relaxor ferroelectric PZN-5%PT (0.95[Pb(Zn 1/3 Nb 2/3)O 3]–0.05PbTiO 3) and detect additional features of the localization process. In the lead, up to phonon localization on cooling, the local resonant modes that drive phonon localization increase in number. The increase in resonant scattering centers is attributed to a known increasemore » in the number of locally off centered Pb atoms on cooling. The transition to phonon localization occurs when these random scattering centers increase to a concentration where the Ioffe-Regel criterion is satisfied for localizing the phonon. Finally, we also model the effects of damped mode coupling on the observed phonons and phonon localization structure.« less

Grain boundaries at the surface of consolidated MgO nanocrystals and acid-base functionality.

PubMed

Vingurt, Dima; Fuks, David; Landau, Miron V; Vidruk, Roxana; Herskowitz, Moti

2013-09-21

The increase of the surface basicity-acidity of MgO material by factors of 1.8-3.0 due to consolidation of its nanocrystals was demonstrated by the indicator titration. It was shown that the parallel increase of surface acidity and basicity is attributed to the formation of grain boundaries (GB) after MgO aerogel densification. A simple model predicting the increase of surface acidity-basicity of MgO that correlates with the results of direct measurements was proposed. The model is based on the study of the fine atomic structure at GB surface areas in consolidated MgO nanocrystals in the framework of Density Functional Theory. It is found that the displacements of coordinatively unsaturated surface ions near the GB are significant at the distances ~3-4 atomic layers from the geometrical contact plane between nanocrystals. The detailed analysis of atomic positions inside GB demonstrated the coordination deficiency of surface atoms at the GB areas leading to the formation of stretched bonds and to creation of low coordinated surface ions due to splitting of coordination numbers of surface atoms belonging to GB areas. Density of states for electrons shows the existence of additional states in the band gap close to the bottom of the conduction band. The adsorption energy of CO2 molecules atop oxygen atoms exposed at surface GB areas is of the same order of magnitude as that reported for oxygen atoms at crystallographic edges and corners of MgO crystals. It provides additional options for bonding of molecules at the surface of nanocrystalline MgO increasing the adsorption capacity and catalytic activity.

Photon interaction study of organic nonlinear optical materials in the energy range 122-1330 keV

NASA Astrophysics Data System (ADS)

Awasarmol, Vishal V.; Gaikwad, Dhammajyot K.; Raut, Siddheshwar D.; Pawar, Pravina P.

2017-01-01

In the present study, the mass attenuation coefficient (μm) of six organic nonlinear optical materials has been calculated in the energy range 122-1330 keV and compared with the obtained values from the WinXCOM program. It is found that there is a good agreement between theoretical and experimental values (<3%). The linear attenuation coefficients (μ) total atomic cross section (σt, a), and total electronic cross section (σt, el) have also been calculated from the obtained μm values and their variations with photon energy have been plotted. From the present work, it is observed that the variation of obtained values of μm, μ, σt, a, and σt, el strongly depends on the photon energy and decreases or increases due to chemical composition and density of the sample. All the samples have been studied extensively using transmission method with a view to utilize the material for radiation dosimetry. Investigated samples are good material for radiation dosimetry due their low effective atomic number. The mass attenuation coefficient (μm), linear attenuation coefficients (μ), total atomic cross section (σt, a), total electronic cross section (σt, el), effective atomic numbers (Zeff), molar extinction coefficient (ε), mass energy absorption coefficient (μen/ρ) and effective atomic energy absorption cross section (σa, en) of all sample materials have been carried out and transmission curves have been plotted. The transmission curve shows that the variation of all sample materials decreases with increasing photon energy.

Coherent single-atom superradiance

NASA Astrophysics Data System (ADS)

Kim, Junki; Yang, Daeho; Oh, Seung-hoon; An, Kyungwon

2018-02-01

Superradiance is a quantum phenomenon emerging in macroscopic systems whereby correlated single atoms cooperatively emit photons. Demonstration of controlled collective atom-field interactions has resulted from the ability to directly imprint correlations with an atomic ensemble. Here we report cavity-mediated coherent single-atom superradiance: Single atoms with predefined correlation traverse a high–quality factor cavity one by one, emitting photons cooperatively with the N atoms that have already gone through the cavity (N represents the number of atoms). Enhanced collective photoemission of N-squared dependence was observed even when the intracavity atom number was less than unity. The correlation among single atoms was achieved by nanometer-precision position control and phase-aligned state manipulation of atoms by using a nanohole-array aperture. Our results demonstrate a platform for phase-controlled atom-field interactions.

Static time-of-flight secondary ion mass spectrometry analysis of microelectronics related substrates using a polyatomic ion source

NASA Astrophysics Data System (ADS)

Ravanel, X.; Trouiller, C.; Juhel, M.; Wyon, C.; Kwakman, L. F. Tz.; Léonard, D.

2008-12-01

Recent time-of-flight secondary ion mass spectrometry studies using primary ion cluster sources such as Au n+, SF 5+, Bi n+ or C 60+ have shown the great advantages in terms of secondary ion yield enhancement and ion formation efficiency of polyatomic ion sources as compared to monoatomic ion sources like the commonly used Ga +. In this work, the effective gains provided by such a source in the static ToF-SIMS analysis of microelectronics devices were investigated. Firstly, the influence of the number of atoms in the primary cluster ion on secondary ion formation was studied for physically adsorbed di-isononyl phthalate (DNP) (plasticizer) and perfluoropolyether (PFPE). A drastic increase in secondary ion formation efficiency and a much lower detection limit were observed when using a polyatomic primary ion. Moreover, the yield of the higher mass species was much enhanced indicating a lower degree of fragmentation that can be explained by the fact that the primary ion energy is spread out more widely, or that there is a lower energy per incoming ion. Secondly, the influence of the number of Bi atoms in the Bi n primary ion on the information depth was studied using reference thermally grown silicon oxide samples. The information depth provided by a Bi n cluster was shown to be lowered when the number of atoms in the aggregate was increased.

The effect of grading the atomic number at resistive guide element interface on magnetic collimation

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

Alraddadi, R. A. B.; Woolsey, N. C.; Robinson, A. P. L.

2016-07-15

Using 3 dimensional numerical simulations, this paper shows that grading the atomic number and thus the resistivity at the interface between an embedded high atomic number guide element and a lower atomic number substrate enhances the growth of a resistive magnetic field. This can lead to a large integrated magnetic flux density, which is fundamental to confining higher energy fast electrons. This results in significant improvements in both magnetic collimation and fast-electron-temperature uniformity across the guiding. The graded interface target provides a method for resistive guiding that is tolerant to laser pointing.

Superradiance in a Large and Dilute Cloud of Cold Atoms in the Linear-Optics Regime.

PubMed

Araújo, Michelle O; Krešić, Ivor; Kaiser, Robin; Guerin, William

2016-08-12

Superradiance has been extensively studied in the 1970s and 1980s in the regime of superfluorescence, where a large number of atoms are initially excited. Cooperative scattering in the linear-optics regime, or "single-photon superradiance," has been investigated much more recently, and superradiant decay has also been predicted, even for a spherical sample of large extent and low density, where the distance between atoms is much larger than the wavelength. Here, we demonstrate this effect experimentally by directly measuring the decay rate of the off-axis fluorescence of a large and dilute cloud of cold rubidium atoms after the sudden switch off of a low-intensity laser driving the atomic transition. We show that, at large detuning, the decay rate increases with the on-resonance optical depth. In contrast to forward scattering, the superradiant decay of off-axis fluorescence is suppressed near resonance due to attenuation and multiple-scattering effects.

ELECTRON IRRADIATION OF SOLIDS

DOEpatents

Damask, A.C.

1959-11-01

A method is presented for altering physical properties of certain solids, such as enhancing the usefulness of solids, in which atomic interchange occurs through a vacancy mechanism, electron irradiation, and temperature control. In a centain class of metals, alloys, and semiconductors, diffusion or displacement of atoms occurs through a vacancy mechanism, i.e., an atom can only move when there exists a vacant atomic or lattice site in an adjacent position. In the process of the invention highenergy electron irradiation produces additional vacancies in a solid over those normally occurring at a given temperature and allows diffusion of the component atoms of the solid to proceed at temperatures at which it would not occur under thermal means alone in any reasonable length of time. The invention offers a precise way to increase the number of vacancies and thereby, to a controlled degree, change the physical properties of some materials, such as resistivity or hardness.

Influence of UV irradiation on hydroxypropyl methylcellulose polymer films

NASA Astrophysics Data System (ADS)

Rao, B. Lakshmeesha; Shivananda, C. S.; Shetty, G. Rajesha; Harish, K. V.; Madhukumar, R.; Sangappa, Y.

2018-05-01

Hydroxypropyl Methylcellulose (HPMC) biopolymer films were prepared by solution casting technique and effects of UV irradiation on the structural and optical properties of the polymer films were analysed using X-ray Diffraction and UV-Visible studies. From XRD data, the microcrystalline parameters (crystallite size (LXRD) and crystallinity (Xc)) were calculated and found to be decreasing with UV irradiation due to photo-degradation process. From the UV-Vis absorption data, the optical bandgap (Eg), average numbers of carbon atoms per conjugation length (N) of the polymer chain and the refractive index (n) at 550 nm (average wavelength of visible light) of virgin and UV irradiated HPMC films were calculated. With increase in UV exposure time, the optical bandgap energy (Eg) increases, and hence average number of carbon atoms per conjugation length (N) decreases, supports the photo-degradation of HPMC polymer films. The refractive index of the HPMC films decreases after UV irradiation, due to photo-degradation induced chain rearrangements.

First stages of oxide growth on Al(1 1 0) and core-level shifts from density functional theory calculations

NASA Astrophysics Data System (ADS)

Lousada, Cláudio M.; Korzhavyi, Pavel A.

2018-05-01

The formation of islands of O-atoms is the dominant mode of growth of the oxide in the first stages of oxidation of Al(1 1 1). It is however unknown if a similar mechanism exists for other low index surfaces of Al. We performed a density functional theory (DFT) and ab initio molecular dynamics investigation of the first stages of the oxidation of Al(1 1 0) using two distinct models: a homogeneous surface disposition of O-atoms; and a model where the O-atoms are close-spaced forming clusters or islands. We investigated the surface reactions with oxygen up to a coverage of 2 ML and found that for both models the adsorption energy per dissociating O2(g) becomes more negative with increasing coverage. Our results show that for coverages up to 1.25 ML the oxide forms clusters or islands while for coverages higher than 1.5 ML the oxide covers the surface homogeneously. This is because the O-atoms bind preferably to neighboring sites even at the minimum coverage. With increasing coverage, the clusters of O start to form stripes along the [1 1 bar 0] direction. The work function (ϕ) of the surface decreases when going from bare Al(1 1 0) to up to 1 ML coverage of O-atoms, but for coverages of 1.25 ML and higher, ϕ increases. The Al 2p surface core level shifts (SCLS) shift towards higher binding energies with increasing surface coverage of O-atoms and start to approach the values of Al 2p in Al2O3 already at a coverage of 2ML. A relation between the SCLS and the coordination number of Al to O-atoms was made. The Al 2p SCLS increases with increasing coordination to O-atoms, for single, twofold and three-fourfold coordinated cations. For the O-atoms that terminate the surface at the short-bridge sites, the SCLS of O 1s, is largely affected by the proximity to other O-atoms. These results demonstrate that the cooperative effects between surface bound O-atoms have important roles in the mechanism of growth of the oxide at Al(1 1 0), and similarly to what happens for Al(1 1 1), the initial oxidation of Al(1 1 0) proceeds via the formation of islands of O-atoms.

Robust determination of effective atomic numbers for electron interactions with TLD-100 and TLD-100H thermoluminescent dosimeters

NASA Astrophysics Data System (ADS)

Taylor, M. L.

2011-04-01

Lithium fluoride thermoluminescent dosimeters (TLD) are the most commonly implemented for clinical dosimetry. The small physical magnitude of TLDs makes them attractive for applications such as small field measurement, in vivo dosimetry and measurement of out-of-field doses to critical structures. The most broadly used TLD is TLD-100 (LiF:Mg,Ti) and, for applications requiring higher sensitivity to low-doses, TLD-100H (LiF:Mg,Cu,P) is frequently employed. The radiological properties of these TLDs are therefore of significant interest. For the first time, in this study effective atomic numbers for radiative, collisional and total electron interaction processes are calculated for TLD-100 and TLD-100H dosimeters over the energy range 1 keV-100 MeV. This is undertaken using a robust, energy-dependent method of calculation rather than typical power-law approximations. The influence of dopant concentrations and unwanted impurities is also investigated. The two TLDs exhibit similar effective atomic numbers, ranging from approximately 5.77-6.51. Differences arising from the different dopants are most pronounced in low-energy radiative effects. The TLDs have atomic numbers approximately 1.48-2.06 times that of water. The effective atomic number of TLD-100H is consistently higher than that of TLD-100 over a broad energy range, due to the greater influence of the higher- Z dopants on the electron interaction cross sections. Typical variation in dopant concentration does not significantly influence the effective atomic number. The influence on TLD-100H is comparatively more pronounced than that on TLD-100. Contrariwise, unwanted hydroxide impurities influence TLD-100 more than TLD-100H. The effective atomic number is a key parameter that influences the radiological properties and energy response of TLDs. Although many properties of these TLDs have been studied rigorously, as yet there has been no investigation of their effective atomic numbers for electron interactions. The discrepancy between the effective atomic numbers of the TLDs and water is significantly higher than would be indicated by comparing effective atomic numbers calculated via the common - but dubious - power-law method. The mean effective numbers over the full energy range are 6.06, 6.09, 3.34 and 3.37 for TLD-100, TLD-100H, soft tissue and water respectively.

Science and Emerging Technology of 2D Atomic Layered Materials and Devices

DTIC Science & Technology

2017-09-09

AFRL-AFOSR-JP-TR-2017-0067 Science & Emerging Technology of 2D Atomic Layered Materials and Devices Angel Rubio UNIVERSIDAD DEL PAIS VASCO - EUSKAL...Emerging Technology of 2D Atomic Layered Materials and Devices 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA2386-15-1-0006 5c.  PROGRAM ELEMENT NUMBER...reporting documents for AOARD project 144088, “2D Materials and Devices Beyond Graphene Science & Emerging Technology of 2D Atomic Layered Materials and

Explanation of the conductivity minimum in tin- and tellurium-doped bismuth

NASA Astrophysics Data System (ADS)

Roy, Arpita; Banerjee, Dipali; Bhattacharya, Ramendranarayan

1995-01-01

The presence of a minimum observed in the variation of conductivity of bismuth with impurity concentrations at a constant temperature (4.2 K) has remained unexplained for a long time. An attempt to explain this anomalous behavior is reported here. In order to do so, a calculation has been made to find the change in the number of free carriers in bismuth with the addition of impurities (donors or acceptors). The calculation has been made using simple parabolic bands. It is known that when tin or tellurium atoms are added as impurities to bismuth all of the atoms are ionized. It has been found here that the number of free carriers initially shows a slow rate of decrease (for donors) or a slow rate of increase (for acceptors) as the impurity concentration is increased, as long as the impurity concentration is small, i.e., as long as the shift of the Fermi level is small. For a higher impurity concentration the number of carriers increases at a rate equal to that of the impurity concentration. This finding, combined with the scattering by impurity ions, could explain the anomalous behavior satisfactorily.

A study of 173 nm light emission from discharge cells in plasma display panel

NASA Astrophysics Data System (ADS)

Uhm, Han S.; Choi, Eun H.; Jung, Kyu B.

2005-03-01

Emission properties of the 173nm lights from the electrical discharge cells of the plasma display panel are investigated. The dimer formation and a theoretical model of 173nm emission are presented. It is shown that the diffusion loss of the excited xenon atoms in the metastable level is one of the most important population depreciation factor of excited xenon atoms. The decay time τd of excited atom number increases from zero, reaches its peak, and then decreases to zero, as the gas pressure p increases from zero, agreeing well with experimental data. A simple analytical expression Y of the total emission intensity is described in terms of the diffusion loss df, the three-body collision η, the gas pressure p, and the xenon mole fraction χ. The emission intensity Y of 173nm photon decreases with an increasing value of parameter df. Moreover, the emission intensity Y increases drastically with an increasing value of the gas pressure p and the xenon mole fraction χ. Results from the theoretical model agree remarkably well with experimental data.

Water-soluble conductive polymers

DOEpatents

Aldissi, Mahmoud

1989-01-01

Polymers which are soluble in water and are electrically conductive. The monomer repeat unit is a thiophene or pyrrole molecule having an alkyl group substituted for the hydrogen atom located in the beta position of the thiophene or pyrrole ring and having a surfactant molecule at the end of the alkyl chain. Polymers of this class having 8 or more carbon atoms in the alkyl chain exhibit liquid crystalline behavior, resulting in high electrical anisotropy. The monomer-to-monomer bonds are located between the carbon atoms which are adjacent to the sulfur or nitrogen atoms. The number of carbon atoms in the alkyl group may vary from 1 to 20 carbon atoms. The surfactant molecule consists of a sulfonate group, or a sulfate group, or a carboxylate group, and hydrogen or an alkali metal. Negative ions from a supporting electrolyte which may be used in the electrochemical synthesis of a polymer may be incorporated into the polymer during the synthesis and serve as a dopant to increase the conductivity.

Water-soluble conductive polymers

DOEpatents

Aldissi, Mahmoud

1990-01-01

Polymers which are soluble in water and are electrically conductive. The monomer repeat unit is a thiophene or pyrrole molecule having an alkyl group substituted for the hydrogen atom located in the beta position of the thiophene or pyrrole ring and having a surfactant molecule at the end of the alkyl chain. Polymers of this class having 8 or more carbon atoms in the alkyl chain exhibit liquid crystalline behavior, resulting in high electrical anisotropy. The monomer-to-monomer bonds are located between the carbon atoms which are adjacent to the sulfur or nitrogen atoms. The number of carbon atoms in the alkyl group may vary from 1 to 20 carbon atoms. The surfactant molecule consists of a sulfonate group, or a sulfate group, or a carboxylate group, and hydrogen or an alkali metal. Negative ions from a supporting electrolyte which may be used in the electrochemical synthesis of a polymer may be incorporated into the polymer during the synthesis and serve as a dopant to increase the conductivity.

Water-soluble conductive polymers

DOEpatents

Aldissi, M.

1988-02-12

Polymers which are soluble in water and are electrically conductive. The monomer repeat unit is a thiophene or pyrrole molecule having an alkyl group substituted for the hydrogen atom located in the beta position of the thiophene or pyrrole ring and having a surfactant molecule at the end of the alkyl chain. Polymers of this class having 8 or more carbon atoms in the alkyl chain exhibit liquid crystalline behavior, resulting in high electrical anisotropy. The monomer-to-monomer bonds are located between the carbon atoms which are adjacent to the sulfur or nitrogen atoms. The number of carbon atoms in the alkyl group may vary from 1 to 20 carbon atoms. The surfactant molecule consists of a sulfonate group, or a sulfate group, or a carboxylate group, and hydrogen or an alkali metal. Negative ions from a supporting electrolyte which may be used in the electrochemical synthesis of a polymer may be incorporated into the polymer during the synthesis and serve as a dopant to increase the conductivity.

Larger sized wire arrays on 1.5 MA Z-pinch generator

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

Safronova, A. S., E-mail: alla@unr.edu; Kantsyrev, V. L., E-mail: alla@unr.edu; Weller, M. E., E-mail: alla@unr.edu

Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes frommore » mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten)« less

Aggregation Number in Water/n-Hexanol Molecular Clusters Formed in Cyclohexane at Different Water/n-Hexanol/Cyclohexane Compositions Calculated by Titration 1H NMR.

PubMed

Flores, Mario E; Shibue, Toshimichi; Sugimura, Natsuhiko; Nishide, Hiroyuki; Moreno-Villoslada, Ignacio

2017-11-09

Upon titration of n-hexanol/cyclohexane mixtures of different molar compositions with water, water/n-hexanol clusters are formed in cyclohexane. Here, we develop a new method to estimate the water and n-hexanol aggregation numbers in the clusters that combines integration analysis in one-dimensional 1 H NMR spectra, diffusion coefficients calculated by diffusion-ordered NMR spectroscopy, and further application of the Stokes-Einstein equation to calculate the hydrodynamic volume of the clusters. Aggregation numbers of 5-15 molecules of n-hexanol per cluster in the absence of water were observed in the whole range of n-hexanol/cyclohexane molar fractions studied. After saturation with water, aggregation numbers of 6-13 n-hexanol and 0.5-5 water molecules per cluster were found. O-H and O-O atom distances related to hydrogen bonds between donor/acceptor molecules were theoretically calculated using density functional theory. The results show that at low n-hexanol molar fractions, where a robust hydrogen-bond network is held between n-hexanol molecules, addition of water makes the intermolecular O-O atom distance shorter, reinforcing molecular association in the clusters, whereas at high n-hexanol molar fractions, where dipole-dipole interactions dominate, addition of water makes the intermolecular O-O atom distance longer, weakening the cluster structure. This correlates with experimental NMR results, which show an increase in the size and aggregation number in the clusters upon addition of water at low n-hexanol molar fractions, and a decrease of these magnitudes at high n-hexanol molar fractions. In addition, water produces an increase in the proton exchange rate between donor/acceptor molecules at all n-hexanol molar fractions.

On-site monitoring of atomic density number for an all-optical atomic magnetometer based on atomic spin exchange relaxation.

PubMed

Zhang, Hong; Zou, Sheng; Chen, Xiyuan; Ding, Ming; Shan, Guangcun; Hu, Zhaohui; Quan, Wei

2016-07-25

We present a method for monitoring the atomic density number on site based on atomic spin exchange relaxation. When the spin polarization P ≪ 1, the atomic density numbers could be estimated by measuring magnetic resonance linewidth in an applied DC magnetic field by using an all-optical atomic magnetometer. The density measurement results showed that the experimental results the theoretical predictions had a good consistency in the investigated temperature range from 413 K to 463 K, while, the experimental results were approximately 1.5 ∼ 2 times less than the theoretical predictions estimated from the saturated vapor pressure curve. These deviations were mainly induced by the radiative heat transfer efficiency, which inevitably leaded to a lower temperature in cell than the setting temperature.

Growth of the camping market in the Northeast

Treesearch

George H. Moeller; George H. Moeller

1971-01-01

Almost like an atomic explosion, the number of commercial campgrounds in the Northeast mushroomed 800 percent between 1961 and 1967. During this same period, the number of public campgrounds increased by only 40 percent. The pattern of commercial and public campground growth in the Northeast was studied over a 6-year period to find how such growth may relate to...

Seniority and orbital symmetry as tools for establishing a full configuration interaction hierarchy.

PubMed

Bytautas, Laimutis; Henderson, Thomas M; Jiménez-Hoyos, Carlos A; Ellis, Jason K; Scuseria, Gustavo E

2011-07-28

We explore the concept of seniority number (defined as the number of unpaired electrons in a determinant) when applied to the problem of electron correlation in atomic and molecular systems. Although seniority is a good quantum number only for certain model Hamiltonians (such as the pairing Hamiltonian), we show that it provides a useful partitioning of the electronic full configuration interaction (FCI) wave function into rapidly convergent Hilbert subspaces whose weight diminishes as its seniority number increases. The primary focus of this study is the adequate description of static correlation effects. The examples considered are the ground states of the helium, beryllium, and neon atoms, the symmetric dissociation of the N(2) and CO(2) molecules, as well as the symmetric dissociation of an H(8) hydrogen chain. It is found that the symmetry constraints that are normally placed on the spatial orbitals greatly affect the convergence rate of the FCI expansion. The energy relevance of the seniority zero sector (determinants with all paired electrons) increases dramatically if orbitals of broken spatial symmetry (as those commonly used for Hubbard Hamiltonian studies) are allowed in the wave function construction. © 2011 American Institute of Physics

Geometry, bonding and magnetism in planar triangulene graphene molecules with D3h symmetry: Zigzag Cm∗∗2+4m+1H3m+3 (m = 2, …, 15)

NASA Astrophysics Data System (ADS)

Philpott, Michael R.; Cimpoesu, Fanica; Kawazoe, Yoshiyuki

2008-12-01

Ab initio plane wave based all valence electron DFT calculations with geometry optimization are reported for the electronic structure of planar zigzag edged triangular shaped graphene molecules CH where the zigzag ring number m = 2, …, 15. The largest molecule C 286H 48 has a 3.8 nm side length and retains D3h symmetric geometry. The zone in the middle of the molecules, where the geometry and electronic properties resemble infinite single sheet graphite (graphene), expands with increasing ring number m, driving deviations in geometry, charge and spin to the perimeter. If a molecule is viewed as a set of nested triangular rings of carbon, then the zone where the lattice resembles an infinite sheet of graphene with CC = 142 pm, extends to the middle of the penultimate ring. The radial bonds joining the perimeter carbon atoms to the interior are long CC = 144 pm, except near the three apexes where the bonds are shorter. Isometric surfaces of the total charge density show that the two bonds joined at the apex have the highest valence charge. The perimeter CC bonds establish a simple pattern as the zigzag number increases, which shares some features with the zigzag edges in the D2h linear acenes C 4m+2H 2m+4 and the D6h hexangulenes CH6m but not the D6h symmetric annulenes (CH). The two CC bonds forming each apex are short (≈139 pm), next comes one long bond CC ≈ 142 pm and a middle region where all the CC bonds have length ≈141 pm. The homo-lumo gap declines from 0.53 eV at m = 2 to approximately 0.29 V at m = 15, the latter being larger than found for linear or hexagonal shaped graphenes with comparable edge lengths. Across the molecule the charge on the carbon atoms undergoes a small oscillation following the bipartite lattice. The magnitude of the charge in the same nested triangle decreases monotonically with the distance of the row from the center of the molecule. These systems are predicted to have spin polarized ground states with S = ½( m - 1), in accord with the theorems of Lieb for a bipartite lattice with unequal numbers of sub-lattice carbon atoms. The magnitude of the spin on the atoms increases monotonically from the center to the edges, this effect being greatest on the majority A-sub lattice atoms. The spins are delocalized, not confined to specific atoms as might result in geometries stabilized by islands of aromatic resonance. In the largest systems the magnetic non-bonding levels (NBL) occur as a narrowly distributed set of homos close to the Fermi level, separated from the lower lying valence bond manifold by a gap of about 1 eV. The NBL are a set of disjoint radical orbitals having charge only on atoms belonging to the A-lattice and this charge is concentrated on the perimeter and penultimate row atoms.

Surface Engineering of a Supported PdAg Catalyst for Hydrogenation of CO2 to Formic Acid: Elucidating the Active Pd Atoms in Alloy Nanoparticles.

PubMed

Mori, Kohsuke; Sano, Taiki; Kobayashi, Hisayoshi; Yamashita, Hiromi

2018-06-22

The hydrogenation of carbon dioxide (CO 2 ) to formic acid (FA; HCOOH), a renewable hydrogen storage material, is a promising means of realizing an economical CO 2 -mediated hydrogen energy cycle. The development of reliable heter-ogeneous catalysts is an urgent yet challenging task associated with such systems, although precise catalytic site design protocols are still lacking. In the present study, we demonstrate that PdAg alloy nanoparticles (NPs) supported on TiO 2 promote the efficient selective hydrogenation of CO 2 to give FA even under mild reaction conditions (2.0 MPa, 100 °C). Specimens made using surface engineering with atomic precision reveal a strong correlation between increased cata-lytic activity and decreased electron density of active Pd atoms resulting from a synergistic effect of alloying with Ag atoms. The isolated and electronically promoted surface-exposed Pd atoms in Pd@Ag alloy NPs exhibit a maximum turnover number of 14,839 based on the quantity of surface Pd atoms, which represents a more than ten-fold increase compared to the activity of monometallic Pd/TiO 2 . Kinetic and density functional theory (DFT) calculations show that the attack on the C atom in HCO 3 - by a dissociated H atom over an active Pd site is the rate-determining step during this reaction, and this step is boosted by PdAg alloy NPs having a low Pd/Ag ratio.

High resistivity iron-based, thermally stable magnetic material for on-chip integrated inductors

DOEpatents

Deligianni, Hariklia; Gallagher, William J.; Mason, Maurice; O'Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang

2017-03-07

An on-chip magnetic structure includes a palladium activated seed layer and a substantially amorphous magnetic material disposed onto the palladium activated seed layer. The substantially amorphous magnetic material includes nickel in a range from about 50 to about 80 atomic % (at. %) based on the total number of atoms of the magnetic material, iron in a range from about 10 to about 50 at. % based on the total number of atoms of the magnetic material, and phosphorous in a range from about 0.1 to about 30 at. % based on the total number of atoms of the magnetic material. The magnetic material can include boron in a range from about 0.1 to about 5 at. % based on the total number of atoms of the magnetic material.

OH radical kinetics in hydrogen-air mixtures at the conditions of strong vibrational nonequilibrium

NASA Astrophysics Data System (ADS)

Winters, Caroline; Hung, Yi-Chen; Jans, Elijah; Eckert, Zak; Frederickson, Kraig; Adamovich, Igor V.; Popov, Nikolay

2017-12-01

This work presents results of time-resolved, absolute measurements of OH number density, nitrogen vibrational temperature, and translational-rotational temperature in air and lean hydrogen-air mixtures excited by a diffuse filament nanosecond pulse discharge, at a pressure of 100 Torr and high specific energy loading. The main objective of these measurements is to study kinetics of OH radicals at the conditions of strong vibrational excitation of nitrogen, below autoignition temperature. N2 vibrational temperature and gas temperature in the discharge and the afterglow are measured by ns broadband coherent anti-Stokes Raman scattering. Hydroxyl radical number density is measured by laser induced fluorescence, calibrated by Rayleigh scattering. The results show that the discharge generates strong vibrational nonequilibrium in air and H2-air mixtures for delay times after the discharge pulse of up to ~1 ms, with a peak vibrational temperature of T v  ≈  1900 K at T  ≈  500 K. Nitrogen vibrational temperature peaks at 100-200 µs after the discharge pulse, before decreasing due to vibrational-translational relaxation by O atoms (on the time scale of several hundred µs) and diffusion (on ms time scale). OH number density increases gradually after the discharge pulse, peaking at t ~ 100-300 µs and decaying on a longer time scale, until t ~ 1 ms. Both OH rise time and decay time decrease as H2 fraction in the mixture is increased from 1% to 5%. Comparison of the experimental data with kinetic modeling predictions shows that OH kinetics is controlled primarily by reactions of H2 and O2 with O and H atoms generated during the discharge. At the present conditions, OH number density is not affected by N2 vibrational excitation directly, i.e. via vibrational energy transfer to HO2. The effect of a reaction between vibrationally excited H2 and O atoms on OH kinetics is also shown to be insignificant. As the discharge pulse coupled energy is increased, the model predicts transient OH number density overshoot due to the temperature rise caused by N2 vibrational relaxation by O atoms, which may well be a dominant effect in discharges with specific energy loading.

Atomic Mass and Nuclear Binding Energy for U-287 (Uranium)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume B `Nuclei with Z = 55 - 100' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms', and additionally including data for nuclei with Z = 101 - 130. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope U-287 (Uranium, atomic number Z = 92, mass number A = 287).

Atomic Mass and Nuclear Binding Energy for Ac-212 (Actinium)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume B `Nuclei with Z = 55 - 100' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms', and additionally including data for nuclei with Z = 101 - 130. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope Ac-212 (Actinium, atomic number Z = 89, mass number A = 212).

Coherent control and storage of a microwave pulse in a one-dimensional array of artificial atoms using the Autler-Townes effect and electromagnetically induced transparency

NASA Astrophysics Data System (ADS)

Ayaz, M. Q.; Waqas, Mohsin; Qamar, Sajid; Qamar, Shahid

2018-02-01

In this paper we propose a scheme for coherent control and storage of a microwave pulse in superconducting circuits exploiting the idea of electromagnetically induced transparency (EIT) and the Aulter-Townes (AT) effect. We show that superconducting artificial atoms in a four-level tripod configuration act as EIT based coherent microwave (μ w ) memories with gain features, when they are attached to a one-dimensional transmission line. These atoms are allowed to interact with three microwave fields, such that there are two control fields and one probe field. Our proposed system works in such a way that one control field with large Rabi frequency when interacting with atoms, produces the AT effect. While the second control field with relatively small Rabi frequency produces EIT in one of the absorption windows produced due to the AT splitting for the weak probe field. The group velocity of the probe pulse reduces significantly through this EIT window. Interestingly, the output intensity of the probe pulse increases as we increase the number of artificial atoms. Our results show that the probe microwave pulse can be stored and retrieved with high fidelity.

Long-term epidemiological studies of atomic bomb survivors in Hiroshima and Nagasaki: study populations, dosimetry and summary of health effects.

PubMed

Okubo, Toshiteru

2012-10-01

The Radiation Effects Research Foundation succeeded 28 years' worth of activities of the Atomic Bomb Casualty Commission on long-term epidemiological studies in Hiroshima and Nagasaki. It has three major cohorts of atomic bomb survivors, i.e. the Life Span Study (LSS) of 120,000 people, the In Utero Cohort of 3600 and the Second Generation Study (F(1)) of 77,000. The LSS and F(1) studies include a periodic health examination for each sub-cohort, i.e. the Adult Health Study and the F(1) Clinical Study, respectively. An extensive individual dose estimation was conducted and the system was published as the Dosimetry System established in 2002 (DS02). As results of these studies, increases of cancers in relation to dose were clearly shown. Increases of other mortality causes were also observed, including heart and respiratory diseases. There has been no evidence of genetic effects in the survivors' children, including cancer and other multi-factorial diseases. The increase in the expected mortality number in the next 10 y would allow the analyses of further details of the observed effects related to atomic bomb exposures.

Structure and functionality of bromine doped graphite.

PubMed

Hamdan, Rashid; Kemper, A F; Cao, Chao; Cheng, H P

2013-04-28

First-principles calculations are used to study the enhanced in-plane conductivity observed experimentally in Br-doped graphite, and to study the effect of external stress on the structure and functionality of such systems. The model used in the numerical calculations is that of stage two doped graphite. The band structure near the Fermi surface of the doped systems with different bromine concentrations is compared to that of pure graphite, and the charge transfer between carbon and bromine atoms is analyzed to understand the conductivity change along different high symmetry directions. Our calculations show that, for large interlayer separation between doped graphite layers, bromine is stable in the molecular form (Br2). However, with increased compression (decreased layer-layer separation) Br2 molecules tend to dissociate. While in both forms, bromine is an electron acceptor. The charge exchange between the graphite layers and Br atoms is higher than that with Br2 molecules. Electron transfer to the Br atoms increases the number of hole carriers in the graphite sheets, resulting in an increase of conductivity.

Nonlinear effects in defect production by atomic and molecular ion implantation

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

David, C., E-mail: david@igcar.gov.in; Dholakia, Manan; Chandra, Sharat

This report deals with studies concerning vacancy related defects created in silicon due to implantation of 200 keV per atom aluminium and its molecular ions up to a plurality of 4. The depth profiles of vacancy defects in samples in their as implanted condition are carried out by Doppler broadening spectroscopy using low energy positron beams. In contrast to studies in the literature reporting a progressive increase in damage with plurality, implantation of aluminium atomic and molecular ions up to Al{sub 3}, resulted in production of similar concentration of vacancy defects. However, a drastic increase in vacancy defects is observed duemore » to Al{sub 4} implantation. The observed behavioural trend with respect to plurality has even translated to the number of vacancies locked in vacancy clusters, as determined through gold labelling experiments. The impact of aluminium atomic and molecular ions simulated using MD showed a monotonic increase in production of vacancy defects for cluster sizes up to 4. The trend in damage production with plurality has been explained on the basis of a defect evolution scheme in which for medium defect concentrations, there is a saturation of the as-implanted damage and an increase for higher defect concentrations.« less

Bonded Radii and the Contraction of the Electron Density of the Oxygen Atom by Bonded Interactions

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

Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.

2013-02-21

The bonded radii for more than 550 bonded pairs of atoms, comprising more than 50 crystals, determined from experimental and theoretical electron density distributions, are compared with the effective ionic, ri(M), and crystal radii, rc(M), for metal atoms, M, bonded to O atoms. At odds with the fixed ionic radius of 1.40 Å, assumed for the O atom in the compilation of the ionic radii, the bonded radius for the atom, rb(O), is not fixed but displays a relatively wide range of values as the O atom is progressively polarized by the M-O bonded interactions: as such, rb(O) decreases systematicallymore » from 1.40 Å (the Pauling radius of the oxide anion) as bond lengths decrease when bonded to an electropositive atom like sodium, to 0.64 Å (Bragg’s atomic radius of the O atom) when bonded to an electronegative atom like nitrogen. Both rb(M) and rb(O) increase in tandum with the increasing coordination number of the M atom. The bonded radii of the M atoms are highly correlated with both ri(M) and rc(M), but they both depart systematically from rb(M) and become smaller as the electronegativity of the M atom increases and the M-O bond length decreases. The well-developed correlations between both sets of radii and rb(M) testifies to the relative precision of both sets of radii and the fact that both sets are highly correlated the M-O bond 1 lengths. On the other hand, the progressive departure of rb(O) from the fixed ionic radius of the O atom with the increasing electronegativity of the bonded M atom indicates that any compilation of sets of ionic radii, assuming that the radius for the oxygen atom is fixed in value, is problematical and impacts on the accuracy of the resulting sets of ionic and crystal radii thus compiled. The assumption of a fixed O atom radius not only results in a negative ionic radii for several atoms, but it also results in values of rb(M) that are much as ~ 0.6 Å larger than the ri(M) and rc(M) values, respectively, particularly for the more electronegative M atoms. On the other hand, the ionic radii are in closer agreement with rb(M) for the more electropositive atoms. Notwithstanding that ionic radii are typically smaller than bonded radii, particularly for the more electronegative atoms, they have been used with considerable success in understanding and rationalizing problems and properties in crystal chemistry primarily because both ionic and crystal radii are highly correlated on a one-to-one basis with both the bonded radii and the associated M-O bond lengths. The lack of agreement between the effective ionic and crystal radii and the bonded radii for the more shared bonded interactions is ascribed to the progressive increase in the polarization of the O atom by the bonded atoms with a concomitant decrease in its radius, a factor that was neglected in the compilation of ionic and crystal radii for fluorides, oxides, sulfides and nitrides. This accounts for ionic radii for these materials being smaller than the bonded radii for the more electronegative atoms.« less

Out-of-plane spin polarization of edge currents in Chern insulator with Rashba spin-orbit interaction

NASA Astrophysics Data System (ADS)

Chen, Tsung-Wei; Hsiao, Chin-Lun; Hu, Chong-Der

2016-07-01

We investigate the change in the non-zero Chern number and out-of-plane spin polarization of the edge currents in a honeycomb lattice with the Haldane-Rashba interaction. This interaction breaks the time-reversal symmetry due to the Haldane phase caused by a current loop at the site-I and site-II atoms, and also accounts for the Rashba-type spin-orbit interaction. The Rashba spin-orbit interaction increases the number of Dirac points and the band-touching phenomenon can be generated by tuning the on-site potential in the non-zero Haldane phase. By using the Pontryagin winding number and numerical Berry curvature methods, we find that the Chern number pattern is {+2, -1, 0} and {-2, +1, 0} for the positive and negative Haldane phase, respectively. A non-zero Chern number is called a Chern-insulating phase. We discovered that changes in both the Haldane phase and on-site potential leads to a change in the orientation of the bulk spin polarization of site-I and site-II atoms. Interestingly, in a ribbon with a zigzag edge, which naturally has site-I atoms at one outer edge and site-II atoms at the opposite outer edge, the spin polarization of the edge states approximately obeys the properties of bulk spin polarization regardless of the change in the Chern number. In addition, even when the Chern number changes from  +2 to  -1 (or  -2 to  +1), by tuning the strength of the on-site potential, the sign of the spin polarization of the edge states persists. This approximate bulk-edge correspondence of the spin polarization in the Haldane-Rashba system would play an important role in spintronics, because it enables us to control the orientation of the spin polarization in a single Chern-insulating phase.

Out-of-plane spin polarization of edge currents in Chern insulator with Rashba spin-orbit interaction.

PubMed

Chen, Tsung-Wei; Hsiao, Chin-Lun; Hu, Chong-Der

2016-07-13

We investigate the change in the non-zero Chern number and out-of-plane spin polarization of the edge currents in a honeycomb lattice with the Haldane-Rashba interaction. This interaction breaks the time-reversal symmetry due to the Haldane phase caused by a current loop at the site-I and site-II atoms, and also accounts for the Rashba-type spin-orbit interaction. The Rashba spin-orbit interaction increases the number of Dirac points and the band-touching phenomenon can be generated by tuning the on-site potential in the non-zero Haldane phase. By using the Pontryagin winding number and numerical Berry curvature methods, we find that the Chern number pattern is {+2, -1, 0} and {-2, +1, 0} for the positive and negative Haldane phase, respectively. A non-zero Chern number is called a Chern-insulating phase. We discovered that changes in both the Haldane phase and on-site potential leads to a change in the orientation of the bulk spin polarization of site-I and site-II atoms. Interestingly, in a ribbon with a zigzag edge, which naturally has site-I atoms at one outer edge and site-II atoms at the opposite outer edge, the spin polarization of the edge states approximately obeys the properties of bulk spin polarization regardless of the change in the Chern number. In addition, even when the Chern number changes from  +2 to  -1 (or  -2 to  +1), by tuning the strength of the on-site potential, the sign of the spin polarization of the edge states persists. This approximate bulk-edge correspondence of the spin polarization in the Haldane-Rashba system would play an important role in spintronics, because it enables us to control the orientation of the spin polarization in a single Chern-insulating phase.

LAS bioconcentration is isomer specific

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

Tolls, J.; Haller, M.; Graaf, I. de

1995-12-31

The authors measured parent compound specific bioconcentration data for linear alkylbenzene sulfonates in Pimephales promelas. They did so by using cold, custom synthesized sulfophenyl alkanes. They observed that, within homologous series of isomers, the uptake rate constants (k{sub 1}) and the bioconcentration factor (BCF) increase with increasing number of carbon atoms in the alkyl chain (n{sub C-atoms}). In contrast, the elimination rate constant k{sub 2} appears to be independent of the alkyl chain length. Regressions of log BCF vs n{sub C-atoms} yielded different slopes for the homologous groups of the 5- and the 2-sulfophenyl alkane isomers. Regression of all logmore » BCF-data vs log 1/CMC yielded a good description of the data. However, when regressing the data for both homologous series separately again very different slopes are obtained. The results therefore indicate that hydrophobicity-bioconcentration relationships may be different for different homologous groups of sulfophenyl alkanes.« less

Aspects of electron transport in zigzag graphene nanoribbons

NASA Astrophysics Data System (ADS)

Bhalla, Pankaj; Pratap, Surender

2018-05-01

In this paper, we investigate the aspects of electron transport in the zigzag graphene nanoribbons (ZGNRs) using the nonequilibrium Green’s function (NEGF) formalism. The latter is an esoteric tool in mesoscopic physics. It is used to perform an analysis of ZGNRs by considering potential well. Within this potential, the dependence of transmission coefficient, local density of states (LDOS) and electron transport properties on number of atoms per unit cell is discussed. It is observed that there is an increment in electron and thermal conductance with increasing number of atoms. In addition to these properties, the dependence of same is also studied in figure of merit. The results infer that the contribution of electrons to enhance the figure of merit is important above the crossover temperature.

High resistivity iron-based, thermally stable magnetic material for on-chip integrated inductors

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

Deligianni, Hariklia; Gallagher, William J.; Mason, Maurice

An on-chip magnetic structure includes a palladium activated seed layer and a substantially amorphous magnetic material disposed onto the palladium activated seed layer. The substantially amorphous magnetic material includes nickel in a range from about 50 to about 80 atomic % (at. %) based on the total number of atoms of the magnetic material, iron in a range from about 10 to about 50 at. % based on the total number of atoms of the magnetic material, and phosphorous in a range from about 0.1 to about 30 at. % based on the total number of atoms of the magneticmore » material. The magnetic material can include boron in a range from about 0.1 to about 5 at. % based on the total number of atoms of the magnetic material.« less

Atomic Scale Investigation of Structural Properties and Glass Forming Ability of Ti100-x Al x Metallic Glasses

NASA Astrophysics Data System (ADS)

Tahiri, M.; Hasnaoui, A.; Sbiaai, K.

2018-03-01

In this work, we employed molecular dynamics (MD) simulations to study Ti-Al metallic glasses (MGs) using the embedded atom method (EAM) potential to model the atomic interaction with different compositions. The results showed evidence of the metallic glass formation induced by the split occurring in the second peak of the radial distribution function (RDF) curves implying both Ti and Al atoms. The common neighbor analysis (CNA) method confirmed the presence of the icosahedral clusters with a maximum amount observed for an alloy with 75 pct of Al. Analysis of coordination numbers (CNs) indicated that the total CNs are nearly unchanged in these systems. Finally, Voronoi tessellation analyses (VTA) showed a higher value of the number of icosahedral units at Ti25Al75 composition. This specific composition represents a nearby peritectic point localized at a low melting point in the Ti-Al binary phase diagram. The glass forming ability (GFA) becomes important when the fraction of Al increases by forming and connecting "icosahedral-like" clusters (12-coordinated <0, 0, 12, 0> and 13-coordinated <0, 1, 10, 2>) and by playing a main role in the structure stability of the Ti-Al MGs.

Atomic Scale Investigation of Structural Properties and Glass Forming Ability of Ti100- x Al x Metallic Glasses

NASA Astrophysics Data System (ADS)

Tahiri, M.; Hasnaoui, A.; Sbiaai, K.

2018-06-01

In this work, we employed molecular dynamics (MD) simulations to study Ti-Al metallic glasses (MGs) using the embedded atom method (EAM) potential to model the atomic interaction with different compositions. The results showed evidence of the metallic glass formation induced by the split occurring in the second peak of the radial distribution function (RDF) curves implying both Ti and Al atoms. The common neighbor analysis (CNA) method confirmed the presence of the icosahedral clusters with a maximum amount observed for an alloy with 75 pct of Al. Analysis of coordination numbers (CNs) indicated that the total CNs are nearly unchanged in these systems. Finally, Voronoi tessellation analyses (VTA) showed a higher value of the number of icosahedral units at Ti25Al75 composition. This specific composition represents a nearby peritectic point localized at a low melting point in the Ti-Al binary phase diagram. The glass forming ability (GFA) becomes important when the fraction of Al increases by forming and connecting "icosahedral-like" clusters (12-coordinated <0, 0, 12, 0> and 13-coordinated <0, 1, 10, 2>) and by playing a main role in the structure stability of the Ti-Al MGs.

[Separation of PM2.5 from coal combustion with phase change].

PubMed

Yan, Jin-pei; Yang, Lin-jun; Zhang, Xia; Sun, Lu-juan; Zhang, Yu; Shen, Xiang-lin

2008-12-01

The influence of two methods of gas moisture conditioning on removal efficiency of PM2.5 from coal combustion with addition of atomized droplets and steam was investigated. The particles size distribution and number concentration were measured in real time by electrical low pressure impactor (ELPI). The results show that collection efficiency of PM2.5 from coal combustion can be highly improved with steam condensational enlargement. Particle stage collection efficiency increases with the particles, especially for those smaller than 0.3 microm. The separation efficiency can be improved by 60% with the size of particles increasing from 0.03 microm to 0.3 microm for 0.1 kg/m3 of steam addition. The removal efficiency is independent of the gas temperature at the inlet of conditioning chamber for steam addition. But it increases with the gas temperature obviously for atomized droplets addition, which can be improved by 30% with increasing gas temperature from 136 degrees C to 256 degrees C. High removal efficiency of PM2.5 from coal combustion can be obtained with atomized droplets evaporation in hot flue gas except for steam addition.

Insights into the crystal chemistry of Earth materials rendered by electron density distributions: Pauling's rules revisited

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

Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.

2014-05-20

Pauling's first two rules are examined in terms of the accumulation of the electron density between bonded pairs of atoms for a relatively large number of oxide and silicate crystals and siloxane molecules. The distribution of the electron density shows that the radius of the oxygen atom is not fixed, but that it actually decreases systematically from ~1.40 Å to ~ 0.65 Å as the polarizing power and the electronegativity of the bonded metal atoms increase and the distribution of the O atom is progressively polarized and contracted along the bond vectors by the impact of the bonded interactions. Themore » contractions result in an aspherical oxygen atom that displays as many different bonded “radii” as it has bonded interactions. The bonded radii for the metal atoms match the Shannon and Prewitt ionic radii for the more electropositive atoms like potassium and sodium, but they are systematically larger for the more electronegative atoms like aluminum, silicon and phosphorous. Pauling's first rule is based on the assumption that the radius of the oxide anion is fixed and that the radii of the cations are such that radius sum of the spherical oxide anion and a cation necessarily equals the separation between the cation-anion bonded pair with the coordination number of the cation being determined by the ratio of the radii of the cation and anion. In the case of the bonded radii, the sum of the bonded radii for the metal atoms and the oxide anion necessarily equals the bond lengths by virtue of the way that the bonded radii were determined in the partitioning of the electron density along the bond path into metal and O atom parts. But, the radius ratio for the O and M atoms is an unsatisfactory rule for determining the coordination number of the metal atom inasmuch as a bonded O atom is not, in general, spherical, and its size varies substantially along its bonded directions. But by counting the number of bond paths that radiate from a bonded atom, the coordination number of the atom is determined uniquely independent of the asphericity and sizes of the atom. A power law connection established between the bond lengths and bond strengths for crystals and molecules is mirrored by a comparable power law connection between bond length and the accumulation of the electron density between bonded pairs of atoms, a connection that is consistent with Pauling's electroneutrality postulate that the charges of the atoms in an oxide are negligibly small. The connection indicates that a one-to-one correspondence exists between the accumulation between a pair of bonded atoms and the Pauling bond strength for M-O bonded interaction for all atoms of the periodic table. The connection provides a common basis for understanding the success of the manifold applications that have been made with the bond valence theory model together with the modeling of crystal structures, chemical zoning, leaching and cation transport in batteries and the like. We believe that the wide spread applications of the model in mineralogy and material science owes much of its success to the direct connection between bond strength and the quantum mechanical observable, the electron density distribution. Comparable power law expressions established for the bonded interactions for both crystals and molecules support Pauling's assertion that his second rule has significance for molecules as well as for crystals. A simple expression is found that provides a one to one connection between the accumulation of the electron density between bonded M and O atoms and the Pauling bond strength for all M atoms of the periodic table with ~ 95 % of the variation of the bond strength being explained in terms of a linear dependence on the accumulated electron density. Compelling evidence is presented that supports the argument that the Si-O bonded interactions for tiny siloxane molecules and silicate crystals are chemically equivalent.« less

Quantum Statistical Properties of the Codirectional Kerr Nonlinear Coupler in Terms of su (2 ) Lie Group in Interaction with a Two-level Atom

NASA Astrophysics Data System (ADS)

Abdalla, M. Sebawe; Khalil, E. M.; Obada, A. S.-F.

2017-08-01

The problem of the codirectional Kerr coupler has been considered several times from different point of view. In the present paper we introduce the interaction between a two-level atom and the codirectional Kerr nonlinear coupler in terms of su (2 ) Lie algebra. Under certain conditions we have adjusted the Kerr coupler and consequently we have managed to handle the problem. The wave function is obtained by using the evolution operator where the Heisnberg equation of motion is invoked to get the constants of the motion. We note that the Kerr parameter χ as well as the quantum number j plays the role of controlling the atomic inversion behavior. Also the maximum entanglement occurs after a short period of time when χ = 0. On the other hand for the entropy and the variance squeezing we observe that there is exchange between the quadrature variances. Furthermore, the variation in the quantum number j as well as in the parameter χ leads to increase or decrease in the number of fluctuations. Finally we examined the second order correlation function where classical and nonclassical phenomena are observed.

Formation of Surface and Quantum-Well States in Ultra Thin Pt Films on the Au(111) Surface

PubMed Central

Silkin, Igor V.; Koroteev, Yury M.; Echenique, Pedro M.; Chulkov, Evgueni V.

2017-01-01

The electronic structure of the Pt/Au(111) heterostructures with a number of Pt monolayers n ranging from one to three is studied in the density-functional-theory framework. The calculations demonstrate that the deposition of the Pt atomic thin films on gold substrate results in strong modifications of the electronic structure at the surface. In particular, the Au(111) s-p-type Shockley surface state becomes completely unoccupied at deposition of any number of Pt monolayers. The Pt adlayer generates numerous quantum-well states in various energy gaps of Au(111) with strong spatial confinement at the surface. As a result, strong enhancement in the local density of state at the surface Pt atomic layer in comparison with clean Pt surface is obtained. The excess in the density of states has maximal magnitude in the case of one monolayer Pt adlayer and gradually reduces with increasing number of Pt atomic layers. The spin–orbit coupling produces strong modification of the energy dispersion of the electronic states generated by the Pt adlayer and gives rise to certain quantum states with a characteristic Dirac-cone shape. PMID:29232833

Future population of atomic bomb survivors in Nagasaki.

PubMed

Yokota, Kenichi; Mine, Mariko; Shibata, Yoshisada

2013-01-01

The Nagasaki University Atomic Bomb Survivor Database, which was established in 1978 for elucidating the long-term health effects of the atomic bombing, has registered since 1970 about 120,000 atomic bomb survivors with a history of residence in Nagasaki city. Since the number of atomic bomb survivors has steadily been decreasing, prediction of future population is important for planning future epidemiologic studies, and we tried to predict the population of atomic bomb survivors in Nagasaki city from 2008 to 2030. In addition, we evaluated our estimated population comparing with the actual number from 2008 to 2011.

Two-mode mazer injected with V-type three-level atoms

NASA Astrophysics Data System (ADS)

Liang, Wen-Qing; Zhang, Zhi-Ming; Xie, Sheng-Wu

2003-12-01

The properties of the two-mode mazer operating on V-type three-level atoms are studied. The effect of the one-atom pumping on the two modes of the cavity field in number-state is asymmetric, that is, the atom emits a photon into one mode with some probability and absorbs a photon from the other mode with some other probability. This effect makes the steady-state photon distribution and the steady-state photon statistics asymmetric for the two modes. The diagram of the probability currents for the photon distribution, given by the analysis of the master equation, reveals that there is no detailed balance solution for the master equation. The computations show that the photon statistics of one mode or both modes can be sub-Poissonian, that the two modes can have anticorrelation or correlation, that the photon statistics increases with the increase of thermal photons and that the resonant position and strength of the photon statistics are influenced by the ratio of the two coupling strengths of the two modes. These properties are also discussed physically.

Does the number of nitrogen atoms have an influence on the conducting properties of diphenylazines? A DFT insight

NASA Astrophysics Data System (ADS)

Moral, Mónica; Granadino-Roldán, José Manuel; Garzón, Andrés; García, Gregorio; Fernández-Gómez, Manuel

2011-01-01

The present study reports on the variation of some structural and electronic properties related to the electron conductivity for the series of diphenylazines represented by the formula Ph sbnd (C 2+nN 4-nH n) sbnd Ph, n = 0 - 4. Properties such as planarity, aromaticity, HOMO → LUMO excitation energy, electron affinity, LUMO level energy, reorganization energy and electron coupling between neighboring molecules in the crystal were analyzed from a theoretical perspective as a function of the number of nitrogen atoms in the molecular structure. As a result, the planarity, aromaticity and electron affinity increase with the number of N atoms in the central ring while the HOMO → LUMO excitation energy and LUMO levels diminish. It is worth noting that up to n = 3, the frontier orbitals appear delocalized throughout the whole system while for n = 4 the localized character of the LUMO might explain the increase in the reorganization energy and thus the higher difficulty to delocalize the excess of negative charge. Electron coupling between neighboring molecules was also estimated on the basis of the energy splitting in dimer method and the reported crystal structures for some of the studied molecules. Accordingly, the highest | t12| value was obtained for Ph 2T N3 (0.06 eV) while Ph 2Tz should be the most advantageous candidate of the series in terms of electron injection.

Tetrabenzoporphyrin and -mono-, -cis-di- and Tetrabenzotriazaporphyrin Derivatives: Electrochemical and Spectroscopic Implications of meso CH Group Replacement with Nitrogen.

PubMed

van As, Adele; Joubert, Chris C; Buitendach, Blenerhassitt E; Erasmus, Elizabeth; Conradie, Jeanet; Cammidge, Andrew N; Chambrier, Isabelle; Cook, Michael J; Swarts, Jannie C

2015-06-01

Nonperipherally hexyl-substituted metal-free tetrabenzoporphyrin (2H-TBP, 1a) tetrabenzomonoazaporphyrin (2H-TBMAP, 2a), tetrabenzo-cis-diazaporphyrin (2H-TBDAP, 3a), tetrabenzotriazaporphyrin (2H-TBTAP, 4a), and phthalocyanine (2H-Pc, 5a), as well as their copper complexes (1b-5b), were synthesized. As the number of meso nitrogen atoms increases from zero to four, λmax of the Q-band absorption peak becomes red-shifted by almost 100 nm, and extinction coefficients increased at least threefold. Simultaneously the blue-shifted Soret (UV) band substantially decreased in intensity. These changes were related to the relative electron-density of each macrocycle expressed as the group electronegativity sum of all meso N and CH atom groups, ∑χR. X-ray photoelectron spectroscopy differentiated between the three different types of macrocyclic nitrogen atoms (the Ninner, (NH)inner, and Nmeso) in the metal-free complexes. Binding energies of the Nmeso and Ninner,Cu atoms in copper chelates could not be resolved. Copper insertion lowered especially the cathodic redox potentials, while all four observed redox processes occurred at larger potentials as the number of meso nitrogens increased. Computational chemical methods using density functional theory confirmed 1b to exhibit a Cu(II) reduction prior to ring-based reductions, while for 2b, Cu(II) reduction is the first reductive step only if the nonperipheral substituents are hydrogen. When they are methyl groups, it is the second reduction process; when they are ethyl, propyl, or hexyl, it becomes the third reductive process. Spectro-electrochemical measurements showed redox processes were associated with a substantial change in intensity of at least two main absorbances (the Q and Soret bands) in the UV spectra of these compounds.

Trapped atom number in millimeter-scale magneto-optical traps

NASA Astrophysics Data System (ADS)

Hoth, Gregory W.; Donley, Elizabeth A.; Kitching, John

2012-06-01

For compact cold-atom instruments, it is desirable to trap a large number of atoms in a small volume to maximize the signal-to-noise ratio. In MOTs with beam diameters of a centimeter or larger, the slowing force is roughly constant versus velocity and the trapped atom number scales as d^4. For millimeter-scale MOTs formed from pyramidal reflectors, a d^6 dependence has been observed [Pollack et al., Opt. Express 17, 14109 (2009)]. A d^6 scaling is expected for small MOTs, where the slowing force is proportional to the atom velocity. For a 1 mm diameter MOT, a d^6 scaling results in 10 atoms, and the difference between a d^4 and a d^6 dependence corresponds to a factor of 1000 in atom number and a factor of 30 in the signal-to-noise ratio. We have observed >10^4 atoms in 1 mm diameter MOTs, consistent with a d^4 dependence. We are currently performing measurements for sub-mm MOTs to determine where the d^4 to d^6 crossover occurs in our system. We are also exploring MOTs based on linear polarization, which can potentially produce stronger slowing forces due to stimulated emission [Emile et al., Europhys. Lett. 20, 687 (1992)]. It may be possible to trap more atoms in small volumes with this method, since high intensities can be easily achieved.

Computational simulation of the effects of oxygen on the electronic states of hydrogenated 3C-porous SiC

PubMed Central

2012-01-01

A computational study of the dependence of the electronic band structure and density of states on the chemical surface passivation of cubic porous silicon carbide (pSiC) was performed using ab initio density functional theory and the supercell method. The effects of the porosity and the surface chemistry composition on the energetic stability of pSiC were also investigated. The porous structures were modeled by removing atoms in the [001] direction to produce two different surface chemistries: one fully composed of silicon atoms and one composed of only carbon atoms. The changes in the electronic states of the porous structures as a function of the oxygen (O) content at the surface were studied. Specifically, the oxygen content was increased by replacing pairs of hydrogen (H) atoms on the pore surface with O atoms attached to the surface via either a double bond (X = O) or a bridge bond (X-O-X, X = Si or C). The calculations show that for the fully H-passivated surfaces, the forbidden energy band is larger for the C-rich phase than for the Si-rich phase. For the partially oxygenated Si-rich surfaces, the band gap behavior depends on the O bond type. The energy gap increases as the number of O atoms increases in the supercell if the O atoms are bridge-bonded, whereas the band gap energy does not exhibit a clear trend if O is double-bonded to the surface. In all cases, the gradual oxygenation decreases the band gap of the C-rich surface due to the presence of trap-like states. PMID:22913486

Accurate identification of layer number for few-layer WS2 and WSe2 via spectroscopic study.

PubMed

Li, Yuanzheng; Li, Xinshu; Yu, Tong; Yang, Guochun; Chen, Heyu; Zhang, Cen; Feng, Qiushi; Ma, Jiangang; Liu, Weizhen; Xu, Haiyang; Liu, Yichun; Liu, Xinfeng

2018-03-23

Transition metal dichalcogenides (TMDs) with a typical layered structure are highly sensitive to their layer number in optical and electronic properties. Seeking a simple and effective method for layer number identification is very important to low-dimensional TMD samples. Herein, a rapid and accurate layer number identification of few-layer WS 2 and WSe 2 is proposed via locking their photoluminescence (PL) peak-positions. As the layer number of WS 2 /WSe 2 increases, it is found that indirect transition emission is more thickness-sensitive than direct transition emission, and the PL peak-position differences between the indirect and direct transitions can be regarded as fingerprints to identify their layer number. Theoretical calculation confirms that the notable thickness-sensitivity of indirect transition derives from the variations of electron density of states of W atom d-orbitals and chalcogen atom p-orbitals. Besides, the PL peak-position differences between the indirect and direct transitions are almost independent of different insulating substrates. This work not only proposes a new method for layer number identification via PL studies, but also provides a valuable insight into the thickness-dependent optical and electronic properties of W-based TMDs.

Conformations and charge distributions of diazocyclopropanes

NASA Astrophysics Data System (ADS)

Borges, Itamar, Jr.

Three diazo-substituted cyclopropane compounds, which have been suggested as new potential high energy compounds, were studied employing the B3LYP-DFT/6-31G(d,p) method. Geometries were optimized. Distributed multipole analysis, computed from the B3LYP-DFT/6-31G(d,p) density matrix, was used to describe the details of the molecular charge distribution of the three molecules. It was verified that electron withdrawing from the C ring atoms and charge build-up on the N atoms bonded to the ring increased with the number of diazo groups. These effects were related to increased sensitivity to impact and easiness of C bond N bond breaking in the three compounds.

Effective atomic number, energy loss and radiation damage studies in some materials commonly used in nuclear applications for heavy charged particles such as H, C, Mg, Fe, Te, Pb and U

NASA Astrophysics Data System (ADS)

Kurudirek, Murat

2016-05-01

Commonly used nuclear physics materials such as water, concrete, Pb-glass, paraffin, freon and P 10 gases, some alloys such as brass, bronze, stainless-steel and some scintillators such as anthracene, stilbene and toluene have been investigated with respect to the heavy charged particle interaction as means of projected range and effective atomic number (Zeff) in the energy region 10 keV to 10 MeV. Calculations were performed for heavy ions such as H, C, Mg, Fe, Te, Pb and U. Also, the energy loss and radiation damage were studied using SRIM Monte Carlo code for anthracene for different heavy ions of 100 keV kinetic energy. It has been observed that the variation in Zeff becomes less when the atomic number of the ions increase. Glass-Pb, bronze, brass, stainless-steel and Freon gas were found to vary less than 10% in the energy region 10 keV to 10 MeV. For total proton interaction, discrepancies up to 10% and 18% between two databases namely PSTAR and SRIM were noted in mass stopping power and Zeff of water, respectively. The range calculations resulted with a conclusion that the metal alloys and glass-Pb have lowest values of ranges confirming best shielding against energetic heavy ions whereas freon and P 10 gases have the highest values of ranges in the entire energy region. The simulation results showed that the energy loss (%) to target electrons decreases as the Z of the incident ion increases. Also, it was observed that the radiation damage first increases with Z of the ion and then keeps almost constant for ions with Z≥52.

Optimal control of complex atomic quantum systems

PubMed Central

van Frank, S.; Bonneau, M.; Schmiedmayer, J.; Hild, S.; Gross, C.; Cheneau, M.; Bloch, I.; Pichler, T.; Negretti, A.; Calarco, T.; Montangero, S.

2016-01-01

Quantum technologies will ultimately require manipulating many-body quantum systems with high precision. Cold atom experiments represent a stepping stone in that direction: a high degree of control has been achieved on systems of increasing complexity. However, this control is still sub-optimal. In many scenarios, achieving a fast transformation is crucial to fight against decoherence and imperfection effects. Optimal control theory is believed to be the ideal candidate to bridge the gap between early stage proof-of-principle demonstrations and experimental protocols suitable for practical applications. Indeed, it can engineer protocols at the quantum speed limit – the fastest achievable timescale of the transformation. Here, we demonstrate such potential by computing theoretically and verifying experimentally the optimal transformations in two very different interacting systems: the coherent manipulation of motional states of an atomic Bose-Einstein condensate and the crossing of a quantum phase transition in small systems of cold atoms in optical lattices. We also show that such processes are robust with respect to perturbations, including temperature and atom number fluctuations. PMID:27725688

Optimal control of complex atomic quantum systems.

PubMed

van Frank, S; Bonneau, M; Schmiedmayer, J; Hild, S; Gross, C; Cheneau, M; Bloch, I; Pichler, T; Negretti, A; Calarco, T; Montangero, S

2016-10-11

Quantum technologies will ultimately require manipulating many-body quantum systems with high precision. Cold atom experiments represent a stepping stone in that direction: a high degree of control has been achieved on systems of increasing complexity. However, this control is still sub-optimal. In many scenarios, achieving a fast transformation is crucial to fight against decoherence and imperfection effects. Optimal control theory is believed to be the ideal candidate to bridge the gap between early stage proof-of-principle demonstrations and experimental protocols suitable for practical applications. Indeed, it can engineer protocols at the quantum speed limit - the fastest achievable timescale of the transformation. Here, we demonstrate such potential by computing theoretically and verifying experimentally the optimal transformations in two very different interacting systems: the coherent manipulation of motional states of an atomic Bose-Einstein condensate and the crossing of a quantum phase transition in small systems of cold atoms in optical lattices. We also show that such processes are robust with respect to perturbations, including temperature and atom number fluctuations.

Investigation on the neutral and anionic BxAlyH2 (x + y = 7, 8, 9) clusters using density functional theory combined with photoelectron spectroscopy.

PubMed

Ding, Li-Ping; Shao, Peng; Lu, Cheng; Zhang, Fang-Hui; Ding, Lei; Yuan, Tao Li

2016-08-17

The structure and bonding nature of neutral and negatively charged BxAlyH2 (x + y = 7, 8, 9) clusters are investigated with the aid of previously published experimental photoelectron spectra combined with the present density functional theory calculations. The comparison between the experimental photoelectron spectra and theoretical simulated spectra helps to identify the ground state structures. The accuracy of the obtained ground state structures is further verified by calculating their adiabatic electron affinities and vertical detachment energies and comparing them against available experimental data. The results show that the structures of BxAlyH2 transform from three-dimensional to planar structures as the number of boron atoms increases. Moreover, boron atoms tend to bind together forming Bn units. The hydrogen atoms prefer to bind with boron atoms rather than aluminum atoms. The analyses of the molecular orbital on the ground state structures further support the abovementioned results.

The long-term outcome of atomic bomb survivors with gastric carcinoma.

PubMed

Yamamoto, Manabu; Matsuyama, Ayumi; Kameyama, Toshifumi; Okamoto, Masahiro; Okazaki, Jin; Utsunomiya, Tohru; Tsutsui, Shinichi; Ishida, Teruyoshi

2009-12-01

During the decade following the 1945 atomic bombing of Hiroshima, a high incidence of leukemia was observed among atomic bomb survivors. Subsequently, the incidence of other cancers gradually increased while that of leukemia decreased. We examined the long-term clinical outcome of gastric cancer and second primary cancer in atomic bomb survivors. Results of surgical treatment of gastric cancer were reviewed in 231 atomic bomb survivors and 759 control patients between 1995 and 2006. Long-term prognosis of gastric cancer in atomic bomb survivors was significantly poorer than that in control patients (P < 0.05). In a multivariate analysis, age, depth of tumor invasion, lymph node metastases, and curability were found to be significant and independent prognostic factors for gastric cancer. The incidence of second primary cancer after gastric cancer was significantly higher in survivors than in control patients (P < 0.01), because the number of elderly patients in the survivors was higher. Gastric cancer in survivors had a significantly poorer prognosis. Although the frequency of second primary cancer after gastric cancer in survivors was higher than that in control patients, it did not influence the prognosis.

Local structure of NiPd solid solution alloys and its response to ion irradiation

DOE PAGES

Zhang, Fuxiang; Ullah, Mohammad Wali; Zhao, Shijun; ...

2018-04-27

The local structure of Ni$-$Pd solid solution alloys with compositions of Ni 80Pd 20 and Ni 50Pd 50 was investigated with anomalous X-ray diffraction, X-ray absorption and theoretical calculation/simulation. The fcc lattice is distorted for both alloys, and the Pd$-$Pd atomic pair distance is +4.4% and +1.4% larger than ideal values in Ni 80Pd 20 and Ni 50Pd 50 alloys, respectively. The corresponding atomic pair distance of Ni$-$Ni is -1.8% and -3.0% less than the ideal values. Different short-range orders in the alloys were quantitatively identified at the atomic level. In Ni 80Pd 20, Pd atoms are likely to formmore » Pd$-$Pd pairs, while Pd atoms are connected with Pd atoms in the second shell in the equiatomic solid solution alloy. Upon ion irradiation, little change of interatomic distance, but modification of chemical short-range order was observed. The number of Pd$-$Pd pairs decreases to the lowest value at 0.1 dpa, and further irradiation make it increase.« less

Local structure of NiPd solid solution alloys and its response to ion irradiation

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

Zhang, Fuxiang; Ullah, Mohammad Wali; Zhao, Shijun

The local structure of Ni$-$Pd solid solution alloys with compositions of Ni 80Pd 20 and Ni 50Pd 50 was investigated with anomalous X-ray diffraction, X-ray absorption and theoretical calculation/simulation. The fcc lattice is distorted for both alloys, and the Pd$-$Pd atomic pair distance is +4.4% and +1.4% larger than ideal values in Ni 80Pd 20 and Ni 50Pd 50 alloys, respectively. The corresponding atomic pair distance of Ni$-$Ni is -1.8% and -3.0% less than the ideal values. Different short-range orders in the alloys were quantitatively identified at the atomic level. In Ni 80Pd 20, Pd atoms are likely to formmore » Pd$-$Pd pairs, while Pd atoms are connected with Pd atoms in the second shell in the equiatomic solid solution alloy. Upon ion irradiation, little change of interatomic distance, but modification of chemical short-range order was observed. The number of Pd$-$Pd pairs decreases to the lowest value at 0.1 dpa, and further irradiation make it increase.« less

Experimental evaluation of effective atomic number of composite materials using back-scattering of gamma photons

NASA Astrophysics Data System (ADS)

Singh, Inderjeet; Singh, Bhajan; Sandhu, B. S.; Sabharwal, Arvind D.

2017-04-01

A method has been presented for calculation of effective atomic number (Zeff) of composite materials, by using back-scattering of 662 keV gamma photons obtained from a 137Cs mono-energetic radioactive source. The present technique is a non-destructive approach, and is employed to evaluate Zeff of different composite materials, by interacting gamma photons with semi-infinite material in a back-scattering geometry, using a 3″ × 3″ NaI(Tl) scintillation detector. The present work is undertaken to study the effect of target thickness on intensity distribution of gamma photons which are multiply back-scattered from targets (pure elements) and composites (mixtures of different elements). The intensity of multiply back-scattered events increases with increasing target thickness and finally saturates. The saturation thickness for multiply back-scattered events is used to assign a number (Zeff) for multi-element materials. Response function of the 3″ × 3″ NaI(Tl) scintillation detector is applied on observed pulse-height distribution to include the contribution of partially absorbed photons. The reduced value of signal-to-noise ratio interprets the increase in multiply back-scattered data of a response corrected spectrum. Data obtained from Monte Carlo simulations and literature also support the present experimental results.

Population Dynamics of Excited Atoms in Dissipative Cavities

NASA Astrophysics Data System (ADS)

Zou, Hong-Mei; Liu, Yu; Fang, Mao-Fa

2016-10-01

Population dynamics of excited atoms in dissipative cavities is investigated in this work. We present a method of controlling populations of excited atoms in dissipative cavities. For the initial state | e e> A B |00> a b , the repopulation of excited atoms can be obtained by using atom-cavity couplings and non-Markovian effects after the atomic excited energy decays to zero. For the initial state | g g> A B |11> a b , the two atoms can also be populated to the excited states from the initial ground states by using atom-cavity couplings and non-Markovian effects. And the stronger the atom-cavity coupling or the non-Markovian effect is, the larger the number of repopulation of excited atoms is. Particularly, when the atom-cavity coupling or the non-Markovian effect is very strong, the number of repopulation of excited atoms can be close to one in a short time and will tend to a steady value in a long time.

Information-theoretic measures of hydrogen-like ions in weakly coupled Debye plasmas

NASA Astrophysics Data System (ADS)

Zan, Li Rong; Jiao, Li Guang; Ma, Jia; Ho, Yew Kam

2017-12-01

Recent development of information theory provides researchers an alternative and useful tool to quantitatively investigate the variation of the electronic structure when atoms interact with the external environment. In this work, we make systematic studies on the information-theoretic measures for hydrogen-like ions immersed in weakly coupled plasmas modeled by Debye-Hückel potential. Shannon entropy, Fisher information, and Fisher-Shannon complexity in both position and momentum spaces are quantified in high accuracy for the hydrogen atom in a large number of stationary states. The plasma screening effect on embedded atoms can significantly affect the electronic density distributions, in both conjugate spaces, and it is quantified by the variation of information quantities. It is shown that the composite quantities (the Shannon entropy sum and the Fisher information product in combined spaces and Fisher-Shannon complexity in individual space) give a more comprehensive description of the atomic structure information than single ones. The nodes of wave functions play a significant role in the changes of composite information quantities caused by plasmas. With the continuously increasing screening strength, all composite quantities in circular states increase monotonously, while in higher-lying excited states where nodal structures exist, they first decrease to a minimum and then increase rapidly before the bound state approaches the continuum limit. The minimum represents the most reduction of uncertainty properties of the atom in plasmas. The lower bounds for the uncertainty product of the system based on composite information quantities are discussed. Our research presents a comprehensive survey in the investigation of information-theoretic measures for simple atoms embedded in Debye model plasmas.

AtomDB: Expanding an Accessible and Accurate Atomic Database for X-ray Astronomy

NASA Astrophysics Data System (ADS)

Smith, Randall

Since its inception in 2001, the AtomDB has become the standard repository of accurate and accessible atomic data for the X-ray astrophysics community, including laboratory astrophysicists, observers, and modelers. Modern calculations of collisional excitation rates now exist - and are in AtomDB - for all abundant ions in a hot plasma. AtomDB has expanded beyond providing just a collisional model, and now also contains photoionization data from XSTAR as well as a charge exchange model, amongst others. However, building and maintaining an accurate and complete database that can fully exploit the diagnostic potential of high-resolution X-ray spectra requires further work. The Hitomi results, sadly limited as they were, demonstrated the urgent need for the best possible wavelength and rate data, not merely for the strongest lines but for the diagnostic features that may have 1% or less of the flux of the strong lines. In particular, incorporation of weak but powerfully diagnostic satellite lines will be crucial to understanding the spectra expected from upcoming deep observations with Chandra and XMM-Newton, as well as the XARM and Athena satellites. Beyond incorporating this new data, a number of groups, both experimental and theoretical, have begun to produce data with errors and/or sensitivity estimates. We plan to use this to create statistically meaningful spectral errors on collisional plasmas, providing practical uncertainties together with model spectra. We propose to continue to (1) engage the X-ray astrophysics community regarding their issues and needs, notably by a critical comparison with other related databases and tools, (2) enhance AtomDB to incorporate a large number of satellite lines as well as updated wavelengths with error estimates, (3) continue to update the AtomDB with the latest calculations and laboratory measurements, in particular velocity-dependent charge exchange rates, and (4) enhance existing tools, and create new ones as needed to increase the functionality of, and access to, AtomDB.

On the bosonic atoms

NASA Astrophysics Data System (ADS)

Amusia, M. Ya.; Chernysheva, L. V.

2018-01-01

We investigate ground state properties of atoms, in which substitute fermions - electrons by bosons, namely π --mesons. We perform some calculations in the frame of modified Hartree-Fock (HF) equation. The modification takes into account symmetry, instead of anti-symmetry of the pair identical bosons wave function. The modified HF approach thus enhances (doubles) the effect of self-action for the boson case. Therefore, we accordingly modify the HF equations by eliminating the self-action terms "by hand". The contribution of meson-meson and meson-nucleon non-Coulomb interaction is inessential at least for atoms with low and intermediate nuclear charge, which is our main subject. We found that the binding energy of pion negative ions A π - , pion atoms A π , and the number of extra bound pions ΔN π increases with the growth of nuclear charge Z. For e.g. Xe ΔN π = 4. As an example of a simple process with a pion atom, we consider photoionization that differs essentially from that for electron atoms. Namely, it is not monotonic decreasing from the threshold but has instead a prominent maximum above threshold. We study also elastic scattering of pions by pion atoms.

Van-der-Waals interaction of atoms in dipolar Rydberg states

NASA Astrophysics Data System (ADS)

Kamenski, Aleksandr A.; Mokhnenko, Sergey N.; Ovsiannikov, Vitaly D.

2018-02-01

An asymptotic expression for the van-der-Waals constant C 6( n) ≈ -0.03 n 12 K p ( x) is derived for the long-range interaction between two highly excited hydrogen atoms A and B in their extreme Stark states of equal principal quantum numbers n A = n B = n ≫ 1 and parabolic quantum numbers n 1(2) = n - 1, n 2(1) = m = 0 in the case of collinear orientation of the Stark-state dipolar electric moments and the interatomic axis. The cubic polynomial K 3( x) in powers of reciprocal values of the principal quantum number x = 1/ n and quadratic polynomial K 2( y) in powers of reciprocal values of the principal quantum number squared y = 1/ n 2 were determined on the basis of the standard curve fitting polynomial procedure from the calculated data for C 6( n). The transformation of attractive van-der-Waals force ( C 6 > 0) for low-energy states n < 23 into repulsive force ( C 6 < 0) for all higher-energy states of n ≥ 23, is observed from the results of numerical calculations based on the second-order perturbation theory for the operator of the long-range interaction between neutral atoms. This transformation is taken into account in the asymptotic formulas (in both cases of p = 2, 3) by polynomials K p tending to unity at n → ∞ ( K p (0) = 1). The transformation from low- n attractive van-der-Waals force into high- n repulsive force demonstrates the gradual increase of the negative contribution to C 6( n) from the lower-energy two-atomic states, of the A(B)-atom principal quantum numbers n'A(B) = n-Δ n (where Δ n = 1, 2, … is significantly smaller than n for the terms providing major contribution to the second-order series), which together with the states of n″B(A) = n+Δ n make the joint contribution proportional to n 12. So, the hydrogen-like manifold structure of the energy spectrum is responsible for the transformation of the power-11 asymptotic dependence C 6( n) ∝ n 11of the low-angular-momenta Rydberg states in many-electron atoms into the power-12 dependence C 6( n) ∝ n 12 for the dipolar states of the Rydberg manifold.

The increase in animal mortality risk following exposure to sparsely ionizing radiation is not linear quadratic with dose

DOE PAGES

Haley, Benjamin M.; Paunesku, Tatjana; Grdina, David J.; ...

2015-12-09

The US government regulates allowable radiation exposures relying, in large part, on the seventh report from the committee to estimate the Biological Effect of Ionizing Radiation (BEIR VII), which estimated that most contemporary exposures- protracted or low-dose, carry 1.5 fold less risk of carcinogenesis and mortality per Gy than acute exposures of atomic bomb survivors. This correction is known as the dose and dose rate effectiveness factor for the life span study of atomic bomb survivors (DDREF LSS). As a result, it was calculated by applying a linear-quadratic dose response model to data from Japanese atomic bomb survivors and amore » limited number of animal studies.« less

The increase in animal mortality risk following exposure to sparsely ionizing radiation is not linear quadratic with dose

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

Haley, Benjamin M.; Paunesku, Tatjana; Grdina, David J.

The US government regulates allowable radiation exposures relying, in large part, on the seventh report from the committee to estimate the Biological Effect of Ionizing Radiation (BEIR VII), which estimated that most contemporary exposures- protracted or low-dose, carry 1.5 fold less risk of carcinogenesis and mortality per Gy than acute exposures of atomic bomb survivors. This correction is known as the dose and dose rate effectiveness factor for the life span study of atomic bomb survivors (DDREF LSS). As a result, it was calculated by applying a linear-quadratic dose response model to data from Japanese atomic bomb survivors and amore » limited number of animal studies.« less

Theoretical study of electron transport along self-assembled graphitic nanowires

NASA Astrophysics Data System (ADS)

Paulsson, Magnus; Stafström, Sven

2000-11-01

Electron transport through stacks of polyaromatic hydrocarbons is studied theoretically using the Landauer formalism. The polyaromatic hydrocarbons can be synthesized in many different sizes and can form molecular stacks with a varying number of molecules and with a rather strong π-overlap along the stack. This allows for a large flexibility in the nanostructure of these materials and makes it possible to study the variation in the conductance with a number of different factors: a near-linear increase in the conductance as a function of the number of atoms in the individual molecule is observed. Furthermore, the conductance drops exponentially with the number of molecules in the stacks, from which it follows that an increase in the intermolecular hopping results in an increase in the conductance which is proportional to the intermolecular hopping to the power of 2(N-1), where N is the number of molecules in the stack.

Optimized evaporative cooling for sodium Bose-Einstein condensation against three-body loss

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

Shobu, Takahiko; Yamaoka, Hironobu; Imai, Hiromitsu

2011-09-15

We report on a highly efficient evaporative cooling optimized experimentally. We successfully created sodium Bose-Einstein condensates with 6.4x10{sup 7} atoms starting from 6.6x10{sup 9} thermal atoms trapped in a magnetic trap by employing a fast linear sweep of radio frequency at the final stage of evaporative cooling so as to overcome the serious three-body losses. The experimental results such as the cooling trajectory and the condensate growth quantitatively agree with the numerical simulations of evaporative cooling on the basis of the kinetic theory of a Bose gas carefully taking into account our specific experimental conditions. We further discuss theoretically amore » possibility of producing large condensates, more than 10{sup 8} sodium atoms, by simply increasing the number of initial thermal trapped atoms and the corresponding optimization of evaporative cooling.« less

Reaction and Protection of Electrical Wire Insulators in Atomic-oxygen Environments

NASA Technical Reports Server (NTRS)

Hung, Ching-Cheh; Cantrell, Gidget

1994-01-01

Atomic-oxygen erosion on spacecraft in low Earth orbit is an issue which is becoming increasingly important because of the growing number of spacecraft that will fly in the orbits which have high concentrations of atomic oxygen. In this investigation, the atomic-oxygen durability of three types of electrical wire insulation (carbon-based, fluoropolymer, and polysiloxane elastomer) were evaluated. These insulation materials were exposed to thermal-energy atomic oxygen, which was obtained by RF excitation of air at a pressure of 11-20 Pa. The effects of atomic-oxygen exposure on insulation materials indicate that all carbon-based materials erode at about the same rate as polyamide Kapton and, therefore, are not atomic-oxygen durable. However, the durability of fluoropolymers needs to be evaluated on a case by case basis because the erosion rates of fluoropolymers vary widely. For example, experimental data suggest the formation of atomic fluorine during atomic-oxygen amorphous-fluorocarbon reactions. Dimethyl polysiloxanes (silicone) do not lose mass during atomic-oxygen exposure, but develop silica surfaces which are under tension and frequently crack as a result of loss of methyl groups. However, if the silicone sample surfaces were properly pretreated to provide a certain roughness, atomic oxygen exposure resulted in a sturdy, non-cracked atomic-oxygen durable SiO2 layer. Since the surface does not crack during such silicone-atomic oxygen reaction, the crack-induced contamination by silicone can be reduced or completely stopped. Therefore, with proper pretreatment, silicone can be either a wire insulation material or a coating on wire insulation materials to provide atomic-oxygen durability.

X-ray Diffraction Study of Order-Disorder Phase Transition in CuMPt6 (M=3d Elements) Alloys

NASA Astrophysics Data System (ADS)

Ahmed, Ejaz; Takahashi, Miwako; Iwasaki, Hiroshi; Ohshima, Ken-ichi

2009-01-01

We investigated the ordering behavior of ternary CuMPt6 alloys with M=Ti, V, Cr, Mn, Fe, Co, and Ni by high-temperature polycrystalline X-ray diffraction. The alloys undergo a phase transition from the fcc disordered state to the Cu3Au-type ordered state, except for the alloy with M=Ni, in which only short-range order forms. The transition temperature Tc is highest (1593 K) for M=Ti and decreases almost monotonically with increasing atomic number to 1153 K for M=Co. The observed dependence of ordering tendency on the atomic number of M is discussed in the light of the theory of ordering in transition-metal alloys and its significance for the study of ordering in ternary alloys.

Quantitative characterization of new supramolecular synthons involving fluorine atoms in the crystal structures of di- and tetrafluorinated benzamides.

PubMed

Mondal, Pradip Kumar; Yadav, Hare Ram; Choudhury, Angshuman Roy; Chopra, Deepak

2017-10-01

Strong hydrogen bonds play a significant role in crystal packing. In particular, the involvement of interactions involving fluorine in controlling the crystal packing requires appropriate attention, especially in the presence of other strong hydrogen bonds. In the present study, a detailed quantitative assessment has been performed of the nature, energetics and topological properties derived from the electron density in model compounds based on fluorinated benzamides (a total of 46 fluorine-substituted benzamides containing multiple fluorine atoms) in the solid state. The primary motivation in the design of such molecules is to enhance the acidity of the interacting H atoms in the presence of an increasing number of F atoms on the molecular scaffold, resulting in increased propensity towards the formation of intermolecular interactions involving organic fluorine. This exercise has resulted in the identification of new and frequently occurring supramolecular synthons involving F atoms in the packing of molecules in the solid state. The energetics associated with short and directional intermolecular Csp 2 -H...F-Csp 2 interactions with significantly high electrostatic contributions is noteworthy, and the topological analysis reveals the bonding character of these ubiquitous interactions in crystal packing in addition to the presence of Csp 2 -F...F-Csp 2 contacts.

The QSAR and docking calculations of fullerene derivatives as HIV-1 protease inhibitors

NASA Astrophysics Data System (ADS)

Saleh, Noha A.

2015-02-01

The inhibition of HIV-1 protease is considered as one of the most important targets for drug design and the deactivation of HIV-1. In the present work, the fullerene surface (C60) is modified by adding oxygen atoms as well as hydroxymethylcarbonyl (HMC) groups to form 6 investigated fullerene derivative compounds. These compounds have one, two, three, four or five O atoms + HMC groups at different positions on phenyl ring. The effect of the repeating of these groups on the ability of suggested compounds to inhibit the HIV protease is studied by calculating both Quantitative Structure Activity Relationship (QSAR) properties and docking simulation. Based on the QSAR descriptors, the solubility and the hydrophilicity of studied fullerene derivatives increased with increasing the number of oxygen atoms + HMC groups in the compound. While docking calculations indicate that, the compound with two oxygen atoms + HMC groups could interact and binds with HIV-1 protease active site. This is could be attributed to the active site residues of HIV-1 protease are hydrophobic except the two aspartic acids. So that, the increase in the hydrophilicity and polarity of the compound is preventing and/or decreasing the hydrophobic interaction between the compound and HIV-1 protease active site.

Enhanced secondary ion emission with a bismuth cluster ion source

NASA Astrophysics Data System (ADS)

Nagy, G.; Walker, A. V.

2007-04-01

We have investigated the mechanism of secondary ion yield enhancement using Bin+ (n = 1-6) primary ions and three different samples - dl-phenylalanine, Irganox 1010 and polystyrene - adsorbed on Al, Si and Ag substrates. The largest changes in secondary ion yields are observed for Bi2+ and Bi3+ primary ions. Smaller increases in secondary ion yield are found using Bi4+, Bi5+ and Bi6+ projectiles. The secondary ion yield enhancements are generally larger on Si than on Al. Using Bin+ structures obtained from density functional theory (DFT) calculations we demonstrate that the yield enhancements cannot be explained by an increase in the deposited energy density (energy per area) into the substrate. These data show that the mechanism of Bin+ sputtering is very similar to that for Aun+ primary ion beams. When a polyatomic primary ion strikes the substrate, its constituent atoms are likely to remain near to each other, and so a substrate atom can be struck simultaneously by multiple atoms. The action of these multiple concerted impacts leads to efficient energy transfer in the near surface region and an increase in the number of secondary ions ejected from the surface. Such concerted impacts involve one, two or three projectile atoms, which explains well the nonlinear yield enhancements observed going from Bi+ to Bi2+ to Bi3+.

Characterization of Incidental Renal Mass With Dual-Energy CT: Diagnostic Accuracy of Effective Atomic Number Maps for Discriminating Nonenhancing Cysts From Enhancing Masses.

PubMed

Mileto, Achille; Allen, Brian C; Pietryga, Jason A; Farjat, Alfredo E; Zarzour, Jessica G; Bellini, Davide; Ebner, Lukas; Morgan, Desiree E

2017-10-01

The purpose of this study was to assess the diagnostic accuracy of effective atomic number maps reconstructed from dual-energy contrast-enhanced data for discriminating between nonenhancing renal cysts and enhancing masses. Two hundred six patients (128 men, 78 women; mean age, 64 years) underwent a CT renal mass protocol (single-energy unenhanced and dual-energy contrast-enhanced nephrographic imaging) at two different hospitals. For each set of patients, two blinded, independent observers performed measurements on effective atomic number maps from contrast-enhanced dual-energy data. Renal mass assessment on unenhanced and nephrographic images, corroborated by imaging and medical records, was the reference standard. The diagnostic accuracy of effective atomic number maps was assessed with ROC analysis. Significant differences in mean effective atomic numbers (Z eff ) were observed between nonenhancing and enhancing masses (set A, 8.19 vs 9.59 Z eff ; set B, 8.05 vs 9.19 Z eff ; sets combined, 8.13 vs 9.37 Z eff ) (p < 0.0001). An effective atomic number value of 8.36 Z eff was the optimal threshold, rendering an AUC of 0.92 (95% CI, 0.89-0.94), sensitivity of 90.8% (158/174 [95% CI, 85.5-94.7%]), specificity of 85.2% (445/522 [95% CI, 81.9-88.2%]), and overall diagnostic accuracy of 86.6% (603/696 [95% CI, 83.9-89.1%]). Nonenhancing renal cysts, including hyperattenuating cysts, can be discriminated from enhancing masses on effective atomic number maps generated from dual-energy contrast-enhanced CT data. This technique may be of clinical usefulness when a CT protocol for comprehensive assessment of renal masses is not available.

Local structure and polarization resistance of Ce doped SrMnO{sub 3} using extended x-ray fine structure analysis

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

Ryu, Jiseung; Lee, Heesoo, E-mail: heesoo@pusan.ac.kr

2014-09-15

Changes to the local structure of Sr and Mn atoms in Sr{sub 1−x}Ce{sub x}MnO{sub 3} (SCM) according to increasing Ce content and the effect of the structural change on the polarization resistance of SCM were investigated. The reduction of manganese was confirmed by the absorption edge shift of the Mn K-edge toward lower energies. The noise of oscillation in extended X-ray absorption fine structure k{sup 3}χ data at Mn K-edge reveals the distortion of the local structure of Mn atoms, and the peak that indicates the bonding length of Mn-O, Sr/Ce, and -Mn decreased with the addition of Ce contentmore » in Fourier transformations of the Mn K-edge. The distortion of the local structure at Mn atoms was affected by the reduced manganese ions having larger ionic radii than Mn{sup 4+}. Meanwhile, few distortions of local atomic structures of Sr atoms occurred, and the average nearest neighboring distances of Sr-O and Sr-Mn are ∼2.13 Å and ∼2.95 Å, respectively. The average bonding lengths of the Ce-O and Ce-Mn increased because the ionic radius of substituted Ce ion with 12 coordination number is smaller than that of Sr ion, which leads the reduction of Mn ions and the distortion of local structure at the substituted A-site. Therefore, we reasoned that the distortion of the local atomic structure at Mn atoms in MnO{sub 6} and Ce atoms in A-site is one of the causes for interrupting oxygen ion transfers as a geometric factor, which results in an increase in the polarization resistance of SCM within the Ce composition range from 10 mol. % to 30 mol. %.« less

Structure and property of metal melt I: The number of residual bonds after solid-liquid phase changes

NASA Astrophysics Data System (ADS)

Mi, Guangbao; Li, Peijie; He, Liangju

2010-09-01

Based on the mechanism of metal solid-liquid phase change and the theory of liquid metal’s micro-inhomogeneity, a physical model is established between latent heats of fusion and vaporization and the numbers of residual bonds and short-range ordered atoms at the melting point inside a metal melt. Meanwhile, the mathematical derivation and proof are also offered. This model produces the numbers of residual bonds and short-range ordered atoms after the solid-liquid phase change only by using basic parameters and thermophysical properties of the crystal structure. Therefore, it presents a more effective way to analyze the melt’s structural information. By using this model, this study calculates the numbers of residual bonds and short-range ordered atoms in Al and Ni melts. The calculated results are consistent with the experimental results. Simultaneously, this study discusses the atomic number’s influence on the numbers of residual bonds and short-range ordered atoms in the melts within the first (IA) and second main group (IIA) elements.

Energy levels for Ac-212 (Actinium-212)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of Subvolume C `Tables of Excitations of Proton- and Neutron-rich Unstable Nuclei' of Volume 19 `Nuclear States from Charged Particle Reactions' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms'. It provides energy levels for atomic nuclei of the isotope Ac-212 (actinium, atomic number Z = 89, mass number A = 212).

Can I solve my structure by SAD phasing? Anomalous signal in SAD phasing

DOE PAGES

Terwilliger, Thomas C.; Bunkóczi, Gábor; Hung, Li-Wei; ...

2016-03-01

A key challenge in the SAD phasing method is solving a structure when the anomalous signal-to-noise ratio is low. We present a simple theoretical framework for describing measurements of anomalous differences and the resulting useful anomalous correlation and anomalous signal in a SAD experiment. Here, the useful anomalous correlation is defined as the correlation of anomalous differences with ideal anomalous differences from the anomalous substructure. The useful anomalous correlation reflects the accuracy of the data and the absence of minor sites. The useful anomalous correlation also reflects the information available for estimating crystallographic phases once the substructure has been determined.more » In contrast, the anomalous signal (the peak height in a model-phased anomalous difference Fourier at the coordinates of atoms in the anomalous substructure) reflects the information available about each site in the substructure and is related to the ability to find the substructure. A theoretical analysis shows that the expected value of the anomalous signal is the product of the useful anomalous correlation, the square root of the ratio of the number of unique reflections in the data set to the number of sites in the substructure, and a function that decreases with increasing values of the atomic displacement factor for the atoms in the substructure. In conclusion, this means that the ability to find the substructure in a SAD experiment is increased by high data quality and by a high ratio of reflections to sites in the substructure, and is decreased by high atomic displacement factors for the substructure.« less

Can I solve my structure by SAD phasing? Anomalous signal in SAD phasing.

PubMed

Terwilliger, Thomas C; Bunkóczi, Gábor; Hung, Li Wei; Zwart, Peter H; Smith, Janet L; Akey, David L; Adams, Paul D

2016-03-01

A key challenge in the SAD phasing method is solving a structure when the anomalous signal-to-noise ratio is low. A simple theoretical framework for describing measurements of anomalous differences and the resulting useful anomalous correlation and anomalous signal in a SAD experiment is presented. Here, the useful anomalous correlation is defined as the correlation of anomalous differences with ideal anomalous differences from the anomalous substructure. The useful anomalous correlation reflects the accuracy of the data and the absence of minor sites. The useful anomalous correlation also reflects the information available for estimating crystallographic phases once the substructure has been determined. In contrast, the anomalous signal (the peak height in a model-phased anomalous difference Fourier at the coordinates of atoms in the anomalous substructure) reflects the information available about each site in the substructure and is related to the ability to find the substructure. A theoretical analysis shows that the expected value of the anomalous signal is the product of the useful anomalous correlation, the square root of the ratio of the number of unique reflections in the data set to the number of sites in the substructure, and a function that decreases with increasing values of the atomic displacement factor for the atoms in the substructure. This means that the ability to find the substructure in a SAD experiment is increased by high data quality and by a high ratio of reflections to sites in the substructure, and is decreased by high atomic displacement factors for the substructure.

The Belgian repository of fundamental atomic data and stellar spectra (BRASS). I. Cross-matching atomic databases of astrophysical interest

NASA Astrophysics Data System (ADS)

Laverick, M.; Lobel, A.; Merle, T.; Royer, P.; Martayan, C.; David, M.; Hensberge, H.; Thienpont, E.

2018-04-01

Context. Fundamental atomic parameters, such as oscillator strengths, play a key role in modelling and understanding the chemical composition of stars in the Universe. Despite the significant work underway to produce these parameters for many astrophysically important ions, uncertainties in these parameters remain large and can propagate throughout the entire field of astronomy. Aims: The Belgian repository of fundamental atomic data and stellar spectra (BRASS) aims to provide the largest systematic and homogeneous quality assessment of atomic data to date in terms of wavelength, atomic and stellar parameter coverage. To prepare for it, we first compiled multiple literature occurrences of many individual atomic transitions, from several atomic databases of astrophysical interest, and assessed their agreement. In a second step synthetic spectra will be compared against extremely high-quality observed spectra, for a large number of BAFGK spectral type stars, in order to critically evaluate the atomic data of a large number of important stellar lines. Methods: Several atomic repositories were searched and their data retrieved and formatted in a consistent manner. Data entries from all repositories were cross-matched against our initial BRASS atomic line list to find multiple occurrences of the same transition. Where possible we used a new non-parametric cross-match depending only on electronic configurations and total angular momentum values. We also checked for duplicate entries of the same physical transition, within each retrieved repository, using the non-parametric cross-match. Results: We report on the number of cross-matched transitions for each repository and compare their fundamental atomic parameters. We find differences in log(gf) values of up to 2 dex or more. We also find and report that 2% of our line list and Vienna atomic line database retrievals are composed of duplicate transitions. Finally we provide a number of examples of atomic spectral lines with different retrieved literature log(gf) values, and discuss the impact of these uncertain log(gf) values on quantitative spectroscopy. All cross-matched atomic data and duplicate transition pairs are available to download at http://brass.sdf.org

An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements

NASA Technical Reports Server (NTRS)

Ross, H. Richard

1993-01-01

A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.

Comparison of femtosecond- and nanosecond-two-photon-absorption laser-induced fluorescence (TALIF) of atomic oxygen in atmospheric-pressure plasmas

NASA Astrophysics Data System (ADS)

Schmidt, Jacob B.; Sands, Brian; Scofield, James; Gord, James R.; Roy, Sukesh

2017-05-01

Absolute number densities of atomic species produced by nanosecond (ns)-duration, repetitively pulsed electric discharges are measured by two-photon-absorption laser-induced fluorescence (TALIF). Unique to this work is the development of femtosecond-laser-based TALIF (fs-TALIF) that offers a number of advantages over more conventional nanosecond (ns)-pulse-duration laser techniques, such as higher-fidelity quenching rate measurements over a wide pressure range, significantly reduced photolytic interference (including photo-dissociation and photo-ionization), ability to collect two-dimensional images of atomic-species number densities with high spatial resolution aided by higher signal level, and efficient and accurate measurements of atomic-species number densities due to the higher repetition rates of the laser. For full quantification of these advantages, atomic-oxygen TALIF signals are collected from an atmospheric-pressure plasma jet employing both ns- and fs-duration laser-excitation pulses and the results are compared and contrasted.

A Water Geochemistry Study of Indian Wells Valley, Inyo and Kern Counties, California. Supplement. Isotope Geochemistry and Appendix H.

DTIC Science & Technology

1990-09-01

accuracy by Carl F. Austin, NWC; James Moore, California Energy Co.; and Robert 0. Fournier, Unites States Geological Survey. Approved by Under authority...protons, electrons , and neutrons. The electrical charge of protons is positive, and that of electrons is negative. Neutrons have no electrical charge...The number of protons determines what element an atom is and gives it its atomic number. In a neutral or nonionized atom the number of electrons

Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications

NASA Technical Reports Server (NTRS)

deGroh, Kim; Berger, Lauren; Roberts, Lily

2009-01-01

The purpose of this study was to determine the effect of atomic oxygen (AO) exposure on the hydrophilicity of nine different polymers for biomedical applications. Atomic oxygen treatment can alter the chemistry and morphology of polymer surfaces, which may increase the adhesion and spreading of cells on Petri dishes and enhance implant growth. Therefore, nine different polymers were exposed to atomic oxygen and water-contact angle, or hydrophilicity, was measured after exposure. To determine whether hydrophilicity remains static after initial atomic oxygen exposure, or changes with higher fluence exposures, the contact angles between the polymer and water droplet placed on the polymer s surface were measured versus AO fluence. The polymers were exposed to atomic oxygen in a 100-W, 13.56-MHz radio frequency (RF) plasma asher, and the treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers. Pristine samples were compared with samples that had been exposed to AO at various fluence levels. Minimum and maximum fluences for the ashing trials were set based on the effective AO erosion of a Kapton witness coupon in the asher. The time intervals for ashing were determined by finding the logarithmic values of the minimum and maximum fluences. The difference of these two values was divided by the desired number of intervals (ideally 10). The initial desired fluence was then multiplied by this result (2.37), as was each subsequent desired fluence. The flux in the asher was determined to be approximately 3.0 x 10(exp 15) atoms/sq cm/sec, and each polymer was exposed to a maximum fluence of 5.16 x 10(exp 20) atoms/sq cm.

Mössbauer spectroscopy and the structure of interfaces on the atomic scale in metallic nanosystems

NASA Astrophysics Data System (ADS)

Uzdin, V. M.

2007-10-01

A microscopic model of the formation of an alloy on the interface has been constructed, which takes into account the exchange of atoms with the substrate atoms and the “floating up” of the latter into the upper layers in the process of epitaxial growth. The self-consistent calculations of atomic magnetic moments of spatially inhomogeneous structures obtained in this case are used for the interpretation of data of Mössbauer spectroscopy. The proposed scenario of mixing leads to the appearance of a preferred direction in the sample and the asymmetry of interfaces in the direction of epitaxial growth. In the multilayer M 1/ M 2 ( M 1,2 = Fe, Cr, V, Sn, or Ag) systems, this asymmetry makes it possible to understand the difference in the magnetic behavior of M 1-on M 2 and M 2-on- M 1 interfaces which has been observed experimentally. The correlation between the calculated distributions of magnetic moments and the measured distributions of hyperfine fields at iron atoms confirms the assumption about their proportionality for a broad class of metallic multilayer systems. However, a linear decrease of hyperfine fields at the 57Fe nuclei with increasing number of impurity atoms among the nearest and next-nearest neighbors is not confirmed for Fe/Cr systems, although is correct in Fe/V superlattices. In the Fe/Cr multilayer systems, the experimentally measured value of magnetoresistance grows with increasing fraction of the “floated up” atoms of 57Fe. Thus, it is the bulk scattering by impurity atoms that gives the basic contribution to the effect of giant magnetoresistance. The problem of the influence of mixing and adsorption of hydrogen in the vanadium layers on the state of the spin-density wave in V/Cr superlattices has been considered.

Note: A 3D-printed alkali metal dispenser

NASA Astrophysics Data System (ADS)

Norrgard, E. B.; Barker, D. S.; Fedchak, J. A.; Klimov, N.; Scherschligt, J.; Eckel, S.

2018-05-01

We demonstrate and characterize a source of Li atoms made from direct metal laser sintered titanium. The source's outgassing rate is measured to be 5(2) × 10-7 Pa L s-1 at a temperature T = 330 °C, which optimizes the number of atoms loaded into a magneto-optical trap. The source loads ≈107 7Li atoms in the trap in ≈1 s. The loaded source weighs 700 mg and is suitable for a number of deployable sensors based on cold atoms.

The adsorption of helium atoms on coronene cations

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

Kurzthaler, Thomas; Rasul, Bilal; Kuhn, Martin

2016-08-14

We report the first experimental study of the attachment of multiple foreign atoms to a cationic polycyclic aromatic hydrocarbon (PAH). The chosen PAH was coronene, C{sub 24}H{sub 12}, which was added to liquid helium nanodroplets and then subjected to electron bombardment. Using mass spectrometry, coronene cations decorated with helium atoms were clearly seen and the spectrum shows peaks with anomalously high intensities (“magic number” peaks), which represent ion-helium complexes with added stability. The data suggest the formation of a rigid helium layer consisting of 38 helium atoms that completely cover both faces of the coronene ion. Additional magic numbers canmore » be seen for the further addition of 3 and 6 helium atoms, which are thought to attach to the edge of the coronene. The observation of magic numbers for the addition of 38 and 44 helium atoms is in good agreement with a recent path integral Monte Carlo prediction for helium atoms on neutral coronene. An understanding of how atoms and molecules attach to PAH ions is important for a number of reasons including the potential role such complexes might play in the chemistry of the interstellar medium.« less

Vacuum Attachment for XRF Scanner

NASA Technical Reports Server (NTRS)

Schramm, Harry F.; Kaiser, Bruce

2005-01-01

Vacuum apparatuses have been developed for increasing the range of elements that can be identified by use of x-ray fluorescent (XRF) scanners of the type mentioned in the two immediately preceding articles. As a consequence of the underlying physical principles, in the presence of air, such an XRF scanner is limited to analysis of chlorine and elements of greater atomic number. When the XRF scanner is operated in a vacuum, it extends the range of analysis to lower atomic numbers - even as far as aluminum and sodium. Hence, more elements will be available for use in XRF labeling of objects as discussed in the two preceding articles. The added benefits of the extended capabilities also have other uses for NASA. Detection of elements of low atomic number is of high interest to the aerospace community. High-strength aluminum alloys will be easily analyzed for composition. Silicon, a major contaminant in certain processes, will be detectable before the process is begun, possibly eliminating weld or adhesion problems. Exotic alloys will be evaluated for composition prior to being placed in service where lives depend on them. And in the less glamorous applications, such as bolts and fasteners, substandard products and counterfeit items will be evaluated at the receiving function and never allowed to enter the operation

Relaxation of energetic S(1D) atoms in Xe gas: comparison of ab initio calculations with experimental data.

PubMed

Bovino, S; Zhang, P; Kharchenko, V; Dalgarno, A

2011-07-14

In this paper, we report our investigation of the translational energy relaxation of fast S((1)D) atoms in a Xe thermal bath. The interaction potential of Xe-S was constructed using ab initio methods. Total and differential cross sections were then calculated. The latter have been incorporated into the construction of the kernel of the Boltzmann equation describing the energy relaxation process. The solution of the Boltzmann equation was obtained and results were compared with those reported in experiments [G. Nan, and P. L. Houston, J. Chem. Phys. 97, 7865 (1992)]. Good agreement with the measured time-dependent relative velocity of fast S((1)D) atoms was obtained except at long relaxation times. The discrepancy may be due to the error accumulation caused by the use of hard sphere approximation and the Monte Carlo analysis of the experimental data. Our accurate description of the energy relaxation process led to an increase in the number of collisions required to achieve equilibrium by an order of magnitude compared to the number given by the hard-sphere approximation.

Local atomic structure inheritance in Ag{sub 50}Sn{sub 50} melt

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

Bai, Yanwen; Bian, Xiufang, E-mail: xfbian@sdu.edu.cn; Qin, Jingyu

2014-01-28

Local structure inheritance signatures were observed during the alloying process of the Ag{sub 50}Sn{sub 50} melt, using high-temperature X-ray diffraction and ab initio molecular dynamics simulations. The coordination number N{sub m} around Ag atom is similar in the alloy and in pure Ag melts (N{sub m} ∼ 10), while, during the alloying process, the local structure around Sn atoms rearranges. Sn-Sn covalent bonds were substituted by Ag-Sn chemical bonds, and the total coordination number around Sn increases by about 70% as compared with those in the pure Sn melt. Changes in the electronic structure of the alloy have been studied by Agmore » and Sn K-edge X-ray absorption spectroscopy, as well as by calculations of the partial density of states. We propose that a leading mechanism for local structure inheritance in Ag{sub 50}Sn{sub 50} is due to s-p dehybridization of Sn and to the interplay between Sn-s and Ag-d electrons.« less

Correlation of martensitic transformation temperatures of Ni- Mn-Ga/Al-X alloys to non-bonding electron concentration

NASA Astrophysics Data System (ADS)

Ramudu, M.; Satish Kumar, A.; Seshubai, V.; Rajasekharan, T.

2015-02-01

The martensitic transformation TM of the alloys of Ni-Mn-Ga and Ni-Mn-Al show a general trend of increase with electron per atom ratio (e/a) calculated from the total number of electrons outside the rare gas shell of the atoms. However prediction of TM fails among iron substituted Ni-Mn-Ga alloys and those with In doped for Ga, due to the absence of a useful trend. A scheme of computing modified electron concentration is presented considering only the non-bonding electrons per atom Ne/a of the compounds, based on Pauling's ideas on the electronic structure of metallic elements. Systematic variation of TM with Ne/a is reproduced for a large number of alloys of Ni-Mn-Ga and the anomaly observed for Fe containing alloys with e/a disappears. The non-bonding electron concentration is thus demonstrated to be effective in predicting TM of shape memory alloys of Ni-Mn-Ga-X system including the isoelectronic compounds of Ni-Mn-Ga-In.

Mesoscale elucidation of laser-assisted chemical deposition of Sn nanostructured electrodes

NASA Astrophysics Data System (ADS)

Liu, Zhixiao; Deng, Biwei; Cheng, Gary J.; Deng, Huiqiu; Mukherjee, Partha P.

2015-06-01

Nanostructured tin (Sn) is a promising high-capacity electrode for improved performance in lithium-ion batteries for electric vehicles. In this work, Sn nanoisland growth for nanostructured electrodes assisted by the pulse laser irradiation has been investigated based on a mesoscale modeling formalism. The influence of pertinent processing conditions, such as pulse duration, heating/cooling rates, and atom flux, on the Sn nanostructure formation is specifically considered. The interaction between the adsorbed atom and the substrate, represented by the adatom diffusion barrier, is carefully studied. It is found that the diffusion barrier predominantly affects the distribution of Sn atoms. For both α-Sn and β-Sn, the averaged coordination number is larger than 3 when the diffusion barrier equals to 0.15 eV. The averaged coordination number decreases as the diffusion barrier increases. The substrate temperature, which is determined by heating/cooling rates and pulse duration, can also affect the formation of Sn nanoislands. For α-Sn, when applied low heating/cooling rates, nanoislands cannot form if the diffusion barrier is larger than 0.35 eV.

Name that compound: The numbers game for CFCs, HFCs, HCFCs, and Halons

DOE Data Explorer

Blasing, T. J.; Jones, Sonja

2012-02-01

Chlorofluorocarbons (CFCs) contain Carbon and some combination of Fluorine and Chlorine atoms. Hydrofluorocarbons (HFCs) contain Hydrogen, Fluorine, and Carbon (no chlorine). Hydrochlorofluorocarbons (HCFCs) contain Hydrogen, Chlorine, Fluorine, and Carbon atoms. Hydrobromofluorocarbons (HBFCs) contain Hydrogen, Bromine, Fluorine, and Carbon atoms. Perfluorocarbons contain Fluorine, Carbon, and Bromine atoms, and some contain Chlorine and/or Hydrogen atoms. These compounds are often designated by a combination of letters and numbers (e.g., CFC-11, HCFC-142b). In the latter example, the lower-case b refers to an isomer, which has no relationship to the chemical formula (C2H3F2Cl), but designates a particular structural arrangement of the atoms included. For example, HCFC-142b identifies the isomer in which all three hydrogen atoms are attached to the same carbon atom, and the structural formula is written as CH3CF2Cl. By contrast, HCFC-142 (without the b) refers to an arrangement in which one carbon atom is attached to two hydrogen atoms and one chlorine atom, while the other carbon atom is attached to the third hydrogen atom and two fluorine atoms. Hence, it has a different structural formula (CH2ClCHF2).

Mechanical properties of biological specimens explored by atomic force microscopy

NASA Astrophysics Data System (ADS)

Kasas, S.; Longo, G.; Dietler, G.

2013-04-01

The atomic force microscope is a widely used surface scanning apparatus capable of reconstructing at a nanometric scale resolution the 3D morphology of biological samples. Due to its unique sensitivity, it is now increasingly used as a force sensor, to characterize the mechanical properties of specimens with a similar lateral resolution. This unique capability has produced, in the last years, a vast increase in the number of groups that have exploited the versatility and sensitivity of the instrument to explore the nanomechanics of various samples in the fields of biology, microbiology and medicine. In this review we outline the state of the art in this field, reporting the most interesting recent works involving the exploration of the nanomechanical properties of various biological samples.

Length-dependent structural stability of linear monatomic Cu wires

NASA Astrophysics Data System (ADS)

Singh, Gurvinder; Kumar, Krishan; Singh, Baljinder; Moudgil, R. K.

2018-05-01

We present first-principle calculations based on density functional theory for the finite-length monatomic Cu atom linear wires. The structure and its stability with increasing wire length in terms of number of atoms (N) is determined. Interestingly, the bond length is found to exhibit an oscillatory structure (the so-called magic length phenomenon), with a qualitative change in oscillatory behavior as one moves from even N wire to odd N wire. The even N wires follow simple even-odd oscillations whereas odd N wires show a phase change at the half length of the wires. The stability of the wire structure, determined in terms of the wire formation energy, also contains even-odd oscillation as a function of wire length. However, the oscillations in formation energy reverse its phase after the wire length is increased beyond N=12. Our findings are seen to be qualitatively consistent with recent simulations for a similar class finite-length metal atom wires.

Electronic and transport properties of BCN alloy nanoribbons

NASA Astrophysics Data System (ADS)

Darvishi Gilan, Mahdi; Chegel, Raad

2018-03-01

The dependence of the carbon (C) concentration on the electronic and transport properties of boron carbonitride (BCN) alloy nanoribbons have been investigated using surface Green's functions technique and random Hamiltonian model by considering random hopping parameters including first and second nearest neighbors. Our calculations indicate that substituting boron (nitrogen) sites with carbon atoms induces a new band close to conduction (valence) band and carbon atoms behave like a donor (acceptor) dopants. Also, while both nitrogen and boron sites are substituted randomly by carbon atoms, new bands are induced close to both valence and conduction bands. The band gap decreases with C substituting and the number of charge carriers increases in low bias voltage. Far from Fermi level in the higher range of energy, transmission coefficient and current of the system are reduced by increasing the C concentration. Based on our results, tuning the electronic and transport properties of BCN alloy nanoribbons by random carbon dopants could be applicable to design nanoelectronics devices.

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

Domengie, F., E-mail: florian.domengie@st.com; Morin, P.; Bauza, D.

We propose a model for dark current induced by metallic contamination in a CMOS image sensor. Based on Shockley-Read-Hall kinetics, the expression of dark current proposed accounts for the electric field enhanced emission factor due to the Poole-Frenkel barrier lowering and phonon-assisted tunneling mechanisms. To that aim, we considered the distribution of the electric field magnitude and metal atoms in the depth of the pixel. Poisson statistics were used to estimate the random distribution of metal atoms in each pixel for a given contamination dose. Then, we performed a Monte-Carlo-based simulation for each pixel to set the number of metalmore » atoms the pixel contained and the enhancement factor each atom underwent, and obtained a histogram of the number of pixels versus dark current for the full sensor. Excellent agreement with the dark current histogram measured on an ion-implanted gold-contaminated imager has been achieved, in particular, for the description of the distribution tails due to the pixel regions in which the contaminant atoms undergo a large electric field. The agreement remains very good when increasing the temperature by 15 °C. We demonstrated that the amplification of the dark current generated for the typical electric fields encountered in the CMOS image sensors, which depends on the nature of the metal contaminant, may become very large at high electric field. The electron and hole emissions and the resulting enhancement factor are described as a function of the trap characteristics, electric field, and temperature.« less

Comparison of subsurface damages on mono-crystalline silicon between traditional nanoscale machining and laser-assisted nanoscale machining via molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Dai, Houfu; Li, Shaobo; Chen, Genyu

2018-01-01

Molecular dynamics is employed to compare nanoscale traditional machining (TM) with laser-assisted machining (LAM). LAM is that the workpiece is locally heated by an intense laser beam prior to material removal. We have a comprehensive comparison between LAM and TM in terms of atomic trajectories, phase transformation, radial distribution function, chips, temperature distribution, number of atoms in different temperature, grinding temperature, grinding force, friction coefficient and atomic potential energy. It can be found that there is a decrease of atoms with five and six nearest neighbors, and LAM generates more chips than that in the TM. It indicates that LAM reduces the subsurface damage of workpiece, gets a better-qualified ground surface and improves the material removal rate. Moreover, laser energy makes the materials fully softened before being removed, the number of atoms with temperature above 500 K is increased, and the average temperature of workpiece higher and faster to reach the equilibrium in LAM. It means that LAM has an absolute advantage in machining materials and greatly reduces the material resistance. Not only the tangential force (Fx) and the normal force (Fy) but also friction coefficients become smaller as laser heating reduces the strength and hardness of the material in LAM. These results show that LAM is a promising technique since it can get a better-qualified workpiece surface with larger material removal rates, less grinding force and lower friction coefficient.

Nanoscopic morphological changes in yeast cell surfaces caused by oxidative stress: an atomic force microscopic study.

PubMed

Canetta, Elisabetta; Walker, Graeme M; Adya, Ashok K

2009-06-01

Nanoscopic changes in the cell surface morphology of the yeasts Saccharomyces cerevisiae (strain NCYC 1681) and Schizosaccharomyces pombe (strain DVPB 1354), due to their exposure to varying concentrations of hydrogen peroxide (oxidative stress), were investigated using an atomic force microscope (AFM). Increasing hydrogen peroxide concentration led to a decrease in cell viabilities and mean cell volumes, and an increase in the surface roughness of the yeasts. In addition, AFM studies revealed that oxidative stress caused cell compression in both S. cerevisiae and Schiz. pombe cells and an increase in the number of aged yeasts. These results confirmed the importance and usefulness of AFM in investigating the morphology of stressed microbial cells at the nanoscale. The results also provided novel information on the relative oxidative stress tolerance of S. cerevisiae and Schiz. pombe.

Lithium effect on the electronic properties of porous silicon for energy storage applications: a DFT study.

PubMed

González, I; Sosa, A N; Trejo, A; Calvino, M; Miranda, A; Cruz-Irisson, M

2018-05-23

Theoretical studies on the effect of Li on the electronic properties of porous silicon are still scarce; these studies could help us in the development of Li-ion batteries of this material which overcomes some limitations that bulk silicon has. In this work, the effect of interstitial and surface Li on the electronic properties of porous Si is studied using the first-principles density functional theory approach and the generalised gradient approximation. The pores are modeled by removing columns of atoms of an otherwise perfect Si crystal, dangling bonds of all surfaces are passivated with H atoms, and then Li is inserted on interstitial positions on the pore wall and compared with the replacement of H atoms with Li. The results show that the interstitial Li creates effects similar to n-type doping where the Fermi level is shifted towards the conduction band with band crossings of the said level thus acquiring metallic characteristics. The surface Li introduces trap-like states in the electronic band structures which increase as the number of Li atom increases with a tendency to become metallic. These results could be important for the application of porous Si nanostructures in Li-ion batteries technology.

Atomic and Molecular Physics

NASA Technical Reports Server (NTRS)

Bhatia, Anand K.

2005-01-01

A symposium on atomic and molecular physics was held on November 18, 2005 at Goddard Space Flight Center. There were a number of talks through the day on various topics such as threshold law of ionization, scattering of electrons from atoms and molecules, muonic physics, positron physics, Rydberg states etc. The conference was attended by a number of physicists from all over the world.

Cold nuclear fusion

NASA Astrophysics Data System (ADS)

Tsyganov, E. N.; Bavizhev, M. D.; Buryakov, M. G.; Dabagov, S. B.; Golovatyuk, V. M.; Lobastov, S. P.

2015-07-01

If target deuterium atoms were implanted in a metal crystal in accelerator experiments, a sharp increase in the probability of DD-fusion reaction was clearly observed when compared with the reaction's theoretical value. The electronic screening potential, which for a collision of free deuterium atoms is about 27 eV, reached 300-700 eV in the case of the DD-fusion in metallic crystals. These data leads to the conclusion that a ban must exist for deuterium atoms to be in the ground state 1s in a niche filled with free conduction electrons. At the same time, the state 2p whose energy level is only 10 eV above that of state 1s is allowed in these conditions. With anisotropy of 2p, 3p or above orbitals, their spatial positions are strictly determined in the lattice coordinate system. When filling out the same potential niches with two deuterium atoms in the states 2p, 3p or higher, the nuclei of these atoms can be permanently positioned without creating much Coulomb repulsion at a very short distance from each other. In this case, the transparency of the potential barrier increases dramatically compared to the ground state 1s for these atoms. The probability of the deuterium nuclei penetrating the Coulomb barrier by zero quantum vibration of the DD-system also increases dramatically. The so-called cold nuclear DD-fusion for a number of years was registered in many experiments, however, was still rejected by mainstream science for allegedly having no consistent scientific explanation. Finally, it received the validation. Below, we outline the concept of this explanation and give the necessary calculations. This paper also considers the further destiny of the formed intermediate state of 4He∗.

Competition H(D) Kinetic Isotope Effects in the Autoxidation of Hydrocarbons

PubMed Central

Muchalski, Hubert; Levonyak, Alexander J.; Xu, Libin; Ingold, Keith U.; Porter, Ned A.

2016-01-01

Hydrogen atom transfer is central to many important radical chain sequences. We report here a method for determination of both the primary and secondary isotope effects for symmetrical substrates by the use of NMR. Intramolecular competition reactions were carried out on substrates having an increasing number of deuterium atoms at symmetry-related sites. Products that arise from peroxyl radical abstraction at each position of the various substrates reflect the competition rates for H(D) abstraction. The primary KIE for autoxidation of tetralin was determined to be 15.9 ± 1.4, a value that exceeds the maximum predicted by differences in H(D) zero-point energies (~7) and strongly suggests that H atom abstraction by the peroxyl radical occurs with substantial quantum mechanical tunneling. PMID:25533605

Effect of atomic size on undercoolability of binary solid solution alloy liquids with Zr, Ti, and Hf using electrostatic levitation

NASA Astrophysics Data System (ADS)

Jeon, S.; Kang, D.-H.; Lee, Y. H.; Lee, S.; Lee, G. W.

2016-11-01

We investigate the relationship between the excess volume and undercoolability of Zr-Ti and Zr-Hf alloy liquids by using electrostatic levitation. Unlike in the case of Zr-Hf alloy liquids in which sizes of the constituent atoms are matched, a remarkable increase of undercoolability and negative excess volumes are observed in Zr-Ti alloy liquids as a function of their compositional ratios. In this work, size mismatch entropies for the liquids were obtained by calculating their hard sphere diameters, number densities, and packing fractions. We also show that the size mismatch entropy, which arises from the differences in atomic sizes of the constituent elements, plays an important role in determining the stabilities of metallic liquids.

Competition H(D) kinetic isotope effects in the autoxidation of hydrocarbons.

PubMed

Muchalski, Hubert; Levonyak, Alexander J; Xu, Libin; Ingold, Keith U; Porter, Ned A

2015-01-14

Hydrogen atom transfer is central to many important radical chain sequences. We report here a method for determination of both the primary and secondary isotope effects for symmetrical substrates by the use of NMR. Intramolecular competition reactions were carried out on substrates having an increasing number of deuterium atoms at symmetry-related sites. Products that arise from peroxyl radical abstraction at each position of the various substrates reflect the competition rates for H(D) abstraction. The primary KIE for autoxidation of tetralin was determined to be 15.9 ± 1.4, a value that exceeds the maximum predicted by differences in H(D) zero-point energies (∼7) and strongly suggests that H atom abstraction by the peroxyl radical occurs with substantial quantum mechanical tunneling.

Tuning oxidation level, electrical conductance and band gap structure on graphene sheets by cyclic atomic layer reduction technique

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

Gu, Si-Yong; Hsieh, Chien-Te; Lin, Tzu-Wei

The present work develops an atomic layer reduction (ALR) method to accurately tune oxidation level, electrical conductance, band-gap structure, and photoluminescence (PL) response of graphene oxide (GO) sheets. The ALR route is carried out at 200 °C within ALR cycle number of 10–100. The ALR treatment is capable of striping surface functionalities (e.g., hydroxyl, carbonyl, and carboxylic groups), producing thermally-reduced GO sheets. The ALR cycle number serves as a controlling factor in adjusting the crystalline, surface chemistry, electrical, optical properties of GO sheets. With increasing the ALR cycle number, ALR-GO sheets display a high crystallinity, a low oxidation level, anmore » improved electrical conductivity, a narrow band gap, and a tunable PL response. Finally, on the basis of the results, the ALR technique offers a great potential for accurately tune electrical and optical properties of carbon materials through the cyclic removal of oxygen functionalities, without any complicated thermal and chemical desorption processes.« less

Tuning oxidation level, electrical conductance and band gap structure on graphene sheets by cyclic atomic layer reduction technique

DOE PAGES

Gu, Si-Yong; Hsieh, Chien-Te; Lin, Tzu-Wei; ...

2018-05-12

The present work develops an atomic layer reduction (ALR) method to accurately tune oxidation level, electrical conductance, band-gap structure, and photoluminescence (PL) response of graphene oxide (GO) sheets. The ALR route is carried out at 200 °C within ALR cycle number of 10–100. The ALR treatment is capable of striping surface functionalities (e.g., hydroxyl, carbonyl, and carboxylic groups), producing thermally-reduced GO sheets. The ALR cycle number serves as a controlling factor in adjusting the crystalline, surface chemistry, electrical, optical properties of GO sheets. With increasing the ALR cycle number, ALR-GO sheets display a high crystallinity, a low oxidation level, anmore » improved electrical conductivity, a narrow band gap, and a tunable PL response. Finally, on the basis of the results, the ALR technique offers a great potential for accurately tune electrical and optical properties of carbon materials through the cyclic removal of oxygen functionalities, without any complicated thermal and chemical desorption processes.« less

Direct Observations of Nucleation in a Nondilute Multicomponent Alloy

NASA Technical Reports Server (NTRS)

Sudbrack, Chantal K.; Noebe, Ronald D.; Seidman, David N.

2006-01-01

The chemical pathways leading to gamma'(L1(sub 2)) nucleation from nondilute Ni-5.2 Al-14.2 Cr at. %, gama(fcc), at 873 K are followed with radial distribution functions and isoconcentration surface analyses of direct-space atom-probe tomographic images. Although Cr atoms initially are randomly distributed, a distribution of congruent Ni3Al short-range-order domains (SRO), [R] approx. equals 0.6 nm, results from Al diffusion during quenching. Domain site occupancy develops as their number density increases leading to Al-rich phase separation by gamma'-nucleation, [R]=0.75 nm, after SRO occurs.

Breakdown of ionic character of molecular alkali bromides in inner-valence photoionization

NASA Astrophysics Data System (ADS)

Karpenko, A.; Iablonskyi, D.; Urpelainen, S.; Kettunen, J. A.; Cao, W.; Huttula, M.; Aksela, H.

2014-05-01

The inner-valence region of alkali bromide XBr (X=Li, Na, K, Rb) vapours has been studied experimentally by means of synchrotron radiation excited photoelectron spectroscopy. Experimental spectra were analyzed by comparing them with available theoretical results and previous experiments. Ionic character of alkali bromides is seen to change in the inner-valence region with increasing atomic number of the alkali atom. A mechanism involving mixing between Br 4s and Rb 4p orbitals has been suggested to account for the fine structure observed in inner-valence ionization region of RbBr.

Organic chemistry of Murchison meteorite: Carbon isotopic fractionation

NASA Technical Reports Server (NTRS)

Yuen, G. U.; Blair, N. E.; Desmarais, D. J.; Cronin, J. R.; Chang, S.

1986-01-01

The carbon isotopic composition of individual organic compounds of meteoritic origin remains unknown, as most reported carbon isotopic ratios are for bulk carbon or solvent extractable fractions. The researchers managed to determine the carbon isotopic ratios for individual hydrocarbons and monocarboxylic acids isolated from a Murchison sample by a freeze-thaw-ultrasonication technique. The abundances of monocarboxylic acids and saturated hydrocarbons decreased with increasing carbon number and the acids are more abundant than the hydrocarbon with the same carbon number. For both classes of compounds, the C-13 to C-12 ratios decreased with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic number than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with a kinetically controlled synthesis of higher homologues for lower ones.

Cancer mortality in residents of the terrain-shielded area exposed to fallout from the Nagasaki atomic bombing

PubMed Central

Mine, Mariko; Kondo, Hisayoshi; Matsuda, Naoki; Shibata, Yoshisada; Takamura, Noboru

2018-01-01

Abstract The health effects of radiation exposure from the atomic bomb fallout remain unclear. The objective of the present study is to elucidate the association between low-dose radiation exposure from the atomic bomb fallout and cancer mortality among Nagasaki atomic bomb survivors. Of 77 884 members in the Nagasaki University Atomic Bomb Survivors Cohort, 610 residents in the terrain-shielded area with fallout were selected for this analysis; 1443 residents in the terrain-shielded area without fallout were selected as a control group; and 3194 residents in the direct exposure area were also selected for study. Fifty-two deaths due to cancer in the terrain-shielded fallout area were observed during the follow-up period from 1 January 1970 to 31 December 2012. The hazard ratio for cancer mortality in the terrain-shielded fallout area was 0.90 (95% confidence interval: 0.65–1.24). No increase in the risk of cancer mortality was observed, probably because the dose of the radiation exposure was low for residents in the terrain-shielded fallout areas of the Nagasaki atomic bomb, and also because the number of study subjects was small. PMID:29036510

Quantum crystallographic charge density of urea

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

Wall, Michael E.

Standard X-ray crystallography methods use free-atom models to calculate mean unit-cell charge densities. Real molecules, however, have shared charge that is not captured accurately using free-atom models. To address this limitation, a charge density model of crystalline urea was calculated using high-level quantum theory and was refined against publicly available ultra-high-resolution experimental Bragg data, including the effects of atomic displacement parameters. The resulting quantum crystallographic model was compared with models obtained using spherical atom or multipole methods. Despite using only the same number of free parameters as the spherical atom model, the agreement of the quantum model with the datamore » is comparable to the multipole model. The static, theoretical crystalline charge density of the quantum model is distinct from the multipole model, indicating the quantum model provides substantially new information. Hydrogen thermal ellipsoids in the quantum model were very similar to those obtained using neutron crystallography, indicating that quantum crystallography can increase the accuracy of the X-ray crystallographic atomic displacement parameters. Lastly, the results demonstrate the feasibility and benefits of integrating fully periodic quantum charge density calculations into ultra-high-resolution X-ray crystallographic model building and refinement.« less

Quantum crystallographic charge density of urea

DOE PAGES

Wall, Michael E.

2016-06-08

Standard X-ray crystallography methods use free-atom models to calculate mean unit-cell charge densities. Real molecules, however, have shared charge that is not captured accurately using free-atom models. To address this limitation, a charge density model of crystalline urea was calculated using high-level quantum theory and was refined against publicly available ultra-high-resolution experimental Bragg data, including the effects of atomic displacement parameters. The resulting quantum crystallographic model was compared with models obtained using spherical atom or multipole methods. Despite using only the same number of free parameters as the spherical atom model, the agreement of the quantum model with the datamore » is comparable to the multipole model. The static, theoretical crystalline charge density of the quantum model is distinct from the multipole model, indicating the quantum model provides substantially new information. Hydrogen thermal ellipsoids in the quantum model were very similar to those obtained using neutron crystallography, indicating that quantum crystallography can increase the accuracy of the X-ray crystallographic atomic displacement parameters. Lastly, the results demonstrate the feasibility and benefits of integrating fully periodic quantum charge density calculations into ultra-high-resolution X-ray crystallographic model building and refinement.« less

Rydberg-Ritz analysis and quantum defects for Rb and Cs atoms on helium nanodroplets

NASA Astrophysics Data System (ADS)

Lackner, Florian; Krois, Günter; Ernst, Wolfgang E.

2013-08-01

A Rydberg-Ritz approach is used for the interpretation of Rb-He? and Cs-He? Rydberg states and Rydberg series. Variations of the quantum defects within a Rydberg series give insight into the interaction between the alkali atom's valence electron and the superfluid helium droplet. A screening of the valence electron from the alkali atom core by the helium droplet is observed for high Rydberg states. For states with lower principal quantum number, the effect decreases and the quantum defects are found to lie closer to free atom values, indicating an increased probability for the electron to be found inside the alkali atom core. An investigation of the spin-orbit splitting of the Cs-He? nP(2Π) components reveals that the splitting of the lowest 2Π states is more atom-like [Hund's case (c) coupling] than at higher n states [Hund's case (a) coupling]. In addition, we report a detailed study of the droplet size dependence of Ak-He? Rydberg series on the example of the Rb-He? D(Δ) series. Higher Rydberg states of this series are strongly redshifted, which is also related to the screening effect.

Effective Atomic Number, Mass Attenuation Coefficient Parameterization, and Implications for High-Energy X-Ray Cargo Inspection Systems

NASA Astrophysics Data System (ADS)

Langeveld, Willem G. J.

The most widely used technology for the non-intrusive active inspection of cargo containers and trucks is x-ray radiography at high energies (4-9 MeV). Technologies such as dual-energy imaging, spectroscopy, and statistical waveform analysis can be used to estimate the effective atomic number (Zeff) of the cargo from the x-ray transmission data, because the mass attenuation coefficient depends on energy as well as atomic number Z. The estimated effective atomic number, Zeff, of the cargo then leads to improved detection capability of contraband and threats, including special nuclear materials (SNM) and shielding. In this context, the exact meaning of effective atomic number (for mixtures and compounds) is generally not well-defined. Physics-based parameterizations of the mass attenuation coefficient have been given in the past, but usually for a limited low-energy range. Definitions of Zeff have been based, in part, on such parameterizations. Here, we give an improved parameterization at low energies (20-1000 keV) which leads to a well-defined Zeff. We then extend this parameterization up to energies relevant for cargo inspection (10 MeV), and examine what happens to the Zeff definition at these higher energies.

Mid-Atomic-Number Cylindrical Wire Array Precursor Plasma Studies on Zebra

DOE PAGES

Stafford, A; Safronova, A. S.; Kantsyrev, V. L.; ...

2014-12-30

The precursor plasmas from low wire number cylindrical wire arrays (CWAs) were previously shown to radiate at temperatures >300 eV for Ni-60 (94% Cu and 6% Ni) wires in experiments on the 1-MA Zebra generator. Continued research into precursor plasmas has studied additional midatomic-number materials including Cu and Alumel (95% Ni, 2% Al, 2% Mn, and 1% Si) to determine if the >300 eV temperatures are common for midatomic-number materials. Additionally, current scaling effects were observed by performing CWA precursor experiments at an increased current of 1.5 MA using a load current multiplier. Our results show an increase in amore » linear radiation yield of ~50% (16 versus 10 kJ/cm) for the experiments at increased current. However, plasma conditions inferred through the modeling of X-ray time-gated spectra are very similar for the precursor plasma in both current conditions.« less

Investigation of the cavitating flow in injector nozzles for diesel and biodiesel

NASA Astrophysics Data System (ADS)

Zhong, Wenjun; He, Zhixia; Wang, Qian; Jiang, Zhaochen; Fu, Yanan

2013-07-01

In diesel engines, the cavitating flow in nozzles greatly affects the fuel atomization characteristics and then the subsequent combustion and exhaust emissions. At present the biodiesel is a kind of prospective alternative fuel in diesel engines, the flow characteristics for the biodiesel fuel need to be investigated. In this paper, based on the third-generation synchrotrons of Shanghai Synchrotron Radiation facility (SSRF), a high-precision three-dimension structure of testing nozzle with detailed internal geometry information was obtained using X-ray radiography for a more accurate physical model. A flow visualization experiment system with a transparent scaled-up vertical multi-hole injector nozzle tip was setup. A high resolution and speed CCD camera equipped with a long distance microscope device was used to acquire flow images of diesel and biodiesel fuel, respectively. Then, the characteristics of cavitating flow and their effects on the fuel atomization characteristics were investigated. The experimental results show that the nozzle cavitating flow of both the diesel and biodiesel fuel could be divided into four regimes: turbulent flow, cavitation inception, development of cavitation and hydraulic flip. The critical pressures of both the cavitating flow and hydraulic flip of biodiesel are higher than those of diesel. The spray cone angle increases as the cavitation occurs, but it decreases when the hydraulic flip appears. Finally, it can be concluded that the Reynolds number decreases with the increase of cavitation number, and the discharge coefficient increases with the increase of cavitation number.

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

Ding, Jun; Ma, Evan; Asta, Mark

Using molecular dynamics simulations, we have studied the atomic correlations characterizing the second peak in the radial distribution function (RDF) of metallic glasses and liquids. The analysis was conducted from the perspective of different connection schemes of atomic packing motifs, based on the number of shared atoms between two linked coordination polyhedra. The results demonstrate that the cluster connections by face-sharing, specifically with three common atoms, are most favored when transitioning from the liquid to glassy state, and exhibit the stiffest elastic response during shear deformation. These properties of the connections and the resultant atomic correlations are generally the samemore » for different types of packing motifs in different alloys. Splitting of the second RDF peak was observed for the inherent structure of the equilibrium liquid, originating solely from cluster connections; this trait can then be inherited in the metallic glass formed via subsequent quenching of the parent liquid through the glass transition, in the absence of any additional type of local structural order. In conclusion, increasing ordering and cluster connection during cooling, however, may tune the position and intensity of the split peaks.« less

Multimillion Atom Simulations and Visualization of Hypervelocity Impact Damage and Oxidation

DTIC Science & Technology

2004-01-01

MULTIMILLION ATOM SIMULATIONS AND VISUALIZATION OF HYPERVELOCITY IMPACT DAMAGE AND OXIDATION Priya Vashishta*, Rajiv K. Kalia, and Aiichiro Nakano...number. 1. REPORT DATE 2. REPORT TYPE 3. DATES COVERED 00 DEC 2004 N/A 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Multimillion Atom Simulations And...Collaboratory for Advanced Computing and Simulations Department of Materials Science & Engineering, Department of Physics & Astronomy, Department of

Cutoff in Potency Implicates Alcohol Inhibition of N-Methyl-D-Aspartate Receptors in Alcohol Intoxication

NASA Astrophysics Data System (ADS)

Peoples, Robert W.; Weight, Forrest F.

1995-03-01

As the number of carbon atoms in an aliphatic n-alcohol is increased from one to five, intoxicating potency, lipid solubility, and membrane lipid disordering potency all increase in a similar exponential manner. However, the potency of aliphatic n-alcohols for producing intoxication reaches a maximum at six to eight carbon atoms and then decreases. The molecular basis of this "cutoff" effect is not understood, as it is not correlated with either the lipid solubility or the membrane disordering potency of the alcohols, which continue to increase exponentially. Since it has been suggested that inhibition of N-methyl-D-aspartate (NMDA) receptors by alcohols may play a role in alcohol intoxication, we investigated whether a series of aliphatic n-alcohols would exhibit a cutoff in potency for inhibition of NMDA receptors. We found that although potency for inhibition of NMDA receptors increased exponentially for alcohols with one to five carbon atoms, potency for inhibition of NMDA receptors reached a maximum at six to eight carbon atoms and then abruptly disappeared. This cutoff for alcohol inhibition of NMDA receptors is consistent with an interaction of the alcohols with a hydrophobic pocket on the receptor protein. In addition, the similarity of the cutoffs for alcohol inhibition of NMDA receptors and alcohol intoxication suggests that the cutoff for NMDA receptor inhibition may contribute to the cutoff for alcohol intoxication, which is consistent with an important role of NMDA receptors in alcohol intoxication.

Hydroxyl migration disorders the surface structure of hydroxyapatite nanoparticles

NASA Astrophysics Data System (ADS)

Cheng, Xiajie; Wu, Hong; Zhang, Li; Ma, Xingtao; Zhang, Xingdong; Yang, Mingli

2017-09-01

The surface structure of nano-hydroxyapatite (HAP) was investigated using a combined simulated annealing and molecular dynamics method. The stationary structures of nano-HAP with 4-7 nm in diameter and annealed under different temperatures were analyzed in terms of pair distribution function, structural factor, mean square displacement and atomic coordination number. The particles possess different structures from bulk crystal. A clear radial change in their atomic arrangements was noted. From core to surface the structures change from ordered to disordered. A three-shell model was proposed to describe the structure evolution of nano-HAP. Atoms in the core zone keep their arrangements as in crystal, while atoms in the surface shell are in short-range order and long-range disorder, adopting a typically amorphous structure. Atoms in the middle shell have small displacements and/or deflections but basically retain their original locations as in crystal. The disordered shell is about 1 nm in thickness, in agreement with experimental observations. The disordering mainly stems from hydroxyl migration during which hydroxyls move to the surface and bond with the exposed Ca ions, and their left vacancies bring about a rearrangement of nearby atoms. The disordering is to some extent different for particles unannealed under different temperatures, resulting from fewer number of migrated hydroxyls at lower temperatures. Particles with different sizes have similar surface structures, and their surface energy decreases with increasing size. Moreover, the surface energy is reduced by hydroxyl migration because the exposed Ca ions on the surface are ionically bonded with the migrated hydroxyls. Our calculations proposed a new structure model for nano-HAP, which indicates a surface structure with activities different from those without surface reorganization. This is particularly interesting because most bioactivities of biomaterials are dominated by their surface activity.

Quantum theory of an atom in proximity to a superconductor

NASA Astrophysics Data System (ADS)

Le Dall, Matthias; Diniz, Igor; Dias da Silva, Luis G. G. V.; de Sousa, Rogério

2018-02-01

The impact of superconducting correlations on localized electronic states is important for a wide range of experiments in fundamental and applied superconductivity. This includes scanning tunneling microscopy of atomic impurities at the surface of superconductors, as well as superconducting-ion-chip spectroscopy of neutral ions and Rydberg states. Moreover, atomlike centers close to the surface are currently believed to be the main source of noise and decoherence in qubits based on superconducting devices. The proximity effect is known to dress atomic orbitals in Cooper-pair-like states known as Yu-Shiba-Rusinov (YSR) states, but the impact of superconductivity on the measured orbital splittings and optical-noise transitions is not known. Here we study the interplay between orbital degeneracy and particle-number admixture in atomic states, beyond the usual classical spin approximation. We model the atom as a generalized Anderson model interacting with a conventional s -wave superconductor. In the limit of zero on-site Coulomb repulsion (U =0 ), we obtain YSR subgap energy levels that are identical to the ones obtained from the classical spin model. When Δ is large and U >0 , the YSR spectra are no longer quasiparticle-like, and the highly degenerate orbital subspaces are split according to their spin, orbital, and number-parity symmetry. We show that U >0 activates additional poles in the atomic Green's function, suggesting an alternative explanation for the peak splittings recently observed in scanning tunneling microscopy of orbitally-degenerate impurities in superconductors. We describe optical excitation and absorption of photons by YSR states, showing that many additional optical channels open up in comparison to the nonsuperconducting case. Conversely, the additional dissipation channels imply increased electromagnetic noise due to impurities in superconducting devices.

Repetitively Coupled Chemical Reduction and Galvanic Exchange as a Synthesis Strategy for Expanding Applicable Number of Pt Atoms in Dendrimer-Encapsulated Pt Nanoparticles.

PubMed

Cho, Taehoon; Yoon, Chang Won; Kim, Joohoon

2018-06-13

In this study, we report the controllable synthesis of dendrimer-encapsulated Pt nanoparticles (Pt DENs) utilizing repetitively coupled chemical reduction and galvanic exchange reactions. The synthesis strategy allows the expansion of the applicable number of Pt atoms encapsulated inside dendrimers to more than 1000 without being limited by the fixed number of complexation sites for Pt 2+ precursor ions in the dendrimers. The synthesis of Pt DENs is achieved in a short period of time (i.e., ∼10 min) simply by the coaddition of appropriate amounts of Cu 2+ and Pt 2+ precursors into aqueous dendrimer solution and subsequent addition of reducing agents such as BH 4 - , resulting in fast and selective complexation of Cu 2+ with the dendrimers and subsequent chemical reduction of the complexed Cu 2+ while uncomplexed Pt 2+ precursors remain oxidized. Interestingly, the chemical reduction of Cu 2+ , leading to the formation of Cu nanoparticles encapsulated inside the dendrimers, is coupled with the galvanic exchange of the Cu nanoparticles with the nearby Pt 2+ . This coupling repetitively proceeds until all of the added Pt 2+ ions form into Pt nanoparticles encapsulated inside the dendrimers. In contrast to the conventional method utilizing direct chemical reduction, this repetitively coupled chemical reduction and galvanic exchange enables a substantial increase in the applicable number of Pt atoms up to 1320 in Pt DENs while maintaining the unique features of DENs.

Understanding Atomic Structure: Is There a More Direct and Compelling Connection between Atomic Line Spectra and the Quantization of an Atom's Energy?

ERIC Educational Resources Information Center

Rittenhouse, Robert C.

2015-01-01

The "atoms first" philosophy, adopted by a growing number of General Chemistry textbook authors, places greater emphasis on atomic structure as a key to a deeper understanding of the field of chemistry. A pivotal concept needed to understand the behavior of atoms is the restriction of an atom's energy to specific allowed values. However,…

Measurements and kinetic modeling of atomic species in fuel-oxidizer mixtures excited by a repetitive nanosecond pulse discharge

NASA Astrophysics Data System (ADS)

Winters, C.; Eckert, Z.; Yin, Z.; Frederickson, K.; Adamovich, I. V.

2018-01-01

This work presents the results of number density measurements of metastable Ar atoms and ground state H atoms in diluted mixtures of H2 and O2 with Ar, as well as ground state O atoms in diluted H2-O2-Ar, CH4-O2-Ar, C3H8-O2-Ar, and C2H4-O2-Ar mixtures excited by a repetitive nanosecond pulse discharge. The measurements have been made in a nanosecond pulse, double dielectric barrier discharge plasma sustained in a flow reactor between two plane electrodes encapsulated within dielectric material, at an initial temperature of 500 K and pressures ranging from 300 Torr to 700 Torr. Metastable Ar atom number density distribution in the afterglow is measured by tunable diode laser absorption spectroscopy, and used to characterize plasma uniformity. Temperature rise in the reacting flow is measured by Rayleigh scattering. H atom and O atom number densities are measured by two-photon absorption laser induced fluorescence. The results are compared with kinetic model predictions, showing good agreement, with the exception of extremely lean mixtures. O atoms and H atoms in the plasma are produced mainly during quenching of electronically excited Ar atoms generated by electron impact. In H2-Ar and O2-Ar mixtures, the atoms decay by three-body recombination. In H2-O2-Ar, CH4-O2-Ar, and C3H8-O2-Ar mixtures, O atoms decay in a reaction with OH, generated during H atom reaction with HO2, with the latter produced by three-body H atom recombination with O2. The net process of O atom decay is O  +  H  →  OH, such that the decay rate is controlled by the amount of H atoms produced in the discharge. In extra lean mixtures of propane and ethylene with O2-Ar the model underpredicts the O atom decay rate. At these conditions, when fuel is completely oxidized by the end of the discharge burst, the net process of O atom decay, O  +  O  →  O2, becomes nearly independent of H atom number density. Lack of agreement with the data at these conditions is likely due to diffusion of H atoms from the partially oxidized regions near the side walls of the reactor into the plasma. Although significant fractions of hydrogen and hydrocarbon fuels are oxidized by O atoms produced in the plasma, chain branching remains a minor effect at these relatively low temperature conditions.

Hydrogen Sorption Kinetics on Bare and Platinum-Modified Palladium Nanofilms, Grown by Electrochemical Atomic Layer Deposition (E-ALD)

DOE PAGES

Jagannathan, Kaushik; Benson, David M.; Robinson, David B.; ...

2016-01-01

Nanofilms of Pd were grown using an electrochemical form of atomic layer deposition (E-ALD) on 100 nm evaporated Au films on glass. Multiple cycles of surface-limited redox replacement (SLRR) were used to grow deposits. Each SLRR involved the underpotential deposition (UPD) of a Cu atomic layer, followed by open circuit replacement via redox exchange with tetrachloropalladate, forming a Pd atomic layer: one E-ALD deposition cycle. That cycle was repeated in order to grow deposits of a desired thickness. 5 cycles of Pd deposition were performed on the Au on glass substrates, resulting in the formation of 2.5 monolayers of Pd.more » Those Pd films were then modified with varying coverages of Pt, also formed using SLRR. The amount of Pt was controlled by changing the potential for Cu UPD, and by increasing the number of Pt deposition cycles. Hydrogen absorption was studied using coulometry and cyclic voltammetry in 0.1 M H 2SO 4 as a function of Pt coverage. The presence of even a small fraction of a Pt monolayer dramatically increased the rate of hydrogen desorption. However, this did not reduce the films’ hydrogen storage capacity. The increase in desorption rate in the presence of Pt was over an order of magnitude.« less

The evolving quality of frictional contact with graphene.

PubMed

Li, Suzhi; Li, Qunyang; Carpick, Robert W; Gumbsch, Peter; Liu, Xin Z; Ding, Xiangdong; Sun, Jun; Li, Ju

2016-11-24

Graphite and other lamellar materials are used as dry lubricants for macroscale metallic sliding components and high-pressure contacts. It has been shown experimentally that monolayer graphene exhibits higher friction than multilayer graphene and graphite, and that this friction increases with continued sliding, but the mechanism behind this remains subject to debate. It has long been conjectured that the true contact area between two rough bodies controls interfacial friction. The true contact area, defined for example by the number of atoms within the range of interatomic forces, is difficult to visualize directly but characterizes the quantity of contact. However, there is emerging evidence that, for a given pair of materials, the quality of the contact can change, and that this can also strongly affect interfacial friction. Recently, it has been found that the frictional behaviour of two-dimensional materials exhibits traits unlike those of conventional bulk materials. This includes the abovementioned finding that for few-layer two-dimensional materials the static friction force gradually strengthens for a few initial atomic periods before reaching a constant value. Such transient behaviour, and the associated enhancement of steady-state friction, diminishes as the number of two-dimensional layers increases, and was observed only when the two-dimensional material was loosely adhering to a substrate. This layer-dependent transient phenomenon has not been captured by any simulations. Here, using atomistic simulations, we reproduce the experimental observations of layer-dependent friction and transient frictional strengthening on graphene. Atomic force analysis reveals that the evolution of static friction is a manifestation of the natural tendency for thinner and less-constrained graphene to re-adjust its configuration as a direct consequence of its greater flexibility. That is, the tip atoms become more strongly pinned, and show greater synchrony in their stick-slip behaviour. While the quantity of atomic-scale contacts (true contact area) evolves, the quality (in this case, the local pinning state of individual atoms and the overall commensurability) also evolves in frictional sliding on graphene. Moreover, the effects can be tuned by pre-wrinkling. The evolving contact quality is critical for explaining the time-dependent friction of configurationally flexible interfaces.

Density functional theory and surface reactivity study of bimetallic AgnYm (n+m = 10) clusters

NASA Astrophysics Data System (ADS)

Hussain, Riaz; Hussain, Abdullah Ijaz; Chatha, Shahzad Ali Shahid; Hussain, Riaz; Hanif, Usman; Ayub, Khurshid

2018-06-01

Density functional theory calculations have been performed on pure silver (Agn), yttrium (Ym) and bimetallic silver yttrium clusters AgnYm (n + m = 2-10) for reactivity descriptors in order to realize sites for nucleophilic and electrophilic attack. The reactivity descriptors of the clusters, studied as a function of cluster size and shape, reveal the presence of different type of reactive sites in a cluster. The size and shape of the pure silver, yttrium and bimetallic silver yttrium cluster (n = 2-10) strongly influences the number and position of active sites for an electrophilic and/or nucleophilic attack. The trends of reactivities through reactivity descriptors are confirmed through comparison with experimental data for CO binding with silver clusters. Moreover, the adsorption of CO on bimetallic silver yttrium clusters is also evaluated. The trends of binding energies support the reactivity descriptors values. Doping of pure cluster with the other element also influence the hardness, softness and chemical reactivity of the clusters. The softness increases as we increase the number of silver atoms in the cluster, whereas the hardness decreases. The chemical reactivity increases with silver doping whereas it decreases by increasing yttrium concentration. Silver atoms are nucleophilic in small clusters but changed to electrophilic in large clusters.

Experimental study of some shielding parameters for composite shields

NASA Astrophysics Data System (ADS)

Mkhaiber, Ahmed F.; Dheyaa, Abdulraheem

2018-05-01

In this study radiation protection shields have been prepared consist of composite materials have epoxy as a basis material and different reinforcing materials C Ni PbO and Bi with various reinforcing ratios 10 20 30 40 50 % and dimensions 1 × 10 × 10 cm. For examination the suitability of using this shields to protect from gamma ray some shielding parameters were calculated like: Linear attenuation coefficient μ, effective atomic number Zeffe, heaviness and half value thickness X1/2 for energy rang 1218 – 1480 KeV. These parameters have been measured by using sodium iodide system NaITI with deferent radiation sources 152Eu 60Co and 137Cs. The results show that these parameters are effected by the reinforcing ratio and gamma ray energy, it is found that the linear attenuation coefficient and atomic effective number increases with reinforcing ratio increases and decreased with energy increasing especially with high concentrations 40 50 % and at low energies Eγ < 0662 MeV with certain energy while the values of X1/2 decrease with reinforcing ratio increases. Heaviness was calculated too for all shields, with respect to lead from its values we found that this shields lighter than lead, which make it preferable to traditional material such as lead and concrete.

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

NASA Astrophysics Data System (ADS)

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

2012-10-01

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

Quantum dynamics of a BEC interacting with a single-mode quantized field under the influence of a dissipation process: thermal and squeezed vacuum reservoirs

NASA Astrophysics Data System (ADS)

Ghasemian, E.; Tavassoly, M. K.

2017-09-01

In this paper we consider a system consisting of a number of two-level atoms in a Bose-Einstein condensate (BEC) and a single-mode quantized field, which interact with each other in the presence of two different damping sources, i.e. cavity and atomic reservoirs. The reservoirs which we consider here are thermal and squeezed vacuum ones corresponding to field and atom modes. Strictly speaking, by considering both types of reservoirs for each of the atom and field modes, we investigate the quantum dynamics of the interacting bosons in the system. Then, via solving the quantum Langevin equations for such a dissipative BEC system, we obtain analytical expressions for the time dependence of atomic population inversion, mean atom as well as photon number and quadrature squeezing in the field and atom modes. Our investigations demonstrate that for modeling the real physical systems, considering the dissipation effects is essential. Also, numerical calculations which are presented show that the atomic population inversion, the mean number of atoms in the BEC and the photons in the cavity possess damped oscillatory behavior due to the presence of reservoirs. In addition, non-classical squeezing effects in the field quadrature can be observed especially when squeezed vacuum reservoirs are taken into account. As an outstanding property of this model, we may refer to the fact that one can extract the atom-field coupling constant from the frequency of oscillations in the mentioned quantities such as atomic population inversion.

RADIOACTIVE ELEMENTS IN THE STANDARD ATOMIC WEIGHTS TABLE

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

Holden, N.E.; Holden, N.; Holden,N.E.

2011-07-27

In the 1949 Report of the Atomic Weights Commission, a series of new elements were added to the Atomic Weights Table. Since these elements had been produced in the laboratory and were not discovered in nature, the atomic weight value of these artificial products would depend upon the production method. Since atomic weight is a property of an element as it occurs in nature, it would be incorrect to assign an atomic weight value to that element. As a result of that discussion, the Commission decided to provide only the mass number of the most stable (or longest-lived) known isotopemore » as the number to be associated with these entries in the Atomic Weights Table. As a function of time, the mass number associated with various elements has changed as longer-lived isotopes of a particular element has been found in nature, or as improved half-life values of an element's isotopes might cause a shift in the longest-lived isotope from one mass to another. In the 1957 Report of the Atomic Weights Commission, it was decided to discontinue the listing of the mass number in the Atomic Weights Table on the grounds that the kind of information supplied by the mass number is inconsistent with the primary purpose of the Table, i.e., to provide accurate values of 'these constants' for use in various chemical calculations. In addition to the Table of Atomic Weights, the Commission included an auxiliary Table of Radioactive Elements for the first time, where the entry would be the isotope of that element which was the most stable, i.e., the one with the longest known half-life. In their 1973 Report, the Commission noted that the users of the main Table of Atomic Weights were dissatisfied with the omission of values for some elements in that Table and it was decided to reintroduce the mass number for the radioactive elements into the main Table. In their 1983 Report, the Commission decided that radioactive elements were considered to lack a characteristic terrestrial isotopic composition, from which an atomic weight value could be calculated to five or more figure accuracy, without prior knowledge of the sample involved. These elements were again listed in the Atomic Weights Table with no further information, i.e., with no mass number or atomic weight value. For the elements, which have no stable characteristic terrestrial isotopic composition, the data on the half-lives and the relative atomic masses for the nuclides of interest for those elements have been evaluated. The values of the half-lives with their uncertainties are listed in the table. The uncertainties are given for the last digit quoted of the half-life and are given in parentheses. A half-life entry for the Table having a value and an uncertainty of 7 {+-} 3 is listed in the half-life column as 7 (3). The criteria to include data in this Table, is to be the same as it has been for over sixty years. It is the same criteria, which are used for all data that are evaluated for inclusion in the Standard Table of Atomic Weights. If a report of data is published in a peer-reviewed journal, that data is evaluated and considered for inclusion in the appropriate table of the biennial report of the Atomic Weights Commission. As better data becomes available in the future, the information that is contained in either of the Tables of Standard Atomic Weights or in the Table of Radioactive Elements may be modified. It should be noted that the appearance of any datum in the Table of the Radioactive Elements is merely for the purposes of calculating an atomic mass value for any sample of a radioactive material, which might have a variety of isotopic compositions and it has no implication as to the priority for claiming discovery of a given element and is not intended to. The atomic mass values have been taken primarily from the 2003 Atomic Mass Table. Mass values for those radioisotopes that do not appear in the 2003 Atomic mass Table have been taken from preliminary data of the Atomic Mass Data Center. Most of the quoted half-lives.« less

Entanglement between atomic thermal states and coherent or squeezed photons in a damping cavity

NASA Astrophysics Data System (ADS)

Yadollahi, F.; Safaiee, R.; Golshan, M. M.

2018-02-01

In the present study, the standard Jaynes-Cummings model, in a lossy cavity, is employed to characterize the entanglement between atoms and photons when the former is initially in a thermal state (mixed ensemble) while the latter is described by either coherent or squeezed distributions. The whole system is thus assumed to be in equilibrium with a heat reservoir at a finite temperature T, and the measure of negativity is used to determine the time evolution of atom-photon entanglement. To this end, the master equation for the density matrix, in the secular approximation, is solved and a partial transposition of the result is made. The degree of atom-photon entanglement is then numerically computed, through the negativity, as a function of time and temperature. To justify the behavior of atom-photon entanglement, moreover, we employ the so obtained total density matrix to compute and analyze the time evolution of the initial photonic coherent or squeezed probability distributions and the squeezing parameters. On more practical points, our results demonstrate that as the initial photon mean number increases, the atom-photon entanglement decays at a faster pace for the coherent distribution compared to the squeezed one. Moreover, it is shown that the degree of atom-photon entanglement is much higher and more stable for the squeezed distribution than that for the coherent one. Consequently, we conclude that the time intervals during which the atom-photon entanglement is distillable is longer for the squeezed distribution. It is also illustrated that as the temperature increases the rate of approaching separability is faster for the coherent initial distribution. The novel point of the present report is the calculation of dynamical density matrix (containing all physical information) for the combined system of atom-photon in a lossy cavity, as well as the corresponding negativity, at a finite temperature.

Coaxial airblast atomizers

NASA Technical Reports Server (NTRS)

Hardalupas, Y.; Whitelaw, J. H.

1993-01-01

An experimental investigation was performed to quantify the characteristics of the sprays of coaxial injectors with particular emphasis on those aspects relevant to the performance of rocket engines. Measurements for coaxial air blast atomizers were obtained using air to represent the gaseous stream and water to represent the liquid stream. A wide range of flow conditions were examined for sprays with and without swirl for gaseous streams. The parameters varied include Weber number, gas flow rate, liquid flow rate, swirl, and nozzle geometry. Measurements were made with a phase Doppler velocimeter. Major conclusions of the study focused upon droplet size as a function of Weber number, effect of gas flow rate on atomization and spray spread, effect of nozzle geometry on atomization and spread, effect of swirl on atomization, spread, jet recirculation and breakup, and secondary atomization.

Inverse associations between obesity indicators and thymic T-cell production levels in aging atomic-bomb survivors.

PubMed

Yoshida, Kengo; Nakashima, Eiji; Kubo, Yoshiko; Yamaoka, Mika; Kajimura, Junko; Kyoizumi, Seishi; Hayashi, Tomonori; Ohishi, Waka; Kusunoki, Yoichiro

2014-01-01

Reduction of the naive T-cell population represents a deteriorating state in the immune system that occurs with advancing age. In animal model studies, obesity compromises the T-cell immune system as a result of enhanced adipogenesis in primary lymphoid organs and systemic inflammation. In this study, to test the hypothesis that obesity may contribute to the aging of human T-cell immunity, a thousand atomic-bomb survivors were examined for obesity status and ability to produce naive T cells, i.e., T-cell receptor excision circle (TREC) numbers in CD4 and CD8 T cells. The number of TRECs showed a strong positive correlation with naive T cell numbers, and lower TREC numbers were associated with higher age. We found that the TREC number was inversely associated with levels of obesity indicators (BMI, hemoglobin A1c) and serum CRP levels. Development of type-2 diabetes and fatty liver was also associated with lower TREC numbers. This population study suggests that obesity with enhanced inflammation is involved in aging of the human T-cell immune system. Given the fact that obesity increases the risk of numerous age-related diseases, attenuated immune competence is a possible mechanistic link between obesity and disease development among the elderly.

Inverse Associations between Obesity Indicators and Thymic T-Cell Production Levels in Aging Atomic-Bomb Survivors

PubMed Central

Yoshida, Kengo; Nakashima, Eiji; Kubo, Yoshiko; Yamaoka, Mika; Kajimura, Junko; Kyoizumi, Seishi; Hayashi, Tomonori; Ohishi, Waka; Kusunoki, Yoichiro

2014-01-01

Reduction of the naive T-cell population represents a deteriorating state in the immune system that occurs with advancing age. In animal model studies, obesity compromises the T-cell immune system as a result of enhanced adipogenesis in primary lymphoid organs and systemic inflammation. In this study, to test the hypothesis that obesity may contribute to the aging of human T-cell immunity, a thousand atomic-bomb survivors were examined for obesity status and ability to produce naive T cells, i.e., T-cell receptor excision circle (TREC) numbers in CD4 and CD8 T cells. The number of TRECs showed a strong positive correlation with naive T cell numbers, and lower TREC numbers were associated with higher age. We found that the TREC number was inversely associated with levels of obesity indicators (BMI, hemoglobin A1c) and serum CRP levels. Development of type-2 diabetes and fatty liver was also associated with lower TREC numbers. This population study suggests that obesity with enhanced inflammation is involved in aging of the human T-cell immune system. Given the fact that obesity increases the risk of numerous age-related diseases, attenuated immune competence is a possible mechanistic link between obesity and disease development among the elderly. PMID:24651652

Dynamical Evolution of Properties for Atom and Field in the Process of Two-Photon Absorption and Emission Between Atomic Levels

NASA Astrophysics Data System (ADS)

Wang, Jian-ming; Xu, Xue-xiang

2018-04-01

Using dressed state method, we cleverly solve the dynamics of atom-field interaction in the process of two-photon absorption and emission between atomic levels. Here we suppose that the atom is initially in the ground state and the optical field is initially in Fock state, coherent state or thermal state, respectively. The properties of the atom, including the population in excited state and ground state, the atom inversion, and the properties for optical field, including the photon number distribution, the mean photon number, the second-order correlation function and the Wigner function, are discussed in detail. We derive their analytical expressions and then make numerical analysis for them. In contrast with Jaynes-Cummings model, some similar results, such as quantum Rabi oscillation, revival and collapse, are also exhibit in our considered model. Besides, some novel nonclassical states are generated.

Nanoarchitectonics for Controlling the Number of Dopant Atoms in Solid Electrolyte Nanodots.

PubMed

Nayak, Alpana; Unayama, Satomi; Tai, Seishiro; Tsuruoka, Tohru; Waser, Rainer; Aono, Masakazu; Valov, Ilia; Hasegawa, Tsuyoshi

2018-02-01

Controlling movements of electrons and holes is the key task in developing today's highly sophisticated information society. As transistors reach their physical limits, the semiconductor industry is seeking the next alternative to sustain its economy and to unfold a new era of human civilization. In this context, a completely new information token, i.e., ions instead of electrons, is promising. The current trend in solid-state nanoionics for applications in energy storage, sensing, and brain-type information processing, requires the ability to control the properties of matter at the ultimate atomic scale. Here, a conceptually novel nanoarchitectonic strategy is proposed for controlling the number of dopant atoms in a solid electrolyte to obtain discrete electrical properties. Using α-Ag 2+ δ S nanodots with a finite number of nonstoichiometry excess dopants as a model system, a theory matched with experiments is presented that reveals the role of physical parameters, namely, the separation between electrochemical energy levels and the cohesive energy, underlying atomic-scale manipulation of dopants in nanodots. This strategy can be applied to different nanoscale materials as their properties strongly depend on the number of doping atoms/ions, and has the potential to create a new paradigm based on controlled single atom/ion transfer. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Kaur, Sandeep, E-mail: sipusukhn@gmail.com; Sharma, Amrish; Mudahar, Isha, E-mail: isha@pbi.ac.in

First principle calculations based on density functional theory were performed to calculate the structural and electronic properties of C{sub 20}-N{sub m}@C{sub n} dimer complexes. The calculated binding energies of the complexes formed are comparable to C{sub 60} dimer which ensures their stability. The bond lengths of these dimer complexes were found to be nearly same as pure complexes C{sub 20}-C{sub n}. Further, nitrogen (N) atoms were encapsulated inside the secondary cage (C{sub n}) of dimer complexes and the number of N atoms depends on diameter of the cage. The HOMO-LUMO gaps of new proposed complexes indicate the increase in gapmore » as compared to pure complexes. Mulliken charge analysis of these complexes has been studied which shows the significant charge transfer from the N atoms to the secondary cage of these complexes. The study propose the formation of the new dimer complexes which are stable and are able to encapsulate atoms which are otherwise reactive in free space.« less

Ab initio simulations of the structure, energetics and mobility of radiation-induced point defects in bcc Nb

NASA Astrophysics Data System (ADS)

Cerdeira, M. A.; Palacios, S. L.; González, C.; Fernández-Pello, D.; Iglesias, R.

2016-09-01

The formation, binding and migration energetics of helium clusters inside a niobium crystal have been analysed via ab initio simulations. The effect of placing several He atoms within an n-vacancy previously formed or as interstitials inside the initial perfect bulk matrix has been studied. DFT-based results show that He atoms prefer to aggregate forming small clusters at n-vacancy sites rather than at interstitial positions in the perfect crystal. The minimum formation energy is found when NHe is equal to the number of vacancies, n. It follows that vacancies act as almost perfect traps for He atoms, as is well known for other metals. The migration barriers of He atoms inside vacancies increase considerably when compared to what happens for vacancies alone. A secondary consequence is that the full set of energies obtained will be highly relevant as an input for new approaches to KMC simulations of defects in Nb.

Strain-engineered diffusive atomic switching in two-dimensional crystals

PubMed Central

Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.

2016-01-01

Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3–GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways. PMID:27329563

Consideration of critical axial properties of pristine and defected carbon nanotubes under compression.

PubMed

Ranjbartoreh, A R; Su, D; Wang, G

2012-06-01

Carbon nanotubes are hexagonally configured carbon atoms in cylindrical structures. Exceptionally high mechanical strength, electrical conductivity, surface area, thermal stability and optical transparency of carbon nanotubes outperformed other known materials in numerous advanced applications. However, their mechanical behaviors under practical loading conditions remain to be demonstrated. This study investigates the critical axial properties of pristine and defected single- and multi-walled carbon nanotubes under axial compression. Molecular dynamics simulation method has been employed to consider the destructive effects of Stone-Wales and atom vacancy defects on mechanical properties of armchair and zigzag carbon nanotubes under compressive loading condition. Armchair carbon nanotube shows higher axial stability than zigzag type. Increase in wall number leads to less susceptibility of multi-walled carbon nanotubes to defects and higher stability of them under axial compression. Atom vacancy defect reveals higher destructive effect than Stone-Wales defect on mechanical properties of carbon nanotubes. Critical axial strain of single-walled carbon nanotube declines by 67% and 26% due to atom vacancy and Stone-Wales defects.

Atomic Cholesky decompositions: a route to unbiased auxiliary basis sets for density fitting approximation with tunable accuracy and efficiency.

PubMed

Aquilante, Francesco; Gagliardi, Laura; Pedersen, Thomas Bondo; Lindh, Roland

2009-04-21

Cholesky decomposition of the atomic two-electron integral matrix has recently been proposed as a procedure for automated generation of auxiliary basis sets for the density fitting approximation [F. Aquilante et al., J. Chem. Phys. 127, 114107 (2007)]. In order to increase computational performance while maintaining accuracy, we propose here to reduce the number of primitive Gaussian functions of the contracted auxiliary basis functions by means of a second Cholesky decomposition. Test calculations show that this procedure is most beneficial in conjunction with highly contracted atomic orbital basis sets such as atomic natural orbitals, and that the error resulting from the second decomposition is negligible. We also demonstrate theoretically as well as computationally that the locality of the fitting coefficients can be controlled by means of the decomposition threshold even with the long-ranged Coulomb metric. Cholesky decomposition-based auxiliary basis sets are thus ideally suited for local density fitting approximations.

Atomic Cholesky decompositions: A route to unbiased auxiliary basis sets for density fitting approximation with tunable accuracy and efficiency

NASA Astrophysics Data System (ADS)

Aquilante, Francesco; Gagliardi, Laura; Pedersen, Thomas Bondo; Lindh, Roland

2009-04-01

Cholesky decomposition of the atomic two-electron integral matrix has recently been proposed as a procedure for automated generation of auxiliary basis sets for the density fitting approximation [F. Aquilante et al., J. Chem. Phys. 127, 114107 (2007)]. In order to increase computational performance while maintaining accuracy, we propose here to reduce the number of primitive Gaussian functions of the contracted auxiliary basis functions by means of a second Cholesky decomposition. Test calculations show that this procedure is most beneficial in conjunction with highly contracted atomic orbital basis sets such as atomic natural orbitals, and that the error resulting from the second decomposition is negligible. We also demonstrate theoretically as well as computationally that the locality of the fitting coefficients can be controlled by means of the decomposition threshold even with the long-ranged Coulomb metric. Cholesky decomposition-based auxiliary basis sets are thus ideally suited for local density fitting approximations.

A computational study on tuning the field emission and electronic properties of BN nanocones by impurity atom doping

NASA Astrophysics Data System (ADS)

Ahmadi, S.; Delir Kheirollahi Nezhad, P.; Hosseinian, A.; Vessally, E.

2018-06-01

We have inspected the effect of substituting a boron or nitrogen atom of a BN nanocone (BNNC) by two impurity atoms with lower and higher atomic numbers based on the density functional theory calculations. Our results explain the experimental observations in a molecular level. Orbital and partial density of states analyses show that the doping processes increase the electrical conductivity by creating new states within the gap of BNNC as follows: BeB > ON > CB > CN. The electron emission current from the surface of BNNC is improved after the CB and BeB dopings, and it is decreased by CN and ON dopings. The BeB and CN dopings make the BNNC a p-type semiconductor and the CB and ON dopings make it an n-type one in good agreement with the experimental results. The ON and BeB doping processes are suggested for the field emission current, and electrical conductivity enhancement, respectively.

Use of Fibonacci numbers in lipidomics - Enumerating various classes of fatty acids.

PubMed

Schuster, Stefan; Fichtner, Maximilian; Sasso, Severin

2017-01-10

In lipid biochemistry, a fundamental question is how the potential number of fatty acids increases with their chain length. Here, we show that it grows according to the famous Fibonacci numbers when cis/trans isomerism is neglected. Since the ratio of two consecutive Fibonacci numbers tends to the Golden section, 1.618, organisms can increase fatty acid variability approximately by that factor per carbon atom invested. Moreover, we show that, under consideration of cis/trans isomerism and/or of modification by hydroxy and/or oxo groups, diversity can be described by generalized Fibonacci numbers (e.g. Pell numbers). For the sake of easy comprehension, we deliberately build the proof on the recursive definitions of these number series. Our results should be of interest for mass spectrometry, combinatorial chemistry, synthetic biology, patent applications, use of fatty acids as biomarkers and the theory of evolution. The recursive definition of Fibonacci numbers paves the way to construct all structural formulas of fatty acids in an automated way.

Gamma-rays attenuation of zircons from Cambodia and South Africa at different energies: A new technique for identifying the origin of gemstone

NASA Astrophysics Data System (ADS)

Limkitjaroenporn, P.; Kaewkhao, J.

2014-10-01

In this work, the gamma-rays interaction properties of zircons from Cambodia and South Africa have been studied. The densities of Cambodian and South African's zircons are 4.6716±0.0040 g/cm3 and 4.5505±0.0018 g/cm3, respectively. The mass attenuation coefficient and the effective atomic number of gemstones were measured with the gamma-ray in energies range 223-662 keV using the Compton scattering technique. The mass attenuation coefficients of both zircons decreased with the increasing of gamma-rays energies. The different mass attenuation coefficients between the two zircons observed at gamma-ray energies below 400 keV are attributed to the differences in the photoelectric interaction. The effective atomic number of zircons was decreased with the increasing of gamma-ray energies and showed totally different values between the Cambodia and South Africa sources. The origins of the two zircons could be successfully identified by the method based on gamma-rays interaction with matter with advantage of being a non-destructive testing.

Radiation-assisted grafting of vinylidene chloride onto high-density polyethylene

NASA Astrophysics Data System (ADS)

Nagesh, N.; Dokhale, P. A.; Bhoraskar, V. N.

1999-06-01

6 MeV electrons and Co-60 icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/>-rays were used for grafting vinylidene chloride (VDC) onto high-density polyethylene (HDPE) samples. The HDPE samples were immersed in vinylidene chloride and irradiated either with Co-60 icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/>-rays or with 6 MeV electrons. In both cases, the radiation dose was varied in the range 1.25-7.5 kGy. The grafted samples were characterized by IR spectroscopy to obtain information about the chemical bonds and with the 14 MeV neutron activation analysis technique for estimating the number of chlorine atoms. The formation of stable bonds between the VDC molecules and the polymer chains could be achieved either with 6 MeV electrons or with Co-60 icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/>-rays. Both the number of chlorine atoms and the sample-surface conductivity increased with the radiation dose but the increases achieved with 6 MeV electrons were greater than those achieved with Co-60 icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/>-rays.

Improving atomic displacement and replacement calculations with physically realistic damage models

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

Nordlund, Kai; Zinkle, Steven J.; Sand, Andrea E.

Atomic collision processes are fundamental to numerous advanced materials technologies such as electron microscopy, semiconductor processing and nuclear power generation. Extensive experimental and computer simulation studies over the past several decades provide the physical basis for understanding the atomic-scale processes occurring during primary displacement events. The current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model, has nowadays several well-known limitations. In particular, the number of radiation defects produced in energetic cascades in metals is only ~1/3 the NRT-dpa prediction, while the number of atoms involved in atomic mixing is about a factor ofmore » 30 larger than the dpa value. Here we propose two new complementary displacement production estimators (athermal recombination corrected dpa, arc-dpa) and atomic mixing (replacements per atom, rpa) functions that extend the NRT-dpa by providing more physically realistic descriptions of primary defect creation in materials and may become additional standard measures for radiation damage quantification.« less

Improving atomic displacement and replacement calculations with physically realistic damage models

DOE PAGES

Nordlund, Kai; Zinkle, Steven J.; Sand, Andrea E.; ...

2018-03-14

Atomic collision processes are fundamental to numerous advanced materials technologies such as electron microscopy, semiconductor processing and nuclear power generation. Extensive experimental and computer simulation studies over the past several decades provide the physical basis for understanding the atomic-scale processes occurring during primary displacement events. The current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model, has nowadays several well-known limitations. In particular, the number of radiation defects produced in energetic cascades in metals is only ~1/3 the NRT-dpa prediction, while the number of atoms involved in atomic mixing is about a factor ofmore » 30 larger than the dpa value. Here we propose two new complementary displacement production estimators (athermal recombination corrected dpa, arc-dpa) and atomic mixing (replacements per atom, rpa) functions that extend the NRT-dpa by providing more physically realistic descriptions of primary defect creation in materials and may become additional standard measures for radiation damage quantification.« less

Improving atomic displacement and replacement calculations with physically realistic damage models.

PubMed

Nordlund, Kai; Zinkle, Steven J; Sand, Andrea E; Granberg, Fredric; Averback, Robert S; Stoller, Roger; Suzudo, Tomoaki; Malerba, Lorenzo; Banhart, Florian; Weber, William J; Willaime, Francois; Dudarev, Sergei L; Simeone, David

2018-03-14

Atomic collision processes are fundamental to numerous advanced materials technologies such as electron microscopy, semiconductor processing and nuclear power generation. Extensive experimental and computer simulation studies over the past several decades provide the physical basis for understanding the atomic-scale processes occurring during primary displacement events. The current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model, has nowadays several well-known limitations. In particular, the number of radiation defects produced in energetic cascades in metals is only ~1/3 the NRT-dpa prediction, while the number of atoms involved in atomic mixing is about a factor of 30 larger than the dpa value. Here we propose two new complementary displacement production estimators (athermal recombination corrected dpa, arc-dpa) and atomic mixing (replacements per atom, rpa) functions that extend the NRT-dpa by providing more physically realistic descriptions of primary defect creation in materials and may become additional standard measures for radiation damage quantification.

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

Jagannathan, Kaushik; Benson, David M.; Robinson, David B.

Nanofilms of Pd were grown using an electrochemical form of atomic layer deposition (E-ALD) on 100 nm evaporated Au films on glass. Multiple cycles of surface-limited redox replacement (SLRR) were used to grow deposits. Each SLRR involved the underpotential deposition (UPD) of a Cu atomic layer, followed by open circuit replacement via redox exchange with tetrachloropalladate, forming a Pd atomic layer: one E-ALD deposition cycle. That cycle was repeated in order to grow deposits of a desired thickness. 5 cycles of Pd deposition were performed on the Au on glass substrates, resulting in the formation of 2.5 monolayers of Pd.more » Those Pd films were then modified with varying coverages of Pt, also formed using SLRR. The amount of Pt was controlled by changing the potential for Cu UPD, and by increasing the number of Pt deposition cycles. Hydrogen absorption was studied using coulometry and cyclic voltammetry in 0.1 M H 2SO 4 as a function of Pt coverage. The presence of even a small fraction of a Pt monolayer dramatically increased the rate of hydrogen desorption. However, this did not reduce the films’ hydrogen storage capacity. The increase in desorption rate in the presence of Pt was over an order of magnitude.« less

Depressing thermal conductivity of fullerene by caging rare gas

NASA Astrophysics Data System (ADS)

Li, Jian; Zheng, Dong-Qin; Zhong, Wei-Rong

2016-01-01

We have investigated the thermal conductivity of C60 and its derivatives caged with rare gas by using the nonequilibrium molecular dynamics method. It is reported that embedding C60 with different rare gas atoms has a significant impact on its thermal conductivity. We analyze the phenomenon through the phonon spectra of rare gas atom and the C-C bonds length of C60. When the number of atoms inside the C60 increases, the phonon spectra band width of rare gas expands and the length of C-C bonds becomes longer, which contributes to the depression of the thermal conductivity of C60. The method is applied to control the thermal conductivity of C60 chains, which maybe a kind of potential materials in thermal circuits. Our results also provide a controllable method for the thermal management in nanoscale materials.

Composition measurement in substitutionally disordered materials by atomic resolution energy dispersive X-ray spectroscopy in scanning transmission electron microscopy.

PubMed

Chen, Z; Taplin, D J; Weyland, M; Allen, L J; Findlay, S D

2017-05-01

The increasing use of energy dispersive X-ray spectroscopy in atomic resolution scanning transmission electron microscopy invites the question of whether its success in precision composition determination at lower magnifications can be replicated in the atomic resolution regime. In this paper, we explore, through simulation, the prospects for composition measurement via the model system of Al x Ga 1-x As, discussing the approximations used in the modelling, the variability in the signal due to changes in configuration at constant composition, and the ability to distinguish between different compositions. Results are presented in such a way that the number of X-ray counts, and thus the expected variation due to counting statistics, can be gauged for a range of operating conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

Considerable improvement of entanglement swapping by considering multiphoton transitions via cavity quantum electrodynamics method

NASA Astrophysics Data System (ADS)

Pakniat, R.; Soltani, M.; Tavassoly, M. K.

2018-03-01

Recently we studied the effect of photon addition in the initial coherent field on the entanglement swapping which causes some improvements in the process [Soltani et al., Int. J. Mod. Phys. B 31, 1750198 (2017)]. In this paper, we investigate the influence of multiphoton transitions in the atom-field interaction based on the cavity quantum electrodynamics on the entanglement swapping and show its considerable constructive effect on this process. The presented model consists of two two-level atoms namely A1 and A2 and two distinct cavity fields F1 and F2. Initially, the atoms are prepared in a maximally entangled state and the fields in the cavities are prepared in hybrid entangled state of number and coherent states, separately. Making the atom A2 to interact with the field F1 (via the generalized Jaynes-Cummings model which allows m-photon transitions between atomic levels in the emission and absorption processes) followed by their detection allows us to arrive at the entanglement swapping from the two atoms A1, A2 and the two fields F1, F2 to the atom-field A1-F2 system. Then, we pay our attention to the time evolution of success probability of detecting processes and fidelity. Also, to determine the amount of entanglement of the generated entangled state in the swapping process, the linear entropy is evaluated and the effect of parameter m concerning the multiphoton transitions on these quantities is investigated, numerically. It is observed that, by increasing the number of photons in the transition process, one may obtain considerable improvement in the relevant quantities of the entanglement swapping. In detail, the satisfactorily acceptable values 1 and 0.5 corresponding to success probability and fidelity are obtained for most of the times during observing of the above-mentioned procedure. We concluded that the presented formalism in this paper is much more advantageous than our presentation model in our earlier work mentioned above.

The Concept of Oxidation States in Metal Complexes

ERIC Educational Resources Information Center

Steinborn, Dirk

2004-01-01

The concepts of oxidation numbers when applied means electrons that are shared between atoms in molecules are assigned to a specific atom. Oxidation numbers are assigned from the Lewis structure of a molecule, with knowledge of the electronegativities of elements.

Diamond like carbon coatings: Categorization by atomic number density

NASA Technical Reports Server (NTRS)

Angus, John C.

1986-01-01

Dense diamond-like hydrocarbon films grown at the NASA Lewis Research Center by radio frequency self bias discharge and by direct ion beam deposition were studied. A new method for categorizing hydrocarbons based on their atomic number density and elemental composition was developed and applied to the diamond-like hydrocarbon films. It was shown that the diamond-like hydrocarbon films are an entirely new class of hydrocarbons with atomic number densities lying between those of single crystal diamond and adamantanes. In addition, a major review article on these new materials was completed in cooperation with NASA Lewis Research Center personnel.

Quantum phases of a three-level matter-radiation interaction model using SU(3) coherent states with different cooperation numbers

NASA Astrophysics Data System (ADS)

Quezada, L. F.; Nahmad-Achar, E.

2018-06-01

We use coherent states as trial states for a variational approach to study a system of a finite number of three-level atoms interacting in a dipolar approximation with a one-mode electromagnetic field. The atoms are treated as semidistinguishable using different cooperation numbers and representations of SU(3). We focus our analysis on the quantum phases of the system as well as the behavior of the most relevant observables near the phase transitions. The results are computed for all three possible configurations (Ξ , Λ , and V ) of the three-level atoms.

Dual-energy dual-source CT with additional spectral filtration can improve the differentiation of non-uric acid renal stones: An ex vivo phantom study

PubMed Central

Qu, Mingliang; Ramirez Giraldo, Juan C.; Leng, Shuai; Williams, James C.; Vrtiska, Terri J.; Lieske, John C.; McCollough, Cynthia H.

2014-01-01

Purpose To determine the ex vivo ability of dual-energy, dual-source computed tomography (DE-DSCT) with additional tin filtration to differentiate between five groups of human renal stone types. Methods Forty-three renal stones of ten types were categorized into five primary groups based on effective atomic numbers, which were calculated as the weighted average of the atomic numbers of constituent atoms. Stones were embedded in porcine kidneys and placed in a 35cm water phantom. DE-DSCT scans were performed with and without tin filtration at 80/140kV. The CT number ratio [CTR=CT(low)/CT(high)] was calculated on a volumetric voxel-by-voxel basis for each stone. Statistical analysis was performed and receiver operating characteristic (ROC) curves were plotted to compare the difference in CTR with and without tin filtration, and to measure the discrimination between stone groups. Results CTR of non-uric acid stones increased on average by 0.17 (range 0.03–0.36) with tin filtration. The CTR values for non-uric acid stone groups were not significantly different (p>0.05) between any of the two adjacent groups without tin filtration. Use of the additional tin filtration on the high-energy x-ray tube significantly improved the separation of non-uric acid stone types by CTR (p<0.05). The area under the ROC curve increased from 0.78–0.84 without fin filtration to 0.89–0.95 with tin filtration. Conclusion Our results demonstrated better separation between different stone types when additional tin filtration was used on DE-DSCT. The increased spectral separation allowed a 5-group stone classification scheme. Some overlapping between particular stone types still exists, including brushite and calcium oxalate. PMID:21606290

Fisher information in confined hydrogen-like ions

NASA Astrophysics Data System (ADS)

Mukherjee, Neetik; Majumdar, Sangita; Roy, Amlan K.

2018-01-01

Fisher information (I) is investigated for confined hydrogen atom (CHA)-like systems in conjugate r and p spaces. A comparative study between CHA and free H atom (with respect to I) is pursued. A detailed systematic result of I with respect to variation of confinement radius rc is presented, with particular emphasis on non-zero- (l, m) states. In certain respect, inferences in CHA are significantly different from free counterpart, such as (i) dependence on n, l quantum numbers (ii) appearance of maxima in Ip plots for | m | ≠ 0 . The role of atomic number and atomic radius is discussed.

Cold Incineration of Chlorophenols in Aqueous Solution by Advanced Electrochemical Process Electro-Fenton. Effect of Number and Position of Chlorine Atoms on the Degradation Kinetics

NASA Astrophysics Data System (ADS)

Oturan, Nihal; Panizza, Marco; Oturan, Mehmet A.

2009-09-01

This study reports the kinetics of the degradation of several chlorophenols (CPs), such as monochlorophenols (2-chlorophenol and 4-chlorophenol), dichlorophenols (2,4-dichlorophenol and 2,6- dichlorophenol), trichlorophenols (2,3,5- trichlorophenol and 2,4,5-trichlorophenol), 2,3,5,6-tetrachlorophenol, and pentachlorophenol, by the electro-Fenton process using a carbon felt cathode and a Pt anode. The effect of number and the position of the chlorine atoms in the aromatic ring on the oxidative degradation rate was evaluated and discussed. The oxidation reaction of all the CPs with hydroxyl radicals evidenced a pseudo-first-order kinetics and the rate constant decreased with increasing the number of chlorine atoms. The absolute rate constant of second-order reaction kinetics between CPs and •OH was determined by the competition kinetics method in the range of (3.56-7.75) × 109 M-1 s-1 and follows the same sequence of the apparent rate constants. The mineralization of several CPs and of a mixture of all CPs under study was monitored by the total organic carbon (TOC) removal and the chlorine release during mineralization was followed by ion chromatography. Our results demonstrated that more chlorinated phenols are more difficult to mineralize; however for all the tested CPs, almost quantitative release of chloride ions was obtained after 6 h of treatment.

Electron capture and excitation processes in H+-H collisions in dense quantum plasmas

NASA Astrophysics Data System (ADS)

Jakimovski, D.; Markovska, N.; Janev, R. K.

2016-10-01

Electron capture and excitation processes in proton-hydrogen atom collisions taking place in dense quantum plasmas are studied by employing the two-centre atomic orbital close-coupling (TC-AOCC) method. The Debye-Hückel cosine (DHC) potential is used to describe the plasma screening effects on the Coulomb interaction between charged particles. The properties of a hydrogen atom with DHC potential are investigated as a function of the screening strength of the potential. It is found that the decrease in binding energy of nl levels with increasing screening strength is considerably faster than in the case of the Debye-Hückel (DH) screening potential, appropriate for description of charged particle interactions in weakly coupled classical plasmas. This results in a reduction in the number of bound states in the DHC potential with respect to that in the DH potential for the same plasma screening strength, and is reflected in the dynamics of excitation and electron capture processes for the two screened potentials. The TC-AOCC cross sections for total and state-selective electron capture and excitation cross sections with the DHC potential are calculated for a number of representative screening strengths in the 1-300 keV energy range and compared with those for the DH and pure Coulomb potential. The total capture cross sections for a selected number of screening strengths are compared with the available results from classical trajectory Monte Carlo calculations.

Quantum phase transitions of light in a dissipative Dicke-Bose-Hubbard model

NASA Astrophysics Data System (ADS)

Wu, Ren-Cun; Tan, Lei; Zhang, Wen-Xuan; Liu, Wu-Ming

2017-09-01

The impact that the environment has on the quantum phase transition of light in the Dicke-Bose-Hubbard model is investigated. Based on the quasibosonic approach, mean-field theory, and perturbation theory, the formulation of the Hamiltonian, the eigenenergies, and the superfluid order parameter are obtained analytically. Compared with the ideal cases, the order parameter of the system evolves with time as the photons naturally decay in their environment. When the system starts with the superfluid state, the dissipation makes the photons more likely to localize, and a greater hopping energy of photons is required to restore the long-range phase coherence of the localized state of the system. Furthermore, the Mott lobes depend crucially on the numbers of atoms and photons (which disappear) of each site, and the system tends to be classical with the number of atoms increasing; however, the atomic number is far lower than that expected under ideal circumstances. As there is an inevitable interaction between the coupled-cavity array and its surrounding environment in the actual experiments, the system is intrinsically dissipative. The results obtained here provide a more realistic image for characterizing the dissipative nature of quantum phase transitions in lossy platforms, which will offer valuable insight into quantum simulation of a dissipative system and which are helpful in guiding experimentalists in open quantum systems.

High Atom Number in Microsized Atom Traps

DTIC Science & Technology

2015-12-14

forces on the order of (hbar)(k) (Omega), where Omega is the laser Rabi frequency. We have observed behavior compatible with bichromatic slowing and... Rabi frequency. We have observed behavior compatible with bichromatic slowing and cooling of some atoms in atomic beam. Results were presented at the

Mesoscopic Dynamical Differences from Quantum State Preparation in a Bose-Hubbard Trimer

NASA Astrophysics Data System (ADS)

Olsen, M. K.; Neely, T. W.; Bradley, A. S.

2018-06-01

Conventional wisdom is that quantum effects will tend to disappear as the number of quanta in a system increases, and the evolution of a system will become closer to that described by mean-field classical equations. In this Letter we combine newly developed theoretical and experimental techniques to propose and analyze an experiment using a Bose-Hubbard trimer where the opposite is the case. We find that differences in the preparation of a centrally evacuated trimer can lead to readily observable differences in the subsequent dynamics which increase with system size. Importantly, these differences can be detected by the simple measurements of atomic number.

Band gap modulation of graphene by metal substrate: A first principles study

NASA Astrophysics Data System (ADS)

Sahoo, Mihir Ranjan; Sahu, Sivabrata; Kushwaha, Anoop Kumar; Nayak, S. K.

2018-04-01

Due to high in-plane charge carrier mobility with high electron velocity and long spin diffusion length, graphene guarantees as a completely unique material for devices with various applications. Unaffected 2pz orbitals of carbon atoms in graphene can be highly influenced by substrates and leads to tuning in electronic properties. We report here a density functional calculation of graphene monolayer based on metallic substrate like nickel surfaces. Band-gap of graphene near K points opens due to interactions between 2pz and d-orbitals of nickel atoms and the gap modulation can be done with the increasing number of layers of substrates.

Role of radial nonuniformities in the interaction of an intense laser with atomic clusters

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

Holkundkar, Amol R.; Gupta, N. K.

A model for the interaction of an intense laser with atomic clusters is presented. The model takes into account the spatial nonuniformities of the cluster as it evolves in time. The cluster is treated as a stratified sphere having an arbitrary number of layers. Electric and magnetic fields are obtained by solving the vector Helmholtz equation coupled with one-dimensional Lagrangian hydrodynamics. Results are compared with the uniform density nanoplasma model. Enhancement in the amount of energy absorbed is seen over the uniform density model. In some cases the absorbed energy increases by as much as a factor of 40.

Recombination activity of nickel, copper, and oxygen atoms segregating at grain boundaries in mono-like silicon crystals

NASA Astrophysics Data System (ADS)

Ohno, Yutaka; Kutsukake, Kentaro; Deura, Momoko; Yonenaga, Ichiro; Shimizu, Yasuo; Ebisawa, Naoki; Inoue, Koji; Nagai, Yasuyoshi; Yoshida, Hideto; Takeda, Seiji

2016-10-01

Three-dimensional distribution of impurity atoms was determined at functional Σ5{013} and small-angle grain boundaries (GBs) in as-grown mono-like silicon crystals by atom probe tomography combined with transmission electron microscopy, and it was correlated with the recombination activity of those GBs, CGB, revealed by photoluminescence imaging. Nickel (Ni), copper (Cu), and oxygen atoms preferentially segregated at the GBs on which arrays of dislocations existed, while those atoms scarcely segregated at Σ5{013} GBs free from dislocations. Silicides containing Ni and Cu about 5 nm in size and oxides about 1 nm in size were formed along the dislocation arrays on those GBs. The number of segregating impurity atoms per unit GB area for Ni and that for Cu, NNi and NCu, were in a trade-off correlation with that for oxygen, NO, as a function of CGB, while the sum of those numbers was almost constant irrespective of the GB character, CGB, and the dislocation density on GBs. CGB would be explained as a linear combination of those numbers: CGB (in %) ˜400(0.38NO + NNi + NCu) (in atoms/nm2). The GB segregation of oxygen atoms would be better for solar cells, rather than that of metal impurities, from a viewpoint of the conversion efficiency of solar cells.

Quantum Fisher information of the GHZ state due to classical phase noise lasers under non-Markovian environment

NASA Astrophysics Data System (ADS)

Chen, Yu; Zou, Jian; Yang, Zi-Yi; Li, Longwu; Li, Hai; Shao, Bin

2016-08-01

The dynamics of N-qubit GHZ state quantum Fisher information (QFI) under phase noise lasers (PNLs) driving is investigated in terms of non-Markovian master equation. We first investigate the non-Markovian dynamics of the QFI of N-qubit GHZ state and show that when the ratio of the PNL rate and the system-environment coupling strength is very small, the oscillations of the QFIs decay slower which corresponds to the non-Markovian region; yet when it becomes large, the QFIs monotonously decay which corresponds to the Markovian region. When the atom number N increases, QFIs in both regions decay faster. We further find that the QFI flow disappears suddenly followed by a sudden birth depending on the ratio of the PNL rate and the system-environment coupling strength and the atom number N, which unveil a fundamental connection between the non-Markovian behaviors and the parameters of system-environment couplings. We discuss two optimal positive operator-valued measures (POVMs) for two different strategies of our model and find the condition of the optimal measurement. At last, we consider the QFI of two atoms with qubit-qubit interaction under random telegraph noises (RTNs).

A new method to measure electron density and effective atomic number using dual-energy CT images

NASA Astrophysics Data System (ADS)

Ramos Garcia, Luis Isaac; Pérez Azorin, José Fernando; Almansa, Julio F.

2016-01-01

The purpose of this work is to present a new method to extract the electron density ({ρ\\text{e}} ) and the effective atomic number (Z eff) from dual-energy CT images, based on a Karhunen-Loeve expansion (KLE) of the atomic cross section per electron. This method was used to calibrate a Siemens Definition CT using the CIRS phantom. The predicted electron density and effective atomic number using 80 kVp and 140 kVp were compared with a calibration phantom and an independent set of samples. The mean absolute deviations between the theoretical and calculated values for all the samples were 1.7 %  ±  0.1 % for {ρ\\text{e}} and 4.1 %  ±  0.3 % for Z eff. Finally, these results were compared with other stoichiometric method. The application of the KLE to represent the atomic cross section per electron is a promising method for calculating {ρ\\text{e}} and Z eff using dual-energy CT images.

On the atomic-number similarity of the binding energies of electrons in filled shells of elements of the periodic table

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

Karpov, V. Ya.; Shpatakovskaya, G. V., E-mail: shpagalya@yandex.ru

An expression for the binding energies of electrons in the ground state of an atom is derived on the basis of the Bohr–Sommerfeld quantization rule within the Thomas–Fermi model. The validity of this relation for all elements from neon to uranium is tested within a more perfect quantum-mechanical model with and without the inclusion of relativistic effects, as well as with experimental binding energies. As a result, the ordering of electronic levels in filled atomic shells is established, manifested in an approximate atomic-number similarity. It is proposed to use this scaling property to analytically estimate the binding energies of electronsmore » in an arbitrary atom.« less

Uranium isotopes quantitatively determined by modified method of atomic absorption spectrophotometry

NASA Technical Reports Server (NTRS)

Lee, G. H.

1967-01-01

Hollow-cathode discharge tubes determine the quantities of uranium isotopes in a sample by using atomic absorption spectrophotometry. Dissociation of the uranium atoms allows a large number of ground state atoms to be produced, absorbing the incident radiation that is different for the two major isotopes.

China's rare-earth industry

USGS Publications Warehouse

Tse, Pui-Kwan

2011-01-01

Introduction China's dominant position as the producer of over 95 percent of the world output of rare-earth minerals and rapid increases in the consumption of rare earths owing to the emergence of new clean-energy and defense-related technologies, combined with China's decisions to restrict exports of rare earths, have resulted in heightened concerns about the future availability of rare earths. As a result, industrial countries such as Japan, the United States, and countries of the European Union face tighter supplies and higher prices for rare earths. This paper briefly reviews China's rare-earth production, consumption, and reserves and the important policies and regulations regarding the production and trade of rare earths, including recently announced export quotas. The 15 lanthanide elements-lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium (atomic numbers 57-71)-were originally known as the rare earths from their occurrence in oxides mixtures. Recently, some researchers have included two other elements-scandium and yttrium-in their discussion of rare earths. Yttrium (atomic number 39), which lies above lanthanum in transition group III of the periodic table and has a similar 3+ ion with a noble gas core, has both atomic and ionic radii similar in size to those of terbium and dysprosium and is generally found in nature with lanthanides. Scandium (atomic number 21) has a smaller ionic radius than yttrium and the lanthanides, and its chemical behavior is intermediate between that of aluminum and the lanthanides. It is found in nature with the lanthanides and yttrium. Rare earths are used widely in high-technology and clean-energy products because they impart special properties of magnetism, luminescence, and strength. Rare earths are also used in weapon systems to obtain the same properties.

Detection of de novo single nucleotide variants in offspring of atomic-bomb survivors close to the hypocenter by whole-genome sequencing.

PubMed

Horai, Makiko; Mishima, Hiroyuki; Hayashida, Chisa; Kinoshita, Akira; Nakane, Yoshibumi; Matsuo, Tatsuki; Tsuruda, Kazuto; Yanagihara, Katsunori; Sato, Shinya; Imanishi, Daisuke; Imaizumi, Yoshitaka; Hata, Tomoko; Miyazaki, Yasushi; Yoshiura, Koh-Ichiro

2018-03-01

Ionizing radiation released by the atomic bombs at Hiroshima and Nagasaki, Japan, in 1945 caused many long-term illnesses, including increased risks of malignancies such as leukemia and solid tumours. Radiation has demonstrated genetic effects in animal models, leading to concerns over the potential hereditary effects of atomic bomb-related radiation. However, no direct analyses of whole DNA have yet been reported. We therefore investigated de novo variants in offspring of atomic-bomb survivors by whole-genome sequencing (WGS). We collected peripheral blood from three trios, each comprising a father (atomic-bomb survivor with acute radiation symptoms), a non-exposed mother, and their child, none of whom had any past history of haematological disorders. One trio of non-exposed individuals was included as a control. DNA was extracted and the numbers of de novo single nucleotide variants in the children were counted by WGS with sequencing confirmation. Gross structural variants were also analysed. Written informed consent was obtained from all participants prior to the study. There were 62, 81, and 42 de novo single nucleotide variants in the children of atomic-bomb survivors, compared with 48 in the control trio. There were no gross structural variants in any trio. These findings are in accord with previously published results that also showed no significant genetic effects of atomic-bomb radiation on second-generation survivors.

Increasing circular synthetic aperture sonar resolution via adapted wave atoms deconvolution.

PubMed

Pailhas, Yan; Petillot, Yvan; Mulgrew, Bernard

2017-04-01

Circular Synthetic Aperture Sonar (CSAS) processing computes coherently Synthetic Aperture Sonar (SAS) data acquired along a circular trajectory. This approach has a number of advantages, in particular it maximises the aperture length of a SAS system, producing very high resolution sonar images. CSAS image reconstruction using back-projection algorithms, however, introduces a dissymmetry in the impulse response, as the imaged point moves away from the centre of the acquisition circle. This paper proposes a sampling scheme for the CSAS image reconstruction which allows every point, within the full field of view of the system, to be considered as the centre of a virtual CSAS acquisition scheme. As a direct consequence of using the proposed resampling scheme, the point spread function (PSF) is uniform for the full CSAS image. Closed form solutions for the CSAS PSF are derived analytically, both in the image and the Fourier domain. The thorough knowledge of the PSF leads naturally to the proposed adapted atom waves basis for CSAS image decomposition. The atom wave deconvolution is successfully applied to simulated data, increasing the image resolution by reducing the PSF energy leakage.

Cancer mortality in residents of the terrain-shielded area exposed to fallout from the Nagasaki atomic bombing.

PubMed

Yokota, Kenichi; Mine, Mariko; Kondo, Hisayoshi; Matsuda, Naoki; Shibata, Yoshisada; Takamura, Noboru

2018-01-01

The health effects of radiation exposure from the atomic bomb fallout remain unclear. The objective of the present study is to elucidate the association between low-dose radiation exposure from the atomic bomb fallout and cancer mortality among Nagasaki atomic bomb survivors. Of 77 884 members in the Nagasaki University Atomic Bomb Survivors Cohort, 610 residents in the terrain-shielded area with fallout were selected for this analysis; 1443 residents in the terrain-shielded area without fallout were selected as a control group; and 3194 residents in the direct exposure area were also selected for study. Fifty-two deaths due to cancer in the terrain-shielded fallout area were observed during the follow-up period from 1 January 1970 to 31 December 2012. The hazard ratio for cancer mortality in the terrain-shielded fallout area was 0.90 (95% confidence interval: 0.65-1.24). No increase in the risk of cancer mortality was observed, probably because the dose of the radiation exposure was low for residents in the terrain-shielded fallout areas of the Nagasaki atomic bomb, and also because the number of study subjects was small. © The Author 2017. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

Multi-technology Investigation of the Atomic Structure of Calcium Silicate Hydrates

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

Geng, Guoqing; Kilcoyne, David A.; Benmore, Chris J.

2015-01-01

In this study, synthetic C-S-H samples were investigated to reveal the feature at atomic scale. Rietveld refinement was applied to high resolution X-ray scattering data, yielding the lattice constants of the pseudocrystal structure, as well as the crystallinity along three axes. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra was collected at calcium L3,2-edge. Evolution of calcium coordination symmetry were studied by investigating spectra characteristics. Pair Distribution Function (PDF) study yields the statistics of atom pair distribution. Coordination number of Ca and Si were obtained by integrating Radial distribution function. Atomic model based on dimeric structure were discussed and comparedmore » with experimental data. Synthetic C-S-H samples with increasing Ca/Si ratio exhibit pseudo-crystal structure, resembling Dreierketten configuration similar to natural tobermorite structure. Along c-axis, the repeated structure could not survives two layers in case of low Ca/Si ratio (0.70, 1.05). But in high Ca/Si ratio (1.42) case, the crystallinity along c-axis is much bigger. The coordination number of Ca decreases with increasing Ca/Si ratio. Octahedrally coordinated Ca are observed in sample with Ca/Si ratio of 1.42. Various dimeric models are compared with experimental data. In case of Ca/Si ratio of 1.42, SiO4 tetrahedron chain needs to be shortened in linkage, most probably by substituting bridging SiO4 tetrahedron with CaO6 octahedron. These octahedrons in interlayer space act like pins to join two adjacent layer structures together. The crystallinity is thus increased along c-axis, and average coordination number is therefore reduced. In case of Ca/Si 1.05, crystallinity is low along c-axis since, indicating that not too many Ca ions exist in interlayer space to hold two layers together. Instead, negative charge of end oxygen could be balanced by proton. Ca/Si 0.70 has long tetrahedron chain linkage within layer while the linkage between adjacent layers are not strong, resulting in low crystallinity along c-axis. Neither Ca/Si ratio 0.70 nor 1.42 sample contains any Ca in octahedral symmetry, as indicated by the weak crystal field splitting of NEXAFS spectra.« less

Monte-Carlo based assessment of MAGIC, MAGICAUG, PAGATUG and PAGATAUG polymer gel dosimeters for ovaries and uterus organ dosimetry in brachytherapy, nuclear medicine and Tele-therapy.

PubMed

Adinehvand, Karim; Rahatabad, Fereidoun Nowshiravan

2018-06-01

Calculation of 3D dose distribution during radiotherapy and nuclear medicine helps us for better treatment of sensitive organs such as ovaries and uterus. In this research, we investigate two groups of normoxic dosimeters based on meta-acrylic acid (MAGIC and MAGICAUG) and polyacrylamide (PAGATUG and PAGATAUG) for brachytherapy, nuclear medicine and Tele-therapy in their sensitive and critical role as organ dosimeters. These polymer gel dosimeters are compared with soft tissue while irradiated by different energy photons in therapeutic applications. This comparison has been simulated by Monte-Carlo based MCNPX code. ORNL phantom-Female has been used to model the critical organs of kidneys, ovaries and uterus. Right kidney is proposed to be the source of irradiation and another two organs are exposed to this irradiation. Effective atomic numbers of soft tissue, MAGIC, MAGICAUG, PAGATUG and PAGATAUG are 6.86, 7.07, 6.95, 7.28, and 7.07 respectively. Results show the polymer gel dosimeters are comparable to soft tissue for using in nuclear medicine and Tele-therapy. Differences between gel dosimeters and soft tissue are defined as the dose responses. This difference is less than 4.1%, 22.6% and 71.9% for Tele-therapy, nuclear medicine and brachytherapy respectively. The results approved that gel dosimeters are the best choice for ovaries and uterus in nuclear medicine and Tele-therapy respectively. Due to the slight difference between the effective atomic numbers of these polymer gel dosimeters and soft tissue, these polymer gels are not suitable for brachytherapy since the dependence of photon interaction to atomic number, for low energy brachytherapy, had been so effective. Also this dependence to atomic number, decrease for photoelectric and increase for Compton. Therefore polymer gel dosimeters are not a good alternative to soft tissue replacement in brachytherapy. Copyright © 2018 Elsevier B.V. All rights reserved.

Dual-Beam Atom Laser Driven by Spinor Dynamics

NASA Technical Reports Server (NTRS)

Thompson, Robert; Lundblad, Nathan; Maleki, Lute; Aveline, David

2007-01-01

An atom laser now undergoing development simultaneously generates two pulsed beams of correlated Rb-87 atoms. (An atom laser is a source of atoms in beams characterized by coherent matter waves, analogous to a conventional laser, which is a source of coherent light waves.) The pumping mechanism of this atom laser is based on spinor dynamics in a Bose-Einstein condensate. By virtue of the angular-momentum conserving collisions that generate the two beams, the number of atoms in one beam is correlated with the number of atoms in the other beam. Such correlations are intimately linked to entanglement and squeezing in atomic ensembles, and atom lasers like this one could be used in exploring related aspects of Bose-Einstein condensates, and as components of future sensors relying on atom interferometry. In this atom-laser apparatus, a Bose-Einstein condensate of about 2 x 10(exp 6) Rb-87 atoms at a temperature of about 120 micro-K is first formed through all-optical means in a relatively weak singlebeam running-wave dipole trap that has been formed by focusing of a CO2-laser beam. By a technique that is established in the art, the trap is loaded from an ultrahigh-vacuum magnetooptical trap that is, itself, loaded via a cold atomic beam from an upstream two-dimensional magneto-optical trap that resides in a rubidium-vapor cell that is differentially pumped from an adjoining vacuum chamber, wherein are performed scientific observations of the beams ultimately generated by the atom laser.

First principles calculation of the structural, electronic, and magnetic properties of Au-Pd atomic chains

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

Dave, Mudra R., E-mail: mdave-phy@yahoo.co.in; Sharma, A. C.

2015-06-24

The structural, electronic and magnetic properties of free standing Au-Pd bimetallic atomic chain is studied using ab-initio method. It is found that electronic and magnetic properties of chains depend on position of atoms and number of atoms. Spin polarization factor for different atomic configuration of atomic chain is calculated predicting a half metallic behavior. It suggests a total spin polarised transport in these chains.

Atomic insight into tribochemical wear mechanism of silicon at the Si/SiO2 interface in aqueous environment: Molecular dynamics simulations using ReaxFF reactive force field

NASA Astrophysics Data System (ADS)

Wen, Jialin; Ma, Tianbao; Zhang, Weiwei; Psofogiannakis, George; van Duin, Adri C. T.; Chen, Lei; Qian, Linmao; Hu, Yuanzhong; Lu, Xinchun

2016-12-01

In this work, the atomic mechanism of tribochemical wear of silicon at the Si/SiO2 interface in aqueous environment was investigated using ReaxFF molecular dynamics (MD) simulations. Two types of Si atom removal pathways were detected in the wear process. The first is caused by the destruction of stretched Si-O-Si bonds on the Si substrate surface and is assisted by the attachment of H atoms on the bridging oxygen atoms of the bonds. The other is caused by the rupture of Si-Si bonds in the stretched Si-Si-O-Si bond chains at the interface. Both pathways effectively remove Si atoms from the silicon surface via interfacial Si-O-Si bridge bonds. Our simulations also demonstrate that higher pressures applied to the silica phase can cause more Si atoms to be removed due to the formation of increased numbers of interfacial Si-O-Si bridge bonds. Besides, water plays a dual role in the wear mechanism, by oxidizing the Si substrate surface as well as by preventing the close contact of the surfaces. This work shows that the removal of Si atoms from the substrate is a result of both chemical reaction and mechanical effects and contributes to the understanding of tribochemical wear behavior in the microelectromechanical systems (MEMS) and Si chemical mechanical polishing (CMP) process.

The New Element Curium (Atomic Number 96)

DOE R&D Accomplishments Database

Seaborg, G. T.; James, R. A.; Ghiorso, A.

1948-01-01

Two isotopes of the element with atomic number 96 have been produced by the helium-ion bombardment of plutonium. The name curium, symbol Cm, is proposed for element 96. The chemical experiments indicate that the most stable oxidation state of curium is the III state.

The measurement of argon metastable atoms in the barrier discharge plasma

NASA Astrophysics Data System (ADS)

Ghildina, Anna R.; Mikheyev, Pavel Anatolyevich; Chernyshov, Aleksandr Konstantinovich; Lunev, Nikolai Nikolaevich; Azyazov, Valeriy Nikolaevich

2018-04-01

The mandatory condition for efficient operation of an optically-pumped all-rare-gas laser (OPRGL) is the presence of rare gas metastable atoms in the discharge plasma with number density of the order of 1012-1013 cm-3. This requirement mainly depends on the choice of a discharge system. In this study the number density values of argon metastable atoms were obtained in the condition of the dielectric-barrier discharge (DBD) at an atmospheric pressure.

Calculation of absorption parameters for selected narcotic drugs in the energy range from 1 keV to 100 GeV

NASA Astrophysics Data System (ADS)

Akman, Ferdi; Kaçal, Mustafa Recep; Akdemir, Fatma; Araz, Aslı; Turhan, Mehmet Fatih; Durak, Rıdvan

2017-04-01

The total mass attenuation coefficients (μ/ρ), total molecular (σt,m), atomic (σt,a) and electronic (σt,e) cross sections, effective atomic numbers (Zeff) and electron density (NE) were computed in the wide energy region from 1 keV to 100 GeV for the selected narcotic drugs such as morphine, heroin, cocaine, ecstasy and cannabis. The changes of μ/ρ, σt,m, σt,a, σt,e, Zeff and NE with photon energy for total photon interaction shows the dominance of different interaction process in different energy regions. The variations of μ/ρ, σt,m, σt,a, σt,e, Zeff and NE depend on the atom number, photon energy and chemical composition of narcotic drugs. Also, these parameters change with number of elements, the range of atomic numbers in narcotic drugs and total molecular weight. These data can be useful in the field of forensic sciences and medical diagnostic.

Antiproton-impact ionization of hydrogen atom with Yukawa interaction

NASA Astrophysics Data System (ADS)

Jakimovski, Dragan; Grozdanov, Tasko P.; Janev, Ratko K.

2018-01-01

The process of ionization of hydrogen atom by antiproton impact is studied when the interparticle interactions in the system are described by screened interactions of Yukawa type. The collision dynamics is described by the semiclassical atomic-orbital close-coupling method in which the bound atomic states and positive energy continuum pseudostates are determined by diagonalization of target Hamiltonian in a sufficiently large even-tempered basis to ensure convergence of the results at each value of the screening length λ of the interaction. With decreasing the screening length, the bound states in the Yukawa potential become unbound, thus increasing the number of continuum pseudostates. At low collision energies, this leads to the increase of the ionization cross section. It is observed that the energies of pseudostates, generated by the exit of nl bound states in the continuum, at certain critical values λ nl c exhibit series of avoided crossings when λ is varied. The avoided crossings appear between the ( n + k) l and ( n + k + 1) l ( n = 1, 2, 3, … ; k = 0, 1, 2, …) states at screening lengths close to the critical screening length λ nl c . The avoided crossings become increasingly less pronounced with increasing n, k and l. The matrix elements for the ( n + k) l - ( n + k + 1) l transitions at the avoided crossings λ x,(n+k)l (n+k+1)l exhibit maxima and are reflected in the structure of the cross sections for population of the lower nl pseudostates. These structures are, however, smeared out in the total ionization cross section.

Quantum dynamics of the vibrations of helium bound to the nanosurface of a large planar organic molecule: phthalocyanine . He van der Waals complex.

PubMed

Gibbons, Brittney R; Xu, Minzhong; Bacić, Zlatko

2009-04-23

We report rigorous quantum three-dimensional calculations of highly excited intermolecular vibrational states of the van der Waals (vdW) complex phthalocyanine.He (Pc.He). The Pc molecule was treated as rigid and the intermolecular potential energy surface (IPES) was represented as a sum of atom-atom Lennard-Jones pair potentials. The IPES has four equivalent global minima on the diagonals of the square-shaped Pc, inside its five-membered rings, and four slightly shallower local minima between them, creating a distinctive corrugation pattern of the molecular nanosurface. The vdW vibrational states analyzed in this work extend to about two-thirds of the well depth of the IPES. For the assignment of the in-plane (xy) vdW vibrational excitations it was necessary to resort to two sets of quantum numbers, the Cartesian quantum numbers [nu(x), nu(y)] and the quantum numbers (v, l) of the 2D isotropic oscillator, depending on the nodal structure and the symmetry of the wave functions. The delocalization of the He atom parallel to the molecular surface is large already in the ground vdW state. It increases rapidly with the number of quanta in the in-plane vdW vibrations, with the maximum root-mean-square amplitudes Deltax and Deltay of about 7 au at the excitation energies around 40 cm(-1). The wave functions of the highly excited states tend to be delocalized over the entire nanosurface and often have a square shape, reflecting that of the substrate.

Enhanced rigid-bond restraints

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

Thorn, Andrea; Dittrich, Birger; Sheldrick, George M., E-mail: gsheldr@shelx.uni-ac.gwdg.de

2012-07-01

An extension is proposed to the rigid-bond description of atomic thermal motion in crystals. The rigid-bond model [Hirshfeld (1976 ▶). Acta Cryst. A32, 239–244] states that the mean-square displacements of two atoms are equal in the direction of the bond joining them. This criterion is widely used for verification (as intended by Hirshfeld) and also as a restraint in structure refinement as suggested by Rollett [Crystallographic Computing (1970 ▶), edited by F. R. Ahmed et al., pp. 167–181. Copenhagen: Munksgaard]. By reformulating this condition, so that the relative motion of the two atoms is required to be perpendicular to themore » bond, the number of restraints that can be applied per anisotropic atom is increased from about one to about three. Application of this condition to 1,3-distances in addition to the 1,2-distances means that on average just over six restraints can be applied to the six anisotropic displacement parameters of each atom. This concept is tested against very high resolution data of a small peptide and employed as a restraint for protein refinement at more modest resolution (e.g. 1.7 Å)« less

Recurrence spectra of a helium atom in parallel electric and magnetic fields

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

Wang, Dehua; Department of Mathematics and Physics, Shandong Architecture and Engineering Institute, Jinan 250014, People's Republic of China; Ding, Shiliang

2003-08-01

A model potential for the general Rydberg atom is put forward, which includes not only the Coulomb interaction potential and the core-attractive potential, but also the exchange potential between the excited electron and other electrons. Using the region-splitting consistent and iterative method, we calculated the scaled recurrence spectra of the helium atom in parallel electric and magnetic fields and the closed orbits in the corresponding classical system have also been obtained. In order to remove the Coulomb singularity of the classical motion of Hamiltonian, we implement the Kustaanheimo-Stiefel transformation, which transforms the system from a three-dimensional to a four-dimensional one.more » The Fourier-transformed spectra of the helium atom has allowed direct comparison between peaks in such a plot and the scaled action values of closed orbits. Considering the exchange potential, the number of the closed orbits increased, which led to more peaks in the recurrence spectra. The results are compared with those of the hydrogen case, which shows that the core-scattered effects and the electron exchange potential play an important role in the multielectron Rydberg atom.« less

The 6-31B(d) basis set and the BMC-QCISD and BMC-CCSD multicoefficient correlation methods.

PubMed

Lynch, Benjamin J; Zhao, Yan; Truhlar, Donald G

2005-03-03

Three new multicoefficient correlation methods (MCCMs) called BMC-QCISD, BMC-CCSD, and BMC-CCSD-C are optimized against 274 data that include atomization energies, electron affinities, ionization potentials, and reaction barrier heights. A new basis set called 6-31B(d) is developed and used as part of the new methods. BMC-QCISD has mean unsigned errors in calculating atomization energies per bond and barrier heights of 0.49 and 0.80 kcal/mol, respectively. BMC-CCSD has mean unsigned errors of 0.42 and 0.71 kcal/mol for the same two quantities. BMC-CCSD-C is an equally effective variant of BMC-CCSD that employs Cartesian rather than spherical harmonic basis sets. The mean unsigned error of BMC-CCSD or BMC-CCSD-C for atomization energies, barrier heights, ionization potentials, and electron affinities is 22% lower than G3SX(MP2) at an order of magnitude less cost for gradients for molecules with 9-13 atoms, and it scales better (N6 vs N,7 where N is the number of atoms) when the size of the molecule is increased.

Atomic bomb testing and its effects on global male to female ratios at birth.

PubMed

Grech, Victor

2015-01-01

Fallout from atomic bomb testing may travel great distances before precipitating. Males are born in excess of females in a ratio that approximates 0.515 (M/T: male live births divided by total live births. Radiation increases M/T by causing lethal malformations that affect female more than male foetuses, decreasing total births. This study was carried out in order to ascertain whether the effects of increased background radiation levels from atomic weapon testing had any widespread effects on M/T and births in the Americas, Europe, Asia and Australasia in relation to the Partial Test Ban Treaty of 1963. Annual live births by gender were obtained from a World Health Organization dataset and annual number of atomic bomb tests were also obtained (historical data). Overall, 94.5% of births studied showed a uniform reduction in M/T between the early 1950s to the late 1960s, followed by an increase to the mid-1970s, with a subsequent decline. A negative correlation of M/T with total births was found in 66% of births studied, and these were the regions which exhibited the rising M/T pattern in the 1970s. The birth deficit for countries with significant correlations of total births with M/T (North America, Europe and Asia) was estimated at 10090701. A rising M/T was found in most regions in temporal association with atomic weapon testing. Most of these regions also had an associated decline in total births. Elevated levels of man-made ambient radiation may have reduced total births, affecting pregnancies carrying female pregnancies more than those carrying male pregnancies, thereby skewing M/T toward a higher male proportion.

Simulation of Rutherford backscattering spectrometry from arbitrary atom structures.

PubMed

Zhang, S; Nordlund, K; Djurabekova, F; Zhang, Y; Velisa, G; Wang, T S

2016-10-01

Rutherford backscattering spectrometry in a channeling direction (RBS/C) is a powerful tool for analysis of the fraction of atoms displaced from their lattice positions. However, it is in many cases not straightforward to analyze what is the actual defect structure underlying the RBS/C signal. To reveal insights of RBS/C signals from arbitrarily complex defective atomic structures, we develop here a method for simulating the RBS/C spectrum from a set of arbitrary read-in atom coordinates (obtained, e.g., from molecular dynamics simulations). We apply the developed method to simulate the RBS/C signals from Ni crystal structures containing randomly displaced atoms, Frenkel point defects, and extended defects, respectively. The RBS/C simulations show that, even for the same number of atoms in defects, the RBS/C signal is much stronger for the extended defects. Comparison with experimental results shows that the disorder profile obtained from RBS/C signals in ion-irradiated Ni is due to a small fraction of extended defects rather than a large number of individual random atoms.

Helium trapping in aluminium near the critical dose on blister formation

NASA Astrophysics Data System (ADS)

Fukahori, T.; Kanda, Y.; Mori, K.; Tobimatsu, H.

1985-08-01

Blistering and flaking caused by energetic He ions emitted from the plasma in fusion reactors possibly contribute to first-wall erosion. In order to study their characteristics, the numbers of He atoms trapped in He-ion-irradiated Al samples have been measured by a He atom measurement system and every sample has been observed by a scanning electron microscope. The samples have been prepared from a polycrystalline plate and irradiated with 20 keV He ions at room temperature. The saw-tooth like variation of the trapped He atoms with the dose has three edges corresponding to the blistering, flaking and double flaking, respectively. The critical doses for the three events are found to be 4 × 10 21, 7 × 10 21, 12 × 10 21 He atoms m -2, respectively. The average number of He atoms included in an event is 5.4 × 10 10 He atoms in the case of the blistering and 2.1 × 10 11 He atoms in the case of flaking.

Simulation of Rutherford backscattering spectrometry from arbitrary atom structures

NASA Astrophysics Data System (ADS)

Zhang, S.; Nordlund, K.; Djurabekova, F.; Zhang, Y.; Velisa, G.; Wang, T. S.

2016-10-01

Rutherford backscattering spectrometry in a channeling direction (RBS/C) is a powerful tool for analysis of the fraction of atoms displaced from their lattice positions. However, it is in many cases not straightforward to analyze what is the actual defect structure underlying the RBS/C signal. To reveal insights of RBS/C signals from arbitrarily complex defective atomic structures, we develop here a method for simulating the RBS/C spectrum from a set of arbitrary read-in atom coordinates (obtained, e.g., from molecular dynamics simulations). We apply the developed method to simulate the RBS/C signals from Ni crystal structures containing randomly displaced atoms, Frenkel point defects, and extended defects, respectively. The RBS/C simulations show that, even for the same number of atoms in defects, the RBS/C signal is much stronger for the extended defects. Comparison with experimental results shows that the disorder profile obtained from RBS/C signals in ion-irradiated Ni is due to a small fraction of extended defects rather than a large number of individual random atoms.

The Pt site reactivity of the molecular graphs of Au6Pt isomers

NASA Astrophysics Data System (ADS)

Xu, Tianlv; Jenkins, Samantha; Xiao, Chen-Xia; Maza, Julio R.; Kirk, Steven R.

2013-12-01

Within the framework of the theory of atoms in molecules (QTAIM), in an exploratory study we propose a new measure of site reactivity equivalent to the atomic coordination number based purely on the electronic structure. It was found that the number of ring critical points (NNRCPs) positioned on the boundary of the atomic basin of the dopant (Pt) nucleus correlated very well with the relative zero point energy (ZPE) corrected energies. A weaker condition (i.e. than the number of associated bond paths) for the association of the dopant Pt nucleus with the Au6Pt molecular graph is found for NNRCP = 0.

Neutral-atom electron binding energies from relaxed-orbital relativistic Hartree-Fock-Slater calculations for Z between 2 and 106

NASA Technical Reports Server (NTRS)

Huang, K.-N.; Aoyagi, M.; Mark, H.; Chen, M. H.; Crasemann, B.

1976-01-01

Electron binding energies in neutral atoms have been calculated relativistically, with the requirement of complete relaxation. Hartree-Fock-Slater wave functions served as zeroth-order eigenfunctions to compute the expectation of the total Hamiltonian. A first-order correction to the local approximation was thus included. Quantum-electrodynamic corrections were made. For all elements with atomic numbers ranging from 2 to 106, the following quantities are listed: total energies, electron kinetic energies, electron-nucleus potential energies, electron-electron potential energies consisting of electrostatic and Breit interaction (magnetic and retardation) terms, and vacuum polarization energies. Binding energies including relaxation are listed for all electrons in all atoms over the indicated range of atomic numbers. A self-energy correction is included for the 1s, 2s, and 2p(1/2) levels. Results for selected atoms are compared with energies calculated by other methods and with experimental values.

Dispersive detection of radio-frequency-dressed states

NASA Astrophysics Data System (ADS)

Jammi, Sindhu; Pyragius, Tadas; Bason, Mark G.; Florez, Hans Marin; Fernholz, Thomas

2018-04-01

We introduce a method to dispersively detect alkali-metal atoms in radio-frequency-dressed states. In particular, we use dressed detection to measure populations and population differences of atoms prepared in their clock states. Linear birefringence of the atomic medium enables atom number detection via polarization homodyning, a form of common path interferometry. In order to achieve low technical noise levels, we perform optical sideband detection after adiabatic transformation of bare states into dressed states. The balanced homodyne signal then oscillates independently of field fluctuations at twice the dressing frequency, thus allowing for robust, phase-locked detection that circumvents low-frequency noise. Using probe pulses of two optical frequencies, we can detect both clock states simultaneously and obtain population difference as well as the total atom number. The scheme also allows for difference measurements by direct subtraction of the homodyne signals at the balanced detector, which should technically enable quantum noise limited measurements with prospects for the preparation of spin squeezed states. The method extends to other Zeeman sublevels and can be employed in a range of atomic clock schemes, atom interferometers, and other experiments using dressed atoms.

The evolution of interaction between grain boundary and irradiation-induced point defects: Symmetric tilt GB in tungsten

NASA Astrophysics Data System (ADS)

Li, Hong; Qin, Yuan; Yang, Yingying; Yao, Man; Wang, Xudong; Xu, Haixuan; Phillpot, Simon R.

2018-03-01

Molecular dynamics method is used and scheme of calculational tests is designed. The atomic evolution view of the interaction between grain boundary (GB) and irradiation-induced point defects is given in six symmetric tilt GB structures of bcc tungsten with the energy of the primary knock-on atom (PKA) EPKA of 3 and 5 keV and the simulated temperature of 300 K. During the collision cascade with GB structure there are synergistic mechanisms to reduce the number of point defects: one is vacancies recombine with interstitials, and another is interstitials diffuse towards the GB with vacancies almost not move. The larger the ratio of the peak defect zone of the cascades overlaps with the GB region, the statistically relative smaller the number of surviving point defects in the grain interior (GI); and when the two almost do not overlap, vacancy-intensive area generally exists nearby GBs, and has a tendency to move toward GB with the increase of EPKA. In contrast, the distribution of interstitials is relatively uniform nearby GBs and is affected by the EPKA far less than the vacancy. The GB has a bias-absorption effect on the interstitials compared with vacancies. It shows that the number of surviving vacancies statistically has increasing trend with the increase of the distance between PKA and GB. While the number of surviving interstitials does not change much, and is less than the number of interstitials in the single crystal at the same conditions. The number of surviving vacancies in the GI is always larger than that of interstitials. The GB local extension after irradiation is observed for which the interstitials absorbed by the GB may be responsible. The designed scheme of calculational tests in the paper is completely applicable to the investigation of the interaction between other types of GBs and irradiation-induced point defects.

Localized spatially nonlinear matter waves in atomic-molecular Bose-Einstein condensates with space-modulated nonlinearity

PubMed Central

Yao, Yu-Qin; Li, Ji; Han, Wei; Wang, Deng-Shan; Liu, Wu-Ming

2016-01-01

The intrinsic nonlinearity is the most remarkable characteristic of the Bose-Einstein condensates (BECs) systems. Many studies have been done on atomic BECs with time- and space- modulated nonlinearities, while there is few work considering the atomic-molecular BECs with space-modulated nonlinearities. Here, we obtain two kinds of Jacobi elliptic solutions and a family of rational solutions of the atomic-molecular BECs with trapping potential and space-modulated nonlinearity and consider the effect of three-body interaction on the localized matter wave solutions. The topological properties of the localized nonlinear matter wave for no coupling are analysed: the parity of nonlinear matter wave functions depends only on the principal quantum number n, and the numbers of the density packets for each quantum state depend on both the principal quantum number n and the secondary quantum number l. When the coupling is not zero, the localized nonlinear matter waves given by the rational function, their topological properties are independent of the principal quantum number n, only depend on the secondary quantum number l. The Raman detuning and the chemical potential can change the number and the shape of the density packets. The stability of the Jacobi elliptic solutions depends on the principal quantum number n, while the stability of the rational solutions depends on the chemical potential and Raman detuning. PMID:27403634

Introducing a Simple Equation to Express Oxidation States as an Alternative to Using Rules Associated with Words Alone

ERIC Educational Resources Information Center

Minkiewicz, Piotr; Darewicz, Malgorzata; Iwaniak, Anna

2018-01-01

A simple equation to calculate the oxidation states (oxidation numbers) of individual atoms in molecules and ions may be introduced instead of rules associated with words alone. The equation includes two of three categories of bonds, classified as proposed by Goodstein: number of bonds with more electronegative atoms and number of bonds with less…

Estimates of point defect production in α-quartz using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Cowen, Benjamin J.; El-Genk, Mohamed S.

2017-07-01

Molecular dynamics (MD) simulations are performed to investigate the production of point defects in α-quartz by oxygen and silicon primary knock-on atoms (PKAs) of 0.25-2 keV. The Wigner-Seitz (WS) defect analysis is used to identify the produced vacancies, interstitials, and antisites, and the coordination defect analysis is used to identify the under and over-coordinated oxygen and silicon atoms. The defects at the end of the ballistic phase and the residual defects, after annealing, increase with increased PKA energy, and are statistically the same for the oxygen and silicon PKAs. The WS defect analysis results show that the numbers of the oxygen vacancies and interstitials (VO, Oi) at the end of the ballistic phase is the highest, followed closely by those of the silicon vacancies and interstitials (VSi, Sii). The number of the residual oxygen and silicon vacancies and interstitials are statistically the same. In addition, the under-coordinated OI and SiIII, which are the primary defects during the ballistic phase, have high annealing efficiencies (>89%). The over-coordinated defects of OIII and SiV, which are not nearly as abundant in the ballistic phase, have much lower annealing efficiencies (<63%) that decrease with increased PKA energy.

Kramers degeneracy and relaxation in vanadium, niobium and tantalum clusters

NASA Astrophysics Data System (ADS)

Diaz-Bachs, A.; Katsnelson, M. I.; Kirilyuk, A.

2018-04-01

In this work we use magnetic deflection of V, Nb, and Ta atomic clusters to measure their magnetic moments. While only a few of the clusters show weak magnetism, all odd-numbered clusters deflect due to the presence of a single unpaired electron. Surprisingly, for the majority of V and Nb clusters an atomic-like behavior is found, which is a direct indication of the absence of spin–lattice interaction. This is in agreement with Kramers degeneracy theorem for systems with a half-integer spin. This purely quantum phenomenon is surprisingly observed for large systems of more than 20 atoms, and also indicates various quantum relaxation processes, via Raman two-phonon and Orbach high-spin mechanisms. In heavier, Ta clusters, the relaxation is always present, probably due to larger masses and thus lower phonon energies, as well as increased spin–orbit coupling.

Formation of fivefold axes in the FCC-metal nanoclusters

NASA Astrophysics Data System (ADS)

Myasnichenko, Vladimir S.; Starostenkov, Mikhail D.

2012-11-01

Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu-Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000 K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu-Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

Influence of Al grain boundaries segregations and La-doping on embrittlement of intermetallic NiAl

NASA Astrophysics Data System (ADS)

Kovalev, Anatoly I.; Wainstein, Dmitry L.; Rashkovskiy, Alexander Yu.

2015-11-01

The microscopic nature of intergranular fracture of NiAl was experimentally investigated by the set of electron spectroscopy techniques. The paper demonstrates that embrittlement of NiAl intermetallic compound is caused by ordering of atomic structure that leads to formation of structural aluminum segregations at grain boundaries (GB). Such segregations contain high number of brittle covalent interatomic bonds. The alloying by La increases the ductility of material avoiding Al GB enrichment and disordering GB atomic structure. The influence of La alloying on NiAl mechanical properties was investigated. GB chemical composition, atomic and electronic structure transformations after La doping were investigated by AES, XPS and EELFS techniques. To qualify the interatomic bonds metallicity the Fermi level (EF) position and electrons density (neff) in conduction band were determined in both undoped and doped NiAl. Basing on experimental results the physical model of GB brittleness formation was proposed.

Thickness dependence of scattering cross-sections in quantitative scanning transmission electron microscopy.

PubMed

Martinez, G T; van den Bos, K H W; Alania, M; Nellist, P D; Van Aert, S

2018-04-01

In quantitative scanning transmission electron microscopy (STEM), scattering cross-sections have been shown to be very sensitive to the number of atoms in a column and its composition. They correspond to the integrated intensity over the atomic column and they outperform other measures. As compared to atomic column peak intensities, which saturate at a given thickness, scattering cross-sections increase monotonically. A study of the electron wave propagation is presented to explain the sensitivity of the scattering cross-sections. Based on the multislice algorithm, we analyse the wave propagation inside the crystal and its link to the scattered signal for the different probe positions contained in the scattering cross-section for detector collection in the low-, middle- and high-angle regimes. The influence to the signal from scattering of neighbouring columns is also discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

The blue light indicator in rubidium 5S-5P-5D cascade excitation

NASA Astrophysics Data System (ADS)

Raja, Waseem; Ali, Md. Sabir; Chakrabarti, Alok; Ray, Ayan

2017-07-01

The cascade system has played an important role in contemporary research areas related to fields like Rydberg excitation, four wave mixing and non-classical light generation, etc. Depending on the specific objective, co or counter propagating pump-probe laser experimental geometry is followed. However, the stepwise excitation of atoms to states higher than the first excited state deals with increasingly much fewer number of atoms even compared to the population at first excited level. Hence, one needs a practical indicator to study the complex photon-atom interaction of the cascade system. Here, we experimentally analyze the case of rubidium 5S → 5P → 5D as a specimen of two-step excitation and highlight the efficacy of monitoring one branch, which emits 420 nm, of associated cascade decay route 5D → 6P → 5S, as an effective monitor of the coherence in the system.

Thermodynamic properties of small aggregates of rare-gas atoms

NASA Technical Reports Server (NTRS)

Etters, R. D.; Kaelberer, J.

1975-01-01

The present work reports on the equilibrium thermodynamic properties of small clusters of xenon, krypton, and argon atoms, determined from a biased random-walk Monte Carlo procedure. Cluster sizes ranged from 3 to 13 atoms. Each cluster was found to have an abrupt liquid-gas phase transition at a temperature much less than for the bulk material. An abrupt solid-liquid transition is observed for thirteen- and eleven-particle clusters. For cluster sizes smaller than 11, a gradual transition from solid to liquid occurred over a fairly broad range of temperatures. Distribution of number of bond lengths as a function of bond length was calculated for several systems at various temperatures. The effects of box boundary conditions are discussed. Results show the importance of a correct description of boundary conditions. A surprising result is the slow rate at which system properties approach bulk behavior as cluster size is increased.

Effect of an atom on a quantum guided field in a weakly driven fiber-Bragg-grating cavity

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

Le Kien, Fam; Hakuta, K.

2010-02-15

We study the interaction of an atom with a quantum guided field in a weakly driven fiber-Bragg-grating (FBG) cavity. We present an effective Hamiltonian and derive the density-matrix equations for the combined atom-cavity system. We calculate the mean photon number, the second-order photon correlation function, and the atomic excited-state population. We show that due to the confinement of the guided cavity field in the fiber cross-section plane and in the space between the FBG mirrors, the presence of the atom in the FBG cavity can significantly affect the mean photon number and the photon statistics even though the cavity finessemore » is moderate, the cavity is long, and the probe field is weak.« less

A triple point in 3-level systems

NASA Astrophysics Data System (ADS)

Nahmad-Achar, E.; Cordero, S.; López-Peña, R.; Castaños, O.

2014-11-01

The energy spectrum of a 3-level atomic system in the Ξ-configuration is studied. This configuration presents a triple point independently of the number of atoms, which remains in the thermodynamic limit. This means that in a vicinity of this point any quantum fluctuation will drastically change the composition of the ground state of the system. We study the expectation values of the atomic population of each level, the number of photons, and the probability distribution of photons at the triple point.

Nonlinear Sensing With Collective States of Ultracold Atoms in Optical Lattices

DTIC Science & Technology

2015-04-02

20) E. Tiesinga, “Particle-hole Pair Coherence in Mott insulator quench dynamics” at the June 2014, Division of atomic, molecular, and optical...Jian, Philip R. Johnson, Eite Tiesinga. Particle-Hole Pair Coherence in Mott Insulator Quench Dynamics, P H Y S I C A L R E V I EW L E T T E R S (01...lattices. We focused on techniques that make use of the coherent superposition states in atom number. These state are not unlike the photon number

SEPARATION OF PLUTONIUM FROM ELEMENTS HAVING AN ATOMIC NUMBER NOT LESS THAN 92

DOEpatents

Fitch, F.T.; Russell, D.S.

1958-09-16

other elements having atomic numbers nnt less than 92, It has been proposed in the past to so separate plutonium by solvent extraction iato an organic solvent using triglycoldichlcride as the organic solvent. The improvement lies in the discovery that triglycoldichloride performs far more efflciently as an extractant, wher certain second organie compounds are added to it. Mentioned as satisfactory additive compounds are benzaldehyde, saturated aliphatic aldehydes containtng at least twc carbon atoms, and certain polyhydric phenols.

Optical, structural, and chemical properties of CR-39 implanted with 5.2 MeV doubly charged carbon ions

NASA Astrophysics Data System (ADS)

Ali, Dilawar; Butt, M. Z.; Ishtiaq, Mohsin; Waqas Khaliq, M.; Bashir, Farooq

2016-11-01

Poly-allyl-diglycol-carbonate (CR-39) specimens were irradiated with 5.2 MeV doubly charged carbon ions using Pelletron accelerator. Ion dose was varied from 5 × 1013 to 5 × 1015 ions cm-2. Optical, structural, and chemical properties were investigated by UV-vis spectroscopy, x-ray diffractometer, and FTIR/Raman spectroscopy, respectively. It was found that optical absorption increases with increasing ion dose. Absorption edge shifts from UV region to visible region. The measured opacity values of pristine and ion implanted CR-39 range from 0.0519 to 4.7959 mm-1 following an exponential growth (9141%) with the increase in ion dose. The values of direct and indirect band gap energy decrease exponentially with an increase in ion dose by 59% and 71%, respectively. However, average refractive index in the visible region increases from 1.443 to 2.864 with an increase in ion dose, by 98%. A linear relation between band gap energy and crystallite size was observed. Both the number of carbon atoms in conjugation length and the number of carbon atoms per cluster increase linearly with the increase in ion dose. FTIR spectra showed that on C+2 ions irradiation, the intensity of all bands decreases gradually without appearance of any new band, indicating degradation of polymer after irradiation. Raman spectra revealed that the density of -CH2- group decreases on C+2 ions irradiation. However, the structure of CR-39 is completely destroyed on irradiation with ion dose 1 × 1015 and 5 × 1015 ions cm-2.

A circularly polarized optical dipole trap and other developments in laser trapping of atoms

NASA Astrophysics Data System (ADS)

Corwin, Kristan Lee

Several innovations in laser trapping and cooling of alkali atoms are described. These topics share a common motivation to develop techniques for efficiently manipulating cold atoms. Such advances facilitate sensitive precision measurements such as parity non- conservation and 8-decay asymmetry in large trapped samples, even when only small quantities of the desired species are available. First, a cold, bright beam of Rb atoms is extracted from a magneto-optical trap (MOT) using a very simple technique. This beam has a flux of 5 × 109 atoms/s and a velocity of 14 m/s, and up to 70% of the atoms in the MOT were transferred to the atomic beam. Next, a highly efficient MOT for radioactive atoms is described, in which more than 50% of 221Fr atoms contained in a vapor cell are loaded into a MOT. Measurements were also made of the 221Fr 7 2P1/2 and 7 2P3/2 energies and hyperfine constants. To perform these experiments, two schemes for stabilizing the frequency of the light from a diode laser were developed and are described in detail. Finally, a new type of trap is described and a powerful cooling technique is demonstrated. The circularly polarized optical dipole trap provides large samples of highly spin-polarized atoms, suitable for many applications. Physical processes that govern the transfer of large numbers of atoms into the trap are described, and spin-polarization is measured to be 98(1)%. In addition, the trap breaks the degeneracy of the atomic spin states much like a magnetic trap does. This allows for RF and microwave cooling via both forced evaporation and a Sisyphus mechanism. Preliminary application of these techniques to the atoms in the circularly polarized dipole trap has successfully decreased the temperature by a factor of 4 while simultaneously increasing phase space density.

Simulation of Laser Cooling and Trapping in Engineering Applications

NASA Technical Reports Server (NTRS)

Ramirez-Serrano, Jaime; Kohel, James; Thompson, Robert; Yu, Nan; Lunblad, Nathan

2005-01-01

An advanced computer code is undergoing development for numerically simulating laser cooling and trapping of large numbers of atoms. The code is expected to be useful in practical engineering applications and to contribute to understanding of the roles that light, atomic collisions, background pressure, and numbers of particles play in experiments using laser-cooled and -trapped atoms. The code is based on semiclassical theories of the forces exerted on atoms by magnetic and optical fields. Whereas computer codes developed previously for the same purpose account for only a few physical mechanisms, this code incorporates many more physical mechanisms (including atomic collisions, sub-Doppler cooling mechanisms, Stark and Zeeman energy shifts, gravitation, and evanescent-wave phenomena) that affect laser-matter interactions and the cooling of atoms to submillikelvin temperatures. Moreover, whereas the prior codes can simulate the interactions of at most a few atoms with a resonant light field, the number of atoms that can be included in a simulation by the present code is limited only by computer memory. Hence, the present code represents more nearly completely the complex physics involved when using laser-cooled and -trapped atoms in engineering applications. Another advantage that the code incorporates is the possibility to analyze the interaction between cold atoms of different atomic number. Some properties that cold atoms of different atomic species have, like cross sections and the particular excited states they can occupy when interacting with each other and light fields, play important roles not yet completely understood in the new experiments that are under way in laboratories worldwide to form ultracold molecules. Other research efforts use cold atoms as holders of quantum information, and more recent developments in cavity quantum electrodynamics also use ultracold atoms to explore and expand new information-technology ideas. These experiments give a hint on the wide range of applications and technology developments that can be tackled using cold atoms and light fields. From more precise atomic clocks and gravity sensors to the development of quantum computers, there will be a need to completely understand the whole ensemble of physical mechanisms that play a role in the development of such technologies. The code also permits the study of the dynamic and steady-state operations of technologies that use cold atoms. The physical characteristics of lasers and fields can be time-controlled to give a realistic simulation of the processes involved such that the design process can determine the best control features to use. It is expected that with the features incorporated into the code it will become a tool for the useful application of ultracold atoms in engineering applications. Currently, the software is being used for the analysis and understanding of simple experiments using cold atoms, and for the design of a modular compact source of cold atoms to be used in future research and development projects. The results so far indicate that the code is a useful design instrument that shows good agreement with experimental measurements (see figure), and a Windows-based user-friendly interface is also under development.

Investigation and Development of Advanced Surface Microanalysis Techniques and Methods

DTIC Science & Technology

1983-04-01

descriminates against isobars since each of the isobaric species will have a different atomic number or Z and, therefore, will be stripped of its...allow descrimination between two elements at the same mass but which have different atomic numbers. Multiply-charged ions are not produced during the

Self-regulated Gd atom trapping in open Fe nanocorrals

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

Cao, R. X.; Liu, Z.; Miao, B. F.

2014-07-01

Utilizing open Fe nanocorrals built by atom manipulation, we demonstrate self-regulated Gd atom trapping in open quantum corrals. The number of Gd atoms trapped is exactly determined by the diameter of the corral. The quantization can be understood as a self-regulating process, arising from the long-range interaction between Gd atoms and the open corral. We illustrate with arrays of open corrals that such atom trapping can suppress unwanted statistical fluctuations. Our approach opens a potential pathway for nanomaterial design and fabrication with atomic-level precision.

Quasi-coarse-grained dynamics: modelling of metallic materials at mesoscales

NASA Astrophysics Data System (ADS)

Dongare, Avinash M.

2014-12-01

A computationally efficient modelling method called quasi-coarse-grained dynamics (QCGD) is developed to expand the capabilities of molecular dynamics (MD) simulations to model behaviour of metallic materials at the mesoscales. This mesoscale method is based on solving the equations of motion for a chosen set of representative atoms from an atomistic microstructure and using scaling relationships for the atomic-scale interatomic potentials in MD simulations to define the interactions between representative atoms. The scaling relationships retain the atomic-scale degrees of freedom and therefore energetics of the representative atoms as would be predicted in MD simulations. The total energetics of the system is retained by scaling the energetics and the atomic-scale degrees of freedom of these representative atoms to account for the missing atoms in the microstructure. This scaling of the energetics renders improved time steps for the QCGD simulations. The success of the QCGD method is demonstrated by the prediction of the structural energetics, high-temperature thermodynamics, deformation behaviour of interfaces, phase transformation behaviour, plastic deformation behaviour, heat generation during plastic deformation, as well as the wave propagation behaviour, as would be predicted using MD simulations for a reduced number of representative atoms. The reduced number of atoms and the improved time steps enables the modelling of metallic materials at the mesoscale in extreme environments.

Atomization, drop size, and penetration for cross-stream water injection at high-altitude reentry conditions with application to the RAM C-1 and C-3 flights

NASA Technical Reports Server (NTRS)

Gooderum, P. B.; Bushnell, D. M.

1972-01-01

Atomization, drop size, and penetration data are presented for cross stream water injection at conditions simulating high altitude reentry (low Weber number, high static temperature, high Knudsen number, and low static pressure). These results are applied to the RAM C-1 and C-3 flights. Two primary breakup modes are considered, vapor pressure or flashing and aerodynamic atomization. Results are given for breakup boundaries and mean drop size for each of these atomization mechanisms. Both standard and flight orifice geometries are investigated. The data were obtained in both a static environment and in conventional aerodynamic facilities at Mach numbers of 4.5 and 8. The high temperature aspects of reentry were simulated in a Mach 5.5 cyanogen-oxygen tunnel with total temperature of 4500 K.

Chemical experiments with superheavy elements.

PubMed

Türler, Andreas

2010-01-01

Unnoticed by many chemists, the Periodic Table of the Elements has been extended significantly in the last couple of years and the 7th period has very recently been completed with eka-Rn (element 118) currently being the heaviest element whose synthesis has been reported. These 'superheavy' elements (also called transactinides with atomic number > or = 104 (Rf)) have been artificially synthesized in fusion reactions at accelerators in minute quantities of a few single atoms. In addition, all isotopes of the transactinide elements are radioactive and decay with rather short half-lives. Nevertheless, it has been possible in some cases to investigate experimentally chemical properties of transactinide elements and even synthesize simple compounds. The experimental investigation of superheavy elements is especially intriguing, since theoretical calculations predict significant deviations from periodic trends due to the influence of strong relativistic effects. In this contribution first experiments with hassium (Hs, atomic number 108), copernicium (Cn, atomic number 112) and element 114 (eka-Pb) are reviewed.

Theoretical studies on structural, magnetic, and spintronic characteristics of sandwiched Eu(n)COT(n+1) (n = 1-4) clusters.

PubMed

Zhang, Xiuyun; Ng, Man-Fai; Wang, Yanbiao; Wang, Jinlan; Yang, Shuo-Wang

2009-09-22

Europium (Eu)-cyclootetatrene (COT = C(8)H(8)) multidecker clusters (Eu(n)COT(n+1), n = 1-4) are studied by relativistic density functional theory calculations. These clusters are found to be thermodynamically stable with freely rotatable COT rings, and their total magnetic moments (MMs) increase linearly along with the number of Eu atoms. Each Eu atom contributes about 7 mu(B) to the cluster. Meanwhile, the internal COT rings have little MM contribution while the external COT rings have about 1 mu(B) MM aligned in opposite direction to that of the Eu atoms. The total MM of the Eu(n)COT(n+1) clusters can thus be generalized as 7n - 2 mu(B) where n is the number of Eu atoms. Besides, the ground states of these clusters are ferromagnetic and energetically competitive with the antiferromagnetic states, meaning that their spin states are very unstable, especially for larger clusters. More importantly, we uncover an interesting bonding characteristic of these clusters in which the interior ionic structure is capped by two hybrid covalent-ionic terminals. We suggest that such a characteristic makes the Eu(n)COT(n+1) clusters extremely stable. Finally, we reveal that for the positively charged clusters, the hybrid covalent-ionic terminals will tip further toward the interior part of the clusters to form deeper covalent-ionic caps. In contrast, the negatively charged clusters turn to pure ionic structures.

Evaluation of Solute Clusters Associated with Bake-Hardening Response in Isothermal Aged Al-Mg-Si Alloys Using a Three-Dimensional Atom Probe

NASA Astrophysics Data System (ADS)

Aruga, Yasuhiro; Kozuka, Masaya; Takaki, Yasuo; Sato, Tatsuo

2014-12-01

Temporal changes in the number density, size distribution, and chemical composition of clusters formed during natural aging at room temperature and pre-aging at 363 K (90 °C) in an Al-0.62Mg-0.93Si (mass pct) alloy were evaluated using atom probe tomography. More than 10 million atoms were examined in the cluster analysis, in which about 1000 clusters were obtained for each material after various aging treatments. The statistically proven records show that both number density and the average radius of clusters in pre-aged materials are larger than in naturally aged materials. It was revealed that the fraction of clusters with a low Mg/Si ratio after natural aging for a short time is higher than with other aging treatments, regardless of cluster size. This indicates that Si-rich clusters form more easily after short-period natural aging, and that Mg atoms can diffuse into the clusters or possibly form another type of Mg-Si cluster after prolonged natural aging. The formation of large clusters with a uniform Mg/Si ratio is encouraged by pre-aging. It can be concluded that an increase of small clusters with various Mg/Si ratios does not promote the bake-hardening (BH) response, whereas large clusters with a uniform Mg/Si ratio play an important role in hardening during the BH treatment at 443 K (170 °C).

Calculated gadolinium atomic electron energy levels and Auger electron emission probability as a function of atomic number Z

NASA Astrophysics Data System (ADS)

Miloshevsky, G. V.; Tolkach, V. I.; Shani, Gad; Rozin, Semion

2002-06-01

Auger electron interaction with matter is gaining importance in particular in medical application of radiation. The production probability and energy spectrum is therefore of great importance. A good source of Auger electrons is the 157Gd(n,γ) 158Gd reaction. The present article describes calculations of electron levels in Gd atoms and provides missing data of outer electron energy levels. The energy of these electron levels missing in published tables, was found to be in the 23-24 and 6-7 eV energy ranges respectively. The probability of Auger emission was calculated as an interaction of wave function of the initial and final electron states. The wave functions were calculated using the Hartree-Fock-Slater approximation with relativistic correction. The equations were solved using a spherical symmetry potential. The error for inner shell level is less than 10%, it is increased to the order of 10-15% for the outer shells. The width of the Auger process changes from 0.1 to 1.2 eV for atomic number Z from 5 to 70. The fluorescence yield width changes five orders of magnitude in this range. Auger electron emission width from the K shell changes from 10 -2 to ˜1 eV with Z changing from 10 to 64, depending on the final state. For the L shell it changes from 0 to 0.25 when it Z changes from 20 to 64.

Handshake electron transfer from hydrogen Rydberg atoms incident at a series of metallic thin films

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

Gibbard, J. A.; Softley, T. P.

2016-06-21

Thin metallic films have a 1D quantum well along the surface normal direction, which yields particle-in-a-box style electronic quantum states. However the quantum well is not infinitely deep and the wavefunctions of these states penetrate outside the surface where the electron is bound by its own image-charge attraction. Therefore a series of discrete, vacant states reach out from the thin film into the vacuum increasing the probability of electron transfer from an external atom or molecule to the thin film, especially for the resonant case where the quantum well energy matches that of the atom. We show that “handshake” electronmore » transfer from a highly excited Rydberg atom to these thin-film states is experimentally measurable. Thicker films have a wider 1D box, changing the energetic distribution and image-state contribution to the thin film wavefunctions, resulting in more resonances. Calculations successfully predict the number of resonances and the nature of the thin-film wavefunctions for a given film thickness.« less

Classification of ligand molecules in PDB with graph match-based structural superposition.

PubMed

Shionyu-Mitsuyama, Clara; Hijikata, Atsushi; Tsuji, Toshiyuki; Shirai, Tsuyoshi

2016-12-01

The fast heuristic graph match algorithm for small molecules, COMPLIG, was improved by adding a structural superposition process to verify the atom-atom matching. The modified method was used to classify the small molecule ligands in the Protein Data Bank (PDB) by their three-dimensional structures, and 16,660 types of ligands in the PDB were classified into 7561 clusters. In contrast, a classification by a previous method (without structure superposition) generated 3371 clusters from the same ligand set. The characteristic feature in the current classification system is the increased number of singleton clusters, which contained only one ligand molecule in a cluster. Inspections of the singletons in the current classification system but not in the previous one implied that the major factors for the isolation were differences in chirality, cyclic conformations, separation of substructures, and bond length. Comparisons between current and previous classification systems revealed that the superposition-based classification was effective in clustering functionally related ligands, such as drugs targeted to specific biological processes, owing to the strictness of the atom-atom matching.

Ultrastrong coupling of a single artificial atom to an electromagnetic continuum in the nonperturbative regime

NASA Astrophysics Data System (ADS)

Forn-Díaz, P.; García-Ripoll, J. J.; Peropadre, B.; Orgiazzi, J.-L.; Yurtalan, M. A.; Belyansky, R.; Wilson, C. M.; Lupascu, A.

2017-01-01

The study of light-matter interaction has led to important advances in quantum optics and enabled numerous technologies. Over recent decades, progress has been made in increasing the strength of this interaction at the single-photon level. More recently, a major achievement has been the demonstration of the so-called strong coupling regime, a key advancement enabling progress in quantum information science. Here, we demonstrate light-matter interaction over an order of magnitude stronger than previously reported, reaching the nonperturbative regime of ultrastrong coupling (USC). We achieve this using a superconducting artificial atom tunably coupled to the electromagnetic continuum of a one-dimensional waveguide. For the largest coupling, the spontaneous emission rate of the atom exceeds its transition frequency. In this USC regime, the description of atom and light as distinct entities breaks down, and a new description in terms of hybrid states is required. Beyond light-matter interaction itself, the tunability of our system makes it a promising tool to study a number of important physical systems, such as the well-known spin-boson and Kondo models.

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

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

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles ismore » tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. Using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe3+ to Fe2+) likely bonded with pyridinic N (FeN4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H2SO4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μgPt/cm2). Enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.« less

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

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

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). We report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunablemore » through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. In using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe 3+ to Fe 2+) likely bonded with pyridinic N (FeN 4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H 2SO 4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μg Pt/cm 2). Finally, enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O 2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.« less

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

DOE PAGES

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu; ...

2017-09-13

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). We report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunablemore » through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. In using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe 3+ to Fe 2+) likely bonded with pyridinic N (FeN 4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H 2SO 4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μg Pt/cm 2). Finally, enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O 2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.« less

Conductance of carbon based macro-molecular structures

NASA Astrophysics Data System (ADS)

Stafström, S.; Hansson, A.; Paulsson, M.

2000-11-01

Electron transport through metallic nanotubes and stacks of wide bandgap polyaromatic hydrocarbons (PAH) are studied theoretically using the Landauer formalism. These two systems constitute examples of different types of carbon based nanostructured materials of potential use in molecular electronics. The studies are carried out for structures with finite length that bridge two contact pads. In the case of perfect metallic nanotubes, the current is observed to increase stepwise with the applied voltage and the resistance is independent on the length of the tube. In the PAH stacks, the off resonance tunneling conductance decreases exponentially with the number of molecules in the stack and shows a near linear increase with the number of carbon atoms in each molecule.

European Scientific Notes. Volume 35, Number 2,

DTIC Science & Technology

1981-02-28

The risk is as- however, that he did not move forward sociated with the absorbed radiation dose in a straight line from his earliest to the ... dose in latter hdbefomdoiialtoa target region rk per iici-h in a source study the fallout from atomic bombs. However as medical aspects increased in ...enables supported from the Unix systems. The the users to manipulate

Study of the optical properties and the carbonaceous clusters in DAM-ADC solid state nuclear track detectors

NASA Astrophysics Data System (ADS)

Rammah, Y. S.; Abdalla, A. M.

2017-12-01

The optical properties of DAM-ADC solid state nuclear track detectors (SSNTDs) were investigated. Samples of DAM-ADC detector were irradiated at room temperature with gamma doses in the range of 100-500 kGy using 1.25 MeV 60Co source of dose rate 4 kGy/h. The optical characterization of these detectors have been studied through the measurements of UV-visible absorption spectra of blank and γ- irradiated samples. The optical energy band gaps, Eg for the detectors were obtained from the direct and the indirect allowed transitions in K-space using two methods (Tauc's model and absorption spectrum fitting (ASF) method). The absorbance of DAM-ADC detector was found to increase with increasing of the gamma absorbed dose. The width of the tail of localized states in the band gap, Eu was evaluated with the Urbach's method. The number of carbon atoms per conjugated length (N), the number of carbon atoms per cluster (M), and refractive index (n) for the present samples were determined. Both of the direct and the indirect band gaps of DAM-ADC detector decrease with increasing of the gamma absorbed dose. Urbach's energy decreased significantly for the detector. An increase in N, M, and n with increasing of the gamma absorbed dose was noticed. Results shed light on the effect of gamma irradiations of DAM-ADC SSNTDs to suitable industrial applications and to modify the optical properties through gamma-induced modifications of the polymer structure.

Modification of the acid/base properties of γ-Al2O3 by oxide additives: An ethanol TPD investigation

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

Kwak, Ja Hun; Lee, Jaekyoung; Szanyi, Janos

2016-02-26

The electronic properties of oxide-modified γ Al2O3 surfaces were investigated by using ethanol TPD. Ethanol TPD showed remarkable sensitivity toward the surface structures and electronic properties of the aluminas modified by various transition metal oxides. Maximum desorption rates for the primary product of ethanol adsorption, ethylene, were observed at 225 °C on non-modified γ-Al2O3. Desorption temperature of ethanol over a γ Al2O3 samples with different amounts of BaO linearly increased with increasing loading. On the contrary, ethanol desorption temperature on Pt modified γ-Al2O3 after calcined at 500 oC linearly decreased with increasing Pt loading. These results clearly suggested that themore » acid/base properties of the γ-Al2O3 surface can be strongly affected by ad-atoms. For confirming these arguments, we performed ethanol TPD experiments on various oxide modified γ-Al2O3 and normalized the maximum desorption temperatures based on the same number of oxide dopants. These normalized ethanol desorption temperatures linearly correlate with the electronegativity of the metal atom in the oxide. This linear relationship clearly demonstrates that the acidic properties of alumina surfaces can be systematically changed by ad-atoms.« less

Transition Probabilities for Hydrogen-Like Atoms

NASA Astrophysics Data System (ADS)

Jitrik, Oliverio; Bunge, Carlos F.

2004-12-01

E1, M1, E2, M2, E3, and M3 transition probabilities for hydrogen-like atoms are calculated with point-nucleus Dirac eigenfunctions for Z=1-118 and up to large quantum numbers l=25 and n=26, increasing existing data more than a thousandfold. A critical evaluation of the accuracy shows a higher reliability with respect to previous works. Tables for hydrogen containing a subset of the results are given explicitly, listing the states involved in each transition, wavelength, term energies, statistical weights, transition probabilities, oscillator strengths, and line strengths. The complete results, including 1 863 574 distinct transition probabilities, lifetimes, and branching fractions are available at http://www.fisica.unam.mx/research/tables/spectra/1el

Measurements of the effective atomic numbers of minerals using bremsstrahlung produced by low-energy electrons

NASA Astrophysics Data System (ADS)

Czarnecki, S.; Williams, S.

2017-12-01

The accuracy of a method for measuring the effective atomic numbers of minerals using bremsstrahlung intensities has been investigated. The method is independent of detector-efficiency and maximum accelerating voltage. In order to test the method, experiments were performed which involved low-energy electrons incident on thick malachite, pyrite, and galena targets. The resultant thick-target bremsstrahlung was compared to bremsstrahlung produced using a standard target, and experimental effective atomic numbers were calculated using data from a previous study (in which the Z-dependence of thick-target bremsstrahlung was studied). Comparisons of the results to theoretical values suggest that the method has potential for implementation in energy-dispersive X-ray spectroscopy systems.

New ion trap for atomic frequency standard applications

NASA Technical Reports Server (NTRS)

Prestage, J. D.; Dick, G. J.; Maleki, L.

1989-01-01

A novel linear ion trap that permits storage of a large number of ions with reduced susceptibility to the second-order Doppler effect caused by the radio frequency (RF) confining fields has been designed and built. This new trap should store about 20 times the number of ions a conventional RF trap stores with no corresponding increase in second-order Doppler shift from the confining field. In addition, the sensitivity of this shift to trapping parameters, i.e., RF voltage, RF frequency, and trap size, is greatly reduced.

Relativistic well-tempered Gaussian basis sets for helium through mercury

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

Okada, S.; Matsuoka, O.

1989-10-01

Exponent parameters of the nonrelativistically optimized well-tempered Gaussian basis sets of Huzinaga and Klobukowski have been employed for Dirac--Fock--Roothaan calculations without their reoptimization. For light atoms He (atomic number {ital Z}=2)--Rh ({ital Z}=45), the number of exponent parameters used has been the same as the nonrelativistic basis sets and for heavier atoms Pd ({ital Z}=46)--Hg({ital Z}=80), two 2{ital p} (and three 3{ital d}) Gaussian basis functions have been augmented. The scheme of kinetic energy balance and the uniformly charged sphere model of atomic nuclei have been adopted. The qualities of the calculated basis sets are close to the Dirac--Fock limit.

Coupled tensorial forms of the second-order effective Hamiltonian for open-subshell atoms in jj-coupling

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

Jursenas, Rytis, E-mail: Rytis.Jursenas@tfai.vu.l; Merkelis, Gintaras

2011-01-15

General expressions for the second-order effective atomic Hamiltonian are derived for open-subshell atoms in jj-coupling. The expansion terms are presented as N-body (N=0,1,2,3) effective operators given in the second quantization representation in coupled tensorial form. Two alternative coupled tensorial forms for each expansion term have been developed. To reduce the number of expressions of the effective Hamiltonian, the reduced matrix elements of antisymmetric two-particle wavefunctions are involved in the consideration. The general expressions presented allow the determination of the spin-angular part of expansion terms when studying correlation effects dealing with a number of problems in atomic structure calculations.

HELIUM EFFECTS ON DISPLACEMENT CASCADE IN TUNGSTEN

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

Setyawan, Wahyu; Nandipati, Giridhar; Roche, Kenneth J.

2013-09-30

Molecular dynamics (MD) simulations were performed to investigate He effects on displacement cascades in W. Helium content, proportion of interstitial and substitutional He and temperature were varied to reveal the various effects. The effect of interstitial He on the number of self-interstitial atoms (SIAs) produced during cascade damage appears to be insignificant. However, interstitial He tends to fill a vacancy (V). Nevertheless, this process is less favorable than SIA-V recombination particularly when excess SIAs are present before a cascade. The efficiency of He filling and SIA-V recombination increases as temperature increases due to increased point defect mobility. Likewise, substitutional Hemore » is more susceptible to displacement during a collision cascade than W. This susceptibility increases towards higher temperatures. Consequently, the number of surviving V is governed by the interplay between displaced substitutional He and SIA-V recombination. The temperature dependence of these processes results in a minimum number of V reached at an intermediate temperature.« less

Orientation observed by Zeeman spectra of dissociated atoms and the interference in photoexcitations

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

Kimura, Yasuyuki; Kasahara, Shunji; Kato, Hajime

2003-06-01

In a magnetic field, the wave number of a pump laser light polarized along the field was fixed to the isolated Cs{sub 2}D {sup 1}{sigma}{sub u}{sup +}(v=46, J=54)(leftarrow)X {sup 1}{sigma}{sub g}{sup +}(v=0, J=55) line, and the excitation spectrum of the dissociated Cs(6p {sup 2}P{sub 3/2}) atoms was measured by scanning the wave number of a probe laser light polarized perpendicular to the field. The population of each sublevel 6p {sup 2}P{sub 3/2,m{sub j}} of the dissociated atoms was determined from the line intensities in the m{sub j}-resolved excitation spectrum. The unequal population between the 6p {sup 2}P{sub 3/2,+verticalbarm{sub j}}{sub verticalbar}more » and 6p {sup 2}P{sub 3/2,-verticalbarm{sub j}}{sub verticalbar} levels (atomic orientation) was observed and it was enhanced as the magnetic-field strength was increased. The atomic orientation is shown to be induced by the interference between the indirect predissociation, which occurs by a combination of the spin-orbit coupling of the D {sup 1}{sigma}{sub u}{sup +} state with the (2){sup 3}{pi}{sub 0u} state and the L-uncoupling and Zeeman interactions between the (2){sup 3}{pi}{sub 0u} and dissociative (2){sup 3}{sigma}{sub u}{sup +} states, and the dissociation following a direct excitation to the (2){sup 3}{sigma}{sub u}{sup +} state, which is allowed by spin-orbit coupling of the (2){sup 3}{sigma}{sub u}{sup +} state with the B {sup 1}{pi}{sub u} state. It is demonstrated that the atomic orientation is produced by the photodissociation in the presence of an external magnetic field even when all degenerated molecular M=J,...,0,...,-J sublevels are excited by a light polarized linearly along the field.« less

Analytical dependence of effective atomic number on the elemental composition of matter and radiation energy in the range 10-1000 keV

NASA Astrophysics Data System (ADS)

Eritenko, A. N.; Tsvetiansky, A. L.; Polev, A. A.

2018-01-01

In the present paper, a universal analytical dependence of effective atomic number on the composition of matter and radiation energy is proposed. This enables one to consider the case of a strong difference in the elemental composition with respect to their atomic numbers over a wide energy range. The contribution of photoelectric absorption and incoherent and coherent scattering during the interaction between radiation and matter is considered. For energy values over 40 keV, the contribution of coherent scattering does not exceed approximately 10% that can be neglected at a further consideration. The effective atomic numbers calculated on the basis of the proposed relationships are compared to the results of calculations based on other methods considered by different authors on the basis of experimental and tabulated data on mass and atomic attenuation coefficients. The examination is carried out for both single-element (e.g., 6C, 14Si, 28Cu, 56Ba, and 82Pb) and multi-element materials. Calculations are performed for W1-xCux alloys (x = 0.35; x = 0.4), PbO, ther moluminescent dosimetry compounds (56Ba, 48Cd, 41Sr, 20Ca, 12Mg, and 11Na), and SO4 in a wide energy range. A case with radiation energy between the K- and L1-absorption edges is considered for 82Pb, 74W, 56Ba, 48Cd, and 38Sr. This enables to substantially simplify the calculation of the atomic number and will be useful in technical and scientific fields related to the interaction between X-ray/gamma radiation and matter.

Some properties of Stark states of hydrogenic atoms and ions

NASA Astrophysics Data System (ADS)

Hey, J. D.

2007-10-01

The motivation for this work is the problem of providing accurate values of the atomic transition matrix elements for the Stark components of Rydberg Rydberg transitions in atomic hydrogen and hydrogenic ions, for use in spectral line broadening calculations applicable to cool, low-density plasmas, such as those found in H II regions. Since conventional methods of calculating these transition matrix elements cannot be used for the high principal quantum numbers now easily attained in radio astronomical spectra, we attempt to show that the recurrence relation (ladder operator) method recently employed by Watson (2006 J. Phys. B: At. Mol. Opt. Phys. 39 1889 97) and Hey (2006 J. Phys. B: At. Mol. Opt. Phys. 39 2641 64) can be taken over into the parabolic coordinate system used to describe the Stark states of the atomic (ionic) radiators. The present method is therefore suggested as potentially useful for extending the work of Griem (1967 Astrophys. J. 148 547 58, 2005 Astrophys. J. 620 L133 4), Watson (2006), Stambulchik et al (2007 Phys. Rev. E 75 016401(9 pp) on Stark broadening in transitions between states of high principal quantum number, to physical conditions where the binary, impact approximation is no longer strictly applicable to both electron and ion perturbers. Another possible field of application is the study of Stark mixing transitions in 'ultracold' Rydberg atoms perturbed by long-range interactions with slow atoms and ions. Preparatory to the derivation of recurrence relations for states of different principal quantum number, a number of properties and recurrence relations are also found for states of identical principal quantum number, including the analogue in parabolic coordinates to the relations of Pasternack (1937 Proc. Natl Acad. Sci. USA 23 91 4, 250) in spherical polar coordinates.

Retrieval of sodium number density profiles in the mesosphere and lower thermosphere from SCIAMACHY limb emission measurements

NASA Astrophysics Data System (ADS)

Langowski, M. P.; von Savigny, C.; Burrows, J. P.; Rozanov, V. V.; Dunker, T.; Hoppe, U.-P.; Sinnhuber, M.; Aikin, A. C.

2015-07-01

An algorithm has been developed for the retrieval of sodium atom (Na) number density on a latitude and altitude grid from SCIAMACHY limb measurements of the Na resonance fluorescence. The results are obtained between 50 and 150 km altitude and the resulting global seasonal variations of Na are analysed. The retrieval approach is adapted from that used for the retrieval of magnesium atom (Mg) and magnesium ion (Mg+) number density profiles recently reported by Langowski et al. (2014). Monthly mean values of Na are presented as a function of altitude and latitude. This data set was retrieved from the 4 years of spectroscopic limb data of the SCIAMACHY mesosphere and lower thermosphere (MLT) measurement mode. The Na layer has a nearly constant altitude of 90-93 km for all latitudes and seasons, and has a full width at half maximum of 5-15 km. Small but substantial seasonal variations in Na are identified for latitudes less than 40°, where the maximum Na number densities are 3000-4000 atoms cm-3. At mid to high latitudes a clear seasonal variation with a winter maximum of up to 6000 atoms cm-3 is observed. The high latitudes, which are only measured in the Summer Hemisphere, have lower number densities with peak densities being approximately 1000 Na atoms cm-3. The full width at half maximum of the peak varies strongly at high latitudes and is 5 km near the polar summer mesopause, while it exceeds 10 km at lower latitudes. In summer the Na atom concentration at high latitudes and at altitudes below 88 km is significantly smaller than that at mid latitudes. The results are compared with other observations and models and there is overall a good agreement with these.

First principles calculations of the magnetic and hyperfine properties of Fe/N/Fe and Fe/O/Fe multilayers in the ground state of cohesive energy

NASA Astrophysics Data System (ADS)

dos Santos, A. V.; Samudio Pérez, C. A.; Muenchen, D.; Anibele, T. P.

2015-01-01

The ground state properties of Fe/N/Fe and Fe/O/Fe multilayers were investigated using the first principles calculations. The calculations were performed using the Linearized Augmented Plane Wave (LAPW) method implemented in the Wien2k code. A supercell consisting of one layer of nitride (or oxide) between two layers of Fe in the bcc structure was used to model the structure of the multilayer. The research in new materials also stimulated theoretical and experimental studies of iron-based nitrides due to their variety of structural and magnetic properties for the potential applications as in high strength steels and for high corrosion resistance. It is obvious from many reports that magnetic iron nitrides such as γ-Fe4N and α-Fe16N2 have interesting magnetic properties, among these a high magnetisation saturation and a high density crimp. However, although Fe-N films and multilayers have many potential applications, they can be produced in many ways and are being extensively studied from the theoretical point of view there is no detailed knowledge of their electronic structure. Clearly, efforts to understand the influence of the nitrogen atoms on the entire electronic structure are needed as to correctly interpret the observed changes in the magnetic properties when going from Fe-N bulk compounds to multilayer structures. Nevertheless, the N atoms are not solely responsible for electronics alterations in solid compounds. Theoretical results showed that Fe4X bulk compounds, where X is a variable atom with increasing atomic number (Z), the nature of bonding between X and adjacent Fe atoms changes from more covalent to more ionic and the magnetic moments of Fe also increase for Z=7, i.e. N. This is an indicative that atoms with a Z number higher than 7, i.e., O, can produce several new alterations in the entire magnetic properties of Fe multilayers. This paper presents the first results of an ab-initio electronic structure calculations, performed for Fe-N and Fe-O multilayers. Firstly, the formation energy and the cohesive energy of the multilayers are discussed. For optimised values, the cohesive energy of the multilayers to obtain the lattice parameters at the equilibrium ground state was used, i.e. a new methodology for this calculus was applied. Secondly, the magnetic properties and hyperfine interactions (magnetic field, electric field gradient and the isomer shift) of the iron atoms of the multilayers are discussed.

Correlation of materials properties with the atomic density concept

NASA Technical Reports Server (NTRS)

1975-01-01

Based on the hypothesis that the number of atoms per unit volume, accurately calculable for any substance of known real density and chemical composition, various characterizing parameters (energy levels of electrons interacting among atoms of the same or different kinds, atomic mass, bond intensity) were chosen for study. A multiple exponential equation was derived to express the relationship. Various properties were examined, and correlated with the various parameters. Some of the properties considered were: (1) heat of atomization, (2) boiling point, (3) melting point, (4) shear elastic modulus of cubic crystals, (5) thermal conductivity, and (6) refractive index for transparent substances. The solid elements and alkali halides were the materials studied. It is concluded that the number of different properties can quantitively be described by a common group of parameters for the solid elements, and a wide variety of compounds.

Macroscopic irreversibility and microscopic paradox: A Constructal law analysis of atoms as open systems

PubMed Central

Lucia, Umberto

2016-01-01

The relation between macroscopic irreversibility and microscopic reversibility is a present unsolved problem. Constructal law is introduced to develop analytically the Einstein’s, Schrödinger’s, and Gibbs’ considerations on the interaction between particles and thermal radiation (photons). The result leads to consider the atoms and molecules as open systems in continuous interaction with flows of photons from their surroundings. The consequent result is that, in any atomic transition, the energy related to the microscopic irreversibility is negligible, while when a great number of atoms (of the order of Avogadro’s number) is considered, this energy related to irreversibility becomes so large that its order of magnitude must be taken into account. Consequently, macroscopic irreversibility results related to microscopic irreversibility by flows of photons and amount of atoms involved in the processes. PMID:27762333

Analyzing For Light Elements By X-Ray Scattering

NASA Technical Reports Server (NTRS)

Ross, H. Richard

1993-01-01

Nondestructive method of determining concentrations of low-atomic-number elements in liquids and solids involves measurements of Compton and Rayleigh scattering of x rays. Applied in quantitative analysis of low-atomic-number constituents of alloys, of contaminants and corrosion products on surfaces of alloys, and of fractions of hydrogen in plastics, oils, and solvents.

Effective atomic numbers and electron density of dosimetric material

PubMed Central

Kaginelli, S. B.; Rajeshwari, T.; Sharanabasappa; Kerur, B. R.; Kumar, Anil S.

2009-01-01

A novel method for determination of mass attenuation coefficient of x-rays employing NaI (Tl) detector system and radioactive sources is described.in this paper. A rigid geometry arrangement and gating of the spectrometer at FWHM position and selection of absorber foils are all done following detailed investigation, to minimize the effect of small angle scattering and multiple scattering on the mass attenuation coefficient, μ/ρ, value. Firstly, for standardization purposes the mass attenuation coefficients of elemental foils such as Aluminum, Copper, Molybdenum, Tantalum and Lead are measured and then, this method is utilized for dosimetric interested material (sulfates). The experimental mass attenuation coefficient values are compared with the theoretical values to find good agreement between the theory and experiment within one to two per cent. The effective atomic numbers of the biological substitute material are calculated by sum rule and from the graph. The electron density of dosimetric material is calculated using the effective atomic number. The study has discussed in detail the attenuation coefficient, effective atomic number and electron density of dosimetric material/biological substitutes. PMID:20098566

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

Kira, M., E-mail: mackillo.kira@physik.uni-marburg.de

Atomic Bose–Einstein condensates (BECs) can be viewed as macroscopic objects where atoms form correlated atom clusters to all orders. Therefore, the presence of a BEC makes the direct use of the cluster-expansion approach–lucrative e.g. in semiconductor quantum optics–inefficient when solving the many-body kinetics of a strongly interacting Bose. An excitation picture is introduced with a nonunitary transformation that describes the system in terms of atom clusters within the normal component alone. The nontrivial properties of this transformation are systematically studied, which yields a cluster-expansion friendly formalism for a strongly interacting Bose gas. Its connections and corrections to the standard Hartree–Fock–Bogoliubov approachmore » are discussed and the role of the order parameter and the Bogoliubov excitations are identified. The resulting interaction effects are shown to visibly modify number fluctuations of the BEC. Even when the BEC has a nearly perfect second-order coherence, the BEC number fluctuations can still resolve interaction-generated non-Poissonian fluctuations. - Highlights: • Excitation picture expresses interacting Bose gas with few atom clusters. • Semiconductor and BEC many-body investigations are connected with cluster expansion. • Quantum statistics of BEC is identified in terms of atom clusters. • BEC number fluctuations show extreme sensitivity to many-body correlations. • Cluster-expansion friendly framework is established for an interacting Bose gas.« less

The origins of particle size effects in heterogeneous catalysis

NASA Astrophysics Data System (ADS)

Bond, Geoffrey C.

1985-06-01

Model calculations are presented to show how the fraction of atoms at the surface of small metal particles increases as their size diminishes in the range 10 to 2 nm. Such particles are prepared either by condensing atoms or aggregates from the vapour phase onto a support, or by chemical methods in the liquid phase, i.e. the traditional routes for preparing supported metal catalysts. The first group of methods leads to artificially pure materials in which the contact between metal and support is poor. The second group of methods leads to the introduction of impurities, to a greater variety of forms of particle, but to a generally firmer binding of metal to support: this permits electronic interactions between the components to occur. Recent literature on the chemisorptive and catalytic properties of metal particles, usually less than 10 nm in size, suggests that certain classes of reaction may be designated as "structure-insensitive" in that their rates depend only minimally on particle size, whereas others, denoted as "structure-sensitive", have rates which either increase or decrease with size. After discounting trivial effects, a hard core of results remains, demanding explanation. Although certain hydrocarbon transformations appear to need sites comprising more than a certain minimum number of atoms, it is thought that the electronic character of surface atoms plays a greater role than their geometric disposition.

Confocal absorption spectral imaging of MoS2: optical transitions depending on the atomic thickness of intrinsic and chemically doped MoS2.

PubMed

Dhakal, Krishna P; Duong, Dinh Loc; Lee, Jubok; Nam, Honggi; Kim, Minsu; Kan, Min; Lee, Young Hee; Kim, Jeongyong

2014-11-07

We performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra (over the range 1.5-3.2 eV) within regions having different numbers of layers and studied the variation of optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to the bulk MoS2 and this shift was attributed to the reduction of the gap energy in the Brillouin zone at the K-point as the atomic thickness increased. We also performed n-type chemical doping of MoS2 films using reduced benzyl viologen (BV) and the confocal absorption spectra modified by the doping showed a strong dependence on the atomic thickness: A and B exciton peaks were greatly quenched in the monolayer MoS2 while much less effect was shown in larger thickness and the BG peak either showed very small quenching for 1 L MoS2 or remained constant for larger thicknesses. Our results indicate that confocal absorption spectral imaging can provide comprehensive information on optical transitions of microscopic size intrinsic and doped two-dimensional layered materials.

The physical properties of Li-doped g-C{sub 3}N{sub 4} monolayer sheet investigated by the first-principles

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

Ruan, Linwei; Xu, Gengsheng; Gu, Lina

2015-06-15

Highlights: • Systematically research on Li-doped g-C{sub 3}N{sub 4} monolayer sheets by first-principles calculation. • Optimal dopant concentration for optical absorption is 7.12%. • Thermodynamics stability of the doped substrate g-C{sub 3}N{sub 4} decreased with Li dopant concentration increasing. • The values of work function Φ decreased monotonously with the increasing of Li dopant concentration. - Abstract: The geometric, electronic, optical properties, thermodynamic stability, and work function of Li-doped g-C{sub 3}N{sub 4} monolayer were investigated by the first-principles calculation. It was found that the Li atoms were preferentially substituted the open-hollow sites of g-C{sub 3}N{sub 4}. Interestingly, the “odd” numbermore » of Li doped g-C{sub 3}N{sub 4} showed metallic properties, while the “even” number of Li atoms widened the band gap of g-C{sub 3}N{sub 4}. The HOMO and LUMO distributions reveal that the active sites located at edge N and C atoms for both pristine and the Li-doped g-C{sub 3}N{sub 4}. In addition, thermodynamic analysis showed that the doped Li atoms reduced the thermodynamic stability of g-C{sub 3}N{sub 4} monolayer sheets.« less

Simulation of Rutherford backscattering spectrometry from arbitrary atom structures

DOE PAGES

Zhang, S.; Univ. of Helsinki; Nordlund, Kai; ...

2016-10-25

Rutherford backscattering spectrometry in a channeling direction (RBS/C) is a powerful tool for analysis of the fraction of atoms displaced from their lattice positions. However, it is in many cases not straightforward to analyze what is the actual defect structure underlying the RBS/C signal. To reveal insights of RBS/C signals from arbitrarily complex defective atomic structures, we develop in this paper a method for simulating the RBS/C spectrum from a set of arbitrary read-in atom coordinates (obtained, e.g., from molecular dynamics simulations). We apply the developed method to simulate the RBS/C signals from Ni crystal structures containing randomly displaced atoms,more » Frenkel point defects, and extended defects, respectively. The RBS/C simulations show that, even for the same number of atoms in defects, the RBS/C signal is much stronger for the extended defects. Finally, comparison with experimental results shows that the disorder profile obtained from RBS/C signals in ion-irradiated Ni is due to a small fraction of extended defects rather than a large number of individual random atoms.« less

Influence of spray nozzle shape upon atomization process

NASA Astrophysics Data System (ADS)

Beniuga, Marius; Mihai, Ioan

2016-12-01

The atomization process is affected by a number of operating parameters (pressure, viscosity, temperature, etc.) [1-6] and the adopted constructive solution. In this article are compared parameters of atomized liquid jet with two nozzles that have different lifespan, one being new and the other one out. The last statement shows that the second nozzle was monitored as time of operation on the one hand and on the other hand, two dimensional nozzles have been analyzed using laser profilometry. To compare the experimental parameters was carried an experimental stand to change the period and pulse width in injecting liquid through two nozzles. Atomized liquid jets were photographed and filmed quickly. Images obtained were analyzed using a Matlab code that allowed to determine a number of parameters that characterize an atomized jet. Knowing the conditions and operating parameters of atomized jet, will establish a new wastewater nozzle block of parameter values that can be implemented in controller that provides dosing of the liquid injected. Experimental measurements to observe the myriad forms of atomized droplets to a wide range of operating conditions, realized using the electronic control module.

Prediction of enthalpy and standard Gibbs energy of vaporization of haloaromatics from atomic properties.

PubMed

Monte, M J S; Almeida, A R R P; Liebman, J F

2015-11-01

Halogenated benzenes form a class of pollutants with a huge number of members - 1504 distinct benzene compounds, where one or more hydrogen atoms are replaced by halogens, may exist theoretically. This study presents a user friendly method for accurate prediction of vapor pressures and enthalpies of vaporization, at 298.15 K, of any mono or poly halobenzene compound. The derived equations for the prediction of those vaporization properties depend just on the number of each constituent halogen atom. This is a consequence of the absence of intramolecular interactions between the halogen atoms, revealed after examining vaporization results of ca. 40 halogenated benzenes. In order to rationalize the estimation equations, the contribution of the halogen atoms for the referred to above properties of vaporization was decomposed into two atomic properties - the volume and electron affinity. Extension of the applicability of the estimation method to substituted benzenes containing other substituent groups beyond halogen atoms as well as to some polycyclic aromatic species was tested with success. Copyright © 2015 Elsevier Ltd. All rights reserved.

Platinum clusters with precise numbers of atoms for preparative-scale catalysis.

PubMed

Imaoka, Takane; Akanuma, Yuki; Haruta, Naoki; Tsuchiya, Shogo; Ishihara, Kentaro; Okayasu, Takeshi; Chun, Wang-Jae; Takahashi, Masaki; Yamamoto, Kimihisa

2017-09-25

Subnanometer noble metal clusters have enormous potential, mainly for catalytic applications. Because a difference of only one atom may cause significant changes in their reactivity, a preparation method with atomic-level precision is essential. Although such a precision with enough scalability has been achieved by gas-phase synthesis, large-scale preparation is still at the frontier, hampering practical applications. We now show the atom-precise and fully scalable synthesis of platinum clusters on a milligram scale from tiara-like platinum complexes with various ring numbers (n = 5-13). Low-temperature calcination of the complexes on a carbon support under hydrogen stream affords monodispersed platinum clusters, whose atomicity is equivalent to that of the precursor complex. One of the clusters (Pt 10 ) exhibits high catalytic activity in the hydrogenation of styrene compared to that of the other clusters. This method opens an avenue for the application of these clusters to preparative-scale catalysis.The catalytic activity of a noble metal nanocluster is tied to its atomicity. Here, the authors report an atom-precise, fully scalable synthesis of platinum clusters from molecular ring precursors, and show that a variation of only one atom can dramatically change a cluster's reactivity.

Circuit QED with qutrits: Coupling three or more atoms via virtual-photon exchange

NASA Astrophysics Data System (ADS)

Zhao, Peng; Tan, Xinsheng; Yu, Haifeng; Zhu, Shi-Liang; Yu, Yang

2017-10-01

We present a model to describe a generic circuit QED system which consists of multiple artificial three-level atoms, namely, qutrits, strongly coupled to a cavity mode. When the state transition of the atoms disobeys the selection rules the process that does not conserve the number of excitations can happen determinatively. Therefore, we can realize coherent exchange interaction among three or more atoms mediated by the exchange of virtual photons. In addition, we generalize the one-cavity-mode mediated interactions to the multicavity situation, providing a method to entangle atoms located in different cavities. Using experimentally feasible parameters, we investigate the dynamics of the model including three cyclic-transition three-level atoms, for which the two lowest energy levels can be treated as qubits. Hence, we have found that two qubits can jointly exchange excitation with one qubit in a coherent and reversible way. In the whole process, the population in the third level of atoms is negligible and the cavity photon number is far smaller than 1. Our model provides a feasible scheme to couple multiple distant atoms together, which may find applications in quantum information processing.

All-atom four-body knowledge-based statistical potential to distinguish native tertiary RNA structures from nonnative folds.

PubMed

Masso, Majid

2018-09-14

Scientific breakthroughs in recent decades have uncovered the capability of RNA molecules to fulfill a wide array of structural, functional, and regulatory roles in living cells, leading to a concomitantly significant increase in both the number and diversity of experimentally determined RNA three-dimensional (3D) structures. Atomic coordinates from a representative training set of solved RNA structures, displaying low sequence and structure similarity, facilitate derivation of knowledge-based energy functions. Here we develop an all-atom four-body statistical potential and evaluate its capacity to distinguish native RNA 3D structures from nonnative folds based on calculated free energy scores. Atomic four-body nearest-neighbors are objectively identified by their occurrence as tetrahedral vertices in the Delaunay tessellations of RNA structures, and rates of atomic quadruplet interactions expected by chance are obtained from a multinomial reference distribution. Our four-body energy function, referred to as RAMP (ribonucleic acids multibody potential), is subsequently derived by applying the inverted Boltzmann principle to the frequency data, yielding an energy score for each type of atomic quadruplet interaction. Several well-known benchmark datasets reveal that RAMP is comparable with, and often outperforms, existing knowledge- and physics-based energy functions. To the best of our knowledge, this is the first study detailing an RNA tertiary structure-based multibody statistical potential and its comparative evaluation. Copyright © 2018 Elsevier Ltd. All rights reserved.

Inner hydrogen atom transfer in benzo-fused low symmetrical metal-free tetraazaporphyrin and phthalocyanine analogues: density functional theory studies.

PubMed

Qi, Dongdong; Zhang, Yuexing; Cai, Xue; Jiang, Jianzhuang; Bai, Ming

2009-02-01

Density functional theory (DFT) calculations were carried out to study the inner hydrogen atom transfer in low symmetrical metal-free tetrapyrrole analogues ranging from tetraazaporphyrin H(2)TAP (A(0)B(0)C(0)D(0)) to naphthalocyanine H(2)Nc (A(2)B(2)C(2)D(2)) via phthalocyanine H(2)Pc (A(1)B(1)C(1)D(1)). All the transition paths of sixteen different compounds (A(0)B(0)C(0)D(0)-A(2)B(2)C(2)D(2) and A(0)B(0)C(m)D(n), m

Fusion barrier characteristics of actinides

NASA Astrophysics Data System (ADS)

Manjunatha, H. C.; Sridhar, K. N.

2018-03-01

We have studied fusion barrier characteristics of actinide compound nuclei with atomic number range 89 ≤ Z ≤ 103 for all projectile target combinations. After the calculation of fusion barrier heights and positions, we have searched for their parameterization. We have achieved the empirical formula for fusion barrier heights (VB), positions (RB), curvature of the inverted parabola (ħω) of actinide compound nuclei with atomic number range 89 ≤ Z ≤ 103 for all projectile target combinations (6

SU-C-BRC-05: Monte Carlo Calculations to Establish a Simple Relation of Backscatter Dose Enhancement Around High-Z Dental Alloy to Its Atomic Number

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

Utsunomiya, S; Kushima, N; Katsura, K

Purpose: To establish a simple relation of backscatter dose enhancement around a high-Z dental alloy in head and neck radiation therapy to its average atomic number based on Monte Carlo calculations. Methods: The PHITS Monte Carlo code was used to calculate dose enhancement, which is quantified by the backscatter dose factor (BSDF). The accuracy of the beam modeling with PHITS was verified by comparing with basic measured data namely PDDs and dose profiles. In the simulation, a high-Z alloy of 1 cm cube was embedded into a tough water phantom irradiated by a 6-MV (nominal) X-ray beam of 10 cmmore » × 10 cm field size of Novalis TX (Brainlab). The ten different materials of high-Z alloys (Al, Ti, Cu, Ag, Au-Pd-Ag, I, Ba, W, Au, Pb) were considered. The accuracy of calculated BSDF was verified by comparing with measured data by Gafchromic EBT3 films placed at from 0 to 10 mm away from a high-Z alloy (Au-Pd-Ag). We derived an approximate equation to determine the relation of BSDF and range of backscatter to average atomic number of high-Z alloy. Results: The calculated BSDF showed excellent agreement with measured one by Gafchromic EBT3 films at from 0 to 10 mm away from the high-Z alloy. We found the simple linear relation of BSDF and range of backscatter to average atomic number of dental alloys. The latter relation was proven by the fact that energy spectrum of backscatter electrons strongly depend on average atomic number. Conclusion: We found a simple relation of backscatter dose enhancement around high-Z alloys to its average atomic number based on Monte Carlo calculations. This work provides a simple and useful method to estimate backscatter dose enhancement from dental alloys and corresponding optimal thickness of dental spacer to prevent mucositis effectively.« less

wACSF—Weighted atom-centered symmetry functions as descriptors in machine learning potentials

NASA Astrophysics Data System (ADS)

Gastegger, M.; Schwiedrzik, L.; Bittermann, M.; Berzsenyi, F.; Marquetand, P.

2018-06-01

We introduce weighted atom-centered symmetry functions (wACSFs) as descriptors of a chemical system's geometry for use in the prediction of chemical properties such as enthalpies or potential energies via machine learning. The wACSFs are based on conventional atom-centered symmetry functions (ACSFs) but overcome the undesirable scaling of the latter with an increasing number of different elements in a chemical system. The performance of these two descriptors is compared using them as inputs in high-dimensional neural network potentials (HDNNPs), employing the molecular structures and associated enthalpies of the 133 855 molecules containing up to five different elements reported in the QM9 database as reference data. A substantially smaller number of wACSFs than ACSFs is needed to obtain a comparable spatial resolution of the molecular structures. At the same time, this smaller set of wACSFs leads to a significantly better generalization performance in the machine learning potential than the large set of conventional ACSFs. Furthermore, we show that the intrinsic parameters of the descriptors can in principle be optimized with a genetic algorithm in a highly automated manner. For the wACSFs employed here, we find however that using a simple empirical parametrization scheme is sufficient in order to obtain HDNNPs with high accuracy.

Computation of heats of transport in crystalline solids: II

NASA Astrophysics Data System (ADS)

Grout, P. J.; Lidiard, A. B.

2008-10-01

This paper explores the application of classical molecular dynamics to the computation of the heat of transport of Au atoms in a model of solid gold at several elevated temperatures above the Debye temperature. It is assumed that the solid shows vacancy disorder. The work shows that to obtain consistent and reliable results it is necessary (a) to use very small time steps (≈1 fs) in the molecular dynamics integration routine and (b) to take averages over a very large number of vacancy displacements—a number which varies with temperature but which is of the order of 105. The results for the reduced heat of transport for the Au atoms show that: (1) it is positive in sign, i.e. that the diffusion of Au atoms in a temperature gradient is biassed towards the cold region or equivalently that the vacancies tend to migrate towards the hotter region; (2) it is predicted to fall as the average temperature increases and that the variation is closely linear in (1/T); (3) its value at high T relative to the energy of activation for vacancy movement is close to the corresponding ratio of experimental quantities. Analysis of these results indicates that the method and model may allow reliable predictions for other metals having the face centred cubic structure.

Chemistry of superheavy elements.

PubMed

Schädel, Matthias

2006-01-09

The number of chemical elements has increased considerably in the last few decades. Most excitingly, these heaviest, man-made elements at the far-end of the Periodic Table are located in the area of the long-awaited superheavy elements. While physical techniques currently play a leading role in these discoveries, the chemistry of superheavy elements is now beginning to be developed. Advanced and very sensitive techniques allow the chemical properties of these elusive elements to be probed. Often, less than ten short-lived atoms, chemically separated one-atom-at-a-time, provide crucial information on basic chemical properties. These results place the architecture of the far-end of the Periodic Table on the test bench and probe the increasingly strong relativistic effects that influence the chemical properties there. This review is focused mainly on the experimental work on superheavy element chemistry. It contains a short contribution on relativistic theory, and some important historical and nuclear aspects.

Mechanical properties of atomically thin boron nitride and the role of interlayer interactions

PubMed Central

Falin, Aleksey; Cai, Qiran; Santos, Elton J. G.; Scullion, Declan; Qian, Dong; Zhang, Rui; Yang, Zhi; Huang, Shaoming; Watanabe, Kenji; Taniguchi, Takashi; Barnett, Matthew R.; Chen, Ying; Ruoff, Rodney S.; Li, Lu Hua

2017-01-01

Atomically thin boron nitride (BN) nanosheets are important two-dimensional nanomaterials with many unique properties distinct from those of graphene, but investigation into their mechanical properties remains incomplete. Here we report that high-quality single-crystalline mono- and few-layer BN nanosheets are one of the strongest electrically insulating materials. More intriguingly, few-layer BN shows mechanical behaviours quite different from those of few-layer graphene under indentation. In striking contrast to graphene, whose strength decreases by more than 30% when the number of layers increases from 1 to 8, the mechanical strength of BN nanosheets is not sensitive to increasing thickness. We attribute this difference to the distinct interlayer interactions and hence sliding tendencies in these two materials under indentation. The significantly better interlayer integrity of BN nanosheets makes them a more attractive candidate than graphene for several applications, for example, as mechanical reinforcements. PMID:28639613

Composition Formulas of Inorganic Compounds in Terms of Cluster Plus Glue Atom Model.

PubMed

Ma, Yanping; Dong, Dandan; Wu, Aimin; Dong, Chuang

2018-01-16

The present paper attempts to identify the molecule-like structural units in inorganic compounds, by applying the so-called "cluster plus glue atom model". This model, originating from metallic glasses and quasi-crystals, describes any structure in terms of a nearest-neighbor cluster and a few outer-shell glue atoms, expressed in the cluster formula [cluster](glue atoms). Similar to the case for normal molecules where the charge transfer occurs within the molecule to meet the commonly known octet electron rule, the octet state is reached after matching the nearest-neighbor cluster with certain outer-shell glue atoms. These kinds of structural units contain information on local atomic configuration, chemical composition, and electron numbers, just as for normal molecules. It is shown that the formulas of typical inorganic compounds, such as fluorides, oxides, and nitrides, satisfy a similar octet electron rule, with the total number of valence electrons per unit formula being multiples of eight.

General properties of quantum optical systems in a strong field limit

NASA Technical Reports Server (NTRS)

Chumakov, S. M.; Klimov, Andrei B.

1994-01-01

We investigate the dynamics of an arbitrary atomic system (n-level atoms or many n-level atoms) interacting with a resonant quantized mode of an em field. If the initial field state is a coherent state with a large photon number then the system dynamics possesses some general features, independently of the particular structure of the atomic system. Namely, trapping states, factorization of the wave function, collapses and revivals of the atomic energy oscillations are discussed.

Atomic and electronic structures of an extremely fragile liquid.

PubMed

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

2014-12-18

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.

Complex magnetic structure of clusters and chains of Ni and Fe on Pt(111)

PubMed Central

Bezerra-Neto, Manoel M.; Ribeiro, Marcelo S.; Sanyal, Biplab; Bergman, Anders; Muniz, Roberto B.; Eriksson, Olle; Klautau, Angela B.

2013-01-01

We present an approach to control the magnetic structure of adatoms adsorbed on a substrate having a high magnetic susceptibility. Using finite Ni-Pt and Fe-Pt nanowires and nanostructures on Pt(111) surfaces, our ab initio results show that it is possible to tune the exchange interaction and magnetic configuration of magnetic adatoms (Fe or Ni) by introducing different numbers of Pt atoms to link them, or by including edge effects. The exchange interaction between Ni (or Fe) adatoms on Pt(111) can be considerably increased by introducing Pt chains to link them. The magnetic ordering can be regulated allowing for ferromagnetic or antiferromagnetic configurations. Noncollinear magnetic alignments can also be stabilized by changing the number of Pt-mediated atoms. An Fe-Pt triangularly-shaped nanostructure adsorbed on Pt(111) shows the most complex magnetic structure of the systems considered here: a spin-spiral type of magnetic order that changes its propagation direction at the triangle vertices. PMID:24165828

Ab initio studies of isolated boron substitutional defects in graphane

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Chetty, N.

2017-10-01

We have systematically studied energetics, structural and electronic properties of different configurations of the B atoms substituting C-H pairs located on a single hexagonal ring in a graphane system using the first-principles density functional theory (DFT). A total number of 12 distinct B dopants configurations were identified and characterized. Based on the formation energy analysis, we found that relative stability of B dopants depends greatly on the defect configurations. Our results suggest that the B substitutions prefer to be distributed randomly but avoiding the formation of homo-elemental B-B bonds in a graphane system, at any concentration. Generally, the values of band gap decrease as the number of B dopants increases, but the low energy configurations have large band gaps compared to those that have homo-elemental bonds. As a result, the band gap of graphane can be fine tuned through the change in the structural arrangement of B atoms. The adequate control of the electronic structure of graphane through doping should be essential for technological device applications.

Undersize solute element effects on defect structure development in copper under electron irradiation

NASA Astrophysics Data System (ADS)

Satoh, Y.; Yoshiie, T.; Arai, S.

2018-03-01

We conducted systematic experiments of defect structure development in Cu base binary alloys under 1000 kV electron irradiation at temperatures higher than 300 K, using in situ observations with high voltage electron microscopy. This report describes the effects of undersize elements: Co (-3.78%), Ni (-8.45%) and Be (-26.45%). The volume size factors are given in parentheses. The amounts of the respective elements were 2, 0.3, 0.05 at.%, or less. In Cu-Ni and Cu-Co and in the reference Cu, temperature dependence of the number density of interstitial-type dislocation loops had a down peak (i.e. loops hardly formed) at approximately 373 K, attributed to unexpected impurity atoms. Above the down-peak temperature, the addition of Co or Ni increased the loop number density through continuous nucleation of loops, extended the loop formation to higher temperatures, and decreased the apparent activation energy of loop growth rate. The addition of Be for 0.3 at.% or more delayed loop formation after formation of stacking fault tetrahedra (SFTs) around 300 K. The apparent mobility of self-interstitial atoms is expected to be smaller than that of vacancies because of strong binding with Be. Loop formation at temperatures higher than 373 K was enhanced by Be for 0.3 or 2 at.%, although it was suppressed greatly for 0.05 at.% or less. All undersize atoms increased the stability of SFTs under irradiation. Mechanisms of those effects were discussed and were briefly compared with earlier results found for oversize elements in Cu.

Low temperature platinum atomic layer deposition on nylon-6 for highly conductive and catalytic fiber mats

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

Mundy, J. Zachary; Shafiefarhood, Arya; Li, Fanxing

2016-01-15

Low temperature platinum atomic layer deposition (Pt-ALD) via (methylcyclopentadienyl)trimethyl platinum and ozone (O{sub 3}) is used to produce highly conductive nonwoven nylon-6 (polyamide-6, PA-6) fiber mats, having effective conductivities as high as ∼5500–6000 S/cm with only a 6% fractional increase in mass. The authors show that an alumina ALD nucleation layer deposited at high temperature is required to promote Pt film nucleation and growth on the polymeric substrate. Fractional mass gain scales linearly with Pt-ALD cycle number while effective conductivity exhibits a nonlinear trend with cycle number, corresponding to film coalescence. Field-emission scanning electron microscopy reveals island growth mode ofmore » the Pt film at low cycle number with a coalesced film observed after 200 cycles. The metallic coating also exhibits exceptional resistance to mechanical flexing, maintaining up to 93% of unstressed conductivity after bending around cylinders with radii as small as 0.3 cm. Catalytic activity of the as-deposited Pt film is demonstrated via carbon monoxide oxidation to carbon dioxide. This novel low temperature processing allows for the inclusion of highly conductive catalytic material on a number of temperature-sensitive substrates with minimal mass gain for use in such areas as smart textiles and flexible electronics.« less

Electronic structure of oxygen-vacancy defects in amorphous In-Ga-Zn-O semiconductors

NASA Astrophysics Data System (ADS)

Noh, Hyeon-Kyun; Chang, K. J.; Ryu, Byungki; Lee, Woo-Jin

2011-09-01

We perform first-principles density functional calculations to investigate the atomic and electronic properties of various O-vacancy (VO) defects in amorphous indium gallium zinc oxides (a-IGZO). The formation energies of VO have a tendency to increase with increasing number of neighboring Ga atoms, whereas they are generally low in the environment surrounded with In atoms. Thus, adding Ga atoms suppresses the formation of O-deficiency defects, which are considered as the origin of device instability in a-IGZO-based thin film transistors. The conduction band edge state is characterized by the In s orbital and insensitive to disorder, in good agreement with the experimental finding that increasing the In content enhances the carrier density and mobility. In a-IGZO, while most VO defects are deep donors, some of the defects act as shallow donors due to local environments different from those in crystalline oxides. As ionized O vacancies can capture electrons, it is suggested that these defects are responsible for positive shifts of the threshold voltage observed under positive gate bias stress. Under light illumination stress, VO defects can be ionized, becoming VO2+ defects due to the negative-U behavior. When electrons are captured by applying a negative bias voltage, ionized VO2+ defects return to the original neutral charge state. Through molecular dynamics simulations, we find that the initial neutral state is restored by annealing, in good agreement with experiments, although the annealing temperature depends on the local environment. Our calculations show that VO defects play an important role in the instability of a-IGZO-based devices.

Experimental investigation on the effect of liquid injection by multiple orifices in the formation of droplets in a Venturi scrubber.

PubMed

Guerra, V G; Gonçalves, J A S; Coury, J R

2009-01-15

Venturi scrubbers are widely utilized in gas cleaning. The cleansing elements in these scrubbers are droplets formed from the atomization of a liquid into a dust-laden gas. In industrial scrubbers, this liquid is injected through several orifices so that the cloud of droplets can be evenly distributed throughout the duct. The interaction between droplets when injected through many orifices, where opposite clouds of atomized liquid can reach each other, is to be expected. This work presents experimental measurements of droplet size measured in situ and the evidence of cloud interaction within a Venturi scrubber operating with multi-orifice jet injection. The influence of gas velocity, liquid flow rate and droplet size variation in the axial position after the point of the injection of the liquid were also evaluated for the different injection configurations. The experimental results showed that an increase in the liquid flow rate generated greater interaction between jets. The number of orifices had a significant influence on droplet size. In general, the increase in the velocity of the liquid jet and in the gas velocity favored the atomization process by reducing the size of the droplets.

Femtosecond, two-photon laser-induced-fluorescence imaging of atomic oxygen in an atmospheric-pressure plasma jet

NASA Astrophysics Data System (ADS)

Schmidt, Jacob B.; Sands, Brian L.; Kulatilaka, Waruna D.; Roy, Sukesh; Scofield, James; Gord, James R.

2015-06-01

Femtosecond, two-photon-absorption laser-induced-fluorescence (fs-TALIF) spectroscopy is employed to measure space- and time-resolved atomic-oxygen distributions in a nanosecond, repetitively pulsed, externally grounded, atmospheric-pressure plasma jet flowing helium with a variable oxygen admixture. The high-peak-intensity, low-average-energy femtosecond pulses result in increased TALIF signal with reduced photolytic inferences. This allows 2D imaging of absolute atomic-oxygen number densities ranging from 5.8   ×   1015 to 2.0   ×   1012cm-3 using a cooled CCD with an external intensifier. Xenon is used for signal and imaging-system calibrations to quantify the atomic-oxygen fluorescence signal. Initial results highlight a transition in discharge morphology from annular to filamentary, corresponding with a change in plasma chemistry from ozone to atomic oxygen production, as the concentration of oxygen in the feed gas is changed at a fixed voltage-pulse-repetition rate. In this configuration, significant concentrations of reactive oxygen species may be remotely generated by sustaining an active discharge beyond the confines of the dielectric capillary, which may benefit applications that require large concentrations of reactive oxygen species such as material processing or biomedical devices.

Self-bound droplets of a dilute magnetic quantum liquid

NASA Astrophysics Data System (ADS)

Schmitt, Matthias; Wenzel, Matthias; Böttcher, Fabian; Ferrier-Barbut, Igor; Pfau, Tilman

2016-11-01

Self-bound many-body systems are formed through a balance of attractive and repulsive forces and occur in many physical scenarios. Liquid droplets are an example of a self-bound system, formed by a balance of the mutual attractive and repulsive forces that derive from different components of the inter-particle potential. It has been suggested that self-bound ensembles of ultracold atoms should exist for atom number densities that are 108 times lower than in a helium droplet, which is formed from a dense quantum liquid. However, such ensembles have been elusive up to now because they require forces other than the usual zero-range contact interaction, which is either attractive or repulsive but never both. On the basis of the recent finding that an unstable bosonic dipolar gas can be stabilized by a repulsive many-body term, it was predicted that three-dimensional self-bound quantum droplets of magnetic atoms should exist. Here we report the observation of such droplets in a trap-free levitation field. We find that this dilute magnetic quantum liquid requires a minimum, critical number of atoms, below which the liquid evaporates into an expanding gas as a result of the quantum pressure of the individual constituents. Consequently, around this critical atom number we observe an interaction-driven phase transition between a gas and a self-bound liquid in the quantum degenerate regime with ultracold atoms. These droplets are the dilute counterpart of strongly correlated self-bound systems such as atomic nuclei and helium droplets.

Self-bound droplets of a dilute magnetic quantum liquid.

PubMed

Schmitt, Matthias; Wenzel, Matthias; Böttcher, Fabian; Ferrier-Barbut, Igor; Pfau, Tilman

2016-11-10

Self-bound many-body systems are formed through a balance of attractive and repulsive forces and occur in many physical scenarios. Liquid droplets are an example of a self-bound system, formed by a balance of the mutual attractive and repulsive forces that derive from different components of the inter-particle potential. It has been suggested that self-bound ensembles of ultracold atoms should exist for atom number densities that are 10 8 times lower than in a helium droplet, which is formed from a dense quantum liquid. However, such ensembles have been elusive up to now because they require forces other than the usual zero-range contact interaction, which is either attractive or repulsive but never both. On the basis of the recent finding that an unstable bosonic dipolar gas can be stabilized by a repulsive many-body term, it was predicted that three-dimensional self-bound quantum droplets of magnetic atoms should exist. Here we report the observation of such droplets in a trap-free levitation field. We find that this dilute magnetic quantum liquid requires a minimum, critical number of atoms, below which the liquid evaporates into an expanding gas as a result of the quantum pressure of the individual constituents. Consequently, around this critical atom number we observe an interaction-driven phase transition between a gas and a self-bound liquid in the quantum degenerate regime with ultracold atoms. These droplets are the dilute counterpart of strongly correlated self-bound systems such as atomic nuclei and helium droplets.

All-atom 3D structure prediction of transmembrane β-barrel proteins from sequences.

PubMed

Hayat, Sikander; Sander, Chris; Marks, Debora S; Elofsson, Arne

2015-04-28

Transmembrane β-barrels (TMBs) carry out major functions in substrate transport and protein biogenesis but experimental determination of their 3D structure is challenging. Encouraged by successful de novo 3D structure prediction of globular and α-helical membrane proteins from sequence alignments alone, we developed an approach to predict the 3D structure of TMBs. The approach combines the maximum-entropy evolutionary coupling method for predicting residue contacts (EVfold) with a machine-learning approach (boctopus2) for predicting β-strands in the barrel. In a blinded test for 19 TMB proteins of known structure that have a sufficient number of diverse homologous sequences available, this combined method (EVfold_bb) predicts hydrogen-bonded residue pairs between adjacent β-strands at an accuracy of ∼70%. This accuracy is sufficient for the generation of all-atom 3D models. In the transmembrane barrel region, the average 3D structure accuracy [template-modeling (TM) score] of top-ranked models is 0.54 (ranging from 0.36 to 0.85), with a higher (44%) number of residue pairs in correct strand-strand registration than in earlier methods (18%). Although the nonbarrel regions are predicted less accurately overall, the evolutionary couplings identify some highly constrained loop residues and, for FecA protein, the barrel including the structure of a plug domain can be accurately modeled (TM score = 0.68). Lower prediction accuracy tends to be associated with insufficient sequence information and we therefore expect increasing numbers of β-barrel families to become accessible to accurate 3D structure prediction as the number of available sequences increases.

Evaluation of Radiation Shielding Properties of the Polyvinyl Alcohol/Iron Oxide Polymer Composite

PubMed Central

Srinivasan, K.; Samuel, E. James Jabaseelan

2017-01-01

Context: Lead is the conventional shielding material against gamma/X-rays. It has some limitations such as toxic, high density, nonflexibility, and also bremsstrahlung production during electron interaction. It may affect the accuracy of radiotherapy outcome. Aims: To theoretically analyze the radiation shielding properties of flexible polyvinyl alcohol/iron oxide polymer composite with five different concentrations of magnetite over the energy range of 15 KeV–20 MeV. Subjects and Methods: Radiological properties were calculated based on the published literature. Attenuation coefficients of pure elements are generated with the help of WinXCOM database. Results: Effective atomic numbers and electron density are increased with the concentration of magnetite. On the other hand, the number of electrons per gram decreased. Mass attenuation coefficient (μ/ϼ) and linear attenuation coefficients (μ) are higher in the lower energy <100 KeV, and their values decreased when the energy increased. Computed tomography numbers (CT) show the significant variation between the concentrations in <60 KeV. Half-value layer and tenth-value layers are directly proportional to the energy and indirectly proportional to the concentration of magnetite. Transmission curve, relaxation length (ƛ), kinetic energy released in the matter, and elemental weight fraction are also calculated and the results are discussed. Conclusions: 0.5% of the magnetite gives superior shielding properties compared with other concentrations. It may be due to the presence of 0.3617% of Fe. Elemental weight fraction, atomic number, photon energy, and mass densities are the important parameters to understand the shielding behavior of any material. PMID:29296043

Valence, Covalence, Hypervalence, Oxidation State, and Coordination Number

ERIC Educational Resources Information Center

Smith, Derek W.

2005-01-01

Valence as a numerical measure of an atom's combining power, expressed by the number of bonds it forms in a molecular formulation of the compound in question, was unable to cope with coordination compounds. The covalence of an atom is the nearest model equivalent, but is subject to ambiguity since it often depends on which bonding model is being…

Cooling by spontaneous decay of highly excited antihydrogen atoms in magnetic traps.

PubMed

Pohl, T; Sadeghpour, H R; Nagata, Y; Yamazaki, Y

2006-11-24

An efficient cooling mechanism of magnetically trapped, highly excited antihydrogen (H) atoms is presented. This cooling, in addition to the expected evaporative cooling, results in trapping of a large number of H atoms in the ground state. It is found that the final fraction of trapped atoms is insensitive to the initial distribution of H magnetic quantum numbers. Expressions are derived for the cooling efficiency, demonstrating that magnetic quadrupole (cusp) traps provide stronger cooling than higher order magnetic multipoles. The final temperature of H confined in a cusp trap is shown to depend as approximately 2.2T(n0)n(0)(-2/3) on the initial Rydberg level n0 and temperature T(n0).

Cooling flexural modes of a mechanical oscillator by magnetically trapped Bose-Einstein-condensate atoms

NASA Astrophysics Data System (ADS)

Xu, Donghong; Xue, Fei

2017-12-01

We theoretically study cooling of flexural modes of a mechanical oscillator by Bose-Einstein-condensate (BEC) atoms (Rb87) trapped in a magnetic trap. The mechanical oscillator with a tiny magnet attached on one of its free ends produces an oscillating magnetic field. When its oscillating frequency matches certain hyperfine Zeeman energy of Rb87 atoms, the trapped BEC atoms are coupled out of the magnetic trap by the mechanical oscillator, flying away from the trap with stolen energy from the mechanical oscillator. Thus the mode temperature of the mechanical oscillator is reduced. The mode temperature of the steady state of mechanical oscillator, measured by the mean steady-state phonon number in the flexural mode of the mechanical oscillator, is analyzed. It is found that ground state (phonon number less than 1) may be accessible with optimal parameters of the hybrid system of mechanical oscillator and trapped BEC atoms.

Introduction to the Contributions of A. Temkin and R. J. Drachman to Atomic Physics

NASA Technical Reports Server (NTRS)

Bhatia, A.K.

2007-01-01

Their work, as is the work of most atomic theorists, is concerned with solving the Schroedinger equation accurately for wave function in cases where there is no exact analytical solution. In particular, Temkin is associated with electron scattering from atoms and ions. When he started there already were a number of methods to study the scattering of electrons from atoms.

Magic Numbers in Small Iron Clusters: A First-Principles Study

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

Kim, Eunja; Mohrland, Andrew B.; Weck, Philippe F.

2014-10-03

We perform ab initio spin-polarized density functional calculations of Fen aggregates with n ≤ 17 atoms to reveal the origin of the observed magic numbers, which indicate particularly high stability of clusters with 7, 13 and 15 atoms. Our results clarify the controversy regarding the ground state geometry of clusters such as Fe5and indicate that magnetism plays an important role in determining the stability and magic numbers in small iron clusters.

Charge transfer and formation of reduced Ce3+ upon adsorption of metal atoms at the ceria (110) surface.

PubMed

Nolan, Michael

2012-04-07

The modification of cerium dioxide with nanoscale metal clusters is intensely researched for catalysis applications, with gold, silver, and copper having been particularly well studied. The interaction of the metal cluster with ceria is driven principally by a localised interaction between a small number of metal atoms (as small as one) and the surface and understanding the fundamentals of the interaction of metal atoms with ceria surfaces is therefore of great interest. Much attention has been focused on the interaction of metals with the (111) surface of ceria, since this is the most stable surface and can be grown as films, which are probed experimentally. However, nanostructures exposing other surfaces such as (110) show high activity for reactions including CO oxidation and require further study; these nanostructures could be modified by deposition of metal atoms or small clusters, but there is no information to date on the atomic level details of metal-ceria interactions involving the (110) surface. This paper presents the results of density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) calculations of the adsorption of a number of different metal atoms at an extended ceria (110) surface; the metals are Au, Ag, Cu, Al, Ga, In, La, Ce, V, Cr, and Fe. Upon adsorption all metals are oxidised, transferring electron(s) to the surface, resulting in localised surface distortions. The precise details depend on the identity of the metal atom. Au, Ag, Cu each transfer one electron to the surface, reducing one Ce ion to Ce(3+), while of the trivalent metals, Al and La are fully oxidised, but Ga and In are only partially oxidised. Ce and the transition metals are also partially oxidised, with the number of reduced Ce ions possible in this surface no more than three per adsorbed metal atom. The predicted oxidation states of the adsorbed metal atoms should be testable in experiments on ceria nanostructures modified with metal atoms.

A Theoretical Search for Supervelocity Semiconductors

DTIC Science & Technology

1992-10-01

interfaces, doping control and compositional uniformity with atomic level dimensions. The development of ALE may very well prove to be the ultimate growth...pseudomorphic or strained-layer devices. These structures permit extended compositional ranges and, thus, have a number of potential advantages such as...in silicon devices For the past fifteen years, the silicon MOSFET industry has been dealing increasingly with prob- lems related to hot electron

Coaxial twin-fluid atomization with pattern air gas streams

NASA Astrophysics Data System (ADS)

Hei Ng, Chin; Aliseda, Alberto

2010-11-01

Coaxial twin-fluid atomization has numerous industrial applications, most notably fuel injection and spray coating. In the coating process of pharmaceutical tablets, the coaxial atomizing air stream is accompanied by two diametrically opposed side jets that impinge on the liquid/gas coaxial jets at an angle to produce an elliptical shape of the spray's cross section. Our study focuses on the influence of these side jets on the break up process and on the droplet velocity and diameter distribution along the cross section. The ultimate goal is to predict the size distribution and volume flux per unit area in the spray. With this predictive model, an optimal atomizing air/pattern air ratio can be found to achieve the desired coating result. This model is also crucial in scaling up the laboratory setup to production level. We have performed experiments with different atomized liquids, such as water and glycerine-water mixtures, that allow us to establish the effect of liquid viscosity, through the Ohnesorge number, in the spray characteristics. The gas Reynolds number of our experiments ranges from 9000 to 18000 and the Weber number ranges from 400 to 1600. We will present the effect of pattern air in terms of the resulting droplets size, droplet number density and velocity at various distances downstream of the nozzle where the effect of pattern air is significant.

Quantum computation with cold bosonic atoms in an optical lattice.

PubMed

García-Ripoll, Juan José; Cirac, Juan Ignacio

2003-07-15

We analyse an implementation of a quantum computer using bosonic atoms in an optical lattice. We show that, even though the number of atoms per site and the tunnelling rate between neighbouring sites is unknown, one may operate a universal set of gates by means of adiabatic passage.

Project Physics Tests 5, Models of the Atom.

ERIC Educational Resources Information Center

Harvard Univ., Cambridge, MA. Harvard Project Physics.

Test items relating to Project Physics Unit 5 are presented in this booklet. Included are 70 multiple-choice and 23 problem-and-essay questions. Concepts of atomic model are examined on aspects of relativistic corrections, electron emission, photoelectric effects, Compton effect, quantum theories, electrolysis experiments, atomic number and mass,…

Stark effect on an excited hydrogen atom

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

Barratt, C.

1983-07-01

The method of degenerate perturbation theory is used to study the dipolar nature of an excited hydrogen atom in an external electric field. The dependence of the atoms perturbed energy levels on the principal and magnetic quantum numbers, n and m, is investigated, along with the perturbed wave functions.

Theory of Reactions at a Solid Surface.

DTIC Science & Technology

1983-03-01

vibrational and rotational motions of X2 and X are separable even at small distances away from the surface, and that the lattice vibra- tions do not...volume of the clean surface, and o(X) is the reaction cross section of X atoms with lattice atoms M. Rearranging Eq. (28), we ,can write d[n(M) - an(R...positions of only a small number, n, of local surface atoms. We designate these as the "primary lattice atoms". The remaining N-n solid atoms serve

Search for novel contrast materials in dual-energy x-ray breast imaging using theoretical modeling of contrast-to-noise ratio

NASA Astrophysics Data System (ADS)

Karunamuni, R.; Maidment, A. D. A.

2014-08-01

Contrast-enhanced (CE) dual-energy (DE) x-ray breast imaging uses a low- and high-energy x-ray spectral pair to eliminate soft-tissue signal variation and thereby increase the detectability of exogenous imaging agents. Currently, CEDE breast imaging is performed with iodinated contrast agents. These compounds are limited by several deficiencies, including rapid clearance and poor tumor targeting ability. The purpose of this work is to identify novel contrast materials whose contrast-to-noise ratio (CNR) is comparable or superior to that of iodine in the mammographic energy range. A monoenergetic DE subtraction framework was developed to calculate the DE signal intensity resulting from the logarithmic subtraction of the low- and high-energy signal intensities. A weighting factor is calculated to remove the dependence of the DE signal on the glandularity of the breast tissue. Using the DE signal intensity and weighting factor, the CNR for materials with atomic numbers (Z) ranging from 1 to 79 are computed for energy pairs between 10 and 50 keV. A group of materials with atomic numbers ranging from 42 to 63 were identified to exhibit the highest levels of CNR in the mammographic energy range. Several of these materials have been formulated as nanoparticles for various applications but none, apart from iodine, have been investigated as CEDE breast imaging agents. Within this group of materials, the necessary dose fraction to the LE image decreases as the atomic number increases. By reducing the dose to the LE image, the DE subtraction technique will not provide an anatomical image of sufficient quality to accompany the contrast information. Therefore, materials with Z from 42 to 52 provide nearly optimal values of CNR with energy pairs and dose fractions that provide good anatomical images. This work is intended to inspire further research into new materials for optimized CEDE breast functional imaging.

Search for novel contrast materials in dual-energy x-ray breast imaging using theoretical modeling of contrast-to-noise ratio.

PubMed

Karunamuni, R; Maidment, A D A

2014-08-07

Contrast-enhanced (CE) dual-energy (DE) x-ray breast imaging uses a low- and high-energy x-ray spectral pair to eliminate soft-tissue signal variation and thereby increase the detectability of exogenous imaging agents. Currently, CEDE breast imaging is performed with iodinated contrast agents. These compounds are limited by several deficiencies, including rapid clearance and poor tumor targeting ability. The purpose of this work is to identify novel contrast materials whose contrast-to-noise ratio (CNR) is comparable or superior to that of iodine in the mammographic energy range. A monoenergetic DE subtraction framework was developed to calculate the DE signal intensity resulting from the logarithmic subtraction of the low- and high-energy signal intensities. A weighting factor is calculated to remove the dependence of the DE signal on the glandularity of the breast tissue. Using the DE signal intensity and weighting factor, the CNR for materials with atomic numbers (Z) ranging from 1 to 79 are computed for energy pairs between 10 and 50 keV. A group of materials with atomic numbers ranging from 42 to 63 were identified to exhibit the highest levels of CNR in the mammographic energy range. Several of these materials have been formulated as nanoparticles for various applications but none, apart from iodine, have been investigated as CEDE breast imaging agents. Within this group of materials, the necessary dose fraction to the LE image decreases as the atomic number increases. By reducing the dose to the LE image, the DE subtraction technique will not provide an anatomical image of sufficient quality to accompany the contrast information. Therefore, materials with Z from 42 to 52 provide nearly optimal values of CNR with energy pairs and dose fractions that provide good anatomical images. This work is intended to inspire further research into new materials for optimized CEDE breast functional imaging.

Grassmann phase space theory and the Jaynes-Cummings model

NASA Astrophysics Data System (ADS)

Dalton, B. J.; Garraway, B. M.; Jeffers, J.; Barnett, S. M.

2013-07-01

The Jaynes-Cummings model of a two-level atom in a single mode cavity is of fundamental importance both in quantum optics and in quantum physics generally, involving the interaction of two simple quantum systems—one fermionic system (the TLA), the other bosonic (the cavity mode). Depending on the initial conditions a variety of interesting effects occur, ranging from ongoing oscillations of the atomic population difference at the Rabi frequency when the atom is excited and the cavity is in an n-photon Fock state, to collapses and revivals of these oscillations starting with the atom unexcited and the cavity mode in a coherent state. The observation of revivals for Rydberg atoms in a high-Q microwave cavity is key experimental evidence for quantisation of the EM field. Theoretical treatments of the Jaynes-Cummings model based on expanding the state vector in terms of products of atomic and n-photon states and deriving coupled equations for the amplitudes are a well-known and simple method for determining the effects. In quantum optics however, the behaviour of the bosonic quantum EM field is often treated using phase space methods, where the bosonic mode annihilation and creation operators are represented by c-number phase space variables, with the density operator represented by a distribution function of these variables. Fokker-Planck equations for the distribution function are obtained, and either used directly to determine quantities of experimental interest or used to develop c-number Langevin equations for stochastic versions of the phase space variables from which experimental quantities are obtained as stochastic averages. Phase space methods have also been developed to include atomic systems, with the atomic spin operators being represented by c-number phase space variables, and distribution functions involving these variables and those for any bosonic modes being shown to satisfy Fokker-Planck equations from which c-number Langevin equations are often developed. However, atomic spin operators satisfy the standard angular momentum commutation rules rather than the commutation rules for bosonic annihilation and creation operators, and are in fact second order combinations of fermionic annihilation and creation operators. Though phase space methods in which the fermionic operators are represented directly by c-number phase space variables have not been successful, the anti-commutation rules for these operators suggest the possibility of using Grassmann variables—which have similar anti-commutation properties. However, in spite of the seminal work by Cahill and Glauber and a few applications, the use of phase space methods in quantum optics to treat fermionic systems by representing fermionic annihilation and creation operators directly by Grassmann phase space variables is rather rare. This paper shows that phase space methods using a positive P type distribution function involving both c-number variables (for the cavity mode) and Grassmann variables (for the TLA) can be used to treat the Jaynes-Cummings model. Although it is a Grassmann function, the distribution function is equivalent to six c-number functions of the two bosonic variables. Experimental quantities are given as bosonic phase space integrals involving the six functions. A Fokker-Planck equation involving both left and right Grassmann differentiations can be obtained for the distribution function, and is equivalent to six coupled equations for the six c-number functions. The approach used involves choosing the canonical form of the (non-unique) positive P distribution function, in which the correspondence rules for the bosonic operators are non-standard and hence the Fokker-Planck equation is also unusual. Initial conditions, such as those above for initially uncorrelated states, are discussed and used to determine the initial distribution function. Transformations to new bosonic variables rotating at the cavity frequency enable the six coupled equations for the new c-number functions-that are also equivalent to the canonical Grassmann distribution function-to be solved analytically, based on an ansatz from an earlier paper by Stenholm. It is then shown that the distribution function is exactly the same as that determined from the well-known solution based on coupled amplitude equations. In quantum-atom optics theories for many atom bosonic and fermionic systems are needed. With large atom numbers, treatments must often take into account many quantum modes—especially for fermions. Generalisations of phase space distribution functions of phase space variables for a few modes to phase space distribution functionals of field functions (which represent the field operators, c-number fields for bosons, Grassmann fields for fermions) are now being developed for large systems. For the fermionic case, the treatment of the simple two mode problem represented by the Jaynes-Cummings model is a useful test case for the future development of phase space Grassmann distribution functional methods for fermionic applications in quantum-atom optics.

Study of variations in structural, optical parameters and bulk etch rate of CR-39 polymer due to electron irradiation

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

Sahoo, G. S.; Joshi, D. S.; Tripathy, S. P., E-mail: sam.tripathy@gmail.com, E-mail: tripathy@barc.gov.in

2016-07-14

In this work, electron induced modifications on the bulk etch rate, structural and optical parameters of CR-39 polymer were studied using gravimetric, FTIR (Fourier Transform Infrared) and UV–vis (Ultraviolet–Visible) techniques, respectively. CR-39 samples were irradiated with 10 MeV electron beam for different durations to have the absorbed doses of 1, 10, 550, 5500, 16 500, and 55 000 kGy. From the FTIR analysis, the peak intensities at different bands were found to be changing with electron dose. A few peaks were observed to shift at high electron doses. From the UV-vis analysis, the optical band gaps for both direct and indirect transitions weremore » found to be decreasing with the increase in electron dose whereas the opacity, number of carbon atoms in conjugation length, and the number of carbon atoms per cluster were found to be increasing. The bulk etch rate was observed to be increasing with the electron dose. The primary objective of this investigation was to study the response of CR-39 to high electron doses and to determine a suitable pre-irradiation condition. The results indicated that, the CR-39 pre-irradiated with electrons can have better sensitivity and thus can be potentially applied for neutron dosimetry.« less

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

Li, Yang; Tu, Xingchen; Wang, Hao

The electronic efficiency and binding energy of contacts formed between graphene electrodes and poly-aromatic hydrocarbon (PAH) anchoring groups have been investigated by the non-equilibrium Green’s function formalism combined with density functional theory. Our calculations show that PAH molecules always bind in the interior and at the edge of graphene in the AB stacking manner, and that the binding energy increases following the increase of the number of carbon and hydrogen atoms constituting the PAH molecule. When we move to analyzing the electronic transport properties of molecular junctions with a six-carbon alkyne chain as the central molecule, the electronic efficiency ofmore » the graphene-PAH contacts is found to depend on the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the corresponding PAH anchoring group, rather than its size. To be specific, the smaller is the HOMO-LUMO gap of the PAH anchoring group, the higher is the electronic efficiency of the graphene-PAH contact. Although the HOMO-LUMO gap of a PAH molecule depends on its specific configuration, PAH molecules with similar atomic structures show a decreasing trend for their HOMO-LUMO gap as the number of fused benzene rings increases. Therefore, graphene-conjugated molecule-graphene junctions with high-binding and high-conducting graphene-PAH contacts can be realized by choosing appropriate PAH anchor groups with a large area and a small HOMO-LUMO gap.« less

The Unimolecular Reactions of CF3CHF2 Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules.

PubMed

Smith, Caleb A; Gillespie, Blanton R; Heard, George L; Setser, D W; Holmes, Bert E

2017-11-22

The recombination of CF 3 and CHF 2 radicals in a room-temperature bath gas was used to prepare vibrationally excited CF 3 CHF 2 * molecules with 101 kcal mol -1 of vibrational energy. The subsequent 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions were observed as a function of bath gas pressure by following the CHF 3 , CF 3 (F)C: and C 2 F 4 product concentrations by gas chromatography using a mass spectrometer as the detector. The singlet CF 3 (F)C: concentration was measured by trapping the carbene with trans-2-butene. The experimental rate constants are 3.6 × 10 4 , 4.7 × 10 4 , and 1.1 × 10 4 s -1 for the 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions, respectively. These experimental rate constants were matched to statistical RRKM calculated rate constants to assign threshold energies (E 0 ) of 88 ± 2, 88 ± 2, and 87 ± 2 kcal mol -1 to the three reactions. Pentafluoroethane is the only fluoroethane that has a competitive H atom transfer decomposition reaction, and it is the only example with 1,1-HF elimination being more important than 1,2-HF elimination. The trend of increasing threshold energies for both 1,1-HF and 1,2-HF processes with the number of F atoms in the fluoroethane molecule is summarized and investigated with electronic-structure calculations. Examination of the intrinsic reaction coordinate associated with the 1,1-HF elimination reaction found an adduct between CF 3 (F)C: and HF in the exit channel with a dissociation energy of ∼5 kcal mol -1 . Hydrogen-bonded complexes between HF and the H atom migration transition state of CH 3 (F)C: and the F atom migration transition state of CF 3 (F)C: also were found by the calculations. The role that these carbene-HF complexes could play in 1,1-HF elimination reactions is discussed.

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

Zheng, Ce; Auger, Maria A.; Moody, Michael P.

In this study, Ferritic/Martensitic (F/M) HT9 steel was irradiated to 20 displacements per atom (dpa) at 600 nm depth at 420 and 440 °C, and to 1, 10 and 20 dpa at 600 nm depth at 470 °C using 5 MeV Fe++ ions. The characterization was conducted using ChemiSTEM and Atom Probe Tomography (APT), with a focus on radiation induced segregation and precipitation. Ni and/or Si segregation at defect sinks (grain boundaries, dislocation lines, carbide/matrix interfaces) together with Ni, Si, Mn rich G-phase precipitation were observed in self-ion irradiated HT9 except in very low dose case (1 dpa at 470more » °C). Some G-phase precipitates were found to nucleate heterogeneously at defect sinks where Ni and/or Si segregated. In contrast to what was previously reported in the literature for neutron irradiated HT9, no Cr-rich α' phase, χ-phases, η phase and voids were found in self-ion irradiated HT9. The difference of observed microstructures is probably due to the difference of irradiation dose rate between ion irradiation and neutron irradiation. In addition, the average size and number density of G-phase precipitates were found to be sensitive to both irradiation temperature and dose. With the same irradiation dose, the average size of G-phase increased whereas the number density decreased with increasing irradiation temperature. Within the same irradiation temperature, the average size increased with increasing irradiation dose.« less

A Method to Estimate the Atomic Number and Mass Thickness of Intervening Materials in Uranium and Plutonium Gamma-Ray Spectroscopy Measurements

NASA Astrophysics Data System (ADS)

Streicher, Michael; Brown, Steven; Zhu, Yuefeng; Goodman, David; He, Zhong

2016-10-01

To accurately characterize shielded special nuclear materials (SNM) using passive gamma-ray spectroscopy measurement techniques, the effective atomic number and the thickness of shielding materials must be measured. Intervening materials between the source and detector may affect the estimated source isotopics (uranium enrichment and plutonium grade) for techniques which rely on raw count rates or photopeak ratios of gamma-ray lines separated in energy. Furthermore, knowledge of the surrounding materials can provide insight regarding the configuration of a device containing SNM. The described method was developed using spectra recorded using high energy resolution CdZnTe detectors, but can be expanded to any gamma-ray spectrometers with energy resolution of better than 1% FWHM at 662 keV. The effective atomic number, Z, and mass thickness of the intervening shielding material are identified by comparing the relative attenuation of different gamma-ray lines and estimating the proportion of Compton scattering interactions to photoelectric absorptions within the shield. While characteristic Kα x-rays can be used to identify shielding materials made of high Z elements, this method can be applied to all shielding materials. This algorithm has adequately estimated the effective atomic number for shields made of iron, aluminum, and polyethylene surrounding uranium samples using experimental data. The mass thicknesses of shielding materials have been estimated with a standard error of less than 1.3 g/cm2 for iron shields up to 2.5 cm thick. The effective atomic number was accurately estimated to 26 ± 5 for all iron thicknesses.

Stability investigation of a high number density Pt1/Fe2O3 single-atom catalyst under different gas environments by HAADF-STEM

NASA Astrophysics Data System (ADS)

Duan, Sibin; Wang, Rongming; Liu, Jingyue

2018-05-01

Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt1/Fe2O3 SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water–gas shift, and hydrogenation reactions. Under the oxidative gas environment, Fe2O3 supported Pt single atoms are stable even at high temperatures. The presence of either CO or H2 molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H2 molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of H2O molecules to the CO or H2 significantly accelerates the sintering of the Fe2O3 supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal–support interaction.

Stability investigation of a high number density Pt1/Fe2O3 single-atom catalyst under different gas environments by HAADF-STEM.

PubMed

Duan, Sibin; Wang, Rongming; Liu, Jingyue

2018-05-18

Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt 1 /Fe 2 O 3 SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water-gas shift, and hydrogenation reactions. Under the oxidative gas environment, Fe 2 O 3 supported Pt single atoms are stable even at high temperatures. The presence of either CO or H 2 molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H 2 molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of H 2 O molecules to the CO or H 2 significantly accelerates the sintering of the Fe 2 O 3 supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal-support interaction.

Structural characterization of graphene layers in various Indian coals by X-Ray Diffraction technique

NASA Astrophysics Data System (ADS)

Manoj, B.; Kunjomana, A. G.

2015-02-01

The results of the structural investigation of three Indian coals showed that, the structural parameters like fa & Lc increased where as interlayer spacing d002 decreased with increase in carbon content, aromaticity and coal rank. These structural parameters change just opposite with increase in volatile matter content. Considering the 'turbostratic' structure for coals, the minimum separation between aromatic lamellae was found to vary between 3.34 to 3.61 A° for these coals. As the aromaticity increased, the interlayer spacing decreased an indication of more graphitization of the sample. Volatile matter and carbon content had a strong influence on the aromaticity, interlayer spacing and stacking height on the sample. The average number of carbon atoms per aromatic lamellae and number of layers in the lamellae was found to be 16-21 and 7-8 for all the samples.

Sensory and short-term memory formations observed in a Ag2S gap-type atomic switch

NASA Astrophysics Data System (ADS)

Ohno, Takeo; Hasegawa, Tsuyoshi; Nayak, Alpana; Tsuruoka, Tohru; Gimzewski, James K.; Aono, Masakazu

2011-11-01

Memorization caused by the change in conductance in a Ag2S gap-type atomic switch was investigated as a function of the amplitude and width of input voltage pulses (Vin). The conductance changed little for the first few Vin, but the information of the input was stored as a redistribution of Ag-ions in the Ag2S, indicating the formation of sensory memory. After a certain number of Vin, the conductance increased abruptly followed by a gradual decrease, indicating the formation of short-term memory (STM). We found that the probability of STM formation depends strongly on the amplitude and width of Vin, which resembles the learning behavior of the human brain.

Atom Interferometry on Atom Chips - A Novel Approach Towards Precision Inertial Navigation System - PINS

DTIC Science & Technology

2010-06-01

Demonstration of an area-enclosing guided-atom interferometer for rotation sensing, Phys. Rev. Lett. 99, 173201 (2007). 4. Heralded Single- Magnon Quantum...excitations are quantized spin waves ( magnons ), such that transitions between its energy levels ( magnon number states) correspond to highly directional...polarization storage in the form of a single collective-spin excitation ( magnon ) that is shared between two spatially overlapped atomic ensembles

Shuttling single metal atom into and out of a metal nanoparticle.

PubMed

Wang, Shuxin; Abroshan, Hadi; Liu, Chong; Luo, Tian-Yi; Zhu, Manzhou; Kim, Hyung J; Rosi, Nathaniel L; Jin, Rongchao

2017-10-10

It has long been a challenge to dope metal nanoparticles with a specific number of heterometal atoms at specific positions. This becomes even more challenging if the heterometal belongs to the same group as the host metal because of the high tendency of forming a distribution of alloy nanoparticles with different numbers of dopants due to the similarities of metals in outmost electron configuration. Herein we report a new strategy for shuttling a single Ag or Cu atom into a centrally hollow, rod-shaped Au 24 nanoparticle, forming AgAu 24 and CuAu 24 nanoparticles in a highly controllable manner. Through a combined approach of experiment and theory, we explain the shuttling pathways of single dopants into and out of the nanoparticles. This study shows that the single dopant is shuttled into the hollow Au 24 nanoparticle either through the apex or side entry, while shuttling a metal atom out of the Au 25 to form the Au 24 nanoparticle occurs mainly through the side entry.Doping a metal nanocluster with heteroatoms dramatically changes its properties, but it remains difficult to dope with single-atom control. Here, the authors devise a strategy to dope single atoms of Ag or Cu into hollow Au nanoclusters, creating precise alloy nanoparticles atom-by-atom.

Atomic-Scale Tuning of Layered Binary Metal Oxides for High Temperature Moving Assemblies

DTIC Science & Technology

2015-06-01

AFRL-OSR-VA-TR-2015-0166 Atomic-Scale Tuning of Layered Binary Metal OxideS ASHLIE MARTINI UNIVERSITY OF CALIFORNIA MERCED Final Report 06/01/2015...Assemblies 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA9550-12-1-0221 5c.  PROGRAM ELEMENT NUMBER 6.  AUTHOR(S) ASHLIE MARTINI 5d.  PROJECT NUMBER 5e...ABSTRACT UU 18.  NUMBER        OF        PAGES 19a.  NAME OF RESPONSIBLE PERSON ASHLIE MARTINI Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18

Cheminoes: A Didactic Game to Learn Chemical Relationships between Valence, Atomic Number, and Symbol

ERIC Educational Resources Information Center

Moreno, Luis F.; Hincapié, Gina; Alzate, María Victoria

2014-01-01

Cheminoes is a didactic game that enables the meaningful learning of some relations between concepts such as chemical element, valence, atomic number, and chemical symbol for the first 36 chemical elements of the periodic system. Among the students who have played the game, their opinions of the activity were positive, considering the game to be a…

PREPARATION OF OXALATES OF METALS OF ATOMIC NUMBER GREATER THAN 88

DOEpatents

Duffield, R.B.

1959-02-01

A method is presented for the preparation of oxalates of metals of atomic number greater than 88. A solid peroxide of the heavy metal is contacted with an aqueous oxalic acid solution ai a temperature of about 50 C for a period of time sufficient to form the insoluble metal oxalate which is subsequentiy recovered as a pures crystalline compound.

A beachhead on the island of stability

DOE PAGES

Oganessian, Yuri Ts.; Rykaczewski, Krzysztof P.

2015-01-01

Remember learning the periodic table of elements in high school? Our chemistry teachers explained that the chemical properties of elements come from the electronic shell structure of atoms. Furthermore, our physics teachers enriched that picture of the atomic world by introducing us to isotopes and the Segrè chart of nuclides, which arranges them by proton number Z and neutron number N.

Fast Computation of High Energy Elastic Collision Scattering Angle for Electric Propulsion Plume Simulation (Conference Paper with Briefing Charts)

DTIC Science & Technology

2016-07-10

Elastic Collision Scattering Angle for Electric Propulsion Plume Simulation 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6...atom needs to be sampled; however, it is confirmed that initial target atom velocity does not play significant role in typical electric propulsion ...by ANSI Std. 239.18 Fast Computation of High Energy Elastic Collision Scattering Angle for Electric Propulsion Plume Simulation∗ Samuel J. Araki1

Non-Evaporative Cooling Using Spin-Exchange Collision in an Optical Trap

DTIC Science & Technology

2009-02-03

transit time of the atoms across the optical trap should damp the atoms’ motion significantly. These processes are described in detail in Ref. [ 18]. The...potentials. Finally, since the optical trap was very shallow compared to a MOT, any light-assisted collision that resulted in almost any net acceleration...EXCHANGE COLLISION IN AN OPTICAL TRAP 5a. CONTRACT NUMBER FA9550-06-1-0190 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S

An accurate full-dimensional potential energy surface for H-Au(111): Importance of nonadiabatic electronic excitation in energy transfer and adsorption.

PubMed

Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M; Kandratsenka, Alexander

2015-09-28

We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ≈3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.

QTAIM charge-charge flux-dipole flux interpretation of electronegativity and potential models of the fluorochloromethane mean dipole moment derivatives.

PubMed

Silva, Arnaldo F; da Silva, João V; Haiduke, R L A; Bruns, Roy E

2011-11-17

Infrared fundamental vibrational intensities and quantum theory atoms in molecules (QTAIM) charge-charge flux-dipole flux (CCFDF) contributions to the polar tensors of the fluorochloromethanes have been calculated at the QCISD/cc-pVTZ level. A root-mean-square error of 20.0 km mol(-1) has been found compared to an experimental error estimate of 14.4 and 21.1 km mol(-1) for MP2/6-311++G(3d,3p) results. The errors in the QCISD polar tensor elements and mean dipole moment derivatives are 0.059 e when compared with the experimental values. Both theoretical levels provide results showing that the dynamical charge and dipole fluxes provide significant contributions to the mean dipole moment derivatives and tend to be of opposite signs canceling one another. Although the experimental mean dipole moment derivative values suggest that all the fluorochloromethane molecules have electronic structures consistent with a simple electronegativity model with transferable atomic charges for their terminal atoms, the QTAIM/CCFDF models confirm this only for the fluoromethanes. Whereas the fluorine atom does not suffer a saturation effect in its capacity to drain electronic charge from carbon atoms that are attached to other fluorine and chlorine atoms, the zero flux electronic charge of the chlorine atom depends on the number and kind of the other substituent atoms. Both the QTAIM carbon charges (r = 0.990) and mean dipole moment derivatives (r = 0.996) are found to obey Siegbahn's potential model for carbon 1s electron ionization energies at the QCISD/cc-pVTZ level. The latter is a consequence of the carbon mean derivatives obeying the electronegativity model and not necessarily to their similarities with atomic charges. Atomic dipole contributions to the neighboring atom electrostatic potentials of the fluorochloromethanes are found to be of comparable size to the atomic charge contributions and increase the accuracy of Siegbahn's model for the QTAIM charge model results. Substitution effects of the hydrogen, fluorine, and chlorine atoms on the charge and dipole flux QTAIM contributions are found to be additive for the mean dipole derivatives of the fluorochloromethanes.

Development of the Science Data System for the International Space Station Cold Atom Lab

NASA Technical Reports Server (NTRS)

van Harmelen, Chris; Soriano, Melissa A.

2015-01-01

Cold Atom Laboratory (CAL) is a facility that will enable scientists to study ultra-cold quantum gases in a microgravity environment on the International Space Station (ISS) beginning in 2016. The primary science data for each experiment consists of two images taken in quick succession. The first image is of the trapped cold atoms and the second image is of the background. The two images are subtracted to obtain optical density. These raw Level 0 atom and background images are processed into the Level 1 optical density data product, and then into the Level 2 data products: atom number, Magneto-Optical Trap (MOT) lifetime, magnetic chip-trap atom lifetime, and condensate fraction. These products can also be used as diagnostics of the instrument health. With experiments being conducted for 8 hours every day, the amount of data being generated poses many technical challenges, such as downlinking and managing the required data volume. A parallel processing design is described, implemented, and benchmarked. In addition to optimizing the data pipeline, accuracy and speed in producing the Level 1 and 2 data products is key. Algorithms for feature recognition are explored, facilitating image cropping and accurate atom number calculations.

V. S. Lebedev and I. L. Beigman, Physics of Highly Excited Atoms and Ions

NASA Astrophysics Data System (ADS)

Mewe, R.

1999-07-01

This book contains a comprehensive description of the basic principles of the theoretical spectroscopy and experimental spectroscopic diagnostics of Rydberg atoms and ions, i.e., atoms in highly excited states with a very large principal quantum number (n≫1). Rydberg atoms are characterized by a number of peculiar physical properties as compared to atoms in the ground or a low excited state. They have a very small ionization potential (∝1/n2), the highly excited electron has a small orbital velocity (∝1/n), the radius (∝n2) is very large, the excited electron has a long orbital period (∝n3), and the radiation lifetime is very long (∝n3-5). At the same time the R. atom is very sensitive to perturbations from external fields in collisions with charged and neutral targets. In recent years, R. atoms have been observed in laboratory and cosmic conditions for n up to ˜1000, which means that the size amounts to about 0.1 mm, ˜106 times that of an atom in the ground state. The scope of this monograph is to familiarize the reader with today's approaches and methods for describing isolated R. atoms and ions, radiative transitions between highly excited states, and photoionization and photorecombination processes. The authors present a number of efficient methods for describing the structure and properties of R. atoms and calculating processes of collisions with neutral and charged particles as well as spectral-line broadening and shift of Rydberg atomic series in gases, cool and hot plasmas in laboratories and in astrophysical sources. Particular attention is paid to a comparison of theoretical results with available experimental data. The book contains 9 chapters. Chapter 1 gives an introduction to the basic properties of R. atoms (ions), Chapter 2 is devoted to an account of general methods describing an isolated Rydberg atom. Chapter 3 is focussed on the recent achievements in calculations of form factors and dipole matrix elements of different types of bound-bound and bound-free radiative transitions. Chapter 4 concentrates on the formulation of basic theoretical methods and physical approaches to collisions involving R. atoms. Chapters 5 to 8 contain a systematic description of major directions and modern techniques in the collision theory of R. atoms and ions with atoms, molecules, electrons, and ions. Finally, Chapter 9 deals with the spectral-line broadening and shift of R. atomic series induced by collisions with neutral and charged particles. A subject index of four pages and 250 references are given. This monograph will be a basic tool and reference for all scientists working in the fields of plasma physics, spectroscopy, physics of electronic and atomic collisions, as well as astrophysics, radio astronomy, and space physics.

A study of the relationship between the performance and dependability of a fault-tolerant computer

NASA Technical Reports Server (NTRS)

Goswami, Kumar K.

1994-01-01

This thesis studies the relationship by creating a tool (FTAPE) that integrates a high stress workload generator with fault injection and by using the tool to evaluate system performance under error conditions. The workloads are comprised of processes which are formed from atomic components that represent CPU, memory, and I/O activity. The fault injector is software-implemented and is capable of injecting any memory addressable location, including special registers and caches. This tool has been used to study a Tandem Integrity S2 Computer. Workloads with varying numbers of processes and varying compositions of CPU, memory, and I/O activity are first characterized in terms of performance. Then faults are injected into these workloads. The results show that as the number of concurrent processes increases, the mean fault latency initially increases due to increased contention for the CPU. However, for even higher numbers of processes (less than 3 processes), the mean latency decreases because long latency faults are paged out before they can be activated.

Suppression and enhancement of decoherence in an atomic Josephson junction

NASA Astrophysics Data System (ADS)

Japha, Yonathan; Zhou, Shuyu; Keil, Mark; Folman, Ron; Henkel, Carsten; Vardi, Amichay

2016-05-01

We investigate the role of interatomic interactions when a Bose gas, in a double-well potential with a finite tunneling probability (a ‘Bose-Josephson junction’), is exposed to external noise. We examine the rate of decoherence of a system initially in its ground state with equal probability amplitudes in both sites. The noise may induce two kinds of effects: firstly, random shifts in the relative phase or number difference between the two wells and secondly, loss of atoms from the trap. The effects of induced phase fluctuations are mitigated by atom-atom interactions and tunneling, such that the dephasing rate may be suppressed by half its single-atom value. Random fluctuations may also be induced in the population difference between the wells, in which case atom-atom interactions considerably enhance the decoherence rate. A similar scenario is predicted for the case of atom loss, even if the loss rates from the two sites are equal. We find that if the initial state is number-squeezed due to interactions, then the loss process induces population fluctuations that reduce the coherence across the junction. We examine the parameters relevant for these effects in a typical atom chip device, using a simple model of the trapping potential, experimental data, and the theory of magnetic field fluctuations near metallic conductors. These results provide a framework for mapping the dynamical range of barriers engineered for specific applications and set the stage for more complex atom circuits (‘atomtronics’).

Experimental demonstration of multiple monoenergetic gamma radiography for effective atomic number identification in cargo inspection

NASA Astrophysics Data System (ADS)

Henderson, Brian S.; Lee, Hin Y.; MacDonald, Thomas D.; Nelson, Roberts G.; Danagoulian, Areg

2018-04-01

The smuggling of special nuclear materials (SNMs) through international borders could enable nuclear terrorism and constitutes a significant threat to global security. This paper presents the experimental demonstration of a novel radiographic technique for quantitatively reconstructing the density and type of material present in commercial cargo containers, as a means of detecting such threats. Unlike traditional techniques which use sources of bremsstrahlung photons with a continuous distribution of energies, multiple monoenergetic gamma radiography utilizes monoenergetic photons from nuclear reactions, specifically the 4.4 and 15.1 MeV photons from the 11B(d,nγ)12C reaction. By exploiting the Z-dependence of the photon interaction cross sections at these two specific energies, it is possible to simultaneously determine the areal density and the effective atomic number as a function of location for a 2D projection of a scanned object. The additional information gleaned from using and detecting photons of specific energies for radiography substantially increases the resolving power between different materials. This paper presents results from the imaging of mock cargo materials ranging from Z ≈5 -92 , demonstrating accurate reconstruction of the effective atomic number and areal density of the materials over the full range. In particular, the system is capable of distinguishing pure materials with Z ≳ 70 , such as lead and uranium—a critical requirement of a system designed to detect SNM. This methodology could be used to screen commercial cargoes with high material specificity, to distinguish most benign materials from SNM, such as uranium and plutonium.

Directed Field Ionization

NASA Astrophysics Data System (ADS)

Gregoric, Vincent C.; Kang, Xinyue; Liu, Zhimin Cheryl; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

2017-04-01

Selective field ionization is an important experimental technique used to study the state distribution of Rydberg atoms. This is achieved by applying a steadily increasing electric field, which successively ionizes more tightly bound states. An atom prepared in an energy eigenstate encounters many avoided Stark level crossings on the way to ionization. As it traverses these avoided crossings, its amplitude is split among multiple different states, spreading out the time resolved electron ionization signal. By perturbing the electric field ramp, we can change how the atoms traverse the avoided crossings, and thus alter the shape of the ionization signal. We have used a genetic algorithm to evolve these perturbations in real time in order to arrive at a target ionization signal shape. This process is robust to large fluctuations in experimental conditions. This work was supported by the National Science Foundation under Grants No. 1607335 and No. 1607377 and used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant Number OCI-1053575.

Safe transport of radioactive materials in Egypt

NASA Astrophysics Data System (ADS)

El-Shinawy, Rifaat M. K.

1994-07-01

In Egypt the national regulations for safe transport of radioactive materials (RAM) are based on the International Atomic Energy Agency (IAEA) regulations. In addition, regulations for the safe transport of these materials through the Suez Canal (SC) were laid down by the Egyptian Atomic Energy Authority (EAEA) and the Suez Canal Authority (SCA). They are continuously updated to meet the increased knowledge and the gained experience. The technical and protective measures taken during transport of RAM through SC are mentioned. Assessment of the impact of transporting radioactive materials through the Suez Canal using the INTERTRAN computer code was carried out in cooperation with IAEA. The transported activities and empty containers, the number of vessels carrying RAM through the canal from 1963 to 1991 and their nationalities are also discussed. The protective measures are mentioned.A review of the present situation of the radioactive wastes storage facilities at the Atomic Energy site at Inshas is given along with the regulation for safe transportation and disposal of radioactive wastes

Three-dimensional quantitative structure-property relationship (3D-QSPR) models for prediction of thermodynamic properties of polychlorinated biphenyls (PCBs): enthalpy of vaporization.

PubMed

Puri, Swati; Chickos, James S; Welsh, William J

2002-01-01

Three-dimensional Quantitative Structure-Property Relationship (QSPR) models have been derived using Comparative Molecular Field Analysis (CoMFA) to correlate the vaporization enthalpies of a representative set of polychlorinated biphenyls (PCBs) at 298.15 K with their CoMFA-calculated physicochemical properties. Various alignment schemes, such as inertial, as is, and atom fit, were employed in this study. The CoMFA models were also developed using different partial charge formalisms, namely, electrostatic potential (ESP) charges and Gasteiger-Marsili (GM) charges. The most predictive model for vaporization enthalpy (Delta(vap)H(m)(298.15 K)), with atom fit alignment and Gasteiger-Marsili charges, yielded r2 values 0.852 (cross-validated) and 0.996 (conventional). The vaporization enthalpies of PCBs increased with the number of chlorine atoms and were found to be larger for the meta- and para-substituted isomers. This model was used to predict Delta(vap)H(m)(298.15 K) of the entire set of 209 PCB congeners.

Cooling rate dependence and local structure in aluminum monatomic metallic glass

NASA Astrophysics Data System (ADS)

Kbirou, M.; Trady, S.; Hasnaoui, A.; Mazroui, M.

2017-10-01

The local atomic structure in aluminium monatomic metallic glass is studied using molecular dynamics simulations combined with the embedded atom method (EAM). We have used a variety of analytical methods to characterise the atomic configurations of our system: the Pair Distribution Function (PDF), the Common Neighbour Analysis (CNA) and the Voronoi Tessellation Analysis. CNA was used to investigate the order change from liquid to amorphous phases, recognising that the amount of icosahedral clusters increases with the decrease of temperature. The Voronoi analysis revealed that the icosahedral-like polyhedral are the predominant ones. It has been observed that the PDF function shows a splitting in the second peak, which cannot be attributed to the only ideal icosahedral polyhedron 〈0, 0, 12, 0〉, but also to the formation of other Voronoi polyhedra 〈0, 1, 10, 2〉 . Further, the PDFs were then integrated giving the cumulative coordination number in order to compute the fractal dimension (df).

Electronic and structural properties of Lu under pressure: Relation to structural phases of the rare-earth metals

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

Min, B.I.; Oguchi, T.; Jansen, H.J.F.

1986-07-15

Ground-state electronic and structural properties of Lu under pressure are investigated with use of the self-consistent all-electron total-energy linear muffin-tin orbital band-structure method within a local-density-functional approximation. Pressure-induced structural transitions are found to occur in the following sequence: hcp--(Sm-type)--dhcp--fcc, which is the same as that observed in the crystal structures of the trivalent rare-earth metals with decreasing atomic number. This structural transition is correlated with the increase in the number of d-italic electrons under pressure.

Resonance and intercombination lines in Mg-like ions of atomic numbers Z = 13 – 92

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

Santana, Juan A.; Trabert, Elmar

2015-02-05

While prominent lines of various Na-like ions have been measured with an accuracy of better than 100 ppm and corroborate equally accurate calculations, there have been remarkably large discrepancies between calculations for Mg-like ions of high atomic number. We present ab initio calculations using the multireference Moller-Plesset approach for Mg-like ions of atomic numbers Z = 13-92 and compare the results with other calculations of this isoelectronic sequence as well as with experimental data. Our results come very close to experiment (typically 100 ppm) over a wide range. Furthermore, data at high values of Z are sparse, which calls formore » further accurate measurements in this range where relativistic and QED effects are large.« less

ATOMIC PHYSICS, AN AUTOINSTRUCTIONAL PROGRAM, VOLUME 2, SUPPLEMENT.

ERIC Educational Resources Information Center

DETERLINE, WILLIAM A.; KLAUS, DAVID J.

THE AUTOINSTRUCTIONAL MATERIALS IN THIS TEXT WERE PREPARED FOR USE IN AN EXPERIMENTAL STUDY, OFFERING SELF-TUTORING MATERIAL FOR LEARNING ATOMIC PHYSICS. THE TOPICS COVERED ARE (1) ISOTOPES AND MASS NUMBERS, (2) MEASURING ATOMIC MASS, (3) DISCOVERY OF THE NUCLEUS, (4) STRUCTURE OF THE NUCLEUS, (5) DISCOVERY OF THE NEUTRON, (6) NUCLEAR REACTIONS,…

The Periodic Pyramid

ERIC Educational Resources Information Center

Hennigan, Jennifer N.; Grubbs, W. Tandy

2013-01-01

The chemical elements present in the modern periodic table are arranged in terms of atomic numbers and chemical periodicity. Periodicity arises from quantum mechanical limitations on how many electrons can occupy various shells and subshells of an atom. The shell model of the atom predicts that a maximum of 2, 8, 18, and 32 electrons can occupy…

Treatment of Ion-Atom Collisions Using a Partial-Wave Expansion of the Projectile Wavefunction

ERIC Educational Resources Information Center

Wong, T. G.; Foster, M.; Colgan, J.; Madison, D. H.

2009-01-01

We present calculations of ion-atom collisions using a partial-wave expansion of the projectile wavefunction. Most calculations of ion-atom collisions have typically used classical or plane-wave approximations for the projectile wavefunction, since partial-wave expansions are expected to require prohibitively large numbers of terms to converge…

The Analog Atomic Force Microscope: Measuring, Modeling, and Graphing for Middle School

ERIC Educational Resources Information Center

Goss, Valerie; Brandt, Sharon; Lieberman, Marya

2013-01-01

using an analog atomic force microscope (A-AFM) made from a cardboard box and mailing tubes. Varying numbers of ping pong balls inside the tubes mimic atoms on a surface. Students use a dowel to make macroscale measurements similar to those of a nanoscale AFM tip as it…

Atomic clusters and atomic surfaces in icosahedral quasicrystals.

PubMed

Quiquandon, Marianne; Portier, Richard; Gratias, Denis

2014-05-01

This paper presents the basic tools commonly used to describe the atomic structures of quasicrystals with a specific focus on the icosahedral phases. After a brief recall of the main properties of quasiperiodic objects, two simple physical rules are discussed that lead one to eventually obtain a surprisingly small number of atomic structures as ideal quasiperiodic models for real quasicrystals. This is due to the fact that the atomic surfaces (ASs) used to describe all known icosahedral phases are located on high-symmetry special points in six-dimensional space. The first rule is maximizing the density using simple polyhedral ASs that leads to two possible sets of ASs according to the value of the six-dimensional lattice parameter A between 0.63 and 0.79 nm. The second rule is maximizing the number of complete orbits of high symmetry to construct as large as possible atomic clusters similar to those observed in complex intermetallic structures and approximant phases. The practical use of these two rules together is demonstrated on two typical examples of icosahedral phases, i-AlMnSi and i-CdRE (RE = Gd, Ho, Tm).

IR investigation on silicon oxycarbide structure obtained from precursors with 1:1 silicon to carbon atoms ratio and various carbon atoms distribution

NASA Astrophysics Data System (ADS)

Niemiec, Wiktor; Szczygieł, Przemysław; Jeleń, Piotr; Handke, Mirosław

2018-07-01

Silicon oxycarbide is a material with a number of advantageous properties that strongly depend on its structure. The most common approach to its tailoring is based on varying the silicon to carbon atoms ratio in the preceramic polymeric precursor. This work is the first comparison of the materials obtained from precursors with the same Si to C atoms ratio, but with various distribution of these atoms in the preceramic polymer. In addition to standard mixtures of monomers containing single silicon atom, a number of monomers with high molar masses and well defined structure was used. The IR was used to investigate the structure of the precursors and materials obtained after their annealing in 800 °C. The results show, that not only the distribution of carbon containing groups among the monomers is important, but also the (in)ability of these groups to end up in each other vicinity in the precursor as well as the degree of condensation of each structural unit.

Nanoscopic analysis of oxygen segregation at tilt boundaries in silicon ingots using atom probe tomography combined with TEM and ab initio calculations.

PubMed

Ohno, Y; Inoue, K; Fujiwara, K; Kutsukake, K; Deura, M; Yonenaga, I; Ebisawa, N; Shimizu, Y; Inoue, K; Nagai, Y; Yoshida, H; Takeda, S; Tanaka, S; Kohyama, M

2017-12-01

We have developed an analytical method to determine the segregation levels on the same tilt boundaries (TBs) at the same nanoscopic location by a joint use of atom probe tomography and scanning transmission electron microscopy, and discussed the mechanism of oxygen segregation at TBs in silicon ingots in terms of bond distortions around the TBs. The three-dimensional distribution of oxygen atoms was determined at the typical small- and large-angle TBs by atom probe tomography with a low impurity detection limit (0.01 at.% on a TB plane) simultaneously with high spatial resolution (about 0.4 nm). The three-dimensional distribution was correlated with the atomic stress around the TBs; the stress at large-angle TBs was estimated by ab initio calculations based on atomic resolution scanning transmission electron microscopy data and that at small-angle TBs were calculated with the elastic theory based on dark-field transmission electron microscopy data. Oxygen atoms would segregate at bond-centred sites under tensile stress above about 2 GPa, so as to attain a more stable bonding network by reducing the local stress. The number of oxygen atoms segregating in a unit TB area N GB (in atoms nm -2 ) was determined to be proportional to both the number of the atomic sites under tensile stress in a unit TB area n bc and the average concentration of oxygen atoms around the TB [O i ] (in at.%) with N GB ∼ 50 n bc [O i ]. © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society.

Design of ultrathin Pt-Mo-Ni nanowire catalysts for ethanol electrooxidation.

PubMed

Mao, Junjie; Chen, Wenxing; He, Dongsheng; Wan, Jiawei; Pei, Jiajing; Dong, Juncai; Wang, Yu; An, Pengfei; Jin, Zhao; Xing, Wei; Tang, Haolin; Zhuang, Zhongbin; Liang, Xin; Huang, Yu; Zhou, Gang; Wang, Leyu; Wang, Dingsheng; Li, Yadong

2017-08-01

Developing cost-effective, active, and durable electrocatalysts is one of the most important issues for the commercialization of fuel cells. Ultrathin Pt-Mo-Ni nanowires (NWs) with a diameter of ~2.5 nm and lengths of up to several micrometers were synthesized via a H 2 -assisted solution route (HASR). This catalyst was designed on the basis of the following three points: (i) ultrathin NWs with high numbers of surface atoms can increase the atomic efficiency of Pt and thus decrease the catalyst cost; (ii) the incorporation of Ni can isolate Pt atoms on the surface and produce surface defects, leading to high catalytic activity (the unique structure and superior activity were confirmed by spherical aberration-corrected electron microscopy measurements and ethanol oxidation tests, respectively); and (iii) the incorporation of Mo can stabilize both Ni and Pt atoms, leading to high catalytic stability, which was confirmed by experiments and density functional theory calculations. Furthermore, the developed HASR strategy can be extended to synthesize a series of Pt-Mo-M (M = Fe, Co, Mn, Ru, etc.) NWs. These multimetallic NWs would open up new opportunities for practical fuel cell applications.

Development of a Plutonium Ceramic Target for the MASHA Separator

NASA Astrophysics Data System (ADS)

Shaughnessy, D. A.; Moody, K. J.; Kenneally, J. M.; Wild, J. F.; Stoyer, M. A.; Lougheed, R. W.; Yeremin, A. V.; Oganessian, Yu. Ts.

2004-04-01

We are participating in the development of the target for the MASHA (Mass Analyzer of Super Heavy Atoms) on-line mass separator in Dubna. Along with recent upgrades of the U400 cyclotron, MASHA will provide for at least a ten-fold increase in the production- and-detection rate for element 114 atoms, and will allow us to measure their atomic masses precisely. The MASHA separator will employ a thick Pu ceramic target capa- ble of tolerating temperatures in the vicinity of 2000 C without vaporizing the actinide compound. Reaction products will diffuse out of the target and will drift to an ECR ion source after which they will be transported through the separator and will impinge on a position-sensitive focal-plane detector array. Furthermore, operation of the MASHA hot target/ion source combination will provide chemical volatility information that will support our assignment of an atomic number of 114 to these nuclei. Taken together, these experiments on MASHA will allow us to make measurements that will cement our identification of element 114 and provide for future experiments in which the chemical properties of the heaviest elements are studied.

Design of ultrathin Pt-Mo-Ni nanowire catalysts for ethanol electrooxidation

PubMed Central

Mao, Junjie; Chen, Wenxing; He, Dongsheng; Wan, Jiawei; Pei, Jiajing; Dong, Juncai; Wang, Yu; An, Pengfei; Jin, Zhao; Xing, Wei; Tang, Haolin; Zhuang, Zhongbin; Liang, Xin; Huang, Yu; Zhou, Gang; Wang, Leyu; Wang, Dingsheng; Li, Yadong

2017-01-01

Developing cost-effective, active, and durable electrocatalysts is one of the most important issues for the commercialization of fuel cells. Ultrathin Pt-Mo-Ni nanowires (NWs) with a diameter of ~2.5 nm and lengths of up to several micrometers were synthesized via a H2-assisted solution route (HASR). This catalyst was designed on the basis of the following three points: (i) ultrathin NWs with high numbers of surface atoms can increase the atomic efficiency of Pt and thus decrease the catalyst cost; (ii) the incorporation of Ni can isolate Pt atoms on the surface and produce surface defects, leading to high catalytic activity (the unique structure and superior activity were confirmed by spherical aberration–corrected electron microscopy measurements and ethanol oxidation tests, respectively); and (iii) the incorporation of Mo can stabilize both Ni and Pt atoms, leading to high catalytic stability, which was confirmed by experiments and density functional theory calculations. Furthermore, the developed HASR strategy can be extended to synthesize a series of Pt-Mo-M (M = Fe, Co, Mn, Ru, etc.) NWs. These multimetallic NWs would open up new opportunities for practical fuel cell applications. PMID:28875160

Atomic and Molecular Databases, VAMDC (Virtual Atomic and Molecular Data Centre)

NASA Astrophysics Data System (ADS)

Dubernet, Marie-Lise; Zwölf, Carlo Maria; Moreau, Nicolas; Awa Ba, Yaya; VAMDC Consortium

2015-08-01

The "Virtual Atomic and Molecular Data Centre Consortium",(VAMDC Consortium, http://www.vamdc.eu) is a Consortium bound by an Memorandum of Understanding aiming at ensuring the sustainability of the VAMDC e-infrastructure. The current VAMDC e-infrastructure inter-connects about 30 atomic and molecular databases with the number of connected databases increasing every year: some databases are well-known databases such as CDMS, JPL, HITRAN, VALD,.., other databases have been created since the start of VAMDC. About 90% of our databases are used for astrophysical applications. The data can be queried, retrieved, visualized in a single format from a general portal (http://portal.vamdc.eu) and VAMDC is also developing standalone tools in order to retrieve and handle the data. VAMDC provides software and support in order to include databases within the VAMDC e-infrastructure. One current feature of VAMDC is the constrained environnement of description of data that ensures a higher quality for distribution of data; a future feature is the link of VAMDC with evaluation/validation groups. The talk will present the VAMDC Consortium and the VAMDC e infrastructure with its underlying technology, its services, its science use cases and its etension towards other communities than the academic research community.

Retrieval of sodium number density profiles in the mesosphere and lower thermosphere from SCIAMACHY limb emission measurements

NASA Astrophysics Data System (ADS)

Langowski, M. P.; von Savigny, C.; Burrows, J. P.; Rozanov, V. V.; Dunker, T.; Hoppe, U.-P.; Sinnhuber, M.; Aikin, A. C.

2016-01-01

An algorithm has been developed for the retrieval of sodium atom (Na) number density on a latitude and altitude grid from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) limb measurements of the Na resonance fluorescence. The results are obtained between 50 and 150 km altitude and the resulting global seasonal variations of Na are analyzed. The retrieval approach is adapted from that used for the retrieval of magnesium atom (Mg) and magnesium ion (Mg+) number density profiles recently reported by Langowski et al. (2014). Monthly mean values of Na are presented as a function of altitude and latitude. This data set was retrieved from the 4 years of spectroscopic limb data of the SCIAMACHY mesosphere and lower thermosphere (MLT) measurement mode (mid-2008 to early 2012). The Na layer has a nearly constant peak altitude of 90-93 km for all latitudes and seasons, and has a full width at half maximum of 5-15 km. Small but significant seasonal variations in Na are identified for latitudes less than 40°, where the maximum Na number densities are 3000-4000 atoms cm-3. At middle to high latitudes a clear seasonal variation with a winter maximum of up to 6000 atoms cm-3 is observed. The high latitudes, which are only measured in the summer hemisphere, have lower number densities, with peak densities being approximately 1000 Na atoms cm-3. The full width at half maximum of the peak varies strongly at high latitudes and is 5 km near the polar summer mesopause, while it exceeds 10 km at lower latitudes. In summer the Na atom concentration at high latitudes and at altitudes below 88 km is significantly smaller than that at middle latitudes. The results are compared with other observations and models and there is overall a good agreement with these.

40 CFR 766.27 - Congeners and LOQs for which quantitation is required.

Code of Federal Regulations, 2014 CFR

2014-07-01

... substances containing predominantly chlorine atoms, only congeners totally chlorinated at the numbered positions need be quantified; for chemical substances containing predominantly bromine atoms, only congeners...

40 CFR 766.27 - Congeners and LOQs for which quantitation is required.

Code of Federal Regulations, 2011 CFR

2011-07-01

... substances containing predominantly chlorine atoms, only congeners totally chlorinated at the numbered positions need be quantified; for chemical substances containing predominantly bromine atoms, only congeners...

40 CFR 766.27 - Congeners and LOQs for which quantitation is required.

Code of Federal Regulations, 2013 CFR

2013-07-01

... substances containing predominantly chlorine atoms, only congeners totally chlorinated at the numbered positions need be quantified; for chemical substances containing predominantly bromine atoms, only congeners...

40 CFR 766.27 - Congeners and LOQs for which quantitation is required.

Code of Federal Regulations, 2012 CFR

2012-07-01

... substances containing predominantly chlorine atoms, only congeners totally chlorinated at the numbered positions need be quantified; for chemical substances containing predominantly bromine atoms, only congeners...

40 CFR 766.27 - Congeners and LOQs for which quantitation is required.

Code of Federal Regulations, 2010 CFR

2010-07-01

... substances containing predominantly chlorine atoms, only congeners totally chlorinated at the numbered positions need be quantified; for chemical substances containing predominantly bromine atoms, only congeners...

Stability chart of small mixed 4He-3He clusters

NASA Astrophysics Data System (ADS)

Guardiola, R.; Navarro, J.

2003-11-01

A stability chart of mixed 4He and 3He clusters has been obtained by means of the diffusion Monte Carlo method, using both the Aziz HFD-B and the Tang-Toennies-Yiu atom-atom interaction. The investigated clusters contain up to eight 4He atoms and up to 20 3He atoms. One single 4He binds 20 3He atoms, and two 4He bind 1, 2, 8, and more than 14 3He atoms. All clusters with three or more 4He atoms are bound, although the combinations 4He33He9,10,11 and 4He34He9 are metastable. Clusters with 2, 8, and 20 3He atoms are particularly stable and define magic 3He numbers.

[Study of emission spectra of N atom generated in multi-needle-to-plate corona discharge].

PubMed

Ge, Hui; Yu, Ran; Zhang, Lu; Mi, Dong; Zhu, Yi-Min

2012-06-01

The emission spectra of nitrogen (N) atom produced by multi-needle-to-plate negative corona discharge in air were detected successfully at one atmosphere, and the excited transition spectral line at 674.5 nm with maximum value of relative intensity was selected to investigate the influences of air and electrical parameters on N atom relative density. The results indicate that N atom relative density in ionization region increases with the increase in power; decreases with increasing discharge gap and relative humidity; and with the increase in N2 content, the relative density of N active atom firstly increases and then decreases. Under present experimental conditions, the maximum value of N atom relative density appears at the axial distance from needle point r = 1 mm.

Method and apparatus for noble gas atom detection with isotopic selectivity

DOEpatents

Hurst, G. Samuel; Payne, Marvin G.; Chen, Chung-Hsuan; Parks, James E.

1984-01-01

Apparatus and methods of operation are described for determining, with isotopic selectivity, the number of noble gas atoms in a sample. The analysis is conducted within an evacuated chamber which can be isolated by a valve from a vacuum pumping system capable of producing a pressure of 10.sup.-8 Torr. Provision is made to pass pulses of laser beams through the chamber, these pulses having wavelengths appropriate for the resonance ionization of atoms of the noble gas under analysis. A mass filter within the chamber selects ions of a specific isotope of the noble gas, and means are provided to accelerate these selected ions sufficiently for implantation into a target. Specific types of targets are discussed. An electron measuring device produces a signal relatable to the number of ions implanted into the target and thus to the number of atoms of the selected isotope of the noble gas removed from the gas sample. The measurement can be continued until a substantial fraction, or all, of the atoms in the sample have been counted. Furthermore, additional embodiments of the apparatus are described for bunching the atoms of a noble gas for more rapid analysis, and for changing the target for repetitive cycling of the gas in the chamber. The number of repetitions of the cyclic steps depend upon the concentration of the isotope of interest, the separative efficiency of the mass filter, etc. The cycles are continued until a desired selectivity is achieved. Also described are components and a method of operation for a pre-enrichment operation for use when an introduction of a total sample would elevate the pressure within the chamber to levels in excess of those for operation of the mass filter, specifically a quadrupole mass filter. Specific examples of three noble gas isotope analyses are described.

Self-organized nanostructure formation on the graphite surface induced by helium ion irradiation

NASA Astrophysics Data System (ADS)

Dutta, N. J.; Mohanty, S. R.; Buzarbaruah, N.; Ranjan, M.; Rawat, R. S.

2018-06-01

The effects of helium ion irradiation on the graphite surface are studied by employing a plasma focus device. The device emits helium ion pulse having energies in the range of a few keV to a few MeV and flux on the order of 1025 m-2 s-1 at 60 mm axial position from the anode tip. The field emission scanning electron microscopy confirms the formation of multi-modal spherical and elongated agglomerated structures on irradiated samples surface with increase in agglomerate size with increasing number of irradiation shots. The transient annealing in each irradiation was not enough to cause the Oswald ripening or sintering of particles into bigger particle or crystal size but only resulted in clustering. The atomic force micrographs reveal an increase in average surface roughness with increasing ion irradiation. The Raman study demonstrates increase in disordered D peak along with reduced crystallite size (La) with increasing number of irradiation shots.

Effect of 0.25 and 2.0 MeV He-Ion Irradiation on Short-Range Ordering in Model (EFDA) Fe-Cr Alloys

NASA Astrophysics Data System (ADS)

Dubiel, Stanisław M.; Żukrowski, Jan; Serruys, Yves

2018-05-01

The effects of He+ irradiation on a distribution of Cr atoms in Fe100-x Cr x (x = 5.8, 10.75, 15.15) alloys were studied by 57Fe Conversion Electron Mössbauer Spectroscopy (CEMS). The alloys were irradiated with doses up to 12 × 1016 ions/cm2 with 0.25 and 2.0 MeV He+ ions. The distribution of Cr atoms within the first two coordination shells around Fe atoms was expressed with short-range order parameters α 1 (first-neighbor shell, 1NN), α 2 (second-neighbor shell, 2NN), and α 12 (1NN + 2NN). In non-irradiated alloys, α 1 >0 and α 2 <0 was revealed for all three samples. The value of α 12 ≈0, i.e., the distribution of Cr atoms averaged over 1NN and 2NN, was random. The effect of the irradiation of the Fe94.2Cr5.8 alloy was similar for the two energies of He+, viz., increase of number of Cr atoms in 1NN and decrease in 2NN. Consequently, the degree of ordering increased. For the other two samples, the effect of the irradiation depends on the composition, and is stronger for the less energetic ions where, for Fe89.25Cr10.75 alloy, the disordering disappeared and some traces of Cr clustering appeared. In Fe84.85Cr15.15 alloy, the clustering was clear. In the samples irradiated with 2. 0 MeV He+ ions, the ordering also survived in the samples with x = 10.75 and 15.15, yet its degree became smaller than in the Fe94.2Cr5.8 alloy.

Enhanced adsorption of Co atoms on grain boundary of boron nitride

NASA Astrophysics Data System (ADS)

Zhang, Tingting; Chen, Guibin; Zhu, Liyan

2017-11-01

Structural, energetic, electronic, and magnetic properties of Co monomer, dimer, and trimer adsorbed on a single-layer boron nitride (BN) with a grain boundary (GB) consisting of tetragons and octagons ( 4|8) are theoretically explored via density functional calculations. Due to the presence of 4|8 GB, the adsorption energies (EAs) of small Co clusters are generally enhanced by 10% as compared with those adsorbed on pristine BN, e.g., the EA of Co monomer, and dimer increase by 0.1 eV on a global amount of 0.87 eV, and 0.2 eV for the case of Co trimer. Most interestingly, the increase in adsorption energy exhibits a strong correlation to the number of atoms directly bonded to the substrate. The enhanced binding of Co adatom on the BN with 4|8 GBs ( BN 48 ) is due to the strong hybridization of d orbitals of Co adatom and the localized defect states at the 4|8 GBs. However, the GBs have negligible influence on the electronic and magnetic properties of adsorbates. Hence, the two-dimensional (2D) nanosheets with linear GBs might be a better candidate for anchoring the transition metal atoms than pristine BN. Such a strategy may also be applied to other 2D materials, e.g., MoS2 and phosphorene, to enhance the binding of adatom on them, or to utilize them as 1D templates to assemble transition metal atoms into nanowires.

DEUTERIUM FRACTIONATION DURING AMINO ACID FORMATION BY PHOTOLYSIS OF INTERSTELLAR ICE ANALOGS CONTAINING DEUTERATED METHANOL

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

Oba, Yasuhiro; Watanabe, Naoki; Kouchi, Akira

2016-08-10

Deuterium (D) atoms in interstellar deuterated methanol might be distributed into complex organic molecules through molecular evolution by photochemical reactions in interstellar grains. In this study, we use a state-of-the-art high-resolution mass spectrometer coupled with a high-performance liquid chromatography system to quantitatively analyze amino acids and their deuterated isotopologues formed by the photolysis of interstellar ice analogs containing singly deuterated methanol CH{sub 2}DOH at 10 K. Five amino acids (glycine, α -alanine, β -alanine, sarcosine, and serine) and their deuterated isotopologues whose D atoms are bound to carbon atoms are detected in organic residues formed by photolysis followed by warmingmore » up to room temperature. The abundances of singly deuterated amino acids are in the range of 0.3–1.1 relative to each nondeuterated counterpart, and the relative abundances of doubly and triply deuterated species decrease with an increasing number of D atoms in a molecule. The abundances of amino acids increase by a factor of more than five upon the hydrolysis of the organic residues, leading to decreases in the relative abundances of deuterated species for α -alanine and β -alanine. On the other hand, the relative abundances of the deuterated isotopologues of the other three amino acids did not decrease upon hydrolysis, indicating different formation mechanisms of these two groups upon hydrolysis. The present study facilitates both qualitative and quantitative evaluations of D fractionation during molecular evolution in the interstellar medium.« less

Atom Interferometer Modeling Tool

DTIC Science & Technology

2011-08-08

present, LiveAtom supports the alkali metals from Lithium to Cesium. LiveAtom will also show where atoms in the equilibrium state will sit if a trap is...Address: 7105 La Vista Pl . Niwot, CO 80503 Phone Number: 303-652-0725 The views and conclusions contained in this document are those of the authors...0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing

A Mapping of the Electron Localization Function for Earth Materials

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

Gibbs, Gerald V.; Cox, David F.; Ross, Nancy

2005-06-01

The electron localization function, ELF, generated for a number of geometry-optimized earth materials, provides a graphical representation of the spatial localization of the probability electron density distribution as embodied in domains ascribed to localized bond and lone pair electrons. The lone pair domains, displayed by the silica polymorphs quartz, coesite and cristobalite, are typically banana-shaped and oriented perpendicular to the plane of the SiOSi angle at ~0.60 Å from the O atom on the reflex side of the angle. With decreasing angle, the domains increase in magnitude, indicating an increase in the nucleophilic character of the O atom, rendering itmore » more susceptible to potential electrophilic attack. The Laplacian isosurface maps of the experimental and theoretical electron density distribution for coesite substantiates the increase in the size of the domain with decreasing angle. Bond pair domains are displayed along each of the SiO bond vectors as discrete concave hemispherically-shaped domains at ~0.70 Å from the O atom. For more closed-shell ionic bonded interactions, the bond and lone pair domains are often coalesced, resulting in concave hemispherical toroidal-shaped domains with local maxima centered along the bond vectors. As the shared covalent character of the bonded interactions increases, the bond and lone pair domains are better developed as discrete domains. ELF isosurface maps generated for the earth materials tremolite, diopside, talc and dickite display banana-shaped lone pair domains associated with the bridging O atoms of SiOSi angles and concave hemispherical toroidal bond pair domains associated with the nonbridging ones. The lone pair domains in dickite and talc provide a basis for understanding the bonded interactions between the adjacent neutral layers. Maps were also generated for beryl, cordierite, quartz, low albite, forsterite, wadeite, åkermanite, pectolite, periclase, hurlbutite, thortveitite and vanthoffite. Strategies are reviewed for finding potential H docking sites in the silica polymorphs and related materials. As observed in an earlier study, the ELF is capable of generating bond and lone pair domains that are similar in number and arrangement to those provided by Laplacian and deformation electron density distributions. The formation of the bond and lone pair domains in the silica polymorphs and the progressive decrease in the SiO length as the value of the electron density at the bond critical point increases indicates that the SiO bonded interaction has a substantial component of covalent character.« less

Spatial atomic layer deposition of ZnO/TiO{sub 2} nanolaminates

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

Chen, Rong, E-mail: rongchen@mail.hust.edu.cn; Lin, Ji-Long; He, Wen-Jie

2016-09-15

Spatial atomic layer deposition (S-ALD) is a potential high-throughput manufacturing technique offering fast and large scale ultrathin films deposition. Here, an S-ALD system with modular injectors is introduced for fabricating binary oxides and their nanolaminates. By optimizing the deposition conditions, both ZnO and TiO{sub 2} films demonstrate linear growth and desired surface morphology. The as-deposited ZnO film has high carrier mobility, and the TiO{sub 2} film shows suitable optical transmittance and band gap. The ZnO/TiO{sub 2} nanolaminates are fabricated by alternating substrate movement between each S-ALD modular units of ZnO and TiO{sub 2}. The grazing incidence x-ray diffraction spectra ofmore » nanolaminates demonstrating the signature peaks are weaker for the same thickness nanolaminates with more bilayers, suggesting tuning nanolaminates from crystalline to amorphous. Optical transmittances of ZnO/TiO{sub 2} laminates are enhanced with the increase of the bilayers' number in the visible range. Refractive indices of nanolaminates increase with the thickness of each bilayer decreasing, which demonstrates the feasibility of obtaining desired refractive indices by controlling the bilayer number. The electronic properties, including mobility, carrier concentration, and conductivity, are also tunable with different bilayers.« less

Rare earth element scavenging in seawater

NASA Astrophysics Data System (ADS)

Byrne, Robert H.; Kim, Ki-Hyun

1990-10-01

Examinations of rare earth element (REE) adsorption in seawater, using a variety of surface-types, indicated that, for most surfaces, light rare earth elements (LREEs) are preferentially adsorbed compared to the heavy rare earths (HREEs). Exceptions to this behavior were observed only for silica phases (glass surfaces, acid-cleaned diatomaceous earth, and synthetic SiO 2). The affinity of the rare earths for surfaces can be strongly affected by thin organic coatings. Glass surfaces which acquired an organic coating through immersion in Tampa Bay exhibited adsorptive behavior typical of organic-rich, rather than glass, surfaces. Models of rare earth distributions between seawater and carboxylate-rich surfaces indicate that scavenging processes which involve such surfaces should exhibit a strong dependence on pH and carbonate complexation. Scavenging models involving carboxylate surfaces produce relative REE abundance patterns in good general agreement with observed shale-normalized REE abundances in seawater. Scavenging by carboxylate-rich surfaces should produce HREE enrichments in seawater relative to the LREEs and may produce enrichments of lanthanum relative to its immediate trivalent neighbors. Due to the origin of distribution coefficients as a difference between REE solution complexation (which increases strongly with atomic number) and surface complexation (which apparently also increases with atomic number) the relative solution abundance patterns of the REEs produced by scavenging reactions can be quite complex.

Synchrotron EXAFS and XANES spectroscopy studies of transition aluminas doped with La and Cr for catalytic applications

NASA Astrophysics Data System (ADS)

Glazoff, Michael V.

2016-04-01

Transition aluminas doped with Cr find widespread application in the dehydrogenation catalysis industry, while La-stabilized transition aluminas are used extensively for high-temperature application as catalytic supports (Wefers and Misra in Oxides and hydroxides of aluminum, Alcoa Laboratories, Pittsburgh, 1987). In this work, detailed synchrotron XAFS spectroscopy studies were conducted to shed light upon the atomic mechanisms of surface and subsurface reconstructions and/or catalytic support stabilization of doped aluminas. It was demonstrated that in four transition aluminas doped with Cr, it is the atoms which are mostly in the state of oxidation Cr3+ and enter nanoparticles of Cr-bearing phases (Cr2O3 in the case of gamma- and chi-alumina). In the transition series aluminas: "gamma- chi- theta- eta-alumina," the change of properties (in particular, the dramatic increase in dehydrogenation catalytic activity and catalyst longevity and the coloration of samples) takes place because of the reduction in the average size of Cr clusters and their appearance on the Al2O3 surface, probably responsible for change in catalytic activity. It was demonstrated that in the samples of gamma-alumina doped with La any substantial change in the local coordination of the La atoms takes place only upon heating up to 1400 °C. This makes the La-stabilized gamma-alumina a perfect catalytic support for the numerous applications, e.g., catalytic three-way conversion of automobile exhaust gases. This change manifested itself in the form of increased La-O bond lengths and the La coordination number (from 8 to 12). Furthermore, it was demonstrated that the local environment of La in this new La-bearing phase cannot be explained in terms of the LaAlO3 formation. The absence of the La atoms in the second coordination sphere favors monoatomic distribution of La atoms on grain boundaries, proving that only very small amount of this rare earth material is required to achieve full stabilization. It is inferred that the tendency of La atoms to get surrounded by oxygen atoms, and also the impossibility of going into the alumina bulk, could be a major reason of the increased thermal stability of gamma-alumina doped with lanthanum.

Formation of nanocolloidal metacinnabar in mercury-DOM-sulfide systems

USGS Publications Warehouse

Gerbig, Chase A.; Kim, Christopher S.; Stegemeier, John P.; Ryan, Joseph N.; Aiken, George R.

2011-01-01

Direct determination of mercury (Hg) speciation in sulfide-containing environments is confounded by low mercury concentrations and poor analytical sensitivity. Here we report the results of experiments designed to assess mercury speciation at environmentally relevant ratios of mercury to dissolved organic matter (DOM) (i.e., <4 nmol Hg (mg DOM)−1) by combining solid phase extraction using C18 resin with extended X-ray absorption fine structure (EXAFS) spectroscopy. Aqueous Hg(II) and a DOM isolate were equilibrated in the presence and absence of 100 μM total sulfide. In the absence of sulfide, mercury adsorption to the resin increased as the Hg:DOM ratio decreased and as the strength of Hg-DOM binding increased. EXAFS analysis indicated that in the absence of sulfide, mercury bonds with an average of 2.4 ± 0.2 sulfur atoms with a bond length typical of mercury-organic thiol ligands (2.35 Å). In the presence of sulfide, mercury showed greater affinity for the C18 resin, and its chromatographic behavior was independent of Hg:DOM ratio. EXAFS analysis showed mercury–sulfur bonds with a longer interatomic distance (2.51–2.53 Å) similar to the mercury–sulfur bond distance in metacinnabar (2.53 Å) regardless of the Hg:DOM ratio. For all samples containing sulfide, the sulfur coordination number was below the ideal four-coordinate structure of metacinnabar. At a low Hg:DOM ratio where strong binding DOM sites may control mercury speciation (1.9 nmol mg–1) mercury was coordinated by 2.3 ± 0.2 sulfur atoms, and the coordination number rose with increasing Hg:DOM ratio. The less-than-ideal coordination numbers indicate metacinnabar-like species on the nanometer scale, and the positive correlation between Hg:DOM ratio and sulfur coordination number suggests progressively increasing particle size or crystalline order with increasing abundance of mercury with respect to DOM. In DOM-containing sulfidic systems nanocolloidal metacinnabar-like species may form, and these species need to be considered when addressing mercury biogeochemistry.

Oxygen concentration dependence of silicon oxide dynamical properties

NASA Astrophysics Data System (ADS)

Yajima, Yuji; Shiraishi, Kenji; Endoh, Tetsuo; Kageshima, Hiroyuki

2018-06-01

To understand oxidation in three-dimensional silicon, dynamic characteristics of a SiO x system with various stoichiometries were investigated. The calculated results show that the self-diffusion coefficient increases as oxygen density decreases, and the increase is large when the temperature is low. It also shows that the self-diffusion coefficient saturates, when the number of removed oxygen atoms is sufficiently large. Then, approximate analytical equations are derived from the calculated results, and the previously reported expression is confirmed in the extremely low-SiO-density range.

Quantum teleportation with atoms trapped in cavities

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

Cho, Jaeyoon; Lee, Hai-Woong

2004-09-01

We propose a scheme to implement the quantum teleportation protocol with single atoms trapped in cavities. The scheme is based on the adiabatic passage and the polarization measurement. We show that it is possible to teleport the internal state of an atom trapped in a cavity to an atom trapped in another cavity with the success probability of 1/2 and the fidelity of 1. The scheme is resistant to a number of considerable imperfections such as the violation of the Lamb-Dicke condition, weak atom-cavity coupling, spontaneous emission, and detection inefficiency.

Watching the Solvation of Atoms in Liquids One Solvent Molecule at a Time

NASA Astrophysics Data System (ADS)

Bragg, Arthur E.; Glover, William J.; Schwartz, Benjamin J.

2010-06-01

We use mixed quantum-classical molecular dynamics simulations and ultrafast transient hole-burning spectroscopy to build a molecular-level picture of the motions of solvent molecules around Na atoms in liquid tetrahydrofuran. We find that even at room temperature, the solvation of Na atoms occurs in discrete steps, with the number of solvent molecules nearest the atom changing one at a time. This explains why the rate of solvent relaxation differs for different initial nonequilibrium states, and reveals how the solvent helps determine the identity of atomic species in liquids.

Interactions of molecules and the properties of crystals

NASA Astrophysics Data System (ADS)

McConnell, Thomas Daniel Leigh

In this thesis the basic theory of the lattice dynamics of molecular crystals is considered, with particular reference to the specific case of linear molecules. The objective is to carry out a critical investigation of a number of empirical potentials as models for real systems. Suitable coordinates are introduced, in particular vibrational coordinates which are used to describe the translational and rotational modes of the free molecule. The Taylor expansion of the intermolecular potential is introduced and its terms considered, in particular the (first-order) equilibrium conditions for such a system and the (second-order) lattice vibrations. The elastic properties are also considered, in particular with reference to the specific case of rhombohedral crystals. The compressibility and a number of conditions for elastic stability are introduced. The total intermolecular interaction potential is divided into three components using perturbation methods, the electrostatic energy, the repulsion energy and the dispersion energy. A number of models are introduced for these various components. The induction energy is neglected. The electrostatic interaction is represented by atomic multipole and molecular multipole models. The repulsion and dispersion energies are modelled together in a central interaction potential, either the Lennard-Jones atom-atom potential or the anisotropic Berne-Pechukas molecule-molecule potential. In each case, the Taylor expansion coefficients, used to calculate the various molecular properties, are determined. An algorithm is described which provides a relatively simple method for calculating cartesian tensors, which are found in the Taylor expansion coefficients of the multipolar potentials. This proves to be particularly useful from a computational viewpoint, both in terms of programming and calculating efficiency. The model system carbonyl sulphide is introduced and its lattice properties are described. Suitable parameters for potentials used to model the system are discussed and the simplifications to the Taylor expansion coefficients due to crystal symmetry are detailed. Four potential parameters are chosen to be fitted to four lattice properties, representing zero, first and second order Taylor expansion coefficients. The supplementary tests of a given fitted potential are detailed. A number of forms for the electrostatic interaction of carbonyl sulphide are considered, each combined with a standard atom-atom potential. The success of the molecular octupole model is considered and the inability of more complex electrostatic potentials to improve on this simple model is noted. The anisotropic Berne-Pechukas potential, which provides an increased estimate of the compressibility is considered as being an improvement on the various atom-atom potentials. The effect of varying the exponents in the atom-atom (or molecule-molecule) potential, representing a systematic variation of the repulsion and dispersion energy models, is examined and a potential which is able to reproduce all of the given lattice properties for carbonyl sulphide is obtained. The molecular crystal of cyanogen iodide is investigated. Superficially it is similar to the crystal of carbonyl sulphide and the potentials used with success for the latter are applied to cyanogen iodide to determine whether they are equally as effective models for this molecule. These potentials are found to be far less successful, in all cases yielding a number of unrealistic results. Reasons for the failure of the model are considered, in particular the 3 differences between the electrostatic properties of the two molecules are discussed. It is concluded that some of the simplifications which proved satisfactory for carbonyl sulphide are invalid for simple extension to the case of cyanogen iodide. A first estimate of the differences in the electrostatic properties is attempted, calculating the induction energies of the two molecules. The assumption that the induction energy may be neglected is justified for the case of carbonyl sulphide but found to be far less satisfactory for cyanogen iodide. Finally details of ab initio calculations are outlined. The amount of experimental data available for the electrostatic properties of the two molecules under consideration is relatively small and the experimental data which is available is supplemented by values obtained from these calculations.

Tuning optical properties of magic number cluster (SiO2)4O2H4 by substitutional bonding with gold atoms.

PubMed

Cai, Xiulong; Zhang, Peng; Ma, Liuxue; Zhang, Wenxian; Ning, Xijing; Zhao, Li; Zhuang, Jun

2009-04-30

By bonding gold atoms to the magic number cluster (SiO(2))(4)O(2)H(4), two groups of Au-adsorbed shell-like clusters Au(n)(SiO(2))(4)O(2)H(4-n) (n = 1-4) and Au(n)(SiO(2))(4)O(2) (n = 5-8) were obtained, and their spectral properties were studied. The ground-state structures of these clusters were optimized by density functional theory, and the results show that in despite of the different numbers and types of the adsorbed Au atoms, the cluster core (SiO(2))(4)O(2) of T(d) point-group symmetry keeps almost unchanged. The absorption spectra were obtained by time-dependent density functional theory. From one group to the other, an extension of absorption wavelength from the UV-visible to the NIR region was observed, and in each group the absorption strengths vary linearly with the number of Au atoms. These features indicate their advantages for exploring novel materials with easily controlled tunable optical properties. Furthermore, due to the weak electronic charge transfer between the Au atoms, the clusters containing Au(2) dimers, especially Au(8)(SiO(2))(4)O(2), absorb strongly NIR light at 900 approximately 1200 nm. Such strong absorption suggests potential applications of these shell-like clusters in tumor cells thermal therapy, like the gold-coated silica nanoshells with larger sizes.

Statistical study of defects caused by primary knock-on atoms in fcc Cu and bcc W using molecular dynamics

NASA Astrophysics Data System (ADS)

Warrier, M.; Bhardwaj, U.; Hemani, H.; Schneider, R.; Mutzke, A.; Valsakumar, M. C.

2015-12-01

We report on molecular Dynamics (MD) simulations carried out in fcc Cu and bcc W using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code to study (i) the statistical variations in the number of interstitials and vacancies produced by energetic primary knock-on atoms (PKA) (0.1-5 keV) directed in random directions and (ii) the in-cascade cluster size distributions. It is seen that around 60-80 random directions have to be explored for the average number of displaced atoms to become steady in the case of fcc Cu, whereas for bcc W around 50-60 random directions need to be explored. The number of Frenkel pairs produced in the MD simulations are compared with that from the Binary Collision Approximation Monte Carlo (BCA-MC) code SDTRIM-SP and the results from the NRT model. It is seen that a proper choice of the damage energy, i.e. the energy required to create a stable interstitial, is essential for the BCA-MC results to match the MD results. On the computational front it is seen that in-situ processing saves the need to input/output (I/O) atomic position data of several tera-bytes when exploring a large number of random directions and there is no difference in run-time because the extra run-time in processing data is offset by the time saved in I/O.

Periodic trends in bond dissociation energies. A theoretical study.

PubMed

Mó, Otilia; Yáñez, Manuel; Eckert-Maksić, Mirjana; Maksić, Zvonimir B; Alkorta, Ibón; Elguero, José

2005-05-19

Bond dissociation energies (BDEs) of all possible A-X single bonds involving the first- and second-row atoms, from Li to Cl, where the free valences are saturated by hydrogens, have been estimated through the use of the G3-theory and at the B3LYP/6-311+G(3df,2pd)//B3LYP/6-31G(2df,p) DFT level of theory. BDEs exhibit a periodical behavior. The A-X (A = Li, Be, B, Na, Mg, Al, and Si) BDEs show a steady increase along the first and the second row of the periodic table as a function of the atomic number Z(X). For A-X bonds involving electronegative atoms (A = C, N, O, F, P, S, and Cl) the bond energies achieve a maximum around Z(X) = 5. The same behavior is observed when BDEs are plotted against the electronegativity chi(X) of the atom X. Thus, for A-X bonds (A = Li, Be, B, Na, Mg, Al, Si), the BDEs for a fixed A increases, grosso modo, as the electronegativity differences between X and A increase, with some exceptions, which reflect the differences in the relaxation energies of the radicals produced upon the bond cleavage. A similar trend, albeit less pronounced, is found for single A-X bonds, where A = C, N, O, F, P, S, and Cl. However, there is an additional feature embodied in the enhancement of the strength of the A-boron bonds due to the ability of boron to act as a strong electron acceptor. The trends in bond lengths and charge densities at the bond critical points are in line with the aforementioned behavior.

Numerical simulations of the seasonal/latitudinal variations of atomic oxygen and nitric oxide in the lower thermosphere and mesosphere

NASA Technical Reports Server (NTRS)

Rees, D.; Fuller-Rowell, T. J.

1989-01-01

A 2-Dimensional zonally-averaged thermospheric model and the global University College London (UCL) thermospheric model have been used to investigate the seasonal, solar activity and geomagnetic variation of atomic oxygen and nitric oxide. The 2-dimensional model includes detailed oxygen and nitrogen chemistry, with appropriate completion of the energy equation, by adding the thermal infrared cooling by O and NO. This solution includes solar and auroral production of odd nitrogen compounds and metastable species. This model has been used for three investigations; firstly, to study the interactions between atmospheric dynamics and minor species transport and density; secondly, to examine the seasonal variations of atomic oxygen and nitric oxide within the upper mesosphere and thermosphere and their response to solar and geomagnetic activity variations; thirdly, to study the factor of 7 to 8 peak nitric oxide density increase as solar F sub 10.7 cm flux increases from 70 to 240 reported from the Solar Mesospheric Explorer. Auroral production of NO is shown to be the dominant source at high latitudes, generating peak NO densities a factor of 10 greater than typical number densities at low latitudes. At low latitudes, the predicted variation of the peak NO density, near 110 km, with the solar F sub 10.7 cm flux is rather smaller than is observed. This is most likely due to an overestimate of the soft X-ray flux at low solar activity, for times of extremely low support number, as occurred in June 1986. As observed on pressure levels, the variation of O density is small. The global circulation during solstice and periods of elevated geomagnetic activity causes depletion of O in regions of upwelling, and enhancements in regions of downwelling.

Novel model of negative secondary ion formation and its use to refine the electronegativity of almost fifty elements.

PubMed

Wittmaack, Klaus

2014-06-17

This study aimed to examine the recently proposed idea that the ionic contribution to atomic bonds is essential in determining the charge state of sputtered atoms. Use was made of negative secondary ion yields reported by Wilson for a large number of elements implanted in silicon and then sputter profiled by Cs bombardment. The derived normalized ion yields (or fractions) P vary by 6 orders of magnitude, but the expected exponential dependence on the electron affinity EA is evident only vaguely. Remarkably, a correlation of similar quality is observed if the data are presented as a function of the ionization potential IP. With IP being the dominant (if not sole) contributor to the electronegativity χ, one is led to assume that P depends on the sum χ + EA. About 72% of the "nonsaturated" ion yields are in accordance with a dependence of the form P ∝ exp[(χ + EA)/ε], with ε ≅ 0.2 eV, provided the appropriate value of χ is selected from the electronegativity tables of Pauling (read in eV), Mulliken or Allen. However, each of the three sources contributes only about one-third to the favorable electronegativity data. This unsatisfactory situation initiated the idea to derive the "true" electronegativity χSIMS from the measured ion yields P(χ + EA), verified for 48 elements. Significant negative deviations of χSIMS from a smooth increase with increasing atomic number are evident for elements with special outer-shell electron configurations such as (n-1)d(g-1)ns(1) or (n-1)d(10)ns(2)np(1). The results strongly support the new model of secondary ion formation and provide means for refining electronegativity data.

RADinfo Glossary of Radiation Terms

MedlinePlus

... electrical charge typically found within an atom's nucleus. nucleus: The central part of an atom that contains ... the number of protons and neutrons in the nucleus. picocurie: One one-trillionth (1/1,000,000, ...

Influence of Fluorine Atoms and Aromatic Rings on the Acidity of Ethanol

NASA Astrophysics Data System (ADS)

Ramírez, Ramsés E.; García-Martínez, Cirilo; Méndez, Francisco

2009-09-01

Absolute gas-phase acidities ΔacidG0(OH) and ΔacidG0(CH) were calculated at the B3LYP and MP2 levels using six different standard basis sets for the OH and CH heterolytic bond cleavage of ethanol and twelve derivatives of the type CH3-nFnCHXrOH, where n ranges from zero to three and represents the number of fluorine atoms and r represents hydrogen and the type of aromatic ring, namely: X0 = hydrogen, X1 = phenyl, X2 = 1-naphthyl, and X3 = 9-anthryl. The similarity between calculated and experimental ΔacidG0(OH) values for ethanol (1a), 2-fluoroethanol (1b), 2,2-difluoroethanol (1c), 2,2,2-trifluoroethanol (1d), and 1-phenylethanol (2a) was used to validate the right theoretical method for this study. Substituent partial contributions to hydroxyl-, methylene-, and methine-hydrogen acidities were evaluated by linear combination. Good parameter fittings of the primary and secondary alcohols were obtained and interpreted as additive contribution of the substituent effects. The nonlinear contributions were identified. Calculations prove that fluoroalcohols exhibit C-H acidity, which is usually lower than O-H acidity. In principle, the inversion of this acidity order is possible by the introduction of a large aromatic ring instead to increase the number of fluorine atoms.

Effective atomic number and electron density of amino acids within the energy range of 0.122-1.330 MeV

NASA Astrophysics Data System (ADS)

More, Chaitali V.; Lokhande, Rajkumar M.; Pawar, Pravina P.

2016-08-01

Photon attenuation coefficient calculation methods have been widely used to accurately study the properties of amino acids such as n-acetyl-L-tryptophan, n-acetyl-L-tyrosine, D-tryptophan, n-acetyl-L-glutamic acid, D-phenylalanine, and D-threonine. In this study, mass attenuation coefficients (μm) of these amino acids for 0.122-, 0.356-, 0.511-, 0.662-, 0.884-, 1.170, 1.275-, 1.330-MeV photons are determined using the radio-nuclides Co57, Ba133, Cs137, Na22, Mn54, and Co60. NaI (Tl) scintillation detection system was used to detect gamma rays with a resolution of 8.2% at 0.662 MeV. The calculated attenuation coefficient values were then used to determine total atomic cross sections (σt), molar extinction coefficients (ε), electronic cross sections (σe), effective atomic numbers (Zeff), and effective electron densities (Neff) of the amino acids. Theoretical values were calculated based on the XCOM data. Theoretical and experimental values are found to be in a good agreement (error<5%). The variations of μm, σt, ε, σe, Zeff, and Neff with energy are shown graphically. The values of μm, σt, ε, σe are higher at lower energies, and they decrease sharply as energy increases; by contrast, Zeff and Neff were found to be almost constant.

Understanding and Controlling the Aggregative Growth of Platinum Nanoparticles in Atomic Layer Deposition: An Avenue to Size Selection

PubMed Central

2017-01-01

We present an atomistic understanding of the evolution of the size distribution with temperature and number of cycles in atomic layer deposition (ALD) of Pt nanoparticles (NPs). Atomistic modeling of our experiments teaches us that the NPs grow mostly via NP diffusion and coalescence rather than through single-atom processes such as precursor chemisorption, atom attachment, and Ostwald ripening. In particular, our analysis shows that the NP aggregation takes place during the oxygen half-reaction and that the NP mobility exhibits a size- and temperature-dependent scaling. Finally, we show that contrary to what has been widely reported, in general, one cannot simply control the NP size by the number of cycles alone. Instead, while the amount of Pt deposited can be precisely controlled over a wide range of temperatures, ALD-like precision over the NP size requires low deposition temperatures (e.g., T < 100 °C) when growth is dominated by atom attachment. PMID:28178779

Selfbound quantum droplets

NASA Astrophysics Data System (ADS)

Langen, Tim; Wenzel, Matthias; Schmitt, Matthias; Boettcher, Fabian; Buehner, Carl; Ferrier-Barbut, Igor; Pfau, Tilman

2017-04-01

Self-bound many-body systems are formed through a balance of attractive and repulsive forces and occur in many physical scenarios. Liquid droplets are an example of a self-bound system, formed by a balance of the mutual attractive and repulsive forces that derive from different components of the inter-particle potential. On the basis of the recent finding that an unstable bosonic dipolar gas can be stabilized by a repulsive many-body term, it was predicted that three-dimensional self-bound quantum droplets of magnetic atoms should exist. Here we report on the observation of such droplets using dysprosium atoms, with densities 108 times lower than a helium droplet, in a trap-free levitation field. We find that this dilute magnetic quantum liquid requires a minimum, critical number of atoms, below which the liquid evaporates into an expanding gas as a result of the quantum pressure of the individual constituents. Consequently, around this critical atom number we observe an interaction-driven phase transition between a gas and a self-bound liquid in the quantum degenerate regime with ultracold atoms.

Atomistic simulations to characterize the influence of applied strain and PKA energy on radiation damage evolution in pure aluminum

NASA Astrophysics Data System (ADS)

Sahi, Qurat-ul-ain; Kim, Yong-Soo

2018-05-01

Knowledge of defects generation, their mobility, growth rate, and spatial distribution is the cornerstone for understanding the surface and structural evolution of a material used under irradiation conditions. In this study, molecular dynamics simulations were used to investigate the coupled effect of primary knock-on atom (PKA) energy and applied strain (uniaxial and hydrostatic) fields on primary radiation damage evolution in pure aluminum. Cascade damage simulations were carried out for PKA energy ranging between 1 and 20 keV and for applied strain values ranging between -2% and 2% at the fixed temperature of 300 K. Simulation results showed that as the atomic displacement cascade proceeds under uniaxial and hydrostatic strains, the peak and surviving number of Frenkel point defects increases with increasing tension; however, these increments were more prominent under larger volume changing deformations (hydrostatic strain). The percentage fraction of point defects that aggregate into clusters increases under tension conditions; compared to the reference conditions with no strain, these increases are around 13% and 7% for interstitials and vacancies, respectively (under 2% uniaxial strain), and 19% and 11% for interstitials and vacancies, respectively (under 2% hydrostatic strain). Clusters formed of vacancies and interstitials were both larger under tensile strain conditions, with increases in both the average and maximum cluster sizes. The rate of increase/decrease in the number of Frenkel pairs, their clustering, and their size distributions under expansion/compression strain conditions were higher for higher PKA energies. Overall, the present results suggest that strain effects should be considered carefully in radiation damage environments, specifically for conditions of low temperature and high radiation energy. Compressive strain conditions could be beneficial for materials used in nuclear reactor power systems.

Optimally Squeezed Spin States

NASA Astrophysics Data System (ADS)

Rojo, Alberto

2004-03-01

We consider optimally spin-squeezed states that maximize the sensitivity of the Ramsey spectroscopy, and for which the signal to noise ratio scales as the number of particles N. Using the variational principle we prove that these states are eigensolutions of the Hamiltonian H(λ)=λ S_z^2-S_x, and that, for large N, the states become equivalent to the quadrature squeezed states of the harmonic oscillator. We present numerical results that illustrate the validity of the equivalence. We also present results of spin squeezing via atom-field interactions within the context of the Tavis-Cummings model. An ensemble of N two-level atoms interacts with a quantized cavity field. For all the atoms initially in their ground states, it is shown that spin squeezing of both the atoms and the field can be achieved provided the initial state of the cavity field has coherence between number states differing by 2. Most of the discussion is restricted to the case of a cavity field initially in a coherent state, but initial squeezed states for the field are also discussed. An analytic solution is found that is valid in the limit that the number of atoms is much greater than unity. References: A. G. Rojo, Phys. Rev A, 68, 013807 (2003); Claudiu Genes, P. R. Berman, and A. G. Rojo Phys. Rev. A 68, 043809 (2003).

A comparative study of gamma-ray interaction and absorption in some building materials using Zeff-toolkit

NASA Astrophysics Data System (ADS)

Mann, Kulwinder Singh; Heer, Manmohan Singh; Rani, Asha

2016-07-01

The gamma-ray shielding behaviour of a material can be investigated by determining its various interaction and energy-absorption parameters (such as mass attenuation coefficients, mass energy absorption coefficients, and corresponding effective atomic numbers and electron densities). Literature review indicates that the effective atomic number (Zeff) has been used as extensive parameters for evaluating the effects and defect in the chosen materials caused by ionising radiations (X-rays and gamma-rays). A computer program (Zeff-toolkit) has been designed for obtaining the mean value of effective atomic number calculated by three different methods. A good agreement between the results obtained with Zeff-toolkit, Auto_Zeff software and experimentally measured values of Zeff has been observed. Although the Zeff-toolkit is capable of computing effective atomic numbers for both photon interaction (Zeff,PI) and energy absorption (Zeff,En) using three methods in each. No similar computer program is available in the literature which simultaneously computes these parameters simultaneously. The computed parameters have been compared and correlated in the wide energy range (0.001-20 MeV) for 10 commonly used building materials. The prominent variations in these parameters with gamma-ray photon energy have been observed due to the dominance of various absorption and scattering phenomena. The mean values of two effective atomic numbers (Zeff,PI and Zeff,En) are equivalent at energies below 0.002 MeV and above 0.3 MeV, indicating the dominance of gamma-ray absorption (photoelectric and pair production) over scattering (Compton) at these energies. Conversely in the energy range 0.002-0.3 MeV, the Compton scattering of gamma-rays dominates the absorption. From the 10 chosen samples of building materials, 2 soils showed better shielding behaviour than did other 8 materials.

40 CFR 63.8000 - What are my general requirements for complying with this subpart?

Code of Federal Regulations, 2011 CFR

2011-07-01

... atoms, and you use a combustion-based control device (excluding a flare) to meet an organic HAP emission... calculating the concentration of each organic compound that contains halogen atoms using the procedures specified in § 63.115(d)(2)(v), multiplying each concentration by the number of halogen atoms in the organic...

40 CFR 63.8000 - What are my general requirements for complying with this subpart?

Code of Federal Regulations, 2010 CFR

2010-07-01

... atoms, and you use a combustion-based control device (excluding a flare) to meet an organic HAP emission... calculating the concentration of each organic compound that contains halogen atoms using the procedures specified in § 63.115(d)(2)(v), multiplying each concentration by the number of halogen atoms in the organic...

40 CFR 63.8000 - What are my general requirements for complying with this subpart?

Code of Federal Regulations, 2014 CFR

2014-07-01

... atoms, and you use a combustion-based control device (excluding a flare) to meet an organic HAP emission... calculating the concentration of each organic compound that contains halogen atoms using the procedures specified in § 63.115(d)(2)(v), multiplying each concentration by the number of halogen atoms in the organic...

An Estimation of the Number and Size of Atoms in a Printed Period

ERIC Educational Resources Information Center

Schaefer, Beth; Collett, Edward; Tabor-Morris, Anne; Croman, Joseph

2011-01-01

Elementary school students learn that atoms are very, very small. Students are also taught that atoms (and molecules) are the fundamental constituents of the material world. Numerical values of their size are often given, but, nevertheless, it is difficult to imagine their size relative to one's everyday surroundings. In order for students to…

40 CFR 63.8000 - What are my general requirements for complying with this subpart?

Code of Federal Regulations, 2013 CFR

2013-07-01

... atoms, and you use a combustion-based control device (excluding a flare) to meet an organic HAP emission... calculating the concentration of each organic compound that contains halogen atoms using the procedures specified in § 63.115(d)(2)(v), multiplying each concentration by the number of halogen atoms in the organic...

40 CFR 63.8000 - What are my general requirements for complying with this subpart?

Code of Federal Regulations, 2012 CFR

2012-07-01

... atoms, and you use a combustion-based control device (excluding a flare) to meet an organic HAP emission... calculating the concentration of each organic compound that contains halogen atoms using the procedures specified in § 63.115(d)(2)(v), multiplying each concentration by the number of halogen atoms in the organic...

Atomically manufactured nickel-silicon quantum dots displaying robust resonant tunneling and negative differential resistance

NASA Astrophysics Data System (ADS)

Cheng, Jian-Yih; Fisher, Brandon L.; Guisinger, Nathan P.; Lilley, Carmen M.

2017-12-01

Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni-Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni-Si clusters. The resonance energy is reproducible and the peak spacing of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I-V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. All of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.

Atomically manufactured nickel–silicon quantum dots displaying robust resonant tunneling and negative differential resistance

DOE PAGES

Cheng, Jian -Yih; Fisher, Brandon L.; Guisinger, Nathan P.; ...

2017-05-22

Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni–Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni–Si clusters. The resonance energy is reproducible and the peak spacingmore » of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I–V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. Furthermore, all of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.« less

Atomically manufactured nickel–silicon quantum dots displaying robust resonant tunneling and negative differential resistance

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

Cheng, Jian -Yih; Fisher, Brandon L.; Guisinger, Nathan P.

Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni–Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni–Si clusters. The resonance energy is reproducible and the peak spacingmore » of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I–V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. Furthermore, all of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.« less

Modelling the atomic structure of Al92U8 metallic glass.

PubMed

Michalik, S; Bednarcik, J; Jóvári, P; Honkimäki, V; Webb, A; Franz, H; Fazakas, E; Varga, L K

2010-10-13

The local atomic structure of the glassy Al(92)U(8) alloy was modelled by the reverse Monte Carlo (RMC) method, fitting x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) signals. The final structural model was analysed by means of partial pair correlation functions, coordination number distributions and Voronoi tessellation. In our study we found that the most probable atomic separations between Al-Al and U-Al pairs in the glassy Al(92)U(8) alloy are 2.7 Å and 3.1 Å with coordination numbers 11.7 and 17.1, respectively. The Voronoi analysis did not support evidence of the existence of well-defined building blocks directly embedded in the amorphous matrix. The dense-random-packing model seems to be adequate for describing the connection between solvent and solute atoms.

Superradiance for Atoms Trapped along a Photonic Crystal Waveguide

NASA Astrophysics Data System (ADS)

Goban, A.; Hung, C.-L.; Hood, J. D.; Yu, S.-P.; Muniz, J. A.; Painter, O.; Kimble, H. J.

2015-08-01

We report observations of superradiance for atoms trapped in the near field of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge near the D1 transition of atomic cesium, strong interaction is achieved between trapped atoms and guided-mode photons. Following short-pulse excitation, we record the decay of guided-mode emission and find a superradiant emission rate scaling as Γ¯SR∝N ¯Γ1 D for average atom number 0.19 ≲N ¯≲2.6 atoms, where Γ1 D/Γ'=1.0 ±0.1 is the peak single-atom radiative decay rate into the PCW guided mode, and Γ' is the radiative decay rate into all the other channels. These advances provide new tools for investigations of photon-mediated atom-atom interactions in the many-body regime.

Soliton Dynamics of an Atomic Spinor Condensate on a Ring Lattice

DTIC Science & Technology

2013-02-22

REPORT Soliton dynamics of an atomic spinor condensate on a Ring Lattice 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: We study the dynamics of...8/98) Prescribed by ANSI Std. Z39.18 - Soliton dynamics of an atomic spinor condensate on a Ring Lattice Report Title ABSTRACT We study the dynamics...Report Number Soliton dynamics of an atomic spinor condensat Block 13: Supplementary Note © 2013 . Published in Physical Review A (accepted), Vol. Ed

DFT Modeling of Cross-Linked Polyethylene: Role of Gold Atoms and Dispersion Interactions.

PubMed

Blaško, Martin; Mach, Pavel; Antušek, Andrej; Urban, Miroslav

2018-02-08

Using DFT modeling, we analyze the concerted action of gold atoms and dispersion interactions in cross-linked polyethylene. Our model consists of two oligomer chains (PEn) with 7, 11, 15, 19, or 23 carbon atoms in each oligomer cross-linked with one to three Au atoms through C-Au-C bonds. In structures with a single gold atom the C-Au-C bond is located in the central position of the oligomer. Binding energies (BEs) with respect to two oligomer radical fragments and Au are as high as 362-489 kJ/mol depending on the length of the oligomer chain. When the dispersion contribution in PEn-Au-PEn oligomers is omitted, BE is almost independent of the number of carbon atoms, lying between 293 and 296 kJ/mol. The dispersion energy contributions to BEs in PEn-Au-PEn rise nearly linearly with the number of carbon atoms in the PEn chain. The carbon-carbon distance in the C-Au-C moiety is around 4.1 Å, similar to the bond distance between saturated closed shell chains in the polyethylene crystal. BEs of pure saturated closed shell PEn-PEn oligomers are 51-187 kJ/mol. Both Au atoms and dispersion interactions contribute considerably to the creation of nearly parallel chains of oligomers with reasonably high binding energies.

Optical Thin Film Thickness Measurement for the Single Atom Microscope

NASA Astrophysics Data System (ADS)

Nelson, Courtney; Frisbie, Dustin; Singh, Jaideep; Spinlab Team

2017-09-01

The Single Atom Microscope Project proposes an efficient, selective, and sensitive method to measure the 1022Ne+24 He ->1225 Mg + n reaction. This rare nuclear reaction is a source of neutrons for heavy element development through the slow neutron capture process. This method embeds Magnesium atoms in a solid neon film. The Magnesium atoms exhibit a shifted fluorescence spectrum allowing for the detection of individual fluorescence photons against the excitation light background. Currently, Ytterbium is used in place of Magnesium-25 because it has been more thoroughly studied than Magnesium and we expect it to have a brighter signal. To identify the signal emitted from the Ytterbium atoms, we need to quantify the amount of signal and background per atom in the neon film. We need to know the film thickness to find the number of atoms in the film to determine the amount of light emitted per atom. In preparation for the neon film measurement, I constructed an experiment to advance the understanding of what is required to optically measure a thin film by using a cover glass slide in place of the thin film. This preliminary experiment has determined a measurement method for finding the thickness of a neon thin film on a sapphire substrate. This work is supported by Michigan State University, U.S. National Science Foundation under Grant Number 1654610, and U.S. NSF REU.