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Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel 2010 Iowa State University

Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

H2S forms a rich variety of structures on Ag(111) at low temperature and submonolayer coverage. The molecules decorate step edges, exist as isolated entities on terraces, and aggregate into clusters and islands, under various conditions. One type of island exhibits a (×)R25.3° unit cell. Typically, molecules in the clusters and islands are separated by about 0.4 nm, the same as the S–S separation in crystalline H2S. Density functional theory indicates that hydrogen-bonded clusters contain two types of molecules. One is very similar to an isolated adsorbed H2S molecule, with both ...


Formation And Coarsening Of Ag(110) Bilayer Islands On Nial(110): Stm Analysis And Atomistic Lattice-Gas Modeling, Yong Han, Barış Ünal, Dapeng Jing, Feili Qin, Cynthia J. Jenks, Da-Jiang Liu, Patricia A. Thiel, James W. Evans 2010 Iowa State University

Formation And Coarsening Of Ag(110) Bilayer Islands On Nial(110): Stm Analysis And Atomistic Lattice-Gas Modeling, Yong Han, Barış Ünal, Dapeng Jing, Feili Qin, Cynthia J. Jenks, Da-Jiang Liu, Patricia A. Thiel, James W. Evans

Chemistry Publications

Scanning tunneling microscopy analysis of the initial stages of film growth during deposition of Ag on NiAl(110) reveals facile formation of bilayer Ag(110) islands at temperatures of 130 K and above. Annealing subsequent to deposition at 130 K induces coarsening of the bilayer island distribution. The thermodynamic driving force for bilayer island formation reflects a lower relative surface energy for films of even layer thicknesses. This feature derives from quantum size effects due to electron confinement in the Ag film. The kinetics of island formation and relaxation is controlled by terrace and edge-diffusion barriers, detachment barriers, interlayer diffusion ...


Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, Barış Ünal, Alex Belianinov, Patricia A. Thiel, Michael C. Tringides 2010 Iowa State University

Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, Barış Ünal, Alex Belianinov, Patricia A. Thiel, Michael C. Tringides

Chemistry Publications

Ag on Si(111)-7×7 was one of the first systems where height selection of metal islands was attributed to electron confinement, i.e., stabilization of selected heights through a quantum size effect (QSE). However, it has been puzzling how the requisite electron standing waves can form, because the Fermi level EF (along the growth [111] direction) is within the gap for bulk Ag. With detailed experiments over a wide coverage and temperature range, we show that a large increase of 12% is present in the interlayer spacing within the bilayer islands. This can shift EF below ...


Islands And Holes As Measures Of Mass Balance In Growth Of The (√3×√3)R30° Phase Of Ag On Si(111), Alex Belianinov, Barış Ünal, Ning Lu, Min Ji, Kai-Ming Ho, Cai-Zhuang Wang, Michael C. Tringides, Patricia A. Thiel 2010 Iowa State University

Islands And Holes As Measures Of Mass Balance In Growth Of The (√3×√3)R30° Phase Of Ag On Si(111), Alex Belianinov, Barış Ünal, Ning Lu, Min Ji, Kai-Ming Ho, Cai-Zhuang Wang, Michael C. Tringides, Patricia A. Thiel

Chemistry Publications

It is well known that conversion of Si(111)-(7×7) into the (√3×√3)R30° phase of adsorbed Ag requires a change in the Si density, and causes formation of islands and holes at the surface. By mass balance, the ratio of areas of islands and holes (RIH) should be approximately 1. However, we find that the ratio is significantly higher, depending on preparation conditions. A possible explanation would be that there are different types of (√3×√3)R30° structures. However, neither scanning tunneling microscopy nor density-functional theory (implemented as a genetic algorithm search) supports this explanation. We ...


Mesoporous Silica Nanoparticles: Structural Design And Applications, Igor I. Slowing, Juan Luis Vivero-escoto, Brian G. Trewyn, Victor S.Y. Lin 2010 Iowa State University

Mesoporous Silica Nanoparticles: Structural Design And Applications, Igor I. Slowing, Juan Luis Vivero-Escoto, Brian G. Trewyn, Victor S.Y. Lin

Chemistry Publications

The structural properties of mesoporous silica nanoparticles are reviewed. Different strategies for the introduction of functional groups are considered. Based on the architectural features of the material, the functionalization at defined regions of the particles is described, along with the properties emerging from the corresponding site-specific modifications of their chemistry. Many applications derived from the unique architecture and chemistry of these nanostructured composite materials are shown.


Multiple Nonstoichiometric Phases With Discrete Composition Ranges In The Caau5-Caau4bi-Biau2 System. A Case Study Of The Chemistry Of Spinodal Decomposition, Qisheng Lin, John D. Corbett 2010 The Ames Laboratory

Multiple Nonstoichiometric Phases With Discrete Composition Ranges In The Caau5-Caau4bi-Biau2 System. A Case Study Of The Chemistry Of Spinodal Decomposition, Qisheng Lin, John D. Corbett

Chemistry Publications

Synthetic explorations in the CaAu5−CaAu4Bi−BiAu2 system at 400 °C reveal five separate solid solution regions that show three distinct substitution patterns in the CaAu5 parent: (I) CaAu4(Au1−mBim) with 0 ≤ m ≤ 0.15(1), (II) 0.33(1) ≤ m ≤ 0.64(1), (III) 0.85(4) ≤ m ≤ 0.90(2); (IV) (Ca1−rAur)Au4(Bi1−sAus) with 0 ≤ r ≤ 0.39(1) and 0 ≤ s ≤ 0.12(2); (V) (Ca1−pqAupBiq)Au4Bi with 0.09(2) ≤ p ≤ 0.13(1) and 0.31(2) ≤ q ≤ 0 ...


M3(Au,Ge)19 And M3.25(Au,Ge)18 (M = Ca, Yb): Distinctive Phase Separations Driven By Configurational Disorder In Cubic Ycd6-Type Derivatives, Qisheng Lin, John D. Corbett 2010 The Ames Laboratory

M3(Au,Ge)19 And M3.25(Au,Ge)18 (M = Ca, Yb): Distinctive Phase Separations Driven By Configurational Disorder In Cubic Ycd6-Type Derivatives, Qisheng Lin, John D. Corbett

Chemistry Publications

Exploratory syntheses in the M−Au−Ge (M = Ca, Yb) systems have led to the discovery of two cleanly separated non-stoichiometric phases M3Au∼14.4Ge∼4.6 (I) and M3.25Au∼12.7Ge∼5.3 (II). Single crystal X-ray studies reveal that both (space group Im3̅) feature body-centered-cubic packing of five-shell multiply endohedral clusters that resemble those in the parent YCd6 (= Y3Cd18) and are akin to approximate phases in other quasicrystal systems. However, differences resulting from various disorders in these are distinctive. The innermost cluster in the M3Au∼14.4Ge∼4.6 phase (I) remains a disordered tetrahedron, as ...


Euagxal11−X With The Bahg11-Type Structure: Composition, Coloring, And Competition With The Bacd11-Type Structure, Fei Wang, Karen N. Pearson, Warren E. Straszheim, Gordon J. Miller 2010 Iowa State University

Euagxal11−X With The Bahg11-Type Structure: Composition, Coloring, And Competition With The Bacd11-Type Structure, Fei Wang, Karen N. Pearson, Warren E. Straszheim, Gordon J. Miller

Chemistry Publications

EuAgxAl11−x phases adopting the BaHg11-type structure (space group Pmm, Z = 3) were synthesized with high yield by arc melting a mixture loaded as “EuAg3.5Al7.5” and annealing at 500 °C for 40 days. This phase has a very narrow phase width around EuAg4.0Al7.0; and it is unstable at 600 and 700 °C, at which it transforms into other phases. Magnetometry indicates that Eu is divalent, which gives the valence electron concentration per Ag/Al atom as 2.45 e/atom, higher than in ...


Structural And Magnetic Characteristics Of Gd5gaxsi4−X, Hui Wang, Sumohan Misra, Fei Wang, Gordon J. Miller 2010 Iowa State University

Structural And Magnetic Characteristics Of Gd5gaxsi4−X, Hui Wang, Sumohan Misra, Fei Wang, Gordon J. Miller

Chemistry Publications

A crystallographic study and theoretical analysis of the Si/Ga site preferences in the Gd5GaxSi4−x series is presented. Gd5GaxSi4−x adopt the orthorhombic Gd5Si4-type structure (space group Pnma, Z = 4) with a maximum Ga content near x = 1.00, as determined by single crystal and powder X-ray diffraction. Refinements from single crystal X-ray diffraction studies of the three independent sites for Si/Ga atoms in the asymmetric unit (interslab T1, intraslab T2 and T3) reveal partial mixing of these elements, with a clear preference for ...


Controlling Magnetism Of A Complex Metallic System Using Atomic Individualism, Yaroslav Mudryk, Durga Paudyal, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Sumohan Misra, Gordon J. Miller 2010 Iowa State University

Controlling Magnetism Of A Complex Metallic System Using Atomic Individualism, Yaroslav Mudryk, Durga Paudyal, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Sumohan Misra, Gordon J. Miller

Chemistry Publications

When the complexity of a metallic compound reaches a certain level, a specific location in the structure may be critically responsible for a given fundamental property of a material while other locations may not play as much of a role in determining such a property. The first-principles theory has pinpointed a critical location in the framework of a complex intermetallic compound—Gd5Ge4—that resulted in a controlled alteration of the magnetism of this compound using precise chemical tools.


Rhombohedrally Distorted Γ-Brasses Cr1−Xfexga, Hyujin Ko, Olivier Gourdon, Delphine Gout, Eun-Deok Mun, Srinivasa Thimmaiah, Gordon J. Miller 2010 Iowa State University

Rhombohedrally Distorted Γ-Brasses Cr1−Xfexga, Hyujin Ko, Olivier Gourdon, Delphine Gout, Eun-Deok Mun, Srinivasa Thimmaiah, Gordon J. Miller

Chemistry Publications

A series of rhombohedrally distorted γ-brass structures containing a mixture of magnetically active 3d elements, Cr and Fe, Cr1−xFexGa, is investigated crystallographically. These structures consist of chains of trans-face-sharing Ga-centered transition metal icosahedra. Neutron powder diffraction specifically on Cr0.5Fe0.5Ga, which could be prepared as a single phase material, gave lattice constants (11 K) a = 12.5172(2) Å and c = 7.8325(2) Å and a refined composition of Cr0.502(6)Fe0.498Ga = Cr6.523Fe6.477Ga13 and revealed partial ordering ...


Scalable Event Tracking On High-End Parallel Systems, Kathryn Marie Mohror 2010 Portland State University

Scalable Event Tracking On High-End Parallel Systems, Kathryn Marie Mohror

Dissertations and Theses

Accurate performance analysis of high end systems requires event-based traces to correctly identify the root cause of a number of the complex performance problems that arise on these highly parallel systems. These high-end architectures contain tens to hundreds of thousands of processors, pushing application scalability challenges to new heights. Unfortunately, the collection of event-based data presents scalability challenges itself: the large volume of collected data increases tool overhead, and results in data files that are difficult to store and analyze. Our solution to these problems is a new measurement technique called trace profiling that collects the information needed to diagnose ...


Scrap Reduction Model: By Combination Of Dmaic And Design Of Experiments, Anoop J. Randive 2010 University of Texas at El Paso

Scrap Reduction Model: By Combination Of Dmaic And Design Of Experiments, Anoop J. Randive

Open Access Theses & Dissertations

This project deals with the experimentation which took place at a cable manufacturing company. The thesis describes and summarizes the various strategies and techniques that has been applied and practiced for scrap reduction. DMAIC and Six Sigma Technology has been proven very help full in order to reduce scrap to a major extent. DMAIC help to identify areas in process where extra expense exist, identify the biggest impact factor related production expenses, introduce appropriate measurement system, optimize process and reduce production cost and time. Many issues were detected by the production, such as a lack of a unified procedure for ...


Seismic Investigation Of The Southern Rio Grande Rift, Lennox Emmanuel Thompson 2010 University of Texas at El Paso

Seismic Investigation Of The Southern Rio Grande Rift, Lennox Emmanuel Thompson

Open Access Theses & Dissertations

Competing models exist to explain what caused the Earth's crust to spread apart 29 million years ago to create a region known today as the Rio Grande Rift (RGR). The RGR extends from central Colorado through New Mexico to northern Mexico, near El Paso. The RGR has different geologic features that distinguish it from most other valleys (e.g., the RGR was not cut by a river nor does a river branch upstream). A growing body of evidence shows that geologic activity still occurs in the RGR, with a continuation of faulting, seismicity and widening at a small rate ...


Sulfur K-Edge Photo-Fragmentation Of Ethylene Sulfide, Wayne C. Stolte, Gunnar Ohrwall 2010 University of Nevada, Las Vegas

Sulfur K-Edge Photo-Fragmentation Of Ethylene Sulfide, Wayne C. Stolte, Gunnar Ohrwall

Chemistry and Biochemistry Faculty Publications

We have investigated the photofragmentation properties of the three-membered ring heterocyclic molecule ethylene sulfide or thiirane, C2H4S, by time-of-flight mass spectroscopy. Positive ions have been collected as a function of photon energy around the S K ionization threshold. Branching ratios were derived for all detected ions, which are informative of the decay dynamics and photofragmentation patterns of the core-excited species. We present a new assignment of the spectral features around the S K-edge.


Climatological Aspects Of The Optical Properties Of Fine/Coarse Mode Aerosol Mixtures, Thomas F. Eck, B. N. Holben, Aliaksandyr Sinyuk, R. T. Pinker, P. Goloub, H. Chen, B. Chatenet, Z. Li, Ramesh P. Singh, Sachchida N. Tripathi, J. S. Reid, D. M. Giles, O. Dubovik, N. T. O'Neill, A. Smirnov, P. Wang, X. Xia 2010 Universities Space Research Association

Climatological Aspects Of The Optical Properties Of Fine/Coarse Mode Aerosol Mixtures, Thomas F. Eck, B. N. Holben, Aliaksandyr Sinyuk, R. T. Pinker, P. Goloub, H. Chen, B. Chatenet, Z. Li, Ramesh P. Singh, Sachchida N. Tripathi, J. S. Reid, D. M. Giles, O. Dubovik, N. T. O'Neill, A. Smirnov, P. Wang, X. Xia

Mathematics, Physics, and Computer Science Faculty Articles and Research

Aerosol mixtures composed of coarse mode desert dust combined with fine mode combustion generated aerosols (from fossil fuel and biomass burning sources) were investigated at three locations that are in and/or downwind of major global aerosol emission source regions. Multiyear monitoring data at Aerosol Robotic Network sites in Beijing (central eastern China), Kanpur (Indo-Gangetic Plain, northern India), and Ilorin (Nigeria, Sudanian zone of West Africa) were utilized to study the climatological characteristics of aerosol optical properties. Multiyear climatological averages of spectral single scattering albedo (SSA) versus fine mode fraction (FMF) of aerosol optical depth at 675 nm at all ...


Limit On Continuous Neutrino Emission From Neutron Stars, Itzhak Goldman, Shmuel Nussinov 2010 Afeka College of Engineering

Limit On Continuous Neutrino Emission From Neutron Stars, Itzhak Goldman, Shmuel Nussinov

Mathematics, Physics, and Computer Science Faculty Articles and Research

The timing data of the binary pulsar PSR1913+16, are used to establish an upper limit on the rate of continuous neutrino emission from neutron stars. Neutrino emission from each of the neutron stars of the binary system, increases the star binding energy and thus translates to a decrease in their masses. This in turn implies an increase with time of the binary period. Using the pulsar data we obtain an upper limit on the allowed rate of mass reduction: vertical bar M vertical bar < 1.1 x 10(-12) yr(-1) M, where M is the total mass of the binary. This constrains exotic nuclear equations of state that predict continuous neutrino emissions. The limit applies also to other channels of energy loss, e. g. axion emission. Continued timing measurements of additional binary pulsars, should yield a stronger limit in the future.


A Time-Symmetric Formulation Of Quantum Mechanics, Yakir Aharonov, Sandu Popescu, Jeff Tollaksen 2010 Chapman University

A Time-Symmetric Formulation Of Quantum Mechanics, Yakir Aharonov, Sandu Popescu, Jeff Tollaksen

Mathematics, Physics, and Computer Science Faculty Articles and Research

Quantum mechanics allows one to independently select both the initial and final states of a single system. Such pre- and postselection reveals novel effects that challenge our ideas about what time is and how it flows.


Linear Stochastic State Space Theory In The White Noise Space Setting, Daniel Alpay, David Levanony, Ariel Pinhas 2010 Chapman University

Linear Stochastic State Space Theory In The White Noise Space Setting, Daniel Alpay, David Levanony, Ariel Pinhas

Mathematics, Physics, and Computer Science Faculty Articles and Research

We study state space equations within the white noise space setting. A commutative ring of power series in a countable number of variables plays an important role. Transfer functions are rational functions with coefficients in this commutative ring, and are characterized in a number of ways. A major feature in our approach is the observation that key characteristics of a linear, time invariant, stochastic system are determined by the corresponding characteristics associated with the deterministic part of the system, namely its average behavior.


On The Characteristics Of A Class Of Gaussian Processes Within The White Noise Space Setting, Daniel Alpay, Haim Attia, David Levanony 2010 Chapman University

On The Characteristics Of A Class Of Gaussian Processes Within The White Noise Space Setting, Daniel Alpay, Haim Attia, David Levanony

Mathematics, Physics, and Computer Science Faculty Articles and Research

Using the white noise space framework, we define a class of stochastic processes which include as a particular case the fractional Brownian motion and its derivative. The covariance functions of these processes are of a special form, studied by Schoenberg, von Neumann and Krein.


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