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Articles 27781 - 27810 of 36715

Full-Text Articles in Physical Sciences and Mathematics

Electronic Properties Of Nacdf3: A First-Principles Prediction, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, Wei-Guo Yin, John R. Hardy, R. W. Smith, M. J. Mehl, L. L. Boyer Jan 2004

Electronic Properties Of Nacdf3: A First-Principles Prediction, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, Wei-Guo Yin, John R. Hardy, R. W. Smith, M. J. Mehl, L. L. Boyer

John R. Hardy Papers

Based on first-principles total energy calculations, we predict that NaCdF3 could be formed in a ferroelectric crystal structure. Using a symmetry guided search with structure optimization, we found two ferroelectric structures, nearly degenerate in energy, competing for the ground state: a rhombohedral structure with space group R3c and an orthorhombic structure with space group Pna21. The energies of both structures are ≈60 meV lower than the sum of those of the constituents, NaF and CdF2, implying chemical stability.

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Tem Study Of Crystalline Structures Of Cr–N Thin Films, Xingzhong Li, J. Zhang, David J. Sellmyer Jan 2004

Tem Study Of Crystalline Structures Of Cr–N Thin Films, Xingzhong Li, J. Zhang, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Cr–N films were grown on Si (001) substrates by reactive magnetron sputtering under an N2/Ar atmosphere at room temperature. The composition of the films, expressed as Cr1–xNx, can be varied by changing the N2/Ar pressure ratio during the synthesis process. Crystalline states of Cr–N films have been studied using electron diffraction. It is well known that two intermediate phases, Cr2N (hexagonal) and CrN (cubic), exist in the Cr–N system, and small variations around the ideal stoichiometry are tolerated. The present study shows that cubic CrN with vacancies rather than hexagonal Cr2 …

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Pupil Phase Apodization For Achromatic Imaging Of Extra-Solar Planets, Weidong Yang Jan 2004

Pupil Phase Apodization For Achromatic Imaging Of Extra-Solar Planets, Weidong Yang

Dissertations, Master's Theses and Master's Reports - Open

Direct imaging of extra-solar planets in the visible and infrared region has generated great interest among scientists and the general public as well. However, this is a challenging problem. Diffculties of detecting a planet (faint source) are caused, mostly, by two factors: sidelobes caused by starlight diffraction from the edge of the pupil and the randomly scattered starlight caused by the phase errors from the imperfections in the optical system. While the latter diffculty can be corrected by high density active deformable mirrors with advanced phase sensing and control technology, the optimized strategy for suppressing the diffraction sidelobes is still …

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Grain Size Distributions And Photoelectric Heating In Ionized Media, P. A. M. Vanhoof, J. C. Weingartner, P. G. Martin, K. Volk, Gary J. Ferland Jan 2004

Grain Size Distributions And Photoelectric Heating In Ionized Media, P. A. M. Vanhoof, J. C. Weingartner, P. G. Martin, K. Volk, Gary J. Ferland

Physics and Astronomy Faculty Publications

Ever since the pioneering study of Spitzer, it has been widely recognized that grains play an important role in the heating and cooling of photoionized environments. This includes the diffuse interstellar medium and H II regions, planetary nebulae and photodissociation regions. A detailed code is necessary to model grains in a photoionized medium since the interactions of grains with their environment include a host of microphysical processes. In this paper we will use the spectral synthesis code CLOUDY for this purpose. A comprehensive upgrade of the grain model has been recently incorporated into CLOUDY. One of these upgrades is the …

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One- And Two-Dimensional Optical Lattices On A Chip For Quantum Computing, Katharina Gillen-Christandl, Gregory P. Lafyatis, Seung-Cheol Lee, Jin-Fa Lee Jan 2004

One- And Two-Dimensional Optical Lattices On A Chip For Quantum Computing, Katharina Gillen-Christandl, Gregory P. Lafyatis, Seung-Cheol Lee, Jin-Fa Lee

Physics

We propose a way to make arrays of optical frequency dipole-force microtraps for cold atoms above a dielectric substrate. Traps are nodes in the evanescent wave fields above an optical waveguide resulting from interference of different waveguide modes. The traps have features sought in developing neutral atom based architectures for quantum computing: ∼1 mW of laser power yields very tight traps 150 nm above a waveguide with trap vibrational frequencies ∼1 MHz and vibrational ground state sizes ∼10 nm. The arrays are scalable and allow addressing of individual sites for quantum logic operations.

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Evolution Dynamics Of A Dense Frozen Rydberg Gas To Plasma, Wenhui Li, Michael W. Noel, Michael P. Robinson, Paul J. Tanner, Thomas F. Gallagher, Daniel Comparat, Bruno Laburthe Tolra, Nicolas Vanhaecke, Thibault Vogt, Nassim Zahzam, Pierre Pillet, Duncan A. Tate Jan 2004

Evolution Dynamics Of A Dense Frozen Rydberg Gas To Plasma, Wenhui Li, Michael W. Noel, Michael P. Robinson, Paul J. Tanner, Thomas F. Gallagher, Daniel Comparat, Bruno Laburthe Tolra, Nicolas Vanhaecke, Thibault Vogt, Nassim Zahzam, Pierre Pillet, Duncan A. Tate

Physics Faculty Research and Scholarship

Dense samples of cold Rydberg atoms have previously been observed to spontaneously evolve to a plasma, despite the fact that each atom may be bound by as much as 100 cm−1. Initially, ionization is caused by blackbody photoionization and Rydberg-Rydberg collisions. After the first electrons leave the interaction re- gion, the net positive charge traps subsequent electrons. As a result, rapid ionization starts to occur after 1 μs caused by electron-Rydberg collisions. The resulting cold plasma expands slowly and persists for tens of microseconds. While the initial report on this process identified the key issues described above, it failed to …

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Magnetic Isomers And Local Moment Distribution In Mn5o And Mn6o Clusters, N. O. Jones, Shiv N. Khanna, T. Baruah, M. R. Pederson, W.-J. Zheng, J. M. Nilles, K. H. Bowen Jan 2004

Magnetic Isomers And Local Moment Distribution In Mn5o And Mn6o Clusters, N. O. Jones, Shiv N. Khanna, T. Baruah, M. R. Pederson, W.-J. Zheng, J. M. Nilles, K. H. Bowen

Physics Publications

A synergistic approach combining the experimental photoelectron spectroscopy and theoretical electronic structure studies is used to demonstrate the existence of magnetic isomers as well as configurations having comparable binding energies, identical spins, and yet differing in the distribution of local moments (called isomags). Our studies carried out on Mn5O and Mn6O clusters show that while the O atom occupies either bridge or hollow site with a binding energy of 6.88eV in Mn5, it prefers a hollow site with a binding energy of 7.18eV in Mn6 clusters. Mn5O is shown to possess two magnetic isomers with total spins of 13 and …

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Spectroscopic Signature Of Magnetic Bistability In Mn2oà Anions And Its Implications For Piezomagnetism At The Nanoscale, Shiv N. Khanna, Puru Jena, W.-J. Zheng, J. M. Nilles, K. H. Bowen Jan 2004

Spectroscopic Signature Of Magnetic Bistability In Mn2oà Anions And Its Implications For Piezomagnetism At The Nanoscale, Shiv N. Khanna, Puru Jena, W.-J. Zheng, J. M. Nilles, K. H. Bowen

Physics Publications

A synergistic study, using gradient corrected density functional theory and photoelectron spectroscopy, shows that the presence of oxygen can fundamentally alter the interaction between two Mn atoms. The normally weak interaction between two Mn atoms exhibits strong bonding when an oxygen atom is added to form Mn2O. This allows the atomiclike magnetic moments of each Mn atom to couple either ferromagnetically or antiferromagnetically depending on whether Mn2O is anionic or neutral. Furthermore, the Mn2O− anion is found to possess an antiferromagnetic isomer that lies only 0.01 eV above its nearly degenerate ferromagnetic ground state. The possibility of exploiting this magnetic …

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Energetics And Local Spin Magnetic Moment Of Single 3,4d Impurities Encapsulated In An Icosahedral Au12 Cage, Shan-Ying Wang, Jing-Zhi Yu, Hiroshi Mizuseki, Qiang Sun, Chong-Yu Wang, Yoshiyuki Kawazoe Jan 2004

Energetics And Local Spin Magnetic Moment Of Single 3,4d Impurities Encapsulated In An Icosahedral Au12 Cage, Shan-Ying Wang, Jing-Zhi Yu, Hiroshi Mizuseki, Qiang Sun, Chong-Yu Wang, Yoshiyuki Kawazoe

Physics Publications

The energetics and local spin magnetic moment of a single 3,4d impurity (Sc-Ni, Y-Pd) encapsulated in an icosahedral Au12 cage have been studied theoretically by using a real-space first-principles cluster method with generalized gradient approximation for exchange-correlation functional. The relativistic effect is considered by scalar relativistic pseudopotentials. All doped clusters show unexpected large relative binding energies compared with icosahedral Au13cluster. The smallest and the largest values appear at Pd and Zr, 2.186 and 7.791eV per cluster, respectively, indicating doping could stabilize the icosahedral Au12 cage and promote the formation of a new binary alloy cluster. Comparatively large magnetic moments are …

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Classical Stern-Gerlach Profiles Of Mn5 And Mn6 Clusters, N. O. Jones, Shiv N. Khanna, Tunna Baruah, M. R. Pederson Jan 2004

Classical Stern-Gerlach Profiles Of Mn5 And Mn6 Clusters, N. O. Jones, Shiv N. Khanna, Tunna Baruah, M. R. Pederson

Physics Publications

Mn5 and Mn6 clusters have recently been found to exhibit Stern-Gerlach profiles marked by a central peak that broadens with the increasing field gradient. The profiles neither exhibit a reminiscence of space quantization as observed through a splitting of beams for the case of free atoms, nor a net deflection characteristic of superparamagnetic relaxations observed in other transition metal clusters. It is proposed that this new behavior results from a weak coupling of localized atomic moments. ab initio electronic structure studies are carried out to show that a Mn5cluster has isomers with spin magnetic moments of 3μB, 13μB, and 23μBwhile …

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Magnetism And Energetics Of Mn-Doped Zno (101¯0) Thin Films, Q. Wang, Q. Sun, B. K. Rao, Puru Jena Jan 2004

Magnetism And Energetics Of Mn-Doped Zno (101¯0) Thin Films, Q. Wang, Q. Sun, B. K. Rao, Puru Jena

Physics Publications

First-principles calculations based on gradient corrected density functional theory are performed on Mn-doped ZnO thin film. Magnetism and energetics are studied for two Mn concentrations and varying Mn configurations. It is found that in the dilute limit when Mn atoms are far apart, the ferro-magnetic and antiferromagnetic states are energetically nearly degenerate. The resulting fluctuation would, therefore, make the system paramagnetic as found in the experiment. But, as the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around oxygen. For such a configuration, the antiferromagnetic coupling between Mn atoms is …

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Interactions Of Au Cluster Anions With Oxygen, Qiang Sun, Puru Jena, Young Dok Kim, Matthias Fischer, Gerd Ganteför Jan 2004

Interactions Of Au Cluster Anions With Oxygen, Qiang Sun, Puru Jena, Young Dok Kim, Matthias Fischer, Gerd Ganteför

Physics Publications

Experimental and theoretical evidence is presented for the nondissociative chemisorption of O2on free Au cluster anions (Au−n, n=number of atoms) with n=2, 4, 6 at room temperature, indicating that the stabilization of the activated di-oxygen species is the key for the unusual catalytic activities of Au-based catalysts. In contrast to Au−n with n=2, 4, 6, O2 adsorbs atomically on Aumonomer anions. For the Aumonomer neutral, calculations based on density functional theory reveal that oxygen should be molecularly bound. On Au dimer and tetramer neutrals, oxygen is molecularly bound with the O–O bond being less activated with respect to their …

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Competition Between Linear And Cyclic Structures In Monochromium Carbide Clusters Crcn- And Crcn (N=2-8): A Photoelectron Spectroscopy And Density Functional Study, Hua-Jin Zhai, Lai-Sheng Wang, P. Jena, G. L. Gutsev, C. W. Bauschlicher Jr. Jan 2004

Competition Between Linear And Cyclic Structures In Monochromium Carbide Clusters Crcn- And Crcn (N=2-8): A Photoelectron Spectroscopy And Density Functional Study, Hua-Jin Zhai, Lai-Sheng Wang, P. Jena, G. L. Gutsev, C. W. Bauschlicher Jr.

Physics Publications

Photoelectron spectroscopy (PES) is combined with density functional theory (DFT) to study the monochromium carbide clusters CrC−n and CrCn (n=2–8). Well-resolved PES spectra were obtained, yielding structural, electronic, and vibrational information about both the anionic and neutral clusters. Experimental evidence was observed for the coexistence of two isomers for CrC−2, CrC−3, CrC−4, and CrC−6. Sharp and well-resolved PES spectra were observed for CrC−n (n=4,6,8), whereas broad spectra were observed for CrC−5 and CrC−7. Extensive DFT calculations using the generalized gradient approximation were carried out for the ground and low-lying excited states of all the CrC−n and CrCn species, as well …

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Geometry And Electronic Structure Of V-N(Bz)(M) Complexes, Anil K. Kandalam, B. K. Rao, P. Jena, Ravindra Pandey Jan 2004

Geometry And Electronic Structure Of V-N(Bz)(M) Complexes, Anil K. Kandalam, B. K. Rao, P. Jena, Ravindra Pandey

Physics Publications

First-principles calculations based on the generalized gradient approximation to the density functional theory are performed to explore the global geometries, ground-state spin multiplicities, relative stabilities, and energetics of neutral and anionic Vn(Bz)m (n51 – 3, m51 – 4, with n ,m) complexes. The calculated results show that the Vn(benzene)m complexes clearly prefer sandwich structures to rice-ball structures. The ground-state spin multiplicities of the Vn(benzene)n11 complexes increased linearly with the size of the system (i.e., n). In the anionic complexes, the V(benzene)2 complex is found to be unstable against the autodetachment of the extra electron. The energy difference between adiabatic and …

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Appearance Of Bulk Properties In Small Tungsten Oxide Clusters, Q. Sun, B. K. Rao, P. Jena, D. Stolcic, Y. D. Kim, Gerd Gantefor, A. W. Castleman Jr. Jan 2004

Appearance Of Bulk Properties In Small Tungsten Oxide Clusters, Q. Sun, B. K. Rao, P. Jena, D. Stolcic, Y. D. Kim, Gerd Gantefor, A. W. Castleman Jr.

Physics Publications

Contrary to the conventional understanding that atomic clusters usually differ in properties and structure from the bulk constituents of which they are comprised, we show that even a dimer of tungsten oxide (WO3)2 possesses bulklike features and the geometry of a small cluster containing only 4 tungsten and 12 oxygen atoms bears the hallmarks of crystalline tungsten oxide, WO3. This observation, based on a synergistic approach involving mass distributions under quasisteady state conditions, photoelectron spectroscopy, and first principles molecular orbital theory, not only illustrates the existence of a class of strongly covalent or ionic materials whose embryonic forms are tiny …

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Formation And Properties Of Halogenated Aluminum Clusters, D. E. Bergeron, A. W. Castleman Jr., T. Morisato, S. N. Khanna Jan 2004

Formation And Properties Of Halogenated Aluminum Clusters, D. E. Bergeron, A. W. Castleman Jr., T. Morisato, S. N. Khanna

Physics Publications

The fast-flow tube reaction apparatus was employed to study the halogenation of aluminum clusters. For reactions with HX (X=Cl, Br, and I), acid-etching pathways are evident, and we present findings for several reactions, whereby AlnX− generation is energetically favorable. Tandem reaction experiments allowed us to establish that for AlnCl−, AlnI−, and AlnI−2, species with n=6, 7, and 15 are particularly resistant to attack by oxygen. Further, trends in reactivity suggest that, in general, iodine incorporation leaves the aluminum clusters’ electronic properties largely unperturbed. Ab initio calculations were performed to better interpret reaction mechanisms and elucidate the characteristics of the products. …

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The Parsec-Scale Structure And Jet Motions Of The Tev Blazars 1es 1959+650, Pks 2155-304, And 1es 2344+514, B. Glenn Piner, Philip G. Edwards Jan 2004

The Parsec-Scale Structure And Jet Motions Of The Tev Blazars 1es 1959+650, Pks 2155-304, And 1es 2344+514, B. Glenn Piner, Philip G. Edwards

Physics

As part of our study of the VLBI properties of TeV blazar jets, we present here a series of high-resolution 15 GHz Very Long Baseline Array (VLBA) images of the parsec-scale jets of the TeV blazars 1ES 1959+650, PKS 2155-304, and 1ES 2344+514, with linear resolutions of ~0.5 pc. Each of these sources was observed with the VLBA at three or four epochs during 1999 and 2000. There is a notable lack of any strong moving components on the VLBI images (in contrast to the rapid superluminal motions seen in EGRET blazars), and the structure of the VLBI jet can …

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Mapping Surface Polarization In Thin Films Of The Ferroelectric Polymer P(Vdf-Trfe)., Bradley W. Peterson, Stephen Ducharme, Vladimir M. Fridkin, Timothy J. Reece Jan 2004

Mapping Surface Polarization In Thin Films Of The Ferroelectric Polymer P(Vdf-Trfe)., Bradley W. Peterson, Stephen Ducharme, Vladimir M. Fridkin, Timothy J. Reece

Stephen Ducharme Publications

Pyroelectric Scanning Microscopy (PSM) has been developed to enable mapping of surface polarization in ferroelectric thin films, in particular the copolymer polyvinylidene fluoride trifluororethylene, or P(VDF-TrFE). The Chynoweth method for dynamically measuring pyroelectric current is employed in conjunction with a micropositioning system to construct two-dimensional images of the film polarization. These images have revealed enhancement of the polarization near the edges of the film below the average coercive field, with the center's polarization increasing thereafter to meet the edge value at saturation.

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Electron Irradiation Effects On Ferroelectric Copolymer Langmuir-Blodgett Films, Christina M. Othon, Stephen Ducharme Jan 2004

Electron Irradiation Effects On Ferroelectric Copolymer Langmuir-Blodgett Films, Christina M. Othon, Stephen Ducharme

Stephen Ducharme Publications

The effect of irradiation on the ferroelectric properties of Langmuir-Blodgett films of the copolymer poly(vinylidene fluoride-trifluorethelene) is investigating using 1.26 MeV electrons with dosages from 16 to 110 Mrad. Irradiation causes a systematic decrease in the phase transition temperature, coercive field and polarization of these thin films.

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Ferroelectricity At Molecular Level, L. M. Blinov, A. V. Bune, Peter A. Dowben, Stephen Ducharme, Vladimir M. Fridkin, S. P. Palto, K. A. Verkhovskaya, G. V. Vizdrik, S. G. Yudin Jan 2004

Ferroelectricity At Molecular Level, L. M. Blinov, A. V. Bune, Peter A. Dowben, Stephen Ducharme, Vladimir M. Fridkin, S. P. Palto, K. A. Verkhovskaya, G. V. Vizdrik, S. G. Yudin

Stephen Ducharme Publications

he synthesis of ultrathin ferroelectric nanostructures by the Langmuir-Blodgett method and their properties are reviewed. It is shown that ferroelectricity exists in one monolayer of the ferroelectric P(VDF-TrFE) copolymer, i.e., at the molecular level. The specific characteristics of switching of ultrathin ferroelectric films are established.

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Apparatus For Studying Wave Motion And Sound At The University Of Nebraska– Lincoln's “Historical Scientific Instrument Gallery”, Lily M. Wang, M. Eugene Rudd Jan 2004

Apparatus For Studying Wave Motion And Sound At The University Of Nebraska– Lincoln's “Historical Scientific Instrument Gallery”, Lily M. Wang, M. Eugene Rudd

M. Eugene Rudd Publications

The University of Nebraska–Lincoln's “Historical Scientific Instrument Gallery,'' compiled by the second author in 1998, contains approximately 700 inventoried items and may be visited on-line at http://physics.unl.edu/outreach/histinstr/. Amidst the collection are several acoustical instruments that were used in the early 1900s. These include equipment that demonstrate wave motion (traveling wave machine, mercury ripple dish, vibration microscope), wave interference (interference machine), resonance conditions (Helmholtz resonators, vibrating rods, singing flames, sonometer), and sound generation (Galton's whistles, high-frequency tuning forks, large tuning forks, organ pipes, siren saw). A review of the equipment and the history of their use at the University of Nebraska …

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Heavy Quark Production By A Quasi-Classical Color Field In Proton-Nucleus Collisions, Kirill Tuchin Jan 2004

Heavy Quark Production By A Quasi-Classical Color Field In Proton-Nucleus Collisions, Kirill Tuchin

Kirill Tuchin

We calculate the inclusive heavy quark production cross section for proton-nucleus collisions at high energies. We perform calculation in a quasi-classical approximation (McLerran-Venugopalan model) neglecting all low-x evolution effects. The derived expression for the differential cross section can be applied for studying the heavy quark production in the central rapidity region at RHIC.

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Nuclear Modification Factor In D + Au Collisions: Onset Of Suppression In The Color Glass Condensate, Dmitri Kharzeev, Yuri V. Kovchegov, Kirill Tuchin Jan 2004

Nuclear Modification Factor In D + Au Collisions: Onset Of Suppression In The Color Glass Condensate, Dmitri Kharzeev, Yuri V. Kovchegov, Kirill Tuchin

Kirill Tuchin

We perform a quantitative analysis of the nuclear modification factor in deuteron-gold collisions R dAu within the Color Glass Condensate approach, and compare our results with the recent data from RHIC experiments. Our model leads to Cronin enhancement at mid-rapidity, while at forward rapidities it predicts strong suppression of R dAu at all PT due to low-x evolution. We demonstrate that our results are consistent with the data for dAu charged hadron spectra, R dAu and R CP recently reported for rapidities in the interval η=0-3.2 by the BRAHMS experiment at RHIC. We also make a prediction for R pA …

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Particle Correlations At High Partonic Density, Kirill Tuchin Jan 2004

Particle Correlations At High Partonic Density, Kirill Tuchin

Kirill Tuchin

We discuss manifestations of the particle correlations at high partonic density in the heavy-ion collisions at RHIC. In particular, we argue that the elliptic flow variable v% is dominated by particle correlations at high PT

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Qcd In Curved Space-Time: A Conformal Bag Model, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin Jan 2004

Qcd In Curved Space-Time: A Conformal Bag Model, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin

Kirill Tuchin

We construct an effective low energy Lagrangian using constraints imposed by the renormalization group. Degrees of freedom are gluons and a scalar glueball. This effective theory has a dual description as classical gluodynamics on a curved conformal background. Color fields are dynamically confined, and the strong coupling freezes at distances larger than the glueball size. We make specific predictions (in particular, on the Nc dependence of glueball properties) which can be tested in lattice simulations of gluodynamics.

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Effects Of Counterion Fluctuations In A Polyelectrolyte Brush, Christian Santangelo, A.W.C. Lau Jan 2004

Effects Of Counterion Fluctuations In A Polyelectrolyte Brush, Christian Santangelo, A.W.C. Lau

Christian Santangelo

We investigate the effect of counterion fluctuations in a single polyelectrolyte brush in the absence of added salt by systematically expanding the counterion free energy about Poisson-Boltzmann mean-field theory. We find that for strongly charged brushes, there is a collapse regime in which the brush height decreases with increasing charge on the polyelectrolyte chains. The transition to this collapsed regime is similar to the liquid-gas transition, which has a first-order line terminating at a critical point. We find that, for monovalent counterions, the transition is discontinuous in theta solvent, while for multivalent counterions, the transition is generally continuous. For collapsed …

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Distribution Of Counterions Near Discretely Charged Planes And Rods, M. L. Henle, Christian Santangelo, D. M. Patel, P. A. Pincus Jan 2004

Distribution Of Counterions Near Discretely Charged Planes And Rods, M. L. Henle, Christian Santangelo, D. M. Patel, P. A. Pincus

Christian Santangelo

Realistic charged macromolecules are characterized by discrete (rather than homogeneous) charge distributions. We investigate the effects of surface charge discretization on the counterion distribution at the level of mean-field theory using a two-state model. Both planar and cylindrical geometries are considered; for the latter case, we compare our results to numerical solutions of the full Poisson-Boltzmann equation. We find that the discretization of the surface charge can cause enhanced localization of the counterions near the surface; for charged cylinders, counterion condensation can exceed Oosawa-Manning condensation.

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Structural And Computational Depth Of Diffusion Limited Aggregation, D. Tillberg, Jonathan Machta Jan 2004

Structural And Computational Depth Of Diffusion Limited Aggregation, D. Tillberg, Jonathan Machta

Jonathan Machta

Diffusion-limited aggregation (DLA) is studied from the perspective of computational complexity. A parallel algorithm is exhibited that requires a number of steps that scales as the depth of the tree defined by the cluster. The existence of this algorithm suggests a connection between a fundamental computational and structural property of DLA.

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Long Distance Chiral Corrections In B Meson Amplitudes, Juan J. Sanz-Cillero, John Donoghue, Andreas Ross Jan 2004

Long Distance Chiral Corrections In B Meson Amplitudes, Juan J. Sanz-Cillero, John Donoghue, Andreas Ross

John Donoghue

We discuss the chiral corrections to f_B and B_B with particular emphasis on determining the portion of the correction that arises from long distance physics. For very small pion and kaon masses all of the usual corrections are truly long distance, while for larger masses the long distance portion decreases. These chiral corrections have been used to extrapolate lattice calculations towards the physical region of lighter masses. We show in particular that the chiral extrapolation is better behaved if only the long distance portion of the correction is used.

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Precision Zeeman-Stark Spectroscopy Of The Metastable A(1)[Σ+3] State Of Pbo, David Kawall, F. Bay, S. Bickman, Y. Jiang, D. Demille Jan 2004

Precision Zeeman-Stark Spectroscopy Of The Metastable A(1)[Σ+3] State Of Pbo, David Kawall, F. Bay, S. Bickman, Y. Jiang, D. Demille

David Kawall

The metastable a(1)[Σ+3] state of PbO has been suggested as a suitable system in which to search for the electric dipole moment of the electron. We report here the development of experimental techniques allowing high-sensitivity measurements of Zeeman and Stark effects in this system, similar to those required for such a search. We observe Zeeman quantum beats in fluorescence from a vapor cell of PbO, with shot-noise limited extraction of the quantum beat frequencies, high counting rates, and long coherence times. We argue that improvement in sensitivity to the electron electric dipole moment by at least 2 orders of magnitude …

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