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Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Anomaly In Conformal Quantum Mechanics: From Molecular Physics To Black Holes, Horacio E. Camblong
Anomaly In Conformal Quantum Mechanics: From Molecular Physics To Black Holes, Horacio E. Camblong
Physics and Astronomy
A number of physical systems exhibit a particular form of asymptotic conformal invariance: within a particular domain of distances, they are characterized by a long-range conformal interaction (inverse square potential), the apparent absence of dimensional scales, and an SO(2,1) symmetry algebra. Examples from molecular physics to black holes are provided and discussed within a unified treatment. When such systems are physically realized in the appropriate strong-coupling regime, the occurrence of quantum symmetry breaking is possible. This anomaly is revealed by the failure of the symmetry generators to close the algebra in a manner shown to be independent of the renormalization …
So(2,1) Conformal Anomaly: Beyond Contact Interactions, Horacio E. Camblong
So(2,1) Conformal Anomaly: Beyond Contact Interactions, Horacio E. Camblong
Physics and Astronomy
The existence of anomalous symmetry-breaking solutions of the SO(2,1) commutator algebra is explicitly extended beyond the case of scale-invariant contact interactions. In particular, the failure of the conservation laws of the dilation and special conformal charges is displayed for the two-dimensional inverse square potential. As a consequence, this anomaly appears to be a generic feature of conformal quantum mechanics and not merely an artifact of contact interactions. Moreover, a renormalization procedure traces the emergence of this conformal anomaly to the ultraviolet sector of the theory, within which lies the apparent singularity.
Anomalous Commutator Algebra For Conformal Quantum Mechanics, Horacio E. Camblong
Anomalous Commutator Algebra For Conformal Quantum Mechanics, Horacio E. Camblong
Physics and Astronomy
The structure of the commutator algebra for conformal quantum mechanics is considered. Specifically, it is shown that the emergence of a dimensional scale by renormalization implies the existence of an anomaly or quantum-mechanical symmetry breaking, which is explicitly displayed at the level of the generators of the SO(2,1) conformal group. Correspondingly, the associated breakdown of the conservation of the dilation and special conformal charges is derived.
Accuracy In Spreadsheet Modelling Systems, Thomas A. Grossman Jr.
Accuracy In Spreadsheet Modelling Systems, Thomas A. Grossman Jr.
Business Analytics and Information Systems
Accuracy in spreadsheet modelling systems can be reduced due to difficulties with the inputs, the model itself, or the spreadsheet implementation of the model. When the "true" outputs from the system are unknowable, accuracy is evaluated subjectively. Less than perfect accuracy can be acceptable depending on the purpose of the model, problems with inputs, or resource constraints. Users build modelling systems iteratively, and choose to allocate limited resources to the inputs, the model, the spreadsheet implementation, and to employing the system for business analysis. When making these choices, users can suffer from expectation bias and diagnosis bias. Existing research results …
Research Strategy And Scoping Survey On Spreadsheet Practices, Thomas A. Grossman Jr., O Ozluk
Research Strategy And Scoping Survey On Spreadsheet Practices, Thomas A. Grossman Jr., O Ozluk
Business Analytics and Information Systems
We propose a research strategy for creating and deploying prescriptive recommendations for spreadsheet practice. Empirical data on usage can be used to create a taxonomy of spreadsheet classes. Within each class, existing practices and ideal practices can he combined into proposed best practices for deployment. As a first step we propose a scoping survey to gather non-anecdotal data on spreadsheet usage. The scoping survey will interview people who develop spreadsheets. We will investigate the determinants of spreadsheet importance, identify current industry practices, and document existing standards for creation and use of spreadsheets. The survey will provide insight into user attributes, …
Species-Rich Plantings Increase Biomass And Nitrogen Accumulation In A Wetland Restoration Experiment, John Callaway, Gary Sullivan, Joy B. Zedler
Species-Rich Plantings Increase Biomass And Nitrogen Accumulation In A Wetland Restoration Experiment, John Callaway, Gary Sullivan, Joy B. Zedler
Environmental Science
Our test of the hypothesis that biomass and nitrogen would increase with more species-rich plantings simultaneously vegetated a salt marsh restoration site and demonstrated that on average, randomly chosen, 6-species plantings accumulated more biomass and nitrogen than the mean for 0- and 1-species assemblages, with the mean for 3-species assemblages being intermediate. In addition, we found that individual species (from the pool of eight native halophytes) differed in their functional capacity, with Salicornia virginica (Sv) and Jaumea carnosa contributing the greatest biomass when planted alone, while Triglochin concinna had the highest tissue N concentrations. When planted alone, Sv accumulated comparable …
Response To “Comment On ‘Atomization Energies And Enthalpies Of Formation Of The Snbi[Sub N] (N=1–3) Gaseous Molecules By Knudsen Cell Mass Spectrometry’ ” [J. Chem. Phys. 118, 4766 (2003)], Giovanni Meloni, Karl A. Gingerich
Response To “Comment On ‘Atomization Energies And Enthalpies Of Formation Of The Snbi[Sub N] (N=1–3) Gaseous Molecules By Knudsen Cell Mass Spectrometry’ ” [J. Chem. Phys. 118, 4766 (2003)], Giovanni Meloni, Karl A. Gingerich
Chemistry Faculty Publications
Discusses atomization energies and enthalpies of formation of gaseous molecules of compounds containing tin and bismuth by Knudsen cell mass spectrometry. Procedure followed to evaluate the mass spectrometric equilibrium data regarding these molecules; Statistics of atomization energies and enthalpies calculated; Factors contributing to the necessity of high level of calculations to obtain these figures.
Anion Photoelectron Spectroscopy Of Solvated Transition State Precursors, Harry Gomez, Giovanni Meloni, James Madrid, D M. Neumark
Anion Photoelectron Spectroscopy Of Solvated Transition State Precursors, Harry Gomez, Giovanni Meloni, James Madrid, D M. Neumark
Chemistry Faculty Publications
Photoelectron (PE) spectra have been collected for the clustered bihalide anions XHX−∙(M) (X=Br, I) and BrHI−∙(M), where M=H2O, HBr, and HI, in order to probe the effects of strongly solvating species on the PE spectra of transition state precursor anions. The PE spectra of the XHX−∙(H2O) ions show similar vibrational progressions as the spectra of the bare BrHBr− and IHI− anions, indicating that photodetachment of the bare and hydrated ions accesses similar XHX transition state geometries on the X+HX reactionpotential energy surfaces. These results are consistent with electronic structure calculations that predict a double hydrogen-bonded XHX−∙(H2O) structure in which the …
The Ionizing Efficiency Of The First Stars, Aparna Venkatesan, James W. Truran
The Ionizing Efficiency Of The First Stars, Aparna Venkatesan, James W. Truran
Physics and Astronomy
We investigate whether a single population of first stars could have influenced both the metal enrichment and reionization of the high-redshift intergalactic medium (IGM), by calculating the generated ionizing radiation per unit metal yield as a function of the metallicity of stellar populations. We examine the relation between the ionizing radiation and carbon created by the first stars, since the evidence for the widespread enrichment of the IGM at redshifts z about 3-4 comes from the detection of C IV absorption. We find that the number of ionizing photons per baryon generated in association with the detected IGM metallicity may …
Feedback From The First Supernovae In Protogalaxies: The Fate Of The Generated Metals, Keiichi Wada, Aparna Venkatesan
Feedback From The First Supernovae In Protogalaxies: The Fate Of The Generated Metals, Keiichi Wada, Aparna Venkatesan
Physics and Astronomy
We investigate the chemo-dynamical effects of multiple supernova explosions in the central region of primordial galaxies using three-dimensional hydrodynamical simulations of the inhomogenous interstellar medium down to parsec-scales. We find that the final protogalactic structure and metal distribution depend strongly on the number of SNe. Specifically, 1) 1000 SNe after an instantaneous burst of star formation are sufficient to almost completely blow away the gas in these systems, whereas 2) 100 SN explosions trigger the collapse of the protogalactic cloud, leading to the formation of a cold, dense clumpy disk (n > 300 cm^-3) with metallicity, Z = 4 10^-4 Z_sun. …
Cosmological Effects Of The First Stars: Evolving Spectra Of Population Iii, Jason Tumlinson, J Shull, Aparna Venkatesan
Cosmological Effects Of The First Stars: Evolving Spectra Of Population Iii, Jason Tumlinson, J Shull, Aparna Venkatesan
Physics and Astronomy
The first stars hold intrinsic interest for their uniqueness and for their potentially important contributions to galaxy formation, chemical enrichment, and feedback on the intergalactic medium (IGM). Although the sources of cosmological reionization are unknown at present, the declining population of large bright quasars at redshifts z > 3 implies that stars are the leading candidates for the sources that reionized the hydrogen in the IGM by z ~ 6. The metal-free composition of the first stars restricts the stellar energy source to proton-proton burning rather than the more efficient CNO cycle. Consequently, they are hotter, smaller, and have harder spectra …
Evolving Spectra Of Population Iii Stars: Consequences For Cosmological Reionization, Aparna Venkatesan, Jason Tumlinson, J Shull
Evolving Spectra Of Population Iii Stars: Consequences For Cosmological Reionization, Aparna Venkatesan, Jason Tumlinson, J Shull
Physics and Astronomy
We examine the significance of the first metal-free stars (Population III) for the cosmological reionization of H I and He II. These stars have unusually hard spectra, with the integrated ionizing photon rates from a Population III stellar cluster for H I and He II being 1.6 and 105 times stronger, respectively, than those from a Population II cluster. For the currently favored cosmology, we find that Population III stars alone can reionize H I at redshifts of z 9 and 4.7 and He II at z 5.1 and 0.7 for continuous and instantaneous modes of star formation, respectively. …
Material Optimization Of Er3+Y2sio5 At 1.5 Μm For Optical Processing, Memory, And Laser Frequency Stabilization Applications, Thomas Böttger, Y Sun, C W. Thiel, R L. Cone
Material Optimization Of Er3+Y2sio5 At 1.5 Μm For Optical Processing, Memory, And Laser Frequency Stabilization Applications, Thomas Böttger, Y Sun, C W. Thiel, R L. Cone
Physics and Astronomy
Spatial-spectral holography using spectral hole burning materials is a powerful technique for performing real-time, wide-bandwidth information storage and signal processing. For operation in the important 1.5 μm communication band, the material Er3+:Y2SiO5 enables applications such as laser frequency stabilization, all-optical correlators, analog signal processing, and data storage. Site-selective absorption and emission spectroscopy identified spectral hole burning transitions and excited state T1 lifetimes in the 1.5 μm spectral region. The effects of crystal temperature, Er3+-dopant concentration, magnetic field strength, and crystal orientation on spectral diffusion were explored using stimulated photon echo spectroscopy, which is the “prototype” interaction mechanism for device applications. …