869 research outputs found
UNUSUAL NEGATIVE MOLECULAR IONS AND DIANIONS AND CHEMICAL BONDS INVOLVING RYDBERG ORBITALS
No full text1. Maciej Gutowski, Piotr Skurski, Kenneth D. Jordan, Jack Simons; Int J. Quant. Chem.; 64, 183 (1997). 2. P. Skurski, M. Gutowski and J. Simons, Int J. Quant Chem. 76. 197 (2000). 3. Alexander I. Boldyrev, Maciej Gutowski, and Jack Simons; Acc. Chem. Res.; 29, 497 (1996). 4. Jack Simons and Maciej Gutowski, Chem. Rev. 91, 669 (1991). 5. A. I. Boldyrev and J. Simons; J. Phys. Chem. 96, 8840 (1992); A. I. Boldyrev and J. Simons. J. Phys. Chem., 103, 3575 (1999).Author Institution: Department of Chemistry and Henry Eyring Center for Theoretical Chemistry, University of UtahIn this presentation, our work and that of several other groups on the species listed in the title will be discussed. Particular emphasis will be given to: (a) dipole bound (which have also been the subject of numerous experimental studies), (b) dipole bound (which remain theoretical speculation), (c) resonance states of anions that can be made stable via ``solvation'', (d) dianions such as that have extremely high second electron binding (which occur in the solid state and in solution), (e) anions in which the ``extra'' electron occupies a Rydberg-like molecular (which have been seen experimentally), and (f) chemical bonds that arise when a Rydberg-like orbital is
ABJ(M) Chiral Primary Three-Point Function at Two-loops
No full textThis article is distributed under the terms of the Creative Commons
Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.archiveprefix: arXiv primaryclass: hep-th reportnumber: QMUL-PH-14-10 slaccitation: %%CITATION = ARXIV:1404.1117;%%archiveprefix: arXiv primaryclass: hep-th reportnumber: QMUL-PH-14-10 slaccitation: %%CITATION = ARXIV:1404.1117;%%archiveprefix: arXiv primaryclass: hep-th reportnumber: QMUL-PH-14-10 slaccitation: %%CITATION = ARXIV:1404.1117;%%Article funded by SCOAP
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A probabilistic assessment of sea level variations within the Last Interglacial stage
No full textThe Last Interglacial (LIG) stage (ca. 130–115 ka) provides a relatively recent example of a world with both poles characterized by greater-than- Holocene temperatures similar to those expected later in this century under a range of greenhouse gas emission scenarios. Previous analyses inferred that LIG mean global sea level (GSL) peaked 6–9 m higher than today (Kopp et al. 2009; Dutton & Lambeck 2012). Here, we extend our earlier work to perform a probabilistic assessment of sea level variability within the LIG highstand. Using the terminology for probability employed in the Intergovernmental Panel on Climate Change (IPCC) assessment reports, we find it extremely likely (95% probability) that the paleo-sea level record allows resolution of at least two intra-LIG sea level peaks and likely (67% probability) that the magnitude of low-to-high swings exceeded 4 m. Moreover, it is likely that there was a period during the LIG in which GSL rose at a 1000-year average rate exceeding 3 m/ky, but unlikely (33% probability) that the rate exceeded 7 m/ky and extremely unlikely (5% probability) that it exceeded 11 m/ky. These rate estimates can provide insight into rates of Greenland and/or Antarctic melt under climate conditions partially analogous to those expected in the twenty- first century.This is the authors’ preprint version of the manuscript: 23 January 2013. Originally submitted 18 September 2012. Accepted for publication in Geophysical Journal International, published by Oxford University Press.Peer reviewe
Two-loop Sudakov form factor in ABJM
No full textThis article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited
Locations of selected small earthquakes in the Zagros mountains
No full textAuthor Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 6 (2005): Q03001, doi:10.1029/2004GC000849.The Zagros mountains of southern Iran are marked by a zone of high seismicity and accommodate a significant portion of the convergence between Arabia and Eurasia. Due to the lack of dense local seismic or geodetic networks, the inferred kinematics of the collision in Iran is mainly based on catalogs of teleseismically determined earthquake locations. We surveyed all M w > 4.5 earthquakes in the Harvard Centroid Moment Tensor (HCMT) and International Seismological Centre (ISC) catalogs that occurred in the Zagros mountains during the period 1992–2002 and that were spanned by Interferometric Synthetic Aperture Radar (InSAR) images from the ERS 1 and 2 satellites. We invert the observed deformation for the best fitting point source, single fault plane, and distributed fault slip for four earthquakes and one unexplained deformation event. We find that we can precisely locate earthquakes that are too small to be well-located by either the HCMT or ISC catalogs, allowing us to tie specific earthquakes to active geologic structures.ERS 1 and 2 data were acquired through an
ESA category-1 proposal. R. Lohman is partially supported by
a NASA New Investigator Program grant award to M. Simons
Riverbed sediment classification using multi-beam echo-sounder backscatter data
No full textA method has recently been developed that employs multi-beam echo-sounder backscatter data to both obtain the number of sediment classes and discriminate between them by applying the Bayes decision rule to multiple hypotheses [ Simons and Snellen, Appl. Acoust. 70, 1258–1268 (2009) ]. In deep water, the number of scatter pixels within the beam footprint is large enough to ensure Gaussian distributions for the backscatter strengths and to increase the discriminative power between acoustic classes. In very shallow water (<10?m), however, this number is too small. This paper presents an extension of this high-frequency methodology for these environments, together with a demonstration of its performance using backscatter data from the river Waal, The Netherlands. The objective of this work is threefold. (i) Increasing the discriminating power of the classification method: high-resolution bathymetry data allow precise bottom slope corrections for obtaining the true incident angle, and the high-resolution backscatter data reduce the statistical fluctuations via an averaging procedure. (ii) Performing a correlation analysis: the dependence of acoustic backscatter classification on sediment physical properties is verified by observing a significant correlation of 0.75 (and a disattenuated correlation of 0.90) between the classification results and sediment mean grain size. (iii) Enhancing the statistical description of the backscatter intensities: angular evolution of the K-distribution shape parameter indicates that the riverbed is a rough surface, in agreement with the results of the core analysis.Remote SensingAerospace Engineerin
Aircraft noise calculation and synthesis in a non-standard atmosphere
No full textThe atmosphere modifies the emitted sound waves of an aircraft during propagation and is therefore important in the calculation of noise contours or synthesis. Noise contours present the resulting noise levels on the ground and are, as such, often applied for regulatory purposes. Aircraft noise synthesis is a technique that allows to transform a calculated prediction into audible sound that can be experienced in a virtual reality environment. Noise synthesis techniques allow people to be subjected to aircraft, routes or procedures that are still being designed. This dissertation describes recent research to improve the modeling of atmospheric propagation effects in aircraft noise contours as well as aircraft noise synthesis. Multi-event noise contours are usually calculated with standardized models that take non-standard propagation into account in an empirical fashion. A propagation algorithm was developed to augment such a model. Signal processing steps can be applied to transform a source noise prediction into an audible result. Furthermore, such steps can be utilized to apply propagation effects to a source noise signal. For a non-standard atmosphere this is not trivial. The role of a non-standard atmosphere is described by a dedicated simulation framework developed in this dissertation. The framework is applied to a flyover to demonstrate the effects associated with multiple ray paths and shadow zones. Besides demonstrating non-standard atmospheric effects, the framework was used to create synthesized results of actual flyovers near an airport. Subsequently, a comparison between measured results and synthesized results was executed. Furthermore, a method was designed to include the effect of turbulence-induced coherence loss of the direct and ground reflected ray in noise synthesis.Aircraft Noise & Climate EffectsAerospace Engineerin
A K-theoretic approach to Chern-Cheeger-Simons invariants
No full textsummary:The aim of this paper is to construct a natural mapping \check C\sb k, , from the multiplicative -theory of a differential manifold , associated to the trivial filtration of the de Rham complex, as defined by {\it M. Karoubi} in [C. R. Acad. Sci., Paris, S\'er. I 302, 321-324 (1986; Zbl 0593.55004)] to the odd cohomology H\sb s\sp{2k-1} (X;C\sp*). By using this mapping, the author associates to any flat complex vector bundle on characteristic classes \check C\sb k(E) \in H\sb{dR}\sp{2k-1} (X;C\sp*) analogous to the classes studied by {\it S. Chern}, {\it J. Cheeger} and {\it J. Simons} in [Differential characters and geometric invariants, in `Geometry and topology', Lect. Notes Math. 1167, 50-80 (1985; Zbl 0621.57010), Characteristic forms and geometric invariants, Ann. Math., II. Ser. 99, 48-69 (1974; Zbl 0283.53036)]
Sediment classification using Sub-bottom profiler
No full textSub bottom profilers are commonly used as mapping tool for the seafloor and sub-bottom structure in the upper few meters of the seafloor. Their recent enhanced performance in terms of resolution adds the potential to classify the sediment layers as well. In this research, the seabed surface and sub layers classification are investigated using model based techniques. The remote sediment classification technique of the seabed surface is achieved by matching the back scatter measurements to the predicted backscatter intensity of the model. The model simulates the returned signals of a monostatic sub bottom profiler operating at 100 kHz. The back scattering strength in the angle domain is estimated using the APL-UW backscattering model. The matching procedure was applied on averaged echo envelopes performed by Hilbert transform. The averaging process is essential to reduce the stochastic variability of the acquired data. The sub layers data was obtained by operating frequencies of (5, 10 and 15 kHz). The layer classification was achieved by estimating the geoacoustic parameters such as reflectivity and impedance contrast. Two techniques were investigated based on a reflectivity model. The first technique is an extension work of D.Simons [11] which aims to estimate the reflection coefficients via the received and transmitted energy ratio. The second technique is an implementation of a similar approach but applies the attenuation on the received frequency components in place of the nominal components. Both models accounted for energy propagation and its corresponding geometrical and sediment attenuation losses. The classification techniques were carried out to a dataset that was acquired in the Baltic Sea near Rostock in 2004. The acquired dataset is characterized by various bottom types such as mud, sand and coarse sediments. The general description of the acquired areas was used as a reference for the final results. Due to the lack of core samples, the classification was evaluated by comparing the results of the backscatter to the energy model. The results were consistent with the general description of the dataset. However, the matching process of the backscatter model is a cumbersome and very sensible to the envelope averaging technique. Averaging the reflected signals from the soft sediments has to ensure to preserve the surficial and volume back scatter information. On the other hand, at rough surfaces, the late arrivals are likely to be irregular reflections or noise that has to be averaged to avoid ambiguous results. The initial results of sub layers reflection models were consistent with the data description. However, due to the high resolution of the sub bottom profile, the computation procedure can easily fail by missing sub layers. In order to reduce the probability of missing layers, an overlapping window concept was implemented, where the reflection coefficients are estimated at shorter intervals. The methods investigated here leaves room for further optimization through model adjustment such as signal interference, backscatters and error propagation.GeomaticsAerospace Engineerin
Mechanisms of top-down facilitation in perception of visual objects studied by fMRI
No full textPrior knowledge regarding the possible identity of an object facilitates its recognition from a degraded visual input, though the underlying mechanisms are unclear. Previous work implicated ventral visual cortex but did not disambiguate whether activity-changes in these regions are causal to or merely reflect an effect of facilitated recognition. We used functional magnetic resonance imaging to study top-down influences on processing of gradually revealed objects, by preceding each object with a name that was congruent or incongruent with the object. Congruently primed objects were recognized earlier than incongruently primed, and this was paralleled by shifts in activation profiles for ventral visual, parietal, and prefrontal cortices. Prior to recognition, defined on a trial-by-trial basis, activity in ventral visual cortex rose gradually but equivalently for congruently and incongruently primed objects. In contrast, prerecognition activity was greater with congruent priming in lateral parietal, retrosplenial, and lateral prefrontal cortices, whereas functional coupling between parietal and ventral visual (and also left lateral prefrontal and parietal) cortices was enhanced in the same context. Thus, when controlling for recognition point and stimulus information, activity in ventral visual cortex mirrors recognition success, independent of condition. Facilitation by top-down cues involves lateral parietal cortex interacting with ventral visual areas, potentially explaining why parietal lesions can lead to deficits in recognizing degraded objects even in the context of top-down knowledge
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