2,864 research outputs found
Foreword; Preface; Introduction
No full textIncludes a foreword, a preface, and an introduction written by John Kallenberg, a member of San Joaquin Valley Library System Administrative Council, Keith Boettcher and Yoshino [Tajiri] Hasegawa, members of San Joaquin Valley Library System.A Japanese American oral history project undertaken in 1979-1980, funded by the National Endowment for the Humanities and archived at the Fresno County Public Library
Physics of the Edwards-Anderson Spin Glass in Dimensions from Heuristic Ground State Optimization
No full textWe present a collection of simulations of the Edwards-Anderson lattice spin glass at to elucidate the nature of low-energy excitations over a range of dimensions that reach from physically realizable systems to the mean-field limit. Using heuristic methods, we sample ground states of instances to determine their energies while eliciting excitations through manipulating boundary conditions. We exploit the universality of the phase diagram of bond-diluted lattices to make such a study in higher dimensions computationally feasible. As a result, we obtain a verity of accurate exponents for domain wall stiffness and finite-size corrections that allow us to examine their dimensional behavior and their connection with predictions from mean-field theory. We also provide an experimentally testable prediction for the thermal-to-percolative crossover exponent in dilute lattices Ising spin glasses.12 pages, 4 figs, 1 table. Review summarizing several dispersed papers with improved figures, published version. Related information can be found at https://physics.emory.edu/faculty/boettcher
Numerical Results for Ground States of Spin Glasses on Bethe Lattices
No full textThe average ground state energy and entropy for +/- J spin glasses on Bethe
lattices of connectivities k+1=3...,26 at T=0 are approximated numerically. To
obtain sufficient accuracy for large system sizes (up to n=2048), the Extremal
Optimization heuristic is employed which provides high-quality results not only
for the ground state energies per spin e_{k+1} but also for their entropies
s_{k+1}. The results show considerable quantitative differences between
lattices of even and odd connectivities. The results for the ground state
energies compare very well with recent one-step replica symmetry breaking
calculations. These energies can be scaled for all even connectivities k+1 to
within a fraction of a percent onto a simple functional form, e_{k+1} = E_{SK}
sqrt(k+1) - {2E_{SK}+sqrt(2)} / sqrt(k+1), where E_{SK} = -0.7633 is the ground
state energy for the broken replica symmetry in the Sherrington-Kirkpatrick
model. But this form is in conflict with perturbative calculations at large
k+1, which do not distinguish between even and odd connectivities. We find
non-zero entropies s_{k+1} at small connectivities. While s_{k+1} seems to
vanish asymptotically with 1/(k+1) for even connectivities, it is
indistinguishable from zero already for odd k+1 >= 9.Comment: 11 pages, RevTex4, 28 ps-figures included, related papers available
at http://www.physics.emory.edu/faculty/boettcher
Synthesis of Chlorosilicates
No full textSteinhauer S, Boettcher T, Schwarze N, Neumann B, Stammler H-G, Hoge B. Synthesis of Chlorosilicates. Angewandte Chemie International Edition. 2014;53(48):13269-13272.Chlorosilicates represent important intermediates in S(N)2 reactions of chlorosilanes. They can be stabilized by the introduction of electron-withdrawing substituents. Salts of various (pentafluoroethyl)chlorosilicates have been isolated and structurally characterized
Investigating Hybrid Search with Eye-Tracking: A Replication of Drew, Boettcher, and Wolfe (2017)
No full textThis is a replication of Drew, T., Boettcher, S. E., & Wolfe, J. M. (2017). One visual search, many memory searches: An eye-tracking investigation of hybrid search. Journal of Vision, 17(11), 5-5.
This study investigates how three factors affect performance of visual search: (1) memory set size: the number of targets the participant must memorize and then search for; (2) visual set size: the number of distractors (not memorized) and targets on the screen; and (3) target presence. By measuring response times and eye-movement patterns, the study tests the hypothesis that observers make a single search through the visual image in a hybrid search. A hybrid search occurs when an observer is searching for one of a number of possible targets that they hold in memory.
We plan to run the same analyses as Drew et al. regarding behavioral results, eye-tracking results, and FVF analysis
Spectral equivalences, Bethe ansatz equations, and reality properties in PT-symmetric quantum mechanics
No full textThe one-dimensional Schrodinger equation for the potential x(6)+alphax(2)+l (l+1)/x(2) has many interesting properties. For certain values of the parameters I and a the equation is in turn supersymmetric (Witten) and quasi-exactly solvable (Turbiner), and it also appears in Lipatov's approach to high-energy QCD. In this paper we signal some further curious features of these theories, namely novel spectral equivalences with particular second- and third-order differential equations. These relationships are obtained via a recently observed connection between the theories of ordinary differential equations and integrable models. Generalized supersymmetry transformations acting at the quasi-exactly solvable points are also pointed out, and an efficient numerical procedure for the study of these and related problems is described. Finally we generalize slightly and then prove a conjecture due to Bessis, Zinn-Justin, Bender and Boettcher, concerning the reality of the spectra of certain PT-symmetric quantum mechanical systems
Pentacoordinate silicon(IV): cationic, anionic and neutral complexes derived from the reaction of NHC -> SiCl4 with highly Lewis acidic (C2F5)(2)SiH2
No full textBoettcher T, Steinhauer S, Neumann B, Stammler H-G, Roeschenthaler G-V, Hoge B. Pentacoordinate silicon(IV): cationic, anionic and neutral complexes derived from the reaction of NHC -> SiCl4 with highly Lewis acidic (C2F5)(2)SiH2. Chemical Communications. 2014;50(47):6204-6206.Addition of NHC -> SiCl4 to the highly Lewis acidic bis(pentafluoroethyl) silane ((C2F5)(2)SiH2) afforded the salt [(NHC)(2)SiCl2H][(C2F5)(2)SiCl3] with pentacoordinate silicon in the cation and the anion. The anion represents the first example of a chlorosilicate structurally characterized in the solid state. In this reaction, the long sought pentacoordinate NHC-adduct of silicochloroform was identified as an intermediate and its crystal structure is presented
The Cost-Optimal Optimization of public buildings in cold and warm climates: two case-studies in Germany and Italy
No full textDirective EU 844/2018, in the matter of energy performance of buildings and future goals of energy efficiency for the EU Member Countries, extends the standard of nearly zero-energy building goals to the existing building stock, with the mandatory aim of almost complete decarbonization of the whole sector within 2050, and thus a strong reduction of greenhouse gas pollution of about 80-95% compared to the levels of '90s. In this frame, the present study purposes the multi-objective optimizations of two office buildings, located in Berlin (Germany, European backcountry, "Cfb" climate in the classification of Köppen and Geiger) and Naples (Italy, Mediterranean coast, "Csa" climate classification), with the aim of finding the best trade-off between two couples of contrasting targets, representative of private and public interests, respectively: minimization of indoor thermal discomfort and operational costs, and minimization of indoor thermal discomfort and environmental impact. In addition, an investment cost analysis is performed by optimizing operational costs and total construction costs. The explored and investigated energy conservation measures, to apply during the building retrofit, involve the main levers of energy efficiency, and thus the building envelope, and the active energy systems. The results underline that the cost-optimal energy measures to apply during the building refurbishments deeply differ based on the building usage, the intensity of required indoor comfort, and depending on the climatic peculiarities and building construction technologies
Hysteretic response to different modes of ramping an external field in sparse and dense Ising spin glasses
No full textWe consider the hysteretic behavior of Ising spin glasses at for various modes of driving. Previous studies mostly focused on an infinitely slow speed by which the external field was ramped to trigger avalanches of spin flips by starting with destabilizing a single spin while few have focused on the effect of different driving methods. First, we show that this conventional protocol imposes a system size dependence. Then, we numerically analyze the response of Ising spin glasses at rates that are fixed as well, to elucidate the differences in the response. Specifically, we compare three different modes of ramping (, , and for constant ) for two types of spin glass systems of size , representing dense networks by the Sherrington-Kirkpatrick model and sparse networks by the lattice spin glass in dimensions known as the Edwards Anderson model. Depending on the mode of ramping, we find that the response of each system, in form of spin-flip avalanches and other observables, can vary considerably. In particular, in the -independent mode applied to the lattice spin glass, which is closest to experimental reality, we observe a percolation transition with a broad avalanche distribution between phases of localized and system-spanning responses. We explore implications for combinatorial optimization problems pertaining to sparse systems.8 pages, 7 figures, RevTex, final version. For related work, see https://physics.emory.edu/faculty/boettcher
Earthquake scaling relations for mid-ocean ridge transform faults
No full textAuthor Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): B12302, doi:10.1029/2004JB003110.A mid-ocean ridge transform fault (RTF) of length L, slip rate V, and moment release rate dot above M can be characterized by a seismic coupling coefficient χ = A E/A T, where A E ∼ dot above M/V is an effective seismic area and A T ∝ L 3/2 V −1/2 is the area above an isotherm T ref. A global set of 65 RTFs with a combined length of 16,410 km is well described by a linear scaling relation (1) A E ∝ A T, which yields χ = 0.15 ± 0.05 for T ref = 600°C. Therefore about 85% of the slip above the 600°C isotherm must be accommodated by subseismic mechanisms, and this slip partitioning does not depend systematically on either V or L. RTF seismicity can be fit by a truncated Gutenberg-Richter distribution with a slope β = 2/3 in which the cumulative number of events N 0 and the upper cutoff moment M C = μD C A C depend on A T. Data for the largest events are consistent with a self-similar slip scaling, D C ∝ A C 1/2, and a square root areal scaling (2) A C ∝ A T 1/2. If relations 1 and 2 apply, then moment balance requires that the dimensionless seismic productivity, ν0 ∝ inline equation 0/A T V, should scale as ν0 ∝ A T −1/4, which we confirm using small events. Hence the frequencies of both small and large earthquakes adjust with A T to maintain constant coupling. RTF scaling relations appear to violate the single-mode hypothesis, which states that a fault patch is either fully seismic or fully aseismic and thus implies A C ≤ A E. The heterogeneities in the stress distribution and fault structure responsible for relation 2 may arise from a thermally regulated, dynamic balance between the growth and coalescence of fault segments within a rapidly evolving fault zone.M.B. was supported by a NSF
Graduate Research Fellowship, a MIT Presidential Fellowship, and the
WHOI DOEI Fellowship. This research was supported by the Southern
California Earthquake Center. SCEC is funded by NSF Cooperative Agreement
EAR-0106924 and USGS Cooperative Agreement 02HQAG0008
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