10,478 research outputs found
Quadratic operators used in deducing exact ground states for correlated systems: ferromagnetism at half filling provided by a dispersive band
Quadratic operators are used in transforming the model Hamiltonian (H) of one
correlated and dispersive band in an unique positive semidefinite form coopting
both the kinetic and interacting part of H. The expression is used in deducing
exact ground states which are minimum energy eigenstates only of the full
Hamiltonian. It is shown in this frame that at half filling, also dispersive
bands can provide ferromagnetism in exact terms by correlation effects .Comment: 7 page
Mechanical and GWP Assessment of Concrete Using Blast Furnace Slag, Silica Fume and Recycled Aggregate
Demolition waste and cement production is responsible for 36% of total waste produced on earth and 8% of the worlds CO2 emissions, respectively. Due to limited research on concrete mixes containing ternary cementitious mixes (Ground Granulated Blast-furnace Slag (GGBS) and Silica Fume (SF)) and demolition waste, the paper reviewed the mechanical properties of concrete, and structural performance of reinforced beams. Thereafter, life cycle analysis (LCA) was investigated to understand the true environmental impact, focusing on Global Warming Potential (GWP). Results show that recycled concrete aggregates (RCA) had no significant negative impact on the compressive strength, tensile strength, and modulus of rupture of concrete. The inclusion of GGBS and SF in mixes containing RCA eliminated any negative impact and for all mixes produced greater strengths in comparison to the control mix, due to the secondary reaction of Ca (OH)2 and pore refinement. The flexural behavior of the concrete beams with 0%, 25%, 50% and 100% RCA, 25% GGBS and 5% SF is similar. LCA results showed that replacing NA with 25%, 50% or 100% RCA has no significant impact on the GWP emissions. This is because of the similar emissions associated with manufacturing and processing of recycled and natural aggregates. However, replacing cement with 5% SF and 25% GGBS improves the GWP environmental response of concrete significantly. Additionally, natural aggregates have a higher GWP contribution than that of recycled concrete aggregates by almost 80% since the process of NA required quarry operation and transportation while the RCA are produced on site from an existing building waste
Intellectualism, Infiltration, and the Imaginary: The Challenge of Conservative Think Tanks in Developing Coherent Democratic Community
This paper extends the question “What should we be doing and what kinds of activities would we be engaged in during the time we take off to craft and assert ourselves as public intellectuals?” Kathleen Kesson and Jim Henderson provided us with historical background (and a delightful song parody) while Kent den Heyer challenges us to take two years off from the academy and engage in research that would better enable us to communicate with and influence those in positions of power. For the purpose of this paper, we wish to join with Kesson, Henderson, and den Heyer, if only momentarily, in crafting new ways to comprehend public intellectualism. To wit, what forms of immigration and infiltration can we imagine and craft to better position ourselves as part of the larger conversations concerning schools and society? We use the term “immigration” specifically to highlight the changing demographics and potentially changing nature of U.S. society in 2005. By sheer numbers, change occurs. In the most unlikely of places in rural Georgia, for example, “se habla Español” regularly appears on store fronts. Beyond sheer numbers, however, infiltration also means doing the grunt work of making our way into otherwise exclusive or elusive conversations where important decisions are made concerning schools and society. To immigrate and infiltrate effectively, however, will require imagination
The Metallicity Dependence of the Fourier Components of RR Lyrae Light Curves is the Oosterhoff/Arp/Preston Period Ratio Effect in Disguise
The correlation of particular Fourier components of the light curves of RR
Lyrae variables with metallicity, discovered by Simon and later by Kovacs and
his coworkers, is shown to have the same explanation as the period ratios
(period shifts in log P) between RRab Lyrae variables that have the same
colors, amplitudes, and light-curve shapes but different metallicities. A
purpose of this paper is to demonstrate that the model which predicts the
period-metallicity relations is the mediating parameters of colors, amplitudes,
and light-curve shapes also explains the Simon/Kovacs et al. correlation
between period, Phi_31, and metallicity. The proof is made by demonstrating
that the combination of the first and third phase terms in a Fourier
decomposition of RRab light curves, called Phi_31 by Simon and Lee, varies
monotonically across the RR Lyrae instability strip in the same way that
amplitude, color, and rise time vary with period within the strip. The premise
of the model is that if horizontal branches at the RR Lyrae strip are stacked
in luminosity according to the metallicity, then there necessarily must be a
log period shift between RR Lyraes with different metallicities at the same
Phi_31 values. However, there are exceptions to the model. (...)Comment: 17 pages, 8 figures, 1 table. Accepted for publication in The A
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