Carbon foam characterization tensile evaluation of carbon foam ligaments

A methodology for ligament isolation and specimen preparation for tensile testing of single ligaments from the unit cell of open-cell carbon foams has been successfully developed and implemented. Results are presented for ligaments of three different carbon foam designations. Two of them are reticulated vitreous carbon (RVC) foams of 20 and 45 pores-per- inch (ppi) coated with SiC by chemical vapor deposition (CVD) and the other is a RVC 20 ppi foam without coating. Scanning electron microscopy and digital imaging analysis is used to analyze the fracture surfaces posts tests. The ultimate strength of each ligament evaluated. Weibull statistics is used to describe the strength distribution of ligaments. While the distribution of strengths of the carbon foam ligaments (RVC) could be described with a one-population distribution, it is found that a two-population Weibull distribution is necessary to describe the distribution of strength of the SiC coated ligaments

Renormalization transformation of periodic and aperiodic lattices

In this work we introduce a similarity transformation acting on transfer matrices describing the propagation of elementary excitations through either periodic or Fibonacci lattices. The proposed transformation can act at two different scale lengths. At the atomic scale the transformation allows one to express the systems' global transfer matrix in terms of an equivalent on-site model one. Correlation effects among different hopping terms are described by a series of local phase factors in that case. When acting on larger scale lengths, corresponding to short segments of the original lattice, the similarity transformation can be properly regarded as describing an effective renormalization of the chain. The nature of the resulting renormalized lattice significantly depends on the kind of order (i.e., periodic or quasiperiodic) of the original lattice, expressing a delicate balance between chemical complexity and topological order as a consequence of the renormalization process

Theoretical assessment on the validity of the Wiedemann-Franz law for icosahedral quasicrystals

©2007 The American Physical Society. We warmly thank Tsunehiro Takeuchi for enlightening comments. We acknowledge M. V. Hernández for a critical reading of the paper. This work has been supported by the Universidad Complutense de Madrid through Project No. PR27/05-14014-BSCH.The validity of the Wiedemann-Franz law (WFL) for icosahedral quasicrystals belonging to the families AlCu(Fe,Ru) and AlPd(Mn,Re) is discussed. We exploit some characteristic features in the electronic structure in order to obtain closed analytical expressions for the transport coefficients in terms of the Hurwitz zeta function. Depending on the Fermi-level position, a systematic deviation from the ideal WFL is observed. The role of self-similar features in the electronic structure on the WFL is discussed. The obtained expression for the Lorenz function may be used in order to refine previous experimental results on the charge-carrier contribution to the thermal conductivity in these materials.Universidad Complutense de MadridDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

English as a Second Language at Californias Community Colleges: An Early Examination of AB 705 Reforms

California's community colleges began implementing Assembly Bill 705 (AB 705) reforms for credit English as a Second Language (ESL) in fall 2021, two years after implementing similar reforms in English and math. With a broad goal of improving success and equity for students pursuing degrees and transfers to four-year colleges, AB 705 reforms are already making notable transformations to ESL placement policies and the ESL courses into which English Learners (ELs) are placed. Building on our previous research, this study reports on the progress colleges have made in implementing AB 705 in ESL across the community college system