Evaluation of the geopolymer/nanofiber interfacial bond strength and their effects on Mode-I fracture toughness of geopolymer matrix at high temperature

The present article has reported the effects of several nanofiller’s aspect ratio, length and interfacial strength on Mode-I fracture toughness (K_IC) of geopolymer as the matrix of continuous fibre reinforced composites. These nanofillers have been chosen based on the variations in the surface chemistry and nature of interfacial bonding with geopolymer, which include Carbon, Alumina and Silicon carbide. Geopolymer matrix was subjected to the addition of single volume fraction, 2% of each type of nanofiller with two aspect ratios, designated as nanoparticles and nanofibers. Notched beam flexure tests (SEVNB) of neat and each nanofiller reinforced samples suggest that, while baseline K_IC of neat geopolymer improved with heat treatment, nanofibers with high interfacial bond strength showed maximum capability in further improving K_IC. Among those nanofibers, 2 vol% Silicon Carbide Whisker (SCW) showed the largest improvement in K_IC of geopolymer, which is ~164%. After heat treatment at 650 °C, SCW reinforcement was also found to be effective, with only ~28% lower than the reinforcing performance at 250 °C, while the performance of Alumina Nanofiber reinforced geopolymer notably reduced. SEM and EDS analysis suggested that the inhomogeneity in neat geopolymer and length of nanofibers control the reinforcing capability as well as crack propagation resistance of geopolymer. For instance, minimum length of nanofillers to toughen this geopolymer at 250 °C was required as ~2 μm. The results further suggested that the sample failure occurred due to the dominance of tensile failure of nanofibers over the interfacial separation.     

Physics with heavy neutron-rich RIBs at the HRIBF

The Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory has recently produced the world's first post-accelerated beams of heavy neutron-rich nuclei. The first experiments with these beam are described, and the results discussed. B(E2;0⁺ → 2⁺) values for neutron-rich ^126,128Sn and ^132,134,136Te isotopes have been measured by Coulomb excitation in inverse kinematics. The results for ¹³²Te and ¹³⁴Te (N = 80, 82) show excellent agreement with systematics of lighter Te isotopes, but the B(E2) value for ¹³⁶Te (N = 84) is unexpectedly small. Single-neutron transfer reactions with a ¹³⁴Te beam on ^natBe and ¹³C targets at energies just above the Coulomb barrier have also been studied. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: radford@mail.phy.ornl.gov     

B(E2) upward arrow measurements for radioactive neutron-rich ge isotopes: reaching the N=50 closed shell

The B(E2;0(+)(1)-->2(+)(1)) values for the radioactive neutron-rich germanium isotopes (78,80)Ge and the closed neutron shell nucleus 82Ge were measured at the HRIBF using Coulomb excitation in inverse kinematics. These data allow a study of the systematic trend between the subshell closures at N=40 and 50. The B(E2) behavior approaching N=50 is similar to the trend observed for heavier isotopic chains. A comparison of the experimental results with a shell model calculation demonstrates persistence of the N=50 shell gap and a strong sensitivity of the B(E2) values to the effective interaction.     

Iconicity and contraction: a semiotic investigation of forms of algebraic generalizations of patterns in different contexts

The aim of this paper is to investigate the progressive manner in which students gain fluency with cultural algebraic modes of reflection and action in pattern generalizing tasks. The first section contains a short discussion of some epistemological aspects of generalization. Drawing on this section, a definition of algebraic generalization of patterns is suggested. This definition is used in the subsequent sections to distinguish between algebraic and arithmetic generalizations and some elementary naïve forms of induction to which students often resort to solve pattern problems. The rest of the paper discusses the implementation of a teaching sequence in a Grade 7 class and focuses on the social, sign-mediated processes of objectification through which the students reached stable forms of algebraic reflection. The semiotic analysis puts into evidence two central processes of objectification—iconicity and contraction.     

The epistemic,the cognitive,the human: a commentary on the mathematical working space approach

ZDM – Mathematics Education - This article is a commentary on the mathematical working space (MWS) approach and draws on the articles contained in this ZDM issue. The article is divided into...     

Observation of the weakly deformedvi 13 2/2 band in188Hg

High-Spin states in¹⁸⁸Hg have been investigated using the¹⁶⁸Er(²⁴Mg,4n) reaction. The rotation aligned vi ₁₃ ^2/2 band, which intersects the weakly oblate ground state band atI≈10, is observed up toI ^π =20⁺ with an isomeric 12⁺ level with T_1/2=134(15)ns. The coexisting strongly deformed band, built on the 825 keV 0⁺ level, is observed up to the 14⁺ state. The systematics of the vi ₁₃ ^2/2 rotation aligned bands is discussed.     

Superdeformation in144Eu

A ridge has been found in a - coincidence matrix obtained from the reaction¹²²Sn(²⁷Al,5n)¹⁴⁴Euat 142 MeV.The half-width of the valley is 59 keV,which is similar to the energy spacings in the superdeformed bands in ¹⁴³Euand ¹⁴²Sm.This indicates the existence of superdeformed bands in ¹⁴⁴Eu.This work was supported by the Natural Sciences and Engineering Research Council of Canada and AECL Research. We thank the crew and staff at TASCC for supplying the beams, and Dr.R.A.Wyss for use of the CSM and TRS codes.     

Pointed Hopf Algebras—from Enveloping Algebras to Quantum Groups and Beyond

A fundamental example of a pointed Hopf algebra is the universal enveloping algebra of a Lie algebra. This example finds its generalization in quantum groups. The class of pointed Hopf algebras is rather extensive and has been the subject of intense study. We recount some of the basic ideas in the development of the theory. A fundamental structure in the general theory is an analog of the enveloping algebra in a certain category, the Nichols algebra.