Strain mapping of a triple junction in nanocrystalline Pd

Aberration-corrected transmission electron microscopy was used to provide structural information on a triple junction in nanocrystalline Pd. This triple junction consists of two intersecting Σ3 twin boundaries with a Σ9 grain boundary and is connected to a quadruple point via the Σ9 grain boundary. A comprehensive strain analysis of this triple junction using geometric phase analysis is presented and compared with a molecular dynamics simulation. The main results are: (i) the strain field of the core of the triple junction shows dislocation character and extends over a distance of about 0.5 nm; (ii) the intersecting boundaries result in a net translation of , which corresponds to a Burgers vector of an dislocation in the fcc lattice; (iii) a disclination emerging from the triple junction along the Σ9 grain boundary is balanced by a disclination of opposite sign emerging from the quadruple point. Based on the observation that the core of the triple junction can be described by the strain field of a dislocation, its energy was estimated using to be about 1.7 × 10⁻⁹ J m⁻¹. The presence of a disclination dipole is thought to be essential for stabilization of the structure observed.     

Prioritizing test cases with string distances

Test case prioritisation aims at finding an ordering which enhances a certain property of an ordered test suite. Traditional techniques rely on the availability of code or a specification of the program under test. We propose to use string distances on the text of test cases for their comparison and elaborate a prioritisation algorithm. Such a prioritisation does not require code or a specification and can be useful for initial testing and in cases when code is difficult to instrument. In this paper, we also report on experiments performed on the “Siemens Test Suite”, where the proposed prioritisation technique was compared with random permutations and four classical string distance metrics were evaluated. The obtained results, confirmed by a statistical analysis, indicate that prioritisation based on string distances is more efficient in finding defects than random ordering of the test suite: the test suites prioritized using string distances are more efficient in detecting the strongest mutants, and, on average, have a better APFD than randomly ordered test suites. The results suggest that string distances can be used for prioritisation purposes, and Manhattan distance could be the best choice.     

Crystal growth of copper-rich ytterbium compounds: The predicted giant unit cell structures YbCu4.4 and YbCu4.25

Two new phases YbCu_4.4 and YbCu_4.25 are found as a result of careful phase diagram investigations. Between the congruent and peritectic formation of YbCu_4.5 and YbCu_3.5, respectively, the phases YbCu_4.4 and YbCu_4.25 are formed peritectically at 934(2) °C and 931(3) °C.Crystal growth was realised using a Bridgman technique and single crystalline grains of about 50–100 μm were analysed by electron diffraction and single crystal X-ray diffraction. Due to the only slight differences in both compositions and formation temperatures the growth of larger single crystals of a defined phase is challenging. The compounds YbCu_4.4 and YbCu_4.25 fit in ?ernýs [J Solid State Chem 2003;174:125] building principle {(RECu₅)_n·(RECu₂)} where RE = Yb with n = 4 and 3. YbCu_4.4 and YbCu_4.25 are based on AuBe₅/MgCu₂-type substructures and contain approximately 4570 and 2780 atoms per unit cell. The new phases close the gap in the series of known copper-rich rare-earth compounds for n = 1, 2 (DyCu_3.5, DyCu_4.0) and n = 5 (YbCu_4.5, DyCu_4.5).     

Surface functionalization by smart coatings: Stimuli-responsive binary polymer brushes

Heterogeneous binary polymer brushes consist of an assembly of polymer chains of two incompatible polymers that are attached by one end to the surface with sufficient grafting density. They have been investigated experimentally only for a short time. Those brushes can be used in the form of ultrathin polymeric layers as a versatile tool for surface engineering to tune physico-chemical surface characteristics as wettability, surface charge, chemical composition or morphology, and furthermore to create switchable and responsive surface properties. For the fabrication of these layers “grafting-from” (as radical polymerization at the interface) and “grafting-to” (as tethering of the polymer chains from solution) methods were developed and investigated in detail.