Peeling behavior and spalling resistance of CFRP sheets bonded to bent concrete surfaces

In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer （CFRP） sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.     

Construction of bent functions via Niho power functions

A Boolean function with an even number n=2k of variables is called bent if it is maximally nonlinear. We present here a new construction of bent functions. Boolean functions of the form f(x)=tr(α₁x^d₁+α₂x^d₂), α₁,α₂,x∈F_2ⁿ, are considered, where the exponents d_i (i=1,2) are of Niho type, i.e. the restriction of x^d_i on F_2^k is linear. We prove for several pairs of (d₁,d₂) that f is a bent function, when α₁ and α₂ fulfill certain conditions. To derive these results we develop a new method to prove that certain rational mappings on F_2ⁿ are bijective.     

Structural characterization of [Fe(NO)(mnt)2] salts

The iron dithiolene compounds [Fe₂(mnt)₄]²⁻ [1]²⁻ and [Fe(NO)(mnt)₂]ⁿ (n = 1−, [2]¹⁻; n = 2−, [2]²⁻) ([mnt]²⁻ = maleonitriledithiolate = [(NC)₂C₂S₂]²⁻) have been characterized structurally by X-ray diffraction as their [Et₄N]⁺ salts at 100 K. Dianion [2]²⁻ is prepared from [2]¹⁻ by reduction with Na[Et₃BH] and is observed to have a bent Fe-NO angle at 149.9(5)° in contrast to the linear configuration of Fe-NO in [2]¹⁻ (180.0°). The change from linear to bent binding mode for NO, an increase of more than 0.1 Å in the Fe-N bond length, and the relative invariance of the Fe-S distances for [2]²⁻ versus [2]¹⁻ indicate that the NO ligand is the site of reduction. The [Et₃NH]⁺ complex of [2]¹⁻ was also identified by crystallography and found to have hydrogen bonding contacts between [Et₃NH]⁺ and the cyano nitrogen atom of an [mnt]²⁻ ligand. Furthermore, relatively close S?S contacts (3.602-3.615 Å) occur between [2]¹⁻ anions, which pack together in an offset, head-to-head fashion. These S?S contacts are absent in the structure of [Et₄N][2]. Infrared spectra show an energy decrease for, and a significant broadening of, the NO bond stretching absorption peak in [2]²⁻, which is consistent with a bent NO ligand sampling a range of conformations both by facile pivoting about the Fe-N axis and by a breathing of the Fe-NO angle.     

A Redox-Responsive Ferrocene-Based Capsule Displaying Unusual Encapsulation-Induced Charge-Transfer Interactions

A ferrocene-based capsule is spontaneously and quantitatively formed in water by the assembly of bent amphiphiles carrying two ferrocene units. The disassembly and assembly of the new organometallic capsule, with a well-defined and highly condensed ferrocene core, are demonstrated by chemical redox stimuli in a fully reversible fashion under ambient conditions. In contrast to previously reported multiferrocene assemblies, only the present capsule efficiently encapsulates typical organic/inorganic dyes as well as electron-accepting molecules in water. As a result, unusual host-guest charge-transfer (CT) interactions, displaying relatively wide absorption bands in the visible to near-infrared region (λ=650–1350 nm), are observed upon the encapsulation of acceptors (i.e., chloranil and TCNQ). The resultant encapsulation-induced CT interactions can be released by a redox stimulus through the disassembly of the capsule.