Method to Determine Tensile Stress Alterations in Prestressing Steel Strands by Means of an Eddy-Current Technique

The increased demand for reinforced concrete elements, for example, in bridge construction, requires long-term monitoring using multisensor techniques. Dynamic load inspection and maximum load detection is now an important requirement to avoid overstressing in light of past building failures in Germany, Austria, Poland, and Russia. Magnetoelastic force measurement of prestressed reinforcing concrete cables is also an investigative method for detecting steel failures (McMaster, 1986; Cullity, 1972; Fabo, 2002). An examination of coil impedance measurements made using eddy-current sensors placed on mechanically stressed steel specimens demonstrates a high dependency on the magnetoelastic effect. This stress measurement on prestressings or other reinforced concrete cables can be achieved by calibration of the material properties and stabilization of the magnetization state at the working point.     

Measurement and evaluation of display scattering

Abstract— A novel approach is introduced for the simple and effective measurement and evaluation of light scattering in general, and its application to electronic displays is described. The method is based on the measurement of the lateral distribution of reflected luminance with an imaging detector. After numerical transformation of the measured luminance distribution, we obtain the characteristics of the BRDF of the sample with high directional resolution within a limited range of inclination angles centered about the specular direction. The method is easy to implement and to carry out. Due to the absence of moving parts, it exhibits only little sensitivity with respect to variations of the geometry parameters and is thus very robust. This paper summarizes the basics of the approach, establishes the relation to conventional BRDF‐measuring methods, it introduces an implementation and presents some typical results for LCD‐monitors.     

Chinon-sensibilisierte photochemische Dediazonierung von Arendiazoniumsalzen

Photochemical Dediazoniation of Arene Diazonium Salts Catalyzed by Quinones The rate constants of the hydrogen abstraction of triplet-excited p-benzoquinone (BQ), duroquinone (DQ), p-chlorophenyl-p-benzoquinone (PQ) and 2, 5-di(p-chlorophenyl)-p-benzoquinone (P₂Q) from n-heptane and acetonitrile are determined by laser flash photolysis as well as the rate constants for the reactions with oxygen. The semiquinones formed are in equilibrium with their respective semiquinone anions; at pH 3 and pH 7, respectively, it was possible in acetonitrile/water solution to determine separately the rate constants for their disproportionation affording quinones and hydroquinones and the rate constants for electron transfer to p-chlorbenzene diazonium tetrafluoroborate. It comes out that the electron transfer to the diazonium compound only competes favorably with the disproportionation in the case of the semiquinone anions.     

Eigenschaften und thermische Reaktionen von Komplexen der Arendiazoniumsalze mit Kronenethern

Properties and Thermal Reactions from Complexes of Arene Diazonium Salts with Crown Ethers In contrast to 18-crown-6, the substituted crown ethers Benzo-18-crown-6, Dibenzo-18-crown-6, and Naphtho-18-crown-6 form in solution complexes with p-CH₃ C₆H₄ N₂⁺BF₄-characterized by a broad charge transfer absorption up to 550 nm. The formation constants lg K_c are 2,32 2,16 and 1,44 for Benzo-, Dibenzo-, and Naphtho-18-crown-6, respectively. Formation enthalpy ΔH = −7,5 kJ/mol and entropy ΔS = +18 J/K mol are measured in the case of p-Cl C₆H₄ N₂⁺BF₄⁻ and Dibenzo-18-crown-6 (20°). K_c depends on substituents in the arene ring of the diazonium salt; ϱ = +0,8. Thermal dediazoniation in the presence of Crown ethers results in high yields of the corresponding arene. This is explained by a fast radical chain reaction between the diazonium salt and the polyether (Meerwein-Reduction).     

Possible and certain keys for SQL

Driven by the dominance of the relational model and the requirements of modern applications, we revisit the fundamental notion of a key in relational databases with NULL. In SQL, primary key columns are NOT NULL, and UNIQUE constraints guarantee uniqueness only for tuples without NULL. We investigate the notions of possible and certain keys, which are keys that hold in some or all possible worlds that originate from an SQL table, respectively. Possible keys coincide with UNIQUE, thus providing a semantics for their syntactic definition in the SQL standard. Certain keys extend primary keys to include NULL columns and can uniquely identify entities whenever feasible, while primary keys may not. In addition to basic characterization, axiomatization, discovery, and extremal combinatorics problems, we investigate the existence and construction of Armstrong tables, and describe an indexing scheme for enforcing certain keys. Our experiments show that certain keys with NULLs occur in real-world data, and related computational problems can be solved efficiently. Certain keys are therefore semantically well founded and able to meet Codd’s entity integrity rule while handling high volumes of incomplete data from different formats.