Performance of the generalized delta rule in structural damage detection

The paper examines the suitability of the generalized data rule in training artificial neural networks (ANN) for damage identification in structures. Several multilayer perceptron architectures are investigated for a typical bridge truss structure with simulated damage stares generated randomly. The training samples have been generated in terms of measurable structural parameters (displacements and strains) at suitable selected locations in the structure. Issues related to the performance of the network with reference to hidden layers and hidden. neurons are examined. Some heuristics are proposed for the design of neural networks for damage identification in structures. These are further supported by an investigation conducted on five other bridge truss configurations.

Phonons and fractons in sol-gel alumina: Raman study

We report Raman scattering from the boehmite, gamma-, delta- and alpha-phases of the alumina gel. Samples are characterized by transmission and scanning electron microscopy, X-ray diffraction and density measurements. The main Raman line in the boehmite phase is red-shifted as well as asymmetrically broadened with respect to that in the crystalline boehmite, signifying the nanocrystalline nature of the gel. Raman signatures are absent in the gamma- and delta-phases due to the disorder in cation vacancies. We also show that low frequency Raman scattering from the boehmite phase resembles that from a fractal network, characterized in terms of fraction dimension ($) over tilde d. Taking Hausdorff dimension D of the boehmite gel to be 2.5 (or 3.0), the value of ($) over tilde d is 1.33 +/- 0.02 (or 1.44 +/- 0.02), which is close to the theoretically predicted value of 4/3.

Intramolecular Reactivity - Keto Participation in the Hydrolysis of N-Methyl-N-(9-Oxobicyclo[3.3.1]Nonan-2-Alpha-YL) Morpholinium Iodide, and A Cannizzaro-Type Reaction of 3-(2-Oxocyclohexyl)Propanal

Mechanistic studies of two intramolecular processes, nucleophilic displacement of N-methylmorpholinium in N-methyl-N-{9-oxobicyclo[3,3,1]nonan-2 alpha-yl}morpholinium iodide, anchimerically assisted by keto carbonyl, and a Cannizzaro-type reaction of 3-(2-oxocyclohexyl)propanal, occurring via axial hydride transfer onto the cyclohexanone, are reported.

Activities in the spinel solid solution FeXMg1−XAl2O4

Abstract: Activities in the spinel solid solution FexMg1-xAl2O4 saturated with alpha-Al2O3 have been measured for the compositional range 0 < X < 1 between 1100 and 1350 K using a bielectrolyte solid-state galvanic cell, which may be represented as Pt, Fe + FexMg1-xAl2O4 + alpha-Al2O3//(Y2O3)ThO2/ (CaO)ZrO2//Fe + FeAl2O4 + alpha-Al2O3, Pt Activities of ferrous and magnesium aluminates exhibit small negative deviations from Raoult's law. The excess free energy of mixing of the solid solution is a symmetric function of composition and is independent of temperature: Delta G(E) = -1990 X(1 - X J/mol. Theoretical analysis of cation distribution in spinel solid solution also suggests mild negative deviations from ideality. The lattice parameter varies linearly with composition in samples quenched from 1300 K. Phase relations in the FeO-MgO-Al2O3 system at 1300 K are deduced from the results of this study and auxiliary thermodynamic data from the literature. The calculation demonstrates the influence of intracrystalline ion exchange equilibrium between nonequivalent crystallographic sites in the spinel structure on intercrystalline ion exchange equilibrium between the monoxide and spinel solid solutions (tie-lines). The composition dependence of oxygen partial pressure at 1300 K is evaluated for three-phase equilibria involving the solid solutions Fe + FexMg1-xAl2O4 + alpha-Al2O3 and Fe + FeyMg1-yO + FexMg1-xAl2O4. Dependence of X, denoting the composition of the spinel solid solution, on parameter Y, characterizing the composition of the monoxide solid solution with rock salt structure, in phase fields involving the two solid solutions is elucidated. The tie-lines are slightly skewed toward the MgAl2O4 corner.

A new strategy for the alpha-vinylation of ketones: Application to an enantioselective synthesis of sesquiterpene (+)-alpha-elemene

A new, simple and preparatively useful protocol for the construction of a-vinyl ketones, particularly those bearing a quaternary carbon centre, from the corresponding alkenes has been devised. Our four-step strategy consists of dichloroketene addition, base catalysed ring contraction to 'push-pull' cyclopropane esters, reduction and eliminative cyclopropane fragmentation to unravel the a-vinyl ketone moiety. The generality of this approach has been demonstrated with a few representative olefins and good regio- and stereocontrol has been observed. As an application of this methodology, an enantioselective synthesis of sesquiterpene hydrocarbon (+)-alpha-elemene (42) from R-(+)-limonene (43) has been accomplished.

Charge-ordering in manganates

Ordering of Mn3+ and Mn4+ ions occurs in the rare earth manganates of the general composition Ln(1-x)A(x)MnO(3) (Ln rare earth, A = Ca, Sr). Such charge-ordering is associated with antiferromagnetic and insulating properties. This phenomenon is to be contrasted with the ferromagnetic metallic behavior that occurs when double-exchange between the Mn3+ and Mn4+ ions predominates. Two distinct types of charge-ordering can be delineated. In one, a ferromagnetic metallic (FMM) state transforms to the charge-ordered (CO) state on cooling. In the other scenario, the CO state is found in the paramagnetic ground stale and there is no ferromagnetism down to the lowest temperatures. Magnetic fields transform the CO state to the FMM state, when the average radius of the A-site cations is sufficiently large ([r(A)] > 1.17 Angstrom). Chemical melting of the CO state by Cr3+ substitution in the Mn site is also found only when [r(A)] greater than or similar to 1.17 Angstrom. The effect of the size of the A-cations on the Mn-O-Mn angle is not enough to explain the observed variations of the charge-ordering temperature as well as the ferromagnetic Curie temperature T-c. An explanation based on a competition between the Mn and A-cation orbitals for sigma-bonding with the oxygen rho(sigma) orbitals is considered to account for the large changes in T-c and hence the true bandwidth, with [r(A]). Effects of radiation, electric field, and other factors on the CO state are discussed along with charge-ordering in other manganate systems. Complex phase transitions, accompanied by changes in electronic and magnetic properties, occur in manganates with critical values of(rA) Or bandwidth. Charge-ordering is found in layered manganates, BixCa1-xMnO3 and CaMnO3-delta.

Electronic conduction in LaNiO3-delta: the dependence on the oxygen stoichiometry delta

We report a systematic study of the electronic transport properties of the metallic perovskite oxide LaNiO3-delta as a function of the oxygen stoichiometry delta (delta less than or equal to 0.14). The electrical resistivity, magnetoresistance, susceptibility, Hall effect and thermopower have been studied, All of the transport coefficients are dependent on the value of delta. The resistivity increases almost exponentially as delta increases. We relate this increase in rho to the creation of Ni2+ with square-planar coordination. We find that there is a distinct T-1.5-contribution to the resistivity over the whole temperature range. The thermopower is negative, as expected for systems with electrons as the carrier, but the Hall coefficient is positive. We have given a qualitative and quantitative explanation for the different quantities observed and their systematic variation with the stoichiometry delta.

Hot deformation and microstructural evolution in an alpha(2)/O titanium aluminide alloy Ti-25Al-15Nb

Deformation processing and microstructural development of an alpha(2)/O aluminide alloy Ti-25Al-15Nb (at.%) was studied in the temperature range of 950 to 1200 degrees C and strain rate range of 10(-3) to 100 s(-1). Regions of processing and instability were identified using dynamic materials model. Dynamic recrystallization (DRX) of alpha(2)/O phase and p phase were seen to occur in the region of 950 to 1050 degrees C/0.001 to 0.05 s(-1) and 1125 to 1175 degrees C/0.001 to 0.1 s(-1), respectively. Unstable flow was seen to occur in the region of 1050 to 1190 degrees C/10 to 100 s(-1). Thermal activation analysis showed that DRX of alpha(2)/O and beta was controlled by cross-slip.

Nonequilibrium phase transitions in a driven sandpile model

We construct a driven sandpile slope model and study it by numerical simulations in one dimension. The model is specified by a threshold slope sigma(c), a parameter alpha, governing the local current-slope relation (beyond threshold), and j(in), the mean input current of sand. A non-equilibrium phase diagram is obtained in the alpha-j(in) plane. We find an infinity of phases, characterized by different mean slopes and separated by continuous or first-order boundaries, some of which we obtain analytically. Extensions to two dimensions are discussed.z

Thermodynamic properties of LaFeO3-delta and LaFe12O19

The standard Gibbs energies of formation of lanthanum orthoferrite (LaFeO3-delta) and hexaferrite (LaFe12O19)were determined using solid-state electrochemical cells incorporating yttria-stabilized zirconia as the electrolyte and pure oxygen gas at ambient pressure as the reference electrode. From emf of the solid-state cell, the Gibbs energy of formation of nonstoichiometric orthoferrite (LaFeO3-delta) is obtained. To derive values for the stoichiometric phase, variation of the oxygen nonstoichiometric parameter with oxygen partial pressure was measured using thermogravimetry under controlled gas mixtures. The results obtained for LaFeO3 and LaFe12O19 can be summarized by the following equations, which represent the formation of ternary oxides from their component binary oxides: 1/2 La2O3 + 1/2 Fe2O3 -> LaFeO3: Delta G degrees (LaFeO3) (+/- 450) (J mol(-1)) = -62920 - 2.12T (K), and 1/2 La2O3 + 9/2Fe(2)O(3) + Fe3O4 -> LaFe12O19; Delta G degrees (LaFe12O19) (+/- 200) (J mol(-1)) = -103900 + 21.25T (K). These data are discussed critically in comparison with thermodynamic values reported in the literature from a variety of measurements. The values obtained in this study are consistent with calorimetric entropy and enthalpy of formation of the perovskite phase and with some of the Gibbs energy measurements reported in the literature. For the lanthanum hexaferrite (LaFe12O19) there are no prior thermodynamic measurements for comparison. (c) 2011 Elsevier B.V. All rights reserved.

Photolysis of arene chromium tricarbonyl complexes in presence of amine-boranes: Observation of sigma-borane complexes in solution

Activation of the B-H sigma-bond of amine-boranes on the chromium(0) center of arene chromium tricarbonyl complexes (eta(6)-arene) Cr(CO)(3) (arene = fluorobenzene, 1a; benzene, 1b and mesitylene, 1c) has been studied. Photolysis of 1b in presence of ammonia-borane (H3N center dot BH3, AB) and tert-butylamine-borane ((BuH2N)-Bu-t center dot BH3, TBAB) resulted in H-2 evolution and precipitation of a BNHx polymer. On the other hand, photolysis in the presence of trimethylamine-borane (Me3N center dot BH3, TMAB) resulted in the formation of a sigma-borane complex (2) along with Cr(CO)(5)(eta(1)-HBH2 center dot NMe3) (3). The sigma-borane complexes (eta(6)-arene) Cr-( CO)(2)(eta(1)-HBH2 center dot NMe3) (arene = fluorobenzene, 2a; benzene, 2b and mesitylene, 2c) were characterized in solution by H-1, B-11, and C-13 NMR spectroscopy. Electron withdrawing substituents on the arene ring provide the more stable sigma-borane moiety in this series of complexes. (C) 2011 Elsevier B.V. All rights reserved.

On the existence of a nickel hydroxide phase which is neither alpha nor beta

A novel phase of nickel hydroxide with an average interlayer spacing 5.4-5.6 Angstrom has been synthesized which is neither ct nor beta type but is an interstratification of both. It ages to the beta form in strong alkali. These observations have implications on the dissolution-reprecipitation mechanism suggested for the alpha-->beta transformation of nickel hydroxide.

Processing map for the hot working of near-alpha titanium alloy 685

Using a dynamic materials model, processing and instability maps have been developed for near-alpha titanium alloy 685 in the temperature range 775-1025 degrees C and strain-rate range of 0.001-10 s(-1) to optimise its hot workability. The alloy's beta-transus temperature lies at about 1020 degrees C. The material undergoes superplasticity with a peak efficiency of 80% at 975 degrees C and 0.001 s(-1), which are the optimum parameters for alpha-beta working. The occurrence of superplasticity is attributed to two-phase microduplex structure, higher strain-rate sensitivity, low flow stress and sigmoidal variation between log flow stress and log strain rate. The material also exhibits how localisation due to adiabatic shear-band formation up to its beta-transus temperature with strain rates greater than 0.02 s(-1) and thus cracking along these regions. (C) 1997 Published by Elsevier Science S.A.

A Change in the 3(10)- to alpha-Helical Transition Point in the Heptapeptides Containing Sulfur and Selenium

Crystal structures of three heptapeptides Boc-Ala-Leu-Aib-XXX-Ala-Leu-Aib-OMe (where XXX = methionine in peptide A, selenomethionine in peptide B, and S-benzyl cysteine in peptide C) reveal mixed 3(10)-/alpha-helical conformations with R factors of 6.94, 5.79, and 5.98, respectively. All the structures were solved in the P2(1)2(1)2(1) space group. 3(10)- to a-helical transitions are observed in all of these peptides. The helices begin as a 3(10)-helical segment at the N-terminus and then transit for peptides A and C at residue Aib(3) carbonyl (O(3)), while for peptide B the transition occurs at residue Leu(2) carbonyl oxygen (O(2)). There are water molecules associated in the crystal of each of these peptides and they form different types of hydrogen bonding patterns in each crystal. The observations suggest that 3(10)- to alpha-helical transition is sequence dependent in these short heptapeptide sequences.

Stereocontrolled synthesis of (+/-)-alpha-pinguisene and (+/-)-pinguisenol

Total synthesis of (+/-)-alpha-pinguisene 1 and (+/-)-pinguisenol 2, employing an orthoester Claisen rearrangement and an intramolecular diazo ketone cyclopropanation reaction for the stereospecific construction of vicinal quaternary carbon atoms, is described.