Large amplitude vibrations and damage detection of rectangular plates

In this work, geometrically nonlinear vibrations of fully clamped rectangular plates are used to study the sensitivity of some nonlinear vibration response parameters to the presence of damage. The geometrically nonlinear version of the Mindlin plate theory is used to model the plate behaviour. Damage is represented as a stiffness reduction in a small area of the plate. The plate is subjected to harmonic loading with a frequency of excitation close to the first natural frequency leading to large amplitude vibrations. The plate vibration response is obtained by a pseudo-load mode superposition method. The main results are focussed on establishing the influence of damage on the vibration response of the plate and the change in the time-history diagrams and the Poincaré maps caused by the damage. Finally, a criterion and a damage index for detecting the presence and the location of the damage is proposed. The criterion is based on analysing the points in the Poincaré sections of the damaged and healthy plate. Numerical results for large amplitude vibrations of damaged and healthy rectangular and square plates are presented and the proposed damage index for the considered cases is calculated. The criterion demonstrates quite good abilities to detect and localize damage.     

Magnetic properties and magnetocaloric effects in ferrimagnetic compounds

Magnetic properties and magnetocaloric effects were studied in (Gd_xY_1?x)₃Co₁₁B₄ ferrimagnetic compounds. Rather high values of the entropy changes were shown in large temperature ranges. The ΔS values were correlated with high temperature dependences of resultant magnetizations determined mainly by the gadolinium sublattice one. Large relative cooling power was also shown.     

Synthesis of Amine Derivatives of the Polyhedral Borane Anion [B(20)H(18)](4)(-)

Ethylenediamine (en) reacts with the polyhedral borane anion [n-B(20)H(18)](2)(-), in the presence or absence of strong nonnucleophilic auxiliary bases, to produce the [ae-B(20)H(17)(en)](3)(-) anion. In either case, substitution is accompanied, to an approximately equal extent, by reduction of the starting material to form [a(2)()-B(20)H(18)](4)(-). As found with similar substituted systems derived from this 20-boron structure, [ae-B(20)H(17)(en)](3)(-) may be conveniently rearranged to the [a(2)()-B(20)H(17)(en)](3)(-) anion. A more convenient synthesis of the known [ae-B(20)H(17)NH(3)](3)(-) ion, which employs acetonitrile as the source of the NH(3) ligand instead of liquid ammonia, is also described.     

Laser assisted selective chemical metalization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films

Thick aluminum oxide films are prepared on Al plates by anodizing. On the ceramic surface thus obtained a very thin Ag film is deposited via vacuum thermal evaporation. The Ag/Al₂O₃/Al samples prepared are irradiated by Nd:YAG laser through a suitable metal mask in order to remove the top metal film in the exposed areas. Thus, a negative silver image of the copied mask is obtained. Further, the samples are processed in Ni electroless chemical bath activated by the rest of silver. All processing steps are studied by scanning electron microscopy (SEM). EDS X-ray mapping is applied to study the final distribution of Al and Ni in the processed areas. In addition, the DC conductivity of the fabricated Ni wires obtained is measured. The proposed new method for selective chemical deposition of electroconductive Ni onto laser microstructured Ag/Al₂O₃/Al samples is simple, versatile and not restricted to the metal/ceramic system studied as well as to the electroless deposited metal.     

Covalent Labeling of Nucleosides with VIII‐ and VI‐Valent Osmium Complexes

Osmium tetroxide complexes with nitrogen ligands [Os(VIII)L] have been widely applied as probes of the DNA structure and as electroactive labels of DNA. Here we describe the electrochemical behavior of Os(VIII)2,2‐bipyridine (Os, bipy)‐base‐labeled nucleosides. We show that electroactive label can be introduced also in the nucleoside ribose residues using six‐valent osmium complex. Cyclic voltammograms of sugar‐Os(VI)‐modified ribosides are similar but not identical to those of the base‐modified ribosides. Our results showing the electroactivity of sugar modified ribosides pave the way to facile end‐labeling of RNA.     

A novel technique for improving interferometric determination of emulsion film thickness by digital filtration

Determination of the thickness of emulsion films by using the film interferometric images is usually less accurate than that of foam films, due to the close values of the refractive indices of the liquid film and adjacent liquid phases (hence, low contrast and high level of noise at high magnification). A new technique was developed to improve the thickness determination by obtaining the interferometric images without directly filtering the illuminating light, as is usually done in the classical Scheludko interferometric technique. The new method then uses digital filtration during the off-line image post-processing to obtain monochromatic interferometric images required for the thickness determination. The technique was tested with foam films stabilised by sodium dodecyl sulfate and successfully applied to determine thickness of toluene-water-toluene emulsion films using the green and red digital filters. Results for emulsion film thickness determined by either the green or red digital filtration are comparable, thus validating the new technique developed here for emulsion films.     

Synthesis and reactivity of [(silox)2Mo=NR]2Hg (R=tBu, tAmyl; silox=OSitBu3): unusual thermal stability and ready nucleophilic cleavage rationalized by electronic factors

Treatment of (DME)Cl2Mo(=NR)2 (R=tBu, (1-tBu), tAmyl (1-tAmyl)) with 2 equiv of tBu3SiOH (siloxH) and 1 equiv of HCl produced (silox)2Cl2Mo=NR (R=tBu, (3-tBu), tAmyl (3-tAmyl)); subsequent reduction by Na/Hg afforded the Mo(V) chloride, (silox)2ClMo=NtBu (4-tBu), and the Mo(IV) mercury derivatives, [(silox)2Mo=NR]2Hg (R=tBu ((5-tBu)2Hg), tAmyl ((5-tAmyl)2Hg)). Reductions of 3-tBu and 3-tAmyl in the presence of L (L=PMe3, pyridine, 4-picoline) led to the isolation of adducts (silox)2(Me3P)Mo=NR (R=tBu (6-tBu), tAmyl (6-tAmyl)) and (silox)2L2Mo=NtBu (L=py (7-py), 4-pic (7-4-pic)). Single-crystal X-ray structural investigations of pseudo-tetrahedral 4-tBu, Hg-capped, pseudo-trigonal planar (5-tBu)2Hg, pseudo-tetrahedral 6-tBu, and trigonal bipyramidal 7-4-pic reveal that all possess a closed O-Mo-O angle when compared to the N=Mo-O angles. A molecular orbital rationale and supporting calculations suggest that this is a manifestation of the greater pi-donating ability of the imido relative to that of the siloxides. While the D(Mo-Hg) of [(HO)2Mo=NH]2Hg ((5')2Hg) was calculated to be 22.4 kcal/mol, (5-R)2Hg (R=tBu, tAmyl) are remarkably stable; (5-tBu)2Hg degraded in a first-order fashion with DeltaG=31.9(1) kcal/mol. In the presence of strong (L=PMe, pyridine, S8) or weak (L=2-butyne, ethylene, N2O, 1,4,7,10-tetrathiacyclododecane, 1,4,7,10,13,16-hexathiacyclooctadecane) nucleophiles, an enhanced rate of Mo-Hg bond cleavage was noted, with some of the former group generating adducts in <5 min; the products were 6-tBu, 7-py, (silox)2(S)Mo=NtBu (10-tBu), (silox)2Mo=NtBu(C2Me2) (8-tBu), (silox)2(C2H4)Mo=NtBu (11-tBu), (silox)2(O)Mo=NtBu (9-tBu), and a mixture of 10-tBu and 11-tBu, respectively. Some of these were independently prepared via substitution of 6-tBu. According to calculations and a molecular orbital rationale, dissociation of the Mo-Hg bond in (5-R)2Hg (R=tBu, tAmyl) is orbitally forbidden, and the addition of a nucleophile to the terminus of the Mo-Hg-Mo linkage mitigates the symmetry requirements. The mechanism of thermal degradation was studied with mixed success. NMR spectroscopy revealed imido exchange between (5-tBu)2Hg and (5-tAmyl)2Hg during an initial induction period and a subsequent rapid exchange period that implicated free 5-R (R=tBu, tAmyl). Further crossover studies revealed siloxide exchange as an additional complication.     

W6S8] octahedral tungsten clusters functionalized with thiophene derivatives: toward polymerizable building blocks

The functionalization of octahedral [W(6)S(8)] clusters with a family of phosphino-thiophene ligands has been investigated with the goal of synthesizing extended networks of [W(6)S(8)] units covalently linked to one another through thiophene-conjugated bridges. In addition to new phosphino-thiophene ligands, eight clusters were synthesized and characterized by (1)H and (31)P NMR spectroscopies, elemental analysis, and UV-vis absorption. These clusters are formulated [W(6)S(8)(T-PPh(2))6] (1a), [W(6)S(8)(T-PEt(2))(6)] (1b), [W(6)S(8)(2T-PPh(2))(6)] (2a), [W(6)S(8)(2T-PEt(2))(6)] (2b), [W(6)S(8)(3T-PPh(2))(6)] (3a), [W(6)S(8)(3T-PEt(2))(6)] (3b), [W(6)S(8)((2T)(3)P)(6)] (4), and [W(6)S(8)(2EDOT-PEt(2))(6)] (5) (T = thiophene and EDOT = 3,4-ethylenedioxythiophene). The molecular structure of six of them has been obtained by single-crystal X-ray diffraction analysis. All of them crystallize in the P1 triclinic space group except 3b, which has the P2(1)/c monoclinic symmetry. The redox behavior of both the ligands and the corresponding functionalized clusters has been investigated by cyclic voltammetry. An attempt to electropolymerize these species is also reported.     

A Novel Method for Surface Free-Energy Determination of Powdered Solids

Interfacial solid/liquid interactions play a crucial role in wetting, spreading, and adhesion processes. In the case of a flat solid surface, contact angle measurements are commonly utilized for the determination of the solid surface free energy and its components. However, if such a surface cannot be obtained, then the contact angle can not be measured directly. Usually methods based on imbibition of probe liquids into a thin porous layer or column are applied. In this paper a novel method, also based on the capillary rise, is proposed for the solid surface free-energy components determination. Actually, it is a modification of the thin column wicking method; similar theoretical background can be applied together with that appropriate for the capillary rise method of liquid surface tension determination. The proposed theoretical approach and procedure are verified by using single glass capillaries, and then alumina and ground glass powders were used for the method testing. Thus obtained surface free-energy components for these solids, for both glass and alumina, agree well with the literature values.