Scale-effects on mean and standard deviation of the mechanical properties of condensed matter: an energy-based unified approach

The size effects on the mean values of the mechanical properties of condensed matter and on the related variances are analysed by means of a unified approach based on the multiscale character of energy dissipation. In particular, the scaling law for fragmentation energy density is obtained taking into account the self-similarity of fragments. It is based on a generalization of the three classical comminution laws that has been performed to evaluate the energy dissipation, computing volume and surface area of the particles for one- two- and three-dimensional fragmented objects. The result is general and can be applied to different fractal energy dissipation mechanisms, e.g., plasticity. Based on this approach, the scaling laws for mean and standard deviation values of the main mechanical properties of materials can be derived, like Young's and shear elastic moduli, ultimate normal and shear stresses and strains, fracture energy and toughness.     

Investigations of delamination criticality and the transferability of growth criteria

This article describes a study of delamination growth along 0 °/0 °, 0 °/ 5 °, ± 5 °, and 0 °/90 ° interfaces sandwiched between unidirectional carbon fibre/epoxy composite material. Relationships between damage criticality, growth rate and acoustic emission activity for delamination growth have been studied and the transferability of results from laboratory coupons to composite structural elements has been examined. Two types of coupon tests, conventional delamination beams and rigidly loaded single edge notched strips, have been compared for different mode ratios. Comparative tests have been made on buckling-induced delamination in plates. A graphite crack gauge has been used to measure delamination length and growth rate, ranging from 0.05–2000 m/s. Damage growth was also followed using visual, ultrasonic C-scan, X-ray radiography, macro-video and acoustic emission measurements. Empirical evaluations of interlaminar toughness for delamination beams are made using the Irwin-Kies relation. Unstable growth is analysed using elasto-dynamic moving finite elements. Bucklinginduced delamination is analysed using plate/shell FE methods with growth/remeshing algorithms.     

Compound formation in the mercury-cadmium-tellurium-oxygen system

We report on compound formation in the system HgCdTeO. Samples were prepared by solid state reaction of mixtures of the binary oxide components. Specific phases were identified and characterized by X-ray and microprobe techniques. For some of these compounds small single crystals could be prepared and structural data of which are reported. Three groups of phases could be distinguished, most of them being of low symmetry, with Te in +4, +6, and in mixed oxidation states. The monotellurites HgTeO₃ and CdTeO₃ are structurally different and exhibit a large miscibility gap, whereas for the di-tellurites complete solid solution between CdTe₂O₅ and HgTe₂O₅ was found. As to the tellurates, phases with the compositions MTeO₄ and M₃Te₂O₉ (M = Hg, Cd) have been prepared. The Cd₃Te₂O₉-structure is stabilized by 30 mole% Hg. Another tellurate, monoclinic Hg₂TeO₄, was found to be isomorphous to the respective selenate and sulfate and is identical with the mineral magnolite. The interaction of Te₂O₅ with the metal oxides led to the formation of mixed valence compounds with both Te(+4) and Te(+6) of the types M₂Te₂O₇ and MTe₂O₆.     

Ischemic preconditioning prior to myocardial protection with cold blood cardioplegia in coronary surgery

OBJECTIVE: Encouraging results on myocardial preconditioning in experimental models of infarction, stunning or prolonged ischemia raise the question whether preconditioning techniques may enhance conventional cardioplegic protection used for routine coronary surgery. METHODS: A prospective clinical trial was conducted to investigate the effect of additional ischemic normothermic preconditioning prior to cardioplegic arrest applying cold blood cardioplegia in patients scheduled for routine coronary surgery (3 vessel disease, left ventricular ejection fraction > 50%). Two cross clamp periods of 5 min with the hearts beating in sinus rhythm were applied followed by 10 min of reperfusion, each (n = 7, group I). Inducing moderate hypothermia cold blood cardioplegia was delivered antegradely. In control groups, cold intermittent blood cardioplegia (n = 7, group II) was used alone. Coronary sinus effluents were analyzed for release of creatine kinase (CK), CK-MB, lactate, and troponin T at 1, 3, 6, 9, and 12 h. In addition, postoperative catecholamine requirements were monitored. RESULTS: The procedure was tolerated well, and no perioperative myocardial infarction in any of the groups studied occurred. Concentrations of lactate tended to be higher in group I, but this difference was not significant. In addition, no significant differences for concentrations of CK, CK-MB, and troponin T were found. Following ischemic preconditioning an increased dosage of dopamine was required within the first 12 h postoperatively (group I: 2.63 +/- 1.44 microg/kg/min, group II: 0.89 +/- 1.06 microg/kg/min). CONCLUSIONS: Combining ischemic preconditioning and cardioplegic protection with cold blood cardioplegia does not appear to ameliorate myocardial protection when compared to cardioplegic protection applying cold blood cardioplegia alone. Inversely, contractile function seemed to be impaired when applying this protocol of ischemic preconditioning.     

Implementation of a quiet hour: effect on noise levels and infant sleep states

It is necessary to decrease environmental stimuli in order to provide developmentally supportive care to the very low birthweight (VLBW) infant, thereby enhancing the sleep/wake cycle and possibly physiologic stability. The purpose of this study was to determine if it was possible to decrease the noise level in the Developmental Unit, and promote sleep states in infants on the unit. After determining control noise levels and infant state, the last hour of each shift was designated a Quiet Hour. During this time, noise levels were monitored in the room in five locations. Infant sleep states were also noted. The results indicate that noise levels decreased significantly on two of the three shifts. Fewer infants were crying during the Quiet Hour than the control period (2.4 vs 14.3 percent), and more were in deep or light sleep (84.5 vs 33.9 percent). This study demonstrates that noise levels in Developmental Units can be significantly decreased, and that the decreased noise levels positively impact infant state. By enhancing sleep states, nurses can enhance the long term developmental outcome of the VLBW infant. However, the reduction of noise is highly dependent on the collaborative efforts of all health care providers within the unit.