: The current proceedings of the third conference, 'Fatigue 87', which was held at the University of Virginia, Charlottesville, covered a wide range of diverse views of the fundamental and applied aspects of fatigue. This includes questions of cyclic deformation, crack initiation and propagation, small cracks, crack closure, variable amplitude effects, and environmentally-influenced behavior. The proceedings should provide a comprehensive state-of-the-art review of the field, suitable for students, researchers and practising engineers alike.
Although healthy dentin is invariably hydrated in vivo, from a perspective of examining the mechanisms of fracture in dentin, it is interesting to consider the role of water hydration. Furthermore, it is feasible that exposure to certain polar solvents, e.g., those found in clinical adhesives, can induce dehydration. In the present study, in vitro deformation and fracture experiments, the latter involving a resistance-curve (R-curve) approach (i.e., toughness evolution with crack extension), were conducted in order to assess changes in the constitutive and fracture behavior induced by three common solvents - acetone, ethanol and methanol. In addition, nanoindentation-based experiments to evaluate the deformation behavior at the level of individual collagen fibers and ultraviolet Raman spectroscopy to evaluate changes in bonding were performed. The results indicate a reversible effect of chemical dehydration, with increased fracture resistance, strength, and stiffness associated with lower hydrogen bonding ability of the solvent. These results are analyzed both in terms of intrinsic and extrinsic toughening phenomena to further understand the micromechanisms of fracture in dentin and the specific role of water hydration.
Recognizing that the earthquake response of many buildings can be estimated by considering only the first two vibration modes in the response spectrum analysis (RSA) procedure a simplified response spectrum analysis (SRSA) procedure is presented. The SRSA method should be very useful in practical application because, although much simpler than the RSA method, it provides very similar estimates of design forces for many buildings. With the development of the SRSA, a hierarchy of four analysis procedures to determine the earthquake forces are available to the building designer: code‐type procedure, SRSA, RSA, and RHA (response history analysis). The criteria presented to evaluate the results from each procedure and to decide whether it is necessary to improve results by proceeding to the next procedure in the hierarchy use all the preceding computations and are, therefore, convenient.
Volterra series have been in the engineering literature for some time now, and yet there have been few attempts to measure Volterra kernels. This paper discusses techniques for measuring the Volterra kernels of weakly nonlinear systems. We introduce a new quick method for measuring the second Volterra kernel which is analogous to pseudonoise testing of a linear device. To illustrate the discussion we present an experimental example, an electro-acoustic transducer. Throughout the paper we emphasize the practical aspects of kernel measurement.
In this paper we seek to make headway on the question of what recovery from Covid-19 recession may look like, focusing on the duration of the recovery - that is, how long it will take to re-attain the levels of output and employment reached at the prior business cycle peak. We start by categorizing all post-1960 recessions in advanced countries and emerging markets into supply-shock, demand-shock and both-shock induced recessions. We measure recovery duration as the number of years required to re-attain pre-recession levels of output or employment. We then rely on the earlier literature on business cycle dynamics to identify candidate variables that can help to account for variations in recovery duration following different kinds of shocks. By asking which of these variables are operative in the Covid-19 recession, we can then draw inferences about the duration of the recovery under different scenarios. A number of our statistical results point in the direction of lengthy recoveries.
The Global Credit Crisis of 2008-09 has underscored the urgency of reforming the international financial architecture.While a number of short-term reforms are already in train, this paper contemplates more ambitious reforms of the international financial architecture that might be implemented over the next ten years.It proposes routinizing the expansion of IMF quotas and the conduct of exchange rate surveillance.It contemplates an expanded role for the SDR in international transactions, which would require someone-like the IMF-to act as market maker.It considers proposals for reimposing Glass-Steagall-like restrictions on commercial and investment banking, something that will have to be coordinated internationally to be feasible.Other proposals would require banks to purchase capital insurance; here the question is who would be on the other side of the market.Again there is likely to be a role for the IMF.Then there are arguments for a new agency or institution to deal with cross-border bank insolvencies.Any such entity will require staff support, which might plausibly come from the Fund.Finally, some insist that international colleges of regulators are not enough-that it is desirable to create a World Financial Organization (WFO) with the power to sanction members whose national regulatory policies are not up to international standards.A WFO will similarly need staff support, of which the IMF would be one possible source.All this of course presupposes meaningful IMF governance reform so that the institution has the legitimacy and efficiency to assume these additional responsibilities.The paper therefore concludes with some conventional and unconventional proposals for IMF governance reform.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Transition-metal boryl complexes of the form Cp'Fe(CO)LBcat and (CO)5MBcat, where Cp' = C5H5, C5Me5, M = Mn, Re, L = CO, PMe3, and cat = 1,2-O2C6H4, were synthesized by reaction of ClBcat with [Cp'Fe(CO)L]- or [M(CO)5]-. X-ray crystal structures of CpFe(CO)2Bcat, Cp*Fe(CO)2Bcat, and (CO)5MnBcat were obtained. Upon irradiation, these metal boryl complexes reacted with arenes and alkenes to form aryl- and vinylboronate ester products in moderate to high yields. Monosubstituted arenes with methyl, chloro, trifluoromethyl, methoxy, and dimethylamino substituents were used as substrates, and the resulting ratios of ortho- to meta- to para-substituted arene products were measured. No significant electronic effects were observed, indicating that the chemistry is not occurring through a typical electrophilic aromatic substitution pathway. Competition experiments between toluene and other substituted arenes were conducted. Reactivity differences were small, but anisole was found to have the fastest rate of reaction. Kinetic isotope effects were measured for the reaction of CpFe(CO)2Bcat, (CO)5MnBcat, or (CO)5ReBcat with benzene/benzene-d6 mixtures and were found to be 3.3 ± 0.4, 2.1 ± 0.1, and 5.4 ± 0.4, respectively. This difference in isotope effect along with differences in selectivities with substituted arsenic reagents rules out a mechanism by which a common free Bcat radical attacks free substrate. Several experiments were also conducted to probe for CO loss. A 13CO-labeling experiment, CO inhibition experiment, and PMe3 trapping experiment indicate that the mechanism most likely proceeds through irreversible CO loss to form a 16-electron intermediate. Functionalization of alkenes to form vinylboronate esters was also observed, and mechanistic studies showed the absence of a measurable kinetic isotope effect for reaction of CpFe(CO)2Bcat or (CO)5ReBcat with ethylene/ethylene-d4 mixtures or for reaction with ethylene-d2.
