The mechanics of crack tip plasticity in dynamic crack growth is considered as it influences two modes of dynamic fracture—cleavage and micro-void nucleation, growth and coalescence. The subject is approached using both the continuum theory of visco-plasticity and dislocation dynamics. The viewpoint underlying each approach is that the crack is traveling through material with a relatively high density of pre-existing mobile dislocations. Analysis is directed at discovering the role played by the associated rate-dependent plasticity in establishing conditions for dynamic crack propagation. The theory is far from complete, but the contents of the paper should serve to aid understanding of basic material fracture phenomena, such as cleavability and the ductile-brittle transition, as well as provide a background for the engineering theory of dynamic fracture.
No abstract is provided for this article.
It is estimated that at least 29.1 million Americans, or 9.3% of the US population, currently have diabetes (1), a disease characterized by impaired insulin action and/or production. Although type 2 diabetes (T2D),4 which accounts for >90% of diagnosed diabetes, is largely predictable through anthropometric, lifestyle, and clinical factors, and is preventable through diet and lifestyle modifications, the metabolic pathways underlying its development and progression are incompletely understood. The rapidly developing area of metabolomics, which is designed to quantitatively profile a large number of small molecules in cells or biofluids, has emerged as a promising approach to elucidate altered metabolic pathways and discover novel biomarkers in T2D. The past several years have seen the initial success of metabolomics in identifying novel biomarkers for insulin resistance and T2D. In 2009, Newgard et al. (2) compared 131 targeted metabolites between 74 obese and 67 lean subjects and found that plasma concentrations of branched-chained amino acids (BCAAs) were strongly correlated with obesity and insulin resistance. In 2011, Wang et al. (3) measured a panel of 61 metabolites and found that 5 BCAAs and aromatic amino acids (i.e., isoleucine, leucine, valine, tyrosine, and phenylalanine) were predictive of developing diabetes in the Framingham Offspring Study and the Malmo Diet and Cancer Study. In 2012, Wang-Sattler et al. (4) quantified 140 metabolites in 4297 fasting serum samples in the Cooperative Health Research in the Region of Augsburg cohort and found that the concentrations of metabolites [i.e., lower values of glycine and lysophosphatidylcholine (18:2), as well as higher values of acetylcarnitine] predicted impaired glucose tolerance 7 years before disease onset. Meanwhile, Cheng et al. (5) observed significant associations of insulin resistance traits with metabolites glutamine and glutamate and the glutamine-to-glutamate ratio, from a panel of 45 metabolites in the Framingham Heart Study. Finally, Wang et al. …
This paper examines the influence of acylation of the Lys-ε-NH3+ groups of bovine carbonic anhydrase (BCA, EC 4.2.1.1) to Lys-ε-NHCOR (R = −CH3, −CH2CH3, and −CH(CH3)2, −CF3) on the rate of denaturation of this protein in buffer containing sodium dodecyl sulfate (SDS). Analysis of the rates suggested separate effects due to electrostatic charge and hydrophobic interactions. Rates of denaturation (kAc,n) of each series of acylated derivatives depended on the number of acylations (n). Plots of log kAc,n vs n followed U-shaped curves. Within each series of derivatives, rates of denaturation decreased as n increased to ∼7; this decrease was compatible with increasingly unfavorable electrostatic interactions between SDS and protein. In this range of n, rates of denaturation also depended on the choice of the acyl group as n increased to ∼7, in a manner compatible with favorable hydrophobic interactions between SDS and the −NHCOR groups. As n increased in the range 7 < n < 14, however, rates of denaturation stayed approximately constant; analysis suggested that these rates were compatible with an increasingly important contribution to denaturation that depended both on the net negative charge of the protein and on the hydrophobicity of the R group. The mechanism of denaturation thus seems to change with the extent of acylation of the protein. For derivatives with the same net electrostatic charge, rates of denaturation increased with the acyl group (by a factor of ∼3 for n ∼ 14) in the order CH3CONH− < CH3CH2CONH− < (CH3)2CHCONH− < CF3CONH−. These results suggested that the hydrophobicity of CF3CONH− is slightly greater (by a factor of <2) than that of RHCONH− with similar surface area.
The effect of small imperfections on the buckling of continuous structures loaded into the plastic range is studied. A simple model study is presented and several additional examples are discussed. The rôle of the load at which elastic unloading first occurs is emphasized, and a general asymptotic analysis is given for the behavior prior to the onset of elastic unloading for a class of elastic-plastic solids subject to loads characterized by a single load parameter. Asymptotic imperfection-sensitivity formulae are obtained whose features are similar to analogous formulae for elastic structures.
Abstract Background Quantitative lipoprotein analytics using nuclear magnetic resonance (NMR) spectroscopy is currently commonplace in large-scale studies. One methodology has become widespread and is currently being utilized also in large biobanks. It allows the comprehensive characterization of 14 lipoprotein subclasses, clinical lipids, apolipoprotein A-I and B. The details of these data are conceptualized here in relation to lipoprotein metabolism with particular attention on the fundamental characteristics of subclass particle numbers, lipid concentrations and compositional measures. Methods and Results The NMR methodology was applied to fasting serum samples from Northern Finland Birth Cohorts 1966 and 1986 with 5651 and 5605 participants, respectively. All results were highly consistent between the cohorts. Circulating lipid concentrations in a particular lipoprotein subclass arise predominantly as the result of the circulating number of those subclass particles. The spherical lipoprotein particle shape, with a radially oriented surface monolayer, imposes size-dependent biophysical constraints for the lipid composition of individual subclass particles and inherently restricts the accommodation of metabolic changes via compositional modifications. The new finding that the relationship between lipoprotein subclass particle concentrations and the particle size is log-linear reveals that circulating lipoprotein particles are also under rather strict metabolic constraints for both their absolute and relative concentrations. Conclusions The fundamental structural and metabolic relationships between lipoprotein subclasses elucidated in this study empower detailed interpretation of lipoprotein metabolism. Understanding the intricate details of these extensive data is important for the precise interpretation of novel therapeutic opportunities and for fully utilizing the potential of forthcoming analyses of genetic and metabolic data in large biobanks.
