The effects of overloads on sustained-load crack growth in a nickel-base superalloy: part I—analysis

Analytical procedures are presented for predicting the retardation effects of cyclic overloads on the sustained load crack growth rate in Inconel 718 at 649°C. The Wheeler model is used in a crack growth computer program, CRACKS, by representing sustained load by equivalent fatigue cycles per unit time and an equivalent stress ratio, R. A new model, the exponential overload (EXPOL) model, is developed based on the concept of a crack growing at a retarded rate through an overload plastic zone. The analytical procedures use a minimum of empirical constants and are capable of accurately representing the time-dependent sustained load crack growth behavior with single or Multiple cyclic overloads.     

On a Smooth Dual Gap Function for a Class of Quasi-Variational Inequalities

A well-known technique for the solution of quasi-variational inequalities (QVIs) consists in the reformulation of this problem as a constrained or unconstrained optimization problem by means of so-called gap functions. In contrast to standard variational inequalities, however, these gap functions turn out to be nonsmooth in general. Here, it is shown that one can obtain an unconstrained optimization reformulation of a class of QVIs with affine operator by using a continuously differentiable dual gap function. This extends an idea from Dietrich (J. Math. Anal. Appl. 235:380–393 [24]). Some numerical results illustrate the practical behavior of this dual gap function approach.     

Total Synthesis of the Postulated Structure of Fulicineroside

A total synthesis of the proposed structures of fulicineroside and its aglycone fulicinerine is reported. The tetrasubstituted dibenzofuran substructure was accessible either through a Pd‐mediated ortho‐metalation or by an Ir‐catalyzed meta‐borylation. The synthesis of the β,β,α‐linked trisaccharide consisting of D ‐olivose, L ‐rhodinose, and L ‐rhamnose was challenged by the unprecedented β‐linked rhodinose. A Pd‐catalyzed β‐selective glycosylation of a 4‐epi‐rhodinose and a subsequent Mitsunobu inversion provided selectively the β‐linked L ‐rhodinose‐L ‐rhamnose disaccharide. Comparison with the reported data for the natural product and the aglycone suggests a misassignment of the structure of the natural product.     

Chip-calorimetric monitoring of biofilm eradication with bacteriophages reveals an unexpected infection-related heat profile

Bacteriophages or phage-derived biological structures are a promising alternative to the application of antibiotics to eradicate biofilms. These countermeasures are highly cell specific. For a better understanding of the sequence of the underlying processes (attachment, infection, multiplication, phage release), for optimization of phage applications, or simply for screening of suitable phages or phage-derived enzymes, real-time monitoring devices are urgently required. Calorimetry is promising because it is non-invasive and quantitatively connected to the metabolic fluxes. Chip-calorimetry provides real-time information about biofilm eradication by phages. This was confirmed by comparison with reference analyses (i.e., confocal laser scanning microscopy, colony plate counts, or phage titre determination). Furthermore, chip-calorimetry provides additional information which was not captured by the reference methods such as the enhanced cell-specific heat production caused by the infection process and a residual activity of seemingly persistent bacteria.     

Xanthomonins I–III: A New Class of Lasso Peptides with a Seven‐Residue Macrolactam Ring

Lasso peptides belong to the class of ribosomally synthesized and post‐translationally modified peptides. Their common distinguishing feature is an N‐terminal macrolactam ring that is threaded by the C‐terminal tail. This lasso fold is maintained through steric interactions. The isolation and characterization of xanthomonins I–III, the first lasso peptides featuring macrolactam rings consisting of only seven amino acids, is now presented. The crystal structure of xanthomonin I and the NMR structure of xanthomonin II were also determined. A total of 25 variants of xanthomonin II were generated to probe different aspects of the biosynthesis, stability, and fold maintenance. These mutational studies reveal the limits such a small ring imposes on the threading and show that every plug amino acid larger than serine is able to maintain a heat‐stable lasso fold in the xanthomonin II scaffold.