Cyclic plate bearing tests

A series of circular and square plate-bearing tests are reported, the load-displacement curves for which can be fitted quite closely by a three parameter curve of modified exponential form. The characteristics features of the response of such plates to loading and unloading cycles are then demonstrated and it is shown that their behaviour can be accurately modelled by a simple modification of the first-load response equation which requires three further parameters to be introduced.The six parameters, from which the cyclic load behaviour of plates of any size can be predicted, can be determined from two in situ tests: a conventional plate test and a single-load-level cyclic plate test.     

Non-axisymmetric modes in viscoelastic taylor-couette flow

In this work, the linear stability analysis of the viscoelastic Taylor-Couette flow against non-axisymmetric disturbances is investigated. A pseudospectrally generated, generalized algebraic eigenvalue problem is constructed from the linearized set of the three-dimensional governing equations around the steady-state azimuthal solution. Numerical evaluation of the critical eigenvalues shows that for an upper-convected Maxwell model and for the specific set of geometric and kinematic parameters examined in this work, the azimuthal Couette (base) flow becomes unstable against non-axisymmetric time periodic disturbances before it does so for axisymmetric ones, provided the elasticity number ε (De/Re) is larger than some non-zero but small value (ε 0.01). In addition, as ε increases, different families of eigensolutions become responsible for the onset of instability. In particular, the azimuthal wavenumber of the critical eigensolution has been found to change from 1 to 2 to 3 and then back to 2 as ε increases from 0.01 to infinity (inertialess flow).In an analogous fashion to the axisymmetric viscoelastic Taylor-Couette flow, two possible patterns of time-dependent solutions (limit cycles) can emerge after the onset of instability: ribbons and spirals, corresponding to azimuthal and traveling waves, respectively. These patterns are dictated solely by the symmetry of the primary flow and have already been observed in conjunction with experiments involving Newtonian fluids but with the two cylinders counter-rotatng instead of co-rotating as considered here. Inclusion of a non-zero solvent viscosity (Oldroyd-B model) has been found to affect the results quantitatively but not qualitatively. These theoretical predictions are of particular importance for the interpretation of the experimental data obtained in a Taylor-Couette flow using highly elastic viscoelastic fluids.     

An integral equation approach to self-similar plane-elastodynamic crack problems

The elastodynamic problem of an expanding crack under homogeneous polynomialform loading was reduced to the solution of a Cauchy singular integral equation. In this manner the solution of the original problem can be obtained by using well-known numerical treatments available for Cauchy SIEs. The procedure was accomplished by means of the Busemann-Chaplygin similarity technique and complex variable methods. The analysis has been restricted to the subsonic case.     

Anelastic to plastic transition in metallic glass-forming liquids

The configurational properties associated with the transition from anelasticity to plasticity in a transiently deforming metallic glass-forming liquid are studied. The data reveal that the underlying transition kinetics for flow can be separated into reversible and irreversible configurational hopping across the liquid energy landscape, identified with beta and alpha relaxation processes, respectively. A critical stress characterizing the transition is recognized as an effective Eshelby "backstress," revealing a link between the apparent anelasticity and the "confinement stress" of the elastic matrix surrounding the plastic core of a shear transformation zone.     

Enhanced aqueous solubilization of tetrachloroethylene by a rhamnolipid biosurfactant

A rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 was isolated, purified and characterized in terms of its ability to mobilize and solubilize tetrachloroethylene (PCE) for potential use in surfactant-enhanced aquifer remediation (SEAR) applications. Using a drop volume method, the PCE-biosurfactant steady-state interfacial tension was determined and found to be ca. 10 mN/m which is not low enough to cause significant PCE nonaqueous phase liquid (NAPL) mobilization. It was observed that the biosurfactant partitioned significantly into PCE at aqueous concentrations higher than the critical micelle concentration (CMC). After accounting for rhamnolipid partitioning into the PCE phase, a weight solubilization ratio (WSR) of 1.2 g(PCE)/g(rhamnolipid) was determined and through this mechanism the biosurfactant significantly improved the apparent aqueous solubility of PCE.     

A versatile annulation protocol toward novel constrained phosphinic peptidomimetics

The development of a novel 3-center 2-component annulation reaction between alpha,omega-carbamoylaldehydes and suitably monoalkylated phosphinic acids is reported. Depending on the starting alpha,omega-carbamoylaldehyde, diverse phosphinic scaffolds varying in the size of their rigidity element, the nature and stereochemistry of substituents, and the participation of heteroatoms in the azacyclic ring system can be obtained in one synthetic step and in high yield. In addition, this methodology allows the synthesis of Fmoc-protected constrained aminophosphinic acids that can be easily converted to suitable pseudodipeptide building blocks compatible with the requirements of peptide synthesis on the solid phase. Finally, the careful choice of both substituents and protecting groups can provide functionally diverse, orthogonally protected constrained scaffolds for extended derivatization of the target phosphinic peptidomimetic structures.     

Practical Synthesis of Phosphinic Dipeptides by Tandem Esterification of Aminophosphinic and Acrylic Acids under Silylating Conditions

In this report, a synthetic protocol for the preparation of phosphinic dipeptides of type 5 is presented. These compounds serve as valuable building blocks for the development of highly potent phosphinopeptidic inhibitors of medicinally relevant Zn-metalloproteases and aspartyl proteases. The proposed method is based on the tandem esterification of α-aminophosphinic and acrylic acids under silylating conditions in order to subsequently participate in a P-Michael reaction. The scope of the transformation was investigated by using a diverse set of readily available acrylic acids and (R)-α-aminophosphinic acids, and high yields were achieved in all cases. In most examples reported herein, the isolation of biologically relevant (R,S)-diastereoisomers became possible by simple crystallization from the crude products, thus enhancing the operational simplicity of the proposed method. Finally, functional groups corresponding to acidic or basic natural amino acids are also compatible with the reaction conditions. Based on the above, we expect that the practicality of the proposed protocol will facilitate the discovery of pharmacologically useful bioactive phosphinic peptides.     

Balance laws and energy release rates for cracks in dipolar gradient elasticity

It is the purpose of this work to derive the balance laws (in the Günther–Knowles–Sternberg sense) pertaining to dipolar gradient elasticity. The theory of dipolar gradient (or grade 2) elasticity derives from considerations of microstructure in elastic continua [Mindlin, R.D., 1964. Microstructure in linear elasticity. Arch. Rational Mech. Anal. 16, 51–78] and is appropriate to model materials with periodic structure. According to this theory, the strain–energy density assumes the form of a positive-definite function of the strain (as in classical elasticity) and the gradient of both strain and rotation (additional terms). The balance laws are derived here through a more straightforward procedure than the one usually employed in classical elasticity (i.e. Noether’s theorem). Indeed, the pertinent balance laws are obtained through the action of the standard operators of vector calculus (grad, curl and div) on appropriate forms of the Hamiltonian of the system under consideration. These laws are directly related to the energy release rates in the processes of crack translation, rotation and self-similar expansion. Under certain conditions, they are identified with conservation laws and path-independent integrals are obtained.     

Alaninyl­tryptophan hydrate,glycyl­tryptophan dihydrate and tryptophyl­glycine hydrate

The crystal structures of the title tryptophan‐containing dipeptides, C₁₄H₁₇N₃O₃·H₂O, (I), C₁₃H₁₅N₃O₃·2H₂O, (II), and C₁₃H₁₅N₃O₃·H₂O, (III), respectively, contain at least one water mol­ecule of solvation. As a result, the crystal packing of these compounds is composed of regions of water‐mediated hydrogen bonding and tryptophan ring‐to‐ring stacking separated by the length of the mol­ecule. The tryptophan rings stack in a continuous layer that, when viewed edge‐on from the outermost part of the tryptophan ring, exhibits a herring‐bone motif. However, owing to the lack of direct overlap of adjacent rings, no degree of π contact or long‐range delocalization of ring systems is possible here. The overall molecular conformations of (I) and (III) contain a folding of one peptide over the other, such that a minimum in molecular volume occurs without any intramolecular hydrogen bonding. In these two dipeptides, extensive hydrogen bonding is observed to and from the single water mol­ecule of solvation. In the crystal structure of (II), however, an extended mol­ecule conformation complements a more extensive hydrogen‐bonding scheme involving two water mol­ecules of solvation per dipeptide.