Mode II brittle fracture assessment using an energy based criterion

In this paper the minimum strain energy density criterion is modified to predict the values of mode II fracture toughness reported in the literature for several brittle and quasi-brittle materials. The experimental results are all related to mode II fracture tests performed on the semicircular bend specimen. The modified mode II fracture criterion takes into account the effect of T-stress (in addition to the singular terms of stresses/strains) when calculating the strain energy density factor at a very small critical distance from the crack tip. It is shown that the proposed criterion provides significantly better predictions for mode II fracture toughness compared with the classical minimum strain energy density criterion.     

A simple and efficient total synthesis of (±)-danshexinkun A, a bioactive diterpenoid from Salvia miltiorrhiza

An efficient 12-step route for the synthesis of the diterpenoid quinone (±)-danshexinkun A in 23% overall yield from the corresponding highly substituted stilbene using a photocyclization strategy is described.     

Microcellular antibacterial polylactide‐based systems prepared by additive extrusion with ALUM

This work investigates preparation by extrusion of microcellular antimicrobial polylactide (PLA) with an additive, the latter comprising 1% potassium aluminum sulfate dodecahydrate (ALUM), and 3% or 5% of a mixture of sodium hydrogen carbonate and sodium dihydrogen phosphate (1:1). Study was made as to the properties of the materials, their hydrolysis, release profiles, and antimicrobial properties in comparison with the pure polymer. Measuring the molecular weight of samples by gel permeation chromatography revealed that, during thermal processing, the molecular weight of the PLA prepared with additives mentiond above had reduced by approximately 43%. A mechanical test confirmed a decline in mechanical properties after processing as compared with the pure PLA. Release of the antimicrobial compound and the subsequent antimicrobial activity against Staphylococcus aureus and Escherichia coli was evaluated according to ISO 22196:2007. The release of ALUM from the microcellular specimens took place in two steps. During the first 10 days, the rate of release was extremely high in contrast with the remaining period. However, the release rate of the nonporous sample was seen to equal less than 1% in the first 10 days, a phenomenon probably arising through its less active surface.     

Generalized Covering Groups

Let v and be two varieties of groups defined by the sets of laws V and W, respectively. In this paper we construct a -v-covering group of a finite v-perfect group G, and show that every automorphism of G may be lifted to its -v-covering group. These generalize the previous work of the first two authors (1999). We also characterize the -v-irreducible extensions in some sense.AMS Mathematics Subject Classification (2000) Primary 20E34 20E36 Secondary 20E10     

On the Flag Curvature of Invariant Randers Metrics

In the present paper, the flag curvature of invariant Randers metrics on homogeneous spaces and Lie groups is studied. We first give an explicit formula for the flag curvature of invariant Randers metrics arising from invariant Riemannian metrics on homogeneous spaces and, in special case, Lie groups. We then study Randers metrics of constant positive flag curvature and complete underlying Riemannian metric on Lie groups. Finally we give some properties of those Lie groups which admit a left invariant non-Riemannian Randers metric of Berwald type arising from a left invariant Riemannian metric and a left invariant vector field.      

Electron transport through SWNT/<Emphasis Type="Italic">trans</Emphasis>-PA/SWNT structure (the role of solitons): A t-matrix technique

Using a tight-binding model and a transfer-matrix technique, we numerically investigate the effects of the coupling strength and the role of solitons on the electronic transmission through a system in which trans-polyacetylene (trans-PA) molecule is sandwiched between two semi-infinite single-walled carbon nanotubes (SWNT). We rely on Landauer formalism as the basis for studying the conductance properties of this system. Our calculations show that the solitons play an important role in the response of this system causing a large enhancement in the conductance. Also our results suggest that the conductance is sensitive to the CNT/molecule coupling strength.      

The Baer-invariant and the direct limit

In this note we establish that the Baer-invariant of a group commutes with direct limit. It has a very useful application so that if one works with the Baerinvariant, or in particular Schur-multiplicator, of arbitrary groups it is only needed to take the groups to be finitely generated.     

Voltammetric determination of droxidopa in the presence of carbidopa using a nanostructured base electrochemical sensor

A novel carbon paste electrode modified with ZnO nanorods and 2-(4-oxo-3-phenyl-3,4-dihydroquinazolinyl)-N′-phenyl-hydrazinecarbothioamide (2PHCZNCPE) was fabricated and employed to study the electrocatalytic oxidation of droxidopa, using cyclic voltammetry, chronoamperometry and square wave voltammetry as diagnostic techniques. It has been found that the oxidation of droxidopa at the surface of modified electrode occurs at a potential of about 435 mV less positive than that of an unmodified carbon paste electrode. Square wave voltammetry exhibits a linear dynamic range from 7.0 × 10^–8 to 3.0×10^?4 M and a detection limit of 45.0 nM for droxidopa. Finally this modified electrode was used for simultaneous determination of droxidopa and carbidopa.     

Synthesis of Tetrahydrothiopyrano[2,3‐b]indole [60]Fullerene Derivatives via Hetero‐Diels–Alder Reaction of C60 and α,β‐Unsaturated Indole‐2‐thiones

Hetero‐Diels–Alder reactions of [60]fullerene with α,β‐unsaturated thio‐oxindoles ( 3a , 3b , 3c ), prepared from thio‐oxindole 1 and heteroaromatic aldehydes ( 2a , 2b , 2c ), to generate tetrahydrothiopyrano[2,3‐b ]indole [60]fullerene cycloadducts ( 5a , 5b , 5c ) under thermal or microwave irradiation were described. The yields were improved, and the reaction time was decreased by conducting the reaction under microwave irradiation.