13C nmr spectroscopy of tetracarbocyclic diterpenes and related substances1

A caarbon shift analysis of hibaene, phyllocladene, cafestol, cafamarine, mascaroside and hilbane-like substances is presented.     

Synthese de sesquiterpenes tricycliques—I: Etude d''un modele derive de la (−)Δ trimethyl 1,1,7β octalone-3 (pulegone acetone)

Photochemical cycloaddition of ethylene on (−)Δ⁴-1,1,7β-trimethyl-octal-3-one leads to a mixture of two isomers. The rearrangement of the major ketone in the presence of toluene-p-sulphonic acid has been studied. Solvolysis of the tertiary alcohols related to the major cycloaddition product gives the same mixture of five substances which have been separated and whose structures have been determined.     

Two new phenolic compounds from the leaves of Alnus sibirica Fisch. ex Turcz.

Two new phenolic compounds, 4-O-glucopyranosyl-5-O-caffeoylshikimic acid (1) and 2,3-digalloyl oregonin (2), were isolated along with eight known phenolic compounds (3–10) from an 80% acetone extract of Alnus sibirica leaves. The chemical structures of these compounds were elucidated using 1D/2D nuclear magnetic resonance and high resolution-MS. The anti-oxidative activities of these compounds were determined by assaying their 1,1-diphenyl-2-picrylhydrazyl radical and nitroblue tetrazolium superoxide anion scavenging activity. All of the isolated phenolic compounds (1–10) exhibited potent anti-oxidative activities. In particular, 2 and 4, which are diarylheptanoids, and 10 which is ellagitannin exhibited excellent anti-oxidative activities with almost the same potency as that of the positive controls L-ascorbic acid and allopurinol.     

Enhanced fracture toughness and mechanical properties of epoxy resin with rice husk-based nano-silica

This paper reports a novel approach to toughen epoxy resin with nano-silica fabricated from rice husk using a thermal treatment method with a particle size distribution in range of 40–80 nm. The nano-silica content was in the range, 0.03–0.10 phr, with respect to epoxy. The mechanical test showed that with the addition of 0.07 phr of rice husk based nano-silica, the fracture toughness of the neat epoxy resin increased 16.3% from 0.61 to 0.71 MPa m^1/2. The dynamic mechanical analysis test results showed that the glass transition temperature (T _g) of a 0.07 phr nano-silica dispersion in epoxy resin shifted to a higher temperature from 140 to 147°C compared to neat epoxy resin. SEM further showed that the nano-silica particles dispersed throughout the epoxy resin prevented and altered the path of crack growth along with a change in the fracture surface morphology of cured epoxy resin.     

Effect of micro/nano white bamboo fibrils on physical characteristics of epoxy resin reinforced composites

As a green filler comprising both nano- and micro-sized fibrils, micro/nano white bamboo fibrils (MWBFs) were treated with a silane coupling agent (S-MWBFs) prior to their introduction in an epoxy resin (EP). The sequential processes of steam explosion, alkaline treatment, and micro grinding were used to prepare to MWBFs. The effects of the S-MWBFs on various characteristics of the cured EP such as compatibility, fracture toughness, morphology, mechanical property, and flame retardation were studied. The fracture toughness and mechanical characteristics of both the storage modulus and tanδ maximum increased following addition of the S-MWBFs to the EP. Notably, the fracture toughness of the EP with 0.3 wt% of S-MWBFs was 22.2% higher than that of unmodified resin. Scanning electron microscopy presented somewhat rougher surfaces with shear deformation and tortuously twisting cracks, resulting in a higher fracture toughness in S-MWBF-modified epoxy samples. However, fire testing showed that the presence of S-MWBFs increased the burning rate of the EP.     

Development of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-based cyclic neutron activation analysis for short-lived radionuclides

The k ₀-based cyclic neutron activation analysis (k ₀-CNAA) technique has been studied to explore the applicability at the Portuguese research reactor (RPI). In particular, for the determination of elements which form short-lived radionuclides, particularly fluorine (²⁰F, 11.16 s half-life) and selenium (^77mSe, 17.36 s half-life) in polymer, biological and environmental samples. The detection limits obtained for F and Se were about 50 and 0.01 mg kg⁻¹, respectively, in the investigated materials. The timing parameters for the procedure were 10 to 20 s for irradiation, 5 s decay, 10 to 20 s counting, 5 s waiting and performed with eight cycles. The k ₀-IAEA program was modified to use millisecond time resolution for irradiation, decay and counting times as needed for interpreting k ₀-CNAA data in terms of concentration, accuracy and detection limit. The quality control of the procedure was performed by preparing a standard solution containing fluorine with different contents as well as using the certified reference materials containing selenium from which the bias between the results and the certified values were within 15% for most elements at the investigated content ranges. The analytical results for several other elements producing short-lived or detectable radionuclides, e.g., Al, Ca, Cl, Cu, Dy, I, Mg, Mn, Ti, and V were also obtained by the k ₀-CNAA procedure with accuracy within 12%.     

Asymptotic of solutions for second IBVP for hyperbolic systems in non-smooth domains

The purpose of this paper is to study the asymptotic behaviour of solutions of the second initial boundary value problem for hyperbolic systems in an infinite cylinder with the base containing conical points. Some new results on the asymptotics of solutions of elliptic problem depending on a parameter are also given.