The first phytochemical investigation of Dobera glabra (Forssk.) Poir. (Salvadoraceae) led to the isolation of seven flavonoids, namely isorhamnetin-3-O-β-glucopyranoside-7-O-α-rhamnopyranoside (1), isorhamnetin-3-O-α-rhamnopyranoside-7-O- β-glucopyranoside (2), kaempferol-3,7-di-O-α-rhamnopyranoside (3), isorhamnetin-3-O-β-glucopyranoside (4), kaempferol-3-O-β-glucopyranoside (5), isorhamnetin (6) and kaempferol (7). Their structure elucidation was performed by chromatographic, chemical and spectroscopic methods. Antioxidant and cytotoxic activities were also determined for five successive extracts of the plant. The ethyl acetate, chloroform, butanol, methanol and aqueous plant extracts exhibited moderate antioxidant effects (DPPH assay). Their cytotoxic activity was carried out against four tumor cell lines (MTT assay). The ethyl acetate and butanol extracts expressed the greatest antiproliferative activity against colon cancer cells (HCT116) with IC50 (8.7 and 5.3 mg/mL), respectively. In addition D. glabra is a highly valued plant species with diverse importance such as drought food and source of feed, a special mineral source feed, a tool for forecasting the droughts [1]. The crude protein content of D. glabra is also high to support animals' requirement and the laboratory analysis on the nutritive value of the edible part of D. glabra also revealed that this plant has nutritive value nearly comparable to the most common wild food fruits [2].

The effects of γ-irradiation on the optical properties of polyoxymethylene (POM) compacts are studied at room temperature. A UV-visible spectrometer is used to study the optical absorbency in the wavelength range 200–1100 nm. The optical energy of both direct and indirect transitions as well as the energy band tail ΔE is determined as a function of γ exposure dose. The results obtained showed that the POM compacts became brittle as the γ-radiation dose reaches 5 Mrad. In the meanwhile, the wavelength of the optical band tail λg increases to a maximum at 2 Mrad and the energy band tail ΔE reaches 5 eV at the same dose. Both direct and indirect energies of transition decrease with the irradiation dose. The results can be explained on the basis of γ-irradiation-induced changes due to cross-linking in the POM.

Tensile samples of low density polyethylene (LDPE) films with different thickness and disc samples for ultrasonic measurements were outdoor exposed to weather for different ageing times before being tested. The strength parameters of the material (yield strength and sonic modulus) decrease with increasing ageing time up to 7 days, then they start to recover, whereas ductility decreases continuously with ageing time. The results are discussed in terms of oxidation and cross-linking. Below 7 days of ageing the oxidation process dominates the degradation whereas above this period the cross-linking overrides the former one. (C) 1998 Elsevier Science Limited. All rights reserved.

The thermal and dielectric spectroscopy of a thiosemicarbazide Schiff base and its nickel and palladium complexes were studied. The Perkin Elmer TGA7 thermal analysis technique was applied to study the effect of the heating rate on the TG curve. A Hioki 3520 RLC tester was used to measure the dielectric spectroscopy in the frequency range 102–105 Hz. The activation energies of the ligand and its complexes were determined, and the d.c. and a.c. conductivities were estimated for the ligand and its Ni(II) complex. The results showed that the Ni(II) complex was present in a dimeric form, while the Pd(II) complex was present in a monomeric form. The insertion of a nickel atom increases the d.c. conductivity. The mechanism of conduction is discussed.

Mechanical properties of engineering polymers which are the most important properties for design and construction purposes are diverse. This has been proved by investigation tensile properties of different grades of LDPE using tensile specimens processed by both injection moulding and compression moulding techniques. A considerable variation in these properties exists among the examined grades for similar chemical structures and similar previous history. The obtained results showed that mechanical properties for compressed samples are better then those obtained for the injected samples. This behaviour could be explained by the difference in the internal stress levels inside the material. Thus, caution must be exercised in selecting the material, its grade and its manufacturing method for a defined design.

The effects of immersion of low-density polyethylene (LDPE) in seawater for times of up to one year were studied using mechanical and ultrasonic techniques. The studies were carried out in the laboratories of the Faculties of Science and Engineering in the University of Qatar. The results demonstrate an interaction between ageing time and seawater immersion. The experimental results indicated that mechanical propenies are sensitive to varying periods of seawater immersion. The results are discussed in terms of the stability of LDPE in seawater and explained in terms of chemical reactions and physical absorption processes taking place in the presence of high ionic concentrations present in seawater. Significant physical interactions are reported and mechanism involving chain scission and deploymerisation are proposed to explain the mechanical test results.

The effect of gamma-radiation and thickness on the optical energy gap of Bi-thin films has been investigated by measuring their optical absorbance. The measurements were carried out on thermally evaporated films having thicknesses in the range 5-20 nm. Different gamma-radiation doses were used ranging from 0-300 Mrad. The optical energy gap as well as the absorption coefficient were found to be gamma-dose dependent.

The dielectric response of some thiosemicarbazide derivatives has been studied as a function of frequency and temperature. The measurements were investigated using a Hioki RLC tester in the 0.1–100 kHz frequency region and in the temperature range 300–400 K. Analysis of a.c. conductivity reveals a faint semiconducting feature based predominantly on a diffusion-like behaviour mechanism followed by hopping of localized electrons.

The effect of gamma-radiation dose up to about 324 kGy on the thermoluminescence and dielectric properties of LiKSO4: Gd was studied. All glow curves exhibited a single peak around 373 K. The activation energy of this peak was estimated to be about 0.82 eV. The variation of the TL intensity with gamma-dose is characterized by a maximum at 6.75 kGy. The dielectric dispersion was studied as a function of irradiation dose. In the low frequency range straight line behaviour was obtained for low dose (up to 12.3 kGy) while for higher gamma-dose, semicircles are obtained. The bulk conductivity was found to increase with dose up to 6.75 kGy.

The effect of γ-radiation dose up to about 324 kGy on the thermoluminescence and dielectric properties of LiKSO4: Gd was studied. All glow curves exhibited a single peak around 373 K. The activation energy of this peak was estimated to be about 0.82 eV. The variation of the TL intensity with γ-dose is characterized by a maximum at 6.75 kGy. The dielectric dispersion was studied as a function of irradiation dose. In the low frequency range straight line behaviour was obtained for low dose (up to 12.3 kGy) while for higher γ-dose, semicircles are obtained. The bulk conductivity was found to increase with dose up to 6.75 kGy.

Isotopic effects in pure and y-irradiated triglycine selenate crystals were investigated using the specific heat (C(p)) technique. The obtained results showed an interesting dependence of the critical behavior of C(p) on the deuterium content. With increasing content of deuterium, the character of the phase transition changed from a second order (lambda-type) to a first order transition. After gamma-irradiation, the behavior of C(p) around the phase transition region was essentially affected. The transition temperature, T(c), decreased and DELTAC(p) depressed, and the transition became broad. It was noted that the effect of gamma-irradiation is opposite to the isotopic effect.

The thermophysical properties of LiKSO4 crystals were studied around the high-temperature phase, at Tc2 = 943 K. A Heraeus (DSC) technique was used to measure the specific heat, c(p), while the thermal conductivity, K, was measured by the linear heat flow steady-state method. The measured parameters showed an anomaly in the temperature dependence of both c(p) and K. Anisotropy in the thermal conductivity coefficient was also observed in the different crystallographic axes.

Thermoluminescence (TL) measurements were carried out for pure and doped LiRbSO4, with different concentrations of thallium (Tl). The glow-curve range of measurement is between room temperature up to 300-degrees-C. The radiation absorbed dose is in the range 56-3.2 x 10(5) Gy. The results show that both pure and doped samples have glow peak temperatures that are dose dependent, and vary between 70-80-degrees-C and 140-170-degrees-C for pure and doped samples respectively. Doped samples display double peaks that increase with dopant concentration up to about 0.7% wt. The second peak which occurs at high temperature increases linearly with dose up to 4500 Gy. From the results it is proposed that LiRbSO4 doped with 0.7% Tl can be used for dosimetric purposes in this range. The activation energies of structural transitions are estimated and the results are discussed on the basis of radiation-induced stable dipoles in the random field system.

Measurements of the direct current conductivity (σ) of different stoichiometric (NaxK1-x)2SO4 crystals with x = 0.1, 0.2 and 0.3 have been carried out in the temperature range 350 to 500 K. The effect of uniaxial pressure up to 9 tons cm-2 along the b-axis was studied in the vicinity of the phase transition temperature. Different behavior of the pressure dependence of the conductivity has been observed with two regions for each stoichiometric ratio. The transition temperature as well as the activation energy were determined for each case. The results were discussed in terms of a uniaxial pressure-induced change in the phase transition. Keywords: uniaxial pressuresodium potassium sulphatephase transition

Structural defects were introduced in lithium ammonium sulphate crystals (LAS) either in the process of crystal growth (in the form of foreign ions) or by neutron irradiation. The effect of such defects on the thermal properties of LAS crystals was studied in the temperature range 300–500 K. It was assumed that the doped LAS crystals are composed of a two-phase system having different thermal parameters in each phase. The specific heat at constant pressure, Cp, of irradiated samples was found to decrease with increasing irradiation doses. The thermal expansion of LAS crystals was found to be dependent on neutron irradiation, and was attributed to two processes: the release of new species and the trapping process.

The influence of stoichiometric ratio on the phase transition of sodium potassium sulphate (NaxK1−x)2SO4 crystals is investigated in the temperature range 300–500 K. The stoichiometric ratiox is chosen to bex=0.2, 0.3, 0.4, 0.8 and 0.9. The study has been carried out by using differential scanning calorimetry, DSC technique. The value of the specific heat,C p, at the transition temperature,T c , increases asx is increased up tox=0.4 and then decreases for higher values ofx. The change in the specific heat, ΔC p, is following a relation of the form ΔC p ΔC p α(T−T c /T c )−α withα = 0.12 which is in a fair agreement with the 3d Ising model. Insertion of Cu2+ ions into the lattice of (NaxK1−x)2SO4 crystals leads to a multiple peak in the temperature dependence ofC p. The results are discussed from thermodynamical point of view.

The direct-current resistivity, β, and Hall coefficient,R H, of lightly dopedn-type InP samples were measured at temperatures (T) down to 12K and magnetic fields up to 4.8 kG. A sharp exponential increase in β, asT was decreased, was observed for temperatures below 80 K. The Hall coefficient showed a similar trend,i.e. R H increased sharply asT was reduced below 80 K. This is attributed to the freeze-out of conduction electrons onto their donor sites. The donor activation energy,E d, calculated from the temperature dependence of the resistivity, was less than the theoretical prediction. An enhanced dielectric constant would be a possible candidate for such behaviour. The initial decrease in β (asT is reduced) recorded in the higher-temperature region is due to impurity scattering probably combined with lattice scattering.

The dielectric constant and the dielectric loss of potassium acetylacetonate, K(acac), are measured as a function of both temperature and frequency. A peak value is obtained at the a critical temperature T(c) = 313 K. X-ray analysis revealed that at T(c), K(acac) undergoes phase transition from orthorhombic to triclinic structure. The Cole-Cole diagrams have been used to determine the molecular relaxation time-tau. The temperature dependence of tau is expressed by thermally activated process. The impedance spectra in the frequency range from 50 Hz to 500 kHz plotted in the complex plane show semicircles. The conduction mechanism, below T(c), is predominantly operating at the surface. Above T(c), the conduction is proceeding in the bulk material with contribution from the surface.