SAID SHEHATA

The composition of the microflora, N2‐fixing bacteria particularly, in different soils cultivated with wheat in Egypt was investigated in some samples collected from the fields after applying the agricultural practices recommended for wheat cultivation and just before sowing. The influence of carbon sources, mineral nitrogen and water regimes on potential dinitrogen fixation (acetylene reduction assay) in soils was investigated. The bacterial population densities including‐N2‐fixing organisms were related to a number of environmental factors such as organic matter content. Among diazotrophs, Azotobacter spp. and Azospirillum spp. were encountered in higher densities in comparison with clostridia. Unamended soils showed a lower acetylene‐reducing activity (0.5–61.5 nmoles C2H4 g−1 h−1). Addition of glucose (1% w/w) greatly enhanced such activity being the highest (86.9–2846.5 nmoles C2H4 g−1 h−1) in the clay soil with the highest organic carbon content (1.42%). Glucose amendment had no significant influence on acetylene reduction in the saline soil. N2‐fixation in barley straw‐amended (1%) soils was not much higher than in unamended soils. Concentrations of up to 70 ppm ammonium‐nitrogen depressed N2‐fixation in soils that received barley straw. Acetylene reduction in submerged soil increased after addition of cellulose. Non‐flooded conditions favoured N2‐fixation in the fertile clay soil amended with sucrose. Copyright © 1989 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

The donor–acceptor interaction of acrylonitrile (AN) with indene (In) has been investigated by means of ultraviolet spectroscopy and dielectric polarization measurements. The latter method yielded a value of 0.5 for the association constant of the charge‐transfer‐complex (CTC) and a 4.02 D for its dipole moment. The copolymerization of the two monomers was characterized by a tendency towards alternation when conducted in the bulk. This might be due to the participation of a weak CTC in the process of copolymerization. However, this tendency disappeared in polar solvents such as DMF. Copyright © 1989 John Wiley & Sons, Inc.

The effect of heat treatment on the structural transformation and electrical conductivity σ of the amorphous alloy Ge20Se5Te75 was studied. X-ray diffraction experiments on annealed samples, at temperatures higher than the glass transition temperature, showed the presence of Te and TeGe crystalline phases. On heating the amorphous sample above the glass transition temperature irreversible electrical conductivity changes were observed. The temporal changes in the σ values of the Ge20Se5Te75 samples at various isothermal annealing temperatures were used to determine the transformation ratios from the amorphous to crystalline state. The kinetic parameters were also calculated. The crystallization is a two-dimensional process. A value of 1.02 ± 0.12 eV was obtained for the activation energy of the crystal growth in the temperature range 230-270 °C. © 1989.

The electrical conductivity of γ irradiated and unirradiated finely divided ferrites of composition Fe3O4, CdFe2O4 and CoxZn1-xFe2O4 (0 ≤ x ≤ 1) was studied in a nitrogen atmosphere as a function of temperature. Fe3O4, ZnFe2O4 and CdFe2O4 showed n-type conduction, whereas CoFe2O4 showed p-type conduction. For CoVxZn1-xFe2O4 it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe3O4 and CoxZn1-xFe2O4 (0 ≤ x ≤1) was explained by a hopping mechanism, whereas the conduction in ZnFe2O4 and in CdFe2O4 is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of γ irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism was discussed. © 1989.

The electrical conductivity of γ-irradiated and unirradiated finely divided ferrites of composition Fe3O4, CdFe2O4 and Cox Fn1-xFe2O4(0 ≤x ≤ 1) was studied in a nitrogen atmosphere as a function of temperature. Fe3O4, ZnFe2O4 and CdFe2O4 showed n-type conduction, whereas CoFe2O4 showed p-type conduction. For CoxZn1-xFe2O4 it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe3O4, and CoxZn1-xFe2O4(0 ≤x ≤ 1) was explained by a hopping mechanism, whereas the conduction in ZnFe2O4 and in CdFe2O4 is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of γ-irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed. © 1989 Chapman and Hall Ltd.

The d.c. and a.c. conductivity and the thermoelectric power of the compounds H3N+(CH2)nN+H 3FeCl4, where n = 2, 3, 7 or 10, have been studied over a temperature range of 150-500 K. The conductivity results confirm the presence of more than one structural phase transition for each compound investigated. The thermoelectric power measurements show that electrons are the main charge carriers in all crystal phases. The conductivity results are explained on the basis of an electron-hopping mechanism over the whole temperature range. © 1989.

DTA, dc-conductivity and thermoelectric power of the compounds RMnCl4, RCoCl4 and RMn0.5Co0.5Cl4; {Mathematical expression}, have been measured over a temperature range of 300-500 K. Both DTA and dc-conductivity results showed the presence of many phase transitions in each one of the complexes investigated. The conductivity results were explained in terms of an electron hopping mechanism. The effect of γ-irradiation on the conductivity data and the type of crystal phases have been investigated and discussed. © 1989 Akadémiai Kiadó.

The magnetic susceptibility of the compounds (4-Cl-C6H4NH3)2FepZn1-pCl4 has been studied according to the change in the magnetic ion concentration (p = 0.1, 0.2, 0.4, 0.6, 0.75, 0.9 and 1.0). The size of the domain was found to vanish at the critical concentration 0.1 mol fraction. For the parent compound, p = 1.0, the investigated magnetic susceptibility showed antiferromagnetic character. Dielectric constant behaviour could be explained on the bases of magnon-phonon interaction. Also the magnetostriction effect of the lattice was found to play a role in this behaviour. © 1989.

The magnetic susceptibility of (IPA)2FeCl4, (IBuA)2FeCl4 and (IPA)2CuCl4, where IPA = (CH3)2CHNH+ 3 and IBuA = (CH3)2CHCH2NH+ 3, were measured in the temperature range form 80 K up to a temperature near the melting points of the samples. The results obtained were interpreted in termw of a canted two-dimensional antiferromagnet. The variation of the magnetic susceptibility with the change in the composition was also discussed. © 1989.

The magnetic susceptibility of (IPA)2FeCl4, (IBuA)2FeCl4 and (IPA)2CuCl4, where IPA = (CH3)2CHNH+ 3 and IBuA = (CH3)2CHCH2NH+ 3, were measured in the temperature range from 80 K up to a temperature near the melting points of the samples. The results obtained were interpreted in terms of a canted two-dimensional antiferromagnet. The variation of the magnetic susceptibility with the change in the composition was also discussed. © 1989.

Underground water samples taken from 15 wells located at 3 municipal water works in Cairo were examined for the presence of fecal streptococci as a fecal pollution indicator. Fecal streptococci were detected in 96.4% of the 111 representative samples. Ranges of such pollution indicator were 1-17, 1-17 and 1-24 MPN/100 ml for water samples collected from wells in Mustorod, El-Marg and El-Maadi water works, respectively. A total of 200 pure strains of streptococci were isolated and subjected to biochemical and serological tests. Biochemical tests showed that only 26 strains could be classified as related to group D streptococci (enterococcus). Fore further identification, serological test was applied using 48 isolates chosen at random. The distribution of isolates among various serological groups showed that only 15 isolates (31%) could be classified into 5 defined groups (A, B, C, F and G). On the other hand, 4 isolates could not be defined serologically. The remaining 29 isolates (60%) gave a mixed reaction.

X-ray structural analysis on (FeCl(DMSO)5)(Fe2-Cl6O) complex have shown that the position of the dimethylsulphoxide molecule (DMSO) became distorted between two positions with increasing temperature. The disorder in this compound is due to the tendency of the angle of the oxobridge of the anion (Cl3Fe-O-FeCl3) to straighten out, the effect being transmitted to the cation via the short Cl-S contact. This letter reports a study of the effect of temperature on the magnetic susceptibility, dielectric constant and electrical conductivity of the neutral complex ((DMSO)2FeCl2). This complex was found to have a distorted square planar complex at room temperature, with two chloride ions and two oxygens of sulphoxide groups lying around the Fe2+ ions. Such studies may yield information about the effect of temperature on the structure and the donor sites of DMSO in this type of complex.

The temperature dependence of the electrical conductivity σ of some two-dimensional chelated compounds ((ODA)FeCl4, (ODA)1 2(Cyst)FeCl4, (ODA)CuCl4 and (ODA)1 2 (GA)CuCl4, where ODA = octanediammonium ion. Cyst = cystinium ion, GA = glucosam- monium ion) was investigated. Differential scanning calorimetry measurements of these compounds show the presence of more than one structural phase transition for each compound. These phase transitions are also observed in the conductivity results. Seebeck voltage measurements show that electrons are the majority charge carriers in all the crystal phases of the complexes. © 1989.

DTA, d.c. conductivity and thermoelectric power of the compounds RMnCl4, RCoCl4 and RMn0.5Co0.5Cl4 (R = H3N-(CH2)8-NH3) were measured over a temperature range of 300-500 K. Both the DTA and the d.c.-conductivity results show the presence of many phase transitions in each of the complexes investigated. The conductivity results are explained on the basis of an electron-hopping mechanism. The effect of γ-irradiation on the conductivity data and the type of crystal phase are investigated and discussed. © 1989.

n/a