مجله علوم جمهوری اسلامی ایران
سال:1382 | دوره:14 | شماره:2 |تعداد مقالات:15

Isotope data from bulk carbonates, micrite, marine calcite cements, non-skeletal grains and brachiopods indicate deposition of a wide spectrum of warm to cold water carbonates during the Ordovician and the Jurassic. This isotopic interpretation is supported by warm to cold climatic models proposed for the Ordovician and the Jurassic. These carbonates formed during the Greenhouse mode (conditions similar to present day) and Icehouse mode. Isotopic equilibrium trends of carbonate minerals indicate an originally aragonite-calcite mixture during the late Ordovician of Tasmania and Late Jurassic of Iran (Kopet-Dagh Basin-Sarakhs area) corresponding to warm temperatures; whereas originally calcitic mineralogy deposited during the Mid Jurassic in England and Scotland, and the Late Jurassic at Mallorca Island, Spain, correspond to cool to cold water temperatures. Sedimentological features of these ancient limestones are similar to modern warm to cold water carbonates.

We previously reported the cloning and expression of cDNA of Human Basic Fibroblast Growth Factor (hbFGF) in Escherichia coli under the control of T7 promoter [6]. In this study we looked for the factor which affects the diminution of Inclusion Bodies (IBs) in E. coli cells which produce heterologous proteins (hbFGF), 6 h after induction. It was shown that the amount of the insoluble hbFGF (as inclusion bodies), reached to the highest level 3 h after induction at 37°C and 42°C, however it decreased gradually afterwards to the lowest level at 6 hrs after induction. To address whether this diminution is the result of destruction of IBs by E. coli proteases, cell death, cell growth inhibition or changing in other physiological characteristics of E. coli, we carried out three experiments. These experiments were continual removal of the E. coli cells which loose their plasmids in culture by adding ampicillin; comparing the number of colonies which loose their plasmids to those which keep the plasmids by growing cells on LB agar plates containing ampicillin or without ampicillin; and adding chloramphenicol to culture 3 h after induction in order to cease protein synthesis in the E. coli cells. The results showed that neither IBs destruction by proteases nor cell death caused the IBs diminution. We showed that the IBs reduction is the immediate result of overgrowth of plasmid-free cells in culture and inhibition of proliferation of the cells containing plasmids and producing the heterologous proteins. Consequently, the ratio of heterologous protein producing cells to the ones lack this character is decreased.

Glucose 6-phosphate dehydrogenase (G6PD) from Streptomyces aureofaciens was purified and denatured in 6 M urea. Denaturation led to complete dissociation of the enzyme into its inactive monomers, 98% loss of the enzyme activity, about 30% decrease in the protein fluorescence and a 10 nm red shift in the emission maximum. Dilution of urea-denatured enzyme resulted in regaining of the enzyme activity and the native protein fluorescence. The renatured enzyme was indistinguishable from the native enzyme based on a number of enzymological and physicochemical criteria. Regaining of the protein fluorescence occurred immediately after diluting the denatured enzyme and before reactivation started. The reactivation process was also monitored by measuring the accessibility of histidine residues toward diethylpyrocarbonate modification. As the reactivation proceeded, less histidine residues were able to be modified. Nicotineamide adenine dinucleotide (NAD+), nicotinamide adenine dinucleotide phosphate (NADP+) and glucose 6-phosphate stimulated the reactivation rate at different degrees. It seemed likely that specific ligands stimulated reactivation by binding to an inactive form of the enzyme leading to a different pathway of refolding. The data are consistent with a model for enzyme renaturation and reactivation in which NAD+ and NADP+ pull the enzyme toward different conformational structures.

Eleven populations of five Avena species were analysed for meiotic characters including chiasma frequency and distribution as well as chromosomal association and segregation. Plants of a single population of A. eriantha showed the presence of 2n = 14 (diploid) and 2n = 4x = 28 chromosome number. Populations of A. barbata and A. wiestii possessed n = 14, while populations of A. sterilis ssp. ludoviciana possessed 2n = 6x = 42 (hexaploid) chromosome number. Tetraploid and hexaploid species showed diplontic behavior and formed only bivalents. The species and populations studied differed significantly in the frequency of chiasmata. B-chromosomes occurred in some of the species studied. Cytomixis and chromosome elimination led to aneuploid and unreduced pollen mother cell formation in the species studied.

Self-association of alcohols; including ethanol, methanol, cyclopentanol and octanol in separate mixtures with inert solvents have been studied using FT-IR spectroscopy. Except for the band at 3640 cm–1 in the IR spectrum of the alcohols which is due to the monomer species, the presence of other bands in the region of stretching vibrational frequencies of OH (3100-3700 cm–1) are attributed to the higher associated species such as dimmer, trimer and multimers. Association models of such as trimer, continuous linear association model, linear association with cyclic trimer (LACT) and dependent equilibrium constant model (DECM) have been used for treating the IR Spectroscopy results. The calculations indicated that the dominant species in the studied concentration range of alcohols is the trimer. The evaluated association constants in the best-fitted model (timer or LACT) were utilized to obtain the excess properties such as hE, gE and activity coefficients for the mixtures.

Soghan complex is one of the major ultramafic-mafic complexes in south-east Iran (Esfandagheh area). Lower part of this complex is composed of dunite, harzburgite and chromitite. The lower part is transitionally converted to lherzoite, dunite, pyroxenite and wehrlite (transition zone). These units are transitionally changed into layered gabbros. This sequence is overlained by the metamorphosed Sargaz-Abshur complexes (Marble and Amphibolites) and has been invaded by an isotropic gabbro in Upper Triassic-lower Jurassic period. The last magmatic phase in this complex is characterised by Cretaceous diabasic dykes. Dunites and harzburgites have coarse granular texture with evidence of grain boundary migration and annealing. In these rocks, there are two generations of minerals; the first generation is completely deformed but the second one is nondeformed which have been probably recrystallized from ascending melts. Soghan peridotites have a weak lattice preferred orientation similar to the mantle peridotites. Layered gabbros have typical cumulate textures and phase layering. There are various shapes of minerals with different chemical composition in Soghan complex. The whole chemical composition of Soghan chromitites in particular TiO2 and Cr2O3 contents are similar to boninitic chromites. However, disseminated chromospinels of harzburgites plot in the field of refractory depleted chromospinels. Geothermometric estimations on orthopyroxene-clinopyroxene and olivine-spinel in the complex show subsolidous equilibrium temperatures ranging from 800-950°C. Based on the petrogeochemical data, Soghan harzburgites have been formed by partial melting of subcontinental lherzolites with minor percolation of later melts. The absence of pillow lavas and tectonites, combined with textures, mineral chemistry and whole rock chemistry indicate this complex is likely a part of mantle diapir. Paleorifting of aborted types in Paleozoic, caused lherzolitic diapirism in this area. At the first stage, the diapir is partially melted and resulting melts form transition zone and layered gabbros. In later stages of partial melting, ultramafic sills and isotropic gabbro were formed and move upward. These could have reacted with host peridotites and formed chromite bearing dunites. It is probable that in early Kimmerian orogenic phase, the whole sequence was metamorphosed up to amphibolite facies.

Multivariate reward processes with reward functions of constant rates, defined  on a semi-Markov process, first were studied by Masuda and Sumita, 1991. Reward processes with nonlinear reward functions were introduced in Soltani, 1996. In this work we study a multivariate process s Z(t) = (Z1 (t),..., Z p (t)), t ≥ 0 , where Z1(t),...,Zp (t) are reward processes with nonlinear reward functions ρ1 ,...,ρ p respectively. The Laplace transform of the covariance matrix, Σ(t), is specified for given ρ1 ,...,ρ p , and if they are real analytic functions, then the covariance matrix is fully specified. This result in particular provides an explicit formula for the variances of univariate reward processes. We also view Σ(t) as a solution of a renewal equation.