Chlorination of silver dosed with potassium and barium in presence of oxygen: An X-ray photoelectron spectroscopy study

XPS studies show that the presence of chemisorbed chlorine stabilizes and also enhances molecular dioxygen species on Ag surfaces dosed with either K or Ba. The surface atomic oxygen is found to become depleted on chlorination. The variation in the nature of surface species with respect to temperature shows chlorine-induced diffusion of atomic oxygen into the subsurface region at 300 K. For coverages of potassium up to 8 × 1014 atoms/cm2, preferential chloridation of Ag occurs while at higher potassium coverages, KCl formation is distinctly observed on the surface. In the case of barium, two types of adsorbed chlorine species, Cl(α) and Cl(β), associated with Ag and Ba, respectively, are clearly seen even at low barium coverages. This is believed to be due to the higher valence occupation of barium compared to potassium. The Cl(α) species associated with Ag is found to occupy a preferred site on both K- and Ba-dosed surfaces, involving chemisorptive replacement of O(α) to the subsurface region.

Multiplication of hybrid aspen (Populus tremula L. x P. tremuloides Michx.) from cuttings

The primary aim of the present study was to find an efficient and simple method of vegetative propagation for producing large numbers of hybrid aspen (Populus tremuloides L. x P. tremula Michx.) plants for forest plantations. The key objectives were to investigate the main physiological factors that affect the ability of cuttings to regenerate and to determine whether these factors could be manipulated by different growth conditions. In addition, clonal variation in traits related to propagation success was examined. According to our results, with the stem cutting method, depending on the clone, it is possible to obtain only 1−8 plants from one stock plant per year. With the root cutting method the corresponding values for two-year-old stock plants are 81−207 plants. The difference in number of cuttings between one- and two-year-old stock plants is so pronounced that it is economically feasible to grow stock plants for two years. There is no reason to use much older stock plants as a source of cuttings, as it has been observed that rooting ability diminishes as root diameter increases. Clonal variation is the most important individual factor in propagation of hybrid aspen. The fact that the efficiently sprouted clones also rooted best facilitates the selection of clones for large-scale propagation. In practice, root cuttings taken from all parts of the root system of hybrid aspen were capable of producing new shoots and roots. However, for efficient rooting it is important to use roots smaller than one centimeter in diameter. Both rooting and sprouting, as well as sprouting rate, were increased by high soil temperature; in our studies the highest temperature tested (30ºC) was the best. Light accelerated the sprouting of root cuttings, but they rooted best in dark conditions. Rooting is essential because without roots the sprouted cutting cannot survive long. For aspen the criteria for clone selection are primarily fiber qualities and growth rate, but ability to regenerate efficiently is also essential. For large-scale propagation it is very important to find clones from which many cuttings per stock plant can be obtained. In light of production costs, however, it is even more important that the regeneration ability of the produced cuttings be high.

The effect of long-term repeated burning and fire exclusion on above- and below-ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

We used a long-term fire experiment in south-east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soil-stored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 19711972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil-stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 37.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil-stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.

Novel Oxidation of Pyridoxal in Ternary Metal Complexes. An X-Ray Study of the Products

Attempts to prepare ternary metal complexes of pyridoxylidene-amino acid Schiff bases culminated in the oxidation of pyridoxal to pyridoxic acid or to its lactone and their complex formation, as evidenced from an X-ray study.

Tautomeric forms of hydroxycyclotriphosphazatrienes; X-ray crystal structure of N3P3Ph2(OMe)3OH

The prefered tautomer(s) of hydroxycyclotriphosphazatrienes and prototropic exchange in solution have been established by 31P n.m.r. spectroscopy, thus confirming predictions deduced from basicity calculations; the X-ray structure of N3P3Ph2(OMe)3OH shows that it exists as the hydrogen-bonded dimer of the oxophosphazadiene tautomer in which a proton is adjacent to the PPh2 group.

X-Ray Spectroscopic Studies of the Surface Species in Co-Mo-Al2O3 Hydrodesulphurization Catalysts

Octahedrally coordinated CoII and MoIV species are present on the surfaces of sulfided Co-Mo-Al2O3 catalysts used for hydrodesulfurization. They were characterized by XPE, EXAFS and XANES data. An excess of sulfur in the surface species can be explained in terms of the presence of S[stack 22 ] ions. Disulfide bridges could play a role in the hydrodesulfurization.

Is Human-X Chromosome Inactivation A Sex-Determining Device

The evolutionary function of X chromosome inactivation is thought to be dosage compensation. However, there is, at present, little evidence to suggest that most X chromosome-linked genes require such compensation. Another view--that X chromosome inactivation may be related to sex determination--is examined here. Consider a hypothetical DNA sequence regulating a major structural gene concerned with the determination of maleness. If this regulatory sequence occurs in both X and Y chromosomes and if its copy number in the Y chromosome is significantly greater than in the X chromosome, then the male-determining properties of the Y chromosome could be attributed to this higher copy number. On the other hand, if the Y chromosome has the same copy number of this sequence as the X chromosome, it is difficult to see how determination of two sexes would occur under such circumstances because XX and XY genomes would then be indistinguishable in this regard. Such a situation seems to occur in the human species with respect to the banded krait minor satellite, a repetitious DNA sequence associated with sex determination. This apparent difficulty may be resolved if X chromosome inactivation renders regulatory as well as structural genes nonfunctional and thereby brings about a significant reduction in the effective copy number of X chromosome-linked DNA sequences concerned with sex determination. It is suggested that X chromosome inactivation brings about, in this manner, a critical inequality between XX and XY embryos and that sex determination in humans is a consequence of this inequality. An analogous situation appears to exist in certain insects in which inactivation of a haploid set of chromosomes (and presumably, therefore, a 50% reduction in the effective copy number of most genes) is associated with maleness. If this line of reasoning is correct, it would suggest that sex determination may be the primary function of X chromosome inactivation.

Valence states and magnetic properties of LaNi1-xMnxO3 (for 0≤x≤0.2 and x=0.5)

Single-phase LaNi1-xMnxO3 samples in the compositional range 00.05, but any motional enthalpy appears to remain small ( Delta Hm approximately=0). The x=0.1 sample exhibits ferrimagnetic spin glass behaviour below 40K, and the ferromagnetic interactions increase with manganese concentration. The oxide with x=0.50 is ferromagnetic with a well defined Curie temperature.

X-Ray Studies On Crystalline Complexes Involving Amino-Acids And Peptides .11. Peptide Aggregation And Water-Structure In The Crystals Of A Hydrated 1-1 Complex Between L-Histidyl-L-Serine And Glycyl-L-Glutamic Acid

The hexahydrate of a 1:1 complex between L-histidyl-L-serine and glycyl-L-glutamic acid crystallizes in space group P1 with a = 4.706(1), b= 8.578(2), c= 16.521(3) ÅA; α= 85.9(1), β= 89.7(1)°, = 77.4(1). The crystal structure, solved by direct methods, has been refined to an R value of 0.046 for 2150 observed reflections. The two peptide molecules in the structure have somewhat extended conformations. The unlike molecules aggregate into separate alternating layers. Each layer is stabilized by hydrogen bonded head-to-tail sequences as well as sequences of hydrogen bonds involving peptide groups. The arrangement of molecules in each layer is similar to one of the plausible idealized arrangements of L-alanyl-L-alanine worked out from simple geometrical considerations. Adjacent layers in the structure are held together by interactions involving side chains as well as water molecules. The water structure observed in the complex provides a good model, at atomic resolution, for that in protein crystals. An interesting feature of the crystal structure is the existence of two water channels in the interfaces between adjacent peptide layers.

Interaction of Gibberellic Acid and Indole-3-acetic Acid in the Growth of Excised Cuscuta Shoot Tips in Vitro1

Gibberellic acid (GA3) induced a marked elongation of 2.5-centimeter shoot tips of Cuscuta chinensis Lamk. cultured in vitro. In terms of the absolute amount of elongation, this growth may be the largest reported for an isolated plant system. The response to hormone was dependent on an exogenous carbohydrate supply. The hormone-stimulated growth was due to both cell division and cell elongation. The growth response progressively decreased if GA3 was given at increasingly later times after culturing, but the decreased growth response could be restored by the application of indole-3-acetic acid (IAA) to the apex. Explants deprived of GA3 gradually lost their ability to transport IAA basipetally, but this ability was also restored by auxin application. The observations are explained on the basis that: (a) the growth of Cuscuta shoot tip in vitro requires, at least, both an auxin and a gibberellin; and (b) in the absence of gibberellin the cultured shoot tip explants lose the ability to produce and/or transport auxin.

ac susceptibility and electrical resistivity in Fe80-xNixCr20 (21 \leq x \leq 30) alloys

ac susceptibility and electrical resistivity studies on polycrystalline Fe80-xNixCr20 (21 \leq x \leq 30) alloys, with x=21, 23, 26, and 30, between 4.2 and 80 K, are reported. A previous dc magnetization study indicated the presence of ferro-spin-glass mixed-phase behavior in x=23 and 26 alloys while the alloys with x=21 and 30 were found to be spin-glass and ferromagnetic, respectively. The present ac susceptibility results support the above picture. In the electrical resistivity study, a low-temperature minimum in the resistivity-temperature curve is observed in all the alloys except the ferromagnetic one.

Water-ethanol mixtures by molecular dynamics and x-ray Compton scattering

Water-ethanol mixtures are commonly used in industry and house holds. However, quite surprisingly their molecular-level structure is still not completely understood. In particular, there is evidence that the local intermolecular geometries depend significantly on the concentration. The aim of this study was to gain information on the molecular-level structures of water-ethanol mixtures by two computational methods. The methods are classical molecular dynamics (MD), where the movement of molecules can be studied, and x-ray Compton scattering, in which the scattering cross section is sensitive to the electron momentum density. Firstly, the water-ethanol mixtures were studied with MD simulations, with the mixture concentration ranging from 0 to 100%. For the simulations well-established force fields were used for the water and ethanol molecules (TIP4P and OPLS-AA, respectively). Moreover, two models were used for ethanol, rigid and non-rigid. In the rigid model the intramolecular bond lengths are fixed, whereas in the non-rigid model the lengths are determined by harmonic potentials. Secondly, mixtures with three different concentrations employing both ethanol models were studied by calculating the experimentally observable x-ray quantity, the Compton profile. In the MD simulations a slight underestimation in the density was observed as compared to experiment. Furthermore, a positive excess of hydrogen bonding with water molecules and a negative one with ethanol was quantified. Also, the mixture was found more structured when the ethanol concentration was higher. Negligible differences in the results were found between the two ethanol models. In contrast, in the Compton scattering results a notable difference between the ethanol models was observed. For the rigid model the Compton profiles were similar for all the concentrations, but for the non-rigid model they were distinct. This leads to two possibilities of how the mixing occurs. Either the mixing is similar in all concentrations (as suggested by the rigid model) or the mixing changes for different concentrations (as suggested by the non-rigid model). Either way, this study shows that the choice of the force field is essential in the microscopic structure formation in the MD simulations. When the sources of uncertainty in the calculated Compton profiles were analyzed, it was found that more statistics needs to be collected to reduce the statistical uncertainty in the final results. The obtained Compton scattering results can be considered somewhat preliminary, but clearly indicative of the behaviour of the water-ethanol mixtures when the force field is modified. The next step is to collect more statistics and compare the results with experimental data to decide which ethanol model describes the mixture better. This way, valuable information on the microscopic structure of water-ethanol mixtures can be found. In addition, information on the force fields in the MD simulations and on the ability of the MD simulations to reproduce the microscopic structure of binary liquids is obtained.

X-ray studies on crystalline complexes involving amino acids. IV. The structure of L-arginine L-ascorbate

L-Arginine ascorbate, C6HIsN40+.C6H706, a 1"1 crystalline complex between the amino acid arginineand the vitamin ascorbic acid, crystallizes in the monoclinic space group P21 with two formula units in a cell of dimensions a = 5.060 (8), b = 9.977 (9), c = 15.330 (13) A, fl = 97.5 (2) °. The structure was solved by the symbolic addition procedure and refined to an R of 0.067 for 1501 photographically observed reflec- tions. The conformation of the arginine molecule in the structure is different from any observed so far. The present structure provides the first description of the ascorbate anion unaffected by the geometrical constraints and disturbances imposed by the requirements of metal coordination. The lactone group and the deprotonated enediol group in the anion are planar and the side chain assumes a conformation which appears to be sterically the most favourable. In the crystals, the arginine molecules and the ascorbate anions aggregate separately into alternating layers. The molecules in the arginine layer are held together by interactions involving a-amino and ~t-carboxylate groups, a situation analogous to that found in proteins. The two layers of unlike molecules are interconnected primarily through the interactions of the side-chain guanidyl group of arginine with the ascorbate ion. These involve a specific ion-pair interaction accompanied by two convergent hydrogen bonds and another pair of nearly parallel hydrogen bonds.

Plan U.S.R.R. Melitopol'skogo okruga Genicheskogo raiona poluostrova Chongar vymezhevannogo v poriadke chastichnogo izmeneniia ustroistva kolfonda s ustroistvom poselkov, razbivkoiu na polia sevooborota, gony soglasno nakazu N.K.Z dnia 1927, n 52-2825. Izmerenie v nature proizvedeno i plan etot sostovlen X. partieiu po ustroistvu kolfondov

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