Upward Inflection Research Articles

An STM study of the oxidation of Mg( [formula omitted

We have studied the oxidation of Mg(0 0 0 1) using electron stimulated desorption ion angular distributions, low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Two structures associated with the oxidation were observed by STM and are identified as a suboxide, consisting of incorporated oxygen, and ionic MgO. We observed that both the clean step edges and oxygen adsorbed on the terraces were highly mobile and interact with the STM tip at room temperature. Ionic oxide is observed to form first at defect sites along step edges and grows as an elongated pillar. These ionic oxide nucleation sites appear to be point defects that pin two terraces forming a double step. A form of suboxide characterized by broad bumps 1.2 Å across and 3.6 Å in height were observed on the terraces. The bumps increase in number and the pillars grow in area and height with increased oxygen exposure. At 12 L (Langmuir=1×10 −6 Torr s), the bumps coalesce to completely cover the surface. LEED shows a diffuse 1×1 pattern indicating that this coalesced phase is in registry with the Mg substrate. At 14 L, protrusions begin to form on the terraces and an upward inflection point is observed in the ESD ion yield, indicating that the oxide is now on the surface. At higher oxygen exposures, these protrusions continue to grow in size leading to an increased coverage of the ionic oxide.

Thermotolerance of leaf discs from four isoprene-emitting species is not enhanced by exposure to exogenous isoprene

The effects of exogenously supplied isoprene on chlorophyll fluorescence characteristics were examined in leaf discs of four isoprene-emitting plant species, kudzu (Pueraria lobata [Willd.] Ohwi.), velvet bean (Mucuna sp.), quaking aspen (Populus tremuloides Michx.), and pussy willow (Salix discolor Muhl). Isoprene, supplied to the leaves at either 18 &mgr;L L-1 in compressed air or 21 &mgr;L L-1 in N2, had no effect on the temperature at which minimal fluorescence exhibited an upward inflection during controlled increases in leaf-disc temperature. During exposure to 1008 &mgr;mol photons m-2 s-1 in an N2 atmosphere, 21 &mgr;L L-1 isoprene had no effect on the thermally induced inflection of steady-state fluorescence. The maximum quantum efficiency of photosystem II photochemistry decreased sharply as leaf-disc temperature was increased; however, this decrease was unaffected by exposure of leaf discs to 21 &mgr;L L-1 isoprene. Therefore, there were no discernible effects of isoprene on the occurrence of symptoms of high-temperature damage to thylakoid membranes. Our data do not support the hypothesis that isoprene enhances leaf thermotolerance.

CHEMISTRY OF MANTLE PERIDOTITES FROM TROODOS OPHIOLITE

A detailed geochemical mapping of the mantle peridotite section in the Troodos ophiolite massif has revealed a kmscale compositional heterogeneity. Based on the Cr# (Cr/(Cr+Al)) of spinel and modal abundance of clinopyroxene (cpx) we subdivided the mantle section into two units: 1) spinel lherzolite with a Cr# of 0.22-0.28, and 5-7 modal % cpx and 2) harzburgite with a Cr# 0.51-0.70, and 0.5-1 modal % cpx. The boundary between spinel lherzolite and harzburgite units coincides with that separating Wilson’s (1959) limit between zone abundant chrysolite veinlets and rare chrysolite veinlets. Small-scale compositional heterogeneity is present within both lherzolite and harzburgite units. The spinel lherzolite contains numerous dunite bodies. Zones of cpx-bearing harzburgites are located between the spinel lherzolites and the dunite bodies and have higher Cr# of spinel (0.32-0.45) and lower modal cpx 1.5-4.5 % than surrounding spinel lherzolite. These harzburgites will be refereed later on as a harzburgites-II to distinguish them from the harzburgites of the main unit (harzburgites-I). The dunites display the highest Cr# of spinel (between 0.70-0.84). Contacts between spinel lherzolite and harzburgite-II are gradational. Contacts between harzburgite-II and dunite are sharp. While cpx is present in the contact zone between harzburgite- II and dunite, dunites themselves are cpx free. Clinopyroxenite and enstatitite veins are associated with dunite bodies. The harzburgite-I unit underlies the ultramafic metacumulates representing the “petrologic” Moho (Allen, 1975; etc). Dunite, plagioclase lherzolite bodies and gabbroic impregnation zones are abundant within the main harzburgite. Spinel lherzolites display a narrow compositional range over the entire unit, well within compositional variations of abyssal peridotites in respect to both trace element concentrations of cpx and mineral chemistry. The incompatible element patterns of cpx are very close to those of abyssal peridotites with only difference in a slight upward inflection of La and Ce of former (Fig. 1A). Cpx from harzburgite- II surrounding the dunite bodies within the lherzolite unit have lower HREE concentrations and extremely low (close to SIMS detection limit) MREE concentrations (Fig. 1B). They show very significant upward inflection of La and Ce relative to Nd. Cpx from the enstatitite vein shows the same trace element pattern. Cpx from the clinopyroxenite veins differs from those of harzburgite-II by having higher MREE concentration (Fig. 1B). All these rocks are close in their cpx trace element composition and mineral chemistry to forearc peridotites and most depleted Oman harzburgite (Fig. 1B). Cpx from the harzburgite-I unit are extremely depleted in HREE (Fig. 1A). Their MREE concentrations are below detection limit of SIMS. The close association of cpx with opx and grains morphology suggests that cpx formed by exsolution from opx during recrystallization accompanying solid-state deformation (Sobolev and Batanova, 1995). The modeling suggest that spinel lherzolite represents the residue of 12% critical melting of a depleted (MORB-like) mantle source with a low residual mantle porosity (0.1%) The upward inflection of La and Ce could be explained by subsequent melt percolation event. The structure of cpx-bearing harzburgite – dunite zones, their position within the spinel lherzolite and their association with magmatic pyroxenite veins allows us to suggest that these zones could be produced by reaction of spinel lherzolite with percolating melts. Dunite bodies and surrounding cpx-bearing harzburgite-II represent pathways of the melts in the mantle. Some of these melts were close to ultra-depleted boninites from Troodos upper pillow lavas. However the majority of analyzed clinopyroxenes suggest a percolation of melts significantly more depleted in MREE than any known so far. Such melts could form by second stage melting of refractory lherzolite but require addition of LREE and Zr enriched component likely of subduction related origin. A more plausible mechanism for the production of the harzburgite-I can be regarded as an open-system reaction between infiltrating melt and the initial spinel lherzolite.

Structural Inversion: Occurrence, Mechanics, and Implications for Petroleum Exploration: ABSTRACT

Structural inversion, defined as the uplift of previously extended, subsiding regions by later contraction, has been recognized on every continent that has been explored for petroleum. The process can occur at the large scale of deformation in orogenic belts, but this presentation focused on inversion affecting sedimentary basins and their associated structures. The mid-continent rift and the Uinta Mountains of northeastern Utah are good examples of basin inversion. Typically, rift and sag basins can be later inverted. Mainly by reactivation of older normal faults, inversion selects rift basins where, in pure shear, weakening because of necking or thinning of lithosphere has occurred, and where, in simple shear, mechanical detachment surfaces are available for subsequent movement. Sag basins can apparently be inverted in the absence of reactivated normal faults, as in the southern altiplano of Bolivia and offshore Sabah, Borneo. Basins can be inverted by dominant strike slip with some convergent component, e.g., offshore northeast Brazil, and by almost direct compression, e.g., Atlas Mountains, Morocco. Structural inversion has important implications for petroleum exploration. Areas of inversion frequently have tighter porosity for a potential reservoir and faster seismic velocity for a particular stratigraphic interval than would be expected for their present depthmore » of burial. Burial history curves characteristically have an upward inflection at the time of inversion, which can affect the hydrocarbon maturation process. Some source rocks may be overmature for present burial depths. In some presently shallow basins, however, maturation would not have occurred had not source rocks once been buried more deeply. Inversion can cause remigration of hydrocarbons. Finally, inversion can create the trapping structures.« less

Time-Temperature Relationships for L1A2 Cells Step-Down Heated from 38 to 45°C in Vitro

The in vitro response of L1A2 cells to a single exposure to one temperature and to step-down heating was investigated. Single heating consisted of heating for a specified time at a constant temperature in the range 38.0-45.0 degrees C, whereas step-down heating involved a pretreatment of either 45.0 degrees C for 10 min or 42.0 degrees C for 90 min. The pretreatments were adjusted to give the same survival level. The survival curves for single heating had an initial shoulder followed by an exponential region, whereas for step-down heating they were strictly exponential and had no shoulder. The time-temperature relationship for cells exposed to single heating showed a biphasic Arrhenius curve with a downward inflection at 40.5 degrees C. Biphasic Arrhenius curves were also observed for step-down heating, but both the 45 degrees C/10 min and the 42 degrees C/90 min pretreatment showed an upward inflection that broke at 42.5 degrees C and 40.5 degrees C, respectively. The downward inflection on the Arrhenius curve for single heating has been attributed to thermotolerance development and the effect of step-down heating to a temporary inhibition of thermotolerance development. However, the present shape of the Arrhenius curves for step-down heating cannot be explained by inhibition of thermotolerance. It is therefore reasonable to assume that step-down heating is more than just the inhibition of thermotolerance, and that step-down heating and thermotolerance are distinct phenomena which act independently.

Electron paramagnetic resonance of the high-T c superconductor Y 0.9Er 0.1Ba 1.9Sr 0.1Cu 3O 7−δ

The Y 0.9Er 0.1Ba 1.9Sr 0.1Cu 3O 7−δ superconductor has been investigated by X-band EPR in the temperature range 4.2–300 K. The superconducting transition temperature of the sample has been determined to be T c = 88 K. No copper EPR line was observed at any temperature, contrary to that observed in the undoped high- T c superconductor YBa 2Cu 3O 7−δ. The sizes of the Josephson junctions are determined to be in the range 0.4–0.7 μm. The dependence of the lower critical field H cl on temperature exhibits an upward inflection at ∼ 15 K, possibly due to the dimensional effect, which is observed in multilayered and granular weakly coupled superconductors. The lower critical field and the upper critical field, as extrapolated to 0 K, have been estimated to be H c1 (0) = 19 mT and H c2 (0) = 83 T, respectively, while the Sommerfeld constant γ = 4.8 mJ mol −1 K −2. The spin-glass nature of the sample, below T c, has also been confirmed by the observed shift in the base line. The values of the critical exponent defined by I ≃ (T c − T) n , where I is the intensity of the low-field microwave absorption, is determined to be n = 1.32.

Upper critical field of V-Ag multilayered superconductors.

We report investigations of the upper critical field (H/sub c//sub 2//sub perpendicular/ and H/sub c//sub 2//sub X/) of V-Ag proximity-coupled superconducting multilayer structures, prepared by ultrahigh-vacuum electron-beam evaporation. By means of x-ray diffraction analysis, successful formation of an artificial superstructure is confirmed. From resistivity measurement parallel to the layers, the electron mean free paths in the V and Ag layers are determined. With reference to these transport properties, characterization of H/sub c//sub 2/ has been made. For three-dimensional multilayer structures, H/sub c//sub 2/ is analyzed in terms of the temperature dependence of H/sub c//sub 2//sub perpendicular/, the zero-temperature coherence length, and the anisotropy H/sub c//sub 2//sub X//H/sub c2//sub perpendicular/. Our results are in quantitative agreement with the relevant theories. For quasi-two-dimensional multilayer structures, a peculiar temperature dependence has been revealed in both H/sub c//sub 2//sub perpendicular/ and H/sub c//sub 2//sub X/. H/sub c//sub 2//sub perpendicular/ exhibits positive curvature near T/sub c/, and it is continuously enhanced with the increase of multilayer period, as predicted theoretically. In contrast with the monotonic variation in H/sub c//sub 2//sub perpendicular/, a drastic upturn at a certain temperature (dimensional crossover) and an upward inflection at a higher temperature have been observed in H/sub c//sub 2//submore » X/. These two types of anomalies in H/sub c//sub 2//sub X/ are discussed in the context of the commensurability between the multilayer structure and the vortex lattice.« less

Electrical properties and membrane currents in the ciliateDidinium

1. The electrical properties of the ciliateDidinium nasutum, aParamecium predator, have been investigated using techniques of constant current injection, voltage-clamp, exchange of solutions, and non-lethal deciliation. The electrical observations have been related to structural characteristics (Fig. 1). 2. The resting potential was primarily K-dependent. K concentrations beyond 1 mmol/1 depolarized the cell and reduced the input resistance. The resting conductance for Ca was low. Partial substitution of Ca by Mg changed the membrane potential very little and had no effect on the input resistance. Chloride did not influence the membrane properties. 3. The late V/I-relationship was characterized by pronounced outward and minimal inward rectification. It was very little modified by Ca concentrations ranging between 0.125 mmol/1 and 8 mmol/1. Raising the K concentration between 0.063 and 16 mmol/1 did not affect membrane rectification. 4. Membrane depolarization triggered a stimulus-graded action potential, which was Ca-dependent. The action potential rose with rates of up to 6 V/s; its overall duration was 100 to 500 ms. Repolarization occurred along a fast and a slow (shoulder) component and was followed by pronounced after-hyperpolarization. 5. Complete deciliation ofDidinium eliminated the regenerative depolarization of the membrane. The resting potential, input resistance and late current/voltage relationship were not modified by the removal of ciliary membranes. Under voltage-clamp deciliation removed the early inward current and the hump component of the late outward current. 6. Depolarizing voltage-clamp pulses of up to + 20 mV revealed a residual inward current following the early transient. The transient included two decay time constants (3.3 ms; 31.8 ms). An 0.8 nA persistent inward current was isolated using the difference current of ciliated and deciliated cells. A late outward current rose with depolarizations beyond 20 mV including an upward inflection (hump) about 50 ms after step onset. 7. A decreasing Ca/Ba mole-fraction increased the frequency and duration of spontaneous action potentials, and depressed the amplitudes of both, early inward and late outward current under voltage-clamp. In Ca-free Ba solution the unclamped membrane fired repetitively; the depolarizations included shoulders of 10 s or more. Inactivation of inward Ba currents was slow under depolarizing voltage-clamp; the late outward current was strongly depressed. In deciliated cells an early inward current was missing in Ca-free Ba solution, and the late I/V relation resembled that of deciliated cells in Ba-free Ca solution. 8. Tail currents following the late outward current of ciliated cells in Ca-solution and of deciliated cells in Ca- or Ba-solutions decayed with similar time constants. 9. In conclusion, the voltage-activated Ca conductance of the ciliary membrane ofDidinium compares well with data from ciliates so far studied. Unique is (i) a persistent inward current isolated using minor step depolarization or the difference current of ciliated and deciliated cells, (ii) a slow activating voltage-dependent K conductance, and (iii) a late, potentially Ca-dependent, outward current, which may be related to spatial separation of the cilia from the majority of the soma membrane. Ba interferes with the Ca channel which favours a previous two-binding site model. Ba can inhibit the K conductance from inside the cell after passing the ciliary Ca channel.

Wind speed limits to work under hot environments for clothed men

Four heat-acclimated clothed young adult men exercised (treadmill) at metabolic rate of 191 W.m-2 (27% VO2 max), under five air temperatures (Ta) between 36 and 53 degrees C and three wind velocities (v), 1, 2, and 4 m.s-1, for 2 h. The 2nd h of each experiment involved progressive increases in the ambient vapor pressure (Pa) to force an upward inflection of the rectal temperature (Tre). The Tre point of inflection identified the critical Pa (Pcrit) for each Ta. The average mean skin temperature (Tsk = 36 degrees C for all Pcrit. Straight-line isotherms for Tsk = 36 degrees C, which agreed with the negative regressions of the Pcrit on Ta, represented the limits of exposure for Ta less than or equal to 44 degrees C. The slope characteristics of the isotherms corresponded with skin wettedness (w) of 0.94, 0.71, and 0.58, respectively, for v of 1, 2, and 4 m.s-1. For Ta greater than 44 degrees C the limit line corresponded with steeper negative regressions indicating a lower w than for Ta less than or equal to 44 degrees C. Despite the increase in the ambient evaporative capacity due to the higher v the limit lines describing exposure limits were not significantly different either at Ta less than or equal to 44 degrees C for v of 2 and 4 m.s-1 or at Ta greater than 44 degrees C for all three v.

Anomalous Light Scattering by Poly(2-vinylpyridine) in Methanol

Abstract The light scattering of a poly(2-vinylpyridine) solution was measured under various conditions. In solvents such as methanol, ethanol, 2-propanol, 2-butanone, and pyridine, anomalous Zimm plots with an upward inflection at lower angles were observed. This anomaly was especially striking in methanol, in which the dissymmetry coefficient was frequently less than unity. Systematic investigations carried out with methanol as a solvent revealed that; (1) the anomaly does not depend appreciably on the concentration or tacticity of the polymer, the temperature, or the wavelength of the incident light; (2) the anomaly diminishes with an increase in the molecular weight of the polymer; (3) the anomaly disappears upon the addition of dry ammonia of 10−2 mol/1 or more in methanol, and (4) similar perturbed Zimm plots are realized by the addition of a trace amount of hydrochloric acid or sulfuric acid in a methanol solution of a higher-molecular-weight fraction which showed a normal Zimm plot in pure methanol. The anomaly can not be explained in terms of the effects of the optical anisotropy of the polymer segment, but the external interference arising from the non-random arrangement of the polymer in solution may contribute to it.

Ammonia Volatilization from Soils1

AbstractIf NH4+‐N fertilizers are used, most agronomic crops grow best if the soil reaction is near neutrality. Previous studies have shown that if the soil pH becomes alkaline, NH3 volatilization losses of N occurs. The objective of this study was to determine whether or not a rapidly growing crop could reduce the volatilization losses of N, especially from soils above pH 7 to which large applications of NH4+‐N fertilizers were made. This study was conducted in a greenhouse using a closed system in which all NH3 evolved from the soil was swept away by a stream of air and collected. The amount of NH3‐N evolved from the soils was measured as a function of time, soil pH, amount of N application, and presence or absence of corn (Zea mays indentata Bailey) seedlings. Ammonia losses with or without plants in the system increased as the soil reaction and amount of NH4+‐N application increased. A sharp upward inflection in NH3‐N loss occurred at pH 7.2. Plants reduced NH3‐N losses by atleast 60% in the alkaline soils and by lesser amounts in the acidic and neutral soils. Rapid absorption of NH4+‐N by plant roots appeared to account for the conservation of N.

Upwelling and nutrient regeneration in the Benguela Current, October, 1968

A hydrographic and nutrient survey in the inner part of the Benguela Current, between Sylvia Hill and Dune Point, South West Africa, was made from 25th to 31st October, 1968. Cool, low salinity, oxygen-poor and nutrient-rich water was present along the coast, this being particularly marked off Sylvia Hill. The upward inflection of the isopycnals was most intense in the south where upwelling was active while some stabilisation of the water was experienced farther north. The upwelled water was derived from depths of 150–250 m.Nutrient concentrations were high in the bottom shelf waters compared with the offshore water at the depth of upwelling. Such high concentrations were produced by in situ regeneration within the upwelled water. The ratios of change of the nutrient concentrations varied across the shelf indicating differing rates of regeneration of the individual nutrients.High bottom nitrite concentrations were accompanied by low nitrate and oxygen concentrations in some areas indicating nitrate reduction. In these cases the Δ N : Δ P ratio was quite different from open sea or outer shelf values.

31. Relative Growth in Amphibia

31. Relative Growth in Amphibia