Abrupt Change In Slope Research Articles

Fast linear sweep voltammetry studies on polycrystalline lead and electrodeposited lead dioxide (α and β) in aqueous sulphuric acid

Fast linear sweep voltammetry experiment on Pb and PbO 2 (α and β) in H 2 SO 4 are described. The magnitude of the peak current for the anodic oxidation of Pb to PbSO 4 and the cathodic reduction of β-PbO 2 to PbSO 4 is a linear function of the square root of the sweep rate at lower sweep rates and low concentrations of H 2 SO 4 , and the plot shows an abrupt change in slope at higher sweep rates. The experimental data support the view that in low H 2 SO 4 concentrations and at lower sweep rates the rate controlling mechanism for the anodic oxidation of Pb and the cathodic reduction of β-PbO 2 is ionic diffusion in solution and in higher H 2 SO 4 concentrations and higher sweep rates ionic diffusion in the solid state. There is evidence from cyclic sweeping experiments with α-PbO 2 that it undergoes a modification to β-PbO 2 .

The mechanism of the anodic formation of peroxodisulphate ion on platinum—II. Time dependence of the anode potential

At constant cd the potential vs log (time) graphs consist of sections with different slopes; so do the steady-state potential vs SO 4 2− concentration graphs. At the same total cd, the abrupt changes in slope occur at practically the same potentials. The change of potential with time is thus interpreted as being caused by the adsorption of sulphate species, which then become inactive in persulphate formation. This process can be described by first-order kinetics in terms of the active sulphate ions.

Heat Capacity and Magnetization of Polycrystalline MnBr2·4H2O as a Function of Temperature at Magnetic Fields up to 30 000 G in the Liquid-Helium Region

The heat capacity and magnetization of a spherical crystalline powder sample of MnBr2·4H2O has been determined as a function of temperature in applied magnetic fields up to 30 000 G. The H−T diagram for the magnetic transformations has been obtained from the loci of the points inflection in the derived values of the rate of change of the entropy and magnetization with temperature at constant applied magnetic field. The loci of these points of inflection exhibit an abrupt change in slope, indicative of a transition occuring in the portion of the sample having the spin axis aligned parallel with the applied field. The observed phenomena are in agreement with the data reported for optical and microwave absorption.

Studies on potassium nutrition of plants III.—Effects of potassium concentration on growth and mineral composition of vegetable seedlings in solution culture

AbstractBecause of diffusion, the effective concentration of nutrients in contact with plant roots in sand culture is much less than the concentration of the nutrient solution supplied. For comparison with earlier observations in sand culture, solution culture experiments have been made with cabbage and red beet seedlings using readily available equipment for the control, within reasonable limits, of the potassium concentration of the root environment.Weight responses and K content of tops and roots, Na content of tops, top: root weight ratios, percentage dry residue of top and root and potassium flux through the roots were influenced in similar ways by increase of K+ concentration in the medium. There were steep slopes to about K0·1 followed by an abrupt change of slope and levelling off or a slight fall at the highest potassium concentrations. The weight responses, K content of top and root and potassium flux increased with increasing nutrient medium K+ concentration whereas the other relationships were in the reverse direction.Root potassium contents increased in a similar manner to those of the tops but were lower than the latter at corresponding medium K+ concentrations. Root sodium contents rose to a maximum at a medium concentration of 0·1 mequiv./1 of K+ and thereafter fell with increasing potassium in the medium. The sums of the cation equivalents (K, Na, Mg, Ca) in the tops and roots were approximately constant.The limiting potassium concentration was determined from the response curves as the lowest concentration at which maximum yield was obtained. For beet in solution culture, the value was 0·15 and the corresponding concentration in sand culture was 0·7 mequiv./1 (ratio, sand/solution = 4·7); the values for cabbage were, respectively, 0·13 and 0·5 mequiv./1 (ratio, 3·8).The rate of removal of potassium by beet seedlings from solutions containing initial concentrations in the range 0·01‐5 mequiv./1 was determined. The flux of potassium through the root surfaces varied from 0·35–1·89 μg K/g root/sec with increasing initial concentration in the medium.

Airway closure as a function of age

Alveolar P an 2 tracings were examined after VC inspirations of O 2 in subjects aged 7–50. Abrupt changes in slope of the alveolar plateau signified the onset of airway closure. Among adults, the volume at which closure occurred increased linearly with age; this accounted for the age dependent increase in ΔP an 2 of the alveolar plateau which was seen in adults. It is suggested that changes in closing volume were likely due to changes in lung elastic recoil, rather than to changes in the tendency for airways to collapse. Children showed evidence for airway closure at the same lung volume as adults aged 20–29. Children also showed very flat plateaux with damped cardiogenic oscillations.

Thermal Conductivity, Electrical Resistivity, and Seebeck Coefficient of Silicon from 100 to 1300°K

Results are presented of measurements of the thermal conductivity (90-1328\ifmmode^\circ\else\textdegree\fi{}K), the electrical resistivity (300-1273\ifmmode^\circ\else\textdegree\fi{}K), and the Seebeck coefficient (350-1273\ifmmode^\circ\else\textdegree\fi{}K) for single-crystal and large-grained polycrystalline specimens of 99.99+% pure silicon. The thermal conductivity above 387\ifmmode^\circ\else\textdegree\fi{}K was measured by an absolute radial-heat-flow technique; below 350\ifmmode^\circ\else\textdegree\fi{}K, by an absolute longitudinal technique. Some intermediate thermal-conductivity measurements from 300-400\ifmmode^\circ\else\textdegree\fi{}K were made on the polycrystalline material using a comparative longitudinal-heat-flow apparatus. The estimated errors of these three thermal-conductivity methods were \ifmmode\pm\else\textpm\fi{}2%\ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}K, \ifmmode\pm\else\textpm\fi{}1.2%\ifmmode\pm\else\textpm\fi{}0.1\ifmmode^\circ\else\textdegree\fi{}K, and \ifmmode\pm\else\textpm\fi{}4.0%\ifmmode\pm\else\textpm\fi{}1\ifmmode^\circ\else\textdegree\fi{}K, respectively. The estimated error for the electrical-resistivity measurements was \ifmmode\pm\else\textpm\fi{}1.4%\ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}K, and for the Seebeck measurements \ifmmode\pm\else\textpm\fi{}1.6%\ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}K. The thermal-conductivity values were compared with conflicting data from the literature, and they corroborate the higher-temperature results obtained by Glassbrenner and Slack. Therefore, we agree with their conclusion that the electronic contribution is reasonably close to theoretical estimates which include a large ambipolar-diffusion term. The temperature dependence of the lattice thermal resistance has been compared to various theoretical models but no approach seems to explain the data in detail. An abrupt slope change in the thermal resistivity at about 670\ifmmode^\circ\else\textdegree\fi{}K is a major cause of the difficulty.

One-dimensional walls

A one-dimensional wall is one in which the magnetization does not vary throughout the thickness of the ferromagnetic film nor along the length of the wall. There are three types of one dimensional walls: Bloch, Néel, and intermediate. The results of calculations of the structure, width, and type of walls as a function of film thickness and wall angle are discussed. The Néel wall width is inversely proportional to wall angle and to film thickness plus a constant. The Bloch wall width is proportional to the square root of film thickness plus a constant. The transition between Néel and intermediate walls is marked by an abrupt change of slope in the hard-axis hysteresis loop.

Further evidence of contour currents in the Western North Atlantic

A study of compass-oriented sea-floor photographs, echograms and sediment cores on the Atlantic continental margin of North America has been made in order to evaluate the role of deep-sea contour currents in the shaping of the continental rise. The sediments on the upper continental rise consist of lutites which are being deposited on the sea floor in an environment devoid of strong bottom currents. Below an abrupt change in regional slope, that marks the boundary between the upper and lower continental rise, a swift bottom current is observed which flows to the southwest parallel to the contours. Beneath this current the surface sediments are distinctly coarser grained and long cores show many quartz silt laminations in the sedimentary column. Further downslope on the lower continental rise the currents are variable in direction and weaker. Measurements of northerly directions indicate that at certain locations the Gulf Stream may intermittently scour the sea floor. In the area of the Lower Continental Rise Hill a swift southwesterly current is again observed. Hyperbolic echo traces on echograms, prolonged multiple echo sequences, and wedging of sub-bottom reflecting interfaces can be mapped as distinct zones. These zones of sea floor micromorphology parallel the regional contours of the continental rise, and are produced by erosional and depositional processes of bottom currents. We conclude that the continental rise is a large sediment wedge which owes its shape to deep geostrophic contour currents.

Some problems on calc-alkali rock series

Variation curves for SiO2, FeO+Fe2O3, and TiO2 for the differentiation of Skaergaard, Palisade and Dillsburg, and Elephant's Head and New Amalfi intrusions, and the pigeonitic rock series of Izu-Hakone region are compared. Abrupt change of slope of the three curves occurs at approximately the same stage of fractionation for each differentiation series. It is also noticed that the later the stage of the change of slope in the series, the higher the concentration of FeO+Fe2O3 during fractionation. The change of slope is probably caused by appearance of titaniferous magnetite (or magnetite+ilmenite) as a solid phase in the crystallizing magmas, or possibly by sudden increase in the amount of the same mineral separating from the magmas. As the stage of the appearance of magnetite is probably determined by oxygen partial pressure of the magmas, which is in turn related to the H2O content, it is inferred that the Skaergaard differentiation series, where the FeO+Fe2O3 concentration is the highest, was produced from magma with lowest H2O, the pigeonitic rock series, where the FeO+Fe2O3 concentration is the lowest, was produced from magma with highest H2O, and the other two from magmas of in ermediate H2O. In the hypersthenic rock series of Izu-Hakone, the maximum concentration of FeO+Fe2O3 is seen at the earliest stage of fractionation and the maximum FeO+Fe2O3 thereof is even lower than that in the pigeonitic rock series, indicating higher H2O content in the magma of the hypersthenic rock series. The high H2O content in this series is also indicated by the occurrence of orthopyroxene in the groundmass and the appearance of hornblende and biotite as phenocrysts which are normally absent in the other series. The variation trend in chemistry of the hypersthenic rock series agrees with that generally accepted as characteristic of the calc-alkali rock series. It is proposed to confine the term calc-alkali rock series to basalt-andesite-dacite-rhyolite of the hypersthenic rock series and to its plutonic equivalent, if any. The essential factor for producing the calc-alkali rock series is therefore the high concentration of H2O in the magma. It should be remembered that the distribution of the calc-alkali rock series is confined to the areas floored by the sialic crust and also that granitic xenoliths and xenocrysts are common in this series. It is not yet certain however whether contamination of the magma by granitic material is a necessary factor for concentrating H2O in the magma and therefore for producing the calc-alkali rock series.

SOME NEW NEUTRON SEPARATION ENERGIES FOR ISOTOPES OF Hg, Tl, Pb, AND Bi

Values derived from mass spectral doublets are reported for the following mass differences: Hg200−Hg198, Hg201−Hg199, Hg202−Hg200, Hg204−Hg202, Tl205−Tl203, Pb206−Pb204, Pb208−Pb206, Bi209−Pb207, Pb207−Tl205, Pb206−Hg204, and Tl203−Hg201. These mass differences are combined with existing reaction and disintegration data to yield single- and double-neutron separation energies for several of the isotopes of the above elements. The resulting neutron separation energy curves for even N are strikingly similar in shape and all exhibit an abrupt change in slope at N = 124. The curves for odd N do not display the same regularity. Currently accepted values for the total decay energies Tl204–Hg204 and Tl202–Hg202 are probably too large and too small, respectively, but current values for Pb205–Tl205 and Bi208–Pb208 are confirmed.

Molecular motions in amorphous random ethylene‐propylene copolymers

AbstractDynamic mechanical properties (sound velocity and damping factor Q−1) have been determined in some amorphous ethylene‐propylene copolymers from −170 to −15°C. by an electrostatic method at a frequency of the order of 104 Hz.Two abrupt changes of slope are observed in the v—T curves, one at T'g (−120°C.) and one at Tg (−30 to −55°C.) and two regions of high dissipation are noticed in the Q−1‐T curves, one at temperatures between T'g and Tg and one at temperatures above Tg.The transition at T'g and the lower temperature relaxation phenomenon are both attributed to molecular motions of CH2 groups in the main chain and of a limited number of chain elements containing CH3 branching. The transition at Tg and the higher temperature relaxation phenomenon are connected with motions of large sections of the chain.The experimental results are discussed on the basis of the structure of ethylene‐propylene copolymers and suggestions are made concerning the use of dynamic mechanical data for the characterization of these materials.

Adsorption of n-butane on silica gel investigated by direct measurement of the adsorption isotherms

1. Use has been made of a method for the direct measurement of adsorption isosteres, which is convenient in investigating the energy characteristics of the adsorptive equilibrium. It gives more accurate results than the method usually used of interpolating between adsorption isotherms measured at different temperatures. 2. The isosteres coming from the rising adsorption or from the falling desorption branch of the hysteresis loop of the initial isotherm correspond over the range of temperatures and pressures studied with constant values of isosteric heats. The isosteres coming from the horizontal end branch of the original adsorption isotherm correspond with two values of isosteric heats. The first isosteric heats are always greater than the second isosteric heats. 3. Inside the hysteresis region of the end part of the isotherm there are two initial points, which correspond with the two different values of the first and second isosteric heats depending upon whether these points are taken during an adsorptive or a desorptive isothermal process. 4. The curves showing the first isosteric heats as a function of adsorption have high maxima. The desorption points have the higher maximum. The occurrence of maxima may be explained in terms of transformations in the adsorbed phase. A direct experimental demonstration of this is provided by the abrupt change in slope of the adsorption isosteres.

Antimalarial Activity and Metabolism of Biguanides

SummaryThe metabolism of chlorguanide (CG) and chlorguanide triazine (CGT) has been investigated following intramuscular and intravenous administration of CG and CGT to monkeys and oral administration of CG to monkeys and man. In confirmation of earlier investigations in this Institute, it has been found that in both species CG is metabolized to CGT and to the free amine, p-chlorophenylbiguanide (PBG). These two derivatives and the parent drug were the only p-chloroaniline (PCA)-containing metabolites which could be detected in urine of either man or monkey.In the monkey 60 to 80% of CG injected intravenously or intramuscularly was recovered in the urine as total PCA-containing metabolites; about one-third of this urinary PCA was CGT. In man the recovery of total PCA in urine after oral administration of CG ranged from 56 to 66%; of this about 60% was CG, 30% was CGT, and the remainder PBG.Studies in monkeys indicated that serum levels of total metabolites (total PCA) after intramuscular or intravenous injection of CG quickly reached a peak and then fell rapidly for 1 to 2 hours. During the next 2 to 6 hours the concentrations of total PCA-containing materials in serum either did not change or showed a slight increase; this rather abrupt change in slope coincided temporally with the appearance of significant amounts of CGT and possibly PBG in the blood stream. The subsequent die-away curves for total PCA were quite flat when compared to the earlier portions of the curves. Similar results were obtained when CG was administered orally except that with slower absorption from the gastrointestinal tract the peculiar changes in slope coincidental with CGT elaboration appeared somewhat later, usually from 3 to 5 hours after drug administration. Also the proportion of CGT to total PCA in the blood stream was much larger in this case, suggesting that greater conversion of CG to CGT occurs when the drug is given orally and must first pass through the liver.When CGT was administered to monkeys, the serum levels fell rapidly for 2 to 4 hours and then dropped more slowly. As a result, the serum levels of CGT during the period from 4 hours to 24 hours after drug administration were similar whether CG or an equal amount of CGT had been administered. In no instance did the levels of CGT derived from CG exceed those obtained when an equal amount of CGT had been given. These findings suggest that the superior activity of CG compared to CGT against primate malarias must be attributed in part to antimalarial activity inherent in the parent drug.

Effect of Pressure on the Resistance of Iodine and Selenium

The effect of pressure from 60 to over 400 kbar has been measured on the resistance of selenium and iodine. Selenium exhibits a very rapid drop in resistance between 60 and 128 kbar; at 128 kbar it shows a discontinuous drop. At higher pressures its behavior is apparently metallic. Iodine shows a rapid drop in resistance from 60 kbar to the region of 225–255 kbar where there is relatively abrupt change of slope. At higher pressures the change in resistance with pressure is much smaller. It is interesting to note that the optical energy gap of selenium extrapolates to zero at about 130 kbar, while the optical gap for iodine extrapolates to zero at 240 kbar.

Heat Contents above 298.15°K. of Oxides of Cobalt and Nickel

High temperature heat content measurements of cobaltous oxide, cobalt spinel and nckelous oxide were conducted from 298 deg K to 1805, 999, and 1810 deg K, respectively. The heat content-temperature curve of nickelous oxide shows abrupt changes in slope at 525 and 565 deg K, indicating secondorder transformations. A table of heat content and entropy increments ahove 298.15 deg K and heat content equations are included for use in thermodynamic calculations. (auth)

Intrinsic Optical Absorption in Germanium-Silicon Alloys

The intrinsic optical absorption spectrum for the germanium-silicon alloy system has been measured as a function of temperature and composition. Over the entire composition range the absorption near the threshold ($Kl100$ ${\mathrm{cm}}^{\ensuremath{-}1}$) exhibits a temperature dependence which is characteristic of phonon-assisted indirect electronic transitions. There appears to be no temperature-independent component of the absorption attributable to disorder-assisted transitions. When the phonon contribution to the absorption is explicitly taken into account, as in a Macfarlane-Roberts type analysis, the experimental data yield an equivalent phonon temperature which varies from 270\ifmmode\pm\else\textpm\fi{}20\ifmmode^\circ\else\textdegree\fi{}K for pure Ge to 550\ifmmode\pm\else\textpm\fi{}50\ifmmode^\circ\else\textdegree\fi{}K for pure Si, with most of the variation occurring in the middle of the composition range. The composition dependence of the derived energy gap shows an abrupt change in slope at about 15 atomic percent Si. This is due to a switch from a Ge-like ([111]) to a Si-like ([100]) conduction band structure. The onset of direct electronic transitions (${10}^{2} {\mathrm{cm}}^{\ensuremath{-}1}lKl{10}^{4} {\mathrm{cm}}^{\ensuremath{-}1}$) was observed as a function of composition in the Ge-rich alloys. The data show that the [000] conduction band minimum moves more rapidly than the [111] minima as Si is added to Ge. In an attempt to account for the observed variation of the phonon equivalent temperature with composition, certain lattice vibrational modes were computed on the basis of a number of simplified models. The one which gives the most realistic results emphasizes the presence of atoms of different masses and some short-range order in the alloy lattice.

Magnetic and Electrical Properties of Manganese Telluride

The temperature dependence of the susceptibility of the antiferromagnetic compound MnTe was measured over a range of temperature between liquid nitrogen temperature and 720°C. An abrupt change in slope and a maximum of the susceptibility curve were found at 37°C and at 55°C respectively. These results are compared with the observed Néel temperatures previously reported by Squire and by Serre. A thermal hysteresis was also found above the Néel temperature, relating to the heat history of the specimen. It is shown that the susceptibility of MnTe 1+ x (0≤ x ≤1), where x is the excess content of tellurium, is explicable in terms of two phases, MnTe and MnTe 2 which posses different susceptibilities. The electrical properties, i.e., the resistivity, the thermo-emf and the Hall emf, were measured as functions of temperature. Evidence was found of anomalous behaviours at the Néel temperature for them. A large thermal hysteresis of the resistivity is also found above the Néel temperature, which suggests a change of the crystal structure at about 130°C.

Evaluation of significance of slope changes in double‐mass curves

The double‐mass method is commonly used in the interpretation of precipitation records. Interpretation of double‐mass curves frequently involves rejection or acceptance of indicated changes in slope. Often, the decision must be based on inadequate station records. In any case, it is important that the analyst should know the probability of getting an abrupt slope change purely by chance. The significance of any slope change can be evaluated by a statistical treatment making use of range instead of standard deviations. The application is simplified by a special protractor and simple nomograph.

The Sorption of Synthetic Surface-Active Compounds by Carbon Black

The sorption on carbon black of a number of types of anionic, cationic, and nonionic surface- active compounds from aqueous solutions has been measured. It is shown that the sorption of these compounds does not conform to the Freundlich adsorption isotherm over the whole of the concentration range studied (0.01%—0.2% by weight). In the majority of cases an abrupt change in slope of the curve occurred at concentrations which appear to correspond, at least approximately, to the critical micelle concentrations of the various compounds. At con centrations above this critical point the plot of log X vs. log C appeared to be linear, but below the critical point considerable deviation from lineality was observed in some cases. The sorption of sodium alkyl sulfates increased with increasing chain length of the alkyl group at constant temperature, and decreased with increasing temperature at constant chain length. A series of compounds differing widely in chemical constitution, and including both anionic and cationic agents, were shown to be remarkably similar with respect to the general level of adsorption. Two typical nonionic compounds were found to be sorbed somewhat more strongly, particularly at higher concentrations, than any of the other compounds investigated. The addition of sodium sulfate to solutions of anionic compounds resulted in an increase in the sorption of the latter in every case.

Origin of Abrupt Change in Slope at Continental Shelf Margin

An abrupt change in slope marks the boundary between the continental shelf and the continental slope. The slope change previously has been attributed to (1) sedimentation at wave base and in equilibrium with present sea-level, (2) sedimentation at wave base but related to some past lowered sea-level, (3) wave abrasion in equilibrium with present sea-level, and (4) wave abrasion related to some past lowered sea-level. To test these various possible origins, the concept of wave base is examined theoretically. It is found that wave base appears unimportant in the regimen of the sea, and it does not account for the observed shelf-break. The break appears to be related to the depth at which breakers form which, excluding rare cases, is at a maximum of about 5 fathoms. The wr ters term this the depth of vigorous abrasion. On theoretical grounds it appears, therefore, that the break-of-slope is caused by wave abrasion related to a sea-level lowered to within about 5 fathoms of the break. This theory is tested with several field facts and these appear to confirm it. For example, the depth of the shelf-break is approximately the same on the windward and the leeward side of islands which is in agreement with the concept of the break being formed at the depth of vigorous abrasion, but is in disagreement with the concept of wave base. Some geological implications of this theory are briefly discussed. These are: (1) sea-level has recently (geologically speaking) risen eustatically, (2) this recent rise has taken place more rapidly than changes of land-level effected by erosion, sedimentation, or diastrophism.