Abrupt Change In Slope Research Articles

Anomalous magnetizations in melt spinning Ni–Mn–Ga

The structural and magnetic characteristics were studied for martensitic and austenitic Ni–Mn–Ga melt-spun ribbons of as quenched and as annealed at different temperatures. No essential structure change was found before and after annealing, but there are some anomalies in the magnetization process. In the austenite state the M(T) curves measured in 100 Oe field exhibit a Hopkinson peak at TC for the ribbons of as quenched and annealed at 573 and 773 K, but the curves monotonically decays to zero with the increasing temperature to TC after annealing at 1073 K. In the martensite phase of both as quenched and 573 K annealed ribbons an abrupt increase in the slope of the M(H) curve was observed; it appears to be due to the onset of magnetic-field-induced twin boundary motion. The abrupt slope change disappeared in the ribbons annealed at temperatures higher than 773 K. The ribbon processing history and particularly the quenched-in internal stress were modeled to probe the possible mechanisms for the anomalous magnetization behaviors, combining the grain-grain strain stored in the polycrystalline. The annealing temperatures were clarified into three groups according to their effects on the magnetization behaviors of the austenite and martensite.

REVEALING PROBABLE UNIVERSAL FEATURES IN THE LOWER RED GIANT BRANCH LUMINOSITY FUNCTIONS OF GALACTIC GLOBULAR CLUSTERS

This paper aims at demonstrating, for the first time, very probable universal peculiarities of the evolution of stars in the lower red giant branch (RGB) of Galactic globular clusters (GCs), reflected in two corresponding dips in the luminosity functions (LFs). By relying on the database of Hubble Space Telescope photometry of GCs, we analyze the lower RGB LFs of a sample of 18 GCs in a wide metallicity range, Δ[Fe/H] ≈ 1.9 dex. We first show that in the F555W–(F439W–F555W) color-magnitude diagrams (CMDs), the lower RGB of GCs, except for the most metal-poor of them, frequently shows an apparent knee. It reveals itself as a fairly abrupt change of the RGB slope. At the same luminosity level, the RGB LFs show a feature in the form of a more or less pronounced dip. We find that the magnitude difference between the RGB base and the given feature is, on average, around Δ F555Wdip base≈ 1.4 mag. It shows a marginal variation with metallicity, if any, comparable to the error. At the same time, the magnitude difference between the dip and the RGB bump, Δ F555Wbump dip, decreases with increasing metallicity and falls within the range 0.8 Δ F555Wbump dip 1.7 mag. Generalized LFs (GLFs) have been obtained for three subsamples of GCs within limited metallicity ranges and with different horizontal branch (HB) morphology. They reproduce the knee-related dip that is statistically significant in two of the GLFs. This feature turns out to be more pronounced in the GLFs of GCs with either the blue or red HB morphology than with the intermediate one. The same GLFs also reveal an additional probable universal dip. It shows up below the RGB bump at Δ F555W slightly increasing from ~0.3 to ~0.5 mag with increasing metallicity. Also, the statistical significance of this prebump dip increases, on average, toward higher metallicity. Except for the well known RGB bump, no other universal features corresponding to those found here were so far empirically revealed or theoretically predicted in the lower RGB of GCs.

Nanoindentation of Ti50Ni48Fe2 and Ti50Ni40Cu10 shape memory alloys

Abstract In the present paper we use nanoindentation to investigate two shape memory alloys, austenitic Ti50Ni48Fe2 and martensitic Ti50Ni40Cu10 which both show two step martensitic transformations on cooling from the high temperature regime. No such two step features were observed during nanoindentation. Load controlled nanoindentation experiments were performed using a Berkovich indenter using maximum loads ranging from 0.5 to 85 mN resulting in maximum indentation depths between 30 and 1350 nm. For small maximum indentation loads below 5 mN, longer indentation times result in larger indentation depths (austenitic Ti50Ni48Fe2). At loads of about 1 mN the indentation curves show an abrupt change in slope which we suggest to be related to an interaction of the deformation and failure of a thin oxide layer and the formation of stress induced martensite (austenitic Ti50Ni48Fe2) or the de-twinning of martensite (martensitic Ti50Ni40Cu10). Nanohardnesses and shape recovery ratios strongly increase with decreasing indentation depths below 400 nm. For larger indentation depths, constant values are observed (austenitic Ti50Ni48Fe2: nanohardness 2.45 GPa/recovery ratio 0.25, martensitic Ti50Ni40Cu10: nanohardness 1.6 GPa/recovery ratio 0.4).

New proposals on “hyperentanglement” of galactomannans: Solution viscosity of fenugreek gum under neutral and alkaline conditions

Previous studies have shown that double-logarithmic plots of ‘zero-shear’ specific viscosity versus degree of space occupancy ( c[ η]) for disordered polysaccharide coils fall into two linear regions, with an abrupt change in slope from ∼1.4 to ∼3.3 at c[ η] ≈ 4, due to interpenetration of neighbouring coils to form an entangled network. For guar gum and other galactomannans of higher mannose:galactose ratio, however, the transition from dilute to semi-dilute solution properties occurs at lower degree of space occupancy (typically at c[ η] ≈ 2.5) and the subsequent slope is steeper (typically ∼5). These departures from “normal” concentration-dependence have been attributed to association (“hyperentanglement”) of unsubstituted mannan regions of the galactomannan chains. The purpose of the present investigation was to test this interpretation by studies of fenugreek gum, in which the mannan backbone is almost fully substituted with galactose sidechains. The plot of log η sp versus log c[ η] for fenugreek gum in water was similar to those reported for galactomannans of lower galactose content and, as also observed for other galactomannans (guar gum and locust bean gum), dissolving in strong alkali caused a reduction in viscosity (in both the dilute and semi-dilute regimes) which was almost fully reversed on neutralisation, consistent with ionisation of hydroxyl groups and consequent dissociation of “hyperentanglements” by electrostatic repulsion. Intrinsic viscosity, [ η], decreased sigmoidally when plotted against the logarithm of alkali (NaOH) concentration, with the midpoint coming at [NaOH] ≈ 50 mM (pH ≈ 12.7). Plots of log η sp versus log c[ η] for fenugreek gum in alkali (0.1 M and 1.0 M sodium hydroxide; 1.0 M tetramethylammonium hydroxide), however, superimposed closely on the plot obtained with water as solvent, but viscosities in the semi-dilute regime were substantially higher when salt (0.9 M NaCl) was incorporated in solutions prepared in 0.1 M NaOH. These observations are interpreted as follows. (i) The original concept of hyperentanglement is broadly correct, but association occurs perpendicular to the direction envisaged initially, with galactose sidechains in the participating strands lying above and below one another, and with therefore no necessary involvement of unsubstituted regions of mannan backbone. (ii) Progressive addition of alkali has two simultaneous opposing effects. The first is to destabilise hyperentanglements by progressive introduction of negative charge along the polymer chains. The second is to cause progressive shielding of the resulting electrostatic repulsions, because of the increase in ionic strength as the concentration of alkali is increased, thus allowing association to persist between the charged chains. (iii) When ionic strength is increased with no accompanying increase in charge density, by addition of salt, the screening effect can be seen in isolation, giving rise to the observed increases in solution viscosity.

Determination of Wrinkling Criteria for an Incompressible Polymer Membrane by Non-Linear Elastic Finite Element Method

A wrinkling criterion for non-linear elastic membrane materials such as thin polymer, fabric or rubber structures has been determined by employing finite element analysis as an alternative to the difficult experimental counterpart. The hyperelastic constitutive equation proposed by Ogden was implemented into the commercial finite element program ABAQUS with user material subroutine VUMAT. The relation between strain energy and the principal values of the stretch tensor was obtained in order to trace the wrinkle/non-wrinkle boundaries. It was shown that the wrinkling of an elastic membrane can be regarded as being initiated at the instance of abrupt slope change of the strain energy-stretch curve, which was verified by comparing the criterion obtained by finite element analysis with the existing analytical solution.

High-Pressure Phase Behavior of the Binary Systems (Propane + Diamantane) and (Ethane + Diamantane)

(Solid + fluid) and (vapor + liquid) equilibria for the binary systems (propane + diamantane) and (ethane + diamantane) were determined according to the synthetic method in the temperature range 360−510 K and in the pressure ranges 0.3−14 and 0.3−200 MPa, respectively. Also, for both systems the high-temperature branch of the three-phase curve (solid diamantane + liquid + vapor) was determined. In both systems, this curve starts at the second critical endpoint where the three-phase curve intersects the vapor—liquid critical curve and runs to higher temperature with a negative slope dP/dT to the triple point of diamantane. Due to a solid—solid transition of pure diamantane, the three-phase curve (solid diamantane + liquid + vapor) of both systems shows an abrupt change in slope at the point where it intersects the solid—solid transition curve of diamantane. This quadruple point SISIILV is found for (propane + diamantane) at T = 442.64 K and P = 4.110 MPa and for (ethane + diamantane) at T = 445.49 K and P ...

Order-disorder transformations in Sm–Co and Sm–Co–ZrC systems with 2-17 stoichiometry

This work investigates the order-disorder transformations utilizing time-resolved x-ray diffraction at the Advanced Photon Source. The metastable phases that can form during the order-disorder transformations in the Sm–Co intermetallics have the potential to produce materials with enhanced permanent magnetic properties. The high-temperature experiments transformed the disordered alloys with the TbCu7-type structure obtained by rapid solidification into the mixture of the hexagonal and rhombohedral ordered structures at 1375K. The ordering process and the role of the ZrC alloying on the phase formation and ordering transformations were examined. The results showed the formation of shoulders of the fundamental peaks and superlattice peak broadening prior to complete ordering. The lattice parameters expanded linearly up to the onset of ordering, after which an abrupt change of slope was observed. The change in slope suggests a nucleation and growth mechanism for the ordering transformation. The effect of ZrC alloying promoted the formation of the disordered structure in the as-solidified state and lowered the onset of the ordering temperature.

Solubility of hydroxyapatite by solid titration at pH 3–4

Objectives The solubility isotherm (S) of hydroxyapatite (HAp) is of fundamental importance to saliva chemistry, dental caries and related contexts. It has previously been shown that the locus of the S[HAp] is substantially lower than is commonly reported, and of different slope, probably due to HAps incongruent dissolution. The aim of the present study was to determine the S[HAp] over a wider pH range and to identify the precipitate formed at equilibrium in HAp solid titration. Methods The solid titration technique of Leung and Darvell (Leung VW-H, Darvell BW. Calcium-phosphate system in saliva-like media. J Chem Soc Faraday Trans 1991; 87(11):1759–64.) was used to investigate the solubility behaviour of HAp at 37.0 ± 0.1 °C in 100 mM aqueous KCl. The pH range studied overlapped that of earlier work from pH 3.6 to 5.2, for a reproducibility check and validation, and extended to pH ∼2.9. XRD and EDX were used to identify the precipitates. SEM and TEM were used to observe the morphology. Results The previous S[HAp] reported by Chen et al. (Chen Z-F, Darvell BW, Leung VW-H. Hydroxyapatite solubility in simple inorganic solutions. Arch Oral Biol 2004; 49(5):359–67.) was reconfirmed. An abrupt change of slope of S[HAp] was detected at pH ∼3.9. No other phase than HAp was found at pH 3.2, 3.6 and 4.1. In particular, brushite (dicalcium phosphate dihydrate) was not detected, even below pH 3.9, where instead calcium-deficient HAp was formed. Conclusion The solid titration method was reconfirmed as reproducible and to yield HAp from pH 2.9 to 5.2. The expected brushite did not appear, but rather a stable calcium-deficient HAp was consistently formed. The chemistry of calcium phosphates needs to be reevaluated.

Abrupt Slope Change in Temperature Dependence of Resistivity in Ni-Fe-O Sintered Body

NiFe2O4+ 0∼100 vol.% NiO sintered bodies were prepared by mixing NiFe2O4 and NiO powders, and subsequent sintering at 800°C in air for 1 hour. Slopes in the temperature dependence of resistivity curves in the system have been found to abruptly changed, except for a composition of NiFe2O4+ 50 vol.% NiO. To investigate the mechanism of this phenomenon, NiFe2O4 powder was analyzed by high temperature X-ray diffraction, a thermo-gravimetry and differential thermo analysis. In the range from 100 to 300°C, the structure of NiFe2O4 phase does not change. Therefore the mechanism of this phenomenon is not related to any phase transition or the contamination of NiO.

A boundary-fitted numerical model for flood routing with shock-capturing capability

Summary The shallow water equations (SWEs) are solved numerically in general curvilinear coordinates for predicting flood flows. Second-order accuracy is achieved both in time and space through the use of the MacCormack scheme, in conjunction with a total variation diminishing (TVD) modification. The method is highly efficient as no local characteristic transformation is needed. The possible numerical imbalance induced by the inconsistent evaluation of the flux gradient and source terms is removed by employing the non-conservative form of the SWEs. All of the flow regimes and their transitions can be modelled. Specific considerations have been given to simulating flows in practical environments. The friction–slope term is discretized semi-implicitly when the water depth is smaller than a prescribed value. The check for flooding/drying (wet/dry status of the cell) is performed at each time step. Validation tests include steady flows along a deflected wall and a converging channel, unsteady wave diffraction around a circular cylinder, and the Malpasset dam-break flood in 1959. The results indicate that the present model is able to predict accurately the shock fronts, even over initially dry beds with friction and abrupt slope changes.

Carbon dioxide-induced melting point depression of biodegradable semicrystalline polymers

The melting point depression of semicrystalline polymers exposed to a compressed fluid allows certain biodegradable polymers to be processed in the molten state using carbon dioxide at modest temperatures. Experimental melting temperature ( T m) data are presented for the aliphatic polyesters, polycaprolactone (PCL) and poly(butylene succinate) (PBS), as a function of the applied pressure of carbon dioxide. The characteristic features of the T m versus P curve – a linear regime at modest P, followed by an abrupt transition to a second regime where T m changes little with P – are interpreted using the Clapeyron equation for two-component, three-phase equilibrium. For PCL and PBS, as well as for other polymers, the slope of the lower pressure linear regime can be quantitatively estimated from the normal T m, the enthalpy of fusion of the polymer, and the Henry's law coefficient for CO 2 dissolved in the melt. The location of the abrupt change in slope is correlated with equivalence of the molar volumes of the compressed fluid and the Kuhn monomer unit of the polymer crystal. The method is also applicable to non-polymeric compounds which have high critical points and low solubility in the compressed fluid.

Two-dimensional diffusion of colloids in polymer solutions

Enhanced digital videomicroscopy is used to study the two-dimensional diffusion of colloidal polystyrene spheres of diameter 0.99 µm in confined aqueous solutions of polymer PEO (polyethyleneoxide) of molecular weight 8 × 106. Diffusion is found to obey the Brownian motion law of linearity of the mean square displacement with time, with a constant appropriate to two dimensions. The diffusivity is determined for various polymer concentrations ranging from zero to those corresponding to dilute and semi-dilute polymer solutions. An abrupt slope change occurs near the polymer concentration of 0.002 wt-%, which lies below the concentration at which the polymer chains begin to overlap.

Temperature-Induced Conformational Change at the Catalytic Site of Sulfolobus solfataricus Alcohol Dehydrogenase Highlighted by Asn249Tyr Substitution. A Hydrogen/Deuterium Exchange, Kinetic, and Fluorescence Quenching Study

A combination of hydrogen/deuterium exchange, fluorescence quenching, and kinetic studies was used to acquire experimental evidence for the crystallographically hypothesized increase in local flexibility which occurs in thermophilic NAD(+)-dependent Sulfolobus solfataricus alcohol dehydrogenase (SsADH) upon substitution Asn249Tyr. The substitution, located at the adenine-binding site, proved to decrease the affinity for both coenzyme and substrate, rendering the mutant enzyme 6-fold more active when compared to the wild-type enzyme [Esposito et al. (2003) FEBS Lett. 539, 14-18]. The amide H/D exchange data show that the wild-type and mutant enzymes have similar global flexibility at 22 and 60 degrees C. However, the temperature dependence of the Stern-Volmer constant determined by acrylamide quenching shows that the increase in temperature affects the local flexibility differently, since the K(SV) increment is significantly higher for the wild-type than for the mutant enzyme over the range 18-45 degrees C. Interestingly, the corresponding van't Hoff plot (log K(SV) vs 1/T) proves nonlinear for the apo and holo wild-type and apo mutant enzymes, with a break at approximately 45 degrees C in all three cases due to a conformational change affecting the tryptophan microenvironment experienced by the quencher molecules. The Arrhenius and van't Hoff plots derived from the k(cat) and K(M) thermodependence measured with cyclohexanol and NAD(+) at different temperatures display an abrupt change of slope at 45-50 degrees C. This proves more pronounced in the case of the mutant enzyme compared to the wild-type enzyme due to a conformational change in the structure rather than to an overlapping of two or more rate-limiting reaction steps with different temperature dependencies of their rate constants. Three-dimensional analysis indicates that the observed conformational change induced by temperature is associated with the flexible loops directly involved in the substrate and coenzyme binding.

Novel dynamic rheological behavior of individual focal adhesions measured within single cells using electromagnetic pulling cytometry

The rheology of cells and sub-cellular structures, such as focal adhesions, are important for cell form and function. Here we describe electromagnetic pulling cytometry (EPC), a technique to analyze cell rheology by applying dynamic tensional forces to ligand-coated magnetic microbeads bound to cell surface integrin receptors. EPC utilizes an electromagnetic microneedle that is integrated with a computerized control and image acquisition system and an inverted microscope and CCD camera to monitor bead displacement. Arbitrary force regimens may be defined over a wide range of frequency (DC to 10 Hz) and force (100 pN to 10 nN). With EPC, the viscoelastic creep response of individual focal adhesions was measured over three decades in time using RGD-coated magnetic microbeads bound to integrins that induce local focal adhesion assembly and coupling to the internal cytoskeleton. These data were compared to the power-law-like predictions from the soft glassy model of cell rheology proposed by Fabry et al. [14]. Although power-law-like behavior was observed in some focal adhesions, 52% of these structures did not exhibit power-law-like behavior, but instead exhibited either a multi-phase response characterized by abrupt changes in slope or experienced a retraction in the opposite direction to the applied force, especially in response to prolonged force application. These data suggest that while the soft glassy model may provide reasonable estimates for aggregate mechanical behavior of living cells, the rheological behavior of individual focal adhesions may be more heterogeneous and complex than suggested by the soft glassy model. These results are considered in context with the hierarchical nature of cytoskeletal architecture.

Analysis of Simple Kinetic Models in Heterogeneous Catalysis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Three and four phase predictions for polyethylene + hydrocarbon systems

Experimental cloud-point isotherms for polyethylene+hydrocarbon systems can exhibit abrupt changes in slope when the polyethylene has a broad molar mass distribution. Equations of state with parameters correlated to qualitatively reproduce this behavior can result in cloud-point curves that fold, crossing themselves. The point of self-intersection is the terminus of a three-phase region, with three liquid-like phases in equilibrium. Teardrop-shaped three-phase boundaries have been calculated using the Modified Sanchez–Lacombe (MSL) equation of state for polyethylene+ethylene and polyethylene+n-hexane systems. We also show some examples of phase boundaries separating two-phase regions from three-phase regions, which exhibit folding and self-intersection, indicating the presence of a region with four liquid-like phases in equilibrium. A boundary isolating a four-phase region inside a three-phase region has been calculated for a polyethylene-co-octene-1+n-hexane system. It has been noted that the polyethylene molar mass distribution, especially the extension to high molar masses, determines whether three-phase regions and four-phase regions occur.

Current driven resistance changes in low resistance x area magnetic tunnel junctions with ultra-thin Al-Ox barriers

Current induced resistance changes were investigated in magnetic tunnel junctions with ultrathin Al-Ox barriers. The nonuniformity of the insulator induced a strong coupling between the two magnetic electrodes and no magnetoresistance. However, the current-voltage (I–V) characteristics at low bias voltages were consistent with a tunnellike behavior. At larger bias voltages, they showed an abrupt change of slope that was reversible for an opposite voltage polarity. The resistance versus current (R–I) curves exhibited reversible resistance changes that reached over 100%. We interpret this as controlled electromigration in local nanoconstrictions of the barrier.

Calibration of the LISEM model for a small Loess Plateau catchment

The Limburg Soil Erosion Model (LISEM) soil erosion model was calibrated for a 2-km 2 catchment on the Chinese Loess Plateau. The most important calibration factors were saturated conductivity and Manning's n. Calibration on catchment discharge was done by using the discharge peak (timing and discharge) followed by an adjustment for the total discharge to obtain the correct amount of sediment output. The results showed that LISEM can be successfully calibrated for a Loess Plateau catchment, and that small runoff events need to be calibrated separately from large runoff events. A separate calibration might even be needed for each event. The model performance was also evaluated using catchment wide spatially distributed data on rill erosion. Rill erosion intensity was mapped in the field and compared to spatial patterns of erosion predicted by LISEM. The simulated erosion patterns do show some resemblance with mapped erosion patterns in a general sense but they are very different in detail. The cause for this can be found in the extremely steep slopes and abrupt slope changes in the catchment. Some of the process descriptions in LISEM are not intended for such an environment, while the grid based kinematic wave routing cannot cope with the abrupt changes in flow conditions. The effects of this are amplified by inaccuracies in the input data and the DEM. For topographically complex catchments it will be very difficult to obtain data that are good enough for an accurate simulation of erosion patterns. This limits the use of a model such as LISEM as a predictive tool for future events. Simulation of different land use scenarios is less problematic, if a known event is used for all scenario simulations.

Surveillance of a Simple Linear Regression

This article considers an important aspect of the general sequential analysis problem where a process is in control up to some unknown point i = ν − 1, after which the distribution from which the observations are generated changes. An extensive sequential analytic literature assumes that the change in distribution is abrupt, for example, from N(0,1) to N(μ,1). There is also an extensive literature that deals with a gradual change in the case where the decision (whether or not a change has occurred) is based on a fixed set of observations, rather than an ongoing process of decision making every time a new observation is obtained. However, there is virtually no literature on the practical case of sequentially detecting a gradual change in distribution (visualize a machine deteriorating gradually). This article considers solutions to this problem. As a first approximation, the gradual change problem can be modeled as a change from a fixed distribution to a model of simple linear regression with respect to time (i.e., there is an abrupt change of slope, from a 0 to a nonzero slope). We study an extension of this case to a general context of sequential detection of a change in the slope of a simple linear regression. The residuals are assumed to be normally distributed. We consider both the case in which the baseline parameters are known and the case in which they are not. Finally, as an application, we monitor for an increase in the rate of global warming.

Energetic Evidence for Formation of a pH-dependent Hydrophobic Cluster in the Denatured State of Thermus thermophilus Ribonuclease H

NMR studies on the denatured states of proteins indicate that residual structure often resides predominantly in hydrophobic clusters. Such hydrophobic cluster formation implies burial of apolar surface and, consequently, is expected to cause a decrease in heat capacity. We report here that, in the case of ribonuclease H from the thermophile Thermus thermophilus, a sharp decrease in denatured-state heat capacity occurs at about pH 3.8; this result points to the formation of hydrophobic clusters triggered by the protonation of several (about four) carboxylic acid groups, and indicates that the burial of apolar surface is favored by the less hydrophilic character of the uncharged forms of Asp and Glu side-chains. The process is not accompanied by large changes in optically active structure, but appears to be highly cooperative, as indicated by the sharpness of the pH-induced transition in the heat capacity. This acid-induced hydrophobic burial in denatured T.thermophilus ribonuclease H is clearly reflected in the pH dependence of the denaturation temperature (i.e. an abrupt change of slope at about pH 3.8 is seen in the plot of denaturation temperature versus pH), supporting a role for such denatured-state hydrophobic clusters in protein stability. The finding of cooperative protonation of several groups coupled to surface burial in denatured T.thermophilus ribonuclease H emphasizes the potential complexity of denatured-state electrostatics and advises caution when attempting to predict denatured-state properties on the basis of simple electrostatic models. Finally, our results suggest a higher propensity for hydrophobic cluster formation in the denatured state of T.thermophilus ribonuclease H as compared with that of its mesophilic counterpart from Escherichia coli.