Steep Negative Slope Research Articles

Phase transitions in H2−HD−D2 mixtures up to 350 GPa

Utilizing the high-pressure low-temperature Raman and optical transmission/absorption spectroscopies, we have mapped out the phase diagram of H2-HD-D2 alloy with the initial H:D concentration 50:50 up to 350 GPa between 10 and 300 K. We followed the phase lines between all known solid phases [I, II, III, IV, and IV′ (IV+V)] of pure H2 and D2 constraining their locations in the wide space. We trace the phase boundary separating phases III and IV(IV′)/V demonstrating that this phase line has a steep negative slope (−0.95 K/GPa), which becomes shallower at above 250 GPa (−0.55 K/GPa). The phase line follows the trend observed in the pure species. Additionally, we find that the band gap of the mixture between 300 and 360 GPa is close to those of the pure species suggesting that alloying one isotope by another would not significantly shift the metallization pressure. These observations imply that hydrogen deuteride (HD) has very similar properties to those exhibited by the pure species. Published by the American Physical Society 2025

Evidence of association between higher cardiorespiratory fitness and higher cerebral myelination in aging

Emerging evidence suggests that altered myelination is an important pathophysiologic correlate of several neurodegenerative diseases, including Alzheimer and Parkinson's diseases. Thus, improving myelin integrity may be an effective intervention to prevent and treat age-associated neurodegenerative pathologies. It has been suggested that cardiorespiratory fitness (CRF) may preserve and enhance cerebral myelination throughout the adult lifespan, but this hypothesis has not been fully tested. Among cognitively normal participants from two well-characterized studies spanning a wide age range, we assessed CRF operationalized as the maximum rate of oxygen consumption (VO2max) and myelin content defined by myelin water fraction (MWF) estimated through our advanced multicomponent relaxometry MRI method. We found significant positive correlations between VO2max and MWF across several white matter regions. Interestingly, the effect size of this association was higher in brain regions susceptible to early degeneration, including the frontal lobes and major white matter fiber tracts. Further, the interaction between age and VO2max exhibited i) a steeper positive slope in the older age group, suggesting that the association of VO2max with MWF is stronger at middle and older ages and ii) a steeper negative slope in the lower VO2max group, indicating that lower VO2max levels are associated with lower myelination with increasing age. Finally, the nonlinear pattern of myelin maturation and decline is VO2max-dependent with the higher VO2max group reaching the MWF peak at later ages. This study provides evidence of an interconnection between CRF and cerebral myelination and suggests therapeutic strategies for promoting brain health and attenuating white matter degeneration.

Anomalous to normal dispersion nonlinear optical dephasing switch in electromagnetically induced transparency using a Kerr effect

The atomic decoherence effect (DE) on a Kerr nonlinear (KNL) electromagnetically induced transparency (EIT)is studied in a Δ system. The DE between the ground state hyperfine levels is caused by the dephasing rate γ d which dramatically modifies the medium response. It controls the normal dispersive region which shows steep positive slopes for linear response at the line center while the nonlinear response experiences steep negative slopes for low γ d . The microwave field strength and γ d modify the nonlinear response from the anomalous dispersion to normal dispersion. The calculations show that room-temperature atoms are used to quantify the quantum interference (QI) on linear and nonlinear absorption with γ d . The EIT spectrum explores the understanding of the subluminal and superluminal wave propagation of probe signal and this study opens a new pathway for the understanding of the QI devices and their nonlinearities based on EIT.

Spatial distribution of woody plants in relation to mistletoe-infected Vachellia karroo trees in a semi-arid African savanna

By increasing resource heterogeneity, mistletoe-infected trees can restructure plant community processes and distribution patterns. No information is available on how mistletoe-infected Vachellia (Acacia) karroo trees within V. karroo dominated stands are spatially distributed, and on how they influence the spatial patterns of their surrounding conspecifics and heterospecifics. Each woody plant was stem mapped using a cartesian plane (x, y) within three 50×50 m plots located in V. karroo dominated stands in a semi-arid savanna, South West Zimbabwe. Pair correlations g(r) were used for the univariate analysis and Poisson process null models were applied to quantify and detect overall departure from randomness. For the bivariate analysis, pair correlations g12(r) under the null model of independence were used, whilst the mark correlation function (kmm(r)) was used to analyse the correlation of tree canopy area and mistletoe infection intensity. For each plot, size class distributions, based on tree height and basal stem diameter displayed negative J curves, with steep negative regression slopes across the size classes, clearly indicating a strongly recruiting population of V. karroo. The univariate patterns of all trees (infected and non-infected) were consistent with a random pattern, which is attributed to unsystematic mistletoe seed dispersal by birds. The univariate analysis of all woody plants (adults and juveniles) exhibited aggregation at small spatial scales due to the high abundance of clustered seedlings and saplings. At small spatial scales, understory woody plants (both conspecifics and non-conspecifics) were positively associated with mistletoe-infected trees due to mistletoephily which is the facilitation (or nurse protégé interactions) within the more resource-rich mistletoe-infected tree subcanopies. These results provide strong evidence suggesting that the variations in spatial pattern modification by mistletoe-infected trees could further increase spatial heterogeneity in this semi-arid savanna. As such, by increasing heterogeneity, mistletoe-infected trees can increase the resilience of semi-arid savannas in the face of perturbations and stochastic events.

A study on the metallicity gradients in the galactic disk using open clusters

We study the metallicity distribution and evolution in the galactic disk based on the largest sample of open star clusters in the galaxy. From the catalog of 1,879 open clusters in the range of galactocentric distance (RGC) from 4 to 20 kpc, we investigate the variation in metallicity in the galactic disk as functions of RGC, vertical distance (Z), and ages of the clusters. In the direction perpendicular to the galactic plane, the variation in metallicity is found to follow a stepped linear relation. We estimate a vertical metallicity gradient d[Fe/H]d|Z| of −0.545 ± 0.046 dex kpc−1 for |Z| < 0.487 kpc and −0.075 ± 0.093 dex kpc−1 for 0.487 < |Z| < 1.8 kpc. On average, metallicity variations above and below the galactic plane are found to change at similar rates. The change in metallicity in the radial direction is also found to follow a two-function linear relation. We obtain a radial metallicity gradient d[Fe/H]dRGC of −0.070 ± 0.002 dex kpc−1 for 4.0 ≲ RGC ≲ 12.8 kpc and −0.005 ± 0.018 dex kpc−1 for 12.8 ≲ RGC ≲ 20.5 kpc, which clearly shows a strong variation in the metallicity gradient when moving from the inner to the outer galactic disk. The age–metallicity relation (AMR) is found to follow a steeper negative slope of −0.031 ± 0.006 dex Gyr−1 for clusters older than 240 Myr; however, there is some hint of positive metallicity age gradient for younger clusters.

Mineralogy and element geochemistry of the Bayan Obo (China) carbonatite dykes: Implications for REE mineralization

The Bayan Obo deposit in China is the world's largest rare earth element (REE) deposit. However, its genesis remains highly debated. It is considered to have a close genetic association with carbonatites because of the presence of nearby carbonatite dykes and the geochemical similarities between these dykes and the orebody. However, the evolution of these dykes and associated REE mineralization remain poorly understood, hindering the origin interpretation of the deposit. This study provides new insights into the petrography, mineralogy, and major- and trace-element geochemistry of these carbonatite dykes and rock-forming minerals to reconstruct the magmatic evolution and REE enrichment of the deposit. The dykes evolved from dolomite- to calcite-dominated (i.e., calcite and fenitized calcite) carbonatites, and their REE content remarkably increased, with the latter developing strong REE mineralization. The dolomites and minor calcites within the dolomite carbonatites exhibit a steep negative slope with high light REE (LREE) enrichment and heavy REE (HREE) depletion, similar to the whole rock. In contrast, the calcites from the calcite-dominated carbonatites exhibit flat REE patterns with HREE enrichment. Combined with previous isotopic data and our petrology, mineralogy, and geochemistry study, we propose that these rocks are derived directly from the low-degree melting of the underlying mantle source. REE mineralization may be related to the progressive crystallization of rock-forming calcites of calcite-dominated carbonatites. Monazite, bastnäsite, parisite, and huanghoite are the dominant REE minerals and exhibit intimate associations with barite and alkaline silicate minerals such as aegirine, biotite, K-feldspar, and albite. This assemblage indicates that the REE were primarily transported via REE–sulfate and REE–alkali complexes, with the latter favoring HREE, and the precipitation of alkaline silicate minerals destabilized these REE complexes, facilitating REE mineralization.

Thermal‐Infrared Emission Spectroscopy of Graybody Minerals (Sulfide): Implications for Extraterrestrial Exploration for Magmatic Ore Deposits

AbstractGraybody materials exhibit systematically low emissivity across their spectrum. This characteristic violates the key assumption of unit emissivity at some wavenumber in the spectrum used to calibrate thermal‐infrared emission data. This assumption makes graybody materials “appear colder” than their actual physical temperature and imparts a slope in emission spectra that is non‐physical in nature, both of which affect interpretations of planetary surfaces. Pyrrhotite derived from the Stillwater Complex's J‐M Reef in Montana, USA exhibits systemic graybody behavior across its mid‐infrared spectrum and thus has a steep negative spectral slope from high to low wavenumbers when calibrated using conventional methods. A new measurement technique is introduced for deriving the absolute emissivity of graybody materials using reference samples with known Christiansen Frequencies during calibration. The reference temperature method significantly reduces the spectral slope of and provides a more accurate estimation of the absolute emissivity of graybody materials. After correcting the temperature of pyrrhotite using results from a series of reference experiments, we conclude that the emission spectrum of pyrrhotite is spectrally featureless and has a maximum emissivity of ∼0.7. If sulfide mineral deposits are exposed on Mars, they will not be identified using spectral features found in the mid‐infrared (5–40 μm). However, they could be located by identifying basaltic terrain that appears colder than their surroundings and with apparent emissivity spectra that exhibit negative spectral slopes from high to low wavenumbers and are spectrally neutral.

Readiness potential reflects the intention of sit-to-stand movement.

The negative-going movement-related cortical potentials are associated with the preparation and execution of thevoluntary movements. Thus far, the readiness potential (RP) for simple movements involving either the upper or lower body segments has been studied. We investigated the ability to decode the sit-to-stand movement's intention from the RP, which uses the upper and lower body segments. Therefore, we performed scalp electroencephalography in healthy volunteers. A gyro sensor was placed on the back to detect the movement of the upper body segment, and an electromyogram electrode was placed on the surface of the hamstrings and quadriceps to detect movement of the lower body segment. Our study revealed that a negative RP was evoked around 2 to 3s before the onset of the upper body movement in the sit-to-stand movement in response to the start cue. The RP had a negative peak and a steeper negative slope from - 0.8 to - 0.001s just before the onset of the upper body movement. Negative-going RPs reflect the intention of preparation/execution of the sit-to-stand movement. Therefore, we used the morphological component analysis method to extract the morphology of RPs from a single trial. This morphology of RPs is a promising aspect for limb neurotrophies or neurorehabilitation devices.

Buckling of Stiffened Cone–Cylinder Structures Under Axial Compression

This paper studies the instability behavior of stringer-stiffened cone–cylinder shells under axial compressive load via computational finite element (FE) code, ABAQUS. First, the FE model was validated using past experiments on four cone–cylinder specimens (two unstiffened and two stringer-stiffened) fabricated in pairs using mild steel. Results show that the comparison between numerical and experimental collapse loads was less than 10%. Second, parametric study was conducted using the validated FE model to investigate the effects of the location and number of stringers on the buckling behavior of axially compressed cone–cylinder structures. It has been found that reinforcing the cone–cylinder structures tends to produce higher buckling load when compared to the unstiffened ones. The presence of stringers changes the failure mode of the structure, and the initial post-buckling curves show a less steep negative slope when compared to that of the unstiffened counterpart. Externally stiffened structures were able to sustain more load as compared to the internally stiffened counterpart. Introducing longitudinal reinforcement on the conical section and ring reinforcement on the cone–cylinder junction produces a much higher buckling load compared to having stringer-stiffeners on the conical part only.

Measuring Ostracism-Induced Changes in Consumption of Palatable Food: Feasibility of a Novel Behavioral Task

PurposeOstracism is a highly aversive interpersonal experience. Previous research suggests that it can increase consumption of highly palatable food in some individuals, but decrease it in others. Thus, we developed the Cyberball-Milkshake Task (CMT), to facilitate research investigating individual differences in ostracism’s effects on consumption of highly palatable food. We present data on feasibility for the CMT in a sample of young adult women.Materials and MethodsParticipants were 22 women, 18–30 years old, reporting very low or very high levels of emotional eating at screening. Participants performed the CMT, which consisted of 12 trials. Each trial included: playing a round of Cyberball (a computerized game of catch with fictitious “other participants” programmed to either include or exclude the participant); viewing a chocolate image; and then consuming a participant-determined amount of milkshake. Participants subsequently played an additional inclusion and exclusion round of Cyberball, each immediately followed by questionnaires assessing current mood and recent Cyberball experience.ResultsCyberball exclusion (vs. inclusion) was associated with large, significant increases in reported ostracism and threats to self-esteem; exclusion’s effects on affect were in the expected direction (e.g., increased negative affect), but generally small and non-significant. Milkshake intake was measurable for 95% of participants, on 96% of trials. Intake decreased quadratically across trials, with a steep negative slope for low trial numbers that decreased to the point of being flat for the highest trial numbers.DiscussionThe CMT is a generally feasible approach to investigating ostracism’s effects on consumption of highly palatable food. The feasibility (and validity) of the CMT may benefit from modification (e.g., fewer trials and longer rounds of Cyberball). Future research should examine whether performance on a modified version of the CMT predicts real-world behavior in a larger sample.

Depressed 660-km discontinuity caused by akimotoite\u2013bridgmanite transition

The 660-kilometre seismic discontinuity is the boundary between the Earth’s lower mantle and transition zone and is commonly interpreted as being due to the dissociation of ringwoodite to bridgmanite plus ferropericlase (post-spinel transition)1–3. A distinct feature of the 660-kilometre discontinuity is its depression to 750 kilometres beneath subduction zones4–10. However, in situ X-ray diffraction studies using multi-anvil techniques have demonstrated negative but gentle Clapeyron slopes (that is, the ratio between pressure and temperature changes) of the post-spinel transition that do not allow a significant depression11–13. On the other hand, conventional high-pressure experiments face difficulties in accurate phase identification due to inevitable pressure changes during heating and the persistent presence of metastable phases1,3. Here we determine the post-spinel and akimotoite–bridgmanite transition boundaries by multi-anvil experiments using in situ X-ray diffraction, with the boundaries strictly based on the definition of phase equilibrium. The post-spinel boundary has almost no temperature dependence, whereas the akimotoite–bridgmanite transition has a very steep negative boundary slope at temperatures lower than ambient mantle geotherms. The large depressions of the 660-kilometre discontinuity in cold subduction zones are thus interpreted as the akimotoite–bridgmanite transition. The steep negative boundary of the akimotoite–bridgmanite transition will cause slab stagnation (a stalling of the slab’s descent) due to significant upward buoyancy14,15.

Negative frequency-dependent prey selection by wolves and its implications on predator–prey dynamics

Many species exhibit selective foraging behaviour, where consumers use a nonrandom subset of available food types. Yet little is known about how selective foraging behaviour varies with environmental conditions and the community level consequences of such selection dynamics. We examined selective foraging by wolves preying primarily on elk in Yellowstone National Park (YNP) over a 12-year period and on moose in Isle Royale National Park (IRNP) over a 47-year period. Specifically, we assessed how selection for calves and senescent adults varied with their frequency in the environment, wolf abundance and winter severity. Selection for senescent adults decreased as the relative abundance of senescent prey increased (i.e. negative frequency-dependent selection) in both study sites. In IRNP, selection for calves was also negatively frequency dependent and declined with increasing wolf abundance. These results are inconsistent with the pattern of positive frequency-dependent selection expected under the prey-switching hypothesis. These results suggest that selection is primarily driven by intraspecific differences in prey vulnerability and wolves’ interest in minimizing their risk of injury, as opposed to maximizing intake rates. Lastly, we ran simulations to evaluate how predator–prey dynamics were influenced by dynamic patterns of selection, like those observed in YNP and IRNP. The simulations indicated that predators are more efficient (i.e. steeper slope of the numerical response) when selection for calves is negatively frequency dependent, which results in a lower mean abundance of prey. More importantly, predation is a stronger destabilizing force when selection for calves is negatively frequency dependent. That stronger destabilizing force is indicated by greater variability in the abundance of prey and predators, prey populations being less resilient and a steeper negative slope of the relationship between predation rate and prey population growth rate. As such, our simulation analyses suggest that some of the observed patterns of negative-frequency dependent selection may have important consequences for predator–prey dynamics. • Wolves showed negative frequency-dependent selection for calves and senescent prey. • Wolves did not exhibit prey-switching behaviour when preferred prey became rare. • Selection is likely driven by the predator's interest to reduce their risk of injury. • Selection for calves may result in more efficient predators and less resilient prey.

Safety and Feasibility Evaluation of Step Count Informed Meal Boluses in Type 1 Diabetes: A Pilot Study.

Physical activity can cause glucose fluctuations both during and after it is performed, leading to hurdles in optimal insulin dosing in people with type 1 diabetes (T1D). We conducted a pilot clinical trial assessing the safety and feasibility of a physical activity-informed mealtime insulin bolus advisor that adjusts the meal bolus according to previous physical activity, based on step count data collected through an off-the-shelf physical activity tracker. Fifteen adults with T1D, each using a continuous glucose monitor (CGM) and an insulin pump with carbohydrate counting, completed two randomized crossover daily visits. Participants performed a 30 to 45-minute brisk walk before lunch and lunchtime insulin boluses were calculated based on either their standard therapy (ST) or the physical activity-informed bolus method. Post-lunch glycemic excursions were assessed using CGM readings. There was no significant difference between visits in the time spent in hypoglycemia in the post-lunch period (median [IQR] standard: 0 [0]% vs physical activity-informed: 0 [0]%, P = NS). Standard therapy bolus yielded a higher time spent in 70 to 180 mg/dL target range (mean ± standard: 77% ± 27% vs physical activity-informed: 59% ± 31%, P = .03) yet, it was associated with a steeper negative slope in the early postprandial phase (P = .032). Use of step count to adjust mealtime insulin following a walking bout has proved to be safe and feasible in a cohort of 15 T1D subjects. Physical activity-informed insulin dosing of meals eaten soon after a walking bout has a potential of mitigating physical activity related glucose reduction in the early postprandial phase.

ASTROPHYSICAL AND STRUCTURAL PARAMETERS, AND DYNAMICAL EVOLUTION OF THE OPEN CLUSTERS NGC 1245 AND NGC 2099

We derive astrophysical and structural parameters of open clusters NGC 1245 and NGC 2099 from 2MASS JHKs and Gaia DR2 photometric / astrometric data bases. Their likely members have been determined from Gaia DR2 proper motion data. Our E(B – V) values (2MASS) are slightly smaller than the literature values, whereas our E(B – V) values (Gaia DR2) agree with the literature within the uncertainties. Their distance moduli/distances and ages are in good coincident with the literature. NGC 1245 has steep negative core mass function slope (MFs) (χ_core=-1.24). It’s at halo (χ_halo=+0.78) and at overall (χ_overall=-0.95) MFs mean that it presents signs of small-scale mass segregation to the outer regions from its core, due to its [t_rlx (overall),τ_overall ]=[302 Myr,5]. The MFs of NGC 2099 is very negative steep (χ_core=-2.67) in the core, and quite positive steep (χ_halo=+1.41) in the halo. This kind of MF slope steeping from the core to the outskirts indicates that low-mass stars in the core are transferred to the cluster's outskirts, while massive stars sink in the core, because of mass segregation. NGC 2099's flat overall MFs (χ_overall=+0.91) and its τ_overall=8 presents a sign of mass segregation. These OCs with the relatively large masses 8700 Msolar (NGC 1245) and 5660 Msolar (NGC 2099), which locate at RGC > 9 kpc, expose to external perturbations such as tidal effects and shock waves, and they lose their stars in low-proportions.

Rhyolites in continental mafic Large Igneous Provinces: Petrology, geochemistry and petrogenesis

We present a detailed review of the petrological and geochemical aspects of rhyolite and associated silicic volcanic rocks (up to 20 ​vol% of all rocks) reported to date from twelve well known Phanerozoic continental mafic Large Igneous Provinces (LIPs). These typically spread over ≤104 ​km2 (rarely 105 ​km2 for Paraná-Etendeka) area and comprise ≤104 ​km3 of extrusive silicic rocks, erupted either during or after the main basaltic eruption within <5 Myr, with some eruption(s) continuing for ≤30 Myr. These rhyolites and associated silicic volcanic rocks (60−81 ​wt.% of SiO2) are mostly metaluminous to peraluminous and are formed via (i) fractional crystallization of parental mafic magma with negligible crustal contamination, and (ii) melting of continental crust or assimilation and fractional crystallization (AFC) of mafic magma with significant crustal contribution. Rhyolites formed by extensive fractional crystallization are characterized by the presence of clinopyroxene phenocrysts, exhibit steep negative slopes in bivariate major oxides plots and weak to no Nb-Ta anomaly; these typically have temperature >900 ​°C. Rhyolites formed by significant crustal contribution are characterized by strong negative Nb-Ta anomalies, absence of clinopyroxene phenocrysts, and are likely to have a magma temperature <900 ​°C. Geochemical signatures suggest rhyolite melt generation in the plagioclase stability field with a minor fraction originating from lower crustal depths. A large part of the compositional variability in rhyolites, particularly the Sr-Nd-Pb-O isotope ratios, suggests a significant role of continental crust (upper crustal melting or AFC) in the evolution of these silicic rocks in the continental mafic LIPs.

Growth trajectories of parental emotion socialization and child adjustment following a military parenting intervention: A randomized controlled trial.

Children of combat deployed parents are at risk of behavioral problems. Parental emotion socialization (PES) has been theorized to influence children's behaviors; many studies lend support to this theory. However, longitudinal studies examining PES with experimental designs are sparse. In this study, we estimated PES growth trajectories following a parenting intervention and evaluated whether intervention induced improvements in PES predict child outcomes in postdeployed military families. National Guard/Reserve families with at least one deployed parent and a child aged 4-13 years were randomized into an intervention or control group. Data from all 255 2-parent married families, who were primarily Caucasian and middle-class, were analyzed. PES was indicated by self-reported nonsupportive and supportive reactions to children's negative emotions (baseline, 1-year, and 2-year follow-up). Child behaviors were assessed through averaged mother- and father- reports (baseline and 2-year follow-up). Results of latent growth models showed that mothers and fathers assigned to the intervention condition reported greater improvements in nonsupportive PES (steeper negative slopes) over 2 years relative to controls. Both mothers' and fathers' intervention-induced improvements in nonsupportive PES were associated with decreased child internalizing behaviors. Mothers' intervention-induced improvements in nonsupportive PES were associated with decreased child externalizing behaviors. No significant findings were detected for intervention effects on supportive PES growth trajectories. Our findings supported the indirect effects of the intervention on child behaviors through nonsupportive PES over two years. PES is an important, malleable skill that can be targeted in parenting interventions for postdeployed military families. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Girls' brain structural connectivity in late adolescence relates to history of depression symptoms.

Girls' depressive symptoms typically increase in adolescence, with individual differences in course and severity being key risk factors for impaired emotional functioning in young adulthood. Given the continued brain white matter (WM) maturation that occurs in adolescence, the present study tested whether structural connectivity patterns in late adolescence are associated with variation in the course of depression symptom severity throughout adolescence. Participants were girls (N=115) enrolled in a multiyear prospective cohort study of risk for depression. Initial depression severity (intercept) at age 10 and change in severity (linear slope) across ages 10-19 were examined in relation to WM tractography collected at age 19. Network-based statistic analyses were used to identify clusters showing variation in structural connectivity in association with depressive symptomintercept, slope, and their interaction. Higher initial depressive severity and steeper positive slope (separately) were associated with greater structural connectivity between temporal, subcortical socioaffective, and occipital regions. Intercept showed more connectivity associations than slope. The interaction effect indicated that higher initial symptom severity and a steeper negative slope (i.e., alleviating symptoms) were related to greater connectivity between cognitive control regions. Moderately severe symptoms that worsened over time were followed by greater connectivity between self-referential and cognitive regions (e.g., posterior cingulate and frontal gyrus). Higher depressive symptomseverity in early adolescence and increasing symptom severity over time may forecast structural connectivity differences in late adolescence, particularly in pathways involving cognitive and emotion-processing regions. Understanding how clinical course relates to neurobiological correlates may inform new treatment approaches to adolescent depression.

Deformation and HCF behavior of A356 aluminum alloys in torsion

In this study, monotonic, cyclic and fatigue properties of the A356 aluminum alloy were identified using torsion tests with rounded solid test specimens of the alloy in four different processing conditions. The monotonic and cyclic shear stress-strain behaviors of the alloys are described using the Ramberg-Osgood model and the materials constitutive parameters were estimated minimizing the difference between the experimental torque and the analytical value. Results of torsion fatigue tests with R = −1 were compared with rotating bending results and the load factor was evaluated. Experimental fatigue results indicated that the alloys at T6 condition showed the best behavior and the results of strontium modified alloys shown slightly lower performance. The fatigue life diagram of T6 alloys has steeper negative slope (shear fatigue strength exponent, b ≅ −0.2) than the others as cast alloys (b ≅ −0.06). The comparisons of experimental rotating bending and reverse torsion fatigue showed exponent b is dependent on the load type for the as cast alloys. For the heat-treated alloys, the variation of exponent b is minimal and its value can be considered constant.

Spectroscopic observations on human pigmentation.

The main chromophores of human skin are melanins and hemoglobins along with carotenoids, bilirubin, and other compounds. In an effort to study the spectral signatures of skin melanin, we measured absorption spectra in a variety of situations, including a method to show early signs of re-pigmentation in vitiligo. To measure skin in vivo, the essential component was a "Bifurcated Optical Fiber" with one end connected to the light source and the second end connected to the spectrometer while the common end was placed on the skin. In a typical in situ "melanin in skin" spectrum, the absorbance values first rise gradually, from 750 to 600nm, then rise moderately from 600 to 450nm, and rise sharply from 450nm to a broad peak at 335nm, below which it gradually rolls down to much lower values. We successfully studied melanin spectroscopically in subjects with vitiligo lesions, obtaining the differential spectra. Higher melanin levels can be shown by steeper negative slopes of a straight line fitted between 620 and 720nm. Also, absorption peak at 335nm showed the presence of melanin.

Mineral chemistry and crystal size distributions of mafic dikes and sills on the eastern border of the Parnaíba Basin, NE Brazil

Crystal size distributions (CSDs) and mineral chemistry of plagioclase and clinopyroxene are used to quantify textures and estimate timescales of Mesozoic mafic sills and dikes exposed on the eastern margin of the Parnaíba Basin (NE Brazil). The diabases consist of plagioclase, clinopyroxene (augite and pigeonite) and FeTi oxides and show textures that vary from holocrystalline, to locally porphyritic, glomerophyric and hypocrystalline. Plagioclase and clinopyroxene CSDs are similar in sills and dikes, with clinopyroxene slopes systematically steeper than plagioclase slopes. Plagioclase usually records nearly log-linear negative slopes that tend to steepen approaching the wall rock contact. Plagioclase typically shows normal zoning with anorthite contents varying (An84-25) from the center to the grain margin. Calculated residence times for the log-linear segments vary from ca. one month (τ = 10−7 mm·s−1) for samples situated 20 cm from the contact to ca. four months for samples ~3 m away from the contact. Clinopyroxene consists of augite (dominant) and pigeonite and shows relatively uniform compositions. Unlike plagioclase, clinopyroxene CSDs tend to be flat or slightly positive towards the finer grains suggesting that the texture was modified during the crystallization of the residual melt. Plagioclase microlites (L < 0.5 mm), in contrast, show kinked CSDs with the steeper negative slopes including minute crystals of sanidine (orthoclase component) and alkali-sodic feldspar in addition to CaNa plagioclase. The modified textures and high nucleation density of microlites in mostly static, deep-seated magmatic reservoirs therefore resulted from chemical disequilibrium between largely solidified tholeiitic magma and late, highly fractionated alkali-rich residual melts. The estimated time for the full crystallization of the largest sills is one and one-half years.