Plateau Stages Research Articles

Deformation behavior of bulk metallic glasses under a mixed-mode (I/II) loading condition

Bulk metallic glasses (BMGs) demonstrate different deformation behavior under varying loading conditions. In the present work, a Zr57Cu20Al10Ni8Ti5 (atomic percent, at.%) BMG was subjected to a mixed-mode (I/II) loading condition by tailoring double-side notches. The findings show stable plastic-flow plateau stages in the loading-displacement curves, and this phenomenon is different from other notched BMG specimens with predominant-mode-I failure. More importantly, due to the stress concentrations between two notches, most of the slip events with large load drops occur on the fracture plane, resulting in a wide smooth region consisting of several shear steps on the fracture surface. We show that despite different deformation behavior, the specimens still display slip-size statistics of the plastic flow, which are similar to those seen in compression tests. The present findings give more insight into the deformation behavior/mechanisms of BMGs under varying loading conditions for practical structural applications.

Fabrication of fly ash cenospheres-hollow glass microspheres/borosilicate glass composites for high temperature application

A temperature resistant buoyant material, namely, fly ash cenospheres-hollow glass microspheres/borosilicate glass (FACs-HGMs/BG) for high temperature application, was prepared through a tert-butyl alcohol-based gelcasting process, with FACs and HGMs as the fillers and BG as the matrix, respectively. The effect of FACs addition on the mechanical and high-temperature performance of the FACs-HGMs/BG composites was studied. The composites containing different amounts of FACs displayed low density (0.44–0.89g/cm3), low Young's modulus (0.05–1.10GPa), and relatively high compressive strength (2.78–9.75MPa). Three stages, namely, elastic, plateau, and fracture stages, could be observed in the stress-strain curves. The compressive strength of the samples at high temperature was lower than the ones at room temperature, and the 10%FACs-HGMs/BG composite tested at 500°C displayed a compressive strength of 6.03MPa. The FACs-HGMs/BG composites demonstrating excellent mechanical properties both at room and high temperatures may be used as promising candidates for structural materials or temperature resistant buoyant materials in the near future.

Lattice Boltzmann modeling for the coalescence between a free droplet in gases and a sessile droplet on wettable substrate with contact angle hysteresis

The coalescence between a free droplet and a sessile droplet on wettable substrate is numerically studied. The axisymmetric lattice Boltzmann method for two-phase flows is used in modeling. Here the contact angle hysteresis (prescribed by advancing angle [Formula: see text] and receding angle [Formula: see text]) is taken into account. The effects of Ohnesorge number ( Oh), contact angle and its hysteresis, and the radius of the free droplet on the coalescence dynamics are investigated in detail. The Oh numbers ranging from 0.02 to 0.15 here makes the radius of the liquid bridge r and the time t follow power law. Also, Oh has remarkable impact on the development of capillary wave and on the amount of kinetic energy released from coalescence. It is found that the curve of the wetting radius varying with time includes several plateau stages, which is a typical characteristic for the effect of contact angle hysteresis. The larger window of contact angle hysteresis would result in smaller steady wetting radius after coalescence. Compared with the existence of contact angle hysteresis, the absence of contact angle hysteresis makes the droplets system release more kinetic energy during the coalescence but the released kinetic energy decays more rapidly and soon reduces to zero. Oppositely, if the contact angle hysteresis exists, the released kinetic energy would oscillate for a period of time before approaching zero.

Mechanical behavior of three-dimensional pyramidal aluminum lattice materials

Al based pyramidal lattice truss materials have been fabricated through 3-D printing and molten metal infiltration technology. It is shown that the designable structures with thin struts and small cells can be realized by this technology. Similar to usual porous materials, the present Al based lattice materials also exhibited three-stage compressive mechanical behavior, i.e. linear elastic, plateau and densification stages. The mechanical properties of the lattice materials showed obvious dependence on the structure parameters including the inclination angle of strut with the bottom plane, strut length and strut diameter etc, but actually all these dependences can be attributed to varied relative densities of the lattice materials. Moreover, it is found that the deformation mode of the lattice materials was different if the inclination angle was obviously changed. When the inclination angle was relatively small, the deformation uniformly took place in the form of strut buckling, while it occurred in a localized zone followed by the extending of the zone if the inclination angle was large enough.

Does aqueductal stenosis influence the lumbar infusion test in normal-pressure hydrocephalus?

Late-onset idiopathic aqueductal stenosis may present with clinical features indistinct from idiopathic normal-pressure hydrocephalus (NPH). Moreover, aqueductal stenosis (AS) is not always detected by conventional magnetic resonance imaging (MRI). The aim of this study was to compare the hydrodynamic pattern among NPH patients according to the patency of the aqueduct. Fifty-six consecutive lumbar infusion tests were performed in patients with NPH syndrome. Precipitating causes of hydrocephalus were excluded, and aqueductal patency was examined through high-resolution, T2-weighted 3D MRI. Patients were classified into two groups: non-patent aqueduct and patent aqueduct. Mean values of pressure and pulse amplitude were obtained from basal and plateau stages of infusion studies. Twelve of 56 patients with NPH-like symptoms presented with morphological AS (21.4%). Patent aqueduct and non-patent aqueduct groups had similar values of mean opening lumbar pressure (8.2 vs. 8.1mmHg), and mean opening pulse amplitude (3.1 vs. 2.9mmHg). Mean pressure in the plateau stage (28.6 vs. 23.2mmHg), and mean pulse amplitude in the plateau stage (12.5 vs. 10.6mmHg) were higher in the patent aqueduct group. These differences were not statistically significant. Only Rout was significantly higher in the patent aqueduct group (13.6 vs. 10.1mmHg/ml/min). One-third of NPH patients with AS presented Rout >12mmHg/ml/min. No differences in mean pressure or pulse amplitude during basal and plateau epochs of the lumbar infusion test in NPH patients were detected, regardless of aqueductal patency. However, Rout was significantly higher in patients with patent aqueduct.

Detection of type I collagen fibrils formation and dissociation by a fluorescence method based on thioflavin T

In this study, fibrillogenesis and thermal dissociation of pepsin-soluble collagen (PSC), extracted from snakehead (Channa argus) skin, were monitored by fluorescence method based on thioflavin T (Th-T), where the accuracy and sensitivity were evaluated and compared with those of turbidity assay. The fluorescence method revealed the fibrillogenesis dynamics of collagen with better sensitivity, especially at nucleation and plateau stages. The melting temperature (Tm) of PSC was estimated to be 47°C by circular dichroism spectroscopy; below this temperature, the triple-helical structure should be intact. After that, the dynamic process of collagen dissociation was explored by the fluorescence method, and verified by morphological analysis of the fibrils and the proportion of retained fibrils. The thermal dissociation critical temperature (TDCT) of PSC fibrils was confirmed to be 39°C. The fluorescence intensity of fibril-incorporated Th-T gradually decreases in the dissociation process, and the decrease rate can be accelerated by increasing temperature. Finally, the thermal stability of triple-helical structures of free-, assembled- and dissociated-PSC was compared. Thus, we demonstrated the formation and thermal dissociation of collagen fibrils in vitro by a fluorescence method based on Th-T. This approach may advance the understanding of fibril formation and inverse dissociation of fish-sourced collagen in vitro.

Characterisation of the complexity of intracranial pressure signals measured from idiopathic and secondary normal pressure hydrocephalus patients.

Hydrocephalus is a condition characterised by enlarged cerebral ventricles, which in turn affects intracranial pressure (ICP); however, the mechanisms regulating ICP are not fully understood. A nonlinear signal processing approach was applied to ICP signals measured during infusion studies from patients with two forms of hydrocephalus, in a bid to compare the differences. This is the first study of its kind. The two forms of hydrocephalus were idiopathic normal pressure hydrocephalus (iNPH) and secondary normal pressure hydrocephalus (SH). Following infusion tests, the Lempel-Ziv (LZ) complexity was calculated from the iNPH and SH ICP signals. The LZ complexity values were averaged for the baseline, infusion, plateau and recovery stages of the tests. It was found that as the ICP increased from basal levels, the LZ complexities decreased, reaching their lowest during the plateau stage. However, the complexities computed from the SH ICP signals decreased to a lesser extent when compared with the iNPH ICP signals. Furthermore, statistically significant differences were found between the plateau and recovery stage complexities when comparing the iNPH and SH results (p = 0.05). This Letter suggests that advanced signal processing of ICP signals with LZ complexity can help characterise different types of hydrocephalus in more detail.

Achieving high energy absorption capacity in cellular bulk metallic glasses.

Cellular bulk metallic glasses (BMGs) have exhibited excellent energy-absorption performance by inheriting superior strength from the parent BMGs. However, how to achieve high energy absorption capacity in cellular BMGs is vital but mysterious. In this work, using step-by-step observations of the deformation evolution of a series of cellular BMGs, the underlying mechanisms for the remarkable energy absorption capacity have been investigated by studying two influencing key factors: the peak stress and the decay of the peak stress during the plastic-flow plateau stages. An analytical model of the peak stress has been proposed, and the predicted results agree well with the experimental data. The decay of the peak stress has been attributed to the geometry change of the macroscopic cells, the formation of shear bands in the middle of the struts, and the “work-softening” nature of BMGs. The influencing factors such as the effect of the strut thickness and the number of unit cells have also been investigated and discussed. Strategies for achieving higher energy absorption capacity in cellular BMGs have been proposed.

Tannin-Ca Complex as Green Thermal Stabilizer Additive for PVC: Viscoelastic Properties

This study investigated the viscoelastic and rheometeric properties of PVC stabilized with tannin-Ca complex as totally bio-based thermal stabilizer. Dynamic mechanical thermal analysis (DMTA) used to characterize the viscoelastic properties of PVC samples obtained by thermal mixing of PVC with three composition percentages (1.0, 2.0, and 3.0) part per hundred ratios (phr) of tannin-Ca complex with this polymer. The torque rheometery test used to monitor the effect of tannins derivative on the thermal stability and mixing properties of PVC formulations during samples processing. For that purpose, PVC sample with 2 phr commercial thermal stabilizer (Reapak B-NT/ 7060) was used for comparison and considered as reference samples. Before the glass transition temperature of PVC at 30°C - 60°C, the DMTA curves show that the values of storage modulus and tan delta of PVC samples stabilized with tannin derivative were very similar with those of PVC sample stabilized with commercial thermal stabilizer. The glass transition temperature (Tg) of PVC stabilized with commercial thermal stabilizer and with tannin-Ca complex occurred at about 76°C. In a sequence, after the glass transition region of PVC samples, the DMTA scans confirmed that the PVC samples with 2 phr tannin-Ca complex have relatively longer flowing stage which occurs at lower temperatures by 18°C per that of PVC sample stabilized with commercial stabilizer. Global results of the torque rheometery which have suitable plateau stages and the DMTA show that the processing thermal stability and thermal flexibility of PVC are clearly increased with the incorporation of tannin-Ca complex. All the PVC formulations with tannins-Ca complex show excellent viscoelastic properties which were found to be slightly best or much closed to those obtained for PVC stabilized with commercial thermal stabilization.

Experimental study on the compression properties and failure mechanism of 3D integrated woven spacer composites

The compressive experiments on the 3D integrated woven spacer composites with different core heights are performed in the flat and warp direction. Macro-fracture morphology and SEM micrographs have been examined to understand the deformation and failure mechanism. The results show that the core height is an important parameter to influence the compressive properties and failure mechanism. For flat compression, the compressive properties decrease with the core height and load–displacement curves exhibit elastic, plasticity plateau and densification stages. For high core height, yet more than one peak load appears. For warp compression, the compressive properties increase greatly with the core height and the curves only have obvious elastic stage. Meanwhile, the failure mechanism is significantly different under the flat and warp compression. For flat compression, core fiber bundles dominate the failure and three typical failure mechanisms have been obtained for different core heights. For warp compression, it is the face sheet rupture and dislocation between the top and bottom face sheets that dominate the failure of the composites.

Crush dynamics of rubber tube under low velocity impact

It is proved that hyperelastic honeycomb coatings can attenuate underwater blast loads impinged on the ship hull. The crush behavior of a unit tube cell of the coating made of rubber material is investigated in this study. A series of tests are conducted to investigate the crush dynamic behavior of the tube under low velocity impact loads. Numerical analyses are carried out to explore the impact process of the rubber tube and the role of some dynamic parameters, thereby serve as a reference in the design of new coating. Some characteristics, such as the geometric imperfections, nonlinear elasticity and material viscosity, are analyzed. The results of simulation and experiments show that the geometric imperfections not only attenuate the shock force in the buckling and the force plateau stages, but also enhance the shock force in the densification stage greatly and promote the global peak force initiation, while the material viscosity enhances the force plateau and attenuates the shock force in the densification stage greatly. These effects are illustrated and quantified with the aid of experiments and numerical calculations.

Dynamic Changes of Clinical Features that Predict the Prognosis of Acute-on-Chronic Hepatitis B Liver Failure: A Retrospective Cohort Study

Objective: The natural history of acute-on-chronic hepatitis B liver failure (ACHBLF) is complex and highly variable. However, the global clinical characteristics of this entity remain ill-defined. We aimed to investigate the dynamic patterns of the natural progression as well as their impact on the outcomes of ACHBLF. Methods: The clinical features and disease states were retrospectively investigated in 54 patients with ACHBLF at the China South Hepatology Center. The clinical and laboratory profiles including hepatic encephalopathy (HE), hepatorenal syndrome (HRS), and spontaneous bacterial peritonitis (SBP) were evaluated. The disease state estimated by the model for end-stage liver disease (MELD) score and the dynamic patterns during the clinical course of ACHBLF were extrapolated. Results: Twenty-two patients died during the 3-month follow-up period (40.74%). The patients were predominantly male (88.89%). Baseline characteristics showed that there were significant differences in only hepatitis B virus (HBV) DNA levels and platelet count between the deceased and surviving patients (P=0.014 and P=0.012, respectively). Other baseline characteristics were similar in both groups. The dynamic state of the MELD score gradually increased from an initial hepatic flare until week 4 of ACHBLF progression. There were notable changes of the dynamic state of the MELD score at two time points (week 2 and week 4) during ACHBLF progression. The MELD scores were significantly greater in the death group (24.80±2.99) than in the survival group (19.49±1.96, P<0.05) during the clinical course of ACHBLF; the MELD scores of the survival group began to decrease from week 4, while they continued to rise and eventually decreased as more patients died. The gradients of the ascent and descent stages could predict exactly the severity and prognosis of ACHBLF. Conclusions: The natural progression of ACHBLF could be divided approximately into four stages including ascent, plateau, descent, and convalescence stages according to different trends of liver failure progression, respectively. Thus, the special patterns of the natural progression of ACHBLF may be regarded as a significant predictor of the 3-month mortality of ACHBLF.

Characterisation of the intracranial pressure waveform during infusion studies by means of central tendency measure

In the present study an attempt was made to quantify and characterise the changes in the intracranial pressure (ICP) waveform over the wide pressure range covered during infusion studies by means of the central tendency measure (CTM). CTM is a non-linear approach using continuous chaotic modelling that summarises the degree of variability in a signal. CTM of the ICP wave in the lumbar subarachnoid space was analysed in 77 infusion studies performed in patients with idiopathic and secondary forms of normal pressure hydrocephalus (median age 74years, range 22-88). Four artefact-free epochs were selected during the baseline, infusion, plateau and relaxation stages of every infusion study. The average pressure, pulse amplitude and CTM were determined for each epoch. Correlations among these parameters were explored. CTM of the ICP waveform decreases, i.e. variability increases, as infusion studies progress from baseline pressure to the plateau stage. Significant correlations were found during all phases of infusion testing, except at baseline, between CTM and pressure, CTM and amplitude and pressure and amplitude. Partial correlations emphasised the relationship between CTM and amplitude. When pulse amplitude is held constant, CTM and the pressure range do not correlate. Volume loading leads to increased variability of the ICP signal measured by means of CTM. This finding summarises numerically the long-established phenomenon of increasing amplitude and rounding of ICP pulses associated with ICP elevation during infusion studies. CTM could be a suitable approach to quantify and characterise the pulsatile nature of the ICP wave.

Statistical signal processing methods for intraoral pressure curve analysis in orthodontics

A thorough understanding of the intraoral pressure conditions of patients with different forms of malocclusion may help to characterize their aetiology in more detail and improve orthodontic treatment approaches by adding strategies to achieve a normalization of intraoral pressure levels. These pressure curve analyses should not only provide information on intraoral activity or during rest but also detail characterization of swallowing features and pressure plateau stages. For this purpose, algorithms for extracting swallowing peaks and plateau stages were developed and evaluated. Established curve characteristics such as the average or maximum pressure as well as the number of swallowing peaks or resting phases were compared between each other. Their usefulness and correlation (Kendall's τ) were evaluated in a data example of different occlusal groups (Angle Class I: n = 30; Angle Class II division 1: n = 12; and Angle Class II division 2: n = 13). Curve characteristics were compared among these groups using the Kruskal-Wallis test. Some of the derived curve characteristics were found to be uncorrelated, thus providing different information concerning the intraoral pressure condition of subjects. Based on these findings, it is recommended to employ the curve characteristics described in this study to obtain a holistic image of factors that may affect the formation of the dentition.

Holocene peat growth and decay dynamics in sub‐arctic peat plateaus, west‐central Canada

Peat and net carbon accumulation rates in two sub‐arctic peat plateaus of west‐central Canada have been studied through geochemical analyses and accelerator mass spectrometry (AMS) radiocarbon dating. The peatland sites started to develop around 6600–5900 cal. yr BP and the peat plateau stages are characterized by Sphagnum fuscum peat alternating with rootlet layers. The long‐term peat and net carbon accumulation rates for both profiles are 0.30–0.31 mm/yr and 12.5–12.7 gC/m2yr, respectively. These values reflect very slow peat accumulation (0.04–0.09 mm/yr) and net carbon accumulation (3.7–5.2 gC/m2yr) in the top rootlet layers. Extensive AMS radiocarbon dating of one profile shows that accumulation rates are variable depending on peat plateau stage. Peat accumulation rates are up to six times higher and net carbon accumulation rates up to four times higher in S. fuscum than in rootlet stages. Local fires represented by charcoal remains in some of the rootlet layers result in very low accumulation rates. High C/N ratios throughout most of the peat profiles suggest low degrees of decomposition due to stable permafrost conditions. Hence, original peat accretion has remained largely unaltered, except in the initial stages of peatland development when permafrost was not yet present.

Angiotensin II triggers EGFR tyrosine kinase-dependent Ca2+ influx in afferent arterioles.

We previously reported that inhibition of epidermal growth factor receptor tyrosine kinase activity attenuates renal arteriolar contractile responses to angiotensin II. We performed the present experiments to determine if epidermal growth factor receptor tyrosine kinase activity contributes to the afferent arteriolar intracellular [Ca2+] response to angiotensin II. Afferent arterioles were dissected from rat kidney and intracellular [Ca2+] was monitored with the use of fura-2. In normal Ringer's bath containing 1.5 mmol/L Ca2+, basal intracellular [Ca2+] averaged 95+/-7 nmol/L and 100 nmol/L angiotensin II caused a rapid rise (peak Delta=75+/-10 nmol/L) that waned to a plateau averaging 24+/-5 nmol/L above baseline. Pretreatment with 100 nmol/L AG1478 (epidermal growth factor receptor tyrosine kinase inhibitor) reduced both the peak and the plateau stages of the angiotensin II response (peak Delta=42+/-7 nmol/L; plateau Delta=8+/-4 nmol/L). A structurally unrelated epidermal growth factor receptor tyrosine kinase inhibitor also suppressed the peak response to angiotensin II, whereas tyrosine phosphatase inhibition enhanced the plateau phase of the response. In the presence of 100 nmol/L extracellular Ca2+, the angiotensin II response was characterized by a peak of diminished magnitude (Delta=49+/-10 nmol/L; P<0.05 versus the response in normal Ringer's bath) with no plateau, and this response was unaffected by AG1478. Moreover, angiotensin II stimulation of divalent cation influx (Mn2+ quench of fura-2 fluorescence) was decreased significantly by AG1478. We conclude that epidermal growth factor receptor tyrosine kinase activity contributes to the afferent arteriolar intracellular [Ca2+] response to angiotensin II and that this process involves promotion of Ca2+ influx.

Length of the plateau and pipping stages of incubation affects the physiology and survival of turkeys

1. The hypothesis tested was that accelerating the vate at which a turkey embryo passes through the Plateau and Pipping stages (incubation days 25 to 28) affects growth and embryonic mortality. 2. Eggs from 4 genetic lines were incubated similarly until 24 d of incubation. The eggs were divided at random, half incubated at 36.8°C (CON) and the remaining half incubated at 37.3°C (FAST). 3. The passage time for each developmental stage was recorded at 4 h intervals. Tissues were collected and measured for growth, and glycogen concentration at each developmental stage in response to the accelerated development. 4. The FAST treatment accelerated passage through the Plateau in some lines but not others, but time to pip was shortened in all genetic lines. Embryonic survival rate was affected differently by FAST . Slower growth in response to FAST enhanced survival. 5. In conclusion the rate at which genetically different embryos grow, mature and survive may involve choices among the 3 processes.

Effects of an oxygen-enriched environment on the survival of turkey embryos between twenty-five and twenty-eight days of age

The hypothesis was tested that increased partial pressure of oxygen during the plateau (25 to 26 d of incubation for turkeys) and paranatal (27 to 28 d of incubation) stages of incubation may increase survival rates of turkeys from selected genetic lines. Partial pressure of oxygen inside the incubator cabinet was increased to 171 + 3 mm Hg of the barometric pressure during the plateau stage in oxygen consumption and compared to ambient oxygen (152 + 3 mm Hg). Turkey embryos from genetic lines selected for egg production (E) or growth (F) were compared to their respective randombred controls. These genetic lines have previously been shown to differ in egg weight, eggshell conductance, length of incubation period, embryonic gluconeogenesis, and survival rates during late incubation. Blood, liver, heart, and pipping muscle samples were obtained prior to pipping, at internal pipping and external pipping, and at hatching. The blood was analyzed for glucose concentration and the remaining tissues were assayed for glycogen concentrations. Survival rates were determined on approximately 2,200 eggs in each of three independent trials of the experiment. Interactions of oxygen treatment and genetic line were observed for embryonic survival, heart growth, and hepatic glycogen content. The data suggest that the response to increased oxygen tension in selected genetic lines has been diminished. It was concluded that embryos have been altered metabolically by genetic selection and the concomitant increase in mortality of selected lines during the plateau and paranatal stages is not simply the result of shell quality and hypoxia.

EUVE Photometry of SS Cygni: Dwarf Nova Outbursts and Oscillations

I present EUVE Deep Survey photometry and AAVSO optical measurements of the 1993 August and 1994 June/July outbursts of the dwarf nova SS Cygni. The EUV and optical light curves are used to illustrate the different response of the accretion disk to outbursts which begin at the inner edge and propagate outward, and those which begin at the outer edge and propagate inward. Furthermore, we describe the properties of the quasi-coherent 7-9 s sinusoidal oscillations in the EUV flux detected during the rise and plateau stages of these outbursts.

The role of mosaic phenomena in natural communities

Interrelations among three groups of ideas are considered. (1) The place where a plant is rooted, or a sessile animal is attached, may be termed a microsite. The microsites for a community form a mosaic that is differentiated by physical environment or biological effects or both. Population function and regulation, and community self-maintenance and response to environmental fluctuation, can be approached in terms of the flow of reproducing populations through the mosaic. (2) Most communities are subject to disturbance followed by succession. Communities are diverse in the kinds and frequencies of disturbances and in kinds of successions and climaxes; and the species of a biota diversify in their relationships to successional time and patterns of successional and climax communities. (3) Although mosaic phenomena are general, two broad groupings may be recognized: intracommunity patterns that relate to microsite differentiation and species response to this, and intercommunity successional mosaics and climax complexes for which community disturbance is a major determining force. Relationships between elements of a mosaic can often be formulated in terms of a chain or network of replacement rates, but formulations should allow for the influence of bath terms and occurrence of semipermanent plateau stages in some successions.