Thermal behaviour of poly(methyl methacrylate)/fullerene composite films

ABSTRACT

Poly(methyl methacrylate) films and poly(methyl methacrylate)/fullerene composite films were fabricated by casting from toluene solutions. The mass fraction of fullerene (C₆₀) was varied from 0.05–3?wt. %. The effect of the fullerene (C₆₀) content on the thermal degradation parameters of the composite films was evaluated by thermogravimetric (TG) analysis. It was found that the incorporation of C₆₀ improved the thermal stability of the polymers. The films eventually decomposed in three stages. Incorporation of fullerene caused a change in the distribution of mass loss over the stages of degradation in comparison with the pristine polymer. Using differential scanning calorimetry (DSC), the phase transitions from the glassy state to the elastic one was studied for the examined polymeric materials. New data relating to the effect of C₆₀ on the glass transition temperature of composites with low weight fractions of filler were obtained. Specifically, for films containing up to 0.1 wt. % of C₆₀, a single glass transition temperature was found, whereas for composites with a higher concentration of filler, two glass transition temperatures were recorded.     

Determination of glass-forming ability of Ge1− x Sn x Se2.5 (0 ≤ x ≤ 0.5) alloys using differential scanning calorimetry

The glass-forming ability of Ge_{1? x} Sn _x Se_2.5 (0 ≤ x ≤ 0.5) alloys was studied using differential scanning calorimetry. Samples were scanned at different heating rates under non-isothermal conditions. Various simple quantitative methods were employed to assess the stability of the glassy materials in the above-mentioned system. All of these methods are based on characteristic temperatures, such as the glass-transition temperature, T _g, the onset-of-crystallization temperature, T _c, and the peak crystallization temperature, T _p. A crystallization rate factor, K, has also been used as a measure of the thermal stability of the glasses. It was found that Ge_0.7Sn_0.3Se_2.5 was the least stable among all the samples.     

Thermal shock resistance of brittle ceramic materials with embedded elliptical cracks

An analytical model is established for the prediction of the thermal shock resistance of a ceramic plate with an embedded elliptical crack with ideal thermal insulation. The thermal stress intensity factors at the crack fronts are formulated by fitting the thermal stress to a polynomial form in an un-cracked plate. The thermal shock resistance of sapphire ceramic is evaluated as an example. In addition, the numerical solution of thermal shock resistance suitable for practical engineering applications is provided. The model developed applies to any brittle material in high temperature applications.     

On convergence of the generalized Maxwell scheme: conductivity of composites containing cubic arrays of spherical particles

The Maxwell concept of equivalent inhomogeneity generalized to account for the interactions between the particles in the cluster and combined with recently reported results on the polarizability of a cube is used to evaluate the effective conductivities of the materials reinforced by cubic arrays of spherical particles. New numerical results demonstrate that the estimates of the effective properties based on the generalized Maxwell scheme with the equivalent inhomogeneity of cubic shape converge to the accurate periodic benchmark solutions, unlike spherical shape-based estimates.     

Thermal stability and glass-forming ability of Se80− x Te20Ag x (x = 0, 3, 5, 7 and 9) chalcogenide glasses

The thermal stability and glass-forming ability (GFA) of Se_{80? x} Te₂₀Ag _x (x?=?0,?3,?5,?7 and 9) chalcogenide glasses have been investigated using differential scanning calorimetry (DSC). The DSC runs have been taken at five different heating rates (10, 20, 30, 40 and 50?K/min) under non-isothermal condition. The thermal stability and GFA are monitored through determination of the temperature difference ΔT?=?T _c???T _g, where T _c is the onset crystallization temperature, T _g is the glass transition temperature, H ^l is the stability parameter, ΔH _c is the enthalpy released during crystallization and F _i is the fragility index. The activation energy of crystallization E _c and crystallization rate factor K have also been determined as indicators of the thermal stability of the above-mentioned samples. It is found that Se₇₁Te₂₀Ag₉ is the most stable among all the samples of the series.     

Crystallization and thermal stability of polypropylene/multi-wall carbon nanotube nanocomposites

Polypropylene (PP)/multi-wall carbon nanotube (MWCNT) nanocomposites were prepared via a melt compounding method using a twin-screw extruder. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the crystallization and thermal stability of the nanocomposites. The DSC analysis results revealed that the existence of MWCNTs in a PP matrix, which acted as a nucleating agent enhancing the crystallization process of PP matrix. This behaviour was manifested by an increase in the crystallization temperature and crystallinity index of the nanocomposites. Additionally, the TGA results showed that the addition of MWCNTs dramatically increased the thermal stability of the PP/MWCNT nanocomposites. Generally, MWCNT type C-70P showed improved crystallization and better thermal stability of the nanocomposites compared to type C-150P.     

Supercapacitor behaviour of cobalt-doped nickel oxide films

Ordered nanostructured cobalt-doped nickel oxide films were prepared on a conducting glass substrate via the sol–gel dip-coating method. X-ray diffraction analysis shows the films to be amorphous. Field-emission scanning electron microscope images showed well-defined, ordered grains with pores in between them. Supercapacitor behaviour was studied using cyclic voltammetry. A maximum specific capacitance of 1982?F/g at a scan rate of 5?mV/s with 1?M KOH was obtained for 5?wt% of cobalt-doped nickel oxide films. AC impedance analysis showed that the solution resistance was R _s?=?27?Ω and the charge transfer resistance R _ct?=?20?Ω.     

A theoretical model of effective electrical conductivity and piezoresistivity of carbon nanotube composites

A theoretical model is developed to predict the electrical conductivity of polymer composites containing carbon nanotubes. It incorporates the effect of two conductivity mechanisms, electron hopping between adjacent nanotubes at the nanoscale and the transmission of electrons through conductive networks formed by nanotubes at the microscale. Based on the model, analytical expressions of both electrical conductivity and piezoresisitivity under stretching are established. The expressions are simple in form, without resorting to heavy computation, and able to give accurate estimations for both electrical conductivity and piezoresistivity.     

High-pressure electrical resistivity behaviour of nanocrystalline perovskite (La,Sr)(Mn,Fe)O3

We report here the electrical resistivity of nanocrystalline perovskite-structured La–Sr manganites as a function of pressures up to 8?GPa, at room temperature. The nanocrystalline perovskite manganites were prepared by the sol–gel technique and found to have crystallite sizes of 12–18?nm. The pressure dependence of the electrical resistivity shows a first-order phase transition at 0.66(2)?GPa and a subtle phase transition between 3.5 and 3.8?GPa. The first-order transition at 0.66?GPa can be related to the transition from localized-electron to band magnetism.     

Precipitation of an icosahedral quasicrystalline phase in Hf59Ni8Cu20Al10Ti3 metallic glass

The crystallization process of a Hf₅₉Ni₈Cu₂₀Al₁₀Ti₃     

High-angle annular dark field scanning transmission electron microscopy of the antiphase boundary in a rapidly solidified B2 type TiPd compound

High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast is applied to characterize the antiphase boundary (APB) of the B2 structure in a rapidly solidified TiPd melt-spun compound. The atomic shift associated with the R ?=?(1/2) a ₀ ?111? type displacement vector is directly observed at the boundary. A microstructure modification of the melt-spun compound with the cooling rate during solidification is also described.     

Effects of measurement aggregation on predicting externalizing problems from preschool behaviour

In long‐term studies of psychological development, the initial assessment of etiologically significant child behaviours is often carried out at a single point in time only. However, one‐time assessments of behaviour are likely to possess limited reliability, leading to attenuated longitudinal correlation coefficient magnitudes. How much this bias might have affected behavioural continuity estimates in longitudinal research is presently unknown. Using a data set from the Mauritius Child Health Project, we particularize the attenuating effects of single‐occasion behavioural assessments on consistency estimates of impulsive–aggressive behaviour over time. Specifically, two nursery teachers provided 15 consecutive weekly ratings of the aggressive behaviour of 99 four‐year‐old children. The same children were reassessed for the presence of externalizing behaviour problems at the ages of 8 and 10. There were substantial increases in both reliability and predictive correlation coefficient magnitudes when the preschool scores were aggregated across several weekly ratings. A further increase resulted after the two outcome assessments were combined into a composite score of school‐age externalizing symptoms. A generalized procedure, developed from the correction for attenuation formula, is introduced to describe the relation of aggregation to predictive validity in longitudinal research.     

The use of implementation intentions and the decision balance sheet in promoting exercise behaviour

Although increasing exercise and fitness has often been associated with positive health outcomes, infrequent exercise participation has remained a problem. Since two distinct motivational and volitional phases to goal pursuit have been proposed, a combined motivational (decision balance sheet, DBS) and volitional (implementation intentions) intervention was predicted to be more effective in increasing exercise behaviour than a control or either strategy alone. A total of 86 students were randomly assigned to one of the four conditions, and were all asked to try to exercise two more times a week than they currently did, over a four week period. Their fitness levels were measured through fitness tests conducted pre- and post-intervention. A priori orthogonal contrasts indicated that the experimental strategies produced a greater increase in exercise frequency and total time spent exercising per week and accordingly showed greater fitness improvements than the control group. Moreover, the volitional groups taken together produced greater increase in time spent exercising and a marginally greater improvement in frequency than the DBS alone. The combined intervention led to improvements in fitness and marginal increases in frequency over the implementation intention alone group. It is proposed that for the combined group the DBS may have aided recall of the implementation intention or increased commitment to it, as remembering and then acting on the plan, in the stated place and time, mediated the implementation intention–behaviour relationship. The combined intervention produced the greatest fitness improvements, indicating that this strategy can lead to important health benefits.     

Phenomenological model of variant change during magnetization of martensite

The present study deals with the straining of ferromagnetic martensite in a magnetizing field. A phenomenological model of the movement of the interface between martensitic variants is developed for calculation of the strength of the magnetic field required for a variant change. The effect of uniaxial stress on interface movement is also examined. The results are applied to the martensite phases of NiMnGa and FePd ferromagnetic shape-memory alloys.     

稳定性/发展性:气质研究视角的嬗变

气质作为心理学研究的一个重要领域,传统研究注重突出气质的先天性与稳定性,而近期研究则逐渐开始强调气质是具有行为基础的发展性的行为特征,表现出与传统研究不同的视角转向。目前这种“暗流涌动”式的转向将对气质研究领域的拓展和深化具有重要的导向意义。     

Microstructure and superconductivity of bulk BPSCCO/LPMO composite

Bulk superconducting (SC) ceramics containing BPSCCO and LPMO (Lanthanum/Lead – manganite phase) have been produced. The initial components were prepared by a low-temperature Pechini method. The submicron powders in weight ratio 90/10 Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_z/La_0.6Pb_0.4MnO₃ (nominal composition) were heat treated at 840°C. The duration of the heat treatment effect (60 and 100?h) of the composite on the transformation of the microstructure was studied. The obtained composites were analyzed by scanning electron microscopy (SEM) and by the method of energy-dispersive X-ray spectroscopy (EDX). They contain several phases. It was established that the SC 2212 phase is predominate in the composite. The phase La_0.6Pb_0.4MnO₃ transforms in solid solution with preliminary composition La_0.5(Sr?+?Ca)_0.5Mn_{1? z} Cu _z O₃, which after full replacement of the La and Mn ions leads to the appearance of phases with nominal composition Sr_{1? x} Ca _x CuO _y . AC and DC magnetization measurements were used to study the SC and magnetic properties of the samples. Both samples are SC with critical temperatures 75 and 77?K, respectively. It was concluded that the SC and magnetic phases stably coexist in the composite sintered at 60?h heat treatment at 840°C.     

An investigation of behaviour and attitudes relevant to the user safety of pedestrian/cyclist shared paths

Bicycle/pedestrian shared paths are an increasingly popular solution to providing cycling infrastructure, despite evidence suggesting safety issues. Improved design and management of shared paths should be informed by understanding of bicyclist and pedestrian behaviour on shared paths, and of relevant safety initiatives (e.g. centreline marking). However, relevant research is lacking. Bicyclist/pedestrian passing events (n = 407) were observed on three relatively busy shared paths in Sydney, Australia – one of them without centreline marking. User characteristics, relevant behaviours and incidents (aggression, near-misses, crashes) were recorded. A tendency toward left-hand travel, as on Australian roads, was stronger for cyclists than for pedestrians, and where centreline was present. Cyclists were often estimated to travel above 10 km/h, a speed limit that has been suggested based on pedestrian safety considerations, but that would be unacceptable for long stretches of commuter cycling. Centreline was associated with lower estimated speeds. Cyclists typically adhered to their responsibility of giving way to pedestrians, but often passed on the left, passed too close, passed without slowing, or passed without warning (e.g. with a bell). Use of mobile telephones and mp3 players is common, particularly amongst pedestrians. Five near collisions were observed, and 53 survey participants reported 2 collisions and 13 near misses. Contributing factors appear to include path users using potentially distracting devices, or straying from the rules of thumb to keep to the left, and to overtake on the right.A survey of cyclists and pedestrians suggested that there are issues with perceptions of space ownership. These results represent an important contribution to the evidence-base for initiatives to improve the safety of shared paths.     

Critical factors governing the thermal stability of austenite in an ultra-fined grained Medium-Mn steel

The time-evolution of retained austenite at 650 °C is shown to be a fair indicator of the factors governing the austenite stability. The grain size contribution to austenite stability is evidenced and a martensite start temperature (M_s) law applicable to medium-Mn steels and including both the chemical and size effects is determined.     

The psychological process of reintegration following a nine month/260 day solo sailboat circumnavigation of the globe

The focus of this case report is on the psychological reintegration process following the achievement of a highly challenging long‐duration and solitary endeavor. The participant was a 29 year old male who successfully circumnavigated the globe during a 260 day solo sailing expedition. We assessed the psychological aftermath in terms of stability and change in personality characteristics and personal beliefs prior to, and at 180 and 360 days after the completion of the journey. Overall, the personality configuration reflected adaptive personality functioning. A belief in an internal locus of control was consistent throughout, as were perceptions of personal growth as a result of the circumnavigation experience. NEO PI‐R Neuroticism, Extraversion, Openness, and Triarchic Psychopathy Measure (Tri‐PM) Boldness scores remained stable. Positive personality change was reflected by an elevation in Conscientiousness; negative change by a decline in Agreeableness and an increase in Tri‐PM Disinhibition. While overall the participant exhibited positive change as a result of his journey, there were also some negative aspects of the reintegration phase in regard to interactions with other persons. This latter change may be related to the effects of isolation from usual social contacts over an extended period.     

Effect of Al-Zr clusters on the thermal stability of Cu-Zr-rich Cu-Zr-Al bulk metallic glasses

The Gibbs free energy of formation, ?G^a, of the amorphous phase of Cu–Zr-rich Cu–Zr–Al bulk metallic glasses (BMGs) has been calculated over a broad composition region to re-evaluate their thermal stability, based on the efficient cluster packing model. It is found that Al–Zr clusters have an important effect on the thermal stability of the Cu–Zr–Al BMGs with the same Cu/Zr content ratio. The crystallisation of the BMGs involves crystallisation of both Al–Zr and Cu–Zr clusters. The results could be useful for predicting the thermal stability and understanding the underlying mechanism of crystallisation of multicomponent metallic glasses.