Some previously unexpected phenomena of volume recovery

We have extensively studied the nonequilibrium behavior of atactic polystyrenes in a broad range of temperatures. Depending on the conditions of the initial temperature (To) and the aging temperature (T), the shapes of isotherms plotted in the form of total fractional free volume (viz., δ) versus logarithmic aging time can be linear or nonlinear. At a T in the vicinity of T_g , the isotherms converge together. When the Tis lowered, the isotherms become increasingly nonlinear; eventually, these isotherms intersect one another at various points, forming a newly discovered crossing phenomenon. Differences in volume contraction persist throughout further aging, regardless of the equality in δ right at the moment of crossing. In a further case, the nonlinear isotherms between the two polystyrenes may be superposable by a simple δ shift, despite their substantial differences in δ. As none of these phenomena can be justified by kinetic arguments, this study seriously questions the validity of the existing kinetic theories as well as the existence of the extrapolated underlying equilibrium state.     

三嵌段共聚物SEBS中自由体积行为的温度及e+辐照时间依赖性的研究

利用正电子湮没寿命谱实验手段研究了²²Na放射源的e⁺自辐射对三 嵌段共聚物SEBS的正电子湮没参数的影响，而后结合Eldrup的经典模型，研究了SEBS的自由体积孔尺寸和自由体积分数随着温度的变化关系，给出了自由体积分数在T_g以上和在Tg以下各自区域内分别与温度呈线性关系，最后结合Williams-Landel-Ferry(WLF)自由体积理论和Eldrup的经典模型讨论了热膨胀系数和自由体积分数中的A常数. 关键词： 正电子湮没技术 嵌段共聚物 自辐射 热膨胀     

Long-term stability of soft magnetic properties of amorphous and nanocrystalline alloys based on iron

In the present paper long-term stability of magnetic properties of different amorphous and nanocrystalline alloys was studied. Magnetic properties were measured for annealed samples (300<Ta<900 K) directly after annealing and after long-term aging at room temperature. It was shown that for the Fe_75.3Cu₁Zr_1.7Si₁₃B₉ alloy magnetic permeability of the optimized samples is stable during 8 years aging. For Fe_86−xNb_xB₁₄ alloys the observed long-term instability (3 years aging) is due to annealing out of free volume leading to formations of small iron clusters coherent with the amorphous surroundings.     

Glass and β transitions of atactic polystyrenes monitored by volume dilatometry

Volume recovery in the temperature range of above T_g to below T _β has been studied for two atactic polystyrene specimens (M _w = 210,000 and 300,000 g/mol). Observations clearly disclose the collapse of free volume even at temperatures well below T_β. In an excess free volume sufficient environment, as the aging temperature is lowered through T_β, the retardation of the initial volume recovery becomes progressively longer, forming a variation in the nonlinearity of the isotherms. Indeed, it is this variation that leads to the observation of the β transition in the V-T plot. The β transition is time dependent, but molecular weight independent. On the other hand, in addition to well-known molecular weight and time dependence, the glass transition has another important feature: The difference in thermal expansion coefficients above and below T_g increases slightly with aging time. Thus, time cannot alter the existence of Tg. Consequently, this study favors thermodynamic theories for the formation of T_g.     

Origin of the constricted hysteresis loop in cobalt ferrites revisited

A series of Co ferrites (Co_xFe_3−xO₄ (x=0−1)) were prepared using solid-state method in this work. The aging effect of their structures and constrictions of hysteresis loops under low magnetic field were investigated. It was found that during the aging process, the migration of trivalent (bivalent) ions between tetrahedral (A-site) and octahedral (B-site) coordination induced a shrinking of the lattice, which would expand again due to the precipitation of Fe³⁺ after a much longer aging time. The first process caused a pronounced constriction of the loops, due to the uniaxial anisotropy led by this migration. The depression of constriction could attribute to both the expansion of lattice and the change of ionic ratios as a result of the second-phase-precipitation. The impacts of Co content, aging time and temperature upon the constriction were also discussed.     

SMMA/SMA共聚物共混物的自由体积的热动态特性与相分离行为的PALS研究

基于自由体积理论，利用正电子湮灭寿命谱仪(PALS)分别研究在不同升温速率条件下，聚苯乙烯-甲基丙烯酸甲酯共聚物(SMMA)和聚苯乙烯-马来酸酐共聚物(SMA)混合物(30/70)的自由体积参数的温度依赖性，探索相容共混物相行为的热动态特性.在PALS实验中，在玻璃化转变温度T_g以上，当结构松弛的弛豫时间与等温停留时间相当，发现在某一段温度范围内，共混物的自由体积参数随着温度的变化明显地偏离线性关系.从自由体积孔的浓度I₃值在该段的变化趋势，初步推断共混物在该温 关键词： 正电子湮没 正电子素 聚合物共混物 相分离     

Temperature invariance ofS 0-parameter of polymers

The parameterS ₀ which is characteristic of molten alkali halides and liquids has also been shown to be characteristic of a wide variety of polymers. Calculated data using the volume expansivity of the polymer establish the temperature invariance and constancy of theS ₀-parameter which retains, on an average, a constant value of 1.11 for polymers. Further understanding of the significance of fractional free volume andS ₀-parameter in describing various thermoacoustic properties and the anharmonic behaviour in polymers, has been developed.     

MRI of human tumor xenografts in vivo: Proton relaxation times and extracellular tumor volume

Proton T₁ and T₂ differ substantially between tumors, but the tumor properties causing heterogeneity in T₁ and T₂ have not been fully recognized. The purpose of the study reported here was to investigate whether differences in T₁ and T₂ between tumors are mainly a consequence of differences in the fractional volume of the extracellular compartment. The study was performed using a single human tumor xenograft line showing large naturally occurring intratumor heterogeneity in the size of the extracellular compartment. The size of the extracellular compartment was calculated from the volume and the density of the tumor cells. Cell volume was measured by an electronic particle counter. Cell density was determined by stereological analysis of histological preparations. T₁ and T₂ were measured by MRI in vivo both in the absence and presence of Gd-DTPA. Two spin-echo pulse sequences were used, one with a repetition time (TR) of 600 ms and echo times (TEs) of 20, 40, 60, and 80 ms and the other with a TR of 2,000 ms and TEs of 20, 40, 60, and 80 ms. Measurements of T₁ and T₂ in the presence of Gd-DTPA were performed in a state of semi-equilibrium between uptake and clearance of Gd-DTPA. MR-images and histological preparations of tumor subregions homogeneous in extracellular volume were analysed in pairs. The extracellular volume differed between tumor subregions from 5 to 70%. T₁ and T₂ measured in the absence of Gd-DTPA differed between tumor subregions by a factor of approximately 1.5 and increased with increasing extracellular volume. The relative decrease in T₁ caused by Gd-DTPA, represented by $\text{(T}{}_{\mathrm{<mtext>1\; control</mtext>}}\text{−T}{}_{\mathrm{<mtext>1\; Gd-DTPA</mtext>}}\text{)}\text{T}{}_{\mathrm{<mtext>1\; control</mtext>}}$, also increased with increasing extracellular volume. The relative decrease in T₂ did not change significantly as the extracellular volume increased. These observations strongly suggest that the size of the extra-cellular compartment is a major determinant of proton T₁s and T₂s of tumors, possibly because the ratios of free to structured and free to bound water increase with increasing extracellular tumor volume.     

Enthalpy recovery of a glass-forming liquid constrained in a nanoporous matrix: Negative pressure effects

The T _g of organic liquids confined to nanoporous matrices and that of thin polymer films can decrease dramatically from the bulk value. One possible explanation for this phenomenon is the development of hydrostatic tension during vitrification under confinement that results in a concomitant increase in the free volume. Here we present experimental evidence and modeling results for ortho-terphenyl (o-TP) confined in pores as small as 11.6 nm that indicate that, although there is an important hydrostatic tension in the liquid in the pores, it does not develop until near the reduced T _g of the constrained material --well below the bulk T _g. Enthalpy recovery for the o-TP in the nanopores exhibits accelerated physical aging relative to the bulk, as well as a leveling off of the fictive temperature at equilibrium values greater than the aging temperature. An adaptation of the structural recovery model that incorporates vitrification under isochoric conditions is able to provide a quantitative explanation for the apparently anomalous aging observed in nanopore confined liquids and in thin polymeric films. The results strongly support the existence of an intrinsic size effect as the cause of the reduced T _g. Received 3 September 2001     

Fractional fermion number on a thermal ø4 soliton backgroud field at finite temperature

We employ a thermal kink soliton field as the background field and discuss the effect of the field on fractional fermion number 〈N〉_β at finite temperature. It is found that the fractional fermion charge will be restored at critical temperature T_c. The expressions of 〈N〉_β at the high-temperarute limit and the low-temperature limit are given.     

Numerical study on effects of hydrothermal aging to composite regeneration in CeO2-based catalyzed diesel particulate filter

The effects of hydrothermal aging on the performance of CeO₂-based catalyzed diesel particulate filter (CDPF) was numerically investigated in this study based on a zero-dimensional model using the plug flow reactor in which a chemical reaction kinetic mechanism was established and validated by the simulated gas environment experiment. The effects of regeneration temperature, O₂ concentration in the ultimate emission conditions, the ratio of NO₂ in NOx (α) and the ratio of NOx to soot (β) on catalyst deactivation temperature and soot oxidation rate were investigated with fresh and hydrothermal aging CeO₂-based CDPF. The results show that hydrothermal aging of CeO₂-based catalysts raises the regeneration temperature from 613 to 783 K and shifts the soot catalytic combustion reaction path from complete to incomplete oxidation. Soot oxidation rate of fresh catalyst first increases rapidly at 516 K and then starts to slow down gradually at 633 K, but for hydrothermal aging catalysts, are 601 K and 789 K, respectively. With O₂ concentration increased from 1.5 mol/m³ to 5.5 mol/m³, the catalyst deactivation of fresh and hydrothermal aging catalyst increased from 609 K to 602 K, 791 K to 818 K, respectively. The increase in α and β leads to an increase in soot oxidation rate and a decrease in regeneration temperature. The deactivation temperature of catalyst is increased in higher α (1.0) and lower β (0.1), which the highest is 821 K. Synergistic mechanisms of NOx, regeneration temperature, and hydrothermal aging effects on soot catalytic combustion in CeO₂-based CDPF are revealed deeply with the help of zero-dimensional model.     

Fractal representation of the Debye theory for studying the heat capacity of macro-and nanostructures

The traditional theory of Debye heat capacity with a single free parameter (characteristic temperature θ_D) is extended to fractal spaces taking into account two more “latent” parameters contained in it, viz., the phonon spectrum dimension d _f and dimension d determining the geometry of the skeleton of the structure under investigation. In the classical version of the Debye theory, d _f = d = 3. In the case under investigation, these parameters can assume arbitrary (including fractional) values, which is typical of materials such as polymers, colloid aggregates, and various porous structures and nanostructures, as well as materials with a complex chemical composition. The application of a fractal approach makes it possible to substantially extend the class of materials with a heat capacity described by the continual Debye approximation.     

Triple convective flow of micropolar nanofluids in double lid-driven enclosures partially filled with LTNE porous layer under effects of an inclined magnetic field

In this paper, free, forced and Marangoni convective flows within an open enclosure partially filled with a porous medium under impacts of an inclined magnetic field are investigated. The forced convection is due to the movement of the side walls, the free convection induces from the heated part in the bottom wall and the Marangoni convection is a responsible on the thermal interaction at the free surface (top wall). The flow domain is partially heated from below and partially filled by a porous medium. The local thermal non-equilibrium model (LTNEM) is used to represent the thermal field in the porous layer (bottom layer) while the two-phase model is used to simulated the micropolar nanofluid behavior. Two cases based on the direction of the movement of the side walls are considered, namely, assisting flow (downward lid motion) and opposing flow (upward lid motion). Numerical analysis based on the finite volume method is conducted and the obtained are presented in terms of the streamlines, isotherms, angular velocity, and the cup-mixing temperature θ_cup, the bulk-averaged temperature θ_ave and the average Nusselt numbers. The controlling parameters, in this situation, are the Darcy number Da, the Marangoni number Ma, the Nield number H, the vortex viscosity Δ, the Biot number Bi and the Hartmann number Ha. The results revealed that the increase in the Nield number enhances the cup-mixing temperature θ_cupand bulk-averaged temperature θ_ave regardless the direction of the side walls motion. Also, the average Nusselt number is boosted as the Marangoni number is grown.     

Study of intermolecular interactions in binary mixtures of 2′-chloro-4-methoxy-3-nitro benzil in various solvents and at different concentrations by the measurement of acoustic properties

Density (ρ), ultrasonic velocity (u), adiabatic compressibility (β), apparent molar volume (Ø), acoustic impedance (Z), intermolecular free length (L_f), relative association (RA) of binary mixtures of 2′-chloro-4-methoxy-3-nitro benzil (abbreviated as 2CBe) in ethanol, acetonitrile, chloroform, dioxane and benzene were measured at different concentrations at 298 K. Several useful parameters such as excess density, excess ultrasonic velocity, excess adiabatic compressibility, excess apparent molar volume, excess acoustic impedance and excess intermolecular free length have been calculated. These parameters are used to explain the nature of intermolecular interactions taking place in the binary mixture. The above study is useful in understanding the solute – solvent interactions occurring in different concentrations at room temperature.     

Thermodynamic parameters of N-(p-n-alkoxybenzylidene)-p-n-(butyloxyanilines), (nO.O4) liquid crystal compounds — A dilatometric study

Different thermodynamic parameters are estimated from volume expansion coefficient, α for a number of N-(p-n-alkoxybenzylidene)-p-n-butyloxyanilines, nO.O4 compounds in isotropic phase (at T_IN + 5 °C) and in liquid crystalline phases. The variation of different thermodynamic parameters with the alkoxy chain length in nO.O4 series and their variation with the temperature in individual liquid crystal compounds are discussed. The parameters like available volume (V_a), inter molecular free length (L_f) and molecular radius (M_r) are also computed from density, and refractive index for these nO.O4 compounds and the nature of molecular free length and molecular radius are analyzed and discussed.     

Pressure effect on structural,electronic and thermodynamic investigations of europium filled skutterudite EuFe4Sb12: LDA and LSDA approximations

Numerical calculations based on the full potential muffin-tin orbitals method (FP-LMTO) within the local density approximation (LDA) and the local spin-density approximation (LSDA) to investigate the structural, electronic and thermodynamic properties of filled skutterudite EuFe₄Sb₁₂ are presented. The electronic band structure and density of states profiles prove that this material is a conductor. The present investigation is also extended to the elastic constants, such as the bulk modulus B, anisotropy factor A, shear modulus G, young's modulus E, Poisson's ratio ν, and the B/G ratio with pressure in the range of 0–40 GPa. The sound velocities and Debye temperatures are also predicted from the above constants. The variations of the primitive cell volume, expansion coefficient α, bulk modulus B, heat capacity (C_p and C_v), Debye temperature θ_D, Helmholtz free energy A, Gibbs free energy G, entropy S, and internal energy U with pressure and temperature in the range 0–3000 K are calculated successfully.     

Aging effects in the nonequilibrium behavior of multilayer magnetic superstructures

A numerical Monte Carlo study of the nonequilibrium behavior of multilayer magnetic superstructures consisting of alternating magnetic and nonmagnetic nanolayers is performed. The calculated two-time autocorrelation function and the staggered magnetization of the structure at its evolution starting from various initial states are analyzed. The analysis reveals aging effects characterized by a slowing down of the relaxation and correlation characteristics in the system with the waiting time. It is shown that, in contrast to bulk magnetic systems, the aging effects in magnetic superstructures arise not only near the ferromagnetic ordering temperature T _c in the films but also within a wide temperature range at T ≤ T _c.     

Analysis of pulsed discharge characteristics of solid-state switch (IGBT) based 16?kHz repetition rate, 100?W average power copper–HBr lasers

We present for the first time a comprehensive analysis (both time resolved and time averaged) of the gas-discharge characteristics of a solid-state switch (IGBT) based on high average power (100?W class), high pulse repetition rate (16?kHz) copper?CHBr laser under various excitation conditions. We evaluate various discharge-plasma parameters such as the electrical inductance, electrical resistance, active laser-head voltage, active electrical power, pre-pulse electron density, and axial gas temperature by numerical processing of the measured laser head voltage?Ccurrent waveforms. For the first time, we evaluate fractional losses at various intermediate stages of the circuit elements as well as effective coupling for the laser excitation process during transfer of energy from the wall plug to the laser-discharge plasma. We conclude that irrespective of the capacitive storage input power (P _in), a constant fraction of ~40% of P _in is coupled into the laser-discharge plasma. With a low to moderate specific input power of 0.4?C0.7?kW/?, the tube produced 70?C110?W average output power at an efficiency of????3.2?C2.8%, respectively. The average laser performances at various P _in are correlated to its time-resolved and average gas-discharge parameters such as the inter-pulse electron density and axial gas temperature.     

Ionic conductivity enhancement during pre-crystallization in amorphous lithium ionic conductor Li2B2O4

It is found from the temperature dependence of the ionic conductivity of amorphous Li₂B₂O₄ that the ion transport process is rather complicated. At temperature below T_k (≈310°C), the ionic conductivity obeys an Arrhenius relation. Above the crystallization temperature T_c (≈410°C) ion transport is dominated by the process in the crystalline state. In between the ionic conductivity is anomalously enhanced. In this pre-crystallization range two distinguishable steps with a transition temperature at T_p (≈380°C) can be identified. At temperature between T_k and T_p, the conductivity increase is due to the redistribution of free volume. For temperature between T_p and T_c the specimen contains a small amount of crystallites but the crystallinity is less than 5%. The ⁷Li NMR spectra show that the line shape of partially crystallized amorphous material is quite similar to that of LiCl containing DSPP but in this case the second-phase particles are crystallites of the parent material.