糖渍野木瓜鲜切片加工及保鲜工艺研究

目的 优化糖渍野木瓜的制作工艺和保鲜工艺参数,并评估其货架期。方法 以糖液质量分数、超声糖渍时间、真空糖渍时间为因素,进行正交实验,筛选出糖渍野木瓜鲜切片的最佳制作工艺。在最佳糖渍工艺基础上,筛选糖渍野木瓜鲜切片的保鲜处理工艺参数。在糖液中添加纳他霉素和D-异抗坏血酸钠,真空包装后巴氏杀菌。根据筛选出的最佳工艺参数制作产品,并进行产品检验。结果 糖渍野木瓜鲜切片最佳工艺参数：超声糖渍时间为60 min,真空糖渍时间为90 min,糖液质量分数为40%,纳他霉质量浓度为60 mg/L,D-异抗坏血酸钠质量浓度为200 mg/L,杀菌条件为70℃、30 min。结论 该工艺生产出的糖渍野木瓜鲜切片相较于市售产品具有更高的安全性和更长的货架期。     

Rehydration ratio of fluid bed-dried vegetables

Fluid-bed drying of vegetable pieces has been investigated. The vegetables used have been potatoes, parsley roots, celery roots and carrots of various dimensions. Starting water content was: potatoes 78%, parsley roots 85.1%, celery roots 93.6%, and carrots 88.6%. Temperatures of fluidisation have varied from 60‡ to 100‡C at velocities of 0.71 ms^-1. The goal has been to obtain dry vegetables with 6% to 10% water content and of good rehydration quality. Experimental data (bed height, gas temperature and velocity, pressure drop over the bed, drying time) have been measured and relevant values have been calculated. The results have shown that drying of vegetables in a fluidized bed produces dry vegetable pieces of excellent quality in a much shorter time than in continuous belt-dryers which are generally used     

Chemical vapour deposition of Si3N4 from a gas mixture of Si2Cl6, NH3 and H2

Si₃N₄ layers were obtained on a quartz substrate from a gas mixture of Si₂Cl₆, NH₃ and H₂ under a reduced pressure in a temperature range of 800 to 1300‡ C. Amorphous Si₃N₄ layers that were dense and adherent to the substrate were obtained in a temperature range of 800 to 1100‡ C. On the other hand,α-Si₃N₄ layers were obtained at 1200‡ C and a source-gas ratio (N/Si) of 1.33 to 1.77. The lowest deposition temperature of amorphous Si₃N₄ was considered to be about 700‡ C. The microhardness of amorphous Si₃N₄ obtained in a temperature range of 800 to 1100‡ C was 2400 to 2600 kg mm⁻² (load: 50 g), and that ofα-Si₃N₄ obtained at 1200‡ C was 3400 kg mm⁻². Chlorine contents in the Si₃N₄ layer decreased with increasing deposition temperature and source-gas ratio (N/Si), and with decreasing total pressure.     

Conductive-convective drying installations: Problems and calculation

We present a procedure to calculate multicylinder conductive-convective drying installations and equations to determine the temperatures of a paper strip when on cylinders and off them. Dependences are obtained to calculate the intensities of moisture evaporation and reduction of the moisture content of fibrous woodpulp paper materials over corresponding portions, as well as a formula to calculate the relationship between evaporated moisture on cylinders and off them in the “on a drying cylinder-off a drying cylinder” cycles. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 1000–1005, November–December, 1998.     

Vibronic states in La{2-x}BaxCuO4BaxCuO4

The temperature dependences of the resistivity R(T) and the thermoelectric power α(itT) under different hydrostatic pressuresP for the system La_{2-x}BavCuO₄, 0.11 ≤ x < -1.6, are reported and interpreted as evidence for strong electron coupling to oxygen vibrations along the CuO-Cu bond axes of the CuO₂ sheets. The sensitivity of the transport properties to the bending Φ of the (180‡-Φ) Cu-O-Cu bond angle and their insensitivity to long-range magnetic order indicate that the segregation into hole-rich and magnetic stripe domains is driven primarily by electron-lattice interactions and not by electron-electron interactions alone.     

Superplastic deformation characteristics of two microduplex titanium alloys

A comparison of the superplastic deformation behaviour of Ti-6Al-4V (wt%) between 760 and 940‡ C and Ti-6Al-2Sn-4Zr-2Mo between 820 and 970‡ C has been carried out on sheet materials possessing similar as-received microstructures. High tensile elongations were obtained with maximum values being recorded at 880‡ C for Ti-6Al-4V (Ti-6/4) and at 940‡ C for Ti-6Al-2Sn-4Zr-2Mo (Ti-6/2/4/2), under which conditions both alloys possessed aΒ phase proportion of approximately 0.40. For a given deformation temperature the Ti-6/4 alloy had a slightly lower flow stress than the Ti-6/2/4/2, and this was attributed to the lowerΒ phase proportion in the latter alloy. However, at the respective optimum deformation temperatures the Ti-6/2/4/2 alloy had the lower flow stress. The results show that suitably processed Ti-6/2/4/2 alloy is capable of withstanding substantial superplastic strains at relatively low flow stresses, although the optimum deformation temperature is higher for this alloy than for Ti-6/4 material possessing a similar microstructure.     

Thermal strain in zinc pyrovanadate

The α- andc-axis thermal expansion coefficients of α-Zn₂V₂O₇ (monoclinic structure) were found to be negative between 20 and 560‡C. The volume expansion coefficient is negative above 260‡C. As a result, the zinc atoms tend to be in sixfold rather than fivefold coordination. Similar behavior results from substitution of larger sized ions on Zn sites. These effects are associated with the shear strain suffered by the soft Zn-0 polyhedra as a result of significant changes in Β. On cooling from 20‡C to liquid-nitrogen temperature, as well as upon substitution of smaller sized ions on Zn sites, the major structural changes occur along theb axis, without changes in theac plane: the soft polyhedra experience uniform compression and the Zn ions remain in fivefold coordination. Only in the latter case is the extent of substitutional solid solutions governed by the relative difference in size between the host and substituent ion.     

The coking kinetics of heat resistant austenitic steels in hydrogen-propylene atmospheres

The kinetics of coke formation on several commercial Fe-Ni-Cr alloys used in the construction of ethylene steam crackers, nickel and copper were investigated over the temperature range 450 to 1000‡ C in hydrogen-propylene atmospheres using a tubular microbalance reactor. Between 900 and 1000‡ C steady state coking was controlled by gas-phase pyrolysis and similar coking rates were observed for all materials. At 900‡ C alloy carburization led to lengthy periods of parabolic kinetics before the onset of steady state. Below 900‡ C alloy coking rates were between those of copper and nickel. Major differences in coking rates of alloys were only observed below 800‡ C and arise from variations in the effectiveness of chromium carbide scales in excluding the hydrocarbon atmosphere from contact with the underlying nickel-rich and iron-rich alloy.     

Gap-to-T c ratio as a function of the Fermi level shift

Within the framework of the BCS theory, the gap-to-T_C ratioR=2‡ ₀/kT_c is evaluated numerically (‡₀ is the energy gap atT = 0 andT> _c is the critical temperature) for a superconductor with a van Hove singularity (vHs) in the density of states as a function of the shifts (δ) of the Fermi level with respect to the vHs. It is found thatR varies asymmetrically with δ and that the variations are strong near δ = 0. Our numerical calculation shows that the largest R’s occur at certain values of δ⊋0.     

Effect of the fluctuation range of formation temperature on the preparation and superconductivity of Bi(Pb)2223 single-phase

Effects of the fluctuation range of formation temperature on preparation and superconducting properties of the Bi(Pb)2223 phase have been investigated in detail. Our results show that knowledge about the temperature distribution and fluctuation in the muffle furnace is necessary for preparation of the Bi(Pb)2223 single-phase. Single-phase samples from Bi_0.17Pb_0.3Sr₂Ca₂Cu₃O_y were obtained by a solid-state reaction in air at 835±5C. The best superconducting property of the as-prepared samples shows a one-step transition of a.c. susceptibility withT _c=109 K. Using this optimum sintering temperature and keeping the temperature fluctuation less than 5C, we have prepared pure Bi(Pb)2223 single-phase samples with good reproducibility.     

Gaseous reduction of Fe2O3 compacts at 600 to 1050° C

Dense Fe₂O₃ briquettes were isothermally reduced with hydrogen, carbon monoxide and H₂-CO mixtures at 600 to 1050‡ C. The course of reduction was followed by measuring the oxygen weight loss, as a function of time, using a thermogravimetric technique. Microscopic examination, X-ray and carbon analyses were also used to elucidate the kinetics and mechanisms of reduction of Fe₂O₃ briquettes. In the initial stages of reduction, the highest reduction rate was obtained in hydrogen while the slowest was in carbon monoxide. In CO-H₂ gas mixtures, the rate decreased with increasing amounts of carbon monoxide. In the later stages of reduction, a minimum reduction rate was only observed during the reduction with hydrogen and hydrogen-rich gas mixtures due to the formation of denseγ-iron at 900 to 950‡ C. This was eliminated in carbon monoxide and carbon-monoxide-rich gas mixtures due to the carbon deposition in the samples and secondary reactions.     

Sr1-xCexFe1-yCoyO3 (x ≤0.15,0<y < 1) solid solutions

Sr,_{1 - x}Ce_xFe_{1 - y}Co_yO_{3-δ(x ≤} 0.15,0 <y < 1) solid solutions with the cubic perovskite structure were prepared by solid-state reactions. The lattice parameter of the solid solutions was shown to depend not only on the metal composition but also on oxygen stoichiometry. With increasing Fe or Ce content, the stability of the materials toward oxygen loss rises, which is accompanied by a reduction in the lattice parameter and thermal expansion coefficient in air and helium between 300 and 1000‡C. The room-temperature electrical conductivity of the solid solutions increases systematically with Co content (y = 0-1.0) and passes through a maximum atx = 0.10 with increasing Ce content.     

A guarded hot-plate apparatus for thermal conductivity measurements over the temperature range −75 to 200‡C

A guarded hot-plate apparatus for small circular samples has been developed for the temperature range from –75 to 200C. To avoid edge losses, the apparatus is immersed in a liquid whose temperature is a few degrees lower than the mean temperature of the samples. A detailed evaluation procedure with several correction calculations leads to a remaining uncertainty of measurement of 0.5% for measurements on glass samples. This has been confirmed by experiment. Measurements on glass and on insulation material showed that the developed apparatus and the evaluation procedure applied can be used in a relatively wide range of thermal conductivity values (factor 50).     

Dynamics of micromechanisms controlling the mechanical behaviour of industrial single crystal superalloys

When deforming bulk material, micromechanisms involving moving defects result in mechanical characteristics observed at a macroscopic scale.In situ straining of microsamples in a Transmission Electron Microscope, provides the unique advantage of observing the dislocation dynamics involved in such micro-deformation processes under the combined effects of stress and temperature. Here the efficiency of this technique is illustrated by describing the different obstacles controlling the movement of dislocations in a two-phase industrial single crystal superalloy. At 25‡ and 850‡C, different core structures of the moving dislocations as well as several ways of crossing obstacles are described, which concern the movement of dislocations inγ channels, at γ/γ′ interfaces and while shearing γ′ precipitates. From these observations, a quantitative analysis is developed leading to the evaluation of the critical propagation stresses involved in the channels of the matrix and when crossing the interfaces. This allows to discuss the various sites of resistance opposed to the dislocation movements and controlling the macroscopic deformation.     

Structural characteristics and dielectric properties of neodymium doped barium titanate

Neodymium (Nd) doped barium titanate powder (Ba_(1−x)Nd _x TiO₃) with x value varying from 0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.13 was prepared using the sol gel method. The powder samples were calcined at 700 °C and tetragonal phase appeared in the powders before they were sintered at 1250 °C for 3 h. The undoped samples have a polycrystalline tetragonal structure, but Nd doping into the BaTiO₃ caused phase transformation from tetragonal to cubic. The smaller grains (0.35 μm) produced with the addition of Nd is associated to the inhibition of grain growth of samples. The powders for each composition were pressed into pellets and tested as dielectric resonator antenna (DRA). It was found that on the actual antenna circuit, each sample showed a resonance frequency at X-band application and a dielectric constant value in the range of 51.25–56.89 and tangent loss was 0.039–0.045, depending on the concentration of the Nd at room temperature.     

Formation and characteristics of lead lanthanum zirconium titanate thin films formed by using the r.f. sputtering method

PLZT (lead lanthanum zirconium titanate) thin films were prepared by using the r.f. magnetron sputtering method and post-annealing for crystallization at 650 C. The films which were annealed at 650 C for 10 min consisted of a metastable phase and a stable phase. However, another film which was annealed at 650 C for 20 min had only stable perfect perovskite phase. The stability of the post-annealed thin film and substrate interfaces was observed by using scanning electron microscopy. The longer the annealing time, the more unstable were the interfaces. By analysing the EDX data, the composition difference between the sputtering target and thin films, and the composition variation between as-deposited and post-annealed PLZT were studied. The films annealed at 650 C for 20 min showed good ferroelectric and electrical properties with a remanent polarization (P _r) of 11.5 C cm^–2, and a coercive field (E _c) of 164 kV cm^–1.     

A Study on Thermoelectric Power and Electrical Properties of Bi-2223 Superconductors Sintered for Different Time Periods

Structure examination, resistivity, and thermopower measurements were made on samples of Bi_1.75Pb_0.35 Sr₂Ca₂Cu₃O _y sintered for different time periods. Thermoelectric power of all samples was found to be positive and changes slightly with sintering time prolongation. The normal state resistivity was analyzed using only the equation ρ _n =ρ(0)+aT which was found to be satisfactory. The superconducting fluctuation behavior has been investigated using the Aslamazov and Larkin (AL), Lawrence and Doniach (LD), and Varlamov and Livanov (VL) models. In agreement with the theoretical prediction, the ln (Δσ/σ ₃₀₀)−ln (ε) plots exhibited three different regions, namely critical, mean field, and short wave fluctuation regions. Some parameters such as critical exponents, zero temperature coherence length ζ(0), the interlayer spacing d, the interlayer coupling ν, and the Fermi energy E _F have been estimated. The effect of sintering time on such estimated parameters has been studied. The critical exponent λ values have indicated dimensionality cross-over from 2D to 3D for all the investigated samples.     

Oxygen permeability of Sr1-x Ce x Co0.2Fe0.8O3-δ ceramic membranes

Sr_1-x Ce _x Fe_0.8Co_0.2O_3-δ (x = 0, 0.05, 0.10, 0.15) ceramics were prepared by solid-state reactions, and their oxygen permeability was measured as a function of cerium content and membrane thickness at temperatures from 400 to 1000‡C and oxygen partial pressures from 10² to 10⁵ Pa. The oxygen permeability of the ceramics was found to decrease systematically with increasing Ce content. The oxygen transport was shown to be limited by volume diffusion. Doping of the ceramics with 20 wt % Ag notably improves their cracking resistance during thermal cycling.     

The Effect of Sintering Temperature Variation on the Superconducting Properties of ErBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Superconductor Prepared via Coprecipitation Method

The effect of heat treatment on the superconducting properties of ErBa₂Cu₃O_7−δ (ErBCO) ceramic materials has been studied. The nano-metal oxalate precursor was prepared using coprecipitation (COP) method. The prepared materials were subjected to calcination process at 900 °C for 12 h and then sintered under oxygen environment for 15 h at 920 °C, 930 °C, 940 °C, and 950 °C, respectively. All samples showed a metallic behavior and single-step transition in the R–T curves. The best zero critical current, T _C(R=0)=91.4 K, was for the sample sintered at 920 °C. XRD data showed single phase of an orthorhombic structure. As the sintering temperature increases, the formation of nonsuperconducting phases (impurities) was observed when the samples sintered above 920 °C. The formation of nano-oxalate powders via COP method is a very efficient procedure to produce high-quality superconductors with less processing temperature required.     

Pressure-density-temperature measurements of ethylene

As a contribution to current projects on the thermophysical properties of ethylene for the preparation of reference tables, measured PVT data are presented. For the measurements in the single-phase region, two types of equipment have been employed: an expansion apparatus to determine isotherms and a constant volume apparatus to determine isochores. Both the design and calibration of each type of equipment and the experimental procedures are described. The accuracy of the 251 measured PVT data on 10 isotherms and 16 isochores, which cover the temperature range from –30 to 80C, with pressures up to 250 bar, is about 0.1% in the compressibility factors. The critical temperature was determined with the result t _c =9.22±0.02C by visual observation of the disappearance of the meniscus.