Cellular/dendritic transition,dendritic growth and microhardness in directionally solidified monophasic Sn-2%Sb alloy

Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb (mass fraction) alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate (V_L) and the cooling rate (T_R). High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for T_R>5.0 K/s. Cellular (l_c) and primary dendrite arm spacings (l₁) are determined along the length of the directionally-solidified casting. Experimental growth laws relating l_c and l₁ to V_L and T_R are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed.     

DISCUSSION

The Water Rights Analysis Package (WRAP) is a generalized river basin simulation model for evaluating water availability within the framework of a prior appropriation water rights system, such as the permit system recently implemented in Texas. WRAP is used to evaluate water supply reliabilities for permitted water users and unappropriated streamflows available for additional permit applicants. The historic hydrologic period-of-record is simulated using a monthly computational time step. For each monthly interval, a network flow programming algorithm allocates streamflow and reservoir storage resources in accordance with water rights. The model is generalized for application to river/reservoir systems of essentially any configuration. WRAP and its application to the Brazos River Basin illustrate the use of network flow programming in modeling the allocation of a limited water resource to numerous users within a complex institutional setting.     

ARTIFICIAL NEURAL NETWORKS FOR CONSTRUCTION BID DECISIONS

An Artificial Neural Network (ANN) approach was explored for supporting construction bid decisions, since such decisions are heavily dependent on practitioner expertise, which in turn is generally encapsulated in case histories. One of the ANNs described here was trained on knowledge from a sample of the entire Sri Lankan construction industry, and was used to predict the preferred job sizes for firms of differing characteristics; such information could help firms in their bid/no-bid decisions. The other ANN was trained on case histories elicited from a single contractor, and was used to predict the percentage mark-up. The network outputs were obtained in both binary output and continuous valued output formats. The former format had some distinct advantages over the latter, as it provided greater information for decision making instead of being a “black box” output. The influences of the middle layer size, output format and allowable error during training, on the training duration and accuracy of prediction were studied.     

Reliability-based settlement analysis of embankments over soft soils reinforced with T-shaped deep cement mixing piles

This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing (TDM) pile-supported embankments over soft soils. The uncertainties of the mechanical properties of the in-situ soil, pile, and embankment, and the effect of the pile shape are considered simultaneously. The analyses are performed using Monte Carlo Simulations in combination with an adaptive Kriging (using adaptive sampling algorithm). Individual and system failure probabilities, in terms of the differential and maximum settlements (serviceability limit state (SLS) requirements), are considered. The reliability results for the embankments supported by TDM piles, with various shapes, are compared and discussed together with the results for conventional deep cement mixing pile-supported embankments with equivalent pile volumes. The influences of the inherent variabilities in the material properties (mean and coefficient of variation values) on the reliability of the piled embankments, are also investigated. This study shows that large TDM piles, particularly those with a shape factor of greater than 3, can enhance the reliability of the embankment in terms of SLS requirements, and even avoid unacceptable reliability levels caused by variability in the material properties.     

定向凝固单相Sn-2%Sb合金的胞/枝晶转变、枝晶生长和显微硬度（英文）

采用单相Sn-2%Sb(质量分数)合金进行水平定向凝固实验,分析凝固热参数对显微组织形貌和长度尺度的影响。在凝固过程中,对沿铸坯长度方向的不同部位进行连续温度测量,用这些温度数据来确定凝固热参数,包括生长速率(V_L)和冷却速率(T_R)。高冷却速率的胞晶和枝晶可以表征铸件不同区域的显微组织,当T_R5.0 K/s时发生枝晶向胞晶的可逆转变。沿定向凝固铸造的长度方向确定胞晶尺寸(λ_c)和一次枝晶间距(λ_1),提出关于λ_c和λ_1与V_L和T_R的实验生长规律,并与垂直向上定向凝固实验结果进行对比分析,并分析显微组织形貌和长度尺度对显微硬度的影响。     

CHANGES IN FREE AMINO ACIDS AND BIOGENIC AMINES DURING RIPENING OF FRESH AND FROZEN SARDINE

A study was carried out on the evolution of free amino acids and biogenic amines throughout the ripening process of fresh and frozen sardine. The effect of the level of fish gutting was also followed. During ripening a general increase of free amino acids content was observed in all samples. Histidine was the exception to this trend and decreased throughout the processing period. On the basis of the ratio of basic/acidic amino acids, as an indicative of the ripened state, the fresh nobbed sardine ripened faster than the gutted fish. During the course of ripening a considerable increase in biogenic amines and particularly histamine occurred until the 20th day in products from fresh fish. The maximum histamine content allowed in ripened fish products in the European Union (400 mg/Kg) was never attained in this period. A general decrease in most amines was observed by the 240th day of ripening. Tyramine behaves differently and increased in the same period. The samples prepared with frozen fish consistently showed the lowest amine values throughout the ripening period. It seems that freezing has a good effect on the final quality of ripened products as it could decrease the bacterial activity responsible for biogenic amine formation.     

GREEN UMBU (SPONDIAS TUBEROSA ARR. CAM.) PRESERVE: PHYSICAL, CHEMICAL AND MICROBIOLOGICAL CHANGES DURING STORAGE

A preserve made from “umbu” in the green state of maturity represents an alternative to avoid losses of the fruit in the mature stage. A factorial experimental design was used to evaluate the effects of formulation, packaging and storage time (0, 45 and 90 days) on the physicochemical, chemical, physical and microbiological characteristics of the preserve during storage under ambient conditions (33C/88% relative humidity). The results showed that the products were microbiologically stable, but that degradation of soluble pectin, reducing sugars and total soluble solids occurred, especially in the cellophane packaging, and this resulted in textural and color changes in the products. The results suggested the incorporation of pectin and glucose syrup and the use of a polypropylene packaging as being the most adequate method of producing and conserving preserves made from this pulp.     

Lethality Distribution within Particles in the Holding Section of an Aseptic Processing System

Residence time distribution (RTD) affected lethal effects of heat on 1.27 cm diameter particles in the holding section of an aseptic processing system. The variations in particle center and particle surface F₀ were determined as a function of particle density, flow rate, and particle to fluid heat transfer coefficient, h_fp. Particles with density ratios of 1.00-1.04 relative to the carrier fluid showed diverse RTD characteristics in the hold tube. Particles with density ratio of 1.01 had the least residence time. The distribution of the particle center F₀ value increased with increase in the h_fp.     

Solidification of Be-free Ni-based dental alloy

A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuous casting to study the microstructure evolution during solidification and its mechanical properties. The solidification of the alloy started with the primary crystallization of FCC-γ, followed by a binary eutectic reaction, with the formation of a heterogeneous constituent: FCC-γ+G-phase, which replaced the low-melting eutectic (FCC-γ+NiBe) in the Be-bearing alloys. AlNi₆Si₃ and γ′ formed during the terminal stages of solidification by investment casting, while the formation of AlNi₆Si₃ was suppressed by continuous casting. The Scheil solidification model agreed very well with the experimental results.