Aluminium precipitates in the primary silicon of as-sprayformed hypereutectic aluminium-silicon alloys

Precipitates have been observed in the primary silicon of as-spray-formed hypereutectic aluminium-silicon alloys with and without various alloy additions. The precipitates have been investigated using transmission electron microscopy and high-resolution transmission electron microscopy. They are aluminium based and generally adopt a spheroidal morphology, with diameters in the range of approximately 5-10nm, unless located on a stacking fault or grain boundary. Spray forming is a rapid solidification process and precipitation occurs because of the low solid solubility of aluminium in silicon (maximum of 0.016 +/- 0.003at.% at 1190 C). The morphology of the precipitates suggests that they form from aluminium or aluminium-rich liquid. The orientation relationships of several precipitates in one of the primary silicon grains have been determined.     

Voids formed from solidifying tin particles in solid aluminium

In this study, voids commonly associated with tin particles in two aluminium alloys containing microalloying additions (0.01 at.%) of tin have been observed by transmission electron microscopy. The voids were generated by quenching the alloys at moderate rates (10²–10³ K s^?1) from a temperature (718 K) in excess of the melting temperature (501 K) of elemental tin in tin–microalloyed aluminium. Estimates of the void volume as a function of the volume of the associated tin particle reveal a linear relationship consistent with the excess volume resulting from the solidification of the tin particle. The formation and stabilisation of shrinkage voids in metallic alloys are suggested to arise from a combination of high vacancy supersaturation, the large volumetric misfit strain of the solidifying tin particle and a reduction in void surface energy associated with segregation of alloying elements.     

团队气氛与团队心理授权：团队信任的中介作用

通过对32家企业156个工作团队568名员工进行问卷调查,采用相关分析、回归分析和结构方程建模等统计分析方法,对中国文化背景下团队气氛与团队心理授权的关系,以及团队信任的作用进行了探讨。结果表明：（1）团队气氛对团队信任、团队心理授权有正向影响;（2）团队信任对团队心理授权有正向影响;③团队信任在团队气氛和团队心理授权之间具有部分中介作用。其中,情感信任在团队气氛和团队心理授权之间具有部分中介作用,认知信任在团队气氛与团队心理授权之间的中介作用不显著。     

Glass formation in the Pd–Si-based alloys

Taking into account the importance of undercooling on glass formation, we propose a new criterion which allowed us to predict the best glass-forming composition, namely Pd₇₈Ag_5.5Si_16.5, among selected Pd–Si-based alloys ranging from binary to quaternary systems. The composition agrees well with that found experimentally. Using conventional copper mould casting, the Pd₇₈Ag_5.5Si_16.5 alloy is capable of forming fully amorphous rods with a diameter of 3 mm. The effects of Au and Ag additions on the glass-forming ability of the selected Pd–Si-based alloys have been investigated.     

Token economy: who responds how?

Token economy programs (TEP) can successfully modify a variety of specific and generalized behaviors in clinical populations (Gripp and Magaro, 1974). but this general success is offset by the frequent occurrence of individual nonresponsiveness (Kazdin. 1973), Two solutions to the problem of nonresponsiveness have been proposed. One proposal regards the nonresponder as needing intensified training with behavioral methods while the other suggests that the operant paradigm may be inappropriate or inefficient with such patients. In either case, it would be helpful to identify potential nonresponders before or shortly after their introduction to a TEP in order that alternative treatments or pretraining might be developed to suit them while reserving the TEP for those who could derive maximum benefit from it. However, little consistent relationship between individual responsiveness and other patient-related characteristics has been found upon which to base such judgements. The present research examined the changes in response to treatment over time of a TEP population and its component diagnostic groups with the hypothesis that distinct and unique patterns of response would be associated with the diagnostic groups and that the patterns would be different from that shown by the total group.     

Generic health-related quality of life amongst patients employing different voice restoration methods following total laryngectomy

Three methods of voice restoration--tracheosophageal speech (TEP), oesophageal speech, electrolarynx--are available following total laryngectomy. TEP produces better voice quality compared with other methods and is assumed to result in better quality of life. Little evidence exists to support the relationship between voice quality and quality of life, however. Advertising this study through several leading laryngectomy charities resulted in the completion of 226 questionnaires (TEP = 147; oesophageal speech = 42; electrolarynx = 37) comprising the Short Form 36 (SF-36) quality of life measure and questions examining perceived voice intelligibility. Additionally, 89 questionnaires comprising only the SF-36 were completed by participants who reported having no serious medical problems, to form a healthy control group. Results indicate that improved voice quality does not result in widespread benefits to quality of life. On only a few dimensions were there differences between voice restoration method: electrolarynx and TEP better than oesophageal speech with respect to pain, TEP better than oesophageal speech with respect to role limitation: physical problems. Additionally whilst widespread differences between voice restoration methods did not occur, all three groups had a worse quality of life compared with the healthy control group. Implications of the results for the selection of voice restoration method to maximize quality of life are discussed.     

Additions are biased by operands: evidence from repeated versus different operands

Recent evidence led to the conclusion that addition problems are biased towards overestimation, regardless of whether information is conveyed by symbolic or non-symbolic stimuli (the Operational Momentum effect). The present study focuses on the role of operands in the overestimation of addition problems. Based on the tie effect, and on recent evidence that the nature of operands biases addition problems towards an underestimation when operands are repeated, but towards an overestimation when different, we aim here to further elucidate the contribution of operands to addition problems. Experiment 1 replicates the underestimation of repeated-operand additions and overestimation of different-operand additions, with large numbers (around 50), and explores whether these effects also apply to small operand additions (around 10). Experiment 2 further explores the overestimation of different-operand additions by investigating the roles of operand order and numerical distance between operands. The results show that both factors have an impact on the overestimation size, but are not crucial for overestimation to occur. The results are discussed in terms of arithmetic strategies, spatial organization of numbers and magnitude representation.     

Synthesis,transformation and superconductivity of dual phase In–Sn alloy nanoparticles embedded in an Al matrix

We report the synthesis of nanoembedded biphasic alloy particles of In–Sn near eutectic alloy compositions embedded in an aluminium matrix by rapid solidification processing. Detailed transmission electron microscopy indicates that the two phases present at room temperature in as-synthesized samples are β and γ phases with tetragonal and hexagonal crystal structures, respectively. These co-exist with a small amount of single phase In or Sn particles with sizes less than 10?nm. Low temperature magnetization measurements indicate a superconducting transition temperature of 5?K, suggesting complete decomposition of the β-phase at small sizes and at low temperature. The small particles show type II behavior with a critical field Hc₁≈44?G and two values for Hc₂ of 250 and 1000?G, respectively. These values are considerably lower than those observed in bulk In–Sn alloys.     

Interfacial reaction between silicon nitride and aluminium

Abstract

The microstructure of a silicon nitride/aluminium interface has been identified by analytical transmission electron microscopy. HIPed silicon nitride without any additive was bonded by pure aluminium at 800°C for 15 min. A thin (～ 5000 Å) reaction layer was recognized at the interface. It consisted of two regions. One an amorphous layer facing the aluminium; it contained aluminium, silicon and oxygen. The other was on the silicon nitride side and consisted of fine particles which were less than 100 Å in diameter. These particles were considered to have β'-sialon type structure.     

Working memory and children's use of retrieval to solve addition problems

This study tested the hypothesis that children with high working memory capacities solve single-digit additions by direct retrieval of the answers from long-term memory more often than do children with low working memory capacities. Counting and reading letter span tasks were administered to groups of third-grade (mean age=107 months) and fourth-grade (mean age=118 months) children who were also asked to solve 40 single-digit additions. High working memory capacity was associated with more frequent use of retrieval and faster responses in solving additions. The effect of span on the use of retrieval increased with the size of the minimum addend. The relation between working memory measures and use and speed of retrieval did not depend on the numerical or verbal nature of the working memory task. Implications for developmental theories of cognitive arithmetic and theories of working memory are discussed.     

Oxygen self-diffusion in corundum (alpha-Al2O3): A conundrum

Recent point-defect calculations for Al2O3 by Lagerlof and Grimes have been used to rationalize oxygen diffusion in undoped, MgO-doped and TiO2-doped Al2O3. The amphoteric nature of Al2O3 is emphasized by the calculations; oxygen and aluminium diffusion will be dominated by oxygen vacancies and aluminium interstitials, or oxygen interstitials or aluminium vacancies, depending on whether divalent or tetravalent impurities are present in greater abundance. The oxygen diffusion data can be rationalized in a reasonably quantitative manner by the calculated concentrations of oxygen vacancies and oxygen interstitials. Oxygen vacancies appear to be 2-2.5 times more mobile than oxygen interstitials, whereas aluminium interstitials appear to be 103 to 104 times more mobile than oxygen vacancies. However, these calculations suggest migration energies of the oxygen point defects of 4.5-5.9eV. These values are large, and it is not known whether they have any physical significance.     

Z-contrast imaging of the arrangement of Cu in precipitates in 6XXX-series aluminium alloys

High-resolution annular dark field imaging has been used to study small precipitates in the Al matrix of 6XXX-series aluminium alloys. Cu-containing columns in precipitates were imaged by atomic number contrast along a 〈100〉 matrix direction. At an under-aged condition, large, lath-shaped particles of the Cu-containing Q′-phase were observed at grain boundaries. At over-aged conditions, Q′ was the main matrix phase. In both cases the laths showed an Al {150} habit plane. A precursor phase was found, with different arrangement of Cu-rich columns from that of the Q′-phase and sharing Al {100} habit planes. Precipitates containing elements of both the Q′-phase and the precursor were found to be common. Annular dark field imaging can differentiate directly between phases. The method complements and aids interpretation of conventional high-resolution TEM images and nano beam diffraction observations. The results obtained contribute to an improved understanding of the crystallography of the precursor and details of the structural transformation taking place during the precipitation process.     

A proposed adaptation of DC: 0‐3R for primary care,developmental research,and prevention of mental disorders

The development of the Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood (DC: 0‐3; Zero to Three: National Center for Clinical Infant Programs, 1994) has been an important step in the field of infant mental health. In this paper, we propose some additions to the existing classification system. These additions include the development of criteria for infant, toddler, and family strengths, and the development of criteria for symptomatology that represents risk for disorder, but not fully manifest disorder. These additions will give DC: 0‐3R greater potential for use in the primary health care of children, thereby increasing the system's utility in diagnosing and preventing infant mental health problems.     

On the construction of weak orders from fragmentary information

An iterative method is proposed for constructing a weak order from a partial order on a set of stimuli that is based on individual pairwise comparison data. The method generalizes Duncan Luce's construction of the weak order induced by a semiorder. Various aspects of the iterative procedure are discussed, including its rationale, the number of iterations required to obtain a weak order, and the extent to which the data support additions to the initial partial order as a function of the number of iterations performed before the additions occur.This work was supported in part by a grant from the Alfred P. Sloan Foundation to The Institute for Advanced Study.The computer simulation programs for this study were written and run by William Gehrlein. I am grateful to him for his assistance.     

Encoding numbers: Behavioral evidence for processing-specific representations

The aim of this study was to test the hypothesis of a complex encoding of numbers according to which each numerical processing requires a specific representational format for input In three experiments, adult participants were given two numbers presented successively on screen through a self-presentation procedure after being asked to add, to subtract, or to compare them. We considered the self-presentation time of the first number as reflecting the complexity of the encoding for a given planned processing. In line with Dehaene's triple-code model, self-presentation times were longer for additions and subtractions than for comparisons with two-digit numbers but longer for subtractions than for additions and comparisons with one-digit numbers. The implications of these results for different theories of number processing are discussed.     

Detecting and identifying change: additions versus deletions

The recognition of changes in the features of objects was examined as a function of the nature of the change (additions, deletions, no change). In two experiments we assessed both detection (noticing whether the stimulus had changed) and identification (specifying the exact nature of the change). Both detection and identification were expected to depend upon the subject's awareness of the subsequent recognition tasks while the original stimuli were encoded. In Experiment 1, subjects were not aware of subsequent detection and identification tasks while they initially viewed study slides of the to-be-changed stimuli. During the subsequent presentation of the test stimuli, detection and identification were superior for additions. On the other hand, in Experiment 2 when subjects were aware of the subsequent recognition tasks while viewing each study slide, a detection advantage for deletions obtained. Identification performance depended upon a further factor, whether the features of a stimulus were codable. Only in codable stimuli were deletions easier to identify than additions. The differences between the two experiments in detecting and identifying additions versus deletions are consistent with Tversky's (1977) research that stresses the importance of specifying which representation (the study stimulus or the test stimulus) is the subject of comparison in the comparative judgment.     

Procedural vs. direct retrieval strategies in arithmetic: A comparison between additive and multiplicative problem solving

The opposition between declarative and procedural knowledge is used to account for the solution by more or less expert and novice arithmeticians of simple additions and multiplications presented either in mixed blocks (Experiments 1 and 3) or unmixed blocks (Experiment 2) in an equation verification task. In the three experiments, presenting the sign (+ vs 2) before the operands had a stronger effect in additions than in multiplications. This priming effect indicates that many participants use a counting procedure for additions that coexists with the declarative knowledge stored in the associative network. In contrast, the small size (and sometimes the absence) of a priming effect for the ''x'' sign, together with the weak effect of size and the frequency of interaction effects, reveals the essentially declarative nature of multiplication solution.     

Phase stability of Al3Nb as a function of nickel additions

Abstract

Phase stability of the intermetallic compound Al₃Nb is investigated as a function of nickel additions by band structure calculations based on an extended Hueckel tight-binding method. With this method, the electronic structure and total energies of the Al_6-n -Ni _n Nb₂ compounds (where n is an integer from 0 to 6) are calculated for both D0₂₂ and L1₂ structures under the assumption that nickel substitutes for aluminium. The electronic total energies obtained from integration of the energy states of all electrons considered have shown that the D0₂₂ structure is stable in the binary Al₃Nb compound as compared with the L1₂ structure; conversely, the L1₂ structure is stable for compounds with n values greater than 1. These calculations are in good agreement with X-ray diffraction results reported by Schubert and co-workers. Differences in the electronic total energy per atom between D0₂₂ and L1₂ are - 0·79 eV and 0·56 eV for n equal to 0 and 2, respectively.     

On the synthesis and characterisation of novel composite-structured high-entropy alloys

A study of novel composite-structured CoCrFeNi₃Si, CoCrFe₂Ni₂Si and Co₂CrFeNi₂Si high-entropy alloys, synthesised by vacuum arc melting, is presented. The designing criteria for the formation of such alloys were based on the enthalpy of mixing and the valence electron concentration. X-ray diffraction analysis revealed that all the alloys were composed of face-centered cubic and intermetallic phases. Scanning electron microscopy, along with elemental analysis, indicated that the face-centered cubic phase mainly contains Co, Cr, Fe and Ni, whereas, the intermetallic compound is Ni-Si rich. All the synthesised high-entropy alloys in the present investigation possess excellent compressive strength along with ductility at room temperature, suggesting significant potential application in the engineering field. Furthermore, enhanced hardness, wear resistance and corrosion resistance were achieved in all the designed high-entropy alloys. The previously given design parameters for the composite-structured high-entropy alloys are in good accord with the current research work.     

Electron back-scatter diffraction study of inoculation of Al

The microstructure of cast commercial-purity aluminium inoculated by addition of an Al-Ti-C grain refiner has been studied by scanning electron microscopy and electron back-scatter diffraction (EBSD). It is found that a small fraction of the TiC particles present in the melt act as nucleation centres for grains. EBSD shows that the aluminium grains have a crystallographic cube-cube orientation relationship with the particles on which they nucleate. Nucleation occurs only on the largest particles, consistent with model predictions. Despite potential thermodynamic instability, TiC particles are effective nucleating agents.