Configurational entropy and solute correlation in disordered alloys

A new approach in expressing the excess configurational entropy of a binary alloy phase is reported, which, through economy of formulation and ease of manipulation, offers a convenient and effective alternative to the widely-used regular solution approximation. The key to this development is the direct use of the diffuse intensity α_k (Fourier transform of the pair correlations) to specify the state of clustering or short-range order in an alloy. Detailed attention is given to the formulaS _XS = 1/2k _B〈lnα_k〉 which sets the excess entropy proportional to the mean value of the logarithm of the intensity. As an example of application, a concise analysis for pair correlations and thermodynamic properties at equilibrium is carried out. The result coincides with the spherical model for alloys, a variant of the Ising model resembling the Gaussian model of Clapp and Moss but far exceeding it in accuracy. In this manner the merit of the proposed entropy formulation is established.     

A solidification diagram for Ni-Cr-Mo-Gd alloys estimated by quantitative microstructural characterization and thermal analysis

A γ-Gd solidification diagram is proposed as an aid to understanding solidification behavior of Ni-Cr-Mo-Gd alloys. In this system, the Ni-Cr-Mo solid solution γ primary austenite phase is treated as the “solvent” and Gd is treated as the solute. The proposed diagram, which has features characteristic of a binary “eutectic” system, was constructed by combining differential thermal analysis and quantitative microstructural analysis data. As a result of the partially divorced solidification microstructure in the ingots studied, determination of the fraction eutectic, and hence the eutectic composition, requires the use of advanced image analysis techniques. The diagram displays a number of features that are very similar to the Ni-Gd binary system and can be used to assess the influence of the Gd concentration on solidification behavior.     

Attention and luminance detection: A quantitative analysis.

Two experiments investigated the effects of spatial cues on the detection of luminance targets in global (nonlocalizing) and local (poststimulus probe) detection tasks. Cuing effects were quantified by fitting a variety of single- and multiple-channel signal-detection models to the data from individual observers. The local detection data showed enhanced sensitivity at cued locations, consistent with previous findings. Models for global detection in which cues affected both sensitivity and criterion or criterion alone could not be distinguished reliably on the basis of goodness-of-fit statistics. However, estimated model parameters showed that under global detection conditions, sensitivity was enhanced at cued locations by a factor of around 2. Results are discussed relative to a model in which Poisson-coded sensory representations are modulated by spatial attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aggression and the EEG: A quantitative analysis.

80 male offenders (mean age 33.93 yrs) at a psychiatric security hospital completed scales of aggression and hostility and were rated on previous history of assaulative behavior. Two psychiatrists agreed that 45 Ss had personality disorders and 35 were psychotic. Low frequency analysis was employed to obtain measures of EEG abundance at rest, during repetitive auditory stimulation, and during the cold pressor test. Neither within the sample as a whole nor within personality disorders alone was any relation found between resting abundance and aggression. More aggressive Ss tended to have a higher dominant frequency at rest, less increase in theta during monotonous stimulation, and greater alpha reactivity to cold pressor stimulation. Results are not in accord with the view that a high prevalence of theta activity characterizes aggressive offenders. The evidence of greater cortical excitability in aggressive patients suggests that persistent aggression is associated with a dominance of the ergotropic system. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Efficacy of rational-emotive therapy: A quantitative analysis.

Meta-analysis of 28 controlled studies on the efficacy of rational-emotive therapy (RET) showed RET to be superior to placebo and no treatment but equally effective in comparison with other types of treatment such as combination therapies and systematic desensitization. No support was found for the view that RET with a main or balanced emphasis on behavioral techniques is more efficacious than RET with a primarily or exclusively cognitive approach. However, given the heterogeneity of the set of studies and its relatively small sample size, interpretations of results have to be made with caution, particularly because evidence was found for a relationship between study characteristics and magnitude of effect size. For the sake of meta-analysis, outcome studies should be required to report at least the means and standard deviations for all experimental groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of weibull statistics to quantify property variability in TiAl alloys

Tensile experiments have been performed on specimens of four different investment-cast TiAl-based alloys with variations in casting conditions. The average ductilities obtained in these experiments vary between approximately 0.8 to 2.0 pct plastic strain to failure in tension. By using the three-parameter form of the Weibull relation, with the 0.2 pct offset yield strength as the minimum failure strength, the resulting variability in the data can be quantified and is found to be similar for those alloys with similar microstructural scale (grain size). Large variations in lamellar volume fraction, segregation, and phase distribution have a minor influence on property variability, compared to changes in the scale of the grain structure caused by either variations in cooling rate during casting or the addition of grain refiners.     

不同热处理状态下镍基耐蚀合金析出相的定性定量分析

镍基耐蚀钢的性能,在很大程度上取决于钢中各种相的数量、组成、大小、分布状况和合金元素在晶界的分配情况。镍基耐蚀钢经过等温热处理,通常会形成碳化物相、金属间相等析出相。这些析出相在合金中的形成将导致钢的脆化,显著降低钢的塑性、韧性和耐蚀性。为了对不同热处理条件下镍基耐蚀合金析出相做定性定量分析,实验在选择好合适的电解制度后,利用电解分离方法将析出相从基体中分离。通过扫描电镜(SEM)和X射线衍射(XRD)定性研究了提取后析出相的形貌以及结构特性的变化过程;并利用Rietveld全谱拟合法计算不同析出相的组成及含量,最后还讨论了析出相含量与材料耐蚀性能间的关系。实验结果表明900 ℃时效形成的析出相最多,且析出相的含量随时间的延长呈明显上升的趋势;腐蚀性能评价结果表明析出相的含量与平均腐蚀速率存在一定的正相关,即随着析出相含量的增加,材料的平均腐蚀速率也增加,耐蚀性能减弱。     

A quantitative analysis of microtubule elongation

Methods have been developed for differentially inhibiting microtubule nucleation and elongation in vitro. By use of polyanions, assembly-competent tubulin solutions of several milligrams/milliliter can be prepared which do not exhibit appreciable spontaneous assembly during the time-course of an experiment. Microtubule elongation can be initiated by the addition of known numbers of microtubule fragments. A detailed analysis of the resulting process demonstrates that: (a) rings are not obligatory intermediates in the nucleation sequence, and neither rings nor protofilament sheets are obligatory intermediates in the elongation reaction. (b) The end of an elongating microtubule often has a short region of open protofilament sheet or "C-microtubule" similar to that observed in vivo. (c) The development of turbidity follows a simple exponential approach to an equilibrium value. (d) The final equilibrium values are independent of the number of added nucleating fragments, while the initial growth rates and half-times to reach equilibrium are dependent on the number of added nuclei. (e) The final lengths of the microtubules at equilibrium are inversely proportional to the number of added fragments. (f) The equilibrium constants are independent of microtubule length. (g) The number of assembly and disassembly sites per microtubule is not a function of microtubule length. (h) The forward rate constants, the final polymer concentrations, and growth rates of microtubules are dependent upon the concentration of polyanion present. These results are strongly supportive of the idea that microtubule assembly is a "condensation-polymerization" and provide basic information on the kinetics and length distributions of the elongation in vitro.     

A quantitative analysis of hydrogen trapping

The complex hydrogen trapping characteristics of iron-titanium-carbon alloys, contain-ing both reversible and irreversible traps have been fully analyzed. The key to this quantitative analysis is a complete identification of the type and number of each operating trap. The trapping parameters were obtained from an analysis of the relevant hydrogen permeation transients. Titanium substitutional atoms have been shown to be reversible, low occupancy traps with an interaction energy with hydrogen,E (Ti-H), of 0.27 eV. Typi-cal rate constants for these alloys are; a hydrogen capture rate constant of approximately 10^-24 cm³/atom .s a release rate constant of approximately 10^-3 s^-1 and a trapping rate of the order of 10¹⁵ atoms, H/cm³ .s. TiC particles are irreversible traps with a large oc-cupancy and an interaction energy, .E(TiC-H), of 0.98 eV. The irreversible trapping parameters are calculated from the first permeation transient, where mixed trapping oc-curs. The trapping kinetics are about an order of magnitude faster than when only rever-sible trapping exists. The role of trapping on the effective diffusivity of hydrogen is dis-cussed as is, briefly, its role in affecting hydrogen-induced damage. Finally, guidelines are given to permit the trapping behavior of more general alloys to be analyzed. Formerly at Carnegie-Mellon University, Pittsburgh.     

On the grain boundary statistics in metals and alloys susceptible to annealing twinning

Grain boundary distribution which includes grain boundary character distribution (i.e. distribution of boundaries by the reciprocal density of coincidence sites Σ) as well as distributions of boundaries by misorientation angles and axes is an important parameter describing polycrystalline microstructure. Numerous experimental data on grain boundary distributions in low stacking fault energy f.c.c. materials that are susceptible to annealing twinning have been analyzed and it has been established that there is a certain stable grain boundary distribution characterized by the dominance of Σ3ⁿ boundaries in all statically recrystallized materials of this class. computer modelling based on the assumption that multiple twinning is the main process controlling structure formation has confirmed this conclusion. It has been also found that distribution of lengths of different types of grain boundaries is more sensitive to the stacking fault energy and treatment of the material. Relation between grain boundary distributions and grain orientation distribution has been studied both experimentally and by computer modelling. It has been established that the grain boundary distribution is not completely determined by texture but is only influenced by it, because the grain boundary spectrum is primarily dependent on the orientation correlations which may exist between various crystallites of a polycrystal. Control of grain boundary distributions by means of various treatments has been demonstrated and possibilities of grain boundary design for improving the bulk properties of polycrystalline materials are discussed.     

In vitro bonding of adhesive resin to dental alloys and dentine

The purpose of this in vitro investigation was to compare the shear bond strength of sandblasted, tin-plated and metal primed Type II gold alloy bonded to Ni-Cr alloy, as well as sandblasted Type II gold bonded to dentine, using two different adhesive resin cements. All bonding surfaces were treated with C&B-Metabond (Parkell, CB) or Imperva Dual (Shofu, ID), according to the manufacturers' instructions. In all, 20 sandblasted, 20 tin-plated and 20 metal-primed gold cylinders were bonded to Ni-Cr, and 20 sandblasted gold cylinders bonded to dentine. Bonds were stressed to failure using a shear load in an Instron testing machine. Data were calculated, statistically analysed (ANOVA and Student-t-test), and the fracture sites examined in a SEM. The CB and ID systems demonstrated significantly higher bond strengths (p < 0.01) when the gold was tin-plated, but CB demonstrated significantly lower bond strengths (p < 0.01) when the gold was pre-treated with metal primer. CB always demonstrated significantly higher metal (p < 0.01) and dentine (p < 0.05) bond strengths than ID.     

A statistics primer. Power analysis and sample size determination

Gynecologic-oncologic patients are at increased risk for complications with closed laparoscopy. Open laparoscopy eliminates the steps of blind insufflation and trocar insertion. This study is the first large series of open laparoscopies to assess the feasibility and safety of the open laparoscopy technique in patients with gynecologic malignancies. We performed 90 open laparoscopies in 89 oncologic patients with previous major surgery (65%) and/or radiotherapy (17%) or a large omental cake (18%). Complications due to the laparoscopic access technique occurred in one patient (1%) for whom a laparotomy was performed for a small bowel perforation. The incidence of complications of the open laparoscopy technique (1%) is favorable compared to the complication rate of closed laparoscopy in gynecologic-oncologic patients. It is concluded that open laparoscopy is a safe and feasible technique in gynecologic-oncologic patients.     

自动统计在夹杂物分析过程中的应用

摘要：为了探明夹杂物自动分析设备在夹杂物统计过程中的准确性,利用夹杂物自动分析和手工统计分析的方法对夹杂物的尺寸、数量和种类进行统计表征,对比分析了2种分析方法在稀土钛处理钢中结果的差异。研究结果表明：夹杂物自动分析不适用于含稀土钢中夹杂物数量和尺寸的统计分析,但对于夹杂物中不同成分组元的含量和面积分数的统计,夹杂物自动分析的结果是准确的。原因主要是自动分析会将一个夹杂物内部成分差异较大的不同区块认定为2个或多个小夹杂物,导致统计得到的夹杂物数量偏高,尺寸偏小,复合夹杂物数量偏少。     

Precipitation of silicon in aluminum-silicon: A calorimetric analysis of liquid-quenched and solid- quenched alloys

The precipitation of silicon in aluminum-silicon was investigated by calorimetric analysis of liquid-quenched (LQ; rapidly solidified) and solid-quenched (SQ: quenched after annealing the solid at elevated temperature) alloys. Nonisothermal annealing experiments (differential scanning calorimetry) were performed using specimens containing 1.3 to 19.1 gross at. pct Si. Initial and resulting microstructures were characterized by X-ray diffraction and transmission electron microscopy. Quantitative analysis showed that heat production in LQ alloys is due to precipitation of dissolved silicon and coarsening of silicon particles already present in the as-liquidquenched state, whereas heat production in SQ alloys can be ascribed solely to precipitation. The kinetics of silicon precipitation are affected by quenched-in excess vacancies in both LQ and SQ alloys. The grain-boundary area as a function of gross silicon content is discussed in terms of its effect on vacancy annihilation and the resulting effective activation energy.     

Contacting surfaces: A problem in fatigue and diffusion bonding

Contact between surfaces usually occurs at asperities under compression or at connecting ligaments, depending on how the interface is formed. This paper deals with the nondestructive evaluation of the topology of contact and with the use of this information to predict the effects that loads borne by these contacts have on mechanical properties. Two specific examples are discussed: a fatigue crack and a diffusion bond. Asperity contact along the fracture surface of a fatigue crack partially shields the crack tip from the externally applied driving force. Using information from acoustic experiments, the geometry of the asperities, the contacting stress, and the shielding stress intensity factor have been estimated. Acoustically, a diffusion bonded interface looks very similar to that joining the two sides of a partially closed crack. In this particular case, the acoustically determined geometry of well-bonded ligaments can be verified by fractography of destructively tested samples whose bond strength has also been determined. Models to determine the bond strength from the ligament geometry are being suggested.