沉淀铁费托合成催化剂焙烧工艺的优化研究

通过DOE实验设计对沉淀铁费托合成催化剂焙烧过程进行了优化,并给出了焙烧过程的分子模拟与粒子长大模型。结果表明,随着焙烧温度的升高和焙烧时间的延长,催化剂的孔容减小,堆比及骨架密度增加,耐磨性改善。BET表面与磨耗的变化趋势一致,即比表面积越小磨耗越小;磨耗与密度成线性反比关系,密度越高磨耗越小。通过焙烧工艺的优化,可调变Cu、Si通过O原子与Fe原子的键合作用及催化剂的粒子粒径,得到较高F-T活性且稳定性好的沉淀铁催化剂。在该实验中,优化的焙烧温度为560℃。     

Grain growth in ultrafine titanium powders during sintering

Grain growth behaviour of fine (∼3 μm) and attrition milled nanocrystalline (∼32 nm) titanium powers during sintering have been studied. The activation energies of grain growth (Q _g) in fine titanium were found to be 192.9 and 142.4 kJ/mol at lower and higher temperature ranges, respectively. The nanocrystalline titanium showed very low values of Q _g (54.6 kJ/mol) at lower temperatures and it increased to 273.2 kJ/mol at higher temperatures. The constant (n) in nano Ti system was found to have unusually very high values of 6.5–8.2. The grain boundary rotation along with the diffusional processes could be the grain growth mechanism in nanocrystalline and in fine titanium powders.     

Equilibrium in a war of attrition with an option to fight decisively

We develop a symmetric incomplete-information continuous-time two-player war-of-attrition game with an option to fight decisively. We show that there exists an essentially unique symmetric Bayesian Nash equilibrium. Under equilibrium, the game does not end immediately, and a costly delay persists even with the availability of the fighting option that ends the game if chosen. In addition, there exists a critical time in which a fight occurs unless a player resigns before that time.     

Exchange bias in ferrimagnetic-antiferromagnetic nanocomposite produced by mechanical attrition

Nanoparticles comprising of magnetite (Fe₃O₄) core-hematite (α-Fe₂O₃) shell with mean diameter around 9 nm were synthesized by mechanical grinding. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization and hysteresis loop measurements were carried out over the temperature range 5-300 K. Exchange bias varying from 140 to 10 Oe was observed. This is explained as arising due to ferrimagnetic-antiferromagnetic coupling at the nanointerfaces between the two phases. Analysis of data shows a pronounced increase in the effective anisotropy constant as the milling time is increased.     

Measurement of Granule Attrition and Fatigue in a Vibrating Box

This paper describes a new test machine that has been designed to measure the strength of single particles in the size range of 10²–10³ μm. The device is a vibrating box that subjects each particle in the sample to a large number of impacts of known but variable strength. By tracking the size and shape of the particles as a function of the number of impacts, their strength characteristics against the mechanisms of fracture, fatigue and attrition can be differentiated. The number of particles tested in one sample is restricted in order to make any particle‐particle interaction negligible but is sufficiently large that the distribution of these characteristics can be determined.     

A Study of College Student Attrition Via Probabilistic Approach

This exploratory paper proposes a probabilistic approach to investigating college student attrition. Through the use of attributable risk, the top risk factors for attrition are identified and ranked. Then the issue of confounding risk between two risk factors is addressed by the means of relative attributable risk. Though it is only illustrated by the eight-year attrition data collected at a private institution, the proposed technique is comparatively simple for institutional researchers to test on their own data.     

Characterization of the Corrosion of Nanostructured 17-4 PH Stainless Steel by Surface Mechanical Attrition Treatment (SMAT)

Abstract

The corrosion properties of nanostructured 17-4PH stainless steel facilitated by a surface mechanical attrition treatment (SMAT) process were studied using electrochemical measurements in 0.6?M NaCl aqueous solution. The microstructure of the surface layer was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrated the formation of a nanostructured surface layer on the surface of the material. By the combination of SMAT and low-temperature annealing processes, the potentiodynamic polarization measurements and X-ray photoelectron spectroscopy (XPS) spectra demonstrated an improvement in the corrosion resistance of 17-4PH stainless steel with a reduced corrosion current density of 0.241?mA/cm² and a higher chromium content. The improved corrosion resistance may be attributed to the formation of nucleation sites through which chromium may freely move from the matrix to the upper surface and thereby form a protective oxide layer on the surface of the material.     

Assessing the impact of derived behavior information on customer attrition in the financial service industry

The value of the customer has been widely recognized in terms of financial planning and efficient resource allocation including the financial service industry. Previous studies have shown that directly observable information can be used in order to make reasonable predictions of customer attrition probabilities. However, these studies do not take full account of customer behavior information. In this paper, we demonstrate that efficient use of information can add value to financial services industry and improve the prediction of customer attrition. To achieve this, we apply an orthogonal polynomial approximation analysis to derive unobservable information, which is then used as explanatory variables in a probit–hazard rate model. Our results show that derived information can help our understanding of customer attrition behavior and give better predictions. We conclude that both researchers and the financial service industry should gather and use derived financial information in addition to directly observable information.     

A non-zero-zum War of Attrition

The division of a cake by two players is modelled by means of a game of timing in which the players have a probability of learning when their opponent acts. It is shown that the game has a unique Nash equilibrium when both players are non-noisy but that there are many Nash equilibria including pure ones when at least one of the players is noisy. Explicit expressions for the strategies used in these Nash equilibria are obtained.This work was carried out while Dr. Garnaev was visiting the University of Southampton on a Postdoctoral Fellowship of The Royal Society of London.     

The effect of nanostructured surface layer on the fatigue behaviors of a carbon steel

A nanostructured surface layer was formed on a carbon steel by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer of the SMATed sample was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness and residual stress distribution along the depth from the SMATed surface layer were measured at the same time. Fatigue behaviors of the carbon steel subjected to the SMAT process were investigated. A nanostructured layer with average grains size of ∼12.7 nm was formed, of which microhardness is more than twice as high as that in matrix and residual compressive stress can reach about −400 MPa with maximum depth of ∼600 μm. The fatigue strength of as-received sample is 267 MPa and that of SMATed sample is 302 MPa based on fatigue life 5 × 10⁶ cycles. The SMAT process has improved the fatigue strength by as much as 13.1% for the carbon steel. It is shown that the SMAT is an effective method to render the material with the features, such as a nanostructured and work-hardened surface layer as well as compressive residual stresses, which can pronouncedly improve the fatigue strength of the carbon steel.