Relationships between process, microstructure and properties of molded zirconia micro specimens

Due to size effects the mechanical behavior of micro-components with dimensions in the range of some 100 μm and structure details of about 10 μm differs markedly from those of larger components. This is a crucial aspect for the design of micro-components for applications where demands for high strength are critical. The present study, which was performed in the frame of the Collaborative Research Centre 499 (SFB 499), approaches this issue by investigating the relationship between production process, microstructure and the mechanical properties of micro-specimens made from zirconia using two different feedstocks. The specimens were produced by a sintering process. The sintering temperature was varied between 1,300 and 1,500°C. Mechanical and tribological behavior of the specimens was determined by three-point bending tests as well as static and sliding friction tests, respectively. Properties derived from these tests were then correlated to the surface states in the specimens such as porosity, edge radius and roughness. The strength of the micro-specimens was found to be significantly influenced by these surface features. Whilst low porosity alone is not sufficient for high strength, notch effects resulting from pores as well as surface roughness can lower the strength. With increasing edge radius the strength of the material also increases. The porosity, edge radius and surface roughness were mathematically correlated with the strength to allow for a forecast. Within the SFB 499 feedstocks with specific properties were designed and reliable processes were developed to guarantee desirable surface roughness and porosity in the specimens. A characteristic bending strength of about 2,000 MPa is realizable in the micro-specimens within a good statistical reliability. The tribological tests revealed that the wear properties of the zirconia micro-components are strongly dependent on the quality of the feedstock.     

Determination of mechanical properties of slip cast, micro powder injection moulded and microcast high aspect ratio microspecimens

In a project of the German Research Council (DFG) Collaborative Research Centre (SFB) 499 Development, production and quality assurance of moulded micro-components made of metallic and ceramic materials [SFB03] three-point bending-specimens (dimension: 1.2 × 0.2 × 0.2 mm) made of slip cast [BAU02] or micro powder injection moulded ZrO₂ [RUP03] as well as tensile specimens (dimension of the gauge length: 0.78 × 0.26 × 0.13 mm) made of the micro-cast AuAgCu-alloy Stabilor G [BAU03] were investigated with respect to their behaviour under quasi-static loading.The support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged. The authors appreciate the co-operation of all the project partners within the SFB 499.     

Modeling of mechanical properties and bond relationship using data mining process

Reinforced concrete is a widely used construction material. Its properties depend on the bond between the reinforcing bar and concrete as much as the compressive strength or properties of the reinforcing bar because of component of construction expose to both flexural and bond together compressive loads. In this paper, the bond properties of concretes with different mix designs were investigated according to the results of compressive, flexural, bond, and flexural-bond tests. The data mining (DM) process was used to determine relationships among the test results and DM algorithms. Seventeen modeling techniques within WEKA were applied to the experimental data for the prediction of bond properties.The results show that the implemented models were good at predicting the bond properties. The best results were obtained from the RepTree algorithm for bond strength, the Multilayer Perceptron algorithm for flexural-bond strength, the MedSq algorithm for bond slippage, and the Pace Regression for flexural-bond deformation. Bond and flexural-bond can be easily predicted using the compressive strength, flexural strength and tensile stress of the rebar. Although a relationship is also existent between these and bond slippage and flexural-bond deformation, these relationships are weaker than the others.These results suggested that the DM algorithms can be used as an alternative approach to predict the bond strength using the results of compressive, flexural, bond, and flexural-bond tests as input parameters. The predictions of the bond slippage and flexural-bond deformation models poorly agreed with the experimental results. It can be obtained more successful results for these variables, when DM models with different inputs like the rebar-concrete interface stress together the measured parameters are used.     

Fuzzy optimization of slab production from mechanical stone properties

This paper aims to conduct slab production optimization by a flexible tool, which is fuzzy linear programming. There is a direct relationship between slab production and mechanical stone characteristics. In this process, the goal and its tolerance cannot be specified firstly due to a lack of knowledge. Therefore, the optimal system design problem for optimal slab production under soft constraints is constructed and solved in a fuzzy environment. The results show that fuzzy linear optimization is a convenient tool for optimizing slab production.     

Mechanical strength and microstructure of Stabilor-G® and ZrO2 microspecimens

For a safe design of micromechanical components reliable data of mechanical properties at static and cyclic loadings are of vital interest. Such data together with a detailed analysis of the microstructure are also useful for a straight forward optimization of the manufacturing process. Therefore, in the present study the mechanical behavior of microcast Stabilor-G^® microspecimens under quasistatic and cyclic loadings and of slip cast and micro powder injection molded ZrO₂ microspecimens under quasistatic loadings was determined. Together with a microscopic characterization of the specimens it could be shown that the elastic-plastic behavior of Stabilor-G^® microspecimens is strongly determined by grain anisotropy. In fatigue tests cyclic hardening occurs. The scatter of the lifetimes is not larger than observed at cast macrospecimens. The failure behavior of ZrO₂ microspecimens under quasistatic bending is mainly determined by surface roughness and near surface porosities as well as by the edge geometry. The highest characteristic bending strength which currently can be reached is nearly 3,200 Mpa.     

Correlations between bugginess and time-based commit characteristics

Modern software is often developed over many years with hundreds of thousands of commits. Commit metadata is a rich source of time-based characteristics, including the commit’s time of day and the commit frequency and seniority of its author. The “bugginess” of a commit is also a critical property of that commit. In this paper, we investigate the correlation between a commit’s time-based characteristics and its “bugginess”; such results can be useful for software developers and software engineering researchers. For instance, developers or code reviewers might be well-advised to thoroughly verify commits that are more likely to be buggy. In this paper, we study the correlation between a commit’s bugginess and the time of day of the commit, the day of week of the commit, the commit frequency and seniority of the commit authors, and whether or not the developers have marked a commit as a “stable” commit. We survey three widely-used open source projects: the Linux kernel, PostgreSQL, and the Xorg server. Our main findings include: (1) commits between midnight and 4 AM (referred to as late-night commits) are significantly buggier and commits between 8 AM and noon are less buggy, implying that developers may want to double-check their own late-night commits; (2) daily-committing developers produce less-buggy commits, indicating that we may want to promote the practice of daily-committing developers reviewing other developers’ commits; (3) the bugginess of commits versus day-of-week varies for different software projects; and (4) stable commits are significantly less buggy than commits in general.     

Microstructure and mechanical properties of micro tensile specimens made of CuAl10Ni5Fe4 produced by micro casting

In this paper the results of micro tensile tests of specimens produced by vacuum pressure casting (VPC) and centrifugal casting (CC) with varied mould temperatures are described. The microstructure of VPC-micro specimens is clearly different from CC-micro specimens. Due to the large tolerance range of the chemical composition of the aluminum bronze CuAl10Ni5Fe4 and process instabilities the microstructure of batches of VPC-micro specimens can be very fine grained as well as very coarse grained even if the process parameters were nominally the same. As a consequence the mechanical properties of micro specimen show a wide range, e.g. the ultimate tensile strength (VPC, mould temperature T _m = 1,000°C) is between 670 and 1,000 MPa. Within one batch (ca. 15 specimens) the scatter of microstructure and mechanical properties is clearly smaller. If the chemical composition of the material is nearly constant for a larger number of batches, then the production process of vacuum pressure casting leads reproducibly to nearly identical microstructure and mechanical properties.     

Stress engineering and mechanical properties of SU-8-layers for mechanical applications

SU-8 is an essential material for manufacturing micromechanical components with high demands in aspect ratio and toughness in the area of micro-system technologies. For reproducible production of SU-8 components, e.g. polymeric AFM-cantilevers and chip carriers, a characterization sequence for the material in its raw state and in all subsequent processing steps was developed. Included in these tests were differential scanning calorimetry of the unprocessed resist, in situ monitoring of the solid content during soft bake, measurement of the stress behaviour during and after post-exposure bake as well as determination of micro-hardness and Young’s modulus at different baking and exposure conditions. The results are promising with respect to definition of a novel procedure for reproducible preparation of micromechanical components from SU-8.     

芳烃生产流程模拟与研究

根据某石化企业芳烃生产数据,运用Petro-SIM软件建立了包括芳烃歧化和烷基转移、芳烃异构化反应模型的流程模型,经校正后,对模型计算值与实际测量值进行对比,验证了模型的准确性。利用软件中的Databook功能,对建立的模型进行了单装置反应条件和原料组成对产品产率影响的研究,结果表明,甲苯歧化及烷基转移反应中,产物的选择性主要受原料中T/C9A的比值的影响;芳烃异构化单元中,提高反应温度,有利于二甲苯达到热力学平衡,增加反应压力,乙苯转化率增加,原料中乙苯和C8环烷烃的含量对乙苯转化率和对二甲苯收率影响较为显著。     

Extremal properties of conditional entropy and quantum discord for XXZ,symmetric quantum states

For the XXZ subclass of symmetric two-qubit X states, we study the behavior of quantum conditional entropy \(S_{cond}\) as a function of measurement angle \(\theta \in [0,\pi /2]\). Numerical calculations show that the function \(S_{cond}(\theta )\) for X states can have at most one local extremum in the open interval from zero to \(\pi /2\) (unimodality property). If the extremum is a minimum, the quantum discord displays region with variable (state-dependent) optimal measurement angle \(\theta ^*\). Such \(\theta \)-regions (phases, fractions) are very tiny in the space of X-state parameters. We also discover the cases when the conditional entropy has a local maximum inside the interval \((0,\pi /2)\). It is remarkable that the maxima exist in surprisingly wide regions, and the boundaries for such regions are defined by the same bifurcation conditions as for those with a minimum.     

基于组件的机械仿真架构及流程控制技术研究

为了协同实现仿真作业的真正流程化,在分析典型工作流应用系统框架基础上,建立了CSE体系框架.结合组件开发思想,提出了仿真组件的概念;根据机械仿真的特点,引入虚拟网络计算(Virtual Network Computing,VNC)技术.项目开发进度表明,该框架对于机械仿真需求变化有强大的适应能力,整体结构清晰,组件化的方法明显提高了系统的适应性和灵活性.     

Explaining Disease: Correlations,Causes, and Mechanisms

Minds and Machines - Why do people get sick? I argue that a disease explanation is best thought of as causal network instantiation, where a causal network describes the interrelations among...     

Quasi-optimal integrated production, inventory and maintenance policies for a single-vendor single-buyer system with imperfect production process

In this paper we deal with the integrated supply chain management problem in the context of a single vendor-single buyer system for which the production unit is assumed to randomly shift from an in-control to an out-of-control state. At the end of each production cycle, a corrective or preventive maintenance action is performed, depending on the state of the production unit, and a new setup is carried out. Two different integrated production, shipment and maintenance strategies are proposed to satisfy the buyer’s demand at minimum total cost. The first one suggests that the buyer orders batches of size nQ and the vendor produces nQ and makes equal shipments of size Q. The second policy proposes that to satisfy the same ordered quantity, the vendor produces separately smaller batches of size Q, n times. The total integrated average cost per time unit corresponding to each strategy is considered as the performance criterion allowing choosing the best policy for any given situation.     

Evaluating the learning process of mechanical CAD students

There is little theoretical or experimental research on how beginner-level trainees learn CAD skills in formal training sessions. This work presents findings on how trainees develop their skills in utilizing a solid mechanical CAD tool (Pro/Engineer version 2000i² and later version Wildfire). Exercises at the beginner and intermediate levels were designed so that several variations of a solid object are built by non-experienced trainees as they accumulate training time. In this case, trainees are fourth year mechanical engineering seniors and as such, they were of a similar technical and gender make-up. This assessment was conducted over the duration of training (16-week long semester). The test exercises were used to assess the trainees’ speed and proficiency in the use of CAD by (1) measuring their performance time and (2) feature count (number of features-of-size used to build the test parts). Using performance time data, empirical learning curves are generated. Breaking these curves into declarative and procedural components provides insight into how fast the trainees develop cognitive and motor CAD skills. In order to confirm that this methodology can be extended to other CAD platforms, a follow-up study was performed on a different set of beginner-level trainees with similar make-up while using the same beginner-level parts but with a more recent version of Pro/Engineer: Wildfire. One significant result of this study is that the procedural and declarative components of CAD learning are largely cognitive.     

Correlations between Horn fractions, satisfiability and solver performance for fixed density random 3-CNF instances

An enhanced concept of sub-optimal reverse Horn fraction of a CNF-formula was introduced in [18]. It was shown that this fraction is very useful in effectively (almost) separating 3-colorable random graphs with fixed node-edge density from the non-3-colorable ones. A correlation between this enhanced sub-optimal reverse Horn fraction and satisfiability of random 3-SAT instances with a fixed density was observed. In this paper, we present experimental evidence that this correlation scales to larger-sized instances and that it extends to solver performances as well, both of complete and incomplete solvers. Furthermore, we give a motivation for various phases in the algorithm aHS, establishing the enhanced sub-optimal reverse Horn fraction, and we present clear evidence for the fact that the observed correlations are stronger than correlations between satisfiability and sub-optimal MAXSAT-fractions established similarly to the enhanced sub-optimal reverse Horn fraction. The latter observation is noteworthy because the correlation between satisfiability and the optimal MAXSAT-fraction is obviously 100%. AMS subject classification 90C05, 03B99, 68Q01, 68W01     

Methodologies for Measuring the Correlations between Post-Editing Effort and Machine Translatability

Against the background of a wider research project that aims to investigate the correlation, if any, between post-editing effort and the presence of negative translatability indicators in source texts submitted to Machine Translation (MT), this paper sets out to assess the potential of two methods for measuring the effort involved in post-editing MT output. The first is based on the use of the keyboard-monitoring program Translog; the second on Choice Network Analysis (CNA). The paper reviews relevant research in both machine translatability and MT post-editing, and appraises, in particular, the suitability of think-aloud protocols in assessing post-editing effort. The combined use of Translog and CNA is proposed as a way of overcoming some of the difficulties presented by the use of think-aloud protocols in the current context. Initial results from a study conducted at Dublin City University confirm that triangulating data from Translog and CNA can cast light on the temporal, cognitive and technical aspects of post-editing effort.     

The mechanical properties, dimensional tolerance and microstructural characterization of micro-molded ceramic and metal components

Metal and ceramic micro-components with 10 m features were fabricated by molding nano-powder-binder mixtures in micro-molds produced from LiGA-formed masters and then sintering to achieve the desired density and properties. The mechanical properties of the metals nickel and 316L stainless steel were measured in tension using miniature dog bone shaped, micro-molded test specimens. The sintering temperature controlled yield stress (YS), the ultimate tensile strength (UTS) and the ductility of the nickel with the YS and the UTS decreasing and the ductility increasing with increasing sintering temperature. For the stainless steel, the YS was nearly 400 MPa, UTS was 650 MPa and the ductility was 3%. The mechanical properties of aluminum oxide ceramics were determined using 4-point bending on miniature micro-molded bend bars. The average modulus of rupture (MOR) was 260 MPa. Careful measurements were made of the dimensional tolerance of the micro-molded parts both before and after sintering using automated optical metrology. The variability in the dimensions of a sintered SS gear after sintering was <3 m. Finally microscopic examination of the micromolded components indicated that the final grain size was generally less than 1 m with minimal residual porosity.This work was performed at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-ACO4–94AL85000. The authors wish to thank Linda Domeier for developing the replicated PMMA molds and Dale Zschiesche, Ralph Tissot, Joe Ceramuga, Paul Hlava and Dave Schmale for technical support.     

Correlations between characteristics of maximum influence and degree distributions in software networks

Software systems can be represented as complex networks and their artificial nature can be investigated with approaches developed in network analysis.Influence maximization has been successfully applied on software networks to identify the important nodes that have the maximum influence on the other parts.However,research is open to study the effects of network fabric on the influence behavior of the highly influential nodes.In this paper,we construct class dependence graph(CDG)networks based on eight practical Java software systems,and apply the procedure of influence maximization to study empirically the correlations between the characteristics of maximum influence and the degree distributions in the software networks.We demonstrate that the artificial nature of CDG networks is reflected partly from the scale free behavior:the in-degree distribution follows power law,and the out-degree distribution is lognormal.For the influence behavior,the expected influence spread of the maximum influence set identified by the greedy method correlates significantly with the degree distributions.In addition,the identified influence set contains influential classes that are complex in both the number of methods and the lines of code(LOC).For the applications in software engineering,the results provide possibilities of new approaches in designing optimization procedures of software systems.     

太湖水体叶绿素浓度与反射光谱特征关系的研究

根据2004年10月在太湖实测的水体反射光谱及实验室分析得到的叶绿素浓度数据,对太湖水体反射光谱特征与叶绿素浓度之间的关系进行探讨与分析。研究结果表明:水体叶绿素浓度与各波长处的反射光谱相关性不大,但是反射光谱经过比值法和微分处理后,两者具有很好的相关性,而且叶绿素浓度与反射光谱700nm附近波峰几何形态特征(波峰位置、面积、净高度)相关性很好,建立太湖水体叶绿素浓度估算模型。