Advances in Electron Beam Melting of Aluminum Alloys

The high thermal conductivity and melt pool optical reflectivity associated with aluminum alloys can pose significant challenges for direct-metal SFF processes. The use of SFF processes to produce aluminum parts is often not cost effective relative to CNC machining for simple geometries. However, the use of SFF techniques for aluminum alloys is justified for some applications such as aerospace forgings or high surface area heat exchangers. This paper describes recent progress in processing aluminum alloys using the Electron Beam Melting process. Structure and properties will be discussed, as well challenges associated with high vapor pressure alloying elements such as zinc and magnesium.Mechanical Engineerin

Preaching With Audio-Visuals

Problem The increasing usage of audio-visuals in modern communication has brought about an increase in communication efficiency, an efficiency that is sometimes lacking in sermons. Audio-visuals can be viewed by the Christian church as either legitimate or illegitimate means of communication in preaching. If the church accepts these media as genuine and valid vehicles of communication of its message, it must then discover ways of employing audio-visuals effectively and responsibly in preaching. Methods For the development of guidelines for the utilization of audio-visuals in preaching, data and information from the following areas have been studied and surveyed: (1) Scriptural data on communication and revelation; (2) the theology of preaching; (3) the literature of communication, education, and audio-visuals; and (A) a survey conducted among the members of one congregation to discover their response to audio-visual sermons. Results A study of the Scriptures reveals that God has employed a variety of multi-sensory methods in seeking to communicate with men. While both Old and New Testaments strongly support the idea of the prominence of the word, yet the oral-auditory channel is by no means exclusive to other forms of communication. The literature of the audio-visual field and audio-visual education is rich in sound theoretical principles that can readily be adapted to preaching to insure efficiency of communication. The model of instructional development is here of particular benefit in that it seeks to consider the totality of the communication situation. This model also suggests that audio-visuals are not necessarily suited for all kinds of sermons and audiences, but that each particular communication situation must be viewed individually. While the employment of audio-visuals may improve information transmission efficiency in preaching, yet the use of such media is not totally without danger to preaching. To insure that the preacher is aware of such dangers, this project report examines in particular the role of the interpersonal relationship in communication as well as the ethics of human persuasion and suggests responsible ways in which audio—visuals may be used in preaching. A survey conducted among the members of one congregation generally showed favorable responses to audio-visual sermons as well as to various issues arising in such preaching. Conclusions The impact of modern media on man makes it necessary for preaching to respond somehow to the contemporary situation. Audiovisuals in preaching is one way through which greater information transmission efficiency may be achieved, for they are media with which modern man is thoroughly familiar. The employment of audiovisuals in preaching, however, needs the guidance of both theoretical principles from the field of communication and also biblically informed theological principles. From a study of Scriptural evidences, communication literature, and a personal survey it is suggested that the use of audio-visuals in preaching may be one viable means of increasing the church\u27s effectiveness in the communication of the gospel

A QUALITATIVE CHOICE ANALYSIS OF FACTORS INFLUENCING POST-CRP LAND USE DECISIONS

The future use of Conservation Reserve Program (CRP) lands is an important agricultural policy issue. To examine the effects of factors that influence landowners' post-contract use of CRP lands, a survey of Texas High Plains CRP contract holders was conducted in 1992. This study analyzes the results of the survey using a qualitative choice model. It was found that the presence of a livestock enterprise in the current contract holder's operation increases the probability of these acres remaining in the established cover. Contract holders who value the commodity base have an increased probability of returning their acres to crop production.Agricultural policy, Conservation Reserve Program, Ordered probit model, Land Economics/Use,

Extensive Characterization of Seismic Laws in Acoustic Emissions of Crumpled Plastic Sheets

Statistical similarities between earthquakes and other systems that emit cracking noises have been explored in diverse contexts, ranging from materials science to financial and social systems. Such analogies give promise of a unified and universal theory for describing the complex responses of those systems. There are, however, very few attempts to simultaneously characterize the most fundamental seismic laws in such systems. Here we present a complete description of the Gutenberg-Richter law, the recurrence times, Omori's law, the productivity law, and Bath's law for the acoustic emissions that happen in the relaxation process of uncrumpling thin plastic sheets. Our results show that these laws also appear in this phenomenon, but (for most cases) with different parameters from those reported for earthquakes and fracture experiments. This study thus contributes to elucidate the parallel between seismic laws and cracking noises in uncrumpling processes, revealing striking qualitative similarities but also showing that these processes display unique features.Comment: Accepted for publication in EP

Distance to the scaling law: a useful approach for unveiling relationships between crime and urban metrics

We report on a quantitative analysis of relationships between the number of homicides, population size and other ten urban metrics. By using data from Brazilian cities, we show that well defined average scaling laws with the population size emerge when investigating the relations between population and number of homicides as well as population and urban metrics. We also show that the fluctuations around the scaling laws are log-normally distributed, which enabled us to model these scaling laws by a stochastic-like equation driven by a multiplicative and log-normally distributed noise. Because of the scaling laws, we argue that it is better to employ logarithms in order to describe the number of homicides in function of the urban metrics via regression analysis. In addition to the regression analysis, we propose an approach to correlate crime and urban metrics via the evaluation of the distance between the actual value of the number of homicides (as well as the value of the urban metrics) and the value that is expected by the scaling law with the population size. This approach have proved to be robust and useful for unveiling relationships/behaviors that were not properly carried out by the regression analysis, such as i) the non-explanatory potential of the elderly population when the number of homicides is much above or much below the scaling law, ii) the fact that unemployment has explanatory potential only when the number of homicides is considerably larger than the expected by the power law, and iii) a gender difference in number of homicides, where cities with female population below the scaling law are characterized by a number of homicides above the power law.Comment: Accepted for publication in PLoS ON

Scale-adjusted metrics for predicting the evolution of urban indicators and quantifying the performance of cities

More than a half of world population is now living in cities and this number is expected to be two-thirds by 2050. Fostered by the relevancy of a scientific characterization of cities and for the availability of an unprecedented amount of data, academics have recently immersed in this topic and one of the most striking and universal finding was the discovery of robust allometric scaling laws between several urban indicators and the population size. Despite that, most governmental reports and several academic works still ignore these nonlinearities by often analyzing the raw or the per capita value of urban indicators, a practice that actually makes the urban metrics biased towards small or large cities depending on whether we have super or sublinear allometries. By following the ideas of Bettencourt et al., we account for this bias by evaluating the difference between the actual value of an urban indicator and the value expected by the allometry with the population size. We show that this scale-adjusted metric provides a more appropriate/informative summary of the evolution of urban indicators and reveals patterns that do not appear in the evolution of per capita values of indicators obtained from Brazilian cities. We also show that these scale-adjusted metrics are strongly correlated with their past values by a linear correspondence and that they also display crosscorrelations among themselves. Simple linear models account for 31%-97% of the observed variance in data and correctly reproduce the average of the scale-adjusted metric when grouping the cities in above and below the allometric laws. We further employ these models to forecast future values of urban indicators and, by visualizing the predicted changes, we verify the emergence of spatial clusters characterized by regions of the Brazilian territory where we expect an increase or a decrease in the values of urban indicators.Comment: Accepted for publication in PLoS ON

Polyamide Nanocomposites for Selective Laser Sintering

Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high heat resistance characteristics for a plethora of finished parts that are desired and required for performance driven applications. It is anticipated that nanomodification of polyamide 11 and 12 will result in enhanced polymer performance, i.e., fire retardancy, high strength and high heat resistance for polyamide 11 and 12. It is expected that these findings will expand the market opportunities for polyamide 11 and 12 resin manufacturers. The objective of this research is to develop improved polyamide 11 and 12 polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into the polyamide 11 and 12 via twin screw extrusion to provide improved material properties of the polymer blends. Arkema RILSAN® polyamide 11 molding polymer pellets and Degussa VESTAMID® L1670 polyamide 12 were examined with three types of nanoparticles: chemically modified montmorillonite (MMT) organoclays, surface modified nanosilica, and carbon nanofibers (CNFs) to create polyamide 11 and 12 nanocomposites. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of dispersion. Injection molded test specimens were fabricated for physical, thermal, mechanical properties, and flammability tests. Thermal stability of these polyamide 11 and 12 nanocomposites was examined by TGA. Mechanical properties such as tensile, flexural, and elongation at break were measured. Flammability properties were also obtained using the Cone Calorimeter at an external heat flux of 50 kW/m2. TEM micrographs, physical, mechanical, and flammability properties are included in the paper. Polyamide 11 and 12 nanocomposites properties are compared with polyamide 11 and 12 baseline polymers. Based on flammability and mechanical material performance, selective polymers including polyamide 11 nanocomposites and control polyamide 11 were cryogenically ground into fine powders and fabricated into SLS parts.Mechanical Engineerin

Analisis Keamanan Sistem Perangkat Lunak

Kesalahan kerentanan dan keamanan perangkat lunak dapat dikurangi jika secure software development process (SSDP) diikuti, seperti memenuhi aspek keamanan pada tahap membangun perangkat lunak. Keamanan perangkat lunak sangat penting dalam perangkat lunak, sebagian besar keamanan perangkat lunak tidak ditangani sejak software development life cycle (SDLC). Sistem perangkat lunak yang aman akan memberikan tingkat kepercayaan yang tinggi dari user, user akan merasa nyaman dan aman ketika berhubungan dengan sistem yang sudah kita bangun. Pada tulisan kali ini, kita akan membahas tentang keamanan pada fase-fase membangun perangkat lunak. Selain itu tulisan ini dapat membantu pengembang perangkat lunak untuk meningkatkan keamanan dan mengurangi vulnerability (kerentanan) pada perangkat lunak, sehingga kedepan keamanan harus terintegrasi ke dalam software development life cycle (SDLC). Keamanan harus dibangun “built-in” ke dalam produk yang yang kita kembangkan