Theoretical foundation of the 80/20 rule

A rigorous analysis of the 80/20 rule is made using an index for the observed values of the variables. Three important findings are identified. First, a sufficient condition is provided for Burrell's inverse relationship between minimum holdings and average circulation rate. Second, an indexed version of Lotka's law is used to derive a sufficient condition for Egghe's finding on the 80/20 rule. Third, through the computer simulations of the Simon-Yule model of Lotka's law, we identify the entry rate of new holdings as well as the number of circulations when the entry rate is a decreasing function to be crucial factors for the pattern of the 80/20-type curve.     

Quantitative measurement of gas hold-up distribution in a stirred chemical reactor using X-ray cone-beam computed tomography

Cone-beam type X-ray computed tomography (CBCT) is a potential method to measure three-dimensional phase distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data are highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transfer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effects of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate measurement of void fraction profiles with CBCT.     

A holistic approach to feature modeling for product line requirements engineering

Requirements engineering (RE) offers the means to discover, model, and manage the requirements of the products that comprise a product line, while software product line engineering (SPLE) offers the means of realizing the products’ requirements from a common base of software assets. In practice, however, RE and SPLE have proven to be less complementary than they should. While some RE techniques, particularly goal modeling, support the exploration of alternative solutions, the appropriate solution is typically conditional on context and a large product line may have many product-defining contexts. Thus, scalability and traceability through into product line features are key challenges for RE. Feature modeling, by contrast, has been widely accepted as a way of modeling commonality and variability of products of a product line that may be very complex. In this paper, we propose a goal-driven feature modeling approach that separates a feature space in terms of problem space and solution space features, and establish explicit mappings between them. This approach contributes to reducing the inherent complexity of a mixed-view feature model, deriving key engineering drivers for developing core assets of a product line, and facilitating the quality-based product configuration.     

New inhibitors of the Tat-TAR RNA interaction found with a "fuzzy" pharmacophore model

TAR RNA is a potential target for AIDS therapy. Ligand-based virtual screening was performed to retrieve novel scaffolds for RNA-binding molecules capable of inhibiting the Tat-TAR interaction, which is essential for HIV replication. We used a "fuzzy" pharmacophore approach (SQUID) and an alignment-free pharmacophore method (CATS3D) to carry out virtual screening of a vendor database of small molecules and to perform "scaffold-hopping". A small subset of 19 candidate molecules were experimentally tested for TAR RNA binding in a fluorescence resonance energy transfer (FRET) assay. Both methods retrieved molecules that exhibited activities comparable to those of the reference molecules acetylpromazine and chlorpromazine, with the best molecule showing ten times better binding behavior (IC50 = 46 microM). The hits had molecular scaffolds different from those of the reference molecules.     

Data collection in global software engineering research: learning from past experience

Global Software Engineering has become a standard in today’s software industry. Research in distributed software development poses severe challenges that are due to the spatial and temporal distribution of the actors, as well as to language, intercultural and organizational aspects. These challenges occur in addition to “traditional” challenges of the domain itself in large-scale software projects, like coordination and communication issues, requirements volatily, lack of domain knowledge, among others. While several authors have reported empirical studies of global software development projects, the methodological difficulties and challenges of this type of studies have not been sufficiently discussed. In this paper, we share our experiences of collecting and analysing qualitative data in the context of Global Software Engineering projects. We discuss strategies for gaining access to field sites, building trust and documenting distributed and complex work practices in the context of several research projects we have conducted in the past 9 years. The experiences described in this paper illustrate the need to deal with fundamental problems, such as understanding local languages and different cultures, observing synchronous interaction, or dealing with barriers imposed by political conflicts between the sites. Based on our findings, we discuss some practical implications and strategies that can be used by other researchers and provide some recommendations for future research in methodological aspects of Global Software Engineering.     

过程自动化系统

读者们觉得新型过程系统更加有用,希望可以购买到更多这样的产品。专家建议:在考虑价格前,首先考虑对系统性能的要求及其拓展性。过程自动化系统较传统的分布式控制系统进步,但用户还是有很多相似的考虑,如可靠性、技术支持和升级等。为了预测出这个价值数     

Video-assisted lateral intertransverse process arthrodesis. Validation of a new minimally invasive lumbar spinal fusion technique in the rabbit and nonhuman primate (rhesus) models

STUDY DESIGN: Cadaveric anatomic and in vivo survival animal studies were performed to develop a new arthrodesis technique for the lumbar spine. OBJECTIVES: To examine the feasibility, efficacy, and safety of a minimally invasive lumbar intertransverse process arthrodesis technique using an osteoinductive growth factor (rhBMP-2) delivered in a collagen sponge carrier. The technique was first developed using a rabbit model and modified for the nonhuman primate (rhesus monkey), a larger animal with the most similar bone biology to humans. SUMMARY OF BACKGROUND DATA: The morbidity of conventional posterolateral lumbar intertransverse process arthrodesis includes graft donor site morbidity; paraspinal muscle devascularization, denervation, and scarring and nonunion in up to 36% of patients. Minimally invasive anterior lumbar interbody arthrodesis techniques have been developed, but these often require a metal implant and carry risks to major vessels and development of retrograde ejaculation. A minimally invasive technique for posterolateral intertransverse process arthrodesis has not been described previously. METHODS: In Part 1, we examined seven New Zealand white rabbits and five rhesus monkeys at necropsy and during nonsurvival surgeries to determine the best access routes and to develop special instruments for video-assisted lateral intertransverse process arthrodesis. In Part 2, 38 New Zealand white rabbits underwent L4-L5 intertransverse process arthrodesis: the "OPEN" group (n = 16) underwent a standard open muscle-splitting approach using rhBMP-2 (bone morphogenetic protein) and collagen as a bone graft substitute; the "video-assisted control" group (n = 6) underwent video-assisted lateral intertransverse process arthrodesis with the collagen implant only (no growth factor); and the "video-assisted-BMP" group (n = 16) underwent video-assisted lateral intertransverse process arthrodesis with rhBMP-2 and collagen as the graft material. In Part 3, rhesus monkeys (n = 4) underwent video-assisted lateral intertransverse process arthrodesis using rhBMP-2 and collagen after laminectomy of L4-L5. RESULTS: In Part 1, we identified expedient, minimally invasive routes to the intertransverse process interval appropriate for each species: an intermuscular approach for the rabbit and a lateral, extramuscular approach for the rhesus monkey. In Part 2, all rabbits in the OPEN and video-assisted-BMP groups achieved solid intertransverse process lumbar fusions when assessed at 10 weeks. There were no neurologic impairments nor any difference between the two groups in the frequency of postoperative infection or other complications. None of the animals in the video-assisted control group showed evidence of fusion. In Part 3, exposure, decortication and grafting with rh-BMP-2 and collagen was accomplished successfully in all four monkeys through the video-assisted minimally invasive approach without complications. CONCLUSION: Video-assisted lateral intertransverse process arthrodesis is a feasible, effective, and safe method of lumbar spinal fusion in the rabbit and rhesus monkey. Use of this arthrodesis procedure will minimize the morbidity of paraspinal muscle denervation and devascularization seen with open intertransverse process fusion techniques, and the use of an osteoinductive growth factor will eliminate the problem of graft donor site morbidity and possibly increase the chances for successful fusion.     

Natural perspective projections for head-mounted displays

The display units integrated in today's head-mounted displays (HMDs) provide only a limited field of view (FOV) to the virtual world. In order to present an undistorted view to the virtual environment (VE), the perspective projection used to render the VE has to be adjusted to the limitations caused by the HMD characteristics. In particular, the geometric field of view (GFOV), which defines the virtual aperture angle used for rendering of the 3D scene, is set up according to the display field of view (DFOV). A discrepancy between these two fields of view distorts the geometry of the VE in a way that either minifies or magnifies the imagery displayed to the user. It has been shown that this distortion has the potential to affect a user's perception of the virtual space, sense of presence, and performance on visual search tasks. In this paper, we analyze the user's perception of a VE displayed in a HMD, which is rendered with different GFOVs. We introduce a psychophysical calibration method to determine the HMD's actual field of view, which may vary from the nominal values specified by the manufacturer. Furthermore, we conducted two experiments to identify perspective projections for HMDs, which are identified as natural by subjects--even if these perspectives deviate from the perspectives that are inherently defined by the DFOV. In the first experiment, subjects had to adjust the GFOV for a rendered virtual laboratory such that their perception of the virtual replica matched the perception of the real laboratory, which they saw before the virtual one. In the second experiment, we displayed the same virtual laboratory, but restricted the viewing condition in the real world to simulate the limited viewing condition in a HMD environment. We found that subjects evaluate a GFOV as natural when it is larger than the actual DFOV of the HMD--in some cases up to 50 percent--even when subjects viewed the real space with a limited field of view.     

Commodified science and social wellbeing

This paper explores the increasing trend towards the commodification of public research and development (R&D) and the impact of this on social wellbeing. In many developed countries, the changes introduced by governments to funding mechanisms for universities and public research institutions has led to a fundamental shift in the focus of public R&D. The focus has shifted from creating useful public, codifiable knowledge to creating a knowledge commodity driven by commercial imperatives. Although there may be an economic argument to be made for the virtues of such change, we argue here that the potential costs to social wellbeing have been largely, and dangerously, ignored.