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.     

Temporal and molecular characteristics of lacZ mutations in somatic tissues of transgenic mice

In order to help establish criteria for optimizing protocols for in vivo mutation studies, lacZ transgenic mice (Muta mouse) were treated with five consecutive daily doses of ethylnitrosourea (50 mg/kg), sampled at times up to 55 days after treatment, and mutant frequencies and DNA sequences determined for liver and bone marrow. In the bone marrow, the mutant frequency rose very rapidly in the first 5 days after treatment to 34 times the control frequency. Subsequently, there was a brood peak where the mutant frequency did not vary significantly, although it did appear to begin to decline after 45 days. In contrast, in the liver, the peak mutant frequency (11 times the control frequency) was not achieved until 35 days, after which there appeared to be a slow decline up to 55 days, which was not statistically significant. Once the maximum mutant frequency was reached, the mutation spectra in the two tissues were indistinguishable. In contrast to the G:C-->A:T transitions in 5'-CpG sites characteristic of untreated mice, A:T-->T:A transversions and A:T-->G:C transitions were prominent in both liver and bone marrow of ENU-treated mice, suggesting the involvement of unrepaired O2- and O4-ethylthymine adducts. In addition, G:C-->T:A transversions were induced in liver. This study demonstrates the possibility that although tissues may have different mutation fixation times, a single mutation fixation time equal to the longest time may be appropriate for in vivo mutation studies, provided that the mutation frequency does not decline appreciably after the peak is reached. This study also illustrates the necessity of ensuring that mutation characteristics are determined after optimal fixation has occurred.     

Sanger DNA-sequencing reactions performed in a solid-phase nanoreactor directly coupled to capillary gel electrophoresis

A miniaturized, solid-phase nanoreactor was developed to prepare Sanger DNA-sequencing ladders which was directly interfaced to a capillary gel electrophoresis system. A biotinylated fragment of the rat brain actin gene (1 kbp) was amplified by PCR and attached to the interior wall of an (aminoalkyl)silane-derivatized fused-silica capillary tube via a biotin/streptavidin/biotin linkage. Coverage of the capillary wall with the biotinylated DNA averaged 77 +/- 10%. Stability of the anchored template under pressure (33 nL/s) and electroosmotic flows (11.3 nL/s) were favorable, requiring rinsing for > 150 h to reduce the surface coverage by only 50%. In addition, the immobilized template was stable toward temperatures required for preparing sequencing ladders, even under cycling conditions. Standard Sanger dideoxynucleotide termination performed in a large-volume (approximately 8 microL) solid-phase reactor using the thermally stable polymerase enzymes Taq and Vent and the polymerases T7 and Bst with off-line slab gel electrophoresis and autoradiographic detection indicated that acceptable fragment generation was achieved only in the case of the thermally stable polymerases. Banding was not apparent for T7 and Bst since all reagents were inserted into the column in a single plug at the beginning of the reaction. A small volume reactor (volume approximately 62 nL) was then used to perform DNA polymerase reactions and was coupled directly to a capillary gel column for separation. The capillary reactor was placed inside a thermocycler to control the temperature during chain extension and was directly connected to the gel column via zero dead volume fused-silica connectors. The complementary DNA fragments generated (C-track only) in the reactor were denatured using heat and directly injected onto the gel-filled capillary for size separation with detection accomplished using near-IR laser-induced fluorescence. Extension and single-base separation resolution of the C-track, which was directly injected onto the gel column, was estimated to be > 450 bases from the primer annealing site with plate numbers ranging from 1 x 10(6) to 2 x 10(6)/m.     

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.     

Nitrogen fixation of and N transfer from cowpea, mungbean and groundnut when intercropped with maize

Grain legumes are used widely in intercropping systems. However, quantitative and comparative data available as to their N₂ fixation and N beneficial effect on the companion crop in intercropping systems are scarce. Hence, studies were conducted to ascertain the above when cowpea (Vigna unguiculata L.), mungbean (Vigna radiata L.) and groundnut (Arachis hypogaea L.) were intercropped with maize. The study was¹⁵N-aided and made outdoors in basins (30 L) filled with 38 kg of soil.¹⁵N labelling was effected by incorporating¹⁵N-tagged plant material or applying¹⁵N-labelled fertilizer along with sucrose to stabilize¹⁵N enrichment in the soil during the experimental period. Intercropped groundnut fixed the highest amount of nitrogen from the atmosphere (i.e. 552 mg plant^–1), deriving 85% of its N from the atmosphere. Intercropped cowpea and mungbean fixed 161 and 197 mg N plant^–1, obtaining 81% and 78% of their N content from the atmosphere, respectively. The proportion of N derived by maize from the associated legume varied from 7-11% for mungbean, 11–20% for cowpea and 12–26% for groundnut which amounted to about 19–22, 29–45 and 33–60 mg N maize plant^–1, respectively. The high nitrogen fixation potential of groundnut in dual stands and its relatively low harvest index for N have apparently contributed to greater N-benefical effect on the associated crop.     

Design and fabrication of an electrochemically actuated microvalve

A microfluidic valve based on electrochemical (ECM) actuation was designed, fabricated using UV-LIGA microfabrication technologies. The valve consists of an ECM actuator, polydimethylsiloxane (PDMS) membrane and a micro chamber. The flow channels and chamber are made of cured SU-8 polymer. The hydrogen gas bubbles were generated in the valve microchamber with Pt black electrodes (coated with platinum nanoparticles) and filled with 1 M of NaCl solution. The nano particles coated on the working electrode helps to boost the surface-to-volume ratio of the electrode for faster reversible electrolysis and faster valve operation. To test the functionality of the microvalve, a simple micropump based on ECM principle was also integrated in the system to deliver a microscopic volume of fluid through the valve. The experimental results have showed that an approximately 300 μm deflection of valve membrane was achieved by applying a bias voltage of ?1.5 V across the electrodes. The pressure in the valve chamber was estimated to be about 200 KPa. Experimental results proved that the valve can be easily operated by controlling the electrical signals supplied to the ECM actuators.     

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     

Management of early-stage epithelial ovarian cancer

"Early" epithelial ovarian carcinoma encompasses a spectrum of patients with diseases that have markedly different survivals, ranging from indolent lesions truly confined to the ovary to high-grade lesions that have a significant chance of occult metastasis at the time of diagnosis. The basic principles of management rest on an adequate primary surgical procedure that removes all gross disease and accurately assesses the sites at risk for metastasis with a comprehensive staging laparotomy. After a comprehensive staging laparotomy, patients can be stratified into low-risk and high-risk groups. Those with low-risk disease have such a low risk of recurrence that the toxicity of adjuvant therapy is not warranted. Although patients with high-risk disease have a high enough of a risk of recurrence to justify consideration of adjuvant therapy, their ultimate prognosis may be determined more by an accurate determination of the stage of disease rather than by currently available, marginally effective or ineffective therapy. Patients who are thought to have early stage disease on the basis of inadequate staging procedures either should undergo a restaging laparotomy or receive therapy for the possibility of occult advanced disease.     

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.