面向服务架构设计的模式与反模式

面向服务架构设计原则 SOA已成为一个大家熟知的，且稍微有些歧义的缩写词。如果让两个人描述一下SOA，可能会得到两个截然不同，甚至相反的答案。有些人将SOA描述为用作业务启动的IT基础结构，而其他人则指望SOA来提高IT效率。在很多方面SOA有点像John Godfrey Saxe所讲的盲人摸象的故事——由于每个人受自己个人体验的影响，描述的大象各不相同。Saxe先生的大象很容易描述，因为它是一个存在的物理实体。然而，SOA却很难描述，因为设计理念不像物理体现那样是存在的。     

Heat transfer coefficient measurements for mixed gas working fluids at cryogenic temperatures

The use of mixed gas working fluids has become common in Joule-Thomson type cryocoolers for a variety of applications. However, there is very little data or theory currently available regarding the heat transfer coefficient associated with these multi-component, multi-phase mixtures at cryogenic temperatures. This paper describes an experimental test facility and procedure that has been used to make careful measurements of the horizontal, flow boiling heat transfer coefficient for several hydrocarbon mixtures that are nominally optimal for small, Joule-Thomson cryocoolers in the 80 K to 120 K operating range. Data are presented over a range of temperatures from 100 K to room temperature and for several pressures and mass flow rates. The results indicate that quality and mass flux are the most important parameters governing the heat transfer coefficient among those that were varied. The experiment is verified by carrying out tests using single-phase, pure nitrogen gas and comparing the results with the Dittus-Boelter equation. The experimental uncertainty of the measurements is estimated from 1st principles; additionally, the repeatability of the experimental measurements was investigated by replicating tests at a nominal set of operating conditions and composition on separate days. The measurements presented here are intended to aid in the design of small, mixed-gas Joule-Thomson cryocoolers.     

Statistical approach and benchmarking for modeling of multi-dimensional behavior in TRISO-coated fuel particles

The fundamental design for a gas-cooled reactor relies on the behavior of the coated particle fuel. The coating layers, termed the TRISO coating, act as a mini-pressure vessel that retains fission products. Results of US irradiation experiments show that many more fuel particles have failed than can be attributed to one-dimensional pressure vessel failures alone. Post-irradiation examinations indicate that multi-dimensional effects, such as the presence of irradiation-induced shrinkage cracks in the inner pyrolytic carbon layer, contribute to these failures. To address these effects, the methods of prior one-dimensional models are expanded to capture the stress intensification associated with multi-dimensional behavior. An approximation of the stress levels enables the treatment of statistical variations in numerous design parameters and Monte Carlo sampling over a large number of particles. The approach is shown to make reasonable predictions when used to calculate failure probabilities for irradiation experiments of the New Production - Modular High Temperature Gas Cooled Reactor Program.     

Linear stochastic approximation driven by slowly varying Markov chains

We study a linear stochastic approximation algorithm that arises in the context of reinforcement learning. The algorithm employs a decreasing step-size, and is driven by Markov noise with time-varying statistics. We show that under suitable conditions, the algorithm can track the changes in the statistics of the Markov noise, as long as these changes are slower than the rate at which the step-size of the algorithm goes to zero.     

The availability of source code in relation to timely response to security vulnerabilities

Once a vulnerability has been found in an application or service that runs on a computer connected to the Internet, fixing that exploit in a timely fashion is of the utmost importance. There are two parts to fixing vulnerability: a party acting on behalf of the application's vendor gives instructions to fix it or makes a patch available that can be downloaded; then someone using that information fixes the computer or application in question. This paper considers the effects of proprietary software versus non-proprietary software in determining the speed with which a security fix is made available, since this can minimize the amount of time that the computer system remains vulnerable.     

Quality management metrics for software development

It can be argued that the quality of software management has an effect on the degree of success or failure of a software development program. We have developed a metric for measuring the quality of software management along four dimensions: requirements management, estimation/planning management, people management, and risk management. The quality management metric (QMM) for a software development program manager is a composite score obtained using a questionnaire administered to both the program manager and a sample of his or her peers. The QMM is intended to both characterize the quality of software management and serve as a template for improving software management performance. We administered the questionnaire to measure the performance of managers responsible for large software development programs within the US Department of Defense (DOD). Informal verification and validation of the metric compared the QMM score to an overall program-success score for the entire program; this resulted in a positive correlation.     

The design of autonomous DNA nano-mechanical devices: Walking and rolling DNA

We provide designs for the first autonomousDNA nanomechanical devices that execute cycles of motion without external environmental changes. These DNA devices translate along a circular strand of ssDNA and rotate simultaneously. The designs use various energy sources to fuel the movements, include (i) ATP consumption by DNA ligase in conjunction with restriction enzyme operations, (ii) DNA hybridization energy in trapped states, and (iii) kinetic (heat) energy. We show that each of these energy sources can be used to fuel random bidirectional movements that acquire after n steps an expected translational deviation of O(√n). For the devices using the first two fuel sources, the rate of stepping is accelerated over the rate of random drift due to kinetic (heat) energy. Our first DNA device, which we call walking DNA, achieves random bidirectional motion around a circular ssDNA strand by use of DNA ligase and two restriction enzymes. Our other DNA device, which we call rolling DNA, achieves random bidirectional motion without use of DNA ligase or any restriction enzyme, and instead using hybridization energy. We also describe how to modify the design for the rolling DNA device to include a ``latching mechanism' that fixes the wheels position at specified location along the road, so as to provide for overall unidirectional translational movement. This revised version was published online in June 2006 with corrections to the Cover Date.     

Estimating subpixel surface temperatures and energy fluxes from the vegetation index-radiometric temperature relationship

Routine (i.e., daily to weekly) monitoring of surface energy fluxes, particularly evapotranspiration (ET), using satellite observations of radiometric surface temperature has not been feasible at high pixel resolution (i.e., ∼10¹-10² m) because of the low frequency in satellite coverage over the region of interest (i.e., approximately every 2 weeks). Cloud cover further reduces the number of useable observations of surface conditions resulting in high-resolution satellite imagery of a region typically being available once a month, which is not very useful for routine ET monitoring. Radiometric surface temperature observations at ∼1- to 5-km pixel resolution are available multiple times per day from several weather satellites. However, this spatial resolution is too coarse for estimating ET from individual agricultural fields or for defining variations in ET due to land cover changes. Satellite data in the visible and near-infrared wavelengths, used for computing vegetation indices, are available at resolutions an order of magnitude smaller than in the thermal-infrared, and hence provide higher resolution information on vegetation cover conditions. A number of studies have exploited the relationship between vegetation indices and radiometric surface temperature for estimating model parameters used in computing spatially distributed fluxes and available moisture. In this paper, the vegetation index-radiometric surface temperature relationship is utilized in a disaggregation procedure for estimating subpixel variation in surface temperature with aircraft imagery collected over the US Southern Great Plains. The disaggregated surface temperatures estimated by this procedure are compared to actual observations at this subpixel resolution. In addition, a remote sensing-based energy balance model is used to compare output using actual versus estimated surface temperatures over a range of pixel resolutions. From these comparisons, the utility of the surface temperature disaggregation technique appears to be most useful for estimating subpixel surface temperatures at resolutions corresponding to length scales defining agricultural field boundaries across the landscape.     

Comparing MODIS and ETM+ data for regional and global land classification

Nearly simultaneous reflectance data sets from the Landsat 7 Enhanced Thematic Mapper Plus (ETM+), at 30-m resolution, and the Terra satellite instrument MODIS, at 500-m resolution, are compared for their ability to map fractional coverage of surface types over large areas. Lower spatial resolution MODIS classification results are generally comparable those of ETM+, with discrepancies for some regions with mixed surface types. Analysis of laboratory and field spectra suggests an ambiguity, the “brightness ambiguity”, which can prevent accurate area estimation of pixels having two or more surface types. This ambiguity, plus general mathematical inversion issues, can account for the discrepancy. Thus, occasional high-resolution measurements, as from Landsat 7, are necessary to refine estimations of large area surface types from MODIS and similar lower spatial resolution instruments.     

Developing an Automated Enzyme Immunoassay for High-Throughput Screening of Bovine Serum Antibodies to Neospora Caninum

An enzyme-linked immunosorbent assay (ELISA) for Neospora caninum antibodies was automated with a robotic workstation, the Beckman Coulter Biomek 2000, to screen 200 bovine sera. Comparing these results with manually run ELISA data, a 95.92% agreement (K = 0.9592) between the two assays was obtained. The automated assay was specific and sensitive with excellent positive and negative predictive values. The results were repeatable and reproducible. The automation flexibility was high and the operation complexity was minimal. High-throughput screening (HTS) for bovine antibodies to Neospora caninum was achieved. The assay was developed according to the internationally recognized ISO17025 standard requirements.