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271.
This investigation was conducted to determine the nature of the strain-rate sensitivity of OFHC copper at room temperature.
In particular, the relative magnitudes of the dynamic contribution (particle inertia, suppression of thermal assistance, and
so forth) and the nondynamic contribution (namely, the accelerated rate of strain hardening observed at high strain rates)
to the strain-rate sensitivity were determined. Specimens were dynamically compressed using the Hopkinson pressure bar technique,
and then were reloaded quasistatically to determine their respective yield strengths. The dynamic contribution to strainrate
sensitivity was taken as the difference between the peak dynamic flow stress and the flow stress of the same specimen when
reloaded quasistatically. The nondynamic contribution to strain-rate sensitivity of the flow stress was taken as the difference
between the quasistatic flow stress in reloading of a specimen prestrained ε0 dynamically and the flow stress at ε0 for a sample deformed in uniaxial quasistatic compression. The room temperature dynamic flow-stress of OFHC copper, deformed
at 500s−1, was found to be 25 pct higher than the conventional quasistatic flow stress for this metal over a strain range of 0.08 to
0.20. The nondynamic contribution to strain-rate sensitivity was found to be about 60 pct of the total flow stress increase
and has been attributed to a difference in strainhardening at different strain rates. Thus, it appears that in OFHC copper
at room temperature and at strain rates of about 500s−1, the nondynamic contribution to strain-rate sensitivity is more significant than the dynamic contribution. 相似文献
272.
Airborne brake wear debris: size distributions, composition, and a comparison of dynamometer and vehicle tests 总被引:1,自引:0,他引:1
Particle size distributions of light-duty vehicle brake wear debris are reported with careful attention paid to avoid sampling biases. Electrical low-pressure impactor and micro-orifice uniform deposit impactor measurements yield consistent size distributions, and the net particulate matter mass from each method is in good agreement with gravimetric filter measurements. The mass mean diameter of wear debris from braking events representative of urban driving is 6 microm, and the number-weighted mean is 1-2 microm for three currently used classes of lining materials: low metallic, semimetallic, and non-asbestos organic (NAO). In contrast, the wear rates are very material dependent, both in number and mass of particles, with 3-4 times higher emissions observed from the low metallic linings as compared to the semimetallic and NAO linings. Wind tunnel and test track measurements demonstrate the appearance of micron size particles that correlate with braking events, with approximately 50% of the wear debris being airborne for the test vehicle in this study. Elemental analysis of the wear debris reveals a consistent presence of the elements Fe, Cu, and Ba in both dynamometer and test track samples. 相似文献
273.
Allometric modeling of plant root growth and its application in rhizosphere remediation of soil contaminants 总被引:1,自引:0,他引:1
Allometric curves relating tree trunk diameter to root biomass, depth, and breadth were compiled for mulberry (Morus sp.). The curves were based on statistical analyses of measurements made on 29 different-sized trees ranging in age from 2 to 15 yr that had grown from seed in a naturally revegetated former sludge basin containing polyaromatic hydrocarbons. Over a 15-yr period, the curves indicate that the fine root biomass (<1.5 mm diameter) increases 60-fold and, under the right circumstances, can be a part of a root system that reaches a 2-m depth. The fine roots of mulberry were shown to produce several flavonoid compounds at concentrations (ranging from 94 to 525 microg/cm3) known to support the growth of organisms capable of degrading xenobiotics. Recognizing the root system as the driver of rhizoremediation, allometry curves presented in this paper can be used to quantify the magnitude of the driver (root system) without damaging plants during the course of a multiyear field study. 相似文献
274.
A combination of controlled annealing and characterization by scanning probe microscopy (SPM) is used to demonstrate that the refractive-index proffle of a commercially available silica-based optical fiber can be accurately reconfigured for use as an evanescent field sensor. The process relies on the controlled relocation of the silica glass dopants across the fiber cross section through heat treatment and the accurate measurement of the resulting dopant redistribution with SPM and differential etching techniques. The effect of variable annealing along a length of fiber is to produce a mode transformer to couple light from a laser source into the sensing region of the fiber. 相似文献
275.
Gómez Alvarez-Arenas TE 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(6):676-685
This work describes the application of an ultrasonic air-coupled characterization technique to membrane filters. Coefficient of transmission of sound at normal incidence through each membrane in the frequency range 0.55 MHz-2.4 MHz was measured. For all cases, at least one thickness resonance was observed. From these measurements density, velocity, and attenuation of ultrasonic longitudinal waves are calculated and compared to available filtration data such as water flux measurements and bubble point data, both provided by manufacturers. Results show that velocity of ultrasonic waves in membrane filters depends on the membrane grade and can be correlated to filtration properties; attenuation per wavelength is independent of membrane grade but sensitive to moisture content. Advantages of this technique over other conventional membrane tests are pointed out. 相似文献
276.
Sepiolite-PAN intercalation used as Si3N4 forming precursor 总被引:2,自引:0,他引:2
Silicon nitride (Si3N4) formation was investigated using sepiolite and polyacrylonitrile as silicon and carbon source, respectively. It was found that purified sepiolite could readily adsorb a sufficient amount of acrylonitrile (AN) reagent without pre-treatment. Polymerisation of sepiolite-AN mixtures and subsequent cyclization of the polymerised complex yielded a precursor, which was found ideal as a starting material in carbothermal reduction-nitridation (CRN) for the formation of silicon nitride powders. The quantity of silicon nitride, grain size and morphology were found to be dependent on the reaction conditions and starting reagent. Fine grain size, high surface area (up to approx. 12.4 m2/g) powders of mainly -Si3N4 were obtained via pyrolysis of sepiolite-PAN complex after 4 h heating at 1400°C in 1000 ml/min nitrogen flow with a heating rate of 300°C/h. Mg retained in the molecular structure of the mineral must have promoted the formation of -grains in CRN process. 相似文献
277.
The paper deals with the problem of automatic verification of programs working with extended linear linked dynamic data structures,
in particular, pattern-based verification is considered. In this approach, one can abstract memory configurations by abstracting
away the exact number of adjacent occurrences of certain memory patterns. With respect to the previous work on the subject
the method presented in the paper has been extended to be able to handle multiple patterns, which allows for verification
of programs working with more types of structures and/or with structures with irregular shapes. The experimental results obtained
from a prototype implementation of the method show that the method is very competitive and offers a big potential for future
extensions. 相似文献
278.
Mirko Viroli Tom Holvoet Alessandro Ricci Kurt Schelfthout Franco Zambonelli 《Autonomous Agents and Multi-Agent Systems》2007,14(1):49-60
The notion of environment is receiving an increasing attention in the development of multiagent applications. This is witnessed by the emergence of a number of infrastructures providing agent designers with useful means to develop the agent environment, and thus to structure an effective multiagent application. In this paper we analyse the role and features of such infrastructures, and survey some relevant examples. We endorse a general viewpoint where the environment of a multiagent system is seen as a set of basic bricks we call environment abstractions, which (i) provide agents with services useful for achieving individual and social goals, and (ii) are supported by some underlying software infrastructure managing their creation and exploitation. Accordingly, we focus the survey on the opportunities that environment infrastructures provide to system designers when developing multiagent applications. 相似文献
279.
Mahesh Tripunitara Tom Messerges 《Computer》2007,40(2):104-106
Cryptography-based alternatives are the most appropriate long-term solution to the micropayment problem, especially compared to the business solution of restructuring transaction fees. We acknowledge that the business solution is easier to deploy in the short term. Cryptography-based solutions face tremendous deployment challenges: they need more market testing, they significantly change payment-ecosystem processes, their legal implications are unclear, and they require new kinds of devices and processes for merchants. Nonetheless, the long-term payoff of investing in such sound solutions are be tremendous 相似文献
280.
美国PTI公司发明的专利技术JetBOxTM超音速氧枪喷射系统被证明是一种能有效提高电弧炉产量同时又能减少电炉改造成本的技术.通过在各个炼钢电炉上使用这种独特而有效的化学能输入方式从而获得了良好的效果.由于每个电炉的JetBOxTM系统都是专门设计,能满足每个炼钢车间的不同要求,因此已经被成功地应用在用料篮加料的普通电炉、Consteel电炉、使用DRI/HBI的电炉以及热装铁水的电炉上,同样都获得了良好的运行效果.自2001年以来JetBOxTM系统已经在全世界超过60台不同的电炉上安全而有效地运行着,满足了不同钢厂的要求. 相似文献