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121.
X.500 is a new and complex electronic directory technology that is still unproven in many organizations. The author presents case studies of 15 pioneering pilot and operational X.500 based directory services, and provides valuable insights into how organizations are coming to understand this new technology and derive benefits from it. The case studies presented cover a reasonably broad spectrum of organizations, including computer suppliers, government organizations, universities, and research institutes, as well as the UK and US defense community. Some of the factors that were critical to the success of the X.500 projects studied are identified 相似文献
122.
This paper proposes a sensorless speed measurement scheme that improves the performance of transducerless induction machine drives, especially for low-frequency operation. Speed-related harmonics that arise from rotor slotting and eccentricity are analyzed using digital signal processing. These current harmonics exist at any nonzero speed and are independent of time-varying parameters, such as stator winding resistance. A spectral estimation technique combines multiple current harmonics to determine the rotor speed with more accuracy and less sensitivity to noise than analog filtering methods or the fast Fourier transform. An on-line initialization routine determines machine-specific parameters required for slot harmonic calculations. This speed detector, which has been verified at frequencies as low as 1 Hz, can provide robust, parameter-independent information for parameter tuning or as an input to a sensorless flux observer for a field-oriented drive. The performance of the algorithm is demonstrated over a wide range of inverter frequencies and load conditions 相似文献
123.
This paper provides a preliminary examination of present and projected land use in Africa to estimate the potential availability of land in 2025 for use in producing biomass energy. Fifty countries are included in the analysis. Future cropland requirements are projected on the basis of average African cereal crop yield improvements since 1972, and minimum nutritional requirements are assumed to be met in 2025 without increasing imports above present absolute levels. Cropland, natural forests and other wilderness areas are excluded from consideration for biomass energy use. Woody biomass energy yields are estimated on the basis of nationally averaged precipitation, using a yield-precipitation correlation for commercial eucalyptus plantations in Brazil. The total African bioenergy production potential in 2025 is estimated to be about 18 EJ per year for a set of baseline assumptions that includes planting only 10% of the available non-crop, non-forest, non-wilderness area with biomass energy crops. A preliminary cost assessment suggests that much of this biomass could be produced for $1–2 GJ−1. A number of uncertainties in the modelling assumptions are examined through a sensitivity analysis. Despite limitations in the model used here, one robust conclusion is that Africa as a whole has a significant biophysical potential for producing biomass energy. This result suggests that more detailed country and sub-country level assessments would be worthwhile to understand better the practical prospects for future biomass energy production in Africa. 相似文献
124.
125.
126.
The effect of na and Sr modification on surface tension and volumetric shrinkage of A356 alloy and their influence on porosity formation 总被引:2,自引:0,他引:2
D. Emadi J. E. Gruzleski J. M. Toguri 《Metallurgical and Materials Transactions B》1993,24(6):1055-1063
Modification of the eutectic Si in Al-Si foundry alloys by adding strontium or sodium is, unfortunately, accompanied by an
increase of porosity in the casting. In an attempt to understand the nature of this problem, this study used a sessile-drop
method to investigate the effect of Sr and Na on surface tension and volumetric shrinkage, two probable causes of porosity
occur-rence. The addition of 0.01 wt pct Sr and 0.005 wt pct Na to A356 alloy decreases the surface tension of the liquid
by about 19 and 10 pct, respectively, and may increase the volume shrink-age by about 12 pct. These changes to surface tension
and volumetric shrinkage promote the early formation of the pores during solidification and give the availability of a longer
period of growth prior to complete solidification, resulting in a larger pore size. The effect of surface tension on the pores
is more significant than volumetric shrinkage. Although the predicted pore diameter increases with lower surface tension or
higher volumetric shrinkage, these two effects alone do not seem able to completely account for the observed increase in porosity
that is associated with modification. 相似文献
127.
Recent work concerning the interstitial modification of permanent magnet alloys based on rare-earth iron intermetallic compounds is reviewed. The crystal structure of the new materials is discussed, then the thermodynamic and statistical aspects of the low-temperature interstitial modification process are considered. Finally, reaction kinetics and thermal stability of the new compounds are discussed and future prospects assessed. 相似文献
128.
JE Myers T Mieczkowski J Perel D Abbondanza TB Cooper JJ Mann 《Canadian Metallurgical Quarterly》1994,35(2):112-120
Serotonergic responsivity was assessed in 20 psychiatric patients by the prolactin response to a fenfluramine challenge test. During the fenfluramine challenge 6 of 20 patients (30%) spontaneously reported psychopathologic reactions that included: increased anxiety/agitation, psychotic symptoms, illusions, mood elevation, and anergia. The time of peak behavioral symptoms (2.5 +/- 0.8 hrs) corresponded closely to the time of peak increase in prolactin levels (3.0 +/- 1.1 hr). Abnormal behavioral responders had statistically significant greater increases in prolactin 1 to 4 hr after fenfluramine when compared to normal responders. Patients who developed an abnormal psychopathologic response to fenfluramine were characterized by higher levels of anxiety and agitation at the time of admission to the hospital but otherwise were not distinguishable on the basis of severity of other psychiatric symptoms. This study suggests that increased serotonergic transmission may trigger anxiety, psychosis, and mood elevation in specific vulnerable individuals, whereas other patients with similar psychiatric illnesses are not affected. 相似文献
129.
Cheng-Hsiung Lid Shou-Chiung Chen Yung-Chi Lee Theodore D. Sokoloski Ming-Thau Sheu 《Drug development and industrial pharmacy》1994,20(11):1911-1922
Polyvinylpyrrolidone (PVP) in aqueous solution was used as a binding agent in a fluidized-bed system to agglomerate acetaminophen powder into directly compressible granules. It was found that a minimal amount of 5% w/w PVP in a concentration of 7.5% w/v or less was needed to produce granules with an acceptable flow and the corresponding tablets having enough hardness without capping. There was a strong correlation between the time for 80% dissolved (T80) and the logarithm of granule volume-surface mean diameter. A directly compressible acetaminophen composition to manufacture tablets having a T80 value less than 30 min can be prepared simply by adding an appropriate amount of disintegrant (crospovidone, sodium starch glycolate, or pregelatinized starch) to the agglomerated granules. 相似文献
130.
N. Balchev D. Kovacheva V. Lovchinov K. Konstantinov K. Petrov 《Journal of Superconductivity》1993,6(1):49-54
The preparation conditions, phase composition, and superconducting properties of Bi-Pb-Sr-Ca-Cu oxide materials from different nominal compositions have been investigated. Nearly single-phase samples from Bi2Pb0.4Sr2Ca3Cu4O
y
, as well as from the proposed compositions Bi1.8Pb0.4Sr2Ca3Cu4O
y
and Bi1.8Pb0.4Sr2Ca2.5Cu3.5O
y
were obtained by a solid-state reaction in air. Samples with the third nominal composition showed the best superconducting properties (T
on=111 K and zero resistance atT
0=103 K). A possible mechanism for the 2223 phase formation in the three investigated compositions has been discussed. 相似文献