Transfer Functions of the Slip-Controlled Induction Machine

The use of a feedback loop to regulate the slip frequency of an inverter-driven induction machine is viewed as replacing the normal independent control of stator frequency with independent control of slip frequency. For steady-state conditions the two modes of operation are shown to produce characteristics analogous to shunt and series dc machines. A method employing closed-form transfer functions, a reduced set of nondimensional parameters, and a general root locus diagram is used to present the dynamic characteristics of controlled slip frequency operation and to compare performance with conventional operation. The parameter range in the general diagram is sufficient to incorporate nearly all standard induction machines over a wide size and frequency range. The results demonstrate that the ratio K? of the rotor transient time constant to the static electromechanical time constant is a critical parameter in the comparison of the two modes. Since this parameter tends to increase with machine size, the relative advantages of slip frequency control are shown to be machine-size dependent. Inclusion of a speed-control loop regulating machine voltage is also Considered and shown to be described by the same general root loci. The performance of this closed-loop system is also shown to be very dependent on K? and hence on machine size.     

聚羧酸减水剂在水泥和泥土表面的吸附行为

采用有机碳测定仪研究了水泥、泥土和水体系中聚羧酸减水剂吸附量与吸附时间、减水剂浓度、体系温度的关系。同时,对减水剂吸附模型和吸附热进行了分析,探讨了聚羧酸减水剂在水泥、泥土颗粒表面的吸附特性。结果表明:水泥和泥土对聚羧酸减水剂的吸附量随时间延长不断增加,最后达到平衡,同时,泥土比水泥对减水剂的吸附量要大,泥土的掺入量为0.5%就会大大降低水泥净浆的流动度;聚羧酸减水剂的吸附基本符合Langmuir等温吸附模型,水泥和泥土对减水剂的饱和吸附量分别为3.7mg/g和10.1mg/g;水泥和泥土对聚羧酸减水剂的吸附量随温度的增大而减小,其吸附是一个放热过程。     

The crystal state binding of dithionite to deoxy-hemoglobin

The crystal state binding of sodium ditbionite to deoxyhemoglobinis reported. Dithionite has been used extensively to deoxygenatehemoglobin and myoglobin and there has been considerable interestamong users of dithionite about its effect on protein structureand binding site(s). We have determined that dithionite bindsto deoxygenated hemoglobin crystals at the interface of twomolecules in the crystal lattice. Specific residues involvedin hydrogen bonds or salt interactions with dithionite includeHisll6 and Hisll7 of the ft subunit and Lysl6 of the ß₂subunit of the adjacent hemoglobin molecule. No binding wasobserved at the symmetry related Hisll6 and 117 ß1 residues.We have shown that dithionite does not affect the native hemoglobinstructure or the binding of several allosteric inhibitors tohemoglobin and can be used to mount T state crystals in theair     

表现出良好带束层边缘粘合性能的冠带层新材料

本文介绍了加工助剂莱茵塑分T和增塑剂A在全钢载重子午线轮胎胎面配方中的胶料性能对比，并着重考察了对胎面挤出性能和外胎性能的影响。试验结果表明，使用加工助剂能降低胎面的挤出温度，提高胎面的挤出速度；两种加工助剂相比，含莱茵塑分T的胶料老化性能、疲劳性能和分散性以及胎面挤出温度和断面气孔情况均比增塑剂A好；外胎的耐久试验均超过国家标准。     

Gas separation performance of 6FDA-based polyimides with different chemical structures

This work reports the gas separation performance of several 6FDA-based polyimides with different chemical structures, to correlate chemical structure with gas transport properties with a special focus on CO₂ and CH₄ transport and plasticization stability of the polyimides membranes relevant to natural gas purification. The consideration of the other gases (He, O₂ and N₂) provided additional insights regarding effects of backbone structure on detailed penetrant properties. The polyimides studied include 6FDA-DAM, 6FDA-mPDA, 6FDA-DABA, 6FDA-DAM:DABA (3:2), 6FDA-DAM:mPDA (3:2) and 6FDA-mPDA:DABA (3:2). Both pure and binary gas permeation were investigated. The packing density, which is tunable by adjusting monomer type and composition of the various samples, correlated with transport permeability and selectivity. The separation performance of the polyimides for various gas pairs were also plotted for comparison to the upper bound curves, and it was found that this family of materials shows attractive performance. The CO₂ plasticization responses for the un-cross-linked polyimides showed good plasticization resistance to CO₂/CH₄ mixed gas with 10% CO₂; however, only the cross-linked polyimides showed good plasticization resistance under aggressive gas feed conditions (CO₂/CH₄ mixed gas with 50% CO₂ or pure CO₂). For future work, asymmetric hollow fibers and carbon molecular sieve membranes based on the most attractive members of the family will be considered.     

Contribution of Charge to Powder Particle Adhesion

We have measured the charge on gold particles attached to the surfaces of beads and found 22 × 10^?15 Coul/particle on these 30 micron particles. In other dusts we had seen charges from 1–70 × 10^?15 Coul/particle attached to similar surfaces. The attachment forces of 0.1–1 dyne reported for gold particles on metal surfaces could be produced by the particle's charge if a suitably thin (～ 100Å) oxide layer insulated the particle's charge from the metal surface. Our gold contained tarnish layers which are both friable and fritable and appear to be suitably thin.

St. John and Montgomery⁵ report the angle of the applied removal force is critical in determining the detachment of particles. We confirm this, but our surface coverage was high enough to allow avalanches to form which complicate the interpretation of the angular phenomena.     

Flexible Backbone Aromatic Polyimide Adhesives

Continuing research at Langley Research Center on the synthesis and development of new inexpensive flexible aromatic polyimides as adhesives has resulted in a material identified as LARC-F-SO₂ with similarities to polyimidesulfone (PISO₂) and other flexible backbone polyimides recently reported by Progar and St. Clair. Also prepared and evaluated was an endcapped version of PISO₂. These two polymers were compared with LARC-TPI and LARC-STPI, polyimides researched in our laboratory and reported in the literature.

The adhesive evaluation, primarily based on lap shear strength (LSS) tests, involved preparing adhesive tapes, conducting bonding studies and exposing lap shear specimens to 204°C air for up to 1000 hrs and to a 72-hour water boil. LSS tests at RT, 177°C and 204°C were performed before (controls) and after these exposures. The type of adhesive failure as well as the Tg was determined for the fractured specimens.

The results indicate that LARC-TPI provides the highest LSSs, 33 MPa at RT, 30 MPa at 177°C, and 26 MPa at 204°C. LARC-F-SO₂, LARC-TPI and LARC-STPI all retain their strengths after thermal exposure for 1000 hrs and PISO₂ retains greater than 80% of its control strengths.

Most of the four adhesive systems showed reduced strengths for all test temperatures although they still retained a high percentage of their original strength (<60%) except for one case.

The predominant failure mode was cohesive with no significant change in the Tgs.

Although the LARC-F-SO₂ could not be prepared in diglyme alone as the solvent, the properties of the resulting adhesive were notable. The darkening of the adhesive during bonding was typical of systems which utilize amide solvents.     

Electron Transfer Reactions in Pulping Systems (III): A Study of Steric Effects in Lignin Model/Aq Reactions

Abstract

The reactions of five B-aryl ether lignin model dimers with three anthrahydroquinone (AHQ) analogs have been studied. Some of the models and AHQ analogs have bulky substituents strategically located in positions which would possibly inhibit adduct reactions but not single electron transfer (SET) reactions. The fact that the model fragmentation efficiencies were the same for both steri-cally hindered and unhindered AHQ analogs indicates that the reaction mechanism cannot involve a rate determining adduct formation step. The results can be best explained either by an SET mechanism or a mechanism which involves quinoneraethide generation as a slow step, followed by adduct, SET, or other steps. Placing methyl groups on the S-carbon of the models favored model fragmentation reactions by NaOH. The B-methyl group may be promoting fragmentation reaction rates and/or retarding the rates of competing side reactions, such as vinyl ether generation.     

NO x and VOC Control and Its Effects on the Formation of Aerosols

This research analyzes the qualitative and quantitative behavior of aerosol dynamics resulting from the control of nitrogen oxide (NO x ) and volatile organic compound (VOC) emissions by calculating detailed pollutant isopleths. Several emission scenarios are evaluated using various norms to study the nonlinear impact of control strategies. The modeling episode studied is the Southern California Air Quality Study on August 27, 28, and 29, 1987. The modeling domain is the South Coast Air Basin of California. Research suggests that the reduction of NO x and VOC emissions traditionally implemented to control ozone also controls particulate matter, but to a limited extent. Furthermore, the effects of reducing NH 3 are more effective in PM control than reducing both NO x and VOC. Simulations indicate that the combined control of NH 3 , NO x , and VOC emissions is most effective to reduce particulate matter and ozone in the South Coast Air Basin of California.