滑线变阻器的安全选用

滑线变阻器的两个额定值是最大电阻和最大电流。变阻器在电路中常用来分压,超过额定值,变阻器可能损坏。例1.电源电压为220V,且恒定,用120Ω,1.5A的变阻器,串一切率足够大,阻值为100Ω的电阻R_2,如图1。

Mode II fracture analysis of double edge cracked circular disk subjected to different diametral compression

A detailed analysis of mode II stress intensity factors(SIFs) for the double edge cracked Brazilian disk subjected to different diametral compression is presented using a weight function method. The mode II SIFs at crack tips can be obtained by simply calculating an integral of the product of mode II weight function and the shear stress on the prospective crack faces of uncracked disk loaded by a diametral compression. A semi-analytical formula for the calculation of normalized mode II SIF, f _Ⅱ, is derived for different crack lengths (from 0.1 to 0.7) and inclination angles (from 10° to 75°) with respect to loading direction. Comparison between the obtained results and finite element method solutions shows that the weight function method is of high precision. Combined with the authors previous work on mode I fracture analysis, the new specimen geometry can be used to study fracture through any combination of mode I and mode II loading by a simple alignment of the crack relative to the diameter of compression loading, and to obtain pure mode II crack extension. Another advantage of this specimen geometry is that it is available directly from rock core and is also easy to fabricate.

Density, Viscosity, and Excess Properties for Binary Mixture of Diethylene Glycol Monoethyl Ether ＋ Water from 293.15 to 333.15 K at Atmospheric Pressure

Densities and viscosities were measured as a function of composition for binary liquid mixture of diethylerie glycol monoethyl ether [CH3CH2O（CH2）2O（CH2）2OH] ＋ water from 293.15 to 333.15 K at atmospheric pressure, with a capillary pycnometer and Ubbelohde capillary viscometer respectively. From the experimental data, the excess molar volume V^E, viscosity deviation △η, and the excess energy of activation for viscous flow △G^＊E were calculated. These data were correlated by the Redlich-Kister type equations to obtain the coefficients and standard deviations. The results showed a strong molecular interaction between diethylene glycol monoethyl ether and water.

Novel Control Structure Design of Differential Pressure Thermally Coupled Reactive Distillation for Methyl Acetate Hydrolysis

In this paper, the novel control structures of differential pressure thermally coupled reactive distillation process for methyl acetate hydrolysis were proposed. The RadFrac module of Aspen Plus was adopted in the steady-state simulation. Sensitive analysis was applied to find the stable intial value and provide a basis for the improved control structure design. The Aspen Dynamics software was adopted to study the process dynamic behaviors, and two novel control structures provided with feed ratio controllers and sensitive tray temperature controllers were proposed. The reflux ratio controllers were applied in the improved novel control structures. Both control structures abandoned the composition controllers that were replaced by simpler controllers with which the product purity could meet the specification requiring under a ± 20% disturbance to the total feed flowrate / MeAc composition.

Potential Connection between the Australian Summer Monsoon Circulation and Summer Precipitation over Central China

This study investigated the connection between the Australian summer monsoon(ASM) and summer precipitation over central China. It was found that,following a weaker-than-normal ASM, the East Asian summer monsoon and western North Pacific subtropical high tend to be stronger, yielding anomalous northward moisture to be transported from the western Pacific to central China. Besides, anomalous upwelling motion emerges over 30–37.5°N, along 110°E. Consequently,significant positive summer precipitation anomalies are located over central China. Further analysis indicated that the boreal winter sea surface temperature(SST) in the Indian Ocean and South China Sea shows positive anomalies in association with a weaker-than-normal ASM. The Indian Ocean warming in boreal winter could persist into the following summer because of its own long memory, emanating a baroclinic Kelvin wave into the Pacific that triggers suppressed convection and an anomalous anticyclone. Besides, the abnormal SST signal in the South China Sea develops eastward with time because of local air-sea interaction, causing summer SST warming in the western Pacific. The SST warming can further affect East Asian atmospheric circulation and precipitation through its impact on convection.

Pressure-induced changes in the magnetic properties of the single crystal of Mn_3 single-molecule magnet

The magnetic measurements of the single crystal of Mn3 single-molecule magnet under high pressure at T=2 K have been performed.We find both the antiferromagnetic intermolecular coupling parameter J and the effective energy barrier to vary compared with the measurements at low pressure.The increase of|J|is estimated to be 12%at 0.7 GPa when compared with that of0 GPa,whereas the effective energy barrier becomes smaller with increasing pressure.Our results demonstrate that the intermolecular interaction of single-molecule magnet can be changed by pressure.Compared with the normal magnetic alloy,the effect of pressure on the magnetic properties of Mn3 is much more prominent,which implies that Mn3 may have great potential in magnetic multifunctional material.

Protective effect of ischemic postconditioning on lung ischemia-reperfusion injury in rats and the role of heme oxygenase-1

Objective： To investigate the effect of ischemic postconditioning （1PO） on acute lung ischemia-reperfusion （I/R） injury and the protein expression of haeme oxygenase-1 （HO-1）, a cytoprotective defense against oxidative injury. Methods： After being anesthetized with chloralhydrate, forty-eight healthy SD rats were randomly divided into 6 groups （8 in each）： sham operation group （S group）; I/R group： left lung hilum was clamped for 40 minutes followed by 105 minutes of reperfusion; IPO group： left lung hilum was clamped for40 minutes and postconditioned by 3 cycles of 30 seconds of reperfusion and 30 seconds of reocclusion; Heroin （HM）＋ I/R group： heroin, an inducer of HO-1 was injected intraperitoneally at 40 μmol·kg^-1·day^-1 for two consecutive days prior to 40 minutes clamping of left lung hilum; ZnPPIX＋IPO group： zinc protoporphyrin IX, an inhibitor of HO-1 was injected intraperitoneally at 20 mg·kg^-1 24 hours prior to 40 minutes clamping of left lung hilum; and HM＋S group： HM was administered as in the HM＋I/R group without inducing lung I/R. Arterial partial pressure of oxygen （PaO2） and malondialdehyde （MDA） content in serum were assessed. The left lung was removed for determination of wet/dry lung weight ratio and expression of HO-1 protein by immuno-histochemical technique and for light microscopic examination. Results： The PaO2 was significantly lower in all the experimental groups compared with sham group （90 roan Hg ±11 mmHg）. However, the values of PaO2in IPO （81 mm Hg±7 mm Hg） and HM＋I/R （80 mm Hg±9 mm Hg） were higher than that in I/R （63 mm Hg±9 mm Hg） and ZnPPIX＋IPO （65 mm Hg±8 mm Hg） groups （P〈0.01）. The protein expression of HO- 1 in lung tissue was significantly increased in I/R group compared with S group （P〈0.01）. While the HO-1 protein expression was higher in IPO and HM＋I/R groups as compared with I/R group （P〈0.05, P〈0.01 ）. The lung wet/ dry （W/D） weight ratio and MDA content in serum were significantly increased in I/R group as compared with S or HM＋S groups （P〈0.01）, accompanied by severe lung tissue histological damage, which was attenuated either by IPO or by HM pretreatment （P〈0.01, IPO or HM＋I/R vs. I/R）. The protective effect of IPO was abolished by ZnPPIX. Conclusion： Ischemic postconditioning can attenuate the lung ischemia-reperfusion injury through upregulating the protein expression of HO-I that leads to reduced postischemic oxidative damage.

Dynamics of the Manakov Solitons in Biased Guest-Host Photorefractive Polymer

In the biased guest-host photorefractive polymer, the Manakov equations can be used to describe the op- tical soliton propagation and interaction. Hereby for such equations, via the Hirota method and syrnbolic computation, analytic soliton solutions in the bright-dark and dark-dark forms are obtained. Based on the choice of photorefrac- rive polymer parameter and incident-optical-beam parameter, the bright-dark and dark-dark solitons as well as their interaction can occur in the polymer when the total intensity is much lower than the background illumination, and our analysis indicates that the incident light with different polarization directions influence little on the soliton propagation. ~, representing the soliton intensity far away from the soliton center, determines the appearance of bright or dark soliton under the background illumination. Through the graphic and asymptotic analysis on the two-soliton solutions along with the different ~, we find that there exist the elastic and inelastic interactions between the bright-dark solitons, while the interactions between the dark-dark solitons are always elastic.