A survey of recent advances in magnetic recording materials

Magnetic recording coatings are still made predominantly of iron oxide particles but the newer particles are significantly better in magnetic properties, dispersibility and orientability than the particles used, say, ten years ago. Chromium dioxide particles show excellent recording performance (particularly at densities above 1000 flux changes per millimeter) but they are presently being challenged by the new cobalt-modified iron oxides. These are formed by diffusing cobalt into the surface of acicular iron oxide particles and it is claimed that the particles prepared in this way are much more stable with respect to temperature and stress than the older cobalt-substituted iron oxides. Metal particles, by virtue of their high moment density and high coercivity, would be ideal for high density recording if they could be passivated permanently. The paper reviews improvements which have been made within the last nine years in the properties of particles for magnetic recording applications and discusses how the improvements were effected.     

变电站风冷变压器冷却器全停故障分析

某220 kV变电站切换站用变压器,约1 h后主变压器三侧断路器跳闸,主变压器“冷却器故障”告警灯亮。综合分析,此次故障主要原因是变压器切换后,风控箱电源接触器未可靠吸合,即主电源KM1交流控制器和备用电源KM2交流控制器下口失电。通过对冷却装置保护回路进行改造,即增加“冷却器全停”和“备用冷却器故障”2个中央信号,实现冷却器全停后经短延时上传远方中央信号,经定值要求延时20 min或60 min后出口跳闸。改造后问题得到了解决。     

Comparative analysis and performance of two predictive fadedetection schemes for Ka-band fade countermeasures

The design of Ka-band satellite fade countermeasure (FCM) systems is conditioned by the detection/prediction algorithm to be included within practical DSP-based FCM controllers. It depends upon the ability of systems to efficiently integrate the dynamic and stochastic nature of the Ka-band fading process which is dominated by rain attenuation and amplitude scintillation. The paper analyzes the modeling and statistical performance of two predictive fade detection algorithms. Prediction is introduced as a way to minimize the impact of the finite response time on the BER/throughput of practical FCM systems. Both fixed (FDM) and variable (VDM) detection margin strategies are introduced and compared in terms of their margin requirements, FCM utilization factor, and channel capacity utilization. The VDM is shown to be more efficient than its fixed counterpart. The long-term BER availability and average user data throughput of a VDM/fixed-FEC/adaptive transmission rate FCM are then evaluated for a typical low-power low-rate Ka-band in-bound VSAT link     

Cancer‐Cell‐Specific Induction of Apoptosis Using Mesoporous Silica Nanoparticles as Drug‐Delivery Vectors

Targeted delivery of the chemotherapeutic agent methotrexate (MTX) to cancer cells using poly(ethyleneimine)‐functionalized mesoporous silica particles as drug‐delivery vectors is reported. Due to its high affinity for folate receptors, the expression of which is elevated in cancer cells, MTX serves as both a targeting ligand and a cytotoxic agent. Enhanced cancer‐cell apoptosis (programmed cell death) relative to free MTX is thus observed at particle concentrations where nonspecific MTX‐induced apoptosis is not observed in the nontargeted healthy cell line, while corresponding amounts of free drug affect both cell lines equally. The particles remain compartmentalized in endo‐/lysosomes during the time of observation (up to 72 h), while the drug is released from the particle only upon cell entry, thereby inducing selective apoptosis in the target cells. As MTX is mainly attached to the particle surface, an additional advantage is that the presented carrier design allows for adsorption (loading) of additional drugs into the pore network for therapies based on a combination of drugs.     

Dynamic grain growth and particle coarsening in Al–3.5Cu

Grain growth and particle coarsening in Al–3.5Cu at a temperature of 450 °C has been studied. Plastic deformation of this Zener-pinned system at strain rates of 10^?3 and 10^?4 s^?1 led to an increase in both the grain growth and particle coarsening rates. The results of mechanical tests and metallography, including in situ studies, showed that the material was deforming primarily by intragranular slip. The dynamic grain growth was ascribed to the geometric effect of deformation on the Zener pinning, and the rate sensitivity of the growth to the dynamic particle coarsening. The principal effect of deformation on particle coarsening was concluded to be increased diffusion due to the dislocation content.     

Inhibition of tumour necrosis factor (TNF) production by antimalarial drugs used in cerebral malaria

A pseudoaneurysm after percutaneous coronary angioplasty (PTCA) of the left anterior descending coronary artery is reported in a 52-year-old woman who underwent PTCA for exertional angina and a significant isolated stenosis of the left anterior descending coronary artery. Intravascular ultrasonography during repeat coronary angiography clearly identified a localized coronary dilation at the PTCA site in conventional coronary angiography as a pseudoaneurysm that was confirmed during surgery.     

Plastic anisotropy in a superplastic Al-Li-Mg-Cu alloy

The plastic anisotropy of AA8090 Al-Li-Cu-Mg alloy sheet has been evaluated by tensile testing and by deep drawing at temperatures in the range 200 °C to 525 °C. At temperatures of about 500 °C and strain rates of about 10^-3 s^-1, this material exhibits a high strain-rate sensitivity of flow stress which reduces any tendency to strain localization in stretching and allows so-called superplastic forming of the sheet. Most models of the material behavior in this regime require highly inhomogeneous deformation on the scale of the material’s grain size. The plastic anisotropy measured in the superplastic regime was similar in form, though of reduced magnitude, to that measured under conditions associated with a much smaller strain-rate sensitivity. Homogeneous slip models predict the correct form of anisotropy, and inclusion of slip-rate senitivity can reduce the magnitude of anisotropy predicted but not sufficiently to give good correlation with the experimental results unless very high values are used. The development of the preferred crystallographic orientation in deep drawing has also been examined. The predictions of homogeneous slip models correlate quite well with experimental results at low temperatures, but the situation is more complex in the superplastic regime where, although there is some evidence of texture changes as predicted, there is a general reduction in the intensity of preferred orientation with deformation. However, the results indicate that a greater contribution of homoeneous slip deformation is involved in superplastic deformation than is assumed in some models of superplasticity.     

Evolution of matt surface topography in aluminium pack rolling. Part II: effect of material properties

A model has been presented in a companion paper [1] to predict the generation of roughness on the matt surface in pack rolling of aluminium foil. The model is based on the finite element method using isotropic plasticity. This model is used in the current paper to investigate the effect of material properties on the generation of surface roughness. There is a large inhomogeneity of strain during deformation, with harder grains generally deforming less than softer ones. It is found that the roughness amplitude is roughly proportional to the standard deviation of the initial grain yield stress distribution, normalised by the initial mean yield stress, so that a wider distribution of the initial yield stress results in greater surface roughness. It is shown that a suitable linear hardening law can be used to approximate the roughening behaviour for real material flow stress curves.