尖晶石LixMn2O4结构的不稳定性及可能对策

描述了锂离子电池用正极活性物质尖晶石锂锰氧化物锂离子嵌入和脱嵌的三维晶体结构;讨论了这种结构经充放电后不稳定的主要原因;介绍了稳定尖晶石锂锰氧化物结构的几种可能方法。     

尖晶石锂锰氧化物合成温度的选择

用TG、DSC实验结果讨论了以Li2 CO3和电解MnO2 为原料合成尖晶石型LiMn2 O4 的温度选择。用X—射线衍射、循环伏安、恒电流充放电等手段研究了合成样品的性能。TG、DSC实验结果表明 ,电解MnO2 在 5 42℃开始分解成Mn2 O3;Li2 CO3在 6 18℃开始熔融 ,718℃分解 ;Li2 CO3和电解MnO2 的混合物在 70 1℃时形成尖晶石型LiMn2 O4 。据此提出在 2 0 0 ,6 0 0 ,70 1,80 0℃分段保温一定时间的加热程序 ,可以得到纯尖晶石的锂锰氧化物。循环伏安和恒电流充放电结果表明 ,合成的尖晶石锂锰氧化物的充放电机理为锂离子二步嵌入和脱嵌过程     

过量锂尖晶石锂锰氧化物的结构与电化学行为

研究了过量锂锰氧化物,合成产品的结构和电化学性能,XRD结果表明,合成产品Li1 xMn2O4仍属于尖晶石结构,过量的锂进入尖晶石八面体位置。随着尖晶石八面体中锂量的增加,样品的晶胞常数减小,晶体体积收缩,循环伏安实验结果表明,过量锂尖晶石锂锰氧化物仍然保持原来的两步脱嵌锂离子过程,恒电流充放电结果表明,初始容量变化不大,稳定性提高,锂含量为1．03时,容量最高,稳定性最好。     

一些金属阳离子的掺杂对尖晶石LiMn2O4的结构和电化学性质的影响

介绍了Co、Cr、Ni、Cu、Al 5种金属元素的掺杂对尖晶石LiMn2 O4 的结构和 4V区电化学性质的影响 :探讨了掺杂元素增加尖晶石锂锰氧化物 4V区循环稳定性的机理 ;减少了尖晶石在电解液中的溶解量 ;抑制了John Teller效应的发生 ;增加了键强度 ,使得尖晶石结构更加牢固。讨论了掺杂对尖晶石高电位 (>4 5V)区容量的影响 :掺杂后的尖晶石锂锰氧化物仍保持尖晶石结构 ,但与未掺杂的尖晶石锂锰氧化物相比 ,它的晶胞常数减小 ,晶胞体积收缩 ;锰元素的平均化合价升高 ;4V区的初始容量减小 ;循环稳定性明显增加。除Al外 ,Co、Cr、Ni、Cu掺杂后的尖晶石锂锰氧化物均在高电位区有一定的放电容量 ,且随掺杂量的增加而增加。     

铬对尖晶石锂锰氧化物电化学性质的影响

研究了纯尖晶石锂锰氧化物和掺铬尖晶石锂锰氧化物粉末微电极的循环伏安曲线和交流阻抗谱图,结果表明;掺铬样品循环稳定性明显增加,但它的氧化还原峰的位置发生正移,峰形宽化,两步嵌脱锂的量也由相等变为不等,反应电阻增加。     

掺杂钴对锂锰氧化物性能的影响

价廉、低毒的锂锰氧化物已成为目前高能锂离子电池最有潜力的正极材料之一,但其在充放电过程中循环稳定性较差,制约了它的应用前景。通过掺钴改性,锂锰氧化物结构趋于稳定,减缓了容量衰减,改善了循环性能。     

锂离子电池正极材料LiMn2O4的改性研究

为改善尖晶石LiMn2O4的循环性能，采用高温固相法合成了由Li2CO3改性的尖晶石锂锰氧化物，研究了Li2CO3添加量对LiMn2O4性能的影响。通过XRD，Rietveld精细XRD分析和模拟电池等方法对产物的结构和电化学性能进行了表征与测试。结果表明，部分Li进入到尖晶石LiMn2O4的晶格中，增强了材料充放电循环过程中的结构稳定性。随着Li2CO3量的增加，产物的循环稳定性增加。当Li2CO3的加入量为0．06摩尔比时，10次循环后的高温容量衰减由改性前的15％降低到6．8％。     

锂锰氧化物离子筛结构和掺杂研究进展

尖晶石型锂锰氧化物作为一种提锂吸附剂材料具有很好的应用前景，但因其溶损率大的问题，严重阻碍着它的商业化应用。介绍了尖晶石型锂锰氧化物离子筛的结构，指出Mn的溶损和Jahn-teller效应是LiMn2O4溶损的主要原因，重点讨论了通过掺杂改性的方法来抑制Mn的溶损和Jahn-teller效应，从而提高尖晶石结构的稳定性。     

S-Y复合掺杂LiMn2O4的电化学性能研究

用高温固相反应法合成了锂离子电池正极材料锂锰氧化物，并对其进行了硫、钇掺杂厦硫和钇的复合掺杂修饰。对材料进行了X射线衍射、恒电流充放电、交流阻抗等测试。实验结果表明：固相反应法合成的硫和钇复合掺杂的材料具有标准尖晶石结构；掺杂硫其首次放电容量达196．1mAh／g，但容量衰减较快；掺杂钇后正极材料在0．2C充放电速率下，循环20次后容量保持率为98．6％，但是初始容量较低；而硫钇复合掺杂综合了硫掺杂效应和钇掺杂效应，有较好的电化学性能。     

掺铬锂锰氧化物的制备和性能研究

用熔盐法制备出掺铬的尖晶石锂锰氧化物LiCr     

铆螺钢冷镦裂纹形成与消除的研究

通过理化检测,对铆螺钢在冷镦时出现开裂现象的原因进行了分析.结果表明: 铆螺钢在冶炼和浇注过程中生成的复合夹杂物,造成其在冷镦过程中开裂的发生.通过调整连铸前的吹氩工艺和中间包的烘烤工艺,有效地避免了铆螺钢冷镦开裂现象的发生.     

Noise detection during bradycardia pacing with a hybrid nonthoracotomy implantable cardioverter defibrillator system: incidence and clinical significance

The purpose of this study was to prospectively evaluate the incidence of noise detection during bradycardia pacing by an FDA approved hybrid nonthoracotomy ICD system. An illustrative case report which prompted this investigation is provided. Backup bradycardia pacing by tiered therapy cardioverter defibrillators has been useful in preventing postshock bradycardia and occasionally for chronic rate support in bradycardic patients. Unexplained "noise" detected by real-time telemetry has been previously described during bradycardia pacing by a device utilizing automatic gain control for sensing. Eighteen patients were prospectively evaluated for noise detection during ventricular pacing by the ICD. Real-time telemetry was analyzed with each patient: (1) supine, (2) supine with deep inspiration/expiration, (3) supine during Valsalva, and (4) during a change in position from supine to sitting. Analysis of pacing threshold and lead impedance was made in each patient. Eleven of 18 patients had noise detected on real-time telemetry during bradycardia pacing. In 10 patients this was noted during deep inspiration/expiration, in 2 during Valsalva maneuver, and in 5 with position change. There was no evidence in any patient of lead malfunction nor any difference in pacing threshold or lead impedance between patients with noise detected versus those without it. Noise detection by an approved hybrid ICD system is common and may be due to the automatic gain control which maximizes sensitivity during bradycardia pacing. This may lead to clinically significant events, with both suppression of bradycardia pacing and triggering of tachycardia therapy in the absence of ventricular tachyarrhythmias in pacemaker-dependent patients.     

Body composition in children receiving recombinant human growth hormone after renal transplantation

BACKGROUND: Recombinant human growth hormone (rhGH) is an anabolic hormone promoting protein synthesis in various tissues. Therefore, changes in body composition may be expected during rhGH treatment. METHODS: We studied changes in body composition during two years of rhGH treatment in 21 children after at least one year with a functioning renal transplant. The mean +/- SD age was 12.9+/-2.5 years at the start of rhGH therapy. A whole body, dual energy X-ray absorptiometry (DEXA) exam was performed before the initiation of rhGH therapy (T0), and was repeated at one and two year intervals after initiation of the therapy (T1 and T2, respectively). RESULTS: Lean body mass increased by a median of 0.48 SDS during the first year of treatment (P = 0.022), and the median increase during two years of therapy was 0.36 SDS (P = 0.061). On the contrary, the median fat body mass decreased by 2.17 SDS during the T0 to T1 period (P = 0.04) and by 1.99 SDS during the T0 to T2 period (P = 0.055). The index for fat body mass/lean body mass (FBM/LBM) decreased by a median of 5.3% during T0 to T1 (P < 0.001), however, a slower but still significant decrease by a median of 4.2% was noted at T2 (P < 0.05). Bone mass content did not change significantly during rhGH treatment. The medians in caloric and protein intakes were stable during rhGH treatment. CONCLUSION: A significant increase of lean body mass and a decrease of fat body mass was noted during rhGH therapy in children after renal transplantation.     

边部组织及切边工艺对低碳SPHC冷轧边裂的影响

针对迁钢低碳系SPHC热卷在冷轧过程中经常出现边裂缺陷,研究了边裂出现的原因。结果表明,精轧过程中,带钢边部温降过大导致边部出现粗大晶粒并伴有混晶,以及边部剪切参数不匹配导致的切边质量不佳是导致低碳系SPHC冷轧边裂的原因。通过调整精轧冷却水以及合理匹配剪切参数,有效解决了这一缺陷。     

Parental drinking problems and children's adjustment: Vagal regulation and emotional reactivity as pathways and moderators of risk.

Children's emotional regulation (as indexed by vagal suppression) and children's emotional reactivity during an argument were examined as moderators and mediators of parental problem drinking and children's adjustment in a sample of 6- to 12-year-olds. Cardiac vagal tone was assessed during both a baseline condition and exposure to an audiotaped argument. Vagal suppression was calculated by subtracting vagal tone during the baseline from that recorded during the argument, with a higher number representing increased suppression of vagal tone during the argument. Emotional reactivity was based on both observations of overt behaviors of children and their reported feelings during the argument. A higher level of vagal suppression was a protective factor against children's externalizing, internalizing, and social problems associated with exposure to parental problem drinking. Emotional reactivity was a vulnerability factor, and children's increased anger and fear, and to a lesser degree sadness, each moderated and exacerbated the effects of parental problem drinking on child outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Secondary structure of sea anemone cytolysins in soluble and membrane bound form by infrared spectroscopy

We investigated the effects of muscle mass and contraction intensity on the cardiorespiratory responses to static exercise and on the contribution afforded by muscle metaboreflex and arterial baroreflex mechanisms. Ten subjects performed static handgrip at 30% maximal voluntary contraction (MVC) (SHG-30) and one-leg extension at 15% (SLE-15) and 30% (SLE-30) MVC, followed by postexercise circulatory occlusion (PECO). Mean arterial pressure (MAP) and heart rate (HR) responses were greater during SLE-30 than during SHG-30. The difference in MAP was maintained by PECO, and the part of the pressor response maintained by PECO was greater after SLE-30 than after SHG-30 (88.3 +/- 10.6 and 67.8 +/- 12.7%, respectively, P = 0. 02). There were no differences in MAP and HR responses between SHG-30 and SLE-15 trials. Baroreflex sensitivity was maintained during SHG-30 and SLE-15, whereas it was significantly reduced during SLE-30 and recovered back to the resting level during PECO. Minute ventilation and oxygen uptake increased more during SLE-30 than during both SHG-30 and SLE-15 trials. Minute ventilation remained significantly elevated above rest only during PECO following SLE-30. These data suggest that during static exercise the muscle mass and contraction intensity affect 1) the magnitude of the cardiorespiratory responses, 2) the contribution of muscle metaboreflex to the cardiorespiratory responses, and 3) the arterial baroreflex contribution to HR control.     

Hot and warm forming of 2618 aluminium alloy

The hot and warm formability of 2618 aluminium alloy, in the as-solutioned condition, was investigated in extended ranges of temperature and strain rate by means of torsion testing. Precipitation was found to occur during deformation. The effect of the precipitation of second phase particles, occurring during deformation, on the flow curve shape and on the stress level was evaluated. At the lowest temperatures, precipitation, during deformation, resulted in a continuous increase of flow stress; by contrast, when testing temperature exceeded 250 °C, precipitation and subsequent coarsening of precipitates, during deformation, resulted in a peak of flow curves, followed by softening. The constitutive equations of the material were calculated and the ductility of the alloy was evaluated as strain to fracture values in all the tested condition.     

Auditory stimulus detection is not suppressed during saccadic eye movements

Auditory detection and pitch discrimination thresholds were measured during saccades and during periods of fixation. The accuracy of auditory localisation under these two conditions was also measured. These thresholds were unaffected by whether the sound was presented during a saccade or during periods of steady fixation: there is no evidence for saccadic suppression of auditory processing.