Polyphenolic glycosides and aglycones utilize opposing pathways to selectively remodel and inactivate toxic oligomers of amyloid β

Substantial evidence suggests that soluble prefibrillar oligomers of the Aβ42 peptide associated with Alzheimer's disease are the most cytotoxic aggregated Aβ isoform. Limited previous work has revealed that aromatic compounds capable of remodeling Aβ oligomers into nontoxic conformers typically do so by converting them into off-pathway aggregates instead of dissociating them into monomers. Towards identifying small-molecule antagonists capable of selectively dissociating toxic Aβ oligomers into soluble peptide at substoichiometric concentrations, we have investigated the pathways used by polyphenol aglycones and their glycosides to remodel Aβ soluble oligomers. We find that eleven polyphenol aglycones of variable size and structure utilize the same remodeling pathway whereby Aβ oligomers are rapidly converted into large, off-pathway aggregates. Strikingly, we find that glycosides of these polyphenols all utilize a distinct remodeling pathway in which Aβ oligomers are rapidly dissociated into soluble, disaggregated peptide. This disaggregation activity is a synergistic combination of the aglycone and glycone moieties because combinations of polyphenols and sugars fail to disaggregate Aβ oligomers. We also find that polyphenolic glycosides and aglycones use the same opposing pathways to remodel Aβ fibrils. Importantly, both classes of polyphenols fail to remodel nontoxic Aβ oligomers (which are indistinguishable in size and morphology to Aβ soluble oligomers) or promote aggregation of freshly disaggregated Aβ peptide; thus revealing that they are specific for remodeling toxic Aβ conformers. We expect that these and related small molecules will be powerful chemical probes for investigating the conformational and cellular underpinnings of Aβ-mediated toxicity.     

驱动频率对超磁致伸缩致动器的损耗和温升特性的影响

从超磁致伸缩材料的压磁效应入手,基于能量极小值条件和磁学理论,分析了磁化过程中磁弹性力对材料中磁场的影响,分析了不同驱动频率下材料的涡流损耗、磁滞损耗以及复数磁导率的频率特性,对致动器中的磁能损耗以及损耗带来的温升特性进行仿真实验.结果表明,利用涡流损耗的计算公式得到的结果与有限元仿真结果吻合较好,该公式可适用于超磁致伸缩材料在中低频下的损耗计算,而高频下复数磁导率的变化将增大材料内部磁场的滞回非线性.实验结果表明,致动器中超磁致伸缩材料轴向温度分布随驱动频率的变化而变化;实验验证了计算与仿真结果的正确性,在此基础上分析了强制水冷对致动器温升的控制,所得结论为超磁致伸缩致动器的设计提供参考.     

超磁致伸缩致动器热变形影响及温控研究

在分析超磁致伸缩致动器热变形影响的基础上，结合实验论证，构建了在大电流、长时间且高精度场合下能对致动器进行整体温控的装置。设计并制作了一台超磁致伸缩致动器样机，在其电磁线圈的骨架中设置了内外两个水冷腔。通过恒温水的循环流动，带走线圈热量，以控制磁致伸缩棒和壳体的温度。进行了多组热变形对比实验，结果表明，致动器的整体温控装置有效地抑制了致动器的热变形影响，适合于大电流、高精度场合。     

超磁致伸缩伺服阀用伺服放大器的设计及分析

为驱动超磁致伸缩伺服阀,结合超磁致伸缩执行器驱动电源与伺服阀用伺服放大器的性能要求设计了超磁致伸缩伺服阀用伺服放大器,并建立了其电路模型,仿真分析了功率运算放大器的开环增益对其输出性能的影响.仿真结果表明,在功率运算放大器开环增益大于80 dB时,电路特性可满足设计要求.在驱动负载为额定值时,测试结果表明,样机的输出电流线性度为3％;输出电流2A时,其阶跃响应的调节时间小于0.5 ms,幅频宽可达2 kHz;在驱动频率小于1 kHz时,输出电流失真小且无相位滞后.     

A Nonvolatile Spintronic Memory Element with a Continuum of Resistance States

A continuum of stable remanent resistance states is reported in perpendicularly magnetized pseudo spin valves with a graded anisotropy free layer. The resistance states can be systematically set by an externally applied magnetic field. The gradual reversal of the free layer with applied field and the field‐independent fixed layer leads to a range of stable and reproducible remanent resistance values, as determined by the giant magnetoresistance of the device. An analysis of first‐order reversal curves combined with magnetic force microscopy shows that the origin of the effect is the field‐dependent population of up and down domains in the free layer.     

Formation of Functionalized Nanowires by Control of Self‐Assembly Using Multiple Modified Amyloid Peptides

Amyloid peptides have great potential as building blocks in the creation of functional nanowires due to their natural ability to self‐assemble into nanofibrillar structures and because they can be easily modified with various functional groups. However, significant modifications of an amyloid peptide generally alter its self‐assembly property, making it difficult to construct functionalized fibrils with a desired structure and function. In this study, a very effective method to overcome this problem is demonstrated by using our structure‐controllable amyloid peptides (SCAPs) terminated with a three‐amino‐acid‐residue cap. The method consists on mixing two or more structurally related amyloid peptides with a fraction of modified SCAPs which co‐assemble into a fibril. This SCAP‐mixing method provides remarkable control over the self‐assembly process both on the small oligomers level and the macroscopic fibrils level. Furthermore, it is shown that the modified peptides imbedded in the resulting fibril can subsequently be functionalized to generate nanowires with the desired properties, highlighting the importance of this SCAP method for nanotechnology applications.     

汽轮机主汽门大型阀壳内型腔的加工

主汽门阀壳是大型汽轮机的关键零件。其内型腔形状复杂，除了有一非圆的盲深孔外，还有一个内球面及一条环形深槽，因此加工难度极大。本文介绍了如何利用一些特殊的工装、刀具在简易的专用机床上加工该内型腔的方法。     

Theoretical and experimental investigation on giant magnetoresistive materials with amorphous ferromagnetic layer

Pseudo-spin-valve （PSV） sandwiches using amorphous CoNbZr alloy as soft magnetic layer were fabricated by magnetron sputtering. The giant magnetoresistance （GMR） and its dependence on the thickness of magnetic layer were investigated. Anti-parallel magnetization alignments were observed in the samples with very thin CoNbZr thickness （2-4 nm） and a maximum GMR ratio of 6.5% was obtained. The Camley-Barnas semiclassical model was extended for amorphous layer based ：nagnetic sandwiches by considering that the mixed layers exist between the ferromagnetic and nonmagnetic layer. The calculated results agree with the experimental results very well, indicating that the new model gives a more realistic picture of the physical processes that take place in the magnetic sandwiches. Moreover, the calculated results for amorphous sandwiches also clarify that the occurrence of maximum GMR at very small thickness of amorphous layer is ascribed to the short mean-flee-path in amorphous materials.     

超磁致伸缩微位移致动器的研究

 基于超磁致伸缩材料的磁致伸缩特性设计了一种用于微位移驱动的致动器．分析了致动器工作磁场的组成，计算了线圈的工作电流，并以此为依据设计了稳流电源．分析结果表明，设计的稳流电源满足工作要求；线圈提供的工作磁场能够保证超磁致伸缩棒工作在线性区域。     

制备条件和退火处理对Fex/(In2O3)1-x颗粒膜结构、磁性及巨磁电阻的影响

用射频溅射法成功制备了金属／半导体型颗粒膜Fex／(In2O3)1-x实验结果表明样品的微结构、磁性和巨磁电阻效应受制备条件(如本底真空度、衬底温度、溅射电压等)以及热退火处理的强烈影响。较高的衬底温度有利于基体In2O3的晶化和Fe颗粒的成长。适当的热退火能促使Fe颗粒生长，使晶格畸变减小，从而改善膜的微结构。室温下，磁性测量表明样品具有超顺磁性，符合朗之万方程。高温退火后，颗粒的大小已超过单畴粒子的临界尺寸，引起矫顽力下降。