How the Aggregates Determine Bound Rubber Models in Silicone Rubber? A Contrast Matching Neutron Scattering Study

The correlation between aggregates and bound rubber structures in silicone rubbers(S(phr)) with various silica fractions(ΦSi) has been investigated by contrast matching small-angle neutron scattering(SANS), swelling kinetics, and low-field nuclear magnetic resonance(NMR).Mixed solvents with deuterated cyclohexane fractions of 4.9% and 53.7% were chosen to match the scattering length densities of the matrix(SMP(phr)) and the filler(SMS(phr)), respectively. All the data consistently suggest that:(i) There is a critical threshold ΦSic between 10 and 30 phr;below ΦSic, the isolated aggregates are dominant, while beyond ΦSic, some rubber fraction is trapped among the agglomerate;(ii) ΦSiindependent thicknesses around 7.5 nm(NMR) and 8.6 nm(SANS) suggest that the bound rubber formation is determined by inherent properties of the components, and the power-law around 4.2 suggests an exponential changed gradient density of the bound rubber;(iii) SMS(80) presents a bicontinuous bound rubber with three characteristic lengths of 41, 100, and 234 nm. The expanded correlation length, a 20 nm smaller aggregate sizes suggest that such existent bicontinuous network in dry samples with less ΦSi is kind of impacted by swelling. With the obtained bound rubber models, the reinforcing mechanism of filled silicone rubber is elucidated.

Miniaturized time-of-flight neutron spin flipper using a high-TC superconductor

A miniaturized neutron spin flipper based on a high-TC superconductor film,developed at the China Spallation Neutron Source(CSNS),is presented.A neutron spin flipper is an essential component for performing polarized neutron experiments and,as such,constitutes a high priority for developing CSNS’s polarized neutron capability.To provide the beamlines with a universal neutron spin flipper operating over a wide wavelength band,the neutron spin flipper utilizes non-adiabatic spin flipping during transit through opposite magnetic fields that are mutually shielded by the superconductor Meissner effect.A compact vacuum heat shield and a low-power consumption sterling refrigerator maintained the superconducting condition while reducing the size and power input of the flipper.The prototype device was tested at the CSNS BL-20,which demonstrated a flipping efficiency of 99%at 4 A°.

Dispersion of neutron spin resonance mode in Ba_(0.67)K_(0.33)Fe_(2)As_(2)

We report an inelastic neutron scattering investigation on the spin resonance mode in the optimally hole-doped ironbased superconductor Ba_(0.67)K_(0.33)Fe_(2)As_(2)with T_c=38.2 K.Although the resonance is nearly two-dimensional with peak energy ER≈14 meV,it splits into two incommensurate peaks along the longitudinal direction([H,0,0])and shows an upward dispersion persisting to 26 meV.Such dispersion breaks through the limit of total superconducting gaps△_(tot)=|△k|+|△k+Q|(about 11-17 meV)on nested Fermi surfaces measured by high resolution angle resolved photoemission spectroscopy(ARPES).These results cannot be fully understood by the magnetic exciton scenario under s^(±)-pairing symmetry of superconductivity,and suggest that the spin resonance may not be restricted by the superconducting gaps in the multi-band systems.

Hardening of Thermal Photons Through Inverse Compton Scattering in Strong Magnetic Fields

A new spectrum function is obtained by use of the Compton scattering cross section in the laboratory frame derived earlier. This spectrum function, besides some modifications in the coefficients of the resonant term, contains also a non-resonant term which is inversely proportional to the square of the magnetic field. Based on this spectrum function, the hardening of thermal photons through inverse Compton scattering by relativistic electron beams on the surface of a strongly magnetized neutron star is investigated. Two new features are found. First, there is a maximum scattered photon energy for a given resonant scattering, beyond which resonance disappears. This maximum depends on the electron energy and the magnetic field, but is independent of the incident photon energy. Second, beyond each resonant scattering, there is a high-energy tail, resulting from non-resonant scattering. It is also found that all the tails have a common upper limit which is the highest scattered photon energy for the given incident photon and electron energies. These two new features are absent in the Monte Carlo simulations and therefore, may have physical implications for y-ray emissions.

吉木萨尔芦草沟组页岩储层孔隙结构与流体可动性研究

利用原子力显微镜、小角中子散射、高压压汞和T_(1)−T_(2)二维核磁共振岩心分析等实验技术,对页岩油储层中不同岩性样品的孔隙结构、表面粗糙度、全尺度孔径分布和可动油饱和度进行定量研究。研究结果表明:粉砂岩的孔径分布曲线多为连续波浪型,孔隙以亚微米孔为主,大多数孔隙直径小于500 nm,宏孔孔容和平均孔径更大。粉砂岩含有狭缝状或楔形粒间孔隙,砂屑云岩中含有粒间孔和粒内溶孔。云质泥岩样品中存在干酪根和沥青核磁信号,并发育中小尺度的有机质孔隙,可动油平均饱和度为15.6%。粉砂岩可动油平均饱和度为53.8%。粉砂岩是优质储层发育的成岩相,也是水平井靶体目的层。

温敏性微凝胶的研究技术

温敏性微凝胶因具有尺寸小、对温度的变化响应速度快、渗透性好等优点,所以在许多领域显示出良好的应用前景。温敏性微凝胶的应用性能取决于由其结构所决定的物理化学性能。为了深入了解温敏性微凝胶的结构与性能关系,研究人员利用不同技术手段进行了广泛研究。本文主要综述了显微技术、示差扫描量热技术、光散射技术、中子散射技术、核磁共振及荧光光谱等在温敏性微凝胶结构与性能研究中的应用、主要研究结果,并对微凝胶未来的研究方向提出了一些建议。

中子散射在新型磁性材料研究中的应用

简单介绍了中子散射在具有一级晶格和磁相变的新型磁制冷材料和具有庞磁致电阻材料中的一些研究进展。中子散射结果表明,在NaZn13型稀土铁基化合物中,晶格与磁性之间存在明显的耦合,这种耦合可能是该体系中大的磁熵变的来源;在CMR(Colossal Magnetoresistant)锰氧化物中,极化中子衍射证明3d电子的轨道分布与Jahn-Teller效应、磁有序等密切相关,并在该体系中,首次测量到纳米尺度的磁性材料中的自旋波。

三轴中子散射谱仪的建造及凝聚态物质中磁相互作用的中子散射研究中期报告

该研究是973计划“高通量中子散射在凝聚态物质磁相互作用方面的前沿研究”的研究- “三轴中子散射谱仪的建造及凝聚态物质中磁相互作用的中子散射研究中期报告”（2012CB 821401）的中期报告.主要进展包括3个部分.首先,我们基本搭建完成了“翠竹”热中子三轴谱仪.其次,我们在铁基自旋动力学方面取得了-些重要进展,包括B a Fe2 -x N ix A s ,中的量子临界性质和低能自旋激发谱的演化,铁基超导体自旋序来源的总结以及L i缺陷对L iF e A s性质的影响.最后,在理论方面,我们提出了一种独特的铁基超导理论,对二维阻挫系统中的金属-绝缘体相变也进行了讨论.

17-4PH不锈钢纳米析出物的磁小角中子散射研究

本文充分发挥中子对磁灵敏、穿透力强等技术优势,利用加载磁场小角中子散射实验技术研究核电站实际服役14年的阀杆17-4PH不锈钢样品。结果表明,与不加磁场时相比,加载磁场条件下二维散射图谱呈明显各向异性,在散射矢量垂直于磁场方向上散射强度显著增强。利用多分散球模型对数据进行拟合,结合原子探针实验结果分析得出,衬度的增加降低了Cu析出物周围元素分布不均匀对散射的相对贡献,从而有助于更加准确地获得Cu纳米析出物的尺寸。

轨道序和巡游性对尖晶石结构钒氧化物AV2O4（A=Mn,Fe,Co）物性影响的研究

在尖晶石钒基氧化物AV2O4中,因为自旋阻挫、轨道序、巡游性等独特的内禀属性间存在着相互合作和竞争,所以该体系常常表现出复杂而有趣的物理现象。通过对A位磁性离子的调控,我们详细研究该体系中不同物性的起源,比如磁相变与结构相变的不同起因,局域和巡游电子的交叉行为等等。我们以Mn1-xCoxV2O4和Fe1-xCoxV2O4体系为研究对象,通过变温X射线衍射、磁化率、比热和中子散射等测试手段,结合第一性原理计算,对其物性起源进行了详细的研究。我们发现:(i)在低Co^2+离子掺杂时,体系受到局域V^3+离子以及A位Fe^2+离子的轨道序作用,往往会在磁有序附近伴随着结构相变的出现,以至于弱化体系中钒离子独立形成的四面体造成的几何阻挫。这也说明Co^2+离子低掺杂下,该体系有着强的自旋-晶格耦合;(ii)在高Co^2+离子掺杂时,由于巡游性的增强,轨道序的弱化,JAB交换相互作用增强,体系也表现出明显的磁各向同性。因此磁相变温度向更高的温度移动,而结构相变温度向低温移动甚至消失。

铁基超导体中的反铁磁序和自旋动力学

类似于其他非常规超导材料,铁基高温超导电性通常出现在静态长程反铁磁序被抑制之后,并且强烈的自旋涨落始终与超导电性相伴相生,因此理解磁性相互作用是建立铁基超导微观机理的重要前提.中子散射作为研究凝聚态物质中磁性相互作用的有力工具,在揭示铁基超导电性的磁性起源方面起到了关键作用.本文系统总结了近十年来铁基超导材料的中子散射研究结果,包括铁基超导材料中的静态磁结构、磁性相变、动态磁激发、电子向列相等,并探讨它们与超导电性之间的关系.

Physical properties and magnetic structure of a layered antiferromagnet PrPd0.82Bi2

We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic(AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at TN^7K. A large Sommerfeld coefficient of 329.23 m J·mol-1·K-2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k =(0 0 0) is formed below TN. The Pr3+ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μBat 4K, which is smaller than the effective moment of the free Pr3+ ion of 3.58 μB.PrPd0.82Bi2 can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity.

Electromagnetic Theory of the Nuclear Interaction

After one century of nuclear physics, its underlying fundamental laws remain a puzzle. Rutherford scattering is well known to be electric at low kinetic energy. Nobody noticed that the Rutherford scattering formula works also at high kinetic energy, needing only to replace the repulsive electric -2 exponent by the also repulsive magnetic -6 exponent. A proton attracts a not so neutral neutron as amber attracts dust. The nucleons have magnetic moments that interact as magnets, equilibrating statically the electric attraction between a proton and a not so neutral neutron. In this paper, the electromagnetic potential energies of the deuteron 2H and the α particle 4He have been calculated statically, using only electromagnetic fundamental laws and constants. Nuclear scattering and binding energy are both electromagnetic.

强磁场中的逆康普顿散射

本文根据非相对论情形(B/B_(cr)《1,hv/m_eC^2《1)强磁场中的康普顿散射微分截面,讨论了强磁场中低频光子与相对论电子的逆康普顿散射,并给出了呈幂律分布的低频光子与呈幂律分布的相对论电子相互作用产生的逆康顿散射谱,这可以用来解释γ射线爆高达几百KeV的低频倒转谱。

利用小角中子核磁散射分离研究AerMet100钢中纳米析出相的形貌和成分

AerMet100超高强度钢以其优异的力学性能广泛应用于飞机起落架。其超高强度主要源于合金回火过程中产生的大量M_(2)C型针状析出相的二次硬化作用。由于AerMet100高强钢中的纳米析出相与马氏体基体共格且尺寸细小,无法进行萃取,很难采用传统成像手段对其尺寸和成分进行准确表征。本工作结合TEM和XRD的观测结果,采用小角中子散射(SANS)技术分别对454、482、486和498℃回火5 h的AerMet100合金钢中M_(2)C型针状析出相的尺寸、分布和含量进行了定量表征。通过在SANS实验时施加1.1 T横向磁场并对数据沿平行和垂直磁场方向按角度规约,实现了对数据的核、磁散射分离。对核散射曲线的模型拟合结果显示,合金中针状析出相平均长度为6~16 nm,平均直径为1~2 nm,针状碳化物相的体积分数随退火温度升高由0.54%逐渐提高至5.19%。磁散射数据得到的碳化物结构参数均大于核散射结果,说明在碳化物与马氏体基体相界面存在自旋错排的纳米磁畴区。此外,通过对碳化物和基体相中子核磁散射长度密度的对比计算,推断出针状碳化物的可能的化学组成和密度分别为:(Cr_(0.4)Mo_(1.6))C和8.55 g/cm^(3)。

Mictomagnetism and suppressed thermal conduction of the prototype high-entropy alloy CrMnFeCoNi

High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices,differing from traditional alloys.Here,we investigate the magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering.Direct-current and alternating-current magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions below room temperature and three anomalies are found at about 80,40,and 20 K,which are related to the paramagnetic to antiferromagnetic transition,the antiferromagnetic to ferromagnetic transition,and the spin freezing,respectively.The electrical and thermal conductivities are significantly reduced compared to Ni,and the temperature dependence of lattice thermal conductivity exhibits a glasslike plateau.Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.

高温超导体的磁激发:探寻不同体系铜氧化合物的共同特征

文章回顾了中子散射在高温超导铜氧化合物磁激发研究中的最新进展.自从铜氧化合物在20年前被发现以后,理解它们超导电性的微观来源一直是凝聚态物理中的核心课题.在传统超导体中,使得电子成对形成超导态的相互作用是以晶格振动(声子)为媒介的.而对于铜氧化合物的超导机理,人们通常认为磁激发可能起到根本的作用,因为超导电性是在可移动的“电子”或“空穴”掺杂到反铁磁母体化合物之后才发生的.文章总结了过去20年来利用非弹性中子散射研究磁激发的关键结果和现状,并指出了将来可能的研究方向.

中子散射技术及其应用

热中子的波长和凝聚态物质的原子/分子间距具有相同的量级,而其能量又和原子/分子的热运动能量相近.因此,利用热中子的弹性和非弹性散射效应,可以从微观层次上获取物质的结构和动力学知识.目前,中子散射技术在物理、化学、化工、生物和材料科学等研究领域的应用已经获得了许多用其他方法无法得到的知识.文章介绍了中子散射的基本原理和特点。

铁基超导体中的长程反铁磁序

文章回顾了用中子散射技术对铁基超导体中所存在的三维长程反铁磁序进行研究的进展.大多数铁基超导体母体的晶体结构在温度降低时都经历了从四方相变化到正交相或单斜相的结构相变.在此相变温度之下,自旋系统也从顺磁变化到三维长程反铁磁.在掺杂之后,结构相变和磁相变都被压制,而超导则最终出现.文章详细介绍了各种母体中的三维反铁磁结构及其自旋波频谱,并讨论了掺杂对反铁磁相变和晶格相变的影响.

Superconductivity and spin fluctuations

In the conventional superconductors, the Cooper pairs are mediated by phonons, which is a pro- cess where only the correlations between the phonons and the charge properties of the electrons are needed. However, superconductivity can also be derived from other types of elementary excitations. The spin fluctuations are arguably the most promising candidate that can mediate such unconventional superconductivity. In some of the important systems such as cuprates, Fe-based superconductors and heavy-fermion superconductors, spin fluctuations play a key role in the mechanism of their superconductivity although there are still many debates. In this paper, we will give a brief review on the correlation between the spin fluctuations and superconductivity.