一维周期调制磁场中二维电子气的热学输运特性

在线性响应理论的框架内讨论了一维调制磁场中二维电子气的热电系数Ｓμｖ，热传导系数ｋμｖ及热阻系数（ｋ＾－１）μｖ等热力学输运特性。结果表明，由于磁场调制部分的存在，使二维电子气的热力学输运系数中除了通常ＳｄＨ振荡特性外，还表现出与磁场调制周期相关的新的振荡特性，即Ｗｅｉｓｓ振荡。     

周期调制磁场中二维电子气的电学特性

讨论了一般形式的弱周期调制磁场中二维电子气的电学特性．调制磁场消除了朗道能级的简并性，使之成为朗道子能带，从而导致磁致电阻的Ｗｅｉｓｓ振荡．结果表明：在纵向电阻ρｘｘ（及△ρｘｘ）和横向电阻ρｙｙ（及△ρｙｙ）中的Ｗｅｉｓｓ振荡位相是相反的，而霍尔电阻△ρｘｙ与△ρｘｘ的位相相同．△ρｘｘ的振幅远大于△ρｙｙ及△ρｘｙ的振幅．在较强磁场下，调制磁场的高阶Ｆｏｕｒｉｅｒ分量的贡献很明显；而弱磁场中，高阶Ｆｏｕｒｉｅｒ分量的贡献可以忽略．     

稀土离子（Ⅲ）与牛血清白蛋白的相互作用Ⅰ．结合反应热力学

在ｐＨ６．３０、３７℃条件下，采用离心超过滤技术测定了１１种稀土离子（Ⅲ）与牛血清白蛋白（Ｂ８Ａ）的专一性结合常数Ｋ＿ｓ和非专一性结合常数Ｋ＿（ｎｓ）观察到Ｋ＿ｓ随稀土系列原子序数（Ｚ＿（ＲＥ））的变化有明显的＂四分组效应＂和＂钆断现象＂，而Ｋ＿（ｎｓ）～Ｚ＿（ＲＥ）类似于一元羧酸－稀土配合物稳定常数的变化规律。求出Ｔｂ（Ⅲ）－ＢＳＡ结合反应的热力学函数分别为ΔＨ＿ｓ＝４４．５±０．８ｋＪ／ｍｏｌ，ΔＳ＿ｓ＝２４３．２±２．４Ｊｍｏｌ·Ｋ，ΔＨ＿（ｎｓ）＝１９．９±１．１ＫＪ／ｍｏｌ，ΔＳ＿（ｎｓ）＝１４１．４±３．２Ｊ／ｍｏｌ·Ｋ。根据不同ｐＨ下测得的Ｔｂ（Ⅲ）与ＢｓＡ结合的Ｋ＿ｓ和Ｋ＿（ｎｓ）拟合出ＢＳＡ分子中参与稀土配位的基团的质子解离常数ｐＫ＝４．６０，进而确定出这些基团主要为天冬氨酸和谷氨酸残基侧链中的β、γ－ＣＯＯ￣－。     

泸定百合居群染色体形态研究

研究了７个泸这百合居群的染色体形态变异,结果如下：（１）南涧居群Ｋ１＝２ｎ＝２ｘ＝２４＝２ｍ（２ＳＡＴ）＋２ｍ＋４ｓｔ（２ＳＡＴ）＋４ｓｔ＋１２ｔ,染色体长度比２．６２,平均臂比８．６３,Ａｓ,Ｋ值８１．２０％。（２）弥勒居群Ｋ２＝２ｎ＝２ｘ＝２４＝２ｍ（２ＳＡＴ）＋２ｍ（２ＳＡＴ）＋２ｓｔ（２ＳＡＴ）＋２ｓｔ＋１４ｔ,染色体长度比２．５７,平均臂比８．６９,Ａｓ．Ｋ．值８１．１２％。（３）峨眉居     

Y_（1－x）Gd_xBa_2Cu_3O_（7－δ）超导体的磁场烧结致各向异性

在磁场下（Ｈ＝１．３Ｔ）烧结得到的Ｙ１－ｘＧｄｘＢａ２Ｃｕ３Ｏ７－δ（ｘ＝０～１．０）系超导体表现出明显的电阻率ρ、超导转变零电阻温度Ｔｃｆ和临界电流Ｊｃ各向异性．样品的常态电阻率在平行于烧结磁场方向上的值ρ比垂直于烧结磁场方向上的值ρ大８％～７０％；零电阻温度Ｔｃｆ比Ｔｃｆ大１．０～５．０Ｋ；临界电流Ｊｃ比Ｊｃ大９％～７３％，而且在外磁场（Ｈｔ＝２．０Ｔ）下测得的临界电流Ｊｃ随外场Ｈｔ与烧结磁场ＨＳ间的夹角α呈椭圆形变化规律．这表明烧结过程中所加的磁场引起了该系超导体的各向异性．     

安徽百合属细胞学研究

本文研究了安徽产百合属（ＬｉｌｉｕｍＬ．）２种和２变种的染色体数目和核型，结果如下：野百合（Ｌ．ｂｒｏｗｎｉｉＦ．Ｅ．Ｂｒｏｗｎ）观察了２个居群。歙县居群观察到两种细胞型，细胞型Ⅰ：２ｎ＝２６＝１ｍ＋２Ｓｍ＋１０Ｓｔ＋１０ｔ＋３Ｔ；细胞型Ⅱ：２ｎ＝２４＋２Ｂｓ＝２ｍ＋２Ｓｍ＋８Ｓｔ（２ｓｃ）＋１２ｔ＋２Ｂｓ；石台居群核型公式为２ｎ＝２４＋１Ｂｓ＝３ｍ＋１Ｂｍ＋６Ｓｔ＋１２ｔ＋２Ｔ＋１Ｂｓ。百合（Ｌ．ｂｒｏｗｎｉｉＦ．Ｅ．Ｂｒｏｗｎｖａｒ．ｖｉｒｉｄｕ－ｌｕｍＢａｋｅｒ）核型公式为２ｎ＝２４＋１Ｂｓ＝４ｍ（２ｓｃ）＋１４Ｓｔ（２ｓｃ）＋６ｔ＋１Ｂｓ；药百合（Ｌ．ｓｐｅｃｉｏｓｕｎＴｈｕｎｂ．ｖａｒ，ｇｌｏｒｉｏｓｏｉｄｅｓＢａｋｅｒ）核型公式为２ｎ＝２４＝４ｍ＋９Ｓｔ（２ｓｃ）＋１０ｔ＋１Ｔ；条叶百合（Ｌ．ｃａｌｌｏｓｕｍＳｉｅｂ．ｅｔＺｕｃｅ．）核型公式为２ｎ＝２４＝２ｍ＋２Ｓｍ＋４Ｓｔ（２ｓｃ）＋１６ｔ。以上的核型类别全部属于“３Ｂ”型，其中野百合２ｎ＝２６的染色体数目和核型为首次记录。     

四苯硼酸铷在甲醇-水混合溶剂中的溶解度及缔合热力学函数

用紫外光度法测定了２８８．１５～３２８．１５Ｋ（间隔１０Ｋ）下,ＲｂＢＰｈ４在甲醇－水混合溶剂中的溶解度．经微机曲线拟合给出ＲｂＢＰｈ４的溶解度Ｓ随混合溶剂中甲醇质量百分比浓度Ｗｔ％及温度Ｔ之间的经验关系：ｌｎＳ＝－１．９７１６－２１３２．５／Ｔ＋２．８９６７×１０－２Ｗｔ％．应用Ｆｕｏｓｓ缔合理论计算了ＲｂＢＰｈ４在甲醇－水混合溶剂中的缔合常数及缔合热力学函数,并对ＲｂＢＰｈ４的缔合热力学函数的变化规律进行了讨论．     

Bi Pb Sr Ca Cu O F超导体的结构

对Ｂｉ￣（１．７）Ｐｂ￣（０．３）Ｓｒ＿２Ｃａ＿２Ｃｕ＿３Ｏ＿（ｙ－ｘ）Ｆ＿ｘ（ｘ＝０．８）超导体Ｔ＿ｃ介于１１４～１１８Ｋ的样品进行ＳＥＭ和ＴＥＭ结构观察．超导体的晶粒尺寸大小不一，内部孔洞较多，元素的成分分布极不均匀．含Ｆ样品存在２种结构的２２２３相，其中含Ｆ的２２２３相沿ｂ＿Ｆ方向的调制周期为１３．８８，不含Ｆ的２２２３相沿ｂ方向的调制周期为９．４２，含Ｆ单胞在ａｂ面的点阵常数略有收缩．Ｆ取代部分Ｏ是产生调制周期变长和Ｔ＿ｃ提高的原因．     

Bakakov-Kantorovich 算子的 Lp 饱和等价定理

引入双线性泛函，利用积分方程技巧得出了ＢａｓｋａｋｏｖＫａｎｔｏｒｏｖｉｃｈ算子在Ｌｐ［０，∞）关于阶１ｎ和平凡类Ｔ＝｛ｆ｜ｆ＝ｃｏｎｓｔ｝是Ｌｐ饱和的，饱和类为Ｓｐ＝｛ｆ｜ｆ∈Ｌｐ［０，∞），φ２（ｘ）ｆ″（ｘ）∈Ｌｐ［０，∞）（１＜ｐ＜∞）｝．     

Optical fiber Bragg grating sensors in smart structures

ＯｐｔｉｃａｌｆｉｂｅｒＢｒａｇｇｇｒａｔｉｎｇｓｅｎｓｏｒｓｉｎｓｍａｒｔｓｔｒｕｃｔｕｒｅｓＷｅｉｃｈｏｎｇＤｕ１，２，ＷＪｉｎ２，ＳＨＬｉｕ１（１ＨｏｎｇＫｏｎｇＰｏｌｙｔｅｃｈｎｉｃＵｎｉｖ．２ＳｏｕｔｈＣｈｉｎａＮｏｒｍａｌＵｎｉｖ．）Ｏｐ...     

Structural, magnetic and transport properties of Sc-doped La0.7Sr0.3MnO3

The Sc-doped La0.7Sr0.3MnO3 polycrystallines were prepared by thermal decomposition of complexes of metal ions with ethylenediamine-tetraacetic acid (EDTA). The dependence of structural, magnetic and transport properties on Sc doping was investigated. Moderate Sc doping level results in a sharp drop in Curie temperature, an increase in resistance and enhancement of magnetoresistance effect. At temperatures above TMI, R(T) can be described as R(T) = R0exp(T0/T)1/4, which indicates that conduction takes place by hopping between the localized states. The experimental data reveal that the change in magnetoresistance property is related to the structure.     

温度和量子线的纵横比对电导振荡现象的影响

利用两端区域为二维自由电子气 ,中间区域为准一维均匀直通道的简单理论模型 ,即 2D_准 1D_2D模型 ,研究了低温下不同纵横比 (通道长宽比 )的量子线电子弹道输运性质 .理论计算结果表明 ,量子线弹道区电子输运性质与通道纵横比和温度两者有密切关系 ,即随重整化标准费米能变化而产生的电导量子化和电导振荡现象强烈地依赖于温度和通道纵横比两者 ,而不仅仅依赖温度 .     

Colossal magnetoresistive p-n junctions of perovskite oxide La0.9Sr0.1MnO3／SrNb0.01Ti0.99O3

We have successfully fabricated the colossal magnetoresistive (CMR) p-n junctions of perovskite oxide La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 (LSMO/SNTO) with laser molecular beam epitaxy. The I-V characteristics of the LSMO/SNTO p-n junctions as a function of applied magnetic field (0—5 T) were studied between 100 and 300 K. We found that the p-n junction exhibited the CMR behavior. The CMR ratio △R/R0 (△R = RH - R0) is positive in magnetic fields below 0.13 T and at high temperature, while it displays a negative CMR near 100 K and in magnetic fields over 0.13 T. The CMR ratio values are 8% at 0.1 T and 13% at 5 T and 300 K, 40% at 0.1 T and 150 K, 10% at 0.13 T and -60% at 5 T and 100 K. The CMR behavior of the p-n junction is different from those of the LaMnO3 compound family.     

掺杂对一维反铁磁海森堡自旋链性质的影响

应用三子格的自旋波理论和格林函数方法研究了由掺杂形成的准一维自旋1/2的反铁磁海森堡系统,得到系统存在3支自旋波激发谱,其中1支没有能隙,2支有能隙;在长波近似下,这3支自旋波激发谱与波矢k成平方关系,系统的低温比热为C∝T1/2关系,其基态具有磁性长程序,这都不同于未掺杂的一维自旋1/2的反铁磁海森堡链模型系统.对系统磁性序的研究表明,T=0是相变点,Mermin-Wagner定理对于该系统成立.     

Driven coherent oscillations of a single electron spin in a quantum dot

The ability to control the quantum state of a single electron spin in a quantum dot is at the heart of recent developments towards a scalable spin-based quantum computer. In combination with the recently demonstrated controlled exchange gate between two neighbouring spins, driven coherent single spin rotations would permit universal quantum operations. Here, we report the experimental realization of single electron spin rotations in a double quantum dot. First, we apply a continuous-wave oscillating magnetic field, generated on-chip, and observe electron spin resonance in spin-dependent transport measurements through the two dots. Next, we coherently control the quantum state of the electron spin by applying short bursts of the oscillating magnetic field and observe about eight oscillations of the spin state (so-called Rabi oscillations) during a microsecond burst. These results demonstrate the feasibility of operating single-electron spins in a quantum dot as quantum bits.     

Quantum oscillations in a molecular magnet

The term 'molecular magnet' generally refers to a molecular entity containing several magnetic ions whose coupled spins generate a collective spin, S (ref. 1). Such complex multi-spin systems provide attractive targets for the study of quantum effects at the mesoscopic scale. In these molecules, the large energy barriers between collective spin states can be crossed by thermal activation or quantum tunnelling, depending on the temperature or an applied magnetic field. There is the hope that these mesoscopic spin states can be harnessed for the realization of quantum bits--'qubits', the basic building blocks of a quantum computer--based on molecular magnets. But strong decoherence must be overcome if the envisaged applications are to become practical. Here we report the observation and analysis of Rabi oscillations (quantum oscillations resulting from the coherent absorption and emission of photons driven by an electromagnetic wave) of a molecular magnet in a hybrid system, in which discrete and well-separated magnetic clusters are embedded in a self-organized non-magnetic environment. Each cluster contains 15 antiferromagnetically coupled S = 1/2 spins, leading to an S = 1/2 collective ground state. When this system is placed into a resonant cavity, the microwave field induces oscillatory transitions between the ground and excited collective spin states, indicative of long-lived quantum coherence. The present observation of quantum oscillations suggests that low-dimension self-organized qubit networks having coherence times of the order of 100 micros (at liquid helium temperatures) are a realistic prospect.     

海森伯格XXZ模型的热纠缠

负值度(Negativity)是一种通用的纠缠度量,可方便地计算两体量子系统的纠缠度.利用负值度研究了两量子比特各向异性海森伯格XXZ模型的热纠缠,讨论了在热平衡时温度和外加磁场对热纠缠的影响.当温度小于临界温度时,热纠缠的大小依赖于外加磁场的强弱;当温度大于临界温度时,纠缠消失.     

La5/6Li1/6MnO3的低频内耗研究

研究了样品La5/6Li1/6MnO3的内耗、直流电阻、交流磁化率.在75—245K的温度范围内,在0.3T的磁场下该样品有明显的磁阻(MR)效应.测量到两个电阻峰(Tp1=224K,Tp2=169K)和一个MR峰(T=218K).内耗(Q-1)测量中发现两个峰(PL=169K,PH=224K)和模量软化;并且内耗峰温与频率无关、内耗峰值与频率成反比.最终,提出在样品中存在相分离的观点.