NMR microimaging studies of water diffusivity in saturated, microporous systems

A novel microimaging method is described for measuring the effective diffusion coefficient (D_∞) of water in saturated, microporous materials. A simple multicompartment computer simulation was used to show how the value of D_∞, when combined with measurements of water proton relaxation times and pulsed field gradient spin-echo amplitudes, allows the pore size distribution and pore connectivity to be characterized.     

Determination of the (Na+) Sternheimer antishielding factor by 23Na NMR spectroscopy on sodium oxide chloride, Na3OCl

The (Na⁺) Sternheimer antishielding factor γ_∞ (Na⁺) was determined by ²³Na NMR spectroscopy on sodium oxide chloride, Na₃OCl. The quadrupolar coupling constant of the sodium ion in Na₃OCl was determined to QCC=11.34 MHz, which presents the largest coupling constant of a sodium nucleus observed so far. Applying a simple point charge model, the largest principal value of the electric field gradient at the sodium site was calculated to V_zz=−6.76762·10²⁰ V/m². From these values we calculated the (Na⁺) Sternheimer antishielding factor to γ_∞ (Na⁺)=−5.36. In sodium oxide, Na₂O, we observed an isotropic chemical shift of δ_CS=55.1 ppm, referenced to 1 M aqueous NaCl (δ=0 ppm).     

Electromagnetic final-state interactions in the leptonic decays of the neutral kaon (I) Kℓ3 mode

We present a calculation of the Coulomb final-state interaction effects in the decays K_L → π ℓ^±V_ℓ. Specifically we investigate the charge asymmetry and the transverse polarization of the charged lepton. We consider the effects of possible ΔQ = −ΔS amplitudes and the q² dependence of the form factors. The variation of the effects over the Dalitz plot is discussed and many numerical results are given.     

Charge ordering characteristics in Y0.5Ca0.5MnO3 manganite

The charge ordering characteristics in Y_0.5Ca_0.5MnO₃ manganite, prepared by sol–gel process, have been investigated experimentally. It is found that the superlattice diffractions appear in the electron diffraction patterns recorded at low temperatures, while only basic Brag diffraction spots can be observed when temperature is higher than 300 K. This provides direct evidence for the existence of charge ordering in Y_0.5Ca_0.5MnO₃. The magnetization and specific heat measurements indicate the charge ordering temperature of Y_0.5Ca_0.5MnO₃ is 290 K, around which both the magnetization and specific heat reveal anomalous behaviors. We also observed that the MnO bond length changed remarkably and the effective number of carriers reduced prominently with decreasing temperature around charge ordering temperature through transform infrared spectra measurements.     

Limits on neutrino electromagnetic properties — an update

Limits on neutrino electromagnetic properties from laboratory experiments and astrophysical arguments are reviewed with an emphasis on the currently favored range of small neutrino masses. We derive a helioseismological limit on the charge and dipole moment for all flavors of e_ν6×10⁻¹⁴e and μ_ν4×10⁻¹⁰μ_B (Bohr magneton). The most restrictive limits remain those from the plasmon decay in globular-cluster stars of e_ν2×10⁻¹⁴e and μ_ν3×10⁻¹²μ_B.     

Counting neutrinos and families in the standard electroweak model

Let n_ν be the number if neutrinos much lighter than their charged lepton partners. In the standard electroweak model, using low-energy particle physics data, we prove that n_ν<137. If moreover the up-type and down type quarks are also highly nondegenerate in mass n_ν<47. The limits are much tighter for nondegenerate leptonic mass spectra. If the ratio of the lepton masses in two consecutive families is about 10 then there are at most two neutrinos beyond the known ν_e, ν_μ and ν_τ. The same result is obtained for a mass spectrum à la Froggat and Nielsen.     

Lattice sternheimer factor of Eu(OH)3 from Mössbauer spectral study

The Mössbauer spectra of powdered Eu(OH)₃ were recorded between 300 and 4.2 K, with ¹⁵¹SmF₃ as source. The spectra showed one single absorption line having definite width but without any fine structure. The lattice Sternheimer factor γ_∞ of ¹⁵¹Eu in Eu(OH)₃ was estimated with the help of these spectra as well as by using the values of some physical parameters obtained from spectral and magnetic susceptibility measurements on pure single crystal of Eu(OH)₃, The value of lattice Sternheimer factor (= -87) thus evaluated is slightly larger than that value ( = - 80) for ¹⁵⁴Eu in ethylsulphate host. This result is consistent with the γ_∞ values of other rare-earth ions and also with the results obtained from magnetic and optical experiments on Eu(OH)₃.     

Transport coefficients and flux motion in Bi2Sr2CaCu2Ox single crystals

We present measurements of the electrical resistivity, thermal conductivity, and Hall, Nernst, and Seebeck effects in the mixed state of single crystalline Bi₂Sr₂CaCu₂O_x. It is shown that the sign of the Hall voltage changes twice as temperature decreases below T_c. From the Nernst effect we estimate the transport entropy S_φ to be about 10⁻¹⁰ erg/K cm. S_φ is equal to zero in the normal state, increases and passes through a maximum at the mixed state as expected. The temperature dependences of the thermoelectric power in magnetic fields are analogous to the resistive transition curves. These phenomena are discussed in terms of flux flow. The contribution of the flux flow to the thermal conductivity is estimated to be negligible. Lowering of the thermal conductivity at temperatures below T_c by a magnetic field is attributed to phonon scattering by the vortex lines.     

Considerations concerning the radiative corrections to muon decay in the Fermi and Standard theories

The FAC, PMS, and BLM optimization methods are applied to the QED corrections to the muon lifetime in the Fermi V-A theory. The FAC and PMS scales are close to m_e, while the BLM scale nearly coincides with the geometric average √m_em_μ. The optimized expressions are employed to estimate the third order coefficient in the (m_μ) expansion and the theoretical error of the perturbative series. Using arguments based on effective field theory and a simple examination of Feynman diagrams, it is shown that, if contributions of (m_μ²/M_W²) are neglected, the corrections to muon decay in the SM factorize into the QED correction of the Fermi V-A theory and the electroweak amplitude g²/(1 − Δr), both of which are strictly scale-independent. We use the results to clarify how the QED corrections to muon decay and the Fermi constant G_F should be used in the SM, and what is the natural choice of scales if running couplings are employed.     

Homotopy algebra morphism and geometry of classical string field theories

We discuss general properties of classical string field theories with symmetric vertices in the context of deformation theory. For a given conformal background, there are many string field theories corresponding to different decomposition of moduli space of Riemann surfaces. It is shown that any classical open string field theories on a fixed conformal background are A_∞-quasi-isomorphic to each other. This indicates that they have isomorphic moduli space of classical solutions. The minimal model theorem in A_∞-algebras plays a key role in these results. Its natural and geometric realization on formal supermanifolds is also given. The same results hold for classical closed string field theories, whose algebraic structures are governed by L_∞-algebras.     

金属/介质薄膜中声子热辐射的空间和各向异性研究

基于理论、实验和仿真相结合的方式,着重研究了金属/介质(MD)薄膜中声子热辐射的空间特性和各向异性。声子是由于晶格振动产生的元激发,是物质的内在属性。尽管声子不易调控,但是声子与其他光学激发的耦合会产生奇异的光学现象。特别是红外到太赫兹范围内的光子与极性介质中的声子强耦合产生表面声子激元（SPhP）。SPhP具有强局域、低损耗等特点,与等离子体（plasmon polaritons）形成互补,使得深亚波长光学成为可能。为了进一步了解声子吸收的内在理论基础,首先通过黄昆方程和超晶格连续介电模型在理论上分析了声子吸收。实验上,主要以SiO₂声子作为研究对象,利用等离子体增强化学气相沉积(PECVD)方法,分别在Si/Al（150 nm）薄膜和Si衬底上制备出500 nm厚的SiO₂薄膜。基于傅里叶红外光谱仪(FTIR),在垂直入射下得到热辐射光谱,通过热辐射光谱分析,并结合由时域有限差分算法（finite-difference time-domain,FDTD）计算得出的仿真光谱图,对比了MD薄膜结构和非MD薄膜结构中声子的热辐射,发现MD薄膜结构更能够有利于声子和SPhP的激发。根据Berreman效应,纵光学波（LO）声子只在倾斜入射时产生。光谱线没有呈现洛伦兹线型,因此,虽然LO声子在垂直入射时测得的热辐射图中不辐射,但同样影响横光学波（TO）声子辐射谱的线型。另外,利用FTIR对金属（Si/Al）/介质（SiO₂薄膜）进行热辐射转角测试,对热辐射转角图分析证明,Si/Al/SiO₂薄膜中SiO₂声子遵循LST(lyddano-sachs-teller)关系,纵横声子成对出现,且两种声子的空间辐射特性不同。改变偏振,发现在S偏振和P偏振下,声子热辐射呈现不同的模式, 体现出声子的空间各向异性。并且,声子与光子耦合可以激发SPhP,反过来,SPhP可以增强声子的吸收。基于MD结构,能够激发并调控SPhP和声子辐射行为,为红外器件的实现奠定了基础。     

Effective activation energy Ue(T,J,H) in textured Bi1.84Pb0.4Sr2Ca2Cu3Oy silver-clamped thick films

We have measured the resistivity of textured Bi_1.84Pb_0.4Sr₂Ca₂Cu₃O_y silver-clamped thick films as a function of temperature, current density ranging from 10 to 1×10³ A/cm² and magnetic field up to 0.3 T. We find that the effective activation energy U_e follows U_e(T,J,H)=U₀(1−T/T_p)^mln(J_c0/J)H⁻ with m=1.75 for Hab-plane and 2.5 for Hc-axis and =0.76 for Hab and 0.97 for Hc, for the current density regime above 100 A/cm², where T_p is a function of applied magnetic field and current density. This result suggests the effective activation energy U_e be correlated with the temperature, current density and magnetic field. The possible dissipative mechanisms responsible for the temperature, current density and magnetic field dependence of the effective activation energy are discussed.     

Electrical properties of pure and Li2O-doped CuO/Fe2O3 system precalcined at different temperatures

The electrical properties of pure and Li₂O-doped CuO/Fe₂O₃ solids were investigated. Pure and variously doped solids were subjected to thermal treatment at 1073–1273 K and the amount of dopant was varied between 0.84 to 3.36 mol%. The effect of precalcination temperature and amount of Li₂O added on the electrical conductivity σ, activation energy E_a and dielectric constant * were studied. The variation of ′ and ″ as a function of frequency for pure and variously doped solids precalcined at different temperatures was also investigated. The results obtained were discussed.     

Eu3+或Tb3+掺杂Y2O3纳米材料紫外激发光谱

采用燃烧法制备了不同Ln³⁺(Ln=Eu或Tb)掺杂浓度和不同平均粒径的Y₂O₃:Ln纳米晶体粉末和体材料样品。研究发现随着粒径的减小,Y₂O₃:Eu电荷迁移带的位置发生红移;并且,由于存在于近表面低结晶度环境中的Eu³⁺数量的增加,小粒径样品(5nm)的电荷迁移带还向长波方向发生了明显的展宽。实验中还观察到Y₂O₃:Tb纳米晶激发谱中4f5d(4f⁸→4f⁷5d¹)跃迁吸收对应激发峰(带)的谱线形状随样品粒径变化存在较大的差异,这是由于Tb³⁺存在于近表面的低结晶度和颗粒内部的高结晶度两种不同环境中,Tb³⁺的4f5d跃迁在两种环境中对应的吸收峰位置不同,当样品粒径发生变化时Tb³⁺处于两种环境中的比例随之变化,造成相应吸收跃迁对应的激发峰(带)强度发生变化,并改变了激发谱的谱线形状。实验中还发现,随着Tb³⁺(或Eu³⁺)浓度的减小,Y₂O₃基质激子跃迁吸收的激发峰对比4f5d跃迁(或电荷迁移带)激发峰的相对强度随之增强。     

玻璃中CdSeS纳米晶体的室温光致发光谱

对掺有过饱和的镉、硒和少量硫的玻璃在500～800℃分别退火4h,生长了不同尺寸的CdSe_1-xS_x纳米晶体。测量了纳米晶体的室温吸收光谱和光致发光(PL)光谱,550℃生长的样品在300～800nm的范围没有观察到吸收和发光峰,表明温度低于550℃玻璃中不能形成纳米晶体。生长温度在600～650℃,纳米晶体的PL光谱主要为两个宽的发光带,即带边激子发光带和通过表面态复合的发光带。随着生长温度的升高,带边复合发光的蓝移减小,通过表面态的发光逐渐消失,并出现了叠加于宽发光带上的一系列明显的弱发射峰。不同温度生长的样品中,叠加峰的能量相同。同一样品中叠加峰的能量不随激发光波长的变化而变化。     

A new measurement of the weak magnetism term in the betaspectra of B and N

The betaspectra of ¹²B and ¹²N have been measured with a NaI crystal as spectrometer. Assuming a shape correction factor 1 + aW + bW² and b₋ = 1.106 × 10⁻⁴ MeV⁻², b₊ = −1.397 × 10⁻⁴ MeV⁻², the spectra yield a₋ = (+0.91 ± 0.11) × 10⁻² MeV⁻¹ and a₊ = (−0.07 ± 0.09) × 10⁻² MeV⁻. the a₋ − a₊ = (+0.98 ± 0.09) × 10⁻² MeV⁻¹ is in agreement with the weak magnetism prediction.     

Upper bound to the charge-transfer energy on a 2D Wigner lattice in high-Tc cuprates

Assuming that the energy of a 2D Wigner lattice, which has been frequently observed on the CuO₂ plane in layered high-T_c cuprates, is composed of Coulomb energy, kinetic energy, and charge-transfer energy which is necessary to transfer electrons or holes onto the CuO₂ plane (the magnitude of the energy is expected to be of the order of the work function of the compound constituting the plane from which the electrons are transferred, if the CuO₂ plane easily accepts the electrons or holes, as if the CuO₂ plane were crystal surface), we find in the mean-field approximation, that the total energy for a unit lattice, E₀, can be given by a function of the charge-transfer energy E_φ as E₀= (E_φ−E_φ⁰+O((E_φ−E_φ⁰)₂)(>0), where the value of E_φ⁰(1.5 in the ground state, for example) is independent of the lattice configuration. This relation implies that the upper bound to the charge-transfer energy is given by E_φ⁰. The smallness of E_φ⁰, compared with the work function of ordinary metals and alloys (with the work function around 4 eV), is necessary for the realization of the 2D Wigner lattice in many layered high-T_c cuprates.     

两种新型芴衍生物的合成、晶体结构及光谱性能

合成了两种新型芴衍生物:2,7-二（3,5-二（三氟甲基）苯基）-9,9-二乙基芴（1）和2,7-二（4-氟苯基）-9,9-二乙基芴（2）。通过元素分析、红外光谱（IR）、核磁共振氢谱（¹H NMR）以及单晶X射线衍射对其结构进行了表征。化合物1属于单斜晶系,P2₁/c空间群;化合物2属于三斜晶系,P-1空间群。通过紫外-可见吸收和荧光光谱研究了化合物的发光性能。结果表明:在CH₂Cl₂溶液和固态薄膜中,化合物1、2在350～400 nm波段有吸收峰,归属于π-π^*电荷跃迁;化合物1、2的光学带隙E_g分别为3.31 eV和3.30 eV,并且均有强烈的蓝色荧光发射现象（激发波长为330 nm）,在二氯甲烷中的荧光量子效率分别为0.62和0.61,固态荧光寿命分别为6.39 ns和9.00 ns。     

An isothermal equation of state for solids

An isothermal equation of state (EOS) for solids, recently suggested by the authors in the realistic form, V/V₀=f(P), with relative volume as the dependent and the pressure as the independent variable, was shown to have an advantage for some close-packed materials in that it allows B′_∞=(∂B_s/∂P)_s(P→∞) to be fitted, and this is where the usual standard equations fail. In the present study, our EOS is applied to a number of inorganic as well as organic solids, including alloys, glasses, rubbers and plastics; varying widely in their bonding and structural characteristics, as well as in their bulk modulus values. A very good agreement is observed between the data and fits. The results obtained are compared with those from two well-known equations, expressible in the realistic form, proposed by Murnaghan and Luban. Further, the results are also compared with those from the widely used two- and three-parameter EOSs, expressible in the unrealistic form only, P=f(V/V₀), proposed by Birch—and also with those from the EOS model of Keane in which B′_∞ is explicitly expressed as an equation of state parameter. The results obtained from our model compare well to these EOSs. Our EOS, in general, yields the smallest mean-squared deviations between data and fits. The values of B′_∞calculated from our EOS are compared with those from Keane's model. Further, we have studied the variation of B′_∞with temperature using the experimental isotherms of Mo and W at 10 different temperatures ranging from 100 to 1000 K, and observed that the values of B′_∞ yielded by our model and that of Keane vary, as expected, within a narrow range. Furthermore, our EOS is applied to study the stability of the fit parameters with variation in the pressure ranges with reference to the isothermal compression data on Mo and W—and also to study the variation of isothermal bulk modulus with pressure, with reference to the ultrasonic data on NaCl and noted a very good agreement with experiment. In addition, our model is applied, with B₀ and B′₀ constrained to the theoretical values, to the five theoretical isotherms of MgO at 300, 500, 1000, 1500 and 2000 K obtained on the basis of a first principles approach—a good agreement is observed with the predictions, and the values of B′_∞ inferred at different temperatures tend to converge to a constant value.