Proton-detected heteronuclear single quantum correlation NMR spectroscopy in rigid solids with ultra-fast MAS

In this article, we show the potential for utilizing proton-detected heteronuclear single quantum correlation (HSQC) NMR in rigid solids under ultra-fast magic angle spinning (MAS) conditions. The indirect detection of carbon-13 from coupled neighboring hydrogen nuclei provides a sensitivity enhancement of 3- to 4-fold in crystalline amino acids over direct-detected versions. Furthermore, the sensitivity enhancement is shown to be significantly larger for disordered solids that display inhomogeneously broadened carbon-13 spectra. Latrodectus hesperus (Black Widow) dragline silk is given as an example where the sample is mass-limited and the sensitivity enhancement for the proton-detected experiment is 8- to 13-fold. The ultra-fast MAS proton-detected HSQC solid-state NMR technique has the added advantage that no proton homonuclear decoupling is applied during the experiment. Further, well-resolved, indirectly observed carbon-13 spectra can be obtained in some cases without heteronuclear proton decoupling.     

71Ga NMR of reference GaIV, GaV, and GaVI compounds by MAS and QPASS, extension of gallium/aluminum NMR parameter correlation

We report new measurements of NMR parameters for 71Ga in gallium bearing oxide reference compounds, ranging from perfectly ordered systems to disordered crystalline structures and their aluminate counterparts. Static, MAS, and QPASS spectra are obtained at magnetic fields ranging from 7.0 to 18.8 T. With these results we enhance the previously established correlation between isotropic chemical shifts of 71Ga and 27Al and propose a correlation between gallium and aluminum electric field gradients (EFG). This correlation shows that the EFG at 71Ga sites are generally three times greater than those at equivalent 27Al sites.     

Low temperature glassy properties of disordered crystals

Low temperature measurements of specific heat, thermal conductivity, dielectric dispersion, ultrasonic dispersion and other properties have disclosed that a variety of disordered crystals exhibit the same anomalous behavior as found in amorphous solids. The anomalies arise from localized excitations having broad spectra in both energy and equilibration time. In some disordered crystals, these spectra may be changed systematically by varying the disorder present. The physical origin of the excitations, in crystals or glasses, lacks a satisfactory theoretical explanation. It is expected that the crystalline systems will be more amenable to theoretical study. The crystalline solids found to harbor the excitations include, at this time, certain fast-ion conductors, ferroelectrics, metallic alloys, and rotationally disordered solids.     

Electroreflectance and Raman scattering investigation of glow-discharge amorphous Si:F:H

The electroreflectance and Raman scattering spectra of several samples of glow-discharge amorphous Si:F:H films have been investigated. We have observed for the first time modulated optical spectroscopy structure above the absorption edge for a disordered semiconductor. The energy positions of these structures, at 3.4 and 4.5 eV, correspond to peaks seen in crystalline silicon. In particular, the latter feature can be related to the degree of disorder in the material. Also we have seen for the first time in disordered silicon (except for ion-damaged, laser annealed samples) peaks in the Raman spectra intermediate between amorphous (465 cm^-1) and crystalline materials (522 cm^-1). These experimental results provide strong evidence that a-Si:F:H possesses “microcrystalline” or some other intermediate range order (i.e., an improved connectivity between the elements of the random network.)     

Dielectric spectra of disordered ferroelectric systems: Polycrystals and composites

The dielectric spectra of heterogeneous systems that have very large dielectric constants and exhibit the Maxwell-Wagner relaxation are analyzed. The spectra of the disordered systems are found to be of a non-Debye type, and attempts to fit them using either the Cole-Cole or Davidson-Cole equations sometimes fail to produce satisfactory results. Experimental spectra of disordered systems are proved to be close to the spectra obtained by computer simulation of statistical mixtures and ferroelectric ceramics. A new formula is suggested to describe the dielectric relaxation in polycrystalline and composite materials, and reasons for the non-Debye nature of the dielectric spectra are examined.     

Quantifying the complexity of excised larynx vibrations from high-speed imaging using spatiotemporal and nonlinear dynamic analyses

In this paper, we investigate the biomechanical applications of spatiotemporal analysis and nonlinear dynamic analysis to quantitatively describe regular and irregular vibrations of twelve excised larynges from high-speed image recordings. Regular vibrations show simple spatial symmetry, temporal periodicity, and discrete frequency spectra, while irregular vibrations show complex spatiotemporal plots, aperiodic time series, and broadband spectra. Furthermore, the global entropy and correlation length from spatiotemporal analysis and the correlation dimension from nonlinear dynamic analysis reveal a statistical difference between regular and irregular vibrations. In comparison with regular vibrations, the global entropy and correlation dimension of irregular vibrations are statistically higher, while the correlation length is significantly lower. These findings show that spatiotemporal analysis and nonlinear dynamic analysis are capable of describing the complex dynamics of vocal fold vibrations from high-speed imaging and may potentially be helpful for understanding disordered behaviors in biomedical laryngeal systems.     

Two-dimensional dynamic-director (13)C NMR of liquid crystals

A novel nuclear magnetic resonance (NMR) experiment for facilitating the resolution and assignment of liquid crystalline (13)C NMR spectra is described. The method involves the motor-driven reorientation of the liquid crystalline director, in synchrony with the acquisition of a 2D chemical shift correlation spectrum. By monitoring in this fashion the (13)C NMR evolution of spins in the liquid crystal at two different director orientations with respect to the magnetic field, the method distinguishes anisotropic from isotropic displacements and can be utilized for assigning the resonances and estimating local degrees of order. Of various potential pairs of angles suitable for such a correlation, the (0 degrees, 90 degrees ) choice was found to be most convenient, as it avoids line broadening complications that may otherwise originate from heterogeneities of the oriented phase. The technique thus derived was employed in the analysis of a series of monomeric and polymeric liquid crystal systems.     

Symmetries of multifractal spectra and field theories of Anderson localization

We uncover the field-theoretical origin of symmetry relations for multifractal spectra at Anderson transitions and at critical points of other disordered systems. We show that such relations follow from the conformal invariance of the critical theory, which implies their general character. We also demonstrate that for the Anderson localization problem the entire probability distribution for the local density of states possesses a symmetry arising from the invariance of correlation functions of the underlying nonlinear σ model with respect to the Weyl group of the target space of the model.     

Multi-dimensional 1H-13C HETCOR and FSLG-HETCOR NMR study of sphingomyelin bilayers containing cholesterol in the gel and liquid crystalline states

(13)C cross polarization magic angle spinning (CP-MAS) and (1)H MAS NMR spectra were collected on egg sphingomyelin (SM) bilayers containing cholesterol above and below the liquid crystalline phase transition temperature (T(m)). Two-dimensional (2D) dipolar heteronuclear correlation (HETCOR) spectra were obtained on SM bilayers in the liquid crystalline (L(alpha)) state for the first time and display improved resolution and chemical shift dispersion compared to the individual (1)H and (13)C spectra and significantly aid in spectral assignment. In the gel (L(beta)) state, the (1)H dimension suffers from line broadening due to the (1)H-(1)H homonuclear dipolar coupling that is not completely averaged by the combination of lipid mobility and MAS. This line broadening is significantly suppressed by implementing frequency switched Lee-Goldburg (FSLG) homonuclear (1)H decoupling during the evolution period. In the liquid crystalline (L(alpha)) phase, no improvement in line width is observed when FSLG is employed. All of the observed resonances are assignable to cholesterol and SM environments. This study demonstrates the ability to obtain 2D heteronuclear correlation experiments in the gel state for biomembranes, expands on previous SM assignments, and presents a comprehensive (1)H/(13)C NMR assignment of SM bilayers containing cholesterol. Comparisons are made to a previous report on cholesterol chemical shifts in dimyristoylphosphatidylcholine (DMPC) bilayers. A number of similarities and some differences are observed and discussed.     

Disorder-Order-Crystalline State Transitions of PEO-b-PPO-b-PEO Copolymers and their Blends: SAXS/WAXS/DSC Study

The structure in the symmetrical triblock copolymers PEO-b-PPO-b-PEO and their blend with PEO, studied by small angle x-ray scattering (SAXS), wide angle x-ray scattering (WAXS), and differential scanning calorimetry (DSC), pass from melt to the solid state on cooling. On subsequent heating back to the melt, they pass through disordered and ordered molten states, crystalline structure, and finally back to a disordered melt state. At high temperatures these systems are in the melt in the disordered state approximately described by the mean-field theory. The characteristic lengths of these systems, obtained from SAXS, are proportional to R _g . At lower temperatures, their structure changes to a disordered state which can be described by the concentration fluctuation theory. During cooling, the disordered melt structure changes abruptly into the ordered melt structure. The crystallization destroys this melt structure, forming a new lamellar structure with different periodicity. During heating near the melting point, lamellar periodicity increases very steeply. After melting, the crystalline structure transforms directly to the disordered state.     

Two-Dimensional Dynamic-Director C NMR of Liquid Crystals

A novel nuclear magnetic resonance (NMR) experiment for facilitating the resolution and assignment of liquid crystalline ¹³C NMR spectra is described. The method involves the motor-driven reorientation of the liquid crystalline director, in synchrony with the acquisition of a 2D chemical shift correlation spectrum. By monitoring in this fashion the ¹³C NMR evolution of spins in the liquid crystal at two different director orientations with respect to the magnetic field, the method distinguishes anisotropic from isotropic displacements and can be utilized for assigning the resonances and estimating local degrees of order. Of various potential pairs of angles suitable for such a correlation, the (0°, 90°) choice was found to be most convenient, as it avoids line broadening complications that may otherwise originate from heterogeneities of the oriented phase. The technique thus derived was employed in the analysis of a series of monomeric and polymeric liquid crystal systems.     

Solid state NMR interaction parameters of oxygens linking titanium and silicon in crystalline cyclic titanodiphenylsiloxanes

17O static and magic angle spinning NMR spectra are reported from three crystalline cyclic titanodiphenylsiloxanes at magnetic fields of 5.6, 14.1, and 17.6 T. These compounds allow the NMR parameters characteristic of Ti-O-Si environments to be determined. It appears from these data that the quadrupole interaction (C(Q)) of such environments is in the range of 3-3.5 MHz and that Si-O-TiO3 sites are less shifted than Si-O-TiO5. The relatively large isotropic chemical range observed suggests that for structurally and atomically disordered titanosilicate-based materials the very highest applied magnetic field may not produce the best 17O solid state NMR spectra. There appears to be a correlation between the 17O shift and Ti-O bondlength.     

Mössbauer effect of119Sn in amorphous superconducting metals

Mössbauer spectra for¹¹⁹Sn in crystalline and disordered Sn, as well as in crystalline and liquid-like amorphous Sn_1-x Cu _x (X=0.10?0.18), have been measured at 2.6 K≦T≦108 K. The Debye-Waller-Factor (DWF) obtained from the spectra is identical for the crystalline and for the disordered phase. The DWF of the amorphous phase is smaller than the DWF of the crystalline phase athigh temperatures, but it shows a stronger temperature dependence than the DWF of the crystalline phase and reaches the latter one at about 4 K. From this low-temperature result we conclude that the differences of the Eliashberg functionα ²(ω)F(ω) and of the superconducting transition temperatureT _c in these two phases cannot be related to changes in the phonon spectrumF(ω), but must result from changes of the interaction parameterα ² (ω). A comparison between DWF,α ² F, and specific heat data is performed. From the values for the isomeric shift of the Mössbauer line we can show that the hybridisation and covalency of the electronic bonds present in the crystalline and in the disordered phases are destroyed in the amorphous phase. Both, the DWF and the isomer shift demonstrate that the electronic properties of crystalline and amorphous Sn(Cu) differ appreciably. The electronic and superconducting properties of amorphous Sn(Cu) are similar to the properties of the high pressure phase of tin.     

Excitonic line shapes of disordered solids

The optical absorption for a disordered one-dimensional excitonic solid has been studied by numerical methods. We have considered both Gaussian and binary energy fluctuations. Our results indicate that the physical properties associated with the spectra are selfaveraging. Results obtained on a single realization of random variables are consistent with recent ensemble averaged results obtained numerically on smaller samples. We also show that for binary disordered solids in the band splitting limit, spectra are dominated by cluster effects and can not be described through analytical treatments.     

Random lasing in strongly disordered medium

Using the time-dependent theory, we calculate the random-laser emission spectra in a two-dimensional strongly disordered medium. The calculation results show that in low dimensional systems, such as thin- film disordered media and planar waveguides, the larger the difference of the refractive indices between the scattering and background media, the smaller the lasing threshold. We also reveal the existence of multi-mode survival and mode competition. We experimentally obtain the emission spectra of a dye solution with Al particles doped at different pumping energies, and the experimental results agree well with the calculated ones.     

Room-Temperature 2.5 eV Pulsed Cathodoluminescence Band of High-Purity Silicon Dioxide

We study the room-temperature (RT) pulsed cathodoluminescence (PCL) spectra of a set of pure synthetic (both crystalline and amorphous) silicon dioxide samples. We show that the PCL spectra of all samples (both amorphous and crystalline) possess bands with intensity maxima in the region of 487 – 500 nm (2.54 – 2.48 eV). These bands are the most intense in the PCL spectra of disordered materials. We investigate the annealing behavior of RT PCL spectra of the crystalline and amorphous samples. Annealing has no significant effect on this emission. We demonstrate that the surface area of the material plays no role in the emission of PCL bands at 415 and 490 nm in the spectra of α-quartz single crystal and crystalline powder with grain sizes of 10 – 100 μm. Our results show that the bands in the region of 2.5 eV are the universal property of all synthetic pure SiO₂ samples. The nature of the SiO₂ emission band in the region of 2.5 eV is not clear; we discuss two possible explanations. The first one is based on considering the intrinsic emission due to self-trapped exciton (STE) decay with the transient O-O (oxygen–oxygen) bond formation. The second one is based on the role of Li ions in the emission process.     

聚氧乙烯-六氟砷酸锂复合物不同结晶结构的13C谱归属

聚氧乙烯-六氟砷酸锂复合物在不同的退火温度下会形成两种不同的结晶结构,其固体核磁共振¹³C谱具有很高的分辨率．利用二维交换¹³C谱和¹³C fp-RFDR(finite-pulse radio-frequency-driven recoupling)双量子-单量子(DQ-SQ)实验对复合物结晶的信号进行归属,为从分子水平上研究结晶区中不同-CH₂-基团的运动提供实验依据．     

Echo-Induced EPR Spectra of Spin Probes as a Method for Identification of Glassy States in Biological Objects

The echo-induced spectra of nitroxide radicals trapped in organic glasses change their shapes with increases in the time interval between echo-forming microwave pulses. The changes are assigned to the presence in a disordered state of a special type of orientational motion (libration) of molecules near their equilibrium positions. This is not observed in a crystalline state. It is proposed that this effect determines the phase state of the different components of biological systems. The potential of the method is demonstrated by studying the embryos and endosperm of wheat kernels (Tritium vulgare L.) and various models.     

掺Er3+钆硼硅酸盐玻璃及玻璃陶瓷的红外发光特性和热稳定性

报道了一种新型可作为掺铒光纤放大器(EDFA)基质材料的Er³⁺掺杂B₂O₃-SiO₂-Gd₂O₃-Na₂O(BSGN)体系玻璃及其玻璃陶瓷。对材料中铒的⁴I_13/2→⁴I_15/2跃迁的1.5μm发射光谱、吸收光谱、时间分辨光谱及寿命进行了测量和分析,讨论了热处理对玻璃材料带宽和寿命的影响。结果表明,铒掺杂玻璃1.5μm发射的带宽和J-O参数Ω₆都随B₂O₃含量的增加而增加,寿命随B₂O₃含量的增加而减小。经过热处理后得到的玻璃陶瓷比具有相同组分的玻璃具有更高的1.5μm发射效率。同时,差热分析的数据表明,该玻璃体系具有极好的热稳定性。     

近周期超晶格中的声学声子及其光散射特性

利用转移矩阵方法计算了近周期超晶格体系（包括有限周期数的超晶格、耦合超晶格、层厚起伏和层厚渐变的超晶格）中声学声子的喇曼散射谱．结果表明上述近周期超晶格的光散射特性与理想严格周期的体系和完全无序的体系都不相同，呈现出许多独特的性质．对有限周期数的超晶格，由于边界的存在，喇曼谱中除了理想超晶格中存在的折叠声学声子峰（主峰）外，还会出现一系列等间距分布的卫星峰．对耦合超晶格体系，理想超晶格中存在的主峰将出现分裂．对层厚起伏变化的超晶格，主峰呈现非对称展宽，展宽主要出现在高波数端．计算结果和实验测得的谱线作了比 关键词：