Specification of infrared detectors and arrays

The possibility is examined of defining a figure of merit covering the widest possible range of infrared detectors and detector arrays. It is concluded that the best figure of merit which can be found is a generalisation of D^*, but that so broadly based a figure of merit is of limited value.     

Variation of molecular alignment as a means of resolving orientational ambiguities in protein structures from dipolar couplings

Residual dipolar couplings for pairs of proximate magnetic nuclei in macromolecules can easily be measured using high-resolution NMR methods when the molecules are dissolved in dilute liquid crystalline media. The resulting couplings can in principle be used to constrain the relative orientation of molecular fragments in macromolecular systems to build a complete structure. However, determination of relative fragment orientations based on a single set of residual dipolar couplings is inherently hindered by the multi-valued nature of the angular dependence of the dipolar interaction. Even with unlimited dipolar data, this gives rise to a fourfold degeneracy in fragment orientations. In this Communication, we demonstrate a procedure based on an order tensor analysis that completely removes this degeneracy by combining residual dipolar coupling measurements from two alignment media. Application is demonstrated on (15)N-(1)H residual dipolar coupling data acquired on the protein zinc rubredoxin from Clostridium pasteurianum dissolved in two different bicelle media.     

Electro-optical characterization of a 2-cyclo-octylamino-5-nitropyridine thin organic crystal film

2-cyclo-octylamino-5-nitropyridine (COANP) single crystals were grown between transparent plates coated with indium tin oxide. The Pockels effect of the crystals was analyzed by an ac modulation method. The figure of merit of electro-optic phase retardation of the COANP crystals is estimated to be 4.2x10(-12) m/V . The crystals were protected by the plates, and the figure of merit of the phase retardation of the crystals did not decrease with time. We believe that the crystal-growth method described is applicable to other organic compounds whose crystal growth from a melt is feasible.     

Comparing,Modeling, and Assigning Chemical-Shift Tensors in the Cartesian,Irreducible Spherical,and Icosahedral Representations

A measure of the difference between two chemical-shift tensors is developed by defining the scalar distance between them. Chemical-shift tensors are treated as functions whose domain is the surface of a sphere and the mathematical definition of the quadratic distance between two functions is invoked. Expressions for the distance between two chemical-shift tensors are developed in the Cartesian and irreducible spherical representations and in a new icosahedral representation. A representation wherein the chemical-shift tensor is specified by the shifts when the magnetic field is along six directions defined by the vertices of an isosahedron is developed and its properties are discussed. The expression for the distance between two tensors is found to be particularly attractive and useful in this icosahedral representation. The distance between tensors computed in the icosahedral representation is useful in fitting linear models to tensor data. It is shown how such fitting can contribute to the assignment of tensors obtained from single-crystal studies. A quantitative figure of merit useful for comparing multiple assignment possibilities is developed. The results derived are applicable to any physical phenomenon described by real zero-rank and second-rank tensors.     

The effect of geometric arrangement on the thermoelectric properties of Phenanthrene coupled to the graphene nanoribbons electrodes

The thermoelectric properties of a Phenanthrene molecule, such as thermopower, electrical conductivity, thermal conductivity and figure of merit, are investigated by applying the non-equilibrium Green's function (NEGF) method combined with the density functional theory (DFT). Phenanthrene is intended to couple to the graphene nanoribbons electrodes in two configurations. The vertical and horizontal orientations of the molecule between the nanoribbons are considered. The results reveal that the thermoelectric properties of the considered structures are dependent on the orientation of Phenanthrene configuration between the electrodes. At high chemical potential, the greatest figure of merit is observed for Phenanthrene, which is vertically attached to the electrodes, because of the small thermal conductivity of this configuration. On the other hand, the symmetric and horizontal configurations of the molecule make it a high-performance thermoelectric device at zero chemical potential.     

The 13C chemical shift tensor principal values and orientations in dialkyl carbonates and trithiocarbonates

The 13C chemical shift tensor principal values for the trigonal carbonate and thiocarbonate carbon atoms in the dialkyl carbonates, dimethyl carbonate, ethylene carbonate, and diphenyl carbonate, and in the trithiocarbonates, ethylene trithiocarbonate and dimethyl trithiocarbonate, respectively, were measured in various solid-state one-dimensional and two-dimensional nuclear magnetic resonance experiments. Furthermore, the chemical shift tensor principal values and orientations were calculated for the corresponding isolated molecules with quantum mechanically fully optimized geometries. Proton-optimized X-ray geometries of ethylene carbonate, ethylene trithiocarbonate, and diphenyl carbonate were used in embedded ion method (EIM) calculations and in calculations on the isolated molecules to obtain the theoretical principal values and to assign the chemical shift tensor orientations in these three compounds. Considerable improvement in the correlation between the experimental and calculated principal values is obtained when the electrostatic crystal potentials are included in EIM calculations. The chemical shift tensor orientations and principal values obtained for the dialkyl compounds in this study complement the previous data on a series of ionic potassium carbonates and thiocarbonates.     

The C Chemical Shift Tensor Principal Values and Orientations in Dialkyl Carbonates and Trithiocarbonates

The ¹³C chemical shift tensor principal values for the trigonal carbonate and thiocarbonate carbon atoms in the dialkyl carbonates, dimethyl carbonate, ethylene carbonate, and diphenyl carbonate, and in the trithiocarbonates, ethylene trithiocarbonate and dimethyl trithiocarbonate, respectively, were measured in various solid-state one-dimensional and two-dimensional nuclear magnetic resonance experiments. Furthermore, the chemical shift tensor principal values and orientations were calculated for the corresponding isolated molecules with quantum mechanically fully optimized geometries. Proton-optimized X-ray geometries of ethylene carbonate, ethylene trithiocarbonate, and diphenyl carbonate were used in embedded ion method (EIM) calculations and in calculations on the isolated molecules to obtain the theoretical principal values and to assign the chemical shift tensor orientations in these three compounds. Considerable improvement in the correlation between the experimental and calculated principal values is obtained when the electrostatic crystal potentials are included in EIM calculations. The chemical shift tensor orientations and principal values obtained for the dialkyl compounds in this study complement the previous data on a series of ionic potassium carbonates and thiocarbonates.     

Fano resonance sensing based on coupled sub-wavelength dielectric grating and periodic photonic crystal

Based on the diffraction effect of sub-wavelength dielectric grating and the optical property of periodic photonic crystal, a hybrid structure of sub-wavelength grating all-dielectric multilayer thin film containing periodic photonic crystal is proposed. The transmission property of the structure is simulated by finite element method (FEM). The result shows that the discrete state generated by the sub-wavelength waveguide grating will be coupled with the continuous state generated by the photonic crystal cavity and the Fano resonance can be formed. The Fano resonance sensing model based on structural parameters and resonance wavelength are established, the influence of structural parameters on the Fano resonance spectral curve is quantitatively analyzed by numerical simulations, and the dynamic detection of the refractive index of samples is realized. The above structure can realize the optical refractive index sensing with high figure of merit (FOM) value and provide an effective theoretical reference for the formation of Fano resonance in the all-dielectric hybrid structure.     

Optimal crystal geometry and orientation in electric field sensing using electro-optic sensors

For optimal sensitivity in electric field measurements, electro-optic (EO) crystals are typically selected based on their EO coefficients and dielectric constants. However, the conventional figure of merit yields sensitivity predictions regarding EO materials that are inconsistent with experimental data. In this Letter, we demonstrate that depolarization effects, which are often ignored, can dramatically enhance responsivity depending on the shape and orientation of the EO crystal. For optimal sensitivity, these effects are best exploited in longitudinal EO sensors, where they yield an optical modulation depth that increases quadratically with crystal length.     

Theoretical investigation of the thermoelectric transport properties of BaSi2

The full-potential linear augmented plane wave method based on density functional theory is employed to investigate the electronic structure of BaSi 2 . With the constant relaxation time and rigid band approximation,the electrical conductivity,Seebeck coefficient and figure of merit are calculated by using Boltzmann transport theory,further evaluated as a function of carrier concentration. We find that the Seebeck coefficient is more anisotropic than electrical conductivity. The figure of merit of BaSi 2 is predicted to be quite high at room temperature,implying that optimal doping may be an effective way to improve thermoelectric properties.     

ADTGSP晶体热释电探测器的最佳切割方向

分析了TGS类晶体在制作热释电探测器件时的最佳切割方向问题,给出了有关参数之间的相应公式;测量了ADTGSP晶体在不同方向上的介电常数、热释电系数以及电压响应优值与温度的依赖关系。结果表明,采用最佳切割将大大提高热释电红外探测器件的电压响应性能。 关键词：     

用于光纤电流传感器的BGO晶体磁光特性研究

在理论分析Bi4Ge3O12（BGO）晶体磁光特性的基础上,利用倍频法测量了不同工作波长下BGO晶体的费尔德常量,获得了与理论相符的实验结果.同时根据BGO晶体费尔德常量随波长的变化关系曲线,通过对该晶体吸收系数的测量,得出了其磁光优值曲线.进而将BGO晶体的磁光特性与光纤电流传感器常用的几种磁光材料作了对比,结果表明BGO晶体适合用于光纤电流传感器.     

化学位移张量的测量

对于刚性晶格中的分子,化学位移是与外加磁场空间取向相关的张量,这个张量有6个独立的分量. 化学位移张量也可以利用其主轴分量及主轴与晶体坐标系的方向余弦来表示. 很显然,知道了固体分子中各不等价位置处的化学位移张量,就可以推测出分子中电子分布的图象,具有重要意义. 本文首先描述了化学位移张量测量的理论,对测量化学位移 各 向异性的各种方法作了介绍和比较,并详细论述了一些常用的方法,如二维魔角跳旋转(M a gic Angle Hopping, MAH)、二维魔角慢旋转(Magic Angle Turning, MAT)和二维变相旋转边带分离（2D phase-adjusted spinning sidebands, 2D-PASS）技术等. 最后,还介绍了单晶化学位移张量的常规测量方法.     

Diffusion anisotropy in excised normal rat spinal cord measured by NMR microscopy

A conventional spin-echo NMR imaging pulse sequence was used to obtain high-resolution images of excised normal rat spinal cord at 7 and 14 T. It was observed that the large pulsed-field gradients necessary for high-resolution imaging caused a diffusion weighting that dominated the image contrast and that could be used to infer microscopic structural organization beyond that defined by the resolution of the image matrix (i.e., fiber orientation could be assigned based on diffusion anisotropy). Anisotropic diffusion coefficients were therefore measured using apparent diffusion tensor (ADT) imaging to assess more accurately fiber orientations in the spinal cord; structural anisotropy information is portrayed in the six unique images of the complete ADT. To reduce the dimensionality of the data, a trace image was generated using a separate color scale for each of the three diagonal element images of the ADT. This new image retains much of the invariance of the trace to the relative orientations of laboratory and sample axes (inherent to a greyscale trace image) but provides, by the use of color, contrast reflecting diffusion anisotropy. The colored trace image yields a pseudo-three-dimensional view of the rat spinal cord, from which it is possible to deduce fiber orientations.     

Spatial anisotropy of linear electro-optic effect in crystal materials: I—Experimental determination of electro-optic tensor in LiNbO3 by means of interferometric technique

The paper presents a technique suitable for the determination of linear electro-optic effect (LEOE) tensor components in crystal materials of any symmetry. The method is based on the Michelson interferometer, where the sample being studied is set into one of its arms to measure the electro-induced changes of the optical path. We describe in detail the sample geometries that are needed to determine a complete set of the LEOE tensor components and derive the corresponding equations. The experimental technique has been tested and verified on lithium niobate crystals as well as applied to MgO-doped LiNbO₃ crystals to study their electro-optic properties. The developed method can be useful for optical engineering, which deals with new materials being used in design or production of devices, such as, e.g., modulators or deflectors.     

Fano resonances in complex plasmonic super-nanoclusters: The effect of environmental modifications on the LSPR sensitivity

In this study, gold nanodisk clusters in heptamer orientations as clusters were used to design a super-heptamer consisting of one central and six peripheral heptamers. We examined the position and movement of the plasmon and Fano resonances by sketching the spectral response of the superstructure for various nanodisk dimensions. The quality of the interference between the superradiant and subradiant plasmon resonance modes of the nanodisk clusters was found to depend strongly on the structural configuration and the refractive index of the environmental medium. We replaced the central heptamer with a nanodisk and probed the position of the Fano resonance by geometrically altering the nanodisk structure. Finally, the effect of the dielectric environment on the plasmon response of both of the studied structures was examined numerically and theoretically. The localized surface plasmon resonance sensitivity of the finite plasmonic structures to the presence of liquid substances was investigated and shown by plotting the linear figure of merit. The finite-difference time-domain method was used as a numerical tool to investigate the plasmon response of the structure.     

Palladium nanoparticles as catalysts for reduction of Cr(VI) and Suzuki coupling reaction

Herein, six kinds of PdNPs (including icosahedron, sphere, spindle, cube, rod, and wire) were synthesized via simple methods. The catalytic activities were investigated by the reduction reaction of Cr(VI) and Suzuki coupling reaction. Chemically synthesized morphologies of the six catalysis were characterized by transmission electron microscopy, field emission scanning electron microscopy, and X-ray diffraction, etc. Pd icosahedron shows a better catalytic property than other PdNPs with a rate constants 0.42 min^?1 for the reduction of Cr(VI). Moreover, the electrocatalyst shows that Pd icosahedron possesses a bigger surface area of 8.56 m²/g than other nanoparticles, which is attributed to the better catalyst. The Pd icosahedron possesses a better catalytic property, attributing to the abundant exposed {111} facets with high activity on Pd icosahedron. The catalytic activities are closely related to the surface area with the following order: icosahedrons ≥ sphere > rod > spindle > cube > wire. The Pd icosahedron catalyst represents a strong activity for Suzuki coupling reaction as well, outweighting is 80%. The results reveal that Pd icosahedron acts as an efficient catalyst compared to other PdNPs (wire, rod, sphere, spindle, and cube).     

Variation in linear susceptibility tensor at crystal surface probed by linear Cherenkov radiation

At the surfaces of crystals, linear susceptibility tensors would differ from their counterparts in the interior of the bulk crystal. However, this phenomenon has not been shown in a visible way yet. In previous researches, numerous types of nonlinear Cherenkov radiation based on different materials have been studied, while linear Cherenkov radiation is barely reported. We experimentally prove the generation of linear Cherenkov radiation on the potassium dihydrogen phosphate(KDP) crystal surface and theoretically analyze its phase-matching scheme. In our study, o-polarized light and e-polarized light can mutually convert through the linear Cherenkov process. According to this result, we figure out new nonzero elements at off-diagonal positions in the linear susceptibility tensor matrix at crystal surfaces, compared with the normal form of a bulk KDP.     

直接法中起始套反射的优化选择方法(Ⅱ)

文通过三个未知结构的测定例子,分别在记号附加法与多解法中采用了起始套反射的优化选择方法。结果表明:优化选择方法为记号附加法提供了一种选择起始套的方法,由此可以获得记号间的明确关系,从而保证结构测定的顺利进行,在多解法中,采用优化选择方法,可以克服由于使用MULTAN程序求解结构的失败例,并且由于正确解的品质因素增加,这就提高了以品质因素值判断结构解正确性的效力。